EP0008552B1 - Process for the recovery of uranium from an organic phase - Google Patents

Abstract

The invention relates to a process for the recovery and the concentration of uranium (VI) contained in an organic phase. The organic phase is treated continuously in a contact zone with an aqueous solution containing an oxidizing-reducing agent in the reduced state, said oxidizing-reducing agent being capable of reducing U+6 to U+4 in said aqueous solution. The aqueous solution employed in the process issues in part or in its entirety from the cathodic compartment of an electrolytic separation cell, which is under a direct current potential, and the aqueous phase issuing from the contact zone feeds in part or in its entirety the anodic compartment of the electrolytic cell. The process is of particular interest when applied to the recovery and concentration of uranium contained in a wet process phosphoric acid.

Description

The present invention relates to a process for recovering uranium contained in a complexing organic phase and it relates more particularly to the concentration and purification of uranium extracted from a wet phosphoric acid.

It is known to recover uranium from aqueous solutions containing it at low concentrations, by separating it from the other species (if applicable recoverable) constituting the ores treated, by means of a set of liquid-liquid extraction and treatments. aiming to isolate uranium and recover it in the form of high purity U30 $ oxide, usable as a source of nuclear fuel. These processes apply to the recovery of ores such as phosphate rocks, which also provide phosphoric acid or to ores of various origins with a higher or lower content of uranium most often present in the form of oxides. The process generally involves the treatment of the ore with a strong and concentrated acid such as sulfuric, phosphoric, hydrochloric, nitric acids to provide an aqueous solution containing uranyl ions in the very diluted state together with other contaminating ions, from which uranium is recovered.

A typical example of treatment of such a solution is described by F. J. Hurst and D. J. Crouse - Ind. Eng. Chem. Process Des. Develop., Vol. 11, n ° 1, 1972, pages 122-128 starting from a crude phosphoric acid of wet way resulting from the attack of a rock phosphated by sulfuric acid.

The resulting solution in which the uranium is found or is transformed in the dehydrated state U (VI) is subjected to a first cycle of extraction of the uranium by means of an oregano solvent constituted by a synergistic mixture of extractants , di- (2 ethylhexyl) phosphoric acid (designated by HDEHP) and trioctylphosphine oxide (designated by TOPO), diluted in a kerosene type hydrocarbon. The uranium is then extracted into the organic solvent in the form of a uranyl complex formed between the uranium (VI) U02 ¹ ions and the synergistic mixture of extractants. The uranium is then recovered from the organic phase in which it was extracted, by contact with an aqueous solution of phosphoric acid containing enough iron (II) ions to reduce the uranium (VI) to uranium (IV) which , not extracted by the organic solvent, is transferred to the aqueous phase. This aqueous phase is then reoxidized to bring the uranium to the oxidation state (VI) again and is then subjected to a second extraction cycle with an organic phase containing the synergistic mixture of HDEHP-TOPO extractants to finally obtain after re-extraction uranium by a solution of ammonium carbonate, a sufficiently pure mixed carbon of uranium and ammonium.

This process has drawbacks in terms of its industrial exploitation. In particular the reductive re-extraction in the first cycle requires the addition of iron ion (11) which is obtained by attacking iron with phosphoric acid, which is a slow and difficult reaction or by introducing an iron salt. (II) - which implies the introduction of an additional anion. Anyway, this way of operating has the disadvantage of introducing a significant amount of iron in phosphoric acid which seriously interferes with the second uranium purification cycle downstream. In addition, this second extraction cycle is carried out on the oxidized aqueous solution and treatment with an oxidant is necessary. If this oxidation is practiced by means of air, the operation is slow and requires substantial equipment. If this oxidation is carried out by means of a chemical oxidant, it involves the introduction of harmful foreign ions; for example, the introduction of chlorate ions provides by reduction of chloride ions which are powerful corrosion agents. Furthermore, the use of hydrogen peroxide is a high cost price.

Furthermore, it is known according to French Patent No. 2,041,169 to modify the valence of a metal with variable valence, contained in an organic solution, by forming by stirring a dispersion of said organic solution with an immiscible aqueous solution and by passing an electric current through said dispersion in the cathode zone of an electrolyser if a lower valence state is desired or in the anode zone, if a higher valence state is desired, said electrolyser comprising a membrane porous zone separation.

• 1) ladite solution aqueuse d'extraction provient en totalité ou en partie du compartiment cathodique d'une cellule électrolytique à séparateur sous tension de courant continu;
• 2) ladite phase aqueuse provenant de ladite zone de contact et chargée en uranium alimente en totalité ou en partie le compartiment anodique de ladite cellule électrolytique à séparateur sous tension de courant continu, ce par quoi l'on recueille une phase aqueuse, concentrée en uranium substantiellement sous forme U (VI) et l'agent d'oxydo-réduction à l'état oxydé qui constitute la production.

