EP0239501B1 - Process for separating iron from an organic solution containing uranium - Google Patents

Description

The invention relates to a process for the separation of iron from an organic solution containing uranium.

More generally, the subject of the invention is a process for extracting uranium present in phosphoric acid solutions, in particular in phosphoric acid solutions obtained from phosphate ores containing iron.

It is known that phosphates ores generally contain quantities of uranium which can be recovered during the attack of phosphates ores by sulfuric acid.

This recovery is interesting, given the large tonnage of phosphate ores treated with sulfuric acid.

During the attack of ores with sulfuric acid, the uranium goes into solution in the phosphoric acid obtained and the processes for recovering uranium from phosphoric acid use appropriate organic solvents such as those described in the french patent ^No. 2,396,803, consist of a synergistic mixture of extractants.

The process developed with these solvents allows the extraction and purification of uranium in a single cycle, and the iron is removed from the decanters in the form of a precipitate, when the uranium is reextracted using carbonate d 'ammonium.

It has also developed new solvents, disclosed in French patent ^No. 2,442,796, the certificate of addition ^No. 2,459,205 and French Patent ^No. 2,494,258.

These new solvents are made up of more powerful synergistic couples. These new solvents extract more uranium, but also more iron, which makes alkaline re-extraction of uranium difficult, given the troublesome presence of iron hydroxides which precipitate in an alkaline medium.

It has also been envisaged to use organic solvents such as trioctylphosphine oxide and di-2-ehtyl hexylphosphoric acid with dilute phosphoric acid which is substantially free of iron, but this process has the drawback of either cause significant coextraction of uranium with iron and therefore lose uranium which passes into the aqueous phase, either to operate in a dilute phosphoric acid medium subsequently requiring a reconcentration of phosphoric acid or a loss of that -C (cf. French patent ^No. 2,459,837).

The subject of the invention is a process for extracting uranium from an organic solution containing it and contaminated with iron.

One aspect of the invention is to propose a method for separating iron contaminating an organic solution containing uranium, which method also makes it possible to extract the uranium at a high rate.

One of the other aspects of the invention is to propose a process allowing the easy use of solvents capable of extracting uranium with a high yield, while eliminating the problems due to the presence of iron.

One of the other aspects of the invention is to propose a method for extracting uranium comprising only one extraction-re-extraction cycle, avoiding a second purification cycle and the double reduction-oxidation operation to re-extract uranium, while overcoming the difficulties of conducting the direct alkaline re-extraction operation of uranium.

One aspect of the invention is to provide a method for separating iron contaminating an organic solution containing uranium, which method does not at any time require changing either the valence of uranium or that of iron.

One of the aspects of the invention is to propose a process for de-ironing phosphoric acid, applicable industrially and advantageously integrable in a plant for the production of phosphoric acid from natural phosphates in which it is also desired to recover the uranium. contained in said phosphates.

ou de formule (R₁)₃-P=O
dans laquelle

• . R₁ et R₂ identiques ou différents, représentent un radical alcoyle linéaire ou ramifié comportant de 4 à 10 atomes de carbone, de préférence 6 ou 8,
• . m est un nombre entier allant de 1 à 3 et valant de préférence 1,
• . n est un nombre entier allant de 4 à 10 et valant de préférence 7,

   et un composé organophosphoré acide répondant à la formule :

dans laquelle R₃, R₄, R₅, R₆ identiques ou différents représentent un radical alcoyle linéaire ou ramifié ayant au moins 4 atomes de carbone, de préférence de 4 à 10 atomes de carbone, avantageusement de 4 à 6 atomes de carbone, ou un radical aryle de 6 à 10 atomes de carbone,
   lequel procédé comprend la réaction de la susdite solution organique uranifère sur un acide choisi parmi l'acide oxalique, un mélange d'acide phosphorique et sulfurique ou un mélange d'acide phosphorique déferrisé et d'acide sulfurique, l'uranium restant dans la solution organique initiale et le fer passant en solution aqueuse.The process for separating iron according to the invention from an initial uranium organic solution containing at least 1 g / l of iron, which initial organic solution contains an organic solvent comprising a system of extractants consisting of:
a neutral phosphine oxide of formula:

or of formula (R₁) ₃-P = O
in which

• . R₁ and R₂, which are identical or different, represent a linear or branched alkyl radical comprising from 4 to 10 carbon atoms, preferably 6 or 8,
• . m is an integer ranging from 1 to 3 and preferably equal to 1,
• . n is an integer ranging from 4 to 10 and preferably equal to 7,

and an acid organophosphorus compound corresponding to the formula:

in which R₃, R₄, R₅, R₆ identical or different represent a linear or branched alkyl radical having at least 4 carbon atoms, preferably from 4 to 10 carbon atoms, advantageously from 4 to 6 carbon atoms, or an aryl radical from 6 to 10 carbon atoms,
which process comprises reacting the above organic uranium solution with an acid chosen from oxalic acid, a mixture of phosphoric and sulfuric acid or a mixture of deferrized phosphoric acid and sulfuric acid, the uranium remaining in the solution initial organic and iron passing into aqueous solution.

It has been found quite unexpectedly, that by using an acid chosen from those mentioned above, in an initial organic solution containing uranium and iron, there was a sufficient separation between the uranium and the iron such that most or all of the uranium remains in the organic phase and most or all of the iron is extracted from the initial organic solution and passes into the aqueous phase, which makes it possible to re-extract the uranium from the organic phase without the uranium re-extraction process being hindered by the presence of iron, which could for example precipitate, and without there being any loss of uranium by passing it into the aqueous phase.

The amount of uranium that remains in the phase organic corresponds to at least about 85%, and is from about 85% to about 95% of the total amount of uranium contained in said initial organic solution, but generally the amount of uranium which passes into the aqueous phase does not exceed about 10%.

The amount of iron which passes into aqueous solution corresponds to approximately at least 60-70% of the total amount of iron contained in the initial organic solution.

In the initial organic solution, the iron is at valence 3 and is advantageously in the form of Fe (PO₄R₂) ₃, R representing the radical of the acid organophosphorus compound defined above and the uranium is at valence 6, and advantageously under form UO₂ (PO₄R₂) ₂, R representing the radical of the acid organophosphorus compound defined above.

The method according to the invention advantageously applies to initial organic solutions, in which the ratio between iron and uranium, Fe / U, is equal to or greater than about 0.8, in particular about 1, without upper limit.

The method according to the invention advantageously applies to initial organic solutions, in which the value of the Fe / U ratio varies from approximately 0.8 to approximately 2.5, and in particular from approximately 1 to approximately 2.5.

