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Environmental Impact Assessment of Hydrometallurgical Processes for Metal Recovery from WEEE Residues Using a Portable Prototype Plant Laura Rocchetti,† Francesco Vegliò,‡ Bernd Kopacek,§ and Francesca Beolchini†,* †

Dipartimento di Scienze della Vita e dell’Ambiente, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy Dipartimento di Ingegneria Industriale e dell’Informazione e di Economia, Università dell’Aquila, L’Aquila, Italy § Austrian Society for Systems Engineering and Automation, Vienna, Austria ‡

S Supporting Information *

ABSTRACT: Life cycle assessment (LCA) was applied to hydrometallurgical treatments carried out using a new portable prototype plant for the recovery of valuable metals from waste electrical and electronic equipment (WEEE). The plant was fed with the WEEE residues from physical processes for the recycling of fluorescent lamps, cathode ray tubes (CRTs), Li-ion accumulators and printed circuit boards (PCBs). Leaching with sulfuric acid was carried out, followed by metal recovery by selective precipitation. A final step of wastewater treatment with lime was performed. The recovered metals included yttrium, zinc, cobalt, lithium, copper, gold, and silver. The category of global warming potential was the most critical one considering the specifications for southern European territories, with 13.3 kg CO2/kg recovered metal from the powders/residues from fluorescent lamps, 19.2 kg CO2/kg from CRTs, 27.0 kg CO2/kg from Li-ion accumulators and 25.9 kg CO2/kg from PCBs. Data also show that metal extraction steps have the highest load for the environment. In general, these processes appear beneficial for the environment in terms of CO2 emissions, especially for metal recovery from WEEE residues from fluorescent lamps and CRTs.

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INTRODUCTION The final disposal of electrical and electronic devices is an issue of current worldwide concern.1 Disposal and incineration can pose threats to the whole environment, from the atmospheric to the aquatic and terrestrial compartments. Indeed, gases produced during thermal treatments (e.g., dioxins, furans, polybrominated organic pollutants, and polycyclic aromatic hydrocarbons) can be released into the environment if adequate flue gas cleaning systems are not implemented.2 Similarly metals can be released from waste electrical and electronic equipment (WEEE) disposed of in landfill sites by leaching processes. Such gaseous and solid waste are hazardous for human beings and for the environment.3,4 As man-made devices such as electrical and electronic equipment, accumulators and fluorescent lamps are rich in valuable metals (e.g., Au, Ag, Cu, Zn, Co, Y), WEEE recycling for the production of secondary materials needs to be encouraged.5−7 In the current scenario, recycling policies are gaining more attention, and many countries have drawn up regulations for the management of WEEE,8, including European Union, the United Kingdom, China, Japan, South Korea, Taiwan, and some states of the U.S.9 In particular, the European WEEE Directive aims at WEEE recycling, to reduce the disposal of waste and “to contribute to the efficient use of resources and the retrieval of valuable secondary raw materials”.10 WEEE represents a source of metals, that have been mined from ore minerals, where they are often present at low concentrations. © 2013 American Chemical Society

These are then included at higher concentrations as the pure metals or metallic alloys in electrical and electronic equipment. For example, the amount of Au in a printed circuit board (PCB) is an order of magnitude higher than in the mineral ore from which it is mined.11 Considering the increasing demand of technological equipment in the industrialized and developing countries, it is a priority and real necessity to recycle metals, rather than to mine them.12 Nowadays, the main technologies used for the recovery of valuable metals from WEEE are based on pyrometallurgical and hydrometallurgical processes.13 Pyrometallurgical processes require the heating of WEEE at high temperatures (often greater than 1000 °C) to recover valuable metals. These thus represent highly energy-consuming treatments that lead to the production of hazardous gases that must be correctly removed from the air with flue gas cleaning systems. Hydrometallurgical treatments are based on the use of leaching agents in aqueous solutions, such as strong acids and bases. These are often applied together with other complexing agents, such as oxalic acid, acetic acid, cyanide, halide, thiourea, and thiosulfate.13 Hydrometallurgical processes are less energy and cost demanding than pyrometallurgical treatments, and they are Received: Revised: Accepted: Published: 1581

