Activated carbons from two precursors (coal and coconut shell) were used to produce low-concentration (i.e., ppb level) mercury adsorbents with various physical and chemical properties via gas- and liquid-phase sulfur impregnation. The goal is to achieve a full-scale production of mercury adsorbents. Results showed that sulfur impregnation altered the physical properties of activated carbons. Sulfur impregnation assembled chemical activation, which created new porous structure as well as sulfur doping. When the impregnation process was scaled-up, gas-phase sulfur impregnation significantly blocked the porous structure, indicating that sulfur impregnation simultaneously causes the pore opening and blocking. Liquid-phase impregnation did not act as activation, the resulting surface area and pore volume thus decreased as the sulfur amount increased, which was more significant in full-scale samples. Mercury adsorption capacity was proportional to the sulfur content of resulting samples, however, with an insignificant correlation. This result suggests that other factors, beside sulfur content, controls the adsorption behaviors as well. The full-scale carbon products had an adsorption capacity > 1000 μg/g. Further study should be focused on evaluating the relationship between surface functional groups, physical properties, and mercury adsorption capacity. The adsorption mechanism of mercury onto the activated carbon surface may be depicted, which may help to improve the current production protocols.

Mercury, adsorbent, impregnation