For values of the Fe / U ratio of less than about 0.8, the method of the invention also applies.

The process of the invention advantageously applies to initial organic solutions containing at least approximately 1,200 mg / l of iron and at least approximately 1,200 mg / l of uranium, since it makes it possible to eliminate the problems due to precipitation. subsequent iron.

The above values are not critical since the method of the invention also applies to initial organic solutions containing less than approximately 1200 mg / l of uranium and which can for example contain approximately 400 mg / l of uranium.

According to a preferred embodiment of the process of the invention, the initial organic solutions contain from approximately 0.3 to approximately 3 g / l of uranium, in particular from approximately 0.4 to approximately 1.5 g / l d uranium and from about 1 to about 4 g / l of iron, especially about 1.2 g / l of iron.

According to a preferred embodiment of the process of the invention, the initial organic solution consists of a mixture of two extractants chosen from tri octyl phosphine oxide (TOPO), di n hexyl octyl methoxy phosphine oxide ( DinHMOPO), bis dibutoxy 1,3 propyl 2 phosphoric acid (BIDIBOPP) and bis dihexyloxy 1,3 propyl 2 phosphoric acid (BIDIHOPP) and in particular the following couples:
(TOPO - BIDIBOPP),
(TOPO - BIDIHOPP),
(DinHMOPO - BIDIBOPP),
(DinHMOPO - BIDIHOPP).

According to an advantageous embodiment of the process of the invention, the initial organic solution containing iron and uranium comes from a starting phosphoric acid solution, containing uranium, in particular at a rate of approximately 50 to approximately 300 mg / l, and iron, in particular at a rate of approximately 1 to approximately 15 g / l, in particular from approximately 1 to approximately 10 g / l.

In the starting phosphoric acid solution, the U / Fe ratio is generally about 1/100 to 1/15, and goes to about 1/1 by adding a system of extractants mentioned above, to constitute the initial organic solution, the uranium passes into the initial organic solution, the iron passes mainly with phosphoric acid and part of the iron remains in the initial organic solution and must be removed.

• 1)
  
          UO₂(PO₄R₂)₂+H₂C₂O₄ ---> UO₂(PO₄R₂)₂+H₂C₂O₄,
  
  
  
  R représentant le radical du composé organophosphoré acide ci-dessus défini,
  en d'autres termes, il n'y a pas déplacement de l'uranium et celui-ci reste dans la solution organique initiale,
  
• 2)
  
          2Fe(PO₄R₂)₃+3H₂C₂O₄ ---> Fe₂(C₂O₄)₃+6HPO₄R₂
  
  
  
  R représentant le radical du composé organophosphoré acide ci-dessus défini,
  l'oxalate de fer passe en solution aqueuse.

Regarding the acid used to extract iron from the initial organic solution, when using oxalic acid, this, on organic uranium and iron compounds, leads to reactions following:

• 1)
  
  UO₂ (PO₄R₂) ₂ + H₂C₂O₄ ---> UO₂ (PO₄R₂) ₂ + H₂C₂O₄,
  
  
  
  R representing the radical of the acid organophosphorus compound defined above,
  in other words, there is no displacement of the uranium and it remains in the initial organic solution,
  
• 2)
  
  2Fe (PO₄R₂) ₃ + 3H₂C₂O₄ ---> Fe₂ (C₂O₄) ₃ + 6HPO₄R₂
  
  
  
  R representing the radical of the acid organophosphorus compound defined above,
  the iron oxalate passes into aqueous solution.

Oxalic acid is advantageously used, in the implementation of the process of the invention, at a rate of approximately 8 to approximately 10 kg per kg of iron to be extracted.

It is also possible to use quantities of oxalic acid (expressed in kg) less than about 8 kg per kg of iron to be extracted.

Oxalic acid is generally used at a concentration of approximately 5 to approximately 50 g / l, in particular approximately 5 to approximately 30 g / l and preferably approximately 20 g / l.

Oxalic acid can be regenerated, for example by using calcium hydroxide Ca (OH) ₂, at a rate of about 1 to about 4 kg, and sulfuric acid, at a rate of about 2 to about 8 kg , per kg of oxalic acid.

Oxalic acid is particularly advantageous insofar as it allows efficient separation iron and uranium, such that all of the uranium remains in the initial organic solution.

According to another advantageous embodiment of the process of the invention, it is also possible to use a mixture of phosphoric acid and sulfuric acid, hereinafter designated by a sulfophosphoric mixture.

We have, in fact, noticed that by modifying the proportion between phosphoric acid and sulfuric acid, we obtain a different behavior of iron and uranium.

According to an advantageous embodiment of the invention, the phosphoric acid used in the sulfophosphoric mixture is desuranized. By desuranized phosphoric acid is meant phosphoric acid containing less than about 10 mg / l of uranium.

It has been found that the mixture of sulfuric acid and phosphoric acid, which is advantageously desuranized, can be used without it being necessary to carry out a step of reconcentration of the sulfophosphoric acid, and without causing excessive co-extraction. uranium.

Advantageously, a mixture of phosphoric acid and sulfuric acid with a total normality of 12 N to 20 N is used.

The normality of sulfuric acid can vary from 3 N to 12 N, and the normality of phosphoric acid can vary from 3 N to 12 N.

Advantageously, a mixture of sulfuric acid of normality 3 N and phosphoric acid of normality 9 N is used, when the content of iron contained in phosphoric acid is equal to or less than about 1.5 g / l.

When the iron content of phosphoric acid is more than about 1.5 g / l, you can proceed an increase in the sulfuric acid concentration, this then being advantageously greater than or equal to 9 N.

The H₂SO₄ / H₃PO₄ ratio in normality can then advantageously vary from 3 to 1/3.

When the iron content of the phosphoric acid is greater than approximately 1.5 g / l, it is also possible to carry out a prior iron removal of the phosphoric acid, advantageously de-uranium-containing, that is to say containing less than approximately 10 mg / l of uranium, before making the sulfophosphoric mixture.

When the iron content of the phosphoric acid is greater than approximately 1.5 g / l, it is possible to increase the concentration of sulfuric acid and together with a deferrization of the phosphoric acid, advantageously desuranized.

According to another embodiment of the process of the invention, it is therefore possible to have recourse to a sulfophosphoric mixture in which the phosphoric acid has been previously de-ironed, and advantageously previously de-ironed and desuranized.

In carrying out the process of the invention, it is possible to obtain deuraniated and deferrized phosphoric acid, intended for the preparation of the sulfophosphoric mixture, by taking deuraniated phosphoric acid, obtained from uraniferous phosphoric acid. containing iron, after the uranium has been extracted using one of the solvents defined above.

