Eu (III) / An (III) separation method based on zirconium phosphonate-based metal organic framework adsorbent

Abstract

The invention relates to the technical field of radionuclide separation, in particular to an Eu (III) / An (III) separation method based on a zirconium phosphonate-based metal organic framework adsorbent, which comprises the following steps: adding the zirconium phosphonate-based metal organic framework adsorbent into an Eu (III) and / or An (III) nuclide-containing aqueous solution with the acid concentration of 0.001-3M to carry out adsorption reaction, and then carrying out solid-liquid separation, wherein the zirconium phosphonate-based metal organic framework adsorbent is a zirconium phosphonate-based metal organic framework material exchanged by metal cations M; the metal cation M is selected from one of alkali metal ions, alkaline earth metal ions or divalent transition metal ions. According to the invention, the interlayer chemical properties of the material are regulated and controlled through ion exchange, so that the adsorbent has ultrahigh selectivity, rapid adsorption kinetics, high adsorption capacity and excellent structural stability on trivalent actinide / simulated nuclides in extremely high-acid, high-salt and intense-radiation environments; the key problems of low separation efficiency and poor stability in a high-acid complex system in the prior art are solved, and the method is suitable for treating high-level liquid waste.

Description

Technical Field

[0001] This invention relates to the field of radionuclide separation technology, and in particular to a method for separating Eu(III) / An(III) based on zirconium phosphonate-based metal-organic framework adsorbents. Background Technology

[0002] The sustainable development of nuclear energy is an important way to address global energy demand growth and reduce greenhouse gas emissions. However, the use of nuclear energy inevitably generates a large amount of radioactive waste, especially high-level radioactive waste (HLW) from spent fuel reprocessing, which has become a key environmental and safety challenge restricting the development of nuclear energy. HLW has an extremely complex composition, high acidity (usually 1-3M or even higher nitric acid or sulfuric acid systems), high salt content, and contains a large number of long-lived, highly radiotoxic fission products and minor actinides. Among them, trivalent minor actinides, such as americium (Am(III)) and curium (Cm(III)) (collectively referred to as An(III)), are the main source of long-term environmental risks due to their million-year-level long half-lives and extremely high radiotoxicity. Achieving efficient and selective separation of An(III) is of vital importance for reducing the volume of radioactive waste, mitigating the long-term risks of geological repositories, and converting it into short-lived or stable nuclides through separation-transmutation technology.

[0003] Currently, the main method for separating An(III) from high-level radioactive waste is solvent extraction, such as the TALSPEAK, DIAMEX, and SANEX processes. Although these methods can achieve separation under specific conditions, they generally have the following inherent drawbacks: (1) They rely on large amounts of toxic and volatile organic solvents and extractants, posing a fire risk and potentially generating secondary organic waste; (2) Under extremely high acid and high salt conditions, extraction efficiency and selectivity are easily suppressed, and emulsification or the formation of a third phase can easily occur, affecting process stability; (3) The operation steps are cumbersome, the equipment is complex, and the operating costs are high; (4) The secondary waste generated is difficult to treat, which does not conform to the concept of green and sustainable nuclear waste management.

[0004] In contrast, separation techniques based on solid adsorbents, such as ion exchange or solid-state extraction, are considered a promising alternative due to their ease of operation, potential environmental friendliness, and low likelihood of generating secondary organic waste. An ideal adsorbent must simultaneously meet stringent requirements, including structural stability in highly acidic environments, high adsorption capacity and selectivity for the target An(III), rapid adsorption kinetics, and excellent radiation resistance.

[0005] In recent years, various adsorbent materials have been developed and used in the separation of radionuclides. For example, inorganic materials (such as titanates, layered metal sulfides, and silicon-based materials) have advantages such as low cost and good stability. Layered metal sulfides (such as KMS-1 and KMS-5) exhibit rapid kinetics and good selectivity for certain trivalent lanthanides / actinides, but they are susceptible to damage from high concentrations of H+ in strongly acidic environments with pH below 2. + Competition has significantly reduced adsorption performance and posed challenges to stability. While layered vanadate materials exhibit broad acid-base stability, their adsorption capacity and selectivity at extremely high acidity levels still need improvement. Traditional materials such as zeolites and activated carbon often lack sufficient selectivity and adsorption capacity in complex high-acid systems.

