Purification and enrichment methods for Pb-212 and Bi-212 product solutions extracted from natural thorium decay chains

Abstract

This invention provides a purification and enrichment method for extracting Pb-212 and Bi-212 product solutions from natural thorium decay chains, belonging to the field of medical radioisotope preparation technology. The method includes: passing a solution containing Th-232 decay chain substances through a first-stage anion exchange resin column to adsorb Pb-212 and Bi-212, with impurity nuclides passing directly through; eluting with a desorption reagent to obtain a first-stage eluent, adjusting its halide ion concentration and acidity to obtain the next-stage feed solution, and passing it through the column again for adsorption and elution with the desorption reagent; repeating the above column passing, desorption, and feed solution adjustment until the Th and Ba concentrations in the final eluent are both below 1 ppm, thus completing the purification and enrichment. This invention solves the problem of high-concentration Th / Ba residues by using a series of successive anion exchange resin column steps, efficiently extracting Pb-212 and Bi-212, and producing high-purity, highly efficient products with minimal organic contamination.

Description

Technical Field

[0001] This invention relates to the field of medical radioisotope preparation technology, and in particular to a purification and enrichment method for extracting Pb-212 and Bi-212 product solutions from natural thorium decay chains. Background Technology

[0002] With the advancement of science and technology, the global demand for more efficient and less invasive methods to treat various cancers is increasingly urgent. Medical radioisotopes are an ideal and effective cancer treatment method, causing minimal damage to normal human tissues and playing a vital role in safeguarding public health. Pb-212 / Bi-212 is one of the few radioisotopes applicable to targeted alpha therapy (TAT), demonstrating good efficacy in treating malignant tumors such as pancreatic cancer, ovarian cancer, prostate cancer, and breast cancer. Pb-212 / Bi-212 is a decay product of Th-232. Extracting Pb-212 / Bi-212 from the monazite hydrometallurgical industry chain requires no reactor or accelerator; sufficient quantities can be obtained solely through the spontaneous decay of Th-232, potentially fundamentally solving the global shortage of Pb-212 / Bi-212.

[0003] Currently, methods for separating and extracting Pb-212 from the Th-232 decay chain are mainly divided into indirect and direct separation methods. The indirect separation method first separates Ra-228, then Th-228 and Ra-224 in a stepwise manner, finally obtaining Pb-212 using a Ra-224 / Pb-212 generator or by capturing Rn-220 gas. This method is relatively mature and facilitates the wide distribution and transportation of Pb-212 (half-life 10.6 hours), but the separation steps are numerous and complex, requiring multiple waiting periods for daughter gas growth and multiple purification and testing processes, resulting in high production costs, long production cycles, and increased risk of radiation hazards to personnel, especially regarding the protection against the short-lived radioactive gas Rn-220. The direct separation method is simple and efficient, suitable for centralized distribution and supply within city, county, and even provincial administrative regions. Its challenge lies in finding suitable separation materials and technologies to achieve highly selective and efficient separation of Pb-212 and Bi-212 from the Th-232 decay chain. Existing literature reports that crown ether extractants (such as Pb resin) can selectively separate Pb-212 from natural thorium based on solid-phase adsorption. However, the elution rate is slow, making industrial production difficult, and Bi-212 cannot be extracted simultaneously, resulting in a waste of scarce nuclide resources. Furthermore, crown ether adsorbents are difficult and expensive to synthesize. In addition, the applicant has previously successfully separated and extracted Pb-212 and Bi-212 from thorium nitrate solution using anion exchange resins or anion exchange fibers, and developed a direct separation method using monazite-processed radium slag as raw material.

