IL33003A - Method of uranium235enrichment by ion exchange - Google Patents

Description

33003/3 235 0*31» «ιι^'π Method of uranium enrichment by ion exchange JOIHE-KUHMAJSir and IBS ECHAIGEURS D»IOHS MINBRAUX Inventors: 1* Gaston CHARIOT 2* Alain DIDIER 3i Gerard RAT 4. Paul SPILLIAERT G% 31277 33005/2 ffihis invention is directed to a method of isotopic enrichment of uranium 235 by means of ion-exchange between uranium ions in two different valence states, respectively.

In order to enrich an isotopic mixture with a predetermined isotope, it has already been proposed to utilize the isotopic exchange phenomena which take place when compounds containing ions of a same element in two different valence states are brought together. However, it is known that ¾he separation factors are but slightl different from 1 by reason of the very closely related properties of the isotopes of a same element.

In order to enhance the separation efficiency, consideration has been given to -the use of an ion exchanger for the selective adsorption of the element in one of its valence states. A known method thus consists in contacting an aqueous solution containing ions of one element in a first valence with particles of an ion exchange resin which has absorbed ions of the same element in a second valence, said particles being circulated countereurrent to the aqueous solution.

However, the efficiency.' of this process is very low and the isotope separation factor between the two different valences of the element remain very far removed from the theoretical Value. Moreover, this method is subject to all the disadvantages attached to the circulation of resin particles, and in particular the very (substantial value of theoretical plate height, with the result that the dimensional requirements of the countercurrent exchange plant are wholly unacceptable from an industrial standpoint, both in regard to the overall size of the installation and in regard to the residence time of the element being processed in such While retaining the advantages of the known profcess referred- o above, the present invention provides the possibility of circumventing the disadvantages of this process by making use of a fixed-bed ion exchanger.

Accordingly, the invention proposes a method of isotopie enrichment of Uranium 235 by means of ion-exchange between uranium ions in a first and in a second valence, respectively, which is essentially characterized in that it consists in placing an ion exchanger in a ixed bed in a form which is capable of selectively adsorbing the uranium ions in the second valence, in circulating through said ion exchanger a solution to be processed which contains uranium in the form of ions in said first valence, and possibly in a minor proportion also in the form of ions in said second valence, in changing the uranium ions in the solution to be processed from said first to said second valence in order to cause the adsorption of said ions on the ion exchanger, in circulating through said ion exchanger after the solution to be processed a solution of a displacement agent which is capable of displacing the uranium Ions from the exchanger and in changing said displaced uranium ions from the second to the first valence fhe uranium ions which are thus displaced and have reverted to the first valence are transported by the solution through the ion exchanger until they have again changed valence and are adsorbed on the ion exchanger further towards the front (in the direction of flow).

There is thus caused to appear within the fixed-bed ion exchanger an exchange zone in which the isotopie exchange takes place between the uranium ions in the second valence solution, and said exchange zone forms a band which is displaced within the ion exchanger.

In a preferred mode of application of the method uranium according to the invention, the /kloiaoafc to be processed which is dissolved in the solution is periodically injected into the band which is formed within the ion exchanger and the uranium withdrawals of the/cignrgart which is either enriched or depleted in a predetermined isotope are carried out periodically at the ends of said band.

Compared with the methods employed in the prior art, the method in accordance with the invention which makes use of a fixed-bed ion exchanger has the advantage of great simplicity of operation _ The method also permits the use of much smaller ion-exchanger particles, thereby resulting in an exchange column having a theoretical plate height which is much smaller and therefore compatible with industrial operation o In the method according to the invention, there is carried out at each end of the band ; uranium - on the one hand a change of phase of the ^lcmcntr- to be processed which is converted from the liquid phase (aqueous solution) to the solid phase (ion exchanger) at the front of the band and from the solid phase to the liquid phase at the rear of the band, - and on the other hand a change of valence by oxidation or uranium reduction, wherein the tfctemeirtr is converted from the first to the second valence at the front of the band and from the second to the first valence, at the rear of the band.

