Fly ash-based magnetic hectorite and preparation method thereof

Abstract

The present invention discloses a fly ash-based magnetic hectorite and a preparation method thereof, belonging to the field of inorganic material synthesis technology. The method uses fly ash-based mineral polymers produced after fly ash depolymerization as raw materials, utilizes its residual surface defect sites to fix magnetic substances, and utilizes microwave progressive irradiation technology to distinguish whether the magnetic substances are chemically loaded. On this basis, hectorite is prepared with the help of the topological structure remaining in the magnetic precursor. During this process, magnetic particles enter the crystals of the synthetic product along with the crystallization behavior of the raw materials, thereby imparting magnetism. The fly ash-based magnetic hectorite obtained by the present invention has the characteristics of high adsorption efficiency and good regeneration performance. At the same time, the preparation process is suitable for industrial production and can be used in the field of heavy metal water pollution control.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic material synthesis, and particularly relates to fly ash-based magnetic hectorite and a preparation method thereof. Background Art

[0002] Hectorite is a synthetic layered silicate material. Its unique nanostructure, high surface area, and adjustable surface charge make it a valuable resource for the treatment of heavy metal, dye, and antibiotic pollution. However, traditional hectorite preparation processes generally rely on chemical raw materials such as high-purity lithium salts, magnesium salts, and silicates. These processes are plagued by high raw material costs and complex synthesis routes (typically using hydrothermal synthesis, which results in low yields due to the low solid-to-liquid ratio per reactor, high wastewater discharge, and low synthesis efficiency). These factors contribute to high costs for large-scale production.

[0003] Fly ash is a solid waste generated by coal combustion in coal-fired power plants, smelting, chemical industries, and other industries. Its main components are SiO2, Al2O3, Fe2O3, and a certain amount of unburned carbon particles. Currently, the global comprehensive utilization rate of fly ash is less than 30%. Existing reports indicate that large-scale fly ash accumulation not only leads to land occupation, but also creates dust pollution and the risk of heavy metal leaching. Traditionally, fly ash is mainly used in building materials (such as cement admixtures) or roadbed fill, but its added value is low and its chemical properties are not fully utilized. Therefore, how to achieve high-value-added utilization of fly ash and transform waste into valuable resources is a major challenge facing academia and industry. Fly ash is mostly in the form of micron-sized particles with a porous structure and high specific surface area (typically 200-400 m² / g), which makes it potentially valuable in the field of adsorption. However, the adsorption capacity of industrial fly ash is limited (typically less than 50 mg / g), and its adsorption capacity for divalent heavy metal ions (such as Pb) is limited. 2+ 、Cd 2+ ) has poor selectivity. In addition, direct use of fly ash in the adsorption field may cause secondary pollution due to alkaline leaching solution (pH>11), and the pH value of the wastewater needs to be additionally adjusted.

[0004] In recent years, with the advent of green chemistry, alternative synthesis processes for preparing industrial adsorption products using fly ash as a raw material have garnered widespread attention. However, fly ash contains a certain amount of mullite and quartz, which are not readily reactive, as well as a high concentration of Al₂O₃ and Fe₂O₃ impurities, necessitating pretreatment. Developing an efficient pretreatment process is currently a key challenge in the comprehensive utilization of fly ash. Furthermore, the concept of magnetic adsorption materials has been proposed in recent years to improve the efficiency of adsorption products. Magnetic adsorption materials are chemically imbued with magnetic properties to enhance their separation and regeneration capabilities. However, the preparation of magnetic materials is plagued by self-aggregation of magnetic materials and the random distribution of functional groups (or defects) on the adsorption material's surface, making it difficult to ensure uniform and efficient loading of the magnetic material. Furthermore, due to the weak interaction between the magnetic material and the adsorption material, the magnetic material is prone to detachment during the regeneration and recycling of the adsorption material, severely reducing the regeneration performance of the magnetic adsorption material. Summary of the Invention

[0005] To address the challenges of preparing magnetic hectorite in existing technologies, the present invention provides a fly ash-based magnetic hectorite and a method for its preparation. This method uses fly ash-based mineral polymers, produced after fly ash depolymerization, as raw material. The residual surface defects in the polymer are used to immobilize magnetic materials, and microwave progressive irradiation is used to identify whether the magnetic materials are chemically loaded. Furthermore, the hectorite is prepared by leveraging the residual topological structure of the magnetic precursor. During this process, magnetic particles are incorporated into the resulting crystals as the raw material crystallizes, imparting magnetic properties.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing fly ash-based magnetic hectorite specifically comprises the following steps:

[0008] A1. The lithium source, magnesium source and magnetic precursor were mixed in a molar ratio of 1.0:3.0:1.7-3.0 and stirred thoroughly. The resulting mixture was designated as mixture I.

