Slow-release ammoniated potassium sulfate compound fertilizer and production process thereof

Abstract

The present application relates to the technical field of compound fertilizer, in particular to a slow-release ammoniated potassium sulfate compound fertilizer and a production process thereof. The production process of the slow-release ammoniated potassium sulfate compound fertilizer comprises the preparation of ammoniated potassium sulfate fertilizer core, the preparation of in-situ crystallization coating layer and the preparation of slow-release ammoniated potassium sulfate compound fertilizer. In the present application, coating liquid A and coating liquid B are alternately sprayed in pulses to synchronously react and crystallize on the surface of the fertilizer core, so that a continuous and dense magnesium ammonium phosphate film layer is grown in-situ. Nano-attapulgite is used as a nucleation site and to fill defects, so that the film layer is combined through chemical bonds and physical anchoring, thereby preventing shedding and having nutrient properties. Then, paraffin-oleic acid-triethanolamine emulsion and hydrophobic fumed silica are compounded to seal, so as to penetrate the interstitial gaps and construct a super-hydrophobic surface, thereby realizing long-acting fertilizer supply through synergistic controlled release. At the same time, EDTA chelated zinc and boron are positioned in the sealing layer to be slowly released, so as to integrate nitrogen, phosphorus, potassium, magnesium, zinc and boron, synchronize nutrient release with crop demand, and realize synergistic slow release.

Description

Technical Field

[0001] This invention relates to the field of compound fertilizer technology, specifically to a slow-release ammonified potassium sulfate compound fertilizer and its production process. Background Technology

[0002] Potassium sulfate ammonium compound fertilizer, rich in potassium, sulfur, and ammonium nitrogen, is an important basic fertilizer for many economic crops. However, this type of fertilizer is highly water-soluble, and its nutrients are released too quickly after being applied to the soil. This not only leads to low fertilizer utilization but also easily causes seedling burn and nutrient loss with water, making it difficult to match the continuous nutrient requirements of crops in the middle and later stages. Therefore, modifying it to have a slow-release effect is a key way to improve the agronomic and environmental benefits of fertilizers.

[0003] Currently, the slow-release modification of fertilizers mainly relies on physical coating technology, which involves coating the surface of fertilizer core granules with a hydrophobic or semi-permeable polymer membrane. Commonly used materials include polyolefins, polyurethane, resins, and paraffin wax. While this traditional coating can slow down water infiltration to some extent, it generally suffers from the following prominent problems: First, the membrane layer and the fertilizer core are only bound by physical adsorption and weak mechanical interlocking forces, making them prone to rupture or detachment under storage, transportation, application, and alternating soil moisture conditions, resulting in loss of controlled release capability and triggering nutrient bursts. Second, the coating materials themselves are mostly chemically inert and difficult-to-degrade synthetic polymers, which can lead to soil microplastic pollution with long-term application. Furthermore, as an ineffective component, they have no nutritional function and effectively reduce the effective nutrient content of the fertilizer. Third, the single-layer homogeneous membrane layer has a simple control mechanism, often exhibiting a high initial leakage rate and significant nutrient bursts, followed by rupture due to the pressure difference between the inside and outside of the membrane layer in the later stages, making it difficult to precisely extend the release period to more than 90 days.

[0004] Furthermore, modern precision fertilization requires fertilizers to not only control the release of macronutrients such as nitrogen, phosphorus, and potassium, but also to simultaneously supply micronutrients such as zinc and boron. Moreover, each nutrient must be released in a coordinated and slow-release manner according to the crop's absorption patterns to prevent nutrient deficiencies at their source. However, traditional slow-release fertilizers containing micronutrients often use a simple method of mixing micronutrient salts with the substrate and then granulating or coating them. Elements such as zinc and boron are easily fixed and deactivated in the soil, or are rapidly lost with water in the early stages of coating, making it difficult to achieve a synchronized and long-lasting release with the main nutrients in both time and space. Especially when using substances such as paraffin for sealing, although the hydrophobic slow-release effect can be enhanced, if the micronutrients are not precisely loaded and released in an orderly manner, it is still impossible to meet the balanced nutritional needs of crops throughout their entire growth cycle. Currently, there is no fertilizer product that integrates ammonium nitrogen, potassium, phosphorus, magnesium, zinc, and boron into one unit and achieves a sequential and continuous synergistic supply of each nutrient through a multi-stage controlled-release system.

[0005] Therefore, this application aims to develop a slow-release compound fertilizer and its production process, which uses ammonium sulfate as the fertilizer core, has a nutrient-rich and high-strength coating layer, and can organically unify macro-elements and micro-elements, and achieve precise fertilization for more than 90 days through a multi-stage controlled-release mechanism, in order to solve the problems in the existing technology. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a slow-release ammonified potassium sulfate compound fertilizer and its production process.

