A urea phosphate composition and a method for preparing the same

Abstract

The application belongs to the technical field of organic fertilizer, and provides a urea phosphate composition and a preparation method thereof.The preparation method comprises the following steps: (1) vacuum drying, crushing, screening and spraying activation of urea phosphate crystals with dilute phosphoric acid; (2) adding the activated urea phosphate crystals and deionized water into a reaction kettle, stirring, heating and keeping warm, then adding calcium nitrate aqueous solution, followed by adding diammonium hydrogen phosphate aqueous solution, adjusting pH and keeping warm to react, and forming a nano-hydroxyapatite coating layer; (3) heating, adding sodium stearate and stirring to react; (4) cooling, adding EGTA aqueous solution, stirring to react, and obtaining slurry; and (5) post-treatment.The composition can effectively solve the technical problems of poor stability, serious phosphorus fixation and single function of the existing urea phosphate, and can improve the nutrient slow-release performance and soil improvement effect of the product.The preparation method has simple process, accurate parameters and large-scale production, the product has stable performance and remarkable effect, no three wastes are discharged, and the method meets the requirements of green agricultural development.

Description

Technical Field

[0001] This invention belongs to the field of organic fertilizer technology, specifically relating to a urea phosphate composition and its preparation method. Background Technology

[0002] Urea phosphate is a high-concentration nitrogen-phosphorus complex salt formed by urea and phosphoric acid. It has the dual function of supplying nitrogen and phosphorus nutrients, has a high total nutrient content, and has a mild soil-improving effect. It is widely used in modern agricultural production and can effectively increase crop yield and improve crop quality. It is especially suitable for crop planting in special soils such as saline-alkali land. However, existing urea phosphate products and related preparation processes still have many technical problems, which seriously limit their large-scale promotion and application, as follows: On the one hand, urea phosphate has a unique crystal structure and weak interlayer bonding, making it highly susceptible to moisture absorption and clumping in high-humidity environments. This reduces the product's dispersibility and makes it difficult to apply mechanically. Simultaneously, its thermal stability is insufficient; during storage and transportation, even slightly elevated temperatures can cause thermal decomposition, leading to nitrogen volatilization and phosphorus loss, significantly reducing fertilizer efficiency and increasing agricultural production costs. On the other hand, after urea phosphate is applied to the soil, the phosphate ions produced by hydrolysis easily combine with metal ions (such as calcium and magnesium ions) in the soil to form insoluble phosphates. This makes it difficult for crops to absorb and utilize phosphorus, resulting in extremely low phosphorus utilization. This not only wastes nutrients but may also cause secondary problems such as soil compaction. Furthermore, existing urea phosphate products can only provide nitrogen and phosphorus nutrition. Even with a small number of improved products, they can only address a single problem and cannot simultaneously address stability, slow release, and soil improvement effects. Moreover, their improvement effect is mild and cannot meet the improvement needs of special soils such as saline-alkali land, nor can they adapt to the development needs of modern agriculture for "quality improvement, efficiency enhancement, and green environmental protection." In addition, current modifications to urea phosphate mostly adopt simple physical mixing methods, which have limited modification effects and are prone to introducing impurities, affecting product purity and fertilizer efficiency. Some chemical modification schemes have complex processes, high costs, and are prone to generating waste, which do not meet the needs of green agricultural development and are difficult to achieve large-scale production.

