Hierarchical Ag-SiO2@Fe3O4 magnetic composites for elemental mercury removal from non-ferrous metal smelting flue gas.

Hierarchical Ag-SiO2@Fe3O4 magnetic composites were selected for elemental mercury (Hg0) removal from non-ferrous metal smelting flue gas in this study. Results showed that the hierarchical Ag-SiO2@Fe3O4 magnetic composites had favorable Hg0 removal ability at low temperature. Moreover, the adsorption capacity of hierarchical magnetic composite is much larger than that of pure Fe3O4 and SiO2@Fe3O4. The Hg0 removal efficiency reached the highest value as approximately 92% under the reaction temperature of 150°C, while the removal efficiency sharply reduced in the absence of O2. The characterization results indicated that Ag nanoparticles grew on the surface of SiO2@Fe3O4 support. The large surface area of SiO2 supplied efficient reaction room for Hg and Ag atoms. Ag-Hg amalgam is generated on the surface of the composites. In addition, this magnetic material could be easily separated from fly ashes when adopted for treating real flue gas, and the spent materials could be regenerated using a simple thermal-desorption method.

Enhancing the catalytic oxidation of elemental mercury and suppressing sulfur-toxic adsorption sites from SO2-containing gas in Mn-SnS2.

It is difficult to stabilize gaseous elemental mercury (Hg°) on a sorbent from SO2-containing industrial flue gas. Enhancing Hg° oxidation and activating surface-active sulfur (S*) can benefit the chemical mercury adsorption process. A Mn-SnS2 composite was prepared using the Mn modification of SnS2 nanosheets to expose more Mn oxidation and sulfur adsorption sites. The results indicate that Mn-Sn2 exhibits better Hg° removal performances at a wide temperature range of 100-250 °C. A sufficient amount of surface Mn with a valance state of Mn4+ is favorable for Hg° oxidation, while the electron transfer properties of Sn can accelerate this oxidation process. Oxidized mercury primary exists as HgS with surface S*. A larger surface area, stable crystal structure, and active valance state of each element are favorable for Hg° oxidation and adsorption. The Mn-SnS2 exhibits an excellent SO2 resistance when the SO2 concentration is lower than 1500 ppm. The effects of H2O and O2 were also evaluated. The results show that O2 has no influence, while H2O and SO2 coexisting in the flue gas have a toxic effect on the Hg° removal performance. The Mn-SnS2 has a great potential for the Hg° removal from SO2-containing flue gas such as non-ferrous smelting gas.

Design of MnO2/CeO2-MnO2 hierarchical binary oxides for elemental mercury removal from coal-fired flue gas.

MnO2/CeO2-MnO2 hierarchical binary oxide was synthesized for elemental mercury (Hg0) removal from coal-fired flue gas. CeO2 in-situ grow on the surface of carbon spheres, and that CeO2@CSs acted as precursor for porous MnO2/CeO2-MnO2. XRD, Raman, XPS, FT-IR, and H2-TPR were selected for the physical structural and chemical surface analysis. The results indicated that the composite has sufficient surface oxygen and hierarchical porous structure. The Hg0 removal experiments results indicated that MnO2/CeO2-MnO2 exhibited excellent Hg0 removal performance, with an 89% removal efficiency of total 300min at 150°C under 4% O2. MnO2 was the primary active site for Hg0 catalytic oxidation. The porous structure was beneficial for gaseous mercury physically adsorption. In addition, CeO2 enhanced the oxygen capture performance of the composite and the oxidation performance for MnO2. Moreover, the effects of O2, SO2 and H2O were also tested in this study. O2 promoted the Hg0 removal reaction. While SO2 and H2O can poison the MnO2 active site, resulted in a low Hg0 removal efficiency.