SO2 Tolerance and Mechanism of Elemental Mercury Removal from Flue Gas by a Magnetic Recyclable Fe6Mn0.8Ce0.2Oy Sorbent

A Ce-doped Fe-Mn magnetic sorbent (Fe6Mn0.8Ce0.2Oy) was developed using the coprecipitation method. The effects of O-2, H2O, flue gas temperature, SO2 concentration, and Ce doping on the SO2 tolerance of the Fe6Mn0.8Ce0.2Oy sorbent for mercury removal were explored in a fixed-bed system. Combined with mercury temperature-programmed desorption (Hg-TPD) and X-ray photoelectron spectroscopy (XPS) analysis, the mechanism of mercury removal by the Fe6Mn0.8Ce0.2Oy sorbent in the presence of SO2 was analyzed. The results show that the Fe6Mn0.8Ce0.2Oy sorbent is a promising sorbent for circulating mercury removal with high SO2 tolerance. Ce doping significantly enhances the SO2 tolerance of the Fe6Mn0.8Ce0.2Oy sorbent for mercury removal by protecting the Mn4+ active sites from SO2 poisoning. This is because Ce has a stronger affinity with SO2 compared to that of Mn, and most of SO(2 )will preferentially react with CeO2 instead of MnO2 to form Ce-2(SO4)(3). O-2 in flue gas improves the SO2 tolerance of the Fe6Mn0.8Ce0.2Oy sorbent by timely supplementing the oxygen vacancies. H2O coexisting with SO2 in flue gas further reduces the mercury removal rate because of the competitive adsorption between H2O and mercury. Mercury is mainly adsorbed by MnO2 in the Fe6Mn0.8Ce0.2Oy sorbent by the Mars-Maessen mechanism, and SO2 in flue gas causes the generation of a small amount of Hg2SO4 and HgSO4.

Automated summary

The Ce-doped Fe6Mn0.8Ce0.2Oy magnetic sorbent exhibits good SO2 tolerance and can be used for the circulating removal of mercury in high-temperature flue gas. Ce protects Mn4+ active sites from SO2 poisoning, while O-2 helps supplement oxygen vacancies in a timely manner, enhancing the sorbent's tolerance.