Unfired aggregate based on ardealite solid waste recycling as well as preparation method and application of unfired aggregate

Abstract

The invention relates to the field of unfired aggregate, in particular to unfired aggregate based on ardealite solid waste recycling, a preparation method and application of the unfired aggregate. The method comprises the following steps: mixing a fertilizer and stearic acid, and extruding into particles; chitosan modification treatment: dissolving the modified chitosan in an acetic acid solution, and adding a plasticizer and a coalescing agent to form an emulsion; chitosan emulsion is uniformly sprayed on the outer layer of the core fertilizer, and is cured to form a compact inner layer film, namely a chitosan coating layer; sulphoaluminate cement, phosphogypsum and nano SiO2 are mixed to form a shell layer material, and cement-based slurry is formed; and spraying cement-based slurry on the surface of the chitosan coating layer, and coating layer by layer through centrifugal force to obtain the aggregate. The method and the aggregate prepared by the method are burning-free, so that the production cost is reduced, the waste utilization of the phosphogypsum is realized, and the nutrient slow release function is improved.

Description

Technical Field

[0001] The present invention relates to the field of unburned aggregates, and in particular to an unburned aggregate based on the resource utilization of phosphogypsum solid waste, a preparation method and an application thereof. Background Art

[0002] Traditional aggregate production has long relied on natural ore mining, resulting in mountain destruction, soil erosion, and a sharp decline in biodiversity, causing irreversible damage to the ecological environment. As high-quality ore resources become increasingly depleted, mining costs continue to rise due to longer transportation distances and environmental restrictions. Although existing sintered aggregate technology can use raw materials such as clay and shale, it needs to be sintered in a high-temperature environment above 1200°C, with energy consumption of more than 80kg of standard coal per ton of product, and is accompanied by large amounts of carbon dioxide, sulfur oxides and dust emissions. This high-carbon, high-pollution process model not only exacerbates the greenhouse effect, but also forms a sharp contradiction with the global green and low-carbon development trend.

[0003] The total amount of phosphogypsum in my country is large, and the annual increase continues to rise. The heavy metals lead and cadmium are easily leached out with rainwater to pollute the soil and groundwater. Traditional treatment processes are mainly landfilled or stored in the open air due to insufficient utilization, which poses environmental safety risks.

[0004] Conventional fertilizers are mostly slow-released through coating or physical mixing. However, the pore structure of the carrier material is uncontrollable, resulting in a mismatch between the nutrient release rate and the needs of the crop during the growth period, which can easily lead to problems such as excessive release in the early stage causing seedling burns and insufficient fertility in the later stage.

[0005] How to comprehensively utilize phosphogypsum to prepare unburned aggregate with nutrient slow-release function remains an urgent problem to be solved. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a fire-free aggregate based on the resource utilization of phosphogypsum solid waste, a preparation method and its application, which realizes the waste utilization of phosphogypsum and reduces the production cost by not burning the aggregate. The aggregate adopts a double-layer slow-release barrier design to improve the nutrient slow-release function.

[0007] The technical solution of the present invention is as follows:

[0008] On the one hand, the present invention provides a method for preparing a burn-free aggregate based on the resource utilization of phosphogypsum solid waste, comprising the following steps:

[0009] (1) mixing the fertilizer and stearic acid and extruding them into granules;

[0010] (2) Chitosan modification: chitosan is added with a cross-linking agent to react and form a three-dimensional network structure;

[0011] (3) dissolving the modified chitosan in an acetic acid solution, adding a plasticizer and a film-forming aid to form an emulsion;

[0012] (4) In step (1), the outer layer of the particles is evenly sprayed with a chitosan emulsion and cured to form a chitosan coating layer.

[0013] (5) Sulfoaluminate cement, phosphogypsum, and nano-SiO₂ are mixed as the shell material and form a cement-based slurry after adding water.

[0014] (6) The cement-based slurry is sprayed on the surface of the chitosan coating layer and wrapped layer by layer through centrifugal force to obtain non-fired aggregates.

