Silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer and preparation method thereof

Abstract

The invention provides a silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer and a preparation method thereof.The silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer comprises an inner core and a protective shell covering at least part of the surface of the inner core; the inner core comprises a spongy framework and particles filled in and on the surface of the spongy framework; the spongy framework is of a spongy structure based on a Si-O-P bridged bond generated by reaction of a framework raw material system containing boron-containing potassium phosphate silicate and silicon phosphate, and the particles comprise boron-containing potassium phosphate silicate, biochar and an inorganic mineral material; the protective shell comprises at least one of zinc silicate or magnesium silicate; the inner core is compounded with a nutrient material through a spongy framework, so that a stable structure and a slow-release basis of nutrients are realized; the spongy framework provides a high specific surface area and a porous structure to adsorb and fix nutrients, so that the physical strength of the particles is improved, the material viscosity is remarkably reduced, the subsequent drying efficiency is improved, the hygroscopicity of the fertilizer particles is reduced, and the effects of high strength, quick drying, low hygroscopicity and capability of realizing gradient release of the nutrients are achieved.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to a silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer and its preparation method. Background Technology

[0002] Silicon and potassium are core elements for ensuring healthy crop growth and improving the quality of agricultural products. Silicon effectively strengthens crop stems, enhances resistance to pests and diseases, improves stress resistance, and enhances fruit appearance and storage life. Potassium and phosphorus are essential nutrients for plant growth. In addition, although micronutrients such as zinc, magnesium, and boron are present in small amounts in crops, they are equally indispensable for physiological processes such as chlorophyll synthesis, pollination and fertilization, and fruit development.

[0003] However, traditional potassium silicate fertilizers have long faced a series of systemic technical bottlenecks in actual production and application. First, potassium silicate itself has strong hygroscopic properties, causing fertilizer products to easily absorb moisture and clump during storage, greatly inconveniencing transportation and application. Second, when using conventional physical mixing and granulation processes to produce high-potassium silicate fertilizers, problems such as low particle strength and slow drying rates are common. This not only leads to low production efficiency but also makes the product prone to pulverization during subsequent processing, affecting its effectiveness.

[0004] In terms of agrochemical functions, conventional silicon-potassium fertilizers have a relatively simple nutrient release pattern. After being applied to the soil, silicon and potassium nutrients dissolve too quickly and are easily lost due to leaching or fixation, resulting in short-lasting fertilizer effects that are difficult to meet the balanced needs of crops throughout their entire growth cycle. Some existing technologies attempt to delay nutrient release through polymer coating or the addition of a single slow-release material, but these methods often significantly sacrifice the rapid effectiveness that silicon-potassium fertilizers should have while pursuing slow-release effects, failing to achieve a synergistic balance between rapid supply and long-term maintenance.

[0005] Existing technologies, such as the high-temperature calcination of potassium-containing rocks to prepare citrate-soluble potassium-silicon fertilizer, can obtain mineral phases with a certain degree of slow release, but the nutrient release depends entirely on the acid solubility of the minerals in the soil, resulting in a rigid release pattern and failing to fundamentally solve the product's hygroscopicity problem. Other technologies focus on the chelation stabilization of liquid potassium-silicon fertilizers, but their research direction is weakly related to the structural design and physical performance improvement of solid fertilizers. Furthermore, although the application of mineral carriers such as biochar or attapulgite in fertilizers is widely known, existing technologies are mostly limited to their soil improvement or simple adsorption functions, and have not yet proposed a systematic solution from the perspective of the synergistic effect of fertilizer particle internal structural design and surface chemical modification.

[0006] Therefore, there is an urgent need in this field for a new fertilizer technology that can systematically solve the above problems, namely, a comprehensive innovative solution that simultaneously achieves slow release of micronutrients, high particle strength, low hygroscopicity, and high drying efficiency while maintaining the rapid effectiveness of silicon and potassium nutrients. Summary of the Invention

[0007] This invention provides a slow-release fertilizer of silicon, potassium, phosphorus, zinc, and magnesium and its preparation method, which solves the problems of low fertilizer strength, slow moisture absorption, and low drying efficiency in the prior art.

