A preparation method of water-retaining controlled-release compound fertilizer and its product

Abstract

The present invention discloses a preparation method of a water-retaining controlled-release compound fertilizer and its product, and belongs to the technical field of fertilizers. The preparation method comprises the following steps: granulating urea, diammonium phosphate, potassium sulfate, superphosphate and zinc sulfate compound fertilizer to obtain fertilizer core particles; then wrapping acid-modified carbon nanotubes and bentonite on the surface of the fertilizer core particles to form an inner coating layer; finally, wrapping modified starch-based water-retaining agent particles on the surface of the inner coating layer to form an outer coating layer to obtain the water-retaining controlled-release compound fertilizer. The water-retaining controlled-release compound fertilizer prepared by the preparation method of the present invention can significantly reduce the water evaporation rate, improve the effectiveness of soil moisture, and improve the ability of soil to release and retain water. The water-retaining slow-release fertilizer has the properties of water absorption, water retention and nutrient slow-release, and is rich in nutrients, and has good development and application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of fertilizers, and in particular to a preparation method of a water-retaining controlled-release compound fertilizer and a product thereof. Background Art

[0002] Drought and water shortage are important factors that restrict agricultural development and accelerate land desertification. Improving the water utilization rate of farmland has become one of the central tasks of agriculture. Agricultural water retainers have the functions of drought resistance, water retention, heat preservation, and improvement of soil structure. They can inhibit soil moisture evaporation, increase soil saturated water content, reduce leaching loss of soluble nutrients, and improve fertilizer utilization. At the same time, they can reduce soil bulk density and improve soil structure and water and heat conditions. Although water retainers have super strong water absorption and water retention effects, they do not have fertilizer nutrients, which are essential nutritional conditions for crop production and vegetation growth. At the same time, the application of water retainers and fertilizers separately is labor-intensive and time-consuming, and is not conducive to the interaction between water and fertilizer and the play of water-fertilizer effects.

[0003] Therefore, combining it with controlled-release fertilizers to prepare multifunctional fertilizers that can both slowly release nutrients and absorb and retain water and resist drought will surely become a new hot spot in the field of fertilizer research and production. Water-retaining controlled-release fertilizers have the functions of both water-retaining agents and controlled-release fertilizers, and have the dual functions of absorbing and retaining water and slowly releasing nutrients, which meets the actual needs of water conservation and dryland agricultural production.

[0004] The existing water-retaining controlled-release fertilizers have the following problems: the preparation of some water-retaining controlled-release fertilizers is limited to laboratory scale by inducing polymerization of the controlled-release fertilizer in a reactor to wrap a layer of water-retaining agent, which is not feasible in terms of process and thus greatly limits its large-scale industrial production; the "fertilizer core" of the water-retaining controlled-release fertilizers is mostly expensive slow-release fertilizers such as urea formaldehyde, but the release period of such products is generally short, the nutrient release performance is not ideal, and the nutrients are relatively single; although the water-retaining controlled-release fertilizers have certain water-retaining and controlled-release properties, both the water-retaining and controlled-release properties are low and cannot meet the requirements of agricultural production. Therefore, it is very necessary to develop a water-retaining controlled-release compound fertilizer that can provide crops with multiple nutrients, has good water-retaining and controlled-release properties, and is suitable for large-scale industrial production. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a water-retaining controlled-release compound fertilizer and a product thereof, so as to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention: a method for preparing a water-retaining controlled-release compound fertilizer, comprising the following steps:

[0008] S1. Grinding urea, diammonium phosphate, potassium sulfate, double superphosphate and zinc sulfate, and granulating them to obtain fertilizer core particles;

[0009] S2, acidifying the carbon nanotubes with a sulfuric acid solution, washing, and drying to obtain modified carbon nanotubes;

[0010] S3, wrapping the modified carbon nanotubes and bentonite on the surface of the fertilizer core particles under the action of a binder to form an inner coating layer to obtain preliminary coated fertilizer particles;

[0011] S4, mixing soluble starch with water, heating and stirring at a temperature of 45-55°C for 40-60 minutes, adding aminosulfonic acid, continuing heating and stirring for 2-2.5 hours, and then drying to obtain modified starch; dissolving the modified starch in water, heating and gelatinizing, then adding acrylic acid and sodium hydroxide solution, and then adding an initiator and a cross-linking agent, reacting at a temperature of 45-55°C for 1-2 hours to obtain a viscoelastic colloid; drying and crushing the viscoelastic colloid to obtain modified starch-based water-retaining agent particles;

[0012] S5. Wrapping the modified starch-based water-retaining agent particles on the surface of the preliminary coated fertilizer particles under the action of a binder to form an outer coating layer to obtain the water-retaining controlled-release compound fertilizer.

