Controlled release potassium element granules and method of making same

Abstract

This invention relates to a controlled-release potassium granule, comprising a potassium nutrient core and a polyurethane coating layer covering the surface of the potassium nutrient core. The potassium nutrient core uses at least one of potassium chloride and potassium sulfate as the potassium source material, and also includes a functional carrier, a potassium activator modifier, and a binder. After the potassium source material, functional carrier, potassium activator modifier, and binder are mixed evenly, the potassium nutrient core is formed through granulation and drying processes. This invention adopts a separate potassium coating design, breaking the limitations of existing nitrogen, phosphorus, and potassium mixed coatings. It can be flexibly mixed with separately coated nitrogen, phosphorus, and other nutrient fertilizers in any proportion, and can precisely adjust the mixing ratio of potassium with other nutrients according to the nutrient requirements of different crops (such as grain crops and fruit and vegetable crops) and different growth stages (such as seedling stage, fruit expansion stage, and grain filling stage), so as to achieve personalized precision fertilization and adapt to the personalized needs of various crops.

Description

Technical Field

[0001] This invention relates to the field of controlled-release fertilizer technology, and in particular to a controlled-release potassium element granule and its preparation method. Background Technology

[0002] Potassium is an essential nutrient for crop growth and development, often referred to as a "quality element." It participates in key physiological processes such as photosynthesis, enzyme activity regulation, osmotic pressure regulation, and stress resistance enhancement, directly impacting crop resistance to lodging, disease, and drought. It plays an irreplaceable role in increasing crop yield and improving fruit quality. Currently, the most common form of potassium supply in agricultural production is traditional fast-acting potassium fertilizer, whose core raw materials mainly include potassium chloride and potassium sulfate. However, these traditional fast-acting potassium fertilizers have significant technical shortcomings. Existing controlled-release potassium granules mostly use a mixed coating model of nitrogen, phosphorus, and potassium, which cannot achieve independent coating of potassium with nitrogen, phosphorus, and other nutrients. Consequently, it is impossible to flexibly adjust the mixing ratio of potassium with other nutrients according to soil type (acidic, alkaline, saline soil), crop variety, and different growth stages, limiting the realization of precision fertilization. Furthermore, after mixed coating, the release rates of each nutrient are mutually restrictive, making it impossible to individually match the differentiated needs of crops for different nutrients. This fails to meet the personalized and precise fertilization requirements of modern agriculture and is also difficult to adapt to specific fertilization programs for different crops. Summary of the Invention

[0003] The purpose of this invention is to provide controlled-release potassium particles and a method for preparing the same, so as to solve the technical problems existing in the prior art.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A controlled-release potassium particle comprises a potassium nutrient core and a polyurethane coating layer covering the surface of the potassium nutrient core. The potassium nutrient core uses at least one of potassium chloride and potassium sulfate as the potassium source material, and also includes a functional carrier, a potassium activating modifier, and a binder. The potassium source material, functional carrier, potassium activating modifier, and binder are mixed evenly and then granulated and dried to form the potassium nutrient core. Furthermore, the polyurethane coating layer is a bio-based modified polyurethane coating layer, formed by gradient curing of a customized bio-based polyurethane coating agent. The coating thickness and crosslinking density can be flexibly adjusted according to the controlled-release requirements to achieve precise control of the potassium release rate.

[0005] Furthermore, in the potassium nutrient core, the mass percentages of each component are as follows: potassium source raw material 70%-92%, functional carrier 5%-22%, potassium activating modifier 1%-5%, and binder 0.5%-3%; the potassium source raw material can be a single raw material or a mixture of raw materials, specifically: 1) Single raw material: Potassium chloride or potassium sulfate is used as the potassium source alone; potassium chloride (KCl) has a potassium content (calculated as K2O) of 58%-62%, good water solubility, and low cost, making it suitable for grain crops and non-chlorine-sensitive crops (such as corn, wheat, and cotton); potassium sulfate (K2SO4) has a potassium content (calculated as K2O) of 50%-54%, is chlorine-free, and is suitable for chlorine-sensitive crops (such as tobacco, potatoes, fruits and vegetables) and saline-alkali land, avoiding the damage to crops caused by chloride ion accumulation and the aggravation of soil salinization; 2) Mixed raw materials: Potassium chloride and potassium sulfate are mixed at a mass ratio of 1:0.3-2.0, which can balance potassium content and applicability, balance cost and chlorine risk, and is suitable for various soils and crops, especially suitable for crops with moderate chlorine sensitivity (such as soybeans and peanuts) and plots with moderate chlorine content in the soil.

[0006] Furthermore, the functional carrier is selected from one or more of attapulgite, bentonite, zeolite powder, diatomaceous earth, straw charcoal, and humic acid, with a particle size of 280-400 mesh. The functional carrier undergoes composite modification treatment to further enhance its adsorption capacity and binding force for potassium ions, while improving the sphericity and stability of the core particles. The specific modification process is as follows: after crushing and sieving the functional carrier, it is first soaked in a 2%-4% dilute hydrochloric acid or dilute nitric acid solution for 15-25 minutes (solid-liquid ratio 1:7-10 g / mL, stirring speed 350-550 rpm), washed until pH=6.5-7.5, dried at 85-95℃ until the moisture content is ≤0.8%, cooled, and 0.3%-1.0% of its mass of silane coupling agent (KH-550 or KH-570) is added. The mixture is stirred at 80-90℃ and 800-1000 rpm for 10-15 minutes. After modification, it is sealed for later use.

[0007] The modified functional carrier has a triple function of "adsorption-buffering-activation": the porous structure of inorganic carriers (attapulgite, zeolite powder, etc.) can adsorb potassium ions, reducing potassium loss and soil fixation; organic carriers (straw charcoal, humic acid, etc.) can provide organic matter, promote soil microbial activity, activate potassium fixed in the soil, and can also degrade, improving environmental friendliness; the introduction of silane coupling agents can enhance the binding force between functional carriers and potassium source raw materials and binders, improve the compressive strength and stability of core particles, and avoid particle loosening and breakage during granulation.

