Novel Counteraction Effect of H2O and SO2 toward HCl on the Chemical Adsorption of Gaseous Hg0 onto Sulfureted HPW/γ-Fe2O3 at Low Temperatures: Mechanism and Its Application in Hg0 Recovery from Coal-Fired Flue Gas.

In this work, sulfureted phosphotungstic acid-grafted γ-Fe2O3 (HPW/γ-Fe2O3) was investigated as a regenerable monolithic sorbent to recover gaseous Hg0 upstream of wet flue gas desulfurizations (FGDs), and the effects of HCl, SO2, and H2O on the chemical adsorption of Hg0 onto sulfureted HPW/γ-Fe2O3 were investigated with Hg balance analysis and kinetic analysis. Hg0 conversion over sulfureted HPW/γ-Fe2O3 was remarkably promoted in the presence of HCl, and most Hg0 was catalytically oxidized to HgCl2. Moreover, the chemical adsorption of Hg0 was notably restrained as the key species for Hg0 transformation to HgS (i.e., S22-) was rapidly oxidized by Cl*. However, the effect of HCl on Hg0 conversion over sulfureted HPW/γ-Fe2O3 was almost counteracted by H2O and SO2 as they competed with physically adsorbed Hg0 and S22- for the consumption of Cl*. Therefore, the chemical adsorption of Hg0 onto sulfureted HPW/γ-Fe2O3 in the presence of SO2 and H2O was slightly inhibited by HCl, and only a small amount of HgCl2 was formed. Moreover, sulfureted HPW/γ-Fe2O3 exhibited a moderate ability for gaseous HgCl2 adsorption. As a result, sulfureted HPW/γ-Fe2O3 showed excellent performance in recovering Hg0 from the flue gas upstream of the FGDs for the centralized control of Hg0 emitted from coal-fired plants.

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 FeTiOx 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 S22- 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 S22- 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.