[0013] Furthermore, in step S1, the mass ratio of urea, diammonium phosphate, potassium sulfate, triple superphosphate and zinc sulfate is: 20-25:15-20:10-15:5-10:1-5.

[0014] Furthermore, in step S1, each raw material is crushed and then passed through a 40-mesh sieve.

[0015] Furthermore, in step S2, the concentration of the sulfuric acid solution is 1 mol / L, the solid-liquid ratio of carbon nanotubes to the sulfuric acid solution is 1 g:15-20 mL, the temperature of the acidification treatment is 80-90° C., and the time is 2-6 h.

[0016] Furthermore, in step S3, the mass ratio of the carbon nanotubes to bentonite is 1:2-4, and the total mass of the carbon nanotubes and bentonite is 40-50% of the mass of the fertilizer core particles.

[0017] Furthermore, in step S3, the binder is a polyvinyl alcohol solution, the concentration of the polyvinyl alcohol solution is 30-40wt.%, and the amount of the binder is 10-20% of the total mass of the carbon nanotubes and bentonite.

[0018] Furthermore, the step S3 of wrapping the modified carbon nanotubes and bentonite on the surface of the fertilizer core particles under the action of a binder is performed multiple times.

[0019] Furthermore, in step S4, the solid-liquid ratio of the soluble starch to water is 1 g:2-3 mL, and the amount of aminosulfonic acid added is 1-1.5 wt.% of the soluble starch.

[0020] Furthermore, in step S4, the initiator is ammonium persulfate, and the cross-linking agent is N,N-methylenebisacrylamide.

[0021] Furthermore, in step S4, the solid-liquid ratio of the modified starch to water is 1 g:20-30 mL, the mass ratio of the modified starch to acrylic acid is 1:10-20, the added amount of the initiator is 1-3 wt.% of the acrylic acid, and the added amount of the crosslinker is 0.01-0.02 wt.% of the acrylic acid.

[0022] Furthermore, the heating gelatinization temperature in step S4 is 90° C. and the time is 60 min.

[0023] Furthermore, when adding acrylic acid and sodium hydroxide solution to the gelatinized modified starch in step S4, the acrylic acid and the sodium hydroxide solution are first mixed and then added to the gelatinized modified starch together, and the gelatinized modified starch is cooled to 45-55° C. before adding the mixture of acrylic acid and sodium hydroxide solution to the gelatinized modified starch.

[0024] Furthermore, the concentration of the sodium hydroxide solution in step S4 is 7.5 mol / L, and the amount of sodium hydroxide added is calculated to neutralize 65-75 mol% of acrylic acid.

[0025] Furthermore, the mass of the modified starch-based water-retaining agent particles in step S5 is 30-40% of the mass of the preliminary coated fertilizer particles.

[0026] Furthermore, in step S5, the binder is a polyvinyl alcohol solution, the concentration of the polyvinyl alcohol solution is 40-50wt.%, and the amount of the binder is 20-25wt.% of the modified starch-based water-retaining agent particles.

[0027] Furthermore, the step S5 of wrapping the modified starch-based water-retaining agent particles on the surface of the preliminary coated fertilizer particles under the action of the binder is performed multiple times.

[0028] The second technical solution of the present invention: a water-retaining controlled-release compound fertilizer prepared according to the above preparation method.

