H2O2 mediated oxidation mechanism of pyrite (001) surface in the presence of oxygen and water

Pyrite (FeS2) is the most common metal sulfide in nature. The oxidation mechanism of the pyrite has attracted intensive research attentions. It has been determined that this process involves multi-step electron transfer reactions between the FeS2 surface and the adsorbed O2 and H2O. In this process, sulfoxide (such as S2O32-, SO42-) and ferrous (Fe2+) are released into solution, and intermediate by-products, such as hydrogen peroxide (H2O2) and other reactive oxygen species (ROS), are produced. However, our understanding of the formation and transformation of these transient species is still limited. In this study, oxidation pathways by O2 and H2O on the pyrite (001) surface are explored by means of density functional theory (DFT) simulation. The oxidation pathway including the H2O2 forms as the inter-mediate is reported for the first time. It is found that the H2O2 molecule forms with low activation energy barriers when the O2 and H2O are co-absorbed on the pyrite surface. The H2O2 dissociates and releases the O atom to promote the sulfur oxidation. The product distribution resulted by the H2O2 mediated oxidation pathway agrees with the isotopic composition experiment that a minor amount of O2 is permanently incorporated into SO42- during pyrite oxidation (O in SO42- is mainly derived from water).