Uranic fluoride

Figure 2. Solubility of maninite as a function of pH at 25°C for different fluoride concentrations. Formation of uranous fluoride complexes greatly enhances maninite solubility below pH 3-4. The increase of maninite solubility at higher pH results from the formation of uranous hydroxyl complexes. [Used with permission of Elsevier Science, fromLangmuir (1978) Geochim Cosmochim Acta, Vol. 42, Fig. 4, p. 555].

Uranium Tetrafluoride, Uranous Fluoride, UF, is the chief product obtained when the metal is acted upon by fluorine. It may be prepared by the action of hydrogen fluoride on urano-uranic oxide or on uranous oxide or by reduction of a solution of uranyl fluoride with stannous chloride. It is also formed with uranium hexafluoride when the pentachloride is acted upon by fluorine at —40° C. thus ... 

Uranous fluoride is a green amorphous powder, insoluble in water, hardly attacked by dilute acids and-only dissolved with difficulty by concentrated acids, except in the case of nitric acid which readily decomposes it. When heated in the air it loses fluorine and leaves a residue of urano-uranic oxide. At ordinary temperatures it is gradually oxidised to the uranyl compound, UOjFj. If heated in absence of air it melts at about 1000° C. ... 

The insolubility of uranous fluoride affords a method of estimating the metal by precipitation with hydrofluoric acid. ... 

IVhen uranous fluoride is dissolved in a solution of ammonium oxalate a dark green liquid results, which exhibits a violet fluorescence and deposits on e -aporation crvstals of the double salt UF4.2(NH4)jC,04. 4H20. ... 

Uranium Hexafluoride, Uranic Fluoride, UFg, is the only known compound of hexavalent uranium (with the possible exception of the boride in which the condition of the uranium is not established) which does not contain oxygen. It was first prepared by Ruff and Heinzel-mann by the action of fluorine on uranium pentachloride at —40° C. The action proceed.s as already described (see equation above), and the volatile hexafluoride is distilled off from the tetrafiuoride. The penta-ehloride, Avhen acted upon by dry hydrogen fluoride, yields a compound, UF5.a HF, which breaks up on distillation into the tetra- and hexafluorides, but this method of preparation is less convenient than the preceding one owing to the difficulty of separating the hexafluoride from hydrogen fluoride. Uranium carbide reacts with fluorine in presence of a little chlorine at —70° C., vith formation of the hexafluoride. 

A.G. Winger, Sorption Processes, membrane processes - ion exchange, Eng. Progr., 1957, 53, 606 W.W. Schlutz, E.W. Neuvar, J.I. Carroll and R.E. Bums, Electrodialytic conversion of uranyl nitrate to uranic fluoride salts, Ind. Eng. Chem., 1958, 50, 1768. 

In sununaiy, the aqueous speciation of U in solutions that are believed to be representative of the relatively oxidizing and reducing groundwaters of the Tono region is dominated by U(OH)4(aq) under reducing conditions, and by the uranyl mono-, di- and tri-carbonato complexes, and (or) U02(0H)3, under relatively oxidizing conditions. Uranous fluoride or phosphate complexes, or their uranyl counterparts, are important in these respective solutions only if pH is less than 6 or 7. 

Uranous complexes tend to be insoluble at low temperatures and at pH 4.5-7. At temperatures above 150°C uranous transport may become dominant. Depending on ligand concentrations, uranous fluoride, phosphate, sulphate and especially hydroxide compounds are important species under these conditions, but uranous carbonate complexes are not. Uranyl species are soluble over a wide range of conditions. In normal groundwater, at temperatures of 25°C, uranyl fluoride complexes are dominant at pH <4, uranyl phosphates at pH 4-7.5 and uranyl di- and tricarbonate complexes at pH >7.5. Uranyl silicate complexes are probably insignificant, and at temperatures near 100°C uranyl hydroxides predominate, whereas uranyl carbonate complexes dissociate. ... 

Uranium Is stripped from the organic solvent by precipitation as uranous fluoride. 

Double fluorides have been obtained by reduction of complex alkali uran d fluoride solutions by means of oxalic or formic acid under the influence of sunlight. The potassium salt, KUFj, is a green powder, insoluble in water. 

