STUDIES OF THE HYDROUS NIOBIUM(V) OXIDE-ION EXCHANGER .7. RATE OF THEISOTOPIC EXCHANGE OF CESIUM IONS BETWEEN THE EXCHANGER IN THE CS-SOLUTION( FORM AND AQUEOUS)

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 degrees C increased w ith pH up to pH7; from 3.0x10(-11) m(2)s(-1) at pH6 to 4.0x10(-11) m(2 )s(-1) at pH7, and became constant above pH8 (5.0x10(-11) m(2) s(-1)). While the diffusion coefficients of Na+ monotonously decrease with in creasing pH; from 7.9x10(-11) m(2)s(-1) at pH6.5 to 2.8x10(-11) m(2)s( -1) at pH11. The difference in the dependence of diffusion coefficient s on pH between Cs+ and Na+ was interpreted in terms of strength of in teraction between counterions and ion-exchange sites since hydrous nio bium(V) oxide has selectivity higher for Cs+ than for Na+.