[0009] The magnetic precursor is prepared by the following method, specifically comprising:

[0010] B1. The fly ash-based mineral polymer and the magnetic material were mixed uniformly in a mass ratio of 1:0.05-1, and the resulting mixture was designated as mixture II;

[0011] B2. The mixture II was transferred to a polytetrafluoroethylene-lined hydrothermal reactor tank, and 3-5 ml of ammonia solution was added to the bottom of the polytetrafluoroethylene-lined hydrothermal reactor tank;

[0012] B3. The polytetrafluoroethylene-lined tank in step B2 of the hydrothermal reactor was loaded into a stainless steel reactor, placed in a constant temperature oven, and reacted at a temperature of 150-170 ° C for 3-6h;

[0013] B4. After the reaction is complete, the polytetrafluoroethylene-lined hydrothermal reactor tank is removed, and the solid product in the reactor tank is removed. The resulting mixture is referred to as mixture III.

[0014] B5. The mixture obtained in step B4 is loaded into a microwave digestion vessel, and 3-5 ml of ammonia solution is added to the bottom of the microwave digestion vessel;

[0015] B6. Place the prepared microwave digestion vessel into a microwave digestion instrument and irradiate at a certain temperature according to specific irradiation conditions: irradiation temperature 120-150°C, irradiation cycles 3-8 times;

[0016] B7. After the reaction is complete, remove the microwave digestion vessel from the microwave irradiation chamber, filter the solid product until it is neutral, and place it in a vacuum oven at 90°C for 12 hours at a vacuum level of 0.07 MPa. The resulting solid powder is the magnetic precursor.

[0017] A2. The mixture Ⅰ was transferred to a polytetrafluoroethylene-lined hydrothermal reactor tank, and 3-5 ml of ammonia solution was added to the bottom of the polytetrafluoroethylene-lined hydrothermal reactor tank;

[0018] A3. Place the loaded polytetrafluoroethylene-lined tank into a stainless steel reactor, place it in a constant temperature oven, and react at a temperature of 110-200°C for 24-72h.

[0019] A4. After the reaction is complete, remove the polytetrafluoroethylene-lined tank from the hydrothermal reactor, centrifuge and wash the solid product until neutral, transfer the solid product with deionized water, and freeze-dry the resulting material. The resulting solid powder is fly ash-based magnetic hectorite.

[0020] Furthermore, in step A1, the lithium source is one of lithium fluoride, lithium carbonate, and lithium hydroxide monohydrate, or a mixture of two of them; the magnesium source is one of magnesium chloride, magnesium carbonate, and magnesium hydroxide, or a mixture of two of them.

[0021] Furthermore, in step A2, the mass concentration of the ammonia water used is 25%; the mixture I and the ammonia solution are separated by a polytetrafluoroethylene mesh, that is, during the reaction, only the alkaline vapor formed by the heating of the ammonia water serves as the reaction medium.

[0022] Furthermore, in step A4, the freeze-drying conditions are: freezing temperature -80°C, and freeze-drying time is 1-3 days.

[0023] Furthermore, in step B1, the magnetic material is one or a combination of Fe2O3, Fe3O4, FeCl2, Co3O4, CoCl2, and NiCl2.

[0024] Furthermore, in step B2, the ammonia solution used has a mass concentration of 25% and is obtained by uniformly mixing the ammonia solution with deionized water in a volume ratio of 1:1; the mixture II and the ammonia solution are separated by a polytetrafluoroethylene mesh, that is, the reaction in step B3 relies solely on the alkaline vapor generated by the heating of the ammonia solution as the reaction medium;

[0025] In step B5, aqueous ammonia is used with a mass concentration of 25%. Mixture III and the aqueous ammonia solution are separated by a polytetrafluoroethylene mesh, that is, the reaction in step B6 relies solely on the alkaline vapor formed by the heating of aqueous ammonia as the reaction medium.

[0026] Furthermore, in step B6, the irradiation cycle is specifically each cycle of 100W irradiation for 10s, 150W irradiation for 10s, 200W irradiation for 10s, 250W irradiation for 10s, 300W irradiation for 10s, and rest for 10s.

