JPS6229373B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering uranium present in phosphoric acid solutions, in particular phosphoric acid solutions obtained from phosphate ores. Phosphate ores contain a non-negligible amount of uranium, which is known to migrate into the resulting phosphoric acid solution during the action of sulfuric acid on these ores. Currently known methods for reliably recovering uranium present in phosphoric acid obtained from phosphate ores include extraction with suitable organic solvents. However, the solvents that had been used until then were found to be relatively ineffective due to the large amount of phosphoric acid to be treated, the high concentration of phosphoric acid, and the simultaneous presence of iron in the solution. are doing. The present invention provides a method for recovering uranium present in a phosphoric acid solution, in which the phosphoric acid concentration is relatively high, e.g.
This article relates to a method that enables a good uranium extraction level to be achieved even at around 8M. That is, the present invention allows uranium present in a phosphoric acid solution to be
A method for recovering uranium by contacting the solution with an organic solvent suitable for uranium extraction, wherein the organic solvent is an acidic organophosphorus compound and the formula: (wherein the groups R ₁ , R ₂ and R ₃ are the same or different and are alkyl, aryl or alkoxyalkyl groups, and at least one of the groups R ₁ , R ₂ and R ₃ is an alkoxyalkyl group) This invention relates to a uranium recovery method using an extractant system consisting of neutral phosphine oxide. The method defined above has the advantage of giving a better uranium extraction rate due to the nature of the extractant system.
Such a system thus makes it possible to obtain a good uranium partition coefficient between the organic phase and the aqueous phase. Furthermore, the system can be used at much higher concentrations than currently known systems, particularly due to the very good solubility of neutral phosphine oxide in the inert diluents conventionally used for this type of extraction. . According to the invention, the acidic organophosphorus compound has the formula: Advantageously, it is a dialkyl phosphoric acid in which R ₄ and R ₅ are the same or different alkyl radicals, preferably branched alkyl radicals having at least 8 carbon atoms. An example of a dialkyl phosphoric acid used is di-2-ethylhexyl phosphoric acid. According to the present invention, as the acidic organophosphorus compound,
formula: It is also possible to use phosphonic acids in which R ₆ and R ₇ are the same or different and are alkyl or aryl groups. Examples of phosphonic acids that can be used include ethyl-2-hexyl monoester of phenylphosphonic acid, n
-octyl monoester and octyl-phenyl monoester of phenylphosphonic acid. According to the invention, the neutral phosphine oxide according to the formula () is selected among the phosphine oxides in which at least one of the R ₁ , R ₂ or R ₃ groups is an alkoxymethyl group having 4 to 12 carbon atoms. It is advantageous to be able to When the phosphine oxide has an alkyl group, it is preferably a straight chain group. Examples of neutral phosphine oxides that can be used include diphenyl-octoxymethylphosphine oxide, diisobutyl-octoxymethylphosphine oxide, di-n-butyl-octoxymethylphosphine oxide, di-n-pentyl ―
Octoxymethylphosphine oxide and di-n
-hexyl-octoxymethylphosphine oxide. According to the method of the invention, preference is given to using di-n-hexyl-octoxymethylphosphine oxide. In the extractant system used in the method of the invention, the concentrations of the acidic organophosphorus compound and the neutral phosphine oxide are such that the molar ratio of acidic organophosphorus compound to neutral phosphine oxide is between 4 and 5. is advantageous. In order to carry out the process of the invention, it is advantageous to dilute the extractant system in an inert solvent composed of a saturated hydrocarbon having at least 8 carbon atoms, such as, for example, dodecane. Advantageously, the total concentration of extractant in the organic solvent is greater than 0.6M in order to obtain good uranium extraction levels. It is noted that the process of the present invention can be carried out in conventional extraction equipment such as mixer-settler sets, pulse columns, centrifugal extractors, and the like. According to the invention, the uranium extracted into the organic solvent is then optionally containing a reducing agent in such a way as to reduce the uranium extracted into the organic solvent to uranium to facilitate its re-extraction. It can be re-extracted by bringing the solvent into contact with an aqueous phosphoric acid solution. Satisfactory uranium recovery can be achieved by this re-extraction method, but the addition of a reducing agent and
It requires the use of concentrated phosphoric acid solutions and has the disadvantage of requiring supplementary purification steps. According to the invention, the uranium re-extraction is preferably carried out in a re-extraction device having at least three stages, by introducing the uranium-containing organic solvent for this re-extraction from the first stage thereof. Recirculate. In all stages, an aqueous ammonium carbonate solution is introduced from the last stage and circulated countercurrently with the organic solvent. The amount introduced is such that it corresponds to 50 to 80% of the stoichiometric amount required to neutralize the acidic organophosphorus compound and convert the uranium present in the organic solvent to uranyl ammonium tricarbonate. In order to maintain the pH of the first stage at a value of 8-8.5, ammonia is added in the form of a gas or an aqueous solution to the ammonium carbonate solution flowing through the first stage. The ammoniacal organic solvent leaving the final re-extraction stage is preferably purified by contacting it with an acid to remove ammonium in the form of an ammonium salt, and the organic solvent thus purified is then subjected to uranium extraction. Reuse to do. Advantageously, the acid is selected from the group comprising sulfuric acid, hydrochloric acid and phosphoric acid. It is also a preferred practice to purify the ammoniacal organic solvent leaving the final re-extraction stage by reacting it with the phosphoric acid recovered after the uranium extraction. This preferred uranium re-extraction method yields an aqueous uranium solution at the end of the re-extraction, which can then be easily converted to uranium in the form of oxides, in the form of alkali or alkaline earth uranates, without any auxiliary purification steps. It can be recovered with a total uranium recovery rate of over 90%. Furthermore, reusable products can thereby be formed. Organic solvents purified, for example by treatment with phosphoric acid, can be further used for the extraction of uranium, and the ammonium phosphate obtained from the organic solvent purification process can be used commercially or recycled to fertilizer plants. . According to the invention, uranium re-extraction is preferably carried out in three stages. In this case, the uranium-containing organic solvent is circulated from the first stage to the third stage in the stoichiometric amount necessary to neutralize the acidic organophosphorus compounds of the organic solvent and convert the uranium to uranyl ammonium tricarbonate. A mixture of ammonia and carbon dioxide gas previously dissolved in water in the form of an aqueous ammonium carbonate solution or carbonate containing 50 to 80% of
Introduce to the stage. This solution is circulated from the third stage to the first stage, and before entering the first stage ammonia is added in the form of a gas or an aqueous solution. The amount to add is the first
