Abstract:

The accelerating global demand for neodymium (Nd) highlights its strategic role in neodymium-iron-boron (NdFeB) permanent magnets, which serve as essential components in electric vehicle motors, wind turbines, and clean energy technologies. Owing to the increasing use of such technologies, sustainable and secure Nd supply has become a global priority. Conventional production routes based on mining and refining of rare earth ores are energy-intensive and environmentally harmful, while current recycling and recovery technologies rarely achieve direct metallic Nd production. Hydrometallurgical processes, though efficient in rare earth dissolution, generate large volumes of aqueous effluents and require extensive purification. Pyrometallurgical methods, conversely, demand high operating temperatures (above 1500°C) and often yield oxides or alloys rather than high-purity Nd metal. Consequently, there remains a critical technological gap for a single-step, energy-efficient, and low-waste process capable of directly producing metallic Nd from End-of-Life (EoL) magnets.

This research investigates molten salt electrowinning (MSE) as a direct, single-step route for Nd recovery. As a high-temperature, non-aqueous electrochemical system, MSE enables selective Nd³⁺ reduction and metallic deposition while suppressing co-reduction of impurity species.

The first step was to establish the state of knowledge in molten salt electrowinning and identify suitable electrolyte compositions, electrode materials, electrochemical operation windows, and impurity control strategies. Based on thermodynamic and kinetic criteria, a LiCl–KCl–MgCl₂ eutectic composition (55:40:5 mol%) was formulated to achieve a low melting temperature (596 K) and was thermally characterized using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Salts were purified and dried under glovebox conditions, and corrosion-resistant crucibles were employed to ensure reproducible and inert electrochemical environments. Following electrolyte development, the solution behavior of neodymium is investigated by preparing controlled NdCl₃ concentrations and quantifying solubility and speciation using ICP-MS.

The electrochemical performance of Nd3+ was evaluated in a three-electrode cell using cyclic voltammetry (10-200 mV/s), revealing a two-step reduction mechanism (Nd³⁺ → Nd²⁺ → Nd) over a potential range of −1.0 to −2.0 V (vs. Cl⁻/Cl₂). Controlled electrolysis experiments were performed at current densities of −10 to −100 mA cm⁻² and temperatures (723-1073 K). Oxygen and moisture impurities were mitigated using sacrificial magnesium getters.

By carefully deoxygenating the LiCl–KCl–MgCl₂–NdCl₃ melt and using an inert cathode, this work directly targets key methodological gaps in distinguishing metallic Nd from oxide or intermetallic products. Within the experimentally defined Nd³⁺ → Nd²⁺ → Nd⁰ potential window, the applied potentials remain significantly more positive than those required for Mg or other cation reduction in the salt, so Nd is selectively reduced and deposited in its metallic form, rather than as Mg–Nd alloys or Nd oxides. Recovered metals and intermediate products were characterized using SEM/EDS and XRD to evaluate morphology, purity, and microstructure and to establish correlations with processing conditions.

These stages provide the scientific foundation for electrowinning studies and future application to real magnet-waste feeds. This work advances practical REE recycling, supporting Canada's critical minerals strategy and fostering sustainable clean energy technologies.

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Ms. Asal Shoaei