A method for the enrichment of radium by multistage countercurrent intersection recrystallization

Abstract

This invention relates to the field of radiochemistry and nuclide separation and purification technology, and discloses a multi-stage countercurrent recrystallization method for enriching radium. This method employs a countercurrent recrystallization operation within the same crystallization stage, where the mother liquor is not mixed across stages during two crystallizations. In each crystallization stage, the mother liquor after the first crystallization is evaporated and crystallized again. The resulting second batch of crystals is combined with the first batch of crystals and enters the next stage. The second batch of mother liquor is directly discarded and does not participate in the cross-stage cycle, allowing radium to be enriched step by step in the solid phase and barium salts to be efficiently removed. The initial solid mass can be reduced after only 5 stages of recrystallization, while the radium recovery rate remains stable. This avoids the radium dispersion loss and operational complexity caused by repeated cross-stage merging of mother liquor in traditional staged recrystallization, ultimately achieving a balance between rapid weight reduction and high recovery rate.

Description

Technical Field

[0001] This invention relates to the fields of radiochemistry and nuclide separation and purification technology, specifically a method for enriching radium by multi-stage countercurrent recrystallization. Background Technology

[0002] Ac-225, a star alpha nuclide, holds a pivotal position in the field of radiopharmaceuticals. Compared to beta nuclides such as Lu-177, Ac-225 exhibits significant advantages in radiation energy, therapeutic efficacy, and safety. Clinical studies have shown that 225Ac-PSMA radioligand therapy demonstrates potent antitumor activity in previously treated metastatic prostate cancer patients. The US FDA granted orphan drug designation to 225Ac-SSO110 for the treatment of small cell lung cancer in the first quarter of 2025, and the National Medical Products Administration of China accepted Novartis' clinical trial application for 225Ac-PMSA-617 in February 2025. According to incomplete statistics, there are over 60 Ac-225 radiopharmaceuticals in development pipelines. However, the supply of Ac-225 nuclides severely restricts the rapid development of this industry. It is estimated that the global annual demand for Ac-225 reaches several hundred curies (Ci), while the current global supply is less than 3 Ci / year, indicating a significant gap. The shortage of the key raw material Ra-226 is the fundamental constraint that limits the supply of Ac-225.

[0003] Since Marie Curie discovered radium through repeated extraction from tens of tons of pitchblende, the industrial extraction of radium has undergone a long period of development. The Radium Institute in the United States achieved industrial-scale radium extraction by processing domestic uranium mines (mainly vanadium-potassium uranium mines in the Colorado region) and exported it to Europe; Belgium established the Oran Radium Plant using high-grade uranium deposits discovered in Zaire, and its radium production once accounted for more than 50% of the global total. In the process of radium enrichment, Ba / Ra separation has always been a key technical challenge. Early studies used a graded recrystallization method, utilizing the difference in solubility between barium chloride and radium chloride to enrich radium in the solid phase through repeated crystallization. Subsequent researchers expanded to systems such as bromides, nitrates, and chromates (e.g., Salutsky SL et al., 1953). However, traditional graded recrystallization is cumbersome, often requiring dozens of stages to achieve ideal separation. For example, five-stage graded recrystallization requires 15 independent crystallization operations, accompanied by multiple solid-liquid mixing, heating and dissolution, recrystallization, and material transfer. This process is not only time-consuming but also places enormous pressure on equipment layout and production line design (especially complex material flow). Furthermore, this process simultaneously generates multiple crystalline products and mother liquor. With increasing stage number, product management becomes increasingly complex, requiring frequent merging and reprocessing. Even if multiple parallel reactors are added to shorten the time, it significantly increases the investment of human and material resources. While subsequent studies have used ion exchange resins (such as Dowex 50 resin) to achieve Ba / Ra separation (e.g., Power WH et al., 1959), this method produces a large volume of waste liquid (typically more than 10 times the column volume), which would impose a heavy economic and environmental burden on its engineering application.

[0004] Therefore, especially in the process of rare earth slag removal and radium extraction, the existing graded recrystallization technology has problems such as complex process, cumbersome operation, inability to achieve rapid weight reduction, and difficulty in conveniently obtaining high-yield radium-enriched crystals. There is an urgent need for a more efficient, economical and engineering-suitable radium enrichment method. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides a method for enriching radium through multi-stage countercurrent recrystallization. This method has the advantages of significantly simplified process, fewer operation steps, rapid weight reduction and high yield, low equipment dependence, and ease of engineering production. It solves the problems of existing graded recrystallization technologies, such as complex and cumbersome processes, chaotic material management, inability to achieve rapid weight reduction, poor economic efficiency, and difficulty in applying them to industrial production.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for enriching radium by multi-stage countercurrent recrystallization, comprising the following steps:

[0009] Step 1: Preparation of raw materials and reagents: Prepare a mixture of barium salt and radium salt as the starting material, and prepare a dilute acid solution as the recrystallization solvent.

[0010] Step 2, First-stage double crystallization: Add the mixture of barium salt and radium salt obtained in Step 1 to the reaction flask, add recrystallization solvent, heat to slight reflux, evaporate until the solution becomes slightly turbid, cool to room temperature, age, and then separate the solid and liquid to obtain the first batch of crystals; evaporate the mother liquor again until slightly turbid, cool and age, and separate the solid and liquid to obtain the second batch of crystals; combine the two batches of crystals and discard the second mother liquor;

[0011] Step 3, Second-stage double crystallization: The crystals obtained in Step 2 are used as the raw material for this stage. A recrystallization solvent is added, and the heating and dissolving → evaporation and concentration → cooling and aging → solid-liquid separation → mother liquor evaporation and crystallization → crystal merging operation of Step 2 is repeated. The evaporation endpoint, aging time and filtration operation are the same as in Step 2.

