Adsorption of nonionic surfactant and hydrophobic organic compounds on clay minerals

The environmental chemistry of the adsorption of nonionic surfactant from aqueous solution on swelling and nonswelling clay minerals, and the distribution of hydrophobic organic compounds (HOCs) in montmorillonite-aqueous systems with and without nonionic surfactant is investigated.; Adsorption isotherms were determined as a function of layer charge density, pH, ionic strength and chemistry, as well as solid concentration. The optical density of TX-100-montmorillonite complexes was determined as a function of ionic strength. The structure of complexes of TX-100 with montmorillonite were determined with x-ray diffraction methods. Adsorption isotherms by low (SWy-2)- and high (SAz-1) charge montmorillonite were obtained for Pyrene and 1,2,4-Trichlorobenzene (TCB) in aqueous systems with and without surfactant.; The affinity of low TX-100 concentrations for SWy-2 depends on the exchangeable cation and increases in the order: Na {dollar}<{dollar} Cs {dollar}<{dollar} Ca. The extent of hydrophobic interaction between sorbed and dissolved surfactant molecules influences the adsorption density and sorption maxima, and is affected by the swelling capacity. Consequently, the sorption maxima increase with swelling capacity in the order: Cs {dollar}<{dollar} Ca {dollar}<{dollar} Na-SWy-2. In general, increasing ionic strength and decreasing pH enhance nonionic surfactant adsorption by montmorillonite. The adsorption density on the surfaces of kaolinite is comparable to that of Na-SWy-2. The low affinity of TX-100 for SAz-1 and the limited interlayer accessibility results in S-shaped isotherms.; The montmorillonite-water distribution coefficients show that the HOC adsorption increases in the order of decreasing hydration energy of the exchangeable cation: Ca {dollar}<{dollar} Na {dollar}<{dollar} Cs. In general, HOC uptake by montmorillonite surfaces is inversely proportional to the aqueous solubility. A net increase in HOC uptake occurs at TX-100 concentrations below the critical micelle concentration (CMC). The apparent distribution coefficient of HOCs between montmorillonite and aqueous surfactant solution decreases at supra-CMCs. Marked increase in HOC sorption concurs with strongly increased TX-100 adsorption, indicating the formation of micelle-like surface aggregates. The smaller TCB has a higher affinity for surfactant surface aggregates than Pyrene. For SWy-2, the HOC affinity increases with surfactant adsorption density in the order: Cs- {dollar}<{dollar} Ca- {dollar}<{dollar} Na-SWy-2. Weak surfactant interaction with the surfaces of Na-SAz-1 gives rise to the formation of a highly effective partitioning phase for HOCs.