X-ray standing wave study of arsenite incorporation at the calcite surface

The location and orientation of arsenite incorporated at the CaCO3 (1014) cleavage surface from a dilute aqueous solution was examined with the X-ray standing wave (XSW) technique. The high coherent fractions measured for As on the (1014) and (0006) Bragg reflections indicate that the arsenite was w...

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Bibliographic Details
Published in:Geochimica et cosmochimica acta 1999-10, Vol.63 (19-20), p.3153-3157
Main Authors: Cheng, Likwan, Fenter, Paul, Sturchio, Neil C., Zhong, Zhong, Bedzyk, Michael J.
Format: Article
Language:English
Subjects:
AQUEOUS SOLUTIONS
ARSENIC OXIDES
BRAGG REFLECTION
CALCITE
CLEAVAGE
CRYSTAL STRUCTURE
GEOSCIENCES
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
ORIENTATION
SORPTION
STANDING WAVES
SURFACE PROPERTIES
X RADIATION
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Summary:The location and orientation of arsenite incorporated at the CaCO3 (1014) cleavage surface from a dilute aqueous solution was examined with the X-ray standing wave (XSW) technique. The high coherent fractions measured for As on the (1014) and (0006) Bragg reflections indicate that the arsenite was well ordered in registration with the calcite surface lattice. The As coherent positions show that arsenite was located at the carbonate site. The XSW analysis is consistent with a structural model in which the pyramidal-shaped arsenite ion was oriented with its oxygen base coincident with the carbonate plane, and its As apex pointing outward from the (1014) surface. The structure observed here for arsenite, and previously for selenite, suggests that other pyramidal trioxyanions could be incorporated at the calcite (1014) surface with the same geometry.
ISSN:0016-7037
1872-9533
DOI:10.1016/S0016-7037(99)00242-2