A magnetic composite material, a preparation method thereof and its use for removing ammonia nitrogen from wastewater

Abstract

The present invention discloses a magnetic composite material, which comprises a porous carrier with the chemical formula 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:porous carrier are 0.5 - 10%:30 - 50%:50 - 70%; the pore diameter of the pores is 0.35 - 0.45 nm. The present invention also discloses a preparation method of the magnetic composite material. The magnetic composite material prepared by the present invention has strong magnetism, and after adsorbing ammonia nitrogen in sewage, it can be recycled through the characteristics of recovery and regeneration, greatly reducing the material cost during sewage treatment and achieving the purpose of reducing the sewage treatment cost.

Description

Technical Field

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

[0002] The methods for removing ammonia nitrogen from wastewater mainly include biochemical methods and physicochemical methods. Traditional biological denitrification refers to the process in which organic nitrogen and ammonia nitrogen in sewage are metabolically converted into nitrogen gas under the combined action of microorganisms. The removal of ammonia nitrogen by biochemical methods is achieved through microbial metabolism, which is affected by water quality fluctuations, carbon-nitrogen ratio, and temperature, and does not have the characteristics of starting and stopping at any time.

[0003] The physicochemical methods for removing ammonia nitrogen include: 1. Stripping method. The stripping method is generally used for high-concentration ammonia nitrogen wastewater, especially for landfill leachate with a concentration greater than 2000 mg / L, and the removal rate can reach more than 90%. However, the stripping method has a low efficiency for ammonia nitrogen removal under low-temperature and low-concentration conditions. 2. Zeolite adsorption method. The cations in zeolite are used to exchange with NH4 + in the wastewater to achieve the purpose of denitrification. Zeolite is generally used to treat low-concentration ammonia-containing wastewater or wastewater containing trace heavy metals. 3. Membrane separation technology. This method has a simple process flow, does not consume chemicals, and the electricity consumption during operation is proportional to the ammonia nitrogen concentration in the wastewater. However, the operation and investment costs are high, and the concentrated liquid generated needs to be treated subsequently. 4. MAP (struvite) precipitation method. Since the content of magnesium salts in most wastewater is relatively low compared to phosphates and ammonia nitrogen, although the generated magnesium ammonium phosphate can be used as agricultural fertilizer to offset part of the cost, the cost of adding magnesium salts still becomes the main factor restricting the implementation of this method. 5. Chemical oxidation method. A method in which strong oxidants are used to directly oxidize ammonia nitrogen into nitrogen gas for removal. Breakpoint chlorination is to use the reaction of ammonia and chlorine in water to generate ammonia gas for deammoniation, which is the most common chemical oxidation method. The operation cost is high, and the by-products chloramines and chlorinated organic compounds will cause secondary pollution. The chlorination method is only applicable to treating low-concentration ammonia nitrogen wastewater.

[0004] In summary, the existing water treatment technologies for removing ammonia nitrogen have certain limitations. All the adsorption materials prepared by the existing preparation methods are consumable materials during use and cannot be regenerated after adsorbing ammonia nitrogen. There is a problem of high sewage treatment cost caused by continuous consumption of materials. Therefore, there is an urgent need in the prior art for a preparation method that can prepare a cyclic adsorption material. Summary of the Invention

[0005] To solve the above technical problems, a first aspect of the present invention provides a magnetic composite material, which comprises a porous carrier with the chemical formula of Na2Al2Si2O8·nH2O, and SmCo5 particles and Fe3O4 particles existing 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 of the pores is 0.35-0.45 nm. The magnetic composite material of the present invention can be denoted as SmCo5-Fe3O4 / Na2Al2Si2O8·nH2O, where " / " indicates that the substance before it is carried on or within the substance after it.

[0006] Preferably, the mass percentages of SmCo5, Fe3O4 and the porous carrier are 1.9-7.5%: 37-40%: 55-59%; more preferably, the mass percentages of SmCo5, Fe3O4 and the porous carrier are 1.96-7.41%: 37-39.2%: 55.6-58.8%.

[0007] A second aspect of the present invention provides a preparation method of the magnetic composite material described in the first aspect, and the preparation method comprises the following steps:

[0008] S1. Mix FeCl2, FeCl3 and pure water to form a first mixture.

