Thermal processes in the metallurgical industry
Suggested Revisions by Environment Canada including comments arising from
discussions in Geneva at EGB II 1 in 2005 and comments submitted by February
2006 to the Stockholm Secretariat.
28.April.2006
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
Table of contents
V.D
Thermal processes in the metallurgical industry: ...................................................................... 5
SUMMARIES BY SOURCE CATEGORIES – PART III OF ANNEX C ...................................................................... 6
VI.B.
Thermal processes in the metallurgical industry not mentioned in Annex C, Part II: ............... 6
SECTION V
8
GUIDANCE/GUIDELINES BY SOURCE CATEGORY: SOURCE CATEGORIES IN PART II OF
ANNEX C
8
V.D. THERMAL PROCESSES IN THE METALLURGICAL INDUSTRY .................................................................... 8
(i)
Secondary copper production .................................................................................................... 8
(ii)
Sinter plants in the iron and steel industry .............................................................................. 17
(iii)
Secondary aluminium production ............................................................................................ 29
(iv)
Secondary zinc production ....................................................................................................... 42
SECTION VI. GUIDANCE/GUIDELINES BY SOURCE CATEGORY SOURCE CATEGORIES IN
PART III OF ANNEX C ............................................................................................................................... 51
VI.B THERMAL PROCESSES IN THE METALLURGICAL INDUSTRY NOT MENTIONED IN ANNEX C, PART II ..... 52
(v)
Secondary lead production ...................................................................................................... 52
(vi)
Primary aluminium production ................................................................................................ 60
(vii)
Magnesium production ............................................................................................................ 70
(viii)
Secondary steel production ...................................................................................................... 80
(ix)
Primary base metals smelting .................................................................................................. 96
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
Section IV. Compilation of summaries of Sections V and VI
V.D
Thermal processes in the metallurgical industry:
(i) Secondary copper production
Secondary copper smelting involves copper production from copper scrap, sludge, computer and
electronic scrap, and drosses from refineries. Processes involved in copper production are feed
pretreatment, smelting, alloying and casting. Organic materials in feed such as oils, plastics and
coatings, and temperatures between 250 °C and 500 °C, may give rise to chemicals listed in Annex
C of the Stockholm Convention.
Best available techniques include presorting, cleaning feed materials, maintaining temperatures
above 850 °C, utilizing afterburners with rapid quenching, activated carbon adsorption and fabric
filter dedusting.
Achievable performance levels for secondary copper smelters: < 0.5 ng I-TEQ/Nm3.1
(ii) Sinter plants in the iron and steel industry
Sinter plants in the iron and steel industry are a pretreatment step in the production of iron whereby
fine particles of iron ores and, in some plants, secondary iron oxide wastes (collected dusts, mill
scale) are agglomerated by combustion. Sintering involves the heating of fine iron ore with flux
and coke fines or coal to produce a semi-molten mass that solidifies into porous pieces of sinter
with the size and strength characteristics necessary for feeding into the blast furnace.
PCDD and PCDF appear to be formed in the iron sintering process via de novo synthesis. PCDF
generally dominate in the waste gas from sinter plants. The PCDD/PCDF formation mechanism
appears to start in the upper regions of the sinter bed shortly after ignition, and then the dioxins,
furans and other compounds condense on cooler burden beneath as the sinter layer advances along
the sinter strand towards the burn-through point.
Primary measures identified to prevent or minimize the formation of PCDD/PCDF during iron
sintering include the stable and consistent operation of the sinter plant, continuous parameter
monitoring, recirculation of waste gases, minimization of feed materials contaminated with
persistent organic pollutants or contaminants leading to formation of such pollutants, and feed
material preparation.
Secondary measures identified to control or reduce releases of PCDD/PCDF from iron sintering
include adsorption/absorption (for example, activated carbon injection) and high-efficiency
dedusting, as well as fine wet scrubbing of waste gases combined with effective treatment of the
scrubber waste waters and disposal of waste-water sludge in a secure landfill.
The achievable performance level for an iron sintering plant operating according to best available
techniques: < 0.2 ng TEQ/Nm3.
(iii) Secondary aluminium production
Secondary aluminium smelting involves the production of aluminium from used aluminium
products processed to recover metals by pretreatment, smelting and refining.
Fuels, fluxes and alloys are used, while magnesium removal is practised by the addition of
chlorine, aluminium chloride or chlorinated organics. Chemicals listed in Annex C of the
1
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured
at 0 °C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present
guidelines. The operating oxygen concentration conditions of exhaust gases are used for metallurgical
sources.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Stockholm Convention probably result from organics in the feed, chlorine compounds and
temperatures between 250 °C and 500 °C.
Best available techniques include high-temperature advanced furnaces, oil- and chlorine-free feeds
(if alternatives are available), afterburners with rapid quench, activated carbon adsorption and
dedusting fabric filters.
The achievable performance level for secondary aluminium smelters: < 0. 5 ng I-TEQ/Nm3.
(iv) Secondary zinc production
Secondary zinc smelting involves the production of zinc from materials such as dusts from copper
alloy production and electric arc steel making, and residues from steel scrap shredding and
galvanizing processes. Production processes include feed sorting, pretreatment cleaning, crushing,
sweating furnaces to 364 °C, melting furnaces, refining, distillation and alloying. Oils and plastics
in feed, and temperatures between 250 °C and 500 °C, may give rise to chemicals listed in Annex
C of the Stockholm Convention.
Best available techniques include feed cleaning, maintaining temperatures above 850 °C, fume and
gas collection, afterburners with quenching, activated carbon adsorption and fabric filter dedusting.
The achievable performance level for secondary zinc smelters: < 0.5 ng I-TEQ/Nm3.
Summaries by source categories – Part III of Annex C
VI.B. Thermal processes in the metallurgical industry not mentioned
in Annex C, Part II:
(i) Secondary lead production
Secondary lead smelting involves the production of lead and lead alloys, primarily from scrap
automobile batteries, and also from other used lead sources (pipe, solder, drosses, lead sheathing).
Production processes include scrap pretreatment, smelting and refining. Oils and plastics in feed,
and temperatures between 250 and 500° C, may give rise to chemicals listed in Annex C of the
Stockholm Convention.
Best available techniques include the use of plastic-free and oil-free feed material, high furnace
temperatures above 850 °C, effective gas collection, afterburners and rapid quench, activated
carbon adsorption, and dedusting fabric filters.
The achievable performance levels for secondary lead smelters: < 0.1 ng I-TEQ/Nm3.
(ii) Primary aluminium production
Primary aluminium is produced directly from the mined ore, bauxite. The bauxite is refined into
alumina through the Bayer process. The alumina is reduced into metallic aluminium by electrolysis
through the Hall-Héroult process (either using self-baking anodes – Söderberg anodes – or using
prebaked anodes).
Primary aluminium production is generally thought not to be a significant source of chemicals
listed in Annex C of the Stockholm Convention. However, contamination with PCDD and PCDF is
possible through the graphite-based electrodes used in the electrolytic smelting process.
Possible techniques to reduce the production and release of chemicals listed in Annex C from the
primary aluminium sector include improved anode production and control, and using advanced
smelting processes. The achievable performance level in this sector should be < 0.1 ng TEQ/Nm3.
(iii) Magnesium production
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
7
Magnesium is produced either from raw magnesium chloride with molten salt electrolysis, or
magnesium oxide reduction with ferrosilicon or aluminium at high temperatures, as well as through
secondary magnesium recovery (for example, from asbestos tailings).
The addition of chlorine or chlorides, the presence of carbon anodes and high process temperatures
in magnesium production can lead to the formation of chemicals listed in Annex C of the
Stockholm Convention and their emission in air and water.
Alternative techniques may include the elimination of the carbon source by using non-graphite
anodes, and the application of activated carbon. However, achievable performance depends on the
type of process and controls utilized.
(iv) Secondary steel production
Secondary steel is produced through direct smelting of ferrous scrap using electric arc furnaces.
The furnace melts and refines a metallic charge of scrap steel to produce carbon, alloy and stainless
steels at non-integrated steel mills. Ferrous feed materials may include scrap, such as shredded
vehicles and metal turnings, or direct reduced iron.
Chemicals listed in Annex C of the Stockholm Convention, such as PCDD and PCDF, appear to be
most probably formed in the electric arc furnace steel-making process via de novo synthesis by the
combustion of non-chlorinated organic matter such as polystyrene, coal and particulate carbon in
the presence of chlorine donors. Many of these substances are contained in trace concentrations in
the steel scrap or are process raw materials such as injected carbon.
Primary measures include adequate off-gas handling and appropriate off-gas conditioning to
prevent conditions leading to de novo synthesis formation of PCDD/PCDF. This may include postcombustion afterburners, followed by rapid quench of off-gases. Secondary measures include
adsorbent injection (for example, activated carbon) and high-level dedusting with fabric filters.
The achievable performance level using best available techniques for secondary steel production is
< 0.1 ng I-TEQ/Nm3.
(v) Primary base metals smelting
Primary base metals smelting involves the extraction and refining of nickel, lead, copper, zinc and
cobalt. Generally, primary base metals smelting facilities process ore concentrates. Most primary
smelters have the technical capability to supplement primary concentrate feed with secondary
materials (for example, recyclables).
Production techniques may include pyrometallurgical or hydrometallurgical processes. Chemicals
listed in Annex C of the Stockholm Convention are thought to originate through high-temperature
thermal metallurgical processes; hydrometallurgical processes are therefore not considered in this
section on best available techniques for primary base metals smelting.
Available information on emissions of PCDD and PCDF from a variety of source sectors (for
example, incinerators, steel electric arc furnaces, iron sintering plants) suggests that process
technologies and techniques, and associated off-gas conditioning, can influence the formation and
subsequent release of PCDD/PCDF. Consideration should be given to hydrometallurgical
processes, where technically feasible, as alternatives to pyrometallurgical processes when
considering proposals for the construction and commissioning of new base metals smelting
facilities or processes.
Primary measures include the use of hydrometallurgical processes, quality control of feed materials
and scrap to minimize contaminants leading to PCDD/PCDF formation, effective process control to
avoid conditions leading to PCDD/PCDF formation, and use of flash smelting technology.
Identified secondary measures include high-efficiency gas cleaning and conversion of sulphur
dioxide to sulphuric acid, effective fume and gas collection and high-efficiency dust removal.
The achievable performance level using best available techniques for base metals smelters is < 0.1
ng I-TEQ/Nm3.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Section V
Guidance/guidelines by source category:
Source categories in Part II of Annex C
V.D. Thermal processes in the metallurgical industry
(i)
Secondary copper production
Summary
Secondary copper smelting involves copper production from copper scrap, sludge, computer
and electronic scrap, and drosses from refineries. Processes involved in copper production are
feed pretreatment, smelting, alloying and casting. Organic materials in feed such as oils, plastics
and coatings, and temperatures between 250 and 500 °C, may give rise to chemicals listed in
Annex C of the Stockholm Convention.
Best available techniques include: presorting, cleaning feed materials, maintaining temperatures
above 850 °C, utilizing afterburners with rapid quenching, activated carbon adsorption and
fabric filter dedusting.
Achievable performance levels for secondary copper smelters: < 0.5 ng I-TEQ/Nm3.
1.
Process description
Secondary copper smelting involves pyrometallurgical processes dependent on the copper content
of the feed material, size distribution and other constituents. Feed sources are copper scrap, sludge,
computer scrap, drosses from refineries and semi-finished products. These materials may contain
organic materials like coatings or oil, and installations take this into account by using de-oiling and
decoating methods or by correct design of the furnace and abatement system (European
Commission 2001, p. 201–202). Copper can be infinitely recycled without loss of its intrinsic
properties.
The quoted material that follows is from Secondary Copper Smelting, Refining and Alloying, a
report of the Environmental Protection Agency of the United States of America (EPA 1995).
“Secondary copper recovery is divided into 4 separate operations: scrap pre-treatment,
smelting, alloying, and casting. Pre-treatment includes the cleaning and consolidation of
scrap in preparation for smelting. Smelting consists of heating and treating the scrap for
separation and purification of specific metals. Alloying involves the addition of 1 or more
other metals to copper to obtain desirable qualities characteristic of the combination of
metals.
Scrap pre-treatment may be achieved through manual, mechanical, pyrometallurgical, or
hydrometallurgical methods. Manual and mechanical methods include sorting, stripping,
shredding, and magnetic separation. Pyrometallurgical pre-treatment may include sweating
(the separation of different metals by slowly staging furnace air temperatures to liquefy
each metal separately), burning insulation from copper wire, and drying in rotary kilns to
volatilize oil and other organic compounds. Hydrometallurgical pre-treatment methods
include flotation and leaching to recover copper from slag. Leaching with sulphuric acid is
used to recover copper from slime, a byproduct of electrolytic refining.
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Smelting of low-grade copper scrap begins with melting in either a blast or a rotary
furnace, resulting in slag and impure copper. If a blast furnace is used, this copper is
charged to a converter, where the purity is increased to about 80 to 90 percent, and then to
a reverberatory furnace, where copper of about 99 percent purity is achieved. In these firerefining furnaces, flux is added to the copper and air is blown upward through the mixture
to oxidize impurities.
These impurities are then removed as slag. Then, by reducing the furnace atmosphere,
cuprous oxide (CuO) is converted to copper. Fire-refined copper is cast into anodes, which
are used during electrolysis. The anodes are submerged in a sulphuric acid solution
containing copper sulphate. As copper is dissolved from the anodes, it deposits on the
cathode. Then the cathode copper, which is as much as 99.99 percent pure, is extracted and
recast. The blast furnace and converter may be omitted from the process if average copper
content of the scrap being used is greater than about 90 percent.
In alloying, copper-containing scrap is charged to a melting furnace along with 1 or more
other metals such as tin, zinc, silver, lead, aluminium, or nickel. Fluxes are added to
remove impurities and to protect the melt against oxidation by air. Air or pure oxygen may
be blown through the melt to adjust the composition by oxidizing excess zinc. The alloying
process is, to some extent, mutually exclusive of the smelting and refining processes
described above that lead to relatively pure copper.
The final recovery process step is the casting of alloyed or refined metal products. The
molten metal is poured into moulds from ladles or small pots serving as surge hoppers and
flow regulators. The resulting products include shot, wire bar, anodes, cathodes, ingots, or
other cast shapes.”
Figure 1 presents the process in diagrammatic form.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Figure 1. Secondary copper smelting
Input
Potential output
Lower grade
residues, fluxes,
coke, oxygen
Smelting
reduction
Black
copper
Slag
Flux, scrap,
air, oxygen
Land releases, filter dust
(recycled), furnace linings
Converter
Converter
copper
Clean scrap,
reductant, air
Air emissions – CO
Dust, metal oxide fume – recycled
Dioxins, volatile organic compounds
Land emissions
Furnace linings
Slag
Air emissions: SO2,
metals, dust
Anode furnace
Anodes
Electrolytic
refining
Anode scrap
Slime
Final slag
Construction
Ni, etc.
Cathodes
Particulate matter
Source: European Commission 2001, p. 217
Artisinal and small enterprise metal recovery activities may be significant, particularly in
developing countries and countries with economies in transition. These activities may contribute
significantly to pollution and have negative health impacts. For example, artisinal zinc smelting is
an important atmospheric mercury emission source. The technique used to smelt both zinc and
mercury is simple; the ores are heated in a furnace for a few hours, and zinc metal and liquid
mercury are produced. In many cases there are no pollution control devices employed at all during
the melting process. Other metals that are known to be produced by artisinal and small enterprise
metal recovery activities include antimony, iron, lead, manganese, tin, tungsten, gold, silver,
copper, and aluminum.
These are not considered best available techniques or best environmental practices.
However, as a minimum, appropriate ventilation and material handling should be carried
out.
2.
Sources of chemicals listed in Annex C of the Stockholm
Convention
The formation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans
(PCDF) is probably due to the presence of chlorine from plastics and trace oils in the feed material.
As copper is the most efficient metal to catalyse PCDD/PCDF formation, copper smelting is a
concern.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
2.1.
11
General information on emissions from secondary copper smelters
Airborne emissions consist of nitrogen oxides (NOx), carbon monoxide (CO), dust and metal
compounds, organic carbon compounds and PCDD/PCDF. Off-gases usually contain little or no
sulphur dioxide (SO2), provided sulphidic material is avoided. Scrap treatment and smelting
generate the largest quantity of atmospheric emissions. Dust and metal compounds are emitted
from most stages of the process and are more prone to fugitive emissions during charging and
tapping cycles. Particulate matter is removed from collected and cooled combustion gases by
electrostatic precipitators or fabric filters. Fume collection hoods are used during the conversion
and refining stages due to the batch process, which prevents a sealed atmosphere. NOx is
minimized in low-NOx burners, while CO is burnt in hydrocarbon afterburners. Burner control
systems are monitored to minimize CO generation during smelting (European Commission 2001, p.
218–229).
2.2.
Emissions of PCDD/PCDF to air
PCDD/PCDF are formed during base metal smelting through incomplete combustion or by de novo
synthesis when organic and chlorine compounds such as oils and plastics are present in the feed
material. Secondary feed often consists of contaminated scrap.
The process is described in European Commission 2001, p. 133:
“PCDD/PCDF or their precursors may be present in some raw materials and there is a
possibility of de-novo synthesis in furnaces or abatement systems. PCDD/PCDF are easily
adsorbed onto solid matter and may be collected by all environmental media as dust,
scrubber solids and filter dust.
The presence of oils and other organic materials on scrap or other sources of carbon
(partially burnt fuels and reductants, such as coke), can produce fine carbon particles which
react with inorganic chlorides or organically bound chlorine in the temperature range of
250 to 500 °C to produce PCDD/PCDF. This process is known as de-novo synthesis and is
catalysed by the presence of metals such as copper or iron.
Although PCDD/PCDF are destroyed at high temperature (above 850 °C) in the presence
of oxygen, the process of de-novo synthesis is still possible as the gases are cooled through
the “reformation window”. This window can be present in abatement systems and in cooler
parts of the furnace e.g. the feed area. Care taken in the design of cooling systems to
minimise the residence time in the window is practised to prevent de-novo synthesis.”
2.3.
Releases to other media
Process, surface and cooling water can be contaminated by suspended solids, metal compounds and
oils. Most process and cooling water is recycled. Waste-water treatment methods are used before
discharge. By-products and residues are recycled in the process as these contain recoverable
quantities of copper and other non-ferrous metals. Waste material generally consists of acid slimes
which are disposed of on site. Care must be taken to ensure the proper disposal of slimes in order
to minimize copper and dioxins exposure to the environment.
3.
Recommended processes
Process design and configuration is influenced by the variation in feed material and quality control.
Processes considered as best available techniques for smelting and reduction include the blast
furnace, the mini-smelter (totally enclosed), the sealed submerged electric arc furnace, and ISA
smelt. The top-blown rotary furnace (totally enclosed) and Pierce-Smith converter are best
available techniques for converting. The submerged electric arc furnace is sealed and is cleaner
than other designs if the gas extraction system is adequately designed and sized.
The use of blast furnaces for scrap melting is becoming less common due to difficulties in
economically preventing pollution. Shaft furnaces without a coal/coke feed are being used instead
(Personal Communication, February 2006).
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Clean copper scrap devoid of organic contamination can be processed using the reverberatory
hearth furnace, the hearth shaft furnace or Contimelt process. These are considered to be best
available techniques in configurations with suitable gas collection and abatement systems.
No information is available on alternative processes to smelting for secondary copper processing.
4.
Primary and secondary measures
Primary and secondary measures of PCDD/PCDF reduction and elimination are discussed below.
4.1.
Primary measures
Primary measures are regarded as pollution prevention techniques to reduce or eliminate the
generation and release of persistent organic pollutants. Possible measures include:
4.1.1.
Presorting of feed material
The presence of oils, plastics and chlorine compounds in the feed material should be avoided to
reduce the generation of PCDD/PCDF during incomplete combustion or by de novo synthesis.
Feed material should be classified according to composition and possible contaminants. Storage,
handling and pretreatment techniques will be determined by feed size distribution and
contamination.
Methods to be considered are (European Commission 2001, p. 232):

Oil removal from feed (for example, thermal decoating and de-oiling processes followed
by afterburning to destroy any organic material in the off-gas);

Use of milling and grinding techniques with good dust extraction and abatement. The
resulting particles can be treated to recover valuable metals using density or pneumatic
separation;

Elimination of plastic by stripping cable insulation (for example, possible cryogenic
techniques to make plastics friable and easily separable);

