Neodymium was electrochemically deposited from NdF₃–LiF–Nd₂O₃ molten salt electrolyte onto the Mo electrode at temperatures close to 1273 K. Cyclic voltammetry and chronoamperometry measurements were the applied electrochemical methods. Metallic neodymium is obtained by potentiostatic deposition. The optical microscopy and XRD were used to analyze the electrolyte, the working electrode surface, and the deposit on the electrode. It was established that Nd(III) ions were reduced to Nd metals in two steps: Nd(III) + e⁻ → Nd(II) at potential ≈−0.55 V vs. W and Nd(II) + 2e⁻ → Nd(0) at ≈−0.83 V vs. W. Both of these processes are reversible and under mass transfer control. Upon deposition under the regime of relatively small deposition overpotential of −0.10 V to −0.20 V, and after the electrolyte was cooled off, Nd metal was observed at the surface of the Mo electrode. CO and CF₄ were gases registered as being evolved at the anode. CO and CF₄ evolution were observed in quantities below 600 ppm and 10 ppm, respectively.

This work is a contribution to the approach for Al purification and extraction from scrap using the thin-layer multiple-capillary molten salt electrochemical system. The single- and multiple-capillary cells were designed and used to study the kinetics of aluminium reduction in LiF–AlF₃ and equimolar NaCl–KCl with 10 wt.% AlF₃ addition at 720–850 °C. The cathodic process on the vertical liquid aluminium electrode in NaCl–KCl (+10 wt.% AlF₃) in the 2.5 mm length capillary had mixed kinetics with signs of both diffusion and chemical reaction control. The apparent mass transport coefficient changed from 5.6∙10⁻³ cm.s⁻¹ to 13.1∙10⁻³ cm.s⁻¹ in the mentioned temperature range. The dependence between the mass transport coefficient and temperature follows an Arrhenius-type behaviour with an activation energy equal to 60.5 kJ.mol⁻¹. In the multiple-capillary laboratory electrolysis cell, galvanostatic electrolysis in a 64LiF–36AlF₃ melt showed that the electrochemical refinery can be performed at a current density of 1 A.cm⁻² or higher with a total voltage drop of around 2.0 V and specific energy consumption of about 6–7 kWh.kg⁻¹. The resistance fluctuated between 0.9 and 1.4 Ω during the electrolysis depending on the current density. Thin-layer aluminium recycling and refinery seems to be a promising approach capable of producing high-purity aluminium with low specific energy consumption.

Electrodeposition processes of neodymium and praseodymium in molten NdF₃ + PrF₃ + LiF + 1 wt.%Pr₆O₁₁ + 1 wt.%Nd₂O₃ and NdF₃ + PrF₃ + LiF + 2 wt.%Pr₆O₁₁ + 2 wt.%Nd₂O₃ electrolytes at 1323 K were investigated. Cyclic voltammetry, square wave voltammetry, and open circuit potentiometry were applied to study the electrochemical reduction of Nd(III) and Pr(III) ions on Mo and W cathodes. It was established that a critical condition for Nd and Pr co-deposition in oxyfluoride electrolytes was a constant praseodymium deposition overpotential of ≈−0.100 V, which was shown to result in co-deposition current densities approaching 6 mAcm⁻². Analysis of the results obtained by applied electrochemical techniques showed that praseodymium deposition proceeds as a one-step process involving exchange of three electrons (Pr(III)→Pr(0)) and that neodymium deposition is a two-step process: the first involves one electron exchange (Nd(III)→Nd(II)), and the second involves an exchange of two electrons (Nd(II)→Nd(0)). X-ray diffraction analyses confirmed the formation of metallic Nd and Pr on the working substrate. Keeping the anodic potential to the glassy carbon working anode low results in very low levels of carbon oxides, fluorine and fluorocarbon gas emissions, which should qualify the studied system as an environmentally friendly option for rare earth metal deposition. The newly reported data for Nd and Pr metals co-deposition provide valuable information for the recycling of neodymium-iron-boron magnets.

The anode effect can occur during neodymium and didymium oxide electrowinning, causing a surge in the electrochemical cell voltage, interrupting the process, and increasing the greenhouse gas emissions. In this work, we develop a mathematical model, based on the mass balance of gas bubbles evolving from the anode, to understand the influence of some process parameters on the anode effect. The anode effect occurs due to bubble coverage and limitations on the mass transfer of the oxide species. Variables such as current density, oxide content, viscosity, and electrolyte composition play an important role in the anodic process. Finally, we propose a mechanism for the occurrence of the anode effect during Nd or Di (Nd–Pr) oxide electrolytic reduction based on models used in aluminum electrolysis.

The impact of rare earth oxide (REO) concentration on the deposition process and selective recovery of the metal being deposited from a molten fluoride salt system was investigated by applying deposition of Nd and Pr and varying the concentration of REO added to the electrolyte. A ternary phase diagram for the liquidus temperature of the NdF₃-PrF₃-LiF system was constructed to better predict the optimal electrolyte constitution. Cyclic voltammetry was used to record three redox signals, reflecting the processes involving Nd(III)/Nd and Pr(III)/Pr transformations. A two-step red/ox process for Nd(III) ions and a single-step red/ox process for Pr(III) ions were confirmed by square-wave voltammetry. The cyclic voltammetry results indicated the possibility of neodymium and praseodymium co-deposition. In order to sustain higher co-deposition rates on the cathode and to avoid increased production of PFC greenhouse gases on the anode, a low-overpotential deposition technique was used for Nd and Pr electrodeposition from the electrolyte with varying Nd₂O₃ and Pr₆O₁₁ concentrations. Co-deposited neodymium and praseodymium metals were characterized by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) analysis. After electrodeposition, concentration profiles of neodymium and praseodymium were recorded, starting from the cathode surface towards the electrolyte bulk. The working temperature of 1050 °C of the molten fluoride salt basic electrolyte, in line with the constructed phase diagram, was validated by improved co-deposition and led to a more effective deposition process.

The Al-V alloys were synthetized by potentiostatic electrodeposition onto a glassy carbon electrode from equimolar AlCl₃ + NaCl bath containing vanadium ions at 200 °C. The alloy deposits were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The deposits were identified as Al₃V and AlV₃ alloys. It was found that intermetallic alloys were synthetized during aluminium underpotential deposition onto vanadium metal that was previously deposited on the glassy carbon electrode by diffusion-controlled overpotential deposition. Alloys were the result of solid-state interdiffusion between the initially deposited vanadium and the subsequently deposited aluminium. As a source to secure a constant concentration of vanadium in the electrolyte during deposition, vanadium anodic dissolution, and VCl₃ melt addition were studied. The effect of vanadium ion concentration in the electrolyte on the composition and the surface morphology of the obtained deposits was investigated. The results indicate that controlled vanadium and aluminium codeposition could be a further step to the successful development of an advanced technology for Al₃V and AlV₃ alloy synthesis.