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).

In this study, CuS x /TiO 2 was developed to selectively remove Hg 2+ from waste acids. X-ray photoelectron spectroscopy and X-ray diffraction analyses demonstrated that there were two reaction routes for Hg 2+ removal by CuS x /TiO 2 , corresponding to the two types of copper sulfides (i.e., CuS and Cu 2 S). The CuS route with the product HgS occurred regardless of the presence of Cl − , while the Cu 2 S route with the product Hg 2 Cl 2 only occurred with Cl − . Therefore, Cl − exhibited a remarkable promotion on Hg 2+ removal. Kinetic analysis demonstrated that the CuS route was markedly faster than the Cu 2 S route, which accounted for the rapid removal of Hg 2+ . CuS x /TiO 2 showed excellent performance for Hg 2+ removal at pH 2.0 with an adsorption rate of 16.3 mg g −1 min −1 , and removed Hg 2+ can be recovered as liquid Hg 0 as a co-benefit of Hg 0 recovery units in smelters. Therefore, CuS x /TiO 2 was a promising sorbent for Hg 2+ recovery in waste acids for centralized control.

The combined technology of selective catalytic reduction and wet flue gas desulfurization (SCR + WFGD) to control Hg0 emissions from coal-fired flue gas is often unsatisfactory due to the undesired Hg0 oxidation efficiency of SCR, the re-emission of Hg0 from WFGD, and the potential secondary pollution. To offset the shortcomings of SCR + WFGD, Cu–ZnS that resulted from Cu2+ activation of natural sphalerite was developed as a difunctional sorbent to sequentially capture gaseous Hg0 in flue gas and aqueous Hg2+ in desulfurization solution. Not only did Cu–ZnS exhibit significant performance in capturing the gaseous Hg0 downstream of an electrostatic precipitator, but it also displayed a superior ability in capturing aqueous Hg2+. Hg0 re-emission from WFGD, which resulted from the reduction of aqueous Hg2+ by SO2, was completely suppressed because Cu–ZnS could adsorb both aqueous Hg2+ and re-emitted Hg0 in desulfurization solution. Spent Cu–ZnS containing Hg can be separated from the desulfurization slurry via flotation for Zn smelting, and adsorbed Hg can be at last recovered as mainly liquid Hg0 in modern smelters for centralized control. Therefore, the sequential capture of gaseous Hg0 and aqueous Hg2+ by Cu–ZnS may be an economically viable and eco-friendly technology to control Hg pollution of coal-fired power plants.

Recently, sulfureted metal oxides have been developed for the catalytic oxidation of Hg 0 to HgCl 2 using HCl as an oxidant at low temperatures, and they exhibit excellent Hg 0 removal performance. Owing to the lack of reaction mechanisms and kinetics, further improvement in their performance for Hg 0 conversion is extremely restricted. In this study, the reaction mechanism of Hg 0 conversion over sulfureted HPMo/γ-Fe 2 O 3 with HCl at low temperatures was investigated using Hg balance analysis and transient reaction. The chemical adsorption of Hg 0 as HgS and the catalytic oxidation of Hg 0 to HgCl 2 both contributed to Hg 0 conversion over sulfureted HPMo/γ-Fe 2 O 3 . Meanwhile, the formed HgCl 2 can adsorb onto sulfureted HPMo/γ-Fe 2 O 3 . Then, the kinetics of Hg 0 conversion, Hg t adsorption, and HgCl 2 desorption were developed, and the kinetic parameters were gained by fitting the Hg balance curves. Subsequently, the inhibition mechanism of H 2 O and SO 2 on Hg 0 conversion over sulfureted HPMo/γ-Fe 2 O 3 was determined by comparing the kinetic parameters. The kinetic model suggested that both HgCl 2 resulting from Hg 0 oxidation and unoxidized Hg 0 can be completely adsorbed on sulfureted HPMo/γ-Fe 2 O 3 with a moderate mass hourly space velocity. Therefore, sulfureted HPMo/γ-Fe 2 O 3 can be developed as a reproducible sorbent for recovering Hg 0 emitted from coal-fired power plants.