Organic-inorganic hybrid material of use for extracting uranium (VI) from aqueous media containing phosphoric acid, processes for preparing same and uses thereof

Abstract

The invention relates to an organic-inorganic hybrid material which comprises an inorganic solid support on which are grafted organic molecules of the general formula (I) hereafter: ##STR00001##
and relates to methods allowing preparation of this hybrid material as well as to the uses of the hybrid material for extracting uranium(VI) from an aqueous medium comprising phosphoric acid.

Claims

1. An organic-inorganic hybrid material, which comprises an inorganic solid support on which is covalently grafted a plurality of organic molecules of formula (I): ##STR00007## wherein: x, y and z are equal to 0 or 1, with the proviso that at least one of x, y and z is equal to 1; m is an integer ranging from 1 to 6; v and w are equal to 0 or 1, with the proviso that v is equal to 1 when w is equal to 0 and v is equal to 0 when w is equal to 1; if x is equal to 0, R.sup.1 represents a hydrogen atom or a linear or branched, saturated or unsaturated hydrocarbon group comprising from 1 to 12 carbon atoms, and, if x is equal to 1, R.sup.1 represents a group bound to the inorganic solid support through at least one covalent bond represented by the dotted line; if y is equal to 0, R.sup.2 represents a hydrogen atom or a linear or branched, saturated or unsaturated hydrocarbon group comprising from 1 to 12 carbon atoms, and, if y is equal to 1, R.sup.2 represents a group bound to the inorganic solid support through at least one covalent bond represented by the dotted line; if z is equal to 0, R.sup.3 represents a hydrogen atom or a linear or branched, saturated or unsaturated hydrocarbon group comprising from 1 to 12 carbon atoms, and, if z is equal to 1, R.sup.3 represents a group bound to the inorganic solid support through at least one covalent bond represented by the dotted line; R.sup.4 and R.sup.5 represent, independently of each other, a hydrogen atom, a linear or branched, saturated or unsaturated hydrocarbon group comprising from 2 to 8 carbon atoms, or a monocyclic aromatic group.

2. The organic-inorganic hybrid material of claim 1, wherein the inorganic solid support comprises a metal oxide, a mixed metal oxide, a mixture of metal oxides, or carbon.

3. The organic-inorganic hybrid material of claim 1, wherein the inorganic solid support is a porous material.

4. The organic-inorganic hybrid material of claim 3, wherein the porous material is a mesoporous or macroporous material.

5. The organic-inorganic hybrid material of claim 4, wherein the porous material is a mesoporous silica, a mesoporous titanium oxide, a mesoporous zirconia or a mesoporous carbon.

6. The organic-inorganic hybrid material of claim 5, wherein the inorganic solid support is a SBA mesoporous silica or a CMK mesoporous carbon.

7. The organic-inorganic hybrid material of claim 1, wherein R.sup.3 represents (CH.sub.2).sub.qX.sup.1 wherein q is an integer ranging from 0 to 12, and X.sup.1 represents a group selected from the group consisting of: ##STR00008## and CHCH.

8. The organic-inorganic hybrid material of claim 1, wherein at least one of R.sup.1 and R.sup.2 represents a group of formula (a), (b), (c), (d), (e), (f) or (g):
(CH.sub.2).sub.pC(O)NH(CH.sub.2).sub.qX.sup.2(a)
(CH.sub.2).sub.pNHC(O)(CH.sub.2).sub.qX.sup.2(b)
(CH.sub.2).sub.pC(O)O(CH.sub.2).sub.qX.sup.2(c)
(CH.sub.2).sub.pOC(O)(CH.sub.2).sub.qX.sup.2(d)
(CH.sub.2).sub.pO(CH.sub.2).sub.qX.sup.2(e)
(CH.sub.2).sub.p-triazole-(CH.sub.2).sub.qX.sup.2(f)
(CH.sub.2).sub.qX.sup.2(g) wherein p is an integer ranging from 1 to 6, q is an integer ranging from 0 to 12, and X.sup.2 represents a group selected from the group consisting of: ##STR00009## and CHCH.

9. The organic-inorganic hybrid material of claim 8, wherein R.sup.3 represents (CH.sub.2).sub.qX.sup.1 wherein q is an integer ranging from 0 to 12 and X.sup.1 is identical with X.sup.2.

