FR3002951A1 - USE OF AMIDE AND PHOSPHONATE FUNCTION COMPOUNDS FOR EXTRACTING URANIUM (VI) FROM AQUEOUS SOLUTIONS OF SULFURIC ACID, IN PARTICULAR FROM THE SULFURIC LIXATION OF URANIFIED MINERALS - Google Patents

Abstract

The invention relates to the use of compounds of general formula (I) below: in which: R1 and R2 represent a hydrocarbon group, saturated or unsaturated, linear or branched, C6 to C12; R3 represents H, a C1 to C12 linear or branched, saturated or unsaturated hydrocarbon-based group optionally comprising one or more heteroatoms, or a C3 to C8 monocyclic, saturated or unsaturated hydrocarbon-based group optionally comprising one or more heteroatoms; ; while R4 represents a linear or branched C2-C8 hydrocarbon group, saturated or unsaturated, or a monocyclic aromatic group; as extractants, for extracting uranium (VI) from an aqueous solution of sulfuric acid. It also relates to a process which makes it possible to recover the uranium present in an aqueous solution of sulfuric acid resulting from the leaching of a uranium-containing ore by sulfuric acid and which uses said compounds asextractants. Applications: treatment of uranium ores in order to valorize the uranium present in these ores.

Description

USE OF AMIDE FUNCTIONAL COMPOUNDS AND PHOSPHONATE FOR EXTRACTING URANIUM (VI) FROM AQUEOUS SOLUTIONS OF SULFURIC ACID, IN PARTICULAR FROM THE SULFURIC LIXATION OF URANESTER MINERALS DESCRIPTION TECHNICAL FIELD The invention relates to the field of the extraction of uranium from aqueous media containing sulfuric acid. More specifically, the invention relates to the use of bifunctional compounds, comprising both an amide function and a phosphonate function, as extractants, for extracting uranium (VI) from an aqueous acid solution. sulfuric acid in which it is present and, in particular, of an aqueous solution resulting from the leaching of a uranium-containing ore by sulfuric acid. The invention also relates to a method for recovering the uranium present in an aqueous sulfuric acid solution resulting from the leaching of a uranium-containing ore by sulfuric acid and which uses said compounds as sulfuric acid. extractants.

The invention finds particular application in the treatment of uranium ores (uraninite, pitchblende, coffinite, brannérite, carnotite, ...) in order to recover the uranium present in these ores. STATE OF THE PRIOR ART Uranium ores (or ores of uranium) are extracted from the mines, crushed and crushed until they reach the consistency of a fine sand, and then they are subjected to an attack, also called leaching, by the Sulfuric acid (except if their gangue is naturally alkaline, in which case this leaching would require a crippling consumption of sulfuric acid). Sulfuric acid was chosen for two reasons: on the one hand, it is the strongest acid cheapest, this acid can be manufactured on the site of the plants for the treatment of uranium ores from sulfur by a process known as "Double catalysis", and secondly, its use leads to effluents that are relatively easy to treat because the sulfate ions can be largely removed by precipitation with lime. The attack of each uranium ore is studied on the basis of an optimization of the dissolution efficiency of uranium (VI) compared to the quantity of sulfuric acid consumed. Some ores are easily attacked in agitated tanks and require only about 25 kg of pure sulfuric acid per ton of ore, while others are only autoclaved and require more than 100 kg of pure sulfuric acid per tonne. ore.

In any case, many other elements such as aluminum, iron and silica, which are generally the elements of the gangue, as well as elements that vary from one ore to another, are also solubilized. by their nature only by their quantity, such as molybdenum, vanadium, zirconium, titanium, copper, nickel, and arsenic.

After filtration to remove insolubles, the aqueous solution resulting from the leaching with sulfuric acid, which generally contains from 0.1 to 10 g / l of uranium, is sent to a purification unit in which it is not only purified but also concentrated either by passage over ion exchange resins or by liquid-liquid extraction (that is to say by means of a solvent phase or organic phase). It undergoes a pH adjustment and a precipitation, which allows to obtain a yellow uranium concentrate which is commonly called "yellow cake". This uranium concentrate is filtered, washed, dried, possibly calcined (to obtain uranium sesquioxide U308), before being put in barrels and shipped to a refinery-conversion plant in which the uranium is transformed into UF6. of nuclear purity. To purify by liquid-liquid extraction the aqueous solution resulting from leaching with sulfuric acid, two processes are used industrially: the AMEX process ("AMine Extraction") and the DAPEX process ("DiAlkylPhosphoric Acid Extraction").

The AMEX process uses, as extractant, a commercial mixture of trialkylated tertiary amines whose alkyl chains are C 8 to C 10, for example Adogen 364 or Alamine 336, in solution in a kerosene-type hydrocarbon, optionally containing a heavy alcohol (C10-C13) which acts as a phase modifier, whereas the DAPEX process uses as extractant a synergistic mixture of di (2-ethylhexyl) phosphoric acid (HDEHP) and tri-n -butylphosphate (TBP), in solution in a kerosene type hydrocarbon. None of these methods is completely satisfactory. Indeed, apart from the fact that the uranium selectivity of the tertiary amine mixture used in the AMEX process deserves to be improved, particularly with respect to molybdenum and vanadium, it is found that, on the one hand, these amines are degraded during the process by secondary and primary amines by acid hydrolysis - which results in a loss of selectivity in the extraction of uranium - and that, on the other hand, the AMEX process leads to the formation of interfacial dirt which disturbs the proper operation of the extractors in which it is used and which are responsible for loss of extractant and phase modifier. As for the DAPEX process, it has the drawbacks of using an extractant which is even less selective for uranium than is the mixture of tertiary amines used in the AMEX process, to have a kinetic of slow extraction (unlike the AMEX process which has fast extraction kinetics) and drastically limit the way in which the uranium is extracted from the aqueous solution after leaching with sulfuric acid. The development of new extractants that perform better than those currently used in the AMEX and DAPEX processes is therefore an important issue for the uranium mining industry. In particular, the supply of extractants that are capable of very efficiently extracting uranium from an aqueous solution of phosphoric acid while being more selective towards uranium than is the mixture of Tertiary amines used in the AMEX process and less acid sensitive than these tertiary amines would result in purer uranium concentrates, which would further facilitate the implementation of subsequent refining-conversion processes. these concentrates. In addition, it would be desirable for these extractants to obtain, on the one hand, rapid extraction kinetics, given the residence time of the aqueous phases and the organic phases in the extractors which are only a few minutes, and, on the other hand, complete separation of the organic and aqueous phases in the presence, both during the extraction of the uranium and its desextraction of the organic phase. DISCLOSURE OF THE INVENTION The object of the invention is precisely to propose the use of compounds, which satisfy all these requirements, for the extraction of uranium from aqueous solutions of sulfuric acid and, in particular, from aqueous solutions derived from the leaching of uranium ores by sulfuric acid. The subject of the invention is therefore first of all the use of a compound corresponding to the following general formula (I): ## STR2 ## in which: R 1 and R 2 R2, which may be identical or different, represent a linear or branched, saturated or unsaturated hydrocarbon-based group comprising from 6 to 12 carbon atoms; R3 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 hydrocarbon group, saturated or unsaturated, monocyclic, comprising from 3 to 8 carbon atoms and optionally one or more heteroatoms; while R4 represents a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 2 to 8 carbon atoms, or a monocyclic aromatic group; as an extractant, for extracting uranium (VI) from an aqueous solution of sulfuric acid in which it is present.

