A method for separating actinium from an irradiated thorium target

Abstract

The present application relates to a kind of methods for separating actinium from irradiated thorium target, belong to medical radioisotope manufacturing technical field, solve the problem that thorium element and lanthanide element impurity content in final actinium product in prior art is higher.The present application discloses a kind of methods for separating actinium from irradiated thorium target, first, irradiated thorium target is dissolved, then using cation exchange resin column, UTEVA or TK200 resin extraction column, DGA resin extraction column, LN resin extraction column four-stage series separation purification process, obtain final actinium product.Actinium is efficiently and selectively recovered, and the thorium element and lanthanide element impurity content in final actinium product is significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of medical radioisotope manufacturing technology, and in particular to a method for separating actinium from an irradiated thorium target. Background Technology

[0002] Targeted radionuclide therapy (TRT) is one of the most promising methods for cancer treatment. This method uses highly selective carriers to deliver radionuclides to the cancerous site, utilizing the energy released from the decay of the radionuclide to kill tumor cells while minimizing damage to surrounding normal cells. Radionuclides used for targeted therapy include alpha nuclides, beta nuclides, and Auger electron nuclides. Alpha nuclides have advantages over the other two types, including high energy, high linear energy transfer (LET), and short tissue penetration distance. These advantages give them unique benefits in treating non-solid tumors and micrometastases. Ac-225 is an alpha nuclide suitable for targeted therapy.

[0003] Currently, there are three main methods for producing Ac-225: (1) separating Th-229 from U-223 with a long storage time, and then producing Ac-225 through the decay of Th-229; (2) producing Ac-225 by bombarding Ra-226 solution with protons or gamma rays; and (3) producing Ac-225 by irradiating Th-232 with protons. Due to the difficulty in obtaining materials and the high irradiation risk during the preparation process in methods one and two, the third method is the most widely used. However, when preparing Ac-225 using a Th-232 thorium target, various nuclear reactions occur, generating nearly a hundred elements. The dissolved target system is complex, and separation is difficult.

[0004] Currently, several research institutions are exploring methods for separating Ac-225 from irradiated thorium targets. For example, Los Alamos added citric acid to the target dissolution solution during Ac purification, converting Th and some fission elements into... Complexes were used to separate matrix thorium from Ac and other elements using cation exchange resin, followed by purification of Ac using DGA resin. TRIUMF in Canada, when separating Ac, first precipitated a large amount of Th and some fragmented elements with hydrogen peroxide, then passed the remaining solution through cation exchange resin, eluted the remaining Th with a citric acid / nitric acid mixture, eluted the Ra / Ac mixture with nitric acid, and finally purified with DGA resin to obtain the Ac product. Oak Ridge Laboratory passed a thorium matrix solution under a high-concentration nitric acid atmosphere through AG-MP1 resin. Similar to the complexation with citric acid, Th and some elements complexed with nitrate ions to form complex anions, which were adsorbed by the ion exchange resin, achieving separation from other elements. The Ac mixture was then sequentially passed through UTEVA / DGA extraction resin to obtain the Ac product. Lomonosov Moscow State University used a two-stage extraction process with HDEHP / toluene solution to remove Th, followed by DGA resin adsorption and TRU resin adsorption to complete the separation of Ac.

[0005] However, the actinium products obtained by existing processes have high levels of thorium and lanthanide impurities, which is not conducive to the further processing and application of actinium products. Summary of the Invention

[0006] In view of the above analysis, the present invention aims to provide a method for separating actinium from an irradiated thorium target, in order to solve the problem that the actinium products separated from irradiated thorium targets by existing processes have high thorium impurity content and lanthanide impurity content.

[0007] This invention discloses a method for separating actinium from an irradiated thorium target. First, the irradiated thorium target is dissolved, and then a four-stage tandem separation and purification process is used, consisting of a cation exchange resin column, a UTEVA or TK200 resin extraction column, a DGA resin extraction column, and an LN resin extraction column, to obtain the final actinium product.

[0008] Specifically, it includes the following steps:

[0009] S1: Dissolve the irradiated thorium target to obtain a thorium-based solution;

[0010] S2: Prepare a cation exchange resin column and pre-wash it with a first inorganic acid;

[0011] S3: Pass the thorium-based solution through a cation exchange resin column to obtain effluent F1; wash the cation exchange resin column with a first inorganic acid to obtain washing solution W1; wash the cation exchange resin column with a weakly acidic buffer solution C1 containing a complexing agent to obtain eluent E1; wash the cation exchange resin column with a second inorganic acid to obtain thorium eluent.

[0012] S4: Mix the effluent F1, washing solution W1 and elution solution E1 to obtain crude product solution FD1. Evaporate and concentrate FD1, and dissolve it with the third inorganic acid to obtain column loading solution FD2.

[0013] S5: Prepare solid phase extraction column I using UTEVA or TK200 resin and pre-wash with a third inorganic acid;

[0014] S6: Pass the loading solution FD2 through solid phase extraction column I to obtain effluent F2; wash solid phase extraction column I with the third inorganic acid to obtain washing solution W2; wash solid phase extraction column I with the fourth inorganic acid to obtain eluent E2;

[0015] S7: Solid phase extraction column II was prepared using DGA extraction resin and pre-washed with the fifth inorganic acid;

[0016] S8: Mix the effluents F2 and W2 and pass them through solid phase extraction column II to obtain effluent F3; wash solid phase extraction column II with the fifth inorganic acid to obtain washing solution W3; wash solid phase extraction column II with the sixth inorganic acid to obtain eluent E3; wash solid phase extraction column II with the seventh inorganic acid to obtain eluent E4.

