STUDIES OF THE HYDROUS NIOBIUM(V) OXIDE ION EXCHANGER. VII.RATE OF THE ISOTOPIC EXCHANGE OF CESIUM IONS BETWEEN THE EXCHANGER IN THE Cs+FORM AND AQUEOUS SOLUTION

The isotopic exchange rate of Cs+ between hydrous niobium(V) oxide in the Cs+ form and aqueous solutions was determined radiochemically. The rate was controlled by the diffusion of Cs+ in the exchanger particle at varying pH. The diffusion coefficients at 10°C increased with pH up to pH7; from 3.0x10−11 m2s−1 at pH6 to 4.0×10−11 m2s−1 at pH7, and became constant above pH8 (5.0x10−11 m2s−1). While the diffusion coefficients of Na+ monotonously decrease with increasing pH; from 7.9×l0−11 m2s−1 at pH6.5 to 2.8×l0−11 m2s−1 at pHll. The difference in the dependence of diffusion coefficients on pH between Cs+ and Na+ was interpreted in terms of strength of interaction between counterions and ion-exchange sites since hydrous niobium(V) oxide has selectivity higher for Cs+ than for Na+.