Changes of phase and changes of valence can either be concomitant or be carried out separately in time and space „ Thus, in the first case and in accordance with a first mode of application of the invention, the ions which uranium are displaced from the ion exchanger by the m±om½uA> being processed (at the front of the band) and the ions which dis- e place this the rear of the band) can be accompanied by an oxidizing agent or reducing agent or themselves also perform an oxidizing or reducing function. For example, a cation which is capable both of oxidizing and of displacing uranium the /&½Θ-&©Η>£- being processed can be selected for this purpose uranium by comparing its properties with those of θβ**-«¾β»·β«.ϊ-insofar as concerns the oxidation-reduction potential and the affinity for the ion exchanger which is employed, In the second case, and according to a second mode uranium of application of the invention, the « cmon; to be processed is reduced or oxidized, advantageously by electrolysis, before being adsorbed on the ion exchanger or after having been displaced therefrom.

According to a secondary feature of the invention, these two modes of application can be combined by carrying out the changes of phase and of valence in a concomitant manner at one end of the band and separately at the other end.

When one of the changes of valence is carried out by the electrolytic process, it is an advantage for the sake of enhanced economy of the process to utilize the by-products of the electrolysis for the purpose of regenerating a reagent which has produced the other change of valence. Similarly, if both changes of valence are carried out by electrolysis, a preferred mode of application of the method consists in circulating the solution for both changes of valence within the two compartments of a same electrolytic cell, namely the anode compartment and the cathode compartment.

A better understanding of the invention will be gained by means of the practical examples which are described hereinafter. It will naturall be a arent that these examples which are illustrated in the accompanying figures 1 and 2 are not to "be interpreted in a limiting sense .

As illustrated diagrammatically in Pigs. 1 and 2, the installation employed for carrying out the method comprises essentially : - a series of columns numbered CI, C2, C3 .... CIO which are filled with ion exchanger in a uniformly packed bed. The complete assembly of columns can be heated between 20° and 100 °C either by means of a double jacket on each column or by placing all the columns within a single casing : in fact, an elevation of temperature generally has the effect of accelerating the isotopic exchange. The liquids are always circulated in downward flow within all the columns. - electrolytic cells ELI and EL2 made up in the conventional manner of two compartments separated by a porous wall or alternatively by an ion exchange membrane. The anode is formed of graphite (chloride medium) or of platinum (sulphate medium) whilst the cathode is formed of titanium coated with platinum. Both cells are electrically connected in series. - a system of valves and piping which permits all possible combinations : isolation of any one column, coupling of a number of consecutive columns in series, and so forth. The coupling between two successive columns comprises a cock for r withdrawals of solution. - pumping and storage equipment for the different solutions employed or recovered during the process.

Example 1 The ion exchanger which is employed is a cation exchanger having a medium degree of cross-linking and known commercially as DOWEX 50 W-X8 (network structure of polyst rene cross-linked b divin lbenzene to which active sulphonic groups are attached) . In the presence of an uranium aqueous solution of the e½emervb to be processed, the exchanger uranium uranium leaves the ions of said -jelQ¾e¾ in solution in a first of its valences while strongly adsorbing the ions in the second valence.

Assuming that said second valence corresponds to uranium the lowest oxidation state of ^he-c^-em ra—teeing proc-e-gae-d, the application of the method according to the invention in the particular example herein described results in the need to carry out at the rear of the isotopic exchange zone an uranium oxidation of the /6¾¾me¾yfe with displacement of the oxidized ions which are transported by the solution and a reduction uranium of the ^lomonfe at the front of the exchange zone. In this case, the reduction is carried out by electrolytic process and oxidation is carried out by means of a suitable reagent. It is apparent that oxidations and reductions would be reversed if the ion exchanger were to display a greater uranium affinity for the gi mesfe-in its most highly oxidized state of valence „ In the particular case herein described, the oxidizing reagent is ferric iron and since the element being processed is uranium to be enriched in the U isotope, ferric iron also performs the function of displacing agent which is capable of being adsorbed on the ion exchanger in the place of tetravalent uranium. It would be possible by way of alternative to add to the iron which produces the change of valence (oxidation of tetravalent uranium to hexa-valent uranium) another cation such as calcium or strontium which would produce the displacement.