[0006] Metal-organic frameworks (MOFs) have shown great potential in adsorption and separation due to their highly tunable porous structure, abundant surface chemistry, and functionalizable sites. However, most MOFs, especially those based on carboxylic acid ligands, are prone to metal-ligand bond hydrolysis in aqueous solutions, particularly under acidic conditions. This leads to framework structural collapse and severely insufficient chemical stability, failing to meet the practical requirements for treating high-level radioactive waste. Although some Zr-based and Ti-based MOFs with better stability have been reported, their selective separation ability of An(III) in complex systems with high acidity, high salt content, and strong radiation, especially their rapid kinetics and resistance to ion interference, still requires significant improvement.

[0007] Chinese invention patent CN112657473B discloses a zirconium phosphonate MOF (SZ-7) for the reaction of Sr under alkaline conditions. 2+ The excellent adsorption performance demonstrates that the strong coordination bond formed between the phosphonic acid group and the tetravalent Zr metal center can endow the material with excellent chemical stability. However, the specific material SZ-7 and its application protected by this patent are specifically targeted at Sr in strongly alkaline environments (pH 12-14). 2+ The removal process differs fundamentally in its material design (fluorine-containing, specific interlayer cations) and application scenarios (strong bases) compared to the separation of trivalent An(III) in highly acidic environments. For highly acidic environments, particularly considering ionic radii, coordination properties, and Sr... 2+ Developing specialized adsorbents that combine ultra-high acid stability, ultra-high selectivity, and rapid kinetics for the significantly different trivalent An(III) / Eu(III) ions remains an unresolved technical challenge.

[0008] Therefore, developing a novel solid adsorbent and separation method that can adapt to strong acid environments from 0.001M to 3M, exhibits ultra-high selectivity for Eu(III) / An(III), rapid adsorption kinetics, excellent anti-interference ability, and radiation stability is of urgent practical need and important scientific value for promoting the development of advanced treatment technologies for high-level radioactive waste liquids and achieving safe, efficient, and green minimization of nuclear waste disposal. Summary of the Invention

[0009] The purpose of this invention is to provide a method for separating Eu(III) / An(III) based on zirconium phosphonate-based metal-organic framework adsorbents. This method overcomes the shortcomings of existing technologies, such as poor stability of adsorbent materials in high acid environments, low selectivity for trivalent An(III) / Eu(III), slow kinetics, and weak anti-interference ability.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a zirconium phosphonate-based metal-organic framework adsorbent, comprising the following steps: Step 1: Preparation of layered zirconium phosphonate MOF precursor; Using zirconium oxychloride as the zirconium source and methylene diphosphonic acid as the organic ligand, a layered zirconium phosphonate MOF precursor was obtained by reacting under solvothermal conditions. Step 2: Ion exchange modification; The layered zirconium phosphonate MOF precursor obtained in step 1 was mixed with a nitrate solution containing metal cation M at a solid-liquid mass ratio of 1:1-2:1 and reacted for 24 hours under stirring conditions at pH 4-5. After centrifugation, washing, and drying, the zirconium phosphonate-based metal-organic framework adsorbent M-ZrPC was obtained.

[0011] Furthermore, the metal cation M is selected from at least one of alkali metal (Na, K, Rb, Cs) ions, alkaline earth metal (Mg, Ca, Sr, Ba) ions, or divalent transition metal (Co, Ni, Cu, Zn) ions, with K being preferred. + or Ca 2+ .

[0012] Furthermore, the salt solution containing the metal cation M is a potassium nitrate solution or a calcium nitrate solution, with a concentration of 100-900 ppm and a pH value of 4-5.

