NEW POLY(ETHERPHOSPHORAMIDE) POLYMER AND METHOD FOR THE REMOVAL OF RARE EARTH ELEMENTS FROM A LIQUID MEDIUM USING THIS POLYMER

Description

[0001] The present invention falls within the field of rare earth valorization.

[0002] More particularly, the present invention relates to a polymer especially suited for the solid-phase extraction of a rare earth element from a liquid medium, as well as a composite material containing such a polymer on a solid support. The invention also relates to the use of such a polymer or such a composite material for the extraction of a rare earth element from a liquid medium containing it. Another object of the invention is a method for extracting a rare earth element from a liquid medium containing it, using such a polymer or such a composite material.

[0003] Rare earth elements, and in particular lanthanum, are used in numerous industrial applications. Examples include the manufacture of glass, especially lenses for cameras and telescopes; the production of nodular steels and cast irons; the manufacture of fuel cells and batteries, particularly rechargeable hydride batteries used in hybrid vehicles; chemical catalysis for oil refining; and the preparation of light alloys, notably for improving their mechanical properties. Rare earth elements are also important in the new technology industry, for the manufacture of electronic components for computers and mobile phones, where they are used in the composition of light-emitting diodes (LEDs) and magnets.

[0004] Sourcing these high-value raw materials proves difficult, particularly due to their limited availability in nature. Lanthanum, for example, does not exist in its free element form.

[0005] Mining effluents, particularly from phosphate deposits such as those in Tunisia, currently constitute a common source of rare earth elements. The ore found in these deposits, a sedimentary phosphorite type, contains several thousand ppm of rare earth oxides, the most abundant of which are cerium and lanthanum.

[0006] This phosphate ore is commonly used for the industrial production of phosphoric acid through its reaction with sulfuric acid in water. This reaction typically leads to the formation of phosphoric acid (H₃PO₄), hydrofluoric acid (HF), and hydrated calcium sulfate (CaSO₄·xH₂O), where x = 0.5 or 2. The reaction yields two main phases: a liquid phase containing phosphoric acid and a solid phase containing hydrated calcium sulfate. The liquid phase, in particular, is rich in rare earth elements. Currently, rare earth elements are extracted using a liquid-liquid extraction technique, such as that described in the publication by Agarwal et al., 2021, Mineral Processing and Extractive Metallurgy, 130(2): 90-97.This technique, however, uses a significant amount of organic solvent, particularly from petrochemicals, such as kerosene, the subsequent disposal of which is environmentally problematic. US2023 / 101316A1 discloses a method for removing, adsorbing, separating, storing, or sequestering a metal from an aqueous fluid stream.

[0007] CHABBAH et al.: Talanta, vol. 247, 2022, page 123550 discloses new poly(ether-phosphoramide) sulfides based on natural resources.

[0008] To overcome this drawback, and to avoid or at least limit the use of polluting organic solvents, several solid-liquid extraction techniques have been proposed in the prior art to recover rare earth elements from a liquid medium containing them. However, none of these techniques offers satisfactory extraction performance.

[0009] The present invention aims to overcome the drawbacks of prior art methods for extracting rare earth elements from aqueous media containing them, particularly the drawbacks described above, by providing a material that can be used in a solid-liquid extraction process and that enables such extraction to be carried out efficiently. Additional objectives of the invention are that this material can be obtained, and that the extraction process using it can be implemented, in the most environmentally friendly manner possible.

[0010] The invention also aims to ensure that rare earths can be easily recovered at the end of the process, and in such a way that the material used to extract them can be reused.

[0011] The inventors have discovered that these objectives are achieved by a polymer with a specific structure, belonging to the poly(ether-phosphoramide) family, which exhibits a particularly high affinity for rare earth elements, especially lanthanum and cerium, as demonstrated by electrochemical impedance measurements at the interface between the polymer and rare earth solutions. This affinity is, surprisingly, significantly higher than that of other polymers with very similar structures. When used in a solid-state extraction process, this polymer enables the extraction of rare earth elements from a liquid medium with a high extraction rate. Furthermore, the adsorption of rare earth elements onto this polymer is reversible, and their desorption is easily achieved, advantageously in the aqueous phase.

[0012] In the present description, rare earths are understood, in a classical manner, to mean scandium, yttrium, and the 15 lanthanides, namely lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0013] Thus, according to a first aspect, the present invention proposes a polymer particularly useful for the solid-phase extraction of a rare earth element from a liquid medium containing it. This polymer comprises a repeating unit of general formula (I): in which R1 and R2, whether identical or different, each represent a hydrogen atom, or a linear, branched and / or cyclic hydrocarbon radical, saturated and / or unsaturated, aromatic or not, possibly substituted, which may have one or more rings, possibly condensed, possibly interrupted by one or more heteroatoms, such as oxygen, sulfur, or nitrogen, and preferably comprising from 1 to 12 carbon atoms; or R1 and R2 together form, with the nitrogen atom to which each is attached, a heterocycle of 3 to 8 members, preferably 4 to 6 members, saturated or unsaturated, possibly aromatic, comprising one or more heteroatoms in the ring, such as an oxygen atom, possibly substituted by one or more linear, branched and / or cyclic alkyl radicals, each of these alkyl radicals being preferably C1-C12, preferably C1-C6, and preferably also in C1-C3,said heterocycle being optionally condensed into one or more rings or heterocycles, each of 3 to 8 members, preferably 4 to 6 members, saturated or unsaturated, possibly aromatic, possibly comprising one or more heteroatoms in the ring, and possibly substituted by one or more linear, branched and / or cyclic alkyl radicals, each of these alkyl radicals being preferably at C1-C12, preferably at C1-C6 and preferably again at C1-C3.

