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

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