Stoichiometric recovery of UF4 from UF6 dissolved in ionic liquid

Abstract

Described herein is a process for recovering uranium tetrafluoride (UF4) from hexafluoride uranium (UF6), the process comprising dissolving UF6 directly in an ionic liquid and recovering UF4, which can be processed to obtain UO2(s) or metallic uranium.

Description

[0001] Cross-reference with related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 986,059, filed March 6, 2020, which is incorporated herein by reference in its entirety.

[0003] Federally funded research

[0004] This invention was made with the support of the U.S. government, under the main contract number DE-NA-0003624, subcontract number 159313, and mission order numbers 26 and 37 granted by the U.S. Department of Energy. The U.S. government holds certain rights in this invention. Technical Field

[0005] This article describes a method for recovering uranium tetrafluoride (UF4) from uranium hexafluoride (UF6), the method comprising dissolving UF6 directly in an ionic liquid and recovering UF4, wherein the UF4 may be processed to obtain UO2(s) or metallic uranium. Background Technology

[0006] Uranium hexafluoride (UF6) is a highly volatile and reactive form of uranium and is part of national nuclear stockpiles. 95% of the world's depleted uranium exists in the form of UF6. UF6 reacts violently with water to produce uranyl fluoride (UO2F2) and hydrofluoric acid (HF), which are highly volatile and sublime at room temperature.

[0007] There is a need for methods to convert reactive UF6 into more stable uranium compounds that can be used for subsequent applications. Summary of the Invention

[0008] One embodiment described herein is a method for converting uranium hexafluoride (UF6) into uranium tetrafluoride (UF4), the method comprising: directly dissolving UF6 at a concentration of 0.01 M to 3.0 M in an ionic liquid at room temperature; incubating the solution for a period of time; and adding water to the solution to precipitate solid UF4. In one case, the UF6 concentration in the ionic liquid is less than about 2.0 M. In another case, the UF6 concentration in the ionic liquid is about 0.01 M, about 0.02 M, about 0.03 M, about 0.04 M, about 0.05 M, about 0.06 M, about 0.07 M, about 0.08 M, about 0.09 M, 0.01 M, about 0.02 M, about 0.03 M, about 0.04 M, about 0.05 M, about 0.06 M, about 0.07 M, about 0.08 M, about 0.09 M, or about 0.1 M. M, about 0.2M, about 0.3M, about 0.4M, about 0.5M, about 0.6M, about 0.7M, about 0.8M, about 0.9M, about 1.0M, about 1.1M, about 1.2M, about 1.3M, about 1.4M, about 1.5M, about 1.6M, about 1.7M, about 1.8M, about 1.9M, about 2.0M, about 2.1M, about 2.2M, about 2.3M, about 2.4M, about 2.5M, or about 3.0M. In another embodiment, the method further includes chilling the UF6 before dissolving it in the ionic liquid. In another embodiment, the time period comprises about 1 hour to about 200 days. In another embodiment, the time period comprises about 1 hour to about 1 day. In another embodiment, the ionic liquid comprises anions with lone pairs of electrons. In another embodiment, the ionic liquid comprises anion selected from n-bis(trifluoromethanesulfonylimide) (TFSI), dicyandiamide, trifluoroacetate, alkyl sulfonate, alkyl sulfate, bis(fluorosulfonyl)imide, and trifluoromethylacetate. In yet another embodiment, the ionic liquid comprises n-bis(trifluoromethanesulfonylimide) anion (TFSI). - In another case, the ionic liquid comprises a cation selected from alkyl-substituted or unsubstituted ammonium cations, alkyl-substituted or unsubstituted piperidinium cations, and alkyl-substituted or unsubstituted pyrrolidineonium cations. In another case, the ionic liquid comprises a cation selected from tetraalkylammonium cations, dialkylpiperidinium cations, and dialkylpyrrolidineonium cations. In another case, the ionic liquid comprises a 1-methyl-1-propylpiperidinium cation. In another case, the ionic liquid comprises 1-methyl-1-propylpiperidinium bis(trifluoromethanesulfonylimide) ([MPPi][TFSI]). In another case, the recovery of UF4 is approximately 100%.

[0009] Another implementation is UF6 produced using any of the methods described above. 2- .

[0010] Another implementation is UF4 produced using any of the methods described above.

[0011] Another implementation is the production of metallic uranium or uranium oxide using any of the methods described above.

[0012] Another implementation method is the production of UF6 2- The method comprises directly dissolving UF6 at a concentration of 0.01 M to 2.5 M in an ionic liquid at room temperature and incubating the solution for a period of time. In one case, the method further comprises chilling the UF6 before dissolving it in the ionic liquid. In another case, the period of time comprises about 1 hour to about 200 days. In another case, the period of time comprises about 1 hour to about 1 day. In another case, the ionic liquid contains anions with lone pairs of electrons. In another case, the ionic liquid contains anions selected from n-bis(trifluoromethanesulfonylimide) (TFSI), dicyandiamide, trifluoroacetate, alkyl sulfonate, alkyl sulfate, bis(fluorosulfonyl)imide, and trifluoromethylacetate. In another case, the ionic liquid contains n-bis(trifluoromethanesulfonylimide) anion (TFSI). - In another instance, the ionic liquid comprises a cation selected from alkyl-substituted or unsubstituted ammonium cations, alkyl-substituted or unsubstituted piperidinium cations, and alkyl-substituted or unsubstituted pyrrolidineonium cations. In another instance, the ionic liquid comprises a cation selected from tetraalkylammonium cations, dialkylpiperidinium cations, and dialkylpyrrolidineonium cations. In another instance, the ionic liquid comprises a 1-methyl-1-propylpiperidinium cation. In another instance, the ionic liquid comprises 1-methyl-1-propylpiperidinium bis(trifluoromethanesulfonylimide) ([MPPi][TFSI]).

