GB829090A - Production of aqueous uranium sulphate solutions - Google Patents

Abstract

Uranium values are recovered as uranyl sulphate from an oxide of less than hexavelent uranium by reaction with dilute sulphuric acid in the presence of an added soluble fluoride. The process is also suitable for the treatment of slags obtained in the manufacture of metallic uranium by reacting uranium tetrafluoride with an alkali or alkaline earth metal, beryllium or aluminium to form metallic uranium and a slag which already contains the requisite fluoride. The invention is particularly applicable to U3O8 and UO2. The fluoride may be added as magnesium, sodium, calcium or hydrogen fluoride. The dissolution may be effected in the presence of an oxidizing agent, particularly if any free metal is present. Thus air, hydrogen peroxide, nitric acid or a permanganate or chromate may be used, such oxidizing agent also converting the dissolved uranium to the hexavalent form. According to examples: (1) a slag obtained from the production of metallic uranium by the tetrafluoride process containing uranium together with a substantial proportion of calcium and magnesium fluorides was heated with 20% sulphuric acid at 85 DEG to 95 DEG C., thereby completely dissolving the uranium values; (2) a uranium oxide product obtained by roasting contaminated uranium metal in air was heated with 12% sulphuric acid and a minor amount of calcium fluoride. The solutions from this and the preceding example may be treated with 27 1/2 % hydrogen peroxide solution to convert the uranium to hexavelent form and the solutions may be heated to 90 DEG C., treated with calcium carbonate to adjust the pH between 2.8 and 3.5 and filtered free from solid matter. (3) Uranium dross obtained when crude uranium from the tetrafluoride process was re-melted, air roasted at 800 DEG C., milled and treated with sulphuric acid at temperatures between 85 DEG and 100 DEG C. The uranium dross contained 3 1/2 % fluorine. The solutions obtained were diluted with water, cooled to 40 DEG C. and treated with 28% aqueous hydrogen peroxide, after which the solution was heated to boiling-point to decompose any uranium peroxide formed. On separation of the solid matter a solution of uranyl sulphate was obtained. A further example shows the use of sodium fluoride. The process may be combined with the process of Specification 829,087 where uranium dross is roasted with lime in air and the product treated with concentrated sulphuric acid at elevated temperature. The product of this sulphuric acid treatment is introduced into water to dissolve the soluble components and the relatively dilute sulphuric acid solution obtained containing uranyl and other sulphates may be employed in the process of the present invention. Specification 829,088 also is referred to.