| Mesophile-Acidithiobacillus ferrooxidans and moderate thermophile -Acidithiobacillus caldus grown on different energy resources were studied in the paper to investigate the alterations of surface properties of chalcopyrite after bacterial treatment by adsorption studies,FT-IR spectra, Zeta-potential,contact angle measurement and AFM images.The adsorption mechanism of microorganisms on chalcopyrite could be illustrated by the surface thermodynamics and extended DLVO theory. The mechanism of microorganism-chalcopyrite interactions could be explored and the way to increase the leaching efficiency could be found as function of leaching effects of two kinds of bacterium.The results of research on surface properties suggested that bacterial cells cultured on different energy resources had the similar surface groups, and the change trend of surface properties of chalcopyrite after conditioning with these bacterium was similar.All types of bacterium adhered to chalcopyrite surface rapidly,but adapted bacteria had the stronger adsorption ability.The isoelectric point of chalcopyrite after bacterial treatment moved towards the isoelectric point of pure cells.Due to the formation of elemental sulfur and intermediate copper sulphides on chalcopyrite surface,the contact angle and surface hydrophobicity of chalcopyrite increased.The images of atomic force microscopy showed that A.ferrooxidans had the stronger corrosion ability than A.caldus. Results supported the direct mechanism of chalcopyrite oxidation in initial bioleaching.The analyse of surface thermodynamics showed that both free energy (△Gadh) of bacterium-chalcopyrite interactions were negative,which indicated that both bacterium could adsorb on chalcopyrite surface.The potential energy curve deduced by extended DLVO theory showed that at pH 2.5,acid-base interaction between A.ferrooxidans-chalcopyrite was repulsive while Lifshitz-van der Waals force and electrostatic force both were strong attractive force.Therefore the total interaction force of A.ferrooxidans-chalcopyrite was attractive when separation distance(d) was over 1.6nm,so adsorption of A.ferrooxidans was possible on chalcopyrite.However the Lifshitz-van der Waals force,electrostatic force and acid-base interaction force of A.caldus-chalcopyrite were all attractive force at pH 2.5,so A.caldus could adhere to chalcopyrite surface.At pH 10.5,the strong repulsive electrostatic interaction of both bacterium-chalcopyrite systems caused that there would be no adsorption of both bacterium on chalcopyrite.Both bacterium aggregated in acid condition and dispersed in the media solution in alkaline condition.The results of bioleaching of chalcopyrite had further proved the conclusion of research on surface properties.Adapted bacteria had the stronger leaching ability than unadapted bacteria.A.ferrooxidans had the better leaching ability than A.caldus in initial stage of bioleaching,while A.caldus had the stronger oxidation activity during the later stage. A.ferrooxidans can bear higher pulp concentration than A.caldus,with the optimum value of 5%and 3%respectively.The finer particle size of chalcopyrite was,the higher leaching rate got.As the increase of inoculum concentration,copper extraction rised up obviously but there was no obvious increase when inoculum concentration increased to some extent. The pulp potential increased with the increase of copper extraction in bioleaching by A.ferrooxidans,while kept in the range of 250mV～300mV by A.caldus.Compared with the initial pH value of 2.0,there was a rise in pH in initial stage of bioleaching and then pH decreased.Research on bioleaching of chalcopyrite by mixed cultures showed that the optimum temperature was 40℃and that the oxidation of A.caldus was dominant during the bioleaching.The dissertation was supported by "National Basic Research Program"(2004CB619204) and "National Nature Science Foundation of China"(50621063).
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