Electrokenetic Remediation
Technology Description:
Components-
Electrokinetic Remediation (EKR) is a developing technology
for in-situ removal of heavy metals and radionuclides. The
application of direct current in a porous medium leads to
two transport phenomena; ionic species in the soil-water
solution will migrate to the oppositely charged electrode
(electromigration), and accompanying this migration, a bulk
flow of soil-water is induced usually toward the cathode
(electroosmosis). The combination of these two transport
phenomena leads to a movement of contaminant ions towards
one or the other electrodes, illustrated by the figure
below. The direction and rate of movement of an ionic
species will depend on its charge, both in magnitude and
polarity, as well as the magnitude of the
electroosmosis-induced flow velocity. Non-ionic species will
be transported along with the electroosmosis induced water
flow.
Electrokinetic Phenomena
The electrokinetic transport phenomena pertinent to in-situ
remediation include electroosmosis (movement of water in
response to an electric field), electrophoresis (movement of
a charged particle or colloid in an electric field), and
electromigration (movement of solute ions in the electric
field).
Electrokinetic remediation is accomplished by implanting
electrodes in the soil whereby a relatively small direct
electrical current is supplied between the electrodes. Ions
in solution will migrate toward an electrode by
electromigration. Experimental results indicate significant
dependence of the electromigration rates on the soil pore
water current density. The process efficiency is not as
dependent on the fluid permeability of soil as it is on the
pore water electrical conductivity and the path length
through the soil, both of which are functions of the soil
moisture content. Removal of contaminants at the electrode
may be accomplished by several means among which are:
electroplating at the electrode; precipitation or
co-precipitation at the electrode; pumping of water near the
electrode; or complexing with ion exchange resins. An
alternate method suggested is adsorption into the electrode
because some ionic species will change valence near the
electrode (depending on the soil pH) making them more likely
to adsorb.
The direction and quantity of contaminant movement is
influenced by contaminant concentration (anions versus
cations), soil type and structure, interfacial chemistry,
and current density in the soil pore water. For the process
to work, the soil moisture content must be above a minimum
value. This minimum moisture content required for
electromigration is related to, and can be estimated from,
the residual moisture content of a soil, also called
"immobile water." Preliminary results indicate that the
optimum soil moisture content for electromigration is less
than saturation due to competing effects of tortuosity and
pore water content.
Procedures/Reliability-
General Applications and Limitations-
Support/Infrastructure Requirements-
Program Integration Issues and Compatibility with
Other Technologies-
Operator Staffing/Skill/Training/Physical Requirements-
Acceptability:
Environmental and Aesthetic Impacts-
Natural Resource Usage-
Land Use Impacts-
Other Socioeconomic Impacts-
For use of EKR in unsaturated soils, the addition of water
is a concern because of the potential of hydraulically
washing contaminants out of the range of capture. SNL's
unsaturated soil extraction electrode system is designed to
minimize this problem and its in situ performance will be
demonstrated in a FY94 field test.
Status:
Maturity-
This is a developing technology. Laboratory bench scale
tests have been conducted, and the results will be used to
develop a predictive model of the migration rates. A pilot
scale test will be conducted in FY94, first in a sand-box
with chromate and then on clean soil. A field test at the
chromic acid pit at SNL will be conducted in FY95. A system
to remove contaminants collected at the electrodes is
currently under development.
Future Development-
The EKR technology is a developing technology. Projected
performance will be determined after a predictive model for
migration rates is developed. The migration rate is a
function of moisture content, sand grain size, ionic
mobility, pore water current density, contaminant
concentration, and total ionic concentration. Others have
projected the total remediation cost to be in the range of
$50 - $150/yd3. The cost of EKR is dependent on specific
chemical and hydraulic properties present at the site.
EKR has many applications for remediation of industrial
process ground contamination. There are many commercial
sites where toxic metallic contamination may be mixed with
other chemical contamination in unsaturated or saturated
soils.
