Uranium tetrachloride is an inorganic compound, a salt of uranium and chlorine, with the formula UCl4. It is a hygroscopic olive-green solid. It was used in the electromagnetic isotope separation (EMIS) process of uranium enrichment. It is one of the main starting materials for organouranium chemistry.
Synthesis and structure
Uranium tetrachloride is synthesised generally by the reaction of uranium trioxide (UO3) and hexachloropropene. Solvent UCl4 adducts can be formed by a simpler reaction of UI4 with hydrogen chloride in organic solvents. Uranium tetrachloride also forms the nonahydrate, which can be produced by evaporating a mildly acidic solution of UCl4. According to X-ray crystallography the uranium centers are eight-coordinate, being surrounded by eight chlorine atoms, four at 264 pm and the other four at 287pm.
Applications Uranium tetrachloride is produced commercially by the reaction of carbon tetrachloride with pure uranium dioxide UO2 at 370 °C. It has been used as feed in the electromagnetic isotope separation (EMIS) process of uranium enrichment. Beginning in 1944, the Oak Ridge Y-12 Plant converted UO3 to UCl4 feed for the Ernest O. Lawrence's calutrons. Its major benefit was that the uranium tetrachloride used in the calutrons is not as corrosive as the uranium hexafluoride used in most other enrichment technologies. This process was abandoned in the 1950s. In the 1980s Iraq revived this option as part of its nuclear weapons program. In the enrichment process, uranium tetrachloride is ionized into a uranium plasma. The uranium ions are then accelerated and passed through a strong magnetic field. After traveling along half of a circle, the beam is split into a region nearer the outside wall, which is depleted, and a region nearer the inside wall, which is enriched in 235U. The large amounts of energy required in maintaining the strong magnetic fields as well as the low recovery rates of the uranium feed material and slower more inconvenient facility operation make this an unlikely choice for large scale enrichment plants. Work is being done in the use of molten uranium chloride–alkali chloride mixtures as reactor fuels in molten salt reactors. Uranium tetrachloride melts dissolved in a lithium chloride–potassium chloride eutectic have also been explored as a means to recover actinides from irradiated nuclear fuels through pyrochemical nuclear reprocessing.
Safety Like all water soluble uranium salts, uranium tetrachloride is nephrotoxic (poisonous to the kidney) and can cause severe renal damage and acute renal failure if ingested.
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