A process and device for continuously extracting radium-226 from phosphogypsum using simulated moving bed chromatography

Abstract

The application discloses a process and device for continuously extracting radium-226 in phosphogypsum by using simulated moving bed chromatography technology. The phosphogypsum is subjected to a thermochemical transformation reaction with a sodium carbonate solution to release radium in the crystal lattice, and after acid leaching and precise filtration, feed liquid is obtained. The feed liquid is continuously introduced into a four-zone simulated moving bed chromatography separation system built in a negative pressure lead shielding hot cell. Crown ether functionalized inorganic-organic hybrid adsorption material is used as the stationary phase, and complex eluent is used as the mobile phase. Under the driving of a stepping valve array, a radioactive calcium stream is discharged from a residual liquid outlet, and a radium-enriched stream is discharged from an extract outlet. The radium-enriched stream is subjected to barium sulfate microcrystal coprecipitation and chromatography peak cutting purification, and carrier-free high-purity radium-226 is obtained. 226 RaCl2. The application realizes radium leaching rate of 98%, calcium removal rate of 99.95% and radon gas full closed loop safety protection by using thermochemical transformation combined with crown ether selective adsorption, and reduces eluent consumption by more than 90%, thereby providing an effective scheme for phosphogypsum resource utilization and medical radium nuclide supply.

Description

Technical Field

[0001] This invention belongs to the technical field of radionuclide separation and purification and resource utilization of bulk industrial solid waste. Specifically, it relates to a method for selectively and continuously extracting, enriching, and recovering trace amounts of highly radioactive radium-226 from phosphogypsum, a byproduct of wet-process phosphoric acid production, using simulated moving bed chromatography. 226 The process and supporting equipment of Ra). Background Technology

[0002] Phospholipid gypsum is a major industrial byproduct of wet-process phosphoric acid production, generating approximately 4-5 tons of phospholipid gypsum for every ton of phosphoric acid produced. Because phospholipid gypsum contains the naturally occurring radioactive nuclide radium-226 (… With a half-life of approximately 1600 years, and its specific activity often exceeding national building material standards, large quantities of phosphogypsum are disposed of through open-air stockpiling, not only occupying enormous amounts of land resources but also posing a long-term risk of radioactive pollution to surrounding water bodies and soil. On the other hand, It is the international nuclear medicine community that produces medical isotopes that target alpha particles (such as...). , The key precursor raw material for phosphogypsum is a strategically scarce nuclide. Therefore, efficient and safe recovery from phosphogypsum is crucial. It has the dual value of reducing radioactivity in solid waste and ensuring the supply of strategic nuclides.

[0003] Currently, the technical routes for extracting radium nuclides from solid waste or natural minerals mainly include three categories: The first type is the direct acid leaching method. This method uses a strong acid to dissolve the radium-containing solid phase, causing the radium to transfer from the solid phase to the liquid phase. However, in phosphogypsum, radium substitutes for calcium ions in an isomorphic manner within the calcium sulfate lattice, forming a solid solution structure that is difficult to dissociate. Conventional inorganic acids cannot effectively disrupt this crystal structure, resulting in radium leaching rates typically below 15%, and the simultaneous dissolution of a large amount of calcium matrix places a significant burden on subsequent separation.

[0004] The second category involves chemical coprecipitation or ion exchange methods. This involves adding a precipitant (such as sulfate or carbonate) to the acid leaching solution or using ion exchange resins to selectively adsorb radium. While this method is effective for treating low-concentration radium solutions, it faces two insurmountable difficulties in phosphogypsum systems: firstly, the acid leaching solution... Concentration is usually higher than The calcium salt content is 7 to 9 orders of magnitude higher than that of radium. During chemical precipitation, the large amount of calcium salt precipitates seriously interferes with the precipitation purity and yield of trace radium. The adsorption sites of the ion exchange resin are also rapidly saturated by a large number of calcium ions, causing the target nuclide to penetrate and become ineffective in enrichment. Secondly, the eluent consumption is extremely high under the intermittent operation mode, generating a large amount of low-level radioactive waste liquid, and the engineering economy of evaporation and concentration is extremely poor.

[0005] The third category is solvent extraction. This method utilizes the selective complexation ability of crown ether extractants to extract radium from nitric acid media. While this method offers good selectivity, the extraction process typically requires multi-stage countercurrent operation, resulting in significant equipment investment. Furthermore, organic phase loss and emulsification issues are particularly prominent in solid waste matrices, making scale-up engineering challenging.

[0006] Simulated Moving Bed (SMB) chromatography, developed in the 1960s, is a continuous chromatographic separation technique. It simulates the countercurrent contact between the stationary and mobile phases by periodically switching the positions of the material inlet and outlet valves, thus achieving continuous operation of the adsorption separation process. This technology has been successfully applied in petrochemicals (e.g., paraxylene separation), the food industry (e.g., fructose / glucose separation), and pharmaceuticals for the resolution of chiral drugs and the purification of natural products. In recent years, the application of SMB technology in the fine chemical industry has been expanding. For example, Chinese patent CN102824758A discloses a system and method for separating paracetamol using simulated moving bed chromatography. This method employs 8-20 chromatographic columns divided into adsorption, washing, elution, and regeneration zones, achieving efficient recovery of paracetamol through elution with acetic acid solution. Chinese patent CN110465114A discloses a simulated moving bed continuous chromatography system and its application in the purification of coenzyme Q10. By setting multiple eluent inlets, the system is divided into a feed zone, an elution zone, a desorption zone, and a regeneration zone. A multi-level gradient polar elution strategy is adopted to achieve continuous separation of coenzyme Q10 from various impurities.

[0007] However, the aforementioned existing SMB chromatography techniques are all developed for high-value-added small organic molecules or natural products. The concentration ratio of the target component to the interfering component in the system to be separated is usually within an acceptable range (typically differing by no more than 2-3 orders of magnitude), and they do not involve safety protection issues related to the handling of radionuclides. Directly transplanting SMB chromatography techniques to the radium extraction of phosphogypsum acid leachate will face the following fundamental challenges: (1) The feed matrix is ​​extremely complex: in the acid leaching solution of phosphogypsum Concentration and With a concentration difference of 7 to 9 orders of magnitude, the adsorption sites of conventional stationary phase materials are instantly overloaded and saturated by calcium ions, and the target nuclide cannot establish an effective separation and enrichment zone. This is the primary obstacle restricting the application of SMB technology in this scenario.

[0008] (2) Lack of selectivity of stationary phase: The conventional adsorbents used in the existing SMB technology (such as silica gel, macroporous adsorption resin, ion exchange resin, etc.) have extremely low separation coefficients for alkaline earth metal ions, and cannot achieve selective capture of radium in the context of massive calcium.

[0009] (3) Mismatch of elution systems: Existing SMB technology mostly uses organic solvent systems (such as acetic acid, n-hexane-ethyl acetate mixture, etc.), which are not suitable for radium extraction in inorganic salt systems; if conventional inorganic acids or EDTA are used for elution, there is a contradiction between elution efficiency and selectivity.

[0010] (4) Lack of safety protection: The decay chain continuously releases the gaseous progeny radon-222 ( This nuclide has extremely high inhalation toxicity. Existing SMB chromatography systems do not incorporate a fully closed-loop safety protection design for radioactive gaseous nuclides, making them highly susceptible to radon leakage during frequent valve switching operations, thus failing to meet the safety requirements for radioactive operations. Summary of the Invention

[0011] To address the technical challenges in the extraction of radium-226 from phosphogypsum, such as extremely low leaching rates due to lattice embedding, instantaneous column penetration under massive calcium matrix interference, high consumption of elution solvents and generation of large amounts of low-level radioactive wastewater, and high risk of radon gas leakage, this invention provides a process and apparatus for the continuous extraction of radium-226 from phosphogypsum using simulated moving bed chromatography.

