Enhancement of Electrokinetic Decontamination with EDTA

Department of Civil & Construction Engineering, Southern Polytechnic State University (SPSU), Marietta, Georgia, USA.
Environmental Technology (Impact Factor: 1.56). 04/2012; 33(20):2291-2298. DOI: 10.1080/09593330.2012.665493


The effect of ethylenediaminetetraacetic acid (EDTA) during electrokinetic decontamination (EKD) was investigated in this research. EDTA is a ligand that can form soluble complexes with precipitated heavy metals inside soil pores. Millpond sludge, primarily contaminated with lead (Pb) and zinc (Zn), was subjected to EKD with and without the presence of EDTA. Dilute EDTA solutions with strengths of 0.05M and 0.125M were injected into the millpond sludge by electroosmosis. Several beneficial effects of using EDTA were observed in this research: EDTA substantially increased the electroosmotic (EO) flow in the millpond sludge indicating that it could significantly reduce the duration of EKD. Another advantage was that a significantly higher percentage of Pb and Zn removal was achieved from the solid phase due to the complexation of EDTA with these heavy metals. Also, EDTA was able to prevent the precipitation of metals at the cathode electrode typically observed in EKD process.

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Available from: M A Karim, Feb 25, 2015
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    • "hardness ions.[7] Mobilization of PTMs in soil by the formation of water-soluble toxic EDTA chelate [8] poses a threat to the environment and EDTA-washed soil must be thoroughly rinsed to remove all mobilized PTM species before remediated soil is returned to the site of excavation. Although EDTA is not a particularly expensive chemical , the cost of chelant use can be significant, since low EDTA concentrations often do not extract PTMs from soil effectively.[9] "
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    ABSTRACT: We demonstrate here, in a pilot-scale experiment, the feasibility of ethylenediaminetetraacetate (EDTA)based washing technology for soils contaminated with potentially toxic metals. Acid precipitation coupled to initial alkaline toxic metal removal and an electrochemical advanced oxidation process were used for average recovery of 76 +/- 2% of EDTA per batch and total recycle of water in a closed process loop. No waste water was generated; solid wastes were efficiently bitumen-stabilized before disposal. The technology embodiment, using conventional process equipment, such as a mixer for soil extraction, screen for soil/gravel separation, filter chamber presses for soil/liquid and recycled EDTA separation and soil rinsing, continuous centrifuge separator for removal of precipitated metals and electrolytic cells for process water cleansing, removed up to 72%, 25% and 66% of Pb, Zn and Cd from garden soil contaminated with up to 6960, 3797 and 32.6 mg kg(-1) of Pb, Zn and Cd, respectively, in nine 60kg soil batches. Concentrations of Pb and Zn remaining in the remediated soil and bioaccessible from the simulated human intestinal phase soil were reduced by 97% and 96% and were brought under the level of determination for Cd. In the most cost-effective operation mode, the material and energy costs of remediation amounted to 50.5 Euros ton(-1) soil and the total cost to 299 Euros ton(-1).
    Environmental Technology 01/2014; 35(9-12):1389-400. DOI:10.1080/09593330.2013.869265 · 1.56 Impact Factor
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    • "These studies mainly focus on in situ soil treatment [12] [13] [14]. In addition, complexing ligands, such as EDTA, are also known to increase the electrochemical remediation of soil [15] [16] [17]. "
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    ABSTRACT: This study examined the efficacy of electrokinetic remediation of chelated mine tailing soils with mixed heavy metals. Electrokinetic experiments were conducted in a nontraditional bench-reactor that contained intermediate liquid collection interfaces within treatment zones between the electrodes. Tests were conducted using 0.05 M Na2EDTA as the chelating permeant. Tap water was used in control experiments. A constant direct current voltage of 20 V (electric field≈0.625 V/cm) was applied across working electrodes for 48 h. Transient and spatial distribution of pH, conductivity, oxidation-reduction potential (Eh), and cumulative mass of the metal species in solution were measured. In all experiments, including controls, a larger portion of soluble metals were found in the anode reservoir, indicating transformation of the metals into complex species of negative charge, reverse electroosmotic advection toward anode, and/or colloidally assisted transport. Na2EDTA was expected to increase the metal extraction into the analyte as it produced negatively charged complexes with the metals. Soluble mass of the metals was markedly low in the catholyte, with heavy precipitation of metal hydroxide salts in the ensuing high pH, low Eh environment. Total removals of all three metals were either unchanged or lower, for the same duration of treatment with 0.05 M Na2EDTA than with tap water. Results showed that chelating agents, as was exemplified with a commonly used ligand in here, may not be advantageous in enhancing electrokinetic remediation of heavily contaminated mine tailings. In such substrates, metals' transport and removal regime (i.e., rate, sequence and preference of extraction) appeared to be influenced more so by the type of metal and transient distribution of the pH-Eh under the electric field than the solubilizing effect of a ligand within the treatment zone.
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