Porous composite material, functionalised by a uranium(VI) ligand, method for preparing same and use thereof for extracting uranium(VI) from an aqueous solution of sulphuric acid

Abstract

The invention relates to a composite material which is provided in the form of porous beads with an open porosity, each bead comprising a plurality of porous carbon-based particles, bound together by an organic polymer, and which is characterised in that at least one organic ligand of uranium(VI) is deposited non-covalently in the pores of the beads. The invention also relates to a method for preparing this material and to the use thereof for extracting uranium(VI) from an aqueous solution comprising sulphuric acid. The invention can be used in the treatment of uranium ores with a view to recovering the uranium contained in these ores.

Description

[0001] POROUS COMPOSITE MATERIAL, FUNCTIONALIZED BY A URANIUM(VI) LIGAND, ITS PREPARATION PROCESS AND ITS USE FOR EXTRACTING URANIUM(VI) FROM AN AQUEOUS SULFURIC ACID SOLUTION

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The invention relates to the field of extraction of uranium(VI) from aqueous media comprising sulfuric acid.

[0005] More specifically, the invention relates to a composite material in the form of porous beads functionalized by a uranium(VI) ligand, to a process for preparing this material and to the use of said material for extracting uranium(VI) from an aqueous sulfuric acid solution.

[0006] The invention finds particular application in the treatment of uranium ores (uraninite, pitchblende, coffinite, brannerite, carnotite, etc.) to recover the uranium(VI) present in these ores with a view to recovering it, in particular from an aqueous solution of sulfuric acid resulting from the leaching of a uranium ore by sulfuric acid.

[0007] STATE OF THE PRIOR ART

[0008] Uranium ores (or uranium ores) are extracted from mines, crushed and ground to a consistency of fine sand, then they are subjected to an attack, called "leaching", by sulfuric acid (unless their gangue is naturally alkaline, in which case this leaching would require prohibitive consumption of sulfuric acid).

[0009] Sulfuric acid was chosen for two reasons: firstly, it is the cheapest strong acid, and can be produced on the site of uranium ore processing plants from sulfur by a process known as "double catalysis" and, secondly, its use leads to effluents that are relatively easy to treat because sulfate ions can be largely eliminated by lime precipitation. The attack of each uranium ore is studied on the basis of an optimization of the uranium(VI) dissolution efficiency in relation to the quantity of sulfuric acid consumed. Some ores are easily attacked in a stirred tank and require only about 25 kg of pure sulfuric acid per ton of ore, while others are only attacked in an autoclave and require more than 100 kg of pure sulfuric acid per ton of ore.

[0010] Currently, there are essentially two techniques for extracting uranium(VI) from an aqueous medium: liquid-liquid extraction and solid-liquid extraction.

[0011] Liquid-liquid extraction (or LLI) is a relatively efficient and simple technique to implement, which consists of bringing the aqueous medium containing the uranium into contact with an organic solution, immiscible with water, which comprises one or more uranium ligand compounds, dissolved in an organic solvent. However, it has a number of disadvantages, particularly when used on an industrial scale, because it requires the use of large volumes of organic solution which, after having back-extracted the uranium(VI) to recover it, must be washed with different aqueous solutions for reuse. In addition, there is the problem of possible contamination of the uranium(VI) by species present in the organic solution as well as that of the formation of a third phase by demixing.

[0012] Solid-liquid extraction, which consists of bringing the aqueous medium containing the uranium into contact with a material comprising a solid, organic or inorganic support impregnated with one or more uranium ligand compounds or on which molecules capable of retaining the uranium by complexing effect or ion exchange are fixed, does not have these drawbacks. It also has the advantage of being more flexible than liquid-liquid extraction and of involving fewer risks for humans and the environment (flammability, toxicity, etc.).

[0013] However, organic solid-support materials have limitations which are mainly due to their poor mechanical and chemical resistance in acidic and / or highly saline environments as well as their tendency to swell and float in aqueous environments, which is a barrier to their use in equipment which is typically used to carry out continuous solid-liquid extractions such as fluidized beds or cartridges.

[0014] Inorganic solid-support materials are more chemically stable than the previous ones and have therefore given rise to a certain number of studies on the possibility of using them to extract uranium from acidic aqueous solutions and, in particular, from aqueous sulfuric acid solutions.