[0008] In a first aspect, the present invention provides a silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer, comprising a core and a protective shell covering at least a portion of the surface of the core; The core consists of a sponge-like framework and particles filling the interior and surface of the sponge-like framework; the sponge-like framework is a sponge-like structure based on Si-OP bridging bonds generated by the reaction of a framework raw material system including potassium borophosphosilicate and silicon phosphate; the particles include potassium borophosphosilicate, biochar and inorganic mineral materials. The protective shell includes at least one of zinc silicate or magnesium silicate.

[0009] Compared with existing technologies, the advantages of this invention are as follows: This invention constructs a composite structure of "core-protective shell". The core, through the combination of a sponge-like skeleton and nutrient materials, achieves structural stability and provides a basis for the slow release of nutrients. The sponge-like skeleton not only provides a high specific surface area and porous structure for adsorbing and fixing nutrients, but also improves the physical strength of the particles. This sponge-like structure can effectively lock free water in the liquid phase, significantly reducing material viscosity, thereby greatly improving subsequent drying efficiency. At the same time, this sponge-like network is tightly bonded to the nutrient materials, like adding steel bars to the particles, resulting in a qualitative leap in the mechanical strength of the particles. The outer protective shell is composed of zinc silicate / magnesium silicate. This dense film, generated through surface chemical reaction, is more firmly bonded than physical coatings, effectively controlling the dissolution rate of zinc and magnesium elements, achieving long-term supply, and significantly reducing the hygroscopicity of fertilizer particles, preventing caking. Ultimately, it achieves the effects of high strength, fast drying, low hygroscopicity, and gradient release of nutrients.

[0010] Furthermore, at least a portion of the surface of the protective shell also includes a hydrophobic outer membrane; and / or, The kernel diameter is 1-5 mm; and / or, The particle size of slow-release fertilizers containing silicon, potassium, phosphorus, zinc, and magnesium is 1.01-5.60 mm.

[0011] Furthermore, the skeleton raw material system includes at least one of boron-containing potassium phosphosilicate, potassium methylsilicate, polyaspartic acid or potassium polyaspartic acid, and silicon phosphate. The hydrophobic outer membrane is made of polymethylsilicic acid.

[0012] Furthermore, the raw materials for silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer, by weight, include: Potassium borophosphosilicate containing: 30-50 parts; Potassium methylsilicate: 1-5 parts; Polyaspartic acid or potassium polyaspartate: 1.5 to 4 parts; Silicon phosphate: 2~3.9 parts; Biochar: 15-20 parts; Inorganic mineral materials: 10-30 parts; Zinc sulfate: 3-5 parts; Magnesium sulfate: 5-15 parts.

[0013] In a second aspect, the present invention provides a method for preparing the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer described in the first aspect, comprising the following steps: S1. Preparation of core premix: Add phosphate silicon to a composite aqueous dispersion containing potassium borophosphosilicate, potassium methylsilicate, polyaspartic acid or potassium polyaspartic acid, mix and perform shear dispersion treatment to obtain a precursor dispersion. S2. Granulation to form the core: Solid materials including biochar and inorganic mineral materials are mixed, a precursor dispersion is added for granulation, and after drying, a core consisting of a sponge-like skeleton and particles filling the interior and surface of the sponge-like skeleton is formed. S3. Surface film formation: A film-forming solution including at least one of zinc sulfate or magnesium sulfate is sprayed onto the core surface, and a protective shell is formed by the reaction to obtain the fertilizer precursor. S4. Drying: The fertilizer precursor is dried to obtain silicon, potassium, phosphorus, zinc and magnesium slow-release fertilizer.

[0014] Further, in step S1, the boron content in the boron-containing potassium phosphosilicate is 1.2%~6%, and the phosphorus content is 2%~5%; the particle size of the boron-containing potassium phosphosilicate is not greater than 300 nm; and / or, In step S1, the amount of silicon phosphate added is 4% to 13% of the mass of potassium borophosphosilicate; and / or, In step S2, the mass ratio of the precursor dispersion to the solid material is 1:(0.25~0.5).

