Macronutrient water-soluble fertilizer and method for producing the same

Abstract

This invention discloses a water-soluble fertilizer containing macronutrients, using mesoporous nano-hydroxyapatite as the first carrier, loading P, K, and Mg nutrients, and then subjecting it to secondary loading / coating with zeolite to form a "dual-carrier synergistic slow-release" system. The production steps include: Step 1, loading macronutrients onto mesoporous nano-hydroxyapatite: dispersing mesoporous nano-hydroxyapatite in deionized water and stirring; adding potassium dihydrogen phosphate and nano-magnesium oxide, stirring at a constant temperature to ensure P, K, and Mg are fully adsorbed and loaded onto the mesoporous nano-hydroxyapatite; drying under reduced pressure and pulverizing to obtain nHAP-based macronutrient powder; Step 2, secondary loading / coating with zeolite: dispersing zeolite in deionized water, adding a water-soluble dispersant to form a stable colloidal solution; adding the nHAP-based macronutrient powder obtained in Step 1 to achieve ion exchange and physical adsorption loading; centrifuging or filtering, low-temperature drying; pulverizing and sieving. This invention solves the problems of excessively rapid release of water-soluble fertilizers, lack of nutrients on the carrier, and potential safety hazards.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to a water-soluble fertilizer containing macro-elements and its production method. Background Technology

[0002] Water-soluble fertilizers containing macronutrients have advantages such as good water solubility, rapid nutrient absorption, and compatibility with fertigation, and have been widely used in modern agricultural production. Currently, commercially available water-soluble fertilizers are mainly divided into inorganic, organic, and suspension types. Their formulations often use urea, monoammonium phosphate, diammonium phosphate, potassium nitrate, and dipotassium hydrogen phosphate as the main sources of nitrogen, phosphorus, and potassium. Some products also contain amino acid chelates, trace elements, growth regulators, and adjuvants to meet the nutritional needs of different crops at different growth stages.

[0003] In existing technologies, to improve the stability, dispersibility, and long-lasting effect of water-soluble fertilizers, relevant research has employed specific carrier or adjuvant systems to load and regulate the slow release of nutrients. For example, the invention disclosed in CN107759346A uses a micellar system formed by compounding polyvinyl alcohol, sodium carboxymethyl cellulose, and sodium alkylbenzene sulfonate to load trace elements such as iron, zinc, and manganese onto a ferromagnetic carrier. This allows for the slow release of effective components while ensuring rapid fertilizer dissolution, extending the fertilizer's effective period and reducing nutrient loss. Another technology uses concentrated yeast waste liquid as an organic carrier, combined with suspending agents, nitrogen, phosphorus, and potassium raw materials, and chelated trace elements, to prepare organic suspension-type water-soluble fertilizer through high-speed dispersion. This solves the problems of low nutrient content, easy stratification and sedimentation, and limited transportation distance of conventional liquid fertilizers, while also replenishing soil organic matter and stimulating crop root growth.

[0004] Although existing water-soluble fertilizers containing macronutrients have shown some effectiveness, they still have significant technical shortcomings. For example, most inorganic carriers only function as physical adsorption, dispersion, or film formation agents, and cannot degrade themselves into nutrients that plants can absorb and utilize. After fertilizer application, the carrier remains in the soil, resulting in low utilization and potential long-term accumulation that could affect soil structure. Secondly, while some organic carriers can provide organic matter, their ability to control the release of macronutrients (phosphorus, potassium, calcium, magnesium, etc.) is limited. Nutrients are released quickly and are easily lost through leaching in water, leading to low fertilizer utilization. Furthermore, micronutrients and macronutrients are prone to chemical reactions and precipitation when combined, resulting in nutrient inactivation. Existing products also struggle to simultaneously achieve a synergistic effect of high water solubility, excellent slow release, and full nutrient availability. Finally, industrial waste-based carriers pose a potential heavy metal risk, lack sufficient biocompatibility and environmental safety, and are unsuitable for green and efficient agricultural production. Previous studies have shown that nano-hydroxyapatite (nHAP) can serve as a slow-release nutrient source for phosphorus and calcium, which degrades slowly in the soil to provide fertilizer. However, direct application of high doses of phosphorus and calcium nutrients can easily trigger ion antagonism / osmotic stress, inhibiting plant growth.