[0015] The following have been proposed: solid-support materials made of mesoporous silica of the SBA-15 type or of mesoporous carbon of the CMK-13 type, functionalized with a uranium(VI) amidophosphonate ligand by covalent grafting of the ligand onto the support after prefunctionalization thereof with amine functions (WO-A-2015 / 067689, hereinafter reference [1]); solid support materials made of mesoporous silica gel (Davisil60, Aldrich), also functionalized with a uranium(VI) amidophosphonate ligand, either by covalent grafting of the ligand onto the silica or by impregnation of the silica with, here too, prefunctionalization by chemical reaction of the silica (A. Dressier et al., Chemical Engineering Journal Advances 2022, 9, 100225, hereinafter reference [2]; A. Dressier et al., Molecules, 2022, 27(14), 4342, hereinafter reference [3]).

[0016] As the global nuclear fleet and, consequently, the demand for uranium continue to increase, inventors considered that it was nevertheless desirable to broaden the range of materials suitable for use in extracting, by solid-liquid extraction, uranium(VI) from aqueous solutions resulting from the leaching of uranium ores by sulfuric acid, these ores currently representing the primary source of uranium supply.

[0017] They therefore set themselves the goal of providing a new material that would enable uranium(VI) to be extracted very efficiently from aqueous sulfuric acid solutions by solid-liquid extraction.

[0018] They also set themselves the goal that, on the one hand, the preparation of this material does not involve any chemical coupling or covalent grafting reaction and, on the other hand, the material can be used in a continuous uranium(VI) extraction process, for example in a fixed bed or column, as implemented on an industrial scale.

[0019] STATEMENT OF THE INVENTION

[0020] The invention aims precisely to propose a material meeting all these criteria.

[0021] The invention therefore has, firstly, a composite material which is in the form of porous balls, with open porosity, each ball comprising a plurality of porous carbon-based particles, linked together by an organic polymer, and which is characterized in that at least one organic ligand of uranium(VI) is deposited non-covalently in the pores of the balls.

[0022] In the foregoing and the following, we understand:

[0023] - by open porosity, a porosity made up of pores (micropores, mesopores and / or macropores) which not only communicate with the exterior of the balls by opening onto the surface of these balls but which also communicate with other pores, themselves opening or not onto the surface of the balls;

[0024] - by particle (...) based on carbon, a particle of which the majority (i.e. more than 50%), or even all, of the atoms which constitute it are carbon atoms;

[0025] - by organic ligand of uranium(VI), any organic compound (and, therefore, comprising carbon and hydrogen atoms) which is capable of forming a coordination complex with one or more uranyl ions UO2 2+ in aqueous solution and, thus, to extract it(them) from this solution;

[0026] - by ligand (....) deposited non-covalently in the pores of the beads, the fact that the molecules of the ligand are present inside the pores of the beads without being fixed there by one or more covalent bonds.

[0027] According to the invention, the porous carbon-based particles are preferably particles with a lamellar structure.

[0028] Such particles may in particular be graphite microplatelets or nanoplatelets, graphite oxide microplatelets or nanoplatelets, graphene microplatelets or nanoplatelets or graphene oxide microplatelets or nanoplatelets. Among these, graphene microplatelets and nanoplatelets and, more specifically, graphene nanoplatelets are preferred.

[0029] Examples of graphene nanoplatelets that can be used include those available from Graphene Production and Merck-Sigma-Aldrich, such as Grade C graphene nanoplatelets.

[0030] The organic polymer, which acts as a binder for the porous carbon-based particles, can be any polymer that has the following characteristics:

[0031] (1) be able to establish interfacial interactions with the porous carbon-based particles capable of leading to a homogeneous particle / polymer mixture and, therefore, to a homogeneous composite material;

[0032] (2) be transformable into beads, in particular by extrusion or by ionic precipitation / crosslinking;

[0033] (3) be insoluble in organic solvents capable of being used for the organic ligand of uranium(VI) to be deposited non-covalently in the pores of the beads by impregnation of these beads with a solution comprising this ligand in an organic solvent, such as ethanol, dichloromethane, tetrahydrofuran, acetone or diethyl ether; and

[0034] (4) if the composite material is intended to be brought into contact with a solution of strong acidity, for example of pH 1 or lower, be capable of maintaining its integrity at this acidity.

