Ammonium uranyl carbonate

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Ammonium uranyl carbonate
Names
IUPAC name
uranium(VI)dioxide tetra-ammonium tricarbonate
Other names
uranyl ammonium carbonate
AUC
Identifiers
Properties
UO2CO3·2(NH4)2CO3
Molar mass 522.199 g/mol
Appearance lemon-yellow crystalline[1]
Density 2.72[1]
Melting point Decomposes between 165 °C and 185 °C
Insoluble
Structure[1]
monoclinic
C2/c
a = 10·68, b = 9·38, c = 12·85
α = 90°, β = 96.45°°, γ = 90°
1279
4
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

Ammonium uranyl carbonate (UO2CO3·2(NH4)2CO3) is known in the uranium processing industry as AUC and is also called uranyl ammonium carbonate. This compound is important as a component in the conversion process of uranium hexafluoride (UF6) to uranium dioxide (UO2). The ammonium uranyl carbonate is combined with steam and hydrogen at 500–600 °C to yield UO2. In another process aqueous uranyl nitrate, known as uranyl nitrate liquor (UNL) is treated with ammonium bicarbonate to form ammonium uranyl carbonate as a solid precipitate. This is separated from the solution, dried with methanol and then calcinated with hydrogen directly to UO2 to obtain a sinterable grade powder. The ex-AUC uranium dioxide powder is free-flowing, relatively coarse (10 µ) and porous with specific surface area in the range of 5 m2/g and suitable for direct pelletisation, avoiding the granulation step. Conversion to UO2 is often performed as the first stage of nuclear fuel fabrication.

The AUC process is followed in South Korea and Argentina. In the AUC route, calcination, reduction and stabilization are simultaneously carried out in a vertical fluidized bed reactor. In most countries, sinterable grade UO2 powder for nuclear fuel is obtained by the ammonium diuranate (ADU) process, which requires several more steps.

Ammonium uranyl carbonate is also one of the many forms called yellowcake; in this case it is the product obtained by the heap leach process.

References[edit]

  1. ^ a b c Graziani, R.; Bombieri, G.; Forsellini, E. (1972). "Crystal structure of tetra-ammonium uranyl tricarbonate". Journal of the Chemical Society, Dalton Transactions (19): 2059. doi:10.1039/DT9720002059. 

Extra reading[edit]

  • Yi-Ming, Pan; Che-Bao, Ma; Nien-Nan, Hsu (September 1981). "The conversion of UO2 via ammonium uranyl carbonate: Study of precipitation, chemical variation and powder properties". Journal of Nuclear Materials. 99 (2-3): 135–147. Bibcode:1981JNuM...99..135Y. doi:10.1016/0022-3115(81)90182-3. 
  • Kan-Sen, Chou; Ding-Yi, Lin; Mu-Chang, Shieh (May 1989). "Precipitation studies of ammonium uranyl carbonate from UO2F2 solutions". Journal of Nuclear Materials. 165 (2): 171–178. Bibcode:1989JNuM..165..171K. doi:10.1016/0022-3115(89)90246-8. 
  • Mellah, A.; Chegrouche, S.; Barkat, M. (March 2007). "The precipitation of ammonium uranyl carbonate (AUC): Thermodynamic and kinetic investigations". Hydrometallurgy. 85 (2-4): 163–171. doi:10.1016/j.hydromet.2006.08.011.