[0012] Step 4: Repeat the process: Following the method in Step 3, sequentially perform the third, fourth, fifth, and so on, on the crystals merged in the previous stage until the preset number of stages is reached;

[0013] Step 5, final product collection: The crystal obtained by combining the last stage double crystallization is taken as the radium enrichment product, that is, the product is a high specific activity barium chloride-radium chloride or barium bromide-radium bromide mixed crystal;

[0014] Step 6: Waste liquid treatment: Collect the second mother liquor discarded in each stage of double crystallization and carry out centralized environmental protection disposal or barium / radium recovery.

[0015] Preferably, in step one, the raw material preparation involves selecting one of the following raw materials: the mixture of barium salt and radium salt.

[0016] (a) A mixture of barium chloride dihydrate or barium bromide dihydrate solid and radium chloride or radium bromide liquid;

[0017] (b) The barium-removed slag from rare earth extraction is converted into carbonate and then dissolved in hydrochloric acid or hydrobromic acid to obtain the solution.

[0018] (c) The barium sulfate-radium coprecipitate is converted and then dissolved in hydrochloric acid or hydrobromic acid to obtain the solution.

[0019] Preferably, in step one, the prepared mass of barium chloride dihydrate or barium bromide dihydrate in the starting raw materials is 200-250g, and the prepared volume of radium salt solution is 1-3mL.

[0020] Preferably, in step one, the reagent preparation is as follows: the dilute acid is selected from dilute hydrochloric acid or dilute hydrobromic acid, wherein the dilute hydrochloric acid is prepared by mixing concentrated hydrochloric acid with deionized water at a mass fraction of 36% to 38% to prepare 0.1 mol / L; the dilute hydrobromic acid is prepared by mixing hydrobromic acid with deionized water at a mass fraction of 40% or 48% to prepare 0.1 to 0.3 mol / L.

[0021] Preferably, in step two, the ratio of the starting material composed of the mixture of barium salt and radium salt to the recrystallization solvent is: 0.6 to 1.2 mL of recrystallization solvent is added per gram of barium salt solid.

[0022] Preferably, the operating parameters for each stage in step two are as follows:

[0023] (1) Heating method: Heat to micro-reflux;

[0024] (2) Evaporation endpoint: The solution becomes slightly turbid;

[0025] (3) Cooling method: Naturally and slowly cool down to 20-25℃;

[0026] (4) Aging time: Stir at room temperature for 4 hours;

[0027] (5) Filtration method: atmospheric pressure filtration or vacuum filtration;

[0028] (6) Merging crystals: The first batch of crystals is mixed with the second batch of crystals as the first-stage product; the second mother liquor is collected and treated as waste liquid.

[0029] Preferably, in step three, the ratio of the volume of the added recrystallization solvent to the mass of the crystal is adjusted according to the system: bromide system: 0.6-0.9 mL / g; chloride system: 1.5-3.0 mL / g.

[0030] Preferably, in step four: the preset number of stages is 5, the crystal mass gradually decreases after each stage, the weight reduction ratio increases step by step, and the final product mass is about 3% to 11% of the starting solid mass.

[0031] Preferably, in step five, the product is a high-specific-activity barium chloride-radium chloride or barium bromide-radium bromide mixed crystal, which can be directly used for subsequent radium extraction or actinium-225 production.

[0032] Preferably, the waste liquid treatment method in step six is: evaporation to recover barium salt, or precipitation and solidification in accordance with radioactive waste liquid standards before disposal.

[0033] Compared with the prior art, the present invention provides a method for enriching radium by multi-stage countercurrent recrystallization, which has the following beneficial effects:

[0034] 1. This invention employs a countercurrent co-current operation within the same crystallization stage, where the mother liquor is not mixed across stages during two crystallization processes. In each crystallization stage, the mother liquor after the first crystallization is evaporated and crystallized again. The resulting second batch of crystals is combined with the first batch and enters the next stage. The second batch of mother liquor is discarded directly and does not participate in the cross-stage cycle. This allows radium to be enriched step by step in the solid phase and barium salts to be efficiently removed. After only 5 stages of recrystallization, the initial solid mass can be reduced by more than 90%, while the radium recovery rate remains stable at over 80%. This avoids the radium dispersion loss and operational complexity caused by repeated cross-stage merging of mother liquor in traditional staged recrystallization, ultimately achieving a balance between rapid weight reduction and high recovery rate.

[0035] 2. This invention achieves the beneficial effects of reducing the total number of crystallization operations from more than 15 times in traditional graded recrystallization to 10 times by performing only two crystallizations per stage and without merging mother liquor across stages. It also provides clear material flow and eliminates the need to repeatedly merge multiple intermediate products, which can greatly simplify the process flow and reduce the number of equipment, operation time and labor costs.

[0036] 3. This invention uses dilute hydrochloric acid or dilute hydrobromic acid as a recrystallization solvent and optimizes the solid-liquid ratio for bromide and chloride systems respectively, so that the crystal growth rate is moderate, the solubility difference between barium and radium is fully utilized, the crystallization rate is moderate, the radium enrichment factor is high, the specific activity of the product is significantly improved, and the process parameters are easy to scale up in engineering. This solves the problem that traditional methods are difficult to industrialize due to complex processes and poor economic efficiency. Attached Figure Description

[0037] Figure 1 This is a flowchart of the method of the present invention;

[0038] Figure 2 This is a flowchart illustrating the recrystallization process according to an embodiment of the present invention. Detailed Implementation

[0039] 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.