Sufficient blending of material to provide a homogeneous feed in order to promote steadystate conditions.
Additional techniques for oil removal are solvent use and caustic scrubbing. Cryogenic stripping
can be used to remove cable coatings.
4.1.2.
Effective process control
Process control systems should be utilized to maintain process stability and operate at parameter
levels that will contribute to the minimization of PCDD/PCDF generation, such as maintaining
furnace temperature above 850 °C to destroy PCDD/PCDF. Ideally, PCDD/PCDF emissions would
be monitored continuously to ensure reduced releases. Continuous emissions sampling of
PCDD/PCDF has been demonstrated for some sectors (for example, waste incineration), but
research is still ongoing for applications to other sources. In the absence of continuous
PCDD/PCDF monitoring, other variables such as temperature, residence time, gas composition and
fume collection damper controls should be continuously monitored and maintained to establish
optimum operating conditions for the reduction of PCDD/PCDF emissions.
4.2.
Secondary measures
Secondary measures are pollution control techniques. These methods do not eliminate the
generation of contaminants, but serve as a means to contain, prevent or reduce emissions.
4.2.1.
Fume and gas collection
Air emissions should be controlled at all stages of the process, from material handling, smelting
and material transfer points, to limit potential emissions of PCDD/PCDF. Sealed furnaces are
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essential to contain fugitive emissions while permitting heat recovery and collecting off-gases for
process recycling. Proper design of hooding and ductwork is essential to trap fumes. Furnace or
reactor enclosures may be necessary. If primary extraction and enclosure of fumes is not possible,
the furnace should be enclosed so that ventilation air can be extracted, treated and discharged.
Roofline collection of fume should be avoided due to high energy requirements. The use of
intelligent damper controls can improve fume capture, reduce fan sizes and hence costs. Sealed
charging cars or skips used with a reverberatory furnace can significantly reduce fugitive emissions
to air by containing emissions during charging (European Commission 2001, p. 187–188).
4.2.2.
High-efficiency dust removal
The smelting process generates large quantities of particulate matter with high surface area on
which PCDD/PCDF can adsorb. These dusts with their associated metal compounds should be
removed to reduce PCDD/PCDF emissions. Fabric filters are the most effective technique,
although wet or dry scrubbers and ceramic filters can also be considered. Collected dust must be
treated in high-temperature furnaces to destroy PCDD/PCDF and recover metals.
Fabric filter operations should be constantly monitored by devices to detect bag failure. Other
relevant technology developments include online cleaning methods and use of catalytic coatings to
destroy PCDD/PCDF (European Commission 2001, p. 139–140).
4.2.3.
Afterburners and quenching
Afterburners (used post-combustion) should be operated at a minimum temperature of 950 °C to
ensure full combustion of organic compounds (Hübner et al. 2000). This stage is to be followed by
rapid quenching of hot gases to temperatures below 250 °C. Oxygen injection in the upper portion
of the furnace will also promote complete combustion (European Commission 2001, p. 189).
It has been observed that PCDD/PCDF are formed, on a net basis, in the temperature range of 250
to 500 °C. They are destroyed above 850 °C in the presence of oxygen. Howerver, de novo
synthesis remains possible as the gases are cooled through the reformation window present in
abatement systems and cooler areas of the furnace if the necessary precursors and metal catalysts
are still present. Proper operation of cooling systems to minimize the time during which exhaust
gases are within the de novo synthesis temperature range should be implemented (European
Commission 2001, p. 133).
4.2.4.
Adsorption on activated carbon
Activated carbon treatment should be considered for PCDD/PCDF removal from smelter off-gases.
Activated carbon possesses a large surface area on which PCDD/PCDF can be adsorbed. Off-gases
can be treated with activated carbon using fixed or moving bed reactors, or by injection of carbon
particulate into the gas stream followed by removal as a filter dust using high-efficiency dust
removal systems such as fabric filters.
5.
Emerging research
5.1.
Catalytic oxidation
Catalytic oxidation is an emerging technology used in waste incinerators to eliminate PCDD/PCDF
emissions. This process should be considered by secondary base metals smelters as it has proven
effective for PCDD/PCDF destruction in waste incinerators. However, catalytic oxidation can, be
subject to poisoning from trace metals and other exhaust gas contaminants.; Validation work would
be necessary before use of this process.
Catalytic oxidation processes organic compounds into water, carbon dioxide (CO2) and
hydrochloric acid using a precious metal catalyst to increase the rate of reaction at 370 to 450 °C.
In comparison, incineration occurs typically at 980 °C. Catalytic oxidation has been shown to
destroy PCDD/PCDF with shorter residence times, lower energy consumption and >99%
efficiency. Particulate matter should be removed from exhaust gases prior to catalytic oxidation for
optimum efficiency. This method is effective for the vapour phase of contaminants. The resulting
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
hydrochloric acid is treated in a scrubber while the water and CO2 are released to the air after
cooling (Parvesse 2001).
Fabric filters used for dust removal can also be treated with a catalytic coating to promote oxidation
of organic compounds at elevated temperature.
6.
Summary of measures
Table 1. Measures for recommended processes for new secondary copper smelters
Measure
Description
Recommended
processes
Various
recommended
smelting processes
should be
considered for new
facilities
Considerations
Processes to consider include:
 Blast furnace, mini-smelter, topblown rotary furnace, sealed
submerged electric arc furnace,
ISA smelt, and the Pierce-Smith
converter
 Reverberatory hearth furnace,
the hearth shaft furnace and
Contimelt process to treat clean
copper scrap devoid of organic
contamination
Other comments
These are considered to be best
available techniques in
configuration with suitable gas
collection and abatement.
The submerged electric arc
furnace is sealed and can be
cleaner than other designs if the
gas extraction system is
adequately designed and sized
Table 2. Summary of primary and secondary measures for secondary copper smelters
Measure
Description
Considerations
Other comments
Primary measures
Presorting of
feed material
Effective process
control
The presence of oils,
plastics and chlorine
compounds in the feed
material should be avoided
to reduce the generation of
PCDD/PCDF during
incomplete combustion or
by de novo synthesis
Processes to consider include:
Process control systems
should be utilized to
maintain process stability
and operate at parameter
levels that will contribute
to the minimization of
PCDD/PCDF generation
PCDD/PCDF emissions may be
minimized by controlling other
variables such as temperature,
residence time, gas composition
and fume collection damper
controls after having established
optimum operating conditions for
the reduction of PCDD/PCDF
Continuous emissions
sampling of PCDD/PCDF
has been demonstrated for
some sectors (for example,
waste incineration), but
research is still ongoing
for applications to other
sources
Processes to consider include:
Roofline collection of
fume is to be avoided due
to high energy
requirements
 Oil removal from feed
material
 Use of milling and grinding
techniques with good dust
extraction and abatement
Thermal decoating and deoiling processes for oil
removal should be
followed by afterburning
to destroy any organic
material in the off-gas
 Elimination of plastic by
stripping cable insulation
Secondary measures
Fume and gas
collection
Effective fume and off-gas
collection should be
implemented in all stages
of the smelting process to
capture PCDD/PCDF
emissions
Guidelines on BAT and Guidance on BEP
 Sealed furnaces to contain
fugitive emissions while
permitting heat recovery and
collecting off-gases. Furnace
or reactor enclosures may be
Environment Canada Revision, April 28, 2006
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Measure
Description
Considerations
15
Other comments
necessary
 Proper design of hooding and
ductwork to trap fumes
High-efficiency
dust removal
Afterburners and
quenching
Dusts and metal
compounds should be
removed as this material
possesses high surface
area on which
PCDD/PCDF easily
adsorb. Removal of these
dusts would contribute to
the reduction of
PCDD/PCDF emissions
Processes to consider include:
Afterburners should be
used at temperatures > 950
°C to ensure full
combustion of organic
compounds, followed by
rapid quenching of hot
gases to temperatures
below 250 °C
Considerations include:
 Fabric filters (most effective
method)
 Wet/dry scrubbers and
ceramic filters
 PCDD/PCDF formation at
250–500 °C, and destruction >
850 °C with O2
Dust removal is to be
followed by afterburners
and quenching.
Collected dust must be
treated in high-temperature
furnaces to destroy
PCDD/PCDF and recover
metals
De novo synthesis is still
possible as the gases are
cooled through the
reformation window
 Requirement for sufficient O2
in the upper region of the
furnace for complete
combustion
 Need for proper design of
cooling systems to minimize
reformation time
Adsorption on
activated carbon
Activated carbon treatment
should be considered as
this material possesses
large surface area on
which PCDD/PCDF can
be adsorbed from smelter
off-gases
Processes to consider include:
Catalytic oxidation is an
emerging technology for
sources in this sector
(demonstrated technology
for incinerator
applications) which
should be considered due
to its high efficiency and
lower energy
consumption. Catalytic
oxidation transforms
organic compounds into
water, CO2 and
hydrochloric acid using a
precious metal catalyst
Considerations include:
 Treatment with activated
carbon using fixed or moving
bed reactors
Lime/carbon mixtures can
also be used
 Injection of powdered carbon
into the gas stream followed
by removal as a filter dust
Emerging research
Catalytic
oxidation
7.
 Process efficiency for the
vapour phase of contaminants
 Hydrochloric acid treatment
using scrubbers while water
and CO2 are released to the air
after cooling
Catalytic oxidation has
been shown to destroy
PCDD/PCDF with shorter
residence times, lower
energy consumption and
>99% efficiency.
Particulate matter should
be removed from -exhaust
gases prior to catalytic
oxidation for optimum
efficiency
Achievable performance levels
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
16
SECTION V. Guidelines/guidance by source category: Part II of Annex C
The achievable performance level2 for emissions of PCDD/PCDF from secondary copper smelters
is < 0.5 ng I-TEQ/Nm3.
References
A.J. Gunson, Yue Jian, Artisanal Mining in The People's Republic of China, Mining,
Minerals and Sustainable Development (MMSD), International Institute for Environment
and Development (IIED), September 2001
EPA (United States Environmental Protection Agency). 1995. Secondary Copper Smelting,
Refining and Alloying. Background Report AP-42, Section 12.9.
www.epa.gov/ttn/chief/ap42/ch12/final/c12s09.pdf.
European Commission. 2001. Reference Document on Best Available Techniques in the NonFerrous Metals Industries. BAT Reference Document (BREF). European IPPC Bureau, Seville,
Spain. eippcb.jrc.es.
Feng Xinbin, Qui Guangle, Li Guanghui, Li Ping, Wang Shaofeng, Mercury Emissions
from Artisanal Zinc and Mercury Smelting in Guizhou, PR China, Goldschmidt
Conference Abstracts 2005, The Geochemistry of Mercury, page A705
Hübner C., Boos R., Bohlmann J., Burtscher K. and Wiesenberger H. 2000. State-of-the-Art
Measures for Dioxin Reduction in Austria. Vienna.
www.ubavie.gv.at/publikationen/Mono/M116s.htm.
Parvesse T. 2001. “Controlling Emissions from Halogenated Solvents.” Chemical
Processing [Chem. Process.]. Vol. 64, no. 4, pp. 48-51. Apr 2001Personal communication from
Expert Group Best Available Techniques Best Environmental Practices, Finland Member,
February 2006
Personal communication, Member, Japan, Expert Group Meeting, 1 December, 2006
UNEP, Compilation of comments received from Parties and others on the draft Guidelines on Best
Available Techniques and provisional Guidance on Best Environmental Practices, October 14,
2005
http://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5
.pdf
UNEP Environment Program News Centre,
http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=
3204&l=en, as read on January 20, 2006
UNEP Environment Program News Centre,
http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=
3204&l=en, as read on January 20, 2006
Xinbin Feng, Xianwu Bi, Guangle Qiu, Guanghui Li, Shunlin Tang, Mercury Pollution in
Guizhou, China - A status Report,
http://pbc.eastwestcenter.org/abstracts2005/abstract2005fengxinbin.htm, as read on
December 29th, 2005
2
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0 °C
and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present guidelines. The
operating oxygen concentration conditions of exhaust gases are used for metallurgical sources.
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
SECTION V. Guidelines/guidance by source category: Part II of Annex C
(ii)
17
Sinter plants in the iron and steel industry
Summary
Sinter plants in the iron and steel industry are a pretreatment step in the production of iron
whereby fine particles of iron ores and, in some plants, secondary iron oxide wastes (collected
dusts, mill scale) are agglomerated by combustion. Sintering involves the heating of fine iron
ore with flux and coke fines or coal to produce a semi-molten mass that solidifies into porous
pieces of sinter with the size and strength characteristics necessary for feeding into the blast
furnace.
PCDD and PCDF appear to be formed in the iron sintering process via de novo synthesis.
PCDF generally dominate in the waste gas from sinter plants. The PCDD/PCDF formation
mechanism appears to start in the upper regions of the sinter bed shortly after ignition, and then
the dioxins, furans and other compounds condense on cooler burden beneath as the sinter layer
advances along the sinter strand towards the burn-through point.
Primary measures identified to prevent or minimize the formation of PCDD/PCDF during iron
sintering include the stable and consistent operation of the sinter plant, continuous parameter
monitoring, recirculation of waste gases, minimization of feed materials contaminated with
persistent organic pollutants or contaminants leading to formation of such pollutants, and feed
material preparation.
Secondary measures identified to control or reduce releases of PCDD/PCDF from iron sintering
include adsorption/absorption (for example, activated carbon injection) and high-efficiency
dedusting, as well as fine wet scrubbing of waste gases combined with effective treatment of
the scrubber waste waters and disposal of waste-water sludge in a secure landfill.
The achievable performance level for an iron sintering plant operating according to best
available techniques: < 0.2 ng TEQ/Nm3.
1.
Process description
Iron sintering plants are associated with the manufacture of iron and steel, often in integrated steel
mills. The sintering process is a pretreatment step in the production of iron whereby fine particles
of iron ores and, in some plants, secondary iron oxide wastes (collected dusts, mill scale) are
agglomerated by combustion. Agglomeration of the fines is necessary to enable the passage of hot
gases during the subsequent blast furnace operation (UNEP 2003, p. 60).
Sintering involves the heating of fine iron ore with flux and coke fines or coal to produce a semimolten mass that solidifies into porous pieces of sinter with the size and strength characteristics
necessary for feeding into the blast furnace. Moistened feed is delivered as a layer onto a
continuously moving grate or strand. The surface is ignited with gas burners at the start of the
strand and air is drawn through the moving bed, causing the fuel to burn. Strand velocity and gas
flow are controlled to ensure that burn-through (i.e., the point at which the burning fuel layer
reaches the base of the strand) occurs just prior to the sinter being discharged. The solidified sinter
is then broken into pieces in a crusher and is air cooled. Product outside the required size range is
screened out, oversize material is recrushed, and undersize material is recycled back to the process.
Sinter plants that are located in a steel plant recycle iron ore fines from the raw material storage and
handling operations and from waste iron oxides from steel plant operations and environmental
control systems. Iron ore may also be processed in on-site sinter plants (Environment Canada 2001,
p. 18).
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
18
SECTION V. Guidelines/guidance by source category: Part II of Annex C
A blast furnace is a vertical furnace using tuyeres to blast heated or cold air into the
furnace burden to smelt the contents. Sinter is charged into the top of the blast furnace in
alternating layers with coke.
The flexibility of the sintering process permits conversion of a variety of materials, including iron
ore fines, captured dusts, ore concentrates, and other iron-bearing materials of small particle size
(for example, mill scale) into a clinker-like agglomerate (Lankford et al. 1985, p. 305–306).
Waste gases are usually treated for dust removal in a cyclone, electrostatic precipitator, wet
scrubber or fabric filter.
Figure 1 provides a schematic of an iron sintering plant using a wet scrubbing system.
It has been suggested that this diagram does not represent the entire steel industry regarding
secondary sinter off-gas cleaning; that wet scrubbing systems will be shut down and replaced by
fabric filters with injection of hydrated lime / activated carbon / zeolite etc.; and that due to
problems and the costs of the waste water treatment this process can only be used effectively where
the waste water (after filtering and dilution to the salt concentration of the sea water) may be
released to the ocean (Personal Communication, February 2006).
Figure 1. Process diagram of a sinter plant using a web scrubbing system
Water
Sinter Machine
ESP
Mashing Stage
Main Fan
Emission
Monitoring
Quench
Fine Scrubbers
Mashing
Water
Sludge
Water
Process Air
Fan
Recycling
Fe-Components
Water
Nat.
Gas
Reheating
Discharge
Water
Water
Treatment
Slag
Immobilisation
Thickener
Sludge Tank
Floating Sludge
to BF
Sludge
Depot
Cleaned Water
Source: Hofstadler et al. 2003.
2.
Sources of chemicals listed in Annex C of the Stockholm
Convention
As regards emissions of chemicals listed in Annex C of the Stockholm Convention, iron sintering
has been identified as a source of PCDD and PCDF. The formation and release of
hexachlorobenzene (HCB) and polychlorinated biphenyls (PCB) are less understood from this
potential source.
2.1.
2.1.1.
Releases to air
General information on emissions from iron sintering plants
The following information is drawn from Environment Canada 2001, p. 23–25.
Guidelines on BAT and Guidance on BEP
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
19
“Emissions from the sintering process arise primarily from materials-handling operations,
which result in airborne dust, and from the combustion reaction on the strand. Combustion
gases from the latter source contain dust entrained directly from the strand along with
products of combustion such as CO, CO2, SOx, NOx, and particulate matter. The
concentrations of these substances vary with the quality of the fuel and raw materials used
and combustion conditions. Atmospheric emissions also include volatile organic
compounds (VOCs) formed from volatile material in the coke breeze, oily mill scale, etc.,
and dioxins and furans, formed from organic material under certain operating conditions.
Metals are volatilized from the raw materials used, and acid vapours are formed from the
halides present in the raw materials.
Combustion gases are most often cleaned in electrostatic precipitators (ESPs), which
significantly reduce dust emissions but have minimal effect on the gaseous emissions.
Water scrubbers, which are sometimes used for sinter plants, may have lower particulate
collection efficiency than ESPs but higher collection efficiency for gaseous emissions.
Significant amounts of oil in the raw material feed may create explosive conditions in the
ESP. Sinter crushing and screening emissions are usually controlled by ESPs or fabric
filters. Wastewater discharges, including runoff from the materials storage areas, are
treated in a wastewater treatment plant that may also be used to treat blast furnace
wastewater.
Solid wastes include refractories and sludge generated by the treatment of emission control
system water in cases where a wet emission control system is used. Undersize sinter is
recycled to the sinter strand.”
2.1.2.
Emissions of PCDD and PCDF
(William Lemmon and Associates Ltd. 2004, p. 20–21)
The processes by which PCDD/PCDF are formed are complex. PCDD/PCDF appear to be formed
in the iron sintering process via de novo synthesis. PCDF generally dominate in the waste gas from
sinter plants.
The PCDD/PCDF formation mechanism appears to start in the upper regions of the sinter bed
shortly after ignition, and then the dioxin/furan and other compounds condense on cooler burden
beneath as the sinter layer advances along the sinter strand towards the burn-through point. The
process of volatilization and condensation continues until the temperature of the cooler burden
beneath rises sufficiently to prevent condensation and the PCDD/PCDF exit with the flue gas. This
appears to increase rapidly and peak just before burn-through and then decrease rapidly to a
minimum. This is supported by the dioxin/furan profile compared to the temperature profile along
the sinter strand in several studies.
The quantity of PCDD and PCDF formed has been shown to increase with increasing carbon and
chlorine content. Carbon and chloride are present in some of the sinter feed materials typically
processed through a sinter plant.
2.1.3.
Research findings of interest
It appears that the composition of the feed mixture has an impact on the formation of PCDD/PCDF,
i.e., increased chlorine content results in increased PCDD/PCDF formation while the replacement
of coke as a fuel with anthracite coal appears to reduce PCDD/PCDF concentration.
The form of the solid fuel may also impact furan emissions. Coal, graphite, and activated coke in a
Japanese laboratory research programme reduced pentachlorinated dibenzofuran emissions by
approximately 90%.
The operating parameters of the sintering process appear to have an impact on the
formation of PCDD/PCDF. (William Lemmon and Associates Ltd. 2004)
2.2.
Releases to other media
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Environment Canada Revision, April 28, 2006
20
SECTION V. Guidelines/guidance by source category: Part II of Annex C
No information was identified on releases of chemicals listed in Annex C from iron sintering
operations to other media such as through waste water or collected dusts.
3.
Alternatives
In accordance with the Stockholm Convention, when consideration is being given to proposals for
construction of a new iron sintering plant, priority consideration should be given to alternative
processes, techniques or practices that have similar usefulness but avoid the formation and release
of chemicals listed in Annex C. Adoption of alternative processes, techniques or practices can
have implications on other parts of the mill, careful assessment is needed on a case by case basis.
Alternative processes to iron sintering include:
4.

Direct reduction processes: This technique, also known as Direct Reduction Iron (DRI) or
Hot Briquetted Iron (HBI), processes iron ore to produce a direct reduced iron product that
can be used as a feed material to steel-manufacturing electric arc furnaces, iron-making
blast furnaces, or steel-making basic oxygen furnaces. Natural gas is reformed to make
hydrogen and carbon dioxide, where hydrogen is the reductant used to produce the direct
reduced iron. The availability and cost of natural gas will impact the feasibility of using
this technique. Two new direct reduction processes for iron ore fines, Circored® and
Circofer® are available. Both processes use a proven two-stage configuration, combining a
Circulating Fluidized Bed (CFB) with a bubbling Fluidized Bed (FB). The Circored
process uses hydrogen as reductant. The first-of-its-kind Circored plant was built in
Trinidad for the production of 500,000 t/a of HBI and commissioned in 1999. In the
Circofer process, coal is used as reductant. (Personal Communication, February 2006). In
some direct reduction process systems (eg. FASTMET®), various carbon sources can be
used as the reductant. Examples of carbon sources that may be used include: coal, coke
breeze and carbon bearing steeel mill wastes (blast furnace dust, sludge, BOF dust, mill
scale, EAF dust, sinter dust). This process converts iron oxide pellet feed, oxide fines,
and/or steel mill wastes into metallic iron, and produces a direct reduced iron product
suitable for use in a blast furnace. Emission concentration of PCDD and PCDF from this
process is reported to be < 0.1 ng TEQ/m3.4

Direct smelting processes: Direct smelting replaces the traditional combination of sinter
plant, coke oven and blast furnace to produce molten iron. A number of direct smelting
processes are evolving and are at various stages of development and commercialization.
Primary and secondary measures
Primary and secondary measures for reducing emissions of PCDD and PCDF from iron sintering
processes are outlined below. Much of this material has been drawn from William Lemmon and
Associates Ltd. 2004.
The extent of emission reduction possible with implementation of primary measures only is not
readily known. It is therefore recommended that consideration be given to implementation of both
primary and secondary measures at existing plants.
4.1.
Primary measures
Primary measures are understood to be pollution prevention measures that will prevent or minimize
the formation and release of chemicals listed in Annex C. These are sometimes referred to as
process optimization or integration measures. Pollution prevention is defined as: “The use of
processes, practices, materials, products or energy that avoid or minimize the creation of
4
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0 °C
and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present guidelines.
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
SECTION V. Guidelines/guidance by source category: Part II of Annex C
21
pollutants and waste, and reduce overall risk to human health or the environment” (see section
III.B of the present guidelines).
Primary measures have been identified that may assist in preventing and minimizing the formation
and release of chemicals listed in Annex C. Emission reductions associated with implementation of
the following primary measures only is not known. It is recommended that the following measures
be implemented together with appropriate secondary measures to ensure the greatest minimization
and reduction of emissions possible. Identified primary measures include the following:
4.1.1.
Stable and consistent operation of the sinter strand
Research has shown that PCDD/PCDF are formed in the sinter bed itself, probably just ahead of
the flame front as the hot gases are drawn through the bed. Disruptions to flame front (i.e., nonsteady-state conditions) have been shown to result in higher PCDD/PCDF emissions.
Sinter strands should be operated to maintain consistent and stable process conditions (i.e., steadystate operations, minimization of process upsets) in order to minimize the formation and release of
PCDD, PCDF and other pollutants. Operating conditions requiring consistent management include
strand speed, bed composition (consistent blending of revert materials, minimization of chloride
input), bed height, use of additives (for example, addition of burnt lime may help reduce
PCDD/PCDF formation), minimization of oil content in mill scale, minimization of air in-leakage
through the strand, ductwork and off-gas conditioning systems, and minimization of strand
stoppages. This approach will also result in beneficial operating performance improvements (for
example, productivity, sinter quality, energy efficiency) (European Commission 2000, p. 47; IPPC
2001, p. 39).
4.1.2.
Continuous parameter monitoring
A continuous parameter monitoring system should be employed to ensure optimum operation of
the sinter strand and off-gas conditioning systems. Various parameters are measured during
emission testing to determine the correlation between the parameter value and the stack emissions.
The identified parameters are then continuously monitored and compared to the optimum
parameter values. Variances in parameter values can be alarmed and corrective action taken to
maintain optimum operation of the sinter strand and emission control system.
Operating parameters to monitor may include damper settings, pressure drop, scrubber water flow
rate, average opacity and strand speed.
Operators of iron sintering plants should prepare a site-specific monitoring plan for the continuous
parameter monitoring system that addresses installation, performance, operation and maintenance,
quality assurance and record keeping, and reporting procedures. Operators should keep records
documenting conformance with the identified monitoring requirements and the operation and
maintenance plan (EPA 2003).
4.1.3.
Recirculation of off-gases
Recycling of sinter off-gas (waste gas) has been shown to minimize pollutant emissions, and
reduce the amount of off-gas requiring end-of-pipe treatment. Recirculation of part of the off-gas
from the entire sinter strand, or sectional recirculation of off-gas, can minimize formation and
release of pollutants. For further information on this technique see ECSC 2003 and European
Commission 2000, p. 56–62.
Recycling of iron sintering off-gases can reduce emissions of PCDD/PCDF, NOx and SO2.
4.1.4.
Feed material selection
Unwanted substances should be minimized in the feed to the sinter strand. Unwanted substances
include persistent organic pollutants and other substances associated with the formation of
PCDD/PCDF, HCB and PCB (for example, chlorine/chlorides, carbon, precursors and oils).
A review of feed inputs should be conducted to determine their composition, structure, and
concentration of substances associated with persistent organic pollutants and their formation.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Options to eliminate or reduce the unwanted substances in the feed material should be identified.
For example:

Removal of the contaminant from the material (for example, de-oiling of mill scales);

Substitution of the material (for example, replacement of coke breeze with anthracite);

Avoidance of the use of the contaminated material (for example, avoid processing
electrostatic precipitator sinter dusts, which have been shown to increase PCDD/PCDF
formation and release) (Kasai et al. 2001);

