Literature Review: Reduction of Np(v) to Np (Iv)-Alternatives to Ferrous Sulfamate

Kessinger, G.; Kyser, Edward A.; Almond, Philip M.

doi:10.2172/969037

Cited by 6 publications

(8 citation statements)

References 9 publications

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“…Ferrous sulfamate has historically been used to reduce Np(V) to Np(IV) in both ion exchange and solvent extraction applications. [12] The two Np spectra presented on Figure 4 are very similar, except for the very broad peak centered at approximately 425 nm which can be attributed to Fe(II) in the solution. Figure 5 compares the UV-vis spectra of Pu solutions in which HAN was added to an aliquot of the Pu stock solution prior to combining with the lactic acid and DTPA and in which Pu was added to a solution containing lactic acid, DTPA, and HAN.…”

Section: Reduction Of Actinide Valences Using Han and Fsmentioning

confidence: 78%

“…Both HAN and FS will reduce Pu(IV) to Pu(III) and FS will reduce Np(V) to Np(IV). [11][12] The four solutions prepared for study included: (1a) Np + HAN added to 1.5 M lactic acid/0.05 M DTPA, (2a) Pu + HAN added to 1.5 M lactic acid/0.05M DTPA, (3a) Np + FS added to 1.5 M lactic acid/0.05 M DTPA, and (4a) Pu + FS added to 1.5 M lactic acid/0.05 M DTPA. Prior to recording the UV-vis spectrum of each solution, the pH was adjusted to nominally 2.8.…”

Section: Srnl-sti-2010-00502mentioning

confidence: 99%

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Distribution of Actinides Between the Aqueous and Organic Phases in the Talspeak Process

Rudisill¹,

Kyser²

2010

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SUMMARYOne objective of the US Department of Energy's Office of Nuclear Energy (DOE-NE) is the development of sustainable nuclear fuel cycles which improve uranium resource utilization, maximize energy generation, minimize waste generation, improve safety, and complement institutional measures limiting proliferation risks.[1] Activities in progress which support this objective include the development of advanced separation technologies to recover the actinides from used nuclear fuels. With the increased interest in the development of technology to allow closure of the nuclear fuel cycle, the TALSPEAK process is being considered for the separation of Am and Cm from the lanthanide fission products in a next generation reprocessing plant. However, at this time, the level of understanding associated with the chemistry and the control of the process variables is not acceptable for deployment of the process on an industrial scale. To address this issue, DOE-NE is supporting basic scientific studies focused on the TALSPEAK process through its Fuel Cycle Research and Development (R&D) program. One aspect of these studies is an experimental program at the Savannah River National Laboratory (SRNL) in which temperature-dependent distribution coefficients for the extraction of actinide elements in the TALSPEAK process were measured. The data were subsequently used to calculate conditional enthalpies and entropies of extraction by van't Hoff analysis to better understand the thermodynamic driving forces for the TALSPEAK process.In the SRNL studies, the distribution of Pu(III) in the TALSPEAK process was of particular interest. A small amount of Pu(III) would be present in the feed due to process losses and valence adjustment in prior recovery operations. Actinide elements such as Np and Pu have multiple stable oxidation states in aqueous solutions; therefore the oxidation state for these elements must be controlled in the TALSPEAK process, as the extraction chemistry is dependent upon the actinide's valence. Since our plans included the measurement of Pu(III) distribution coefficients using a Np(V) solution containing small amounts of 238 Pu, it was necessary to demonstrate that the desired oxidation states of Np and Pu are produced and could be stabilized in a buffered lactate solution containing diethylenetriaminepentaacetic (DTPA). The stability of Np(V) and Pu(III) in lactic acid/DTPA solutions was evaluated by ultraviolet-visible (UV-vis) spectroscopy. To perform the evaluation, Np and Pu were added to solutions containing either hydroxylamine nitrate (HAN) or ferrous sulfamate (FS) as the reductant and nominally 1.5 M lactic acid/0.05 M DTPA. The pH of the solution was subsequently adjusted to nominally 2.8 as would be performed in the TALSPEAK process.In the valence adjustment study, we found that it was necessary to reduce Pu to Pu(III) prior to combining with the lactic acid and DTPA. The Pu reduction was performed using either HAN or FS. When FS was used, Np was reduced to Np(IV). The spectroscopic studies showed t...

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Section: Reduction Of Actinide Valences Using Han and Fsmentioning

confidence: 78%

Section: Srnl-sti-2010-00502mentioning

confidence: 99%

Distribution of Actinides Between the Aqueous and Organic Phases in the Talspeak Process

Rudisill¹,

Kyser²

2010

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“…The proposed mechanism of the partitioning of lactate into the organic phase matches very well with recent 14 C-labeled lactate liquidliquid distribution studies reported by Grimes. 12 Del Cul also observed the presence of lactate in the organic phase. 13 The agreement between our data and the slopes reported by Kosyakov is striking; however, Figure 8 clearly shows that the extractant dependency for the extraction of europium from aqueous solutions without lactate is characterized by a slope of 2.…”

Section: Equationmentioning

confidence: 89%

“…As with HAN, it is well documented that FS will reduce Pu to Pu(III). [12] The spectra of the solutions which resulted from the addition of Pu(III) to the lactic acid and DTPA are very similar. Both spectra contain the three peaks between 550 and 630 nm which were attributed to Pu(III).…”

