Reduction of Contaminants in Soil and Water By Direct Electric Current - Electrokinetics for Petroleum and Environmental Engineers - page 54

1.4

Average linear fit to test data in soil; y=0.93+0.01x

1.0 0.6[Fe]/[Cr]

3[Fe]/[Cr]
5[Fe]/[Cr]
11[Fe]/[Cr]

0.37V

0.6

0.2

-0.2 0

-20 -40 -60 -80 -100

Nernst equation prediction for an aqueous system: y=0.56+0.01x

-0.6

Log({[Cr 2 O 7 -2 [H + ] 14 ]/[Cr +3 ]}.{[Fe +2 ] 6 /[Fe +3 ] 6 })

pH range 2-3 pH range 3-4 pH range 4-6

Figure 2.12 Measured and predicted redox potential variation with reaction quotient of
species concentration in Nernst relation (average redox potential shift =0.37V) (Pamukcu
et al., 2004)

pH, the DDL is compressed with a higher ion concentration, higher electric
field (Israelachvili and Adams, 1978), hence higher degree of polarization,
and lowered capacitance. At higher pH, the DDL is expanded with reduced
degree of polarization, consequently higher capacitance. The ions in an
expanded DDL are less restricted to move, therefore discernable fluctua-
tions are likely to occur in the potential development across the diffuse layer.

2.3 Electrokinetically-Aided Environmental
Mitigation

The main and best-known advantage of electrokinetically aided environ-
mental mitigation is its ability to move water, dissolved contaminants and,
colloidal/micellar particles through low permeability soils and porous for-
mations that are not amenable to hydraulic treatments (Hamed et. al, 1991;
Pamukcu and Wittle, 1992; Wittle and Pamukcu, 1993; Acar, et al., 1986,
1989, 1990, 1992; Shapiro and Probstein, 1993, Probstein and Hicks, 1993;
Pamukcu et al. 1995, 1997; Pamukcu, 1994, 1998). The electrokinetically
aided transport is based on well-known electrokinetic processes (Hunter,
1981; Cassagrande, 1949; Mitchel, 1993), primarily comprised of electro-
osmosis, electrophoresis , and ion migration in wet soil. The electrokinetic
treatment involves applying a low direct current (on the order of milliamps
per unit cross-sectional area), or a low potential gradient (on the order of
few volts per unit distance) between the power electrodes inserted in the