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XAFS study of Sb and As in Cretaceous-Tertiary boundary sediments: an index of soiling of the global environment with dust and ashes from impact ejecta falls

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Title: XAFS study of Sb and As in Cretaceous-Tertiary boundary sediments: an index of soiling of the global environment with dust and ashes from impact ejecta falls
Authors: Hongu, Hidetomo Browse this author
Yoshiasa, Akira Browse this author
Tobase, Tsubasa Browse this author
Okube, Maki Browse this author
Sugiyama, Kazumasa Browse this author
Sato, Tsutomu Browse this author →KAKEN DB
Keywords: Local structures of Sb and As
K-T boundary sediments
XANES
EXAFS
Coprecipitation
Issue Date: Dec-2019
Publisher: Mineralogical Society of Japan , Japanese association of Mineralogists, Petrologists and Economic Geologists
Journal Title: Journal of mineralogical and petrological sciences
Volume: 114
Issue: 5
Start Page: 224
End Page: 230
Publisher DOI: 10.2465/jmps.180927
Abstract: The local structure around antimony (Sb) atoms in Cretaceous-Tertiary (K-T) boundary sediments from Stevns Klint in Denmark was studied using Sb K-edge X-ray absorption fine structure (XAFS) spectroscopy to obtain information about the chemical state and coordination environment. We also performed arsenic (As) K-edge XAFS measurements. The Sb K-edge X-ray absorption near edge structure (XANES) spectrum of K-T boundary sediments was compared with those of various kinds of reference Sb minerals, such as Sb sulfides and Sb5+ complex oxides, and soils containing ferrihydrite (schwertmannite), Sb2O3, and Sb2O5. The XANES pattern and threshold energy of K-T boundary sediments are similar to those of ferrihydrite (schwertmannite) soil samples. There is no chemical shift in the threshold energies among K-T boundary sediments, Sb5+ oxide complex minerals, and Sb2O5. In As XAFS analyses, the threshold energy of K-T boundary sediments is approximately similar to those of As5+ minerals, and the XANES pattern of K-T boundary sediments is almost similar to those of ferrihydrite (schwertmannite) soil samples. The oxidation states of Sb and As of K-T boundary sediments are estimated to be Sb5+ and As5+, respectively. Sb and As in K-T boundary sediments are coordinated with oxide ions, and Sb and As exist in the same local structure positions as Sb and As in ferrihydrite (schwertmannite) The XANES spectra and radial structure function for Sb atoms also showed that Sb in K-T boundary sediments is stored in a SbO6 octahedral coordination environment. The Sb-O interatomic distance in the K-T boundary sediments sample is 1.99(1) angstrom. Abundant ferric hydroxides occur in K-T boundary sediments. Sb is considered to be coprecipitated with As and Fe ions, and Sb and As in K-T boundary sediments are incorporated in low crystalline ferrihydrite (schwertmannite) throughout precipitation and sedimentation. The environment at K-T boundary sediments resembles that of soil contaminated by Sb and As in local areas at the present age. However, in an unusual environment, such as widely distributed K-T boundary sediments in the world, unusually high concentrations of Sb5+ and As5+ could become an index of the soiling of the global environment with dust and ashes derived from asteroid impact ejecta falls.
Type: article
URI: http://hdl.handle.net/2115/76517
Appears in Collections:工学院・工学研究院 (Graduate School of Engineering / Faculty of Engineering) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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