[0009] S2. Add metakaolin to the first mixture and mix well to form a second mixture; the chemical formula of the metakaolin is Al2O3·2SiO2, which is the product of natural kaolin after calcination and dehydration.

[0010] S3. Add a NaOH solution to the second mixture, adjust the pH of the reaction system to 13-14, and then react at a temperature of 70-100 °C for 0.5-1 h to form a third mixture.

[0011] S4. Then add SmCl3, CoCl2 and NaBH4 to the third mixture for hydrothermal reaction, control the reaction temperature to be 60-100 °C, the pH to be 13-14, and the reaction time to be 6-10 h, and the magnetic composite material is obtained.

[0012] Among them, the reactions in steps S1-S4 are all carried out under the protection of an inert gas.

[0013] The inert gas is understood in a broad sense, and any gas that does not affect the synthesis of the materials of the present invention can be used as an inert gas, such as nitrogen, argon, etc.

[0014] In step S1, the amounts of FeCl2 and FeCl3 can be prepared according to the stoichiometric ratio capable of generating Fe3O4. Of course, they can also be prepared without following the stoichiometric ratio. For example, in the first solution, the mass ratio of FeCl2, FeCl3, and pure water is 2.36:1:20.

[0015] In step S2, the mass ratio of the metakaolin added to the first solution can be adjusted arbitrarily by those skilled in the art. For example, it can be 1.5:20.

[0016] In step S3, after adding NaOH to form the third mixture, Fe 2+ and Fe 3+ react with it to produce Fe3O4, and the metakaolin will also react in an alkaline environment to form a part of sodium aluminosilicate substances;

[0017] In step S4, under hydrothermal conditions, the sodium aluminosilicate substances can undergo hydrothermal crystallization reaction to form porous molecular sieve Na2Al2Si2O8·nH2O. The metakaolin that was not completely reacted in step S3 also continues to react with NaOH to form sodium aluminosilicate substances and then undergoes hydrothermal crystallization reaction to form porous molecular sieve Na2Al2Si2O8·nH2O. At the same time, SmCl3, CoCl2, and NaBH4 react and co-precipitate according to the following equation in the hydrothermal reaction:

[0018] 2SmCl3 + 10CoCl2 + 12NaBH4 + 26NaOH → 2SmCo5↓ + 12NaBO2 + 26NaCl + 35H2↑ + 2H2O

[0019] The newly formed SmCo5 particles and Fe3O4 particles will deposit in the pores of the porous molecular sieve, which is the magnetic composite material prepared by the present invention.

[0020] 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.

[0021] After the magnetic composite material adsorbs ammonia nitrogen in the sewage, the magnetic composite material can be recovered by applying an additional magnetic field.

[0022] Na2Al2Si2O8 in the magnetic composite material is a kind of molecular sieve, and the crystal cell pores of the molecular sieve can adsorb ammonia nitrogen in the sewage. The ammonia nitrogen exists in the sewage in the form of ammonium ions. The pore diameter range of the crystal cell pores of this molecular sieve is generally 0.35 nm - 0.45 nm, that is, the pore diameter of the crystal cell pores is at the 4A level. This level of molecular sieve is also called 4A molecular sieve. Molecules and ions larger than this pore diameter cannot enter, while the particle diameter of ammonium ions is 0.286 nm. Therefore, ammonium ions can enter the crystal cell pores.

[0023] The Na in the molecular sieve + Ionization can displace with ammonium ions and attract ammonium ions into the crystal cell pores through ionic bonds. The crystal cell pores of the molecular sieve have strong polarity and Coulomb field, and ammonium ions in sewage are adsorbed by physical attraction. Thus, the present invention adsorbs ammonium ions in sewage through chemical displacement and physical adsorption.

