Removal of elemental Mercury from flue gas using wheat straw chars modified by K₂FeO₄ reagent

In this article, wheat straw (WS) char, a common agricultural waste and renewable biomass, was pyrolyzed and then modified by K₂FeO₄ reagent to develop an efficient sorbent for removal of Hg⁰ from flue gas. Brunauer-Emmett-Teller, scanning electron microscopy with energy spectrum and X-ray diffraction (XRD) were employed to characterize the sorbents. The effects of K₂FeO₄ loading, reaction temperature, Hg⁰ inlet concentration and concentrations of gas mixtures O₂, NO and SO₂ in flue gas on Hg⁰ removal were investigated in a fixed-bed reactor. The results show that K₂FeO₄-impregnation can improve pore structure of WS char and produce new active sites, which significantly enhance Hg⁰ removal. Increasing Hg⁰ inlet concentration significantly decreases Hg⁰ removal efficiency. O₂ in flue gas promotes Hg⁰ oxidation by replenishing the oxygen groups on the surface of modified chars. The presence of NO obviously promotes Hg⁰ removal since it can oxidize Hg⁰ to Hg(NO₃)₂. SO₂ in flue gas significantly decreases Hg⁰ removal efficiency due to the competition adsorption between SO₂ and Hg⁰. The increase in reaction temperature has a dual impact on Hg⁰ removal.