Process for the separation and purification of radium-224 and radium-228 in the natural thorium-232 decay chain

Abstract

The application provides a method for separating and purifying radium-224 and radium-228 in a natural thorium-232 decay chain, and belongs to the technical field of radioisotope separation. The method comprises the following steps: dissolving thorium-containing raw materials, selectively precipitating and solid-liquid separating, and obtaining a radium-containing filtrate; introducing the radium-containing filtrate into a cation exchange chromatographic column after dilution for one-dimensional radium enrichment, collecting an eluate after elution to obtain a radium enrichment sample; performing two-dimensional radium refining and purifying on the radium enrichment sample by high performance liquid chromatography, and selectively collecting a fraction containing target radium isotopes; and performing three-dimensional radium concentration and salt conversion on the fraction to obtain a target radium sample with high purity and high concentration. The application realizes the separation and purification of Ra-228 and Ra-224 in the same thorium-232 raw material system in sequence, and completes the acquisition of target nuclides in different decay stages through a highly consistent separation process, thereby having significant process universality and resource utilization advantages.

Description

Technical Field

[0001] This invention belongs to the field of radioactive isotope separation technology, and specifically relates to a method for separating and purifying radium-224 and radium-228 from the decay chain of natural thorium-232. Background Technology

[0002] Lead-212 (Pb-212, half-life of 10.64 hours) is a promising medical radionuclide, particularly suitable for targeted alpha therapy (TAT). The decay products of Pb-212, such as bismuth-212 (Bi-212) and polonium-212 (Po-212), release highly linearly energy-transfer (LET) alpha particles, exhibiting strong cytotoxic effects against tumor cells while causing relatively little radiation damage to surrounding normal tissues. Existing research indicates that Pb-212 shows promising potential in the treatment of various malignant tumors, including ovarian, prostate, and pancreatic cancer. However, its clinical application remains limited by factors such as insufficient stable sources and complex separation and purification processes.

[0003] Currently, Pb-212 is mainly obtained through Ra-224 / Pb-212 radionuclide generators. A significant source of radium-224 (Ra-224) is the decay of thorium-228 (Th-228), which in turn originates from the decay of radium-228 (Ra-228). Ra-228 further originates from the decay of natural thorium-232 (Th-232), such as... Figure 1 As shown, efficient acquisition of Ra-224 and Ra-228 is a key prerequisite for a stable supply of Pb-212. my country has abundant natural thorium resources, but due to limitations in utilization technology, thorium-containing materials or smelting residues are mostly treated directly as radioactive waste, resulting in low resource utilization. If Ra-224 and Ra-228 could be directly separated from natural Th-232, it would not only effectively alleviate the Pb-212 supply shortage but also contribute to the high-value utilization of thorium resources. Calculations show that 1 kg of Th-232 decay equilibrium can produce 0.11 mCi Ra-224 or Ra-228. However, due to the short half-life of Th-232 (1.4 × 10⁻⁶ mCi), the yield of Ra-224 and Ra-228 is significantly reduced. 10 The half-life of Ra-224 (3.63 days) and Ra-228 (5.75 years) is much longer than that of Th-232, making the isolation and purification of trace amounts of high-purity Ra-224 and Ra-228 from large quantities of Th-232 a huge challenge.

[0004] Existing radionuclide separation and purification processes mostly rely on manual operation, have low automation levels, pose a high risk of radiation exposure to personnel, and have difficulty in guaranteeing repeatability and stability.

[0005] Therefore, developing an efficient, simple, and low-cost separation and purification technology for Ra-224 and Ra-228 is crucial for improving Pb-212 production capacity and application prospects. This technology not only needs to improve the separation efficiency and purity of Ra-224 and Ra-228, but also needs to simplify operational procedures and reduce production costs, providing a reliable guarantee for their widespread application in the medical field. Summary of the Invention

[0006] In view of this, the present invention provides a method for separating and purifying radium-224 and radium-228 from the decay chain of natural thorium-232, aiming to solve at least one of the technical problems in the background art.

[0007] This invention is implemented as follows: A method for separating and purifying radium-224 and radium-228 from the decay chain of natural thorium-232, comprising the following steps: S1. Dissolve, selectively precipitate, and separate the thorium-containing raw materials (including but not limited to the following: thorium nitrate, thorium hydroxide, rare earth slag, nuclear fuel, natural minerals (such as monazite, thorium, etc.), thorium oxalate, and thorium citrate) of the natural thorium-232 decay chain to obtain radium-containing filtrate.

[0008] S2. The radium-containing filtrate is diluted and introduced into a chromatographic column filled with polymer matrix cation exchange material (sulfonated cross-linked polystyrene spheres) for one-dimensional radium enrichment. Radium is adsorbed onto the polymer matrix cation exchange chromatographic column. After elution, the eluent is collected to obtain a radium-enriched sample. The radium-containing sample is then evaporated to dryness and subsequently reconstituted with water or a weak acid (such as 0.001M~0.8M (preferably 0.2M~0.7M, more preferably 0.4M~0.6M), such as one or two of nitric acid or hydrochloric acid).

[0009] S3. Using a hybrid silica matrix cation exchange material (sulfonic acid hybrid silica) as the stationary phase, the radium enriched sample is purified by two-dimensional radium purification by high performance liquid chromatography, and fractions containing the target radium isotopes are selectively collected, the fractions being rich in Ra-224 and Ra-228.

[0010] S4. Three-dimensional radium concentration and salt conversion, specifically: the fraction obtained in step S3 is adjusted to pH < 2 with nitric acid or hydrochloric acid, while the concentration of anions or cations is controlled to be ≤ 0.5 M (preferably ≤ 0.45 M, more preferably ≤ 0.4 M) by dilution with water. The diluted fraction is introduced into a chromatographic column packed with polymer matrix cation exchange resin for adsorption, followed by elution to obtain a high-purity, high-concentration target radium sample.

[0011] Furthermore, the polymer matrix cation exchange resin in S4 is modified with sulfonic acid functional groups; the eluent is collected after elution with inorganic acid (such as 2M~15M (preferably 4M~12M, more preferably 7M~9M) nitric acid, 1M~12M (preferably 3M~8M, more preferably 4M~6M) hydrochloric acid) or organic acid (such as 50mM~500mM (pH =3~6) citric acid (preferably 100mM~400mM (pH =3.5~5.5), more preferably 200mM~300mM (pH =4~5))).

[0012] Furthermore, step S1 specifically includes: S11. Dissolve the thorium-containing raw material of the natural thorium-232 decay chain in water or an acidic solution of 0.001M to 15M (preferably 0.1M to 10M, more preferably 1M to 4M) (such as one or both of nitric acid and hydrochloric acid) to obtain a thorium solution, wherein the concentration of thorium ions is in the range of 0.1M to 1.5M (preferably 0.3M to 1.2M, more preferably 0.5M to 0.8M).

