Liquid Electrodes for An/Ln Separation in Pyroprocessing

Abstract

The aim of this work is to evaluate and compare the possibility of Cd, Hg, Al, Ga, Sn, Pb and Bi as candidate cathode materials based on their physicochemical and electrochemical properties and theoretical separation ability for actinides over lanthanides. First, the comparison of melting points and vapor pressures about those metals shows that Group 12 elements Cd and Zn are more practically suitable for the electrowinning process. Then, cyclic voltammetry conducted at 773 K on these cathodes in LiCl-KCl eutectic presents a trend of electrochemical reactivity (Bi > Sn > Ga ≥ Pb > Zn > Cd > Al), nobility (Bi > Pb ≥ Sn > Ga > Cd > Zn > Al) and electrochemical window (Cd > Al > Pb > Bi > Ga > Sn > Zn), respectively. Moreover, cyclic voltammograms of U3+ and La3+ collected at 773 K on these cathodes demonstrate different electrochemical reactivity scales Ec(U): Ga ≥ Bi > Sn > Al > Zn > Pb > Cd) and Ec(La): Bi > Sn ≥ Ga > Zn > Pb > Cd > Al), respectively, from the anodic to the cathodic side. From these results, a favorable trend for electrochemical separation of U over La can be obtained (Al > Ga > Zn > Bi > Sn > Pb > Cd). In addition, the theoretical Mediema model shows the relationships of the enthalpy of formation and the activity of different alloys as, a U − M : Al < Ga < Sn < Zn < Bi < Pb < Cd, a ( L a − M ) : Bi < Sn < Pb < Al < Ga < Cd < Zn, suggests the interaction of Al and Ga to uranium is the strongest with the best theoretical separation performance.