Recent Work on the Recovery of Rare Earths Using Ionic Liquids and Deep Eutectic Solvents

With the development of smart technologies, the use of rare-earth elements (REEs) has been widespread; thus, their importance as valuable and strategic metals has been boosted to levels never known before. Due to their scarcity in the Earth's crust, the recovery of these elements from secondary resources has also witnessed further developments. Traditional pyrometallurgical and hydrometallurgical processing techniques, though widely used in the recovery of these REEs, have some environmental drawbacks; thus, new recovery approaches are under development. Here, Solvometallurgy has emerged as an environmentally friendly technology, and ionic liquids and deep eutectic solvents have turned out to be first-line chemicals to be used in the different unit operations employed in solvometallurgical processing, i.e., leaching, liquid-liquid extraction, ion exchange (adsorption), precipitation, and electrolysis. This manuscript reviews the most recent literature (2002-June 2023) concerning the use of ionic liquids and deep eutectic solvents in the recovery of REEs from various sources.