Fluoroaluminophosphate ammonium magnesium salt, preparation method, application and wastewater treatment method

Abstract

The application discloses fluorinated aluminum magnesium ammonium phosphate salt, a preparation method and application thereof and a wastewater treatment method, and relates to the technical field of phosphoaluminate. The chemical formula of the fluorinated aluminum magnesium ammonium phosphate salt is (NH4)2MgAlP2O5F2(OH)5, and the fluorinated aluminum magnesium ammonium phosphate salt belongs to a triclinic system and has a P-1 space group. The structure of the fluorinated aluminum magnesium ammonium phosphate salt is formed by co-apex connection of PO4 tetrahedrons, AlO4F2 octahedrons and MgO4F2 octahedrons to form an anion layer. The anion layer is filled with ammonium ions. The material is prepared by a low-temperature hydrothermal method. The material can effectively remove strontium ions in radioactive wastewater as an ion exchange material. The structure of the material is stable in a pH range of 2 to 12. The adsorption equilibrium time is only 1 minute to 3 minutes. The maximum adsorption capacity is 260.77 mg / g. The material can be used as a high-efficiency and stable radioactive wastewater treatment material.

Description

Technical Field

[0001] This invention relates to the field of phosphoaluminate technology, and particularly to magnesium aluminum fluoride phosphate, its preparation method, application and wastewater treatment method. Background Technology

[0002] The application of nuclear energy technology has generated a large amount of radioactive waste liquid, which contains highly toxic radioactive nuclides with long half-lives, such as strontium ions.

[0003] Currently used materials for treatment include organic resins and inorganic molecular sieves. Organic resins are prone to chemical degradation under strong radiation or high temperature environments, leading to structural collapse and shortened service life. Traditional zeolite molecular sieves, while possessing some radiation resistance, have small micropore sizes and are susceptible to skeletal aluminum dissolution under strongly acidic conditions, resulting in structural damage. Some layered metal sulfides, although capable of adsorbing specific nuclides, have complex synthesis processes and high costs, limiting their large-scale applications. Furthermore, existing materials exhibit poor adsorption kinetics, with the time required to reach adsorption equilibrium typically being long, making it difficult to meet the rapid response requirements for nuclear accident emergency treatment.

[0004] Therefore, how to provide a novel ion exchange material with simple preparation process, strong chemical stability and fast adsorption rate has become an urgent technical problem to be solved. Summary of the Invention

[0005] The main objective of this invention is to provide magnesium aluminum fluoride ammonium salt, its preparation method, its application, and its wastewater treatment method, aiming to provide a novel ion exchange material with a simple preparation process, strong chemical stability, and fast adsorption rate.

[0006] To achieve the above objectives, this invention proposes a magnesium aluminum phosphate (MgA) fluoride salt with the chemical formula (NH4)2MgAlP2O5F2(OH)5, belonging to the triclinic crystal system with space group P-1. Its basic structural units include isolated PO4 tetrahedra, AlO4F2 octahedra, and MgO4F2 octahedra. The PO4 tetrahedra are connected to the AlO4F2 octahedra and MgO4F2 octahedra via shared vertices, forming anion layers. The spaces between the anion layers are filled with interlayer cations NH4+. + And form a layered structure.

[0007] Preferably, the unit cell parameters of the aluminum magnesium ammonium fluorophosphate are: a = 5.0011(2) Å, b = 7.0837(4) Å, c = 7.9338(3) Å; α = 91.954(4)°, β = 94.099(3)°, γ = 110.609(4)°; unit cell volume V = 261.88(2) ų, and number of molecules in unit cell Z = 2.

[0008] Preferably, in the layered structure, each PO4 tetrahedron is connected to a first AlO4F2 octahedron, a second AlO4F2 octahedron, and a first MgO4F2 octahedron; each AlO4F2 octahedron is connected to four PO4 tetrahedrons, a second MgO4F2 octahedron, and a third MgO4F2 octahedron; and each MgO4F2 octahedron is connected to two PO4 tetrahedrons, a third AlO4F2 octahedron, and a fourth AlO4F2 octahedron.

