CN111848292A

CN111848292A - Urea slow-release compound fertilizer and preparation method thereof

Info

Publication number: CN111848292A
Application number: CN202010666163.9A
Authority: CN
Inventors: 刘强; 魏萍; 张培; 徐萌琦
Original assignee: University of Shanghai for Science and Technology
Current assignee: University of Shanghai for Science and Technology
Priority date: 2020-07-13
Filing date: 2020-07-13
Publication date: 2020-10-30

Abstract

The invention discloses a urea slow-release compound fertilizer and a preparation method thereof, belonging to the field of fertilizers. The urea slow-release compound fertilizer which is simple in method, small in pollution and good in slow-release effect is realized. The invention achieves the purpose of slow release by reducing the release rate of urea, and the biochar adsorbs the urea by utilizing the porous structure and the larger specific surface area of the biochar, and can further enhance the absorption of plants to fertilizers as a soil conditioner. The addition of montmorillonite enhances the retention of urea while also enhancing the stability of the overall material. The material is further protected by utilizing a polyvinyl alcohol coating, and a layer of coating is formed outside the material to protect the urea. The invention achieves the purpose of slow release by reducing the release rate of urea, improves the quality of nitrogen fertilizer, reduces fertilizer loss and improves the utilization rate of soil fertilizer; the method is simple and easy to implement, realizes the resource utilization of the waste, has low cost and is suitable for popularization and application.

Description

Urea slow-release compound fertilizer and preparation method thereof

Technical Field

The invention relates to a nitrogen fertilizer and a preparation method thereof, in particular to a urea compound fertilizer and a preparation method thereof, which are applied to the technical field of fertilizer industry.

Background

At present, nitrogen fertilizer is used as one of the chemical fertilizer types with the largest yield and utilization amount all over the world, and plays a vital role in improving the grain yield in China. It is known that nitrogen is a nutrient element required by plants in all growth periods, so that the utilization rate of nitrogen is closely related to the growth of plants, but the utilization rate of nitrogen fertilizer is extremely low, so that the utilization rate of nitrogen fertilizer should be improved. The urea is one of the simplest organic compounds consisting of C, H, N, O four elements, and is neutral and suitable for any soil, and hardly causes any damage to the soil, but the utilization process of the urea still has many problems to be solved.

At present, there are many materials and methods for preparing the urea slow release fertilizer, such as using elemental sulfur as an external coating of urea, using starch as a sealing layer of urea, or using a polymer to form a thin film outside urea to protect urea, and the combination methods include direct mixing, granulation, and casting. Granulation is a simple and convenient technology, and substances can be directly and tightly combined by utilizing granulation and then combined with a coating to form a compact structure so as to protect urea.

The biochar is a substance rich in carbon, is produced by pyrolyzing biomass under the condition of limited oxygen, has developed internal pores and larger specific surface area, and can be used as an adsorbing material; meanwhile, because the surface of the biochar contains rich oxygen-containing functional groups and a graphite-like structure in the biochar, the biochar has certain conductivity, and people begin to use the biochar as a catalytic material to degrade pollutants. Biochar is commonly used as a catalyst support, and is less useful for fertilizer raw materials.

The clay mineral is water-containing aluminosilicate mineral, and the common clay mineral is kaolinite, montmorillonite, illite, etc. The clay mineral has higher cation exchange CEC. In addition, the clay mineral has a layered structure due to the characteristic property, and under the condition that water exists, part of neutral molecules can be inserted into the middle of the layered structure, so that the property lays a foundation for retaining urea. Montmorillonite (MMT) is a clay mineral with a layered structure. Under the action of water, the layered structure of MMT can effectively retain neutral molecules. In addition, the montmorillonite has excellent plasticity and viscosity, and the property enables the whole composite material to be processed and manufactured to a certain extent. Meanwhile, researches show that the montmorillonite also has a certain adsorption effect on environmental pollutants after being applied to water and soil.

