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]
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