Mercury Control and Mercury Stability in Byproducts - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 146

Based on the results, ZS-MnO 2 , PT-MnO 2 , FS-MnO 2 , and ZS-FeCl 3 were found
to be applicable for use in the future because of their better adsorption efficiencies,
lower costs and easier modified operation.
The adsorption of Hg 0 by AC proceeded through the chemical adsorption
process either in N 2 gas or in simulated flue gas. In addition, Hg 0 was oxidized to
HgCl 2 by the Cl element that remained on a carbon surface and adsorbed by AC in
N 2 gas. Thus, chemical modification enhanced the Hg adsorption of AC in certain
flue gas environments. The Cl element was consumed as adsorption proceeded, AC
then lost the ability to adsorb Hg 0 through chemical oxidization, and a breakthrough
occurred as Hg 0 was measured at the outlet of the reactor. However, the adsorption
of Hg 0 by AC did not reach its full capacity. When the gas flow was switched from
N 2 to the simulated gas compounds one by one, the AC resumed its absorption of
Hg 0 . The oxidation factor of Hg 0 was not the Cl element in AC, but the components
in the simulated flue gas, such as NO, NO 2 , HCl, etc., with the help of carbon on the
AC surface. When the adsorption capacity of AC for Hg 0 reached its full capacity,
Hg 0 oxidation continued, and the breakthrough occurred when Hg 2+ was detected at
the reactor outlet.
Mercury appeared to be stable in untreated AC according to leaching tests.
Thus, when using oxidation treatment to enhance the mercury sorption capacity of
sorbents, it is very important to consider first the stability of mercury on the surface
of sorbents. As the temperature increases, more mercury is released from the control
products of AC and gypsum. Furthermore, it is not a good idea to place mer-
cury-contaminated AC and gypsum under direct sunlight for long periods of time
and in high-temperature environments. Finally, Hg was found to be stable on actual
fly ash and AC in a natural storage environment.

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