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Title:
ACTINIDE EXTRACTION METHODS AND ACTINIDE SEPARATION COMPOSITIONS
Document Type and Number:
WIPO Patent Application WO/2008/088576
Kind Code:
A3
Abstract:
The invention includes methods of separating actinides from lanthanides. A regio-/stereo-specific dithiophosphinic acid having organic moieties is provided in an organic solvent which is then contacted with an acidic media containing an actinide and a lanthanide. The method can extend to separating actinides from one another. Actinides are extracted as a complex with the dithiophosphinic acid. Separation compositions include an aqueous phase, an organic phase, dithiophosphinic acid, and at least one actinide. The compositions may include additional actinides and/or lanthanides. The invention includes a method of producing a dithiophosphinic acid comprising at least two organic moieties selected from aromatics and alkyls, each moiety having at least one functional group. A source of sulfur is reacted with a halophosphine. An ammonium salt of the dithiophosphinic acid product is precipitated out of the reaction mixture. The precipitated salt is dissolved in ether. The ether is removed to yield the dithiophosphinic acid.

Inventors:
PETERMAN DEAN R (US)
KLAEHN JOHN R (US)
HARRUP MASON K (US)
TILLOTSON RICHARD D (US)
LAW JACK D (US)
Application Number:
PCT/US2007/073229
Publication Date:
October 02, 2008
Filing Date:
July 11, 2007
Export Citation:
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Assignee:
BATTELLE ENERGY ALLIANCE LLC (US)
International Classes:
B01D11/00; C01F17/00; C01G56/00; C01G99/00
Foreign References:
US6312654B12001-11-06
US20040230079A12004-11-18
US4867951A1989-09-19
US3463619A1969-08-26
US4318893A1982-03-09
US20050203314A12005-09-15
US3018301A1962-01-23
US5475146A1995-12-12
Other References:
MODOLO ET AL.: "Influence of the Purity and Irradiation Stability of Cyanex 301 on the Separation of Trivalent Actinides from Lanthanides by Solvent Extraction", JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY, vol. 228, 1998, pages 83 - 89
Attorney, Agent or Firm:
KIRSCH, Alan, D. (LLC.P.O. Box 162, Idaho Falls ID, US)
Download PDF:
Claims:

CLAIMS

1. A method of separating at least one actinide from at least one lanthanide comprising: providing an organic solvent containing a dithiophosphinic acid comprising a first re gio-/stereo- specific moiety and a second re gio-/stereo- specific moiety, the first regio- /stereo-specific moiety being an aromatic group comprising a first functional group, the second re gio-/stereo- specific moiety comprising a member of the group consisting of aromatics and alkyls and comprising a second functional group, the first and second functional groups being independently selected from the group consisting of substituted or non- substituted alkyls, alkenyls, alkynyls, single-ring aryls, multi-ring aryls or mixtures thereof; with substitutions being selected from the group consisting of oxygen, nitrogen, fluorine, chlorine, bromine, iodine, boron, gallium, silicon, germanium, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, and oxides thereof, and combinations thereof; and contacting an acidic media containing at least one actinide and at least one lanthanide with the organic solvent.

2. The method of claim 1 wherein the dithiophosphinic acid is symmetric.

3. The method of claim 1 wherein the dithiophosphinic acid is bis-(ortho- trifluoromethylphenyl)dithiophosphinic acid.

4. The method of claim 1 wherein the acidic media comprises nitric acid.

5. The method of claim 1 wherein the at least one actinide comprises trivalent amencmm.

6. The method of claim 1 wherein the at least one lanthanide comprises trivalent europium.

7. The method of claim 1 wherein the at least one actinide comprises trivalent curium.

8. The method of claim 1 further comprising extracting a complex of the dithiophosphinic acid and the at least one actinide in an organic phase of a biphasic media.

9. The method of claim 1 wherein the acidic media has a pH of greater than or equal to 2.

10. The method of claim 1 wherein the organic phase comprises trifluoromethylphenyl sulfone.

11. A separation method comprising: providing an acidic media comprising a first actinide and a second actinide; contacting the acidic media with an organic solution containing at least one dithiophosphinic acid comprising a first regio-/stereo-specific moiety and a second re gio-/stereo- specific moiety, the first regio-/stereo- specific moiety being an aromatic group comprising a first functional group, the second re gio-/stereo- specific moiety comprising a member of the group consisting of aromatics and alkyls and comprising

a second functional group, the first and second functional groups being independently selected from the group consisting of substituted or non-substituted alkyls, alkenyls, alkynyls, single-ring aryls, multi-ring aryls or mixtures thereof; with substitutions being selected from the group consisting of oxygen, nitrogen, fluorine, chlorine, bromine, iodine, boron, gallium, silicon, germanium, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, and oxides thereof, and combinations thereof; and extracting the first actinide into the organic solution.

