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Study of Aluminium-Lanthanide Extraction in MoltenFluorides by Electrochemical Co-Reduction


Study of Aluminium-Lanthanide Extraction in Molten Fluorides by Electrochemical Co-Reduction

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									   Study of Aluminium-Lanthanide Extraction in Molten
        Fluorides by Electrochemical Co-Reduction
           Mathieu Gibilaro, Laurent Massot*, Pierre Chamelot, Pierre Taxil
     Laboratoire de Génie Chimique UMR 5503, Département Procédés Electrochimiques,
                     Université Paul Sabatier, 31062 Toulouse Cedex 9

Since 1991, French nuclear industries investigate solutions for treatment of the
radioactive wastes. The actual hydrometallurgical process PUREX allows uranium and
plutonium to be extracted for further recycling. In novel generation reactors, this
process is no more available for extraction of lanthanides and actinides which exhibit
too low solubility in aqueous medium. An alternative route should be the use of
pyrochemical processes using molten fluorides.
The process for actinides recovery by reductive extraction on liquid aluminium in LiF-
AlF3 medium seems to be promising according to [1]. So, for recycling the solvent, the
step of extraction of the other fission products, such as lanthanides (Ln), in presence of
aluminium ions must be expected; it is the aim of this work.
Due to lanthanides reduction potential close to the solvent reduction in lithium molten
fluorides, the extraction efficiency is limited at around 90% on inert electrode; this is
not enough for nuclear applications [2].
So this work concerns the co-deposition process of Al-Ln in LiF-CaF2 medium (79-
21% mol.) at 860 °C using electrochemical techniques: cyclic voltammetry, square
wave voltammetry and potentiostatic electrolyses on tungsten electrode.
Al-Ln alloys formation peaks were observed in cyclic voltammetry between the
reduction waves of LnIII and AlIII, when both lanthanide and aluminium ions are present
in the melt.
The difference of potential measured between the solvent reduction and the alloys
formation allows reaching an extraction efficiency of 99.99%.
Then, obtained alloys were characterised by Scanning Electron Microscopy (SEM)
with EDS probe.
Preliminary similar experiments of extraction of samarium and cerium were performed
to validate the process.

[1] O. Conocar, J. Serp, “Promising pyrochemical Actinide/Lanthanide separation
processes using Aluminium”, Nucl. Sci. Eng., 153, 2006, 253-261

[2] P. Chamelot, L. Massot, C. Hamel, C. Nourry, P. Taxil, “Feasibility of the
electrochemical way in molten fluorides for separating thorium and lanthanides and
extracting lanthanides from the solvent”, J. of Nucl. Mater, 360, 1, 2007, 64-74x

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