CYCLIC AMINE MONOAMIDES FOR EXTRACTING URANIUM(VI) AND PLUTONIUM(IV) AND FOR SEPARATING THEM WITHOUT REDUCING PLUTONIUM(IV)

Abstract

Uses of cyclic amine monoamides for extracting uranium(VI) and/or plutonium(IV) from an acidic aqueous solution, as well as for totally or partially separating uranium(VI) from plutonium(IV) from an acidic aqueous solution. A method for treating an aqueous solution resulting from the dissolution of spent nuclear fuel in nitric acid to extract, separate and decontaminate uranium(VI) and plutonium(IV) in a single cycle and without resorting to any operation of reducing plutonium(IV), and wherein a cyclic amine monoamide or a mixture of cyclic amine monoamides is used as extractant. The cyclic amine monoamides have formula (I):

##STR00001##

Claims

1. A method for extracting uranium(VI) and/or plutonium(IV) from an acidic aqueous solution with a PH of less than 0, comprising contacting the acidic aqueous solution with an organic solution comprising a monoamide or a mixture of monoamides in an organic diluent, and then separating the aqueous and organic solutions from each other, wherein the monoamide(s) is (are) of formula (I): ##STR00017## wherein: n=1, 2 or 3; R.sup.1 is a straight or branched chain alkyl group comprising from 4 to 12 carbon atoms; and R.sup.2 is a straight or branched chain alkyl or alkoxy group, the chain of which is optionally interrupted one or more times by an oxygen atom and the total number of carbon atoms and, if applicable, of oxygen atoms is between 3 and 10.

2. (canceled)

3. The method of claim 1, wherein the organic solution comprises from 1 mol/L to 2 mol/L of the monoamide or of the mixture of monoamides.

4. The method of claim 1, wherein the acidic aqueous solution with a pH of less than 0 is an aqueous solution resulting from the dissolution of a spent nuclear fuel in nitric acid.

5. A method for totally or partially separating uranium(VI) from plutonium(IV) from an acidic aqueous solution with a pH of less than 0, comprising: a) a co-extraction of uranium(VI) and plutonium(IV) from the acidic aqueous solution with a pH of less than 0, the co-extraction comprising at least one contacting of the aqueous solution with an organic solution S1 comprising a monoamide or a mixture of monoamides in an organic diluent, followed by a separation of the aqueous and organic solutions from each other, the monoamide(s) being of formula (I): ##STR00018## wherein: n=1, 2 or 3; R.sup.1 is a straight or branched chain alkyl group comprising from 4 to 12 carbon atoms; and R.sup.2 is a straight or branched chain alkyl or alkoxy group, the chain of which is optionally interrupted one or more times by an oxygen atom and the total number of carbon and, if applicable, oxygen atoms is between 3 and 10; b) a stripping of plutonium, in the +IV oxidation state, and of a fraction of the uranium(VI) from the organic solution issued from a), the stripping comprising at least one contacting of the organic solution with an acidic aqueous solution with a pH greater than 0, followed by a separation of the organic and aqueous solutions from each other; and c) a re-extraction of all or part of the uranium(VI) fraction present in the aqueous solution issued from b), the re-extraction comprising at least one contacting of the aqueous solution with an organic solution S2 comprising the monoamide or the mixture of monoamides in the organic diluent, followed by a separation of the aqueous and organic solutions from each other; whereby an aqueous solution comprising either plutonium(IV) without uranium(VI), or a mixture of plutonium(IV) and uranium(VI), and an organic solution comprising uranium(VI) without plutonium(IV) are obtained.

6. The method of claim 5, wherein the organic solutions S1 and S2 comprise from 1 mol/L to 2 mol/L of the monoamide or of the mixture of monoamides.

7. The method of claim 5, wherein the acidic aqueous solution with a pH less than 0 is an aqueous solution resulting from the dissolution of a spent nuclear fuel in nitric acid, while the acidic aqueous solution with a pH greater than 0 is a solution comprising from 0.1 mol/L to 0.5 mol/L of nitric acid.

8. The method of claim 5, wherein n=2 or 3.

9. The method of claim 5, wherein: R.sup.1 is a straight or branched chain alkyl group comprising from 6 to 10 carbon atoms; and/or R.sup.2 is a straight or branched chain alkyl group comprising from 4 to 10 carbon atoms.

10. The method of claim 9, wherein the monoamide is: N-(2-heptylpyrrolidinyl)-(2-ethyl)hexanamide, N-(2-hexylpiperidinyl)-(2-ethyl)hexanamide, N-(3-hexylpiperidinyl)-(2-ethyl)hexanamide, N-(4-hexylpiperidinyl)-(2-ethyl)hexanamide, or N-(3-hexylpiperidinyl)-(2-propyl)pentanamide.

