Method for extracting prenuclide and preparing medical alpha isotope in large scale based on monazite waste slag

Abstract

The invention discloses a method for extracting prenuclide and preparing medical alpha isotope on a large scale based on monazite discharged waste slag. According to the method, high-value conversion of radioactive waste is realized by comprehensively utilizing the monazite waste slag. The alpha isotope is used as a core raw material for extracting preposed nuclide, so that the environmental harm of radioactive waste residues is reduced, waste is turned into wealth, and a stable raw material source is provided for preparing the medical alpha isotope. A complete technical chain for extracting the medical alpha isotope 225Ac / 212Pb from the monazite waste slag containing 226Ra and 228Ra is constructed, and efficient output of high-value nuclides is achieved. 226Ra and 228Ra in the discharged waste slag are obtained through a step-by-step extraction process flow of a coarse radium product and a fine radium product, a radium target of an ECANS device is manufactured, and hot medical alpha isotopes such as 225Ac, 212Pb and the like can be prepared on a large scale by utilizing a photo-nuclear reaction. According to the preparation mode, the utilization rate of the discharged waste slag is increased, and the requirement of radioactive diagnosis and treatment on the medical alpha isotope can be met.

Description

Technical Field

[0001] This invention belongs to the field of nuclear medical technology, specifically a method for extracting precursor radionuclides from monazite waste slag and preparing medical α isotopes on a large scale. Background Technology

[0002] Nuclear medicine is a field of "medical-engineering integration" that combines medicine and nuclear technology. It integrates diagnosis and treatment through radiopharmaceuticals, its core being the precise targeting of lesions with the nuclear energy released by radioactive isotopes. Compared to traditional tumor therapies, radiopharmaceutical therapy has advantages in efficacy and broad applicability, demonstrating unique value, especially in the treatment of metastatic tumors and small lesions, making it an important direction for current nuclear medicine development. Medical isotopes are the "core raw materials" of nuclear medicine, with alpha isotopes becoming a research hotspot due to their unique physical properties. Alpha radiation has a linear energy transfer density (LET) 1000 times higher than beta radiation, with a range of only 25-60 μm (cellular level), which can kill tumor cells while minimizing damage to surrounding normal tissues, making it particularly suitable for targeted therapy of small lesions. Currently, 223 Ra (radium chloride injection) has been approved by the FDA for the treatment of bone metastases in castration-resistant prostate cancer, and it works by targeting and accumulating in bone destruction lesions. 225 Ac is a more promising alpha nuclide. It and its daughter nuclide can undergo four consecutive alpha decays, and the decay process is accompanied by low-energy gamma radiation. It is expected to achieve "therapeutic integration". Currently, there are more than 20 actinide products under development worldwide, some of which have entered Phase III clinical trials.

[0003] However, in existing technologies, radioactive waste such as monazite slag is not effectively utilized and instead becomes an environmental burden requiring high disposal costs, with the enriched radium and thorium nuclides remaining idle for a long time. Traditional methods of directly extracting medical nuclides from natural uranium and thorium ores face problems such as low grade, high extraction difficulty, and high cost. Furthermore, there is a lack of a complete technological chain from precursor nuclides to medical alpha isotopes. The extraction of short-lived nuclides is prone to low efficiency due to decay and loss, which restricts the development of the nuclear medicine industry. Summary of the Invention

[0004] The purpose of this invention is to provide a method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale in order to solve the problems mentioned above.