The isotopic exchange is carried out in a band corresponding to the columns (which are two in number in the example considered) in which the oxidized solution containing hexavalent uranium is circulated in contact with the ion exchanger which is loaded with tetravalent uranium ; the U23*5 isotope has a tendency to collect in the hexavalent uranium. The band is displaced within the exchanger from one column to the next progressively as the displacing agent is introduced at the rear of the band.

Prior to starting up the installation, all the ion exchange columns are put in the hydrogen form in the usual manner by circulating a solution of strong acid through the exchange columns. The acid employed in this case is 2 to 3 M hydrochloric acid, A short washing operation is finally carried out with a more dilute acid solution (0.4 to 0.5 M).

The following procedure is adopted in order to form the band ; - The columns CI, C2 and C3 are connected in series, the bottom outlet of C being connected to a tank Bl which is intended for the storage of the effluent hydrochloric acid solution. The electrolytic cells ELI and EL2 are put into service and supplied with uranyl chloride solution derived from a storage tank B4 by means of a pump P4.

The reduced solution constitutes the solution to be processed. This solution is re- irculated by a pump P8 and delivered to the top of the column CI. The tetravalent uranium is immediately adsorbed on the ion exchanger and replaces the H' ions. The formation of the band can readily be followed by observing the change of coloring of the ion exchanger ; brown amber in the H + form, dark green in the U4+ form. - Delivery of the solution is stopped when the front of the band arrives near the bottom of the column C « The step which immediatel follows the formation of the band consists in causing the migration of this latter by carrying out simultaneously the oxidation and displacement of the uranium which is adsorbed on the exchanger, this being carried out in the example described by introducing after the solution to be processed a 0,1 to 0.2 M ferric chloride solution which is drawn up from a tank B2 by a pump P2„ The bottom of the column C3 is connected to the cathode compartment of the electrolytic cell ELI as illustrated in Fig. 1 ; the outlet of the cathode compartment of 10 the electrolytic cell EL2 supplies the top of the column C by means of the pump P8. The bottom of the column C4 is connected to the tank Bl which is used for the storage of hydrochloric acid.

The ferric chloride solution is delivered to the top of the column CI by means of the pump P2. The ferric ions Fe3+ oxidize and displace the uranium according to the general reaction : Fed* + 3 ¾U * 6 HO → 4 i Fe + 3 UOgC^ + 12 HC1 + 6 FeCl≥ (1 ) where R designates the radical of the polystyrene-sulphonic ion exchanger The ion exchanger turns from a dark green color which is characteristic of the U ' ions to a brown color which is characteristic of the ferric ions Fe 3+. This makes it possible to localize the rear boundary of the band with accuracy and to follow its displacement within the column.

The uranium which is displaced in the form of uranyl ions UC^ is driven towards the front of the band together with the ferrous ions Fe"'"'. The uranyl chloride solution reaches the electrolytic cells ELI and EL2 5 the solution then flows successively into the cathode compartment of ELI and then into the cathode compartment of EL2 in which it undergoes an electrolytic reduction according to the reaction s At the exit of the second electrolytic cell EL2, the reduced solution in which uranium is now present in the tetravalent state is recycled "by the pump P8 and passed to the top of the column 04. The ion exchanger which is contained in this column immediately adsorbs the uranous ions U 4+ as well as the ferrous ions Fe+*r. By reason of the differences in respective affinities, a greenish band is formed at the front and contains only ferrous ions Fe whilst a dark green band of substantially equal length is formed at the rear and contains all the uranous ions U 4+ The effluent from the column 04 consists of dilute hydrochloric acid which is directed to the storage tank Bl .

Progressively as the ferric ions Fe 3+ which are passed to the top of the column CI oxidize and displace the uranium, this latter is transported through the columns 01, .form C2 and 03 in the ta e of uranyl ions U02 in solution, passes into the electrolytic cells ELI and EL2 and is readsorbed on the ion exchanger of column 04 in the of uranous ions U4+β The ion exchanger which is contained in column 04 is progressively saturated with uranous ions U 4+ and ferrous ions Fe++. When saturation is achieved, the effluent which had hitherto consisted of a dilute solution of hydrochloric acid HC1 becomes a dilute solution of ferrous chloride. As soon as the ferrous ions appear, the effluent is directed towards a tank B3 in which the ferrous chloride is stored, then recycled by the pump P3 and delivered into an oxidation column Cll„ Said effluent flows through said column within a glass packing countereurrent to the chlorine which is evolved within the anode com artments of the electrol tic cells ELI and EL2 ; this makes it possible to regenerate that part of the ferric chloride which has served to oxidize the tetravalent uranium in the reaction of displacement of the rear boundary of the band.

