Calcium superphosphate granules with good stability and preparation method thereof
Through chemical modification and physical envelope combination, superphosphate particles with good stability were prepared, which solved the problems of moisture absorption and agglomeration and phosphorus fixation in traditional powdered superphosphate, and achieved particle stability and phosphorus utilization in high humidity environments.
Patent Information
- Application Number
- CN202510794434.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-13
- Publication Date
- 2025-08-08
AI Technical Summary
Traditional powdered superphosphate is prone to moisture absorption and agglomeration, and after application to the soil, it is easy to react with calcium, iron, and aluminum plasma to form insoluble phosphates, resulting in phosphorus fixation and low utilization.
The method of combining chemical modification (humidic acid-montmorillonite) with physical envelope (bio-based polyurethane) is used to prepare the calcium superphosphate particles with good stability. Through the synergy between the modified core and the envelope layer, a chemically stable network is formed to prevent moisture absorption and agglomeration and regulate nutrient release.
Leave it in an environment with a humidity of 75% for 7 days, the moisture absorption rate is less than 1.5%, the compressive strength of the particles is ≥15N/pellet, and the pH is stable between 4.5 and 5.5, reducing the fixed loss of phosphorus in the soil and meeting the requirements of mechanized fertilization.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of fertilizers, and more particularly to a superphosphate granule with good stability and a preparation method thereof. Background Art
[0002] Superphosphate is a fast-acting phosphate fertilizer with monocalcium phosphate (Ca(H2PO4)2) and calcium sulfate (CaSO4) as its main ingredients. It is produced by reacting phosphate rock powder with sulfuric acid. Its effective phosphorus content (calculated as P2O5) is usually 12%-20%. It has both water-soluble and citrate-soluble phosphorus forms. It is suitable for directly providing phosphorus nutrition to crops in acidic or neutral soils. It also contains secondary elements such as sulfur and calcium. As a traditional phosphate fertilizer, superphosphate has long had the following problems: powdered superphosphate produced by traditional technology easily absorbs moisture and clumps, and after being applied to the soil, it easily reacts with calcium, iron, aluminum and other ions to form insoluble phosphates, resulting in phosphorus fixation and an utilization rate of only 10%-15%. Summary of the Invention
[0003] In order to overcome the deficiencies of the prior art, the present invention provides a superphosphate granule with good stability and a preparation method thereof. The prepared superphosphate granule meets the requirements of mechanized fertilization and can reduce the fixed loss of phosphorus in the soil.
[0004] The technical solution adopted by the present invention to solve its technical problem is: The first object of the present application is to provide a superphosphate granule with good stability, comprising: a modified core material and a coating layer coated on the modified core material; The raw materials for forming the modified core material include the following components: Phosphate rock 50-70 parts; Sulfuric acid, the molar amount of phosphorus in phosphate rock and the molar amount of sulfuric acid are in a ratio of 1:2-1:3; 0.2-0.4 parts of anionic polyacrylamide; 100-200 parts water; 3-5 parts humic acid 2-3 parts montmorillonite 1-2 parts of diatomaceous earth.
[0005] Optionally, the coating solution for forming the coating layer includes the following components: 50-60 parts of apple tree branch liquefied matter 20-50 parts castor oil 15-20 parts of diisocyanate 3-5 parts of silicon dioxide 1-2 parts of coupling agent.
[0006] Optionally, the content of P2O5 in the phosphate rock is 22%-25%; And / or, the particle size of the phosphate rock is 20-30 mesh; And / or, the particle size of the montmorillonite is 50nm-100nm; And / or, the particle size of the diatomaceous earth is 10 μm-20 μm.
[0007] Optionally, the preparation process of the modified core material includes: The phosphate rock is dispersed in water, sulfuric acid is added according to a molar ratio and mixed, and dissolved to form a mixed liquid; anionic polyacrylamide is added, stirred and mixed to form flocs, and the flocs are filtered out to obtain a monocalcium phosphate liquid; adding humic acid, montmorillonite, and diatomaceous earth to the monocalcium phosphate solution in sequence and mixing them thoroughly to form a modified mixture; The modified mixture is extruded into granules and dried to obtain a modified core material.
