Chemistry of inorganic compounds – Radioactive – Uranium compound
Patent
1983-12-05
1986-04-29
Miller, Edward A.
Chemistry of inorganic compounds
Radioactive
Uranium compound
C01G 4301
Patent
active
045856346
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the production of uranium trioxide having a large specific surface by the thermal denitration in two stages of hydrated uranyl nitrates corresponding to the formula UO.sub.2 (NO.sub.3).sub.2.xH.sub.2 O, with 2.ltoreq.x.ltoreq.6.
It is well known that the production of uranium trioxide (UO.sub.3) by the thermal denitration of uranyl nitrate hexahydrate in accordance with the following reaction scheme: +6H.sub.2 O hexafluoride comprising the reduction of uranium trioxide to uranium dioxide, fluorination of the uranium dioxide with hydrofluoric acid and, finally, the action of fluorine on the uranium tetrafluoride to form the desired uranium hexafluoride. However, it is equally well known that the UO.sub.2 obtained by thermal denitration followed by reduction affords low productivity through lack of reactivity with hydrofluoric acid during its conversion into UF.sub.4.
Numerous processes for the production of uranium trioxide have already been described in the specialist literature. Thus, the work entitled "URANIUM PRODUCTION TECHNOLOGY", edited by Charles D. Harrington and Archie E. Ruchle, New York, Edition 1959, pages 181 to 191, describes several processes for the thermal denitration of uranyl nitrate hexahydrate.
A first process, of the batch type, comprises heat-treating a continuously stirred concentrated solution of uranyl nitrate hexahydrate first for 1.5 hours at a controlled temperature of 621.degree. C. of the combustion gases and then for 5 hours at a temperature of 510.degree. C. of those gases and finally, cooling the powder-form product obtained for approximately 30 minutes.
However, as the author himself states, this process is attended by certain disadvantages which limit its development. Firstly, the powder-form product obtained is in fact made up of a mixture of UO.sub.3 and U.sub.3 O.sub.8, this second oxide forming on the walls of the reactor heated to a temperature higher than that prevailing inside said reactor. In addition, if the denitration temperature is too high, it may result in solidification of the above-mentioned mixture of oxides whereas, if it is too low, the mixture of oxides still contains uranyl nitrate and water. Finally, in the most favorable case, i.e. where the powder-form product obtained is UO.sub.3 subsequently reduced to UO.sub.2, the UO.sub.2 obtained shows minimal capacity to react with HF during its fluorination. This minimal capacity of the UO.sub.2 to react with HF, which is a measure of the lack of reactivity of the product, is considered by the author himself as being attributable to the small specific surface of the uranium trioxide obtained (0.73 m.sup.2 /g).
In order to improve the reactivity of the uranium dioxide, the author advises the use of certain aids such as, for example, the introduction of sulfuric acid into the uranyl nitrate solution subjected to the thermal denitration process. However, these aids are limited in their effectiveness because the UO.sub.3 obtained has a specific surface not exceeding 2 m.sup.2.g.sup.-1.
In another, continuous process, uranyl nitrate hexahydrate is thermally decomposed by introducing an aqueous solution thereof into a stirred bed of powder-form uranium trioxide kept at the denitration temperature. The thermal decomposition of the uranyl nitrate in solution is carried out in a crucible-type reactor, the base of which is electrically heated, by direct contact between the uranyl nitrate solution and the hot UO.sub.3 powder filling the crucible of said reactor, the temperature of the denitration medium being kept between 510.degree. C. and 530.degree. C. To enable the bed of powder to be continuously stirred, the denitration reactor is equipped with a stirrer having a horiziontal shaft and T-shaped arms which keep the bed stirred. As it is formed, the UO.sub.3 is withdrawn from the reactor while the gaseous effluents are collected and treated.
Although this process has the advantage of being continuous, it is attended by disadvantages similar to those mentioned above in refere
REFERENCES:
patent: 2981592 (1961-04-01), Lawroski et al.
patent: 3761547 (1973-09-01), Grossman et al.
Bridge et al., Chem. Abst., 50, (#22), abs. #16498i (1956).
Bachelard Roland
Lakodey Pierre
Comurhex
Miller Edward A.
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