[0008] Furthermore, the potassium activating modifier is selected from one or more of potassium polyaspartate, seaweed extract, potassium humate, and potassium amino acids. This potassium activating modifier can form stable chelates with potassium ions in the potassium source material, effectively preventing potassium ions from being fixed by the soil lattice, prolonging the retention time of potassium in the soil solution, activating crop root development, promoting root absorption of potassium, and synergistically activating potential mineral potassium in the soil, thereby enhancing the soil's potassium supply capacity and addressing the industry pain points of easy potassium fixation and low utilization rate. Among these, potassium polyaspartate, as a chelating agent, can increase potassium availability by more than 28%, while also promoting lateral root growth and expanding the root absorption area.

[0009] Furthermore, the binder is selected from one or more of sodium carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), starch modifier, and xanthan gum, with a molecular weight of 8000-20000 Da. The binder can improve the molding rate and sphericity of the potassium nutrient core, making the core particle surface smooth and dense, avoiding particle agglomeration and clumping, while enhancing the bonding force between the core and the polyurethane coating layer, preventing the coating layer from falling off, and solving the problems of irregular core particles and poor coating uniformity in existing systems.

[0010] Further, the thickness of the polyurethane coating layer is 10-40 μm, and the coating rate is 5%-15%; the polyurethane coating layer is formed by curing a customized bio-based polyurethane coating agent, which includes an isocyanate component, a bio-based polyol component, functional additives, and a crosslinking agent, wherein the molar ratio (NCO:OH) of the isocyanate component to the bio-based polyol component is 1:1.1-2.2, the amount of functional additives added is 1.0%-7.0% of the total mass of the isocyanate component and the bio-based polyol component, and the amount of crosslinking agent added is 0.3%-1.5% of the total mass of the isocyanate component and the bio-based polyol component.

[0011] Compared with existing coatings, the polyurethane coating layer of this invention has two core improvements: First, it uses bio-based polyols to replace some petrochemical-based polyols, improving the biodegradability of the coating material and reducing the risk of soil residue; second, it introduces a crosslinking agent to optimize the density and flexibility of the coating layer by controlling the crosslinking density, thereby achieving precise control of the potassium release rate and improving the coating layer's resistance to mechanical damage, thus avoiding coating damage during transportation and fertilization.

[0012] Furthermore, the isocyanate component is one or more of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), and polymethylene polyphenyl isocyanate (PAPI); the bio-based polyol component is one or more of castor oil-based polyol, palm oil-based polyol, soybean oil-based polyol, and cellulose-based polyol, with a molecular weight of 1200-4000 Da, a bio-based content of ≥85%, and is biodegradable with a degradation rate of over 88% (after 6 months of application to the soil), thus balancing environmental friendliness and economic efficiency; the functional additives include toughening agents. The coating contains a toughening agent, an anti-aging agent, a defoamer, and a hydrophobic modifier. The toughening agent is one of epoxidized soybean oil and polycaprolactone. The anti-aging agent is one of 2,6-di-tert-butyl-p-cresol (BHT) and UV absorber UV-531. The defoamer is an organosilicon defoamer. The hydrophobic modifier is methyl silicone oil or polydimethylsiloxane. The crosslinking agent is one or more of trimethylolpropane (TMP), glycerol, and pentaerythritol. The crosslinking density of the coating layer can be flexibly adjusted by controlling the amount of crosslinking agent, thereby precisely controlling the potassium release rate. The higher the crosslinking density, the denser the coating layer, and the slower the potassium release. Conversely, the lower the crosslinking density, the faster the release rate.

[0013] Preferably, by controlling the chain length of the bio-based polyol (such as using short-chain polytetrahydrofuran compounded with castor oil-based polyol), the crosslinking density and mechanical strength of the coating layer can be further improved, and the tensile strength can be increased by more than 100% compared with the traditional coating layer. Long-term controlled release can still be achieved even with a low coating rate (5%), reducing the amount of coating material used and production costs.

[0014] Furthermore, the controlled-release potassium particles have a particle size of 1.5-4.8 mm, a bulk density of 1.20-1.40 g / cm³, a compressive strength ≥20 N / particle, and a sphericity ≥0.85. Compared to existing products, the particle stability and resistance to mechanical damage are significantly improved, effectively preventing breakage during transportation and storage. Under conditions of 25℃ and deionized water, the cumulative potassium release rate meets the following requirements: ≤10% within 24 hours (to avoid premature release and seedling burn), ≤22% within 7 days, and ≤45% within 30 days. Within 60 days, the release rate is ≤70%; within 90 days, it is ≥90%; and within 120 days, it is ≥96%, meeting the requirements of HG / T4215-2011 "Controlled-Release Fertilizer" standard. It can achieve slow and continuous release of potassium, precisely matching the potassium requirements of crops from seedling to maturity, especially during the fruit expansion and grain filling stages. It can be coated a second time according to the controlled-release requirements to form a double-layer polyurethane coating layer, with a total coating rate of 12%-20%, extending the controlled-release period to 150-180 days, making it suitable for crops with longer growth periods (such as cotton and fruit trees).

[0015] Meanwhile, these controlled-release potassium granules can tolerate different soil environments. In acidic soils (pH=5.0-6.5), the potassium release rate can be increased by 15%-20%, preventing potassium from being fixed by hydrogen ions. In alkaline soils (pH=7.5-8.5), the release rate is stable, which can alleviate the interference of calcium ions on potassium absorption. In saline soils, it can reduce the inhibitory effect of sodium ions on potassium absorption and improve the salt resistance of crops.

