Magnetic composite material, preparation method therefor, and use thereof in removal of ammonia nitrogen from wastewater

Abstract

Disclosed is a magnetic composite material, comprising a porous carrier the chemical formula of which is Na2Al2Si2O8·nH2O, and SmCo5 particles and Fe3O4 particles present within the pores of the porous carrier, n≥0. The mass percentages of SmCo5:Fe3O4:the porous carrier are 0.5-10%:30-50%:50-70%. The pore diameters of the pores are 0.35-0.45 nm. Further disclosed is a preparation method for the magnetic composite material. The magnetic composite material prepared according to the present invention has strong magnetism, and after ammonia nitrogen in wastewater is adsorbed, the magnetic composite material can be cyclically utilized due to the recyclability and regenerability thereof, so that material costs during wastewater treatment are greatly reduced, achieving the purpose of reducing wastewater treatment costs.

Description

A magnetic composite material, its preparation method and its use in removing ammonia nitrogen from wastewater Technical Field

[0001] The present invention belongs to the technical field of water treatment, and in particular relates to a magnetic composite material, a preparation method thereof and use thereof in removing ammonia nitrogen from wastewater. Background Art

[0002] Methods for removing ammonia nitrogen from wastewater primarily include biochemical and physicochemical methods. Traditional biological denitrification involves the conversion of organic nitrogen and ammonia nitrogen in wastewater into nitrogen gas through the combined action of microorganisms. Biochemical ammonia nitrogen removal, which relies on microbial metabolism, is affected by fluctuations in water quality, the carbon-nitrogen ratio, and temperature, and lacks the ability to start or stop at will.

[0003] Physical and chemical methods for removing ammonia nitrogen include: 1. Air stripping method. Air stripping method is generally used for wastewater with high concentration of ammonia nitrogen, especially for leachate with concentration greater than 2000 mg / L, the removal rate can reach more than 90%. However, the air stripping method is not very efficient in removing ammonia nitrogen under low temperature and low concentration conditions. 2. Zeolite adsorption method. The cations in zeolite are used to react with NH4 + Exchange is performed to achieve denitrification. Zeolite is generally used to treat low-concentration ammonia-containing wastewater or wastewater containing trace amounts of heavy metals. 3. Membrane separation technology. This method has a simple process flow, does not consume reagents, and the amount of electricity consumed during operation is proportional to the ammonia nitrogen concentration in the wastewater. However, the operating and investment costs are high, and the resulting concentrate requires subsequent treatment. 4. MAP (struvite) precipitation method. Since the content of magnesium salts in most wastewaters is relatively low compared to phosphates and ammonia nitrogen, although the resulting magnesium ammonium phosphate can be used as agricultural fertilizer to offset some of the cost, the cost of adding magnesium salts remains a major factor limiting the implementation of this method. 5. Chemical oxidation method. A method of removing ammonia nitrogen by directly oxidizing it to nitrogen gas using a strong oxidant. Breakpoint chlorination, which utilizes the reaction of ammonia in water with chlorine to produce ammonia gas for deamination, is the most common chemical oxidation method. Operating costs are high, and the byproducts chloramines and chlorinated organic matter can cause secondary pollution. Chlorination is only suitable for treating low-concentration ammonia nitrogen wastewater.

[0004] In summary, the existing ammonia nitrogen removal water treatment technology has certain limitations. The adsorption materials produced by all preparation methods are consumable materials when used and cannot be regenerated after adsorbing ammonia nitrogen. There is a problem of high sewage treatment costs caused by continuous consumption of materials. Therefore, there is an urgent need in the existing technology for a preparation method that can prepare a circulating adsorption material.

[0005] Summary of the Invention

[0006] To solve the above technical problems, the first aspect of the present invention provides a magnetic composite material, which includes a porous carrier with a chemical formula of Na2Al2Si2O8·nH2O and SmCo5 particles and Fe3O4 particles present in the pores of the porous carrier, wherein n ≥ 0, and the mass percentages of SmCo5, Fe3O4, and the porous carrier are 0.4-10%:30-50%:50-70%; and the pore diameter of the pores is 0.35-0.45nm. The magnetic composite material of the present invention can be recorded as SmCo5-Fe3O4 / Na2Al2Si2O8·nH2O, where the " / " indicates that the substance in front is supported on or within the substance behind.

