Study on Water-Heat-Solution Transport Law in Cr(VI)-Contaminated Soil during Electric Remediation

Abstract

In order to understand the water-thermal-solute transport pattern during the electrokinetic remediation of Cr(VI)-contaminated soil, this study selected 2.46 m3 of Cr(VI)-contaminated soil from a chemical plant plot for an indoor experiment of electrokinetic remediation, which monitored the changes of three indicators of soil volumetric water content, temperature and Cr(VI) content over time under the conditions of a voltage of 90 V and 110 V and an electrode distance of 1.5 m for 7 days. A numerical model was also developed using the finite element software COMSOL, which was evaluated and calibrated to predict the changes in soil volumetric water content and hexavalent chromium concentration within 15 days. The results showed that the soil volumetric water content near the anode showed a decreasing trend at the beginning, and then gradually increased when the external supplemental water arrived. The decrease in soil volume water content became larger when the voltage increased. During the electrokinetic remediation experiment, the maximum temperature could reach 36.9 °C at 5 cm from the anode under the conditions of 90 V and 1.5 m distance between electrodes, while the maximum temperature could reach 52.4 °C at a voltage of 110 V. Moreover, the higher the voltage, the faster the temperature rise of the soil at the same location. A higher voltage increased the removal rate of hexavalent chromium, and the removal rate of hexavalent chromium in shallow soils was higher than that in deep soils. At 90 V and an electrode distance of 1.5 m, the removal rates of hexavalent chromium at sampling points 6 and 7 reached 66.03% and 60.80%, respectively. The removal rates of points 6 and 7 at 110 V were able to reach 75.96% and 70.74%, respectively.