Study on catalytic mechanism of silver ions in bioleaching of chalcopyrite by SR-XRD and XANES

Ag+ is one of the efficient and recoverable catalysts to improve chalcopyrite bioleaching. Because of the complexity of the surface reaction during chalcopyrite bioleaching, there is still controversy on catalytic mechanism of Ag+ in improving dissolution of chalcopyrite. In the present study, we studied the catalytic effect of Ag+ on bioleaching of chalcopyrite by extreme thermophile Acidianus manzaensis. Based on synchrotron radiation X-ray diffraction (SR-XRD) and X-ray absorption near edge structure (XANES) spectroscopy, the relevant iron and sulfur speciation of leaching residues was analyzed. Bioleaching experiments showed that copper extraction was significantly promoted by adding Ag+, and the optimum concentration of Ag+ was 0.05% (mass fraction of Ag+ to chalcopyrite). SR-XRD and XANES analyses showed that, during bioleaching in the presence of 0.05% of Ag+ and in the absence of Ag+, the intermediates S, jarosite and secondary minerals (chalcocite, bomite and covellite) were formed. The linear combination fitting of XANES spectra further revealed that the addition of silver ions remarkably promoted the formation of bornite and covellite, while had no effect on formation of chalcocite, indicating that bioleaching of chalcopyrite should be catalyzed by Ag+ with promoting the generation of bornite and its conversion to covellite. This model suggested that the rapid formation of bornite like species contributed to positive effect of Ag+ on chalcopyrite bioleaching, while the accumulation of covellite slowed leaching rate at the end period of chalcopyrite bioleaching.