Mercury Control and Mercury Stability in Byproducts - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 141

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FeCl 3 -AC Leaching

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H 2 OH 2 SO 4 FeCl 3 Na 2 CO 3 NaOH

TCLP

Different leaching methods

Fig. 5.37 The leaching results of AC(FeCl 3 -MZ)
The leaching results of AC(MnO 2 -MZ) are shown in Fig. 5.36. Evidently, the
average Hg concentrations in the leachates of H 2 O, 1% H 2 SO 4 , and TCLP were over
the safe limit of 25 μg/L. In addition, although the Hg concentrations in the
leachates of 1% FeCl 3 , 1% Na 2 CO 3 , and 1% NaOH were much lower than those in
the leachates of H 2 O, 1% H 2 SO 4 and TCLP, respectively, those values were still
much larger than the results shown in Fig. 5.35. According to these results, it
seemed that the Hg adsorbed on the surface of AC(MnO 2 -MZ) was not firm. The
average Hg concentration in each leachate for AC(FeCl 3 -MZ) was low except in the
1% H 2 SO 4 leachate (Fig. 5.37). However, all the leaching results of AC(FeCl 3 -MZ)
were still less than the safe limit. Considering both Fig. 5.36 and Fig. 5.37, the Hg
adsorbed by the oxidation treatment of ACs, especially by AC(MnO 2 -MZ), was not
stable in the acid solution environment. The concentrations of Hg were relatively
lower in the alkaline solution environment for both. Further research may be done
to clarify these facts.
All the conditions in the Hg adsorption experiments and the original Hg-laden
were the same for the three kinds of ACs. However, it was very clear that the
amounts of Hg that leached out from the AC(MnO 2 -MZ) were greater than those
from the other two kinds of ACs (Fig. 5.38). There was very little amount of Hg that
leached out from the AC(MZ) relative to the AC(MnO 2 -MZ) and the
AC(FeCl 3 -MZ). The oxidation treatment induced the differences in the stability of
mercury on ACs. In other words, the influences of the oxidized or acidic flue gas
components, such as O 2 , NO 2 , NO, SO 2 and HCl, can be omitted as compared with
that of the oxidation treatment on the stability of mercury on AC. It can be assumed
that the oxidation treatment changed the physical and chemical characteristics of
mercury on the surface of the ACs, or the adsorption affinity between the mercury
and the surface of ACs. These changes induced the instability of mercury in AC in
the solution environment.