[0029] The present invention discloses the following technical effects:

[0030] (1) The present invention uses urea, diammonium phosphate, potassium sulfate, superphosphate and zinc sulfate as raw materials for fertilizer core particles, and provides various nutrients required for the growth of crops. A mixture of bentonite and modified carbon nanotubes is used as a slow-release material to form an inner coating layer on the surface of the fertilizer core particles. Bentonite has good adhesion, cation exchange and hygroscopicity, which have good effects on regulating the physical and chemical properties of soil and improving soil water, fertilizer, gas and heat. At the same time, it can also adsorb nutrients to achieve a slow-release effect. Carbon nanotubes have a cavity structure and a large specific surface area, and have a strong adsorption capacity. After acidification treatment and modification, the cavity lattice inside the carbon nanotubes is cracked, the cavity is expanded, and the adsorption capacity is improved, so that its water absorption and water retention performance and the adsorption and slow-release effect on nutrients are further enhanced. Bentonite and modified carbon nanotubes work synergistically, giving the fertilizer a good adsorption performance while giving the fertilizer a certain water absorption and water retention performance. The modified starch-based water-retaining agent particles are used as the main water-retaining component to form an outer coating layer on the surface of the inner coating layer. The starch itself is hydrophilic. The starch is denatured with aminosulfonic acid and then grafted with polypropylene. The hydrophilic groups such as sulfonic acid group and amine group are further introduced into the formed starch-based graft copolymer, and the number and type of hydrophilic functional groups are increased. The higher the content of the hydrophilic functional groups, the greater the water absorption and water retention capacity. And when the modified starch-based water-retaining agent particles absorb water, they will become an elastic body, protecting the inner coating layer from damage during use, further improving the slow-release effect of the fertilizer. The inner coating layer and the outer coating layer work synergistically, which can effectively improve the slow-release performance and water retention performance of the fertilizer. The water-retaining controlled-release composite fertilizer prepared by the preparation method of the present invention can significantly reduce the water evaporation rate, improve the effectiveness of soil moisture, and improve the ability of soil to release and retain water. The water-retaining slow-release fertilizer has the properties of water absorption, water retention and nutrient slow-release, and is rich in nutrients, and has good development and application prospects.

[0031] (2) When the water-retaining controlled-release compound fertilizer is prepared by the preparation method of the present invention, the steps of granulation, wrapping the inner film layer and wrapping the inner film layer can all be completed in a granulator, which is simple to operate and suitable for large-scale industrial production. DETAILED DESCRIPTION

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0034] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0035] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0036] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0037] The experimental methods described in the following examples and comparative examples are conventional methods unless otherwise specified; the reagents and raw materials described are commercially available unless otherwise specified; and the parts described are parts by mass.

[0038] Example 1

[0039] S1. Weigh 20 parts of urea, 15 parts of diammonium phosphate, 10 parts of potassium sulfate, 5 parts of double superphosphate and 1 part of zinc sulfate, grind them through a 40-mesh sieve respectively, then mix the sieved raw materials evenly and put them into a drum granulator, introduce steam and perform rolling humidification granulation. The granulation particle size is 3 mm to obtain fertilizer core particles.

[0040] S2. Add carbon nanotubes and 1 mol / L H2SO4 solution into a three-necked flask (solid-liquid ratio is 1 g:20 mL), stir the mixture at 90°C for 4 hours, wash the product with distilled water after the reaction is completed, and dry it in a vacuum oven at 50°C to obtain modified carbon nanotubes.

[0041] S3. Grind the modified carbon nanotubes and bentonite separately through an 80-mesh sieve, and then mix them in a mass ratio of 1:2, spray a binder polyvinyl alcohol solution (concentration of 30wt.%) on the surface of the fertilizer core particles, and slowly sprinkle the mixture of the modified carbon nanotubes and bentonite at the same time, rotate until the sprinkled modified carbon nanotubes and bentonite are completely wrapped on the surface of the fertilizer core particles, and then spray the binder polyvinyl alcohol solution (concentration of 30wt.%), repeat the above operation 4 times, form an inner coating layer on the surface of the fertilizer core particles, and obtain preliminary coated fertilizer particles (the total amount of the mixture of modified carbon nanotubes and bentonite is 40% of the mass of the fertilizer core particles, sprinkled in 5 times, each time sprinkling 1 / 5 of the total amount, the total amount of polyvinyl alcohol solution is 15% of the mass of the mixture of modified carbon nanotubes and bentonite, sprayed in 5 times, each time spraying 1 / 5 of the total amount).