[0005] The technical solution adopted in this invention is as follows: A method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale, the method comprising the following steps: Step 1: Select waste tailings generated during the development of monazite mines as raw materials. These tailings are enriched with... 226 Ra、 228Ra and other precursor nuclides; through physical pretreatment such as screening and crushing, large impurities in the slag are removed to obtain raw material particles with uniform particle size, thereby improving the subsequent leaching efficiency; Step 2: Add NaOH solution to the pretreated slag to convert the phosphorus element in the slag into soluble sodium salt and enter the liquid phase, while rare earth, radium, uranium, thorium and other nuclides remain in the solid phase; perform solid-liquid separation, discard the sodium phosphate waste liquid, and retain the solid phase residue; Step 3: Add HCl solution to the solid residue obtained in Step 2 to dissolve nuclides such as uranium and thorium into the liquid phase, extract uranium and thorium and remove waste residue; collect the insoluble residue by centrifugation to obtain target substances containing radium, rare earth elements and other materials; Step 4: Add (NH4)2SO4 solution and BaCl2 solution to the solid substance from Step 3, so that Ra 2 ⁺ co-precipitates with BaSO4 to form a barium sulfate-radium complex; by static precipitation and filtration separation, a product containing... 226 Ra、 228 Ra crude radium products; rare earth products are recovered from waste liquid through concentration and crystallization. Step 5: Wash the crude radium product obtained in Step 4 with deionized water to remove residual soluble salt impurities, and then vacuum dry it at 60~80℃ to obtain crude barium radium sulfate, which will be used as a raw material for subsequent refining. Step 6: Add at least 5 times its weight of Na₂CO₃ solid to the crude radium product to convert barium sulfate radium into barium carbonate radium precipitate; leach the insoluble precipitate with deionized water, then add dilute hydrochloric acid to remove impurities, and separate excess Na₂CO₃, H₂S, etc. by adding sulfuric acid and filtering; repeat the above process to perform a secondary conversion treatment on the crude radium product to obtain high-purity radium. 226 Ra / 228 Ra's product is barium radium carbonate. Step 7: The refined radium product obtained in Step 6 is directly sealed in a platinum-iridium alloy shell to prepare a solid radium target suitable for accelerator irradiation; the radium target is irradiated with a high-power photon source generated by the neutron source of the Donghua Accelerator, and photonuclear reactions are used to generate... 225 Ra、 224 Ra and other medical alpha isotope precursor nuclides; Step 8: After irradiation, the radium target decays to produce the target medical alpha isotope. 225 Ac / 212 Pb; the target material was dissolved in dilute nitric acid and extracted sequentially. 225 Ac、 212 Medical alpha isotopes such as Pb were used to ultimately obtain a radiopharmaceutical raw material solution that meets medical standards.

[0006] The beneficial effects of this invention are as follows: 1. This invention achieves high-value transformation of radioactive waste through the comprehensive utilization of monazite waste tailings. The waste tailings generated during monazite mining are originally an environmental burden, with the enriched radium and thorium nuclides remaining largely unused. This method uses them as a core raw material for extracting precursor nuclides, not only reducing the environmental hazards of radioactive waste but also turning waste into treasure, providing a stable source of raw materials for the preparation of medical alpha isotopes. Traditional methods of directly extracting medical nuclides from natural uranium and thorium ores face problems such as low grade and high extraction difficulty. However, after radium enrichment in the waste tailings through preliminary processes, the extraction efficiency is significantly improved, reducing raw material acquisition costs and laying the foundation for large-scale production.

[0007] 2. This invention establishes a complete technological chain from pre-extraction of radionuclides to the preparation of medical alpha isotopes, achieving efficient production of various high-value radionuclides. This is achieved by extracting radionuclides from waste slag. 226 Ra and 228 Ra can be prepared on a large scale using ECANS devices and accelerator technology via photonuclear reactions. 212 Pb, 225 Ac and other popular medical alpha isotopes. This preparation method not only improves the utilization rate of radioactive waste slag, but also meets the demand for medical alpha isotopes in radiodiagnosis and treatment, facilitates the preparation of medical alpha isotopes and radiopharmaceuticals, and promotes the future development of the nuclear medicine industry. Attached Figure Description

[0008] Figure 1 This is a schematic diagram illustrating the process principle of the present invention; Figure 2 To separate rare earth elements, uranium, thorium, and radium-containing compounds from uranium-thorium associated minerals in this invention. 226 Ra / 228 Process flow diagram of Ra) waste residue; Figure 3 This is a flowchart illustrating the separation and purification technology and process flow from crude radium product to refined radium product in this invention. Detailed Implementation

[0009] 1. Radionuclide analysis of monazite waste slag (1) In order to comprehensively utilize monazite, research was carried out on the utilization of waste slag. 228 Ra / 226 Ra / 228 Th / 212 A preliminary study on the recovery technology of medical isotopes such as Pb was conducted. 1g of waste slag from a monazite mine was used for radionuclide measurement over a period of 1500s. 232 Th and 228 The analysis results of Ra are shown in Table 1 below.

