Uranium oxide fluorides

The balance of hydrogen fluoride is used ia appHcations such as stainless steel pickling inorganic fluoride production, alkylation (qv), uranium enrichment, and fluorine production. Hydrogen fluoride is used to convert uranium oxide to UF which then reacts with elemental fluorine to produce volatile UF. ... 

Dioxygea difluoride has fouad some appHcatioa ia the coaversioa of uranium oxides to UF (66), ia fluoriaatioa of actinide fluorides and oxyfluorides to AcF (67), and in the recovery of actinides from nuclear wastes (68) (see Actinides and transactinides Nuclear reaction, waste managel nt). 

Figure 4.21 The equilibrium concentrations of HF in a mixture with H20 for the reduction of uranium oxide by hydrogen fluoride versus temperature.

Calcium metal is used in the reduction of zirconium fluorides, thorium and uranium oxides to obtain the metals. 

Tungsten(VI) fluoride (WF6) and molybdenum(VI) fluoride (MoF6) are available commercially, and can be made by reaction of the metals with fluorine.4 In the case of uranium(VI) fluoride (UF6), a preparation that is claimed5 to be feasible in the laboratory uses uranium metal and chlorine trifluoride uranium(VI) fluoride is prepared6 commercially by the fluorination of uranium(IV) fluoride, itself prepared from an oxide and hydrogen fluoride. 

Uranium(VI) fluoride can react35 as a Lewis acid or an oxidizing agent with alcohols. In the vapor phase at 80 °C (note that this is considerably lower than the temperatures used in the examples given vide supra) it behaves as a Lewis acid and gives35 mixtures of the corresponding fluorides, alkenes and ethers (Table 1). 

In solution (l,l,2-trichloro-l,2,2-trifluoroethane) the oxidizing power of uranium(VI) fluoride predominates with alcohols and they are converted13 into ketones and aldehydes, which then go on to acid fluorides. 

The amino acids alanine and threonine have been treated40 with uranium(VI) fluoride both form gels from which alanine can be recovered unchanged while threonine is converted into 1-aminoacetone via oxidation of the secondary alcohol (> CHOH) moiety to a carbonyl group (> C = 0). 

Calcium serves as a reductant for such reactive metals as zirconium, thorium, vanadium, and uranium. In zirconium reduction, zirconium fluoride is reacted with culcium metal. The high heat of the reaction melts the zirconium. The zirconium ingot resulting is remelted undet vacuum for purilicatinn. Thorium and uranium oxides are reduced with an excess of calcium in reactors or trays under an atmosphere of argon. The resulting tnetals are leached with acetic acid tu remove the lime. 

Thorium oxide fluoride (Th2OF5) (277) has been prepared from ThF4 and ThOF, and the reaction of uranium oxides with UF4 at 400-500°C is said to produce U205F as one of the products (278). 

Finally, some DOE sites also have stored hexavalent uranium fluoride (UFs). The approach to stabilize this compound is to calcine it to form stable uranium oxide. There is no study reported in the literature on treatment of fluorides using a CBPC matrix, but considering that fluroapatites are stable minerals, they should be applicable to stabilization of actinide compounds. 

Synonyms Common names Uranium 1 Uranium oxide Brown oxide Uranyl oxide Orange oxide Uranium octaoxide Yellow cake Block oxide Uranium fluoride ... 

Uranium can exist in five oxidation states +2, +3, +4, +5, and +6 (Lide 1994) however, only the +4 and +6 states are stable enough to be of practical importance. Tetravalent uranium is reasonably stable and forms hydroxides, hydrated fluorides, and phosphates of low solubility. Hexavalent uranium is the most stable state, and the most commonly occurring state is UjOg, although there are a few localized storage locations for anthropogenic uranium hexafluoride (UFg) (EPA 1991). Major compounds of uranium include oxides, fluorides, carbides, nitrates, chlorides, acetates, and others. One of the characteristics of 002" ions is their ability to fluoresce under ultraviolet light. 

Table 12.4 lists the signatures for processes using UF gas. In the conversion step, one could look for uranyl fluoride, but the isotopic ratio would not change from uranium ore (i.e., no fractionation). However, an analytical method that yielded oxidation states of atomic uranium and fluoride, such as ESCA (electron spectrometry for chemical analysis), could be used to identify the uranyl compound. 

Uranium(III) fluoride is insoluble in water and surprisingly resistant to aerial oxidation and hydrolysis. 

