Electrolyte diffusive flux determination through a highly selective cationexchange membrane

A new method for evaluating highly selective ion exchange membranes is devi sed, which is competitive with the counter-ion transport number determinati on method. It is based on the evaluation of a strong electrolyte leakage th rough a membrane. This study uses a CM2 polystyrene and divinylbenzene sulf onated cation exchange membrane, separating two solutions, one containing t he electrolyte at a given concentration C-0 and the other permuted water. T he electrolyte diffuses under its concentration gradient and induces an inc rease of the conductivity in the diluted compartment, allowing the determin ation of its flux. This new method is shown to be reliable and sufficiently accurate over a large concentration range. The bilogarithmic variation of the flux versus the concentration, for the KCl (10(-2) less than or equal t o C, less than or equal to 4 mol L-1)/CM2/H2O system, shows the existence o f three linear sections, each one corresponding to a diffusion state. The c oncentration range 10(-1)-2 mol L-1 seems to be the most interesting one fo r experimental and theoretical studies of the diffusion phenomenon of a str ong electrolyte through an ion exchange membrane. In this domain the concen tration is high enough that the proton contribution to the measured values of the conductivity can be neglected and sufficiently low that the osmosis flux, which would slow down the electrolyte as it diffuses, is not importan t.