Magnesium-aluminum composite magnetic adsorbent and preparation method thereof

Abstract

The invention discloses a magnesium-aluminum composite magnetic adsorbent and a preparation method thereof, and relates to the technical field of sewage treatment materials. According to the preparation method disclosed by the invention, a specific hierarchical pore structure is formed in the adsorbent by pertinently controlling the molar ratio of magnesium ions to aluminum ions and combining the guiding effect of the template agent, so that the specific surface area and the total pore volume of the adsorbent are remarkably increased, and the adsorption efficiency and the adsorption quantity of the adsorbent are greatly improved; the Fe3O4 is subjected to surface hydroxylation treatment by using alkali liquor, so that the Fe3O4 can be combined with a magnesium aluminum hydroxide hydrogen bond, the loading stability of the Fe3O4 is remarkably improved, and efficient recovery and repeated use of the adsorbent are facilitated; according to the preparation method, the specific surface area and the total pore volume of the magnesium-aluminum composite magnetic adsorbent can be remarkably increased, the loading stability of Fe3O4 is enhanced, the adsorption performance and the recovery rate of the adsorbent are greatly improved, and efficient removal of phosphate and heavy metal in a water body and cyclic utilization of the adsorbent are facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment materials, in particular to a water body phosphate and heavy metal adsorption material, and particularly to a magnesium-aluminum composite magnetic adsorbent and a preparation method thereof. BACKGROUND

[0002] With the acceleration of industrialization and the continuous growth of population, water body eutrophication has attracted widespread attention. Water body eutrophication is mainly caused by excessive accumulation of nitrogen, phosphorus and other nutrients in water, leading to excessive growth of algae and other aquatic organisms, thereby disrupting the ecological balance of water bodies. Among them, phosphate is one of the main causes of water body eutrophication, so developing efficient phosphate removal technology has important environmental significance.

[0003] Adsorption technology has been widely used in water treatment due to its high efficiency, economy and simple operation. The performance of the adsorbent largely determines the effect of the adsorption technology, so developing efficient and reusable adsorbents has become a hot research topic. As a new type of adsorbent, magnesium-aluminum hydroxide magnetic composite adsorbent has gradually attracted the attention of researchers due to its good adsorption performance and magnetic recovery capacity. For example, patent CN108889266A discloses a magnetic magnesium-aluminum composite oxide and its preparation method and application; patent CN110876917A discloses a superparamagnetic response nano-phosphorus adsorbent and its preparation method. However, the existing method for preparing magnesium-aluminum hydroxide magnetic composite adsorbent still has some defects, which limits its widespread use in practical applications.

[0004] The main adsorption sites of magnesium-aluminum hydroxide magnetic composite adsorbent come from the hydroxyl (-OH) groups on its surface. These hydroxyl groups can adsorb phosphate molecules through hydrogen bonding or ion exchange. However, the number of hydroxyl groups on the surface of the composite adsorbent prepared by the existing method is limited, resulting in fewer adsorption sites. When treating high-concentration phosphate wastewater, the adsorption capacity of the adsorbent is often insufficient, making it difficult to meet the actual demand.

[0005] Specific surface area is one of the important factors affecting the adsorption performance of adsorbents. A larger specific surface area can provide more adsorption sites, thereby improving the adsorption capacity of the adsorbent. However, the specific surface area of the magnesium-aluminum hydroxide magnetic composite adsorbent prepared by the existing method is small, limiting the further improvement of its adsorption performance. A smaller specific surface area means that the number of active sites on the surface of the adsorbent is limited, making it difficult to fully utilize its adsorption potential. In addition, a smaller specific surface area may also lead to adsorption saturation phenomenon during the adsorption process, further reducing the adsorption efficiency of the adsorbent.

[0006] Therefore, it is of great significance to develop a magnesium aluminum hydroxide magnetic composite adsorbent with high specific surface area and multiple active sites to meet the increasingly stringent environmental protection requirements and improve resource utilization efficiency. SUMMARY

[0007] The present application aims to overcome the problems of small specific surface area and few active sites of the magnesium aluminum hydroxide magnetic composite adsorbent prepared by the prior art method, and provides a magnesium aluminum composite magnetic adsorbent and a preparation method thereof.

