Controlled Ion Transport in the Subsurface: A Coupled Advection-Diffusion-Electromigration System

TL;DR

This paper presents a coupled advection-diffusion-electromigration model for controlling ion transport in groundwater, introducing a new classification based on Peclet number and Electrodiffusivity index, validated through simulations.

Contribution

It introduces a novel ion transport regime classification and demonstrates how manipulating electric potential, pressure, and concentration can control transport regimes in porous media.

Findings

Identification of four distinct ion transport regimes.

Validation of regimes through simulations in heterogeneous models.

Highlighting the importance of tailoring Pe and EDI for optimal control.

Abstract

Groundwater pollution poses a significant threat to environmental sustainability during urbanization. Existing remediation methods like pump-and-treat and electrokinetics have limited ion transport control. This study introduces a coupled advection-diffusion-electromigration system for controlled ion transport in the subsurface. Using the Lattice-Boltzmann-Poisson method, we simulate ion transport in various two- and three-dimensional porous media. We establish an ion transport regime classification based on the Peclet number (Pe) and a novel Electrodiffusivity index (EDI). By manipulating the electric potential, hydrostatic pressure, and ion concentration, we identify four transport regimes: large channeling, uniform flow, small channeling, and no flow. Large channeling occurs when advection dominates, while uniform flow arises when diffusion and electromigration are more prevalent. Small channeling happens when the advection opposes electromigration and diffusion, and no flow occurs when the advection or electromigration impedes ion transport via diffusion. Simulations in heterogeneous models confirm these transport regimes, highlighting the influence of pore size variation on transport regimes. Consequently, $Pe$ and $EDI$ must be tailored for optimal transport control. These findings enable better control over ion transport, optimizing processes such as heavy metal removal, bioremediation, and contaminant degradation in groundwater management.