[0014] The polymer according to the invention preferably comprises 10 to 50 repetitions of the general formula repeating motif (I).

[0015] Furthermore, it is preferably linear.

[0016] Preferably, the general formula repeating motif (I) is the only repeating motif of the polymer.

[0017] In preferred embodiments of the invention, the polymer structure can thus be expressed by the general formula (II): in which n is a positive integer greater than or equal to 2, preferably greater than or equal to 10, and preferably between 10 and 50, and R 1 and R 2 are such as defined with reference to the general formula (I).

[0018] The polymer according to the invention can, for example, correspond to the formula (Ila): in which n is a positive integer greater than or equal to 2, preferably greater than or equal to 10, and preferably between 10 and 50, R 1 and R 2 are as defined with reference to the general formula (I), and A represents a fluorine atom, a chlorine atom, a hydrogen atom, or a hydroxyl group.

[0019] The polymer according to the invention advantageously incorporates an isosorbide motif in its structure. Thus, its synthesis involves an isosorbide synthon, with general formula (III): compound derived from agricultural resources. Thus, the polymer according to the invention is advantageously at least partially bio-based.

[0020] As mentioned above, this polymer, particularly in its embodiments corresponding to general formulas (II) and (IIa), exhibits a particularly high affinity for rare earth elements, and especially for the two most abundant rare earth elements in nature, lanthanum and cerium. This affinity is significantly greater than that of polymers with a similar structure, and in particular polymers with a similar formula, but in which: the oxygen atom bonded to the phosphorus atom is replaced by a sulfur atom, and / or the nitrogen atom bonded to the phosphorus atom is replaced by a carbon atom, and / or the isosorbide motif is replaced by a motif derived from bisphenol A, of formula (IV):

[0021] We will not speculate here on the mechanisms explaining the particularly high affinity of the polymer according to the invention for rare earth elements. We can only observe that it appears to be specifically linked to the combination, within the polymer structure, of the oxygen and nitrogen atoms respectively bonded to the phosphorus atom, the whole forming a phosphoramide functional group, and to the isosorbide motif. Nothing in the prior art suggested that such a specific combination would be associated with an affinity for rare earth elements significantly higher than that of polymers lacking this specific combination, even those with very similar structures.

[0022] In particularly preferred embodiments of the invention, in the general formula (I), as well as in the general formulas (II) and (IIa), R 1 and R 2 together form, with the nitrogen atom to which each is attached, a saturated heterocycle of 3 to 8 links, preferably of 6 links, comprising one or more heteroatoms in the ring, optionally substituted by one or more linear, branched and / or cyclic alkyl radicals, each of these alkyl radicals being preferably in C1-C12, preferably in C1-C6 and preferably again in C1-C3.

[0023] Preferably, in the general formula (I), as well as in the general formulas (II) and (IIa), R1 and R2 together form, with the nitrogen atom to which each is attached, a morpholine nucleus, possibly substituted by one or more linear, branched and / or cyclic alkyl radicals, each of these alkyl radicals being preferably in C1-C12, preferably in C1-C6 and preferably again in C1-C3.

[0024] In particular embodiments of the invention, the morpholine core is not substituted.

[0025] Thus, the polymer according to the invention may comprise a repeating motif of general formula (V):

[0026] The polymer can notably conform to the general formula [VI): in which n is a positive integer greater than or equal to 2, preferably greater than or equal to 10, and preferably between 10 and 50. The polymer corresponding to this general formula (VI) exhibits an affinity for rare earths, especially lanthanum and cerium, which is particularly important.

[0027] The polymer according to the invention can, for example, correspond to the formula (Vla): in which n is a positive integer greater than or equal to 2, preferably greater than or equal to 10, and preferably between 10 and 50, and A represents a fluorine atom, a chlorine atom, a hydrogen atom, or a hydroxyl group.

[0028] In alternative embodiments of the invention, in the general formula (I), as well as in the general formulas (II) and (IIa), R 1 and R 2, identical or different, each represent a hydrogen atom or a linear or branched C1-C6 alkyl radical, preferably a methyl radical or an ethyl radical.

[0029] In this configuration, preferably, R1 and R2, whether identical or different, each represent a methyl radical or an ethyl radical.

[0030] In variants of the invention, in the general formula (I), as well as in the general formulas (II) and (IIa), R 1 and R 2, identical or different, each represent a hydrogen atom or an aromatic cyclic group comprising preferably from 1 to 12 carbon atoms, comprising a single ring or several rings, possibly condensed, possibly containing one or more heteroatoms in the ring(s), and possibly substituted by one or more linear, branched and / or cyclic alkyl radicals, each of these alkyl radicals being preferably C1-C6 and preferably C1-C3.

