Oxalic acid ferrous ammonium phosphate, preparation method thereof and application of oxalic acid ferrous ammonium phosphate in enrichment of strontium in strontium-containing wastewater

Abstract

The invention provides oxalic acid ammonium ferrous phosphate and a preparation method and application thereof in enrichment of strontium in strontium-containing wastewater, the oxalic acid ammonium ferrous phosphate is mixed according to the molar ratio of (1-1.5): (1-2): (6-12): (3-6), a hydrothermal reaction is performed at 150-180 DEG C for 60-100 hours, and a single-phase crystal is prepared. The material has a three-dimensional tunnel structure, template cations can be rapidly migrated, and oxalate provides high-density adsorption sites. Experiments show that the NFPO has adsorption equilibrium within 60 minutes, and the removal rate is gt; 90%; when coexisting, the capacity reaches 281 mg / g, the pH value is 2-11, the stability is realized at 300 DEG C, and the removal rate gt is obtained after 5 times of circulation; 85%. The defect of an amorphous structure of a traditional adsorbent is overcome, and an efficient scheme is provided for deep purification of low-concentration radioactive strontium.

Description

Technical Field

[0001] This invention relates to the field of radioactive wastewater treatment technology, specifically to a ferrous ammonium oxalate phosphate, its preparation method, and its application in the enrichment of strontium in strontium-containing wastewater. Background Technology

[0002] Since the mid-20th century, nuclear energy has been widely used globally as an important form of energy. Nuclear energy has a high energy density, capable of generating large amounts of electricity in a relatively small volume. However, accidental leakage of radioactive nuclides has always been a key factor restricting the development of nuclear energy, as even trace amounts of radioactive nuclides can cause significant harm to the environment and human health. 90Sr (with a half-life of approximately 28.8 years) is one of the most environmentally harmful radioactive nuclides, exhibiting high biological activity and bioaccumulation. 90Sr has osteophagocytic properties similar to Ca(II), and once it enters the human body through the food chain, it deposits in bones and continuously releases high-energy beta rays, causing irreversible radiation damage to surrounding tissues. Long-term exposure to 90Sr radiation may lead to serious diseases such as bone cancer and cardiovascular disease, posing a significant threat to human health. The hazards of radioactive strontium have received widespread attention internationally. For example, after the Fukushima nuclear accident in Japan, research on the environmental behavior and biological effects of radioactive strontium became a hot topic. Scientists point out that the migration and transformation processes of radioactive strontium in the marine environment are complex, and its impact on marine life cannot be ignored. In addition, organizations such as the International Atomic Energy Agency (IAEA) have emphasized the importance of effective regulation of radioactive strontium to prevent its long-term effects on public health and the environment.

[0003] In the field of radioactive wastewater treatment, given the relationship between 90Sr and its stable state... They exhibit highly similar physicochemical behaviors, and current research generally uses... The purification process was simulated. Compared to techniques such as chemical precipitation, membrane separation, and solvent extraction, adsorption is considered the preferred method for the deep purification of low-concentration radioactive strontium due to its advantages of simple operation, strong environmental compatibility, and adjustable selectivity. Currently, various adsorbent materials have been reported for purification. These include zeolites, metal oxides, titanates, layered double hydroxides, metal phosphates, and layered metal sulfides. Among them, metal phosphates have become popular due to their readily available raw materials, simple synthesis routes, high specific surface area, and strong surface chemical modifiability. A research hotspot for efficient capture. Hydroxyapatite and zirconium phosphate have long been used in aqueous phases. Classic metal phosphate adsorbents are used for adsorption. However, these materials often have significant limitations due to their predominantly amorphous structure: (1) solid-liquid separation of nanoparticles is difficult; (2) the actual adsorption capacity is significantly lower than the theoretical value and the kinetics are slow; (3) the disordered structure hinders the analysis of the adsorption structure-activity relationship. Therefore, the development of novel metal phosphate materials with well-defined crystal structures, rapid mass transfer kinetics, and high stability is the current research focus.

