Magnetic aluminum-iron loaded modified sludge hydrothermal carbon, and preparation method and application thereof

Abstract

This invention relates to the field of environmental functional material preparation technology, specifically to a magnetic aluminum-iron supported modified sludge hydrothermal carbon, its preparation method, and its application. The sludge hydrothermal carbon prepared using hydrothermal carbonization technology is a porous carbonaceous carrier with a high specific surface area and abundant oxygen-containing functional groups. The product obtained by impregnating and precipitating the sludge hydrothermal carbon with an aluminum precursor, ferrous salt, and ferric salt is an aluminum-iron oxide (mainly Fe3O4) supported on a porous sludge carbon body. Utilizing the abundant acidic functional groups and active sites of metal oxides on the product surface, highly efficient chemical adsorption of fluoride ions is achieved. This adsorption mainly relies on the complexation, exchange, and surface binding of Al(OH)3 and other phases with fluoride ions. After adsorption, the fluoride ions can be rapidly recovered and reused through an external magnetic field, avoiding secondary pollution. Therefore, the magnetic aluminum-iron supported modified sludge hydrothermal carbon possesses the dual advantages of highly efficient fluoride removal and magnetic recovery.

Description

Technical Field

[0001] This invention belongs to the field of functional material preparation technology, and specifically relates to a magnetic aluminum-iron supported modified sludge hydrothermal carbon, its preparation method, and its application. Background Technology

[0002] Fluoride pollution is a significant environmental and health issue. Fluoride-containing water treatment technologies are widely used in drinking water and industrial wastewater treatment. Adsorption methods are recognized as an economical and effective method for fluoride removal due to their low cost, ease of operation, and high removal efficiency. Existing research has reported on various fluoride removal adsorbents, including alumina, activated carbon, layered double hydroxides, and other natural and synthetic materials. These materials have attracted attention due to their abundant and readily available sources. However, these traditional adsorbents typically suffer from limited adsorption capacity and difficulty in further improving adsorption efficiency. Furthermore, in practical applications, because the adsorbents are often in powder form, they are prone to clogging and high pressure drops during filtration, making efficient recovery difficult.

[0003] To address the challenge of adsorbent recovery, researchers have begun developing new adsorption materials. Some literature indicates that preparing biochar from waste sludge and loading it with metal ions can improve fluoride removal performance. For example, the material obtained by combining sludge biochar with lanthanum ions can achieve a maximum fluoride ion adsorption capacity of approximately 40 mg / g, demonstrating that metal modification can enhance the fluoride removal capacity of sludge biochar. However, the aforementioned studies often struggle to simultaneously achieve high adsorption capacity and easy recovery. Therefore, there is an urgent need to design a fluoride removal adsorption material that possesses both excellent adsorption performance and can be easily recovered magnetically to improve fluoride removal efficiency and facilitate adsorbent regeneration. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, the present invention aims to provide a magnetic aluminum-iron supported modified sludge hydrothermal carbon, its preparation method, and its application. This method utilizes waste sludge to prepare porous hydrothermal carbon as a carbonaceous carrier, and employs an impregnation and precipitation method to support aluminum-iron precursors. The resulting material possesses both excellent fluoride ion adsorption capacity and magnetic recyclability.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon, comprising the following steps:

[0006] After mixing dry sludge with deionized water, the mixture is reacted in a hydrothermal reaction at a temperature of 160℃~260℃ for 0.5h~2h to obtain sludge hydrothermal carbon.

[0007] The obtained hydrothermal sludge carbon was combined with aluminum precursor, ferrous salt and ferric salt by impregnation and precipitation method to prepare magnetic aluminum-iron supported modified hydrothermal sludge carbon.

[0008] The hydrothermal reaction temperature is controlled between 160℃ and 260℃. This temperature range is sufficient to convert sludge into stable carbonized material while maintaining a high yield and good pore structure. A shorter hydrothermal reaction time may lead to incomplete conversion, while an excessively long reaction time may result in unnecessary energy consumption and excessive decomposition of organic matter, affecting the adsorption performance of the hydrothermal carbon.

[0009] Preferably, the impregnation precipitation method is a stepwise impregnation precipitation method, and the steps are as follows:

[0010] Ferrous salt and ferric salt were dissolved in deionized water to prepare an iron precursor solution. The iron precursor solution was then mixed with sludge hydrothermal carbon to obtain mixed solution B.

[0011] The pH of mixed solution B is adjusted to 9-10, stirred, allowed to stand overnight, filtered, washed, dried, and pulverized to obtain pretreated material B. Pretreated material B is calcined under a nitrogen atmosphere to obtain magnetic pretreated material C. Then, an aluminum precursor is dissolved in deionized water to prepare an aluminum precursor solution. The aluminum precursor solution is then mixed with the magnetic pretreated material to obtain mixed solution C. The pH of mixed solution C is then adjusted to 9-10, stirred, allowed to stand overnight, filtered, washed, dried, and pulverized to obtain pretreated material D. Pretreated material D is calcined under a nitrogen atmosphere or not calcined to obtain magnetic aluminum-iron supported modified sludge hydrothermal carbon.

[0012] When the pH of mixed solution B is 9-10, Fe 2+ It mainly precipitates as Fe(OH)2, Fe 3+ Precipitated in the form of Fe(OH)3, it can be fully deposited on the surface of the hydrothermal carbon carrier of sludge, forming a uniformly distributed iron hydroxide, which lays the foundation for the subsequent calcination to form magnetic Fe3O4.

[0013] If pH < 9, Fe(OH)2 and Fe(OH)3 precipitation is incomplete, resulting in iron ions remaining in the solution, low loading, and affecting the magnetic properties and number of active sites of the material.

[0014] If pH > 10, some iron ions may be present as soluble [Fe(OH)4]. - The presence of iron ions leads to a decrease in loading efficiency and may also cause damage to the surface structure of the carbon support.

[0015] When the pH of mixed solution C is 9-10, Al 3+ It mainly precipitates in the form of Al(OH)3.

[0016] Preferably, the impregnation precipitation method is a one-step impregnation precipitation method, and the steps are as follows:

[0017] An aluminum-iron precursor solution was prepared by dissolving the aluminum precursor, ferrous salt, and ferric salt in deionized water.

[0018] A mixed solution A is obtained by mixing aluminum-iron precursor solution with sludge hydrothermal carbon.

[0019] The pH of the mixed solution A was adjusted to 9-10, and after stirring and standing overnight, it was filtered, washed, dried and pulverized to obtain pretreated material A. The pretreated material A was then calcined under a nitrogen atmosphere to obtain magnetic aluminum-iron supported modified sludge hydrothermal carbon.

[0020] When the pH of mixed solution A is alkaline, a black precipitate will form. However, when the pH of mixed solution A is in the range of pH 9-10, Al... 3+ It mainly precipitates as Al(OH)3, while Fe 2+ / Fe 3+ They precipitate as Fe(OH)₂ and Fe(OH)₃, respectively. If the pH of mixed solution A is < 9, the precipitation of Al(OH)₃ will be incomplete; if the pH of mixed solution A is > 10, soluble [Al(OH)₄] will be formed. - Or [Fe(OH)4] - This reduces load efficiency.