The advantage presented by deuraniated and deferrized phosphoric acid is that this phosphoric acid can intervene in the process of the invention, in particular when the initial organic solution comes from a solution of uraniferous phosphoric acid, itself coming from ores phosphates.

The quantity of phosphoric acid sampled corresponds at most to approximately 10% of the quantity of phosphoric acid obtained from desuraniated phosphoric acid containing iron.

This desuranylated phosphoric acid is then reacted with one of the new or regenerated solvents defined above.

The iron contained in the deuranic phosphoric acid is extracted from the deuraniated phosphoric acid and passes into the new or regenerated solvent, and deuraniated and deferrized phosphoric acid is obtained.

In practice, the preparation of de-ironed phosphoric acid is carried out by countercurrent extraction, for example, in five stages, with an organic solvent chosen from those mentioned above and new or regenerated on deuraniated phosphoric acid.

New or regenerated solvent is defined as the solvent practically free of uranium and iron, that is to say containing less than approximately 100 mg / l of iron, in particular less than approximately 10 mg / l of iron and less than about 10 mg / l of uranium, and containing in particular about 2 to 3 mg / l of uranium.

It is considered that a solvent is regenerated when it has undergone an alkaline re-extraction, in particular using ammonium carbonate and ammonia before being reused either for the extraction of uranium or for iron removal phosphoric acid.

The deferrized and advantageously desuranized phosphoric acid used in the preparation of the sulfophosphoric mixture involved in the process of the invention generally has a concentration of approximately 1 M to 3 M.

It has been found that the iron removal of advantageously desuranized phosphoric acid is all the more effective that the concentration of advantageously desuranized phosphoric acid to be ironed is low.

It has thus been observed that the use of a deuranified phosphoric acid to be iron-depleted, of a concentration of approximately 3M, leads to the production of a de-uraniumized and de-ironed phosphoric acid, using a new or regenerated solvent, generally in one or two stages, while a deuranified phosphoric acid to be ironed at a higher concentration, for example around 4.5M, requires 3 to 5 stages to be ironed.

What is said about the iron removal of phosphoric acid, in particular deuranic acid, containing an amount greater than 1.5 g / l of iron applies to phosphoric acid containing from 0 to 1.5 g / l of iron.

After iron removal, the iron removal of phosphoric acid used in the constitution of the sulfophosphoric mixture used in the process of the invention contains from approximately 50 mg / l to approximately 600 mg / l of iron.

The de-ironed phosphoric acid used in the composition of the sulfophosphoric mixture is advantageously from approximately 3 N to approximately 5 N.

Advantageously, a mixture of sulfuric acid of normality 9 N and deferrized phosphoric acid of normality 3 N is used, or a mixture of sulfuric acid of normality of about 12 N and phosphoric acid normality 4 N.

The choice of the normality value of sulfuric acid and that of phosphoric acid deferrized or not depends on the nature of the phosphoric acid used, and in particular on its iron content.

It is also possible to use a mixture of sulfuric acid and phosphoric acid in which part of the phosphoric acid is de-ironed. As an example, not limiting, we can have recourse to sulfuric acid of normality 12 N, phosphoric acid of normality 2 N, containing more than approximately 1.5 g / l of iron, and phosphoric acid deferrized (containing less than approximately 0.6 g / l of iron) of normality 2 N.

According to a preferred embodiment of the process of the invention, the concentration of sulfophosphoric acid is approximately 450 g / l, taking into account the fact that sulfuric acid has two acid functions and that phosphoric acid has three acid functions.

• de ne pas avoir à effectuer de reconcentration du mélange sulfophosphorique qui peut être directement réutilisé à l'attaque des phosphates,
• de limiter la coextraction en uranium.
  Selon un mode de réalisation préféré de l'invention, le procédé de l'invention comprend les étapes suivantes :
• on fait agir un solvant choisi parmi les systèmes d'extractants suivants :
     (TOPO - BIDIBOPP),
     (TOPO - BIDIHOPP),
     (DinHMOPO - BIDIBOPP),
     (DinHMOPO - BidiHOPP),
  sur une solution d'acide phosphorique de départ contenant de l'uranium et du fer, et dont le rapport en poids U/Fe est d'environ 1/10 à environ 3/1000 pour obtenir
• d'une part une solution organique initiale constituée du susdit solvant, contenant au moins environ 95 % de la quantité d'uranium contenu dans l'acide phosphorique de départ et au moins 1 g/l de fer dans laquelle le rapport en poids Fe/U est supérieur ou égal à environ 0,8, notamment compris d'environ 1/1 à environ 2,5/1,
• et d'autre part une phase aqueuse désuraniée contenant l'acide phosphorique et environ 80 % à environ 90 % du fer contenu dans la solution d'acide phosphorique de départ ;
• on fait agir sur la susdite solution organique initiale un acide choisi parmi l'acide oxalique, un mélange d'acide phosphorique et sulfurique, ou un mélange d'acide phosphorique déferrisé et d'acide sulfurique pour obtenir
• d'une part une phase aqueuse contenant environ 50 % à environ 90 %, notamment environ 70 %, du fer contenu dans la solution organique initiale et
• d'autre part une phase organique contenant au moins 85 % en poids de l'uranium contenu dans la solution organique initiale.
  Selon un autre mode de réalisation préféré de l'invention, le procédé de séparation du fer à partir d'une solution d'acide phosphorique de départ contenant de l'uranium et du fer est caractérisé en ce qu'il comprend les étapes suivantes :
• on fait agir un solvant choisi parmi les systèmes d'extractants suivants:
     (TOPO - BIDIBOPP),
     (TOPO - BIDIHOPP),
     (DinHMOPO - BIDIBOPP),
     (DinHMOPO - BIDIHOPP),
  sur la solution d'acide phosphorique de dpéart contenant de l'uranium et du fer, et dont le rapport en poids U/Fe est d'environ 1/10 à environ 3/1000 pour obtenir
• d'une part solution organique initiale contenant le susdit solvant contenant au moins environ 95 % de la quantité d'uranium contenu dans l'acide phosphorique de départ, et au moins 1 g/l de fer dans laquelle le rapport en poids Fe/U est supérieur ou égal à environ 0,8, notamment compris d'environ 1/1 à environ 2,5/1,
• et d'autre part une phase aqueuse désuraniée contenant l'acide phosphorique et environ 80 % à environ 90 % du fer contenu dans la solution d'acide phosphorique de départ,
• on fait agir sur la susdite solution organique initiale un acide choisi parmi l'acide oxalique, un mélange d'acide phosphorique et sulfurique, ou un mélange d'acide phosphorique déferrisé et d'acide sulfurique pour obtenir
• d'une part une phase aqueuse contenant environ 50 % à environ 90 %, notamment environ 70 % du fer contenu dans la solution organique initiale et
• d'autre part une phase organique contenant au moins 85 % en poids de l'uranium contenu dans la solution organique initiale.

