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1.
A narrow span (E o ±0.1 V) controlled potential coulometric method has been developed for the determination of neptunium in 1M H2SO4 with a RSD of 0.2%. The main advantage of this method over the existing coulometric methods is that it can tolerate up to a 5-fold excess of plutonium. The method involves carrying out the electrolysis to about 97% and calculating by an iterative computation the formal electrode potential in situ, which is used to calculate the total amount present in the sample. The method consists in oxidation of all the neptunium to Np (VI) by Ce(IV), destruction of excess Ce(IV) and reduction of Np(VI) to Np(V) by NaNO2, destruction of excess nitrite by sulfamic acid followed by coulometric titration of Np(V) to Np(VI).  相似文献   

2.
A method for controlled potential coulometric determination of neptunium by titration with internally electrolytically generated iron(II) has been developed. The method involves oxidation of Np to Np(VI) by Ce(IV), destruction of excess of Ce(IV) by NaNO2 followed by determination of neptunium by reduction of Np(VI) to Np(IV) by internal generation of Fe(II). The method was employed for various neptunium solution samples and a precision of ±0.25% at 2–5 mg level of neptunium was obtained.  相似文献   

3.
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   

4.
A rapid and sensitive method for the photometric determination of trace amounts of neptunium and plutonium from their mixtures is described. Np(IV) is selectively extracted from about 1 M HNO3 medium with TTA in xylene retaining Pu in the nonextractable trivalent state in the aq. phase with ferrous sulfamate. Plutonium in the aqueous phase is subsequently oxidized with NaNO2 to the highly extractable tetravalent state and extracted with TTA. Np(IV) as well as Pu(IV) thus extracted are finally estimated in the organic phase itself spectrophotometrically employing xylenol orange as the chromogenic reagent. Their molar absorptivities are in the 5 × 104 range. Beer's law is valid up to 2.4 ppm Np and 3.5 ppm Pu. The color of the solutions is stable for at least 48 hr. The method tolerates large excess of several common contaminants encountered during spent fuel reprocessing. Cerium(IV) and phosphoric acid, however, interfere with the final estimation.  相似文献   

5.
Hg2+2 can be determined gravimetrically as Hg2Cl2 provided that its disproportionation is avoided by the presence of a mercury(II) salt and the use of a slight excess only (0.01 M) of chloride ions. The determination of Hg2+2 in a Ce(IV)-Hg(1) reaction mixture in 1 M perchloric acid was achieved by the prior removal of the remaining Ce(IV) with Fe(II).  相似文献   

6.
The interaction of Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) with Al(III) in solutions at pH 0–4 was studied by the spectrophotometric method. It was shown that, in the range of pH 3–4, the hydrolyzed forms of neptunyl and plutonyl react with the hydrolyzed forms of aluminium. In the case of Pu(VI), the mixed hydroxoaqua complexes (H2O)3PuO2(-OH)2Al(OH)(H2O)3 2+ or (H2O)4PuO2OAl(OH)(H2O)4 2+ are formed at the first stage of hydrolysis. Np(VI) also forms similar hydroxoaqua complexes with Al(III). The formation of the mixed hydroxoaqua complexes was also observed when Np(IV) or Pu(IV) was simultaneously hydrolyzed with Al(III) at pH 1.5–2.5. The Np(IV) complex with Al(III) has, most likely, the formula (H2O) n (OH)Np(-OH)2Al(OH)(H2O)3 3+. At pH from 2 to 4.1 (when aluminium hydroxide precipitates), the Np(V) or Nd(III) ions exist in solutions with or without Al(III) in similar forms. When pH is increased to 5–5.5, these ions are almost not captured by the aluminium hydroxide precipitate.  相似文献   

7.
The reactions of the ions of tervalent and quadrivalent actinides and lanthanides with hydrated electrons eaq and CO3 radicals in concentrated carbonate solutions have been studied by microsecond pulse radiolysis, using spectrophotometric recording of short-lived particles. It is shown that the rate of the reactions of eaq with carbonato complexes of Ce(IV), Pu(IV), and Np(IV) is controlled by diffusion. The carbonato complex of Eu(III) reacts with eaq appreciably more slowly. A linear relationship is obtained between the logarithm of the rate constant for the reactions of CO3 with the carbonato complexes of Am(III), Ce(III), and Pu(III) and the redox potential of the complexes. The rate of the reaction of CO3 with Np(III) in carbonate solutions is controlled by diffusion.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 28–32, January, 1990.  相似文献   

8.
Godbole AG  Patil SK 《Talanta》1979,26(4):330-332
A simple and quick method for the potentiometric determination of neptunium on the 2-5 mg scale has been developed. It consists of oxidation to Np(VI) by AgO or fuming with HClO(4), destruction of excess of AgO by sulphamic acid, reduction of Np(VI) to Np(IV) with a slight excess of standard Fe(II) in 2M H(2)SO(4) and potentiometric titration of the excess of Fe(II) with standard Ce(IV). The precision is +/-0.5%.  相似文献   

