Solid-waste-based water-retention slow-release fertilizer and preparation method thereof

Abstract

The invention discloses a solid-waste-based water-retention slow-release fertilizer and a preparation method thereof, and belongs to the technical field of slow-release fertilizer preparation. The preparation method comprises the following steps: (1) mixing coal series kaolinite with a nitrogen source solution, and stirring to enable a nitrogen source intercalation to enter a kaolinite interlayer to obtain nitrogen source intercalated kaolinite; and (2) mixing the nitrogen source intercalated kaolinite, nitrogen source particles and macromolecular polysaccharide, ultrasonically dispersing uniformly, adding into a calcium chloride solution, crosslinking to form hydrogel, then removing the residual calcium chloride solution, and freeze-drying to obtain the solid waste-based water-retaining slow-release fertilizer. The slow-release fertilizer with the water retention function provided by the invention has the advantages of excellent slow release performance, excellent water retention performance, environmental friendliness, simple preparation process and the like, can effectively promote crop growth, improve the utilization rate of the fertilizer and improve the soil environment, and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of slow-release fertilizer preparation, and in particular relates to a solid waste-based water-retaining slow-release fertilizer and a preparation method thereof. Background Art

[0002] Fertilizer plays an important role in the entire agricultural production activities. It is of great significance to increase food production and ensure food security. However, the traditional method of applying fertilizers has low fertilizer utilization rate due to the influence of the environment (such as rain, temperature, microorganisms, etc.), resulting in excessive use of fertilizers, which in turn has a serious impact on the ecological environment (such as water pollution, destruction of the soil ecological chain, etc.). Fertilizer slow-release technology can achieve the slow release of fertilizers and greatly improve the utilization efficiency of fertilizers. Slow release refers to the use of certain technical means to control the dissolution and diffusion of fertilizers into the soil and reduce the diffusion rate. The use of slow-release fertilizer technology can effectively avoid the rapid dissolution of traditional fertilizers in the soil or during rainfall, and achieve the control of the diffusion rate of fertilizers into the soil, thereby improving the overall bioavailability of fertilizers.

[0003] At present, slow-release fertilizers are generally obtained through the following methods:

[0004] (1) Chemical synthesis

[0005] The nutrient release rate is controlled by forming complexes or chelates through chemical synthesis. For example, urea reacts with formaldehyde to form urea-formaldehyde resin-type slow-release fertilizers. However, the nutrient release rate of such fertilizers in the soil is still too fast to meet the needs of crop growth, resulting in low fertilizer utilization and high environmental pollution risks. In addition, chemical synthesis requires specific reaction conditions and catalysts, which is costly and limits its promotion and application.

[0006] (2) Inorganic mineral loading method

[0007] Load nutrients into inorganic minerals with layered or porous structures, such as montmorillonite, zeolite, etc. For example, urea is intercalated into the interlayer of montmorillonite to form a urea-montmorillonite complex. Although this type of fertilizer has good slow-release properties, its water retention performance is poor and it cannot provide sufficient water for crops in arid areas or drought periods, affecting crop growth and development. In addition, the preparation process of the inorganic mineral loading method is relatively complex and has high requirements for the selection of materials.

[0008] (3) Coating method

[0009] Inorganic minerals, organic polymers and other materials are used as coatings on the surface of nutrients to form slow-release fertilizers with biodegradable functional coatings. For example, urea particles are coated in polymer materials such as polyvinyl alcohol. This type of fertilizer needs to control the coating thickness and uniformity to achieve the ideal slow-release effect. In addition, the degradation rate of the coating material needs to match the crop growth cycle, otherwise it will affect the slow-release performance and environmental impact of the fertilizer.

[0010] (4) Hydrogel method

[0011] Prepare hydrogel-type slow-release fertilizers that have the ability to retain water multiple times their own weight, and use physical and chemical interactions to effectively load nutrients. For example, urea is dissolved in a sodium alginate solution and cross-linked with CaCl2 to form a hydrogel. However, slow-release fertilizers prepared from a single sodium alginate still have great limitations, and their slow-release and water-retention capabilities still need to be further improved. In addition, the mechanical strength and stability of the hydrogel also need to be further optimized.

