Slow-release selenium-rich nitrogen fertilizer and preparation method thereof

Abstract

The invention discloses a slow-release selenium-rich nitrogen fertilizer and a preparation method thereof in the technical field of functional fertilizer production, and the slow-release selenium-rich nitrogen fertilizer comprises the following raw materials in parts by weight: 7.5-10 parts of urea, 7-9 parts of formaldehyde, 0.01-0.5 part of chitosan, 0.1-0.8 part of phosphoric acid, 0.01-0.1 part of sodium selenite, 0.01-0.1 part of seleninic acid and 0.03-0.3 part of ascorbic acid. The technical design is novel, the preparation method is simple, the preparation reaction process is carried out at normal temperature and normal pressure, and all the used raw materials are converted into products; the nitrogen element and the selenium element in the slow-release selenium-rich nitrogen fertilizer both show a good slow-release effect, so that the slow-release selenium-rich nitrogen fertilizer can promote crop growth, increase the content of selenium in agricultural products and improve the quality of the agricultural products.

Description

Technical Field

[0001] The present invention relates to the technical field of functional fertilizer production, and specifically relates to a slow-release selenium-rich nitrogen fertilizer and a preparation method thereof. Background Art

[0002] Ordinary chemical fertilizers are easily soluble and decomposable, and a large amount of their nutrients are lost into the air and water bodies through leaching, volatilization and other ways, which not only causes huge economic losses but also pollutes the ecological environment. Moreover, due to the phenomenon of "burning seedlings" caused by excessive application, the soil aggregate structure will also be damaged. Therefore, ordinary chemical fertilizers must be applied in small amounts and multiple times, which is time-consuming and laborious and increases production costs. The main way to improve the utilization rate of chemical fertilizers and reduce environmental pollution is to apply slow-release fertilizers.

[0003] Slow-release fertilizers can slowly release nutrients, improve nutrient utilization rate, reduce economic costs, reduce environmental pollution, and can also improve the soil. However, the common problems of current slow-release fertilizers are complex preparation processes and high production costs. Not only are the auxiliary materials used difficult to degrade, but organic solvents are also required in the production process, thus increasing the environmental burden. Therefore, there is an urgent need to develop slow-release fertilizers with simple processes and environmental friendliness. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a slow-release selenium-rich nitrogen fertilizer and a preparation method thereof to solve the problems raised in the above background art.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A slow-release selenium-rich nitrogen fertilizer, comprising the following raw materials in parts by weight: 7.5 - 10 parts of urea, 7 - 9 parts of formaldehyde, 0.01 - 0.5 parts of chitosan, 0.1 - 0.8 parts of phosphoric acid, 0.01 - 0.1 parts of sodium selenite, 0.01 - 0.1 parts of selenious acid, 0.03 - 0.3 parts of ascorbic acid, wherein the concentration of formaldehyde is 37%.

[0007] Preferably, it comprises the following raw materials in parts by weight: 8 - 10 parts of urea, 8 parts of formaldehyde, 0.1 - 0.3 parts of chitosan, 0.3 - 0.5 parts of phosphoric acid, 0.05 - 0.1 parts of sodium selenite, 0.03 - 0.08 parts of selenious acid, 0.05 - 0.1 parts of ascorbic acid, wherein the concentration of formaldehyde is 37%.

[0008] Preferably, it comprises the following raw materials in parts by weight: 8.5 parts of urea, 8 parts of formaldehyde, 0.1 part of chitosan, 0.05 parts of sodium selenite, 0.05 parts of selenious acid, 0.08 parts of ascorbic acid, wherein the concentration of formaldehyde is 37%.

[0009] A preparation method of a slow-release selenium-rich nitrogen fertilizer, the preparation method comprising the following steps

[0010] Step 1: Add urea into the formaldehyde solution, stir until the urea is completely dissolved, dropwise add the sodium selenite solution, stir evenly, and let it stand at room temperature for 1.5 - 2 hours;

[0011] Step 2: Add the selenious acid solution containing chitosan into the reaction solution, stir well, and let it stand at room temperature for 10 - 20 minutes;

[0012] Step 3: Add the aqueous solution of ascorbic acid, stir well, let it stand for 1 hour to obtain a light red viscous product, dry it at 60 °C, and pulverize it to obtain the product.