[0042] S4. Put the soluble starch in a three-necked flask, add deionized water at a solid-liquid ratio of 1g:2.5mL and stir until it is in a homogenous state, keep mechanical stirring at a constant speed of 200r / min, heat in a water bath at 50°C for 40min, add aminosulfonic acid (1.2wt.% of the soluble starch), continue to keep heating in a water bath at 50°C and mechanical stirring at a constant speed of 200r / min to react, transfer the denatured solution to a polytetrafluoroethylene plate after 2h, and dry it in an electric oven at 50°C to obtain denatured starch;

[0043] Take modified starch and add water according to the solid-liquid ratio of 1g:30mL to dissolve it in a four-necked flask, heat it to 90℃, introduce nitrogen, stir and gelatinize it, and cool it to 50℃ after gelatinization for 60min; weigh acrylic acid (15 times the mass of modified starch) in a small beaker, then add sodium hydroxide with a concentration of 7.5mol / L (the amount is calculated based on neutralizing 70%mol of acrylic acid), add it to the four-necked flask after mixing, add initiator ammonium persulfate (the amount is 1.6wt.% of acrylic acid), stir it in a water bath at 50℃ for 5min to generate free radicals; then add crosslinking agent N,N-methylenebisacrylamide (the amount is 0.015wt.% of acrylic acid), stir and react in a water bath at 50℃, generate a viscoelastic colloid after 1h, take it out and dry it at 50℃ for 72h, crush it, and pass it through a 20-mesh sieve to obtain modified starch-based water-retaining agent particles.

[0044] S5. Spray a binder polyvinyl alcohol solution (at a concentration of 40 wt.%) onto the surface of the preliminary coated fertilizer particles, and at the same time slowly sprinkle in modified starch-based water-retaining agent particles, rotate until the sprinkled modified starch-based water-retaining agent particles are all wrapped on the surface of the preliminary coated fertilizer particles, and then spray a binder polyvinyl alcohol solution (at a concentration of 40 wt.%), repeat the above operation twice, form an outer coating layer on the surface of the preliminary coated fertilizer particles, and obtain a water-retaining controlled-release compound fertilizer (the total amount of modified starch-based water-retaining agent particles is 30% of the mass of the preliminary coated fertilizer particles, sprinkled in 3 times, 1 / 3 of the total amount each time, the total amount of polyvinyl alcohol solution is 20 wt.% of the modified starch-based water-retaining agent particles, sprayed in 3 times, 1 / 3 of the total amount each time).

[0045] Example 2

[0046] S1. Weigh 23 parts of urea, 18 parts of diammonium phosphate, 13 parts of potassium sulfate, 8 parts of double superphosphate and 3 parts of zinc sulfate, grind them through a 40-mesh sieve respectively, then mix the sieved raw materials evenly and put them into a drum granulator, introduce steam and perform rolling humidification granulation. The granulation particle size is 3 mm to obtain fertilizer core particles.

[0047] S2. Same as step S2 in Example 1.

[0048] S3. Grind the modified carbon nanotubes and bentonite separately through an 80-mesh sieve, and then mix them in a mass ratio of 1:3, spray a binder polyvinyl alcohol solution (concentration of 35wt.%) on the surface of the fertilizer core particles, and slowly sprinkle the mixture of the modified carbon nanotubes and bentonite at the same time, rotate until the sprinkled modified carbon nanotubes and bentonite are completely wrapped on the surface of the fertilizer core particles, and then spray the binder polyvinyl alcohol solution (concentration of 35wt.%), repeat the above operation 4 times, form an inner coating layer on the surface of the fertilizer core particles, and obtain preliminary coated fertilizer particles (the total amount of the mixture of modified carbon nanotubes and bentonite is 45% of the mass of the fertilizer core particles, sprinkled in 5 times, each time sprinkling 1 / 5 of the total amount, the total amount of polyvinyl alcohol solution is 18% of the mass of the mixture of modified carbon nanotubes and bentonite, sprayed in 5 times, each time spraying 1 / 5 of the total amount).

[0049] S4. Same as step S4 in Example 1.

