Electrokinetic transport mechanisms of rare earth elements in ion-adsorption deposits: An integrated model approach

Abstract

Heavy rare earth elements (REEs) are critical strategic resources for advanced technologies and the low-carbon economy transition. Ion-adsorption deposits (IADs) represent the primary sources of heavy REEs, yet their mining has caused severe environmental impacts. Electrokinetic mining (EKM), a sustainable alternative, promises efficient REE recovery from IADs. However, the electrokinetic transport mechanisms of REEs in IADs remain unclear, and predictive models are lacking. Here, we develop an integrated EKM (IEKM) model that rigorously incorporates coupled effects of diffusion, convection, electromigration, electroosmosis, and electrolysis to resolve REE transport in IADs. The IEKM model was validated using a 14-ton-scale IAD EKM, accurately simulating REE and leaching agent (NH₄⁺) ion transport. The predicted REE recovery efficiency is 80.97 % after 11 days of EKM, aligning with experimental results (88.28 ± 17.00 %). Significantly, the IEKM model quantitatively determines that diffusion, convection, electromigration, electroosmosis, and electrolysis contribute 3.06 %, 2.90 %, 82.91 %, 0.20 %, and 10.93 %, respectively, to REE transport. Unexpectedly, electromigration emerges as the dominant mechanism governing REE electrokinetic transport in IADs with significant influence by electrolysis, while electroosmosis exhibits negligible contribution, contradicting conventional expectations. Furthermore, electrolysis consumed 57.95 % of input energy due to water splitting, leaving only 42.05 % for direct REE transport. This work advances fundamental understanding of REE electrokinetic transport in IADs and establishes an industrially viable model, bridging experimental and numerical modeling to facilitate practical applications of environmentally sustainable EKM technology in resource recovery.