[0027] Furthermore, in step B1, the fly ash-based mineral polymer is prepared by the following method, specifically comprising:

[0028] C1. Mixing sodium hydroxide and fly ash in a mass ratio of 1:1.4, calcining in a muffle furnace at 720-900° C. for 2-4 hours, or calcining in a microwave muffle furnace at 720-900° C. for 0.5-1 hour; after calcination, removing from the muffle furnace, grinding into powder, and sieving through an 80-mesh sieve to obtain an alkali-fused powder;

[0029] C2. Filter the alkali molten powder with deionized water until it is neutral, and dry it in an oven at 90°C for 12 hours to obtain a neutral alkali molten powder;

[0030] C3. The neutral alkali molten powder and the acid solution are loaded into a microwave digestion tank according to a certain solid-liquid ratio, wherein the mass volume ratio of the alkali molten powder to the acid solution is in the range of 1:2.5-5 g / ml;

[0031] C4. Place the microwave digestion vessel prepared in step C3 into a microwave digestion instrument and irradiate at a certain temperature according to specific irradiation conditions, specifically, an irradiation temperature of 150-200° C. and 30-60 irradiation cycles;

[0032] C5. Take out the microwave digestion tank after microwave irradiation, filter the solid product until it is neutral, and place it in a constant temperature oven at 80-90°C to dry for 12 hours. The obtained solid powder is the fly ash-based mineral polymer.

[0033] Furthermore, in step C3, the acid solution is hydrochloric acid with a concentration of 2-4 mol / L;

[0034] In step C3, the fly ash and the acid solution are separated by a polytetrafluoroethylene mesh, that is, during the microwave irradiation process, only the acid solution is heated to form acidic steam as the reaction medium;

[0035] In step C4, the irradiation cycle is specifically each cycle of 200W irradiation for 10s, 230W irradiation for 10s, 270W irradiation for 10s, 330W irradiation for 10s, 350W irradiation for 10s, and rest for 10s.

[0036] Compared with the prior art, the advantages of the present invention are as follows:

[0037] 1. The use of fly ash as a synthetic raw material to prepare magnetic hectorite adsorption materials provides a feasible way for the high value-added utilization of fly ash to a certain extent, and also provides a green raw material source for the functional synthesis of hectorite, and also provides cheap raw materials for the preparation of industrial adsorbents.

[0038] 2. Regarding the process of obtaining fly ash geopolymer, the alkali melting process of fly ash can be treated not only with a muffle furnace, but also with a microwave muffle furnace, which can provide multiple solutions for industrial production.

[0039] 3. During the microwave acid leaching process, the fly ash powder after alkali melting is directly irradiated with microwaves. Due to the differences in the microwave response of chemical bonds between different elements, direct activation is achieved, resulting in consistent activation and rupture of chemical bonds. These ruptured chemical bonds can better bind firmly and uniformly to the magnetic particles through chemical interactions. This also allows Al2O3, Fe2O3, and other components to be separated from the acid vapor, facilitating the separation of fly ash components.

[0040] 4. In the process of preparing magnetic precursors, a solid-phase preparation method and a microwave progressive irradiation screening method are used to weaken the influence of the synthesis process on the magnetic properties of magnetic particles. At the same time, microwave irradiation technology is used to quickly identify the chemical loading behavior between magnetic particles and geopolymers.

[0041] 5. In the process of preparing magnetic hectorite, a solid-phase preparation method is combined with a freeze-drying process, which eliminates the inconveniences of hydrothermal synthesis of hectorite and can also fully reduce the loss of magnetic particles, thereby preparing magnetic hectorite with maximum efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0043] Figure 1 For implementation case 1, the XRD pattern of fly ash is shown;

[0044] Figure 2 The SEM image of fly ash is shown in the implementation case 1;

[0045] Figure 3 The XRD pattern of fly ash-based mineral polymer is shown in implementation case 1;

[0046] Figure 4 The SEM image of fly ash-based mineral polymer is shown in Example 1;

[0047] Figure 5 This is the XRD pattern of fly ash-based magnetic hectorite for implementation case 1;

[0048] Figure 6 This is the SEM image of fly ash-based magnetic hectorite in implementation case 1;

[0049] Table 1 shows the test results of the lead ion adsorption capacity of fly ash-based magnetic hectorite and the lead ion adsorption capacity after 8 regenerations in Examples 1-8;

