Uranium dioxide fluorination

One of the most important examples of the fluorination of oxides is the fluorination of uranium dioxide. Uranium tetrafluoride (UF4) is the intermediate compound which is reduced to uranium metal. The gaseous higher fluoride, uranium hexafluoride (UF6) is used for the separation of uranium isotopes to obtain enriched uranium (i.e., uranium containing a higher proportion of the isotope, U235, than natural uranium). 

Another preparative method involves converting triuranium octaoxide to uranyl nitrate, U02(N0s)2, by treatment with nitric acid. Uranyl nitrate then is decomposed to uranium trioxide, UO3, which is reduced to the dioxide, UO2, with hydrogen. A fluidized bed of uranium dioxide is treated with hydrogen fluoride to produce uranium tetrafluoride, UF4, which then is treated with fluorine to form hexafluoride. The preparation should be done in copper apparatus. 

In TBP extraction, the yellowcake is dissolved in nitric acid and extracted with tributyl phosphate in a kerosene or hexane diluent. The uranyl ion forms the mixed complex U02(N03)2(TBP)2 which is extracted into the diluent. The purified uranium is then back-extracted into nitric acid or water, and concentrated. The uranyl nitrate solution is evaporated to uranyl nitrate hexahydrate [13520-83-7], U02(N03)2 6H20. The uranyl nitrate hexahydrate is dehydrated and denitrated during a pyrolysis step to form uranium trioxide [1344-58-7], U03, as shown in equation 10. The pyrolysis is most often carried out in either a batch reactor (Fig. 2) or a fluidized-bed denitrator (Fig. 3). The U03 is reduced with hydrogen to uranium dioxide [1344-57-6], U02 (eq. 11), and converted to uranium tetrafluoride [10049-14-6], UF4, with HF at elevated temperatures (eq. 12). The UF4 can be either reduced to uranium metal or fluorinated to uranium hexafluoride [7783-81-5], UF6, for isotope enrichment. The chemistry and operating conditions of the TBP refining process, and conversion to U03, U02, and ultimately UF4 have been discussed in detail (40). 

Burner designed to introduce reactants into the combustion zone. Be careful to ensure that the system is not operating within the estplosive limits. Examples include the fluorination of UF4 to UF4 at 350-600 °C with solids feed at rate of 1 Mg/d uranyl nitrate dehydrated and denitrified to uranium dioxide at rate of 1 Mg/d. Air oxidation of phosphorous to P2O5 at 2500 °C at 1.5 Mg/h. This reactor is 1.8 m diameter, 10 m high with gas flow of 1 m/s and molten flow of 0.4 kg/s. 

If the uranium is to be used as a metal or as feed material for isotope enrichment plants, the uranium dioxide is treated with anhydrous hydrogen fluoride (AHF) to form UF4 (Figure 1.11). The UF4 can then be reduced metallothermically with magnesium or calcium to produce metallic uranium (still of natural isotope composition), which can also be used to fuel some types of reactors. However, if enrichment of the U isotope is planned, the UF4 is fluorinated to produce UFg, which is the feed material for most commercial enrichment plants. The uranium hexafluoride is then transferred into 10-14 ton cylinders where it solidifies. These cylinders with the solid UFg are stored until ready to be shipped to the enrichment plant. 

Total chlorine and fluorine by pyrohydrolysis ion-selective electrode method C1502 standard test method for the determination of total chlorine and fluorine in uranium dioxide and gadoUnium oxide... 

Conditions must be carefully controlled to prevent sintering of the oxide particles during reaction in order to keep a high specific surface area of the oxide needed in the fluorination reaction. Nevertheless, in certain cases, if the uranium dioxide is to be used directly as nuclear fuel in heavy-water nuclear reactors (i.e., CANDU), sintering can be allowed to produce a denser ceramic fuel. 

Conversion of uranium dioxide to tetrafluoride in contact with hydrofluoric acid Production of caustic alkalis, particularly in the presence of sulfur compounds Reactor vessels and heat-exchanger tubing used in the production of vinyl chloride Process equipment used in the production of chlorinated and fluorinated hydrocarbons... 

CBr4 Noncombustible solid. Violent reaction with fluorine, hexylcyclo-hexyldilead, oxygen, potassium, potassium acetylene-1,2-dioxide, sodium azide, uranium(III) hydride. Mixtures with finely divided aluminum, lithium, magnesium, potassium-sodium alloy, titanium, zinc can form a friction- or shock-sensitive explosive material. Incompatible with decaborane. Attacks active metals. 

TOLUOL (108-88-3) C7H, CsHjCHj Forms explosive mixture with air [explosion limits in air (vol %) 1.4 to 6.7 flash point 39°F/4°C cc autoignition temp 896°F/480°C Fire Rating 3]. Violent reaction with strong oxidizers, bromine, bromine trifluoride, chlorine, hydrochloric acid-sulfuric acid mixture, l,3-dichloro-5,5-dimethyl-2,4-imidazolididione, dinitrogen tetraoxide, fluorine, nitric acid (cone.), nitrogen dioxide, silver chloride, sulfur dichloride, uranium fluoride, vinyl acetate. Forms explosive mixture with strong acids, strong oxidizers, silver perchlorate. 

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