Improving Gold (Bio)Leaching Efficiency Through Pretreatment Using Hydrogen Peroxide Assisted Sulfuric Acid

Compared to conventional recycling methods, the recovery of gold from electronic waste (e-waste) using bioleaching is more environmentally friendly and sustainable. E-wastes contain large amounts of copper that forms stable complexes with cyanide and competes with gold during bioleaching. To overcome this, e-waste from printed circuit boards was pretreated with sulfuric acid and hydrogen peroxide to remove copper from the waste. The kinetics of the copper removal process was examined by varying sulfuric acid concentrations, hydrogen peroxide concentrations, e-waste particle sizes, and temperature. Both sulfuric acid and hydrogen peroxide showed a significant effect on pretreatment; copper removal from the e-waste was found to fit the diffusion-controlled model. Under optimal pretreatment conditions (5M H2SO4, 5M H2O2, T = 313 K, and d(o) = 50-75 mm, 85.5% of copper was removed from the e-waste. Two-step bioleaching (where e-waste was added only after the bacteria has grown and produced significant lixiviant) and spent medium leaching (i.e., using cell-free medium containing the lixiviant) were examined using the metabolically engineered Chromobacterium violaceum pBAD strain for extraction of gold from e-waste. Spent medium leaching achieved a gold recovery of 36.4% as compared to 24.7% under two-step bioleaching for pretreated e-waste.