Increased oxidation of UO2 in molten alkali-metal carbonate based mixtures by increasing oxygen solubility and by controlled generation of superoxide ions, and evidence for a new sodium uranate / Volkovich VA,Griffiths TR,Fray DJ,Fields M // JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS. - 1997. - V. 93, l. 21. - P. 3819-3826.

ISSN/EISSN:

0956-5000 / нет данных

Type:

Article

Abstract:

The oxidation of uranium dioxide to uranates in the ternary alkali-metal carbonate melt (Li-Na-K)(2)CO3 containing added chlorides or sulfates has been studied in the range 723-1023 K and a variety of uranium(vr) species was obtained. Increased oxygen solubility in fused carbonates was achieved by adding alkali-metal chloride or sulfate. The yield of uranates in chloride-containing melts decreased with increasing radius of the alkali-metal chloride cation, Li greater than or equal to Na > K > Cs. When UO2 was oxidised in alkali chloride containing carbonate melts no intermediate uranium chloride complexes were observed The temperature required for complete oxidation of UO2 can be lowered by 100-150 K by the addition of alkali-metal chlorides to carbonate melts. The addition of chloride and aluminium ions to form AlCl4--effected UO2 oxidation by a different mechanism, through intermediate formation of uranyl complexes, but the yield of uranates was not significantly altered. Attempts at oxidation by direct addition of potassium superoxide at 723 K were inefficient owing to thermal instability of the reagent, but UO2 oxidation was enhanced, by more than 10\%, by superoxide formed in situ by the reaction of peroxide and nitrate, compared with oxidation by peroxide or nitrate individually. Optimum conditions for complete;oxidation at 723 K required a peroxide :nitrate mole ratio of ca. 3. The major reaction pathway in melts containing nitrate and peroxide, at various concentrations of these reactants, was determined. At a mole ratio of oxidiser to UO2 of 0.3, the percentage of UO2 oxidised and the yield of uranates, increased in the order Na2O2 approximate to KO2 < KNO2 < KNO3 < KNO3 + Na2O2. Evidence has been obtained for a new sodium uranate, Na2O(UO3-y)(x)(1 < x < 2; y<0.02).

Author keywords:

MELTS

DOI:

10.1039/a704450j

Web of Science ID:

ISI:A1997YD74700011

Соавторы в МНС:

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Другие поля

Поле	Значение
Month	NOV 7
Publisher	ROYAL SOC CHEMISTRY
Address	THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON ROAD, CAMBRIDGE, CAMBS, ENGLAND CB4 4WF
Language	English
Keywords-Plus	MELTS
Research-Areas	Chemistry; Physics
Web-of-Science-Categories	Chemistry, Physical; Physics, Atomic, Molecular \& Chemical
ResearcherID-Numbers	Volkovich, Vladimir/K-8339-2012
ORCID-Numbers	Volkovich, Vladimir/0000-0003-4438-1194
Number-of-Cited-References	32
Usage-Count-Since-2013	7
Journal-ISO	J. Chem. Soc.-Faraday Trans.
Doc-Delivery-Number	YD747