Oxidative Adsorption of Elemental Mercury by Activated Carbon in Simulated Coal-Fired Flue Gas

Abstract

Bench-scale adsorption experiments were conducted to explore and verify the change of mercury speciation during elemental mercury (Hg0) adsorption by activated carbon (AC) impregnated with chlorine using a continuous mercury monitor. Results uniquely demonstrated that Hg0 was completely oxidized to divalent mercury (Hg2+) during the adsorption process of Hg0 by AC whether in N2 gas or in simulated coal-fired flue gas. Without the presence of a chemical oxidizing element, such as chlorine, on the surface of the sorbent, AC would not adsorb Hg0 in N2 gas. When the oxidizing element was consumed, the breakthrough of Hg0 adsorption by AC occurred. Hg0 was detected as the only Hg species at the outlet of the adsorption bed. However, the adsorption of Hg0 by AC did not reach its full capacity. When the adsorption atmosphere was switched from N2 gas to simulated flue gas, AC started to absorb Hg0 again. When the AC reached its full capacity for Hg0, oxidation of Hg0 continued, because when breakthrough occurred, Hg2+ was detected at the reactor outlet. However, the oxidation of Hg0 was not due to chlorine on the surface of AC but the components in simulated flue gas, such as NO, NO2, HCl, etc., which catalyzed oxidation of Hg0 on the AC surface.