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Hexavalent actinides

The Table shows a great spread in Kd-values even at the same location. This is due to the fact that the environmental conditions influence the partition of plutonium species between different valency states and complexes. For the different actinides, it is found that the Kd-values under otherwise identical conditions (e.g. for the uptake of plutonium on geologic materials or in organisms) decrease in the order Pu>Am>U>Np (15). Because neptunium is usually pentavalent, uranium hexavalent and americium trivalent, while plutonium in natural systems is mainly tetravalent, it is clear from the actinide homologue properties that the oxidation state of plutonium will affect the observed Kd-value. The oxidation state of plutonium depends on the redox potential (Eh-value) of the ground water and its content of oxidants or reductants. It is also found that natural ligands like C032- and fulvic acids, which complex plutonium (see next section), also influence the Kd-value. [Pg.278]

Three classes of carbamoylmethylphosphoryl extractants were studied for their ability to extract selected tri-, tetra-, and hexavalent actinides from nitric acid. The three extractants are dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP), hexyl hexyl-N,N-diethylcarbamoylmethylphosphinate (HHDECMP), and octyl(phenyl)-N,N-diisobutylcarbamoylmethylphos-phine oxide 0< >D[IB]CMP0. The above three extrac-trants were compared on the basis of nitric acid and extractant dependencies for Am(III), solubility of complexes on loading with Nd(III) and U(VI), and selectivity of actinide(III) over fission products. [Pg.428]

Hexavalent Pu—See Valence states Hexyl hexyl- V, V-diethylcarbamoyl-methylphosphinate, actinide... [Pg.462]

One of the first bed materials was based on the extractant diamyl amylphosphonate (DAAP marketed under the name U-TEVA-Spec ) and was designed for purification of the tetravalent actinides (U (IV), Th (IV), Pu (IV)) and hexavalent uranium (U(VI)). This material is characterized by high (>10-100) distribution coefficients for U and Th in significant (>3 M) concentrations of both nitric and hydrochloric acids, and so is useful for both U and Th purification (Horwitz et al. 1992 Goldstein et al. 1997 Eikenberg et al. 2001a). [Pg.28]

The use of HDEHP for extraction of actinides from waste solutions also has several drawbacks, including extraction of trivalent ions at a pH at which tetravalent ions such as Zr(IV) and Pu(IV) are hydrolyzed, and difficulties in stripping tetravalent and hexavalent actinides. All in all, monofunctional organophosphorus reagents are vastly inferior to their bifunctional counterparts for extracting Am(III) and other actinides from strong HNO3 media. [Pg.538]

The first and thus far only silsesquioxane complex of an actinide element is [Cy7Si70i2]2U (100). This colorless, nicely crystalline uranium(VI) compound is formed upon reaction of 3 with any uranium precursor, e.g., UCI4 in the presence of NEt3. In all cases oxidation of uranium to the hexavalent oxidation state is observed. The best synthetic route leading to 100 in ca. 80% yield is the reaction of 3 with uranocene as outlined in Scheme 33. [Pg.125]

In Section 6 we will consider one of the actinides, viz. hexavalent uranium. Its luminescence has been studied extensively, but many problems remain still unresolved. The position of the c.t. bands appears to be very important. [Pg.45]

Removes trivalent, tetravalenf and hexavalent lanthanides and actinides equally well no valence adjustment is necessary. [Pg.375]

The mobility of humic/fulvic colloid-borne tri-, tetra-, penta- and hexavalent actinide ions has been clearly observed in sand column experiments (Kim et al. 1994 Artinger et al. [Pg.538]

The obvious first step in checking for the consistency of the data is comparing equilibrium constants of cations with the same charge and similar ionic radius. Comparison of the formation constants of complexes and solids of tet-ravalent actinides (Th, U4+, Np4+, Pu4+), Zr4+, and Sn4+ reveals that the selected data are very similar, which is to be expected from a chemical point of view, and none of the formation constants appears to be improbable (for details see Hummel et al. 2002). Similar pictures of chemical consistency emerge from the triva-lent Np3+, Pu3+, Am, and Eu3+ complexes and solids, and from the hexavalent UOz"1", NpOl4, and PuO complexes and solids (Hummel et al. 2002). [Pg.565]

The Purex process is used for almost all fuel reprocessing today. Irradiated UO2 fuel is dissolved in HNO3 with the uranium being oxidized to U02(N03)2 and the plutonium oxidized to Pu(NC>3)4. A solution of TBP in a high-boiling hydrocarbon, such as n-dodecane, is used to selectively extract the hexavalent U02(N03)2 and the tetravalent Pu(NC>3)4 from the other actinides and fission products in the aqueous phase. The overall reactions are... [Pg.481]