[0008] Optionally, the moisture content of the modified core material is less than 2%; And / or, the particle size of the modified core material is 2 mm to 5 mm.
[0009] Optionally, the thickness of the envelope layer is 15 μm-25 μm.
[0010] Optionally, the silica has a particle size of 10 nm to 30 nm; Optionally, filter out the flocs with a filter cloth having a mesh size of 20.
[0011] And / or, the coupling agent is a silane coupling agent.
[0012] Optionally, the coating solution for forming the coating layer is prepared by: The apple tree branch liquefied material, castor oil and diisocyanate are mixed, nano silicon dioxide and a coupling agent are added, and the mixture is fully stirred to form a coating liquid.
[0013] The second object of the present application is to provide a method for preparing the above-mentioned superphosphate particles, comprising the following steps: The modified core material is added into a fluidized bed, and a coating liquid is sprayed to form a coating layer to obtain superphosphate particles.
[0014] Optionally, during the process of spraying the coating liquid, the coating weight gain rate is controlled at 3% to 5%.
[0015] The beneficial effects of this application are: 1. This application solves the moisture absorption and slow-release problems of traditional phosphate fertilizers by combining chemical modification (humic acid-montmorillonite) with physical coating (bio-based polyurethane).
[0016] 2. This application uses apple tree branch liquefied material to replace petroleum-based materials to reduce the cost of coating.
[0017] 3. The superphosphate granules prepared in this application, when placed in a humidity environment of 75% for 7 days, have a moisture absorption rate of less than 1.5% and a granule compressive strength of ≥15N / granule, meeting the requirements of mechanized fertilization; and the pH is stable at 4.5-5.5, reducing the fixed loss of phosphorus in the soil. DETAILED DESCRIPTION
[0018] In order to facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the embodiments. The contents mentioned in the embodiments are not intended to limit the present invention.
[0019] As used herein, "and / or" includes the term of any and all combinations of one or more of the associated listed items. The terms used herein are only used to describe specific embodiments and are not intended to limit the invention. As used herein, the singular forms "a", "an", "an" and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. It is further understood that "including", when used in this specification, specifies the stated features, integers, steps, operations, elements and / or components, but does not preclude the existence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.
[0020] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It is further understood that terms, such as those defined in commonly used dictionaries, are interpreted in accordance with their meanings in the context of the relevant art and are not idealized or overly formalized unless expressly defined otherwise herein.
[0021] The exemplary inventions described herein may suitably lack any one or more element limitations not specifically disclosed herein. Therefore, terms such as "comprises," "includes," "contains," and the like should be understood broadly and non-restrictively. In addition, the terminology used herein is used as a description, not a limitation, and it is unintentional to use these terminology expressions that do not include any equivalent characteristics, but only describe a portion of their characteristics, but various modifications are possible within the scope of the invention according to the rights. Therefore, although the present invention has been specifically disclosed through preferred embodiments and optional features, the modifications disclosed herein to embody the changes of the invention may be recorded by those skilled in the art, and such modifications and changes will be considered to be within the scope of the invention.
[0022] The raw material or reagent used in the embodiments of the present invention and the comparative example are all purchased from the market mainstream manufacturers, and the manufacturer or concentration are not specified. They are all the raw material or reagent of the analytical grade that can be conventionally obtained. As long as the desired effect can be achieved, there are no particular restrictions. The instrument and equipment used in the present embodiment are all purchased from the main manufacturers in the market. As long as the desired effect can be achieved, there are no particular restrictions. In the present embodiment, the specific technology or conditions are not specified. The technology or conditions described in the document in this area or the product specification are carried out.