12. The method of claim 11, wherein the organic solution is a first organic solution, and further comprising: separating the first organic solution from the acidic media; adjusting the pH of the acidic media; after adjusting the pH, contacting the acidic media with a second organic solution comprising at least one dithiophosphinic acid comprising a third regio-/stereo-specific moiety and a fourth regio-/stereo-specific moiety, the third re gio-/stereo- specific moiety being an aromatic group comprising a third functional group, the fourth regio-/stereo- specific moiety comprising a member of the group consisting of aromatics and alkyls and comprising a fourth functional group, the third and fourth functional groups being independently selected from the group consisting of substituted or non-substituted alkyls, alkenyls, alkynyls, single-ring aryls, multi-ring aryls or mixtures thereof; with substitutions being selected from the group consisting of oxygen, nitrogen, fluorine, chlorine, bromine, iodine, boron, gallium, silicon, germanium, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, and oxides thereof, and combinations thereof; and extracting the second actinide into the second organic solution.

13. The method of claim 12 wherein the pH of the acidic media after the adjusting is greater than about 2.14.

14. The method of claim 12 wherein the pH of the acidic media prior the adjusting is about 2

15. The method of claim 12 wherein the first actinide is americium and the second actinide is curium.

16. A separation method comprising: providing a first acidic media comprising a first actinide and a second actinide, the first acidic media having a first pH; contacting the first acidic media with an organic solution comprising at least one dithiophosphinic acid comprising a first regio-/stereo-specific moiety and a second re gio-/stereo- specific moiety, the first re gio-/stereo- specific moiety being an aromatic group comprising a first functional group, the second regio-/stereo-specific moiety comprising a member of the group consisting of aromatics and alkyls and comprising a second functional group, the first and second functional groups being independently selected from the group consisting of substituted or non-substituted alkyls, alkenyls, alkynyls, single-ring aryls, multi-ring aryls or mixtures thereof; with substitutions being selected from the group consisting of oxygen, nitrogen, fluorine, chlorine, bromine, iodine, boron, gallium, silicon, germanium, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, and oxides thereof, and combinations thereof; extracting the first actinide and second into the organic solution; separating the organic solution from the first acidic media;

contacting a second acidic media with the organic solution, the second acidic media having a second pH that differs from the first pH; and extracting the first actinide from the organic solution into the second acidic media.

17. The method of claim 16 wherein the pH of the first acidic media is greater than about 2.14.

18. The method of claim 16 wherein the pH of the second acidic media is about 2

19. The method of claim 16 wherein the first actinide is curium and the second actinide is americium.

20. A separation method comprising: providing an acidic media containing americium and europium; contacting the acidic media with an organic solution containing bis-(ortho- trifluoromethylphenyl)dithiophosphinic acid dissolved in trifluoromethylphenyl sulfone; forming a bis-(ortho-trifluoromethylphenyl)dithiophosphinic acid and americium complex; and collecting the complex in the organic solution.

21. The separation method of claim 20 wherein the acidic media has a pH of from about 2 to about 2.5.

22. The separation method of claim 20 wherein the acidic media contains at least one additional lanthanide.

23. The separation method of claim 20 wherein the acidic media contains at least one additional actinide.

24. An actinide-lanthanide separation composition comprising: an aqueous phase; an organic phase; at least one dithiophosphinic acid comprising a first regio-/stereo-specific moiety and a second re gio-/stereo- specific moiety, the first regio-/stereo- specific moiety being an aromatic group comprising a first functional group, the second regio-/stereo-specific moiety comprising a member of the group consisting of aromatics and alkyls and comprising a second functional group, the first and second functional groups being independently selected from the group consisting of substituted or non-substituted alkyls, alkenyls, alkynyls, single- ring aryls, multi-ring aryls or mixtures thereof; with substitutions being selected from the group consisting of oxygen, nitrogen, fluorine, chlorine, bromine, iodine, boron, gallium, silicon, germanium, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, and oxides thereof, and combinations thereof; at least one actinide; and at least one lanthanide.

25. The separation composition of claim 24 wherein the at least one dithiophosphinic acid comprises bis-(ortho-trifluoromethylphenyl)dithiophosphinic acid.

26. The separation composition of claim 24 wherein at least some actinide is present in the organic phase complexed with at least some of the dithiophosphinic acid.

27. The separation composition of claim 24 wherein the at least one actinide comprises americium.

28. The separation composition of claim 24 wherein the at least one actinide comprises curium.

29. The separation composition of claim 24 wherein the at least one actinide comprises americium and curium.

30. The separation composition of claim 29 wherein a majority of the americium is present in the organic phase and a majority of the curium is present in the aqueous phase.

31. The separation composition of claim 29 wherein a majority of the curium is present in the organic phase and a majority of the americium is present in the aqueous phase.

32. The separation composition of claim 29 wherein a majority of the americium is present and a majority of the curium are present in the organic phase.

33. The separation composition of claim 24 wherein the majority of the at least one lanthanide is present in the aqueous phase and at least some of the at least one actinide is complexed with dithiophosphinic acid in the organic phase.

