Recovery of Metals from Wastes and Effluents
Electrochemical processes offer elegant, environmentally-benign, energy-efficient engineering solutions for metal recovery from industrial effluents and wastes. Electrical energy is used to effect the required chemical change(s) by oxidation reactions at anodes and reduction reactions at cathodes.
The Electrochemical Engineering research group has extensive experience of the electrochemical science and engineering required to develop recovery and recycling processes for metals from industrial effluents[i],[ii],[iii] and end-of-life materials, such as waste electrical and electronic equipment (WEEE) [iv],[v],[vi],[vii],[viii],[ix],[x],[xi] and spent catalysts[xii],[xiii]. The feasibility of (near-) closed loop processes have been demonstrated using aqueous solutions containing chloride and iodide. A current project is extending these electrolytes to ionic liquids.
WEEE was shredded and if necessary ground to liberate encapsulated metals; as the mechanical energy requirement increases sharply with decreasing particle sizes below ca. micrometres, optimisation of the liberated metal value is required with respect to the energy input. The resulting particles were dissolved in coupled leach and electrochemical reactors (Fig.1); chlorine was generated by reaction (4) to effect non-selective dissolution of metallic components by reaction (1), with simultaneous selective or non-selective electrodeposition by reaction (2). The fluid phases were operated in closed loop with recycle of the electrolyte solution, so the overall process involved inputting electrical energy to move the metals from waste to cathode (reaction (5)) and, in principle, additionally produced only de-metallised material (polymer and glass), for further processing.
With multi-metallic wastes, control of electrode potential may be used to deposit metals selectively, or alloy deposits can be electrorefined subsequently to achieve the required purity for recycling (e.g. commercial purity copper ³ 99.99 %). Mathematical models enable process options and optimal strategies (selective vs. non-selective dissolution, simultaneous or sequential electrodeposition) to be explored depending on the properties of particular wastes, and enable rational reactor and process design to minimise dissolution times, maximise charge yields, and optimise specific electrical energy consumptions and overall process energy requirements (ca. 0.4 MW h (tonne Au)-1; 2 MW h (tonne Cu)-1 etc.) and (capital + running) costs.
A similar process (Fig.2) was developed for recovery of Pd and Pt from spent catalysts, using aqueous iodide solutions and tri-iodide as oxidant at neutral pHs, so Pd and Pt could be dissolved selectively from Al2O3 supports that also could be recycled.
|Fig. 1. Concept of metal recovery from shredded WEEE.||Fig. 2. Electrochemical and leach reactors for metal recovery from spent catalysts.|
List of Publications
[i]. N.P. Brandon, D. Pilone, G.H. Kelsall and Q. Yin, Simultaneous Recovery of Pb and PbO2 from Battery Plant Effluents. II., J.Appl.Electrochem., 33 (2003) 853-862.
[ii]. C.Y. Cheng, G.H. Kelsall and D.Pilone, Modelling Potentials, Concentrations and Current Densities in Porous Electrodes for Metal Recovery from Dilute Aqueous Effluents, J.Appl.Electrochem., 35(12) 1191 - 1202 (2005).
[iii]. A. Hankin G.H. Kelsall, Electrochemical recovery of nickel from nickel sulfamate plating effluents, J.Appl.Electrochem. (2012) 42:629–643
[iv]. N.P.Brandon, G.H.Kelsall, T.Müller, R.Olijve, M.Schmidt and Q.Yin, Metal Recovery from Electronic Scrap by Leaching and Electrowinning. 200th Electrochemical Society Meeting, San Francisco, 2-7 September 2001 and Proc.Electrochem.Soc. Vol.2001-23, Energy and Electrochemical Processes for a Cleaner Environment, C.Comninellis, M.Doyle and J.Winnick (Eds.), Electrochem.Soc., N.J., 2001, pp.323-338. (ISBN 1-56677-356-3).
[v]. N.P. Brandon, G.H. Kelsall, M.J. Schmidt and Q.Yin, Metal recovery from electronic scrap by leaching and electrowinning II. TMS Meeting on Recycling and Waste Treatment in Mineral and Metal Processing: Technical and Economic Aspects, 16-20 June 2002, Luleå, Sweden, B.Björkman, C.Samuelsson, J-O.Wilkström (Eds.), TMS, Warrendale, PA, 2002, pp.359-368. (ISBN 91-631-2361-4).
[vi]. N.P. Brandon, G.H. Kelsall, R. Olijve, M. Schmidt and Q. Yin, Metal Recovery from Electronic Scrap by Leaching and Electrowinning III, in "Chloride Metallurgy 2002, Proceedings of the International Conference on the Practice and Theory of Chloride/Metal Interaction", Vol.II, E.Peek, G. van Weert (Eds.), CIM, Montréal, Canada, 2002, pp.743-757.
[vii]. C-y. Cheng, G.H. Kelsall and A. Robson, Model Predictions of Metal Leaching from Waste Electrical and Electronic Equipment (WEEE) in Chlorine-containing Acidic Aqueous Chloride, Electrochemical Society Transactions Vol.2. No.3, Electrochemistry in Mineral and Metal Processing VII, R.Woods, F.Doyle and G.H.Kelsall (Editors), Electrochemical Society, Pennington, NJ, 2006, pp. 231-242.
[viii]. N.P. Brandon, G.H. Kelsall, R. Olijve, M. Schmidt and Q. Yin, in ’Chloride Metallurgy 2002, Proceedings of the International Conference on the Practice and Theory of Chloride/Metal Interaction’, Vol.II, E.Peek, G. van Weert (Eds.), CIM, Montréal, Canada, 2002, pp.743-757.
[ix]. D.Pilone and G.H.Kelsall, Prediction and Measurement of Multi-Metal Electrodeposition Rates And Efficiencies In Aqueous Acidic Chloride Media, Electrochim.Acta, 51 (2006) 3802–3808.
[x]. C-Y. Cheng, M. A. Diaz, G. H. Kelsall and A. Robson, Gold Electrowinning from Acidic Aqueous Chloride in a Packed Bed Electrode, Electrochemical Society Transactions Vol.2. No.3, Electrochemistry in Mineral and Metal Processing VII, R.Woods, F.Doyle and G.H.Kelsall (Editors), Electrochemical Society, Pennington, NJ, May 2006, pp. 317-328.
[xi]. D.Pilone and G.H.Kelsall, Model Of Multiple Metal Electrodeposition In Porous Electrodes, J.Electrochem.Soc., 153(5) D85-D90, 2006.
[xii]. R.J. Dawson and G.H. Kelsall, Recovery of Platinum Group Metals from Secondary Materials. I. Palladium Dissolution in Iodide Solutions, J.Appl.Electrochem., (2007) 37:3–14.
[xiii]. R.J. Dawson and G.H. Kelsall, Pt dissolution and deposition in high concentration aqueous tri-iodide / iodide solutions, Electrochemical Letters, 2(11) D55-D57 (2013).