Ammonium uranyl carbonate (UO₂CO₃·2(NH₄)₂CO₃) is known in the

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

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 the inorganic compound with the formula . Uranium hexafluoride is a volatile, white solid that is used in enriching uranium for nuclear reactors and nuclear weapons. Preparation Uranium dioxide is co ...

(UF₆) to

uranium dioxide Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reac ...

(UO₂). The ammonium uranyl carbonate is combined with

steam Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...

and

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

at 500–600 °C to yield UO₂. In another process aqueous

uranyl nitrate Uranyl nitrate is a water-soluble yellow uranium salt with the formula . The hexa-, tri-, and dihydrates are known. The compound is mainly of interest because it is an intermediate in the preparation of nuclear fuels. In the nuclear industry, it ...

, known as uranyl nitrate liquor (UNL) is treated with

ammonium bicarbonate Ammonium bicarbonate is an inorganic compound with formula (NH4)HCO3. The compound has many names, reflecting its long history. Chemically speaking, it is the bicarbonate salt of the ammonium ion. It is a colourless solid that degrades readily to ...

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 compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

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 Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other atomic nucleus, nuclear devices to generate energy. Oxide fuel For fission reactors, the fuel (typically based on uranium) is ...

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 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 Yellowcake (also called urania) is a type of powdered uranium concentrate obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before ...

; in this case it is the product obtained by the heap leach process.

References

Further reading