Abstract
Rare earth elements (REEs) are indispensable to modern technologies, including renewable energy systems, advanced electronics, catalysts, and defense applications, yet their separation remains technically demanding due to their similar ionic radii and identical trivalent oxidation state. This review critically examines contemporary methods for the extraction and separation of REEs from both primary mineral deposits and secondary technogenic resources. Emphasis is placed on hydrometallurgical leaching strategies, including environmentally oriented bioleaching approaches, as well as downstream separation technologies such as solvent extraction, ion exchange, ion-imprinted polymers, and membrane-based systems. The aqueous chemistry and coordination behavior of REEs are discussed to elucidate the thermodynamic and kinetic factors governing selectivity across the lanthanide series. Recent advances in tailored polymeric resins, solvent-impregnated materials, polymer inclusion membranes, and biomimetic ion channels demonstrate significant progress toward molecular-level discrimination among closely related REEs. Although solvent extraction remains industrially dominant, emerging ion-exchange and membrane technologies offer promising pathways toward improved selectivity, reduced chemical consumption, and enhanced sustainability. The integration of advanced materials design, green chemistry principles, and process intensification strategies is identified as essential for developing scalable, environmentally responsible REE recovery systems capable of strengthening global supply resilience.