- Electrochemical oxidation of Am(III) and Am(V) ions in HNO3 solutions containing potassium phosphotungstate K10P 2W17O61
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The kinetics of electrochemical oxidation of Am(III) and Am(V) on Pt electrode in solutions of concentrated nitric acid containing potassium phosphotungstate was studied spectrophotometrically. The processes occurring in the system follow the rate law for reversible reaction. The direct reaction is first-order with respect to the concentration of Am(III) ions, and the reverse process is a zero-order reaction.
- Erin,Baranov,Volkov,Chistyakov
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p. 563 - 566
(2008/10/09)
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- Reduction of Am(IV) with water in KHCO3 + K2CO 3 solutions
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Reduction of Am(IV) with water in KHCO3 and K2CO 3 solutions (pH 8.5-10.5) was studied spectrophotometrically at 54-70°C. The Am(IV) concentration decreases, following the first-order rate law. The reduction rate increases with pH (Δ log k/ΔpH = 0.4), but decreases with increase in (HCO3- + CO3 2-) concentration. It was assumed that the thermally excited Am(IV) ion forms a dimer with unexcited Am(IV). The dimer dissociates into two Am(III) ions and H2O2. Hydrogen peroxide reduces two more Am(IV) ions. In this process, the excited Am(III) ion appears, which transfers the excitation to Am(IV) at collision. Thus, a chain process is initiated. This scheme can also explain the kinetics of Am(VI) and Np(VII) reduction in carbonate solutions.
- Shilov
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p. 279 - 282
(2008/10/08)
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- Electrochemical Oxidation of Am(III) Ions in HNO3 Solutions
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Formal oxidation potentials (E(0)p) of the Am(IV)/Am(III) couple were measured and the kinetics of electrochemical oxidation of Am(III) on platinum electrode in concentrated solutions of nitric acid (1-6 M) containing potassium phosphotungstate K10P2W17O61 (KPW) was studied. The formal potential E(0)p only slightly depends on the concentration of HNO3 and isshifted toward the negative region by ~1.0 V as compared with t he standard values. The extent of Am(III) oxidation increases with increasing KPW concentration and decreasing concentration of nitric acid. Electrochemical oxidation of Am(III) is accompanied by radiochemical reduction of Am(IV) and is described by the equation -dC(Am(III))/dt=(k + k1)*C(Am(III)) - k1*C0 - k0, where k is the apparent rate constant of electrochemical oxidation of Am(III), k1 is the apparent rate constant of Am(IV) reduction, and k0 is the constant of radiation-chemical reduction of Am(IV).
- Erin, E. A.,Baranov, A. A.,Volkov, A. Yu.,Chistyakov, V. M.,Timofeev, G. A.
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p. 350 - 353
(2008/10/08)
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- Investigation of 137Cs+, 85Sr2+ and 241Am3+ ion exchange on thorium phosphate hydrogenphosphate and their immobilization in the thorium phosphate diphosphate
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Thorium phosphate diphosphate (TPD) has been proposed as a host matrix for the long-term storage of tetravalent actinides such as U(IV), Np(IV) and Pu(IV), which form solid solutions with TPD. Small amounts of di- or trivalent cations can also be immobilized in this matrix. Another method of loading of TPD, using the ion-exchange properties of thorium phosphate hydrogenphosphate (TPHP), a precursor of TPD, was applied to 137Cs+, 85Sr2+ and 241Am3+. The adsorption of these cations on TPHP was studied in terms of pH in NaClO4 and NaNO3 media. The ion-exchange process on TPHP was found to be reversible for 85Sr2+ and 241Am3+. Doped TPHP obtained in this way was heated at 1050°C until TPD was formed. Several leaching tests were performed in acidic media on TPD doped with radionuclides with ionic strength equal to 0.1 M. The average partial order related to the proton was found to be equal to 0.24 ± 0.10 and the normalized leaching rate constant was in the range of 3 × 10-6 to 2 × 10-5 gm-2 d-1. These results are similar to those obtained for thorium plutonium(IV) phosphate diphosphate solid solutions. On the basis of the results obtained from the adsorption and leaching studies, this adsorption-immobilization process, based on the TPHP matrix, can be proposed for the decontamination of low level radioactive liquid wastes.
- Pichot,Dacheux,Brandel,Genet
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p. 1017 - 1023
(2007/10/03)
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- Kinetics of dissociation of trivalent actiniae chelates of TMDTA
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Measurements by a radiotracer technique show that the dissociation of TMDTA (trimethylenediamine-N,N-tetraacetic acid) chelates with Am, Cm, Bk, Cf, and Eu proceeds through an acid-catalyzed pathway. The rates of dissociation of An(TMDTA)- are 2 orders of magnitude faster than those of the corresponding EDTA chelates, presumably due to the greater lability of the nitrogen atom in the six-membered nitrogen-metal-nitrogen ring of TMDTA chelates. The rate of dissociation also decreased with decreasing metal ion radius. A proton-catalyzed mechanism similar to that for dissociation of EDTA complexes of lanthanide and actinide cations is consistent with the rate data.
- Muscatello, Anthony C.,Choppin, Gregory R.,D'Olieslager, Willem
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p. 993 - 997
(2008/10/08)
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- Preparation and properties of americium(VI) in aqueous carbonate solutions
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Hexavalent americium is conveniently prepared as a soluble, red-brown complex in aqueous Na2CO3 or NaHCO3 by O3 or S2O8-2 oxidation of americium in lower valence states. The solutions in 0.1 to 0.5 M NaHCO3 are stable at 90° to reduction by H2O, Cl-, and Br-, but are readily reduced by I-, N2H4, H2O2, NO2-, and NH2OH. Reduction by water occurs at 90° in 2 M Na2CO3. The spectra of Am(VI) in the 500-1300 mμ region are markedly different in carbonate solutions than in acid. The infrared spectra of solid sodium americyl(VI) carbonates establish the presence of the O-Am-O group in the carbonate complex. Based on the properties of Am(VI) in carbonate solution, a new procedure for the preparation of Am(V) free from traces of Am(III) and a useful process for the separation of americium and curium are reported.
- Coleman,Keenan,Jones,Carnall,Penneman
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