[0031] In particular, R1 and R2, identical or different, can then each represent a nucleus chosen from a benzene nucleus and a naphthalene nucleus, this nucleus being optionally substituted by one or more linear, branched and / or cyclic alkyl radicals, preferably in C1-C6 and preferably in C1-C3.

[0032] In general, when they do not form a ring together, R1 and R2 are preferably both different by one hydrogen atom. They are also preferably identical.

[0033] Thus, in particular embodiments of the invention, in the general formula (I) and the general formulas (II) and (IIa) above, R1 and R2 each represent, simultaneously: a methyl radical, an ethyl radical, a benzene ring, or a naphthalene ring.

[0034] The polymer according to the invention can be prepared by any synthesis route within the capabilities of a person skilled in the art.

[0035] For example, it can be prepared from the isosorbide synthon, of formula (III) above, and a synthon of general formula (VII): in which A, R 1 and R 2 are such as defined previously, in particular of formula (VIIa): by an aromatic nucleophilic substitution reaction (SnAr).

[0036] The synthon of formula (VII) or (VIIa) can be obtained by any classical method in itself, in particular by an oxidation reaction of the corresponding thiophosphoryl compound of formula respectively (VIII) or (VIIIa): in which A, R1 and R2 are as defined previously,

[0037] An example of a synthesis process for such a thiophosphoryl-type compound is described in particular in the publication by Chabbah et al., 2022, Talanta, 247: 123550.

[0038] The polymer according to the invention can be used as is, in powder form, for the extraction of a rare earth from a liquid medium containing it.

[0039] The powder form of the polymer can be obtained from a solution of the polymer in a solvent in which it is soluble, for example dimethylformamide, dimethyl sulfoxide or N-methylmorpholine, by precipitation in a solvent or mixture of solvents in which it is insoluble, such as a water / methanol mixture, then drying the precipitate formed by evaporation of the solvents, this drying being optionally followed by sieving through a sieve, for example with a mesh size of 50 µm to 200 µm.

[0040] The polymer according to the invention can otherwise be used for the extraction of a rare earth from a liquid medium containing it, in a form in which it is integrated into a composite material, within which it is supported by a solid support.

[0041] Thus, another aspect of the invention relates to a composite material comprising a polymer according to the invention on a solid support in divided form.

[0042] By solid support in divided form, we mean that the solid support is presented as a set of distinct individual elements, preferably identical.

[0043] The solid support is preferably inert with respect to rare earths, and more generally with respect to the liquid medium containing the rare earth from which it is desired to extract.

[0044] It is preferably presented in the most divided form possible, so as to maximize the contact surface between the polymer according to the invention and the liquid medium containing the rare earth to be extracted.

[0045] The solid support can notably take the form of fibers, beads or irregularly shaped particles.

[0046] Examples of fibers that can form the solid support of the composite material according to the invention include hydrophilic fibers, preferably of natural origin, such as cellulose fibers, in particular with a diameter between 10 and 50 µm, or carbon fibers, in particular with a diameter between 5 and 20 µm.

[0047] Such fibers can advantageously be easily impregnated with the polymer according to the invention, by any technique for impregnating a conventional solid support in itself, in particular by immersing the fibers in a solution of the polymer, ultrasonication and heating then controlled evaporation under vacuum.

[0048] The composite material can then, for example, be used in a chromatography column, through which the medium containing the rare earth to be extracted is made to circulate.

[0049] The solid support can also, for example, be in the form of particles, in particular in the form of beads, especially with a diameter between 200 and 2000 nm, or irregularly shaped particles.

[0050] Such particles can for example be formed from inorganic oxide(s), for example silicon oxide or metallic oxide, in particular copper oxide, nickel oxide, zinc oxide, iron oxide, etc., such a list being in no way limiting of the invention.

[0051] The solid support can advantageously take the form of spheres with magnetic properties, such as magnetite spheres, combining the advantages of a large contact surface and easy separation of liquid media, and are particularly well-suited for processing large volumes of liquid media. These magnetite spheres can, for example, have a diameter between 200 and 2000 nm.

[0052] Such beads, or other sphere-shaped or irregularly shaped solid particles, can advantageously be easily coated with a polymer layer according to the invention, using any conventional solid support coating technique, for example, immersion in a polymer solution, ultrasonication, heating, and then controlled evaporation under vacuum. The thickness of the polymer coating layer is preferably between 10 nm and 100 nm.

[0053] In general, the polymer according to the invention is impregnated onto, or forms a coating layer on, the solid support, more precisely on the individual elements that compose it.

[0054] An additional aspect of the invention relates to a method for extracting a rare earth from a liquid medium, in particular an aqueous liquid medium, containing it.

[0055] This process comprises contacting this liquid medium with a polymer according to the invention, in solid form, particularly powdered, or with a composite material according to the invention, comprising this polymer, so as to achieve the adsorption of the rare earth by the latter. It then comprises separating the polymer, or the composite material, comprising the rare earth that has been adsorbed onto the polymer, from this liquid medium.