[0024] In the obtained magnetic composite material, sometimes due to the regular and ordered structure of Fe3O4, the magnetism of Fe3O4 is weak, and because it is located at the core of the magnetic composite material, the magnetism of the overall magnetic composite material is weak. Experiments have found that 10%-30% of the magnetic composite materials cannot be adsorbed by the magnetic field due to weak magnetism, that is, the yield rate of the magnetic composite material is not high. Therefore, the following step S5 can be used to screen out the magnetic materials with strong magnetism among them:

[0025] S5. The solid product after the hydrothermal reaction is selected by magnetic separation to obtain 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. Among them, the purpose of washing is to wash away the impurities in the crystal cell pores of the magnetic composite material to ensure the adsorption capacity of the magnetic composite material. For the magnetic composite material that needs to be transported as a product, there is also a drying process after washing to remove the moisture of the magnetic composite material, which is convenient for the collection of the magnetic composite material, and the weight after removing the moisture after drying 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.

[0026] Preferably, the metakaolin in step S2 also includes pretreatment. Before adding the aqueous solution, the metakaolin is uniformly mixed into pure water and then added to the first mixture.

[0027] The purpose of using pure water is to avoid impurities entering the reaction system and prevent impurities from occupying the position of Na + in the eutectic, so as to avoid the problem that the performance of the product changes and the yield rate of the magnetic composite material decreases.

[0028] Preferably, in step S4, the reaction time is shortened by continuously supplementing NaOH to the third mixture.

[0029] More preferably, the pH value in step S4 is controlled at 13.4.

[0030] The present invention has the following beneficial effects:

[0031] 1. The magnetic composite material obtained by the present invention has a higher magnetic susceptibility and a higher ammonia nitrogen adsorption performance compared with the Fe3O4 / Na2Al2Si2O8·nH2O magnetic composite material without adding SmCo5 particles known in the prior art.

[0032] 2. In the preparation method of the present invention, in order to better combine SmCo5, Fe3O4, and Na2Al2Si2O8, after the third mixture starts to react, it is necessary to strictly control the time and continue to react for 0.5 - 1 h, and then add SmCl3, CoCl2, and NaBH4. If added when < 0.5 h, the adsorption performance of the prepared material will deteriorate; if greater than 1 h, it will affect the combination between SmCo5, Fe3O4, and Na2Al2Si2O8. And in order to make the combination between crystals closer, the present invention does not directly add SmCo5, but makes it react and precipitate while building the porous structure of the molecular sieve through SmCl3, CoCl2, and NaBH4, so that SmCo5 is better distributed in the pores of the molecular sieve.

[0033] 2. After the magnetic composite material completes adsorption and is recycled, it is put into the regenerant NaCl solution to regenerate the magnetic composite material and obtain repeated use. The recycling and regeneration of the magnetic composite material reduce the material cost of sewage treatment. The adsorption materials that cannot be recycled and regenerated in the prior art need to be continuously consumed when treating sewage, so the material cost is very high. The magnetic composite material prepared by the present invention can be recycled through the characteristics of recycling and regeneration, greatly reducing the material cost during sewage treatment and achieving the purpose of reducing the sewage treatment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solution of the present invention, the drawings required for describing the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0035] Figure 1 It is an electron micrograph of the magnetic composite material

[0036] Figure 2 It is a schematic flow chart of the cyclic adsorption of ammonia nitrogen using the magnetic composite material

[0037] Figure 3 It is a curve graph of pH value and reaction time in Example 4. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The technical solution of the present invention will be clearly and completely described below in combination with the specific implementation manners of the embodiments of the present invention with reference to the drawings.

[0039] Example 1

[0040] A preparation method of a magnetic composite material for adsorbing ammonia nitrogen, comprising the following steps:

[0041] S1. Dissolve 2.36 g of FeCl3·6H2O and 1 g of FeCl2·4H2O into 20 g of water to form a first mixture.

[0042] S2. Under the assistance of ultrasonic waves, disperse 1.5 g of metakaolin into 20 g of pure water and mix evenly. Then add it to the first mixture, pass nitrogen for 10 min, and seal and stir for 1 h to form a second mixture.

[0043] S3. Add 20 ml of a NaOH solution with a concentration of 6 mol / L to the above-mentioned second mixture to adjust the acidity and alkalinity of the overall aqueous solution. The pH of the reaction system is 13 - 14. When adding the NaOH solution, stir the overall aqueous solution for 5 min. Then heat and react the third mixture at a temperature control of 95°C for 0.5 h.

