Method for improving balling rate of fly ash hollow microspheres

Abstract

The invention provides a method for improving the balling rate of fly ash hollow microspheres, which comprises the following steps: carrying out ball milling on fly ash to enable the average particle size of the fly ash after ball milling to be 1t; 2 [mu] m; fully and mechanically mixing the fly ash subjected to ball milling, water, an inorganic phosphate additive and clay to obtain spray slurry; carrying out spray drying on the spray slurry to obtain a fly ash hollow microsphere green body; and sintering the fly ash hollow microsphere green body to obtain the fly ash hollow microsphere. According to the method, the fly ash raw material is modified by utilizing inorganic phosphate and clay before spray drying, and the viscosity and stability of spray slurry are improved by utilizing the high plasticity of the clay and the moisture absorption capability and the water retention and shaping capability of an inorganic phosphate additive, so that the balling rate of the fly ash hollow microspheres can be improved, and the fly ash hollow microspheres can be prepared. The balling rate can be increased to 90-95% and is far higher than that of a production mode of common hollow microspheres, and the feasibility of high-value utilization of the solid waste fly ash is improved.

Description

Technical Field

[0001] This invention relates to a method for treating fly ash solid waste, and more particularly to a method for improving the pelletizing rate of hollow microspheres from fly ash, belonging to the field of solid waste resource recycling technology. Background Technology

[0002] Fly ash from waste incineration is a byproduct of waste incineration and is classified as hazardous solid waste, with a particle size generally between 1 and 100 μm. Fly ash contains harmful substances such as heavy metals, the carcinogen dioxins, and soluble salts. The leaching of heavy metals can pollute surrounding soil and groundwater, directly threatening human health. Currently, the disposal of fly ash faces challenges including large stockpiles, secondary pollution, and low resource utilization rates.

[0003] Hollow microspheres are hollow inorganic non-metallic materials with micron-sized particles ranging from 0.01 to 1 mm. They are lightweight, possess excellent thermal insulation properties, and exhibit strong adsorption capacity, making them widely used in insulation materials, aerospace materials, and composite materials. Fly ash contains valuable elements and useful components such as alumina and silicon dioxide, which are the main components of hollow microspheres. Therefore, using fly ash as a raw material to produce hollow microspheres is of great significance for reducing environmental pollution and improving the economic benefits of solid waste resources. However, due to the complex and highly variable composition of fly ash raw materials, their poor plasticity, and current hollow microsphere production processes, it is difficult to produce hollow microspheres with a high pelletizing rate using fly ash. Therefore, there is an urgent need to develop a simple and low-cost production process to meet the growing demand for waste incineration fly ash and coal-fired fly ash treatment, and to further improve fly ash utilization. Summary of the Invention

[0004] To address the aforementioned shortcomings and deficiencies, the present invention aims to provide a method for improving the pelletizing rate of fly ash hollow microspheres. This method not only improves raw material utilization but also significantly increases the pelletizing rate of fly ash hollow microspheres, thus solving the problem of low pelletizing rate in existing technologies.

[0005] To achieve the above objectives, the present invention provides a method for improving the pelletizing rate of hollow fly ash microspheres, wherein the method includes:

[0006] Step (1) Ball milling and screening of fly ash raw materials: The fly ash is ball milled so that the average particle size of the ball-milled fly ash is <2μm;

[0007] Step (2) Preparation of spray slurry: The fly ash after ball milling, water, inorganic phosphate additives and clay are thoroughly mechanically mixed to obtain spray slurry;

[0008] Step (3) Spray forming: The spray slurry is spray-dried to obtain fly ash hollow microsphere green bodies;

[0009] Step (4) Sintering of fly ash hollow microspheres: Sinter the fly ash hollow microsphere green body to obtain fly ash hollow microspheres.

[0010] As a specific embodiment of the method described above in this invention, in step (1), the fly ash includes, but is not limited to, waste incineration fly ash and coal-fired fly ash.