The method of the invention comprises the continuous treatment in a contact zone of an organic phase containing a uranyl complex formed between the uranium (VI) U02 ⁺ ions and an extractant or a mixture of extractants not miscible with water, optionally an excess of extractant or mixture of extractants not complexed with uranium, optionally diluted with an inert organic solvent that is not miscible with water, using an aqueous extraction solution containing an oxidoreducing agent, in the reduced state, which is reducing uranium (VI) to uranium (IV), in said aqueous solution, whereby the uranium is reduced and extracted in said aqueous solution in the form of U (IV) ions, then the separation of an organic phase depleted in uranium and an aqueous phase charged with uranium, the process being characterized in that:

• 1) said aqueous extraction solution comes in whole or in part from the cathode compartment of an electrolytic cell with a separator under direct current voltage;
• 2) said aqueous phase coming from said contact zone and loaded with uranium supplies all or part of the anode compartment of said electrolytic cell with separator under direct current voltage, whereby an aqueous phase is collected, concentrated in uranium substantially in U (VI) form and the redox agent in the oxidized state which constitutes the production.

According to the invention, the starting organic phase contains an extractant for uranium (VI) ions but little extraction of uranium (IV). This type of extractant is well known in the art. It includes cationic extractants, among which non-limiting examples may be mentioned, products such as certain mono or dialkylphosphoric, alkylphosphonic, alkylphenylphosphoric, alkylphosphinic, alkylpyrophosphoric acids used alone or as a mixture, the alkyl chains generally comprising 4 to 10 carbon atoms. If necessary, the extraction agent as defined above can be combined with a well-known synergistic extraction agent such as, for example, alkylphosphates, alkylphosphonates, alkylphosphinates or trialkylphosphine oxides. Among the pairs which are very suitable for the extraction of uranium from phosphoric acid, there may be mentioned, for example, the mixture of di (2 ethylhexyl) phosphoric acid - trioctylphosphine oxide. It likewise comprises anionic extractants such as certain secondary or tertiary alkylamines which are not soluble in water and well-known extractants, of neutral nature, immiscible in water such as trialkyl phosphates.

The organic phase contains, where appropriate, an organic diluent which is inert towards the extractants in order to improve the hydrodynamic properties of the organic phase. According to the invention, many organic solvents or their mixtures can be used as a diluent. By way of illustration, mention may be made of aliphatic hydrocarbons such as kerosene, aromatic, halogenated and petroleum ethers, etc. In general, the characteristics of the inert diluent are not critical although some have advantages under particular conditions. 'use.

The concentration of extractant in the diluent can vary within wide limits between 0.05 mol and the pure extractant. However, from a practical point of view, extractant solutions of between 0.1 and 2 molar are usually used. In the case of the use of an extractant together with a synergistic extracting agent, the solution ranges from 0.1 to 2 molar for the extractant and from 0.01 to 2 molar for the synergistic agent.

The starting organic phase contains uranium at the oxidation state (VI), taking into account the conditions for producing this solution. It also contains other chemical species depending on its production conditions. Especially in the case of a solution obtained by liquid-liquid extraction of a crude wet phosphoric acid, it usually contains phosphoric acid and other anions and metal cations such as AI, Fe, Ti, V , etc ... in the weakly concentrated state. The uranium concentration of the organic phase is generally between 20 and 3000 mg expressed as metal uranium per liter of phase, preferably between 50 and 500 mg per liter.

The aqueous solution which is brought into contact with the preceding organic phase generally contains a strong and complexing acid such as phosphoric or hydrochloric acid and optionally other acids or their mixtures, with the restriction that the presence of these acids does not lead to precipitation of uranium. The aqueous solution also contains a redox agent from uranium (VI) to uranium (IV), the agent being in the reduced state. The electrochemical potential of the preceding redox couple in the aqueous solution considered is such that it is less than that of the uranium (VI) - uranium (IV) couple in said solution. A representative redox couple is the iron (III) / iron (II) couple. Consequently, when this pair is used, the aqueous solution contains iron with the degree of oxidation (II). In order to shift the equilibrium of the reaction between the ions U (VI) and Fe (II) on the one hand and U (IV) and Fe (III) on the other hand, in the direction favorable to the production of ions U (IV), the solution should contain a large excess of iron (II) ion compared to uranium ions. The concentration of the iron solution in the oxidation state (II) is usually between 0.5 and 100 grams per liter. The concentration of strong acid in the solution can vary within wide limits. However, in practice, with a view to obtaining maximum uranium depletion of the organic solution, the concentration will be chosen according to the specific phases used and the temperature. In the case where the strong and complexing acid of the aqueous solution is phosphoric acid, its concentration in the solution must be between 18 and 70%, preferably greater than 35% by weight of P _Z O _S. The solution may also contain iron ions with the degree of oxidation (III); the ratio of the concentration of iron (11) ions to the concentration of iron (III) ions can vary within very wide limits. In practice, however, a value greater than 0.1 is indicated, but preferably it is greater than 10.

