Temperature dependence of isotope effects in uranium chemical exchange reactions

Abstract

Temperature dependence of isotope effects in U(IV)-U(VI) exchange reaction was experimentally studied by means of redox chromatography using columns packed with anion exchange resin in the temperature range 87-160°C (360-433 K). The experimentally observed isotopic separation coefficient, ε, was converted to the isotopic equilibrium constant, InK=ε0, of the U(IV)-U(VI) exchange reaction with the aid of the experimentally measured ionic mole fractions of U(IV) and U(VI) in the resin phase and the aqueous solution phase. The plots of εo vs. 1/T led to the temperature dependence of εo=0.69/T-82/T2, where the first term is due to the nuclear field effect (nuclear-electron interaction effect) and the second term is due to the molecular-vibration mass effect. The discussion is extended to the temperature dependence of the previously reported isotope effects in the U(III)-U(IV) electron exchange reaction, and the U(VI)-malate-complex ligand exchange reaction. © Atomic Energy Society of Japan.