Influence of Rare Earth Oxide Concentration on Electrochemical Co-Deposition of Nd and Pr from NdF3-PrF3-LiF Based Melts

• Published in: Metals (Basel ) Vol. 12; no. 7; p. 1204
• Main Authors: Cvetković, Vesna S., Feldhaus, Dominic, Vukićević, Nataša M., Milicevic-Neumann, Ksenija, Barudžija, Tanja S., Friedrich, Bernd, Jovićević, Jovan N.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-07-2022
• Subjects: Carbon; Cathodes; co-deposition; Codeposition; Electrodeposition; Electrodes; Electrolytes; Electron probe microanalysis; EPMA; Experiments; fluoride melts; Fluorides; Gases; Greenhouse gases; Liquidus; Lithium fluoride; Metals; Neodymium; Phase diagrams; Praseodymium; Praseodymium oxide; Rare earth oxides; Signal processing; ternary phase diagram; Ternary systems; Trace elements; Voltammetry; Netherlands
• ISSN: 2075-4701; 2075-4701
• DOI: 10.3390/met12071204

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.