11. A method for treating in one cycle an aqueous solution resulting from a dissolution of a spent nuclear fuel in nitric acid, the aqueous solution comprising uranium(VI), plutonium(IV), americium(III), curium(III) and fission and activation products including ruthenium and technetium, the cycle comprising: a) a co-extraction of uranium(VI) and plutonium(IV) from the aqueous solution, the co-extraction comprising at least one contacting, in an extractor, of the aqueous solution with an organic solution S1 comprising a monoamide or a mixture of monoamides in an organic diluent, followed by a separation of the aqueous and organic solutions from each other, the monoamide(s) being of formula (I): ##STR00019## wherein: n=1, 2 or 3; R.sup.1 is a straight or branched chain alkyl group comprising from 4 to 12 carbon atoms; and R.sup.2 is a straight or branched chain alkyl or alkoxy group, the chain of which is optionally interrupted one or more times by an oxygen atom and the total number of carbon atoms and, if applicable, of oxygen atoms is between 3 and 10; b) a decontamination of the organic solution issued from a) with respect to americium(III), curium(III) and fission and activation products, the decontamination comprising at least one contacting, in an extractor, of the organic solution with an aqueous solution comprising from 0.5 mol/L to 6 mol/L of nitric acid, followed by a separation of the organic and aqueous solutions from each other; c) a partitioning of the uranium(VI) and plutonium(IV) present in the organic solution issued from b) into an aqueous solution comprising either plutonium(IV) without uranium(VI), or a mixture of plutonium(IV) and uranium(VI), and an organic solution comprising uranium(VI) without plutonium(IV), the partitioning comprising: c.sub.1) a stripping of plutonium, in the +IV oxidation state, and of a fraction of the uranium(VI) from the organic solution issued from b), the stripping comprising at least one contacting, in an extractor, of the organic solution with an aqueous solution comprising from 0.1 mol/L to 0.5 mol/L of nitric acid, followed by a separation of the organic and aqueous solutions from each other; c.sub.2) a re-extraction of all or part of the uranium(VI) fraction present in the aqueous solution issued from c.sub.1), the re-extraction comprising at least one contacting, in an extractor, of the aqueous solution with an organic solution S2 comprising the monoamide or the mixture of monoamides in the organic diluent, followed by a separation of the aqueous and organic solutions from each other; d) a decontamination of the organic solution issued from c.sub.1) with respect to technetium, the decontamination comprising: d.sub.1) a stripping of technetium, in the +IV oxidation state, from the organic solution issued from c.sub.1), the stripping comprising at least one contacting, in an extractor, of the organic solution with an aqueous solution comprising from 0.1 mol/L to 3 mol/L of nitric acid and at least one reducing agent capable of reducing technetium from the +VII oxidation state to the +IV oxidation state, followed by a separation of the organic and aqueous solutions from each other; d.sub.2) a re-extraction of the uranium(VI) fraction present in the aqueous solution issued from d.sub.1), the re-extraction comprising at least one contacting, in an extractor, of the aqueous solution with an organic solution S3 comprising the monoamide or the mixture of monoamides in the organic diluent, followed by a separation of the aqueous and organic solutions from each other; e) a stripping of uranium(VI) from the organic solution issued from d.sub.1), the stripping comprising at least one contacting, in an extractor, of the organic solution with an aqueous solution comprising at most 0.05 mol/L of nitric acid, followed by a separation of the organic and aqueous solutions from each other; and f) optionally, a regeneration of the organic solution issued from e); whereby a first and a second aqueous solution decontaminated with respect americium(III), curium(III) and fission and activation products are obtained, the first aqueous solution comprising either plutonium(IV) without uranium(VI), or a mixture of plutonium(IV) and uranium(VI), and the second aqueous solution comprising uranium(VI) without plutonium(IV).

12. The method of claim 11, wherein the organic solutions S1, S2 and S3 comprise from 1 mol/L to 2 mol/L of the monoamide or mixture of monoamides.

13. The method of claim 11, wherein the aqueous solution of b) comprises from 4 mol/L to 6 mol/L of nitric acid before being contacted with the organic solution.

14. The method of claim 11, wherein the contacting of the organic and aqueous solutions in the extractor of c.sub.1) comprises circulating the organic and aqueous solutions with a ratio of a flow rate of the organic solution to a flow rate of the aqueous solution greater than 1.

15. The method of claim 11, wherein the reducing agent is uranous nitrate, hydrazinium nitrate, hydroxylammonium nitrate, acetaldoxime, hydroxyiminoalkanoic acid, or a mixture thereof.

16. The method of claim 11, wherein: the extractor of d.sub.1) is heated to a temperature of 30 C. to 40 C. and/or the extractor of e) is heated to a temperature of 40 C. to 50 C.

17. The method of claim 11, wherein the contacting of the organic and aqueous solutions in the extractor of e) comprises circulating the organic and aqueous solutions with a ratio of the flow rate of the organic solution to the flow rate of the aqueous solution greater than 1.

18. The method of claim 11, wherein the organic solution issued from e) is regenerated and then divided into a first and a second fraction, the first fraction forming the organic solution S1 and the second fraction forming the organic solution S2.

19. The method of claim 11, wherein n=2 or 3.

20. The method of claim 11, wherein: R.sub.1 is a straight or branched chain alkyl group comprising from 6 to 10 carbon atoms; and/or R.sub.2 is a straight or branched chain alkyl group comprising from 4 to 10 carbon atoms.

21. The method of claim 11, wherein the monoamide is: N-(2-heptylpyrrolidinyl)-(2-ethyl)hexanamide, N-(2-hexylpiperidinyl)-(2-ethyl)hexanamide, N-(3-hexylpiperidinyl)-(2-ethyl)hexanamide, N-(4-hexylpiperidinyl)-(2-ethyl)hexanamide, or N-(3-hexylpiperidinyl)-(2-propyl)pentanamide.

22. Monoamide, which is: N-(2-heptylpyrrolidinyl)-(2-ethyl)hexanamide, N-(2-hexylpiperidinyl)-(2-ethyl)hexanamide, N-(3-hexylpiperidinyl)-(2-ethyl)hexanamide, N-(4-hexylpiperidinyl)-(2-ethyl)hexanamide, or N-(3-hexylpiperidinyl)-(2-propyl)pentanamide.

