LCA modelling of metal recovery from 1 tonne
high grade WEEE
M. BIGUM*, L. BROGAARD*
*DTU Environment, Department of Environmental Engineering, Technical
University of Denmark (DTU)
SUMMARY: The high grade fraction of waste electrical and electronic equipment (WEEE)
(WEEE directive category 3 and 4) is considered to be valuable because of its high content of
silver (Ag), gold (Au), palladium (Pd), copper (Cu), aluminium (Al) and iron (Fe) which can be
recycled thus substituting virgin resources. Life cycle assessment (LCA) has been used for the
environmental assessment of the recovery of these metals from 1 tonne high grade WEEE and
significant savings for the resource consumption was found even with a significant loss of metals
during the pre-treatment step. The most significant saving was obtained for Pd with a saving of
64 Person Equivalents (PE).
1. INTRODUCTION
Waste electrical and electronic equipment (WEEE) is considered to be one of the fastest growing
waste streams in Europe. The European community has by the implementation of the RoHS and
WEEE directive recognized the environmental significance of WEEE both regarding its content
of hazardous substances but also regarding its high content of recyclable materials. This paper
focuses on WEEE as a source of recyclable metals (gold, silver, copper, aluminium, nickel, iron
and palladium), and is not considering the treatment of the hazardous materials (more on this in
Chapter 4). The recycling of WEEE plastics is as well not included.
Printed circuit boards has been collected and treated for some time due to the high content of
copper, gold, silver and palladium, but WEEE is now overall beginning to be viewed as a
resource and is even referred to as “a mine above ground” (Hagelüken, 2006). The valuable metal
content is considered an economic driver for the recovering of WEEE (Cui and Zhang, 2008).
The amount of gold in an ore is approximately 9 g per tonne (Classen et al., 2007) compared to a
concentration of approximately 22 g per tonne in the high grade fraction of WEEE (Chancerel et
al., 2008). WEEE is therefore today considered to be a commodity rather than a waste and is
therefore traded by and among various treatment industries.
Most research on WEEE focuses on local conditions and only single waste fractions such as
printed circuit boards (Vasile et al., 2008) or CRT glass from televisions (Andreola et al., 2007)
and do not give a complete picture of the WEEE management system. In reality many fractions
are treated together (so called treatment categories) and not as single equipment types. When
evaluating the treatment of WEEE there is therefore a need for data on the different treatment
categories. These are rarely available as the political focus on the WEEE treatment in Europe is
relatively new - initiated by the WEEE directive in 2002, but also because the sampling and
characterization of the treatment categories is much more difficult than simply considering one
equipment type.
2. BACKGROUND
2.1 Definition of WEEE
Electric and electronic equipment (EEE) can be defined as: "Components which are reliant on
electricity or electromagnetic fields to work" and "Equipments used for production, transmission
and measurements of electricity and electromagnetic fields" (Danish WEEE declaration, 2005).
Waste Electric and Electronic Equipment (WEEE) is defined as the discarded EEE. The
definition of WEEE is therefore very broad and includes many different types of equipment and
is therefore considered to be a very heterogeneous waste type. The European WEEE directive
categorizes the waste type into 10 WEEE categories (Table 1), which can be further divided into
5 treatment categories (Table 2), where WEEE which needs similar treatment is grouped together
and routed for further processing.
Table 1 – The 10 WEEE directive categories (WEEE directive, 2002)
#
1
2
3
4
5
6
7
8
9
10
Category name
Large household appliances
Small household appliances
IT and telecommunications equipment
Consumer equipment
Lighting equipment
Electrical and electronic tools
Toys, leisure and sports equipment
Medical devices
Monitoring and control instruments
Automatic dispensers
Table 2 – The 5 WEEE treatment categories and their associated WEEE directive category
numbers (Bigum and Brogaard, 2009)
#
1, 10
1, 10
2, 6, 7, 8, 9
3, 4
4
5
Treatment categories
Cooling white goods
Heating white goods
Low grade fraction
High grade fraction
TV and monitors
Lighting equipment
2.2 Life cycle assessment (LCA)
Life cycle assessment (LCA) is a method in where a product or system and its upstream and
downstream processes are evaluated according to their impact on the environment. The
Environmental Development of Industrial Products (EDIP) method is just one of the available
LCA methods, but is the one chosen for this assessment. The EDIP method includes three general
impact categories: Environmental impacts, resource consumption and impact on working
environment, the latter is not included in this study.
