WO2024066260A1 - Selenium-tungsten polyoxometalate and preparation method therefor, and use thereof in ultra-filtration separation of actinide ions - Google Patents

Abstract

Disclosed in the present invention are a selenium-tungsten polyoxometalate and a preparation method therefor, and the use thereof in the ultra-filtration separation of actinide ions. The selenium-tungsten polyoxometalate {Se6W45} is [(CH3)2NH2]15Na0.8(H3O)8.2[Se6W45O159(H2O)9]·27H2O, and belongs to a monoclinic system; the space group is P21/m; and the cell parameters are: a = 15.6207(6), b = 33.5801(11), c = 20.8294(7), α = 90º, β = 98.130(2)º, γ = 90º, and V = 10816.1(7) Å3. By dissolving an Na24[H6Se6W39O144]·74H2O precursor in water and sequentially adding an organic amine and an inorganic acid thereto to treat same, the selenium-tungsten polyoxometalate {Se6W45} is obtained. The selenium-tungsten polyoxometalate {Se6W45} is provided with a hole having a planar donor site, and the site is precisely coordinated with a pentagonal pyramid coordination geometrical shape of a hexavalent actinide ion. The selenium-tungsten polyoxometalate {Se6W45} prepared in the present invention can be selectively coordinated with a hexavalent actinide ion to form a nanocluster, such that efficient complexing and separation of the actinide ions are achieved, the interception coefficient of the actinide ions is up to 96%, the recovery rate of americium recovered by means of ultra-filtration separation reaches 92% or higher, and the problem of hexavalent americium being difficult to stabilize and separate is effectively solved.

Description

A selenotungstic polyacid and its preparation method and application in ultrafiltration separation of actinide ions Technical Field

The present invention relates to the technical field of adsorption separation, and in particular to a seleno-tungsten polyacid {Se ₆ W ₄₅ } and a preparation method thereof and application thereof in ultrafiltration separation of actinide ions.

Background technique

Americium (Am), as a byproduct of nuclear power generation, is the main contributor to the long-term radiotoxicity of high-level radioactive waste (HLW) in the nuclear fuel cycle. The effective recovery of Am and its conversion into short-lived or stable nuclides will greatly reduce the environmental impact of nuclear energy. In HLW, the coexistence of lanthanides (Lns) with high neutron cross-sections seriously affects its transmutation efficiency, thus requiring an effective separation between Am and Lns, which is one of the most challenging chemical separations in modern industry. This difficulty mainly stems from their similar chemical behaviors, because both Am and Lns exist in solution as thermodynamically stable trivalent cations, especially with almost identical ionic radii and coordination chemistries.

Traditional separation methods take advantage of the subtle bonding differences between trivalent Am ions and Lns ions, where nitrogen- or sulfur-containing extractants preferentially distribute Am over Lns through a solvent extraction process. However, this separation strategy remains hampered by the limited ability to distinguish between Am(III) and Ln(III) and the generation of large amounts of secondary radioactive organic waste. Currently, although researchers from various countries have explored various techniques, including solvent extraction, precipitation, and ion exchange, the reduction potentials of AmO ₂ ²⁺ /AmO ₂ ⁺ and AmO ₂ ²⁺ /Am ³⁺ are 1.60 V and 1.68 V (relative to SCE at pH 0), respectively. Therefore, when Am(VI) ions contact organic extractants/solvents or pass through chromatographic columns, Am(III) species can be produced within seconds, greatly reducing the efficiency of these separations. Therefore, there is an urgent need for a method that can efficiently separate actinide ions (including americium) from lanthanide ions.

