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.

Hg0 Conversion over Sulfureted HPMo/γ-Fe2O3 with HCl at Low Temperatures: Mechanism, Kinetics, and Application in Hg0 Removal from Coal-Fired Flue Gas.

Recently, sulfureted metal oxides have been developed for the catalytic oxidation of Hg0 to HgCl2 using HCl as an oxidant at low temperatures, and they exhibit excellent Hg0 removal performance. Owing to the lack of reaction mechanisms and kinetics, further improvement in their performance for Hg0 conversion is extremely restricted. In this study, the reaction mechanism of Hg0 conversion over sulfureted HPMo/γ-Fe2O3 with HCl at low temperatures was investigated using Hg balance analysis and transient reaction. The chemical adsorption of Hg0 as HgS and the catalytic oxidation of Hg0 to HgCl2 both contributed to Hg0 conversion over sulfureted HPMo/γ-Fe2O3. Meanwhile, the formed HgCl2 can adsorb onto sulfureted HPMo/γ-Fe2O3. Then, the kinetics of Hg0 conversion, Hgt adsorption, and HgCl2 desorption were developed, and the kinetic parameters were gained by fitting the Hg balance curves. Subsequently, the inhibition mechanism of H2O and SO2 on Hg0 conversion over sulfureted HPMo/γ-Fe2O3 was determined by comparing the kinetic parameters. The kinetic model suggested that both HgCl2 resulting from Hg0 oxidation and unoxidized Hg0 can be completely adsorbed on sulfureted HPMo/γ-Fe2O3 with a moderate mass hourly space velocity. Therefore, sulfureted HPMo/γ-Fe2O3 can be developed as a reproducible sorbent for recovering Hg0 emitted from coal-fired power plants.

Simultaneous Adsorption of Gaseous Hg0 and Hg(II) by Regenerable Monolithic FeMoSx/TiO2: Mechanism and its Application in the Centralized Control of Hg Pollution in Coal-Fired Flue Gas.

FeMoSx/TiO2 was investigated as a regenerable sorbent to simultaneously adsorb Hg0 and Hg(II) from coal-fired flue gas for the centralized control of Hg pollution discharged from coal-fired power plants. The performance of FeMoSx/TiO2 for Hg(II) and/or Hg0 adsorption was evaluated on a fixed-bed reactor at 80 oC, and the mutual interference between Hg0 adsorption and Hg(II) adsorption was analyzed using individual adsorption, simultaneous adsorption, and two-stage adsorption. FeMoSx/TiO2 displayed an excellent capacity for individual Hg0 adsorption (41.8 mg g-1) and a moderate capacity for individual Hg(II) adsorption (0.48 mg g-1). Two types of adsorption sites were present on FeMoSx/TiO2 for gaseous Hg adsorption (S0 and FeS2/MoS3 sites). X-ray photoelectron spectroscope and kinetic analyses demonstrated that Hg0 and Hg(II) could adsorb onto S0 sites, whereas only Hg0 was adsorbed onto FeS2/MoS3 sites. As Hg0 competed with Hg(II) for the S0 sites, the amount of Hg(II) adsorbed slightly decreased by 16% in the presence of Hg0. However, Hg0 adsorption onto the FeS2/MoS3 sites predominated over the Hg0 adsorption onto FeMoSx/TiO2 and it was not inhibited in the presence of Hg(II). Therefore, the amount of Hg0 adsorbed on FeMoSx/TiO2 was only decreased by 2% in the presence of Hg(II).