Mechanistic Insights into H2O-Enhanced Iron Sulfide Formation: A DFT Study for Sulfur Fire Prevention and Environmental Hazard Mitigation.

The presence of water (H2O) has been found to increase the susceptibility of sulfur to ignition during production and transportation, primarily due to the spontaneous combustion of iron-sulfide compounds generated by friction. In this study, the interaction mechanisms of iron-sulfur reactions under wet and dry conditions were investigated using density functional theory (DFT). Reactant cluster models were constructed, and the structures of all stationary points along the reaction potential energy surface were fully optimized for the 13-fold spin state. The adsorption mechanisms of Fe4 and S2 clusters, with and without H2O, were systematically examined. Key parameters, including differential charge density, Mulliken charge distribution, and energy gap between Fe4 and S2 before and after H2O adsorption, were calculated to elucidate the role of water. The results demonstrate that the addition of H2O enhances the adsorption energy between Fe4 and S2 clusters, reduces the system's energy gap, and increases reactivity. Furthermore, the chemical reaction pathways of Fe4 and S2 clusters, with and without H2O, were analyzed along with their associated thermodynamic and kinetic parameters. The presence of H2O promotes Fe-S bond formation, lowers the energy barrier of the rate-determining step, and accelerates the production of iron-sulfide compounds.