Revealing the mechanism of electrokinetic remediation for lead-contaminated clayey soil by using molecular dynamics simulations

This study uses molecular dynamics (MD) simulations to investigate the electrokinetic properties of lead-contaminated Na-montmorillonite under varying cation exchange capacities (CEC) and lead ion concentrations in coupled electric and hydraulic fields, aiming to elucidate mechanisms that govern lead ion distribution and pore water flow. Results reveal that Pb²⁺ and Na⁺ ions form hydration layers in water, migrating under an electric field and contributing to electro-osmotic flow. Electro-driven and hydraulic-driven processes are shown to be independent and can be linearly superimposed, with maximum removal efficiency achieved when the electric field aligns with the hydraulic gradient. The concentration of wall charges ϕ_e is employed to integrate MD simulation results with the traditional electro-osmosis model, which is confirmed by literature data and illustrates the validation of the established molecular model. Analysis indicates that CEC enhances electro-osmotic flow within a specific range (<100 cmol kg⁻¹), while the presence of lead ions has an inhibitory effect. Based on electric double layer (EDL) theory, the coupling impact of these two factors on electric potential ψ(z), ζ-potential, and thickness of the diffuse layer are investigated. The results show that increasing CEC significantly raises potential ψ(z) and ζ-potential, while higher lead ion concentrations compress the EDL and reduce electro-osmotic efficiency. This study provides theoretical and technical insights to optimize electrodynamic remediation parameters for practical applications in lead-contaminated soil remediation.