[0015] Furthermore, the inorganic mineral material is at least one of attapulgite, calcium-based bentonite, sepiolite, or magnesite slag powder; and / or, Biochar is produced by low-temperature, oxygen-limited pyrolysis at 200-400℃ from at least one of coconut shells, fruit shells, sawdust, straw, or rice husks; and / or, Magnesium sulfate and zinc sulfate are byproducts of industrial acid wastewater treatment.

[0016] Further, in step S1, the rotation speed of the shear dispersion treatment is 6000-10000 rpm, and the treatment time is 3-10 min; and / or, In step S3, the spraying is carried out in a rotary granulator or a fluidized bed; and / or, In step S4, the drying temperature is 60-80℃, and the drying process continues until the moisture content in the fertilizer precursor is no higher than 3%.

[0017] Furthermore, it also includes: before step S4, it includes: Waterproofing post-treatment: Atomize and spray an aqueous solution of potassium methylsilicate onto the surface of the fertilizer precursor, and perform low-temperature drying treatment to form a hydrophobic outer film on at least a portion of the surface of the protective shell.

[0018] Furthermore, in the post-waterproofing treatment, the mass concentration of the potassium methylsilicate aqueous solution is 1%-3%; the temperature of the low-temperature drying treatment is 60-80℃, and the treatment time is 15-25 minutes. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] In a first aspect, the present invention provides a silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer, comprising a core and a protective shell covering at least a portion of the surface of the core; the core comprises a sponge-like skeleton and particles filling the interior and surface of the sponge-like skeleton; the sponge-like skeleton comprises a sponge-like structure based on Si-OP bridging bonds generated by reacting a skeleton raw material system comprising potassium borophosphorus silicate and silicon phosphate, and the particles comprise potassium borophosphorus silicate, biochar and inorganic mineral materials; the protective shell comprises at least one of zinc silicate or magnesium silicate.

[0021] The silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer provided by this invention constructs a composite structure of "sponge-like core-protective shell". The core, through the combination of a sponge-like skeleton and nutrient materials, achieves structural stability and provides a basis for slow nutrient release. The sponge-like skeleton not only provides a high specific surface area and porous structure for adsorbing and fixing nutrients, but also improves the physical strength of the particles. This sponge-like structure can effectively lock free water in the liquid phase, significantly reducing material viscosity, thereby greatly improving subsequent drying efficiency. At the same time, this sponge-like network is tightly bonded to the nutrient materials, like adding steel bars to the particles, resulting in a qualitative leap in the mechanical strength of the particles. The outer protective shell is composed of zinc silicate / magnesium silicate. This dense film, generated through surface chemical reaction, is more firmly bonded than a physical coating, effectively controlling the dissolution rate of zinc and magnesium elements, achieving long-term supply, and significantly reducing the hygroscopicity of fertilizer particles, preventing caking. Ultimately, it achieves the effects of high strength, fast drying, low hygroscopicity, and gradient nutrient release.

[0022] Furthermore, at least part of the surface of the protective shell also includes a hydrophobic outer membrane.

[0023] By introducing a hydrophobic barrier formed by potassium methylsilicate, together with the internal zinc / magnesium silicate protective shell, a composite waterproof layer is formed, which can more effectively resist environmental moisture and make the product more stable in high humidity environments.

[0024] Optionally, the core particle size is 1-5 mm; the particle size of the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer is 1.01-5.60 mm. Further, the core particle size is 1.00 mm-4.75 mm or 3.35 mm-5.60 mm, and correspondingly, the particle size of the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer is 1.01-4.75 mm or 3.36-5.60 mm.

[0025] By limiting the particle size of the fertilizer, its mechanical properties are further improved, and it is also convenient for mechanized fertilization operations, thus meeting the needs of practical agricultural applications.

[0026] Furthermore, the skeleton raw material system includes at least one of boron-containing potassium phosphosilicate, potassium methylsilicate, polyaspartic acid or potassium polyaspartic acid, and silicon phosphate. The hydrophobic outer membrane is made of polymethylsilicic acid.