[0017] S9: Solid phase extraction column III was prepared using LN resin and pre-washed with the eighth inorganic acid;

[0018] S10: Evaporate and concentrate the eluent E3, redissolve it with the eighth inorganic acid, and pass it into solid phase extraction column III. Collect the effluent and treat it as waste liquid. Continuously wash with the eighth inorganic acid to obtain eluent E5-1 and eluent E5-2. E5-1 is the final purified product.

[0019] Specifically, the first inorganic acid is a 5-5.5 mol / L nitric acid solution.

[0020] Specifically, the weakly acidic buffer solution C1 containing the complexing agent is a mixture of the complexing agent and nitric acid. The complexing agent is ammonium lactate or ethylenediaminetetraacetic acid, and the concentration of the complexing agent is 0.15-0.25 mol / L. The pH is adjusted to 5.5-6.5 with ammonium acetate.

[0021] Specifically, the third inorganic acid is a 3.5–4.5 mol / L nitric acid solution or a 1.8–2.5 mol / L hydrochloric acid solution.

[0022] Specifically, when the second inorganic acid is a nitric acid solution, the solid-phase extraction column I in step S5 is a UTEVA resin column with dipentylphosphonate as the extractant and resin particles with a particle size of 100μm to 150μm.

[0023] Specifically, when the second inorganic acid is a hydrochloric acid solution, the solid-phase extraction column I in step S5 is a TK200 resin column with tri-n-octylphosphine oxide as the extractant and resin particles of 100μm to 150μm.

[0024] Specifically, the fourth inorganic acid is a hydrochloric acid solution of 0.01–0.1 mol / L.

[0025] Specifically, the loading extractant for the LN resin is di(2-ethylhexyl) phosphate.

[0026] Specifically, the eighth inorganic acid is a hydrochloric acid solution of 0.1–0.25 mol / L.

[0027] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0028] 1. This invention innovatively employs LN resin for the separation of actinium and lanthanides, achieving excellent results and providing a new approach for the separation of radioactive elements, especially actinium and lanthanides. LN resin can utilize the subtle differences between lanthanides to separate most of them. Because LN resin has a relatively weak adsorption capacity for actinium, it is washed away first under dilute acid, followed by the sequential elution of the lanthanides. Although some actinium is mixed with the lanthanides at the end of the elution process, according to the elution curve, over 95% of the actinium can be separated purely.

[0029] 2. This invention can effectively separate impurity elements from irradiated thorium targets (thorium-based solutions). Two extraction columns, one using cation exchange resin and the other using UTEVA extraction resin (or TK200 resin), are used to effectively separate thorium from other impurity elements. DGA resin is then used to separate divalent elements, transition metals, and lanthanide elements. Finally, LN resin is used to separate actinium from lanthanides, completing the purification of actinium.

[0030] 3. This invention can effectively separate a large amount of Th element from an irradiated thorium target (thorium-based solution). Since thorium constitutes a high mass proportion in the thorium-based solution, separating thorium from other elements (including actinium) is a primary concern. Thorium is a tetravalent element, and the partition coefficient of cation exchange resin for it is very high, much greater than that of divalent and trivalent elements in the solution. By controlling the acidity to reduce the partition coefficients of other elements on the cation exchange column while maintaining effective adsorption of thorium, thorium can be separated from most other elements. At this point, some of the higher-valence trivalent elements will adhere to the resin. A complexing agent can then be used to elute the trivalent elements, especially the target element actinium, achieving a higher actinium recovery rate. Furthermore, the UTEVA extraction resin further removes thorium from the lower-valence elements, enhancing the purification of thorium.

[0031] 4. This invention can effectively separate large amounts of lanthanides from irradiated thorium targets (thorium-based solutions). DGA resin is currently a commonly used material for separating lanthanides and actinium, using a method of high-acid elution of actinium and low-acid elution of lanthanides to remove contaminants from the lanthanides. However, many experiments have shown that actinium cannot be eluted under high-acid conditions, or only a small portion of actinium is eluted. Therefore, in this method, further purification of actinium with LN resin can yield actinium products with higher purity.

[0032] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0033] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0034] Figure 1 This is a schematic diagram of a method for separating actinium from an irradiated thorium target. Detailed Implementation

[0035] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0036] This invention discloses a method for separating actinium from an irradiated thorium target. First, the irradiated thorium target is dissolved, and then a four-stage tandem separation and purification process is used, consisting of a cation exchange resin column, a UTEVA / TK200 resin extraction column, a DGA resin extraction column, and an LN resin extraction column, to obtain the final Ac product.

[0037] Specifically, it includes the following steps:

[0038] S1: Irradiate the thorium target to dissolve it, and obtain a thorium-based solution;

[0039] S2: Prepare a cation exchange resin column and pre-wash it with a first inorganic acid;

[0040] S3: Pass the thorium-based solution through a cation exchange resin column to obtain effluent F1; wash the cation exchange resin column with a first inorganic acid to obtain washing solution W1; wash the cation exchange resin column with a weakly acidic buffer solution C1 containing a complexing agent to obtain eluent E1; wash the cation exchange resin column with a second inorganic acid to obtain thorium eluent.

[0041] S4: Mix the effluent F1, washing solution W1 and elution solution E1 to obtain crude product solution FD1. Evaporate and concentrate FD1, and dissolve it with the third inorganic acid to obtain column loading solution FD2.

