Compound phosphate fertilizer slow-release carboxylation modified hydrogel microbead and preparation method thereof

Abstract

The invention provides a compound phosphate fertilizer slow-release carboxylated modified hydrogel microbead and a preparation method thereof. The preparation method comprises the following steps: adding a composite phosphate fertilizer into a sodium alginate aqueous solution to obtain a mixed suspension; the mixed suspension liquid is injected into a calcium ion-containing solution, a sodium alginate aqueous solution is crosslinked with calcium ions to form sodium alginate gel, loading of the composite phosphate fertilizer is realized by virtue of the gelation process, and a gel microbead structure is constructed; the release time of the phosphate fertilizer in the soil can be prolonged by utilizing the structural characteristics of the gel microbeads; the hydrogel microbeads are subjected to carboxylation modification by using a modifier, so that more carboxyl groups are loaded on the gel microbeads, and the water absorption and retention performance of the microbeads is further improved; according to the preparation method, the raw materials are wide in source, low in cost, safe and harmless, the preparation process is simple, and the prepared hydrogel microbeads have high water absorption and water retention performance and a fertilizer slow release function and can effectively improve soil, increase the water retention performance of the soil and the effectiveness of a phosphate fertilizer and reduce soil moisture and fertility loss.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water-retaining materials, and particularly relates to a composite phosphorus fertilizer slow-release carboxyl-modified hydrogel microsphere 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 a high requirement for the types of raw materials. Generally, the water retention agent is mainly a superabsorbent polymer, which is derived from a physically or chemically cross-linked polymer. Due to its porous structure and rich 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 the soil, is easy to cause environmental hazards, and has few products with both water retention and fertilizer retention functions, so the application is limited.

[0003] Sodium alginate (SA) as a renewable resource existing in the ocean is a polysaccharide biological macromolecule extracted from kelp or sargassum after iodine and mannitol, and the molecular formula is (C6H7O6Na)n. Sodium alginate is non-toxic and has good biocompatibility and gel-forming properties, and is widely used in food, environment and other fields. In addition, sodium alginate can also be cross-linked with divalent metal cations (commonly used Ca 2+ ) to form a lattice structure, and gel balls can be obtained after drying or carbonization under specific conditions. 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.

[0004] Sodium alginate is a natural polysaccharide-based water-absorbing material with strong adsorption properties and is a good biological hydrogel material. The hydrogel formed by the combination of sodium alginate and cations has strong sensitivity to pH and belongs to an alkaliphilic hydrogel. Generally, under acidic conditions, the hydroxyl groups on the network structure of the hydrogel combine with free hydrogen ions to form carboxylic acid, and the free hydrogen ions in water decrease, resulting in the collapse of the gel. When the pH value of the hydrogel solution is alkaline, the free hydrogen ions combine with hydroxyl ions to form water, and the combination reaction of carboxyl groups and hydrogen ions will be inhibited, so that they exist in the form of hydroxyl ions. Under the condition of electrostatic repulsion, the hydrogel swells and absorbs water.

[0005] The prior art discloses a high water-absorbing sodium alginate-based composite material and a preparation method thereof, the invention mixes sodium alginate, polyvinyl alcohol, acrylic acid, ammonium persulfate and N,N'-methylene bisacrylamide in a crosslinking manner to form a gel, and is used for soil improvement and has good water absorption and water retention capacity. SUMMARY

[0006] In order to solve the defects in the prior art, the present application provides a kind of composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres and its preparation method;The present application uses inorganic composite phosphorus fertilizer and carboxylated modified sodium alginate hydrogel to form a hydrogel microsphere with high water absorption and phosphorus slow-release type, which has high water absorption and water retention and fertilizer slow-release function, can effectively improve the soil, increase the soil water retention and phosphorus fertilizer availability, reduce soil water loss and fertility loss.

[0007] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0008] In the first aspect, the present application provides a preparation method of composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres, comprising the following steps:

[0009] Disperse the composite phosphorus fertilizer in the sodium alginate aqueous solution to obtain a mixed suspension;

[0010] Inject the mixed suspension into a calcium ion-containing solution, filter, and obtain the composite phosphorus fertilizer slow-release microspheres;

[0011] Soak the composite phosphorus fertilizer slow-release microspheres in a modifier solution, adjust the pH to 7-9, stir, filter, and obtain the composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres;

[0012] The modifier solution is an acid solution containing carboxyl groups.