[0027] The specific chemical substances constituting the framework raw material system and the hydrophobic outer membrane were identified. Among them, boron-containing potassium phosphate not only provides the core silicon and potassium nutrients, but its boron element, as an essential micronutrient, works synergistically with silicon, potassium, and phosphorus to make the fertilizer nutrients more comprehensive. Potassium methylsilicate plays a dual role in the premixing stage, acting as a dispersant to promote the homogeneity and stability of the precursor dispersion, and as a water-resistant additive to initially improve the stability of the system. Polyaspartic acid or its potassium salt, as a highly efficient organic polymer dispersant, can effectively prevent the agglomeration of nanoparticles and ensure the uniformity and thoroughness of subsequent reactions. Silicon phosphate, as a key internal curing agent, is introduced in limited quantities and is the core of constructing a controllable three-dimensional cross-linked network with potassium silicate.

[0028] Meanwhile, it was determined that the hydrophobic outer membrane is polymethylsilicic acid, which has extremely low surface energy and can form a robust monomolecular hydrophobic membrane, further enhancing the fertilizer's ability to resist environmental moisture.

[0029] Specifically, the raw materials of the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer, by weight, include: 30-50 parts of boron-containing potassium phosphate silicate; 1-5 parts of methyl silicate; 1.5-4 parts of polyaspartic acid or potassium polyaspartic acid; and 2-3.9 parts of silicon phosphate. Biochar: 15-20 parts; Inorganic mineral materials: 10-30 parts; Zinc sulfate: 3-5 parts; Magnesium sulfate: 5-15 parts.

[0030] By precisely defining the mass ratio of each component, it is further ensured that the internal solidification network can be effectively formed without blocking nutrient channels, guaranteeing the porosity and strength of the sponge-like skeleton, and allowing the surface film-forming reaction to proceed fully, thereby further improving the fertilizer's drying efficiency, particle strength, moisture resistance, and nutrient release performance.

[0031] In a second aspect, the present invention provides a method for preparing a silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer as described in the first aspect, comprising the following steps: S1. Preparation of core premix: Add phosphate silicon to a composite aqueous dispersion containing potassium borophosphosilicate, potassium methylsilicate, polyaspartic acid or potassium polyaspartic acid, mix and perform shear dispersion treatment to obtain a precursor dispersion. S2. Granulation to form the core: Solid materials including biochar and inorganic mineral materials are mixed, a precursor dispersion is added for granulation, and after drying, a core consisting of a sponge-like skeleton and particles filling the interior and surface of the sponge-like skeleton is formed. S3. Surface film formation: A film-forming solution including at least one of zinc sulfate or magnesium sulfate is sprayed onto the core surface, and a protective shell is formed by the reaction to obtain the fertilizer precursor. S4. Drying: The fertilizer precursor is dried to obtain silicon, potassium, phosphorus, zinc and magnesium slow-release fertilizer.

[0032] The preparation method provided by this invention employs an internal solidification and surface film-forming process. By homogenizing silicon phosphate and a composite aqueous dispersion under shear dispersion, an internal silicon-oxygen-phosphorus cross-linking network is actively induced and constructed, providing the structural basis and fast-acting nutrient channels for the entire particle. In step S2, granulation causes biochar and inorganic minerals to form particles, which fill the pores of the sponge-like skeleton formed by the precursor dispersion in step S1, forming a core with a specific structure. In step S3, surface reaction film formation utilizes the residual active silicates inside the core to undergo an in-situ chemical reaction with the externally sprayed zinc and magnesium salt solutions, generating a chemically bonded reaction to form a robust protective shell of zinc silicate / magnesium silicate. This method is far more advanced than physical coating technology, achieving gradient slow release of nutrients. The method is simple, operates under mild conditions (no high-temperature calcination required), consumes little energy, and effectively utilizes industrial by-products, making it suitable for large-scale industrial production and key to achieving this high-performance fertilizer.

