Remarkable differences between copper-based sulfides and iron-based sulfides for the adsorption of high concentrations of gaseous elemental mercury: Mechanisms, kinetics, and significance

Abstract

Copper sulfides (CuSx) and iron sulfides (FeSx) have been developed to capture gaseous elemental mercury (Hg0) originating from the smelting flue gas. However, these compounds exhibit different Hg0 adsorption characteristics and Hg species adsorbed on CuSx can be spontaneously released as gaseous Hg0. Following these findings, the adsorption/desorption kinetics of Hg0 onto and from FeSx and CuSx were determined. After comparing the kinetic parameters, the mechanisms behind some of the remarkable differences between FeSx and CuSx with respect to Hg0 adsorption were discovered. The Cu-S bond in CuSx was not completely broken during Hg0 oxidation, but the SS bond in FeSx was. Hence, the activation energy for the oxidation of Hg0 physically adsorbed on CuSx was much lower than that for FeSx, resulting in a much higher efficiency of CuSx to oxidize Hg0 than FeSx. However, the bond strength of Hg-S for HgS on CuSx was weaker due to the sharing of S2− in HgS with Cu+, resulting in a decrease in the thermal stability of HgS on CuSx. Therefore, HgS adsorbed on Cu-based sulfides was metastable, and could be spontaneously decomposed to release moderate concentrations of gaseous Hg0, which was not preferable for capturing high concentrations of Hg0.