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

Abstract

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.

Electrochemical Study of Nd and Pr Co-Deposition onto Mo and W from Molten Oxyfluorides

“…They were represented as four reduction (cathodic) current waves (C1, C2, C3 and C4) and four oxidation (anodic) counterparts (A1, A2, A3 and A4). Comparing the current wave peak potentials shown in Figure 2 to the similar current wave potentials obtained in our previous study from NdF3 + LiF + 2wt.%Nd2O3 electrolyte on W and Mo electrodes under the same conditions for the neodymium deposition and dissolution, helped attribution of C1/A1 and C2/A2 to the deposition and dissolution of neodymium and C4/A4 to the deposition and dissolution of lithium [12,15]. According to the data published in our earlier work, in the fluoride electrolyte, neodymium reduces to the metal form in two steps, seen as C1 and C2 in Figure 2 [12,15].…”

“…As a result, in some applications, such as permanent magnets, the term didymium (Di), which is an Nd-Pr alloy, is used [8]. For deposition processing of neodymium and praseodymium via molten salt electrolysis, in terms of efficiency and environmental footprint, molten fluorides or chlorides are commonly used as electrolytes [8][9][10][11][12].…”

“…A series of studies have been successfully performed to determine not only the electrochemical behaviour of Nd or Pr in different electrolyte media, but also to obtain RE metal alone or RE-alloy samples by selective electrochemical deposition on chosen working substrates [11][12][13][14][15][16]. Nevertheless, the processes for Nd-Pr alloy production by electrolysis from molten chloride or fluoride were difficult to execute and only limited research has been published [17,18].…”

NdFeB Magnets Recycling Process: An Alternative Method to Produce Mixed Rare Earth Oxide from Scrap NdFeB Magnets

“…Generally, we developed one combined environmentally friendly process for recovery of nanosized powder mixture of Nd 2 O 3 and Pr 2 O 3 from spent magnets and re-use of nitric acid. The final winning of the mixture of metallic Nd and Pr will be ensured using molten salt electrolysis [34].…”

Advances in Understanding of the Application of Unit Operations in Metallurgy of Rare Earth Elements

“…Hydrometallurgy contains technologies derived from science of geochemistry where metals are extracted into an aqueous solution and subsequently recovered by a variety of methods. The hydrometallurgical unit operations are mostly used for metal recovery from ores, concentrates, and secondary materials: leaching under atmospheric pressure [1], treatment under high pressure in an autoclave [2], bioleaching [3], microwave dissolution [4], dry digestion [5], acid baking [6], filtration [7], neutralization [8], solvent extraction [9], purification of solution using anionic exchange resin [10], cementation [11], precipitation [12][13][14][15][16][17], crystallization [18], electrocoagulation [19][20][21], reduction in aqueous phase [22], aqueous electrolysis [23], electrochemical deposition with molten salt electrolysis [24], and ultrasonic spray pyrolysis [25][26][27][28][29][30][31][32].…”