Uranyl chloride

Uranyl chloride, UO₂Cl₂ is an unstable, bright yellow coloured chemical compound of uranium. It forms large sand-like crystals which are highly soluble in water, alcohols and ethers. Uranyl chloride, and its two hydrates (UO₂Cl₂·H₂0 and UO₂Cl₂·3H₂0) decomposes in the presence of light, a fact discovered by Adolph Gehlen in 1804, This photosensitivity periodically attracted scientific curiosity and various unsuccessful attempts to develop photographic applications using the salts. As with most other uranic species this compound also exhibits fluorescence.

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Uranyl chloride is formed when chlorine gas is passed over uranium dioxide at a red heat. However it is more usually obtained by dissolving uranium oxide in hydrochloric acid and evaporating.

Industrial importance

The company Indian Rare Earths Limited (IREL) has developed a process to extract uranium from the Western and Eastern coastal dune sands of India. After pre-processing with high intensity magnetic separators and fine grinding, the mineral sands (known as monazite), are digested with caustic soda at about 120C and water. The hydroxide concentrate is further digested with concentrated hydrochloric acid to solubilise all hydroxides to form a feed solution composed of chlorides of uranium and other rare earth elements including thorium. The solution is subjected to solvent extraction with dual solvent systems to produce uranyl chloride and thorium oxalate. The crude uranyl chloride solution is subsequently refined to nuclear grade ammonium diuranate by a purification process involving precipitation and solvent extraction in a nitrate media.

Health and environmental

Uranyl chloride is spectacularly toxic by inhalation and if swallowed. There is also a danger of cumulative effects. The target organs are the liver and kidneys. It is toxic to aquatic organisms, and may cause long-term adverse effects in the aquatic environment. As with all compounds of uranium it is radioactive to a degree dependent on its isotopic ratios.

References

• Uranium, Volume V27, Page 788 of the 1911 Encyclopedia Britannica
• Lanthanides & Actinides, Four Lectures in 2^nd Year Inorganic Chemistry, S.J. Heyes, Oxford, 1997-8