[0007] This invention provides a production process for a slow-release ammonified potassium sulfate compound fertilizer, comprising: S1: Preparation of ammonified potassium sulfate fertilizer core; Ammonium sulfate, potassium sulfate and binder are added to deionized water, heated and stirred, and then concentrated by vacuum evaporation to a water content of 12-15% to obtain a hot viscous slurry containing complex salt microcrystals; then extruded and granulated, and dried by staged fluidized bed drying at 40-65℃ to a water content of ≤1.5%, and sieved to obtain 3-4 mm ammonified potassium sulfate fertilizer core. S2: Preparation of in-situ crystallized coating layer; Prepare a coating solution A containing magnesium / phosphorus and a coating solution B containing struvite seeds and alkaline pH; apply the coating solution to the surface of the fertilizer core in a fluidized bed using pulsed alternating spraying, and generate an insoluble magnesium ammonium phosphate crystal film through in-situ chemical reaction. Repeat the coating process until the weight gain is 22-30%, and obtain coated particles. S3: Preparation of slow-release ammonified potassium sulfate compound fertilizer; Low-melting-point paraffin, oleic acid, and triethanolamine were emulsified and then compounded with hydrophobic silica, EDTA-chelated zinc, and borax to form a composite sealing liquid. This liquid was sprayed onto the surface of coated particles, dried at low temperature, and then sieved to obtain a slow-release ammonified potassium sulfate compound fertilizer.

[0008] As a preferred aspect, S1: the preparation of ammonified potassium sulfate fertilizer cores specifically includes the following steps: S1.1: Add 60-70 parts by weight of deionized water to a reactor equipped with a stirrer, a reflux condenser and a vacuum interface, heat to 80-90℃, then add 55-65 parts by weight of ammonium sulfate crystals at 30-50 rpm, stir to dissolve, then add 100-120 parts by weight of potassium sulfate powder and 2-3 parts by weight of binder and stir well. Maintain the temperature at 80-90℃ and stir for 1.5-2 hours. After the temperature is maintained, stop heating and cool the material to 65-75℃. Connect the reactor to a vacuum system and perform reduced pressure evaporation and concentration at a vacuum degree of -0.07 to -0.08 MPa until the water content of the mixture drops to 12-15%, to obtain a hot viscous slurry containing a large number of potassium ammonium sulfate double salt micro crystals. S1.2: Heat the hot viscous slurry to 85-95℃, feed it into an extrusion granulator, and under an extrusion pressure of 6-8MPa, extrude the material from the die hole into a continuous cylindrical strip, and then cut it into wet granules by a cutter. S1.3: The wet granules are fed into a vibrating fluidized bed for pre-drying. The inlet air temperature is strictly controlled at 40-50℃. The surface moisture is slowly removed until the granule moisture content drops to 6-8%. Then, the pre-dried granules are fed into a fluidized bed dryer. The inlet air temperature is controlled at 60-65℃. The granules are dried until the granule moisture content is ≤1.5%. After drying, the granules are cooled to 30-35℃ and sieved to obtain 3-4mm granules, which are the ammonified potassium sulfate fertilizer cores.

[0009] As a preferred aspect, the binder in step S1.1 is specifically attapulgite.

[0010] As a preferred aspect, S2: the preparation of the in-situ crystallized coating layer specifically includes the following steps: S2.1: Add 18-22 parts by weight of magnesium sulfate heptahydrate and 14-17 parts by weight of ammonium dihydrogen phosphate to 50-60 parts by weight of deionized water, stir and dissolve at 40-50℃, then add 0.5-1.0 parts by weight of nano-attapulgite clay, and ultrasonically disperse for 15-20 min to obtain coating solution A. Take 20-25 parts by weight of deionized water, add 0.3-0.5 parts by weight of diammonium hydrogen phosphate, stir and dissolve, then adjust the pH to 8.5-9.0 with 5-6 wt% dilute ammonia water, then add 0.8-1.2 parts by weight of struvite seed crystals pulverized to 200 mesh, stir to suspend and ultrasonically disperse for 10-15 min to obtain coating solution B. S2.2: Add 100 parts by weight of ammonified potassium sulfate fertilizer core into a fluidized bed coating machine, preheat for 5-10 minutes under the conditions of fluidization air velocity of 1.5-2.0 m / s and inlet air temperature of 55-65℃, and then switch to a dual-fluid nozzle to alternately spray coating liquid A and coating liquid B in a pulse manner. S2.3: After stopping the spraying, maintain the inlet air temperature at 60-65℃ and continue fluidized drying for 15-20 minutes to make the free water content on the particle surface ≤2% to obtain a primary coating intermediate. Then, the primary coating intermediate is subjected to a second coating and drying under the conditions of S2.2 and S2.3 to make the coating weight gain reach 22-30wt% to obtain coated particles.

