Diffusion and sorption of simple ions in cellulose: ion exchange

Abstract

The sorption and diffusion properties in a cellulose membrane of KCl, NaCl, KI and NaI have been studied. These salts show a similar degree of absorption. Sorption is not reversible and residual solute remains which can only be removed by cationic exchange. Thus, H⁺, K⁺ and Na⁺ cellulose membranes were prepared. The degree of absorption depends strongly on membrane pH, increasing with pH. Diffusion coefficients were smaller in magnitude at lower concentrations of solute, the concentration gradient showing a diffusion “barrier” at the low concentration side of the membrane, with energy estimated at 9.4 × 10³ J mol^–1. The observations are explained via an electrokinetic approach, the core of the double layer being the network of electronegative oxygen-bearing cellulose molecular chains. The salt retention properties of cellulose in reverse osmosis are similarly explained thus including more effective retention at lower solute concentrations.