The advantage of the sulfophosphoric mixture of normality and chosen concentration, allows:

• not to have to reconcentrate the sulfophosphoric mixture which can be directly reused to attack phosphates,
• limit coextraction into uranium.
  According to a preferred embodiment of the invention, the method of the invention comprises the following steps:
• a solvent chosen from the following extractant systems is made to act:
  (TOPO - BIDIBOPP),
  (TOPO - BIDIHOPP),
  (DinHMOPO - BIDIBOPP),
  (DinHMOPO - BidiHOPP),
  on a starting phosphoric acid solution containing uranium and iron, and whose weight ratio U / Fe is from about 1/10 to about 3/1000 to obtain
• on the one hand, an initial organic solution consisting of the above-mentioned solvent, containing at least about 95% of the amount of uranium contained in the starting phosphoric acid and at least 1 g / l of iron in which the weight ratio Fe / U is greater than or equal to about 0.8, in particular from about 1/1 to about 2.5 / 1,
• and on the other hand a desuranized aqueous phase containing phosphoric acid and about 80% to about 90% of the iron contained in the starting phosphoric acid solution;
• an acid chosen from oxalic acid, a mixture of phosphoric and sulfuric acid, or a mixture of deferrized phosphoric acid and sulfuric acid is made to act on the above initial organic solution
• on the one hand, an aqueous phase containing approximately 50% to approximately 90%, in particular approximately 70%, of the iron contained in the initial organic solution and
• on the other hand an organic phase containing at least 85% by weight of the uranium contained in the initial organic solution.
  According to another preferred embodiment of the invention, the process for the separation of iron from a starting phosphoric acid solution containing uranium and iron is characterized in that it comprises the following stages:
• a solvent chosen from the following extractant systems is made to act:
  (TOPO - BIDIBOPP),
  (TOPO - BIDIHOPP),
  (DinHMOPO - BIDIBOPP),
  (DinHMOPO - BIDIHOPP),
  on the dpéart phosphoric acid solution containing uranium and iron, and whose weight ratio U / Fe is from about 1/10 to about 3/1000 to obtain
• on the one hand, initial organic solution containing the above-mentioned solvent containing at least about 95% of the amount of uranium contained in the starting phosphoric acid, and at least 1 g / l of iron in which the weight ratio Fe / U is greater than or equal to about 0.8, in particular from about 1/1 to about 2.5 / 1,
• and on the other hand, a desuranized aqueous phase containing phosphoric acid and approximately 80% to approximately 90% of the iron contained in the starting phosphoric acid solution,
• an acid chosen from oxalic acid, a mixture of phosphoric and sulfuric acid, or a mixture of deferrized phosphoric acid and sulfuric acid is made to act on the said initial organic solution
• on the one hand an aqueous phase containing approximately 50% to approximately 90%, in particular approximately 70% of the iron contained in the initial organic solution and
• on the other hand an organic phase containing at least 85% by weight of the uranium contained in the initial organic solution.

In practice, the iron removal of the initial organic solution generally takes place by circulating one of the acids mentioned above against the current with respect to the circulation of the initial organic solution.

The number of stages used is approximately 1 to 6, and preferably 2 to 4.

The contact time between the initial organic solution and the acid is generally around 3 to 10 minutes.

The above organic phase obtained from the iron removal of the initial organic solution and containing the major part of the uranium is then advantageously washed, in particular with water, until a PO₄ content in the solution is obtained. organic less than or equal to about 1 g / l.

The uranium is then re-extracted in an alkaline medium, from the washed organic phase. Uranium is for example re-extracted using ammonium carbonate and ammonia to regulate the pH. This re-extraction makes it possible to dissolve in the ammonium carbonate a quantity of uranium corresponding to approximately 95% to approximately 100% of the total quantity contained in the initial organic solution.

The process of the invention which allows the separation between iron and uranium and the elimination of iron, limits the precipitation of iron in the ammonium carbonate medium.

In the process of the invention, the following practical details can also be specified.

In practice, in the process of the invention, the solvent travels through a loop.

The solvent is in a first step brought into contact with a starting phosphoric acid solution (uraniferous phosphoric acid containing iron) to extract the uranium).

The solvent thus loaded with uranium but also with iron constitutes the initial organic solution defined above.

This initial organic solution is de-ironed in a second step, and the solvent thus de-ironed is subjected, in a third step, to washing, then to be subjected in a fourth step, to re-extraction, to re-extract the uranium.

The solvent thus deuranized is then subjected in a fifth step to acidification, since the previously mentioned re-extraction step generally takes place in an alkaline medium.

The acidification generally consists of phosphoric acid, advantageously de-ironed or sulfuric acid, which can come from the effluents obtained at the end of the first extraction step.

However, it is not necessary to do an iron purge of the solvent thus acidified with phosphoric acid containing iron, because when the acidified solvent is placed in the presence of the starting phosphoric acid solution, the iron equilibria are not modified.

One of the preferred variants of the process of the invention is shown diagrammatically in FIG. 1.

The influent (a), essentially containing phosphates and also containing uranium and iron, is treated, in particular with sulfuric acid, to be transformed into phosphoric acid (b). The stage for the preparation of phosphoric acid is shown in (1).

• d'une part à des effluents désuraniés (d) contenant du fer,
• et d'autre part à la solution organique initiale (e) qui s'est constituée à partir du solvant (c) qui s'est chargé en uranium et également en fer.

The phosphoric acid containing uranium and iron is subjected to an extraction step represented in (2), using one of the solvents mentioned above, introduced against the current to lead

• on the one hand to desuranic effluents (d) containing iron,
• and on the other hand to the initial organic solution (e) which is formed from the solvent (c) which is loaded with uranium and also with iron.

The initial organic solution (e) containing uranium and iron is subjected to a deferrization step (3), using one of the acids (f) mentioned above, introduced against the current.

This iron removal leads to an organic iron removal solution, represented by (g) and to acid loaded with iron, represented by (t).

The de-ironed organic solution (g) containing the uranium is then subjected to the washing step represented by (4) using water (h) introduced against the current.

The de-ironed organic solution (g) containing the uranium is represented by (i) at the end of the washing step.

The organic solution (i) is subjected to a re-extraction step represented in (5), using ammonium carbonate and ammonia (j) introduced against the current. On the one hand, an eluate of ammonium carbonate rich in uranium (k) is obtained, and on the other hand the desuranized solvent (m) leaving the re-extraction step.

