Novel Counteraction Effect of H<sub>2</sub>O and SO<sub>2</sub> toward HCl on the Chemical Adsorption of Gaseous Hg<sup>0</sup> onto Sulfureted HPW/γ-Fe<sub>2</sub>O<sub>3</sub> at Low Temperatures: Mechanism and Its Application in Hg<sup>0</sup> Recovery from Coal-Fired Flue Gas
Chang Wang, Fangtian Xie, Shuai Chang, Zhen Ding, Jian Mei, Shijian Yang
Abstract
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.