Introducing hybrid electrokinetic-permeable reactive barrier-membrane systems for remediation of soil-slag mixtures contaminated with Pb and Zn.

Abstract

This study investigates the effectiveness of electrokinetic (EK) remediation for the removal of lead (Pb) and zinc (Zn) from a contaminated soil-slag mixture collected from the Isfahan Steel Industry. The mixture exhibited high buffering capacity, significant organic matter content, and elevated Pb and Zn concentrations. The electrokinetic setup, which was constructed from transparent plexiglass, consists of three main sections: a soil chamber, two electrolyte reservoirs and two stainless steel electrodes and they were placed at the ends of the soil chamber within electrode compartments. Nine experiments were performed under a constant voltage gradient of 1.5 V/cm over 120 h to evaluate different enhancement strategies, including (1) coupling EK with pistachio shell-derived activated carbon as a permeable reactive barrier (PRB) near the cathode and both electrolytes, (2) incorporating a cation exchange membrane (CEM) near the cathode, (3) conditioning the electrolyte with ethylenediaminetetraacetic acid (EDTA), both alone and in combination with PRB and CEM, and (4) pre-treating the mixture with EDTA. Visual Minteq modeling indicated that, in the absence of EDTA, the dominant Pb and Zn species were Pb₃(OH)₄²⁺ and Zn(OH)₂, while the presence of EDTA led to the formation of PbEDTA^2- and ZnEDTA^2-, enhancing metal mobility. The highest removal efficiencies were obtained in the experiment where EDTA (0.1 M) was used in the catholyte, PRB was placed at the center of the cell, and CEM was applied near the cathode, achieving 68.7% Pb and 48.3% Zn removal with lower energy consumption. SEM-EDS analysis confirmed significant Pb and Zn adsorption onto the activated carbon. The findings suggest that the integration of PRB, CEM, and EDTA-enhanced electrolyte conditioning improves electrokinetic remediation performance and offers a feasible approach for treating heavy metal-contaminated soil-slag mixtures.