[0005] Therefore, developing a novel water-soluble fertilizer with a dual-function carrier that can be degraded into nutrients, and which combines high water solubility, stable slow release, synergistic nutrient enhancement, and environmental friendliness, is of great practical significance and application value. This would overcome the problems of existing technologies, such as carriers not contributing nutrients, excessively rapid nutrient release, easy precipitation and loss, and low utilization rate. Summary of the Invention

[0006] To address the problems of existing water-soluble fertilizers such as rapid release, easy leaching, lack of nutrient contribution from the carrier, and potential safety hazards, this invention provides a water-soluble fertilizer containing macronutrients and its production method. Specifically, it uses mesoporous nano-hydroxyapatite loaded with macronutrients as the first carrier, and then zeolite is used to load and coat the macronutrients to form a double-layer slow-release, dual-carrier fertilizer that is biodegradable. This achieves the effects of the carrier being biodegradable into nutrients, slow release without leaching, and long-lasting fertilizer effect.

[0007] This invention is achieved through the following technical solution:

[0008] On the one hand, the present invention provides a water-soluble fertilizer containing macroelements, wherein the water-soluble fertilizer contains macroelements using mesoporous nano-hydroxyapatite as the first carrier, and loads P, K and Mg nutrients, and then loads / coats them with zeolite to form a dual-carrier composite slow-release system.

[0009] Specifically, the water-soluble fertilizer containing macro-elements is made from the following raw materials in parts by weight:

[0010] 30-50 parts of mesoporous nano-hydroxyapatite (nHAP), 40-60 parts of zeolite, 15-25 parts of potassium dihydrogen phosphate (KH2PO4), 3-8 parts of nano-magnesium oxide (MgO), 1-3 parts of water-soluble dispersant, and 100-200 parts of deionized water.

[0011] As a preferred embodiment of the present invention, the water-soluble dispersant is composed of polyvinyl alcohol and sodium carboxymethyl cellulose in a mass ratio of 1:2 to 4.

[0012] As a preferred embodiment of the present invention, the mesoporous nano-hydroxyapatite is a rod-shaped nanoparticle with a rod diameter of 30-50 nm, a rod length of 150-300 nm, and a mesopore diameter of 5-20 nm.

[0013] As a preferred embodiment of the present invention, the zeolite is clinoptilolite with a particle size of 60-120 μm. The zeolite has a microporous-mesoporous hierarchical pore structure, wherein the micropore diameter is 0.3-0.8 nm and the mesopore and intergranular gap size is 20-80 nm.

[0014] Mesoporous nHAP nanorods partially penetrate the mesoporous channels of zeolite, while others are fixed to the outer surface of zeolite through surface adsorption, intergranular intercalation, and electrostatic interactions. The micropores (0.3–0.8 nm) of the zeolite are also responsible for adsorbing K+. + Mg 2+ Plasma, mesopores (20–80 nm), and intergranular spaces are responsible for providing anchoring sites.

[0015] On the other hand, the present invention provides a method for producing a water-soluble fertilizer containing macro-elements, comprising the following steps:

[0016] Step 1: Loading macroelements onto mesoporous nano-hydroxyapatite: Disperse 30-50 parts by mass of mesoporous nano-hydroxyapatite in deionized water and stir for 30 min; add 15-25 parts of KH2PO4 and 3-8 parts of MgO, and stir at a constant temperature of 50℃ for 60 min to allow P, K, and Mg to be fully adsorbed and loaded onto the nHAP surface; dry under reduced pressure and pulverize to obtain nHAP-based macroelement powder.

[0017] Step 2: Zeolite secondary loading / coating by mass: Disperse 40-60 parts of zeolite in deionized water, add 1-3 parts of dispersant to form a stable colloidal solution; add the nHAP-based macro-element powder obtained in Step 1, react for 60-90 minutes to achieve ion exchange and physical adsorption loading; then, centrifuge or filter, and dry at low temperature at 60℃; finally, pulverize and pass through a 200-mesh sieve to obtain zeolite@nHAP-macro-element water-soluble fertilizer.

[0018] As a preferred embodiment of the present invention, the total amount of deionized water used is 100 to 200 parts. If the amount of deionized water is too low, the solid-liquid ratio of the system will be too high, the carrier will easily agglomerate, and the nutrient loading will be uneven. If the amount of deionized water is too high, the subsequent drying energy consumption will be high, and the powder will easily clump together, affecting the sustained-release performance.