The organic phase containing the uranium at the oxidation state (VI) and the aqueous solution which have been described above, are brought into contact in a conventional liquid-liquid extraction apparatus. This contacting can be carried out in mixers- decanters, packed or pulsed columns, or any other suitable device, the contact being co-current or counter-current. The temperature during contacting is not critical but for practical reasons it is preferred to operate between 20 ° C and 80 ° C, preferably in the vicinity of 50 ° C.

The ratio of the flow rates of the organic phase to the aqueous extraction solution entering the contact zone is not critical but must be kept as high as possible in order to recover the uranium in the form of a concentrated solution. However, a value between 20 and 50 leads to the best results. This value range does not take into account the internal recycling in the extraction zone.

During contacting, it is believed that the uranium (VI) partition equilibrium between the organic phase and the aqueous solution is quickly established, while the reduction of uranium (VI) in the solution aqueous by the reducing agent is slow. Knowledge of this reduction kinetics and of the isotherms for sharing U (VI) and U (IV) between the two phases makes it possible to adjust the various parameters of the bringing into contact with a view to a maximum result of the extraction.

The aqueous phase leaving, after separation, from the previous contact zone, containing the U (IV) ions and the oxidation-reduction agent in the partially oxidized state, is preferably divided into two streams each supplying a compartment d '' an electrolytic cell with separator under direct current voltage. The first derivative current feeds the cathode compartment of said cell under direct current voltage, whereby the redox agent is electrolytically reduced. Thus, in the case of the use of the iron III / iron II couple as an oxidation-reduction agent, iron (III) ions are reduced to iron (II) ions. Then, this first current again supplies the contact zone with the organic phase previously defined, to form a closed circulation loop. After derivation of this first current, before its introduction into the cathode compartment of the electrolytic cell, an aqueous solution is added to it, preferably containing strong and complexing acid, and containing ions of the redox couple, in amounts corresponding to those withdrawn in the second derivative current, this in order to balance the material balance. In the specific case of application of the present process to the treatment of an organic phase containing uranium (VI) and originating from the extraction of a crude phosphoric acid from the wet process, the aqueous solution added to the first derivative stream comprises phosphoric acid at a concentration equivalent to that of the aqueous solution circulating in the previous loop. In the case of the use of the iron (III) / iron (II) couple as an oxidation-reducing agent, the iron of this added solution can be in the form of iron (II) or iron (III) ions and can come from either iron present in phosphoric acid, or iron (II) or iron (III) salt added to this solution, or iron attack by phosphoric acid.

The second derivative current feeds the anode compartment of said electrolytic cell with separator under direct current voltage, the intensity in the two compartments being equal, whereby an aqueous phase is collected, as a result, substantially concentrated in uranium. in U (VI) form and containing the redox agent in the oxidized state, which constitutes the production. The aqueous phase leaving the anode compartment with a high concentration of uranium at the oxidation state (VI) undergoes subsequent physical and chemical treatments, which are not part of the invention, with a view to recovering the uranium therefrom.

The electrolytic cell used for implementing the method of the invention is a well-known separator cell. As a separator, one can use a porous material such as a ceramic or a plastic material made porous by sintering or by introduction of porophore or an ion exchange membrane. Among these separators, a cationic ion exchange membrane is preferred, preferably consisting of perfluorinated polymer with sulfonic acid groups. The anode is generally made of graphite or a metal covered with an electroactive coating such as the Ti / precious metal alloy pair. The cathode can be made up of different metals such as platinum, lead, the Ti / precious metal alloy pair. The configuration of the cell is generally of the planar type with a large electrode surface and a small spacing between the electrodes. In a preferred form of industrial implementation, a battery of electrolysis elements mounted in series in a multicellular device of the well-known filter press type is used. In this embodiment, the supply of the cathode compartments can be in parallel or in series, this in order to regulate the flow rates of liquid in each element. In order to promote electrochemical reactions, it may be advisable to increase the active surface of the electrodes or to cause significant agitation of the solutions by sets of baffles. Similarly, the supply of the anode compartments is due in series or in parallel. In addition, in order to balance the pressures of the two compartments, the anode compartment may include recycling of the outgoing solution.

