RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

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 (pH_ZPC = 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.