Computer-munching microbes: metal leaching from electronic scrap by bacteria and fungi

Microbiological processes were applied to mobilize metals from electronic w aste materials. Bacteria (Thiobacillus thiooxidans, T. ferrooxidans) and fu ngi (Aspergillus niger, Penicillium simplicissimum) were grown in the prese nce of electronic scrap. The formation of inorganic and organic acids cause d the mobilization of metals. Initial experiments showed that microbial gro wth was inhibited when the concentration of scrap in the medium exceeded 10 g L-1. However, after a prolonged adaptation time, fungi as well as bacter ia grew also at concentrations of 100 g L-1. Both fungal strains were able to mobilize Cu and Sn by 65%, and Al, Ni, Pb, and Zn by more than 95%. At s crap concentrations of 5-10 g L-1, Thiobacilli were able to leach more than 90% of the available Cu, Zn, Ni, and Al. Pb precipitated as PbSO4 while Sn precipitated probably as SnO. For a more efficient metal mobilization, a t wo-step leaching process is proposed where biomass growth is separated from metal leaching. (C) 2001 Elsevier Science B.V. All rights reserved.