Technical Note Improvement in electrokinetic remediation of heavy metal spiked kaolin with the polarity exchange technique M. Pazos, M.A. Sanroma ´n, C. Cameselle * Department of Chemical Engineering, University of Vigo, E-36200 Vigo, Spain Received 28 June 2004; received in revised form 21 April 2005; accepted 22 April 2005 Available online 20 June 2005 Abstract In the electrokinetic treatment of heavy metal polluted soil, an alkaline environment is generated at the cathode side. It provokes the precipitation of metal ions as hydroxides into the soil and diminishes the capability of the electroreme- diation to clean the polluted site. In this work the ‘‘polarity exchange’’ technique is presented as a simple way to avoid the negative effect of OH À on metal transportation. This technique lies in the operation during short time intervals at inverted polarity, so that the generation of H + ions from the oxidation of water neutralize in the alkaline zone where the metal is precipitated, favouring its dissolution. Once the metals are redissolved, the polarity is set to the original posi- tion to transport them to the desired direction. Kaolin clay contaminated with Mn was used to test the feasibility of the polarity exchange technique. The application of the ‘‘conventional technique’’ dealt with a removal of 14% of the initial Mn in 7.6 d. For a similar treatment time the polarity exchange technique resulted in 72% of removed Mn. Successive polarity exchanges will yield with a complete decontamination of the soil with a moderate increment in the electric power consumption. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Polarity exchange; Heavy metals; Soil remediation; Electrokinetic remediation 1. Introduction Electrokinetic remediation is an innovative technique for the decontamination and restoration of polluted soils, sludges and other solid wastes. The principle of electrokinetic remediation relies upon the application of a low-intensity direct current through a porous solid medium between appropriately distributed electrodes. This technique can be performed in situ and resulted effective for the treatment of low hydraulic permeability soils, which are difficult to treat with other techniques. It advantages include low power consumption, close con- trol over the direction of water and dissolved conta- minants, and the confinement of pollutants in the electrode chambers that makes easier the subsequent treatment (Page and Page, 2002). During the electrokinetic treatment of a soil, pollu- tants are transported towards the electrodes by electro- migration (migration of ions towards the opposite charged electrode) and electroosmosis (movement of liquid relative to the charged soil particles) (Acar and Alshawabkeh, 1993). The electroremediation process is governed in part by the electrode reactions that are inherent to the process, i.e. the electrolysis of water (Yeung et al., 1997). The oxidation of water at the anode 0045-6535/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2005.04.071 * Corresponding author. Tel.: +34 986 812318; fax: +34 986 812382. E-mail address: claudio@uvigo.es (C. Cameselle). Chemosphere 62 (2006) 817–822 www.elsevier.com/locate/chemosphere