Reengineering electrokinetics: EDTA-enhanced mobilization of organic soil pollutants

• EDTA boosts COC transport in EKR, enabling efficient organic pollutant remediation. • Low temperatures (10 °C) enhance electro-osmotic flux and contaminant mobilization. • EDTA extraction peaks at 0.1 M; higher concentrations show no added benefit. • Electro-osmosis drives cathodic COC transport more than electromigration. • 26 mmol EDTA needed per mmol COC at 10 °C, key for scalable EKR design. • EDTA expands EKR use beyond metals, targeting persistent organic pollutants. The lack of mobility of chlorinated organic compounds in electrokinetic systems requires enhancement of the operational parameters. In this study, we investigated the role of ethylenediaminetetraacetic acid (EDTA) as a catholyte additive in enhancing the electrokinetic remediation (EKR) of real-contaminated soils containing chlorinated organic compounds (COCs). Initial soil washing experiments confirmed EDTA’s chelating efficacy, with extraction increasing from 0.006 mmol using pure water to 0.15 mmol with 0.1 M EDTA. Subsequent EKR trials at varying temperatures revealed that EDTA significantly improves COC mobilization, particularly toward the anode, where a 120% increase in molar transport was observed at 10 °C. This enhancement is attributed to the interaction between negatively charged EDTA complexes and chloro-substituted aromatic and alicyclic compounds, facilitating directional migration under an electric field. Temperature played a critical role in optimizing electro-osmotic flux and minimizing evaporation, with sub-25 °C conditions favoring contaminant transport. However, EDTA’s anionic nature also contributed to reduced soil electrical resistance, indirectly supporting electrokinetic performance. Notably, COC mobilization toward the cathode was less pronounced, with only a 20% increase, primarily driven by water movement rather than electrophoretic or electromigration. The study quantified EDTA demand, indicating that 26 mmol and 8 mmol of EDTA are required per mmol of COC mobilized at 10 °C and 25 °C, respectively. Despite lower extraction yields in EKR (0.086 mmol L⁻¹) compared to soil washing (0.149 mmol L⁻¹), the findings underscore EDTA’s potential to enhance organic pollutant mobility in electrokinetic systems. This work expands the applicability of chelating agents beyond heavy metals, offering new pathways for remediating complex organic-contaminated matrices.