[0021] Preferably, the aluminum precursor is selected from any one of aluminum chloride, aluminum sulfate, and aluminum nitrate; the ferrous salt is ferrous chloride or ferrous sulfate, and the ferric salt is ferric chloride and ferric sulfate.

[0022] Aluminum chloride, aluminum sulfate, and aluminum nitrate were chosen as aluminum precursors primarily because of their good solubility, high reactivity, and ability to form Al(OH)3 colloids under hydrothermal conditions. Furthermore, these three aluminum salts are widely available and inexpensive, making them suitable for large-scale applications. Different aluminum salts have limited impact on the structure and adsorption performance of the final material, therefore all can be selected as precursors. Ferrous chloride or ferrous sulfate were chosen as ferrous salts because of their good solubility and high reactivity, facilitating the formation of Fe... 2+ They are uniformly dispersed and react with the carrier to form magnetic oxides such as Fe3O4. These salts are widely available and inexpensive, making them suitable for large-scale preparation.

[0023] Ferric chloride and ferric sulfate were chosen as iron salts because, for the same reason, they have high solubility, which can ensure the iron content of Fe is reduced. 3+ They fully participate in the reaction. Furthermore, these salts are widely available and inexpensive, making them suitable for large-scale preparation.

[0024] Preferably, the concentration of the aluminum precursor solution is 0.1 mol / L to 0.5 mol / L, the concentration of the aluminum-iron precursor solution is 0.01 mol / L to 0.5 mol / L, and the concentration of the iron precursor solution is ≥0.4 mol / L, wherein the molar ratio of ferrous salt to ferric salt in both the aluminum-iron precursor solution and the iron precursor solution is 1:2.

[0025] The reason for setting the molar ratio of ferrous salt to ferric salt in both the aluminum-iron precursor solution and the iron precursor solution to 1:2 is based on Fe 2+ +2Fe 3+ +4OH - The reaction equation →Fe3O4 + 2H2O ensures optimal formation of Fe3O4. Theoretically, this ratio can be adjusted, but deviations from 1:2 will lead to an excess of certain iron ions, affecting the product composition and magnetism.

[0026] The concentration of the aluminum precursor solution was selected from 0.1 mol / L to 0.5 mol / L. The concentration of the aluminum-iron precursor solution was chosen to ensure that aluminum ions could fully react with the carbon support surface to form a uniform loaded layer. Too low a concentration would result in insufficient loading and affect adsorption performance; too high a concentration might lead to aluminum salt agglomeration, pore blockage, and a reduction in the specific surface area of ​​the material. Therefore, this concentration range balanced the uniformity of loading and the optimization of the material's pore structure. The concentration of the iron precursor solution was selected to be ≥0.4 mol / L. Under this concentration condition, the prepared magnetic pretreated material exhibited good magnetic properties.

[0027] Preferably, the molar ratio of total iron to aluminum in the aluminum-iron precursor solution is 1:1 to 5:1.

[0028] This ratio range is beneficial for forming a uniform aluminum-iron oxide layer on the carbon support surface, ensuring sufficient iron to impart magnetism while also taking into account the adsorption activity of aluminum. Too much iron will clog the pores, while too much aluminum will result in insufficient magnetism.

[0029] Preferably, the mass ratio of sludge hydrothermal carbon to the volume ratio of the aluminum-iron precursor solution in mixed solution A is 2.5 g / L to 10 g / L. This ratio is selected based on the optimal loading of metal oxides during adsorbent preparation. This range ensures that metal ions are fully dispersed on the carbon support surface, forming abundant active sites, while avoiding pore blockage and structural collapse due to excessive metal oxides.

[0030] The mass ratio of sludge hydrothermal carbon to iron precursor solution in mixed solution B is 2.5 g / L to 10 g / L; the mass-to-volume ratio of magnetic pretreatment material to aluminum precursor solution in mixed solution C is ≥10 g / L.

[0031] In mixed solution B, the volume ratio of sludge hydrothermal carbon to iron precursor solution is 2.5 g / L to 10 g / L; in mixed solution C, the volume ratio of magnetic pretreatment material to aluminum precursor solution is ≥10 g / L. This setting ensures sufficient dispersion of metal ions, forming abundant active sites and avoiding pore blockage.

[0032] Preferably, sodium hydroxide or ammonia is used to adjust the pH values ​​of mixed solution A, mixed solution B, and mixed solution C.

[0033] NaOH and ammonia are both commonly used alkalis that can effectively adjust the pH of the solution to 9-10, causing metal ions to precipitate in the form of hydroxides, promoting their binding with the functional groups on the surface of the carbon support, and ensuring the loading efficiency and material structure.

[0034] Preferably, pretreatment materials A, B, and D are all calcined in a tube furnace at a temperature of 300℃~500℃ for a duration of 0.5h~2h.

[0035] The selection of temperature and duration for calcining both pretreatment materials A and B in a tube furnace is based on the synergistic optimization of the crystallinity of the metal oxide and the structure of the carbon support. Too low a calcination temperature will prevent the formation of a highly active aluminum hydroxide / Fe3O4 phase, while too high a temperature will lead to carbon support ablation and loss of pore structure. This temperature and duration range balances the high adsorption performance and magnetic stability of the materials.

[0036] The present invention also provides a method for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon.

[0037] This invention also provides the application of magnetic aluminum-iron supported modified sludge hydrothermal carbon in the adsorption of fluoride ions.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] This invention involves mixing dried sludge with deionized water and reacting the mixture in a hydrothermal reaction at 160℃~260℃ for 0.5h~2h to convert it into sludge hydrothermal carbon (carbonized body). This process not only improves the yield of sludge hydrothermal carbon but also endows it with a good pore structure. The sludge hydrothermal carbon obtained in this step is a carbon-based support with a high specific surface area and abundant pores, providing an ideal support platform for the uniform loading of metal oxides and an ideal support for the diffusion and adsorption of fluoride ions.

[0040] The product obtained by impregnation and precipitation of sludge hydrothermal carbon with aluminum precursors, ferrous salts, and ferric salts is an aluminum-iron oxide (mainly Fe3O4) supported on porous sludge carbon. Utilizing the abundant acidic functional groups and active sites of metal oxides on the surface of this product, highly efficient chemical adsorption of fluoride ions is achieved. This adsorption mainly relies on the complexation, exchange, and surface binding of fluoride ions with phases such as Al(OH)3. Furthermore, the adsorbed fluoride ions can be rapidly recovered and reused using an external magnetic field, avoiding secondary pollution. Therefore, magnetic aluminum-iron supported modified sludge hydrothermal carbon possesses the dual advantages of highly efficient fluoride removal and magnetic recovery.

