UPTAKE OF ELEMENTAL MERCURY VAPORS BY ACTIVATED CARBONS

The adsorptive capacities of virgin and sulfur-impregnated activated c arbons (GAC) for gas-phase mercury were evaluated as a function of tem perature and influent mercury concentration. The virgin activated carb on showed little adsorptive capacity, especially at temperatures above 90 degrees C. The isothermal representation of the adsorptive capacit y for virgin GAC exhibited a semi-logarithmic relationship at 50 degre es C, 90 degrees C, and 140 degrees C. The pronounced effect of temper ature on the adsorptive capacity evidences a physical adsorption mecha nism between the mercury and virgin GAG. Sulfur-impregnated activated carbons exhibited enhanced mercury removal efficiency over the non-imp regnated varieties, due to formation of mercuric sulfide on the carbon surface. This chemisorption process is enhanced by increased temperat ures between 25 degrees C and 90 degrees C, yielding increased removal efficiency of elemental mercury. However, at 140 degrees C a decrease in adsorptive capacity occurs, indicating reduced formation of mercur ic sulfide. The method used for impregnating GAC with sulfur had a pro nounced effect on mercury removal capacity. The chemical bonding of su lfur at 600 degrees C provides a more uniform distribution of sulfur t hroughout the GAC pore structure than is achieved by conventional cond ensation techniques, yielding improved performance.