Bioleaching of cadmium and nickel from synthetic sediments by Acidithiobacillus ferrooxidans

Abstract

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 Cd2+ leaching with A. ferrooxidans, cell-free filtrate, and Fe3+ suggest that abiotic oxidation of CdS by Fe3+ controls the overall leaching rate, and the role of A. ferrooxidans is most likely not to oxidize CdS mineral directly but to regenerate Fe3+ as an oxidant.