Selenium ligands doped ZnS for highly efficient immobilization of elemental mercury from coal combustion flue gas

Abstract At the upstream of electrostatic precipitator (ESP) or bag house (BH), using sorbents with excellent adsorption capacity is a common method for capturing mercury (Hg) from coal-fired power plant flue gas. ZnS, an inexpensively and conveniently prepared metal sulfide, can even be collected from nature, and is a promising candidate for its sulfur resistance. In this work, selenium ligands (Se2- and Se0) were introduced into ZnS for enhancing Hg0 capture capability. The experimental results showed that the Hg0 removal efficiency can reach 100% in a wide temperature range from 40 ℃ to 300 ℃ when the Se ratio was 30 wt.% (30SZ). Compared with pure ZnS and Se powder, Se/ZnS were all exhibited an excellent absorbent capability. A long term experiment was imposed on 30SZ, and the sample adsorption capacity remained unchanged. Moreover, O2 and SO2 had insignificant effects on Hg0 adsorption, NO showed a slight competition for Hg0 adsorption. It was found that Se ligands(Se2- and Se0) and surface active S (S2- and S) sites immobilized Hg0 over the Se/ZnS surface, and in turn the adsorbed Hg0 was basically converted to HgSe and HgS, and the adsorption mechanism was also proposed. With these advantageous performances, 30SZ is expected to be an economically feasible and scientifically sound sorbent. This work also provides a promising way for Hg0 capture from coal combustion flue gas.