[0004] However, the Pb-212 and Bi-212 product solutions obtained by the single process using only a single anion exchange column still contain a certain amount of impurity ions, especially Th and Ba ions. The Th ion content in thorium nitrate feedstock is as high as tens of thousands or even hundreds of thousands of ppm, and the Ba ion content in radium slag dissolution solution is also as high as tens of thousands or hundreds of thousands of ppm. During the extraction process, high concentrations of Th / Ba are prone to tailing residues during elution, resulting in low elution efficiency, large elution solution volume, and long extraction time, which is not conducive to the rapid extraction of short-lived radionuclides Pb-212 and Bi-212. Furthermore, the specific activities of Pb-212 and Bi-212 in the products obtained by the single-stage column process are generally only several hundred to several thousand Bq / mL, requiring further enrichment and concentration to be suitable for the subsequent preparation of targeted radiopharmaceuticals. Therefore, there is an urgent need to provide a purification and enrichment method that can efficiently remove Th / Ba impurities and improve the specific activity of the product. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a purification and enrichment method for extracting Pb-212 and Bi-212 product solutions from natural thorium decay chains. This method solves the problem of high concentration Th / Ba residues by using a series of stepwise anion exchange resin columns, efficiently extracting Pb-212 and Bi-212, and producing products with high purity and high enrichment efficiency, while minimizing organic pollution of the products.

[0006] To achieve the above objectives, this invention provides a method for purifying and enriching Pb-212 and Bi-212 product solutions extracted from natural thorium decay chains, comprising the following steps: S1. Obtain a solution containing a substance with the Th-232 decay chain, wherein the solution contains halide ions and is acidic; S2. The obtained solution is passed through a first-stage anion exchange resin column, so that Pb-212 and Bi-212 are adsorbed onto the resin column, while the impurity nuclides pass through the resin column. S3. Use a desorption reagent to desorb Pb-212 and Bi-212 adsorbed on the first-stage anion exchange resin column to obtain the first-stage desorption solution; S4. Adjust the concentration and acidity of halide ions in the first-stage desorption solution to meet the conditions suitable for adsorption by the next-stage anion exchange resin column, and use it as the feed solution for the next stage. S5. Pass the next stage feed solution through the next stage anion exchange resin column to adsorb Pb-212 and Bi-212, and then desorb with a desorption reagent to obtain the desorption solution of this stage. S6. Repeat steps S4 to S5 until the concentrations of Th and Ba in the final desorption solution are both below 1 ppm, thus completing the purification and enrichment of Pb-212 and Bi-212 product solutions extracted from the natural thorium decay chain.

[0007] Preferably, the solution containing the Th-232 decay chain substance is a nitric acid solution with a nitric acid concentration greater than 0.01 mol / L.

[0008] Preferably, the concentration of halide ions in the solution is 0.2~2 mol / L, and the concentration of hydrogen ions is greater than 0.01 mol / L.

[0009] Preferably, the halide ions exist in the form of an acid or salt solution containing chloride ions, bromide ions, or iodide ions.

[0010] Preferably, the anion exchange resin is a silicon-based anion exchange resin, which is a composite resin formed by loading an organic anion exchange resin with polyvinylpyridine functional groups onto porous silica support particles, and the effective particle size of the silicon-based anion exchange resin is 35~150μm, and the BET specific surface area is 50~100m². 2 / g, with a pore size of 10~100nm.

[0011] Preferably, after adsorption and before desorption of each stage of the anion exchange resin column, an acid or salt solution containing halide ions is used as a rinsing agent for rinsing, and the concentration of the rinsing agent is 0.001~5 mol / L.

[0012] Preferably, the desorption reagent is a non-hydrohalic acid aqueous solution or pure water with an acid concentration of less than 1.0 mol / L.

[0013] Preferably, the desorption reagent is a perchloric acid solution with a concentration of 0.001~4 mol / L.

[0014] Preferably, in two adjacent anion exchange resin columns, the volume of the latter column is 1 / 2 to 1 / 10 of the volume of the former column.

[0015] Preferably, in step S4, when adjusting the halide ion concentration and acidity, an acid containing bromide ions is used to adjust the acidity as the feed solution for the lower-stage anion exchange resin column, wherein the bromide ion concentration is 0.001~5 mol / L and the hydrogen ion concentration is greater than 0.01 mol / L.

