Effect of Acidithiobacillus ferrooxidans on Humic-Acid Passivation Layer on Pyrite Surface

The effect of Acidithiobacillus ferrooxidans on the humic-acid passivation layer on pyrite surfaces was studied by atomic-force microscopy, leaching experiments, and adsorption experiments. Atomic-force-microscopy results showed that humic-acid was adsorbed onto the pyrite surface. The bacteria grew and reproduced on the humic-acid layer. Leaching experiments showed that the humic-acid passivation layer prevented the oxidation of pyrite by Fe3+ under aseptic conditions. Bacteria destroyed the humic-acid layer, promoted pyrite oxidation, and increased the oxidation of pyrite from 1.64% to 67.9%. Bacterial adsorption experiments showed that the humic-acid passivation layer decreased the speed of bacterial adsorption on the pyrite surface but had no effect on the number of bacteria adsorbed on the pyrite surface. The maximum number of bacteria adsorbed by pyrite with and without the humic-acid layer was 4.17 × 1010 cells∙mL−1 and 4.4 × 1010 cells∙mL−1, respectively. Extracellular polymeric stratum layer of bacteria cultured at different concentrations of humic-acid was extracted and analyzed. This layer could destroy the humic-acid layer and promote pyrite oxidation