Thermal analysis studies of the reactions occurring during the decomposition of ammonium uranyl carbonate in different atmospheres

Hälldahl, Lars; Nygren, Mats

doi:10.1016/0022-3115(86)90260-6

Cited by 14 publications

(11 citation statements)

References 10 publications

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“…By analyzing this mass variation, the material balance calculations unequivocally indicated that the AUC compound was (NH 4 ) 4 UO 2 (CO 3 ) 3 . Consequently, our study successfully identified the conditions conducive to the formation of AUC precipitates, which are very similar to the findings reported in the literature [ [37] , [38] , [39] , [40] , [41] , [42] ]. Therefore, to achieve the precipitation of free AUF, a C/U molar ratio greater than six is required.…”

Section: Resultssupporting

confidence: 86%

Uranyl ammonium carbonate precipitation and conversion into triuranium octaoxide

Hung,

Thuan,

Thuy

et al. 2024

Heliyon

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Section: Resultssupporting

confidence: 86%

Uranyl ammonium carbonate precipitation and conversion into triuranium octaoxide

Hung,

Thuan,

Thuy

et al. 2024

Heliyon

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“…An exothermic reaction took place at 440 °C, then shortly after another exothermic reaction started at around 590 °C. Halldahl and Nygren [4] also observed a similar phenomenon, the DTA curves for decomposition of (NH 4 ) 2 UO 2 (NO 3 ) 4 ·2H 2 O were dependent upon the atmospheric gas used during the decomposition. Halldahl also reported that the maximum peak temperature when AUC was thermally decomposed into UO 3 under a nitrogen, air, and hydrogen atmosphere was 195, 198, and 185 °C, respectively.…”

Section: Resultsmentioning

confidence: 62%

“…It is assumed that such a difference in the reaction temperature between an air and a nitrogen atmosphere was due to the different activation energy that was dependent on the atmospheric under which the decomposition was carried out. Also, it has been reported that if the composition of a compound is different or an impurity is present, the peak of the DTA curve moves toward a higher temperature [4]. …”

Section: Resultsmentioning

confidence: 99%

“…Meanwhile, AUC decomposes at around 190 °C, giving off CO 2 , NH 3 , and H 2 O with the formation of an amorphous phase. In a N 2 , Ar, or CO 2 atmosphere, the amorphous phase crystallizes to α-UO 3 before decomposing to U 3 O 8 [4]. Various reports have been published on thermal analysis studies of the reactions occurring during a decomposition of AUC and ADU.…”

Section: Introductionmentioning

confidence: 99%

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Thermal and X-ray diffraction analysis studies during the decomposition of ammonium uranyl nitrate

Kim

Lee

Prelas

et al. 2012

J Radioanal Nucl Chem

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Two types of ammonium uranyl nitrate (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3, were thermally decomposed and reduced in a TG-DTA unit in nitrogen, air, and hydrogen atmospheres. Various intermediate phases produced by the thermal decomposition and reduction process were investigated by an X-ray diffraction analysis and a TG/DTA analysis. Both (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3 decomposed to amorphous UO3 regardless of the atmosphere used. The amorphous UO3 from (NH4)2UO2(NO3)4·2H2O was crystallized to γ-UO3 regardless of the atmosphere used without a change in weight. The amorphous UO3 obtained from decomposition of NH4UO2(NO3)3 was crystallized to α-UO3 under a nitrogen and air atmosphere, and to β-UO3 under a hydrogen atmosphere without a change in weight. Under each atmosphere, the reaction paths of (NH4)2UO2(NO3)4·2H2O and NH4UO2(NO3)3 were as follows: under a nitrogen atmosphere: (NH4)2UO2(NO3)4·2H2O → (NH4)2UO2(NO3)4·H2O → (NH4)2UO2(NO3)4 → NH4UO2(NO3)3 → A-UO3 → γ-UO3 → U3O8, NH4UO2(NO3)3 → A-UO3 → α-UO3 → U3O8; under an air atmosphere: (NH4)2UO2(NO3)4·2H2O → (NH4)2UO2(NO3)4·H2O → (NH4)2UO2(NO3)4 → NH4UO2(NO3)3 → A-UO3 → γ-UO3 → U3O8, NH4UO2(NO3)3 → A-UO3 → α-UO3 → U3O8; and under a hydrogen atmosphere: (NH4)2UO2(NO3)4·2H2O → (NH4)2UO2(NO3)4·H2O → (NH4)2UO2(NO3)4 → NH4UO2(NO3)3 → A-UO3 → γ-UO3 → α-U3O8 → UO2, NH4 UO2(NO3)3 → A-UO3 → β-UO3 → α-U3O8 → UO2.

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“…The XRD result showed that the initial precipitate was UO 4 4H 2 O. After sintering the precipitate at 800 °C, the precipitate changed to U 3 O 8 , the TG results shows that the UO 4 4H 2 O changes to UO 4 2H 2 O at about 90 °C, and UO 4 at about 200 °C, which are considered to be attributed to the losses of water from the structure, i.e., a loss of water of crystallization, and finally to U 3 O 8 at 550 °C. The change of the TG weight loss shows exactly the same change of weight due to the change of UO 4 to U 3 O 8 .…”

Section: Resultsmentioning

confidence: 98%

Precipitation Characteristics of Uranyl Ions at Different pHs Depending on the Presence of Carbonate Ions and Hydrogen Peroxide

Kim

Lee

et al. 2009

Environ. Sci. Technol.

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This work studied the dissolution of uranium dioxide and precipitation characteristics of uranyl ions in alkaline and acidic solutions depending on the presence of carbonate ions and H2O2 in the solutions at different pHs controlled by adding HNO3 or NaOH in the solution. The chemical structures of the precipitates generated in different conditions were evaluated and compared by using XRD, SEM, TG-DT, and IR analyses together. The sizes and forms of the precipitates in the solutions were evaluated, as well. The uranyl ions were precipitated in the various forms, depending on the solution pH and the presences of hydrogen peroxide and carbonate ions in the solution. In a 0.5 M Na2CO3 solution with H2O2, where the uranyl ions formed mixed uranyl peroxy-carbonato complexes, the uranyl ions were precipitated as a uranium peroxide of UO4(H20)4 at pH 3-4, and precipitated as a clarkeite of Na2U2Ox(OH)y(H2O)z above pH 13. In the same carbonate solution without H2O2, where the uranyl ions formed uranyl tris-carbonato complex, the uranyl ions were observed to be precipitated as a different form of clarkeite above pH 13. The precipitate of uranyl ions in a nitrate solution without carbonate ions and H2O2 at a high pH were studied together to compare the precipitate forms in the carbonate solutions.

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Thermal analysis studies of the reactions occurring during the decomposition of ammonium uranyl carbonate in different atmospheres

Cited by 14 publications

References 10 publications

Uranyl ammonium carbonate precipitation and conversion into triuranium octaoxide

Uranyl ammonium carbonate precipitation and conversion into triuranium octaoxide

Thermal and X-ray diffraction analysis studies during the decomposition of ammonium uranyl nitrate

Precipitation Characteristics of Uranyl Ions at Different pHs Depending on the Presence of Carbonate Ions and Hydrogen Peroxide

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