Novel strategies of bioleaching metals from printed circuit boards (PCBs) in mixed cultivation of two acidophiles

Effects of two acidophiles on metals recovery in printed circuit boards (PCBs) were investigated. Based on the phenomenon that PCBs addition times and amounts adversely inhibited bacterial growth and thus lowered metals bioleaching capacity, novel strategies of multiple PCBs additions (4 g/l at 48 h, 6 g/l at 96 h and 8 g/l at 144 h) were developed in separated culture of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans. As a result, percentages of Cu, Ni, Zn and Pb leached by A. thiooxidans were 78, 73, 75 and 71%, and corresponding values were 80, 73, 76 and 72% by A. ferrooxidans after 240 h cultivation. Further applying the strategies to mixed culture of two acidophiles, extraction percentages of Cu, Ni, Zn and Pb were 94, 89, 90 and 86%, respectively. Moreover, increased redox potential and lowered pH in filtrate were observed, suggesting the mechanism involved in enhancing metals recovery in mixed culture.