INSITUHIGH TEMPERATURE NMR AND EXAFS SPECTROSCOPY IN MOLTEN LANTHANIDE FLUORIDES APPLICATION TO NUCLEAR WASTES RECYCLING

摘要

High temperature ~(19)F Nuclear Magnetic Resonance (NMR) experiments have been performed in different lanthanide fluoride-lithium fluoride (LnF_3-LiF) molten mixtures. The results can be explained with three kinds of fluorine depending on the composition: from free fluorine in pure LiF, to bridging fluorine in melts rich in LnF_3. The chemical shifts evolution over the whole range of composition includes also the presence of non-bridging fluorine involved in the coordination polyhedra around the lanthanide cation. Different molten mixtures of LaF_3-LiF and YF_3-LiF binaries have been followed by ~(139)La and ~(89)Y NMR and spectra show that the coordination is constant and independent of the composition. NMR data were combined with EXAFS measurements at the K edge of Yttrium using a specially designed cell.