[0013] Preferably, the room temperature is 25 °C.

[0014] Preferably, the sodium selenite solution provides an alkaline environment for the addition reaction in Step 1.

[0015] Preferably, the selenious acid solution containing chitosan provides an acidic environment for the condensation reaction in Step 2.

[0016] Advantages of the present invention:

[0017] The technical design of the present invention is novel, the preparation method is simple, the preparation reaction process is carried out under normal temperature and pressure, all the raw materials used are converted into products, the reaction conditions are easy to control, and there will be no "explosive polymerization" phenomenon to form urea - formaldehyde resin. The synthesis process is environmentally friendly, without waste gas and waste generation;

[0018] In the slow - release selenium - rich nitrogen fertilizer product of the present invention, the selenium element mainly exists in the form of amorphous nano - selenium, and the nano - selenium is coated by urea - formaldehyde and chitosan. The nano - selenium will not agglomerate and crystallize after long - term storage. In fertilizer application, the nano - selenium gradually releases selenium elements as the urea - formaldehyde molecules decompose. Both the nitrogen element and the selenium element in the obtained product show good slow - release effects, which can promote crop growth, increase the selenium content in agricultural products, and improve the quality of agricultural products; in addition, all components in the obtained product can be completely decomposed, and long - term application will not cause environmental pollution, and it has the functions of improving soil and enhancing the disease - resistance ability of crops; the obtained slow - release selenium - rich nitrogen fertilizer can be used to produce various selenium - rich agricultural products; it can be applied alone or mixed with organic fertilizer or inorganic fertilizer in a certain proportion to form a compound fertilizer for application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 It is the electron micrograph of a typical product in the present invention;

[0021] Figure 2 is the electron diffraction pattern of a typical product in the present invention;

[0022] Figure 3 is the dissolution curve of a typical product in the present invention Figure 1 ;

[0023] Figure 4 is the dissolution curve of a typical product in the present invention Figure 2 。 Detailed implementation manners

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0025] The present invention provides a slow-release selenium-rich nitrogen fertilizer and its preparation method. Selenium elements are added during the preparation of urea formaldehyde to form a selenium-rich slow-release nitrogen fertilizer. First, determine the form and method of adding selenium elements during the condensation reaction of formaldehyde and urea; then determine the reaction conditions of the synthesis system, including the pH value, reaction temperature, reaction time, etc. of the reaction solution; finally, determine the existing forms of nitrogen elements and selenium elements in the final product.

[0026] Currently, common methods use inorganic acids such as acetic acid and hydrochloric acid to dissolve chitosan. The present invention uses selenious acid to dissolve chitosan and adds it to the reaction system when an acidic catalyst is needed. In this way, not only the solubility problem of chitosan is solved, but also selenium elements and chitosan are introduced into the reaction system.

[0027] The slow-release selenium-rich nitrogen fertilizer to be prepared by the present invention involves the following three main components: urea formaldehyde, selenium elements, and chitosan;

[0028] Among them, urea formaldehyde slow-release fertilizer is a chain-type condensate formed by the condensation of urea and formaldehyde under certain conditions, and it is a slow-release nitrogen fertilizer with the earliest research and the largest usage. Compared with urea, urea formaldehyde fertilizer can reduce nitrogen loss by 37%. The ratio of urea to formaldehyde must be controlled within a certain range. The first addition reaction of the condensation reaction requires using a basic catalyst to control the reaction solution within a certain alkaline range, and the second polycondensation reaction requires using an acidic catalyst to control the reaction solution within a certain acidic range. In addition, the temperature and reaction time of the reaction solution must be strictly controlled, so as to obtain a slow-release nitrogen fertilizer with "limited polymerization" of urea and formaldehyde;