[0056] The process according to the invention, which falls within the field of solid-liquid extraction, advantageously avoids the use of organic solvents required by the liquid-liquid extraction method proposed by the prior art. The contact step in the process according to the invention is preferably carried out at a pH of 3 or less, and preferably 2 or less. Thus, the process according to the invention may include an initial step of measuring the pH of the liquid medium containing the rare earth, and, if necessary, a step of adjusting this pH to the required value, for example, by means of a strong acid, such as sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid. Establishing such a pH advantageously allows the rare earth to be released in ionic form within the medium, thereby facilitating its extraction.

[0057] The contact time is advantageously chosen to allow the adsorption of the greatest possible quantity of the rare earth by the polymer according to the invention. This time can, for example, be between 1 minute and 2 hours.

[0058] The contact can be achieved in any manner known to those skilled in the art, for example, by circulating the liquid medium through a chromatography column containing the composite material according to the invention, the solid support of which is then preferably in the form of fibers, or by mixing the liquid medium and the composite material, the solid support of which is then preferably in the form of particles, and / or by mixing the liquid medium and particles of the polymer according to the invention in powder form. In these last two cases, the polymer powder and / or the composite material are preferably dispersed in a substantially homogeneous manner throughout the entire volume of the liquid medium.

[0059] The contacting step can advantageously be carried out at room temperature.

[0060] The step of separating the polymer or composite material from the liquid medium can be carried out in any conventional way in itself, depending in particular on the type of solid support in the composite material, and on the method of implementation of the contact step of the process.

[0061] For example, separation can be achieved by simply flowing the liquid medium out of a chromatography column used in the process, or by any conventional solid-liquid separation method, such as filtration, centrifugation, etc., or even magnetically in embodiments where the solid support for the composite material consists of beads with magnetic properties. This last embodiment is particularly preferred in the context of the invention.

[0062] The process according to the invention preferably includes a final step of separating the rare earth from the polymer or composite material on which it was adsorbed during the contact step of the process.

[0063] This separation step, known as desorption, can be carried out by any method known to those skilled in the art. In particular, it can be performed by washing the polymer or composite material particles with an aqueous solution containing a rare-earth complexing agent, such as tributyl phosphate or cis-1,3,5-triamino 2,4,6-trihydroxycyclohexane (also called 1,3,5-triamino-1,3,5-trideoxy-cis-inositol), known as a regeneration solution. Such washing is preferably carried out for a sufficient time to desorb all the rare earth that had been adsorbed from the polymer.

[0064] After separation of the polymer or composite material from the regeneration solution, which can be achieved by any known solid-liquid separation technique, including one of the techniques described above, an aqueous solution containing the rare earth is advantageously obtained. The polymer or composite material can then be advantageously reused for a new implementation of the process according to the invention on a new liquid medium containing a rare earth to be extracted.

[0065] The rare earth element for the extraction of which the process according to the invention is applied can be a lanthanide, scandium, or yttrium. Preferably, it is a lanthanide, and in particular lanthanum or cerium. Of course, the process according to the invention can be used to simultaneously extract a plurality of rare earth elements from a liquid medium containing them in mixture.

[0066] The process according to the invention finds a particularly advantageous application for the extraction of rare earths from mining effluents, such a field of application being in no way limiting of the invention.

[0067] Thus, in particular embodiments of the invention, the liquid medium to which the process according to the invention is applied is a mining effluent, in particular from a phosphate deposit, for example from a phosphate deposit in Tunisia.

[0068] This effluent can notably be a solution of phosphoric acid such as produced from a phosphate ore extracted from such a deposit.

[0069] Alternatively, it could be a leachate from washing such a phosphate ore. The liquid medium to which the process according to the invention is applied could also be an industrial effluent, for example, an effluent from the chemical industry.

[0070] The invention also relates to the use of a polymer or composite material according to the invention, meeting one or more of the characteristics described above, for the extraction of a rare earth from a liquid medium, in particular aqueous, containing it.

[0071] This use may meet one or more of the characteristics described above with reference to the process according to the invention of extracting a rare earth from a liquid medium containing it.

[0072] In particular, the rare earth element can be a lanthanide, notably lanthanum or cerium.

[0073] The liquid medium can be a mining effluent, for example from a phosphate deposit, such as a phosphoric acid solution obtained from phosphate ore or a leachate from washing such an ore. Alternatively, it can be, for example, an industrial effluent.

