A one-pot process based on P44414Cl-HCl aqueous biphasic system for recovering rare earth elements from NdFeB permanent magnet

Abstract

Recovering critical metals from secondary resources have attracted great interest recently. In this work, a green one-pot leaching-extraction process based on tributyl(tetradecyl)phosphonium chloride (P44414Cl) aqueous biphasic system (ABS) was developed to efficiently recover rare earth elements (REEs) from NdFeB permanent magnet. The reaction process, phase separation mechanism, and operation conditions were thoroughly investigated. It is found that the P44414Cl-HCl ABS showed strong extraction ability towards Fe (> 99%) whereas only a few REEs (< 10%) were extracted, leading to extremely high separation selectivity between Fe and REEs. The characterization results showed that the coordination differences of Fe and Nd in HCl were the main driving forces for such highly selective separation. The phase diagram of P44414Cl-NdCl3 ABS indicated that the salting-out effect of NdCl3 was stronger than common chlorides. Due to the hydrophobic property of P44414[FeCl4] and salting-out effect of NdCl3, the P44414Cl could directly form ABS at room temperature after dissolving practical roasted NdFeB samples without any other operations and reagents. REEs and Fe could be mutually separated in just one step. Compared with traditional liquid-liquid extraction or ABS separation, this recovery process is green and facile and shows great application prospects in the field of rare-earth recovery.