Retention of ions in nanofiltration at various ionic strength

Retention of a single salt solution was investigated versus the applied pressure, ion valencies and feed concentration using positively-charged membranes, obtained by chemical modification of ZrO2 layer of UF membranes with a cross-linked polymer. Retention of colon was in agreement with the Donnan effect but coupling with either divalent counterion or the smallest colon (proton) was not accounted for. Mixtures of big positive organic solutes (antibiotics) and small cations were studied at increasing ionic strength (I). Retentions of membrane colons were plotted versus I--0.5 according to the semi-empirical model of ionic strength controlled retention the applicability of which was discussed and compared to the Donnan effect.