[0011] As a preferred aspect, in step S2.2, the bed temperature is controlled at 50-60℃, the bed pH is controlled at 8.0-9.0, and the total spraying time is 50-70 minutes.

[0012] As a preferred aspect, S3: The preparation of slow-release ammonified potassium sulfate compound fertilizer specifically includes the following steps: S3.1: Take 3-5 parts by weight of paraffin, 0.5-1.0 parts by weight of oleic acid, and 0.3-0.5 parts by weight of triethanolamine, add them to 30-40 parts by weight of deionized water at 80-85℃, and emulsify at high speed of 10000-12000 rpm for 10-15 min. Then add 0.5-1.0 parts by weight of hydrophobic fumed silica, 0.15-0.3 parts by weight of EDTA chelated zinc, and 0.08-0.15 parts by weight of borax. After stirring evenly, cool to 40-50℃ to obtain a composite blocking solution. S3.2: Place the coated granules in a rotary drum coating machine. At 40-50℃ and 30-40 rpm, use an air atomizing nozzle to evenly spray the composite closed emulsion onto the surface of the granules. After spraying, raise the air inlet temperature of the coating machine to 60-65℃ and continue to dry for 12-15 minutes. After drying, cool to 30-35℃ and use a vibrating screen to separate the finished granules to 3-5mm, thus obtaining slow-release ammonified potassium sulfate compound fertilizer.

[0013] As a preferred aspect, the paraffin in step S3.1 is specifically a low-melting-point paraffin with a temperature of 52-56°C.

[0014] As a preferred aspect, the amount of composite blocking emulsion used in step S3.2 is controlled to be 3-5% of the total mass of the coated particles.

[0015] The present invention also provides a slow-release potassium ammonium sulfate compound fertilizer, which is prepared by the production process of any one of the slow-release potassium ammonium sulfate compound fertilizers described in any one of the claims.

[0016] The present invention has the following advantages: 1. This invention innovatively employs a pulsed, alternating spraying method of coating solution A and coating solution B in a fluidized bed to simultaneously carry out chemical reactions and crystallization on the fertilizer core surface, resulting in the in-situ growth of a continuous and dense magnesium ammonium phosphate crystalline film. This film is firmly bonded to the fertilizer core through chemical bonds and physical anchoring, exhibiting a bonding strength far superior to traditional physical coatings, thus preventing film detachment. The introduction of nano-attapulgite serves as a nucleation site for crystallization, promoting uniform deposition of struvite, and also fills film defects, significantly improving density and mechanical stability. Simultaneously, the struvite coating layer itself is an excellent slow-dissolving nitrogen, phosphorus, and magnesium fertilizer, leaving no residue after degradation and being absorbable by crops. This represents a fundamental innovation in coating materials, transforming them from "inert controlled-release layers" to "functional nutrient layers," and enabling long-term slow-release effects.

[0017] 2. This invention uses a repeated coating process to increase the weight of the struvite layer by 22-30 wt%, forming a multi-layered crystalline barrier with increasing thickness and density gradients. Then, a composite sealing liquid composed of paraffin-oleic acid-triethanolamine high-shear emulsion and hydrophobic fumed silica is used for surface treatment. The emulsion can penetrate and seal the gaps between struvite crystals, while the hydrophobic silica constructs a micro-nano superhydrophobic structure on the outermost layer of the particles, effectively inhibiting initial water penetration and nutrient burst release. Through a three-level synergistic controlled-release mechanism—the low solubility of the fertilizer core salt, the slightly soluble and degradable nature of the struvite membrane, and the hydrophobic barrier properties of the sealing layer—nutrient release is stable and long-lasting, enabling precise fertilization for 90-180 days and greatly improving fertilizer utilization.

[0018] 3. The fertilizer core of this invention provides high levels of potassium and ammonium nitrogen, while the coating layer introduces active phosphorus and magnesium. The sealing liquid uses EDTA-chelated zinc and borax to precisely position trace elements within the sealing layer. These trace elements are slowly released as the paraffin sealing layer gradually degrades, effectively preventing rapid fixation of trace elements after they are applied to the soil. The entire fertilizer integrates nitrogen, phosphorus, potassium, magnesium, zinc, and boron, with the release order of each nutrient highly matched to the crop's absorption patterns. This comprehensively prevents crop nutrient deficiencies and achieves synergistic slow-release of four-dimensional nutrition. Attached Figure Description