Recovery of the ferrous chloride at the outlet of column 04 takes place only during the second part of the loading cycle of column 0 whilst the evolution of chlorine at the anode of ELI and EL2 is continuous „ It is therefore necessary to ensure that the tank B3 performs the function of a buffer reservoir in order to permit continuous recovery of chlorine throughout the period in which the column 04 does not produce ferrous chloride.

The mode of operation which has just been described 4-i-is carried on up to the moment when the uranous ions U appear in the effluent from column 04. This takes place when almost the entire quantity of ion exchanger which is present within the column 04 has been converted into the form U4+. At this moment, delivery of the ferric chloride solution to the top of the column 01 is stopped and the changeover operations which are necessary for the performance of the second cycle are then carried out. The changeover operations referred-to can be broken down as follows : a) The column 01 which no longer contains any uranium but only ferric ions Fe 3+ is isolated and placed in a stand-by position, P b) The pump 2 which serves to convey the ferric chloride solution is connected to the top of column 02, c) The discharge end of column 0 is connected directly to the top of column 04. d) The electrolytic cells ELI and EL2 are stopped momentarily and connected between columns 04 and 05. e) The discharge end of column 05 is connected to the hydrochloric acid storage tank Bl .

Once these changeover operations have been completed either manually or in some cases automatically, the delivery of ferric chloride solution is resumed and the electrolytic cells ELI and EL2 are restored to normal service.

This mode of operation is continued until the moment when ferrous iron appears in the effluent from column 05 ; the effluent is then directed towards the tank B3. When the uranous ions U 4-+ appear in their turn, the cycle is completed and the entire series of changeover operations described above is again carried out before proceeding with the third cycle.

The following cycles constitute an exact reproduction of the cycles which have just been described and all comprise two stages during which the effluent from the column which serves to store the reflux is successively an hydrochloric acid solution then a ferrous chloride solution.

In each cycle, the front of the band passes into a new column which contains the ion exchanger in the hydrogen ion (H+) form and the rear of the band leaves a column in which the ion exchanger is saturated with ferric ions Fe 3-s-, In order to ensure indefinite continuity of the cycles with a finite number of columns, it is possible to regenerate progressively the columns which are saturated with ferric ions Fe3+, that is to say to replace the ion exchanger contained in said columns m the hydrogen ion (H form. To this end, it is an advantage to recover the ferric icon in the form of ferric chloride which can again be employed as band displacing agent .

Thus, in Fig. 1, the columns 06, 07 and 08 are assumed to be in process of regeneration. These columns which are saturated with ferric ions Fe 3+ are coupled together in series and the hydrochloric acid which was recovered during the previous cycles and stored in the tank Bl is delivered by means of a pump PI to the top of column C6. The effluent from column G8 is then constituted by a ferric chloride solution which is delivered into the tank B2. The operation is interrupted when the column 06 is regenerated, that is to say when the solution which passes from column G6 to column C7 practically no longer contains any ferric ions. Column C7 is then only partially regenerated, and column C8 is still almost entirely in the ferric ion (3?e^+) form. In the following cycle, column C9 which is entirely in the ferric ion (Fe^"' ) form is connected in series with columns C7 and C8 and hydrochloric acid is passed through the top of column C7 whilst the ferric chloride solution which flows out of column C9 is collected in the tank B2.

After a few cycles, the quantities of reagents in the recovery tanks stabilize at a substantially constant level and it is only necessary from time to time to add a few make-up quantities of hydrochloric acid, of ferric chloride or of water in order to compensate for inevitable losses .

Withdrawals of uranium depleted in the U 235 isotope are periodically carried out at the rear of the band and compensated by injections of natural uranium. After a starting period, withdrawals of enriched uranium are also made at the front of the band and are also compensated by injections of natural uranium in order to maintain the length of band at a constant value.

