Electrochemical Studies of Uranium and Thorium in Molten LiF-NaF-KF at 500°C

Electrochemical studies of U(IV) in molten LiF ‐ NaF ‐ KF (46.5‐11.5‐42.0 mole per cent) at 500°C reveal a two‐step reduction process at a platinum electrode. The first step is complicated by disproportionation of U(III) to regenerate U(IV); the second step involves formation of uranium metal. Standard electrode potentials with respect to a unit mole fraction Ni(II)/Ni electrode are estimated for the U(IV)/U(III) and U(III)/U couples as −1.41 and −1.81V, respectively. These values must be considered tentative because of complications in the electrode processes. The voltammetric oxidation of U(IV) at platinum and pyrolytic graphite electrodes in LiF ‐ NaF ‐ KF occurs at ∼ + 1.3V vs. a Ni(II) (saturated)/Ni reference electrode. The results point to the disproportionation of electrochemically generated U(V). In voltammetric studies of Th(IV) in molten LiF ‐ NaF ‐ KF at 500°C, a reduction wave is obtained at nickel and tungsten electrodes, with a peak potential of −2.02V ( vs. a Ni(II) (saturated)/Ni reference electrode). Analysis indicated that Th(IV) is reversibly reduced to the metal with alloy formation between the deposited thorium and the nickel. A standard electrode potential for the Th(IV)/Th couple in this melt is calculated to be −2.13V vs. a unit mole fraction Ni(II)/Ni electrode.