Specific adsorption of cations on hydrous γ-Al2O3

✍ Scribed by Chin-Pao Huang; Werner Stumm

• Publisher: Elsevier Science
• Year: 1973
• Tongue: English
• Weight: 805 KB
• Volume: 43
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1016/0021-9797(73)90387-1

✦ Synopsis

The amphoteric properties of hydrous ~-A1203 and the distribution of earth alkaline cations in the oxide-electrolyte interface was evaluated from alkalimetric and acidimetric titration curves of aqueous dispersions. In NaC1 electrolytes (25°C), pH of zero point of charge is pHzpo = 8.5; acid-base properties can be characterized in terms of a heterogeneous two-protic acid with intrinsic acidity constants pKint 1 = 7.9 and pKin, 2 = 9.1.

The extent of adsorption of Ca 2+ and other earth alkaline cations on hydrous 7-AI2Oa increases with increasing pH; finite adsorption is observed at pH~p~ and at pH values slightly lower than pHz,o. Evaluation of adsorption measurements and alkalimetric titration curves indicates that the adsorption of M 2+ can be described by: AIOH + M 2+ ~-ATOM++ H +. Operational association constants for this equilibrium were determined ; the extent of adsorption increases in the series Mg 2+ > Ca 2+ > Sr ~+ > Ba 2+. In the pH-range above pHzp~, these ions, upon being adsorbed may reverse the surface charge of the oxide suspension.