34. The separation composition of claim 24 wherein the organic phase comprises trifluoromethylphenyl sulfone.

35. The separation composition of claim 24 wherein the aqueous phase is acidic.

36. The separation composition of claim 24 wherein the aqueous phase has a pH of greater than or equal to about 2.

37. A method of producing an actinide extractant agent comprising: providing a halophosphine; reducing the halophosphine with a metal hydride; reacting the halophosphine with a source of sulfur; forming a re gio-/stereo- specific dithiophosphinic acid; adding an excess of ammonium carbonate relative to the dithiophosphinic acid; precipitating an ammonium salt of the dithiophosphinic acid; dissolving the ammonium salt of the dithiophosphinic acid in an organic solvent; contacting the organic solvent with an acid; and removing the organic solvent to produce the acid form of the extractant agent, the extractant agent being a dithiophosphinic acid comprising a first re gio-/stereo- specific moiety and a second regio-/stereo- specific moiety, the first regio-/stereo-specific moiety being an aromatic group comprising a first functional group, the second regio-/stereo-specific moiety comprising a member of the group consisting of aromatics and alkyls and comprising a second functional group, the first and second functional groups being independently selected from the group consisting of substituted or non- substituted alkyls, alkenyls, alkynyls, single- ring aryls, multi-ring aryls or mixtures thereof; with substitutions being selected from the group consisting of oxygen, nitrogen, fluorine, chlorine, bromine, iodine, boron, gallium,

silicon, germanium, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, and oxides thereof, and combinations thereof.

38. The method of claim 37 wherein the halophosphine is bis-(ortho- trifluoromethylphenyl)chlorophosphine and the acid form of the extractant agent is bis- (ortho-trifluoromethylphenyl)dithiophosphinic acid.

39. The method of claim 37 wherein the organic solvent is an ether.

40. The method of claim 37 wherein the acid is hydrochloric acid.

Description:

Actinide Extraction Methods and Actinide Separation Compositions

RELATED APPLICATIONS

This application claims benefit of U.S. Non-provisional application No. 11/530,508, filed September 11, 2006, entitled ACTINIDE EXTRACTION METHODS AND ACTINIDE SEPARATION COMPOSITIONS, which is incorporated herein by reference in its entirety.

GOVERNMENT RIGHTS

This invention was made with Government support under Contract No. DE-AC07- 05ID 14517 awarded by the United States Department of Energy. The Government has certain rights in the invention.

TECHNICAL FIELD

The invention pertains to methods of separating actinides, methods of separating actinides from lanthanides, separation compositions and methods for production and isolation of symmetric or asymmetric regio-/stereo-specific dithiophosphinic acids.

BACKGROUND OF THE INVENTION

Heretofore, the primary commercially available extractant employed to separate trivalent actinides from trivalent lanthanides has been bis-2,4,4-trimethylpentyl dithiophosphinic acid, having the trade name CYANEX ® -301 (Cytec Technology Corp., Wilmington DE). This conventional extractant is an effective agent for the separation of trivalent actinides (Am(III), Cm(III), etc.) from lanthanides in an acidic media.

While this extraction agent has worked with some degree of success, there are shortcomings with this compound which have detracted from its usefulness. Chief among these shortcomings is that this compound requires the use of mildly acidic processing conditions. In practice, the use of this compound requires complex adjustments to the aqueous process-feed that complicates the operation of this very complex extraction process, and tends to increase the amount of secondary waste material. In addition to the foregoing, it

has long been known that CYANEX ® -301 is easily decomposed in acidic solutions, further

limiting its usefulness in production scale processes.

An extraction agent and method of extraction for actinides from lanthanides which avoids the shortcomings in the prior art compounds and methodology used heretofore is the subject matter of the present application. The extraction can additionally be utilized to separate actinides from one another.

SUMMARY In one aspect the invention pertains to methods of separating at least one actinide from at least one lanthanide. A symmetric or asymmetric dithiophosphinic acid having regio- specificity and/or stereo- specificity is provided into an acidic media containing at least one actinide and at least one lanthanide. The dithiophosphinic acid can have aromatic and/or alkyl groups having single or multiple functional groups. In one aspect the invention pertains to a separation method for separating a first actinide from a second actinide. An acidic media containing a first actinide and a second actinide is provided. An organic solution containing at least one dithiophosphinic acid is contacted with an acidic media and the first actinide is extracted into the organic solution.

In one aspect the invention pertains to an actinide/lanthanide separation composition. The composition contains an aqueous phase and an organic phase. At least one

dithiophosphinic acid is present in the composition along with at least one actinide and at least one lanthanide.

In one aspect the invention pertains to an actinide- actinide separation composition having an aqueous phase and an organic phase. The composition includes at least one dithiophosphinic acid and at least two actinides.

