Actinide Metals

doi:10.1002/9783527656189.ch9

Cited by 3 publications

(4 citation statements)

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“…In contrast, Neck et al reported that no significant Np(V) hydrolysis occurred in carbonate-free perchlorate solutions at pH below 10 . This remarkable difference in the hydrolytic properties of Np(V) was debated in the literature, , and following critical reviews, it was assigned to the effect of carbonate complexation due to infiltration of CO 2 during the experiments by Rao et al , In the present experiments, no protective environment was applied, and hence, interaction with CO 2 cannot be ruled out. The extent of carbonate complexation can be assessed from the spectrophotometric data, as it is associated to a distinct absorption band at 991 nm, or as a shoulder on the intense 980 nm band, depending on the exposure time. ,, Only a small shoulder could be observed at 991 nm in our experiments, compared to the appearance of much stronger absorbance effects reported in the literature (see Figure S6).…”

Section: Discussioncontrasting

confidence: 56%

“…Kato et al reported on the characterization of such a dark reddish–brown precipitate as NpO 3 ·H 2 O while performing solubility studies on Np(VI) . However, other solid phases such as NpO 3 ·2H 2 O and NpO 2 (OH) 2 have been reported to form as well . No NpO 2 2+ remained in solution at pH values above pH 5.9.…”

Section: Discussionmentioning

confidence: 99%

“…The Np(VI) ion NpO 2 2+ is less stable than the hexavalent UO 2 2+ and PuO 2 2+ ions and is hydrolyzed quickly into polynuclear hydroxo complexes such as (NpO 2 ) 2 (OH) 2 2+ . ,, An exchange between hydrated water molecules and nitrate ions can take place depending on the nitrate concentration . Similar to Np(V), carbonate complexation may occur, and hydrolysis experiments on Np(VI) in a NaClO 4 solution (0.1 M) at either 80 or 0.03% CO 2 partial pressure resulted in precipitation of NpO 2 CO 3 (tan greenish powder) or NpO 3 ·H 2 O (dark reddish–brown powder), respectively, rather than the hydroxide NpO 2 (OH) 2 …”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussioncontrasting

confidence: 56%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Speciation and Ammonia-Induced Precipitation of Neptunium and Uranium Ions

et al. 2023

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“…Knowing the metal partition and the total concentrations, each column experiment allows evaluation of the formation of the metal-protein complex. Speciation calculations were performed with the computer program Hyperquad Simulation and Speciation (HySS) ( 58 ) and taking into account the metal hydrolysis constants ( 59 ). Under the studied conditions, the metal hydroxide species account for <1% for Ac 3+ and <15% for Y 3+ .…”

Section: Methodsmentioning

confidence: 99%