Patent Number: 
Section: claims

1. Process for separating, in an aqueous medium, at least one actinide element from one or more lanthanide elements by using, in combination, at least one molecule which sequesters the at least one actinide element to be separated and membrane filtration, the process successively comprising:a) bringing the at least one molecule which sequesters the at least one actinide element in contact with the aqueous medium, the at least one molecule not being retained in a non-complexed state by the membrane and being capable of forming a complex with the at least one actinide element to be separated, the complex comprising the at least one actinide element and at least two of the at least one sequestering molecules, which complex is capable of being retained by the membrane; andb) passing the aqueous medium over the membrane in order to form a permeate on one side, the permeate comprising an aqueous effluent depleted of the at least one actinide element, and a retentate comprising the complex,wherein the at least one sequestering molecule is a monoaromatic compound carrying at least two sequestering functions on its ring, which are selected from —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group, andwherein the monoaromatic compound corresponds to the following formula:wherein:A, B, D independently represent a carbon atom or a nitrogen atom;X1 and X2 independently represent a —COOH, —CONHOH, —SO3H, —PO3H2 or —P(O)OHQ group, with Q representing an alkyl, hydroxyalkyl or oxoalkyl group; andZ1, Z2 and Z3 are selected independently from the group consisting of —H, —F, —Cl, —Br, —I, —OH, —OR, —SR, —NHR, —CHO, —COOR, —CONR1R2, —NR1R2, —NR1—NR2R3, —R′—SO2R, —SO3R, when A, B and/or D represents a carbon atom, with:R, R1, R2, R3 independently representing H, an alkyl or hydroxyalkyl group comprising from 1 to 6 carbon atoms; andR′ representing an alkene or hydroxyalkene group comprising from 1 to 6 carbon atoms. 2. Process according to claim 1, wherein the at least one actinide element to be separated is americium. 3. Process according to claim 1, wherein step b) is carried out by ultrafiltration or nanofiltration. 4. Process according to claim 1, wherein the contacting step a) is carried out with a predetermined pH. 5. The process of claim 1,wherein the monoaromatic compound corresponds to the following formula: 6. Process according to claim 5, wherein the at least one actinide element to be separated is americium. 7. Process according to claim 5, wherein step b) is carried out by ultrafiltration or nanofiltration. 8. Process according to claim 5, wherein the contacting step a) is carried out with a predetermined pH. 9. Process for separating, in an aqueous medium, at least one actinide element from one or more lanthanide elements by using, in combination, at least one molecule which sequesters the at least one actinide element to be separated and membrane filtration, the process successively comprising:a) bringing the at least one molecule which sequesters the at least one actinide element in contact with the aqueous medium, the at least one molecule not being retained in a non-complexed state by the membrane and being capable of forming a complex with the at least one actinide element to be separated, the complex comprising the at least one actinide element and at least two of the at least one sequestering molecules, which complex is capable of being retained by the membrane; andb) passing the aqueous medium over the membrane in order to form a permeate on one side, the permeate comprising an aqueous effluent depleted of the at least one actinide element, and a retentate comprising the complex,wherein the at least one sequestering molecule is a monoaromatic compound carrying at least two sequestering functions on its ring, which are selected from —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group, andwherein the monoaromatic compound corresponds to one of the following formulae:wherein:X1 and X2 independently represent a —COOH, —CONHOH, —SO3H, —PO3H2 or —P(O)OHQ group, with Q representing an alkyl, hydroxyalkyl or oxoalkyl group; andZ1, Z2 and Z3 are selected independently from the group consisting of —H, —F, —Cl, —Br, —I, —OH, —OR, —SR, —NHR, —CHO, —COOR, —CONR1R2, —NR1R2, —NR1—NR2R3, —R′—SO2R, —SO3R, with:R, R1, R2, R3 independently representing H, an alkyl or hydroxyalkyl group comprising from 1 to 6 carbon atoms; andR′ representing an alkene or hydroxyalkene group comprising from 1 to 6 carbon atoms. 10. Process according to claim 9, wherein the at least one actinide element to be separated is americium. 11. Process according to claim 9, wherein step b) is carried out by ultrafiltration or nanofiltration. 12. Process according to claim 9, wherein the contacting step a) is carried out with a predetermined pH. 13. Process for separating, in an aqueous medium, at least one actinide element from one or more lanthanide elements by using, in combination, at least one molecule which sequesters the at least one actinide element to be separated and membrane filtration, the process successively comprising:a) bringing the at least one molecule which sequesters the at least one actinide element in contact with the aqueous medium, the at least one molecule not being retained in a non-complexed state by the membrane and being capable of forming a complex with the at least one actinide element to be separated, the complex comprising the at least one actinide element and at least two of the at least one sequestering molecules, which complex is capable of being retained by the membrane; andb) passing the aqueous medium over the membrane in order to form a permeate on one side, the permeate comprising an aqueous effluent depleted of the at least one actinide element, and a retentate comprising the complex,wherein the at least one sequestering molecule is a monoaromatic compound carrying at least two sequestering functions on its ring, which are selected from —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group, andwherein the monoaromatic compound is a 5-membered ring. 14. Process according to claim 13, wherein the monoaromatic compound comprises one or more oxygen, sulphur and/or nitrogen atoms in its ring. 15. Process according to claim 13, wherein the monoaromatic compound comprises one or more nitrogen atoms in its ring. 16. Process according to claim 13, wherein the at least one actinide element to be separated is americium. 17. Process according to claim 13, wherein step b) is carried out by ultrafiltration or nanofiltration. 18. Process according to claim 13, wherein the contacting step a) is carried out with a predetermined pH. 19. Process for separating, in an aqueous medium, at least one actinide element from one or more lanthanide elements by using, in combination, at least one molecule which sequesters the at least one actinide element to be separated and membrane filtration, the process successively comprising:a) bringing the at least one molecule which sequesters the at least one actinide element in contact with the aqueous medium, the at least one molecule not being retained in a non-complexed state by the membrane and being capable of forming a complex with the at least one actinide element to be separated, the complex comprising the at least one actinide element and at least two of the at least one sequestering molecules, which complex is capable of being retained by the membrane; andb) passing the aqueous medium over the membrane in order to form a permeate on one side, the permeate comprising an aqueous effluent depleted of the at least one actinide element, and a retentate comprising the complex,wherein the at least one sequestering molecule is a monoaromatic compound carrying at least two sequestering functions on its ring, which are selected from —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group, andwherein the monoaromatic compound corresponds to the following formula:wherein:A represents a sulphur or oxygen atom;X1 and X2 are selected independently from the group consisting of —COOH, —CONHOH, —SO3H, —PO3H2, —P(O)OHQ with Q representing an alkyl, hydroxyalkyl or oxoalkyl group; andZ1 and Z2 are selected independently from the group consisting of —H, —F, —Cl, —Br, —I, —OH, —OR, —SR, —NHR, —CHO, —COOR, —CONR1R2, —NR1R2, —NR1—NR2R3, —R′—SO2R, —SO3R with:R, R1, R2, R3 independently representing H, an alkyl or hydroxyalkyl group comprising from 1 to 6 carbon atoms; andR′ representing an alkene or hydroxyalkene group comprising from 1 to 6 carbon atoms. 20. Process according to claim 19, wherein the at least one actinide element to be separated is americium. 21. Process according to claim 19, wherein step b) is carried out by ultrafiltration or nanofiltration. 22. Process according to claim 19, wherein the contacting step a) is carried out with a predetermined pH.