Silicon oxide / hydrotalcite composite slow-release fertilizer and preparation method thereof

Abstract

The present invention provides a silica / hydrotalcite composite slow-release fertilizer and a preparation method thereof, comprising the following steps: uniformly mixing amorphous silica, a divalent metal salt, a trivalent metal salt, and water to obtain a mixed solution; subjecting the mixed solution to a hydrothermal reaction, followed by filtering, washing, and drying to obtain a silica / hydrotalcite nanocomposite material; calcining the silica / hydrotalcite nanocomposite material to obtain a silica / metal oxide nanocomposite material; and loading inorganic and organic fertilizers onto the silica / metal oxide nanocomposite material to obtain a silica / hydrotalcite composite slow-release fertilizer. This preparation method is simple, highly feasible, low-cost, and easily scalable for industrial production. The layered and pore-channel structure of the silica / hydrotalcite nanocomposite material effectively provides ample space for the loading of nutrients, thereby improving the slow-release efficiency of nutrients in the fertilizer, increasing nutrient utilization efficiency, reducing fertilization frequency, and minimizing potential environmental impacts.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural cultivation, and in particular to a silicon oxide / hydrotalcite composite slow-release fertilizer and a preparation method thereof. Background Art

[0002] With the growth of the global population and the reduction of arable land resources, the sustainability of agricultural production faces major challenges. Traditional fertilizers often release nutrients quickly, resulting in a short fertilizer effect time, low utilization rate, and easy to cause environmental pollution. In particular, the efficient utilization of nitrogen (N), phosphorus (P), potassium (K) and selenium (Se), which are essential nutrients for crop growth, has become a key topic in agricultural research. Slow-release fertilizers are favored because they can reduce the loss of nutrients, prolong the fertilizer effect time, and improve fertilizer utilization efficiency. However, most slow-release fertilizers on the market currently have limitations in terms of cost, slow-release effect and environmental friendliness. Therefore, the development of a new, efficient and environmentally friendly slow-release fertilizer is of great practical significance.

[0003] As a layered material, hydrotalcite has demonstrated excellent performance in areas such as drug release and pollutant adsorption. However, single hydrotalcite materials still have limitations in fertilizer carrier applications, such as low nutrient loading and poor release performance for cationic nutrients and urea. Summary of the Invention

[0004] Based on this, the present invention provides a method for preparing a silicon oxide / hydrotalcite composite slow-release fertilizer with good slow-release performance.

[0005] A method for preparing a silicon oxide / hydrotalcite composite slow-release fertilizer comprises the following steps:

[0006] uniformly mixing amorphous silicon oxide, a divalent metal salt, a trivalent metal salt and water to obtain a mixed solution;

[0007] The mixed solution is subjected to a hydrothermal reaction, and then filtered, washed and dried to obtain a silicon oxide / hydrotalcite nanocomposite material;

[0008] calcining the silicon oxide / hydrotalcite nanocomposite material to obtain a silicon oxide / metal oxide nanocomposite material;

[0009] Inorganic and organic fertilizers are loaded on the silicon oxide / metal oxide nanocomposite material to obtain a silicon oxide / hydrotalcite composite slow-release fertilizer.

[0010] In one embodiment, loading inorganic and organic fertilizers on the silica / metal oxide nanocomposite material comprises the following steps: dissolving phosphorus and potassium fertilizers and selenium fertilizers in water, adding the silica / metal oxide nanocomposite material, mixing uniformly, and then drying to obtain a silica / hydrotalcite-based phosphorus, potassium, and selenium complex; and melting urea and mixing uniformly with the silica / hydrotalcite-based phosphorus, potassium, and selenium complex, followed by extrusion and granulation.

[0011] In one embodiment, the phosphorus and potassium fertilizers are one of potassium phosphate, potassium hydrogen phosphate and potassium dihydrogen phosphate, and the selenium fertilizer is sodium selenite or sodium selenate.

[0012] In one embodiment, the mass ratio of phosphorus and potassium fertilizers to selenium fertilizers is 10:1 to 100:1, the mass ratio of phosphorus and potassium fertilizers to the silicon oxide / metal oxide nanocomposite material is 1:1 to 3:1, and the mass ratio of water to the silicon oxide / metal oxide nanocomposite material is 5:1 to 10:1.

