Selective permeability of a perfluorosulphonic membrane to different valency cations. Ion-exchange isotherms and kinetic aspects

摘要

Transport competition between protons and Ag+, Co2+ and Ce3+ ions across a Nafion(TM) cation exchange membrane (CEM) has been studied in the Donnan exclusion domain. In such conditions the membrane does not contain any mobile anion but only cations (the counter-ions) which electrically equilibrate the sulphonic sites. In the frame of the gel-model, the ion transport flux depends on both the composition of the membrane resulting from the solution-membrane exchange equilibrium and the mobility of the counter-ions within the membrane. As the charge of the ion increases, so does its affinity for the membrane which is greater for multivalent counter-ions than for protons due to their larger electrostatic attraction towards the exchange sites of opposite polarity. On the other hand, as the charge of the ion increases, its mobility in the membrane is reduced. Modelling of this transport takes into account these two aspects as well as ionic concentration variations in the diffusion layer. (C) 1998 Elsevier Science B.V. [References: 21]