[0007] Preferably, the mass percentage of SmCo5, Fe3O4 and porous carrier is 1.9-7.5%: 37-40%: 55-59%; more preferably, the mass percentage of SmCo5, Fe3O4 and porous carrier is 1.96-7.41%: 37-39.2%: 55.6-58.8%.

[0008] The second aspect of the present invention provides a method for preparing the magnetic composite material according to the first aspect, the preparation method comprising the following steps:

[0009] S1, mixing FeCl2, FeCl3 and pure water to form a first mixture;

[0010] S2. Adding metakaolin to the first mixture and mixing well to form a second mixture; the metakaolin has a chemical formula of Al2O3·2SiO2 and is a product of natural kaolin that has been calcined and dehydrated;

[0011] S3, adding NaOH solution to the second mixture, adjusting the pH of the reaction system to 13-14, and then reacting at 70-100° C. for 0.5-1 h to form a third mixture;

[0012] S4, adding SmCl3, CoCl2 and NaBH4 to the third mixture for hydrothermal reaction, controlling the reaction temperature to 60-100°C, the pH to 13-14, and the reaction time to 6-10 hours to obtain the magnetic composite material;

[0013] The reactions in steps S1 to S4 are all carried out under the protection of inert gas.

[0014] The inert gas mentioned herein is understood in a broad sense, and any gas that does not affect the synthesis of the material of the present invention can be used as an inert gas, such as nitrogen, argon, etc.

[0015] In step S1, the amounts of FeCl2 and FeCl3 can be prepared according to a stoichiometric ratio that can generate Fe3O4, or they can be prepared according to a non-stoichiometric ratio. For example, in the first solution, the mass ratio of FeCl2, FeCl3 and pure water is 2.36:1:20.

[0016] In step S2, the mass ratio of the added metakaolin to the first solution can be adjusted by technicians at will, for example, it can be 1.5:20.

[0017] In step S3, after adding NaOH to form a third mixture, Fe 2+ and Fe 3+ It reacts with it to produce Fe3O4, and metakaolin will also react in an alkaline environment to produce some sodium aluminosilicate substances;

[0018] In step S4, the sodium aluminosilicate substance can undergo a hydrothermal crystallization reaction under the hydrothermal conditions to generate a porous molecular sieve Na2Al2Si2O8·nH2O. The metakaolin that is not completely reacted in step S3 also continues to react with NaOH to generate a sodium aluminosilicate substance and then undergoes a hydrothermal crystallization reaction to generate a porous molecular sieve Na2Al2Si2O8·nH2O. At the same time, SmCl3, CoCl2 and NaBH4 react according to the following equation in the hydrothermal reaction and co-precipitate:

[0019] 2SmCl3+10CoCl2+12NaBH4+26NaOH→2SmCo5↓+12NaBO2+26NaCl+35H2↑+2H2O

[0020] The newly generated SmCo5 particles and Fe3O4 particles will be deposited in the pores of the porous molecular sieve, which is the magnetic composite material prepared by the present invention.

[0021] The third aspect of the present invention relates to the use of the magnetic composite material described in the first aspect for removing ammonia nitrogen from wastewater.

[0022] After the magnetic composite material adsorbs ammonia nitrogen in sewage, the magnetic composite material can be recovered by adding a magnetic field.

[0023] The Na2Al2Si2O8 in the magnetic composite material is a molecular sieve whose unit cell pores are capable of adsorbing ammonia nitrogen from wastewater. Ammonia nitrogen exists in wastewater as ammonium ions. The unit cell pores of this molecular sieve generally have a pore size range of 0.35nm-0.45nm, meaning they are rated 4A. Molecules and ions larger than this pore size are unable to enter, while ammonium ions have a particle size of 0.286nm, allowing them to enter the unit cell pores.

[0024] The Na in the molecular sieve + Ionization can replace ammonium ions, attracting them into the unit cell pores through ionic bonds. The unit cell pores of the molecular sieve have strong polarity and Coulomb field, which adsorb ammonium ions in the wastewater through physical attraction. Thus, the present invention adsorbs ammonium ions in wastewater through chemical replacement and physical adsorption.

