Optimizing mixed culture of two acidophiles to improve copper recovery from printed circuit boards (PCBs)

► Mixed culture of two acidophiles was optimized for maximizing PCBs addition amounts and copper leaching efficiency at the same time. ► Inoculums ratio showed remarkable effect on A. thiooxidans and A. ferrooxidans growth status. ► Initial pH, and S0 and Fe2+concentrations were optimized by response surface methodology to enhance copper recovery. ► Compared with both S0 and Fe2+ which significantly influenced copper leaching, pH did not show a notable effect. ► Higher Fe3+ and lowered pH value kept in filtrate elucidated the mechanism involved in achieving efficient copper recovery.