Coadsorption of phenol and nonionic surfactants onto clays

The influence of nonionic surfactants on the adsorption behaviour of phenol onto kaolinite and montmorillonite is studied by determining its adsorption isotherm separately or in the presence of various concentrations of the nonionic surfactants. An enhancement of the adsorption of phenol is observed. Phenol alone can be adsorbed both by kaolinite and montmorillonite, but in the presence of surfactant molecules, a large part of the adsorption is the solubilisation of the phenol molecule inside surfactant surface aggregates. Partition coefficients between aqueous solution and surface aggregates are determined and compared with that calculated for bulk micelles. They show a larger affinity of phenol for surface micelles than for bulk micelles. A microcalorimetric study shows that the solubilisation process in surface or bulk micelles is nearly athermal. The process is entropically driven.