[0050] from Figure 1 and Figure 3 It can be seen that the fly ash has been deagglomerated into an amorphous state;

[0051] from Figure 2 and Figure 4 It can be seen that the morphology breaks from spherical to irregular flakes, which indicates that the fly ash has been fully deagglomerated;

[0052] Figure 5 It is a typical hectorite crystal peak, among which the peak around 2θ=30° is the characteristic peak of Fe3O4, which indicates that the synthetic product is magnetic nanohectorite;

[0053] according to Figure 6 It can be seen that the sample as a whole presents a typical flaky morphology, which is the typical morphology of hectorite, and there are evenly distributed nano-concave-convex particles on its surface, which should be magnetic particles. DETAILED DESCRIPTION

[0054] In order to clearly and completely describe the technical solution and specific working process of the present invention, the specific implementation methods of the present invention are as follows in conjunction with the accompanying drawings:

[0055] Example 1

[0056] This embodiment provides a method for preparing fly ash-based magnetic hectorite, and the specific steps of the method are as follows:

[0057] A1. Mix a lithium source, a magnesium source, and a magnetic precursor in a molar ratio of 1.0:3.0:1.7-3.0 and stir thoroughly. The resulting mixture is designated Mixture I.

[0058] The preparation method of the magnetic precursor is as follows:

[0059] B1. The fly ash-based mineral polymer and the magnetic material were mixed uniformly in a mass ratio of 1:1. The resulting mixture was designated as mixture II.

[0060] B2. Transfer the mixture II to a 100 ml polytetrafluoroethylene-lined hydrothermal reactor and add 5 ml of ammonia solution to the bottom of the polytetrafluoroethylene-lined hydrothermal reactor.

[0061] B3. The polytetrafluoroethylene-lined tank in step B2 was loaded into a stainless steel reactor and placed in a constant temperature oven at a temperature of 170°C for 3h;

[0062] B4. After the reaction is complete, the polytetrafluoroethylene-lined hydrothermal reactor tank is removed, and the solid product in the reactor tank is removed. The resulting mixture is referred to as mixture III.

[0063] B5. The mixture obtained in step B4 was loaded into a microwave digestion vessel, and 5 ml of ammonia solution was added to the bottom of the microwave digestion vessel;

[0064] B6. Place the microwave digestion vessel into a microwave digestion instrument and irradiate at a specific temperature and under specific irradiation conditions, specifically, 120°C for eight irradiation cycles.

[0065] B7. After the reaction is completed, remove the microwave digestion vessel after microwave irradiation, filter the solid product until it is neutral, and place it in a vacuum oven at 90°C for 12 hours. The vacuum degree of the vacuum oven is 0.07 MPa. The resulting solid powder is the magnetic precursor.

[0066] A2. Transfer the mixture Ⅰ to a 100 ml polytetrafluoroethylene-lined hydrothermal reactor and add 5 ml of ammonia solution to the bottom of the polytetrafluoroethylene-lined hydrothermal reactor.

[0067] A3. The polytetrafluoroethylene-lined tank in step A2 was loaded into a stainless steel reactor and placed in a constant temperature oven at a temperature of 110°C for 72h.

[0068] A4. After the reaction is complete, remove the polytetrafluoroethylene-lined tank from the hydrothermal reactor, centrifuge and wash the solid product until neutral, transfer the solid product with deionized water, and freeze-dry the resulting material. The resulting solid powder is fly ash-based magnetic hectorite.

[0069] In this embodiment, in step A1, the lithium source is lithium hydroxide monohydrate; and the magnesium source is magnesium chloride.

[0070] In this embodiment, in step A2, the mass concentration of the ammonia water used is 25%; the mixture I and the ammonia solution are separated by a polytetrafluoroethylene mesh, that is, during the reaction process, only the alkaline vapor formed by the heating of the ammonia water serves as the reaction medium.

[0071] In this embodiment, in step A4, the freeze-drying conditions are: freezing temperature -80°C, and freeze-drying time is 1 day.

[0072] In this embodiment, the ammonia solution used in step B2 is an ammonia solution obtained by uniformly mixing ammonia solution with a laboratory-labeled concentration of 25% and deionized water in a volume ratio of 1:1. Mixture II and the ammonia solution are separated by a polytetrafluoroethylene mesh, that is, the reaction in step B3 relies solely on the alkaline vapor formed by heating the ammonia solution as the reaction medium.