[0008] In order to achieve the above-mentioned application purposes, the present application provides a preparation method of a magnesium aluminum composite magnetic adsorbent, comprising the following steps: (1) mixing and dissolving an aluminum source, a magnesium source, a template agent and a surfactant with an ethanol aqueous solution to obtain a mixed solution; In the mixed solution, the molar ratio of aluminum ions to magnesium ions is 3-5:1, the concentration of the template agent is 0.05-0.1 g / L, and the concentration of the surfactant is 5-10 mg / L; in the ethanol aqueous solution, the concentration of water is 10-25 mL / L; (2) adding a precipitating agent to the mixed solution to obtain a sol solution with a pH value of 8-10; (3) subjecting the sol solution to a solvothermal reaction at a temperature of 160-200℃ for 1-5h, and cooling to obtain a suspension; (4) adding Fe3O4 nanoparticles to the suspension, stirring uniformly, and then adding a lye to obtain a precursor solution with a pH value of 9-10; (5) separating the precursor solution, washing the separated solid with deionized water and ethanol alternately, and drying to obtain a precursor powder; (6) subjecting the precursor powder to aminization treatment to obtain a magnesium aluminum composite magnetic adsorbent.

[0009] The preparation method of the magnesium-aluminum composite magnetic adsorbent not only controls the molar ratio of magnesium ions and aluminum ions, and combines the guiding action of the template agent, so that a specific multi-stage pore structure is formed in the adsorbent, the specific surface area and the total pore volume of the adsorbent are significantly increased, and the adsorption efficiency and the adsorption capacity of the adsorbent are greatly improved; and the surface of Fe3O4 is hydroxylated by using lye, so that the Fe3O4 can be combined with magnesium-aluminum hydroxide by hydrogen bond, the load stability of the Fe3O4 is significantly improved, and the efficient recovery and reuse of the adsorbent are facilitated; meanwhile, in the preparation process, the ethanol aqueous solution is used as the solvent for the solvothermal reaction, the diffusion rate of ions in the reaction process is reduced, the precipitation growth rate can be effectively controlled, the uniformity of the growth of the adsorbent particles is promoted, the particle size of the adsorbent is more reasonable and uniform, and the specific surface area is larger; the preparation method can significantly increase the specific surface area and the total pore volume of the magnesium-aluminum composite magnetic adsorbent, enhance the load stability of the Fe3O4, greatly improve the adsorption performance and the recovery rate of the adsorbent, and facilitate the efficient removal of water body phosphates and heavy metals and the recycling of the adsorbent; the preparation method is simple in steps, controllable in process, stable in product performance, and suitable for large-scale production of the magnesium-aluminum composite magnetic adsorbent.

[0010] In step (1), preferably, the aluminum source is aluminum potassium sulfate dodecahydrate; the magnesium source is magnesium nitrate hexahydrate; the template agent is cetyltrimethylammonium bromide, which guides the self-assembly of aluminum ions into spherical porous particles under solvothermal conditions during hydrolysis; and the surfactant is polyethylene glycol, which is used to inhibit particle agglomeration; preferably, the types of reactants are widely available, stable in performance, and low in cost, and are suitable for industrialized production of the magnesium-aluminum composite magnetic adsorbent.

[0011] Preferably, the concentration of magnesium ions in the mixed solution is 0.01-0.1 mol / L; preferably, the concentration of magnesium ions is better for the adsorption performance of the prepared adsorbent; if the concentration is too large, the particle size of the generated adsorbent is too small and easy to agglomerate; and if the concentration is too small, the particle size of the generated adsorbent is too large, and the specific surface area is significantly reduced.

[0012] Preferably, the content of water in the ethanol aqueous solution is 15-20 ml / L; preferably, the water content makes the particle size of the adsorbent more uniform and the dispersibility better.

[0013] In step (2), preferably, the precipitant is at least one of sodium hydroxide solution and potassium hydroxide solution.

[0014] In step (3), preferably, the solvothermal reaction is carried out in an ultrasonic or microwave environment; the heating is more uniform, the reaction time can be significantly shortened, and the energy consumption is reduced; more preferably, the power of the ultrasonic or microwave is 500-800 w.