[0013] In one embodiment, the melting temperature of urea is 133-145° C., and the mass ratio of urea to silicon oxide / hydrotalcite-based potassium phosphorus-selenium complex is 2.5:1-7.5:1.

[0014] In one embodiment, the specific surface area of ​​the amorphous silicon oxide is 100 to 600 m 2 / g, and its proportion in the silicon oxide / hydrotalcite nanocomposite material is 3wt% to 50wt%.

[0015] In one embodiment, the divalent metal salt is selected from Mg 2+ and Ca 2+ One or more soluble salts, wherein the trivalent metal salt is Al 3+ The soluble salt has a molar ratio of the divalent metal salt to the trivalent metal salt of 2 to 4.

[0016] In one embodiment, the process further includes the following steps before the hydrothermal reaction: adjusting the pH value of the mixed solution to 9-11.

[0017] In one embodiment, the temperature of the hydrothermal reaction is 40-120° C., and the time is 12-48 hours; the temperature of the calcination is 450-550° C., and the time is 30-120 minutes.

[0018] The present invention also provides a silicon oxide / hydrotalcite composite slow-release fertilizer, which is prepared according to the above preparation method.

[0019] The above solution of the present invention has the following beneficial effects:

[0020] The present invention utilizes the characteristics of silicon oxide and hydrotalcite and forms a nanocomposite material with good slow-release performance and high adsorption capacity through a specific synthesis process, thereby preparing a silicon oxide / hydrotalcite composite slow-release fertilizer with excellent slow-release performance, thereby improving the utilization efficiency of the fertilizer and reducing the impact on the environment.

[0021] Specifically, the preparation method begins with lightweight, porous amorphous silica, divalent metal salts, and trivalent metal salts. These readily available, inexpensive raw materials are then co-precipitated in aqueous solution to produce a silica / hydrotalcite nanocomposite. A subsequent calcination step promotes bonding between the two materials, removing components like carbonate ions and providing the necessary space for subsequent nutrient loading. This simple process is suitable for large-scale production and cleverly utilizes silica's inherent "carrier" function to load hydrotalcite onto it, forming a nanocomposite structure. The entire synthesis process is environmentally friendly and in line with current trends in green chemistry.

[0022] Furthermore, key nutrient elements such as nitrogen, phosphorus, potassium, and selenium are combined with the silicon oxide / hydrotalcite nanocomposite material through a simple step of wet mixing and blending. The process is easy to operate and convenient for large-scale production. The simplified preparation process reduces production costs, making the silicon oxide / hydrotalcite composite slow-release fertilizer both efficient and economical, and improving market competitiveness. The present invention utilizes the synergistic effect of silicon oxide / hydrotalcite nanocomposite materials and urea coatings. This innovative combination significantly improves the slow-release performance of elements such as nitrogen, phosphorus, potassium, and selenium in fertilizers, and optimizes the supply efficiency of nutrients. In addition, the present invention can regulate the nutrient element loading according to different crops and soil conditions. By adjusting the ratio of nitrogen, phosphorus, potassium, and selenium, the slow-release characteristics of the composite material can be customized, thereby realizing the production of personalized fertilizer products.

[0023] The present invention first combines phosphorus, potassium, and selenium with silicon oxide / metal oxide through wet mixing. Since the oxide in the composite material will be converted into hydrotalcite again after contacting the aqueous solution of phosphorus, potassium, and selenium, this process is conducive to the intercalation and loading of phosphate and selenite anion groups in the hydrotalcite. At the same time, silicon oxide will also form a large amount of silicon hydroxyl groups that are conducive to the adsorption of potassium ions, thereby forming a composite slow-release fertilizer. In addition, molten urea and silicon oxide / hydrotalcite-based phosphorus, potassium, and selenium complex are fused together. Due to the fluidity and reactivity of urea, urea molecules can be promoted to enter the micropores of the material and react with surface hydroxyl groups, promoting the immobilization of urea molecules by the composite material. Excess urea molecules will form a urea layer on the surface of the composite material, which will wrap the nitrogen, phosphorus, potassium, and selenium elements in the inner layer to form a core-shell structure. This slow-release fertilizer system will greatly improve the slow-release performance of nutrients. Compared with currently available slow-release fertilizers, this structure has significant innovation.

