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

Abstract

A Ce-doped Fe–Mn magnetic sorbent (Fe₆Mn₀.₈Ce₀.₂Oy) was developed using the coprecipitation method. The effects of O₂, 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 SO₂ will preferentially react with CeO₂ instead of MnO₂ to form Ce₂(SO₄)₃. O₂ 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.