Chitosan-based hydrogel ball as well as preparation method and application thereof

Abstract

The invention relates to the technical field of water treatment materials and resource recovery, in particular to a chitosan-based hydrogel ball as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing an acidic aqueous solution of chitosan with soluble ferric salt to obtain an M-chitosan solution; wherein the metal salt is selected from soluble ferric salt or a mixture of soluble ferric salt and soluble calcium salt; the M-chitosan solution forms charged liquid drops by adopting electronic injection treatment, the charged liquid drops are dropped into alkaline solidification liquid, and the chitosan-based hydrogel balls are obtained after solidification treatment. The chitosan-based hydrogel ball prepared by the preparation method provided by the invention solves the bottleneck that a traditional phosphorus removal adsorbent is difficult to have efficient adsorption performance and recoverability at the same time. Besides, the chitosan-based hydrogel ball can be applied as a fertilizer after adsorbing phosphorus, so that a'pollution control-resource recovery 'closed loop is realized, and the chitosan-based hydrogel ball has the dual functions of efficient phosphorus removal and agricultural recycling.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment materials and resource recovery, and in particular to a chitosan-based hydrogel ball and a preparation method and application thereof. Background Art

[0002] With the continued advancement of industrialization and rapid economic development, large amounts of phosphorus-containing wastewater are being discharged into the aquatic environment, making the problem of eutrophication increasingly serious. While phosphorus content in water bodies seriously exceeds the standard, the contradiction of phosphorus resource shortage is becoming increasingly prominent. As a non-renewable resource, phosphorus is currently used in a one-way, linear manner worldwide, with a lack of recycling and utilization channels, and low production and utilization efficiency. More than 90% of mined phosphate rock is used for phosphate fertilizer production, and agricultural non-point source pollution caused by the application of phosphate fertilizer is the main cause of eutrophication of water bodies. If the excess phosphorus in water can be recovered and reused, it will not only effectively prevent and control eutrophication of water bodies, but also alleviate the current shortage of phosphorus resources, thereby forming a closed loop of "pollution control and resource recovery."

[0003] The adsorption method has been widely used in the field of water treatment due to its significant advantages of simple operation, low cost and wide application range. However, when the adsorbent has been regenerated many times and its adsorption capacity has dropped significantly or the loss is large, it is usually treated as solid waste and landfilled, which not only occupies land resources and damages the ecological environment, but also causes a waste of phosphorus resources. In terms of phosphorus removal, iron or calcium metal-based nanomaterials have shown excellent performance, and the materials are easy to obtain and inexpensive. However, iron or calcium metal-based nanomaterials are powdery on a macroscopic scale and are difficult to recycle after use, which has limitations in practical applications. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a chitosan-based hydrogel sphere and a preparation method and application thereof. The present invention uses chitosan as a carrier, loads a metal salt functional component, adopts electrospray treatment to form an M-chitosan solution into charged droplets, and drips it into an alkaline coagulation liquid to solidify, thereby obtaining a chitosan-based hydrogel sphere. The present invention adjusts the parameters of the electrospray treatment so that the particle size of the chitosan-based hydrogel sphere is uniform and the size is controllable. In addition, the chitosan-based hydrogel sphere of the present invention has a high adsorption efficiency and is recyclable while ensuring a high phosphorus adsorption efficiency. It can be used as a fertilizer after being discarded, and has a significant promoting effect on the growth of hydroponic soybeans, can realize a "pollution control-resource recovery" closed loop, and has the dual functions of efficient phosphorus removal and agricultural resource utilization.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: The first object of the present invention is to provide a method for preparing the chitosan-based hydrogel spheres, comprising the following steps: S1. Mixing an acidic aqueous solution of chitosan with a metal salt to obtain an M-chitosan solution; wherein the metal salt is selected from a soluble iron salt or a mixture of a soluble iron salt and a water-soluble calcium salt.

[0006] S2. Using electrospray treatment, the M-chitosan solution is formed into charged droplets, which are dropped into an alkaline coagulation liquid. After solidification treatment, chitosan-based hydrogel spheres are obtained.

