Research Trends in Rare Metal Recovery Processes Using Deep Eutectic Solvents

With the recent advances in modern technologies, the mass production and widespread use of electronic devices have led to a considerable increase in electronic waste (E-waste), creating a crucial need for efficient and environmentally sustainable E-waste recycling. Conventional metal recovery techniques, including pyrometallurgical and hydrometallurgical processes, often suffer from low economic efficiency and severe environmental burdens, necessitating the development of alternative recovery strategies. Metal recovery using deep eutectic solvents (DESs), which are formed through hydrogen bonding interactions between hydrogen bond donors (HBDs) and acceptors (HBAs), has emerged as a promising alternative to traditional leaching media due to their tunable physicochemical properties, low toxicity, and cost-effectiveness. DESs are environmentally friendly solvents that have recently gained increasing attention due to their various advantages, including mild design, property adjustment, and high solubility. In this review, we summarize the current status of technologies applied to lithium-ion battery recycling and rare earth element recovery using DESs. First, we provide the concept and principles of deep eutectic solvent technology and analyze key factors affecting their efficiency, including hydrogen bonding, coordination interactions, redox behavior, density, and viscosity. In addition, we summarize industrial applications and the current status of related technology development, analyze technological developments in key unit operations of DES-based metal recovery, such as leaching, precipitation, electrodeposition and solvent extraction, and provide available information on recycling of waste lithium-ion batteries and rare earth metals recovery using DESs, presenting prospects for the technology and industry.