pH-value. Thus, major shifts in chemical equilibrium and subsequent
reactions of Hg(II) complexes are expected during the alkalization
process of FGD waste water. Ligand exchange reactions of
Hg(II) are generally considered as very fast reactions, their reaction
rates are usually close to the diffusion controlled limit [23].
The actual Cl concentration in FGD waste water resulting from
the combustion of various coals is reported to be as high as
0.84 mol/l [11,24]. For pH 9, which represents the maximum of
the pH-range of the experimental runs, the impact of total Cl concentration
on the speciation of Hg(II) compounds is presented in
Fig. 3. It can be concluded, that for high Cl concentration, the predominant
Hg(II) compound is shifted to [HgCl4]
2, whereas the
share of Hg(II) complexes with OH ligands decreases. This is in
good agreement with calculations in [25]