Specification of limits on permissible concentrations of unwanted substances (for example,
oil content in feed should be limited to less than 0.02%) (EPA 2003).
Documented procedures should be developed and implemented to carry out the appropriate
changes.
4.1.5.
Feed material preparation
Fine feed materials (for example, collected dusts) should be adequately agglomerated before they
are placed on the sinter strand and feed materials should be intimately mixed or blended. These
measures will minimize formation and entrainment of pollutants in the waste gas, and will also
minimize fugitive emissions.
4.1.6.
Urea injection
Tests using urea injection to suppress formation of dioxins and furans have been conducted at an
iron sintering plant in the United Kingdom. Controlled quantities of urea prills were added to the
sinter strand, and this technique is thought to prevent or reduce both PCDD/PCDF and sulphur
dioxide emissions. The trials indicate that PCDD/PCDF formation was reduced by approximately
50%. It is estimated that a 50% reduction in PCDD/PCDF would achieve a 0.5 ng TEQ/m3
emission concentration. Capital costs are estimated at UK£0.5 to £1.0 million per plant
(approximately US$0.9 million to $1.8 million) (Entec UK Ltd. 2003, p. D10–D20).
At Canada’s only sinter plant, operated by Stelco Inc. in Hamilton, Ontario, trials have been
completed using a new similar process in order to reduce dioxins emissions. Stelco found that
sealing the furnace to reduce the amount of oxygen and adding a small amount of urea interfered
with the chemical reaction that produces dioxins, resulting in reduced emissions. This new process
configuration, combined with air-scrubbing systems released 177 pg/m3 of dioxins in a test. This
result surpasses the 2005 Canada-wide Standard limit of 500 pg/Rm3 and is below the 200 pg/Rm3
limit for 2010. It also represents a 93% reduction from the 1998 measured levels of 2700 pg/Rm3.
The improvement clearly does not depend on scrubbing dioxins out of the stack gases, but is
thought to result from "true pollution prevention", as chlorine is needed to produce dioxins and the
urea releases ammonia, which captures chlorides in the dust, reducing its availability for dioxin
formation. (The Hamilton Spectator, March 1, 2006)
4.2.
Secondary measures
Secondary measures are understood to be pollution control technologies or techniques, sometimes
described as end-of-pipe treatments.
Primary measures identified earlier should be implemented together with appropriate secondary
measures to ensure the greatest minimization and reduction of emissions possible. Measures that
have been shown to effectively minimize and reduce PCDD and PCDF emissions include:
4.2.1.
4.2.1.1.
Removal techniques
Adsorption/absorption and high-efficiency dedusting
This technique involves sorption of PCDD/PCDF to a material such as activated carbon, together
with effective particulate matter (dedusting) control.
Guidelines on BAT and Guidance on BEP
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
23
For regenerative activated carbon technology (William Lemmon and Associates Ltd. 2004) an
electrostatic precipitator is used to reduce dust concentration in the off-gases prior to entry to the
activated carbon unit. The waste gas passes through a slowly moving bed of char granules which
acts as a filter/adsorption medium. The used char is discharged and transferred to a regenerator,
where it is heated to elevated temperatures. PCDD/PCDF adsorbed to the char are decomposed and
destroyed within the inert atmosphere of the regenerator. This technique has been shown to reduce
emissions to 0.1 to < 0.3 ng TEQ/m3.
Another sorption technique is the use of lignite or activated carbon injection, together with a fabric
filter. PCDD/PCDF are sorbed onto the injected material, and the material is collected in the fabric
filter. Along with good operation of the sinter strand, this technique is associated with
PCDD/PCDF emission concentrations ranging from 0.1 to 0.5 ng TEQ/m3 (IPPC 2001, p. 135).
4.2.1.2.
Fine wet scrubbing system
The Airfine scrubbing system, developed by Voest Alpine Industries (Austria), has been shown to
effectively reduce emission concentrations to 0.2 to 0.4 ng TEQ/m3. The scrubbing system uses a
countercurrent flow of water against the rising waste gas to scrub out coarse particles and gaseous
components (for example, sulphur dioxide (SO2)), and to quench the waste gas. (An electrostatic
precipitator may also be used upstream for preliminary dedusting.) Caustic soda may be added to
improve SO2 absorption. A fine scrubber, the main feature of the system, follows, employing highpressure mist jet co-current with the gas flow to remove impurities. Dual flow nozzles eject water
and compressed air (creating microscopic droplets) to remove fine dust particles, PCDD and PCDF
(William Lemmon and Associates Ltd. 2004, p. 29–30; European Commission 2000, p. 72–74).
This technique should be combined with effective treatment of the scrubber waste waters and
waste-water sludge should be disposed of in a secure landfill (European Commission 2000).
4.2.2.
General measures
The following measures can assist in minimizing pollutant emissions, but should be combined with
other measures (for example, adsorption/absorption, recirculation of off-gases) for effective control
of PCDD/PCDF formation and release.
4.2.2.1.
Removal of particulate matter from the sinter off-gases
It has been suggested that effective removal of dust can help reduce emissions of PCDD and
PCDF. Fine particles in the sinter off-gas have an extremely large surface area for adsorption and
condensation of gaseous pollutants, including PCDD and PCDF (Hofstadler et al. 2003). The best
available technique for removal of particulate matter is the use of fabric filters. Fabric filters used
at sinter plants are associated with particulate matter emission concentrations of < 10 to < 30
mg/m3 (UNECE 1998; IPPC 2001, p. 131).
Other particulate control options that are commonly used for sinter plant off-gases include
electrostatic precipitators and wet scrubbers, however their particulate removal efficiencies are not
as high as for fabric filters. Good performance of electrostatic precipitators and high-efficiency wet
gas scrubbers is associated with particulate matter concentrations of < 30 to 50 mg/m3 (IPPC 2001;
William Lemmon and Associates Ltd. 2004, p. 26; UNECE 1998).
Adequately sized capture and particulate emission controls for both the feed and discharge ends
should be required and put in place.
4.2.2.2.
Hooding of the sinter strand
Hooding of the sinter strand reduces fugitive emissions from the process, and enables use of other
techniques, such as waste gas recirculation.
5.
Emerging research
5.1.
Catalytic oxidation
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Selective catalytic reduction has been used for controlling NOx emissions from a number of
industrial processes, including iron sintering. Modified selective catalytic reduction technology
(i.e., increased reactive area) and select catalytic processes have been shown to decompose PCDD
and PCDF contained in off-gases, probably through catalytic oxidation reactions. This may be
considered an emerging technique with potential for reducing emissions of persistent organic
pollutants from iron sintering plants and other applications.
A study investigating stack emissions from four sinter plants noted lower concentrations of
PCDD/PCDF (0.995 – 2.06 ng TEQ/Nm3) in the stack gases of sinter plants with selective catalytic
reduction than a sinter plant without (3.10 ng TEQ/Nm3), and that the PCDD/PCDF degree of
chlorination was lower for plants with selective catalytic reduction. It was concluded that selective
catalytic reduction did indeed decompose PCDD/PCDF, but would not necessarily be sufficient as
a stand alone PCDD/PCDF destruction technology to meet stringent emission limits. Add-on
techniques (for example, activated carbon injection) may be required (Wang et al. 2003, p. 1123–
1129).
Catalytic oxidation can, subject to catalyst selection, be subject to poisoning from trace metals and
other exhaust gas contaminants. Validation work would be necessary before use of this process.
Further study of the use of selective catalytic reduction and other catalytic oxidation techniques at
iron sintering applications is needed to determine its value and effectiveness in destroying and
reducing PCDD/PCDF released from this source.
6.
Summary of measures
Tables 1 and 2 present a summary of the measures discussed in previous sections.
Table 1. Alternatives and requirements for new iron sintering plants
Measure
Alternative
processes
Description
Priority consideration should
be given to alternative
processes with potentially less
environmental impacts than
traditional iron sintering
Considerations
Other comments
Examples include:
 Pelletisation Plants
 Direct reduction of iron
(FASTMET®,
Circored® and
Circofer®)
 Direct smelting
Performance
requirements
New iron sintering plants
should be permitted to
achieve stringent performance
and reporting requirements
associated with best available
techniques
Consideration should be
given to the primary and
secondary measures listed
in Table 2 below
Performance requirements
for achievement should
include:
< 0.2 ng TEQ/Rm3 for
PCDD/PCDF
< 20 mg/Rm3 for particulate
matter
Table 2. Summary of primary and secondary measures for iron sintering plants
Measure
Description
Considerations
Other comments
Primary measures
Stable and
consistent
operation of the
sinter plant
The sinter strand should be
operated to maintain stable
consistent operating
conditions (e.g., steady-state
conditions, minimization of
Guidelines on BAT and Guidance on BEP
Conditions to optimize
operation of the strand
include:
 Minimization of
This approach will have
co-benefits such as
increased productivity,
increased sinter quality
and improved energy
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Measure
Description
process upsets) to minimize
formation of PCDD, PCDF
and other pollutants
Considerations
stoppages
25
Other comments
efficiency
 Consistent strand speed
 Bed composition
 Bed height
 Additives (e.g., burnt
lime)
 Minimization of oil
content
 Minimization of air inleakage
Continuous
parameter
monitoring
A continuous parameter
monitoring system should be
employed to ensure optimum
operation of the sinter strand
and off-gas conditioning
systems.
Operators should prepare a
site-specific monitoring plan
for the continuous parameter
monitoring system and keep
records that document
conformance with the plan
Correlations between
parameter values and stack
emissions (stable operation)
should be established.
Parameters are then
continuously monitored in
comparison to optimum
values. System can be
alarmed and corrective
action taken when
significant deviations occur
Recirculation of
waste gases
Waste gases should be
recycled back to the sinter
strand to minimize pollutant
emissions and reduce the
amount of off-gas requiring
end-of-pipe treatment
Recirculation of the waste
gases can entail recycling of
part of the off-gas from the
entire sinter strand, or
sectional recirculation of offgas
Feed material
selection:
Minimization of
feed materials
contaminated
with persistent
organic
pollutants or
leading to their
formation
A review of feed materials and
identification of alternative
inputs and/or procedures to
minimize unwanted inputs
should be conducted.
Documented procedures
should be developed and
implemented to carry out the
appropriate changes
Examples include:
This technique will result
in only a modest
reduction of
PCDD/PCDF
 Removal of the
contaminant from the
material (e.g., de-oiling
of mill scales)
 Substitution of the
material (e.g.,
replacement of coke
breeze with anthracite)
 Avoid use of the material
(e.g., collected sinter
electrostatic precipitator
dust)
 Specification of limits on
permissible
concentrations of
unwanted substances
(e.g., oil content in feed
should be limited to less
than 0.02%)
Feed material
preparation
Fine material (e.g., collected
dusts) should be agglomerated
before being placed on the
Guidelines on BAT and Guidance on BEP
These measures will help
reduce entrainment of
pollutants in the waste
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Measure
Description
Considerations
sinter strand. Feed materials
should be intimately mixed
before placement on the sinter
strand
Other comments
gas, and minimize
fugitive emissions
Secondary measures
The following secondary measures can effectively reduce emissions of PCDD/PCDF and should be
considered as examples of best available techniques
Adsorption/
absorption and
high-efficiency
dedusting
Use of this technique should
include an adsorption stage
together with high-efficiency
particulate control as key
components of the off-gas
conditioning system
Two adsorption techniques
have been demonstrated:
 Regenerative activated
carbon technology
whereby off-gases are
first cleaned by
electrostatic precipitator,
and passed through
moving adsorption bed
(char) to both adsorb
PCDD/PCDF and to
filter particulates.
Adsorptive material is
then regenerated
These techniques are
associated with the
following emission
concentration levels:
< 0.3 ng TEQ/m3
0.1 to 0.5 ng TEQ/ m3
 Injection of activated
carbon, lignite or other
similar adsorptive
material into the gas
stream followed by
fabric filter dedusting
Fine wet
scrubbing of
waste gases
Use of this technique should
include a preliminary
countercurrent wet scrubber to
quench gases and remove
larger particles, followed by a
fine scrubber using high
pressure mist jet co-current
with off-gases to remove fine
particles and impurities
The fine wet scrubbing
system under the trade
name Airfine®, as
developed by Voest
Alpine Industries, has
been shown to reduce
emission concentrations
to 0.2 to 0.4 ng TEQ/m3
The following secondary measures should not be considered best available techniques on their own. For
effective minimization and reduction of PCDD, PCDF and other persistent organic pollutants, the following
should be employed in concert with other identified measures
Removal of
particulate
matter from
waste gases
Waste gases should be treated
using high-efficiency
techniques, as this can help
minimize PCDD/PCDF
emissions. A recommended
best available technique for
particulate control is the use of
fabric filters.
Feed and discharge ends of the
sinter strand should be
adequately hooded and
controlled to capture and
Guidelines on BAT and Guidance on BEP
Fabric filters have been
shown to reduce sinter offgas particulate emissions to
< 10 to < 30 mg/m3
Other particulate control
techniques used include
electrostatic precipitators
and high-efficiency
scrubbers. Good
performance of these
technologies is associated
with particulate
concentrations of < 30 to
50 mg/m3
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Measure
Description
Considerations
27
Other comments
mitigate fugitive emissions
Hooding of the
sinter strand
7.
The sinter strand should be
hooded to minimize fugitive
process emissions
Hooding of the strand
will enable use of other
measures, such as waste
gas recirculation
Achievable performance levels
Achievable levels were identified for emissions of PCDD/PCDF only. No levels were identified for
other chemicals listed in Annex C or for releases to other media.
The achievable performance levels for emissions of PCDD/PCDF from iron sintering plants are
identified in Table 3.
Table 3. Achievable performance for emissions of PCDD/PCDF
Source type
Emission limit value5
New plants
< 0.2 ng TEQ/Nm3
Adsorption/absorption and high-efficiency dedusting
< 0.5 ng TEQ/Nm3
Fine wet scrubbing system
< 0.4 ng TEQ/Nm3
References
ECSC (European Coal and Steel Community). 2003. The Impact of ECSC Steel Research on Steel
Production and Sustainability. www.stahlonline.de/medien_lounge/medieninformationen/hintergrundmaterial.htm.
Entec UK Ltd. 2003. Development of UK Cost Curves for Abatement of Dioxins Emissions to Air,
Final Report. Draft for consultation, November 2003.
Environment Canada. 2001. Environmental Code of Practice for Integrated Steel Mills – CEPA
1999 Code of Practice. Public Works and Government Services, Canada.
EPA (United States Environmental Protection Agency). 2003. National Emission Standards for
Hazardous Air Pollutants: Integrated Iron and Steel Manufacturing: Final Rule. 40 CFR Part 63,
Federal Register 68:97. EPA, Washington, D.C. www.epa.gov.
European Commission. 2000. Reference Document on Best Available Techniques for the
Production of Iron and Steel. BAT Reference Document (BREF). European IPPC Bureau, Seville,
Spain. eippcb.jrc.es.
Hofstadler K. et al. 2003. Dioxin at Sinter Plants and Electric Arc Furnaces – Emission Profiles
and Removal Efficiency. Voest Alpine Indstrienlagenbau GmbH, Austria.
g5006m.unileoben.ac.at/downloads/Dioxin.doc.
IPPC (European Integrated Pollution Prevention and Control Bureau). 2001. Guidance for the
Coke, Iron and Steel Sector. Sector Guidance Note IPPC S2.01. UK Environment Agency.
5
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured
at 0 °C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present
guidelines. The operating oxygen concentration conditions of exhaust gases are used for metallurgical
sources.
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Kasai E. et al. 2001. “Effect of Additives on the Dioxins Emissions in the Iron Ore Sintering
Process.” ISIJ International 41:1.
Lankford W.T., Samways N.L., Craven R.F. and MacGannon H.E. (eds.) 1985. The Making,
Shaping and Treating of Steel. 10th Edition. Association of Iron and Steel Engineers, USA.
Personal communication from Expert Group Best Available Techniques Best Environmental
Practices, Finland Member, February 2006
The Hamilton Spectator, Canada. March 1, 2006
UNECE (United Nations Economic Commission for Europe). 1998. “Best Available Techniques
for Controlling Emission of Heavy Metals.” Annex III, Protocol to the 1979 Convention on LongRange Transboundary Pollution on Heavy Metals. UNECE, Geneva. www.unece.org.
UNEP (United Nations Environment Programme). 2003. Standardized Toolkit for Identification
and Quantification of Dioxin and Furan Releases. UNEP, Geneva.
www.pops.int/documents/guidance/Toolkit_2003.pdf.
UNEP, September 16, 2005. Overview and Summary of Outcomes from the Regional
Consultations on the Draft Guidelines on Best Available Techniques (BAT) and Best
Environmental Practices (BEP) relevant to Article 5 and Annex C of the Stockholm Convention on
Persistent Organic Pollutants (POPs), February – April 2005. UNEP, Geneva.
http://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_%201
_inf_4_final.pdf
UNEP, October 14, 2005. Compilation of comments received from Parties and others on the draft
Guidelines on Best Available Techniques and provisional Guidance on Best Environmental
Practices,
http://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5
.pdf
Wang L.-C. et al. 2003. “Emission of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans from
Stack Flue Gases of Sinter Plants.” Chemosphere 50:9.
William Lemmon and Associates Ltd. 2004. Research on Technical Pollution Prevention Options
for Iron Sintering. Prepared for the Canadian Council of Ministers of the Environment, Canada.
www.ccme.ca/assets/pdf/df_is_p2_ctxt_p2_strtgy_e.pdf .
Guidelines on BAT and Guidance on BEP
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
(iii)
29
Secondary aluminium production
Summary
Secondary aluminium smelting involves the production of aluminium from used aluminium
products processed to recover metals by pre-treatment, smelting and refining.
Fuels, fluxes and alloys are used, while magnesium removal is practised by the addition of
chlorine, aluminium chloride or chlorinated organics. Chemicals listed in Annex C of the
Stockholm Convention probably result from organics in the feed, chlorine compounds and
temperatures between 250 and 500 °C.
Best available techniques include high-temperature advanced furnaces, oil- and chlorine-free
feeds (if alternatives are available), afterburners with rapid quench, activated carbon adsorption
and dedusting fabric filters.
The achievable performance level for secondary aluminium smelters: < 0.5 ng I-TEQ/Nm3.
1.
Process description
Processes used in secondary aluminium smelting are dependent on feed material. Pre-treatment,
furnace type and fluxes used will vary with each installation. Production processes involve scrap
pre treatment and smelting/refining. Pre-treatment methods include mechanical, pyrometallurgical
and hydrometallurgical cleaning. Smelting is conducted using reverberatory or rotary furnaces.
Induction furnaces may also be used to smelt the cleaner aluminium feed materials.
Reverberatory furnaces consist of two sections: a smelting chamber heated by a heavy oil burner
and an open well where aluminium scraps of various sizes are supplied. Rotary furnaces consist of
a horizontal cylindrical shell mounted on rollers and lined with refractory material. The furnace is
fired from one end usually using gas or oil as the fuel.
Feed consists of process scrap, used beverage cans, foils, extrusions, commercial scraps, turnings
and old rolled or cast metal. Skimmings and salt slags from the secondary smelting process are also
recycled as feed. Pre-sorting of scrap into desired alloy groups can reduce processing time. Scrap is
often contaminated with oil or coatings which must be removed to reduce emissions and improve
melting rate (European Commission 2001, p. 279).
The following summary of the process is drawn from EPA 1994:
“Most secondary aluminium recovery facilities use batch processing in smelting and
refining operations. The melting furnace is used to melt the scrap, and remove impurities
and entrained gases. The molten aluminium is then pumped into a holding furnace.
Holding furnaces are better suited for final alloying, and for making any additional
adjustments necessary to ensure that the aluminium meets product specifications. Pouring
takes place from holding furnaces, either into molds or as feedstock for continuous casters.
Smelting and refining operations can involve the following steps: charging, melting,
fluxing, demagging, degassing, alloying, skimming, and pouring. Charging consists of
placing pre-treated aluminium scrap into a melted aluminium pool (heel) that is maintained
in melting furnaces. The scrap, mixed with flux material, is normally placed into the
furnace charging well, where heat from the molten aluminium surrounding the scrap causes
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
it to melt by conduction. Flux materials combine with contaminates and float to the surface
of the aluminium, trapping impurities and providing a barrier (up to 6 inches thick) that
reduces oxidation of the melted aluminium. To minimize aluminium oxidation (melt loss),
mechanical methods are used to submerge scrap into the heel as quickly as possible.
Demagging reduces the magnesium content of the molten charge. In the past, when
demagging with liquid chlorine, chlorine was injected under pressure to react with
magnesium as the chlorine bubbled to the surface. The pressurized chlorine was released
through carbon lances directed under the heel surface, resulting in high chlorine emissions.
A more recent chlorine aluminium demagging process has replaced the carbon lance
procedure. Chlorine gas is metered into the circulation pump discharge pipe. It is
anticipated that reductions of chlorine emissions (in the form of chloride compounds) will
be reported in the future. Other chlorinating agents or fluxes, such as anhydrous aluminium
chloride or chlorinated organics, are used in demagging operations.
Degassing is a process used to remove gases entrained in molten aluminium. High-pressure
inert gases are released below the molten surface to violently agitate the melt. This
agitation causes the entrained gasses to rise to the surface to be absorbed in the floating
flux.
Alloying combines aluminium with an alloying agent in order to change its strength and
ductility. The skimming operation physically removes contaminated semisolid fluxes
(dross, slag, or skimmings) by ladling them from the surface of the melt.”
Figure 1. Secondary aluminium smelting
Pretreatment
Smelting/refining
Chlorine
Flux
Products
Fuel
Reverberatory
smelting/refining
(chlorine)
Fluorine
Flux
Fuel
Reverberatory
smelting/refining
(fluorine)
Treated aluminium
scrap
Flux
Alloy ingots
Billets
Notched bars
Shot
Hot metal
Fuel
Crucible
smelting/refining
Induction
smelting/refining
Electricity
Guidelines on BAT and Guidance on BEP
Hardeners
Flux
Environment Canada Revision, April 28, 2006
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31
Source: EPA 1994.
Artisinal and other small scale aluminium recovery processes are used in a number of
countries. Achievable performance limits are not applicable to artisinal and small scale
aluminium recovery processes as the processes used cannot be considered best available
techniques or best environmental practices and ideally would not be practised at all.
Current practice includes melting largely unsorted scrap in small crucibles or furnaces
typically housed in areas with inadequate ventilation. The crucible or furnace may be fired
with charcoal, oil, waste oil or coal depending on economies and the local fuel supply
situation. In larger furnaces, the melt may be treated with fluxes and degasifying
chemicals to improve the quality of the molten metal. Artisinal and other small scale
aluminium recovery processes may release many chemicals into the environment,
including POPs; these processes should be discouraged. However, in many countries,
artisinal and other small scale aluminium recovery processes are practiced. Certain
measures can be put in place in order to reduce the amount of pollutants released into the
environment. Using the proper air pollution controls on larger scale secondary aluminium
smelting operations, instead of artisinal processes, should be encouraged. Measures to
reduce POPs emissions and other pollutants from artisinal processes include: pre-sorting
of scrap material, selecting a better fuel supply (oil or gas fuels instead of coal), adequate
ventilation, filtration of exhaust gases, proper management of wastes and proper choice of
degassifiers. These measures can be achieved by education and outreach programs working
with craft groups and town authorities.
Manual scrap sorting is feasible in some economies rather than mechanical sorting, and
with proper training and supervision this could be highly effective. Pre-sorting of scrap
can lead to improvements in energy consumption and product quality and reduce the
amount of slag to be disposed of. The drying of feed materials and the pre-warming of
refractories can reduce hydrogen production in the melt and therefore can improve product
quality without the use of chemicals.
Proper ventilation by extraction of fumes and off-gases through a chimney and hood
enclosure around the crucible, thereby providing natural draught and some dispersion, will
improve the quality of combustion and reduce occupational exposure of workers to
pollutants.
Filters, dry scrubbers or wet scrubbers for particle abatement can be effective at pollution
control but require a reliable electricity supply to power the fans. Wet scrubbers require
appropriate arrangements for the collection, treatment and safe disposal of effluent. All
pollution control systems require appropriate residue handling arrangements and disposal
routes to be in place before installation. If effluent treatment is not in place then dry air
pollution control devices should be preferred. However, storage of fine particulate matter
is demanding in many environments and appropriate storage and waste arrangements are
required for the captured material until a safe disposal route is identified. Co-location of
facilities and regional cooperation to manage and dispose wastes would be beneficial.
The use of hexachloroethane as a degasifier for reducing melts has been thought to lead to
significant release of POPs. The use of potassium fluoride or potassium aluminium
fluoride as a degassing agent has been used successfully in some larger plants. Other large
plants have successfully used chlorine as a degasifier, however at these locations
appropriate handling and safety arrangements are in place including appropriately trained
staff.(Personal Communication, February 2006)
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2.
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Sources of chemicals listed in Annex C of the Stockholm
Convention
The generation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans
(PCDF) is probable due to the presence of organic contaminants and plastics in the feed material
with the addition of chlorine and chlorides during the smelting process.
2.1.
General information on emissions from secondary aluminium smelters
(European Commission 2001, p. 294–300)
Potential emissions to air include dust, metal compounds, chlorides, nitrogen oxides (NOx), sulphur
dioxide (SO2) and organic compounds such as PCDD/PCDF and carbon monoxide (CO). Ammonia
can also be generated from the improper storage, treatment and transport of skimmings. Chlorine
compounds can be removed using wet or dry scrubbers and their formation minimized by good
control and the use of mixtures of chlorine and inert gases. Low-NOx burners and low-sulphur fuels
can be used to decrease emissions of NOx and SO2.
“After burning is used to destroy organic materials that escapes the combustion zone, while
injection of treatment materials such as lime, sodium bi-carbonate and carbon is also
practised. Most installations then use (high efficiency) bag filters or ceramic filters to
remove dust and emissions can lie in the range 0.6 to 20 mg/Nm3. A spark arrester or
cooling chamber often precedes them to provide filter protection. Energy recovery can be
practised, most commonly re-cuperative burners are used” (European Commission 2001).
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33
Figure 2: Input and output from secondary aluminium production
NB smoke and dust can be associated with organic compounds such as VOC and dioxins (IPPC 2001)
2.2.
Emissions of PCDD/PCDF to air
PCDD/PCDF are formed during aluminium smelting through incomplete combustion or by de novo
synthesis when organic and chlorine compounds such as oils and plastics are present in the feed
material. Secondary feed often consists of contaminated scrap.
“The presence of oils and other organic materials on scrap or other sources of carbon
(partially burnt fuels and reductants, such as coke), can produce fine carbon particles which
react with inorganic chlorides or organically bound chlorine in the temperature range of
250 to 500 °C to produce PCDD/PCDF. This process is known as de-novo synthesis and is
catalysed by the presence of metals such as copper or iron.
Although PCDD/PCDF are destroyed at high temperature (above 850 °C) in the presence
of oxygen, the process of de-novo synthesis is still possible as the gases are cooled through
the “reformation window”. This window can be present in abatement systems and in cooler
parts of the furnace e.g. the feed area. Care taken in the design of cooling systems to
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
minimise the residence time in the window is practised to prevent de-novo synthesis”
(European Commission 2001, p. 133).
“Poor combustion of fuel or the organic content of the feed material can result in the
emission of organic materials. The provision of effective burner and furnace to controls is
used to optimise combustion. Peak combustion rates from included organic materials need
to be taken into account if they are fed to the furnace. It is reported that pre-cleaning of
scrap removes much of the organic material and improves the melting rate. The use of
chlorine mixtures for degassing and magnesium removal and the use of chlorides (salt flux)
will provide a source of chlorine for the potential formation of PCDD/PCDF” (European
Commission 2001, p. 297).
Based on information obtained from Japanese secondary aluminum operations, emissions have
been found to vary according to the furnace type employed. The highest-emitting furnace type in
this study was the open well reverberatory furnace. These units were found to average 0.38 ng
TEQ/Nm3. These results are believed to relate to the fact that this is the only furncace design which
permits the introduction of large pieces of scrap material, and this material is often the most
contaminated with organic compounds which may contribute to PCDD/PCDF formation
(Government of Japan, 2005).
2.3.
Releases to other media
(European Commission 2001, p. 294–300)
“Production of aluminium from secondary raw materials is essentially a dry process.
Discharge of wastewater is usually limited to cooling water, which is often re-circulated,
and rainwater run-off from surfaces and roofs. The rainwater run-off can be contaminated
by open storage of raw materials such as oily scrap and deposited solids.
Salt slags arise when mixtures of sodium and potassium chloride are used to cover the
molten metal to prevent oxidation, increase yield and increase thermal efficiency. These
slags are generally produced in rotary furnaces and can have an environmental impact if
they are deposited on land. Skimmings are used as a raw material in other parts of the
secondary aluminium industry and are sometimes pre-treated by milling and air
classification to separate aluminium from aluminium oxide. Spent filters from metal
treatment are usually disposed. In some cases when sodium bicarbonate is used for gas
cleaning, solid residues can be recovered with the salt flux. Alternatively filter dust can be
treated thermally to destroy dioxins. Furnace linings and dust can be recovered in the salt
slag treatment processes or disposed.”
3.
Recommended processes
Process design and configuration is influenced by the variations in feed material and quality
control. Processes considered as best available practices are the reverberatory furnace, rotary and
tilting rotary furnaces, the induction furnace and the Meltower shaft furnace. All techniques should
be applied in conjunction with suitable gas collection and abatement systems.
No information is available on alternative processes to smelting for secondary aluminium
processing.
4.
Primary and secondary measures
Primary and secondary measures for PCDD/PCDF reduction and elimination are discussed below.
4.1.
Primary measures
Primary measures are regarded as pollution prevention techniques to reduce or eliminate the
generation and release of persistent organic pollutants. Possible measures include:
4.1.1.
Pre-sorting of feed material
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35
The presence of oils, plastics and chlorine compounds in the feed material should be avoided to
reduce the generation of PCDD/PCDF during incomplete combustion or by de novo synthesis.
Sorting of feed material should be conducted prior to smelting to suit furnace type and abatement
and to permit the transfer of unsuitable raw materials to other facilities better suited for their
treatment. This will prevent or minimize the use of chloride salt fluxes during smelting.
Scrap material should be cleaned of oils, paints and plastics during pre-treatment. The removal of
organic and chlorine compounds will reduce the potential for PCDD/PCDF formation. Methods
used include the swarf centrifuge, swarf drying or other thermal decoating techniques. Thermal
decoating and de-oiling processes for oil removal should be followed by afterburning to destroy
any organic material in the off-gas (European Commission 2001, p. 310).
Scrap sorting using laser and eddy current technology is being tested. These methods could provide
more efficient selection of materials for recycling and the ability to produce desired alloys in
recycling plants (European Commission 2001, p. 294–300).
4.1.2.
Effective process control
Process control systems should be utilized to maintain process stability and operate at parameter
levels that will contribute to the minimization of PCDD/PCDF generation, such as maintaining
furnace temperature above 850 °C to destroy PCDD/PCDF. Ideally, PCDD/PCDF emissions would
be monitored continuously to ensure reduced releases. Continuous emissions sampling of
PCDD/PCDF has been demonstrated for some sectors (for example, waste incineration), but
research is still developing in this field. In the absence of continuous PCDD/PCDF monitoring,
other variables such as temperature, residence time, gas components and fume collection damper
controls should be continuously monitored and maintained to establish optimum operating
conditions for the reduction of PCDD/PCDF.
4.2.
Secondary measures
Secondary measures are pollution control techniques. These methods do not eliminate the
generation of contaminants, but serve as a means to contain and prevent emissions.
4.2.1.
Fume and gas collection
Fume and off-gas collection should be implemented in the control of air emissions from all stages
of the process. The use of sealed feeding systems and furnaces should be practised. Fugitive
emissions should be controlled by maintaining negative air pressure within the furnace to prevent
leaks. If a sealed unit is not possible, hooding should be used. Furnace or reactor enclosures may be
necessary. Where primary extraction and enclosure of fumes is not practicable, the furnace should
be enclosed so that ventilation air can be extracted, treated and discharged (European Commission
2001, p. 187–188). Additional benefits of fume and off-gas collection from rooflines include
reducing exposure of fumes and heavy metals to the workforce.
4.2.2.
High-efficiency dust removal
Particulate matter generated during the smelting process should be removed as this material
possesses a large surface area on which PCDD/PCDF can adsorb. Proper isolation and disposal of
these dusts will aid in PCDD/PCDF control. Collected particulate should be treated in hightemperature furnaces to destroy PCDD/PCDF and recover metals. Methods to consider are the use
of fabric filters, wet and dry scrubbers and ceramic filters.
Scrubbing off-gases with sodium bicarbonate will remove chlorides produced by the salt flux,
resulting in sodium chloride, which can then be removed by fabric filters to be recharged to the
furnace. In addition, use of a catalytic coating on fabric filter bags could destroy PCDD/PCDF by
oxidation while collecting particulate matter on which these contaminants have adsorbed
(European Commission 2001, p. 294–300).
4.2.3.
Afterburners and quenching
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Environment Canada Revision, April 28, 2006
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Afterburners (post-combustion) should be used at a minimum temperature of 950 °C to ensure full
combustion of organic compounds (Hübner et al. 2000). This stage is to be followed by rapid
quenching of hot gases to temperatures below 250 °C. Oxygen injection in the upper portion of the
furnace will promote complete combustion (European Commission 2001, p. 189).
It has been observed that PCDD/PCDF are formed in the temperature range of 250 to 500 °C. They
are destroyed above 850 °C in the presence of oxygen. Yet, de novo synthesis is still possible as the
gases are cooled through the reformation window present in abatement systems and cooler areas of
the furnace. Proper operation of cooling systems to minimize reformation time should be
implemented (European Commission 2001, p. 133). A benefit of cooling the flue gases before
scrubbbing would be reduced gas volume, hence reducing the size of abatement equipment, the
duct size and the energy needs for gas movement.
4.2.4.
Adsorption on activated carbon
Activated carbon treatment should be considered as this material is an ideal medium on which
PCDD/PCDF can adsorb due to its large surface area. Off-gas treatment techniques include using
fixed or moving bed reactors or injection of carbon into the gas stream followed by high-efficiency
dust removal systems such as fabric filters. Lime/carbon mixtures can also be used.
4.2.5.
Catalyst-Coated Filter
Japanese researchers have used a catalyst-coated filter on an experimental basis, and results are
encouraging. This filter system consists of two filters, one to collect the soot and a second which is
coated with a catalyst to decompose dioxins and furans. The experiemtnal work has demonstrated
that the catalyst was effective at decomposing dioxins and furans at temperatures in the range of
180 to 200 ºC.
4.3
Best Environmental Practices
The following guidelines are derived from the Japan Aluminium Alloy Refiners Assocation (March
2004) and may be considered as best environmental practices:

Concrete operation guidelines are shown below. The following main items are common to
these guidelines.
1. Do not purchase anything that are likely to generate smoke. Melt materials gradually.
2. Perform smelting and combustion with no soot or smoke generation.
3. Perfectly burn generated soot and smoke promptly.
4. Quickly cool down exhaust gas at high or middle temperatures to 170 oC or below promptly.
5. CO control in exhaust gas (CO ≤ 50 ppm, air-fuel ratio management)
<Concrete operation guidelines>
1. Matters Related to Materials and Scraps
Reinforce sorting on and after accepting materials.
(1) Sort and eliminate resin and oil
(2) Sort and eliminate foreign substances and resin after shredder processing.
(3) Return materials where resin or oil is stuck. Do not accept them at discount prices.
2. At Time of Combustion and Smelting at Smelting Chamber
(1) Avoid turning the burner ON and OFF as much as possible in order to reduce imperfect
combustion and soot generation.
(2) Supply materials while the burner is ON, and set generated smoke and soot in flame for
secondary combustion.
3. At Time of Combustion and Smelting in Open Well
Guidelines on BAT and Guidance on BEP
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
37
(1) Adjust the air-fuel ratio by measuring the CO and O2 concentration in flue exhaust gas.
(2) In order to heat and burn smoke and soot generated from materials supplied to the open well,
put the smoke and soot in burner flame.
(3) Adjust the supply of smelting materials according to the extent of smoke and flame (soot)
generation.
 Equalize the supply of burnable material (repetitively and little by little).
 Keep the combustion space with no imperfect combustion.
 Do not leak smoke from the exhaust gas hood.
(4) Maintain the performance of the dust collector (with regular inspection and bag replacement).
4. At Time of Demagnesium Processing
(1) Maintain the interval between the extinguishment of the burner and the start of chlorine
processing, and between the completion of chlorine processing and burner ignition. For 5 to 10
minutes, while performing air suction (residual gas discharge).
(2) Make improvement in efficiency by an increase in the initial temperature of molten metal
processing.
(3) Sort combined materials according to the quantity of Mg contained.
(4) Standardize the quantity of chlorine and that of flux used.
5. At Time of Drying Turnings
(1) Demand improvement in cut dust with excessive cutting oil (cutting oil with a high chlorine
content).
(2) Reheat at high temperature, maintain the exhaust gas of the drying furnace, and quickly cool
down the exhaust gas (i.e., keep good temperature control).
(3) Measure the CO concentration in exhaust gas regularly.
6. At Time of Paint Removal and Baking of Can Scraps (UBC)
(1) Removal of mixing foreign substances, such as resin and resin bags.
(2) Stable operation of the reheating furnace at constant circulation and exhaust gas temperature.
7. General
(1) Maintenance and inspection of the capacity of the dust collector, bag replacement, shaking
cycle, and suction pressure.
(2) Regular implementation of in-house environmental education for smelting workers.
(3) Targeting at the DXNs concentration in exhaust gas (< 1 ng-TEQ/Nm3) for existing facilities.
5.
Emerging research
5.1.
Catalytic oxidation
Catalytic oxidation is an emerging technology used in waste incinerators to eliminate PCDD/PCDF
emissions. This process should be considered by secondary base metals smelters as it has proven
effective for PCDD/PCDF destruction in waste incinerators. However, catalytic oxidation can,
subject to catalyst selection, be subject to poisoning from trace metals and other exhaust gas
contaminants. Validation work would be necessary before use of this process.
Catalytic oxidation processes organic compounds into water, carbon dioxide (CO2) and
hydrochloric acid using a precious metal catalyst to increase the rate of reaction between 370 and
450 °C, whereas incineration occurs typically at 980 °C. Catalytic oxidation has been shown to
destroy PCDD/PCDF with shorter residence times, lower energy consumption and 99% efficiency,
and should be considered. Off-gases should be treated for particulate removal prior to catalytic
oxidation for optimum efficiency. This method is effective for the vapour phase of contaminants.
The resulting hydrochloric acid is treated in a scrubber while the water and CO2 are released to the
air after cooling (Parvesse 2001).
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
6.
Summary of measures
Table 1. Measures for recommended processes for new secondary aluminium smelters
Measure
Description
Recommended
processes
Various
recommended
smelting processes
should be considered
for new facilities
Considerations
Processes to consider include:
reverberatory furnace, rotary
and tilting rotary furnaces,
induction furnace, and
Meltower shaft furnace
Other comments
All techniques should be
applied in conjunction with
suitable gas collection and
abatement systems
Table 2. Summary of primary and secondary measures for secondary aluminium smelters
Measure
Description
Considerations
Other comments
Primary measures
Presorting of
feed material
Effective
process control
The presence of oils,
plastics and chlorine
compounds in the
feed material should
be avoided to reduce
the generation of
PCDD/PCDF during
incomplete
combustion or by de
novo synthesis
Processes to consider include:
Process control
systems should be
utilized to maintain
process stability and
operate at parameter
levels that will
contribute to the
minimization of
PCDD/PCDF
generation
PCDD/PCDF emissions may be
minimized by controlling other
variables such as temperature,
residence time, gas components
and fume collection damper
controls after having
established optimum operating
conditions for the reduction of
PCDD/PCDF
Continuous emissions
sampling of PCDD/PCDF has
been demonstrated for some
sectors (e.g. waste
incineration), but research is
still developing in this field
Processes to consider include:
Where primary extraction and
enclosure of fumes is not
practicable, the furnace
should be enclosed so that
ventilation air can be
extracted, treated and
discharged
 Prevention or minimization
of the use of chloride salts
where possible
 Cleaning scrap material of
oils, paints and plastics
during pretreatment
 Using thermal decoating
techniques such as the swarf
centrifuge or swarf dryer
Sorting of feed material
should be conducted prior to
smelting to suit furnace type
and abatement and to permit
the transfer of unsuitable raw
materials to other facilities
better suited for their
treatment.
Thermal decoating and deoiling processes for oil
removal should be followed
by afterburning to destroy
any organic material in the
off-gas
Secondary measures
Fume and gas
collection
Effective fume and
off-gas collection
should be
implemented in the
capture of air
emissions from all
stages of the process
 Use of sealed feeding
systems and furnaces
 Control of fugitive
emissions by maintaining
negative air pressure within
the furnace to prevent leaks
 Use of hooding if a sealed
unit is not possible
 Use of furnace or reactor
enclosures
High-efficiency
Particulate matter
Guidelines on BAT and Guidance on BEP
Processes to consider include:
Collected particulate should
Environment Canada Revision, April 28, 2006
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Measure
dust removal
Afterburners
and quenching
Adsorption on
activated carbon
Description
Considerations
generated during the
smelting process
should be removed as
this material
possesses large
surface area on which
PCDD/PCDF can
adsorb. Proper
isolation and disposal
of these dusts will aid
in PCDD/PCDF
control
 Fabric filters, wet/dry
scrubbers and ceramic
filters
Afterburners should
be used at
temperatures > 950
°C to ensure full
combustion of
organic compounds,
followed by rapid
quenching of hot
gases to temperatures
below 250 °C
Considerations include:
Activated carbon
treatment should be
considered as this
material is an ideal
medium on which
PCDD/PCDF can
adsorb due to its large
surface area
Processes to consider include:
 Catalytic coatings on fabric
filter bags to destroy
PCDD/PCDF by oxidation
while collecting particulate
matter on which these
contaminants have adsorbed
 PCDD/PCDF formation at
250to 500 °C, and
destruction > 850 °C with
O2
39
Other comments
be treated in hightemperature furnaces to
destroy PCDD/PCDF and
recover metals
De novo synthesis is still
possible as the gases are
cooled through the
reformation window
 Requirement for sufficient
O2 in the upper region of the
furnace for complete
combustion
 Need for proper design of
cooling systems to
minimize reformation time
 Treatment with activated
carbon using fixed or
moving bed reactors
Lime/carbon mixtures can
also be used
 Injection of carbon into the
gas stream followed by
high-efficiency dedusting
methods such as fabric
filters
Emerging research
Catalytic
oxidation
Catalytic oxidation is
an emerging
technology which
should be considered
due to its high
efficiency and lower
energy consumption.
Catalytic oxidation
transforms organic
compounds into
water, carbon dioxide
(CO2) and
hydrochloric acid
using a precious
metal catalyst
Guidelines on BAT and Guidance on BEP
Considerations include:
 Process efficiency for the
vapour phase of
contaminants
 Hydrochloric acid treatment
using scrubbers while water
and CO2 are released to the
air after cooling
Has been shown to destroy
PCDD/PCDF with shorter
residence times, lower energy
consumption and 99%
efficiency.
Off-gases should be dedusted
prior to catalytic oxidation
for optimum efficiency
Environment Canada Revision, April 28, 2006
40
7.
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Achievable performance levels
The achievable performance level6 for emissions of PCDD/PCDF from secondary aluminium
smelters is < 0.5 ng I-TEQ/Nm3.
References
A.J. Gunson, Yue Jian, Artisanal Mining in The People's Republic of China, Mining,
Minerals and Sustainable Development (MMSD), International Institute for Environment
and Development (IIED), September 2001
EPA (United States Environmental Protection Agency). 1994. Secondary Aluminium Operations.
Background Report AP-42, Section 12.8. www.epa.gov/ttn/chief/ap42/ch12/final/c12s08.pdf.
European Commission. 2001. Reference Document on Best Available Techniques in the NonFerrous Metals Industries. BAT Reference Document (BREF). European IPPC Bureau, Seville,
Spain. eippcb.jrc.es.
Feng Xinbin, Qui Guangle, Li Guanghui, Li Ping, Wang Shaofeng, Mercury Emissions from
Artisanal Zinc and Mercury Smelting in Guizhou, PR China, Goldschmidt Conference Abstracts
2005, The Geochemistry of Mercury, page A705
Government of Japan, Ministry of Economy, Trade and Industry. Technical Information on
Measures for Dioxins Discharge Control at Secondary Aluminum Refineries. November
2005
Hübner C., Boos R., Bohlmann J., Burtscher K. and Wiesenberger H. 2000. State-of-the-Art
Measures for Dioxin Reduction in Austria. Vienna.
www.ubavie.gv.at/publikationen/Mono/M116s.htm.
Integrated Pollution Prevention and Control (IPPC), Reference Document on Best Available
Techniques in the Non Ferrous Metals Industries, December 2001
Parvesse T. 2001. “Controlling Emissions from Halogenated Solvents.” Chemical Processing
[Chem. Process.]. Vol. 64, no. 4, pp. 48-51. Apr 2001
Personal communication from Expert Group Best Available Techniques Best Environmental
Practices, Finland Member, February 2006
Personal communication from Expert Group Best Available Techniques Best Environmental
Practices, UK Member, February 2006
Personal communication, Member, Japan, Expert Group Meeting, 1 December, 2006
New Operation Guidelines to Suppress DXNs Emissions Exhaust Gas, Japan Aluminium
Alloy Refiners Association, March 30, 2004
UNEP, Compilation of comments received from Parties and others on the draft Guidelines on Best
Available Techniques and provisional Guidance on Best Environmental Practices, October 14,
6
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured
at 0 °C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present
guidelines. The operating oxygen concentration conditions of exhaust gases are used for metallurgical
sources.
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
SECTION V. Guidelines/guidance by source category: Part II of Annex C
41
2005
http://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5
.pdf
UNEP Environment Program News Centre,
http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=
3204&l=en, as read on January 20, 2006
Xinbin Feng, Xianwu Bi, Guangle Qiu, Guanghui Li, Shunlin Tang, Mercury Pollution in
Guizhou, China - A status Report,
http://pbc.eastwestcenter.org/abstracts2005/abstract2005fengxinbin.htm, as read on
December 29th, 2005
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
42
(iv)
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Secondary zinc production
Summary
Secondary zinc smelting involves the production of zinc from materials such as dusts from
copper alloy production and electric arc steel making, and residues from steel scrap shredding
and galvanizing processes.
Production processes include feed sorting, pretreatment cleaning, crushing, sweating furnaces to
364 °C, melting furnaces, refining, distillation and alloying. Oils and plastics in feed, and
temperatures between 250 and 500 °C, may give rise to chemicals listed in Annex C of the
Stockholm Convention.
Best available techniques include feed cleaning, maintaining temperatures above 850 °C, fume
and gas collection, afterburners with quenching, activated carbon adsorption and fabric filter
dedusting.
The achievable performance level for secondary zinc smelters: < 0.5 ng I-TEQ/Nm3.
1.
Process description
(EPA 1981)
Secondary zinc smelting involves the processing of zinc scrap from various sources. Feed material
includes dusts from copper alloy production and electric arc steel making, residues from steel scrap
shredding, and scrap from galvanizing processes. The process method is dependent on zinc purity,
form and degree of contamination. Scrap is processed as zinc dust, oxides or slabs. The three
general stages of production are pretreatment, melting and refining.
During pretreatment scrap is sorted according to zinc content and processing requirements, cleaned,
crushed and classified by size. A sweating furnace is used to heat the scrap to 364 °C. At this
temperature only zinc is melted, while other metals remain solid. The molten zinc is collected at the
bottom of the sweat furnace and recovered. The leftover scrap is cooled, recovered and sold to
other processors.
Pretreatment can involve leaching with sodium carbonate solution to convert dross and skimmings
to zinc oxide, to be reduced to zinc metal. The zinc oxide product is refined at primary zinc
smelters.
Melting processes use kettle, crucible, reverberatory, reduction and electric induction furnaces.
Impurities are separated from molten zinc by flux materials. Agitation allows flux and impurities to
float on the surface as dross, which can be skimmed off. The remaining zinc is poured into moulds
or transferred in a molten state for refining. Alloys can be produced from pretreated scrap during
sweating and melting.
Refining removes further impurities in clean zinc alloy scrap and in zinc vaporized during the melt
phase in retort furnaces. Distillation involves vaporization of zinc at temperatures from 982 to
1,249 °C in muffle or retort furnaces and condensation as zinc dust or liquid zinc. Several forms
can be recovered depending on temperature, recovery time, absence or presence of oxygen and
equipment used during zinc vapour condensation. Pot melting is a simple indirect heat melting
operation whereby the final alloy cast into zinc alloy slabs is controlled by the scrap input into the
pot. Distillation is not involved.
Final products from refining processes include zinc ingots, zinc dust, zinc oxide and zinc alloys.
Figure 1 shows the production process in diagrammatic form.
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
SECTION V. Guidelines/guidance by source category: Part II of Annex C
43
Figure 1. Secondary zinc smelting
Pretreatment
Die-cast
products,
residues,
skimmings,
other mixed
scrap
Sweating:
Reverberatory
Rotary
Muffle
Kettle (pot)
Melting
Alloying
Melting:
Kettle (pot)
Crucible
Reverberatory
Fuel
Sweated
scrap (melt
or ingots)
Refining/alloying
Flux
Alloy
Flux Fuel Alloying agent
Distillation:
Retort
Muffle
Fuel
Fuel
Water
Zinc
ingot,
zinc
dust
Graphite rod
distillation
Fuel
Electric
induction
melting
Clean
scrap
Electricity
Electric resistance
sweating
Flux
Zinc
alloys
Contaminated zinc
oxide baghouse dust
Distillation
Oxidation:
Retort
Muffle
Fuel
Crushing/
screening
Residues,
skimmings
Electricity
Sodium
carbonate
leaching
Water
Water
Air Water
Retort
reduction
Crude zinc oxide to
primary smelters
Fuel Water Carbon
monoxide
Sodium
carbonate
Source: EPA 1981.
Artisinal and small enterprise metal recovery activities may play a significant international role, in
particular in developing countries and countries with economies in transition. These activities may
contribute significantly to pollution and have negative health impacts. For example, artisinal zinc
smelting is an important atmospheric mercury emission source. The technique used to smelt both
zinc and mercury are very simple. The ores are heated in a furnace for a few hours, and zinc metal
and liquid mercury are produced. In many cases there are no pollution control devices employed at
all during the melting process. Other metals that are known to be produced by artisinal and small
enterprise metal recovery activities include antimony, iron, lead, manganese, tin, tungsten, gold,
silver, copper, and aluminum.
These are not considered best available techniques or best environmental practices. However, as a
minimum, appropriate ventilation and material handling should be carried out.
2.
Sources of chemicals listed in Annex C of the Stockholm
Convention
Guidelines on BAT and Guidance on BEP
Zinc
oxide
Environment Canada Revision, April 28, 2006
Zinc
44
SECTION V. Guidelines/guidance by source category: Part II of Annex C
The formation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans
(PCDF) may be possible if plastics and oils are present in the feed material.
2.1.
General information on emissions from secondary zinc smelters
Air emissions from secondary zinc smelting can escape as stack or fugitive emissions, depending
on the facility age or technology. Main contaminants are sulphur dioxide (SO2), other sulphur
compounds and acid mists, nitrogen oxides (NOx), metals (especially zinc) and their compounds,
dusts and PCDD/PCDF. SO2 is collected and processed into sulphuric acid in acid plants when
processing secondary material with high sulphur content. Fugitive SO2 emissions can be controlled
by good extraction and sealing of furnaces. NOx can be reduced using low-NOx or oxy-fuel
burners. Particulate matter is collected using high-efficiency dust removal methods such as fabric
filters and returned to the process (European Commission 2001, p.359–368).
2.2.
Emissions of PCDD/PCDF to air
PCDD/PCDF are formed during base metals smelting through incomplete combustion or by de
novo synthesis when organic and chlorine compounds such as oils and plastics are present in the
feed material. Secondary feed often consists of contaminated scrap.
“The processing of impure scrap such as the non-metallic fraction from shredders is likely
to involve production of pollutants including PCDD/PCDF. Relatively low temperatures
are used to recover lead and zinc (340 and 440°C). Melting of zinc may occur with the
addition of fluxes including zinc and magnesium chlorides” (UNEP 2003, p. 78).
The low temperatures used in zinc smelting fall directly within the 250 to 500 °C range in which
PCDD/PCDF are generated. The addition of chloride fluxes provides a chlorine source. Formation
is possible in the combustion zone by incomplete combustion of organic compounds and in the offgas treatment cooling section through de novo synthesis. PCDD/PCDF adsorb easily onto
particulate matter such as dust, filter cake and scrubber products and can be discharged to the
environment through air emissions, waste water and residue disposal.
“Although PCDD/PCDF are destroyed at high temperature (above 850 °C) in the presence
of oxygen, the process of de-novo synthesis is still possible as the gases are cooled through
the “reformation window”. This window can be present in abatement systems and in cooler
parts of the furnace e.g. the feed area. Care taken in the design of cooling systems to
minimise the residence time in the window is practised to prevent de-novo synthesis”
(European Commission 2001, p. 133).
A report prepared by the Government of Japan studied dioxin reduction technologies and their
effects in secondary zinc production facilities of Japan. Various exhaust gas technologies were
introduced in line with guidelines on BAT/BEP at five existing facilities. Dioxin emissions were
found to vary depending on the type of furnace employed. Dioxin discharge concentrations before
and after the introduction of technologies, were found to range from 0.91-40.00 ng TEQ/Nm3 and
0.32-11.700 ng TEQ/Nm3, respectively. When a state-of-the-art two-step bag filter and two-step
activated carbon injection system was introduced into the reduction furnace at one facility, dioxin
concentration was reduced from 3.30 ng TEQ/Nm3 to 0.49 ng TEQ/Nm3 (Government of Japan,
2005).
2.3.
Releases to other media
Waste water originates from process effluent, cooling water and run-off and is treated using wastewater treatment techniques. Process residues are recycled, treated using downstream methods to
recover other metals, or safely disposed.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
3.
45
Recommended processes
Variation in feed material and desired product quality influences process design and configuration.
These processes should be applied in combination with good process control, gas collection and
abatement systems. Processes considered to be best available practices include:
“Physical separation, melting and other high temperature treatment techniques followed by
the removal of chlorides.
The use of Waelz kilns, cyclone or converter type furnaces to raise the temperature to
volatilise the metals and then form the oxides that are then recovered from the gases in a
filtration stage” (European Commission 2001, p. 396).
No information is available on alternative processes to smelting for secondary zinc processing.
4.
Primary and secondary measures
Primary and secondary measures of PCDD/PCDF reduction and elimination are discussed below.
4.1.
Primary measures
Primary measures are regarded as pollution prevention techniques to reduce or eliminate the
generation and release of persistent organic pollutants. Possible measures include:
4.1.1.
Presorting of feed material
Oils and plastics in zinc scrap should be separated from the furnace feed to reduce the formation of
PCDD/PCDF from the incomplete combustion of organic compounds or by de novo synthesis.
Methods for feed storage, handling and pretreatment are influenced by material size distribution,
contaminants and metal content.
Milling and grinding, in conjunction with pneumatic or density separation techniques, can be used
to remove plastics. Thermal decoating and de-oiling processes for oil removal should be followed
by afterburning to destroy any organic material in the off-gas (European Commission 2001, p.
232).
4.1.2.
Effective process control
Process control systems should be utilized to maintain process stability and operate at parameter
levels that will contribute to the minimization of PCDD/PCDF generation, such as maintaining
furnace temperature above 850 °C to destroy PCDD/PCDF. Ideally, PCDD/PCDF emissions would
be monitored continuously to ensure reduced releases. Continuous emissions sampling of
PCDD/PCDF has been demonstrated for some sectors (for example, waste incineration), but
research is still developing in this field. In the absence of continuous PCDD/PCDF monitoring,
other variables such as temperature, residence time, gas components and fume collection damper
controls should be continuously monitored and maintained to establish optimum operating
conditions for the reduction of PCDD/PCDF.
4.2.
Secondary measures
Secondary measures are pollution control techniques to contain and prevent emissions. These
methods do not prevent the formation of contaminants.
4.2.1.
Fume and gas collection
Effective fume and off-gas collection should be implemented in all stages of the smelting process
to capture PCDD/PCDF emissions.
“The fume collection systems used can exploit furnace-sealing systems and be designed to
maintain a suitable furnace [vacuum] that avoids leaks and fugitive emissions. Systems that
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
46
SECTION V. Guidelines/guidance by source category: Part II of Annex C
maintain furnace sealing or hood deployment can be used. Examples are through hood
additions of material, additions via tuyeres or lances and the use of robust rotary valves on
feed systems. An [effective] fume collection system capable of targeting the fume
extraction to the source and duration of any fume will consume less energy. BAT for gas
and fume treatment systems are those that use cooling and heat recovery if practical before
a fabric filter…” (European Commission 2001, p. 397).
4.2.2.
High-efficiency dust removal
Dusts and metal compounds generated from the smelting process should be removed as this
particulate matter possesses high surface area on which PCDD/PCDF easily adsorb. Removal of
these dusts would contribute to the reduction of PCDD/PCDF emissions. Techniques to be
considered are the use of fabric filters, wet and dry scrubbers and ceramic filters. Collected
particulate matter is usually recycled in the furnace.
Fabric filters using high-performance materials are the most effective option. Innovations regarding
this method include bag burst detection systems, online cleaning methods, and catalytic coatings to
destroy PCDD/PCDF (European Commission 2001, p. 139–140).
4.2.3.
Afterburners and quenching
Afterburners (post-combustion) should be used at a minimum temperature of 950 °C to ensure full
combustion of organic compounds (Hübner et al. 2000). This stage is to be followed by rapid
quenching of hot gases to temperatures below 250 °C. Oxygen injection in the upper portion of the
furnace will promote complete combustion (European Commission 2001, p. 189).
It has been observed that PCDD/PCDF are formed in the temperature range of 250 to 500 °C.
These are destroyed above 850 °C in the presence of oxygen. Yet, de novo synthesis is still
possible as the gases are cooled through the reformation window present in abatement systems and
cooler areas of the furnace. Operation of cooling systems to minimize reformation time should be
implemented (European Commission 2001, p. 133).
4.2.4.
Adsorption on activated carbon
Activated carbon treatment should be considered for PCDD/PCDF removal from smelter off-gases.
Activated carbon possesses large surface area on which PCDD/PCDF can be adsorbed. Off-gases
can be treated with activated carbon using fixed or moving bed reactors, or injection of carbon
particulate into the gas stream followed by removal as a filter dust using high-efficiency dust
removal systems such as fabric filters.
5.
Emerging research
5.1.
Catalytic oxidation
Catalytic oxidation is an emerging technology used in waste incinerators to eliminate PCDD/PCDF
emissions. This process should be considered by secondary base metals smelters as it has proven
effective for PCDD/PCDF destruction in waste incinerators. Catalytic oxidation can, subject to
catalyst selection, be subject to poisoning from trace metals and other exhaust gas contaminants.
Validation work would be necessary before use of this process.
Catalytic oxidation processes organic compounds into water, carbon dioxide (CO2) and
hydrochloric acid using a precious metal catalyst to increase the rate of reaction at 370 to 450 °C.
In comparison, incineration occurs typically at 980 °C. Catalytic oxidation has been shown to
destroy PCDD/PCDF with shorter residence times, lower energy consumption and 99% efficiency,
and should be considered. Off-gases should be treated for particulate removal prior to catalytic
oxidation for optimum efficiency. This method is effective for the vapour phase of contaminants.
The resulting hydrochloric acid is treated in a scrubber while the water and CO2 are released to the
air after cooling (Parvesse 2001).
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
SECTION V. Guidelines/guidance by source category: Part II of Annex C
6.
47
Summary of measures
Table 1. Measures for recommended processes for new secondary zinc smelters
Measure
Recommended
Processes
Description
Various recommended
smelting processes
should be considered
for new facilities
Considerations
Processes to consider include:
 Physical separation, melting
and other high-temperature
treatment techniques
followed by the removal of
chlorides
Other comments
These processes should be
applied in combination
with good process
control, gas collection and
abatement systems
 The use of Waelz kilns,
cyclone- or converter-type
furnaces to raise the
temperature to volatilize the
metals and then form the
oxides that are then recovered
from the gases in a filtration
stage
Table 2. Summary of primary and secondary measures for secondary zinc smelters
Measure
Description
Considerations
Other comments
Primary measures
Presorting of feed
material
Effective process
control
Oils and plastic in zinc
scrap should be
separated from the
furnace feed to reduce
the formation of
PCDD/PCDF from
incomplete combustion
or by de novo synthesis
Processes to consider include:
Process control systems
should be utilized to
maintain process
stability and operate at
parameter levels that
will contribute to the
minimization of
PCDD/PCDF generation
PCDD/PCDF emissions may be
minimized by controlling other
variables such as temperature,
residence time, gas components
and fume collection damper
controls, after having
established optimum operating
conditions for the reduction of
PCDD/PCDF
Continuous emissions
sampling of
PCDD/PCDF has been
demonstrated for some
sectors (e.g. waste
incineration), but
research is still
developing in this field
Effective fume and offgas collection should be
implemented in all
stages of the smelting
process to capture
PCDD/PCDF emissions
Processes to consider include:
Best available
techniques for gas and
fume treatment systems
are those that use
cooling and heat
recovery if practical
before a fabric filter
except when carried out
as part of the production
 Milling and grinding, in
conjunction with pneumatic
or density separation
techniques, can be used to
remove plastics
Thermal decoating and
de-oiling processes for
oil removal should be
followed by afterburning
to destroy any organic
material in the off-gas
 Oil removal conducted
through thermal decoating
and de-oiling processes
Secondary measures
Fume and gas
collection
 Furnace-sealing systems to
maintain a suitable furnace
vacuum that avoids leaks
and fugitive emissions
 Use of hooding
 Hood additions of material,
additions via tuyeres or
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
48
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Measure
Description
Considerations
lances and the use of robust
rotary valves on feed
systems
High-efficiency
dust removal
Dusts and metal
compounds should be
removed as this material
possesses high surface
area on which
PCDD/PCDF easily
adsorb. Removal of
these dusts would
contribute to the
reduction of
PCDD/PCDF emissions
Processes to consider include:
Afterburners and
quenching
Afterburners should be
used at temperatures >
950 °C to ensure full
combustion of organic
compounds, followed by
rapid quenching of hot
gases to temperatures
below 250 °C
Considerations include:
 Use of fabric filters, wet/dry
scrubbers and ceramic filters
 PCDD/PCDF formation at
250 to 500 °C, and
destruction > 850 °C with O2
Other comments
of sulphuric acid
Fabric filters using highperformance materials
are the most effective
option. Collected
particulate matter should
be recycled in the
furnace
De novo synthesis is still
possible as the gases are
cooled through the
reformation window
 Requirement for sufficient
O2 in the upper region of the
furnace for complete
combustion
 Need for proper design of
cooling systems to minimize
reformation time
Adsorption on
activated carbon
Activated carbon
treatment should be
considered as this
material is an ideal
medium for adsorption
of PCDD/PCDF due to
its large surface area
Processes to consider include:
Catalytic oxidation is an
emerging technology
which should be
considered due to its
high efficiency and
lower energy
consumption. Catalytic
oxidation transforms
organic compounds into
water, CO2 and
hydrochloric acid using
a precious metal catalyst
Considerations include:
 Treatment with activated
carbon using fixed or
moving bed reactors
Lime/carbon mixtures
can also be used
 Injection of carbon
particulate into the gas
stream followed by removal
as a filter dust
Emerging research
Catalytic oxidation
Guidelines on BAT and Guidance on BEP
 Process efficiency for the
vapour phase of
contaminants
 Hydrochloric acid treatment
using scrubbers while water
and CO2 are released to the
air after cooling
Catalytic oxidation has
been shown to destroy
PCDD/PCDF with
shorter residence times,
lower energy
consumption and 99%
efficiency.
Off-gases should be
treated for particulate
removal prior to
catalytic oxidation for
optimum efficiency
Environment Canada Revision, April 28, 2006
SECTION V. Guidelines/guidance by source category: Part II of Annex C
7.
49
Achievable performance levels
The achievable performance level7 for emissions of PCDD/PCDF from secondary zinc smelters is
< 0.5 ng I-TEQ/Nm3.
References
A.J. Gunson, Yue Jian, Artisanal Mining in The People's Republic of China, Mining,
Minerals and Sustainable Development (MMSD), International Institute for Environment
and Development (IIED), September 2001
EPA (United States Environmental Protection Agency). 1981. Secondary Zinc Processing.
Background Report AP-42, Section 12.14. epa.gov/ttn/chief/ap42/ch12/final/c12s14.pdf.
European Commission. 2001. Reference Document on Best Available Techniques in the
Non-Ferrous Metals Industries. BAT Reference Document (BREF). European IPPC
Bureau, Seville, Spain. eippcb.jrc.es.
Feng Xinbin, Qui Guangle, Li Guanghui, Li Ping, Wang Shaofeng, Mercury Emissions
from Artisanal Zinc and Mercury Smelting in Guizhou, PR China, Goldschmidt
Conference Abstracts 2005, The Geochemistry of Mercury, page A705
Government of Japan, Ministry of Economy, Trade and Industry. Report on Dioxin
Reduction Technologies and their Effects in Secondary Zinc Production Facilities of
Japan. November 2005.
Hübner C., Boos R., Bohlmann J., Burtscher K. and Wiesenberger H. 2000. State-of-the-Art
Measures for Dioxin Reduction in Austria. Vienna.
http://www.umweltbundesamt.at/fileadmin/site/publikationen/M116.pdf.
Parvesse T. 2001. “Controlling Emissions from Halogenated Solvents.” Chemical Processing
[Chem. Process.]. Vol. 64, no. 4, pp. 48-51. Apr 2001
Personal communication, Member, Japan, Expert Group Meeting, 1 December, 2006
UNEP (United Nations Environment Programme). 2003. Standardized Toolkit for Identification
and Quantification of Dioxin and Furan Releases. UNEP, Geneva.
www.pops.int/documents/guidance/Toolkit_2003.pdf
UNEP, Compilation of comments received from Parties and others on the draft Guidelines on Best
Available Techniques and provisional Guidance on Best Environmental Practices, October 14,
2005
http://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5
.pdf
7
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0 °C
and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present guidelines. The
operating oxygen concentration conditions of exhaust gases are used for metallurgical sources.
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
50
SECTION V. Guidelines/guidance by source category: Part II of Annex C
UNEP Environment Program News Centre,
http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=
3204&l=en, as read on January 20, 2006
Xinbin Feng, Xianwu Bi, Guangle Qiu, Guanghui Li, Shunlin Tang, Mercury Pollution in
Guizhou, China - A status Report,
http://pbc.eastwestcenter.org/abstracts2005/abstract2005fengxinbin.htm, as read on
December 29th, 2005
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
Section VI.
Guidance/Guidelines by source category
Source categories in Part III of Annex C
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
52
SECTION V. Guidelines/guidance by source category: Part II of Annex C
VI.B Thermal processes in the metallurgical industry not
mentioned in Annex C, Part II
(v)
Secondary lead production
Summary
Secondary lead smelting involves the production of lead and lead alloys, primarily from scrap
automobile batteries, and also from other used lead sources (pipe, solder, drosses, lead
sheathing). Production processes include scrap pretreatment, smelting and refining. Oils and
plastics in feed, and temperatures between 250 and 500 °C, may give rise to chemicals listed in
Annex C of the Stockholm Convention.
Best available techniques include the use of plastic-free and oil-free feed material, high furnace
temperatures above 850 °C, effective gas collection, afterburners and rapid quench, activated
carbon adsorption, and dedusting fabric filters.
The achievable performance level for secondary lead smelters: < 0.1 ng I-TEQ/Nm3.
1.
Process description
The following summary of the process is drawn from Environmental Protection Agency (United
States EPA) 1986. Figure 1 summarizes the process in diagrammatic form.
“Secondary lead smelters produce lead and lead alloys from lead-bearing scrap material.
More than 60 percent of all secondary lead is derived from scrap automobile batteries.
Other raw materials used in secondary lead smelting include wheel balance weights, pipe,
solder, drosses, and lead sheathing.
Secondary lead smelting includes 3 major operations: scrap pre-treatment, smelting, and
refining. Scrap pre-treatment is the partial removal of metal and nonmetal contaminants
from leadbearing scrap and residue. Processes used for scrap pre-treatment include battery
breaking, crushing, and sweating. Battery breaking is the draining and crushing of
batteries, followed by manual separation of the lead from nonmetallic materials. This
separated lead scrap is then sweated in a gas- or oil-fired reverberatory or rotary furnace to
separate lead from metals with higher melting points. Rotary furnaces are usually used to
process low-lead-content scrap and residue, while reverberatory furnaces are used to
process high-lead-content scrap. The partially purified lead is periodically tapped from
these furnaces for further processing in smelting furnaces or pot furnaces.
Smelting produces lead by melting and separating the lead from metal and non-metallic
contaminants and by reducing oxides to elemental lead. Smelting is carried out in blast,
reverberatory, and rotary kiln furnaces. In blast furnaces pre-treated scrap metal, rerun slag,
scrap iron, coke, recycled dross, flue dust, and limestone are used as charge materials to the
furnace. The process heat needed to melt the lead is produced by the reaction of the
charged coke with blast air that is blown into the furnace. Some of the coke combusts to
melt the charge, while the remainder reduces lead oxides to elemental lead. As the lead
charge melts, limestone and iron float to the top of the molten bath and form a flux that
retards oxidation of the product lead. The molten lead flows from the furnace into a
holding pot at a nearly continuous rate.
Refining and casting the crude lead from the smelting furnaces can consist of softening,
alloying, and oxidation depending on the degree of purity or alloy type desired. These
Guidelines on BAT and Guidance on BEP
Environment Canada Revision – April 28, 2006
SECTION VI. Guidance/guidelines by source category: Part III of Annex C
53
operations can be performed in reverberatory furnaces; however, kettle-type furnaces are
most commonly used. Alloying furnaces simply melt and mix ingots of lead and alloy
materials. Antimony, tin, arsenic, copper, and nickel are the most common alloying
materials. Oxidizing furnaces, either kettle or reverberatory units, are used to oxidize lead
and to entrain the product lead oxides in the combustion air stream for subsequent recovery
in high-efficiency baghouses.”
Figure 1. Secondary lead smelting
Pretreatment
Smelting
Refining
Fume
Soft
lead
ingots
Kettle (softening)
refining
SO2
Dust
&
fume
Reverberatory
smelting
Fume
Kettle (alloying)
refining
Storage
Flux
Recycled
dust, rare
scrap, fuel
Pretreated
scrap
Dust
&
fume
Crude
lead
bullion
Fuel
Alloying
agent
Alloys
Sawdust
Fume
Battery
lead oxide
Kettle
oxidation
Blast furnace
smelting
Fume
Fuel Air
Limestone,
recycled dust,
coke, slag
residue, lead
oxide, scrap
iron, pure scrap,
return slag
Reverberatory
oxidation
Fuel
Red lead oxide
Pb3O4
Yellow lead
oxide
PbO
Air
Source: EPA 1986.
2.
Sources of chemicals listed in Annex C of the Stockholm
Convention
The formation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans
(PCDF) is probably due to the presence of chlorine from plastics and trace oils in the feed material.
2.1.
General information on emissions from secondary lead smelters
Air emissions from secondary lead smelting can escape as stack or fugitive emissions, depending
on the facility age or technology. Main contaminants are sulphur dioxide (SO2), other sulphur
compounds and acid mists, nitrogen oxides (NOx), metals (especially lead) and their compounds,
dusts and PCDD/PCDF. SO2 is collected and processed into sulphuric acid in acid plants. Fugitive
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
54
SECTION V. Guidelines/guidance by source category: Part II of Annex C
SO2 emissions can be controlled by good extraction and sealing of furnaces. NOx can be reduced
using low-NOx or oxy-fuel burners. Particulate matter is collected using high-efficiency dust
removal methods such as fabric filters and returned to the process (European Commission 2001, p.
359–368).
2.2.
Emissions of PCDD/PCDF to air
PCDD/PCDF are formed during base metals smelting through incomplete combustion or by de
novo synthesis when organic and chlorine compounds such as oils and plastics are present in the
feed material.
The process is described in European Commission 2001, p. 133:
“PCDD/PCDF or their precursors may be present in some raw materials and there is a
possibility of de-novo synthesis in furnaces or abatement systems. PCDD/PCDF are easily
adsorbed onto solid matter and may be collected by all environmental media as dust,
scrubber solids and filter dust.
The presence of oils and other organic materials on scrap or other sources of carbon
(partially burnt fuels and reductants, such as coke), can produce fine carbon particles which
react with inorganic chlorides or organically bound chlorine in the temperature range of
250 to 500 °C to produce PCDD/PCDF. This process is known as de-novo synthesis and is
catalysed by the presence of metals such as copper or iron.
Although PCDD/PCDF are destroyed at high temperature (above 850 °C) in the presence
of oxygen, the process of denovo synthesis is still possible as the gases are cooled through
the “reformation window”. This window can be present in abatement systems and in cooler
parts of the furnace e.g. the feed area. Care taken in the design of cooling systems to
minimise the residence time in the window is practised to prevent de-novo synthesis.”
2.3.
Releases to other media
Waste water originates from process effluent, cooling water and run-off and is treated
using waste-water treatment techniques. Process residues are recycled, treated using
downstream methods to recover other metals, or safely disposed.
3.
Recommended processes
Variation in feed material and desired product quality influences process design and configuration.
These processes should be applied in combination with good process control, gas collection and
abatement systems. Processes considered as best available techniques include the blast furnace
(with good process control), the ISA Smelt/Ausmelt furnace, the top-blown rotary furnace, the
electric furnace and the rotary furnace (European Commission 2001, p. 379).
The submerged electric arc furnace is a sealed unit for mixed copper and lead materials. It is
cleaner than other processes if the gas extraction system is well designed and sized (European
Commission, p. 395).
“The injection of fine material via the tuyeres of a blast furnace has been successfully used
and reduces the handling of dusty material and the energy involved in returning the fines to
a sinter plant” (European Commission, p. 404). This technique minimizes dust emissions
during charging and thus reduces the release of PCDD/PCDF through adsorption on
particulate matter.
No information is available on alternative processes to smelting for secondary lead processing.
4.
Primary and secondary measures
Primary and secondary measures of PCDD/PCDF reduction and elimination are discussed below.
Guidelines on BAT and Guidance on BEP
Environment Canada Revision – April 28, 2006
SECTION VI. Guidance/guidelines by source category: Part III of Annex C
4.1.
55
Primary measures
Primary measures are regarded as pollution prevention techniques to reduce or eliminate the
generation and release of persistent organic pollutants. Possible measures include:
4.1.1.
Presorting of feed material
Scrap should be sorted and pretreated to remove organic compounds and plastics to reduce
PCDD/PCDF generation from incomplete combustion or by de novo synthesis. Whole battery feed
or incomplete separation should be avoided. Feed storage, handling and pretreatment techniques
will be determined by material size, distribution, contaminants and metal content.
Milling and grinding, in conjunction with pneumatic or density separation techniques, can be used
to remove plastics. Oil removal can be achieved through thermal decoating and de-oiling processes.
Thermal decoating and de-oiling processes for oil removal should be followed by afterburning to
destroy any organic material in the off-gas (European Commission 2001, p. 232).
4.1.2.
Effective process control
Process control systems should be utilized to maintain process stability and operate at parameter
levels that will contribute to the minimization of PCDD/PCDF generation, such as maintaining
furnace temperature above 850 °C to destroy PCDD/PCDF. Ideally, PCDD/PCDF emissions would
be monitored continuously to ensure reduced releases. Continuous emissions sampling of
PCDD/PCDF has been demonstrated for some sectors (for example, waste incineration), but
research is still developing in this field. In the absence of continuous PCDD/PCDF monitoring,
other variables such as temperature, residence time, gas components and fume collection damper
controls should be continuously monitored and maintained to establish optimum operating
conditions for the reduction of PCDD/PCDF.
“Particular attention is needed for the temperature measurement and control for furnaces
and kettles used for melting the metals in this group so that fume formation is prevented or
minimised” (European Commission 2001, p. 390).
4.2.
Secondary measures
Secondary measures are pollution control techniques to contain and prevent emissions.
These methods do not prevent the formation of contaminants.
4.2.1.
Fume and gas collection
Fume and off-gas collection should be implemented in all stages of the smelting process to control
PCDD/PCDF emissions.
“The fume collection systems used can exploit furnace-sealing systems and be designed to
maintain a suitable furnace depression that avoids leaks and fugitive emissions. Systems
that maintain furnace sealing or hood deployment can be used. Examples are through hood
additions of material, additions via tuyeres or lances and the use of robust rotary valves on
feed systems. An [efficient] fume collection system capable of targeting the fume
extraction to the source and duration of any fume will consume less energy. BAT for gas
and fume treatment systems are those that use cooling and heat recovery if practical before
a fabric filter except when carried out as part of the production of sulphuric acid”
(European Commission 2001, p. 397).
4.2.2.
High-efficiency dust removal
Dusts and metal compounds generated from the smelting process should be removed. This
particulate matter possesses high surface area on which PCDD/PCDF easily adsorb. Removal of
these dusts would contribute to the reduction of PCDD/PCDF emissions. Techniques to be
considered are the use of fabric filters, wet and dry scrubbers and ceramic filters. Collected
particulate should be recycled in the furnace.
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
56
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Fabric filters using high-performance materials are the most effective option. Innovations regarding
this method include bag burst detection systems, online cleaning methods and catalytic coatings to
destroy PCDD/PCDF (European Commission 2001, p. 139–140).
4.2.3.
Afterburners and quenching
Afterburners (post-combustion) should be used at a minimum temperature of 950 °C to ensure full
combustion of organic compounds (Hübner et al. 2000). This stage is to be followed by rapid
quenching of hot gases to temperatures below 250 °C. Oxygen injection in the upper portion of the
furnace will promote complete combustion (European Commission 2001, p. 189).
It has been observed that PCDD/PCDF are formed in the temperature range of 250 to 500 °C.
These are destroyed above 850 °C in the presence of oxygen. Yet, de novo synthesis is still
possible as the gases are cooled through the reformation window present in abatement systems and
cooler areas of the furnace. Proper operation of cooling systems to minimize reformation time
should be implemented (European Commission 2001, p. 133).
4.2.4.
Adsorption on activated carbon
Activated carbon treatment should be considered for PCDD/PCDF removal from smelter off-gases.
Activated carbon possesses large surface area on which PCDD/PCDF can be adsorbed. Off-gases
can be treated with activated carbon using fixed or moving bed reactors, or injection of carbon
particulate into the gas stream followed by removal as a filter dust using high-efficiency dust
removal systems such as fabric filters.
5.
Emerging research
5.1.
Catalytic oxidation
Catalytic oxidation is an emerging technology used in waste incinerators to eliminate PCDD/PCDF
emissions. This process should be considered by secondary base metals smelters as it has proven
effective for PCDD/PCDF destruction in waste incinerators. Catalytic oxidation can, subject to
catalyst selection, be subject to poisoning from trace metalsand other exhaust gas contaminants.
Validation work would be necessary before use of this process.
Catalytic oxidation processes organic compounds into water, carbon dioxide (CO2) and
hydrochloric acid using a precious metal catalyst to increase the rate of reaction at 370 to 450 °C.
In comparison, incineration occurs typically at 980 °C. Catalytic oxidation has been shown to
destroy PCDD/PCDF with shorter residence times, lower energy consumption and 99% efficiency,
and should be considered. Off-gases should be treated for particulate removal prior to catalytic
oxidation for optimum efficiency. This method is effective for the vapour phase of contaminants.
The resulting hydrochloric acid is treated in a scrubber while the water and CO2 are released to the
air after cooling (Parvesse 2001).
6.
Summary of measures
Table 1. Measures for new secondary lead smelters
Measure
Recommended
processes
Description
Various recommended
smelting processes
should be considered
for new facilities
Considerations
Processes to consider include:
 Blast furnace (with good
process control), ISA
Smelt/Ausmelt furnace, topblown rotary furnace, electric
furnace and rotary furnace
Other comments
These processes should
be applied in
combination with good
process control, gas
collection and
abatement systems
 Submerged electric arc furnace
Guidelines on BAT and Guidance on BEP
Environment Canada Revision – April 28, 2006
SECTION VI. Guidance/guidelines by source category: Part III of Annex C
Measure
Description
Considerations
57
Other comments
(it is a sealed unit for mixed
copper and lead materials,
cleaner than other processes if
the gas extraction system is
well designed and sized)
 Injection of fine material via
the tuyeres of a blast furnace
reduces handling of dusty
material
Table 2. Summary of primary and secondary measures for secondary lead smelters
Measure
Description
Considerations
Other comments
Primary measures
Presorting of
feed material
Effective process
control
Scrap should be sorted
and pretreated to
remove organic
compounds and
plastics to reduce
PCDD/PCDF
generation from
incomplete combustion
or by de novo synthesis
Processes to consider include:
Process control
systems should be
utilized to maintain
process stability and
operate at parameter
levels that will
contribute to the
minimization of
PCDD/PCDF
generation
PCDD/PCDF emissions may be
minimized by controlling other
variables such as temperature,
residence time, gas components
and fume collection damper
controls after having established
optimum operating conditions for
the reduction of PCDD/PCDF
Continuous emissions
sampling of
PCDD/PCDF has been
demonstrated for some
sectors (e.g. waste
incineration), but
research is still
developing in this field.
Particular attention is
needed for the
temperature
measurement and
control for furnaces and
kettles used for melting
the metals in this group
so that fume formation
is prevented or
minimized
Processes to consider include:
Best available
techniques for gas and
fume treatment systems
are those that use
cooling and heat
recovery if practical
before a fabric filter
 Avoidance of whole battery
feed or incomplete separation
 Milling and grinding, followed
by pneumatic or density
separation techniques, to
remove plastics
Thermal decoating and
de-oiling processes for
oil removal should be
followed by
afterburning to destroy
any organic material in
the off-gas
 Oil removal conducted through
thermal decoating and de-oiling
processes
Secondary measures
Fume and gas
collection
Fume and off-gas
collection should be
implemented in all
stages of the smelting
process to capture
PCDD/PCDF
Guidelines on BAT and Guidance on BEP
 Furnace-sealing systems to
maintain a suitable furnace
vacuum that avoids leaks and
fugitive emissions
 Use of hooding
Environment Canada Revision, April 28, 2006
58
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Measure
Description
Considerations
emissions
 Hood additions of material,
additions via tuyeres or lances
and the use of robust rotary
valves on feed systems
High-efficiency
dust removal
Dusts and metal
compounds should be
removed as this
material possesses high
surface area on which
PCDD/PCDF easily
adsorb. Removal of
these dusts would
contribute to the
reduction of
PCDD/PCDF
emissions
Processes to consider include:
Afterburners and
quenching
Afterburners should be
used at temperatures >
950 °C to ensure full
combustion of organic
compounds, followed
by rapid quenching of
hot gases to
temperatures below
250 °C
Considerations include:
Activated carbon
treatment should be
considered as this
material is an ideal
medium for adsorption
of PCDD/PCDF due to
its large surface area
Processes to consider include:
Catalytic oxidation is
an emerging
technology which
should be considered
due to its high
efficiency and lower
energy consumption.
Catalytic oxidation
transforms organic
compounds into water,
CO2 and hydrochloric
acid using a precious
metal catalyst
Considerations include:
Adsorption on
activated carbon
 Use of fabric filters, wet/dry
scrubbers and ceramic filters
 PCDD/PCDF formation
between 250 and 500 °C, and
destruction > 850 °C with O2
 Requirement for sufficient O2 in
the upper region of the furnace
for complete combustion
Other comments
Fabric filters using
high-performance
materials are the most
effective option.
Collected particulate
matter should be
recycled in the furnace
De novo synthesis is
still possible as the
gases are cooled
through the reformation
window
 Need for proper design of
cooling systems to minimize
reformation time
 Treatment with activated
carbon using fixed or moving
bed reactors
Lime/carbon mixtures
can also be used
 Injection of carbon particulate
into the gas stream followed by
removal as a filter dust
Emerging research
Catalytic
oxidation
Guidelines on BAT and Guidance on BEP
 Process efficiency for the
vapour phase of contaminants
 Hydrochloric acid treatment
using scrubbers while water and
CO2 are released to the air after
cooling
Catalytic oxidation has
been shown to destroy
PCDD/PCDF with
shorter residence times,
lower energy
consumption and 99%
efficiency.
Off-gases should be
treated for particulate
removal prior to
catalytic oxidation for
optimum efficiency
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7.
59
Achievable performance level
The achievable performance level for emissions of PCDD/PCDF from secondary lead smelters is <
0.1 ng I-TEQ/Nm3.1
References
EPA (United States Environmental Protection Agency). 1986. Secondary Lead Processing.
Background Report AP-42, Section 12.11. www.epa.gov/ttn/chief/ap42/ch12/final/c12s11.pdf.
European Commission. 2001. Reference Document on Best Available Techniques in the NonFerrous Metals Industries. BAT Reference Document (BREF). European IPPC Bureau, Seville,
Spain. eippcb.jrc.es.
Hübner C., Boos R., Bohlmann J., Burtscher K. and Wiesenberger H. 2000. State-of-the-Art
Measures for Dioxin Reduction in Austria. Vienna.
www.ubavie.gv.at/publikationen/Mono/M116s.htm.
Parvesse T. 2001. “Controlling Emissions from Halogenated Solvents.” Chemical Processing
[Chem. Process.]. Vol. 64, no. 4, pp. 48-51. Apr 2001
1
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0 °C
and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present guidelines. The
operating oxygen concentration conditions of exhaust gases are used for metallurgical sources.
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(vi)
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Primary aluminium production
Summary
Primary aluminium is produced directly from the mined ore, bauxite. The bauxite is refined into
alumina through the Bayer process. The alumina is reduced into metallic aluminium by
electrolysis through the Hall-Héroult process (either using self-baking anodes – Söderberg
anodes – or using prebaked anodes).
Primary aluminium production is generally thought not to be a significant source of chemicals
listed in Annex C of the Stockholm Convention. However, contamination with PCDD and
PCDF is possible through the graphite-based electrodes used in the electrolytic smelting
process.
Possible techniques to reduce the production and release of chemicals listed in Annex C from
the primary aluminium sector include improved anode production and control, and using
advanced smelting processes. The achievable performance level in this sector should be < 0.1
ng TEQ/Nm3.
1.
Process description
Primary aluminium production refers to aluminium produced directly from the mined ore, bauxite.
The bauxite is refined into alumina by the Bayer process, and then the alumina is reduced by
electrolysis (the Hall-Héroult process) into metallic aluminium. This section does not cover the
secondary aluminium processes, which is covered in section V.D (iii) of the present guidelines.
1.1.
The Bayer process: Refining bauxite to alumina
Bauxite is converted to alumina using the Bayer process (Figure 1). The bauxite ore is dried,
crushed and ground into a powder and mixed with a solution of caustic soda to extract the alumina
at elevated temperatures and pressures in digesters. A slurry is produced which contains dissolved
sodium aluminate and a mixture of metal oxides, called red mud, which is removed in thickeners.
The red mud is washed to recover the chemicals and is disposed of. The aluminate solution is
cooled and seeded with alumina to crystallize the hydrated alumina in precipitator tanks. The
crystals are washed and then calcined in rotary kilns or fluid bed/fluid flash calciners to produce the
aluminium oxide or alumina, which is a white powder resembling table salt.
1.2.
The Hall-Héroult process: Reduction by electrolysis of alumina to
aluminium
Aluminium is produced from alumina by electrolysis in a process known as the Hall-Héroult
process. The alumina is dissolved in an electrolytic bath of molten cryolite (sodium aluminium
fluoride). An electric current is passed through the electrolyte and flows between the anode and
cathode. Molten aluminium is produced, deposited at the bottom of the electrolytic cell or pot, and
periodically siphoned off and transferred to a reverberatory holding furnace. There it is alloyed,
fluxed and degassed to remove trace impurities. Finally, the aluminium is cast or transported to the
fabricating plants.
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61
Figure 1. Simplified flow sheet for alumina production
Source: Aluminium Association of Canada.
1.3.
Production of aluminium
There are two types of technologies used for the production of aluminium (Figure 2): those using
self-baking anodes (Söderberg anodes) and those using prebaked anodes.
The older Söderberg anodes are made in situ from a paste of calcined petroleum coke and coal tar
pitch, and are baked by the heat from the molten electrolytic bath. As the anode is consumed, more
paste descends through the anode shell in a process that does not require anode changes. Alumina
is added periodically to Söderberg cells through holes made by breaking the crust alumina and
frozen electrolyte which covers the molten bath. Depending on the placement of the anode studs,
these are known as vertical stud Söderberg or horizontal stud Söderberg cells or pots. Automatic
point feeding systems are used in upgraded plants, eliminating the need for regular breaking of the
crust.
Prebaked anodes are manufactured in a carbon plant from a mixture of calcined petroleum coke
and coal tar pitch, which is formed into a block and baked in an anode furnace. The prebaked anode
production plants are often an integrated part of the primary aluminium plant. The prebaked anodes
are gradually lowered into the pots as they are consumed, and need to be replaced before the entire
block has been consumed. The anode remnants, known as anode butts, are cleaned and returned to
the carbon plant for recycling. Depending on the method of feeding the alumina into the
electrolytic cells, the cells are called side-worked prebake or centre-worked prebake. For sideworked prebake cells, the alumina is fed to the cells after the crust is broken around the perimeter.
For centre-worked prebake cells, the alumina is fed to the cells after the crust is broken along the
centre line or at selected points on the centre line of the cell.
The cathode typically has to be replaced every five to eight years because of deterioration, which
can allow the molten electrolyte and aluminium to penetrate the cathode conductor bar and steel
shell. The spent cathode, known as spent pot lining, contains hazardous and toxic substances such
as cyanides and fluorides which must be disposed of properly.
Molten alumina is periodically withdrawn from the cells by vacuum siphon and is transferred to
crucibles. The crucibles containing liquid metal are transported to the casting plant, where the
aluminium is transferred to the holding furnaces. Alloying elements are added in these furnaces.
Dross (“skimmings”) formed by the oxidation of molten aluminium is skimmed off, and sealed
containers are used to minimize further oxidation of the dross. Nitrogen and argon blanketing is
used. This is followed by removal of sodium, magnesium, calcium and hydrogen. The treatment
gas used varies depending on the impurities. Argon or nitrogen is used to remove hydrogen;
mixtures of chlorine with nitrogen or argon are used to remove metallic impurities.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Figure 2. General schematic of the electrolytic process for aluminium production
Source: Aluminium Association of Canada.
2.
Sources of chemicals listed in Annex C of the Stockholm
Convention
Primary aluminium production is unlikely to be a significant source of releases of polychlorinated
dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF), although contamination is
possible through the graphite-based electrodes (AEA Technology Environment 1999, p. 63).
PCDD/PCDF release levels are generally thought to be low and the main interest is in the thermal
processing of scrap materials (UNEP 2003, p. 73). This is discussed further in Section 2.3 below.
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2.1.
63
Emissions of PCDD/PCDF
There is limited information available on PCDD/PCDF formation from primary aluminium
processes. Some literature suggests that initial emissions testing indicates that PCDD/PCDF are not
considered significant from this sector.
It is reported that it is unlikely that the Söderberg and prebaked processes release significantly
different emissions per ton of aluminium produced (AEA Technology Environment 1999, p. 63).
Test results on emission sources and abatement units associated with prebaked anode
manufacturing indicate that PCDD are not significant from these sources. However, if chlorine
compounds or additives are used, emissions will need to be examined (European Commission
2001, p. 669).
Some studies have tested for PCDD in fume from the casting process because the use of chlorine
for degassing and the presence of carbon from the combustion gases may lead to the formation of
PCDD. Results from primary smelter cast houses have shown that releases are significantly below
1 gram per year (European Commission 2001, p. 289). The potential for PCDD/PCDF formation
during the refining processes for both primary and secondary aluminium production has not been
fully investigated. It has been recommended that this source be quantified (European Commission
2001, p. 318).
2.2.
Releases to land
The production of primary aluminium from ores is not thought to produce significant quantities of
PCDD/PCDF (New Zealand Ministry for the Environment 2000). The Review of Dioxin Releases
to Land and Water in the UK states that there may be the possibility of graphite-based electrodes
having some PCDD/PCDF contamination (UK Environment Agency 1997). Swedish data suggest
that the spent sludge from the cells may contain 7.8 ng Nordic-TEQ kg-1. However, if the cathode
is high-purity carbon material and the reduction process does not involve chlorine or chloride
materials, it is unlikely that PCDD/PCDF will be present.
Metal reclaim fines may contain PCDD/PCDF because chlorine or chlorine-based products are
used to degas the fraction of the aluminium that is poured into the extrusion billets.
2.3.
Research findings of interest
Limited information exists on the unintentional formation of PCDD/PCDF from this
sector. It has been suggested that primary aluminium production is not considered to be a
significant source of releases. A paper (Anglesey Aluminium Dioxin and Furan Emission
Survey, July 2000) reports non-detect levels for dioxins and furans emissions. However, a
2001 Russian study of the PCDD/PCDF emissions in the city of Krasnoyarsk concluded
that the aluminium factory was responsible for 70% of industrial PCDD/PCDF emissions
to air and 22% of industrial releases to land. More studies in this area would be needed in
order to show whether or not primary aluminium production is a significant source of
dioxins and furans.
2.4.
General information on releases from primary aluminium plants
Greenhouse gases are a major pollutant from aluminium production and result from fossil fuel
combustion, carbon anode consumption, and perfluorocarbons from anode effects. In addition to
greenhouse gases, aluminium smelters also discharge other atmospheric emissions, as well as some
solid wastes (spent potliners) and liquid effluents (SNC-Lavalin Environment 2002, p. 3:14).
“The use of carbon anodes leads to emissions of sulphur dioxide (SO2), carbonyl sulphide
(COS), polycyclic aromatic hydrocarbons (PAHs) and nitrogen oxides (NOx). Most of the
sulphur in the carbon anode is released as COS, which is not entirely oxidized to SO2
before being emitted at the potroom gas scrubber stacks. Sulphur emissions are
predominately in the form of SO2 with a minor component of COS. The emission of
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
sulphur gases from aluminium reduction is expected to rise with the increasing sulphur
content of petroleum cokes used for anode manufacture. PAHs are the result of incomplete
combustion of hydrocarbons found in certain pitch used to form the anodes. The use of
prebake anodes has virtually eliminated the emissions of PAHs, mainly associated with
Söderberg anodes. The NOx emissions mainly come from the combustion of fuel in the
anode baking furnace” (SNC-Lavalin Environment 2002, p. 3:14).
“The electrolysis of alumina also leads to the emission of fluorides (particulate fluorides
and gaseous HF) and other particulates. The removal of fluorides from the cell gases in
modern alumina injection dry scrubber systems is now greater than 99% efficient and the
final fluoride emissions from modern prebake smelters are significantly lower. Anode
changing and cooling of spent anode butts are the most important sources of fugitive
fluoride emissions from an aluminium smelter and these are estimated to 4 to 5 times
greater than stack emissions (after the scrubber)” (SNC-Lavalin Environment 2002, p.
3:16).
The “anode effect” results in generation of perfluorocarbons in smelting pots when the
concentration of alumina falls below a certain level due to the lack of fresh feed. The carbon anode
preferentially reacts with the fluorine in the cryolite solution because there is insufficient oxygen
available from the alumina. When this event occurs, carbon tetrafluoride (CF 4) and
hexafluoroethane (C2F6) are produced, along with a surge in voltage. The amount of
perfluorocarbons generated depends on the efficiency of feed control in the pot. For pots not
equipped with proper controls, perfluorocarbon emissions from anode effects can be the largest
source, accounting for over 50% of the total smelter emissions (on a CO2-equivalent basis).
Practically any point-fed, computer-controlled pot can operate at low anode effect frequency. Older
technologies, such as horizontal stud and vertical stud Söderberg cells, have higher perfluorocarbon
generation rates. These technologies typically do not have individual pot sensing systems and the
feed is usually a non-automated bulk system. The process control techniques in modern prebaked
smelters are such that perfluorocarbon emissions can be reduced to less than 5% of the total
greenhouse gas emissions from the smelter. CO2 emissions from anode consumption are the next
largest source for pots without modern controls (SNC-Lavalin Environment 2002, p. 3:10–11).
Table 1. Emissions, effluents, by-products and solid wastes from primary aluminium
production
Air emissionsa
Process
Effluents
By-products and
solid wastes
Alumina refining
Particulate
Waste water containing
starch, sand, and caustic
Red mud, sodium
oxalate
Anode production
Particulates, fluorides, polycyclic
aromatic hydrocarbons, SO2,
PCDD/PCDFb
Waste water containing
suspended solids,
fluorides, and organics
Carbon dust, tar,
refractory waste
Aluminium
smelting
CO, CO2, SO2, fluorides
(gaseous and particulate),
perfluorocarbons (CF4, C2F6),
polycyclic aromatic
hydrocarbons, PCDD/PCDFb
Wet air pollution control
effluents (wet
electrostatic precipitator)
Spent potliners,
wet air pollution
control wastes,
sludges
a. Excluding combustion-related emissions.
b. Based on the Krasnoyarsk study (Kucherenko et al. 2001).
Source: Energetics Inc. 1997.
3.
New primary aluminium plants
The Stockholm Convention states that when consideration is being given to proposals for
construction of a new primary aluminium plant, priority consideration should be given to
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65
alternative processes, techniques or practices that have similar usefulness but which avoid the
formation and release of the identified substances.
3.1.
Alternative processes to primary aluminium smelting (emerging
technologies)
There are a number of research initiatives currently under way to produce primary aluminium while
concurrently reducing energy consumption and emissions (European Commission 2001, p. 335;
SNC-Lavalin Environment 2002; Welch 1999; USGS 2001; BCS Inc. 2003, p. 41–58). These
initiatives include:

Inert anodes: Carbon-free anodes that are inert, dimensionally stable, that are slowly
consumed, and produce oxygen instead of CO2. The use of inert anodes eliminates the need
for an anode carbon plant (and emissions of polycyclic aromatic hydrocarbons from the
process);

Wettable cathodes: New cathode materials or coatings for existing cathode materials that
allow for better energy efficiency;

Vertical electrodes – low-temperature electrolysis (VELTE): The process uses a nonconsumable metal alloy anode, a wetted cathode and an electrolytic bath, which is kept
saturated with alumina at the relatively low temperature of 750 °C by means of free
alumina particles suspended in the bath. This technology could produce primary aluminium
metal with lower energy consumption, lower cost, and lower environmental degradation
than the conventional Hall-Héroult process;

Drained cell technology: Features the coating of aluminium cell cathodes with titanium
dibromide and eliminating the metal pad, which reduces the distance between anode and
cathode, thereby lowering the required cell voltage and reducing heat loss;

Carbothermic technology: Carbothermic reduction produces aluminium using a chemical
reaction that takes place within a reactor and requires much less physical space than the
Hall-Héroult reaction. This process would result in significantly reduced electrical
consumption, and the elimination of perfluorocarbon emissions resulting from carbon
anode effects, hazardous spent pot liners, and hydrocarbon emissions associated with the
baking of consumable carbon anodes;

Kaolinite reduction technology: The production of aluminium by reduction of aluminium
chloride using clays holds appeal because the raw materials are readily available and
inexpensive. The thermodynamics also provide high-speed conversion reactions with lower
electrical demand and no bauxite residue is produced.
4.
Primary and secondary measures
Primary and secondary measures for reducing emissions of PCDD/PCDF from primary aluminium
production processes are outlined below.
The extent of emission reduction possible with the implementation of primary measures only is not
readily known. It is therefore recommended that consideration be given to implementation of both
primary and secondary measures at existing plants.
Note that no secondary measures have been developed specifically for primary aluminium smelters
to control the unintentional formation of PCDD/PCDF. The following are general measures that
may result in lower pollutant emissions at primary aluminium smelters, including releases of
PCDD/PCDF.
4.1.
Primary measures
Primary measures are understood to be pollution prevention measures that prevent or minimize the
formation and release of the identified substances (particulates, fluorides, polycyclic aromatic
hydrocarbons, sulphur dioxide, carbon dioxide, carbon monoxide, and perfluorocarbons). Note that
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
there are no primary measures identified for PCDD/PCDF. These are sometimes referred to as
process optimization or integration measures. Pollution prevention is defined as: “The use of
processes, practices, materials, products or energy that avoid or minimize the creation of pollutants
and waste, and reduce overall risk to human health or the environment.” (See section III.B of the
present guidelines.)
For new smelters, using the prebake technology rather than the Söderberg technology for
aluminium smelting is a significant pollution prevention measure (World Bank 1998). The use of
centre-worked prebaked cells with automatic multiple feeding points is considered to be a best
available technique for the production of primary aluminium (European Commission 2001, p. 325).
“Point feeders enable more precise, incremental feeding for better cell operation. They are
generally located at the centre of the cell and thereby cut down on the diffusion required to
move dissolved alumina to the anodic reaction sites. The controlled addition of discrete
amounts of alumina enhances the dissolution process, which aids in improving cell stability
and control, minimizing anode effects, and decreasing the formation of undissolved sludge
on the cathode. In the jargon of modern commerce, point feeders enable ‘just-in-time
alumina supply’ to permit optimum cell operation. Point feeder improvements continue to
be made as more accurate cell controllers become available” (BCS Inc. 2003, p. 47).
Advanced process controllers are also being adopted by industry to reduce the frequency of anode
effects and control operational variables, particularly bath chemistry and alumina saturation, so that
cells remain at their optimal conditions (BCS Inc. 2003).
Primary measures which may assist in reducing the formation and release of the identified
substances include (European Commission 2001, p. 326, 675–676):

An established system for environmental management, operational control and
maintenance;

Computer control of the electrolysis process based on active cell databases and monitoring
of cell operating parameters to minimize the energy consumption and reduce the number
and duration of anode effects;

If local, regional or long-range environmental impacts require SO2 reductions, the use of
low-sulphur carbon for the anodes or anode paste if practicable, or an SO2 scrubbing
system.
4.2.
Secondary measures
Secondary measures are understood to be pollution control technologies or techniques, sometimes
described as end-of-pipe treatments. Note that the following are not considered secondary measures
specific to minimization of PCDD/PCDF releases, but for pollutant releases generally.
The following measures have been shown to effectively reduce releases from primary aluminium
production and should be considered best available techniques (European Commission 2001, p.
326, 675–676):

Feed preparation: Enclosed and extracted grinding and blending of raw materials, fabric
filters for abatement;

Complete hood coverage of the cells, which is connected to a gas exhaust and filter. The
use of robust cell covers and adequate extraction rates. Sealed anode butt cooling system;

Better than 99% fume collection from cells on a long-term basis. Minimization of the time
taken for opening covers and changing anodes;

Gases from the primary smelting process should be treated to remove dust, fluorides and
hydrogen fluoride using an alumina scrubber and fabric filter. The scrubbing efficiency for
total fluoride should be > 99.8%, and the collected alumina used in the electrolytic cells;
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67

Use of low-NOx burners or oxy-fuel firing. Control of firing of furnaces to optimize the
energy use and reduce polycyclic aromatic hydrocarbons and NOx emissions;

If there is an integrated anode plant the process gases should be treated in an alumina
scrubber and fabric filter system and the collected alumina used in the electrolytic cells.
Tars from mixing and forming processes can be treated in a coke filter;

Destruction of cyanides, tars and hydrocarbons in an afterburner if they have not been
removed by other abatement techniques;

Use of wet or semi-dry scrubbing to remove SO2 if necessary;

Use of biofilters to remove odorous components if necessary;