[0040] Please see Figures 1-2 A method for enriching radium by multi-stage countercurrent recrystallization includes the following steps:

[0041] Step 1: Preparation of raw materials and reagents: Prepare a mixture of barium salts and radium salts as the starting material. Alternatively, a solution can be obtained by converting rare earth residues into carbonates and then dissolving them in hydrochloric acid or hydrobromic acid (the main components are a mixture of barium chloride and radium chloride or a mixture of barium bromide and radium bromide). Or, the remaining materials can be enriched by barium sulfate and radium precipitation, then converted into carbonates and dissolved in hydrochloric acid or hydrobromic acid. Also, prepare a dilute acid solution as a recrystallization solvent.

[0042] Step 2, First-stage double crystallization: Add the mixture of barium salt and radium salt obtained in Step 1 to the reaction flask, add the recrystallization solvent (dilute hydrochloric acid or dilute hydrobromic acid), heat to slight reflux, evaporate until the solution becomes slightly turbid, slowly cool to room temperature, and after aging, separate the solid and liquid to obtain the first batch of crystals; evaporate the mother liquor again until slightly turbid, cool and age, and separate the solid and liquid to obtain the second batch of crystals; combine the two batches of crystals and discard the second mother liquor;

[0043] Step 3, Second-stage double crystallization: The crystals obtained in Step 2 are used as the raw material for this stage. A recrystallization solvent is added, and the heating and dissolving → evaporation and concentration → cooling and aging → solid-liquid separation → mother liquor evaporation and crystallization → crystal merging operation of Step 2 is repeated. The evaporation endpoint, aging time and filtration operation are the same as in Step 2.

[0044] Step 4: Repeat the process: Following the method in Step 3, sequentially perform the third, fourth, fifth, and so on, on the crystals merged in the previous stage until the preset number of stages is reached;

[0045] Step 5, final product collection: The crystal obtained by combining the last stage double crystallization is taken as the radium enrichment product, that is, the product is a high specific activity barium chloride-radium chloride or barium bromide-radium bromide mixed crystal;

[0046] Step 6, Waste liquid treatment: Collect the second mother liquor discarded in each stage of double crystallization (such as 2L1, 2L2...2L5) and carry out centralized environmental protection treatment or barium / radium recovery.

[0047] Specifically, in step one, the raw material preparation is as follows: Barium salt is a solid raw material, selected from either barium chloride dihydrate (BaCl2·2H2O) or barium bromide dihydrate (BaBr2·2H2O). Both raw materials have good solubility in dilute acid, excellent crystallization properties, and can be subsequently converted to obtain radium chloride or radium bromide. Radium salt is a liquid raw material, selected from either radium chloride (RaCl2) or radium bromide (RaBr2), or a solution obtained by converting barium residue generated during rare earth extraction into carbonate and then dissolving it with hydrochloric acid or hydrobromic acid, or a solution obtained by converting barium sulfate-radium coprecipitation and then dissolving it with hydrochloric acid or hydrobromic acid. This solution is obtained from radium-containing waste liquid through a coprecipitation-dissolution process, which facilitates uniform mixing with barium salt.

[0048] Specifically, in step one, the prepared mass of barium chloride dihydrate or barium bromide dihydrate in the starting raw materials is 200-250g, and the prepared volume of radium salt solution is 1-3mL. Through the verification of the ratio of 243g and 244g to 2mL of radium solution in Examples 1-3, the recrystallization operation is stable within this range, the crystal precipitation is good, and it is convenient for subsequent scale-up.

[0049] Specifically, in step one, the reagent preparation is as follows: the dilute acid is selected from either dilute hydrochloric acid or dilute hydrobromic acid. The dilute hydrochloric acid is prepared by mixing concentrated hydrochloric acid with deionized water at a mass fraction of 36%–38% to obtain a concentration of 0.1 mol / L. By measuring the solubility curves of barium chloride / radium chloride at different concentrations, it was found that the crystallization rate was moderate and the radium enrichment factor was the highest at 0.1 mol / L. The dilute hydrobromic acid is prepared by mixing hydrobromic acid with deionized water at a mass fraction of 40% or 48% to obtain a concentration of 0.1–0.3 mol / L. By comparing Example 1 (0.3 mol / L) and Example 2 (0.1 mol / L), both are effective, but the crystal yield is slightly higher at 0.3 mol / L. Therefore, the preferred range of 0.1–0.3 mol / L is given.

[0050] Specifically, in step two: the ratio of the starting material, consisting of a mixture of barium salt and radium salt, to the recrystallization solvent is: 0.5 to 1.8 mL of recrystallization solvent is added per gram of barium salt solid, preferably 0.6 to 1.2 mL / g. Through single-factor experiments on solvent volume, it was found that: when the solvent volume is below 0.5 mL / g, the solid dissolves incompletely; when the solvent volume is above 1.8 mL / g, the evaporation and concentration time is too long and the radium loss increases; the dissolution and crystallization efficiency is optimal within the range of 0.6 to 1.2 mL / g.

[0051] Specifically, the operational parameters for each stage in step two are as follows:

[0052] (1) Heating method: Heat to slight reflux (the solution boils slightly);

[0053] (2) Evaporation endpoint: The solution becomes slightly turbid (i.e., a small amount of solid begins to precipitate).

