Piezodialytic transport across charge-mosaic membranes

Abstract

The study reported in this paper is a continuation of a study presented earlier'*/Proceedings of the Internat, Congress on Desalination and water Re-use, Nice, France, Oct. 21-27, 1979, Water for life, Vol. III Part 3/. The title membranes were prepared on the basis of polyethylene modified with the copolymers of styrene, 4-vinyl-pyridine and 2-vinyl-benzene. They were designed for the piezodialytic desalination and concentration of brakish waters and seawater. Symmetric and asymmetric electrolytes, KCl, MgCl 2,Mncl 2 CaCl 2 and Na 2So 4, /of an initial concentration between 0.05 and 0.5 M/ contained in brackish waters were concentrated, and the results obtained are discussed. The investigations were carried out in a laboratory system which permitted a recirculation of the liquid under study, and a mixing in the dialysate cell. The pressure at which the electrolytes were concentrated varied from 10.3 to 15.3 Pa /100 to 150 atm/ and was kept constant throughout each measurement. The applicability of the membranes in question to a dialytic concentration was estimated, in terms of the coefficient α which describes the concentration effect. The concentration effect depends on the degree of crosslinking in the ion-exchange elements, on the type concentration of the electrolyte and the value of pressure difference. For electrolytes of an initial concentration of 0.5 M no concentration effect was obtained. In the case of asymmetric electrolytes /but only for an initial concentration of 0.05 M/ the concentration effect was insignificant The experimental results indicate that the concentration effect decreases with the increase in electrolyte concentration and in the pressure applied.