Mechanisms of Gas-Phase Mercury Immobilized by Metal Sulfides from Combustion Flue Gas: A Mini Review

Atmospheric mercury (Hg) pollution has attracted global attention as a result of its great harm to the ecosystem. By virtue of abundant surface Hg-philic sulfur sites, metal sulfides have been regarded as a promising Hg adsorbent. The Hg adsorption performance of metal sulfides is mainly determined by the distribution of surface active sites; thus, it is crucial to understand the interactions between the Hg atom and different surface sites. In this review, the immobilization mechanism of the Hg atom over metal sulfides was systematically summarized. First, the roles of surface active sites, i.e., metal and sulfur sites, played in Hg0 adsorption were systematically elaborated, to explain the excellent performance of metal sulfides. Second, the improvement on the Hg0 adsorption ability of engineered metal sulfides was attributed to the reasonable regulation of surface unsaturation and the introduction of alien active sites. Eventually, the effects of flue gas components on mineral sulfides were illuminated from the perspective of the introduction/consumption of surface active sites. The objective of this review was to interpret the detailed Hg0 immobilization mechanism and to provide guidance for developing metal-sulfide-based sorbents, and the future prospects and challenges related to the Hg0 adsorption mechanism by metal sulfides were discussed.