[0011] As a specific embodiment of the method described above in this invention, in step (1), a high-speed ball mill is used to ball mill the fly ash for 8-12 hours, with a rotation speed of 300-600 r / min. The grinding balls are alumina balls, and the mass ratio of alumina balls, fly ash and water is 2-4:1:1-2, preferably 2:1:2.

[0012] As a specific embodiment of the method described above in this invention, in step (1), after ball milling, a laser particle size analyzer is used to test the particle size distribution of fly ash until the average particle size of the fly ash after ball milling is measured to be <2μm.

[0013] As a specific embodiment of the method described above in this invention, in step (2), the amount of the inorganic phosphate additive is 5-10% of the fly ash mass.

[0014] As a specific embodiment of the method described above in this invention, in step (2), the inorganic phosphate additive includes one or a combination of several of aluminum dihydrogen phosphate, potassium dihydrogen phosphate, and sodium dihydrogen phosphate.

[0015] As a specific embodiment of the method described above in this invention, in step (2), the amount of clay used is 10-15% of the mass of fly ash.

[0016] As a specific embodiment of the method described above in this invention, in step (2), the clay includes clay with a plasticity index greater than 2.5;

[0017] Preferably, the clay includes white clay, etc.

[0018] As a specific embodiment of the method described above in this invention, in step (2), the mass ratio of fly ash and water after ball milling is 1:5-1:3.

[0019] As a specific embodiment of the method described above in this invention, in step (2), the fly ash, water, inorganic phosphate additives and clay after ball milling are fully mechanically mixed in a rotary vane mixer, wherein the rotary vane mixer is set to a speed of 50-100 r / min and a mixing time of 1-3 h.

[0020] As a specific embodiment of the method described above in this invention, in step (3), the spray slurry is fed into the rotating atomizing disc in the spray forming tower through the feeding pipe by the feeding pump, and the hot air generated in the hot air furnace is fed into the spray forming tower through the air supply pipe to spray dry the spray slurry. After the spray drying is completed, fly ash hollow microsphere green blanks are collected through the receiving bin below the spray forming tower.

[0021] As a specific embodiment of the method described above in this invention, in step (3), the feeding speed of the feeding pump is 1-10 kg / min, and / or the rotation speed of the rotating atomizing disc is 200-400 r / min, and / or the airflow rate of the hot air is 500-1000 m³ / min. 3 / h, and / or the spray drying temperature is 150-200℃.

[0022] As a specific embodiment of the method described above in this invention, in step (4), the sintering includes first heating to 500°C at a heating rate of 0.5-1°C / min, then heating to 800-950°C at a heating rate of 2-3°C / min, and holding at 800-950°C for 60-90 minutes.

[0023] As a specific embodiment of the method described above in this invention, in step (4), the sintering is carried out in a muffle furnace.

[0024] The beneficial effects that the method for improving the pelletizing rate of hollow fly ash microspheres provided by this invention can achieve include at least the following:

[0025] The method for improving the pelletizing rate of fly ash hollow microspheres provided by this invention modifies the fly ash raw material with inorganic phosphate and clay before spray drying. By utilizing the high plasticity of clay and the hygroscopic and water-retaining shaping capabilities of inorganic phosphate additives, the viscosity and stability of the spray slurry are improved, thereby increasing the pelletizing rate of fly ash hollow microspheres to 90-95%, which is much higher than that of ordinary hollow microsphere production methods, thus increasing the feasibility of high-value utilization of solid waste fly ash. Detailed Implementation

[0026] It should be noted that the term "comprising" and any variations thereof in the specification and claims of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0027] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0028] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0029] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0030] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0031] In this invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0033] In this embodiment, the process of obtaining the sphericity of fly ash hollow microspheres includes: placing at least 300 fly ash hollow microspheres under an optical microscope for observation, and calculating the sphericity of fly ash hollow microspheres using the following formula 1).

[0034] Spherical formation rate = (1 - number of non-spherical, broken fly ash hollow microspheres / total number of fly ash hollow microspheres in the field of view) × 100% (Formula 1).