[0013] Another implementation is UF6 produced using any of the methods described above. 2- .

[0014] Another implementation is UF4 produced using any of the methods described above.

[0015] Another implementation is the production of metallic uranium or uranium oxide using any of the methods described above. Attached Figure Description

[0016] This patent or application document contains at least one color drawing. A copy of this patent or patent application publication with the color drawing will be provided by the Patent Office after the application is filed and the necessary fees are paid.

[0017] Figure 1A –C. Figure 1A The image shows the 0.1M solution that was just added; Figure 1B The same solution is shown after shaking and incubation for 2 days.

[0018] Figure 2 The UV-Vis spectrum of 0.1 M UF6 in [MPPi][TFSI] as a function of time is shown.

[0019] Figure 3 The IR spectrum of UF6 in [MPPi][TFSI] over time and the identified peaks are shown.

[0020] Figure 4 Normalized XANES spectra of UF4, 700 mM UF6 at 169 days old, 100 mM UF6 at 169 days old, and 100 mM UF6 at 10 days old are shown at the U–L3 edge.

[0021] Figure 5A –D. Figure 5A The image shows 0.95MUF6 in [MPPi][TFSI] after it was just added; Figure 5B The same solution is shown 24 hours later; Figure 5C The solution is shown after 8 days.

[0022] Figure 6A –C. Figure 6A UF6 in [MPPi][TFSI] mixed with water is shown. Figure 6B It shows the source Figure 6A The precipitate from the centrifuged solution. Figure 6C The precipitate is shown after rinsing with acetone and drying overnight at room temperature in a fume hood. The precipitate changed from dark green to light green during drying.

[0023] Figure 7 It shows Figure 6C The XRPD curve of the green precipitate shows characteristics of hydrated UF4. Detailed Implementation

[0024] This article describes a method for recovering uranium tetrafluoride (UF4) from uranium hexafluoride (UF6), the method comprising dissolving UF6 directly in an ionic liquid and recovering UF4, wherein the UF4 may be processed to obtain UO2(s) or metallic uranium.

[0025] Uranium hexafluoride (UF6) is a highly volatile and reactive form of uranium and is part of a national nuclear material stockpile. Previous work has involved methods for converting reactive UF6 into a more stable material, as UF6 sublimates at room temperature and reacts violently with water to produce uranyl fluoride (UO2F2) and HF. See International Patent Application No. PCT / US2019 / 024870, filed March 29, 2019, the contents of which are incorporated herein by reference. As described therein, the direct dissolution of uranium hexafluoride in an ionic liquid (IL) has been demonstrated. Stoichiometric amounts of uranium hexafluoride (UF6) are directly dissolved in the IL and chemically converted to uranium tetrafluoride (UF4). The dissolution is carried out through a spontaneous chemical process involving the reduction of uranium hexafluoride by the anions of the ionic liquid. The resulting product is UF4, which is very stable and relatively mild compared to the reactive and volatile UF6. The complete recovery of uranium as UF4 from the IL is described herein. UF4 can then be used in different processes to obtain UO2(s) or metallic uranium using methods known in the art. The process described herein is ~100% efficient in the recovery of metallic uranium materials. The process provides a novel and safe route for converting uranium hexafluoride into more useful uranium materials.

[0026] When used herein, the terms “comprising,” “including,” “having,” “may,” “containing,” and variations thereof are intended as open-ended transitional phrases, terms, or words that do not exclude the possibility of additional actions or structures. The singular forms include plural references unless the context clearly indicates otherwise. This disclosure also relates to other embodiments that “comprising,” “consisting of,” and “substantially constitute” the embodiments or elements stated herein, whether or not explicitly stated.

[0027] The modifier “about” used in connection with quantity includes the value of the statement and has a meaning determined by the context (e.g., it at least includes the degree of error associated with the measurement of the particular quantity). The modifier “about” should also be considered to disclose a range defined by the absolute values ​​of the two endpoints. For example, the statement “about 2 to about 4” also discloses a range of “2 to 4”. The term “about” can refer to plus or minus 10% of the specified number. For example, “about 10%” might indicate a range of 9% to 11%, and “about 1” might mean 0.9 to 1.1. Other meanings of “about” can be apparent from the context, such as rounding, so “about 1” might also mean 0.5 to 1.4.

[0028] For the description of number ranges in this article, each intermediate number with the same precision between them is explicitly assumed. For example, for the range of 6-9, the numbers 7 and 8 are taken into account in addition to 6 and 9, and for the range of 6.0-7.0, the numbers 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly taken into account.