[0016] Compared with the prior art, the present invention discloses at least the following technical effects: (1) This invention provides a purification and enrichment method for the stepwise separation and extraction of Pb-212 and Bi-212 product solutions from thorium nitrate or monazite processing radium slag solutions. The method uses a solution containing Th-232 decay chain substances as raw material, passing it through an anion exchange resin column several times to efficiently remove impurities such as Th and Ba from the recovered product, achieving rapid separation and efficient enrichment of Pb-212 and Bi-212. Simultaneously, gamma spectroscopy and ICP-AES and ICP-MS analysis show that the obtained products have extremely high purity and are essentially free of impurity nuclides such as Th, Ac, and Ra.

[0017] (2) The present invention preferably uses a silicon-based anion exchange resin, which has the advantages of low price, fast adsorption / desorption kinetics, low column pressure, excellent hydraulic properties, stable chemical properties and is not easily soluble, and is applicable in the temperature range of 5℃ to 95℃. Compared with conventional all-organic commercial resins or crown ether materials, the present invention effectively solves the technical problems of slow elution rate, high synthesis difficulty, high price and inability to extract Bi-212 simultaneously. It can simultaneously separate and extract Pb-12 and Bi-212 from the Th-232 decay chain, ensuring the maximum utilization of scarce nuclide resources.

[0018] (3) This invention uses an acidic solution containing halide ions as the feed solution, enabling the anion exchange resin to rapidly adsorb Pb-212 and Bi-212 simultaneously, while essentially not adsorbing other metal elements; rinsing is performed using a halide-containing acid or salt solution with a concentration of 0.001~5 mol / L, and perchloric acid is used as the desorbent to achieve rapid desorption and efficient separation of Pb-212 and Bi-212. The above method is not only applicable to the selective extraction of Pb-212 and Bi-212 from the Th-232 decay chain (including Ra-228, Ra-224, Pb-212, Bi-212, etc.), but can also be extended to various application scenarios for the selective extraction of lead and bismuth from complex systems such as thorium, radium, actinium, lanthanum, barium, lead, and bismuth. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of a purification and enrichment method for extracting Pb-212 and Bi-212 product solutions from the decay chain of natural thorium according to the present invention.

[0021] Figure 2 This is the decay chain path of Th-232.

[0022] Figure 3 The image shows the elution curve of Th after the thorium nitrate solution passes through an anion exchange column.

[0023] Figure 4 The enrichment results of Pb-212 and Bi-212 activity in the monazite processing radium slag solution provided in Example 2 were obtained in two stepwise separation experiments.

[0024] Figure 5 The changes in elemental concentrations of the monazite processing radium slag solution provided in Example 2 after separation by a two-stage anion exchange column.

[0025] Figure 6 The activity enrichment results of Pb-212 and Bi-212 in the thorium nitrate solution provided in Example 3 during three stepwise separation experiments.

[0026] Figure 7 The image shows the gamma spectrum of the thorium nitrate solution provided in Example 3.

[0027] Figure 8 The gamma spectrum of the recovered solution after three staged column separation experiments of the thorium nitrate solution provided in Example 3. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, this invention provides a method for purifying and enriching Pb-212 and Bi-212 product solutions extracted from natural thorium decay chains, comprising the following steps: S1. Obtain a solution containing a substance with the Th-232 decay chain, wherein the solution contains halide ions and is acidic.

[0031] S2. The obtained solution is passed through a first-stage anion exchange resin column, so that Pb-212 and Bi-212 are adsorbed onto the resin column, while the impurity nuclides pass through the resin column.

[0032] S3. Use a desorption reagent to desorb Pb-212 and Bi-212 adsorbed on the first-stage anion exchange resin column to obtain the first-stage desorption solution.

[0033] S4. Adjust the concentration and acidity of halide ions in the first-stage desorption solution to meet the conditions suitable for adsorption by the next-stage anion exchange resin column, and use it as the feed solution for the next stage.

[0034] S5. Pass the next stage feed solution through the next stage anion exchange resin column to adsorb Pb-212 and Bi-212, and then desorb with a desorption reagent to obtain the desorption solution of this stage.

[0035] S6. Repeat steps S4 to S5 until the concentrations of Th and Ba in the final desorption solution are both below 1 ppm, thus completing the purification and enrichment of Pb-212 and Bi-212 product solutions extracted from the natural thorium decay chain.

