oa South African Journal of Chemistry - The effect of pH on the ion-exchange properties of hydrated alumina : part 1. capacity and selectivity



A study has been made of ion-exchange processes Involving univalent cations and anions on hydrated alumina, which, being amphoteric, acts as a cation-exchanger at high pH, and as an anion-exchanger at low pH. The cation-exchange capacity and selectivity both increase with increasing pH, while the anion-exchange capacity and selectivity decrease. Selectivity has been found to depend also upon the relative amounts of the exchanging ions on the exchanger. Titration curves show that hydrated alumina behaves as a monofunctional cation-exchanger, but as a polyfunctional anion-exchanger, the presence of three different types of exchangeable hydroxyl ions being indicated by the curves obtained on titration with acids. Possible reasons for this are discussed


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