Solubility of Nd2O3 in LiF and LiF–NdF3 molten salts

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.