Phosphate adsorbent, method for preparing the same, and use thereof

Abstract

The application provides a phosphate adsorbent and a preparation method and application thereof. The specific surface area of the clay-iron composite prepared by the application is 87.6 m 2 / g, which is higher than 63.6 m 2 / g of the clay. The adsorbent prepared by the application has a large specific surface area. The adsorption capacity of the clay-iron composite prepared by the application to the phosphate is 1.936 mg / g, and the adsorption rate is 88.165%. The bentonite selected by the application has a strong phosphate adsorption capacity and an expansion structure, which is beneficial to the loading of iron. After the iron is combined with the bentonite, the iron ion solution and the composite are separated, and then the iron oxide is synthesized again. Compared with the prior art of directly mixing the iron oxide and the clay mineral or synthesizing the iron oxide in the state that the clay mineral is dispersed in the iron ion solution, the method of the application retains the increased phosphate adsorption capacity of the iron oxide and reduces the content of iron in the composite, and has a higher environmental protection value.

Description

Technical Field

[0001] This invention relates to the field of adsorbent technology, and in particular to a phosphate adsorbent, its preparation method, and its application. Background Technology

[0002] Phosphorus is a key factor in eutrophication of water bodies, which can cause severe environmental pollution and ecological damage. In recent years, driven by the national policy of ecological civilization construction, the treatment of phosphorus eutrophication in aquatic environments has gradually shifted towards methods that have no impact on the ecological environment. Currently, common phosphorus removal technologies are mainly divided into three categories: physical, chemical, and biological phosphorus removal. For water environment treatment, chemical precipitation is costly and prone to causing secondary pollution, while biological phosphorus removal is time-consuming and affected by factors such as water quality, temperature, and pH, making it unsuitable for a wide range of water bodies. Therefore, physical remediation is currently the main measure for treating phosphorus pollution in water bodies, with adsorption being considered the most commonly used phosphate removal technology due to its simple principle, convenient operation, and significant effects.

[0003] Currently, commonly used adsorption methods mainly involve synthesizing new materials or improving the physicochemical properties of common adsorbent materials to enhance their adsorption capacity for phosphates. Activated carbon, metal oxides, and clay minerals are widely used adsorbents, each with its own advantages and disadvantages. For example, activated carbon has extremely strong adsorption capacity but is very expensive; metal oxides, especially iron oxides, also have strong phosphorus adsorption capacity and are more affordable than activated carbon, but may cause iron pollution and other impacts when introduced into water bodies; clay mineral iron oxides are more affordable than activated carbon and are also harmless, but their adsorption capacity is slightly weaker.

[0004] Given the shortcomings of current phosphorus adsorbents, it is necessary to improve them. Summary of the Invention

[0005] In view of this, the present invention addresses the shortcomings of the prior art by proposing a phosphate adsorbent, its preparation method, and its application, in order to solve or at least partially solve the defects of the prior art.

[0006] This invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a phosphate adsorbent, comprising the following steps:

[0008] Bentonite was added to a ferric solution and shaken to obtain an iron-loaded bentonite solution.

[0009] After centrifuging the bentonite solution loaded with iron, the supernatant was discarded to obtain the first precipitate;

[0010] Add water to the first precipitate and adjust the pH to neutral. Shake to obtain a complex solution.

[0011] After centrifuging the complex solution, the supernatant was discarded to obtain the second precipitate;

[0012] After freezing and drying the second precipitate, a clay-iron composite is obtained, which is the phosphate adsorbent.

[0013] Preferably, the trivalent iron solution includes at least one of FeCl3 solution, Fe(NO3)3 solution, and Fe2(SO4)3 solution.

[0014] Preferably, bentonite is added to a ferric solution and shaken in a shaker at a speed of 200-250 rpm and a temperature of 20-30°C for 20-30 hours to obtain a bentonite solution loaded with iron.

[0015] Preferably, the bentonite solution loaded with iron is centrifuged at 3000-5000 rpm and 20-30°C for 5-20 min, the supernatant is discarded, and the solution is washed to obtain the first precipitate.

