Patent Application
20180333697
The present invention relates to the field concerning the extraction of uranium present in an aqueous medium containing phosphoric acid.
More particularly, it relates to an organic material allowing the extraction of uranium, and more specifically uranium in oxidation state +VI, denoted uranium(VI) or U(VI), this uranium being present in an aqueous solution also comprising phosphoric acid.
The invention also relates to a method for extracting and to a method for recovering uranium(VI) present in said aqueous solution.
The aqueous solution from which the uranium(VI) can be extracted, or from which it can be recovered, may notably be an aqueous solution resulting from the attack of a natural phosphate by sulfuric acid.
The present invention particularly finds application in the treatment of natural phosphates to recover the uranium value contained in these phosphates.
Natural phosphates, also called phosphate ores, are used for the production of phosphoric acid and fertilizer. They contain uranium in amounts that can vary from a few tens of ppm to several thousand ppm, as well as variable amounts of other metals.
The potential recovery of the uranium contained in these natural phosphates is a few thousand tonnes per year, this representing a non-negligible source of uranium supply.
In methods currently used to recover this uranium contained in natural phosphates, these natural phosphates are subjected to attack by sulfuric acid. This attack converts tricalcium phosphate to phosphoric acid and results in solubilising the uranium together with various other metals, in particular iron which remains the majority impurity.
The actual recovery of uranium(VI) is therefore carried out from these concentrated aqueous phosphoric acid solutions that shall be called “aqueous phosphoric acid solutions” in the remainder of the present description.
At the present time, several routes are known for extracting the uranium contained in said aqueous phosphoric acid solutions.
According to a first route, the aqueous solution containing phosphoric acid and uranium is subjected to hydrometallurgical treatment based on liquid-liquid extraction, a technique whereby this aqueous solution, or aqueous phase, is placed in contact with an organic phase comprising one or more extractants to obtain extraction, in the organic phase, of the uranium contained in the aqueous phosphoric acid solution.
However, this liquid-liquid extraction technique has recourse to substantial volumes of organic solvents which generally have very low flash points or flammability points. Said organic solvents are therefore flammable, and both the use and storage thereof can raise problems of industrial safety but also of environmental safety.
To overcome these disadvantages generated by the use of organic solvents, a second route to extract uranium has been proposed.
This second route uses solid-liquid extraction, whereby uranium is extracted from an aqueous phosphoric acid solution by contacting this aqueous solution with a water-insoluble material comprising functional chemical groups capable of retaining the uranium either by ion exchange or by chelation.
Among the proposed materials recognized as allowing the extraction of uranium from aqueous phosphoric acid solutions, particular mention can be made of the organic materials such as taught in documents U.S. Pat. No. 4,599,221 and U.S. Pat. No. 4,402,917, respectively referenced [1] and [2].
However, in these documents [1] and [2], the extraction processes require that the uranium present in oxidation state +VI in the aqueous phosphoric acid solutions resulting from sulfuric attack of natural phosphates, should be previously reduced to oxidation state +IV before it is possible to carry out actual extraction of the uranium.
It is therefore the objective of the invention to propose novel materials allowing the extraction, via the solid-liquid extraction technique, of uranium(VI) contained in an aqueous phosphoric acid solution, with a reduced number of steps.
In particular, these novel materials must not have recourse either to a reduction step of uranium(VI) to uranium(IV) prior to extraction properly so-called, but they must allow direct extraction of this uranium when present at oxidation state +VI in said aqueous phosphoric acid solutions.
The novel materials of the invention must also allow extraction of uranium(VI) that is particularly efficient irrespective of the concentration of phosphoric acid in this aqueous solution. In particular, it must be possible to use these novel materials to extract uranium(VI) from so-called “concentrated” aqueous phosphoric acid solutions, such as aqueous solutions resulting from attack of a natural phosphate by sulfuric acid having a typical phosphoric acid concentration of at least 5 mol/L.
The novel materials of the invention must also allow highly selective extraction of uranium(VI) over other metal cations likely to be contained in the aqueous phosphoric acid solution and, in particular, over iron(III).
