Fulvic acid coated urea controlled-release fertilizer and preparation method thereof

Abstract

The invention discloses a fulvic acid coated urea controlled-release fertilizer and a preparation method thereof, and belongs to the technical field of coated controlled-release fertilizers. The preparation method comprises the following steps: dissolving fulvic acid in water, adding nano calcium carbonate, a small amount of inorganic salt ferric trichloride containing bivalent or higher cations and calcium chloride, then adding curdlan as a thickening agent, keeping the temperature for a certain time to prepare fulvic acid hydrogel as a coating, and finally obtaining the fulvic acid coated slow / controlled release fertilizer. The physical cross-linked hydrogel prepared by the invention has self-healing performance and can completely wrap urea particles serving as a fertilizer core, so that rapid release of nutrients caused by exposure of urea is avoided, the release time of the nutrients is prolonged, and the utilization efficiency of the nutrients is improved. The material provided by the invention is biodegradable, does not introduce a new pollution source, can be applied to agriculture on a large scale, and has important economic value and social benefit.

Description

Technical Field

[0001] The present invention relates to the technical field of coated slow-release fertilizers, and particularly relates to a fulvic acid-coated urea controlled-release fertilizer and a preparation method thereof. Background Art

[0002] Currently, traditional slow-release fertilizers on the market are coated fertilizers. Commonly used coating materials include insoluble inorganic materials such as sulfur; and petroleum-based polymers such as polyethylene, polypropylene, polyvinyl chloride, and polystyrene. Generally, coated fertilizers are made by physically encapsulating soluble fertilizers with hydrophobic inorganic and / or polymer materials, and the hydrophobic inorganic and / or polymer materials act as a barrier to inhibit the rapid release of nutrients to avoid the "burst effect". Encapsulation does extend the release time of nutrients and then improves the utilization efficiency of nutrients. However, due to the non-biodegradability of the coating during use, it may also introduce new pollution sources. These disadvantages of coated fertilizers limit their large-scale application in agriculture.

[0003] Fulvic acid is a water-soluble reddish-brown or grayish-black powdery substance. It can promote plant growth, improve the stress resistance of plants, and has the effects of increasing production and improving crop quality. Its main application targets are wheat, corn, sweet potato, millet, rice, cotton, peanut, rapeseed, tobacco, mulberry, etc. Using fulvic acid as a raw material for crop fertilizer production has been reported. The patent "CN117185859B A nano-fertilizer for improving the fruit quality of Hami melons" introduces a nano-fertilizer that directly mixes fulvic acid with other components such as potassium dihydrogen phosphate and sodium nitrate to form a nano-fertilizer for promoting fruit growth. However, reports on using fulvic acid as a coating material are still relatively few. Gel is a special dispersion system in which colloidal particles or macromolecules in a sol or solution are connected to each other under certain conditions to form a spatial network structure. How to use fulvic acid as a coating material by selecting a suitable physical cross-linking agent while achieving effective substance slow release and soil environmental protection is still an unsolved problem. Summary of the Invention

[0004] Aiming at the above-mentioned prior art, the purpose of the present invention is to provide a fulvic acid-coated urea controlled-release fertilizer and a preparation method thereof.

[0005] In the first aspect of the present invention, a fulvic acid coating material is provided. The fulvic acid coating material comprises the following raw materials: fulvic acid, water, nano calcium carbonate, inorganic salts, and thickener; the mass ratio of fulvic acid, water, nano calcium carbonate, inorganic salts, and thickener is (50 - 100):(100 - 200):(0.1 - 1):(0.5 - 5):(0.5 - 10).

[0006] Further, in the inorganic salts, the mass ratio of ferric chloride to calcium chloride is 1:1.

[0007] Further, the thickening agent is curdlan.

[0008] In the second aspect of the present invention, there is provided a method for preparing the fulvic acid coating material, comprising the following steps:

[0009] Mix fulvic acid, water, nano calcium carbonate, inorganic salts and a thickening agent evenly, and react at 20 - 50 °C for 30 - 120 minutes to obtain a fulvic acid hydrogel; pulverize the fulvic acid hydrogel to prepare the fulvic acid coating material.

[0010] In the third aspect of the present invention, there is provided the application of the fulvic acid coating material in coated fertilizers.