Description

BRIEF DESCRIPTION OF THE FIGURE

[0106] FIG. 1 illustrates a schematic diagram of a method for treating an aqueous solution resulting from the dissolution of a spent nuclear fuel in nitric acid in accordance with the invention; in this FIGURE, rectangles 1 to 7 represent multi-step extractors such as those conventionally used in the treatment of spent nuclear fuel (mixer-settlers, pulsed columns or centrifugal extractors); the organic phases are symbolised by solid lines while the aqueous phases are symbolised by dotted lines.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

ISynthesis of Monoamides of Formula (I)

[0107] The monoamides of formula (I) can be synthesised by two different procedures, referred to below as A and B respectively.

Procedure A:

[0108] This is based on the reaction of a carboxylic acid of the formula: R.sup.1COOH wherein R.sup.1 has the same meaning as in formula (I) with a cyclic amine of the formula:

##STR00004##

wherein n and R.sup.2 have the same meaning as in formula (I).

[0109] This reaction can, for example, be conducted as follows: a solution comprising 1-hydroxybenzotriazole monohydrate (or HOBt1.20 eq.) and N,N-dicyclohexylcarbodiimide (or DCC1.20 eq.) in 2-methyltetrahydrofuran (0.2 mol/L) is stirred at room temperature for 10 min until completely dissolved. Carboxylic acid (1.00 eq.) is then added to the mixture. The resulting solution is stirred for 10 min and then a solution of the cyclic amine (1.00 eq.), optionally in salt form, in 2-methyltetrahydrofuran is added. The resulting suspension is stirred overnight at room temperature and then filtered on Celite. The filtrate is washed twice with a saturated sodium bicarbonate solution, and then once with a saturated sodium chloride solution. The solution is finally dried with magnesium sulphate, filtered and then concentrated in vacuo.

Procedure B:

[0110] This is based on the reaction of an acid halide of the formula: R.sup.1C(O)X wherein X represents a halogen atom, for example a chlorine atom, and R.sup.1 has the same meaning as in formula (I) with a cyclic amine of the formula as represented hereinabove.

[0111] This reaction can be conducted as follows: triethylamine (1.50-4.00 eq.) is added to a solution of the cyclic amine (1.00 eq.), optionally in salt form, in dichloromethane (or DCM). The resulting solution is stirred at room temperature for 10 min then acid halide (1.50 eq.) is added. After stirring for two hours at room temperature, water is added to the reaction medium. The aqueous phase is then extracted 3 times with dichloromethane. The organic phases are combined and washed with a saturated sodium bicarbonate solution, and then with a saturated sodium chloride solution, dried with magnesium sulphate, filtered and concentrated in vacuo.

Application of Procedures A and B to the Synthesis of Particular Monoamides of Formula (I):

[0112] The different monoamides of formula (I) whose synthesis is reported hereinafter may possess several stereogenic centres leading to the formation of diastereoisomers. These diastereoisomers are visible in .sup.1H or .sup.13C NMR. In addition, each diastereomer may have rotamers, which are also visible in NMR. To aid understanding of their NMR analysis, the percentage proportion of each peak has been added below where possible.

Synthesis of Monoamide EHPip2

[0113] Monoamide EHPip2, which has the particular formula hereinafter:

##STR00005##

is synthesised using procedure B wherein 2-ethylhexanoyl chloride (3.00 mL, 17.4 mmol, 1.05 eq.) as the acid chloride, 2-hexylpiperidine hydrochloride (3.40 g, 16.5 mmol, 1.00 eq.) as the cyclic amine salt, triethylamine (5.6 mL, 41.3 mmol, 2.50 eq.) and DCM (165 mL) are used.

[0114] This yielded 4.42 g (15.7 mmol) of EHPip2 as a yellow oil. Yield: 95%.

[0115] .sup.1H NMR (CDCl.sub.3, 400 MHz): (ppm): 4.92-4.83 (m, 1H, 56%), 4.67-4.63 (m, 1H, 22%), 4.63-4.57 (m, 1H, 22%), 4.07-3.97 (m, 1H, 44%), 3.87-3.81 (m, 1H, 28%), 3.81-3.74 (m, 1H, 28%), 3.07 (t, J=13.7 Hz, 1H, 28%), 3.06 (t, J=13.8 Hz, 1H, 28%), 2.64-2.55 (m, 1H, 44%+1H, 100%), 1.76-1.54 (m, 8H), 1.51-1.36 (m, 4H), 1.34-1.12 (m, 12H), 0.95-0.82 (m, 100%)

[0116] .sup.13C NMR (CDCl.sub.3, 101 MHz): (ppm): 174.92 (CO, 22%), 174.87 (CO, 22%), 174.6 (CO, 56%), 53.0 (CO, 56%), 52.9 (CO, 44%), 48.1, 48.0, 42.8 (78%), 42.6 (22%), 40.99 (44%), 40.95 (56%), 36.68, 36.66, 33.1, 32.9, 32.6, 32.3, 32.02, 31.98, 31.93, 31.90, 30.63, 30.57, 30.5, 30.2, 30.0, 29.9, 29.6, 29.52, 29.48, 29.45, 29.4, 28.6, 28.5, 26.9, 26.83, 26.76, 26.45, 26.41, 26.39, 26.3, 26.2, 26.00, 25.95, 25.7, 23,2, 23.12, 23.07, 23.06, 22.74, 22.71, 19.35 (44%), 19.34 (56%), 14.23, 14.19, 12.7, 12.5, 12.20, 12.16

[0117] IR (cm.sup.1): 2955, 2924, 2872, 2855, 1636, 1437, 1250, 1217

[0118] HRMS (CI+): Theoretical exact mass for C.sub.19H.sub.38NO.sup.+ [M+H].sup.+: 296.2953; experimental: 296.2963.