[0016] A method for preparing the above-mentioned controlled-release potassium particles includes the following steps: (1) Raw material pretreatment: Potassium source raw materials, functional carriers, potassium activator modifiers and binders are pretreated respectively, and customized bio-based polyurethane coating liquid is prepared for later use. (2) Mixed granulation: The pretreated potassium source material, functional carrier and binder are mixed, potassium activator modifier solution is sprayed, and then deionized water is sprayed for granulation. The qualified wet potassium nutrient core particles are obtained by sieving. (3) Drying treatment: Dry the wet potassium element nutrient core particles to a moisture content of ≤1.0% and cool to room temperature for later use; (4) Gradient coating and curing: Dry potassium nutrient core particles are placed into the coating equipment, and customized bio-based polyurethane coating liquid is sprayed using a gradient spraying method. The coating is cured in stages to form a polyurethane coating layer. After curing, the coating is cooled to room temperature. (5) Screening and packaging: The coated granules are screened a second time and their performance is sampled. After passing the test, they are weighed and packaged.

[0017] Furthermore, in step (1), the raw material pretreatment specifically includes: ① Potassium source raw material processing: Remove impurities (such as stones, soil, weeds, etc.), put them into a universal pulverizer, adjust the pulverizing speed to 3000-3500 rpm, pulverize to 120-160 mesh, after pulverizing, screen through a vibrating screen to remove un-pulverized coarse particles, put the qualified potassium source raw material powder into a dry and sealed container for later use to prevent moisture absorption and clumping. ② Functional carrier treatment: Modify the functional carrier according to the above composite modification process, and seal it for later use after modification; if no modification is required, remove impurities directly, crush to 280-400 mesh, and sieve for later use. ③ Potassium activator modifier pretreatment: Dissolve the potassium activator modifier in deionized water to prepare a modifier solution with a mass concentration of 8%-20%. Stir evenly and put it into a sealed container for later use. Ensure that the modifier is fully dissolved to facilitate uniform mixing with other raw materials in the future. ④ Adhesive pretreatment: Dissolve the adhesive in deionized water to prepare an adhesive solution with a mass concentration of 3%-8%, stir until completely dissolved, without precipitation or clumping, and seal for later use; ⑤ Preparation of customized bio-based polyurethane coating solution: Weigh the isocyanate component, bio-based polyol component, functional additive and crosslinking agent according to the preset ratio. First, put the isocyanate component and bio-based polyol component into a high-speed stirrer, adjust the stirring speed to 1000-1200 rpm, and stir for 20-25 minutes at room temperature (20-25℃) until the mixture is uniform. Then, add the crosslinking agent and functional additive in sequence, stirring for 3-5 minutes after each addition to ensure that all components are completely dispersed in the mixture system, and prepare a uniform and transparent customized bio-based polyurethane coating solution. Place it in a constant temperature sealed container and store it in an environment of 20-25℃ for later use. Avoid direct sunlight and high temperature exposure to prevent the coating solution from curing prematurely.

[0018] Further, in step (2), the mixing and granulation is carried out using a disc granulator, a drum granulator, or an extrusion granulator. The specific operation includes: putting the potassium source raw material powder, functional carrier powder, and binder solution into the feed inlet of the mixing and granulation equipment according to the preset mass ratio, closing the feed door, adjusting the stirring speed of the equipment to 45-60 rpm, and carrying out dry mixing for 10-22 minutes. During this period, the machine is stopped every 4 minutes to observe the mixing uniformity until the material color is consistent and there is no obvious layering or clumping; then the spray system is turned on to spray the pretreated potassium activator modifier solution into the mixture at a uniform speed of 5-7 mL / min, and stirring is continued for 6-9 minutes to ensure that the potassium activator modifier is fully mixed with the material; after the mixing is completed, the spray system of the equipment is turned on to spray deionized water (the amount added is 7% of the total mass of the mixture) -13% potassium nutrient core particles are sprayed evenly into the mixture at a rate of 5-7 mL / min, while maintaining a constant stirring speed. Granulation is carried out for 30-50 minutes. During granulation, the particle formation is observed in real time. If the particle size is too small or loose, the amount of deionized water sprayed can be increased appropriately (0.5%-1% each time). If the particles are clumped or too large, the amount of deionized water sprayed can be reduced appropriately, and the stirring speed can be increased by 5-10 rpm. After granulation, the discharge port of the granulation equipment is opened, and the formed wet potassium nutrient core particles are placed into a vibrating screen (screen mesh size of 1.5-4.8 mm). Unqualified particles with a particle size that is too small (<1.5 mm) or too large (>4.8 mm) are removed. Unqualified particles can be crushed again and returned to the mixing and granulation step. Qualified wet particles are placed in a transfer container for later use.

[0019] Preferably, a disc granulator is used for granulation. Adjusting the disc tilt angle to 38°-52° can further improve the granulation rate, particle roundness and sphericity, and ensure the uniformity of subsequent coating.

[0020] Further, step (3) uses a hot air circulating drying box. The specific operation includes: turning on the drying equipment in advance, adjusting the drying temperature to 90-115℃, preheating for 15-20 minutes to ensure that the internal temperature of the equipment is uniform and there are no local overheated areas; spreading the qualified wet potassium nutrient core particles in the transfer container evenly on the drying tray, with a particle thickness of 1.5-2.5cm to avoid uneven drying due to excessive stacking; placing the tray on the layered support of the drying equipment, ensuring that there is a gap of 8-12cm between the trays to facilitate the flow of hot air; closing the drying equipment door and maintaining the drying temperature. The drying time is 25-40 minutes, and the equipment vents are opened every 6 minutes during the drying process to remove moisture from the equipment. The drying status of the particles is observed at the same time. After drying, the power of the equipment is turned off. When the temperature inside the equipment drops to 30-40℃, a small amount of particles are taken out and the moisture content is tested with a moisture meter. If the moisture content is >1.0%, the particles are put back into the drying equipment and dried for another 5-7 minutes until the moisture content is ≤1.0%. If the moisture content is qualified, the dried potassium nutrient core particles are taken out and placed on a cooling tray to cool naturally to room temperature (20-25℃) for later use.