[0013] Preferably, the acid solution containing carboxyl groups comprises at least one of chloroacetic acid, succinic anhydride, citric acid and polyacrylic acid.

[0014] Preferably, the concentration of the modifier solution is 0.2-0.5 mol / L.

[0015] Preferably, the composite phosphorus fertilizer slow-release microspheres are soaked in the modifier solution, the pH is adjusted to 7-9, and the stirring is carried out at 60-200 rpm and 16-25℃ for 8-11 h, then filtered, washed to neutral and dried to obtain the composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres.

[0016] Preferably, the calcium ion-containing solution comprises at least one of CaCl2 solution, CaSO4 solution, Ca(NO)3 and phosphogypsum leaching solution.

[0017] Preferably, the composite phosphorus fertilizer comprises superphosphate, triple superphosphate, potassium dihydrogen phosphate;

[0018] The mass ratio of the potassium dihydrogen phosphate, the superphosphate and the triple superphosphate is (1-2):(1-3):(0-2).

[0019] Preferably, the composite phosphorus fertilizer is ultrasonically dispersed in the sodium alginate aqueous solution, and then stirred at 16-25℃ and 550-650rpm for 1-2h to obtain a mixed suspension;

[0020] The mixed suspension is injected into a calcium ion-containing solution by using a syringe pump with a needle diameter of 1-1.5mm, and stirred at 200-250rpm and 16-25℃ for 45-60min, and then left to stand for 2-3h, filtered and washed to obtain the composite phosphorus fertilizer slow-release microbeads.

[0021] Preferably, the mass concentration of the sodium alginate aqueous solution is 1-2%;

[0022] The mass concentration of the calcium ion-containing solution is 2-4%;

[0023] The mass-volume ratio of the composite phosphorus fertilizer, the sodium alginate aqueous solution and the calcium ion-containing solution is (3-4)g:(5-6)g:(100-250)mL.

[0024] Preferably, the composite phosphorus fertilizer slow-release microbeads are soaked in a modifier solution, and the pH is adjusted to 7-9 by using a 0.02-0.1mol / L sodium hydroxide aqueous solution, and then stirred and filtered to obtain the composite phosphorus fertilizer slow-release carboxylated modified hydrogel microbeads.

[0025] In the second aspect, the present application further provides a composite phosphorus fertilizer slow-release carboxylated modified hydrogel microbead prepared by using the preparation method.

[0026] The composite phosphorus fertilizer slow-release carboxylated modified hydrogel microbead and the preparation method thereof have the following effects compared with the prior art:

[0027] 1. The preparation method of the composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres of the present application, by mixing the composite phosphorus fertilizer with the sodium alginate aqueous solution to obtain a mixed suspension; injecting the mixed suspension into a calcium ion-containing solution, the sodium alginate aqueous solution will form a sodium alginate gel after crosslinking with the calcium ion, and by means of this gelation process, the loading of the composite phosphorus fertilizer is realized, 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 prolonged; at the same time, by mixing the composite phosphorus fertilizer with the sodium alginate, the mechanical strength and structural stability of the sodium alginate gel microspheres can be effectively improved; by using the modifier to carboxylate the composite phosphorus fertilizer slow-release hydrogel microspheres, more carboxyl groups are loaded on the gel microspheres, the water absorption units in the gel microspheres are improved, and the water absorption and water retention performance of the microspheres is further improved.

[0028] 2. The composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres prepared by the present application have good pH responsiveness, the carboxylation modification loads more carboxyl groups on the gel microsphere structure, the change of pH is accompanied by the protonation and deprotonation process of the carboxyl groups, thereby affecting the stability of the chemical bond and the stability of the overall structure, further affecting the water absorption and water release rate of the material and the release rate of the contents.

