Electrokinetic remediation of chromium (Cr)-contaminated soil with citric acid (CA) and polyaspartic acid (PASP) as electrolytes

Abstract

In this study, the electrokinetic (EK) remediation of industrial soil contaminated by chromium (Cr) was explored using two electrolytes, citric acid (CA) and polyaspartic acid (PASP). All of the EK experiments were conducted in a 2-L soil cell reactor with a moisture level of 23.1% blended with a total Cr of 11.20±1.03mgg−1 under a constant voltage gradient (2Vcm−1) for 7d. The experimental results showed that electric energy was wasted to heat up the soil in EK remediation as the soil temperature increased. The temperature difference in soil-cell positions was likely caused by a variety of soil characteristics, such as ionic strength. Compared with deionized water (DW), using CA in the contaminated soil was found to effectively improve the removal efficiencies of both the total Cr and Cr6+. However, using PASP only improved the Cr6+ removal efficiency, mainly because the CA and PASP could restore Cr6+ to Cr3+. When using both CA and PASP as electrolytes, the α-OH and –COOH groups play a key role in chromium reduction. In the EK experiment, the relatively lower removal efficiency of the total Cr with PASP was partially due to the transformation of the exchangeable portion of Cr into carbon-bounded Cr. Carbon-bounded Cr has a lower migration rate than that of the exchangeable portion. Compared with the addition of DW, additional energy consumption was increased in the EK remediation after adding the two electrolytes to reach the same removal rates of Cr. Consequently, utilization efficiency of the accumulated electrical energy consumption decreased.