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1.
Zusammenfassung Die Verteilungskoeffizienten (D) von Neptunium zwischen salpetersauren Lösungen, in denen dieses Transuranelement in (IV)-, (V)- und (VI)-wertigen Oxydationsstufen vorlag, und einem Anionenaustauscher wurden gemessen.Die VerteilungskoeffizientenD(IV) für das Np(IV) wurden nach Reduktion einer Probenreihe bestimmt, währendD(V) aus der Literatur bekannt war undD(VI) aus Analogiegründen gleichD(V) gesetzt wurde. Die Anteile der einzelnen Oxydationsstufen in der jeweiligen Lösung wurden quantitativ bestimmt. Aus diesen Daten ließen sich nun dieD-Werte auch rechnerisch ermitteln. Dabei stellte sich heraus, da\ in Systemen mit Oxydationsmitteln (Cr2O7 2- und Ce4+) im Austauscherharz nach kurzer Zeit eine Reduktion eintritt, die das Gleichgewicht nach Np(IV) verschiebt, und daßD dann nur durch den Anteil an Np(IV) bestimmt wird. In nichtoxydierenden Lösungen tragen alle Oxydationsstufen entsprechend ihrer Konzentration additiv zur Größe desD-Wertes bei.
Distribution of Np in nitric acid solution containing uranyl ion
The distribution coefficients (D) of Neptunium in the valence states (IV), (V) and (VI) between nitric acid solutions and an anion exchanger were determined.The distribution coefficientD(IV) for Np(IV) was determined after reduction of a series of samples,D(V) being taken from literature, andD(VI) was assumed to be equal toD(V) for reasons of analogy. The ratios of the valence states in the respective solutions were determined quantitatively. From this data, theD-values could also be ascertained by calculations. It was found that reduction takes place in the exchanger resin, which displaces the equilibrium towards Np(IV), andD is only determined by the protion of Np(IV). In solutions free of oxidizers,D is an additive value of all valence states and their respective concentrations.


Mit 7 Abbildungen

Herrn Univ.-Prof. Dr.Engelbert Broda zum 60. Geburtstag gewidmet.  相似文献   

2.
Nuclear test explosions and nuclear reactor wastes and accidents have released large amounts of radioactivity into the environment. Actinideions in waters often are not in a state of thermodynamic equilibrium and their solubility and migration behavior is related to the form in which the nuclides are introduced into the aquatic system. Chemical speciation, oxidation state, redox reactions, and sorption characteristics are necessary in predicting solubility of the different actinides, their migration behaviors and their potential effects on marine biota. The most significant of these variables is the oxidation state of the metal ion as the simultaneous presence of more than one oxidation state for some actinides in a solution complicates actinide environmental behavior. Both Np(V)O2 + and Pu(V)O2 +, the most significant soluble states in natural oxic waters, are relatively noncomplexing and resistant to hydrolysis and subsequent precipitation. The solubility of NpO2 + can be as high as 10−4M while that of PuO2 + is much more limited by reduction to the insoluble tetravalent species, Pu(OH)4, (pKsp≥56) but which can be present in the pentavalent form in aqautic phases as colloidal material. The solubility of hexavalent UO2 2+ in sea water is relatively high due to formation of carbonate complexes. The insoluble trivalent americium hydroxocarbonate, Am(OH)(CO3) is the limiting species for the solubility of Am(III) in sea water. Thorium(IV) is present as Th(OH)4, in colloidal form. The chemistry of actinide ions in the environment is reviewed to show the spectrum of reactions that can occur in natural waters which must be considered in assessing the environmental behavior of actinides. Much is understood about sorption of actinides on surfaces, the mode of migration of actinides in such waters and the potential effects of these radioactive species on marine biota, but much more understanding of the behavior of the actinides in the environment is needed to allow proper and reliable modeling needed for disposition of nuclear waste over many thousands of years. This paper has been presented as a Hevesy Medal Award Lecture by the medalist author at the 1st International Nuclear Chemistry Congress (1st-INCC), 22–29 May 2005, Kusadasi, Turkey  相似文献   