[0073] In step B5, the ammonia water used is a laboratory-labeled concentrated ammonia water with a concentration of 25%; the mixture III and the ammonia solution are separated by a polytetrafluoroethylene mesh, that is, the reaction in step B6 relies solely on the alkaline vapor formed by the heating of the ammonia water as the reaction medium.

[0074] In this embodiment, in step B6, the irradiation cycles mentioned are as follows: 100W irradiation for 10s, 150W irradiation for 10s, 200W irradiation for 10s, 250W irradiation for 10s, 300W irradiation for 10s, and rest for 10s.

[0075] In this embodiment, in step B1, the magnetic material is Fe3O4.

[0076] In this embodiment, in step B1, the fly ash-based mineral polymer is prepared by the following method, specifically comprising:

[0077] C1. Sodium hydroxide and fly ash were mixed in a mass ratio of 1:1.4 and calcined in a muffle furnace at 720° C. for 4 h. After calcination, the mixture was removed from the muffle furnace, ground into powder, and sieved through an 80-mesh sieve to obtain an alkali-fused powder.

[0078] C2. Filter the alkali molten powder with deionized water until it is neutral, and dry it in an oven at 90°C for 12 hours to obtain a neutral alkali molten powder;

[0079] C3. Load the neutral alkali molten powder and acid solution into a microwave digestion tank at a certain solid-liquid ratio, with the ratio range of alkali molten powder: acid solution = 1:5 g / ml;

[0080] C4, placing the microwave digestion vessel prepared in step C3 into a microwave digestion instrument, and irradiating the solution at a certain temperature according to specific irradiation conditions, specifically, an irradiation temperature of 150° C. and 60 irradiation cycles;

[0081] C5. Take out the microwave digestion tank after microwave irradiation, filter the solid product until it is neutral, and place it in a constant temperature oven at 80-90°C to dry for 12 hours. The obtained solid powder is the fly ash-based mineral polymer.

[0082] In this embodiment, in step C3, the acid solution used is hydrochloric acid with a concentration of 4 mol / L;

[0083] In step C3, the fly ash and the acid solution are isolated by a polytetrafluoroethylene mesh, that is, during the microwave irradiation process, only the acid solution is heated to form acidic steam as the reaction medium.

[0084] In step C4, the irradiation cycle mentioned is specifically each cycle of 200W irradiation for 10s, 230W irradiation for 10s, 270W irradiation for 10s, 330W irradiation for 10s, 350W irradiation for 10s, and rest for 10s.

[0085] The rest of Example 2 is the same as Example 1, except that, in step A1, the molar ratio of the lithium source, magnesium source, and magnetic precursor is 1.0:3.0:1.7; in step A2, 3 ml of ammonia solution is added to the bottom of the polytetrafluoroethylene hydrothermal reaction lined kettle; in step A3, the constant temperature oven temperature is 200°C, and the reaction is carried out for 24 hours; in step A1, the lithium source is lithium fluoride; the magnesium source is magnesium hydroxide; in step A4, the freeze-drying condition is a freezing temperature of -80°C, and the freeze-drying time is 3 days.

[0086] The rest of Example 3 is the same as Example 1, except that, in step B1, the mass ratio of fly ash-based mineral polymer to magnetic material is 1:0.05; in step B2, 3 ml of ammonia solution is added to the bottom of the polytetrafluoroethylene hydrothermal reaction kettle lined with a reactor; in step B3, the constant temperature oven temperature is 150 ° C, and the reaction is carried out for 6 hours; in step B5, 3 ml of ammonia solution is added to the bottom of the microwave digestion tank; in step B6, the irradiation temperature is 150 ° C, and the irradiation cycle is 3.

[0087] The rest of Example 4 is the same as Example 1, except that the magnetic material in step B1 is CoCl2.

[0088] The rest of Example 5 is the same as Example 1, except that in step C1, calcination is performed at 900°C in a muffle furnace for 2 h; in step C3, the ratio of alkali molten powder: acid solution is 1:2.5 g / ml; in step C4, the irradiation temperature is 200°C, and the irradiation cycle is 30; in step C5, drying is performed in a constant temperature oven at 90°C for 12 h.

[0089] The rest of Example 6 is the same as Example 1, except that, in step C1, the calcination is carried out in a microwave muffle furnace at 720° C. for 1 h.

