FI75603C - FOERFARANDE FOER GEMENSAM UTVINNING AV URAN, YTTRIUM, TORIUM OCH SAELLSYNTA JORDARTSMETALLER UR EN ORGANISK FAS. - Google Patents

Description

1 75603

The present invention relates to a process for the combined recovery of uranium, thorium, yttrium and rare earths contained in an organic phase. In particular, this method can be used for the co-recovery of the above-mentioned mineral species contained in the crude phosphoric acid obtained by the wet process.

In the past, in particular from European patent application O 026 132, a method for the recovery of these species together from an organic solvent is known. This patent application describes a process in which an aqueous solution of an acid, for example a crude crude phosphoric acid, is contacted with an organic phase containing in particular dialkylphenylphosphoric acid. After separation of the phases, the organic phase is re-extracted with a solution containing hydrofluoric acid and phosphoric acid.

This re-extraction is effective, but it has some drawbacks.

First, the cost of reactants can be expensive. Namely, hydrofluoric acid and phosphoric acid are partially transferred to the organic phase during the extraction. This causes a decrease in the concentrations of these acids in the recirculation water phase cycle. Substantial amounts of these acids therefore have to be added.

An attempt has been made to solve this problem of reagent consumption by washing the organic phase from which the metal species have been emptied with an aqueous solution after the re-extraction step before returning it to the regeneration zone of the original acid-water solution. The organic phase is then emptied of phosphoric and hydrofluoric acids and the aqueous solution 2 75603 from the washing zone is then combined with the re-extraction aqueous solution. In such a case, however, the acid concentrations of the solution from the washing zone are generally lower than the concentration of the re-extraction cycle, so that the combination of the two solutions results in a low-acid flow. This flow then has to be concentrated and consumes energy, which can also be detrimental to the economics of the process.

In addition, this method requires a special technique to perform the three-step separation. The machines used to make this separation are expensive, difficult to maintain, and have to be built from raw materials that are very resistant to corrosion by hydrofluoric acid and phosphoric acid.

Thus, there is a need to develop a method for the re-extraction of target species that is simple and economical on an industrial scale.

This object is achieved by a process according to the invention for the combined recovery of uranium, yttrium, thorium and rare earth metals in an organic phase, which process is characterized in that said organic phase is contacted with at least one diluent which is an ether, alcohol, polyol, amide , a sulfoxide or ketone, with at least one precipitating agent which is ammonia, an ammonium salt or a fluoride other than hydrofluoric acid, and an aqueous phase, the diluent being chosen so as to obtain a homogeneous environment with the organic phase and the aqueous phase to give a liquid phase and a precipitate, containing the aforementioned mineral species, which are then separated from the liquid phase.

The use of a miscible diluent generally results in a two-phase system in which decantation is easily performed in simple equipment.

Other features and advantages of the invention will be best understood by reading the following description and specific, but non-limiting, examples of the practice of the invention.

Il 3 75603

The process according to the invention is suitable for any organic phase containing uranium and / or at least one substance from the group consisting of yttrium, thorium and rare earth metals. These species may have been added to this organic phase by contacting it with an acid-water solution containing these species.

This aqueous phase may be of different origins. It may contain some strong mineral acid such as phosphoric, sulfuric, hydrochloric acid and the target species in small amounts.

Any acid-water phase of the type described in European patent application O 026 132 can be used in the context of the present invention. Thus, this aqueous phase can be formed from crude phosphoric acid obtained by the wet process. It may also be an aqueous phase obtained by treating a residual phosphorus gypsum containing the above-mentioned species in an insoluble form as an aqueous solution with a concentrated mineral acid. It may also be an aqueous raffinate obtained by a solvent process from phosphoric acid from a wet process.

With regard to the organic phase, on the other hand, the process according to the invention can be applied particularly well to all organic phases which contain a solvent capable of dissolving uranium and at least one substance from the group consisting of yttrium, thorium and rare earth metals from the above-mentioned aqueous acid phases.

Suitable extractants useful in the context of the invention are alkyl, aryl or alkylaryl (mono- or dialkylaryl) esters of phosphoric, phosphinic and phosphonic acids or mixtures of these esters. Thus, an organic phase based on diethyl 2-hexylphosphoric acid, monoethyl-2-hexylphosphoric acid, monooctylphenylphosphoric acid or dioctylphenylphosphoric acid can be used.

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In addition, extractants containing at least two phosphorus atoms can be used, in particular extractants of the type dialkylpyrophosphoric acid, dialkyldiphosphonic acid, dialkylphosphinic acid or mixtures thereof. Mention may be made, for example, of octylpyrophosphoric acid OPPA, in particular that obtained by reacting phosphorus pentoxide with octanol, or also didodecyl-vinylenediphosphonic acid (C12H250 ^ 0H op (CH-CH) - ΡΟΗ (0 ^ 2Η250 ^ 'ch2

Of course, mixtures of the various groups of extractants mentioned above can also be used.