[0029] For the purposes of this disclosure, chemical elements are identified according to the periodic table (CAS edition, Handbook of Chemistry and Physics, 75th edition, inner cover), and specific functional groups are generally as described therein. Furthermore, the general principles of organic chemistry, as well as descriptions of specific functional groups and reactivity, are found in the following references: *Organic Chemistry*, Thomas Sorrell, University Science Books, Sausalito, 1999; Smith and March, *March's Advanced Organic Chemistry* (5th edition, John Wiley & Sons, Inc., New York, 2001); Larock, *Comprehensive Organic Transformations*, VCH Publishers, Inc., New York, 1989; Carruthers, *Some Modern Methods of Organic Synthesis* (3rd edition, Cambridge University Press, Cambridge, 1987); the entire contents of each of these references are incorporated herein by reference.

[0030] When used herein, the term "alkyl" means a straight-chain or branched saturated hydrocarbon chain. Representative examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, 3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl, 4,4-dimethylpent-2-yl, n-heptyl, n-octyl, n-nonyl, and n-decyl.

[0031] The term "substituted" means that a group can be substituted by one or more non-hydrogen substituents. For example, an alkyl-substituted ammonium cation refers to an ammonium group that can be substituted by at least one alkyl group described herein. In some embodiments, the group can be substituted by two alkyl groups, making it dialkyl-substituted, or by four alkyl groups, making it tetraalkyl-substituted.

[0032] The term "ionic liquid" or "IL" refers to a salt that melts at a relatively low temperature. Ionic liquids are essentially salts in a liquid state. Some ionic liquids are room-temperature ionic liquids, or "RTILs," indicating that they are liquids at room temperature. While common liquids such as water and gasoline are primarily composed of electrically neutral molecules, ionic liquids are primarily composed of ions and ion pairs (i.e., cations and anions). The physical properties of an IL vary depending on the identity of the cation / anion. Any salt that melts without decomposing or vaporizing typically produces an ionic liquid. For example, sodium chloride (NaCl) melts at 801°C (1,474°F) into a liquid primarily composed of sodium cations (Na+, Na ... + ) and chloride anion (Cl - A liquid composed of ).

[0033] In some embodiments, the ionic liquid contains anions, particularly selected from n-bis(trifluoromethanesulfonylimide) (TFSI), dicyandiamide, acetate, trifluoroacetate, trifluoromethanesulfonate, alkylsulfonate, alkyl sulfate, bis(fluorosulfonyl)imide, trifluoromethylacetate, tetrafluoroborate, hexafluorophosphate, chloride, and nitrate.

[0034] In some embodiments, the ionic liquid comprises, in particular, a cation selected from tetraalkylammonium cations, dialkylpiperidinium cations, dialkylpyrrolidinium, carboxy-N,N-trimethylethylammonium (Hbet), 1-butyl-1-methylpyrrolidinium (BMPyrr), 1-propyl-1-methylpiperidinium (MPPi), 1-butyl-3-methylpiperidinium (C4MPIP), 3-butyl-1-methylimidazolium (BMIM), 3-ethyl-1-methylimidazolium (EMIM), and tri-n-octylmethylammonium (TOMA).

[0035] Exemplary ionic liquids particularly include butyltrimethylammonium n-bis(trifluoromethanesulfonylimide), 3-ethyl-1-methylimidazolium acetate, 3-butyl-1-methylimidazolium tetrafluoroborate, 3-butyl-1-methylimidazolium n-bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidineonium n-bis(trifluoromethanesulfonyl)imide, 1-methyl-1-propylpiperidinium n-bis(trifluoromethanesulfonylimide), or 1-methyl-1-propylpyrrolidineonium n-bis(trifluoromethanesulfonylimide).

[0036] method

[0037] This disclosure provides a method for recovering uranium tetrafluoride (UF4) from uranium hexafluoride (UF6), the method comprising dissolving the UF6 in an ionic liquid:

[0038]

[0039] When UF6 is dissolved in an ionic liquid, evidence of reduction can be observed by the transformation from a white solid to a green solution. Higher concentrations of the sample form a green precipitate. Not wishing to be limited by theory, it is assumed that the potential mechanism of this dissolution is as shown in reaction route 1:

[0040]

[0041] Characterization of the dissolved uranium material using UV-Vis, FTIR, and XAFS indicates that uranium was rapidly reduced to UF6. - The form of U(V) (uranium V). The reduction is achieved by an ionic liquid anion (e.g., TFSI). - The oxidation of uranium (U(IV)) is promoted, and the aforementioned anion has been reported to be a stable free radical. A second electron transfer appears to occur over time to produce the U(IV) anion, UF6. 2- See reaction route 1.

[0042] The uranium material can be recovered by adding water to the dissolved UF6 solution to precipitate UF4, thus recovering 70% of the uranium dissolved in the ionic liquid. The inclusion of water removes residual F. - and taking UO2 2+ The remaining 30% of U in the form of soluble uranium results in less than 0.3% soluble uranium remaining in the ionic liquid. Characterization of the solid recovered from the ionic liquid indicates, according to X-ray diffraction (XRPD), that the uranium material obtained from the dissolved UF6 is hydrated UF4 material (100%). The remaining UO2 is precipitated from the aqueous solution using a simple reducing agent such as a mixture of ferrous chloride (II) or ferric hydroxide (II / III). 2+ This allows for the complete recovery of the soluble uranium as UO2(s). Furthermore, metallic uranium can be recovered from precipitated UF4 using methods known in the art. A possible mechanism for the reaction of UF6 – an ionic liquid solution – with water to produce UF4 is illustrated in reaction route 2:

[0043]

[0044] As described herein, the method for recovering uranium includes dissolving uranium hexafluoride (UF6) directly in an ionic liquid at a concentration of about 0.01 M to about 3.0 M to form a solution in the ionic liquid, and incubating the solution for a period of time. The method may also include quenching the UF6 prior to dissolving it in the ionic liquid.