June 1, 2012 January 15, 2013 January 16, 2013 January 16, 2013 dx.doi.org/10.1021/es302192t | Environ. Sci. Technol. 2013, 47, 1581−1588

Environmental Science & Technology

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Figure 1. System boundaries for the processes carried out in the HydroWEEE portable plant that were aimed at metal recovery from fluorescent powders from used fluorescent lamps and CRTs and from ground electrode material from used Li-ion accumulators. *EEE (electrical and electronic equipment): fluorescent lamps/CRT TV-monitor sets/Li-ion accumulators; x Pretreatment: Hg distillation (fluorescent lamps)/CRT recycling process/grinding (Li-ion accumulators); + WEEE residues that enter the portable plant: fluorescent powders (fluorescent lamps and CRTs)/ ground electrode material (Li-ion accumulators). The physical processes carried out before the treatment of the WEEE residues were collecting, sorting and dismantling of the WEEEs. The products were recovered with extraction efficiencies of around 90% for Y, 93% for Li and 97% for Co, with purities of 95%, 18%, and 43%, respectively.

also applicable in plants with relatively small capacities.14 Recently hybrid technologies have also been applied, which integrate the chemical approach (more efficient) with biological strategies (more ecocompatible), thus taking advantage of the benefits of both chemical and biological leaching.15 The present study was performed as a part of the research project called HydroWEEE 231962 (Innovative Hydrometallurgical Process to recover Metals from WEEE including lamps and batteries), which was funded by the European Commission within the FP7 Capacities Work Program. The aim of the project was the recovery of base and precious metals from WEEE residues. Within the HydroWEEE project, different processes for the exploitation of WEEE residues were developed to extract high-purity metals. In particular, a portable demonstration prototype was installed in a container lorry, for the application of the processes that were developed. These used the WEEE residues for the recovery of Y from fluorescent lamps; Y and Zn from CRTs; Li and Co from Li-ion accumulators; and Cu, Ag, and Au from PCBs. The advantages and novelty of this portable plant include its cost-effectiveness and the use of innovative processes that can be applied anywhere where the plant is based. This last arises from the portable nature of this plant, which allows small enterprises without their own recycling plant, along with the many collection facilities that can now be found in most countries, to take advantage of its transportability. The aim of the present study was to assess the environmental impact of the processes implemented with this portable plant, by means of life cycle assessment (LCA) and according to selected environmental impact categories. The unit operations that have a high load on the environment were also identified in each of these processes,

and primary production processes were considered as reference. This innovative approach applied in the field of WEEE residue recycling covers the final step of the recycling processes, which deals with the dangerous fractions (fluorescent powders are classified as hazardous waste by the European Waste Directive)16 that are rich in metals. In Europe at present, these fractions are mainly either disposed of in landfill sites or treated in large pyrometallurgical plants. It is very important at this stage of the worldwide state of the art in WEEE residue recycling to determine whether the proposed strategy is the correct way to proceed in this extremely critical field of recycling and secondary raw materials production.

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EXPERIMENTAL SECTION Processes for Metal Recovery from WEEE Residues. The processes addressed for this exploitation of WEEE residues (from fluorescent lamps, CRTs, Li-ion accumulators and PCBs) were carried out in the portable plant from the HydroWEEE research project. Specific, essentially physical, pretreatments were carried out according to the kind of WEEE, which were aimed at the recovery of the main fractions (e.g., glass, plastics, metals) and at the production of the WEEE residues that are not treated by most small and medium enterprise (SME) recyclers at present . In particular, the pretreatments included crushing, sieving and Hg removal by distillation, for the fluorescent lamps (Figure 1); disassembly and CRT recycling (e.g., with diamond cutting technology), for the CRTs (Figure 1); sorting, dismantling and grinding for the Li-ion accumulators (Figure 1); and sorting, shredding, magnetic separation and aluminum separation, for the PCBs (Figure 2). The initial characterization and preliminary tests of the WEEE 1582

