DFT study of ferric ion interaction with passive layer on chalcopyrite surface: Elemental sulfur, defective sulfur and replacement of M2+(M=Cu and Fe) ions

Abstract

The acidic dissolution of chalcopyrite in the sulfated medium is dependent on the rate of ferric (F3+) ion reduction. Due to the formation of elemental sulfur passive layer on the chalcopyrite surface, the ferric ion reduction rate decreases at the surface and prevents electron transfer from the surface to ferric ion. In this research, the interaction of ferric ion with sulfur passive layer in different modes has been studied using studio material software and density functional theory method. The results showed that the sulfur passive layer is insulated and ferric ion does not react on this surface, but the layer can be activated by changes in the structure. Defects in the passive layer structure (removal of sulfur atoms) or substitution of metal ions (iron and copper) cause surface reactivity, which by interaction with ferric ion will result in electron transfer to 3d orbital of Fe3+ ion. The overlap of 3p orbital surface sulfur atoms and the 3d orbital ferric ion conduction band provide the conditions for electron transfer. Also, the Fe3+ ion adsorption energies for different surface states, structure defects; ferrous and cupric ions substitution were obtained at −244, −229 and −228 kcal/mol, respectively. In addition, energy change (ΔE) due to the reduction of Fe3+ ion for structure defects more than the other two surfaces.