In one aspect the invention pertains to a method of specifically producing either a symmetric or an asymmetric dithiophosphinic acid having regio-specificity and/or stereo- specificity. A source of sulfur is reacted with a phosphine to produce a dithiophosphinic acid product. A reaction mixture is formed and an excess of ammonium carbonate is added to the reaction mixture. An ammonium salt of the dithiophosphinic acid is precipitated out of the reaction mixture. The precipitated ammonium salt is dissolved in ether. The ether phase is contacted with hydrochloric acid and the ether is removed to yield the dithiophosphinic acid.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention are described below with reference to the following accompanying drawings.

Fig. 1 is a graph showing distribution ratios for americium and europium as a function of aqueous phase acid concentration.

Fig. 2 is a graph showing distribution ratios for curium as a function of aqueous phase acid concentration.

Fig. 3 is a graph showing distribution ratios for the lanthanide ions as a function of ionic radius.

Fig. 4 shows distribution ratios for americium and europium as a function of aqueous phase nitrate ion concentration.

Fig. 5 is a graph showing distribution ratios for americium and europium as a function of organic phase bis-(ortho-trifluoromethylphenyl) dithiophosphinic acid concentration.

Fig. 6 is a graph showing separation factors (S=D AπI /D EU , etc.) as a function of nitric acid concentration. Fig. 7 is a graph showing separation factors for various lanthanide ions in aqueous solution.

Fig. 8 is 31 P nuclear magnetic resonance (NMR) spectra of bis-(ortho- trifluoromethylphenyl) dithiophosphinic acid in trifluoromethylphenyl sulfone organic solvent; and as initially prepared or after 57 days of incubation in a 2-phase sample system containing an acidic aqueous phase (various [H + ]) and trifluoromethylphenyl sulfone organic solvent phase.

Fig. 9 is 19 F nuclear magnetic resonance (NMR) spectra of bis-(ortho- trifluoromethylphenyl) dithiophosphinic acid in trifluoromethylphenyl sulfone organic solvent; and as initially prepared or after 57 days of incubation in a 2-phase sample system containing an acidic aqueous phase (various [H + ]) and trifluoromethylphenyl sulfone organic solvent phase.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In general, the invention encompasses an extraction agent, methods of producing the extraction agent, and extraction methodology. The extraction includes methodology can be utilized for extracting an actinide from one or more differing actinides and/or extracting an actinide from one or more lanthanides.

The extraction agent (extractant) can typically comprise a symmetric or asymmetric dithiophosphinic acid . The dithiophosphinic acid can contain alkyl and/or aromatic groups having various functional groups. The dithiophosphinic acid can preferably be prepared to

have at least two regio-specific and/or stereo- specific organic moieties. These may include a first organic moiety which is an aromatic having a first functional group selected from the group consisting of substituted or non-substituted alkyls, alkenyls, alkynyls, single-ring aryls, multi-ring aryls or mixtures thereof. The substitutions can be for example, oxygen, nitrogen, fluorine, chlorine, bromine, iodine, boron, gallium, silicon, germanium, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, and oxides thereof. Multiple substitutions may be present on a given functional group.

The second organic moiety can be either an aromatic or an alkyl. The second moiety has a second functional group which can be the same as or can differ from the first function group and can be selected from the group consisting of substituted or non-substituted alkyls, alkenyls, alkynyls, single-ring aryls, multi-ring aryls, or mixtures thereof. The substitutions can be for example, oxygen, nitrogen, fluorine, chlorine, bromine, iodine, boron, gallium, silicon, germanium, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, and oxides thereof. Multiple substitutions may be present on the second functional group. In particular instances, a symmetric extractant can be a bis-phenyl dithiophosphinic acid. Preferably the extraction agent is bis-(ortho-trifluoromethylphenyl) dithiophosphinic acid (hereinafter referred to as 0-CF 3 ), shown below.

Bis(o-trifluoromethylphenyl)dithiophosphinic Acid ; ( 0 -CF 3 )

The 0-CF 3 (or alternative regio-/stereo-specific dithiophosphinic acid) utilized for the invention can be prepared by, for example, utilizing methodology as set forth in co-pending application serial number 11/232,541, entitled Extraction Agent and Method for Forming an

Extraction Agent for the Separation of Actinides from Lanthanides, the contents of which is hereby incorporated by reference. As set forth in the co-pending application, various reagents can be reacted to produce halophosphines that are symmetric or asymmetric, and which contain aromatic and/or alkyl groups with various regio-/stereo specific functional groups, for example, bis-(ortho-trifluoromethylphenyl) chlorophosphine. The halophosphine can be reduced to the phosphine by various metal hydrides. The corresponding phosphine can then be reacted with a source of sulfur to produce a dithiophosphinic acid product that is symmetric or asymmetric, containing aromatic/alkyl groups having various functionalities. An example symmetric dithiophosphinic acid that can be produced using such methodology is bis-(ortho-trifluoromethylphenyl)dithiophosphinic acid. The product can be in acid form as set forth in the co-pending application. The product can be collected by alternative methodology such as distillation as described in the co-pending application, or by salt precipitation as set forth below.