[0011] In the fourth aspect of the present invention, there is provided a fulvic acid coated controlled-release fertilizer, which is composed of the fulvic acid coating material and a fertilizer core wrapped with microcrystalline wax;

[0012] The mass ratio of the fulvic acid coating material, microcrystalline wax and the fertilizer core is (2 - 6):(0.1 - 1):100.

[0013] Further, the fertilizer core is urea.

[0014] In the fifth aspect of the present invention, there is provided a method for preparing the fulvic acid coated controlled-release fertilizer, comprising the following steps:

[0015] Preheat the fertilizer core, add microcrystalline wax, mix evenly, then spray the fulvic acid coating material, and dry to prepare the fulvic acid coated controlled-release fertilizer.

[0016] Further, preheat the fertilizer core to 70 - 80 °C.

[0017] Further, the drying temperature is 70 - 80 °C.

[0018] The beneficial effects of the present invention:

[0019] In the present invention, fulvic acid is dissolved in water, nano calcium carbonate, a small amount of inorganic salts containing divalent or higher cations such as ferric chloride and calcium chloride are added, and then curdlan is added as a thickener, and a fulvic acid hydrogel is prepared by maintaining a constant temperature for a certain time. Under rapid rotation, the pulverized hydrogel is evenly and slowly sprayed onto the surface of urea wrapped with microcrystalline wax by a spray gun, so that the surface of all urea particles is wrapped with a fulvic acid coating material, and the obtained product is dried to obtain a fulvic acid-coated controlled-release fertilizer. The physically cross-linked hydrogel prepared in the present invention has self-healing performance, can completely wrap the urea particles as the fertilizer core, avoids the rapid release of nutrients caused by the exposure of urea, prolongs the release time of nutrients, and improves the utilization efficiency of nutrients. The materials of the present invention are biodegradable, do not introduce new pollution sources, can be widely applied in agriculture, and have important economic value and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 are the self-healing and tensile tests of the hydrogel containing fulvic acid, Figure 1 in which a is the gel before healing, Figure 1 in which b is the gel after healing, Figure 1 and c is the tensile test of the gel. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0022] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below with reference to specific embodiments.

[0023] The test materials not specifically described used in the embodiments of the present invention are all conventional test materials in the art and can be obtained through commercial channels. The CAS number of the fulvic acid (fulvic acid, Fulvic acid) used in the present invention is 479-66-3; the CAS number of the nano calcium carbonate used is 471-34-1; the CAS number of the ferric chloride used is 7705-08-0; the CAS number of the curdlan used is 54724-00-4.

[0024] Example 1

[0025] (1) Preparation of fulvic acid film material

[0026] Mix fulvic acid, nano calcium carbonate, ferric trichloride, calcium chloride, curdlan and water in a mass ratio of 50:0.5:0.25:0.25:5:100, stir evenly, react at 30 °C for 60 minutes to prepare a fulvic acid hydrogel, and then crush the hydrogel with a pulverizer to obtain a fulvic acid film material.

[0027] (2) Coating of slow-release fertilizer

[0028] Place 500 kg of urea as the fertilizer core in a rotating drum, preheat to 70 °C, add 2.0 kg of microcrystalline wax, mix evenly, heat the fulvic acid film material to 60 °C, and slowly spray the fulvic acid film material onto the surface of the urea with a spray gun under rapid rotation. Ensure that the surface of all urea particles is coated with the fulvic acid film material (the mass ratio of the fulvic acid film material to the fertilizer core is 4:100). Dry the obtained product at 70 °C and cool to room temperature to obtain a fulvic acid-coated slow-release fertilizer.

[0029] Example 2

[0030] (1) Preparation of fulvic acid film material

[0031] Mix fulvic acid, nano calcium carbonate, ferric trichloride, calcium chloride, curdlan and water in a mass ratio of 70:0.8:1:1:5:150, stir evenly, react at 30 °C for 60 minutes to prepare a fulvic acid hydrogel, and then crush the hydrogel with a pulverizer to obtain a fulvic acid film material.

[0032] (2) Coating of slow-release fertilizer

[0033] Place 500 kg of urea as the fertilizer core in a rotating drum, preheat to 70 °C, add 2.0 kg of microcrystalline wax, mix evenly, heat the fulvic acid film material to 60 °C, and slowly spray the fulvic acid film material onto the surface of the urea with a spray gun under rapid rotation. Ensure that the surface of all urea particles is coated with the fulvic acid film material (the mass ratio of the fulvic acid film material to the fertilizer core is 4:100). Dry the obtained product at 70 °C and cool to room temperature to obtain a fulvic acid-coated slow-release fertilizer.

