Multifunctional hydrogel microbead with water retention and fertilizer retention functions and preparation method of multifunctional hydrogel microbead

Abstract

The invention provides a multifunctional hydrogel microbead with water retention and fertilizer retention functions and a preparation method of the multifunctional hydrogel microbead. The multifunctional hydrogel microbead provided by the invention is prepared from various raw materials such as sodium alginate, humic acid, microalgae and a compound phosphate fertilizer, the hydrogel microbead with high water absorption and phosphorus slow release property is formed by cross-linking and reaction combination among the components, and meanwhile, due to the addition of humic acid and microbial components, the interaction among the materials can be promoted; therefore, the material has the functions of soil conditioning and the like, and has a certain effect of improving the water-retaining property of soil and the effectiveness of phosphate fertilizer. The hydrogel microsphere prepared by the invention is wide in raw material source, low in cost, safe and harmless, and simple in preparation process, has high water absorption and water retention property and fertilizer slow release function, and can effectively improve soil, increase the water retention property of the soil and the effectiveness of a phosphate fertilizer, and reduce the loss of water and fertility of the soil.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hydrogel and soil remediation, and particularly relates to a multifunctional hydrogel microsphere with water retention and fertilizer retention and a preparation method thereof. BACKGROUND

[0002] With the rapid development of agricultural economy, the utilization rate of soil is gradually increasing, but this high-intensity and high-frequency utilization also brings a series of serious problems to the soil. For the soil which is extremely short of water and poor in water and fertilizer retention, a high water and fertilizer retention agent is needed, which has high requirements for the types of raw materials. Generally, the water retention agent is mainly a superabsorbent polymer derived from a physically or chemically cross-linked polymer. Due to its porous structure and abundant hydrophilic groups, it can absorb and store a large amount of water for the soil to use. However, the superabsorbent polymer currently used mainly comes from petrochemical products, which is not only expensive, but also has poor degradability when applied to soil, is easy to cause environmental hazards, and there are few products with both water retention and fertilizer retention functions, so the application is limited.

[0003] Sodium alginate is a polysaccharide biomacromolecule extracted from brown algae or sargassum after iodine and mannitol, which has no toxicity, good biocompatibility and gelation characteristics, etc., and can be cross-linked with divalent metal cations (commonly used Ca 2+ ) to form a lattice structure. After drying or carbonization under specific conditions, a gel ball can be obtained. This structure has a certain swelling property, so it is often used as a slow-release agent outer packaging material and applied to the field of soil or water pollution control. At present, there are many studies on the preparation of gel balls using sodium alginate, but most of them use traditional methods, and the prepared gel balls have single function and limited application range. SUMMARY

[0004] In order to solve the defects in the prior art, the present application provides a multifunctional hydrogel microsphere with water retention and fertilizer retention and a preparation method thereof. The present application mixes humic acid, yeast and sodium alginate, which not only improves the water absorption and retention performance of the material, but also improves the form of phosphorus in the soil by using the complexation of humic acid and phosphorus and the phosphorus absorption of yeast cells, and increases the content and proportion of slow-release phosphorus and available phosphorus. Further, the above mixed product is compounded with compound phosphorus fertilizer, and the slow release of phosphorus in the soil is realized by using the barrier effect of cell wall, the complexation and the slow release effect of gel ball, and the availability of phosphorus fertilizer is increased. The hydrogel microsphere prepared by the present application has the functions of water retention, fertilizer retention and conditioning, and the raw materials used have good biocompatibility and are safe to the environment.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] In a first aspect, the present application provides a method for preparing multifunctional hydrogel microbeads with water and fertilizer conservation, comprising the following steps:

[0007] dispersing humic acid and yeast in a sodium alginate aqueous solution to obtain a first mixed suspension;

[0008] dispersing compound phosphate fertilizer in the first mixed suspension to obtain a second mixed suspension;

[0009] injecting the second mixed suspension into a calcium ion-containing solution, filtering to obtain compound phosphate fertilizer slow-release microbeads;

[0010] immersing the compound phosphate fertilizer slow-release microbeads in a chloroacetic acid solution, adjusting the pH to 7-9, stirring, filtering to obtain multifunctional hydrogel microbeads with water and fertilizer conservation.

[0011] Preferably, the humic acid and yeast are dispersed in the sodium alginate aqueous solution, stirred at 16-25°C and 550-650 rpm for 2-3 h to obtain the first mixed suspension.

[0012] Preferably, the compound phosphate fertilizer is dispersed in the first mixed suspension, stirred at 16-25°C and 550-650 rpm for 1-2 h to obtain the second mixed suspension.