[0010] For Table 1, take 1g of waste slag, from the slag... 228Ac activity calculation 228 Ra activity (by) 214 Bior 214 Pb estimation 226 Ra activity), obtained 228 Ra activity is 17200 Bq (equivalent to 4.6487 × 10⁻⁶). -7 Ci), the equivalent mass is 1.7042 × 10 -9 g indicates the amount of waste slag in the mine. 228 Ra content is very low, and it contains many other impurities.

[0011] Table 1. Sample analysis results of monazite mining and comprehensive utilization of waste slag. Serial Number Nuclide γ energy (keV) Branch ratio (%) Activity (Bq) 1 <![CDATA[ 212 Pb]]> 238.6 44.6 7810.0 2 <![CDATA[ 228 And ( 228 Ra)]]> 911.6 27.7 17200.0 3 <![CDATA[ 214 With]]> 609.3 46.3 2030.0 4 <![CDATA[ 214 Pb]]> 351.9 37.2 1920.0 Table 1 shows the waste slag... 214 Bihe 214 The Pb activity is approximately 2000 Bq (mean), from which the following can be calculated. 226 The mass of Ra is 5.4657 × 10⁻⁶. -8 g, corresponding to the activity 238 The mass of U is 0.1607 g, accounting for approximately 16.07% of the mass of the monazite waste slag, classifying it as a high-grade uranium ore. This indicates the presence of radium (U) in the monazite waste slag. 226 Ra and 228 The extraction of Ra is economical.

[0012] 2. Process for obtaining crude radium from monazite slag The slag is crushed to a particle size of no more than 5 mm using a jaw crusher, and then screened through a vibrating screen with a mesh size of 100-200 to ensure uniform particle size. During pretreatment, large impurities and metal fragments are removed from the slag to improve subsequent leaching efficiency. The moisture content of the treated raw material particles is controlled below 10% for later use.

[0013] according to Figure 2 The process flow shown can extract crude radium and recover rare earth / uranium / thorium, etc. The process flow is as follows: ① Add NaOH for alkaline dissolution (hydrolysis) and solid-liquid separation. The alkali (sodium phosphate product) is recovered in the liquid phase, and the solid phase enters the downstream end; ② Add HCl to the solid phase (target substances such as rare earth / uranium / thorium / barium radium, etc.) for acid dissolution, so that the target substances such as uranium / thorium enter the liquid phase, uranium / thorium is extracted and its waste residue is removed, and the target substances such as rare earth / barium radium, etc. in the solid phase enter the downstream end; ③ Add (NH4)2SO4 and BaCl2 to the solid phase (target substances such as rare earth / barium radium, etc.) for acid dissolution (hydrolysis), so that the rare earth is concentrated and crystallized to achieve recovery. The remaining waste slag (containing barium radium sulfate) is the target substance of this process, barium radium sulfate crude product (referred to as crude radium product).

[0014] 3. Purification process for radium products The refined radium product is primarily composed of a barium radium carbonate mixture. During the concentration and purification of the crude radium product, chemical separation techniques are employed to remove impurities such as mineral components and residual chemical reagents. Through a combination of multi-stage precipitation, centrifugation, and solvent extraction, the impurity content is gradually reduced, thereby improving the purity of the barium radium carbonate. This process requires strict control of the pH value of the reaction system between 8 and 10, and the reaction temperature maintained between 60 and 80°C to promote the crystallization and separation of the target analyte. After purification, a high-purity refined radium product is obtained, with a significantly increased radionuclide activity concentration, meeting the requirements for further processing of medical pre-treatment radionuclides.

