Harnessing Electric Fields for Rare Earth Element Recovery: A Computational Study of Electromigration and Flow Dynamics Using Dilute Feedstock

The extraction of critical metals, such as rare earth elements (REEs), from dilute feedstocks like geothermal brine, mine tailings, and produced water is crucial for advancing clean energy technologies and sustainable manufacturing. However, the efficient separation of REE ions from these sources remains challenging due to their similar chemical properties and the complex interactions within dilute mixtures. This study explores an electrohydrodynamic-based approach for separating REE ions from a dilute feedstock containing competing cations using a Computational Fluid Dynamics (CFD) continuum model that incorporates ion transport via diffusion, advection, and electromigration. Numerical simulations highlight the competition between flow velocity, microfluidic channel dimensions, and electrohydrodynamic effects in determining separation selectivity. We showed that the e-field-based separation process is governed by three distinct regimes: (i) a diffusion-advection balance regime, where diffusion counteracts flow-induced advection, resulting in limited ion separation and reducing separation selectivity by promoting a more uniform ion concentration distribution; (ii) an electromigration-dominant regime, where the applied electric field overcomes advection effects, enabling selective ion migration and enhanced separation selectivity; and (iii) an advection-dominant regime, where high flow velocities dominate electromigration, leading to poor separation performance. Our results reveal that optimal separation is achieved when electromigration dominates over both diffusion and advection, which occurs under conditions of slow flow and strong electric fields. Additionally, narrower channel geometries intensify local electric field gradients, further enhancing electromigration and improving ion selectivity but also increasing sensitivity to flow velocity variations. This work emphasizes the need to address charge neutrality issues in CFD modeling and, more importantly, a fundamental understanding of the interplay between flow dynamics, channel design, and electrohydrodynamic forces to develop efficient methods for extracting critical metals from dilute feedstocks. These advancements are essential for enabling sustainable resource recovery and supporting emerging technologies.