MODEL FOR CAPACITY VARIATIONS OF WEAK-ACID AND WEAK-BASE ION-EXCHANGERS AS A FUNCTION OF THE IONIC ENVIRONMENT

The ionization of weak-acid and weak-base ion-exchangers is investigated using acid-base titrations. Experiments are performed with gel-type resins Duolite A368 and A375, and with pellicular silica-based supports IBF CM and DEAE Spherodex LS. A method to write reaction schemes is proposed with special attention to weak-base anion-exchangers, and results are modelled with the aid of a computer program. A good agreement between experimental and calculated results is observed. General trends of the titration curves are explained, as well as the influence of adjustable parameters. The question of the variations of the apparent capacity is treated.