[0029] 3. The preparation method of the composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres of the present application has wide raw material sources, low cost, safety and harmlessness, simple preparation process, and the prepared composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres have high water absorption and water retention and fertilizer slow-release functions, can effectively improve the soil, increase the soil water retention and phosphorus fertilizer effectiveness, and reduce the loss of soil water and fertility. DETAILED DESCRIPTION

[0030] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to specific embodiments. In the specific embodiments, preferred embodiments of the present application are given. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0031] The order of description of the following embodiments is not intended to imply a preferred order of embodiments. Additionally, in the description of the application, the term "including" means "including but not limited to". Various embodiments of the application can exist in a range of forms; it should be understood that the description in a range form is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the application; therefore, it should be considered that the range described has been specifically disclosed all possible sub-ranges and single values within the 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., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) within the indicated range.

[0032] The application provides a preparation method of composite phosphorus fertilizer slow-release carboxylated modified hydrogel microbeads, comprising the following steps:

[0033] S1, dispersing the composite phosphorus fertilizer in a sodium alginate aqueous solution to obtain a mixed suspension;

[0034] S2, injecting the mixed suspension into a calcium ion-containing solution, filtering to obtain composite phosphorus fertilizer slow-release microbeads;

[0035] S3, soaking the composite phosphorus fertilizer slow-release microbeads in a modifier solution, adjusting the pH to 7-9, stirring, filtering to obtain composite phosphorus fertilizer slow-release carboxylated modified hydrogel microbeads;

[0036] The modifier solution is an acid solution containing carboxyl groups.

[0037] The preparation method of the composite phosphorus fertilizer slow-release carboxylated modified hydrogel microbeads of the application, by dispersing the composite phosphorus fertilizer in the sodium alginate aqueous solution to obtain the mixed suspension, injecting the mixed suspension into the calcium ion-containing solution, the sodium alginate aqueous solution will form a sodium alginate gel after crosslinking with the calcium ion, by means of this gelation process, the loading of the composite phosphorus fertilizer is realized, and the gel microbead structure is constructed; by utilizing the structural characteristics of the gel microbeads, the release rate of the phosphorus fertilizer in the soil can be effectively reduced, and the action time is prolonged; at the same time, by mixing the composite phosphorus fertilizer with the sodium alginate, the mechanical strength and structural stability of the sodium alginate gel microbeads can be effectively improved; further, the composite phosphorus fertilizer slow-release microbeads are soaked in the modifier solution, the pH is adjusted to 7-9, stirring, filtering to obtain the composite phosphorus fertilizer slow-release carboxylated modified hydrogel microbeads; the modifier solution is an acid solution containing carboxyl groups, the composite phosphorus fertilizer slow-release hydrogel microbeads are carboxylated modified by using the modifier, more carboxyl groups are loaded on the gel microbeads, the water absorption units in the gel microbeads are improved, and the water absorption and water retention performance of the microbeads is further improved.

[0038] Further, the carboxyl-modified hydrogel microspheres prepared by the present application have good pH responsiveness. The carboxyl modification loads more carboxyl groups on the structure of the gel microspheres. The change of pH is accompanied by the processes of protonation and deprotonation of the carboxyl groups, thereby affecting the stability of chemical bonds and the stability of the overall structure, and further affecting the water absorption and release rate of the material and the release rate of the contents.

[0039] In some embodiments, the carboxyl-containing acidic solution comprises at least one of chloroacetic acid, succinic anhydride, citric acid, and polyacrylic acid.

[0040] In some embodiments, the concentration of the modifier solution is 0.2-0.5 mol / L.

[0041] In some embodiments, the composite phosphorus fertilizer slow-release microspheres are soaked in the modifier solution, the pH is adjusted to 7-9, stirring is carried out at 60-200 rpm and 16-25°C for 8-11 h, filtration is carried out, washing is carried out until neutral, and drying is carried out, to obtain the composite phosphorus fertilizer slow-release carboxyl-modified hydrogel microspheres.

[0042] In some embodiments, the calcium ion-containing solution comprises at least one of CaCl2 solution, CaSO4 solution, Ca(NO)3, and phosphogypsum leaching solution.