[0021] Further, in step (4), gradient coating and curing is the core improved process. The specific operations include: ① Equipment debugging: turn on the coating equipment (fluidized bed coating machine or rotary drum coating machine), adjust the equipment speed to 28-38 rpm, turn on the hot air system, preheat the internal temperature of the equipment to 65-80℃, and at the same time debug the atomization spraying system, adjust the atomization pressure to 0.45-0.65MPa, and adjust the spraying speed to 7-20mL / min to ensure that the spraying system is unblocked and the spraying is uniform; ② Gradient spraying: put the dried potassium element nutrient core particles cooled to room temperature into the feed port of the coating equipment at a uniform speed. After the particles are evenly dispersed in the equipment, turn on the customized bio-based polyurethane coating liquid spraying switch, and adopt the gradient spraying method from "low concentration, slow speed" to "medium concentration, medium speed" to "high concentration, slow speed". Spray the coating liquid in 3-4 stages. After each stage of spraying is completed, keep the equipment speed and temperature unchanged and stir for 5-8 minutes to ensure that the coating liquid covers the entire surface. ③ Staged curing: After gradient spraying, the equipment temperature is adjusted in stages for curing. First stage (10-15 minutes): The temperature is maintained at 65-70℃ to allow the coating liquid to initially solidify and form a dense bottom layer coating. Second stage (15-20 minutes): The temperature is raised to 70-75℃ to promote full cross-linking and curing of the coating liquid, improving the flexibility and adhesion of the coating layer. Third stage (5-10 minutes): The temperature is lowered to 60-65℃ for slow curing to avoid cracking of the coating layer due to rapid curing. During the curing process, the curing status of the coating layer is observed every 12 minutes to avoid insufficient curing leading to coating layer peeling off, or over-curing leading to coating layer becoming brittle. ④ Cooling and discharging: After curing, the hot air system and spraying system are turned off, and the equipment speed is maintained. When the temperature inside the equipment drops to room temperature (20-25℃), the discharge port is opened to remove the controlled-release potassium element particles after coating and place them in a transfer container for later use. If a secondary coating is required, repeat the above gradient coating and curing steps to control the total coating rate to 12%-20%.

[0022] Compared to traditional one-time coating, gradient coating and curing technology can effectively improve the uniformity, density and flexibility of the coating layer, avoid problems such as cracks and leakage in the coating layer, and at the same time, it can precisely control the coating thickness and cross-linking density, realize personalized regulation of potassium release rate, and adapt to the growth stage needs of different crops.

[0023] Further, in step (5), the screening and packaging specifically includes: ① Secondary screening: The controlled-release potassium particles after coating and solidification are placed into a vibrating screen (screen mesh size is 1.5-4.8mm) for secondary screening to remove damaged particles, uncoated particles and particles of unqualified size generated during the coating process. Unqualified particles can be reused in the mixing and granulation step after being crushed, and qualified particles are placed in a clean transfer container; ② Performance sampling inspection: 50-100 particles are randomly selected from the qualified particles to test the particle size, sphericity, compressive strength, moisture content and potassium release rate. At the same time, the integrity of the coating is tested (using the static water immersion method, the coating damage rate is ≤5% after immersion for 24 hours) to ensure that it meets the preset standards (particle size 1.5-4.8mm, sphericity ≥0. .85, compressive strength ≥20N / particle, moisture content ≤1.0%), if the sampling inspection fails, the coating and drying steps need to be re-inspected, and the sampling inspection is carried out again after rectification; ③ Metering and packaging: Put the qualified controlled-release potassium granules into the automatic metering and packaging machine, and measure them according to the preset specifications (such as 25kg / bag, 50kg / bag). The packaging adopts waterproof, moisture-proof and damage-proof composite woven bags. After the packaging is completed, the product name, specifications, production date, shelf life, coating rate, controlled release period, potassium content (calculated as K2O), applicable crops and HG / T4215-2011 standard number are marked on the packaging bag. Then, the packaged products are placed in the warehouse and sealed in a dry, ventilated and cool environment to avoid moisture, exposure to the sun and compression.

[0024] By adopting the above technical solution, the present invention has the following beneficial effects: This invention employs a separate potassium coating design, breaking the limitations of existing nitrogen, phosphorus, and potassium mixed coatings. It can be flexibly mixed with separately coated nitrogen, phosphorus, and other nutrients in any proportion. It can precisely adjust the mixing ratio of potassium with other nutrients according to the nutrient requirements of different crops (such as grain crops and fruit and vegetable crops) and different growth stages (such as seedling stage, fruit expansion stage, and grain filling stage), achieving personalized and precise fertilization and adapting to the individual needs of various crops. At the same time, it can be adapted to various soil types such as acidic, alkaline, and saline soils, further broadening the product's applicability. Detailed Implementation