[0013] Secondly, the present invention provides a method for separating Eu(III) / An(III) based on a zirconium phosphonate-based metal-organic framework adsorbent, comprising: Add 0.5-2 g / L of the above zirconium phosphonate-based metal-organic framework adsorbent to an aqueous solution containing the target nuclide with an acid concentration of 0.001-3 M, carry out the adsorption reaction at room temperature, and perform solid-liquid separation after 5-240 minutes. The adsorbent is a zirconium phosphonate-based metal-organic framework material exchanged with metal cation M, wherein M is selected from at least one of alkali metal ions, alkaline earth metal ions, or divalent transition metal ions.

[0014] Furthermore, the acid system containing the target nuclide aqueous solution is nitric acid or sulfuric acid; the target nuclide is Eu(III) and / or trivalent actinide An(III), where An(III) includes americium (Am) and curium (Cm).

[0015] Furthermore, the aqueous solution containing the target nuclide also contains Na. + Mg 2+ Even with competitive cations, and a molar ratio of competitive cations to target nuclides of up to 200,000:1, the adsorbent can still maintain highly efficient separation selectivity.

[0016] Thirdly, the present invention provides the application of the above-mentioned zirconium phosphonate-based metal-organic framework adsorbent in the separation and removal of Eu(III) and / or An(III) from acidic radioactive waste liquid.

[0017] Preferably, the acidic radioactive waste liquid is a high-level radioactive waste liquid (HLW) of nitric acid system or sulfuric acid system.

[0018] Preferably, the adsorbent maintains stable adsorption performance after being subjected to 100-200 kGy of β or γ radiation.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) By employing a strongly stable zirconium phosphonate framework and interlayer specific metal ions (K) + / Ca 2+ The synergistic design of the exchange process allows the adsorbent M-ZrPC to maintain its structural integrity in nitric acid or sulfuric acid environments ranging from 0.001M to 3M, and its affinity for the target nuclide is not diminished by high concentrations of H₂. + Strong inhibition. Experimental verification showed that the adsorbent Ca-ZrPC still adsorbed 64.2 mg / g of Eu(III) in 3.0 M concentrated nitric acid.

[0020] (2) After specific metal ion exchange, the material exhibits a unique pore matching and soft-hard synergistic adsorption mechanism for trivalent nuclides; experimental verification shows that the adsorbent K-ZrPC removes 97% of Eu(III) in the solution within 20 minutes; even with coexisting competing ions (Na+) + Mg 2+Even with a molar ratio of up to 200,000:1 between the adsorbent and the target nuclide, the removal rate of Eu(III) by the adsorbent Ca-ZrPC can still be maintained at 93% (Na). + (system) and 75% (Mg) 2+ (System) and above.

[0021] (3) The adsorbent M-ZrPC has passed the dual tests of high acidity and high irradiation, showing stable performance in a wide range of acidity. After being irradiated with a large dose of β / γ rays of 100-200kGy, the material structure is intact and the removal rate of Eu(III) remains above 96% without performance degradation. This allows the adsorbent M-ZrPC to be directly applied to the high-radiation waste liquid treatment system under strong radiation field.

[0022] (4) The entire separation process is an all-aqueous, room-temperature, solid-liquid operation, which eliminates the large amount of toxic and flammable organic solvents required by traditional solvent extraction methods, achieving a balance between efficient separation and green environmental protection, and conforming to the development trend of minimizing nuclear waste and being environmentally friendly. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the synthesis and structure of the adsorbent M-ZrPC of this invention.

[0024] Figure 2 These are the adsorption kinetic curves and adsorption isotherms of Eu(III) by the adsorbent M-ZrPC of this invention.

[0025] Figure 3 This is a graph showing the adsorption performance of the adsorbent M-ZrPC of this invention for Eu(III) in nitric acid solutions of different concentrations.

[0026] Figure 4 The adsorbent M-ZrPC of this invention is in Na + and Mg 2+ Removal rate of Eu(III) in the presence of interfering ions.

[0027] Figure 5 This is a graph showing the removal performance of the adsorbent M-ZrPC of this invention on Eu(III) after irradiation with different doses.

