Green recovery of Cu-Ni-Fe from a mixture of spent PCBs using adapted A. ferrooxidans in a bubble column bioreactor

The high amount of base metals poses an important challenge in gold bioleaching from spent printed circuit boards (PCBs). This study aims to investigate the bioleaching of important base metals (Cu, Ni, and Fe) from a mixture of spent PCBs (E-waste) using adapted Acidithiobacillus ferrooxidans in the bubble column bioreactors. Firstly, the adaptation process is done from 1 to 15 g/L in Erlenmeyer flasks in 187 days, then the concentration of E-waste increased to 40 g/L in bubble column bioreactors in 44 days. The concurrent recovery of copper, nickel, and iron using adapted bacterium in a bioreactor was optimized by central composite design. Various effective parameters such as aeration rate, initial ferrous sulfate concentration, and solid waste loading that significantly affected bioleaching yields were studied. 54% of Cu (6% dissolution/d), 75% of Ni (8% dissolution/ d), and 55% of Fe (6.1% dissolution/d) were simultaneously recovered under the optimum condition of 20 g/L of solid content, 1.5 vvm of aeration rate, and 40 g/L of the initial concentration of ferrous sulfate after only 9 days. The results proved 100% recovery of each metal is separately possible; 100% of Cu and Fe are extracted maximally on the 4th and 13th day, respectively. Ni is recovered maximally 96% on the 17th day. This is the first report of an ecofriendly method for the bioleaching of important base metals from E-waste in a bubble column bioreactor. Thus, the obtained results contribute to the knowledge of microbial hydrometallurgy on a large scale.