Decontamination of Clay Using Electrokinetic Phenomena
IGC 2009, Guntur, INDIA
DECONTAMINATION OF CLAY USING ELECTROKINETIC PHENOMENA
V.K. Stalin
Astt. Professor, Division of Soil Mechanics and Foundation Engineering, Anna University Chennai, Chennai– 600025, India.
E-mail: [email protected]
C.A. Poornima
P.G. Student, Division of Soil Mechanics and Foundation Engineering, Anna University Chennai, Chennai–600025, India.
E-mail: [email protected]
M.R. Nanda Gopalan
Senior Engineer, Larsen and Toubro Ltd, Chennai, India.
ABSTRACT: The electrokinetic phenomena is also used for decontamination and enhancement of soil–chemical interaction,
apart from electro-osmotic consolidation of dewatering. In this paper, an attempt is made to decontaminate the Na +
contaminated clay using electro-kinetic principle for varying voltage, spacing and number of electrodes. Box type electrokinetic cell was used for this purpose. Results indicated that % reduction of Na concentration level in the contaminated soil
increases with increasing voltage and decreasing spacing of electrodes. It is concluded that effective decontamination of clays
using electro-kinetic principle is largely influenced by spacing, voltage and number of electrodes.
1. INTRODUCTION
In order to stabilize and decontaminate the days, electrokinetic process are being widely used because of their
advantages are: low cost, non-intrusive character, applicability
to a wide range of contaminants and insensitivity to pore size
soil that makes it suitable for fine-grained soils.
Pascal Suer & Thomas Lifvergren (2003) studied on the
remediation of mercury-contaminated soil using iodide.
Iodide was added to the cathode compartment moved
through the soil and oxidized to iodine near the anode. After
5 days, some 50% of the total mercury content was found to
have migrated to the anode compartment and another 25%
was recovered from the soil water in the vicinity of the
anode. Krishna Reddy and Chintham Reddy (2003) studied
sequential enhancement of kaolin which is contaminated by
chromium, nickel and cadmium. In this process voltage and
spacing of the electrode are kept constant. When tap water is
used as purging solution the efficiency of removal was very
low.
Henrik Hansen & Adrian Bojo (2004) investigated the
decontamination of copper. When tap water is used as a
purging solution the removal was 8%. They have used
bipolar electrodes which increases the efficiency. The
advantages are shorter migration pathway for the
contaminants, an increased electrical conductivity, less time
and voltage applied. The removal was increased by 42%
sulphuric acid when used as a purging solution gives better
efficiency. Krishna Reddy & Chintham Reddy (2004) the
glacial till soils is contaminated by nickel, chromium and
cadmium. When tap water is used chromium and cadmium
were not removed. Garcia Nogueira, et al. (2007) investigated
the decontamination of manganese in kaolinite clay. Initially
26% of the Manganese is removed when tap water is being
used. When EDTA, is used as a purging solution 42% is
decontaminated.
Korolev et al. (2007) investigated the removal of oil from oil
contaminated soil. Platinum electrodes were mounted at the
tube ends, contacting with the sample. Current was applied to
the soil sample for 4–8 hours. Then the collected filtrate was
analyzed. As a result of it one of the samples near cathode
was cleared of oil, and another was enriched. They
concluded that the intensity of the migration of oil grows
with an increase of the quantity of clay minerals in the soil.
In the present investigation, an attempt is made to
decontaminate the artificially contaminated soil for varying
voltage, spacing and number of electrodes using electrokinetic principle.
2. MATERIALS
Soil samples were collected from SIPCOT, Chennai for the
present study. The soil is pure and expansive in nature. The
liquid and plastic limit of soil is 67% and 31% respectively.
The % clay is more than 80%. The soil is classified as ‘CH’
type. The physical properties of soil is shown in Table 1.
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Decontamination of Clay Using Electrokinetic Phenomena
Table 1: Physical Properties of Soil
Properties
Specific gravity
Liquid limit, %
Plastic limit, %
Plasticity index, %
Shrinkage limit, %
Free swell index, %
Max. dry density, kg/m3
Optimum moisture content, %
Swell classification
Soil classification as per IS
concentration of contaminants using spectro photometer.
Then the soil sample was remoulded and filled in the tank.
The test was carried for four hours and the concentration of
contaminants was determined by digital flame photometer.
The results are compared with the initial concentration of
contaminants before passage of current.
Soil
2.71
62.5
31.0
35
9.3
78
1.65
23.36
Very high
CH
The following procedure
Contamination of Soil.
1.
2.
