Significant Enhancement of Gaseous Elemental Mercury Recovery from Coal-Fired Flue Gas by Phosphomolybdic Acid Grafting on Sulfurated γ-Fe2O3: Performance and Mechanism

The existing technologies to control Hg emissions from coal-fired power plants can be improved to achieve the centralized control of Hg-0 emissions, which continue to pose a risk of Hg exposure to human populations. In this work, MoSx@gamma-Fe2O3, formed by the sulfuration of phosphomolybdic acid (HPMo)-grafted y-Fe2O3, was developed as a magnetic and regenerable sorbent to recover gaseous Hg-0 from coal-fired flue gas as a cobenefit to the use of wet electrostatic precipitators. The thermal stability of gamma-Fe2O3 was notably enhanced by HPMo grafting; thus, the magnetization of MoS@gamma-Fe2O3 hardly decreased during the application. The kinetic analysis indicates that the chemical adsorption of gaseous He was mainly dependent on the amounts of surface S(2)(2-)and surface adsorption sites. Although the amount of S-2(2-) on sulfurated gamma-Fe2O3 decreased after HPMo grafting, the amount of surface adsorption sites significantly increased due to the formation of a layered MoSx structure on the surface. Therefore, the ability of sulfurated gamma-Fe2O3 to capture Hg-0 was improved considerably after HPMo grafting. Furthermore, low concentrations of gaseous He in coal-fired flue gas can be gradually enriched by at least 1000 times by MoSx@gamma-Fe2O3, which facilitates the recovery and centralized control of gaseous Hg-0 in flue gas.