[0033] Both the boron-containing potassium phosphosilicate and the methyl potassium silicate used in this invention are in liquid form. The solid content of the liquid boron-containing potassium phosphosilicate is 22-42%, and the solid content of the liquid methyl potassium silicate is 30-40%.

[0034] Further, in step S1, the boron content in the boron-containing potassium phosphosilicate is 1.2%~6%, the phosphorus content in the boron-containing potassium phosphosilicate is 2%~5%, and the particle size of the boron-containing potassium phosphosilicate is no greater than 300nm; in step S1, the amount of silicon phosphate added is 4%~13% of the mass of the boron-containing potassium phosphosilicate; in step S2, the mass ratio of the precursor dispersion to the solid material is 1:(0.25~0.5).

[0035] The particle size of the boron-containing potassium phosphosilicate is the same as that of the liquid boron-containing potassium phosphosilicate. Optionally, the inorganic mineral material is at least one of attapulgite, calcium-based bentonite, sepiolite, or magnesite slag powder; the biochar is obtained by low-temperature oxygen-limited pyrolysis at 200-400℃ using at least one of coconut shell, fruit shell, wood chips, straw, or rice husk as raw material.

[0036] In one specific embodiment, magnesium sulfate and zinc sulfate are derived from byproducts of industrial acidic wastewater treatment.

[0037] By utilizing industrial waste resources, raw material costs are reduced, environmental burden is decreased, and economic and social benefits are improved.

[0038] Specifically, in step S1, the rotation speed of the shear dispersion treatment is 6000-10000 rpm, and the treatment time is 3-10 min; in step S3, the spraying is carried out in a rolling granulator or fluidized bed; in step S4, the drying temperature is 60-80℃, and the drying treatment continues until the moisture content in the fertilizer precursor is no higher than 3%.

[0039] Furthermore, it also includes: before step S4, it includes: Waterproofing post-treatment: Atomize and spray an aqueous solution of potassium methylsilicate onto the surface of the fertilizer precursor, and perform low-temperature drying treatment to form a hydrophobic outer film on at least a portion of the surface of the protective shell.

[0040] The potassium methylsilicate aqueous solution was diluted to a mass concentration of 1%-3%; the low-temperature drying treatment was carried out at a temperature of 60-80℃ for 15-25 minutes.

[0041] By constructing a hydrophobic barrier made of potassium methylsilicate on top of the surface protective shell, a dual protection system of chemical film + physical waterproof film is formed, which greatly improves the fertilizer product's moisture resistance and anti-caking ability, enabling it to adapt to more demanding storage environments.

[0042] The following detailed description of the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer and its preparation method provided by the present invention is provided through specific embodiments. Example 1

[0043] The raw materials in this embodiment, by weight, include: Liquid potassium silicate (B element content: 3.5%, P element content: 3%, <300nm): 40 parts; Liquid potassium methylsilicate: 3 parts; Potassium polyaspartate: 2.5 parts; Silicon phosphate: 2.5 parts (containing 6.25% of the mass of potassium borophosphosilicate); Coconut shell biochar (300℃ oxygen-limited pyrolysis): 18 parts; Attapulgite: 20 parts; Zinc sulfate heptahydrate (industrial byproduct): 5 parts; Magnesium sulfate heptahydrate (industrial by-product): 10 parts.

[0044] The preparation method includes the following steps: S1. Preparation of core premix: Potassium borophosphosilicate, potassium methylsilicate, and potassium polyaspartate are mixed evenly in a stirred tank to form a composite aqueous dispersion premix; then silicon phosphate is added, and the mixture is immediately homogenized at 8000 rpm for 5 minutes using a high-speed shear disperser. It can be observed that the viscosity of the system first increases slightly and then tends to stabilize, indicating that the internal cross-linking network has been initially formed, and the precursor dispersion is obtained. S2. Granulation to form the core: Mix coconut shell biochar and attapulgite evenly in a dry state, then place them in a disc granulator, slowly add the precursor dispersion prepared in step S1, and roll to form a core with a particle size of 2-3 mm.

