Efficient scandium recovery with deep eutectic solvents confined in carbon nanopores

Abstract

Scandium (Sc) is a rare, yet strategically vital element used in high-performance applications such as aerospace alloys, modern defense systems, fuel cells, and advanced electronics. However, extensive research is currently directed toward the recovery of Sc from secondary sources, such as red mud, which are characterized by trace concentrations and highly complex matrices. In these systems, conventional extractants frequently exhibit insufficient selectivity for Sc³⁺ in the presence of dominant co-leached ions such as Al³⁺ and Fe³⁺. Therefore, developing efficient and selective adsorbents for the recovery of Sc is a top priority. In this study, we investigate the potential of confining a deep eutectic solvent (DES) within the nanopores of mesoporous carbon (CMK-8) materials as a stable, customized adsorbent for highly selective extraction and purification of Sc. The synthesized materials demonstrated good extraction capacity, with a maximum adsorption of 3.3 mg g⁻¹ and high selectivity for Sc, along with excellent chemical stability over multiple cycles, even under harsh extraction conditions (pH = 1), making them suitable for recovering Sc from various sources and ultimately reducing waste during primary production. The batch extraction tests demonstrated rapid Sc uptake, achieving nearly 100% removal within 30 s. Additionally, the CMK-8-DES material maintains high selectivity for Sc even under challenging conditions, such as extraction from simulated red mud solutions, where competing elements are present at significantly higher concentrations than Sc (i.e., pH = 2, [Sc] = 8 ppm, [Al] = 2050 ppm, and [Fe] = 1330 ppm). These findings indicate that immobilizing DES within a porous carbon matrix offers a sustainable tactic for developing advanced adsorbents for real-world applications.