[0019] As a preferred embodiment of the present invention, the ratio of the amount of deionized water used in step 1 to the total mass of mesoporous nano-hydroxyapatite, potassium dihydrogen phosphate, and nano-magnesium oxide is 1 to 2:1, and the remainder is the deionized water used in step 2.

[0020] As a preferred embodiment of the present invention, the mesoporous nano-hydroxyapatite is prepared by a hydrothermal method with a Ca / P molar ratio of 1.67. The specific steps are as follows: First, 6 mmol of Na₂HPO₄·12H₂O is weighed and dissolved in 50 mL of deionized water, stirred until completely dissolved; then, 1 mol / L NaOH solution is added dropwise to adjust the pH of the solution to 11-12, obtaining solution A; 10 mmol of Ca(NO₃)₂·4H₂O is weighed and dissolved in 30 mL of deionized water, stirred until completely dissolved, obtaining solution B. Under magnetic stirring, solution B is slowly added dropwise to solution A, forming a white emulsion suspension; this suspension is transferred to a polytetrafluoroethylene-lined stainless steel autoclave, sealed, and reacted at 200°C for 7-9 hours. After the reaction was completed, the autoclave was allowed to cool naturally to room temperature, and the precipitate was separated by centrifugation. The product was washed 2 to 4 times with deionized water and anhydrous ethanol to remove residual ions. The product was then placed in an oven and dried at 100°C for 5 to 7 hours to obtain mesoporous hydroxyapatite.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) This invention constructs a two-layer sustained-release mechanism. On the one hand, the mesoporous nano-hydroxyapatite described in this invention is a rod-shaped nanoparticle with a mesoporous structure and Ca 2+ Sites and OH - Nutrient ion loading can be achieved through mesoporous physical adsorption, surface ion exchange, or electrostatic adsorption at specific sites; furthermore, the nHAP crystal surface contains a large number of uncoordinated phosphate ions (PO42-). 3- / HPO4 2- These negatively charged groups can react with K in the solution. + Mg 2+ Weak ionic / coordinate bonds are formed when K + Mg 2+ At higher concentrations, trace amounts of magnesium phosphate (Mg3(PO4)2) and potassium hydrogen phosphate (K2HPO4) precipitates form on the nHAP surface. These precipitates adhere to the pores, effectively "locking" nutrients within the carrier. Multiple mechanisms work synergistically to load P, K, and Mg, achieving the slow release of a large number of elements. Furthermore, the clinoptilolite possesses a microporous-mesoporous structure, allowing mesoporous nano-hydroxyapatite to be stably loaded / coated onto the zeolite's outer surface or inside its pores through surface physical adsorption, pore anchoring, intergranular intergrowth, and electrostatic interactions. Simultaneously, exchangeable cations (such as Na+) on the zeolite framework... + Ca 2+ ) and K in solution + Mg 2+Nutrient cations undergo a displacement reaction, fixing nutrients within the micropores of zeolite and forming strong binding sites; or, some nutrient ions are adsorbed into the mesopores and intergranular spaces of zeolite through van der Waals forces, forming weak binding sites. The "dual-carrier synergistic slow-release" system enables continuous nutrient release.

[0023] (2) On the other hand, as a natural mineral carrier, clinoptilolite contains a variety of beneficial elements such as silicon, calcium, magnesium, and potassium, which can be slowly dissolved and released in the soil to provide long-term nutritional supplements for crops, promote the growth and development of phosphorus-loving and calcium-loving crops such as tomatoes, increase chlorophyll content, promote root growth, and ultimately achieve the effect of increasing yield and improving quality. Attached Figure Description

[0024] Figure 1 Data graphs showing the slow-release performance (25℃) in water of zeolite@nHAP-macronutrient water-soluble fertilizers prepared in Examples 1-3, zeolite@macronutrient water-soluble fertilizers (Comparative Example 2), and nHAP-based macronutrient powders (Comparative Example 3). Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments.