According to the invention, the term "hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 6 to 12 carbon atoms", any alkyl, alkenyl or alkynyl group, straight or branched chain, which comprises at least 6 carbon atoms but which does not comprise more than 12 carbon atoms. In an analogous manner, the term "linear or branched, saturated or unsaturated hydrocarbon group comprising from 2 to 8 carbon atoms" means any linear or branched chain alkyl, alkenyl or alkynyl group which comprises at least 2 carbon atoms. carbon but does not include more than 8 carbon atoms. Furthermore, the term "hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 1 to 12 carbon atoms and optionally one or more heteroatoms", any group consisting of a hydrocarbon chain, linear or branched, which comprises at least minus 1 carbon atom but not more than 12 carbon atoms, the chain of which may be saturated or, on the contrary, contain one or more double or triple bonds and the chain of which may be interrupted by one or more heteroatoms or substituted by one or more heteroatoms or by one or more substituents comprising a heteroatom. In this respect, it is specified that the term "heteroatom" means any atom other than carbon and hydrogen, this atom typically being a nitrogen, oxygen or sulfur atom. Furthermore, the term "hydrocarbon group, saturated or unsaturated, monocyclic, comprising from 3 to 8 carbon atoms and optionally one or more heteroatoms", any cyclic hydrocarbon group which comprises only one ring and whose cycle includes minus 3 carbon atoms but not more than 8 carbon atoms, may be saturated or, on the contrary, have one or more double or triple bonds, and may include one or more heteroatoms or may be substituted by one or more heteroatoms or by one or more substituents comprising a heteroatom. Thus, this group can in particular be a cycloalkyl, cycloalkenyl or cycloalkynyl group (for example a cyclopropane, cyclopentane, cyclohexane, cyclopropenyl, cyclopentenyl or cyclohexenyl group), a saturated heterocyclic group (for example, a tetrahydrofuryl, tetrahydro-thiophenyl or pyrrolidinyl group). or piperidinyl), an unsaturated but nonaromatic heterocyclic group (eg, pyrrolinyl or pyridinyl), an aromatic group or a heteroaromatic group. In this regard, it is specified that the term "aromatic group" means any group whose cycle satisfies Hückel's aromaticity rule and therefore has a number of delocalized Tc electrons equal to 4n + 2 (for example, a phenyl or benzyl group), while the term "heteroaromatic group" is intended to mean any aromatic group such as has just been defined but whose ring comprises one or more heteroatoms, this heteroatom or these heteroatoms being typically chosen from among the atoms nitrogen, oxygen, and sulfur (e.g., furanyl, thiophenyl, or pyrrolyl).

According to the invention, in the general formula (I) above, R 1 and R 2, which may be identical or different, advantageously represent a linear or branched alkyl group comprising from 6 to 12 carbon atoms. More preferably, it is preferred that R 1 and R 2 are identical to each other and that they both represent a branched alkyl group comprising from 8 to 10 carbon atoms, the 2-ethylhexyl group being very particularly preferred. Furthermore, in the general formula (I) above, R 3 advantageously represents a linear or branched alkyl group comprising from 1 to 12 carbon atoms, or a monocyclic aromatic group. More preferably, it is preferred that R3 represents a linear or branched alkyl group comprising from 6 to 10 carbon atoms, especially 2-ethylhexyl or n-octyl, or a phenyl group. Finally, in the general formula (I) above, R4 preferably represents a linear or branched alkyl group comprising from 2 to 8 carbon atoms and, more preferably, from 2 to 4 carbon atoms such as an ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl group, the ethyl, isopropyl, n-butyl and isobutyl groups being very particularly preferred. Compounds of general formula (1) above which have these characteristics are in particular: n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, which corresponds to the general formula (1) below. wherein R1 and R2 are each 2-ethylhexyl, R3 is n-octyl, and R4 is n-butyl; isopropyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, which corresponds to the general formula (1) above in which R1 and R2 each represent a 2-ethylhexyl group, R3 represents a group n -octyl while R4 represents an isopropyl group; the isopropyl 1- (N, N-di-2-ethylhexylcarbamoyl) -2-ethylhexylphosphonate, which corresponds to the general formula (1) above in which R1, R2 and R3 each represent a 2-ethylhexyl group while that R4 represents an isopropyl group; isobutyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, which has the general formula (1) above wherein R1 and R2 each represent a 2-ethylhexyl group, R3 represents a group n -octyl while R4 is isobutyl; isobutyl 1- (N, N-di-2-ethylhexylcarbamoyl) -2-ethylhexylphosphonate, which corresponds to the general formula (1) above in which R1, R2 and R3 each represent a 2-ethylhexyl group while R4 is isobutyl; - Isobutyl (N, N-di-n-octylcarbamoyl) nonylphosphonate, which corresponds to the general formula (1) above wherein R1, R2 and R3 each represent an n-octyl group while R4 represents a group isobutyl; n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) -2-ethylhexylphosphonate, which corresponds to the general formula (1) above in which R1, R2 and R3 each represent a 2-ethylhexyl group while R4 is n-butyl; ethyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, which corresponds to the general formula (I) above wherein R 1 and R 2 each represent a 2-ethylhexyl group, R 3 represents a group n -octyl while R4 represents an ethyl group; and n-butyl (N, N-di-n-octylcarbamoyl) nonylphosphonate, which corresponds to the general formula (I) above in which R1, R2 and R3 each represent an n-octyl group while R4 represents n-butyl group.