dx.doi.org/10.1021/es302192t | Environ. Sci. Technol. 2013, 47, 1581−1588


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Figure 2. System boundaries for the process carried out in the HydroWEEE portable plant aimed at metal recovery from PCB residues. The unit processes included in the LCA study are production of electricity, thiourea, ferric sulfate, hydrogen peroxide, sulfuric acid, zinc, and calcium hydroxide. The products were recovered with extraction efficiencies of around 90% for Cu, Au, and Ag), with purities of 99.5% for Cu and 80% for (Au+Ag).

with respective purities of 95%, 99.5%, 80% (Au+Ag), 18% and 43% . These relatively low purities are not suitable for direct commercialization (where at least 99% would be needed), but these products are marketable to companies that use them as feed for a final purification. A final step of wastewater treatment was also considered, based on the use of lime for precipitation and neutralization processes. Figures 1 and 2 show the detailed system boundaries considered for the LCA and the processes included in the data elaboration. All of the details concerning the processes developed can be found elsewhere.17−20 It should be noted that only the hydrometallurgical processes that are carried out in the portable plant are considered in the analysis, and not the recycling pretreatments. Furthermore, the transport step of the WEEE residues to the hydrometallurgical plant was not considered, as the plant can be moved from one SME recycler site to another, throughout Europe. The transport of the recovered metals was considered to be outside of the system boundaries, even if this might be of relevance and should or could be considered on a case-by-case basis (i.e., this will depend on the sites of the plant and the purchasing companies).21 Goal and Scope Definition of the LCA. As indicated above, the main goal of the present study was the estimation of the environmental impact of the processes carried out in the HydroWEEE portable plant for the recovery of metals from these four WEEE residues following the initial physical

residues were carried out on the powders produced from these pretreatments. From the fluorescent tubes, these contained 5− 7% Y, as oxides, with rare earth elements also present, such as Eu (although these were not targets of the purification within the HydroWEEE project). From the CRTs, there were 15− 20% Y and 30−35% Zn, which were present as oxides and sulfur compounds. The ground electrode material produced after the Li-ion accumulator pretreatment contained 23−25% Li and 2−3% Co. Finally, for the PCBs, there were 25−28% Cu, 400−800 g/tonne Au, and 1400−1900 g/tonne Ag. These were thus the starting point for achieving the most suitable and effective treatments for metal extraction and recovery.17−19 The feed materials for the portable plant were thus the WEEE residues: fluorescent powders from fluorescent lamps and CRTs, ground electrode material from Li-ion accumulators and waste granulate material from PCBs. A leaching operation with sulfuric acid was a common unit operation for metal extraction (Y, Zn, Cu, Li, Co) from WEEE residues. For the Li-ion accumulator and PCB WEEE residues, hydrogen peroxide was also added under acidic conditions, as a reducing agent. In the case of PCBs, this was followed by a thiourea leaching step (for Au and Ag dissolution). The metal recovery from the leach liquor was carried out by selective precipitation operations, according to each of the specific metals to be recovered. The products were recovered here with extraction efficiencies of around 90% for Y, Cu, Au, Ag, 93% for Li, and 97% for Co, 1583