The novel materials of the invention must also be able to be synthesised with relative ease, i.e. only having recourse to reactions conventionally performed in the field of chemical synthesis.
These objectives set forth above and others are reached first with an organic material of the aforementioned type, i.e. a water-insoluble material comprising chemical functional groups capable of retaining uranium.
According to the invention, this material is an organic material comprising a solid polymeric substrate on which is covalently grafted a plurality of molecules having the following general formula (I):
where:
The inventors have unexpectedly and surprisingly ascertained that an organic material comprising a solid polymeric substrate on which is covalently grafted a plurality of molecules having general formula (I) such as defined above, allows uranium(VI) to be extracted directly from an aqueous phosphoric acid solution, without a prior reduction step.
Additionally, this extraction is obtained with high performance and selectively irrespective of the concentration of phosphoric acid in this aqueous solution. More particularly, this extraction is obtained by adsorption of this uranium(VI) on the organic material.
This high extraction performance, in particular in aqueous solutions comprising a high concentration of phosphoric acid, typically higher than 5 mol/L, is all the more unexpected and surprising since it goes against the teaching of document WO 2014/127860, referenced [3], which also concerns the field of extracting uranium contained in an aqueous medium comprising phosphoric acid.
The material described in document [3] for uranium extraction is a material comprising an inorganic solid substrate on which is covalently grafted a plurality of organic molecules comprising a diamidophosphonate unit. Yet the choice of an inorganic solid substrate is presented, in document [3], as being far more preferable to the choice of an organic solid substrate, in particular on account of the greater chemical stability of a solid substrate of inorganic type.
It is specified that in the meaning of the present invention:
Therefore, depending on the meaning of R2 and R3, the plurality of molecules of the organic material according to the invention may meet:
where:
where m, n, R1, R4, R5 and G are such as previously defined.
In one advantageous variant, the plurality of molecules of the organic material of the invention meets formula (I-a).
In one preferred variant, the plurality of molecules of the organic material of the invention meets formula (I-a) where m=0 and/or R3 is a hydrogen atom.
In particular, this plurality of molecules may particularly meet the following particular formula (I-c) where R1, R2, R4 and R5 are such as defined previously for the plurality of molecules in particular formula (I-a), m=0 and R3 is a hydrogen atom:
As indicated above, R5 is attached to at least one group G. This bond between R5 and G is a covalent bond.
This group G is itself attached to the solid polymeric substrate of the organic material of the invention by at least one covalent bond, this covalent bond between the group G and the solid polymeric substrate being represented by the dotted line in general formula (I) and in the particular formulas (I-a), (I-b) and (I-c) above.
Groupe G is selected from among an amide group, alkenyl group, alkynyl group, amine group, thioether group, ether-oxide group and 1,2,3-triazole group.
Table 1 below specifies, for each type of group G, the corresponding structural or condensed structural formula.
As illustrated in Table 1, when group G is an amide group, this group may be a secondary amide group or a tertiary amide group. In the same manner, when the group is an amine group, this group may be a secondary amine group or a tertiary amine group.
Table 1 also evidences the fact that, when group G is a secondary or tertiary amide, the polymeric solid substrate may be attached to the plurality of corresponding molecules on the carbon side or else on the nitrogen side of this amide group.
Irrespective of the group G selected, it is observed that it is capable of withstanding the operating conditions applied by the method for extracting uranium(VI) contained in an aqueous phosphoric acid solution.
In one particular variant, the plurality of molecules of the organic material of the invention meets the following particular formula (I-d):
where:
In one variant, the groups R1 and R2 of the plurality of molecules of the organic material of the invention, irrespective of which above formula (I-a) to (I-d) they meet, are each identical and advantageously represent a branched alkyl group which may particularly comprise 8 to 10 carbon atoms. The 2-ethylhexyl group is most particularly preferred.
In one advantageous version, the plurality of molecules of the organic material of the invention meets the following particular formula (I-e):
where the abbreviations “Bu” and “EtHex” respectively correspond to n-butyl and 2-ethylhexyl groups.
