First-principles study on the effect of arsenic impurity on oxidation of pyrite surfaces

Arsenic (As) frequently exists in pyrite (FeS2) in the form of impurities. The oxidation behavior of As in FeS2 is important in environmental science, mineral processing, and other related fields. The adsorption behaviors of H2O and O2 molecules on the As-bearing pyrite (100) surface (As-FeS2(100)) are studied using the density functional theory (DFT). The results show that As prefers the S site on the pyrite (100) surface (FeS2(100)). In the absence of O2, an isolated H2O molecule does not dissociate when adsorbed at an iron (Fe) site and is repelled at an As site. Furthermore, the surface area around the As atoms exhibits a hydrophobic behavior. Adsorption energy analysis reveals that the presence of As atoms is unfavorable for the adsorption of H2O molecules on the pure FeS2 surface, and that the adsorption of H2O molecules on the As-FeS2(100) is physical adsorption. In the absence of H2O, it is suggested that the O2 molecule easily dissociates on both the pure FeS2(100) and As-FeS2(100). The adsorption of O2 on the As-bearing surface is weaker than that on the pure FeS2(100). For the co-adsorption of H2O and O2, the adsorption energy on the As-bearing surface is more negative than that on the pure surface. This indicates that the presence of As promotes surface oxidation. Additionally, two -OH and O (AsO or SO) or -O (Fe-O) species are formed on the surface of pyrite when the H2O molecule is dissociated. The ability of the H2O molecule to adsorb on the pyrite surface is decreased, due to the As atom. Additionally, the presence of the Arsenic (As) impurity weakens the adsorption of the O2 molecule on the pyrite surface. However, the results indicate that the presence of As will promote surface oxidation during the co-adsorption of both water and oxygen (H2O-O2).image