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

The impacts of O-2, HCl, SO2, and NO existing in simulated coal-combustion flue gases on Hg-0 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 N-2. The effectiveness of enhancing Hg-0 adsorption capacity for these components, in a declining order, was NO, HCl, O-2, and SO2. When two acidic/oxidizing gas components were present in the baseline gases, especially when NO coexisted, sulfur-impregnated activated carbon had increasing Hg-0 adsorption capacities compared to that obtained at the baseline condition. In contrast, the presence of SO2 with O-2 had deteriorating effects on Hg-0 adsorption. The reduction in Hg-0 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/O-2/HCl/NO gas resulted in the largest Hg-0 adsorption capacity. Full factorial analysis further suggested that NO possessed the greatest effects on enhancing the Hg-0 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. (C) 2012 Elsevier Ltd. All rights reserved.