[0025] The following detailed description, in conjunction with specific embodiments of the present invention, is provided. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0026] Example 1: Preparation of controlled-release potassium particles from a single potassium source (potassium chloride) 1) Raw material pretreatment: Potassium chloride was pulverized to 140 mesh and set aside; attapulgite was pulverized to 320 mesh, soaked in 3% dilute hydrochloric acid solution for 20 minutes (solid-liquid ratio 1:8 g / mL, stirring speed 450 rpm), washed until pH=7.0, dried at 90℃ to a moisture content of 0.7%, and 0.6% silane coupling agent KH-550 was added. The mixture was stirred at 85℃ and 900 rpm for 12 minutes after modification and set aside; potassium polyaspartate was dissolved in deionized water to prepare a 15% (w / w) potassium polyaspartate solution and set aside; sodium carboxymethyl cellulose (CMC) was dissolved in deionized water. In this process, a 5% CMC solution was prepared and set aside. Hexamethylene diisocyanate (HDI) and castor oil-based polyol (molecular weight 2500 Da, bio-based content 88%) were mixed at a molar ratio of NCO:OH = 1:1.4. 3.5% epoxidized soybean oil (toughening agent), 1.0% BHT (anti-aging agent), 0.8% silicone defoamer, 1.5% methyl silicone oil (hydrophobic modifier), and 0.8% trimethylolpropane (TMP, crosslinking agent) were added. The mixture was stirred at 1100 rpm at room temperature for 22 minutes to prepare a customized bio-based polyurethane coating solution for later use. 2) Mixing and granulation: Take 85kg of potassium chloride powder, 12kg of modified attapulgite, and 1.5kg of 5% CMC solution and put them into a disc granulator. Adjust the disc tilt angle to 42° and the rotation speed to 50rpm. Dry mix for 15 minutes until uniform. Spray 1.5kg of 15% potassium polyaspartate solution and continue stirring for 7 minutes. Then spray 9kg of deionized water and granulate for 38 minutes to obtain wet potassium nutrient core particles with a particle size of 1.5-4.8mm. 3) Drying treatment: The wet kernel particles are placed in a hot air circulating drying oven, preheated at 100℃ for 18 minutes, and dried for 30 minutes. After drying, the moisture content of the particles is 0.8%, and the dried potassium nutrient kernel is obtained. 4) Gradient coating and curing: The dried core particles are placed in a fluidized bed coating machine, the rotation speed is adjusted to 32 rpm, the temperature is preheated to 70°C, the atomization pressure is 0.5 MPa, and the customized bio-based polyurethane coating liquid is sprayed using a gradient spraying method. The coating rate is controlled at 8%, and the coating is carried out in 3 stages and cured. After cooling to room temperature, controlled-release potassium particles are obtained. 5) Screening and packaging: Screening removes unqualified particles, weighs and packages them, and seals them for storage.

[0027] Performance testing: The controlled-release potassium granules have a particle size of 1.5-4.8mm, a sphericity of 0.88, a compressive strength of 22N / granule, and a bulk density of 1.28g / cm³. Under deionized water conditions at 25℃, the cumulative potassium release rate is 8% after 24 hours, 20% after 7 days, 42% after 30 days, 68% after 60 days, 92% after 90 days, and 97% after 120 days. Coating integrity testing: After 24 hours of soaking, the breakage rate is 3.2%, meeting the standard requirements. When used for corn planting, the application rate is 30kg per mu (approximately 0.067 hectares). Compared with traditional potassium chloride fertilization, corn yield per mu increases by 9.8%, potassium utilization rate increases to 65%, and soil potassium fixation is reduced by more than 75%. It can be mixed with separately coated nitrogen fertilizer at a ratio of 1:1.3 according to the needs of corn during the tasseling and grain-filling stages to further increase the thousand-grain weight and yield per mu by an additional 2.5%.

[0028] Example 2: Preparation of controlled-release potassium particles from a mixed potassium source (potassium chloride + potassium sulfate) 1) Raw material pretreatment: Potassium chloride and potassium sulfate are mixed at a mass ratio of 1:1 (containing 57% K2O after mixing), pulverized to 130 mesh, and set aside; zeolite powder and straw charcoal are mixed at a mass ratio of 3:2, pulverized to 300 mesh, soaked in 2.5% dilute nitric acid solution for 22 minutes, washed until pH=7.2, dried at 92℃ to a moisture content of 0.6%, 0.5% silane coupling agent KH-570 is added, and stirred at 88℃ and 950rpm for 10 minutes, and set aside after modification; seaweed extract is dissolved in deionized water to prepare a 12% seaweed extract solution, set aside; polyvinyl alcohol (PVA) Dissolve PVA in deionized water to prepare a 4% PVA solution for later use; mix isophorone diisocyanate (IPDI) and palm oil-based polyol (molecular weight 2000 Da, bio-based content 90%) in a molar ratio of NCO:OH = 1:1.3, add 3.0% polycaprolactone (toughening agent), 0.9% UV-531 (anti-aging agent), 0.7% silicone defoamer, 1.2% polydimethylsiloxane (hydrophobic modifier) ​​and 0.6% glycerol (crosslinking agent), stir at 1050 rpm at room temperature for 24 minutes to prepare a customized bio-based polyurethane coating solution for later use; 2) Mixing and granulation: Take 82kg of mixed potassium source powder, 15kg of modified composite carrier and 1.8kg of 4% PVA solution and put them into a rotary drum granulator. Mix them dry for 18 minutes at 55rpm until uniform. Spray 1.2kg of 12% seaweed extract solution and continue stirring for 8 minutes. Then spray 8.5kg of deionized water and granulate for 42 minutes to obtain wet potassium nutrient core particles with a particle size of 1.5-4.8mm. 3) Drying treatment: The wet kernel particles are placed in a hot air circulating drying oven, preheated at 95℃ for 16 minutes, and dried for 32 minutes. After drying, the moisture content of the particles is 0.9%, and the dried potassium nutrient kernel is obtained. 4) Gradient coating and curing: The dried core particles are placed in a rotary drum coating machine, the speed is adjusted to 35 rpm, the temperature is preheated to 75℃, the atomization pressure is 0.55 MPa, and a customized bio-based polyurethane coating liquid is sprayed using a gradient spraying method. The coating rate is controlled at 10%, and the coating is carried out in 4 stages and cured. After cooling to room temperature, controlled-release potassium particles are obtained. 5) Screening and packaging: Screening removes unqualified particles, weighs and packages them, and seals them for storage.

