Interaction of Pb2+ with hydrous γ-Al2O3

Significant adsorption of Pb(II) on to hydrous γ-Al2O3 from dilute solutions is observed even at pH values far below the zero point of charge. The specific binding of Pb2+ on hydrous γ-Al2O3 in dilute electrolyte is interpreted as surface complex formation. The amphoteric properties of the coordinating surface are characterized in 0.1 M NaC1O4 in terms of a two-protic acid-base system (pHZPC = 8.3). The extent of Pb2+ interaction with the Al2O3 surface was determined both from measurements of residual [Pb2+] with a Pb2+ electrode and from the displacement of alkalimetric titration curves by the presence of Pb(II). The complex forming properties of the surface coordination reaction can be quantified by the equilibria: ≡ AlOH + Pb2+ ⇄ ≡ AlOPb+ + H+; 2 ≡ AlOH +Pb2+ ⇄ (≡ AlO)2Pb + 2H+. Hydrolysis need not be invoked to describe the interaction.