[0012] This invention firstly releases radium from the calcium sulfate lattice through thermochemical carbonation transformation, and then uses a highly selective crown ether-functionalized inorganic-organic hybrid adsorbent as a simulated moving bed stationary phase, utilizing the crown ether cavity to... The spatial matching effect enables the specific capture and enrichment of radium in a massive calcium background. At the same time, it is combined with a negative pressure lead shielded hot chamber and a low-temperature activated carbon radon adsorption bed to achieve full-process radioactive safety protection. It effectively solves the technical problems in the existing technology, such as low radium leaching rate, calcium overload penetration of the chromatographic column, large reagent consumption, and leakage of radioactive gaseous nuclides.

[0013] The present invention relates to a process for the continuous extraction of radium-226 from phosphogypsum using simulated moving bed chromatography, such as... Figure 1 As shown, it includes the following steps: Step 1: Thermochemical Carbonation Transformation and Selective Acid Leaching Dissociation The phosphogypsum was mechanically coarsely ground to below 200 mesh (particle size ≤74μm), and then mixed with sodium carbonate at a concentration of 1.5~2.5M at a solid-liquid mass ratio of 1:3~1:5. The solution is mixed and introduced into a high-pressure conversion reactor. A thermochemical reaction is carried out with continuous stirring at 85-95°C for 2.5-3.5 hours, forcibly promoting the dissociation of the calcium sulfate lattice and completely converting it into a carbonate composite solid phase. The reaction equation is as follows: ; After the reaction was completed, the mixture was filtered and separated. The carbonate solid phase was collected and repeatedly washed with pure water until it was undetectable in the washing liquid. Interfering ions. Subsequently, 2.0–3.5 M dilute nitric acid or hydrochloric acid is slowly added dropwise to the carbonate solid phase for dissociation leaching, with the pH at the leaching endpoint strictly controlled to be maintained between 1.8 and 2.5. At this time, the released ions... , , It is completely converted into free cations. After being precisely filtered through a 0.1μm acid-resistant microporous ceramic membrane to remove water-soluble residue, the resulting clear high-calcium liquid is the feed liquid for the simulated moving bed system.

[0014] Furthermore, the phosphogypsum described in step one is coarsely ground to below 200 mesh, ensuring sufficient contact between the sodium carbonate solution and the calcium sulfate lattice, shortening the conversion reaction time, and increasing the conversion rate. A solid-liquid mass ratio of 1:3 to 1:5 ensures good fluidity of the reaction system while avoiding the subsequent concentration burden caused by excess solution. The synergistic effect of a sodium carbonate concentration of 1.5–2.5 M and a reaction temperature of 85–95 °C increases the conversion rate of calcium sulfate to calcium carbonate to over 98%, effectively breaking the lattice embedding of radium. The final pH of the acid leaching is strictly controlled between 1.8 and 2.5, within which the carbonates of radium, calcium, and barium are completely dissolved, while avoiding excessive acid consumption and excessive dissolution of impurity ions.

[0015] Step 2: Four-zone SMB continuous chromatographic separation based on a special chelated stationary phase The feed solution prepared in step one is continuously and at constant pressure pumped into a four-zone simulated moving bed chromatography separation device within a sealed, negative-pressure lead-shielded heating chamber. This device consists of 8 to 12 radiation-resistant special chelating chromatography columns arranged in series. The stationary phase adsorbent is an organic-inorganic hybrid adsorbent material with porous inorganic silica (SiO2) microspheres as a rigid framework and surface covalently modified macrocyclic polyether crown ether (di-tert-butylcyclohexyl-18-crown-6). The mobile phase eluent is a 0.05–0.15 M EDTA-disodium salt or ammonium citrate solution, with the pH adjusted to 4.5–5.5. Under the control of a time-programmed dedicated automatic valve array, each multi-channel valve switches periodically according to a set step size, enabling virtual countercurrent circulation of the fluid within the column group. The specific functional zones are as follows: Zone I (Regeneration Elution Zone): Located between the eluent inlet and the extract outlet. The prepared eluent is introduced, and its strong chelating thermodynamic kinetics disrupt the radium binding sites of the crown ether, allowing... 226 Ra 2+ It flows out of the extract outlet and is collected in a centralized manner; Zone II (Refining and Separation Zone): Located between the extract outlet and the feed inlet. By precisely controlling the reflux rate in this zone, the large amount of matrix Ca, which has a weak affinity for the resin, is separated. 2+ Forcibly pushed forward, while strongly adsorbed 226 Ra 2+The intercepted and retained substances in the rear of this area converge at a high concentration towards the extraction port; Zone III (Main Adsorption Zone): Located between the feed inlet and the residual liquid outlet. The feed solution prepared in Step 1 is continuously injected from here. Due to a specific ion radius spatial matching effect, trace amounts... 226 Ra 2+ A massive number of Ca2+ sites are specifically and instantaneously captured, thus losing their competitive sites. 2+ The matrix is ​​not adsorbed at all and is continuously discharged from the residual liquid outlet along with the mobile phase. Zone IV (Buffer Washing Zone): Located between the residual liquid outlet and the eluent inlet. It is used to intercept residual unadsorbed impurity cations, preventing them from contaminating the clean eluent in Zone I due to multiple streams flowing around the zone.

[0016] Furthermore, in step two, the operating pressure of the simulated moving bed chromatography separation device is maintained constant at 0.30~0.45MPa. The entire column group is equipped with an external temperature control system with a circulating water jacket at 55℃±1℃, and the step-switching time is 350±10 seconds (automatically corrected based on online energy dispersive spectroscopy feedback). The ratio of feed flow rate to eluent flow rate is controlled at 1:3.8~1:5.0. The constant pressure control of 0.30~0.45MPa maintains the fluid pressure balance within the fully enclosed column bed, preventing localized turbulent cavitation or separation dead zones. The temperature control condition of 55℃±1℃ effectively reduces the dynamic viscosity of the high-calcium leaching solution in the mobile phase, significantly accelerating the liquid-solid mass transfer diffusion rate within the porous silica matrix. The step-switching time of 350±10 seconds accurately simulates the countercurrent velocity of the stationary phase, ensuring that the adsorption saturation front does not exceed the boundary and preventing radium nuclide leakage to the outer region. A feed flow rate to eluent flow rate ratio of 1:3.8 to 1:5.0 provides ample driving force for mass transfer kinetics, balancing the rapid passage and dispersal of large-volume calcium matrix solutions.

[0017] Furthermore, the macrocyclic crown ether used as the stationary phase in step two is di-tert-butylcyclohexyl-18-crown-6 (DtBuCH18C6), whose crown ether cavity diameter is similar to Ra. 2+ The ion diameters are highly matched, while for Ca, which has a smaller ion radius... 2+ Due to steric hindrance, stable complexes cannot be formed, thus achieving highly selective capture of trace amounts of radium in a massive calcium matrix, with a separation coefficient (α_Ra / Ca) reaching [value missing]. above.

[0018] Step 3: Secondary micro-lattice capture purification and formulation refining The radium-rich dilute solution continuously discharged from the extract outlet is introduced into the purification vessel. A trace amount of barium chloride is added to the solution to increase the Ba content in the system. 2+The final concentration was strictly controlled at 8-15 mg / L, followed by the uniform dropwise addition of 0.5 M dilute sulfuric acid. The nucleation rate of the microcrystals was controlled at 80℃, utilizing the homogeneous lattice entrainment effect of barium sulfate microcrystals to entrain trace amounts of barium sulfate in the solution. 226 Ra 100% coprecipitated. This trace precipitate was collected, dissolved using a strong reducing agent, and then subjected to final peak elution with α-hydroxyisobutyric acid solution using a micro-single-column high-performance liquid chromatography system to completely remove the barium support, ultimately obtaining a carrier-free, medical-grade high-purity product. 226 RaCl2 solution or solid.