[0019] Figure 1 This is a flow chart of the production process of the slow-release ammonified potassium sulfate compound fertilizer used in the embodiments of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0021] Example 1: A production process for a slow-release ammonified potassium sulfate compound fertilizer, referring to... Figure 1 ,include: S1: Preparation of potassium sulfate ammonium sulfate fertilizer core S1.1: Add 60 parts by weight of deionized water to a reactor equipped with a stirrer, a reflux condenser and a vacuum interface, heat to 80°C, then add 55 parts by weight of ammonium sulfate crystals at 30 rpm, stir to dissolve, then add 100 parts by weight of potassium sulfate powder and 2 parts by weight of binder attapulgite clay and stir well. Maintain the temperature at 80°C and stir for 1.5 hours. After the temperature is maintained, stop heating and cool the material to 65°C. Connect the reactor to a vacuum system and perform reduced pressure evaporation and concentration at a vacuum degree of -0.07 MPa until the water content of the mixture drops to 12%, to obtain a hot viscous slurry containing a large number of potassium ammonium sulfate double salt micro crystals. S1.2: Heat the hot viscous slurry to 85°C and feed it into an extrusion granulator. Under an extrusion pressure of 6MPa, the material is extruded from the die hole into a continuous cylindrical strip, which is then cut into wet granules by a cutter. S1.3: The wet granules are fed into a vibrating fluidized bed for pre-drying. The inlet air temperature is strictly controlled at 40℃. The surface moisture is slowly removed until the granule moisture content drops to 6%. Then the pre-dried granules are fed into a fluidized bed dryer. The inlet air temperature is controlled at 60℃. The granules are dried until the granule moisture content is ≤1.5%. After drying, the granules are cooled to 30℃ and sieved to obtain 3-4mm granules, which are the ammonified potassium sulfate fertilizer cores. S2: Preparation of in-situ crystallized coating layer S2.1: Add 18 parts by weight of magnesium sulfate heptahydrate and 14 parts by weight of ammonium dihydrogen phosphate to 50 parts by weight of deionized water, stir and dissolve at 40°C, then add 0.5 parts by weight of nano-attapulgite clay, and ultrasonically disperse for 15 min to obtain coating solution A. Take 20 parts by weight of deionized water, add 0.3 parts by weight of diammonium hydrogen phosphate and stir to dissolve, then adjust the pH to 8.5 with 5 wt% dilute ammonia water, then add 0.8 parts by weight of struvite seed crystals pulverized to 200 mesh, stir to suspend and ultrasonically disperse for 10 min to obtain coating solution B. S2.2: 100 parts by weight of ammonified potassium sulfate fertilizer cores are put into a fluidized bed coating machine and preheated for 5 minutes under the conditions of fluidization air velocity of 1.5 m / s and inlet air temperature of 55℃. Then switch to dual-fluid nozzles and alternately spray coating liquid A and coating liquid B in a pulse manner, controlling the bed temperature at 50℃ and the bed pH at 8.0, with a total spraying time of 50 minutes. S2.3: After stopping the spraying, maintain the inlet air temperature at 60℃ and continue fluidized drying for 15 minutes to make the free water content on the particle surface ≤2% to obtain a primary coating intermediate. Then, the primary coating intermediate is subjected to a second coating and drying according to the conditions of S2.2 and S2.3 to make the coating weight gain reach 22wt% to obtain coated particles. S3: Preparation of slow-release ammonified potassium sulfate compound fertilizer S3.1: Take 3 parts by weight of low-melting-point paraffin with a melting point of 52-56℃, 0.5 parts by weight of oleic acid, and 0.3 parts by weight of triethanolamine, add them to 30 parts by weight of deionized water at 80℃, and emulsify at high speed of 10000rpm for 10min. Then add 0.5 parts by weight of hydrophobic fumed silica, 0.15 parts by weight of EDTA chelated zinc and 0.08 parts by weight of borax, stir evenly and cool to 40℃ to obtain a composite blocking solution. S3.2: Place the coated granules in a rotary drum coating machine. At 40℃ and 30 rpm, use an air atomizing nozzle to evenly spray the composite sealing emulsion onto the surface of the granules. The amount of composite sealing emulsion is controlled at 3% of the total mass of the coated granules. After spraying, raise the air inlet temperature of the coating machine to 60℃ and continue to dry for 12 minutes. After drying, cool to 30℃ and use a vibrating screen to separate the finished granules of 3-5 mm to obtain slow-release ammonified potassium sulfate compound fertilizer.

