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.

A schematic flowsheet showing the potential process options for recovery of metals from e-scrap (Adapted from Yazıcı and Deveci, 2009).Figure optionsDownload as PowerPoint slideHighlights
► The generation of WEEE rapidly increases with ever increasing environmental concern.
► WEEE is a secondary resource for base and precious metals, compared with ores.
► Recycling of WEEE is the best environmental and economical waste management option.
► Pilot scale tests generate operational and cost data for commercialization.