[0029] Performance testing: The controlled-release potassium granules have a particle size of 1.5-4.8 mm, a sphericity of 0.87, a compressive strength of 23 N / granule, and a bulk density of 1.32 g / cm³. Under deionized water conditions at 25℃, the cumulative potassium release rate is 7% after 24 hours, 18% after 7 days, 40% after 30 days, 65% after 60 days, 93% after 90 days, and 98% after 120 days. When used for tomato cultivation (a chlorine-sensitive crop), the application rate is 35 kg per mu (approximately 0.067 hectares). Compared with traditional potassium sulfate fertilization, tomato yield increases by 12.3% per mu, potassium utilization rate increases to 70%, and soil potassium loss is reduced by more than 80%. It can be mixed with separately coated nitrogen and phosphorus fertilizers at a ratio of 1:1.6:1.0 according to the needs of tomato fruit expansion period, increasing the sugar content of tomato fruits by 1.6 percentage points and reducing the rate of deformed fruits by 5.0%.

[0030] Example 3: Preparation of controlled-release potassium particles (potassium sulfate as raw material) with a double-layer third polyurethane coating 1) Raw material pretreatment: Potassium sulfate (containing 2% K₂O₅) is pulverized to 150 mesh and set aside; bentonite is pulverized to 350 mesh, soaked in 3.5% dilute hydrochloric acid solution for 18 minutes, washed until pH=6.8, dried at 88℃ to a moisture content of 0.7%, and 0.8% silane coupling agent KH-550 is added. The mixture is stirred at 82℃ and 850 rpm for 14 minutes after modification and set aside; potassium humate is dissolved in deionized water to prepare an 18% potassium humate solution and set aside; starch-modified material is dissolved in deionized water to prepare a 6% potassium humate solution. Prepare a starch-modified solution (%); mix diphenylmethane diisocyanate (MDI) and soybean oil-based polyol (molecular weight 3000 Da, bio-based content 86%) at a molar ratio of NCO:OH = 1:1.6, add 4.0% epoxidized soybean oil (toughening agent), 1.1% BHT (anti-aging agent), 0.9% organosilicon defoamer, 1.8% methyl silicone oil (hydrophobic modifier), and 1.0% pentaerythritol (crosslinking agent), stir at 1150 rpm at room temperature for 20 minutes to prepare a customized bio-based polyurethane coating solution (for later use); 2) Mixing and granulation: Take 88 kg of potassium sulfate powder, 10 kg of modified bentonite, and 1.2 kg of 6% starch-modified solution and put them into an extrusion granulator. Mix them dry for 12 minutes at 58 rpm until uniform. Spray 0.8 kg of 18% potassium humate solution and continue stirring for 6 minutes. Then spray 9.5 kg of deionized water and granulate for 35 minutes to obtain wet potassium nutrient core particles with a particle size of 1.5-4.8 mm. 3) Drying treatment: The wet kernel particles are placed in a hot air circulating drying oven, preheated at 105℃ for 15 minutes, and dried for 28 minutes. After drying, the moisture content of the particles is 0.7%, and the dried potassium nutrient kernel is obtained. 4) Gradient coating and curing: First coating: The dried core particles are placed in a fluidized bed coating machine, the rotation speed is adjusted to 30 rpm, preheated to 68℃, and the atomization pressure is 0.48 MPa. The customized bio-based polyurethane coating liquid is sprayed using a gradient spraying method, and the coating rate is controlled at 7%. The coating is cured in 3 stages. Second coating: The customized bio-based polyurethane coating liquid is sprayed again on the surface of the particles after the first coating using a gradient spraying method, and the total coating rate is controlled at 16%. The coating is cured in 3 stages and cooled to room temperature to obtain double-layer third polyurethane coated controlled-release potassium particles. 5) Screening and packaging: Screening removes unqualified particles, weighs and packages them, and seals them for storage.

[0031] Performance testing: The controlled-release potassium granules have a particle size of 1.5-4.8mm, a sphericity of 0.89, a compressive strength of 25N / granule, and a bulk density of 1.35g / cm³. Under deionized water conditions at 25℃, the cumulative potassium release rate is 6% after 24 hours, 15% after 7 days, 36% after 30 days, 60% after 60 days, 91% after 90 days, and 96% after 180 days. For apple cultivation (a long-growing crop), the application rate is 40kg per acre, applied as a single base fertilizer. No additional potassium fertilizer is needed during the growing season. Apple yield increases by 11.5% per acre, potassium utilization rate increases to 68%, and soil potassium fixation decreases by more than 78%. It can be mixed with separately coated nitrogen and phosphorus fertilizers at a ratio of 1:1.5:1.2 for topdressing according to the needs of apple fruit expansion period, improving apple fruit surface smoothness and increasing fruit firmness by 0.3kg / cm².