[0013] Preferably, the compound phosphate fertilizer comprises superphosphate, triple superphosphate, and potassium dihydrogen phosphate.

[0014] The mass ratio of the potassium dihydrogen phosphate, superphosphate, and triple superphosphate is (1-2):(1-3):(0-2).

[0015] Preferably, the second mixed suspension is injected into the calcium ion-containing solution using a syringe pump with a needle diameter of 1-1.5 mm, stirred at 200-250 rpm and 16-25°C for 45-60 min, left standing for 2-3 h, filtered, and washed to obtain the compound phosphate fertilizer slow-release microbeads.

[0016] Preferably, the compound phosphate fertilizer slow-release microbeads are immersed in the chloroacetic acid solution, the pH is adjusted to 7-9, stirred at 60-200 rpm and 16-25°C for 8-11 h, filtered, washed to neutral, and dried to obtain the multifunctional hydrogel microbeads with water and fertilizer conservation.

[0017] Preferably, the mass concentration of the sodium alginate aqueous solution is 1-2%.

[0018] The mass concentration of the calcium ion-containing solution is 2-4%.

[0019] The concentration of the chloroacetic acid solution is 0.2-0.5 mol / L.

[0020] The calcium ion-containing solution comprises at least one of CaCl2 solution, CaSO4 solution, Ca(NO)3 solution, and phosphogypsum leaching solution.

[0021] Preferably, the mass-volume ratio of the humic acid, yeast, sodium alginate aqueous solution, compound phosphate fertilizer, and calcium ion-containing solution is (2-5) g:(1-3) g:(5-8) g:(1-4) g:(100-250) mL.

[0022] Preferably, the compound phosphate fertilizer slow-release microbeads are soaked in a chloroacetic acid solution, 0.02-0.1 mol / L sodium hydroxide aqueous solution is used to adjust the pH to 7-9, stirring, filtration, and a multifunctional hydrogel microbead with water-retention and fertilizer-retention is obtained.

[0023] In the second aspect, the application further provides a multifunctional hydrogel microbead with water-retention and fertilizer-retention, which is prepared by the preparation method.

[0024] The multifunctional hydrogel microbead with water-retention and fertilizer-retention and the preparation method thereof have the following effects compared with the prior art:

[0025] 1. The preparation method of the multifunctional hydrogel microbead with water-retention and fertilizer-retention utilizes the mixing of humic acid, yeast, and sodium alginate, which not only improves the water absorption and water retention performance of the material, but also improves the existing form of phosphorus in the soil by utilizing the complexation of humic acid and phosphorus and the phosphorus absorption of yeast cells, and increases the content and proportion of slow-release phosphorus and effective phosphorus; further, the mixing product is compounded with a compound phosphate fertilizer, the slow release of phosphorus in the soil is realized by utilizing the barrier effect of the cell wall, the complexation, and the slow release effect of the gel ball, and the effectiveness of the phosphate fertilizer is increased.

[0026] 2、The prepared hydrogel microspheres of the application have the three functions of water retention, fertilizer retention and conditioning (conditioning soil), and the raw materials used all have good biocompatibility and are safe and harmless to the environment; the application obtains a second mixed suspension by mixing the composite phosphorus fertilizer with the first mixed suspension containing a sodium alginate aqueous solution, injects the second mixed suspension into a calcium ion-containing solution, the sodium alginate aqueous solution forms a sodium alginate gel after crosslinking with calcium ions, the loading of the composite phosphorus fertilizer is realized by means of this gelation process, and the gel microsphere structure is constructed; by utilizing the structural characteristics of the gel microspheres, the release rate of the phosphorus fertilizer in the soil can be effectively reduced, and the action time is prolonged; at the same time, the mixing of the composite phosphorus fertilizer and the sodium alginate can also effectively improve the mechanical strength and structural stability of the sodium alginate gel microspheres; the carboxylation modification of the composite phosphorus fertilizer slow-release hydrogel microspheres by chloroacetic acid loads more carboxyl groups on the gel microspheres, improves the water absorption units in the gel microspheres, and further improves the water absorption and swelling properties of the microspheres; the addition of humic acid and yeast fills the large-area cavities inside the microspheres, provides more action sites for crosslinking, and the carboxylation modification and the filler jointly form the cavities inside the microspheres, which are uniform in size, uniform in distribution and tortuous in channel, can provide more space for water molecules and effectively prevent the rapid release of water molecules.