[0074] The features and advantages of the invention will become more apparent in light of the following implementation examples, provided by way of illustration only and in no way limiting the invention, with the support of figures 1 to 7 , in which: There figure 1 shows a reaction scheme for the production of phosphorylated monomers with a morpholine motif, components of a polymer according to the invention or of comparative polymers not according to the invention. figure 2 shows a reaction scheme for the production of phosphorylated monomers with a methyl phenyl motif, which are components of comparative polymers not conforming to the invention. figure 3shows the impedance spectra, in the form of Nyquist diagrams representing the imaginary part of the impedance as a function of the real part of the impedance, obtained in an electrochemical impedance measurement experiment using a polymer-coated electrode in a lanthanum solution at different concentrations between 5.10⁻¹¹ M and 5.10⁻⁶ M, in a) for a polymer according to the invention, in b) for a comparative polymer not according to the invention. figure 4 shows a graph representing the sensitivity to lanthanum, defined as the ratio of the relative change in polarization resistance to the logarithm of the lanthanum concentration, determined from electrochemical impedance spectroscopy measurements, for a polymer according to the invention (P8) and comparative polymers not conforming to the invention (P1 to P7). figure 5shows the impedance spectra, in the form of Nyquist diagrams representing the imaginary part of the impedance as a function of the real part of the impedance, obtained in an electrochemical impedance measurement experiment using a polymer-coated electrode in a cerium solution at different concentrations between 10⁻⁸ M and 10⁻³ M, in a) for a polymer according to the invention, in b) for a comparative polymer not according to the invention. figure 6 shows a graph representing the sensitivity to cerium, defined as the ratio of the relative change in polarization resistance to the logarithm of the cerium concentration, determined from electrochemical impedance spectroscopy measurements, for a polymer according to the invention (P8) and comparative polymers not conforming to the invention (P1 to P7). figure 7shows photographs of particles of a polymer according to the invention, under illumination at 482 nm, with luminescence reading at 425 nm, in a / , in the initial state, and in b / , after 24 h of incubation in an acidic aqueous medium containing lanthanum. HAS / Polymer synthesis

[0075] A polymer according to the invention P8 and comparative polymers not according to the invention, P1 to P7, are synthesized as indicated below. A.1 / Synthesis of phosphorylated monomers

[0076] Morpholine-core monomers of formula (4a) and (5a) are synthesized according to the reaction scheme shown in the figure 1 Monomers of formula (2a) and (3a) with a methyl phenyl motif are synthesized according to the reaction scheme shown in the figure 2 . A.1.1 / Synthesis of bis(4-fluorophenyl)chloro thiophosphore (1a)

[0077] In a 250 mL three-necked round-bottom flask equipped with a condenser topped with a HCl trap (KOH dissolved in water), a magnetic stirrer, an addition funnel, and a nitrogen-swept system, 11.94 g (0.070 mol) of trichlorothiophosphorus (PSCl₃) and 14.00 g (0.105 mol) of anhydrous AlCl₃ are introduced. The mixture is stirred at 40°C, and 26.90 g (0.280 mol) of fluorobenzene is added dropwise. The solution is stirred at 85°C for 3 h.

[0078] The reaction mixture is poured into 500 mL of an ice / water mixture and then extracted with ethyl acetate. The organic phase is washed with water and dried over anhydrous sodium sulfate. The solvent is evaporated under vacuum, yielding 17.20 g, with an 85% yield, of a white solid (1a). A.1.2 / Synthesis of bis(4-fluorophenyl)(4-methylphenyl)phosphine thiooxide (2a)

[0079] In a 250 mL three-necked round-bottom flask equipped with a condenser topped with a HCl trap (KOH dissolved in water), a magnetic stirrer, an addition funnel, and a nitrogen-swept system, the following are introduced: 10.00 g (0.034 mol) of bis(4-fluorophenyl)chlorothiophosphorus (1a) and 13.84 g (0.104 mol) of anhydrous AlCl3. The mixture is stirred at 40°C, and 12.75 g (0.138 mol) of toluene is added dropwise. The solution is stirred at 110°C for 3 h.

[0080] The reaction mixture is poured into 500 mL of an ice / water mixture and then extracted with ethyl acetate. The organic phase is washed with water and dried over anhydrous sodium sulfate. The solvent is evaporated under vacuum, and the resulting solid is recrystallized in hexane and then washed with petroleum ether. 7.740 g of a brown solid (2a) is obtained with a 65% yield. 1<H NMR: (CDCl 3): δ (ppm): 7.77-7.68 (m, 4H, H2); 7.63-7.56 (m, 2H, H3); 7.31-7.27 (m, 2H, H4); 7.19-7.12 (m, 4H, H1) and 2.43 (s, 3H, H5) NMR 19< F: (CDCl 3): δ (ppm): -107.43 NMR 31< P: (CDCl 3): δ (ppm): 41.40 A.1.3 / Synthesis of bis(4-fluorophenyl)(morpholino)phosphine (4a) thiooxide

[0081] In a 250 mL three-necked round-bottom flask equipped with a condenser, magnetic stirrer, addition funnel, and a nitrogen-swept stream, 10.0 g (0.034 mol) of bis(4-fluorophenyl)chlorothiophosphorus (1a) and 16 mL of chloroform are mixed in an ice bath for 3 min. Then, 6.64 g of morpholine dissolved in 16.0 mL of chloroform are added over 30 min. Finally, 7.71 g of trimethylamine are added to the solution. After completing the addition, the solution is heated to 85°C for 6 h.

[0082] Finally, the reaction mixture is cooled to room temperature and then filtered. The filtrate is washed with water and then extracted with dichloromethane, dried over anhydrous sodium sulfate. The solvent is evaporated under vacuum.