[0013] S12. A precipitant selected from sodium hydroxide (e.g., 0.5M~8M (preferably 1M~6M, more preferably 3M~5M)), potassium hydroxide (e.g., 0.5M~6M (preferably 1M~6M, more preferably 3M~5M)), oxalic acid (e.g., 0.5M~1M (preferably 0.6M~0.9M, more preferably 0.7M~0.8M)), citric acid (e.g., 0.2M~1.5M (preferably 0.4M~1.2M, more preferably 0.6M~0.7M)), or ammonia (e.g., 4M-10M (preferably 5M~8M, more preferably 6M~7M)) is added to the thorium solution. To ensure precipitation, the molar ratio of sodium hydroxide to thorium should be controlled at approximately 7:2~4:1 (preferably 15:4~4:1, more preferably...). The molar ratio of potassium hydroxide to thorium is approximately 7:2 to 4:1 (preferably 15:4 to 4:1, more preferably 19:5 to 4:1); the molar ratio of oxalic acid to thorium should be in the range of 2:1 to 4:1 (preferably 2 to 3:1, more preferably 5:2 to 8:3); the molar ratio of citric acid to thorium should be in the range of 1:1 to 6:1 (preferably 3:2 to 4:1, more preferably 2 to 3:1); the molar ratio of ammonia to thorium is approximately 7:2 to 4:1 (preferably 15:4 to 4:1, more preferably 19:5 to 4:1); in order to precipitate thorium as completely as possible and reduce the influence of errors in the experiment, this step adopts a method of synergistic regulation of the amount (molar ratio) of precipitant and pH value to achieve precise control of the precipitation process. First, by controlling the molar ratio of precipitant to thorium within the aforementioned range, initial precipitation of thorium in the system is achieved. Based on this, considering that the buffering capacity of the solution decreases when pH > 4.5 and that pH is highly sensitive to changes in the amount of alkali added, relying solely on theoretical calculations is prone to deviation. Therefore, a small amount of alkali solution is used for fine adjustment. Specifically, by adding a trace amount of alkali solution (such as sodium hydroxide and / or potassium hydroxide), the pH of the system is finely adjusted a second time, so that the final pH is controlled between 5 and 10 (preferably 6 to 9, more preferably 7 to 8), thereby achieving stable control of the thorium precipitant system.

[0014] S13. Solid-liquid separation, wherein the main component of the solid is thorium precipitate and the liquid is radium-containing filtrate.

[0015] Furthermore, the thorium precipitate is recycled as the thorium-containing raw material in S1. Step S1 is repeated, and the eluent is collected to obtain a filtrate rich in Ra-224. The thorium precipitate is then recycled after being placed as the thorium-containing raw material in S1 for 2 to 20 days (preferably 5 to 15 days, more preferably 8 to 10 days). Step S1 is repeated, and the eluent is collected to obtain a filtrate rich in Ra-224.

[0016] Further, the one-dimensional radium enrichment includes column equilibration, sample loading, elution, and radium elution of a chromatographic column packed with a polymer matrix cation exchange material. Before sample loading, the concentration of cations (such as thorium, sodium, potassium, and ammonium ions) in the radium filtrate is reduced to below 0.5 M (preferably to 0.45 M, more preferably to 0.4 M) by dilution with water. The column equilibration is performed using water or acid (0.001 M to 0.5 M (preferably 0.01 M to 0.3 M, more preferably 0.1 M to 0.2 M), such as one or two of nitric acid or hydrochloric acid) to equilibrate to 1 BV to 5 BV (preferably 1 BV to 4 BV, more preferably 2 BV to 3 BV). The sample volume loaded does not exceed 500 BV (preferably not more than 500 BV). The elution process uses 0.001M to 0.8M (preferably 0.01M to 0.5M, more preferably 0.1M to 0.2M) of dilute acid (such as one or both of nitric acid and hydrochloric acid) to elute for 1BV to 20BV (preferably 5BV to 15BV, more preferably 8BV to 12BV); the elution process uses 1M to 15M of concentrated acid (such as one or both of nitric acid and hydrochloric acid, 2M to 15M (preferably 4M to 12M, more preferably 7M to 9M) of nitric acid, 1M to 12M (preferably 3M to 8M, more preferably 4M to 6M) of hydrochloric acid) to elute for 3BV to 6BV, and the target radium component is generally eluted within the first 1BV to 3BV column volume.

[0017] Furthermore, during the two-dimensional radium purification operation, at least the following conditions (a) and (b) must be met: (a) Before loading the sample, the concentration of cations (such as thorium ions, sodium ions, potassium ions, ammonium ions, etc.) in the radium sample is reduced to below 0.2M by dilution.

[0018] (b) When loading the sample, the solution pH should be controlled at 0.5~10.

[0019] The separation process includes column equilibration, sample loading, and elution of a chromatographic column packed with a hybrid silica matrix cation exchange material. The column equilibration is carried out with water or acid (0.001M~0.5M) for 1BV~5BV. The sample volume loaded does not exceed 1BV. The elution process uses a chelating agent of 0.1M~1M (such as citric acid, α-hydroxyisobutyric acid) (pH 1~6) for elution of 3BV~10BV. The target radium component is generally eluted within 3BV~3.4BV.

[0020] Furthermore, in the two-dimensional radium purification process of S3, the functional group of the hybrid silica matrix cation exchange material is a sulfonic acid group (propanesulfonic acid), and the matrix is ​​a vinyl hybrid silica. This cation exchange material is synthesized through an olefin-thiol click reaction.

[0021] Furthermore, in S3, the collected fractions are left to stand for 1 hour before their radioactivity is measured, and selective collection is performed based on the level of radioactivity. The polymer matrix cation exchange material is sulfonated cross-linked polystyrene spheres. The preparation process of the sulfonated cross-linked polystyrene spheres is as follows: 2L~6L of 0.4%~0.6% polyvinyl alcohol aqueous solution, 8g~12g of azobisisobutyronitrile, 180g~220g of divinylbenzene, and 360g~440g of xylene are mixed evenly and heated and stirred at 80℃~120℃ for 5h~7h. The reaction solution is filtered, washed with water and ethanol sequentially, and dried at 50℃~70℃ for 12h~20h to obtain polystyrene microspheres. 80mL~120mL of 96%-98% concentrated sulfuric acid and 8g~12g of polystyrene microspheres are mixed evenly and reacted at 25℃~35℃ for 45h~50h. The reaction solution is diluted with water and filtered, washed with water and ethanol sequentially, and dried at 50℃~70℃ for 12h~20h to obtain the sulfonated cation exchange packing material.

[0022] This invention uses thorium-232 as a starting material. First, through the dissolution, selective precipitation, and solid-liquid separation of natural thorium, a thorium-based solution suitable for radium separation is obtained. Subsequently, through one-dimensional radium enrichment and separation, two-dimensional radium purification, and three-dimensional radium concentration and salt conversion steps, efficient separation and purification of the target radium isotope is achieved. The above separation process is used initially to separate and purify Ra-228 from the natural Th-232 system. After Ra-228 separation, the thorium-based system decays to Ra-224 over a certain period, and the same separation process is used again to separate and purify Ra-224. The core of this invention lies in optimizing precipitation conditions, multidimensional chromatographic parameters, and process connections, enabling the same separation process system to be applied simultaneously to the separation and purification of Ra-228 and Ra-224. This eliminates the need to redesign independent processes for different Ra isotopes, thereby significantly improving the utilization efficiency of Th-232 resources and reducing process complexity and production costs.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention combines precipitation separation and multidimensional chromatographic separation strategies to address the problem of multiple nuclides coexisting and complex matrix in natural Th-232, achieving highly selective separation of Ra-224 and Ra-228, with the obtained products exhibiting high separation yield and radiochemical purity.

[0024] 2. The separation method described in this invention has stable process and good repeatability within the allowable experimental error range, making it suitable for continuous and standardized operation.

[0025] 3. The separation process of this invention is reasonably designed, the steps are simple, the operating conditions are mild, and the operability is strong, which helps to reduce the risk of human intervention and radiation exposure to personnel. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the decay chain of Th-232. Figure 2 This is a schematic diagram illustrating the process of extracting Ra-224 and Ra-228 from Th-232 in this invention; Figure 3 This is a flowchart of the separation and purification process of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] A method for separating and purifying radium-224 and radium-228 from the decay chain of natural thorium-232, the principle and process of which are as follows: Figure 2 and Figure 3 As shown. The method includes the following steps: S1. Dissolve, selectively precipitate and separate the thorium-containing raw materials of the natural thorium-232 decay chain (including but not limited to the following: thorium nitrate, thorium hydroxide, rare earth slag, nuclear fuel, natural minerals (such as monazite, thorium, etc.), thorium oxalate, thorium citrate, or one or more of these) to obtain radium-containing filtrate.

