Preparation method of slow-release fertilizer

Abstract

The invention relates to the technical field of fertilizer preparation, in particular to a preparation method of a slow-release fertilizer. The method aims at improving the utilization efficiency of the fertilizer, reducing nutrient loss, promoting nitrogen absorption of crops and reducing environmental pollution at the same time. The composite iron oxide and the zeolite form the supported biochar, so that the adsorption capacity of the supported biochar on nutrient ions such as ammonium nitrogen and nitrate nitrogen is improved, the loss of nutrients is reduced, and the utilization efficiency of the fertilizer is improved. The supported biochar can adjust the surface property and the pore structure of the biochar and enhance the ion exchange capacity.

Description

Technical Field

[0001] This invention relates to the field of fertilizer preparation technology, specifically a method for preparing slow-release fertilizer. This method aims to improve fertilizer utilization efficiency, reduce nutrient loss, promote nitrogen absorption by crops, and simultaneously reduce environmental pollution. Background Technology

[0002] Slow-release fertilizer is a new type of fertilizer whose core characteristic is its ability to slowly release nutrients to meet the needs of crops at different growth stages. This type of fertilizer controls the nutrient release rate through special chemical or physical mechanisms, thereby ensuring a continuous and stable supply of nutrients to crops over a long period. The application of slow-release fertilizer significantly improves fertilizer utilization efficiency, reduces nutrient loss and waste, and also lowers the risk of environmental pollution caused by excessive fertilization. In agricultural production, slow-release fertilizer has become an important type of fertilizer, widely used in various crops and soil conditions.

[0003] Biochar, as a natural organic material, has played an important role in the preparation of slow-release fertilizers in recent years. Originating from the high-temperature pyrolysis of biomass, it is rich in carbon and retains some of the original biomass' nutrients. In slow-release fertilizers, biochar not only serves as a nutrient carrier but also improves the fertilizer's physical properties, such as increasing porosity and specific surface area, thereby enhancing its adsorption and release capacity. Furthermore, the addition of biochar can promote the activity of soil microorganisms, further activating soil nutrients and creating a more favorable soil environment for crop growth. Therefore, the application of biochar in slow-release fertilizers helps improve the overall performance of fertilizers and better meet the nutrient needs of crops.

[0004] While biochar offers numerous advantages in slow-release fertilizers, its alkaline nature presents certain challenges. Nitrogen fertilizer is a commonly used nutrient source in slow-release fertilizers, primarily providing the nitrogen nutrients needed for crop growth. However, the alkalinity of biochar may react with nitrogen fertilizer, accelerating its volatilization and reducing its effective residence time in the soil. This volatilization not only results in nutrient loss but may also lead to environmental pollution. These factors combined reduce fertilizer utilization efficiency, impacting crop growth and yield. Therefore, addressing the problems posed by the alkaline nature of biochar is crucial for improving the utilization efficiency of slow-release fertilizers and promoting sustainable agricultural development. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing a slow-release fertilizer for nitrogen fertilizer applications. By combining biochar with iron oxides and zeolite to form supported biochar, the method solves the problem that the alkaline properties of biochar affect nitrogen fertilizer volatilization and crop nitrogen uptake, thereby impacting fertilizer utilization efficiency. 1. This invention provides a method for preparing a slow-release fertilizer, comprising the following steps: (a) Biochar was prepared by pyrolysis using lignin as raw material, with the particle size controlled at 0.5-2 mm; (b) Biochar, iron oxide and zeolite were mixed in a mass ratio of 40-50:10-30:10-30, and 2wt%-5wt% sodium carboxymethyl cellulose (CMC) was added as a binder. The mixture was then ball-milled to obtain supported biochar. (c) The supported biochar and the inorganic film-forming agent are mixed at a mass ratio of 88-95:5-15 to form a sustained-release coating agent; (d) The above-mentioned slow-release coating agent is applied to the surface of fertilizer granules containing nitrogen fertilizer with a coating thickness of 0.1-0.2 mm, and then dried and cured to obtain the final slow-release fertilizer product.

[0006] Specifically, the lignin pyrolysis temperature is 400°C-600°C, and the time is 1-3 hours.

[0007] Specifically, the iron oxide includes Fe2O3 and Fe3O4 in a mass ratio of 0.5-2:1, both with a particle size of 0.1-0.5 mm.

[0008] Specifically, the zeolite is one or more of clinoptilolite, mordenite, anticline, chalcogenite, or calcium cruciformite, with a particle size of 0.1-0.3 mm.

[0009] Specifically, the ball milling process is performed at a speed of 150-300 rpm for 1-4 hours.

[0010] Specifically, the inorganic film-forming agent is selected from silicates and phosphates.

