Ionic liquid as an emerging alternative for the separation and recovery of Nd, Sm and Eu using solvent extraction technique-A review

Rare earth metals (REMs), especially neodymium, samarium and europium are termed as critical metals since their supply is experiencing shortfall due to sudden rise in demand. Solvent extraction as an effective separation technique has been widely adopted for the recovery and recycling of these metals from a collection of several primary and secondary resources. Ionic liquids possessing negligible volatility have potential usefulness in rare earth extraction, either as the diluents or as extractants. The diversity in terms of structural properties, superior physico chemical characteristics and tunability to achieve higher selectivity have made these ionic liquids interesting and potential stakeholders for the application in liquid-liquid extraction and separation of Nd, Sm and Eu. The extractive separation of these elements by quaternary ammonium, phosphonium ionic liquids occurs mostly through ion exchange mechanism while it follows neutral complexation pathway when functionalized ionic liquids are in action. The present review comprehensively describes the separation and recovery of Nd, Sm and Eu employing different types of ionic liquids based on various operating conditions, extraction mechanism and efficiency. The process schemes for the recovery of these metals from post-cosumer products like magnets and phosphors using ionic liquids have also been summarized and discussed in detail.