Aqueous metal recovery techniques from e-scrap: Hydrometallurgy in recycling

Waste of electric-electronic equipment (WEEE) with an annual growth rate of about 3-5% is the fastest growing waste stream in municipal wastes. Notwithstanding their environmental pollution potential, waste of electrical and electronic equipment (WEEE) with their high content of base and precious metals, in particular, are regarded as a potential secondary resource when compared with ores. For the recovery of metals from WEEE, various treatment options based on conventional physical, hydrometallurgical and pyrometallurgical processes are available. These process options with particular reference to hydrometallurgical processes were reviewed in this study. With their relatively low capital cost, reduced environmental impact (e.g. no hazardous gases/dusts), potential for high metal recoveries and suitability for small scale applications, hydrometallurgical processes are promising options for the treatment of WEEE. Since the metals are present in native form and/or as alloys, an oxidative leaching process is required for the effective extraction of base and precious metals of interest. A two-stage process based on oxidative acid leaching of base metals (Cu in particular) followed by leaching of precious metals using cyanide, thiosulfate, thiourea or halide as lixiviant(s) can be suitably developed for the hydrometallurgical treatment of WEEE. However, further research is required to develop new, cost effective and environmentally friendly processes and/or refine existing ones for leaching and, in particular, downstream processes. © 2011 Elsevier Ltd. All rights reserved

Reclamation of Precious Metals from Small Electronic Components of Computer Hard Disks

Present research work focuses on the recovery of precious metals (Ag, Au, Pd, and Pt) from the leach liquor of small populated chips present in the hard disk of computers. Initially, the hard disks were dismantled to separate the printed circuit boards (PCBs) followed by its depopulation to liberate the mounted small electronic components. The liberated black chips were pulverized to *100 mesh and chemically analysed. The powdered black chips containing *0.6% Ag, *0.3% Au, *0.01% Pd, *0.0003% Pt, and 20% Cu on mass basis were first leached in nitrate medium for maximum dissolution of non-ferrous metals along with Ag leaving Au, Pd, and Pt in the residue. About 99.99% of precious metals were leached out from the residue using suitable lixiviant. The obtained leach liquor was purified using advanced separation techniques (solvent extraction/ion-exchange/ precipitation) from which marketable products (metals/salts) could be produced