[0036] In this invention, thorium nitrate or monazite-processed radium slag is selected as the raw material. Thorium nitrate products are typically obtained by separating and extracting Th-232-rich slag (thorium slag, highly soluble slag) from monazite hydrometallurgical processes. Monazite-processed radium slag, on the other hand, is radium-containing waste residue formed during the rare earth processing of monazite, where radioactive radium is removed through co-precipitation of barium ions and sulfate ions. The natural thorium-232 decay chain includes a parent chain. 232 Th and its successive decay products, such as 228 Ra、 228 Ac、 228 Th、 224 Ra、 212 Pb, 212 Bi、 208 Tl, etc., their decay relationships are as follows Figure 2 As shown. The radium slag solution processed from thorium nitrate or monazite is used as raw material, which contains high concentrations of Th or Ba (tens of thousands to hundreds of thousands of ppm), as well as target nuclides such as Pb-212 and Bi-212.

[0037] The above steps are further described below, including the following: Specifically, in step S1, the solution containing the Th-232 decay chain substance is a nitric acid solution with a concentration greater than 0.01 mol / L, wherein the halide ion concentration is 0.2~2 mol / L and the hydrogen ion concentration is greater than 0.01 mol / L. The halide ions exist in the form of chloride ions (Cl). - ), bromide ions (Br) - ) or iodide ions (I - Pb is a solution of acid or salt. In an acidic medium containing halide ions, Pb 2+ and Bi 3+ It can form stable halide anion complexes, such as PbBr4.2- BiBr4 - The target nuclide is selectively adsorbed by the anion exchange resin, while impurity nuclides such as Th, Ba, U, and Ce do not form anion complexes or the complexes are unstable in the medium and pass directly through the resin column, thus achieving the initial separation of the target nuclide from the impurity nuclide.

[0038] Specifically, the anion exchange resin in steps S2 and S5 is a silicon-based anion exchange resin. This resin is a composite resin formed by loading an organic anion exchange resin with polyvinylpyridine functional groups onto porous silica support particles, such as SiPyR-N4. This resin has been described in the applicant's previous patent ZL202411261811.7, with an effective particle size of 35~150 μm and a BET specific surface area of ​​50~100 m². 2 / g, with a pore size of 10~100nm. Compared with conventional all-organic commercial resins, this silica-based resin has the advantages of fast adsorption / desorption rate, low column pressure, good hydraulic properties, stable chemical properties, low solubility, and low price, and is applicable in a temperature range of 5℃~95℃. In each step, after adsorption and before desorption, the anion exchange resin column is eluted with an acid or salt solution containing halide ions, with a concentration of 0.001~5mol / L, to remove Th, Ba, and other impurity ions remaining in the resin column gaps or non-specifically adsorbed.

[0039] Specifically, the desorption reagent in step S3 is a perchloric acid solution with a concentration of 0.001~4 mol / L. Perchloric acid can simultaneously and rapidly desorb Pb-212 and Bi-212 adsorbed on the anion exchange resin, and the resulting first-stage desorption solution is the preliminarily purified target nuclide product solution. Alternatively, a non-hydrohalic acid aqueous solution or pure water with an acid concentration less than 1.0 mol / L can also be used as the desorption reagent, which can also achieve effective desorption of Pb-212 and Bi-212.

[0040] Specifically, in step S4, the acidity of the first-stage desorption solution is adjusted using an acid containing bromide ions, which serves as the feed solution for the next-stage anion exchange resin column. The bromide ion concentration is 0.001–5 mol / L, and the hydrogen ion concentration is greater than 0.01 mol / L. By adjusting the halide ion concentration and acidity, the feed solution regains the adsorption conditions required by the anion exchange resin, preparing it for the next stage of separation and enrichment. When repeating the above steps, the volume of the feed solution in each stage gradually decreases, and the volume of each anion exchange resin column also gradually decreases. In adjacent stages, the volume of the subsequent column is 1 / 2 to 1 / 10 of the volume of the preceding column, thus achieving high-level enrichment of the target nuclide while simultaneously purifying it step by step.