10. The organic-inorganic hybrid material of claim 1, wherein the organic molecules have the formula (Ia): ##STR00010##

11. The organic-inorganic hybrid material of claim 10, wherein x and y are 0, R.sup.1 and R.sup.2 represent, independently of each other, a linear or branched alkyl group comprising from 1 to 12 carbon atoms; z is 1 and R.sup.3 represents a group bound to the inorganic solid support through at least one covalent bond, and R.sup.4 and R.sup.5 represent, independently of each other, a hydrogen atom or a linear or branched alkyl group comprising from 2 to 8 carbon atoms.

12. The organic-inorganic hybrid material of claim 11, wherein R.sup.1 and R.sup.2 are identical with each other and represent a branched alkyl group comprising from 6 to 12 carbon atoms.

13. The organic-inorganic hybrid material of claim 11, wherein R.sup.4 and R.sup.5 represent, independently of each other, a hydrogen atom or a linear or branched alkyl group comprising from 2 to 4 carbon atoms.

14. The organic-inorganic hybrid material of claim 10, wherein the inorganic solid support is based on a metal oxide, a mixed metal oxide or on a mixture of metal oxides and R.sup.3 represents: ##STR00011## wherein q is 1 to 5.

15. The organic-inorganic hybrid material of claim 10, wherein the inorganic solid support is based on carbon and R.sup.3 represents: ##STR00012## wherein q is 1 to 5.

16. A method for extracting uranium(VI) from an aqueous medium comprising phosphoric acid comprising contacting the aqueous medium with the organic-inorganic hybrid material of claim 1 and then separating the aqueous medium and the organic-inorganic hybrid material.

17. The method of claim 16, wherein the aqueous medium comprises from 0.012 mol/L to 9 mol/L of phosphoric acid.

18. The method of claim 17, wherein the aqueous medium results from the attack of a phosphate ore with sulfuric acid.

19. A method for recovering uranium(VI) from an aqueous medium comprising phosphoric acid, comprising: extraction of uranium(VI) from the aqueous medium, the extraction comprising contacting the aqueous medium with the organic-inorganic hybrid material of claim 1, and then separating the aqueous medium and the organic-inorganic hybrid material; and stripping of uranium(VI) from the organic-inorganic hybrid material obtained at the end of the extraction, the stripping comprising contacting the organic-inorganic hybrid material with a basic aqueous solution, and then separating the organic-inorganic hybrid material and the basic aqueous solution.

20. The method of claim 19, wherein the aqueous medium results from the attack of a phosphate ore with sulfuric acid.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically illustrates the preparation of a first organic-inorganic hybrid material according to the invention, in which the inorganic solid support is a mesoporous silica and in which the organic molecules fit the general formula (I) hereinbefore in which R.sup.1 and R.sup.2 both represent a 2-ethylhexyl group, R.sup.3 represents a group (CH.sub.2).sub.3SiO.sub.3, R.sup.4 represents an ethyl group, while R.sup.5 represents a hydrogen atom.

(2) FIG. 2 schematically illustrates the preparation of a second organic-inorganic hybrid material according to the invention in which the inorganic solid support is a mesoporous carbon and in which the organic molecules fit the general formula (I) hereinbefore wherein R.sup.1 and R.sup.2 both represent a 2-ethylhexyl group, R.sup.3 represents a group CH.sub.2C, R.sup.4 represents an ethyl group, while R.sup.5 represents a hydrogen atom.

(3) FIG. 3 schematically illustrates the reaction schemes of the synthesis of organic compounds useful for preparing the organic-inorganic hybrid materials shown in FIGS. 1 and 2.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

EXAMPLE 1

Preparation of a First Organic-Inorganic Hybrid Material According to the Invention

(4) A first organic-inorganic hybrid material according to the invention is prepared, called hereafter material M1, which comprises a mesoporous silica with a hexagonal periodic structure, of the SBA-15 type, on which are grafted organic molecules fitting the general formula (I) hereinbefore wherein: m is 1; v is 1 (and therefore w is 0); R.sup.1 and R.sup.2 both represent a 2-ethylhexyl group, R.sup.3 represents a group (CH.sub.2).sub.3SiO.sub.3, R.sup.4 represents an ethyl group, while R.sup.5 represents a hydrogen atom.

