GB854235A - Improvements in the preparation of ammonium diuranate - Google Patents

Abstract

Ammonium diuranate having a bulk density not less than 1.4 g./ml. and having a particle size below 3 microns is prepared by precipitating finely divided ammonium diuranate from an aqueous solution containing per gallon, between 0.3 and 0.6 pounds of uranium, 0.15 and 0.3 pounds of fluoride and an excess of at least 0.3 pounds of ammonia over that stoichiometrically required to neutralise any acid present and to form ammonium diuranate. The ammonium diuranate precipitate is separated from the mother liquor without washing and the fluoride - containing ammonium diuranate is thereafter dried. It is particularly suitable for converting to uranium dioxide of bulk density of 2.4 g./ml. or more, from which high density compacts having at least 60% theoretical density may be obtained. Such compacts may be sintered to obtain uranium dioxide bodies of more than 90% theoretical density. The ammonium diuranate may be formed by hydrolising uranium hexafluoride in an ammonia solution. For example uranium hexafluoride may be added to a solution of ammonia in the mol ratio of 1 to 4 after which the required excess ammonia is rapidly added in the form of a 27% solution to precipitate the uranium diuranate. Alternatively ammonium diuranate from any source may be dissolved in a solution containing sufficient ammonium bifluoride to produce a U/F ratio of about 2 and the required excess ammonia rapidly added to precipitate the high density finely divided ammonium diuranate of the invention. Alternatively ammonium diuranate may be precipitated from a neutral solution of uranyl fluoride and ammonium fluoride by adding the required excess of ammonia thereto. Specification 850,957 is referred to.