Upon formation of the final phosphinic acid product utilizing methodology as set forth in the co-pending application, the product can be precipitated as its corresponding salt from the reaction mixture. The reaction mixture containing the acid product can be transferred to an appropriate flask, preferably while still hot. The original reaction flask can be washed with an organic solvent such as, for example, toluene, which is then added to the flask into which the reaction mixture has been transferred. Subsequently, while maintaining the reaction mixture at a temperature near boiling, an excess of an appropriate salt such as, for example, ammonium carbonate ((NH 4 ) 2 3 ) is added to the reaction mixture. The corresponding product phosphinate salt is then precipitated out of the hot mixture as a solid. The salt can be collected by filtration over an appropriate filter such as, for example, filter paper.

The resulting precipitate can be washed with an appropriate organic solvent such as, for example, toluene. The salt can be allowed to dry and can subsequently be converted to its corresponding acid by, for example, dissolving the salt in an appropriate organic solvent such as diethyl ether and an acid such as, for example, aqueous hydrochloric acid. The organic solvent layer can be separated from the aqueous phase to collect the product acid in the ether/organic layer. Further purification can be achieved utilizing appropriate purification techniques such as recrystallization in hexane or other appropriate organic solvent.

Example: Salt Precipitation of Product A dark-green reaction mixture containing 0-CF 3 was produced utilizing methodology as set forth in the co-pending application. The reaction mixture was transferred to a 250 mL Erlenmeyer flask equipped with a magnetic stir bar while the mixture was still hot. 75 mL of toluene was utilized to wash the reaction flask and was subsequently transferred into the Erlenmeyer flask. A hot plate/stirrer was utilized to keep the toluene stirring at a temperature near boiling. A slight excess of ammonium carbonate (0.75 g, 0.008 mol) was slowly added to the reaction mixture. The ammonium salt (0-(CF 3 )CoH 4 ) I PS 2 (NH 4 ) slowly precipitated out of the hot toluene as a white powdery solid. The solution remained heated and was stirred for about 1 hour. The ammonium salt was filtered through fluted filter paper while the solution was still hot. Additional chilled toluene was utilized to wash the precipitate. The ammonium salt was collected on a watch glass and allowed to air dry overnight. 50 mL of diethyl ether was provided within a 125 mL separatory funnel and subsequently 25 mL of 4.0 M hydrochloric acid was added to the separatory funnel. The ammonium salt product was introduced into the funnel and was shaken vigorously to dissolve the salt into the ether. After the ammonium salt was dissolved the ether layer was isolated and the water layer was washed twice with 25 mL of diethyl ether which was then combined with the originally separated

ether layer. The ether was then removed from the product 0-CF 3 utilizing a roto-evaporator. The resulting product was a light green solid and the overall yield of the isolated product was about 75%. The product was subsequently recrystallized in hexanes to result in light green prismatic crystals.

The yield, physical and nuclear magnetic resonance (NMR) characteristics for the resulting Bis-(o-trifluoromethylphenyl)dithiophosphinic acid (0-CF 3 ) were as follows: [-40% overall yield; mp = 93-94 0 C; bp = 0.07-0.125 mmHg / 150-160 0 C; 31 P NMR δ (CDCl 3 ) = (t, JPH = 19.6 Hz) 58.1; 19 F NMR δ (CDCl 3 ) = (s) -55.7; 1 H NMR δ (CDCl 3 ) = (dd, J PH = 18.0 Hz, J FH = 9.0 Hz, H) 8.43, (m, 3H) 7.65-7.85, (s, H) 3.31; 13 C NMR δ (CDCl 3 ) = (doublet, J PC = 78.5 Hz, ipso) 134.3, (doublet, J PC = 12.8 Hz, ortho) 134.2, (doublet, J PC = 3.0 Hz, para) 132.1, (doublet, J PC = 14.3 Hz, meta) 131.7, (doublet of quartets, J PC = 6.0 Hz, J CF = 38.5 Hz, ortho) 129.7, (multiplet, meta) 128.0, (quartet, J CF = 274.7 Hz, CF 3 ) 123.4].

From the results of the alternative isolation method set forth above it can be noted that for particular products such as 0-CF 3 the salt precipitation method can be preferred since such results in increased yields relative to distillation techniques described in the co-pending application. Although the methodology above is described in terms of particular dithiophosphinic acids it is to be understood that the methodology can be utilized to produce alternative dithiophosphinic acids. Extraction methodology of the invention can be utilized to separate one or more actinides from one or more lanthanides and/or to separate one actinide from one or more additional differing actinides. Such methodology typically involves formation of a separation composition having an organic phase and an aqueous phase. The aqueous phase of the separation composition is preferably acidic (has a pH of less than about 7). Where the separation involves extraction of one or more actinide from lanthanides the pH of the aqueous

