Manufacturing of Dysprosium-Iron Alloys by Electrolysis in Fluoride-Based Electrolytes: Oxide Solubility Determinations

Electrolytic production of light rare earth elements and alloys takes place in a fluoride-based electrolyte using rare earth oxides as raw material. The optimization of this method, mainly in terms of the energy efficiency and environmental impact control, is rather challenging. Anode effects, evolution of fluorine-containing compounds, and side cathode reactions could largely be minimized by a good control of the amount of rare earth oxide species dissolved in the fluoride-based electrolyte and their dissolution rate. The oxide content of the fluoride melts REF₃-LiF (RE = Nd, Dy) at different compositions and temperatures were experimentally determined by carbothermal analysis of melt samples. The highest solubility values of oxide species, added as Dy₂O₃ and Dy₂(CO₃)₃, were obtained to be of ca. 3 wt pct (expressed as Dy₂O₃) in the case of the equimolar DyF₃-LiF melt at 1323 K (1050 °C). The oxide saturation values increased with the amount of REF₃ present in the molten bath and the working temperature.