Solubilities and raman spectra of NdOCl in some chloride melts of interest for the electrowinning of magnesium from its oxide

Abstract

Some fundamental data related to the solvent proposed for a new technical electrolytic process for magnesium production based on MgO as the raw material are presented. Liquidus data are obtained for MgCl2-rich melts in the MgCl2-NdOCl system. The solubility of MgO and NdOCl in pure liquid NdCl3, MgO in NdCl3-MgCl2 and in MgCl2-NdCl3-NaCl liquid mixtures, and NdOCl in CaCl2 and Cs2MgCl4 have also been studied. The solubility of MgO decreases when MgCl2 is added to the pure NdCl3 and further by additions of NaCl as expected. A so far unidentified compound having the composition MgxNdyOCl2x-3y-2 where x and y are larger than 1 seems to be formed in very small amounts in these melts. This compound seems to precipitate at temperatures higher than 910 °C in the NdCl3-MgO quasi-binary system containing about 8 mol pct MgO and seems to remain suspended in the melt in small quantities. The first liquid-solid phase transition observed, however, was the NdCl3 (1)=NdCl3 (s) transition <758 °C. X-ray diffraction (XRD) data of filtered samples of this solid show new X-ray lines not detected in MgCl2, NdCl3, NaCl, MgO, and NdOCl. The published phase diagram of the quasi binary system MgCl2-NdOCl is, according to the present work, not correct because the solubility of MgO seems to be much less than previously reported. Raman spectroscopic data of NdCl3-MgCl2-NdOCl melts show the known features of the NdCl3-MgCl2 and NdCl3-NdOCl melts. Raman bands due to dissolved species of the unidentified compound were not detected. In view of the obvious small concentration of this species in the liquid phase, this was reasonable.