Synthesis of Monoamide EHPip3

[0119] The monoamide EHPip3, which has the particular formula hereinafter:

##STR00006##

is synthesised using procedure B wherein 2-ethylhexanoyl chloride (890 L, 5.10 mmol, 1.50 eq.) as the acid chloride, 3-hexylpiperidine hydrochloride as the cyclic amine salt (700 mg, 3.40 mmol, 1.00 eq.), triethylamine (1.84 mL, 13.6 mmol, 4.00 eq.) and DCM (12 mL) are used.

[0120] This yielded 990 mg (3.35 mmol) of EHPip3 as a yellow oil. Yield: 99%.

[0121] .sup.1H NMR (CDCl.sub.3, 400 MHz): (ppm): 4.52 (t, J=11.8 Hz, 1H, 100%), 3.89 (d, J=13.2 Hz, 1H, 100%), 2.99 (t, J=12.3 Hz, 1H, 50%), 2.69-2.51 (m, 2H, 100%), 2.32 (q, J=10.7, 12.3, 1H, 50%), 1.86 (d, J=12.3 Hz, 1H, 100%), 1.74-1.57 (m, 3H, 100%), 1.49-1.35 (m, 4H, 100%), 1.33-1.05 (m, 15H, 100%), 0.86 (m, 18H, 100%)

[0122] .sup.13C NMR (CDCl.sub.3, 101 MHz): (ppm): 174.4 (CO), 52.10, 52.06, 48.2, 46.7, 42.97, 42.94, 42.65, 42.63, 42.55, 42.52, 37.4, 36.35, 36.31, 34.05, 33.91, 32.81, 32.80, 32.6, 32.5, 31.9, 31.70, 31.68, 31.4, 30.2, 30.1, 30.02, 29.95, 29.7, 29.6, 26.9, 26.8, 26.4, 26.23, 26.19, 26.14, 26.11, 25.4, 23.04, 22.8, 22.7, 14.21, 14.16, 12.44 (50%), 12.42 (50%), 12.3 (50%), 12.2 (50%)

[0123] IR (cm.sup.1): 2957, 2928, 2872, 2855, 1639, 1460, 1439

[0124] HRMS (CI+): Theoretical exact mass for C.sub.19H.sub.38NO [M+H].sup.+: 296.2953; experimental: 296.2973

Synthesis of Monoamide PPPip3

[0125] The monoamide PPPip3, which has the particular formula hereinafter:

##STR00007##

is synthesised using procedure A wherein 2-propylpentanoic acid is used as the carboxylic acid (2.93 mL, 18.4 mmol, 1.00 eq.), 3-hexylpiperidine hydrochloride as cyclic amine salt (3.00 g, 18.4 mmol, 1.00 eq.), HOBt (2.99 g, 22.1 mmol, 1.20 eq.), DCC (4.56, 22.1, 1.20 eq.) and 2-methyltetrahydrofuran (184 mL). N,N-diisopropylethylamine (or DIPEA6.6 mL, 36.8 mmol, 2.00 eq.) is added initially to deprotonate 3-hexylpiperidine hydrochloride.

[0126] This yielded 4.03 g (13.63 mmol) of PPPip3 as a clear oil. Yield: 74%.

[0127] .sup.2H NMR (CDCl.sub.3, 400 MHz): (ppm): 4.54 (t, J=12.1 Hz, 1H), 3.91 (d, J=13.3 Hz, 1H), 2.99 (td, J=12.7, 2.6 Hz, 1H, 50%), 2.74-2.51 (m, 2H), 2, 36-2.26 (m, 1H, 50%), 1.91-1.83 (m, 1H), 1.73-1.58 (m, 3H), 1.45-1.17 (m, 19H), 0.95-0.83 (m, 9H, CH.sub.3)

[0128] .sup.13C NMR (CDCl.sub.3, 101 MHz): (ppm): 174.6 (CO), 52.1, 48.2, 46.7, 43.0, 40.6, 40.5, 37.4, 36.3, 35.7, 35.6, 35.5, 34.1, 34.0, 31.9, 31.7, 31.4, 29.7, 29.6, 26.9, 26.8, 26.4, 25.4, 22.79, 22.76, 21.2, 21.1, 21.0, 20.9, 14.42, 14.40, 14.38, 14.2

[0129] IR (cm.sup.1): 2957, 2922, 2855, 1636, 1441

[0130] HRMS (CI+): Theoretical exact mass for C.sub.19H.sub.38NO [M+H].sup.+: 296.2953, experimental: 296.2895

Synthesis of Monoamide EHPip4

[0131] The monoamide EHPip4, which has the particular formula hereinafter:

##STR00008##

is synthesised using procedure B wherein 2-ethylhexanoyl chloride as the acid chloride (2.48 mL, 14.3 mmol, 1.05 eq.), 4-hexylpiperidine hydrochloride as the cyclic amine salt (2.80 g, 13.6 mmol, 1.00 eq.), triethylamine (4.60 mL, 34.0 mmol, 2.50 eq.) and DCM (136 mL) are used.

[0132] This yielded 3.51 g (12.5 mmol) of EHPip4 as a yellow oil. Yield: 92%.