[0054] (3) Cooling method: Naturally and slowly cool down to 20-25℃ (room temperature);

[0055] (4) Aging time: Stir at room temperature for 2 to 8 hours, preferably 4 hours;

[0056] (5) Filtration method: atmospheric pressure filtration or vacuum filtration;

[0057] (6) Combined crystals: The first batch of crystals is mixed with the second batch of crystals as the first-stage product; the second mother liquor (such as 2L1) is collected and treated as waste liquid.

[0058] The advantages are: the above process can effectively enrich radium in the solid phase through two crystallizations in the same stage, without the need for cross-stage mixing of mother liquor, with fewer operation steps, clear material flow direction, and significant single-stage weight reduction effect.

[0059] Specifically, in step three: the ratio of the volume of the added recrystallization solvent to the mass of the crystals is adjusted according to the system: bromide system (barium bromide + radium bromide): 0.6-0.9 mL / g; chloride system (barium chloride + radium chloride): 1.5-3.0 mL / g.

[0060] Specifically, in step four: the preset number of stages is 2 to 10, preferably 5 stages. After each stage, the crystal mass gradually decreases, the weight reduction ratio increases step by step, and the final product mass is about 3% to 11% of the starting solid mass.

[0061] Specifically, in step five: the product is a high-specific-activity barium chloride-radium chloride or barium bromide-radium bromide mixed crystal; the radium recovery rate is over 80%; the product can be directly used for subsequent radium extraction or actinium-225 production.

[0062] Specifically, in step six: since the radium content of the second mother liquor is extremely low (radium preferentially enters the crystalline phase), and the main components are barium bromide or barium chloride, the waste liquid treatment method is: to evaporate and recover barium salts, or to dispose of it after precipitation and solidification in accordance with the standards for radioactive waste liquid.

[0063] The advantages are: the above process only requires 5 stages of operation to achieve a reduction of more than 90% in the mass of the starting solid (to 3.7% to 10.9%), while maintaining a radium recovery rate of more than 80%. It requires fewer pieces of equipment and has a shorter operation cycle, which is significantly better than the traditional fractional recrystallization process and is easy to scale up in engineering.

[0064] The method of this invention is applied to the enrichment and separation of radium in radium-containing barium salt waste liquid or radium-containing solid waste, and is especially suitable for rare earth slag removal and extraction processes, ultimately achieving the beneficial effect of maximizing radium extraction.

[0065] Example 1

[0066] The barium bromide dihydrate and a small amount of radium bromide solution were dissolved in a dilute hydrobromic acid solution (0.3 mol / L) and then recrystallized.

[0067] S1. First-stage crystallization: Weigh 243g of barium bromide dihydrate and 2mL of radium bromide solution, add them to a 500mL reaction flask, then add 158mL of 0.3mol / L hydrobromic acid solution, heat to micro-reflux, evaporate until the solution becomes slightly turbid, stop heating, and slowly cool the solution to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter, the first batch of crystals is recorded as 1C1, and the first batch of mother liquor is recorded as 1L1. Transfer 1L1 to a 250mL reaction flask, heat to micro-reflux again, evaporate again until the solution becomes slightly turbid, stop heating, and slowly cool the solution to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for another 4 hours. Filter, the second batch of crystals is recorded as 2C1, and the second batch of mother liquor is recorded as 2L1. Combine 1C1 and 2C1 to obtain a total of 124g of crystals. Discard the mother liquor 2L1 as waste liquid.

[0068] S2, Second-stage crystallization: The combined crystals from the previous stage were added to a 250 mL reaction flask, along with 80 mL of 0.3 mol / L hydrobromic acid solution. The mixture was heated to a slight reflux and evaporated until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, a large amount of white crystalline solid precipitated. The mixture was then stirred at room temperature for 4 hours. After filtration, the first batch of crystals was designated 1C2, and the first batch of mother liquor was designated 1L2. 1L2 was then transferred to a 250 mL reaction flask, heated to a slight reflux again, and evaporated again until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, the amount of white crystalline solid gradually increased again. The mixture was then stirred at room temperature for 4 hours. After filtration, the second batch of crystals was designated 2C2, and the second batch of mother liquor was designated 2L2. 1C2 and 2C2 were combined to obtain a total of 84.5 g of crystals. The mother liquor 2L2 was discarded as waste.

[0069] S3, Third-stage crystallization: The combined crystals from the previous stage were added to a 250 mL reaction flask, along with 62 mL of 0.3 mol / L hydrobromic acid solution. The mixture was heated to a slight reflux and evaporated until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, a large amount of white crystalline solid precipitated. The mixture was then stirred at room temperature for 4 hours. After filtration, the first batch of crystals was designated 1C3, and the first batch of mother liquor was designated 1L3. 1L3 was then transferred to a 100 mL reaction flask, heated to a slight reflux again, and evaporated again until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, the amount of white crystalline solid gradually increased again. The mixture was then stirred at room temperature for 4 hours. After filtration, the second batch of crystals was designated 2C3, and the second batch of mother liquor was designated 2L3. 1C3 and 2C3 were combined to obtain a total of 43.6 g of crystals. Mother liquor 2L3 was discarded as waste.

[0070] S4, Fourth-stage crystallization: Combine the crystals obtained in the previous stage and add the solid to a 100mL reaction flask. Add 35mL of 0.3mol / L hydrobromic acid solution, heat to micro-reflux, and evaporate until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is designated 1C4, and the first batch of mother liquor is designated 1L4. Transfer 1L4 to a 100mL reaction flask, heat to micro-reflux again, and evaporate again until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for 4 hours. Filter the solution. The second batch of crystals obtained is designated 2C4, and the second batch of mother liquor is designated 2L4. Combine 1C4 and 2C4 to obtain a total of 23.2g of crystals. Discard the mother liquor 2L4 as waste liquid.

