Microbial Pb(II) precipitation : the influence of elevated Pb(II) concentrations

Abstract

The objective of the study was to determine the influence of elevated lead concentrations on the rates of lead precipitation by a local industrially-obtained consortium. The consortium was sourced from a lead battery recycling plant located in Gauteng, South Africa. The experiments were performed under anaerobic conditions using commercial Luria Bertani (LB) broth and simulated LB broth (reduced NaCl concentration) as the growth media. The respective media were spiked with various concentrations of lead, ranging from 80 ppm to 1000 ppm. All concentrations of lead resulted in a black precipitate with a final medium pH of between 6 and 8, indicating the presence of lead(0). A 99 % removal of lead occurred with 500 ppm lead after 11 days. A lead concentration of 1000 ppm was reduced by 87 % after 22 days. The higher NaCl concentration in the commercial LB broth formed a white precipitate (PbCl2) upon initiation of the high lead(II) concentration experiments. These experiments also presented with a black precipitate at a later stage, indicating that the lead in the PbCl2 precipitate remained available for reduction to elemental lead. No white precipitate was observed during experimentation where the simulated LB broth was used with a lower concentration of NaCl. The results indicate that the consortium precipitates lead concentrations up to 1000 ppm. This provides support that biological precipitation has potential application in industry for the hydrometallurgical processing of lead as well as industrial lead bioremediation.