[0090] The rest of Example 7 is the same as Example 5, except that, in step C1, the calcination is carried out at 900° C. in a microwave muffle furnace for 0.5 h.

[0091] The rest of Example 8 is the same as Example 1, except that in step C3, the acid solution used is hydrochloric acid with a concentration of 2 mol / L.

[0092] Experimental data

[0093] Table 1 shows the test results of the lead ion adsorption capacity of fly ash-based magnetic hectorite and the lead ion adsorption capacity after 8 regenerations in implementation cases 1-8.

[0094] serial number Adsorption efficiency (first time) Adsorption efficiency (9th time) Implementation Case 1 99% 94% Implementation Case 2 99% 94% Implementation Case 3 99% 93% Implementation Case 4 99% 94% Implementation Case 5 99% 92% Implementation Case 6 98% 93% Implementation Case 7 99% 91% Implementation Case 8 99% 93%

[0095] Adsorption experiments

[0096] A certain mass of fly ash-based magnetic hectorite (0.2 g) was weighed and placed in a conical flask, and a certain volume of aqueous solution containing lead ions (100 mL) was added. The mixture was shaken at 30 °C for 2 h. After the adsorption was completed, the supernatant was taken and centrifuged at 8000 r / min for 15 min. The concentration of heavy metal ions in the wastewater before and after adsorption was determined by X-ray fluorescence diffractometer (the initial concentration C0 was 1000.0 mg·L¹, C t is the concentration of heavy metal ions in the solution after adsorption), and then calculate the removal rate of heavy metal ions (R, %) according to the following formula.

[0097]

[0098] The adsorbed material is collected under the action of an external magnetic field, and then a regeneration adsorption experiment is carried out. Before each regeneration adsorption, it needs to be ultrasonically treated at room temperature (20-30°C) (the ultrasonic frequency used is 40KHz, and the ultrasonic time is 15min). After the ultrasonic treatment is completed, the adsorption experiment is carried out.

[0099] It can be seen from the experimental results of lead ion adsorption in Table 1 that the fly ash-based magnetic hectorite prepared in each implementation case has relatively excellent adsorption performance and regeneration performance.

[0100] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0101] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0102] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing fly ash-based magnetic hectorite, characterized in that: The specific steps include: A1. The lithium source, magnesium source and magnetic precursor were mixed in a molar ratio of 1.0:3.0:1.7-3.0 and stirred thoroughly. The resulting mixture was designated as mixture I. The magnetic precursor is prepared by the following method, specifically comprising: B1. The fly ash-based mineral polymer and the magnetic material were mixed uniformly in a mass ratio of 1:0.05-1, and the resulting mixture was designated as mixture II; B2. The mixture II was transferred to a polytetrafluoroethylene-lined hydrothermal reactor tank, and 3-5 ml of ammonia solution was added to the bottom of the polytetrafluoroethylene-lined hydrothermal reactor tank; B3. The polytetrafluoroethylene-lined tank in step B2 of the hydrothermal reactor was loaded into a stainless steel reactor, placed in a constant temperature oven, and reacted at a temperature of 150-170 ° C for 3-6h; B4. After the reaction is complete, the polytetrafluoroethylene-lined hydrothermal reactor tank is removed, and the solid product in the reactor tank is removed. The resulting mixture is referred to as mixture III. B5. The mixture obtained in step B4 is loaded into a microwave digestion vessel, and 3-5 ml of ammonia solution is added to the bottom of the microwave digestion vessel; B6. Place the prepared microwave digestion vessel into a microwave digestion instrument and irradiate at a certain temperature according to specific irradiation conditions: irradiation temperature 120-150°C, irradiation cycles 3-8 times; B7. After the reaction is complete, remove the microwave digestion vessel from the microwave irradiation chamber, filter the solid product until it is neutral, and place it in a vacuum oven at 90°C for 12 hours at a vacuum level of 0.07 MPa. The resulting solid powder is the magnetic precursor. A2. The mixture Ⅰ was transferred to a polytetrafluoroethylene-lined hydrothermal reactor tank, and 3-5 ml of ammonia solution was added to the bottom of the polytetrafluoroethylene-lined hydrothermal reactor tank; A3. Place the loaded polytetrafluoroethylene-lined tank into a stainless steel reactor, place it in a constant temperature oven, and react at a temperature of 110-200°C for 24-72h. A4. After the reaction is complete, remove the polytetrafluoroethylene-lined tank from the hydrothermal reactor, centrifuge and wash the solid product until neutral, transfer the solid product with deionized water, and freeze-dry the resulting material. The resulting solid powder is fly ash-based magnetic hectorite.

