Deep eutectic solvents for sustainable recovery of critical and rare metals from primary and secondary resources: A review

The growing demand for critical raw materials and increasing environmental concerns have intensified interest in sustainable metal recovery from both primary ores and secondary resources. While conventional extraction from ores remains essential, it is often associated with high energy consumption, reagent use, and environmental impacts. In parallel, recovery from secondary sources such as electronic waste (e-waste), industrial by-products, and end-of-life products has emerged as a key strategy within urban mining and circular resource utilization. Deep eutectic solvents (DESs) have recently gained attention as tunable solvent systems due to their adjustable physicochemical properties, relatively simple preparation, and potential environmental advantages. DES-related research has increased significantly, with a notable rise in DES-based leaching studies since 2018. This review provides a comprehensive overview of DES applications in the recovery of critical and rare metals from both primary ores and secondary resources, emphasizing physicochemical properties, selective leaching behavior, operating conditions, process flowsheet considerations, and downstream recovery challenges. DESs have been applied in spent lithium-ion batteries, permanent magnets, primary ores, waste printed circuit boards (WPCBs), coal fly ash, metallurgical slags, and red mud. These studies highlight the potential of DESs for processing complex matrices and enabling selectively dissolution of target metals under specific solvent and process conditions. By integrating this review critically evaluates the scientific and practical significance of DESs in improving metal selectivity, reducing reliance on aggressive mineral acids, and supporting circular economy strategies, while identifying key challenges related to solvent stability, recyclability, downstream recovery, process integration, and scale-up.