GB836771A - Process of producing and recovering uranium enriched with u - Google Patents

Abstract

Uranium enriched in U235 is recovered from a calutron by scrubbing the source region thereof with hot water, sieving out solid impurities and treating the solution with hydrogen peroxide and then with ammonia to precipitate ammonium diuranate and ferric and chromium hydroxides. The caultron, described in Specification 816,772, [Group XL (a)], is a device for separating a plurality of isotopes of an element by vaporizing a compound of the element and subjecting the vapour to ionization, electrically segregating ions from the unionized vapour and accelerating the segregated ions to high velocities through an electromagnetic field which deflects the ions along the curved paths, the radii of curvature of which are proportional to the square root of the masses of the ions. The ions are thereby concentrated in a collector member of the calutron which consists of two pockets in a stainless steel block. Thus after vaporizing a charge of uranium tetrachloride, the first pocket of the collector will contain uranium enriched with U235 whilst principally U238 will be collected in the second pocket. Such calutrons are preferably employed in series, whereby the U235 from the first pocket of the collector is removed by an acid wash and reconverted to uranium tetrachloride and subjected to ionization in a second calutron, thereby obtaining a doubly enriched fraction of U235 in the first pocket of the second calutron. In the second pocket of the second calutron there is deposited uranium which has been first enriched in U235 in the first calutron and depleted in the second stage calutron: this may be recycled, as tetrachloride, to the first calutron. At the same time in both calutrons a considerable amount of the uranium tetrachloride charge is condensed on various parts of the calutron particularly near the source and such deposited uranium values are subjected to recovery according to the invention. In practice a relatively large number of first stage calutrons are associated with a small number of second stage calutrons and the solutions obtained by treating the various parts and collectors of these calutrons are grouped together according to their U235 content for treatment as shown in detail below. Alternatively precipitates obtained from the washings of the various parts of the calutron are combined for further treatment according to their U235 content. Thus a first solution or precipitate is derived from the second pocket of the second stage calutron and the parts of the first stage calutron in the source region thereof, this composite being normal in U235 content. Similarly, a composite is made from solution or precipitate from the parts of the second stage calutron in the source region thereof with the solution or precipitate from the first pocket of the collector of the first stage calutron such composite being singly enriched in U235. The first pocket of the collector of the second stage calutron yields a product doubly enriched in U235. The uranium values deposited in the source region of either the first or second stage calutron is recovered as shown in Fig. 2 by scrubbing and washing the parts with hot water, thereby dissolving the uranium tetrachloride together with impurities such as copper, iron, chromium, nickel and carbon. The carbon is sieved out and the remaining metal values are oxidized with hydrogen peroxide, whereby the uranium values are converted to uranyl irons as shown. After filtration to remove carbon, the filtrate, with or without evaporating, is treated with ammonium hydroxide to precipitate ammonium uranate together with iron and chromium hydroxides leaving the copper and nickel in solution as amine complexes. The specification as open to inspection under Sect. 91 of the Patents and Designs Acts, 1907 to 1942 comprises also recovery of the uranium deposited in the calutron collectors. As shown in Fig. 3 (Cancelled) the deposited metal is dissolved in nitric, sulphuric or hydrochloric acids, and, with or without evaporating, such solution is treated with ammonium hydroxide to produce ammonium uranate precipitate. The precipitates are combined according to their U235 content as referred to above, and treated as shown in Fig. 4 (Cancelled) by dissolving in sulphuric acid and then employing the solution as an electrolyte in an electrolytic cell having a platinum anode and a mercury cathode which is vigorously agitated with the electrolyte. On electrolysis at a current density of about 0.1 amps./sq. cm., the uranous ion formed remains in the electrolyte, whilst iron and chromium are reduced to metals and accumulate in the mercury cathode. After separating the electrolyte from the mercury it is treated with ammonium hydroxide to bring the solution to pH 4.0 to 4.8 to precipitate uranous hydroxide. The <PICT:0836771/III/1> <PICT:0836771/III/2> <PICT:0836771/III/3> <PICT:0836771/III/4> latter is separated