Studies of a hydrous tin(IV) oxide ion exchanger. VI. Rate of the isotopic exchange of cobalt ions between the exchanger in the cobalt form and aqueous solutions.

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The isotopic exchange rate of cobalt ions between a hydrous tin(IV) oxide ion exchanger and aqueous solutions was radiochemically measured in order to obtain fundamental data which could be useful for elucidating the ion-exchange kinetics of the material for the transition metal elements. This rate can be understood by considering that the cobalt in an exchanger exists as three species: (A1) dissociated ions which can diffuse in the exchanger particles; (A2) weakly bound ions to the exchange sites, which are in local equilibrium with A1; and (B) covalently fixed ions to the exchange sites, which are exchanged very slowly with A1. At a small ratio of the amount of B to the total amount of cobalt sorbed on the exchanger, the rate is controlled by the diffusion of A1, with effective diffusion coefficient, \barDeff, a value which depends on the concentration ratio of A2 to A1. When B predominates over A, the concentration ratio of B to A1 greatly affects \barDeff. The values of \barDeff and their activation energy (20 kJ mol−1) were also estimated.
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