[0016] Preferably, water is added to the first precipitate, ultrasonically dispersed for 5-15 minutes, the pH is adjusted to neutral using NaOH solution, and the mixture is shaken in a shaker at 200-250 rpm and 20-30°C for 20-30 hours to obtain the complex solution.

[0017] Preferably, the complex solution is centrifuged at 3000–5000 rpm and 20–30°C for 5–20 min, the supernatant is discarded, and the mixture is washed to obtain the second precipitate.

[0018] Preferably, in the step of freezing the second precipitate, the freezing temperature is -20 to -25°C and the freezing time is 20 to 30 hours.

[0019] Preferably, the concentration of the ferric iron solution is 0.05–0.2 M;

[0020] The mass-to-volume ratio of the bentonite to the ferric solution is (3-7) g:(1-2) L.

[0021] Secondly, the present invention also provides a phosphate adsorbent, which is prepared by the preparation method described above.

[0022] Thirdly, the present invention also provides an application of the phosphate adsorbent described above in the removal of phosphate from water.

[0023] The method for preparing the phosphate adsorbent of the present invention has the following advantages over the prior art:

[0024] The preparation method of the phosphate adsorbent of the present invention greatly enhances the adsorption capacity of clay minerals by combining iron oxides and clay minerals (i.e., bentonite); the clay-iron composite phosphate adsorbent prepared by the present invention has a specific surface area of ​​87.6 m². 2 / g, higher than 63.6m of clay. 2 The adsorbent prepared by this invention has a large specific surface area. Experiments show that the clay-iron composite prepared by this invention has the highest phosphate adsorption capacity of 1.936 mg / g and an adsorption rate of 88.165%. In contrast, clay has the highest phosphate adsorption capacity of 0.054 mg / g and an adsorption rate of 4.314%, while the clay-goethite mixture has the highest phosphate adsorption capacity of 0.668 ± 0.036 mg / g and an adsorption rate of 86.482%. Compared to clay and the clay-goethite mixture, the clay-iron composite prepared by this invention has a significantly higher phosphate adsorption capacity. Furthermore, this invention combines iron oxides and clay minerals (i.e., bentonite), which improves the adsorption capacity of clay minerals while reducing the influence of iron oxides. Compared to previous similar bonding methods, the bentonite selected in this invention has a strong phosphorus adsorption capacity and an expansion structure that facilitates iron loading. Furthermore, the iron oxide is synthesized by separating the iron ion solution and the composite after the iron is combined with the bentonite. Compared to the previous method of directly mixing iron oxide and clay minerals or synthesizing iron oxide while the clay minerals are dispersed in the iron ion solution, this method retains the increased phosphorus adsorption capacity of the iron oxide while reducing the iron content in the composite, thus having higher environmental value. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The image shows the X-ray diffraction pattern of the clay-iron composite prepared in Example 1 and the clay.

[0027] Figure 2 The diagram shows the clay-iron composite prepared in Example 1 and the zeta potential changes of the clay at pH 2 to 8.

[0028] Figure 3 This is an atomic force microscope image of the clay-iron composite prepared in Example 1.

[0029] Figure 4 The images shown are transmission electron microscopy (TEM) images and EDS (energy dispersive spectroscopy) images of the clay-iron composite prepared in Example 1.

[0030] Figure 5 The nitrogen adsorption and desorption curves of the clay-iron composite and clay prepared in Example 1 are shown.

[0031] Figure 6 The Mössbauer spectrum of the clay-iron composite prepared in Example 1;

[0032] Figure 7 The adsorption capacity of clay-iron composites for phosphorus under different phosphorus concentrations;

[0033] Figure 8 The isothermal adsorption curves and adsorption kinetic curves of phosphate ions on the clay-iron composite prepared in Example 1 are shown.

[0034] Figure 9 The adsorption capacity of clay for phosphorus at different phosphorus concentrations in Comparative Example 1 is shown.

[0035] Figure 10 This represents the phosphorus adsorption capacity of the clay-goethite mixture under different phosphorus concentrations in Comparative Example 2. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present 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 digits 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.

