The Pressure Dependence of Oxygen Isotope Exchange Rates Between Solution and Apical Oxygen Atoms on the [UO2(OH)4]~(2-) Ion

摘要

A key concern in the use of nuclear energy is the disposal and long term storage of spent fuel. The aqueous chemistry of the uranyl(VI) ion under strongly alkaline conditions, such as those found in many above-ground waste storage tanks, remains poorly understood. To this effect, the oxygen atom exchange between the uranyl oxygen atoms and bulk solvent water has been studied by ~(17)O NMR spectroscopy under acidic and alkaline conditions using line-broadening by Clark et al. and, recently, saturation-transfer methods by Szabo, Grenthe et al., but no determination of activation volumes has been attempted. Such data are invaluable in verifying theoretical models for reaction pathways. The activation volume probes the transition state and complements molecular dynamics simulations. Herein, the activation volume of the oxygen atom exchange of the uranyl oxygen atoms with bulk water has been determined by experiments at 60 °C between 0.1 and 350 MPa as a function of uranyl and hydroxide concentrations.