Effects of Permeable Reactive Composite Electrodes on Hexavalent Chromium in the Electrokinetic Remediation of Contaminated Soil

Abstract

Electrokinetic transport processes have been shown to have potential for effective removal of heavy metals from soils. However, pH changes near the anode and cathode limit their widespread application in remediation of contaminated soils. Permeable reactive composite electrodes (PRCEs) were constructed by attaching reactive materials such as Fe(0) and zeolite to electrodes, and effects of composite electrodes on pH control, chromium (Cr) removal efficiency, and adjustment of speciation of Cr were studied in the electrokinetic remediation of Cr(VI)-spiked soil. Composite electrodes consisting of permeable reactive materials gave better pH control and Cr removal efficiency compared to application of traditional electrodes, and a reactive layer of Fe(0) and zeolite in the anode exhibited the best performance compared to zeolite or Fe(0) alone. After 5 d of electrokinetic remediation with a DC voltage of 2.0 V/cm, the Fe(0)+zeolite reactive layer buffered pH fluctuation, maintained soil pH in the range of 5.5–8.5, and increased Cr(VI) remediation efficiency up to 97% in each section of soil. Additionally, it resulted in lower Cr(III) residues, enhancement of the amount of Cr retention up to 8× and 1.8×, respectively, and transformation of 98% of the Cr(VI) to lower toxicity Cr(III). After remediation, heavy metal ions were removed from the remediation system simply by unplugging the composite electrodes, which theoretically needed no further treatment—a major advantage over traditional electrokinetic remediation methods. This study provides a theoretical basis for exploitation of PRCEs, which is a practical option for future applications.