Mechanism of SeO{sub 4}{sup 2{minus}} substitution in calcite: An XAFS study

Journal Article · Thu Dec 01 04:00:00 EST 1994 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/0016-7037(94)90256-9· OSTI ID:28817

Reeder, R J; Staudt, W J ^[1]; Lamble, G M ^[2]; Lee, Jyh-Fu ^[3]

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1. State Univ. of New York, Stony Brook, NY (United States)
2. Brookhaven National Lab., Upton, NY (United States)
3. Synchrotron Radiation Research Center, Taiwan (China)

Analysis of Se K-edge XAFS spectra of calcite grown from SeO{sub 4}{sup 2{minus}}-bearing aqueous solutions at 25{degrees}C reveals the local environment of Se incorporated in calcite. The position of the Se K-edge is consistent with oxidation state 6+, and the first shell contains four O atoms at a distance of 1.63 {angstrom}, confirming that Se is present as the tetrahedral SeO{sub 4}{sup 2{minus}} complex ion. The second shell is split and is best fitted by approximately 2 Ca atoms at 3.17 {angstrom} and approximately 4 Ca atoms at 3.49 {angstrom}. The coordination indicated by the split second shell is consistent with substitution of the SeO{sub 4}{sup 2{minus}} ion in the CO{sub 3} site of the calcite, which has six nearest-neighbor Ca atoms. The large size of the SeO{sub 4}{sup 2{minus}} ion and its tetrahedral geometry cause significant distortion of the site that is consistent with the observed Se-Ca distances. Two possible models for the local coordination of the SeO{sub 4}{sup 2{minus}} ion are suggested that involve corner sharing of the SeO{sub 4} tetrahedron with neighboring Ca octahedra. The results suggest that other complex anions - particularly the geochemically important SO{sub 4}{sup 2{minus}} ion, which is also tetrahedral but slightly smaller than SeO{sub 4}{sup 2{minus}} - may also substitute in the CO{sub 3} site of carbonates.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY
• DOE Contract Number: FG05-89ER45384; AC02-76CH00016
• OSTI ID: 28817
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 24 Vol. 58; ISSN 0016-7037; ISSN GCACAK
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
ABSORPTION SPECTROSCOPY
AQUEOUS SOLUTIONS
CALCITE
CHEMICAL REACTIONS
GEOCHEMISTRY
GEOMETRY
OXIDATION
ROCK-FLUID INTERACTIONS
SELENIUM OXIDES
TRACE AMOUNTS
X-RAY SPECTROSCOPY