Geoscience Reference
In-Depth Information
Table 13.1
Principal salts of soils and waters (Al Droubi
et al.
1976; Gueddari
1984; Rieu
et al
. 1998; Mees and Singer 2006).
Mineral
Nature/Occurrence
Mineral
Nature/Occurrence
Anhydrite
CaSO
4
(salt mine)
Kainite
MgSO
4
,
KCl
,3
H
2
O
(K deposits)
Bassanite
CaSO
4
,0.5
H
2
O
Kieserite
MgSO
4
,
H
2
O (waters from
(plaster of Paris)
the oceans)
Bischofite
MgCl
2
,6
H
2
O
(K mines)
Leonite
K
2
SO
4
,
MgSO
4
,4
H
2
O
(K mines)
Calcite
CaCO
3
(rocks)
Mirabilite
Na
2
SO
4
,10
H
2
O
(saline lakes)
Dolomite
CaMg
(
CO
3
)
2
(rocks)
Natron
Na
2
CO
3
,10
H
2
O
(soda lakes)
Epsomite
MgSO
4
,7
H
2
O
Picromerite
K
2
SO
4
,
MgSO
4
,6
H
2
O
(salt
(salt lakes)
deposits from oceans)
Eugsterite
Na
4
Ca
(
SO
4
)
3
,2
H
2
O
(lakes) Sylvinite
KCl
Gaylussite
Na
2
Ca
(
CO
3
)
2
,5
H
2
O
Thenardite
Na
2
SO
4
(salt lakes)
(alkali lakes)
Gypsum
CaSO
4
,2
H
2
O
(soils,
Thermonatrite
Na
2
CO
3
,
H
2
O
(salt lakes)
deposits)
Halite
NaCl
Trona
Na
2
CO
3
,NaHCO
3
,2
H
2
O
(salt lakes)
Hexahydrite
MgSO
4
,6
H
2
O
(some rivers)
On a first analysis, it seems that the least soluble salts must precipitate
first. This leads to simplified schemes such as that in Fig. 13.11.
The hygroscopic encrustation absorbs moisture from the air during
the night and is dark by morning. It gets dehydrated and lightened
in colour during the day (CaCl
2
is used in some dehumidifiers). The
white crust, when rich in mirabilite crystallized in the form of needles,
shatters the soil aggregates that become powdery (powdery crust). The
black crust, very alkaline, dissolves organic matter, whence its colour.
Modelling
The diagram in Fig. 13.11 reveals important facts:
Discussion
Mainly, the concentration process leads to precipitation in the
following order: calcium carbonate more or less contaminated
with magnesium and additional dolomite, then gypsum,
followed by sodium chloride and lastly, salts of potassium and
magnesium.
According to the proportion of various ions at the start, the pH of
the residual bittern can change very variably and this is one of the