[0045] S3. Surface film formation: Prepare a 30% mixed aqueous solution of zinc sulfate heptahydrate and magnesium sulfate heptahydrate. In a fluidized bed, atomize the above solution and spray it evenly onto the surface of the fluidized core. Maintain the reaction for 5 minutes to form a protective shell. S4. Waterproofing post-treatment: A 2% (w / w) potassium methylsilicate aqueous solution is atomized and sprayed onto the surface of the granules to form a hydrophobic outer film on at least part of the protective shell, thus obtaining the fertilizer precursor. S5. Drying and sieving: The treated fertilizer precursor is dried at 70℃ for 2.5 hours until the moisture content is less than 5%, and then sieved to obtain silicon, potassium, phosphorus, zinc and magnesium slow-release fertilizer. Example 2

[0046] The difference between this embodiment and Embodiment 1 is that in step S1, the amount of silicon phosphate added is 8 parts (accounting for 18% of the total mass of the liquid premix).

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that silicon phosphate is not added in step S1.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that steps S3 and S4 are not performed.

[0049] Experimental Example 1 Performance tests were conducted on the above embodiments and comparative examples. The drying time to a moisture content of <3% was determined using an oven drying method at (105±2)℃ (referencing standard NY / T3036-2016); particle compressive strength was measured using a particle strength tester; the moisture absorption weight gain rate was measured over 4 hours at constant temperature and humidity (40±3℃, 80%±5%RH) (referencing relevant methods in HG / T5520-2019); the potassium leaching rate over 1 hour and the zinc cumulative release rate over 7 days were tested using the purified water leaching method (referencing standard GB / T23348).

[0050] The test results are shown in Table 1.

[0051] Table 1

[0052] Results analysis: Example 1 vs Example 2: This demonstrates that excessive internal solidification, while resulting in extremely high strength, negatively impacts the rapid availability of nutrients (potassium leaching rate is only 45%).

[0053] Example 1 vs. Comparative Example 1: Demonstrates that the lack of internal curing leads to slow drying, low strength, and high hygroscopicity. Although potassium dissolves quickly, the slow-release ability of zinc is also reduced.

[0054] Example 1 vs Comparative Example 2: This demonstrates that without surface film formation, even with good internal curing (decent drying and strength), the moisture-proof ability of the particles and the slow-release function of zinc are severely reduced.

[0055] The complete "inner solid and outer membrane" solution of this invention achieves the best balance and comprehensive improvement in four mutually restrictive performance indicators: drying efficiency, particle strength, storage stability, and rapid and slow release of nutrients, resulting in a synergistic effect of "1+1>2". This is the concentrated embodiment of the inventiveness of this invention.

[0056] In summary, the present invention has the following beneficial effects: 1. Synergistic curing and efficient production: The internal cross-linking network formed by the limited introduction of silicon phosphate significantly shortens the drying time by 20%-30% and increases particle strength by more than 50%, greatly improving production efficiency and product physical quality.

[0057] 2. Intelligent release and high stability: The internal "porous sponge-like" structure and the surface chemical / physical composite film work together to ensure the rapid release of silicon and potassium (dissolution rate >40% within 1 hour) and the long-term supply of zinc and magnesium (cumulative release rate <80% in 7 days). At the same time, the product does not caking when stored in a high humidity environment for 30 days.

[0058] 3. Multi-element synergy and green environmental protection: The product provides Si, K, Zn, Mg, B, P, and organic matter in one go, providing comprehensive nutrients. It utilizes raw materials derived from industrial and agricultural waste (such as by-product magnesium sulfate and biochar), embodying the concept of a circular economy.

[0059] 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; if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should all be considered to be within the protection scope of the present invention.

Claims

1. A silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer, characterized in that, Includes the core and a protective shell covering at least part of the core's surface; The core consists of a sponge-like framework and particles filling the interior and surface of the sponge-like framework; the sponge-like framework is a sponge-like structure based on Si-OP bridging bonds generated by the reaction of a framework raw material system including potassium borophosphosilicate and silicon phosphate; the particles include potassium borophosphosilicate, biochar and inorganic mineral materials. The protective shell includes at least one of zinc silicate or magnesium silicate.

