Isotope separation of 233U by anion exchange chromatography based on the U(IV)−U(VI) exchange is studied. After long-distance migration, 233U enrichment is observed at the rear band boundary. To examine the isotope effects of 233U, 234U, and 238U, three-isotope plots of local enrichment factors are constructed for the isotopes contained in sample fractions of the eluted uranium band. The results clearly show an anomalous mass dependence for 233U. We previously reported that the even-mass nuclides 232U, 234U, 236U, and 238U show a regular mass-dependence in their isotope separation behaviors, while 235U does not fall on the same line. The isotope effects of the odd-mass nuclides 233U and 235U deviate from the linear mass dependence observed among the even-mass nuclides. The isotope effects observed in chemical exchange are shown to be closely related to the isotope shifts in the atomic spectra of uranium isotopes.

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, ", was converted to the isotopic equilibrium constant, ln K¼" o , 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 " o vs. 1=T led to the temperature dependence of " o ¼0:69=TÀ82=T 2 , 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.

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