[0022] Example 2, a production process for a slow-release ammonified potassium sulfate compound fertilizer, see [link to example]. Figure 1 ,include: S1: Preparation of potassium sulfate ammonium sulfate fertilizer core S1.1: Add 70 parts by weight of deionized water to a reactor equipped with a stirrer, a reflux condenser and a vacuum interface, heat to 90°C, then add 65 parts by weight of ammonium sulfate crystals at 50 rpm, stir to dissolve, then add 120 parts by weight of potassium sulfate powder and 3 parts by weight of binder attapulgite clay and stir well. Maintain the temperature at 90°C and stir for 2 hours. After the temperature is maintained, stop heating and cool the material to 75°C. Connect the reactor to a vacuum system and perform reduced pressure evaporation and concentration at a vacuum degree of -0.08 MPa until the water content of the mixture drops to 15%, to obtain a hot viscous slurry containing a large number of potassium ammonium sulfate double salt micro crystals. S1.2: Heat the hot viscous slurry to 95°C and feed it into an extrusion granulator. Under an extrusion pressure of 8MPa, the material is extruded from the die hole into a continuous cylindrical strip, which is then cut into wet granules by a cutter. S1.3: The wet granules are fed into a vibrating fluidized bed for pre-drying. The inlet air temperature is strictly controlled at 50℃. The surface moisture is slowly removed until the granule moisture content drops to 8%. Then the pre-dried granules are fed into a fluidized bed dryer. The inlet air temperature is controlled at 65℃. The granules are dried until the granule moisture content is ≤1.5%. After drying, the granules are cooled to 35℃ and sieved to obtain 3-4mm granules, which are the ammonified potassium sulfate fertilizer cores. S2: Preparation of in-situ crystallized coating layer S2.1: Add 22 parts by weight of magnesium sulfate heptahydrate and 17 parts by weight of ammonium dihydrogen phosphate to 60 parts by weight of deionized water, stir and dissolve at 50°C, then add 1.0 part by weight of nano-attapulgite clay, and ultrasonically disperse for 20 min to obtain coating solution A. Take 25 parts by weight of deionized water, add 0.5 parts by weight of diammonium hydrogen phosphate and stir to dissolve, then adjust the pH to 9.0 with 6 wt% dilute ammonia water, then add 1.2 parts by weight of struvite seed crystals pulverized to 200 mesh, stir to suspend and ultrasonically disperse for 15 min to obtain coating solution B. S2.2: 100 parts by weight of ammonified potassium sulfate fertilizer cores are put into a fluidized bed coating machine and preheated for 10 minutes under the conditions of fluidization air velocity of 2.0 m / s and inlet air temperature of 65℃. Then switch to dual-fluid nozzles and alternately spray coating liquid A and coating liquid B in a pulse manner, controlling the bed temperature at 60℃ and the bed pH at 9.0, with a total spraying time of 70 minutes. S2.3: After stopping the spraying, maintain the air inlet temperature at 65℃ and continue fluidized drying for 20 minutes to make the free water content on the particle surface ≤2% to obtain a primary coating intermediate. Then, the primary coating intermediate is subjected to a second coating and drying under the conditions of S2.2 and S2.3 to make the coating weight gain reach 30wt% to obtain coated particles. S3: Preparation of slow-release ammonified potassium sulfate compound fertilizer S3.1: Take 5 parts by weight of low-melting-point paraffin with a melting point of 52-56℃, 1.0 part by weight of oleic acid, and 0.5 parts by weight of triethanolamine, add them to 40 parts by weight of deionized water at 85℃, and emulsify at high speed of 12000rpm for 15min. Then add 1.0 part by weight of hydrophobic fumed silica, 0.3 parts by weight of EDTA chelated zinc and 0.15 parts by weight of borax, stir evenly and cool to 50℃ to obtain a composite blocking solution. S3.2: Place the coated granules in a rotary drum coating machine. At 50℃ and 40 rpm, use an air atomizing nozzle to evenly spray the composite sealing emulsion onto the surface of the granules. The amount of composite sealing emulsion is controlled at 5% of the total mass of the coated granules. After spraying, raise the air inlet temperature of the coating machine to 65℃ and continue to dry for 15 minutes. After drying, cool to 35℃ and use a vibrating screen to separate the finished granules of 3-5 mm to obtain slow-release ammonified potassium sulfate compound fertilizer.