Of these compounds, n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate and isopropyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate are particularly preferred. The compounds which correspond to the general formula (I) above in which R 1, R 2 and R 4 are as previously defined and R 3 represents a hydrogen atom can in particular be synthesized by a process which comprises: the reaction of a amine of formula HNR1R2 in which R1 and R2 are as previously defined with a compound of formula (II) below: X in which X represents a halogen atom, for example a chlorine or bromine atom, to obtain a compound of formula (III) below: R ', N R2 wherein R1, R2 and X are as previously defined; the reaction of the compound of formula (III) above with a compound of formula HP (O) (OR 4) 2 in which R 4 is as defined above, to obtain a compound of formula (IV) below: R. 1, N R2 wherein R1, R2 and R4 are as previously defined; and treating the compound of formula (IV) above with a strong base. These steps correspond to the steps noted A, B and C in Figure 1 attached in the appendix. As for the compounds which correspond to the general formula (I) above in which R 1, R 2 and R 4 are as previously defined and R 3 represents either a linear or branched, saturated or unsaturated hydrocarbon group comprising from 1 to 12 carbon atoms. carbon and optionally one or more heteroatoms, a hydrocarbon group, saturated or unsaturated, monocyclic, comprising from 3 to 8 carbon atoms and optionally one or more heteroatoms, they can be synthesized by a process which comprises: - the reaction of a amine of formula HNR 1 R 2 in which R 1 and R 2 are as previously defined with a compound of formula (II) below: X in which X represents a halogen atom, for example a chlorine or bromine atom, in order to obtain a compound of formula (III) below: R ', N R2 wherein R1, R2 and X are as previously defined; the reaction of the compound of formula (III) above with a compound of formula HP (O) (OR 4) 2 in which R 4 is as defined above, to obtain a compound of formula (IV) below: R 1, Wherein R ', R2 and R4 are as previously defined; the reaction of the compound of formula (IV) above with a compound of formula R 3 -Y in which Y represents a halogen atom, for example a chlorine or bromine atom, to obtain the compound of formula (V) hereinafter: R, N R2 wherein R ', R2, R3 and R4 are as previously defined; and treating the compound of formula (V) above with a strong base. These steps correspond to the steps noted A, B, D and E in Figure 1 attached in the appendix. Stage A is, for example, carried out in the presence of triethylamine in an organic solvent of the dichloromethane type. Steps B and D are, for example, carried out in the presence of n-butyllithium and 2,2'-bipyridine, or sodium hydride and 2,2'-bipyridine, in an organic solvent of the tetrahydrofuran type, while that steps C and E are, for example, carried out using potash as a strong base, in a solvent composed of water and dimethylformamide. Typically, the compound of general formula (I) above is used to extract uranium (VI) from the aqueous solution of sulfuric acid by liquid-liquid extraction, that is to say by bringing this solution into contact with one another. aqueous solution with an organic phase comprising said compound and then separating said aqueous solution from the organic phase, in which case this organic phase preferably comprises the compound in solution, at a concentration of 0.01 to 1 mol / L, in a diluent organic, advantageously of the aliphatic type such as n-dodecane, hydrogenated tetrapropylene (TPH) or kerosene, for example that marketed by TOTAL under the trade name Isane IP-185. According to the invention, the aqueous solution from which the uranium (VI) is extracted is advantageously an aqueous solution of sulfuric acid which is derived from the leaching of a uranium-containing ore by sulfuric acid, in which case this aqueous solution comprises typically from 0.1 to 10 g / l of uranium, from 0.1 to 2 mol / l of sulfate ions, at an acidity of 0.01 to 0.5 mol / l. The invention also relates to a process for recovering uranium present in an aqueous solution of sulfuric acid resulting from the leaching of a uranium-containing ore by sulfuric acid, which process comprises: a) extraction of uranium from sulfuric acid; uranium, in the VI oxidation state, of the aqueous sulfuric acid solution, by bringing this solution into contact with an organic phase comprising a compound as defined above, and then separating said aqueous solution from said organic phase; and b) the desextraction of the uranium (VI) present in the organic phase obtained after step a), by contacting this organic phase with an aqueous phase comprising a carbonate, for example ammonium or sodium, and then separating said organic phase and said aqueous phase. In this process, the compound is preferably used in solution, at a concentration of 0.01 to 1 mol / L, in an organic diluent, advantageously of the aliphatic type such as n-dodecane, TPH or isane. . The aqueous sulfuric acid solution, which is used in step a), preferably comprises from 0.1 to 10 g / l of uranium and from 0.1 to 2 mol / l of sulfate ions, with an acidity from 0.01 to 0.5 mol / L, while the aqueous phase comprising the carbonate, which is used in step b), preferably comprises from 0.1 to 1 mol / l of carbonate. Furthermore, according to the invention, the volume ratio between the organic phase and the sulfuric acid solution, which are used in step a), and / or the volume ratio between the organic phase and the aqueous phase comprising the carbonate, which are used in step b), are (are) adjusted so that the aqueous phase obtained at the end of step b) has a concentration of uranium which makes it possible to precipitate this uranium later in good conditions, that is to say a uranium concentration typically 40 to 100 g / L. It is possible to favor a concentrated extraction (step a)) or, on the contrary, a concentrated (step b)) extraction or even an intermediate situation, each of these steps contributing to the concentration of uranium up to the target value. . Thus, the volume ratio between the organic phase and the aqueous solution of sulfuric acid may, for example, be less than or equal to 1 and, more preferably, between 0.2 and 1, while the volume ratio between the organic phase and the aqueous phase comprising the carbonate may, for example, be greater than 1, to induce both a concentration of uranium in the organic phase in step a) and a concentration of uranium in aqueous phase at step b). According to the invention, step a) of the process may further comprise washing the organic phase after its separation from the aqueous solution, to eliminate from this phase: either traces of acid likely to have were co-extracted with uranium, in which case this washing is preferably carried out by contacting the organic phase with an aqueous phase consisting solely of water, and then separating said organic phase and said aqueous phase; or, depending on the level of purity required, the traces of unwanted cations such as molybdenum, vanadium or titanium, which may have been co-extracted with the uranium, in which case this washing is preferably carried out by bringing the organic phase into contact with an aqueous phase comprising sulfuric acid or a strong complexing agent for impurities such as an oxalate or a citrate, for example ammonium or sodium, and then separating said organic phase and said aqueous phase .