[0083] The product (4a) obtained is in the form of a brick-red powder following column separation with a 9:1 (dichloromethane / acetonitrile) mixture. The yield is 75%. 1<H NMR: (CDCl 3): δ (ppm): 8.02-7.93 (m, 4H, H2); 7.12-7.05 (m, 4H, H1); 3.70-3.66 (m, 4H, H4) and 2.80-2.75 (m, 4H, H3) NMR 19< F: (CDCl 3): δ (ppm): -106.94 NMR 31< P: (CDCl 3): δ (ppm): 65.43 A.1.4 / Synthesis of monomers (3a) and (5a)

[0084] In a 100 mL three-necked flask equipped with a condenser, magnetic stirrer, and addition funnel, 0.0155 mol of (2a) or (4a) and 17.0 mL of glacial acetic acid are introduced. The reaction mixture is placed at 90°C. 1.67 g (0.0490 mol) of hydrogen peroxide (35% wt. solution in water) is added very slowly and dropwise. After 2 h of reaction, an additional 0.83 g of hydrogen peroxide is added more rapidly. The reaction is monitored by 31P NMR. After 3 h of reaction, the reaction mixture is cooled and left at room temperature for 30 min without stirring. The mixture is filtered through Celite to remove the sulfur formed. The Celite is rinsed twice with acetic acid. The filtrate is evaporated under vacuum and then extracted with 100 mL of ethyl acetate, neutralized with a saturated sodium carbonate solution to pH 8-9, washed with distilled water, and dried over sodium sulfate.The solvent is evaporated under vacuum, and the resulting solid is washed with hot petroleum ether. Monomer (3a) is obtained with a 68% yield, and monomer (5a) with a 60% yield, both as brown solids. (3a) 1<H NMR: (CDCl 3): δ (ppm): 7.68-7.63 (m, 4H, H2); 7.55-7.51 (m, 2H, H3); 7.31-7.28 (m, 2H, H4); 7.18-7.14 (m, 4H, H1) and 2.43 (s, 3H, H5) NMR 19< F: (CDCl 3): δ (ppm): -106.57 NMR 31< P: (CDCl 3): δ (ppm): 27.71 (5a) NMR 1< H: (CDCl 3): δ (ppm): 7.91-7.85 (m, 4H, H2); 7.20-7.16 (m, 4H, H1); 3.74-3.71 (m, 4H, H4) and 3.10-3.05 (m, 4H, H3) NMR 19< F: (CDCl 3): δ (ppm): -106.43 NMR 31< P: (CDCl 3): δ (ppm): 27.21 A.2 / Polymer synthesis

[0085] The experimental protocol applied for the formation of polymers, from the above monomers and, depending on the polymers, from bisphenol A or isosorbide, is as follows.

[0086] In a 50 mL three-necked flask equipped with a mechanical stirrer and a nitrogen flow, 5.0 mmol of difluorinated phosphorylated monomer (2a, 3a, 4a, or 5a), 5.0 mmol of diol (bisphenol A or isosorbide), and 11 mmol of potassium carbonate are added to dimethylacetamide (DMAC). The solids content in the DMAC is 25%. The reaction mixture is stirred at 160–165°C for 24 h. The reaction mixture is then cooled and precipitated with water. After several rinses with distilled water, the polymer is dried under vacuum at 100°C and then washed several times with methanol. The resulting polymer is separated by filtration and then dried under vacuum to a constant mass. It is in the form of a solid powder.

[0087] This process is applied for the preparation of polymer P8 (according to the invention) and the following polymers P1 to P7 (not according to the invention) (for each of these polymers, the glass transition temperature Tg is measured by thermogravimetric analysis TGA): NMR 1< H: (CDCl 3): δ (ppm): 7.80-7.75 (m, 4H, H8), 7.03-6.98 (m, 4H, H7), 5.00-4.96 (m, 1H, H2), 4.86-4.80 (m, 2H, H5 and H3), 4.64-4.63 (m, 1H, H4), 4.19-4.03 (m, 4H, H1 and H6), 3.69 (s, 4H, H10), 3.05 (s, 4H, H9), NMR 31< P: (CDCl 3): δ (ppm): 29.5 Tg = 198°C; NMR 1< H: (CDCl3): δ (ppm): 7.63-7.53 (m, 6H, H8 and H9), 7.25-7.22 (m, 6H, H10 and H2), 7.04-6.95 (m, 8H, H7 and H1), 2.41 (s, 3H, H11), 1.69 (s, 6H, H3) NMR 31< P: (CDCl3): δ (ppm): 28.65 Tg = 184°C; RMN 1< H : (CDCl3) : δ (ppm) : 7.69-7.58 (m, 6H, H8 et H9), 7.25-7.22 (m, 6H, H10 et H2), 7.02-6.95 (m, 8H, H7 etH1), 2.40 (s, 3H, H11), 1.70 (s, 6H, H3) RMN 31< P : (CDCl3) : δ (ppm) : 41.46 Tg = 185°C ; RMN 1< H : (CDCl3) : δ (ppm) : 7.68-7.56 (m, 6H, H8 et H9), 7.26-7.24 (m, 2H, H10), 7.02-6.97 (m, 4H, H7), 5.02-4.98 (m, 1H, H2), 4.88-4.81 (m, 2H, H5 et H3), 4.66-4.65 (m, 1H, H4), 4.05-4.03 (m, 4H, H1 et H6), 2.41 (s, 3H, H11) RMN 31< P : (CDCl3) : δ (ppm) : 41.26 Tg = 196°C ; RMN 1< H : (CDCl3) : δ (ppm) : 7.62-7.51 (m, 6H, H8 et H9), 7.28-7.26 (m, 2H, H10), 7.04-6.98 (m, 4H, H7), 5.02-4.99 (m, 1H, H2), 4.89-4.82 (m, 2H, H5 et H3), 4.67-4.65 (m, 1H, H4) 4.05-4.04 (m, 4H, H1 et H6), 2.41 (s, 3H, H11) RMN 31< P : (CDCl3) : δ (ppm) : 28.57 Tg = 202°C ; RMN 1< H : (CDCl 3 ) : δ (ppm) : 8.00-7.93 (m, 4H, H8), 7.03-6.96 (m, 4H, H7), 5.00-4.96 (m, 1H, H2), 4.86-4.80 (m, 2H, H5 et H3), 4.64-4.63 (m, 1H, H4), 4.19-4.03 (m, 4H, H1 et H6), 3,65 (s, 4H, H10), 2.75 (s, 4H, H9) RMN 31< P : (CDCl 3 ) : δ (ppm) : 66.05 Tg = 218°C ; RMN 1< H : (CDCl 3 ) : δ (ppm) : 7.82-7.77 (m, 4H, H8), 7.28-7.24 (m, 4H, H2), 7.04-6.95 (m, 8H, H1 et H7), 3.70 (s, 4H, H10), 3.08 (s, 4H, H9), 1.71 (s, 6H, H3) RMN 31< P : (CDCl 3 ) : δ (ppm) : 29.08 Tg = 187°C ; RMN 1< H : (CDCl 3 ) : δ (ppm) : 8.02-7.95 (m, 4H, H8), 7.26-7.23 (m, 4H, H2), 7.04-6.94 (m, 8H, H1 et H7), 3.75 (s, 4H, H10), 2.88 (s, 4H, H9), 1.71 (s, 6H, H3) RMN 31< P : (CDCl 3 ) : δ (ppm) : 66.09 Tg = 206°C. B / Rare earth affinity measurements