The amount is such that the pH of the stage is maintained at a value of 8-8.5. When the pH value is lower than 8, the uranium re-extraction rate decreases,
If the pH value is higher than 8.5, the amount of ammonia introduced will form an emulsion, which will not improve the uranium reextraction rate. Preferably, the ammonia is added in the form of a solution having an ammonia molar concentration of 5M to 7.5M. During these stages, the uranium-containing organic solvent, which also contains iron on contact with ammonia, gradually transforms into hydrated ammonium salts, and the countercurrently circulating aqueous phase becomes enriched in uranium and iron. Ammonium carbonate forms uranyl ammonium tricarbonate with uranium, which remains in solution and iron precipitates as ferric hydroxide, which is separated from the aqueous phase by precipitation. Upon exiting the third stage, the ammoniacal organic solvent is purified by treatment with an acid such as sulfuric acid, hydrochloric acid or phosphoric acid to recover an organic phase no longer containing ammonium ions and an aqueous phase containing ammonium salts. It is preferable to make it possible to do so. Preferably, the phosphoric acid portion recovered at the end of the uranium extraction step is used for this treatment. BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention will be understood by reference to the following description and accompanying drawings, which are given by way of example and not in a restrictive sense. In Figure 1, the symbol A designates the uranium extraction device, the symbol B designates the device for washing the organic solvent leaving the extraction device, and the symbols C ₁ , C ₂ and C ₃ represent the three re-extraction stages. The symbol D represents a uranium separation device, and the symbol E represents an organic solvent purification device. 0.05-0.20g/uranium from production equipment,
Phosphoric acid containing 2 to 5 g of iron and up to 2 g of calcium is introduced into extractor A via 1a. The acid is pre-oxidized to bring all the uranium into the hexavalent state and the iron into the trivalent state. In extractor A, phosphoric acid is brought into countercurrent contact with an organic solvent introduced via line 3a. This organic solvent contains an extractant system composed of an acidic organophosphorus compound and a neutral phosphine oxide of the formula - Advantageously, it consists of a mixture with octoxymethylphosphine oxide (POX11) diluted with dodecane, the concentration of di-2-ethyl-hexyl-phosphoric acid being
0.1~1M/, and the concentration of di-n-hexyl-octoxymethylphosphine oxide is 0.025~
Advantageously, it is 0.25M/. The extraction is carried out at a volume ratio of phosphoric acid to organic solvent of preferably 1 to 10 and at a temperature of 25 to 65°C, preferably close to 40°C. On leaving the extractor A, the phosphoric acid, which essentially no longer contains uranium, is discharged through line 1b, and the uranium-containing organic solvent, slightly contaminated with metal ions, in particular ferric ions, is discharged through line 3b. . This organic solvent is then sent to washing unit B where it is washed with water to essentially remove the phosphate ions contained in the solvent. After leaving the washing device it is connected to the first line by line 3c.
introduced into re-extraction stage C ₁ , followed by stages C ₂ and
Cycle to _C3 . In stages C ₂ and C ₃ it is countercurrently contacted with the ammonium carbonate solution introduced by line 4a into the final stage C ₃ , in stage C ₁ with the carbonate solution from stage C ₂ and finally with its Countercurrent contact is made with ammonia in the form of gaseous ammonia or an ammonia solution injected via line 5 into the carbonate solution entering stage _C1 . According to the invention, the flow of ammonia or ammonia is regulated by a valve controlled by a PH meter to maintain the PH value of the first stage _C1 at a value of 8-8.5. Similarly, the flow of ammonium carbonate solution introduced by line 4a into the final stage _C3 , which on the one hand neutralizes the di-2-ethyl-hexyl phosphate and on the other hand converts the uranium into uranyl ammonium tricarbonate of the stoichiometric amount required for
Adjust in such a way that it corresponds to 50-80%. During re-extraction, the uranium that first came into contact with the ammonia
Iron-containing organic solvents gradually form hydrated ammonium salts and the countercurrently migrating aqueous phase becomes rich in uranium and iron, whereas ammonium carbonate reacts with uranium to form uranyl ammonium tricarbonate. , which remains dissolved, whereas iron precipitates in the form of hydroxide. The aqueous phase containing uranyl ammonium tricarbonate leaves the first re-extraction stage C ₁ by line 4b and then flows towards the uranium separation unit D. It should be pointed out that uranium can be separated from this solution in oxide form or in the form of sodium uranate. To obtain uranium in the form of uranium trioxide, add 90~
Air is bubbled through the reactor at a temperature of 100° C. for about 6 hours, then the precipitate is filtered and washed with water.
Uranium trioxide is obtained by drying at 120℃ and roasting at about 400℃. To obtain uranium in the form of sodium uranate, a uranyl ammonium tricarbonate solution, previously degassed by bubbling air at about 90 °C to remove carbon dioxide gas and ammonia, is heated to about 80 °C. C. and then precipitate the uranium by adding sodium hydroxide to the solution while operating for 1 hour at a temperature of 80.degree. After filtration and washing with 50°C water, the sodium uranate is collected, which can later be converted into ammonium diuranate or uranium trioxide. After leaving the third re-extraction stage _C3 , the organic solvent from which the uranium has been removed is discharged via line 3d, and the refining stage E
and there treated with phosphoric acid introduced via line 1c. This phosphoric acid is part of the phosphoric acid leaving extraction step A via tube 1b. By contacting the organic solvent with phosphoric acid, the ammonium salt of the extractant decomposes to form ammonium phosphate which is discharged through line 6 and a purified organic solvent is obtained. The latter is recycled by line 3a and reused in extraction step A. The ammonium phosphate recovered in this way is
It is noted that it can be used directly commercially or in fertilizer manufacturing plants. The following examples are intended to illustrate the results obtained by practicing the method of the invention. EXAMPLE 1 This example relates to the recovery of uranium from a 6M phosphoric acid solution containing 1 g/g uranium and 1 g/iron. The organic solvent used in this example was
A mixture of ethyl-hexyl phosphoric acid (DEHP) and di-n-hexyl-octoxymethylphosphine oxide (POX11) was diluted with dodecane, and the concentration of DEHP was 0.5 M, and the concentration of POX11 was varied. . Extraction involves combining an aqueous phosphoric acid solution and a certain volume of an organic solvent.
This was accomplished by contacting both phases for approximately 15 minutes with mechanical stirring. The two phases were then separated by centrifugation, and samples were then taken and analyzed to determine their uranium concentration. It should be noted that uranium concentrations were determined potentiometrically (redox using potassium dichromate) or colorimetrically (using dibenzoylmethane). The distribution or distribution coefficient D is then determined. is equal to the ratio of the uranium concentration in the organic phase to the uranium concentration in the aqueous phase. The results obtained are shown in the table and FIG. Figure 1 shows the change in uranium distribution coefficient D of organic solvent POX11.
It is shown as a function of content, and the organic solvent contained 0.5M/DEHP in all cases.