[0035] Examples of suitable polymers include polysaccharides such as cyclodextrins or alginates (i.e. salts of alginic acid), for example sodium alginate, potassium alginate or calcium alginate, chitosan.

[0036] Alternatively, it is also possible to use animal protein nanofibers, for example amyloid nanofibers (as obtained from whey protein (P-lactoglobulin), egg white (lysozyme) or bovine blood (bovine serum albumin)) or water-soluble polymers such as a polyamide and a formophenolic polymer. In any case, the material has a porous particle / organic polymer mass ratio which is preferably between 1 and 15 and, more preferably, between 5 and 10.

[0037] According to the invention, the organic ligand of uranium(VI) is preferably one of the amidophosphonate ligands which are described in international application WO-A-2014 / 139869, hereinafter reference [4],

[0038] It is recalled that these ligands correspond to the general formula (I) below: in which:

[0039] R 1 and R 2, identical or different, represent a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 6 to 12 carbon atoms;

[0040] R 3 represents:

[0041] - a hydrogen atom;

[0042] - a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 1 to 12 carbon atoms and optionally one or more heteroatoms; or

[0043] - a saturated or unsaturated, monocyclic hydrocarbon group comprising from 3 to 8 carbon atoms and optionally one or more heteroatoms; while

[0044] R 4 represents a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 2 to 8 carbon atoms or a monocyclic aromatic group.

[0045] Among these ligands, those in which R 1 and R 2are identical to each other and each represents a branched alkyl group, comprising from 8 to 10 carbon atoms, R 3 represents a linear or branched alkyl group comprising from 1 to 10 carbon atoms, while R 4 represents a linear or branched alkyl group comprising from 2 to 4 carbon atoms. Examples of such ligands include:

[0046] - n-butyl (di-2-ethylhexylcarbamoyl)ethylphosphonate (more simply denoted DEHCEBP), which corresponds to the general formula (I) in which R 1 and R 2 each represent a 2-ethylhexyl group, R 3 represents a methyl group and R 4 represents an n-butyl group;

[0047] - n-butyl (di-2-ethylhexylcarbamoyl)nonylphosphonate (more simply denoted DEHCNBP), which corresponds to the general formula (I) in which R 1 and R 2 each represent a 2-ethylhexyl group, R 3represents an n-octyl group and R 4 represents an n-butyl group;

[0048] - ethyl (di-2-ethylhexylcarbamoyl)nonylphosphonate (more simply denoted DEHCNBE), which corresponds to the general formula (I) in which R 1 and R 2 each represent a 2-ethylhexyl group, R 3 represents an n-octyl group and R 4 represents an ethyl group;

[0049] - n-butyl (dioctylcarbamoyl)ethylphosphonate (more simply DOCEBP), which corresponds to the general formula (I) in which R 1 and R 2 each represent an n-octyl group, R 3 represents a methyl group and R 4 represents an n-butyl group.

[0050] Alternatively, the organic ligand of uranium(VI) may also be a di- or trialkylated phosphate such as di-n-octylphosphate or tri-n-butylphosphate, a trialkylated tertiary amine such as tri-n-octylamine or a mixture of trialkylated tertiary amines such as that known under the commercial references Adogen 364 and Alamine 336, an aminophosphonate of the type described in FR-A-3 072 824 (hereinafter [5]), for example diethylhexyl diethylhexylaminonon(l)ylphosphonate, or DEHANPDEH or a phosphine oxide amine of the type described in WO-A-2016 / 156591 (hereinafter [6]).

[0051] In any event, the pores of the porous beads constituting the material of the invention are preferably saturated with ligand, that is to say they contain the maximum quantity of ligand that they are likely to contain.

[0052] The composite material as previously described may in particular be prepared by a process which comprises at least the following steps: a) preparation of a homogeneous suspension comprising the carbon-based porous particles and the organic polymer in a solvent; b) transformation of the suspension obtained in step a) into porous beads by extrusion or ionic precipitation / crosslinking; c) washing, for example with water, preferably distilled, then drying, for example in an oven or by freeze-drying, of the porous beads obtained in step b); d) impregnation of the porous beads obtained in step c) with a solution comprising the organic ligand of uranium(VI) in an organic solvent; and e) removal of the organic solvent from the porous beads obtained in step d) and, optionally, drying of these beads, for example under vacuum.

[0053] Therefore, the invention also relates to this method.