3.
The irradiation of aqueous nitric acid solutions generates transient, reactive species that are known to oxidize neptunium. However, nitrous acid is also a long-lived product of nitric acid irradiation, which reduces neptunium. When we irradiated nitric acid solutions of neptunium and measured its speciation by UV/Vis spectroscopy, we found that at short irradiation times, oxidation of Np(V) to Np(VI) occurred due to reactions with radicals such as ?OH, ?NO3 and ?NO2. However, at higher absorbed doses and after a sufficient amount of nitrous acid was produced, reduction of Np(VI) to Np(V) began to occur, eventually reaching an equilibrium distribution of these species depending on nitric acid concentration. Neptunium(IV) was not produced.  相似文献   

4.
Spectrophotometric investigations have been carried out on the disproportionation of Np(V) to form Np(IV) and Np(VI) in 1.1 mol⋅L−1 solutions of tributyl phosphate (TBP) and in N,N-dihexyl octanamide (DHOA) in n-dodecane medium. The Np(V) was found to coordinate with Np(IV) in 1.1 mol⋅L−1 TBP solution in n-dodecane to form a mixed valence “cation–cation” complex by bonding through an axial oxo group on Np(V). By contrast, this interaction was less prominent in the case of 1.1 mol⋅L−1 DHOA solutions. The effect of 1-octanol, added as phase modifier, on the disproportionation behavior of Np(V) was also investigated. An attempt was made to calculate the disproportionation/reduction rate constants for Np(V) under the conditions of these studies. Absorbance measurements on the Np stripped from organic phases revealed the occurrence of Np(V) in the aqueous phase.  相似文献   

5.
Capillary electrophoresis (CE) was used to separate the neptunium oxidation states Np(IV) and Np(V), which are the only oxidation states of Np that are stable under environmental conditions. The CE setup was coupled to an inductively coupled plasma mass spectrometer (Agilent 7500ce) using a Mira Mist CE nebulizer and a Scott-type spray chamber. The combination of the separation capacity of CE with the detection sensitivity of inductively coupled plasma mass spectrometry (ICP-MS) allows identification and quantification of Np(IV) and Np(V) at the trace levels expected in the far field of a nuclear waste repository. Limits of detection of 1?×?10-9 and 5?×?10-10 mol L-1 for Np(IV) and Np(V), respectively, were achieved, with a linear range from 10-9 to 10-6 mol L-1. The method was applied to study the redox speciation of the Np remaining in solution after interaction of 5?×?10-7 mol L-1 Np(V) with Opalinus Clay. Under mildly oxidizing conditions, a Np sorption of 31% was found, with all the Np remaining in solution being Np(V). A second sorption experiment performed in the presence of Fe2+ led to complete sorption of the Np onto the clay. After desorption with HClO4, a mixture of Np(IV) and Np(V) was found in solution by CE–ICP–MS, indicating that some of the sorbed Np had been reduced to Np(IV) by Fe2+.  相似文献   

6.
In this paper, to separation Cs(I) effectively from HLW, a kind of chromatographic rein was synthesized through immobiling calix[4]-bis-crown-6 on the macroporous polystyrene -divinylbenzene polymeric material. The synthesized chromatographic resin showed high ability to absorb Cs(I). While the radioactive elements Pu(III), Np(V), U(VI), Th(IV), as well as all of the fission and non-fission products showed almost no sorption towards chromatographic rein. The separation of Cs from HLW can be realized through adjusting the valence of Np and Pu or adding H2C2O4. All the results showed that the application of the new chromatographic rein to the analysis of HLW is possible.  相似文献   