[0009] Preferably, the magnesium aluminum fluoride phosphate is a colorless, transparent, elongated, sheet-like crystal with a size of approximately 2 mm.

[0010] The present invention also provides an application of magnesium aluminum fluoride phosphate as described above as an ion exchange material in the adsorption of radionuclides.

[0011] Preferably, the radionuclide includes Sr². + .

[0012] Preferably, the magnesium aluminum fluoride phosphate maintains structural stability in a solution environment with a pH of 2 to 12, and has good resistance to the Sr²⁺ ions. + The adsorption equilibrium time is 1 min to 3 min, and its adsorption of the strontium ion Sr² is... + The maximum adsorption capacity is 260.77 mg / g.

[0013] The present invention also provides a method for treating radioactive wastewater, wherein the method utilizes aluminum magnesium ammonium fluorophosphate as described in any of the preceding claims to contact wastewater containing radionuclides, thereby removing the radionuclides from the wastewater through ion exchange.

[0014] The present invention also provides a method for preparing magnesium aluminum fluorophosphate as described in any of the preceding claims, characterized by comprising the following steps: Step 1: Dissolve boric acid, magnesium dihydrogen phosphate, aluminum fluoride, ammonium carbonate and ammonia in deionized water, mix well and transfer to a polytetrafluoroethylene (PTFE) liner, place the PTFE liner in a high-pressure reactor and seal it. Step 2: Place the reactor in a furnace and heat it at a constant temperature. After the reaction is complete, allow it to cool naturally to room temperature. Step 3: Remove the liner, wash the solid mixture with boiling water and dry it to obtain the magnesium aluminum fluoride phosphate.

[0015] Preferably, in step 1, the amounts of reactants added are: 10 mmol to 15 mmol of boric acid, 1.0 mmol to 1.2 mmol of magnesium dihydrogen phosphate, 1.0 mmol to 1.2 mmol of aluminum fluoride, 1.0 mmol to 1.2 mmol of ammonium carbonate, and 0.5 mL of ammonia water with a mass fraction of 25% to 28%; in step 2, the reaction temperature is 175 °C, and the reaction time is 4 to 5 days.

[0016] The above technical solution has the following advantages: The magnesium aluminum fluoride ammonium salt provided by this invention possesses a unique two-dimensional layered structure. This structure consists of isolated PO4 tetrahedra connected to AlO4F2 octahedra and MgO4F2 octahedra sharing vertices. This robust framework connection ensures good structural stability of the material over a wide pH range from 2 to 12. The ammonium ions filling the interlayer provide active sites for ion exchange. The open two-dimensional channels facilitate the rapid migration of radionuclides. This material exhibits an extremely fast kinetic response during the adsorption of strontium ions, reaching adsorption equilibrium within 1 to 3 minutes. (Regarding Sr²⁺) + The maximum adsorption capacity can reach 260.77 mg / g. The material is prepared using a low-temperature hydrothermal synthesis method. The process is simple, with high yield, and possesses good economic benefits and promising industrial application prospects. Attached Figure Description

[0017] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a schematic diagram of the crystal structure of magnesium aluminum fluoride phosphate provided in an embodiment of the present invention, wherein, Figure 1 (a) in the diagram is a schematic diagram of the octahedral structure of MgO4F2. Figure 1 (b) in the diagram is a schematic diagram of the AlO4F2 octahedral structure. Figure 1 (c) in the diagram is a schematic diagram of the tetrahedral structure of PO4. Figure 1 (d) in the diagram is a schematic diagram of the local atomic connection relationship. Figure 1 (e) in the diagram is a schematic diagram of the connection relationship of local polyhedra. Figure 1 (f) in the diagram is a schematic diagram of the anion layer structure. Figure 1 (g) in the diagram is a schematic diagram of a layered crystal structure.

