Retention of mineral salts by a polyamide nanofiltration membrane

Retention measurements with single salt solutions (KCl, K2SO4, MgSO4 and MgCl2) were carried out with an AFC 30 organic membrane. The membrane showed high retentions for K2SO4 and MgSO4 solutions and moderate ones for MgCl2 and KCl solutions. The effective pore radius and the effective thickness to the porosity ratio of the membrane were determined from the limiting retention of glucose and permeability measurements, respectively. The Dorman Steric Pore Model (DSPM), based on the extended Nernst-Planck equation and a modified Dorman equilibrium accounting for steric effects, was used to characterize the membrane in terms of effective membrane volume charge. It appears that the membrane is positively charged in presence of MgCl2 and MgSO4 solutions and negatively charged for KCl and K2SO4 solutions. This was attributed to ionic adsorption at the interface membrane/solution. (C) 2002 Elsevier Science B.V. All rights reserved.