[0071] S5. Fifth Crystallization: Combine the crystals obtained in the previous stage and add the solid to a 50 mL reaction flask. Add 18 mL of 0.3 mol / L hydrobromic acid solution, heat to micro-reflux, and evaporate until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is denoted as 1C5, and the first batch of mother liquor is denoted as 1L5. Transfer 1L5 to a 50 mL reaction flask, heat to micro-reflux again, and evaporate again until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for 4 hours. Filter the solution. The second batch of crystals obtained is denoted as 2C5, and the second batch of mother liquor is denoted as 2L5. Combine 1C5 and 2C5 to obtain a total of 10.4 g of crystals. Discard the mother liquor 2L5 as waste liquid.

[0072] Example 2

[0073] The barium bromide dihydrate and a small amount of radium bromide solution were dissolved in a dilute hydrobromic acid solution (0.1 mol / L) and then recrystallized.

[0074] S1. First-stage crystallization: Weigh 243g of barium bromide dihydrate and 2mL of radium bromide solution, add them to a 500mL reaction flask, then add 158mL of 0.1mol / L hydrobromic acid solution. Heat to micro-reflux and evaporate until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is denoted as 1C1, and the first batch of mother liquor is denoted as 1L1. Transfer 1L1 to a 250mL reaction flask, heat to micro-reflux again, and evaporate again until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for 4 hours. Filter the solution to obtain the second batch of crystals, denoted as 2C1, and the second batch of mother liquor, denoted as 2L1. Combine 1C1 and 2C1 to obtain a total of 126g of crystals. Discard the mother liquor 2L1 as waste liquid.

[0075] S2, Second-stage crystallization: The combined crystals from the previous stage were added to a 250 mL reaction flask, along with 80 mL of 0.1 mol / L hydrobromic acid solution. The mixture was heated to a slight reflux and evaporated until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, a large amount of white crystalline solid precipitated. The mixture was then stirred at room temperature for 4 hours. After filtration, the first batch of crystals was designated 1C2, and the first batch of mother liquor was designated 1L2. 1L2 was then transferred to a 250 mL reaction flask, heated to a slight reflux again, and evaporated again until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, the amount of white crystalline solid gradually increased again. The mixture was then stirred at room temperature for 4 hours. After filtration, the second batch of crystals was designated 2C2, and the second batch of mother liquor was designated 2L2. 1C2 and 2C2 were combined to obtain a total of 64.3 g of crystals. The mother liquor 2L2 was discarded as waste.

[0076] S3, Third-stage crystallization: The combined solid crystals from the previous stage were added to a 250 mL reaction flask, along with 62 mL of 0.1 mol / L hydrobromic acid solution. The mixture was heated to a slight reflux and evaporated until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, a large amount of white crystalline solid precipitated. The mixture was then stirred at room temperature for 4 hours. After filtration, the first batch of crystals was designated 1C3, and the first batch of mother liquor was designated 1L3. 1L3 was then transferred to a 100 mL reaction flask, heated to a slight reflux again, and evaporated again until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, the amount of white crystalline solid gradually increased again. The mixture was then stirred at room temperature for 4 hours. After filtration, the second batch of crystals was designated 2C3, and the second batch of mother liquor was designated 2L3. 1C3 and 2C3 were combined to obtain a total of 34.3 g of crystals. The mother liquor 2L3 was discarded as waste.

[0077] S4, Fourth-stage crystallization: Combine the crystals obtained in the previous stage and add the solid to a 100mL reaction flask. Add 35mL of 0.1mol / L hydrobromic acid solution, heat to micro-reflux, and evaporate until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is designated 1C4, and the first batch of mother liquor is designated 1L4. Transfer 1L4 to a 100mL reaction flask, heat to micro-reflux again, and evaporate again until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for 4 hours. Filter the solution. The second batch of crystals obtained is designated 2C4, and the second batch of mother liquor is designated 2L4. Combine 1C4 and 2C4 to obtain a total of 18.0g of crystals. Discard the mother liquor 2L4 as waste liquid.

[0078] S5. Fifth Crystallization: Combine the crystals obtained in the previous stage and add the solid to a 50 mL reaction flask. Add 18 mL of 0.1 mol / L hydrobromic acid solution, heat to micro-reflux, and evaporate until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is denoted as 1C5, and the first batch of mother liquor is denoted as 1L5. Transfer 1L5 to a 50 mL reaction flask, heat to micro-reflux again, and evaporate again until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for 4 hours. Filter the solution. The second batch of crystals obtained is denoted as 2C5, and the second batch of mother liquor is denoted as 2L5. Combine 1C5 and 2C5 to obtain a total of 8.9 g of crystals. Discard the mother liquor 2L5 as waste liquid.

[0079] Example 3

[0080] The barium chloride dihydrate and a small amount of radium chloride solution were dissolved in a dilute hydrochloric acid solution (0.1 mol / L) and then recrystallized.

[0081] S1. First-stage crystallization: 244g of barium chloride dihydrate and 2mL of radium chloride solution were added to a 1L reaction flask, followed by 440mL of 0.1mol / L hydrochloric acid solution. The mixture was heated to a slight reflux and evaporated until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, a large amount of white crystalline solid precipitated. The mixture was then stirred at room temperature for 4 hours. After filtration, the first batch of crystals was designated 1C1, and the first batch of mother liquor was designated 1L1. 1L1 was then transferred to a 1L reaction flask, heated to a slight reflux again, and evaporated again until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, the amount of white crystalline solid gradually increased again. The mixture was then stirred at room temperature for 4 hours. After filtration, the second batch of crystals was designated 2C1, and the second batch of mother liquor was designated 2L1. 1C1 and 2C1 were combined to obtain a total of 154g of crystals. The mother liquor 2L1 was discarded as waste liquid.