[0029] Th usually exists in the form of thorium nitrate or other soluble thorium salts; after one Ra-228 separation, the remaining Th mostly exists in the form of thorium precipitates (such as thorium hydroxide, thorium oxalate, and thorium citrate).

[0030] S1 specifically includes: S11. Dissolve the above-mentioned thorium-containing raw material solid in water or an acidic solution (such as nitric acid or hydrochloric acid solution). The concentration range of the acidic solution can be controlled within the range of 0.001M to 15M, and the concentration range of thorium ions is 0.1M to 1.5M.

[0031] S12. After the Th-containing sample is dissolved to obtain a thorium solution, a precipitant solution (selected from sodium hydroxide (e.g., 0.5M~8M), potassium hydroxide (e.g., 0.5M~6M), oxalic acid (e.g., 0.5M~1M), citric acid (e.g., 0.2M~1.5M), or ammonia (e.g., 4M~10M)) is added to the thorium solution at a temperature of room temperature to 120℃. To ensure precipitation, the molar ratio of sodium hydroxide to thorium should be controlled at 7:2 to 4:1. The molar ratio of potassium hydroxide to thorium is approximately 7:2 to 4:1 (preferably 15:4 to 4:1, more preferably 19:5 to 4:1); the molar ratio of oxalic acid to thorium should be in the range of 2:1 to 4:1 (preferably 2 to 3:1, more preferably 5:2 to 8:3); the molar ratio of citric acid to thorium should be in the range of 1:1 to 6:1 (preferably 3:2 to 4:1, more preferably 2 to 3:1). The molar ratio of ammonia to thorium is approximately 7:2 to 4:1 (preferably 15:4 to 4:1, more preferably 19:5 to 4:1). To ensure complete thorium precipitation and minimize experimental errors, this step employs a coordinated approach of controlling the amount of precipitant (molar ratio) and pH value to achieve precise precipitation control. First, by controlling the molar ratio of precipitant to thorium within the aforementioned range, initial thorium precipitation is achieved in the system. Based on this, considering the reduced buffering capacity of the solution at pH > 4.5 and the high sensitivity of pH to changes in the amount of alkali added, relying solely on theoretical calculations is prone to deviation. Therefore, a small amount of alkali solution is used for fine-tuning. Specifically, by adding a trace amount of alkali solution (such as sodium hydroxide and / or potassium hydroxide), the pH of the system is fine-tuned a second time, ensuring the final pH is controlled between 5 and 10 (preferably 6 to 9, more preferably 7 to 8), thereby achieving stable control of the thorium precipitant system.

[0032] Separation is achieved by utilizing the difference in solubility between Th and Ra under certain reaction conditions. Under these conditions, Th ions react with the precipitant to form insoluble precipitates (such as thorium oxalate, thorium citrate, and thorium hydroxide), which deposit at the bottom of the reaction vessel. Meanwhile, Ra ions, due to their high solubility in this system, remain stably in the liquid phase, thus achieving the initial separation of Ra from a large amount of Th. This step significantly reduces the load and interference of Th on subsequent chromatographic separation processes. The key to this step lies in the precise control of reaction conditions to ensure sufficient precipitation of Th while avoiding co-precipitation loss of Ra, thereby ensuring the recovery rate of the target Ra.

[0033] The examples below use alkaline hydroxides (such as potassium hydroxide) as examples, but are not limited thereto; other unlisted precipitants are also applicable within this scope.

[0034] After S13 and thorium precipitate are formed, the resulting solid-liquid mixture is subjected to solid-liquid separation. The radium-containing filtrate is filtered and then flows into the sample loading tank for subsequent enrichment treatment; while the solid precipitate is retained in the filter tank.

[0035] The collected thorium precipitate can be recycled and reused. Specifically, after filtration, an acidic solution (such as one or both of 1M-10M nitric acid or hydrochloric acid) can be added to the precipitate to redissolve it. In this invention, the fresh Th-232 raw material system is preferentially used for the separation of Ra-228; after one Ra-228 extraction and 2-20 days, the same Th-232 system can be used again for the separation and purification of Ra-224, thereby achieving the phased and efficient utilization of Th resources.

[0036] S2, one-dimensional radium enrichment: The radium-containing filtrate is diluted and introduced into a chromatographic column filled with polymer matrix cation exchange material. Radium is adsorbed onto the cation exchange chromatographic column. After elution, the eluent is collected to obtain a radium-enriched sample. After solid-liquid separation is completed, the radium-containing filtrate collected in step S1 is appropriately diluted with water to reduce the cation concentration (such as thorium ions, sodium ions, potassium ions, ammonium ions, etc.) to below 0.5M. The diluted radium-containing filtrate is used as the loading solution.

[0037] Subsequently, the treated sample was introduced into a cation exchange chromatography column, where radium was selectively adsorbed onto the column by utilizing its cation exchange properties in the system.

[0038] One-dimensional radium enrichment typically involves column equilibration, sample loading, elution, and radium elution. Column equilibration is performed using water or acid (0.001M~0.5M) for 1 BV~5 BV. The sample volume loaded does not exceed 500 BV. The elution process uses 0.001M~0.8M dilute acid (such as one or two of nitric acid or hydrochloric acid) for 1 BV~20 BV. Elution is performed using 1M~15M concentrated acid (such as one or two of nitric acid or hydrochloric acid) for 3 BV~6 BV. The target radium component is generally eluted within 1 BV~3 BV.

[0039] The resulting radium-enriched samples typically contain trace amounts of other metal ions. Therefore, these Ra samples often fail to meet the purity requirements for medical isotope production and require further separation and purification.

[0040] Ra-224 and Ra-228 obtained through one-dimensional radium enrichment can be used directly as needed; alternatively, the samples can be concentrated using an evaporation device. Specifically, the sample is evaporated to dryness and then re-dissolved in a suitable solvent for subsequent use. The concentration or evaporation process can be flexibly selected according to process conditions, including but not limited to rotary evaporators, nitrogen blowing devices, or infrared lamp heating.

[0041] S3, Two-dimensional radium purification: Using a hybrid silica matrix cation exchange material (sulfonic acid-based hybrid silica, patent pending) as the stationary phase, the radium-enriched sample obtained by S3 is purified by two-dimensional radium purification by high performance liquid chromatography. Fractions containing the target radium isotopes are selectively collected, and the fractions are rich in Ra-224 and Ra-228.

[0042] Since the Ra-224 and Ra-228 radium-enriched samples obtained by S2 one-dimensional radium enrichment still contain impurity metal ions, this step of the two-dimensional radium purification process employs high-performance chromatography (HPLC) to further refine the target radium isotopes. The stationary phase used is a hybrid silica matrix cation exchange material with sulfonic acid groups (propanesulfonic acid) as the functional group and vinyl hybrid silica as the matrix. This cation exchange material is synthesized via an olefin-thiol click reaction.

[0043] In the process of two-dimensional radium purification, the control of sample loading conditions is particularly critical: First, the concentration of cations in the sample needs to be controlled, usually by diluting with water to reduce the concentration of cations (such as thorium ions, sodium ions, potassium ions, ammonium ions, etc.) to below 0.2M; second, the acidity of the sample needs to be adjusted, and the pH of the solution is generally controlled in the range of 0.5~10 when loading the sample.

