Kinetics of sodium dodecyl benzene sulfonate adsorption on hematite

Abstract

The adsorption of sodium dodecyl benzene sulfonate (Na-DBS), an anionic surfactant, on hematite mineral surface has been studied through equilibration and during kinetic measurement. The surfactant adsorbs strongly on the hematite surface. The adsorption isotherms have shown different regions in accordance with the definition reported elsewhere, which reflect different modes of collector adsorption as the equilibrium concentration is increased. The concentration at which the isotherm reaches saturation is higher than that which corresponds to the critical micelle concentration. The adsorption density as well as the rate of adsorption are dependent on the suspension pH. The adsorption decreases with increasing pH value. The rate of Na-DBS adsorption on hematite is a slow process which reaches 77 to 83% of the corresponding equilibrium values depending upon pH after 10 min. The adsorption density reaches its equilibrium values sooner in the case of alkaline suspension and conversely later in case of acidic pH. The initial adsorption density is lower at pH 4 than that at higher pH (neutral and basic), whereas the adsorption density near to saturation is higher at pH 4 when compared to that at higher pH. Adsorption in stages: firstly, at the Stern layer, and secondly at the mineral surface, has been proposed which explains the nature of the kinetics curves at different pH levels.