Studies of the hydrous tin(IV) oxide ion exchanger. V. The sodium isotopic exchange rate between the exchanger in the Na+ form and aqueous solutions.

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The sodium isotopic exchange rate between the hydrous tin(IV) oxide ion exchanger in the Na<SUP>+</SUP> form and aqueous solutions was determined radiochemically. When the dried exchanger was used, the rate of the first step was controlled by the rate of the equilibration of water in the exchanger with the solutions, while the second step was found to be controlled by the diffusion of sodium ions in the particles (particle diffusion). When the exchanger had been sufficiently immersed in solutions in advance, the particle diffusion controlled the rate from the beginning. From the dependency of the rate of particle diffusion on the apparent particle size and the specific surface area of the exchanger, and on the sodium-ion concentrations in the solutions, the process controlling the rate is considered to be the diffusion in the primary particles, which are formed at the initial stage of precipitation and which aggregate to form the hydrous tin(IV) oxide gel. The diffusion constants and their activation energy (35±2 KJ mol<SUP>−1</SUP>) were also evaluated.
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