7.
Sulfate, one of the inorganic constituents in the groundwater of nuclear waste repository, could affect the migration of radioactive materials by forming complexes. Spectrophotometric and microcalorimetric titrations were performed to identify the Np(V)/sulfate complex and determine the equilibrium constants and enthalpy of complexation at 10–70°C. Results show that the complexation of Np(V) with sulfate is weak but slightly enhanced by the increase in temperature. The complexation is endothermic and becomes more endothermic with the increase in temperature. The enhanced complexation at elevated temperatures is due to the increasingly larger entropy of complexation that exceeds the increase in enthalpy, indicating that the complexation of Np(V) with sulfate is entropy-driven.  相似文献   

8.
The solubilities of NpO2(s) in the KURT (KAERI Underground Research Tunnel) granitic groundwater with low ionic strength were measured experimentally and calculated by a geochemical code. Then these results were compared with each other as well as with foreign results. The concentrations of neptunium were measured as 6·10−8−2·10−8 mol/L at a pH = 9.5–11.1 and Eh = −0.2 V, and less than 5·10−9 mol/L at a pH = 11.8–13.0 and Eh = −0.3–0.44 V. The dominant aqueous species were presumed as Np(OH)x(CO3)y 4−x−2y complexes and Np(OH)4(aq) at pH = 9.5–13 under the Eh<−0.2 V reducing condition.  相似文献   

9.
Preparation of source and sample holder is described for the Mössbauer studies of237Np and238U. For the Mössbauer measurement of237Np, a source assembly with small sources of241Am metal was developed taking account of the transport regulations for radioactive substances. The source assembly of241Am showed a sufficient activity enough to measure the Mössbauer spectra of237Np. In order to handle237Np compounds safely, trebly sealed holders were designed which could encapsulate237Np samples without the seepage of liquid helium. A source for238U Mössbauer measurement was also developed from a highly pure242PuO2.  相似文献   

10.
Photolysis of benzyl phenylacetate (ACO2A), benzyl p-methylphenylacetate (BCO2A) and 1-naphthyl phenylacetate (ACO2Np) in homogeneous and micellar solutions results in products typical of radical coupling reactions and loss of carbon dioxide. The cage effects upon direct photolysis of these esters in acetonitrile are significantly greater than zero and those in SDS or HDTBr micellar solutions are even greater. In the triplet sensitization reaction of ACO2Np in micellar solutions the cage effects are smaller than those obtained upon direct irradiation. However, the application of a 0.05 or 0.2 T external magnetic field in the photolysis in micellar solutions decreases the cage effects dramatically. All these results suggest that the photoextrusions of carbon dioxide from these esters proceed via radical intermediates, and upon direct photolysis the reactive states for the cleavage reaction involve both singlet and triplet excited states.  相似文献   

11.
Zusammenfassung Das Verteilungsverhalten von237Np–239Np zwischen salpetersauren Lösungen verschiedener Konzentration und einem Anionenaustauscher (Dowex 1X8) wurde untersucht. Durch Reduktion mit Fe2++Hydrazin konnte quantitativ das Np(IV) hergestellt und dessen Verteilungskoeffizient (D) in 1n-10n-HNO3 bestimmt werden. Mit Hydrazin allein und bei Lösungen ohne Reduktionsmittel wurden stark schwankendeD-Werte gefunden, die auf unterschiedliche Prozentsätze an Np(IV), Np(V) und Np(VI) zurückzuführen waren. Durch die Bestimmung der Anteile der einzelnen Oxidationsstufen konnten jedoch die jeweiligenD-Werte [D(IV),D(V),D(VI)] berechnet werden. Die mit dieser Methode erhaltenen Werte stimmten gut mit den Daten überein, die an Systemen gewonnen wurden, in denen jeweils nur eine Neptuniumoxidations-stufe vorlag.
The ion exchange behaviour of neptunium in nitric acid solutions
The distribution of237Np–239Np between nitric acid solutions of different concentration and an anion exchanger (Dowex 1X8) was investigated. By reduction with Fe2++hydrazine, the Np(IV) was obtained quantitatively and its distribution coefficients (D) in 1n to 10n-HNO3 were determined. With hydrazine alone and without any reduction media, strongly varyingD-values were found. This was due to different amounts of Np(IV), Np(V), and Np(VI) in the solutions. By determining the fractions of the individual oxidation states the correspondingD-values [D(IV),D(V), andD(VI)] could be calculated. The data obtained by this method agreed well with theD-values resulting from determinations of systems, in which the individual Np-oxidation state was the only component of the corresponding solution.


