Surface sulfidation modification of magnetospheres from fly ash for elemental mercury removal from coal combustion flue gas

Reduction of elemental mercury (Hg-0) emission from coal-fired power plants is an enormous challenge. In this work, magnetospheres separated from fly ash was modified through H2S as an efficient sorbent (i.e., S-MS) for Hg-0. Elemental sulfur with high affinity towards Hg-0 was formed on the S-MS surface through selective catalytic oxidation of H2S. The sulfidation temperature played an important role in Hg-0 adsorption over S-MS, ascribing to the variation of sulfur species on S-MS. The S-MS exhibited above 80% Hg-0 adsorption efficiency with a sulfidation temperature of 150 degrees C for 30 min. The optimal Hg-0 adsorption performance was obtained at 50 and 75 degrees C, implying that the S-MS could be adopted by injecting into the duct upstream of wet electrostatic precipitator (WESP) system. The gaseous Hg-0 was immobilized by S-MS as stable mercury sulfide (HgS) owing to the presence of abundant sulfur species that is active for binding Hg-0. The leaching ratio of mercury from spent S-MS in WESP effluent was as low as 1%, hence minimizing the secondary mercury pollution from the industrial waste. The cost analysis demonstrates that the mercury removal technology on the basis of magnetospheres adsorbents exhibited much superiority in operation cost compared with commercial activated carbon injection technology. Thus, the S-MS, with specific features, such as high Hg-0 adsorption performance, minimized environmental hazardous and recyclability, displayed great potential in Hg-0 sequestration.

Automated summary

This research proposes a method to reduce elemental mercury emission from coal-fired power plants by modifying magnetospheres with H2S as a sorbent. The modified magnetospheres show high affinity towards Hg-0 and can achieve over 80% adsorption efficiency. The technology has low cost, high recyclability, and minimal impact on environmental mercury pollution.