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REEs are selectively separated from REPM wastes. The separated REEs are recycled in the form of rare-earth metals which can be directly applied in industry. Forming anode channels make the separation of REEs in the inside of REPM wastes feasible. • Rare-earth metal was directly recycled from REPM waste. • Forming anodic channels facilitated the oxidation of rare-earth elements inside the REPM waste. • The formation parameter and process of channels were proposed. Tens of thousands of tons of rare-earth permanent magnet (REPM) wastes are produced worldwide every year. The recovery of rare-earth elements from the wastes can effectively reduce the exploitation of rare-earth minerals. The recovery of neodymium and praseodymium from a REPM waste is investigated by electrolysis in molten LiF-CaF 2 where no anode gas releases, making the process environmentally attractive. Neodymium and praseodymium are selectively oxidized from the REPM waste and transformed into rare-earth ions. To facilitate the oxidation of rare-earth elements inside the REPM waste, we intended to make REPM electrode form channels by oxidation of Nd-Pr and Nd 2 Fe 14 B alloys. By analyzing the microstructure of REPM electrode after forming channels, it can be found that the channels provide continuous transport access of the electrolyte to the inside of the REPM electrode. The separation rates of Nd and Pr increase with increasing current, while the rate of oxidation reaction is proportional to current. In addition, the oxidation of Fe initially occurs at the inside of the REPM electrode where rare-earth elements have been first depleted. The separated rare-earth ions are directly prepared as rare-earth metals at the cathode by electrolysis, leaving the porous Fe 2 B alloy and metallic Fe. [ABSTRACT FROM AUTHOR]

We proposed a simple and sustainable approach to recover rare earths and iron from an ultrafine NdFeB waste. Rare earths were directly recovered by one-step precipitation in hydrofluoric acid and the dissolved iron was recovered in the form of nano-scale FeF 2 (s) and Fe(s) by electrodeposition. The hydrofluoric acid, which has removed iron by electrodeposition, could be still used for the leaching of the waste, making the hydrofluoric acid recyclable. • A simple and sustainable approach was proposed to recover rare earths and iron from an ultrafine NdFeB waste. • Rare earths were directly recovered by one-step precipitation. • The chemicals used in this approach were recyclable. In this work, a simple and sustainable approach is proposed to recover rare earths and iron from an ultrafine NdFeB waste. Rare earths are directly recovered by one-step precipitation in hydrofluoric acid and the dissolved iron by electrodeposition. The rate constant and activation energy of the reaction of rare earth hydroxide with hydrofluoric acid are investigated to understand the kinetics of iron leaching and rare earth precipitation. The rare earth precipitation is much faster than the iron leaching, enabling the rare earths separation from iron after a complete iron dissolution. The cathodic deposits of iron were characterized by X-ray photoelectron spectrometer (XPS) and scanning electron microscope (SEM). The nano-scale FeF 2 (s) and Fe(s) were deposited on Pt electrode in hydrofluoric acid solution with pH 2.3 and pH 2.89, respectively. The reduction of Fe(III) to Fe(0) was investigated by cyclic voltammetry, chronopotentiometry and open circuit chronopotentiometry. This reduction was a quasi-reversible process which was controlled by diffusion. The temperature dependence of the diffusion coefficient was established as lnD = −9.84 − 1805.43/ T and the activation energy value of the diffusion process was calculated to be −15.01 kJ mol−1. The relationship between the Gibbs energy of intermetallic Fe-Pt formation and the temperature was established to be Δ G = −487.53 + 0.936 T. The hydrofluoric acid after the electrodeposition could be recycled for the leaching of the ultrafine NdFeB waste again. [ABSTRACT FROM AUTHOR]