[0034] Example 3

[0035] (1) Preparation of fulvic acid film material

[0036] Mix fulvic acid, nano calcium carbonate, ferric trichloride, calcium chloride, curdlan and water in a mass ratio of 100:1:2.5:2.5:5:200, stir evenly, react at 30 °C for 60 minutes to prepare a fulvic acid hydrogel, and then crush the hydrogel with a pulverizer to obtain a fulvic acid film material.

[0037] (2) Coating of slow-release fertilizer

[0038] Place 500 kg of urea as the fertilizer core in a rotating drum, preheat it to 70 °C, add 2.0 kg of microcrystalline wax, and after mixing evenly, heat the fulvic acid film material to 60 °C. Under rapid rotation, spray the fulvic acid film material evenly and slowly onto the surface of the urea with a spray gun. Ensure that all urea particles are wrapped with the fulvic acid film material (the mass ratio of the fulvic acid film material to the fertilizer core is 4:100). Dry the obtained product at 70 °C and cool it to room temperature to obtain the fulvic acid-coated controlled-release fertilizer.

[0039] Comparative Example 1

[0040] Mix fulvic acid, nano calcium carbonate, curdlan and water in a mass ratio of 50:0.5:5:100, stir evenly, react at 30 °C for 60 minutes to prepare a fulvic acid hydrogel, and then crush the hydrogel with a pulverizer to obtain the fulvic acid film material.

[0041] Place 500 kg of urea as the fertilizer core in a rotating drum, preheat it to 70 °C, add 2.0 kg of microcrystalline wax, and after mixing evenly, heat the fulvic acid film material to 60 °C. Under rapid rotation, spray the fulvic acid film material evenly and slowly onto the surface of the urea with a spray gun. Ensure that all urea particles are wrapped with the fulvic acid film material (the mass ratio of the fulvic acid film material to the fertilizer core is 4:100). Dry the obtained product at 70 °C and cool it to room temperature to obtain the fulvic acid-coated controlled-release fertilizer.

[0042] Comparative Example 2

[0043] Mix fulvic acid, nano calcium carbonate, ferric trichloride, curdlan and water in a mass ratio of 50:0.5:0.25:5:100, stir evenly, react at 30 °C for 60 minutes to prepare a fulvic acid hydrogel, and then crush the hydrogel with a pulverizer to obtain the fulvic acid film material.

[0044] Place 500 kg of urea as the fertilizer core in a rotating drum, preheat it to 70 °C, add 2.0 kg of microcrystalline wax, and after mixing evenly, heat the fulvic acid film material to 60 °C. Under rapid rotation, spray the fulvic acid film material evenly and slowly onto the surface of the urea with a spray gun. Ensure that all urea particles are wrapped with the fulvic acid film material (the mass ratio of the fulvic acid film material to the fertilizer core is 4:100). Dry the obtained product at 70 °C and cool it to room temperature to obtain the fulvic acid-coated controlled-release fertilizer.

[0045] Comparative Example 3

[0046] Mix fulvic acid, nano calcium carbonate, calcium chloride, curdlan and water in a mass ratio of 50:0.5:0.25:5:100, stir evenly, react at 30 °C for 60 minutes to prepare a fulvic acid hydrogel, and then crush the hydrogel with a pulverizer to obtain the fulvic acid film material.

[0047] Place 500 kg of urea as the fertilizer core in a rotary drum, preheat it to 70 °C, add 2.0 kg of microcrystalline wax, mix evenly, heat the fulvic acid film material to 60 °C, and under rapid rotation, spray the fulvic acid film material evenly and slowly onto the surface of the urea with a spray gun. Ensure that all urea particles are wrapped with the fulvic acid film material (the mass ratio of the fulvic acid film material to the fertilizer core is 4:100). Dry the obtained product at 70 °C and cool it to room temperature to obtain the fulvic acid-coated sustained-release fertilizer.