Summary of the invention

The technical problem to be solved by the present invention is to provide a selenotungsten polyacid {Se ₆ W ₄₅ } and a preparation method thereof and an application thereof in ultrafiltration separation of actinide ions. The present invention prepares a selenotungsten polyacid {Se ₆ W ₄₅ } with a hole having a planar donor site, the site can be precisely coordinated with the pentagonal bipyramidal coordination geometry of actinyl ions (AnO ₂ ²⁺ ), but is not suitable for spherical coordination with lanthanide ions. Nanoscale clusters are formed by the coordination of selenotungsten polyacid {Se ₆ W ₄₅ } with hexavalent actinide ions, thereby realizing efficient separation of actinide ions and lanthanide ions.

In order to solve the above technical problems, the present invention provides the following technical solutions:

The first aspect of the present invention provides a selenotungsten polyacid {Se ₆ W ₄₅ }, whose chemical formula is [(CH ₃ ) ₂ NH ₂ ] ₁₅ Na _0.8 (H ₃ O) _8.2 [Se ₆ W ₄₅ O ₁₅₉ (H ₂ O) ₉ ]·27H ₂ O; the polyacid {Se ₆ W ₄₅ } belongs to the monoclinic system, the space group is P2 ₁ /m, and the unit cell parameters are: a=15.6207(6), b=33.5801(11), c=20.8294(7), α=90°, β=98.130(2)°, γ=90°,

The second aspect of the present invention provides a method for preparing the seleno-tungsten polyacid {Se ₆ W ₄₅ } described in the first aspect, comprising adding an organic amine salt and an inorganic acid to an aqueous solution of a precursor polyacid {Se ₆ W ₃₉ }, acidifying the solution and allowing the solution to stand to obtain the seleno-tungsten polyacid {Se ₆ W ₄₅ }; the precursor polyacid {Se ₆ W ₃₉ } is Na ₂₄ [H ₆ Se ₆ W ₃₉ O ₁₄₄ ]·74H ₂ O.

Furthermore, an organic amine salt is added to the aqueous solution of the precursor polyacid {Se ₆ W ₃₉ }, stirred and dissolved, and then an inorganic acid is added for acidification, and the selenotungsten polyacid {Se ₆ W ₄₅ } is obtained after standing for 12 to 36 hours.

Furthermore, the organic amine salt is dimethylammonium chloride and/or dimethylammonium nitrate.

Furthermore, the inorganic acid is nitric acid and/or hydrochloric acid.

Furthermore, the molar ratio of the precursor polyacid {Se ₆ W ₃₉ }, the organic amine salt and the inorganic acid is 1:100-150:100-150, for example, 1:145:126.

Furthermore, the selenotungstate polyacid {Se ₆ W ₄₅ } crystals obtained after standing are washed with cold water and then air-dried at room temperature for later use.

The third aspect of the present invention provides a method for separating tungsten selenoic acid {Se ₆ W ₄₅ } in ultrafiltration. Applications in actinide ions.

Further, an oxidant is added to the aqueous solution containing actinide ions, and after the actinide ions are converted into AnO ₂ ²⁺ , selenotungstic acid {Se ₆ W ₄₅ } is added to form nanoscale clusters with AnO ₂ ²⁺ , and ultrafiltration separation is performed; wherein An is U, Np, Pu or Am;

Furthermore, in step (1), the oxidant is cupric periodate.

Furthermore, in step (1), the nanoscale clusters are formed under the condition of pH ≤ 1.

The fourth aspect of the present invention provides a use of the seleno-tungsten polyacid {Se ₆ W ₄₅ } described in the first aspect in separating americium ions from lanthanide ions.

Furthermore, an oxidant is added to a solution containing americium ions and lanthanide ions to convert the americium ions into AmO ₂ ²⁺ , and then selenotungstic polyacid {Se ₆ W ₄₅ } is added to form nanoscale clusters with AmO ₂ ²⁺ , and the nanoscale clusters are separated by ultrafiltration, and the nanoscale clusters retained after separation are collected.

Furthermore, the nano-scale clusters formed by selenotungsten polyacid {Se ₆ W ₄₅ } and AmO ₂ ²⁺ are reduced to obtain trivalent americium ions, and the released selenotungsten polyacid {Se ₆ W ₄₅ } is recovered by ultrafiltration.