[0025] In the resulting magnetic composite material, the magnetism of Fe3O4 is sometimes weak due to its regular and orderly structure. Furthermore, due to its location in the core of the magnetic composite material, the magnetism of the entire magnetic composite material is weak. Experiments have found that 10%-30% of the magnetic composite material cannot be adsorbed by the magnetic field due to its weak magnetism, which means that the yield rate of the magnetic composite material is low. To this end, the following step S5 can be used to screen out the magnetic material with strong magnetism:

[0026] S5. The solid product after the hydrothermal reaction is subjected to magnetic separation to select the part that can be adsorbed by the additional magnetic field, and then washed and dried to obtain a magnetic composite material with guaranteed magnetism. The purpose of washing is to wash away impurities in the unit cell pores of the magnetic composite material to ensure the adsorption capacity of the magnetic composite material. For magnetic composite materials that need to be transported as products, there is a drying process after washing to remove moisture from the magnetic composite material, which is convenient for the collection of the magnetic composite material. The weight of the magnetic composite material after drying after the moisture is removed is also more convenient for transportation. The weight ratio of the magnetic composite material with guaranteed magnetism obtained after magnetic separation to the magnetic composite material before magnetic separation is defined as the yield rate.

[0027] Preferably, the metakaolin in step S2 further includes pretreatment, that is, before adding the aqueous solution, the metakaolin is uniformly mixed with pure water and then added to the first mixture.

[0028] The purpose of using pure water is to prevent impurities from entering the reaction system and to prevent impurities from occupying Na + The position within the eutectic is achieved to avoid the problem of product performance changes leading to a decrease in the yield of the magnetic composite material.

[0029] Preferably, in step S4, the reaction time is shortened by continuously adding NaOH to the third mixture.

[0030] More preferably, the pH value is controlled at 13.4 in step S4.

[0031] The present invention has the following beneficial effects:

[0032] 1. The magnetic composite material obtained by the present invention has a higher magnetic susceptibility and a higher ammonia nitrogen adsorption performance than the Fe3O4 / Na2Al2Si2O8·nH2O magnetic composite material known in the prior art without adding SmCo5 particles.

[0033] 2. In the preparation method of the present invention, in order to better combine SmCo5, Fe3O4, and Na2Al2Si2O8, the time must be strictly controlled after the third mixture starts to react and the reaction is continued for 0.5 to 1 hour before adding SmCl3, CoCl2, and NaBH4. If they are added at <0.5 hours, the adsorption performance of the obtained material will deteriorate; if they are added at more than 1 hour, it will affect the combination of SmCo5, Fe3O4, and Na2Al2Si2O8; and in order to make the crystals more tightly bonded, the present invention does not directly add SmCo5, but uses SmCl3, CoCl2, and NaBH4 to make them react and precipitate at the same time, and the precipitation process is synchronized with the construction of the porous structure of the molecular sieve, so that SmCo5 is better distributed in the pores of the molecular sieve.

[0034] 2. After the magnetic composite material is adsorbed and recovered, it is placed in a regeneration agent, NaCl solution, to regenerate the magnetic composite material and reuse it. The recovery and reuse of the magnetic composite material reduces the material cost of sewage treatment. In the prior art, adsorption materials that cannot be recycled and regenerated are constantly consumed during sewage treatment, resulting in very high material costs. The magnetic composite material prepared by the present invention can be recycled and reused due to its recyclable and regenerative properties, significantly reducing the material cost of sewage treatment and achieving the purpose of reducing sewage treatment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 is an electron microscope image of the magnetic composite material

[0037] Figure 2 is a schematic diagram of the process of cyclic adsorption of ammonia nitrogen using magnetic composite materials

[0038] FIG3 is a graph showing the pH value and the reaction time in Example 4. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings through specific implementations of the embodiments of the present invention.

[0040] Example 1

[0041] A method for preparing a magnetic composite material for adsorbing ammonia nitrogen comprises the following steps:

[0042] S1. Dissolve 2.36 g of FeCl 3 ·6H 2 O and 1 g of FeCl 2 ·4H 2 O in 20 g of water to form a first mixture.

[0043] S2. 1.5 g of metakaolin was diffused into 20 g of pure water under the assistance of ultrasound and mixed evenly, and then added to the first mixture, purged with nitrogen for 10 minutes, and sealed and stirred for 1 hour to form a second mixture;

[0044] S3. Add 20 ml of 6 mol / L NaOH solution to the second mixture to adjust the pH of the entire aqueous solution to 13-14. Stir the entire aqueous solution for 5 minutes while adding the NaOH solution. Then, heat the third mixture at 95° C. for 0.5 h.

