CONCURRENCE ADSORPTION OF ALKYLBENZENESULFONATES AND POLYANIONS FROM AQUEOUS-SOLUTIONS ON GAMMA ALUMINUM-OXIDE

The interaction of γ-Al2O3 with three homologous n-alkyl-benzene sulfonates and different polyanions as well as with mixtures of surfactants and polyanions has been investigated by measurements of adsorption and electrokinetic potentials at 70 °C. The adsorption isotherms of the anionic surfactants at pH 7 follow the Langmuir adsorption equation. The interaction with the alumina surface consists in a hydroxyl ion exchange as is indicated by the observed liberation of hydroxyl ions during the adsorption. At higher surfactant concentrations hydrophobic bonding of the surfactant ions in the adsorption layer contributes to the interaction. This is shown by the fact that even above the isoelectric point (IEP) a significant adsorption occurs, and that even far below the IEP the negative electrokinetic potential is approximately constant. The adsorption isotherms of Na5P3O10, HEDP and citrate at pH 7 follow the high affinity type indicating that these polyanions exert a stronger interaction with the alumina surface than the surfactants. The adsorption is specific and very strong even at pH 10. The adsorption of the surfactants is highly inhibited at pH 7 and 9 by STP, HEDP or citrate, sometimes even at very small concentrations of the polyanions. The polyanions themselves are strongly adsorbed at the same time. At lower pH values, on the other hand, the adsorption of the surfactants is only little influenced by the polyanions although the latter are strongly adsorbed. © 1979 Dr. Dietrich Steinkopff Verlag.