Environmental Engineering Reference
In-Depth Information
12
1.8
1.6
1.4
1.2
1
Numeric C/C0; 1d; C0=0.05M; L=20cm
Test C/C0; 1day; C0=0.03M; L=10cm
Numeric pH; 1d
Test pH; 1day
10
8
6
1d C/C 0
0.8
0.6
0.4
0.2
0
1d pH
4
2
0
0
0.2
0.4
Distance from anode end, X/L
0.6
0.8
1
Figure 5.2 Variation of total lead (Pb) concentration and pH distribution as predicted by
the Cao (1997) model and measured by experiment for a 1-day duration (After Pamukcu,
2009)
well as the length of the physical and numerical specimens employed, the
normalized distributions are comparable.
As shown in figure 5.2, the pH distribution of the model agrees well with
the experimental pH after 1 day of treatment, but the distribution of lead
does not agree as well for the same duration. The model predicts conserva-
tively a uniform concentration distribution of the metal ion at around 80%
of the original, while the available data at three points along the soil col-
umn indicate a substantial reduction at the anode and a substantial accu-
mulation at the cathode. It is noted that the model makes a conservative
prediction of pH at the cathode end, leading to inadequate capture of the
actual lead accumulation by precipitation.
Figure 5.3 shows the long-term model predictions and the matching
experimental data from the same series of tests for 35-day treatment. As
observed, the model predicts well the long-term behavior of both the lead
and the pH distribution, including the accumulation of the metal in a nar-
row zone adjacent to the cathode.
5.6
Coupling of Electrical and Pressure Gradients
Electrical boundary layers that form a solid-fluid interface in the porous
medium create the elektrokinetic potential that result fluid flow under an
electric gradient, or charge flow under a hydraulic gradient (Grahame,
1947; Davis et al., 1978). Researchers have investigated the coupling
 
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