The sorption of mercury, as Hg-0 and HgCl2, in a synthetic flue gas (SFG) b
y three activated carbons has been examined by XAFS spectroscopy. The three
carbons consisted of a sulfur-activated carbon, an iodine-activated carbon
, and an activated carbon derived from lignite. In addition to mercury, the
occurrence and behavior of sulfur, chlorine, calcium, and iodine were also
examined by XAFS spectroscopy. These other elements were present either as
activating species on the carbons or as reactive components (SO2, HCl) in
the SFG. The XAFS results showed that each type of activated carbon behaves
differently with respect to sorption of mercury and other species from the
SFG. For the iodine- and sulfur-activated carbons, the XAFS data confirm t
hat it is the activating element (I or S) that forms a sorption complex wit
h mercury. However, the activated carbon from lignite exhibited a more vari
able behavior that reflected the conditions of the experiments, in particul
ar whether HCl or HgCl2 was present in the SFG. This study reveals some of
the complexities that are involved in low-temperature sorption of mercury b
y activated carbons in that the sorption mechanism clearly involves acidic
species of sulfur and chlorine in the gas phase, the affinity of the carbon
for such species, and the nature of the active sites on the carbons, in ad
dition to the mercury speciation.