Polyvinyl alcohol is commonly used as one of the coating materials. The polyvinyl alcohol has certain moldability, and can form a layer of film outside the fertilizer so as to prevent the fertilizer from directly contacting with water to achieve the slow release effect. The film formed by the polyvinyl alcohol has compact structure and the formed film is flexible and smooth. Meanwhile, the polyvinyl alcohol is used as an organic coating material, so that the health of human bodies is not influenced, and the environment is not polluted. After the urea is released from the composite, the polyvinyl alcohol can be degraded later by soil microorganisms into carbon dioxide and water to accelerate the degradation.

Urea is one of the most widely used nitrogen fertilizers at present, but urea reacts rapidly after being applied to soil, so that nutrients are released rapidly in the process of converting urea in soil, most plants require less nutrients in the early growth stage, so that the utilization rate of the plants is low, and the nutrients produced by rapid reaction also face problems, such as ammonium ions and nitrate ions, wherein the nitrate ions mainly cause leaching loss under rainwater or irrigation, ammonium nitrogen mainly reacts to generate ammonia gas to volatilize and cause loss, and the ammonium nitrogen also easily generates nitrate nitrogen to cause leaching loss; this is a technical problem to be solved. So far, no report related to the formation of the multi-mode slow-release fertilizer granular material by mixing montmorillonite, biochar and urea and coating polyvinyl alcohol is seen.

Disclosure of Invention

In order to solve the problems of the prior art, the invention aims to overcome the defects of the prior art, provide the urea slow-release compound fertilizer and the preparation method thereof, and realize the urea slow-release compound fertilizer with simple method, little pollution and good slow-release effect. The invention achieves the purpose of slow release by reducing the release rate of urea, and the biochar adsorbs the urea by utilizing the porous structure and the larger specific surface area of the biochar, and can further enhance the absorption of plants to fertilizers as a soil conditioner. The addition of montmorillonite enhances the retention of urea while also enhancing the stability of the overall material. The material is further protected by utilizing a polyvinyl alcohol coating, and a layer of coating is formed outside the material to protect the urea.

In order to achieve the purpose of the invention, the invention adopts the following technical scheme:

a urea slow release compound fertilizer is prepared by taking urea, biochar, montmorillonite and polyvinyl alcohol as raw materials and carrying out the processes of uniformly mixing, granulating and drying, wherein the biochar adsorbs the urea by utilizing the porous structure and the larger specific surface area of the biochar, and the biochar is used as a carrier of the urea and is combined with the urea to form urea composite material particles; montmorillonite is used as a retention agent for enhancing the urea composite material to urea, and the composite particle structure of the urea composite material is stabilized; polyvinyl alcohol is often used as a coating material, and a composite material formed by mixing urea, biochar and montmorillonite is subjected to film encapsulation to obtain coated urea particles, so that the urea slow-release compound fertilizer is obtained.

The preferred mixing mass percentage ratio of the montmorillonite, the urea and the biochar is 1 (1-3) to 1-3.

Further preferably, the mixing mass percentage ratio of the montmorillonite, the urea and the biochar is 1:1: 1.

A preparation method of a urea slow-release compound fertilizer comprises the following steps:

a. preparing ingredients:

weighing montmorillonite, urea and biochar as raw materials according to the mass percentage ratio of (1) - (3) to (1-3) for mixing corresponding raw material components;

b. pretreatment of raw materials:

sieving the urea, the biochar and the montmorillonite prepared in the step a, and adding water to uniformly mix to obtain a mixture soft material for later use;

c. and (3) granulation:

at normal temperature, extruding the soft mixture material prepared in the step b through a screen with a fixed aperture by using a granulator under the action of mechanical force, then granulating to form composite particles, and drying the composite particles in a dark place for at least 48 hours to obtain a biochar/urea/montmorillonite composite fertilizer particle material with the particle size of 0.5-1 mm;

d. urea coating treatment:

and c, placing the compound fertilizer granular material granulated and dried in the step c in a polyvinyl alcohol solution with the concentration of not less than 10g/L for coating treatment, thereby obtaining a finished coated urea granular fertilizer.