Two processes are employed for the production of uranium(VI) fluoride, namely the wet and dry processes. In both processes uranium(IV) oxide and uranium(lV) fluoride are formed as intermediates. In the wet process the uranium(IV) oxide is produced from the uranium concentrate by way of uranyl nitrate, whereas in the dry process the uranium concentrate is directly reduced to uranium(IV) oxide. The methods of purification used are also different in the wet process the purification proceeds at the uranyl nitrate stage, by solvent extraction, whereas in the dry process the end product uranium hexafluoride is itself distillatively purified. 

Uranium(IV) oxide is the starting material for uranium(lV) fluoride production in which uranium(lV) oxide is generally reacted with anhydrous hydrogen fluoride. This difficult to carry out exothermic reaction proceeds either in a fluidized bed, in moving bed reactors, or in screw-reactors. To achieve as complete as possible reaction in fluidized bed reactors, two fluidized bed reactors are connected in series. Screw-reaetors are also preferably connected in series. In moving bed reactors the reduction zone and the hydrofluorination are arranged above one another in a plant. The uranium(IV) oxide produced by the reduction of uranium(VI) oxide with hydrogen is very reactive and is eompletely reaeted with HF at temperatures between 500 and 650°C to uranium(lV) fluoride. 

In the dry process, introduced by Allied Chemical Corp., the uranium concentrate is pelletized and directly reduced with hydrogen to uranium(IV) oxide at temperatures between 540 and 650°C in a fluidized bed reactor. Hydrofluorination to uranium(IV) fluoride proceeds in two fluidized bed reactors connected in series. After fluorinating the uranium(IV) fluoride formed in a production unit consisting of a flame-reactor and a fluidized bed reactor, the uranium(Vl) fluoride produced is purified in a two stage pressure distillation process. This distillative purification process is necessary, because, in contrast with the wet process, no purification is carried out in earlier stages. 

There are three processes which are industrially convert enriched uranium(VI) fluoride into sinterable uranium(IV) oxide two wet processes and one dry process. 

The IDR (Integrated Dry Route) process consists of reacting gaseous uranium(VI) fluoride with superheated steam, whereupon solid UO2F2 is formed, which is reduced with hydrogen to uranium(IV) oxide. This reaction can be carried out in both a fluidized bed reactor and in a rotary kiln, whereby the latter appears more suitable. 

Uranium metal. Metallic uranium as a nuclear fuel is unimportant compared with uranium(IV) oxide. It is manufactured by reducing uranium(IV) fluoride with metallic magnesium or calcium, whereby the mixture as a result of the temperature increase (Mg), or with the help of ignition pellets, burns up producing liquid uranium metal ... 

The further processing of the uranyl nitrate solution, which in some plants is postpurified with silica gel, is directed towards further enrichment of the uranium. If this is not worthwhile due to a too low - U-content, the product is converted into uranium(Vl) oxide, a storable compound. This can serve as a starting material for possible later utilization in fast breeder reactors. The uranium(VI) oxide is either produced indirectly by way of ammonium diuranate or by direct calcination. If further enrichment is foreseen, uranium(Vl) fluoride or uranium(lV) fiuoride is produced, the latter being fluorinated in the enrichment plant to uranium(VI) fluoride. 

Uranium(Vl) oxide has been converted almost quantitatively into uranium(VI) fluoride, in a COj flow system, at 1023 K [1498] ... 

The Zr-ECR method has been applied for determination of fluoride in water [38], air [84], rocks and minerals [85-87], iron ore and apatite [15], and various reagents [39]. Various above-mentioned coloured systems Zr-organic reagent were used for determining fluoride in bones [49], waters [16], silicate rocks [47], phosphates [44], and uranium oxides [50]. 

The plutonium purification may be achieved by additional TBP extraction cycles. U(IV) cannot be used as reductant in this part of the process. The final uranium and plutonium products are nitrate solutions whose conversion to oxides, fluorides, etc., have been described earlier ( 5.5.3). 

The conventional approach starts with uranium oxide (UO2) and includes two technological stages. The first one is exothermic conversion of the oxide into fluoride with HF ... 

Radioactivity is spontaneous. This means that it does not require any help to start or to continue. The rate of disintegration does not depend upon temperature. This is in contrast to chemical reactions, whose rates are often drastically affected by changes in temperature. The radioactive decay of the nucleus of an atom is unaffected by the presence of other atoms and cannot be catalysed. For example, uranium-235 decays at the same speed (and into the same products) whether it is pure uranium, combined as uranium oxide (UO2) or as uranium fluoride (UFg). 

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