Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Li, Y. Articles by Gault, R. A. Search for Related Content GeoRef GeoRef Citation

A NEW RARE-EARTH-ELEMENT URANYL CARBONATE SHEET IN THE STRUCTURE OF BIJVOETITE-(Y)

Yaping Li¹, Peter C. Burns^1, and Robert A. Gault²

¹ Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, Indiana 46556-0767, U.S.A.
² Research Division, Canadian Museum of Nature, P.O. Box 3443, Station "D", Ottawa, Ontario K1P 6P4, Canada

E-mail address: pburns{at}nd.edu

The crystal structure of bijvoetite-(Y), [M₈³⁺(H₂O)₂₅(UO₂)₁₆O₈(OH)₈(CO₃)₁₆](H₂O)₁₄, M = (Y, REE), pseudo-orthorhombic, monoclinic, a 21.234(3), b 12.958(2), c 44.911(6) Å, ß 90.00(2)°, V 12,357(6) ų, space group B12₁1, Z = 4, was solved by direct methods and refined by least-squares techniques to an agreement index (R) of 8.4% and a goodness of fit (S) of 0.81 for 6622 unique observed (|F_o| > 4_F) reflections collected for a twinned crystal using graphite-monochromatic MoK X-radiation and a CCD area detector. There are 16 symmetrically independent U⁶⁺ positions, each of which is part of near-linear (U⁶⁺O₂)²⁺ uranyl ion. Eight uranyl ions are coordinated by three O^2– and two (OH)^– anions each, resulting in uranyl pentagonal bipyramids, and eight uranyl ions are coordinated by six O^2– anions each, forming uranyl hexagonal bipyramids. The structure contains 16 unique carbonate groups and eight unique M³⁺ sites that are occupied by variable amounts of Y, Dy and other REEs. The structure of bijvoetite-(Y) is based on a novel uranyl carbonate chain that is parallel to [100], involving edge-sharing dimers of uranyl pentagonal bipyramids, edge-sharing dimers of uranyl hexagonal bipyramids, and carbonate groups. The chains are cross-linked by irregular M³⁺_n (: unspecified ligand) polyhedra, forming (Y,REE)-bearing uranyl carbonate sheets that are parallel to (010). The sheet in bijvoetite-(Y) is based upon a new sheet anion-topology. There are 39 symmetrically unique H₂O groups in the structure, 25 of which are bonded to M³⁺ and 14 of which are located in the interlayer, where they are held in place by H bonds. The interlayer of the structure contains only H₂O groups, and adjacent sheets are connected by H bonds only. The discovery of the structure may have implications for nuclear waste disposal because uranyl carbonates may be abundant in a geological repository due to the corrosion of uranium oxide nuclear fuel. It is proposed that the structure may incorporate transuranium elements.

Keywords: bijvoetite-(Y), uranyl carbonate, uranyl mineral, structure determination, nuclear waste disposal.

This article has been cited by other articles:

				P. C. Burns U6+ MINERALS AND INORGANIC COMPOUNDS: INSIGHTS INTO AN EXPANDED STRUCTURAL HIERARCHY OF CRYSTAL STRUCTURES Can Mineral, December 1, 2005; 43(6): 1839 - 1894. [Abstract] [Full Text] [PDF]

				Y. Li and P. C. Burns THE CRYSTAL STRUCTURE OF SYNTHETIC GRIMSELITE, K3Na[(UO2)(CO3)3](H2O) Can Mineral, August 1, 2001; 39(4): 1147 - 1151. [Abstract] [Full Text] [PDF]