Mit 4 Abbildungen

Herrn Prof. Dr.Hans Nowotny gewidmet.  相似文献   

12.
We have, previously, reported on the HPLC elution behavior of the Th, Pa, U, Np, and Am metallofullerenes and the UV/vis/NIR absorption spectra of the Th@C84 and U@C82 species. In this paper, the followings are reported: (1) Pu metallofullerenes were produced and their HPLC elution behavior was investigated using a radiotracer technique. The HPLC chromatogram of this metallofullerene was found to be almost the same as that of the Np and Am metallofullerenes. (2) The oxidation states of Th@C84 and U@C82 produced in macroscopic quantities were examined by XANES (X-ray absorption near edge structure) measurements. The oxidation state of the U atom in the C82 fullerene cage was estimated to be 3+ with the formal charge of the ionic molecule being U3+@C82 3-.  相似文献   

13.
Migration experiments with 237Np(V) and 241Am(III) have been performed using a column system, packed with loess, taken from Shanxi, China. The adsorption mechanism of 237Np and 241Am on the loess was examined by a chemical extraction method. Most of 237Np was adsorbed on the influent edge of the column, and the adsorbtion was mainly controlled by surface complexation. However, the migration of 237Np in loess media could be roughly evaluated by the distribution coefficient. In the case of 241Am, particulate, the 241Am species was formed in the influent solution and moved in the column. The 241Am adsorbed on loess was controlled by irreversible reactions. The migration behavior of particulate 241Am in loess media could be expressed by the filtration theory.  相似文献   

14.
The reliable separation of neptunium from dissolved nuclear fuel assumes the ability to maintain a preferred oxidation state. However, regardless of its initial redox speciation, a series of reactions occurs in nitric acid to create a mixture of oxidation states including Np(V), Np(VI) and sometimes Np(IV). To further complicate the situation, irradiated solutions such as fuel dissolution contain both transient and long-lived radiolysis products which may be strongly oxidizing or reducing. Thus, irradiation may be expected to impact the equilibrium distributions of the various neptunium valences.We have irradiated nitric acid solutions of neptunium with 60Co gamma-rays, and measured radiolytically-induced changes in neptunium valences, as well as the nitrous acid concentration, by UV/Vis spectroscopy. It was found that in 4 M HNO3 at low absorbed doses, the oxidizing radicals oxidized Np(V) to Np(VI). However, as the irradiation proceeded the concentration of nitrous acid became sufficient to reduce Np(VI) to Np(V), and then continued irradiation favored this reduction until an equilibrium was achieved in balance with the oxidation of Np(V) by nitric acid itself. The starting abundances of the two neptunium valences did not affect the final equilibrium concentrations of Np(V) and Np(VI), and no Np(IV) was detected.  相似文献   

15.
An establishéd electrodeposition method for separating americium and plutonium from highly saline used-fuel-leaching solutions has been extended to the determination of Np and U in saline groundwaters. The interference of major ionic species in groundwater on the yield was investigated using three groundwaters of varying salinity (ionic strength I=1.37, 0.0748 and 0.0253 mol/l). High average yields (>92%), and good reproducibility were obtained for Np and U electroplated from solutions with ionic strength less than 0.1. The greatest interferences from individual ions were caused by Mg2+ and HCO 3 .  相似文献   

16.
Systematics of hyperfine parameters from 237Np Mössbauer resonance data of compounds with Np in a high formal charge state are discussed with respect to electronic structure properties. In neptunyl(VI) species, we find a linear correlation between the isomer shift and the strength of quadrupole interaction. Both scale linearly with the actinide-oxygen bond length, stressing the central role of this parameter. Some compounds show paramagnetic relaxation spectra which makes their analysis difficult. The hyperfine interactions are often not rotational symmetric indicating a deviation from the simple linear O-Np-O configuration. Mössbauer spectra of NpO3·2H2O reveal that this compound should be described as a neptunyl. A comparison of hyperfine parameter systematics indicates that the Np valence electron properties in Np(VII) species are basically similar to those in Np(VI) neptunyls.  相似文献   