[0015] Preferably, the particle size of the Fe3O4 nanoparticles is not less than 30 nm in step (4), which can avoid plugging the pores of the adsorbent, reduce the adsorption effect of the adsorbent, and cause plugging when the particle size is too small, and the bonding strength between the Fe3O4 nanoparticles and the substrate is reduced when the particle size is too small. More preferably, the particle size of the Fe3O4 nanoparticles is 30-200 nm.

[0016] Preferably, the alkali solution is at least one of sodium hydroxide solution, potassium hydroxide solution and ammonia water.

[0017] Preferably, the separation method in step (5) is at least one of centrifugal separation, filtration separation, membrane separation and sedimentation separation.

[0018] Preferably, the number of washing is not less than 3 times, which can better remove impurity ions.

[0019] Preferably, the drying temperature is 60-80℃ and the time is 8-15h.

[0020] Preferably, the mass fraction of Fe3O4 nanoparticles in the magnesium-aluminum composite magnetic adsorbent is 5-10% in step (6).

[0021] Preferably, the aminosilane solution is an ethanol aqueous solution, the volume concentration of aminosilane in the ethanol aqueous solution is 2-5%, and the volume ratio of ethanol to water in the ethanol aqueous solution is 8-10:1.

[0022] Preferably, the aminosilane solution is an ethanol aqueous solution, the volume concentration of aminosilane in the ethanol aqueous solution is 2-5%, and the volume ratio of ethanol to water in the ethanol aqueous solution is 8-10:1.

[0023] Preferably, the aminosilane is 3-aminopropyl triethoxysilane.

[0024] Preferably, the aminosilane is 3-aminopropyl triethoxysilane.

[0025] In order to achieve the above-mentioned purposes, the application further provides a magnesium-aluminum composite magnetic adsorbent prepared by the above preparation method, which has the advantages of good adsorption performance and high recovery rate, the specific surface area is not less than 150 m 2 / g, and the total pore volume is not less than 0.3 cm 3 / g, the average pore size is 10-20 nm, and the magnetic response time is not more than 2 min (magnetic field intensity 0.5T).

[0026] Compared with the prior art, the present application has the following advantages: 1. The preparation method of the magnesium-aluminum composite magnetic adsorbent can form a specific multi-level pore structure in the adsorbent by controlling the molar ratio of magnesium ions and aluminum ions and combining the guiding action of the template agent, thereby significantly increasing the specific surface area and total pore volume of the adsorbent and greatly improving the adsorption efficiency and adsorption capacity of the adsorbent.

[0027] 2. The preparation method of the magnesium-aluminum composite magnetic adsorbent can significantly improve the loading stability of Fe3O4 by performing surface hydroxylation treatment on Fe3O4 with alkali and then performing aminoization treatment, which is beneficial to the efficient recovery and reuse of the adsorbent.

[0028] 3. In the preparation process of the magnesium-aluminum composite magnetic adsorbent, ethanol aqueous solution is used as the solvent thermal reaction solvent, which reduces the diffusion rate of ions in the reaction process, effectively controls the precipitation growth rate, promotes the uniform growth of the adsorbent particles, and makes the particle size of the adsorbent more reasonable and uniform, and the specific surface area larger.

[0029] 4. The preparation method of the magnesium-aluminum composite magnetic adsorbent can significantly improve the specific surface area and total pore volume of the magnesium-aluminum composite magnetic adsorbent, enhance the loading stability of Fe3O4, greatly improve the adsorption performance and recovery rate of the adsorbent, and is beneficial to the large-scale popularization and application of the magnesium-aluminum composite magnetic adsorbent.