[0043] Specifically, the preparation method of the phosphogypsum leaching solution is as follows: phosphogypsum is crushed and then soaked in water, filtration is carried out, and the phosphogypsum leaching solution is obtained; wherein the mass concentration of calcium ions in the phosphogypsum leaching solution is 2-4%.

[0044] The chemical composition of the phosphogypsum is shown in Table 1.

[0045] Table 1-Chemical composition of phosphogypsum

[0046]

[0047]

[0048] Loss in Table 1 represents the loss on ignition.

[0049] In some embodiments, the composite phosphorus fertilizer comprises superphosphate, triple superphosphate, and potassium dihydrogen phosphate.

[0050] The mass ratio of potassium dihydrogen phosphate, superphosphate, and triple superphosphate is (1-2):(1-3):(0-2).

[0051] In some embodiments, the composite phosphorus fertilizer is ultrasonically dispersed in a sodium alginate aqueous solution, and then stirring is carried out at 16-25°C and 550-650 rpm for 1-2 h, to obtain a mixed suspension.

[0052] The mixed suspension is injected into a calcium ion-containing solution by using a syringe pump with a needle diameter of 1-1.5 mm, stirred at 200-250 rpm and 16-25℃ for 45-60 min, left for 2-3 h, filtered, and washed to obtain the composite phosphate fertilizer slow-release microbeads.

[0053] In some embodiments, the mass concentration of the sodium alginate aqueous solution is 1-2%;

[0054] The mass concentration of the calcium ion-containing solution is 2-4%;

[0055] The mass-volume ratio of the composite phosphate fertilizer, the sodium alginate aqueous solution, and the calcium ion-containing solution is (3-4) g:(5-6) g:(100-250) mL.

[0056] Specifically, the volume of the modifier solution is not limited, as long as the composite phosphate fertilizer slow-release microbeads are completely soaked.

[0057] In some embodiments, the composite phosphate fertilizer slow-release microbeads are soaked in the modifier solution, 0.02-0.1 mol / L sodium hydroxide aqueous solution is used to adjust the pH to 7-9, stirring, filtering, and obtaining the composite phosphate fertilizer slow-release carboxylated modified hydrogel microbeads.

[0058] Based on the same inventive concept, the application also provides a composite phosphate fertilizer slow-release carboxylated modified hydrogel microbead prepared by the above preparation method.

[0059] The preparation method of the composite phosphate fertilizer slow-release carboxylated modified hydrogel microbead of the application is further illustrated in the following specific embodiments. This part further illustrates 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 examples and comparative examples, the sodium alginate is purchased from Macklin Reagent, specifically S817374 sodium alginate, Cas No.: 9005-38-3;

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

[0062] The polyacrylic acid is purchased from Macklin Reagent, specifically P822497 polyacrylic acid, Cas No.: 9003-01-4.

[0063] Example 1

[0064] The present embodiment provides a preparation method of a composite phosphate fertilizer slow-release carboxylated modified hydrogel microbead, comprising the following steps:

[0065] S1, 2 g of potassium dihydrogen phosphate, 1 g of calcium superphosphate was ultrasonically dispersed in 5 g of 1 wt% sodium alginate aqueous solution, then stirred at 25°C, 550 rpm for 2 h to obtain a mixed suspension, ready for use;

[0066] S2, the mixed suspension in S1 was injected into 250 mL of 2 wt% CaCl2 aqueous solution by a syringe pump with a needle diameter of 1 mm, stirred at 200 rpm, 25°C for 60 min, and then left to stand for 3 h. The obtained spheres were filtered and washed with deionized water for 3 times to obtain the composite slow-release phosphate fertilizer microspheres;

[0067] S3, the composite slow-release phosphate fertilizer microspheres in S2 were soaked in a 0.5 mol / L chloroacetic acid aqueous solution (the volume of the chloroacetic acid solution was 500 mL to completely immerse the composite slow-release phosphate fertilizer microspheres), and the pH was adjusted to 7 with a 0.1 mol / L sodium hydroxide aqueous solution. The mixture was stirred at 150 rpm, 25°C for 11 h, filtered, washed with deionized water until neutral, and dried at room temperature (25°C) to obtain the composite slow-release carboxylated modified hydrogel microspheres.