9.
Polymerization of methyl methacrylate was carried out in aqueous nitric acid in the temperature range 26–40°C, with the redox initiator system ceric ammonium nitrate–isopropyl alcohol. A short induction period was observed, as well as the attainment of a limiting conversion, and the total ceric ion consumption with reaction time. The reaction orders were 1/2 and 3/2 with respect to the IPA and monomer concentration, respectively, within the range (3–5) × 10?3M of Ce(IV). But at lower Ce(IV) concentration (≤ 1 × 10?3M), the order with respect to monomer and Ce(IV) changed to 1 and 1/2, respectively. The rate of ceric ion disappearance was first order with respect to Ce(IV) concentration and (RCe)?1 was proportional to [IPA]?1. Both the rate of polymerization and the rate of ceric ion consumption increase with rise in temperature. The average-molecular weight can be controlled by variations in IPA, Ce(IV), and monomer concentrations, and in temperature. A kinetic scheme involving oxidation of IPA by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by bimolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included.  相似文献   

10.
The extraction of Np(IV), Zr, Nb, Cs, Ce(III) and Am(III) from nitric acid solutions containing oxalate and phosphate ions by solutions of 1-phenyl-3-methyl-4-benzoylpyrazolon-5 (PMBP) and tri-n-butyl phosphate (TBP) in benzene has been investigated. A solution 0.1M in respect to PMBP and 0.25M in respect to TBP was found to extract 99% of neptunium from aqueous solutions 1M in respect to H3PO4 and 0.5M in respect to HNO3. Under these conditions, the extraction of the other investigated elements does not exceed 0.1%. Based on this finding, a procedure was developed to determine243Am through its daughter product239Np in solutions containing large quantities of curium and its fission products. The sensitivity of the procedure is 1·10−7 mg of243Am in the sample. The243Am content is obtained by calculation from measurements of the γ-activity of the extracted239Np. The purification ratio of239Np is∼105 from Zr, Nb and Ru, ∼108 from Ce and Cm and >1012 from Cs.  相似文献   

11.
The polymerization of acrylonitrile (M) initiated by the sorbitol (R)-Ce(IV) redox system has been studied in sulphuric acid in the range 30–40° under nitrogen. At moderately high concentrations of Ce(IV) (0.00015-0.02 M), the rate of polymerization (Rp) is proportional to [M]32 and [R]12 and the rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. At lower concentration of Ce(IV) (0.00005–0.00015 M) Rp is proportional to [M], [R]1/2 and [Ce(IV)]1/2 and rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. The effects of certain salts, acid, solvent and temperature on both rates have been investigated. A kinetic scheme involving mutual termination has been proposed and various rate and energy parameters evaluated. At still higher concentration of Ce(IV) (0.02 M), a linear mode of termination seems to operate.  相似文献   

12.
The redox potential of the Ce(IV)/Ce(III) DOTA is determined to be 0.65 V versus SCE, pointing out a stabilization of ~13 orders of magnitude for the Ce(IV)DOTA complex, as compared to Ce(IV)aq. The Ce(III)DOTA after electrochemical oxidation yields a Ce(IV)DOTA complex with a t1/2 ~3 h and which is suggested to retain the “in cage” geometry. Chemical oxidation of Ce(III)DOTA by diperoxosulfate renders a similar Ce(IV)DOTA complex with the same t1/2. From the electrochemical measurements, one calculates logK (Ce(IV)DOTA2?) ~ 35.9. Surprisingly, when Ce(IV)DOTA is obtained by mixing Ce(IV)aq with DOTA, a different species is obtained with a 2 : 1(M : L) stoichiometry. This new complex, Ce(IV)DOTACe(IV), shows redox and spectroscopic features which are different from the electrochemically prepared Ce(IV)DOTA. When one uses thiosulfate as a reducing agent of Ce(IV)DOTACe(IV), one gets a prolonged lifetime of the latter. The reductant seems to serve primarily as a coordinating ligand with a geometry which does not facilitate inner sphere electron transfer. The reduction process rate in this case could be dictated by an outer sphere electron transfer or DOTA exchange by S2O32?. Both Ce(IV)DOTA and Ce(IV)DOTACe(IV) have similar kinetic stability and presumably decompose via decarboxylation of the polyaminocarboxylate ligand.  相似文献   

13.
A milking process is described for preparing 239Np from 243Am. The process includes the stabilization of Np(IV) with ascorbic acid, isolation of Np(IV) by extraction with TOPO/dodecane and stripping of Np with (NH4)2CO3. The yield amounts to 60%. During milking, about 2% of the 243Am ends up in the scrub which is collected and reprocessed together with the remaining feed after 25 operations using extraction chromatography.  相似文献   

