Investigating the oxidation mechanism of facet-dependent pyrite: implications for the environment and sulfur evolution.

The oxidation of pyrite (FeS) not only adversely affects the environment, but also plays a critical role in the geochemical evolution of Fe and S elements. However, the oxidation rate of FeS is often controlled by its exposed crystal facets. Herein, the oxidation behaviors and mechanisms of naturally existing FeS(100) and FeS(210) crystals are investigated. The adsorption models of O on FeS(100) and FeS(210) facets are established, additionally, their corresponding surface energies, O adsorption sites and energies are also obtained using Density Functional Theory (DFT) calculations. These results suggest that the FeS(210) facet more readily reacts with O because it has more unsaturated coordination of Fe atoms compared with the FeS(100) facet. Moreover, electrochemical results such as EIS, Tafel and CV curves further prove that FeS(210) possesses a higher oxidation rate than that of FeS(100). The results of chemical oxidation experiments and XPS analyses show that FeS(210) can produce more total Fe, SO and H than FeS(100). Furthermore, various intermediate S species such as SO, SO, SO, SO and SO are also detected. This work can provide a basis for understanding the oxidation mechanism of facet-dependent FeS and the geochemical evolution of Fe and S elements.