Reduction of Fluorides

Fluorides are nonhygroscopic, and their melting points are higher than those of the corresponding chlorides. Besides, the fluoride reduction reactions are considerably more exothermic. The prime examples of the use of fluorides as intermediates are the reduction of uranium tetrafluoride by calcium or magnesium the reduction of rare earth fluorides by calcium, reduction of beryllium fluoride by magnesium and the reduction of potassium tantalum double fluoride by sodium. 

Magnesium can be obtained in high purity at low cost. It is the preferred reducing agent whenever feasible. The reduction of uranium tetrafluoride by magnesium involves the reaction 

The reduction of uranium tetrafluoride by calcium, in accordance with the reaction 

As mentioned earlier, magnesiothermic reduction is carried out in a sealed bomb. This steel bomb (400 mm in diameter and 1000-1200 mm in height for about 100 kg of uranium) is provided with a 25 mm MgF2 lining, which is thin enough to permit the influx of 

All the rare earth metals except samarium, europium, and ytterbium can be prepared in a pure form by reducing their trifluorides with calcium. Magnesium fluoride is less stable than the rare earth fluorides and so magnesium does not figure as a reductant. Lithium forms a fluoride which is stabler than some of the rare earth fluorides and thus finds some use as a reductant. 

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The production of tantalum and niobium metals by reduction of fluoride melts... 

Modem refining technology uses tantalum and niobium fluoride compounds, and includes fluorination of raw material, separation and purification of tantalum and niobium by liquid-liquid extraction from such fluoride solutions. Preparation of additional products and by-products is also related to the treatment of fluoride solutions oxide production is based on the hydrolysis of tantalum and niobium fluorides into hydroxides production of potassium fluorotantalate (K - salt) requires the precipitation of fine crystals and finishing avoiding hydrolysis. Tantalum metal production is related to the chemistry of fluoride melts and is performed by sodium reduction of fluoride melts. Thus, the refining technology of tantalum and niobium involves work with tantalum and niobium fluoride compounds in solid, dissolved and molten states. 

Table 3-13. Percent reduction of fluoride peak height upon addition of bicarbonate as a function of the fluoride content in solution.

Production of Elements by Reduction of Fluorides and Chlorides with Sodium... 

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... 

The reduction of fluoride [Sb(V) complexed with HI to Sb(lII) which is then precipitated with H S] is a little tricky. If difficulty is encountered, boil longer with HI and afterwards saturate longer with H S. 

Cm Th reduction of oxide gram Li reduction of fluoride (for multi-milligram batch)... 

Smelting to give the metals involves metallothermic reduction of fluorides or oxides, or electrochemical methods. Metal oxides are converted to fluorides by HF/Ar and purified by melting in an HF/Ar atmosphere. The fluorides are then reduced by the more electropositive calcium metal. 

Oxidizing nature of the fission process. The fission of a mole of UF.1 would yield more equivalents of cation than of anion if the noble gas isotopes of half-life greater than 10 min were lost and if all other elements formed fluorides of their lowe.st reported valence state. If this were the case the system would, presumably, retain cation-anion equivalence by reduction of fluorides of the most noble fission products to metal and perhaps by reduction of some U + to U +. If, however, all the elements of uncertain valence state listed in Article 12-6.2 deposit as metals, the balance would be in the opposite direction. Only about 3.2 equivalents of coml)iiicd cations result, and since the number of active anion equivalents is a minimum of 4 (from the four fluorines of UF4), the deficiency must 1)0 alleviated by oxidation of the container. The evidence from the Aircraft Reactor Experiment, the in-pile loops, and the in-pile capsules has not shown the fission process to cause serious oxidation of the container it is possible that these experiments burned too little uranium to yield significant results. If fission of UF4 is shown to be oxidizing, the detrimental effect could be overcome by deliberate and occasional addition of a reducing agent to create a small and stable concentration of soluble UF3 in the fuel mixture. 

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