Ionic surfactants adsorption on heterogeneous surfaces

Abstract The adsorption of surfactants from aqueous solution is a phenomenon of major importance in applications ranging from ore flotation and paint technology to enhanced oil recovery. As this paper will illustrate, the process is very complex and of high scientific interest; its results can be extended to the retention of organic compounds (humic and fulvic acids, pollutants...) on solids in the biosphere. For a good understanding of the mechanisms involved in surfactants adsorption at the hydrophilic solid–aqueous solution interface, thermodynamic models have to take into account: ( i ) the physical chemistry of the surfactant in aqueous solution for choosing the appropriate reference phase, ( ii ) the surface heterogeneity of the adsorbing solid, ( iii ) the intensity of normal adsorbate–adsorbent bonds responsible for adsorption, ( iv ) the intensity of lateral bonds that favour the formation of surface aggregates through cooperative process and finally, ( v ) suitable theoretical models to describe adsorption phenomena. Once this has been achieved, two systems can be discussed: systems characterised by strong normal adsorbate–adsorbent bonds, currently used in ore flotation, which lead, in the case of heterogeneous surfaces, to the formation of lamellar aggregates at monolayer concentration and bilayer formation for higher concentrations. Systems characterised by weak normal adsorbate–adsorbent bonds, currently used in enhanced oil recovery and hydrocarbon (bio)remediation, which correspond to: ( i ) formation of globular micelles at the solid surface near the CMC when the temperature is higher than the Krafft point, ( ii ) formation of bilayered lamellar aggregates in the opposite case, ( iii ) three-dimensional condensation on substrate ( T T Krafft ) if the ionic surfactant interacts with cations in the bulk. To cite this article: J.-M. Cases et al., C. R. Geoscience 334 (2002) 675–688.