Simultaneous Removal of Pb, Cd, and Zn from Heavily Contaminated Mine Tailing Soil Using Enhanced Electrochemical Process Aydeniz Demir, 1, * Sibel Pamukcu, 2 and Reena Amatya Shrestha 2 1 Department of Environmental Engineering, Mersin University, Mersin, Turkey. 2 Department of Civil and Environmental Engineering, Lehigh University, Bethlehem, Pennsylvania. Received: August 9, 2014 Accepted in revised form: December 31, 2014 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 interme- diate liquid collection interfaces within treatment zones between the electrodes. Tests were conducted using 0.05 M Na 2 EDTA 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 (E h ), 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. Na 2 EDTA 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 E h environment. Total removals of all three metals were either unchanged or lower, for the same duration of treatment with 0.05 M Na 2 EDTA 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-E h under the electric field than the solubilizing effect of a ligand within the treatment zone. Key words: electrochemical remediation; mine tailings; mixed heavy metals; Na 2 EDTA enhanced remediation; sequential extraction Introduction A s soil contamination increasingly threatens human health and ecosystem functioning, heavy metal mitiga- tion of soils, sediments, and tailings has become an acute geo- environmental engineering problem of the 21st century (Pociecha and Lestan, 2010; Saleem et al., 2012). Cleaning of heavy metal-contaminated soils is difficult because metals are nondegradable and they persist when adsorbed onto the soil colloids and other constituents (Dermont et al., 2008; Voglar and Lestan, 2012). Among the commonly used cleanup methods are: washing with aqueous solutions of strong ligands (Shrestha et al., 2003; Dermont et al., 2008), and physicochemical stabilization methods (Di Palma et al., 2003; Kim et al., 2003; Rao et al., 2008). Chelating agents and ligands have been used to enhance in-situ (e.g., flushing, phytoextraction) or ex-situ (e.g., washing, heaping) remedi- ation of heavy metal-contaminated soils. The problem with soil washing is by-production of a complex solution that often requires further treatment (Ortega et al., 2008; Voglar and Lestan, 2012; Demir and Koleli, 2013). Finding a sustainable method of recycling the used soil washing solutions remains an unsolved technical problem. Enhanced electrochemical processes have been shown to produce effective results in lowering the levels of contami- nants in soils, sediments, and industrial waste water (Pa- mukcu et al., 1997; Ottosen et al., 2001, 2009; Hansen et al., 2005; Garcia-Gutierrez et al., 2007; Reddy et al., 2010). Among these, electrokinetic method is the process of ap- plying a low-voltage direct-current electric field across the treatment zone or contaminated soil mass to transport charged particles, ionic constituents, and polar molecules (e.g., ions, water, micelles, and colloids) toward the working *Corresponding author: Department of Environmental Engineering, Mersin University, Mersin 33342, Turkey. Phone: +90 324 361 0001; +90 324 361 7033; Fax: +90 324 361 0015; E-mail: demiraydeniz@ gmail.com; aydenizdemir@mersin.edu.tr ENVIRONMENTAL ENGINEERING SCIENCE Volume 32, Number 5, 2015 ª Mary Ann Liebert, Inc. DOI: 10.1089/ees.2014.0384 416