The solvent (m) is subjected to an acidification step shown in (6), in particular using phosphoric acid (d₁), introduced against the current and coming from the deuraniated effluents (d).

The solvent thus acidified (s) is taken up in the extraction step (2).

The invention will be better understood from the examples below, given by way of illustration and without implied limitation.

EXAMPLE 1 Iron removal by oxalic acid -

This example relates to the process of the invention in which oxalic acid is used to extract iron from an initial organic solution.

There is no reaction between uranium and oxalic acid, uranium therefore remains in the organic solution and the iron oxalate goes into aqueous solution.

• . Concentration en H₂C₂O₄, 2H₂O..... 23 g/l
• . Nombre d'étages................... 5
• . Rapport organique/aqueux (en volume).... 1/2,7
• . Débit de la solution organique initiale ... 0,1 1/h
• . Débit de la solution d'acide oxalique...... 0,27 1/h
• . Recyclage interne de la phase aqueuse..... 0,126 1/h
• . Temps de fonctionnement................... 62 h
• . Taux moyen d'élimination.............. 80 à 85% en Fe
• . Consommation d'acide oxalique.......8 à 10 kg/kg de Fe

This operation was carried out against the current continuously over 5 stages, under the experimental conditions indicated below.

• . Concentration of H₂C₂O₄, 2H₂O ..... 23 g / l
• . Number of floors ................... 5
• . Organic / aqueous ratio (by volume) .... 1 / 2.7
• . Flow rate of the initial organic solution ... 0.1 1 / h
• . Flow rate of the oxalic acid solution ...... 0.27 1 / h
• . Internal recycling of the aqueous phase ..... 0.126 1 / h
• . Operating time ................... 62 h
• . Average elimination rate .............. 80 to 85% Fe
• . Oxalic acid consumption ....... 8 to 10 kg / kg of Fe

The results obtained over five stages with three initial organic solutions having different iron contents are the following:

During this operation, the uranium is not re-extracted at all. Except for the analytical dispersion, the contents of the uranium solvent on all the stages are identical.

The extraction of iron with oxalic acid gives remarkable technical results, and requires between approximately 8 and approximately 10 kg of oxalic acid to remove 1 kg of iron.

Oxalic acid can then be regenerated by transforming iron oxalate into calcium oxalate by lime and the latter into oxalic acid by the action of sulfuric acid. The reactions are as follows:



Fe₂ (C₂O₄) ₃ + 3 Ca (OH) ₂ ---> 2 Fe (OH) ₃ + 3 CaC₂O₄ + 3H₂O




CaC₂O₄ + H₂SO₄ ---> CaSO₄ + H₂C₂O₄

Figure ^No. 2 is a block diagram of the inventive method, with removal of iron by oxalic acid. The figures are given for information only for a plant processing 80 m³ / h of phosphoric acid.

There is shown in (1), the step of extracting uranium from the influent (a) consisting of phosphoric acid (442 g / l daniumH₃PO₄), containing uranium (0.08 g / l) and iron (1.31 g / l), and whose flow rate is 80 m₃ / h.

This extraction is carried out using a solvent (s) introduced against the current.

After the uranium extraction, an effluent of phosphoric acid (b) containing iron and free of uranium is obtained, and the solvent containing uranium and iron (c) and which has been previously designated. by initial organic solution.

This initial organic solution (c) is subjected to a deferrization step shown in (2), using an oxalic acid solution (d) introduced against the current, at a flow rate of 3.5 m³ / h , to lead on the one hand to an iron oxalate (d₁), at a flow rate of 3.5 m₃ / h, and on the other hand to the deferrized organic solution containing uranium (e).

The deferrized organic solution containing the uranium (e) in step (3) is then washed, using neutral water (f), at a flow rate of 1.5 m³ / h, which leads to water acid (g) with a flow rate of 1.5 m³ / h and with the washed organic solution with iron removal containing uranium (h).

• d'une part à un éluat uranifère (j), dans lequel l'uranium est à l'état UO₂(CO₃)₃ (NH₄)₄ et est présent à raison d'environ 10 g/l
• et d'autre part au solvant désuranié (k).

The uranium is reextracted from the deferrized organic solution (h) in the re-extraction step shown in (4), using an ammonium carbonate solution (i), introduced against the flow rate 0 , 6 m₃ / h, which leads

• on the one hand to a uranium eluate (j), in which the uranium is in the UO U (CO₃) ₃ (NH₄) ₄ state and is present at a rate of approximately 10 g / l
• and on the other hand with the deuranized solvent (k).

The deuranified solvent (k) is then acidified in step (5) using non-iron-depleted phosphoric acid (b¹), introduced against the current, at a flow rate of 1.5 m³ / h from a portion phosphoric effluent (b).

At the end of step (5), an ammonium phosphate solution (m) is obtained, and the acidified solvent (s), at the rate of 4.9 m³ / h which is reintegrated in step d uranium extraction (1).

EXAMPLE 2 Process for the iron removal of phosphoric acid

This example relates to the preparation of de-ironed phosphoric acid, advantageously de-uranium entering into the preparation of a sulfophosphoric mixture.

• une préparation de l'acide phosphorique désuranié à contre-courant avec du solvant "neuf" ou régénéré, (exempt de fer et d'uranium),
• le mélange de l'acide sulfurique et de l'acide phosphorique déferrisé,
• une élimination du fer à partir du solvant organique, à contre-courant, à l'aide du mélange sulfophosphorique dans lequel l'acide phosphorique a été déferrisé.

The process of the invention in which sulfophosphoric acid is used in which the phosphoric acid is previously iron-removed and advantageously comprises the following steps:

• a preparation of desuranized phosphoric acid against the current with "new" or regenerated solvent (free of iron and uranium),
• the mixture of sulfuric acid and deferrized phosphoric acid,
• removal of iron from the organic solvent, against the current, using the sulfophosphoric mixture in which the phosphoric acid has been de-ironed.

Desuranic phosphoric acid usually always contains significant amounts of iron. A certain amount of this iron-free acid may be available, by performing a continuous operation on an appropriate number of stages.

• 1) sur l'acide phosphorique désuranié à 4,62 M dont les caractéristiques sont les suivantes :
  • . U : < 3 mg/l
  • . Fe : 1 290 mg/l
  • . P₂O₅ : 328 g/l ;
  Le temps de contact et le pourcentage correspondant de fer extrait sont les suivants :
  
  La teneur en fer résiduel de l'acide est de 48 mg/l ;
• 2) sur l'acide phosphorique désuranié à 3,4 M dont les caractéristiques principales sont les suivantes :
  • . U : < 3 mg/l
  • . Fe : 950 mg/l
  • . P₂O₅ : 242 g/l
  Le temps de contact et le pourcentage correspondant de fer extrait sont les suivants :
  
  La teneur en fer résiduel de l'acide est de 10 mg/l.