[0133] .sup.1H NMR (CDCl.sub.3, 400 MHz): (ppm): 4.75-4.69 (m, 1H, 50%), 4.69-4.64 (m, 1H, 50%), 4.07-4.01 (m, 1H, 50%), 4.01-3.95 (m, 1H, 50%), 2.98 (t, J=12.4 Hz, 1H, 50%), 2.98 (t, J=12.4 Hz, 1H, 50%), 2.64-2.48 (m, 2H), 1.78-1.59 (m, 4H), 1.53-1.37 (m, 3H), 1.34-1.16 (m, 14H), 1.11-0.98 (m, 2H), 0.93-0.82 (m, 9H)

[0134] .sup.13C NMR (CDCl.sub.3, 101 MHz): (ppm): 173.5 (CO), 45.2, 41.6, 41.54, 41.45, 41.4, 35.6, 35.4, 32.5, 31.8, 31.6, 31.5, 31.0, 29.1, 29.0, 28.6, 25.7, 25.2, 25.1, 22.1, 22.0, 21.8, 13.24, 13.18, 11.4, 11.2

[0135] IR (cm.sup.1): 2953, 2926, 2868, 2856, 1628, 1429, 1246

[0136] HRMS (CI+): Theoretical exact mass for C.sub.19H.sub.38NO [M+H].sup.+: 296.2953, experimental: 296.2963

Synthesis of Monoamide EHPyr2

[0137] The monoamide EHPyr2, which has the particular formula hereinafter:

##STR00009##

is synthesised using procedure B wherein 2-ethylhexanoyl chloride as the acid chloride (2.53 mL, 14.6 mmol, 1.20 eq.), 2-heptylpyrrolidine as the cyclic amine (2.17 g, 12.2 mmol, 1.00 eq.), triethylamine (2.46 mL, 18.3 mmol, 1.50 eq.) and DCM (165 mL) are used.

[0138] This yielded 4.42 g (15.7 mmol) of EHPyr2 as a yellow oil. Yield: 82%.

[0139] .sup.1H NMR (CDCl.sub.3, 400 MHz): (ppm): 4.17-4.08 (m, 1H, 67%), 3.89-3.80 (m, 1H, 33%), 3.61-3.39 (m, 2H, 100%), 2.42-2.31 (m, 1H, 100%), 2.03-1.78 (m, 4H), 1.72-1.39 (s, 5H), 1.35-1.16 (m, 15H), 0.92-0.83 (m, 9H)

[0140] .sup.13C NMR (CDCl.sub.3, 101 MHz): (ppm): 175.14 (CO, 16%), 175.06 (CO, 16%), 174.73 (CO, 33%), 174.71 (CO, 33%), 57.65 (16%), 57.63 (16%), 57.3 (33%), 57.2 (33%), 47.0 (100%), 45.73, 45.71, 45.35, 45.32, 45.25, 35.65 (16%), 35.62 (16%), 33.48, 33.47, 33.4, 33.0, 32.6, 32.5, 32.0 (67%), 31.93 (16%), 31.91 (16%), 30.5, 30.23, 30.22, 30.19, 29.95, 29.92, 29.74, 29.72, 29.64, 29.56, 29.5, 29.4, 29.3, 29.2, 26.7, 26.7, 26.6, 26.5, 26.0, 25.9, 24.2, 23.2, 23.1, 23.0, 22.8, 22.2, 14.24, 14.21, 14.18, 12.70, 12.41, 12.18, 12.15

[0141] IR (cm.sup.1): 2957, 2924, 2864, 2855, 2636, 1419

[0142] HRMS (CI+): Theoretical exact mass for C.sub.19H.sub.38NO [M+H].sup.+: 296.2953, experimental: 296.2962

IIExtractive Properties of Monoamides of Formula (I)

[0143] Extraction tests are carried out using: [0144] as organic phases: solutions comprising 1.2 mol/L of one of the following monoamides: EHPip2, EHPip3, PPPip3, EHPip4 and EHPyr2 in TPH; and [0145] as aqueous phases: aqueous solutions comprising 10 g/L of uranium(VI), 200 kBq/mL of .sup.239-240plutonium(IV) and nitric acid at a concentration of either 4 mol/L (to simulate the acidity likely to be exhibited by an aqueous solution resulting from the dissolution of a spent nuclear fuel in nitric acid) or 0.5 mol/L (to simulate the acidity that would be exhibited by an aqueous solution likely to be used to strip plutonium).

[0146] Each of these tests is carried out by bringing one of the organic phases into contact with one of the aqueous phases, in a tube and under stirring, for 30 min at 25 C. The O/A volume ratio used is 1. These phases are then separated from each other after centrifugation.

[0147] The uranium(VI) concentrations and the plutonium(IV) activities are measured in the organic and aqueous phases thus separated, respectively by plasma inductively coupled-atomic emission spectrometry (or ICP-AES) and by a spectrometry.

[0148] The distribution coefficients of uranium(VI) and plutonium(IV) as well as the U/Pu separation factors were determined in accordance with conventions in the field of liquid-liquid extractions, namely that: [0149] the distribution coefficient of a metal element M, noted D.sub.M, between two, respectively organic and aqueous, phases is equal to:

[00001]$D_M=\frac{{\left[M\right]}_{\mathrm{org}.}}{{\left[M\right]}_{\mathrm{aq}.}}$

where: [0150] [M].sub.org.=concentration of the metal element in the organic phase at extraction equilibrium (in mg/L); and [0151] [M].sub.aq.=concentration of the metal element in the aqueous phase at extraction equilibrium (in mg/L); [0152] the separation factor between two metal elements M1 and M2, noted FS.sub.M1/M2, is equal to:

[00002]${\mathrm{FS}}_{M1/M2}=\frac{D_{M1}}{D_{M2}}$ [0153] where: [0154] D.sub.M1=distribution coefficient of the metal element M1; and [0155] D.sub.M2=distribution coefficient of the metal element M2.