Beneficial effects of the present invention:

1. The present invention designs and synthesizes a water-soluble cryptic selenotungsten polyacid {Se ₆ W ₄₅ }, which is equipped with a cavity with a planar donor site, which can accurately match the pentagonal bipyramidal coordination geometry of AnO ₂ ²⁺ and is completely unsuitable for the spherical coordination of lanthanide ions. Therefore, the selenotungsten polyacid {Se ₆ W ₄₅ } synthesized by the present invention can accurately coordinate with AnO ₂ ²⁺ to form nanoscale clusters, so that hexavalent actinide ions, especially hexavalent americium ions, can be stabilized to a level sufficient to achieve separation applications, effectively solving the problem of instability of hexavalent americium ions in the oxidation method, and realizing efficient separation of americium ions and lanthanide ions.

2. The present invention is based on the recognition of selenotungstic polyacid {Se ₆ W ₄₅ } to coordinate AnO ₂ ²⁺ to form nano-scale clusters, which improves the stability of hexavalent actinide ions, and utilizes the size difference between nano-scale clusters and lanthanide ions to achieve rapid and efficient separation of actinide ions and lanthanide ions through ultrafiltration separation. The technical method is simple to operate, has low energy consumption, and has no secondary organic waste liquid, is environmentally friendly, and provides a new method for the separation of actinide ions and the efficient separation of lanthanum and actinide ions. Separation provides new ideas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the assembly of synthesizing selenotungsten polyacid {Se ₆ W ₄₅ } from precursor polyacid {Se ₆ W ₃₉ } in Example 1;

Fig. 2 is a UV-vis-NIR spectrogram of UO ₂ ²⁺ (a), PuO ₂ ²⁺ (b), NpO ₂ ²⁺ (c), and AmO ₂ ²⁺ (d) during the spectral titration process of Example 2;

FIG3 is the UV-vis-NIR spectrum of a 0.25 mM Am solution in 0.1 M HNO ₃ oxidized by copper (III) periodate in the presence of 2.0 eq selenotungstic acid {Se ₆ W ₄₅ } after standing for 24 h;

Figure 4 shows the self-reduction of Am(VI) in the presence of polyacid {Se ₆ W ₄₅ } or dodecane;

FIG5 is a chemical equation for the assembly reaction of selenotungstate polyacid {Se ₆ W ₄₅ } and hexavalent actinide ions;

Figure 6 shows the structure of An(VI)-POM, An(VI) and the average bond length of An＝O;

FIG7 shows single crystal images of U(VI)-POM, Np(VI)-POM, Pu(VI)-POM and Am(VI)-POM and their UV-vis-NIR spectra;

FIG8 shows the rejection coefficients of ultrafiltration separation of U(VI), Np(VI), Pu(VI), and Am(VI);

FIG9 is a comparison of separation factors and recoveries between the nano-polyacid ultrafiltration described in Example 4 and other americium oxidation separation techniques;

FIG. 10 is a schematic diagram of separating americium ions and lanthanide ions by ultrafiltration separation using selenotungstic acid {Se ₆ W ₄₅ }.

Detailed ways

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and/or" includes any and all combinations of one or more of the associated listed items.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

Example 1 Synthesis of selenotungstic acid {Se ₆ W ₄₅ }

This embodiment involves the synthesis of selenotungstic polyacid {Se ₆ W ₄₅ }. The synthesis schematic diagram is shown in FIG1 . The specific preparation process is as follows:

30 mg of Na ₂₄ [H ₆ Se ₆ W ₃₉ O ₁₄₄ ]·74H ₂ O ({Se ₆ W ₃₉ }) (0.0024 mmol) was added to a small glass bottle, dissolved with 800 μL of aqueous solution, 30 mg of (CH ₃ ) ₂ NH ₂ Cl (0.368 mmol) was added thereto, stirred to dissolve, and then 20 μL of 6M HNO ₃ solution was added to acidify. After standing for one day, colorless block crystals were obtained at the bottom of the solution. The obtained crystalline product was washed with cold water and then dried at room temperature.