The iron removal tests are carried out on two phosphoric acids: an effluent of deuraniated phosphoric acid, without dilution, the concentration of which is 4.62 M, and an effluent of deuranied phosphoric acid, diluted with part of the washing water for lead to a concentration of 3.4 M. The reaction kinetics are as follows:

• 1) on desuranized phosphoric acid at 4.62 M, the characteristics of which are as follows:
  • . U: <3 mg / l
  • . Fe: 1290 mg / l
  • . P₂O₅: 328 g / l;
  The contact time and the corresponding percentage of iron extracted are as follows:
  
  The residual iron content of the acid is 48 mg / l;
• 2) on desuranized phosphoric acid at 3.4 M, the main characteristics of which are as follows:
  • . U: <3 mg / l
  • . Fe: 950 mg / l
  • . P₂O₅: 242 g / l
  The contact time and the corresponding percentage of iron extracted are as follows:
  
  The residual iron content of the acid is 10 mg / l.

Figures ^No. 3 and 4 show schematically the method steps of the invention to realize the removal of iron from an initial organic solution, respectively, using a sulfophosphorique mixture in which the phosphoric acid is uranium-depleted and ironed.

In Figure ^No. 3 is shown by (a) the influent consisting sulfophosphorique mixture containing 1290 mg / l of iron and uranium.

• d'une part à l'obtention d'un effluent (b), constitué par l'acide phosphorique désuranié, de concentration 4,62 M et contenant 890 mg/l de fer,
• et d'autre part à une solution organique initiale contenant 2 125 mg/l de fer et 1 375 mg/l d'uranium.

In (2), there is shown the extraction of uranium using one of the solvents mentioned above, introduced against the current; which leads

• on the one hand, to the production of an effluent (b), consisting of desuranic phosphoric acid, of concentration 4.62 M and containing 890 mg / l of iron,
• and on the other hand to an initial organic solution containing 2,125 mg / l of iron and 1,375 mg / l of uranium.

The initial organic solution (c) is subjected to a de-ironing step represented by (3) using the sulfophosporic mixture in which the phosphoric acid has been previously de-ironed, introduced against the current over 2 to 6 stages. On the one hand, the iron-free organic solution (d) is obtained (containing approximately 300 mg / l of iron) containing uranium and an effluent consisting of sulfophosphoric mixture loaded with iron (q), which is recycled into the defined influent above.

The deferrized organic solution (d) containing uranium is subjected to a washing step represented by (4), using water (e) introduced against the current and, on the one hand, acidic water (f) and the de-ironed and washed organic solution (g), containing uranium.

• d'une part le solvant désuranié, déferrisé et acidifié (k),
• et d'autre part du phosphate d'ammonium (m).

The organic solution (g) is subjected to a step of re-extracting the uranium represented by (5), using ammonium carbonate and ammonia (h) introduced against the current. On the one hand, a uranium eluate (i) and the desuranic solvent (j) are obtained. The solvent (j) is then acidified in an acidification step represented by (6) using deuranified phosphoric acid (b₂) with iron removal at a concentration of 4.62 M, introduced against the current and containing only 48 mg / l of iron. The phosphoric acid (b₂) is introduced against the current and one obtains

• on the one hand, the deuranized, de-ironed and acidified solvent (k),
• and on the other hand ammonium phosphate (m).

(1) shows the step of iron removal of deuranified phosphoric acid (b₁) using the deuranized and iron removal solvent (k), introduced against the current.

Uranium phosphoric acid (b₁) is an aliquot of uranium phosphoric acid (b), phosphoric acid (b₁) representing approximately 10% by volume of uranium phosphoric acid (b).

The iron removal step leads to iron removal of phosphoric acid (b₂) with a concentration of 4.62 M and containing 48 mg / l of iron, to which sulfuric acid is added (the addition of sulfuric acid is represented by (p)), under conditions such that the appropriate composition and acidity of the sulfophosphoric mixture.

It is this sulfophosphoric mixture (p₁) which is introduced in the iron removal step (3) of the initial organic solution.

The iron removal of phosphoric acid (b₁) using the solvent (k) leads to the solvent (s) containing 297 mg / l of iron.

The amount of iron in the solvent (s) relative to that of the solvent (k) is little modified, taking into account the fact that the solvent (k) serves to iron a small amount of phosphoric acid.

In Figure ^No. 4 is shown by (a) the influent consisting sulfophosphorique mixture in which the phosphoric acid has previously been de-ironed, containing 1290 mg / l of iron and uranium.

In (2), the extraction of uranium is represented using one of the solvents mentioned above, introduced against the current, which leads on the one hand to obtaining d '' an effluent (b), consisting of desuranium phosphoric acid at 4.2 M containing 1190 mg / l of iron, and on the other hand to an initial organic solution (c) containing 2021 mg / l of iron and 1,313 mg / l uranium.

The initial organic solution (c) is subjected to a de-ironing step represented by (3) using a sulfophosphoric mixture in which the phosphoric acid has been previously de-ironed, introduced against the current over 5 stages.

On the one hand, the iron-free solvent (d) (containing approximately 300 mg / l of iron) containing uranium and an effluent consisting of sulfophosphoric mixture charged with iron (q) is obtained, which is reintroduced into the influent defined above. -above.

The de-ironed solvent (d) containing uranium is subjected to a washing step represented by (4) using water (e) introduced against the current and, on the one hand, acidic water (f) and the deferrized and washed solvent (g), containing uranium, are obtained.

The solvent (g) is subjected to a step of re-extracting the uranium represented by (5) using ammonium carbonate and ammonia (h) introduced against the current. On the one hand, a uranium eluate (i) and the desuranic solvent (j) are obtained. The solvent (j) is then acidified in an acidification step represented by (6) using deuranified and de-ironed phosphoric acid (b₂) with a concentration of 3.4 M and containing 10 mg / l of iron, to obtain deuranized, iron-depleted solvent (k) and ammonium phosphate (m).

(1) shows the step of de-ironing of deuranified phosphoric acid (b₁) using the de-uraniumized and de-ironed solvent (k).

Uranium phosphoric acid (b1) is an aliquot of uranium phosphoric acid (b), phosphoric acid (b₁) representing approximately 10% by volume of phosphoric acid (b).

To obtain the phosphoric acid (b₁), a fraction of the phosphoric acid (b) defined above is taken and it is subjected to a dilution using the washing water (f).

