Influence of sulfur vacancy on pyrite oxidization by water and oxygen molecules

Abstract

Pyrite (FeS2) is one of the widely existed sulfide minerals, which plays a very significant role in acid mine drainage (AMD) and other aspects. Natural and synthetic pyrite has often been found to contain vacancy and impurity defects. Nevertheless, the effect of S-vacancy on pyrite oxidization by water and oxygen molecules has not been researched in detail. In this work, the adsorption of water and oxygen molecules is simulated based on density functional theory (DFT). It is found that the adsorption energy of water molecules on S-vacancy surface is relatively low and the dissociative adsorption of water molecules does not occur readily. When oxygen molecules are adsorbed, it is shown that the adsorption is stronger than that of water molecules and a SO specie is formed. And through the change of density of states (DOS), charges and magnetic moments of Fe1 and Fe2 on the S-vacancy surface before and after oxygen molecule adsorption, this indicated that due to the adsorption of oxygen molecule, the property of the S-vacancy surface is changed. Furthermore, the co-adsorption of water and oxygen molecules on S-vacancy surface is calculated. It is manifested that the Fe-OH and S-O species are formed. When the filling of O atom (captured from water molecules) at S-vacancy site restores the surface and the O atom bonds to the surrounding two Fe atoms and one S atom, the adsorption configuration is the most stable.