[0088] Affinity measurements are performed using electrochemical impedance spectroscopy at the polymer / rare earth salt solution interface. Experiments are conducted for the following rare earths: lanthanum, cerium.

[0089] For this purpose, each of the polymers P1 to P8 above is deposited on a flat gold or platinum electrode as follows. The electrode is rinsed with acetone for 15 min, rinsed with demineralized water, and then dried under a nitrogen stream. Next, the electrode surface is cleaned for approximately 5 min in a piranha solution (a mixture of 25% by volume of (H₂O₂ 35%) and 75% by volume of (H₂SO₄ 96%)) to activate the surface, then rinsed with ultrapure water under ultrasound for 10 min, and finally dried under a nitrogen stream.

[0090] A solution of the polymer in chloroform (5 µL, 1% w / w) is then deposited, by droplet application, onto the surface of the electrode. The solvent is evaporated under a flow of nitrogen at room temperature.

[0091] Each electrode is immersed in rare-earth solutions (lanthanum or cerium) at different concentrations (between 5 x 10⁻¹¹ M and 5 x 10⁻⁶ M for lanthanum, and between 10⁻⁸ M and 10⁻³ M for cerium) in water at room temperature. Measurements are taken after 20 minutes of immersion to ensure that equilibrium conditions have been reached between the polymer-coated electrode and the solution.

[0092] Impedance spectroscopy measurements are performed using a BioLogic EC-Lab® VMP3 multi-channel potentiostat at open-circuit potential, applying a 10 mV sinusoidal perturbation in the frequency range of 100 mHz to 100 kHz. The impedance spectra are modeled by a Randles equivalent circuit to extract the bias resistance value.

[0093] As an example, the following are shown on the figure 3 the spectra obtained, in a / , for the P8 polymer according to the invention, and, in b / for the P5 polymer, very close in structure but not according to the invention, for the lanthanum solutions.

[0094] From these results, we deduce the affinity of the different polymers for lanthanum (in terms of sensitivity, defined as the ratio of the relative change in polarization resistance to the logarithm of the lanthanum concentration). The results obtained are shown on the figure 4. It is observed that the P8 polymer according to the invention has a much greater affinity for lanthanum than the comparative polymers tested, which have very similar structures.

[0095] It is deduced from this experiment that the impedimetric sensor obtained from the P8 polymer according to the invention allows the detection of lanthanum in a concentration range from 7.2.10 -11< M to 7.2.10 -6< M (a lanthanum concentration range for which the relative variation of resistance is linear as a function of the logarithm of the lanthanum concentration), with a detection limit of 7.2.10 -11< M, and a sensitivity of 0.112.

[0096] They are shown as examples on the figure 5 the spectra obtained, in a / , for the P8 polymer according to the invention, and, in b / for the P5 polymer, very close in structure but not according to the invention, for the cerium solutions.

[0097] From these results, we deduce the affinity of the different polymers for cerium (in terms of sensitivity, defined as the ratio of the relative change in polarization resistance to the logarithm of the cerium concentration). The results obtained are shown on the figure 6 Here again, we observe that the P8 polymer according to the invention has a much greater affinity for cerium than the comparative polymers tested, which have very similar structures.

