Nitrate, uranyl

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. 

Uranium. The uranium product from the PUREX process is in the form of uranyl nitrate which must be converted to some other chemical depending on anticipated use. One route to MO fuel is to mix uranium and plutonium nitrates and perform a coprecipitation step. The precipitate is... 

Homogeneous Aqueous Reactors. As a part of the research on neutron multiphcation at Los Alamos in the 1940s, a small low power reactor was built using a solution of uranium salt. Uranyl nitrate [36478-76-9] U02(N0 2> dissolved in ordinary water, resulted in a homogeneous reactor, having uniformly distributed fuel. This water boiler reactor was spherical. The 235u... 

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). 

These can be converted to their uranyl nitrate addition compounds. The crude or partially purified ester is saturated with uranyl nitrate solution and the adduct filtered off. It is recrystallised from -hexane, toluene or ethanol. For the more soluble members crystallisation from hexane using low temperatures (-40°) has been successful. The adduct is decomposed by shaking with sodium carbonate solution and water, the solvent is steam distilled (if hexane or toluene is used) and the ester is collected by filtration. Alternatively, after decomposition, the organic layer is separated, dried with CaCl or BaO, filtered, and fractionally distilled under high vacuum. 

Di-n-amyl n-amylphosphonate [6418-56-0] M 292.4, b 150-151°/2mm, n 1.4378. Purified by three crystns of its uranyl nitrate complex from hexane (see tributyl phosphate). Extracts Zr " from NaCl solns. 

Di-n-butyl n-butylphosphonate [78-46-6] M 250.3, b 150-151°/10mm, 160-162°/20mm, n 1.4302. Purified by three recrystallisations of its compound with uranyl nitrate, from hexane. For method, see tributyl phosphate. 

Triisoamyl phosphate [919-62-0] M 308.4, b 143"/3mm. Purified by repeated crystallisation, from hexane, of its addition compound with uranyl nitrate, (see tributyl phosphate.) [Siddall J Am Chem Soc 81 4176 7959]. 

URANIUM HEXAFLUORIDE URANYL ACETATE URANYL NITRATE URANYL NITRATE HEXAHYDRATE... 

Figure 31.7 (a) The octahedral anion in Cs2[U02CU]. (b) Pentagonal bipyramidal coordination of U in dinuclear [U02(02CMe)2L]2 (L = OPPhs, OAsPhs). (c) Hexagonal bipyramidal coordination of U in uranyl nitrate, U02(N03)2-6H20. 

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. 

Uranyl Nitrate (Uranium Nitrate, UNH, Yellow Salt). U02(N03)2.6H20, mw 502.18, N 5.58% yellow rhomb crysts, greenish luster by reflected light mp 60.2°, bp 118°, d 2.807g/cc, RI 1.4967. Sol in 1.5p w, freely in ale and eth. Prepd by the action of nitric acid on U octoxide. When shaken, rubbed, or crushed, the crysts show remarkable triboluminescence with occasional detonations. It is highly toxic, and a severe fire and expln risk when shocked or heated,... 

There have been many instances of examination of the effect of additive product on the initiation of nucleation and growth processes. In early work on the dehydration of crystalline hydrates, reaction was initiated on all surfaces by rubbing with the anhydrous material [400]. An interesting application of the opposite effect was used by Franklin and Flanagan [62] to inhibit reaction at selected crystal faces of uranyl nitrate hexa-hydrate by coating with an impermeable material. In other reactions, the product does not so readily interact with reactant surfaces, e.g. nickel metal (having oxidized boundaries) does not detectably catalyze the decomposition of nickel formate [222],... 

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... 

Chemical analyses reveal that measurable amounts of uranyl ion are actually present in Pu(IV) polymers grown in mixtures of Pu(IV) and uranyl nitrate suggesting that uranyl ion is being taken up in the polymer network and consequently hampers the growth through a chain termination process as suggested in Fig. 3. The uranyl serves to terminate active sites because it does not typically form extensive polymeric aggregates as does Pu(IV) instead it tends only to dimerize and, at most, tri-merize (4). 

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

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