Uranyl nitrate complex with tributyl phosphate

In TBP extraction, the yeUowcake is dissolved ia nitric acid and extracted with tributyl phosphate ia a kerosene or hexane diluent. The uranyl ion forms the mixed complex U02(N02)2(TBP)2 which is extracted iato the diluent. The purified uranium is then back-extracted iato nitric acid or water, and concentrated. The uranyl nitrate solution is evaporated to uranyl nitrate hexahydrate [13520-83-7], U02(N02)2 6H20. The uranyl nitrate hexahydrate is dehydrated and denitrated duting a pyrolysis step to form uranium trioxide [1344-58-7], UO, as shown ia equation 10. The pyrolysis is most often carried out ia either a batch reactor (Fig. 2) or a fluidized-bed denitrator (Fig. 3). The UO is reduced with hydrogen to uranium dioxide [1344-57-6], UO2 (eq. 11), and converted to uranium tetrafluoride [10049-14-6], UF, with HF at elevated temperatures (eq. 12). The UF can be either reduced to uranium metal or fluotinated to uranium hexafluoride [7783-81-5], UF, for isotope enrichment. The chemistry and operating conditions of the TBP refining process, and conversion to UO, UO2, and ultimately UF have been discussed ia detail (40). 

Purification of the precipitated concentrates is often carried out by dissolution in nitric acid followed by extraction with tributyl phosphate (TBP) dissolved in kerosene or n-hexane. The extraction is based on the formation of a complex between the uranyl nitrate and TBP according to the equation ... 

Spectrophotometric methods may often be applied directly to the solvent extract utilising the absorption of the extracted species in the ultraviolet or visible region. A typical example is the extraction and determination of nickel as dimethylglyoximate in chloroform by measuring the absorption of the complex at 366 nm. Direct measurement of absorbance may also be made with appropriate ion association complexes, e.g. the ferroin anionic detergent system, but improved results can sometimes be obtained by developing a chelate complex after extraction. An example is the extraction of uranyl nitrate from nitric acid into tributyl phosphate and the subsequent addition of dibenzoylmethane to the solvent to form a soluble coloured chelate. 

Uranium is deposited widely in the Earth s crust, hence it has few ores, notably the oxides uraninite and pitchblende. The ores are leached with H2SO4 in the presence of an oxidizing agent such as NaClOs or Mn02, to oxidize all the uranium to the (+6) state as a sulfate or chloride complex. On neutralization with ammonia a precipitate of yellow cake , a yellow solid with the approximate composition (NH4)2U207 is formed. This is converted into UO3 on ignition at 300 °C. This can be purified further by conversion into uranyl nitrate, followed by solvent extraction using tributyl phosphate in kerosene as the extractant. 

Trllsoamyl phosphate [919-62-0] M 308.4, b 143 /3mm. Purify the ester by repeated crystallisation, from hexane, of its addition compound with uranyl nitrate. Decompose the complex, and distil the ester at high vacuum. [Siddall J Am Chem Soc 81 4176 7959.] [see tributyl phosphate and Cherbuhez in Organo Phosphorus Compounds (Kosolapoff Maier eds) Wiley Vol 6 pp 211-577 1973.]... 

The principle of the Purex process, now commonly used for processing irradiated uranium by solvent extraction, is illustrated in Fig. 1.18. The solvent used in this process is a solution of tributyl phosphate (TBP) in a high-boiling hydrocarbon, frequently n-dodecane or a mixture of similar hydrocarbons. TBP forms complexes with uranyl nitrate [U0i(N03)2] and tetravalent plutonium nitrate [Pu(N03)4] whose concentration in the hydrocarbon phase is higher than in an aqueous solution of nitric acid in equilibrium with the hydrocarbon phase. On the other hand, TBP complexes of most fission products and trivalent plutonium nitrate have lower concentrations in the hydrocarbon phase than in the aqueous phase in equilibrium. 

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