[0012] In addition, the type and performance of slow-release fertilizer materials have a direct impact on the slow-release performance and water retention performance. For example, although inorganic minerals such as montmorillonite and zeolite have good slow-release properties, their water retention performance is poor; while organic polymer materials may lack ideal slow-release properties. In addition, its preparation process also has an important influence on the slow-release performance and water retention performance. For example, the coating method needs to control the coating thickness and uniformity to achieve the ideal slow-release effect; in the hydrogel preparation process, the selection and dosage of the cross-linking agent will affect the water retention and mechanical strength of the hydrogel. Moreover, the choice of materials also needs to consider their cost and environmental impact. For example, the use of expensive organic polymer materials or complex preparation processes will lead to increased production costs, and the production scale of slow-release fertilizers will also affect their cost and promotion and application. Summary of the invention

[0013] In view of the above-mentioned deficiencies in the prior art, the present invention provides a solid waste-based water-retaining slow-release fertilizer and a preparation method thereof, which can better adapt to the needs of different crops and environments, effectively promote plant growth, improve crop yield and quality, reduce the amount of chemical fertilizer application, and protect the environment.

[0014] To achieve the above purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0015] The object of the present invention is to provide a method for preparing a solid waste-based water-retaining slow-release fertilizer, comprising the following steps:

[0016] (1) mixing coal-bearing kaolinite with a nitrogen source solution, and stirring to allow the nitrogen source to be intercalated into the interlayers of the kaolinite to obtain nitrogen source intercalated kaolinite;

[0017] (2) The nitrogen source intercalated kaolinite, nitrogen source particles and high molecular weight polysaccharide are mixed, ultrasonically dispersed evenly, and then added to a calcium chloride solution to cross-link them to form a hydrogel. The excess residual calcium chloride solution is then removed and freeze-dried to obtain the solid waste-based water-retaining slow-release fertilizer.

[0018] The present invention introduces coal-based kaolinite and high molecular weight polysaccharides to give fertilizers good water retention capacity, effectively improve soil structure, increase soil water retention capacity, and enhance crop drought resistance. It is prepared from natural materials, biodegradable, and pollution-free to the environment, meeting the requirements of green and sustainable development. In addition, it adopts liquid intercalation method and gel cross-linking technology, and the preparation process is simple and easy, with low cost.

[0019] Furthermore, 10-15 wt% of coal-based kaolinite is added to the nitrogen source solution at 50-60° C., and stirred to allow the nitrogen source to be intercalated into the interlayers of the kaolinite to obtain nitrogen source intercalated kaolinite.

[0020] Furthermore, in step (1), the temperature for preparing the nitrogen source intercalated kaolinite is 60° C., the amount of coal-based kaolinite is 10 wt %, and the concentration of the nitrogen source solution is 60%.

[0021] Furthermore, the nitrogen source is at least one of ammonium bicarbonate, ammonium nitrate and ammonium sulfate.

[0022] Furthermore, in step (1), the mixture is stirred at a temperature of 60°C.

[0023] Furthermore, in step (2), the weight ratio of the nitrogen source intercalated kaolinite to the high molecular weight polysaccharide is 1:1.5 to 1:2.

[0024] Furthermore, the weight ratio of the nitrogen source intercalated kaolinite and the high molecular weight polysaccharide is 1:2.

[0025] Furthermore, the high molecular weight polysaccharide is at least one of starch, cellulose, chitosan, hyaluronic acid, polyacrylic acid, polymethacrylic acid, polyacrylamide and poly-N-polyacrylamide.

[0026] Furthermore, the nitrogen source particles are ammonium bicarbonate, ammonium nitrate or ammonium sulfate particles.