[0011] Specifically, the fertilizer granules have a particle size of 0.5-1 mm, and the nitrogen fertilizer is selected from ammonium nitrogen and nitrate nitrogen.

[0012] Specifically, the drying and curing process is selected from one of natural air drying, heating drying, and vacuum drying; the drying and curing temperature is 50°C-60°C, and the time is 24-48 hours.

[0013] Specifically, the coating method of the slow-release fertilizer is selected from spraying or rolling.

[0014] Specifically, the fertilizer granules also include one or more of the following: phosphate fertilizer, trace elements, and plant growth regulators.

[0015] Compared with the prior art, the present invention has the following advantages: First, this invention forms supported biochar by combining iron oxides and zeolite, increasing its adsorption capacity for nutrient ions such as ammonium nitrogen and nitrate nitrogen, which helps reduce nutrient loss and improve fertilizer utilization efficiency. This is because supported biochar can adjust the surface properties and pore structure of biochar and enhance its ion exchange capacity.

[0016] Secondly, this invention uses silicates or phosphates as inorganic film-forming agents, which can chemically react with the inorganic components in biochar, iron oxides, and zeolites to form strong chemical bonds. Compared to other types of film-forming agents, the bonding of the inorganic film-forming agent used in this invention helps to enhance the stability and durability of the film and improve its anti-aging properties.

[0017] Finally, by adjusting the ratio of Fe2O3 to Fe3O4, this invention can optimize the adsorption capacity, ion exchange performance, and nutrient release characteristics of supported biochar, thereby achieving optimal fertilizer efficiency and economic benefits. Detailed Implementation

[0018] Slow-release fertilizers were prepared based on fertilizer granules containing the following components: Nitrogen fertilizer (ammonium nitrogen): accounts for 25% of the total fertilizer mass; Phosphate fertilizer (calculated as P2O5): accounts for 15% of the total fertilizer mass; Micronutrients: including zinc, copper, iron, manganese, etc., accounting for 2% of the total mass of fertilizer; Plant growth regulators: Select appropriate plant growth regulators, accounting for 1% of the total fertilizer mass.

[0019] Example 1 A method for preparing a slow-release fertilizer, the specific steps of which are as follows: (a) Biochar was prepared by pyrolysis of lignin. The pyrolysis temperature was 500°C, the time was 2 hours, and the particle size was controlled at 1 mm.

[0020] (b) Biochar, iron oxides, and zeolite were mixed in a mass ratio of 45:20:25. The iron oxides consisted of Fe₂O₃ and Fe₃O₄ in a 1:1 mass ratio, both with a particle size of 0.3 mm. Clinoptilolite with a particle size of 0.2 mm was selected as the zeolite. 3 wt% sodium carboxymethyl cellulose (CMC) was added as a binder, and the mixture was ball-milled to obtain supported biochar. The ball milling process was performed at 200 rpm for 2.5 hours.

[0021] (c) The supported biochar and the inorganic film-forming agent are mixed at a mass ratio of 90:10 to form a slow-release coating agent; the inorganic film-forming agent contains 15 wt% silicate (modulus 3) and 1 wt% CMC.

[0022] (d) The above-mentioned slow-release coating agent was applied to the surface of fertilizer granules containing nitrogen fertilizer, with a coating thickness of 0.15 mm. The particle size of the fertilizer granules was 0.75 mm, and ammonium nitrogen was selected as the nitrogen fertilizer. The coating method was spraying. A drying and curing treatment was then performed using heat drying at 55°C for 36 hours to obtain the final slow-release fertilizer product.

[0023] Comparative Example 1 A method for preparing a slow-release fertilizer, the specific steps of which are as follows: (a) Biochar was prepared by pyrolysis of lignin. The pyrolysis temperature was 500°C, the time was 2 hours, and the particle size was controlled at 1 mm.

[0024] (b) Biochar and zeolite were mixed at a mass ratio of 45:25. The zeolite used was clinoptilolite with a particle size of 0.2 mm. 3% sodium carboxymethyl cellulose (CMC) was added as a binder, and the mixture was ball-milled to obtain supported biochar. The ball milling process was performed at 200 rpm for 2.5 hours.

[0025] (c) The supported biochar and the inorganic film-forming agent are mixed at a mass ratio of 90:10 to form a slow-release coating agent; the inorganic film-forming agent contains 15 wt% sodium silicate (modulus 3) and 1 wt% CMC.

[0026] (d) The above-mentioned slow-release coating agent was applied to the surface of fertilizer granules containing nitrogen fertilizer, with a coating thickness of 0.15 mm. The particle size of the fertilizer granules was 0.75 mm, and ammonium nitrogen was selected as the nitrogen fertilizer. The coating method was spraying. A drying and curing treatment was then performed using heat drying at 55°C for 36 hours to obtain the final slow-release fertilizer product.