[0045] S4, adding 0.0058g SmCl3, 0.0146g CoCl2, and 0.0051g NaBH4 to form a fourth mixture, transferring the fourth mixture into a hydrothermal reactor, and continuing the reaction at 80°C for 8h, during which a precipitate is continuously precipitated, and the precipitate is the magnetic composite material of the present invention;

[0046] S5. Using magnetic separation to select the portion of the precipitate that can be adsorbed by the additional magnetic field, and obtaining a magnetic composite material with guaranteed magnetism after washing and drying.

[0047] Example 2

[0048] Example 2 is relative to Example 1, except that in Example 2, SmCl3, CoCl2, and NaBH4 are configured in a molar ratio of 1:5:6 in step S4, and the total amount of SmCl3, CoCl2, and NaBH4 is controlled to generate a series of samples with different SmCo5 contents shown in sequence numbers 2-6 in Table 1 below (wherein sequence number 1 is a blank control sample), which are put into a reaction vessel to form a fourth mixture, and the fourth mixture is transferred to a hydrothermal reactor, and the reaction is continued at 80°C for 8 hours, during which a precipitate is continuously precipitated, and the precipitate is the magnetic composite material of the present invention.

[0049] The precipitate was subjected to magnetic separation to select the portion that could be adsorbed by the additional magnetic field, and after washing and drying, a magnetic composite material with guaranteed magnetic properties was obtained. Specific data on the magnetic susceptibility, magnetic composite material yield, and magnetic composite material output of the magnetic composite material are shown in Table 1 below.

[0050] Table 1 Magnetic susceptibility and yield of magnetic composite materials with different SmCo5 contents

[0051] As shown in Table 1, as the SmCo5 content in the magnetic composite increases, the magnetic susceptibility and yield of the magnetic composite increase accordingly. When the SmCo5 content reaches 5% of the total mass of the magnetic material, the production of the magnetic composite increases significantly and then stabilizes. Magnetic composites produced at this mass ratio have a high yield, minimize raw material waste, and reduce the cost of producing the magnetic composite. The higher magnetic susceptibility of the magnetic composite produced at this mass ratio makes it easier to adsorb when subjected to an additional magnetic field. This makes it easier to recover the magnetic composite after it is added to wastewater, minimizing losses and thus reducing wastewater treatment costs. The corresponding equilibrium ammonia nitrogen adsorption concentration is 40.5 mg / g, and the yield of the magnetic composite is 98.1%. At this point, the magnetic composite has a strong adsorption capacity for ammonia nitrogen, while maintaining a high yield, resulting in a good yield during production and a high recovery rate during use.

[0052] Example 3

[0053] The difference between Example 1 and Example 3 is that this example adopts a jacket heating method, and NaOH is intermittently added to the heating kettle through the feeding port during the heating process to keep the pH value of the third mixture within the range of 13-14.

[0054] As the reaction proceeds, the metakaolin, OH - 、Fe 3+ 、Fe 2+ 、Sm 3 、Co 2+ The concentration of the corresponding ions in the third mixture will gradually decrease, resulting in a decrease in reaction efficiency and a prolonged reaction time. During the heating process, NaOH was added to the third mixture to maintain the pH value of the third mixture. After heating for 8 hours, no precipitate was produced in the third mixture.

[0055] It can be seen that by adding NaOH to the third mixture to maintain the pH value, the heating time is greatly shortened by the time required for the reaction, thereby achieving the effect of reducing the preparation time of the magnetic composite material.

[0056] At the same time, the OH in the third mixture is increased - 、Na + The concentration of metakaolin and Fe 3+ 、Fe 2+ 、Sm 3+ 、Co 2+ Able to react more quickly and completely.

[0057] Example 4

[0058] The pH value of the third mixture affects the efficiency of forming the magnetic composite material. The magnetic composite material was prepared using 2 g of FeCl3·H2O, 1 g of FeCl2·H2O, and 1.5 g of kaolin. The heating temperature was controlled at 100°C.

[0059] In combination with the technical solution of Example 3, NaOH was added to adjust the pH value of the third mixture to 12, 12.2, 12.4, 12.6, 12.8, 13, 13.2, 13.4, 13.6, 13.8, and 14, respectively, forming a total of 11 groups of data, as shown in serial numbers 1-11 in Table 2 below.

[0060] In addition, during the heating process of the third mixture, NaOH was added to stabilize the pH value of each group of the third mixture. The reaction time of the magnetic composite material in the third mixture is shown in Table 2.