[0004] Metal oxalate phosphate open frameworks (MOPOFs) are a class of organic-inorganic hybrid crystalline materials constructed from oxalate-crosslinked transition metal phosphates. Their multidimensional structure can encapsulate various template cations (such as...). As a bidentate ligand for dicarboxylic acids, the introduction of oxalate significantly enhances the stability of the material framework, lowers the synthesis energy barrier through the spatial regulation of organic ligands, and provides a two-dimensional diffusion channel for interlayer cation migration. Furthermore, oxalate provides four oxygen coordination sites, effectively increasing the adsorption site density and thus improving the material's adsorption capacity. Therefore, the introduction of oxalate can solve the aforementioned defects of metal phosphates. Among them, ferrous oxalate phosphate has a stable three-dimensional tunnel structure, providing an effective transfer channel for the template cations within it, and has the potential to be used as an adsorbent. However, in the currently existing ferrous oxalate phosphate sodium, sodium ions are tightly bound to the oxygen-containing sites in the tunnel, resulting in poor adsorption capacity and kinetics when used as a strontium adsorbent. Considering the inclusion of sodium ferrous oxalate phosphate... The aim is to replace ionic bonds with hydrogen bonds to weaken the binding ability of template ions to oxygen-containing sites, thereby designing a highly efficient strontium removal adsorbent that primarily relies on ion exchange. Although ferrous oxalate phosphate sodium salt already exists, its product is not single-phase, and its three-dimensional structure changes when the template ion is changed to NH4+. Therefore, designing a novel ferrous oxalate phosphate with a single-phase product remains a challenge.

[0005] Nuclear energy, as a high-energy-density clean energy source, carries the risk of radioactive nuclide leakage. Among these, 90Sr, due to its long half-life (28.8 years), high bioaccumulation, and bone affinity, poses a serious threat to the ecological environment and human health. 90Sr accumulates in bones through the food chain, continuously releasing beta rays that cause irreversible damage such as bone cancer and cardiovascular disease. Its remediation has become a research hotspot in the international nuclear safety field. Currently, the purification of low-concentration radioactive strontium relies on adsorption methods. Metal phosphates are preferred adsorbent materials due to their readily available raw materials and strong surface modifiability. However, their amorphous structure generally suffers from difficulties in solid-liquid separation, low adsorption capacity (actual values ​​are far lower than theoretical values), and slow kinetics, which restricts their practical application.

[0006] Metal oxalate phosphate open frameworks (MOPOFs) form organic-inorganic hybrid crystal structures by crosslinking transition metal phosphates with oxalate, exhibiting both high stability and controllable pore size. Oxalate, as a bidentate ligand, provides four oxygen coordination sites to increase adsorption site density and constructs two-dimensional diffusion channels through spatial regulation, significantly improving mass transfer efficiency. Among these, ferri-based oxalate phosphates show strontium adsorption potential due to their three-dimensional tunnel structure, but their existing sodium salt forms (such as sodium ferri-based oxalate phosphate) contain template ions (…). Due to defects such as excessive binding to oxygen-containing sites in the framework, product heterogeneity, and slow adsorption kinetics, it is difficult to meet the requirements for efficient strontium removal.

[0007] Therefore, developing novel ferri-based oxalate phosphate materials with a well-defined single-phase crystal structure, rapid ion diffusion channels, and high selectivity has become the key to breaking through existing technological bottlenecks and achieving deep purification of low-concentration radioactive strontium. Summary of the Invention

[0008] This invention provides a method for preparing ferrous ammonium oxalate phosphate and its application in strontium enrichment in strontium-containing wastewater. By optimizing the template cation and synthesis process, single-phase ferrous ammonium oxalate phosphate (NFPO) crystals are prepared, aiming to solve the structural defects and adsorption performance limitations of traditional materials and provide an efficient solution for the treatment of strontium-containing wastewater.

[0009] A method for preparing ferrous ammonium oxalate phosphate includes the following steps:

[0010] Will Mix the ingredients in a molar ratio of 1-1.5:1-2:6-12:3-6, add to a solvent containing 65% water, stir until homogeneous, adjust the pH, transfer to an autoclave, and react at 150-180℃ for 60-100 hours. After washing and drying, the product yields ferrous ammonium oxalate phosphate crystals. .

[0011] Furthermore, the aforementioned and The molar ratio is 1:1.5:8:4.

[0012] Furthermore, the washing step includes washing three times with deionized water, washing three times with methanol, and achieving solid-liquid separation by high-speed centrifugation.

[0013] Furthermore, the drying step involves drying in a vacuum drying oven for 12 hours, followed by grinding and sieving.

[0014] A ferrous ammonium oxalate phosphate crystal, prepared by the above method, has the chemical formula... It has a single-phase crystal structure.