[0054] According to the invention, the suspension, which is prepared in step a), has a porous particles / organic polymer mass ratio which is preferably between 1 and 15 and, better still, between 5 and 10.

[0055] The beads obtained at the end of step c), advantageously have a size of between 100 μm and 4 mm, are preferably macroporous beads - i.e. having pores having a diameter greater than 50 nm in accordance with the definition of UlPAC - and / or mesoporous beads - i.e. having pores having a diameter of between 2 nm and 50 nm in accordance with the definition of UlPAC - and have a BET specific surface area of, preferably, between 10 m 2 / g and 1000 m 2 / g.

[0056] The pore size of the beads can be determined by - as known per se - the methods of mercury porosimetry and nitrogen porosimetry.

[0057] In a preferred embodiment of this method, the organic polymer is a polysaccharide which can be solubilized, optionally by heating, in aqueous solution (of neutral, acidic or alkaline pH), such as an alginate or chitosan, in which case:

[0058] - step a) advantageously comprises solubilization of the polymer, preferably at a concentration of at most 3% by mass, in an aqueous solution (for example, water for sodium alginate and an acidic aqueous solution such as an acetic acid solution for chitosan), then dispersion, with stirring, of the porous carbon-based particles in the aqueous solution thus obtained until a homogeneous suspension is obtained;

[0059] - step b) advantageously comprises a dropwise addition of the suspension obtained in step a) to an aqueous solution comprising an ionic crosslinking agent, typically a salt such as a calcium salt (for example, calcium chloride) for sodium alginate, or sodium hydroxide for chitosan, which allows the transformation of the suspension into porous beads.

[0060] In any event, step d) of impregnating the porous beads, as obtained in step c), is preferably carried out by immersing these beads in the ligand solution, this solution having a sufficient ligand concentration to allow saturation of the pores of said beads by the ligand, and maintaining the beads in this solution, with stirring, for several hours, for example 24 hours.

[0061] The invention further relates to the use of a composite material as previously defined for extracting uranium(VI) from an aqueous sulfuric acid solution in which this uranium is present.

[0062] In accordance with the invention, the aqueous solution from which the uranium(VI) is extracted is advantageously an aqueous solution of sulfuric acid which is obtained from the leaching of a uranium-bearing ore by sulfuric acid, in which case this aqueous solution typically comprises from 0.1 g / L to 10 g / L of uranium, from 0.1 mol / L to 2 mol / L of sulfate ions, at an acidity of 0.01 mol / L to 0.5 mol / L.

[0063] The extraction of uranium(VI) from an aqueous solution of sulfuric acid using an organic-inorganic hybrid material as previously defined is extremely simple to implement since it is sufficient to place this aqueous solution in contact with the material, for example in a stirred reactor or in a column, for a sufficient time to allow the uranium(VI) to be complexed by the material, then to separate the aqueous solution from the material.

[0064] It should be noted that the volume of the aqueous solution from which the uranium(VI) is to be extracted depends on the functionalization rate of the organic-inorganic hybrid material. Thus, for example, it is possible to use 20 mL of an aqueous solution with 50 mg of a material comprising 0.6 mmol of ligand per gram of bead. Once the uranium(VI) has been extracted, it is possible to recover the uranium by back-extraction, which is carried out, for example, by bringing the composite material loaded with uranium(VI) into contact with a concentrated aqueous acid solution, for example an aqueous solution comprising from 0.01 mol / L to 3 mol / L of sulfuric acid, then separating the liquid phase from the solid phase.

[0065] Other characteristics and advantages of the invention will emerge from the additional description which follows.

[0066] It goes without saying that this additional description is given only as an illustration of the subject of the invention and must in no case be interpreted as a limitation of this subject.

[0067] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0068] EXAMPLE 1 TEST OF EXTRACTION OF URANIUM(VI) BY A FIRST MATERIAL Ml

[0069] ACCORDING TO THE INVENTION

[0070] 1.1 - Preparation of material Ml:

[0071] Graphene nanoplatelets (GnPs - grade C, from Sigma-Aldrich) are mixed, under vigorous stirring (from 50 rpm to 300 rpm), with 1000 mL of an aqueous SI solution comprising 1% by mass of sodium alginate (from Sigma-Aldrich), in a GnP / sodium alginate mass ratio of 7.