Other features and advantages of the invention will appear better on reading the additional description which follows, which refers to examples of synthesis of useful compounds according to the invention and demonstration of their properties. Of course, these examples are given as an illustration of the subject of the invention and do not constitute in any way a limitation of this object.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 illustrates the steps of the methods for synthesizing the compounds that are useful according to the invention. FIG. 2 illustrates the isotherm of the extraction of uranium (VI) by a compound that is useful according to the invention. FIG. 3 illustrates the kinetics of the extraction of uranium (VI) by a compound useful according to the invention (curve A) and by Alamine 336 (curve B). FIG. 4 illustrates the evolution of the distribution coefficient of uranium, denoted Du, as a function of the molar concentration of total sulphates (denoted by [total SO4] and expressed in mol / L) of the solution from which this uranium is extracted by a compound which is useful according to the invention, for three different initial concentrations of H + ions of this solution: 0.2 N (curve A), 0.35 N (curve B) and 0.5 N (curve C). DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS EXAMPLE 1 Synthesis of Compounds Useful According to the Invention 1.1 Synthesis of N-Butyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate: 1- (N, N-di) N-butyl 2-ethylhexylcarbamoyl) nonylphosphonate, denoted DEHCNPB, which corresponds to the general formula (I) above in which R 1 - R 2 = 2-ethylhexyl, R 3 = n-octyl, R 4 = n-butyl, is synthesized by carrying out the steps A, B, D and E shown in FIG. 1. Step A: Synthesis of 2-chloro-N, N-di-2-ethylhexylacetamide The mixture is introduced into a three-necked mixture, with stirring and under nitrogen, 7.46 mL (2 eq) of bis (2-ethylhexyl) amine, 50 mL of dichloromethane and 3.5 mL (1 eq) of triethylamine, which is cooled to -30 ° C. with a dry ice bath. /acetone. Then, 2 mL (1 eq) of chloroacetyl chloride is added dropwise and the reaction mixture is left for 3 hours at room temperature. After which, it is poured into 50 ml of distilled water, decanted and extracted with 50 ml of dichloromethane. The dichloromethane phases are washed with 50 ml of distilled water, dried over magnesium sulphate, filtered and evaporated to dryness on a rotary evaporator. The 7.26 g of yellow oil thus obtained are subjected to chromatography on a column of silica gel (80 g - 63-200 μm of particle size) with a dichloromethane / methanol mixture 98/2, v / v, as eluent. . There is thus obtained 7.20 g of 2-chloro-N, N-di-2-ethylhexylacetamide in the form of a pale yellow oil (yield: 92%), of which the characterizations by 1 H and 13 C NMR as well as spectrometry of mass are given below. 1H NMR (400MHz, CDCl3) δ (ppm): 4.08 (2H, s, CH2Cl); 3.23-3.28 (2H, m, NCH 2); 3.20 (2H, d, J = 7.5 Hz, NCH 2); 1.76-1.65 (1H, m, NCH 2 CH); 1.64-1.52 (1H, m, NCH2CH); 1.40-1.15 (16H, m, CH3 (CH2) 3CH (CH2CH3) CH2N); 0.95-0.78 (12H, m, CH 3) - 13 C NMR (100.13 MHz, CDCl3) δ (ppm): 166.64 (C = O); 51.27 (NCH 2); 48.3 (NCH2); 41.17 (CH2Cl); 38.10 (CH); 36.40 (CH); 30.16 (NCH 2 CH (Et) CH 2 (CH 2) 2 CH 3); 30.00 (NCH 2 CH (Et) CH 2 (CH 2) 2 CH 3); 28.40 (NCH 2 CH (Et) -CH 2 CH 2 CH 2 CH 3); 28.24 (NCH 2 CH (Et) CH 2 CH 2 CH 2 CH 3); 23.49 (-CHCH2CH3); 23.35 (-CHCH2CH3); 22.65 (NCH 2 CH (Et) - CH 2 CH 2 CH 2 CH 3); 22.62 (NCH 2 CH (Et) CH 2 CH 2 CH 2 CH 3); 13.67 (-CH 2 CH 2 CH 3); 13.63 (- CH 2 CH 2 CH 3); 10.49 (-CHCH2CH3); 10.20 (-CHCH2CH3) - ESI +: [M + H] = 318, [M + Na] = 340, [2M + Na] = 657 Step B: Synthesis of 1- (N, N-di-2-ethylhexylcarbamoyl) Di-n-butyl methylphosphonate 1 ml (1 eq.) of di-n-butylphosphite, some crystals of 2,2'-bipyridine and 50 ml of tetrahydrofuran, which is introduced under stirring and under nitrogen, are introduced into a tricolor under stirring and under nitrogen. it is cooled to -50 ° C. with a dry ice / acetone bath. 4.6 ml (1.5 eq) of a 1.6 mol / L solution of n-butyllithium in hexane are then added dropwise. A clear red reaction mixture is obtained. 1.95 g (1.25 eq) of 2-chloro-N, N-di-2-ethylhexylacetamide are then added dropwise. A yellow reaction mixture is obtained which is left overnight at room temperature. After which, it is poured into 100 ml of distilled water and acidified by addition of N HCl in an amount sufficient to obtain an acidic pH. The whole is extracted with 2 times 50 ml of ethyl ether. The ethereal phases are washed with twice 50 ml of distilled water and 50 ml of water saturated with NaCl, dried over magnesium sulphate, filtered and evaporated to dryness on a rotary evaporator. The 2.69 g of yellow oil thus obtained are subjected to chromatography on a silica column (125 g - 63-200 .mu.m of particle size) using a cyclohexane / ethyl acetate mixture 8/2, v / v, as an eluent. 1.03 g of di-n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) methylphosphonate are thus obtained in the form of a colorless oil (yield: 44%), the characteristics of which are determined by 1H NMR. , 1-3C and 3I-P as well as by mass spectrometry are given below. 1 H NMR (400 MHz, CDCl 3)? (Ppm): 4.18-4.04 (4H, m, OCH 2); 3.37-3.20 (4H, m, NCH 2); 3.07 (2H, d, J = 22Hz, COCH2P); 1.78-1.51 (6H, m, OCH2CH2, CH); 1.47-1.14 (20H, m, OCH 2 CH 2 CH 2, CH 3 (CH 2) 3 CH (CH 2 CH 3) CH 2 N); 0.99 - 0.82 (18H, m, CH 3) - 13 C NMR (100.13 MHz, CDCl 3) δ (ppm): 165.15 (C = O); 66.15 (d, 2 Pdc = 6.6 Hz); 52.26 (NCH 2); 48.86 (NCH 2), 38.58 (CH); 36.98 (CH); 33.61 (d, 1 Jpc = 133 Hz, CH 2 P); 30.52 and 30.27 (NCH 2 CH (Et) CH 2 (CH 2) 2 CH 3); 30.17 (OCH 2 CH 2 CH 2 CH 3); 28.81 and 28.67 (NCH 2 CH (Et) CH 2 CH 2 CH 2 CH 3), 26.86 (OCH 2 CH 2 CH 2 CH 3); 23.83 and 23.39 (-CHCH2CH3); 23.11 and 23.03 (NCH 2 CH (Et) CH 2 CH 2 CH 2 CH 3); 18.72 (OCH 2 CH 2 CH 2 CH 3); 14.12 and 14.03 (OCH 2 CH 2 CH 2 CH 3); 13.61 (CH 2 CH 2 CH 3); 10.91 and 10.51 (-CHCH2CH3). 31 P NMR (162 MHz, CDCl 3, decoupling 1H) δ (ppm): 22.03 (s, P = 0) ES: (M + H) = 476, [2M + Na] = 973 Step D: Synthesis of 1 (N, N-di-2-ethylhexylcarbamoyl) non-butylphosphonate of di-n-butyl 1.99 g (1 eq.) Of 1- (N, N-di) dihydrate are introduced into a tricolor under stirring and under nitrogen. Di-n-butyl 2-ethylhexylcarbamoyl) methylphosphonate, 50 mL of tetrahydrofuran and some crystals of 2,2'-bipyridine, which is cooled to -50 ° C with a dry ice / acetone bath. Then, bromooctane is added dropwise. A clear red reaction mixture is obtained which is left for 20 minutes at this temperature. 3.92 mL (1.5 eq) of a solution of n-butyllithium at 1.6 mol / L in hexane are then added dropwise. The dry ice / acetone bath is removed and the reaction slowly rises to room temperature. The reaction mixture is then heated overnight at 60 ° C. After which, the reaction mixture is poured into 100 ml of distilled water and acidified by addition of N HCl in an amount sufficient to obtain an acidic pH. It is extracted twice with 50 ml of ethyl ether. The ethereal phases are washed with twice 50 ml of distilled water and 50 ml of water saturated with NaCl, dried over magnesium sulphate, filtered and evaporated to dryness on a rotary evaporator. The 3.45 g of yellow oil thus obtained are subjected to chromatography on a silica column (125 g - 63-200 μm particle size) using a cyclohexane / ethyl acetate mixture 9/1, v / v, as an eluent. 1.1 g of di-n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate are thus obtained in the form of a colorless oil (yield: 44%), whose characterizations by 1-NMR. 1-1.13C and 3I-P as well as by mass spectrometry are given below. 1H NMR (400MHz, CDCl3) δ (Ppm): 0.81-0.93 (m, 21H, CH3); 1.17 - 1.42 (m, 32H, CH 2, OCH 2 CH 2 CH 2 CH 3); 1.59-1.66 (m, 5H, CHCH2N, OCH2CH2CH2CH3); 1.69-1.84 (m, 2H, CHCH2N, C71-115CH2CH (CO) P); 2.02 - 2.13 (m, 1H, C 71-115 CH 2 CH (CO) P); 2.80 - 2.92 (m, 1H, CH 2 N); 2.95 - 3.03 (m, 1H, CH 2 N); 3.14- 3.22 (m, 1H, COCH (Oct) P); 3.43 - 3.55 (m, 1H, CH 2 N); 3.62 - 3.78 (m, 1H, CH 2 N); 3.96 -4.11 (m, 4H, OCH 2 CH 2 CH 2 CH 3) - 13 C NMR (100 MHz, CDCl 3) δ (ppm): 10.4; 10.7; 10.9; 11.0 (CH3); 13.8 (OCH 2 CH 2 CH 2 CH 3); 14.2; 14.3 (CH3); 18.9 (OCH 2 CH 2 CH 2 CH 3); 22.8; 23.2; 23.3; 23.7; 23.9; 24.0; (CH2); 28.2 (C71-115CH2CH (CO) P); 28.8; 28.9; 29.0; 29.1; 29.4; 29.5; 29.8; 29.9; 30.4; 30.5; 30.7; 30.8; 32.0 (CH2); 32.7; 32.8 (d, J = 6.5 Hz, OCH 2 CH 2 CH 2 CH 3); 37.2; 37.3; 37.4; 39.2; 39.3; 39.5; 39.6 (CHCH2N); 41.9; 43.2 (d, J = 131.0 Hz, COCH (Oct) P); 50.0; 50.2; 50.9; 51.1; 51.9; 52.0; 52.6; 52.7 (CH2N); 66.1 (d, J = 6.5 Hz, OCH 2 CH 2); 66.3 (d, J = 6.5 Hz, OCH 2 CH 2); 168.5 (d, J = 5.0 Hz, C = O). 31 P NMR (160 MHz, CDCl 3) δ (ppm): 24.6.

