Studies On Bioleaching And Electrochemical Behavior Of Chalcopyrite

In this research, the rate of chalcopyrite oxidation is examined by leaching in the presence of A.ferrooxidans and L.ferriphilum, and the XRD, SEM and dialysis bag are also used to reveal the dissolution of chalcopyrite. The preliminary analysis of surface passivation in leaching process is also investigated. Electrochemical analysis methods (such as cyclic voltammetry (CV), polarization curves and electrochemical impedance spectroscopy) are employed to investigate electrochemical behavior of chalcophanite in bioleaching system with or without bacteria in order to reveal the oxidation mechanism in microbial metallurgy system.The results of bioleaching tests show that bacteria can improve significantly the leaching rate of chalcopyrite, and copper concentrations after 21 days in both absence and presence of A.ferrooxidans are 0.18 g/L and 0.51 g/L; copper concentrations after 21 days in both absence and presence of L.ferriphilum are 0.31 g/L and 1.87g/L. The addition of ferric ion is conductive to chalcopyrite leaching. The results also show that the behaviors of chalcopyrite leaching including the oxidation of bacteria on elemental sulfur as well as the oxidation of ferric ion, the oxidation product of ferrous ion, on chalcopyrite dissolution in the microbe-mineral contact model; however, the dissolution of chalcopyrite is determined by the oxidation of ferric ion in the microbe-mineral uncontact model. The leaching rate of chalcopyrite is controlled mainly by potentials of leaching system, and high potential is more conductive to chalcopyrite leaching. The microbe-mineral contact model is more conductive to the increasing of potentials than microbe-mineral uncontact model, and also can eliminate the sulfur film on chalcopyrite surface. Therefore, it is more profitable for leaching of chalcopyrite than uncontact model. The jarosite easily generated on chalcopyrite surface at high potentials is the main cause of surface passivation of chalcopyrite.The electrochemical behaviors of chalcopyrite oxidization show that chalcopyrite gives priority to the release of iron and is oxidized to Cu1-xFe1-yS2-z or CuS and S at the potential of 50mV(vs. SCE) in leaching without bacteria, and the CuS and S will also be oxidized further to Cu2+å’ŒSO42- at the potential of 400mV(vs. SCE). The decline of pH or addition of ferric ion can increase the the corrosion potential and corrosion current of chalcopyrite. It indicates that the decomposition mechanism of chalcopyrite in both bacterial and sterile conditions is basically the same, but corrosion current increases and impedance declines under the condition of bacteria. The addition of bacteria is conducive to the decomposition of chalcopyrite. Adding Fe3+ in sterile solution, corrosion current of chalcopyrite increases and impedance declines, revealing addition of Fe3+ is conductive to electron transfer and corrosion of chalcopyrite.It has been shown that the surface passivation of chalcopyrite in leaching process is determined by decomposition mechanism of itself and leaching conditions together. In acid leaching conditions, the cause of low leaching rate and surface passivation is mainly due to the formation of Cu1-xFe1-yS2-z and CuS on the surface of chalcopyrite, which is stable and insoluble at low potential. In bacterial leaching conditions, the surface of chalcopyrite is seriously covered by a great amount of jarosite and FeOOH, which cause the surface passivation as well as the low leaching rate.The dissertation was supported by "National Basic Research Program" (2004CB619204,2010CB630903) and "National Nature Science Foundation of China" (50621063).