2. The silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer according to claim 1, characterized in that, At least a portion of the surface of the protective shell also includes a hydrophobic outer membrane; and / or, The kernel diameter is 1-5 mm; and / or, The particle size of slow-release fertilizers containing silicon, potassium, phosphorus, zinc, and magnesium is 1.01-5.60 mm.

3. The silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer according to claim 2, characterized in that, The skeleton material system includes at least one of boron-containing potassium phosphosilicate, potassium methylsilicate, polyaspartic acid or potassium polyaspartic acid, and silicon phosphate. The hydrophobic outer membrane is made of polymethylsilicic acid.

4. The silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer according to claim 3, characterized in that, The raw materials for slow-release fertilizers containing silicon, potassium, phosphorus, zinc, and magnesium, by weight, include: Potassium borophosphosilicate containing: 30-50 parts; Potassium methylsilicate: 1-5 parts; Polyaspartic acid or potassium polyaspartate: 1.5 to 4 parts; Silicon phosphate: 2~3.9 parts; Biochar: 15-20 parts; Inorganic mineral materials: 10-30 parts; Zinc sulfate: 3-5 parts; Magnesium sulfate: 5-15 parts.

5. A method for preparing the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of core premix: Add phosphate silicon to a composite aqueous dispersion containing potassium borophosphosilicate, potassium methylsilicate, polyaspartic acid or potassium polyaspartic acid, mix and perform shear dispersion treatment to obtain a precursor dispersion. S2. Granulation to form the core: Solid materials including biochar and inorganic mineral materials are mixed, a precursor dispersion is added for granulation, and after drying, a core consisting of a sponge-like skeleton and particles filling the interior and surface of the sponge-like skeleton is formed. S3. Surface film formation: A film-forming solution including at least one of zinc sulfate or magnesium sulfate is sprayed onto the core surface, and a protective shell is formed by the reaction to obtain the fertilizer precursor. S4. Drying: The fertilizer precursor is dried to obtain silicon, potassium, phosphorus, zinc and magnesium slow-release fertilizer.

6. The method for preparing the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer according to claim 5, characterized in that, In step S1, the boron content in the boron-containing potassium phosphosilicate is 1.2%~6%, and the phosphorus content is 2%~5%; the particle size of the boron-containing potassium phosphosilicate is no greater than 300 nm; and / or, In step S1, the amount of silicon phosphate added is 4% to 13% of the mass of potassium borophosphosilicate; and / or, In step S2, the mass ratio of the precursor dispersion to the solid material is 1:(0.25~0.5).

7. The method for preparing the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer according to claim 5, characterized in that, The inorganic mineral material is at least one of attapulgite, calcium-based bentonite, sepiolite, or magnesite slag powder; and / or, Biochar is produced by low-temperature, oxygen-limited pyrolysis at 200-400℃ from at least one of coconut shells, fruit shells, sawdust, straw, or rice husks; and / or, Magnesium sulfate and zinc sulfate are byproducts of industrial acid wastewater treatment.

8. The method for preparing the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer according to any one of claims 5-7, characterized in that, In step S1, the rotation speed for shear dispersion treatment is 6000-10000 rpm, and the treatment time is 3-10 min; and / or, In step S3, the spraying is carried out in a rotary granulator or a fluidized bed; and / or, In step S4, the drying temperature is 60-80℃, and the drying process continues until the moisture content in the fertilizer precursor is no higher than 3%.

9. The method for preparing the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer according to claim 5, characterized in that, It also includes: Before step S4, it also includes: Waterproofing post-treatment: Atomize and spray an aqueous solution of potassium methylsilicate onto the surface of the fertilizer precursor, and perform low-temperature drying treatment to form a hydrophobic outer film on at least a portion of the surface of the protective shell.

10. The method for preparing the silicon-potassium-phosphorus-zinc-magnesium slow-release fertilizer according to claim 9, characterized in that, In the post-waterproofing treatment, the mass concentration of potassium methylsilicate aqueous solution is 1%-3%; the temperature for low-temperature drying is 60-80℃, and the treatment time is 15-25 minutes.

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