[0068] Example 2

[0069] The present embodiment provides a preparation method of composite slow-release carboxylated modified hydrogel microspheres, comprising the following steps:

[0070] S1, 1 g of potassium dihydrogen phosphate, 3 g of calcium superphosphate was ultrasonically dispersed in 6 g of 2 wt% sodium alginate aqueous solution, then stirred at 25°C, 600 rpm for 1 h to obtain a mixed suspension, ready for use;

[0071] S2, the mixed suspension in S1 was injected into 250 mL of 4 wt% calcium ion-containing phosphogypsum leaching solution (the preparation of the phosphogypsum leaching solution is as shown above) by a syringe pump with a needle diameter of 1.5 mm, stirred at 180 rpm, 25°C for 45 min, and then left to stand for 3 h. The obtained spheres were filtered and washed with deionized water for 3 times to obtain the composite slow-release phosphate fertilizer microspheres;

[0072] S3, the composite slow-release phosphate fertilizer microspheres in S2 were soaked in a mixed solution containing 0.3 mol / L citric acid and 0.3 mol / L polyacrylic acid (the volume of the mixed solution was 500 mL to completely immerse the composite slow-release phosphate fertilizer microspheres, and the concentration of citric acid in the mixed solution was 0.3 mol / L, and the concentration of polyacrylic acid was 0.3 mol / L), and the pH was adjusted to 8 with a 0.05 mol / L sodium hydroxide aqueous solution. The mixture was stirred at 150 rpm, 25°C for 10 h, filtered, washed with deionized water until neutral, and dried at room temperature (25°C) to obtain the composite slow-release carboxylated modified hydrogel microspheres.

[0073] Comparative Example 1

[0074] The present comparative example provides a preparation method of modified hydrogel microspheres, which is the same as Example 2, except that no composite phosphate fertilizer is added, and specifically comprises the following steps:

[0075] S1, 6g of 2wt% sodium alginate aqueous solution is stirred at 25°C and 600rpm for 1h to obtain a suspension, which is ready for use;

[0076] S2, the suspension in S1 is injected into 250mL of 4wt% CaCl2 solution using a syringe pump with a needle diameter of 1.5mm, stirred at 180rpm and 25°C for 45min, and then left to stand for 3h. The obtained microspheres are filtered and washed with deionized water for 3 times to obtain slow-release microspheres;

[0077] S3, the slow-release microspheres are soaked in a mixed solution containing 0.3mol / L citric acid and 0.3mol / L polyacrylic acid (the volume of the mixed solution is 500mL to completely immerse the slow-release microspheres, and the concentration of citric acid in the mixed solution is 0.3mol / L and the concentration of polyacrylic acid is 0.3mol / L), and the pH is adjusted to 8 using 0.05mol / L sodium hydroxide aqueous solution. The mixed solution is stirred at 150rpm and 25°C for 10h, filtered, washed with deionized water until neutral, and dried at room temperature (25°C) to obtain modified hydrogel microspheres.

[0078] Comparative Example 2

[0079] The present comparative example provides a preparation method of modified hydrogel microspheres, which is the same as Example 1, except that step S3 is removed, and specifically comprises the following steps:

[0080] S1, 2g of potassium dihydrogen phosphate and 1g of calcium superphosphate are ultrasonically dispersed in 5g of 1wt% sodium alginate aqueous solution, and then stirred at 25°C and 550rpm for 2h to obtain a mixed suspension, which is ready for use;

[0081] S2, the mixed suspension in S1 is injected into 250mL of 2wt% CaCl2 aqueous solution using a syringe pump with a needle diameter of 1mm, stirred at 200rpm and 25°C for 60min, left to stand for 3h, filtered, washed with deionized water for 3 times, and dried to obtain composite phosphate fertilizer slow-release microspheres, which are modified hydrogel microspheres.

