The growing demand for rare earth elements (REEs), particularly Nd, Pr, and Dy, has intensified the need for their efficient recovery from secondary resources such as NdFeB magnet waste. As part of hydrometallurgical processing, this review focuses on purification strategies at the pregnant leach solution (PLS) stage — the key bottleneck in REE recycling — addressing the challenge of selective separation and individual recovery from chemically complex feeds. It critically evaluates solvent extraction (SX), ion exchange (IX), and adsorption-based processes, including recent advances and their industrial applications. SX remains the industrial benchmark due to its scalability and high efficiency, but is constrained by significant chemical consumption, solvent losses, and poor selectivity among closely related REEs such as Nd and Pr. IX provides selective recovery and pre-concentration for dilute and impurity-rich streams, with advanced chromatographic systems (ligand-assisted displacement, MGDA-based elution) achieving >99% purity for adjacent REE pairs. Adsorption is emerging as a tunable and operationally simpler alternative, competitive for dilute streams and group REE recovery, but currently limited by a TRL and capacity gap relative to commercial IX and SX under industrially relevant conditions. Post-processing methods including precipitation, crystallization, and electrodeposition are also reviewed. The review concludes that no single technology provides a universal solution — the most promising pathway lies in chemistry-driven integrated flowsheets in which leaching, SX, IX, and adsorption are deliberately combined to match each technology to the feed stream for which it is best suited.
Asasian-Kolur et al. (Mon,) studied this question.