LAUSR

Abstract Sorption of pure electrolytes and binary electrolyte mixtures in non-ionic microporous adsorbents was studied in batch and fixed-bed systems. Hypercrosslinked polystyrene (HCPS) and densely crosslinked dextran gel (G10) were used as adsorbents and the studied model systems were HCl/CaCl 2 /HCPS at 25 °C and Na 2 -tartrate/NaOH/G10 at 50 °C. The results were explained in terms of cooperative sorption and the experimental data were correlated using a generalized Donnan equilibrium model together with Pitzer model for evaluation of the ion-ion and ion-adsorbent interactions. Moreover, a model was included for partial ion dehydration at high concentrations. Non-linear sorption observed at very low and high concentrations of pure electrolytes was explained by electrostatic exclusion and partial ion dehydration. In binary mixtures, a more complex behavior was observed because of cooperativity and good separation of the electrolyte mixtures was obtained in the fixed-bed experiments involving pulse feed and elution with pure water. In the HCl/CaCl 2 /HCPS system, selective uptake of HCl was enhanced by increasing the total electrolyte concentration. This trend can be explained by taking into account both size exclusion of CaCl 2 and the non-ideal behavior of the electrolyte mixture. Separation of Na 2 -tartrate and NaOH was dominated by size exclusion of the tartrate anion and well-defined separation is possible even at very high column loading. Moreover, the observed splitting of Na 2 -tartrate to NaH-tartrate and NaOH can be explained on the basis of cooperativity. The results suggest that the proposed model applies equally well to materials having rigid microporous structure and to densely cross-linked gels.