[0023] In order to solve the problems of traditional products being prone to moisture absorption and agglomeration, water-soluble phosphorus being easily fixed by the soil, and concentrated nutrient release, the present application provides a superphosphate granule with good stability, comprising: a modified core material and a coating layer coated on the modified core material; The raw materials for forming the modified core material include the following components: Phosphate rock 50-70 parts; Sulfuric acid, the molar amount of phosphorus in phosphate rock and the molar amount of sulfuric acid are in a ratio of 1:2-1:3; 0.2-0.4 parts of anionic polyacrylamide; 100-200 parts water; 3-5 parts humic acid 2-3 parts montmorillonite 1-2 parts of diatomaceous earth.
[0024] In some specific embodiments, the content of P2O5 in the phosphate rock is 22%-25%. In the present application, low-quality phosphate rock is used as the basic phosphorus source. By utilizing low-quality phosphate rock to prepare superphosphate particles, production costs are reduced and resources are fully utilized.
[0025] In some examples, the particle size of the phosphate rock is 20-30 mesh, for example, 20 mesh, 22 mesh, 25 mesh, and 30 mesh; the weight of the phosphate rock is 50-70 parts, for example, 50 parts, 55 parts, 60 parts, 65 parts, 66 parts, and 70 parts.
[0026] In some examples, sulfuric acid is concentrated sulfuric acid with a mass concentration of 98% to decompose the phosphate rock to produce monocalcium phosphate and calcium sulfate. The molar ratio of phosphorus in the phosphate rock to the molar amount of sulfuric acid is 1:2-1:3, which is sufficient to decompose the phosphate rock.
[0027] In some embodiments, humic acid can chelate metal ions, reduce phosphorus fixation, and improve soil structure. The weight of humic acid can be 3 parts, 4 parts, or 5 parts.
[0028] In some embodiments, the montmorillonite has a particle size of 50 nm to 100 nm, and the nanosheet structure absorbs nutrients, thereby improving the particle's compressive strength and moisture absorption resistance. The montmorillonite particle size can be 50 nm, 60 nm, 90 nm, or 100 nm.
[0029] In some specific embodiments, the particle size of the diatomaceous earth is 10 μm-20 μm, and the porous structure adjusts the phosphorus release rate and enhances air permeability.
[0030] In some embodiments, the preparation process of the modified core material comprises: The phosphate rock is dispersed in water, sulfuric acid is added according to a molar ratio and mixed, and dissolved to form a mixed liquid; anionic polyacrylamide is added, stirred and mixed to form flocs, and the flocs are filtered out to obtain a monocalcium phosphate liquid; adding humic acid, montmorillonite, and diatomaceous earth to the monocalcium phosphate solution in sequence and mixing them thoroughly to form a modified mixture; The modified mixture is extruded into granules and dried to obtain a modified core material.
[0031] Exemplarily, the preparation process of the modified core material comprises the following steps: Step 1: Acid hydrolysis Prepare the materials according to the raw material composition of the modified core material; disperse the phosphate rock powder into the water Concentrated sulfuric acid was added according to the molar ratio and mixed, and the temperature was raised to 60°C to 80°C in the reactor. The mixture was stirred and reacted for 5 to 6 hours to generate a mixed liquid.
[0032] Step 2: Flocculation Filtration The mixed liquid was cooled to 40-50°C, anionic polyacrylamide was added, and the mixture was stirred and mixed for 2-3 hours to form flocs. The flocs were filtered out using a 20-mesh filter cloth to obtain a monocalcium phosphate liquid.
[0033] Step 3: Composite modification Humic acid, montmorillonite and diatomaceous earth were added to the monocalcium phosphate solution in sequence, the temperature was maintained at 50°C to 60°C, and the mixture was stirred for 30 minutes to form a mixed solution.
[0034] Step 4: Granulation and Drying The mixture liquid is formed into particles (particle size 2mm~5mm) by an extrusion granulator, and dried at 100℃~120℃ until the moisture content is less than 2% to form a modified core material.