Of course, these extractants can be used in combination with a neutral organic solvent selected, alone or in admixture, from aromatic or aliphatic hydrocarbons. As the neutral solvent, for example, heptane, dodecane, hexane, fuel oil-type oil fractions, aromatic compounds such as benzene, toluene, ethylbenzene, xylene and Solvesso-type (trademark of the EXXON group) used alone or in mixtures can be mentioned.

In addition, the organic phase may contain a solvating agent (modifier) selected from trialkylphosphine oxides, alkylphosphinates, alkylphosphonates, alkylphosphates and alkylsulfoxides. In practice, tri-octylphosphine oxide (TOPO), dibutylbutylphosphonate or tributylphosphate is preferably used.

Finally, in some other cases, it may be advantageous to incorporate into the organic phase a modifier selected from aliphatic hydroxyl compounds containing more than 4 carbon atoms or alkylaryl compounds containing more than 10 carbon atoms. Preferably, an aliphatic alcohol having 10 carbon atoms or an alkylphenol such as nonylphenol is used for this purpose.

Il 5 75603

According to a particular embodiment of the invention, an organic phase is used which comprises, from a co-extractant of one of the above species, aqueous solutions of an acid of the type described above, which is a dialkylphenylphosphoric acid substantially without a monoalkylphenylphosphoric derivative, and a neutral solvent of the type described above.

More specifically, an acid is used in which the alkyl group is a straight-chain or branched aliphatic group containing 4 to 12 carbon atoms. Preferably the alkyl group is an octyl group, more particularly the 1,1,3,3-tetramethylbutyl group, preferably in the 4-position. Of course, mixtures of one dialkylphenylphosphoryl acid can be used instead of one.

Furthermore, according to this same specific embodiment, the organic phase may further contain a solvating agent and / or a modifying agent of the same type as described above.

The conditions of use of these organic phase components are described in European patent application O 026 132.

The contacting of the aqueous starting acid solution with the organic extraction phase takes place in a manner known per se and is not within the scope of the present invention.

The organic phase containing uranium, thorium, yttrium and rare earth metals is then contacted with a diluent which is at least partially mixed with this phase.

Preferably, a readily distillable diluent is used to facilitate separation of the mixture of diluent and organic phase after separation of the precipitate. In particular, diluents with a low boiling point are well suited to the process of the invention. According to a particular embodiment of the invention, this diluent is an ether.

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In another embodiment, the diluent is an alcohol or polyol. In particular, lower aliphatic alcohols with preferably less than 6 or 6 and especially less than 4 or 4 carbon atoms are selected.

According to yet another embodiment, an amide can be used as the diluent, preferably an amide having less than 6 or 6 and more specifically less than 4 or 4 carbon atoms.

For example, dimethylformamide can be used.

In another variation of the invention, the diluent is a sulfoxide such as dimethyl sulfoxide.

According to a preferred embodiment of the invention, a ketone is used as diluent. Ketones prove to be very effective and give good quantitative yields of the target species. In particular, a short-chain aliphatic ketone having a number of carbon atoms of less than 6 or 6 is preferably used. For example, acetone, methyl ethyl ketone or diethyl ketone can be used.

It is, of course, entirely possible to use a mixture of the different types of diluents described above.

The amount of diluent used can vary widely. Preferably, an amount of diluent is used which provides a homogeneous medium with the organic phase and optionally the aqueous phase of the precipitant, if used as a solution.

As the precipitant, for example, ammonia or ammonia salts such as ammonium carbonate or bicarbonate can be used.

Preferably some fluoride is used. Examples of fluorides which may be mentioned are ammonium fluoride or alkali metal fluorides. Alkali earth metal fluorides, hydrogen fluoride or

II

7 75603 silicofluorides. Mention should also be made of hydrofluoric acid.

Of course, it is entirely possible to use some precipitant mixture.

The amount of precipitant can vary within wide limits, which can depend on the quality of the diluent.

The precipitant can be added in various forms, in particular as a solid or a more or less concentrated solution. For example, when ammonium fluoride is used, and especially when acetone is used as the diluent, solutions having a concentration of 300 to 400 g / l can be used.

Generally, the organic phase is first contacted with a diluent. A precipitant is then added to the resulting medium. However, it is also entirely possible to contact the organic phase simultaneously with both the diluent and the precipitator and also first with the precipitator and then only with the diluent.