[0045] In one embodiment, the concentration of uranium hexafluoride (UF6) in the ionic liquid solvent is less than 0.01M, less than 0.05M, less than 0.1M, less than 0.5M, less than 1.0M, less than 1.5M, less than 2.0M, or less than 2.5M. In another case, the concentration of uranium hexafluoride (UF6) in the ionic liquid solvent is about 0.01M to about 1M, about 0.01M to 0.5M, about 0.01M to 0.4M, about 0.1M to about 1M, about 0.1M to about 0.5M, about 0.1M to about 0.4M, about 0.1M to about 0.6M, about 0.1M to about 2.0M, or about 0.1M to about 2.5M. In one case, the concentration of uranium hexafluoride (UF6) in the ionic liquid solvent is about 0.01 M, about 0.02 M, about 0.03 M, about 0.04 M, about 0.05 M, about 0.06 M, about 0.07 M, about 0.08 M, about 0.09 M, 0.01 M, about 0.02 M, about 0.03 M, about 0.04 M, about 0.05 M, about... 0.06M, approximately 0.07M, approximately 0.08M, approximately 0.09M, approximately 1.0M, approximately 1.1M, approximately 1.2M, approximately 1.3M, approximately 1.4M, approximately 1.5M, approximately 1.6M, approximately 1.7M, approximately 1.8M, approximately 1.9M, approximately 2.0M, approximately 2.1M, approximately 2.2M, approximately 2.3M, approximately 2.4M, approximately 2.5M, or approximately 3.0M.

[0046] The ionic liquid can be any combination of cations and anions. For optimization within the method described herein, the combination of cations and anions can be selected as needed to influence the properties of the solution. The ionic liquid can be a room-temperature ionic liquid (RTIL). RTILs are ionic liquids that are liquids at room temperature. RTILs exhibit similar electrochemical properties to other ionic liquids without requiring increased temperature.

[0047] The ionic liquid can be a simple ionic liquid containing one type of cation and one type of anion. The ionic liquid can also be a complex or mixed ionic liquid containing several types of anions and cations or double salts.

[0048] The ionic liquid may contain anions with lone pairs of electrons. In some embodiments, the anion is selected from n-bis(trifluoromethanesulfonylimide) (TFSI), dicyandiamide, trifluoroacetate, alkyl sulfonate, alkyl sulfate, bis(fluorosulfonyl)imide, and trifluoromethylacetate. In one exemplary embodiment, the ionic liquid contains an n-bis(trifluoromethanesulfonylimide) (TFSI) anion.

[0049] The ionic liquid may contain cations, particularly those selected from tetraalkylammonium cations, dialkylpiperidine cations, dialkylpyrrolidine cations, carboxy-N,N-trimethylethylammonium (Hbet), 1-butyl-1-methylpyrrolidine cations (BMPyrr), 1-methyl-1-propylpiperidine cations (MPPi), 1-butyl-3-methylpiperidine cations (C4MPIP), 3-butyl-1-methylimidazolium cations (BMIM), 3-ethyl-1-methylimidazolium cations (EMIM), and tri-n-octylmethylammonium cations (TOMA).

[0050] Exemplary ionic liquids particularly include butyltrimethylammonium n-bis(trifluoromethanesulfonylimide), 3-ethyl-1-methylimidazolium acetate, 3-butyl-1-methylimidazolium tetrafluoroborate, 3-butyl-1-methylimidazolium n-bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidineonium n-bis(trifluoromethanesulfonyl)imide, 1-methyl-1-propylpiperidinium n-bis(trifluoromethanesulfonylimide), or 1-methyl-1-propylpyrrolidineonium n-bis(trifluoromethanesulfonylimide).

[0051] In one exemplary embodiment, the ionic liquid is 1-methyl-1-propyl-methylpiperidinium n-bis(trifluoromethanesulfonylimide).

[0052] After uranium hexafluoride (UF6) is directly dissolved in an ionic liquid, the solution is incubated for a period of time. This period can range from 1 hour to 1500 days. In one case, the period is 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours; 1 day, 2 days, 5 days, 10 days, 20 days, 30 days, 45 days, 60 days, 90 days, 180 days, 210 days, 1 year, 2 years, 5 years, or even longer. In one case, the time period is 0.5h to 2h, 1h to 12h, 1h to 24h, 8h to 16h, 8h to 24h, 0.5–1 day, 1–2 days, 2–5 days, 1–15 days, 1–30 days, 1–45 days, 1–60 days, 1–90 days, 1–180 days, 1–365 days, or 1–5 years, including all integers within the specified range and their endpoints.

[0053] The incubation can be carried out at a specific temperature. In one case, the incubation can be carried out at ambient temperature or at a temperature in the range of 1°C to 100°C, including all integers and endpoints of the specified range. In another case, the incubation is carried out at room temperature, i.e., ~25°C. Without any theoretical limitations, the initial reaction temperature is determined by the exothermic nature of the ionic liquid; therefore, higher concentrations of UF6 dissolve more quickly due to the increased dissolution temperature.