As shown in Figure 1, the precursor polyacid {Se ₆ W ₃₉ } and organic amine form the target seleno-tungsten polyacid {Se ₆ W ₄₅ } under acidic conditions, and the pore size of the pore is becomes And the hole carried by the polyacid {Se ₆ W ₄₅ } has four planar oxygen ligand sites. According to single crystal X-ray diffraction (SCXRD) analysis, the prepared polyacid [(CH ₃ ) ₂ NH ₂ ] ₁₅ Na _0.8 (H ₃ O) _8.2 [Se ₆ W ₄₅ O ₁₅₉ (H ₂ O) ₉ ]·27H ₂ O (abbreviated as {Se ₆ W ₄₅ }). Theoretical value of elemental analysis: C, 2.81; H 1.70; N, 1.64; Na, 0.14; Se, 3.69; W, 64.60. Experimental value ((%)): C, 3.18; H, 1.34; N, 1.68; Na, 0.14; Se, 3.73; W, 63.29. {Se ₆ W ₄₅ } belongs to the monoclinic system, the space group is P2 ₁ /m, the unit cell parameters are: a＝15.6207(6), b＝33.5801(11), c＝20.8294(7), α＝90°, β＝98.130(2)°, γ＝90°,

Example 2 Complexation of Selenotungstate Polyacid {Se ₆ W ₄₅ } with Hexavalent Actinide Ions

This example takes actinide elements (An) ²³⁸ U, ²³⁷ Np, ²⁴² Pu and ²⁴³ Am as examples to study the complexing ability of selenotungsten polyacid {Se ₆ W ₄₅ } to hexavalent actinide ions. The specific operation is as follows:

(1) Preparation of hexavalent actinide ions AnO ₂ ²⁺ : 1.7 mg of cupric periodate was added to 400 μL of a 0.1 M HNO ₃ aqueous solution of actinide ions (0.575 mM), and the mixture was shaken for 10 min. The generation of AnO ₂ ²⁺ ions was monitored by UV-vis-NIR spectrometry.

(2) Complexation of selenotungsten polyacid {Se ₆ W ₄₅ } with hexavalent actinide ions: The method described in Example 1 The prepared selenotungsten polyacid {Se ₆ W ₄₅ } was dissolved in a 0.1 M HNO ₃ aqueous solution to prepare a 2.0 mM selenotungsten polyacid {Se ₆ W ₄₅ } solution. The selenotungsten polyacid {Se ₆ W ₄₅ } solution was added dropwise to the solution containing hexavalent actinide ions AnO ₂ ²⁺ in step (1) (10 μL each time). After shaking, the changes in the characteristic absorption peak of An(VI) were observed by a spectrometer.

The results of spectral titration are shown in Figures 2a to 2d, wherein Figures 2b to 2d are the spectral changes after adding selenotungsten polyacid {Se ₆ W ₄₅ } to NpO ₂ ²⁺ , PuO ₂ ²⁺ , and AmO ₂ ²⁺ solutions, respectively. It can be seen from the figures that the corresponding characteristic absorption peaks change significantly after adding selenotungsten polyacid {Se ₆ W ₄₅ }; the wavelength 831nm in Figure 2b corresponds to the characteristic peak of PuO ₂ ²⁺ , and 841nm corresponds to the characteristic peak of PuO ₂ ²⁺ -polyacid {Se ₆ W ₄₅ } complex (abbreviated as Pu(VI)-POM). With the increase of the titration amount of selenotungsten polyacid {Se ₆ W ₄₅ }, the absorption of the characteristic peak corresponding to 831nm decreases, and the absorption of the characteristic peak of Pu(VI)-POM corresponding to 841nm increases; the wavelength 1224nm in Figure 2c corresponds to NpO ₂ The wavelength ^666nm in Figure 2d corresponds to the characteristic peak of AmO ₂ ²⁺ , and 677nm corresponds to the characteristic peak of AmO ₂ ²⁺ -polyacid {Se ₆ W ₄₅ } complex (abbreviated as Np(VI)-POM). The ^titration data show that a 1 _{:1 complex is formed between AnO 2 2+} ^and selenotungstic polyacid {Se ₆ W _{45 } .}

