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

The adsorption behavior of 2,4-dichlorophenol and of nonionic surfactants o f the Triton-X series on soil colloids, separately and in mixed systems, wa s studied at different pH values. Particular attention was paid to the infl uence of the adsorption process of the pollutant in the case of small, envi ronmentally relevant surfactant coverages. The adsorption isotherms of 2,4- dichlorophenol on Ca montmorillonite were of the Henry type and no intercal ation into the interlayer space of the clay mineral was observed using X-ra y diffraction. The pollutant did not show any significant affinity to the n ative silica surface. The different courses of the isotherms of the nonioni c surfactant and their pH dependence indicate significantly different adsor ption mechanisms for the two adsorbents. This results in a greater effectiv eness 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.