The organic material of the invention comprises a solid polymeric substrate. This solid polymeric substrate is formed of a polymer comprising at least one repeat unit selected from among an olefin unit, a unit comprising an aromatic group, an acrylic ester unit and mixtures of these units.
The polymer of the solid polymeric substrate is advantageously a divinylbenzene/styrene copolymer or an acrylic ester polymer.
As previously indicated, irrespective of the group G selected to ensure the covalent bond between the solid polymeric substrate and the plurality of molecules, the organic material of the invention has particularly high affinity and high selectivity for uranium(VI) when this uranium(VI) is contained in an aqueous solution also comprising phosphoric acid.
Therefore, a second subject of the invention relates to the use of an organic material such as defined above, to extract uranium(VI) from an aqueous solution comprising phosphoric acid, it being specified that the advantageous characteristics of this organic material, such as those relating to the molecules and/or to the solid polymeric substrate, can be taken alone or in combination.
According to the invention, this aqueous solution may comprise phosphoric acid over a very broad range of molar concentrations.
More particularly, the aqueous solution may comprise at least 0.1 mol/L, advantageously from 1 mol/L to 10 mol/L, preferably from 2 mol/L to 9 mol/L and more preferably from 3 mol/L to 7 mol/L of phosphoric acid.
Said aqueous solution may particularly be a solution resulting from attack of a natural phosphate by sulfuric acid.
A third subject of the invention relates to a method for extracting uranium(VI) from an aqueous solution comprising phosphoric acid, said aqueous solution in particular possibly being a solution resulting from attack of a natural phosphate by sulfuric acid.
According to the invention, this method comprises:
A fourth subject of the invention relates to a method for recovering uranium(VI) from an aqueous solution comprising phosphoric acid, said aqueous solution in particular possibly being a solution resulting from the attack of a natural phosphate by sulfuric acid.
According to the invention, this method comprises:
A fifth subject of the invention relates to a molecule able to be grafted onto a solid polymeric substrate and to form an organic material such as defined above.
According to the invention, the molecule meets the following general formula (II):
where:
Reference will be made to the different definitions given above for m and the different groups R1 to R5, in connection with the organic material.
When G′ is a hydroxyl group, it may be an activated hydroxyl group, e.g. with a tosyl denoted Ts, or with a mesyl denoted Ms.
Therefore, depending on the meaning of R2 and R3, the molecule of the invention may meet:
where:
where m, n, R1, R4, R5 and G′ are such as previously defined.
In one advantageous variant, the molecule of the invention meets formula (II-a).
In one preferred variant, the molecule of the invention meets formula (II-a) where m=0 and/or R3 is a hydrogen atom.
In particular, this molecule may meet the following particular formula (II-c), where R1, R2, R4 and R5 are such as previously defined for the molecule in the particular formula (II-a), m=0 and R3 is a hydrogen atom:
As indicated above, R5 is attached to at least one group G′. This bond between R5 and G′ is a covalent bond.
Group G′ is selected from among a thiol, azide, aldehyde, acyl chloride, acetylene group, alkene group, amine group, hydroxyl group and halide group.
Table 2 below specifies, for each type of group G′, the corresponding condensed structural formula.
As illustrated in Table 2, when group G′ is an amine group, this group may be a primary amine group or a secondary amine group.
In one particular variant, the molecule of the invention meets the following particular formula (II-d):
where:
In one variant, the groups R1 and R2 of the molecule of the invention, irrespective of which above particular formula (II-a) to (II-d) they meet, are each identical and advantageously represent a branched alkyl group that may in particular comprise S to 10 carbon atoms. The 2-ethylhexyl group is most particularly preferred.
In one advantageous version, the molecule of the invention meets the following particular formula (II-e):
where the abbreviations “Bu” and “EtHex” respectively correspond to n-butyl and 2-ethylhexyl groups.
A sixth subject of the invention relates to the use of a specific molecule as precursor for the synthesis of the organic material of the invention.
