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Recycling 2017, 2(3), 14;

The Effect of the Redox Potential of Aqua Regia and Temperature on the Au, Cu, and Fe Dissolution from WPCBs

Laboratory of Hydrometallurgy and Corrosion, Department of Chemical and Metallurgical Engineering, School of Chemical Engineering, Aalto University, P.O. Box 16200, FI-00076 Espoo, Finland
This paper is an extended version of our paper published in 6th International Conference Quo Vadis Recycling, High Tatras, Slovak Republic, 6–9 June 2017.
Author to whom correspondence should be addressed.
Received: 22 August 2017 / Revised: 28 August 2017 / Accepted: 31 August 2017 / Published: 1 September 2017
(This article belongs to the Special Issue Quo Vadis Recycling 6)
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Constant growth in waste electrical and electronic equipment (WEEE) levels necessitates the development of new, commercially viable recycling processes. Waste printed circuit boards (WPCBs) are a sub-group of WEEE that are of increasing interest due to their relatively high level of valuable metal content including Au, Ag, and platinum group metals (PGMs). Currently, precious metals like gold are mainly recycled from WEEE streams through copper smelting/refining; however, the possibility to peel gold from WPCBs prior to smelting, could offer advantages for recycling. In this study, the suitability of aqua regia for selective or partially selective gold leaching from un-crushed WPCBs was investigated. The redox potential of aqua regia solutions and the dissolution efficiencies of Au, Cu, and Fe from WPCBs were investigated at different temperatures (40–80 °C) and concentrations (2–32%) in batch leaching tests. The redox potential of aqua regia solution was found to depend on concentration and temperature. It is suggested that Au dissolution in aqua regia requires dissolved Cu2+ ions originating from the WPCB material to work. Au extraction (>50%) was shown to require a redox potential >700 mV with [Cu2+] > 2500 ppm, as a potential >850 mV alone was insufficient without cupric ions. Significant amounts of Au and Cu could be dissolved with only minor Fe dissolution at ≥8% aqua regia at 80 °C. Results suggest that leaching of uncrushed WPCBs in 8% aqua regia (T = 80 °C) can provide the opportunity for partial Au recovery prior to further processing. View Full-Text
Keywords: waste printed circuit boards; gold leaching; copper leaching waste printed circuit boards; gold leaching; copper leaching

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Elomaa, H.; Seisko, S.; Junnila, T.; Sirviö, T.; Wilson, B.P.; Aromaa, J.; Lundström, M. The Effect of the Redox Potential of Aqua Regia and Temperature on the Au, Cu, and Fe Dissolution from WPCBs
. Recycling 2017, 2, 14.

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