Activated carbon based sorbents are the most widely tested sorbents for mercury removal in coal-fired power plants. A major problem in mercury removal is the limited understanding of the mechanism associated with heterogeneous elemental mercury oxidation and subsequent adsorption. The current work involves the investigation of the possible binding mechanism of mercury on chemically-impregnated powder and fiber activated carbon sorbents through experimental characterization techniques such as X-ray Photoelectron Spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy.
Experiments are conducted using a bench-scale packed-bed system. As a first step only elemental Hg vapor and air is injected onto activated carbon to isolate the chemistry of elemental mercury with the carbon surface. Hg-adsorbed carbon samples are investigated to identify the possible binding mechanism of mercury on activated carbon sorbents using X-ray spectroscopy. Through XPS surface characterization of brominated activated carbon sorbent, it was found that elemental mercury primarily binds to surface as oxidized mercury in the form of either HgO or HgBr2 . However the identification of the exact oxidation state of Hg on these samples could not be determined.
Flue gas components such as SO2, NOx, H2O, and HCl are known to have effects on mercury oxidation and subsequent adsorption. Experiments are also conducted in a simulated flue gas to determine the interaction of halogen species with the carbon sorbent. Methane will be combusted in a laminar flow tubular burner and mixed with mercury and chlorine to simulate the flue gas environment. Additional flue gas species will be introduced to the reactor system to understand the effect of individual flue gas species on mercury adsorption and oxidation. Mercury adsorbed samples will be characterized using XPS and XAFS to elucidate mercury sorption mechanism and its chemical state.