X-ray absorption spectroscopy of Co(II) sorption complexes on quartz ({alpha}-SiO{sub 2}) and rutile (TiO{sub 2})
- Arizona State Univ., Tempe, AZ (United States)
- Virginia Inst. of Marine Science, Gloucester Point, VA (United States)
- Stanford Univ., CA (United States)
The local molecular structure of Co(II) surface complexes sorbed to two pure mineral substrates, quartz ({alpha}-SiO{sub 2}) and rutile (TiO{sub 2}), was examined with X-ray absorption spectroscopy (XAS) are extended X-ray absorption fine structure (EXAFS) analysis. Absorption spectra were collected for samples equilibrated with Co solutions under- and over-saturated with respect to solid Co-hydroxide phases (0.15-3.00 mM) at Co surface coverages of 0.63-9.51 {mu}mol m{sup {minus}2} and for equilibration times of 23 h to 21 days. Quantitative analysis of the EXAFS spectra indicates no significant structural differences in the local atomic environment around Co sorbed to quartz, regardless of the surface coverage or the equilibration time. For all Co/quartz samples, the local Co environment is similar (but not identical) to that of Co in solid, crystalline cobalt hydroxide (Co(OH){sub 2}(s)). Cobalt is octahedrally coordinated by six O atoms at 2.06-2.11 {Angstrom}; second-neighbor Co backscatterers are found at 3.11-3.12 {Angstrom}, slightly contracted relative to the Co-Co distance in Co (OH){sub 2}(s) (3.173 {Angstrom}). Analysis of these high coverage Co/rutile samples indicates Ti backscatterers at distances near those expected for anatase, a TiO{sub 2} polymorph, suggesting a local geometry for Co and Ti octahedra at the rutile/water interface similar to that of the cation octahedra in anatase. We suggest that differences in Co sorption on quartz and rutile may be attributed to the availability of reactive surface sites on quartz and rutile which are structurally favorable for the sorption of octahedrally-coordinated Co{sup 2+}. 102 refs., 7 figs.
- OSTI ID:
- 457469
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 60, Issue 14; Other Information: PBD: Jul 1996
- Country of Publication:
- United States
- Language:
- English
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