[0156] Table I hereinafter shows, for each monoamide tested, the distribution coefficients of uranium(VI), noted D.sub.U, and of plutonium(IV), noted D.sub.Pu, as obtained for the aqueous phases at 4 mol/L of HNO.sub.3 and at 0.5 mol/L of HNO.sub.3, as well as the separation factors U/Pu, noted FS.sub.U/Pu, as obtained for the aqueous phases at 0.5 mol/L of HNO.sub.3.

TABLE-US-00001 TABLE I [C] [HNO.sub.3] Extractants tested (mol/L) (mol/L) D.sub.U D.sub.Pu FS.sub.U/Pu [00010] 1.2 4 0.5 9.7 0.31 1.8 0.014 22 [00011] 1.2 4 0.5 15.1 0.42 5.1 0.027 16 [00012] 1.2 4 0.5 14.8 0.54 5.3 0.029 19 [00013] 1.2 4 0.5 8.4 0.29 3.2 0.022 13 [00014] 1.2 4 0.5 16.8 1.07 14.1 0.032 33 [00015] 1.2 4 0.5 9.1 0.32 4.3 0.018 18 [00016] 1.1 4 0.5 23.5 2.6 20.3 0.85 3.1

[0157] By way of comparison, also reported in this table are the results of tests carried out under the same operating conditions but using as the organic phases: [0158] on the one hand, a solution comprising 1.2 mol/L of MDEHA (N-decyl-N-methyl-2-ethylhexanamide) provided in reference [2], in TPH, MDEHA being a dissymmetric monoamide free of a cyclic amine which has the same molecular formula (C.sub.19H.sub.38NO) as the monoamides tested and which comprises, like the monoamides EHPip2, EHPip3, EHPip4 and EHPyr2, a carbonyl group carrying a 1-ethylpentyl group; and [0159] on the other hand, a solution comprising 1.1 mol/L of TBP in TPH since TBP is the solvent for the PUREX method.

[0160] Table I shows that all the monoamides tested co-extract uranium(VI) and plutonium(IV) at high acidity (D>1 for [HNO.sub.3]=4 mol/L) and selectively strip plutonium (IV) at moderate acidity (D.sub.Pu<0.05 for [HNO.sub.3]=0.5 mol/L).

[0161] The piperidine ring monoamides EHPip3 and PPPip3 lead, at high acidity ([HNO.sub.3]=4 mol/L), to distribution coefficients for uranium(VI) and plutonium(IV) that are higher than those obtained, at the same acidity and identical concentration in the organic phase, for MDEHA, while retaining good U/Pu selectivity at moderate acidity (FS.sub.U/Pu>10 for [HNO.sub.3]=0.5 mol/L).

[0162] However, the most interesting monoamide is the pyrrolidine ring monoamide EHPyr2. Indeed, this monoamide strongly extracts uranium(VI) and plutonium(IV) at high acidity ([HNO.sub.3]=4 mol/L) while achieving a high U/Pu separation factor at moderate acidity (FS.sub.U/Pu=33 for [HNO.sub.3]=0.5 mol/L).

[0163] In addition, unlike monoamides such as MDEHA, which extract uranium(VI) more strongly than plutonium(IV), the monoamide EHPyr2 leads, at high acidity ([HNO.sub.3]=4 mol/L), to similar distribution coefficients for uranium(VI) and plutonium(IV). These distribution coefficients are higher than those obtained, at the same acidity and identical concentration in the organic phase, for MDEHA. The U/Pu separation factor obtained, at moderate acidity ([HNO.sub.3]=0.5 mol/L), for monoamide EHPyr2 is also higher than that obtained, at the same acidity, for MDEHA.

[0164] It should be noted that the uranium(VI) and plutonium(IV) distribution coefficients obtained for monoamide EHPyr2 at high acidity ([HNO.sub.3]=4 mol/L are lower than those obtained at the same acidity for TBP. On the other hand, at moderate acidity ([HNO.sub.3]=0.5 mol/L, the monoamide EHPyr2 has a U/Pu selectivity that is much higher than that of TBP, since it leads to a FS.sub.U/Pu separation factor that is 10 times higher than that obtained for TBP at the same acidity.

IIIUranium(VI) Loading Capacity of Monoamides of Formula (I):

[0165] Uranium (VI) loading capacity tests are carried out by subjecting an organic phase comprising 1.2 mol/L of monoamide EHPip3 in TPH to 5 successive contacts with an aqueous solution comprising 135 g/L uranium(VI) and 4 mol/L nitric acid.

[0166] Each contact is made in a tube under stirring, for 30 min at 25 C. and with an O/A volume ratio of 2, and is followed by centrifugation, separation of the aqueous and organic phases that have been brought into contact and measurement of the uranium(VI) concentration in the organic phase.

[0167] Table II hereinafter sets forth the uranium(VI) concentrations, noted [U].sub.org and expressed in g/L, as obtained in the organic phases after each of the 5 contacts.