[0029] Selenium has multiple biological functions and is an essential trace element for the human body. Inorganic selenium is highly toxic, and the preparation process of organic selenium is complex. Applying selenium-rich fertilizers to increase the biological selenium content in agricultural products is a safe and effective way to solve the problem of selenium deficiency in humans. Moreover, adding selenium to fertilizers can also inhibit the absorption of harmful elements such as cadmium by crops;

[0030] Chitosan is a product obtained by partially or completely deacetylating chitin. It is a natural amino polysaccharide compound. When applied as a fertilizer, chitosan can be completely decomposed by soil organisms, and the nutrients such as nitrogen produced can be absorbed by crops. Chitosan has antibacterial and antifungal effects, can enhance the disease resistance of crops, and is known as the "plant vaccine". Chitosan can change the soil microflora, promote the growth of beneficial microorganisms, increase the soil aggregate structure, and improve the soil quality. In addition, the molecular chain of chitosan contains abundant polar groups such as hydroxyl and amino groups, which have the function of chelating divalent metal ions and can reduce the absorption of heavy metal ions by crops.

[0031] Example 1:

[0032] A slow-release selenium-rich nitrogen fertilizer, which comprises the following raw materials in parts by weight: 7.5 parts of urea, 9 parts of formaldehyde (37%), 0.01 - 0.1 part of chitosan, 0.01 - 0.05 part of sodium selenite, 0.01 - 0.1 part of selenious acid, and 0.05 - 0.2 part of ascorbic acid.

[0033] A preparation method of selenium-rich slow-release nitrogen fertilizer, comprising the following steps:

[0034] Step 1: Add urea to the formaldehyde solution, stir to completely dissolve the urea, dropwise add the sodium selenite solution, stir evenly, and let it stand at room temperature (25°C) for 1.5 - 2 hours;

[0035] Step 2: Add the selenious acid solution containing chitosan to the reaction solution, stir well, and let it stand at room temperature (25°C) for 10 - 2oth minutes;

[0036] Step 3: Add the ascorbic acid aqueous solution, stir well, let it stand for 1 hour to obtain a light red viscous product. Dry it at 60°C and pulverize it to obtain the product.

[0037] To obtain selenium-rich products, soluble inorganic selenium compounds are added to the condensation reaction system of urea and formaldehyde. Specifically, there are two ways to add: 1. In the first addition reaction, add the sodium selenite solution; 2. In the second condensation reaction, add the selenious acid solution; Considering that both sodium selenite and selenious acid are highly water-soluble compounds, in order to reduce the loss of selenium, a reducing agent is added during the preparation process to reduce most of the selenium to insoluble nano-selenium, and the remaining small part of tetravalent selenium is also adsorbed and encapsulated, with slow-release properties.

[0038] Sodium selenite solution is added in the step 1 reaction of urea and formaldehyde. Sodium selenite provides an alkaline environment for the addition reaction. As the reaction proceeds, selenite ions are adsorbed and wrapped by the generated chain-like condensate molecules and stably exist in the solution.

[0039] In the step 2 reaction of urea and formaldehyde, selenious acid solution containing chitosan is added. Selenious acid provides an acidic environment for the condensation reaction. The functions of introducing chitosan are as follows: 1. Chitosan (existing in the form of cations in acidic solution) can combine with hydrogen selenite anions in the reaction solution to form a stable complex, and can adsorb and stabilize the later formed nano-selenium particles; 2. Chitosan undergoes a cross-linking reaction with the residual formaldehyde in the solution, reducing the environmental pollution caused by formaldehyde; 3. The abundant amino and hydroxyl groups on the chitosan molecule can form hydrogen bonds with the ureido group, destroying the regularity of the intermolecular chain arrangement structure of urea-formaldehyde and reducing the crystallinity of urea-formaldehyde molecules, thereby preventing the formation of urea-formaldehyde resin that is extremely difficult to decompose.