[0007] Among them, the conditions for electrospray treatment are: jetting at an output voltage of 0.1kV~10kV and a propulsion speed of 0.5mL / min~6mL / min; below or above this range will cause the particle size of the chitosan-based hydrogel spheres to be uneven, affecting the subsequent adsorption effect and recyclability.

[0008] Preferably, in the M-chitosan solution, when the metal salt is selected from a mixture of a soluble iron salt and a soluble calcium salt, the mass percentage of chitosan in the M-chitosan solution is 1wt% to 3wt%, the mass ratio of chitosan to metal salt is 1:0.5-2, and the mass ratio of soluble iron salt to soluble calcium salt is 1:1-3, where the mass of the metal salt is calculated as anhydrous metal salt. The chitosan solution prepared within this concentration range has moderate viscosity, is easy to process and shape, and forms a uniform and stable structure. The resulting chitosan-based hydrogel spheres have diffusion and permeability, can effectively transport phosphate, iron ions, and calcium ions, and achieve good economic benefits while meeting performance requirements.

[0009] Preferably, when the metal salt is selected from soluble iron salt, the mass ratio of chitosan to soluble iron salt in the M-chitosan solution is 1:0.5-2, wherein the mass of the soluble iron salt is calculated based on the anhydrous soluble iron salt.

[0010] Preferably, the specific operations of the electrospray treatment are: The M-chitosan solution was loaded into a syringe, the syringe needle was connected to the positive electrode of a high-voltage DC power supply, a receiving tray containing an alkaline coagulant solution was placed under the syringe needle, an aluminum foil was placed under the receiving tray, and the aluminum foil was connected to the negative electrode of the power supply. A high-voltage DC power was applied and the propulsion pump was turned on for electrospray treatment, so that the M-chitosan solution dripped out of the needle and formed charged droplets, which dripped into the alkaline coagulant solution.

[0011] Preferably, the vertical distance between the liquid surface of the alkaline coagulation liquid and the syringe needle is 5 cm to 20 cm. A distance that is too large or too small will affect the volatilization of the acid in the acidic aqueous solution of chitosan, thereby causing the chitosan-based hydrogel spheres to have irregular shapes, uneven particle sizes, and poor mechanical properties.

[0012] Preferably, the curing treatment conditions are: curing at room temperature for 12 hours to 24 hours.

[0013] Preferably, the alkaline coagulation liquid is a NaOH solution, and the concentration of the NaOH solution is 0.5 mol / L~2 mol / L. If the concentration is too low, the curing process will be slow, resulting in the chitosan-based hydrogel spheres formed being easily adhered and having poor mechanical strength, which will directly affect the yield and mechanical properties of the chitosan-based hydrogel spheres. If the concentration is too high, the chitosan-based hydrogel spheres will be cured on the outside but incompletely cured on the inside, which will affect the permeability, mechanical properties and release behavior of the chitosan-based hydrogel spheres, and a large amount of water will be required for long-term washing, which will increase the cost.

[0014] Preferably, the prepared chitosan-based hydrogel balls are further subjected to a washing treatment, and the chitosan-based hydrogel balls are washed with deionized water until they are neutral, otherwise the subsequent use effect will be affected.

[0015] The second object of the present invention is to provide chitosan-based hydrogel balls prepared by the above-mentioned preparation method. The surface of the chitosan-based hydrogel balls is wrinkled, the cross section is densely arranged in a tube bundle, and there are nano-scale pores on the tube wall.

[0016] Preferably, the chitosan-based hydrogel spheres are uniform in size, with a particle size of 1.5 mm to 2.0 mm.

[0017] The third object of the present invention is to provide the use of the chitosan-based hydrogel spheres in preparing chitosan-based hydrogel sphere adsorbents.