It has otherwise been found that it might be advantageous to add water to the liquid phase when the organic phase is contacted with or immediately after the diluent and precipitator. This addition of water usually significantly increases the precipitated amount of the target species. This effect is particularly noticeable when ketones and especially acetone are used as diluents.

This addition of water can be made at any time when the organic phase is brought into contact with the diluent and precipitator or even before or after it.

This water may be the water or it may be added to the water that could already be or could be added to the medium when the precipitant is used as a solution.

The amount of water added may vary. In general, it is recommended that an attempt be made to work in a homogeneous medium, in which case the maximum amount of water to be added is that after which the homogeneity of the 8 75603 medium would no longer be ensured.

It should be noted, moreover, that if the uranium is not in the organic phase such that its oxidation state is IV, but VI, and if it is desired to precipitate quantitatively, it is desirable to reduce it in advance. This reduction can take place either in the organic phase or in a mixture of the organic phase and the diluent. Any suitable reducing agent such as ferrous metal, aluminum or zinc can be used.

The reaction temperature is usually between room temperature, about 20 ° C and 40 ° C.

The process according to the invention can be carried out continuously or intermittently. The reaction is carried out in devices known per se.

When the organic phase, the diluent and the precipitant are contacted, a precipitate containing uranium, yttrium, thorium and rare earth metals appears. This precipitate is easily separated by precipitation or filtration of the liquid phase and forms the product.

The components of the liquid phase can be separated by washing or distillation. The diluent and precipitant can thus be recycled.

The following are illustrative examples of the method.

Example 1 Starting from phosphoric acid obtained from a wet process from ore extracted in Florida and having the following concentrations of uranium and rare earths: U 150 mg / l, Y2O2 75 mg / l, rare earth oxides 120 mg / l.

It is extracted with the following solvent: DOPPA (dioctylphenyl-phosphoric acid) 0.5 M, TOPO 0.125 M, Solvesso 300 g / l, fuel oil in phase ratio A / 0 = 5. An extraction product is obtained which contains: li 9 75603 U 540 mg / l, Y2 ° 3 350 mg / l and rare earth oxides 300 mg / l.

To 1 liter of the extract product add 1 liter of acetic anhydride and 2 g of ferrous metal to reduce to U (VI) U (IV) and then 3 minutes 5 minutes later 90 cm of ammonium fluoride solution with a concentration of 185 g / l. It is found that a precipitate is formed which can be easily separated by decantation or filtration.

The amount of uranium, yttrium and rare earths in the supernatant solution shows that the precipitation yield is more than 98% for uranium, more than 97% for yttrium and more than 95% for rare earths.

The separated liquid phase is then distilled at atmospheric pressure to give a recyclable azeotropic mixture of water and acetone at the top and a biphasic mixture at the bottom consisting of a recyclable ammonium fluoride solution on the one hand and a solvent of the extraction solvent composition on the other.

Example 2 Starting from ore originating in Morocco, wet phosphoric acid to which europium and thorium have been added. The concentrations in this acid are as follows: U 150 mg / l, Y2 ° 3 68 mg / l, 50 mg / l, ThO2 50 mg / l. The acid is extracted at the same time as the solvent and under the same conditions as in Example 1.

To one liter of the extraction product are added 1 liter of acetonic anhydride and 2 g of iron in the form of 3 3 3 and then 85 cm of the same ammonium fluoride solution as in Example 1.

ThO 2 more than 95%, Y 2 O 3 more than 97%.

Example 3 Starting from ore originating in Morocco, wet phosphoric acid has the following concentrations: 75 753 U 148 mg / l, Y ^ O ^ 68 mg / l. Powdered iron 4 g / l is added to the acid. The acid is extracted as a solvent containing 0PPA in a mixture of 4 g / l with a fuel oil having a phase ratio of A / 0 = 5. To 1 liter of the extract product is added 2.75 liters of acetone anhydride and then 80 ml of the same type of ammonium fluoride solution as above. Precipitation is obtained. The precipitation yields are as follows: U more than 98%, Y 2 O 3 more than 90%.

Example 4 This example shows the results obtained using different types of diluents in an organic extraction phase having the following composition: DOPPA 0.5 M, TOPO 0.125 M, Solvesso 300 g / l, fuel oil; to this phase was added 2 g / l Y 2 O 2.

The results are summarized in the following table.

