SYNERGISTIC EFFECTS BETWEEN CATIONIC SURFACTANTS AND ORGANIC POLLUTANTS ON CLAY-MINERALS

The adsorption of the model pollutant 2-naphthol and cationic surfactants (C-12-trimethylammonium bromide, C-16-trimethylammonium bromide and 2C-12-dimethylammonium bromide) on clays (Ca2+-bentonite and illite) was studied. The hydrophobic part of the adsorbed cationic surfactants enhances 2-naphthol adsorption/adsolubilization. The hydrophobic/hydrophilic structure of 2-naphthol promotes the adsorption of surfactant at surfactant concentrations above the cation exchange capacity (CEC) of the clay (synergism). In this case 2-naphthol acts as a cosurfactant. At small surfactant concentrations (below the CEC), the surface coverage and the density of the adsorbed surfactant layer are decisive for the enhancement of 2-naphthol adsorption. At high surfactant concentrations (above the CMC) the solubilization of 2-naphthol in the bulk phase competes with adsolubilization on the surface. Here the 2-naphthol molecules, enhancing surfactant adsorption, migrate into the micelles, thus reducing the amount of adsorbed surfactant. Kinetic studies show an increase in the rate of adsorption of the 2-naphthol upon addition of a cationic surfactant. The sequence of this addition plays an important role. An intercalation of 2-naphthol into the interlayers can bc detected only for bentonite densely loaded with 2C-12-surfactant by X-ray measurements.