[0026] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0027] Preparation of mesoporous nHAp: Based on a Ca / P molar ratio of 1.67, a hydrothermal method was used to prepare the nanorods. First, 6 mmol of Na₂HPO₄·12H₂O was weighed and dissolved in 50 mL of deionized water, stirred until completely dissolved. Then, 1 mol / L NaOH solution was added dropwise to adjust the pH of the solution to 11.5, obtaining solution A. 10 mmol of Ca(NO₃)₂·4H₂O was weighed and dissolved in 30 mL of deionized water, stirred until completely dissolved, obtaining solution B. Under magnetic stirring, solution B was slowly added dropwise to solution A, forming a white emulsion suspension. This suspension was transferred to a 100 mL PTFE-lined stainless steel autoclave, sealed, and reacted at 200 °C for 8 h. After the reaction, the autoclave was allowed to cool naturally to room temperature, and the precipitate was separated by centrifugation. The precipitate was washed three times each with deionized water and anhydrous ethanol to remove residual ions. The product was then placed in an oven and dried at 100 °C for 6 h to obtain mesoporous hydroxyapatite nanorods.

[0028] Clinoptilolite, commercially available from Wuhu Honghuashan Zeolite Mining Co., Ltd., has a particle size of 60–120 μm, containing micropores of 0.3–0.8 nm and mesopores and intergranular gaps of 20–80 nm.

[0029] Preparation of water-soluble dispersant: Polyvinyl alcohol and sodium carboxymethyl cellulose were compounded in a mass ratio of 1:3.

[0030] Example 1

[0031] A water-soluble fertilizer containing macronutrients, wherein the macronutrient water-soluble fertilizer uses mesoporous nano-hydroxyapatite as the first carrier, loads P, K, and Mg nutrients, and then loads / coats them with zeolite to form a dual-carrier composite slow-release system. The macronutrient water-soluble fertilizer is made from the following raw materials in parts by weight: 30 parts mesoporous nano-hydroxyapatite (nHAP), 40 parts zeolite, 15 parts potassium dihydrogen phosphate (KH2PO4), 3 parts nano-magnesium oxide (MgO), 1 part water-soluble dispersant, and 120 parts deionized water.

[0032] Specifically, the production steps of a water-soluble fertilizer containing macro-elements are as follows:

[0033] Step 1: Mesoporous nano-hydroxyapatite loaded with macro-elements:

[0034] By mass, 30 parts of mesoporous nHAP were dispersed in 50 parts of deionized water and stirred for 30 min; 15 parts of KH2PO4 and 3 parts of MgO were added and stirred at a constant temperature of 50℃ for 60 min to allow P, K and Mg to be fully adsorbed and loaded on the nHAP surface; the powder was dried under reduced pressure and pulverized to obtain nHAP-based macro-element powder.

[0035] Step 2, Zeolite secondary loading / coating:

[0036] By mass, 40 parts of zeolite were dispersed in 70 parts of deionized water, and 1 part of dispersant was added to form a stable colloidal solution; the nHAP-based macro-element powder prepared in step 1 was added, and the reaction was carried out for 75 minutes to achieve ion exchange and physical adsorption loading; centrifugation or filtration was performed, and the solution was dried at a low temperature below 60°C; the solution was pulverized and passed through a 200-mesh sieve to obtain 1# zeolite@nHAP-macro-element water-soluble fertilizer.

[0037] Example 2

[0038] A water-soluble fertilizer containing macronutrients, wherein the macronutrient water-soluble fertilizer uses mesoporous nano-hydroxyapatite as the first carrier, loads P, K, and Mg nutrients, and then loads / coats them with zeolite to form a dual-carrier composite slow-release system. The macronutrient water-soluble fertilizer is made from the following raw materials in parts by weight: 40 parts mesoporous nano-hydroxyapatite (nHAP), 50 parts zeolite, 20 parts potassium dihydrogen phosphate (KH2PO4), 5 parts nano-magnesium oxide (MgO), 2 parts water-soluble dispersant, and 150 parts deionized water.

[0039] Specifically, the production steps of a water-soluble fertilizer containing macro-elements are as follows:

[0040] Step 1: Mesoporous nano-hydroxyapatite loaded with macro-elements:

[0041] By mass, 40 parts of mesoporous nHAP were dispersed in 70 parts of deionized water and stirred for 30 min; 20 parts of KH2PO4 and 5 parts of MgO were added and stirred at a constant temperature of 50℃ for 60 min to allow P, K and Mg to be fully adsorbed and loaded onto the nHAP surface; the powder was dried under reduced pressure and pulverized to obtain nHAP-based macro-element powder.