[0039] This application provides a method for preparing a phosphate adsorbent, comprising the following steps:

[0040] S1. Add bentonite to the ferric solution and shake to obtain a bentonite solution loaded with iron.

[0041] S2. After centrifuging the bentonite solution loaded with iron, discard the supernatant to obtain the first precipitate;

[0042] S3. Add water to the first precipitate and adjust the pH to neutral. Shake to obtain a complex solution.

[0043] S4. After centrifuging the complex solution, discard the supernatant to obtain the second precipitate;

[0044] S5. After freezing the second precipitate, dry it to obtain a clay-iron composite, which is the phosphate adsorbent.

[0045] This invention combines iron oxides and clay minerals (i.e., bentonite) to greatly enhance the adsorption capacity of clay minerals; the clay-iron composite phosphate adsorbent prepared by this invention has a specific surface area of ​​87.6 m². 2 / g, higher than 63.6m of clay. 2The adsorbent prepared by this invention has a large specific surface area. Experiments show that the clay-iron composite prepared by this invention has the highest phosphate adsorption capacity of 1.936 mg / g and an adsorption rate of 88.165%. In contrast, clay has the highest phosphate adsorption capacity of 0.054 mg / g and an adsorption rate of 4.314%, while the clay-goethite mixture has the highest phosphate adsorption capacity of 0.668 ± 0.036 mg / g and an adsorption rate of 86.482%. Compared to clay and the clay-goethite mixture, the clay-iron composite prepared by this invention has a significantly higher phosphate adsorption capacity. Furthermore, this invention combines iron oxides and clay minerals (i.e., bentonite), which improves the adsorption capacity of clay minerals while reducing the influence of iron oxides. Compared to previous similar bonding methods, the bentonite selected in this invention has a strong phosphorus adsorption capacity and an expansion structure that facilitates iron loading. Furthermore, the iron oxide is synthesized by separating the iron ion solution and the composite after the iron and bentonite are combined. Compared to the previous method of directly mixing iron oxide and clay minerals or synthesizing iron oxide while the clay minerals are dispersed in the iron ion solution, this method retains the increased phosphorus adsorption capacity of iron oxide while reducing the iron content in the composite (the iron content in the clay-iron composite prepared in Example 1 of this invention is about 5%, while the iron content in the previous mixture of iron oxide and clay minerals was about 20%. This invention, while reducing the iron content in the composite, also has extremely high phosphorus adsorption capacity), thus having higher environmental value.

[0046] In some embodiments, the ferric solution includes at least one of FeCl3 solution, Fe(NO3)3 solution, and Fe2(SO4)3 solution.

[0047] In some embodiments, bentonite is added to a ferric solution and shaken in a shaker at a speed of 200-250 rpm and a temperature of 20-30°C for 20-30 hours to obtain a bentonite solution loaded with iron.

[0048] In some embodiments, the bentonite solution loaded with iron is centrifuged at 3000-5000 rpm and 20-30°C for 5-20 min, the supernatant is discarded, and the solution is washed to obtain the first precipitate.

[0049] In some embodiments, water is added to the first precipitate, ultrasonically dispersed for 5–15 min, the pH is adjusted to neutral using NaOH solution, and the mixture is shaken in a shaker at 200–250 rpm and 20–30 °C for 20–30 h to obtain a composite solution.

[0050] Specifically, in the above embodiments, the concentration of the NaOH solution was 0.5–1 M.

[0051] In some embodiments, the complex solution is centrifuged at 3000–5000 rpm and 20–30°C for 5–20 min, the supernatant is discarded, and the solution is washed to obtain a second precipitate.

[0052] In some embodiments, in the step of freezing the second precipitate, the freezing temperature is -20 to -25°C and the freezing time is 20 to 30 hours.

[0053] In some embodiments, the concentration of the ferric solution is 0.05–0.2 M;

[0054] In some embodiments, the mass-to-volume ratio of bentonite to ferric solution is (3-7) g:(1-2) L.

