Bioleaching of chalcocite started at different pH: Response of the microbial community to environmental stress and leaching kinetics

Bioleaching of chalcocite mineral was conducted in two stirred reactors at 30 °C. Bacteria culture from the Zijin copper mine bio-heap was applied in this test. Leaching test started from pH 1.2 was carried in reactor A, and for reactor B, a start-up pH of 1.5 was used. Results showed that low pH could effectively facilitate copper dissolution and the affected microbial community structure thus inhibited iron dissolution. By using the 16 S rRNA gene clone library technique, bacterial community structure and change in the two reactors was revealed. In the inoculated culture, the dominant bacteria groups were Leptospillium, Acidithiobacillus and Sulfobacillus. While as leaching tests continued, the bacteria community in the two reactors presented different structures. A decrease in the proportion of Leptospillium from 22.2% to 10% and an increase in the proportion of Acidithiobacillus from 31.1% to 86% was detected in reactor A under relative higher redox potential (from 651 mV to 705 mV) and low pH (pH1.2). While for reactor B, an increase in the proportion of Leptospillium and Acidithiobacillus under relative low redox potential (from 530 mV to 631 mV) and high pH (pH 1.5–1.6) was observed, each from 22.2% to 59.2% and 31.1% to 40.8% respectively. Leaching experiment data were fitted to the shrinking core model. Diffusion control was found to be more significant at pH 1.2 bioleaching than it was at pH 1.5 bioleaching. These results may help us understand bioleaching behavior of secondary copper sulfide and improve commercial plant operation.