[0050] S5. Spray a binder polyvinyl alcohol solution (at a concentration of 45 wt.%) onto the surface of the preliminary coated fertilizer particles, and at the same time slowly sprinkle in modified starch-based water-retaining agent particles, rotate until the sprinkled modified starch-based water-retaining agent particles are all wrapped on the surface of the preliminary coated fertilizer particles, and then spray a binder polyvinyl alcohol solution (at a concentration of 45 wt.%), repeat the above operation twice, form an outer coating layer on the surface of the preliminary coated fertilizer particles, and obtain a water-retaining controlled-release compound fertilizer (the total amount of modified starch-based water-retaining agent particles is 35% of the mass of the preliminary coated fertilizer particles, sprinkled in 3 times, 1 / 3 of the total amount each time, the total amount of polyvinyl alcohol solution is 22 wt.% of the modified starch-based water-retaining agent particles, sprayed in 3 times, 1 / 3 of the total amount each time).

[0051] Example 3

[0052] S1. Weigh 25 parts of urea, 20 parts of diammonium phosphate, 15 parts of potassium sulfate, 10 parts of double superphosphate, and 5 parts of zinc sulfate, grind them through a 40-mesh sieve respectively, then mix the sieved raw materials evenly and put them into a drum granulator, introduce steam, perform rolling humidification granulation, and the granulation particle size is 3 mm to obtain fertilizer core particles.

[0053] S2. Same as step S2 in Example 1.

[0054] S3. Grind the modified carbon nanotubes and bentonite separately through an 80-mesh sieve, and then mix them in a mass ratio of 1:4, spray a binder polyvinyl alcohol solution (concentration of 40wt.%) on the surface of the fertilizer core particles, and slowly sprinkle the mixture of the modified carbon nanotubes and bentonite at the same time, rotate until the sprinkled modified carbon nanotubes and bentonite are completely wrapped on the surface of the fertilizer core particles, and then spray the binder polyvinyl alcohol solution (concentration of 40wt.%), repeat the above operation 4 times, form an inner coating layer on the surface of the fertilizer core particles, and obtain preliminary coated fertilizer particles (the total amount of the mixture of modified carbon nanotubes and bentonite is 50% of the mass of the fertilizer core particles, sprinkled in 5 times, each time sprinkling 1 / 5 of the total amount, the total amount of polyvinyl alcohol solution is 20% of the mass of the mixture of modified carbon nanotubes and bentonite, sprayed in 5 times, each time spraying 1 / 5 of the total amount).

[0055] S4. Same as step S4 in Example 1.

[0056] S5. Spray a binder polyvinyl alcohol solution (at a concentration of 50 wt.%) onto the surface of the preliminary coated fertilizer particles, and at the same time slowly sprinkle in modified starch-based water-retaining agent particles, rotate until the sprinkled modified starch-based water-retaining agent particles are all wrapped on the surface of the preliminary coated fertilizer particles, and then spray a binder polyvinyl alcohol solution (at a concentration of 50 wt.%), repeat the above operation twice, form an outer coating layer on the surface of the preliminary coated fertilizer particles, and obtain a water-retaining controlled-release compound fertilizer (the total amount of modified starch-based water-retaining agent particles is 40% of the mass of the preliminary coated fertilizer particles, sprinkled in 3 times, 1 / 3 of the total amount each time, the total amount of polyvinyl alcohol solution is 25 wt.% of the modified starch-based water-retaining agent particles, sprayed in 3 times, 1 / 3 of the total amount each time).

[0057] Comparative Example 1

[0058] The same as Example 1, except that step S2 is omitted and ordinary commercially available carbon nanotubes of equal mass are used to replace the modified carbon nanotubes in step S3.

[0059] Comparative Example 2

[0060] The same as Example 1, except that in step S3, an equal mass of modified carbon nanotubes is used instead of bentonite.

[0061] Comparative Example 3

[0062] The same as comparative example 1, except that step S2 is omitted and bentonite of equal mass is used to replace the modified carbon nanotubes in step S3.

[0063] Comparative Example 4

[0064] S1. Weigh 20 parts of urea, 15 parts of diammonium phosphate, 10 parts of potassium sulfate, 5 parts of double superphosphate and 1 part of zinc sulfate, grind them through a 40-mesh sieve respectively, then mix the sieved raw materials evenly and put them into a drum granulator, introduce steam and perform rolling humidification granulation. The granulation particle size is 3 mm to obtain fertilizer core particles.

