Solubility of Nd2O3 in LiF and LiF–NdF3 molten salts

Abstract

Accurately measuring the solubility of Nd₂O₃ in the LiF–NdF₃ molten salt system is of great significance for establishing a reasonable feeding system for the electrolytic production of the rare earth metal neodymium and its alloys. Based on the isothermal saturation method, this article developed a membrane method for accurately measuring the solubility of rare earth oxides in molten salts, which solves the problem that the solubility values obtained by traditional isothermal saturation methods are too high due to the presence of undissolved Nd₂O₃ or NdOF in the molten salt supernatant. This method also has reference value for studying the solubility of other substances in molten salts. Simultaneously, the experimental process uses NdOF instead of Nd₂O₃ to indirectly study the solubility of Nd₂O₃ in LiF–NdF₃ molten salt, solving the problem of analysis errors caused by chemical reactions between Nd₂O₃ and NdF₃ in the molten salt system. The effects of dissolution time, dissolution temperature, and NdF₃ concentration on the solubility of Nd₂O₃ were studied in detail. The experimental results show that, under the conditions of 1373 K and 9 h dissolution time in LiF molten salt, the maximum solubility of Nd₂O₃ is 0.32% (wt%). In the LiF–NdF₃ binary molten salt system, when the concentration of NdF₃ is 23 mol%, the maximum solubility of Nd₂O₃ is 2.77% (wt%) in the temperature range of 1173 K to 1373 K. At 1273 K, when the concentration of NdF₃ is in the range of 16 mol% to 45.5 mol%, the maximum solubility is 3.37% (wt%), which provides basic data for the formulation of an accurate feeding system for electrolytic neodymium production. Using EPMA, the analysis of the quenched sample of the LiF–23 mol% NdF₃–3.5 wt% Nd₂O₃ molten salt system at 1473 K revealed the presence of the Nd₃O₂F₅ compound in the system.