(5) This organic-inorganic hybrid material is prepared by the method illustrated in FIG. 1, which comprises:

(6) (1) the functionalization of the mesoporous silica with amine functions, which is achieved by a silanization reaction, i.e. by reacting silanol functions (SiOH) of this silica with ethoxysilane functions of the 3-amino-propyl-triethoxysilane (commercially available), noted as APTS in FIG. 1; and then

(7) (2) the grafting of 3-(N,N-di(2-ethylhexyl)carbamoyl)-3-(ethoxy)-hydroxyphosphono)propanoic acid, or compound RT141, on the amine functions of the thereby functionalized silica, which is achieved by a peptide coupling, i.e. by reacting said amine functions with the carboxylic acid functions of this compound.

(8) 1.1Synthesis of the Mesoporous Silica

(9) The mesoporous silica is synthesized by following an operating procedure identical with the one described by Zhao et al. in Science 1998, 279, 548-552, reference [12]. It has pores with a diameter of 9.1 nm (as determined according to the BJH method) and a BET specific surface area of 800 m.sup.2/g (as determined by adsorption-desorption of nitrogen).

(10) 1.2Functionalization of the Mesoporous Silica

(11) After activation (i.e. heating in vacuo to 130 C. for 24 hours), the mesoporous silica (1.8 g) is suspended in a solution containing 0.5 g of 3-aminopropyltriethoxysilane in 20 mL of toluene. The mixture is heated to 90 C. for 48 hours under nitrogen, and then filtered and washed with acetone before being treated with acetone in the Soxhlet apparatus for 48 hours. The thereby obtained aminosilica is dried in the oven (80 C.) for 20 hours.

(12) Its physico-chemical characteristics are the following: pore diameter (BJH method): 8.4 nm; BET specific surface area (nitrogen adsorption-desorption): 460 m.sup.2/g; mass loss (ATG analysis): 9%; elementary analysis, found: C, 5.0%, N, 1.7%, P, 0%. amount of grafted amine functions: 1.4 mmol/g of mesoporous silica.

(13) 1.3Synthesis of the RT141 Compound

(14) The RT141 compound is synthesized by using the reaction scheme comprising the steps A, B, C and D, which is illustrated in FIG. 3.

(15) As visible in this figure, this synthesis consists of reacting in a first step, noted as A, 2,2-diethylhexylamine, noted as 1, with chloroacetyl chloride, noted as 2, in order to obtain 2-chloro-N,N-diethylhexylacetamide, noted as 3 in this figure.

(16) To do this, to a solution of 2,2-diethylhexylamine at 0.7 mol/L in dichloromethane, potassium carbonate (2 equiv.) is added with stirring. The thereby obtained suspension is cooled to 0 C. and chloroacetyl chloride is added to it drop wise (1.5 equiv.). The mixture is left to return to room temperature. Once the amine is consumed (which may be checked by thin layer chromatography (TLC) by using ethyl acetate as an eluent and ninhydrin as a developer), 4 equivalents of water are added drop wise to the mixture, which produces effervescence. When this effervescence is completed, an amount of water equal to half the volume of dichloromethane having been used for dissolving the amine is added to this mixture. The mixture is maintained with stirring for 15 minutes. The aqueous and organic phases are then separated and the organic phase is dried on Na.sub.2SO.sub.4, filtered and concentrated. The expected compound (yield: 97%) is thereby obtained, for which the characterizations by .sup.1H and .sup.13C NMR are given hereafter.

(17) .sup.1H NMR (400 MHz, CDCl.sub.3) (ppm): 0.85-0.91 (m, 12H, CH.sub.3); 1.23-1.33 (m, 16H, CH.sub.2); 1.55-1.60 (m, 1H, CHCH.sub.2N); 1.67-1.73 (m, 1H, CHCH.sub.2N); 3.18 (d, 2H, J=7.5 Hz, CH.sub.2N); 3.22-3.32 (m, 2H, CH.sub.2N); 4.09 (s, 2H, CH.sub.2Cl);

(18) .sup.13C NMR (100 MHz, CDCl.sub.3) (ppm): 10.7; 11.0; 14.1 (CH.sub.3); 23.1; 23.9; 24.0; 28.7; 28.9; 30.4; 30.6 (CH.sub.2); 36.8; 38.5 (CH); 41.6 (CH.sub.2Cl); 48.8 (CH.sub.2N); 51.7 (CH.sub.2N); 167.1 (CO).