[0098] It is deduced from this experiment that the impedimetric sensor obtained from the P8 polymer according to the invention allows the detection of cerium in a concentration range from 1.43.10 -10< M to 1.43.10 -5< M (cerium concentration range for which the relative variation of the resistance is linear as a function of the logarithm of the cerium concentration), with a detection limit of 5.2.10 -10< M, and a sensitivity of 0.15. C / Rare earth adsorption studies on powdered polymer

[0099] Adsorption studies are conducted by mixing 100 mg of powdered P8 polymer with aqueous solutions containing lanthanum or cerium (at a concentration of 10 µg / L - 10 ppb) and 0.42% phosphoric acid (10 mL) (4 × 10⁻² M, pH 1.4), and then stirring the resulting mixture for 24 h. A sample of the mixture is then taken using a syringe and filtered through a 0.45 µm polytetrafluoroethylene (PTFE) filter to separate the polymer from the liquid. The concentration of lanthanum or cerium in the filtrate is measured by inductively coupled plasma mass spectrometry (CP-MS) using an Agilent ICP-MS / MS 8800 instrument.

[0100] From this measurement, we can deduce the concentration of lanthanum or cerium that has been adsorbed by the polymer. This concentration turns out to be particularly high: 0.317 ppm for lanthanum (0.317 µg / g of polymer) and 0.321 ppm (0.321 µg / g of polymer) for cerium.

[0101] The presence of lanthanum on the surface of the P8 polymer according to the invention is further demonstrated by the luminescence properties of lanthanum, as illustrated in the figure 7 Significant luminescence is observed at the end of the contact step (in b / on the figure), whereas no luminescence was observed for the initial polymer (in a / on the figure). D / Rare earth desorption

[0102] The P8 polymer powders obtained from the above experiment of lanthanum or cerium adsorption on the powdered polymer are recovered from the liquid medium by filtration.

[0103] Each of the powders obtained is immersed in an aqueous solution comprising a rare earth complexant, tributyl phosphate or cis-1,3,5-triamino 2,4,6-trihydroxycyclohexane, at a concentration of 1 M. After an incubation time of 24 h, the polymer powder free of lanthanum or cerium is recovered by filtration, and an aqueous solution containing lanthanum or cerium is recovered separately.

Claims

1. Polymer comprising a repeating unit of the general formula (I): wherein R1 and R2, identical or different, each represent a hydrogen atom, or a linear, branched and / or cyclic, saturated and / or unsaturated, aromatic or nonaromatic, hydrocarbon radical, optionally interrupted by one or more heteroatom(s), which can comprise a single ring or several rings, optionally condensed, or R1 and R2 together, with the nitrogen atom to which each is attached, form a saturated or unsaturated, optionally aromatic, 3- to 8- membered heterocycle, comprising one or more heteroatom(s) in the cycle, optionally substituted with one or more linear, branched and / or cyclic alkyl radical(s), said heterocycle being optionally condensed to one or more saturated or unsaturated, optionally aromatic, 3- to 8- membered cycle(s) or heterocycle(s), optionally comprising one or more heteroatom(s) in the cycle, and optionally substituted with one or more linear, branched and / or cyclic alkyl radical(s).

2. Polymer according to claim 1, comprising 10 to 50 repeats of the repeating unit of the general formula (I).

3. Polymer according to claim 1 or 2, which is linear.

4. Polymer according to any one of claims 1 to 3, having the general formula (IIa): wherein n is an integer between 10 and 50, and A represents a fluorine atom, a chlorine atom, a hydrogen atom or a hydroxyl group.

5. Polymer according to any one of claims 1 to 4, wherein R1 and R2 together form, with the nitrogen atom to which each is attached, a morpholine nucleus.

6. Polymer according to any one of claims 1 to 4, wherein R1 and R2, identical or different, each represent a hydrogen atom, a methyl radical or an ethyl radical.

7. Polymer according to any one of claims 1 to 4, wherein R1 and R2, identical or different, each represent a hydrogen atom, or a nucleus chosen from a benzene nucleus and a naphthalene nucleus, said nucleus being optionally substituted with one or more linear, branched and / or cyclic alkyl radical(s).

8. Composite material, comprising a polymer according to any one of claims 1 to 7 on a solid support in divided form.

9. Composite material according to claim 8, wherein said solid support is in the form of fibers, beads or irregularly shaped particles.

10. Composite material according to claim 8 or 9, wherein said polymer is impregnated on or forms a coating layer on said solid support.

11. Use of a polymer according to any one of claims 1 to 7 or a composite material according to any one of claims 8 to 10, for the extraction of a rare earth from an aqueous liquid medium containing it.

12. Extraction method for extracting a rare earth from an aqueous liquid medium containing it, characterized in that it comprises contacting said liquid medium with a polymer according to any one of claims 1 to 7 or a composite material according to any one of claims 8 to 10, and then separating said polymer or composite material from said medium.

13. Extraction method according to claim 12, wherein said contacting is carried out at a pH less than or equal to 3.

14. Extraction method according to claim 12 or 13, comprising a final step of separating said rare earth from said polymer or said composite material.

15. Extraction method according to any one of claims 12 to 14, wherein said rare earth is a lanthanide, preferably lanthanum or cerium.

16. Extraction method according to any one of claims 12 to 15, wherein said liquid medium is a mining effluent.