Effects of microorganisms on surface properties of chalcopyrite and bioleaching

The alteration of surface properties of chalcopyrite after biological conditioning with Acidithiobacillus ferrooxidans and Acidithiobacillus caldus was evaluated by Zeta-potential, adsorption studies, FT-IR spectra and contact angle measurement. The Zeta-potential studies show that the iso-electric point(IEP) of chalcopyrite after bacterial treatment moves towards the IEP of pure cells, indicating the adsorption of cells on chalcopyrite surface. The FT-IR spectra of chalcopyrite treated with bacterial cells show the presence of the cell functional groups signifying cells adsorption. Due to the formation of elemental sulfur and intermediate copper sulphides on chalcopyrite surface, the contact angle and surface hydrophobicity of chalcopyrite increase at the initial bioleaching stage. Chalcopyrite bioleaching by Acidithiobacillus ferrooxidans has higher copper extraction, which agrees with the fact that Acidithiobacillus ferrooxidans adsorbed on chalcopyrite surface is much more than Acidithiobacillus caldus. The results support the direct mechanism of sulfide oxidations in bioleaching chalcopyrite.