An EXAFS Spectroscopy Study of Speciation of Uranium and Some Fission Product Elements in Chloride Melts

The various chloro complexes of the transition metals U, Y, Zr, Ru, Tc and Re in high-temperature chloride melts (both liquid and quenched) have been investigated using EXAFS spectroscopy. All the oxidation states of uranium (III, IV, V and VI) are stable in molten LiCl U(III) and U(IV) form UCl 6 X− ions and U(V) and U(VI) form UO 2 Cl 4 X− ions. U(III) and U(IV) are the most stable oxidation states in LiCl-BeCl 2 eutectic melt; even under a Cl 2 atmosphere (but in the absence of oxygen) U(VI) species are converted into U(IV){can't make sense of this sentence: do you really mean this, +6 reduced to +4 by chlorine?}. U(III) and U(IV) are present in the melt as hexachloro complexes. Yttrium(III) forms YCl 6 3− ions and there is evidence that these units are joined together into chains by sharing two Cl ligands between every two Y atoms. Zr in LiCl melt forms Zr(II) and Zr(IV) ions, both six-coordinated. Ruthenium in LiCl-KCl and NaCl-KCl between 450 and 750 °C, and in quenched samples forms six-coordinated complexes with Ru–Cl distances essentially independent of temperature and melt composition. Only quenched melt samples of technetium and rhenium have so far were investigated. Tc can form Tc(IV) and Tc(VIII) ions, TcCl 6 2− and TcO 4 − , and rhenium under the same conditions always yielded the Re(IV) species, ReCl 6 2− .