[0035] In the present application, the raw material composition and preparation process of the modified core material are as follows: phosphate rock reacts with sulfuric acid to generate phosphoric acid and calcium sulfate, and phosphoric acid further reacts with calcium sulfate to form monocalcium phosphate; anionic polyacrylamide, through charge neutralization and bridging effects, causes colloidal impurities (such as silicates and metal hydroxides) in the reaction solution to form flocs, which are removed by filtration through a 20-mesh filter cloth, thereby improving the purity of monocalcium phosphate and reducing ineffective components; humic acid reacts with the Ca in superphosphate through carboxyl groups and phenolic hydroxyl groups. 2+ It forms chelates to inhibit the growth of calcium phosphate crystals. At the same time, the nanosheet structure of montmorillonite fixes phosphate through electrostatic adsorption and interlayer ion exchange, reducing the chemical fixation of phosphorus in the soil; the porous structure of diatomaceous earth adsorbs free water and reduces the humidity inside the particles. The three work together to form a chemically stable network to prevent moisture absorption and agglomeration.
[0036] In some specific implementation methods, the coating solution for forming the coating layer includes the following components: 50-60 parts of apple tree branch liquefied matter 20-50 parts castor oil 15-20 parts of diisocyanate 3-5 parts of silicon dioxide 1-2 parts of coupling agent.
[0037] In this application, apple tree branch liquefaction, containing bio-based polyols, provides a film-forming skeleton; castor oil acts as a plasticizer to improve the flexibility and hydrophobicity of the film; diisocyanate acts as a cross-linking agent to solidify the film; silica enhances the mechanical strength and aging resistance of the film, and a coupling agent can improve the inorganic-organic interface compatibility.
[0038] In some examples, the silica has a particle size of 10 nm to 30 nm; In some examples, the coupling agent is a silane coupling agent, such as γ-aminopropyltriethoxysilane.
[0039] In some examples, the coating solution for forming the coating layer is prepared by: The apple tree branch liquefied material, castor oil and diisocyanate are mixed, nano silicon dioxide and a coupling agent are added, and the mixture is fully stirred to form a coating liquid.
[0040] Exemplary, a method for preparing a coating solution for the coating layer comprises the following steps: Step 1: Liquefactant Preparation The apple tree branches were crushed and passed through a 60-mesh sieve, mixed with ethylene glycol / polyethylene glycol at a solid-liquid ratio of 1:3, and 1% sulfuric acid catalyst was added. The mixture was liquefied at 140-150°C under normal pressure for 60-80 minutes to obtain hydroxyl-containing bio-based polyols.
[0041] Step 2: Coating solution preparation Mix apple tree branch liquefaction, castor oil, and isocyanate in proportion, add nano-silica and coupling agent, and stir at 50-60°C for 30 minutes to form a uniform coating liquid. The method for preparing the superphosphate granules comprises the following steps: The modified core material is added into a fluidized bed, and a coating liquid is sprayed to form a coating layer to obtain superphosphate particles.
[0042] In some cases, the modified core material is added to a fluidized bed, hot air preheated to 50°C is introduced (flow rate 1.5-2.0 m / s), and the coating liquid is sprayed (atomization pressure 0.3-0.5 MPa). The coating weight gain rate is controlled at 3%-5%, forming a continuous coating layer with a thickness of 15-25 μm.
[0043] In this application, the polyols in the liquefied apple tree branches and castor oil are cross-linked through diisocyanate to form a polyurethane network structure, and nano-silica is evenly dispersed in the membrane layer through a coupling agent to form a "microporous barrier" to regulate the nutrient release rate; the coating layer isolates the external moisture intrusion, and at the same time, the bio-based material can be gradually degraded under the action of soil microorganisms, and the released small molecules (such as humic acid derivatives) further promote the activation of soil nutrients.
[0044] Example 1 A superphosphate granule with good stability comprises: a modified core material and a coating layer coated on the modified core material; The raw materials for forming the modified core material include the following components: 50 parts of phosphate rock (P2O5 content 22%); Sulfuric acid, the ratio of the molar amount of phosphorus in phosphate rock to the molar amount of sulfuric acid is 1:2; 3 parts of humic acid; 2 parts of montmorillonite; 1 part diatomaceous earth; 100 parts water; 0.2 parts of anionic polyacrylamide.