In the step d, the compound fertilizer granular material is put into a reagent bottle filled with a polyvinyl alcohol solution, placed in a constant temperature oscillation box for at least 10min, dried and subjected to coating treatment, so that a finished coated urea granular fertilizer product is obtained.

As a preferred technical solution of the present invention, in the step a, the preparation process of the biochar is as follows:

placing the pretreated clean and dry corn straw biomass in a quartz boat, fully compacting, placing the quartz boat loaded with the biomass in a quartz tube, and placing the quartz tube in a tubular electric furnace; and then connecting the quartz tube with a nitrogen bottle to maintain a nitrogen atmosphere environment in the quartz tube, adjusting the heating temperature of the tube furnace through a temperature control device to maintain the required pyrolysis temperature of the charcoal, automatically closing the temperature control device after the pyrolysis process is finished, taking out the quartz boat from the quartz tube when the temperature is cooled to room temperature, grinding the pyrolysis product, sieving the product to obtain charcoal powder, and sealing and storing the charcoal powder.

Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:

1. The biochar in the urea slow-release compound fertilizer disclosed by the invention adsorbs urea by utilizing the porous structure and the larger specific surface area of the biochar, and meanwhile, the biochar serving as a soil conditioner can further enhance the absorption of plants on the fertilizer; the addition of the montmorillonite not only strengthens the retention of the composite material to urea, but also strengthens the stability of the whole material; the polyvinyl alcohol coating further protects the material, and a layer of coating is formed outside the material to protect urea; meanwhile, the biochar and the montmorillonite can adsorb other pollutants, and the polyvinyl alcohol can be degraded in soil, so that the environment is not polluted while the slow release performance is improved;

2. the invention achieves the purpose of slow release by reducing the release rate of urea, improves the quality of the nitrogen fertilizer, reduces the loss of the fertilizer and improves the utilization rate of the soil fertilizer;

3. the method is simple and easy to implement, realizes the resource utilization of the waste, has low cost and is suitable for popularization and application.

Drawings

Fig. 1 is a schematic view of a soil bollard according to a second embodiment of the present invention.

Fig. 2 is a schematic view of a soil bollard provided by the present invention.

FIG. 3 is a graph showing the slow-release effect of a urea slow-release compound fertilizer without being coated in water according to a first embodiment of the present invention.

FIG. 4 is a graph showing the slow-release effect of the coated urea slow-release compound fertilizer in water according to the first embodiment of the present invention.

FIG. 5 is a graph of the cumulative release rate of a coated urea granular fertilizer according to an example of the present invention.

Detailed Description

The present invention will be further described with reference to the following examples.

The first embodiment is as follows:

the above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:

in the embodiment, the urea slow-release compound fertilizer is prepared by taking urea, biochar, montmorillonite and polyvinyl alcohol as raw materials and performing the processes of uniformly mixing, granulating and drying, wherein the biochar adsorbs the urea by utilizing the porous structure and the larger specific surface area of the biochar, and the biochar is used as a carrier of the urea and is combined with the urea to form urea composite material particles; montmorillonite is used as a retention agent for enhancing the urea composite material to urea, and the composite particle structure of the urea composite material is stabilized; polyvinyl alcohol is often used as a coating material, and a composite material formed by mixing urea, biochar and montmorillonite is subjected to film encapsulation to obtain coated urea particles, so that the urea slow-release compound fertilizer is obtained.