[0041] To further clarify the necessity of using a multi-stage column, the inventors verified the elution behavior of Th in a thorium nitrate solution after passing it through a single-stage anion exchange column: Uniformly sized SiPyR-N4 silicon-based anion exchange resin was packed into a column with a specification of [missing information]. In a 10mm × 200mm glass adsorption column, the resin column was pretreated with pure water to remove air bubbles and with 0.5M HBr. Thorium nitrate solution (0.5M HBr medium) was then passed through the resin adsorption column at a flow rate of 5 mL / min, followed by elution with 0.5M HBr. The eluent was collected using a distillation collector every 2 minutes per tube, and the concentration of Th in the eluent was then determined by ICP-OES. Figure 3 As shown, when the concentration of Th was eluted from a high concentration to 60 mg / L, the elution efficiency became very low, and the concentration of Th in the eluent decreased slowly, forming a clear tailing trend. This indicates that when using only a single-stage anion exchange column, a large volume and long elution time are required to elute the residual Th, which is not conducive to the rapid extraction of Pb-212 and Bi-212 and the improvement of product purity.

[0042] Furthermore, the adsorption / desorption operation of the ion exchange column described in this invention is carried out under ambient temperature and pressure conditions. Acidic solutions containing halide ions allow the anion exchange resin to simultaneously and rapidly adsorb Pb-212 and Bi-212, while exhibiting minimal adsorption of other metal elements. Perchloric acid as a desorbent enables rapid elution of both Pb-212 and Bi-212, thereby achieving efficient separation, purification, and enrichment of Pb-212 and Bi-212. This method is not only applicable to the selective extraction of Pb-212 and Bi-212 from the Th-232 decay chain, but can also be extended to various applications requiring the selective extraction of lead and bismuth from complex systems such as thorium, radium, actinium, lanthanum, barium, lead, and bismuth.

[0043] To further illustrate the technical solution of this invention in detail, the following embodiments are set up in conjunction with specific experimental data. The composite silicon-based anion exchange resin used in this invention has stable physicochemical properties and excellent adsorption / desorption performance, and is suitable for the purification and enrichment of thorium nitrate and monazite processing radium slag solution of this invention.

[0044] Example 1 This embodiment aims to provide a pre-adsorption treatment method for removing stable Pb and non-target Pb / Bi radionuclides from thorium nitrate solution and radium slag solution from monazite processing, thereby improving the purity of Pb-212 and Bi-212 extracted subsequently. The specific steps are as follows: (1) Take a number of uniformly sized silicon-based anion exchange resin SiPyR-N4 and fill it into a glass adsorption column with a specification of Ф×H=10mm×200mm until it is full.

[0045] (2) Adopt the bottom-up flow mode, adjust the flow rate to 10 mL / min, and first pass pure water to remove air bubbles in the glass adsorption column.

[0046] (3) Pretreatment of the glass adsorption column resin by introducing 150 mL of 0.5 M HBr in a top-down flow mode.

[0047] (4) Prepare the solution into a 0.5M HBr medium, and pass the solution through a glass resin adsorption column at a flow rate of 10mL / min for pre-adsorption treatment so that the resin adsorbs all the lead and bismuth in the solution. Collect the effluent, let it stand and decay, and use it for secondary adsorption.

[0048] (5) Then, 1M HClO4 is introduced at a flow rate of 10mL / min to elute the resin, so as to remove stable Pb and other radionuclides of Pb and Bi adsorbed on the resin.

[0049] The pretreatment results are shown in Table 1-2. After pretreatment, stable Pb-208 and its related isotopes in the thorium nitrate solution and the radium slag solution from monazite processing were removed. After standing for 4 days, the solution decayed and generated new Pb-212 and Bi-212. Pretreatment is beneficial to improving the purity of the separated and extracted Pb-212 and Bi-212.

[0050] Table 1. Nuclide specific activities and elemental concentrations in monazite-processed radium slag solutions after secondary column separation.

[0051] Table 2. Specific activities and elemental concentrations of thorium nitrate solutions in triple column separation.

