Uranyl Ion Complexation

Allen PG, Shuh DK, Bucher JJ, Edelstein NM, Reich T, Denecke MA, Nitsche H (1996a) EXAFS determinations of uranium structures The uranyl ion complexed with tartaric, citric, and malic acids. Inorg Chem 35 784-787... 

Denecke MA, Reich T, Bubner M, Pompe S, Heise KH, Nitsche H, Allen PG, Bucher JJ, Edelstein NM, Shuh DK (1998a) Determination of structural parameters of uranyl ions complexed with organic acids using EXAFS. J Alloys and Compounds 271-273 123-127. 

Hanowfield. J.M. Ogden. M.I. White, A.H. Actinide complexes of the calixarenes. Part 1. Syntheses and crystal structure of bis(homo-oxa)-/ -r rr-butylcalix[4]arene and its uranyl ion complex. J. Chem. Soc.. Dalton Trans. 1991. 

Masci, B. Gabrielli. M. Mortera. S.E. Nierlich. M. Thuery, P. Hydrogen bonded supramolecular assemblies from uranyl ion complexes of tetrahomodioxacalix[4]ar-enes with various counterions. Polyhedron 2002, 21 (11). 1125-1131. 

Thus, while past experiments with sulfonate containing resins far outweighs past experiments employing carboxylate containing resins, the carboxylate moieties have been shown in the present study to be superior with respect to uranyl ion complexation when the particular reactive groups are contained in polymers or as difunctional monomers. 

Previous work involved the s3mthesis and physical characterization of linear uranyl polyesters obtained from both interfacial and aqueous solution polycondensation routes. Uranyl ion complexation, i.e. removal, was effected to a 10" molar (concentration in aqueous solution) level. 

The present work focuses on the formation of uranyl ion complexes with polysodium acrylate to investigate the isolation of the uranyl ion. This paper concentrates on the structural identification of the coordination product between polysodium acrylate, polyacrylic acid and the uranyl ion. 

Thuery P (2006) Uranyl ion complexation by citric and tricarballylic acids hydrothermal synthesis and structure of two- and three-dimensional uranium-organic frameworks. Chem Commun 853-855... 

The solvent, a solution of either sulfuric acid or sodium carbonate, forms the stable complex uranyl ions U02(S04) "2) U02(SO ) )... 

In TBP extraction, the yeUowcake is dissolved ia nitric acid and extracted with tributyl phosphate ia a kerosene or hexane diluent. The uranyl ion forms the mixed complex U02(N02)2(TBP)2 which is extracted iato the diluent. The purified uranium is then back-extracted iato nitric acid or water, and concentrated. The uranyl nitrate solution is evaporated to uranyl nitrate hexahydrate [13520-83-7], U02(N02)2 6H20. The uranyl nitrate hexahydrate is dehydrated and denitrated duting a pyrolysis step to form uranium trioxide [1344-58-7], UO, as shown ia equation 10. The pyrolysis is most often carried out ia either a batch reactor (Fig. 2) or a fluidized-bed denitrator (Fig. 3). The UO is reduced with hydrogen to uranium dioxide [1344-57-6], UO2 (eq. 11), and converted to uranium tetrafluoride [10049-14-6], UF, with HF at elevated temperatures (eq. 12). The UF can be either reduced to uranium metal or fluotinated to uranium hexafluoride [7783-81-5], UF, for isotope enrichment. The chemistry and operating conditions of the TBP refining process, and conversion to UO, UO2, and ultimately UF have been discussed ia detail (40). 

Crystals of uranyl perchlorate, U02(C10[13093-00-0] have been obtained with six and seven hydration water molecules. The uranyl ion is coordinated with five water molecules (4) in the equatorial plane with a U—O(aquo) distance of 245 nm (2.45 E). The perchlorate anion does not complex the uranyl center. The unit cells contain two [0104] and one or two molecules of hydration water held together by hydrogen bonding (164). 

The hydrolysis of the uranyl(VI) ion, UO " 2> has been studied extensively and begins at about pH 3. In solutions containing less than lO " M uranium, the first hydrolysis product is the monomeric U02(OH)", as confirmed using time-resolved laser induced fluorescence spectroscopy. At higher uranium concentrations, it is accepted that polymeric U(VI) species are predominant in solution, and the first hydrolysis product is then the dimer, (U02)2(0H) " 2 (154,170). Further hydrolysis products include the trimeric uranyl hydroxide complexes (U02)3(0H) " 4 and (1102)3(OH)(154). At higher pH, hydrous uranyl hydroxide precipitate is the stable species (171). In studying the sol-gel U02-ceramic fuel process, O nmr was used to observe the formation of a trimeric hydrolysis product, ((U02)3( -l3-0)(p.2-0H)3) which then condenses into polymeric layers of a gel based on the... 

The 0s 02 " group has a formal similarity to the more familiar uranyl ion [U02] " and is present in a variety of octahedral complexes... 

