Effect of Sulfur Impregnation Method on Activated Carbon Uptake of Gas-Phase Mercury

Abstract

The dynamics of granular activated carbon (GAC) adsorbers for the uptake of gas-phase mercury was evaluated as a function of temperature, influent mercury concentration, and empty bed contact time. Sulfur-impregnated carbons exhibited enhanced mercury removal efficiency over virgin carbon due to the formation of mercuric sulfide on the carbon surface. The effect of the sulfur impregnation method on mercury removal efficiency was examined through experi ments conducted on commercially available sulfur-impregnated carbon (HGR) and carbon impregnated with sulfur in our laboratory (BPL-S). Although HGR and BPL-S possess similar sulfur contents, BPL-S is impregnated at a higher temperature, which promotes a more uniform distribution of sulfur in the GAC pore structure. At low influent mercury concentrations and low temperatures, HGR and BPL-S performed similarly in the removal of mercury gas. However, as the temperature was increased above the melting point of sulfur, the performance of HGR deteriorated significantly, while the performance of BPL-S slightly improved. At high influent mercury concentrations, HGR performed better than BPL-S, regardless of temperature. For both HGR and BPL-S, the observed dynamic mercury adsorptive capacities were far below the capacities predicted by the stoichiometry of mercuric sulfide formation. In HGR carbon the sulfur is very accessible, but ag glomeration that occurs at high temperatures causes the sulfur to be relatively unreactive. In BPL-S carbon, on the other hand, the sulfur remains in a highly reactive form, but its location deep in the internal pores makes it relatively inaccessible and prone to blockage by HgS formation.