Bacterial leaching of copper, zinc, nickel and aluminum from discarded printed circuit boards using acidophilic bacteria

Abstract

E-waste is an important secondary source of precious metals. Especially discarded printed circuit boards (PCBs) contain high concentrations of precious metals. In recent years, the bacterial leaching was more widely preferred due to its low environmental impact and cost in the recovery of these precious metals. In this study, a PCBs-adapted pure culture of A. ferrooxidans, A. thiooxidans and PCBs-adapted mixed culture of A. ferrooxidans and A. thiooxidans were used for recovery of the copper, zinc, nickel and aluminum. The effects of initial pH, inoculum bacteria and pulp density were investigated to determine the optimum conditions in bioleaching experiments. Optimum experimental conditions in mixed culture experiments were determined as 10% inoculum bacteria, 10% pulp density, 10 days leaching time, 1.8 initial pH, 30 ± 2 ℃ initial temperature, 125 µm particle size and 180 rpm stirring speed. As a result of triple experiments conducted under optimum conditions, metal recovery efficiencies for copper, nickel, zinc and aluminum were 94, 89, 88 and 59%, respectively. These results were demonstrated that the experiments with mixed culture were more effective in recovering precious metals such as copper, nickel, zinc and aluminum than others.