[0015] Furthermore, the crystal has a three-dimensional tunnel structure, with encapsulation within the tunnel. Template cations, and the interlayer provides two-dimensional diffusion channels through oxalate.

[0016] An application of the ferrous ammonium oxalate phosphate crystals described above in the treatment of strontium-containing wastewater, wherein the application is to remove strontium from the wastewater by adsorption. .

[0017] Furthermore, the pH range of the adsorption process is 2-11.

[0018] The present invention has the following beneficial effects:

[0019] 1. Controllable synthesis of single-phase crystal structures: through optimization By using a molar ratio of 1-1.5:1-2:6-12:3-6 and a hydrothermal reaction at 150-180℃ for 60-100 hours, single-phase ferrous ammonium oxalate phosphate (NFPO) crystals were successfully prepared for the first time, solving the problems of difficult solid-liquid separation and low adsorption capacity caused by the amorphous structure of traditional metal phosphates.

[0020] 2. Highly efficient adsorption performance: The weak hydrogen bonding between the three-dimensional tunnel structure and the NH4⁺ template cation, combined with the two-dimensional diffusion channels provided by the oxalate ion, achieves... Rapid mass transfer (adsorption equilibrium reached in 60 minutes, removal rate >90%), Langmuir adsorption capacity reaches 281 mg / g ( (When coexisting), it represents a relatively high level among existing materials.

[0021] 3. Synergistic adsorption and anti-interference properties: In The adsorption capacity was significantly increased in the presence of (50 mg / L), and in When multiple ions coexist, The removal rate is still >92.8%, breaking through the bottleneck of high-salinity wastewater interference.

[0022] 4. Stability under extreme conditions: The structure is stable within the pH range of 2-11. Thermal decomposition only occurs above 300℃. After 5 cycles, the removal rate is >85%, making it suitable for complex radioactive wastewater environments. Attached Figure Description

[0023] Figure 1 (a) shows the NFPO adsorption kinetics curve; (b) shows the curve fitted by the intraparticle diffusion model; and (c) shows the isotherm fitting results.

[0024] Figure 2 For NFPO at different concentrations Under the condition of existence Adsorption capacity;

[0025] Figure 3 In (a) and (b), NFPO pairs with a single interfering ion and multiple cations, respectively. The distribution coefficient and removal efficiency;

[0026] Figure 4 In (a) and (b), NFPO is shown in the presence of no interfering ions and Adsorption under coexistence conditions The desorption efficiency and removal efficiency after desorption;

[0027] Figure 5 (a) shows the ORTEP plot of the asymmetric unit corresponding to NFPO (thermal ellipsoid probability is 50%); (b) shows the comparison between the simulated PXRD of the analytical structure of NFPO and the experimentally obtained PXRD spectrum.

[0028] Figure 6 (a) and (b) are XRD patterns of NFPO under different pH and different adsorbate conditions, respectively; (c) is the adsorption of NFPO. Comparison of thermogravimetric curves before and after treatment; (d) shows the results after treatment with aqueous solutions of different pH values ​​and adsorption. FTIR spectrum after NFPO;

[0029] Figure 7 NFPO adsorption XPS spectra before and after, where (a) is the total spectrum; (bf) are the high-resolution spectra of Fe 2p, O 1s, N 1s, Sr 3d, and Ca 2p. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1: A method for preparing ferrous ammonium oxalate phosphate, comprising the following steps:

[0032] Will The mixture was prepared by mixing (molar ratio) 150 mmol of FeCl2 and adding all reagents to a beaker containing water (65% liquid). The mixture was stirred thoroughly, and the pH was measured. The mixture was then magnetically stirred in a 50°C water bath for 20 min, followed by transfer to a 500 mL PTFE-lined autoclave. The mixture was then heated to 165°C and maintained for 96 hours. The pH of the reaction product was measured, and the product was washed three times with deionized water and three times with methanol (solid-liquid separation was achieved using a high-speed centrifuge). Finally, the product was dried in a vacuum drying oven for 12 hours. The resulting powder was ground and sieved to obtain NFPO with a yield of 68%.