[0044] After sample loading, a gradient elution method can be used to effectively separate Ra-224 and Ra-228 from other metal ions, thereby selectively collecting the fraction rich in the target radium isotope. This step yields Ra-224 and Ra-228 with extremely high radiochemical purity, which can be directly used in the construction of Ra / Pb generators or further converted into other organic salts or inorganic acid systems.

[0045] S4. Three-dimensional radium concentration and salt conversion: Adjust the pH of the fraction obtained in step S3 to <2 (dilution is required if necessary), introduce the diluted fraction onto the polymer matrix cation exchange material for adsorption, and then perform rinsing and elution to obtain a high-purity, high-concentration target radium sample.

[0046] The fraction rich in Ra-224 and Ra-228 obtained from the S3 two-dimensional radium purification process can be used directly; alternatively, it can be further concentrated and converted to salt according to the actual situation.

[0047] Specifically: Radon fractions of Ra-224 and Ra-228 obtained from two-dimensional radium purification are selectively collected based on their radioactivity levels. The sample pH (e.g., pH < 2) and ionic strength (anion or cation metal ion concentration ≤ 0.5 M) are controlled. The diluted fraction is then introduced onto a polymer-matrix cation exchange resin column for adsorption / desorption. The separation process includes column equilibration with acid (e.g., 0.001 M–1 M nitric acid or hydrochloric acid), with an equilibration volume of not less than 1 BV. Radon-containing samples are then loaded. After loading, the column is eluted with acid (e.g., 0.001 M–1 M nitric acid or hydrochloric acid), with an elution volume of not less than 1 BV. Finally, radium is eluted with a strong acid (e.g., 2–15 M nitric acid or 1 M–12 M hydrochloric acid), with an elution volume of not less than 2 BV. The eluent is collected, yielding the target radium sample with a radionuclear purity > 99.8% and a yield > 90%.

[0048] Ra-224 and Ra-228 obtained through three-dimensional radium concentration and salt conversion can be used directly. When the eluent is an inorganic acid system, the sample can be further concentrated by evaporation, or it can be directly evaporated to dryness and then reconstituted for use. The evaporation or concentration process can be completed by rotary evaporator, nitrogen blowing device, or infrared lamp heating, depending on the process requirements.

[0049] Example 1 This example describes the extraction of Ra-228 and Ra-224 from 9 kg of thorium nitrate, including the following steps: S1. Dissolution, precipitation, and solid-liquid separation of Th-containing raw materials. In a plastic container containing 9 kg of thorium nitrate hexahydrate (Shanghai Yi'en Chemical Technology Co., Ltd., Ron brand, 98% purity, tested to contain approximately 200 μCi of Ra-228 and 300 μCi of Ra-224; due to the shorter half-life of Ra-224, the yield was calculated based on Ra-228), 0.1 M nitric acid was added directly (dissolves quickly with no significant exothermic reaction). The solution was slowly shaken to dissolve. Due to the high viscosity of the thorium nitrate solution, it was added directly to the precipitation vessel via a peristaltic pump and tubing. As the thorium nitrate solution in the container decreased, dilute nitric acid was added multiple times until all the thorium nitrate was dissolved and added to the precipitation vessel. A total of 10 L of 0.1 M nitric acid and 1 L of pure water were added (to rinse the container and tubing). The thorium nitrate solution in the precipitation vessel was diluted with water to a total volume of approximately 25 L. Stirring was started at a speed of 320-350 rpm (330 rpm in this case). The heating vessel was turned on, and when the internal temperature reached 80-100℃ (90℃ in this case), 4M potassium hydroxide solution was added. After adding 15 L of potassium hydroxide solution (flow rate 100 mL / min), the online pH meter and its associated peristaltic pump were turned on (speed 320-350 rpm, 330 rpm in this case). The molar ratio of potassium hydroxide to thorium was also 4:1. Due to slight changes in the water absorption of thorium nitrate, several tens of milliliters of 4M potassium hydroxide were added to raise the pH of the system to 6.3. The total volume of the system in the precipitation vessel was 40 L. After filtration, thorium precipitate and radium-containing filtrate were obtained, with a volume of 30 L of radium-containing filtrate.

[0050] S2, one-dimensional radium enrichment The specific synthesis process of the polymer matrix cation exchange material (sulfonated cross-linked polystyrene spheres) used for one-dimensional radium enrichment and three-dimensional concentration-conversion is as follows: 4 L of 0.5% polyvinyl alcohol aqueous solution, 10 g of azobisisobutyronitrile, 200 g of divinylbenzene, and 400 g of xylene were mixed evenly and heated and stirred at 100 °C for 6 h. The reaction solution was filtered, washed successively with water and ethanol, and dried at 60 °C for 16 h to obtain polystyrene microspheres. 100 mL of 96%-98% concentrated sulfuric acid and 10 g of polystyrene microspheres were mixed evenly and reacted at 30 °C for 48 h. The reaction solution was diluted with water, filtered, washed successively with water and ethanol, and dried at 60 °C for 16 h to obtain the sulfonated cation exchange packing material.

[0051] The obtained radium-containing filtrate was further processed by introducing it into a polymer-based cation exchange column (sulfonated cross-linked polystyrene spheres) (column specifications: 50mm × 250mm, inner diameter × height). The specific steps are as follows: (1) Sample loading: First, use 1 L of water to equilibrate the column. Take 30 L of filtrate, add 90 L of water to dilute it, and then load the diluted filtrate at a flow rate of 400 mL / min.

[0052] (2) Washing: After the sample loading is completed, the column is washed with 0.2M nitric acid aqueous solution at a flow rate of 200mL / min to remove impurities.

[0053] (3) Elution: The column was eluted with 8M nitric acid aqueous solution at a flow rate of 200 mL / min. The eluent was collected in sample vials at volumes of 400 mL for the first fraction, 600 mL for the second fraction, 500 mL for the third fraction, and 500 mL for the fourth fraction. Testing showed that Ra-228 and Ra-224 were mainly concentrated in the second 600 mL sample vial. The activity of Ra-228 was approximately 192 μCi, and the yield was 96%. The obtained Ra-228 and Ra-224 samples were evaporated to dryness using a rotary evaporator.

[0054] This embodiment demonstrates that the precipitation filtration and chromatographic enrichment elution process can effectively separate and enrich trace amounts of Ra-228 and Ra-224 from a large amount of thorium nitrate.

[0055] S3, Two-dimensional radium purification Add 50 mL of pure water to 600 mL of evaporated sample containing Ra-228 (approximately 192 μCi) and Ra-224. The solid Ra sample completely dissolves in the water, forming a pale green transparent solution with a pH of approximately 1–1.5. The concentration of cations in the sample (such as thorium, sodium, potassium, and ammonium ions) is less than 0.2 M.

[0056] The specific synthesis process of the hybrid silica matrix cation exchange material used in the two-dimensional purification is as follows: 1142g of vinyltriethoxysilane and 2917g of tetraethyl orthosilicate were dissolved in 2040g of anhydrous ethanol, and 10mL of triethylamine was added. The mixture was stirred at 35℃ for 16h. The reaction solution was distilled under reduced pressure at 80℃ until no liquid was distilled off, yielding silica sol. After cooling to room temperature, 1000g of xylene was added and stirred until homogeneous. Separately, 12L of water, 240g of Tween 20, and 2160g of anhydrous ethanol were mixed and added, and emulsified at 500rpm for 10min. Immediately afterward, 500g of ammonia solution with a mass concentration of 26-28% was added, and the mixture was reacted at 55℃ for 16h. The product was washed successively with methanol and water, and dried to obtain vinyl hybrid silica microspheres. Under nitrogen protection, 50g of sodium 3-mercapto-1-propanesulfonate and 10g of azobisisobutyramidine hydrochloride were dissolved in 150mL of water, and 50g of... The mixture of microspheres and 350 mL of methanol was reacted at 56 °C for 24 h; the product was filtered, washed successively with water and methanol, dried, and then dried to obtain sulfonic acid-based hybrid silica gel chromatographic packing material.

