Adsorption of sodium dodecylbenzene sulfonate on organophilic bentonites

A bentonite from the Cauca Valley in Colombia was treated with tetramethylammonium bromide (TAB), hexadecyltrimethylammonium bromide (CTAB), hexadecylbenzyldimethylammonium chloride (CDAC), and alkylbenzyldimethylammonium chloride (BTC), in order to obtain organophilic compounds. The treatment was carried out at 50% and 100% of the cationic exchange capacity (CEC) of the natural bentonite (NB). The adsorption of an aqueous solution of sodium dodecylbenzene sulfonate (DBS) over the natural and modified bentonites was studied. The experimental data points were fitted to several equations applicable to adsorption in solution such as: Langmuir, BET and Freundlich. The Langmuir isotherm adequately describes the adsorption process in all cases. The adsorption grade can be quantified by the distribution coefficient, for low concentrations in solution expressed in molality, Kdm. The affinity of organophilic bentonites by DBS can be expressed in terms of the standard adsorption Gibbs energy. The class and structure of the hydrocarbon chains of the quaternary ammonium ions adsorbed over the bentonite determine the DBS adsorption grade.