Selective Growth of Nb-Fe-B Intermetallic Compounds for the Direct Separation of Rare Earths Based on Manipulating Liquation

Abstract

Since the primary goal of industrialization has changed to carbon neutrality, the importance of rare earths (REs) has increased due to their criticality in green industries. The attainment of sustainable resources via green production processes is necessary due to the increasing need for REs. Liquid metal extraction is regarded as a leading technology for supporting the sustainability of resources based on the selective reactivity between REs and extractants. However, this process requires multiple stages, including pretreatment, extraction and separation, which are considered bottlenecks in industrialization. In this work, reverse selectivity is applied instead of conventional liquid metal extraction (c-LME) for the direct separation of REs in a single stage. Niobium (Nb) is selected because of its thermodynamic properties for enhancing the selectivity of the reactions between the extractant and other elements, excluding REs. The process is thermodynamically designed for liquation systems, and it reflects the interactions between the extractant and magnets. The solidification behavior based on the selective growth of phases without REs is shown with variations in the composition and cooling rate to confirm the kinetics. The composition prevents the formation of RE-Fe intermetallic compounds, and excess Nb is considered a bottleneck for separating REs. In addition, the cooling rate influences the agglomeration of RE as a layer. Because of the manipulation of the liquation, 92.89% of the REs are successfully separated in the form of accumulated layers. This effective process for the direct separation of REs is verified through thermodynamic and experimental assessments. Overall, this investigation can provide new guidelines for the construction of a circular economy after improving the energy efficiency of this system in future research.