ES +: [M + H] = 588, [M + Na] = 610, [2M + Na] = 1197 Step E: Synthesis of n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate 0.4 g (1 eq.) Of di-n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, 5 ml of distilled water, 5 ml are introduced into a CEM DiscoverTM microwave reactor. of dimethylformamide and 0.23 g (6 eq) of potash, which is heated at 150 ° C for 15 hours. After which, the reaction mixture is poured into 100 ml of distilled water and acidified by addition of N HCl in an amount sufficient to obtain an acidic pH. It is extracted twice with 50 ml of ethyl ether. The ethereal phases are washed twice with 50 ml of distilled water, dried over magnesium sulphate, filtered and evaporated to dryness on a rotary evaporator. The 0.34 g of oil thus obtained are subjected to chromatography on a silica column (17 g - 63-200 .mu.m of particle size) using a dichloromethane / methanol mixture 97/3, v / v, as eluent. 0.14 g of n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate are thus obtained in the form of a colorless oil (yield: 39%), of which the characterizations by 1 H, 13 C NMR and 31P as well as by mass spectrometry are given below. 1 H NMR (400 MHz, CDCl 3) δ (Ppm): 0.83-0.94 (m, 15H, CH 3); 1.20 - 1.41 (m, 30H, CH 2, OCH 2 CH 2 CH 2 CH 3); 1.59 - 1.73 (m, 4H, OCH 2 CH 2 CH 2 CH 3, C 7 H 15 CH 2 CH (CO) P); 1.85 - 2.06 (m, 2H, CHCH2N); 3.07-3.21 (m, 3H, CH2N, COCH (Oct) P); 3.24 - 3.50 (m, 2H, CH 2 N); 3.98 -4.10 (m, 2H, OCH 2 CH 2 CH 2 CH 3); 9.34 (s, 1H, OH). 13 C NMR (100 MHz, CDO 3) δ (Ppm): 10.5; 10.8; 10.9; (CH3); 13.7 (OCH 2 CH 2 CH 2 CH 3); 14.1; 14.2 (CH3); 18.8 (OCH 2 CH 2 CH 2 CH 3); 22.8; 23.2; 23.3; 23.7; 23.8; 23.9; (CH2); 28.2 (C7H15CH2CH (CO) P); 28.7; 28.9; 29.4; 29.5; 29.8; 29.9; 30.4; 30.5; 30.7; 32.0 (CH2); 32.6 (d, J = 6.5 Hz, OCH 2 CH 2 CH 2 CH 3); 37.2; 37.3; 39.0; 39.2; 39.4 (CHCH2N); 41.9; 43.2 (d, J = 134.0 Hz, COCH (Oct) P); 49.9; 50.5; 50.7; 51.2; 52.0; 52.1; 52.7; 52.8 (CH2N); 65.6 (d, J = 6.5 Hz, OCH 2 CH 2); 169.3 (d, J = 5.0 Hz, C = O). 31 P NMR (160 MHz, CDCl 3) δ (ppm): 26.8. ES: MH = 530, [2M-H] = 1061 1.2 Synthesis of Other Useful Compounds According to the Invention The following compounds: 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate isopropyl, denoted DEHCNPiP, which corresponds to the general formula (I) above in which R1 = R2 = 2-ethylhexyl, R3 = n-octyl and R4 = isopropyl; Isopropyl 1- (N, N-di-2-ethylhexylcarbamoyl) -2-ethylhexylphosphonate, denoted DEHCEHPiP, which corresponds to the general formula (1) above in which R1 = R2 = R3 = 2-ethylhexyl, and R4 = isopropyl; Isobutyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, denoted DEHCNPiB, which corresponds to the general formula (1) above in which R1 = R2 = 2-ethylhexyl, R3 = n- octyl and R4 = isobutyl; Isobutyl 1- (N, N-di-2-ethylhexylcarbamoyl) -2-ethylhexylphosphonate, denoted DEHCEHPiB, which corresponds to the general formula (I) above in which R1 = R2 = R3 = 2-ethylhexyl and R4; = isobutyl; Isobutyl 1- (N, N-di-n-octylcarbamoyl) nonylphosphonate, noted DOCNPiB, which has the general formula (1) above wherein R1 = R2 = R3 = n-octyl and R4 = isobutyl; N-Butyl 1- (N, N-di-2-ethylhexylcarbamoyl) -2-ethylhexylphosphonate, denoted DEHCEHPB, which corresponds to the general formula (1) above in which R1 = R2 = R3 = 2-ethylhexyl and R4 = n-butyl; Ethyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, denoted DEHCNPE, which corresponds to the general formula (1) above in which R1 = R2 = 2-ethylhexyl, R3 = n-octyl and R4 = ethyl; and n-butyl 1- (N, N-di-n-octylcarbamoyl) nonylphosphonate, noted DOCNPB, which corresponds to the general formula (1) above in which R1 = R2 = R3 = n-octyl and R4 = n-butyl; are synthesized by carrying out the steps A, B, D and E shown in FIG. 1 and using, for each of these steps, an operating protocol similar to that described in point 1.1 above.