[0045] The preparation process of the modified core material comprises the following steps: Step 1: Acid hydrolysis According to the raw material composition of the modified core material, the materials are prepared; the phosphate rock powder is dispersed in water, concentrated sulfuric acid is added according to the molar ratio, the mixture is heated to 60° C. in a reactor, and stirred for reaction for 5 hours to generate a mixed liquid.
[0046] Step 2: Flocculation Filtration The mixed liquid was cooled to 40° C., anionic polyacrylamide was added, and the mixture was stirred and mixed for 2 hours to form flocs. The flocs were filtered out using a 20-mesh filter cloth to obtain a monocalcium phosphate liquid.
[0047] Step 3: Composite modification Humic acid, montmorillonite and diatomaceous earth were added to the monocalcium phosphate solution in sequence, the temperature was maintained at 50° C., and the mixture was stirred for 30 minutes to form a mixed solution.
[0048] Step 4: Granulation and Drying The mixture liquid is formed by an extrusion granulator (the particle size is controlled at 2-5 mm), and dried at 100°C to a moisture content of less than 2% to form a modified core material.
[0049] The coating solution for forming the coating layer comprises the following components: 50 parts of apple tree branch liquefied matter 20 parts castor oil 15 parts of diisocyanate 3 parts of silicon dioxide 1 part coupling agent.
[0050] The method for preparing the coating liquid of the coating layer comprises the following steps: Step 1: Liquefactant Preparation Apple tree branches were crushed and passed through a 60-mesh sieve, mixed with ethylene glycol / polyethylene glycol at a solid-liquid ratio of 1:3 to obtain a mixed liquid; sulfuric acid (98% by mass) was added as a catalyst at 1% by mass of the mixed liquid, and liquefied at normal pressure at 140°C for 80 minutes to obtain an apple tree branch liquefied product.
[0051] Step 2: Coating solution preparation Mix apple tree branch liquefaction, castor oil, and diisocyanate in proportion, add nano-silica and coupling agent, and stir at 50-60°C for 30 minutes to form a uniform coating liquid. The preparation method of superphosphate granules comprises the following steps: The modified core material is added to the fluidized bed, hot air preheated to 50°C is introduced (the flow rate is controlled at 1.5~2.0 m / s), the coating liquid is sprayed (atomization pressure 0.3MPa), the coating weight gain rate is controlled at 3%, and a continuous coating layer with a thickness controlled at 15~25μm is formed.
[0052] The specific raw material compositions and preparation processes of Examples 2 to 10 and Comparative Examples 1 to 5 were designed and adjusted according to the contents of Table 1 below, and the rest were consistent with Example 1.
[0053] Table 1 In Examples 4, 6, and 8, 70 parts of phosphate rock and 200 parts of water were used.
[0054] The superphosphates of the examples and comparative examples were tested according to the following test items. The test results are summarized in Table 2.
[0055] 1. Stability testing 1. Anti-moisture absorption Test method: Place the sample in a constant temperature and humidity chamber (temperature 25°C, humidity 75% RH) for 7 days, and measure the mass change before and after.
[0056] Calculation method: Moisture absorption rate = (mass after moisture absorption - mass before moisture absorption) / mass before moisture absorption.
[0057] Standard basis (for reference): Refer to GB / T 8573-2017, which requires a moisture absorption rate of less than 1.5%.
[0058] 2. Compressive strength Testing method: Use a particle strength tester to randomly select 50 particles, apply pressure to each particle until they break, and record the peak pressure.
[0059] Standard basis (for reference): GB / T 24890-2010, requirement ≥15N / piece.
[0060] 3. Chemical stability (pH value) Detection method: Weigh 5g of sample, dissolve it in 50mL of deionized water, stir for 30min, let it stand, and measure the pH of the supernatant with a pH meter.
[0061] 2. Nutrient slow-release performance test 1. Phosphorus release rate Detection method: Using the water solubility method, weigh 2g of sample and place it in a nylon mesh bag, immerse it in 200mL of deionized water (constant temperature and oscillation at 25℃), collect the supernatant at 1, 3, 7, 14, and 28 days, and determine the phosphorus content using the molybdenum antimony colorimetric method.