[0041] This invention also provides a method for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon via a one-step impregnation-precipitation method. Under alkaline pH (9-10) conditions in the one-step impregnation-precipitation method, aluminum-iron precursors are co-mixed with sludge hydrothermal carbon, and metal ions are co-deposited on the carbon support surface, forming an aluminum-iron composite hydroxide / oxide. The one-step impregnation-precipitation method achieves full penetration and uniform precipitation of the aluminum-iron precursor in the form of hydroxides, enabling the formation of stable chemical bonds with the functional groups on the sludge hydrothermal carbon surface, ensuring the dispersion and binding strength of the hydroxides on the support. Furthermore, during the calcination process, under controlled temperature and atmosphere, the carbon is transformed into a highly active aluminum hydroxide / Fe3O4 composite, greatly enriching the adsorption active sites, promoting the crystallization of magnetic Fe3O4 and the formation of active sites, while maintaining the structural integrity of the carbon support and optimizing the pore structure and the distribution of surface functional groups. The rational control of these process parameters results in a composite material with high specific surface area, abundant acidic functional groups, and excellent chemical stability, thereby significantly improving its adsorption capacity for fluoride ions.

[0042] This invention also provides a method for preparing magnetic aluminum-iron-supported modified hydrothermal sludge carbon via a stepwise impregnation-precipitation method. Under the alkaline pH (9-10) conditions of the stepwise impregnation-precipitation method, the iron precursor solution, in the form of hydroxide, fully penetrates and uniformly precipitates, forming stable chemical bonds with the functional groups on the carbon support surface. This ensures the dispersion and binding strength of the hydroxide on the support. During the calcination process, under controlled temperature and atmosphere, a magnetic pretreated material C is obtained, which is then loaded with an aluminum precursor. In this way, the iron oxide first forms a magnetic framework, and then the molten aluminum precursor is loaded onto the surface of the magnetic pretreated material C, preparing a pretreated material D, aluminum hydroxide precipitate, with more fully exposed active sites, greatly enriching the adsorption active sites. After calcination, the aluminum hydroxide precipitate dehydrates to form AlOOH, which is fixed on the surface of the hydrothermal carbon. The reasonable control of these process parameters results in a composite material with high specific surface area, abundant acidic functional groups, and excellent chemical stability, thereby significantly improving its adsorption capacity for fluoride ions. In addition, compared with the stepwise impregnation and precipitation method, although the metal distribution in the magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared by the one-step impregnation and precipitation method is more uniform, some active sites may be buried. Therefore, the adsorption activity of the magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared by the one-step impregnation and precipitation method is slightly lower than that of the stepwise method.

[0043] This invention utilizes waste sludge as raw material to prepare functional adsorbents, realizing the resource utilization of sludge. The preparation process is simple and low-cost, and has good economic and environmental benefits. Attached Figure Description

[0044] Figure 1 The images are SEM images of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon in this invention, wherein (1) is the SEM image of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by one-step impregnation and precipitation method, and (2) is the SEM image of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by stepwise impregnation and precipitation method.

[0045] Figure 2The above are EDS mapping images of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon in this invention, wherein (1) is the SEM image corresponding to the selected region of the EDS of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by one-step impregnation and precipitation method, (2) is the EDS Al mapping image of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by one-step impregnation and precipitation method, (3) is the EDS Fe mapping image of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by one-step impregnation and precipitation method, (4) is the SEM image corresponding to the selected region of the EDS of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by stepwise impregnation and precipitation method, (5) is the EDS Al mapping image of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by stepwise impregnation and precipitation method, and (6) is the EDS Fe mapping image of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by stepwise impregnation and precipitation method.

[0046] Figure 3 The images are SEM images of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon after fluorine adsorption in this invention. (1) is the SEM image of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon after fluorine adsorption prepared by one-step impregnation and precipitation method, and (2) is the SEM image of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon after fluorine adsorption prepared by stepwise impregnation and precipitation method.

[0047] Figure 4 Figure 1 shows the EDS mapping diagrams of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon after fluoride adsorption in this invention. Figure 2 shows the F mapping diagram of the EDS after fluoride adsorption in the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by the one-step impregnation and precipitation method. Figure 3 shows the Al mapping diagram of the EDS after fluoride adsorption in the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by the one-step impregnation and precipitation method. Figure 4 shows the Fe mapping diagram of the EDS after fluoride adsorption in the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by the one-step impregnation and precipitation method. Figure 5 shows the SEM diagram of the selected area of ​​the EDS after fluoride adsorption in the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by the stepwise impregnation and precipitation method. Figure 6 shows the F mapping diagram of the EDS after fluoride adsorption in the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared by the stepwise impregnation and precipitation method. Figure (7) is the EDS Al mapping diagram of the hydrothermal carbon of magnetic aluminum-iron-loaded modified sludge prepared by stepwise impregnation and precipitation method after fluorine adsorption. Figure (8) is the EDS Fe mapping diagram of the hydrothermal carbon of magnetic aluminum-iron-loaded modified sludge prepared by stepwise impregnation and precipitation method after fluorine adsorption.

[0048] Figure 5The images show the VSM diagrams of the magnetic aluminum-iron supported modified sludge hydrothermal carbon in this invention. The left image shows the VSM diagram of the magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared by the one-step impregnation and precipitation method, and the right image shows the VSM diagram of the magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared by the stepwise impregnation and precipitation method. Detailed Implementation

[0049] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0050] The inventors discovered that hydrothermal carbonization technology can transform municipal or industrial sludge into a porous carbonaceous carrier with high specific surface area and abundant oxygen-containing functional groups under subcritical water conditions, thus achieving both sludge reduction and material performance optimization in the process. Subsequently, an aluminum-iron precursor solution is uniformly loaded onto the surface of the carbonaceous carrier using a one-step impregnation-precipitation method. Under alkaline conditions with a pH of 9-10, aluminum ions form stable chemical bonds with the carrier functional groups in the form of hydroxides, while iron ions synergistically generate magnetic oxide nanoparticles, laying the foundation for subsequent magnetic recovery. Finally, the pretreated material is precisely calcined under a nitrogen atmosphere, promoting the transformation of the aluminum-iron precursor into a highly active aluminum hydroxide / Fe3O4 composite crystalline phase, forming a multi-scale porous structure and abundant active sites, achieving efficient chemical adsorption and rapid magnetic recovery of fluoride ions. Alternatively, a stepwise impregnation-precipitation method can be employed. First, an iron precursor solution is uniformly loaded onto the surface of a carbonaceous support. Under an alkaline environment of pH 9-10, ferrous and ferric ions are deposited as hydroxides and combine with the functional groups of the support. After calcination under a nitrogen atmosphere, they are transformed into stable magnetic iron oxide nanoparticles, endowing the material with excellent magnetic properties. Next, the magnetically pretreated material is impregnated again with an aluminum precursor solution. Under the same alkaline conditions, aluminum ions are loaded onto the surface of the magnetic material as hydroxides, forming abundant aluminum active sites. Finally, after calcination or without calcination, magnetic aluminum-iron supported modified sludge hydrothermal carbon is obtained. This material combines high specific surface area, multi-scale porous structure, and highly dispersed aluminum-iron oxide active sites, achieving efficient chemical adsorption and rapid magnetic recovery of fluoride ions. This overcomes the technical bottlenecks of traditional adsorbents, such as difficulty in recovery and secondary pollution, embodying the innovative concept of green circular economy and sustainable development.