[0040] Ascorbic acid is added in step 3. The functions of introducing ascorbic acid are as follows: 1. Ascorbic acid not only acts as a reducing agent to reduce selenite to nano-selenium, but also acts as an acidic catalyst to accelerate the urea-formaldehyde condensation reaction, enabling the condensation process to be completed quickly; 2. At this time, the selenite ions in the reaction solution have been adsorbed and wrapped by the macromolecules of urea-formaldehyde condensate or chitosan macromolecules. Therefore, the reduction reaction proceeds in situ on the macromolecules, and the generated nano-selenium particles will be immediately adsorbed and wrapped by the macromolecules and stably exist in the system, thus avoiding the phenomenon of nano-selenium particles agglomerating to form large particles.

[0041] Example 2:

[0042] A slow-release selenium-rich nitrogen fertilizer, which comprises the following raw materials in parts by weight: 8.5 parts of urea, 8.5 parts of formaldehyde (37%), 0.01 - 0.1 part of chitosan, 0.1 - 0.5 part of phosphoric acid, 0.01 - 0.05 part of sodium selenite, 0.01 - 0.08 part of ascorbic acid.

[0043] A preparation method of selenium-rich slow-release nitrogen fertilizer, comprising the following steps:

[0044] Step 1: Add urea to the formaldehyde solution, stir until the urea is completely dissolved, dropwise add sodium selenite solution, stir evenly, and let it stand at room temperature (25°C) for 1.5 - 2 hours;

[0045] Step 2: Add phosphoric acid solution containing chitosan to the reaction solution, stir well, and let it stand at room temperature (25°C) for 5 - 10 minutes;

[0046] Step 3: Add ascorbic acid aqueous solution, stir well, let it stand for 1 hour to obtain a light red viscous product. Dry it at 60°C and pulverize to obtain the product.

[0047] Example 3:

[0048] A slow-release selenium-enriched nitrogen fertilizer, which comprises the following raw materials in parts by weight: 9.5 parts of urea, 8 parts of formaldehyde (37%), 0.1-0.5 part of chitosan, 0.01-0.05 part of sodium selenite, 0.01-0.1 part of selenious acid, and 0.06-0.15 part of ascorbic acid.

[0049] A preparation method of selenium-enriched slow-release nitrogen fertilizer, comprising the following steps:

[0050] Step 1: Add urea to the formaldehyde solution, stir to completely dissolve the urea, dropwise add the sodium selenite solution, stir evenly, and let stand at room temperature (25°C) for 1.5-2 hours;

[0051] Step 2: Add the selenious acid solution containing chitosan to the reaction solution, stir well, and let stand at room temperature (25°C) for 10-20 minutes;

[0052] Step 3: Add the ascorbic acid aqueous solution, stir well, let stand for 1 hour to obtain a light red viscous product. Dry at 60°C and pulverize to obtain the product.

[0053] Example 4:

[0054] A slow-release selenium-enriched nitrogen fertilizer, which comprises the following raw materials in parts by weight: 10 parts of urea, 7 parts of formaldehyde (37%), 0.1-0.5 part of chitosan, 0.2-0.8 part of phosphoric acid, 0.01-0.05 part of sodium selenite, and 0.01-0.08 part of ascorbic acid.

[0055] A preparation method of selenium-enriched slow-release nitrogen fertilizer, comprising the following steps:

[0056] Step 1: Add urea to the formaldehyde solution, add an appropriate amount of water to completely dissolve the urea, stir evenly, dropwise add the sodium selenite solution, stir evenly, and let stand at room temperature (25°C) for 1.5-2 hours;

[0057] Step 2: Add the phosphoric acid solution containing chitosan to the reaction solution, stir well, and let stand at room temperature (25°C) for 5-10 minutes;

[0058] Step 3: Add the ascorbic acid aqueous solution, stir well, let stand for 1 hour to obtain a light red viscous product. Dry at 60°C and pulverize to obtain the product.

[0059] The electron micrograph of the typical product is as Figure 1 shown, and it can be seen from Figure 1 that the black nano-selenium particles are dispersed and encapsulated in macromolecules such as urea-formaldehyde, and the particle size is about 10-80 nanometers. Different particle sizes result in different solubilities, which is helpful for slow release; Figure 2 This is the electron diffraction pattern of the typical product. It can be seen from Figure 2It is known that nano-selenium is an amorphous particle; Figure 3 , Figure 4 is the dissolution curve of a typical product. It can be seen from the curve that both nitrogen and selenium elements have good slow-release properties. The measured product activity index is 54%-68%, meeting the requirements of slow-release fertilizers.