[0035] According to a specific embodiment of the present invention, the method for improving the pelletizing rate of fly ash hollow microspheres includes:

[0036] Step (1) Ball milling and screening of fly ash raw materials: The fly ash is ball milled using a high-speed ball mill for 8-12 hours at a speed of 300-600 r / min. The grinding balls are alumina balls, and the mass ratio of alumina balls, fly ash and water is 2:1:2. The fly ash includes, but is not limited to, waste incineration fly ash and coal-fired fly ash. After ball milling, the fly ash particle size distribution is tested using a laser particle size analyzer until the average particle size of the ball-milled fly ash is <2 μm.

[0037] Step (2) Preparation of spray slurry: Weigh the ball-milled fly ash, water, inorganic phosphate additives and clay according to the mass ratio, and put them into a rotary vane mixer for thorough mechanical mixing. Set the speed of the mixer to 50-100 r / min and the mixing time to 1-3 h. After thorough mechanical mixing, the spray slurry is obtained.

[0038] The inorganic phosphate additive is used at 5-10% of the fly ash mass, and the inorganic phosphate additive includes one or a combination of several of aluminum dihydrogen phosphate, potassium dihydrogen phosphate, and sodium dihydrogen phosphate.

[0039] The amount of clay used is 10-15% of the fly ash mass;

[0040] The mass ratio of fly ash to water after ball milling is 1:5 to 1:3.

[0041] Step (3) Spray forming: The mixed material, i.e., the spray slurry, is fed into the rotating atomizing disc in the spray forming tower through the feeding pipe using a feeding pump. The feeding speed is set to 1-10 kg / min, and the rotation speed of the rotating atomizing disc is set to 200-400 r / min. Hot air generated in the hot air furnace is then introduced into the spray forming tower through the air supply pipe to spray dry the spray slurry. The air supply flow rate is 500-1000 m³ / min. 3 / h, the spray drying temperature is set to 150-200℃, and after spray drying, fly ash hollow microsphere green bodies are collected through the receiving hopper below the spray forming tower.

[0042] Step (4) Sintering of fly ash hollow microspheres: The fly ash hollow microsphere green blanks are placed in a muffle furnace for sintering and sintering is completed at a certain sintering temperature regime to obtain the fly ash hollow microspheres.

[0043] The sintering temperature regime includes first heating to 500℃ at a heating rate of 0.5-1℃ / min, then heating to 800-950℃ at a heating rate of 2-3℃ / min, and holding at 800-950℃ for 60-90min.

[0044] The method of this invention can increase the spheroidization rate of fly ash hollow microspheres to 90-95%.

[0045] The technical solution of the present invention will be described in detail below with reference to embodiments and comparative examples.

[0046] Example 1

[0047] This embodiment provides a method for improving the pelletizing rate of hollow fly ash microspheres, which includes the following specific steps:

[0048] Step (1) Ball milling and screening of fly ash raw materials: The fly ash from waste incineration was ball milled using a high-speed ball mill for 8 hours at a speed of 300 r / min. The grinding balls were alumina balls, and the mass ratio of alumina balls, fly ash, and water was 2:1:2. After ball milling, the particle size distribution of the fly ash was tested using a laser particle size analyzer, and the average particle size of the ball-milled fly ash was measured to be 2 μm.

[0049] Step (2) Preparation of spray slurry: Weigh the ball-milled fly ash, water, inorganic phosphate additive and white mud according to the mass ratio, put them into a rotary vane mixer for thorough mechanical mixing to obtain the mixed material, i.e., spray slurry. The mixer speed is set to 50 r / min and the mixing time is 1 h. The inorganic phosphate additive is aluminum dihydrogen phosphate, and the amount added is 5% of the mass of fly ash; the amount of white mud added is 10% of the mass of fly ash; the mass ratio of fly ash to water is 1:5.

[0050] Step (3) Spray forming: The mixed material is fed into the rotating atomizing disc in the spray forming tower through the feeding pipe using a feeding pump. The feeding speed is set to 1 kg / min, and the rotation speed of the rotating atomizing disc is set to 200 r / min. Hot air generated in the hot air furnace is then introduced into the spray forming tower through the air supply pipe to spray dry the mixed material. The air supply flow rate is 500 m³ / min. 3 / h, the spray drying temperature is set to 150℃; after spray drying, fly ash hollow microsphere green bodies are collected through the receiving hopper below the spray forming tower.