[0023] Example 3, a production process for a slow-release ammonified potassium sulfate compound fertilizer, see [link to example]. Figure 1 ,include: S1: Preparation of potassium sulfate ammonium sulfate fertilizer core S1.1: Add 65 parts by weight of deionized water to a reactor equipped with a stirrer, a reflux condenser and a vacuum interface, heat to 85°C, then add 60 parts by weight of ammonium sulfate crystals at 35 rpm, stir to dissolve, then add 110 parts by weight of potassium sulfate powder and 2.5 parts by weight of binder attapulgite clay and stir well. Maintain the temperature at 85°C and stir for 1.7 hours. After the temperature is maintained, stop heating and cool the material to 70°C. Connect the reactor to a vacuum system and perform reduced pressure evaporation and concentration at a vacuum degree of -0.075 MPa until the water content of the mixture drops to 13%, to obtain a hot viscous slurry containing a large number of potassium ammonium sulfate double salt micro crystals. S1.2: Heat the hot viscous slurry to 90°C and feed it into an extrusion granulator. Under an extrusion pressure of 7MPa, the material is extruded from the die hole into a continuous cylindrical strip, which is then cut into wet granules by a cutter. S1.3: The wet granules are fed into a vibrating fluidized bed for pre-drying. The inlet air temperature is strictly controlled at 45℃. The surface moisture is slowly removed until the granule moisture content drops to 7%. Then the pre-dried granules are fed into a fluidized bed dryer. The inlet air temperature is controlled at 63℃. The granules are dried until the granule moisture content is ≤1.5%. After drying, the granules are cooled to 33℃ and sieved to obtain 3-4mm granules, which are the ammonified potassium sulfate fertilizer cores. S2: Preparation of in-situ crystallized coating layer S2.1: Add 20 parts by weight of magnesium sulfate heptahydrate and 15 parts by weight of ammonium dihydrogen phosphate to 55 parts by weight of deionized water, stir and dissolve at 45°C, then add 0.7 parts by weight of nano-attapulgite clay, and ultrasonically disperse for 17 min to obtain coating solution A. Take 23 parts by weight of deionized water, add 0.4 parts by weight of diammonium hydrogen phosphate and stir to dissolve, then adjust the pH to 8.5 with 5.5 wt% dilute ammonia water, then add 1 part by weight of struvite seed crystals that have been crushed to 200 mesh, stir to suspend and ultrasonically disperse for 13 min to obtain coating solution B. S2.2: 100 parts by weight of ammonified potassium sulfate fertilizer cores are put into a fluidized bed coating machine and preheated for 7 minutes under the conditions of fluidized air velocity of 1.7 m / s and inlet air temperature of 60℃. Then switch to dual fluid nozzles and alternately spray coating liquid A and coating liquid B in a pulse manner, controlling the bed temperature at 55℃ and the bed pH at 8.5, with a total spraying time of 60 minutes. S2.3: After stopping the spraying, maintain the inlet air temperature at 63℃ and continue fluidized drying for 17 minutes to make the free water content on the particle surface ≤2% to obtain a primary coating intermediate. Then, the primary coating intermediate is subjected to a second coating and drying under the conditions of S2.2 and S2.3 to make the coating weight gain reach 26wt% to obtain coated particles. S3: Preparation of slow-release ammonified potassium sulfate compound fertilizer S3.1: Take 4 parts by weight of low-melting-point paraffin with a melting point of 52-56℃, 0.7 parts by weight of oleic acid, and 0.4 parts by weight of triethanolamine, add them to 35 parts by weight of deionized water at 83℃, and emulsify at high speed of 11000rpm for 13min. Then add 0.7 parts by weight of hydrophobic fumed silica, 0.2 parts by weight of EDTA chelated zinc and 0.12 parts by weight of borax, stir evenly and cool to 45℃ to obtain a composite blocking solution. S3.2: Place the coated granules in a rotary drum coating machine. At 45℃ and 35 rpm, use an air atomizing nozzle to evenly spray the composite sealing emulsion onto the surface of the granules. The amount of composite sealing emulsion is controlled at 4% of the total mass of the coated granules. After spraying, raise the air inlet temperature of the coating machine to 63℃ and continue to dry for 13 minutes. After drying, cool to 33℃ and use a vibrating screen to separate the finished granules of 3-5 mm to obtain slow-release ammonified potassium sulfate compound fertilizer.

[0024] Comparative Example 1 differs from Example 1 in that, in step S2.2, coating liquid A and coating liquid B are not alternately sprayed in a pulse manner. Instead, coating liquid A and coating liquid B are mixed and directly sprayed into the fluidized bed coating machine in one continuous motion using a single-fluid nozzle. Furthermore, coating liquid A does not contain nano-attapulgite. The remaining steps remain unchanged in preparing the slow-release ammonified potassium sulfate compound fertilizer, which is Comparative Example 1.

[0025] Comparative Example 2 differs from Example 1 in that the composite sealing liquid is prepared by adding 3 parts by weight of low melting point paraffin, 0.3 parts by weight of Span 80, and 35 parts by weight of water at 80°C, and emulsifying at 8000 rpm for 10 min. The remaining steps are unchanged to prepare a slow-release ammonified potassium sulfate compound fertilizer, which is referred to as Comparative Example 2.

