Influences of acidic/oxidizing gases on elemental mercury adsorption equilibrium and kinetics of sulfur-impregnated activated carbon

Abstract

The impacts of O2, HCl, SO2, and NO existing in simulated coal-combustion flue gases on Hg0 adsorption equilibrium and kinetics of sulfur-impregnated activated carbon were evaluated. The adsorption capacities increased when one acidic/oxidizing gas component coexisted with the baseline components, including CO2, H2O, and N2. The effectiveness of enhancing Hg0 adsorption capacity for these components, in a declining order, was NO, HCl, O2, and SO2. When two acidic/oxidizing gas components were present in the baseline gases, especially when NO coexisted, sulfur-impregnated activated carbon had increasing Hg0 adsorption capacities compared to that obtained at the baseline condition. In contrast, the presence of SO2 with O2 had deteriorating effects on Hg0 adsorption. The reduction in Hg0 adsorption capacity may be attributed to the formation of SO3 known to compete for adsorption sites. When the flue gas contained at least three acidic/oxidizing components, the baseline/O2/HCl/NO gas resulted in the largest Hg0 adsorption capacity. Full factorial analysis further suggested that NO possessed the greatest effects on enhancing the Hg0 adsorption capacity in the simulated coal-combustion flue gases. Kinetic results also showed that sulfur-impregnated activated carbon with a larger equilibrium adsorption capacity under a given gas condition in general possessed poor adsorption kinetics.