SYNTHESIS AND STRUCTURE OF A NEW Ca URANYL OXIDE HYDRATE, Ca[(UO2)4O3(OH)4](H2O)2, AND ITS RELATIONSHIP TO BECQUERELITE

A new Ca uranyl oxide hydrate, Ca[(UO2)4O3(OH)4](H2O)2, has been synthesized by hydrothermal reaction of a solution of 0.03 M UO3 with calcite crystals. Fifteen hydrothermal synthesis experiments at 140, 180 and 220°C, with starting solution pH in the range 2 to 6, resulted in Ca[(UO2)4O3(OH)4](H2O)2. The structure, space group P 1, a 8.0556(8), b 8.4214(8), c 10.958(1) A, α 78.878(2), β 87.922(2), γ 72.277(2)°, V 649.6(2) A3, Z = 2, has been solved and refined on the basis of F 2 for all unique data collected with monochromatic Mo K α X-radiation and a CCD-based detector to an agreement factor ( R 1) of 3.47%, calculated using 2523 unique observed reflections ( F o ≥ 4σ F ). The structure contains four symmetrically distinct U6+ cations, each of which is part of a nearly linear (UO2)2+ uranyl ion. Three of the uranyl ions are coordinated by five ligands arranged at the equatorial vertices of pentagonal bipyramids, and the other is coordinated by four ligands at the equatorial vertices of a square bipyramid. Polymerization of the uranyl polyhedra by the sharing of vertices and edges results in a novel sheet. The single unique Ca2+ cation is located in the interlayer, together with two H2O groups, one of which is bonded to the Ca2+ cation, whereas the other is held in the structure by hydrogen bonding only. The phase Ca[(UO2)4O3(OH)4](H2O)2 contains more Ca than becquerelite, Ca[(UO2)6O4(OH)6](H2O)8, and polymerization of Ca polyhedra occurs in the interlayer, whereas in becquerelite, the Ca polyhedra do not share polyhedron elements.

[1]  P. Burns,et al.  SYNTHESIS AND CRYSTAL STRUCTURE OF A NEW Pb URANYL OXIDE HYDRATE WITH A FRAMEWORK STRUCTURE THAT CONTAINS CHANNELS , 2000 .

[2]  P. Burns,et al.  The structure of agrinierite: a Sr-containing uranyl oxide hydrate mineral , 2000 .

[3]  P. Burns,et al.  INVESTIGATIONS OF CRYSTAL-CHEMICAL VARIABILITY IN LEAD URANYL OXIDE HYDRATES. II. FOURMARIERITE , 2000 .

[4]  P. Burns,et al.  IMPLICATIONS OF THE SYNTHESIS AND STRUCTURE OF THE Sr ANALOGUE OF CURITE , 2000 .

[5]  P. Burns,et al.  A NEW URANYL SHEET IN K5[(UO2)10O8(OH)9](H2O): NEW INSIGHT INTO SHEET ANION-TOPOLOGIES , 2000 .

[6]  Edgar C. Buck,et al.  Oxidative corrosion of spent UO{sub 2} fuel in vapor and dripping groundwater at 90{degree}C. , 1999 .

[7]  R. Ewing,et al.  The crystal chemistry of hexavalent uranium; polyhedron geometries, bond-valence parameters, and polymerization of polyhedra , 1997 .

[8]  P. Finn,et al.  The Release of Uranium, Plutonium, Cesium, Strontium, Technetium and Iodine from Spent Fuel under Unsaturated Conditions , 1996 .

[9]  R. Ewing,et al.  Description and classification of uranium oxide hydrate sheet anion topologies , 1996 .

[10]  Edgar C. Buck,et al.  Ten-year results from unsaturated drip tests with UO2 at 90°C: implications for the corrosion of spent nuclear fuel , 1996 .

[11]  Peter C. Burns,et al.  U (super 6+) minerals and inorganic phases; a comparison and hierarchy of crystal structures , 1996 .

[12]  E. C. Pearcy,et al.  Alteration of uraninite from the Nopal I deposit, Pen˜a Blanca District, Chihuahua, Mexico, compared to degradation of spent nuclear fuel in the proposed U.S. high-level nuclear waste repository at Yucca Mountain, Nevada , 1994 .

[13]  Robert J. Finch,et al.  The corrosion of uraninite under oxidizing conditions , 1992 .

[14]  David J. Wronkiewicz,et al.  Uranium release and secondary phase formation during unsaturated testing of UO2 at 90°C , 1992 .

[15]  Michael O'Keeffe,et al.  Bond-valence parameters for solids , 1991 .

[16]  G. Ivaldi,et al.  Bond valence vs bond length in O…O hydrogen bonds , 1988 .

[17]  D. Appleman,et al.  Crystal structures and crystal chemistry of the uranyl oxide hydrates becquerelite, billietite, and protasite , 1987 .

[18]  K. Mereiter.  The crystal structure of curite, [Pb6.56(H2O, OH)4] [(UO2)8O8(OH)6]2 , 1979 .

[19]  V. P. Rogova,et al.  Calciouranoite, a new hydroxide of uranium , 1974 .

[20]  V. P. Rogova,et al.  Bauranoite and metacalciouranoite, new minerals of the hydrous uranium oxides group , 1974 .

[21]  W. L. Brown,et al.  Rameauite and agrinierite, two new hydrated complex uranyl oxides from Margnac, France , 1972, Mineralogical Magazine.

[22]  R. J. Williams.  INVESTIGATIONS OF CRYSTAL MODIFICATION OF UREA , 1968 .

[23]  Peter C. Burns,et al.  The crystal chemistry of uranium , 1999 .

[24]  E. Buck,et al.  Contaminant Uranium Phases and Leaching at the Fernald Site in Ohio , 1996 .

[25]  R. Ewing,et al.  Description and Classification of Uranium Oxide Hydrate Sheet Topologies , 1995 .

[26]  G. D. Rieck,et al.  International tables for X-ray crystallography , 1962 .

[27]  C. Frondel.  Systematic mineralogy of uranium and thorium , 1958 .

[28]  Peter C. Burnsi,et al.  U 6 * MINERALS AND INORGANIC PHASES : A COMPARISON AND HIERARCHY OF CRYSTAL STRUCTURES , 2022 .