[0042] S5: Prepare solid phase extraction column I using UTEVA or TK200 resin and pre-wash with a third inorganic acid;

[0043] S6: Pass the loading solution FD2 through solid phase extraction column I to obtain effluent F2; wash solid phase extraction column I with the third inorganic acid to obtain washing solution W2; wash solid phase extraction column I with the fourth inorganic acid to obtain eluent E2;

[0044] S7: Solid phase extraction column II was prepared using DGA extraction resin and pre-washed with the fifth inorganic acid;

[0045] S8: Mix the effluents F2 and W2 and pass them through solid phase extraction column II to obtain effluent F3; wash solid phase extraction column II with the fifth inorganic acid to obtain washing solution W3; wash solid phase extraction column II with the sixth inorganic acid to obtain eluent E3; wash solid phase extraction column II with the seventh inorganic acid to obtain eluent E4.

[0046] S9: Solid phase extraction column III was prepared using LN resin and pre-washed with the eighth inorganic acid;

[0047] S10: Evaporate and concentrate eluent E3, redissolve it with the eighth inorganic acid, and pass it into solid-phase extraction column III. Collect the effluent and treat it as waste liquid. Continuously wash with the eighth inorganic acid to obtain eluents E5-1 and E5-2, with E5-1 being the final purified product. E5-1 is the eluent for the first 7 to 11 bed volumes, containing high-purity actinium; E5-2 is the subsequent eluent, containing not only actinium but also a certain amount of lanthanide elements and other impurities.

[0048] Specifically, step S1 involves dissolving the irradiated thorium target in 10–12 mol / L nitric acid and 0.01 mol / L hydrogen fluoride to obtain a thorium-based solution. The solution contains over 99.9% Th(NO3)4, and other impurities (collectively referred to as spallation elements) mainly include monovalent alkali metal elements (Rb). + Cs + ), divalent alkaline earth metals and transition metals (Ca) 2+ 、Sr 2+ Ba 2+ Ra 2+ Mn 2+ Cd 2 + ), trivalent lanthanide actinides (Ac 3+ La 3+ Ce 3+ 、Sm 3+ Eu3+ (etc.) and transition metals in different valence states (Ag, etc.) + Co 2+ Cr 3+ (etc.), SP-block metallic elements ([WO4]) 2- Po 4+ Pb 2+ (etc.) and halogens (Br) - I - At - The total mass of spallation elements is less than 0.1 Wt%.

[0049] Specifically, the acidity of the thorium-based solution should be adjusted to be the same as that of the first inorganic acid before loading it onto the column.

[0050] Specifically, step S2 involves pre-equilibrating the cation exchange resin with a first inorganic acid to ensure sufficient hydrogen ion exchange equilibrium between the resin and the solution; packing the ion exchange resin into a column and pre-washing the column with two bed volumes of the first inorganic acid. These steps allow the cation exchange resin to begin separating the thorium-based solution under these acidity conditions, preventing excessively high or low acidity levels that could lead to thorium leakage or affect the separation of other elements.

[0051] Specifically, in step S2, the cation exchange resin packed in the column is AG50W-X4 or AG50W-X8, or any sulfonated styrene-divinylbenzene copolymer with a crosslinking degree greater than 4. Resins with higher crosslinking degrees have a larger adsorption capacity for the elements to be adsorbed, higher strength, and better selectivity, thus enabling better removal of thorium.

[0052] Specifically, the cation exchange resin has a mesh size of 150-400 mesh, preferably 200-300 mesh. The resin exchange capacity is 0.5-4.5 meq / mL, preferably 1.5-2 meq / mL. The mesh size of the resin represents the resin particle size; larger mesh resin particles have higher selectivity, which is beneficial for improving the separation coefficient of thorium from other elements. A low exchange capacity means that more resin is needed to complete the separation; therefore, 1.5-2 meq / mL is more suitable.

[0053] Specifically, the resin-to-thorium ratio is 15–25 g resin / g thorium, preferably 19–21 g resin / g thorium, ensuring the optimal ratio of saturated to exchange sections in the separation column is 30%–70%. This prevents thorium leakage and ensures good separation of thorium from impurity elements. The height-to-diameter ratio of the resin column significantly affects the flow rate. In radioactive isotope separation, the longer the operation time, the greater the isotope consumption. A higher height-to-diameter ratio results in a slower flow rate. The height-to-diameter ratio also affects the separation effect; generally, a higher ratio leads to better element separation. The ideal height-to-diameter ratio is 4.5–7.5, preferably 5–7.

[0054] Specifically, the first inorganic acid is a nitric acid solution of 5–5.5 mol / L, preferably a nitric acid solution of 5.3–5.5 mol / L. If the acidity is too high, the hydrogen ion concentration in the solution is very high, preventing the hydrogen ions on the cation column from completing the exchange with thorium, which may cause thorium leakage. If the acidity is too low, other low-valence elements will be adsorbed on the column, reducing the recovery rate of the target element.

[0055] Specifically, a thorium-based solution is injected into a cation exchange resin column, which is loaded with a large number of tetravalent thorium ions from the solution. Other low-valence elements flow out with the solution, resulting in effluent F1, which mainly consists of fragmented elements, most of Ra, some Ac, and lanthanides.

[0056] Specifically, the cation exchange resin column is washed with a first inorganic acid at a rate of 0.5 mL / min to 0.75 mL / min, for a washing volume of 2 to 3 column volumes, yielding washing solution W1. The purpose of this washing is to flush away low-valence elements physically attached to the column, thereby improving the initial recovery rate of actinium. At this point, W1 contains trace amounts of thorium and other low-valence elements besides thorium.