Also synthesized are: ethyl 1- (N, N-di-2-ethylhexylcarbamoyl) methylphosphonate, denoted DEHCMPE, which corresponds to the general formula (1) above in which R1 = R2 = 2-ethylhexyl, R3 = H, R4 = ethyl; and - n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) methylphosphonate, denoted DEHCMPB, which corresponds to the general formula (1) above in which RI- = R2 = 2-ethylhexyl, R3 = H, R5 = n-butyl; implementing steps A, B and C shown in FIG. 1 and using, for steps A and B, an operating protocol similar to that described in point 1.1 above for these steps, and, for the step C, an operating procedure similar to that described in point 1.1 above for step E. EXAMPLE II: PROPERTIES OF COMPOUNDS USEFUL IN ACCORDANCE WITH THE INVENTION 11.1 - Selectivity of the extraction of uranium (VI) from a solution aqueous sulfuric leaching by some of the compounds useful according to the invention: The ability of the compounds useful in the invention to selectively extract uranium (VI) from an aqueous solution of sulfuric acid was evaluated by extraction which is carried out in tubes, using: - as organic phases, phases comprising one of the following compounds: DEHCNPiP, DEHCEHPiP, DEHCNPiB, DEHCEHPiB, DEHCEHPB and DEHCNPB, as an extractant, at a concentration of 0.05 mol / L in TPH, the solubilization of these compounds in the TPH having been previously carried out without using phase modifiers or heating; and - as aqueous phases, aliquots of an aqueous solution resulting from the leaching of a mixture of uranium ores from Canada and Niger by sulfuric acid. This mixture of ores makes it possible to dispose, in the lixiviation solution, all the metallic elements likely to be present in leaching solutions by sulfuric acid, namely: uranium (VI), arsenic, molybdenum, tungsten , iron, vanadium, titanium and zirconium.

The composition in metallic elements of this aqueous phase is presented in Table 1 below. Its content of total sulphates (sulfate ions + hydrogen sulphate ions) is 0.40 mol / L while its H + ion concentration is 0.13 mol / L. Its redox potential, which is 680 mV / ENH, indicates that the iron it contains is predominantly at the oxidation state II while the vanadium is at the oxidation degree IV. Table I Elements Metal concentrations (mg / L) U 3 320 As 1 780 Mo 420 Fe 3 290 V 208 Ti 67 Zr 33 Each of the organic phases was brought into contact with an aqueous phase in an organic phase / aqueous phase volume ratio, denoted 0 / A, of 1, and these phases were maintained for 30 minutes at room temperature (23-24 ° C), in an incubator that imparts horizontal reciprocating motion to the extraction tubes. After that, the organic and aqueous phases were separated by gravity settling in less than 2 minutes. Concentrations of metallic elements were measured in the aqueous phases before and after extraction by plasma atomic emission spectrometry (ICP-AES). Their concentrations in the organic phases were either measured either by X-ray fluorescence or by analytical stripping with ammonium oxalate followed by ammonium carbonate. Table II below shows, for each compound tested, the distribution coefficients of uranium, arsenic, molybdenum, iron, vanadium and titanium respectively denoted Du, DAs, DM °, DFe. DV and DTI, having been obtained from the concentrations thus measured.

