Surface modification of sepiolite with quaternary amines. 
This study was aimed at elucidating the mechanism of adsorption of quaternary amines, stearyldimethylbenzylammoniumchloride (SDBAC), as monomers and as micelles, distearyldimethylammoniumchloride (DDAC) and hexadecyltrimethylammoniumchloride (HTAC), on the surface of sepiolite.  The adsorption capacity for these surfactants onto sepiolite, calculated by fitting the experimental data to the Langmuir-Freundlich equation, were 324% (SDBAC), 278% (DDAC), and 258% (HTAC) of the cation exchange capacity of sepiolite.  The Mg(2+) ions released during the exchange process were higher than the CEC value of sepiolite because of the simultaneous dissolution of the present minerals.  The water adsorption decreased with the increasing surfactant loading up to 250 mmol/kg of sepiolite, which can be ascribed to an intensification of the hydrophobic properties.  With loadings above 250 mmol/kg, the water adsorption increases.  Simple kinetic analysis of SDBAC adsorption was performed.  The properties and the type of bonding between the surfactants and sepiolite were investigated by DT, TG, and DTG analysis.  During the gradual heating in oxidizing atmosphere, the adsorbed organic material is oxidized giving rise to significant exothermic peaks.  The exothermic peak temperatures in the range 200-500 degrees C depended on the surfactant loadings and provided evidence of the formation of multilayers on the sepiolite surface.