[Table] The uranium distribution coefficient D is 0.5M/organic solvent.
It shows that the maximum value is reached when it contains DEHP of 0.1M and POX11 of 0.1M/. In addition, DEHP
It is also seen that good results are obtained when the molar ratio of POX11 to POX11 is 3 to 4. Example 2 This example relates to the extraction of uranium from a 6M phosphorus solution that also contains 1 g/g uranium and 1 g/iron. In this example, uranium extraction was performed under the same conditions as in Example 1, and once again a mixture of DEHP and POX11 diluted with dodecane was used as the organic solvent. Although the total concentration of extractant in the organic solvent was varied in this example, the molar ratio of DEHP to POX11 was in each case 5.
was equal to After each extraction, the uranium () and iron () concentrations in the aqueous and organic phases were measured and the uranium partition coefficient D was determined. The results obtained are shown in the table and FIG. FIG. 2 shows the variation of the uranium-iron partition coefficient D as a function of the total extractant concentration.

[Table] It can be seen that the partition coefficient increases regularly with extractant content, and it increases more rapidly for iron than for uranium. Example 3 In this example, with various uranium concentrations
From 6M phosphoric acid solution, dilute with dodecane to 0.5M/
The uranium was extracted with an organic solvent containing a mixture of DEHP and 0.1M/POX11. Each extraction was performed at a temperature of 20°C for approximately 15 minutes with stirring.
This was accomplished by contacting one volume of an aqueous solution with one volume of an organic solvent. Next, the uranium distribution coefficient D was determined. The results obtained are shown in the table.

