Removal of elemental mercury using magnetic Fe-containing carbon prepared from sludge flocculated with ferrous sulfate by zinc chloride activation

Abstract

In this work, sewage sludge flocculated with ferrous sulfate (SFS) was treated by one-step pyrolysis and ZnCl2 activation to obtain magnetic Fe-containing carbon, which was used to remove elemental mercury (Hg0) from flue gas. When 30% ZnCl2 was added to SFS (names as SFS-30), sulfides, chloride, magnetic FexOy, as well as a suitable BET surface area were produced during pyrolysis. SFS-30 showed a maximum mercury removal efficiency of 96.1%. The presence of O2 and a low SO2 concentration enhanced Hg0 removal, while H2O vapor and a high concentration of SO2 inhibited it. The addition of ZnCl2 increased the BET surface area as well as the conversion of sulfate to sulfide, which were both beneficial for Hg0 removal. In addition, the generated magnetism during the pyrolysis process assisted in the recovery and utilization of SFS-30 in flue gas. After being magnetically separated from a mixture with fly ash, spent SFS-30 was thermally regenerated and recycled. After 8 Hg0 capture and regeneration cycles, the removal efficiency was not notably degraded, demonstrating that SFS-30 prepared by one-step pyrolysis with ZnCl2 activation can be used for Hg0 removal. The results of this study have guiding significance for practical engineering applications of this material.