Different roles of FeS and FeS2 on magnetic FeSx for the selective adsorption of Hg2+ from waste acids in smelters: Reaction mechanism, kinetics, and structure-activity relationship

Magnetic FeSx was developed as a high-performance sorbent for selectively adsorbing Hg2+ from waste acids in smelters. However, further improvement of its ability for Hg2+ adsorption was extremely restricted due to the lack of reaction mechanisms and structure-activity relationships. In this study, the roles of FeS and FeS2 on magnetic FeSx for Hg2+ adsorption were investigated with alternate adsorption of Hg2+ without/with Cl-. The structure-activity relationship of magnetic FeSx for Hg2+ adsorption and the negative effect of acid erosion were elucidated using kinetic analysis. FeS can react with Hg2+ with 1:1 stoichiometric ratio to form HgS, while FeS2 can react with Hg2+ in the presence of Cl- with novel 1:3 stoichiometric ratio to form Hg3S2Cl2. The rate of magnetic FeSx for Hg2+ adsorption was related to the instantaneous amounts of FeS and threefold FeS2 on magnetic FeSx and the amount of Hg2+ adsorbed. Meanwhile, its capacity for Hg2+ adsorption was related to the initial sum of FeS amount and threefold FeS2 amount on the surface and their ratios by acid erosion. Then, magnetic FeSx-400 was devised with adsorption rate of 2.12 mg g-1 min-1 and capacity of 1092 mg g-1 to recover Hg2+ from waste acids for centralized control.

Ash problems and prevention measures in power plants burning high alkali fuel: Brief review and future perspectives

Large-scale utilization of high-alkali fuels is considered an effective solution for alleviating energy shortages and reducing CO2 emissions. However, combustion of high-alkali fuels in boilers releases alkali metals into the flue gas, which leads to severe ash deposition and corrosion on the heating surface. Consequently, research into the efficient use of highly alkaline fuels has been conducted in recent years. In this review, ash issues and measures for their prevention during high-alkali fuel combustion are summarized. First, the characteristics of fly ash produced from high-alkali fuel combustion are reviewed, and the form, migration, and deposition characteristics of alkali metals are summarized. Subsequently, research progress of high alkali fuel ash is introduced in detail. Mechanisms of slagging, fouling, corrosion on the heating surface and the selective catalytic reduction (SCR) unit deactivation are summarized. Prevention and control methods for the high-alkali fuel ash problem are then introduced. Finally, based on current research, existing problems and future development directions for high-alkali fuel research are proposed. Through this review, we hope to provide insights into the effective utilization of high-alkali fuels.

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.