Conceptual Flowsheet for the Extraction of Actinides from HLLW. Figure 5 shows a conceptual flowsheet for the extraction of all the actinides (U, Np, Pu, Am, and Cm) from HLLW using 0.4 M 0< >D[IB]CMP0 in DEB. The CMPO compound was selected for this process because of the high D m values attainable with a small concentration of extractant and because of the absence of macro-concentrations of uranyl ion. Distribution ratios relevant to the flowsheet are shown in previous tables, IV, V, VI, and VII and figures 1 and 2. One of the key features of the flowsheet is that plutonium is extracted from the feed solution and stripped from the organic phase without the addition of any nitric acid or use of ferrous sulfamate. However, oxalic acid is added to complex Zr and Mo (see Table IV). The presence of oxalic acid reduces any Np(VI) to Np(IV) (15). The presence of ferrous ion, which is... 

Leciejewicz J, Alcock NW, Kemp TJ (1995) Carboxylato Complexes of The Uranyl Ion Effects of Ligand Size and Coordinat. Geometry Upon Molecular and Crystal Structure. 82 43-84... 

Uranium is readily mobilized in the meteoric environment, principally as the highly soluble uranyl ion (U02 ) and its complexes, the most important of which are the stable carbonate complexes that form in typical groundwaters (pH > 5, pC02 = 10 bar) (Gascoyne 1992b Grenthe et al. 1992 see also Langmuir (1997) for review). Uranium is... 

Figure 3. Distribution of uranyl complexes as a function of pH at 25°C in presence of typical ligands in surface and ground waters (PCO2 = 10 atm, E F = 0.3 ppm, E Cl = 10 ppm, E SO4 = 100 ppm, E PO4 = 0.1 ppm, E Si02 = 30 ppm). Below pH 4-5 uranyl (U02 ) ion and uranyl fluoride complexes predominate, at intermediaiy pHs (4.5 < pH < 7.5) U02(HP04)2 is the predominant species, whereas at higher pH uranyl is complexed with carbonates. [Used with permission of Elsevier Science, from Langmuir (1978) Geochim Cosmochim Acta, Vol. 42, Fig. 11, p. 558].

Czerwinski KR, Buckau G, Scherbaum F, Kim JI (1994) Complexation of the uranyl ion with aquatic humic acid. Radiochim Acta 65 111-119... 

The ion exchange process involves the ability of hexavalent uranium as the uranyl ion, UO+, to form anionic complexes with sulfate ions, SO2-, and carbonate ions, CO2-. In a general way, it may be mentioned that the uranyl ion exits in dynamic equilibrium with its sulfate complexes,... 

Vidali, M. et al J. Inorg. Nucl. Chem., 1975, 37, 1715-1719 A series of uranyl complexes of macrocyclic azomethines were used as ligands for transition metal ions, with perchlorate anions. Raman spectra of the uranyl-metal complexes could not be recorded because the samples exploded during attempted measurements. 

Cabell, M. J. The complexes formed by thorium and uranyl ions with com-plexones. Analyst 77, 859 (1952). 

Humic acids and fulvic acids interact with a wide variety of cations. In addition to interacting with iron and aluminium, the species with which they are complexed in soils (57), they also form stable complexes with zirconium, thorium, the lanthanides and the uranyl ion. In the case of uranium it has been suggested that humic acids could be of considerable importance in the geological formation of secondary deposits of uranium (58). 

The sequence neutrality for random stretches of double-stranded DNA makes uranyl ion a very useful reagent for examining contact regions in protein-DNA complexes. Such photo-footprinting studies have been carried out with the A-repressor/ORl [185], E. Coli RNA polymerase/deo Plpromoter [187] and transcription factor IIIA-ICR [188]. 

H-atom abstraction has been demonstrated to be the mechanism of action of excited uranyl ions, and in this case negligible base oxidation is found. Nucleo-base (especially guanine) oxidation is the principal reaction caused by singlet oxygen and this reactive species can be generated by a number of the complexes (e.g. many Ru(II)polypyridyls and porphyrins). It is worth pointing out, however, that the yield of may be lower when the sensitiser is bound to DNA, and it is the authors view that some of the reactions claimed to proceed via 62 may be caused by direct reaction of the photo-oxidised sensitiser with the DNA. 

The extractabilities of metal-organic complexes depend on whether inner or outer sphere complexes are formed. Case 1, section 4.2.1, the extraction of ura-nyl nitrate by TBP, is a good example. The free uranyl ion is surrounded by water of hydration, forming U02(H20)f, which from nitric acid solutions can be crystallized out as the salt U02(H20)6 (N03), though it commonly is written U02(N03)2(H20)6. Thus, in solution as well as in the solid salt, the UOf is surrounded by 6 HjO in an inner coordination sphere. In the solid nitrate salt, the distance du.o(nitrate) between the closest oxygen atoms of the nitrate anions, (0)2N0, and the U-atom is longer than the corresponding distance, du-o(water), to the water molecules, OH2, i.e., du.o(nitrate) > 4u.o(water) thus the nitrate anions are in an outer coordination sphere. 

Two other actinyl ions, UO (5/°) and NpO (5/ ), are worth mentioning here. Although the uranyl ion contains no unpaired/electrons, its complexes may display a weak temperature-independent paramagnetism because of... 

Natural inorganic ligands of heavy metals in subsurface water, which are present in a concentration of about 1 millimolar, include nitrite, sulfate, chloride, carbonate, and bicarbonate. These potential ligands generally are efficient only under special conditions. For example, in an alkaline environment, carbonate and bicarbonate can be significant complexors of transition metals like Cu or the uranyl ion, and cadmium may be complexed with Cl" or SO to form... 

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