[0003] In summary, developing a stable, high phosphorus utilization, multifunctional, and simple urea phosphate composition and its preparation method has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the prior art, the first objective of the present invention is to provide a urea phosphate composition. This composition, through reasonable formulation design, can achieve synergistic effects among raw materials, effectively solve the technical problems of poor stability, serious phosphorus fixation, and single function of existing urea phosphate, and at the same time improve the nutrient slow-release performance and soil improvement effect of the product. In view of the above-mentioned shortcomings in the prior art, the second objective of the present invention is to provide a method for preparing the above-mentioned urea phosphate composition. This method is simple in process, precise in parameters, and can be mass-produced. Through the synergistic cooperation of steps such as activation, in-situ growth, hydrophobic modification, and chelation stabilization, the synergistic effect of each raw material can be fully utilized to ensure stable product performance and significant effect, and there is no discharge of waste gas, wastewater, and solid waste, which meets the requirements of green agricultural development. To achieve the above objectives, the solution adopted by the present invention is as follows: A urea phosphate composition, by weight, comprises the following raw materials: 75-88 parts of urea phosphate crystals (Shifang Hongyu Chemical Co., Ltd., in accordance with GB / T 27805-2011, industrial grade, purity ≥98%, nitrogen content ≥17.5%, P2O5 content ≥44.5%), 4-10 parts of nano-hydroxyapatite precursor, 1.5-3.5 parts of sodium stearate (Jingzhou Yinjie Chemical Co., Ltd., model ST-99, purity ≥95%, C18 type, melting point 250–255℃, water solubility ≤0.1g / 100mL at 25℃), and EGTA (ethylene glycol diethyl ether). Diaminetetraacetic acid (EGTA-99, Hubei Bojie Biotechnology Co., Ltd., purity ≥99%) 0.8–2.0 parts; Nano-hydroxyapatite precursors include calcium nitrate (Shanxi Jiaocheng Tianlong Chemical Industry Co., Ltd., compliance with Q / 140000JTL001-2014, purity ≥99%) and diammonium hydrogen phosphate (CF-DAP621, HG / T 4132-2021, purity ≥99%) in a molar ratio of 1.5–2:1. A method for preparing the above-mentioned urea phosphate composition includes the following steps: (1) After vacuum drying, crushing and sieving the urea phosphate crystals to a particle size of 0.3-0.6 mm, activate them by spraying with 0.1 mol / L dilute phosphoric acid and air drying for later use; (2) The activated urea phosphate crystals and deionized water were added to the reaction vessel at a solid-liquid ratio of 1:1-1.5. The mixture was stirred and heated to 45-50℃ and kept at that temperature for 10 min. Then, a 0.5 mol / L calcium nitrate aqueous solution was added dropwise, followed by a 0.3 mol / L diammonium hydrogen phosphate aqueous solution. The pH was adjusted and the reaction was kept at that temperature to form a nano-hydroxyapatite coating layer. (3) Heat to 55–60℃, add sodium stearate in batches, and stir to react; (4) Cool down to 40℃, add EGTA aqueous solution, stir and react to obtain slurry; the solid-liquid ratio of EGTA aqueous solution is 1:5; (5) After the slurry is concentrated, crystallized, centrifuged to dehydrate, dried, and sieved, it is sealed and packaged. Furthermore, in a preferred embodiment of the present invention, in step (1), the vacuum drying temperature is 50–55°C, the vacuum degree is -0.06–0.07 MPa, and the drying time is 1.5 h.

[0005] Furthermore, in a preferred embodiment of the present invention, in step (1), the spraying amount is 8% of the mass of urea phosphate crystals, and the spraying time is 1 min.

[0006] Furthermore, in a preferred embodiment of the present invention, in step (1), the air-drying temperature is 40°C and the air-drying time is 20 min. Furthermore, in a preferred embodiment of the present invention, in step (2), the stirring speed is 120 r / min.

[0007] Furthermore, in a preferred embodiment of the present invention, in step (2), the calcium nitrate aqueous solution is added at a rate of 1.5 mL / min, and after 15 min, diammonium hydrogen phosphate aqueous solution is added at a rate of 0.9 mL / min. The pH of the system is adjusted to 7.2–7.4, and the reaction time is kept warm for 60–90 min.

[0008] Furthermore, in a preferred embodiment of the present invention, in step (3), the stirring speed is 150 r / min, sodium stearate is added in 3 batches with an interval of 10 min between each batch, and the stirring reaction is carried out for 30 min.

[0009] Furthermore, in a preferred embodiment of the present invention, in step (4), the stirring speed is 100 r / min and the stirring reaction is carried out for 20 min.

[0010] Furthermore, in a preferred embodiment of the present invention, in step (5), the concentration temperature is 48–50°C, the vacuum degree is -0.07MPa, the concentration is made up to a moisture content of ≤12%, the crystallization temperature is 25°C, the drying temperature is 45°C, and the drying time is 1.5h.

[0011] Furthermore, in a preferred embodiment of the present invention, in step (5), the particle size of the finished product is 0.4–0.8 mm.

