United States
Environmental Protection
Agency
EPA/540/F-95/504
March 1995
&EPA
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Emerging Technology Bulletin
Electrokinetic Soil Processing
Electrokinetics, Inc.
Process Description: Electrokinetic Soil Processing (or Elec-
trokinetic Remediation) uses two series of electrodes (anodes
and cathodes) positioned inside compartments that allow egress
and ingress of pore fluids to the porous media. The compart-
ments are filled with water or other process fluids and inserted
into contaminated soil. A direct current (DC) is applied across the
electrodes. Under such conditions, moist soil acts as an aqueous
electrolyte and ions and solution move toward the electrodes.
The coupling between electrical, chemical, and hydraulic gradi-
ents is responsible for the movement of both contaminants and
the processing solution through the soil.
Figure 1 presents a schematic diagram of the process. Chemical
species present in the process fluid/and or desorbed from the soil
surface will be transported toward respective electrodes depend-
ing on their charge. Ion migration, advection and diffusion con-
tribute to the movement of the species through the soil mass.
Cations will collect at the cathode and anions at the anode.
Heavy metals and other cationic species will be removed with the
processing fluid, or they will be deposited at the cathode. Pro-
cessing involves the regeneration of the solution through removal
and recovery of the contaminants and return of the regenerated
solution to the electrode compartments.
Waste Applicability: This technology extracts heavy metals,
radionuclides and other inorganic species and polar organic spe-
cies below their solubility limits. Bench scale tests have shown
removal of arsenic, benzene, cadmium, chromium, copper,
ethylbenzene, lead, nickel, phenol, trichloroethane, toluene, xy-
lene, and zinc from soils. Limited pilot-scale field tests displayed
zinc and arsenic removal from clays and sandy clay deposits.
Treatment efficiency depended on the specific chemicals, their
absolute and relative concentrations with respect to other avail-
able species, the buffering capacity of the soil, the duration of
treatment, the current level used and the conditioning scheme
employed. In bench-scale tests, the technique proved 85-95%
Acid Front
and/or Anodic
Process Fluid
Figure 1. A schematic diagram of electrokinetic soil processing and one configuration used in remediation of soils.
Printed on Recycled Paper
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effective when removing phenol at concentrations of 500 ppm.
Removal efficiency for lead, cadmium, chromium, and uranium at
levels up to 4,000 mg/kg ranged between 75% and 95%. The
efficiencies of radium and thorium removal from soils were very
low due to formation of insoluble precipitates in soil.
Test Results: Three pilot-scale studies using 1-ton specimens
were conducted by Electrokinetics Inc. under the SITE program;
two pilot-scale tests using kaolinite spiked with lead at initial
concentrations of 850 mg/kg, 1,500 mg/kg and another using fine
sand and kaolinite mixture spiked with lead at 5,322 mg/kg. The
kaolinite had lead adsorption capacity of about 1,100 mg/kg. Lead
nitrate salt is used as the source of lead. Tap water is used both
as the catholyte and the anolyte. The electrode spacing was 70
cm and a one-dimensional electrical field was applied. Energy
expenditure in the pilot-scale tests ranged from 300-700 kWh/m3.
Processing times in pilot-scale tests ranged from 1,300 h-2,950 h.
Figure 2 shows the lead concentration profile after 123 days of
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processing at a current density of 133 jiA/cm2. More than 90% of
the lead in the soil is transported across to the cathode compart-
ment and preciptitated wiithin the last 7 cm of the specimen.
Lead prematurely precipitates close to the cathode compartment
at its hydroxide solubility value if the chemistry of the electrolyte
at the electrodes is not altered or controlled (unenhanced elec-
trokinetic remediation). One objective of these pilot-scale tests
was to formalize and validate the principles of multi-species
transport under electric fields and develop design/analysis pack-
ages. Therefore, pilot-scale tests did not employ any enhance-
ment technique. Enhancement techniques which employ cathode
depolarization schemes such as acetic acid depolarization tech-
nique prevent the precipitation close to the cathode compart-
ment. A special electrode system (CADEX™) designed and
manufactured by Electrokinetics Inc. efficiently depolarizes the
cathode reaction and promotes electrodeposition of species on
the cathode.
For Further Information:
EPA Project Manager
Randy Parker
Risk Reduction Engineering Laboratory-USEPA
26 West Martin Luther King Drive
Cincinnati, OH 4528
(513)569-7271
Technology Developer Contact:
Yalcin Acar
Electrokinetics, Inc.
Louisiana Business and Technology Center
Louisiana State University
South Stadium Drive
Baton Rouge, LA. 70803-6100
(504) 388-3992
Figure 2. Lead concentration profile after 123 days of processing kaolin-
ite/fine sand mixture spiked at 5,322 mg/kg. [Precipitation close to the
cathode compartment is avoided and transport of species in the cathode
compartment are promoted through cathode depolarization techniques and
the CADEX™ electrode system].
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/540/F-95/504
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