[0082] S2, Second-stage crystallization: Combine the crystals obtained in the previous stage and add the solid to a 500mL reaction flask. Add 290mL of 0.1mol / L hydrochloric acid solution, heat to slight reflux, and evaporate until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is denoted as 1C2, and the first batch of mother liquor is denoted as 1L2. Transfer 1L2 to a 500mL reaction flask, heat to slight reflux again, and evaporate again until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for 4 hours. Filter the solution. The second batch of crystals obtained is denoted as 2C2, and the second batch of mother liquor is denoted as 2L2. Combine 1C2 and 2C2 to obtain a total of 104g of crystals. Discard the mother liquor 2L2 as waste liquid.

[0083] S3, Third-stage crystallization: Combine the crystals obtained in the previous stage and add the solid to a 500mL reaction flask. Add 180mL of 0.1mol / L hydrochloric acid solution, heat to slight reflux, and evaporate until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is denoted as 1C3, and the first batch of mother liquor is denoted as 1L3. Transfer 1L3 to a 500mL reaction flask, heat to slight reflux again, and evaporate again until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for 4 hours. Filter the solution. The second batch of crystals obtained is denoted as 2C3, and the second batch of mother liquor is denoted as 2L3. Combine 1C3 and 2C3 to obtain a total of 63.9g of crystals. Discard the mother liquor 2L3 as waste liquid.

[0084] S4, Fourth-stage crystallization: Combine the crystals obtained in the previous stage and add the solid to a 250mL reaction flask. Add 113mL of 0.1mol / L hydrochloric acid solution, heat to slight reflux, and evaporate until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is designated 1C4, and the first batch of mother liquor is designated 1L4. Transfer 1L4 to a 250mL reaction flask, heat to slight reflux again, and evaporate again until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for 4 hours. Filter the solution. The second batch of crystals obtained is designated 2C4, and the second batch of mother liquor is designated 2L4. Combine 1C4 and 2C4 to obtain a total of 40.5g of crystals. Discard the mother liquor 2L4 as waste liquid.

[0085] S5. Fifth Crystallization: Combine the crystals obtained in the previous stage and add the solid to a 250mL reaction flask. Add 72mL of 0.1mol / L hydrochloric acid solution, heat to slight reflux, and evaporate until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is designated 1C5, and the first batch of mother liquor is designated 1L5. Transfer 1L5 to a 100mL reaction flask, heat to slight reflux again, and evaporate again until the solution becomes slightly turbid. Stop heating and allow the solution to slowly cool to room temperature. During this process, the amount of white crystalline solid gradually increases again. Continue stirring at room temperature for 4 hours. Filter the solution. The second batch of crystals obtained is designated 2C5, and the second batch of mother liquor is designated 2L5. Combine 1C5 and 2C5 to obtain a total of 26.6g of crystals. Discard the mother liquor 2L5 as waste liquid.

[0086] Comparative Example 1

[0087] This comparative example was performed using a five-stage recrystallization process. Barium bromide dihydrate and a small amount of radium bromide solution were dissolved in a dilute hydrobromic acid solution (0.3 mol / L) and then recrystallized.

[0088] T1, First-stage crystallization: Weigh 243g of barium bromide dihydrate and 2mL of radium bromide solution, add them to a 500mL reaction flask, then add 158mL of 0.3mol / L hydrobromic acid solution, heat to slight reflux, evaporate until the solution becomes slightly turbid, stop heating, and slowly cool the solution to room temperature. During this process, a large amount of white crystalline solid precipitates. Then continue stirring at room temperature for 4 hours; filter, the first batch of crystals is recorded as 1C1 86.1g, and the first batch of mother liquor is recorded as 1L1;

[0089] T2, Secondary Crystallization: Transfer 1C1 to a 250mL reaction flask, then add 52mL of 0.3mol / L hydrobromic acid solution. Heat to slight reflux and evaporate until the solution becomes slightly turbid. Stop heating and slowly cool the solution to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is recorded as 1C2 26.4g, and the first batch of mother liquor is recorded as 1L2.

[0090] 1 L1 was transferred to a 250 mL reaction flask, heated again to micro-reflux, and evaporated again until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this period, white crystalline solids gradually increased again. Stirring was continued at room temperature for 4 hours. After filtration, the second batch of crystals was recorded as 2C1 57.6 g, and the second batch of mother liquor was recorded as 2 L1.

[0091] T3, Third-stage crystallization: Transfer 1C2 to a 100mL reaction flask, then add 19mL of 0.3mol / L hydrobromic acid solution, heat to slight reflux, evaporate until the solution becomes slightly turbid, stop heating, and slowly cool the solution to room temperature. During this process, a large amount of white crystalline solid precipitates. Then continue stirring at room temperature for 4 hours; filter, and record the first batch of crystals as 1C3 11.2g, and the first batch of mother liquor as 1L3;

[0092] The excess 1L2 and 2C1 from the second-stage crystals were mixed, heated to micro-reflux, and a small amount of 0.3 mol / L hydrobromic acid solution was added until completely dissolved. Heating was stopped, and the solution was slowly cooled to room temperature. During this period, white crystalline solids gradually increased again. The mixture was then stirred at room temperature for 4 hours. After filtration, the second batch of crystals was recorded as 2C2 31.1 g, and the second batch of mother liquor was recorded as 2L2.