[0012] The beneficial effects of the urea phosphate composition and its preparation method provided by this invention are: (1) The urea phosphate composition provided by the present invention can significantly improve product stability through the synergistic effect of each raw material: urea phosphate crystals, as the core nutrient supplier, can provide sufficient nitrogen and phosphorus nutrition; the nano-hydroxyapatite (n-HAP) generated in situ by the nano-hydroxyapatite precursor matches the crystal lattice of urea phosphate crystals and forms a dense coating layer through chemical bonding, which effectively blocks moisture and heat, and improves the product's resistance to moisture absorption and thermal decomposition; the hydrophobic layer formed by sodium stearate further blocks moisture contact and works synergistically with the n-HAP coating layer to completely solve the problem of urea phosphate absorbing moisture and clumping; EGTA chelates free metal ions, which can not only block the catalytic decomposition of urea phosphate by metal ions, but also work synergistically with n-HAP to reduce phosphorus fixation. The synergistic effect of the four ingredients greatly improves the product stability, prevents clumping in high humidity environments, and has an extremely low nutrient loss rate during heat storage, thus solving the core problem of poor stability of urea phosphate in the prior art. (2) The urea phosphate composition provided by the present invention has a double barrier structure formed by the n-HAP coating layer and the hydrophobic layer, which can precisely control the release rate of nitrogen and phosphorus nutrients and avoid rapid loss of nutrients; the EGTA chelation effect reduces phosphorus fixation, making phosphorus easier for crops to absorb, and at the same time, in synergy with urea phosphate, achieves a balanced supply of nitrogen and phosphorus nutrients, greatly improves nitrogen and phosphorus utilization, reduces the number of topdressings, reduces agricultural production costs, and solves the problems of low phosphorus utilization and serious nutrient waste in the prior art; (3) The urea phosphate composition provided by the present invention slowly releases Ca²⁺ from n-HAP, which can improve the soil aggregate structure. Combined with the slightly acidic properties of urea phosphate, it can effectively improve saline-alkali land and reduce soil pH. EGTA chelates excess metal ions in the soil to prevent soil compaction. In synergy with other raw materials, it can meet the needs of various soils and crops, and solve the problem of the single function and limited soil improvement effect of urea phosphate in the prior art. (4) The preparation method of the urea phosphate composition provided by this invention uses industrial-grade, readily available raw materials that are widely sourced and cost-controllable. The preparation process requires no complex equipment, is simple, and produces no waste, meeting the requirements of green agriculture development. Simultaneously, the synergistic effect between raw materials reduces the amount of any single raw material used, improving product performance while further controlling production costs. The cost-effectiveness is significantly better than existing products, solving the problems of high cost and pollution associated with existing modification schemes. (5) The preparation method of the urea phosphate composition provided by the present invention has a preparation process and raw materials that are synergistically adapted to ensure stable product performance: the activation, in-situ growth, hydrophobic modification, chelation stabilization and other steps in the preparation process are all designed for the characteristics of each raw material, which can give full play to the synergistic effect of each raw material, ensure that the n-HAP coating layer and the hydrophobic layer are tightly combined, and that EGTA fully chelates free metal ions, and finally obtains a finished product with uniform and stable performance. Moreover, the process parameters are accurate and can be mass-produced, which solves the problem of complex modification process and difficulty in mass production in the prior art. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0014] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products. Example

[0015] This embodiment provides a urea phosphate composition, which, by weight, comprises: 80 parts of urea phosphate crystals, 8 parts of nano-hydroxyapatite precursor, 2.5 parts of sodium stearate, and 1 part of EGTA; the nano-hydroxyapatite precursor comprises calcium nitrate and diammonium hydrogen phosphate in a molar ratio of 1.8:1. This embodiment also provides a method for preparing the urea phosphate composition, including: (1) Dry urea phosphate crystals at 52℃ and vacuum degree of -0.065MPa for 1.5h, crush and sieve to a particle size of 0.5mm, activate them by spraying with dilute phosphoric acid with a concentration of 0.1mol / L, the spray amount is 8% of the mass of urea phosphate crystals, the spraying time is 1min, and air dry at 40℃ for 20min for later use. (2) The activated urea phosphate crystals and deionized water were added to the reaction vessel at a solid-liquid ratio of 1:1.2. The mixture was stirred at 120 r / min and heated to 48°C. After holding the temperature for 10 min, calcium nitrate aqueous solution with a concentration of 0.5 mol / L was added dropwise at a rate of 1.5 mL / min for 15 min. Then, diammonium hydrogen phosphate aqueous solution with a concentration of 0.3 mol / L was added dropwise at a rate of 0.9 mL / min. The pH of the system was adjusted to 7.3. The reaction was held at the temperature for 70 min to form a nano-hydroxyapatite coating layer. (3) Heat to 58°C, add sodium stearate in 3 batches, with an interval of 10 min between each batch, and stir at 150 r / min for 30 min; (4) Cool down to 40℃, add EGTA aqueous solution, stir at 100r / min for 20min to obtain slurry; the solid-liquid ratio of EGTA aqueous solution is 1:5; (5) The slurry is concentrated at 49°C and vacuum degree of -0.07MPa until the moisture content is ≤12%. Then it is crystallized at 25°C, centrifuged to dehydrate, dried at 45°C for 1.5h, sieved to a particle size of 0.6mm, and then sealed and packaged. Example