[0055] In some embodiments, the second precipitate is frozen, dried, ground in a mortar and pestle, and then passed through a 50-150 mesh sieve to obtain a clay-iron composite, which is a phosphate adsorbent.

[0056] Based on the same inventive concept, the present invention also provides a phosphate adsorbent, which is prepared by the above-described preparation method.

[0057] Based on the same inventive concept, the present invention also provides the application of the above-mentioned phosphate adsorbent in the removal of phosphate from water.

[0058] The following specific embodiments further illustrate the phosphate adsorbent of this application, its preparation method, and its application. This section further illustrates the content of the present invention in conjunction with specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0059] Example 1

[0060] This application provides a method for preparing a phosphate adsorbent, comprising the following steps:

[0061] S1. Add 5g of bentonite to 1L of 0.1M FeCl3 solution and shake in a shaker at 220rpm and 25℃ for 24h to obtain a bentonite solution loaded with iron.

[0062] S2. Centrifuge the iron-loaded bentonite solution at 3000 rpm and 25°C for 10 min, discard the supernatant, and wash three times with ultrapure water to obtain the first precipitate.

[0063] S3. Add 1L of water to the first precipitate, sonicate for 10min, adjust the pH to 7 with 0.5M NaOH solution, and shake in a shaker at 220rpm and 25℃ for 24h to obtain the complex solution.

[0064] S4. Centrifuge the complex solution at 3000 rpm and 25°C for 10 min, discard the supernatant, and wash three times with ultrapure water to obtain the second precipitate.

[0065] S5. Freeze the second precipitate at -20℃ for 24 hours, dry it, grind it in a mortar and pestle and pass it through a 100-mesh sieve to obtain a clay-iron composite, which is the phosphate adsorbent.

[0066] Example 2

[0067] This embodiment provides an application of a phosphate adsorbent in removing phosphate from water, including the following steps:

[0068] 0.04 g of the clay-iron composite prepared in Example 1 was added to 20 mL of solutions with phosphorus concentrations of 1 mg / L, 2 mg / L, 3 mg / L, 4 mg / L, and 5 mg / L (specifically, KH2PO4 solutions). After shaking at 220 rpm for 24 h, the remaining phosphorus content was measured by centrifugation, and the adsorption capacity of the clay-iron composite for phosphorus was calculated.

[0069] Comparative Example 1

[0070] This comparative example provides an application of a phosphate adsorbent in removing phosphate from water, including the following steps:

[0071] S1. Add 0.04g of clay (i.e., the bentonite used in Example 1) to 20mL of solutions with phosphorus concentrations of 1mg / L, 2mg / L, 3mg / L, 4mg / L, and 5mg / L respectively (specifically, KH2PO4 solution). After shaking at 220rpm for 24h, centrifuge to measure the remaining phosphorus content and calculate the adsorption capacity of the clay for phosphorus.

[0072] Comparative Example 2

[0073] This comparative example provides a method for preparing a phosphate adsorbent, comprising the following steps:

[0074] S1. Mix clay (i.e., the bentonite used in Example 1) and goethite in a mass ratio of 1:1 to obtain a clay-goethite mixture.

[0075] The synthesis method of goethite is as follows: 27.03g of ferric chloride hexahydrate is added to 1L of water to prepare 0.1M FeCl3 solution. 0.1M KOH is added to adjust the pH to 7. The solution is then transferred to a reaction vessel and aged at 70℃ for 48h. After centrifugation at 5000rpm for 10min, the solution is rinsed with water and centrifuged again at 5000rpm for 10min. This process is repeated three times. The precipitate is collected, freeze-dried, and stored at -20℃ for later use.

[0076] S2. Add 0.04g of the clay-goethite mixture from step S1 to 20mL of solutions with phosphorus concentrations of 1mg / L, 2mg / L, 3mg / L, 4mg / L, and 5mg / L (specifically, KH2PO4 solutions). After shaking at 220rpm for 24h, centrifuge to measure the remaining phosphorus content and calculate the adsorption capacity of the clay-goethite mixture for phosphorus.

