Interfacial characterization of α-alumina with small surface area by streaming potential and chromatography

Interfacial properties of porous media are important to study adsorption and transport of solutes and colloids in the natural environment. In the present study, alpha alumina beads with small surface area were modified by several techniques, interfacial properties of alpha alumina before and after modifications were characterized by streaming potential and chromatographic charge density methods. The zeta potential and the surface charge density of α-Al2O3 materials were obtained as a function of pH. Streaming potential was used to monitor the zeta potential at several pH values to compare electrokinetic property and to identify isoelectric point of α-Al2O3 materials. The surface charge density of α-Al2O3 materials was evaluated by chromatographic method from measuring pH breakthrough curves. A good agreement between the charge density obtained from column pH breakthrough curves and 1-pK Stern model was confirmed in the pH range of 4.7–9.4 irrespective of ionic strength between 0.001 M NaCl and 0.01 M NaCl. The dissolution of alumina below pH 4.7 and above pH 9.4 influenced the net proton consumption and induced the difference between the experimental data and the calculated curves from the model. The adsorption of sodium dodecyl sulfate (SDS) followed by desorption during the washing process increased proton binding on the surface of alumina material. The zeta potential and surface charge density increase significantly in the pH range higher than 5.5. Nevertheless, the charging behavior of α-Al2O3 can be recovered by heating at high temperature 550 °C and 1.0 M NaOH cleaning.