[0052] Example 2 This embodiment aims to verify the enrichment effect of Pb-212 and Bi-212 and the removal efficiency of impurities such as Th and Ba after separation of monazite processing radium slag solution by a two-stage tandem anion exchange resin column. The specific steps are as follows: (1) Take a number of uniformly sized SiPyR-N4 silicon-based anion exchange resins and fill them into adsorption columns of different specifications. Column 1: Ф×H=7.8mm×100mm; Column 2: Ф×H=4.6mm×75mm; fill until full.

[0053] (2) Adopt the bottom-up flow mode, adjust the flow rate to 10 mL / min, and introduce pure water into the column to remove air bubbles in the adsorption column.

[0054] (3) Pretreatment of the resin in the adsorption column by introducing 200 mL of 0.5 M HBr in a top-down flow mode.

[0055] (4) The pretreated monazite processing radium slag solution was passed through the resin adsorption column 1 at a flow rate of 10 mL / min. At this time, Pb-212 and Bi-212 were adsorbed and fixed on the resin column.

[0056] (5) Then 100 mL of 0.5 M HBr is introduced for rinsing to remove residual thorium, uranium, barium and other elements attached to the resin column. The washing solution is collected and the content of impurity elements in the solution is tested by ICP.

[0057] (6) Elute with 0.1M HClO4 at a flow rate of 5mL / min to desorb and elute Pb-212 and Bi-212 from the resin column. Collect the eluent, with a collection time of 2min per column. The activities of Pb-212 and Bi-212 in the eluent were determined using a high-purity germanium gamma-ray spectrometer.

[0058] (7) Collect and mix the two solutions with the highest activity in the desorption solution of column 1, add 1.25 mL of 48% HBr, and adjust the acidity of the solution.

[0059] (8) Pass the above solution through the resin adsorption column 2 at a flow rate of 5 mL / min.

[0060] (9) Then 50 mL of 0.5 M HBr was introduced for rinsing to remove elements such as thorium remaining in the resin column. The washing solution was collected and the content of impurity elements in the solution was tested by ICP.

[0061] (10) Elute with 0.1M HClO4 at a flow rate of 2mL / min to desorb and elute Pb-212 and Bi-212 from the resin column. Collect the eluent, with a volume of 2mL per column. Determine the activities of Pb-212 and Bi-212 in the eluent using a high-purity germanium gamma-ray spectrometer.

[0062] Figure 4 The activity enrichment results of Pb-212 and Bi-212 in the radium slag solution for monazite processing in two stepwise separation experiments are shown. In the figure, I is the dead volume, II is the radium slag solution (raw material), III is the column 1-0.5M HBr eluent, IV is the column 1-0.1M HClO4 desorption solution, V is the column 2-feed solution after adding HBr again, VI is the column 2-0.5M HBr eluent, and VII is the column 2-0.1M HClO4 desorption solution. Figure 5 The changes in elemental concentrations in the radium slag solution from monazite processing after separation by a two-stage anion exchange column. Figure 4 and Figure 5As shown in Table 1, after the monazite processing radium slag solution passed through a two-stage series ion exchange resin column, the specific activity of Pb-212 increased from 676 Bq / mL in the original solution to 8081 Bq / mL in the product solution, and the specific activity of Bi-212 increased from 536.8 Bq / mL in the original solution to 2104 Bq / mL in the product solution. At the same time, the high concentration of Ba decreased from 65600 ppm to below 1 ppm, and elements such as Th, U, and Ce were successfully removed. The resulting product solution had high purity and high specific activity.

[0063] Example 3 This embodiment aims to verify the enrichment effect of Pb-212 and Bi-212 and the removal efficiency of impurities such as Th after separation of thorium nitrate solution by a three-stage series anion exchange resin column, and to examine the effect of stepwise separation on improving product purity and specific activity. The specific steps are as follows: (1) Take a number of uniformly sized SiPyR-N4 silicon-based anion exchange resins and fill them into adsorption columns of different specifications: Column 1: Ф×H=10mm×250mm; Column 2: Ф×H=7.8mm×100mm; Column 3: Ф×H=4.6mm×75mm; until full.

[0064] (2) Adopt the bottom-up flow mode, adjust the flow rate to 10 mL / min, and introduce pure water into the three columns to remove air bubbles in the adsorption column.

