Elemental mercury (Hg0) removal over spinel LiMn2O4 from coal-fired flue gas

Spinel LiMn2O4 was prepared using a sol-gel method to investigate gaseous elemental mercury (Hg0) removal performance from coal-fired power plants. The physical and chemical characterization results indicated that LiMn2O4 had a basic MnO6 unit and Li ions in the spinel λ-MnO2 structure. LiMn2O4 exhibited better Hg0 removal performance than that of pure Mn2O3 and mixed oxides of Li2O-Mn2O3. Hg0 removal efficiency of LiMn2O4 was 93.09% (600 min reaction) at an optimum temperature of 150 °C. Higher temperature (>200 °C) was not favorable for Hg0 removal. O2 enhanced the Hg0 removal efficiency of LiMn2O4, while SO2 and H2O inhibited the reaction, and the co-existence of them had a poison effect on Hg0 removal. The primary Hg0 removal mechanism was chemical-adsorption, Hg0 was firstly catalytic oxidized to Hg2+ along with the reduction of high valance of Mn (Mn4+/Mn3+) to low valance (Mn3+/Mn2+). Hg2+ was combined with adsorbed oxygen and existed as Hg-O on LiMn2O4 surface. The existence of Li ions constructs a λ-MnO2 structure and benefits the oxidation process. Furthermore, based on the Hg-TPD results, the desorption activation energy was 58.82 kJ/mol.