Experimental and theoretical studies of the mechanism of oxidation of arsenopyrite in the presence of hydrogen peroxide

Arsenopyrite, which is a typical gold-bearing mineral, is widely distributed in gold tailings. In this study, we have examined the surface morphology of arsenopyrite before and after oxidation, the types of oxidation products, and the oxidation mechanism. We have carried out froth flotation and contact angle measurements and found that the wettability, which is a descriptor of the hydrophilicity of the arsenopyrite surfaces, increases with the levels of surface oxidation. X-ray photoelectron spectroscopy (XPS) was used to analyze the elemental composition before and after oxidation, which has demonstrated that both Fe(II) and As(III) oxidize to Fe(III) and As(V), respectively. The microscopic changes of the surface at the atomic level were also examined by atomic force microscopy (AFM), which indicated that the oxidation products gradually and partially cover the surface of the arsenopyrite upon reaction with hydrogen peroxide. These observations explain why the arsenopyrite XPS signal and the uniform change in wettability do not vanish completely during oxidation. Finally, density functional theory (DFT) calculations were used to describe the oxidation of the surface As atoms by the O of the chemisorbed hydrogen peroxide molecules. The computational results also show that the hydrogen peroxide dissociates into two hydroxyl groups that coordinate the Fe and As atoms on the surface of the arsenopyrite. The results of this study have important implications for the reuse of gold tailings containing arsenopyrite.