3. METHODS
In order to study the electrokinetic phenomena in soils, an
electrokinetic cell was designed and fabricated which has the
components like rectangular box open at top, electrodes,
voltmeter, ammeter, AC to DC transformer and multimeter.
Figure 1 shows the schematic diagram of the fabricated cell.
The dimensions of box are 500 × 150 × 150 mm. The soil
sample of varying initial moisture content will be placed in
the tube up to a height of 10cm by hand remolding. At the
cathode end, provision is given at bottom of box to collect
the drained water during the process of passage of current
across the soil sample. The voltmeter is provided to measure
the voltage applied. The voltage can be varied as 40 V and
80 V. The ammeter is used to measure the amount of current
passing through the soil sample. The ammeter is capable of
measuring current from 1 A to 10 A. The cathodic electrode
is made up of copper with perforations to facilitate removal
of water and the anodic electrode is made up of zinc. The
transformer converts the incoming AC current to DC current.
The transformer, voltmeter and ammeter are fitted together in
a small box so that the apparatus is compact.
Slit provided for fitting electrode
Cathode
Anode
Transformer
Ammeter
soil sample
Water collected
Voltmeter
at Cathode
Fig. 1: Schematic Diagram of Electrokinetic Cell.
The soil sample was artificially contaminated with known
Na+ whose concentration is fixed initially and kept for one
day. Thus the contaminated soil was subjected to passage of
electric current in the electro-kinetic cell. After the lapse of
four hours interval the soil samples was tested for
3.
4.
is
adopted
for
artificial
Initially the soil sample was taken and test was
performed for Na concentration in the soil sample, by
using digital flame photometer. It is found that soil
contains 125 ppm of Na concentration.
Take 80% of water content to the total soil sample and
add 50 ppm of Na concentration to the water content.
Add the 80% of water content which contains 50 ppm
Na concentration to the soil sample which already has
125 ppm of Na concentration present in it.
Now the total Na concentration present present in the
sample is 17 5ppm (125 ppm +50 ppm).
4. RESULTS AND DISCUSSIONS
The initial concentration of Na in soil is found as 125 ppm
and to which 50 ppm of Na concentration was added in order
to contaminate the soil externally. Now total initial
concentration of the Na before the start of test is 175 ppm for
all the cases of varying IMC. Table 2 shows the effect of
voltage, IMC and spacing on Na concentration at the end of
test.
4.1 Effect of Voltage
Figures 2 and 3 show the variation of Na concentration with
voltage of 40 V and 80 V respectively for IMC 80% for 10,
20 and 30 cm spacing. In all the cases the reduction in the Na
concentration decreases with increasing voltage at any given
moisture content and at any specified time (Table 2). These
may be because as the voltage increases the charged Na+ ion
particles attracted toward cathode also significantly increases
and because of which Na concentration decreases with
voltage. This is one of the important aspects to be brought
out for decontamination techniques. If concentration of the
contaminants is high in the affected ground, the increase of
voltage is expected to drag more contaminants towards the
anodic and cathodic points at less time interval depends on
positive or negative charges of the contaminants. The
reduction in Na concentration in two electrodes for 40 V and
80 V is 85.14%, 82.33%, 80% and 86.86%, 85.71%, 82.86%
for 10, 20, 30 cm respectively. Similar to this, The reduction
in Na concentration in two electrodes for 40 V and 80 V is
93.14%, 92.57%, 92% and 95.43%, 94.30%, 93.71% for 10,
20, 30 cm respectively (Table 2). Reddy et al. (2003) obtained
a maximum of 77% of mercury reduction removed from
glacial till after electro-kinetic treatment using higher iodide
concentration and high voltage gradient.
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Decontamination of Clay Using Electrokinetic Phenomena
Table 2: Effect of Voltage, IMC and Spacing and Number of Electrodes on Reduction in Na + Concentration
No. of
electrodes
Voltage
IMC (%)
40 V
80%
80 V
80%
40 V
80%
80 V
80%
Spacing
Na concentration*
(ppm)
Reduction in Na
concentration (ppm)
10
20
30
10
20
30
10
20
30
10
20
30
26
31
35
23
25
30
12
13
14
8
10
11
85.14
82.33
80.00
86.86
85.71
82.86
93.14
92.57
92.00
95.43
94.30
93.71
2
3
*Initial Na Concentration of contaminated soil is 175 ppm.
spacing for two electrodes, in three electrodes (Table 2) at 40 V
DC and 80% IMC the % Na concentration 93.14%, 92.57%
and 92% corresponding to 10 cm, 20 cm and 30 cm spacing
(Figure 3). As the spacing between electrodes decreases, the
removal of Na concentration also increases due to effective
electric field in the soil mass is available between two
successive electrodes. For a voltage of 80 V and IMC of 80%
the % reduction in Na concentration is 86%, 85.71% and
82.71% respectively in two electrodes for 10 cm, 20 cm and
30 cm spacing, in three electrode 80% initial moisture
content of 80%, the % reduction in Na concentration for
95%, 94.30% and 93.71% respectively (Fig. 3).
