The Influence of the Solid/Liquid Ratio on the Point of Zero Charge of Alumina

The point of zero charge (pHpzc) of three samples of commercial aluminum oxide in aqueous KNO3 (10-3 - 10-1 mol/dm3) solution was investigated using batch equilibration, mass titration and acid-base titration methods. Structural and chemical characteristics of the alumina samples were determined by X-ray diffraction (XRD) and energy-dispersive X-ray fluorescence spectroscopy (EDXRFS). The obtained pHpzc values (5 to 8.5) dependent on the alumina/solution ratio increase with increasing ratio to a constant value. The concentration of dissolved aluminum ions as a function of solution pH (pH = 3.5 - 11) exhibit a parabolic trend, with the minimum solubility at pHpzc.