Section: Reduction Of Actinide Valences Using Han and Fsmentioning

confidence: 94%

“…In addition evidence has been provided that lactate is seen to partition into HDEHP only when metal ions are present. 12 Studies by Danesi 27 and Kolaric 25 both elude to the mechanism of phase transfer being assisted by the existence of ternary complexes of metal:DTPA:lactate in the aqueous phase. However, recent work by Jensen et al 28 and work performed in this program in FY 2010 (see section 3.3) would seem to dispel the hypothesis that these species exist in the TALSPEAK media and hence, another mechanistic interpretation of the phase transfer process has to be formulated.…”

Section: Kineticsmentioning

confidence: 99%

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Thermodynamics and Kinetics of Advanced Separations Systems ? FY 2010 Summary Report

Martin¹,

Zalupski²

2010

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SUMMARYThis report presents a summary of the work performed in the area of thermodynamics and kinetics of advanced separations systems under the Fuel Cycle Research and Development (FCR&D) program during FY 2010. Thermodynamic investigations into metal extraction dependencies on lactate and HDEHP have been performed. These metal distribution studies indicate a substantial deviation from the expected behavior at conditions that are typical of TALSPEAK process operational platform. These studies also identify that no thermodynamically stable mixed complexes exist in the aqueous solutions and increasing the complexity of the organic medium appears to influence the observed deviations. Following on from this, the first calorimetric measurement of the heat of extraction of americium across a liquid-liquid boundary was performed.Interesting discoveries have been made during the investigation of the phase transfer kinetics of the lanthanides in the TALSPEAK process. These studies have been performed using macro metal concentrations in the aqueous phase, something that has not been previously studied in detail. It has been determined that under the conditions studied here, the phase transfer kinetics of the light lanthanides is extremely fast, as a result the distribution coefficient is seen to vary until the slowest lanthanide to extract has come to equilibrium. This will have significant effects on process scale-up and requires further attention. These results have also identified that the kinetics of DTPA binding to the lanthanides and actinides is of higher significance than first thought. The continuing work into this area has highlighted the fact that the binding kinetics show very little difference across the lanthanide series indicating that the binding rate is essentially independent of ionic radii or physical properties of the lanthanides. However, americium is seen to complex to DTPA significantly faster than the lanthanide ions. This has lead to the suggestion that the nature of the interaction is chemically different between americium and DTPA than the lanthanides and DTPA.Additional scope than originally planned for FY10 was also completed. Investigations into the use of different buffers for a TALSPEAK type process have been performed with promising results. The use of amino acids as the buffer instead of lactic acid results in significantly faster phase transfer kinetics and somewhat increased separation factors. In addition, the use of amino acids would allow for the process to be operated in a more acidic regime. Finally, investigations into the presence of ternary complexes in TALSPEAK aqueous phases have added additional weight to the argument that inner-sphere ternary complexes do not exist in solution. However, evidence presented here suggests that the lactate may be dehydrating the outer hydration sphere and facilitating phase transfer in this manner.

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Speciation and Ammonia-Induced Precipitation of Neptunium and Uranium Ions

et al. 2023

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The pH evolution and corresponding changes in the UV−Vis−NIR absorption spectra of oxygenated neptunium (NpO 2 + and NpO 2 2+) and uranyl ions (UO 2 2+ ) in nitric acid are investigated during titration with an aqueous NH 3 solution. The speciation and precipitation regimes between acidic (pH 1.5) and alkaline (pH 10) conditions at room temperature are discussed to assess the suitability of Np(V) or Np(VI) in sol−gel conversion processes for fuel target fabrication. Under the applied experimental conditions, Np(V) hydrolyzes and precipitates into the insoluble hydroxide NpO 2 OH only above pH values 7.5 and an increase up to pH 10.0 is required to precipitate quantitatively. Np(VI) displays changes in the coordination environment of NpO 2 2+ ions in the pH interval 1.6− 4.0, similar to what is observed for U(VI). Precipitation into NpO 3 •H 2 O or other hydroxide compounds takes place between pH 4.0 and 5.9, which overlaps largely with precipitation of ammonium diuranate species from the U(VI) solution. The use of concentrated NH 3 aqueous solution, as commonly used in the external gelation process, will allow to quantitatively precipitate both Np(V) and Np(VI) species. Internal gelation process conditions, on the other hand, seem incompatible with the high pH required to precipitate Np(V) completely. For fabricating mixed-oxide (U,Np) targets using sol−gel conversion, a feed broth containing Np(VI) and U(VI) will be required to achieve homogeneous gelation.

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Literature Review: Reduction of Np(v) to Np (Iv)-Alternatives to Ferrous Sulfamate

Cited by 6 publications

References 9 publications

Distribution of Actinides Between the Aqueous and Organic Phases in the Talspeak Process

Distribution of Actinides Between the Aqueous and Organic Phases in the Talspeak Process

Thermodynamics and Kinetics of Advanced Separations Systems ? FY 2010 Summary Report

Speciation and Ammonia-Induced Precipitation of Neptunium and Uranium Ions

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