[0028] Figure 6 This is a comparison chart of the adsorption performance of the adsorbents M-ZrPC and SZ-4 of the present invention for Eu(III) in nitric acid solutions of different concentrations. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0030] Example 1 This embodiment provides a method for preparing adsorbents K-ZrPC and Ca-ZrPC, as well as the adsorbents K-ZrPC and Ca-ZrPC prepared by this method.

[0031] like Figure 1 As shown, its preparation method includes: (1) Preparation of precursor SZ-4: Zirconium oxychloride (ZrOCl2·8H2O) and methylene diphosphonic acid (H2O3P-CH3-PO3H2) were dissolved in deionized water at a certain molar ratio and placed in a stainless steel reactor lined with polytetrafluoroethylene. The reaction was carried out at a certain temperature for several days in a solvothermal manner. After the reaction was completed, the product was naturally cooled, centrifuged, washed with water and ethanol, and then dried under vacuum at 60℃ to obtain the layered zirconium phosphonate MOF precursor SZ-4.

[0032] (2) Preparation of M-ZrPC by ion exchange: 1.0 g of each of the SZ-4 precursors prepared above were placed in 200 mL of potassium nitrate (pH=4.5) and calcium nitrate (pH=4.5) solutions with a concentration of 500 ppm, respectively. Ion exchange was carried out by stirring continuously at room temperature for 24 hours. After the exchange was completed, the solid products were centrifuged, washed several times with deionized water to remove residual salts on the surface, and finally dried at 60 °C to obtain K. + Exchange of K-ZrPC and Ca 2+ Exchanged Ca-ZrPC adsorbent.

[0033] Example 2

[0034] This embodiment is a rapid Eu(III) adsorption kinetics test, which includes: Prepare a nitric acid solution with pH=1, containing an initial Eu(III) concentration of 10 ppm. Weigh 10 mg each of the adsorbents K-ZrPC and Ca-ZrPC prepared in Example 1 and add them to 10 mL of the nitric acid solution containing 10 ppm Eu(III), resulting in an adsorbent concentration of 1 g / L. The solution is incubated at room temperature with shaking, and samples are taken at different time points (5, 10, 20, 30, 60, 120, and 240 min). The samples are then filtered through a 0.2 μm filter membrane. The remaining Eu(III) concentration in the filtrate is determined using inductively coupled plasma mass spectrometry (ICP-MS), and the removal rate is calculated.

[0035] The results are as follows Figure 2 As shown in (a) and (c), the adsorbent K-ZrPC achieved a removal rate of 97% for Eu(III) after 20 minutes, while the adsorbent Ca-ZrPC achieved the same removal effect after 25 minutes, indicating that the adsorbent M-ZrPC has ultrafast adsorption kinetics.

[0036] Example 3

[0037] This example demonstrates an extremely high Eu(III) adsorption capacity test, which includes: Prepare a series of nitric acid solutions with pH=1 and different initial Eu(III) concentrations (0-700 ppm). Weigh 10 mg each of adsorbent K-ZrPC and Ca-ZrPC and add them to 10 mL of solutions of different concentrations (adsorbent concentration 1 g / L). Shake the reaction mixture at room temperature for 120 minutes to ensure adsorption equilibrium is reached. After the reaction, centrifuge and collect the supernatant to determine the Eu(III) equilibrium concentration. Calculate the adsorption capacity (q, mg / g) based on the concentration difference before and after adsorption, and plot the adsorption isotherm.

[0038] The results are as follows Figure 2 As shown in (b) and (d): by fitting the Langmuir model, the maximum saturated adsorption capacities of adsorbents K-ZrPC and Ca-ZrPC for Eu(III) are 144.0 mg / g and 167.8 mg / g, respectively, indicating that the materials have extremely high adsorption capacity.

[0039] Example 4

[0040] This embodiment describes the Eu(III) adsorption performance test under high acid conditions, which includes: A series of solutions with different nitric acid concentrations (0.1, 0.5, 1.0, 1.5, 2.0, 3.0 M) were prepared, with the initial Eu(III) concentration fixed at 400 ppm, and the pH value determined by the nitric acid concentration. 10 mg each of adsorbent K-ZrPC and Ca-ZrPC were weighed and added to 10 mL of each of the above solutions with different acidities. After shaking at room temperature for 120 minutes, the Eu(III) concentration in the supernatant was measured by centrifugation, and the adsorption capacity was calculated.