[0018] Figure 2 shows the scanning electron microscope image, energy dispersive spectroscopy (EDS) spectrum, and elemental distribution diagram of magnesium aluminum fluoride phosphate provided in the embodiments of the present invention.

[0019] Figure 3 shows the scanning electron microscope image, energy spectrum, and elemental distribution diagram of the magnesium aluminum fluoride phosphate provided in the embodiment of the present invention after strontium ion exchange.

[0020] Figure 4 is a crystal photograph of magnesium aluminum fluoride phosphate provided in an embodiment of the present invention.

[0021] Figure 5 shows the simulated powder XRD pattern, the measured powder XRD pattern, and the powder XRD pattern after strontium ion exchange of the magnesium aluminum fluoride phosphate provided in the embodiments of the present invention.

[0022] Figure 6 shows the adsorption effect of magnesium aluminum fluoride phosphate provided in the embodiments of the present invention on strontium ions under different pH conditions.

[0023] Figure 7 shows the XRD patterns of magnesium aluminum fluoride phosphate provided in the embodiments of the present invention under different pH conditions.

[0024] Figure 8 is a kinetic model diagram of magnesium aluminum fluoride phosphate provided in the embodiment of the present invention.

[0025] Figure 9 is a diagram of the isothermal adsorption model of magnesium aluminum fluoride phosphate provided in the embodiment of the present invention.

[0026] Figure 10 is a comparison of the adsorption effects of magnesium aluminum fluoride phosphate provided in the embodiments of the present invention and similar materials on strontium ions. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages 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. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example 1 This embodiment provides a magnesium aluminum fluoride ammonium salt. The material is magnesium aluminum fluoride ammonium salt, which can be abbreviated as NMAPOF. The chemical formula of the magnesium aluminum fluoride ammonium salt is (NH4)2MgAlP2O5F2(OH)5, and its composition is consistent with the chemical formula after elemental analysis or structural analysis. The crystal belongs to the triclinic crystal system and the space group is P-1. The specific unit cell parameters determined by single crystal X-ray diffraction analysis are: a = 5.0011(2) Å, b = 7.0837(4) Å, c = 7.9338(3) Å; the unit cell angles are α = 91.954(4)°, β = 94.099(3)°, γ = 110.609(4)°; the unit cell volume V = 261.88(2) ų, and the number of molecules in the unit cell Z = 2.

[0029] Referring to Figure 1, from a molecular structural perspective, the basic structural units of this magnesium aluminum fluoride phosphate salt include isolated PO4 tetrahedra, AlO4F2 octahedra, and MgO4F2 octahedra. These structural units exhibit a unique connection pattern in their spatial arrangement. Specifically, each PO4 tetrahedron is connected to two AlO4F2 octahedra and one MgO4F2 octahedron through a shared vertex arrangement. Each AlO4F2 octahedron is connected to four PO4 tetrahedra and two MgO4F2 octahedra. Each MgO4F2 octahedron is connected to two PO4 tetrahedra and two AlO4F2 octahedra.

[0030] By connecting the common vertices of the aforementioned structural units, the related polyhedra extend along the xy plane, thereby constructing an anionic layer with stable physicochemical properties. In this layered structure, the interlayer cations, namely ammonium ions, of magnesium aluminum fluoride phosphate fill the two-dimensional interlayer spacing, playing a role in balancing the charge, and ultimately forming a complete layered crystal structure.

[0031] The magnesium aluminum fluoride ammonium salt prepared in this embodiment appears macroscopically as colorless, transparent, elongated, plate-like crystals. (See Figure 2 and...) Figure 4 Scanning electron microscopy revealed that the crystal surface was neat and the morphology was regular, with a crystal size of approximately 2 mm. Further electron energy dispersive spectroscopy indicated that its main constituent elements included aluminum, magnesium, fluorine, phosphorus, and oxygen; the presence of nitrogen and ammonium ions was confirmed by other characterization results, and the atomic ratios of each element closely matched the chemical formula (NH4)2MgAlP2O5F2(OH)5.

