Adsorption-desorption and hysteresis of sulfonates on kaolinite: pH effects

Adsorption and desorption behavior of dodecylbenzenesulfonate on kaolinite was investigated under carefully controlled conditions of pH, ionic strength, and dissolved mineral species. The nature of the adsorption maximum and the hysteresis obtained is found to strongly depend on the pH change that occurs during equilibration and dilution. Interestingly, hysteresis can be positive or negative depending mainly on the pH perturbations that take place during the experiment. The results are examined on the basis of available data for the pH-dependent dissolution equilibria for kaolinite. Kaolinite dissolution and subsequent sulfonate precipitation and redissolution are identified to be the major factors in determining abstraction in this system. Many complex interactions are involved in determining surfactant adsorption; studies of desorption behavior along with that of adsorption have proved to be a powerful tool for studying the mechanisms involved.