[0027] 3、The application is based on the three purposes of water retention, fertilizer retention and conditioning, and humic acid and yeast are blended in the hydrogel microspheres, and the synergistic effect between the components enhances the effect of the material in water retention, fertilizer retention and conditioning. Humic acid can not only adjust the soil acid-base environment and the activity of nutrient elements by using its own characteristics, but also provide substrates for soil and microbial enzyme activities; yeast can secrete various enzymes during the mixing process with humic acid, accelerating the conversion of organic matter; humic acid and yeast both contain a large number of hydrophilic functional groups, which can improve the overall water retention, and can also promote the activation of nutrient elements during contact with the gel microspheres. DETAILED DESCRIPTION

[0028] In order to facilitate the understanding of the application, the application will be described more fully below with reference to specific embodiments. The preferred embodiments of the application are given in the specific embodiments. However, the application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the application more thorough and comprehensive.

[0029] The order in which the embodiments are described below is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0030] This invention provides a method for preparing multifunctional hydrogel microspheres that combine water retention and fertilizer retention, comprising the following steps:

[0031] Humic acid and yeast were dispersed in an aqueous solution of sodium alginate to obtain a first mixed suspension;

[0032] The compound phosphate fertilizer is dispersed in the first mixed suspension to obtain the second mixed suspension;

[0033] The second mixed suspension was injected into a calcium ion-containing solution and filtered to obtain compound phosphate fertilizer slow-release microbeads.

[0034] The compound phosphate fertilizer slow-release microbeads were soaked in chloroacetic acid solution, the pH was adjusted to 7-9, stirred, and filtered to obtain multifunctional hydrogel microbeads that have both water retention and fertilizer retention properties.

[0035] The multifunctional hydrogel microspheres provided by this invention are made from a variety of raw materials, including sodium alginate, humic acid, microalgae, and compound phosphate fertilizer. The cross-linking and reaction between these components forms hydrogel microspheres with high water absorption and slow-release phosphate properties. Furthermore, the addition of humic acid and microbial components promotes the interaction between the materials, thus giving the material soil conditioning functions as well. This improves soil water retention and phosphate fertilizer effectiveness. The hydrogel microspheres prepared by this invention use widely available, low-cost, safe, and harmless raw materials, and the preparation process is simple. They possess high water absorption and retention capabilities, as well as slow-release phosphate fertilizer properties, effectively improving soil, increasing soil water retention and phosphate fertilizer effectiveness, and reducing soil moisture and fertility loss.

[0036] The preparation method of the multifunctional water gel microbeads with water and fertilizer preservation of the application utilizes the mixing of humic acid, yeast and sodium alginate, which can not only improve the water absorption and water retention performance of the material, but also improve the form of phosphorus in the soil, increase the content and proportion of slow-release phosphorus and available phosphorus by using the complexation of humic acid and phosphorus and the phosphorus absorption of yeast cells; further, the above mixed product is compounded with compound phosphorus fertilizer, and the slow release of phosphorus in the soil is realized by using the barrier effect, complexation of cell wall and the slow release effect of gel ball, and the availability of phosphorus fertilizer is increased.

[0037] Humic acid is a kind of organic matter formed by the decomposition and transformation of plant and animal remains by microorganisms, which contains rich functional groups, can promote the formation of soil aggregate structure, improve soil permeability and water retention, promote nutrient absorption, and stabilize soil pH. Mixing it with phosphorus fertilizer and other fertilizers can also reduce the fixation of soil to fertilizer elements through complexation, thereby achieving the purpose of slow release of fertilizer effect; yeast is a kind of aquatic single-celled eukaryote, which has a large number of hydrophilic functional groups, including amide group, phosphate group, amine, carboxyl group and hydroxyl group, which can provide a large number of hydrophilic groups, thereby improving the water absorption and water retention capacity of the material.

