Recovery of rare earth elements from weathering crust soils using electrokinetic mining technology☆

Abstract

Ion-absorption deposits (IADs) of rare earth elements (REEs) constitute the main economic resources of the essential heavy rare earth elements (HREE). Nonetheless, the existing leaching methods for extracting REEs from IADs face limitations stemming from significant environmental consequences and a poor REE recovery rate. In a recent development, electrokinetic mining (EKM) has emerged as a novel technology for extracting REEs from ion-adsorption deposits, demonstrating the potential for environmentally friendly and efficient recovery of REEs from weathering crusts. However, the transport mechanism of REE in weathering crust soil in an applied electric field remains poorly understood, and the influence of the EKM process has yet to be studied. In this study, we systematically investigated the transport characteristics of REE in weathering crust soil under the influence of an electric field. We demonstrate that the transport of REE is simultaneous with the transport of water, H+, and OH– in the applied electric field, where the EKM process is influenced by the voltage gradient, initial soil water content, electrode numbers, and power-on time. Under the optimal EKM conditions, 78.8% of REE is recovered from a 45 kg-scale weathering crust soil. Additionally, we identify the transport diversity between light REE (LREE) and HREE, which assists in the separation and pre-enrichment of LREE and HREE. Furthermore, we demonstrate that the mechanism for REE transport under an electric field involves a combination of electromigration, electroosmosis, and electrolysis working synergistically. This study provides new perspectives on the transport behavior and mechanism of REEs in weathering crust soil under an electric field. These findings pave the way for the practical implementation of EKM technology.