[0051] In view of this, the present invention provides a magnetic aluminum-iron supported modified sludge hydrothermal carbon, its preparation method, and its application in fluoride adsorption. The method utilizes waste sludge to prepare porous hydrothermal carbon as a carbonaceous carrier, and uses an impregnation precipitation method to support aluminum-iron precursors. The resulting material has both excellent fluoride ion adsorption capacity and magnetic recyclability.

[0052] The technical solution of the present invention will be further described below through specific embodiments.

[0053] Experiments have shown that any one of aluminum chloride, aluminum sulfate, and aluminum nitrate, any one of ferrous chloride or ferrous sulfate, any one of ferric chloride and ferric sulfate, and any one of sodium hydroxide or ammonia can be used in the preparation method of magnetic aluminum-iron supported modified sludge hydrothermal carbon. The preparation method of magnetic aluminum-iron supported modified sludge hydrothermal carbon in the following examples uses aluminum chloride, ammonia, ferric chloride, and ferrous chloride.

[0054] Example 1

[0055] A one-step impregnation and precipitation process for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon includes the following steps:

[0056] 7g of dry sludge was mixed evenly with 45mL of deionized water and then placed into a pressure-resistant hydrothermal reactor. The reactor was sealed and placed in a constant temperature heating device for hydrothermal reaction at 180℃ for 1 hour. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The reaction product was collected, and the resulting solid was collected by filtration. The solid was repeatedly washed with deionized water until the filtrate was neutral and then dried at 80℃ to obtain porous sludge hydrothermal carbon.

[0057] 2.413g of aluminum chloride (AlCl3·6H2O) and Fe were added according to the following formula: aluminum:total iron molar ratio of 1:3. 2+ :Fe 3+ The molar ratio was 1:2, resulting in 1.2675 g of ferrous chloride (Fe). 2+ (source) and 3.244g ferric chloride (Fe) 3+ Add the source to 100 mL of deionized water, and at the same time add an appropriate amount of ascorbic acid to prevent the oxidation of ferrous chloride. Stir to dissolve and obtain a 0.4 mol / L aluminum-iron precursor solution.

[0058] The obtained hydrothermal sludge carbon was slowly added to the aluminum-iron precursor solution to obtain a mixed solution A with a volume ratio of 2.5 g / L. Ammonia solution was slowly added dropwise to mixed solution A to adjust the pH to 9, and stirring was continued for 4 hours to allow aluminum and iron to precipitate as hydroxides on the carbon support surface. After stirring, the mixture was allowed to stand overnight to promote complete precipitation. The precipitate was collected by filtration, dried at 80°C, and ground to obtain pretreated material A.

[0059] Pretreated material A was placed in a tube furnace under a nitrogen protective atmosphere and heated to 300°C at a rate of approximately 5°C / min. It was then held at this temperature for 1 hour to promote the conversion of aluminum-iron hydroxide into aluminum-iron composite oxide and magnetic iron oxide. After calcination, the material was cooled to room temperature with the furnace to obtain the final magnetic aluminum-iron supported sludge hydrothermal carbon.

[0060] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 83.17%.

[0061] Adsorption experiments were conducted in a 100 mg / L fluoride ion solution. With the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion adsorption capacity reached 54.1 mg / g.

[0062] Example 2

[0063] A one-step impregnation and precipitation process for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon includes the following steps:

[0064] 7g of dry sludge was mixed evenly with 45mL of deionized water and then placed into a pressure-resistant hydrothermal reactor. The reactor was sealed and placed in a constant temperature heating device for hydrothermal reaction at 180℃ for 1.0h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The reaction product was collected, and the resulting solid was collected by filtration. The solid was repeatedly washed with deionized water until the filtrate was neutral and then dried at 80℃ to obtain porous sludge hydrothermal carbon.

[0065] 2.413g of aluminum chloride (AlCl3·6H2O) and Fe were added according to the following formula: aluminum:total iron molar ratio of 1:1. 2+ :Fe 3+ The molar ratio was 1:2, resulting in 0.4225 g of ferrous chloride (Fe). 2+ (source) and 1.0813g ferric chloride (Fe) 3+ Add the source to 100 mL of deionized water, and at the same time add an appropriate amount of ascorbic acid to prevent the oxidation of ferrous chloride. Stir to dissolve and obtain a 0.2 mol / L aluminum-iron precursor solution.

[0066] The obtained hydrothermal sludge carbon was slowly added to the aluminum-iron precursor solution to obtain a mixed solution A with a volume ratio of 5 g / L. Ammonia solution was slowly added dropwise to mixed solution A to adjust the pH to 9, and stirring was continued for 4 hours to allow aluminum and iron to precipitate as hydroxides on the carbon carrier surface. After stirring, the mixture was allowed to stand overnight to promote complete precipitation. The precipitate was collected by filtration, dried at 80°C, and ground to obtain pretreated material A.

[0067] Pretreated material A was placed in a tube furnace under a nitrogen protective atmosphere and heated to 300°C at a heating rate of approximately 5°C / min. This temperature was then maintained for 1.0 h to promote the conversion of aluminum-iron hydroxide into aluminum-iron composite oxide and magnetic iron oxide. After calcination, the material was cooled to room temperature with the furnace to obtain the final magnetic aluminum-iron supported sludge hydrothermal carbon.

[0068] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 80.56%.

[0069] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 47.63 mg / g of fluoride ions.

[0070] Example 3

[0071] A one-step impregnation and precipitation process for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon includes the following steps:

[0072] 7g of dry sludge was mixed evenly with 45mL of deionized water and then placed into a pressure-resistant hydrothermal reactor. The reactor was sealed and placed in a constant temperature heating device for hydrothermal reaction at 180℃ for 1 hour. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the reaction product was collected. The resulting solid was collected by filtration, repeatedly washed with deionized water until the filtrate was neutral, and then dried at any temperature of 80℃ to obtain porous sludge hydrothermal carbon.

[0073] Add 2.0g of aluminum chloride (AlCl3·6H2O) and Fe according to the molar ratio of aluminum to total iron of 1:5. 2+ :Fe 3+ The molar ratio was 1:2, resulting in 1.74915 g of ferrous chloride (Fe). 2+ (source) and 4.47872g ferric chloride (Fe) 3+ Add the source to 100 mL of deionized water, and at the same time add an appropriate amount of ascorbic acid to prevent the oxidation of ferrous chloride. Stir to dissolve and obtain a 0.5 mol / L aluminum-iron precursor solution.