[0062] Calculation method: Cumulative release rate = dissolved phosphorus amount at each time point / total phosphorus amount Standard basis (for reference): GB / T 23348-2009 "Slow-release fertilizers", which requires that the cumulative release rate over 28 days be ≤75%.
[0063] 3. Environmental protection and soil improvement effect testing 1. Encapsulation degradation rate Detection method: Use the soil burial method to bury the coated samples in farmland soil (humidity 60% field water holding capacity, constant temperature 25℃), take them out and weigh them regularly, and calculate the weight loss rate.
[0064] Calculation method: Degradation rate = (initial mass - residual mass) / initial mass.
[0065] 2. Soil porosity Testing method: Soil bulk density is measured using the knife ring method and porosity is calculated (the soil density is 2.65 g / cm³ and the bulk density is measured using the knife ring sampling and drying method) Standard basis (for reference): GB / T 22105.1-2008 "Soil quality - Determination of soil porosity - Ring knife method" 4. Yield increase and nitrogen efficiency testing 1. Field trial design Test group: superphosphate of Example and Comparative Example, with equal nutrient application amount.
[0066] Measurement indicators: Grain number per ear: 20 plants were randomly selected at maturity and the number of grains per ear was counted; Nitrogen fertilizer utilization rate: calculated by subtraction method, formula: Nitrogen fertilizer utilization rate = nitrogen absorption of crops in the fertilization area / nitrogen application amount.
[0067] Standard basis (for reference): NY / T 497-2002 "Technical Procedures for Field Tests for Fertilizer Effect Identification", which requires a 10%~15% increase in yield per mu and a 15%~20% increase in nitrogen fertilizer utilization rate.
[0068] 5. Other key tests 1. Available phosphorus content (P2O5) Detection method: The quinoline phosphomolybdic acid weight method is used. After the sample is acid-hydrolyzed, phosphorus is precipitated with quinomolybdate reagent and the available phosphorus content is calculated by weighing.
[0069] Standard basis (for reference): GB / T 20413-2017 "Superphosphate", requirement ≥32%.
[0070] Table 2 As shown in Table 2, the following improvements were achieved by optimizing the component ratios and process parameters through the synergistic effect of the chemically modified core (humic acid + montmorillonite + diatomaceous earth) and the bio-based coating layer (liquefied apple tree branches + castor oil + nano-silica). 1. Significantly improved moisture absorption resistance The moisture absorption resistance of Examples 1-10 is all less than 1.5%, while the moisture absorption resistance of Comparative Examples 1-8 is generally greater than 2% (even as high as 8.5%).
[0071] Reason: In this application, the coating layer (bio-based polyurethane + nano-silica) forms a hydrophobic barrier to block moisture intrusion; the porous structure of diatomaceous earth absorbs internal free water and reduces the humidity of the particles.
[0072] 2. The compressive strength meets the requirements of mechanized fertilization The compressive strength of the embodiment is ≥15N / particle (maximum 18.1N), while the strength of the uncoated particles or particles with process defects in the comparative example is <15N.
[0073] Reason: The chemical modification of humic acid-montmorillonite enhances the structural stability of the core material; the diisocyanate in the coating liquid cross-links to form a rigid network, which improves the mechanical strength of the particles.
[0074] 3. Stable pH value (4.5-5.5) reduces phosphorus fixation The pH value of the examples was 4.5-5.5, while the pH value of the comparative examples was generally >5.3 (even up to 6.2).
[0075] Reason: The carboxyl and phenolic hydroxyl groups of humic acid form chelates with Ca²+, inhibiting the growth of calcium phosphate crystals and maintaining an acidic environment; the interlayer ion exchange of montmorillonite reduces the release of alkaline substances.
[0076] 4. Excellent sustained-release performance (phosphorus release rate ≤ 72% in 28 days) The phosphorus release rate of the embodiment over 28 days is 60%-72%, while that of the comparative example is as high as 83%-94%.