[0038] The prepared water gel microbeads of the application have the functions of water retention, fertilizer preservation and conditioning (soil conditioning), and the raw materials used have good biocompatibility and are safe and harmless to the environment; the application mixes the compound phosphorus fertilizer with the first mixed suspension containing sodium alginate solution to obtain the second mixed suspension, and injects the second mixed suspension into a calcium ion-containing solution; after the crosslinking of the sodium alginate solution with calcium ions, sodium alginate gel is formed, and by means of this gelation process, the loading of the compound phosphorus fertilizer is realized, and the gel microbead structure is constructed; by utilizing the structural characteristics of the gel microbead, the release rate of the phosphorus fertilizer in the soil can be effectively reduced, and the action time can be prolonged; at the same time, by mixing the compound phosphorus fertilizer with sodium alginate, the mechanical strength and structural stability of the sodium alginate gel microbead can be effectively improved; by carboxylating modification of the compound phosphorus fertilizer slow-release water gel microbead with chloroacetic acid, more carboxyl groups are loaded on the gel microbead, the water absorption unit in the gel microbead is improved, and the water absorption and swelling performance of the microbead is further improved; the addition of humic acid and yeast fills the large-area cavities inside the microspheres, providing more action sites for crosslinking. The carboxylation modification and the filler jointly form the cavities inside the microspheres, which are uniform in size, uniform in distribution and tortuous in channel, which can not only provide more space for water molecules but also effectively prevent their rapid release.

[0039] The present application is based on the three purposes of water retention, fertilizer retention and conditioning, humic acid and yeast are blended in hydrogel microbeads, and the synergistic effect between the components enhances the effect of the material in water retention, fertilizer retention and conditioning. Humic acid can not only adjust the soil acid-base environment and nutrient element activity by its own characteristics, but also provide substrates for soil and microbial enzyme activity; yeast can secrete various enzymes during the mixing process with humic acid, accelerating the transformation of organic matter; humic acid and yeast both contain a large number of hydrophilic functional groups, which can improve the overall water retention, and can also promote the activation of nutrient elements during the contact with the gel microbeads.

[0040] In some embodiments, humic acid and yeast are dispersed in a sodium alginate aqueous solution, stirred at 16-25℃ and 550-650rpm for 2-3h to obtain a first mixed suspension.

[0041] In some embodiments, the composite phosphorus fertilizer is dispersed in the first mixed suspension, stirred at 16-25℃ and 550-650rpm for 1-2h to obtain a second mixed suspension.

[0042] In some embodiments, the composite phosphorus fertilizer includes superphosphate, triple superphosphate and potassium dihydrogen phosphate;

[0043] The mass ratio of potassium dihydrogen phosphate, superphosphate and triple superphosphate is (1-2):(1-3):(0-2).

[0044] In some embodiments, the second mixed suspension is injected into a calcium ion-containing solution using a syringe pump with a needle diameter of 1-1.5mm, stirred at 200-250rpm and 16-25℃ for 45-60min, and then left to stand for 2-3h, filtered, washed and dried to obtain composite phosphorus fertilizer slow-release microbeads.

[0045] In some embodiments, the composite phosphorus fertilizer slow-release microbeads are soaked in a chloroacetic acid solution, the pH is adjusted to 7-9, stirred at 60-200rpm and 16-25℃ for 8-11h, filtered, washed to neutral and dried to obtain multifunctional hydrogel microbeads with water retention and fertilizer retention.

[0046] In some embodiments, the mass concentration of the sodium alginate aqueous solution is 1-2%;

[0047] The mass concentration of the calcium ion-containing solution is 2-4%;

[0048] The concentration of the chloroacetic acid solution is 0.2-0.5mol / L;

[0049] The calcium ion-containing solution includes at least one of CaCl2 solution, CaSO4 solution, Ca(NO)3 solution and phosphogypsum leaching solution.

[0050] Specifically, the preparation method of the phosphogypsum leaching solution is as follows: the phosphogypsum is crushed and then soaked in water, and filtration is performed to obtain the phosphogypsum leaching solution; wherein the mass concentration of calcium ions in the phosphogypsum leaching solution is 2-4%.

[0051] The chemical composition of the phosphogypsum is shown in Table 1.

[0052] Table 1-chemical composition of phosphogypsum

[0053]

[0054] Loss in Table 1 represents the loss on ignition.

[0055] In some embodiments, the mass-volume ratio of the humic acid, the yeast, the sodium alginate aqueous solution, the compound phosphate fertilizer, and the calcium ion-containing solution is (2-5) g:(1-3) g:(5-8) g:(1-4) g:(100-250) mL.

[0056] In some embodiments, the compound phosphate fertilizer slow-release microbeads are soaked in a chloroacetic acid solution, 0.02-0.1 mol / L sodium hydroxide aqueous solution is used to adjust the pH to 7-9, stirring is performed, and filtration is performed to obtain the multifunctional hydrogel microbeads with water-retaining and fertilizer-retaining functions.

[0057] Specifically, the volume of the chloroacetic acid solution is not limited, as long as the compound phosphate fertilizer slow-release microbeads are completely soaked.

[0058] Based on the same inventive concept, the application further provides a multifunctional hydrogel microbead with water-retaining and fertilizer-retaining functions, which is prepared by the above preparation method.

