NdF 3 and Nd 2 O 3 Effect on the Physicochemical and Volume Properties of Cryolite-Based Melts and the NaF + NdF 3 Systems

This study investigates the physicochemical and volume properties of neodymium-containing cryolite-based melts and the NaF + NdF 3 system. Densities were measured using the Archimedean method, showing a linear decrease with increasing temperature and an increase with the NdF 3 or Nd 2 O 3 content. Calculated molar and partial molar volumes indicate local expansion upon addition of neodymium compounds. However, the partial molar volumes of NdF 3 at infinite dilution are lower than those of Nd 2 O 3, due to stronger Nd 3 + –F – interactions and more compact local structures in fluoride melts. In cryolite-based melts, the [AlF 6 ] 3– network enhances packing, resulting in higher partial molar volumes for Nd 2 O 3 . 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.