Use of sealed or indirect cooling systems.
5.
Summary of measures
Tables 2 and 3 present a summary of the measures discussed in previous sections.
Table 2. Measures for new primary aluminium production plants
Measure
Alternative
processes
Description
Priority should be given to
alternative processes with
less environmental impacts
than tradition primary
aluminium production
plants
Considerations
Examples include:
 Inert anodes
 Wettable cathodes
Other comments
These processes are still
in the development
phase
 Vertical electrodes – lowtemperature electrolysis
 Drained cell technology
 Carbothermic technology
 Kaolinite reduction
technology
Prebake
technology
The use of centre-worked
prebaked cells with
automatic multiple feeding
points is considered a best
available technique
Performance
requirements
New primary aluminium
production plants should be
required to achieve stringent
performance and reporting
requirements associated
with best available
technologies and techniques
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Consideration should be given
to the primary and secondary
measures listed in Table 3
No performance
requirements have been
determined for releases
of PCDD/PCDF from
primary aluminium
plants
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Table 3. Summary of primary and secondary measures for primary aluminium production
plants
Measure
Description
Considerations
Other comments
Primary measures
Environmental
management system,
operational control and
maintenance
Computer-controlled
process and monitoring
To minimize energy consumption
and reduce number and duration of
anode effects
Feed selection: Use of
low sulphur carbon for
anodes or anode paste
To control sulphur dioxide
emissions, if necessary
SO2 scrubbing
system may be
used
Secondary measures
Feed preparation:
Enclosed grinding and
blending of raw
materials. Use of fabric
filters
To prevent the releases of
particulates
Complete hood
coverage of cells
The use of hoods that completely
cover cells to collect gases to the
exhaust and filter
Fume collection and
treatment
Fume collection efficiency should
be greater than 99%.
Gases should be treated to remove
dust, fluorides and HF using an
alumina scrubber and fabric filter
Low NOx burners or
oxy-fuel firing
The firing of the furnace should be
optimized to reduce emissions of
polycyclic aromatic hydrocarbons
and NOx
Alumina scrubber
Process gases from anode plant
should be treated in an alumina
scrubber and fabric filter system
Afterburner
To destroy cyanides, tars and
polycyclic aromatic hydrocarbons
if not removed by other abatement
Wet or semi-dry
scrubbing
To remove SO2 if necessary
Biofilters
To remove odorous components if
necessary
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The time taken for
opening the covers
and changing the
anodes should be
minimized
The alumina should be
used in the electrolytic
cells. Tars can be
treated in a coke filter
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6.
69
Achievable performance level
The achievable performance level for emissions of PCDD/PCDF in the primary aluminium sector
is < 0.1 ng TEQ/Nm3.2
References
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Europe. Prepared for Landesumweltamt Nordrhein-Westfalen, Germany, on behalf of European
Commission DG Environment.
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01269
831606, Fax: 01269 841867
BCS Inc. 2003. U.S. Energy Requirements for Aluminum Production: Historical Perspectives,
Theoretical Limits and New Opportunities. Prepared under contract for the United States
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Energetics Inc. 1997. Energy and Environmental Profile of the U.S. Aluminum Industry. Prepared
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European Commission. 2001. Reference Document on Best Available Techniques in the NonFerrous Metals Industries. BAT Reference Document (BREF). European IPPC Bureau, Seville,
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Kucherenko A., Kluyev N., Yufit S., Cheleptchikov A. and Brodskj E. 2001. “Study of Dioxin
Sources in Krasnoyarsk, Russia.” Organohalogen Compounds 53:275–278.
New Zealand Ministry for the Environment. 2000. New Zealand Inventory of Dioxin Emissions to
Air, Land and Water, and Reservoir Sources. www.mfe.govt.nz/publications/hazardous/dioxinemissions-inventory-mar00.pdf.
SNC-Lavalin Environment. 2002. Evaluation of Feasibility and Roadmap for Implementing
Aluminium Production Technologies That Reduce/Eliminate Greenhouse Gases and Other
Emissions. Prepared for Environment Canada.
UK Environment Agency. 1997. A Review of Dioxin Releases to Land and Water in the UK.
Research and Development Publication 3. Environment Agency, Bristol, United Kingdom.
UNEP (United Nations Environment Programme). 2003. Standardized Toolkit for Identification
and Quantification of Dioxin and Furan Releases. UNEP, Geneva.
www.pops.int/documents/guidance/Toolkit_2003.pdf.
USGS (United States Geological Survey). 2001. Aluminium Case Study. Appendix 2,
Technological Advancement: A Factor in Increasing Resource Use. Open-File Report 01-197.
pubs.usgs.gov/of/2001/of01-197 .
Welch B.J. 1999. “Aluminum Production Paths in the New Millennium.” Journal of Metals 51:5.
www.tms.org/pubs/journals/JOM/9905/Welch-9905.html.
World Bank. 1998. “Industry Sector Guidelines – Aluminum Manufacturing.” In: Pollution
Prevention and Abatement Handbook. World Bank, Washington, D.C
2
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0 °C
and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present guidelines. The
operating oxygen concentration conditions of exhaust gases are used for metallurgical sources.
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(vii)
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Magnesium production
Summary
Magnesium is produced either from raw magnesium chloride with molten salt electrolysis, or
magnesium oxide reduction with ferrosilicon or aluminium at high temperatures, as well as
through secondary magnesium recovery (for example, from asbestos tailings).
The addition of chlorine or chlorides, the presence of carbon anodes and high process
temperatures in magnesium production can lead to the formation of chemicals listed in Annex C
of the Stockholm Convention and their emission in air and water.
Alternative techniques may include the elimination of the carbon source by using non-graphite
anodes, and the application of activated carbon. However, achievable performance depends on
the type of process and controls utilized.
1.
Process description
There are two major process routes utilized for production of magnesium metal. The first process
recovers magnesium chloride from the raw materials and converts it to metal through molten salt
electrolysis. The second type of process involves reducing magnesium oxide with ferrosilicon or
aluminium at high temperatures. Examples of the two types of processes are described below.
Magnesium can also be recovered and produced from a variety of magnesium-containing
secondary raw materials (VAMI 2004).
1.1.
Magnesium production process from magnesium oxide resources
The process allows magnesium to be produced from oxide raw materials: magnesite, brusite,
serpentine and others. It is also suitable for magnesium production from raw materials containing
magnesium sulphate or its mixture with chlorides, including sea water. In all cases chlorine
produced by electrolysis is recycled and used for conversion of magnesium oxide or sulphate into
magnesium chloride (VAMI 2004).
Thermal processes for magnesium production are used in a number of countries, however these
processes are not considered best available techniques nor best environmental practices. In
countries where it is the only means of production, the following measures can be taken to reduce
the POPs that are being released into the environment.
Proper raw material selection: Knowledge of the composition of the raw materials can minimize
fuel usage by avoiding excessive quantities of one reagent which is heated and then disposed of as
waste. Control of the purity of raw materials through purchasing strategies and quality control
processes of suppliers assist in minimizing the energy usage and hence POPs release through
heating inserts.
The selection of a process which minimizes energy consumption will minimize the production of
POPs. Continuous processes tend to be more energy efficient as there is less heat used to return the
reactor to operating temperatures between cycles. One widely used process available for license is
the Magnatherm process which replaces the coal heating of the retort with electrical induction
heating.
In larger facilities coal flue gases may be passed through particle abatement. These require a
reliable electricity supply. However, storage of fine particulate matter is demanding in many
environments and appropriate storage and waste arrangements are required for the captured
material until a safe disposal route is identified. Co-location of facilities and regional cooperation
to manage and dispose wastes would be beneficial.
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71
The process consists of the following stages (see Figure 1):

Leaching of raw material by hydrochloric acid and purification of the solution produced;

Separation of magnesium chloride product in the form of synthetic carnallite or mixture of
chlorides from said solution;

Dehydration of said product in a fluidized bed by the stream of hot gases, containing
hydrogen chloride, with production of solid dehydrated product, containing not more than
0.3 wt.% of magnesium oxide and water each;

Feeding of said product into electrolyzers or head unit of flow line and its electrolysis, with
production of magnesium and chlorine.
Chlorine produced by electrolysis is fed into the burners of fluidized bed furnaces, where it is
converted into hydrogen chloride (HCl). Waste gases of the fluidized bed furnaces, containing HCl,
are either treated by water to produce hydrochloric acid, which is used for raw material leaching, or
neutralized by aqueous suspension of magnesium oxide to produce magnesium chloride solution.
Spent electrolyte forming in the course of electrolysis is used for synthetic carnallite production.
All the waste products containing chlorine are utilized with the production of neutral oxides. It is a
significant advantage of the process from an environmental point of view.
Figure 1. Flow diagram of magnesium production process from magnesium oxide resources
Source: VAMI 2004.
1.2.
The Pidgeon process (thermal reduction process)
In the Pidgeon process, magnesium is produced from calcined dolomite under vacuum and at high
temperatures using silicon as a reducing agent. In the process, the finely crushed dolomite
(magnesium/calcium) carbonate is fed to rotary kilns where it is calcined, and where the carbon
dioxide is driven off, leaving a product of calcined dolomite. The calcined dolomite is then
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pulverized in a roller mill prior to mixing with finely ground ferrosilicon and fluorspar. The fine
calcined dolomite, ferrosilicon, and fluorspar are weighed in batch lots and mixed in a rotary
blender. This mixture is then briquetted in briquetting presses (Noranda Magnesium website).
Briquettes are then conveyed to the reduction furnaces. The reduction operation is a batch process
releasing magnesium in vapour form, which condenses in the water-cooled section of the retort
outside the furnace wall. After removal from the furnace, the magnesium crown is pressed from the
sleeve in a hydraulic press. The residue from the reduction charge is removed from the retort and
sent to a waste dump.
Figure 2 illustrates the process in diagrammatic form.
Figure 2. Process flow chart: Timminco magnesium plant
Magnesite
Crushing
Kiln fines (sales)
Calcination
CO2, off-gases
(to atmosphere)
Stack
Grinding
Mixing
Ferrosilicon
Briquetting
Residue
(to waste dump)
Retorting
SF6
Melting
Casting
Magnesium ingots
(to markets)
Billets
(to markets)
Billets
Extrusion
Extrusions
(to markets)
Source: Hatch and Associates 1995.
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73
2.
Sources of chemicals listed in Annex C of the Stockholm
Convention
2.1.
Emissions to air
2.1.1.
General information on emission from magnesium production
Magnesium production facilities generate several types of pollutants, including dust, sulphur
dioxide (SO2), nitrogen oxides (NOx), chlorine (Cl2), hydrochloric acid (HCl), and in several cases
emission of sulphur hexafluoride (SF6) throughout the manufacturing process.
Dust and sulphur dioxide are mainly emitted from the calcinations of dolomite and magnesium
oxide (MgO), from pellet drying as well as from chlorination off-gas treatment.
The source of nitrogen oxides emissions are dolomite and MgO calcinations and pellet drying.
Chlorine and hydrochloric acid are released from electrolysis and chlorination processes, and the
chlorination off-gas treatment system.
While carbon dioxide is emitted from the whole manufacturing process, the source of sulphur
hexafluoride discharges is the cast-house.
2.1.2.
Emissions of PCDD and PCDF
According to tests conducted on an electrolytic process in a magnesium production plant in
Norway, the main process causing the formation of polychlorinated dibenzo-p-dioxins (PCDD) and
polychlorinated dibenzofurans (PCDF) was a furnace converting pellets of MgO and coke to
magnesium chloride (MgCl2) by heating in a Cl2 atmosphere at 700–800 °C (Oehme, Manø and
Bjerke 1989; European Commission 2001).
The purification of MgO using HCl and graphite blades (“chlorination”) or electrolysis of MgCl2
using graphite electrodes are also possible other sources of PCDD/PCDF formation (UNEP 2003).
Timminco Ltd, in Ontario, Canada, which utilizes the thermal reduction Pidgeon process
technology, reported PCDD/PCDF release to air of 0.416 g TEQ/year (CCME 2003).
Table 1 shows emissions to air from different magnesium production processes.
Table 1. PCDD/PCDF emissions to air from different magnesium production processes
Process type
Electrolytic
Source
Emissions3
(ng/Nm3)
From chlorination of offgas treatment
0.8
12
From chlorination vent gas
0.8
28
From
electrolysis/chlorination
Thermal
Reduction, refining and
melting
Norsk Hydro
process
3
Concentration
(µg TEQ/t)
13
0.08
3
< 1.0
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0 °C
and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present guidelines.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Hydro Magnesium Canada reported a total of 0.456 g TEQ/year4 emissions of PCDD/PCDF to air,
broken down as shown in Table 2.
Table 2. Emissions of PCDD/PCDF by source: Hydro Magnesium Canada
Source
g TEQ/year
Dissolving
0.001
Dehydration
0.112
Electrolysis
0.277
Foundry
0.025
HCl synthesis
0.0003
Mg remelting
0.050
2.2.
2.2.1.
Releases to other media
Water
The main water pollutants in the magnesium manufacturing process are metal compounds as
suspended solids. However, chlorinated hydrocarbons and PCDD/PCDF are also found in waste
water from the magnesium electrolysis process (Table 3)
Table 3. Releases of PCDD/PCDF to water from different magnesium production processes
ng/m3
ug TEQ/t of Mg
Electrolytic
100
13
Thermal
0.08
3
Type
Norsk Hydro process
< 0.1
Source: Hydro Magnesium Canada.
2.2.2.
Land
The wet scrubbing process utilized in treatment of gas streams would be expected to generate
residues containing PCDD/PCDF. A water treatment system that includes settling of these residues
in a lagoon would then constitute a release to land (UNEP 2003).
3.
Alternative processes for magnesium production
Although process efficiency and productivity could be the main driving forces in the advancement
and development of alternative new technologies, it is expected that environmental aspects will be
given due consideration This means elimination or minimization of the formation of pollutants at
source, and the incorporation of effective pollution abatement systems, should be part of the initial
design of the project.
3.1.
4
Norsk Hydro dehydration process
Hydro Magnesium Canada presentation at Electrolytic Magnesium Industry Bi-national Informative Meeting,
Montreal, 12 December 2000, by Jean Laperriere, Environment Chief.
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75
Norsk Hydro has developed and successfully implemented a new technology, an MgCl 2
dehydration process, in its plant in Canada (European Commission 2001). Releases of pollutants,
especially PCDD/PCDF, generated from this process are significantly lower than existing processes
(Tables 1 and 3).
The plant produces MgCl2 brine by dissolving magnesite rock in hydrochloric acid. Impurities such
as aluminium, iron and manganese are removed from the leach liquor by purification. The brine is
then subjected to evaporation and prilling and drying using the fluidized bed technique. This will
result in an anhydrous MgCl2 product.
Hydro’s electrolysis cells are operated at around 400 kA. The MgCl 2 prills are fed continuously
from the dehydration plant into the electrolysis cells. This operation produces magnesium metal
and chlorine gas. The chlorine gas is reacted with hydrogen to produce hydrochloric acid, which is
recycled to the magnesite dissolving stage. The molten magnesium is cast under controlled
conditions. The final products are pure metal and alloys in the form of ingots and grinding slabs.
3.2.
Noranda’s magnesium recovery from asbestos tailings
A new technology in use by Noranda5 involves recovery of magnesium from asbestos tailings
(Noranda Inc. website). The process description is as follows:
Transforming serpentine into high-grade magnesium: In Noranda’s proprietary magnesium process,
serpentine undergoes a series of chemical processes and filtration steps to produce a very pure
anhydrous magnesium chloride. This is electrolytically reduced in state-of-the-art high-efficiency
cells into magnesium and chlorine. The chlorine is completely captured and recycled. The
company’s projections for its environmental performance include emission levels of no more than
0.09 g TEQ of PCDD/PCDF to air, using an activated carbon adsorption system.
Feed preparation: Noranda’s magnesium process starts with crysotile serpentine
(3MgO•2SiO2•2H2O), a mining residue containing 23% magnesium. The material is already mined
and above ground, adjacent to the plant. Serpentine is crushed, screened and magnetically
separated. The material is then leached with hydrochloric acid to create magnesium chloride brine,
along with a silica and iron residue.
Brine purification: To purify the magnesium chloride solution, the brine goes through further
purification steps to remove major impurities such as boron. The impurities are extracted from the
brine by precipitation.
Fluid bed drying: High-purity brine is dried to produce granular magnesium chloride. This yields
partially dehydrated magnesium chloride (MgCl2). HCl is recycled for use in the leaching phase.
Melt chlorinator: The magnesium chloride granules are melted in an electrolyte and treated by a
chlorination process involving the injection of gaseous HCl. The acid and water are recovered in
the process for use in the leaching phase.
Electrolytic cell: Metallic magnesium is produced through electrolysis by sending a strong
electrical current through the electrolyte. The chlorine gas that is produced during the electrolysis
phase is washed and combined with hydrogen and thereby reconverted into acid, which will be
reconverted into gas and reused for the chlorination process.
Casting: The metallic magnesium is tapped and then cast in ingots.
Purification of emissions: The production facility is equipped with gas scrubbers throughout the
process to purify the process and ventilation emissions. The chlorine is completely captured,
recycled and returned to the process. Emissions are washed to extract particles and other
contaminants before being released into the atmosphere. The process releases no water effluent to
the environment.
4.
5
Primary and secondary measures
In April 2003 this plant was shut down for an indefinite time due to market conditions.
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4.1.
Primary measures
The electrolysis process is of most interest from the point of view of PCDD/PCDF emissions
because of the presence of carbon and of chlorine in the process and the high temperature
conditions.
Primary measures that may assist in reducing the formation and release of the identified substances
include eliminating the carbon source by substituting the graphite by non-graphite anodes, possibly
metal anodes. Replacement of graphite anodes by metal anodes took place in the chlorine industry
at the start of the 1970s, and very minor amounts of PCDF were formed (Eurochlor 2001).
The new MgCl2 dehydrating process has been found to produce much lower levels of PCDD/PCDF
(Tables 1 and 3).
It is expected that in the proposed Cogburn magnesium project in British Columbia the STI/VAMI
technology will produce less chlorinated hydrocarbons than produced at Magnola due to the
absence of chlorinators. See subsection 5 below for additional information.
4.2.
Secondary measures
Measures include:

Treatment of effluents using techniques such as nanofiltration and use of specially
designed containment for solid residues and effluents;

Treatment of off-gases by cleaning of the off-gas from the chlorinators in a series of wet
scrubbers and wet electrostatic precipitators before incineration, and using bag filters to
clean and remove entrained salts from the magnesium electrolysis process;