[Table] Example 4 In this example, various mixtures of acidic organophosphorus compounds and neutral phosphine oxides diluted with dodecane were prepared from a 6M phosphoric acid solution containing 1 g/g of uranium and 1 g/iron. It was used as a solvent to extract uranium. Extraction was carried out by contacting 1 volume of aqueous solution with 1 volume of organic solvent for about 15 minutes in each case, and then the partition coefficients of uranium () and iron () were determined. The results obtained are shown in the table. In all of the above embodiments, the uranium extracted in an organic solvent is combined with a phosphoric acid solution containing a reducing agent for reducing uranium () to uranium (), preferably having a phosphoric acid concentration of 10M or more, and the organic solvent. It should be pointed out that it can be recovered by contacting with.

【table】

[Table] Example 5 This example concerns the treatment of 2.5 m ³ of phosphoric acid obtained by the action of sulfuric acid on phosphate ore. It had been oxidized in advance with hydrogen peroxide. In this example, 25.6/h of phosphoric acid solution was introduced into extractor A via line 1a at a temperature of 40°C. The solution contained 345 g/P ₂ O ₅ , 0.08 g/U and
It contained 1.91 g of iron, with uranium and iron in the +6 and +3 oxidation states, respectively. Also using line 3a, add 0.5M di-2-ethyl-hexyl phosphoric acid and 0.125M di-n-hexyl-octoxymethylphosphine oxide to extractor A, which consists of five mixer-settler sets. 3.85/hr of an organic solvent consisting of dodecane was introduced. The phosphoric acid solution leaving extractor A was discharged via line 1b at a flow rate of 25.6/h, and a portion of this stream corresponding to 0.45/h was transferred to purifier E via line 1c. The uranium-containing organic solvent leaving extraction device A is line 3b.
and introduced into a washing device B consisting of two mixer-settler sets, where 0.7
Countercurrent contact was made at a temperature of 40° C. with wash water introduced at a flow rate of /h. 0.52g/ of uranium and 0.16g/
The washed organic solvent containing iron was then introduced into the first re-extraction stage _C1 via line 3c. For this re-extraction operated at a temperature of 40 °C,
The organic solvent is introduced into the first stage _C1 at a rate of 3.85/h and the 5M ammonia solution is introduced at 0.17% using line 5a.
/h was also introduced into the first stage. This allows the PH of the first stage to be maintained at a value of 8.5. Using line 4a, a solution of ammonium carbonate with a concentration of 100 g/h was introduced into the third stage _C3 at a rate of 0.7/h. This represented 74% of the stoichiometric amount required to neutralize di-2-ethyl-hexyl phosphate and convert uranium to uranyl ammonium tricarbonate. The organic solvent leaving the third re-extraction stage was discharged via line 3b at a rate of 4.15/hr, with a uranium concentration of 0.002 g/hr. This uranium-free solvent was then introduced via line 3d at a rate of 4.15/hr into refiner E, where it was contacted with phosphoric acid introduced from extractor A via line 1c at a flow rate of 0.45/hr. The purified organic solvent is transferred to purifier E via line 3a.
and recycled to extractor A at a rate of 3.85/hr. In the re-extraction stage, in particular the first stage, iron is precipitated in the form of hydroxide, which is removed by continuous or discontinuous filtration and the solution circulating through the re-extraction stage is recycled. 0.75 Kg of wet precipitate was removed per 2.5 m ³ of acid treated in this way. The aqueous solution containing uranyl ammonium tricarbonate leaving the first re-extraction stage C ₁ was discharged via line 4b at a rate of 0.57/h. This aqueous solution
It contained 3.57 g/U of uranium and was then processed in Uranium Separator D. In this apparatus, the solution was first clarified and then maintained in a reactor at 95° C. for 6 hours with air bubbled through. Filtered, washed with water, dried at 120℃, 400℃
After roasting at °C, uranium in the form of uranium trioxide
190 g were obtained for every 2.5 m ³ of acid treated, corresponding to a total uranium yield of 95%.