[0059] The preparation method of the multifunctional hydrogel microbead with water-retaining and fertilizer-retaining functions of the application is further described in the following specific embodiments. This part further describes the content of the application in combination with specific embodiments, but should not be understood as a limitation of the application. If not specifically stated, the technical means used in the embodiments are conventional means familiar to those skilled in the art. Unless specifically stated, the reagents, methods and equipment used in the application are conventional reagents, methods and equipment in the art.

[0060] In the following embodiments, the sodium alginate is purchased from Macklin Reagent, specifically S817374 sodium alginate, Cas No.: 9005-38-3;

[0061] The superphosphate is purchased from Macklin Reagent, specifically C822236 superphosphate monohydrate, Cas No.: 10031-30-8;

[0062] The humic acid is purchased from Macklin Reagent, specifically H742187 humic acid, Cas No.: 1415-93-6;

[0063] Yeast was purchased from Macron Reagent, specifically Y750241 yeast powder.

[0064] Example 1

[0065] The present embodiment provides a preparation method of multifunctional hydrogel microspheres with water and fertilizer retention, comprising the following steps:

[0066] S1, ultrasonic dispersion 3g humic acid and 1g yeast in 5g 1wt% sodium alginate aqueous solution, stirring at 25℃ and 650rpm for 3h, to obtain a first mixed suspension, ready for use;

[0067] S2, ultrasonic dispersion 2g potassium dihydrogen phosphate and 2g calcium superphosphate in the first mixed suspension in S1, stirring at 25℃ and 550rpm for 2h, to obtain a second mixed suspension, ready for use;

[0068] S3, inject the second mixed suspension in S2 into 250mL 3wt% CaCl2 aqueous solution by a syringe pump with a needle diameter of 1.5mm, stirring at 250rpm and 25℃ for 60min, standing for 3h, filtering, and rinsing the filtered spheres with deionized water for 3 times, to obtain composite phosphorus fertilizer slow-release microspheres;

[0069] S4, immerse the composite phosphorus fertilizer slow-release microspheres in S3 in 0.5mol / L chloroacetic acid solution (the volume of chloroacetic acid solution is 500mL to completely immerse the composite phosphorus fertilizer slow-release microspheres), adjust the pH to 9 with 0.1mol / L sodium hydroxide aqueous solution, stirring at 200rpm and 25℃ for 11h, filtering, rinsing the filtered spheres to neutral with deionized water, and drying at room temperature, to obtain multifunctional hydrogel microspheres with water and fertilizer retention.

[0070] Example 2

[0071] The present embodiment provides a preparation method of multifunctional hydrogel microspheres with water and fertilizer retention, comprising the following steps:

[0072] S1, ultrasonic dispersion 5g humic acid and 3g yeast in 8g 1wt% sodium alginate aqueous solution, stirring at 25℃ and 600rpm for 3h, to obtain a first mixed suspension, ready for use;

[0073] S2, ultrasonic dispersion 1g potassium dihydrogen phosphate and 3g calcium superphosphate in the first mixed suspension in S1, stirring at 25℃ and 550rpm for 2h, to obtain a second mixed suspension, ready for use;

[0074] S3, the second mixed suspension in S2 was injected into 250 mL of calcium ion-containing 3 wt% phosphogypsum leaching solution (the preparation of the phosphogypsum leaching solution is as shown above) using a syringe pump with a needle diameter of 1.5 mm, stirred at 200 rpm and 25°C for 45 min, left to stand for 3 h, filtered, and the filtered spheres were rinsed with deionized water for 3 times to obtain composite phosphate slow-release microspheres;

[0075] S4, the composite phosphate slow-release microspheres in S3 were immersed in a 0.3 mol / L chloroacetic acid solution (the volume of the chloroacetic acid solution was 500 mL to completely immerse the composite phosphate slow-release microspheres), and the pH was adjusted to 8 using a 0.1 mol / L sodium hydroxide aqueous solution, stirred at 180 rpm and 25°C for 10 h, filtered, the filtered spheres were rinsed to neutral with deionized water, and dried at room temperature to obtain multifunctional hydrogel microspheres with water retention and fertilizer retention.