Diluent Volume Organic NH .F 10 M Precipitation yield (ml) phase 4 (ml) yo ° t (ml) 370 g / l

Ethyl alcohol 20 10 0.5> 96% n-propyl alcohol 25 10 0.5> 96% isopropyl alcohol 25 10 0.5> 96% methyl ethyl ketone 25 10 0.5> 96% diethyl ether 20 10 0.3 90%

Example 5 This example shows the results obtained using different diluents, dimethylformamide (DMF) on the one hand and dimethyl sulfoxide (DMSO) in the presence of acetone on the other hand, in an organic extraction phase having the following composition: DOPPA 0.5 M, TOPO 0.125 M, Solvesso (addition ), to which 2 g / l Y2 ° 3 *

The results are summarized in the table below.

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Diluent Volume Temperature Organic NH 4 F 10 M Precipitation phase 4. yield _ _ _ (ml) (ml) Y 2 O 3 DMF 10 40 ° C 10 0.5> 98% DMS? +. j? 25 ° C 0.5 0.5 94% acetone 5

Of course, the invention is in no way limited to the described embodiments, which are given by way of example only. In particular, it encompasses all methods that are technically equivalent to the methods described herein, as well as combinations thereof, when used within the scope of the protection defined in the claims.

Claims (20)

A process for the combined recovery of uranium, yttrium, thorium and rare earth metals contained in an organic phase, characterized in that said organic phase is contacted with at least one diluent which is an ether, alcohol, polyol, amide, sulfoxide or ketone, at least one precipitant with ammonia, an ammonium salt or a fluoride other than hydrofluoric acid, and an aqueous phase, the diluent being selected so as to achieve a homogeneous environment with the organic phase and the aqueous phase to give a liquid phase and a precipitate containing the above-mentioned mineral species which then separated from the liquid phase. Process according to Claim 1, characterized in that the diluent is a ketone, preferably a short-chain aliphatic ketone, in particular one having less than 6 or 6 carbon atoms. Process according to Claim 2, characterized in that the ketone is acetone, methyl ethyl ketone or diethyl ketone. Process according to Claim 1, characterized in that the diluent is an alcohol or a polyol, in particular a lower aliphatic alcohol, preferably having less than 6 or 6, in particular less than 4 or 4 carbon atoms. Process according to Claim 1, characterized in that the diluent is an amide, preferably having less than 6 or 6 and, in particular, less than 4 or 4 carbon atoms. Process according to Claim 6, characterized in that the amide is dimethylformamide. Il 75603 Process according to Claim 1, characterized in that the diluent is a sulfoxide, in particular dimethyl sulfoxide. Process according to Claim 1, characterized in that the fluoride is ammonium fluoride or alkali metal fluoride. Process according to one of the preceding claims, characterized in that the organic phase is first contacted with a diluent and then a precipitant is added. Process according to one of the preceding claims, characterized in that water is added to the liquid phase when or after contacting the organic phase with the diluent and the precipitant. Process according to one of the preceding claims, characterized in that when the uranium is in the organic phase with an oxidation state of VI, it is reduced by adding a reducing agent to the organic phase or to a mixture of the organic phase and the diluent. Process according to any one of the preceding claims, characterized in that the above-mentioned mineral species are added to the organic phase by contacting it with an aqueous phase of an acid containing said species. Process according to any one of the preceding claims, characterized in that said organic phase contains at least one substance from the group consisting of alkyl esters, aryl esters and alkylaryl esters of phosphoric, phosphinic and phosphonic acids. Process according to one of Claims 1 to 12, characterized in that said organic phase contains at least one substance from the group consisting of dialkylpyrophosphoric acid, dialkyldiphosphonic acid and dialkyldiphosphinic acid. _ - TT - 75603 Process according to Claim 14, characterized in that the organic phase contains octylpyrophosphoric acid. Process according to one of Claims 13 to 15, characterized in that the organic phase further contains a neutral solvent selected from aliphatic hydrocarbons, including heptane, hexane, dodecane and kerosene-type oil fractions, aromatic hydrocarbons, including benzene, ethylbenzene, toluene, xylene and aromatic oil fractions. Process according to one of Claims 13 to 16, characterized in that the organic phase additionally contains a solvation derivative selected from trialkylphosphine oxides, alkylphosphinates, alkylphosphonates, alkylphosphates and alkylsulfoxides. Process according to one of Claims 13 to 17, characterized in that the organic phase contains a modifying agent selected from aliphatic hydroxyl compounds having more than 4 carbon atoms or alkylaryl compounds having more than 10 carbon atoms. Process according to Claim 13 and one of Claims 16 to 18, characterized in that said organic phase contains a dialkylphenylphosphoric acid substantially without a monoalkylphenylphosphorus derivative, in which the alkyl group is an aliphatic straight-chain or branched group having 4 to 12 carbon atoms. Process according to Claim 19, characterized in that the alkyl group is an octyl group, in particular a 1,1,3,3-tetramethylbutyl group, preferably in the 4-position. 75603