[0060] In the preparation method of the present invention, the entire preparation process is carried out at normal temperature and pressure. The process is simple, the reaction conditions are easy to control, and there will be no "explosive polymerization" phenomenon to form urea-formaldehyde resin. The synthesis process is environmentally friendly, and all raw materials used are converted into products without the generation of waste and waste gas. In the obtained slow-release selenium-rich nitrogen fertilizer product, the selenium element mainly exists in the form of amorphous nano-selenium, and the nano-selenium is coated with urea-formaldehyde and chitosan. Nano-selenium will not agglomerate and crystallize after long-term storage. In the application of fertilizers, nano-selenium gradually releases selenium elements as the urea-formaldehyde molecules decompose. Therefore, like the nitrogen element, the selenium element has a good slow-release effect;

[0061] In addition, all components in the obtained product can be completely decomposed, and long-term application will not cause environmental pollution. Moreover, it has the effects of improving soil and enhancing the disease resistance of crops. The obtained slow-release selenium-rich nitrogen fertilizer can be used to produce various selenium-rich agricultural products. It can be applied alone or mixed with organic fertilizers or inorganic fertilizers in a certain proportion to form compound fertilizers for application.

[0062] In the description of this specification, the description with reference to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent substitutions can still be made to the specific implementation manners of the present invention. Any modification or equivalent substitution that does not depart from the spirit and scope of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A slow-release selenium-rich nitrogen fertilizer, characterized in that, It includes the following raw materials by weight: 7.5 - 10 parts of urea, 7 - 9 parts of formaldehyde, 0.01 - 0.5 part of chitosan, 0.1 - 0.8 part of phosphoric acid, 0.01 - 0.1 part of sodium selenite, 0.01 - 0.1 part of selenious acid, 0.03 - 0.3 part of ascorbic acid, wherein the concentration of formaldehyde is 37%.

2. The slow-release selenium-rich nitrogen fertilizer according to claim 1, characterized in that It includes the following raw materials by weight: 8 - 10 parts of urea, 8 parts of formaldehyde, 0.1 - 0.3 part of chitosan, 0.3 - 0.5 part of phosphoric acid, 0.05 - 0.1 part of sodium selenite, 0.03 - 0.08 part of selenious acid, 0.05 - 0.1 part of ascorbic acid, wherein the concentration of formaldehyde is 37%.

3. A slow-release selenium-rich nitrogen fertilizer according to claim 1, characterized in that, It includes the following raw materials by weight: 8.5 parts of urea, 8 parts of formaldehyde, 0.1 part of chitosan, 0.05 part of sodium selenite, 0.05 part of selenious acid, 0.08 part of ascorbic acid, wherein the concentration of formaldehyde is 37%.

4. A method for preparing a slow-release selenium-enriched nitrogen fertilizer according to any one of claims 1 to 3, characterized in that, The preparation method includes the following steps Step 1: Add urea to the formaldehyde solution, stir until the urea is completely dissolved, dropwise add the sodium selenite solution, stir evenly, and let it stand at room temperature for 1.5 - 2 hours; Step 2: Add the selenious acid solution containing chitosan to the reaction solution, stir well, and let it stand at room temperature for 10 - 20 minutes; Step 3: Add the ascorbic acid aqueous solution, stir well, let it stand for 1 hour to obtain a light red viscous product, dry it at 60°C, and pulverize it to obtain the product.

5. The preparation method of a slow-release selenium-rich nitrogen fertilizer according to claim 4, characterized in that, The room temperature is 25°C.

6. The preparation method of a slow-release selenium-rich nitrogen fertilizer according to claim 4, wherein, The sodium selenite solution provides an alkaline environment for the addition reaction in Step 1.

7. The preparation method of a slow-release selenium-rich nitrogen fertilizer according to claim 4, characterized in that, The selenious acid solution containing chitosan provides an acidic environment for the condensation reaction in Step 2.

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