[0076] Comparative Example 1

[0077] This comparative example provides a method for preparing hydrogel microspheres, which is the same as Example 1 except that humic acid is not added, and specifically includes the following steps:

[0078] S1, 1 g of yeast was ultrasonically dispersed in 5 g of a 1 wt% sodium alginate aqueous solution, stirred at 25°C and 650 rpm for 3 h to obtain a first mixed suspension, which was prepared for use;

[0079] S2, 2 g of potassium dihydrogen phosphate and 2 g of calcium superphosphate were ultrasonically dispersed in the first mixed suspension in S1, stirred at 25°C and 550 rpm for 2 h to obtain a second mixed suspension, which was prepared for use;

[0080] S3, the second mixed suspension in S2 was injected into 250 mL of 3 wt% CaCl2 aqueous solution using a syringe pump with a needle diameter of 1.5 mm, stirred at 250 rpm and 25°C for 60 min, left to stand for 3 h, filtered, and the filtered spheres were rinsed with deionized water for 3 times to obtain composite phosphate slow-release microspheres;

[0081] S4, the composite phosphate slow-release microspheres in S3 were immersed in a 0.5 mol / L chloroacetic acid solution (the volume of the chloroacetic acid solution was 500 mL to completely immerse the composite phosphate slow-release microspheres), and the pH was adjusted to 9 using a 0.1 mol / L sodium hydroxide aqueous solution, stirred at 200 rpm and 25°C for 11 h, filtered, the filtered spheres were rinsed to neutral with deionized water, and dried at room temperature to obtain hydrogel microspheres.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing hydrogel microspheres, which is the same as Example 1 except that yeast is not added, and specifically includes the following steps:

[0084] S1, 3 g humic acid was ultrasonically dispersed in 5 g 1 wt% sodium alginate aqueous solution, stirred at 25°C, 650 rpm for 3 h to obtain a first mixed suspension, ready for use;

[0085] S2, 2 g potassium dihydrogen phosphate, 2 g calcium superphosphate was ultrasonically dispersed in the first mixed suspension in S1, stirred at 25°C, 550 rpm for 2 h to obtain a second mixed suspension, ready for use;

[0086] S3, the second mixed suspension in S2 was injected into 250 mL, 3 wt% CaCl2 aqueous solution by using a syringe pump with a needle diameter of 1.5 mm, stirred at 250 rpm, 25°C for 60 min, stood for 3 h, filtered, and the filtered spheres were rinsed with deionized water for 3 times to obtain composite slow-release phosphate fertilizer microspheres;

[0087] S4, the composite slow-release phosphate fertilizer microspheres in S3 were immersed in 0.5 mol / L chloroacetic acid solution (the volume of chloroacetic acid solution was 500 mL to completely immerse the composite slow-release phosphate fertilizer microspheres), the pH was adjusted to 9 by using 0.1 mol / L sodium hydroxide aqueous solution, stirred at 200 rpm, 25°C for 11 h, filtered, the filtered spheres were rinsed to neutral with deionized water, and dried at room temperature to obtain hydrogel microspheres.

[0088] Comparative Example 3

[0089] This comparative example provides a preparation method of hydrogel microspheres, which is the same as Example 2, except that no phosphate fertilizer is added, and specifically comprising the following steps:

[0090] S1, 5 g humic acid, 3 g yeast was ultrasonically dispersed in 8 g 1 wt% sodium alginate aqueous solution, stirred at 25°C, 600 rpm for 3 h to obtain a first mixed suspension, ready for use;

[0091] S2, the first mixed suspension was stirred at 25°C, 550 rpm for 2 h to obtain a second mixed suspension, ready for use;

[0092] S3, the second mixed suspension in S2 was injected into 250 mL, 3 wt% calcium ion-containing phosphogypsum leaching solution (the preparation of phosphogypsum leaching solution is as shown above) by using a syringe pump with a needle diameter of 1.5 mm, stirred at 200 rpm, 25°C for 45 min, stood for 3 h, filtered, and the filtered spheres were rinsed with deionized water for 3 times to obtain composite slow-release phosphate fertilizer microspheres;

[0093] S4, immerse the composite phosphorus fertilizer slow-release microspheres in S3 in 0.3 mol / L chloroacetic acid solution (the volume of the chloroacetic acid solution is 500 mL to completely immerse the composite phosphorus fertilizer slow-release microspheres), adjust the pH to 8 with 0.1 mol / L sodium hydroxide aqueous solution, stir at 180 rpm and 25°C for 10 h, filter, rinse the filtered microspheres to neutral with deionized water, and dry at room temperature to obtain the hydrogel microspheres.

