The document discusses the widespread issue of land degradation in India and introduces electrokinetic soil remediation as an effective method for removing heavy metals from contaminated soil. It investigates the effectiveness of fixed and approaching anode techniques, emphasizing the advantages and enhancements of the latter for facilitating lead migration. The study highlights the importance of factors like soil type, current density, and electrode materials in optimizing the electrokinetic remediation process.

1. 1
Electrokinetic Soil Remediation
GAYATHRY T J
M-Tech Second Semester in Geotechnical Engineering
School of Engineering, CUSAT
npspark17@gmail.com
Abstract
In India around 147 million hectares (Mha) of land is under degradation, this includes 94 Mha from water erosion, 16 Mha
from acidification, 14 Mha from flooding, 9 Mha from wind erosion, 6 Mha from salinity, and 7 Mha from a combination of
factors. Even though The total land area of India is just 2.4% of the world’s land area , it ranks second in the world in farming.
Agriculture employs almost 50% of the total workforce in India. So there is an increased need for monitoring and researching
the various facets of land degradation. Electrokinetics is defined as the physicochemical transport of charge, action of charged
particles and effects of applied electric potentials on formation and fluid transport in porous media. The utilization of
electrokinetic in geotechnical engineering for dewatering, consolidation and stabilization of low permeability and to transport
certain chemical species in an electrolyte system had opened new opportunities for application in geo environmental
engineering. Approaching anode is one of the enhancement techniques in electrokinetic soil remediation. This technique is
reported to give promising migration for heavy metals under shorter treatment time and at lower cost in comparison to normal
fixed anode system. In the present study, the effectiveness of fixed anode and approaching anode techniques in electrokinetic
soil remediation for lead migration under different types of wetting agents (0.01M NaNO3 and 0.1M citric acid) was
investigated.
Key Words: Acidification , Failure, Land Degradation, Electrokinetics
I. INTRODUCTION
Due to rapid industrialization and
urbanization, soils are increasingly getting
polluted. Many industries are generating
wastes which contain heavy metals.
Nowadays, industries are practicing open
dumping, since it is an economical means
of waste disposal. Waste, which contains
heavy metal, either in liquid or solid form,
will pollute soil and ground water, when it
gets disposed off to the soil. It has become
a major social issue. So removal of heavy
metal from soil or decontamination of soil
is now gaining importance.
Heavy metals consist of group of metals
and metalloids. Their atomic density is
more than 5 times that of water. Heavy
metal contamination of soil is a common
occurrence in industrial areas and in areas
with high traffic volume. Heavy metal
contamination of soil occurs during mining,
manufacturing and the use of synthetic
products such as pesticides, paints,
batteries, industrial waste and land
application of industrial or domestic sludge.
The density of heavy metal is more than 5
g/cm3. Most common problem causing
heavy metals are Lead, Mercury, Cadmium,
Arsenic, etc. Other problems associated
with heavy metals is, it is non-
biodegradable. Unlike carbon based
molecules, it remains in the soil for decades
(Giannis et al., 2009). So it is important to
have an effective and economical soil
remediation technique.
A number of technologies have been
developed in response to address increasing
environmental problems. Over the past few
decades, electrokinetic (EK) remediation
has been demonstrated to be one of the most
effective methods for in situ or ex situ soil
decontamination. Numerous EK
remediation investigations have shown
success in degrading soil contaminants and
removing heavy metals.
II. ELECTROKINETIC
REMEDIATION
Electrokinetics is defined as the
physicochemical transport of charge, action

2. 2
of charged particles and effects of applied
electric potentials on formation and fluid
transport in porous media. The utilization of
electrokinetic in geotechnical engineering
for dewatering, consolidation and
stabilization of low permeability and to
transport certain chemical species in an
electrolyte system had opened new
opportunities for application in geo
environmental engineering. Recently the
electrical treatment technique has been
applied to in-situ remediation, which was
used to clean up contaminated sites
containing heavy metals and hydrocarbons.
The idea of electrokinetic remediation
started in the 1980s after it was noticed that
water transported by electroosmosis
contained high amounts of heavy metals
and other chemical species.
III.COMPONENTS OF THE
ELECTROLYTIC PROCESS
The main components of the electrolytic
process are:
1) Electrolyte: is a substance that
dissociates in solution into positive and
negative ions to produce an electrically
conductive medium.
2) Electrolysis: the passage of an electric
current through an electrolyte decomposing
it in the process: negative ions (anions) are
attracted to the anode, where they are
oxidized (lose electrons). Positive ions
(cations) are attracted to the cathode, where
they are reduced (gain electrons).
3) Electrolytic Cell: a cell containing an
electrolyte through which an externally
generated electric current is passed by a
system of electrodes in order to produce an
electrochemical reaction.
4) Electrode: Any terminal by which an
electric current passes in or out of an
electrolytic cell. The anode is the positive
electrode and the cathode is the negative
electrode.
5) Electrokinetics: is the movement of
water (electroosmosis), ions and polar
molecules (electromigration), and charged
solid particles (electrophoresis) relative to
one another between two electrodes under
the action of an applied direct electric
current.
Figure1: Electrolytic cell
Electrokinetic process is a soil remediation
method which uses electricity as driving
force for contaminant transport in the soil.
Figure2: Schematic diagram of in-situ
electrokinetic remediation system
This process is initiated by applying low
magnitude direct current from the
electrodes injected into the soil. During
electrokinetic process, electrolysis occurs
in both anode and cathode chambers which
produce H+ and OH-, respectively. Due to
the potential difference between the
electrodes, H+ and OH- transport to the
respective electrode and these are named as

