Mechanistic study for stibnite oxidative dissolution and sequestration on pyrite.

Stibnite (Sb2S3) dissolution and transformation on mineral surfaces are the fundamental steps controlling the fate of antimony (Sb) in the environment. The molecular-level understanding of Sb2S3-mineral-water interfacial reactions is of great importance. Herein, Sb2S3 oxidative dissolution and sequestration on pyrite (FeS2) were explored. The results show that FeS2 accelerated the rate of Sb2S3 oxidative dissolution by a factor of 11.4-fold under sunlight due to heterogeneous electron transfer. The electron transfer from Sb2S3 to FeS2 separated photogenerated hole (h+) and electron (e-) pairs, facilitating the generation of hydroxyl radicals (OH) on Sb2S3 and FeS2, and superoxide radicals (O2-) on FeS2. Surface O2- was the dominant oxidant for Sb(III) oxidation with 91% contribution, as evidenced by radical trapping experiments. OH was preferentially adsorbed on Sb2S3, but was released with Sb2S3 dissolution, and subsequently contributable to Sb(III) oxidation in solution. The Sb(III) oxidation and sequestration on FeS2 surface coupled Fe2+/Fe3+ cycling and inhibited FeS2 dissolution, as evidenced by X-ray absorption near edge structure and X-ray photoelectron spectroscopy. The insights gained from this study further our understanding of Sb2S3 transformation and transport at the environmental mineral-water interfaces.