[0027] Another object of the present invention is to provide a solid waste-based water-retaining slow-release fertilizer, which is prepared by the above method.

[0028] Beneficial effects of the present invention:

[0029] 1. The present invention provides a slow-release fertilizer (UKS) with water-retaining function, which has the advantages of excellent slow-release performance, excellent water-retaining performance, environmental friendliness, simple preparation process, etc. It can effectively promote crop growth, improve fertilizer utilization, and improve soil environment, and has good application prospects.

[0030] 2. The intercalation complex (UK) formed by the nitrogen source and kaolinite in the present invention can effectively control the release rate of the nitrogen source, avoid nutrient loss, achieve slow nutrient release in synchronization with crop demand, and improve fertilizer utilization. The introduction of coal-based kaolinite and high molecular weight polysaccharides gives fertilizers good water retention capacity, can effectively improve soil structure, improve soil water retention capacity, and enhance crop drought resistance.

[0031] 3. Through the wheat growth experiment, it was verified that the slow-release fertilizer prepared by the present invention can significantly promote wheat growth, increase wheat leaf length and root length, enhance crop stress resistance, and improve crop yield and quality. In addition, the water-retaining slow-release fertilizer prepared by the present invention can effectively improve soil structure, improve soil water retention capacity, enhance soil fertility, and promote sustainable agricultural development. It can also effectively control the nutrient release rate, avoid nutrient loss, improve fertilizer utilization, and reduce agricultural production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The diffraction patterns and intercalation rate detection diagrams of coal-bearing kaolinite at different intercalation times;

[0033] Figure 2 This is a test chart of the water retention performance of the slow-release fertilizer UKS;

[0034] Figure 3 This is the nitrogen source release rate detection diagram of the slow-release fertilizer UKS;

[0035] Figure 4 This is a picture of the growth status of wheat after adding slow-release fertilizer UKS;

[0036] Figure 5 This is a test chart showing the effects of slow-release fertilizers UKS and urea on wheat leaf and root length. DETAILED DESCRIPTION

[0037] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0038] Example 1

[0039] A method for preparing a solid waste-based water-retaining slow-release fertilizer comprises the following steps:

[0040] (1) Coal-bearing kaolinite is mixed with a 60% ammonium bicarbonate solution, stirred at 60° C. to allow the ammonium bicarbonate to intercalate into the interlayers of the kaolinite, centrifuged, washed three times with ethanol to remove free ammonium bicarbonate, and then dried in an oven at 60° C. to obtain ammonium bicarbonate intercalated kaolinite;

[0041] (2) Ammonium bicarbonate intercalated kaolinite, ammonium nitrate particles and cellulose are mixed, wherein the weight ratio of nitrogen source intercalated kaolinite to cellulose is 1:2. After being uniformly dispersed by ultrasonic, the mixture is added to a calcium chloride solution to form a hydrogel by crosslinking, and the excess residual calcium chloride solution is removed by washing with distilled water for 3-5 times. The sample is frozen for 24 hours and then freeze-dried to obtain a solid waste-based water-retaining slow-release fertilizer.

[0042] Example 2

[0043] A method for preparing a solid waste-based water-retaining slow-release fertilizer comprises the following steps:

[0044] (1) Coal-bearing kaolinite is mixed with a 60% ammonium sulfate solution, stirred at 50° C. to allow the ammonium sulfate to intercalate into the interlayers of the kaolinite, centrifuged, washed three times with ethanol to remove free ammonium sulfate, and then dried in an oven at 60° C. to obtain ammonium sulfate intercalated kaolinite;

[0045] (2) Ammonium sulfate intercalated kaolinite, ammonium nitrate particles and starch are mixed, wherein the weight ratio of nitrogen source intercalated kaolinite to starch is 1:1.5. After being uniformly dispersed by ultrasonic, the mixture is added to a calcium chloride solution to form a hydrogel by crosslinking, and the excess residual calcium chloride solution is removed by washing with distilled water for 3-5 times. The sample is frozen for 24 hours and then freeze-dried to obtain a solid waste-based water-retaining slow-release fertilizer.