[0015] The separation and purification technology from crude radium product to refined radium product was validated, and the results of refined radium product extraction are shown in Table 2. The table includes four waste slag (crude radium product) samples, categorized as follows: Figure 3 The process involves adding 1, 2, 5, or 10 times the amount of sodium carbonate, followed by two conversions, which can essentially extract most of the barium carbonate radium. Specifically, when the amount of sodium carbonate reaches 5 times or more of the waste slag sample, two conversions are sufficient to completely extract the barium carbonate radium, resulting in a refined radium product (a mixture of barium carbonate and radium).

[0016] Table 2 Preliminary experiments on the comprehensive development of monazite and the extraction of radium from waste slag. Serial Number: Sodium Carbonate from Slag The first two items mass ratio Radium conversion rate in slag: First conversion rate, Second conversion rate: 10.302g, 0.332g, 132%, 59%; 20.283g, 0.569g, 241%, 69%; 30.255g, 1.297g, 568%, 100%; 40.290g, 2.904g, 1086%, 100%. Figure 3 Process flow: ① Anhydrous sodium carbonate solid is roasted to convert barium sulfate radium into barium carbonate radium precipitate; ② The insoluble precipitate is washed with deionized water, and then the barium carbonate radium is introduced into the liquid phase with dilute hydrochloric acid to remove insoluble impurities; ③ Sulfuric acid is added to collect the solid barium sulfate radium with further improved purity; ④ Sodium carbonate is added for secondary recycling to obtain high-purity barium carbonate radium, i.e., refined radium product.

[0017] 4. Preparation using an ECANS device 225 Ac / 212 Medical alpha isotopes such as Pb After obtaining high-purity barium radium carbonate, it is used to fabricate accelerator radium targets. The outer shell of the radium target is made of platinum-iridium alloy, sealing the solid barium radium carbonate within the platinum-iridium alloy shell. The radium target is designed in a sheet shape, with a thickness controlled between 0.5 and 1 mm. Its surface area matches the left, right, or bottom surface of the tungsten target of the ECANS device to ensure maximum photon irradiation efficiency.

[0018] When conducting photonuclear reactions on the ECANS device, long-pulse operating parameters in scientific experimental mode are used: electron energy set to 35 MeV (deviation range -2.5~5 MeV), electron current maintained at 2.0±0.5 mA (average current), pulse width 1~16 μs, and repetition frequency 5~500 Hz. The radium target is mounted in a U-shaped position on the tungsten target (left, right, or bottom face), ensuring the target surface is perpendicular to the direction of the photon beam generated by the electron beam bombarding the tungsten target. At this point, the photon yield of the target station can reach 1.0 × 10⁻⁶. 16 p / s, of which high-energy photons above 6 MeV account for no less than 6.1%, satisfying the requirement 228 Ra(γ,n) 226 Ra、 226 Ra(γ,n) 225 Ra、 226 Ra(γ,n) 224 The energy requirements of Ra photonuclear reactions. Irradiation time is generally controlled within 5 days based on the target nuclide yield requirements.

[0019] After being irradiated with photons, the radium target needs to be cooled in a lead-shielded container for 15 days to transform into β decay. 225 Ac / 212 After cooling, Pb was separated and purified using an ion-exchange chromatography column packed with AG MP-50 cation exchange resin. The column temperature was controlled at 30℃, and 1-2 mol / L nitric acid solution was used as the eluent at a flow rate of 1-2 ml / min for sequential elution and separation. 225 Ac and 212 Pb was used to obtain a radioactive nuclide solution that met medical standards. 225 Ac radioactivity purity is not less than 99%. 212 The radioactive purity of Pb is not less than 90%.