Fig. 2: Reduction in Na+ Concentration with Varying
Spacing for 40 V and 80% IMC
4.3 Effect of Number of Electrodes
With reference to figure 2 and 3, it is noticed that as the
number of electrodes increases, the % reduction in Na
concentration also drastically increases. While for two
electrodes, the Na concentration reduction is steep with
spacing, the same is almost marginal for three electrodes. On
observing table 2, it may be noticed that % reduction is
between 92 to 95 % for three electrode case for the spacing
of 10 to 30 cm. In the case of two electrodes % reduction of
Na is between 80 to 85 % only. This is because, as the
number of electrode increases, the spacing between two
successive electrodes (Anode and Cathode) reduces and
result of which there is effective flow of electrical current in
to the soil sample.
Fig. 3: Reduction in Na+ Concentration with Varying
Spacing for 40 V and 80% IMC
4. CONCLUSIONS
4.2 Effect of Spacing
As the spacing decreases (from 30 cm to 10 cm) the volume
of water collected at cathode also increases at any given time
interval, voltage and initial moisture content and the time
taken to reach a steady state of volume of water decreases. At
40 V DC and IMC of 80% for % Na reduction 85.14%,
82.33% and 80% corresponding to 10 cm, 20 cm and 30 cm
Artificially Na+ contaminated soil has been subjected to
electrokinetic phenomena and based on the results, the
following conclusions may be drawn.
1.
278
As the spacing of electrodes decreases the time taken to
reach a steady state of volume of water decreases. At 40V
DC and IMC of 80% the reduction in Na concentration
Decontamination of Clay Using Electrokinetic Phenomena
2.
3.
is 85.14%, 82.33% and 80% corresponding to 10 cm, 20
cm and 30 cm spacing for using two electrodes.
For three electrodes at 40V DC and 80% IMC for %
reduction in Na concentration is 93.14%, 92.57% and
92% corresponding to 10 cm, 20 cm and 30 cm spacing.
As the spacing between electrodes increases, the
reduction in Na concentration decreases due to
ineffective electric field in the soil mass available
between two successive electrodes. For a voltage of 80
V and IMC of 80% the % reduction in Na concentration
is 86%, 85.71% and 82.71% respectively two electrode
for 10 cm, 20cm and 30cm spacing and three electrode
80% initial moisture content of 80 V DC also the %
reduction in Na concentration for 95%, 94.30% and
93.71% respectively.
Thus, it is suggested that spacing, initial moisture content,
voltage and number of electrodes may be considered for
effective decontamination of soils, to be employed under
electrokinetic principle.
REFERENCES
García Nogueira. M, Pazos. M., Sanromán. M.A. and
Cameselle. C. (2007). “Improving on Electrokinetic
Remediation in Spiked Mn kaolinite by Addition of
Complexing Agents”, Electrochimica Acta, Vol. 52, pp.
3349– 3354.
Henrik Hansen and Adrian Bojo (2007). “Electrokinetic
Remediation of Copper Mine Tailings Implementing
Bipolar Electrodes”, Electrochimica Acta , Vol. 52, pp.
3355–3359.
Korolov, Romanyukha and Abyzova (2007). “Electrokinetic
Remediation of the Oil Contaminated Soils”, 6th
Symposium on Electrokinetic Remediation, Spain, Vol. 1,
pp. 60–66.
Krishna Reddy and Chintham Reddy (2003). “Sequentially
Enhanced Electrokinetic Remediation of Heavy Metals in
Low Buffering Clayey Soils”, ASCE, Vol. 12 (9), pp.
445–450.
Krishna Reddy and Chintham Reddy (2004). “Enhanced
Electrokinetic Remediation of Heavy Metals in Glacial
Till Soils Using Different Electrolyte Solutions”, ASCE
Journal, Vol. 13, pp. 460–466.
Pascal Suer & Thomas Lifvergren, (2003). “Mercury
Contaminated Soil Remediation by Iodide and Electroreclamation”, Journal of Environmental Engineering,
Vol. 2, pp. 441–446.
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