• -la figure 1 est une représentation schématique de la circulation des courants liquides selon un mode de réalisation principal qui peut comporter plusieurs variantes d'exécution, et fonctionnant à une zone de contact et un élément ou une batterie d'éléments électrolytiques.
• -la figure 2 est une autre forme de réalisation à une zone et une batterie d'éléments.
• -la figure 3 est un mode de réalisation comportant deux zones de contact et deux batteries d'éléments électrolytiques avec les courants associés.
• -la figure 4 est une représentation schématique d'un mode de réalisation comportant une zone de contact et deux batteries d'éléments électrolytiques.
• -la figure 5 illustre un mode de réalisation comportant un autre mode de circulation des solutions à une zone de contact et une batterie d'éléments électrolytiques.

The invention will be better understood using the attached figures in which:

• FIG. 1 is a schematic representation of the circulation of liquid streams according to a main embodiment which may include several variant embodiments, and operating at a contact zone and an element or a battery of electrolytic elements.
• FIG. 2 is another embodiment with a zone and a battery of elements.
• FIG. 3 is an embodiment comprising two contact zones and two batteries of electrolytic elements with the associated currents.
• FIG. 4 is a schematic representation of an embodiment comprising a contact zone and two batteries of electrolytic elements.
• FIG. 5 illustrates an embodiment comprising another mode of circulation of the solutions to a contact zone and a battery of electrolytic elements.

In FIG. 1, the circulation of the liquid streams according to the main embodiment is illustrated. An organic phase containing the extractant, if necessary an inert organic diluent and uranium to the oxidation state (VI), is introduced via the stream (1) into a liquid-liquid contact zone (2). Through the current (6), an aqueous extraction solution containing the redox agent in the reduced state is also introduced there. After settling of the phases, it leaves the zone (2), an organic phase current (3) depleted in uranium and an aqueous phase current (4) containing uranium (IV), and the redox agent partly oxidized. This stream (4) is divided into a stream (5) which is added to the stream (6) to form a recycling loop. The remaining stream is in turn divided into two streams (7) and (8). The current (8) feeds the cathode compartments of an electrolytic cell battery represented schematically by (12) and the current (7) feeds the anode compartments of said battery and are represented schematically by (13). Furthermore, to the stream (8) is added a stream (10) consisting of an aqueous solution containing the redox agent. From the cathode compartments a current (9) comes out which, after adding the current (5) constitutes the aqueous solution entering the contact zone (2). Anodic compartments (13) leaves an aqueous solution which is sent to a storage not shown and containing, where appropriate, the complexing acid, uranium in the concentrated state substantially in U (VI) and l oxidizing agent in the oxidized state, which constitutes the production. This solution then undergoes subsequent treatments to recover the uranium.

In a first variant of this main embodiment, all of the current (4) is sent to the anode compartments (13). Therefore, the current (5) is zero and the current (8) is zero, so that the cathode compartments (12) are only continuously supplied with a fresh aqueous solution, containing, if necessary, the complexing acid. and the redox couple.

In a second variant, the streams (5) and (8) not being zero, the stream (10) is introduced into the stream (8) to form, after the addition of the stream (5), the stream of aqueous solution supplying zone (2).

Of course, in the case of using the iron (11) / iron (III) pair, the solution (6) must satisfy the conditions described above with regard to the iron (11) / iron (III) ratio and the power solution reducer. In this case, only the derivative current (8) feeds the cathode compartments (12) to undergo a reduction of the iron ions (III) there.

In a third optional variant, the production solution (11) leaving the anode compartments (13) and which contains the uranium substantially in U form (VI) can be added with a very small amount of chemical oxidant such as hydrogen peroxide, in order to perfect during storage, the transformation into U (VI) of U (IV) ions; but in any event, the amount of chemical oxidant added represents a very small fraction, preferably (of the order of a few percent) of the amount of oxidant which would have been necessary to achieve total oxidation of the uranium and the redox agent chemically without using the process of the invention.

Referring to Figure 2, an embodiment is illustrated comprising a contact area and a battery of electrolytic elements. For the sake of simplification, the aqueous contact extraction solution comprises a strong and complexing acid and an oxidoreducing agent consisting of iron ions. Of course, it is possible to use another redox agent provided that it satisfies the requirements required above.