[0030] 5. The magnesium-aluminum composite magnetic adsorbent has the advantages of good adsorption performance and high recovery rate, the specific surface area is not less than 150 m 2 / g, the total pore volume is not less than 0.3 cm 3 / g, the average pore size is 10-20 nm, and the magnetic response time is not more than 2 min (magnetic field intensity 0.5T). DETAILED DESCRIPTION

[0031] In order to more clearly describe the invention purpose, technical solutions and technical effect advantages in the specific implementation cases of the present invention, the following will be described in detail with reference to the solutions in the specific embodiments of the present invention. The specific technical solutions involved in the following specific embodiments are only for the purpose of clearly and completely describing the innovative technical solutions of the present invention. They themselves are only part of the specific implementation plans that can be adopted by the present invention, not all embodiments, and should not be understood as limiting the innovative solutions of the present invention. Any solution that adopts the same inventive concept of the present invention should be included in the scope of protection of the present invention.

[0032] For those skilled in the art, when understanding the solutions described in the specific embodiments of the present invention, they can refer to conventional technical manuals in the field. At the same time, for the places where the above-mentioned terms appear, they can make appropriate understanding or adjustments for reference, and deduce the implementation of the same or similar technical solutions without paying any creative work.

[0033] Example 1 A magnesium-aluminum composite magnetic adsorbent, the preparation method of which is as follows: (1) mixing and dissolving potassium aluminum sulfate dodecahydrate, magnesium nitrate hexahydrate, hexadecyltrimethylammonium bromide, and polyethylene glycol with an ethanol aqueous solution (water content of 15 ml / L) to obtain a mixed solution; In the mixed solution, the concentration of magnesium ions is 0.05 mol / L, the concentration of aluminum ions is 0.2 mol / L, the concentration of cetyltrimethylammonium bromide is 0.08 g / L, and the concentration of polyethylene glycol is 8 mg / L; (2) Adding a precipitant (0.1 mol / L sodium hydroxide solution) to the mixed solution to obtain a sol solution with a pH value of 8; (3) placing the sol solution at 180°C for 4 h for solvothermal reaction and cooling to obtain a suspension; (4) Add Fe3O4 nanoparticles (particle size 35nm, accounting for 8% of the magnesium-aluminum composite magnetic adsorbent product) to the suspension, stir evenly, and then slowly add 0.1mol / L sodium hydroxide solution to pH = 10 to fully hydroxylate the Fe3O4 surface; (5) Separating the precursor solution (centrifugation: 8000 rpm, 10 min), washing the separated solid with deionized water and ethanol alternately three times, and drying (70 °C, 12 h) to obtain the precursor powder; (6) The precursor powder was stirred and soaked in an ethanol aqueous solution (ethanol to water volume ratio of 9:1) with a volume percentage of 3% by volume of 3-aminopropyltriethoxysilane for 2 h, and then solid-liquid separation (centrifugal separation: 8000 rpm, 5 min) was performed to obtain a magnesium-aluminum composite magnetic adsorbent.

[0034] Example 2 A magnesium-aluminum composite magnetic adsorbent, the preparation method of which is as follows: (1) mixing and dissolving potassium aluminum sulfate dodecahydrate, magnesium nitrate hexahydrate, hexadecyltrimethylammonium bromide and polyethylene glycol with an ethanol aqueous solution (water content is 10 ml / L) to obtain a mixed solution; In the mixed solution, the concentration of magnesium ions is 0.01 mol / L, the concentration of aluminum ions is 0.05 mol / L, the concentration of cetyltrimethylammonium bromide is 0.05 g / L, and the concentration of polyethylene glycol is 5 mg / L; (2) Add a precipitant (0.1 mol / L potassium hydroxide solution) to the mixed solution and cool it to obtain a sol solution with a pH of 9; (3) The sol solution was subjected to solvothermal reaction under 800W ultrasound and 160°C for 1 hour to obtain a suspension; (4) Add Fe3O4 nanoparticles (particle size 40nm, accounting for 5% of the magnesium-aluminum composite magnetic adsorbent product) to the suspension, stir evenly, and then slowly add 0.2mol / L sodium hydroxide solution to pH = 10 to fully hydroxylate the Fe3O4 surface; (5) Separating the precursor solution (filtration), washing the separated solid with deionized water and ethanol alternately three times, and drying (60°C, 15h) to obtain the precursor powder; (6) The precursor powder was stirred and soaked in an ethanol aqueous solution (ethanol to water volume ratio of 10:1) containing 2% by volume of 3-aminopropyltriethoxysilane for 3 h, and then solid-liquid separation (filtration) was performed to obtain a magnesium-aluminum composite magnetic adsorbent.