phase is typically greater about 2. However, where two or more actinides are to be separated from lanthanides, pH values of less than or equal to 2 can be utilized in particular instances to selectively extract a specific actinide while leaving additional actinides and lanthanides in the aqueous phase (discussed more fully below). Extraction methodology in accordance with the invention can be performed by dissolving the dithiophosphinic acid to be used as extractant in an appropriate organic solvent. Where an actinide-lanthanide separation is to be conducted, an acidic aqueous phase is provided having a first actinide and a first lanthanide. The aqueous phase may comprise a second or multiple additional actinides. The aqueous phase may also contain a second lanthanide or multiple lanthanides in addition to the first lanthanide. Once formed, the organic solution containing the extractant can be added directly to the aqueous solution containing the actinide to be extracted. A complex is then formed which contains the extractant and extracted metal. This complex is present in the organic phase and can be separated from non-extracted metals by removal of the organic phase from the two-phase separation composition.

In particular instances, the extractant can preferably be bis-(ortho- trifluoromethylphenyl)dithiophosphinic acid. This compound can be used independently or in combination with one or more additional dithiophosphinic acid extractants. Studies utilizing the present methodology indicate that independent utilization of 0-CF 3 is sufficient to extract one or more actinides from one or more lanthanides and additionally indicate that specific actinides such as Am(III) can be selectively extracted from additional actinides such as Cm(III). Accordingly, extractions in accordance with the invention can efficiently separate one or both of Am(III) and Cm(III) from a composition containing one or more lanthanides and where a solution contains both Am(III) and Cm(III), the extraction methodology can be utilized to selectively remove Am(III) from Cm(III).

The results of tests utilizing the methodology of the invention additionally indicated that bis-(ortho-trifluoromethylphenyl)dithiophosphinic acid has improved separation efficiency and extractant stability relative to conventional actinide/lanthanide extractants. As presented below, the extractant stability extends to methodology where the 0-CF 3 is dissolved in a suitable organic diluent and wherein the aqueous solution contains significant concentrations of acid. The extractant additionally is capable of efficiently separating Am(III) from Eu(III) in such extraction composition.

The organic solvent is not limited to any particular solvent and can preferably be a polar hydrophobic solvent. In particular instances where the extractant comprises 0-CF 3 an appropriate preferred solvent can be trifluoromethylphenyl sulfone (henceforth referred to as FS- 13). It is to be understood, however, that the invention contemplates utilization of alternative polar hydrophobic solvents.

Although not limited to particular concentrations, the organic solution can typically contain an appropriate amount of extractant to fully extract the desired actinide(s) from the acidic aqueous phase into the organic phase of the resulting 2-phase separation composition. An appropriate concentration for a particular extractant and solvent system can be determined based upon the solubility limit of the extractant in the particular solvent utilized. Where the extractant comprises 0-CF 3 , an appropriate extractant concentration can be 0.1 M of 0-CF 3 in FS- 13. The acidic aqueous solution is contacted with this organic solution containing the extractant to form the biphasic solvent system extraction composition.

The pH of the aqueous phase is not limited to a particular value and can depend upon the particular actinides and/or lanthanides present in the solution. The distribution ratio D M and separation factor S can be utilized to determine separation efficiency of a particular separation and can assist in determining appropriate pH values of the aqueous phase. The distribution ratio D M is utilized to quantify the separation of a component of a solution in a

biphasic solvent system. In the case of actinide/lanthanide separations (or actinide/actinide separations) the distribution ratio is defined as the sum of the concentrations of metal containing species in the organic phase divided by the sum of the concentrations of metal containing species in the aqueous phase: D M = ∑[M n+ ]org/∑[M n+ ]aq. The separation factor is defined as the ratio of the distribution ratios for the metal species of interest: S = D M /D M '-

An example separation quantification study was performed in a biphasic solvent system composition for Am(III) and Eu(III) as a function of aqueous phase nitric acid concentration. In the extraction composition, the extractant forms a complex with metal ions to form an extracted metal complex present in the organic phase. The data presented in Table 1 shows the distribution ratios (average of three independent determinations for Am (D Am ) and Eu (D EU ) as function of nitric acid concentration. The aqueous phase contained 0.001 M Eu(NO 3 ) 3 and 1.0 M [NO3 ~ ] to tai as sodium nitrate in varying concentrations of HNO 3 . Unless otherwise noted the organic phase composition used in these studies was 0.1 M o-CF 3 dissolved in FS- 13. The logarithms of the distribution data shown in Table 1 are plotted in Fig. 1. The type of plot presented in Fig. 1 is useful for examination of the stoichiometry of extracted metal complex. The data presented in Table 1 and Fig. 1 indicates that Am(III) is extracted (D Am > 1) by 0-CF 3 at pH values of > 2.00 and is not extracted (UAm < 1) at pH values < 2.0. TABLE 1: Am and Eu Distribution Ratios

The same data set shows that Eu(III) is not extracted by 0-CF 3 at any of the pH values studied. The linear equation presented in Fig. 1 shows that the slope of the linear regression of log-log data plot is approximately -3.2. This indicates that the extracted complex contains three 0-CF 3 ligands for each Am(III) metal center. This stoichiometry is consistent with the expected acidic ion exchange extraction mechanism.