[0074] The obtained hydrothermal sludge carbon was slowly added to the aluminum-iron precursor solution to obtain a mixed solution A with a volume ratio of 10 g / L. Ammonia solution was slowly added dropwise to mixed solution A to adjust the pH to 9, and stirring was continued for 4 hours to allow aluminum and iron to precipitate as hydroxides on the carbon carrier surface. After stirring, the mixture was allowed to stand overnight to promote complete precipitation. The precipitate was collected by filtration, dried at 80°C, and ground to obtain pretreated material A.

[0075] Pretreated material A was placed in a tube furnace under a nitrogen protective atmosphere and heated to 300°C at a rate of approximately 5°C / min. It was then held at this temperature for 1 hour to promote the conversion of aluminum-iron hydroxide into aluminum-iron composite oxide and magnetic iron oxide. After calcination, the material was cooled to room temperature with the furnace to obtain the final magnetic aluminum-iron supported sludge hydrothermal carbon.

[0076] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 84.28%.

[0077] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 56.78 mg / g of fluoride ions.

[0078] Example 4

[0079] A one-step impregnation and precipitation process for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon includes the following steps:

[0080] 7g of dry sludge was mixed evenly with 45mL of deionized water and then placed into a pressure-resistant hydrothermal reactor. The reactor was sealed and placed in a constant temperature heating device for hydrothermal reaction at 180℃ for 1 hour. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the reaction product was collected. The resulting solid was collected by filtration, repeatedly washed with deionized water until the filtrate was neutral, and then dried at any temperature of 80℃ to obtain porous sludge hydrothermal carbon.

[0081] Add 1.3g of aluminum chloride (AlCl3·6H2O) and Fe according to the molar ratio of aluminum to total iron of 1:1. 2+ :Fe 3+ The molar ratio of 1:2 yielded 0.227 g of ferrous chloride (Fe). 2+ (source) and 0.582g ferric chloride (Fe) 3+ Add the source (aluminum-iron precursor) to 100 mL of deionized water, and add an appropriate amount of ascorbic acid to prevent the oxidation of ferrous chloride. Stir to dissolve and obtain a 0.01 mol / L aluminum-iron precursor solution.

[0082] The obtained hydrothermal sludge carbon was slowly added to the aluminum-iron precursor solution to obtain a mixed solution A with a volume ratio of 10 g / L. Ammonia solution was slowly added dropwise to mixed solution A to adjust the pH to 9, and stirring was continued for 4 hours to allow aluminum and iron to precipitate as hydroxides on the carbon carrier surface. After stirring, the mixture was allowed to stand overnight to promote complete precipitation. The precipitate was collected by filtration, dried at 80°C, and ground to obtain pretreated material A.

[0083] Pretreated material A was placed in a tube furnace under a nitrogen protective atmosphere and heated to 300°C at a rate of approximately 5°C / min. It was then held at this temperature for 1 hour to promote the conversion of aluminum-iron hydroxide into aluminum-iron composite oxide and magnetic iron oxide. After calcination, the material was cooled to room temperature with the furnace to obtain the final magnetic aluminum-iron supported sludge hydrothermal carbon.

[0084] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 80.13%.

[0085] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 45.74 mg / g of fluoride ions.

[0086] Example 5

[0087] The only difference between Example 5 and Example 1 is that the hydrothermal reaction temperature is 260°C and the hydrothermal reaction time is 2 hours.

[0088] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 83.08%.

[0089] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 53.79 mg / g of fluoride ions.

[0090] Example 6

[0091] The only difference between Example 6 and Example 1 is that the hydrothermal reaction temperature is 160°C and the hydrothermal reaction time is 0.5h.

[0092] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 84.17%.

[0093] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 54.98 mg / g of fluoride ions.

[0094] Example 7

[0095] The only difference between Example 7 and Example 1 is the pH value. In this example, ammonia solution is slowly added dropwise to the mixture to adjust the pH to 9.5.

[0096] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 83.27%.

[0097] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 54.19 mg / g of fluoride ions.

[0098] Example 8

[0099] The only difference between Example 8 and Example 1 is the pH value. In this example, ammonia solution is slowly added dropwise to the mixture to adjust the pH to 10.

[0100] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 82.96%.

[0101] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 53.78 mg / g of fluoride ions.

[0102] Example 9

[0103] The only difference between Example 9 and Example 1 is that the calcination temperature is 350°C.

[0104] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 83.11%.

[0105] Adsorption experiments were conducted in a 100 mg / L fluoride ion solution. With the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion adsorption capacity reached 54.52 mg / g.

[0106] Example 10

[0107] The only difference between Example 10 and Example 1 is that the calcination temperature is 400°C.

[0108] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 82.16%.

[0109] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 52.13 mg / g of fluoride ions.

[0110] Example 11

[0111] The process for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon by stepwise impregnation and precipitation includes the following steps:

[0112] 7g of dry sludge was mixed evenly with 45mL of deionized water and then placed into a pressure-resistant hydrothermal reactor. The reactor was sealed and placed in a constant temperature heating device for hydrothermal reaction at 180℃ for 1 hour. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the reaction product was collected. The resulting solid was collected by filtration, repeatedly washed with deionized water until the filtrate was neutral, and then dried at 80℃ to obtain porous sludge hydrothermal carbon.

[0113] 2.535g of ferrous chloride (Fe) 2+ (source) and 6.488g ferric chloride (Fe) 3+ (Source) according to Fe 2+ :Fe 3+ Add the iron precursor solution to 100 mL of deionized water at a molar ratio of 1:2, and simultaneously add an appropriate amount of ascorbic acid. Stir to dissolve and obtain an iron precursor solution with a total iron concentration of 0.6 mol / L.

[0114] Sludge hydrothermal carbon was slowly added to the iron precursor solution and stirred to disperse it evenly, resulting in mixed solution B. Ammonia solution was slowly added dropwise to mixed solution B to adjust its pH to 9. Stirring continued for 4 hours, allowing iron to precipitate as hydroxide on the carbon support surface. After standing overnight, the solution was filtered, washed, dried at 80°C, and pulverized to obtain pretreated material A. Pretreated material A was placed in a tube furnace under a nitrogen atmosphere and heated to 400°C at a rate of approximately 5°C / min, and held at this temperature for 1 hour to obtain magnetic pretreated material B.

[0115] Add 2.413g of aluminum chloride AlCl3·6H2O to 100mL of deionized water and stir to dissolve, to obtain a 0.1mol / L aluminum precursor solution.

[0116] Magnetic pretreatment material B was slowly added to a 0.1 mol / L aluminum precursor solution and stirred to ensure uniform dispersion. Ammonia solution was slowly added dropwise to the mixture to adjust the pH to 9, and stirring was continued for 4 hours to allow aluminum to precipitate as hydroxide on the carbon support surface. After stirring, the mixture was allowed to stand overnight to promote complete precipitation. The precipitate was collected by filtration, dried at 80°C, and ground to obtain pretreatment material C.

