Quantitative Study on Dissolution Behavior of Nd₂O₃in Fluoride Melts

Abstract

The dissolution of rare earth oxides in molten fluorides is a critical step in the preparation of the corresponding rare earth metals by oxide-fluoride electrolysis. However, quantitatively understanding the nature of dissolution, especially in the case of molten salts, is usually difficult to be achieved by postmortem characterization. In this paper, the dissolution behavior of Nd2O3 particles in molten fluorides was studied via in situ observation with confocal scanning laser microscopy. Combining direct observation with thermodynamic analyses on the oxide dissolution, the rate-limiting step(s) and the effects of parameters like temperature, salt type, and composition on the dissolution rate are identified. This study provides a methodology to estimate the dissolution kinetics of rare earth oxides in molten fluorides during their primary and secondary processing.

Investigation on the Electrochemical Behaviour and Deposition Mechanism of Neodymium in NdF3–LiF–Nd2O3 Melt on Mo Electrode

“…The same conclusions based on very similar voltammograms obtained from identical or very similar fluoride electrolytes support the said deliberations [18,20,25]. The dissolution of Nd2O3 in molten fluoride (LiF-NdF3) is a diffusion-controlled process which can be accelerated if the temperature and NdF3 concentration in the melt are increased [30]. However, Nd2O3 has very limited solubility in fluoride melts (LiF-CaF2-NdF3, LiF-KF-NdF3, etc.).…”

“…Which of the two species will be predominantly involved in the neodymium deposition reaction should depend on the neodymium oxyfluoride ions/neodymium fluoride ions molar ratio [17,29], electrode potential, and current density applied [24]. The dissolution of Nd 2 O 3 in molten fluoride (LiF-NdF 3 ) is a diffusion-controlled process which can be accelerated if the temperature and NdF 3 concentration in the melt are increased [30]. However, Nd 2 O 3 has very limited solubility in fluoride melts (LiF-CaF 2 -NdF 3 , LiF-KF-NdF 3 , etc.).…”

Dissolution and Online Monitoring of Nd and Pr Oxides in NdF3–PrF3–LiF Electrolytes

“…The current high demand for neodymium (Nd) and praseodymium (Pr) and their alloys is attributed to their superior magnetic flux density needed for developing very strong permanent magnets [1,2]. These rare earth (RE) metals are mostly extracted from their oxides via molten salt electrolysis.…”

“…These rare earth (RE) metals are mostly extracted from their oxides via molten salt electrolysis. The electrolytic production of Nd and Pr has advantages, such as high purity of end product, low energy consumption, and high efficiency [2][3][4]. The efficiency and environmental footprint of the electrolysis process, however, largely depend on the effective dissolution of the rare earth metal oxide (REO) in the electrolyte.…”

“…The efficiency and environmental footprint of the electrolysis process, however, largely depend on the effective dissolution of the rare earth metal oxide (REO) in the electrolyte. The most suitable electrolyte composition for dissolving REO consists of rare earth fluoride (REF), alkali metal fluoride (AF), and in some cases small amounts of alkali earth metal fluorides (AEF) [2,3,5]. In general, the solubility of the REO increases with increasing content of REF in the fluoride electrolyte [5].…”