An organic phase containing the extractant, if necessary, the inert organic diluent and the uranium (VI) is introduced into (14) into a contact zone (16). Through the stream (21) an aqueous complexing acid solution containing iron (II) is also introduced there. After settling of the phases, an organic phase current (15) exhausted in uranium and an aqueous phase current (17) containing uranium (IV), iron (II) and iron leave the zone (16). (III). This stream (17) is divided into two streams (18) and (20). The current (18) feeds the anode compartments of a battery of electrolytic elements schematically represented by (24) and exits by the current (19) which is the production current and containing the complexing acid, from uranium to l 'state substantially concentrated in U (VI) form and iron in iron (III) form, which is sent to storage for further processing. The current (20) is added to the current (22) consisting of an aqueous solution of complexing acid and iron ions. The combined current (25) supplies the cathode compartments of a battery of electrolytic elements schematically represented by (23). Compartments (23) output the current (21) in the reduced state which feeds the contact zone (16). Likewise, optionally, the current of produc tion (19) can be added with a very small amount of a chemical oxidizing agent.

FIG. 3 illustrates an embodiment comprising the use of two contact zones and two batteries of electrolysis elements. An organic phase containing the extractant, if necessary, the inert organic diluent, and the uranium (VI) is introduced via the stream (30) into a first contact zone (31). The organic phase partially depleted of uranium leaves this first zone by the current (32) which feeds a second contact zone (33). After separation of the phases, the organic phase exhausted in uranium leaves by the current (34). By the combined current (39) and (45) which will be explained below, an aqueous solution comprising complexing acid, iron ions and a small proportion of uranium ion (IV) is also introduced into the first zone (31). ). After contact and separation of the phases in the zone (31), an aqueous phase (35) containing uranium (IV), iron (II) and iron (III) is removed. This stream is divided into two streams (36) and (37). Current (36) feeds the cathode compartments of a first battery of electrolytic elements schematically represented by (38). This current, after reduction, constitutes the current (39) which partially supplies the first contact zone (31). The current (37) successively supplies the anode compartments of a second battery of electrolysis elements represented diagrammatically by (40) and then by the current (41) the anode compartments (42) of the first battery of electrolytic elements already mentioned. From the compartments (42) there flows a current (43) which constitutes the production and which is sent to storage, not shown. In the second contact zone (33), the organic phase stream (32) is brought into contact with an aqueous solution (44) containing the complexing acid, iron (II) and iron (III) and a small proportion of 'uranium (IV). After separation of the phases, an aqueous phase is removed from the zone (33) which is divided into a current (45) which feeds together with the current (39) described above, the first contact zone, and into a current (46), which after adding a fresh current containing the complexing acid and iron ions supplies the cathode compartments of the second battery of electrolytic elements already mentioned, and represented schematically by (48). Of course, according to this scheme of implementation and circulation, the material balance requires that the amounts of complexing acid and iron entering by the stream (47) are equal to those leaving in the production stream (43).

FIG. 4 represents another embodiment comprising several contact zones and a single battery of electrolytic elements. The organic starting phase is represented by the current (50) which is successively brought into contact in the zones (58), (56) and (54) with an aqueous solution as will be explained below. After separation, the spent uranium phase leaves the zone (54) by the current (60). Furthermore, an aqueous solution containing the complexing acid and iron ions is introduced by the stream (51). This solution supplies the cathode compartments of a battery of electrolytic cells, represented schematically by (52). The reduced current (53) outgoing, successively supplies a first contact zone (54) with the organic phase then after separation of the phases, a second zone (56) and finally a third zone (58) in the contact order (54 ), (56), (58) while the organic starting phase is brought into contact in successive order (58), (56), (54). In each of the zones (54), (56) and (58), which consist of three banks of mixer-settlers, a fraction of the mixture is taken from the final mixer-settler, in the direction of circulation of the aqueous phase. aqueous phase which is reintroduced respectively into the first mixer-settler of each battery in the form of the streams (55), (57) and (59). From the contact zone (58) comes an aqueous phase (61) enriched in uranium (IV) which is sent entirely into the anode compartments of the battery of electrolytic elements represented diagrammatically by (62), from which an aqueous stream (63) enriched in uranium (VI) is recovered which constitutes the production and which is sent to a storage not shown.

As with the previous embodiments, this mode may include the optional variant of processing the production by means of a very small quantity of chemical oxidizing agent.