[0042] Step 2, Zeolite secondary loading / coating:

[0043] By weight, 50 parts of zeolite were dispersed in 80 parts of deionized water, and 2 parts of dispersant were added to form a stable colloidal solution; the nHAP-based powder obtained in step 1 was added, and the reaction was carried out for 75 minutes to achieve ion exchange and physical adsorption loading; centrifugation or filtration was performed, and the solution was dried at a low temperature below 60°C; the solution was pulverized and passed through a 200-mesh sieve to obtain 2# zeolite@nHAP-macronutrient water-soluble fertilizer.

[0044] Example 3

[0045] A water-soluble fertilizer containing macronutrients, wherein the macronutrient water-soluble fertilizer uses mesoporous nano-hydroxyapatite as the first carrier, loads P, K, and Mg nutrients, and then loads / coats them with zeolite to form a dual-carrier composite slow-release system. The macronutrient water-soluble fertilizer is made from the following raw materials in parts by weight: 50 parts mesoporous nano-hydroxyapatite (nHAP), 60 parts zeolite, 25 parts potassium dihydrogen phosphate (KH2PO4), 8 parts nano-magnesium oxide (MgO), 2 parts water-soluble dispersant, and 180 parts deionized water.

[0046] Specifically, the production steps of a water-soluble fertilizer containing macro-elements are as follows:

[0047] Step 1: Nano-hydroxyapatite loaded with a large number of elements:

[0048] By mass, 50 parts of mesoporous nHAP were dispersed in 90 parts of deionized water and stirred for 30 min; 25 parts of KH2PO4 and 8 parts of MgO were added and stirred at a constant temperature of 50℃ for 60 min to allow P, K and Mg to be fully adsorbed and loaded onto the nHAP surface; the powder was dried under reduced pressure and pulverized to obtain nHAP-based macro-element powder.

[0049] Step 2, Zeolite secondary loading / coating:

[0050] By mass, 60 parts of zeolite were dispersed in 90 parts of deionized water, and 3 parts of dispersant were added to form a stable colloidal solution; the nHAP-based macro-element powder obtained in step 1 was added, and the reaction was carried out for 75 minutes to achieve ion exchange and physical adsorption loading; centrifugation or filtration was performed, and the solution was dried at a low temperature below 60°C; the solution was pulverized and passed through a 200-mesh sieve to obtain 3# zeolite@nHAP-macro-element water-soluble fertilizer.

[0051] Comparative Example 1 (Conventional water-soluble fertilizer containing macronutrients)

[0052] First, add 1 part of dispersant to 20 parts of deionized water and stir evenly; then add 15 parts of potassium dihydrogen phosphate and stir until completely dissolved; slowly add 3 parts of nano magnesium oxide and continue stirring for 50 minutes to form a uniform suspension; spray dry the suspension, set the inlet air temperature to 170℃ and the outlet air temperature to 85℃ to obtain a water-soluble fertilizer powder with good flowability, which is No. 1 conventional macro-element water-soluble fertilizer. It is used as a control group for No. 1 zeolite@nHAP-macro-element water-soluble fertilizer to compare soil leaching loss.

[0053] Similarly, following the steps above, 20 parts of potassium dihydrogen phosphate (KH2PO4), 5 parts of nano magnesium oxide (MgO), 2 parts of water-soluble dispersant, and 30 parts of deionized water were adjusted, while keeping the other steps unchanged, to obtain No. 2 conventional macro-element water-soluble fertilizer. This fertilizer was used as a control group for No. 2 zeolite@nHAP-macro-element water-soluble fertilizer to compare soil leaching losses.

[0054] Similarly, following the steps described above, 25 parts of potassium dihydrogen phosphate (KH2PO4), 8 parts of nano magnesium oxide (MgO), 3 parts of water-soluble dispersant, and 40 parts of deionized water were added, while keeping the other steps unchanged, to obtain No. 3 conventional macro-element water-soluble fertilizer. This fertilizer was used as a control group for No. 3 zeolite@nHAP-macro-element water-soluble fertilizer to compare soil leaching losses.

[0055] Comparative Example 2

[0056] In step 1, the amount of nHAP in the mesopores was 0, and the remaining steps were consistent with those in Example 1, resulting in zeolite@macronutrient water-soluble fertilizer.

