Ammonium uranates

While Cordfuncke [997] believes that there are only four stable compounds in the U03—NH3—H20 system, the results of Stuart et al. [998, 999] indicate the existence of a continuous non-stoichiometric phase containing the NH4 ion and possessing zeolitic properties U02(0H)2 x (ONH4 )x yH20. 

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J. L. Woolfrey, Preparation and Caldnation of Ammonium Uranates—-A Eiterature Survey, AEC/TM-476, AustraUm Atomic Energy Commission, Lucas Heights, Austraha, Sept. 1968. 

U is also found in the Soviet Union where there are sources in Karelia, near Dnepropetrovsk, the Kirghiz Soviet Republic and in Transcaucasia Whereas once U ores were processed for their Ra content, Ra has now lost its commercial importance and it is considered a contaminant. Only two U ores have been processed extensively, pitchblende and carnotite. The general procedure is to solubilize the U with an acid, convert the ion to a complex carbonate (thereby removing the Fe, A1 and Mn), ppt the Pb and Cu as the sulfide, and finally, to recover the U as the ammonium uranate and hence, as the oxide U metal can be obtained from the oxide or the halide by reduction with alkali metals or alkaline earth metals. U, being highly electropositive, cannot be deposited electrolytically from aq solns. Thermal decompn of the tetra-iodide is possible (Ref 1)... 

The main oxides are U02, which is brown-black and highly non-stoichiometric, U308, greenish-black, and U03 orange yellow. The latter is best made by heating uranyl nitrate or ammonium uranate (see below) and the other oxides can be made from U03 ... 

Uranium Oxysulphide, U3O2S4 or UO3.2US2, is formed when uranous oxide, urano-uranic oxide, or ammonium uranate is heated in a stream of hydrogen sulphide or carbon disulphide vapour when one of the oxides is heated with a mixture of ammonium chloride and sulphur or when uranyl sulphate is heated in hydrogen or with potassium pentasulphide. It is a greyish-black powder, which is decomposed by nitric acid %vith deposition of sulphur. 

Ammonium Uranyl Carbonate, (NH4)4U0,(C03)3.2H20, is obtained by dissohnng freshly precipitated ammonium uranate in a solution of ammonium carbonate at 60° to 70° C. or by treating a soluble uranyl salt with ammonium carbonate and ammonia. In either case a yellow solution is formed which on evaporation deposits yellow monoclinic ery> stals of the double carbonate. The same compound results on mixing concentrated solutions of ammonium carbonate (3 molecules) and uranyl nitrate (1 molecule) at 50° to 55° C.,... 

Precipitation with ammonium sulphide is best performed at 80° C. in presence of ammonium chloride. Some ammonium uranate is always formed, and complete separation from the alkali metals is only obtained by repeating the precipitation. The results obtained by this method are liable to be high owing to some sulphide being oxidised to sulphate during ignition. ... 

Results of an i.r. study of the thermal decomposition of ammonium uranate have been interpreted in terms of the final self-reduction of the amide as represented by the equation... 

The thermal decomposition of ammonium uranate in flowing hydrogen has been shown to be accompanied by an initial decrease in the surface area of the pellets as the temperature was increased to 100 °C, but thereafter to be accompanied by an increase in the surface area as dehydration occurred. A sudden increase in the surface area at 325 °C was reported to be associated with nitrate decomposition. No significant evolution of ammonia was recorded below 190°C the maximum release of ammonia occurred at 330 °C with decomposition of the ammonium uranate. At 300 °C the predominant phases were identified as ammonium uranate and U03,2H20 with very minor amounts of P-UO3. At 350 °C complete disruption of the ammonium uranate lattice was observed. 

Uranium trioxide or uranic oxide, UOs, may be prepared in pure form by long continued heating of uranyl-ammonium carbonate at 300° or of ammonium uranate at 250° uranyl nitrate also yields UOs on ignition, but the product contains basic nitrates unless the heating is done thoroughly. The color of the oxide varies from orange to red, depending on the method... 

Ammonium uranate(VI) (NH3)3U30, 7783-22-4 624.131 red-yel amorp powder i EIjO, alk s acid... 

As mentioned earlier, the two most common and stable types of uranium compounds are those in which uranium is in the tetravalent and hexavalent states. As far as the NFC is concerned, the binary oxides, binary fluorides, and oxyfluorides are of major importance, although several other compounds (e.g., uranyl nitrate, uranyl sulfate, and ammonium uranates) also play a role in the processing and handling of uranium (Table 1.5). Uranium metal and especially uranium alloys also play a significant role in commercial and military applications of uranium. 

The mined uranium ore is crushed and ground into a fine powder. After ore dressing, the concentrate is leached with sulfuric acid. The solution is treated in a Hq-uid-Hquid extraction, in which uranium is transferred to an organic phase. It is extracted from that with ammonia, and ammonium uranate is precipitated. At 1000°C it is decomposed to yellow uranium oxide UOj. Uranium hexafluoride is prepared by treating the oxide with hydrogen fluoride to make uranium tetrafluoride. This in turn is treated with elemental fluorine to prepare the gaseous hexafluoride UF (sub-Hmation point 56°C). 

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