The injections of natural uranium are carried out in the form of a 0.05 to 0.1 M uranyl chloride solution which is introduced at the level of the second third of the band. Between two cycles, and since the band takes up three successive columns, namely 0n_-1, Cn and C lt the delivery of ferric chloride is momentarily delayed and the desired quantity of solution is fed in between the columns Cn-1 and C by means of the pump P4.

Withdrawals of uranium which is enriched or depleted in the isotope are carried out in the same way in the form of a uranyl chloride solution, respectively at the front and at the rear of the band. At the front of the band, the withdrawal can also be carried out by periodic removal of tetravalent uranium chloride solution on the discharge side of the pump P8. At the rear, when the rear boundary of the band comes close to the bottom of a column, the displaced uranium is withdrawn instead of being passed into the following column.

By means of a plant which operates in the manner described hereinabove and comprises ten columns having an internal diameter of 5 cm and a useful height of exchanger of 140 to 1 5 cm with a rate of progression of the band of approximately 10 cm per hour, it has been possible to collect during 30 days of productive operation j 266 g of uranium enriched in the uranium-235 isotope and having a mean U2^ content of 0.76 %. 276 g of uranium depleted in the uranium-235 isotope and having a mean content of 0.68 .

During this same period, there were fed into the band 4-2 g of uranium having a natural isotopic content, namely 0.72 of U 235. Consumption of reagents resulting from purges of circulation systems and from inevitable losses amounted to approximately 0. 75 kg in the case of hydrochloric acid (expressed as anhydrous HC1) and to 0.70 kg in the case of ferric chloride (expressed as anhydrous PeCl^). During this same period, the total consumption of energy of the electrolytic cells was of the order of 25-26 kWh.

Example 2 The plant employed and the principles of operation are the same as in Example 1 except for the fact that the displacing agent is a ferric sulphate solution. In con- sequence, the solutions which are recovered during each stage of the operating cycle are respectively a dilute sulphuric acid solution and a ferrous sulphate solution whilst the anode compartments of the electrolytic cells supply oxygen.

The tank Bl is filled with a 1 to 1,5 M sulphuric acid solution, the tank B2 with a ferric sulphate solution having a concentration between 0.1 and 0.2 .

Regeneration of the exchange columns in the H"' form is carried out with sulphuric acid from the tank Bl . The ferric sulphate solution is delivered by the pump P2 to the rear of the band in order to cause the displacement of this latter.

At each cycle and during the first stage of the cycle, there is collected a dilute sulphuric acid solution which is conveyed towards the tank Bl and serves to regenerate the columns which are saturated with ferric iron 5 the ferric sulphate which is thus recovered is directed into the tank B2. During the second stage of the cycle, there is collected a ferrous sulphate solution which is directed to and stored in the tank B5. The oxygen which is evolved at the anodes of the electrolytic cells is used to reoxidize said ferrous sulphate to ferric sulphate. It is preferable to carry out this oxidation, directly rather than to utilize the packed column Oil by continuously circulating the ferrous sulphate solution through the anode compartments of the electrolytic cells ; the diaphragm which forms a separation between the cathode and anode compartments of each electrolytic cell is accordingly constituted by an ion exchange membrane of the anionic type. The ferric sulphate solution which is thus recovered is passed into the tank B2 in order to be employed again as band displacing agent .

During fifteen days of productive operation, there were collected : 132.2 g of uranium enriched in the uranium -235 isotope and having a mean content of 0.76 %. 131 g of uranium depleted in the uranium-235 isotope and having a mean content equal to 0.68 .

During this period, there were introduced into the band 264· g of uranium having a natural isotopic composition (0.72 % of The consumption of reagents amounted to approximately 1.42 kg of sulphuric acid (expressed as anhydrous H^SO^) and 0.37 kg of anhydrous ferric sulphate whilst the energy consumption of the electrolytic cells attained 14.5 kWh.

Example 3 The mode of execution which is described in this example differs essentially from those described in the foregoing by reason of the fact that - on the one hand, the element in its oxidized form (uranium VI ) is adsorbed on the ion exchanger whilst the reduced form (uranium IV) remains in the solution ; - on the other hand, use is made of a displacement solution which has neither an oxidizing nor a reducing function, the changes of valence of the uranium being effected solely by the electrolytic cells either directly or indirectly .

