Complicating factors of using ethylenediamine tetraacetic acid to enhance electrokinetic remediation of multiple heavy metals in clayey soils

Batch and electrokinetic experiments were conducted to investigate the removal of three different heavy metals, chromium(VI), nickel(H), and cadmium(II), from a clayey soil by using ethylenediamine tetraacetic acid (EDTA) as a complexing agent. The batch experiments revealed that high removal of these heavy metals (62-100%) was possible by using either a 0.1 M or 0.2 M EDTA concentration over a wide range of pH conditions (2-10). However, the results of the electrokinetic experiments using EDTA at the cathode showed low heavy metal removal efficiency. Using EDTA at the cathode along with the pH control at the anode with NaOH increased the pH throughout the soil and achieved high (95%) Cr(VI) removal, but the removal of Ni(II) and Cd(II) was limited due to the precipitation of these metals near the cathode. Apparently, the low mobility of EDTA and its migration direction, which opposed electroosmotic flow, prevented EDTA complexation from occurring. Overall, this study found that many complicating factors affect EDTA-enhanced electrokinetic remediation, and further research is necessary to optimize this process to achieve high contaminant removal efficiency.