Uranyl peroxide

Uranyl peroxide or uranium peroxide hydrate (UO4·nH2O) is a pale-yellow, soluble peroxide of uranium. It is found to be present at one stage of the enriched uranium fuel cycle and in yellowcake prepared via the in situ leaching and resin ion exchange system. This compound, also expressed as UO3·(H2O2)·(H2O), is very similar to uranium trioxide hydrate UO3·nH2O. The dissolution behaviour of both compounds are very sensitive to the hydration state (n can vary between 0 and 4). One main characteristic of uranium peroxide is that it consists of small needles with an average AMAD of about 1.1 μm.

Uranyl peroxide
Uranyl peroxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.671
EC Number
  • 234-852-1
UNII
UN number 2909
  • InChI=1S/O2.2O.U/c1-2;;;/q3*-2;+6
    Key: XFDGHOMYEXQKDC-UHFFFAOYSA-N
  • [O-2].[O-2].[O-][O-].[U+6]
Properties
UO4·nH2O
Molar mass 302.03 g/mol (as UO4)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

The uranyl minerals studtite, UO4·4H2O, and metastudtite, UO4·2H2O, are the only minerals discovered to date found to contain peroxide. The product is a light yellow powder.

Synthesis

In general, uranyl peroxide can be obtained from a solution of uranium (VI) by adding a peroxide, usually hydrogen peroxide solution. The dihydrate is obtained from a boiling solution of uranyl nitrate with the addition of hydrogen peroxide and drying of the precipitate, while the trihydrate is precipitated from a solution of ammonium uranyl oxalate.[1]

Crystal structure

The unit cell consists of uranyl cations coordinated to two water molecules and two peroxide anions. The latter are μ2-coordinated to the cation—that is, end-on. Additional water molecules are bound in the crystal by hydrogen bonding.[2] Only the tetrahydrate has been characterized by X-ray crystallography, but density functional theory offers a good approximation to the dihydrate.[3]

Poly­peroxo­uranylate allotrope

When uranyl nitrate is dissolved in an aqueous solution of hydrogen peroxide and an alkali metal hydroxide, it forms cage clusters akin to polyoxometalates or fullerenes.[4] Syntheses also typically add organic materials, such as amines, to serve as templates, akin to zeolites.[5]

  • A 50-uranium-atom peroxo­uranate cluster
    A 50-uranium-atom peroxo­uranate cluster[4]
  • Peroxide-bridged uranyl dimers in K6(H2O)4[(UO2)2(O2)(C2O4)4]
    Peroxide-bridged uranyl dimers in K6(H2O)4[(UO2)2(O2)(C2O4)4][5]
  • Pentagonal oxalo­peroxo­uranates in K10[(UO2)(C2O4)]5(H2O)13
    Pentagonal oxalo­peroxo­uranates in K10[(UO2)(C2O4)]5(H2O)13[5]

Applications

Radiolysis of uranium salts dissolved in water produces peroxides; uranyl peroxide has been studied as a possible end component of spent radioactive waste.[6]

References
  1. Rabald (1954). "Handbuch der präparativen anorganischen Chemie. Unter Mitarbeit zahlreicher Fachleute herausg. v. G. Brauer. Stuttgart: Ferdinand Enke Verlag 1954. XIX, 1439 S., 318 Abb., Ln. DM 199,—". Materials and Corrosion. 5 (11): 475–476. doi:10.1002/maco.19540051117. ISSN 1521-4176.
  2. Burns, Peter C.; Hughes, Karrie-Ann (2003). "Studtite, [(UO2)(O2)(H2O)2](H2O)2: The first structure of a peroxide mineral". American Mineralogist. Mineralogical Society of America. 88 (7): 1165–1168. Bibcode:2003AmMin..88.1165B. doi:10.2138/am-2003-0725. S2CID 100198554. (abstract; 39 kB PDF.)
  3. Weck, Philippe F.; Kim, Kim; Jové-Colón, Carlos F.; Sassani, David C. (2012). "Structures of uranyl peroxide hydrates: a first-principles study of studtite and metastudtite". Dalton Transactions. 41 (32): 9748–9752. doi:10.1039/c2dt31242e. PMID 22763414.
  4. Forbes, Tori Z.; McAlpin, J. Gregory; Murphy, Rachel; Burns, Peter C. (2008). "Metal-Oxygen Isopolyhedra Assembled into Fullerene Topologies". Angew. Chem. Int. Ed. 120 (47): 2824–2827. Bibcode:2008AngCh.120.2866F. doi:10.1002/ange.200705563.
  5. Sigmon, Ginger E.; Jie Ling; Unruh, Daniel K.; Moore-Shay, Laura; Ward, Matthew; Weaver, Brittany; Burns, Peter C. (2009). "Uranyl-Peroxide Interactions Favor Nanocluster Self-Assembly". J. Am. Chem. Soc. 131 (46): 16648–16649. doi:10.1021/ja907837u. PMID 19919139.
  6. Nilsson, Sara; Jonsson, Mats (2011). "H2O2 and radiation induced dissolution of UO2 and SIMFUEL pellets". Journal of Nuclear Materials. 1–3 (410): 89–93. Bibcode:2011JNuM..410...89N. doi:10.1016/j.jnucmat.2011.01.020.


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