[0057] Comparative Example 3

[0058] The nHAP-based macroelement powder obtained in step 1 of Example 1.

[0059] Performance testing:

[0060] (1) The appearance, particle size, pH value, moisture, water-insoluble matter and suspension rate of 1#, 2# and 3# zeolite@nHAP-macro element water-soluble fertilizer products were measured and recorded in Table 1.

[0061] (2) Nutrient determination of 1#, 2#, and 3# zeolite@nHAP-macronutrient water-soluble fertilizer products: Total phosphorus (as P2O5) was determined according to GB / T 8573-2017 "Determination of available phosphorus content in compound fertilizers"; total potassium (as K2O) content was determined according to GB / T 8574-2024 "Determination of potassium content in compound fertilizers"; available magnesium and calcium content were determined according to GB / T 19203-2003 "Determination of calcium, magnesium, and sulfur content in compound fertilizers"; silicon (as SiO2) content was determined according to GB / T 36207-2018 "Silicon-calcium-potassium-magnesium fertilizers". The corresponding results are recorded in Table 2.

[0062] (3) The slow-release performance of the fertilizers in Examples 1-3 and Comparative Examples 2 and 3 was characterized by static slow-release experiments in water. Specific procedures were as follows: 1.00 g of sample dried to constant weight was weighed and placed in a 250 mL stoppered conical flask. 200 mL of deionized water was added, and the flask was sealed and placed in a constant temperature water bath at 25 ± 1 °C. At 2 h, 24 h, and 7 d, 5.0 mL of the supernatant was transferred, filtered through a 0.45 μm filter membrane, and the concentrations of phosphorus, potassium, and magnesium in the filtrate were determined using ICP-OES. 5.0 mL of fresh deionized water was added after each sampling to maintain a constant system volume. The relevant results are attached. Figure 1 As shown.

[0063] (4) By conducting a soil leaching experiment, the nutrient leaching amount of conventional water-soluble fertilizer containing macro-elements (prepared in Comparative Example 1) was compared with that of the fertilizer prepared in the embodiment of this invention. The specific operation was as follows: the test soil that had been air-dried and passed through a 2mm sieve was weighed and placed into an organic glass leaching column with an inner diameter of 5cm and a height of 30cm. The height of the soil column was 20cm, and the bulk density was controlled at 1.2g / cm³. 3 Following the principle of equal nutrient content, slow-release fertilizer samples (1#, 2#, and 3#) and conventional fertilizer control samples were uniformly mixed into the top 3 cm of the soil. After pre-culturing for 24 hours, deionized water was used for leaching, with each leaching volume being 100 mL and the leaching rate being 2–3 mL / min, for a total of 10 leaching cycles. All filtrates from each leaching were collected. After filtering the filtrate through a 0.45 μm filter membrane, the concentrations of phosphorus, potassium, and magnesium in the filtrate were determined using ICP-OES. The nutrient leaching volume and total leaching rate for each leaching cycle were calculated, and the relevant results are recorded in Table 3.

[0064] Application performance:

[0065] The effects of the fertilizer of this invention on crop growth were evaluated through a tomato pot experiment. The relevant results are recorded in Table 4. The blank group was the group that did not apply any fertilizer.

[0066] Table 1: Physicochemical Properties

[0067]

[0068] Table 2: Nutrient Content Indicators

[0069]

[0070] Table 3: Comparison of soil leaching losses (relative to conventional water-soluble fertilizers)

[0071]

[0072] Table 4: Results of pot experiment (taking tomatoes as an example, relative to the control group)

[0073]

[0074] As shown in Table 1, the zeolite@nHAP-macronutrient water-soluble fertilizer prepared by this invention is a uniform grayish-white powder with a particle size ≤0.13mm after passing through a 200-mesh sieve. When prepared as a 1% aqueous solution, its pH is 6.5-7.0, which is a neutral to slightly acidic / weakly alkaline environment, which is very friendly to crops and soil. The moisture content is ≤4.2%, indicating that the powder has good flowability, is not easy to absorb moisture and clump, and has good storage stability. The water-insoluble matter content is ≤3.5%, indicating that after the fertilizer is dissolved in water, there is little undissolved residue, and it is not easy to clog pipes and drippers during drip irrigation / fertigation. The suspended solids content is ≥85%, indicating that the fertilizer has good water dispersibility, is not easy to settle and stratify after standing, and can be stably applied with water with uniform nutrient distribution.