[0032] The preparation method of magnesium aluminum fluoride phosphate provided in this embodiment is achieved by low-temperature hydrothermal synthesis, and the specific steps are as follows: Step 1: Prepare the reaction raw materials. Weigh out 10 mmol of boric acid, 1.0 mmol of magnesium dihydrogen phosphate, 1.0 mmol of aluminum fluoride, and 1.0 mmol of ammonium carbonate according to the stoichiometric ratio and excess auxiliary reagent requirements. Add the above solid raw materials sequentially to a beaker containing deionized water, followed by 0.5 mL of ammonia solution with a concentration of 25% to 28%.

[0033] Step 2, Mixing and Loading. The mixture is mechanically stirred at room temperature to dissolve and homogenize the reactants sequentially, ensuring complete dissolution. The resulting solution is then transferred to a 25 mL polytetrafluoroethylene (PTFE) liner. The liner is placed inside a stainless steel outer casing and sealed to form a complete reaction vessel.

[0034] Step 3, hydrothermal reaction. The reactor is placed in an oven, i.e., a hydrothermal reactor. The reaction temperature is set at 175 ℃, and the crystallization reaction is carried out under this constant temperature condition for 5 days. During this process, components such as boric acid and phosphate promote the nucleation and growth of the aluminum-magnesium-oxygen-fluorine framework under high temperature and high pressure.

[0035] Step 4, Cooling and Post-processing. After the reaction is complete, turn off the power to the reactor and allow it to cool naturally to room temperature inside the furnace. Remove the polytetrafluoroethylene liner and collect the solid mixture. Wash the obtained solid repeatedly with boiling water to remove residual mineralizing agent and unreacted impurities. Finally, dry the washed crystals in an oven at 60 °C for 12 hours to obtain blocky, transparent, single-phase magnesium ammonium aluminum fluoride phosphate crystals. The mass of the obtained product is approximately 0.085 g, with a yield of approximately 85% based on metallic aluminum (Al).

[0036] This magnesium aluminum fluoride phosphate salt demonstrates good technical performance in the treatment of radioactive wastewater. Referring to Figures 3 to 10, the material exhibits strong ion exchange properties, particularly suitable for adsorbing the radioactive element Sr². + In the experimental verification, 10 mg of the crystalline powder was added to Sr²⁺ solution with an initial concentration of 10 mg / L and a pH of 12. + The solution was centrifuged and stirred at room temperature for 8 h. The results showed that this material exhibited a high degree of seroconversion towards Sr²⁺. + The adsorption effect is significant. See Figure 5, where NMAPOF is the sample before ion exchange and NMAPOF-Sr is the sample after strontium ion exchange; the powder XRD pattern of this material and the theoretical spectrum of magnesium aluminum fluoride ammonium salt are also shown. Figure 1 The crystal planes coincided, verifying the accuracy of the material structure.

[0037] Furthermore, this material maintains structural stability over a very wide pH range from 2 to 12, particularly under strong acid or strong base conditions for Sr²⁺. + It has a better adsorption effect and overcomes the defect of traditional molecular sieves that are prone to structural damage caused by the dissolution of skeletal aluminum in strong acid environment.

[0038] Through kinetic experiments, this material's effect on Sr² + The adsorption process is extremely rapid, reaching equilibrium in just 1 to 3 minutes. This is attributed to its open two-dimensional layered structure, which provides channels for the rapid migration of ions. The adsorption process conforms to a pseudo-second-order kinetic model. Calculations using an isothermal adsorption model show that its adsorption on Sr²⁺ is... + The maximum theoretical adsorption capacity reached 260.77 mg / g, and the isothermal adsorption experiments conformed to the Langmuir model, the Freundlich model, and the Langmuir-Freundlich model. Referring to Figure 3, obvious cracks appeared on the crystal surface after ion exchange, which is due to the Sr²⁺... + The ion exchange process is caused by microscopic stress changes induced after ammonium ions enter the crystal lattice, which further verifies the occurrence of the ion exchange process from a morphological perspective. This excellent adsorption performance and extremely short equilibrium time make it of significant application value in fields such as nuclear power plant wastewater treatment and nuclear accident emergency response.

