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

•CuSx and FeSx exhibited different characteristics of Hg0 adsorption.•Hg species adsorbed on CuSx can be spontaneously released as gaseous Hg0.•The Cu-S bond in CuSx was not completely broken during Hg0 oxidation, but the SS bond in FeSx was.•The bond strength of Hg-S for HgS that adsorbed on CuSx was weaker due to the sharing of S2− in HgS with Cu+.•Cu-based sulfides were not preferable for capturing high concentrations of Hg0.