[XAS Analysis upon Dissolved Species of Orpiment in Anoxic Environment]

The orpiment[As2S3(s)] is an important secondary mineral in the geochemical process of arsenic in the environment. The study upon orpiment dissolution is important to investigate the migration and transformation of arsenic in the environment. The environmental pH and sulfur content have vital influence on species changing and stability of arsenic species in orpiment. Here we analyzed the stable arsenic species of anoxic orpiment dissolution in sulfidic and the absence of sulfide solutions at neutral condition with simulation test via X-ray absorption near edge spectroscopy(XANES) and extended X-ray absorption fine structure(EXAFS). The results showed that orpiment dissolution contained a mixture of arsenite and thioarsenite species at neutral condition, and arsenic species in sulfidic solutions is mainly thioarsenic, while arsenic species in the absence of sulfide solutions is oxythioarsenic. The results of Linear Combination of Fits showed that arsenic species were arsenite (88. 2%) and thioarsenite(11. 8%) in sulfidic solutions, and there were arsenite (56. 3%) and thioarsenite(43. 7%) in the absence of sulfide solutions. Our results confirmed that the formation of arsenite was related to the total sulfur to total arsenic ratios, and the form of thioarsenite species could be enriched by increasing of the total sulfur to total arsenic ratio.