[0024] In addition, after the nutrients in the silica / hydrotalcite composite slow-release fertilizer prepared by the present invention are released, the silica / hydrotalcite nanomaterial remains in the soil, which has the beneficial effects of improving soil structure, increasing soil porosity and water retention capacity, and promoting the development of plant roots. In addition, the negative surface charge and porosity of the silica in the composite material are conducive to the adsorption and fixation of heavy metal cations in the soil, and the hydrotalcite interlayers can adsorb and fix anionic group pollutants such as fluoride ions, dichromate ions, and arsenate ions. Therefore, the silica / hydrotalcite nanocomposite material remaining in the soil can serve as an environmentally friendly soil conditioner. Furthermore, the abundant pores and residual nutrients in the composite material can provide a habitat and nutrition for soil microorganisms, promote microbial activity, and enhance the biological activity of the soil. Finally, elements such as Si and Mg in the composite material can be slowly dissolved, providing plants with beneficial elements such as Si and Mg, promoting plant growth, enhancing plant resistance to pests and diseases, and regulating the acid-base environment of the soil. The silica / hydrotalcite composite slow-release fertilizer prepared by the present invention demonstrates the effect of a single fertilizer with multiple uses.

[0025] In summary, the silica / hydrotalcite composite slow-release fertilizer of the present invention has multiple advantages in terms of innovation, environmental friendliness, cost-effectiveness, slow-release performance, and late beneficial effects, and has broad application prospects in modern agricultural production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 XRD patterns of the silicon oxide / hydrotalcite nanocomposite material prepared in Example 1 of the present invention before and after calcination and after loading phosphorus, potassium and selenium elements;

[0027] Figure 2 This is the release curve of nitrogen, phosphorus, potassium and selenium of the silicon oxide / hydrotalcite composite slow-release fertilizer prepared in Example 1 of the present invention;

[0028] Figure 3 This is the release curve of nitrogen, phosphorus, potassium and selenium of the silicon oxide / hydrotalcite composite slow-release fertilizer prepared in Example 2 of the present invention;

[0029] Figure 4 This is the release curve of nitrogen, phosphorus, potassium and selenium of the silicon oxide / hydrotalcite composite slow-release fertilizer prepared in Example 3 of the present invention;

[0030] Figure 5 This is the release curve of nitrogen, phosphorus, potassium and selenium of the hydrotalcite slow-release fertilizer prepared in Comparative Example 1 of the present invention;

[0031] Figure 6 This is the release curve of nitrogen, phosphorus, potassium and selenium of the silicon oxide / hydrotalcite composite slow-release fertilizer prepared in Comparative Example 2 of the present invention;

[0032] Figure 7 This is the release curve of nitrogen, phosphorus, potassium and selenium of the silicon oxide / hydrotalcite composite slow-release fertilizer prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0033] To make the technical problems, technical solutions, and advantages to be solved by the present invention more clear, the following is a detailed description with reference to the accompanying drawings and specific embodiments. It is obvious that the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0034] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified, the reagents and instruments used in the examples are all conventionally selected in the art. Experimental methods without specific conditions in the examples were carried out according to conventional conditions, such as those described in the literature, books, or methods recommended by the manufacturer.

[0035] A method for preparing a silicon oxide / hydrotalcite composite slow-release fertilizer according to an embodiment of the present invention comprises the following steps:

[0036] S1. Evenly mixing amorphous silicon oxide, a divalent metal salt, a trivalent metal salt, and water to obtain a mixed solution;

[0037] S2, subjecting the mixed solution to a hydrothermal reaction, and then filtering, washing, and drying to obtain a silicon oxide / hydrotalcite nanocomposite material;

[0038] S3, calcining the silicon oxide / hydrotalcite nanocomposite material to obtain a silicon oxide / metal oxide nanocomposite material;

[0039] S4. Loading inorganic and organic fertilizers on the silicon oxide / metal oxide nanocomposite material to obtain a silicon oxide / hydrotalcite composite slow-release fertilizer.