[0015] In a further improvement of this solution, in step (1), the fertilizer is a nitrogen-phosphorus-potassium compound fertilizer, the mass of stearic acid is 3-5% of the fertilizer, and the particle size is 1-3 mm.

[0016] In a further improvement of this solution, in step (2), chitosan and a cross-linking agent are treated at 40-50 °C for 20-40 minutes to obtain modified chitosan. The cross-linking agent is glutaraldehyde or epichlorohydrin, and the mass ratio of chitosan to the cross-linking agent is 1:4-1:6.

[0017] In a further improvement of this solution, in step (3), the modified chitosan is dissolved in a 2% acetic acid solution, and monolaurin and propylene glycol are added to form an emulsion with a solid content of 8-14%. The dosage of monolaurin is 1.5-3.5% of the dry basis mass of the modified chitosan, and the dosage of propylene glycol is 2.5-5.5% of the dry basis mass of the modified chitosan.

[0018] In a further improvement of this solution, in step (4), the fertilizer particles obtained in step (1) are evenly sprayed with a chitosan emulsion in a granulator. The dosage of the chitosan emulsion is 10-15% of the weight of the fertilizer particles, and an inner layer film is formed after curing. The rotation speed of the granulator is 40-60 r / min, and the inclination angle is 30-50°.

[0019] In a further improvement of this solution, the weight fractions of each raw material in step (5) are: 30-50 parts of sulfoaluminate cement, 20-40 parts of phosphogypsum, 1-3 parts of nano-SiO₂, the water-cement ratio is 0.1-0.3, and the size of nano-SiO₂ is 10-30 nm.

[0020] In a further improvement of this solution, in step (6), the cement-based slurry is sprayed on the surface of the chitosan coating layer through a granulator. The rotation speed of the granulator is 25-35 r / min, and it is wrapped layer by layer. The aggregate is obtained through curing at room temperature, and the mass of the slow-release fertilizer accounts for 8-15% of the cement-based slurry.

[0021] For a further improvement of this solution, the granulator includes a base, on the surface of which a horizontal frame is fixedly connected. On the surface of the horizontal frame, a first motor is fixedly connected. The output end of the first motor is fixedly connected with a reinforcement base, and on the surface of the reinforcement base, a granulation disc is fixedly connected. On the surface of the base, an extension frame is fixedly connected. On the surface of the extension frame, a mounting plate is fixedly connected. On one side of the surface of the mounting plate, a liquid spraying pipe is fixedly connected, and on the other side of the surface of the mounting plate, a material spraying pipe is fixedly connected. Universal joint pipes are fixedly connected to the tops of the liquid spraying pipe and the material spraying pipe. The bottom end of the liquid spraying pipe is fixedly connected with a nozzle pipe, and several atomizing nozzles are fixedly connected to the surface of the nozzle pipe. A diversion pipe is fixedly connected to the surface of the material spraying pipe, and several blanking heads are fixedly connected to the surface of the diversion pipe.

[0022] On the other hand, the present invention provides the non-fired aggregate obtained by the above method.

[0023] In the third aspect, the present invention provides the application of the above non-fired aggregate in plant growth materials.

[0024] The beneficial effects of the present invention are as follows:

[0025] (1) Sulfoaluminate cement can rapidly form hydration products such as ettringite and aluminosilicate gel through hydration reaction at normal temperature (20 - 30 °C), and the aggregate can be hardened without high-temperature sintering, reducing the production cost. Its early strength develops rapidly, meeting the requirements of aggregate forming. Nano-SiO₂ reacts with the cement hydration product Ca(OH)₂ through the pozzolanic effect to generate C-S-H gel, improving the density of the slurry. At the same time, it acts as a crystal nucleus to promote hydration and accelerate the hardening process at normal temperature. In addition, through centrifugal spraying of the granulator, it is wrapped layer by layer, and the centrifugal force is used to achieve uniform distribution and dense packing of the cement slurry. (2) Trace impurities such as P₂O₅ and F - contained in phosphogypsum (CaSO₄·2H₂O) are solidified through the hydration reaction of calcium sulfoaluminate in sulfoaluminate cement. Phosphogypsum, as an inert filler, can reduce the cement dosage. Its micron-sized particles fill the gaps between cement particles, reducing the porosity, improving the volume stability of the aggregate, and realizing the resource utilization of phosphogypsum waste.

