Deep eutectic solvents and electrochemical metal recycling: a comprehensive method review

The increasing reliance on critical metals is exhausting the primary resources, while also intensifying the environmental problems associated with traditional and harmful metal recycling processes. The present paper responds to the pressing need for sustainable recycling of critical metals by providing a comprehensive review of Deep Eutectic Solvents (DESs), which are efficient, low-cost alternatives to conventional acid leaching. Unlike existing literature focused solely on leaching performance, this study explores the cohesive relationship linking the physicochemical properties of DESs to metal dissolution and electrochemical recovery. The paper highlights the rapidly growing DES research and the exceptional efficiency of DESs for recovering metals such as copper, nickel, cobalt, and manganese from spent batteries or waste printed circuit boards, etc. The review highlights the limitations of DES, relationship between leaching and physicochemical properties of DESs and suggests integrated approach of DES leaching followed by electrochemical recovery. Techniques, including cyclic voltammetry and chronoamperometry, are suggested for potential extractability confirmation and selective and pure recovery of metals. The review acknowledges a marked preference for Choline Chloride-based DESs, focuses on ternary DESs in recycling a myriad of metals (i.e., Co, Li, U) and upcycling the recovered metals into functional cathode precursors. The study discusses important challenges of scaling up for industrial purposes, such as high viscosity, low thermal stability, and controlling complex metal speciation. It also recommends identifying more unexplored components that can be used to produce DES and can act as an efficient substitute for the commonly used Choline Chloride. In closing, the paper proposes a development pathway for industrial-scale, circular hydrometallurgy by combining molecular design, process intensification strategies, and comprehensive TEA/LCA frameworks. • Deep Eutectic Solvents (DESs) for metal recovery. • Types and components of DESs. • Efficiency of DESs for the leaching of heavy or critical metals. • Compatibility of DESs with the electrochemical process for metal reclamation. • Preparation of DESs for metal recovery.