TABLE-US-00002 TABLE II Contacts [U].sub.org (g/L) 1.sup.st 68 2.sup.nd 107 3.sup.rd 126 4.sup.th 141 5.sup.th 142

[0168] Further to the fact that no demixing (i.e. formation of a third phase) was noticed during the 5 contacts, Table II shows that it is possible to load an organic phase comprising a monoamide with 142 g/L of uranium(VI), which represents a high loading capacity, compatible with the development of a method for treating spent nuclear fuels.

IVSchematic Diagram of One Implementation of the Treatment Method of the Invention:

[0169] Reference is made to FIG. 1, which represents a schematic diagram of one implementation of a method for treating an aqueous solution resulting from the dissolution of a spent nuclear fuel in nitric acid in accordance with the invention.

[0170] As shown in the FIGURE, the method comprises 8 steps.

[0171] The first of these steps, noted U/Pu co-extraction in FIG. 1, is aimed at jointly extracting uranium and plutonium, the former in the +VI oxidation state and the latter in the +IV oxidation state, from the aqueous nitric solution resulting from the dissolution of a spent nuclear fuel.

[0172] Such a solution typically comprises from 3 to 6 mol/L of HNO.sub.3, uranium(VI), plutonium(IV), minor actinides (americium, curium and neptunium), fission products (La, Ce, Pr, Nd, Sm, Eu, Gd, Mo, Ru, Tc, Rh, Ru, Pd, Y, Cs, Ba, Zr, Nb, . . . ) as well as a number of activation products such as chromium, manganese, iron, cobalt and nickel.

[0173] The U/Pu co-extraction step is carried out by circulating, in the extractor 1, the dissolution solution countercurrently to an organic phase (noted PO in FIG. 1) which comprises from 1 mol/L to 2 mol/L and, better still, from 1.1 mol/L to 1.3 mol/L, for example 1.2 mol/L, of a monoamide or a mixture of monoamides of formula (I), in solution in an organic diluent.

[0174] The organic diluent can especially be a straight or branched chain hydrocarbon such as n-dodecane, TPH or an isoparaffin such as that marketed under the trade name Isane IP 185T, preference being given to TPH.

[0175] The second step of the method, called PF washing in FIG. 1, aims at stripping, from the organic phase issued from the U/Pu co-extraction, the fraction of fission and activation products that was extracted together with the uranium(VI) and plutonium(IV) from the dissolution solution.

[0176] To do this, the PF washing step comprises one or more operations of washing the organic phase issued from the U/Pu Co-extraction, each washing operation being carried out by circulating this organic phase in the extractor 2, countercurrently to an aqueous nitric solution whose concentration can range from 1 mol/L to 6 mol/L of HNO.sub.3 but is preferably from 4 mol/L to 6 mol/L of HNO.sub.3 and, even better, from 4 mol/L to 5 mol/L of HNO.sub.3 so as to facilitate the stripping of ruthenium and technetium.

[0177] If the PF washing step is carried out with one or more highly acidic aqueous solutions, i.e. typically equal to or greater than 3 mol/L of HNO.sub.3, then this step also comprises deacidifying the organic phase, which is carried out by circulating this organic phase countercurrently to a weakly acidic nitric aqueous solution, i.e. comprising from 0.1 mol/L to 1 mol/L of HNO.sub.3, such as an aqueous solution comprising 0.5 mol/L of HNO.sub.3, in order to prevent too large an amount of acid from being carried to the extractor assigned to the third step, noted Pu stripping in FIG. 1, and impairing performance of this third step.

[0178] The Pu stripping step, which represents the first step of U/Pu partitioning, aims at stripping plutonium in the +IV oxidation state, and therefore without reduction of this plutonium, from the organic phase issued from the PF washing.

[0179] It is carried out by circulating this organic phase in the extractor 3 countercurrently to an aqueous solution comprising from 0.1 mol/L to 0.5 mol/L of HNO.sub.3 and preferably using an O/A flow rate ratio greater than 1, preferably equal to or greater than 3 and, better still, equal to or greater than 5 so that the plutonium(IV) is stripped in a concentrating manner.

[0180] The stripping of plutonium(IV), which is carried out in the Pu stripping step, is accompanied with a stripping of a uranium(VI) fraction which is also present in the organic phase issued from the PF washing.

[0181] Thus, the fourth step of the method, noted 1st U washing in FIG. 1 and representing the second step of the U/Pu partitioning, aims at extracting from the aqueous phase issued from Pu Stripping: [0182] either all the uranium(VI) present in this aqueous phase, if the U/Pu partitioning is desired to lead to an aqueous solution comprising plutonium(IV) without uranium(VI), and to an organic solution comprising uranium(VI) without plutonium(IV); [0183] or the amount of uranium(VI) making it possible to obtain, at the end of the 1st U washing, an aqueous solution comprising uranium(VI) and plutonium(IV) in a pre-selected ratio, if it is desired that the U/Pu partitioning lead to an aqueous solution comprising a mixture of plutonium(IV) and uranium(VI) in this ratio and an organic solution comprising uranium(VI) without plutonium (IV).

[0184] In both cases, the 1st U washing is carried out by circulating, in extractor 4, the aqueous phase issued from the Pu stripping countercurrently to an organic phase (especially noted as PO in FIG. 1) of identical composition to that of the organic phase used for the U/Pu co-extraction. The amount of uranium(VI) extracted is adjusted by varying, on the one hand, the O/A flow rate ratio and, on the other hand, the acidity of the aqueous phase, as the higher the organic phase/aqueous phase flow rate ratio and the higher the acidity of the aqueous phase, the better the extraction of uranium(VI). An addition of more or less concentrated HNO.sub.3 to the aqueous phase circulating in the extractor 4 can therefore be provided depending on the acidity desired to be provided to this aqueous phase.

