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Comparison of the structures of natural and synthetic Pb-Cu-jarosite-type compounds

Karen A. Hudson-Edwards, Adrian M. L. Smith, William E. Dubbin, Andrew J. Bennett, Pamela J. Murphy and Kate Wright
Comparison of the structures of natural and synthetic Pb-Cu-jarosite-type compounds
European Journal of Mineralogy (May 2008) 20 (2): 241-252

Abstract

Jarosite minerals are effective scavengers of potentially toxic elements such as Pb and Cu, and are abundant in acid rock drainage systems, acid sulfate soils and metallurgical wastes. We used XRD, SEM, and infrared, Raman and X-ray absorption (EXAFS and XANES) spectroscopy to determine the structural differences between natural and synthetic Pb-Cu-jarosites. Differences in the a (sub 0) unit cell dimensions for the natural and synthetic samples (7.2288(27) Aa and 7.32088(26) Aa, respectively), and c (sub 0) unit cell values (34.407(14) Aa and 17.0336(7) Aa, respectively) are attributed to different proportions of H (sub 3) O, Fe and Pb in the jarosite structures. The synthetic Pb-Cu-jarosite has sharper Raman and IR spectra, with narrower and more intense bands, suggesting that it is more crystalline than the natural sample. EXAFS fitting of the Fe and Pb data for the natural and synthetic Pb-Cu-jarosite samples are similar to each other, and are also similar to previously reported EXAFS data for jarosites, suggesting that Fe occupies the B sites, and Pb the A sites. The natural sample's Pb EXAFS data are only fitted over a short k-range, however, and the comparison is based on only the first two shells around Pb. Our Cu fits for the natural Pb-Cu-jarosite are similar to the first and third shell fittings for Fe, except that the Cu occupies a tetrahedral rather than an octahedral site (4 O in first shell at r = 1.94-1.95 Aa; 4 Fe in third shell at r = 3.59-3.60 Aa). In the synthetic Pb-Cu-jarosite, Cu also shares the B site with Fe, but fits of 4 Cu around the Cu atom at a bond distance of 2.60 Aa and XANES evidence also suggest the presence of metallic Cu within the structure. Variations in the structures of the natural and synthetic samples are likely due to their differing chemistries and conditions of formation.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 20
Serial Issue: 2
Title: Comparison of the structures of natural and synthetic Pb-Cu-jarosite-type compounds
Affiliation: University of London, Research School of Earth Sciences at UCL-Birkbeck, London, United Kingdom
Pages: 241-252
Published: 200805
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 62
Accession Number: 2008-086483
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: Natural History Museum, GBR, United KingdomRoyal Institution of Great Britain, GBR, United KingdomSTFC Daresbury Laboratory, GBR, United KingdomKingston University, GBR, United Kingdom
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200826
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