3. 3
acid front and base front. The major
contaminant transport mechanisms under
an induced electric potential are:
(1) Electroosmosis – bulk movement of
pore fluid through the electrical double
layer in clayey soils, generally occurring
from anode to cathode;
(2) Electromigration – transport of ions and
ion complexes within the pore fluid towards
oppositely charged electrodes;
(3) Electrophoresis – transport of charged
colloids, micelles, bacterial cells, etc.
within the pore fluid towards oppositely
charged electrodes; and
(4) Diffusion – transport of chemicals due
to concentration gradients
These forces are responsible for
contaminants removal from the soil,
whereby the contaminants are concentrated
in the electrolyte chambers or enriched in a
smaller soil volume.
In the EK remediation process, electrode
reactions take place on the surface to
generate protons (H+) and hydroxyl (OH−)
at the anode and the cathode, respectively.
The concentration of these ions near the
electrodes creates an acid front that moves
from anode to cathode and a basic front that
moves the other way. At the same time, the
generation of OH− ions at the cathode leads
to the precipitation of the heavy metals,
called the focusing effect. This is the main
barrier to electrokinetic remediation of
heavy- metal contaminated soils (Lu et al.
2012). Many studies have been performed
with the aim to control the soil pH and
enhance the capability of electrokinetic
remediation for heavy-metal removal.
Measures include adding strong
complexing agents such as ethylene
diamine tetra acetic acid (EDTA) into soil
(Ottosen et al. 2005) and using ion-
exchange membranes (IEM) to control the
pH and zeta potential (Amrate et al. 2006).
Electrokinetic remediation technology can
be used for the in-situ treatment of
contaminated sites. It consists of drilling
wells (drains or trenches) in which
electrodes are installed and then applying a
very low direct current electric potential.
Pumping and conditioning systems may be
needed at the electrodes depending on the
site conditions. Similarly, electrokinetic
treatment may be accomplished ex-situ by
using specially designed above-ground
reactors. Generally, the contaminants
accumulated at the electrodes are removed
by either adsorption onto the electrodes or
withdrawal followed by treatment.
IV. ADVANTAGES OF ER
Electrokinetic remediation offers the
following advantages as compared to
conventional remediation methods:
(1) Simplicity – requires simple equipment;
(2) Safety – the personnel or the public in
the vicinity are not exposed to
contaminants;
(3) Wide range of contaminated media –
can be used for soils, sludge, sediments, and
groundwater (particularly well-suited for
low-permeability clays and heterogeneous
soil deposits within the vadose zone where
conventional remedial methods have
proven to be ineffective or expensive);
(4) Wide range of contaminants – can be
used for metals, organic compounds,
radionuclide, or a combination of these
contaminants;
(5) Flexibility – can be used as an insitu or
ex-situ remediation system, and it can be
easily integrated with other remediation
technologies such as bioremediation; and
(6) Cost effectiveness- requires low
electrical energy (relative to other thermal
technologies) leading to lower overall cost.
V. FACTORS THAT AFFECT THE
ELECTROKINETIC SOIL
REMEDIATION TECHNIQUE