17.
Symmetry restricted and unrestricted Hartree-Fock calculations at theab initio LCAO-MO-SCF level have been carried out on the ground, core and valence hole states of N2 at various N-N distances. A one-particle criterion for symmetry breaking is discussed. Strong broken-symmetry effects in the inner valence molecular region of N2 have been found at larger N-N distances. This breaking of symmetry accompanying the symmetry unrestricted Hartree-Fock calculations of the inner valence hole states at large internuclear separations can be considered to be a common phenomenon with all highly symmetric molecules. The outer valence broken-symmetry effects with N2 have showed some deviations as compared with these effects in the inner valence and core molecular regions.  相似文献   

18.
A substoichiometric isotope-dilution method is described for the determination of monomethylarsonate, MeAs(V), and dimethylarsinate, Me2As(V). After the separation of MeAs(V) and Me2As(V) by extraction as their iodides into benzene, these methylated arsenic species are complexed with a substoichiometric amount of diethyldithiocarbamate in benzene, and the uncomplexed methylarsenic species are removed. The relative standard deviations for the substoichiometric extraction of MeAs(V) and Me2As(V) are 0.55% and 1.1%, respectively. This substoichiometric speciation of methylated arsenic together with an earlier substoichiometric method for speciation of inorganic arsenic species was applied to the speciation of arsenic in an acid-digested solution of a macro-algae sample. It was demonstrated that almost all the arsenic in this solution was Me2As(V) even after the digestion with nitric acid.  相似文献   

19.
The study of the redox chemistry of mid-actinides (U−Pu) has historically relied on cerium as a model, due to the accessibility of trivalent and tetravalent oxidation states for these ions. Recently, dramatic shifts of lanthanide 4+/3+ non-aqueous redox couples have been established within a homoleptic imidophosphorane ligand framework. Herein we extend the chemistry of the imidophosphorane ligand (NPC=[N=PtBu(pyrr)2]; pyrr=pyrrolidinyl) to tetrahomoleptic NPC complexes of neptunium and cerium ( 1-M , 2-M , M=Np, Ce) and present comparative structural, electrochemical, and theoretical studies of these complexes. Large cathodic shifts in the M4+/3+ (M=Ce, U, Np) couples underpin the stabilization of higher metal oxidation states owing to the strongly donating nature of the NPC ligands, providing access to the U5+/4+, U6+/5+, and to an unprecedented, well-behaved Np5+/4+ redox couple. The differences in the chemical redox properties of the U vs. Ce and Np complexes are rationalized based on their redox potentials, degree of structural rearrangement upon reduction/oxidation, relative molecular orbital energies, and orbital composition analyses employing density functional theory.  相似文献   

20.
Hydroxamic acids are salt free, organic compounds with affinities for cations such as Fe3+, Np4+ and Pu4+, and have been identified as suitable reagents for the control of Pu and Np in advanced nuclear fuel reprocessing. The results of a UV-visible, near-IR spectrophotometric study of the 1:1 and 2:1 complexes formed between formo- and aceto-hydroxamic acids (FHA, AHA) and Np(IV) ions are interpreted using speciation diagrams for the identification of the species present at different pH and ligand to metal ratios. A kinetic model that describes the instability of the complex due to hydrolysis of the hydroxamate moiety, previously developed for the Fe(III)-AHA complexes (Andrieux et al. in J. Solution Chem. 36:1201–1217, [2007]), is tested here against experimental Np(IV)-FHA data. Consequently, the complexation constant for formation of the 1:1 Np(IV)-FHA complex in nitric acid is estimated at K 1=2715 and indications are that complexation protects the ligand against hydrolysis at 0.1>pH>−0.1.  相似文献   

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