[0027] Comparative Example 2 A method for preparing a slow-release fertilizer, the specific steps of which are as follows: (a) Biochar was prepared by pyrolysis of lignin. The pyrolysis temperature was 500°C, the time was 2 hours, and the particle size was controlled at 1 mm.

[0028] (b) Biochar and iron oxide were mixed at a mass ratio of 45:20. The iron oxide consisted of Fe₂O₃ and Fe₃O₄ in a mass ratio of 1:1, both with a particle size of 0.3 mm. 3% sodium carboxymethyl cellulose (CMC) was added as a binder, and the mixture was ball-milled to obtain supported biochar. The ball milling process was performed at 200 rpm for 2.5 hours.

[0029] (c) The supported biochar and the inorganic film-forming agent are mixed at a mass ratio of 90:10 to form a slow-release coating agent; the inorganic film-forming agent contains 15 wt% sodium silicate (modulus 3) and 1 wt% CMC.

[0030] (d) The above-mentioned slow-release coating agent was applied to the surface of fertilizer granules containing nitrogen fertilizer, with a coating thickness of 0.15 mm. The particle size of the fertilizer granules was 0.75 mm, and ammonium nitrogen was selected as the nitrogen fertilizer. The coating method was spraying. A drying and curing treatment was then performed using heat drying at 55°C for 36 hours to obtain the final slow-release fertilizer product.

[0031] Comparative Example 3 A method for preparing a slow-release fertilizer, the specific steps of which are as follows: (a) Biochar was prepared by pyrolysis of lignin. The pyrolysis temperature was 500°C, the time was 2 hours, and the particle size was controlled at 1 mm.

[0032] (b) Biochar, iron oxides, and zeolite were mixed at a mass ratio of 45:20:25. The iron oxides consisted of Fe₂O₃ and Fe₃O₄ in a 1:1 mass ratio, both with a particle size of 0.3 mm. Clinoptilolite with a particle size of 0.2 mm was selected as the zeolite. 3% sodium carboxymethyl cellulose (CMC) was added as a binder, and the mixture was stirred for 2.5 hours to obtain supported biochar.

[0033] (c) The supported biochar and the inorganic film-forming agent are mixed at a mass ratio of 90:10 to form a slow-release coating agent; the inorganic film-forming agent contains 15 wt% sodium silicate (modulus 3) and 1 wt% CMC.

[0034] (d) The above-mentioned slow-release coating agent was applied to the surface of fertilizer granules containing nitrogen fertilizer, with a coating thickness of 0.15 mm. The particle size of the fertilizer granules was 0.75 mm, and ammonium nitrogen was selected as the nitrogen fertilizer. The coating method was spraying. A drying and curing treatment was then performed using heat drying at 55°C for 36 hours to obtain the final slow-release fertilizer product.

[0035] Comparative Example 4 A method for preparing a slow-release fertilizer, the specific steps of which are as follows: (a) Biochar was prepared by pyrolysis of lignin. The pyrolysis temperature was 500°C, the time was 2 hours, and the particle size was controlled at 1 mm.

[0036] (b) Biochar, iron oxides, and zeolite were mixed in a mass ratio of 45:20:25. The iron oxides consisted of Fe₂O₃ and Fe₃O₄ in a 1:1 mass ratio, both with a particle size of 0.3 mm. Clinoptilolite with a particle size of 0.2 mm was selected as the zeolite. 3% sodium carboxymethyl cellulose (CMC) was added as a binder, and the mixture was ball-milled to obtain supported biochar. The ball milling process was performed at 200 rpm for 2.5 hours.

[0037] (c) The supported biochar and the inorganic film-forming agent are mixed at a mass ratio of 90:10 to form a slow-release coating agent; the inorganic film-forming agent contains 15 wt% silicate (modulus 3) and 1 wt% CMC.

[0038] (d) The above-mentioned slow-release coating agent was applied to the surface of fertilizer granules containing nitrogen fertilizer, with a coating thickness of 0.15 mm. The particle size of the fertilizer granules was 0.75 mm, and ammonium nitrogen was selected as the nitrogen fertilizer. The coating method was spraying. A drying and curing treatment was then performed using heat drying at 55°C for 36 hours to obtain the final slow-release fertilizer product.

[0039] Nutrient release characteristics characterization experiments, soil tests, and environmental adaptability tests were conducted on the samples from the above embodiments and comparative examples.