FIG. 5 represents an alternative embodiment of the invention with a contact zone and a battery of electrolytic elements. The organic phase loaded with uranium represented by the stream (70) is introduced into the contact zone (74) from which it leaves exhausted after settling by the stream (79). An aqueous solution of complexing acid containing iron (II) is also introduced into this zone and which comes from the cathode compartments of a battery of electrolytic cells with separator, represented schematically by (72), these compartments being supplied by a current. (71) of a fresh solution of complexing acid and iron ion. After contact and decantation in said zone, an aqueous phase (76) charged with uranium (IV) is collected at the exit from the zone. In the contact zone (74) consisting of a set of mixer-settlers, a derivative current (75) is withdrawn from the last mixer-settler which is reintroduced into the first mixer-settler of said battery in order to form a loop. recycling (75-74). The current (76) feeds the anode compartments of said battery of electrolytic elements, which are schematically represented by (77) and exits by the current (78) which constitutes the production. This stream enriched in uranium (VI) is sent to storage for further processing. As for the embodiments of the preceding figures, the embodiment of FIG. 5 can optionally comprise the treatment of the production stream (78) by means of a very small quantity of chemical oxidizing agent.

It is understood that the embodiments shown in the preceding figures are given only by way of illustration and do not constitute a limitation of the invention. On the contrary, those skilled in the art can envisage alternative embodiments which fall within the scope of the invention as defined by the claims.

The advantages provided by the present process are: lower consumption of energy for oxidation and reduction than that consumed in separate cells and therefore a corresponding lower cost. In addition, the process makes it possible not to introduce foreign ions and in the case of the use of iron as agent of redox agent, the iron content in the production is limited to a concentration acceptable for the simple recovery of uranium of high purity, compared to the processes of the prior art.

The invention is illustrated by means of the following nonlimiting examples, the percentages being expressed by weight, unless otherwise indicated.

Example 1:

This example illustrates the embodiment shown in FIG. 2.

sous un débit de 5,00 litres par heure.An organic phase is introduced in (14) comprising, as an inert organic diluent, kerosene. This phase has a concentration 0.5 molar di- (ethyl-2-hexyl) phosphoric acid, 0.125 molar trioctyl oxide. ¹ phosphine and additionally containing 190 mg / liter of uranium (VI) ions. The phase flow is 5 liters per hour. The organic phase is brought into contact at 50 ° C in zone (16), consisting of a mixer-settler with an aqueous solution (21) of composition:

at a flow rate of 5.00 liters per hour.

After decantation, the outgoing aqueous phase (17) is divided into a stream (20) with a flow rate of 4.87 liters per hour and into a stream (18) with a flow rate of 0.13 liters per hour.

To the stream (20) is added a stream (22) consisting of an aqueous 35% phosphoric acid solution of P ₂ 0 ₅ containing 8 g / liter of iron in ferric form at a flow rate of 0.13 I / hour.

The current (25) resulting feeds the cathode compartment (23) of an electrolysis cell with a membrane made up of perfluorosulfonic polymer (trademark NAFION by Du Pont de Nemours). The electrolysis cell has two compartments of dimension 7 x 20 cm with planar electrodes, the anode being in graphite and the cathode being in lead. The distance from the cathode to the membrane is 3 mm and that from the anode to the membrane is 3 mm.

The anode compartment (24) is provided with staggered baffles making it possible to lengthen the path of the electrolyte and to increase its speed. A continuous electric current of 1 ampere is applied to the cell, the voltage at the terminals being established at 2 volts.

The organic phase (15) after extraction contains 18 mg / i of uranium.

The current (18) feeds the anode compartment (24) of the electrolysis cell.

A solution (19) of phosphoric acid 35% of P ₂ O ₅ containing the ions is collected:

The electrical energy consumption in the electrolytic cell necessary to process 1 kg of uranium is 2KW hour.

Example 2:

This example illustrates the embodiment shown in FIG. 3.

The temperature throughout the device is maintained at 50 ° C.

An organic phase is introduced via stream (30) comprising kerosene as an inert organic diluent. This phase has a concentration of 0.5 molar di- (ethyl-2-hexyl) phosphoric acid, 0.125 molar trioctylphosphine oxide and additionally containing uranium (VI) ions at a concentration of 230 mg / liter. The flow rate of the phase is 5 liters per hour and its temperature of 50 ° C.

et d'autre part, d'un courant (45) qui sera explicité ci-après.Is introduced in (47) a stream of fresh aqueous solution of phosphoric acid 34% P ₂ 0 ₅ and brought to 50 ° C containing 9 g / liter of iron in ferric form, at a rate of 0.15 liter / hour. Phase (30) is brought into contact with an aqueous solution which is the union of two streams, on the one hand stream (39) with a flow rate of 5 liters per hour of the following composition:

and on the other hand, of a current (45) which will be explained below.

