Gold Bioleaching of Electronic scrap material by cyanogenic bacteria and its enhancement with biooxidation

Abstract

Electronic waste is recognized as a fast growing waste stream, and the presence of hazardous as well as precious metals in the waste has attracted attention. Bioleaching is explored as an environmentally sustainable alternative to conventional chemical processes in treating such wastes. Chromobacterium violaceum and Pseudomonas fluorescens were used to bioleach gold from Electronic Scrap Material (ESM) at various pulp densities, using both one-step and two-step methods. Increasing pulp density led to decreased leaching efficiencies, as well as strong inhibition of bacterial growth, particularly for C. violaceum. Two-step bioleaching gave improved gold recovery. Pre-treatment by biooxidation (using Acidithiobacillus. ferrooxidans) was applied to reduce the competing copper ions. Bioleaching of biooxidized ESM showed improvement of leaching gold, particularly by C. violaceum, with much higher gold/copper ratio in the leachate. Bioleaching of 2%w/v ESM by P. fluorescens was also conducted in a bioreactor to examine the potential for scale-up.