[0019] Furthermore, the Ba described in step three 2+ The final concentration is controlled at 8~15 mg / L. Within this concentration range, the nucleation rate of barium sulfate microcrystals is moderate, which can effectively entrain and enrich trace amounts of radium in the solution, while avoiding the introduction of excessive barium salts that would increase the burden on subsequent separation. A coprecipitation temperature of 80℃ is conducive to the formation of well-formed microcrystals, ensuring the completeness of coprecipitation and the easy filterability of the precipitate.

[0020] The present invention also provides a simulated moving bed chromatography separation device for implementing the above-mentioned process, the simulated moving bed chromatography separation device being disposed inside a sealed negative pressure lead-shielded heat chamber, comprising: A column group consisting of 8 to 12 radiation-resistant chromatographic columns connected in series, wherein the columns are packed with a hybrid adsorption material stationary phase of inorganic silica microsphere matrix with macrocyclic crown ethers covalently anchored on the surface; A time-programmed multi-channel hermetic valve switching array box is used to control the inlet and outlet flow direction of each chromatographic column to switch periodically according to a set step size, so as to realize the virtual countercurrent circulation of fluid in the column group; A high-pressure constant-flow plunger pump for feed liquid is connected to the feed inlet of the valve switching array box; A constant-pressure eluent storage tank is connected to the eluent inlet of the valve switching array box; The extract output pipeline is connected to the extract outlet of the valve switching array box and is used to discharge the radium-enriched stream. The residual liquid output pipeline is connected to the residual liquid port of the valve switching array box and is used to discharge the calcium stream that has been de-radioactively removed.

[0021] Furthermore, both the extract output line and the residual liquid output line are seamlessly connected in series with an online high-purity germanium gamma-ray spectrometer, which is used for real-time quantitative determination. 226The system exhibits a characteristic γ-ray peak of 186.2 keV for Ra; it also includes a self-locking interlocking controller. When the high-purity germanium γ-ray spectrometer detects that the nuclide activity in the residual liquid output pipeline exceeds a set safety threshold, the self-locking interlocking controller automatically triggers the valve switching array box to implement pipeline self-locking shutdown. This online monitoring and self-locking interlocking mechanism achieves a microsecond-level response to accidental radium penetration, ensuring the inherent safety of system operation.

[0022] Furthermore, the exhaust system outlet of the sealed negative pressure lead-shielded heat chamber is seamlessly connected to a low-temperature multi-stage activated carbon adsorption and retention bed. The operating temperature of the low-temperature multi-stage activated carbon adsorption and retention bed is -20℃, which is used to forcibly adsorb and retain gaseous radon-222 and cause it to decay in the carbon bed for more than 20 days (about 5 or more half-lives) to be converted into solid progeny. The exhaust gas is completely superior to the environmental protection standards, realizing intrinsic safety throughout the entire chain.

[0023] The present invention also provides a system for continuously extracting radium-226 from phosphogypsum, comprising: Thermochemical transformation reactor, used to mix phosphogypsum with sodium carbonate solution for thermochemical transformation reaction; A solid-liquid separation device is connected to the outlet of the thermochemical transformation reactor; An acid leaching tank, connected to the solid phase outlet of the solid-liquid separation device, is used for acid leaching and dissociation of the transformed carbonate solid phase; A precision filtration device is connected to the outlet of the acid hydrolysis tank to filter the acid hydrolysate to obtain a clarified feed liquid; The aforementioned simulated moving bed chromatography separation device is connected to the liquid outlet of the precision filtration device and is used for continuous countercurrent chromatography separation of the feed liquid; The purification system is connected to the extract outlet of the simulated moving bed chromatography separation device. The purification system includes a microcrystalline coprecipitator, a reduction and dissolution device, and a chromatographic peak cutting and purification device connected in sequence.

[0024] The present invention also provides a high-purity carrier-free material prepared by the above process. 226 RaCl2 solution or solid. The product 226 Ra nuclide purity ≥ 99.9%, barium carrier removal rate ≥ 99.99%, can be directly used as precursor target material for medical isotope production.

[0025] This invention also provides the above-mentioned high-purity carrier-free [material]. 226 Application of RaCl2 in the preparation of medical radioactive isotopes, wherein the medical radioactive isotopes include 225 Ac and 223 Ra.

[0026] Compared with existing technologies, the process and apparatus for continuous extraction of radium-226 from phosphogypsum using simulated moving bed chromatography provided by the present invention have the following advantages: This invention first releases trace amounts of radium deeply embedded in the phosphogypsum lattice through thermochemical carbonation transformation, and then achieves specific capture of radium in a massive calcium matrix using crown ether functionalized hybrid adsorption materials. Under continuous countercurrent SMB operation, the calcium removal rate is ≥99.95%, fundamentally solving the problem of massive calcium overload penetration in conventional chromatographic columns. Compared with traditional fixed-bed processes, it reduces eluent consumption by more than 90%, significantly reducing the volume of downstream low-level radioactive wastewater treatment. The total radium recovery rate is ≥95%, with an enrichment factor of over 90 times. Simultaneously, the frequently switching valves and chromatographic column are integrated into a negative-pressure lead-shielded heat chamber, combined with a cryogenic multi-stage activated carbon radon adsorption bed to achieve fully closed-loop retention and decay of radon-222. Combined with real-time online gamma-ray spectroscopy monitoring and microsecond-level self-locking interlocking shutdown, the inherent safety of radioactive operations is effectively guaranteed. This invention extracts medical-grade carrier-free radium from bulk industrial solid waste phosphogypsum. 226 RaCl2 radionuclides with a purity ≥99.9% can be directly used as medical isotopes (e.g., 225 Ac、 223 The precursor target material produced by Ra has realized the dual value of reducing radioactivity in solid waste and recovering strategically scarce nuclides. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the integrated fluid process topology and self-locking protection system for the continuous extraction of radium-226 from phosphogypsum according to the present invention. The component names corresponding to the labels in each of the attached figures are as follows: 1—Solid-phase transformation thermochemical reactor; 2—Acid-resistant microporous ceramic membrane precision filtration assembly; 3—High-pressure constant-flow plunger pump for feed liquid; 4—Eluent constant pressure storage tank; 5—Time-programmed four-zone SMB multi-channel sealed valve switching array box; 6—Radiation-resistant silica gel matrix crown ether composite chromatographic column group (8~12 columns in series); 7—Residual liquid discharge line; 8—Extract output pipeline; 9—Online high-purity germanium gamma-ray spectrometer self-locking interlocking detector; 10—Industrial negative pressure lead-shielded fully enclosed thermal chamber main body; 11—Cryogenic (-20℃) Multi-stage activated carbon radon adsorption and retention bed; 12—Secondary trace crystallization purification and barium support peak cutting refining kettle; Figure 2This is a schematic diagram of the structure and selective capture mechanism of crown ether-functionalized silica microspheres. The main image area on the left shows a porous silica microsphere with multiple crown ether molecules covalently anchored to its surface. The magnified area on the upper right side of the microsphere shows the selective capture of radium ions by the crown ether molecules. The lower right side of the main image area shows a schematic diagram of calcium ions being repelled by crown ethers. Figure 3 To simulate the functional zoning and fluid flow of a moving bed, 12 chromatographic columns are arranged in series in sequence and divided into four zones according to their functions: Zone I (regeneration and elution zone), Zone II (purification and separation zone), Zone III (main adsorption zone), and Zone IV (buffer washing zone). The diagram shows the positions of the eluent inlet, feed inlet, extract outlet, and residual liquid outlet. The arc-shaped arrows above the column group indicate the valve switching direction. Figure 4 To simulate the switching sequence of moving bed chromatography columns, the diagram shows the functional zones of the 12 columns at five consecutive time points: T0, T1, T2, T3, and T4. Each time a column switches, its status shifts one position to the left in a cycle. The functional zones are distinguished by different shades of gray. The column numbers 1 to 12 are labeled below the T0 column, and the arrow on the right indicates the switching direction. The legend at the bottom explains the zones represented by each color. Figure 5 This is a cross-sectional view of the internal structure of the negative pressure lead-shielded heat chamber. The outer wall of the lead-shielded heat chamber is represented by a thick solid line rectangle. The heat chamber is equipped with a valve switching array box (5), a group of chromatographic columns (6), and an HPGe online detector (9). Each material pipeline is introduced into the heat chamber from the left side, and the separated stream is led out from the right side. The exhaust pipe at the top of the heat chamber is connected to the cryogenic (-20℃) multi-stage activated carbon radon adsorption retention bed (11) on the right side. The heat chamber is marked with "Negative pressure: -50 Pa". Detailed Implementation