(19) In a second step, noted as B in FIG. 3, 2-chloro-N,N-diethylhexyl-acetamide is subject to an Arbuzov reaction in order to obtain diethyl 1-(N,N-diethyl-hexylcarbamoyl)methylphosphonate, noted as 4 in this figure.

(20) This Arbuzov reaction is conducted by bringing a mixture consisting of 2-chloro-N,N-diethylhexylacetamide (1 equiv.) and of triethylphosphite (1.2 equiv.) at 160 C. with reflux for 3 hours. Once the acetamide is consumed (which is checked by TLC by using dichloromethane as an eluent and UV or phosphomolybdic acid as a developer), the phosphite excess is distilled under reduced pressure. The expected compound is thereby obtained (yield: quantitative) for which the characterizations by .sup.1H, .sup.13C and .sup.31P NMR are given hereafter.

(21) .sup.1H NMR (400 MHz, CDCl.sub.3) (ppm): 0.81-0.86 (m, 12H, CH.sub.3); 1.21-1.32 (m, 22H, CH.sub.2, OCH.sub.2CH.sub.3); 1.51-1.57 (m, 1H, CHCH.sub.2N); 1.64-1.71 (m, 1H, CHCH.sub.2N); 3.02 (d, 2H, J=22.0 Hz, COCH.sub.2P); 3.21-3.27 (m, 4H, CH.sub.2N); 4.08-4.16 (m, 4H, OCH.sub.2CH.sub.3);

(22) .sup.13C NMR (100 MHz, CDCl.sub.3) (ppm): 10.6; 11.0; 14.1; 14.2 (CH.sub.3); 16.3; 16.4 (OCH.sub.2CH.sub.3); 23.1; 23.2; 23.5; 23.9; 28.8; 28.9; 30.4; 30.6 (CH.sub.2); 33.1; 34.5 (d, J=134.0 Hz, CH.sub.2P); 37.0; 38.6 (CH); 48.9; 52.3 (CH.sub.2N); 62.5 (d, J=6.5 Hz, OCH.sub.2CH.sub.3); 165.2 (d, J=6.0 Hz, CO);

(23) .sup.31P NMR (160 MHz, CDCl.sub.3) (ppm): 21.8.

(24) In a third step, noted as C in FIG. 3, the diethyl 1-(N,N-diethylhexyl-carbamoyl)methylphosphonate is subject to a C-alkylation reaction in order to obtain the ethyl 3-(N,N-di(2-ethylhexyl)carbamoyl)-3-(diethoxy)phosphono)propanoate, noted as 5 in this figure.

(25) To do this, a solution of diethyl 1-(N,N-diethylhexylcarbamoyl)-methylphosphonate (dried beforehand for 2.5 hours at 80 C. in vacuo) is added dropwise and with stirring in anhydrous tetrahydrofuran (THF1 equiv.1 mol/L) to a suspension of sodium hydride (1.5 equiv.washed beforehand with pentane) in anhydrous THF (2 mol/L). The mixture is stirred for 1 hour at room temperature and the solution is then cooled to 0 C. and a solution of ethyl acetate bromide (1.5 equiv.) is added drop wise. This mixture is left to return to room temperature which is then stirred for 1 hour, after which the crude product is acidified down to a pH of 1 by means of an aqueous solution of hydrochloric acid at 1 mol/L and extracted with dichloromethane. The aqueous and organic phases are separated and the organic phase is dried on Na.sub.2SO.sub.4, filtered and concentrated. The bromide excess is removed by distillation in vacuo. The expected compound (yield: quantitative) is thereby obtained, for which the characterizations by .sup.1H, .sup.13C and .sup.31P NMR are given hereafter.

(26) .sup.1H NMR (400 MHz, CDCl.sub.3) (ppm): 0.77-0.89 (m, 12H); 1.16-1.28 (m, 27H); 1.63-1.70 (m, 1H); 1.74-1.83 (m, 1H); 2.68-2.76 (m, 1H); 2.70-2.90 (m, 1H); 3.01-3.18 (m, 2H); 3.50-3.75 (m, 3H); 4.01-4.13 (m, 6H);

(27) .sup.13C NMR (100 MHz, CDCl.sub.3) (ppm): 10.3; 10.5; 10.6; 10.9; 14.0; 14.1; 16.3; 16.4; 23.1; 23.5; 23.7; 24.0; 28.6; 28.7; 28.8; 28.9 30.2; 30.3; 30.6; 30.7; 32.7; 37.0; 37.1; 37.2; 37.3; 37.7-39.1 (d, J=132.0 Hz); 38.6; 38.7; 38.9; 50.2; 50.6; 50.9; 51.2; 51.9; 52.4; 60.8; 62.4; 62.5; 63.1; 63.2; 63.3; 167.4; 168.5; 171.3-171.5 (dd, J=18.5 Hz, d=4.5 Hz);

(28) .sup.31P NMR (160 MHz, CDCl.sub.3) (ppm): 23.1.

