Novel Counteraction Effect of H 2 O and SO 2 toward HCl on the Chemical Adsorption of Gaseous Hg 0 onto Sulfureted HPW/γ-Fe 2 O 3 at Low Temperatures: Mechanism and Its Application in Hg 0 Recovery from Coal-Fired Flue Gas.

In this work, sulfureted phosphotungstic acid-grafted γ-Fe 2 O 3 (HPW/γ-Fe 2 O 3 ) was investigated as a regenerable monolithic sorbent to recover gaseous Hg 0 upstream of wet flue gas desulfurizations (FGDs), and the effects of HCl, SO 2 , and H 2 O on the chemical adsorption of Hg 0 onto sulfureted HPW/γ-Fe 2 O 3 were investigated with Hg balance analysis and kinetic analysis. Hg 0 conversion over sulfureted HPW/γ-Fe 2 O 3 was remarkably promoted in the presence of HCl, and most Hg 0 was catalytically oxidized to HgCl 2 . Moreover, the chemical adsorption of Hg 0 was notably restrained as the key species for Hg 0 transformation to HgS (i.e., S 2 2- ) was rapidly oxidized by Cl*. However, the effect of HCl on Hg 0 conversion over sulfureted HPW/γ-Fe 2 O 3 was almost counteracted by H 2 O and SO 2 as they competed with physically adsorbed Hg 0 and S 2 2- for the consumption of Cl*. Therefore, the chemical adsorption of Hg 0 onto sulfureted HPW/γ-Fe 2 O 3 in the presence of SO 2 and H 2 O was slightly inhibited by HCl, and only a small amount of HgCl 2 was formed. Moreover, sulfureted HPW/γ-Fe 2 O 3 exhibited a moderate ability for gaseous HgCl 2 adsorption. As a result, sulfureted HPW/γ-Fe 2 O 3 showed excellent performance in recovering Hg 0 from the flue gas upstream of the FGDs for the centralized control of Hg 0 emitted from coal-fired plants.