[0040] (1) Nutrient release characteristic characterization experiment Experimental parameters Measurement indicators: nitrogen (N) release amount and form Temperature: 25℃ (simulating normal temperature environment) Time intervals: 1 day, 3 days, 7 days, 15 days, 30 days, 60 days, 90 days Solution: Deionized water Experimental steps Sample preparation: Weigh 0.5g of a certain amount of slow-release fertilizer sample and place it in a polyethylene bottle.

[0041] Solution preparation: Add 100mL of deionized water to the bottle to ensure the fertilizer is completely submerged.

[0042] Static incubation: Place the polyethylene bottle in a constant temperature and humidity chamber, set the temperature to 25℃, and begin incubation.

[0043] Periodic sampling: Sampling is performed at set time intervals. After each sampling, the sample is filtered, and the filtrate is used to determine the content of various nutrient forms. Fresh deionized water is added to the original volume after sampling.

[0044] Nutrient determination: The nitrogen content in the filtrate was determined using the Kjeldahl method.

[0045] The experimental results are as follows: Table 1. Experimental data characterizing nutrient release properties

[0046] (2) Soil test Experimental parameters Soil type: Loam Fertilizer dosage: 0.3g slow-release fertilizer Soil moisture content: 40% Incubation temperature: 25℃ Culture time: 90 days Experimental steps Soil preparation: Collect representative soil samples, air dry, remove impurities, and sieve (1mm sieve mesh).

[0047] Fertilizer mixing: Mix the slow-release fertilizer evenly with the air-dried soil and adjust the moisture content to the set level according to the soil's maximum water holding capacity.

[0048] Incubation treatment: Place the mixed soil sample in a constant temperature and humidity chamber, set the temperature to 25℃, and begin incubation.

[0049] Regular sampling: Samples are taken at regular intervals to determine the nitrogen nutrient content in the soil.

[0050] Table 2 Soil test data

[0051] (3) Environmental adaptability test Experimental parameters Environmental conditions: High temperature (50℃), low temperature (-10℃), humidity variation (RH 30%-90%), salt spray (5% NaCl solution), vibration (random vibration). Experiment duration: 48 hours for each condition. Experimental steps Sample preparation: Place the slow-release fertilizer sample in a standard test container.

[0052] Environmental conditions setting: Set the corresponding environmental conditions according to the test requirements, such as high temperature chamber, low temperature chamber, humidity chamber, salt spray test chamber, vibration test bench, etc.

[0053] Exposure treatment: The sample is exposed to pre-defined environmental conditions.

[0054] Performance evaluation: After treatment, check whether there are any changes in the appearance, structural integrity and nutrient release performance of the sample.

[0055] Table 3 Environmental adaptability test data

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a slow-release fertilizer, characterized by The method comprises the following steps: (a) preparing biochar by pyrolysis of lignin as raw material, with particle size controlled at 0.5-2mm; (b) mixing biochar, iron oxide and zeolite at a mass ratio of 40-50:10-30:10-30, adding 2%-5% sodium carboxymethyl cellulose (CMC) as a binder, and obtaining a loaded biochar through ball milling treatment; (c) mixing the loaded biochar with an inorganic film-forming agent at a mass ratio of 88-95:5-15 to form a slow-release coating agent; (d) coating the slow-release coating agent on the surface of fertilizer particles containing nitrogen fertilizer, with a coating thickness of 0.1-0.2mm, and performing drying and curing treatment to obtain the final slow-release fertilizer product.

2. The production method according to claim 1, characterized by, The temperature for pyrolysis of lignin is 400°C-600°C, and the time is 1-3 hours.

3. The preparation method according to claim 1, characterized in that, The iron oxide includes Fe2O3 and Fe3O4 at a mass ratio of 0.5-2:1, and the particle size is 0.1-0.5mm.

4. The method of claim 1, wherein, The zeolite is one or more of clinoptilolite, mordenite, analcime, chabazite or edingtonite, and the particle size is 0.1-0.3mm.

5. The preparation method according to claim 1, characterized in that, The rotation speed for ball milling treatment is 150-300rpm, and the time is 1-4 hours.

6. The method of claim 1, wherein, The inorganic film-forming agent is selected from one of silicates and phosphates, and the concentration is 5-30wt%.

7. The preparation method according to claim 1, characterized in that, The particle size of the fertilizer particles is 0.5-1mm, and the nitrogen fertilizer is selected from one of ammonium nitrogen and nitrate nitrogen.

8. The method of claim 1, wherein, The drying and curing treatment is selected from one of natural air drying, heating drying and vacuum drying, and the temperature for drying and curing is 50°C-60°C, and the time is 24-48 hours.

9. The method of claim 1, wherein, The coating method for slow-release fertilizer is selected from one of spraying and rolling.

10. The method of claim 1, wherein, The fertilizer particles further include one or more of phosphorus fertilizer, trace elements and plant growth regulators.

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