[0057] Specifically, the cation exchange resin column is washed with a weakly acidic buffer solution C1 containing a complexing agent to elute the remaining Ac loaded on the cation exchange resin column, yielding eluent E1; the cation exchange resin column is then washed with a second inorganic acid to elute a large amount of Th, yielding waste liquid.

[0058] Specifically, the weakly acidic buffer solution C1 containing the complexing agent is a mixture of the complexing agent and nitric acid. The complexing agent is used to improve the recovery rate of the target element. Under the same acidity as the first inorganic acid, a small amount of the target element and other trivalent elements will be adsorbed on the column. Therefore, the remaining actinium is eluted with the complexing agent, which is ammonium lactate or EDTA (ethylenediaminetetraacetic acid). The concentration of the complexing agent is 0.15–0.25 mol / L, and the pH is adjusted to 5.5–6.5 with ammonium acetate. The carboxylic acid oxygen in ammonium lactate and the N / O functional groups in EDTA have a good complexing effect on the target element, which can elute actinium from the resin. The concentration of the complexing agent and the pH are important; a high concentration will elute a large amount of thorium from the resin, while a low concentration will not elute actinium completely. The complexing efficiency of actinium is highest in the pH range of 5.5–6.5.

[0059] Specifically, the second inorganic acid is any one or a mixture of nitric acid and hydrochloric acid solutions with a concentration of 6-8 mol / L; preferably, the concentration of the acidic solution A2 is 6.5-8.0 mol / L; the elution volume of the A2 acid solution is 18-25 bed volumes. Under high acid conditions, the hydrogen ion concentration is very high, displacing the thorium ions on the resin column and completing the thorium elution. The type of acid has little effect on the elution; it is preferable to avoid introducing other anions outside the system. An elution volume of 18-25 bed volumes can achieve complete thorium recovery.

[0060] Specifically, step S4 involves heating the crude product liquid FD1 to 82–92°C. At this temperature, HF evaporation is facilitated without causing the solution to boil. Heating is stopped when white crystals precipitate, and the remaining liquid is evaporated to dryness using residual heat.

[0061] Specifically, the third inorganic acid is a 3.5–4.5 mol / L nitric acid solution or a 1.8–2.5 mol / L hydrochloric acid solution; at this acidity, the adsorption capacity for thorium is strongest. The volume of the third inorganic acid used for dissolving in step S4 is 5–10 mL to facilitate column loading.

[0062] Specifically, the UTEVA or TK200 resin is a resin that has a specific adsorption effect on Th and other fragmented elements. This type of resin has no adsorption capacity for divalent elements such as Ba, Sr, and Ra, as well as trivalent lanthanide elements.

[0063] Preferably, when the third inorganic acid is a nitric acid solution, the solid-phase extraction column I in step S5 is a UTEVA resin column with dipentylphosphonate as the extractant. The coordinating group is a phosphonooxy atom, which has the ability to complex thorium metal, thus adsorbing thorium ions. Under nitric acid conditions, the adsorption capacity of UTEVA resin for thorium increases with increasing acidity; when the acidity is greater than 3 mol / L, K... d >2×102 The resin particle size is 100μm to 150μm. When the resin particle size is small, the selectivity for the target element will be reduced. d is the distribution coefficient, representing the proportion of a certain substance distributed in the two phases after equilibrium is reached. It can be obtained from the following formula:

[0064]

[0065] In the formula D w V represents the weight of metal ions adsorbed by a certain weight of resin in a given volume of solution; s and V m These represent the volumes of the stationary phase and the mobile phase, respectively.

[0066] Preferably, when the third inorganic acid is a hydrochloric acid solution, the solid-phase extraction column I in step S5 is a TK200 resin column with tri-n-octylphosphine oxide as the extractant. The phosphine-oxygen atoms, whose coordinating groups have a specific adsorption effect on thorium, exhibit D-type adsorption of thorium across almost all acidity ranges. w All are 10 4 It exhibits strong adsorption capacity for thorium in the vicinity. It also shows strong adsorption capacity for lanthanum-actinide elements (D). w All values ​​are less than 10, which can effectively separate thorium from other elements; the resin particle size is 100μm~150μm; however, smaller resin particle size will reduce the selectivity for the target element. w (Mass distribution ratio) refers to the weight of metal ions adsorbed by a certain weight of resin in a given volume of solution. It can be calculated using the following formula:

[0067]

[0068] A0-A S Metal ions adsorbed onto a known weight (in g) of resin; A S The metal ions in a known solution volume (in mL) are given.

[0069] Specifically, the aspect ratio of the solid-phase extraction column I is 10–15, preferably 11–13. Within this aspect ratio range, the separation effect of thorium and other elements is better.

[0070] Specifically, the fourth inorganic acid is a hydrochloric acid solution of 0.01–0.1 mol / L, preferably with a concentration of 0.01–0.03 mol / L. Within the concentration range of 0.01–0.03 mol / L, the adsorption capacity for thorium is very small, thus achieving better elution of thorium.

[0071] Specifically, the loading solution FD2 passes through solid phase extraction column I, while the non-adsorbed metal elements Ba, Pb, Sr, Ra, Ac and lanthanides flow out with the effluent F2.

[0072] Specifically, the solid-phase extraction column I was washed with a third inorganic acid to obtain washing solution W2. Other elements except thorium that were physically attached to the column were then rinsed off.

[0073] Specifically, in step S6, the volume of the third inorganic acid wash is 2 to 4 column volumes, and the flow rate is 0.75 to 1.25 mL / min, preferably 0.9 to 1.0 mL / min. If the washing rate is too high, the elements will not be completely washed; if it is too slow, thorium will be eluted.

