Uranyl chloride

Synthesis and structures

The hydrates are obtained by dissolving uranyl sulfate or uranyl acetate in hydrochloric acid followed by crystallization from concentrated solutions. Depending on the method of drying, one obtains the mono- or the trihydrate. The monohydrate is described as a yellow, sulfur-like powder. It is very hygroscopic. The trihydrate is greenish-yellow. Both hydrates are fluorescent solids that are highly soluble in water.

The anhydrous material can be obtained by the reaction of oxygen with uranium tetrachloride: :

In terms of structures, all three of these compounds feature the uranyl center (trans-) bound to five additional ligands, which can include (bridging) chloride, water, or another uranyl oxygen.

Reactions

The aquo ligands can be replaced by a variety of donors, e.g. THF. Uranyl chloride, and its two hydrates, ( and ) decompose in the presence of light. This photosensitivity over the years, from time to time, has attracted scientific interest and there have been various unsuccessful attempts to develop applications in photography using these compounds.

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 120 C 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, rare earth elements and thorium. The solution is subjected to liquid–liquid 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.

Safety

Uranyl chloride is highly toxic by ingestion and inhalation. Cumulative toxic effects are also probable, with the target organs being the liver and the kidneys. It is toxic to aquatic organisms, and may cause long-term catastrophic effects in the aquatic environment. As all uranium compounds, this salt is radioactive.

References

References

1. https://www.2spi.com/item/z02411/#:~:text=Uranyl%20chloride%20(UO2Cl,yellow%20colored%20compound%20of%20uranium.
2. (1968). "The structures of uranyl chloride and its hydrates". Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry.
3. (1963). "Inorganic Syntheses".
4. F. Hein, S. Herzog. (1963). "Handbook of Preparative Inorganic Chemistry, 2nd Ed.". Academic Press.
5. (1973). "The Structure of Anhydrous Uranyl Chloride by Powder Neutron Diffraction". Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry.
6. (1957). "Inorganic Syntheses".
7. (1999). "Synthesis and Crystal Structure of UO₂Cl₂(THF)₃: A Simple Preparation of an Anhydrous Uranyl Reagent". Inorganic Chemistry.