Environmental Engineering Reference
In-Depth Information
the clay soils. Hydroxide ions are potential makers, which
subsequently cause the cation adsorption capacity of the soil
to increase. Therefore, at high pH the surface potential will
increase, leading to thicker diffuse layers and increased sur-
face conductivity. Since, the bulk liquid conductivity would
be reduced with precipitation, the combined effect should
signal increased electroosmotic water transport and current
efficiency. This suggests that with extended duration of treat-
ment, the accumulated metal may eventually be transported
into the electrode chamber by the steady but slower action of
electroosmotic advection.
Figure 2.26 shows the variation of zeta potential with pH
for two clay-electrolyte systems of high ionic concentration.
As observed, the PZC of either the Sr or Pb spiked kaolin-
ite clay lie at about 4 pH units. The potential increases in
negative values, then reverses at high pH. The changing zeta
potential trends can also explain the interfacial accumula-
tion of some compounds in response to reversed EO flow
regimes. A typical example of post-EK metal accumulation
near the soil-water interface at cathode side is displayed in
Figure 2.27 for lead in various clay soils.
I. Extraction of VOCs, PAHs and organic acids:
The application of electrokinetic phenomena to the trans-
port of NAPL pollutants has not been widely investigated.
Bruell et al., (1992) showed transport TCE and several gaso-
line hydrocarbons by electroosmosis, assuming a constant
40
20
0
-20
-40
Kaolinite Clay
-60
0
2
4
6
8
10
12
14
pH
PbCl2: 33333 ppm
SrCl2: 33333 ppm
Figure 2.26 Evolution of zeta-potential with pH in kaolinite clay of high salt
concentration ( Pamukcu et al., 1997)
 
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