[0026] (3) The double-layer slow-release barrier design is adopted. Inner layer: chitosan membrane - crosslinked chitosan forms a three-dimensional network structure, and monolaurin is used as a hydrophobic plasticizer to reduce the membrane water permeability; Outer layer: cement-based shell - nano-SiO₂ makes the pore size distribution concentrated in 10 - 100 nm, forming a diffusion-controlled release mechanism. In addition, stearic acid forms a hydrophobic layer on the surface of the fertilizer particles, reducing the initial dissolution rate, and forming a multi-level slow-release effect with the shell structure. Based on this, the nutrient slow-release function is improved.

[0027] (4) For crops with a long fertilizer requirement cycle, this aggregate reduces the number of topdressings. Through the above process, the ecological engineering can prepare a coated fertilizer with the advantages of slow release, environmental adaptability and low cost, promoting the green transformation of agriculture; in addition, when used as an aggregate for permeable pavements, the slow-release fertilizer and water retention function cooperate to reduce the maintenance cost. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a schematic diagram of the overall structure of the granulator;

[0030] Figure 2 It is a schematic diagram of the structure of the reinforcement seat of the granulator;

[0031] Figure 3 It is a schematic diagram of the structure of the mounting plate of the granulator;

[0032] Figure 4 It is a schematic diagram of the structure of the atomizing nozzle of the granulator.

[0033] In the figure, 1, base; 2, cross frame; 3, first motor; 4, reinforcement seat; 5, granulating disc; 6, extension frame; 7, mounting plate; 8, liquid spraying pipe; 9, material spraying pipe; 10, universal joint pipe; 11, nozzle pipe; 12, atomizing nozzle; 13, diversion pipe; 14, blanking head; 15, second motor; 16, driving disc; 17, mixing rod; 18, support seat. Detailed Embodiments

[0034] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] Embodiment 1: Preparation of Chitosan Coating

[0036] 1. Pretreatment of Raw Materials and Preparation of Core Fertilizer

[0037] (1) Granulation of Core Fertilizer

[0038] Granulation process: Using a drum granulator, the nitrogen-phosphorus-potassium compound fertilizer (15:15:15) is mixed with stearic acid and then extruded into particles with a particle size of 1 - 3 mm, and pre-dried to a moisture content of ≤3%; the mass of stearic acid is 4% of the fertilizer.

[0039] (2) Chitosan modification treatment

[0040] Crosslinking modification: Chitosan is added with glutaraldehyde as a crosslinking agent and reacted at 50 °C for 30 minutes to form a three-dimensional network structure to delay the degradation rate. The mass ratio of chitosan to the crosslinking agent is 1:5.

[0041] 2. Double-layer coating process design

[0042] (1) Inner layer coating with chitosan

[0043] The modified chitosan is dissolved in a 2% acetic acid solution, and glyceryl monolaurate (plasticizer) and propylene glycol (film-forming aid) are added to form an emulsion (solid content 12%). The dosage of glyceryl monolaurate is 2% of the dry basis mass of the modified chitosan, and the dosage of propylene glycol is 4% of the dry basis mass of the modified chitosan.

[0044] The core fertilizer is evenly sprayed with the chitosan emulsion in the granulator. The dosage of the chitosan emulsion is 12% of the fertilizer weight. After curing, a dense inner layer film is formed. The rotation speed of the granulator is 50 r / min, and the inclination angle is 40°. A dense inner layer film is formed by curing, that is, the chitosan coating layer.

[0045] Example 2:

[0046] 1. Raw material pretreatment and core fertilizer preparation

[0047] (1) Using a drum granulator, the nitrogen-phosphorus-potassium compound fertilizer is mixed with stearic acid and then extruded into particles with a particle size of 1 - 3 mm, and pre-dried to a moisture content of ≤3%; the mass of stearic acid is 3% of the fertilizer.