[0026] Comparative Example 3 differs from Example 1 in that it involves removing nano-attapulgite from coating solution A while keeping the other steps unchanged to prepare a slow-release ammonified potassium sulfate compound fertilizer. This is referred to as Comparative Example 3.

[0027] The sustained-release performance of Examples 1-3 and Comparative Examples 1-3 was determined: Following GB / T23348-2009, the initial dissolution rate and cumulative nitrogen release rate at 24 hours were measured. Three measurements were performed, and the average value was taken. The results are shown in Table 1.

[0028]

[0029] As can be seen from the data in Table 1, the release rate of Examples 1-3 of the present invention is very uniform from 28 days to 180 days, with a cumulative release rate between 80.2% and 84.5% after 180 days. The expected complete release period can exceed 180 days, achieving true "long-term slow release". Comparative Examples 1-3 showed that 61.5%-83.9% of nutrients were released at 28 days, and almost all were released by 90 days, exhibiting a typical "high at the beginning and low at the end" release pattern. Excess nutrients in the early stage cannot be absorbed by crops and will be lost through volatilization, leaching, etc.; while nutrient deficiency in the later stage will seriously affect crop yield and quality. This fully verifies that the present invention achieves stable fertilization that is highly matched with the crop's absorption pattern through a three-level synergistic controlled release mechanism of "low solubility in the fertilizer core - micro-soluble degradation in the membrane layer - hydrophobic barrier in the sealing layer", thereby greatly improving fertilizer utilization.

[0030] Comparative Example 1 eliminated both pulse feeding and nano-attapulgite, completely destroying the membrane's density and bonding strength, resulting in the worst controlled release effect. Comparative Example 2 simply replaced the composite sealing liquid with ordinary paraffin emulsion, losing its superhydrophobic and permeable sealing ability between crystal gaps, leading to severe initial burst release, demonstrating that the sealing layer technology of this invention is an indispensable part of the three-stage controlled release process. Comparative Example 3 only removed nano-attapulgite; although it retained the pulse in-situ crystallization process, the membrane lacked nucleation sites and defect-filling materials, resulting in decreased density and a significantly worse controlled release effect than the examples, proving the crucial reinforcing role of nano-attapulgite in constructing high-performance membranes.

[0031] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A production process for a slow-release ammonified potassium sulfate compound fertilizer, characterized in that, include: S1: Preparation of ammonified potassium sulfate fertilizer core; Ammonium sulfate, potassium sulfate and binder are added to deionized water, heated and stirred, and then concentrated by vacuum evaporation to a water content of 12-15% to obtain a hot viscous slurry containing complex salt microcrystals; then extruded and granulated, and dried by staged fluidized bed drying at 40-65℃ to a water content of ≤1.5%, and sieved to obtain 3-4 mm ammonified potassium sulfate fertilizer core. S2: Preparation of in-situ crystallized coating layer; Prepare a coating solution A containing magnesium / phosphorus and a coating solution B containing struvite seeds and alkaline pH; apply the coating solution to the surface of the fertilizer core in a fluidized bed using pulsed alternating spraying, and generate an insoluble magnesium ammonium phosphate crystal film through in-situ chemical reaction. Repeat the coating process until the weight gain is 22-30%, and obtain coated particles. S3: Preparation of slow-release ammonified potassium sulfate compound fertilizer; Low-melting-point paraffin, oleic acid, and triethanolamine were emulsified and then compounded with hydrophobic silica, EDTA-chelated zinc, and borax to form a composite sealing liquid. This liquid was sprayed onto the surface of coated particles, dried at low temperature, and then sieved to obtain a slow-release ammonified potassium sulfate compound fertilizer.

2. The production process of a slow-release ammonified potassium sulfate compound fertilizer according to claim 1, characterized in that, S1: The preparation of ammonified potassium sulfate fertilizer cores specifically includes the following steps: S1.1: Add 60-70 parts by weight of deionized water to a reactor equipped with a stirrer, a reflux condenser and a vacuum interface, heat to 80-90℃, then add 55-65 parts by weight of ammonium sulfate crystals at 30-50 rpm, stir to dissolve, then add 100-120 parts by weight of potassium sulfate powder and 2-3 parts by weight of binder and stir well. Maintain the temperature at 80-90℃ and stir for 1.5-2 hours. After the temperature is maintained, stop heating and cool the material to 65-75℃. Connect the reactor to a vacuum system and perform reduced pressure evaporation and concentration at a vacuum degree of -0.07 to -0.08 MPa until the water content of the mixture drops to 12-15%, to obtain a hot viscous slurry containing a large number of potassium ammonium sulfate double salt micro crystals. S1.2: Heat the hot viscous slurry to 85-95℃, feed it into an extrusion granulator, and under an extrusion pressure of 6-8MPa, extrude the material from the die hole into a continuous cylindrical strip, and then cut it into wet granules by a cutter. S1.3: The wet granules are fed into a vibrating fluidized bed for pre-drying. The inlet air temperature is strictly controlled at 40-50℃. The surface moisture is slowly removed until the granule moisture content drops to 6-8%. Then, the pre-dried granules are fed into a fluidized bed dryer. The inlet air temperature is controlled at 60-65℃. The granules are dried until the granule moisture content is ≤1.5%. After drying, the granules are cooled to 30-35℃ and sieved to obtain 3-4mm granules, which are the ammonified potassium sulfate fertilizer cores.