[0077] Reason: In this application, the nutrient release rate is regulated by the microporous structure formed by the coating layer; the chemical adsorption of humic acid and montmorillonite delays the diffusion of phosphorus.
[0078] 5. Significant environmental protection and soil improvement effects The degradation rate of the coating in the embodiment is 80%-88% (only 35%-81% in the comparative example), and the bio-based material can be naturally degraded.
[0079] The soil porosity of the embodiment is increased by 4%-7% (only 1.5%-4% in the comparative example), and the porous structure of diatomaceous earth improves the air permeability of the soil.
[0080] The yield per mu of the embodiment increased by 12%-14% (only 3%-8% in the comparative example), and the humic acid derivatives promoted root development and nutrient absorption.
[0081] Comparative analysis of the results: Comparative Example 1 (uncoated), moisture absorption resistance: 8.5% (far exceeding the standard 1.5%), compressive strength: 8.2N / piece (far below 15N / piece), 28-day phosphorus release rate: 92% (fast-acting but easy to lose), pH value: 6.2 (alkaline, promotes phosphorus fixation); Comparative Example 1 lacks a coating layer and a hydrophobic barrier, leaving the particles directly exposed to the environment and causing them to absorb moisture and clump. The lack of mechanical protection also makes the particles fragile. The lack of a coating results in rapid phosphorus release, resulting in low utilization rates, and the alkaline environment exacerbates phosphorus fixation.
[0082] Comparative Example 2 (without apple tree branch liquefied material) Moisture absorption resistance: 4% (not up to standard) Compressive strength: 12.5N / piece (close to but lower than the standard) Phosphorus release rate in 28 days: 85% (released too quickly) In Comparative Example 2, the coating framework was missing. The bio-based polyol film-forming framework provided by the liquefied apple tree branches resulted in an incomplete coating structure, insufficient hydrophobicity and mechanical strength. Release control failed, and the incomplete coating accelerated phosphorus diffusion.
[0083] Comparative Example 3 (no anionic polyacrylamide), moisture absorption resistance: 5.2% (not up to standard); Compressive strength: 10.3N / piece (lower than standard); Available phosphorus content: 28.8% (significantly lower than 33%+ in the example); In Comparative Example 3, flocculation and filtration were missing: anionic polyacrylamide removes impurities (such as silicates and metal hydroxides) through flocculation. This omission resulted in a high concentration of impurities in the core material, reducing purity and stability. Impurities interfered with particle formation, resulting in insufficient mechanical strength.
[0084] Comparative Example 4 (no apple branch liquefied material + no anionic polyacrylamide): moisture absorption resistance: 6.8% (not up to standard), compressive strength: 9.5N / piece (significantly below standard), 28-day phosphorus release rate: 94% (fast-acting but easy to lose); Comparative Example 4 lacked both a coating skeleton (liquefied apple tree branches) and flocculation filtration (anionic polyacrylamide), resulting in a high concentration of impurities within the particles and a lack of a coating structure, which reduced their hygroscopicity and strength. The coating completely failed, leading to rapid phosphorus release.
[0085] Comparative Example 5 (without diisocyanate): compressive strength: 14.1N / particle (close to the standard but poor stability), 28-day phosphorus release rate: 78% (released too quickly), pH value: 5.3 (alkaline, promoting phosphorus fixation); In Comparative Example 5, the absence of diisocyanate as the coating crosslinker resulted in the polyurethane network not curing, making the film flexible but easily ruptured, and the release control ineffective. The lack of humic acid-montmorillonite synergy resulted in insufficient core acidity, leading to an increase in pH.
[0086] Comparative Example 6 (without silicon dioxide), moisture absorption resistance: 2.8% (meets the standard but better than the example), compressive strength: 13.2N / piece (lower than the standard), Phosphorus release rate in 28 days: 75% (released too quickly); In Comparative Example 6, silicon dioxide is a nano-reinforcer, and its absence leads to a decrease in the mechanical strength of the film layer and brittle particles; the microporous structure of silicon dioxide regulates the release rate, and the release is accelerated after its absence.
