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

Synergistic removal of Hg0, HCl, and SO2 from flue gas in municipal solid waste incineration by mechanically modified fly ash

The emissions of flue gas components (such as Hg0, SO2, HCl) and the generation of hazardous waste fly ash from municipal waste incineration pose a significant threat to environmental integrity. In this study, a mechanochemical method combined with a modifier is innovatively proposed for the modification of fly ash to remove Hg0. In the fixed bed adsorption experiment, the removal efficiency of up to 60 percent can be achieved by ball milling (700rap,30min) alone. The modification of fly ash by mechanical force coupling with pyrite can achieve Hg0 removal efficiency is increased to more than 90 percent. By taking advantage of the excellent adsorption capacity of modified fly ash for acidic gases, the enhancement of S and Cl∗ active sites on the surface of modified fly ash strengthened the removal efficiency of modified fly ash for Hg0. DFT simulations evidenced that the defective S sites caused by the ball milling process could enhance the adsorption capacity of pyrite for Hg0. The fly ash was modified with mechanically coupled pyrite and alkalis and was able to have good adsorption capacity for acidic gases, the highest removal effect reached 93.1% and 96.7% for SO2 and HCl, respectively. The adsorbed acid gases increased the S and Cl∗ active sites, which led to the removal of Hg0 from the modified fly ash to more than 94.4%, achieving the synergistic removal of acid gases and Hg0. This method can realize the integrated technical route of "Fly ash collection - Online modification - Timely injection". A novel investigation was conducted on the elimination of flue gas contaminants and the reutilization of perilous fly ash.

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.

Effecting pattern study of SO2 on Hg0 removal over α-MnO2 in-situ supported magnetic composite

α-MnO₂ was in-situ supported onto silica coated magnetite nanoparticles (MagS-Mn) to study the adsorption and oxidation of Hg⁰ as well as the effecting patterns of SO₂ and O₂ on Hg⁰ removal. MagS-Mn showed Hg⁰ removal capacity of 1122.6 μg/g at 150 °C with the presence of SO₂. Hg⁰ adsorption and oxidation efficiencies were 2.4% and 90.6%, respectively. Hg⁰ removal capability deteriorated at elevated temperatures. Surface oxygen and manganese chemistry analysis indicated that SO₂ inhibited the Hg⁰ removal through consumption of adsorbed oxygen and reduction of high valence manganese. This inhibiting effect was observed to be counteracted by O₂ at lower temperatures. O₂ tended to compete with SO₂ for active sites and further create additional adsorbed oxygen sites for Hg⁰ surface reaction via surface dissociative adsorption rather than replenish the active sites consumed by SO₂. The high valence manganese was also preserved by O₂ which was essential to Hg⁰ oxidation. The intervention of O₂ in the inhibition of SO₂ on Hg⁰ removal was weakened at temperatures higher than 250 °C. Aa a result, Hg⁰ tends to be catalytic oxidized in the condition of low reaction temperatures and with the presence of O₂ over α-MnO₂ oriented composites.

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, Hg^t 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.

Mercury removal using various modified V/Ti-based SCR catalysts: A review

Growing levels of mercury pollution has made countries urgently need a suitable mercury treatment technology. Among various technologies, heterogeneous oxidative mercury removal via different modified V/Ti-based SCR catalysts is considered as a promising approach due to excellent economic value and removal efficiency. Although various related modification experiments have been worked in recent years, the research on the performance, including activity and resistance, and mechanism of catalysts still needs to be improved, so it is necessary to summarize these experiments to guide further work. This article will review many modifications start from the V/Ti catalyst. Not only the performance of these catalysts, but also a lot of speculation about the mercury removal mechanism are include in our research. In addition, the characteristics of some modified catalysts have been linked with their oxidation mechanism and structural changes by comparing many studies, and finally attributed to some special properties of the corresponding modifiers. We expect this study will clarify the research progress of modified V/Ti-based SCR catalysts in mercury removal, and guide future modification so that some properties of the catalyst can be improved in a targeted manner.

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

FeMoS_x/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 FeMoS_x/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. FeMoS_x/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 FeMoS_x/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 FeMoS_x/TiO₂ and it was not inhibited in the presence of Hg(II). Therefore, the amount of Hg⁰ adsorbed on FeMoS_x/TiO₂ was only decreased by 2% in the presence of Hg(II).