(29) In a last step, noted as D in FIG. 3, ethyl 3-(N,N-di(2-ethylhexyl)-carbamoyl)-3-(diethoxy)phosphono)propanoate is subject to a saponification reaction in order to obtain the compound RT141.

(30) This saponification is achieved by adding to a solution of 0.4 mol/L of ethyl 3-(N,N-di(2-ethylhexyl)carbamoyl)-3-(diethoxy)phosphono)propanoate in ethanol, a 20% soda solution (6 equiv.). The mixture is refluxed for 3 hours. After cooling, the mixture is acidified down to a pH of 1 by means of an aqueous hydrochloric acid solution at 1 mol/L, and then extracted twice with dichloromethane. The aqueous and organic phases are separated and the organic phase is dried on Na.sub.2SO.sub.4, filtered and concentrated. The expected compound (yield: quantitative) is thereby obtained for which the characterizations by .sup.1H, .sup.13C and .sup.31P NMR are given hereafter.

(31) .sup.1H NMR (400 MHz, CDCl.sub.3) (ppm): 0.82-0.92 (m, 12H); 1.22-1.38 (m, 19H); 1.66-1.73 (m, 1H); 1.74-1.82 (m, 1H); 2.88-3.0 (m, 2H); 3.01-3.23 (m, 2H); 3.46-3.80 (m, 3H); 4.07-4.17 (m, 2H); 8.96 (Is, 2H);

(32) .sup.13C NMR (100 MHz, CDCl.sub.3) (ppm): 10.3; 10.5; 10.7; 10.8; 14.0; 16.2; 16.3; 23.0; 23.4; 23.6; 23.8; 28.5; 28.6; 28.7; 30.2; 30.3; 30.4; 32.9; 37.1; 37.7-39.0 (d, J=132.0 Hz); 38.5; 38.6; 50.4; 50.6; 52.3; 52.8; 62.4 168.8; 174.2 (d, J=9.0 Hz); 174.4 (d, J=9.0 Hz);

(33) .sup.31P NMR (160 MHz, CDCl.sub.3) (ppm): 24.0.

(34) 1.4Grafting of the Compound RT141 on the Aminosilica

(35) The aminosilica (1 equiv. of amine functions) and the compound RT141 (2 equiv.) are reacted in anhydrous THF in the presence of dicyclohexylcarbodiimide (DDC2 equiv.), N-hydroxybenzotriazole (HOBt2 equiv.) and of diisopropylethylamine (DIPEA1.5 equiv.) for 48 hours, at room temperature and under an argon flow.

(36) After which, the reaction medium is filtered, the residue is washed several times with dichloromethane and with methanol and is dried in vacuo at 90 C.

(37) The material 1 is thereby obtained for which the characterizations by .sup.13C, .sup.31P and .sup.29Si CPMAS NMR and the physico-chemical characteristics are given hereafter.

(38) .sup.13C NMR (ppm): 8.5; 11.73; 15.23; 22.39; 28.34; 37.23; 40.74; 48.30; 60.07; 172.44;

(39) .sup.31P NMR (ppm): 18.11;

(40) .sup.29Si NMR (ppm): 59.01; 66.05 (sites T.sup.2 and T.sup.3); 101.12; 110.01 (sites Q.sup.3 and Q.sup.4);

(41) Pore diameter (BJH model): 5.5 nm;

(42) BET specific surface area (nitrogen adsorption-desorption): 400 m.sup.2/g;

(43) Mass loss (ATG analysis): 19%;

(44) Elementary analysis, found: C, 12.4%, N, 1.9%, P, 1.1%.

(45) Amount of grafted molecules of the compound RT141: 0.46 mmol/g of material M1.