14.
The redox-initiated polymerization of methyl methacrylate (MMA) by the Ce(IV)-malic acid system has been carried out in aqueous medium under an inert atmosphere. The rate of polymerization was found to be proportional to [MMA]3/2 [MA]1/2 [Ce(IV)]1/2 and the rate of ceric ion disappearance was proportional to [Ce(IV)] but independent of [MMA]. The rate increased linearly up to a certain range of [MA], above which it remained constant. Increasing [H2SO4] decreased the rate. The activation energy was found to be 57.44 kJ/mol.  相似文献   

15.
Abstract

Polymerizations of methyl methacrylate (MMA) and acrylonitrile (AN) were carried out in aqueous nitric acid at 30°C with the redox initiator system ammonium ceric nitrate-ethyl cellosolve (EC). A short induction period was observed as well as the attainment of a limiting conversion for polymerization reactions. The consumption of ceric ion was first order with respect to Ce(IV) concentration in the concentration range (0.2–0.4) × 10?2 M, and the points at higher and lower concentrations show deviations from a linear fit. The plots of the inverse of pseudo-first-order rate constant for ceric ion consumption, (k 1)?1 vs [EC]?1, gave straight lines for both the monomer systems with nonzero intercepts supporting complex formation between Ce(IV) and EC. The rate of polymerization increases regularly with [Ce(IV)] up to 0.003 M, yielding an order of 0.41, then falls to 0.0055 M and again shows a rise at 0.00645 M for MMA polymerization. For AN polymerization, R p shows a steep rise with [Ce(IV)] up to 0.001 M, and beyond this concentration R p shows a regular increase with [Ce(IV)], yielding an order of 0.48. In the presence of constant [NO? 3], MMA and AN polymerizations yield orders of 0.36 and 0.58 for [Ce(IV)] variation, respectively. The rates of polymerization increased with an increase in EC and monomer concentrations: only at a higher concentration of EC (0.5 M) was a steep fall in R p observed for both monomer systems. The orders with respect to EC and monomer for MMA polymerization were 0.19 and 1.6, respectively. The orders with respect to EC and monomer for AN polymerization were 0.2 and 1.5, respectively. A kinetic scheme involving oxidation of EC by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by biomolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included.  相似文献   

16.
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   

17.
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   

18.
The oxidation—reduction reactions o f neptunium in molten RbCl—CsCl.Standard potentials of the systems NpO2(VI)—NpO2(V) and Np(IV)—Np(III) and the equilibrium constant of the following disproportionation reaction 2NP4+ + 2H2O + 2Cl- ? NpO+2 + Np3++ 4HCI have been determined in a (Rb 0,25; Cs 0,75 )C1 melt in the temperature range 660—750°C by absorption spectrophotometry. The results are com- pared with those obtained previously in (Li 0,7; K 0,3)C1, (Li, K)C1 eutectic and (Li 0,55; CsO,45)Cl.  相似文献   

19.
Americium(III) can be quantitatively extracted with 1 M diisoamylsulphoxide in Solvesso-100 from aqueous 0.02 M HNO3—2.5 Al(NO3)3 solutions and, after dilution of the extract with ethanol and nitric acid, determined in the organic phase with arsenazo-III. The apparent molar absorptivity is 1.58 × 105 l mol-1 cm-1 at 652 nm. The system obeys Beer's law within the range 0.1–1.6 μg Am ml-1; 0.11 μg Am ml-1 is determined with a reproducibility better than ±2%. Relatively large amounts of Ca(II), Cr(III), Fe (III), U(VI), Cl-, NO2-, NO3- and F- are tolerated. Interferences of Ce(IV), Pu(IV) and Th(IV) are eliminated by prior extraction with 2-thenoyltrifluoroacetone; only europium(III) interferes appreciably. Colour development is almost instantaneous and absorbances are virtually constant for 12 h.  相似文献   

20.
Four types of neptunyl(VI) hydroxides have been synthesized by chemical oxidation of Np(IV) instead of ozone oxidation of Np(V) which caused the partial oxidation to the heptavalent state. NpO2(OH)2 (I) and NpO2(OH)2·H2O (orthorhombic type) (II) have been obtained by adding pyridine to the solution at 373K and 343K, respectively. NpO2(OH)2·H2O (hexagonal type) (III) and NpO2(OH)2·xH2yNH3 (x+y=1) (IV) have been prepared by using LiOH and NH4OH, respectively. The four materials have been characterized by X-ray powder diffraction patterns, thermogravimetric analysis and237Np Mössbauer spectra. The237Np Mössbauer spectrum of (I) measured first time as anhydrous neptunyl(VI) hydroxide (δ=?46.2 mm/s,e 2 qQ=193 mm/s and η=0.16 at 4.8K) has more distinct five-line Mössbauer pattern than those of (II), (III) and (IV). The Mössbauer spectra for (II), (III) and (IV) are slightly different from each other. The structural information has been obtained from these data.  相似文献   

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