Reactors fluoride reduction

Figure 4.24 Reactor for uranium fluoride reduction with calcium.

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. 

The sequence of events described above occurs at any given spot in a CVD flow reactor. As an example, one can consider the deposition of tungsten on the interior wall of a graphite tube by the hydrogen reduction of the fluoride as follows ... 

Beryllium fluoride is the intermediate compound in the magnesium-reduction process to produce beryllium metal. The compound also is used in the manufacture of glass, and in nuclear reactors. 

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. 

The dioxide difluorides of U, Np, Pu, and Am have all been isolated. Uranyl fluoride, being an important intermediate in the conversion of enriched UF6 to UO2 for the production of fuel rods for Advanced Gas-Cooled Nuclear Reactors, is undoubtedly the most studied. The majority of papers on UO2F2, therefore, are concerned with its formation from the reaction of UF6 with steam or its conversion to UO2 by reduction with hydrogen. 

Uranium tetrafluoride is a key intermediate in the production of thermal reactor fuels. It may be prepared directly from uranyl solutions by reduction of the U to U and addition of HF to precipitate UF4. A number of processes have been developed to produce UF4 by this wet route, which may be used to produce UF4 at the ore processing site. These employ iron, S02/Cu or electrolysis for the reduction step, the latter being preferred since it introduces no contaminants into the solution. The reduction of u in various media has been studied to assess the effect of complexation on the reduction reaction. The standard potential for the reduction of U02 to in 1 M HCIO4 has been given as +0.32 V. " The overall formation constants of fluoride complexes in 1 M NaCl were found to be log 82= 13.12, logj83 = 17.46 and log/84 = 21.8. Although wet processes have been developed as a short cut to UF4, the most widely used process at present involves dry processing. 

The formaldehyde, or other redox by-products from the reduction of Cr/silica by ethylene, probably stay in the reactor and act as mild poisons. Addition of a strong adsorbent or Lewis-acidic carrier, such as zeolites or alumina treated with fluoride or sulfate, to the reactor together with the catalyst significantly increases the activity of the Cr/silica catalyst. Presumably, the Lewis-acidic carrier adsorbs and removes the redox by-products from the reaction mixture (Section 17.6). 

Sodium reduction of fluorides has also been used to produce metal powders. The reductions can be performed in simple mild steel or stainkss-steel unlined reactors, without introducing large quantities of iron into the... 

Other salt compounds are added in the reactor for lowering the temperature between 4(X) °C and 900 °C below the fusion point of pure K2TaF7 [13], Another reduction mode involves the electrochemical reduction of K2Tap7 in molten fluoride salts [5]. It is well stated now that the electroreduction of Ta in fluorides proceeds in a five-electron single step directly leading to Ta metal [14], and thus current efficiency of the preparation of Ta by the electrochemical route is close to 100 %. 

N2F4 was first prepared by thermal reaction of NF3 with various fluoride acceptors such as Cu, As, Sb, Bi, or stainless steel [1, 2]. Thus, N2F4 was produced in 62 to 71% yield based on NF3 consumed (42 to 62% conversion) in a Cu-packed flow reactor at 375°C with a residence time of 13 min [1,2]. Oxygen or nitrogen oxides are added to the NF3 to reduce the induction period of the reaction and residence time in the Cu-packed reactor [3]. Although Cu is the most effective in producing N2F4 the reaction is erratic and often leads to complete reduction of NF3 to... 

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