[0082] Performance test

[0083] Slow-release rate test

[0084] The modified hydrogel microspheres prepared in 0.5g of Example 1, 2 and Comparative Example 2 were placed in 100mL of distilled water, and the system was stabilized in a room temperature environment for 10h, 20h, 40h, 80h, 160h, 300h, respectively, then 5mL of supernatant was extracted, and 5mL of distilled water was added to the system. Then, the extracted supernatant was filtered with a water filter membrane of 0.45μm, the phosphorus concentration was detected, and the cumulative release amount of phosphorus was calculated as follows:

[0085] Phosphorus release amount (%) = (C t ×V 总 ) / m0×100%

[0086] In the formula: C t is the mass concentration of phosphorus in the supernatant at time t, g / L; V 总 is the total volume of the solution, 100mL; m0 refers to the total weight of phosphorus in the modified hydrogel microspheres, g.

[0087] The test results are shown in Table 2.

[0088] Table 2 - Phosphorus release amount of modified hydrogel microspheres in different examples

[0089]

[0090] From the phosphorus release data, Examples 1 and 2 show a gradual increase in phosphorus release amount over time, with a relatively flat short-term (10-40h) release, an accelerated medium-term (80-160h) release, and a long-term (300h) continuous release, which reflects good long-term phosphorus slow-release capability and helps to meet the continuous fertilizer needs of crops; after removing the carboxylation modification step (S3) in Comparative Example 2, there is still phosphorus release, but compared with Example 1, the stability and controllability of the release process are poor, which shows that carboxylation modification can effectively regulate the release rate of phosphorus and make the release more suitable for slow-release needs. Overall, reasonable formulation and process (loading of composite phosphorus fertilizer, carboxylation modification, etc.) give the composite phosphorus slow-release carboxylated modified hydrogel microspheres good phosphorus slow-release effect, which has application potential in the field of agricultural slow-release fertilizer, and the comparative examples also inversely prove the necessity of key steps and components for achieving slow-release function.

[0091] Material water absorption capacity test

[0092] The modified hydrogel microspheres prepared in 0.5g of Example 1, 2 and Comparative Example 1, 2 were placed in 100mL of distilled water, and the system was stabilized in a room temperature environment for 2h, 4h, 8h, 12h, respectively, then the hydrogel microspheres were filtered out, the excess water on the surface was wiped off, weighed, and the weight of the gel microspheres at that time (m t ) was obtained and the swelling rate SR (g / g) was calculated as follows:

[0093] SR (g / g) = (mt -0.5) / 0.5

[0094] The test results are shown in Table 3.

[0095] Table 3 - Water absorption capacity of modified hydrogel microspheres in different examples

[0096]

[0097] From the water absorption and swelling data, the swelling rate of Examples 1, 2 and Comparative Example 1 increases with time at each time point, which reflects that the water absorption capacity of the modified hydrogel microspheres increases with the extension of the soaking time. The overall swelling rate of Examples 1 and 2 is higher than that of Comparative Example 2, which indicates that the addition of composite phosphorus fertilizer and other ingredients (Examples 1 and 2) and the modification step of carboxylation (Comparative Example 2 removes the S3 step, and the swelling rate is low) can improve the water absorption performance of the microspheres. Although the early swelling rate of Comparative Example 1 is similar to that of Example 1, the late growth is relatively slow, which reflects that the sustained improvement of the water absorption of the microspheres is affected without composite phosphorus fertilizer.

[0098] In summary, reasonable ingredient loading (such as composite phosphorus fertilizer) and modification process (such as carboxylation) can optimize the water absorption and swelling characteristics of the composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres, which is of great significance for its use as a slow-release carrier to regulate nutrient release through the correlation between water absorption and fertilizer release. It also indicates that the absence of key steps or ingredients in the comparative examples can weaken the water absorption performance of the microspheres, which may affect the stable performance of the slow-release function.

[0099] Soil water retention capacity test

[0100] Determination of soil water loss rate: 100 g of dry soil was mixed with 2 g of modified hydrogel microspheres prepared in Examples 1, 2 and Comparative Examples 1, 2 in a container, and another 100 g of dry soil without modified hydrogel microspheres was used as a control group. 100 mL of distilled water was poured into each container and weighed (W0), then each group of mixed soil was placed in natural light conditions, and the weight (W n ) was measured at 4, 8, 12 and 20 days, respectively. The soil water loss rate was calculated as follows:

[0101] Soil water loss rate (%) = (W0-W n ) / W0x100%

[0102] The test results are shown in Table 4.