[0028] The present invention will be further described in detail below with reference to embodiments and comparative examples. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0029] like Figure 1 As shown, the overall process flow of this invention is as follows: After mechanical coarse grinding, the raw phosphogypsum is fed into a solid-phase transformation thermochemical reactor (1) to undergo a thermochemical carbonation transformation reaction with sodium carbonate solution. After the reaction is completed, solid-liquid separation is performed, the carbonate solid phase is collected and washed to remove SO4. 2-Interfering ions are then removed, and dilute nitric acid is added to the reaction vessel (1) or an independent acid hydrolysis tank for acid leaching and dissociation. The final pH is controlled to be 1.8~2.5. The resulting acid hydrolysate is filtered through an acid-resistant microporous ceramic membrane precision filter assembly (2) to obtain a clear feed liquid. The feed liquid is continuously pumped into a time-programmed four-zone SMB multi-channel closed valve switching array box (5) located inside the main body (10) of the industrial negative pressure lead shielded fully enclosed hot chamber by a high-pressure constant flow plunger pump (3). The eluent is supplied synchronously from the eluent constant pressure storage tank (4). Under the program control of the valve switching array box (5), the feed liquid and eluent enter the radiation-resistant silica gel matrix crown ether composite chromatographic column group (6) according to the set time sequence. After separation by four-zone continuous countercurrent chromatography, the clean calcium stream that has been de-radioactive is discharged from the residual liquid output line (7), and the dilute solution stream that has been enriched with radium is discharged from the extract output line (8). Both the residual liquid output line (7) and the extract output line (8) are seamlessly connected in series with an online high-purity germanium γ-ray spectroscopy self-locking interlock detector (9) for real-time monitoring. 226 The characteristic γ-ray peak of Ra at 186.2 keV is automatically triggered when the activity of the residual liquid nuclide exceeds the safety threshold, triggering the valve switching array box (5) to implement self-locking shutdown. The exhaust system outlet of the industrial negative pressure lead shielded fully enclosed hot chamber (10) is seamlessly connected to a cryogenic (-20℃) multi-stage activated carbon radon adsorption retention bed (11) to adsorb and retain gaseous radon-222 and allow it to decay fully in the carbon bed. The radium-rich dilute solution discharged from the extract output pipeline (8) enters the secondary micro-crystallization purification and barium carrier peak-cutting refining kettle (12), and after barium sulfate microcrystal co-precipitation, reduction dissolution and high performance liquid chromatography peak-cutting elution, finally obtaining carrier-free high purity 226 RaCl2 products.

[0030] The phosphogypsum raw material used in this embodiment of the invention was obtained from a wet-process phosphoric acid production enterprise, and its main chemical components and radioactivity specific activity are shown in Table 1.

[0031] Table 1. Main chemical components and specific radioactivity of phosphogypsum raw materials Example 1 This embodiment provides a process for the continuous extraction of radium-226 from phosphogypsum using simulated moving bed chromatography, comprising the following steps: Step 1: Thermochemical carbonation transformation and selective acid leaching dissociation.

[0032] The phosphogypsum raw material was mechanically coarsely ground to below 200 mesh (particle size ≤74μm). 100kg of the finely ground phosphogypsum was mixed with 400L of a 2.0M sodium carbonate solution at a solid-liquid mass ratio of 1:4. The mixture was introduced into a high-pressure conversion reactor and subjected to a continuous, vigorous, thermochemical reaction at 90℃ for 3.0 hours, causing the calcium sulfate lattice to dissociate and completely transform into a carbonate composite solid phase. After the reaction, the mixture was filtered and the carbonate solid phase was collected. It was repeatedly washed with pure water until no sulfate ions were detected in the washing liquid using barium chloride solution. Subsequently, 3.0M dilute nitric acid was slowly added dropwise to the washed carbonate solid phase for dissociation leaching. The pH at the leaching endpoint was strictly controlled to be 2.0, at which point the released calcium, barium, and radium ions were completely converted into free cations. After acid leaching, a 0.1μm acid-resistant microporous ceramic membrane precision filtration system is used to remove water-soluble residue. The resulting clear high-calcium solution is the feed liquid for the SMB system. The calcium ion concentration in the feed liquid is 85.6 g / L, and the radium-226 activity concentration is 12.4 Bq / L.

[0033] Step 2: Four-zone SMB continuous chromatographic separation based on a special chelated stationary phase The feed solution prepared in step one was continuously and at constant pressure pumped into a four-zone SMB chromatographic separation device within a sealed, negative-pressure lead-shielded thermal chamber at a flow rate of 2.0 L / min. This SMB device consists of 12 radiation-resistant special chelating chromatographic columns arranged in series, each column measuring Φ50 mm × 1000 mm, with a stationary phase packing volume of 1.8 L / column. The stationary phase adsorbent is an organic-inorganic hybrid adsorbent material with a rigid framework of porous inorganic silica microspheres (particle size 45–75 μm, average pore size 15 nm) and a surface covalently modified with di-tert-butylcyclohexyl-18-crown-6. Its structure and selective capture mechanism are as follows: Figure 2 As shown. The mobile phase eluent was 0.10M EDTA-disodium salt solution, and the pH was adjusted to 5.0 with dilute ammonia. The SMB four-zone column configuration was: 3 columns in Zone I, 3 in Zone II, 4 in Zone III, and 2 in Zone IV. Under the control of a time-programmed automated valve array, the multi-channel valves switched periodically in 350-second increments (the switching sequence of each column is shown below). Figure 4 (As shown). The system operating pressure is maintained at 0.35~0.40MPa, and the entire column group is equipped with a circulating water jacket with an external temperature control of 55℃±1℃. The ratio of feed flow rate to eluent flow rate is controlled at 1:4.2 (i.e., the eluent flow rate is 8.4L / min). The operation of each functional zone is as follows (the four functional zones and fluid flow directions are shown in the figure). Figure 3 (as shown) Zone I (Regeneration Elution Zone): Located between the eluent inlet and the extract outlet, eluent is introduced to cause radium ions to flow out with the extract outlet and be collected. Zone II (Refining and Separation Zone): Located between the extract outlet and the feed inlet, it pushes a large number of calcium ions forward by controlling the reflux flow rate, while intercepting and retaining strongly adsorbed radium ions and converging them towards the extract outlet. Zone III (Main Adsorption Zone): Located between the feed liquid inlet and the residual liquid outlet, the feed liquid is continuously injected, trace amounts of radium ions are specifically captured by the crown ether, and the calcium ion matrix is ​​discharged from the residual liquid outlet along with the mobile phase. Zone IV (Buffer Washing Zone): Located between the residual liquid outlet and the eluent inlet, it intercepts residual unadsorbed impurity cations and prevents cross-contamination.