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Table 1. Inventory Analysis of the LCA of the Four HydroWEEE Processesa WEEE residues resources

emissions

energy (GJ) material (104 kg) air (104 kg) water (kg) soil (kg)

fluorescent powder from fluorescent lamps

fluorescent powder from CRTs

1700 310

4000 700

9000 870

12 000 910

18 1500 36

48 4500 79

300 25 000 42

380 16 000 63

ground electrodic material from Li-ion accumulators

PCB granulate from PCBs

The functional unit is 100 tonnes WEEE residues: fluorescent powder from fluorescent lamps, fluorescent powder from CRTs, ground electrodic material from Li-ion accumulators and PCB granulate from PCBs. The energy resources are expressed as gross calorific value. The use of the resources includes energy and materials. Air, water and soil emissions are considered. a

recycling processes (Figures 1 and 2): fluorescent powders from fluorescent lamps and CRTs, ground electrode material from Li-ion accumulators and waste granulate from PCBs. The assessment was addressed specifically at the identification within each process of the most critical step for the environment, to be able to suggest further directions for research activities aimed at lowering the environmental impact of metal recovery strategies from WEEE residues. A comparison with primary production processes was also performed, to determine whether the chosen approach follows the right direction for the protection of the environment. The present study thus aims to be a suitable document for all companies involved in metal recycling from WEEE, to help with the choice of the most eco-friendly strategies. The functional unit was 100 tonnes of WEEE residue, which corresponds to the annual capacity of the portable plant and to different quantities of the WEEE: around 1800 tonnes of fluorescent lamps, 3300 tonnes of CRTs, 500 tonnes of Li-ion accumulators, 100 tonnes of PCBs). The system boundaries considered for the LCA and the processes included in the data elaboration are reported in Figures 1 and 2. The impacts of these processes were evaluated according to the problem-oriented methods of the Institute of Environmental Sciences, Leiden University, Leiden, The Netherlands (previously the Centrum voor Milieukunde Leiden; hence CML), as integrated into the GaBi software that is used for LCA.22,23 This methodology includes the following categories: abiotic depletion, acidification potential, eutrophication potential, global warming potential, ozone layer depletion potential, and photochemical ozone creation potential. The methodology chosen for the evaluation of the impact here was CML2001 November 09. Normalization was carried out according to CML2001 - December 07, EU25 + 3, and weighting was evaluated following CML2001 - December 07, according to the experts of the Institute for Polymer Testing and Polymer Science (IKP), University of Stuttgart, Germany, and referred to southern Europe, the area where this study was carried out and where there are no large recycling facilities, such as that of Umicore in northern Europe. The weighting was carried out with the aim of comparing the results obtained across each impact category, and defining where the highest criticalities for the environment were; it should be noted that some controversies exist relating to this procedure.24,25 The flow that was considered to contribute to the potential environmental impact was the processes of the production of energy and chemicals used for the metal extraction, the recovery and the wastewater treatment, which were taken from the databases within the GaBi software. Two of the reagents involved in the production processes were not available in the databases (sodium sulfide and oxalic acid), and so information

reported in the literature26−30 was considered to build these processes within GaBi. In particular, for oxalic acid, the route of biological production was taken into account due to the high impact of the chemical route, in terms of emissions. For the processes developed in the HydroWEEE project, allocation procedures were generally avoided, except for the process created for oxalic acid production. In this case, a 50% mass allocation was hypothesized, considering that the biological process produces both citric and oxalic acid.29−31 An assessment was also carried out considering several potential electricity sources, to determine the sensitivity of the results to this variable. Indeed, the portable plant can be used in different countries where the energy required might come from various origins. We considered the following: hydropower, wind, nuclear, natural gas, power mix (mix of energy produced in Italy), lignite, heavy fuel oil, and hard coal. For the sensitivity analysis, an overall indicator was used as the sum of the normalized (CML2001 - December 07, EU25 + 3) and weighted (CML2001, December 07, IKP experts, southern Europe) impacts of abiotic depletion, acidification, eutrophication, global warming, ozone layer depletion and photochemical ozone creation. Regarding eventual uncertainties associated with the composition of the WEEE residues, the processes were optimized considering an excess of reagents, and consequently it is reasonable to assume that this composition would not affect the environmental impact of the portable plant. Life Cycle Inventory Analysis. The inventory analysis for the LCA was obtained directly by the research activity within the HydroWEEE project for the quantitative and qualitative data (reagents and energy) for the unit processes of the hydrometallurgical treatments. The production processes of the chemicals and energy are available in the EcoInvent 2.2 database,32 except for the sodium sulfide and oxalic acid production processes, which we built by ourselves within GaBi from a consideration of the literature data. For energy, the power mix produced in Italy was used in all of the processes, unless otherwise specified. Table 1 gives the details of the inventory analyses for the four HydroWEEE processes, divided into the use of energy and materials, and the production of air, water and soil emissions. Software for the LCA. For the production processes of energy and raw materials and the estimation of the potential environmental impact of the processes developed, we used the GaBi 4.4 software (PE International) integrated with the EcoInvent database v.2.2.32