At the exit from the contact zone (31), an aqueous stream (35) is recovered which is divided into two streams (36) and (37). The current (37), with a flow rate of 0.15 liters / hour, feeds the anode compartment (40) of a second electrolysis cell of the same constitution as that of Example 1, while the current (36) supplies the cathode compartment (38) of a first cell. A current of 0.40 amperes is applied to the terminals of the first cell. The current (37) after having passed through the anode compartment (40) of the second cell at an intensity of 0.75 amperes, is introduced by the current (41) into the anode compartment (42) of the first cell and leaves in the form a current (43) at a flow rate of 0.15 liters / hour with the following composition:

This current which constitutes the preduction is then sent to storage.

The organic phase current (32) leaving the first contact zone (31) then enters a second zone (33) consisting of a mixer-settler. It is brought into contact there with an aqueous solution (44) at a flow rate of 5 liters per hour, the composition of which is:

The organic phase leaves zone (33) at a uranium concentration of 2 mg / liter. The aqueous phase leaving the zone (33) is divided into two streams, the first (45), with a flow rate of 0.15 liters / hour, is combined with the stream (39) to supply the first area (31) while the second (46), with a flow rate of 5 liters / hour, after having added the fresh current (47) already described, feeds the cathode compartment (48) of the second electrolytic cell. It emerges in the form of the reduced current (44) to supply the second contact zone (33). The quantities of phosphate and iron ions introduced in (47) are equal to those leaving by (43).

Example 3:

This example illustrates the embodiment represented by FIG. 4.

Is introduced in (50) an organic phase consisting of kerosene containing di (ethyl-2-hexyl) phosphoric acid, with a concentration of 0.5 molar, trioctylphosphine oxide (0.125 molar) and 120 mg / 1 of U (VI) ions. The flow rate of the phase is 8 liters / hour and the temperature in the entire device is 50 ° C.

An aqueous solution of phosphoric acid containing 33% P ₂ O ₅ at 50 ° C. and containing 18 g / liter of Fe ³⁺ ions and 12 g / liter of Fe2 + ions is introduced in (51) at a flow rate of 0.20 liters / hour, in the cathode compartment (52) of an electrolysis cell identical to that of Example 1, the electrical intensity being 2.5 amperes.

The outgoing aqueous solution (53) contains:

This solution is sent against the current of the organic phase (50) successively in three mixer-settlers (54), (56), (58) provided with internal recirculations respectively (55), (57), (59) whose flow rates are 4 liters per hour.

The organic phase (60) leaving the zone (54) is depleted of uranium at a concentration of less than 1 mg / liter.

The aqueous phase (61) leaving the zone (58) is sent to the anode compartment of the electrolysis cell at a flow rate of 0.2 liters / hour. The aqueous phase (63) which constitutes the production contains 30 g / liter of Fe (III) ions and 4.76 g / liter of uranium ion, of which 4.2 g / liter in U (VI) form.

Example 4:

This example illustrates the embodiment shown in Figure 5. The temperature throughout the device is 55 ° C.

A solution of kerosene containing 0.5 mol / l of di (ethyl-2-hexyl) phosphoric acid, 0.125 mol / l of trioctylphosphine oxide and 150 mg / l of U (VI) ions is introduced in (70). ). The flow rate is 41 / h, the temperature 55 ° C.

0.1 I / h of a 37% P ₂ O ₅ phosphoric acid solution (71) is introduced into the cathode compartment (72) of a cell identical to that described in Example 1. ° C, containing 30 g / I of iron ions introduced in the form of sulfate, of which 20 g / I are in Fe ³⁺ form. The applied intensity is 1.0 amperes.

The outgoing solution (73) containing 28 g / I of ferrous ions is brought into contact with the organic phase (50) in the mixer-settler (74) provided with an internal circulation (75) having a flow rate of 3 I / h.

The outgoing organic phase (79) contains 15 mg / I of uranium.

The aqueous solution leaving the mixer-settler (76) is introduced into the anode compartment (77) of the cell and leaves at (78) with the following ionic concentration:

The solution that constitutes the production is sent to storage for further processing.

Claims (25)

1. A continuous process for the recovery and concentration of uranium in a degree of oxidation of (VI) which is contained in a water-immiscible organic phase, with little extracting action in respect of uranium (IV), comprising the treatment of said phase in one or more liquid- liquid contact zones, by means of an aqueous extraction solution containing a soluble oxidoreduction agent, in the partially or totally reduced state, which is capable of reducing uranium (VI) to uranium (IV) in said aqueous solution, whereby the uranium is reduced and extracted in said aqueous solution, in the form of U (IV) ions, then separation of an organic phase which is exhausted in respect of uranium and an aqueous phase which is charged in respect of uranium, the process being characterised in that:

1. said aqueous extraction solution originates totally or partly from the cathodic compartment of a separator-type d.c. voltage electrolytic cell; and

2. said aqueous phase originating from said contact zone, which is charged in respect of uranium, totally or partially feeds the anodic compartment of said separator-type d.c. voltage electrolytic cell, whereby there is collected an aqueous phase which is concentrated in respect of uranium substantially in the form U (VI), and containing the oxidoreduction agent in the oxidised state, which forms the production.

