Rare earth elements (REEs) are becoming more and more significant as they play crucial roles in many advanced technologies. Therefore, the development of optimized processes for their recovery, whether from primary resources or from secondary sources, has become necessary, including recovery from mine tailings, recycling of end-of-life products and urban and industrial waste. Ionic solvents, including ionic liquids (ILs) and deep-eutectic solvents (DESs), have attracted much attention since they represent an alternative to conventional processes for metal recovery. These systems are used as reactive agents in leaching and extraction processes. The most significant studies reported in the last decade regarding the recovery of REEs are presented in this review.

Ionic liquids have many favorable properties over conventional diluents in solvent extraction. They provide an environmentally benign feature, adjustable polarity and, in some cases, higher extraction performances that remain however not predictable. As it may have a major role in extraction mechanisms, we evidence the supramolecular aggregation of HDEHP/TOPO extractant molecules in the [OMim][NTf₂] ionic liquid.