[0077] Performance Characterization

[0078] Figure 1 The X-ray diffraction patterns are those of the clay-iron composite prepared in Example 1 and the clay (i.e., the bentonite used in Example 1).

[0079] from Figure 1 As can be seen, the iron loading process altered the structure of the 001 crystal plane of the clay.

[0080] Figure 2 The graph shows the zeta potential changes of the clay-iron composite prepared in Example 1 and the clay (i.e., the bentonite used in Example 1) at pH 2 to 8.

[0081] from Figure 2 As can be seen, the material potential gradually increases as the environmental pH decreases, and the potential of the clay-iron composite is higher than that of the clay, indicating that the loading of iron into the clay changes the electrical properties of the clay.

[0082] Figure 3 This is an atomic force microscope image of the clay-iron composite prepared in Example 1. Figure 3 In the diagram, A, B, and C represent atomic force microscope images at different magnifications.

[0083] from Figure 3 As can be seen, the clay-iron composite prepared in Example 1 exhibits a tightly aggregated cluster morphology.

[0084] Figure 4 The images show the transmission electron microscope (TEM) image and EDS spectrum of the clay-iron composite prepared in Example 1. Figure 4 In Figure A, the image is a transmission electron microscope image; in Figure B, the image is a magnified view of the area within the box in Figure A; and in Figure C, the image is an EDS spectrum.

[0085] from Figure 4 As can be seen, particles resembling amorphous iron oxides were found on the surface of the clay, and elemental analysis showed that the distribution of iron and silicon was extremely similar, indicating that the clay and iron were tightly bound together in space.

[0086] Figure 5 The nitrogen adsorption and desorption curves are shown for the clay-iron composite and clay (i.e., the bentonite used in Example 1) prepared in Example 1.

[0087] The specific surface areas of the clay-iron composite prepared in Example 1 and the clay (i.e., the bentonite used in Example 1) are shown in Table 1 below.

[0088]

[0089]

[0090] As can be seen from Table 1, the specific surface area of ​​the clay-iron composite prepared by this invention is 87.6 m². 2 / g, higher than 63.6m of clay. 2 / g.

[0091] Figure 6 The Mössbauer spectrum is shown for the clay-iron composite prepared in Example 1.

[0092] from Figure 6 As can be seen from the example, the main form of iron in the clay-iron composite prepared in Example 1 is ferrohydrate.

[0093] Following the method in Example 2, the adsorption capacity of the clay-iron composite for phosphorus at different phosphorus concentrations was calculated, and the results are as follows: Figure 7 As shown.

[0094] from Figure 7 As can be seen, the clay-iron composite prepared in Example 1 has the highest phosphate adsorption capacity of 1.936 mg / g, with an adsorption rate of 88.165%.

[0095] Figure 8 The isothermal adsorption curves and adsorption kinetic curves of phosphate ions prepared in Example 1 are shown. Specifically, 0.01 g of the clay-iron composite prepared in Example 1 was added to 20 mL of solutions with phosphorus concentrations of 0.5 mg / L, 1 mg / L, 2 mg / L, 3 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, and 30 mg / L (specifically KH2PO4 solution). After shaking at 220 rpm for 24 h, the remaining phosphorus content was measured by centrifugation. The adsorption capacity of the clay-iron composite for phosphorus was calculated, and the isothermal adsorption curves were fitted using Langmuir and Freundlich models. Similarly, 0.01 g of the clay-iron composite was added to 20 mL of a solution with a phosphorus concentration of 10 mg / L. After shaking at 220 rpm for 24 h, the remaining phosphorus content was measured by centrifugation. The phosphorus adsorption capacity of the composite was calculated, and the adsorption kinetic curves were fitted using pseudo-first-order and pseudo-second-order kinetic models.