The specific molecule that is the subject of this use meets the following general formula (III):
where:
Reference can be made to the different definitions given above for m and the different groups R1 to R5, in connection with the organic material.
The invention particularly concerns the use, as synthesis precursor of the organic material of the invention, of the molecule of the invention such as described above and meeting the general formula (II) and/or the particular formulas (II-a) to (II-e), the advantageous characteristics of this molecule able to be taken alone or in combination.
In fact, the specific molecule that meets the general formula (II), (Ill) and/or the particular formulas (II-a) to (II-e), can be grafted onto a solid polymeric substrate to form an organic material such as defined above.
Therefore, conforming to the invention, the covalent grafting of these specific molecules of general formula (III) and/or (II) onto the solid polymeric substrate can be obtained using a method, optionally in a single step, allowing the group or groups G″ or G′ of the specific molecule, including that of the invention, to react with one or more reactive functions belonging to the solid polymeric substrate, via implementation of conventional reactions in the field of chemical synthesis.
Such reactions between the group or groups G″ or G′ with the reactive function(s) present on the solid polymeric substrate to form the covalent bond(s) can be conducted in particular via substitution, addition, or cycloaddition.
Other characteristics and advantages of the invention will become apparent on reading the following additional description given with reference to appended
Evidently, these examples are only given to illustrate the subject of the invention and do not in any manner limit this subject-matter.
The molecule 11 was synthesised in accordance with the reaction scheme illustrated in
As illustrated in this
1.1 Synthesis of Dibutyl 1-(N,N-Diethylhexylcarbamoyl)-Methylphosphonate
The synthesis of dibutyl 1-(N,N-diethylhexylcarbamoyl)-methylphosphonate can be carried out in particular in accordance with the teaching of document WO 2013/167516, referenced [4], or by implementing steps A and then B of the protocol described in Chapter 1.1 of Example 1 with reference to
At a first step, denoted A, 2,2′-diéthylhexylamine, denoted 1, is caused to react with chloroacetyl chloride, denoted 2, to obtain 2-chloro-N,N-diethylhexylacetamide, denoted 3. This reaction A can particularly be conducted in the presence of dichloromethane and potassium carbonate.
At a second step, denoted B, 2-chloro-N,N-diethylhexylacetamide 3 is caused to react with tributylphosphite, denoted 4, to obtain dibutyl 1-(N,N-diethylhexylcarbamoyl)methylphosphonate, denoted 5.
1.2 Synthesis of Tert-Butyl 6-Bromohexanoate
This synthesis is conducted in one step, denoted C, by causing 6-bromohexanoic acid, denoted 6, to react in the presence of tert-butanol, denoted 7, with dicyclohexylcarbodiimide (DCC) to obtain tert-butyl 6-bromohexanoate, denoted 8.
This step C provides protection of the carboxylic acid function of compound 6, thereby minimising secondary reactions.
1.3 Synthesis of the Molecule 11
First, at an alkylation step denoted D, dibutyl 1-(N,N-diethylhexylcarbamoyl)methylphosphonate 5 is caused to react with tert-butyl 6-bromohexanoate 8, previously synthesised, to obtain tert-butyl 1-(N,N-diethylhexyl-7-dibutoxyphosphoryl)-8-oxooctanoate, denoted 9.
A first saponification step, denoted E, is then performed, to deprotect the carboxylic acid and to obtain 1-(N,N-diethylhexyl-7-dibutoxyphosphoryl)-8-oxooctanoic acid 10, followed by a second mono-saponification step, denoted F, allowing the molecule 11, which corresponds to 1-(N,N-diethylhexyl-7-butoxyhydroxyphosphoryl)-8-oxooctanoic acid, to be obtained.
A solid polymeric substrate formed by a divinylbenzene/styrene copolymer was first functionalised with amine functions to obtain the functionalised solid polymeric substrate denoted IV in
The molecule 11 was then grafted via peptide coupling onto all or part of the amine functions of the functionalised solid polymeric substrate, to obtain an organic material conforming to the invention and denoted V in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1561142 | Nov 2015 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/078293 | 11/21/2016 | WO | 00 |
