Combined effects of high voltage gradient and electrolyte conditioning on electrokinetic remediation for chromium (VI)-contaminated soils

Abstract

Disposal of chromium-containing industrial waste has led to soil contamination at dispersed locations around the globe. Considering the carcinogenic, non-biodegradable, and bioaccumulating nature of hexavalent chromium Cr (VI), it is per-tinent to treat the contaminated soils. Electrokinetic Remediation (EKR) is a promising technology to remediate metal-contaminated soils under the influence of an electric field. This study investigated the removal of Cr (VI) by EKR, enhanced with a combination of high voltage (50 V), electrolyte conditioning using EDTA (0.1 M), and type of electrode material. Under controlled conditions using distilled water, low voltage (20 V at 1 V/cm) resulted in 22% removal, while high volt-age (50 V at 2.5 V/cm) resulted in 55% removal of Cr (VI) in 10 h of treatment period. The removal was further enhanced to 77% by amending with ethylenediaminetetraacetic acid (EDTA 0.1 M) as an electrolyte at a high voltage gradient of 2.5 V/cm. Classifying the role of electrode (graphite and stainless steel), based on the removal efficiency and corrosion of electrodes, graphite resulted in higher removal compared to stainless steel but with a significantly higher corrosion effect. Characterization of soil after EKR experiments exhibited improved liquid and plastic limits, and insignificant difference in Total Organic Carbon (TOC) and other parameters related to soil health. Energy consumption and cost-estimation revealed that application of high voltage, along with conditioning of electrolyte with EDTA can significantly increase removal of Cr (VI) in short period of time in a cost-effective (0.8 US$/g) way, thereby can be applied for rapid treatment of large volumes of soil without affecting the properties of soil.