[0051] Step (4) Sintering of fly ash hollow microspheres: Place the fly ash hollow microsphere green blanks in a muffle furnace for sintering, and complete the sintering at a certain sintering temperature regime to obtain fly ash hollow microspheres.

[0052] The sintering temperature regime includes first heating to 500°C at a heating rate of 1°C / min, then heating to 950°C at a heating rate of 3°C / min, and holding at 950°C for 60 min.

[0053] The sphericity of the fly ash hollow microspheres obtained in this embodiment is 90%.

[0054] Example 2

[0055] This embodiment provides a method for improving the pelletizing rate of hollow fly ash microspheres, which includes the following specific steps:

[0056] Step (1) Ball milling and screening of fly ash raw materials: The fly ash from waste incineration was ball milled using a high-speed ball mill for 12 hours at a speed of 600 r / min. The grinding balls were alumina balls, and the mass ratio of alumina balls, fly ash, and water was 2:1:2. After ball milling, the particle size distribution of the fly ash was tested using a laser particle size analyzer, and the average particle size of the ball-milled fly ash was measured to be 0.8 μm.

[0057] Step (2) Preparation of spray slurry: Weigh the ball-milled fly ash, water, inorganic phosphate additive and white mud according to the mass ratio, put them into a rotary vane mixer for thorough mechanical mixing to obtain the mixed material, i.e., spray slurry. The mixer speed is set to 100 r / min and the mixing time is 3 h. The inorganic phosphate additive is potassium dihydrogen phosphate, and the amount added is 10% of the mass of fly ash; the amount of white mud added is 15% of the mass of fly ash; the mass ratio of fly ash to water is 1:3.

[0058] Step (3) Spray forming: The mixed material is fed into the rotating atomizing disc in the spray forming tower through the feeding pipe using a feeding pump. The feeding speed is set to 10 kg / min, and the rotation speed of the rotating atomizing disc is set to 400 r / min. Hot air generated in the hot air furnace is then introduced into the spray forming tower through the air supply pipe to spray dry the mixed material. The air supply flow rate is 1000 m³ / min. 3 / h, the spray drying temperature is set to 200℃; after spray drying, fly ash hollow microsphere green bodies are collected through the receiving bin below the spray forming tower;

[0059] Step (4) Sintering of fly ash hollow microspheres: Place the fly ash hollow microsphere green blanks in a muffle furnace for sintering, and complete the sintering at a certain sintering temperature regime to obtain fly ash hollow microspheres.

[0060] The sintering temperature regime includes first heating to 500°C at a heating rate of 0.5°C / min, then heating to 800°C at a heating rate of 2°C / min, and holding at 800°C for 90 min.

[0061] The sphericity of the fly ash hollow microspheres obtained in this embodiment is 95%.

[0062] Example 3

[0063] This embodiment provides a method for improving the pelletizing rate of hollow fly ash microspheres, which includes the following specific steps:

[0064] Step (1) Ball milling and screening of fly ash raw materials: The fly ash from waste incineration was ball milled using a high-speed ball mill for 10 hours at a speed of 500 r / min. The grinding balls were alumina balls, and the mass ratio of alumina balls, fly ash, and water was 2:1:2. After ball milling, the particle size distribution of the fly ash was tested using a laser particle size analyzer, and the average particle size of the ball-milled fly ash was measured to be 1.5 μm.

[0065] Step (2) Preparation of spray slurry: Weigh the ball-milled fly ash, water, inorganic phosphate additive and white mud according to the mass ratio, put them into a rotary vane mixer for thorough mechanical mixing to obtain the mixed material, i.e., spray slurry. The mixer speed is set to 80 r / min and the mixing time is 2 h. The inorganic phosphate additive is sodium dihydrogen phosphate, and the amount added is 7% of the mass of fly ash; the amount of white mud added is 12% of the mass of fly ash; the mass ratio of fly ash to water is 1:4.

