Geoscience Reference
In-Depth Information
Table 6.2 The effect of various CMOS on the activity coefficient, c or mole fraction solubility of
naphthalene, for two different solvent-water ratios, f v,solv (Schwarzenbach et al. 2003 )
Cosolvent
Structure
Solubility parameter
(MPa) 1/2
Naphthalene
c sat
iw = c sat
il ¼ x sat
il = x sat
iw
f v ; solv
ð r c
i Þ
¼ 0 : 2
f v ; solv ¼ 0 : 4
Glycerol
36.2
2.5 (2.0)
5.5
Ethylene glycol
HOCH 2 -CH 2 OH
34.9
3 (2.4)
9
Methanol
CH 3 OH
29.7
3.5 (2.7)
14
Dimethylsulfoxide
(DMSO)
26.7
5.5 (3.7)
3.6
Ethanol
H 3 CCH 2 OH
26.1
7 (4.2)
48
Propanol
H 3 CCH 2 CH 2 OH
24.9
17 (6.2)
180
Acetonitrile
H 3 C-C=N
24.8
14 (5.7)
140
Dimethylformamide
24.8
15 (5.9)
130
1,4-Dioxane
20.7
14 (5.7)
180
Acetone
19.7
20 (6.5)
270
amount of the cosolvent. In general, cosolvents can completely change the sol-
vation properties of subsurface water; the solubility of hydrophobic organic con-
taminants increases exponentially as the cosolvent fraction increases. The extent of
solubility enhancement is controlled by the types of cosolvent and solute.
An increase in solubilization of nonpolar organic chemicals in water is obtained
when surfactants are present in the water solution, the solvating strength of sur-
factants being much greater than that of simple cosolvents. This situation may
occur, for example, during effluent disposal on land surface, sewage water irri-
gation, or point disposal of municipal wastes. The structure of a surfactant solu-
tion, above a rather well-defined critical micelle concentration (denoted CMC), is
that of an ultrafine emulsion. The surfactant molecules are aggregated forming a
cluster of 20-200 units or more. The hydrophobic tails are oriented to the interior
of the cluster, and the hydrophilic heads are oriented to the exterior in contact with
the water phase. The total solvent strength is determined by the number of
micelles, their size, and their structure, but it is not proportional to surfactant
concentration.
This type of dissolving action has been called solubilization, despite the fact
that it does not correspond to the mechanism involved. Hartley and Graham-Bryce
( 1980 ) showed that the solubility of a crystalline solute of low water solubility
cannot increase continuously with the expansion of the micelle. The limitation
comes from the fact that the micelle cannot increase indefinitely in size without
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