[0074] Specifically, solid-phase extraction column I is washed with a fourth inorganic acid to obtain eluent E2. The fourth inorganic acid can be either hydrochloric acid or nitric acid solution, with hydrochloric acid being preferred. The UTEVA / TK200 resin column exhibits a low partition coefficient for thorium at any acidity, enabling thorium elution. The eluent then contains trace amounts of thorium mixed with lower valence elements after the thorium removal process using ion exchange resin, thus completing the purification of thorium from lower valence elements.

[0075] Specifically, when the extraction resin column is UTEVA resin, the elution volume of the fourth inorganic acid is 10 to 12 bed volumes, because the partition coefficient of thorium in UTEVA resin is very low under low acid conditions, and thorium is easily eluted. When the extraction resin column is TK200 resin, the elution volume of the fourth inorganic acid is 20 to 25 bed volumes. Under this acidity condition, the partition coefficient of thorium is still relatively high, so a larger elution volume is required, and the eluent flow rate is 0.5 to 0.75 mL / min.

[0076] Specifically, the fifth inorganic acid in step S7 is 3.5–5 mol / L nitric acid, preferably a 3.5–4 mol / L nitric acid solution. Under this acidity condition, the DGA resin has a strong adsorption capacity for lanthanum-actinide elements, thus completing the separation of lanthanum-actinide elements from other elements.

[0077] Specifically, the resin used is DGA resin, and the loading extractant is N,N,N',N'-tetraoctyl diethylene glycol amide. DGA resin has specific adsorption for lanthanides and Ac (Log kd > 3); the resin particle size is 100 μm to 150 μm.

[0078] Specifically, the height-to-diameter ratio of the resin column is 12 to 16.

[0079] Specifically, the F2 and W2 mixed solution is a mixture of Ac and lanthanide elements, including fission elements such as Ra, Ru, Cs, Mo, Ba, Te, Ag, Nb, and Sb.

[0080] Specifically, the effluents F2 and W2 are mixed and passed through solid-phase extraction column II to obtain effluent F3. F3 contains elements such as Ra, Ru, Cs, Mo, Ba, Te, Ag, Nb, and Sb that are not adsorbed. The amide groups in the DGA resin have no specific adsorption effect on these elements, or their adsorption capacity is very low, while their adsorption capacity for lanthanide elements is relatively high. The solid-phase extraction column II is washed with a fifth inorganic acid to obtain washing solution W3, which contains a small amount of unadsorbed elements. Ac and Lns elements are adsorbed onto the column. The solid-phase extraction column II is washed with a sixth inorganic acid to obtain eluent E3, which mainly consists of actinium and a small amount of lanthanide elements. Under high acid conditions, the DGA resin has a very low adsorption capacity for actinium. The solid-phase extraction column II is washed with a seventh inorganic acid to obtain eluent E4, which has a very low adsorption capacity for lanthanide elements under dilute acid conditions. Its main components are lanthanide elements such as La, Ce, and Nd.

[0081] Specifically, the fifth inorganic acid was a nitric acid solution with a concentration of 4.0–4.5 mol / L, a flow rate of 1.0–1.5 mL / min, and a washing volume of 2 column volumes. At an acidity of 4.0–4.5 mol / L, the adsorption capacity for lanthanides and actinides was high, enabling the separation of lanthanides and actinides from other divalent elements and impurity elements.

[0082] Specifically, the sixth inorganic acid is a nitric acid solution with a concentration of 10–12 mol / L. Under this acidity condition, the DGA resin has a low adsorption capacity for actinium, which allows for complete elution. Preferably, the nitric acid solution has a concentration of 10.5–11.5 mol / L, the washing rate is 1.0–1.5 mL / min, and the elution volume is 12–18 bed volumes. This ensures complete elution of actinium and increases its recovery rate.

[0083] Specifically, the seventh inorganic acid is a hydrochloric acid solution with a concentration of 0.1–0.01 mol / L, preferably 0.01–0.03 mol / L, the washing rate is 1.0–1.5 mL / min, and the washing volume is 12–16 bed volumes. At low acid levels, the partition coefficient of the DGA resin for lanthanides is very low, thus enabling the elution of lanthanides.

[0084] Specifically, the loading extractant of the LN resin is di(2-ethylhexyl) phosphate, and the resin particle size is 100 μm to 150 μm. The oxygen atoms in the phosphate ester have adsorption capacity for lanthanides and actinides, which can separate most lanthanides from each other under certain conditions. Because the LN resin has relatively low adsorption capacity for actinides, it will be washed off first under dilute acid washing, followed by the sequential elution of the lanthanides.

[0085] Specifically, the eighth inorganic acid is a hydrochloric acid solution of 0.1–0.25 mol / L, preferably 0.2–0.25 mol / L. At this acidity, it has a certain adsorption capacity for lanthanides and actinides, and can adsorb the elements onto the resin. In step S10, the washing flow rate is 0.3–0.5 mL / min, and the washing volume is 25–30 bed volumes. The detergent flow rate should be relatively low at this time to improve the separation coefficient between actinides and lanthanides.

[0086] Specifically, the first 7-11 bed volume of eluent, E5-1, is the final product, while the subsequent eluent, E5-2, is lanthanide waste liquid. The smaller the bed volume of E5-1, the higher the purity of Ac and the lower the recovery rate; conversely, the larger the bed volume, the lower the purity of Ac and the higher the recovery rate. This is because Ac is eluted preferentially over lanthanides.