[0018] Preferably, the chitosan-based hydrogel ball adsorbent is used to adsorb phosphorus in wastewater, and the chitosan-based hydrogel ball adsorbent after adsorbing phosphorus can be used as a fertilizer.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a method for preparing chitosan-based hydrogel balls, wherein an acidic aqueous solution of chitosan is mixed with a metal salt to obtain an M-chitosan solution; wherein the metal salt is selected from a soluble iron salt or a mixture of a soluble iron salt and a soluble calcium salt; an electrospray treatment is adopted to form the M-chitosan solution into charged droplets, which are dropped into an alkaline coagulation liquid, and after curing treatment, chitosan-based hydrogel balls are obtained; the conditions for the electrospray treatment are: at an output voltage of 0.1kV to 10kV, a jet is carried out at a propulsion speed of 0.5mL / min to 6mL / min. The present invention accurately controls the formation of charged droplets through the electrospray treatment conditions, combines the synergistic effect of the metal salt component and the chitosan carrier, and prepares millimeter-level uniform chitosan-based hydrogel balls in one step, overcoming the bottleneck that traditional phosphorus removal adsorbents are difficult to have both efficient adsorption performance and recyclability. In addition, the chitosan-based hydrogel balls of the present invention can be used as fertilizer after adsorbing phosphorus, which solves the problem of low resource utilization rate of waste after adsorbents adsorb phosphorus, realizes the "pollution control-resource recovery" closed loop, and has the dual functions of efficient phosphorus removal and agricultural resource utilization.

[0020] 2. The chitosan-based hydrogel spheres of the present invention can simultaneously remove phosphorus and recover it for reuse. Specifically, the chitosan hydrogel spheres produced by the present invention have a uniform particle size, which can be controlled by adjusting the applied DC voltage. The size is on the millimeter scale and is recyclable. Furthermore, the phosphorus-adsorbing functional components are evenly distributed within the chitosan carrier, effectively adsorbing and removing phosphorus from water.

[0021] 3. Chitosan-based hydrogel spheres, a polymer material with a three-dimensional cross-linked structure, possess rich pores and a large specific surface area. They are excellent carriers for nanomaterials and are readily available. Loading Fe and Ca metal-based nanomaterials onto chitosan hydrogels allows for the quantification of nano-phosphorus removal materials, facilitating subsequent recycling and reuse.

[0022] 4. The chitosan-based hydrogel balls prepared by the present invention can be used as fertilizers after absorbing phosphorus, and have a significant promoting effect on the growth of hydroponic soybeans, and can realize the "pollution control-resource recovery" closed loop. Among them, chitosan is a natural high molecular polymer with good biocompatibility, and can increase the yield of vegetables and improve the quality of vegetables. Fe and Ca are mineral elements necessary for plant growth and reproduction, and can promote plant growth. As the fourth most essential element required by plants, calcium participates in the process of carbohydrate metabolism, protein biosynthesis and physiological system balance regulation, plays a key role in cell walls and middle layer structures, and can not only maintain the structural stability of cell membranes, but also enhance plant resistance to stress. Iron plays a key role in the core processes of chlorophyll synthesis, photosynthesis, respiration, redox reaction, enzyme activity and nucleic acid metabolism, and is an indispensable "catalyst" and "electron transporter" in plant life activities. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a photo of the Fe / Ca-CS of Example 1.

[0024] Figure 2 These are the scanning electron microscope images and element distribution maps of Fe / Ca-CS of Example 1, where (a), (b), and (c) are surface scanning electron microscope images, with (a) at a magnification of 50 times, (b) at a magnification of 500 times, and (c) at a magnification of 10,000 times; (d), (e), and (f) are cross-sectional scanning electron microscope images, with (d) at a magnification of 45 times, (e) at a magnification of 400 times, and (f) at a magnification of 20,000 times; and (g) is an element distribution map, with g1 representing C, g2 representing Ca, g3 representing O, and g4 representing Fe.

[0025] Figure 3 Graph showing the effect of phosphorus adsorption on Fe / Ca-CS of Example 1, where (a) is the adsorption isotherm and (b) is the adsorption kinetics.

[0026] Figure 4 The amount of phosphorus released from the Fe / Ca-CS in Example 1 in deionized water after saturation of phosphorus adsorption under simulated plant utilization conditions, where (a) represents phosphorus and calcium, and (b) represents iron.

[0027] Figure 5 These are photos of the hydroponic soybean system, where (a) is the overall picture of the hydroponic soybean, (b) is the bean sprout picture, and (c) is the corrosion picture of the hydroponic soybean.

