ON THE ADSORPTION OF HYDROPHOBIC POLLUTANTS ON SURFACTANT CLAY COMPLEXES - COMPARISON OF THE INFLUENCE OF A CATIONIC AND A NONIONIC SURFACTANT/

The adsorption of the cationic surfactant dodecyl trimethyl ammonium b romide (DTAB) and of the nonionic surfactant dodecyl octaethylene glyc ol ether (C12E8) on four different layer silicates and their influence on the sorption processes of the fungizide biphenyl were studied. Une xpectedly, no great differences were found in comparing the adsorption of the two surfactants on the basis of physicochemical investigations , although the adsorption mechanism up to monolayer formation is funda mentally different lion exchange and physisorption). Thus, the plateau values of the adsorption isotherms and the molar enthalpies of displa cement Delta(21)h are of the same order of magnitude for both surfacta nts and the same basal spacing by intercalation is observed in the cas e of swelling clays. The isotherms of the hydrophobic contaminant biph enyl are of the linear C1-type at all layer silicates and very low ads orption takes place approximately proportionally to the BET (N-2) surf ace area. If the surface is weakly hydrophobized by surfactants (c(sur factant)<<critical micelle concentration (CMC)), biphenyl adsorption i s clearly increased. These processes can be adequately described using the distribution coefficients K and K-OC (Henry coefficient related t o the organic carbon content). K-OC is hardly influenced by the type o f layer silicate for DTA(+)-layer silicates, whereas the C12E8 layer s ilicate complexes generally show higher, but also different K-OC value s. If the surfactant concentrations are above the CMC, solubilization and adsorption compete for the pollutant molecules, which leads to a s ignificant decrease in biphenyl adsorption.