A variety of processing technologies are available for recovering metals or metal compounds from raw or unrefined materials. These treatments typically involve several successive reactions that are best performed under different chemical conditions. Two or more separate reactors are often used, or a single reactor running the reactions sequentially. The individual reactions are batch operations, and the entire process would be improved if all of the reactions were run continuously in the same reactor.
A common example of a metal recovery operation is the reduction of uranium oxide for the production of uranium metal. Metallic uranium is used in uranium enrichment facilities and in the reprocessing of light water reactor fuel. The recycling of spent nuclear fuel minimizes the amount of high level nuclear waste that must be stored. The present invention is applicable in nuclear fuel technology for reprocessing high level radioactive waste and supplying feed material for uranium enrichment facilities.
The reduction of uranium oxide to uranium metal is performed by several methods: oxide and chloride electrolysis, chloride metallothermic reduction, saltless direct oxide reduction, and uranium fluorination with bomb reduction. Currently, the conventional method for producing uranium metal is by the reduction of uranium fluoride, which is obtained from hydrofluorination of uranium oxide. Uranium fluoride is reacted with a reducing metal, such as calcium, in a sealed bomb to produce the free metal and a halide by-product.
This bomb reduction method for producing uranium metal generates large amounts of uranium-containing waste salts that are hazardous and that present waste handling problems. The hydrogen fluoride used in the fluorination of uranium oxide is an extremely corrosive gas that presents environmental and occupational hazards. The direct reduction of metal oxides with calcium in solvent chloride salts also creates large volumes of salt residues that are difficult to process due to the corrosive nature of chloride solutions.
The development of a continuous uranium oxide reduction system that avoids the use of hydrogen fluoride will increase the safety for operating personnel, will decrease the amount of hazardous waste produced, and will be more economical than the current technologies. The present invention reduces metal-containing compounds in a molten salt carrier and produces metals with minimum formation of hazardous waste material. The invention achieves in situ regeneration of the liquid salt phase and full recycling of the liquid carrier within a single dual zone reactor to allow continuous processing of metal-containing compounds.