Adsorption of 2,4-dichlorophenol on montmorillonite and silica: Influence of nonionic surfactants

The adsorption behavior of 2,4-dichlorophenol and of nonionic surfactants of the Triton-X series on soil colloids, separately and in mixed systems, was studied at different pH values. Particular attention was paid to the influence of the adsorption process of the pollutant in the case of small, environmentally relevant surfactant coverages. The adsorption isotherms of 2,4-dichlorophenol on Ca montmorillonite were of the Henry type and no intercalation into the interlayer space of the clay mineral was observed using X-ray diffraction. The pollutant did not show any significant affinity to the native silica surface. The different courses of the isotherms of the nonionic surfactant and their pH dependence indicate significantly different adsorption mechanisms for the two adsorbents. This results in a greater effectiveness concerning the hydrophobization of the silica surface by the nonionic surfactant compared to the montmorillonite surface, as can be seen from a comparison of the partitioning coefficients K-oc for 2,4-dichlorophenol. On both the untreated and the surfactant-covered adsorbents the increasing pH reduces 2,4-dichlorophenol adsorption drastically due to Coulomb repulsion and solubility effects. (C) 2001 Academic Press.