Mercury Control and Mercury Stability in Byproducts - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 112

5) Dipping treatment of FeCl 3 ;
6) Sulphurization with different temperature.
The mercury adsorption abilities of modified fly ash, modified zeolite, modified
bentonite, and modified vermiculite are discussed below.

5.3.2.1 Hg 0 Adsorption Ability of Modified Fly Ash

In order to improve Hg 0 adsorption ability, various methods were used to modify fly
ash. The experiments showed that the Hg 0 adsorption ability of modified fly ash
remained at the same level as that of regular fly ash. The main reason for this was
that the carbon-in-ash was lower; hence, modification did not change the physical
surface structure of fly ash.

5.3.2.2 Hg 0 Adsorption Ability of Modified Zeolite

After modification, there was some improvement in the Hg 0 adsorption ability of
zeolite. The zeolite treated by dipping into active MnO 2 had the best Hg 0 adsorption
ability (as shown in Fig. 5.11) among all modified zeolites. The time for 100%
mercury breakthrough increased significantly, extending the effective absorption
time and improving the Hg 0 adsorption ability of zeolite.

120

100

80

60

40

Treated zeolite
Zeolite

20

0

0 20 40 60 80 100 120 140 160

Time (min)

Fig. 5.11 Hg 0 adsorption ability of zeolite treated by dipping of active MnO 2

The zeolite treated by dipping into active MnO 2 had a strong Hg 0 adsorption
ability, which can be attributed to several factors including: (1) Mn had multiva-
lence as a cation; (2) valence transformation of Mn ions was easier, hence the
number of valence Mn ions was reduced more easily than that by mercury; (3) the
adsorption product had a catalytic action, which accelerated Hg 0 adsorption of
modified zeolite; and (4) active MnO 2 was widely distributed on the surface of
zeolite, which enhanced the contact probability of Hg 0 and Mn.