Removal of elemental mercury by bio-chars derived from seaweed impregnated with potassium iodine

Abstract

Two kinds of bio-chars derived from seaweed, such as sargassum and enteromorpha, are modified by halides impregnation. The modified bio-chars are used to capture Hg0 from simulated flue gas. The physical and chemical properties of the samples are investigated by various characterization technologies, including proximate and ultimate analysis, Brunauer-Emmett-Teller (BET), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The effects of different types of halides impregnation, halide loading values, individual flue gas component and adsorption temperature on removal of Hg0 over adsorbents were studied. The mechanism and kinetics of Hg0 removal were also studied. The results show that potassium iodide modified bio-chars have better Hg0 adsorption performance than bio-chars modified by potassium chloride and potassium bromide. The optimal potassium iodide loading value is 3 wt%. As the reaction temperature increases, Hg0 removal efficiency significantly increases. O2 promotes the Hg0 removal. Addition of SO2 inhibits Hg0 removal over enteromorpha-chars, and shows a double impact on Hg0 removal over sargassum-chars. Low concentrations of NO and H2O are beneficial to Hg0 removal, whereas high concentrations of NO and H2O inhibit Hg0 removal. Chemisorption is found to be the main control factor for Hg0 adsorption at 120 °C and 160 °C based on kinetic simulation analysis. The covalent groups (C-I) and the chemisorbed oxygen and/or weakly bonded oxygen species participate in the Hg0 removal process and are the dominant chemical adsorption sites on the suface of the iodide modified seaweed bio-chars.