Mobility of uranium during weathering

University of Tokyo, Mineralogical Institute, Tokyo, Japan

Mineralogical and geochemical mechanisms of U fixation under oxidizing conditions in the vicinity of the secondary U ore deposit at Koongarra, Australia, were examined using transmission and scanning electron microscopy and thermodynamic calculations. The formation of saleeite, Mg(UO ₂ ) ₂ (PO ₄ ) ₂ .1OH ₂ O, is the predominant mechanism for U fixation upstream from the deposit, where saleeite replaces sklodowskite and granular apatite. Within the deposit and further downstream, U is fixed in microcrystals (10-50 nm) of saleeite and (meta)torbernite scattered within veins of fine-grained (2-50 nm) Fe (super 3+) minerals (primarily goethite and hematite). Thermodynamic calculations indicate the groundwater is undersaturated with respect to saleeite and metatorbernite and that these minerals should precipitate at higher U or P concentrations than observed. This suggests that the upstream saleeite precipitated at the reaction interfaces of dissolving sklodowskite and apatite under local saturation conditions. Observed textural relationships of saleeite and (meta)torbernite microcrystals with the Fe minerals, combined with thermodynamic calculations, suggest surface precipitation as the formation mechanism for saleeite and (meta)torbernite microcrystals within, and downstream from, the secondary ore deposit. Phosphorous released during the aging of ferrihydrite and U adsorbed onto Fe minerals are probably the sources of the major components of the microcrystals. Downstream, the microcrystals exist where groundwater U concentrations are as low as 10-30 mu g/L. Once released from the ore deposit, U is fixed in uranyl phosphates even where measured groundwater is undersaturated with respect to uranyl phosphates. The surface precipitation is an important example of long-term post-adsorption U fixation in a natural system. The fully crystalline and radiation-damaged microstructures of saleeite indicate uranyl phosphates have formed continuously (or intermittently) for the last few million years.

This record provided courtesy of AGI/GeoRef.

This article has been cited by other articles:

				S. J. Mills, W. D. Birch, U. Kolitsch, W. G. Mumme, and I. E. Grey Lakebogaite, CaNaFe23+H(UO2)2(PO4)4(OH)2(H2O)8, a new uranyl phosphate with a unique crystal structure from Victoria, Australia American Mineralogist, April 1, 2008; 93(4): 691 - 697. [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]

				D. M. Wellman, J. P. Icenhower, A. P. Gamerdinger, and S. W. Forrester Effects of pH, temperature, and aqueous organic material on the dissolution kinetics of meta-autunite minerals, (Na, Ca)2-1[(UO2)(PO4)]2{middle dot} 3H2O American Mineralogist, January 1, 2006; 91(1): 143 - 158. [Abstract] [Full Text] [PDF]

				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. Suzuki, T. Sato, H. Isobe, T. Kogure, and T. Murakami Dehydration processes in the meta-autunite group minerals meta-autunite, metasaleeite, and metatorbernite American Mineralogist, August 1, 2005; 90(8-9): 1308 - 1314. [Abstract] [Full Text] [PDF]

				A. J. Locock, P. C. Burns, and T. M. Flynn STRUCTURES OF STRONTIUM- AND BARIUM-DOMINANT COMPOUNDS THAT CONTAIN THE AUTUNITE-TYPE SHEET Can Mineral, April 1, 2005; 43(2): 721 - 733. [Abstract] [Full Text] [PDF]

				A. J. Locock, P. C. Burns, M. J. M. Duke, and T. M. Flynn MONOVALENT CATIONS IN STRUCTURES OF THE META-AUTUNITE GROUP Can Mineral, August 1, 2004; 42(4): 973 - 996. [Abstract] [Full Text] [PDF]

				E. C. Buck, B. D. Hanson, and B. K. McNamara The geochemical behaviour of Tc, Np and Pu in spent nuclear fuel in an oxidizing environment Geological Society, London, Special Publications, January 1, 2004; 236(1): 65 - 88. [Abstract] [PDF]

				M. Del Nero, A. Froideval, C. Gaillard, G. Mignot, R. Barillon, I. Munier, and A. Ozgumus Mechanisms of uranyl sorption Geological Society, London, Special Publications, January 1, 2004; 236(1): 545 - 560. [Abstract] [PDF]

				A. J. Locock, A. J. Locock, and P. C. Burns The structure of hugelite, an arsenate of the phosphuranylite group, and its relationship to dumontite Mineralogical Magazine, October 1, 2003; 67(5): 1109 - 1120. [Abstract] [Full Text] [PDF]

				P. W. O. Hoskin, P. W. O. Hoskin, and P. C. Burns Ion exchange between aqueous fluid and spent nuclear fuel alteration products: Implications for the mobility of Cs in the probable repository at Yucca Mountain Mineralogical Magazine, August 1, 2003; 67(4): 689 - 696. [Abstract] [Full Text] [PDF]

				A. G. Sowder, P. M. Bertsch, and P. J. Morris Partitioning and Availability of Uranium and Nickel in Contaminated Riparian Sediments J. Environ. Qual., May 1, 2003; 32(3): 885 - 898. [Abstract] [Full Text] [PDF]

				A. J. Locock and P. C. Burns CRYSTAL STRUCTURES AND SYNTHESIS OF THE COPPER-DOMINANT MEMBERS OF THE AUTUNITE AND META-AUTUNITE GROUPS: TORBERNITE, ZEUNERITE, METATORBERNITE AND METAZEUNERITE Can Mineral, April 1, 2003; 41(2): 489 - 502. [Abstract] [Full Text] [PDF]

				A. J. Locock and P. C. Burns THE CRYSTAL STRUCTURE OF BERGENITE, A NEW GEOMETRICAL ISOMER OF THE PHOSPHURANYLITE GROUP Can Mineral, February 1, 2003; 41(1): 91 - 101. [Abstract] [Full Text] [PDF]

				F. Chabaux, F. Chabaux, J. Riotte, and O. Dequincey U-Th-Ra Fractionation During Weathering and River Transport Reviews in Mineralogy and Geochemistry, January 1, 2003; 52(1): 533 - 576. [Full Text] [PDF]

				A. J. Locock, A. J. Locock, and P. C. Burns The crystal structure of synthetic autunite, Ca[(UO2)(PO4)]2(H2O)11 American Mineralogist, January 1, 2003; 88(1): 240 - 244. [Abstract] [Full Text] [PDF]

				D. Read and C. T. Williams Degradation of phosphatic waste forms incorporating long-lived radioactive isotopes Mineralogical Magazine, October 1, 2001; 65(5): 589 - 601. [Abstract] [Full Text] [PDF]

				P. C. Burns A new uranyl phosphate chain in the structure of parsonsite American Mineralogist, May 1, 2000; 85(5-6): 801 - 805. [Abstract] [Full Text] [PDF]