Use of activated carbon: In the Cogburn magnesium project, there are two chlorinated
hydrocarbon removal systems; both are based on activated carbon removal of chlorinated
hyrdocarbons in liquid effluents.
5.
Emerging research
5.1.
The Cogburn magnesium project
A Cogburn magnesium project in British Columbia is expected to utilize the STI/VAMI
electrolytic cell technology for the decomposition of MgCl 2 to magnesium metal and chlorine gas
(Figure 3). Presently in the magnesium industry, this is done largely in monopolar diaphragmless
electrolytic cells. The STI/VAMI technology is based on a flow-through design in which all the
cells in the cell hall are linked together. Each cell is fed individually. The magnesium and
electrolyte flow from one cell to the next via a system of enclosed launders. The magnesium is
collected at the end of the flow line in a separator cell, and is siphoned out for casting at the cast
house. This system is currently utilized at the Dead Sea magnesium plant in Israel (Hatch and
Associates 2003).
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77
Figure 3. Simplified flow diagram: Cogburn magnesium plant
Source: Hatch and Associates 2003.
6.
Summary of measures
Tables 4 and 5 present a summary of the measures discussed in previous sections.
Table 4. Summary of primary measures for magnesium plants
Measure
Alternative
processes
Description
Considerations
Priority consideration should be given to
alternative processes with less
environmental impacts than traditional
magnesium manufacturing processes
Examples include:
Feed quality
Increasing availability of magnesium
scrap and other magnesium-containing
raw materials would make it attractive
for smelters to use it in their process
Smelter should ensure that only high-grade
scrap, free of contaminants, is used
Pre-treatment
techniques
The calcinations of dolomite creates
significant amount of dust
Use of gas suspension calciner could reduce
it significantly
Guidelines on BAT and Guidance on BEP
 Norsk Hydro’s MgCl2 brine dehydration
process
 Elimination of carbon source: replaces
graphite with non-graphite anode
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Table 5. Summary of secondary measures for magnesium plants
Measure
Description
Treatment of
off-gases
Treatment of
effluent
7.
Considerations
Off-gases from chlorination furnaces in
magnesium plants contain pollutants
such as PCDD, PCDF and chlorinated
hydrocarbons
Use of wet scrubbers and wet electrostatic
precipitators remove aerosols, followed by
incineration to destroy PCDD/PCDF and
other volatile organic compounds.
Activated carbon is also used to absorb
pollutants
Waste water collected from the various
parts of the magnesium plant, such as the
scrubbing effluent from the chlorination
stage, contain PCDD/PCDF and
chlorinated hydrocarbons
Removal of solids by flocculation,
sedimentation and filtration, followed by
activated carbon injection to remove
contaminants
Achievable performance levels
Table 6. Emission factors in the magnesium industry: PCDD/PCDF
Classification
Emission factors: µg TEQ/t of Mg
Air
Water
Land
Product
Residue
Production using MgO/C thermal
treatment in Cl2 no effluent, limited gas
treatment
250
9,000
n.a.
n.a.
0
Production using MgO/C thermal
treatment
50
30
n.a.
n.a.
n.a.
Thermal reduction process
3
n.d.
n.a.
n.a.
n.a.
n.a. Not applicable.
n.d. Not determined.
Source: UNEP 2003.
Table 7. Emission factors in the magnesium industry: Hexachlorobenzene (HCB)
Location
Emission factors: µg/kg
Air
Water
Land
Process
generated
Volatilized
from land
Norsk Hydro,
Posrgrunn*
700–3,000
n.d.
n.d.
n.d.
n.d.
Norsk Hydro,
Bécancour*
90–170
2.4
60–120
n.d.
n.d.
439
0
8
Not estimated
~6
Noranda,
Asbestos**
n.d. Not determined.
* Source: Bramley 1998.
** Source: Kemp 2004; note facility was operating at only 50% of design capacity and emission
factor is believed to be overstated as a result.
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79
References
Bramley M.J. 1998. Dioxin and Hexachlorobenzene Releases from Magnesium Production in
North America: Lessons from Noranda’s Magnola Project in Asbestos, Quebec. Greenpeace,
Canada.
CCME (Canadian Council of Ministers of the Environment). 2003. Status of Activities Related to
Dioxins and Furans Canada-Wide Standards. CCME, Winnipeg.
www.ccme.ca/assets/pdf/d_f_sector_status_rpt_e.pdf.
Eurochlor. 2001. Effect of Dioxins on Human Health.
http://www.eurochlor.org/chlorine/issues/dioxins.htm.
European Commission. 2001. Reference Document on Best Available Techniques in the NonFerrous Metals Industries. BAT Reference Document (BREF). European IPPC Bureau, Seville,
Spain. eippcb.jrc.es.
Hatch and Associates. 1995. Addendum to Primary NonFerrous Smelting and Refining Sector in
Canada - Magnesium. Prepared for Environment Canada.
Hatch and Associates. 2003. Binder No. 1 Project Summary For Production Feasibility Study For
Cogburn Magnesium Plant. Prepared for Leader Mining International.
www.leadermining.com/Binder_No1_Project_Summary.pdf.
Noranda Inc. Noranda Magnesium – A Production Breakthrough.
my.noranda.com/Noranda/magnesium/Introducing+Noranda+Magnesium/A+Production+Breakthr
ough/_A+Production+Breakthrough.htm.
Noranda Magnesium. Magnesium Production: Thermal Reduction - Pidgeon Process.
www.norandamagnesium.com/.
Norsk Hydro. 2001. Environmental Report 2001, Light Metals: Specific Values.
www.hydro.com/de/global_commitment/environment/reports/light_metals_main.html.
Oehme M., Manø S. and Bjerke B. 1989. “Formation of Polychlorinated Dibenzofurans and
Dibenzo-p-dioxins by Production Processes for Magnesium and Refined Nickel.” Chemosphere
18:7–8.
Personal Communication, D. Kemp, 2004
Personal communication from Expert Group Best Available Techniques Best Environmental
Practices, UK Member, February 2006
UNEP (United Nations Environment Programme). 2003. Standardized Toolkit for Identification
and Quantification of Dioxin and Furan Releases. UNEP, Geneva.
www.pops.int/documents/guidance/Toolkit_2003.pdf.
VAMI (Russian National Aluminium-Magnesium Institute). 2004. Magnesium Production
Process from Magnesium Oxide Resources.
http://www.vami.ru/processes/magnesium/sposob_proizvod_magnia_is_oksidnogo_siria.htm.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
(viii) Secondary steel production
Summary
Secondary steel is produced through direct smelting of ferrous scrap using electric arc furnaces.
The furnace melts and refines a metallic charge of scrap steel to produce carbon, alloy and
stainless steels at non-integrated steel mills. Ferrous feed materials may include scrap, such as
shredded vehicles and metal turnings, or direct reduced iron.
Chemicals listed in Annex C of the Stockholm Convention, such as PCDD and PCDF, appear
to be most probably formed in the electric arc furnace steel-making process via de novo
synthesis by the combustion of non-chlorinated organic matter such as polystyrene, coal and
particulate carbon in the presence of chlorine donors. Many of these substances are contained in
trace concentrations in the steel scrap or are process raw materials such as injected carbon.
Primary measures include adequate off-gas handling and appropriate off-gas conditioning to
prevent conditions leading to de novo synthesis formation of PCDD/PCDF. This may include
post-combustion afterburners, followed by rapid quench of off-gases. Secondary measures
include adsorbent injection (for example, activated carbon) and high-level dedusting with fabric
filters.
The achievable performance level using best available techniques for secondary steel
production is < 0.1 ng/Nm3.
1.
Process description
1.1.
General process description
The direct smelting of iron-containing materials, such as scrap, is usually performed in electric arc
furnaces, which play an important and increasing role in modern steelworks. The furnace melts and
refines a metallic charge of scrap steel to produce carbon, alloy and stainless steels at nonintegrated (secondary steel) mills.
An electric arc furnace is a cylindrical vessel with a dish-shaped refractory hearth and electrodes
that lower from the dome-shaped, removable roof. Refractory bricks form the lining of the furnace.
The walls typically contain water-cooled panels, which are covered to minimize heat loss. The
electrodes may also be equipped with water-cooling systems.
Electric arc furnace steel making consists of scrap charging, melting, refining, deslagging and
tapping. In addition to scrap steel, the charge may include pig iron and alloying elements. As the
steel scrap is melted, additional scrap may be added to the furnace. The electric arc furnace
generates heat by passing an electric current between electrodes through the charge in the furnace.
This energy is supplemented by natural gas, oxygen and other fuels.
Other technologies used to smelt iron-containing materials are: cupola furnaces (hot and cold),
induction furnaces, and blast furnaces.
Cupola furnaces are used for the production of cast iron and cast steel. Cupola furnaces are cokeheated vertical furnaces that are charged batch-wise with raw materials, or sometimes charged
continuously using vibrating chutes. The necessary heat for smelting of the charged materials is
produced by means of coke combustion and air (hot or cold) blown in through tuyeres at the sides
of the furnace. The actual smelting zone is found in the lower third of the vertical furnace. With
regard to heat utilization the operation is similar to residential coal-fired stoves. The smelting
capacity depends mainly on the air volume blown in for combustion, the amount of fuel and the
diameter of the furnace. (The European Dioxin Emission Inventory Stage II, December 2000)
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81
Induction furnaces are simple crucibles or channels that are heated by an external electrical coil,
channel induction furnaces are mainly used for melting items with large dimensions. Current is
induced in the metal that has been charged into the furnace and heat is generated. The furnaces may
be equipped with fume extraction hoods and dust abatement that can be used during drossing and
pouring operations. Access to an induction furnace for charging and tapping means that a movable
hooding system is often used. The hoods are robust so that they can withstand some mechanical
impact. Alternatively, efficient fixed or lip extraction is used. The efficiency of this furnace can be
low for some materials but can be increased particularly if the feed material is small. Large items
can be cut to improve efficiency and also to allow the fume collection hoods to be deployed
properly. Some continuous processes also retain a “heel” of molten metal in the bottom of the
furnace between charges if the operation allows it. They may also be operated under vacuum, for
example when melting super alloys, high alloyed steel, pure metals and in some cases for metal
distillation. The temperature of the furnace can be automatically controlled to minimise the
production of fume when melting volatile or oxidisable metals such as zinc or alloys containing
zinc. These furnaces are also used to “Hold” molten metal for alloying and casting. The current
induced in these furnaces causes the metal to be stirred electro-magnetically, which promotes
mixing of the charge and any alloying materials that are added. (IPPC 2001)
A blast furnace is a vertical furnace using tuyeres to blast heated or cold air into the furnace burden
to smelt the contents. Sinter is charged into the top of the blast furnace in alternating layers with
coke.
1.2.
Furnace feedstock
The major feedstock for the furnace is ferrous scrap, which may include ferrous scrap from inside
the steelworks (for example, offcuts), cut-offs from steel product manufacturers (for example,
vehicle builders) and capital or post-consumer scrap (for example, end-of-life vehicles and
appliances) (European Commission 2000). Additional inputs are fluxes and additions like
deoxidants or alloying elements. Direct reduced iron is also increasingly being used as a feedstock,
due to both its low gangue content and variable scrap prices (European Commission 2000).
Fluxing materials are added to combine with unwanted materials and form a slag. Slag removes the
steel impurities (for example, silicon, sulphur and phosphorus) from the molten steel. Oxygen may
be added to the furnace to speed up the steel-making process. At the end of a heat, the furnace tips
forward and the molten steel is poured off.
1.3.
The electric arc furnace
Many steel plants increase productivity by using the electric arc furnace for the melting phase and a
ladle metallurgy facility for the final refining and alloying phase. In some cases the steel ladle is
taken to a vacuum degassing station where the gas content of the molten steel is reduced for quality
requirements.
The molten steel from the electric arc furnace or the ladle metallurgical facility is cast in a
continuous casting machine to produce cast shapes including slabs, billets or beam blanks. In some
processes, the cast shape is torch cut to length and transported hot to the hot rolling mill for further
processing. Other steel mills have reheat furnaces. Steel billets are allowed to cool, and are then
reheated in a furnace prior to rolling the billets into bars or other shapes.
Production of steel from scrap consumes considerably less energy than production of steel from
iron ores (EPRI 1997). Electric arc furnace steel manufacturing is an important recycling activity
that contributes to the recovery of steel resources and waste minimization.
The use of electric arc furnaces in the production of steel provides three major benefits: lower
capital cost for a steel-making shop, significantly less energy required to produce steel compared to
the coke oven/blast furnace/basic oxygen furnace method of the integrated steel makers, and
avoidance of coke ovens.
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Electric arc furnace steel making is a dynamic batch process with steel tap-to-tap times of one hour
or less for a heat except for stainless and specialty steel producers. The process is constantly
changing from the removal of the furnace roof for charging the steel scrap to the meltdown of the
steel scrap, with the resultant emissions from scrap contaminants such as oils and plastics, to the
refining period, and finally tapping of the steel. The conditions within the electric arc furnace and
the combustion processes vary throughout the heat production cycle.
In recent years, more new and existing electric arc furnaces have been equipped with a system for
preheating the scrap in the off-gas in order to recover energy. The so-called shaft technology and
the Consteel process are the two proven systems that have been introduced. The shaft system can
be designed to reheat 100% of the scrap (European Commission 2000).
Some electric arc furnaces also use a water spray or evaporative cooling system to cool the hot offgases, and some use heat exchangers ahead of the emission control device. The furnaces may be
equipped with dry, semi-wet or wet air pollution controls. Semi-wet and wet gas cleaning systems
may be sources of waste water.
Figure 1 shows the electric arc furnace and a generic fabric filter emission control system.
Figure 1. Generic electric arc furnace emission control system
Canopy
hood
Post
Combustion
Evaporative
Cooler
Optional
Optional
EAF
Oxygen injection/
carbon injection/
oxyfuel burner
Spark
Arrestor
Baghouse
Stack
Air-to-gas
cooler
Optional
Source: William Lemmon and Associates Ltd. 2004.
2.
Sources of chemicals listed in Annex C of the Stockholm
Convention
2.1.
Emissions
2.1.1.
PCDD/PCDF formation
Electric arc furnace steel making is a batch process that can result in fluctuating emissions during
heating of the charge and from heat to heat. Gas handling systems vary from facility to facility,
both in configuration and design. These factors contribute to a varying concentration in process offgases.
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As a high-temperature metallurgical process, particulate matter that contains a fine fume of metal
and metal oxides is generated. High-efficiency pollution control systems are required to remove the
fine particulate matter in the off-gases.
Aromatic organohalogen compounds, including polychlorinated dibenzo-p-dioxins (PCDD),
polychlorinated dibenzofurans (PCDF), chlorobenzenes and polychlorinated biphenyls (PCB) may
be formed as a consequence of the thermal process and have been detected in electric arc furnace
off-gas. The most important members of this group of compounds are PCDD/PCDF. Scrap
preheating may result in higher emissions of aromatic organohalogen compounds.
A report entitled Research on Technical Pollution Prevention Options for Steel Manufacturing
Electric Arc Furnaces (William Lemmon and Associates Ltd. 2004), prepared for the Canadian
Council of Ministers of the Environment, takes into account the United Nations Environment
Programme (UNEP) document Formation of PCDD/PCDF – An Overview (UNEP 2003), and
provides an understanding of the basic formation mechanism of PCDD/PCDF. Information from
this report is summarized below.
1. The processes by which PCDD/PCDF are formed are not completely understood. Most
information about these substances in combustion processes has been obtained from
laboratory experiments, pilot-scale systems and municipal waste incinerators.
2. PCDD/PCDF appear to be most probably formed in the electric arc furnace steel-making
process via de novo synthesis by the combustion of non-chlorinated organic matter such
as polystyrene, coal and particulate carbon in the presence of chlorine donors. Many of
these substances are contained in trace concentrations in the steel scrap or are process
raw materials such as injected carbon. Ovaco has commented that it is well known that
the emission of PCDD/F is very low when using stainless steel scrap as raw material: a
fraction only of that of other EAFs. Possibly due to catalytic effects of compounds of Ni
or Cr present in the dusts.
3. There is an inherent dualism of formation and dechlorination of PCDD/PCDF which
occurs in the same temperature range and especially under the conditions present in the
electric arc furnace. In general, dechlorination of PCDD/PCDF appears to take place at
temperatures above 750 °C in the presence of oxygen. As the temperature increases
above 750 °C, the rate of dechlorination increases and the required residence time
decreases.
4. Increasing the oxygen concentrations results in increasing formation of PCDD/PCDF. It
is not known whether this continues at elevated oxygen concentrations (for example,
above 10% O2). Under pyrolytic conditions (oxygen deficiency) dechlorination of
PCDD/PCDF occurs at temperatures above 300 °C.
5. Some metals act as catalysts in the formation of PCDD/PCDF. Copper is a strong catalyst
and iron is a weaker one.
6. Condensation starts in the 125 – 60 °C range with the higher-chlorinated PCDD and
increases very rapidly as the temperature drops. The lower-chlorinated PCDF are the last
to condense, which explains why the tetra and penta PCDF constitute the majority of the
PCDF in electric arc furnace emission tests.
7. Emission test results had higher PCDD/PCDF emission concentrations when the gas
temperature exiting the gas conditioning system/gas cooling device was consistently
above 225 °C, indicating that de novo synthesis had taken place in the gas conditioning
system.
8. PCDF consistently accounted for 60–90% of the PCDD/PCDF concentration in electric
arc furnace emission tests.
9. Two furan congeners, 2,3,7,8-TCDF (tetrachlorodibenzofuran) and 2,3,4,7,8-TCDF,
consistently accounted for 60–75% of the PCDD/PCDF I-TEQ concentration in electric
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arc furnace emission tests. These results are comparable to the theoretical condensation
calculations for PCDD/PCDF, as these two congeners would be the last to condense as
the gas temperature decreases.
10. These latter findings indicate that there is a predominant PCDD/PCDF formation
mechanism, de novo synthesis, for the electric arc furnace steel-making process. It
appears likely that variations in the PCDD/PCDF fingerprint for the process are due to
variations in the constituents of the scrap charge, varying conditions in the furnace
resulting from changes in operating practices from heat to heat and plant to plant, varying
conditions in the gas conditioning and cleaning system, and differences in baghouse
collection efficiencies.
Electric induction furnaces require cleaner scrap charges than electric arc furnaces can tolerate, and
melt their charge using magnetic fields. While there are some similarities to electric arc furnaces,
dioxin and furan generation in such units is expected to be significantly lower than from electric arc
furnaces.
With regard to emissions from cupola furnaces employed in cast iron and steel foundries, a German
submission to the European Dioxin Inventory – Stage II summarized the results of a study
collecting data on 25 cold-blast cupolas located in Germany. Cold blast cupola furnaces (also
termed cold air or cold wind cupolas) were identified in the Standardized Toolkit for Identification
and Quantification of Dioxin and Furan Releases (UNEP 2001) as having a higher potential than
other designs for significant emissions:
“For foundries, there are hardly any data available: testing in Germany (SCEP 1994) showed
that hot air cupolas and induction furnaces fitted with fabric filters had low emissions to air,
an emission factor of 0.03 μg TEQ/t of product should be used.
Cold air cupolas showed higher emissions and a factor of 1 μg TEQ/t is used for plants with
fabric filters.
Limited testing on rotary drum furnaces showed higher levels again and a factor of 4.3 μg
TEQ/t is applied to plants with fabric filters for gas cleaning.
Where cold air cupolas or rotary drum furnaces are used which do not have fabric filters or
equivalent for gas cleaning a higher emission factor of 10 μg TEQ/t should be used.
If poor quality scrap (high contamination) or poorly controlled furnaces with gas cleaning
other than effective fabric filters is found this should be noted.”
The more recent work reported for the European Dioxin Inventory – Stage II focussed on wellcontrolled cold blast cupolas producing iron for castings, equipped with fabric filters for particulate
emission control. This studyindicates that the range of the 18 individual emission samples obtained
was 0.003 to 0.184 ng I-TEQ/Nm3, and that the three-run averages for four of the six furnaces
tested were below 0.1 ng I-TEQ/Nm3 (the emission limit value for municipal waste incinerators).
It also concluded that “For all furnaces studied the average emission factor was found to amount to
0,35 μg I-TEQ/t of smelted iron in the furnaces with a maximum value reaching 1,45 μg I-TEQ/t”
(European Commission, 2000). The conclusions of this chapter of the document were (Ibid):
“Looking at the concentrations found in the waste gases cold-blast cupola furnaces operated in
iron and steel foundries cannot be considered as important sources of dioxins and furans due to
their emitted total amounts of PCDDs and PCDFs. Thus, the results of the measurements agree
with a few known data that existed before the investigations were started.
Note however, that the emissions for North Rhine-Westphalia were extrapolated from only 6
furnaces. It cannot be said with certainty that these furnaces are representative for all cold-blast
cupola furnaces operated in Germany. Within this project one furnace was found having PCDD
and PCDF concentrations in the filter-collected dust of up to approximately 12 μg I-TEQ/kg. This
is considerably higher than from those plants where emissions were measured (highest
concentration in the filter-collected dust from these plants was 0,4 μg I-TEQ). In addition, a high
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temporal fluctuation of PCDD and PCDF concentrations in the filter-collected dusts became
apparent. Therefore, despite of an indication of a positive correlation between the concentrations
in the filter-collected dust and the concentrations in the waste gas — obtained from measurement
results — it is not allowed to assume that this correlation may be extrapolated on furnaces with
higher concentrations in the filter-collected dusts. For clarification, a further study programme
would be necessary which, for example, would allow measurements of PCDD and PCDF
concentrations in the filter-collected dust of a furnace over a longer period of time.
From the observed interdependence of PCDD and PCDF emissions and the amounts of cast scrap
and recycled material applied it can be concluded that the contaminants adhering to the cast scrap
(remnants of paint, oils etc.) have an influence on the emissions. In order to reduce dioxin
concentrations a decrease of the amount of cast scrap would make sense, however, this would
considerably reduce the cost efficiency of foundries. The question arises, whether certain
contaminants on the cast scrap play a major role in the development and emission of PCDDs and
PCDFs. If this is so, it would require a selective elimination from the charged input material.”
2.1.2.
PCDD/PCDF research on electric arc furnaces
Most of the research on PCDD/PCDF formation and control has been carried out for electric arc
furnaces in Europe. The earliest reported work was by Badische Stahlwerke GmbH (BSW) in
Kehl/Rheim, Germany, in the early 1990s (Weiss and Karcher 1996). Other European steel
companies followed BSW’s lead under regulatory pressure from national environmental agencies.
A summary of the electric arc furnace operational findings follows:
1. The BSW research project confirmed that a high concentration of hydrocarbon material
in the steel scrap significantly increased the emissions of volatile organic compounds and
PCDD/PCDF.
2. Emission test results from BSW, ProfilARBED, Differdange and Gerdau Ameristeel
Cambridge emission-testing programmes had higher PCDD/PCDF emission
concentrations when the gas temperature exiting the gas conditioning system/gas cooling
device was consistently above 225 °C, indicating that de novo synthesis had taken place
in the gas conditioning system.
3. PCDF consistently accounted for 60–90% of the PCDD/PCDF I-TEQ concentration in
the Canadian electric arc furnace emission tests. Similar results have been reported in
European emission tests of electric arc furnaces.
4. Two PCDF congeners, 2,3,7,8-TCDF and 2,3,4,7,8-TCDF, consistently accounted for
60–75% of the PCDD/PCDF I-TEQ concentration in the Canadian electric arc furnace
emission tests. Similar results have been reported in European emission tests of electric
arc furnaces. These results are comparable to the theoretical condensation calculations for
PCDD/PCDF, as these two congeners would be the last to condense as the gas
temperature decreases.
5. The congener I-TEQ concentration distributions in the Canadian electric arc furnace
emission tests were similar regardless of the total PCDD/PCDF I-TEQ concentrations.
6. The findings indicate that de novo synthesis is the predominant PCDD/PCDF formation
mechanism for the electric arc furnace steel-making process.
7. It appears likely that variations in the PCDD/PCDF emission fingerprint for the electric
arc furnace steel-making process are due to variations in the constituents of the scrap
charge, varying conditions in the furnace resulting from changes in operating practices
from heat to heat and plant to plant, varying conditions in the gas conditioning and
cleaning system, and differences in baghouse collection efficiencies. There is insufficient
publicly available information to determine the relative importance of these factors.
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2.1.3.
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Review of electric arc combustion chemistry and PCDD/PCDF formation
A review of the relationship of electric arc furnace combustion chemistry with PCDD/PCDF
formation in the furnace may be summarized as follows:
1. PCDD/PCDF can be formed from related chlorinated precursors such as PCB,
chlorinated phenols and chlorinated benzenes.
2. The environment inside a steel-making electric arc furnace is very complex and is
constantly varying. The combustion chemistry produces conditions that are amenable to
PCDD/PCDF formation. The hydrocarbons entering the furnace in the scrap may be
vaporized, cracked, partially combusted or completely combusted, depending on the
conditions in the furnace or parts of the furnace during or after charging. Other sources of
carbon include injected carbon and the graphite electrodes. The dual processes of
PCDD/PCDF formation and dechlorination may be proceeding at the same time if the
oxygen concentration and temperature are such that some PCDD or PCDF congeners are
being formed while other congeners are being dechlorinated.
3. The research on optimization of internal post-combustion indicates that under normal
steel-making operations, conditions favourable to PCDD/PCDF formation – oxygen-rich
atmosphere, reactive carbon particles and temperatures under 800 °C – are present in
parts of the furnace during the meltdown phase and possibly for some time afterwards.
Given that metals that act as catalysts are present and that trace amounts of chlorine may
be present in some of the charge materials and fluxes, the conditions appear to be present
for de novo synthesis to occur. Since ideal mixing conditions are not present, it appears
that a portion of the PCDD/PCDF that are formed will leave the electric arc furnace in
the off-gas without encountering sufficiently high temperatures for dechlorination to take
place.
4. Most of the research on combustion chemistry and internal post-combustion in electric
arc furnace steel making has aimed to increase productivity by taking advantage of fuels
within the furnace – such as hydrocarbons, carbon monoxide and hydrogen – to replace
electric energy with chemical energy, thus reducing the total energy input, which results
in lower production costs per ton of product.
5. Scrap preheating may result in elevated emissions of chlorinated aromatic compounds
such as PCDD/PCDF, chlorobenzenes, PCB, as well as polycyclic aromatic
hydrocarbons, and other products of incomplete combustion from scrap contaminated
with paints, plastics, lubricants or other organic compounds. The formation of these
pollutants may be minimized by post-combustion within the furnace (as opposed to
external post-combustion of the off-gas) by additional oxygen burners developed for
burning the carbon monoxide and hydrocarbons, which recovers chemical energy. It has
been suggested that scrap preheating increases the organic matter in the flue gas and
maybe the formation of chlorinated compounds too. What happens to the emissions
depends on total heat energy balance of the flue gas system. In Ovaco’s case, scrap
preheating decreases the emission of PCDD/F (and most probably increases emission of
light organic compounds). It depends on the fact that scrap preheating acts as an efficient
gas cooler. Low gas temperature at the filter means that heavy organic compounds are
separated with dust. (Ovaco, 2006)
6. Indications are that internal post-combustion may be a more attractive option than
external post-combustion for PCDD/PCDF formation prevention.
2.2.
PCDD/PCDF releases in solid waste and waste-water sources
Most mills worldwide operate electric arc furnaces with dry off-gas cleaning systems (i.e., fabric
filter dust collectors), which produce no process waste water that would require treatment.
Some existing electric arc furnaces may be equipped with semi-wet air pollution control systems
(European Commission 2000). Semi-wet systems apply water to the furnace off-gases in order to
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partially cool and condition the off-gases prior to particulate removal in an electrostatic
precipitator. Sites are able to achieve zero waste-water discharge from semi-wet systems by
balancing the applied water with water that evaporates in the conditioning process. Non-contact
cooling water is the predominant water source; however, some facilities may use treated process
water and plant service water (EPA 2002).
Standards of some jurisdictions identify zero discharge as the best available technique for semi-dry
gas cleaning systems.
In some European Union countries wet scrubbers are used to clean the off-gases from electric arc
furnaces at some mills. However, no information from these facilities is available on waste-water
quantities and methods of treatment (European Commission 2000). Consequently, no findings were
concluded as to best available techniques for treating and minimizing PCDD/PCDF releases from
waste water from wet air pollution control systems.
Residues in the form of dust collected by the dry air pollution control system for electric arc
furnaces may contain trace levels of PCDD/PCDF.
Cupola furnaces may be controlled by wet scrubbers or dry filter systems. The work done on cold
blast cupola furnaces in North Rhine-Westphalia noted earlier found significant levels of
PCDD/PCDF in some collected filter dust samples. The study found 7 samples below 0.1 µg ITEQ/kg dry mass, 19 between 0.1 and 1.0 µg/kg, and 8 above 1.0 µg/kg. One sample had levels of
approximately 12 µg I-TEQ/kg dry mass. While these levels were sufficient that all of the majority
(27) of the samples would have been considered contaminated for the purposes of a German guide
requiring remediation of sites designated as childrens’ playgrounds (i.e., 0.1 ng I-TEQ/kg dry
mass), none of the samples exceeded levels (100 µg total PCDD/PCDF per kg dry mass) which
would have triggered the requirement for special actions to be undertaken by plant operators under
German ordinances on dangerous substances and prohibited chemicals. It was also determined that
15 samples would not have been permitted to be sold or traded under the provisions of the
ordinance respecting dangerous substances (European Commission, 2000). No data has been
located relating to dioxin levels in scrubber blow-down effluents from cupola furnace operations.,
although given the results noted above for dry collection systems there is a potential for dioxin
releases to the environment from such streams.
3.
Electric arc furnace process improvements and alternative
processes for electric steel making
3.1.
Process improvements
The electric arc furnace steel-making process has been undergoing change over the past decades.
Research and development for electric arc furnace steel making, especially in Europe, is focused on
furnace design improvements to increase productivity and energy efficiency, and to reduce steelmaking costs.
There are two major driving forces – reduction of steel-making costs as exemplified by increased
productivity, and increased product quality as exemplified by quality demands from the automotive
industry. Added to these is a third driving force – environmental pressures. Productivity
improvements have resulted in shorter tap-to-tap times, increased energy efficiency and increased
use of chemical energy.
Quality demands have been met through selection of scrap, furnace operating practices and
increased use of ancillary processes such as ladle metallurgy and vacuum degassing.
Environmental pressures include the requirements for PCDD/PCDF emission reduction and smog
precursor reduction of substances such as fine particulate. One option for these producers is to use
higher-quality scrap with lower contaminant levels (William Lemmon and Associates Ltd. 2004).
A second option is to replace part of the scrap charge by direct reduced iron or similar products that
are produced from iron ore and have contaminant concentrations lower than the lower-quality scrap
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steel grades. Merchant direct reduced iron production is increasing and the international market is
growing, so greater availability may mean that some electric arc furnace steel makers have the
option of buying direct reduced iron rather than on-site production. There is very limited available
information on PCDD/PCDF emissions from the direct reduced iron process but, given the
characteristics of the process, PCDD/PCDF emissions are likely to be very small. Information on
the formation and emissions of PCDD/PCDF from the use of direct reduced iron in electric arc
furnace steel making is not available.
A third option is the use of hot metal in electric arc furnace steel making. This is forecast to
increase as steel makers strive for shorter heat cycles and higher productivity (Fruehan 1998).
Information on the impact of this option on PCDD/PCDF emissions is not available. With
preheating of part of the scrap about 60 kWh/t can be saved; in the case of preheating the total
scrap amount up to 100 kWh/t liquid steel can be saved. The applicability of scrap preheating
depends on the local circumstances and has to be proved on a plant-by-plant basis.
Advances in the electric arc furnace steel-making process often have collateral benefits, including
the reduction of particulate matter and PCDD/PCDF emissions, except for scrap preheating as
noted above. Usually the objective of advanced operating practices is improved operational and
energy efficiency to increase productivity and thus increase production and reduce operating costs.
3.2.
Alternative processes
No alternative steel-making technology would replace the electric arc furnace for the high
production operations of steel plants. While other electrode materials have been used for a few
furnaces in the past, there are no alternatives to the graphite electrode at the present time.
4.
Primary and secondary measures
Primary and secondary measures for reducing emissions of PCDD/PCDF from electric arc furnaces
are outlined in the ensuing section. Much of this material has been drawn from William Lemmon
and Associates Ltd. 2004. Some of these also apply to cupola and electric induction furnaces.
The extent of emission reductions possible with implementation of primary measures only is not
readily known. Implementation of both primary and secondary measures at existing and new plants
is probably necessary to achieve the desired emission levels.
It should be feasible for all plants to implement some or all of the pollution prevention practices
identified below.
4.1.
Primary measures for emissions
Primary measures, often called pollution prevention techniques, are able to avoid, suppress or
minimize the formation of PCDD/PCDF or dechlorinate PCDD/PCDF in the steel-making process.
As a general measure, an integral part of a facility’s pollution prevention programme should
include best environmental, operating and maintenance practices for all operations and aspects of
the electric arc furnace steel-making process.
The following list presents a range of options as primary measures; some may not be applicable to
all furnace designs or plants, and some may require further investigation. This list of techniques
has been developed based on work done with electric arc furnaces, and while many of the same
principles are expected to hold for electric induction and cupola furnaces, they have not been
documented for those applications. However, the fact that most of the existing test results for the
other furnace types are below 0.1 ng I-TEQ/Nm3 indicates that a combination of these measures
and the secondary measures listed below should be effective to limit emissions.
4.1.1.
Raw material quality
The major raw material used in the steel-making process is iron or steel scrap. Contaminants,
including oil, plastics and other hydrocarbons, are often present in the scrap. Pollution prevention
practices to prevent or minimize the entry of contaminants into furnaces for iron and steel making
include changes in material specifications, improved quality control programmes, changes in the
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types of raw materials (such as avoidance of oily scrap or cleaning oily scrap) and programmes to
prevent the entry of contaminants.
4.1.2.
Furnace operation
Recent changes in electric arc furnace operational practices that have been adopted to improve
operational and energy efficiency appear to have collateral benefits to reduce PCDD/PCDF or, in
certain conditions, to dechlorinate PCDD/PCDF. Pollution prevention practices that appear to
reduce PCDD/PCDF emissions include minimizing the duration of the roof being open for
charging, reduction of air infiltration into the furnace and avoiding or minimizing operational
delays. Condensation of PCDD/PCDF increases rapidly at temperatures below 125 °C, starting
with the higher-chlorinated dioxins.
4.1.3.
Off-gas conditioning system design
Off-gas conditioning includes the collection, cooling and ducting of furnace off-gases prior to
cleaning in a baghouse. Off-gas conditioning system conditions may be conducive to de novo
synthesis formation of PCDD/PCDF unless care is taken to avoid conditions leading to de novo
synthesis. Pollution prevention techniques include an adequately sized system, maximization of
off-gas mixing, rapid cooling of off-gas to below 200 °C and development and implementation of
good operating and maintenance practices.
4.1.4.
Continuous parameter monitoring system
A continuous parameter monitoring system based on optimizing the appropriate parameters for the
operation of the gas conditioning system and documented operating and maintenance procedures
should minimize the formation of PCDD/PCDF by de novo synthesis in the gas conditioning
system.
4.2.
Secondary measures for emissions
Secondary measures, often called pollution control techniques, may be summarized as follows:
4.2.1.
Off-gas dust collection
Capturing all of the off-gas, including fugitive emissions, from the electric arc furnace area is an
important part of the control system. Dust collection efficiency of primary and secondary emissions
from the furnace should be maximized by a combination off-gas and hood system, or doghouse and
hood system, or building air evacuation.
4.2.2.
Fabric filter dust collectors (or baghouses)
Some of the PCDD/PCDF in the electric arc furnace off-gases adsorb onto fine particulate matter.
As the gas temperature decreases through the PCDD/PCDF condensation temperature of the
various congeners, more of the PCDD/PCDF either adsorb onto the fine particulate matter or
condense and form fine particulate matter. Well-designed fabric filters achieve less than 5 mg
dust/Nm3 for new plants and less than 15 mg dust/Nm3 for existing plants. Minimizing dust levels
also minimizes PCDD/PCDF emissions.
4.2.3.
External post-combustion system coupled with a rapid water quench
This technique was the early PCDD/PCDF emission control technique applied to electric arc
furnace steel making. External post-combustion systems were originally developed to combust
carbon monoxide (CO) and hydrogen (H2) in the furnace off-gas in a refractory lined combustion
chamber, usually with supplementary fuel. Subsequently a number of European electric arc furnace
steel-making plants adopted the external post-combustion technology to dechlorinate PCDD/PCDF
emissions by maintaining the post-combustion temperature above 800 °C. This emission control
technique is not able to consistently meet the Canada-wide standard of 100 pg TEQ/Nm3 (0.1 ng
TEQ/Nm3). It may not be feasible for some plants to install external post-combustion and
improvements to gas conditioning systems due to site-specific space considerations.
4.2.4.
Adsorbent injection
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This control technique was originally developed to control PCDD/PCDF emissions from waste
incinerators. Sized lignite coke (activated carbon is a similar adsorbent) injection technology is
used in a number of European electric arc furnace steel-making plants to supplement the fabric
filter baghouse technology to achieve low PCDD/PCDF emission concentrations consistently. This
technique also reduces emissions of mercury. Reported emission test results from electric arc
furnace steel-making plants in Europe indicate that this technique, in combination with a highefficiency fabric filter baghouse, consistently achieves PCDD/PCDF emission concentrations of
less than 0.1 ng TEQ/Nm3.6
The sized lignite coke is injected into the off-gas upstream of the baghouse. The coke (or activated
carbon) adsorbs the PCDD/PCDF in the off-gas. Good mixing of the coke with the off-gas, and
appropriate sizing of the coke (to a size similar to particles in the gas stream), are essential for
optimum PCDD/PCDF removal.
Sized lignite coke production and activated carbon do not release captured PCDD/PCDF at normal
product storage and landfill temperatures, and are resistant to leaching. Use of sized lignite coke as
an adsorbent increases baghouse dust volume by 2%.
Activated carbon or sized coke injection systems should be considered for use at steel plants to
reduce emissions of PCDD/PCDF. Site-specific considerations, such as lack of available space,
configuration of existing emission control systems and cost impacts may influence the feasibility of
using this technique.
Selective catalytic reduction technology used for removal of nitrogen oxides (No x) in other
industrial sectors has been shown to reduce PCDD/PCDF emissions to significantly less than 0.1
ng I-TEQ/Nm3. This technology has not been applied to steel-making electric arc furnaces but may
be in the future.
4.3.
Primary and secondary measures for solid wastes and waste water
The measures in this section generally apply for electric arc, electric induction, and cupola
furnaces. With respect to solid wastes, electric furnace slag and filter dusts from any furnace
should be recycled to the maximum extent possible. Filter dust from high-alloy steel production,
where possible, may be treated to recover valuable metals. Excess solid waste should be disposed
of in an environmentally sound manner.
Ovaco has commented that the landfilling of EAF-dust is no longer allowed in most industrial
countries. The standard method is recovery of valuable metals in a separate treatment process or
processes outside the steel work. If stainless steel scrap is used as raw material, Cr, Ni, Zn and Pb
are recovered, otherwise (for the main part of dust) Zn and Pb is separated only. The measured
dioxin content of Ovaco’s dust is around 1300 pg I-TE/g and it represents 96% of the total amount
synthesized in our process. If we use this concentration and 50000 t/a as a typical capacity of a
treatment plant, the input material of it contains dioxins some 60 - 70 g I-TE per year.
With respect to waste water, closed-loop water-cooling systems for electric furnace components
avoid waste water being generated, or ensure it is recycled to the maximum extent possible to
minimize waste volume for treatment.
It has been suggested that EAF cooling water is carefully kept separated from molten steel of safety
reasons (risk of explosions). (Ovaco, February 2006)
Semi-dry emission control systems may be used at some plants. While replacement with dry dust
collectors would be the desirable option, semi-dry systems can be designed to avoid the generation
of waste water.
Waste water may originate at facilities that use wet scrubbing systems. The desired approach is the
replacement of existing systems with dry dust collectors. If replacement of existing emission
6
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0 °C
and 101.3 kPa.
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91
control systems is not feasible, the waste water would need treatment. However, standards for
treated waste-water quality concerning PCDD/PCDF discharge levels or other parameters were not
found.
5.
Summary of measures
Tables 1 and 2 present a summary of the measures discussed in previous sections.
Table 1. Measures for new electric arc furnaces
Measure
Description
Considerations
Process design
Priority consideration
should be given to the
latest proven process
designs based on process
and emissions performance
An example is internal
post-combustion design
for a new electric arc
furnace
Performance
requirements
New electric arc furnaces
should be required by the
applicable jurisdiction to
achieve stringent
performance and reporting
requirements associated
with best available
techniques
Consideration should be
given to the primary and
secondary measures listed
in Table 2
Other comments
Achievable emission limits
should be specified as
follows:
< 0.1 ng TEQ/Rm3 for
PCDD/PCDF
< 5 mg/Rm3 for particulate
matter
Table 2. Measures for new and existing electric arc furnaces
Measure
Description
Considerations
Other comments
Primary measures
General
operating
practices
An integral part of a facility’s
pollution prevention program should
include best environmental, operating
and maintenance practices for all
operations and aspects of the electric
arc furnace steel-making process
Generally applicable;
part of an integrated
concept for pollution
prevention
Raw material
quality
A review of feed materials and
identification of alternative inputs
and/or procedures to minimize
unwanted inputs should be conducted.
Documented procedures should be
developed and implemented to carry
out the appropriate changes
Generally applicable.
Measures include
changes in material
specifications, improved
quality control
programs, changes in the
types of raw materials
(such as avoidance of
oily scrap) and programs
to prevent the entry of
contaminants
Electric arc
furnace
operation
Minimizing the duration of the roof
being open for charging, reduction of
air infiltration into the furnace, and
avoiding or minimizing operational
delays
Collateral benefit is
reduced PCDD/PCDF
Guidelines on BAT and Guidance on BEP
Other pollutants are
reduced, including
aromatic
organohalogen
compounds, carbon
monoxide,
hydrocarbons and
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
Measure
Description
Considerations
Other comments
greenhouse gases
Off-gas
conditioning
Design and installation of an
adequately sized gas conditioning
system based on optimum system
parameters should prevent or
minimize formation of PCDD/PCDF
in the gas conditioning system.
Development and implementation of
documented operating and
maintenance procedures should be
developed to assist in optimizing the
operation of the gas conditioning
system
A reduction in de novo
synthesis in the gas
conditioning system has
been linked to the rapid
cooling of the furnace
off-gases to below a
range of 225 to 200 °C
Continuous
parameter
monitoring
A continuous parameter monitoring
system should be employed to ensure
optimum operation of the sinter strand
and off-gas conditioning systems.
Operators should prepare a sitespecific monitoring plan for the
continuous parameter monitoring
system and keep records that
document conformance with the plan
Correlations between
parameter values and
stack emissions (stable
operation) should be
established. Parameters
are then continuously
monitored in
comparison to optimum
values
System can be
alarmed and
corrective action
taken when
significant
deviations occur
Secondary measures
The following secondary measures can effectively reduce releases of PCDD/PCDF and serve as examples
of best available techniques
Off-gas
collection
Dust collection efficiency of primary
and secondary emissions from the
electric arc furnace should be
maximized by a combination off-gas
and hood system, or doghouse and
hood system, or building air
evacuation
Fabric filters
Well-designed fabric filters achieve
low dust emissions.
Procedures should be developed for
the operation and maintenance of the
fabric filter dust collector to optimize
and improve collection performance,
including optimization of fabric bag
cleaning cycles, improved fabric bag
material and preventive maintenance
practices.
A continuous temperature monitoring
and alarm system should be provided
to monitor the off-gas inlet
temperature to the emission control
device.
A bag leak detection system should be
provided with documented operating
and maintenance procedures for
responding to monitoring system
alarms
Guidelines on BAT and Guidance on BEP
98% efficiency or
more of dust
collection is
achievable
There is close
correlation between the
PCDD/PCDF content in
collected dust of a fabric
filter and dust
concentration. Lower
exhaust PCDD/PCDF
levels accompany lower
dust levels
Maintaining the offgases in the
baghouse to below
60 °C will prevent
PCDD/PCDF
evaporation in the
baghouse and
collected dust.
Enclosing the filter
dust collection areas
and transfer points
minimizes fugitive
dust
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SECTION VI. Guidance/guidelines by source category: Part III of Annex C
Measure
Description
Postcombustion of
off-gas
PCDD/PCDF formation may be
minimized by post-combustion within
the off-gas duct system or in a
separate post-combustion chamber.
Indications are that internal postcombustion may be a more attractive
option than external post-combustion
for PCDD/PCDF formation
prevention
Adsorbent
injection
Injection of activated carbon or
similar adsorptive material into the
off-gas upstream of high-efficiency
fabric filters in electric arc furnaces at
European steel-making plants has
consistently achieved low levels of
PCDD/PCDF emissions, according to
data from demonstration projects
Minimize
solid waste
generation
Electric arc furnace slag and filter
dust should be recycled to the extent
possible.
Filter dust from high-alloy steel
production, where possible, may be
treated to recover valuable metals.
Best management practices should be
developed and implemented for
hauling and handling dust-generating
solid wastes.
Excess solid waste should be disposed
of in an environmentally sound
manner
Minimize
waste water
Closed-loop water-cooling systems
for electric arc furnace components
avoid waste water being generated.
Recycle waste water to the maximum
extent possible.
Residual waste water should be
treated.
Semi-dry air pollution control systems
can be designed to have zero
discharge of excess waste water.
Waste water from wet gas cleaning
systems should be treated before
discharging to the environment
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Considerations
93
Other comments
PCDD/PCDF that
have been formed in
the process undergo
dechlorination
reactions as the offgas is burned by the
additional oxygen
burners.
This technique with
a rapid water
quench has been an
early PCDD/PCDF
emission control
technique applied to
electric arc furnace
steel making
These measures would
be primarily associated
with general pollution
prevention and control
practices rather than
being applied
specifically, or only, for
the purpose of
PCDD/PCDF
No standards were
found on
PCDD/PCDF limits
for treated waste
water discharged as
final effluent from
wet off-gas cleaning
systems
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94
6.
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Achievable performance level
The achievable performance level for emissions of PCDD/PCDF from secondary iron and steelmanufacturing electric arc, electric induction and cupola furnaces that incorporate best available
techniques is < 0.1 ng I-TEQ/Nm3.7
References
EPA (United States Environmental Protection Agency). 2002. Development Document for Final
Effluent Limitations Guidelines and Standards for the Iron and Steel Manufacturing Point Source
Category. EPA, Washington, D.C. epa.gov/waterscience/ironsteel/pdf/tdd/complete.pdf.
EPRI (Electric Power Research Institute). 1997. Understanding Electric Arc Furnace Operations.
EPRI, Centre for Materials Production, Palo Alto, California.
European Commission. 2000. Reference Document on Best Available Techniques for the
Production of Iron and Steel. BAT Reference Document (BREF). European IPPC Bureau, Seville,
Spain. eippcb.jrc.es.
European Commission. 2000. The European Dioxin Emission Inventory Stage II, Volume 2,
Destop studies and case studies. North Rhine Estphalia State Environmental Agency, NordrheinWestfalen, Germany. http://europa.eu.int/comm/environment/dioxin/pdf/stage2/volume_2.pdf
European commission, Integrated Pollution Prevention and Control (IPPC), Reference Document
on Best Available Techniques in the Non Ferrous Metals Industries, December 2001.
Fruehan R.J. (ed.) 1998. The Making, Shaping and Treating of Steel 11th Edition: Steelmaking and
Refining Vol. AISE Steel Foundation, Pittsburgh, PA.
Personal Communication, Ovaco, February 2006
Weiss D. and Karcher A. 1996. Evaluation and Reduction of Dioxin and Furan Emissions from
Thermal Processes: Investigation of the Effect of Electric Arc Furnace Charge Materials and
Emission Control Technologies on the Formation of Dioxin and Furan Emissions. Prepared for
BSW.
William Lemmon and Associates Ltd. 2004. Research on Technical Pollution Prevention Options
for Steel Manufacturing Electric Arc Furnaces. Final Report. Prepared for the Canadian Council of
Ministers of the Environment (CCME), Contract No. 283-2003.
www.ccme.ca/assets/pdf/df_eaf_p2_ctxt_p2_strtgy_e.pdf .
UNEP (United Nations Environment Programme). 2001. Standardized Toolkit for Identification
and Quantification of Dioxin and Furan Releases. Draft.
http://www.chem.unep.ch/pops/pdf/toolkit/toolkit.pdf
UNEP (United Nations Environment Programme). 2003. Formation of PCCD/PCDF – An
Overview. Draft. UNEP/POPS/EGB.1/INF/5. UNEP Chemicals, Geneva.
www.pops.int/documents/meetings/bat_bep/1st_session/meetdocen.htm.
7
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured
at 0 °C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present
guidelines. The operating oxygen concentration conditions of exhaust gases are used for metallurgical
sources.
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95
UNEP, Compilation of comments received from Parties and others on the draft Guidelines on Best
Available Techniques and provisional Guidance on Best Environmental Practices, October 14,
2005
http://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5
.pdf
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96
SECTION V. Guidelines/guidance by source category: Part II of Annex C
(ix)
Primary base metals smelting
Summary
Primary base metals smelting involves the extraction and refining of nickel, lead, copper, zinc
and cobalt. Generally, primary base metals smelting facilities process ore concentrates. Most
primary smelters have the technical capability to supplement primary concentrate feed with
secondary materials (for example, recyclables).
Production techniques may include pyrometallurgical or hydrometallurgical processes.
Chemicals listed in Annex C of the Stockholm Convention are thought to originate through
high-temperature thermal metallurgical processes; hydrometallurgical processes are therefore
not considered in this section on best available techniques for primary base metals smelting.
Available information on emissions of PCDD and PCDF from a variety of source sectors (for
example, incinerators, steel electric arc furnaces, iron sintering plants) suggests that process
technologies and techniques, and associated off-gas conditioning, can influence the formation
and subsequent release of PCDD/PCDF. Consideration should be given to hydrometallurgical
processes, where technically and economically feasible, as alternatives to pyrometallurgical
processes when considering proposals for the construction and commissioning of new base
metals smelting facilities or processes.
Primary measures include the use of hydrometallurgical processes, quality control of feed
materials and scrap to minimize contaminants leading to PCDD/PCDF formation, effective
process control to avoid conditions leading to PCDD/PCDF formation, and use of flash
smelting technology. Identified secondary measures include high-efficiency gas cleaning and
conversion of sulphur dioxide to sulphuric acid, effective fume and gas collection and highefficiency dust removal.
The achievable performance level using best available techniques for base metals smelters is <
0.1 ng TEQ/Nm3.
1.
Process description
The technical processes involved in the extraction and refining of base metals (nickel, lead, copper,
zinc and cobalt) generally proceed as shown in Figure 1. Key metal recovery technologies that are
used to produce refined metals can be categorized as follows:

Pyrometallurgical technologies use heat to separate desired metals from unwanted
materials. These processes exploit the differences between constituent oxidation potential,
melting point, vapour pressure, density and miscibility when melted;

Hydrometallurgical technologies use differences between constituent’s solubility and
electrochemical properties while in aqueous acid solutions to separate desired metals from
unwanted materials;

Vapometallurgical technologies apply to the Inco carbonyl process whereby nickel alloys
are treated with carbon monoxide gas to form nickel carbonyl.
Generally, primary base metals smelting facilities process ore concentrates. Most primary smelters
have the technical capability to supplement primary concentrate feed with secondary materials (for
example, recyclables).
Figure 1 provides a generic flowsheet showing the main production processes associated with
primary smelting and refining.
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97
Chemicals listed in Annex C of the Stockholm Convention are thought to originate through hightemperature thermal metallurgical processes; hydrometallurgical processes are therefore not
considered in this section on best available techniques for primary base metals smelting.
Figure 1. Generic flowsheet for primary base metals smelting and refining
Consumed
Scrap
New Scrap
Ore
Mining
Pre-treatment
Minerals
Concentrating
Sintering/
Smelting
Distillation
Smelting
Roasting/
Smelting/
Converting
Electro-refining
Smelting/
Converting
Drossing/
Refining
Roasting and
Leaching
Purification/
Electrolysis
Leaching
Solvent
Extraction/
Electrowinning
Refined Metal
Air Pollution
and
Abatement
Systems
Melting/ Casting/
Manufacturing
New Scrap
Manufacturing/
Applications and Use
Consumed
Scrap
Artisinal and small enterprise metal recovery activities are sometimes used in developing countries
and countires with economies in transition. These artisinal processes may be significant sources of
pollution and of adverse human health impacts. Metals that are known to be produced by artisinal
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
and small enterprise metal recovery activities include aluminium, antimony, copper, gold, iron,
lead, manganese, mercury, tin, tungsten, silver, and zinc. These activities usually do not have any
pollution controls and may be sources of unintentionally produced persistent organic pollutants.
While artisinal metal recovery activities are not consider best available techniques or best
environmental practices, it is recommended that, as a minimum, appropriate ventilation and
material handling should be carried out to minimize human exposure to pollutants from these
activities.
2.
Sources of chemicals listed in Annex C of the Stockholm
Convention
Primary base metals smelters can be sources of chemicals listed in Annex C. The formation and
release of such chemicals from primary smelters are not well understood, and it has been shown
that emissions of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans
(PCDF) can range significantly between operations using similar processes.
2.1.
2.1.1.
Releases to air
General information on emissions from base metals smelting
“The main environmental issues for the production of most non-ferrous metals from
primary raw materials are the potential emission to air of dust and metals/metal compounds
and of sulphur dioxide if roasting and smelting sulphide concentrates or using sulphur
containing fuels or other materials. The capture of sulphur and its conversion or removal is
therefore an important factor in the production of non-ferrous metals. The
pyrometallurgical processes are potential sources of dust and metals from furnaces,
reactors and the transfer of molten metal” (European Commission 2001).
2.1.2.
Emissions of PCDD and PCDF
“There is limited published information on dioxin/furan mechanisms of formation for the
base metals smelting sector, most of which is based on European experience for secondary
base metal smelters. There are a few general statements that dioxins and furans might be
present in some of the raw materials for secondary base metals smelting and that oils and
organic materials are present in many of these raw materials. The presence of oils and other
organic materials in scrap or other sources of carbon (partially burnt fuels and reductants
such as coke) can produce fine carbon particles which react with inorganic chlorides or
organically bound chlorine in the temperature range of 250 to 500°C to produce dioxins
and furans. This process is known as de novo synthesis which is dependent on catalysts
such as copper and iron. Although dioxins and furans are destroyed at high temperature
(above 850°C) in the presence of oxygen, the process of de novo synthesis is still possible
as the gases are cooled” (Charles E. Napier Co. Ltd. 2002).
Available information on emissions of PCDD and PCDF from a variety of source sectors (for
example, incinerators, steel electric arc furnaces, iron sintering plants) suggests that process
technologies and techniques, and associated off-gas conditioning, can influence the formation and
subsequent release of PCDD/PCDF.
Canadian base metals smelting and refining facilities undertook emissions testing for PCDD and
PCDF, and results from their work showed that concentration levels varied with the type of off-gas
conditioning system.
Smelting facilities in Canada generally process sulphide concentrates, and, at some facilities, also
process some secondary materials. Off-gas conditioning varies from extensive cleaning (for
example, high efficiency dedusting) and conversion to sulphuric acid, to dedusting by fabric filters,
to dedusting by electrostatic precipitator. These facilities produce nickel, copper, lead, zinc and coproduct metals. There were 11 participating facilities in the Canadian test program, conducting
approximately 20 emission tests on 16 different sources. No two facilities had the same
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combination and configuration of production processes and off-gas conditioning systems, further
complicating any possible analysis. As such, the observations noted below are general in nature.
Where off-gases were cleaned (i.e., dedusted, scrubbed) and processed through an acid plant for
conversion of off-gases rich in sulphur dioxide (SO2) to sulphuric acid, emission test results
showed concentrations below 5 pg (0.005 ng) TEQ/m3.8
Where off-gases were dedusted by baghouse, concentration levels typically ranged from a few pg
TEQ/m3 to < 30 pg TEQ/m3.
Where off-gases were dedusted by electrostatic precipitator, concentration levels ranged from
approximately 30 pg TEQ/m3 to approximately 500 pg TEQ/m3.
2.2.
Releases to other media
No information was found on releases of chemicals listed in Annex C from primary base metals
smelters to media other than air.
3.
Alternative processes for base metals smelting
In accordance with the Stockholm Convention, when consideration is being given to proposals for
construction of a new base metals smelting facility, priority consideration should be given to
alternative processes, techniques or practices that have similar usefulness but which avoid the
formation and release of the identified substances.
As indicated in Figure 1, there is a wide range of processes used in the primary production of base
metals smelting. The processes used to produce crude or refined base metals from primary sources
will depend to a large extent on the available ore or concentrate (i.e., laterite ore or sulphide ore),
and other considerations (for example, properties of the desired metal(s), properties of the feed
materials, available fuel and energy sources, capacity and economic considerations).
The formation and release of chemicals listed in Annex C is considered to be a result of hightemperature thermal metallurgical operations. Consideration should be given to hydrometallurgical
processes (for example, leaching, electrowinning), where technically feasible, as alternatives to
pyrometallurgical processes (for example, roasting, smelting, converting, fire refining) when
considering proposals for the construction and commissioning of new base metals smelting
facilities or processes.
4.
Primary and secondary measures
There is a paucity of information on the release of chemicals listed in Annex C from primary base
metals smelting operations. No techniques were identified specifically for the primary base metals
smelting sector to prevent or control the unintentional formation and release of PCDD/PCDF and
other chemicals listed in Annex C. The following measures constitute general measures which may
result in lower pollutant emissions at primary base metals smelters, including releases of
PCDD/PCDF.
The extent of emission reduction possible with implementation of primary measures only is not
readily known. It is therefore recommended that consideration be given to implementation of both
primary and secondary measures.
4.1.
Primary measures
Primary measures are regarded as pollution prevention measures that will prevent or minimize the
formation and release of the identified substances, namely PCDD, PCDF, hexachlorobenzene
(HCB) and polychlorinated biphenyls (PCB). These are sometimes referred to as process
optimization or integration measures. Pollution prevention is defined as: “The use of processes,
8
1 pg (picogram) = 1 x 10-15 kilogram (1 x 10-12 gram); 1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram). For
information on toxicity measurement see section I.C, paragraph 3 of the present guidelines.
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
practices, materials, products or energy that avoid or minimize the creation of pollutants and
waste, and reduce overall risk to human health or the environment.” (See section III.B of the
present guidelines.)
Primary measures that may assist in reducing the formation and release of pollutant emissions
include:
4.1.1.
Use of hydrometallurgical processes
Use of hydrometallurgical processes rather than pyrometallurgical processes where possible is a
significant means of preventing emissions. Closed-loop electrolysis plants will contribute to
prevention of pollution.
4.1.2.
Quality control of (scrap) feed material
The presence of oils, plastics and chlorine compounds in scrap feed materials should be avoided to
reduce the generation of PCDD/PCDF during incomplete combustion or by de novo synthesis.
Feed material should be classified according to composition and possible contaminants. Selection
and sorting to prevent the addition of material that is contaminated with organic matter or
precursors can reduce the potential for PCDD/PCDF formation. Storage, handling and pretreatment
techniques will be determined by feed size distribution and contamination.
Methods to be considered are (European Commission 2001, p.232):

Oil removal from feed (for example, thermal decoating and de-oiling processes followed
by afterburning to destroy any organic material in the off-gas);

Use of milling and grinding techniques with good dust extraction and abatement. The
resulting particles can be treated to recover valuable metals using density or pneumatic
separation;

Elimination of plastic by stripping cable insulation (for example, possible cryogenic
techniques to make plastics friable and easily separable);

Sufficient blending of material to provide a homogeneous feed in order to promote steadystate conditions.
4.1.3.
Effective process control
Process control systems should be utilized to maintain process stability and ensure operation at
parameter levels that will contribute to the minimization of PCDD/PCDF generation, such as
maintaining furnace temperature above 850 °C to destroy PCDD/PCDF. Ideally, PCDD/PCDF
emissions would be monitored continuously to ensure reduced releases. Continuous emissions
sampling of PCDD/PCDF has been demonstrated for some sectors (for example, waste
incineration), but research is still developing in this field. In the absence of continuous
PCDD/PCDF monitoring, other variables such as temperature, residence time, gas components and
fume collection damper controls should be continuously monitored and maintained to establish
optimum operating conditions for the reduction of PCDD/PCDF.
4.1.4.
Use of flash smelting technology
The most effective pollution prevention option is to choose a process that entails lower energy
usage and lower emissions. Where pyrometallurgical techniques are used, use of flash smelting
technology rather than older technologies (for example, roasters, blast furnace) is a significant
means of reducing energy use and reducing emissions. Flash smelting will also result in high
concentration of sulphur dioxide in the off-gas stream, which would permit the efficient fixation or
recovery of sulphur dioxide prior to off-gas venting.
4.1.5.
Maximization of SO2 content for sulphur fixation
A general measure involves operation of processes in a manner that maximizes the concentration of
the SO2 in the off-gas (when processing sulphide ores or concentrates). It is important, therefore,
that a process be selected that uses oxygen-enriched air (or pure oxygen) to raise the SO2 content of
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the process gas stream and reduce the total volume of the stream, thus permitting efficient fixation
of SO2.
4.2.
Secondary measures
Secondary measures are understood to be pollution control technologies or techniques, sometimes
described as end-of-pipe treatments.
Secondary measures that may assist in reducing the formation and release of pollutant emissions
include:
4.2.1.
High-efficiency gas cleaning and conversion of SO2 to sulphuric acid
For SO2-rich off-gases (typically 5% or greater) generated by pyrometallurgical processing of
sulphide ores or concentrates, high-efficiency precleaning of off-gases followed by conversion of
SO2 to sulphuric acid are together considered best available techniques for this type of source.
Emission concentrations of PCDD/PCDF with use of this combination of techniques are < 0.005 ng
TEQ/m3.
For conversion to sulphuric acid, a double-contact, double-absorption process is considered a best
available technique. A double-contact, double-absorption plant should emit no more than 0.2 kg of
SO2 per ton of sulphuric acid produced (based on a conversion efficiency of 99.7%) (World Bank
1998).
SO2-rich off-gases from smelting facilities pass through a gas-cleaning train, which typically
includes high-efficiency dedusting, prior to the sulphuric acid plant.
This combination of techniques has the co-benefit of controlling dust and SO2 emissions, in
addition to PCDD/PCDF.
Other techniques for sulphur fixation, which may require precleaning of off-gases prior to
conversion or recovery, may potentially contribute to the minimization of PCDD/PCDF emissions
(World Bank 1998). These techniques include:

Recovery as liquid sulphur dioxide (absorption of clean, dry off-gas in water or chemical
absorption by ammonium bisulphite or dimethyl aniline);

Recovery as elemental sulphur, using reductants such as hydrocarbons, carbon or hydrogen
sulphide. Normally the sulfur content in the gas is still higher than acceptable when using
this technique. The reduction conditions are also favourable for dioxins formation. Thus,
after the recovery, the gas should be post combusted and cleaned using techniques such as
scrubbing.
4.2.2.
Fume and gas collection
Air emissions should be controlled at all stages of the process, from material handling, smelting
and material transfer points, to control of the emission of PCDD/PCDF. Sealed furnaces are
essential to contain fugitive emissions while permitting heat recovery and collecting off-gases for
process recycling. Proper design of hooding and ductwork is essential to trap fumes. Furnace or
reactor enclosures may be necessary. If primary extraction and enclosure of fumes is not possible,
the furnace should be enclosed so that ventilation air can be extracted, treated and discharged.
Roofline collection of fume should be avoided due to high energy requirements. The use of
intelligent damper controls can improve fume capture and reduce fan sizes and hence costs. Sealed
charging cars or skips used with a reverberatory furnace can significantly reduce fugitive emissions
to air by containing emissions during charging (European Commission 2001, p. 187–188).
Fortunately the number of reverberatory furnaces is steadily decreasing in the world because of the
difficulty to control the emissions and the high costs involved. It is difficult to imagine that new
reverberatory furnaces would be built today. (Personal Communication, February 2006)
4.2.3.
High-efficiency dust removal
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SECTION V. Guidelines/guidance by source category: Part II of Annex C
The smelting process generates high volumes of particulate matter with large surface area on which
PCDD/PCDF can adsorb. These dusts and metal compounds should be removed to reduce
PCDD/PCDF emissions. Very high-efficiency dust removal techniques should be employed, for
example, ceramic filters, high-efficiency fabric filters or the gas-cleaning train prior to a sulphuric
acid plant.
Preference should be given to fabric filters over wet scrubbers, wet electrostatic precipitators, or
hot electrostatic precipitators for dust control. Dust from dust control equipment should be returned
to the process. Returned or collected dust should be treated in high-temperature furnaces to destroy
PCDD/PCDF and recover metals preferably by recycling the dust back into the smelting process.
Dust that is captured but not recycled will need to be disposed of in a secure landfill or other
acceptable manner.
Fabric filter operations should be constantly monitored by devices to detect bag failure.
5.
Emerging research
5.1.
Catalytic oxidation
Selective catalytic reduction has been used for controlling emissions of nitrogen oxides (NO x) from
a number of industrial processes. Modified selective catalytic reduction technology (i.e., increased
reactive area) and select catalytic processes have been shown to decompose PCDD and PCDF
contained in off-gases, probably through catalytic oxidation reactions. This may be considered as
an evolving technique with potential for effectively reducing emissions of persistent organic
pollutants from base metals smelting operations and other applications. However, catalytic
oxidation can, subject to catalyst selection, be subject to poisoning from trace metals and other
exhaust gas contaminants. Validation work would be necessary before use of this process.
6.
Summary of measures
Tables 1 and 2 present a summary of the measures discussed in previous sections.
Table 1. Measures for new primary base metals smelting operations
Measure
Description
Considerations
Alternative
processes
Priority consideration should
be given to alternative
processes with potentially
less environmental impacts
than pyrometallurgical base
metals smelting
Hydrometallurgical
processes are a significant
means of preventing
emissions.
It has been commented that
direct atmospheric leaching
of sulfide concentrations
(Fex to Zn concentrates)
should be considered.
(Finnish representative,
2006)
Closed-loop electrolysis
plants will contribute to
prevention of pollution
Performance
requirements
New primary base metals
smelting operations should
be permitted to achieve
stringent performance and
reporting requirements
associated with best
available techniques
Consideration should be
given to the primary and
secondary measures listed
in table 2
Guidelines on BAT and Guidance on BEP
Other comments
Performance requirements
for achievement should
take into consideration
achievable emission levels
of PCDD/PCDF identified
in subsection 7
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SECTION VI. Guidance/guidelines by source category: Part III of Annex C
103
Table 2. Summary of primary and secondary measures for primary base metals smelting
operations
Measure
Description
Considerations
Use of
hydrometallurgical
processes
Use of hydrometallurgical
processes rather than
pyrometallurgical processes where
possible, as a significant means of
preventing emissions. Closed-loop
electrolysis plants will contribute
to prevention of pollution
Use of hydrometallurgical
processes will depend in
large part on the ore and
concentrate to be processed
(e.g. laterite or sulphide)
It has been commented that
the combination of hydro
and pyro metallurgy for Zn,
emerging for other metals
like Ni and Cu, should be
considered. (Finnish
representative, 2006)
Quality control of
(scrap) feed material
Selection and sorting to prevent
the addition of material that is
contaminated with organic matter
or precursors can reduce the
potential for PCDD/PCDF
formation
Methods to be considered
are:
Oil removal from feed (e.g.
thermal decoating and deoiling processes followed
by afterburning to destroy
any organic material in the
off-gas)
Use of milling and grinding
techniques with good dust
extraction and abatement.
The resulting particles can
be treated to recover
valuable metals using
density or pneumatic
separation
Elimination of plastic by
stripping cable insulation
(e.g. possible cryogenic
techniques to make plastics
friable and easily separable)
Sufficient blending of
material to provide a
homogeneous feed in order
to promote steady-state
conditions. It has been
commented that this should
be the first priority. (Finnish
representative, 2006)
Effective process
control
Process control systems should be
utilized to maintain process
stability and operate at parameter
levels that will contribute to the
minimization of PCDD/PCDF
generation. In the absence of
continuous PCDD/PCDF
For example, furnace
temperatures should be
maintained above 850 °C to
destroy PCDD/PCDF
Other
comments
Primary measures
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Environment Canada Revision, April 28, 2006
104
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Measure
Description
Considerations
Other
comments
monitoring, other variables such
as temperature, residence time, gas
components and fume collection
damper controls should be
continuously monitored and
maintained to establish optimum
operating conditions for the
reduction of PCDD/PCDF
Use flash smelting
technology
Where pyrometallurgical
techniques are used, use of flash
smelting technology rather than
older technologies (e.g. roasters,
blast furnace) is a significant
means of reducing energy use and
reducing emissions
Flash smelting will also
result in high concentration
of SO2 in the off-gas
stream, which would permit
the efficient fixation or
recovery of SO2 prior to
off-gas venting
Maximize SO2 content
for sulphur fixation
This general measure involves
operation of processes in a manner
that maximizes the concentration
of the SO2 in the off-gas (where
processing sulphide ores or
concentrates), to enable recovery
or fixation of the sulphur.
Preference should be given to
processes that use oxygenenriched air (or pure oxygen) to
raise the SO2 content of the
process gas stream and reduce the
total volume of the stream
Secondary measures
The following secondary measures can effectively reduce emissions of PCDD/PCDF and should be
considered as examples of best available techniques
High-efficiency gas
cleaning and
conversion of SO2 to
sulphuric acid
SO2-rich off-gases, high-efficiency
precleaning of off-gases followed
by conversion of SO2 to sulphuric
acid should be employed, and are
together considered best available
techniques
Fume and gas
collection
Air emissions should be controlled
at all stages of the process, from
material handling, smelting and
material transfer points, to control
the emission of PCDD/PCDF
High-efficiency dust
removal
Dusts and metal compounds
should be removed to reduce
PCDD/PCDF emissions. Very
high-efficiency dust removal
Guidelines on BAT and Guidance on BEP
This combination of
techniques has the cobenefit of controlling dust
and SO2 emissions, in
addition to PCDD/PCDF
Emission
concentrations
of
PCDD/PCDF
with use of
high-efficiency
gas cleaning
and conversion
of SO2 to
sulphuric acid
are < 0.005 ng
TEQ/m3
Preference should be given
to fabric filters over wet
scrubbers, wet electrostatic
precipitators, or hot
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SECTION VI. Guidance/guidelines by source category: Part III of Annex C
Measure
7.
Description
Considerations
techniques should be employed,
for example, ceramic filters, highefficiency fabric filters or the gascleaning train prior to a sulphuric
acid plant.
Dust from dust control equipment
should be returned to the process.
Returned/collected dust should be
treated in high-temperature
furnaces to destroy PCDD/PCDF
and recover metals.
Fabric filter operations should be
constantly monitored by devices to
detect bag failure
electrostatic precipitators
for dust control.
Dust that is captured but not
recycled will need to be
disposed of in a secure
landfill or other acceptable
manner
105
Other
comments
Achievable performance levels
Emission levels achieved at primary base metals smelting operations are noted in Table 3.
Table 3. Performance levels achieved at primary base metals smelting operations9
Primary base metals smelting source type
Achievable performance
New primary smelters
< 0.1 ng TEQ/Nm3
Acid plant tail gas (recovery of sulphur dioxide in
off-gas from pyrometallurgical sources)
< 0.005 pg TEQ/m3
Off-gas dedusted by baghouse
< 0.005 ng TEQ/m3 to < 0.03 ng TEQ/m3
Off-gas dedusted by electrostatic precipitator
0.03 ng TEQ/m3 to < 0.5 ng TEQ/m3
References
A.J. Gunson, Yue Jian, Artisanal Mining in The People's Republic of China, Mining, Minerals and
Sustainable Development (MMSD), International Institute for Environment and Development
(IIED), September 2001
Charles E. Napier Co. Ltd. 2002. Generic Dioxin/Furan Emission Testing Protocol for the Base
Metals Smelting Sector. Prepared for Environment Canada.
European Commission. 2001. Reference Document on Best Available Techniques in the NonFerrous Metals Industries. BAT Reference Document (BREF). European IPPC Bureau, Seville,
Spain. eippcb.jrc.es.
9
1 ng (nanogram) = 1 × 10-12 kilogram (1 × 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured
at 0 °C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present
guidelines. The operating oxygen concentration conditions of exhaust gases are used for metallurgical
sources.
Guidelines on BAT and Guidance on BEP
Environment Canada Revision, April 28, 2006
106
SECTION V. Guidelines/guidance by source category: Part II of Annex C
Feng Xinbin, Qui Guangle, Li Guanghui, Li Ping, Wang Shaofeng, Mercury Emissions from
Artisanal Zinc and Mercury Smelting in Guizhou, PR China, Goldschmidt Conference Abstracts
2005, The Geochemistry of Mercury, page A705
Personal communication from Expert Group Best Available Techniques Best Environmental
Practices, Finland Member, February 2006
World Bank. 1998. Pollution Prevention and Abatement Handbook. Chapters on copper, nickel,
lead and zinc smelting. www.worldbank.org.
UNEP Environment Program News Centre,
http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=
en, as read on January 20, 2006
Xinbin Feng, Xianwu Bi, Guangle Qiu, Guanghui Li, Shunlin Tang, Mercury Pollution in Guizhou,
China - A status Report, http://pbc.eastwestcenter.org/abstracts2005/abstract2005fengxinbin.htm,
as read on December 29th, 2005
Guidelines on BAT and Guidance on BEP
Environment Canada Revision – April 28, 2006