[0057] Two-dimensional chromatography was performed using a column packed with a hybrid silica matrix cation exchange material. The specific steps are as follows: Two mobile phases were prepared in the experiment: mobile phase A was citric acid solution (5 L, 600 mM, pH=4.5), and mobile phase B was pure water. Separation was performed using a hybrid silica gel-based cation exchange column (column dimensions: 30 mm × 250 mm, inner diameter × height). The column was equilibrated with 300 mL of water, and 50 mL of Ra-containing sample was loaded at a flow rate of 20 mL / min. A gradient elution method was used, divided into two stages. In the first stage, the volume fraction of mobile phase A was gradually increased from 30% to 100%, while the volume fraction of mobile phase B was gradually decreased from 70% to 0%. The elution flow rate was 20 mL / min (total flow rate of mobile phases A and B), and the elution time was 18 min. Subsequently, the volume fraction of mobile phase A was maintained at 100%, the elution flow rate was 20 mL / min, and the elution time was 7 min. The total elution volume for two-dimensional purification was approximately 500 mL.

[0058] Radium elution occurred approximately 21 minutes later. A 20 mL fraction was collected every 1 minute. The radioactivity of each fraction was measured (Table 1). The results showed that radioactivity was detected in fractions 1 through 4, and the activity increased continuously over time, indicating that all fractions contained radium. The total Ra-228 activity in the four fractions was approximately 188 μCi. The second fraction had the highest activity, followed by the first and third fractions, while the fourth fraction had a relatively lower activity. Overall, the experiment was stable, the separation was effective, and the expected experimental objectives were largely achieved.

[0059] Table 1

[0060] S4, Three-dimensional radium concentration and salt conversion Fractions 1-4 containing Ra were mixed and loaded onto a polymer-based cation exchange medium (sulfonated cross-linked polystyrene spheres, synthesis process see S2, one-dimensional radium enrichment) (column specifications: 10mm*150mm, inner diameter × height). The column was first equilibrated with 40mL of 0.1M nitric acid at a flow rate of 20mL / min, followed by loading of the sample (188μCi, 80mL) at a flow rate of 4mL / min. The mobile phase for online dilution of the loaded sample was 0.1M nitric acid at a flow rate of 16mL / min. After loading, the column was eluted with 0.1M nitric acid at a flow rate of 20mL / min for 10min. Subsequently, the column was eluted with 8M nitric acid at a rate of 5mL / min, with an elution volume of 75mL. The specific fraction activities are shown in Table 2, and a total of 184μCi Ra-228 was collected. The overall yield of three-dimensional Ra-228 was 92%, and the radionuclide purity was >99.8%.

[0061] This embodiment demonstrates through a full-process experiment that the method can effectively separate and purify Ra-228 and Ra-224 from thorium nitrate.

[0062] Table 2

[0063] This embodiment successfully separated and purified Ra-228 and Ra-224 from 9 kg of thorium nitrate precursor through a full-process experiment. S1 selective precipitation effectively separated Ra from Th, with a Ra loss rate of less than 5%. S2 one-dimensional radium enrichment successfully enriched Ra from the bulk sample into a smaller volume sample; the selected polymer matrix cation exchange material exhibited excellent adsorption capacity for Ra. S3 two-dimensional radium purification, using gradient elution, successfully separated Ra from other residual impurity ions, achieving efficient Ra purification. Finally, S4 three-dimensional concentration and salt conversion resulted in a stable Ra yield of approximately 92%, with a radionuclear purity exceeding 99.8%. The experimental process parameters were stable and controllable, fully verifying the feasibility and superiority of the method described in this invention for the efficient separation and purification of Ra-228 and Ra-224 in the thorium-232 system.

[0064] Example 2 The process and conditions in this embodiment are basically the same as the dissolution and precipitation process of Th raw material in step S1 of embodiment 1, except that the pH at the precipitation endpoint is higher (pH = 11.27).

[0065] This example describes a 109g-grade thorium nitrate precipitation experiment, including the following steps: 109 g of thorium nitrate hexahydrate (Shanghai Maclean Biochemical Technology Co., Ltd., reagent grade, 98% purity) was dissolved in 300 mL of 0.01 M nitric acid solution, resulting in a total volume of 332 mL. A 60 mL sample was taken, and the Ra-228 concentration was measured to be 0.54 μCi. Subsequently, approximately 185 mL of 4 M potassium hydroxide solution was added under stirring (290 rpm), and the pH reading was 11.27 using a precision pH meter. After filtration, 60 mL of the filtrate was collected one day later, and the Ra-228 concentration was measured to be approximately 0.05 μCi, indicating that Ra-228 had been largely precipitated or adsorbed onto a precipitate.

[0066] This example demonstrates that Ra may be lost through co-precipitation or adsorption under high pH (pH=11.27) or excessive alkaline conditions.

[0067] Example 3 The process and conditions in this embodiment are basically the same as those in S1 (dissolution, precipitation and solid-liquid separation of Th-containing raw materials) and S2 (one-dimensional radium enrichment) in Example 1. The difference is that sodium hydroxide is used as the precipitant in this embodiment.

[0068] This example describes the extraction of Ra-228 and Ra-224 from 801.11g of thorium nitrate, and includes the following steps: S1. Dissolution, precipitation, and solid-liquid separation of Th-containing samples Weigh 801.11 g of thorium nitrate hexahydrate solid (provided by the Institute of Modern Physics, Chinese Academy of Sciences, Ra-228 approximately 30 μCi) and place it in a beaker. Add 0.01 M nitric acid solution in batches, stirring until completely dissolved. Transfer the resulting solution to a 5 L four-necked flask, with a final dissolved volume of 2.656 L. While stirring at 320 rpm, slowly add approximately 1.4 L of 4 M sodium hydroxide solution to the solution until the mixture volume is approximately 4 L. Adjust the pH to 6.64 using a few milliliters of 4 M sodium hydroxide. After standing, the precipitate rapidly separates into layers within 10 min. Filter the precipitate using a sintered glass funnel, collecting approximately 3.5 L of filtrate.

[0069] S2, one-dimensional radium enrichment (1) Sample loading: Enrichment was performed using a chromatographic column filled with a polymer matrix cation exchange material (material from Example 1) measuring 20 mm × 250 mm (inner diameter × height). 3.5 L of filtrate was diluted with water to 10.5 L. The column was equilibrated with 150 mL of 0.1 M nitric acid at a flow rate of 80 mL / min, followed by loading 10.5 L of the sample solution onto the column at a flow rate of 80 mL / min. After sample loading, the radioactivity of the eluent was close to background levels, indicating that radium was effectively adsorbed and no flow-through occurred.

[0070] (2) Eluting: After the sample loading was completed, the column was eluted with 160 mL of 0.01 M nitric acid solution at a flow rate of 80 mL / min. The radioactivity of the eluent increased only slightly, mainly due to system residue, which confirmed that the radium adsorbed on the column was not eluted under low acidity.

[0071] (3) Elution: After elution, the column was eluted with 8M nitric acid solution at a flow rate of 50 mL / min. The eluent was collected and aliquoted for analysis, showing a concentrated distribution of radioactivity. For example, in one elution collection, the activity of the first 80 mL eluent was as high as 27.5 μCi, the second 80 mL was 1 μCi, and the third 80 mL was 0.2 μCi, showing a similar trend of high activity at the beginning and low activity at the end, proving that Ra was efficiently eluted and concentrated in small volumes of eluent. The Ra-228 yield was approximately 95%, and the Th concentration was approximately 20 ppm. Therefore, two-dimensional purification was required to further remove trace impurities such as Th.