[0185] The fifth step, called -Tc barrier in FIG. 1, aims at stripping, from the organic phase issued from the Stripping Pu, the technetium fraction which was extracted during the Co-extraction U/Pu but which was not stripped during the PF washing, in order to enhance the decontamination of this organic phase with respect to technetium.

[0186] It also enables the fraction of neptunium that was extracted during the U/Pu co-extraction and that followed the technetium to the -Tc barrier, as well as any traces of plutonium(IV) that this organic phase is likely to still contain, to be stripped from the organic phase issued from the Pu stripping.

[0187] It is carried out by circulating, in extractor 5, the organic phase issued from the Pu stripping countercurrently to an aqueous nitric solution comprising from 0.1 mol/L to 3 mol/L of HNO.sub.3 and, even better, 1 mol/L of HNO.sub.3, as well as one or more reducing agents for reducing technetiumwhich is present in the organic phase in the +VII oxidation stateto technetium(IV), neptunium(VI) to neptunium(IV) or neptunium(V), and plutonium(IV) to plutonium(III) respectively, without reducing uranium(VI). For this type of acidity, technetium(IV) and neptunium(IV) are not extractable by monoamides of formula (I), while plutonium(III) is less extractable than plutonium(IV).

[0188] As reducing agents, uranous nitrate (or U(IV)), hydrazinium nitrate (or NH), hydroxylammonium nitrate (or NHA) and acetaldoxime, a hydroxyiminoalkanoic acid (6-hydroxyiminohexanoic acid for example) or a mixture thereof such as a U(IV)/NH, U(IV)/NHA or U(IV)/acetaldoxime mixture can thus be used, preference being given to a U(IV)/NH or U(VI)/NHA mixture. If necessary, gluconic acid can be added to the aqueous solution to decrease technetium(IV) reoxidation phenomena in the aqueous phase and thus limit consumption of reducing agent(s).

[0189] This step can be carried out at room temperature (i.e. at 20-25 C.) but is preferably carried out at a temperature of between 30 C. and 40 C. and, better still, 32 C. so as to promote the stripping kinetics of technetium(IV) while limiting technetium(IV) reoxidation phenomena in the aqueous phase and, therefore, the risk of having technetium, once stripped, re-extracted in the organic phase.

[0190] The sixth step, noted 2nd U washing in FIG. 1, aims at extracting, from the aqueous phase issued from the -Tc Barrier, the uranium(VI) which was stripped, together with technetium, in the previous step in order to prevent the -Tc Barrier step from resulting in too great a loss of uranium(VI) in the aqueous phase.

[0191] It is carried out by circulating, in extractor 6, the aqueous phase issued from the -Tc Barrier countercurrently to an organic phase (also noted as PO in FIG. 1) with a composition identical to that of the organic phases used for the U/Pu Co-extraction and the 1st U washing, after acidifying this aqueous phase by adding concentrated nitric acid, especially at 10 mol/L, to promote extraction of uranium(VI).

[0192] The seventh step, noted U stripping in FIG. 1, aims at stripping uranium(VI) from the organic phase issued from the -Tc Barrier.

[0193] It is carried out by circulating, in extractor 7, the organic phase issued from the -Tc barrier countercurrently to a nitric aqueous solution comprising at most 0.5 mol/L and, even better, at most 0.05 mol/L of HNO.sub.3, such as, for example, an aqueous solution comprising 0.01 mol/L of HNO.sub.3. This step can be carried out at room temperature (i.e. at 20-25 C.) but is preferably carried out while hot (i.e. typically at a temperature of 40-50 C.) and using an O/A flow rate ratio greater than 1 so that uranium(VI) is extracted in a concentrating manner.

[0194] At the end of these 7 steps, the following are obtained: [0195] two raffinates, which correspond to the aqueous phases leaving extractors 1 and 6 respectively and which comprise, for the first one, fission and activation products as well as americium and curium (Primary raffinate in FIG. 1) and, for the second one, technetium, neptunium and, optionally, traces of plutonium (Secondary raffinate in FIG. 1); [0196] the aqueous phase leaving the extractor 4, which comprises either decontaminated plutonium(IV) or a mixture of decontaminated plutonium(IV) and uranium(VI) and which is called Pu flow or Pu+U flow depending on the case; [0197] the aqueous phase leaving extractor 7, which comprises decontaminated uranium(VI) and which is called U flow; and [0198] the organic phase leaving extractor 7, which no longer comprises either plutonium(IV) or uranium(VI) but which may contain a number of impurities and degradation products (formed by hydrolysis and radiolysis) of the extractant, which would have accumulated during the previous steps.

[0199] Thus, the eighth step, noted PO washing in FIG. 1, aims at regenerating this organic phase by subjecting it to one or more washes with a basic aqueous solution, for example a first wash with a 0.3 mol/L aqueous sodium carbonate solution, followed by a second wash with a 0.1 mol/L sodium hydroxide, followed by one or more washes with a nitric aqueous solution for reacidification, for example an aqueous solution comprising 2 mol/L HNO.sub.3, each wash being carried out by circulating said organic phase in an extractor countercurrently to the aqueous washing solution.

[0200] As is visible in FIG. 1, the organic phase thus regenerated can then be returned to extractors 1 and 4 for reintroduction into the treatment cycle.

REFERENCES CITED

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