Uranium refining

In Allied Chemical s uranium refinery the sequence of process operations is reversed, with conversion to UF preceding purification, and with UF as the sole purified product. The Allied Chemical process will be described briefly in Sec. 9.7. 

As received by the uranium refinery, uranium ore concentrates now usually consist of uranium oxide or sodium, magnesium, or ammonium diuranate. These concentrates still contain appreciable amounts of elements other than uranium and some of uranium s radioactive decay products present in the original uranium ore, such as radium and radon. 

The first step in the conventional process for refining manium is dissolution in nitric acid. When the concentrates have been produced by chemical leaching and are in the form of diuranates, dissolution proceeds rapidly and leaves little solid residue. When the concentrates have been separated mechanically and are in the form of the original uranium mineral, dissolution may require more concentrated acid, higher temperatures, longer times, and addition of oxidants such as MnO. Also, filtration to remove undissolved residues is usually required. In either case, dissolution produces an aqueous solution of uranyl nitrate hexahydrate U02(N03)2 6H2 0, containing excess nitric acid and variable amounts of nitrates of metallic impurities present in the concentrates. 

The next step in purification is separation of uranyl nitrate from the other metallic impurities in the dissolver solution by solvent extraction. Practically aU uranium refineries now use as solvent tributyl phosphate (TBP) dissolved in an inert hydrocarbon diluent. The first U.S. refinery used diethyl ether as solvent and later refineries have used methyl isobutyl ketone or organic amines, but practically all have now adopted TBP. It is nonvolatile, chemically stable, selective for uranium, and has a uranium distribution coefficient greater than unity when the aqueous phase contains nitric acid or inorganic nitrates. 

Althougji uranium refineries use widely different types of solvent extraction contactors, their basic process flow sheets are similar, along the lines of Fig. 5.22, hich illustrates the 

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Catalyst in alkylation and polymerization reactions Additives to liquid rocket fuels Uranium refining Cyclosarin (GF) 9.01... 

Uranium refining, 25 404—405 Uranium reserves, 17 521-522 Uranium resources, 17 522-525,... 

Protactinium-231 can he recovered from the residues of uranium refining hy various chemical processes. One such recovery process is highlighted helow (Maddock, A.G. 1968. Protactinium. In The Encyclopedia of Chemical Elements, ed. C.A. Hampel, pp 580-585. New York Reinhold Book Corp). 

Other reagents can he employed to recover protactinium from uranium refining residues or wastes. For example, treatment with 4M phosphoric or iodic acid precipitates protactinium as phosphate or iodate which is soluble in HF. 

Stelling JHE. 1980. Source category survey Uranium refining industry. Report. EPA-450/3-80-010. NITS PB80-192867. 

Figure 5.21 Steps in conventional uranium refining processes.

About 450 million metric tons (500 million tons) per year of mill tailings are generated vom copper, iron, taconite, lead, and zinc ore concentration processes and uranium refining, as well as other ores, such as barite, feldspar, gold, molybdenum, nickel, and silver... 

UREX, UREX+ (Uranium Refinement by extraction) No pure Pu stream (UREX) removal of Tc (UREX-L) TBP/dodecane Mitchell et al. (2009)... 

The later methods of uranium refining in the United States similarly involve TBP extraction. The National Lead Company s plant at Femald came into operation during 1954. This uses a 3N nitric acid feed solution prepared from chemical concentrates or high-grade pitchblende with a uranium concentration of 200 g/1. The solvent is 33-5 per cent TBP in a purified kerosene diluent. Phosphoric acid is added in quantities up to 15 per cent on a uranium basis, in order to complex any thorium impurity and prevent its extraction into the solvent. Three separate sieve-plate pulse columns are employed for extraction into solvent, stripping of... 

Metallurgical processes By-product coke ovens Foundries gray iron Foundries steel Secondary aluminum Secondary copper Secondary zinc Uranium refining... 

Uranium refining hydrofluorinator and fluorinator reactors 600 °C HF, F2-corrosion... 

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