The EDIP method includes the construction of the life cycle inventory (LCI) where the
information and data on the different processes within a system is collected and presented. The
environmental assessment of the inventory data is then done by transforming the data into a list
of resource consumptions and impact potentials using the best available background knowledge
on the significance of the different substances. The impact potentials are calculated by
multiplying the quantity of a given substance with the substance’s impact potential (equivalency
factor). The impact potentials can subsequently be normalized, which will give an impression of
the magnitude of the resource consumption and environmental impact. When normalizing
resource consumptions and environmental impact potentials the units of the assessment are given
in person equivalents (PE) (Wenzel et al., 1997). Normalized resource consumption refers to the
resource consumption for an average person in the world in 2004 where 1 [PE] of a given
resource is equal to an average person’s use of that particular substance in 2004. As for the
environmental impact potentials 1 [PE] refers to the annual emission of a given substance in
2004.
When performing a LCA on a multiple input and/or output system it is sometimes necessary to
either use system expansion or allocation. System expansion is very rarely possible for a system
including metals production or recycling. The virgin production of e.g. palladium includes the coproduction of platinum, rhodium, copper and nickel. If only the virgin production of palladium
was to be assessed in a study, the burdens of the co-products would therefore have to be
subtracted from the LCI data. In order to subtract the burdens of the co-products it would entail
the quantification of the burdens of a mine only producing platinum, rhodium, copper and nickel
and the burdens of such a mine is not likely to exist. Allocation is therefore the only remaining
alternative. Allocation means that the burdens of a system have to be distributed among the
different outputs or inputs, which should be done with a criterion relevant to the systems
considered in the LCA.
3. EASEWASTE
At the Technical University of Denmark (DTU) a LCA tool has been developed specifically for
the assessment of waste management systems which is called Environmental Assessment of Solid
Waste Systems and Technologies (EASEWASTE). EASEWASTE models the resource use and
recovery associated with a waste management system and makes it possible to include waste
specific material fractions, source separation, collection and transport, mechanical treatment and
material recycling facilities, use of materials, use and substitution of energy etc. in the
assessment. Overall it can be said that with EASEWASTE it is possible to assess the
environmental impacts of a waste management system from the waste generation to the final
disposal of waste residuals to where they are no longer considered to have further environmental
impacts. EASEWASTE uses the EDIP method for the environmental assessment (Kirkeby et al.,
2006).
4. GOAL AND SCOPE
The treatment of WEEE includes the recovery of valuable metals and materials that substitutes
virgin materials. The goal of this study is to environmentally asses the treatment and subsequent
recovery of metals from high grade WEEE (WEEE directive categories 3 and 4) in Europe
compared to the mining of the same virgin metals. An environmental assessment of the treatment
of WEEE should therefore include the environmental impacts of the WEEE treatment as well as
any benefit from substituting virgin metal production.
The functional unit of the study is “Recovering of gold, silver, copper, aluminium, nickel, iron
and palladium from 1 tonne of high grade WEEE”. The assessment is performed using the
programme EASEWASTE and is attributional (using average data for the energy substitution).
The assessment is comparative and compares the recovery of metals from WEEE to the
extraction of the same metals from virgin sources, or in other words it compares two scenarios A)
Extraction of metals via recycling of high grade WEEE to B) Extraction of metals from virgin
sources. The removal and treatment of hazardous components is determined by law in the WEEE
directive and will therefore occur in both scenarios, and it is therefore possible to exclude these in
a comparative LCA.
5. DATA BACKGROUND PRE-TREATMENT AND METALLURGICAL TREATMENT
High grade WEEE is after collection and sorting sent to a pre-treatment facility. There are
numerous pre-treatment facilities in Europe and the treatment steps within these vary. For this
study a general pre-treatment facility consisting of manual de-pollution, shredding, air sorting,
magnetic sorting, Eddy current separation and optical sorting was suggested (Figure 1). The
modelling of the pre-treatment of high grade WEEE included the significant loss of metals as
determined by Chancerel et al., (2008), gold (74%), silver (89%), copper (40%), aluminium
(15%), and iron (4%), no loss of nickel was considered.