[0046] Example 3

[0047] A method for preparing a solid waste-based water-retaining slow-release fertilizer comprises the following steps:

[0048] (1) Coal-bearing kaolinite is mixed with a 60% ammonium bicarbonate solution, stirred at 55° C. to allow the ammonium bicarbonate to intercalate into the interlayers of the kaolinite, centrifuged, washed three times with ethanol to remove free ammonium bicarbonate, and then dried in an oven at 60° C. to obtain ammonium bicarbonate intercalated kaolinite;

[0049] (2) Ammonium bicarbonate intercalated kaolinite, ammonium sulfate particles and hyaluronic acid are mixed, wherein the weight ratio of nitrogen source intercalated kaolinite to hyaluronic acid is 1:2. After being uniformly dispersed by ultrasonic, the mixture is added to a calcium chloride solution to form a hydrogel by crosslinking, and the excess residual calcium chloride solution is removed by washing with distilled water for 3-5 times. The sample is frozen for 24 hours and then freeze-dried to obtain a solid waste-based water-retaining slow-release fertilizer.

[0050] Experimental example

[0051] 1. Determination of intercalation rate

[0052] The diffraction patterns of coal-bearing kaolinite at different intercalation times were analyzed by XRD, and the urea intercalation rate was calculated. The results are shown in Figure 1 .

[0053] Depend on Figure 1 (a) The (001) diffraction peak of the original coal-bearing kaolinite is at ≈12.3°, and the interlayer spacing is d 001 =0.72nm. After the addition of urea intercalation, the (001) plane diffraction peak shifts to a small angle to the position of the diffraction peak ≈8.2°, and the interlayer spacing changes to d 001 =1.08nm, while the peak intensity of the original (001) plane diffraction peak gradually weakened. The increase in interlayer spacing indicates that urea molecules have entered the interlayer of kaolinite, increasing the interlayer spacing of kaolinite, thereby forming an intercalation complex, which is consistent with previous reports in the literature. It can be found from the figure that with the increase of intercalation time, the peak intensity of the (001) plane diffraction peak shifted to a small angle gradually increases, and the intercalation rate of urea also increases accordingly.

[0054] By calculating the reflection integrated intensity of the (001) diffraction peak in the X-ray powder diffraction results, we know that ( Figure 1 (b)) When the intercalation time was the first day, the urea intercalation rate was at a low level, with an intercalation rate of only 10.6%. As the intercalation time progressed, the intercalation rate on the second day increased significantly, reaching 34.6%. Finally, when the time came to the fifth day, the intercalation rate reached 53.3%, indicating that this intercalation method is a more feasible option.

[0055] 2. Water retention performance test and nitrogen source release performance test of solid waste-based water-retaining slow-release fertilizer (UKS)

[0056] (1) Water retention test

[0057] UKS containing 0%, 1%, 1.5%, 2% and 2.5% UK content were mixed with sand to simulate the water retention behavior of UKS in soil under soil environment and test its water retention capacity in soil. The results are shown in Figure 2 .

[0058] like Figure 2 As shown in the figure, UKS has a significant water retention property, and the water retention capacity increases with the increase of UK content.

[0059] (2) Nitrogen source release performance test

[0060] The urea release rates of UKS containing 0%, 1%, 1.5%, 2% and 2.5% UK in distilled water were tested by UV spectrophotometry. The results are shown in Table 2. Figure 3 .

[0061] like Figure 3 As shown, in a distilled water environment, the nitrogen release rate of the UKS prepared by the present invention is significantly lower than that of the control group (pure urea granules Urea), and the release rate decreases with the increase of UK content, indicating that it has the function of slow release of nitrogen source.