[0040] The preparation method of the present embodiment effectively synthesizes silicon oxide and hydrotalcite into a composite structure with nanometer size by coprecipitation, and then promotes the combination between the two materials through a calcination step, removes components such as carbonate ions, and provides the necessary space for the subsequent loading of nutrient elements. Subsequently, inorganic and organic fertilizers are loaded on the silicon oxide / metal oxide nanocomposite material. The layered structure and pore structure of the silicon oxide / hydrotalcite nanocomposite material can effectively provide sufficient space for the loading of nitrogen, phosphorus, potassium and selenium elements, significantly improving the slow-release efficiency of nutrients in the fertilizer, thereby improving the utilization efficiency of nutrients, reducing the frequency of fertilization, and significantly reducing the potential impact on the environment. Therefore, the present invention not only provides a new way of efficient and environmentally friendly for the technological advancement of slow-release fertilizers, but also has great significance for promoting sustainable agricultural development.

[0041] In a specific example, loading inorganic and organic fertilizers on silica / metal oxide nanocomposites includes the following steps: dissolving phosphorus and potassium fertilizers and selenium fertilizers in water, adding silica / metal oxide nanocomposites, mixing evenly and then drying to obtain a silica / hydrotalcite-based phosphorus, potassium and selenium complex; melting urea and mixing evenly with the silica / hydrotalcite-based phosphorus, potassium and selenium complex, and extruding and granulating.

[0042] In this way, phosphorus, potassium and selenium are compounded with silicon oxide / metal oxide through wet mixing. Since the oxides in the composite material will be converted into hydrotalcite again after contacting the aqueous solution of phosphorus, potassium and selenium, this process is conducive to the intercalation and loading of phosphate and selenite anion groups in the hydrotalcite. At the same time, silicon oxide will also form a large number of silicon hydroxyl groups, which is conducive to the adsorption of potassium ions, thereby forming a composite slow-release fertilizer. In addition, molten urea is co-melted with the silicon oxide / hydrotalcite-based phosphorus, potassium and selenium complex. Due to the fluidity and reactivity of urea, urea molecules can be promoted to enter the micropores of the material and react with the surface hydroxyl groups, promoting the composite material to fix urea molecules. Excess urea molecules will form a urea layer on the surface of the composite material, wrapping the nitrogen, phosphorus, potassium and selenium elements in the inner layer to form a core-shell structure. This slow-release fertilizer system will greatly improve the slow-release performance of nutrients.

[0043] In a specific example, the phosphorus and potassium fertilizers are selected from potassium phosphate, potassium hydrogen phosphate, and potassium dihydrogen phosphate, and the selenium fertilizer is sodium selenite or sodium selenate. It is understood that the specific types of fertilizers are not limited thereto and can be selected and replaced as needed.

[0044] In a specific example, the mass ratio of phosphate fertilizers and selenium fertilizers is 10:1 to 100:1, preferably 10:1 to 20:1, the mass ratio of phosphate fertilizers and silicon oxide / metal oxide nanocomposites is 1:1 to 3:1, and the mass ratio of water (water for dissolving phosphate fertilizers and selenium fertilizers) and silicon oxide / metal oxide nanocomposites is 5:1 to 10:1.

[0045] In a specific example, the melting temperature of urea is 133-145° C., and the mass ratio of urea to the silicon oxide / hydrotalcite-based potassium phosphorus-selenium complex is 2.5:1-7.5:1.

[0046] In a specific example, the specific surface area of ​​amorphous silicon oxide is 100 to 600 m 2 / g, preferably 250 to 400 m 2 / g, and the proportion of amorphous silica in the silica / hydrotalcite nanocomposite is 3wt% to 50wt%, preferably 6wt% to 30wt%, to achieve better fertilizer loading and sustained-release performance. Lightweight and porous amorphous silica has excellent physical and chemical stability, high specific surface area, developed pores, good adsorption properties, and environmental friendliness. Combining this silica with hydrotalcite to form a composite material can fully utilize the advantages of both to increase nutrient loading and regulate release behavior.

