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

Abstract

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.