Also given in this table are the distribution coefficients obtained for these same elements, under the same experimental conditions, but with an organic phase comprising Alamine 336, which is currently the most widely used extractant in the treatment plants. of uranium ores at a concentration of 0.1 mol / L in TPH plus 2% isodecanol. Table II Distribution Coefficients of Dm, DFe DAs DV DTi Extractants DEHCNPiP 0.02 0.015 - 0.01 <10-3 0.015 DEHCEHPiP 7.6 0.06 0.015 - 3.10-3 G 10-3 G 10-3 DEHCNPiB 14 0.015 0.015 - 3.10-3 <10-3 0.033 DEHCEHPiB 14 0.02 0.02 - 3.10-3 <10-3 DEHCEHPB 0.04 0.015 - 5.10-3 <10-3 DEHCNPB 34 0.1 0.03 < 0.01-0.01 0.1 Alanine 336 278 3.10-3 0.04 <0.01 <i0 This table shows that the compounds useful according to the invention have an ability to extract uranium (VI) from an aqueous solution of sulfuric acid and this, with a higher selectivity than that of Alamine 336, especially with respect to molybdenum. The steric hindrance, provided by the branching of the alkyl group on the phosphonate (R4) or on the spacer between the amide function and the phosphonate (R3), causes a slight decrease in the distribution coefficient of the uranium compared to that DEHCNPB compound, but further enhances the selectivity of compounds for uranium to molybdenum and titanium, which are the main potentially coextracted impurities of an aqueous solution of sulfuric acid from the leaching of a uranium ore by sulfuric acid. A separation factor of the order of 1 500 is thus obtained for U / Mo with the compound DEHCNPiP, whereas it is only 19 in the case of Alamine 336 at 0.1 mol / L. The selectivity of the compounds useful according to the invention for uranium is very good with respect to vanadium and titanium; for arsenic, it is better than with Alamine 336. The selectivity of this family of extractants for uranium to iron is less good than for Alamine 336, with which iron does not. is not extracted at all, but it remains very high. 11.2 - Isotherm of the extraction of uranium (VI) with a compound useful according to the invention: In order to determine the isotherm of the extraction of uranium (VI) by a compound according to the invention, tests Extraction methods were performed using: - as organic phases, phases comprising the compound DEHCNPB as an extractant at a concentration of 0.05 mol / L in TPH; and as aqueous phases, aqueous solutions of sulfuric acid comprising 1.9 g / l of uranium (VI), 0.5 mol / l of total sulphates and having a free acidity of 0.2 N, the latter two parameters. being representative of the concentrations of total sulphates and free acidity conventionally presented by solutions resulting from the leaching of uranium ores by sulfuric acid; and gradually lowering, from one test to another, the volume ratio 0 / A of 2 to 0.067, so as to approach the uranium saturation of the organic phase. These tests were carried out in stirred beakers at a temperature of 23-24 ° C., with contact times between the organic phases and the aqueous phases of 30 minutes. After separation of the organic and aqueous phases, the concentrations of uranium and other metallic elements were measured: - in aqueous phases, by ICP-AES or, for very low uranium concentrations by plasma torch mass spectrometry (ICP-MS); in the organic phases, by X-ray fluorescence; and in aqueous solutions containing 0.5 mol / L of ammonium carbonate and in which the uranium and other metallic elements have been extracted from the organic phases by ICP-AES.

The results of these tests are given in Table III below. Table III Volume Ratios 0 / A 2 1 0.33 0.20 0.1 0.067 [U] aqueous phase 0.018 0.83 538 818 (mg / L) [U] organic phase 954 1 908 3 789 4 005 3,720,400 (mg / L) Of 53,000 2,299 7,1 4,0 2,6 2,4 They are also illustrated in Figure 2, in the form of a curve that shows the relationship to the equilibrium between the concentration of uranium in the organic phase and the concentration of this same element in the aqueous phase. The slope of the tangent of the curve at any point gives the distribution coefficient of uranium in the absence of other metallic elements. Table III and Figure 2 show, on the one hand, that the distribution coefficient of uranium, denoted Du, which is very high for the low concentrations of uranium in the aqueous phase (almost vertical slope of the tangent of the curve), falls sharply as the concentration of uranium increases in the aqueous phase, and, secondly, that we obtain a uranium saturation of the organic phase of the order of 4 g d uranium / L. 11.3 - Influence of the acidity and the concentration of total sulphates of the aqueous solution of sulfuric acid on the extraction of uranium (VI) by a useful compound according to the invention: The solutions resulting from the leaching of ores uranifers with sulfuric acid have a free acidity generally between 0.05 and 0.5 N and a concentration of total sulphates (sulfate ions + hydrogen sulfate ions) of between 0.1 and 2 mol / L, or even beyond, depending on the amount of sulfuric acid consumed to achieve this leaching and the amount of calcium leached since during this leaching occurs a partial reprecipitation of calcium sulfate dihydrate (or gypsum) whose solubility is 2.4 g / L in the water. Knowing that, during the extraction of uranium (VI), this uranium is extracted in the form of UO22 + ions and that H + ions are released, it seemed interesting to know what is the influence of uranium. acidity and the total sulphate concentration of the aqueous solution from which uranium (VI) is to be extracted on this extraction. To do this, extraction tests were carried out in stirred tubes using: as organic phases, phases comprising the compound DEHCNPB as an extractant at a concentration of 0.05 mol / L in TPH; and as aqueous phases, solutions comprising 3.7 g / L of uranium (VI) and having total sulphate concentrations ranging from 0.3 to 1 mol / L (by addition of ammonium sulphate) and concentrations of H + ions equal to 0.2 N, 0.35 N and 0.5 N. The results of these tests are illustrated in Figure 4 in which the curves A, B and C represent the evolution of the distribution coefficient of the uranium, denoted by Du, for a concentration of total sulphates ranging from 0.3 to 1 mol / L and for a concentration of H + ions of 0.2 N (curve A), 0.35 N (curve B) and 0.5 N (curve C). As this figure shows, there is a decrease in the distribution coefficient of uranium when the concentration of total sulphates and acidity increase, but this decrease is slight, which allows to maintain a good extraction efficiency while offering flexibility of use depending on the type of uranium ore processed or, possibly, for a given uranium ore, depending on the evolution over time of the leaching conditions.

