Bioleaching of Gold and Copper from Electronic Waste Using Sulphate Reducing Bacteria

Abstract

This thesis examined a novel hybrid method to recover gold and copper from electronic waste (e-waste) based on combination of biological and chemical generation of thiosulphate reagent. E-waste is growing waste stream rich with copper and gold. Thiosulphate is an effective leaching reagent to recover these metals however it is hampered by high cost deeming it economically unfeasible. Currently there are no alternative technologies that are able to overcome this limitation. To establish the need for this new hybrid method, we examined the economics of e-waste and current available technologies. The evaluation revealed these metals with will continue to exist in future e-waste stream and their value will continue to increase. Existing technologies were capital cost intensive and required large e-waste volumes to achieve operational cost parity. These findings were indications that copper and gold are appropriate target metals for our new technology. The novel technology exploits the natural ability of sulphate reducing bacteria (SRB) to generate sulphide that is subsequently oxidised to thiosulphate. The approach involved the isolation of SRB to generate sulphide; conversion of sulphide to thiosulphate using sulphite; and metal leaching studies using generated thiosulphate. This study showed thiosulphate was generated from bioreduced sulphide by isolated SRB. Leaching studies compared the efficiency of reagent grade thiosulphate with thiosulphate generated by the hybrid technology. The gold recoveries of the hybrid generated thiosulphate ranged from 9 to 99%. These favourable results demonstrated for the first time the technical feasibility of generating thiosulphate via biological and chemical route and the thiosulphate generated can effectively leach gold from e-waste. Thus paving for a novel and sustainable method of leaching gold from e-waste.