[0117] Pretreated material C was placed in a tube furnace and heated to 300°C at a rate of approximately 5°C / min under a nitrogen protective atmosphere. This temperature was then maintained for 1 hour to promote the conversion of aluminum-iron hydroxide into aluminum-iron composite oxides and magnetic iron oxides. After calcination, the material was cooled to room temperature with the furnace to obtain the final magnetic aluminum-iron supported sludge hydrothermal carbon composite material.

[0118] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 86.79%.

[0119] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 58.72 mg / g of fluoride ions.

[0120] Example 12

[0121] The process for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon by stepwise impregnation and precipitation includes the following steps:

[0122] 7g of dry sludge was mixed evenly with 45mL of deionized water and then placed into a pressure-resistant hydrothermal reactor. The reactor was sealed and placed in a constant temperature heating device for hydrothermal reaction at 160℃ for 0.5h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the reaction product was collected. The resulting solid was collected by filtration, repeatedly washed with deionized water until the filtrate was neutral, and then dried at 80℃ to obtain porous sludge hydrothermal carbon.

[0123] 1.69g of ferrous chloride (Fe) 2+ (source) and 4.32g ferric chloride (Fe) 3+ (Source) according to Fe 2+ :Fe 3+ Add the iron precursor solution to 100 mL of deionized water at a molar ratio of 1:2, and simultaneously add an appropriate amount of ascorbic acid. Stir to dissolve and obtain an iron precursor solution with a total iron concentration of 0.4 mol / L.

[0124] Sludge hydrothermal carbon was slowly added to the iron precursor solution and stirred to disperse it evenly, resulting in mixed solution B. Ammonia solution was slowly added dropwise to mixed solution B to adjust its pH to 10. Stirring continued for 4 hours, allowing iron to precipitate as hydroxide on the carbon support surface. After standing overnight, the solution was filtered, washed, dried at 80°C, and pulverized to obtain pretreated material A. Pretreated material A was placed in a tube furnace under a nitrogen atmosphere and heated to 400°C at a rate of approximately 5°C / min, and held at this temperature for 1 hour to obtain magnetic pretreated material B.

[0125] Add 4.826g of aluminum chloride AlCl3·6H2O to 100mL of deionized water and stir to dissolve, to obtain a 0.2mol / L aluminum precursor solution.

[0126] Magnetic pretreatment material B was slowly added to a 0.2 mol / L aluminum precursor solution and stirred to ensure uniform dispersion. Ammonia solution was slowly added dropwise to the mixture to adjust the pH to 10, and stirring was continued for 4 hours to allow aluminum to precipitate as hydroxide on the carbon support surface. After stirring, the mixture was allowed to stand overnight to promote complete precipitation. The precipitate was collected by filtration, dried at 80°C, and ground to obtain pretreatment material C.

[0127] Pretreated material C was placed in a tube furnace and heated to 350°C at a rate of approximately 5°C / min under a nitrogen protective atmosphere. This temperature was then maintained for 1 hour to promote the conversion of aluminum-iron hydroxide into aluminum-iron composite oxides and magnetic iron oxides. After calcination, the material was cooled to room temperature with the furnace to obtain the final magnetic aluminum-iron supported sludge hydrothermal carbon composite material.

[0128] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 87.49%.

[0129] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 58.78 mg / g of fluoride ions.

[0130] Example 13

[0131] The process for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon by stepwise impregnation and precipitation includes the following steps:

[0132] 7g of dry sludge was mixed evenly with 45mL of deionized water and then placed into a pressure-resistant hydrothermal reactor. The reactor was sealed and placed in a constant temperature heating device for hydrothermal reaction at 160℃ for 0.5h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the reaction product was collected. The resulting solid was collected by filtration, repeatedly washed with deionized water until the filtrate was neutral, and then dried at 80℃ to obtain porous sludge hydrothermal carbon.

[0133] 2.11g of ferrous chloride (Fe) 2+ (source) and 5.41g ferric chloride (Fe) 3+ (Source) according to Fe 2+ :Fe 3+ Add the iron precursor solution to 100 mL of deionized water at a molar ratio of 1:2, and simultaneously add an appropriate amount of ascorbic acid. Stir to dissolve and obtain an iron precursor solution with a total iron concentration of 0.5 mol / L.

[0134] Sludge hydrothermal carbon was slowly added to the iron precursor solution and stirred to achieve uniform dispersion, resulting in mixed solution B. Ammonia solution was slowly added dropwise to mixed solution B to adjust its pH to 9.5. Stirring continued for 4 hours, allowing iron to precipitate as hydroxide on the carbon support surface. After standing overnight, the solution was filtered, washed, dried at 80°C, and pulverized to obtain pretreated material A. Pretreated material A was placed in a tube furnace under a nitrogen protective atmosphere and heated to 400°C at a rate of approximately 5°C / min, and held at this temperature for 1 hour to obtain magnetic pretreated material B.

[0135] Add 4.826g of aluminum chloride AlCl3·6H2O to 100mL of deionized water and stir to dissolve, to obtain a 0.2mol / L aluminum precursor solution.

[0136] Magnetic pretreatment material B was slowly added to a 0.2 mol / L aluminum precursor solution and stirred to ensure uniform dispersion. Ammonia solution was slowly added dropwise to the mixture to adjust the pH to 9.5, and stirring was continued for 4 hours to allow aluminum to precipitate as hydroxide on the carbon support surface. After stirring, the mixture was allowed to stand overnight to promote complete precipitation. The precipitate was collected by filtration, dried at 80°C, and ground to obtain pretreatment material C.

[0137] Pretreated material C was placed in a tube furnace and heated to 400°C at a rate of approximately 5°C / min under a nitrogen protective atmosphere. This temperature was then maintained for 1 hour to promote the conversion of aluminum-iron hydroxide into aluminum-iron composite oxides and magnetic iron oxides. After calcination, the material was cooled to room temperature with the furnace to obtain the final magnetic aluminum-iron supported sludge hydrothermal carbon composite material.

[0138] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 87.26%.

[0139] In an adsorption experiment conducted in a 100 mg / L fluoride ion solution, the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon resulted in an adsorption capacity of 58.19 mg / g of fluoride ions.

[0140] Example 14

[0141] The only difference between Example 14 and Example 11 is that the pretreatment material C is not carbonized.

[0142] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion removal rate reached 88.17%.

[0143] Adsorption experiments were conducted in a 100 mg / L fluoride ion solution. With the addition of 0.1 g of magnetic aluminum-iron supported sludge hydrothermal carbon, the fluoride ion adsorption capacity reached 60.18 mg / g.

[0144] Comparative Example 1

[0145] Preparation steps of sludge hydrothermal carbon:

[0146] 7g of dry sludge was mixed with 45mL of deionized water and placed in a hydrothermal reactor. The hydrothermal reaction was carried out at 180℃ for 1 hour to obtain hydrothermal char. The hydrothermal char was then filtered, washed, dried at 75℃, and pulverized.

