Adsorption of Sodium Oleate on Kaolinite

Abstract

In this paper the effect of additives on adsorption of sodium oleate on kaolinite in aqueous solution is examined. Kaolinite with specific surface area 20.2 m2/g and zero point of charge 2.0 is used as adsorbent. Adsorption of sodium oleate on kaolinite has been investigated with or without additives such as NaCl, n-butanol, n-penanol, PHPAM (partially hydrolyzed polyacrylamide) and AEO (a nonionic polyoxyethylene surfactant). The adsorption isotherm of sodium oleate, which is different from that of other anionic surfactants on kaolinite, showed two plateaus (i.e. LS type). But it is interesting that an adsorption maximum is found in the isotherms when these additives are added in the liquid/solid adsorption system. Basically, three different adsorption behaviors have been found when the additives are added. The adsorbed amount of sodium oleate decreases considerably when alcohols are added to the solution, while the amount increases when NaCl or PHPAM is added; only a slight alteration is observed when AEO is added to the solution. The adsorption process on kaolinite is found to follow a two-step first-order kinetic rate equation with two different (k1 and k2) rates constants. Values of the energy of activation Ea1 and Ea2 are calculated from the slope of the linear plot of –lnk against 1/T for different systems. The enthalpies of activation (ΔH), entropies of activation (ΔS) and free energies of activation (ΔG) are calculated by using thermodynamic equations. It is found that there is an entropy-enthalpy compensation effect in the adsorption process from the values of ΔH and ΔS. These results are useful in controlling the surfactant's adsorbent loss in tertiary oil recovery.