Removal of elemental mercury by iodine-modified rice husk ash sorbents

Abstract

Iodine-modified calcium-based rice husk ash sorbents (I 2/CaO/RHA) were synthesized and characterized by X-ray diffraction, X-ray fluorescence, and N 2 isotherm adsorption/desorption. Adsorption experiments of vapor-phase elemental mercury (Hg 0) were performed in a laboratory-scale fixed-bed reactor. I 2/CaO/RHA performances on Hg 0 adsorption were compared with those of modified Ca-based fly ash sorbents (I 2/CaO/FA) and modified fly ash sorbents (I 2/FA). Effects of oxidant loading, supports, pore size distribution, iodine impregnation modes, and temperature were investigated as well to understand the mechanism in capturing Hg 0. The modified sorbents exhibited reasonable efficiency for Hg 0 removal under simulated flue gas. The surface area, pore size distribution, and iodine impregnation modes of the sorbents did not produce a strong effect on Hg 0 capture efficiency, while fair correlation was observed between Hg 0 uptake capacity and iodine concentration. Therefore, the content of I 2 impregnated on the sorbents was identified as the most important factor influencing the capacity of these sorbents for Hg 0 uptake. Increasing temperature in the range of 80–140°C caused a rise in Hg 0 removal. A reaction mechanism that may explain the experimental results was presumed based on the characterizations and adsorption study.