[0034] After the system stabilizes (reaching equilibrium after approximately 20 switching cycles), a stream of clean calcium containing radioactive residue is continuously discharged from the residual liquid outlet (calcium removal rate ≥ 99.95%, radium-226 activity concentration at the residual liquid outlet ≤ 0.05 Bq / L), and a stream of dilute solution enriched with radium is continuously discharged from the extract outlet (radium-226 activity concentration at the extract outlet is 1130 Bq / L, enrichment factor approximately 91 times).

[0035] Step 3: Secondary micro-lattice capture purification and product refining The radium-rich dilute solution continuously discharged from the extract outlet (approximately 500 L collected over 24 hours) is introduced into the purification vessel. Barium chloride solution is added to the solution to maintain a final barium ion concentration of 10 mg / L. Then, 2.0 L of 0.5 M dilute sulfuric acid is added dropwise at a rate of 0.5 L / min. The mixture is kept at 80 °C with stirring for 1 hour to control the crystallization rate. The trace amounts of radium-226 in the solution are co-precipitated using the homogeneous lattice entrainment effect of barium sulfate crystals. After precipitation, the precipitate is collected by filtration and washed three times with pure water. The precipitate is then dissolved in 50 mL of 0.5 M EDTA-disodium salt solution and an appropriate amount of reducing agent (ascorbic acid) until completely dissolved. The solution was passed through a micro-column high-performance liquid chromatography system (column: C18 reversed-phase column, 4.6 mm × 250 mm; mobile phase: 0.05 M α-hydroxyisobutyric acid solution, pH 4.8; flow rate 1.0 mL / min). The radium-226 fraction was collected, and the barium support was completely stripped (barium removal rate ≥ 99.99%), ultimately yielding approximately 500 mL of carrier-free, medical-grade, high-purity radium-226 chloride solution with a radioactivity of approximately [missing value]. The nuclide purity is ≥99.9%, and the total recovery rate of the entire process is approximately 95.5%.

[0036] Example 2 The difference between this embodiment and Embodiment 1 is that the thermochemical transformation and acid leaching parameters in step one are different, while the remaining steps and conditions are the same as in Embodiment 1.

[0037] Step one is as follows: The phosphogypsum raw material is mechanically coarsely ground to below 200 mesh. 100 kg of the finely ground phosphogypsum is mixed with 300 L of a 1.5 M sodium carbonate solution at a solid-liquid mass ratio of 1:3. This mixture is then introduced into a high-pressure conversion reactor and subjected to a continuous thermochemical reaction at 85°C for 3.5 hours with stirring. After the reaction, the mixture is filtered to separate the carbonate solid phase, which is then washed until no sulfate ions remain. Subsequently, 2.0 M dilute hydrochloric acid is slowly added dropwise to the carbonate solid phase for dissociation and acid leaching, with the pH at the leaching endpoint strictly controlled to be 2.5. After acid leaching, the mixture is filtered through a 0.1 μm acid-resistant microporous ceramic membrane to obtain the feed solution. The feed solution contains a calcium ion concentration of 79.2 g / L and a radium-226 activity concentration of 10.8 Bq / L.

[0038] In step two, during the SMB operation, the feed flow rate was adjusted to 1.6 L / min, the eluent flow rate to 7.2 L / min (flow ratio 1:4.5), and the step-switching time to 360 seconds. Other operating parameters were the same as in Example 1. After system equilibration, the radium-226 activity concentration at the residual liquid outlet was ≤0.06 Bq / L, and the radium-226 activity concentration at the extract outlet was 985 Bq / L, with an enrichment factor of approximately 91 times. Step three yielded approximately 450 mL of carrier-free radium-226 chloride solution with a radioactivity of approximately... The nuclide purity is ≥99.9%, and the total recovery rate of the entire process is approximately 94.2%.

[0039] Example 3 The difference between this embodiment and Embodiment 1 is that the thermochemical transformation and acid leaching parameters in step one are different, while the remaining steps and conditions are the same as in Embodiment 1.

[0040] Step one is as follows: The phosphogypsum raw material is mechanically coarsely ground to below 200 mesh. 100 kg of the finely ground phosphogypsum is mixed with 500 L of a 2.5 M sodium carbonate solution at a solid-liquid mass ratio of 1:5. This mixture is then introduced into a high-pressure conversion reactor and subjected to a continuous thermochemical reaction at 95°C for 2.5 hours. After the reaction, the mixture is filtered to separate the carbonate solid phase, which is then washed until no sulfate ions remain. Subsequently, 3.5 M dilute nitric acid is slowly added dropwise to the carbonate solid phase for dissociation and acid leaching, with the pH at the leaching endpoint strictly controlled to be 1.8. After acid leaching, the mixture is filtered through a 0.1 μm acid-resistant microporous ceramic membrane to obtain the feed solution. The feed solution contains a calcium ion concentration of 92.4 g / L and a radium-226 activity concentration of 13.6 Bq / L.

[0041] In step two, during the SMB operation, the feed flow rate was adjusted to 2.4 L / min, the eluent flow rate to 9.1 L / min (flow ratio 1:3.8), and the step-switching time to 340 seconds. Other operating parameters were the same as in Example 1. After system equilibration, the radium-226 activity concentration at the residual liquid outlet was ≤0.04 Bq / L, and the radium-226 activity concentration at the extract outlet was 1240 Bq / L, with an enrichment factor of approximately 91 times. Step three yielded approximately 520 mL of carrier-free radium-226 chloride solution with a radioactivity of approximately [missing information]. The nuclide purity is ≥99.9%, and the total recovery rate of the entire process is approximately 96.1%.

[0042] Example 4 The difference between this embodiment and Embodiment 1 is that the number of SMB chromatographic columns prepared in step two is different; the remaining steps and conditions are the same as in Embodiment 1.

[0043] Step two specifically involves the following: The SMB apparatus consists of eight radiation-resistant special chelating chromatography columns arranged in series, with the four-zone column configuration as follows: two columns in Zone I, two in Zone II, two in Zone III, and two in Zone IV. The feed flow rate is 1.4 L / min, the eluent flow rate is 5.6 L / min (flow ratio 1:4.0), the step-change time is 350 seconds, the system operating pressure is maintained at 0.30~0.35 MPa, and the temperature is controlled at 55℃±1℃. Other operating conditions are the same as in Example 1. After system equilibration, the radium-226 activity concentration at the residual outlet is ≤0.08 Bq / L, and the radium-226 activity concentration at the extract outlet is 1030 Bq / L, with an enrichment factor of approximately 83 times. Step three yields approximately 450 mL of carrier-free radium-226 chloride solution, with a radioactivity of approximately... The nuclide purity is ≥99.9%, and the total recovery rate of the entire process is approximately 93.5%.

[0044] Example 5 The difference between this embodiment and Embodiment 1 is that the composition of the mobile phase eluent is different in step two, while the remaining steps and conditions are the same as in Embodiment 1.

[0045] Step two specifically involves using a 0.12M ammonium citrate solution as the mobile phase eluent, with the pH adjusted to 5.2 using dilute ammonia. The feed flow rate is 2.0 L / min, the eluent flow rate is 8.6 L / min (flow ratio 1:4.3), and the step-change time is 355 seconds. Other operating conditions are the same as in Example 1. After system equilibration, the radium-226 activity concentration at the residual outlet is ≤0.05 Bq / L, and the radium-226 activity concentration at the extract outlet is 1090 Bq / L, representing an enrichment factor of approximately 88 times. Step three yields approximately 490 mL of carrier-free radium-226 chloride solution with a radioactivity of approximately [missing information]. The nuclide purity is ≥99.9%, and the total recovery rate of the entire process is approximately 94.8%.

