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Structural state of rare earth elements in eudialyte-group minerals

Borst, Anouk M.; Finch, Adrian A.; Friis, Henrik; Horsburgh, Nicola J.; Gamaletsos, Platon N.; Goettlicher, Joerg; Steininger, Ralph; Geraki, Kalotina

Abstract:
Eudialyte-group minerals (EGM) attract global interest as potential resources for high-field-strength elements (e.g. Zr, Nb, Ta, and rare-earth elements), i.e. critical materials for modern technologies. They are particularly valued for their relative enrichment in the most critical lanthanides, i.e. Nd and heavy rare earth elements (Gd–Lu). However, rare earth element (REE) substitution mechanisms into the EGM structure are still poorly understood. Light and heavy REE may occupy different sites and there may be ordering and/or defect clustering in the structure. This study uses X-ray absorption spectroscopy to determine the structural state of REE in EGM from prospective eudialyte-bearing complexes. Yttrium K-edge and Nd L$_{3}$-edge spectra were collected as proxies for heavy and light REE, respectively, and compared to natural and synthetic REE-bearing standards. Extended X-ray absorption fine structure data yield best fits for Y in six-fold coordination with Y–O distances of 2.24–2.32 Å, and a second coordination sphere comprising Fe, Na, Ca, Si and O at radial distances of 3.6–3.8 Å. These findings are consistent with dominant Y$^{3+}$ substitution for Ca$^{2+}$ on the octahedral M1 site in all the samples studied, and exclude preferential substitution of Y$^{3+}$ onto the smaller octahedral Z site or the large low-symmetry N4 site.
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Verlagsausgabe §
DOI: 10.5445/IR/1000119645
Veröffentlicht am 19.06.2020
Originalveröffentlichung
DOI: 10.1180/mgm.2019.50
Scopus
Zitationen: 3
Web of Science
Zitationen: 1
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Photonenforschung und Synchrotronstrahlung (IPS)
Publikationstyp Zeitschriftenaufsatz
Publikationsjahr 2019
Sprache Englisch
Identifikator ISSN: 0026-461X, 1471-8022
KITopen-ID: 1000119645
HGF-Programm 56.98.01 (POF III, LK 01)
Betrieb in MML
Erschienen in Mineralogical magazine
Band 84
Heft 1
Seiten 19–34
Vorab online veröffentlicht am 02.08.2019
Nachgewiesen in Web of Science
Scopus
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