and calcined in a non-oxidizing atmosphere to produce uranium dioxide. An alternative purification process of the precipitate derived from Figs. 2 and 3 is shown in Fig. 5 (Cancelled) where the precipitates are subjected to an ether extraction process. As shown, if the composite precipitate contains as much or more iron than uranium, it is first dissolved in hydrochloric acid and the solution vigorously agitated with ether to remove the iron chloride. After repetition of this step the aqueous solution is concentrated by evaporation and treated with concentrated nitric acid to produce a solution of uranyl nitrate with chromium nitrate, and is then diluted to bring the nitric acid concentration between three and six normal. Alternatively, if the iron content is low, the initial precipitate is directly dissolved in nitric acid and the acidity adjusted as before. The aqueous solution of uranyl nitrate is then extracted with ether, the uranyl nitrate passing to the ether phase and dissolving therein leaving iron and chromium in aqueous solution. The ether is then evaporated off, and the solid uranyl nitrate is calcined to uranium trioxide for further treatment. Diethyl ether or isopropyl ether may be employed. Alternative chromatographic <PICT:0836771/III/5> <PICT:0836771/III/6> <PICT:0836771/III/7> <PICT:0836771/III/8> treatment of the precipitates is shown in Fig. 6 (cancelled) where the composite precipitates are dissolved in dilute hydrochloric acid and then treated in a chromatographic absorption column containing for example activated alumina, silica gel, 8 hydroxy quinoline or activated charcoal. A chromatogram develops with the chromium and trivalent iron, uranyl, copper, nickel and divalent iron, and manganese forming as distinct rings in that order with activated alumina. The lower three rings may be washed through and the ring containing the uranyl iron may then be washed through with for example hydrochloric or sulphuric acid, or water. Alternatively, the uranyl ring may be separated. The acid solution of the uranyl is treated with sodium hydroxide to precipitate ammonium diuranate which is washed with aqueous ammonia. The treatment of the recovered products, ammonium diuranate, uranium trioxide or uranium dioxide is shown in Fig. 7 (Cancelled) where ammonium diuranate is first calcined to produce uranium trioxide and this, with any other trioxide produced in the process, is as in Specification 812,121 with methane to the dioxide and, with or without any further dioxide from the process, treated with gaseous carbon tetrachloride at <PICT:0836771/III/9> about 450 DEG C. to produce uranium tetrachloride, which, after subliming, constitutes the end product for recycling to the calutron or recovery as product. Alternatively, the uranium trioxide may be directly reacted with carbon tetrachloride in the liquid phase in an autoclave at about 140 DEG to 160 DEG C. and a pressure of about 200 lbs. per sq. inch gauge, as in Specification 807,261. Uranium pentachloride so produced is calcined and the uranium tetrachloride is sublimed and recovered as before. All precipitates and filtrates incident to the above processes might contain some uranium and are subjected to salvage as shown in Fig. 8 (Cancelled) where solutions low in uranyl ion are treated with ammonium hydroxide or excess gaseous ammonia to precipitate ammonium diuranate with iron and chromium hydroxides. If the salvage material is in solid form it is first dissolved in nitric acid before treatment with ammonium hydroxide. Copper and nickel are dissolved in the form of complex amines and the impure ammonium diuranate precipitate is washed with dilute ammonium hydroxide containing ammonium sulphate to eliminate copper and nickel amine complexes. The purified precipitate is dissolved in dilute sulphuric acid and the concentration adjusted to about 1 normal. The solution is then placed in an electrolytic cell containing a platinum anode and a mercury cathode and with agitation is electrolysed at about 0.1 amps. per sq. cm. current. Iron and chromium are reduced to metals and dissolved in the mercury cathode whilst the purified uranyl ion-containing solution is withdrawn. Such a solution or a solution low in uranyl ion derived from elsewhere in the process may be treated as shown in Fig. 9 (Cancelled) with ion exchange resins. The salvage solutions are first adjusted to a pH of 2 to 4 and then percolated through a cation exchange material in the sodium, ammonium or hydrogen form. After the column has absorbed the uranium, the extracted ion may be recovered by washing with 6 normal sulphuric or hydrochloric acid after which the resin is reprocessed and reused. Final traces of uranium are recovered from solutions incident to any of the above processes as shown in Fig. 10 where an acidified salvage solution containing uranium in the uranous state and in low concentration is divided into portions to the first of which is added lanthanum nitrate to amount to