[0087] Examples and comparative examples:

[0088] Example 1:

[0089] (1) After pretreatment of the cation exchange resin, the resin was soaked in 5.5 mol / L nitric acid for more than 2 hours. The resin was then loaded into the exchange column, and two bed volumes were washed with nitric acid of the same concentration. Thorium-based solution was passed through the cation exchange column at an acidity of 5.5 mol / L and a flow rate of 0.50 mL / min. The effluent was collected, containing monovalent, divalent, and some trivalent elements. The resin used was a hydrogen sulfonate-based styrene-divinylbenzene copolymer with a particle size of 200-400 mesh. The cation exchange resin column was washed with two bed volumes of 5.5 mol / L nitric acid to obtain the washing solution. The residual Ac on the column was eluted with a buffer solution of the complexing agent (0.15 mol / L ammonium lactate, ammonium acetate to maintain pH at 5.5 ± 0.2) at a washing rate of 0.3 mL / min to obtain the eluent E1 of Ac and lanthanides. The Th on the ion exchange column was then eluted with 7.5 mol / L nitric acid, with an elution volume of 20 bed volumes, representing over 90% of the thorium in the thorium-based solution. The effluent, washings, and eluent were mixed, evaporated, concentrated, and redissolved. The evaporation temperature was maintained at 85 ± 5 °C. When white crystals began to precipitate in the evaporation tank, the heating device was turned off, and the remaining liquid was evaporated to dryness using residual heat. 10 mL of 4.2 mol / L nitric acid was added for redissolution.

[0090] (2) UTEVA resin was pretreated by immersing it in a 6 mol / L nitric acid solution and packed into a solid-phase extraction column (SPE) I. The UTEVA resin particle size was 100–150 μm. The resin column (φ4 mm × H45 mm) was washed with two column volumes of 4.2 mol / L nitric acid. The mixed solution, excluding a large amount of Th, was passed through SPE column I. The remaining Th, Zr, Mo, and some Ag in the solution were adsorbed onto the column, and the remaining elements eluted with the effluent. The solution was washed again with two column volumes of nitric acid of column concentration to obtain the washing solution. Th and other elements on SPE column I were eluted with either 0.01 mol / L nitric acid solution or a mixture of both, and then separated from the cation exchange resin column to obtain a thorium-containing eluent (impurity eluent).

[0091] (3) Next, the DGA resin was pretreated and packed into a solid-phase extraction column II. The resin particle size was 100-150 μm, and the resin column (φ4 mm × H45 mm) was washed with 4.0 mol / L nitric acid. The effluent and washing liquid from solid-phase extraction column I were passed through solid-phase extraction column II at a flow rate of 0.75 mL / min. The effluent contained non-adsorbed elements such as Ra, Ru, Cs, Mo, Ba, Te, Ag, Nb, and Sb. Ac and Lns elements were adsorbed onto the column and solid-phase extracted with 10.0 mol / L nitric acid solution. Ac was eluted with a volume of 18 column volumes. Lns elements were eluted with a mixture of 0.01 mol / L nitric acid solution and hydrochloric acid solution (HCl: HNO3 = 1:1) with a volume of 16 column volumes.

[0092] (4) After pretreatment of LN resin, a solid-phase extraction column (SPE) III was prepared and packed into a column with a resin particle size of 100–150 μm. The resin column (φ4 mm × H35 mm) was washed with two column volumes of 0.25 mol / L hydrochloric acid solution. The eluent of Ac from SPE II was evaporated and concentrated, and then redissolved with 0.25 mol / L hydrochloric acid. The solution was passed through SPE III and the column was washed with hydrochloric acid solution of the same concentration at a washing rate of 0.35 mL / min. The first nine column volumes were collected as the final total product of Ac, and the last ten bed volumes were collected as the eluent for lanthanides (impurities).

[0093] The final Ac recovery rate reached 88.9%, with Th content less than 0.03±0.01 ng / g, La content less than 0.23±0.01 ng / g, Ce content less than 0.15±0.02 ng / g, and Eu content less than 0.08±0.01 ng / g. After dual Th removal using cation exchange resin and UTEVA resin, the thorium impurity content was reduced to a very low level. The Ac eluted from the DGA resin column was further purified by LN resin, resulting in further purification of the lanthanides.

[0094] Example 2:

[0095] (1) After pretreatment of the cation exchange resin, the resin was soaked in 5.3 mol / L nitric acid for more than 2 hours. The resin was then loaded into an exchange column and washed with two bed volumes of nitric acid of the same concentration. Thorium-based solutions were passed through the cation exchange resin column at an acidity of 5.3 mol / L and a flow rate of 0.50 mL / min. The effluent was collected, containing monovalent, divalent, and some trivalent elements. The resin used was a hydrogen-form sulfonated styrene-divinylbenzene copolymer with a particle size of 200-400 mesh. The cation exchange resin column was washed with two bed volumes of 5.3 mol / L nitric acid to obtain the washing solution. The residual Ac on the column was eluted with a buffer solution of the complexing agent (0.15 mol / L EDTA, with ammonium acetate maintaining the pH at 5.5 ± 0.2) at a washing rate of 0.5 mL / min to obtain the eluent E1 containing Ac and lanthanides. Subsequently, Th on the cation exchange resin column was eluted with 7.5 mol / L nitric acid at a volume of 20 bed layers, with over 90% of the thorium in the thorium-based solution entering this stream. The effluent, washing liquid, and eluent stream were mixed, evaporated, concentrated, and redissolved. The evaporation temperature was maintained at 85 ± 5 °C. When white crystals began to precipitate in the evaporation tank, the heating device was turned off, and the remaining liquid was evaporated to dryness using residual heat. 10 mL of 2.1 mol / L hydrochloric acid was added to redissolve the thorium.