[0035] Example 3 A magnesium-aluminum composite magnetic adsorbent, the preparation method of which is as follows: (1) mixing and dissolving potassium aluminum sulfate dodecahydrate, magnesium nitrate hexahydrate, hexadecyltrimethylammonium bromide, and polyethylene glycol with an ethanol aqueous solution (water content of 25 ml / L) to obtain a mixed solution; In the mixed solution, the concentration of magnesium ions is 0.1 mol / L, the concentration of aluminum ions is 0.3 mol / L, the concentration of cetyltrimethylammonium bromide is 0.1 g / L, and the concentration of polyethylene glycol is 10 mg / L; (2) Add a precipitant (0.1 mol / L sodium hydroxide solution) to the mixed solution and cool it to obtain a sol solution with a pH of 10; (3) placing the sol solution at 200°C for 2 h to undergo solvothermal reaction to obtain a suspension; (4) Add Fe3O4 nanoparticles (particle size 30 nm, 10% of the magnesium-aluminum composite magnetic adsorbent product) into the suspension, stir until uniform, and then slowly add 0.1 mol / L ammonia water until pH = 10, so as to fully hydroxylate the surface of the Fe3O4; (5) Separate the precursor solution (centrifugal separation: 8000 rpm, 10 min), wash the separated solid with deionized water and ethanol alternately for 5 times, and dry (80°C, 8 h) to obtain the precursor powder; (6) Stir and soak the precursor powder in a 5% (volume percentage) 3-aminopropyltriethoxysilane ethanol aqueous solution (volume ratio of ethanol to water 8:1) for 0.5 h, and then separate the solid and liquid (centrifugal separation: 8000 rpm, 5 min) to obtain the magnesium-aluminum composite magnetic adsorbent.

[0036] Comparative Example 1 A magnesium-aluminum composite magnetic adsorbent was prepared by the same method as in Example 1, except that the concentration of aluminum ions was 0.1 mol / L (molar ratio of aluminum ions to magnesium ions 2:1).

[0037] Comparative Example 2 A magnesium-aluminum composite magnetic adsorbent was prepared by the same method as in Example 1, except that the concentration of aluminum ions was 0.3 mol / L (molar ratio of aluminum ions to magnesium ions 6:1).

[0038] Comparative Example 3 A magnesium-aluminum composite magnetic adsorbent was prepared by the same method as in Example 1, except that the content of water in the ethanol aqueous solution in step (1) was 8 ml / L.

[0039] Comparative Example 4 A magnesium-aluminum composite magnetic adsorbent was prepared by the same method as in Example 1, except that the content of water in the ethanol aqueous solution in step (1) was 30 ml / L.

[0040] Comparative Example 5 A magnesium-aluminum composite magnetic adsorbent was prepared by the same method as in Example 1, except that in step (2), after adding the sodium hydroxide solution, a sol solution with pH value of 11 was obtained.

[0041] Comparative Example 6 A magnesium-aluminum composite magnetic adsorbent was prepared by the same method as in Example 1, except that in step (4), after adding the Fe3O4 nanoparticles, no alkali solution was added to adjust the pH value of the precursor solution.

[0042] Comparative Example 7 A magnesium-aluminum composite magnetic adsorbent is prepared by the method of Example 1, except that the particle size of the Fe3O4 nanoparticles is 25 nm.

[0043] Comparative Example 8 A magnesium-aluminum composite magnetic adsorbent is prepared by the method of Example 1, except that the aminoization treatment is not performed, i.e., step (6) is not performed.