Additional studies were performed to determine distribution ratios as a function of aqueous phase nitric acid concentration for Cm(III), (Dc m ). The aqueous phase contained 0.001 M Eu(NO 3 )3 and 1.0 M [NO3 ~ ] to tai as sodium nitrate in varying concentrations of HNO 3 . The organic phase was 0.1 M 0-CF 3 dissolved in FS-13. The logarithms of the distribution data shown in Table 2 are plotted in Fig. 2. Such study was performed using only 244 Cm radio tracer.

TABLE 2: Cm Distribution Ratios

The data presented in Table 2 and Fig. 2 indicates that Cm(III) is extracted (D Cm > 1) by 0-CF 3 at pH values of > 2.14 and is not extracted (D Cm < 1) at pH values < 1.92. The linear equation presented in Fig. 2 indicates that the slope of linear regression of log-log data plot is approximately -2.3.

The lanthanides present in the extraction composition are not limited to particular elements. Studies utilizing the present methodology indicate that one or more actinides can be separated from compositions comprising one or multiple lanthanides. Distribution ratios D for lanthanide ions determined by methodology of the invention are presented in Table 3 and in Fig. 3.

TABLE 3: Lanthanide Distribution Ratios

The lanthanide distribution ratios were calculated from the results of inductively coupled plasma mass spectrometry (ICP-MS) analysis of the aqueous phase (0.01 M HNO 3 + 1.0 M NaNO 3 ) and the organic phase (0.1 M 0-CF 3 in FS-13) following a single phase contact. In each case the calculated values of D Ln are significantly less than one. These results indicate that the 0-CF 3 ligand dissolved in FS-13 does not extract any lanthanide ions. The distribution ratios for Eu(III), (D Eu ) determined from radiometric and ICP-MS analysis

agree to within the experimental error. Accordingly, the lanthanide distribution ratios appear to be sufficiently low to allow efficient separation of actinides from any lanthanide or combination of lanthanides present in the composition.

Additional studies were performed to determine distribution ratios for Am(III) and Eu(III) as a function of nitrate ion concentration in the aqueous phase. The organic phase was 0.1 M 0-CF 3 in FS-13. The aqueous phase was 0.001 M Eu(NO 3 ) 3 , 0.010 M HNO 3 and varying concentration of NO 3 " as sodium nitrate. The results of such studies are presented in Table 4 and plotted in Fig. 4. The nitric acid concentration was maintained at 0.010 M HNO 3 for these experiments.

TABLE 4: Am and Eu Distribution Ratios as a Function of [NO 3 ]

The data presented in Table 4 and Fig. 4 indicates that there is not significant dependence of the measured distribution ratios on the aqueous phase nitrate ion concentration. This indicates that the nitrate ion is not present in the Am (III)-(o-CF 3 ) n complex present in the organic phase.

Further studies were performed to determine distribution ratios for Am(III) and Eu(III) determined as a function of o-CF 3 concentration in the organic phase. The organic phase utilized varying concentration of o-CF 3 in FS-13. The aqueous phase was 0.001 M Eu(NO 3 ) 3 , 0.010 M HNO 3 and 1 M NO 3 " as sodium nitrate. The results of such studies are presented in Table 5 and plotted in Fig. 5. The nitric acid concentration was maintained at 0.010 M HNO 3 for these experiments. The results of the linear regression of the log-log data

indicate that approximately three 0-CF 3 ligands are associated with each Am(III) metal ion in the organic phase.

TABLE 5: Am and Eu Distribution ratios as a Function of [0-CF 3 ]

The separation factors (defined above) for Am(III) from Eu(III), Cm(III) from Eu(III), and Am(III) from Cm(III) determined using radiotracer techniques are presented in Table 6 and Fig. 6. The separation factors for Am relative to Cm are not included in Fig. 6 for clarity purposes. The separation factors are calculated using data presented in Tables 1 and 2.

TABLE 6: Separation Factors

A separation factor significantly greater than 1 is indicative of efficient separation. It should be noted that in the case of both distribution ratios being greater than 1 it is possible to have a separation factor greater than 1 and still not have particularly efficient separation. However, this is not the case for this solvent extraction system (where D Am > 1 and D Eu < 1). The data reveals that at a pH greater than 2.0 it is possible to achieve separation factors of greater than S=100,000.

