Surface complexation of Pb(II) at oxide-water interfaces: I. XAFS and bond-valence determination of mononuclear and polynuclear Pb(II) sorption products on aluminum oxides
- Stanford Univ., CA (United States)
Pb(II) sorption on Al{sub 2}-O{sub 3} powders was studied as functions of sorption density (from 0.5 to 5.2 {mu}moles/m{sup 2}) and [Pb]{sub eq} (0.03-1.4 mM) in 0.1 M NaNO{sub 3} electrolyte solution using XAFS spectroscopy. At pH 6 and 7, Pb(II) ions were found to be fully hydrolyzed and adsorbed preferentially as mononuclear bidentate complexes to edges of AlO{sub 6} octahedra. At higher sorption densities ({Gamma} {ge}3.4 {mu}moles - m{sup -2}), XAFS results suggest the presence of dimeric Pb(II) surface complexes. A bond-valence model was used in conjunction with these results to constrain the compositions and reaction stoichiometries of adsorption complexes. We conclude that Pb(II) adsorption on alumina is attributable to complexation by [Al{sub Al}{sup Al}(>)O{sup -{1/2}}] and [Al-OH{sup -{1/2}}] surface functional groups. Several plausible Pb(II) adsorption reactions are proposed, based on these results, which provide a basis for chemically realistic descriptions of surface complexation of Pb(II) on aluminum oxides. 46 refs., 7 figs., 4 tabs.
- DOE Contract Number:
- FG03-93ER14347
- OSTI ID:
- 576306
- Journal Information:
- Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 13 Vol. 61; ISSN 0016-7037; ISSN GCACAK
- Country of Publication:
- United States
- Language:
- English
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