Environmental Engineering Reference
In-Depth Information
Figure 6.30
Solubility of NiO in fused Na
2
SO
4
at 1200 K [57].
details in Sec. 6.7.4. These terminologies are the commonly accepted nomencla-
ture in describing oxyanion salts in terms of acid-base equilibria. In such sys-
tems, the O
2
ions have the same role as that of the hydroxide ion in aqueous
solutions:
Base
acid
O
2
(6.34)
Sodium sulfate may be considered to consist of a basic component, Na
2
O (or O
2
ions) and an acid component, SO
3
. In liquid sodium sulfate deposit, the sulfate ion
decomposes according to
1
2
O
2
(g)
SO
4
2
SO
2
(g)
O
2
(6.35)
So a Na
2
SO
4
melt is composed of an oxygen ion or Na
2
O, whose activity is
defined by the oxygen and SO
2
potentials. When the oxygen ion concentration
of the melt is low compared to the value required for maintaining equilibrium
in the dissociation reaction of the metal oxide according to
NiO s Ni
2
O
2
(6.36)
