Coadsorption of alkylphenols and nonionic surfactants onto kaolinite

The influence of a nonionic surfactant on the adsorption behaviour of alkylphenols onto kaolinite is studied by determining their adsorption isotherms separately or in the presence of various concentrations of the nonionic surfactant. When alone, alkylphenols are adsorbed with a mechanism close to that of surfactants. If the nonionic surfactant TX100 is added in the medium, the adsorbing properties are modified according to the alkyl chain length. The longer the alkyl chain length of alkylphenol molecule, the weakest is the influence of TX100 surface aggregates on their adsorption behaviour. This unexpected behaviour, according to the relative hydrophobicity of the molecules, may be due in a part to the adsorbing properties of the alkylphenols that are able to self-aggregate at the kaolinite/water interface and in a part to the limited swelling capacity of the TX100 micelles or surface micelles. Partition coefficients between aqueous solution and surface aggregates are determined and compared with that calculated for bulk micelles.