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., S2 2–) 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 S2 2– 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.