[0054] The incubation can be carried out in air or in an atmosphere of an inert gas such as nitrogen, argon, helium, etc. The incubation can be carried out at standard atmospheric pressure, in a vacuum, or at high pressure, such as 1–10 bar (~100 kPa to ~1000 kPa). In one case, the incubation is carried out in air at standard atmospheric pressure (~100 kPa).

[0055] It will be apparent to those skilled in the art that suitable modifications and alterations can be made to the compositions, formulations, methods, processes, and applications described herein without departing from the scope of any embodiment or aspect thereof. The compositions and methods provided are exemplary and are not intended to limit the scope of any particular embodiment. Various different embodiments, aspects, and options disclosed herein can be combined in any variation or iterative manner. The scope of the compositions, formulations, methods, and processes described herein includes all actual or potential combinations of the embodiments, aspects, options, examples, and preferences described herein. The exemplary compositions and formulations described herein may omit any component disclosed herein, substitute any component disclosed herein, or include any component disclosed herein elsewhere. The methods described herein may be performed in any suitable order unless otherwise indicated herein or clearly contradicted by the context. The ratio of the mass of any component of any composition or formulation disclosed herein to the mass of any other component in the formulation or the total mass of the other components in the formulation is disclosed herein as if they were explicitly disclosed. In the event of any conflict between the meaning of any term in any patent or publication incorporated by reference and the meaning of the term used in this disclosure, the meaning of the term or phrase in this disclosure shall prevail. Furthermore, the foregoing discussion merely discloses and describes exemplary embodiments. All patents and publications cited in this article are incorporated herein by reference with respect to their specific teachings.

[0056] The various embodiments and aspects of the invention described herein are summarized by the following clauses:

[0057] Clause 1. A method for converting uranium hexafluoride (UF6) into uranium tetrafluoride (UF4), the method comprising: directly dissolving UF6 at a concentration of 0.01 M to 3.0 M in an ionic liquid at room temperature; incubating the solution for a period of time; and adding water to the solution to precipitate solid UF4.

[0058] Clause 2. The method described in Clause 1, wherein the concentration of UF6 in the ionic liquid is less than about 2.0 M.

[0059] Clause 3. The method described in Clause 1 or 2, wherein the UF6 concentration in the ionic liquid is approximately 0.01 M, approximately 0.02 M, approximately 0.03 M, approximately 0.04 M, approximately 0.05 M, approximately 0.06 M, approximately 0.07 M, approximately 0.08 M, approximately 0.09 M, 0.01 M, approximately 0.02 M, approximately 0.03 M, approximately 0.04 M, approximately 0.05 M, approximately 0.06 M, approximately 0.07 M, approximately 0.08 M, or approximately 0.09 M. Approximately 0.1M, approximately 0.2M, approximately 0.3M, approximately 0.4M, approximately 0.5M, approximately 0.6M, approximately 0.7M, approximately 0.8M, approximately 0.9M, approximately 1.0M, approximately 1.1M, approximately 1.2M, approximately 1.3M, approximately 1.4M, approximately 1.5M, approximately 1.6M, approximately 1.7M, approximately 1.8M, approximately 1.9M, approximately 2.0M, approximately 2.1M, approximately 2.2M, approximately 2.3M, approximately 2.4M, approximately 2.5M, or approximately 3.0M.

[0060] Clause 4. The method of any one of Clauses 1-3, further comprising chilling the UF6 prior to dissolving the UF6 in the ionic liquid.

[0061] Clause 5. The method described in any of Clauses 1-4, wherein the time period comprises about 1 hour to about 200 days.

[0062] Clause 6. The method described in any of Clauses 1-5, wherein the time period comprises about 1 hour to about 1 day.

[0063] Clause 7. The method described in any one of Clauses 1-6, wherein the ionic liquid comprises anion with a lone pair of electrons.

[0064] Clause 8. The method of any one of Clauses 1-7, wherein the ionic liquid comprises anion selected from n-bis(trifluoromethanesulfonylimide) (TFSI), dicyandiamide, trifluoroacetate, alkyl sulfonate, alkyl sulfate, bis(fluorosulfonyl)imide and trifluoromethylacetate.

[0065] Clause 9. The method described in any of Clauses 1-8, wherein the ionic liquid comprises n-bis(trifluoromethanesulfonylimide) anion (TFSI) - ).

[0066] Clause 10. The method of any one of Clauses 1-9, wherein the ionic liquid comprises a cation selected from alkyl-substituted or unsubstituted ammonium cations, alkyl-substituted or unsubstituted piperidinium cations, and alkyl-substituted or unsubstituted pyrrolidineium cations.

[0067] Clause 11. The method of any one of Clauses 1-10, wherein the ionic liquid comprises a cation selected from tetraalkylammonium cation, dialkylpiperidine onium cation and dialkylpyrrolidine onium cation.

[0068] Clause 12. The method of any one of Clauses 1-11, wherein the ionic liquid comprises a 1-methyl-1-propylpiperidinium cation.

