Enhancing electrokinetic remediation of soil contaminated with As, Cd, Cu, and Pb using the biodegradable chelator GLDA: A pilot study

Abstract

Purpose

This study aims to assess the feasibility and efficiency of electrokinetic (EK) remediation of soil contaminated with As, Cd, Cu, and Pb using the biodegradable chelator N, N-bis(carboxymethyl)-tetrasodium salt (GLDA) at the pilot scale.

Materials and methods

The experiments were performed under a constant voltage (40 V) in an EK reactor (100 cm (length) × 50 cm (width) × 25 cm (height)) for over 100 days using various enhancement strategies. The current, electroosmotic flow (EOF), microstructure, mineral composition of the soil samples (before and after EK remediation), removal efficiencies, chemical forms, and ecotoxicity risks of As, Cd, Cu, and Pb were determined.

Results and discussion

The results showed gradual decreases in the electrical current and EOF over time. The spatial distribution of As, Cd, Cu, and Pb in the soil solution and electrolyte revealed that the removed metals primarily accumulated in anolytes. The soil As, Cd, and Cu contents, especially near the anode, showed gradual reductions. The total removal efficiencies of As, Cd, Cu, and Pb were 49.4%, 44.0%, 53.6%, and 36.6%, respectively. Overall, the ecotoxicity risks of the remaining As, Cd, Cu, and Pb were below the initial values. A soil microstructure and mineral composition analysis indicated that the GLDA-enhanced EK technology effectively removed As, Cd, Cu, and Pb by dissolving soil minerals and breaking chemical bonds. The unit energy consumption ranged from 1.25 to 1.83 kW·h/t/%, indicating lower or comparable values to the data in the literature.

Conclusions

The biodegradable chelator, GLDA, has been shown to remove different types of potentially toxic elements using enhancement strategies on a pilot scale with low unit energy consumption. Arsenic migrated to the anode in the anionic form, and the complexes formed by Cd, Cu, and Pb with GLDA were negatively charged and moved toward the cathode. After the EK treatment, the ecotoxicity risks of As, Cd, Cu, and Pb decreased with a reduction in the contents and the chemical form changes of As, Cd, Cu, and Pb.