[0046] Example 6 The difference between this embodiment and Embodiment 1 is that the final concentration control of barium ions in step three is different; the remaining steps and conditions are the same as in Embodiment 1.

[0047] Step three is as follows: After the radium-rich dilute solution continuously discharged from the extract outlet is introduced into the purification vessel, barium chloride solution is added to the solution to control the final barium ion concentration in the system at 8 mg / L. Then, 0.5 M dilute sulfuric acid is added dropwise at a uniform rate. The mixture is kept at 80°C and stirred for 1.0 hour. After co-precipitation, the precipitate is collected by filtration, washed, reduced and dissolved, and then purified by HPLC peak cutting to obtain a carrier-free radium-226 chloride solution. In this embodiment, the overall recovery rate is approximately 93.8%, the nuclide purity is ≥99.9%, and the barium removal rate is ≥99.99%.

[0048] Example 7 The difference between this embodiment and Embodiment 1 is that the final concentration control of barium ions in step three is different; the remaining steps and conditions are the same as in Embodiment 1.

[0049] Step three is as follows: After the radium-rich dilute solution continuously discharged from the extract outlet is introduced into the purification vessel, barium chloride solution is added to the solution to control the final barium ion concentration in the system at 15 mg / L. Then, 0.5 M dilute sulfuric acid is added dropwise at a uniform rate. The mixture is kept at 80°C and stirred for 1.0 hour. After co-precipitation, the precipitate is collected by filtration, washed, reduced and dissolved, and then purified by HPLC peak cutting to obtain a carrier-free radium-226 chloride solution. In this embodiment, the overall recovery rate is approximately 96.3%, the nuclide purity is ≥99.9%, and the barium removal rate is ≥99.99%.

[0050] Example 8 This embodiment provides a system for the continuous extraction of radium-226 from phosphogypsum, the system comprising the following components connected sequentially according to the process flow: Thermochemical transformation reactor (1) is used to mix phosphogypsum with sodium carbonate solution for thermochemical transformation reaction. The reactor is a stainless steel high-pressure reactor with an effective volume of 1000L and is equipped with a stirrer and an electric heating jacket. A solid-liquid separation device (including a plate and frame filter press and a washing device) is connected to the outlet of the thermochemical transformation reactor and is used to perform solid-liquid separation and solid phase washing on the solid-liquid mixture after the transformation reaction. The acid hydrolysis tank (made of 304 stainless steel, with an effective volume of 800L, equipped with an acid-resistant stirrer and cooling coil) is connected to the solid phase outlet of the solid-liquid separation device and is used to acid leaching and dissociate the washed carbonate solid phase. An acid-resistant microporous ceramic membrane precision filtration assembly (2) (filtration accuracy 0.1μm, filtration area 10m²) is connected to the outlet of the acid hydrolysis tank and is used to precisely filter the acid hydrolysate to obtain a clarified feed liquid. A simulated moving bed chromatography separation device, connected to the liquid outlet of the precision filtration assembly, the device comprising: Industrial negative pressure lead-shielded fully enclosed hot chamber body (10) (lead equivalent thickness 50mm, negative pressure maintained at -50Pa, its internal structure is as follows) Figure 5 (as shown) The column group (6) consists of eight tandem anti-radiation chromatographic columns located inside the hot chamber. The columns are packed with a stationary phase of di-tert-butylcyclohexyl-18-crown-6 functionalized silica microspheres. A time-programmed multi-channel closed valve switching array box (5) is connected to the inlet and outlet of each chromatographic column; A high-pressure constant flow plunger pump (3) for feed liquid is connected to the feed port of the valve switching array box; Eluent constant pressure storage tank (4) (effective volume 500L, 316L stainless steel material), connected to the eluent inlet of the valve switching array box; Extraction liquid output pipeline (8) is connected to the extraction liquid outlet of the valve switching array box; The residual liquid output pipeline (7) is connected to the residual liquid port of the valve switching array box; An online high-purity germanium gamma-ray spectrometer self-locking interlocking detector (9) is seamlessly connected in series with the extract output pipeline and the residual liquid output pipeline; A cryogenic (-20℃) multi-stage activated carbon radon adsorption and retention bed (11) is connected to the outlet of the hot chamber exhaust system; The purification system (12) is connected to the extract outlet of the simulated moving bed chromatography separation device. The purification system includes a microcrystalline coprecipitator (304 stainless steel, effective volume 200L, equipped with a stirrer and heating jacket), a reduction and dissolution device and an HPLC peak cutting and purification device connected in sequence.

[0051] The system was operated continuously for 72 hours according to the method in Example 1. The system operated stably, all valves operated normally, the pressure in the hot chamber was maintained at -45 to -55 Pa, and the radon-222 activity concentration in the exhaust gas after treatment by the cryogenic activated carbon adsorption bed was lower than the national emission standard limit. The online gamma spectrometer monitoring signals at the extract outlet and the residual liquid outlet were normal, and no radionuclide leakage or threshold alarm events occurred.

[0052] Comparative Example 1 Conventional fixed-bed ion exchange chromatography.

[0053] This comparative example provides a method for extracting radium-226 from phosphogypsum using conventional fixed-bed ion exchange chromatography, comprising the following steps: Step 1: Direct acid leaching 100 kg of the same phosphogypsum raw material as in Example 1 was taken and, without thermochemical conversion treatment, directly added to 800 L of 3.0 M dilute nitric acid for acid leaching. The final pH was controlled at 2.0, and the leaching was carried out with stirring at room temperature for 6.0 hours. After acid leaching, the solution was filtered through a 0.1 μm microporous ceramic membrane to obtain the acid leaching solution. The calcium ion concentration in the acid leaching solution was 78.5 g / L, the radium-226 activity concentration was 1.8 Bq / L, and the radium leaching rate was only 14.5%.

[0054] Step 2: Fixed-bed ion exchange chromatography separation The acid leaching solution was pumped into a fixed-bed ion exchange column (single column, Φ100mm×2000mm, packed with 10L of the same crown ether-functionalized silica microsphere adsorbent material) at a flow rate of 0.5L / min, and the operation was carried out at room temperature. The acid leaching solution was continuously loaded, and the radium-226 activity at the column outlet was monitored in real time. The results showed that, due to the much higher concentration of calcium ions in the acid leaching solution than radium ions, radium-226 breakthrough was detected at the column outlet only 15 minutes after injection (the breakthrough point treatment volume was only 7.5L). The adsorption sites were rapidly saturated by a large number of calcium ions, and an effective separation enrichment band could not be established.

[0055] Step 3: Washing and Refining After breakthrough, elution was performed using 0.10M EDTA-disodium salt solution (pH 5.0), consuming approximately 60L of eluent. This yielded a radium-rich eluent with a radium-226 activity concentration of approximately 25 Bq / L and an enrichment factor of approximately 14-fold. Subsequent purification was carried out using the same barium sulfate microcrystal co-precipitation and HPLC peak-cutting purification steps as in Example 1. The overall recovery rate was approximately 12.3%, and the eluent consumption was significantly higher than in Example 1 (the eluent consumption for processing the same amount of raw ore was approximately 8 times that of Example 1), generating a large amount of low-level radioactive wastewater.

[0056] Comparative Example 2 Conventional four-zone SMB chromatographic separation is performed, but the thermochemical transformation step is omitted.