[0032] Example 4: Preparation of unmodified carrier-controlled release potassium particles (potassium chloride + potassium sulfate as raw materials) 1) Raw material pretreatment: Potassium chloride and potassium sulfate are mixed at a mass ratio of 1:0.5 and pulverized to 120 mesh for later use; diatomaceous earth is pulverized to 280 mesh to remove impurities and is set aside for later use (unmodified); potassium amino acids are dissolved in deionized water to prepare an 8% potassium amino acid solution for later use; xanthan gum is dissolved in deionized water to prepare a 3% xanthan gum solution for later use; HDI and cellulose-based polyol (molecular weight 1800 Da, bio-based content 85%) are mixed at a molar ratio of NCO:OH = 1:1.2, and 2.5% polycaprolactone (toughening agent), 0.8% UV-531 (anti-aging agent), 0.6% silicone defoamer, 1.0% methyl silicone oil (hydrophobic modifier) ​​and 0.5% glycerol (crosslinking agent) are added. The mixture is stirred at 1000 rpm at room temperature for 25 minutes to prepare a customized bio-based polyurethane coating solution for later use. 2) Mixing and granulation: Take 78 kg of mixed potassium source powder, 20 kg of unmodified diatomaceous earth, and 1.5 kg of 3% xanthan gum solution and put them into a disc granulator. Adjust the disc tilt angle to 40° and the rotation speed to 45 rpm. Dry mix for 20 minutes until uniform. Spray 0.5 kg of 8% amino acid potassium solution and continue stirring for 9 minutes. Then spray 8 kg of deionized water and granulate for 45 minutes to obtain wet potassium nutrient core particles with a particle size of 1.5-4.8 mm. 3) Drying treatment: The wet kernel particles are placed in a hot air circulating drying oven, preheated at 90℃ for 20 minutes, and dried for 35 minutes. After drying, the moisture content of the particles is 1.0%, and the dried potassium nutrient kernel is obtained. 4) Gradient coating and curing: The dried core particles are placed in a rotary drum coating machine, the speed is adjusted to 28 rpm, the temperature is preheated to 65℃, the atomization pressure is 0.45 MPa, and a customized bio-based polyurethane coating liquid is sprayed using a gradient spraying method. The coating rate is controlled at 7%, and the process is cured in 3 stages. After cooling to room temperature, controlled-release potassium particles are obtained. 5) Screening and packaging: Screening removes unqualified particles, weighs and packages them, and seals them for storage.

[0033] Performance testing: The controlled-release potassium granules have a particle size of 1.5-4.8mm, a sphericity of 0.85, a compressive strength of 20N / granule, and a bulk density of 1.22g / cm³. Under deionized water conditions at 25℃, the cumulative potassium release rate is 9% after 24 hours, 21% after 7 days, 44% after 30 days, 70% after 60 days, 90% after 90 days, and 96% after 120 days. When used for wheat cultivation, the application rate is 28kg per mu (approximately 0.067 hectares). Compared with traditional mixed potassium fertilizer application, wheat yield per mu increases by 8.2%, potassium utilization rate increases to 58%, and soil potassium fixation decreases by more than 65%. It can be mixed with separately coated nitrogen fertilizer at a ratio of 1:1.4 according to the needs of wheat during the jointing stage to reduce wheat lodging and increase the grain filling rate by 3.8%.

[0034] Example 5: Bio-based short-chain polyol coated with composite activator controlled-release potassium particles This embodiment uses a bio-based short-chain polyol (castor oil-based polyol compounded with PTMEG-250) to prepare a coating solution, combined with a potassium aspartate-seaweed extract composite activator, to further enhance the mechanical strength of the coating layer and the potassium activation effect. This addresses the technical shortcomings of existing coating layers, such as insufficient resistance to damage and short-lived potassium activation effect, and achieves precise controlled release of potassium, synergistic enhancement of activation and soil improvement, while retaining the flexible blending characteristics of individual coatings.

[0035] 1) Raw material pretreatment: ① Potassium source raw material treatment: Potassium chloride was selected as the single potassium source raw material. After removing impurities, it was placed in a universal pulverizer, the speed was adjusted to 3200 rpm, and pulverized to 140 mesh. After sieving, it was placed in a dry and sealed container for later use; ② Composite carrier modification treatment: Attapulgite and humic acid were mixed at a mass ratio of 4:1, pulverized to 320 mesh, and a 3% dilute hydrochloric acid solution (solid-liquid ratio 1:8 g / mL) was added. The mixture was soaked at 450 rpm at room temperature for 22 minutes, washed until pH=7.0, dried at 90℃ until the moisture content was ≤0.8%, and 0.7% silane coupling agent KH-550 was added. The mixture was stirred at 85℃ for 12 minutes to obtain the modified composite carrier for later use; ③ Composite activator pretreatment: Potassium polyaspartate and seaweed extract were mixed at a mass ratio of 2:1 and dissolved... Dissolve in deionized water to prepare a 15% (w / w) composite activator solution for later use; ④ Preparation of bio-based short-chain polyol coating solution: Using castor oil-based polyol (molecular weight 2200 Da), PTMEG-250 (short-chain polyol), and MDI as raw materials, mix them in a molar ratio of NCO∶OH=1∶1.5 (castor oil-based polyol to PTMEG-250 mass ratio 3∶1), add 3.5% epoxidized soybean oil (toughening agent), 1.0% BHT (anti-aging agent), 0.8% organosilicon defoamer, 1.5% methyl silicone oil (hydrophobic modifier), and 0.9% TMP (crosslinking agent), stir at 1100 rpm at room temperature for 22 minutes to prepare a uniform and transparent bio-based short-chain polyol coating solution, and seal it at 25℃ for later use; 2) Mixing and granulation: Take 86 kg of potassium chloride powder, 11 kg of modified composite carrier, and 1.6 kg of 5% CMC solution and put them into a disc granulator. Adjust the speed to 52 rpm and dry mix for 14 minutes until uniform. Spray 1.4 kg of 15% composite activator solution and continue stirring for 7 minutes. Spray 8.8 kg of deionized water. Set the disc inclination angle to 43° and granulate for 38 minutes. After sieving through a 1.5-4.8 mm vibrating screen, qualified wet potassium element nutrient core particles are obtained. 3) Drying treatment: Spread the wet kernel particles evenly on the drying tray (2.0cm thick), put it into the hot air circulating drying oven, preheat at 98℃ for 17 minutes, dry for 28 minutes, and check the moisture content to be 0.7%. Cool to room temperature for later use. 4) Gradient coating and curing: The dried core particles are placed in a fluidized bed coating machine, the rotation speed is adjusted to 33 rpm, the temperature is preheated to 72°C, the atomization pressure is 0.52 MPa, and the bio-based short-chain polyol coating liquid is sprayed in a gradient spraying manner. The coating rate is controlled at 9%, and the particles are cured in 3 stages and cooled to room temperature to obtain controlled-release potassium particles. 5) Screening and Packaging: Secondary screening removes unqualified particles. 80 particles are randomly sampled for inspection. After confirming that all performance meets the standards, the particles are weighed, packaged, and sealed for storage.