[0041] The results are as follows Figure 3 As shown, although the adsorption capacity of K-ZrPC and Ca-ZrPC decreased with increasing nitric acid concentration from 0.1M to 3.0M, it remained at a relatively high level. Particularly in 3.0M concentrated nitric acid, the adsorption capacity of Ca-ZrPC for Eu(III) reached 64.2 mg / g, while the adsorption capacity of K-ZrPC in 1.5M nitric acid was 66.3 mg / g, and Ca-ZrPC reached as high as 131.7 mg / g in 1.5M nitric acid. This indicates that the adsorbents in this embodiment can still effectively adsorb Eu(III) under extremely high acid conditions.

[0042] Example 5

[0043] This embodiment describes a selective adsorption test in the presence of competing cations, which includes: Prepare a nitric acid background solution with pH=1, where the Eu(III) concentration is fixed at 10 ppm. Add either NaNO3 or Mg(NO3)2 to the solution to adjust the Na... + or Mg 2+ The molar ratios of the adsorbents to Eu(III) were 200:1, 1000:1, 1500:1, 2000:1, 20000:1, 100000:1, and 200000:1, respectively. 10 mg each of K-ZrPC and Ca-ZrPC were weighed and added to 10 mL of solutions containing different interfering ions. After shaking at room temperature for 120 minutes, samples were taken, filtered, and the Eu(III) concentration was determined. The removal rate was calculated.

[0044] The results are as follows Figure 4 As shown: In Na + or Mg 2+ When the excess was 1000 times, the removal rate of Eu(III) by both adsorbents was greater than 95%. Even with a 200,000-fold excess of competing ions (molar ratio 200,000:1), adsorbent K-ZrPC showed better removal of Eu(III) in Na+. + or Mg 2+ The removal rates of Eu(III) in the system remained above 63% and 70%, respectively; the adsorbent Ca-ZrPC performed even better, in the Na... + The removal rate in the system remained above 93%, in Mg 2+ The concentration in the system is also above 75%. This demonstrates that the adsorbent in this embodiment still exhibits remarkable selectivity and anti-interference ability in complex waste liquids with extremely high salinity and a large number of competing ions.

[0045] Example 6

[0046] This embodiment is an irradiation stability test, which includes: The adsorbent samples K-ZrPC and Ca-ZrPC prepared in Example 1 were placed in a radiation field and irradiated with Co-60 γ-rays at doses of 100 kGy and 200 kGy, respectively. After irradiation, 10 mg of the irradiated adsorbent was added to 10 mL of nitric acid solution with pH=1 and an Eu(III) concentration of 10 ppm. After shaking at room temperature for 120 minutes, the Eu(III) removal rate was measured.

[0047] The results are as follows Figure 5 As shown, after high-dose γ-irradiation of 100 kGy and 200 kGy, the removal rate of Eu(III) by adsorbent K-ZrPC remained at approximately 97%, and the removal rate by adsorbent Ca-ZrPC also remained above 96%, showing no significant difference compared to the unirradiated sample. This indicates that the adsorbents in this embodiment possess excellent irradiation stability and are fully suitable for the treatment of highly radioactive waste liquids.

[0048] Comparative Example 1: In this embodiment, the precursors SZ-4, K-ZrPC, and Ca-ZrPC were used as adsorbents to compare the material properties.