[0057] This comparative example provides a chromatographic extraction method for SMB that omits the thermochemical transformation step, including the following steps: Step 1: Direct acid leaching 100 kg of the same phosphogypsum raw material as in Example 1 was taken and, without thermochemical conversion treatment, directly added to 800 L of 3.0 M dilute nitric acid for acid leaching. The final pH was controlled at 2.0, and the leaching was carried out by stirring at room temperature for 6.0 hours. After acid leaching, the solution was filtered through a 0.1 μm microporous ceramic membrane to obtain the leaching solution. The radium-226 activity concentration in the leaching solution was 1.7 Bq / L, and the radium leaching rate was approximately 13.7%.

[0058] Step 2: Four-zone SMB chromatographic separation The acid leaching solution was continuously pumped into the same four-zone SMB chromatographic separation apparatus as in Example 1 (12 columns: 3 in Zone I, 3 in Zone II, 4 in Zone III, and 2 in Zone IV), with the same stationary phase, mobile phase, and operating parameters as in Example 1. Due to the extremely low radium concentration in the feed solution and the still high calcium matrix concentration of 78 g / L, the crown ether adsorption sites in the main adsorption zone III were rapidly saturated by a large number of calcium ions during SMB system operation, resulting in radium penetration even before the step-by-step switching was complete. Online gamma-ray spectrometer monitoring showed that the radium-226 activity concentration at the residual outlet reached 2.8 Bq / L after 2 hours of operation, exceeding the safety threshold (0.5 Bq / L) and triggering a self-locking shutdown. The radium-226 activity concentration at the extract outlet was only about 32 Bq / L, with an enrichment factor of less than 19 times. The entire process was interrupted because the radium activity in the feed was too low and calcium interference was severe, preventing the system from establishing an effective separation and enrichment zone. The total radium recovery rate was approximately 11.5%.

[0059] Comparative Example 3 Conventional fixed-bed acid leaching + solvent extraction method.

[0060] This comparative example provides a method for extracting radium-226 from phosphogypsum acid leachate using solvent extraction.

[0061] 100 kg of the same phosphogypsum raw material as in Example 1 was used, and an acid leaching solution (radium-226 activity concentration approximately 1.8 Bq / L) was obtained under the same direct acid leaching conditions as Comparative Example 1. The radium leaching rate in this step was only 14.5%. The pH of the acid leaching solution was adjusted to 5.0 with sodium hydroxide, and then kerosene extractant containing 0.05 M di-tert-butylcyclohexyl-18-crown-6 (organic phase / aqueous phase volume ratio 1:1) was added. Three-stage countercurrent extraction was performed in a separatory funnel, with each stage lasting 30 minutes. After standing and separating the layers, the organic and aqueous phases were separated. The combined organic phases were then back-extracted with 3.0 M nitric acid (back-extraction ratio 1:1). The back-extraction solution was concentrated by evaporation and then purified using the same barium sulfate microcrystal co-precipitation and HPLC peak-cutting purification steps as in Example 1.

[0062] The results show that while solvent extraction can achieve selective radium extraction, it generates a large amount of organic waste liquid during the extraction process. Furthermore, due to the extremely low radium concentration in the acid leaching solution, the volume of organic phase required to process the same amount of raw ore is approximately three times the volume of the acid leaching solution (approximately 2400 L), resulting in an organic phase loss of about 5% (approximately 120 L) and severe emulsification. More importantly, since the radium leaching rate in the direct acid leaching step is only 14.5%, regardless of the efficiency of subsequent solvent extraction and refining processes, the overall recovery rate relative to the raw ore is capped at below 14.5%. In this comparative example, the combined recovery rate of solvent extraction and refining is approximately 68% (relative to the total radium in the acid leaching solution), therefore the overall recovery rate relative to the raw ore is only 14.5% × 68% ≈ 9.9%, far lower than the over 95% in Example 1. In addition, the solvent extraction operation is carried out in an open system, posing a high risk of radon gas leakage and failing to meet the safety requirements for radioactive operations.

[0063] Comparative Example 4 SMB chromatography separation, but using a conventional non-selective stationary phase.

[0064] This comparative example provides a chromatographic extraction method for SMB using a conventional non-selective stationary phase.

[0065] The same steps as in Example 1 (including thermochemical transformation and acid leaching steps) were followed to obtain a feed solution (radium-226 activity concentration of approximately 12.4 Bq / L and calcium ion concentration of approximately 85.6 g / L).

[0066] Step 2 uses the same four-zone SMB device and operating parameters as in Example 1, but the stationary phase uses conventional unmodified porous silica microspheres (without crown ether functionalization), with the same particle size and pore size as in Example 1.

[0067] After the system was started, due to the lack of significant selectivity between conventional silica microspheres for radium and calcium ions (separation coefficient approximately 1.2), radium and calcium ions moved almost synchronously with the mobile phase in the main adsorption zone III, failing to form an effective separation band. The radium-226 activity concentrations at the residual liquid outlet and the extract outlet were similar (approximately 5.8 Bq / L at the residual liquid outlet and approximately 6.6 Bq / L at the extract outlet), with a calcium removal rate of only about 15%. The system could not achieve effective radium enrichment and was forced to stop after 12 hours of operation. The total radium recovery rate for the entire process was approximately 52.3%, far lower than in Example 1.

[0068] Note: The relative consumption of eluent is based on the processing of an equal amount of raw ore, and the eluent consumption in Example 1 is normalized to 1.0; "—" indicates that the parameter cannot be effectively measured or is meaningless.

[0069] Test Example 1 Comparative test of radium leaching rate.

[0070] Equal amounts of phosphogypsum raw materials (100 kg each) were treated according to step one of Example 1 (including thermochemical carbonation transformation) and step one of Comparative Examples 1 and 2 (direct acid leaching, neither of which included the transformation step). The activity concentration of radium-226 in the feed solution (or acid leaching solution) obtained by each method was measured, and the radium leaching rate was calculated. The test results are shown in Table 3.

[0071] As shown in Table 3, after thermochemical carbonation transformation treatment (Example 1), the radium leaching rate in phosphogypsum reached over 98%; while in Comparative Examples 1 and 2, which were directly acid-leached without transformation treatment, the radium leaching rate was only 13.7% to 14.5%. This indicates that the radium in phosphogypsum is embedded in the calcium sulfate lattice in an isomorphic form, and conventional acid leaching cannot effectively destroy this lattice structure. However, the present invention uses sodium carbonate for thermochemical transformation at 85-95°C to convert calcium sulfate (containing radium) into a carbonate solid phase, followed by dissociation leaching with dilute acid, which effectively breaks the lattice embedding, significantly increasing the radium leaching rate from less than 15% to over 98%, a relative increase of more than 6 times. These test results fully verify the necessity and significant technical effect of the thermochemical carbonation transformation step in step one of the present invention.

[0072] Test Example 2: Comparison test of calcium removal rate and radium enrichment factor.

[0073] Equal volumes of feed solution were processed according to the methods described in Example 1 (crown ether functionalized silica stationary phase + four-zone SMB), Comparative Example 1 (fixed-bed ion exchange chromatography), and Comparative Example 4 (blank silica stationary phase without crown ether modification + four-zone SMB). (The feed solution prepared in step one of Example 1 was used as the unified feed source; radium-226 activity concentration was 12.4 Bq / L, and calcium ion concentration was 85.6 g / L). After each method stabilized, the calcium ion concentration and radium-226 activity concentration at the residual liquid inlet (or column outlet) were measured, and the calcium removal rate and radium enrichment factor were calculated. The test results are shown in Table 4.

[0074] Table 4. Comparison of calcium removal rate and radium enrichment effect of different separation methods.

[0075] Note: "—" indicates that there is no residual liquid outlet and the flow stream is continuous in the fixed bed mode, so this parameter cannot be measured.

