Outstanding Performance of Magnetically Separable Sulfureted MoO₃/Fe–Ti Spinel for Gaseous Hg⁰ Recovery from Smelting Flue Gas: Mechanism and Adsorption Kinetics

Abstract

To replace the hazardous and complicated Boliden−Norzink technology, the technology of Hg 0 recovery from smelting flue gas by a magnetic and reproducible sulfureted MoO 3 /Fe−Ti spinel was employed to keep the produced H 2 SO 4 free of Hg. The sulfureted MoO 3 /Fe−Ti spinel showed excellent performance in capturing gaseous Hg 0 , with an average adsorption rate of 93.3 μg g −1 min −1 and an adsorption capacity of 66.3 mg g −1 at 60 °C, which were much better than those of most of the other reported sorbents. Meanwhile, the sulfureted MoO 3 /Fe−Ti spinel exhibited excellent superparamagnetism and magnetization of 19.9 emu g −1 , which ensured that it could easily be magnetically separated without a specialized precipitator or the molding of pulverous sorbents to monolithic sorbents. To investigate the promotion mechanism of MoO 3 loading on Hg 0 adsorption onto the sulfureted Fe−Ti spinel, the Hg 0 adsorption kinetic parameters of the sulfureted MoO 3 /Fe−Ti spinel and sulfureted Fe−Ti spinel, resulting from the fitting of the adsorption breakthrough curves based on the kinetic model, were compared. The promotion of MoO 3 loading was attributed to the remarkable increase in the adsorption sites on the sulfureted Fe−Ti spinel for Hg 0 physical adsorption, which was mainly related to the formation of the MoS 3 layer.

Different Design Strategies for Metal Sulfide Sorbents to Capture Low Concentrations of Gaseous Hg0 in Coal-Fired Flue Gas and High Concentrations of Gaseous Hg0 in Smelting Flue Gas

“…Therefore, the peak corresponding to the decomposition of HgSO 4 appeared at 330 °C (see Figure 2a). 34,36,40 The amount of Hg 0 desorbed in air (8.33 μg) was approximately equal to that adsorbed amount (8.41 μg), suggesting that most Hg 0 adsorbed on sulfureted Mo/FeTiO x can be thermally desorbed as Hg 0 . According to Figure 2a, the thermal desorption of Hg adsorbed was performed in air at 400 °C.…”

“…The binding energies of Hg 4f for sulfureted Mo/FeTiO x after capturing high concentrations of Hg 0 for 12 h were mainly centered at 104.9 and 100.9 eV (see Figure S2 in Supporting Information), suggesting that Hg species adsorbed on sulfureted Mo/FeTiO x was mainly HgS. , Hg-TPD profile in N 2 of sulfureted Mo/FeTiO x after Hg 0 adsorption showed one Hg 0 desorption peak at approximately 200 °C (see Figure a), which was attributed to HgS decomposition. , As Hg-TPD profile was obtained in air, partial HgS was oxidized to HgSO 4 . Therefore, the peak corresponding to the decomposition of HgSO 4 appeared at 330 °C (see Figure a). ,, The amount of Hg 0 desorbed in air (8.33 μg) was approximately equal to that adsorbed amount (8.41 μg), suggesting that most Hg 0 adsorbed on sulfureted Mo/FeTiO x can be thermally desorbed as Hg 0 . According to Figure a, the thermal desorption of Hg adsorbed was performed in air at 400 °C.…”

“…FeTiO x (Fe/Ti = 2:1) was prepared with a co-precipitation method. , Afterward, Mo/FeTiO x (5 wt % of MoO 3 ) was prepared with the wet impregnation of ammonium molybdate on FeTiO x followed by calcination at 500 °C under an air atmosphere for 3 h . Finally, sulfureted FeTiO x and sulfureted Mo/FeTiO x were obtained by the treatment of FeTiO x and Mo/FeTiO x at 300 °C with 600 ppm of H 2 S, respectively …”

“…To further improve its ability for Hg 0 capture, sulfureted FeTiO x was modified with MoO 3 loading before sulfuration. The performance of sulfureted FeTiO x to capture high concentrations of Hg 0 from SFG was remarkably improved by MoO 3 loading due to the remarkable increase of adsorption sites for the physical adsorption of Hg 0 . However, its performance to capture low concentrations of Hg 0 from CFG was only slightly improved.…”

Mercury Removal from Flue Gas by Noncarbon Sorbents

“…The adsorption of Hg 0 on metal sulfides would consume the sulfur species. Different from the easy replenishing of consumed surface oxygen on metal oxides soon by O 2 in the flue gas, , the sulfur species was hardly replenished. − Since only the surface layer of sulfur on the sorbent was accessible for Hg 0 adsorption, the traditional bulk-phase heteroatom dopant may cause an insufficient utilization of doping elements. Hong et al developed a stepwise Cu 2+ ions incorporation method for activating PbS to immobilize Hg 0 , as shown in Figure .…”