Interactions Between Different Energy Sources Adapted Acidithiobacillus Ferrooxidans And Chalcopyrite Or Pyrite

In this paper, interactions between FeSO4·7H2O, sulfur, pyrite or chalcopyrite adapted Acidithiobacillus ferrooxidans and chalcopyrite or pyrite were studied. Contact angle, zeta potential, fourier transform infrared spectroscopy and acid-base titration experiments were used to analyze the surface properties of bacteria and minerals. Interaction energies between bacteria and minerals were calculated by thermodynamics and extended-DLVO theories. Adhesion forces between bacteria and minerals were measured by atomic force microscope (AFM). Attachment behaviors of bacteria to minerals were monitored within two hours, and the data were simulated by pseudo-first and second-order kinetic models. The differences of interactions between bacteria and minerals were used to reveal the nature of bacterial attachment, the links among prediction of extended-DLVO theory, adhesion force measured by AFM, attachment experiment and simulation of attachment were explored, the relationship between bacterial surface properties and their adhesion forces was also discussed. It will develop further bacteria-mineral interaction mechanisms and provide more favorable conditions for bioleaching.According to surface properties analyses of different energy sources adapted bacteria and minerals, in the iron-free9K medium, negative zeta potential of pyrite was lower than that of chalcopyrite. Contact angle of chalcopyrite was greater than that of pyrite. Positive zeta potential, different contact angles, no difference in surface groups, different amount of EPS and different effect degrees to the nature of NaCl buffer solution were observed from different energy sources adapted bacteria. Bacterial surface properties changed when EPS were deficient. Experiment results showed that EPS have a significant impact on bacterial surface properties and that the nature of substrate affects the properties of bacterial EPS.Extend-DLVO theoretical predictions indicated that the main contribution of total potential energy between bacteria and chalcopyrite was from van der Waals interaction energy (GLW), the main contributions of total potential energy between bacteria and pyrite were from electrostatic interaction energy (GEL) and van der Waals interaction energy (GLW). EPS-deficient bacteria could still attach to chalcopyrite surface, but it will be harder than untreated bacteria. EPS-deficient bacteria needed to cross energy barrier to attach to pyrite surface. Based on extend-DLVO theoretical predictions, bacterial attachment to chalcopyrite surface was easier than to pyrite surface.According to force-distance curves between bacteria and chalcopyrite or pyrite, adhesion forces between bacteria and pyrite were greater, and adhesion forces between different energy sources adapted bacteria and the same kind of mineral were also different, this indicated that the interactions between bacteria and minerals were decided by both bacterial surface properties and the types of minerals. Combined force-distance curves between different energy sources adapted bacteria and minerals, mineral adapted bacteria had the largest adhesion force, followed by sulfur adapted bacteria, FeSO4·7H2O adapted bacteria were the smallest. Combined contact angle and Zeta potential experiments, it could be deduced that hydrophobicity plays a dominant role during attachment of bacteria to chalcopyrite surface and static electricity plays a dominant role during attachment of bacteria to pyrite surface. Adhesion forces between EPS-deficient bacteria and minerals were smaller than untreated bacteria, which is due to defect of surface charge, change of contact angle and extracellular polymers.Attachment experiments showed that the amounts of attached bacteria to pyrite were greater than chalcopyrite. To the same mineral, mineral adapted bacteria had the largest amount of attached bacteria, followed by sulfur adapted bacteria, FeSO4·7H2O adapted bacteria were the smallest. The attachment amounts of EPS-deficient bacteria were smaller than untreated bacteria. Pseudo first-order kinetic model and second-order kinetic model were used to simulate attachments of bacteria to mineral surfaces. From both bacterial attachment rate and attachment capacity, the values of mineral adapted bacteria were the largest, followed by sulfur adapted bacteria, FeSO4·7H2O adapted bacteria was the smallest. When EPS were deficient, bacterial attachment rate and attachment capacity decreased. These indicated that bacterial surface properties are very important to attachment of bacteria to mineral surfaces.