Analysis of the salt retention of a titania membrane using the "DSPM" model: effect of pH, salt concentration and nature

Retention measurements with single salt solutions of KCl, LiCl, K2SO4, MgCl2 and MgSO4 were carried out as a function of the permeate flux for a commercial titania membrane close to the nanofiltration (NF) range. The effect of both pH and salt concentration was studied. The membrane shows amphoteric behavior with an isoelectric point (iep) at pH 6.2 (in presence of an indifferent electrolyte: KCl or LiCl). The obtained results agree qualitatively with the Dorman exclusion principle, characteristic of electrically charged membranes: a higher co-ion valence leads to a higher retention, a higher counter-ion valence leads to lower retention and retention decreases with increasing concentration.