[0016] This embodiment provides a urea phosphate composition and its preparation method, which differs from Example 1 in that: the urea phosphate composition, by weight, comprises: 75 parts of urea phosphate crystals, 10 parts of nano-hydroxyapatite precursor, 1.5 parts of sodium stearate and 2.0 parts of EGTA; the nano-hydroxyapatite precursor comprises calcium nitrate and diammonium hydrogen phosphate in a molar ratio of 1.5:1. Example

[0017] This embodiment provides a urea phosphate composition and its preparation method, which differs from Example 1 in that: the urea phosphate composition, by weight, comprises: 88 parts of urea phosphate crystals, 4 parts of nano-hydroxyapatite precursor, 3.5 parts of sodium stearate and 0.8 parts of EGTA; the nano-hydroxyapatite precursor comprises calcium nitrate and diammonium hydrogen phosphate in a molar ratio of 2:1. Example

[0018] This embodiment provides a urea phosphate composition and its preparation method, which differs from Example 1 in that: The method for preparing the urea phosphate composition provided in this embodiment includes: (1) Dry urea phosphate crystals at 50℃ and vacuum degree of -0.06MPa for 1.5h, crush and sieve to a particle size of 0.3mm, activate them by spraying with 0.1mol / L dilute phosphoric acid, the spray amount is 8% of the mass of urea phosphate crystals, the spraying time is 1min, and air dry at 40℃ for 20min for later use. (2) The activated urea phosphate crystals and deionized water were added to the reaction vessel at a solid-liquid ratio of 1:1.5. The mixture was stirred at 120 r / min and heated to 45°C. After holding the temperature for 10 min, a 0.5 mol / L calcium nitrate aqueous solution was added dropwise at a rate of 1.5 mL / min for 15 min. Then, a 0.3 mol / L diammonium hydrogen phosphate aqueous solution was added dropwise at a rate of 0.9 mL / min. The pH of the system was adjusted to 7.4. The reaction was held at the temperature for 60 min to form a nano-hydroxyapatite coating layer. (3) Heat to 60°C, add sodium stearate in 3 batches, with an interval of 10 min between each batch, and stir at 150 r / min for 30 min; (4) Cool down to 40℃, add EGTA aqueous solution, stir at 100r / min for 20min to obtain slurry; the solid-liquid ratio of EGTA aqueous solution is 1:5; (5) After the slurry is concentrated, crystallized, centrifuged to dehydrate, dried, and sieved, it is sealed and packaged. The concentration temperature is 48℃, the vacuum degree is -0.07MPa, the moisture content is ≤12%, the crystallization temperature is 25℃, the drying temperature is 45℃, the drying time is 1.5h, and the finished product particle size is 0.8mm. Example

[0019] This embodiment provides a urea phosphate composition and its preparation method, which differs from Example 1 in that: The method for preparing the urea phosphate composition provided in this embodiment includes: (1) Dry urea phosphate crystals at 55℃ and vacuum degree of -0.07MPa for 1.5h, crush and sieve to a particle size of 0.6mm, activate them by spraying with 0.1mol / L dilute phosphoric acid, the spray amount is 8% of the mass of urea phosphate crystals, the spraying time is 1min, and air dry at 40℃ for 20min for later use. (2) The activated urea phosphate crystals and deionized water were added to the reaction vessel at a solid-liquid ratio of 1:1. The mixture was stirred at 120 r / min and heated to 50 °C. After holding the temperature for 10 min, the mixture was added dropwise at a rate of 1.5 mL / min for 15 min. Then, a calcium nitrate aqueous solution with a concentration of 0.5 mol / L was added dropwise for 15 min. Next, a diammonium hydrogen phosphate aqueous solution with a concentration of 0.3 mol / L was added dropwise at a rate of 0.9 mL / min. The pH of the system was adjusted to 7.2. The reaction was held at the temperature for 90 min to form a nano-hydroxyapatite coating layer. (3) Heat to 55°C, add sodium stearate in 3 batches, with an interval of 10 min between each batch, and stir at 150 r / min for 30 min; (4) Cool down to 40℃, add EGTA aqueous solution, stir at 100r / min for 20min to obtain slurry; the solid-liquid ratio of EGTA aqueous solution is 1:5; (5) After the slurry is concentrated, crystallized, centrifuged to dehydrate, dried, and sieved, it is sealed and packaged. The concentration temperature is 50℃, the vacuum degree is -0.07MPa, the moisture content is ≤12%, the crystallization temperature is 25℃, the drying temperature is 45℃, the drying time is 1.5h, and the finished product particle size is 0.4mm.