The stability of the complex formed by selenotungsten polyacid {Se ₆ W ₄₅ } and hexavalent actinide ion AnO ₂ ²⁺ was further studied. Taking the extremely unstable Am(VI) as an example, the UV-vis-NIR spectrum of 0.25 mM Am in 0.1 M HNO ₃ aqueous solution oxidized by copper (III) periodate in the presence of 2.0 eq selenotungsten polyacid {Se ₆ W ₄₅ } changed within 24 hours as shown in Figure 3, and the complex product was only reduced by 0.67%. In addition, the self-reduction rate of Am(VI) in the presence of selenotungsten polyacid {Se ₆ W ₄₅ } or dodecane was studied. The results are shown in Figure 4. The reduction kinetic rate of Am(VI) in the polyacid system is only -5.71×10 ^-4 mM/h, which is at least two orders of magnitude slower than the self-reduction of free AmO ₂ ²⁺ ions or the reduction kinetic rate induced by dodecane. The above solution chemistry test results show that with the help of the strong complexation of inorganic selenotungstic polyacid {Se ₆ W ₄₅ }, Am(VI) can be continuously stabilized to a level of separation application that was previously unattainable.

Example 3 Crystal structure of hexavalent actinide polyacid (An(VI)-POM)

To further explore the interaction between AnO ₂ ²⁺ ions and selenotungstic acid {Se ₆ W ₄₅ }, this example A series of An(VI)-POM crystals were prepared by reacting AnO ₂ ²⁺ ions (An = ²³⁸ U, ²³⁷ Np, ²⁴² Pu and ²⁴³ Am) with selenotungstic acid {Se ₆ W ₄₅ } in solution. The preparation conditions and results are shown in Figure 5, wherein UO ₂ ²⁺ , NpO ₂ ²⁺ , and PuO ₂ ²⁺ were reacted with selenotungstic acid {Se ₆ W ₄₅ } at room temperature and pH 1 for 1 day to obtain the corresponding An(VI)-POM crystals, and AmO ₂ ²⁺ was reacted with selenotungstic acid {Se ₆ W ₄₅ } at 4°C and pH 1 for 6 h to obtain Am(VI)-POM single crystals.

Single crystal X-ray diffraction (SCXRD) analysis shows that the above An(VI)-POM single crystals have an isomorphous structure and belong to the monoclinic space group P2 ₁ /m; as shown in Figure 6, the AnO ₂ ²⁺ ions are completely encapsulated in the pre-designed cavities, and the equatorial oxygen atoms of the AnO ₂ ²⁺ ions are provided by four different WO ₆ ^6- groups and one coordinated water, forming a pentagonal bipyramidal coordination geometry. In An(VI)-POM, the average An＝O axial bond lengths of U(VI), Np(VI), Pu(VI) and Am(VI) are 1.734(2), 1.727(3), 1.714(4) and 1.806(5), respectively. In order to prove the oxidation state of AnO ₂ ²⁺ ions in selenotungstic polyacid {Se ₆ W ₄₅ }, solid-state UV-vis-NIR absorption spectra were tested using these single crystal samples. As shown in Figure 7, typical electronic transitions are displayed, including charge transfer transitions at 349 nm (UO ₂ ²⁺ ) and 5f→5f transitions at 841 nm (PuO ₂ ²⁺ ), 1242 nm (NpO ₂ ²⁺ ) and 674 nm (AmO ₂ ²⁺ ), which are consistent with the spectral titration results in Example 2.

