ADSORPTION OF POLYELECTROLYTES ON SOLUBLE OXIDES INDUCED BY POLYION COMPLEXATION WITH DISSOLUTION SPECIES

We investigated the adsorption of high molecular weight polyacrylic acid on partially soluble alumina in aqueous suspension containing 10−3N KCl and 3 × 10−4N AlCl3 ions. The polymer solution and the colloidal suspension at pH 5 were mixed and the pH was recorded as a function of time. We first studied the interaction of polyacrylic acid with aluminum ions in solution in order to characterize the polymer ionization and complexation as a function of pH. We determined that the carboxylic acid group strongly reacts with the aluminum ion to form a metal-polymer complex characterized by a possibly large degree of complexation. When the polymer was added to the oxide suspension, we also determined the concentration of the different species by titration and characterized the polyelectrolyte adsorption by determining the temporal variation of the amount of free and complexed polymer segment adsorbed as well as the concentration of free and complexed aluminum ions in the supernatant liquid phase. Two different situations were investigated depending on the carboxylic acid to aluminum ion ratio. For low value of this ratio, the polymer was rapidly adsorbed in the form of a highly complexed polyelectrolyte whose counterions were the numerous aluminum ions existing in the medium. For high value of the ratio, the adsorption was long delayed. Before adsorption, the polyacid also underwent an aluminum-hydrogen ion-exchange, the extent of which depended on the oxide dissolution rate; it appeared that only the complexed form was able to adsorb on the oxide. © 1993 by Academic Press, Inc.