[0094] Performance test

[0095] Release rate test

[0096] Put 0.5 g of the hydrogel microspheres prepared in Examples 1, 2 and Comparative Examples 1-2, respectively, into 100 mL of distilled water, and place the system in a room temperature environment for 10 h, 20 h, 40 h, 80 h, 160 h and 300 h, respectively, then extract 5 mL of supernatant, and supplement 5 mL of distilled water to the system. Then, filter the extracted supernatant with a 0.45 μm water filter membrane, detect the phosphorus concentration, and calculate the cumulative release amount of phosphorus according to the following formula:

[0097] Phosphorus release amount (%) = (C t × V 总 ) / m0 x 100%

[0098] In the formula, C t is the mass concentration of the solution at time t, g / L; V 总 is the total volume of the solution, mL; and m0 is the total weight of phosphorus in the hydrogel microspheres, g.

[0099] The test results are shown in Table 2.

[0100] Table 2 - Phosphorus release amount of hydrogel microspheres prepared in different examples

[0101]

[0102]

[0103] From Table 2, from the phosphorus release data, it can be seen that the phosphorus release amount of Examples 1 and 2 gradually increases over time, the release is relatively flat from 10 to 40 h, the rate accelerates from 80 to 160 h, and the release continues for 300 h, showing good long-term slow-release capability and suitability for crop sustained fertilizer needs; the release amount at each time point of Comparative Example 1 (without humic acid) and Comparative Example 2 (without yeast) is higher than that of the corresponding examples, such as 10 h, Comparative Example 1 reaches 10.14%, and Example 1 is 5.78%, indicating that humic acid and yeast can delay release and optimize release rhythm; overall, the examples have good phosphorus slow-release performance of hydrogel microspheres by reasonable components (humic acid, yeast, phosphorus fertilizer, etc.) and process, and the counterexamples demonstrate the necessity of key ingredients and formula for slow-release function, which has application potential in agricultural fertilizer conservation (slow-release phosphorus fertilizer) scenarios, and subsequent optimization of crop fertilizer needs can further improve the adaptability.

[0104] Material water absorption capacity test

[0105] 0.5 g of hydrogel microspheres prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were placed in 100 mL of distilled water, and the system was stabilized in a room temperature environment for 2 h, 4 h, 8 h, and 12 h, respectively. Then the hydrogel microspheres were filtered out, the excess water on the surface was wiped off, weighed, and the weight (m t ) of the gel microspheres at that time was obtained, and the swelling rate SR (g / g) was calculated according to the following formula:

[0106] SR (g / g) = (m t -0.5) / 0.5

[0107] The test results are shown in Table 3.

[0108] Table 3 - Water absorption capacity of hydrogel microspheres prepared by different examples

[0109]

[0110] From Table 3, it can be seen that the swelling rate of Examples 1 and 2 is higher than that of Comparative Examples 1 and 2 without adding the corresponding components, indicating that humic acid and yeast can improve the water absorption capacity of hydrogel microspheres; and the swelling rate of each example gradually increases over time, which reflects the continuous water absorption characteristics of hydrogel microspheres, which is beneficial to agricultural water conservation scenarios.

[0111] Soil water retention capacity test

[0112] Determination of soil water loss rate: 100 g of dry soil was mixed with 2 g of hydrogel microspheres prepared in Examples 1 and 2 and Comparative Examples 1 to 3 in a container, and 100 g of dry soil without adding hydrogel microspheres was taken as a control group. 100 mL of distilled water was poured into each container and weighed (W0), and then each group of mixed soil was placed in natural light conditions, and the weight (W1) was measured at 4, 8, 12, and 20 days, respectively.​​​​​​​​​​n The soil water loss rate is calculated by the following formula:

[0113] Soil water loss rate (%) = (W0-W n ) / W0x 100%

[0114] The test results are shown in Table 4.

[0115] Table 4 - Soil water retention capacity of hydrogel microbeads prepared in different examples

[0116]

[0117] As can be seen from Table 4, compared with the control group, the soil water loss rate of Examples 1, 2 and each comparative example after adding hydrogel microbeads is lower, which shows that the hydrogel microbeads can improve the soil water retention capacity. Among them, Examples 1 and 2 generally have lower water loss rates at each time point (4d, 8d, 12d, 20d) due to the addition of humic acid, yeast and other components than Comparative Examples 1 and 2 without the corresponding components. For example, at 20d, Example 1 is 41.19%, Example 2 is 43.22%, Comparative Example 1 is 50.22%, and Comparative Example 2 is 51.85%, which shows that humic acid and yeast can help to enhance the water retention effect.

