Comparison of the reaction kinetics and mechanisms of Sb(III) oxidation by reactive oxygen species from pristine and surface-oxidized pyrite

With the rapid increase in the antimony (Sb) concentration in the environment, the environmental risk and pollution control of Sb has gradually attracted wide attention. The oxidation of Sb by pyrite influences its toxicity and mobility. Pyrite is oxidized by dissolved oxygen (DO) in an aerobic environment to form a surface oxide coating. However, the effect of the surface oxide coating on the reaction activity of pyrite is poorly understood. In this study, the influence of oxidation products on the surface morphology of pyrite and its interfacial reaction with Sb were investigated comprehensively. The amount of surface oxide coating increased with increasing pH. The main oxidation products under acidic conditions were mainly iron (II) hydroxy complex, and those under neutral conditions were iron (III) hydroxy complex. In a suspension of surface-oxidized pyrite (SOP), the oxidation efficiency of Sb(III) decreased significantly, and inhibition became more significant with increasing pH. As a result of the formation of the surface oxide coating, the contents of hydrogen peroxide (H2O2) and hydroxyl radicals (·OH), which are the main oxidants of Sb(III), were found to be lower in the SOP suspension than in pristine pyrite. The reasons are as follows. On the one hand, surface oxidation products decompose H2O2. On the other hand, they retard the production of H2O2 and ·OH by inhibiting Fe(II) release into the solution and O2 diffusion into the surface of pyrite. In addition, the adsorption capacity of Sb was enhanced after aqueous oxidation because Fe hydroxy complex have a strong affinity to Sb and large specific surface area. Aqueous oxidation of pyrite greatly influences the geochemical cycling and existence of Sb in the environment. The study lays a solid foundation for assessing the environmental risk of and developing pollution controls for Sb.