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

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 Cabased 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 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 degrees 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.