[0048] Experimental Example 1 Self-healing experiment of fulvic acid hydrogel

[0049] The electrostatic interaction between the positive charge carried by the cation and the negative charge -COO- of the fulvic acid is the reason for the formation of the gel network structure. The reversibility of this physical interaction endows the gel with self-healing properties. Figure 1 This is the self-healing process of the gel. Cut the fulvic acid hydrogel sample prepared according to the method of Example 1 into three sections. Two of the sections are stained with fruit green and carmine respectively. Docking the three cut specimens in situ, placing them in the corresponding plastic molds, sealing the molds, and after standing at room temperature for 12 h, the gel can heal. At the same time, the healed gel can be stretched. When the gel sample is cut, under the action of an external force, the network of electrostatic interactions within the cutting range will be cut off. When the cut surfaces of the gel are brought into contact, the hydrophilic polymer chains near the interface diffuse with each other and re-form non-covalent bonds. Under the electrostatic action, the cut gel binds together again.

[0050] Experimental Example 2 Fertilizer slow-release effect test

[0051] According to the method of "GBT23348-2009 Slow-release Fertilizers", measure the nutrient release rate of the fulvic acid-coated sustained-release fertilizers prepared in Examples 1-3 and Comparative Examples 1-3 every day. The cumulative nutrient release rate results are shown in Table 1.

[0052] Table 1 Cumulative nutrient release rate (%)

[0053] Number Day 1 Day 7 Day 14 Day 28 Day 60 Day 75 Example 1 1.81 6.15 24.88 56.57 74.20 87.19 Example 2 2.57 5.53 26.13 57.17 75.52 89.27 Example 3 2.83 6.23 28.65 57.14 75.08 86.63 Comparative Example 1 3.59 20.4 48.51 76.74 91.04 100 Comparative Example 2 2.52 13.26 41.55 69.64 85.87 100 Comparative Example 3 2.93 14.03 41.16 71.78 89.32 100

[0054] According to the daily measurement results, count the slow-release days based on the 80% nutrient release amount. The slow-release days of Examples 1-3 are 71 days, 68 days, and 70 days respectively, and the slow-release days of Comparative Examples 1-3 are 49 days, 58 days, and 53 days respectively. According to the data of Examples 1-3 and Comparative Examples 1-3, it shows that compared with not adding inorganic salts, the effects of adding ferric chloride and calcium chloride alone are improved, but they are not as good as the effect of adding both inorganic salts at the same time. Ferric chloride and calcium chloride play a synergistic effect. Among them, the fertilizer prepared in Example 1 has a slow-release period of up to 71 days, and the sustained-release and controlled-release period is long, which can meet the long-term nutritional needs of crops for slow-release and controlled-release.

Claims

1. A fulvic acid coating material, characterized in that: The fulvic acid coating material comprises the following raw materials: fulvic acid, water, nano calcium carbonate, inorganic salt and thickener; the mass ratio of fulvic acid, water, nano calcium carbonate, inorganic salt and thickener is (50-100): (100-200): (0.1-1): (0.5-5): (0.5-10).

2. The fulvic acid coating material according to claim 1, characterized in that: In the inorganic salt, the mass ratio of ferric chloride to calcium chloride is 1:

1.

3. The fulvic acid coating material according to claim 1, characterized in that: The thickener is curdlan.

4. The method for preparing the fulvic acid coating material according to any one of claims 1 to 3, characterized in that: The following steps are involved: The fulvic acid, water, nano calcium carbonate, inorganic salt and thickener are mixed evenly, and reacted at 20-50° C. for 30-120 minutes to obtain the fulvic acid hydrogel; the fulvic acid hydrogel is crushed to prepare the fulvic acid coating material.

5. Use of the fulvic acid coating material according to any one of claims 1 to 3 in coated fertilizers.

6. A fulvic acid coated slow-release fertilizer, characterized in that: The fulvic acid coated slow-release fertilizer is composed of the fulvic acid coating material according to claim 1 and a fertilizer core coated with microcrystalline wax; The mass ratio of fulvic acid coating material, microcrystalline wax and fertilizer core is (2-6):(0.1-1):

100.

7. The fulvic acid coated slow-release fertilizer according to claim 6, characterized in that: The fertilizer core is urea.

8. The method for preparing the fulvic acid coated slow-release fertilizer according to claim 6 or 7, characterized in that: The steps include: The fertilizer core is preheated, microcrystalline wax is added, the mixture is evenly mixed, and then the fulvic acid coating material is sprayed on the mixture and dried to prepare a fulvic acid coated slow-release fertilizer.

9. The preparation method according to claim 8, characterized in that: Preheat the fertilizer core to 70-80℃.

10. The preparation method according to claim 8, characterized in that: The drying temperature is 70-80℃.

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