Different Design Strategies for Metal Sulfide Sorbents to Capture Low Concentrations of Gaseous Hg0 in Coal-Fired Flue Gas and High Concentrations of Gaseous Hg0 in Smelting Flue Gas

Capturing gaseous Hg⁰ using regenerable metal sulfides is a promising technology to recover gaseous Hg⁰ from both coal-fired flue gas (CFG) and smelting flue gas (SFG) for the centralized control. Gaseous Hg⁰ concentration in SFG is 2-3 orders of magnitude higher than that in CFG; therefore, the design strategy of metal sulfides for capturing gaseous Hg⁰ from CFG is quite different from that from SGF. In this work, the structure-activity relationship of metal sulfides to capture Hg⁰ was investigated according to the remarkable difference in MoO₃ loading on sulfureted FeTiO_x to capture low/high concentrations of gaseous Hg⁰. The rate of Hg⁰ adsorption onto metal sulfides was mainly related to the amounts of adsorption sites and S₂^2- on the surface, the affinity of adsorption sites to gaseous Hg⁰, and the gaseous Hg⁰ concentration. Meanwhile, the capacity for Hg⁰ adsorption was approximately equal to the less of the amount of adsorption sites and S₂^2- on the surface. Furthermore, capturing low concentrations of gaseous Hg⁰ from CFG required the metal sulfide sorbents having more adsorption sites with strong affinity to gaseous Hg⁰, while capturing high concentrations of gaseous Hg⁰ from SFG required the sorbents with enough adsorption sites.