[0062] 3. Impact of UKS on wheat growth:

[0063] Through pot experiments, the effects of UKS, urea and clean water on wheat growth at 0, 3, 5 and 7 days were compared. The results are shown in Figure 4 and Figure 5 , the specific process is as follows:

[0064] Control group: irrigated with clean water and no fertilizer was applied.

[0065] Experimental group 1: 0.3 g of urea granules (Urea) were applied.

[0066] Experimental group 2: 0.3 g of UKS slow-release fertilizer (the slow-release fertilizer prepared in Example 1 of the present invention) was applied.

[0067] like Figure 4 and 5 As shown in the pot experiment, the wheat planted in Experimental Group 2 (UKS slow-release fertilizer group) grew fastest, followed by Experimental Group 1 (urea granules group, Urea), and the water control group grew the slowest. At the same time, it was observed that the wheat plants in Experimental Group 2 were taller, stronger, and had a more developed root system, significantly higher than the other two groups.

[0068] according to Figure 5 The test data shown show that on the 5th day, the length of wheat leaves in the UKS group had the largest difference with the Urea group and the water control group, increasing by 31.9% and 34.9% respectively. On the 7th day, the difference in leaf length decreased, but still reached 19.9% ​​and 16.8%.

[0069] For root length, on the 7th day, the root length of wheat in the UKS group had the largest difference with that of the Urea group and the water control group, and its root length increased by 76.5% and 16.9% compared with that of the Urea group and the water control group, respectively.

[0070] The above results show that the slow-release fertilizer UKS prepared by the present invention can effectively promote wheat growth, increase leaf length and root length, and the effect is better than traditional urea granules. It also further proves that it has the effect of slow-release nitrogen and improving soil water retention capacity, and can provide sufficient water for crop growth, synchronize with crop growth needs, and improve nitrogen fertilizer utilization rate.

[0071] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a solid waste-based water-retaining slow-release fertilizer, characterized in that: The following steps are involved: (1) mixing coal-bearing kaolinite with a nitrogen source solution, and stirring to allow the nitrogen source to be intercalated into the interlayers of the kaolinite to obtain nitrogen source intercalated kaolinite; (2) The nitrogen source intercalated kaolinite, nitrogen source particles and high molecular weight polysaccharide are mixed, ultrasonically dispersed evenly, and then added to a calcium chloride solution to cross-link them to form a hydrogel. The excess residual calcium chloride solution is then removed and freeze-dried to obtain the solid waste-based water-retaining slow-release fertilizer.

2. The preparation method according to claim 1, characterized in that: The specific process of step (1) is as follows: At 50-60° C., 10-15 wt % of coal-based kaolinite is added to a nitrogen source solution, and stirred to allow the nitrogen source to be intercalated into the kaolinite interlayers to obtain nitrogen source intercalated kaolinite.

3. The preparation method according to claim 2, characterized in that: The temperature for preparing the nitrogen source intercalated kaolinite in step (1) is 60° C., and the amount of coal-based kaolinite used is 10 wt %.

4. The preparation method according to claim 1 or 2, characterized in that: The nitrogen source includes at least one of ammonium bicarbonate, ammonium nitrate and ammonium sulfate.

5. The preparation method according to claim 1, characterized in that: In step (2), the weight ratio of the nitrogen source intercalated kaolinite to the high molecular weight polysaccharide is 1:1.5 to 1:

2.

6. The preparation method according to claim 5, characterized in that: The weight ratio of nitrogen source intercalated kaolinite and high molecular weight polysaccharide is 1:

2.

7. The preparation method according to claim 1 or 5, characterized in that: The high molecular weight polysaccharide includes at least one of starch, cellulose, chitosan, hyaluronic acid, polyacrylic acid, polymethacrylic acid, polyacrylamide and poly-N-polyacrylamide.

8. The preparation method according to claim 1, characterized in that: The nitrogen source particles in step (2) are ammonium bicarbonate, ammonium nitrate or ammonium sulfate particles.

9. A solid waste-based water-retaining slow-release fertilizer, characterized in that: The method is prepared by any one of claims 1 to 8.

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