[0049] A series of solutions with different nitric acid concentrations (0.1, 0.5, 1.0, 1.5, 2.0 M) were prepared, with the initial Eu(III) concentration fixed at 400 ppm, and the pH value determined by the nitric acid concentration. 10 mg each of adsorbents SZ-4, K-ZrPC, and Ca-ZrPC were weighed and added to 10 mL of each of the above solutions with different acidities. After shaking at room temperature for 120 minutes, the supernatant was centrifuged and the adsorption capacity of the three materials for Eu(III) at different nitric acid concentrations was tested and compared. Figure 6 As shown, the adsorption capacity of all three materials decreased as the nitric acid concentration increased from 0.1 M to 2.0 M. This is due to the high concentration of H+. + Competitive adsorption sites are a common phenomenon. In 1.5M nitric acid, the adsorption capacity of Ca-ZrPC (132 mg / g) remained at a high level, while the adsorption capacity of SZ-4 decreased to below 35 mg / g. The capacity of Ca-ZrPC was approximately three times that of SZ-4, indicating that Ca-ZrPC has significantly stronger tolerance to highly acidic environments. 2+ Interlayer chemical modification by ion exchange is not a simple physical mixing or surface modification, but rather enhances the inherent affinity of the material framework for trivalent Eu(III) and its resistance to protonation, resulting in unexpected technical effects.

[0050] The above examples demonstrate that the adsorbent M-ZrPC exhibits rapid kinetics, good selectivity, and efficient decontamination capability for Eu(III) / An(III) ions under high acid conditions. It can be used for Eu(III) / An(III) ion decontamination in real aquatic environments or high acid aqueous solutions, and is suitable for high-level radioactive waste liquid treatment scenarios.

[0051] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for Eu(III) / An(III) separation based on zirconium phosphonate metal-organic framework adsorbent, characterized in that, The application relates to a method for separating Eu(III) and / or An(III) from an acidic radioactive waste liquid. The method comprises the following steps: adding 0.5-2 g / L of a zirconium phosphonate metal organic framework adsorbent into an Eu(III) and / or An(III) containing aqueous solution with an acid concentration of 0.001-3 M to carry out an adsorption reaction, and then carrying out solid-liquid separation. The application realizes a method for separating Eu(III) / An(III). The zirconium phosphonate metal organic framework adsorbent is a zirconium phosphonate metal organic framework material exchanged by metal cations M; the metal cations M are selected from at least one of alkali metal ions, alkaline earth metal ions or divalent transition metal ions.

2. The method for Eu(III) / An(III) separation based on zirconium phosphonate metal-organic framework adsorbent according to claim 1, characterized in that, The trivalent minor actinide An(III) includes americium (Am) and curium (Cm).

3. The method for Eu(III) / An(III) separation based on zirconium phosphonate metal-organic framework adsorbent according to claim 1, characterized in that, The metal cation M is K + or Ca 2+ .

4. The method for Eu(III) / An(III) separation based on zirconium phosphonate metal-organic framework adsorbent according to claim 3, characterized in that, The preparation of the zirconium phosphonate metal organic framework adsorbent comprises the following steps: Step 1: preparing a layered zirconium phosphonate MOF precursor; The layered zirconium phosphonate MOF precursor is obtained by using zirconium oxychloride as a zirconium source and methylene diphosphonic acid as an organic ligand under a solvothermal condition; Step 2: ion exchange modification; The layered zirconium phosphonate MOF precursor obtained in step 1 is mixed with a nitrate solution containing metal cations M at a solid-liquid mass ratio of 1:1-2:1, and is reacted under stirring at pH 4-5 for 24 hours, and then is centrifuged, washed and dried to obtain the zirconium phosphonate metal organic framework adsorbent M-ZrPC.

5. The method for Eu(III) / An(III) separation based on zirconium phosphonate metal-organic framework adsorbent according to claim 4, characterized in that, The nitrate solution is a potassium nitrate solution or a calcium nitrate solution; the concentration is 200-900 ppm.

6. The method for Eu(III) / An(III) separation based on zirconium phosphonate metal-organic framework adsorbent according to claim 5, characterized in that, The application of the zirconium phosphonate metal organic framework adsorbent to the separation and removal of Eu(III) and / or An(III) from an acidic radioactive waste liquid.

7. The method for Eu(III) / An(III) separation based on zirconium phosphonate metal-organic framework adsorbent according to claim 6, characterized in that, The acidic radioactive waste liquid is a high-level waste liquid of a nitric acid system or a sulfuric acid system.

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