[0020] Comparative Example 1 This comparative example provides a urea phosphate product, the preparation method of which includes: placing industrial-grade urea phosphate crystals into a vacuum drying oven and vacuum drying them at 52℃ and -0.065MPa for 1.5h; placing them into a universal pulverizer and pulverizing them at a speed of 2800r / min for 30s; sieving them using a standard sieve and collecting crystals with a particle size of 0.3–0.6mm; directly placing the sieved crystals into a hot air dryer and drying them at 45℃ and a wind speed of 2.0m / s for 1.5h, controlling the moisture content of the finished product to ≤5%; sieving them using a standard sieve and collecting the finished product with a particle size of 0.6mm; and sealing and packaging the product.

[0021] Comparative Example 2 This comparative example provides a urea phosphate composition, which, by weight, comprises: 80 parts of urea phosphate crystals, 8 parts of humic acid, and 2.5 parts of sodium stearate; The preparation method of the urea phosphate composition provided in this comparative example includes: placing industrial-grade urea phosphate crystals into a vacuum drying oven and vacuum drying them for 1.5 h at 52 °C and -0.065 MPa; pulverizing and sieving the crystals to collect crystals with a particle size of 0.3–0.6 mm; adding urea phosphate crystals, humic acid, and sodium stearate to a reaction vessel, adding deionized water to make the solid-liquid ratio of the system 1:1.2, and stirring at 120 r / min for 30 min; transferring the slurry to a vacuum concentrator and concentrating it to a moisture content of ≤12% at 48 °C and -0.07 MPa; cooling to 25 °C and allowing it to crystallize for 3 h; centrifuging to dehydrate and then hot-air drying at 45 °C for 1.5 h, controlling the moisture content of the finished product to ≤5%; collecting the finished product with a particle size of 0.4–0.8 mm after sieving and sealing it in packaging.

[0022] Comparative Example 3 This comparative example provides a urea phosphate composition, which, by weight, comprises: 80 parts of urea phosphate crystals, 8 parts of humic acid, and 2.5 parts of sodium stearate; The method for preparing the urea phosphate composition provided in this comparative example includes: (1) Place the urea phosphate crystals into a vacuum drying oven and vacuum dry them for 1.5 h at 52 ℃ and -0.065 MPa; after crushing, sieve and collect crystals with a particle size of 0.3-0.6 mm; spray them evenly with 0.1 mol / L dilute phosphoric acid, the spray amount is 8% of the crystal mass, the spray time is 1 min, and air dry at 40 ℃ for 20 min for later use; (2) Add the activated urea phosphate crystals and deionized water to the reactor, control the solid-liquid ratio to 1:1.2, stir at 120 r / min, heat to 58℃, adjust the stirring speed to 150 r / min, crush sodium stearate to a particle size ≤0.1 mm, add it to the reactor in 3 batches with an interval of 10 min between each batch, and stir for 30 min. (3) Reduce the temperature inside the reactor to 40°C, adjust the stirring speed to 100 r / min, dissolve EGTA in deionized water (mass ratio 1:5) to prepare an EGTA aqueous solution, slowly add it to the reactor, and stir for 20 min. (4) Transfer the slurry in the reactor to a vacuum concentrator and concentrate it at 48℃ and -0.07MPa for 40 min, controlling the moisture content of the slurry to ≤12%; cool it to 25℃ and let it stand to crystallize for 3 h; after centrifugation and dehydration, dry it with hot air at 45℃ for 1.5 h; after sieving, collect the finished product with a particle size of 0.6 mm and seal it for packaging.