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RESULTS Life Cycle Impact Assessment. The environmental impact of the hydrometallurgical processes carried out in the

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portable plant were estimated according to the main categories of global warming, abiotic depletion, acidification, eutrophication, photochemical ozone creation, and ozone layer depletion. Table 2 gives the estimated values for the four WEEE residues Table 2. Emissions for the Treatment of 100 Tonnes WEEE Residues: Fluorescent Powder from Fluorescent Lamps, Fluorescent Powder from CRTs, Ground Electrodic Material From Li-Ion Accumulators and PCB Granulate from PCBsa

impact categories global warming (kg CO2-eq.) abiotic depletion (kg Sb-eq.) acidification (kg SO2-eq.) eutrophication (kg phosphateeq.) ozone layer depletion (kg R11-eq.) photochem. ozone creation (kg ethene-eq.)

fluorescent powder from fluorescent lamps

fluorescent powder from CRTs

ground electrodic material from Liion accumulators

PCB granulate from PCBs

9.4 × 104

2.0 × 105

5.4 × 105

7.8 × 105

0.03

0.8

2.0

2.2

505

1225

1365

2044

83

182

130

137

0.008

0.02

0.04

0.05

34

122

98

154

Figure 3. Results of data normalization (CML2001 - December 07, EU25 + 3) and weighting (for southern Europe) for the treatment of 100 tonnes fluorescent powder from fluorescent lamps. The impacts of leaching, Y recovery and wastewater treatment are represented in the categories of abiotic depletion, acidification, eutrophication, global warming, ozone layer depletion, and photochemical ozone creation.

ground electrode material from Li-ion accumulators, the leaching step with sulfuric acid and hydrogen peroxide was the unit operation with the greatest impact in the categories of global warming, acidification, ozone depletion and photochemical ozone creation (SI Figure S1). In this case, the wastewater treatment was the step with the lowest impact. In the process for the recovery of Y and Zn from CRT powders, the highest potential impact in the category of global warming was due to the Y recovery operation, while the leaching and metal recovery sections contributed in similar ways to the photochemical ozone creation potential (SI Figure S2). The process for the recovery of valuable metals from end of life PCBs is more complex than the others, because of the need for two leaching steps for the extraction of Cu and the precious metal (Au and Ag). In any case, the Cu-leaching phase that is carried out with sulfuric acid and hydrogen peroxide was responsible for the highest impact across all of the categories considered (SI Figure S3).

a

The selected impact categories were global warming, abiotic depletion, acidification, eutrophication, ozone layer depletion and photochemical ozone creation (problem oriented method, CML).