[0066] Step (3) Spray forming: The mixed material is fed into the rotating atomizing disc in the spray forming tower through the feeding pipe using a feeding pump. The feeding speed is set to 5 kg / min, and the rotation speed of the rotating atomizing disc is set to 300 r / min. Hot air generated in the hot air furnace is then introduced into the spray forming tower through the air supply pipe to spray dry the mixed material. The air supply flow rate is 800 m³ / min. 3 / h, the spray drying temperature is set to 185℃; after spray drying, fly ash hollow microsphere green bodies are collected through the receiving hopper below the spray forming tower.

[0067] Step (4) Sintering of fly ash hollow microspheres: Place the fly ash hollow microsphere green blanks in a muffle furnace for sintering, and complete the sintering at a certain sintering temperature regime to obtain fly ash hollow microspheres.

[0068] The sintering temperature regime includes first heating to 500°C at a heating rate of 0.8°C / min, then heating to 900°C at a heating rate of 2°C / min, and holding at 900°C for 90 min.

[0069] The pelletizing rate of the fly ash hollow microspheres obtained in this embodiment is 92%.

[0070] Example 4

[0071] This embodiment provides a method for improving the pelletizing rate of hollow fly ash microspheres, which includes the following specific steps:

[0072] Step (1) Ball milling and screening of fly ash raw materials: The fly ash from waste incineration was ball milled using a high-speed ball mill for 12 hours at a speed of 500 r / min. The grinding balls were alumina balls, and the mass ratio of alumina balls, fly ash, and water was 2:1:2. After ball milling, the particle size distribution of the fly ash was tested using a laser particle size analyzer, and the average particle size of the ball-milled fly ash was measured to be 1.2 μm.

[0073] Step (2) Preparation of spray slurry: Weigh the ball-milled fly ash, water, inorganic phosphate additive and white mud according to the mass ratio, put them into a rotary vane mixer for thorough mechanical mixing to obtain the mixed material, i.e., spray slurry. The mixer speed is set to 70 r / min and the mixing time is 3 h. The inorganic phosphate additive is aluminum dihydrogen phosphate, and the amount added is 8% of the mass of fly ash; the amount of white mud added is 15% of the mass of fly ash; the mass ratio of fly ash to water is 1:5.

[0074] Step (3) Spray forming: The mixed material is fed into the rotating atomizing disc in the spray forming tower through the feeding pipe using a feeding pump. The feeding speed is set to 8 kg / min, and the rotation speed of the rotating atomizing disc is set to 200 r / min. Hot air generated in the hot air furnace is then introduced into the spray forming tower through the air supply pipe to spray dry the mixed material. The air supply flow rate is 600 m³ / min. 3 / h, the spray drying temperature is set to 170℃; after spray drying, fly ash hollow microsphere green bodies are collected through the receiving bin below the spray forming tower;

[0075] Step (4) Sintering of fly ash hollow microspheres: Place the fly ash hollow microsphere green blanks in a muffle furnace for sintering, and complete the sintering at a certain sintering temperature regime to obtain fly ash hollow microspheres.

[0076] The sintering temperature regime includes first heating to 500°C at a heating rate of 1°C / min, then heating to 925°C at a heating rate of 2°C / min, and holding at 925°C for 80 min.

[0077] The pelletization rate of the fly ash hollow microspheres obtained in this embodiment is 94%.

[0078] Comparative Example 1

[0079] This comparative example provides a method for preparing fly ash hollow microspheres, which differs from Example 1 only in that:

[0080] No inorganic phosphate additives or white mud were added in step (2).

[0081] The pelletization rate of the fly ash hollow microspheres obtained in this comparative example was 78%.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing fly ash hollow microspheres, which differs from Example 1 only in that:

[0084] No inorganic phosphate additives were added in step (2).

[0085] The pelletization rate of the fly ash hollow microspheres obtained in this comparative example was 83%.

[0086] Comparative Example 3

[0087] This comparative example provides a method for preparing fly ash hollow microspheres, which differs from Example 1 only in that:

[0088] No white clay was added in step (2).

[0089] The pelletization rate of the fly ash hollow microspheres obtained in this comparative example was 86%.