[0147] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of sludge hydrothermal carbon, the fluoride ion removal rate reached 29.75%.

[0148] Adsorption experiments were conducted in a 100 mg / L fluoride ion solution with the addition of 0.1 g of hydrothermal char from sludge. Under the same adsorption conditions, the fluoride ion adsorption capacity reached 2.34 mg / g.

[0149] Comparative Example 2

[0150] The only difference between Comparative Example 2 and Example 1 is that the pretreatment material A is not carbonized.

[0151] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of hydrothermal char from sludge, the fluoride ion removal rate reached 50.75%.

[0152] Adsorption experiments were conducted in a 100 mg / L fluoride ion solution with the addition of 0.1 g of hydrothermal char from sludge. Under the same adsorption conditions, the fluoride ion adsorption capacity reached 20.18 mg / g.

[0153] Comparative Example 3

[0154] The only difference between Comparative Example 3 and Example 1 is that the pH value of the mixed solution A is not adjusted.

[0155] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution, and the addition of 0.25 g of sludge hydrothermal carbon resulted in a fluoride ion removal rate of 66.78%.

[0156] Adsorption experiments were conducted in a 100 mg / L fluoride ion solution with the addition of 0.1 g of hydrothermal char from sludge. Under the same adsorption conditions, the fluoride ion adsorption capacity reached 23.67 mg / g.

[0157] Comparative Example 4

[0158] The only difference between Comparative Example 4 and Example 11 is that the pH value of either Mixed Solution B or Mixed Solution C was adjusted.

[0159] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution, and the addition of 0.25 g of sludge hydrothermal carbon resulted in a fluoride ion removal rate of 67.85%.

[0160] Adsorption experiments were conducted in a 100 mg / L fluoride ion solution with the addition of 0.1 g of hydrothermal char from sludge. Under the same adsorption conditions, the fluoride ion adsorption capacity reached 22.35 mg / g.

[0161] Comparative Example 5

[0162] The only difference between Comparative Example 5 and Example 11 is the magnetic pretreated material prepared.

[0163] Adsorption experiments were conducted in a 20 mg / L fluoride ion solution. With the addition of 0.25 g of sludge hydrothermal carbon, the fluoride ion removal rate reached 16.78%.

[0164] Adsorption experiments were conducted in a 100 mg / L fluoride ion solution with the addition of 0.1 g of hydrothermal char from sludge. Under the same adsorption conditions, the fluoride ion adsorption capacity reached 5.67 mg / g.

[0165] The magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared in Examples 1 to 14 all exhibited fluoride ion removal rates greater than 80% and fluoride ion adsorption capacities greater than 45 mg / g. Compared with Comparative Examples 1 to 5, Examples 1 to 14 showed significantly higher fluoride ion removal rates and adsorption capacities. This is because the sludge hydrothermal carbon prepared by hydrothermal carbonization technology possesses abundant pores and a large specific surface area, providing an ideal carrier basis for the uniform loading of aluminum-iron oxides and the efficient diffusion adsorption of fluoride ions. In the impregnation and precipitation method, aluminum and iron precipitate as hydroxides and are uniformly distributed on the carbon carrier surface. After calcination, they are transformed into highly active aluminum-iron oxides, greatly enriching the adsorption active sites and improving the adsorption capacity for fluoride ions.

[0166] Examples 1 to 14 above all successfully prepared magnetic aluminum-iron supported modified sludge hydrothermal carbon. Figure 1 (1) SEM image of the magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared in Example 1. Figure 1 (2) is a SEM image of the magnetic aluminum-iron-loaded modified sludge hydrothermal carbon prepared in Example 11.

[0167] pass Figure 1 It is evident that the surface of the magnetic aluminum-iron supported modified sludge hydrothermal carbon exhibits irregular wrinkles, lamellar structures, and granular textures, indicating that the aluminum-iron precursor forms uniformly distributed metal oxide particles on the carbon support surface through impregnation and precipitation. This rough and layered structure enhances the surface activity of the material and improves its adsorption capacity for target ions. The material as a whole exhibits a three-dimensional porous network structure, which helps improve its mechanical strength and structural stability during recycling, while also providing channels for adsorption and magnetic separation.

[0168] Magnetic aluminum-iron supported modified sludge hydrothermal carbon was prepared in all of Examples 1 to 14 above. Therefore, EDS Al mapping was performed on the aluminum-supported hydrothermal carbon prepared in Example 1. Figure 2 (1) The SEM image corresponding to the area selected by EDS. Figure 2 (2) is the EDS Al mapping diagram; Figure 2 (3) EDS Fe mapping diagram. The aluminum-loaded hydrothermal carbon prepared in Example 11 was subjected to EDS Al mapping, wherein... Figure 2 (4) The SEM image corresponding to the area selected by EDS. Figure 2 (5) EDS Almapping plot; Figure 2 (6) is the EDS Fe mapping diagram.

[0169] Figure 2 (2) and Figure 2 (5) shows the spatial distribution of aluminum (Al) using a blue-green dot matrix. It can be seen that the Al element is distributed very evenly throughout the selected area, without obvious agglomeration or blank areas, indicating that the aluminum precursor can be uniformly loaded onto the carbonaceous support surface regardless of whether it is obtained through a one-step or stepwise method. The uniform distribution of Al is conducive to the formation of a large number of active sites, enhancing the material's adsorption capacity for fluoride ions. Figure 2 (3) and Figure 2 (6) shows the spatial distribution of iron (Fe) in a red dot matrix. Fe is also uniformly distributed throughout the region and highly overlaps with the distribution area of ​​Al, indicating that the iron precursor can be uniformly loaded onto the carbon support surface. The uniformly distributed Fe not only imparts magnetism to the material but also provides more active sites for adsorption and synergistic fluoride removal. EDS mapping results show that aluminum and iron are uniformly distributed on the porous sludge hydrothermal carbon surface, without significant agglomeration or stratification, demonstrating the excellent loading effect of the impregnation-sedimentation method.

[0170] Figure 3 (1) SEM image of the magnetic aluminum-iron supported modified sludge hydrothermal carbon after adsorption experiment in 100 mg / L fluoride ion solution after adding 0.1 g of magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared in Example 1. Figure 3 (2) SEM image of the magnetic aluminum-iron supported modified sludge hydrothermal carbon after adsorption of fluoride in a 100 mg / L fluoride ion solution after adding 0.1 g of magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared in Example 11.

[0171] pass Figure 3 It can be seen that after fluorine adsorption, Figure 3 (1) and Figure 3 (2) No obvious collapse or blockage was observed on the surface of the materials, and the structure remained stable. Fine particles or deposits were visible in some areas, which were presumably adsorbed fluoride ions and their complexes with aluminum and iron oxides. This indicates that the material has good structural stability during the adsorption process and has the potential for recycling.

