Page 192 - Partition & Adsorption of Organic Contaminants in Environmental Systems

SORPTION FROM WATER SOLUTION 183

TABLE 7.18. Composition and Properties of Commercial Petroleum Sulfonate
Surfactants
Composition/Property Petronate L Petronate HL Pyronate 40
Percent petroleum sulfonate 62 62 41
Fraction as hydrocarbon 46.9 48.0 28.6
15.1 14.0 12.4
Fraction as -NaSO 3
Percent free mineral oil 33.0 32.5 12.0
Percent inorganic salts 0.5 0.5 8.5
Percent water 4.5 4.5 38.5
Percent total hydrocarbon 83.7 84.3 66.0
(water-free basis) a
MW of petroleum sulfonate 415–430 440–470 330–350
Source: Data from Kile et al. (1990).
a Sum of hydrocarbons in petroleum sulfonate and free mineral oil on a moisture-free basis.

factants because of their abilities to reduce the surface tension of water, they
exhibit virtually no monomer–micelle transitions (i.e., no CMCs), and hence
possess a separate-phase property even at very low concentrations. An
example of emulsion-forming commercial products is the class of petroleum
sulfonate–oil (PSO) surfactants, formulated by mixing free mineral oil with
surface-active petroleum sulfonate in certain proportions, as shown in Table
7.18. The solute solubility enhancement in water by microemulsions can be
described in a form similar to Eq. (7.27) as

(7.28)
S* S w = 1 + X emK em
w
where X em is the concentration of microemulsion in water (dimensionless) and
K em is the solute partition coefficient between the emulsified phase and water.
Thus a plot of S* versus X em for a solute should produce a single straight line
w
with a slope of S w K em , which is characteristically different from the plot with
a normal surfactant. The measured K em values for DDT and TCB with PSO
microemulsions have about the same magnitude as the K mc values, confirming
the separate-phase property of microemulsions (Kile et al., 1990). In com-
parison with normal surfactants, however, the emulsified oil phase enhances
the solute solubility at low concentrations more effectively than do normal
surfactants at concentrations below their CMC values. In natural water, the
possible formation of an emulsified oil phase from components of untreated
organic wastes near waste-discharge sites could have a strong impact on the
fate of certain organic pollutants.
The strong enhancement of the solute solubility by surfactants offers a
potential means of remediating contaminated soils or natural solids by appli-
cation of surfactant solutions. If the solution of a normal surfactant (or a
microemulsion) is applied to remove contaminants in soil that exist as a
separate nonaqueous-phase liquid (NAPL), the efficiency of the NAPL