Bioleaching of metals from electronic scrap in a stirred tank reactor

The purpose of the present work was to investigate the effect of aeration, O-2, CO2, agitation, various sulfur types and dosages and pulp density on the growth of Sulfobacillus thermosulfidooxidans and bioleaching efficiency of electronic scrap in stirred tank reactors. Sulfur bioavailability, metabolism, and oxidation degree were also evaluated. The leaching trends show that the optimum extraction of metals in media-1 supplemented using biogenic S were observed using 25% O-2 + 0.03% CO2 enriched air at a 2.5% S-0 dosage with an overall leaching of 91% Al, 95% Cu, 96% Zn and 94% Ni at a 10% pulp density compared to 74% Al, 81% Cu, 83% Zn and 78% Ni using 30% O-2 + 2% CO2 enriched air at a 3.5% S-0 dosage and 10% pulp density with technical sulfur supplementation in media-2. The FT-IR and XANES analyses indicate a significant modification of the spectra of the technical and biogenic sulfur due to the addition of several new groups (-NH, -OH, -S(=O)(2)(-), -SO2-O-, -CH3, or -CH2) and the presence of polythionates, C-S-H, sulfanes and sulfonate species in both media at different degrees and time period. The significantly higher PEP carboxylase activity (5.1 nmol/min mg protein) in media-1 and PEP carboxykinase and pyruvate carboxylase activities (1.10 and 0.5 nmol/min mg protein) in media-2 indicates different preferential modes of growth. An economical feasibility study indicated that the results of the leaching process might have the potential for increased scale. (C) 2014 Elsevier B.V. All rights reserved.