Uranium isotope effects in some ion exchange systems involving uranyl–carboxylate complexes

Abstract

Isotope fractionation between uranyl complexes in aqueous solution and uranyl ions in cation exchange resin was experimentally studied. The isotope separation coefficients ε of the uranyl complex systems determined by a chromatographic method were (0.25±0.1)×10−4 (uranyl–chloride system), (0.88±0.1)×10−4 (acetate), (1.03±0.1)×10−4 (glycolate), (1.42±0.15)×10−4 (lactate), and (2.18±0.2)×10−4 (malate) at 25 °C. IR spectroscopic measurements were conducted on the uranyl complexes of which isotope effects were determined. It was found that the separation coefficients are linearly proportional to the shift of the asymmetric stretching vibration ν3 of O=U=O in uranyl complexes. The observed relation is ε=4.62×10−6 (960−ν3/cm−1). A theoretical treatment indicated that approximately one third of the observed isotope effects could be attributed to the asymmetric stretching vibration.