Chapter 6 - Chalcopyrite bioleaching catalyzed by silver

Abstract

Combined techniques were used to interpret the catalytic mechanism of Ag+ ions in chalcopyrite bioleaching. Density functional theory calculations indicated the favorable adsorption of Ag+ ions on reconstructed (001)-S and (112)-S surfaces of chalcopyrite and confirmed the possibility of silver sulfide and sulfur vacancy formations. X-ray photoelectron spectroscopy analysis further indicated the formation of silver sulfide on the chalcopyrite surface. Electrochemical analysis showed that silver catalyzed chalcopyrite dissolution by enhancing electrochemical reactivity. In addition, incorporating silver atoms into the chalcopyrite surface might cause a major distortion in its structure and accelerate the diffusion rate of copper atoms. Because of that, the Cu+ ionic radius is much smaller than that of Ag+. As a consequence, the accumulation of passivating species was prevented and the adverse effect of a passivation layer consisting of polysulfide and metallic oxides was reduced, resulting in high dissolution kinetics. Furthermore, two types of abandoned silver-bearing solid waste of zinc leaching residue and firebrick were used for silver catalysis in chalcopyrite bioleaching. The bioleaching residues were subsequently leached by thiourea to recover silver. Results indicated that silver was more easily extracted from bioleaching residues than from untreated silver-bearing solid waste.