The preparation method of the urea slow-release compound fertilizer comprises the following steps:

a. preparing ingredients:

weighing montmorillonite, urea and biochar as raw materials according to the mass percentage ratios of 1:1:1, 1:2:2 and 1:3:3 respectively;

b. pretreatment of raw materials:

c. and (3) granulation:

at normal temperature, extruding the mixture soft material prepared in the step b through a screen with a fixed aperture BY using a BY400 granulator under the action of mechanical force, then carrying out granulation to form composite material particles, and drying the composite material particles in a dark place for 48 hours to obtain a biochar/urea/montmorillonite composite fertilizer particle material with the particle size of 0.5-1.0 mm;

d. urea coating treatment:

and c, putting the compound fertilizer granular material granulated and dried in the step c into a reagent bottle filled with a polyvinyl alcohol solution with the concentration of 10g/L, placing the compound fertilizer granular material in a constant-temperature oscillation box for 10min, drying, and performing coating treatment to obtain a finished coated urea granular fertilizer.

Experimental test analysis:

First, test and analysis of slow release performance of compound fertilizer in water body

The method for testing and analyzing the slow release performance of the compound fertilizer comprises the following steps:

in this example, a montmorillonite biochar-based urea fertilizer, in which montmorillonite, urea and biochar are mixed at a mass percentage ratio of 1:1:1, 1:2:2, and 1:3:3, is placed in a water system, and is placed in a polyvinyl alcohol (PVA) reagent bottle of 10g/L, the reagent bottle is placed in a shaking table and is oscillated for 10min, so that the polyvinyl alcohol uniformly covers the composite material, the composite material is dried and is placed in the water system for testing, 1mL of an equal sample is taken out after reaction for 20min, 50min, 110min, 200min, 320min, 470min, 620min, and 1340min, respectively, and is centrifuged at 10000rpm for 10min, and is filtered by a 0.45um syringe, and then the absorbance of urea is measured at 430nm by an ultraviolet spectrophotometer, thereby studying the urea.

A water system experiment is carried out through a slow release test of the urea slow release compound fertilizer in water, and the optimal configuration ratio of the material is explored. And (3) filtering the solution by using a 0.45um syringe, and measuring the absorbance of the urea at 430nm by using an ultraviolet spectrophotometer to obtain the release rate of the urea. The results are shown in fig. 3, and it is found that when the proportion of montmorillonite, urea and biochar is 1:1:1, the slow release performance of the whole composite material is optimal. The slow release performance after coating is shown in figure 4: the slow release performance of the composite material is optimal after coating.

Second, testing and analyzing the slow release performance of the compound fertilizer in the soil

The method for researching the slow release performance of the compound fertilizer comprises the steps of preparing 50g of soil, injecting one half of the soil into a soil column device in advance, and injecting the other half of the soil into the device after mixing with the montmorillonite biochar-based urea-coated compound fertilizer with the mass percentage ratio of 1:1:1, 1:2:2 and 1:3:3 respectively. The soil was wetted with 25mL of distilled water as a pre-treatment for the leaching experiments. After standing for 24 hours, a soil leaching experiment is started, 50mL of distilled water is added into a soil column device, the leaching solution is collected by a triangular flask at the lower end of the device, and the total nitrogen content in the leaching solution is measured by an alkaline potassium persulfate method. A total of 6 times was performed by adding 50mL of distilled water to the column every three days. Finally, the cumulative release rate of nitrogen is calculated. And (3) placing the granulated and dried composite material in 10g/L polyvinyl alcohol solution for coating, and further researching the influence of the coating on the slow release performance of the urea.

Through the slow release experimental test of the urea slow release compound fertilizer in the soil, see fig. 2, three sets of parallel controls were required for each treatment by adding 25g of soil into the bottom of the earth pillar device, then mixing the montmorillonite biochar-based urea compound fertilizer with the other 25g of soil and injecting into the earth pillar. Soil is required to be wetted before the experiment, the soil leaching experiment is carried out after the standing for 24 hours, and the total nitrogen content in the leaching solution is measured by using an alkaline potassium persulfate method. Finally, the cumulative release rate of nitrogen is calculated. The results are shown in FIG. 5: when the ratio of montmorillonite to urea to biochar is 1:1:1, the slow release performance is optimal.