[0028] Figure 6 These are photos of hydroponic soybean growth on the second day after applying Fe / Ca-CS-P, where (a) is deionized water and Fe / Ca-CS-P, and (b) is deionized water.

[0029] Figure 7 Figure 2 shows the growth of soybeans on the 7th day after application of Fe / Ca-CS-P, where (a) is a photo of soybeans, (b) is plant height, (c) is fresh weight, and (d) is dry weight.

[0030] Figure 8 This is a comparison chart of the total length of soybeans on the 15th day after application of Fe / Ca-CS-P and the blank. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solution of the present invention in conjunction with the data in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0033] In the existing technology, on the one hand, although there is adsorption water treatment technology to address the eutrophication problem caused by excessive phosphorus content in water bodies, the adsorption capacity of traditional adsorbents decreases after multiple regenerations. Landfill disposal not only occupies land and damages the ecology, but also wastes phosphorus resources; on the other hand, metal-based nanomaterials of iron or calcium have excellent performance in phosphorus removal and are low-cost, but they are powdery on a macro scale and difficult to recycle after use, which limits their practical application.

[0034] In response to the problems existing in the above-mentioned prior art, the present invention provides a method for preparing chitosan-based hydrogel spheres, comprising the following steps: mixing an acidic aqueous solution of chitosan with a metal salt to obtain an M-chitosan solution; wherein the metal salt is selected from a soluble iron salt or a mixture of a soluble iron salt and a soluble calcium salt; using electrospraying to form charged droplets of the M-chitosan solution, dripping the charged droplets into an alkaline coagulation liquid, and obtaining chitosan-based hydrogel spheres after curing; the electrospraying treatment is performed under the following conditions: at an output voltage of 0.1 kV to 10 kV and a propulsion speed of 0.5 mL / min to 6 mL / min.

[0035] In response to the problems in the prior art that traditional adsorbents have reduced adsorption capacity after multiple regenerations, and are landfilled for disposal, occupying land, damaging the ecology, and wasting phosphorus resources, the present invention prepares chitosan-based hydrogel balls, which not only have high adsorption efficiency but can also be used as fertilizer after being discarded, thereby realizing the recycling and reuse of phosphorus resources and avoiding the problems caused by the landfill of traditional adsorbents. In response to the problems in the prior art that iron or calcium metal-based nanomaterials are powdery on a macro scale, difficult to recycle after use, and have limited practical applications, the present invention uses electrospraying to form charged droplets from an M-chitosan solution and solidify them to obtain chitosan-based hydrogel balls. The chitosan-based hydrogel balls have a uniform particle size of the millimeter level and are recyclable, thus solving the problem of the difficulty in recycling metal-based nanomaterials.

[0036] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments: Example 1 A method for preparing chitosan-based hydrogel spheres comprises the following steps: S1. Dissolve 2 g of chitosan in 100 mL of deionized water, add 2 mL of acetic acid, and heat at 90°C with stirring until the solution is completely dissolved and becomes a viscous liquid to obtain a 2 wt% chitosan solution. Add 1.66 g of FeCl3·6H2O and 1 g of CaCl2 to the chitosan solution and stir evenly to obtain an M-chitosan solution, which is designated as the Fe / Ca chitosan solution. 1 g of FeCl3 is contained in 1.66 g of FeCl3·6H2O.

[0037] S2. The Fe / Ca chitosan solution was loaded into a 20 mL syringe and installed on a syringe pump. The metal needle of the syringe had an inner diameter of 1.19 mm and was connected to the positive electrode of a high-voltage DC power supply. A receiving tray containing 1.25 mol / L NaOH coagulation liquid was placed directly below the needle. The distance between the needle and the liquid surface was 10 cm. A piece of aluminum foil was placed below the receiving tray and connected to the negative electrode of the high-voltage DC power supply. The output voltage of the high-voltage DC power supply was adjusted to 5 kV. The propulsion speed of the syringe pump was set to 1 mL / min. The chitosan solution was allowed to drip out of the needle to form charged droplets. The droplets fell into the NaOH coagulation liquid and solidified at room temperature for 24 hours to obtain solidified balls.