One example of an important application is near
dated steel processing plants, such as in Poland where lead
contamination in soil and groundwater is a significant
problem. In addition, there are locations in the U.S. where
soil has been contaminated after paint stripping operations
on comparatively old structures where the paint contained
high concentrations of lead. EKR has been used by both the
former Soviet Union and India in applications in unsaturated
soils for mining exploration.
Previous Applications (refs.)-
Patents-
A patent application for SNL's unsaturated soil electrode
system is being prepared.
Industrial Partnerships-
Electro Petroleum Inc., Wayne, PA
United Technologies Corp., East Hartford, CT
University of Washington, Seattle, WA
New Mexico Institute of Mining and Technology, Soccorro, NM
Competing Technologies:
The conventional technology to remediate heavy metal
contaminated soils is excavation and solidification. There
have been some field-scale attempts to use EKR methods to
remove heavy metals from saturated soils in the Netherlands.
A field-scale trial funded by the Environmental Protection
Agency for removal of chromium contamination from soils has
met with partial success, but the success was limited by
inadequate site characterization.
Effectiveness:
EKR is being studied at Sandia National Laboratories (SNL)
by means of laboratory bench-top experiments. Separate
experiments were performed using an anionic dye (FD&C Red
No. 40) and chromate. The electrokinetic behavior of the dye
was found to be similar to that of the chromate. The dye is
used as a surrogate for the hazardous chromate ion. The
initial goals of the benchtop study were to determine the
effects of moisture content and soil grain size on the
electromigration rate.
Experimental results indicate that the minimum moisture
content for which electromigration can take place was 3.5
wt% for the prepared medium grit sand (50-100 mesh) test
bed. Optimum moisture content was determined to be between
14 and 18%.
The EKR technology is a developing technology. Projected
performance will be determined after a predictive model for
migration rates is developed. The migration rate is a
function of moisture content, sand grain size, ionic
mobility, pore water current density, contaminant
concentration, and total ionic concentration. Others have
projected the total remediation cost to be in the range of
$50 - $150/yd3. The cost of EKR is dependent on specific
chemical and hydraulic properties present at the site.
Cost:
Start-up-
O&M-
Decommissioning-
Regulatory Oversight-
Rate/Schedule:
Safety (worker exposure, safety impacts, etc.):
References:
1. Lindgren, E.R., M.W. Kozak, "Electrokinetic Remediation
of Contaminated Soils: an Update", in Waste Management '92,
1992 (Technology and Programs for Radioactive Waste
Management and Environmental Restoration); pp 1309
2. Lindgren, E.R., E.D. Mattson, and M.W. Kozak,
"Electrokinetic Remediation of Unsaturated Soils", Presented
at the I&EC Special Symposium of the American Chemical
Society, Atlanta, GA, September 1992; (Draft copy, submitted
for peer review).
3. DOE-MWLID, "Electrokinetic Remediation", FY92 Technical
Task Description, TTP No. ALZE21J2, October 10, 1991.
Contacts:
Principal Investigator(s)
Eric R. Lindgren
TEL (505) 844-3820
FAX (505) 844-1480
Sandia National Laboratories, Org. 6622
P.O. Box 5800
Albuquerque, NM 87185
Additional Contacts
DOE/OTD Environmental Technology Information Service
1-800-845-2096
DOE Program Manager
Skip Chamberlain
EM-551, Trevion II
U.S. Department of Energy
Washington, DC 20585
(301) 903-7248
Industrial/University Partnership
Electro Petroleum Inc., Wayne, PA
United Technologies Corp., East Hartford, CT
University of Washington, Seattle, WA
New Mexico Institute of Mining and Technology, Soccorro, NM
Reporter:
Peter C. Wallmann
Senior Geologist
Golder Associates Inc.
4104 148th Ave NE
Redmond, WA 98052 USA
TEL 206-883-0777
FAX 206-882-5498
Processed 6/29/94 17:53
Validation:
Processed from Technology Catalogue, First Edition, 1994,
DOE/EM-0138P, U.S. Department of Energy, Office of
Environmental Restoration and Waste Management, Office of
Technology Development.