In the embodiment, the biochar not only has an adsorption effect on urea, but also is a good soil conditioner, and can enhance the retention of nitrogen in soil and promote the growth of plants. In an aqueous system, when biochar, urea: when the proportion of the montmorillonite is 1:1:1, the equilibrium release rate is 65%, and compared with the release rate of pure urea which is almost 100%, the composite material can improve the slow release performance of the urea. After the polyvinyl alcohol coating, the equilibrium release rate is 57%, which shows that the coating can further enhance the retention of the composite material for urea. In a soil system, when the proportion of the biochar, the urea and the montmorillonite is 1:1:1, the nitrogen accumulation and release rate of the composite material is the lowest. The initial nitrogen release rate is reduced by 14.6 percent compared with pure urea, and the cumulative nitrogen release rate of 18d is 52 percent and is reduced by 20.1 percent compared with pure urea. The slow release performance of the compound fertilizer coated by the polyvinyl alcohol is optimal, and the cumulative release rate of nitrogen at 18 days is only 44.1%. In addition, the above scheme of the above embodiment of the present invention can improve the slow release effect of urea by adding other materials in addition to the above materials and combination basic mode.

The biochar of the embodiment utilizes the porous structure and the larger specific surface area to adsorb urea, and meanwhile, the biochar can be used as a soil conditioner to further enhance the absorption of plants to fertilizers. The addition of the montmorillonite not only enhances the retention of the composite material to urea, but also enhances the stability of the whole material. Finally, the polyvinyl alcohol coating further protects the material, and a layer of coating is formed outside the material to protect urea. Meanwhile, the biochar and the montmorillonite can adsorb other pollutants, and the polyvinyl alcohol can be degraded in soil, so that the environment cannot be polluted while the slow release performance is improved.

Example two:

this embodiment is substantially the same as the first embodiment, and is characterized in that:

in the embodiment, referring to fig. 1, the preparation method of the urea slow-release compound fertilizer, wherein the raw material biochar is prepared by the biochar pyrolysis preparation device shown in fig. 1, and the preparation method is divided into three parts, namely a carrier gas, pyrolysis and tail gas treatment, and comprises a nitrogen cylinder 1, a tubular electric furnace 4 and a flow meter 2. The carrier gas part comprises a nitrogen gas bottle 1 and a flow meter 2, and mainly makes an oxygen-free environment of the pyrolysis process by continuously providing nitrogen gas. The pyrolysis part is the main device of biological charcoal preparation, and this embodiment adopts program temperature controller 3 to control the tubular furnace as the pyrolysis device, and living beings are pyrolyzed into biological charcoal at this part, and tail gas processing part 5 mainly collects and absorbs the waste gas that produces in the pyrolysis process. In step a of the preparation method of the urea slow-release compound fertilizer, the preparation process of the biochar is as follows:

Placing the pretreated clean and dry corn straw biomass in a quartz boat, fully compacting, placing the quartz boat loaded with the biomass in a quartz tube, and placing the quartz tube in a tubular electric furnace; then the quartz tube is connected with a nitrogen bottle, so that the quartz tube is maintained in a nitrogen atmosphere environment, and nitrogen is continuously filled in the whole experiment process so as to achieve the anoxic condition. The nitrogen valve was opened and the entire apparatus was checked for gas tightness before starting the system. Before starting the system, a flow meter is arranged to ensure that the nitrogen introduction amount of the system reaches 120 mL/min. The heating temperature of the tubular furnace is adjusted through the temperature control device, the required charcoal pyrolysis temperature is maintained, after the pyrolysis process is finished, the temperature control device is automatically closed, the quartz boat is taken out of the quartz tube after the temperature is cooled to reach the room temperature, the pyrolysis product is ground, and after the product is sieved, charcoal powder is obtained and is stored in a sealed mode.

In the embodiment, the biochar is prepared from the corn straws, and comprehensive environmental protection benefits are realized by recycling waste.