[0103] Table 4 - Soil water retention capacity of modified hydrogel microspheres in different examples

[0104]

[0105] These data show that the composite phosphorus fertilizer slow-release carboxylated modified hydrogel microspheres can significantly improve the soil water retention capacity. Compared with the control group, the soil added with the gel microspheres of examples 1 and 2 has a water loss rate of only 53.17% and 51.44% respectively in 20 days, which is much lower than the control group of 84.39%, effectively delaying water loss. The examples optimize water retention through composite phosphorus fertilizer loading and modification process optimization. The comparative examples have a decreased water retention capacity due to the absence of composite phosphorus fertilizer or the absence of key modification steps, which reversely verifies the necessity of the formula and process. The water loss rate of all groups increases with time, but the loss of the gel-added group is slower, which reflects the advantages of short-term water locking and long-term water retention, and has practical value for maintaining soil water content in agricultural production.

[0106] It can be understood that any combination of the technical features of the above-described examples can be made. In order to make the description simple, all possible combinations of the technical features in the above-described examples are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present disclosure.

[0107] 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 for the purpose of explaining 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 carboxylated modified hydrogel microspheres of a composite phosphate fertilizer slow-release process, characterized in that, Includes the following steps: The compound phosphate fertilizer was dispersed in an aqueous solution of sodium alginate to obtain a mixed suspension; The 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 immersed in a modifier solution, the pH was adjusted to 7-9, stirred, and filtered to obtain compound phosphate fertilizer slow-release carboxylated modified hydrogel microbeads. The modifier solution is an acidic solution containing carboxyl groups.

2. The preparation method of the composite phosphate fertilizer slow-release carboxylated modified hydrogel microspheres as described in claim 1, characterized in that, The acidic solution containing carboxyl groups includes at least one of chloroacetic acid, succinic anhydride, citric acid, and polyacrylic acid.

3. The preparation method of the composite phosphate fertilizer slow-release carboxylated modified hydrogel microspheres as described in claim 1, characterized in that, The concentration of the modifier solution is 0.2–0.5 mol / L.

4. The preparation method of the composite phosphate fertilizer slow-release carboxylated modified hydrogel microspheres as described in claim 1, characterized in that, The compound phosphate fertilizer slow-release microbeads were immersed in a modifier solution, the pH was adjusted to 7-9, and the mixture was stirred at 60-200 rpm and 16-25℃ for 8-11 hours. The mixture was then filtered, washed until neutral, and dried to obtain compound phosphate fertilizer slow-release carboxylated modified hydrogel microbeads.

5. The method for preparing the composite phosphate fertilizer slow-release carboxylated modified hydrogel microspheres as described in claim 1, characterized in that, Calcium ion-containing solutions include at least one of CaCl2 solution, CaSO4 solution, Ca(NO)3, and phosphogypsum leachate.

6. The method for preparing the composite phosphate fertilizer slow-release carboxylated modified hydrogel microspheres 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).

7. The method for preparing the composite phosphate fertilizer slow-release carboxylated modified hydrogel microspheres as described in claim 1, characterized in that, The compound phosphate fertilizer was ultrasonically dispersed in an aqueous solution of sodium alginate, and then stirred at 16–25°C and 550–650 rpm for 1–2 hours to obtain a mixed suspension. The 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.

8. The method for preparing the compound phosphate fertilizer slow-release carboxylated modified hydrogel microspheres 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 mass-to-volume ratio of the compound phosphate fertilizer, sodium alginate aqueous solution, and calcium ion-containing solution is (3-4) g:(5-6) g:(100-250) mL.

9. The method for preparing the composite phosphate fertilizer slow-release carboxylated modified hydrogel microspheres as described in claim 1, characterized in that, The compound phosphate fertilizer slow-release microbeads were immersed in a modifier solution, and the pH was adjusted to 7-9 using a 0.02-0.1 mol / L sodium hydroxide aqueous solution. After stirring and filtration, the compound phosphate fertilizer slow-release carboxylated modified hydrogel microbeads were obtained.

10. A composite phosphate fertilizer slow-release carboxylated modified hydrogel microsphere, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 9.

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