[0096] (2) TK200 resin was pretreated by immersing it in 2.1 mol / L hydrochloric acid solution and packed into a solid-phase extraction column I. The TK200 resin particle size was 100–150 μm. The resin column (φ4 mm × H32 mm) was washed with two column volumes of 2.1 mol / L hydrochloric acid. The mixed solution, after removing a large amount of Th, was passed through solid-phase extraction column I. The remaining Th and most of the elements such as Mo, Ti, Hf, Nb, Zr, In, Sn, and Bi in the solution were adsorbed onto the column. The remaining elements eluted with the effluent and were washed again with two column volumes of nitric acid of the same concentration as the loading solution to obtain the washing solution. The fragmented elements such as Th and Mo on the solid-phase extraction column I were eluted with 0.02 mol / L nitric acid solution and separated from the cation exchange resin column to obtain a thorium-containing eluent (impurity eluent).

[0097] (3) Next, the DGA resin was pretreated and packed into a solid-phase extraction column II with a resin particle size of 100–150 μm. The resin column (φ4 mm × H45 mm) was washed with a 4.5 mol / L nitric acid solution. The effluent and washing solution from solid-phase extraction column I were passed through solid-phase extraction column II at a flow rate of 0.75 mL / min. The effluent contained non-adsorbed elements such as Ra, Ru, Cs, Mo, Ba, Te, Ag, Nb, and Sb. Ac and Lns elements were adsorbed onto the column. Column II was washed with a 10.0 mol / L nitric acid solution. Ac was eluted, with an elution column volume of 18 column volumes. Lns elements were eluted with a 0.01 mol / L nitric acid solution.

[0098] (4) After pretreatment of LN resin, a solid-phase extraction column (SPE) III was prepared and packed into a column with a resin particle size of 100–150 μm. The resin column (φ4 mm × H35 mm) was washed with two column volumes of 0.25 mol / L hydrochloric acid solution. The eluent of Ac from extraction column II was evaporated and concentrated, and then redissolved with 0.25 mol / L hydrochloric acid. The solution was passed through SPE column III and the column was washed with hydrochloric acid solution of the same concentration at a washing rate of 0.35 mL / min. The first 12 column volumes were collected as the final total product of Ac, and the last 10 bed volumes were collected as the eluent for lanthanides (impurities).

[0099] The final Ac recovery rate reached 92.8%, with Th content less than 0.02±0.01 ng / g, La content less than 0.85±0.01 ng / g, Ce content less than 0.48±0.02 ng / g, and Eu content less than 0.28±0.02 ng / g. After dual Th removal using cation exchange resin and TK200 resin, the thorium impurity content was reduced to a very low level. The Ac eluted from the DGA resin column was further purified by LN resin, resulting in further purification of the lanthanides.

[0100] Comparative Example 1:

[0101] (1) After pretreatment of the cation exchange resin, the resin was soaked in 5.5 mol / L nitric acid for more than 2 hours. The resin was then loaded into an exchange column and washed with two bed volumes of nitric acid of the same concentration. Thorium-based solutions were passed through the cation exchange column at an acidity of 5.5 mol / L and a flow rate of 0.50 mL / min. The effluent was collected, containing monovalent, divalent, and some trivalent elements. The resin used was a hydrogen-form sulfonated styrene-divinylbenzene copolymer with a particle size of 200-400 mesh. The cation exchange resin column was washed with two bed volumes of 5.5 mol / L nitric acid to obtain the washing solution. The residual Ac on the column was eluted with a complexing agent buffer solution (0.15 mol / L ammonium lactate, ammonium acetate to maintain pH at 5.5 ± 0.2) at a washing rate of 0.3 mL / min to obtain the eluent E1 containing Ac and lanthanides. The Th on the ion exchange column was then eluted with 7.5 mol / L nitric acid, with an elution volume of 20 bed volumes, representing over 90% of the thorium in the thorium-based solution. The effluent, washings, and eluent were mixed, evaporated, concentrated, and redissolved. The evaporation temperature was maintained at 85 ± 5 °C. When white crystals began to precipitate in the evaporation tank, the heating device was turned off, and the remaining liquid was evaporated to dryness using residual heat. 10 mL of 4.2 mol / L nitric acid was added for redissolution.

[0102] (2) UTEVA resin was pretreated by immersing it in a 6 mol / L nitric acid solution and then packed into a solid-phase extraction column (SPE) I. The UTEVA resin particle size was 100–150 μm. The resin column (φ4 mm × H45 mm) was washed with two column volumes of 4.2 mol / L nitric acid. The mixed solution, excluding a large amount of Th, was passed through SPE column I. The remaining Th, Zr, Mo, and some Ag in the solution were adsorbed onto the column, and the remaining elements eluted with the effluent. The solution was washed again with two column volumes of nitric acid of the same concentration used for loading, to obtain the washing solution. Th and other elements on SPE column I were eluted with a 0.01 mol / L nitric acid solution and separated from the cation exchange resin column to obtain a thorium-containing eluent (impurity eluent).

[0103] (3) Next, the DGA resin was pretreated and packed into a solid-phase extraction column II. The resin particle size was 100-150 μm. The resin column (φ4 mm × H45 mm) was washed with 4.0 mol / L nitric acid. The effluent and washing liquid from solid-phase extraction column I were passed through solid-phase extraction column II at a flow rate of 0.75 mL / min. The effluent contained non-adsorbed elements such as Ra, Ru, Cs, Mo, Ba, Te, Ag, Nb, and Sb. Ac and Lns elements were adsorbed onto the column. Column II was washed with a 10.0 mol / L nitric acid solution. Ac was eluted, with an elution volume of 18 column volumes. Lns elements were eluted with a mixed solution of 0.01 mol / L nitric acid and hydrochloric acid (HCl: HNO3 = 1:1), with an elution volume of 16 column volumes.