[0065] S2. Add carbon nanotubes and 1 mol / L H2SO4 solution into a three-necked flask (solid-liquid ratio is 1 g:20 mL), stir the mixture at 90°C for 4 hours, wash the product with distilled water after the reaction is completed, and dry it in a vacuum oven at 50°C to obtain modified carbon nanotubes.

[0066] S3. Grind the modified carbon nanotubes and bentonite separately through an 80-mesh sieve, and then mix them in a mass ratio of 1:2, spray a binder polyvinyl alcohol solution (concentration of 30wt.%) on the surface of the fertilizer core particles, and slowly sprinkle the mixture of the modified carbon nanotubes and bentonite at the same time, rotate until the sprinkled modified carbon nanotubes and bentonite are completely wrapped on the surface of the fertilizer core particles, and then spray the binder polyvinyl alcohol solution (concentration of 30wt.%), repeat the above operation 4 times, form an inner coating layer on the surface of the fertilizer core particles, and obtain preliminary coated fertilizer particles (the total amount of the mixture of modified carbon nanotubes and bentonite is 40% of the mass of the fertilizer core particles, sprinkled in 5 times, each time sprinkling 1 / 5 of the total amount, the total amount of polyvinyl alcohol solution is 15% of the mass of the mixture of modified carbon nanotubes and bentonite, sprayed in 5 times, each time spraying 1 / 5 of the total amount).

[0067] S4. Take soluble starch and add water at a solid-liquid ratio of 1g:30mL to dissolve it in a four-necked flask, heat it to 90°C, introduce nitrogen, stir and gelatinize it, and cool it to 50°C after gelatinization for 60 minutes; weigh acrylic acid (15 times the mass of soluble starch) in a small beaker, then add sodium hydroxide with a concentration of 7.5mol / L (the amount is calculated based on neutralizing 70%mol of acrylic acid), add it to the four-necked flask after mixing, add initiator ammonium persulfate (the amount is 1.6wt.% of acrylic acid), stir it in a water bath at 50°C for 5min to generate free radicals; then add crosslinking agent N,N-methylenebisacrylamide (the amount is 0.015wt.% of acrylic acid), stir and react in a water bath at 50°C, and generate a viscoelastic colloid after 1h. Take it out and dry it with air at 50°C for 72h, crush it, and pass it through a 20-mesh sieve to obtain starch water-retaining agent particles.

[0068] S5. Spray a binder polyvinyl alcohol solution (at a concentration of 40 wt.%) onto the surface of the preliminary coated fertilizer particles, and at the same time slowly sprinkle in modified starch-based water-retaining agent particles, rotate until the sprinkled modified starch-based water-retaining agent particles are all wrapped on the surface of the preliminary coated fertilizer particles, and then spray a binder polyvinyl alcohol solution (at a concentration of 40 wt.%), repeat the above operation twice, form an outer coating layer on the surface of the preliminary coated fertilizer particles, and obtain a water-retaining controlled-release compound fertilizer (the total amount of modified starch-based water-retaining agent particles is 30% of the mass of the preliminary coated fertilizer particles, sprinkled in 3 times, 1 / 3 of the total amount each time, the total amount of polyvinyl alcohol solution is 20 wt.% of the modified starch-based water-retaining agent particles, sprayed in 3 times, 1 / 3 of the total amount each time).

[0069] Comparative Example 5

[0070] S1, weighing 20 parts of urea, 15 parts of diammonium phosphate, 10 parts of potassium sulfate, 5 parts of double superphosphate, and 1 part of zinc sulfate, respectively grinding them through a 40-mesh sieve, then mixing the sieved raw materials evenly and entering a drum granulator into which steam is introduced for rolling humidification granulation, the granulation particle size is 3 mm, and the fertilizer core particles are obtained;

[0071] S2. Same as step S4 in Example 1 (preparing a modified starch-based water-retaining agent).

