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Adsorption and desorption of cationic surfactants, cetyl pyridinium bromide, cetyl trimethyl ammonium bromide, dodecyl pyridinium bromide on bentonite, kaolinite and illite, and their diffusion through a bentonite membrane have been studied.The binding of these compounds on the mineral surface takes place much beyond the exchange capacity. For excessive saturations with long chain compounds like these, the chains stand erect to the surface. A correlation of area per exchange site and area associated with surfactant molecule on clay surface also supports this view. The increase in the extent of adsorption with the size of the organic cation is due to an increase in the van der Waal's forces between clay and surfactant molecule. Isosteric heats of adsorption at different stages of surface covered with surfactant have also been determined and the same was found to pass through a minimum point. Larger ions desorb less, owing to the lesser solubility and larger contribution of dispersion forces.Permeability of these surfactants and energy of activation of the diffusion process through the H-bentonite membrane has also been investigated. Diffusion of these cations takes place via exchange positions through the membrane and the order is exactly the reverse of their adsorption on the clay surface.

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