Effects of Leptospirillum ferriphilum and Acidithiobacillus caldus on surface properties of pyrrhotite

The variation of surface properties of pyrrhotite after biological conditioning with Leptospirillum ferriphilum and Acidithiobacillus caldus was evaluated by zeta-potential, adsorption and contact angle measurements. Previous work showed that the pyrrhotite isoelectric point (IEP) shifts towards the cell isoelectric point after interacting with bacterial cells, indicating the adsorption of cells on the pyrrhotite surface. The degree of interaction of pyrrhotite with A. caldus was observed to be much more pronounced than that of L. ferriphilum, because of the different affinity of A. caldus and L. ferriphilum to pyrrhotite. After treatment by A. caldus, the pyrrhotite surface formed a membrane of sulfur, which was shown by X-ray diffractograms (XRD) and the energy dispersion spectrum (EDS), which explains the increasing hydrophobicity of pyrrhotite. However, the contact angle and surface hydrophobicity of pyrrhotite treated by the L. ferriphilum kept decreasing during bioleaching. The results indicate that the energy source for the microorganism growth determines its function mechanism in the bioleaching system. The iron-oxidizing bacteria offer an indirect mechanism function during bioleaching of pyrrhotite and the sulfur-oxidizing bacteria offer a direct mechanism function.