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Ba(NpO₂)(PO₄)(H₂O), its relationship to the uranophane group, and implications for Np incorporation in uranyl minerals

Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, Indiana 46556, U.S.A

Correspondence: ^* E-mail: pburns{at}nd.edu

Single crystals of Ba(NpO₂)(PO₄)(H₂O) were obtained using hydrothermal synthesis techniques. The structure was determined using single-crystal X-ray diffraction data collected using MoK radiation and an APEX II CCD detector and was refined on the basis of F² for all unique data to R₁ = 2.41%. Ba(NpO₂)(PO₄)(H₂O) crystallized in monoclinic space group P2₁/n with a = 6.905(3), b = 7.108(3), c = 13.321(6) Å, ß= 105.02°, and V = 631.4 ų. The structure contains chains of edge-sharing neptunyl pentagonal bipyramids that link through phosphate tetrahedra to form infinite sheets. This sheet-type is identical to the anion topology of the uranophane group, in particular to that of oursinite, Co[(UO₂)(SiO₃OH)]₂(H₂O)₆. Similarities between Ba(NpO₂)(PO₄)(H₂O) and the uranophane group of minerals suggests a charge-balancing mechanism for incorporation of Np⁵⁺ into uranyl minerals.

Key Words: Neptunium • uranyl mineral • uranophane • nuclear waste • crystal structure • actinide

This article has been cited by other articles:

				A. L. Klingensmith and P. C. Burns Neptunium substitution in synthetic uranophane and soddyite American Mineralogist, November 1, 2007; 92(11-12): 1946 - 1951. [Abstract] [Full Text] [PDF]

				T. Z. Forbes and P. C. Burns THE CRYSTAL STRUCTURES OF X(NpO2)(PO4)(H2O)3 (X = K+, Na+, Rb+, NH4+) AND THEIR RELATIONSHIP TO THE AUTUNITE GROUP Can Mineral, June 1, 2007; 45(3): 471 - 477. [Abstract] [Full Text] [PDF]

				P. C. Burns and A. L. Klingensmith Uranium Mineralogy and Neptunium Mobility Elements, December 1, 2006; 2(6): 351 - 356. [Abstract] [Full Text] [PDF]