Uranium IV fluoride

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. 

UF3 is the most difficult of the trihalides to obtain in the pure state. It can be obtained by the reduction of uranium(IV) fluoride by aluminum (137), hydrogen (138-141), or uranium metal (139, 141-144). Reduction by aluminum can be carried out at 1173 K, when the aluminum fluoride can be sublimed off as the monofluoride. But the product is not very pure. 

Table 22 Uranium(IV) fluoride complexes produced by hydrothermal syntheses.

A wet process is also utilized for the production of uranium(IV) fluoride, namely the EXCER process (Ion Exchange Conversion Electrolytic Reduction). In this process the ion exchange- or extraction-purified uranium(VI) solution is either electrolytically or chemically reduced to uranium(IV), which is precipitated with hydrofluoric acid as uranium(IV) fluoride hydrate (UF4 O.75H2O). This is subsequently dehydrated at 400 to 450°C. 

The conversion of uranium(IV) fluoride to uranium(VI) fluoride proceeds exclusively with elemental fluorine. 

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. 

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 starting material for the manufacture of enriched uranium metal, uranium(IV) fluoride, is produced by reducing enriched uranium(VI) fluoride with hydrogen or chlorohydrocarbons. 

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