First-Principles Study of Hg⁰ Immobilization on a Defective Pyrite Surface

Abstract

The formation of defects over a crystal surface could significantly improve the elemental mercury (Hg 0 ) removal performance of pyrite (FeS 2 ). Herein, the role of surface defects in Hg 0 immobilization over FeS 2 (100) was investigated by adopting quantum chemistry. The contribution of surface defects to mercury immobilization over pyrite was mainly manifested in facilitating Hg 0 adsorption. Compared with a perfect pyrite surface, a defective pyrite surface exhibited a higher affinity to Hg 0 , whose adsorption energy was up to −53.03 kJ/mol. In addition, surface defects could induce the dissociation of HCl, a common component in coal combustion flue gas, which provided active chlorine (Cl*) for subsequent Hg 0 oxidation. The Langmuir−Hinshelwood mechanism is responsible for Hg 0 oxidation over the defective FeS 2 (100) surface. First, Hg 0 and HCl were simultaneously adsorbed over the defective surface, and the presence of defects could promote Hg 0 adsorption and HCl dissociation. Subsequently, adsorbed Hg 0 would combine with the adjacent active Cl* site, whose energy barrier was 92.60 kJ/mol. Eventually, HgCl could spontaneously react with another Cl* site to form a HgCl 2 molecule. Thus, the formation of a HgCl intermediate was the rate-determining step for Hg 0 oxidation over a defective pyrite surface. This work reveals the role of defects in Hg 0 immobilization over a pyrite surface, which provides a scientific basis for the design and modification of natural mineral sulfide sorbents.