[0072] This embodiment confirms that the precipitation filtration and chromatographic enrichment elution process can effectively separate and enrich trace amounts of Ra-228 and Ra-224 from a large amount of thorium nitrate. However, the purity of Ra needs to be improved, which indirectly proves the necessity of two-dimensional purification.

[0073] Example 4 The process and conditions in this embodiment are basically the same as those in S1 (dissolution, precipitation and solid-liquid separation of Th raw material) and S2 (one-dimensional radium enrichment) in Example 1. The difference is that the Th raw material used in this embodiment is thorium hydroxide.

[0074] This embodiment uses 300g of thorium precipitate (thorium hydroxide) to crude Ra-224 sample. The thorium precipitate used is the thorium precipitate obtained from the solid-liquid separation in S1 of Example 3. In this embodiment, Ra-224 that grows in a short time from the thorium precipitate after the previous extraction of Ra-228 and Ra-224 is extracted. Due to the significant difference in half-lives between Ra-228 and Ra-224, the Ra-224 extracted again in a short time has high purity, and the content of Ra-228 is extremely low. This embodiment uses 300g of thorium precipitate to extract Ra-224, including the following steps: S1. Dissolution, precipitation, and solid-liquid separation of thorium-containing precipitates Take 300g of the thorium hydroxide precipitate from Example 3 (Ra-224 approximately 20 μCi, left for 15 days) and add it to a large beaker. Then add 450mL of 8M nitric acid and stir slowly to dissolve it into a light yellow, translucent liquid. Pour the solution into a 2L glass reactor, continue stirring until homogeneous, and let it stand. The solution gradually turns into a light-colored, transparent Th solution. Dilute the Th solution with water to 900mL and heat to 90°C. Start stirring at 400 rpm and add 490mL of 3.5M potassium hydroxide solution. Filter the precipitate using a sintered glass funnel and collect 1442.2g of the Ra-containing solution to be separated.

[0075] S2, one-dimensional radium enrichment The Ra-containing solution to be separated was diluted with deionized water to a total mass of 3822.5 g, yielding the loading solution. Enrichment was performed using a 10 mm * 250 mm (inner diameter × height) column packed with polymer-based cation exchange material (material from Example 1). The column was equilibrated with 30 mL of 0.1 M nitric acid at a flow rate of 20 mL / min, followed by loading the loading solution onto the column at a flow rate of 20 mL / min. After loading, the column was eluted with 0.5 M nitric acid solution at a flow rate of 20 mL / min to remove unadsorbed or weakly adsorbed impurities. After elution, the column was further eluted with 8 M nitric acid solution at a flow rate of 20 mL / min. The eluent was collected sequentially, yielding four vials of 20 mL each. After testing, Ra-228 and Ra-224 were mainly concentrated in the second 20mL sample container, with Ra-228 activity of approximately 18.7 μCi and a yield of 93.5%.

[0076] This embodiment demonstrates that the precipitation filtration and chromatographic enrichment elution process can effectively separate and enrich trace amounts of Ra-224 from thorium hydroxide.

[0077] Example 5 The process and conditions in this embodiment are basically the same as those in S3 (two-dimensional radium purification) in Example 1. The difference is that 50mM citric acid is used for isocratic elution in this embodiment.

[0078] This example describes the purification experiment of 10 μCi Ra-228 (1 mL, taken from S2 in Example 3), including the following steps: A chromatographic column with dimensions of 4.6 mm * 250 mm (inner diameter × height) packed with a hybrid silica matrix cation exchange material (material from Example 1) was used. A 10 mL 0.1 M nitric acid-equilibrated column was used, with a sample volume of 1 mL loaded at a flow rate of 1 mL / min. Elution was performed using 50 mM citric acid at a flow rate of 1 mL / min for 120 min. No Ra-228 was found in the collected fraction, but an activity meter test of the column showed that Ra-228 was still present on the column.

[0079] This example demonstrates that a low eluent concentration makes it difficult to achieve effective elution of Ra-228.

[0080] Example 6 The process and conditions in this embodiment are basically the same as those in S3 (two-dimensional radium purification) in Example 1. The difference is that this embodiment uses a larger Ra-containing sample volume, which is 2.4 BV.

[0081] This example describes the purification experiment of 15 μCi Ra-228 (1 mL, taken from S2 in Example 3), including the following steps: A chromatographic column with a 4.6 mm * 250 mm (inner diameter × height) matrix of hybrid silica-based cation exchange material (material from Example 1) was used. A 10 mL 0.1 M nitric acid equilibrated column was used; subsequently, 15 μCi Ra-228 (1 mL) was diluted to 10 mL before loading, with a flow rate controlled at 1 mL / min. After loading 8 mL, radioactivity was detected in the eluent, and after standing for one day, it was confirmed to be Ra-228. Some Ra-228 in the surface sample flowed through during loading, with a flow-through activity of 10 μCi Ra-228.

[0082] This embodiment confirms that an excessively large sample volume can cause the Ra-228 sample to flow through.

[0083] Example 7 The process and conditions in this embodiment are basically the same as those in S3 (two-dimensional radium purification) in Example 1. The difference is that the concentration of citric acid, the chelating agent (eluting agent), is higher in this embodiment, which is 1.5M.

[0084] This example describes the purification experiment of 15 μCi Ra-228 (0.8 mL, repeating the Ra-228 obtained in S1 and S2 of Example 3), including the following steps: A chromatographic column with dimensions of 4.6 mm * 250 mm (inner diameter × height) packed with a hybrid silica matrix cation exchange material (material from Example 1) was used. A 10 mL 0.1 M nitric acid equilibrated column was used; subsequently, 15 μCi Ra-228 (0.8 mL) sample was loaded at a flow rate of 1 mL / min. Elution was performed using 1.5 M citric acid (pH = 4.5) solution at a flow rate of 1 mL / min. Ra-228 was eluted in the first column volume, and the Th ion concentration in the sample was 20 ppm. No Th removal was observed after this step, indicating that the separation and purification effect under these elution conditions was not ideal.

[0085] This example demonstrates that excessively high concentrations of chelating agents (eluting agents) can weaken the separation and purification effect.

[0086] Example 8 The process and conditions in this embodiment are basically the same as those in S3 (two-dimensional radium purification) in Example 1. The difference is that in this embodiment, the concentration of citric acid solution is reduced to 500mM and the pH is increased to 5.

[0087] This example describes the purification experiment of 10 μCi Ra-228 (1 mL, repeating the Ra-228 obtained in S1 and S2 of Example 3), including the following steps: A chromatographic column with dimensions of 4.6 mm × 250 mm (inner diameter × height) packed with a hybrid silica matrix cation exchange material (material from Example 1) was used. A 10 mL 0.1 M nitric acid equilibrated column was used; then 10 μCi Ra-228 (1 mL) sample was loaded at a flow rate of 1 mL / min. Gradient elution was used, with mobile phase A being citric acid solution (1 L, 500 mM, pH=5) and mobile phase B being pure water. The elution was performed in two stages: the volume fraction of mobile phase A was gradually increased from 30% to 100%, and the volume fraction of mobile phase B was gradually decreased from 70% to 0%, with an elution flow rate of 0.5 mL / min (total flow rate of mobile phases A and B) and an elution time of 17 min. Subsequently, mobile phase A was maintained at 100% volume fraction, with an elution flow rate of 0.5 mL / min and an elution time of 7 min. The total elution volume for two-dimensional purification was approximately 12 mL.