[0033] Example 2: A method for preparing ferrous ammonium oxalate phosphate, comprising the following steps:

[0034] Will The mixture was prepared by mixing (molar ratio) 150 mmol of FeCl2 and adding all reagents to a beaker containing water (65% liquid). The mixture was stirred thoroughly, and the pH was measured. The mixture was then magnetically stirred in a 50°C water bath for 20 min, followed by transfer to a 500 mL PTFE-lined autoclave. The mixture was then heated to 150°C and maintained for 100 hours. The pH of the reaction product was measured, and the product was washed three times with deionized water and three times with methanol (solid-liquid separation was achieved using a high-speed centrifuge). Finally, the product was dried in a vacuum drying oven for 12 hours. The resulting powder was ground and sieved to obtain NFPO, with a yield of 59%.

[0035] Example 3: A method for preparing ferrous ammonium oxalate phosphate, comprising the following steps:

[0036] Will The mixture was prepared by mixing (molar ratio) 150 mmol of FeCl2 and adding all reagents to a beaker containing water (65% liquid). The mixture was stirred thoroughly, and the pH was measured. The mixture was then magnetically stirred in a 50°C water bath for 20 min, followed by transfer to a 500 mL PTFE-lined autoclave. The mixture was then heated to 180°C and maintained for 70 hours. The pH of the reaction product was measured, and the product was washed three times with deionized water and three times with methanol (solid-liquid separation was achieved using a high-speed centrifuge). Finally, the product was dried in a vacuum drying oven for 12 hours. The resulting powder was ground and sieved to obtain NFPO with a yield of 63%.

[0037] This study conducted multiple experiments and finally determined...

[0038] The optimal formulation was chosen primarily because it exhibited favorable reaction and product characteristics during the experiment. The key reasons are as follows:

[0039] (1) Reaction stability. During the preparation experiment, the formulation showed high solubility and system stability during the reaction, and no large amount of undissolved precipitate appeared.

[0040] (2) Product characteristics. Experimental results show that the product obtained using this formulation has good crystal morphology and color characteristics. The obtained crystals have regular shapes and good uniformity. (3) Optimization of experimental conditions. In the experiment, the reaction conditions were further optimized by adjusting parameters such as solvent conditions (e.g., solvent with a water content of 65%) and reaction time (e.g., 96 hours), which improved the quality and performance of the product. (4) Balance of proportions. The molar ratio of various raw materials in this formulation is relatively balanced, which can ensure the full reaction of each substance during the reaction process, thereby obtaining a high-quality product.

[0041] The formulation scheme showed good performance in terms of reaction stability, product characteristics, experimental condition optimization, and formulation balance. Therefore, the NFPO obtained by this formulation scheme was selected as the standard material for subsequent experimental research.

[0042] The performance tests of the products in the embodiments of the present invention are described below:

[0043] (1) Adsorption kinetics and isotherm studies

[0044] Adsorption kinetics studies showed that NFPO exhibits a high adsorption rate, reaching adsorption equilibrium within 60 minutes, while achieving a removal rate exceeding 90%. Figure 1 a) The adsorption data showed a higher fit to the pseudo-second-order kinetic model (PSO), indicating that the adsorption process was dominated by chemisorption. The fitting results of the intraparticle diffusion model showed that the adsorption process could be divided into three stages: a rapid adsorption stage (dominated by membrane diffusion or boundary layer diffusion), a gradual diffusion stage (dominated by intraparticle diffusion), and a final equilibrium stage. Isotherm results showed... (50 mg / L) in the presence of the adsorbent It exhibits higher adsorption capacity. Furthermore, the adsorption curves all conform to the Langmuir model, indicating that it is a uniform monolayer adsorption.

[0045] (2) Synergistic adsorption research

[0046] Figure 2 The results showed that, with the solution With increasing ion concentration, NFPO has an effect on The adsorption capacity showed a trend of first increasing and then decreasing. When At an ion concentration of 50 mg / L, the adsorption capacity of NFPO reaches a maximum of 281 mg / g. This is currently the only known adsorption capacity for NFPO in the presence of cations. Adsorbents that promote ion adsorption.

[0047] (3) Research on anti-interference performance

[0048] First, the study was conducted on single ions ( When NFPO exists The adsorption performance (initial concentration 5 mg / L) was studied. The results showed that... At a concentration of 250 mg / L, The distribution coefficient and removal rate reached their highest values, at 21538.46 mL / g and 89.62%, respectively. At a concentration of 200 times... In its presence, the adsorption process is most disturbed, but for The removal rate is still above 50%. In multi-ion ( Under coexisting conditions (initial concentration of 5 mg / L), NFPO has the effect of The removal rate was higher than 92.8%, followed by... (67.40%), demonstrating excellent performance. Selective adsorption properties.

