Mechanism-Guided Deep Eutectic Solvents for Selective Metal Recovery from Solid Wastes: Linking Occurrence States to Closed-Loop Separation

Complex metal-containing solid wastes pose major recovery challenges because target metals and impurities coexist in different occurrence states and may be simultaneously transferred into deep eutectic solvent (DES) leachates. DESs offer tunable acidity, redox capacity, coordination environments, and solvation properties, enabling regulation of metal release and recovery. However, existing studies rarely integrate metal occurrence states, release barriers, liquid-phase speciation, phase partitioning, and downstream recovery. This Review develops a mechanism-guided framework linking solid-state characteristics with protonation, redox regulation, coordination stabilization, solvation, and mass transfer. Density functional theory, COSMO-RS, and machine learning are further integrated to elucidate molecular interactions, predict solvation and phase behavior, and identify multivariable relationships governing recovery performance. The framework extends from leaching to selective separation, product recovery, and DES regeneration. The analysis shows that high leaching efficiency alone does not ensure process viability, which also depends on selectivity, downstream recovery, solvent regeneration, and material and energy demands. By integrating these factors with environmental, economic, and engineering considerations, this Review provides a basis for designing selective, recyclable, and more sustainable DES-based metal recovery processes.