[0104] Without subsequent LN resin purification, Ac still contains certain lanthanides. The final Ac recovery rate reached 88.6%, with Th content less than 0.3±0.01 ng / g, La content less than 4.8±0.2 ng / g, Ce content less than 8.5±0.1 ng / g, and Eu content less than 5.5±0.1 ng / g.

[0105] According to the examples and comparative examples, LN resin has a good effect on the separation of actinium from other impurity elements, with a recovery rate of over 88.9%. The lowest possible thorium content is below 0.02 ng / g, the lowest possible lanthanide content is below 0.23 ng / g, the lowest possible Ce content is below 0.15 ng / g, and the lowest possible Eu content is below 0.08 ng / g. This effectively reduces the content of thorium, lanthanides, and other impurities in actinium products, resulting in a significant improvement in the purity of the final product.

[0106] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of separating actinium from an irradiated thorium target, characterized by: First, the irradiated thorium target is dissolved, and then a four-stage separation and purification process of cation exchange resin column, TK200 resin extraction column, DGA resin extraction column, and LN resin extraction column is used to obtain the final actinium product; The cation exchange resin column is pre-washed with a first inorganic acid; The thorium-based dissolution solution is passed through the cation exchange resin column to obtain effluent F1; the cation exchange resin column is washed with a first inorganic acid to obtain washing liquid W1; The cation exchange resin column is washed with a weakly acidic buffer solution C1 containing a complexing agent to obtain eluate E1; the cation exchange resin column is washed with a second inorganic acid to obtain a thorium eluate; The first inorganic acid is a 5-5.5 mol / L nitric acid solution, and the second inorganic acid is any one or a mixed solution of a 6-8 mol / L nitric acid solution or a hydrochloric acid solution; The method has an actinium recovery rate of 88.9% or more, a thorium element content of 0.02 ng / g or less, a lanthanide element content of 0.23 ng / g or less, a Ce content of 0.15 ng / g or less, and a Eu content of 0.08 ng / g or less.

2. The method of claim 1, wherein, Comprise the following steps: S1: Dissolve the irradiated thorium target to obtain a thorium-based dissolution solution; S2: Prepare a cation exchange resin column and pre-wash it with a first inorganic acid; S3: Pass the thorium-based dissolution solution through the cation exchange resin column to obtain effluent F1; wash the cation exchange resin column with a first inorganic acid to obtain washing liquid W1; Wash the cation exchange resin column with a weakly acidic buffer solution C1 containing a complexing agent to obtain eluate E1; wash the cation exchange resin column with a second inorganic acid to obtain a thorium eluate; S4: Mix effluent F1, washing liquid W1, and eluate E1 to obtain crude product liquid FD1, evaporate and concentrate FD1, and dissolve it with a third inorganic acid to obtain column feed liquid FD2; S5: Prepare a solid-phase extraction column I with TK200 resin and pre-wash it with a third inorganic acid; S6: Pass column feed liquid FD2 through solid-phase extraction column I to obtain effluent F2; wash solid-phase extraction column I with a third inorganic acid to obtain washing liquid W2; wash solid-phase extraction column I with a fourth inorganic acid to obtain eluate E2; S7: Prepare a solid-phase extraction column II with DGA extraction resin and pre-wash it with a fifth inorganic acid; S8: Mix effluent F2 and W2 and pass them through solid-phase extraction column II to obtain effluent F3; wash solid-phase extraction column II with a fifth inorganic acid to obtain washing liquid W3; wash solid-phase extraction column II with a sixth inorganic acid to obtain eluate E3; wash solid-phase extraction column II with a seventh inorganic acid to obtain eluate E4; S9: Prepare a solid-phase extraction column III with LN resin and pre-wash it with an eighth inorganic acid; S10: Evaporate and concentrate eluate E3, redissolve it with an eighth inorganic acid, and pass it through solid-phase extraction column III; collect the effluent as waste liquid; Wash continuously with an eighth inorganic acid to obtain eluate E5-1 and eluate E5-2, with E5-1 being the final purified product.

3. The method of claim 2, wherein: The weak acid buffer solution C1 containing a complexing agent is a mixture of a complexing agent and nitric acid, the complexing agent is ammonium lactate or ethylenediaminetetraacetic acid, the concentration of the complexing agent is 0.15-0.25 mol / L, and the pH is adjusted to 5.5-6.5 by ammonium acetate.

4. The method of claim 2, wherein: The third inorganic acid is a 3.5-4.5 mol / L nitric acid solution or a 1.8-2.5 mol / L hydrochloric acid solution.

5. The method of claim 2, wherein: When the second inorganic acid is a hydrochloric acid solution, the solid-phase extraction column I in step S5 is a TK200 resin column with a particle size of 100-150 μm and a load extraction agent of tri-n-octylphosphine oxide.

6. The method of claim 2, wherein: The fourth inorganic acid is a 0.01-0.1 mol / L hydrochloric acid solution.

7. The method of claim 2, wherein: The load extraction agent of the LN resin is di(2-ethylhexyl)phosphate.

8. The method of claim 2, wherein: The eighth inorganic acid is a 0.1-0.25 mol / L hydrochloric acid solution.

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