[0072] Stirring is maintained until a macroscopically homogeneous suspension is obtained.

[0073] This suspension is poured dropwise using a syringe, with stirring (from 5 rpm to 50 rpm), into 300 mL of an aqueous solution S2 comprising 30 g / L of calcium chloride, whereby the graphene nanoplatelets, interconnected by sodium alginate, form porous beads.

[0074] The balls thus obtained are left in the calcium chloride solution for 24 hours.

[0075] A step of filtration and washing of the beads with distilled water is then carried out, until a neutral pH of the filtrate is obtained, then the beads are dried in an oven at 80 °C until their mass becomes constant. For their impregnation, 7.4 g of the beads thus obtained are added, with stirring (from 50 rpm to 300 rpm), to 25 mL of an organic solution S3 comprising 6 mmol of DEHCEBP (i.e. 0.6 mmol / g of beads) in dichloromethane. The concentration of DEHCEBP was chosen considering a saturation of the pores of the beads by this ligand.

[0076] Stirring is maintained for 24 hours, then the dichloromethane is evaporated and the beads dried by evaporation under vacuum (100 Pa for a few hours).

[0077] 1.2 - Extraction of uranium(VI) from an aqueous solution of sulfuric acid by material Ml:

[0078] The capacity of the material Ml obtained in point 1.1 above to extract uranium(VI) from an aqueous solution of sulfuric acid is assessed by an extraction test which consists of: mixing 50 mg of this material with 20 mL of an aqueous solution of sulfuric acid with a pH equal to 1, comprising uranium(VI) and having a molar ratio between the sulfate ions and the uranium(VI) (SO4 2 7U(VI)) equal to 900 (pH 1); leave the mixture for 24 hours under agitation (in Turbula™), at room temperature (» 25 °C); then separate by filtration the solid and liquid phases of this mixture.

[0079] Uranium(VI) concentrations are determined by the ICP OES (Inductively Coupled Plasma Optical Emission Spectrometry) method in the aqueous sulfuric acid solution before it is mixed with the Ml material as well as in the filtrate.

[0080] From the concentrations obtained, the quantity of uranium(VI) extracted per g of said material Ml is calculated, noted Qext and expressed in mg / g, according to the following formula:

[0081] Qext =(C ini — C fin ) x — in which:

[0082] Gni represents the initial concentration of uranium(VI) in the aqueous sulfuric acid solution (in mg / L);

[0083] Cfin represents the concentration of uranium(VI) in the filtrate (in mg / L); V represents the volume of aqueous sulfuric acid solution having been mixed with the material Ml (in L); and m represents the mass of material Ml used in the test (in g).

[0084] This test then shows that the said Ml material has a uranium(VI) extraction capacity of approximately 45 mg per g of porous Ml material.

[0085] EXAMPLE 2: TESTS FOR EXTRACTION OF URANIUM(VI) BY THREE OTHER MATERIALS, RESPECTIVELY M2, M3 AND M4, ACCORDING TO THE INVENTION

[0086] 2.1 - Preparation of materials M2, M3 and M4:

[0087] Materials M2, M3 and M4 are prepared from GnPs identical to those used in point 1.1 above, using the aqueous solutions SI, the GnP / polymer mass ratios and the aqueous solutions S2 indicated in Table I below, and DEHCEBP as ligand.

[0088] The methods of preparing the porous beads constituting these materials and of impregnating these beads with DEHCEBP are similar to those previously described.

[0089] Table I

[0090] 2.2 - Tests for the extraction of uranium(VI) from an aqueous solution of sulfuric acid using materials M2, M3 and M4:

[0091] The capacity of materials M2, M3 and M4 obtained in point 2.1 above to extract uranium(VI) from an aqueous solution of sulfuric acid is determined by tests which are conducted in the same way as that described in point 1.2 above for material Ml. The extracted quantities of uranium(VI) Q ex t obtained at the end of these tests are presented in Table II below.

[0092] Table II REFERENCES CITED

[0093] [1] WO-A-2015 / 067689

[0094] [2] A. Dressier et al., Chemical Engineering Journal Advances 2022, 9, 100225

[0095] [3] A. Dressier et al., Molecules 2022, 27(14), 4342

[0096] [4] WO-A-2014 / 139869 [5] FR-A-3 072 824

[0097] [6] WO-A-2016 / 156591

Claims

CLAIMS 1. Composite material in the form of porous beads, with open porosity, each bead comprising a plurality of porous carbon-based particles, linked together by an organic polymer, characterized in that at least one organic ligand of uranium(VI) is deposited non-covalently in the pores of the beads.