[0075] Table 2 records the nutrient content indicators of the fertilizers prepared by this invention. The nutrient content varies in gradient with the amount of carrier and nutrient raw materials added. Each formula contains sufficient phosphorus and potassium macroelements, while also supplementing magnesium, calcium, silicon and other microelements, resulting in a comprehensive and balanced nutrient composition. With the increase of the amount of mesoporous nano-hydroxyapatite and clinoptilolite added, the calcium and silicon contents increase simultaneously, demonstrating that the carrier material has the dual functions of a slow-release framework and nutrient supplementation.

[0076] Table 3 shows a comparison of soil leaching losses. Compared with conventional fertilizers (prepared in Comparative Example 1), the leaching of P, K, and Mg by zeolite@nHAP-water-soluble fertilizers prepared in Examples 1-3 of this invention is significantly reduced.

[0077] Appendix Figure 1This figure compares the cumulative release rates of phosphorus, potassium, and magnesium nutrients at three time points: 2h, 24h, and 7d for zeolite@nHAP-water-soluble fertilizers (prepared in Examples 1-3), zeolite@nHAP-water-soluble fertilizer (comparative Example 2), and nHAP-based macronutrient powder (comparative Example 3). The graph shows a clear stepwise increase in nutrient release for all fertilizers. Notably, in the initial 2h, the release rates of phosphorus, potassium, and magnesium for fertilizers 1, 2, and 3 were all below 30%, avoiding rapid nutrient loss and the risk of root burn. In contrast, the release rates of zeolite@nHAP-water-soluble fertilizer and nHAP-based macronutrient powder were greater than 30%, especially for phosphorus and potassium, which reached 50%. This is because zeolite loads nutrients through physical adsorption, lacking the binding of mesoporous nHAP and the slow-release barrier of a double-layered coating structure. Nutrients easily dissolve rapidly in water, resulting in poor slow-release performance of zeolite-loaded fertilizers. During the first 24 hours, the release rates of fertilizers #1, #2, and #3 were below 60%, while the release rates of zeolite@macronutrient water-soluble fertilizer and nHAP-based macronutrient powder exceeded 60%, especially the cumulative potassium release rate of zeolite@macronutrient water-soluble fertilizer, which reached 81%. In the later stages (7 days), the nutrient release rates of each fertilizer tended to be between 70% and 90%, indicating that the "dual-carrier coating structure" indeed played a slow-release role, avoiding the one-time burst release of nutrients found in ordinary water-soluble fertilizers, and allowing for continuous nutrient release to better meet crop needs.

[0078] Table 4 shows the results of the tomato pot experiment. From the table, it can be seen that the fertilizers prepared in Examples 1-3 can significantly promote plant growth, verifying the application effect of the series of fertilizers of this invention on actual crops.

[0079] In summary, this invention provides a zeolite@nHAP-macro-element water-soluble fertilizer and its production method. By loading P, K, and Mg onto mesoporous nano-hydroxyapatite to form a first carrier, and then loading / coating it with clinoptilolite, a "dual-carrier synergistic slow-release" system is constructed.

[0080] The fertilizer boasts multiple advantages, including excellent physicochemical properties, abundant nutrient content, significant slow-release and fertilizer retention effects, and outstanding application results. For example, the product has a uniform appearance, low moisture content, low water-insoluble matter, and high suspension rate, meeting the requirements of various application methods such as drip irrigation and fertigation. Secondly, it is rich in total phosphorus, total potassium, and available magnesium, while also containing beneficial elements such as calcium and silicon, providing balanced nutrition for crops. Nutrient release is stable, with a low initial burst release rate and a long-lasting nutrient supply period, significantly reducing leaching losses of phosphorus, potassium, and magnesium and greatly improving fertilizer utilization. Pot experiments show that the fertilizer of this invention can significantly promote the growth and development of phosphorus- and calcium-loving crops such as tomatoes, increase chlorophyll content, promote root growth, and ultimately achieve the effect of increasing yield and improving quality.

Claims

1. A water-soluble fertilizer containing macro-elements, characterized in that, The aforementioned water-soluble fertilizer containing macronutrients uses mesoporous nano-hydroxyapatite as the first carrier, loads P, K, and Mg nutrients, and then forms a two-layer composite slow-release system through zeolite loading / coating.