[Brief explanation of the drawing]

FIG. 1 is a schematic representation of the various steps of the method of the invention. FIG. 2 is a graph showing the change in the distribution or distribution coefficient of uranium as a function of the concentration of neutral extractant in the mixture used for extraction. FIG. 3 is a graph showing the variation in the distribution coefficient D of uranium and iron as a function of the total concentration of the organic solvent extractant used.

Claims (1)

[Scope of Claims] 1. A method for recovering uranium present in a phosphoric acid solution by contacting the solution with an organic solvent suitable for uranium extraction, wherein the organic solvent is an acidic organophosphorus compound and the formula: (In the formula, R ₁ , R ₂ and R ₃ are the same or different,
alkyl, aryl or alkoxyalkyl group, in which at least one of R ₁ , R ₂ and R ₃ is an alkoxyalkyl group); and a neutral phosphine oxide. 2 The acidic organophosphorus compound has the formula: The method according to claim 1, wherein R ₄ and R ₅ are the same or different alkyl groups. 3. The method according to item 2, wherein R ₄ and R ₅ are the same or different and are branched alkyl groups having at least 8 carbon atoms. 4. The method according to item 2 above, wherein the dialkyl phosphoric acid is di-2-ethyl-hexyl phosphoric acid. 5 The acidic organophosphorus compound has the formula: The method according to claim 1, wherein R ₆ and R ₇ are the same or different and are alkyl or aryl groups. 6 Neutral phosphine oxide group of formula ()
2. A method according to claim 1, wherein at least one of _R1 , _R2 or _R3 is an alkoxymethyl group having 4 to 12 carbon atoms. 7. The method according to item 6 above, wherein the neutral phosphine oxide is di-n-hexyl-octoxymethylphosphine oxide. 8. According to claim 1, the concentration of the acidic organophosphorus compound and the neutral phosphine oxide in the extractant system is such that the molar ratio of the acidic organophosphorus compound to the neutral phosphine oxide is 4 to 5. the method of. 9. comprising a step of re-extracting the uranium extracted into an organic solvent, the re-extraction step being carried out in a re-extraction apparatus having at least two stages, the uranium-containing organic solvent being introduced from the first stage; an aqueous ammonium carbonate solution is introduced from the last stage and circulated countercurrently to the organic solvent in all stages, but the amount of ammonium carbonate introduced is controlled by The amount is 50 to 80% of the stoichiometric amount required to neutralize the compound and convert the uranium present in the organic solvent into uranyl ammonium tricarbonate, and the first
2. A process according to claim 1, comprising adding ammonia in the form of gas or aqueous solution to the ammonium carbonate solution flowing through the stage to maintain the pH of the first stage at a value between 8 and 8.5. 10 The ammonia organic solvent leaving the final re-extraction stage is purified by reacting it with an acid to remove it in the form of ammonium salts, and the organic solvent so purified is reused for carrying out the uranium extraction. The method described in Section 9. 11. The method according to item 10 above, wherein the acid is selected from the group consisting of sulfuric acid, hydrochloric acid and phosphoric acid. 12. The method of paragraph 10, wherein the ammonia organic solvent leaving the final re-extraction step is purified by reacting it with phosphoric acid recovered after the uranium extraction has ended.