NdF3 and Nd2O3 Effect on the Physicochemical and Volume Properties of Cryolite-Based Melts and the NaF + NdF3 Systems

This study investigates the physicochemical and volume properties of neodymium-containing cryolite-based melts and the NaF + NdF3 system. Densities were measured using the Archimedean method, showing a linear decrease with increasing temperature and an increase with the NdF3 or Nd2O3 content. Calculated molar and partial molar volumes indicate local expansion upon addition of neodymium compounds. However, the partial molar volumes of NdF3 at infinite dilution are lower than those of Nd2O3, due to stronger Nd3+–F– interactions and more compact local structures in fluoride melts. In cryolite-based melts, the [AlF6]3– network enhances packing, resulting in higher partial molar volumes for Nd2O3. Direct calculations are in good agreement with predictive procedures (1A and 1B), validating the data set. These results provide a detailed thermophysical description of Nd-containing melts, offering a valuable basis for modeling and optimizing industrial processes for neodymium separation and refining.