By combining the above embodiments, the embodiments of the present invention relate to a method for preparing coated urea, and belong to the field of fertilizers. Urea is currently one of the most widely used nitrogen fertilizers, but since urea reacts relatively rapidly after application to soil, it releases nutrients relatively quickly during the conversion of urea in soil, and most plants require less nutrients during the early stages of growth, resulting in low plant availability. The nutrients produced by the rapid reaction also face problems, such as ammonium ions and nitrate ions, wherein the nitrate ions mainly cause leaching loss under rainwater or irrigation, the ammonium nitrogen mainly reacts to generate ammonia gas to volatilize and cause loss, and the ammonium nitrogen also easily generates nitrate nitrogen to cause leaching loss. In the above embodiment of the present invention, Urea (Urea), Biochar (Biochar), and montmorillonite (MMT) are sieved, and then mixed with water at three different ratios (Urea: Biochar: montmorillonite: 1:1:1, 2:2:1, and 3:3:1) for use. At normal temperature, a granulator is used to extrude the mixture soft materials in three proportions through a screen with a fixed aperture under the action of mechanical force, and then a polymer with a certain height is formed by granulation. And placing the granulated mixture in a dark place for drying to obtain the Biochar/Urea/MMT compound fertilizer with the thickness of 0.5-1 mm. The above embodiments of the present invention are directed to achieving sustained release by reducing the rate of release of urea. The biochar adsorbs urea by utilizing a porous structure and a large specific surface area of the biochar, and can further enhance the absorption of plants to fertilizers as a soil conditioner. The addition of montmorillonite enhances the retention of urea while also enhancing the stability of the overall material. Finally, the material is further protected by utilizing a polyvinyl alcohol coating, and a layer of coating is formed outside the material to protect the urea.

The embodiments of the present invention have been described with reference to the accompanying drawings, but the present invention is not limited to the embodiments, and various changes and modifications can be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention shall be equivalent substitutions, as long as the purpose of the present invention is met, and the present invention shall fall within the protection scope of the present invention without departing from the technical principle and inventive concept of the present invention.

Claims

1. A slow-release urea compound fertilizer is characterized in that: the urea composite material is prepared by taking urea, biochar, montmorillonite and polyvinyl alcohol as raw materials and performing the processes of uniformly mixing, granulating and drying, wherein the biochar adsorbs the urea by utilizing the porous structure and the larger specific surface area of the biochar, and is used as a carrier of the urea and combined with the urea to form urea composite material particles; montmorillonite is used as a retention agent for enhancing the urea composite material to urea, and the composite particle structure of the urea composite material is stabilized; polyvinyl alcohol is often used as a coating material, and a composite material formed by mixing urea, biochar and montmorillonite is subjected to film encapsulation to obtain coated urea particles, so that the urea slow-release compound fertilizer is obtained.

2. The slow release compound urea fertilizer as claimed in claim 1, wherein: the mixing mass percentage ratio of montmorillonite, urea and biochar is 1 (1-3) to 1-3.

3. The slow release compound urea fertilizer as claimed in claim 2, wherein: the mixing mass percentage ratio of montmorillonite, urea and biochar is 1:1: 1.

4. A preparation method of a urea slow-release compound fertilizer is characterized by comprising the following steps:

a. preparing ingredients:

b. pretreatment of raw materials:

c. and (3) granulation:

d. Urea coating treatment:

5. The method for preparing the slow-release compound urea fertilizer as claimed in claim 4, wherein in the step d, the compound fertilizer granular materials are put into a reagent bottle filled with the polyvinyl alcohol solution, are placed in a constant-temperature shaking box for at least 10min, are dried and are subjected to coating treatment, and thus finished coated urea granular fertilizer is obtained.

6. The method for preparing the slow-release urea compound fertilizer as claimed in claim 4, wherein in the step a, the biochar is prepared by the following steps: