An improved method of recovering uranium from solution

摘要

A solution of a uranyl salt is mixed with an alkali metal or ammonium fluoride and formic acid, and heated to 90 DEG C.; sulphur dioxide is passed in to precipitate a double fluoride of the alkali metal or ammonium and uranium which is then separated, mixed with calcium and magnesium and heated to obtain metallic uranium. Alternatively, where ammonium uranium fluoride is obtained, this may be separated, washed, dried and heated to 250 DEG C. in a dry inert atmosphere to form uranium fluoride and ammonium fluoride (which volatilizes) and the uranium fluoride mixed with calcium or magnesium chips and heated to obtain metallic uranium. In one embodiment, an ore such as pitchblende or autunite which is poor in uranium is attacked with nitric acid to form uranyl nitrate in solution, the solids are separated and the solution extracted with a solvent for the uranium such as tributyl phosphate; the extract is re-extracted with water and the organic phase reused in the first extraction. Ammonium fluoride and formic acid are added and sulphur dioxide bubbled in whereby dense green UF4.NH4F is formed. This reaction may be performed in the apparatus shown in Fig. 2, the solution entering a steamjacketed reactor 11 through line 16 and leaving through line 17, sulphur dioxide being passed in through perforated ring conduit 15 whilst gases (CO2) arising in the reaction are vented at 18 and the precipitate being withdrawn through tube 10. Radial bars 14 are connected to shaft 13 which agitates the mixture by continuous rotation. The precipitate is washed, dried and heated to 250 DEG C., e.g. in a current of nitrogen, and then reduced to metal by reaction with calcium or magnesium chips. Uranyl sulphate may also be used as the starting material. In a statement of prior art for the recovery of uranium from ores, the following steps are referred to: attacking the ore with mineral acid and separating the residues; precipitating some metallic hydroxides with sodium carbonate; breaking-up the uranyl-carbonate complex with nitric or sulphuric acid; precipitating sodium uranate with caustic soda and dissolving the precipitate in nitric acid; extracting with an organic solvent; treating with hydrogen peroxide to precipitate UO4, which is then calcined to UO3; reducing the latter to WO2 with hydrogen or ammonia; converting to UF4 with gaseous hydrofluoric acid and finally reacting the fluoride with calcium or magnesium to give metallic uranium.