Separation factors for Am from the lanthanide ions are presented in Table 7 and are plotted in Fig. 7. These separation factors are calculated utilizing data presented in Tables 1 and 3. In each case the calculated separation factor demonstrates efficient separation of Am(III) from all of the lanthanides in aqueous solution. TABLE 7: Am Separation Factors

Stability studies were performed to determine the stability of dithiophosphinic acids in 2-phase separation compositions utilized in accordance with the invention. NMR studies were compared for o-CF 3 solutions in contact with acidic solutions and were compared to NMR studies of o-CF 3 neat solution phase samples. The results of such stability studies were

benchmarked against conventional commercially available CYANEX ® -301. Five

composition samples were prepared each with 0.1 M o-CF 3 in FS-13. These were placed individually in sealed sample tubes with an aqueous phase containing 1.0 M NO 3 " (as the sodium salt) and A: 0.100 M H + , B: 0.010 M H + , C: 0.005 M H + , or D: without added acid. A fifth sample, E was a blank sample was prepared utilizing an organic phase only (no aqueous phase). The samples were placed on a continuous rotation wheel and the phases kept in constant intimate contact.

Samples were periodically withdrawn and examined by multinuclear NMR techniques ( 19 F and 31 P). The obtained 19 F NMR studies are presented in Fig. 8. The results of the 31 P NMR studies are presented in Fig. 9. The results of these studies were very positive in that the compound proved to be stable in strong acidic environments for prolonged periods of time. The 0-CF 3 appears to be stable for weeks at 0.01 M HNO 3 and shows little degradation at 0.1 M HNO 3 even after months. Additionally, the equilibrium between the organic phase (trifluoromethylphenyl sulfone, CF 3 SO 2 Ph) and aqueous phase shows that virtually none of 0-CF 3 partitions over into the aqueous phase. The new 0-CF 3 was found to be more stable not only in contact with molar acid concentrations, but also in solid-phase atmospheric

exposure tests in which CYANEX ® -301 decomposes noticeably over the given time frame

(approximately 7 months) where 0-CF 3 exhibited no detectable decomposition. In general, this stability represents a significant improvement in the state of the art relative to conventional extractants.

The totality of the results indicates that a regio-/stereo- specific dithiophosphinic acid such as 0-CF 3 can effectively separate actinides from lanthanides and can additionally be utilized to separate various actinides from one another. For actinide-actinide separation, an acidic media can be provided which contains a first actinide and a second actinide. An organic solution containing at least one bis-phenyl or alkyl-phenyl dithiophosphinic acid can be added to the acidic media and the first actinide can be extracted into the organic solution. In particular embodiments, both the first actinide and the second actinide will be extracted into the organic phase. Separation of the organic and the aqueous phases can be utilized to recover the first and second actinides in the organic solution. An additional aqueous phase can then be added to the organic solution where the second aqueous solution has a pH which differs from the original aqueous solution from which the first and second actinide were extracted. Such change in aqueous phase pH can be utilized to effectively re-extract the

second actinide into the aqueous phase thereby separating first and second actinides upon removal of the organic from the aqueous phase.

For example, an acidic aqueous solution can be provided containing a first actinide (e.g. americium) and a second actinide (e.g. curium). Such solution can optionally contain one or more lanthanides, including but not limited to europium. The pH of the acidic solution can be about 2.3-2.5. An organic solution containing 0-CF 3 can be added to the aqueous solution to form a two-phase separation composition. The 0-CF 3 can form a complex with Cm(III) and can form a complex with Am(III), and such complexes can be collected by removing the organic phase from the separation composition. A second aqueous phase having a pH about 2 can be added to the collected organic phase. The Cm(III) can be selectively dissociated from the 0-CF 3 at this lower pH relative to the Am(III), and can be recovered in the second aqueous phase.

Alternatively, where first and second actinides are present in an aqueous solution, the pH of such aqueous phase can be such that upon addition of organic phase containing the bis- phenyl or phenyl-alkyl dithiophosphinic acid only one of the first and second actinides is extracted into the organic phase. The organic phase can then be removed to isolate the first actinide while the second actinide is retained in the aqueous phase. The pH of the aqueous phase can then be adjusted followed by addition of a second organic phase containing the same or a differing bis-phenyl or phenyl-alkyl dithiophosphinic acid. The second actinide is then extracted from the aqueous phase under the adjusted pH conditions to isolate the second actinide.

For example, an acidic aqueous solution can be provided containing a first actinide (e.g. americium) and a second actinide (e.g. curium). Such solution can optionally contain one or more lanthanides, including but not limited to europium. The acid solution can preferably be provided to have a pH of about 2.0. An organic solution containing 0-CF 3 can

be added to the aqueous solution to form a two-phase separation composition. The 0-CF 3 can selectively form a complex with Am(III) relative to Cm(III) and lanthanides, and such complex can be collected by removing the organic phase from the separation composition. The pH of the aqueous phase can then be adjusted to greater than 2, preferably greater than about 2.14. A second organic solution containing 0-CF 3 can then be added to the aqueous solution to form a second two-phase separation composition. The Cm(III) can be selectively complexed with 0-CF 3 relative to the lanthanides, and can be recovered in the second organic phase.

Either of these alternative actinide-actinide separation techniques can be utilized in the presence of one or more lanthanides and can successfully separate actinides from the lanthanides and actinides from each other.