Uranyl nitrate concentration

TBP and nitric acid also tend to form a complex with each other, but at sufftcientiy high uranyl nitrate concentrations the nitric acid is mainly displaced into the aqueous phase. 

The square of the uranyl nitrate concentration is required in the kinetic analysis. Mass transfer with chemical reaction (16, 83) is, however, too specialized a subject to be discussed fully here. 

The purification of uranium by fractional crystallization involves repeated recrystallizations of U02(N03)2 from water or nitric acid, three usually being sufficient. The composition of the crystalline product may range from U02(N03)v2H20 to U02(N03)2 6H20 depending upon the temperature, acidity and uranyl nitrate concentration of the solution.198... 

Table II. Effect of Uranyl Nitrate Concentration in UV Grafting of Methyl Methacrylate (30% v/v) in Methanol to Cellulose0...

Distribution coefficients of neptunium in 30 v/o TBP depend on neptunium valence, temperature, and concentrations of uranyl nitrate, nitric acid, and other nitrates. At the nitric acid concentraticHis below 4 M usually used in Purex processes, the distribution coefficient of hexavalent neptunium is hi er than that of tetravalent neptunium at the same nitric acid and uranyl nitrate concentrations. Both are much higher than that of pentavalent neptunium. Both tetravalent and hexavalent neptunium are extracted as the complexes with two molecules of TBP, Np (N03)4 2TBP and Np 02(N03)2-2TBP. 

Tetravalent neptunium. Srinivasan et al. [S18, S19] measured distribution coefficients of tetravalent and hexavalent neptunium and hexavalent uranium as functions of nitric acid and uranyl nitrate concentrations. At 45 and 60°C, the ratio of the observed [S19] separation factor for tetravalent neptunium to that of hexavalent uranium can be correlated within an average deviation of 6 percent by Eq. (10.25),... 

Fig. 9. Electrophoretic velocity of Si02 particles suspended in a 0.1% Na arabinate sol as a function of the uranyl nitrate concentration, measured at and at /.> ceil height.

Pu(IV) as a function of nitric acid concentration and uranyl nitrate concentration (Figs. 

The particle size also tends to grow with increasing residence time in the bed, and this is particularly the case with uranyl nitrate concentrations above 70 per cent. This can be counteracted by recycling a proportion of the product continuously, after grinding. The finely ground particles act as nuclei for the deposition of further oxide and a satisfactory average particle size can be achieved. In practice, it is more convenient to employ a uranly nitrate concentration of about 70 per cent. 

Hydration. In partition studies of uranyl nitrate between aqueous solution and organic solvent (alcohols, esters, ethers euid ketones) It Is generally found that the water content of the organic phase Increases with uranyl nitrate concentration.por alcohols, the relation between the water content and uranyl nitrate concentration appears to be a complex function. Por esters, ethers, and ketones the relation Is linear except possibly at hl values of This relation may be expressed... 

For cyclohexane, considerably larger values were found for low uranyl nitrate concentrations. 

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). 

In practice, uranium ore concentrates are first purified by solvent extraction with tributyl phosphate in kerosene to give uranyl nitrate hexahydrate. The purified uranyl nitrate is then decomposed thermally to UO (eq. 10), which is reduced with H2 to UO2 (eq. 11), which in turn is converted to UF by high temperature hydrofluorination (eq. 12). The UF is then converted to uranium metal with Mg (eq. 19). 

We solved the first problem by bombarding large amounts of uranyl nitrate with neutrons at the cyclotrons at the University of California and Washington University plutonium concentrates were derived from these sources through the efforts of teams of chemists who used ether extractions to separate the bulk of the uranium and an oxidation-reduction cycle with rare earth fluoride carrier to concentrate the product. I managed to convince chemists trained in the techniques of ultramicrochemistry to join us to solve the second problem—Burris B. Cunningham and Louis B. Werner of the University of California and Michael Cefola from New York University. 

The last paragraph in this extract refers to work on the separation of uranium by ether extraction as a step toward obtaining a plutonium concentrate from a large sample of neutron-irradiated uranyl nitrate. 

Uranyl Nitrate Influence on Polymer Growth. The effect of a solute such as uranyl nitrate on this polymer formation is so complex that the net effect on the polymer growth rate cannot be predicted. Experimentally, it is observed that the rates of growth at given initial HNO3 concentration are always slower in the presence of as indicated by the solid curve in... 

Concentration dependence, polymerization of hydrolysis products with uranyl nitrate.231, 237-39... 

Crystallisation was one of the earliest methods used for separation of radioactive microcomponents from a mass of inert material. Uranium X, a thorium isotope, is readily concentrated in good yield in the mother liquors of crystallisation of uranyl nitrate (11), (33), (108). A similar method has been used to separate sulphur-35 [produced by the (n, p) reaction on chlorine-35] from pile irradiated sodium ot potassium chloride (54), (133). Advantage is taken of the low solubility of the target materials in concentrated ice-cold hydrochloric acid, when the sulphur-35 as sulphate remains in the mother-liquors. Subsequent purification of the sulphur-35 from small amounts of phosphorus-32 produced by the (n, a) reaction on the chlorine is, of course, required. Other examples are the precipitation of barium chloride containing barium-1 from concentrated hydrochloric acid solution, leaving the daughter product, carrier-free caesium-131, in solution (21) and a similar separation of calcium-45 from added barium carrier has been used (60). 

Uranium dioxide occurs in mineral uraninite. Purified oxide may be obtained from uraninite after purification. The commercial material, however, also is recovered from other uranium sources. Uranium dioxide is obtained as an intermediate during production of uranium metal (See Uranium). Uranyl nitrate, U02(N03)2, obtained from digesting the mineral uraninite or pitchblende with concentrated nitric acid and separated by solvent extraction, is reduced with hydrogen at high temperatures to yield the dioxide. 

Figure 16 The extraction of uranyl nitrate (5gdm 3) from nitric acid by HDEHP in kerosene at 2(1 C.112 Curves are labelled with HDEHP concentration (M)...

The purification of uranium by precipitation may involve the formation of insoluble oxalate or peroxide complexes.50 In the oxalate method the ore concentrate is dissolved in nitric acid to give a uranyl nitrate solution from which uranyl oxalate is precipitated according to equation (101), leaving the bulk of the impurities in solution. This approach is favoured over dissolution in hydrochloric acid and reduction to UIV prior to U(C204)2 precipitation since it is simpler and... 

In the solvent extraction purification of the uranium ore concentrate, TBP is the extractant of choice although, in the past, Butex, diethyl ether and MIBK have also been used for this purpose. The uranium ore concentrate is first dissolved in nitric acid to produce a solution of uranyl nitrate from which insoluble impurities are separated. The consumption of nitric acid in this step will depend upon the nature of the concentrate, as shown in equations (104)-( 109). Many impurities... 

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