Removal of elemental mercury from flue gas using the magnetic Fe-containing carbon prepared from the sludge flocculated with ferrous sulfate.

The sewage sludge flocculated with ferrous sulfate (SFS) was prepared by one-step pyrolysis to obtain magnetic Fe-containing carbon. Results showed that only a small amount of FexOy as well as extremely weak magnetism were observed at pyrolysis temperatures of less than 500 °C. SFS tended to exhibit intensive agglomeration, leading to the drastic increase of the crystalline-phase particle size at high pyrolysis temperature. The optimal pyrolysis temperature is 700 °C, corresponding to the production of some sulfides, an optimal content of FexOy, and a suitable BET surface. Hg0 removal efficiency of SFS700 (SFS pyrolyzed at 700 °C) reached 80.7% at the reaction temperature of 125 °C. The presence of O2 and low concentration of SO2 enhanced the Hg0 removal, while the H2O vapor and high SO2 concentration inhibited it. Meanwhile, good resistance for the adsorbent to moderate concentrations of SO2 and H2O was observed. Moreover, the good magnetism performance is conducive to the recovery and utilization of the SFS700 in flue gas. Therefore, SFS can be used for Hg0 removal without any chemical modification after undergoing one-step pyrolysis and this study has guiding significance for the resource utilization and engineering practices.