Bioleaching of heavy metals from electronic scrap material (ESM) by Aspergillus niger and Penicillium simplicissimum

Abstract

This study investigates the use of Aspergillus niger, and Penicillium simplicissimum for the bioleaching of electronic scrap materials (ESM). The fine ESM powder (of heterogeneous matrix, with a low specific surface area and bulk density) contains high concentration of base metals and trace amounts of precious metals. Optimum pulp density for the bioleaching occurred at 0.1% w/v. Spent medium leaching was generally more efficient than two-step and one-step bioleaching in the removal of heavy metals from ESM. P. simplicissimum generally gave higher metal extraction yields than A. niger, but not for Fe, Al, Sn and Au. Both fungi did not effectively extract precious metals from ESM. Acidolysis was the main mechanism in the organic acids leaching, and extracellular enzymes were not responsible in the spent medium leaching of the fungi. Citric, gluconic and oxalic acids were found to be the leaching agents in the bioleaching processes. Although chemical leaching appears to be more effective compared to bioleaching (at the same molarity), the results for Fe, Au, Cu, Pb, Ni and Zn were either comparable or higher in bioleaching, depending on the processes and fungal strains.