[0038] S3, the solidified balls were washed with deionized water until the pH was neutral, and chitosan-based hydrogel balls were obtained, which were recorded as Fe / Ca-CS and stored in deionized water for later use. Figure 1 shown.

[0039] Example 2 A method for preparing chitosan-based hydrogel spheres comprises the following steps: S1. Dissolve 2 g of chitosan in 100 mL of deionized water, add 2 mL of acetic acid, and heat at 90°C with stirring until completely dissolved and a viscous liquid forms, yielding a 2 wt% chitosan solution. Add 0.83 g of FeCl₃·6H₂O and 1 g of CaCl₂ to the chitosan solution and stir thoroughly to yield an M-chitosan solution, designated as the Fe / Ca chitosan solution. The 0.83 g of FeCl₃·6H₂O contains 0.5 g of FeCl₃.

[0040] S2. The Fe / Ca chitosan solution was loaded into a 20 mL syringe and installed on a syringe pump. The metal needle of the syringe had an inner diameter of 1.19 mm and was connected to the positive electrode of a high-voltage DC power supply. A receiving tray containing 1.25 mol / L NaOH coagulation liquid was placed directly below the needle. The distance between the needle and the liquid surface was 20 cm. A piece of aluminum foil was placed below the receiving tray and connected to the negative electrode of the high-voltage DC power supply. The output voltage of the high-voltage DC power supply was adjusted to 10 kV. The propulsion speed of the syringe pump was set to 1 mL / min. The chitosan solution was allowed to drip out of the needle to form charged droplets. The droplets fell into the NaOH coagulation liquid and solidified at room temperature for 24 hours to obtain solidified balls.

[0041] S3. The solidified balls were washed with deionized water until the pH was neutral to obtain chitosan-based hydrogel balls, which were recorded as Fe / Ca-CS and stored in deionized water for future use.

[0042] Example 3 A method for preparing chitosan-based hydrogel spheres comprises the following steps: S1. Dissolve 3 g of chitosan in 100 mL of deionized water, add 3 mL of acetic acid, and heat at 90°C with stirring until completely dissolved and a viscous liquid forms, yielding a 3 wt% chitosan solution. Add 1.66 g of FeCl₃·6H₂O and 1 g of CaCl₂ to the chitosan solution and stir thoroughly to yield an M-chitosan solution, designated as the Fe / Ca chitosan solution. 1 g of FeCl₃ is contained in 1.66 g of FeCl₃·6H₂O.

[0043] S2. The Fe / Ca chitosan solution was loaded into a 20 mL syringe and installed on a syringe pump. The metal needle of the syringe had an inner diameter of 1.19 mm and was connected to the positive electrode of a high-voltage DC power supply. A receiving tray containing 0.5 mol / L NaOH coagulation liquid was placed directly below the needle. The distance between the needle and the liquid surface was 5 cm. A piece of aluminum foil was placed below the receiving tray and connected to the negative electrode of the high-voltage DC power supply. The output voltage of the high-voltage DC power supply was adjusted to 0.1 kV. The propulsion speed of the syringe pump was set to 6 mL / min. The chitosan solution was allowed to drip out of the needle to form charged droplets. The droplets fell into the NaOH coagulation liquid and solidified at room temperature for 24 hours to obtain solidified balls.

[0044] S3. The solidified balls were washed with deionized water until the pH was neutral to obtain chitosan-based hydrogel balls, which were recorded as Fe / Ca-CS and stored in deionized water for future use.

[0045] Example 4 A method for preparing chitosan-based hydrogel spheres comprises the following steps: S1. Dissolve 1 g of chitosan in 100 mL of deionized water, add 1 mL of acetic acid, and heat at 90°C with stirring until completely dissolved and a viscous liquid forms, yielding a 1 wt% chitosan solution. Add 1.66 g of FeCl₃·6H₂O and 0.5 g of CaCl₂ to the chitosan solution and stir thoroughly to yield an M-chitosan solution, designated as the Fe / Ca chitosan solution. 1 g of FeCl₃ is contained in 1.66 g of FeCl₃·6H₂O.

