Limiting transport properties and hydration numbers of actinyl ions in pure water

The transport properties in pure water, i.e. the limiting ionic conductivity (lambdadegrees) and the limiting diffusion coefficient (Ddegrees), and the hydration numbers (N) of the singly and doubly charged uranyl, neptunyl, plutonyl and americyl ions MO2n+ (n = 1 or 2) have been calculated at 298.15 K. A geometric model was applied in which the actinyl ions described by ellipsoids of revolution, with the axis O-M-O as axis of revolution, were transformed into spherical ions. The microscopic version of the Stokes-Einstein law has been used to derive the limiting transport properties of the ions. The main parameters involved in the calculations were the size of the bare ion, the effective cationic charge of the central actinide M, the viscosity of the water molecules in the first hydration shell of the ion and the size of this first hydration shell. The results obtained for the limiting transport properties and for the hydration numbers of the actinyl ions were found in good agreement with experimental data from the literature.