[0036] Performance testing: The controlled-release potassium particles have a particle size of 1.5-4.8 mm, a sphericity of 0.88, a compressive strength of 24 N / particle, and a bulk density of 1.30 g / cm³. Under deionized water conditions at 25℃, the cumulative potassium release rate is 7% after 24 hours, 17% after 7 days, 41% after 30 days, 66% after 60 days, 94% after 90 days, and 98% after 120 days. The tensile strength of the coating layer reaches 6.5 MPa, which is 150% higher than that of traditional coating layers, and the resistance to mechanical damage is significantly enhanced. It is suitable for use in corn-wheat rotation planting. The dosage is 32 kg per mu. Compared with Example 1 (ordinary bio-based coating), the potassium utilization rate is increased to 72%, the soil organic matter content is increased by 22%, the soil potassium fixation is reduced by 82%, and the coating layer degradation rate reaches 92% (8 months after application to the soil). The mixing ratio can be flexibly adjusted according to the differences in crop rotation. During the wheat growing season, it is mixed with separately coated nitrogen fertilizer at a ratio of 1:1.3, and during the corn growing season, it is mixed with separately coated nitrogen and potassium fertilizer at a ratio of 1:1.4:1.0, so as to achieve precise nutrient matching in crop rotation plots. The overall yield per mu is increased by 13.5% compared with traditional fertilization, which is significantly better than the existing ordinary coated controlled-release potassium granules.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A controlled-release potassium element granule, characterized in that, It includes a potassium nutrient core and a polyurethane coating layer covering the surface of the potassium nutrient core; the potassium nutrient core uses at least one of potassium chloride and potassium sulfate as the potassium source material, and also includes a functional carrier, a potassium activator modifier and a binder. After the potassium source material, functional carrier, potassium activator modifier and binder are mixed evenly, the potassium nutrient core is formed by granulation and drying processes.

2. The controlled-release potassium element particles according to claim 1, characterized in that, In the potassium nutrient core, the mass percentages of each component are as follows: potassium source raw material 70%-92%, functional carrier 5%-22%, potassium activator modifier 1%-5%, and binder 0.5%-3%.

3. The controlled-release potassium element particles according to claim 1 or 2, characterized in that, The potassium source material can be a single material or a mixture of materials; the single material is potassium chloride or potassium sulfate, wherein the potassium chloride contains 58%-62% potassium (calculated as K2O) and the potassium sulfate contains 50%-54% potassium (calculated as K2O); the mixture of materials is potassium chloride and potassium sulfate mixed at a mass ratio of 1:0.3-2.

0.

4. The controlled-release potassium element particles according to claim 1, characterized in that, The functional carrier is selected from one or more of attapulgite, bentonite, zeolite powder, diatomite, straw charcoal, and humic acid, with a particle size of 280-400 mesh, and the functional carrier undergoes composite modification treatment.

5. The controlled-release potassium element particles according to claim 4, characterized in that, The composite modification process of the functional carrier is as follows: after crushing and sieving the functional carrier, it is soaked in a 2%-4% dilute hydrochloric acid or dilute nitric acid solution for 15-25 minutes with a solid-liquid ratio of 1:7-10 g / mL and a stirring speed of 350-550 rpm. The carrier is washed until the pH is 6.5-7.5, dried at 85-95℃ until the moisture content is ≤0.8%, cooled, and 0.3%-1.0% of its mass of silane coupling agent is added. The carrier is stirred at 80-90℃ and 800-1000 rpm for 10-15 minutes and then sealed for later use.

6. The controlled-release potassium element particles according to claim 1, characterized in that, The potassium activator modifier is selected from one or more of potassium polyaspartate, seaweed extract, potassium humate, and potassium amino acids; the binder is selected from one or more of sodium carboxymethyl cellulose, polyvinyl alcohol, starch modifier, and xanthan gum, with a molecular weight of 8000-20000 Da.

7. The controlled-release potassium element particles according to claim 1, characterized in that, The thickness of the polyurethane coating layer is 10-40 μm, and the coating rate is 5%-15%. The polyurethane coating layer is a bio-based modified polyurethane coating layer, which is formed by gradient curing of a customized bio-based polyurethane coating agent. The customized bio-based polyurethane coating agent includes isocyanate components, bio-based polyol components, functional additives and crosslinking agents, and the molar ratio (NCO:OH) of the isocyanate component to the bio-based polyol component is 1:1.1-2.

2.

8. The controlled-release potassium element particles according to claim 7, characterized in that, The bio-based polyol component is one or more of castor oil-based polyol, palm oil-based polyol, soybean oil-based polyol, and cellulose-based polyol, with a molecular weight of 1200-4000 Da and a bio-based content of ≥85%; the crosslinking agent is one or more of trimethylolpropane, glycerol, and pentaerythritol, and the amount added is 0.3%-1.5% of the total mass of the isocyanate component and the bio-based polyol component.

9. The controlled-release potassium element particles according to claim 1, characterized in that, The controlled-release potassium particles have a particle size of 1.5-4.8 mm, a bulk density of 1.20-1.40 g / cm³, a compressive strength ≥20 N / particle, and a sphericity ≥0.

85. Under conditions of 25℃ and deionized water, the cumulative potassium release rate meets the following requirements: ≤10% within 24 h, ≤22% within 7 days, ≤45% within 30 days, ≤70% within 60 days, ≥90% within 90 days, and ≥96% within 120 days.

10. A method for preparing controlled-release potassium element particles according to any one of claims 1-9, characterized in that, Includes the following steps: (1) Raw material pretreatment; (2) Mixing and granulation; (3) Drying treatment; (4) Gradient coating and curing; (5) Screening and packaging.