[0118] It can be understood that each technical feature of the above-described examples can be combined arbitrarily. In order to make the description simple, each technical feature in the above-described examples is not described in all possible combinations, however, as long as the combination of these technical features does not exist contradictory, it should be considered as the scope of the present disclosure.

[0119] The above is only a preferred embodiment of the present application, and only the technical principles of the present application are specifically described. These descriptions are only to explain the principles of the present application and cannot be interpreted in any way as a limitation on the scope of protection of the present application. Based on the explanation here, any modification, equivalent replacement and improvement made within the spirit and principles of the present application, and other specific embodiments of the present application that can be easily conceived by those skilled in the art without creative labor, should be included in the scope of protection of the present application.

Claims

1. A method for preparing multifunctional hydrogel microspheres that combine water retention and fertilizer retention, characterized in that, Includes the following steps: Humic acid and yeast were dispersed in an aqueous solution of sodium alginate to obtain a first mixed suspension; The compound phosphate fertilizer is dispersed in the first mixed suspension to obtain the second mixed suspension; The second mixed suspension was injected into a calcium ion-containing solution and filtered to obtain compound phosphate fertilizer slow-release microbeads. The compound phosphate fertilizer slow-release microbeads were soaked in chloroacetic acid solution, the pH was adjusted to 7-9, stirred, and filtered to obtain multifunctional hydrogel microbeads that have both water retention and fertilizer retention properties.

2. The method for preparing multifunctional hydrogel microspheres with both water retention and fertilizer retention as described in claim 1, characterized in that, Humic acid and yeast were dispersed in an aqueous solution of sodium alginate and stirred at 16–25°C and 550–650 rpm for 2–3 hours to obtain a first mixed suspension.

3. The method for preparing multifunctional hydrogel microspheres with both water retention and fertilizer retention as described in claim 1, characterized in that, The compound phosphate fertilizer is dispersed in the first mixed suspension and stirred at 16-25℃ and 550-650rpm for 1-2 hours to obtain the second mixed suspension.

4. The method for preparing multifunctional hydrogel microspheres with both water retention and fertilizer retention as described in claim 1, characterized in that, The compound phosphate fertilizer includes superphosphate, triple superphosphate, and potassium dihydrogen phosphate. The mass ratio of potassium dihydrogen phosphate, superphosphate, and triple superphosphate is (1-2):(1-3):(0-2).

5. The method for preparing multifunctional hydrogel microspheres with both water retention and fertilizer retention as described in claim 1, characterized in that, The second mixed suspension was injected into a calcium ion-containing solution using a syringe pump with a needle diameter of 1–1.5 mm. The mixture was stirred at 200–250 rpm and 16–25°C for 45–60 min, allowed to stand for 2–3 h, filtered, and washed to obtain compound phosphate fertilizer slow-release microbeads.

6. The method for preparing multifunctional hydrogel microspheres with both water retention and fertilizer retention as described in claim 1, characterized in that, The compound phosphate fertilizer slow-release microbeads were soaked in chloroacetic acid solution, the pH was adjusted to 7-9, and the mixture was stirred at 60-200 rpm and 16-25℃ for 8-11 hours. After filtration, washing until neutral, and drying, multifunctional hydrogel microbeads with both water retention and fertilizer retention properties were obtained.

7. The method for preparing multifunctional hydrogel microspheres with both water retention and fertilizer retention as described in claim 1, characterized in that, The mass concentration of the sodium alginate aqueous solution is 1-2%; The mass concentration of the calcium ion-containing solution is 2-4%; The concentration of the chloroacetic acid solution is 0.2–0.5 mol / L; The calcium ion-containing solution includes at least one of CaCl2 solution, CaSO4 solution, Ca(NO)3 solution, and phosphogypsum leachate.

8. The method for preparing multifunctional hydrogel microspheres with both water retention and fertilizer retention as described in claim 1, characterized in that, The mass-to-volume ratio of the humic acid, yeast, sodium alginate aqueous solution, compound phosphate fertilizer, and calcium ion-containing solution is (2-5)g:(1-3)g:(5-8)g:(1-4)g:(100-250)mL.

9. The method for preparing multifunctional hydrogel microspheres with both water retention and fertilizer retention as described in claim 1, characterized in that, The compound phosphate fertilizer slow-release microbeads were soaked in chloroacetic acid solution, and the pH was adjusted to 7-9 with 0.02-0.1 mol / L sodium hydroxide aqueous solution. After stirring and filtration, multifunctional hydrogel microbeads with both water retention and fertilizer retention properties were obtained.

10. A multifunctional hydrogel microsphere that combines water retention and fertilizer retention, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 9.

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