Interaction between ionic surfactants and soil colloids: adsorption, wetting and structural properties

The adsorption of ionic surfactants on different soil components such as silica, clay minerals, and humic acids was studied. The adsorption processes were controlled by flow microcalorimetry to determine the molar adsorption enthalpies of surfactant accumulation on clay and silicate surfaces. The evaluation of adsorption results for cationic surfactants has shown different mechanisms for solids having permanent (kaolinite, illite, montmorillonite) and pH-dependent surface charges (silica gels and powders). The adsorption mechanism for surfactants on silica surfaces with pH-dependent charges has been explained in terms of the development of charges on the surfaces and their interaction with surfactant cations and micelles. The surface hydrophobicity of clay-organocomplexes was characterized by batch microcalorimetry using pure liquids. The fractal dimensions of clays and their organocomplexes were determined by SAXS. The intercalation of organic compounds in the interlamellar space of layered silicates and humates was measured by x-ray diffraction using powder samples and suspensions. The structural properties of the surfactant coated clay suspension were characterized by rheology.