Diffusion and selective transport of alkali cations in a polysulfone ion exchange membrane

Abstract

he diffusion of alkali metals through a charged polysulfonated ICE-450 ion exchange membrane has been measured as a function of pH and conservation of the external solution at 25 degrees C. The permeability and diffusion coefficients were found to increase in the sequence Cs(+)greater than or equal to K+>Na+>Li+ and with the external concentration. This sequence can be explained by considering the hydration of the ions in the membrane. The modes of membrane/solution distribution and the diffusion of cations as a controlling factor in the membrane permselectivity and hydration values of cations both correlated consistently with the flux data, as well as with the estimated membrane permselectivity parameters. The selective transport of K/Na and K/Li binary systems at various pH gradients through the membrane was also investigated under various conditions. The selectivity depended on both the hydrated ionic size and the interaction between the fixed groups in the membrane and the metal ions. A good agreement was found between the observed diffusion coefficients and the selectivity values and the limiting mobility ratio in water.