Lanthanides extraction processes in molten fluoride media: Application to nuclear spent fuel reprocessing

This paper describes four techniques of extraction of lanthanide (Ln) elements from molten salts in the general frame of reprocessing nuclear wastes; one of them is chemical: the precipitation of Ln ions in insoluble compounds (oxides or oxyfluorides); the others use electrochemical methodology in molten fluorides for extraction and measurement of the progress of the processes: first electrodeposition of pure Ln metals on an inert cathode material was proved to be incomplete and cause problems for recovering the metal; electrodeposition of Ln in the form of alloys seems to be far more promising because on one hand the low activity of Ln shifts the electrodeposition potential in a more anodic range avoiding any overlapping with the solvent reduction and furthermore exhibit rapid process kinetics; two ways were examined: (i) obtention of alloys by reaction of the electroreducing Ln and the cathode in Ni or preferably in Cu, because in this case we obtain easily liquid compounds, that enhances sensibly the process kinetics; (ii) codeposition of Ln ions with aluminium ions on an inert cathode giving a well defined composition of the alloy. Each way was proved to give extraction efficiency close to unity in a moderate time.

Overlapping of the neodymium and solvent respective potential ranges, is avoided by co-reduction with Al, which shifts equilibrium potential towards anodic sense, as observed on square wave voltammetry of Nd and Al, where we observe the alloys formation (peaks 2a, 3a and 4a) containing Nd at more positive potentials than pure Nd.Figure optionsDownload as PowerPoint slide