Enhanced recovery of valuable metals from spent lithium-ion batteries through optimization of organic acids produced by Aspergillus niger

[Display omitted] •Optimization of four organic acids produced by Aspergillus niger was performed.•Sucrose concentration is the most important factor for producing organic acids.•LIBs leaching test in optimum conditions through spent medium bioleaching was done.•Cu, Li, Mn, and Al recovery was highest at 2% and for Co and Ni at 1% pulp density. In the present study, spent medium bioleaching method was performed using organic acids produced by Aspergillus niger to dissolve Ni, Co, Mn, Li, Cu and Al from spent lithium-ion batteries (LIBs). Response surface methodology was used to investigate the effects and interactions between the effective factors of sucrose concentration, initial pH, and inoculum size to optimize organic acid production. Maximum citric acid, malic acid, and gluconic acid concentrations of 26,478, 1832.53 and 8433.76ppm, respectively, and a minimum oxalic acid concentration of 305.558ppm were obtained under optimal conditions of 116.90 (gl−1) sucrose concentration, 3.45% (vv−1) inoculum size, and a pH value of 5.44. Biogenically-produced organic acids are used for leaching of spent LIBs at different pulp densities. The highest metal recovery of 100% Cu, 100% Li, 77% Mn, and 75% Al occurred at 2% (wv−1) pulp density; 64% Co and 54% Ni recovery occurred at 1% (wv−1) pulp density. The bioleaching of metals from spent LIBs can decrease the environmental impact of this waste. The results of this study suggest that the process can be used for large scale industrial purposes.