The crystal structure of ianthinite, a mixed-valence uranium oxide hydrate
- Univ. of Illinois, Urbana, IL (United States). Dept. of Geology
- Argonne National Lab., IL (United States). Chemical Technology Div.
- Univ. of Manitoba, Winnipeg, Manitoba (Canada). Dept. of Geological Sciences
- Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences
Ianthinite, [U{sup 4+}{sub 2}(UO{sub 2}){sub 4}O{sub 6}(OH){sub 4}(H{sub 2}O){sub 4}](H{sub 2}O){sub 5}, is the only known uranyl oxide hydrate mineral that contains U{sup 4+}, and it has been proposed that ianthinite may be an important Pu{sup 4+}-bearing phase during the oxidative dissolution of spent nuclear fuel. The crystal structure of ianthinite, orthorhombic, a 7.178(2), b 11.473(2), c 30.39(1) {angstrom}, V 2502.7 {angstrom}{sup 3}, Z = 4, space group P2{sub 1}cn, has been solved by direct methods and refined by least-squares methods to an R index of 9.7% and a wR index of 12.6% using 888 unique observed [{vert_bar}F{vert_bar} {ge} 5{sigma} {vert_bar}F{vert_bar}] reflections. The structure contains both U{sup 6+} and U{sup 4+}. The U{sup 6+} cations are present as roughly linear uranyl ions (Ur) that are in turn coordinated by five O{sup 2{minus}} and OH{sup {minus}} located at the equatorial positions of pentagonal bipyramids. The U{sup 4+} cations are coordinated by O{sup 2{minus}}, OH{sup {minus}} and H{sub 2}O in a distorted octahedral arrangement. The Ur{phi}{sub 5} and U{sup 4+}{phi}{sub 6}({phi}: O{sup 2{minus}}, OH{sup {minus}}, H{sub 2}O) polyhedra link by sharing edges to form two symmetrically distinct sheets at z {approx} 0.0 and z {approx}0.25 that are parallel to (001). There are five symmetrically distinct H{sub 2}O groups between the sheets of U{phi}{sub n} polyhedra, and the sheets of U{phi}{sub n} polyhedra are linked together only by hydrogen bonding to the intersheet H{sub 2}O groups. The crystal-chemical requirements of U{sup 4+} and Pu{sup 4+} are very similar, indicating that extensive Pu{sup 4+} {leftrightarrow} U{sup 4+} substitution can occur within the structure of ianthinite.
- Sponsoring Organization:
- Natural Sciences and Engineering Research Council of Canada, Ottawa, ON (Canada); USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG03-95ER14540
- OSTI ID:
- 572273
- Report Number(s):
- CONF-961202--
- Country of Publication:
- United States
- Language:
- English
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