Distinguishing between interlayer and external sorption sites of clay minerals using x-ray absorption
- University System of Nevada, Las Vegas, NV (United States)
- Univ. of Michigan, Ann Arbor, MI (United States)
Metals dissolved in natural aquatic environments are often sorbed on high surface area, smectite-clay minerals. Using X-ray Absorption Spectroscopy (XAS), it is shown that at low pH and Na ion concentration Co(II) forms outer-sphere, mononuclear surface complexes with permanent-charge sites in the interlayer region of smectites. The Co-O distance 2.10{plus_minus}0.01 {Angstrom} and coordination number (CN, 6.5{plus_minus}20%) are in good agreement with the distance and CN expected for hydrated Co(II). At high pH or Na ion concentration, the presence of a second Co-Co shell at 3.13{plus_minus}0.01 {Angstrom} and a fourth Co-Co shell at 6.06{plus_minus}0.01 {Angstrom} indicates that Co(II) is excluded from the interlayer permanent-charge sites and forms polynuclear species or a surface precipitate on external surface-hydroxyl sites. These studies confirm the relative importance of interlayer and external sites for trace metal sorption on smectites as a function of changing solution conditions.
- OSTI ID:
- 126367
- Report Number(s):
- CONF-950402--
- Country of Publication:
- United States
- Language:
- English
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