Ammonium uranyl carbonate (UO
2CO
3·2(NH
4)
2CO
3) 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
Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...
(UF
6) to
uranium dioxide (UO
2). The ammonium uranyl carbonate is combined with
steam
Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...
and
hydrogen at 500–600 °C to yield UO
2. 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
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
and then calcinated with hydrogen directly to UO
2 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 m
2/g and suitable for direct pelletisation, avoiding the granulation step. Conversion to UO
2 is often performed as the first stage of
nuclear fuel
Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission.
Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing ...
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 UO
2 powder for nuclear fuel is obtained by the
ammonium diuranate Ammonium diuranate or (ADU) ((NH4)2U2O7), is one of the intermediate chemical forms of uranium produced during yellowcake production. The name "yellowcake" originally given to this bright yellow salt, now applies to mixtures of uranium oxides which ...
(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
Extra reading
*
*
*
{{Ammonium salts
Ammonium compounds
Uranyl compounds
Carbonates
Nuclear materials