[0061] Table 2 pH value and complete reaction timetable

[0062] The time required for the complete reaction of the third mixture refers to the time required for various raw materials used to prepare the magnetic composite material in the third mixture to completely react and the third mixture no longer produces the magnetic composite material.

[0063] As shown in Figure 3, the time required for the third mixture to completely react is a curve as the pH value of the third mixture changes. As the pH value increases, the reaction time generally decreases. However, when the pH value rises to a certain level, the reaction time actually increases slightly.

[0064] At a pH of 13.4, the curve reaches a low point. At this point, the time required to prepare the magnetic composite material is the shortest, and the efficiency of preparing the magnetic composite material is the highest. By controlling the pH value of the reaction, the reaction time can be shortened and the efficiency of preparing the magnetic composite material can be improved.

[0065] It can be seen that controlling the pH value can improve the material preparation efficiency, and a pH value of 13.4 is the optimal pH value for preparing magnetic composite materials.

[0066] Example 5

[0067] The reaction time of the fourth mixture affects the material's adsorption properties. After the third mixture begins reacting, the reaction time must be strictly controlled and continued for 0.5-1 hour before adding SmCl₃, CoCl₂, and NaBH₄. If added before 0.5 hours, the resulting material's adsorption properties will deteriorate. If added after 1 hour, it will affect the bonding between SmCo₅, Fe₃O₄, and Na₂Al₂Si₂O₄, resulting in a lower material yield. The effect of the fourth mixture's reaction time on material adsorption properties is shown in Table 3.

[0068] Table 3 Effect of reaction time of the fourth mixture on material adsorption performance

[0069] Table 4 shows that the magnetic composite formed by SmCo5 has an increased magnetic susceptibility and a higher proportion of Na2Al2Si2O8·4.5H2O with adsorption properties, improving adsorption performance. Table 4 compares the equilibrium ammonia nitrogen adsorption concentration, yield rate, and magnetic susceptibility of SmCo5-Fe3O4 / Na2Al2Si2O8·4.5H2O and Fe3O4 / Na2Al2Si2O8·4.5H2O.

[0070] Table 4 Comparison of the two materials

[0071] The above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A magnetic composite material, characterized in that: It includes a porous carrier with a chemical formula of Na2Al2Si2O8·nH2O and SmCo5 particles and Fe3O4 particles present in the pores of the porous carrier, wherein n≥0, and the mass percentages of SmCo5, Fe3O4 and the porous carrier are 0.4-10%: 30-50%: 50-70%; the pore diameter is 0.35-0.45nm.

2. The magnetic composite material according to claim 1, characterized in that: The mass percentages of SmCo5, Fe3O4 and porous carrier are 1.9-7.5%: 37-40%: 55-59%.

3. The magnetic composite material according to claim 1, characterized in that: The mass percentages of SmCo5, Fe3O4 and porous carrier are 1.96-7.41%: 37-39.2%: 55.6-58.8%.

4. The method for preparing the magnetic composite material according to claim 1, characterized in that: The following steps are involved: S1, mixing FeCl2, FeCl3 and pure water to form a first mixture; S2, adding metakaolin to the first mixture and mixing to form a second mixture; S3, adding NaOH solution to the second mixture, adjusting the pH of the reaction system to 13-14, and then reacting at 70-100° C. for 0.5-1 h to form a third mixture; S4, adding SmCl3, CoCl2 and NaBH4 to the third mixture for hydrothermal reaction, controlling the reaction temperature to 60-100°C, the pH to 13-14, and the reaction time to 6-10h, and the obtained solid product is the magnetic composite material; The reactions in steps S1 to S4 are all carried out under the protection of inert gas.

5. The preparation method according to claim 4, characterized in that: The metakaolin in step S2 is uniformly mixed into pure water before being added into the aqueous solution, and then added into the first mixture.

6. The preparation method according to claim 4, characterized in that: After step S4, the method further includes step S5; S5. Screening and separating the magnetic composite material by magnetic separation, and washing and drying the part of the magnetic composite material that can be attracted by magnetic force.

7. The preparation method according to claim 4, characterized in that: The inert gas includes nitrogen or argon.

8. The preparation method according to claim 4, characterized in that: In step S4, the reaction time is shortened by continuously adding NaOH to the third mixture.

9. The preparation method according to claim 4, characterized in that: In step S4, the pH value is controlled at 13.

4.

10. Use of the magnetic composite material according to claim 1 for removing ammonia nitrogen from wastewater.

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