[0096] The fitting parameters for the isothermal adsorption curves of phosphate by the clay-iron composite prepared in Example 1 are shown in Table 2 below. max To fit the Langmuir model, the maximum phosphate adsorption capacity of the complex, kL and k F 1 / n represents the adsorption rate fitted by the Langmuir and Freundlich models, respectively, where n is the affinity of the adsorbent for the adsorbate fitted by the Freundlich model. Generally, an adsorption reaction is considered to occur readily when the value of 1 / n is between 0.1 and 0.5, with Freundlich exhibiting a higher R1. 2 This indicates that the adsorption of phosphate by the clay-iron complex is more inclined to irregular multilayer adsorption, and it has a stronger adsorption effect and a more stable binding capacity for phosphate.

[0097] Table 2 - Fitting parameters for the isothermal adsorption curves of phosphate by clay-iron composites

[0098]

[0099] The fitting parameters for the adsorption kinetics curves of the clay-iron composite for phosphate prepared in Example 1 are shown in Table 3 below. Q1 and Q2 represent the maximum adsorption capacity of the composite for phosphate fitted by the pseudo-first-order and pseudo-second-order kinetic models, respectively. k1 and k2 represent the adsorption rates fitted by the pseudo-first-order and pseudo-second-order kinetic models, respectively. The pseudo-second-order kinetic model has a higher R1. 2 This indicates that the adsorption of phosphate by the clay-iron complex is more inclined to irregular multilayer adsorption, and it has a stronger adsorption effect and a more stable binding capacity for phosphate.

[0100] Table 3 - Fitting parameters for the adsorption kinetics curves of phosphate by clay-iron composites

[0101]

[0102] Following the method in Comparative Example 1, the adsorption capacity of clay for phosphorus at different phosphorus concentrations was calculated, and the results are as follows: Figure 9 As shown.

[0103] from Figure 9 As can be seen from the data, the clay in Comparative Example 1 has the highest phosphate adsorption capacity of 0.054 mg / g, with an adsorption rate of 4.314%.

[0104] Following the method in Comparative Example 2, the adsorption capacity of the clay-goethite mixture for phosphorus under different phosphorus concentrations was calculated, and the results are as follows: Figure 10 As shown.

[0105] from Figure 10 As can be seen from the data, the clay-goethite mixture in Comparative Example 2 has the highest phosphate adsorption capacity of 0.668±0.036 mg / g, with an adsorption rate of 86.482%.

[0106] Following the methods described in Example 2 and Comparative Examples 1-2, the adsorption capacity of different adsorbents for phosphorus at different phosphorus concentrations was calculated, and the results are shown in Table 4 below.

[0107] Table 4 - Adsorption capacity of different adsorbents for phosphorus

[0108]

[0109] As can be seen from Table 4, as the phosphate concentration increases, the amount of phosphorus adsorbed increases while the adsorption rate decreases. Therefore, the strongest adsorption capacity of the clay-iron composite of the present invention is at an initial concentration of 5 mg / L, while the maximum adsorption rate is at an initial concentration of 1 mg / L (test concentration). Furthermore, the adsorption capacity of the clay-iron composite of the present invention for phosphorus is much higher than that of clay and clay-goethite mixture.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of a phosphate adsorbent in the removal of phosphates from water; The phosphate is KH2PO4; The preparation method of the phosphate adsorbent includes the following steps: S1. Add 5g of bentonite to 1L of 0.1M FeCl3 solution and shake in a shaker at 220rpm and 25℃ for 24h to obtain a bentonite solution loaded with iron. S2. Centrifuge the iron-loaded bentonite solution at 3000 rpm and 25°C for 10 min, discard the supernatant, and wash three times with ultrapure water to obtain the first precipitate. S3. Add 1L of water to the first precipitate, sonicate for 10min, adjust the pH to 7 with 0.5M NaOH solution, and shake in a shaker at 220rpm and 25℃ for 24h to obtain the complex solution. S4. Centrifuge the complex solution at 3000 rpm and 25°C for 10 min, discard the supernatant, and wash three times with ultrapure water to obtain the second precipitate. S5. Freeze the second precipitate at -20℃ for 24 hours, dry it, grind it in a mortar and pestle and pass it through a 100-mesh sieve to obtain a clay-iron composite, which is the phosphate adsorbent.

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