[0046] S2. The Fe / Ca chitosan solution was loaded into a 20 mL syringe and installed on a syringe pump. The metal needle of the syringe had an inner diameter of 1.19 mm and was connected to the positive electrode of a high-voltage DC power supply. A receiving tray containing 2 mol / L NaOH coagulation liquid was placed directly below the needle. The distance between the needle and the liquid surface was 10 cm. A piece of aluminum foil was placed below the receiving tray and connected to the negative electrode of the high-voltage DC power supply. The output voltage of the high-voltage DC power supply was adjusted to 5 kV. The propulsion speed of the syringe pump was set to 0.5 mL / min. The chitosan solution was allowed to drip out of the needle to form charged droplets. The droplets fell into the NaOH coagulation liquid and solidified at room temperature for 24 hours to obtain solidified balls.

[0047] S3. The solidified balls were washed with deionized water until the pH was neutral to obtain chitosan-based hydrogel balls, which were recorded as Fe / Ca-CS and stored in deionized water for future use.

[0048] Example 5 A method for preparing chitosan-based hydrogel spheres comprises the following steps: S1. Dissolve 2 g of chitosan in 100 mL of deionized water, add 2 mL of acetic acid, and heat at 90°C with stirring until completely dissolved and a viscous liquid forms, yielding a 1 wt% chitosan solution. Add 1.66 g of FeCl₃·6H₂O to the chitosan solution and stir thoroughly to yield an M-chitosan solution, designated as the Fe-chitosan solution. 1 g of FeCl₃ is contained in 1.66 g of FeCl₃·6H₂O.

[0049] S2. The Fe / Ca chitosan solution was loaded into a 20 mL syringe and installed on a syringe pump. The inner diameter of the metal needle of the syringe was 1.19 mm, which was connected to the positive electrode of a high-voltage DC power supply. A receiving tray containing 2 mol / L NaOH coagulation liquid was placed directly below the needle. The distance between the needle and the liquid surface was 10 cm. A piece of aluminum foil was placed below the receiving tray, which was connected to the negative electrode of the high-voltage DC power supply. The output voltage of the high-voltage DC power supply was adjusted to 5 kV, and the propulsion speed of the syringe pump was set to 5 mL / min. The chitosan solution was allowed to drip out of the needle to form charged droplets. The droplets fell into the NaOH coagulation liquid and solidified at room temperature for 24 hours to obtain solidified balls.

[0050] S3. The solidified balls were washed with deionized water until the pH was neutral to obtain chitosan-based hydrogel balls, which were recorded as Fe / Ca-CS and stored in deionized water for future use.

[0051] The chitosan-based hydrogel balls of the present invention have uniform size, a particle size of 1.5 mm to 2.0 mm, and are recyclable. Figure 2 From Figures (a), (b) and (c), it can be seen that the surface of the chitosan-based hydrogel sphere is rough and wrinkled; Figure 2 As shown in Figure (d), the chitosan-based hydrogel balls are cut and densely arranged in a tube-like shape, with nano-scale pores on the tube wall and a tube diameter of about 10 μm. Figure 2 As shown in Figures (e) and (f), it can provide a transmission channel for the entry and exit of phosphorus, effectively improving the utilization rate of adsorption sites inside the chitosan-based hydrogel balls, while also facilitating the release of phosphorus as phosphorus fertilizer for plants to use.

[0052] Depend on Figure 2Figure (g) shows that Ca is relatively sparsely distributed compared to Fe. This is because equal masses of FeCl₃ and CaCl₂ were added during preparation, and the relative molecular mass of FeCl₃ is greater than that of CaCl₂, resulting in fewer Fe atoms than Ca. However, in terms of uniformity, both Fe and Ca are evenly distributed throughout the chitosan-based hydrogel spheres, indicating abundant and evenly distributed adsorption sites, enabling effective adsorption and removal of phosphorus from water, and ensuring relatively uniform phosphorus removal across each chitosan-based hydrogel sphere.

