Multi-objective optimization of heavy metals bioleaching from discarded mobile phone PCBs: Simultaneous Cu and Ni recovery using Acidithiobacillus ferrooxidans

•Bioleaching ability was examined for heavy metals recovery from mobile phone PCBs.•Multi-objective optimization under RSM was applied to maximize Cu and Ni recovery.•Two modified quadratic models were constructed to predict bioleaching efficiency.•Particle size was detected with a high important positive effect on the Cu recovery.•pH was found as the most important factor on the Ni recovery with a negative effect. The present study examined bioleaching of heavy metals from mobile phone printed circuit boards (MPPCBs) using adapted Acidithiobacillus ferrooxidans. The adaptation phase (10% v/v inoculum) began with 1g PCB powder per 1L culture medium and continued for 55days to a level of 20g PCB powder per 1L medium. The factors that examined for metal bioleaching were initial pH, initial Fe3+ concentration, pulp density and particle size. To maximize simultaneous extraction of Cu and Ni from MPPCBs, these factors were optimized under a multi-objective optimization strategy using the central composite design of response surface methodology. Two modified quadratic models were selected to predict the interactions and behavior of the influence parameters on the bioleaching of Cu and Ni from e-waste samples. An initial pH of 1, initial Fe3+ concentration of 4.18g/l, pulp density of 8.5g/l and particle size of 114.02μm (#100mesh) were determined as the optimal conditions. Under these conditions, 100% extraction of Cu and Ni was achieved. The pH, Eh, bacterial count, and Fe3+ concentration were varied over time and measured under optimal conditions.