Patent GB-812793-A (GB)
Title: Method of recovering uranium
IPC: C01G43/08
Filed: 1945-04-11
Abstract: Uranium values are recovered from a metallic surface on which they are present by immersing the surface in a sulphuric acid solution, electrolysing with the metallic surface as an anode to cause dissolution of the uranium values therefrom to form a sulphuric acid solution containing uranium and metal impurities, treating the solution to remove from it the metal inpurities by electrolysing it in a mercury cathode electrolytic cell so that the metal values other than those of uranium are reduced <PICT:0812793/III/1> <PICT:0812793/III/2> <PICT:0812793/III/3> to the metallic state and are deposited in the mercury cathode and thereafter recovering the uranium values from the solution remaining.  The invention is particularly applicable to the removal of uranium from the metallic collector of a calutron, described below.  The calutron consists of a means for vaporizing a quantity of an uranium compound for example, uranium tetrachloride and subjecting such vapour to ionization whereby ions of the several isotopes of uranium are produced, which ions are segregated from the unionized vapour, accelerated at high velocities and deflected by an electromagnetic field along a curved path, the radius of curvature being proportional to the square root of the masses of the ions, whereby the ions are concentrated in accordance with their masses in a suitably placed collector in the calutron.  The collector has two pockets, one receiving U235 and the other, U238.  Such a device is described in U.S.A.  Specification 2,709,222.  After a suitable number of charges have been vaporized, deposits of the uranium isotopes are formed in pockets in the collector block and these deposits are treated according to the invention.  The majority of the uranium tetrachloride vapour is however unionized and is largely condensed upon parts of the calutron near the source region.  The calutrons are suitably employed in series whereby a first stage calutron gives an enrichment factor of 20 in respect of U235 and a second stage calutron is fed with the enriched product from the first calutron whereby an enrichment factor of 20 gives a final enrichment factor of about 400.  Thus the U235 collected in the pocket of the first calutron is recovered and after conversion to the tetrachloride is treated in a second stage calutron whereby a deposit of uranium in the appropriate pocket of the second calutron is doubly enriched in U235.  Uranium tetrachloride, deposited near the source region of both first and second stage calutrons during operation, is recovered as shown in Fig. 2, by scrubbing these parts with hot water whereby the uranium tetrachloride together with copper, iron, chromium and nickel impurities are dissolved.  The wash water is then treated with hydrogen peroxide and thereafter concentrated by evaporation.  The water vapour driven off is condensed to constitute a new wash solution and the concentrated solution is treated with ammonia to precipitate ammonium uranate, together with the hydroxides of iron and chromium.  The solution is filtered and the precipitate dissolved in 1N sulphuric acid.  Such an acid solution from the source region of the first stage calutron will have a normal content of U235 whilst the acid solution derived from the second stage calutron will be enriched in U235.  The metallic uranium deposited in the first pocket of the collector of the first stage calutron, singly enriched with U235 and the metallic uranium doubly enriched with U235 from the first pocket of the collector of the second stage calutron are recovered by treatment as shown in Fig. 3 by forming the collector of the calutron concerned as an anode of an electrolytic cell containing 0.1 to 0.01 normal sulphuric acid.  With a current density of about 0.1 to 0.3 amps. per cm. sq. the uranium either singly or doubly enriched with U235 passes into solution together with iron, chromium and nickel; these elements enter in the electrolyte in their lower valent state.  Composite solutions are then made up for further treatment, the first composite solution containing the acid solution from the source region of the first stage calutron, together with the electrolyte derived from the second pocket of the collector of the second stage calutron, this composite solution containing the normal content of U235.  The second composite solution consists of the acid solution from the source region of the second stage calutron and the electrolyte derived from the first pocket of the collector of the first stage calutron, this second composite solution comprising uranium singly enriched with U235; the third solution is derived from the electrolyte from the first pocket of the collector of the second stage calutron and this latter solution comprises uranium which is doubly enriched with U235.  These composite solutions are individually treated as indicated in Fig. 4.  The sulphuric acid concentration is first adjusted to 0.5 to 3 normal by adding water or acid.  The solution is then electrolysed between a plantinum anode and a mercury cathode which is vigorously agitated.  With a current density of about 0.1 amps. per sq. cm. of the anode, the uranium is reduced to the uranous state and iron, chromium and nickel impurities are reduced to metal which accumulates in the mercury cathode.  The electrolyte freed from impurities is then subjected to ammonia treatment whereby uranium hydroxide is precipitated and separated; this precipitate is calcined in a nonoxidizing atmosphere at about 250 DEG  C. to produce UO2. The UO2 derived from the first composite solution is normal with respect to U235, and that from the second composite solution is singly enriched with U235.  Both of these batches of UO2 are re-cycled to the process as described below whilst the batch of UO2 derived from the third composite solution doubly enriched with U235 is retained as a commercial product.  The UO2 for re-cycling is converted into uranium tetrachloride by the action with carbon tetrachloride vapour at 450 DEG  C., preferably according to the process of Specification 812,121.  Such uranium tetrachloride is sublimed in a molecular still at about 600 DEG  C. and re-cycled to the first or second stage calutron dependent on its content of U235. The invention is equally applicable to the utilization of uranium hexachloride or tetrabromide.