[0048] (2) Crosslinking modification: Chitosan is added with epichlorohydrin as a crosslinking agent and reacted at 40 °C for 20 minutes to form a three-dimensional network structure to delay the degradation rate. The mass ratio of chitosan to the crosslinking agent is 1:4.

[0049] 2. Double-layer coating process design

[0050] The modified chitosan is dissolved in a 2% acetic acid solution, and glyceryl monolaurate (plasticizer) and propylene glycol (film-forming aid) are added to form an emulsion. The dosage of glyceryl monolaurate is 1.5% of the dry basis mass of the modified chitosan, and the dosage of propylene glycol is 2.5% of the dry basis mass of the modified chitosan.

[0051] The core fertilizer is evenly sprayed with a chitosan emulsion in a granulator. The dosage of the chitosan emulsion is 10% of the fertilizer weight. After curing, a dense inner layer film is formed. The rotation speed of the granulator is 40 r / min, and the inclination angle is 30°. The cured dense inner layer film is the chitosan coating layer.

[0052] Example 3:

[0053] 1. Raw material pretreatment and core fertilizer preparation

[0054] (1) Using a drum granulator, the nitrogen-phosphorus-potassium compound fertilizer and stearic acid are mixed and extruded into particles with a particle size of 1 - 3 mm, and pre-dried to a moisture content of ≤ 3%; the mass of stearic acid is 5% of the fertilizer.

[0055] (2) Crosslinking modification: Chitosan is added with glutaraldehyde as a crosslinking agent and reacted at 50 °C for 40 minutes to form a three-dimensional network structure to delay the degradation rate. The mass ratio of chitosan to the crosslinking agent is 1:6.

[0056] 2. Double-layer coating process design

[0057] The modified chitosan is dissolved in a 2% acetic acid solution, and glycerol monolaurate (plasticizer) and propylene glycol (film-forming aid) are added to form an emulsion. The dosage of glycerol monolaurate is 3.5% of the dry basis mass of the modified chitosan, and the dosage of propylene glycol is 5.5% of the dry basis mass of the modified chitosan.

[0058] The core fertilizer is evenly sprayed with the chitosan emulsion in a granulator. The dosage of the chitosan emulsion is 15% of the fertilizer weight. After curing, a dense inner layer film is formed. The rotation speed of the granulator is 60 r / min, and the inclination angle is 50°. The cured dense inner layer film is the chitosan coating layer.

[0059] Example 4: Verification experiment on the slow-release performance of the chitosan coating layer

[0060] Sample preparation: Take 1.00 g of chitosan-coated fertilizer particles (experimental group) and uncoated particles (the same batch of nitrogen-phosphorus-potassium compound fertilizer, control group), with 3 parallel samples each; place them in 500 mL conical flasks respectively, add 250 mL of leaching solution (pH = 5.0 acetic acid buffer solution), oscillate at a constant temperature of 25 °C (120 rpm), and store in the dark.

[0061] Sampling and analysis: Take 5 mL of the supernatant at 1 h, 6 h, 24 h, 3 d, 7 d, 14 d, and 28 d, and filter through a 0.45 μm filter membrane.

[0062] Nitrogen determination: Using the indophenol blue colorimetric method, determine the concentration of NH4 + -N, and calculate the cumulative release rate. The experimental results are shown in Table 1.

[0063] Table 1

[0064]

[0065] It can be seen from the experiment that the chitosan coating layer can reduce the fertilizer 24h release rate to less than 15% through modification; the parameters of Example 1 are selected for subsequent experiments.

[0066] Example 5: Preparation of unburned aggregate

[0067] Material ratio: 40 parts of sulphoaluminate cement, 20 parts of phosphogypsum, and 2 parts of nano-SiO2 are mixed as shell material, with a water-cement ratio of 0.3.

[0068] Cement-based slurry is sprayed on the surface of the chitosan coating layer, with the mass of the slow-release fertilizer accounting for 10% of the cement-based slurry. The chitosan coating layer is coated layer by layer by centrifugal force (rotation speed 25-35 r / min), and the aggregate is obtained by curing at room temperature.