The plant employed is illustrated diagrammatically in Fig. 2 and differs from the plant described earlier only in the circulation systems for the storage and pumping of reagents, these systems being of slightly more simple design. In particular, there are again shown the ion exchange columns CI to CIO and the electrolytic cells ELI and EL2.

The displacing agent consists of a monosodium citrate solution having a concentration of approximately 0.2 M, said solution being stored in a tank B7 and drawn up by a pump P5>, the expression "monosodium citrate'1 being-intended to designate the citric acid salt in which the Na/citric acid ratio is substantially equal to 1/1. A tank B8 contains a citric acid solution having a concentration of approximately 0.2 M, said solution being recovered at the bottom of the column at which the front of the band is located (column 05 in the figure). This citric acid solution has two purposes : one part of the solution which is drawn up by the pump P6 serves to convert the columns from the sodium ion (Na+) form to the hydrogen ion en"1 ) form after passage of the band ; this operation provides a monosodium citrate solution which is passed into the tank B7. Another part of the solution is delivered by the pump P7 towards the cathode compartments of the electrolytic cells.

The electrolytic cells ELI and EL2 which are electrically connected in series are each provided with a partition in the form of a cation exchange membrane „ The anode com artments are filled with a sul huric acid solution having a concentration of 1 to 2 M whilst the solution to be reduced circulates successively within the cathode compartment of ELI, then within the cathode compartment of EL2„ The oxygen which is collected at the anodes is directed towards the oxidation column Cll which is continuously wetted by the solution to be oxidized at the front of the band.

The element to be treated is uranium in the form of a uranyl nitrate solution having a concentration of the order of 0.1 M. The uranyl ions are adsorbed on the exchanger in accordance with the known reaction : υθ2(ΝΟ^)2 +2^BH » U02 R2 -i-Z^WO^ (3) (R designates the pol st rene-sulphonic radical).

During the period of formation of the band, the dilute nitric acid which is produced by this reaction is rejected. Delivery of the uranyl nitrate solution is stopped when the front boundary of the uranium band comes to within approximately 10 - 20 cm from the bottom of the column C4. deionized The columns are then washed by passing Ί?¾ θ«Βΐ*·ΐ« water to the top of the column CI until final disappearance of the nitric acid ions in the effluent of the column C4. The band is then formed and ready to be displaced.

For the first displacement cycle, the connections between the different elements of the equipment are as . follows : The discharge side of the pump P5 which conveys the monosodium citrate solution stored in the tank B7 is connected to the top of column CI. The bottom of column CI is connected to the top of column C2 via the cathode compartments of the electrolytic cells ELI and EL2 and via the circulating pump P8.

The columns C2, C3 and C4 remain connected in series o The outlet of column G4 is connected to the inlet of the oxidation column Gil, at the outlet of which the solution is recycled by the pump P9 in order to be passed to the inlet of column C5. The oxidation column additionally receives the oxygen which is evolved in the anode compartments of the electrolytic cells ELI and EL2.

The outlet of column C5 is connected to the tank B8 which collects the citric acid solutions.

The displacement of the band is started by feeding monosodium citrate solution to the column Cl , the flow rate of solution being so regulated that the band is displaced substantially at a rate of 10 cm per hour. The electrolytic cells are temporarily maintained in the inoperative condition. They are started up only when the uranium appears at the outlet of the column C4. In order to prevent precipitations within the cathode compartment, an additional quantity of citric acid solution is fed into said electrolytic cells by means of the pump P7.