[0172] Figure 4 (1) ~ Figure 4(4) All images show the EDS mapping of fluoride adsorption after the addition of 0.1g of the magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared in Example 1 to a 100mg / L fluoride ion solution. Figure 4 (1) The SEM image corresponding to the area selected by EDS. Figure 4 (2) is the EDS F mapping diagram. Figure 4 (3) is the EDS Al mapping diagram. Figure 4 (4) is the EDS Fe mapping diagram; Figure 4 (5) ~ Figure 4 (8) These are EDS mapping images of magnetic aluminum-iron supported modified sludge hydrothermal carbon after adsorption of fluoride in a 100 mg / L fluoride ion solution, all prepared in Example 11. Figure 4 (5) The SEM image corresponding to the area selected by EDS. Figure 4 (6) is the EDS F mapping diagram. Figure 4 (7) is the EDS Al mapping diagram. Figure 4 (8) is the EDS Fe mapping diagram.

[0173] Depend on Figure 4 (2) and Figure 4 (6) It can be seen that fluorine is uniformly distributed on the material surface, indicating that fluoride ions are adsorbed in large quantities and uniformly on the material surface and in the pores. This directly proves the material's high adsorption capacity for fluoride ions, and the adsorption sites are widely distributed without local enrichment or blank areas. The distribution of fluorine highly overlaps with the distribution areas of Al and Fe, indicating that fluoride ions have undergone effective chemical complexation or electrostatic adsorption with the surface aluminum and iron oxides, confirming the material's high-efficiency capture capacity for fluoride ions. Figure 4 (3) and Figure 4 (7) It can be seen that aluminum is highly dispersed on the material surface, with no obvious agglomeration. This is conducive to the formation of a large number of aluminum active sites, enhancing the specific adsorption capacity for fluoride ions. Figure 4 (4) and Figure 4 (8) It can be seen that the red and reddish-brown signals are evenly distributed, indicating that the iron oxides are well dispersed and have not agglomerated.

[0174] Figure 5 The left figure is the VSM diagram of the magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared in Example 1; Figure 5 The right figure is a VSM diagram of the magnetic aluminum-iron supported modified sludge hydrothermal carbon prepared in Example 11.

[0175] Depend on Figure 5 It can be seen that, Figure 5 Left image and Figure 5 The magnetic aluminum-iron-loaded modified sludge hydrothermal carbon materials shown in the right figure all exhibit high saturation magnetization, low coercivity, and low remanence, demonstrating excellent soft magnetism and magnetic recovery capabilities. This magnetic property ensures that after adsorbing fluoride ions, the materials can be efficiently separated and recovered using an external magnetic field, which is a key foundation for achieving green recycling and large-scale water treatment applications.

[0176] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing magnetic aluminum-iron loaded modified sludge hydrothermal carbon, characterized in that, Comprising the following steps: After mixing the dry sludge with deionized water, the sludge hydrothermal carbon is obtained by reacting in a hydrothermal reaction at a temperature of 160-260 DEG C for 0.5-2 hours; The magnetic aluminum-iron loaded modified sludge hydrothermal carbon is prepared by impregnation precipitation method using the obtained sludge hydrothermal carbon, aluminum precursor, ferrous salt and ferric salt; The impregnation precipitation method is a step-by-step impregnation precipitation method or a one-step impregnation precipitation method, The step-by-step impregnation precipitation method is as follows: Dissolve the ferrous salt and ferric salt in deionized water to prepare a ferrous precursor solution, mix the ferrous precursor solution with the sludge hydrothermal carbon to obtain a mixed solution B; Adjust the pH value of the mixed solution B to 9-10, stir, stand overnight, filter, wash, dry, crush to obtain pretreated material B, and calcine the pretreated material B under a nitrogen atmosphere to obtain magnetic pretreated material C; Then dissolve the aluminum precursor in deionized water to prepare an aluminum precursor solution, mix the aluminum precursor solution with the magnetic pretreated material to obtain a mixed solution C, and then adjust the pH value of the mixed solution C to 9-10, stir, stand overnight, filter, wash, dry, crush to obtain pretreated material D; calcine or do not calcine the pretreated material D under a nitrogen atmosphere to obtain the magnetic aluminum-iron loaded modified sludge hydrothermal carbon; The one-step impregnation precipitation method is as follows: Dissolve the aluminum precursor, ferrous salt and ferric salt in deionized water to prepare an aluminum-iron precursor solution with a concentration of 0.01-0.5 mol / L, wherein the molar ratio of ferrous salt to ferric salt in the aluminum-iron precursor solution is 1:2, and the molar ratio of total iron to aluminum in the aluminum-iron precursor solution is 1:1-5:1; Mix the aluminum-iron precursor solution with the sludge hydrothermal carbon to obtain a mixed solution A, wherein the mass of sludge hydrothermal carbon in the mixed solution A to the volume of aluminum-iron precursor solution is 2.5-10 g / L; Adjust the pH of the mixed solution A to 9-10, stir and stand overnight, then perform suction filtration, rinsing, drying and crushing to obtain pretreated material A, and calcine the pretreated material A under a nitrogen atmosphere to obtain the magnetic aluminum-iron loaded modified sludge hydrothermal carbon.

2. The method for preparing magnetic aluminum-iron supported modified sludge hydrothermal carbon according to claim 1, characterized in that, The concentration of the aluminum precursor solution is 0.1-0.5 mol / L, and the concentration of the iron precursor solution is ≥0.4 mol / L, wherein the molar ratio of ferrous salt to ferric salt in the iron precursor solution is 1:

2.

3. The method according to claim 1, wherein the magnetic aluminum-iron loaded modified sludge hydrothermal carbon is characterized in that, The mass of sludge hydrothermal carbon in the mixed solution B to the volume of iron precursor solution is 2.5-10 g / L, and the mass of magnetic pretreated material in the mixed solution C to the volume of aluminum precursor solution is ≥10 g / L.

4. The method according to claim 1, wherein the magnetic aluminum-iron loaded modified sludge hydrothermal carbon is characterized in that, The calcination temperature of the pretreated material B and the pretreated material D in the tube furnace is 300-500 DEG C, and the calcination time is 0.5-2 hours.

5. The method according to claim 1, wherein the magnetic aluminum-iron loaded modified sludge hydrothermal carbon is characterized in that, The aluminum precursor is selected from any one of aluminum chloride, aluminum sulfate and aluminum nitrate; the ferrous salt is ferrous chloride or ferrous sulfate, and the ferric salt is ferric chloride and ferric sulfate.

6. The method for preparing magnetic aluminum-iron loaded modified sludge hydrothermal carbon according to claim 1, characterized in that, The calcination temperature of the pretreated material A in the tube furnace is 300-500 DEG C, and the calcination time is 0.5-2 hours.

7. The magnetic aluminum-iron loaded modified sludge hydrothermal carbon prepared by the method according to any one of claims 1-6.

8. The use of the magnetic aluminum-iron loaded modified sludge hydrothermal carbon according to claim 7 in adsorbing fluorine ions.

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