Abstract:
The biohydrometallurgical processing of metals have generated significant interest due to the potential for
bioleaching and biological electrowinning processes to replace current energy intensive, costly, and
environmentally contaminating smelting and hydrometallurgical processes. An ongoing research project aims
to identify, study, and refine a Pb(II) bioremediation and biorecovery process for industrial application.
Previous work has successfully demonstrated Pb(II) bioprecipitation of 86.5% of a 1,000 ppm Pb(II) initial
concentration batch experiment within 22 days.
The objectives of the current study were: (1) to determine the minimum inhibitory concentration (MIC) at which
a specific industrial consortium would cease to grow and/or precipitate Pb(II) from solution, (2) to determine
the identity of the precipitate formed. The consortium was obtained from a borehole at an automotive battery
recycling plant in Gauteng province South Africa. The MIC was studied using inoculated nutrient and
simulated (reduced NaCl) agar plates. Pb(II) concentrations from 500 ppm to 200,000 ppm were tested in the
nutrient agar, and Pb(II) concentrations of 50,000 ppm to the solubility limit of Pb(NO3)2 of 310,000 ppm Pb
were tested in the simulated agar.
The results from the MIC study showed that the industrially obtained consortium was able to grow and
precipitate Pb(II) at concentrations up to approximately 30,000 ppm. MIC values for the reduced NaCl and no
NaCl runs of 34,914±5,995 ppm and 27,164±5,728 ppm, respectively. The results from the nutrient agar
showed no evidence of inhibition, likely a result of decreased effective Pb(II) as a result of PbCl2 precipitation.
The XPS analysis of the metallic ring on the surface of the nutrient agar indicated the presence of PbS and
elemental Pb, in the ratio 0.818:0.182. These results confirm a Pb-reduction (Pb(II) to Pb0) capability is
present in the consortium.
From the results, it can be concluded that the industrial consortium has the ability to grow and precipitate
Pb(II) in significantly high concentrations. In addition, a biological Pb(II) reduction to elemental lead capability
was confirmed, potentially providing a replacement for the electrowinning step in traditional hydrometallurgical
processing of Pb(II).