Uranyl Fluoride, UO Fg, is formed with uranous oxyfluoride (see above) by the action of hydrofluoric acid on urano-uranic oxide Us08-f6HF=U0F2-f2U02F2+3H20. 

The green insoluble uranous oxyfluoride is removed by filtration, and the uranyl fluoride remains as a yellow mass after evaporation of the solution. It is also obtained as a yellow powder by repeated evaporation of uranyl acetate with hydrofluoric acid. A white crystalline form has been described by Smithells, who obtained it by carefully heating the tetrafluoride in air it dissolved in water yielding a yellow solution. 

Other methods, such as precipitation with hydrogen peroxide, or precipitation with hydrogen fluoride after reduction to the uranous condition, are less satisfactory. ... 

Uranium Z, also thought to be a product of uranium X, was discovered by Hahn in 1921, who isolated it in the following manner. The mother-liquors from repeated fractional crj stallisations of uranous nitrate, containing uranium X and uranium Z, w ere treated with ferric chloride solution, and the iron precipitated by means of ammonia and ammonium carbonate. The precipitate, which contained both the uranium Xj and uranium Z, was treated with a solution of tantalum in hydrofluoric acid, lanthanum nitrate added, and the mixture digested on a water-bath with dilute hydrofluoric and sulphuric acids. Lanthanum fluoride was precipitated, and carried do%vn with it uranium The filtrate was evaporated to dryness and the residue ignited. The tantalum was thus rendered insoluble, whilst the iron could be removed by means of concentrated hydrochloric acid. The uranium Z remained with the tantalum. By this means Hahn obtained specimens of uranium Z which were 99-5 per cent, radioactively pure. 

Ammonium uranyl carbonate (AUC) process This process was developed in the 1960 s in the Federal Republic of Germany. It comprises the simultaneous feeding of uranium(Vl) fluoride, carbon dioxide and ammonia into an aqueous ammonium carbonate solution at 70°C, whereupon tetra-ammonium tricarbonato-dioxo-uranate (ammonium uranyl carbonate) precipitates out ... 

The structures of the metal, hydrides, and carbides are described in other chapters, as also are the halides MX3, MX4, and MX5. Here we devote sections to certain halide structures peculiar to U, complex fluorides of Th and U, oxides of U, uranyl compounds and uranates, nitrides and related compounds, and conclude with a note on the sulphides of U, Th, and Ce. 

Luminescence Properties of Uranate Centres in Sodium Fluoride Single Crystals. 117... 

Figure 11 shows the atomic configurations of the uranate centres proposed by Runciman (a) and by Kaplyanskii (b). In contrast to these proposals Pant et al. ) ascribe the luminescence properties to square-planar U04-groups. Recently, E.P.R. measurements have been performed on X- or 7-irradiated crystals of uranium-activated lithium fluoride and uranium-activated sodium fluoride " ). The authors propose (UOsF) ), (UOs—or (UOs)" ) to be the uranium centres, containing pentavalent uranium. 

In the course of a study of the luminescence properties of uranium-doped sodium fluoride single crystals, the complicated uranate luminescence spectra have been unraveled, using chemical variation of the crystal compositions and by applying site selective laser excitation techniques Using the results from both luminescence and electrical conductivity experiments a model was deduced for the configurations of the uranium centres ). 

F3M0OK2, Molybdate(V), pentafluorooxo-, dipotassium, 21 170 FjU, Uranium fluoride, 0-, 21 163 FoKU, Uranate(V), hexafluoro-, potassium, 21 166... 

Fluorocarbons Polychloro- trifluoroe- thylene, polytetra- fluoro- ethylene, polyvinyl fluoride, polymono- chlorotri- fluoro- ethylene Trichloro- ethylene 1. Wipe vrith solvent and treat with the following for 15 min at RT Naphthalene (128 g) dissolved in tetrahydrof uran (11) to which is added sodium (23 g) during a stirring period of 2 h. Rinse in deionized water, and dry in water air Sodium-treated surfaces must not be abraded before use. Hazardous etching solutions requirii skillful handling. Proprietary etching solutions are... 

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