Bioleaching of cadmium and nickel from synthetic sediments by Acidithiobacillus ferrooxidans.

The microbial leaching process was evaluated for the treatment of synthetic sediments contaminated with cadmium and nickel sulfides. A series of batch leaching experiments was conducted to compare metal solubilization in sediment inoculated with Acidithiobacillus ferrooxidans -inoculated sediments to that in sterile control sediment. The rate and extent of metal solubilization were significantly higher in A. ferrooxidans -inoculated reactors than in acidified sterile reactors. The efficiency of cadmium (Cd) solubilization (80) in the bioleaching process was higher than that of nickel (Ni) solubilization (60). The performance of leaching reactors containing only culture supernatants was comparable to that of A. ferrooxidans -inoculated reactors, indicating that indirect non-contact leaching by the products of microbial metabolism is the predominant mechanism for metal solubilization rather than direct microbial sulfide oxidation. Moreover, the similar (60-75%) extents of Cd(2+) leaching with A. ferrooxidans , cell-free filtrate, and Fe(3+) suggest that abiotic oxidation of CdS by Fe(3+) controls the overall leaching rate, and the role of A. ferrooxidans is most likely not to oxidize CdS mineral directly but to regenerate Fe(3+) as an oxidant.