[0020] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale, the method comprising the following steps: Step 1: Select waste tailings generated during the development of monazite mines as raw materials. These tailings are enriched with... 226 Ra、 228 Ra and other precursor nuclides; through physical pretreatment such as screening and crushing, large impurities in the slag are removed to obtain raw material particles with uniform particle size, thereby improving the subsequent leaching efficiency; Step 2: Add NaOH solution to the pretreated slag to convert the phosphorus element in the slag into soluble sodium salt and enter the liquid phase, while rare earth, radium, uranium, thorium and other nuclides remain in the solid phase; Solid-liquid separation is performed, discarding the sodium phosphate-containing waste liquid and retaining the solid residue; Step 3: Add HCl solution to the solid residue obtained in Step 2 to dissolve nuclides such as uranium and thorium into the liquid phase, extract uranium and thorium, and remove waste residue; Insoluble residues were collected by centrifugation to obtain target substances containing radium, rare earth elements, etc. Step 4: Add (NH4)2SO4 solution and BaCl2 solution to the solid substance from Step 3, so that Ra 2 ⁺ co-precipitates with BaSO4 to form a barium sulfate-radium complex; by static precipitation and filtration separation, a product containing... 226 Ra、 228 Ra crude radium products; rare earth products are recovered from waste liquid through concentration and crystallization. Step 5: Wash the crude radium product obtained in Step 4 with deionized water to remove residual soluble salt impurities, and then vacuum dry it at 60~80℃ to obtain crude barium radium sulfate, which will be used as a raw material for subsequent refining. Step 6: Add at least 5 times its weight of Na₂CO₃ solid to the crude radium product to convert barium sulfate radium into barium carbonate radium precipitate; leach the insoluble precipitate with deionized water, then add dilute hydrochloric acid to remove impurities, and separate excess Na₂CO₃, H₂S, etc. by adding sulfuric acid and filtering; repeat the above process to perform a secondary conversion treatment on the crude radium product to obtain high-purity radium. 226 Ra / 228 Ra's product is barium radium carbonate. Step 7: The refined radium product obtained in Step 6 is directly sealed in a platinum-iridium alloy shell to prepare a solid radium target suitable for accelerator irradiation; the radium target is irradiated with a high-power photon source generated by the neutron source of the Donghua Accelerator, and photonuclear reactions are used to generate... 225 Ra、 224 Ra and other medical alpha isotope precursor nuclides; Step 8: After irradiation, the radium target decays to produce the target medical alpha isotope. 225 Ac / 212 Pb; the target material was dissolved in dilute nitric acid and extracted sequentially. 225 Ac、 212 Medical alpha isotopes such as Pb were used to ultimately obtain a radiopharmaceutical raw material solution that meets medical standards.

2. The method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale, as described in claim 1, is characterized in that: In step 1, a jaw crusher is used to crush the slag to a particle size of no more than 5 mm, and then it is screened by a vibrating screen with the screen mesh number controlled at 100~200 mesh to ensure that uniform particle size is obtained.

3. The method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale, as described in claim 1, is characterized in that: In step 2, a sodium hydroxide solution with a mass concentration of 30% to 50% is added to the pretreated slag, and the liquid-to-solid ratio is controlled between 4:1 and 6:

1. The alkaline dissolution reaction is carried out in a reactor equipped with a stirring device. The reaction temperature is maintained at 80 to 100°C, the stirring rate is 200 to 300 rpm, and the reaction is continued for 2 to 4 hours. After the reaction is completed, a plate and frame filter is used for solid-liquid separation. The sodium phosphate waste liquid is discarded, the solid residue is collected, and it is washed with deionized water 2 to 3 times to remove the residual alkaline waste liquid. The obtained solid phase is used for subsequent acid dissolution treatment.

4. The method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale, as described in claim 1, is characterized in that: In step 3, the solid residue after alkali dissolution is transferred to a corrosion-resistant reactor, and a hydrochloric acid solution with a concentration of 6-8 mol / L is added, with a liquid-to-solid ratio of 5:1-7:

1. The reactor is stirred at 60-80°C for 3-5 hours at a stirring rate of 150-250 rpm. During the reaction, the acidity of the solution is monitored by an online pH meter to ensure that the pH value remains below 1, promoting the full dissolution of nuclides such as radium and thorium. The waste residue is removed by extraction to obtain a uranium-thorium solution. Centrifuge the mixture at a speed of 3000-4000 rpm for 15-20 minutes, and collect the insoluble residue.