EXAMPLE 2

Preparation of a Second Organic-Inorganic Hybrid Material According to the Invention

(46) A second organic-inorganic hybrid material according to the invention is prepared, designated hereafter as material M2, which comprises a mesoporous carbon with a hexagonal periodic structure, of the CMK-3 type, on which are grafted organic molecules fitting the general formula (I) hereinbefore wherein: m is 1; v is 1 (and therefore w is 0); R.sup.1 and R.sup.2 both represent a 2-ethylhexyl group, R.sup.3 represents a group CH.sub.2C, R.sup.4 represents an ethyl group, while R.sup.5 represents a hydrogen atom.

(47) This organic-inorganic hybrid material is prepared by the method illustrated in FIG. 2, which comprises:

(48) (1) the functionalization of the mesoporous carbon with amine functions, which is achieved by a Diels-Alder reaction, i.e. by reacting conjugate diene functions of this carbon with alkynyl functions of propargylamine, noted as 9 in FIG. 2; and

(49) (2) the grafting of the compound RT141 on the amine functions of the thereby functionalized carbon which is achieved by peptide coupling like in Example 1 hereinbefore.

(50) 2.1 Synthesis of the Mesoporous Carbon

(51) The mesoporous carbon is synthesized by following the operating procedure described by Jun et al. in Journal of the American Chemical Society 2000, 122, 10712-10713, reference [13]. It has pores with a diameter of 3.5 nm (as determined according to the BJH method) and a BET specific surface area of 1,400 m.sup.2/g (as determined by adsorption-desorption of nitrogen).

(52) 2.2 Functionalization of the Mesoporous Carbon

(53) The mesoporous carbon (0.5 g) is suspended in pure propargylamine. The mixture is placed in an autoclave heated to 100 C. for 48 hours. After which, it is washed with acetone in the Soxhlet for 48 hours.

(54) The thereby obtained aminocarbon is dried in an oven (80 C.) for 20 hours.

(55) Its physico-chemical characteristics are the following: pore diameter (BJH method): 3.0 nm; BET specific surface area (nitrogen adsorption-desorption): 600 m.sup.2/g; elementary analysis, found: N, 1.1%, P, 0%; O,: 2.6%. amount of grafted amines: 0.79 mmol/g of mesoporous carbon.

(56) 2.3 Grafting of the Compound RT141 on the Aminocarbon

(57) This grafting is achieved by following an operating procedure identical with the one described in Example 1 hereinbefore for grafting the compound RT141 on the aminosilica.

(58) It leads to the material 2 for which the physico-chemical characteristics are the following: pore diameter (BJH method): 2.8 nm; BET specific surface area (nitrogen adsorption-desorption): 300 m.sup.2/g; elementary analysis, found: N, 1.3%, P, 0.9%; O, 3.9%. amount of grafted RT141 molecules: 0.38 mmol/g of material M2.

EXAMPLE 3

Properties of the Organic-Inorganic Hybrid Materials According to the Invention

(59) 3.1 Capability of the Organic-Inorganic Hybrid Materials According to the Invention of Extracting Uranium(VI) from Phosphoric Media

(60) The capability of the materials M1 and M2, as obtained in Examples 1 and 2 hereinbefore, of extracting uranium(VI) from aqueous phosphoric media is appreciated by extraction tests which consist of: mixing 250 mg of one of these materials as a powder with 10 mL of a synthetic solution of phosphoric acid containing either exclusively uranium(VI) or uranium(VI) and iron(III); leaving the mixture for 24 hours with stirring (with the vortex), at room temperature (25 C.); and then separating by filtration the solid and liquid phases of this mixture.

(61) The concentrations of uranium(VI) and optionally of iron(III) are measured by X fluorescence in the synthetic solution of phosphoric acid before the latter is mixed with the material as well as in the filtrate.

(62) Thus, for uranium(VI) and if required for iron(III) are determined: the amount of these elements extracted per g of material, noted as Q.sub.ext and expressed in mg/g, which is determined by the following formula:

(63) $Q_{\mathrm{ext}}=\left(C_{\mathrm{ini}}-C_{\mathrm{fin}}\right)\frac{V}{m}$
with: C.sub.ini=initial concentration of the element in the synthetic solution of phosphoric acid (in mg/L); C.sub.fin=concentration of the element in the filtrate (in mg/L); V=the volume of the synthetic solution of phosphoric acid mixed with the material (in L); m=mass of material used in the test (in g); the distribution coefficient, noted as K.sub.d and expressed in L/g, which is determined by the following formula:

(64) $\mathrm{Kd}=\frac{Q_{\mathrm{ext}}}{C_{\mathrm{fin}}}$
wherein Q.sub.ext and C.sub.fin have the same meaning as earlier.

