A new strategy of thin oil film extraction for enhanced recovery and separation of praseodymium and neodymium

Abstract

Recycling of rare earths from their secondary resources such as waste neodymium magnets has attracted extensive attention in recent years. However, to obtain the high purity products, the separation of praseodymium (Pr) and neodymium (Nd) with extremely similar physic-chemical properties is very difficult. In this study, a new strategy of thin-layer oil film extraction was proposed for enhanced mutual separation of Pr3+/Nd3+. Experimental results revealed that the separation factors between Pr3+/Nd3+ were considerably improved comparing with the conventional extraction. Decreasing the thickness of oil layer spreading on the surface of feed liquid was beneficial for the interface renewal. Therefore, the adsorption of Tricaprylmethylammonium nitrate molecules and their arrangement in order at the interface were promoted. Regulating an appropriate flow rate of feed liquid was favorable for intensifying the difference in mass transfer rate of Pr3+ and Nd3+ ions perpendicular to the oil/water interface. The enhanced separation of Pr3+/Nd3+ during the process of thin-layer oil film extraction is mainly dependent on their diffusion mass transfer kinetic difference. The maximum separation factor can reach above 10, which is difficult to achieve in the conventional processes based on the thermodynamic difference. Molecular dynamics simulations and attenuated total reflectance infrared spectroscopy provided detailed mechanisms on enhanced separation at the molecular level. The present work highlights a possible approach of kinetic separation to achieve the selective recovery of Pr and Nd from the leaching solutions of waste neodymium magnets.