Insight into the elemental mercury immobilization mechanism with carbon and sulfur over the mackinawite (FeS) surface via density functional theory.

[Display omitted] • Hg0 adsorption with C and S on the FeS surface has been studied via DFT-D2 method. • DOS and ICOHP demonstrated the interaction between the adsorbates and the surfaces. • Carbon can promote mercury physisorption on the pristine FeS(0 0 1)-S surface. • The HgS generation process occurs through Langmuir-Hinshelwood Mechanism. Elemental mercury (Hg0) adsorption behaviors and mechanisms on the low-Miller index mackinawite surface (FeS(0 0 1)-S surface), with the engagement of carbon or sulfur, were investigated via DFT-D2 theoretical calculations. The simulation results show that the most favorable adsorption site for the C and Hg atoms was the lower-S site on the pristine surface, while S atom preferred the upper-S site. C atom could cause charge transfer and inter-atomic charge redistribution during adsorption. The carbon atom performs as a linker to connect the substrate and the Hg atom in the most stable mercury adsorption geometry onto the carbon-doped surface. Hg0 is physically adsorbed over the sulfur-doped surface. The HgS molecule chemically attached to the surface at the upper-S site via the Hg atom to form a S-Hg-S structure, and its generation process follows Langmuir-Hinshelwood Mechanism. Firstly, the Hg and S atoms were pre-adsorbed on the FeS(0 0 1)-S surface. Then the system needed to overcome an activation energy barrier (E b) of 89.82 kJ·mol−1. It was an endothermic process in which two separate atoms generated HgS*. However, C atom will impede the reaction as occupying the adsorption sites of mercury and sulfur. [ABSTRACT FROM AUTHOR]