[0047] In a specific example, the divalent metal salt is selected from Mg 2+ and Ca 2+ One or more soluble salts, trivalent metal salt is Al 3+ The molar ratio of the soluble salt, the divalent metal salt and the trivalent metal salt is 2 to 4.

[0048] Preferably, before the hydrothermal reaction, the method further comprises adjusting the pH of the mixed solution to 9 to 11. For example, a mixed solution of sodium hydroxide and sodium carbonate can be used to adjust the pH, but the method is not limited thereto. Preferably, the concentrations of sodium hydroxide and sodium carbonate are 1.0 to 2.0 mol / L and 0.1 to 0.2 mol / L, respectively.

[0049] In a specific example, the temperature of the hydrothermal reaction is 40 to 120° C., preferably 60 to 80° C., and the time is 12 to 48 hours, preferably 12 to 24 hours.

[0050] In a specific example, the calcination temperature is 450-550° C., and the calcination time is 30-120 minutes, preferably 60-90 minutes.

[0051] Preferably, the molten urea is mixed with the silicon oxide / hydrotalcite-based potassium phosphorus selenium complex and stirred for 1 to 5 minutes to make the materials more uniform.

[0052] Preferably, before calcination, the silicon oxide / hydrotalcite nanocomposite material may be ground through a 100-mesh sieve to disperse the material more evenly and finely, and to allow for a more thorough subsequent reaction.

[0053] The following are specific examples.

[0054] Example 1

[0055] The steps for preparing the silicon oxide / hydrotalcite composite slow-release fertilizer in this embodiment are as follows:

[0056] 3.0g, with a specific surface area of ​​301.7m 21 / g of silica, 12.2g (0.048mol) of magnesium nitrate hexahydrate, and 7.5g (0.02mol) of aluminum nitrate nonahydrate were added to 300ml of deionized water, stirred for 10 minutes, and then sonicated for 20 minutes. The pH was adjusted to 10 using a mixed solution of sodium hydroxide and sodium carbonate. The mixture was then transferred to a 60°C oven for a sealed hydrothermal reaction for 24 hours. It was then filtered while hot, washed with deionized water until neutral, and dried to obtain a silica / hydrotalcite nanocomposite. After grinding through a 100-mesh sieve, the mixture was calcined at 450°C in a muffle furnace for 90 minutes to obtain a silica / metal oxide nanocomposite. 2.0g of potassium phosphate and 0.2g of sodium selenite were dissolved in 10ml of deionized water. 2.0g of the silica / metal oxide nanocomposite was added, mixed thoroughly, and dried to obtain a silica / hydrotalcite-based potassium-phosphorus-selenium complex. Then, 10.0 g of urea was completely melted at 133°C, and then 2.0 g of silicon oxide / hydrotalcite-based phosphorus potassium selenium complex was added, stirred for 1 minute, and extruded and granulated while hot to obtain silicon oxide / hydrotalcite composite slow-release fertilizer granules. Figure 1 As shown, the XRD patterns of the silicon oxide / hydrotalcite nanocomposite material before and after calcination and loading of phosphorus, potassium and selenium elements in this embodiment are shown, indicating that the silicon oxide / hydrotalcite nanocomposite material was successfully synthesized, and after calcination, the carbonate and water molecules between the hydrotalcite layers were removed and converted into bimetallic oxides. After loading of phosphorus, potassium and selenium elements, the hydrotalcite phase was restored again, indicating that phosphate and selenite successfully entered the interlayers of the hydrotalcite, which is beneficial to the sustained release of phosphorus and selenium elements.

[0057] The slow-release fertilizer uses the static water release method to test the slow-release effect. Figure 2 As shown in the data, the cumulative release rates of N and Se elements within 240 hours are about 75%, while the cumulative release rates of Se and K are 60% and 40% respectively. It has excellent sustained-release performance and comprehensive nutrition, which has exceeded most of the current slow-release materials, such as biochar, bentonite, hydroxyapatite, etc.

