Ammonium uranyl carbonate
Chemical compound
From Wikipedia, the free encyclopedia
Ammonium uranyl carbonate (UO2CO3·2(NH4)2CO3) is known in the uranium processing industry as AUC[2] 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).[3] 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.[4] 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.[5]
| Names | |
|---|---|
| IUPAC name
uranium(VI)dioxide tetra-ammonium tricarbonate | |
| Other names
uranyl ammonium carbonate AUC | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.038.156 |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| 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° | |
Lattice volume (V) |
1279 |
Formula units (Z) |
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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The AUC process is followed in South Korea[6] and Argentina.[7] 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.[citation needed]
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.[citation needed]