[0088] Radium peaked approximately 17 minutes later. One fraction was collected every 1 minute, with each fraction having a volume of 20 mL. The radioactivity of each collected fraction was measured (Table 3). The results showed that radioactivity was detected in fractions 1 through 4, and the activity continued to increase over time, indicating that each fraction contained radium. The total activity of Ra-228 in the three fractions was approximately 9.8 μCi.

[0089] Table 3

[0090] This embodiment demonstrates that gradient elution can achieve efficient separation and purification of Ra-228, resulting in good yield and purity, and the separation effect meets the expected target.

[0091] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for separating and purifying radium-224 and radium-228 from the decay chain of natural thorium-232, characterized in that, The method includes the following steps: S1. Dissolve, selectively precipitate and separate the thorium-containing raw material of the natural thorium-232 decay chain to obtain radium-containing filtrate; S2. The radium-containing filtrate is diluted and then introduced into a polymer matrix cation exchange material (e.g., sulfonated cross-linked polystyrene spheres) for one-dimensional radium enrichment. Radium is adsorbed onto the polymer matrix cation exchange column. After elution, the eluent is collected to obtain a radium-enriched sample. The radium-containing sample is then evaporated to dryness and subsequently reconstituted with water or a weak acid (e.g., 0.001M~0.8M (preferably 0.2M~0.7M, more preferably 0.4M~0.6M), such as one or two of nitric acid or hydrochloric acid). S3. Using a hybrid silica matrix cation exchange material (e.g., sulfonic acid-based hybrid silica) as the stationary phase, the radium-enriched sample is purified by two-dimensional radium purification using high performance liquid chromatography. Fractions containing the target radium isotopes are selectively collected, and the fractions are rich in Ra-224 and Ra-228.

2. The method according to claim 1, characterized in that, The method also includes S4 three-dimensional radium enrichment and salt conversion. S4. Using a polymer-based cation exchange material (e.g., sulfonated cross-linked polystyrene spheres) as the stationary phase, three-dimensional radium concentration and salt conversion are performed. The target radium fraction obtained from two-dimensional purification is introduced onto a polymer-based cation exchange chromatography column and eluted with inorganic acids (e.g., 2M~15M (preferably 4M~12M, more preferably 7M~9M) nitric acid, 1M~12M (preferably 3M~8M, more preferably 4M~6M) hydrochloric acid) or organic acids (e.g., 50mM~500mM (pH = 3~6) citric acid (preferably 100mM~400mM (pH = 3.5~5.5), more preferably 200mM~300mM (pH = 4~5)). The eluent is then collected to obtain the radium-enriched sample.

3. The method according to claim 1, characterized in that, The thorium raw materials include, but are not limited to, the following: thorium nitrate, thorium hydroxide, rare earth slag, nuclear fuel, natural minerals (such as monazite, thorium, etc.), thorium oxalate, and thorium citrate, one or more of these.

4. The method according to claim 1 or 3, characterized in that, The steps in S1 specifically include: S11. Dissolve the thorium-containing raw material of the natural thorium-232 decay chain in water or an acidic solution (such as one or two of nitric acid or hydrochloric acid) of 0.001M to 15M (preferably 0.1M to 10M, more preferably 1M to 4M) to obtain a thorium solution, wherein the concentration of thorium ions is in the range of 0.1M to 1.5M (preferably 0.3M to 1.2M, more preferably 0.5M to 0.8M). S12. Add a precipitant to the thorium solution. The precipitant is selected from sodium hydroxide (e.g., 0.5M~8M (preferably 1M~6M, more preferably 3M~5M)), potassium hydroxide (e.g., 0.5M~6M (preferably 1M~6M, more preferably 3M~5M)), oxalic acid (e.g., 0.5M~1M (preferably 0.6M~0.9M, more preferably 0.7M~0.8M)), citric acid (e.g., 0.2M~1.5M (preferably 0.4M~1.2M, more preferably 0.6M~0.7M)), or ammonia (e.g., 4M-10M (preferably...)). 5M~8M, more preferably 6M~7M); wherein, to ensure precipitation effect, the molar ratio of sodium hydroxide to thorium should be controlled at about 7:2~4:1 (preferably 15:4~4:1, more preferably 19:5~4:1); the molar ratio of potassium hydroxide to thorium is also about 7:2~4:1 (preferably 15:4~4:1, more preferably 19:5~4:1); the molar ratio of oxalic acid to thorium needs to be in the range of 2:1~4:1 (preferably 2~3:1, more preferably 5:2~8:3); the molar ratio of citric acid to thorium The molar ratio should be within the range of 1 to 6:1 (preferably 3:2 to 4:1, more preferably 2 to 3:1); the molar ratio of ammonia to thorium should be around 7:2 to 4:1 (preferably 15:4 to 4:1, more preferably 19:5 to 4:1). To ensure complete precipitation of thorium and reduce the impact of errors during the experiment, this step employs a coordinated control of the amount of precipitant (molar ratio) and pH value to achieve precise control of the precipitation process. First, by controlling the molar ratio of precipitant to thorium within the above range, preliminary precipitation of thorium in the system is achieved. Based on this, considering that the buffering capacity of the solution decreases when pH > 4.5 and the pH value is highly sensitive to changes in the amount of alkali added, relying solely on theoretical calculations is prone to deviation. Therefore, a small amount of alkali solution is further used for fine adjustment. Specifically, by adding a trace amount of alkali solution (such as sodium hydroxide and / or potassium hydroxide), the pH of the system is finely adjusted a second time, so that the final pH is controlled between 5 and 10 (preferably 6 to 9, more preferably 7 to 8), thereby achieving stable control of the thorium precipitant system. S13. Solid-liquid separation, wherein the main component of the solid is thorium precipitate and the liquid is radium-containing filtrate.

5. The method according to claim 4, characterized in that, The thorium precipitate is used as the thorium-containing raw material in S1. After being placed for 2 to 20 days (preferably 5 to 15 days, more preferably 8 to 10 days), it is recycled. Step S1 is repeated, and the eluent is collected to obtain a filtrate rich in Ra-224.

6. The method according to claim 1, characterized in that, The one-dimensional radium enrichment includes column equilibration, sample loading, elution, and radium elution of a polymer-based cation exchange material column. Before sample loading, the concentration of cations (such as thorium, sodium, potassium, and ammonium ions) in the radium filtrate is reduced to below 0.5 M (preferably to 0.45 M, more preferably to 0.4 M) by dilution with water. The column equilibration is performed using water or acid (0.001 M to 0.5 M (preferably 0.01 M to 0.3 M, more preferably 0.1 M to 0.2 M), such as one or two of nitric acid or hydrochloric acid) to equilibrate to 1 BV to 5 BV (preferably 1 BV to 4 BV, more preferably 2 BV to 3 BV). The sample volume loaded does not exceed 500 BV (preferably not more than 450 BV). The elution process uses 0.001M~0.8M (preferably 0.01M~0.5M, more preferably 0.1M~0.2M) of dilute acid (such as one or two of nitric acid or hydrochloric acid) to elute 1BV~20BV (preferably 5BV~15BV, more preferably 8BV~12BV); the elution process uses 1M~15M of concentrated acid (such as one or two of nitric acid or hydrochloric acid, 2M~15M (preferably 4M~12M, more preferably 7M~9M) of nitric acid, 1M~12M (preferably 3M~8M, more preferably 4M~6M) of hydrochloric acid) to elute 3BV~6BV, and the target radium component is generally eluted within the first 1BV~3BV column volume; The polymer matrix cation exchange material is sulfonated cross-linked polystyrene spheres. The preparation process of the sulfonated cross-linked polystyrene spheres is as follows: 2L~6L of 0.4%~0.6% polyvinyl alcohol aqueous solution, 8g~12g of azobisisobutyronitrile, 180g~220g of divinylbenzene, and 360g~440g of xylene are mixed evenly and heated and stirred at 80℃~120℃ for 5h~7h. The reaction solution is filtered, washed with water and ethanol sequentially, and dried at 50℃~70℃ for 12h~20h to obtain polystyrene microspheres. 80mL~120mL of 96%-98% concentrated sulfuric acid and 8g~12g of polystyrene microspheres are mixed evenly and reacted at 25℃~35℃ for 45h~50h. The reaction solution is diluted with water and filtered, washed with water and ethanol sequentially, and dried at 50℃~70℃ for 12h~20h to obtain the sulfonated cation exchange packing material.