2. The water-soluble fertilizer containing macro-elements according to claim 1, characterized in that, The water-soluble fertilizer containing macro-elements is made from the following raw materials in parts by weight: 30-50 parts of mesoporous nano-hydroxyapatite, 40-60 parts of zeolite, 15-25 parts of potassium dihydrogen phosphate, 3-8 parts of nano-magnesium oxide, 1-3 parts of water-soluble dispersant, and 100-200 parts of deionized water.

3. A water-soluble fertilizer containing macro-elements according to claim 2, characterized in that, The water-soluble dispersant is composed of polyvinyl alcohol and sodium carboxymethyl cellulose in a mass ratio of 1:2 to 4.

4. A water-soluble fertilizer containing macro-elements according to claim 2, characterized in that, The mesoporous nano-hydroxyapatite is a rod-shaped nanoparticle with a rod diameter of 30-50 nm, a rod length of 150-300 nm, and a mesopore diameter of 5-20 nm.

5. A water-soluble fertilizer containing macro-elements according to claim 2, characterized in that, The zeolite is clinoptilolite, the particle size of the zeolite is 60-120 μm, and the zeolite has a microporous-mesoporous hierarchical pore structure, wherein the micropore diameter is 0.3-0.8 nm, and the mesopore and intergranular gap size is 20-80 nm.

6. A method for producing a water-soluble fertilizer containing macro-elements as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Loading macro-elements onto mesoporous nano-hydroxyapatite: Disperse mesoporous nano-hydroxyapatite in deionized water and stir to disperse; add potassium dihydrogen phosphate and nano-magnesium oxide, and stir at a constant temperature to allow P, K, and Mg to be fully adsorbed and loaded onto the surface of mesoporous nano-hydroxyapatite. Reduced pressure drying and pulverization were performed to obtain nHAP-based macro-element powder. Step 2, Zeolite secondary loading / coating: Disperse zeolite in deionized water and add a water-soluble dispersant to form a stable colloidal solution; add the nHAP-based macro-element powder obtained in Step 1, react for 60-90 min to achieve ion exchange and physical adsorption loading; centrifuge or filter, dry at low temperature at 60℃; pulverize and pass through a 200-mesh sieve to obtain zeolite@nHAP-macro-element water-soluble fertilizer.

7. The method for producing a water-soluble fertilizer containing macro-elements according to claim 6, characterized in that, In step 1, the ratio of deionized water to mesoporous nano-hydroxyapatite, potassium dihydrogen phosphate, and nano-magnesium oxide is 1 to 2:

1.

8. The method for producing a water-soluble fertilizer containing macro-elements according to claim 6, characterized in that, By mass, in step 1, the amount of mesoporous nano-hydroxyapatite is 30-50 parts, the amount of potassium dihydrogen phosphate is 15-25 parts, and the amount of nano-magnesium oxide is 3-8 parts; in step 2, the amount of zeolite is 40-60 parts, and the amount of water-soluble dispersant is 1-3 parts; and the total amount of deionized water in steps 1 and 2 is 100-200 parts.

9. The method for producing a water-soluble fertilizer containing macro-elements according to claim 6, characterized in that, The mesoporous nano-hydroxyapatite was prepared by a hydrothermal method with a Ca / P molar ratio of 1.

67.

10. A method for producing a water-soluble fertilizer containing macro-elements according to claim 9, characterized in that, The preparation steps of the mesoporous nano-hydroxyapatite include: weighing 6 mmol of Na2HPO4·12H2O, dissolving it in 50 mL of deionized water, adding 1 mol / L NaOH solution dropwise, adjusting the pH of the solution to 11-12, and obtaining solution A; weighing 10 mmol of Ca(NO3)2·4H2O, dissolving it in 30 mL of deionized water, and obtaining solution B; under magnetic stirring, slowly adding solution B to solution A to form a white emulsion suspension; transferring the suspension to a polytetrafluoroethylene-lined stainless steel autoclave, sealing it, and keeping it at 200℃ for 7-9 h; after the reaction, allowing the autoclave to cool naturally to room temperature, centrifuging to separate the precipitate; washing it 2-4 times each with deionized water and anhydrous ethanol to remove residual ions; placing the product in an oven and drying it at 100℃ for 5-7 h to obtain mesoporous hydroxyapatite.

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