The electrochemical oxidation behavior of pyrite in bioleaching system of Acidthiobacillusferrooxidans was investigated by cyclic voltammetry （CV）, polarization curve and electrochemical impedance spectroscopy （EIS）. The results show that in the presence or absence of A. ferrooxidans, the oxidation reaction of pyrite is divided into two steps： the first reaction step involves the oxidation of pyrite to S, and the second reaction step is the oxidation of S to SO4^2-. The oxidation mechanism of pyrite is not changed in the presence of A. ferrooxidans, but the oxidation rate of pyrite is accelerated. With the extension of reaction time of A. ferrooxidan with pyrite, the polarization current density of pyrite increases and the breakdown potential at which the passive film dissolves decreases. The impedance in the presence ofA. ferrooxidans is obviously lower than that in the absence of A. ferrooxidans, further indicating that microorganism accelerates the corrosion process of pyrite.
The alteration of surface properties of chalcopyrite after biological conditioning with Leptospirillum ferriphilum was studied by adsorption,zeta-potential,contact angle and bioleaching tests.The strains of L.ferriphilum cultured using different energy sources（either soluble ferrous ion or chalcopyrite） were used.The adhesion of bacteria to the chalcopyrite surface was a fast process.Additionally,the adsorption of substrate-grown bacteria was greater and faster than that of liquid-grown ones.The isoelectric point（IEP） of chalcopyrite moved toward that of pure L.ferriphilum after conditioning with bacteria.The chalcopyrite contact angle curves motioned diversely in the culture with or without energy source.The results of X-ray diffraction patterns（XRD）,scanning electron microscopy（SEM） and energy-dispersive X-ray spectroscopy（EDS） analysis indicate that the surface of chalcopyrite is covered with sulfur and jarosite during the bioleaching process by L.ferriphilum.Furthermore,EDS results imply that iron phase dissolves preferentially from chalcopyrite surface during bioleaching.The copper extraction is low,resulting from the formation of a passivation layer on the surface of chalcopyrite.The major component of the passivation layer that blocked continuous copper extraction is sulfur instead of jarosite.
The effects of several variables on the bioleaching of marmatite with pure L. ferrooxidans were investigated. The results show that zinc extraction increases with the decrease of pulp density. Adjusting pH tol.6 during the bioleaching process has a positive effect to the dissolution of marmatite. External addition of Fe^3＋ ions accelerates the bioleaching, while the concentration of additional Fe^3＋ over 2.5 g/L weakens the acceleration effect due to the inhibition effect on bacteria growth and the promotion of jarosite production. The electrochemical measurements were used to make further understanding on the dissolution of marmatite with and without additional Fe^3＋ in the presence of L. ferrooxidans. The experimental data illustrate that additional Fe^3＋ ions could increase the corrosion current density, which is favorable to zinc extraction. The EIS spectra show that rate-limiting step does not change when Fe^3＋ is added.
