Tailoring the Use of 8-Hydroxyquinolines for the Facile Separation of Iron, Dysprosium and Neodymium.

Abstract

Permanent magnets (PMs) containing rare earth elements (REEs) can generate energy in a sustainable manner. With an anticipated tenfold increase in REEs demand by 2050, one of the crucial strategies to meet the demand is developing of efficient recycling methods. NdFeB PMs are the most widely employed, however, the similar chemical properties of Nd (20-30 % wt.) and Dy (0-10 % wt.) make their recycling challenging, but possible using appropriate ligands. In this work, we investigated commercially available 8-hydroxyquinolines (HQs) as potential Fe/Nd/Dy complexing agents enabling metal separation by selective precipitation playing on specific structure/property (solubility) relationship. Specifically, test ethanolic solutions of nitrate salts, prepared to mimic the main components of a PM leachate, were treated with functionalized HQs. We demonstrated that Fe³⁺ can be separated as insoluble [Fe(Q_Cl,I)₃] from soluble [REE(Q_Cl,I)₄]^- complexes (Q_Cl,I ^-: 5-Cl-7-I-8-hydoxyquinolinate). Following that, Q_Cl ^- (5-Cl-8-hydroxyquinolinate) formed insoluble [Nd₃(Q_Cl)₉] and soluble (Bu₄N)[Dy(Q_Cl)₄]. The process ultimately gave a solution phase containing Dy with only traces of Nd. In a preliminary attempt to assess the potentiality of a low environmental impact process, REEs were recovered as oxalates, while the ligands as well as Bu₄N⁺ ions, were regenerated and internally reused, thus contributing to the sustainability of a possible metal recovery process.