[0058] Example 2

[0059] The steps for preparing the silicon oxide / hydrotalcite composite slow-release fertilizer in this embodiment are as follows:

[0060] 1.0g, with a specific surface area of ​​254.7m 21g of silica, 12.2g of magnesium nitrate hexahydrate, and 7.5g of aluminum nitrate nonahydrate were added to 300ml of deionized water, stirred for 10 minutes, and then sonicated for 20 minutes. The pH was adjusted to 11 using a mixture of sodium hydroxide and sodium carbonate. The mixture was then transferred to a 60°C oven for a sealed hydrothermal reaction for 12 hours. It was then filtered while hot, washed with deionized water until neutral, and dried to obtain a silica / hydrotalcite nanocomposite. After grinding through a 100-mesh sieve, the mixture was calcined at 550°C in a muffle furnace for 60 minutes to obtain a silica / metal oxide nanocomposite. 2.0g of potassium phosphate and 0.2g of sodium selenite were dissolved in 10ml of deionized water. 2.0g of the silica / metal oxide nanocomposite was added, mixed thoroughly, and dried to obtain a silica / hydrotalcite-based potassium-phosphorus-selenium complex. 5.0 g of urea was melted at 133° C., and then 2.0 g of silicon oxide / hydrotalcite-based phosphorus potassium selenium complex was added, stirred for 1 minute, and extruded and granulated while hot to obtain silicon oxide / hydrotalcite composite slow-release fertilizer granules.

[0061] The slow-release fertilizer uses the static water release method to test the slow-release effect. Figure 3 As shown in the figure, the cumulative release rate of N, Se and K elements within 240 hours is about 80%, while the cumulative release rate of P is 70%. It has excellent sustained-release performance and comprehensive nutrition, which has exceeded most of the current slow-release materials, such as biochar, bentonite, hydroxyapatite, etc.

[0062] Example 3

[0063] The steps for preparing the silicon oxide / hydrotalcite composite slow-release compound fertilizer in this embodiment are as follows:

[0064] 5.0 g, with a specific surface area of ​​385.6 m 2 1g of silica, 12.2g of magnesium nitrate hexahydrate, and 7.5g of aluminum nitrate nonahydrate were added to 300ml of deionized water, stirred for 10 minutes, and then sonicated for 20 minutes. The pH was adjusted to 9 using a mixed solution of sodium hydroxide and sodium carbonate. The mixture was then transferred to a 60°C oven for a sealed hydrothermal reaction for 24 hours. It was then filtered while hot, washed with deionized water until neutral, and dried to obtain a silica / hydrotalcite nanocomposite. After grinding through a 100-mesh sieve, the mixture was calcined at 450°C in a muffle furnace for 60 minutes to obtain a silica / metal oxide nanocomposite. 6.0g of potassium phosphate and 0.6g of sodium selenite were dissolved in 10ml of deionized water. 2.0g of the silica / metal oxide nanocomposite was added, mixed thoroughly, and dried to obtain a silica / hydrotalcite-based potassium-phosphorus-selenium complex. 15.0 g of urea was melted at 140° C., and then 2.0 g of silicon oxide / hydrotalcite-based potassium-phosphorus-selenium complex was added, stirred for 5 minutes, and extruded and granulated while hot to obtain silicon oxide / hydrotalcite composite slow-release fertilizer granules.

[0065] The slow-release fertilizer uses the static water release method to test the slow-release effect. Figure 4 As shown in the data, the cumulative release rate of Se element within 240 hours is about 80%, while the cumulative release rates of N and P are about 70%, and the cumulative release rate of K is 40%. It has excellent sustained-release performance and comprehensive nutrition, which has exceeded most of the current slow-release materials, such as biochar, bentonite, hydroxyapatite, etc.

