Electrochemical Behaviors Of Dy(â…¢) And Its Extraction By Forming Alloys With Al In Molten Li Cl-KCl Salts

Partitioning and Transmutation(P&T), is universally accepted to be one of the key-steps in any future sustainable nuclear fuel cycles, in which high efficient separations of actinides(An) and rare earth(RE) are generally needed. RE could account for much in fission products(FP), and the strong neutron absorption cross sections of RE would largely pull down the transmutation efficiency. Al based pyrochemical electrorefining process has been regarded to be a promising alternative for the separation of RE and An, especially for RE and minor actinides(MA), and the key to achieve this goal is that Al can form Al-RE or Al-An alloys. Dysprosium, as an important RE element, its electrochemistry in molten salts and whether it can form Al-Dy alloys have not been fully disclosed, only a few of related studies have been performed, while they are of importance for the recovery of dysprosium. In addition, even the electroreduction mechanism of Dy(III) ions in molten salts is still controversial according to literature reports. Hence, the basic idea of this work is to reassess the electrochemical behaviors of dysprosium in Li Cl-KCl molten salt and better understand the formation process and related mechanisms of Al-Dy alloys through the co-reduction of Dy(III) and Al(III) ions.This paper mainly focused on four parts as following:1. Anhydrous Al Cl3 was applied as a chlorination to Dy2O3 to abtain Dy(III) ion at temperature of 773 K in Li Cl-KCl melt. The prepared pure Li Cl-KCl-Dy Cl3 melts was measured by ICP-MS analysis, and the concentration of Dy(III) ions in which was measured at the same time.2. The electrochemical behaviors of Dy(III) on an inert tungsten electrode or an active Al electrode was investigated in Li Cl-KCl-Dy Cl3 melts at the temperature of 773 K by using cyclic voltammetry(CV), chronopotentiometry(CP), square wave voltammetry(SWV) and open circuit potential(OCP) techniques.The results showed that the reduction of Dy(III) ions in Li Cl-KCl salts is a reversible diffusion controlled process through a one-step three electron transfered reaction: Dy(III) + 3e- ? Dy(0), and the reaction potential of which is-2.04 V. The diffusion coefficient of Dy(III) ions was calculated by both the CV and CP methods, of which the magnitudes is 10-5 cm2s-1. Compared with W electrode, active Al electrode allows Dy(III) ions deposit at a more positive potential(-1.46 V) by under potential deposition.3. The co-reduction behavior of Dy(III) ions and Al(III) ions was investigated in Li Cl-KCl-Dy Cl3-Al Cl3 melts at the temperature of 773 K by using cyclic voltammetry(CV), square wave voltammetry(SWV) and open circuit potential(OCP) techniques. The results showed that the concentration ratio of Al(III) cations to Dy(III) cations has a large impact on the formation of Al-Dy alloys. In a Dy(III) ion rich system, three signals attributed to the formation of Al-Dy intermetallic compounds were observed in CV and SWV analyses, while only two signals corresponding to Al-Dy intermetallic compounds were observed in the Dy(III) ion poor system.4.Potentiostatic and galvanostatic electrolysis performed on an aluminum electrode identified the co-reduction by the formation of one(Al3Dy) and two Al-Dy alloys(Al3Dy, Al Dy), respectively.