7. The method according to claim 1, characterized in that, During the two-dimensional radium purification operation, at least the following conditions (a) and (b) must be met: (a) Before loading the sample, the concentration of cations (such as thorium ions, sodium ions, potassium ions, ammonium ions, etc.) in the radium sample is reduced to below 0.2M (preferably to 0.18M, ​​more preferably to 0.15M) by diluting with water; (b) The solution pH is controlled at 0.5-10 (preferably 0.8-7, more preferably 1.0-3.0) during sample loading; the separation process includes column equilibration, sample loading, and elution of a chromatographic column packed with a hybrid silica matrix cation exchange material; the column equilibration is performed using water or acid (0.001M-0.5M (preferably 0.01M-0.3M, more preferably 0.1M-0.2M), such as one or two of nitric acid or hydrochloric acid) equilibration at 1 BV-5 BV (preferably 2 BV-5 BV). The sample volume should not exceed 1 BV (preferably not more than 0.9 BV, more preferably not more than 0.8 BV); the elution process adopts a gradient elution method, and the eluent is composed of a mixture of a chelating agent (such as one or two of citric acid or α-hydroxyisobutyric acid) aqueous solution and water. The concentration of the chelating agent aqueous solution is 0.1M~1M (preferably 0.3M~0.8M, more preferably 0.5M~0.7M), and the pH is 1~6 (preferably pH = 2~5, more preferably pH = 4~5); during the elution process, the volume fraction of the chelating agent aqueous solution is gradually increased from 30%~50% to 80%~100%, and the elution is 3BV~10BV (preferably 4BV~80BV, more preferably 4BV~5BV); the target radium component is collected and eluted within 2.5BV~4.0BV (preferably 2.8BV~3.8, more preferably 3BV~3.4BV).

8. The method according to claim 1 or 7, characterized in that, The hybrid silica matrix cation exchange material used in the two-dimensional radium purification of S3 is a sulfonic acid-based hybrid silica gel, with sulfonic acid (propanesulfonic acid) as its functional group and vinyl hybrid silica gel as its matrix. The preparation process of the hybrid silica matrix cation exchange material is as follows: 800g-1200g of vinyltriethoxysilane and 2500g-3500g of tetraethyl orthosilicate are dissolved in 1500g-2500g of anhydrous ethanol, and 5mL-15mL of triethylamine is added. The mixture is stirred at 30℃-40℃ for 10-20 hours. The reaction solution is then distilled under reduced pressure at 70℃-90℃ until no liquid is distilled off, yielding a silica sol. After cooling to room temperature, 900g-1100g of xylene is added and stirred until homogeneous. Separately, 10L-24L of water, 200g-300g of Tween 20, and 1800g-2400g of anhydrous ethanol are mixed and added, and emulsified at 400rpm-600rpm for 6min-12min. min; immediately add 400g~600g of 26%-28% ammonia solution, and react at 50℃~60℃ for 10h~20h; the product is washed successively with methanol and water, and dried to obtain vinyl hybrid silica microspheres; under nitrogen protection, dissolve 30g~80g of sodium 3-mercapto-1-propanesulfonate and 8g~12g of azobisisobutyramidine hydrochloride in 100mL~200mL of water, add a mixture of 40g~60g of microspheres and 300mL~400mL of methanol, and react at 50℃~60℃ for 20h~30h; filter the product, wash successively with water and methanol, and dry to obtain sulfonic acid hybrid silica chromatographic packing material.

9. The method according to claim 1, characterized in that, In S3, the collected fractions are left to stand for more than 1 hour to allow the decayed daughter nuclides to grow fully. Then, their radioactivity or characteristic energy spectrum peaks are measured using an activity meter or gamma spectrometer. Based on the measurement results, fractions with high radioactivity or obvious energy spectrum peak characteristics are selectively collected. Since the daughter nuclides (Ac-228 and Pb-212, respectively) in the newly separated Ra-228 and Ra-224 are extremely low in content, the fractions containing the target nuclides can be accurately identified only after the daughter nuclides have grown to a detectable level through the above-mentioned standing process. Usually, the target nuclides have obvious characteristic peaks of Ac-228 or Pb-212 and measurable activity, while the activity of other components is zero or very low.

10. The method according to claim 2, characterized in that, The method further includes S4 three-dimensional radium concentration and salt conversion, specifically: the target fraction obtained in step S3 is adjusted to pH < 2 with 0.1M~15M nitric acid or hydrochloric acid, while its anion or cationic metal ion concentration is controlled to be ≤ 0.5M (preferably ≤ 0.45M, more preferably ≤ 0.4M) by dilution with water; then the diluted fraction is introduced into a polymer-matrix cation exchange resin chromatographic column for adsorption / desorption; the separation process includes column equilibration with an acid (such as 0.001-1M (preferably 0.01M~0.3M, more preferably 0.1M~0.2M) nitric acid or hydrochloric acid or one or two of them), with an equilibration volume of not less than 1 BV; Subsequently, the radium-containing sample is loaded, with a sample volume not exceeding 500 BV (preferably not exceeding 450 BV, more preferably not exceeding 400 BV). After loading, the column is eluted with an acid (such as 0.001 M to 1 M (preferably 0.01 M to 0.8 M, more preferably 0.1 M to 0.5 M) nitric acid or hydrochloric acid, or one or two of these), with an elution volume of not less than 1 BV (preferably 2 BV to 20 BV, more preferably 8 BV to 12 BV). Finally, the radium is eluted with a strong acid (such as 2 M to 15 M (preferably 4 M to 12 M, more preferably 7 M to 9 M) nitric acid or 1 M to 12 M (preferably 3 M to 8 M, more preferably 4 M to 6 M) hydrochloric acid), with an elution volume of not less than 2 BV (preferably 6 BV to 20 BV, more preferably 8 BV to 10 BV). The eluent is collected to obtain the target radium sample with a radionuclear purity >99.8% and a yield >90%. The polymer matrix cation exchange material is sulfonated cross-linked polystyrene spheres. The preparation process of the sulfonated cross-linked polystyrene spheres is as follows: 2L~6L of 0.4%~0.6% polyvinyl alcohol aqueous solution, 8g~12g of azobisisobutyronitrile, 180g~220g of divinylbenzene, and 360g~440g of xylene are mixed evenly and heated and stirred at 80℃~120℃ for 5h~7h. The reaction solution is filtered, washed with water and ethanol sequentially, and dried at 50℃~70℃ for 12h~20h to obtain polystyrene microspheres. 80mL~120mL of 96%-98% concentrated sulfuric acid and 8g~12g of polystyrene microspheres are mixed evenly and reacted at 25℃~35℃ for 45h~50h. The reaction solution is diluted with water and filtered, washed with water and ethanol sequentially, and dried at 50℃~70℃ for 12h~20h to obtain the sulfonated cation exchange packing material.

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