[0066] Comparative Example 1

[0067] This comparative example does not use silicon oxide, but only uses hydrotalcite to prepare slow-release fertilizer:

[0068] 12.2g (0.048mol) of magnesium nitrate hexahydrate and 7.5g (0.02mol) of aluminum nitrate nonahydrate were added to 300ml of deionized water, stirred for 10 minutes, and then sonicated for 20 minutes. The pH was adjusted to 10 using a mixed solution of sodium hydroxide and sodium carbonate. The mixture was then transferred to a 60°C oven for a sealed hydrothermal reaction for 24 hours. The mixture was filtered while hot, washed with deionized water until neutral, and dried to obtain a hydrotalcite nanomaterial. After grinding through a 100-mesh sieve, the mixture was calcined at 450°C in a muffle furnace for 90 minutes to obtain a metal oxide nanomaterial. 2.0g of potassium phosphate and 0.2g of sodium selenite were dissolved in 10ml of deionized water. 2.0g of the metal oxide nanomaterial was added, mixed thoroughly, and dried to obtain a hydrotalcite-based potassium-phosphorus-selenium complex. 10.0 g of urea was completely melted at 133° C., and then 2.0 g of the hydrotalcite-based phosphorus, potassium, and selenium complex was added, stirred for 1 minute, and extruded and granulated while hot to obtain hydrotalcite slow-release fertilizer granules.

[0069] The slow-release fertilizer uses the static water release method to test the slow-release effect. Figure 5 The results show that compared with the slow-release fertilizer of the present application, the release rates of P and Se did not change significantly, with cumulative release rates of 60% and 45% respectively within 240 hours. However, the release rates of N and K elements increased significantly, exceeding 70% within 2 hours, and the release rates were significantly accelerated. Therefore, the addition of silicon oxide greatly slowed the release rates of N and K elements.

[0070] Comparative Example 2

[0071] This comparative example was not calcined after the hydrothermal reaction:

[0072] 3.0g, with a specific surface area of ​​301.7m 21 / g of silica, 12.2g (0.048mol) of magnesium nitrate hexahydrate, and 7.5g (0.02mol) of aluminum nitrate nonahydrate were added to 300ml of deionized water, stirred for 10 minutes, and then sonicated for 20 minutes. The pH was adjusted to 10 using a mixed solution of sodium hydroxide and sodium carbonate. The mixture was then transferred to a 60°C oven for a sealed hydrothermal reaction for 24 hours. The mixture was filtered while hot, washed with deionized water until neutral, and dried to obtain a silica / hydrotalcite nanocomposite. 2.0g of potassium phosphate and 0.2g of sodium selenite were dissolved in 10ml of deionized water, and 2.0g of the silica / hydrotalcite nanocomposite was added. The mixture was thoroughly mixed and dried to obtain a silica / hydrotalcite-based phosphorus, potassium, and selenium complex. 10.0g of urea was then completely melted at 133°C, followed by the addition of 2.0g of the silica / hydrotalcite-based phosphorus, potassium, and selenium complex. The mixture was stirred for 1 minute and extruded while hot to obtain silica / hydrotalcite composite slow-release fertilizer granules.

[0073] The slow-release fertilizer uses the static water release method to test the slow-release effect. Figure 6 As shown, the results are as follows: Compared with the present application, the release rate of P and Se in the uncalcined composite material is significantly higher than that in the calcined composite material, and the cumulative release rate within 50 hours exceeds 70%, while the release rate of N and K does not change significantly. This is mainly because the interlayer of hydrotalcite in the uncalcined composite material is mainly carbonate, and it is difficult for phosphate and selenite to exchange them, resulting in P and Se mainly existing on the surface of the composite material.

[0074] Example 4

[0075] In this embodiment, urea is not heated to melt:

[0076] 3.0g, with a specific surface area of ​​301.7m 2 1 / g of silica, 12.2g (0.048mol) of magnesium nitrate hexahydrate, and 7.5g (0.02mol) of aluminum nitrate nonahydrate were added to 300ml of deionized water, stirred for 10 minutes, and then sonicated for 20 minutes. The pH was adjusted to 10 using a mixed solution of sodium hydroxide and sodium carbonate. The mixture was then transferred to a 60°C oven for a sealed hydrothermal reaction for 24 hours. It was then filtered while hot, washed with deionized water until neutral, and dried to obtain a silica / hydrotalcite nanocomposite. After grinding through a 100-mesh sieve, the mixture was calcined at 450°C in a muffle furnace for 90 minutes to obtain a silica / metal oxide nanocomposite. 2.0g of potassium phosphate and 0.2g of sodium selenite were dissolved in 10ml of deionized water. 2.0g of the silica / metal oxide nanocomposite was added, mixed thoroughly, and dried to obtain a silica / hydrotalcite-based potassium-phosphorus-selenium complex. Then, 10.0 g of urea was dissolved in water, and then 2.0 g of silicon oxide / hydrotalcite-based phosphorus potassium selenium complex was added, mixed thoroughly, and dried to obtain silicon oxide / hydrotalcite composite slow-release fertilizer particles.

