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 degrees 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-delta)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-delta)O(4)-400 for elemental mercury capture was generally much better than those of MnO(x)/gamma-Fe(2)O(3), (Fe(2.2)Mn(0.8))(1-delta)O(4)-200 and Fe(2.2)Mn(0.8)O(4). Furthermore, the saturation magnetization of (Fe(2.2)Mn(0.8))(1-delta)O(4) obviously increased after the thermal treatment under air at 400 degrees 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-delta)O(4)-400 may be a promising sorbent for elemental mercury capture.