The above crystallographic results and spectral data show that the vacancies in selenotungstic acid {Se ₆ W ₄₅ } can accurately match the coordination geometry of AnO ₂ ²⁺ ions.

Example 4 Ultrafiltration Separation of Actinide Ions by Selenotungstate Polyacid {Se ₆ W ₄₅ }

This embodiment uses selenotungstic polyacid {Se ₆ W ₄₅ } to perform ultrafiltration separation on hexavalent americium ions, which mainly includes oxidation, nano-scale cluster assembly, ultrafiltration separation and reduction recovery process. The specific operation steps are as follows:

(1) Oxidation: 400 μL of Am(III) (0.25 mM) in 0.1 M HNO ₃ aqueous solution was added with 1.7 mg of copper(III) periodate and shaken for 10 min. The spectroscopy confirmed that there was about 99% Am(VI).

(2) Nanoscale cluster assembly: 80 μL of the oxidized Am solution was added to 1.0 mL of a 0.1 M HNO ₃ aqueous solution containing selenotungstic polyacid {Se ₆ W ₄₅ } (polyacid concentration 0.5 mg/mL), and then placed on a shaker and shaken for 5 min;

(3) Ultrafiltration separation: Take 450 μL and use a 0.5 mL ultrafiltration tube (Pall, 3 kDa MWCO) The nano-sized clusters Am(VI)-POM were separated by centrifugation at 5000×g for 10 to 20 minutes;

(4) Reduction and recovery: Hydrogen peroxide is added to the purified Am(VI)-POM to reduce it to obtain Am(III), and then the released selenotungstic acid {Se ₆ W ₄₅ } is recovered by ultrafiltration for the next separation cycle.

Take 100 μL of each of the starting americium polyacid mixed solution, the permeate after ultrafiltration separation in step (3), and the permeate after ultrafiltration separation in step (4), add 2 mL of liquid scintillator and mix them evenly, and then measure their radioactivity with a liquid scintillation instrument. In order to quantify the separation effect, the rejection coefficient (R) is calculated by the following formula:
R＝(1-C _p /C _f )×100％ (I)

Wherein, _Cf and _Cp are the α radioactivity counts (CPM) in the starting americium polyacid mixed solution and the permeate after ultrafiltration in step (3), respectively.

In addition, this embodiment uses the above-mentioned polyacid complex ultrafiltration method to treat U(VI), Np(VI), Pu(VI) and Eu(III) respectively. The results are shown in Figure 8, where the retention coefficients of U(VI), Np(VI), Pu(VI) and Am(VI) are all over 90%. Eu is still a trivalent ion after the above-mentioned oxidation treatment, and its retention coefficient is only 1.7±0.6%. As shown in Figure 9, the separation factor of americium and lanthanide ions separated by the ultrafiltration separation method of the present invention is greater than 750, which is much higher than other separation technologies. The recovery rate is obtained by calculating the ratio of the α radioactive counts in the permeate after ultrafiltration separation in step (4) to the initial americium polyacid mixed solution. It is calculated that the recovery rate of Am after treatment by the above-mentioned method is higher than 92%, which is significantly higher than other americium oxidation-related separation technologies currently disclosed. The corresponding data are summarized in the following Table 1.

Table 1 Americium recovery rate in americium oxidation separation technology


Ref.1: BJ Mincher, LR Martin, NC Schmitt, Solv. Extract. Ion Exch. 30, 445-456 (2012).
Ref.2: M.Kamoshida, T.Fukasawa, J.Nucl.Sci.Technol.33,403-408(1996).
Ref.3: M. Kamoshida, T. Fukasawa, F. Kawamura, J. Nucl. Sci. Technol. 35, 185-189 (1998).
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Ref.5: JD Burns, BA Moyer, Inorg. Chem. 55, 8913-8919 (2016).
Ref.6:Y.Koma,A.Aoshima,M.Kamoshida,A.Sasahira,J.Nucl.Sci.Technol.3,317-32
(2002).

