ION-EXCHANGE EQUILIBRIUM AND DIFFUSION OF YTTRIUM AND LANTHANUM IN A CATION-EXCHANGE MEMBRANE

The ion-exchange equilibrium and transport rate of yttrium and lanthanum were examined for a cation-exchange membrane, SELEMION CMV. Yttrium and lanthanum were selectively sorbed by the membrane in a low-concentration region. Their selectivity coefficients were higher than those of divalent ions, depending on the degree of solution concentration. Experimental results were successfully correlated with separate experimental equations for Y-H and La-H systems over a wide range of solution concentration. In Donnan dialysis experiments with YCl3-HCl and LaCl3-HCl systems under the conditions of membrane diffusion control, the apparent diffusivities of yttrium and lanthanum were considerably affected by solution concentration. Self -diffusivities of ions in the membrane were estimated from a part of the experimental results with a model using the Nernst-Planck equation by means of the Marquardt optimizing method. Those of H+, Y3+, and La3+ were 1.1 x 10(-10), 1.1 x 10(-12), and 4.4 x 10(-13) m2/s respectively. The model with the self-diffusivities explained the experimental results well.