Effect of electrolyte, potential gradient and treatment time on remediation of hexavalent chromium contaminated soil by electrokinetic remediation and adsorption

摘要

Chromium pollution of soil is a serious environmental problem. The methods for remediating heavy metal contaminated soil include: containment, leaching, microbial remediation and phytoremediation. However, the drawbacks, such as high chemical cost, secondary pollution and lack of long-term stability, have limited the practical application of these methods. In this study, an environmentally friendly method of electrokinetic remediation (EKR) combined with adsorption was used to remediate chromium contaminated soil. Two groups of EKR experiments were conducted in the laboratory to study the factors affecting the electric current, pH, and removal efficiency. First, the variation in electric current and electrolyte pH when using different electrolytes (citric acid, sodium chloride, and deionized water) was compared. Then, the effect of remediation time (3, 5, and 7 days) and potential gradient (2, 1, and 0.5 V/cm) on Cr~(6+) removal efficiency was studied. Moreover, the mechanisms of heavy metal removal were analysed. The results showed that the citric acid cannot only neutralize hydroxide ions produced by water electrolysis in the cathode but also reduce some of Cr~(6+) anions to nontoxic Cr~(3+) cations. The Cr~(6+) concentration in section S2 and S3 was higher than that in section SI, S4 and S5, because the migration direction of Cr~(6+) anion was opposite under the functions of electromigration and electroosmosis. The Cr~(6+) removal efficiency reached up to 72.4 under potential gradient of 2 V/cm and remediation time of 5 days, and no toxic chemicals were added or produced. EKR combined with exchange resin adsorption is environmentally friendly and efficient and can be applied in situ.