EFFECT OF DISSOCIATION EQUILIBRIA ON ION-EXCHANGE PROCESSES OF WEAK ELECTROLYTES

Ion-exchange processes involving weak electrolytes are influenced stro ngly by the pH via the occurrence of association/dissociation equilibr ia. This influence was investigated quantitatively through binary disp lacement experiments with different electrolytes to gain better insigh t in the role of the FH and to test it fixed-bed ion-exchange model us ed for the description of multicomponent processes. The two major fact ors determining the ion-exchange behavior of weak electrolytes are the actual exchange of counterions and the sorption of neutral species. T he sorption of neutral species resulted in concentration fluctuations superimposed on the normal ion-exchange profiles, whereas pH fluctuati ons inherent to ion-exchange processes in general also influenced conc entration through modified ionic fractions. The relative importance of these contributions is determined by the magnitude of parameters such as resin capacity distribution coefficients of neutral species, and s electivities of ions, as well as by operating conditions such as conce ntrations of all species.