SUbstance flow analysis of the recycling of small waste electrical ...

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42 Substance flow analysis of the recycling of small WEEE Concentration rate (quality of the output) Recovery rate (quantity of recovered material) Figure 5 The grade-recovery function in mechanical processing (Hagelüken 2006a) Most of precious metal in WEEE is found at trace level concentrations in the printed circuit boards. Pre-processing usually aims at grouping the printed circuit boards in one or several precious metal-rich output fractions to send them to a facility able to recover precious metals. If pre-processing sends a substance, for example gold, to a recovery process that is not able to recover it, it is “lost” for the recycle-economy. This cannot be completely avoided, so that some printed circuit boards end up in side-streams like plastics or ferrous metals that are not set up for precious metal recovery (Hagelüken 2006a). Because of the concentration dilemma shown by Figure 5, all processes used to recover precious metals involve losses (Kreibe et al. 1996). A reduction of the losses of precious metals possibly means reducing the concentration of precious metals in the fraction sent for precious metal recovery and increasing the losses of other materials like ferrous metals that cannot be recovered in processes for precious metals. The printed circuit boards coming from pre-processing can either be intact (for example if the WEEE was manually dismantled) or shredded. Sometimes, the precious-metal rich outputs coming out of pre-processing are not sent directly to facilities for precious metals refining, but are first concentrated in another upstream process using mechanical or melting processes like pyrolisis (Goosey & Kellner 2003; Hall & Williams 2007; Kreibe et al. 1996; Veit et al. 2002; Yoo et al. 2009). 2.4.4.2. Recovery of precious metals According to the WEEE Directive, ‘recovery’ means any of the applicable operations provided for in Annex IIB to Directive 75/442/EEC of the European Commission. Recovery of precious metals is listed in Annex IIB as ‘Recycling/reclamation of metals and metal
2. Background and definitions 43 compounds’. Like all metals, precious metals are characterised by metallic bonding that is not affected by melting, so that they can be recycled over and over again (Heinrich 2007). Reviews on metallurgical processes to recover and refine (precious) metals from printed circuit boards were issued by Cui & Zhang (2008), Goosey & Kellner (2003) and Huang et al. (2009). The European Commission (2001) provided an overview of the “Best Available Techniques” to recover precious and other non-ferrous metals. Currently, mainly pyrometallurgical and hydrometallurgical processes are used to recover the precious metals. Modern facilities using a complex succession of processes including pyrometallurgical techniques, hydrometallurgical process, and electrochemical technology are able recover base metals, precious metals and special metals (Cui & Zhang 2008; Hagelüken 2006b). Pyrometallurgical processing involves heating the crushed WEEE in a furnace or in a molten bath to remove plastics, so that the refractory oxides form a slag phase together with some metal oxides (Cui & Zhang 2008). Incineration, smelting in a plasma arc furnace or blast furnace, drossing, sintering, melting and reactions in a gas phase at high temperatures are techniques presently applied (Cui & Zhang 2008; Hagelüken 2006b; Lee et al. 2007; Lehner 1998; Veldhuizen & Sippel 1994). The main steps in hydrometallurgical processing consist of a series of acidic or caustic leaches of solid material. The most common leaching agents used in recovery of precious metals include cyanide, halide, thiourea, and thiosulfate (Cui & Zhang 2008). The solutions are then subjected to separation and purification procedures such as precipitation of impurities, solvent extraction, adsorption and ion-exchange to isolate and concentrate the metals of interest. Subsequently, the solutions are treated by electrorefining, chemical reduction, or crystallization for metal recovery (Cui & Zhang 2008). Chmielewski et al. (1997), Mishra (2002), Park & Fray (2009), Quinet et al. (2005) and Sheng & Etsell (2007) have published experimental results on the application of hydrometallurgical processes to recover precious metals from printed circuit boards. The efficiency of hydrometallurgical recovery highly depends on the technology used for size reduction and liberation before the recovery process itself. In addition to the precious metal-rich materials coming from pre-processing facilities, precious metals can be recovered out of other material flows related to WEEE. Several plastic recycling companies in Europe and in the USA reported during interviews that some of the precious metals contained in the plastic fractions are recovered in the course of the separation out of the disturbing substances, to which metals belong (Biddle et al. 1998; Novak 2001). More precise data on these processes are not available. In addition, research
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7. Recommendations 109 7. Recommend
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7. Recommendations 111 WEEE contai
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7. Recommendations 113 After collec
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7. Recommendations 115 in the case
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7. Recommendations 117 In many case
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7. Recommendations 119 manufacturer
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7. Recommendations 121 the manufact
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7. Recommendations 123 Reuter et al
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8. Conclusion 125 All the equipment
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References 127 Binder 2007 BITKOM 2
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References 129 CIWMB 2004b Clift &
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References 131 Greenpeace 2005 Gree
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References 133 Janz & Bilitewski 20
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References 135 Melissen 2006 Mesker
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References 137 Rhein et al. 2008 Rh
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References 139 StEP 2009 Stevels 20
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References 141 Veldhuizen & Sippel
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References 143 Legislative texts Ba
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Appendices 145 Appendix 1 Equipment
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Appendices 147 Appendix 2 Average c
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Appendices 149 Appendix 4 Past and
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Appendices 151 Eq. group Equipment
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Appendices 153 2 Assumptions based
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Appendices 159 Appendix 8 Flows of
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Appendices 161 Appendix 10 Flows of
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