The deferrized phosphoric acid (b₂) with a concentration of 3.4 M and containing 10 mg / l of iron is then mixed with introduced sulfuric acid, represented by (p) and it is the sulfophosphoric mixture (p₁), which is introduced in the iron removal step (3) of the initial organic solution.

The iron removal of phosphoric acid (b₁) using the solvent (k) leads to the solvent (s) containing 184 mg / l of iron.

The amount of iron in the solvent (s) compared to that of the solvent (k) is little changed, account given that the solvent (k) is used to iron a small amount of phosphoric acid.

Example 3 : Iron removal using a mixture of sulfuric and phosphoric acid.

This embodiment of the process of the invention has the advantage that sulfuric acid, which is the complementary reagent for carrying out the iron removal of the initial organic solution containing uranium and iron, can be recycled to the attack phosphates and the weight thereof in the balance of reagents for the overall operation will be zero or almost zero.

It has been found that the addition of sulfuric acid to a desuranic phosphoric acid makes it possible to increase the acid concentration and makes it possible to avoid having to use evaporation to reconcentrate while making the minimum necessary concentration of the acid used lower.

It has also been found that there are suitable proportions between phosphoric acid and sulfuric acid making it possible to limit the re-extraction of uranium.

• 1) l'utilisation d'un mélange sulfophosphorique de concentration élevée (400 à 550 g/l) (exprimé en H₂SO₄+H₃PO₄), directement utilisable à l'attaque des phosphates ,
• 2) l'obtention d'une acidité finale qui soit moins élevée que dans le cas de l'acide phosphorique pur (700 g/l) ;
• 3) la limitation de la coextraction de l'uranium.

It has been found that there are sulfophosphoric mixtures which take account of a certain number of industrial constraints, namely

• 1) the use of a sulfophosphoric mixture of high concentration (400 to 550 g / l) (expressed in H₂SO₄ + H₃PO₄), directly usable for attacking phosphates,
• 2) obtaining a final acidity which is lower than in the case of pure phosphoric acid (700 g / l);
• 3) limiting the coextraction of uranium.

Solvent re-extraction tests were carried out using 12 N sulfuric acid (as comparison) and two sulphophosphoric mixtures, in which the phosphoric acid is de-ironed (containing less than about 50 mg / l of iron) and in which the normalities of sulfuric and phosphoric acid are respectively 9 N and 3 N and 3 N and 9 N.

% U : pourcentage d'U extrait du solvant
% Fe : pourcentage de Fe extrait du solvantThe results of these tests are collated in Table III below.

% U: percentage of U extracted from the solvent
% Fe: percentage of Fe extracted from the solvent

The results of these tests show the effectiveness of sulfophosphoric mixtures for re-extracting iron from the organic solvent. We also note that uranium is only co-extracted in small, or even very small, quantity, which is the goal.

FIG. 5 shows the process of the invention in which the sulfophosphoric mixture is used.

In Figure 5, there is shown in (a) the influent consisting of phosphoric acid (442 g / l) containing 0.08 g / l of uranium and 1.31 g / l of iron, the flow of which is 80 m³ / h.

The uranium extraction is carried out in the step represented by (2) using one of the solvents organic mentioned above (s), introduced against the current, to give, on the one hand, effluents (b) made up of desuranic phosphoric acid and, on the other hand, an initial organic solution containing uranium and iron ( vs).

The initial organic solution (c) is then de-ironed in step (2), using a mixture of sulfuric acid and phosphoric acid, introduced against the current at a rate of 4.9 m³ / h (f), to lead on the one hand to an organic iron removal solution (e) containing uranium, and on the other hand to an iron removal effluent (g) consisting of the sulfophosphoric mixture loaded with iron, which is taken back to l attack of phosphates, which allows sulfuric acid to be reused.

The de-ironed organic solution (e) is then washed in step (3), using water (h) introduced against the current at a rate of 1.24 m³ / h, which gives water. acid (i) at a flow rate of 1.24 m³ / h and a washed organic solution containing uranium (k).

The solution (k) is then subjected to a step of re-extracting the uranium represented by (4), using ammonium carbonate (m) introduced against the current at a flow rate of 0.6 m³ / h, to lead on the one hand to a uranium-bearing eluate (n) and to a deferrized and deuranified, alkaline solvent (p).

The solvent (p) is then acidified in step (5) using non-iron-depleted phosphoric acid (b), introduced against the current, which leads to an ammonium phosphate solution (q) and with acid solvent (s) with a flow rate of 4.5 m³ / h.

The non-iron removal phosphoric acid (b₁) comes from the effluent of phosphoric acid (b). Another part (b₂) of the phosphoric acid effluent (b) and whose flow rate is 3.259 m³ / h, is used to form the mixture of sulfophosphoric acid, sulfuric acid (t) being added at a rate of 0.4 m³ / h.

The formation of the above mixture of sulfophosphoric acid of normality 12 N is shown in step (6).

Claims (14)

1. Process for the separation of iron from a uranium-containing initial organic solution which contains at least 1 g/l of iron, which initial organic solution contains an organic solvent comprising an extractant system consisting of:
      a neutral phosphine oxide of formula:

   

   or of formula (R₁)-P=O
   in which
      R₁ and R₂, which may be identical or different, represent a straight-chain or branched alkyl radical containing from 4 to 10, preferably 6, carbon atoms,
      m is an integer ranging from 1 to 3 and preferably taking the value 1,
      n is an integer ranging from 4 to 10 and preferably taking the value 7, and
      an acid organophosphorus compound corresponding to the formula:

   