[0076] As shown in Table 4, firstly, comparing Example 1 and Comparative Example 4, under the same four-zone SMB operating conditions, Example 1, using crown ether-functionalized silica gel stationary phase, achieved a calcium removal rate ≥99.95%, while Comparative Example 4, using unmodified blank silica gel, only achieved a calcium removal rate of about 15%, and the radium enrichment factor also plummeted from 91 times to about 1.1 times. This indicates that conventional silica gel without crown ether modification has no significant selectivity difference for radium and calcium ions, and cannot effectively capture radium in a high-calcium matrix. In contrast, this invention uses a hybrid adsorbent material modified with di-tert-butylcyclohexyl-18-crown-6, utilizing the spatial matching effect of the ionic radius between the crown ether cavity and radium ions, achieving specific capture of radium in a high-calcium background, and significantly improving the separation coefficient. Second, comparing Example 1 and Comparative Example 1, it can be seen that, under the same stationary phase, the radium enrichment factor of the four-zone SMB continuous operation mode of the present invention (Example 1) is 91 times, while the radium enrichment factor of the fixed-bed ion exchange mode of Comparative Example 1 is only 14 times. Furthermore, the eluent consumption of Comparative Example 1 is more than 8 times that of Example 1 (see Table 2). This indicates that, compared with the traditional fixed-bed intermittent operation, the continuous countercurrent SMB operation of the present invention significantly improves the separation efficiency and enrichment factor through the recycling of the mobile phase and continuous feed and discharge, while greatly reducing reagent consumption. These test results fully verify the significant technical effect of the synergistic effect between the crown ether functionalized stationary phase and the four-zone SMB continuous operation in step two of the present invention.

[0077] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A process for the continuous extraction of radium-226 from phosphogypsum, characterized in that, Includes the following steps: (1) Phosphogypsum is mixed with sodium carbonate solution to carry out thermochemical transformation reaction, so that radium in calcium sulfate lattice is converted into carbonate solid phase. After solid-liquid separation, carbonate solid phase is collected, washed and then acid leached and dissociated with inorganic acid. The endpoint pH is controlled to be 1.8~2.

5. After filtration, a feed liquid containing calcium and radium is obtained. (2) The feed liquid is continuously fed into a simulated moving bed chromatography separation system for continuous countercurrent chromatography separation. The stationary phase of the simulated moving bed chromatography separation system adopts a hybrid adsorption material with covalently anchored macrocyclic crown ethers on the surface of an inorganic silica microsphere matrix, and the mobile phase adopts a complexing eluent. Under the program drive of the stepping valve array, the simulated moving bed chromatography separation system forms four functional zones: Zone I is the regeneration elution zone, Zone II is the purification separation zone, Zone III is the main adsorption zone, and Zone IV is the buffer washing zone. The feed liquid is injected from Zone III, and the calcium stream for removing radioactivity is discharged from the residual liquid port, and the radium-enriched stream is discharged from the extract liquid port. (3) The enriched radium stream discharged from the extract outlet is introduced into the purification system, and a barium salt precipitant is added to carry out sulfate microcrystal coprecipitation. After the precipitate is collected and dissolved by reduction, the barium carrier is stripped by chromatographic peak cutting to obtain purified radium-226.

2. The process according to claim 1, characterized in that, The conditions for the thermochemical transformation reaction in step (1) are: solid-liquid mass ratio 1:3~1:5, sodium carbonate concentration 1.5~2.5M, reaction temperature 85~95℃, reaction time 2.5~3.5 hours; the inorganic acid is nitric acid or hydrochloric acid, and the pH of the acid leaching dissociation endpoint is 1.8~2.

5.

3. The process according to claim 1, characterized in that, The simulated moving bed chromatography separation system described in step (2) consists of 8 to 12 chromatographic columns connected in series. The system working pressure is maintained at a constant 0.30 to 0.45 MPa. The entire column group is equipped with a circulating water jacket temperature control system of 55℃±1℃. The column step switching time is 350±10 seconds.

4. The process according to claim 1, characterized in that, The macrocyclic crown ether is di-tert-butylcyclohexyl-18-crown-6, the inorganic silica microspheres are porous silica microspheres, and the mobile phase is a 0.05~0.15M EDTA-disodium salt solution or ammonium citrate solution with a pH of 4.5~5.

5.

5. The process according to claim 1, characterized in that, In the simulated moving bed chromatography separation system described in step (2), the ratio of feed flow rate to eluent flow rate is controlled at 1:3.8 to 1:5.

0.

6. The process according to claim 1, characterized in that, The barium salt mentioned in step (3) is barium chloride, and the control system contains... The final concentration is 8~15 mg / L. The sulfate microcrystal coprecipitation is carried out at 80℃, and the precipitant is 0.5M dilute sulfuric acid.

7. A simulated moving bed chromatography separation apparatus for implementing the process described in any one of claims 1-6, characterized in that, The simulated moving bed chromatography separation device is located inside a sealed, negative-pressure, lead-shielded heat chamber, and includes: A column group consisting of 8 to 12 radiation-resistant chromatographic columns connected in series, wherein the columns are packed with a hybrid adsorption material stationary phase of inorganic silica microsphere matrix with macrocyclic crown ethers covalently anchored on the surface; A time-programmed multi-channel hermetic valve switching array box is used to control the inlet and outlet flow direction of each chromatographic column to switch periodically according to a set step size, so as to realize the virtual countercurrent circulation of fluid in the column group; A high-pressure constant-flow plunger pump for feed liquid is connected to the feed inlet of the valve switching array box; A constant-pressure eluent storage tank is connected to the eluent inlet of the valve switching array box; The extract output pipeline is connected to the extract outlet of the valve switching array box and is used to discharge the radium-enriched stream. The residual liquid output pipeline is connected to the residual liquid port of the valve switching array box and is used to discharge the calcium stream that has been de-radioactively removed.

8. The simulated moving bed chromatography separation apparatus according to claim 7, characterized in that, Both the extract output line and the residual liquid output line are seamlessly connected in series with an online high-purity germanium gamma-ray spectrometer, which is used for real-time quantitative determination. The high-purity germanium gamma-ray detector also includes a characteristic gamma-ray peak of 186.2 keV; and a self-locking interlocking controller, which automatically triggers the valve switching array box to lock the pipeline shut-off when the high-purity germanium gamma-ray energy spectrum detector detects that the activity of the nuclide in the residual liquid output pipeline exceeds the set safety threshold.

9. The simulated moving bed chromatography separation apparatus according to claim 7, characterized in that, The exhaust system outlet of the sealed negative pressure lead shielded heat chamber is seamlessly connected to a low-temperature multi-stage activated carbon adsorption retention bed. The low-temperature multi-stage activated carbon adsorption retention bed operates at a temperature of -20℃ and is used to adsorb and retain gaseous radon-222 and cause it to decay within the carbon bed.

10. A system for the continuous extraction of radium-226 from phosphogypsum, characterized in that, Including those connected sequentially: Thermochemical transformation reactor, used to mix phosphogypsum with sodium carbonate solution for thermochemical transformation reaction; A solid-liquid separation device is connected to the outlet of the thermochemical transformation reactor; An acid leaching tank, connected to the solid phase outlet of the solid-liquid separation device, is used for acid leaching and dissociation of the transformed carbonate solid phase; A precision filtration device is connected to the outlet of the acid hydrolysis tank to filter the acid hydrolysate to obtain a clarified feed liquid; The simulated moving bed chromatography separation device according to claim 7 is connected to the liquid outlet of the precision filtration device and is used for continuous countercurrent chromatography separation of the feed liquid; A purification system is connected to the extract outlet of the simulated moving bed chromatography separation device. The purification system includes a microcrystalline coprecipitator, a reduction and dissolution device, and a chromatographic peak-cutting and purification device connected in sequence.

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