[0039] Example 2 This embodiment further optimizes and adjusts the preparation process parameters of magnesium aluminum fluoride ammonium salt based on Embodiment 1 above, to verify the structural stability and performance consistency of the material under different synthesis conditions. In this embodiment, the specific amounts of each reactant added are set as follows: 15 mmol of boric acid, 1.2 mmol of magnesium dihydrogen phosphate, 1.2 mmol of aluminum fluoride, and 1.2 mmol of ammonium carbonate are weighed. During the mixing process, 0.5 mL of ammonia water is added as a regulator. By increasing the initial raw material concentration, the effect of a high-concentration system on crystal yield and crystal size is observed.

[0040] The specific preparation steps are as follows: First, the measured amounts of boric acid, magnesium dihydrogen phosphate, aluminum fluoride, and ammonium carbonate are sequentially added to 10 mL of deionized water. A homogeneous mixture or suspension is formed under continuous stirring, followed by the dropwise addition of ammonia. The homogeneously mixed material is transferred to a polytetrafluoroethylene liner and sealed in a stainless steel autoclave (reactor). The reactor is placed in a constant-temperature furnace, maintaining the reaction temperature at 175 °C, and the reaction time is shortened to 4 days. After the reaction, the solid product is treated according to the cooling, washing, and drying steps described in Example 1. Experimental results show that although the reaction time is shortened, the obtained product is still a high-purity (NH4)2MgAlP2O5F2(OH)5 crystal, and the yield remains above 80%.

[0041] This embodiment further elucidates the microstructure details of the magnesium ammonium aluminum fluoride phosphate salt to support the features regarding specific atom coordination in the claims. In this layered structure, each PO4 tetrahedron is not randomly connected but exhibits a high degree of order. Specifically, each PO4 tetrahedron is connected to a first AlO4F2 octahedron, a second AlO4F2 octahedron, and a first MgO4F2 octahedron. Simultaneously, each AlO4F2 octahedron is connected to four PO4 tetrahedrons and shares vertices with a second MgO4F2 octahedron and a third MgO4F2 octahedron. Correspondingly, each MgO4F2 octahedron is connected to two PO4 tetrahedrons, a third AlO4F2 octahedron, and a fourth AlO4F2 octahedron. This complex shared-vertex connection constructs a stable [Mg2Al2P2O] structure. 18 F6]²² - Clusters, which constitute the basic framework units of the anion layer.

[0042] This embodiment underwent extensive environmental adaptability testing for the application of this material in the adsorption of radionuclides. See [link to documentation]. Figure 5 As shown in Figure 10, this material maintains good crystal structure integrity in solution environments with pH values ​​ranging from 2 to 12. Particularly under simulated strongly alkaline radioactive wastewater at pH 12, XRD patterns show no significant changes in the position and intensity of its characteristic diffraction peaks, proving that its framework aluminum and magnesium elements have not dissolved. Regarding strontium ions (Sr²⁺)... + In the adsorption test, the material prepared in this embodiment exhibited an extremely fast kinetic response. Referring to Figure 8, the adsorption reaction completed more than 90% of the exchange within the first 1 minute and basically reached adsorption equilibrium within 3 minutes.

[0043] Furthermore, this embodiment highlights the technical superiority of the material of the present invention through comparative experiments. Referring to Figure 10, the material of the present invention is compared with various currently known adsorbent materials, such as flower-like α-ZrP, layered metal sulfides FJSM-SnS, and some aluminophosphate materials. Experimental data show that although some zirconium-based materials have high theoretical adsorption capacities, their equilibrium time typically takes several hours or even longer. In contrast, the magnesium ammonium aluminum fluoride phosphate provided by the present invention significantly shortens the treatment cycle while maintaining a high adsorption capacity of 260.77 mg / g.