Under the conditions which have just been described, the uranium VI which is contained in the exchanger is displaced quantitatively in the state of uranium VI citrate in solution, passes through the column Gl and thence into the cathode compartments of the electrolytic cells ELI, EL2 in which the reduction takes place. The IT^ citrate solution thus obtained passes successively through the columns C2, G3 and C4 in which the isotopic exchange takes place between the IT" of the solution and the U which is adsorbed on the ion exchanger, then into the oxidation column in which the is oxidized to . The JJ^~ is then adsorbed on the ion ex-changer of column 05, the citric acid which has served to transport the uranium being recovered at the outlet of said When the column 05 is practically saturated with uranium, that is to say at the moment when traces of uranium appear in the citric acid effluent solution, the displacement of the band is momentarily stopped by interrupting the delivery of the monosodium citrate solution and the changeover operations required for the following cycle are then carried out. On completion of these changeover operations, all the connections are displaced by one row and are accordingly as follows j The column 01 in which the ion exchanger has changed entirely to the sodium ion (Na ) form is isolated. The monosodium citrate supply is connected to the inlet of the column 02, the lower end of which is connected to the electrolytic cells ELI and EL2. The reduced solution passes through the columns 03, 04 and 05, then through the oxidation column Gil whilst the column 06 /agai-a serves to adsorb the displaced uranium on the ion exchanger.

The displacement of the band through the series of ten columns is thus carried on from cycle to cycle. When the column CIO is saturated with uranium, the front of the band is directed towards the column 01 and during the following cycles the band again passes through the series of ten columns.

After passage of the band, the columns which are taken put/out of service are saturated with sodium ions Na"1 and their regeneration, that is to say the replacement of the sodium ions Na by hydrogen ions H is carried out in such a manner so as to supply a monosodium citrate solution which can be employed as displacing agent. In Fig, 2, the columns 07, 08 and 09 are in process of regeneration. These columns are coupled together in series and the citric acid solution which is held in reserve in the tank B8 is fed into the top of the first column C7 by means of the pump P6 throughout the duration of one cycle whilst the sodium citrate solution which is collected at the bottom of the column 09 is directed towards the tank B? .

The operation of the plant being performed under the conditions hereina ove described, the displacement of the band is continued for a period of 48 days. During this time, uranium which is enriched in the isotope accumulates at the rear of the band whilst uranium which is depleted in the isotope accumulates at the front of the band.

There then begins on the 49th day the withdrawal of uranium at each end and the injection of natural uranium in accordance with the procedure which is described in Example 1, the only difference being that it is preferable in this case to carry out the injections substantially at the center of the band. By way of example, and starting from uranium having a natural isotopic content (0.72 of U ), there are thus obtained in the course of 24 days of productive operation . 210 g of enriched uranium having a mean content of 0.76 216 g of depleted uranium having a mean content of 0.96 %,

Claims (9)

-22 - 33003/2 Claims :

1. A method of isotopic enrichment of uranium 235 by means of ion-exchange between uranium ions in a first and in a second valence thereof, respectively, characterized in that it consists : - in placing an ion exchanger in a fixed bed i a form which is capable of selectively adsorbing the uranium ions in the second valence, - in circulating through said ion exchanger a solution to be processed which contains uranium in the form of ions in said first valence, and possibly in a minor proportion in the form of ions in said second valence, - in changing the uranium ions in the solution to be processed from said first to said second valence in order to cause the adsorption of said lone on the ion exchanger, - in circulating through said ion exchanger after the solution to be processed a solution of a displacement agent which is capable of displacing the uranium ions from the exchanger, - and in changing said displaced uranium ions from the second to the first valence.

2. A metliod in accordance with claim 1, characterized in that at least one of the changes of valence of said element is carried out by reaction with an oxidizing or reducing reagent.

3. A method in accordance with claim 2, characterized in that said reagent is present in the ion exchanger downstream of the solution to be processed.

4. A method in accordance with claim 2, characterized

5. A method i accordance with claim 2, characterized in that said reagent is a salt which constitutes the displacing agent at the same time, especially a ferric salt ΛΆ—■ tho oaoo in which the method is applied to the

6. A method in accordance with any one of the preceding claims, characterized in that at least one of the changes of valence of said element is carried out by electrolytic process.

7. A method in accordance with claim 6, characterized in that the by-products of electrolysis are employed for the purpose of regenerating a reagent which has caused the other change of valence.

8. A method in accordance with claim 6, characterized in that the two changes of valence are carried out by electrolytic process by circulating the solution respectively within the two compartments of a same electrolytic cell, namely the anode compartment and cathode compartment of said cell.

9. A method of isotopic exchange in accordance with claim 1 , substantially as hereinbefore described with reference to the accompanying drawings. For the App'fcants B 2807.34