[0049] (4) Regeneration performance study

[0050] Figure 4 This indicates that NFPO possesses excellent regeneration performance. After five cycles of adsorption-desorption experiments, under deionized water background and at 50 mg / L... Background The removal rates were higher than 70% and 85%, respectively.

[0051] 2. Characterization Analysis

[0052] The synthesized NFPO was subjected to single-crystal XRD (SC-XRD) testing, and its structure was analyzed, yielding the ORTEP diagram of its asymmetric units. Figure 5 (a) verified the structural formula of NFPO: (NH4)2Fe3(C2O4)2(HPO4)2. Comparison of the simulated PXRD pattern with the experimental PXRD pattern showed a high degree of overlap of the Bragg sites, indicating that the synthesized NFPO is a single crystal.

[0053] XRD analysis was performed on the synthesized materials in the above three embodiments. Figure 6Figure a) shows that the three materials have the same diffraction peak sites and high peak intensity similarity, therefore, the synthesis of NFPO can be considered successful. Since the structures of the three examples are consistent, the NFPO with the molar ratio of 1:1.5:8:4 (which has the highest yield) was selected for adsorption batch experiments and subsequent characterization analysis. After treatment with solutions at different pH values, the XRD patterns of NFPO did not change significantly, indicating its excellent stability in the pH range of 2-11. Figure 6 (b) Meanwhile, adsorption under different solute types and concentrations... Subsequently, the peaks in the XRD pattern showed only minor changes, indicating that its main structure remained unchanged. Figure 6 c). Thermogravimetric results show that ( Figure 6 (d) NFPO only experiences a significant weight reduction at temperatures above 300℃, providing preliminary verification of its thermal stability. FTIR ( Figure 6 (e) The stability of NFPO was further verified by displaying functional groups. The changes in the peaks indicate that the adsorption is mainly related to PO, Fe-O and hydroxyl groups.

[0054] See XPS full spectrum and detailed plot. Figure 7 The score shows the specific types of elements, combined with... Figure 7 e, verifying the successful preparation of the adsorbent and The successful adsorption of Fe2p indicates that Fe is in the +2 valence state, further verifying the accuracy of the single-crystal analytical structure. The increase in the binding energy of different oxygen-containing bonds in O1s indicates that this bond successfully adsorbed Fe2p. Bonding occurs. The presence and increased content of MO bonds further confirm this. Successful adsorption and The synergistic promoting effect of adsorption. The decrease in the intensity of the N 1s peak after adsorption indicates a reduction in ammonium ions in the adsorbent, suggesting its synergistic effect with... Ion exchange occurs. Figure 7 f indicates It also binds to NFPO, which is of great significance for explaining its synergistic adsorption.

[0055] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing ferrous ammonium oxalate phosphate, characterized in that, Includes the following steps: Will Mix the ingredients in a molar ratio of 1-1.5:1-2:6-12:3-6, add to a solvent containing 65% water, stir until homogeneous, adjust the pH, transfer to an autoclave, and react at 150-180℃ for 60-100 hours. After washing and drying, the product yields ferrous ammonium oxalate phosphate crystals. .

2. The method as described in claim 1, characterized in that, The and The molar ratio is 1:1.5:8:

4.

3. The method as described in claim 1, characterized in that, The washing steps include washing three times with deionized water, washing three times with methanol, and achieving solid-liquid separation by high-speed centrifugation.

4. The method as described in claim 1, characterized in that, The drying step involves drying in a vacuum drying oven for 12 hours, followed by grinding and sieving.

5. A ferrous ammonium oxalate phosphate crystal, characterized in that, Prepared by the method according to any one of claims 1-4, having the chemical formula It has a single-phase crystal structure.

6. The ferrous ammonium oxalate phosphate crystal as described in claim 5, characterized in that, The crystal has a three-dimensional tunnel structure, with encapsulation within the tunnel. Template cations, and the interlayer provides two-dimensional diffusion channels through oxalate.

7. The application of the ferrous ammonium oxalate phosphate crystals according to claim 5 or 6 in the treatment of strontium-containing wastewater, characterized in that, The application is to remove wastewater by adsorption. .

8. The application as described in claim 7, characterized in that, The pH range for the adsorption process is 2-11.

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