Interaction of ferric ion with (001)-S and (001)-M surfaces of chalcopyrite (M = Fe and Cu): Electrochemical insights from DFT calculations

Abstract

Chalcopyrite is oxidized in the sulfate medium by reducing the ferric ion (Fe3+), which means that the further leaching of chalcopyrite is dependent on the reduction rate of Fe3+. Considering the important role of Fe3+ ion, density functional theory (DFT) calculations were used to better understand its reduction mechanism on the chalcopyrite surface. DFT calculations showed that (001)-S surface of chalcopyrite is more reactive toward the Fe3+than (001)-M (M = Cu, Fe), due to the presence of sulfur atoms. The reduction of the Fe3+ is a result of the charge-transfer from the 3p orbitals of sulfur atom to the 3d orbitals of Fe3+. In the (001)-M surface, in addition to sulfur atoms, coordination decrease of cations is effective in the ferric ion adsorption. According to the obtained thermodynamic data, the reduction of the Fe3+ ion is generally performed better on the (001)-S surface than (001)-M. The free energy change (ΔG) of the Fe3+ + e → Fe2+ reaction on the (001)-S and (001)-M surface is −23 and −22 kcal/mol, respectively. Also, the existence of a Fe defect could significantly enhance the reactivity of the (001)-M surface toward the Fe3+ ion.