[0044] Based on the above-mentioned excellent ion exchange performance and extreme environmental stability, the aluminum magnesium ammonium fluoride phosphate provided by this invention is a highly efficient inorganic ion exchange material that can be applied to the treatment of strontium-containing wastewater, radioactive wastewater, and emergency water treatment in nuclear accidents.

[0045] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are 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 modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A magnesium aluminum fluoride phosphate, characterized in that, The magnesium aluminum fluoride ammonium salt has the chemical formula (NH4)2MgAlP2O5F2(OH)5, belongs to the triclinic crystal system, and has a space group of P-1. Its basic structural units include isolated PO4 tetrahedra, AlO4F2 octahedra, and MgO4F2 octahedra. The PO4 tetrahedra are connected to the AlO4F2 octahedra and MgO4F2 octahedra through shared vertices, forming anion layers. The spaces between these anion layers are filled with interlayer cations NH4+. + And form a layered structure.

2. The magnesium aluminum fluoride ammonium salt according to claim 1, characterized in that, The unit cell parameters of the aluminum magnesium ammonium fluoride phosphate are: a = 5.0011(2) Å, b = 7.0837(4) Å, c = 7.9338(3) Å; α = 91.954(4)°, β = 94.099(3)°, γ = 110.609(4)°; unit cell volume V = 261.88(2) ų, and number of molecules in unit cell Z = 2.

3. The magnesium aluminum fluoride ammonium salt according to claim 1, characterized in that, In the layered structure, each PO4 tetrahedron is connected to a first AlO4F2 octahedron, a second AlO4F2 octahedron, and a first MgO4F2 octahedron; each AlO4F2 octahedron is connected to four PO4 tetrahedrons, a second MgO4F2 octahedron, and a third MgO4F2 octahedron; and each MgO4F2 octahedron is connected to two PO4 tetrahedrons, a third AlO4F2 octahedron, and a fourth AlO4F2 octahedron.

4. The magnesium aluminum fluoride ammonium salt according to claim 1, characterized in that, The aluminum magnesium ammonium fluorophosphate is a colorless, transparent, elongated, sheet-like crystal.

5. The application of magnesium aluminum fluoride phosphate as described in any one of claims 1 to 4 as an ion exchange material in the adsorption of radionuclides.

6. The application according to claim 5, characterized in that, The radionuclides include radioactive isotopes of strontium, and they are present in solution as Sr². + It exists in form.

7. The application according to claim 6, characterized in that, The aluminum magnesium ammonium fluorophosphate maintains structural stability in solution environments with pH values ​​ranging from 2 to 12, and is effective against Sr²⁺. + The adsorption equilibrium time is 1 min to 3 min, and its effect on Sr² + The maximum adsorption capacity is 260.77 mg / g.

8. A method for treating radioactive wastewater, characterized in that, By contacting wastewater containing radionuclides with magnesium aluminum fluoride as described in any one of claims 1 to 4, radionuclides in the wastewater are removed by ion exchange.

9. A method for preparing magnesium aluminum fluorophosphate as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Add boric acid, magnesium dihydrogen phosphate, aluminum fluoride, ammonium carbonate and ammonia to deionized water and mix evenly. After mixing evenly, transfer the mixture to a polytetrafluoroethylene (PTFE) liner. Place the PTFE liner in a high-pressure reactor and seal it. Step 2: Place the reactor in a furnace and heat it at a constant temperature. After the reaction is complete, allow it to cool naturally to room temperature. Step 3: Remove the liner, wash the solid mixture with boiling water and dry it to obtain the magnesium aluminum fluoride phosphate.

10. The preparation method according to claim 9, characterized in that, In step 1, the reactants added are: 10 mmol to 15 mmol of boric acid, 1.0 mmol to 1.2 mmol of magnesium dihydrogen phosphate, 1.0 mmol to 1.2 mmol of aluminum fluoride, 1.0 mmol to 1.2 mmol of ammonium carbonate, and 0.5 mL of ammonia water with a mass fraction of 25% to 28%; in step 2, the reaction temperature is 175 °C, and the reaction time is 4 to 5 days.

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