[0077] The slow-release fertilizer uses the static water release method to test the slow-release effect. Figure 7 As shown in the figure, the cumulative release rate of N within 10 hours reached about 90%, and the release rate was significantly faster than that of loading by heating, while the release rates of K, P and Se did not change significantly. This is because the unheated urea has low reaction activity and is difficult to form chemical bonds with the composite material, resulting in a weak binding effect.

[0078] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon oxide / hydrotalcite composite slow-release fertilizer, characterized in that: The following steps are involved: Amorphous silicon oxide, divalent metal salt, trivalent metal salt and water are mixed uniformly to obtain a mixed solution; wherein the specific surface area of ​​the amorphous silicon oxide is 250~400 m 2 / g; The mixed solution is subjected to a hydrothermal reaction, and then filtered, washed and dried to obtain a silicon oxide / hydrotalcite nanocomposite material; calcining the silicon oxide / hydrotalcite nanocomposite material to obtain a silicon oxide / metal oxide nanocomposite material; Inorganic and organic fertilizers are loaded on the silicon oxide / metal oxide nanocomposite material to obtain a silicon oxide / hydrotalcite composite slow-release fertilizer; wherein the proportion of amorphous silicon oxide in the silicon oxide / hydrotalcite nanocomposite material is 6wt% to 30wt%; the inorganic fertilizer is at least one of phosphorus and potassium fertilizers and selenium fertilizers, and the organic fertilizer is urea.

2. The preparation method according to claim 1, characterized in that The method of loading inorganic and organic fertilizers on the silicon oxide / metal oxide nanocomposite material comprises the following steps: dissolving phosphorus and potassium fertilizers and selenium fertilizers in water, adding the silicon oxide / metal oxide nanocomposite material, mixing them uniformly and then drying to obtain a silicon oxide / hydrotalcite-based phosphorus, potassium and selenium complex; and melting urea, mixing the mixture uniformly with the silicon oxide / hydrotalcite-based phosphorus, potassium and selenium complex, and extruding and granulating the mixture.

3. The preparation method according to claim 2, characterized in that The phosphorus and potassium fertilizer is one of potassium phosphate, potassium hydrogen phosphate and potassium dihydrogen phosphate, and the selenium fertilizer is sodium selenite or sodium selenate.

4. The preparation method according to claim 2, characterized in that The mass ratio of phosphorus and potassium fertilizers to selenium fertilizers is 10:1-100:1, the mass ratio of phosphorus and potassium fertilizers to the silicon oxide / metal oxide nanocomposite material is 1:1-3:1, and the mass ratio of water to the silicon oxide / metal oxide nanocomposite material is 5:1-10:

1.

5. The preparation method according to claim 2, characterized in that The melting temperature of urea is 133-145° C., and the mass ratio of urea to the silicon oxide / hydrotalcite-based phosphorus potassium selenium complex is 2.5:1-7.5:

1.

6. The preparation method according to claim 1, characterized in that The divalent metal salt is selected from Mg 2+ and Ca 2+ One or more soluble salts, wherein the trivalent metal salt is Al 3+ The soluble salt has a molar ratio of the divalent metal salt to the trivalent metal salt of 2 to 4.

7. The preparation method according to claim 1, characterized in that Before carrying out the hydrothermal reaction, the method further comprises the following steps: adjusting the pH value of the mixed solution to 9-11.

8. The preparation method according to any one of claims 1 to 7, characterized in that The temperature of the hydrothermal reaction is 40-120° C., and the time is 12-48 hours; the temperature of the calcination is 450-550° C., and the time is 30-120 minutes.

9. A silicon oxide / hydrotalcite composite slow-release fertilizer, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 8.

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