The recycling of aluminium and iron were modelled as being recycled according to the
available EASEWASTE data. Gold, silver, copper, nickel and palladium were modelled as being
metallurgically treated at the integrated metals smelter Rönnskär belonging to the Boliden
cooperation in Sweden using data from the company’s public environmental reports. Data on the
virgin production of metals are primarily from Classen et al. (2007). The detailed LCI data used
in the assessment can be found in Bigum and Brogaard (2009).
Figure 1. Schematically presentation of the general pre-treatment facility used in the
environmental assessment (Bigum and Brogaard, 2009).
5.1 Allocation aspects
Allocation is necessary as the processes connected to treatment of high grade WEEE and the
productions of virgin metals are multiple input and output processes. A relevant criterion for the
allocation should reflect the function of the process which requires allocation. From a waste
management perspective the allocation should be performed according to the incoming mass of
WEEE as the “function” is to treat the received waste. For the production of virgin materials the
allocation should however be conducted according to the value of the output of metals, as it is the
value of the metals that are the reason for the production taking place. However because the
metallurgical processing of both WEEE and the virgin materials (metal concentrates) in reality
takes place at the same facility, the allocation method therefore also has to be the same, which
creates a dilemma of choice. It was not possible to find a third common allocation method for the
two scenarios and two LCAs was therefore conducted using mass allocation and economic
allocation respectively, and the results thereafter compared.
Mass allocation requires that the inputs to the various processing steps are known as the LCI
data are given on a processing step level. The inputs to the different processes connected to the
extraction of metals are however often not quantified and measured as it is the output of metals
from the processing steps that are relevant to the company. The inputs of the Rönnskär facility
therefore had to be estimated by the construction of a mass balance. The details of the mass
balance can be found in Bigum and Brogaard (2009) but included a rough estimate of an
unknown input of 146 000 tonnes per year (~10% of the total input) in order to balance.
Value allocation requires the value of a given metal as well as the produced amount of the
metals (the product outputs). The product outputs are relatively easily found, as this is important
for the economy of the company. The value of the metals however changes on a daily basis, and
the value allocated data can therefore quickly become outdated. The value allocation was based
on metal prices from January 2009. More details regarding the allocation can be found in Bigum
and Brogaard (2009).
6. RESULTS AND DISCUSSION
The results for the comparative LCA showed environmental savings both with respect to the
environmental impacts categories as well as resource consumption (Table 3). The savings in the
environmental impact categories were however not significant compared to the resource savings,
and are therefore not included in this paper but can be found in Bigum and Brogaard (2009). The
most significant resource saving was found for palladium (Pd), but the recovery of the other
metals considered in this study also showed significant environmental savings. The recovery of
Pd showed an overall saving of 64 PE – even including the significant loss during pre-treatment.
The results were also found to be relatively independent of choice of allocation method.
The LCI data is the essential part of any LCA, and will in all cases directly influence the
results. The LCI data for this study has been collected from many different sources and its
validity has not been double checked by own measurements. All the LCI data has however been
clearly stated in Bigum and Brogaard (2009).
The two allocation methods were shown not to change the results significantly. This was
unexpected as the two methods differ much in the way they are performed. It is however a very
significant result and indicates that the choice of allocation method might not be as significant as
it is usually considered.
The loss of metals during the pre-treatment was considered but no loss during the
metallurgical treatment was. The loss of metals during the metallurgical treatment is most likely
significantly less, than during the pre-treatment and the results presented in Table 3, is therefore
not expected to change much. On the other hand if the significant loss during pre-treatment was
minimized the savings in resource consumption would increase.
The main uncertainty for this LCA is the mass balance of the Rönnskär facility which was
used for the mass allocation, primarily due to the relatively large amount of unknown input. The
significance of the mass balance for the overall result has not been investigated.
Table 3 – Environmental benefits for the extraction of Al, Cu, Au, Fe, Pd and Ag from 1 tonne
of WEEE compared to the extraction of the same metals from virgin sources (Bigum
and Brogaard, 2009).
Resource
Mass allocated
Value allocated
PE
PE
Aluminium -7
-6
Copper
-11
-11
Gold
-15
-15
Iron
-4
-4
Palladium -63
-64
Silver
-12
-12
7. CONCLUSION
The environmental savings from the extraction of metals from high grade WEEE was found to be
significant for aluminum, copper, gold, iron, and palladium and silver, even though a significant
loss of most of the metals occurred during pre-treatment. The environmental benefits of recycling
of high grade WEEE could be greater if the recovery of the metals was improved in the pretreatment step. The results were not significantly influenced by the choice of allocation method.
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