[0090] The experimental results of Examples 1-4 show that the pelletizing rate of the obtained fly ash hollow microspheres is 90-95%. Compared with Example 1, no inorganic phosphate additives and white mud were added in step (2) of Comparative Example 1, no inorganic phosphate additives were added in step (2) of Comparative Example 2, and no white mud was added in step (2) of Comparative Example 3. The pelletizing rate of the fly ash hollow microspheres obtained by Comparative Examples 1-3 is significantly lower than that of the fly ash hollow microspheres obtained in Example 1.

[0091] In summary, the method for improving the pelletizing rate of hollow fly ash microspheres provided in this embodiment of the invention modifies the fly ash raw material with inorganic phosphate and white mud before spray drying. By utilizing the high plasticity of white mud and the hygroscopic and water-retaining shaping capabilities of inorganic phosphate additives, the viscosity and stability of the spray slurry are improved, thereby increasing the pelletizing rate of hollow fly ash microspheres to 90-95%, which is far higher than that of ordinary hollow microsphere production methods, thus increasing the feasibility of high-value utilization of solid waste fly ash.

[0092] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. A method for improving the pelletizing rate of hollow fly ash microspheres, characterized in that, The method includes: Step (1) Ball milling and screening of fly ash raw materials: The fly ash is ball milled so that the average particle size of the ball-milled fly ash is <2μm; Step (2) Preparation of spray slurry: The fly ash after ball milling, water, inorganic phosphate additives and clay are thoroughly mechanically mixed to obtain spray slurry; Step (3) Spray forming: The spray slurry is spray-dried to obtain fly ash hollow microsphere green bodies; Step (4) Sintering of fly ash hollow microspheres: Sinter the fly ash hollow microsphere green body to obtain fly ash hollow microspheres.

2. The method according to claim 1, characterized in that, In step (1), the fly ash is ball-milled using a high-speed ball mill for 8-12 hours at a speed of 300-600 r / min. The grinding balls are alumina balls, and the mass ratio of alumina balls, fly ash and water is 2-4:1:1-2.

3. The method according to claim 1, characterized in that, In step (2), the amount of the inorganic phosphate additive is 5-10% of the fly ash mass.

4. The method according to claim 1 or 3, characterized in that, In step (2), the inorganic phosphate additive includes one or a combination of several of aluminum dihydrogen phosphate, potassium dihydrogen phosphate, and sodium dihydrogen phosphate.

5. The method according to claim 1, characterized in that, In step (2), the amount of clay used is 10-15% of the mass of fly ash.

6. The method according to claim 1 or 5, characterized in that, The clay includes clay with a plasticity index greater than 2.5; Preferably, the clay includes white clay.

7. The method according to claim 1, characterized in that, In step (2), the mass ratio of fly ash and water after ball milling is 1:5-1:

3.

8. The method according to any one of claims 1, 3, 5 and 7, characterized in that, In step (2), the fly ash, water, inorganic phosphate additives and clay after ball milling are fully mechanically mixed in a rotary vane mixer. The rotary vane mixer is set to a speed of 50-100 r / min and a mixing time of 1-3 h.

9. The method according to claim 1, characterized in that, In step (3), the spray slurry is fed into the rotating atomizing disc in the spray forming tower through the feeding pipe using a feeding pump, and the hot air generated in the hot air furnace is fed into the spray forming tower through the air supply pipe to spray dry the spray slurry. After the spray drying is completed, fly ash hollow microsphere green blanks are collected through the receiving bin below the spray forming tower.

10. The method according to claim 9, characterized in that, The feeding speed of the feeding pump is 1-10 kg / min, and / or the rotation speed of the rotating atomizing disc is 200-400 r / min, and / or the airflow rate of the hot air is 500-1000 m³ / min. 3 / h, and / or the spray drying temperature is 150-200℃.

11. The method according to claim 1, characterized in that, In step (4), the sintering includes first heating to 500°C at a heating rate of 0.5-1°C / min, then heating to 800-950°C at a heating rate of 2-3°C / min, and holding at 800-950°C for 60-90 min.