   in which R₃, R₄, R₅ and R₆, which may be identical or different, represent a straight-chain or branched alkyl radical containing at least 4 carbon atoms, preferably from 4 to 10 carbon atoms, advantageously from 4 to 6 carbon atoms, or an aryl radical containing from 6 to 10 carbon atoms,
      which process comprises the reaction of the abovementioned uranium-containing organic solution with an acid chosen from amongst oxalic acid, a mixture of phosphoric acid and sulfuric acid or a mixture of de-ironed phosphoric acid and sulfuric acid, the uranium remaining in the initial organic solution and the iron passing into aqueous solution.
2. Process as claimed in claim 1, wherein the iron is in the form of Fe(PO₄R₂)₃, R representing a radical of the acid organophosphorus compound defined above, and the uranium is in the form of UO₂(PO₄R₂)₂, R representing a radical of the acid organophosphorous compound defined above.
3. Process as claimed in any one of the preceding claims, wherein the initial organic solution consists of a mixture of two extractants chosen from amongst trioctylphosphine oxide (TOPO), di-n-hexyloctylmethoxyphosphine oxide (DinHMOPO), bis-1,3-dibutoxy-2-propylphosphoric acid (BIDIBOPP) and bis-1,3-dihexyloxy-2-propylphosphoric acid (BIDIHOPP) and especially the following pairs:
      (TOPO - BIDIBOPP),
      (TOPO - BIDIHOPP),
      (DinHMOPO - BIDIBOPP) and
      (DinHMOPO - BIDIHOPP).
4. Process as claimed in any one of claims 1 to 3, wherein, in the initial organic solution, uranium is present at a rate of approximately 0.3 to approximately 3 g/l, especially approximately 0.4 to approximately 1.4 g/l, and iron is present at a rate of approximately 1 to 4 g/l, especially at a rate of approximately 1.2 g/l.
5. Process as claimed in any one of claims 1 to 4, wherein the initial organic solution containing iron and uranium originates from a starting phosphoric acid solution which contains uranium at a rate of approximately 50 to approximately 300 mg/l, and iron at a rate of approximately 1 to approximately 15 g/l, especially approximately 1 to approximately 10 g/l.
6. Process for separating iron from a starting phosphoric acid solution which contains uranium and iron, which comprises the following stages:
      a solvent chosen from amongst the following extractant systems:
      (TOPO - BIDIBOPP),
      (TOPO - BIDIHOPP),
      (DinHMOPO - BIDIBOPP), and
      (DinHMOPO - BIDIHOPP),
   is reacted with a starting phosphoric acid solution which contains uranium and iron and which has a gravimetric ratio Fe/U of approximately 1:10 to approximately 3:1000 to obtain
      on the one hand an initial organic solution which consists of the abovementioned solvent, containing at least approximately 95% of the quantity of uranium contained in the starting phosphoric acid and at least 1 g/l of iron, and in which the gravimetric ratio Fe/in is greater than or equal to approximately 0.8, especially approximately 1:1 to approximately 2.5:1,
      and on the other hand a uranium-depleted aqueous phase containing the phosphoric acid and approximately 80% to approximately 90% of the iron contained in the starting phosphoric acid solution;
      an acid chosen from amongst oxalic acid, a mixture of phosphoric acid and sulfuric acid, or a mixture of de-ironed phosphoric acid and sulfuric acid is reacted with the initial organic solution mentioned above to obtain
      on the one hand an aqueous phase containing approximately 50% to approximately 90%, especially approximately 70%, of the iron contained in the initial organic solution and
      on the other hand an organic phase containing at least approximately 85% by weight of the uranium contained in the initial organic solution.
7. Process for separating iron from a phosphoric acid solution which contains uranium and iron, which comprises the following stages:
      a solvent chosen from amongst the following extractant systems:
      (TOPO - BIDIBOPP),
      (TOPO - BIDIHOPP),
      (DinHMOPO - BIDIBOPP), and
      (DinHMOPO - BIDIHOPP),
   is reacted with the starting phosphoric acid solution which contains uranium and iron, and which has a gravimetric ratio U/Fe of approximately 1:10 to approximately 3:1000 to obtain
      on the one hand an initial organic solution containing the abovementioned solvent which contains at least approximately 95% of the quantity of uranium contained in the starting phosphoric acid, and at least 1 g/l of iron, in which the gravimetric ratio Fe/U is greater than or equal to approximately 1: 1, especially approximately 1:1 to approximately 2.5:1, and
      on the other hand a uranium-depleted aqueous phase which contains the phosphoric acid and approximately 80% to approximately 90% of the iron contained in the starting phosphoric acid solution and
      an acid chosen from amongst oxalic acid, a mixture of phosphoric acid and sulfuric acid or a mixture of deironed phosphoric acid and sulfuric acid is reacted with the abovementioned initial organic solution to obtain
      on the one hand an aqueous phase containing approximately 50% to approximately 90%, especially approximately 70%, of the iron contained in the initial organic solution and
      on the other hand an organic phase containing the uranium contained in the initial organic solution.
8. Process for the separation of iron from a starting phosphoric acid solution which contains uranium and iron, which comprises the following stages:
      phosphoric acid is treated with a solvent chosen from amongst the following extractant systems:
      (TOPO - BIDIBOPP),
      (TOPO - BIDIHOPP),
      (DinHMOPO - BIDIBOPP), and
      (DinHMOPO - BIDIHOPP),
   so as to obtain, on the one hand, an aqueous solution containing uranium-depleted phosphoric acid and iron and, on the other hand, an initial organic solution containing at least 1 g/l of iron and at least approximately 95% by weight of the uranium contained in the starting phosphoric acid solution;
      the iron is separated from the uranium by reacting an acid chosen from amongst oxalic acid, a mixture of phosphoric acid and sulfuric acid or a mixture of de-ironed phosphoric acid and sulfuric acid with the initial organic solution to obtain
      on the one hand an organic phase containing at least approximately 85% by weight of uranium and
      on the other hand an aqeuous phase containing iron;
      the organic phase is washed until the PO₄ concentration is equal to or less than approximately 1 g/l, and
      the uranium contained in the organic phase which is washed with ammonium carbonate is reextracted in an alkaline medium, especially an ammonium carbonate medium.
9. Process as claimed in claim 8, wherein, when oxalic acid is used, the latter is used at a rate of approximately 8 to approximately 10 kg per kg of iron, and is regenerated using calcium hydroxide Ca(OH)₂, at a rate of approximately 1 to approximately 4 kg, and sulfuric acid, at a rate of approximately 2 to approximately 8 kg, per kg of oxalic acid.
10. Process as claimed in one of claims 1 to 8, wherein the acid used is a mixture of sulfuric acid and phosphoric acid, the total normality of which is 12 N to 20 N.
11. Process as claimed in claims 1 to 8 and 10, wherein the normality of the phosphoric acid varies from 3 N to 12 N and the normality of the sulfuric acid varies from 3 N to 12 N.
12. Process as claimed in any one of claims 1 to 8 and 10, wherein the acid used is a mixture of sulfuric acid of normality 3 N and phosphoric acid of normality 9 N, the phosphoric acid containing a quantity of iron equal to or less than approximately 1.5 g/l.
13. Process as claimed in one of claims 1 to 8 and 10, wherein the acid used is a mixture of 9 N sulfuric acid and 3 N phosphoric acid which is de-ironed and contains less than approximately 50 mg/l to approximately 600 mg/l of iron.
14. Process as claimed in one of claims 1 to 8 and 10 to 13, wherein the phosphoric acid used in the mixture of sulfuric acid and phosphoric acid is uranium-depleted and contains less than approximately 10 mg/l of uranium.

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