5. The method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale, as described in claim 1, is characterized in that: In step 4, ammonium sulfate solution and barium chloride solution are slowly added to the solid phase collected in the above steps, controlling the molar ratio of barium ions to sulfate ions to be 1:1.2, wherein the concentration of ammonium sulfate solution is 1 mol / L and the concentration of barium chloride solution is 0.5 mol / L; the reaction is stirred at room temperature for 1 to 2 hours at a stirring rate of 100 to 150 rpm, so that radium ions and barium sulfate form a co-precipitate; after the reaction is completed, the precipitate is allowed to stand for 2 to 3 hours, and the precipitate is separated by vacuum filtration. The precipitate obtained is the crude barium sulfate radium product.

6. The method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale as described in claim 1, characterized in that: In step 5, the crude barium sulfate radium product is placed in a Buchner funnel and washed repeatedly with deionized water 3 to 5 times. The amount of water used for each wash is 2 to 3 times the volume of the precipitate, until the conductivity of the washing solution is less than 50 microsiemens per centimeter. After washing, the precipitate is transferred to a vacuum drying oven and dried at 60-80°C for 4-6 hours. During the drying process, the vacuum degree is maintained at 0.08 to 0.1 MPa. The resulting crude barium radium sulfate product is the raw material for subsequent refining.

7. The method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale, as described in claim 1, is characterized in that: In step 6, anhydrous sodium carbonate solid, at least 5 times its weight in weight, is added to the crude barium radium sulfate. The mixture is then ground in an agate mortar until the particle size is less than 100 micrometers. The mixture is then transferred to a muffle furnace for calcination. The calcination temperature is controlled at 600-700℃, the holding time is 2-3 hours, and the heating rate is 5℃ per minute. After calcination, the mixture is allowed to cool naturally to room temperature. The product is then leached with deionized water at 80-90℃, with a liquid-to-solid ratio of 10:

1. After stirring for 30 minutes, the mixture is filtered, and the solid precipitate is collected and dried. 2-3 mol / L dilute hydrochloric acid is added to remove insoluble impurities. Then, 1-2 mol / L sulfuric acid is added, and the solid precipitate is collected. The above operations are repeated on the collected crude radium solid product for secondary conversion treatment to obtain high-purity barium radium carbonate. 226 Ra / 228 Ra products.

8. The method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale, as described in claim 1, is characterized in that: In step 7, a platinum-iridium alloy with a thickness of 0.5 to 1 mm is selected as the outer shell. The barium carbonate radium solid obtained in the previous steps is directly sealed in the platinum-iridium alloy shell to prepare a solid radium target of suitable size for accelerator irradiation. The radium target is installed in the target chamber of the neutron source of the Donghua Accelerator. The tungsten target is irradiated with electrons accelerated by the device to generate high-power photons, and the prepared radium target is then irradiated with the high-power photon source. The radium is generated through photonuclear reaction. 225 Ra、 224 Ra and other medical alpha isotope precursor nuclides; the irradiation time is generally controlled within 5 days according to the production demand of the target nuclide.

9. The method for extracting precursor radionuclides from monazite waste slag and preparing medical α-isotopes on a large scale, as described in claim 1, is characterized in that: In step 8, after irradiation, the radium target is removed from the target chamber, cooled in a lead-shielded container, and left to decay for more than 15 days. 225 Ac / 212 Medical α isotopes such as Pb were separated and purified using ion exchange chromatography. The column was packed with AG MP-50 cation exchange resin, and the column temperature was controlled at 30℃. A 1-2 mol / L nitric acid solution was used as the eluent, and the flow rate was 1-2 ml / min. Separation was carried out sequentially. 225 Ac and 212 Pb was used to obtain a radioactive nuclide solution that met medical standards. 225 Ac radioactivity purity is not less than 99%. 212 The radioactive purity of Pb is not less than 90%.

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