under study: fluorescent lamps, CRTs, Li-ion accumulators and PCBs. The process for the recovery of Y from the powders residue from the recycling of fluorescent lamps has the lowest impact of all of the categories, with 0.94 kg CO2 eq. (global warming), 0.3 mg Sb eq. (abiotic depletion), 5 g SO2 eq. (acidification), 0.8 g phosphate eq. (eutrophication), 80 μg R11 eq. (ozone layer depletion), 0.3 kg ethene eq. (photochemical ozone creation), all per kg of WEEE residue. On the other hand, the highest impact appears to be associated with the process for the recovery of copper, gold and silver from PCBs, with 78 kg CO2 eq. (global warming), 22 mg Sb eq. (abiotic depletion), 20 g SO2 eq. (acidification), 1.4 g phosphate eq. (eutrophication), 500 μg R11 eq. (ozone layer depletion) and1.5 kg ethene eq. (photochemical ozone creation), all per kg of WEEE residue. These data are discussed considering the three macrosections of the hydrometallurgical treatments: metal extraction by leaching; metal purification and recovery; and wastewater treatment. This last section is very important, especially for small and medium size recyclers, which are usually not allowed to discharge wastewater into the environment. In all of these investigated processes, the highest impact was seen for the category of global warming potential, followed by the impact categories of abiotic depletion potential and photochemical ozone creation potential (Figure 3, Supporting Information (SI) Figures S1−S3). For the identification of the high environmental load section within each process, the emissions of carbon dioxide for the treatment of fluorescent lamp powder were shared relatively evenly among the three macro-sections that comprise the complete treatment (Figure 3). The major contribution to all of the other impact categories - abiotic depletion, acidification, eutrophication, ozone layer depletion, and photochemical ozone creation- was due to the Y recovery phase that was carried out with oxalic acid. For the

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DISCUSSION Life Cycle Interpretation. As indicated above, this LCA has allowed the estimation as a whole of the environmental impact of the four processes for metal recovery from WEEE residues (Table 2). Furthermore, the most environmentalthreatening step for each process has been identified. Indeed, the data obtained show that the production processes of oxalic acid on the one hand (for fluorescent powders from fluorescent lamps and CRTs) and hydrogen peroxide on the other (for Liion accumulators and PCBs) are the most critical for the environment. Consequently further research that addresses the identification of an alternative agent for yttrium precipitation (instead of oxalic acid) and an alternative reducing agent instead of (hydrogen peroxide) would improve the ecocompatibility of the processes developed here. Thus, it is important to improve the processes aimed at metal recycling in the end of life phase of these WEEE residues. We have also highlighted that considering the whole life cycle of a piece of electrical and electronic equipment, the benefits that result from the final step of its life can often be greater than the impacts associated with the phases of its production and use.33 1585



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In conclusion, from the comparisons in Table 3, the processes under study within the HydroWEEE project appear to be beneficial for the environment in terms of the carbon dioxide emissions, especially for the metal recovery from the WEEE residues from fluorescent lamps and CRTs. A further aspect that has to be taken into account is associated with the portable nature of this prototype plant, which is an innovative idea in this field. Indeed, in this way, the impact that would result from the transport of the WEEE to a centralized recycling plant is eliminated. Obviously, there is an impact associated with the plant transfer, although this will be negligible with respect to the WEEE transport to the plant, which will be over longer distances. To assess the influence of the eventual transportation of WEEE to the plant, the HydroWEEE impact has been corrected and the CO2 emissions have been calculated inclusive of this transport, where the previously estimated values are reduced by the transport saving. A mean value for the CO2 emissions due to the transport of 100 tonnes of WEEE over the distance of 2000 km was considered, using a 16−32 tonne Euro 4 lorry.34 For the treatment of fluorescent lamps and CRTs we found that the amounts of CO2 per kg metal recovered net of transport for each were about 18-fold and 7-fold less, respectively, than those resulting from the primary production. However, the savings associated with the transport of the WEEE will be higher if the trucks have lower capacities and/or are relatively old (Euro3 or lower). The portable nature of the plant might also allow to different sources for the required energy. Consequently, a sensitivity analysis was performed considering the energy source as variable (SI Figures S4−S7). The global indicator of the environmental impact (calculated as the sum of the six normalized and weighted CML categories; see Experimental Section) for the Italian power mix used in this study was, as expected, intermediate between the group of hydropower, wind and nuclear power, which were characterized by the lowest values, and the group made up of natural gas and lignite, heavy fuel oil and hard coal. The highest variation was estimated for fluorescent lamps and CRTs, where savings in the environmental impact in the range of 24−28% would be achieved in the case of energy produced by renewable sources. Therefore, according to the source of energy selected, different impacts will be realized. Overall, the present study has identified the critical points of the process under study that are important for its optimization. These data will be useful for professionals and researchers working in the framework of metal recycling from WEEE residues.

