LABORATORY EXPERIMENT
(KGP002)
LEACHING OF DUST FROM AN ELECTRIC ARC FURNACE
Theory
The yearly consumption of iron and steel within the EU is approximately 150 million tonnes.
Roughly 50 million tonnes of this is produced by recirculation of iron scrap in electric arc
furnaces. The recirculated scrap is often coated with zinc leading to the formation and
collection of dust with relatively high zinc content in the gas cleaning system. It is estimated
that about 0, 5-1 million tonnes of this type of dust is produced yearly within the EU. Since
the dust also contains smaller amounts of Pb, Cd and Cr it is classified as an environmentally
hazardous waste. The dust is very fine-grained, which makes it prone to spread by wind and
which also increases the leaching rates of heavy metals when exposed to acid rain. The dust
is, due to this, regarded as a threat for soil and earth as well as surface- and groundwater.
On account of these possible risks and also because of the possible value in the dust as a raw
material, especially regarding zinc, intense research has been conducted during many years
with the purpose of making recirculation of the dust possible. Several pyro- as well as
hydrometallurgical processes have been developed of which some has been used in industrial
applications. Some unsolved problems regarding recycling of the dust makes the research on
the subject still intense. The content of chlorides in the dust leads to problem in
pyrometallurgical processes as the chlorides react with the refractories in the furnace. The
content of zinc ferrites constitutes a problem in hydrometallurgical processes where also other
heavy metals bring adversities in the following solution purification.
A possible process could be to combine pyro- and hydrometallurgical methods by performing
a relatively mild leaching where only the content of free zinc oxide is leached. The leaching
residue that contains zinc ferrites and other iron oxides are brought back to the electric arc
furnace while the solution, after solution purification, is used for production of zinc oxide.
Aim
The aim with this experiment is to investigate the proportion in percentage of zinc oxide and
zinc ferrite, respectively, in the dust. Since the content of manganese in solution can cause
problems in the production of zinc oxide (discoloration of the white zinc oxide) it is of
interest to study how much of the manganese that is brought into solution. With the conditions
used during the experiment only Mn2+ is soluble which implies that only MnO is being
leached from the dust.
Analysis of the dust
Ovako
Zn
%
Fe
%
Pb
%
Ca
%
Mn
%
21.9
29.6
0.7
9.1
2.7
Performance
Place the required experimental equipment in a ventilation hood. The leaching is performed
according to:






Temperature:
Leaching solution volume:
Amount of solids:
Amount of NaCl:
pH:
Leaching time:
80C
800 ml water
160 g
120 g
3.0
1 hour
Start by heating up 800 ml water containing 120 grams NaCl. When the temperature is 75C
the heat is turned of and the electric arc furnace dust is added (exothermic reaction). Carefully
add the material and wash down eventual dust sticking on to the edges using small amounts of
water from a spray can. Add concentrated HCl in small portions with pipette to keep the pH at
a constant value of 3.0 during the experiment. In the beginning of the experiment some gas
can be developed, due to the presence of small amounts of carbonates in the dust. Regulate
the temperature to 80C during the experiment. Remember to keep all of the solid material
agitated to avoid cake formation at the bottom of the leaching vessel.
When the leaching is finished the agitator, pH-electrode and temperature sensor are
dismantled. Filter the product using an OOR filter. When the filtration is almost finished and
the last of the remaining solution is entering into the filter cake, 100 ml wash water is added.
When the filtration is ready the total volume (leachate + wash water) is measured. The
leaching residue is placed in a weighed bowl and dried at 120C for 2 hours or until it is dry.
Weigh the leaching residue when it is dry.
OBS! 1.
The total consumption of HCl should be determined (start by measuring out 200
ml of HCl in a measuring cylinder).
OBS! 2.
Protect eyes and clothes when handling HCl.
Analysis with AAS
The leachate is analysed for its zinc, iron and manganese content.
Manganese and iron:
1.0 ml leachate + 2 ml HCl is diluted with deionised water to 100
ml in a measuring flask.
Zinc:
Take 1.0 ml of the solution made for the analysis of iron and
manganese and add 2 ml HCl and dilute with deionised water to
100 ml in another measuring flask.
The leaching residue is analysed for its zinc content.
Dissolve a precise amount of leaching residue (~ 1 gram) by adding 25 ml of concentrated
HCl in a 100 ml measuring flask. Possibly the sample needs to be heated carefully to be
completely dissolved. When the sample has dissolved, dilute with deionised water up to the
marking of the flask
Then take 200 l of the solution + 2 ml HCl and dilute with deionised water to 100 ml in a
measuring flask.
Report
The report shall contain a short introduction, experimental, result and discussion. State the
leaching yield for zinc, iron and manganese from the experiment. Calculate the percentage
amount of zinc oxide respective zinc ferrite in the dust. Is the material balance okay for the
zinc content? Discuss possible deviations. Also, account for how the amount of acid added
agrees with the assumption that all metal oxides except zinc ferrite and iron oxides are soluble
under the leaching conditions used. Discuss conceivable methods, both pyro- and
hydrometallurgical, to avoid manganese in the leachate.
Calculations are accounted for in a separate enclosure.