While pH plays an important role in the extraction of metal ions by the acidic chelating extractants, counteranions such as N03, CE, etc., significantly influence the extraction of metal ions by solvating extractants (L) like TBP, TOPO, etc. The extracted species thus forms solvating species such as MX4 n. or M02X2 nL for tetravalent and hexavalent actinide ions, respectively, where X is a representative counteranion and n is the number of ligand molecules in the extracted species. In... [Pg.71]

The largest number of automated extraction-chromatographic separations for actinides have used TRU-Resin, and many of these have coupled the column to ICP-MS as an on-line separation (see Table 9.3). TRU-Resin is impregnated with the neutral bifunctional organophosphorus complexant, octyl(phenyl)-A,A-diisobu-tylcarbamoylmethylphosphine oxide (CMPO) in tri-n-butyl phosphate (TBP).26 127 128 The organic stationary phase in this resin binds trivalent, tetravalent, and hexavalent actinide nitrato complexes from nitric acid solutions (see Figure 9.11). The extraction equilibria for representative species are shown in Equations 9.3-9.5, where the bar above a species indicates that it is immobilized on the resin.4... [Pg.539]

Actinide retention increases with increasing nitric acid concentration. Tetravalent actinides are more strongly retained than trivalent actinides. Chloro complexes of tetravalent and hexavalent actinides, but not trivalent actinides, are retained from hydrochloric acid solutions (see Figure 9.12). Actinides retained on TRU-Resin columns from nitric acid load solutions can be recovered, individually or in groups, using different acid solutions and/or complexants as eluents. In addition, on-column redox chemistry can be used to shift the valence state of Pu through multistep separation processes so that Pu can be isolated individually. [Pg.540]

Loading the sample in nitric acid solution, the tetravalent actinides are strongly retained along with hexavalent uranium. However, trivalent actinides like Am(III) and Pu(III) are not retained from nitric acid solutions (unlike TRU-Resin). Pu retained as Pu(IV) can be removed from the column by reducing it to Pu(III). Tetravalent actinides and U(VI) are also retained in strong hydrochloric acid solution, with retention sharply dropping off as hydrochloric acid concentrations decrease (see Figure 9.12). Th(IV) is less retained in hydrochloric acid solutions than U(VI). Actinides retained on UTEVA-Resin from nitric acid solutions can be released with diluted nitric acid or low hydrochloric acid concentrations. [Pg.546]

K) -1690 10 kJ mol 1. The preparation and properties of this and other actinide (IV) complex oxides are described and are compared with other perovskites BaM03. The relative stabilities of tetravalent and hexavalent uranium in various environments are compared in terms of the oxidation-reduction behavior of uranium in geological nuclear waste storage media in perovskite, uranium(IV) is very unstable in comparison with uranium(VI). ... [Pg.312]

The hexavalent state of uranium ion is the usually encountered ion in the solution chemistry of uranium and its exceptional stability, relative to its other oxidation states as well as to other hexavalent actinide ions, makes studies with this ion much simple. Though chelating acids, in general, extract U(VI) by the equilibrium,... [Pg.45]

In the hexavalent state these elements are similar to uranium in the quadrivalent state however they have, like uranium and protactinium in this valency state, externally the inert gas configuration of the thorium ion in the trivalent state that of the trivalent actinium ion. The name 5f series may perhaps be the best in place of actinides, thorides or uranides. [Pg.14]


See other pages where Hexavalent actinides is mentioned: [Pg.241]    [Pg.241]    [Pg.80]    [Pg.205]    [Pg.329]    [Pg.148]    [Pg.446]    [Pg.214]    [Pg.510]    [Pg.532]    [Pg.44]    [Pg.238]    [Pg.598]    [Pg.67]    [Pg.70]    [Pg.71]    [Pg.72]    [Pg.73]    [Pg.74]    [Pg.76]    [Pg.77]    [Pg.77]    [Pg.97]    [Pg.132]    [Pg.540]    [Pg.320]    [Pg.83]    [Pg.329]    [Pg.73]    [Pg.88]    [Pg.15]   
See also in sourсe #XX -- [ Pg.67 , Pg.70 , Pg.71 , Pg.72 , Pg.77 , Pg.132 , Pg.540 ]

See also in sourсe #XX -- [ Pg.335 ]




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