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EXAFS signature of structural Zn at trace levels in natural and synthetic trioctahedral 2:1 phyllosilicates

Farid Juillot, Guillaume Morin, Philippe Ildefonse, Georges Calas and Gordon E. Brown
EXAFS signature of structural Zn at trace levels in natural and synthetic trioctahedral 2:1 phyllosilicates
American Mineralogist (August 2006) 91 (8-9): 1432-1441

Abstract

EXAFS spectroscopy has been used to determine the medium-range structural environment (within a radius of 7 Aa) of trace levels of Zn (super 2+) ions within the octahedral sheets of trioctahedral 2:1 phyllosilicates. EXAFS signatures of trace quantities (800-4000 ppm) of Zn in natural and synthetic trioctahedral 2:1 phyllosilicates (talcs and biotite) were analyzed using ab initio FEFF calculations (FEFF 8.10 code) in which various second-neighbor atomic configurations around a Zn-containing octahedral site were examined. Comparison of the results of these model calculations with observed Zn K-edge EXAFS spectra provides constraints on the distribution of Zn within the octahedral sheet. Zn was found to be randomly distributed within the octahedral sheets of the synthetic talc containing 4000 ppm Zn. In the natural biotite containing 800 ppm Zn, the distribution of Zn could not be determined because of significant Fe content, which precluded unambiguous FEFF analysis. Finally, FEFF analysis of single-scattering and multiple-scattering contributions to the EXAFS data of the Zn-dilute talc sample, followed by comparison with EXAFS data from a natural dioctahedral illite sample containing 140 ppm Zn, allowed unambiguous identification of spectral features characteristic of Zn (super 2+) ions incorporated within the octahedral sheets of trioctahedral phyllosilicates. These results indicate that EXAFS spectroscopy can be used to distinguish between incorporation of trace levels of Zn (super 2+) ions within the octahedral sheet of di- or trioctahedral phyllosilicates. They also provide a strong basis for determining the speciation of Zn at trace concentration levels in natural phyllosilicates from Zn-contaminated soils and sediments using Zn K-edge EXAFS spectroscopy. Because the crystal chemistry of other potentially toxic first-row divalent transition elements (i.e., Co (super 2+) , Ni (super 2+) , and Cu (super 2+) ) is similar to that of Zn (super 2+) , this FEFF-based EXAFS approach could be used to (1) complement existing FTIR and polarized-EXAFS approaches in assessing the distribution of these elements within the octahedral sheets of di- and trioctahedral plyllosilicates and (2) better determine the speciation of these elements in contaminated soils and sediments.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 91
Serial Issue: 8-9
Title: EXAFS signature of structural Zn at trace levels in natural and synthetic trioctahedral 2:1 phyllosilicates
Affiliation: Universites de Paris VI et VII, Institut de Mineralogie et de Physique des Milieux Condenses, Paris, France
Pages: 1432-1441
Published: 200608
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 42
Accession Number: 2006-079777
Categories: General geochemistryEnvironmental geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
Secondary Affiliation: Stanford University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200645
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