[0093] 2L1 was transferred to a 250mL reaction flask, heated again to micro-reflux, and evaporated again until the solution became slightly turbid. Heating was stopped, and the solution was slowly cooled to room temperature. During this period, white crystalline solids gradually increased again. Stirring was continued at room temperature for 4 hours. After filtration, the second batch of crystals was recorded as 3C1 36.1g, and the second batch of mother liquor was recorded as 2L1.

[0094] T4, Fourth-stage crystallization: Transfer 1C3 to a 50mL reaction flask, then add 9mL of 0.3mol / L hydrobromic acid solution, heat to slight reflux, evaporate until the solution becomes slightly turbid, stop heating, and slowly cool the solution to room temperature. During this process, a large amount of white crystalline solid precipitates. Then continue stirring at room temperature for 4 hours; filter, and record the first batch of crystals as 3.8g of 1C4 and the first batch of mother liquor as 1L4;

[0095] Mix 1L3 and 2C2 from the third-stage crystallization, heat to micro-reflux, add a small amount of 0.3mol / L hydrobromic acid solution until completely dissolved, stop heating, and slowly cool the solution to room temperature. During this period, white crystalline solids reappear and gradually increase in quantity. Then continue stirring at room temperature for 4 hours. Filter to obtain the second batch of crystals, denoted as 2C3 17.4g, and the second batch of mother liquor, denoted as 2L3.

[0096] The 2L2 and 3C1 from the third-stage crystallization were mixed, heated to micro-reflux, and a small amount of 0.3 mol / L hydrobromic acid solution was added until completely dissolved. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, white crystalline solids gradually increased in number. The mixture was then stirred at room temperature for 4 hours. After filtration, the second batch of crystals was recorded as 3C2 (39.4 g), and the second batch of mother liquor was recorded as 3L2.

[0097] The 3L1 solution in the third-stage crystallization was heated to a slight reflux and evaporated until the solution became slightly turbid. Heating was then stopped, and the solution was slowly cooled to room temperature. During this process, a large amount of white crystalline solid precipitated out. The solution was then stirred at room temperature for another 4 hours. After filtration, the first batch of crystals was recorded as 4Cl 37.8g, and the first batch of mother liquor was recorded as 4L1.

[0098] T5, Fifth-stage crystallization: Transfer 1C4 to a 25mL reaction flask, then add 3mL of 0.3mol / L hydrobromic acid solution. Heat to slight reflux and evaporate until the solution becomes slightly turbid. Stop heating and slowly cool the solution to room temperature. During this process, a large amount of white crystalline solid precipitates. Continue stirring at room temperature for 4 hours. Filter the solution. The first batch of crystals obtained is recorded as 1.8g of 1C5, and the first batch of mother liquor is recorded as 1L5.

[0099] Mix 1L4 and 2C3 from the fourth-stage crystallization, heat to micro-reflux, add a small amount of 0.3mol / L hydrobromic acid solution until completely dissolved, stop heating, and slowly cool the solution to room temperature. During this period, white crystalline solids reappear and gradually increase in quantity. Then continue stirring at room temperature for 4 hours. Filter to obtain the second batch of crystals, denoted as 2C4 11.8g, and the second batch of mother liquor, denoted as 2L4.

[0100] The 2L3 and 3C2 from the fourth-stage crystallization were mixed, heated to micro-reflux, and a small amount of 0.3 mol / L hydrobromic acid solution was added until completely dissolved. Heating was stopped, and the solution was slowly cooled to room temperature. During this period, white crystalline solids gradually increased again. The mixture was then stirred at room temperature for 4 hours. After filtration, the second batch of crystals was recorded as 3C3 22.8 g, and the second batch of mother liquor was recorded as 3L3.

[0101] The 3L2 and 4C1 from the fourth-stage crystallization were mixed, heated to a slight reflux, and a small amount of 0.3 mol / L hydrobromic acid solution was added until completely dissolved. Heating was stopped, and the solution was slowly cooled to room temperature. During this process, white crystalline solids gradually increased in number. The mixture was then stirred at room temperature for 4 hours. After filtration, the second batch of crystals was recorded as 4C2 (31.9 g), and the second batch of mother liquor was recorded as 4L2.

[0102] The 4L1 solution in the fourth-stage crystallization was heated to a slight reflux and evaporated until the solution became slightly turbid. Heating was then stopped, and the solution was slowly cooled to room temperature. During this process, a large amount of white crystalline solid precipitated out. The solution was then stirred at room temperature for another 4 hours. After filtration, the first batch of crystals was recorded as 5Cl 12.1g, and the first batch of mother liquor was recorded as 5L1.

[0103] The examples and comparative examples were analyzed and tested: the activity test was performed using the gas injection method, and the results are shown in Table 1-2:

[0104] Table 1: Results of the Example

[0105]

[0106] Table 2: Comparative Results

[0107]

[0108] Note: Other solids obtained from the fifth stage in the comparative example were not included in the statistics due to their low activity.

[0109] Analysis of Table 1-2 yields the following results:

[0110] Compared with the traditional fractional recrystallization method of Comparative Example 1, Examples 1-3 of the present invention achieve similar or even better radium recovery rates (81.3%-84.7% vs 79.8%) while the final product is lighter (8.9-26.6 g vs 13.6 g) and the weight reduction ratio is greater (3.7%-10.9% vs 5.6%). In particular, Example 1 (bromide system, 0.3 mol / L HBr) has the highest radium recovery rate (84.7%) while reducing the weight to only 4.3%, showing the best overall performance. In addition, the present invention requires only 2 crystallization operations per stage, for a total of 10 crystallization operations across 5 stages, while Comparative Example 1 requires more than 15 crystallization operations and multiple cross-stage mergings. The operational complexity and equipment requirements are greatly reduced, indicating that the method provided by the present invention can achieve efficient and high-yield radium enrichment with a simpler process, and has significant advantages for industrial applications.