(65) In the case of tests having been conducted with a synthetic solution of phosphoric acid containing both uranium(VI) and iron(III), the selectivity coefficient of the material for uranium(VI) towards iron(III) is also determined. This coefficient which is noted as S.sub.U/Fe is determined by the following formula:

(66) $S_{U/\mathrm{Fe}}=\frac{{\mathrm{Kd}}_U}{{\mathrm{Kd}}_{\mathrm{Fe}}}$
wherein Kd.sub.u is the distribution coefficient of the uranium(VI) while Kd.sub.Fe is the distribution coefficient of the iron(III).

(67) Table I hereafter shows the results obtained with different synthetic solutions of phosphoric acid, for which the phosphoric acid concentration and the initial concentrations of uranium(VI) and of iron(III) have been varied.

(68) TABLE-US-00001 TABLE I Uranium(VI) Fe(III) [H.sub.3PO.sub.4] C.sub.ini C.sub.fin Q.sub.ext Kd.sub.U C.sub.ini C.sub.fin Q.sub.ext Kd.sub.Fe Material (mol/L) (mg/L) (mg/L) (mg/g) (L/g) (mg/L) (mg/L) (mg/g) (L/g) S.sub.U/Fe M1 0.1 504 185 12.76 0.069 429 147 11.28 0.077 2 845 2 793 2.08 0.0007 103 1 268 94 6.96 0.074 526 283 9.72 0.034 374 188 7.44 0.040 3 295 3 261 1.36 0.0004 95 M2 0.1 535 64 18.84 0.294 1 250 100 6 0.060 490 205 11.40 0.056

(69) These results show that for an initial concentration of uranium(VI) of 500 ppm and for a phosphoric acid concentration of 0.1 mol/L, 1 kg of material M1 allows extraction of about 13 g of uranium(VI) while 1 kg of material M2 allows extraction of about 19 g of uranium(VI). When the phosphoric acid concentration increases by a factor 10 (1 mol/L), the extracted amount of uranium(VI) drops but remains however very high since it is of about 10 g for material M1 and of about 11 g for material M2.

(70) Moreover, they show that the presence of iron(III) does not have any real influence on the extraction of uranium(VI) by the materials and that the selectivity of the latter towards uranium with respect to the iron is highly satisfactory. Indeed, the selectivity coefficient S.sub.U/Fe is of the order of 100 (which means that the uranium is 100 times better extracted than iron) including when the ratio of the initial concentrations Fe/U is close to 10.

(71) Finally, these results show the fact that the inorganic support is a carbon rather than a silica (or vice versa) does not notably modify the efficiency of the extraction of uranium(VI) in an aqueous phosphoric medium.

(72) 3.2 Stripping of the Uranium(VI) from an Organic-Inorganic Hybrid Material According to the Invention

(73) The possibility of stripping from the material M2 the uranium having been extracted beforehand with this material is appreciated by tests which consist of: mixing 250 mg of one of the materials M2, as obtained at the end of the extraction tests described in point 3.1 hereinbefore, with 10 ml of a potash solution at 0.5 mol/L; leaving the mixture for 24 hours with stirring (with the vortex), at room temperature (25 C.); separating by filtration the solid and liquid phases of this mixture; and then measuring the uranium(VI) concentration of the filtrate by X fluorescence.

(74) Table II hereafter shows the stripped uranium(VI) concentrations, noted as C.sub.str, by comparing them with the uranium concentrations having been extracted beforehand with the material M2, noted as C.sub.ext.

(75) TABLE-US-00002 TABLE II Uranium(VI) [HNO.sub.3] C.sub.ext C.sub.str (mol/L) (mg/g) (mg/g) 1 150 50 285 90

(76) This table shows that about of the uranium having been extracted with the material M2 is stripped from this material after a single stripping cycle with potash for 24 hours, which is very satisfactory. These results actually suggest that it should be possible to optimize the stripping of the uranium by submitting the material to several successive stripping cycles.

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