[0069] Clause 13. The method of any one of Clauses 1-12, wherein the ionic liquid comprises 1-methyl-1-propylpiperidinium bis(trifluoromethanesulfonylimide) ([MPPi][TFSI]).

[0070] Clause 14. The method described in Clauses 1-13, wherein the recovery rate of UF4 is approximately 100%.

[0071] Clause 15.UF6 2- It is produced by the method described in any of the foregoing clauses.

[0072] Clause 16.UF4, which is produced by the method described in any of the preceding clauses.

[0073] Clause 17. Metallic uranium or uranium oxide, produced by the method described in any of the preceding clauses.

[0074] Clause 18. A method for producing UF6 2- The method includes dissolving UF6 directly in an ionic liquid at a concentration of 0.01M to 2.5M at room temperature and incubating the solution for a period of time.

[0075] Clause 19. The method of Clause 18 further includes chilling the UF6 before dissolving it in the ionic liquid.

[0076] The methods described in Clause 20. Clause 18 or 19, wherein the time period comprises approximately 1 hour to approximately 200 days.

[0077] Clause 21. The method described in any of Clauses 18-20, wherein the time period comprises about 1 hour to about 1 day.

[0078] Clause 22. The method of any one of Clauses 18-21, wherein the ionic liquid comprises anion with a lone pair of electrons.

[0079] Clause 23. The method of any one of Clauses 18-22, wherein the ionic liquid comprises anion selected from n-bis(trifluoromethanesulfonylimide) (TFSI), dicyandiamide, trifluoroacetate, alkyl sulfonate, alkyl sulfate, bis(fluorosulfonyl)imide and trifluoromethylacetate.

[0080] Clause 24. The method of any one of Clauses 18-23, wherein the ionic liquid comprises n-bis(trifluoromethanesulfonylimide) anion (TFSI) - ).

[0081] Clause 25. The method of any one of Clauses 18-24, wherein the ionic liquid comprises a cation selected from alkyl-substituted or unsubstituted ammonium cations, alkyl-substituted or unsubstituted piperidinium cations, and alkyl-substituted or unsubstituted pyrrolidineium cations.

[0082] Clause 26. The method of any one of Clauses 18-25, wherein the ionic liquid comprises a cation selected from tetraalkylammonium cation, dialkylpiperidine onium cation, and dialkylpyrrolidine onium cation.

[0083] Clause 27. The method of any one of Clauses 18-26, wherein the ionic liquid comprises a 1-methyl-1-propylpiperidinium cation.

[0084] Clause 28. The method of any one of Clauses 18-27, wherein the ionic liquid comprises 1-methyl-1-propylpiperidinium bis(trifluoromethanesulfonylimide) ([MPPi][TFSI]).

[0085] Clause 29.UF6 2- It is produced by the method described in any of the foregoing clauses.

[0086] Clause 30.UF4, which is produced by the method described in any of the preceding clauses.

[0087] Clause 31. Metallic uranium or uranium oxide, produced by any of the methods described in the preceding clauses.

[0088] Example

[0089] Example 1

[0090] Dissolution of uranium hexafluoride in [MPPi][TFSI]

[0091] The dissolution method for UF6 involves directly dissolving solid UF6 material in [MPPi][TFSI] at a concentration of 0.1M to 1.4M. The UF6 is stored in sealed 10mL test tubes. These tubes are stored at -15°C in a glove box freezer to ensure the substance does not volatilize before use. The test tubes are placed in the jacket hole at the bottom of a VAC glove box containing LN2 and chilled to the LN2 temperature for 1 hour. The test tubes are opened while the UF6 is chilled. Simultaneously with chilling, UF6 is scraped out with a metal scraper and added directly to a scintillation vial containing measured [MPPi][TFSI] at room temperature. The added mass is calculated from the change in the mass of the scintillation vial. When UF6 is heated, it becomes waxy and more difficult to remove from the test tube. If this occurs, briefly rechilling the test tube makes removal easier. The freshly prepared solution is stirred overnight to aid dissolution.

[0092] Example 2

[0093] Characterization of UF6 solutions in ionic liquids

[0094] The UF6 undergoes an instant color change upon addition to [MPPi][TFSI]. Solid UF6 is white. Upon addition to IL, it instantly turns yellow and then dissolves into a blue-green solution. Figure 1A And B). Over the course of 1 day, the 0.1M solution turned green (and B). Figure 1C And it retains this color for a long time (>150 days).

[0095] UV-Vis and FTIR

[0096] Over time, the spectroscopic analysis of 0.1 M UF6 [MPPi][TFSI] solution was performed using UV-Vis and FTIR. The dissolved UF6 sample was pipetteed into a 1 cm path length quartz cuvette until it was at least 75% full. The cuvette was then sealed with a screw cap. UV-Vis spectral measurements were performed daily. Figure 2 However, little change in UV-Vis was observed in the short term, despite a change in color. The first measurements were performed 4 hours after adding UF6 to [MPPi][TFSI]. Changes were minimal in the first week, but the maximum value of the 1350 nm peak decreased over time. Absorption shoulders in the UV region shifted. The peaks at 600–800 nm remained relatively constant throughout the week.