[0111] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for enriching radium through multi-stage countercurrent recrystallization, characterized in that, Includes the following steps: Step 1: Preparation of raw materials and reagents: Prepare a mixture of barium salt and radium salt as the starting material, and prepare a dilute acid solution as the recrystallization solvent. Step 2, First-stage double crystallization: Add the mixture of barium salt and radium salt obtained in Step 1 to the reaction flask, add recrystallization solvent, heat to slight reflux, evaporate until the solution becomes slightly turbid, cool to room temperature, age, and then separate the solid and liquid to obtain the first batch of crystals; evaporate the mother liquor again until slightly turbid, cool and age, and separate the solid and liquid to obtain the second batch of crystals; combine the two batches of crystals and discard the second mother liquor; Step 3, Second-stage double crystallization: The crystals obtained in Step 2 are used as the raw material for this stage. A recrystallization solvent is added, and the heating and dissolving → evaporation and concentration → cooling and aging → solid-liquid separation → mother liquor evaporation and crystallization → crystal merging operation of Step 2 is repeated. The evaporation endpoint, aging time and filtration operation are the same as in Step 2. Step 4: Repeat the process: Following the method in Step 3, sequentially perform the third, fourth, fifth, and so on, on the crystals merged in the previous stage until the preset number of stages is reached; Step 5, final product collection: The crystal obtained by combining the last stage double crystallization is taken as the radium enrichment product, that is, the product is a high specific activity barium chloride-radium chloride or barium bromide-radium bromide mixed crystal; Step 6: Waste liquid treatment: Collect the second mother liquor discarded in each stage of double crystallization and carry out centralized environmental protection disposal or barium / radium recovery.

2. The method for enriching radium by multi-stage countercurrent recrystallization according to claim 1, characterized in that, In step one, the raw material preparation involves selecting one of the following raw materials: the mixture of barium salt and radium salt. (a) A mixture of barium chloride dihydrate or barium bromide dihydrate solid and radium chloride or radium bromide liquid; (b) The barium-removed slag from rare earth extraction is converted into carbonate and then dissolved in hydrochloric acid or hydrobromic acid to obtain the solution. (c) The barium sulfate-radium coprecipitate is converted and then dissolved in hydrochloric acid or hydrobromic acid to obtain the solution.

3. The method for enriching radium by multi-stage countercurrent recrystallization according to claim 2, characterized in that, In step one, the mass of barium chloride dihydrate or barium bromide dihydrate in the starting materials is 200-250g, and the volume of radium salt solution is 1-3mL.

4. The method for enriching radium by multi-stage countercurrent recrystallization according to claim 1, characterized in that, In step one, the reagent preparation is as follows: the dilute acid is selected from either dilute hydrochloric acid or dilute hydrobromic acid. The dilute hydrochloric acid is prepared by mixing concentrated hydrochloric acid with deionized water at a mass fraction of 36% to 38% to prepare a solution of 0.1 mol / L; the dilute hydrobromic acid is prepared by mixing hydrobromic acid with deionized water at a mass fraction of 40% or 48% to prepare a solution of 0.1 to 0.3 mol / L.

5. The method for enriching radium by multi-stage countercurrent recrystallization according to claim 1, characterized in that, In step two: the ratio of the starting material, which is a mixture of barium salt and radium salt, to the recrystallization solvent is: 0.5 to 1.8 mL of recrystallization solvent is added per gram of barium salt solid.

6. The method for enriching radium by multi-stage countercurrent recrystallization according to claim 1, characterized in that, The operational parameters for each stage in step two are as follows: (1) Heating method: Heat to micro-reflux; (2) Evaporation endpoint: The solution becomes slightly turbid; (3) Cooling method: Naturally and slowly cool down to 20-25℃; (4) Aging time: Stir at room temperature for 2 to 8 hours; (5) Filtration method: atmospheric pressure filtration or vacuum filtration; (6) Merging crystals: The first batch of crystals is mixed with the second batch of crystals as the first-stage product; the second mother liquor is collected and treated as waste liquid.

7. The method for enriching radium by multi-stage countercurrent recrystallization according to claim 1, characterized in that, In step three: the ratio of the volume of the added recrystallization solvent to the mass of the crystals is adjusted according to the system: bromide system: 0.6-0.9 mL / g; Chloride system: 1.5~3.0mL / g.

8. The method for enriching radium by multi-stage countercurrent recrystallization according to claim 1, characterized in that, In step four: the preset number of stages is 2 to 10. After each stage, the crystal mass gradually decreases and the weight reduction ratio increases step by step. The final product mass is about 3% to 11% of the starting solid mass.

9. The method for enriching radium by multi-stage countercurrent recrystallization according to claim 1, characterized in that, In step five, the product is a high-specific-activity barium chloride-radium chloride or barium bromide-radium bromide mixed crystal, which can be directly used for subsequent radium extraction or actinium-225 production.

10. The method for enriching radium by multi-stage countercurrent recrystallization according to claim 1, characterized in that, The waste liquid treatment method in step six is: evaporation to recover barium salt, or precipitation and solidification in accordance with radioactive waste liquid standards before disposal.

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