GB829088A - Separation of uranium peroxide from mixtures - Google Patents

Abstract

Uranium peroxide is precipitated from aqueous uranyl sulphate solutions by treatment with a peroxide at a pH between 2 and 5. The uranyl sulphate solution may be derived from the process of Specification 829,087, where uranium dross is burned in air and the product mixed with lime, air roasted and the roasted product thereafter mixed with sulphuric acid in the presence of an oxidizing agent, or by the process of Specification 646,836, where uranium dross is crushed, air roasted, heated with concentrated sulphuric acid and an oxidizing agent and thereafter leached with water. Such uranyl sulphate solutions are then mixed with acidic water to provide a 5-10% uranyl sulphate concentration and treated with an oxidizing agent such as air, nitric acid, permanganate, chromate or a peroxide to convert the uranium to hexavalent form. The oxidized mixture is heated to 70-100 DEG C. and an alkali such as a hydroxide or carbonate of an alkali metal, alkaline earth metal or ammonium is added to adjust the pH to 3-4. Iron precipitates after heating and is separated by filtration and the solution is then cooled to 20-45 DEG C. and filtered. Hydrogen peroxide in an amount equal to 105-200% theoretical quantity necessary is added while the solution is maintained at 30-65 DEG C. and thereafter an alkali is added to restore the pH to between 2 1/2 and 3 1/2 , peferably 2.8, thereby precipitating uranium peroxide. The precipitation is preferably effected from a solution having a content of soluble salts other than uranyl sulphate, from 10-15% by weight and to this end if the soluble salt concentration is low the alkaline reagent used may be one which forms a soluble salt. The precipitation may also take place in the presence of uranium peroxide seeds. The uranium peroxide precipitate may be washed with dilute sulphuric or nitric acids at 30-50 DEG C. According to an example, a uranium sulphate solution prepared as described below, was treated at 40-45 DEG C. with aqueous hydrogen peroxide, the pH falling to 1.5 and being readjusted to 3 by the addition of sodium hydroxide. The uranium peroxide dihydrate was separated and water washed. The initial sulphate solution was prepared by aerating an aqueous uranium sulphate solution and treating it with a small amount of hydrogen peroxide to complete the conversion of tetravalent uranium to hexavalent. The mixture is then heated to 90-95 DEG C. and the pH was adjusted to 3.7 by the addition of calcium carbonate, thereby precipitating iron which was filtered. The solution was then cooled to 40 DEG C. and filtered to produce the purified uranyl sulphate solution. The process of the invention is applicable to the removal from uranium of the following impurities:-magnesium, sodium, boron, copper, cobalt, chromium, molybdenum, manganese and nickel, vanadium, gallium and samarium. Specification 829,090 also is referred to.