[0069] Example 6: Plant growth experiment

[0070] Blank control: no fertilizer, total nitrogen content 0g;

[0071] T1 (ordinary fertilizer): uncoated nitrogen, phosphorus and potassium compound fertilizer, total nitrogen content 0.5g;

[0072] T2 (single-layer coating): chitosan-coated fertilizer only (without cement shell), total nitrogen content 0.5 g;

[0073] The other processes are the same as in Example 5.

[0074] Test plants: Chinese cabbage, environmental control: greenhouse conditions (25±3℃, light 12h / d, humidity 60-70%). Place in pots, each pot is filled with 3kg of soil, and 4 seedlings are planted; each treatment is repeated 4 times. Fertilization method: fertilizer / aggregate is evenly mixed into the top 5cm soil. The experimental results are shown in Table 2.

[0075] Table 2

[0076]

[0077] It can be seen from Table 2 that the nitrogen supply capacity of the basic soil of the blank group is limited. The plant heights of T1, T2, and Example 5 are similar, but the weight of the aboveground part is very different, indicating that the ordinary fertilizer of the T1 group is released quickly in the early stage, but insufficient in the later stage, and there is a problem of burning seedlings. The chitosan film of the T2 group delays release and reduces losses. The double-layer slow-release nitrogen utilization rate of Example 5 is improved to synchronize supply and demand. At the same time, the aggregate provides a suitable gap, which has both water permeability and water retention and plant root growth space, which is more suitable for plant growth.

[0078] Embodiment 7:

[0079] Material ratio: 30 parts of sulfoaluminate cement, 20 parts of phosphogypsum, and 1 part of nano-SiO₂ are mixed as the shell material, and the water-cement ratio is 0.1.

[0080] High-pressure spraying: Spray the cement-based slurry on the surface of the chitosan coating layer. The mass of the slow-release fertilizer accounts for 8% of the cement-based slurry, and it is wrapped layer by layer through centrifugal force (rotation speed 25 - 35 r / min), and cured at room temperature to obtain the aggregate. The average above-ground weight measured in the same experiment 6 is 4.5 catties.

[0081] Example 8:

[0082] Material ratio: 50 parts of sulfoaluminate cement, 40 parts of phosphogypsum, and 3 parts of nano-SiO₂ are mixed as the shell material, and the water-cement ratio is 0.3.

[0083] High-pressure spraying: Spray the cement-based slurry on the surface of the chitosan coating layer. The mass of the slow-release fertilizer accounts for 15% of the cement-based slurry, and it is wrapped layer by layer through centrifugal force (rotation speed 25 - 35 r / min), and cured at room temperature to obtain the aggregate. The average above-ground weight measured in the same experiment 6 is 5.1 catties.

[0084] Example 9:

[0085] The granulator of this embodiment includes a base 1. A cross-frame 2 is fixedly connected to the surface of the base 1. A first motor 3 is fixedly connected to the surface of the cross-frame 2. The output end of the first motor 3 is fixedly connected to a reinforcement seat 4. A granulation disk 5 is fixedly connected to the surface of the reinforcement seat 4. An extension frame 6 is fixedly connected to the surface of the base 1. A mounting plate 7 is fixedly connected to the surface of the extension frame 6. A liquid spraying pipe 8 is fixedly connected to one side of the surface of the mounting plate 7. A material spraying pipe 9 is fixedly connected to the other side of the surface of the mounting plate 7. Universal joint pipes 10 are fixedly connected to the tops of the liquid spraying pipe 8 and the material spraying pipe 9. A nozzle pipe 11 is fixedly connected to the bottom end of the liquid spraying pipe 8. Several atomizing nozzles 12 are fixedly connected to the surface of the nozzle pipe 11. A diversion pipe 13 is fixedly connected to the surface of the material spraying pipe 9. Several feeding heads 14 are fixedly connected to the surface of the diversion pipe 13. The base 1 provides support for the entire granulator. The first motor 3 drives the granulation disk 5 to rotate through the reinforcement seat 4. The liquid spraying pipe 8 and the material spraying pipe 9 are connected to external equipment through the universal joint pipes 10, and can spray liquid or material as needed. The atomizing nozzles 12 on the nozzle pipe 11 can evenly spray water, and the feeding heads 14 on the diversion pipe 13 can evenly drop the material into the granulation disk 5, improving the uniformity of granulation, and there is no need for manual operation to add materials and water, saving manpower.