2. Material according to claim 1, wherein the carbon-based particles are particles with a lamellar structure.

3. The material of claim 2, wherein the porous carbon-based particles are graphite microplatelets or nanoplatelets, graphite oxide microplatelets or nanoplatelets, graphene microplatelets or nanoplatelets, or graphene oxide microplatelets or nanoplatelets.

4. Material according to claim 3, wherein the carbon particles are graphene microplatelets and nanoplatelets, preferably graphene nanoplatelets.

5. Material according to any one of claims 1 to 4, in which the organic polymer is a polysaccharide.

6. Material according to claim 5, in which the polysaccharide is an alginate, preferably sodium, or chitosan.

7. Material according to any one of claims 1 to 6, which has a mass ratio of porous carbon-based particles / organic polymer of between 1 and 15, preferably between 5 and 10.

8. Material according to any one of claims 1 to 7, in which the organic ligand corresponds to the general formula (I) below: (H in which: R 1 and R 2, identical or different, represent a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 6 to 12 carbon atoms; R 3 represents: - a hydrogen atom; - a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 1 to 12 carbon atoms and optionally one or more heteroatoms; or - a saturated or unsaturated, monocyclic hydrocarbon group comprising from 3 to 8 carbon atoms and optionally one or more heteroatoms; and R 4 represents a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 2 to 8 carbon atoms or a monocyclic aromatic group.

9. Material according to claim 8, wherein R 1 and R 2 are identical to each other and each represents a branched alkyl group, comprising from 8 to 10 carbon atoms, R 3represents a linear or branched alkyl group comprising from 1 to 10 carbon atoms and R 4 represents a linear or branched alkyl group comprising from 2 to 4 carbon atoms.

10. Material according to claim 8 or claim 9, wherein said at least one ligand corresponds to the general formula (I) in which R 1 and R 2 each represent a 2-ethylhexyl group, R 3 represents a methyl group and R 4 represents an n-butyl group.

11. Material according to any one of claims 1 to 10, in which the pores of the beads are saturated with organic ligand.

12. A method for preparing a material according to any one of claims 1 to 11, comprising at least the following steps: a) preparation of a homogeneous suspension comprising the carbon-based porous particles and the organic polymer in a solvent; b) transformation of the suspension obtained in step a) into porous beads by extrusion or ionic precipitation / crosslinking; c) washing and drying the porous beads obtained in step b); d) impregnation of the porous beads obtained in step c) with a solution comprising the organic ligand of uranium(VI) in an organic solvent; and e) removal of the organic solvent from the porous beads obtained in step d) and, optionally, drying these beads.

13. Method according to claim 12, in which the suspension of step a) has a mass ratio of porous carbon-based particles / organic polymer of between 1 and 15, preferably between 7 and 10.

14. A method according to claim 12 or claim 13, wherein the organic polymer is a polysaccharide which can be solubilized in aqueous solution, in which case: - step a) comprises solubilization of the polymer, preferably at a concentration of at most 3% by mass, in an aqueous solution, then dispersion, with stirring, of the porous carbon-based particles in the aqueous solution thus obtained until a homogeneous suspension is obtained; and - step b) comprises a dropwise addition of the suspension obtained in step a) to an aqueous solution comprising an ionic crosslinking agent, preferably a salt.

15. Method according to any one of claims 12 to 14, in which step d) comprises immersing the porous beads in the ligand solution, the solution having a sufficient ligand concentration to allow saturation of the pores of the porous beads by the ligand, and maintaining the beads in the solution, with stirring.

16. Use of a material according to any one of claims 1 to 11 for extracting uranium(VI) from an aqueous sulfuric acid solution.

17. Use according to claim 16, wherein the aqueous sulfuric acid solution is a solution resulting from the leaching of a uranium ore by sulfuric acid.

18. Use according to claim 16 or claim 17, wherein the aqueous sulfuric acid solution comprises from 0.1 g / L to 10 g / L of uranium(VI), from 0.1 mol / L to 2 mol / L of sulfate ions, at an acidity of 0.01 mol / L to 0.5 mol / L.