Study of formation and composition of ammonium uranates

Urbanek, V.; Šára, V.; Moravec, J.

doi:10.1016/0022-1902(79)80440-6

Cited by 14 publications

(7 citation statements)

References 7 publications

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“…The term ''ammonium diuranate'' is actually a misnomer, but it remains of common use. Controversies over the composition and structure of ADU have sparked numerous studies [7][8][9][10][11][12][13]. Its morphology has also attracted a great deal of attention, as it is well established that the characteristics of precursor materials are inherited into the final product [14,15].…”

Section: Introductionmentioning

confidence: 99%

Investigation of ammonium diuranate calcination with high-temperature X-ray diffraction

et al. 2014

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The thermal decomposition of ammonium diuranate (ADU) in air is investigated using in situ hightemperature X-ray diffraction (HT-XRD), thermogravimetry and differential thermal analysis. Data have been collected in the temperature range from 30 to 1000°C, allowing the observation of phase transformation and the assessment of the energy changes involved in the calcination of ADU. The starting material 2UO 3 ÁNH 3 Á3H 2 O undergoes a process involving several endothermic and exothermic reactions. In situ HT-XRD shows that amorphous UO 3 is obtained after achieving complete dehydration at 300°C, and denitration at about 450°C. After cooling from heat treatment at 600°C, a crystalline UO 3 phase appears, as displayed by ex situ XRD. The selfreduction of UO 3 into orthorhombic U 3 O 8 takes place at about 600°C, but a long heat treatment or higher temperature is required to stabilise the structure of U 3 O 8 at room temperature. U 3 O 8 remains stable in air up to 850°C. Above this temperature, oxygen losses lead to the formation of U 3 O 8-x , as demonstrated by subtle changes in the diffraction pattern and by a mass loss recorded by TGA.

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Section: Introductionmentioning

confidence: 99%

Investigation of ammonium diuranate calcination with high-temperature X-ray diffraction

et al. 2014

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“…The most common methods of uranium ore processing use ammonium hydroxide as a precipitating reagent and produce AU (commonly referred to as ADU) products, which have the general formula (NH 4 ) 2 U 2 O 7 , UO 3 · x H 2 O · y NH 3 , or UO 2 (OH)2· x H 2 O· y NH 3 . 16,19,20,28 The spectra of several AU samples are given in Fig. 3, with the NIR1 and NIR2 ranges presented separately due to the shift in the detector response.…”

Section: Resultsmentioning

confidence: 99%

Application of Visible/Near-Infrared Reflectance Spectroscopy to Uranium Ore Concentrates for Nuclear Forensic Analysis and Attribution

et al. 2013

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Uranium ore concentrates (UOCs) are produced at mining facilities from the various types of uranium-bearing ores using several processes that can include different reagents, separation procedures, and drying conditions. The final UOC products can consist of different uranium species, which are important to identify to trace interdicted samples back to their origins. Color has been used as a simple indicator; however, visual determination is subjective and no chemical information is provided. In this work, we report the application of near-infrared (NIR) spectroscopy as a non-contact, non-destructive method to rapidly analyze UOC materials for species and/or process information. Diffuse reflectance spectra from 350 to 2500 nm were measured from a number UOC samples that were also characterized by X-ray diffraction. Combination and overtone bands were used to identify the amine and hydroxyl-containing species, such as ammonium uranates or ammonium uranyl carbonate, while other uranium oxide species (e.g., uranium trioxide [UO3] and triuranium octoxide [U3O8]) exhibit absorption bands arising from crystal field effects and electronic transitions. Principal component analysis was used to classify the different UOC materials.

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“…The precipitation with ammonia agrees with the fact that no precipitate with a zero ammonia content could be prepared by the precipitation with NH4OH. The mother liquor makes possible the Saturation of the solid phase at the very beginning of precipitation [22]. This may contribute to the Variation in the Eg value of the corresponding UO3 obtained on calcination at 500°C from 2.175 to 2.12 eV.…”

Section: The Energy Gap {Eg) Value Of Ammonium Uranatementioning

confidence: 98%