[0072] S3. Spray a binder polyvinyl alcohol solution (with a concentration of 40 wt.%) onto the surface of the fertilizer core particles, and at the same time slowly sprinkle in modified starch-based water-retaining agent particles, rotate until the sprinkled modified starch-based water-retaining agent particles are all wrapped on the surface of the fertilizer core particles, and then spray a binder polyvinyl alcohol solution (with a concentration of 40 wt.%), repeat the above operation twice, and form an outer coating layer on the surface of the fertilizer core particles to obtain a water-retaining controlled-release compound fertilizer (the total amount of modified starch-based water-retaining agent particles is 30% of the mass of the fertilizer core particles, sprinkled in 3 times, 1 / 3 of the total amount each time, the total amount of polyvinyl alcohol solution is 20 wt.% of the modified starch-based water-retaining agent particles, sprayed in 3 times, 1 / 3 of the total amount each time).

[0073] Effect verification

[0074] 1. Water retention determination

[0075] Accurately weigh 200g of dry soil that has passed through a 0.2mm sieve, mix it evenly with 6g of water-retaining controlled-release compound fertilizer, and put it into a 500mL beaker. Then add a certain amount of tap water to the beaker (based on the fact that there is no water accumulation on the soil surface and a small amount of water seeps out between the inner wall of the beaker and the soil when the beaker is tilted). Place it in an oven at 35°C, weigh the total mass of the beaker at regular intervals, and perform a blank test (without adding water-retaining controlled-release compound fertilizer, and other conditions are the same as above). Record the data and calculate the soil water retention rate Ri according to the following formula.

[0076]

[0077] Wherein, m0 is the total mass of the water-retaining controlled-release compound fertilizer and soil when fully absorbing water to reach saturation (g); m'0 is the total mass of dry soil and dry water-retaining controlled-release compound fertilizer (g); m i is the total mass (g) of the soil and the water-retaining controlled-release compound fertilizer at the i-th weighing. The water-retaining properties of the water-retaining controlled-release compound fertilizers prepared in the examples and comparative examples are shown in Table 1 (three parallel experiments were conducted for each group, and the results were averaged).

[0078] Table 1

[0079]

[0080] As can be seen from Table 1, under the same experimental conditions, the soil water retention rate of the soil with the water-retaining controlled-release compound fertilizer added is greater than that without the water-retaining controlled-release compound fertilizer, that is, the soil water evaporation rate of the soil with the water-retaining controlled-release compound fertilizer added is significantly lower than that without the water-retaining controlled-release compound fertilizer. It shows that the water-retaining controlled-release compound fertilizer prepared by the present invention has a good water-retaining capacity after being applied to the soil, and can slow down the evaporation of water in the soil. On rainy days, the water-retaining slow-release fertilizer stores excess water. When it is dry, the water adsorbed in the water-retaining slow-release fertilizer can be adsorbed by the capillaries of the plant roots and then transported to the plant body, playing the role of a "micro-reservoir", thereby reducing the number of irrigation times and improving water utilization. And the water retention rate of the soil with the water-retaining controlled-release compound fertilizer prepared by Examples 1-3 of the present invention is better than that of the soil with the water-retaining controlled-release compound fertilizer prepared by Comparative Examples 1-5, indicating that the excellent water-retaining performance of the water-retaining controlled-release compound fertilizer provided by the present invention is brought about by the synergistic effect of various factors in the preparation steps. If any factor is missing, the water-retaining effect will be reduced.

[0081] 2. Controlled release effect test

[0082] Soil is a complex natural body composed of three phases: gas, liquid and solid. It is the main body of crop growth. The intermittent soil column leaching method is used to simulate the slow release of water-retaining controlled-release compound fertilizer in the soil, and the N element is used as the test component for characterization. A small amount of fine sand is added to a PVC tube about 30 cm long and 5 cm in diameter, which is sealed with a filter cloth with a pore size of 0.074 mm. 250 g (about 10 cm high) of air-dried soil (passed through a 2 cm sieve) is loaded into the PVC tube. According to the standard of N1g / kg air-dried soil, 250 g of air-dried soil mixed evenly with water-retaining slow-release fertilizer is loaded on it. A small amount of fine sand (25 g) is covered on the soil column to avoid disturbing the soil layer during leaching. After the soil column is prepared, distilled water is added in small amounts and multiple times to make the soil moisture close to saturation, but no excessive distilled water will seep out of the soil column. After standing for 24 hours, 100 mL of distilled water was poured into the PCV tube, and the leaching solution was collected with a conical flask until no more water dripped out. The leaching solution was taken and the cumulative release rate of N in the fertilizer was determined by the Kjeldahl method. The leaching was performed every 10 days for 40 days. The control effect test results of the water-retaining controlled-release compound fertilizers prepared in each embodiment and comparative example are shown in Table 2 (three parallel experiments were conducted in each group, and the results were averaged).

