Studies of the Hydrous Niobium(V) Oxide Ion Exchanger. IV. The Rate of the Isotopic Exchange of Sodium Ions between the Exchanger in the Na+ Form and Aqueous Solutions

The rate of the isotopic exchange of sodium ions between the hydrous niobium(V) oxide ion exchanger in the Na+ form and aqueous solutions was determined radiochemically. Since the fractional attainment of equilibrium was independent of the sodium-ion concentration in the solutions (≥0.1 mol dm−3), and inversely proportional to the square of the particle radius, the isotopic exchange rate on the hydrous niobium(V) oxide is controlled by the diffusion of the sodium ions in exchanger particles. The self-diffusion coefficients of sodium ions (D=3.1×10−7 cm2 s−1 at 25 °C) and their activation energy (Ea=27±4 kJ mol−1) were also determined.