[0065] (3) Pretreatment of the resin in the adsorption column was carried out by introducing 200 mL, 150 mL and 100 mL of 0.5 M HBr in a top-down flow mode.

[0066] (4) The thorium nitrate solution was passed through the resin adsorption column 1 at a flow rate of 10 mL / min. At this time, Pb-212 and Bi-212 were adsorbed and fixed on the resin column.

[0067] (5) Then 200 mL of 0.5 M HBr is introduced for rinsing to remove the thorium, uranium and other substances that remain attached to the resin column.

[0068] (6) Elute with 0.1M HClO4 to desorb and elute Pb-212 and Bi-212 from the resin column. Collect the eluent, and set the collection time for each column to 4 min. The activities of Pb-212 and Bi-212 in the eluent are determined using a high-purity germanium gamma spectrometer.

[0069] (7) Collect and mix the two tubes with the highest activity in the desorption solution of column 1, add 4.52 mL of 48% HBr, and adjust the acidity of the solution.

[0070] (8) Pass the above solution through the resin adsorption column 2 at a flow rate of 10 mL / min.

[0071] (9) Then 100 mL of 0.5 M HBr is passed through for rinsing to remove elements such as thorium remaining in the resin column.

[0072] (10) Eluent was produced by passing 0.1M HClO4 at a flow rate of 10 mL / min to desorb and elute Pb-212 and Bi-212 from the resin column. The eluent was collected, with a volume of 11 mL per column. The activities of Pb-212 and Bi-212 in the eluent were determined using a high-purity germanium gamma-ray spectrometer.

[0073] (11) Repeat the above (7) to (10) operations on column 3. The volume of 48% HBr added is 1.25 mL, the flow rate is 2 mL / min, the volume of desorption liquid collected on column 3 is 2 mL / tube, and the activities of Pb-212 and Bi-212 in the eluent are determined by high purity germanium gamma spectrometer.

[0074] Figure 6 The results show the activity enrichment of Pb-212 and Bi-212 in the thorium nitrate solution during three stepwise separation experiments. In the figure, I is the dead volume, II is the thorium nitrate solution (raw material), III is the column 1 eluent with 0.5M HBr, IV is the column 1 eluent with 0.1M HClO4, V is the column 2 feed after adding HBr again, VI is the column 2 eluent with 0.5M HBr, VII is the column 2 eluent with 0.1M HClO4, VIII is the column 3 feed after adding HBr again, IX is the column 3 eluent with 0.5M HBr, and X is the column 3 eluent with 0.1M HClO4. Figure 7 The image shows the gamma-ray spectrum of a thorium nitrate solution. Figure 8 This is the gamma-ray spectra of the recovered solution after three successive column separation experiments of thorium nitrate solution. Combined with... Figure 6 , Figure 7 , Figure 8 As shown in Table 2, after passing through a three-stage series of ion exchange resin columns, the specific activity of Pb-212 increased from 502 Bq / mL in the original solution to 19980 Bq / mL, and the specific activity of Bi-212 increased from 500 Bq / mL in the original solution to 4422 Bq / mL. The concentrations of Th, U, and Fe ions in the product solution were all below 0.5 ppm, with the Th concentration decreasing from 181000 ppm to below 0.5 ppm. Compared with the γ-ray spectral peaks of the thorium nitrate solution, the Pb-212 and Bi-212 samples obtained by this invention showed fewer γ-ray peaks. The Ra-224 and Ac-228 nuclides present in the decay chain of the solution were removed, while Pb-212 and Bi-212 were largely retained and exhibited high purity.

[0075] In summary, through Examples 1-3, this invention first removes existing stable Pb and other Pb / Bi radionuclides from the solution through pre-adsorption treatment, providing a purer decay source for separation. Furthermore, through the step-by-step tandem separation experiments in Examples 2 and 3, it is demonstrated that the step-by-step method employed in this invention can successfully remove high-concentration impurity ions such as Th / Ba from thorium nitrate solution and monazite processing radium slag solution, while simultaneously achieving efficient enrichment of Pb-212 and Bi-212, significantly improving the specific activity of the product, greatly saving the amount of elution solution and extraction time, and resulting in a product solution with higher purity and specific activity.

