Application of enhanced electrokinetic approach to remediate Cr-contaminated soil: Effect of chelating agents and permeable reactive barrier

Enhanced electrokinetic (EK) technique was employed to remediate Cr-contaminated soil using a permeable reactive barrier (PRB) and chelating agents. Synthesized nanomagnetic Fe3O4 was used as a reactive material in PRB. Moreover, EDTA and citric acid (CA) were used as chelating agents. Sequential extraction method (SEM) was employed to determine Cr-elimination mechanism during the EK process. The results revealed that EDTA (78% Cr removal) was more effective than CA (54% Cr removal) in eliminating Cr from the contaminated soil during the EK process. The application of PRB in combination with EDTA was able to reduce the Cr removal rate to 70 and 66% by locating PRB in the middle section and near the anode/cathode reservoir, respectively. The use of PRB coupled with EDTA near the anode and cathode led to a more uniform Cr removal from the soil during the EK process. The highest energy consumption was 0.12 KWh during the EK remediation using PRB. Traditional EK remediation could only remove exchangeable and carbonate fractions of Cr. The use of chelating agents led to a significant (more than 90%) increase in Cr removal from the following fractions: exchangeable phase, carbonate phase, and bond to Fe-Mn oxides. In addition to electromigration (EM) mechanism, electroosmotic flow (EOF) played an important role in Cr removal during the EK process, especially when coupled with PRB.