Environmental Engineering Reference
In-Depth Information
8.3.2.2.1. Solubility
Salt solubility is extremely diverse (see Table 8.6). When a solution containing
cations and anions evaporates, salts with the lower solubility will precipitate first.
Q-equilibrium relative
humidity % at 20°C
and 25°C
Solubility in g/100 cm
3
cold water
T°C
(hot water
T°C
)
Salt
279
0
− (536
20
)
Antarcticite, CaCl
2
.6H
2
O
30.8 − 28.6
Arcanite, K
2
SO
4
12
25
− (24.1
100
)
97.6 − 97.3
Bischofite, MgCl
2
.6H
2
O
167 − (367)
33.1 − 32.8
71
20
− (91
40
)
Epsomite, MgSO
4
.7H
2
O
90.1 − 88.3
0.241
0
− (0.222
100
)
Gypsum, CaSO
4
.2H
2
O
> 95
35.7
0
− (39.12
100
)
Halite, NaCl
75.3 − 75.1
Mirabilite, Na
2
SO
4
.10H
2
O
11
0
− (92.7
30
)
93.6 − 91.4
21.52 − (421
54
)
Natron, Na
2
CO
3
.10H2O
97.9 − 88.2
13.3
0
− (247
100
)
Potassium nitrate, KNO
3
94.6 − 93.6
92.129 − (180
100
)
Sodium nitrate, NaNO
3
75.4 − 74.3
Nitrocalcite, Ca(NO
3
)
2
.4H
2
O
266
0
− (660
80
)
53.6 − 50.5
Sylvite, KCl
23.8
20
− (56.7
100
)
85.1 − 84.3
Table 8.6.
Solubility and relative humidity equilibrium of salts at
different temperatures [ARN 89, WEA 80]
The sequential precipitation of salts from sea water gives a good example of such
a property (see Table 8.7).
Precipitation order
Name
Chemical formula
1
Calcite
CaCO
3
2
Dolomite
CaMg(CO
3
)
2
3
Gypsum
CaSO
4
2H
2
O
4
Anhydrite
CaSO
4
5
Halite
NaCl
6
Carnallite
KMgCl
3
.6H
2
O
7
Sylvite
KCl
Table 8.7.
Precipitation sequence of salts during sea water evaporation [FOU 80]