[0023] Comparative Example 4 This comparative example provides a urea phosphate composition, which, by weight, comprises: 80 parts of urea phosphate crystals, 8 parts of nano-hydroxyapatite precursor, and 2.5 parts of sodium stearate; the nano-hydroxyapatite precursor comprises calcium nitrate and diammonium hydrogen phosphate in a molar ratio of 1.8:1. This comparative example also provides a method for preparing the urea phosphate composition, including: (1) Place industrial-grade urea phosphate crystals into a vacuum drying oven and vacuum dry them for 1.5 h at 52 ℃ and -0.065 MPa; after crushing, sieve and collect crystals with a particle size of 0.3–0.6 mm; spray them evenly with 0.1 mol / L dilute phosphoric acid, the spray amount is 8% of the crystal mass, the spray time is 1 min, and air dry at 40 ℃ for 20 min for later use; (2) Add the activated urea phosphate crystals and deionized water to the reaction vessel, control the solid-liquid ratio to 1:1.2, stir at 120 r / min, heat to 48℃ and keep warm for 10 min; first add 0.5 mol / L Ca(NO3)2・4H2O aqueous solution at a rate of 1.5 mL / min, and after adding for 15 min, add 0.3 mol / L (NH4)2HPO4 aqueous solution at a rate of 0.9 mL / min. During the addition, adjust the pH of the system to 7.3 with 0.1 mol / L NaOH solution and keep warm for 75 min. (3) Raise the temperature inside the reactor to 58°C, adjust the stirring speed to 150 r / min, crush the sodium stearate to a particle size ≤ 0.1 mm, add it to the reactor in 3 batches with an interval of 10 min between each batch, and stir for 30 min. (4) Transfer the slurry in the reactor to a vacuum concentrator and concentrate it at 48℃ and -0.07MPa for 40 min, controlling the moisture content of the slurry to ≤12%; cool it to 25℃ and let it stand for crystallization for 3 h; after centrifugation and dehydration, dry it with hot air at 45℃ for 1.5 h, controlling the moisture content of the finished product to ≤5%; after sieving, collect the finished product with a particle size of 0.6 mm and seal it for packaging.

[0024] Comparative Example 5 This comparative example provides a urea phosphate composition and its preparation method, which differs from Example 1 in that: the urea phosphate composition, by weight, comprises: 70 parts of urea phosphate crystals, 15 parts of nano-hydroxyapatite precursor, 1 part of sodium stearate and 3 parts of EGTA; the nano-hydroxyapatite precursor comprises calcium nitrate and diammonium hydrogen phosphate in a molar ratio of 1.5:1. Comparative Example 6 This comparative example provides a urea phosphate composition and its preparation method, which differs from Example 1 in that: the preparation method of the urea phosphate composition provided in this comparative example includes: placing urea phosphate crystals into a vacuum drying oven and vacuum drying at 52°C and -0.065MPa for 1.5h; pulverizing and sieving, collecting crystals with a particle size of 0.3–0.6mm; adding urea phosphate crystals, nano-hydroxyapatite precursor, sodium stearate and EGTA into a reaction vessel, adding deionized water to make the solid-liquid ratio of the system 1:1.2, and stirring at 120r / min for 30min; transferring the slurry into a vacuum concentrator and concentrating it at 48°C and -0.07MPa until the moisture content is ≤12%; cooling to 25°C and allowing it to crystallize for 3h; centrifuging to dehydrate, and then hot air drying at 45°C for 1.5h, controlling the moisture content of the finished product to ≤5%; collecting the finished product with a particle size of 0.4–0.8mm after sieving and sealing and packaging.