The distribution coefficient of uranium decreases with increasing acidity, which was expected given the extraction mechanism that releases two protons per mole of uranium extracted. At constant acidity, the increase in the concentration of sulphate ions also has a negative effect on the extraction of uranium, but less marked.

Claims (22)

REVENDICATIONS1. Use of a compound corresponding to the following general formula (I): embedded image in which: R 1 and R 2, which may be identical or different, represent a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 6 to 12 carbon atoms; R3 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 hydrocarbon group, saturated or unsaturated, monocyclic, comprising from 3 to 8 carbon atoms and optionally one or more heteroatoms; while R4 represents a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 2 to 8 carbon atoms, or a monocyclic aromatic group; as an extractant, for extracting uranium (VI) from an aqueous solution of sulfuric acid in which it is present. 2. Use according to claim 1, wherein R1 and R2, identical or different, represent a linear or branched alkyl group comprising from 6 to 12 carbon atoms. 3. Use according to claim 2, wherein R1 and R2 are identical to each other and both represent a branched alkyl group comprising from 8 to 10 carbon atoms. The use of claim 3, wherein R1 and R2 are both 2-ethylhexyl. 5. Use according to any one of claims 1 to 4, wherein R3 represents a linear or branched alkyl group having 1 to 12 carbon atoms, or a monocyclic aromatic group. 6. Use according to claim 5, wherein R3 represents a linear or branched alkyl group comprising from 6 to 10 carbon atoms, preferably 2-ethylhexyl or n-octyl. 7. Use according to any one of claims 1 to 5, wherein R4 represents a linear or branched alkyl group comprising from 2 to 8 carbon atoms. 8. Use according to claim 7, wherein R4 represents a linear or branched alkyl group comprising from 2 to 4 carbon atoms. Use according to claim 8, wherein R4 is ethyl, isopropyl, n-butyl or isobutyl. 10. Use according to any one of claims 1 to 9, wherein the compound is chosen from: - 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate of n-butyl, which corresponds to the general formula ( I) wherein R1 and R2 are each 2-ethylhexyl, R3 is n-octyl, and R4 is n-butyl; isopropyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, 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 R4 represents an isopropyl group; isopropyl 1- (N, N-di-2-ethylhexylcarbamoyl) -2-ethylhexylphosphonate, which has the general formula (1) in which R1, R2 and R3 each represent a 2-ethylhexyl group while R4 represents an isopropyl group; isobutyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, which has the general formula (1) in which R 1 and R 2 each represent a 2-ethylhexyl group, R 3 represents an n-octyl group while R4 is isobutyl; isobutyl 1- (N, N-di-2-ethylhexylcarbamoyl) -2-ethylhexylphosphonate, which has the general formula (1) in which R1, R2 and R3 each represent a 2-ethylhexyl group while R4 represents an isobutyl group; isobutyl 1- (N, N-di-n-octylcarbamoyl) nonylphosphonate, which corresponds to the general formula (1) in which R1, R2 and R3 each represent an n-octyl group while R4 represents an isobutyl group; ; n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) -2-ethylhexylphosphonate, which corresponds to the general formula (1) in which R1, R2 and R3 each represent a 2-ethylhexyl group while R4 represents an n-butyl group; ethyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate, which has the general formula (1) wherein R 1 and R 2 each represent a 2-ethylhexyl group, R 3 represents an n-octyl group, and R4 represents an ethyl group; and - n-butyl 1- (N, N-di-n-octylcarbamoyl) nonylphosphonate, which has the general formula (1) in which R1, R2 and R3 each represent an n-octyl group while R4 represents a n-butyl group. 11. Use according to claim 10, which is n-butyl 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate or 1- (N, N-di-2-ethylhexylcarbamoyl) nonylphosphonate. isopropyle.30 Use according to any one of claims 1 to 11, wherein the compound is used to extract uranium (VI) from the aqueous sulfuric acid solution by liquid-liquid extraction. 13. Use according to any one of claims 1 to 12, wherein the compound is used in solution, at a concentration of 0.01 to 1 mol / L, in an organic diluent. 14. Use according to any one of claims 1 to 13, wherein the aqueous solution of sulfuric acid is derived from the leaching of a uranium ore by sulfuric acid. 15. Use according to claim 14, wherein the aqueous solution of sulfuric acid comprises from 0.1 to 10 g / l of uranium (VI) and from 0.1 to 2 mol / l of sulfate ions, at an acidity. from 0.01 to 0.5 mol / L. 16. A process for recovering uranium from an aqueous solution of sulfuric acid from the leaching of a uranium-containing ore by sulfuric acid, which process comprises: a) extracting the uranium, at the oxidation state VI, of the aqueous solution of sulfuric acid, by bringing this solution into contact with an organic phase comprising a compound as defined in any one of claims 1 to 11, and then separating said aqueous solution and said organic phase; and b) the desextraction of the uranium (VI) present in the organic phase obtained at the end of step a), by bringing this organic phase into contact with an aqueous phase comprising a carbonate, and then separating said phase organic and of said aqueous phase. 17. The method of claim 16, wherein the compound is used in solution, at a concentration of 0.01 to 1 mol / L, in an organic diluent. 18. A process according to claim 16 or claim 17, wherein the aqueous solution of sulfuric acid comprises from 0.1 to 10 g / L of uranium and from 0.1 to 2 mol / L of sulfate ions, an acidity of 0.01 to 0.5 mol / L. 19. A process according to any one of claims 16 to 18, wherein the aqueous phase comprising the carbonate comprises from 0.1 to 1 mol / L of carbonate. 20. Process according to any one of claims 16 to 19, wherein the volume ratio between the organic phase and the sulfuric acid solution used in step a) and / or the volume ratio between the organic phase and the phase. The aqueous solution comprising the carbonate used in step b) is (are) adjusted so that the aqueous phase obtained at the end of step b) has a uranium concentration of 40 to 100 g / l. 21. The method of claim 20, wherein the volume ratio between the organic phase and the aqueous sulfuric acid solution used in step a) is less than or equal to 1, while the volume ratio between the organic phase and the aqueous phase comprising the carbonate used in step b) is greater than 1. 22. The method of any one of claims 16 to 21, wherein step a) further comprises washing the organic phase after separating it from the aqueous solution.