Outstanding Resistance of H2S-Modified Cu/TiO2 to SO2 for Capturing Gaseous Hg0 from Nonferrous Metal Smelting Flue Gas: Performance and Reaction Mechanism.

The utilization of H2SO4, produced using SO2 from nonferrous metal smelting flue gas as a source of S, is extremely restricted due to Hg contamination; therefore, there is great demand to remove Hg0 from smelting flue gas. Although the ability of Cu/TiO2 to capture Hg0 is excellent, its resistance to H2O and SO2 is very poor. In this study, Cu/TiO2 was treated with H2S to improve its resistance to H2O and SO2 for capturing Hg0. The chemical adsorption of Hg0 on Cu/TiO2 was primarily through the HgO route, which was almost suppressed by H2O and SO2 due to the transformation of CuO into CuSO4. Besides the HgO route, the HgS route also contributed to the chemical adsorption of Hg0 on modified Cu/TiO2. As the CuS on modified Cu/TiO2 was inert to H2O and SO2, the chemical adsorption of Hg0 on modified Cu/TiO2 through the HgS route was barely inhibited. Meanwhile, the HgS route was predominant in the chemical adsorption of Hg0 on modified Cu/TiO2. Therefore, modified Cu/TiO2 exhibited an excellent resistance to H2O and SO2, and its Hg0 capture capacity from simulated flue gas was up to 12.7 mg g-1 at 100 °C.

H2S-Modified Fe-Ti Spinel: A Recyclable Magnetic Sorbent for Recovering Gaseous Elemental Mercury from Flue Gas as a Co-Benefit of Wet Electrostatic Precipitators.

The nonrecyclability of the sorbents used to capture Hg0 from flue gas causes a high operation cost and the potential risk of exposure to Hg. The installation of wet electrostatic precipitators (WESPs) in coal-fired plants makes possible the recovery of spent sorbents for recycling and the centralized control of Hg pollution. In this work, a H2S-modified Fe-Ti spinel was developed as a recyclable magnetic sorbent to recover Hg0 from flue gas as a co-benefit of the WESP. Although the Fe-Ti spinel exhibited poor Hg0 capture activity in the temperature range of flue gas downstream of flue gas desulfurization, the H2S-modified Fe-Ti spinel exhibited excellent Hg0 capture performance with an average adsorption rate of 1.92 µg g-1 min-1 at 60 °C and a capacity of 0.69 mg g-1 (5% of the breakthrough threshold) due to the presence of S22- on its surface. The five cycles of Hg0 capture, Hg0 recovery, and sorbent regeneration demonstrated that the ability of the modified Fe-Ti spinel to capture Hg0 did not degrade remarkably. Meanwhile, the ultralow concentration of Hg0 in flue gas was increased to a high concentration of Hg0, which facilitated the centralized control of Hg pollution.

Elemental Mercury Oxidation over Fe-Ti-Mn Spinel: Performance, Mechanism, and Reaction Kinetics.

The design of a high-performance catalyst for Hg0 oxidation and predicting the extent of Hg0 oxidation are both extremely limited due to the uncertainties of the reaction mechanism and the reaction kinetics. In this work, Fe-Ti-Mn spinel was developed as a high-performance catalyst for Hg0 oxidation, and the reaction mechanism and the reaction kinetics of Hg0 oxidation over Fe-Ti-Mn spinel were studied. The reaction orders of Hg0 oxidation over Fe-Ti-Mn spinel with respect to gaseous Hg0 concentration and gaseous HCl concentration were approximately 1 and 0, respectively. Therefore, Hg0 oxidation over Fe-Ti-Mn spinel mainly followed the Eley-Rideal mechanism (i.e., the reaction of gaseous Hg0 with adsorbed HCl), and the rate of Hg0 oxidation mainly depended on Cl• concentration on the surface. As H2O, SO2, and NO not only inhibited Cl• formation on the surface but also interfered with the interface reaction between gaseous Hg0 and Cl• on the surface, Hg0 oxidation over Fe-Ti-Mn spinel was obviously inhibited in the presence of H2O, SO2, and NO. Furthermore, the extent of Hg0 oxidation over Fe-Ti-Mn spinel can be predicted according to the kinetic parameter kE-R, and the predicted result was consistent with the experimental result.

Recyclable Naturally Derived Magnetic Pyrrhotite for Elemental Mercury Recovery from Flue Gas.

Magnetic pyrrhotite, derived from the thermal treatment of natural pyrite, was developed as a recyclable sorbent to recover elemental mercury (Hg0) from the flue gas as a cobenefit of wet electrostatic precipitators (WESP). The performance of naturally derived pyrrhotite for Hg0 capture from the flue gas was much better than those of other reported magnetic sorbents, for example Mn-Fe spinel and Mn-Fe-Ti spinel. The rate of pyrrhotite for gaseous Hg0 capture at 60 °C was 0.28 µg g min-1 and its capacity was 0.22 mg g-1 with the breakthrough threshold of 4%. After the magnetic separation from the mixture collected by the WESP, the spent pyrrhotite can be thermally regenerated for recycle. The experiment of 5 cycles of Hg0 capture and regeneration demonstrated that both the adsorption efficiency and the magnetization were not notably degraded. Meanwhile, the ultralow concentration of gaseous Hg0 in the flue gas was concentrated to high concentrations of gaseous Hg0 and Hg2+ during the regeneration process, which facilitated the centralized control of mercury pollution. Therefore, the control of Hg0 emission from coal-fired plants by the recyclable pyrrhotite was cost-effective and did not have secondary pollution.