[0025] Comparative Example 7 This comparative example provides a urea phosphate composition and its preparation method, which differs from Example 1 in that: the preparation method of the urea phosphate composition provided in this comparative example includes: (1) Dry urea phosphate crystals at 60℃ and vacuum degree of -0.08MPa for 1.5h, crush and sieve to a particle size of 0.3-0.6mm, activate them by spraying with 0.2mol / L dilute phosphoric acid, the spray amount is 10% of the mass of urea phosphate crystals, the spraying time is 1min, and then air dry at 40℃ for 20min for later use. (2) The activated urea phosphate crystals and deionized water were added to the reaction vessel at a solid-liquid ratio of 1:2. The mixture was stirred at 120 r / min and heated to 55 °C. After holding the temperature for 10 min, calcium nitrate aqueous solution with a concentration of 0.8 mol / L was added dropwise at a rate of 2 mL / min for 10 min. Then, diammonium hydrogen phosphate aqueous solution with a concentration of 0.5 mol / L was added dropwise at a rate of 1 mL / min. The pH of the system was adjusted to 7.3. The reaction was held at the temperature for 100 min to form a nano-hydroxyapatite coating layer. (3) Heat to 50°C, add sodium stearate in 3 batches, with an interval of 10 min between each batch, and stir at 200 r / min for 20 min; (4) Cool down to 35°C, add EGTA aqueous solution, stir at 80 r / min for 15 min to obtain slurry; the solid-liquid ratio of EGTA aqueous solution is 1:8; (5) After the slurry is concentrated, crystallized, centrifuged to dehydrate, dried, and sieved, it is sealed and packaged. The concentration temperature is 55℃, the vacuum degree is -0.07MPa, the moisture content is ≤12%, the crystallization temperature is 25℃, the drying temperature is 45℃, the drying time is 1.5h, and the finished product particle size is 0.6mm. Comparative Example 8 This comparative example provides a urea phosphate composition and its preparation method, which differs from Example 1 in that: the nano-hydroxyapatite precursor includes calcium nitrate and diammonium hydrogen phosphate in a molar ratio of 3:1.

[0026] Experimental Example 1 The moisture absorption rate, nutrient loss rate, nitrogen and phosphorus nutrient release cycle and utilization rate, and soil improvement effect of the urea phosphate products prepared in Examples 1-5 and Comparative Examples 1-8 were tested.

[0027] The performance testing method of this invention is as follows: (1) Moisture absorption rate (%): The sample was placed in an environment of 25℃ and 90% relative humidity for 30 days, and the moisture absorption rate was calculated by the mass difference method; (2) Thermal stability (nutrient loss rate (%)): According to GB / T 8572-2010 and GB / T 8573-2010, the sample was stored at 45℃ for 60 days, and the nutrient content before and after was measured and the loss rate was calculated; (3) Nitrogen and phosphorus nutrient release period (d): The nitrogen and phosphorus nutrient release period (d) was determined by static water extraction at 25℃, referring to GB / T 23348-2009. (4) Nitrogen and phosphorus utilization rate (%): Nitrogen and phosphorus utilization rate (%) was determined by static water extraction at 25℃, referring to GB / T 23348-2009. (5) Soil improvement effect: Select saline-alkali land with pH 8.5, apply 50 kg / mu of soil to the sample, and measure soil pH in accordance with NY / T1121.2-2006 and available phosphorus in soil in accordance with NY / T 1121.7-2021 after 30 days.

[0028] The test results for moisture absorption rate, nutrient loss rate, and nitrogen and phosphorus nutrient release cycle are shown in Table 1:

[0029] As shown in Table 1, the 30-day moisture absorption rate of Examples 1-5 of the present invention is ≤1.2%, the nutrient loss rate after 60 days of storage at 45℃ is ≤2.5%, the nitrogen release period is 78-85 days, and the phosphorus release period is 108-120 days. Overall, the products exhibit low moisture absorption, low loss, and long-term slow release. Moreover, the performance remains stable and controllable when the ratio and process change within the protection range.

[0030] Comparative Example 1, using unmodified urea phosphate and conventional preparation process, exhibited severe hygroscopicity, significant nutrient loss, and an extremely short fertilizer effect period. Comparative Example 3, lacking the nano-hydroxyapatite precursor, showed a significant increase in hygroscopicity and loss rate, and a markedly shortened release cycle, indicating that in-situ nano-hydroxyapatite coating is the core for improving stability and sustained-release properties. Comparative Example 6 used simple mixing, the process parameters of Comparative Example 7 exceeded the limits of this application, and the calcium-phosphorus molar ratio used in Comparative Example 8 was not within the limits of this application; none of these examples could form an effective coating structure, and their stability and sustained-release properties were significantly inferior to the examples.

[0031] The results show that the present invention, through the synergistic process of crystal activation, in-situ growth coating, hydrophobic end-capping, and chelation stabilization, can significantly improve the hygroscopic clumping defects of urea phosphate, enhance thermal stability, and extend the nutrient release cycle, with effects significantly superior to existing technologies.

[0032] The test results of nitrogen and phosphorus utilization rates and soil improvement effects are shown in Table 2:

[0033] As shown in Table 2, the nitrogen utilization rate of Examples 1-5 of this invention is 48-52%, the phosphorus utilization rate is 38-42%, and after 30 days of application in saline-alkali land with pH 8.5, the soil pH drops to 7.1-7.3, the available phosphorus increases by 29-32%, and there is no clumping. The overall performance is excellent.

