Removal of elemental mercury from flue gas over a low-cost and magnetic sorbent derived from FeSO4-flocculated sludge and rice straw. (December 2022) - Li, Honghu
Abstract: Capture of elemental mercury (Hg 0 ) from coal combustion flue gas by sorbent injection is still associated with challenges, such as high-cost starting materials, difficulty in separation/reuse of sorbent and SO2 poisoning, in its large-scale application. This work highlighted a facile method to prepare a cost-effective and magnetically responsive mercury sorbent by pyrolysis of FeSO4 -flocculated sludge and rice straw. Fe3 O4, Fe2 O3 and short-chain polysulfide in the sorbent were proven to be the main active sites for Hg 0 adsorption/oxidation. Appropriate addition of rice straw into sludge boosted the development of porous structure of the sorbent, which facilitated the migration of Hg 0 onto the absorption sites. With straw/sludge mixing ratio of 1:1 and pyrolysis temperature of 700 °C, the obtained SR1 T7 exhibited good Hg 0 capture ability under harsh gas conditions (1000 ppm SO2 and 3% H2 O). At 125 °C, the Hg 0 adsorption capacity and average adsorption rate were estimated to be 9.63 mg/g and 1.96 × 10 −3 mg/(g⋅min), respectively. To extend its service life, the spent SR1 T7 could be collected by magnetic separation, followed by thermal regeneration. SR1 T7 might be a prospective alternative to traditional carbon-based mercury sorbent, due to its excellent Hg 0 capture ability, good recyclability, decent SO2 resistance and low cost. Graphical abstract: Image 1 Highlights: A cost-effective sorbent prepared from sewage sludge and rice straw was used for Hg 0 capture. Fe3 O4, Fe2 O3 and short-chain polysulfide were the main active sites for Hg 0 adsorption/oxidation. Rice straw addition boosted the development of porous structure of the sorbent. The sorbent showed excellent Hg 0 capture ability, good recyclability, decent SO2 resistance.