Biorecovery of gold by Escherichia coli and Desulfovibrio desulfuricans

Microbial precipitation of gold was achieved using Escherichia coli and Desulfovibrio desulfuricans provided with H-2 as the electron donor. No precipitation was observed using H-2 alone or with heat-killed cells. Reduction of aqueous Au(III) ions by both strains was demonstrated at pH 7 using 2 mM HAuCl4 solution and the concept was successfully applied to recover 100% of the gold from acidic leachate (115 ppm of Au(III)) obtained from jewellery waste. Bioreductive recovery of gold from aqueous solution was achieved within 2 h, giving crystalline Au(0) particles (2050 nm), in the periplasmic space and on the cell surface, and small intracellular nanoparticles. The nanoparticle size was smaller (red suspension) at acidic pH (2.0) as compared to that obtained at pH 6.0 and 7.0 (purple) and 9.0 (dark blue). Comparable nanoparticles were obtained from Au(III) test solutions and jewellery leachate.