Comparison of pyrite-phase transition metal sulfides for capturing leaked high concentrations of gaseous elemental mercury in indoor air: Mechanism and adsorption/desorption kinetics

Abstract

Understanding the characteristics of pyrite-phase transition metal sulfides for the adsorption and desorption of gaseous elemental mercury (Hg⁰) is of vital significance for their applications in gaseous Hg⁰ capture. In this study, the adsorption and desorption of gaseous Hg⁰ onto pyrite-phase transition metal sulfides (i.e., FeS₂/TiO₂, CoS₂/TiO₂, and NiS₂/TiO₂) were compared, and the mechanisms of their differences were revealed by the kinetic analysis. The Co/NiS and SS bonds in dumbbell-shaped CoS₂ and NiS₂ were not entirely broken after oxidizing physically adsorbed Hg⁰, whereas the FeS and SS bonds in dumbbell-shaped FeS₂ were. Thus, the activation energies of CoS₂/TiO₂ and NiS₂/TiO₂ for oxidizing physically adsorbed Hg⁰ were smaller than that of FeS₂/TiO₂, causing the stronger abilities of CoS₂/TiO₂ and NiS₂/TiO₂ to oxidize physically adsorbed Hg⁰ than that of FeS₂/TiO₂. However, the bonding strengths of Hg-S in HgS adsorbed on dumbbell-shaped CoS₂ and NiS₂ were relatively weaker because of the sharing of S^2- in HgS with S^- and Co²⁺/Ni²⁺, causing the decreases in heat stabilities of HgS adsorbed on CoS₂/TiO₂ and NiS₂/TiO₂. Therefore, HgS adsorbed on CoS₂/TiO₂ and NiS₂/TiO₂ can be voluntarily decomposed to release gaseous Hg⁰, which should be combined with FeS₂/TiO₂ for the emergency treatment of liquid Hg⁰ leakage indoors.

Keywords: Gaseous Hg(0) adsorption; Gaseous Hg(0) desorption; Kinetics of adsorption and desorption; Liquid Hg(0) leakage indoors; Pyrite-phase transition metal sulfides.