4. 4
A number of factors determine the direction
and extent of the migration of the
contaminant. Such factors include: the type
and structure of the soil, applied current
density, sample conditioning and the
electrode material.
1. Soil Type and Physical Properties
According to Acar (1992), there should not
be any technical restriction on the type of
soil to be cleaned. However, metal
contaminant mobility and transport
efficiencies depend heavily on the physical
properties of the soil and environmental
variables. Soils with fine particles (<100
gm) are more reactive and have a higher
specific surface area than coarser material.
As a result, the fine fraction of a soil often
contains the majority of the contamination.
The distribution of particle sizes with which
a metal contaminant is associated can
therefore determine the effectiveness of the
technology.
2. Voltage and Current Levels
The electric current intensities used in most
studies are of the order of a few tens of
milliamperes per square centimeter.
Although a high current intensity can
generate more acid and increase the rate of
transport to facilitate the contaminant
removal process, it increases power
consumption tremendously as power
consumption is proportional to the square
of electric current. An electric current
density in the range of 1-10 A/rn2 has been
demonstrated to be the most efficient for the
process (Alshawabkeh et al 1999).
However, appropriate selection of electric
current density and electric field strength
Depends on the electrochemical properties
of the soil to be treated in particular the
electric conductivity. The higher the
electric conductivity of the soil is, the
higher the required electric current density
will need to maintain the electric field
strength required. An optimum electric
current density or electric field strength
should be selected based on soil properties,
electrode spacing, and time requirements of
the process.
3. Enhancement
In some cases, an acid front may not be able
to develop by electrokinetic processes
because of the high acid/base buffer
capacity of the soil and reverse
electroosmotic flow,
i.e., from the cathode toward the anode.
Under these circumstances and in order to
promote solubilization and transport of the
metallic species, enhancement agents may
be needed.
Different schemes have been proposed and
evaluated to enhance transport and
extraction of cationic species under a DC
electric field and to prevent the formation
of immobile precipitates. To neutralize the
hydroxyl ions generated by electrolytic
reduction of water, acids such as acetic
acid, hydrochloric acid may be introduced
at the cathode. Chelating or complexing
agents, such as citric acid and ethylene
diamine tetra acetic acid (EDTA), have also
been demonstrated to be feasible for the
extraction of different types of metal
contaminants from fine-gained soils. The
choice of enhancement agent is
contaminant specific. If the primary
function of the enhancement agent is to
desorb the contaminant from the soil
particle surface, the sorption characteristics
of the contaminant on the soil particle
surface in the presence of the enhancement
agent as a function of the value of pH must
be carefully studied. This is because the
presence of the enhancement agent can
change the sorption characteristics
completely.
4. Electrode Material and Spacing
To prevent dissolution of the electrode and
generation of undesirable corrosion
products during electrolysis, chemically
inert and electrically conducting materials
such as graphite, coated titanium, or
platinum should be used. Important
Considerations for the choice of electrode
material are:

5. 5
a) Electrical conduction properties of the
material
b) Availability of the material
c) Ease of fabrication to the form required
for the process
d) Ease of installation in the field
e) Material, fabrication, and installation
costs
Regardless of the material selected for the
electrode, the electrode has to be installed
properly in the field so that it can make
good electrical contact with the subsurface.
Moreover, the design must make provisions
to facilitate exchange of solution with the
subsurface through the electrode. When
selecting spacing between electrodes,
issues of costs and processing time need to
be considered. Larger electrode spacing
will reduce the number of boreholes and
installation costs, but will increase the
processing time required and operation
costs.
VI.COMPARISON OF FIXED
ANODE AND APPROACHING
ANODE TECHNIQUES
Usually, the EK process is operated with
one fixed anode (FA). An enhanced EK
method with approaching anodes (AAs) is
believed to strengthen the remediation
effect. Compared with other remediation
methods, this study speculates that if the
area of the focusing effect can be migrated
towards the cathode in a step-by-step
manner with approaching anodes (AAs),
more heavy metal ions will be precipitated
in a narrow area and extracted from the
contaminated soil (Li et al. 2012b), which
will improve the removal of ions in the
remediation of soils. It may hugely save
remediation time and energy. Approaching
electrode can be categorized into two types,
namely approaching anode and
approaching cathode. This technique
involves sequential switching of either
anode (approaching anode) or cathode
(approaching cathode) close to the other
fixed electrode during electrokinetic
process. This can provide progressive soil
conditioning while compressing the
undesired pH region, which can further
enhance the desorption of heavy metal ions
while reducing the focusing effect for better
electromigration. From the cost aspect,
approaching electrode is reported to
provide saving in energy consumption and
treatment time by 16-44% and 20-40%,
respectively. These advantages generally
improve the feasibility of electrokinetic
process in soil remediation. To date,
approaching electrode technique is mainly
studied for remediating single-
contaminated soil such as Cr (Li et al.
2012), Cd (Shen et al. 2007) and Pb (Zhang
et al. 2014), Hg (Shen et al. 2009) and
fluorine (Zhou et al. 2014) and the results
are promising. However, it is noted that the
investigation of approaching electrode
assisted electrokinetic process in treating
co- contaminated soil is scarce, especially
for the metals that have opposite charge.
This is important as electro migration
would concentrate both metal cations and
anions in cathode and anode regions,
respectively, which fails the purpose of
contaminated soil volume reduction.
Figure3: General diagram for approaching
anode electrokinetic process with a total
treatment time of 5t
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