Elemental Mercury Capture from Flue Gas by Magnetic Mn–Fe Spinel: Effect of Chemical Heterogeneity

A stoichiometric nanosized Mn–Fe spinel (Fe 2.2 Mn 0.8 O 4 ) was synthesized using a coprecipitation method. After the thermal treatment at 400 °C under air, chemical heterogeneity deriving from the oxidation kinetic difference between Fe 2+ and Mn 2+ /Mn 3+ was observed in (Fe 2.2 Mn 0.8 ) 1-δ O 4 . XPS and TEM analyses both pointed a Mn enrichment (especially Mn 4+ cation) on the particle’s surface. Furthermore, the percent of cation vacancy on the surface increased obviously due to the enrichment of Mn 4+ cation on the surface. As a result, the capacity of (Fe 2.2 Mn 0.8 ) 1-δ O 4 -400 for elemental mercury capture was generally much better than those of MnO x /γ-Fe 2 O 3, (Fe 2.2 Mn 0.8 ) 1-δ O 4 -200 and Fe 2.2 Mn 0.8 O 4 . Furthermore, the saturation magnetization of (Fe 2.2 Mn 0.8 ) 1-δ O 4 obviously increased after the thermal treatment under air at 400 °C, which made it easier to separate the sorbent and adsorbed mercury from the fly ash for recycling, regeneration, and safe disposal of the adsorbed mercury. Therefore, (Fe 2.2 Mn 0.8 ) 1-δ O 4 -400 may be a promising sorbent for elemental mercury capture.