The investigation of electrokinetic behaviour of micro-particles produced by CTA+ ions and Na-montmorillonite

In this study, the interactions between clay platelets and CTA+ ions in aqueous dispersions of Na-montmorillonite (Na-MMT) were examined in detail by using electro kinetic parameters such as electrical conductivity and zeta potential and by considering XRD patterns and d-spacing values of the organoclay samples as a function of both surfactant concentration (CTAB, cetyltrimethylammonium bromide) and clay amount. The amounts adsorbed and zeta potentials of the particles increased with an increase in the initial concentration of CTAB in parallel with the electrical conductivity values. The adsorption mechanisms which predominate at certain ranges of CTAB concentration were proposed and schematized by considering the d-spacing values calculated and the zeta potential values of particles. For the different solid/liquid ratios, the initial concentrations of CTAB, in which appeared significant increases in the d-spacing values were found as 200, 280 and 300 mg/L, respectively. The d-spacing values which correspond to these concentrations are, respectively 1.82, 1.82 and 1.68 nm. It is remarkable that at first three solid/liquid ratios, a “stress region” to be related with hydrophobic binding appeared. Thermodynamic parameters such as Gibbs free energy (ΔGo), isosteric enthalpy (ΔHoads)q, and isosteric entropy (ΔSoads)q were also calculated by using experimental data. These parameters indicate that adsorption of CTAB onto Na-montmorillonite is spontaneous and exothermic in the temperature range studied. The ((ΔSoads)q, (ΔHoads)q and (ΔGo)) values calculated are highly negative. This reveals that the adsorption of CTA+ ions at the interlayer region of clay carried out with more order stacking of CTA+ ions.