2. The method for preparing a fly ash-based magnetic hectorite according to claim 1, wherein: In step A1, the lithium source is one of lithium fluoride, lithium carbonate, and lithium hydroxide monohydrate, or a mixture of two of them; the magnesium source is one of magnesium chloride, magnesium carbonate, and magnesium hydroxide, or a mixture of two of them.

3. The method for preparing a fly ash-based magnetic hectorite according to claim 1, wherein: In step A2, the mass concentration of the ammonia water used is 25%; the mixture I and the ammonia solution are separated by a polytetrafluoroethylene mesh, that is, during the reaction, only the alkaline vapor formed by the heating of the ammonia water serves as the reaction medium.

4. The method for preparing a fly ash-based magnetic hectorite according to claim 1, wherein: In step A4, the freeze-drying conditions are: freezing temperature -80°C, and freeze-drying time is 1-3 days.

5. The method for preparing a fly ash-based magnetic hectorite according to claim 1, wherein: In step B1, the magnetic material is one or a combination of Fe2O3, Fe3O4, FeCl2, Co3O4, CoCl2, and NiCl2.

6. The method for preparing a fly ash-based magnetic hectorite according to claim 1, wherein: In step B2, the ammonia solution used has a mass concentration of 25% and is obtained by uniformly mixing it with deionized water in a volume ratio of 1:1; the mixture II and the ammonia solution are separated by a polytetrafluoroethylene mesh, that is, the reaction in step B3 relies solely on the alkaline vapor generated by the heating of the ammonia solution as the reaction medium; In step B5, the mass concentration of the ammonia water used is 25%; the mixture III and the ammonia solution are separated by a polytetrafluoroethylene mesh, that is, the reaction in step B6 relies solely on the alkaline steam formed by the heating of the ammonia water as the reaction medium.

7. The method for preparing fly ash-based magnetic hectorite according to claim 1, wherein: In step B6, the irradiation cycle is specifically each cycle of 100W irradiation for 10s, 150W irradiation for 10s, 200W irradiation for 10s, 250W irradiation for 10s, 300W irradiation for 10s, and rest for 10s.

8. The method for preparing fly ash-based magnetic hectorite according to claim 1, wherein: In step B1, the fly ash-based mineral polymer is prepared by the following method, specifically comprising: C1. Mixing sodium hydroxide and fly ash in a mass ratio of 1:1.4, calcining in a muffle furnace at 720-900° C. for 2-4 hours, or calcining in a microwave muffle furnace at 720-900° C. for 0.5-1 hour; after calcination, removing from the muffle furnace, grinding into powder, and sieving through an 80-mesh sieve to obtain an alkali-fused powder; C2. Filter the alkali molten powder with deionized water until it is neutral, and dry it in an oven at 90°C for 12 hours to obtain a neutral alkali molten powder; C3. The neutral alkali molten powder and the acid solution are loaded into a microwave digestion tank according to a certain solid-liquid ratio, wherein the mass volume ratio of the alkali molten powder to the acid solution is in the range of 1:2.5-5 g / ml; C4, placing the microwave digestion vessel prepared in step C3 into a microwave digestion instrument, and irradiating the solution at a certain temperature according to specific irradiation conditions, specifically, an irradiation temperature of 150-200° C. and 30-60 irradiation cycles; C5. Take out the microwave digestion tank after microwave irradiation, filter the solid product until it is neutral, and place it in a constant temperature oven at 80-90°C to dry for 12 hours. The obtained solid powder is the fly ash-based mineral polymer.

9. The method for preparing fly ash-based magnetic hectorite according to claim 8, wherein: In step C3, the acid solution is hydrochloric acid with a concentration of 2-4 mol / L; In step C3, the fly ash and the acid solution are separated by a polytetrafluoroethylene mesh, that is, during the microwave irradiation process, only the acid solution is heated to form acidic steam as the reaction medium; In step C4, the irradiation cycle is specifically each cycle of 200W irradiation for 10s, 230W irradiation for 10s, 270W irradiation for 10s, 330W irradiation for 10s, 350W irradiation for 10s, and rest for 10s.

10. A fly ash-based magnetic hectorite, characterized in that: The method is prepared by any one of claims 1 to 9.

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