Selectivity of Anion Exchange Resin Modified with Anionic Polyelectrolyte

Abstract

In order to change the ion-exchange selectivity of anion exchange resin, especially to make the ion-exchange of divalent anions more difficult, the surface of gel-type anion exchange resin was modified by the adsorption of an anionic polyelectrolyte: polycondensation product of sodium naphthalene sulfonate and formaldehyde. After the adsorption of the polymer, ion exchange capacity decreased and the rate of ion exchange reaction became slow, though ion exchange equilibrium constants between two anions did not change. Especially, the ion exchange rate of divalent anions was slower than that of the monovalent anions. Because an anionic polyelectrolyte layer was formed on the resin particle, the ion exchange of anions with anion exchange site was retarded by a sieving effect due to the layer. The divalent anions became difficult to ion exchange compared with the monovalent anions due to the existence of the layer which was charged opposite to the charge of the ion exchange groups. Using the modified anion exchange resin, separation of nitrate ions from sulfate ions was attempted.