Geoscience Reference
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140
120
100
80
60
40
0.00
0.02
0.04 0.06
Humic acid conc (%)
0.08
0.10
0.12
Fig. 6.5 Effect of humic substances in an aqueous solution on the dissolution of kerosene (Dror
et al. 2000a )
The solubility of nonaqueous phase liquids in distilled water may be regarded
as an unambiguous physical constant, whereas the apparent enhanced solubility
might be due to the presence of naturally occurring organic macromolecules in
subsurface solutions. Such macromolecules, including humic and fulvic sub-
stances, and negatively charged polysaccharides may increase the dissolution of
organic contaminants in the subsurface aqueous solution. All the organic mole-
cules that are constituents in subsurface organic matter and may be dissolved in the
subsurface water are referred to as dissolved organic matter (DOM). Solubility in
water in the presence of DOM is given by the relation
C sat ; DOM ¼ C sat ð 1 þ ½DOM K DOM Þ;
ð 6 : 10 Þ
where C sat,DOM and C sat are the saturated concentrations of the organic compound
measured in the presence and absence of DOM, respectively; [DOM] denotes
concentration of DOM in water (kg/L); and K DOM is the DOM-water partition
coefficient. Note that the intrinsic solubility of the compound is not affected.
As mentioned previously, the physical state of a solute is susceptible to mod-
ifications by interaction with cosolvents. In principle, a cosolvent can enhance
solute solubility by changing the solvency of the medium, by direct solute inter-
action, by adsorption, or by partitioning (Chiou et al. 1986 ). In a batch experiment
testing the effect of humic acid on kerosene dissolution in an aqueous solution,
Dror et al. ( 2000a ) found a linear correlation between the amount of humic acid
and the amount of kerosene that dissolved (Fig. 6.5 ).
The enhancement of kerosene dissolution occurs even at low humic acid con-
tent in the aqueous solution. In view of the fact that humic substances are rela-
tively high molecular weight species containing nonpolar organic moieties, Chiou
et al. ( 1986 ) assumed that a partition-like interaction between a solute of very low
 
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