Uranium complexes carbonates

Sorption in most soils attains a maximum when the neutral hydroxy complex of uranium is at a maximum. However, at pH 6 and above, and in the presence of high carbonate or hydroxide concentrations, uranium may form anionic complexes such as [U02(0H)4]. The mobility of anionic uranium complexes in soil is dependent upon the nature of the soil. For example, the decrease in sorption in soil with little anion-exchange capacity may result in increased mobility however, increased sorption in soil with high anion-exchange may result in decreased mobility (Allard et al. 1982 Ames et al. 1982 Brookins et al. 1993 Ho and Doern 1985 Hsi and Langmuir 1985 Tichnor 1994). 

It is noted that terminal alkynes add to the carbon of an isonitrile in the presence of a uranium complex, giving a propargylic imine. ... 

Bagnall, K. W. Edwards, J. Heatley, F. Uranium (IV) poly(pyrazol-l-yl)borate complexes—carbon-13 NMR spectra. Transplutonium 1975, Proc. 4 Int. Transplutonium Elem. Symp. Baden-Baden Sept. 1975 Muller, W. Lindner, R., Eds., North-Holland Amsterdam, 1976, 119. 

The aquatic transport of uranium as carbonate complexes is reflected in the formation of the uranyl carbonate minerals Rutherfordine, U02(C03), Leibigite, Ca2[U02(C03)3]-10-llH20, and Andersonite, Na2Ca[U02(C03)3]-6H20. Both natural and synthetic UO2CO3 have similar structures which contain sheets of planar ions. The uranyl groups have the normal trans... 

Treatment of U02C12(THF)3 in THF with 1 equiv. of Na[CH(Ph2P=NSiMe3)2] led to formation of an unusual red uranyl chloro-bridged dimer (70% yield) containing a uranium(vi)-carbon bond as part of a tridentate bis(imino-phosphorano)methanide chelate complex (Scheme 9). This was the first example of a uranyl-methine carbon bond. The methine carbon is displaced significantly from the uranyl equatorial plane.33... 

One advantage of hydrometaiiurgy over the traditionai processes is that sometimes the leaching agent can be pumped directiy into the ore deposits in the earth. For example, aqueous sodium carbonate (Na2C03) can be injected into uranium-bearing ores to form water-soluble complex carbonate ions. 

Uranium complexes have also shown imprecedented reactivity with carbon monoxide. Addition of carbon monoxide to [(COT)(Cp )U(THF)j [122] produced a dimeric 0303 debate uranium complex, [ ( j -Cp )( j -COT)U 2... 

Phosphines metallated at remote atoms other than carbon have also been applied in synthesis, including the bis(phosphinophenyl)amide salt (44), used to prepare various uranium complexes, N-metallated 2-phosphi-noindoles, used to prepare new chiral hybrid phosphino-phosphito... 

More then 150 minerals containing uranium are known. Typically, however, uranium ores contain only about 0.1% uranium. In the commercial production of uranium metal, the ore is crushed, concentrated, roasted, and in most cases leached with sulfuric acid in the presence of an oxidizing agent such as manganese dioxide or chlorate ions to convert all of the uranium to uranyl sulfato complexes. Carbonate leaching is used to extract uranium from ores containing minerals such as calcite. The recovery of uranium... 

Uranium.— The thermolysis reactions of the alkyl complexes [UR( j-C6H6)3] are first order in uranium complex. Rate constants and free energies of activation are given in the Table. The order of stability of the alkyl compounds is primary > secondary > tertiary. In the thermolysis reaction intramolecular abstraction of hydrogen from a cyclopentadienyl occurs, giving RH with retention of configuration at carbon. ... 

To summarize uranium complexing in hydrothermal solutions, the predominant species will depend on the concentration of complexing anions, which is, in turn, dependent on temperature and pH. The activity of fluoride in many uranium mineralizing systems appears to be significant, as is indicated by the abundance of fluorite and other fluoride-containing gangue minerals. In these systems uranyl fluoride complexes would predominate in acid to neutral solutions. At low temperatures carbonate complexes predominate in alkaline solutions, but, as temperature increases, carbonate complexes become less important. Phosphate complexes may be important in nearneutral solutions in which as little as 0.1 ppm phosphate is present. As temperature increases, hydroxide complexes become more important. At temperatures of 300°C and above hydroxide complexes may be the only soluble uranium species. 

According to Naumov and Mitronova, the decomposition of uranyl carbonate complexes and the simultaneous reduction of uranium proceed the more readily w ith decreasing carbonate ion concentration. In fact, the potential of the couple in the presence of CO3" ions is lower than that in carbonate-free waters—that is, more reducing conditions are required to remove uranium from carbonate-rich water in comparison with waters low in carbonate. 

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