Electrokinetic demonstration at Sandia National Laboratories: Use of transference numbers for site characterization and process evaluation Page: 1 of 9
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Electrokinetic Demonstration at Sandia National Laboratories:
Use of Transference Numbers for Site Characterization and Process Evaluation*
E. R. Lindgren Cok F-
Sandia National Laboratories, Environmental Restoration Technologies,
Albuquerque, NM 87185-0719, 505/844-3820 voice, 505/A44-0543 fax, firstname.lastname@example.org
E. D. Mattson
SAT-UNSAT Inc., 12004 Del Rey NE, Albuquerque, NM 87122 S
Electrokinetic remediation is generally an in situ method using direct current electric
potentials to move ionic contaminants and/or water to collection electrodes. The method has been
extensively studied for application in saturated clayey soils. Over the past few years, an
electrokinetic extraction method specific for sandy, unsaturated soils has been developed and
patented by Sandia National Laboratories. A RCRA RD&D permitted demonstration of this
technology for the in situ removal of chromate contamination from unsaturated soils in a former
chromic acid disposal pit was operated during the summer and fall of 1996. This large scale field
test represents the first use of electrokinetics for the removal of heavy metal contamination from
unsaturated soils in the United States and is part of the US EPA Superfund Innovative Technology
Evaluation (SITE) Program.
Guidelines for characterizing a site for electrokinetic remediation are lacking, especially for
applications in unsaturated soil. The transference number of an ion is the fraction of the current
carried by that ion in an electric field and represents the best measure of contaminant removal
efficiency in most electrokinetic remediation processes. In this paper we compare the transference
number of chromate initially present in the contaminated unsaturated soil, with the transference
number in the electrokinetic process effluent to demonstrate the utility of evaluating this parameter.
Heavy metal contamination of soils and ground water is a widespread problem at EPA
Superfund sites, DOE-operated sites, and privately-owned facilities throughout the nation.
Currently, the only available method for remediating heavy-metal contaminated soil is by
excavation followed by soil washing or relocation. One possible technique for in-situ removal of
such contaminants is through the use of electrokinetics. To conduct electrokinetic remediation,
electrodes are implanted into the ground and a direct current is imposed between the electrodes.
Metal ions migrate toward an electrode where they can be removed.
Methodologies for evaluating a site for electrokinetic remediation and designing an
approach with associated predictions of cleanup level, remediation time, and cost are not well
established. The design problem should be considered in two parts. First, an estimate of the total
amount of electrical current required must be made. This will require knowing not only the mass
of contaminant to be removed, but also the efficiency of current usage or transference number
which depends primarily on the chemical nature of the contamination problem. Secondly, a
determination must be made of how the current will be applied over what time period. This
requires additional physical knowledge of the site such as contaminant plume geometry, soil
resistivity and expected temperature changes which when coupled with the electrode layout
determines the voltage and electrical power requirements.
* This work was performed at Sandia National Laboratories which is operated for the U.S. Department of Energy
under Contract No. DE-AC04-94AL85000 and funded by DOE/OST through the Subsurface Contaminant Focus
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Lindgren, E.R. & Mattson, E.D. Electrokinetic demonstration at Sandia National Laboratories: Use of transference numbers for site characterization and process evaluation, article, March 1, 1997; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc675667/m1/1/: accessed February 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.