[0034] Comparative Example 1, prepared using unmodified urea phosphate and conventional processes, exhibited extremely low nutrient utilization, weak soil improvement effects, and severe caking. Comparative Example 4, lacking EGTA in its raw materials, showed a significant decrease in phosphorus utilization and the increase in available phosphorus, indicating that EGTA has an irreplaceable synergistic effect in inhibiting phosphorus fixation and improving phosphorus utilization. Comparative Examples 2, 5, 6, 7, and 8, due to the lack of core components, out-of-range formulations, or the use of simple mixing processes, failed to achieve efficient nutrient utilization and good soil improvement effects.

[0035] The results show that the present invention can significantly improve the utilization rate of nitrogen and phosphorus nutrients, effectively regulate the pH of saline-alkali soil and increase the available phosphorus content through the synergistic effect of nano-hydroxyapatite and EGTA, solve the problem of caking, and achieve synergistic effect of efficient fertilizer utilization and soil improvement, thus possessing outstanding technical advantages.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A urea phosphate composition, characterized in that, By weight, the raw materials include: 75-88 parts of urea phosphate crystals, 4-10 parts of nano-hydroxyapatite precursor, 1.5-3.5 parts of sodium stearate, and 0.8-2.0 parts of EGTA; the nano-hydroxyapatite precursor comprises calcium nitrate and diammonium hydrogen phosphate in a molar ratio of 1.5-2:

1.

2. A method for preparing the urea phosphate composition according to claim 1, characterized in that, Includes the following steps: (1) The urea phosphate crystals are vacuum dried, pulverized and sieved to a particle size of 0.3-0.6 mm, activated by spraying with 0.1 mol / L dilute phosphoric acid, and then air-dried for later use; (2) The activated urea phosphate crystals and deionized water were added to the reaction vessel at a solid-liquid ratio of 1:1-1.

5. The mixture was stirred and heated to 45-50℃ and kept at that temperature for 10 min. A calcium nitrate aqueous solution with a concentration of 0.5 mol / L was added dropwise, followed by a diammonium hydrogen phosphate aqueous solution with a concentration of 0.3 mol / L. The pH was adjusted and the reaction was kept at that temperature to form a nano-hydroxyapatite coating layer. (3) Heat to 55–60°C, add the sodium stearate in batches, and stir to react; (4) Cool down to 40°C, add EGTA aqueous solution, stir and react to obtain slurry; the solid-liquid ratio of the EGTA aqueous solution is 1:5; (5) After the slurry is concentrated, crystallized, centrifuged to dehydrate, dried and sieved, it is sealed and packaged.

3. The preparation method according to claim 2, characterized in that, In step (1), the vacuum drying temperature is 50–55℃, the vacuum degree is -0.06–-0.07MPa, and the drying time is 1.5h.

4. The preparation method according to claim 2, characterized in that, In step (1), the spraying amount is 8% of the mass of the urea phosphate crystals, the spraying time is 1 min, the air drying temperature is 40℃, and the air drying time is 20 min.

5. The preparation method according to claim 2, characterized in that, In step (2), the stirring speed is 120 r / min.

6. The preparation method according to claim 2, characterized in that, In step (2), the calcium nitrate aqueous solution is added at a rate of 1.5 mL / min. After 15 min of addition, the diammonium hydrogen phosphate aqueous solution is added at a rate of 0.9 mL / min. The pH of the system is adjusted to 7.2–7.4, and the reaction time is kept warm for 60–90 min.

7. The preparation method according to claim 2, characterized in that, In step (3), the stirring speed is 150 r / min, the sodium stearate is added in 3 batches with an interval of 10 min between each batch, and the stirring reaction is carried out for 30 min.

8. The preparation method according to claim 2, characterized in that, In step (4), the stirring speed is 100 r / min and the stirring reaction is carried out for 20 min.

9. The preparation method according to claim 2, characterized in that, In step (5), the concentration temperature is 48–50℃, the vacuum degree is -0.07MPa, the concentration is made up to ≤12% moisture content, the crystallization temperature is 25℃, the drying temperature is 45℃, and the drying time is 1.5h.

10. The preparation method according to claim 2, characterized in that, In step (5), the particle size of the finished product is 0.4–0.8 mm.

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