Adsorption and Stability of Mercury on Different Types of Impregnated Activated Carbon

A method for control of mercury emissions from combustion processes involves removal of elemental mercury from the flue gas by injection of activated carbon. The adsorption and stability of mercury was determined on a commercial activated carbon and two activated carbons that were impregnated with bromine and chlorine. The results of the adsorption experiments show Hg sorption capacities of bromine and chlorine impregnated activated carbon were higher than that of original activated carbon. After capture and disposal in a landfill, the stability of adsorbed mercury on activated carbon is very important for avoiding reemission. After loading with mercury using a static technique, the nature of the adsorbed mercury on activated carbons was characterized by sequential extraction experiment that was specifically optimized to distinguish clearly among the stable phases of mercury. This analysis revealed that mercury was found to be sequestered in two distinct forms - elemental mercury adsorption on the carbon surface and by formation of highly stable mercury compound. The predominant type of mercury capture depends on the type of activated carbon adsorbent used. In the sorbent that bromine-impregnated activated carbon BrIPAC, the mercury is present predominantly stable compound. In chlorine-impregnated activated carbon ClIPAC, at least 75% of the Hg was present in the elemental form, physically adsorbed or chemisorbed onto the carbon surface. In PAC, content of the two forms was closed.