[0083] Table 2

[0084]

[0085] It can be seen from Table 2 that the water-retaining controlled-release compound fertilizers prepared in Examples 1-3 of the present invention have good slow-release effects. Comparison of the data of Example 1, Comparative Example 1 and Comparative Example 5 shows that the material composition of the inner coating layer has a greater influence on the slow-release effect of the water-retaining controlled-release compound fertilizer, and the slow-release effect of the fertilizer obtained when the mixture of acid-modified carbon nanotubes and bentonite is used as the slow-release material to prepare the inner coating layer is the best.

[0086] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a water-retaining controlled-release compound fertilizer, characterized in that: The following steps are involved: S1. Grinding urea, diammonium phosphate, potassium sulfate, double superphosphate and zinc sulfate, and granulating them to obtain fertilizer core particles; S2, acidifying the carbon nanotubes with a sulfuric acid solution, washing, and drying to obtain modified carbon nanotubes; S3, wrapping the modified carbon nanotubes and bentonite on the surface of the fertilizer core particles under the action of a binder to form an inner coating layer to obtain preliminary coated fertilizer particles; S4, mixing soluble starch with water, heating and stirring at a temperature of 45-55° C. for 40-60 minutes, adding aminosulfonic acid, continuing heating and stirring for 2-2.5 hours, and then drying to obtain modified starch; dissolving the modified starch in water, heating and gelatinizing, then adding acrylic acid and sodium hydroxide solution, and then adding an initiator and a cross-linking agent, reacting at a temperature of 45-55° C. for 1-2 hours to obtain a viscoelastic colloid; drying the viscoelastic colloid, crushing, and obtaining modified starch-based water-retaining agent particles; S5, wrapping the modified starch-based water-retaining agent particles on the surface of the preliminary coated fertilizer particles under the action of a binder to form an outer coating layer to obtain the water-retaining controlled-release compound fertilizer; In step S3, the mass ratio of the modified carbon nanotubes to bentonite is 1:2-4, and the total mass of the modified carbon nanotubes and bentonite is 40-50% of the mass of the fertilizer core particles; In step S3, the binder is a polyvinyl alcohol solution, the concentration of the polyvinyl alcohol solution is 30-40wt.%, and the amount of the binder is 15-20% of the total mass of the modified carbon nanotubes and bentonite; The mass of the modified starch-based water-retaining agent particles in step S5 is 30-40% of the mass of the preliminary coated fertilizer particles; In step S5, the binder is a polyvinyl alcohol solution, the concentration of the polyvinyl alcohol solution is 40-50wt.%, and the amount of the binder is 20-25wt.% of the modified starch-based water-retaining agent particles.

2. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of urea, diammonium phosphate, potassium sulfate, triple superphosphate and zinc sulfate is: 20-25:15-20:10-15:5-10:1-5.

3. The preparation method according to claim 1, characterized in that: The concentration of the sulfuric acid solution in step S2 is 1 mol / L, the solid-liquid ratio of carbon nanotubes to sulfuric acid solution is 1 g:15-20 mL, the temperature of the acidification treatment is 80-90° C., and the time is 2-6 h.

4. The preparation method according to claim 1, characterized in that: In step S4, the solid-liquid ratio of the soluble starch to water is 1 g:2-3 mL, and the amount of aminosulfonic acid added is 1-1.5 wt.% of the soluble starch.

5. The preparation method according to claim 1, characterized in that: In step S4, the solid-liquid ratio of the modified starch to water is 1g:20-30mL, the mass ratio of the modified starch to acrylic acid is 1:10-20, the amount of the initiator added is 1-3wt.% of the acrylic acid, and the amount of the crosslinker added is 0.01-0.02wt.% of the acrylic acid.

6. A water-retaining controlled-release compound fertilizer prepared according to the preparation method according to any one of claims 1 to 5.

Images