Hexafluoride purification

The hexachloride, uranium hexachloride [13763-23-0], UCl, is best prepared by chlorination of UCl [10026-10-5] with SbCl. An alternative preparative approach is the disproportionation UCl [13470-21 -8] to UCl and UCl under reduced pressure. The obvious disadvantage of the second method is contamination by UCl, however, sublimation is a possible purification technique. Isostmctural with the hexafluoride, the hexachloride is monomeric with an octahedral arrangement of the chlorine atoms around the uranium center. 

Uranium Hexafluoride (Uranyl hexafluoride). UF6 mw 352.02 colorless, deliq monocl crysts mp 64.5—64.8° bp, subl at 56.2° d 4.68g/cc at 21°. Sol in liq Br, Cl2, C tetrachloride, sym-tetrachlorethane and fluorocarbons. Reacts with extreme violence with benz, ethanol, toluene, w or xylene. Prepn is by reaction of dried, powdered U308 with F gas above 600°. Product purification is by vac sublimation in a quartz appar. The vapor behaves as a nearly perfect gas. The compd has a AHf of 2197.7 1,8KJ/mole. It is used in the gaseous diffusion process for the sepn of U isotopes Refs 1) Gmelin, Syst Nr 55 (1940), 124-31 2) G. Brauer, Handbook of Preparative Inorganic Chemistry , Academic Press, NY (1963), 262 3) CondChemDict (1977), 904-05... 

Sulphur Hexafluoride, SF6.—Sulphur hexafluoride, the first hexahalide to be discovered, is prepared by submitting sulphur to the action of fluorine in a copper tube. The issuing gas on condensation in a spiral tube of the same metal at —80° C. becomes partly solidified by allowing the solid to vaporise gradually and passing the vapours through potassium hydroxide solution and solid potassium hydroxide successively, the substance is rendered purer, complete purification being effected subsequently by re-solidification followed by fractional evaporation.4... 

Selenium dioxide, by oxidation of selenium by nitric acid, 119 purification, 120 Selenium hexafluoride, 121 Silica gel, platinized, use in preparation of hydrogen bromide, 152 Silicobromoform, 38 analysis of, 41 Silicoethane, hexachlor, 42 Silicoformic anhydride, 42 Silicomolybdic acid, 127 analysis, 128... 

Silicon, higher chlorides of, 42 Silicon tetrabromide, 38, 40 Silicon tetrachloride, 44 Silicopropane, octachloro, 44 Silicotungstic acid, 129 analysis, 131 ether complex, 131 Silver, metallic, 4 Silver chloride, reduction of, 3 Silver cyanamide, 98 Silver residues, purification of, 2 Sodium amalgam, 10 Sodium amide, 74 Sodium azide, purification of, 79 Sodium azidodithiocarbonate, 82 Sodium butoxide, 88 Sodium hypochlorite (solution), 90 Sodium iodate, 168 Sodium metaperiodate, 170 Sodium paraperiodate, chlorine method, 169 persulfate method, 170 Strontium amalgam, 11 Sulfur hexafluoride, 121 Sulfuryl chloride, 114... 

Sirrce XeF4, as usually obtained, is contaminated with the difluoride or hexafluoride, and the mixtures are difficult to separate physically, a chemical purification is of considerable value. 

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. 

Effective purification of plutonium hexafluoride is proved through the selective adsorption of FPs on NaAlFi. A rather high decontamination factor (more than 5 x 103) is attained for ruthenium fluoride (36). A new separation process of PuF6 from UF6 by the selective adsorption onto UO2F2 is proposed (37). 

Exxon Nuclear Company has conducted various development programs to support the design and licensing of a commercial nuclear fuel reprocessing plant. The uranium conversion portion of the reprocessing plant will use fluidized-bed processes for conversion of uranyl nitrate hexahydrate (UNH) to uranium hexafluoride (UF ). This paper describes the laboratory and pilot plant studies conducted at Oak Ridge National Laboratory (1) for Exxon Nuclear Company on the conversion of UNH to UF, and on the purification of UF. ... 

Concentrates are shipped from the uranium mill to a uranium refinery or conversion plant. Here chemical impurities are removed and the purified uranium is converted into the chemical form needed for the next step in the fuel cycle. Figure 1.14 shows concentrates being converted into uranium hexafluoride (UF ), the form used as process gas in the gaseous diffusion process for enriching U. Other possible products of a uranium refinery used in other fuel cycles are uranium metal, uranium dioxide, or uranium carbide. Uranium purification and conversion processes are also described in Chap. 5. 

As usually prepared, uranium hexafluoride may he contaminated with other volatile fluorides, and hydrogen fluoride, molybdenum hexafluoride, vanadium oxyfluoride are among the common and objectionable impurities that may be present. Purification is usually achieved by distillation procedures and a considerable amount of useful and practical information on purification procedures has recently become available (24, 62, 81). A procedure for the purification of UFe that has been recently introduced by Gathers el al. (16) involves the formation of a complex compound between uranium hexafluoride and an alkali metal fluoride. Ruff and Heinzelmann (68) first observed complex formation between uranium hexafluoride and sodium or potassium fluoride, and this was confirmed by Martin et al. (69). These reports were received with a certain reserve, because efforts made during World War II to prepare addition compounds of uranium hexafluoride were singularly unsuccessful (41). Nevertheless, complex compounds are indeed formed, according to the reaction... 

The reaction is reversible, and uranium hexafluoride is evolved on heating it is this factor that makes the addition compound useful for the recovery or purification of uranium hexafluoride. The dissociation pressure of the complex compound in the temperature range 80-320° is given by the equation log p = 10.88 — (5.09 X 103/ T), where p is the partial pressure of UF6 in millimeters of mercury, and T is the absolute temperature. A decomposition pressure of 1 atm is calculated to occur at 363°, and an enthalpy of formation of —23.2 kcal/mole of UF6 is deduced for the formation of the complex. The kinetics of the reaction between uranium hexafluoride and sodium fluoride have been studied by Massoth and Hensel (60, 61). The reaction appears to proceed initially at a rate determined by the surface area of the sodium fluoride, and then to become diffusion limited, The rate of the reaction is given by the expression k = 5.0 X 106 exp (—13,000// r) per hour the activation energy is thus 13,1 zk 0.2 kcal/mole of uranium hexafluoride. 

Xenon tetrafluoride was first prepared by heating a gaseous mixture of xenon and fluorine under moderate pressure. However, the product obtained by this method is always contaminated with xenon difluoride and hexafluoride, which are in chemical equilibrium with xenon tetrafluoride. Xenon tetrafluoride obtained in this way can be purified by subsequent chemical purification with arsenic pentafluoride." ... 

Because my co-workers at that time (March 23,1962) were still not sufficiently experienced to help me with the glassblowing and the preparation and purification ofPtFg [platinum hexafluoride] necessary for the experiment, I was not ready to carry it out until about 7 p.m. on that Friday. When I broke the seal between the red PtFg gas and the colorless xenon gas, there was an immediate interaction, causing an orange-yellow solid to precipitate. At once I tried to find someone with whom to share the exciting finding, but it appeared that everyone had left for dinner ... 

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