[0053] Table 1 Parameters of the adsorption isotherm model of phosphate on Fe / Ca-CS at 25°C Table 2 Parameters of the adsorption kinetic model of phosphate on Fe / Ca-CS at 25°C The phosphorus adsorption capacity of Fe / Ca-CS at different equilibrium concentrations and different adsorption times at 25°C was fitted and it was found that the adsorption of phosphorus by Fe / Ca-CS was more consistent with the Freundlich model and the pseudo-second-order kinetic model, see Figure 3 Figures (a) and (b) in the figure are shown, and the corresponding fitting parameters are obtained in Tables 1 and 2 based on the fitting model. The 1 / n ratio obtained by the Freundlich model is less than 1, indicating that phosphate is readily adsorbed by Fe / Ca-CS. At an equilibrium mass concentration of 78 mgP / L, the phosphorus adsorption capacity of Fe / Ca-CS is 21.49 mgP / g. The adsorption rate constant k2 obtained by the pseudo-second-order kinetic model is 0.0032 g / mg·min.

[0054] Whether the discarded phosphorus removal adsorbent can be recycled as fertilizer, the release of P, Fe, and Ca is a key factor, which directly determines the effect of the discarded phosphorus removal adsorbent on plants. The release amount depends on the environmental concentration. When the environmental concentration is high, it is not easy to release. When the environmental concentration is low, the elements in the material will be released and eventually reach a state of equilibrium. To this end, 1g / L dry weight of Fe / Ca-CS saturated with adsorbed phosphorus, recorded as Fe / Ca-CS-P, was added to deionized water. Samples were taken every 24 hours to detect the content of P, Fe, and Ca released by the material into the deionized water. After sampling, the deionized water was replaced with an equal volume to simulate the situation where the environmental concentration dropped due to plant absorption. The results are as follows Figure 4As shown in the figure. Initially, due to the large concentration difference between the Fe / Ca-CS-P and the surrounding water, the driving force for the release of phosphorus, calcium, and iron into the water was strong. Phosphorus and calcium release peaked on the first day, while iron reached its maximum on the second day. Thereafter, phosphorus and iron release gradually decreased over time, reaching equilibrium by the fourth day. Calcium release initially decreased, then rebounded, and finally reached equilibrium. The six-day cumulative releases of phosphorus, calcium, and iron were 5.58 mg / L, 15.86 mg / L, and 182.08 μg / L, respectively, all of which were non-toxic to plants.

[0055] To further verify the fertilizer effect of Fe / Ca-CS-P, Fe / Ca-CS-P was applied to hydroponic soybeans, and the effects of Fe / Ca-CS-P on the growth of hydroponic soybeans were studied as follows: Randomly select soybean seeds with similar morphology and sterilize them by soaking them in 3% hydrogen peroxide. Wash the seeds and soak them in a beaker overnight. Drain the water and transfer them to a petri dish. Cover the seeds with a clean, wet cloth to suffocate the germination. After the soybeans sprout, select soybean seedlings with a bud length of 1.5 cm and in good condition and transfer them to the hydroponic system. Place 15 soybeans evenly in each hydroponic pot and add 540 mL of deionized water to the hydroponic pot so that the water covers the roots. Figure 5 shown.

[0056] The experiment set up two groups, one group did not add any materials and served as a deionized water blank control group, and the other group added 5g of Fe / Ca-CS-P into the water. Figure 6 The results showed that the roots of hydroponic soybeans treated with Fe / Ca-CS-P were significantly longer than those of the deionized water blank control group.

[0057] observe Figure 7 Figures (a) and (b) show that the root and shoot lengths of hydroponic soybeans treated with Fe / Ca-CS-P were significantly longer than those of the blank control group, with average root and shoot lengths of 8.8 cm and 14.8 cm, respectively. On the seventh day of hydroponic cultivation, soybean plants were removed from the hydroponic system, allowed to air dry, and the fresh weights of the soybean shoots and roots were measured. Figure 7 The plants were then placed in an oven at 105°C for 30 minutes to cure, and the temperature was lowered to 80°C to dry to constant weight. The dry weight of soybean sprouts and roots was then measured, as shown in Figure (c). Figure 7 As shown in Figure (d). Figure 7 Figures (c) and (d) show that the hydroponic soybean sprouts and roots treated with Fe / Ca-CS-P were heavier than those in the blank control group, both in fresh weight and dry weight.