[0097] Infrared spectroscopy was used to analyze the vibrational energy of the solution. The sample exhibits absorption at wavelengths resonating with the stretching, rotation, or rocking stretching of molecules. The frequencies of these absorptions vary with changes in molecular structure. The IR spectra of [MPPi][TFSI] with and without UF6 change over time (…). Figure 3The IR spectrum shows almost no change in the short term. However, over extended time periods, the IR spectrum changes at 1500 and 900 cm⁻¹. -1 Significant changes occur in the peak shape at this location. These changes are within the spectral range related to the chemical functional groups associated with the IL cation [MPPi].

[0098] Long-term changes in UV-Vis and FTIR indicate the interaction between the dissolved UF6 and [MPPi][TFSI] over time. These interactions develop slowly, likely due to the large size of the cations and anions. However, electrostatic interactions dominate over time, and the resulting salt exhibits low solubility in ILs, leading to precipitation. At 1500 cm⁻¹ -1 The interaction between the cation and anion was observed in a nearby FTIR peak, corresponding to the C–H stretching in the six-membered ring of piperazine with two NH groups at positions 1 and 4. (Approximately 1475 cm⁻¹) -1 The peak at 900 cm⁻¹ may be due to a CH₂ group adjacent to the N atom in the [MPPi] cation. -1 The peak at [a certain point] corresponds to the rocking motion of the nitrogen methyl group. These changes indicate the coordination of UF6 with the cation in solution. [MPPi][TFSI] exhibits significant absorption in the UV range. The shift of the UV shoulder in UV-Vis also indicates a change in the interaction between UF6 and [MPPi][TFSI]. [MPPi][TFSI], UF6, and UF6 have been studied... - and UF6 2- Computer calculations were performed to determine the oxidation state of uranium using FTIR spectroscopy. However, the absorption band of UF6 was extremely small compared to [MPPi][TFSI].

[0099] Example 3

[0100] X-ray absorption fine structure (XAFS)

[0101] To determine the coordination, structure, and oxidation state of uranium, XAFS was performed on UF6 solutions. XAFS was conducted in 100 mM UF6 solutions at 10-day and 169-day ages. Older samples were compared with uranium... It shows 5.0 ± 1 fluorine atoms. There is also evidence showing... There were 3.1 ± 0.6 sulfur atoms present, but further analysis of the samples and data is underway. In the 10-day-old sample, at... There are 5.8 ± 1.2 fluorine atoms present, and no other coordinating atoms. This supports previous evidence that the coordination of UF6 with [MPPi][TFSI] is kinetically slow. Compared with using UF6... 2- The observed bond distance of the substance (i.e., in (TEA)2UF6) )compared to, The U–F bond distance and in UF6 - The bond length (i.e., (PPN)(UF6)) found in the substance The results are more consistent. This indicates that the UF6 compound is U(V) when in an ionic liquid. The XAFS and XANES results are listed in Table 1.

[0102]

[0103] Normalized XANES data of dissolved substances in UF4 standard samples and IL are shown in Figure 4 In the XANES analysis of 169-day and 10-day-old samples, the absorption edges and white lines were located close to each other, indicating that they all had the same oxidation state. However, it remains unclear whether uranium was in the 4th oxidation state. + Still 5 + Oxidation state. A solid UF4 sample was taken as 4. + The reference material was in a certain state, but 5 was not used. + Uranium samples were used as references. The difference in peak shape of normalized XANES in the 100 mM samples aged 169 days and 10 days indicates that the coordination of uranium is different in each of these samples.

[0104] Figure 4 The third sample was a 169-day-old 700mM UF6 sample. This sample showed precipitation at the bottom of the vial from which the solution was removed. This sample showed... There are 6.5 ± 1.3 U–F bonds at this location. The XANES peak shape further indicates different coordination around U.

[0105] A second set of XAFS experiments is underway, using new solutions and several reference materials with various oxidation states. Computational studies are also being conducted to simulate the system and confirm the 4' oxidation state of uranium in solution. + / 5 + Oxidized state.

[0106] Example 4

[0107] Characterization of UF6 precipitates from RTIL

[0108] Even in low-concentration samples (below 0.5 M UF6), precipitation occurred in the UF6 solution. Therefore, a high-concentration solution of 0.95 M was prepared to observe the color change and confirm the presence of cation / anion (IL / UF6). 2-Salt formation in the form of precipitates. A color change pattern similar to that observed in low-concentration samples was observed (Figure 5). The dissolution of UF6 is exothermic, and the heat can be felt through the glove box during the production of high-concentration samples. Heating the solution also accelerates the dissolution of UF6, reducing the need for stirring the solution. Initially, UF6 dissolves into a blue solution, which turns green over a period of one week.

[0109] Example 5

[0110] Uranium recovery from RTIL water

[0111] It has been found that adding water to low-concentration UF6 solutions removes F from the dissolved substances. - This accelerated the formation of the precipitate. In a 15 mL centrifuge tube, 2.93 mL of 0.21 M UF6 solution was combined with 3.0 mL of deionized H2O. The tube was placed on a microplate shaker and mixed for 1 hour. The mixture was then centrifuged at 5500 rpm for 15 minutes. A green solid precipitate was observed mainly at the bottom of the tube. A small amount of precipitate was present in the layer between water and [MPPi][TFSI]. Figure 6A -B shows similar centrifuge tubes before and after centrifugation.