[0086] Support seats 18 are fixedly connected to the surfaces of the nozzle pipe 11 and the diversion pipe 13. The support seats 18 on the surfaces of the nozzle pipe 11 and the diversion pipe 13 play a role in fixing and supporting the nozzle pipe 11 and the diversion pipe 13, ensuring their stability during operation, so as to ensure that water and materials can be accurately sprayed into and dropped into the granulation disk 5.

[0087] The support base 18 is fixedly connected to the lower surface of the mounting plate 7.

[0088] A second motor 15 is fixedly connected to the upper surface of the mounting plate 7.

[0089] The output end of the second motor 15 is fixedly connected to a drive disk 16. The output end of the second motor 15 is connected to the drive disk 16 to transmit the power of the second motor 15 to the drive disk 16, enabling the drive disk 16 to drive stably.

[0090] Several mixing rods 17 are fixedly connected to the lower surface of the drive disk 16. A telescopic stirring rod (not shown in the drawing) is detachably connected to the mixing pipe. The mixing rods 17 on the lower surface of the drive disk 16 stir the materials inside the granulating disk 5 as the drive disk 16 rotates, making the materials fully mixed. The telescopic stirring rod stirs the corner materials as needed.

[0091] The implementation principle of a granulator with a uniform mixing effect in the embodiment of the present application is as follows: First, start the first motor 3. The first motor 3 drives the granulating disk 5 to start rotating through the reinforcement base 4. Open the external feeding device. The materials pass through the spraying pipe 9 and the diversion pipe 13 and are evenly dropped into the granulating disk 5 from the feeding head 14. Then start the second motor 15. The second motor 15 drives the drive disk 16 to rotate. The mixing rods 17 on the lower surface of the drive disk 16 start to stir and mix the materials inside the granulating disk 5. According to the actual requirements of granulation, open the external liquid supply device. The liquid flows out of the liquid supply device and enters the liquid spraying pipe 8. The liquid spraying pipe 8 is connected to the nozzle pipe 11. The liquid flows along the nozzle pipe 11 to the atomizing nozzles 12 connected to its surface. The atomizing nozzles 12 are selected as needed. The atomizing nozzles 12 can evenly spray the liquid into tiny liquid drops. These liquid drops are evenly sprayed into the granulating disk 5. The support base 18 ensures that the nozzle pipe 11 and the diversion pipe 13 will not shake or displace during operation, thus ensuring that the liquid and the materials can be accurately sprayed into and dropped into the granulating disk 5, guaranteeing the smooth progress of the entire granulation process.

[0092] During use, when preparing the chitosan coating layer, the spraying pipe 9 is connected to the fertilizer, and the liquid spraying pipe 8 is connected to the chitosan emulsion. When preparing the non-burned aggregate, the spraying pipe 9 is connected to the chitosan coating layer, and the liquid spraying pipe 8 is connected to the cement-based slurry.

[0093] By setting up the liquid spraying pipe and the material spraying pipe, it is convenient for personnel to add liquid and materials according to requirements. Moreover, the liquid spraying pipe and the material spraying pipe are connected to external equipment through a universal joint pipe, enabling quick connection and also quick disassembly when not in use. The atomizing nozzles on the nozzle pipe can evenly spray the liquid, and the feeding head of the diversion pipe can evenly drop the materials into the granulation pan, improving the uniformity of granulation. At the same time, there is no need for manual operation to add liquid and materials, saving labor. The rotation of the mixing rod in the granulation pan makes the materials mix more evenly, which is beneficial to improving the quality and efficiency of granulation and ensuring stable particle quality.

