A DFT study on flotation behavior of sphalerite with indium and iron impurities

Abstract

Indium (In) is a rare precious metal with extremely low abundance in the Earth's crust, mostly occurring as impurities in sphalerite, and it is closely related to the high iron content in sphalerite. Flotation is generally used to recover such minerals. However, there are few for the flotation mechanism of sphalerite containing indium and iron impurities. In this paper, the adsorption of xanthate (C4H9OCSS−) and depressants (CN–, CaOH+, OH–) on the surface of sphalerite that contains indium and iron impurities is investigated by employing density functional theory (DFT), and compared with pure sphalerite. The findings demonstrate that the presence of indium ions results in stronger adsorption of H2O on sphalerite surface and sphalerite containing InFe exhibits higher hydrophilicity. C4H9OCSS− forms strong covalent InS and FeS bonds on InFe-containing sphalerite surface, transforming the adsorption of C4H9OCSS− on sphalerite surface from weak physical adsorption to strong chemisorption. This enhances the collecting power of C4H9OCSS− on sphalerite and improves the floatability of InFe-containing sphalerite. Studies on electronic interactions have revealed that in the interaction with C4H9OCSS−, the outer s and p orbitals of the indium atom are primarily involved, which is different from the pure sphalerite surface where only the s orbital of zinc is involved. The participation of the p orbitals significantly enhances the interaction of In with xanthate. Additionally, the Fe 3d orbitals can provide a pair of π electrons that can form π-backbonding with C4H9OCSS−. These two factors contribute to the increased adsorption capability of C4H9OCSS− on InFe sphalerite. The adsorption of CN–, CaOH+ and OH– on both In and Fe sites on the surface of InFe-containing sphalerite is stronger than that on the surface of pure sphalerite, with CN– adsorption being the strongest, indicating that CN–, CaOH+ and OH– have stronger depressing effects on InFe-containing sphalerite.