[0087] Comparative Example 7 (without coupling agent): moisture absorption resistance: 2.5% (meets the standard but slightly worse), compressive strength: 12.8N / piece (below the standard), 28-day phosphorus release rate: 73% (released too quickly); In Comparative Example 7, the coupling agent (silane coupling agent) improves the inorganic-organic interface bonding, but its absence leads to weak adhesion between the coating layer and the core material, and the film layer is easy to fall off; the interface defects lead to decreased integrity of the coating and failure of release control.
[0088] Comparative Example 8 (without flocculation and filtration), poor results: moisture absorption resistance: 6.0% (not up to standard), available phosphorus content: 22.4% (significantly lower than 33%+ in Example), 28-day phosphorus release rate: 83% (released too quickly); In Comparative Example 8, the absence of filtration resulted in colloidal impurities (such as silicates and metal hydroxides) remaining in the core material, reducing the purity of the monocalcium phosphate. The impurities interfered with particle formation, resulting in poor hygroscopicity and release properties.
[0089] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious replacement without departing from the concept of the present invention is within the scope of protection of the present invention.
Claims
1. A superphosphate granule with good stability, characterized in that: include: A modified core material and a coating layer coated on the modified core material; The raw materials for forming the modified core material include the following components: Phosphate rock 50-70 parts; Sulfuric acid, the molar amount of phosphorus in phosphate rock and the molar amount of sulfuric acid are in a ratio of 1:2-1:3; 0.2-0.4 parts of anionic polyacrylamide; 100-200 parts water; 3-5 parts of humic acid; 2-3 parts of montmorillonite; 1-2 parts of diatomaceous earth.
2. Superphosphate granules according to claim 1, characterized in that The coating solution for forming the coating layer comprises the following components: 50-60 parts of apple tree branch liquefied matter 20-50 parts castor oil 15-20 parts of diisocyanate 3-5 parts of silicon dioxide 1-2 parts of coupling agent.
3. Superphosphate granules according to claim 1, characterized in that The content of P2O5 in the phosphate rock is 22%-25%; And / or, the particle size of the phosphate rock is 20-30 mesh; And / or, the particle size of the montmorillonite is 50nm-100nm; And / or, the particle size of the diatomaceous earth is 10 μm-20 μm.
4. The superphosphate granules according to claim 1, wherein The preparation process of the modified core material comprises: The phosphate rock is dispersed in water, sulfuric acid is added according to a molar ratio and mixed, and dissolved to form a mixed liquid; anionic polyacrylamide is added, stirred and mixed to form flocs, and the flocs are filtered out to obtain a monocalcium phosphate liquid; adding humic acid, montmorillonite, and diatomaceous earth to the monocalcium phosphate solution in sequence and mixing them thoroughly to form a modified mixture; The modified mixture is extruded into granules and dried to obtain a modified core material.
5. The superphosphate granules according to claim 1, characterized in that The moisture content of the modified core material is less than 2%; And / or, the particle size of the modified core material is 2 mm to 5 mm.
6. The superphosphate granules according to claim 1, characterized in that The thickness of the coating layer is 15 μm-25 μm.
7. The superphosphate granules according to claim 2, characterized in that The particle size of the silicon dioxide is 10nm-30nm; And / or, the coupling agent is a silane coupling agent.
8. The superphosphate granules according to claim 1, characterized in that The coating solution for forming the coating layer comprises the following steps: The apple tree branch liquefied material, castor oil and diisocyanate are mixed, nano silicon dioxide and a coupling agent are added, and the mixture is fully stirred to form a coating liquid.
9. The method for preparing superphosphate granules according to any one of claims 1 to 8, characterized in that The following steps are involved: The modified core material is added into a fluidized bed, and a coating liquid is sprayed to form a coating layer to obtain superphosphate particles.
10. The method according to claim 9, characterized in that During the spraying of the coating liquid, the coating weight gain rate is controlled at 3% to 5%.