Claims

1. Preparation method of non-fired aggregate based on resource utilization of phosphogypsum waste, characterized in that: It includes the following steps: (1) Mix the fertilizer with stearic acid and extrude it into granules; (2) Chitosan modification treatment: Add chitosan to the crosslinking agent and react to form a three-dimensional network structure; (3) Dissolve the modified chitosan in acetic acid solution, add plasticizer and film-forming aid to form an emulsion; (4) Uniformly spray the chitosan emulsion on the outer layer of the granules in step (1) and cure to form a chitosan coating layer; (5) Mix calcium sulfoaluminate cement, phosphogypsum, and nano-SiO2 as the shell material, and add water to form a cement-based slurry; (6) Spray the cement-based slurry on the surface of the chitosan coating layer and wrap it layer by layer through centrifugal force to obtain non-burned aggregates.

2. The preparation method of the non-fired aggregate based on the resource utilization of phosphogypsum solid waste according to claim 1, wherein: In the step (1), the fertilizer is a nitrogen-phosphorus-potassium compound fertilizer, the mass of stearic acid is 3-5% of the fertilizer, and the particle size is 1-3 mm.

3. The preparation method of the non-fired aggregate based on the resource utilization of phosphogypsum solid waste according to claim 1, wherein: In the step (2), the chitosan and the crosslinking agent are treated at 40-50 °C for 20-40 minutes to obtain modified chitosan. The crosslinking agent is glutaraldehyde or epichlorohydrin, and the mass ratio of chitosan to the crosslinking agent is 1:4-1:

6.

4. The preparation method of the non-fired aggregate based on the resource utilization of phosphogypsum solid waste according to claim 1, characterized in that: In the step (3), the modified chitosan is dissolved in 2% acetic acid solution, and monolaurin and propylene glycol are added to form an emulsion with a solid content of 8-14%. The dosage of monolaurin is 1.5-3.5% of the dry basis mass of the modified chitosan, and the dosage of propylene glycol is 2.5-5.5% of the dry basis mass of the modified chitosan.

5. The preparation method of the non-fired aggregate based on the resource utilization of phosphogypsum solid waste according to claim 1, characterized in that: In the step (4), the fertilizer granules obtained in step (1) are uniformly sprayed with the chitosan emulsion in a granulator. The dosage of the chitosan emulsion is 10-15% of the weight of the fertilizer granules. After curing, an inner layer film is formed. The rotation speed of the granulator is 40-60 r / min, and the inclination angle is 30-50°.

6. The preparation method of the non-fired aggregate based on the resource utilization of phosphogypsum solid waste according to claim 1, wherein: In the step (5), the weight fractions of each raw material are: 30-50 parts of calcium sulfoaluminate cement, 20-40 parts of phosphogypsum, 1-3 parts of nano-SiO2, the water-cement ratio is 0.1-0.3, and the size of nano-SiO2 is 10-30 nm.

7. The preparation method of the non-fired aggregate based on the resource utilization of phosphogypsum solid waste according to claim 1, characterized in that: In the step (6), the cement-based slurry is sprayed on the surface of the chitosan coating layer through a granulator. The rotation speed of the granulator is 25-35 r / min, and it is wrapped layer by layer. After curing at room temperature, aggregates are obtained. The mass of the slow-release fertilizer accounts for 8-15% of the cement-based slurry.

8. The preparation method of the non-fired aggregate based on the resource utilization of phosphogypsum solid waste according to claim 1, characterized in that, The granulator includes a base (1), a cross frame (2) is fixedly connected to the surface of the base (1), an extension frame (6) is fixedly connected to the surface of the base (1), a mounting plate (7) is fixedly connected to the surface of the extension frame (6), a liquid spraying pipe (8) is fixedly connected to one side of the surface of the mounting plate (7), a material spraying pipe (9) is fixedly connected to the other side of the surface of the mounting plate (7), and a universal joint pipe (10) is fixedly connected to the top ends of the liquid spraying pipe (8) and the material spraying pipe (9).

9. The non-burned aggregate obtained by the method according to any one of claims 1-8.

10. The application of the non-burned aggregate according to claim 9 in plant growth materials.

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