The above-mentioned U(VI), Np(VI), Pu(VI) and Am(VI) respectively refer to UO ₂ ²⁺ , NpO ₂ ²⁺ , PuO ₂ ²⁺ and AmO ₂ ²⁺ ; Am(III) and Eu(III) respectively refer to trivalent ions of corresponding elements.

The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims (10)

1. A seleno-tungsten polyacid {Se ₆ W ₄₅ }, characterized in that its chemical formula is [(CH ₃ ) ₂ NH ₂ ] ₁₅ Na _0.8 (H ₃ O) _8.2 [Se ₆ W ₄₅ O ₁₅₉ (H ₂ O) ₉ ]·27H ₂ O; the polyacid {Se ₆ W ₄₅ } belongs to the monoclinic system, the space group is P2 ₁ /m, the unit cell parameters are: a=15.6207(6), b=33.5801(11), c=20.8294(7), α=90°, β=98.130(2)°, γ=90°,
2. A method for preparing seleno-tungsten polyacid {Se ₆ W ₄₅ } according to claim 1, characterized in that an organic amine salt and an inorganic acid are added to an aqueous solution of a precursor polyacid {Se ₆ W ₃₉ }, and the solution is acidified and allowed to stand to obtain the seleno-tungsten polyacid {Se ₆ W ₄₅ }; the precursor polyacid {Se ₆ W ₃₉ } is Na ₂₄ [H ₆ Se ₆ W ₃₉ O ₁₄₄ ]·74H ₂ O.
3. The preparation method according to claim 2, characterized in that the organic amine salt is dimethylammonium chloride and/or dimethylammonium nitrate.
4. The preparation method according to claim 2, characterized in that the inorganic acid is nitric acid and/or hydrochloric acid.
5. The preparation method according to claim 2 is characterized in that an organic amine salt is added to the aqueous solution of the precursor polyacid {Se ₆ W ₃₉ }, stirred and dissolved, and then an inorganic acid is added for acidification treatment, and the selenotungsten polyacid {Se ₆ W ₄₅ } is obtained after standing for 12 to 36 hours.
6. The preparation method according to claim 2, characterized in that the molar ratio of the precursor polyacid {Se ₆ W ₃₉ }, the organic amine salt and the inorganic acid is 1:100-150:100-150.
7. A use of the selenotungstic polyacid {Se ₆ W ₄₅ } as claimed in claim 1 in ultrafiltration separation of actinide ions.
8. The use according to claim 7 is characterized in that an oxidant is added to an aqueous solution containing actinide ions, and after the actinide ions are converted into AnO ₂ ²⁺ , selenotungstic acid {Se ₆ W ₄₅ } is added to form nanoscale clusters with AnO ₂ ²⁺ , and ultrafiltration separation is performed; wherein An is U, Np, Pu or Am;
9. The use according to claim 8, characterized in that in step (1), the oxidant is cupric periodate; and the nanoscale clusters are formed under the condition of pH ≤ 1.
10. An application of the seleno-tungsten polyacid {Se ₆ W ₄₅ } described in claim 1 in separating americium ions from lanthanide ions, characterized in that an oxidant is added to a solution containing americium ions and lanthanide ions to convert the americium ions into AmO ₂ ²⁺ , and then the seleno-tungsten polyacid {Se ₆ W ₄₅ } is added to form nanoscale clusters with AmO ₂ ²⁺ , and the nanoscale clusters are obtained by ultrafiltration separation, the nanoscale clusters retained after separation are collected, and reduction treatment is performed to obtain trivalent americium ions, and the released seleno-tungsten polyacid {Se ₆ W ₄₅ } is recovered by ultrafiltration.