[0058] observe Figure 8The results showed that the total length of soybeans treated with Fe / Ca-CS-P was still significantly longer than that of the blank control group, with average lengths of 55.3 cm and 29.3 cm, respectively. Compared with the blank control group, the length of hydroponic soybeans treated with Fe / Ca-CS-P increased by 66.5%, which was more significant than the 28% increase after 7 days of hydroponics. In summary, the growth of hydroponic soybeans treated with Fe / Ca-CS-P was significantly better than that of the deionized water control group without Fe / Ca-CS-P, indicating that the elements released by Fe / Ca-CS-P play a positive role in plant growth and have a fertilizer effect.

[0059] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes preferred embodiments. Although preferred embodiments of the present invention have been described, those skilled in the art will be able to make additional changes and modifications to these embodiments once they understand the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

Claims

1. A method for preparing chitosan-based hydrogel spheres, characterized in that: The steps include: mixing an acidic aqueous solution of chitosan with a metal salt to obtain an M-chitosan solution; Wherein, the metal salt is selected from a soluble iron salt or a mixture of a soluble iron salt and a soluble calcium salt; Electrospraying was used to form charged droplets from the M-chitosan solution, which were then dropped into an alkaline coagulation solution. After solidification, chitosan-based hydrogel spheres were obtained. The conditions for the electrospray treatment are: an output voltage of 0.1 kV to 10 kV and a propulsion speed of 0.5 mL / min to 6 mL / min.

2. The method for preparing chitosan-based hydrogel spheres according to claim 1, wherein When the metal salt is selected from a mixture of soluble iron salt and soluble calcium salt, in the M-chitosan solution, the mass percentage of chitosan is 1wt%~3wt%, the ratio of chitosan to the total mass of the metal salt is 1:0.5~2, and the mass ratio of the soluble iron salt to the soluble calcium salt is 1:1~3.

3. The method for preparing chitosan-based hydrogel spheres according to claim 1, wherein When the metal salt is selected from soluble iron salt, the mass ratio of chitosan to soluble iron salt in the M-chitosan solution is 1:0.5~2.

4. The method for preparing chitosan-based hydrogel spheres according to claim 1, wherein The operation of EFI treatment is: The M-chitosan solution was loaded into a syringe, the syringe needle was connected to the positive electrode of a high-voltage DC power supply, a receiving tray containing an alkaline coagulant solution was placed under the syringe needle, an aluminum foil was placed under the receiving tray, and the aluminum foil was connected to the negative electrode of the power supply. A high-voltage DC power was applied and the propulsion pump was turned on for electrospray treatment, so that the M-chitosan solution dripped out of the needle and formed charged droplets, which dripped into the alkaline coagulant solution.

5. The method for preparing chitosan-based hydrogel spheres according to claim 4, characterized in that: The vertical distance between the liquid surface of the alkaline coagulation solution and the syringe needle is 5 cm to 20 cm.

6. The method for preparing chitosan-based hydrogel spheres according to claim 1, characterized in that: The curing conditions are: curing at room temperature for 12h~24h.

7. The method for preparing chitosan-based hydrogel spheres according to claim 1, characterized in that: The alkaline coagulation liquid is a NaOH solution, and the concentration of the NaOH solution is 0.5 mol / L~2 mol / L.

8. A chitosan-based hydrogel sphere, characterized in that: The chitosan-based hydrogel spheres are prepared by the preparation method according to any one of claims 1 to 7. The microscopic surface of the chitosan-based hydrogel spheres is wrinkled, the cross section is densely arranged in a tube bundle, and there are nano-scale pores on the tube wall.

9. Use of the chitosan-based hydrogel spheres according to claim 8 in preparing a chitosan-based hydrogel sphere adsorbent.

10. The use according to claim 9, characterized in that The chitosan-based hydrogel ball adsorbent is used for adsorbing phosphorus in wastewater, and the chitosan-based hydrogel ball adsorbent after adsorbing phosphorus can be used as a fertilizer.

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