[0112] Most of the aqueous and [MPPi][TFSI] layers were removed using a pipette for analysis of the remaining uranium. The precipitate was then vacuum filtered from the remaining solution. The solid was rinsed with acetone to remove most of the [MPPi][TFSI]. The filter paper was removed from the filter and dried under vacuum overnight. Figure 6C As shown, the precipitate changes from dark green to light green when dried.

[0113] The recovered precipitate weighed 0.1404 g. (PXRD) Figure 7 TGA analysis showed that the precipitate was UF4·2.5H2O. This represents a precipitate recovery rate of 31.6%. ICP-AES analysis of the aqueous phase revealed the presence of 31.6% water. UV-Vis analysis of the aqueous phase showed UO2. 2+ The five-finger characteristic was observed. A mixture of [MPPi][TFSI] and deionized water was incubated overnight to extract any remaining uranium from the organic phase. ICP-AES analysis of the second aqueous phase showed less than 0.5% uranium remaining in the [MPPi][TFSI].

[0114] After being heated to 1300°C, the hydrated UF4 is U3O8.

Claims

1. A method for converting uranium hexafluoride (UF6) into uranium tetrafluoride (UF4), the method comprising: UF6 was directly dissolved in ionic liquids at concentrations ranging from 0.01 M to 3.0 M at room temperature; The solution is incubated for a period of time; and water is added to the solution to precipitate solid UF4.

2. The method according to claim 1, wherein the concentration of UF6 in the ionic liquid is less than 2.0 M.

3. The method according to claim 1, wherein the UF6 concentration in the ionic liquid is 0.01 M, 0.02 M, 0.03 M, 0.04 M, 0.05 M, 0.06 M, 0.07 M, 0.08 M, 0.09 M, 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M, 0.6 M, 0.7 M, 0.8 M, 0.9 M, 1.0 M, 1.1 M, 1.2 M, 1.3 M, 1.4 M, 1.5 M, 1.6 M, 1.7 M, 1.8 M, 1.9 M, 2.0 M, 2.1 M, 2.2 M, 2.3 M, 2.4 M, 2.5 M, or 3.0 M.

4. The method of claim 1, further comprising chilling the UF6 before dissolving the UF6 in the ionic liquid.

5. The method of claim 1, wherein the time period includes 1 hour to 200 days.

6. The method of claim 1, wherein the time period includes 1 hour to 1 day.

7. The method of claim 1, wherein the ionic liquid comprises anions with lone pairs of electrons.

8. The method of claim 1, wherein the ionic liquid comprises a product selected from... n - Anions of bis(trifluoromethanesulfonylimide) (TFSI), dicyandiamide, trifluoroacetate, alkyl sulfonate, alkyl sulfate, bis(fluorosulfonyl)imide and trifluoromethylacetate.

9. The method according to claim 1, wherein the ionic liquid comprises n -Bis(trifluoromethanesulfonylimide) anion (TFSI) - ).

10. The method of claim 1, wherein the ionic liquid comprises a cation selected from alkyl-substituted or unsubstituted ammonium cations, alkyl-substituted or unsubstituted piperidinium cations, and alkyl-substituted or unsubstituted pyrrolidineium cations.

11. The method of claim 1, wherein the ionic liquid comprises a cation selected from tetraalkylammonium cation, dialkylpiperidine onium cation, and dialkylpyrrolidine onium cation.

12. The method of claim 1, wherein the ionic liquid comprises a 1-methyl-1-propylpiperidinium cation.

13. The method of claim 1, wherein the ionic liquid comprises 1-methyl-1-propylpiperidinium bis(trifluoromethanesulfonylimide) ([MPPi][TFSI]).

14. The method of claim 1, wherein the recovery rate of UF4 is 100%.

15. A method for producing UF6 2- The method comprises dissolving UF6 directly in an ionic liquid at a concentration of 0.01 M to 2.5 M at room temperature and incubating the solution for a period of time.

16. The method of claim 15, further comprising chilling the UF6 prior to dissolving the UF6 in the ionic liquid.

17. The method of claim 15, wherein the time period comprises 1 hour to 200 days.

18. The method of claim 15, wherein the time period comprises 1 hour to 1 day.

19. The method of claim 15, wherein the ionic liquid comprises anion with a lone pair of electrons.

20. The method of claim 15, wherein the ionic liquid comprises a selection from... n - Anions of bis(trifluoromethanesulfonylimide) (TFSI), dicyandiamide, trifluoroacetate, alkyl sulfonate, alkyl sulfate, bis(fluorosulfonyl)imide and trifluoromethylacetate.

21. The method of claim 15, wherein the ionic liquid comprises n -Bis(trifluoromethanesulfonylimide) anion (TFSI) - ).

22. The method of claim 15, wherein the ionic liquid comprises a cation selected from alkyl-substituted or unsubstituted ammonium cations, alkyl-substituted or unsubstituted piperidinium cations, and alkyl-substituted or unsubstituted pyrrolidineium cations.

23. The method of claim 15, wherein the ionic liquid comprises a cation selected from tetraalkylammonium cation, dialkylpiperidine cation, and dialkylpyrrolidine cation.

24. The method of claim 15, wherein the ionic liquid comprises a 1-methyl-1-propylpiperidinium cation.

25. The method of claim 15, wherein the ionic liquid comprises 1-methyl-1-propylpiperidinium bis(trifluoromethanesulfonylimide) ([MPPi][TFSI]).

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