[0076] Furthermore, those skilled in the art should understand that the results and discussions of any of the above embodiments are merely illustrative and are not intended to imply that the scope of protection of this application is limited to these examples. They can also be applied to any other situation involving the selective extraction of lead and bismuth from complex systems such as thorium, radium, actinium, lanthanum, barium, lead, and bismuth. Under the framework of this application, two to several successive experiments are applicable, and the technical features of the above embodiments or different embodiments can be combined. The steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not mentioned in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made under the spirit and principles of one or more embodiments of this application should be included within the scope of protection of this patent application.

[0077] Therefore, the present invention adopts the above-mentioned purification and enrichment method for extracting Pb-212 and Bi-212 product solutions from natural thorium decay chains. The method solves the problem of high concentration Th / Ba residue by using a series of step-by-step anion exchange resin columns, efficiently extracting Pb-212 and Bi-212, and the extracted products have high purity, high enrichment efficiency, and are not prone to causing organic pollution of the products.

[0078] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0079] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for purifying and enriching Pb-212 and Bi-212 product solutions extracted from the decay chain of natural thorium, characterized in that, Includes the following steps: S1. Obtain a solution containing a substance with the Th-232 decay chain, wherein the solution contains halide ions and is acidic; S2. The obtained solution is passed through a first-stage anion exchange resin column, so that Pb-212 and Bi-212 are adsorbed onto the resin column, while the impurity nuclides pass through the resin column. S3. Use a desorption reagent to desorb Pb-212 and Bi-212 adsorbed on the first-stage anion exchange resin column to obtain the first-stage desorption solution; S4. Adjust the concentration and acidity of halide ions in the first-stage desorption solution to meet the conditions suitable for adsorption by the next-stage anion exchange resin column, and use it as the feed solution for the next stage. S5. Pass the next stage feed solution through the next stage anion exchange resin column to adsorb Pb-212 and Bi-212, and then desorb with a desorption reagent to obtain the desorption solution of this stage. S6. Repeat steps S4 to S5 until the concentrations of Th and Ba in the final desorption solution are both below 1 ppm, thus completing the purification and enrichment of Pb-212 and Bi-212 product solutions extracted from the natural thorium decay chain.

2. The method according to claim 1, characterized in that, The solution containing the Th-232 decay chain substance is a nitric acid solution with a nitric acid concentration greater than 0.01 mol / L.

3. The method according to claim 1, characterized in that, The concentration of halide ions in the solution is 0.2~2 mol / L, and the concentration of hydrogen ions is greater than 0.01 mol / L.

4. The method according to claim 3, characterized in that, The halide ions exist in the form of acid or salt solutions containing chloride, bromide, or iodide ions.

5. The method according to claim 1, characterized in that, The anion exchange resin is a silicon-based anion exchange resin, which is a composite resin formed by loading an organic anion exchange resin with polyvinylpyridine functional groups onto porous silica support particles. The effective particle size of the silicon-based anion exchange resin is 35-150 μm, and the BET specific surface area is 50-100 m². 2 / g, with a pore size of 10~100nm.

6. The method according to claim 1, characterized in that, After adsorption and before desorption in each stage of the anion exchange resin column, an acid or salt solution containing halide ions is used as a rinsing agent for rinsing, and the concentration of the rinsing agent is 0.001~5 mol / L.

7. The method according to claim 1, characterized in that, The desorption reagent is a non-hydrohalic acid aqueous solution or pure water with an acid concentration of less than 1.0 mol / L.

8. The method according to claim 1, characterized in that, The desorption reagent is a perchloric acid solution with a concentration of 0.001~4 mol / L.

9. The method according to claim 1, characterized in that, In adjacent anion exchange resin columns, the volume of the later column is 1 / 2 to 1 / 10 of the volume of the earlier column.

10. The method according to claim 1, characterized in that, In step S4, when adjusting the concentration of halide ions and acidity, an acid containing bromide ions is used to adjust the acidity as the feed solution for the next stage anion exchange resin column, wherein the concentration of bromide ions is 0.001~5 mol / L and the concentration of hydrogen ions is greater than 0.01 mol / L.

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