A comparison with the primary production processes was also performed. Such a comparison between the primary and secondary production processes in our case has some limitations, due to the different purities of the recovered metals (around 95% for metals in the HydroWEEE processes vs 99.9% in the primary production). Nevertheless, this allows the determination of whether the chosen approach goes in the right direction for environmental protection. We considered only the CO2 emissions here, because from the data we observed that in all of the processes investigated the greatest impact was seen for the category of global warming potential. Estimated values previously reported for the selected functional units (100 tonnes) are presented here as referred to the unit mass of the WEEE residues and the recovered metals. Table 3 shows the Table 3. Carbon Dioxide Emissions from the Treatment of Selected Fractions of the WEEE Residues (Fluorescent Powder from Fluorescent Lamps, Fluorescent Powder from CRTs, Ground Electrodic Material from Li-Ion Accumulators and PCB Granulate from PCBs) for the HydroWEEE Processes Referred to Unit Mass of the WEEE Residues Entering the Plant and to the Unit Mass of the Recovered Metal (The Contribute of Each Metal Is Also Given), and for the Primary Processes (144.9 g CO2/g Y,35 3.5 g CO2/g Zn,32 8.8 g CO2/g Co,32 18.8 g CO2/g Li,32 18740 g CO2/g Au,32 438 g CO2/g Ag,32 3.5 g CO2/g Cu32) hydroWEEE process

WEEE residues fluorescent powder from fluorescent lamps fluorescent powder from CRTs ground electrodic material from Li-ion accumulators PCB granulate from PCBs

g CO2/g WEEE residues

g CO2/g metal

primary process g CO2/ g metal

0.9

13.3 g CO2/g Y

144.9

2.0

19.2 g CO2/g metals (13.7 g for Y ; 5.5 g for Zn) 27.0 g CO2/g metals (24.5 g for Li; 2.5 g for Co)

104.5

25.8 g CO2/g metals (0.1 g for Au; 0.2 g for Ag; 25.5 g for Cu)

55.7

5.4 7.8

27.4

CO2 emissions for the treatments of the WEEE residues in the HydroWEEE processes, referred both to the unit mass of the WEEE residues fed to the plant, and to the unit mass of the recovered metal. To compare these data with the primary production processes, Table 3 also shows the carbon dioxide emissions that were estimated considering the amounts of the metals recovered through the HydroWEEE processes produced by the primary processes. Indeed, as suggested in other studies, the emissions saved by the avoidance of the metal extraction from virgin sources will be relevant.34 It can be seen that the environmental impact of the HydroWEEE processes for the fluorescent powders from the fluorescent lamps and CRTs are significantly lower than the primary production (by 1 order of magnitude). Also, in the case of PCBs, a significant saving in CO2 emissions was estimated for the HydroWEEE process. In the case of Li-ion accumulators, the estimated impact for the recovered metals was comparable to that of the primary production processes. This was mainly due to the use of hydrogen peroxide, the production process for which contributes about 60% of the total impact in the global warming category.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information includes Figures S1−S7. This information is available free of charge via the Internet at http:// pubs.acs.org/.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +39 071 2204225; fax: +39 071 2204650; e- mail: f. [email protected]. 1586



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Author Contributions

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The manuscript was written through contributions from all of the authors. All of the authors have approved the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was funded by the European Commission within the FP7 Capacities Work Program, and all of the partners of the HydroWEEE 231962 project are acknowledged. We thank the five anonymous reviewers for their helpful comments and to Christopher Paul Berrie for his important support in the English revision of the manuscript.

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