3. The production process of a slow-release ammonified potassium sulfate compound fertilizer according to claim 2, characterized in that, The binder in step S1.1 is specifically attapulgite.

4. The production process of a slow-release ammonified potassium sulfate compound fertilizer according to claim 1, characterized in that, S2: Preparation of the in-situ crystallized coating layer, specifically including the following steps: S2.1: Add 18-22 parts by weight of magnesium sulfate heptahydrate and 14-17 parts by weight of ammonium dihydrogen phosphate to 50-60 parts by weight of deionized water, stir and dissolve at 40-50℃, then add 0.5-1.0 parts by weight of nano-attapulgite clay, and ultrasonically disperse for 15-20 min to obtain coating solution A. Take 20-25 parts by weight of deionized water, add 0.3-0.5 parts by weight of diammonium hydrogen phosphate, stir and dissolve, then adjust the pH to 8.5-9.0 with 5-6 wt% dilute ammonia water, then add 0.8-1.2 parts by weight of struvite seed crystals pulverized to 200 mesh, stir to suspend and ultrasonically disperse for 10-15 min to obtain coating solution B. S2.2: Add 100 parts by weight of ammonified potassium sulfate fertilizer core into a fluidized bed coating machine, preheat for 5-10 minutes under the conditions of fluidization air velocity of 1.5-2.0 m / s and inlet air temperature of 55-65℃, and then switch to a dual-fluid nozzle to alternately spray coating liquid A and coating liquid B in a pulse manner. S2.3: After stopping the spraying, maintain the inlet air temperature at 60-65℃ and continue fluidized drying for 15-20 minutes to make the free water content on the particle surface ≤2% to obtain a primary coating intermediate. Then, the primary coating intermediate is subjected to a second coating and drying under the conditions of S2.2 and S2.3 to make the coating weight gain reach 22-30wt% to obtain coated particles.

5. The production process of a slow-release ammonified potassium sulfate compound fertilizer according to claim 4, characterized in that, In step S2.2, during the liquid spraying process, the bed temperature is controlled at 50-60℃, the bed pH is controlled at 8.0-9.0, and the total spraying time is 50-70 minutes.

6. The production process of a slow-release ammonified potassium sulfate compound fertilizer according to claim 1, characterized in that, S3: The preparation of slow-release ammonified potassium sulfate compound fertilizer includes the following steps: S3.1: Take 3-5 parts by weight of paraffin, 0.5-1.0 parts by weight of oleic acid, and 0.3-0.5 parts by weight of triethanolamine, add them to 30-40 parts by weight of deionized water at 80-85℃, and emulsify at high speed of 10000-12000 rpm for 10-15 min. Then add 0.5-1.0 parts by weight of hydrophobic fumed silica, 0.15-0.3 parts by weight of EDTA chelated zinc, and 0.08-0.15 parts by weight of borax. After stirring evenly, cool to 40-50℃ to obtain a composite blocking solution. S3.2: Place the coated granules in a rotary drum coating machine. At 40-50℃ and 30-40 rpm, use an air atomizing nozzle to evenly spray the composite closed emulsion onto the surface of the granules. After spraying, raise the air inlet temperature of the coating machine to 60-65℃ and continue to dry for 12-15 minutes. After drying, cool to 30-35℃ and use a vibrating screen to separate the finished granules to 3-5mm, thus obtaining slow-release ammonified potassium sulfate compound fertilizer.

7. The production process of a slow-release ammonified potassium sulfate compound fertilizer according to claim 6, characterized in that, The paraffin in step S3.1 is specifically low-melting-point paraffin at 52-56℃.

8. The production process of a slow-release ammonified potassium sulfate compound fertilizer according to claim 6, characterized in that, In step S3.2, the amount of composite blocking emulsion used is controlled to be 3-5% of the total mass of the coated particles.

9. A slow-release ammonified potassium sulfate compound fertilizer, characterized in that, It is prepared by the production process of a slow-release ammonified potassium sulfate compound fertilizer as described in any one of claims 1-8.

Images