Electrochemical and Spectroscopic Properties of Europium in AlCl₃-NaCl Melts

Abstract

The physicochemical properties of Eu cations in AlCl3-NaCl melt have been studied for the purpose of spent nuclear fuel recycling via electrochemical and spectroscopic methods. Eu metal dissolves in the AlCl3-NaCl melt to generate divalent europium and Al metal while releasing chlorine gas. The effect of Lewis acidity of melt on the electrochemical behaviors of Eu(II) has been studied. In Lewis base melt of AlCl3-NaCl, Eu3+, and AlCl4- can be co-reduced at the potential between Al deposition and Eu(II) oxidation. With the enhanced Lewis acidity of the molten salt, Eu(II) diffusion becomes more facile. The in-situ absorption spectra of Eu(II) in AlCl3-NaCl melt reveal that the complexation ligand of Eu(II) changes with the melt Lewis acidity, thereby affecting the electrochemical behaviors of Eu(II) species. In addition, the redox potential of the Eu(II)/Eu(III) conversion reaction is more positive than that of Sm(II)/Sm(III).