Uptake of Elemental Mercury Vapors by Activated Carbons

Abstract

The adsorptive capacities of virgin and sulfur-impregnated activated carbons (GAC) for gas-phase mercury were evaluated as a function of temperature and influent mercury concentration. The virgin activated carbon showed little adsorptive capacity, especially at temperatures above 90 °C. The isothermal representation of the adsorptive capacity for virgin GAC exhibited a semi-logarithmic relationship at 50 °C, 90 °C, and 140 °C. The pronounced effect of temperature on the adsorptive capacity evidences a physical adsorption mechanism between the mercury and virgin GAC. Sulfur-impregnated activated carbons exhibited enhanced mercury removal efficiency over the non-impregnated varieties, due to formation of mercuric sulfide on the carbon surface. This chemisorption process is enhanced by increased temperatures between 25 °C and 90 °C, yielding increased removal efficiency of elemental mercury. However, at 140 °C a decrease in adsorptive capacity occurs, indicating reduced formation of mercuric sulfide. The method used for impregnating GAC with sulfur had a pronounced effect on mercury removal capacity. The chemical bonding of sulfur at 600 °C provides a more uniform distribution of sulfur throughout the GAC pore structure than is achieved by conventional condensation techniques, yielding improved performance.