The performance and mechanism of Hg0 removal by Mn-Fe modified magnetic carbon sorbent
In this study,a series of Mn-Fe modified carbon-based magnetic sorbents(MnxFey/C)were prepared by the sol-gel method and further evaluated for gaseous elemental mercury(Hg0)removal and anti-SO2 poisoning.SEM,TEM,BET,XRD,H2-TPR,Raman and XPS were employed to analyze the physicochemical structure of sorbents.According to the characterization results,the inherent reasons for the performance differences of MnxFey/C sorbents were clarified.The results indicated that Mn2Fe1/C achieved best Hg0 removal performance(99.99％)under 150℃ and 250μg/m3 Hg0.The addition of an appropriate amount of Fe could cause strong interaction between Mn and Fe.It led to an oxidation-reduction cycle of Mn3++Fe3+↔Mn4++Fe2+,thus promoting the generation of Mn4+and weakening the chemical bond strength of Mn-O-Mn.Resultantly,the concentration of oxygen vacancies(Ov)and reactive oxygen species(Oa)was increased,which facilitated Hg0 removal over Mn2Fe1/C.In addition,Mn2Fe1/C showed good resistance to SO2.Its Hg0removal efficiency remained above 80％at a concentration of 2000× 10-6 SO2.XPS showed that Fe could protect most of the Mn active sites from SO2 poisoning,thus inhibiting the formation and deposition of sulfate on the sorbent surface.Mn2Fe1/C could be separated from fly ash through magnetic separation.After four cycles of adsorption and regeneration,Mn2Fe1/C still exhibited a Hg0removal efficiency of 95.69％.It showed superior regeneration ability and might be a promising mercury sorbent for coal-fired flue gas.
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