2. A process according to claim 1 characterised in that the organic phase contains an extracting agent of cationic nature for uranium in a degree of oxidation of (VI).

3. A process according to claim 2 characterised in that the cationic extracting agent is at least one member selected from mono- or dialkylphosphoric, alkylphenylphosphoric, alkyl- phosphinic, alkylphosphonic, and alkylpyrophos- phoric acids, the alkyl groups containing from 4 to 10 carbon atoms.

4. A process according to claim 2 characterised in that the cationic extracting agent is di-(2-ethylhexylfphosphorfc acid.

5. A process according to claim 3 or claim 4 characterised in that the organic phase further contains a synergic extraction agent.

6. A process according to claim 5 characterised in that the organic phase contains di-(2-ethylhexyl)phosphoric acid and trioctylphosphine oxide.

7. A process according to claim 1 characterised in that the organic phase contains an extracting agent of anionic nature selected from water-insoluble secondary or tertiary amines.

8. A process according to claim 1 characterised in that the organic phase contains an extracting agent of neutral nature, which is water-immiscible and which is selected from trialkyl phosphates.

9. A process according to one of the preceding claims characterised in that in addition the organic phase contains an organic diluent or solvent which is inert with respect to the extracting mixture, selected from halogenated or unhalogenated aromatic or aliphatic hydrocarbons or petroleum ethers.

10. A process according to claim 6 characterised in that the inert diluent is kerosene.

11. A process according to claim 6, claim 9 and claim 10 characterised in that the concentration in the inert diluent of di-(2-ethylhexyl) phosphoric acid is from 0.1 to 2 molar and that the concentration of the synergic agent is from 0.01 to 2 molar.

12. A process according to any one of the preceding claims characterised in that the uranium concentration in the organic phase is from 20 to 3000 mg/litre, preferably from 50 to 500 mg/litre.

13. A process according to claim 1 characterised in that the aqueous contacting solution is a solution of a strong acid, complexing in respect of uranium (IV), which is selected from phosphoric, hydrochloric and sulphuric acids.

14. A process according to claim 13 characterised in that the phosphoric acid concentration in the aqueous extraction solution is from 18 to 70% by weight of P₂0₅, preferably more than 35%

15. A process according to claim 1 characterised in that the oxidoreduction agent in the reduced state, which is present in the aqueous extraction solution, includes iron (II) ions.

16. A process according to claim 15 characterised in that the iron (II) ions are present in an amount of from 0.5 to 100 grams per litre of aqueous solution.

17. A process according to any one of the preceding claims characterised in that operation is at a temperature of from 20 to 80°C, preferably in the vicinity of 50°C.

18. A process according to one of the preceding claims characterised in that the ratio between the flow rates of the organic phase and the aqueous solution is from 20 to 50.

19. A process according to any one of the preceding claims characterised in that a fraction of the aqueous phase issuing from said contact zone or zones is recycled into said contact zone or zones.

20. A process according to one of the preceding claims characterised in that the whole of the aqueous solution entering the contact zone or zones originates from the cathodic compartment of the electrolysis cell, possibly with internal recycling of a fraction of the phase issuing from said zone or zones; and that the whole of the phase issuing from the zone or zones or the whole reduced by the internal recycling feeds the anodic compartment of said cell.

21. A process according to one of claims 13 to 19 characterised in that the whole of the aqueous solution entering said contact zone or zones originates from the cathodic compartment of the electrolytic cell, that the aqueous phase flow issuing from the contact zone or zones is divided into an aqueous flow for feeding the anodic compartment and constitutes the production and into an aqueous flow for feeding the cathodic compartment of said cell, after having received an aqueous flow containing the strong, complexing acid and the oxidoreduction agent, in amounts corresponding to those drawn off in the production flow.

22. A process according to claim 19 characterised in that the recycled aqueous phase-organic phase ratio is from 0.1 to 10, preferably from 0.5 to 2.

23. A process according to one of claims 1 to 19 characterised in that a plurality of contact zones and a plurality of electrolytic cells are used.

24. A process according to one of the preceding clais characterised in that the separator-type electrolytic cell comprises a membrane of perfluorinated sulphonic polymer.

25. A process according to one of the preceding claims characterised in that in addition a chemical oxidation agent is added to the production flow, in an amount sufficient to oxidise the uranium (IV) ions remaining in said flow.

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