[0044] Experimental Example 1 The magnesium-aluminum composite magnetic adsorbents prepared in Examples 1-3 and Comparative Examples 1-8 are subjected to experimental tests of specific surface area, total pore volume, average pore size, and pore size distribution, and the relevant test results are recorded in the following table:

[0045] Experimental Example 2 The magnesium-aluminum composite magnetic adsorbents prepared in Examples 1-3 and Comparative Examples 1-8 are subjected to determination experiments of phosphate equilibrium adsorption capacity, phosphorus removal efficiency, and adsorbent recovery rate (0.5 T) for a solution to be treated (a sodium phosphate solution with a concentration of 0.05 mol / L and a pH value of 3.5) (dosing amount: 0.5 g / L), and the results are as follows:

[0046] Analysis of the data of Experimental Examples 1 and 2 shows that, in the process of preparing the magnesium-aluminum composite magnetic adsorbent by the method of the present application, the molar ratio of magnesium ions to aluminum ions, the hydroxylation treatment of Fe3O4, the water content in the ethanol aqueous solution, the pH value during the reaction, the particle size selection of Fe3O4, and whether to perform the aminoization treatment, all have a significant influence on the adsorption performance or recovery efficiency of the adsorbent, and are also the keys to preparing the high-performance magnesium-aluminum composite magnetic adsorbent of the present application.

Claims

1. A method for preparing a magnesium-aluminum composite magnetic adsorbent, characterized in that: The following steps are involved: (1) mixing and dissolving an aluminum source, a magnesium source, a template, and a surfactant with an ethanol aqueous solution to obtain a mixed solution; In the mixed solution, the concentration of magnesium ions is 0.01-0.1 mol / L, the molar ratio of aluminum ions to magnesium ions is 3-5:1, the concentration of the template is 0.05-0.1 g / L, and the concentration of the surfactant is 5-10 mg / L; in the ethanol aqueous solution, the concentration of water is 10-25 mL / L; (2) adding a precipitant to the mixed solution to obtain a sol solution with a pH value of 8-10; (3) placing the sol solution at a temperature of 160-200°C for a solvothermal reaction for 1-5 hours, and cooling to obtain a suspension; (4) Add Fe3O4 nanoparticles to the suspension, stir evenly, and then add alkali solution to obtain a precursor solution with a pH value of 9-10; (5) separating the precursor solution, washing the separated solid with deionized water and ethanol alternately, and drying to obtain a precursor powder; (6) The precursor powder is subjected to amino treatment to obtain a magnesium-aluminum composite magnetic adsorbent.

2. The method for preparing the magnesium-aluminum composite magnetic adsorbent according to claim 1, characterized in that: In step (1), the aluminum source is potassium aluminum sulfate dodecahydrate; the magnesium source is magnesium nitrate hexahydrate; the template agent is hexadecyltrimethylammonium bromide; and the surfactant is polyethylene glycol.

3. The method for preparing the magnesium-aluminum composite magnetic adsorbent according to claim 1, characterized in that: In step (2), the precipitant is at least one of a sodium hydroxide solution and a potassium hydroxide solution.

4. The method for preparing the magnesium-aluminum composite magnetic adsorbent according to claim 1, characterized in that: In step (3), a solvothermal reaction is carried out in an ultrasonic or microwave environment.

5. The method for preparing the magnesium-aluminum composite magnetic adsorbent according to claim 1, characterized in that: In step (4), the particle size of the Fe3O4 nanoparticles is not less than 30 nm.

6. The method for preparing the magnesium-aluminum composite magnetic adsorbent according to claim 1, characterized in that: In step (4), the alkaline solution is at least one of sodium hydroxide solution, potassium hydroxide solution, and ammonia water.

7. The method for preparing the magnesium-aluminum composite magnetic adsorbent according to claim 1, characterized in that: In step (6), the mass fraction of Fe3O4 nanoparticles in the magnesium-aluminum composite magnetic adsorbent is 5-10%.

8. The method for preparing the magnesium-aluminum composite magnetic adsorbent according to claim 1, characterized in that: In step (6), the amination treatment method includes: stirring and soaking the precursor powder in an ethanol aqueous solution of aminosilane for 0.5-3 hours, and then separating the solid and liquid.

9. The method for preparing the magnesium-aluminum composite magnetic adsorbent according to claim 8, characterized in that: In the ethanol aqueous solution of the aminosilane solution, the volume concentration of aminosilane is 2-5%; in the ethanol aqueous solution, the volume ratio of ethanol to water is 8-10:

1.

10. A magnesium-aluminum composite magnetic adsorbent, characterized in that: The magnesium-aluminum composite magnetic adsorbent is prepared by the preparation method of any one of claims 1 to 9.

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