[0044] S4. Add 0.0058 g of SmCl3, 0.0146 g of CoCl2, and 0.0051 g of NaBH4 to form a fourth mixture. Transfer the fourth mixture into a hydrothermal reaction kettle and continue to react at a temperature control of 80°C for 8 h. During this period, precipitates continuously precipitate out. This precipitate is the magnetic composite material of the present invention.

[0045] S5. Select the part of the precipitate that can be adsorbed by an additional magnetic field by magnetic separation, and obtain a magnetic composite material with guaranteed magnetism after washing and drying.

[0046] Example 2

[0047] Compared with Example 1, the difference in Example 2 is that in step S4, SmCl3, CoCl2, and NaBH4 are configured in a molar ratio of 1:5:6, and the total amount of SmCl3, CoCl2, and NaBH4 is controlled to generate a series of samples with different SmCo5 contents shown in No. 2 - 6 in Table 1 below (where No. 1 is a blank control sample). Put them into a reaction vessel to form a fourth mixture. Transfer the fourth mixture into a hydrothermal reaction kettle and continue to react at a temperature control of 80°C for 8 h. During this period, precipitates continuously precipitate out. This precipitate is the magnetic composite material of the present invention.

[0048] Select the part of the precipitate that can be adsorbed by an additional magnetic field by magnetic separation, and obtain a magnetic composite material with guaranteed magnetism after washing and drying. The specific data of the magnetic susceptibility, the yield rate of the magnetic composite material, and the output of the magnetic composite material are shown in Table 1 below.

[0049] Table 1 Magnetic susceptibility and good product rate of magnetic composite materials with different SmCo5 contents

[0050]

[0051] As can be seen from Table 1, as the content of SmCo5 in the magnetic composite material increases, the magnetic susceptibility of the magnetic composite material increases, and the yield rate of the magnetic composite material increases. When the production amount of SmCo5 accounts for 5% of the total mass of the magnetic substance, the output of the magnetic composite material increases significantly and then tends to be stable. The yield rate of the magnetic composite material corresponding to the magnetic composite material produced according to this mass ratio is relatively high, with less waste of raw materials, reducing the cost of preparing the magnetic composite material. The magnetic composite material prepared according to this mass ratio has a higher magnetic susceptibility, making it easier to be adsorbed when the magnetic composite material is adsorbed by an additional magnetic field. Therefore, it is easier to be recovered after the magnetic composite material is put into sewage, reducing the loss of the magnetic composite material and thus reducing the cost of sewage treatment. At the same time, the corresponding ammonia nitrogen equilibrium adsorption concentration is 40.5 mg / g, and the yield rate of the magnetic composite material is 98.1%. At this time, the magnetic composite material has a strong adsorption capacity for ammonia nitrogen, and the yield rate of the magnetic composite material also remains at a relatively high level, making the magnetic composite material have a good yield rate during preparation and a high recovery rate during use.

[0052] Example 3

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

[0054] As the reaction proceeds, metakaolin, OH - , Fe 3+ , Fe 2+ , Sm 3 , Co 2+ in the fourth mixture will gradually decrease, resulting in a decrease in the concentration of the corresponding ions in the third mixture, a decrease in the reaction efficiency, and an extension of the reaction time. During the heating process, NaOH is supplemented into the third mixture to maintain the pH value of the third mixture. When heated to the 8th hour, no more precipitates are produced in the third mixture.

[0055] Thus, it can be seen that by supplementing NaOH to the third mixture to maintain the PH value, the heating time significantly shortens the time required for the reaction, achieving the effect of reducing the preparation time of the magnetic composite material.

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

[0057] Example 4

[0058] The pH value of the third mixture affects the production efficiency of the magnetic composite material. The magnetic composite material is prepared with 2 g of FeCl3·H2O, 1 g of FeCl2·H2O, and 1.5 g of kaolin. The heating temperature is controlled at 100 °C for all cases.

[0059] Combined with the technical solution of Example 3, NaOH is 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 by the serial numbers 1 - 11 in Table 2 below.

[0060] And during the heating process of the third mixture, the pH value of each group of the third mixture is kept stable by supplementing NaOH. 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 time table

[0062] Serial number pH value of the third mixture Time required for the complete reaction of the third mixture ( / h) 1 12.0 18.0 2 12.2 17.8 3 12.4 17.2 4 12.6 16.2 5 12.8 14.0 6 13.0 11.0 7 13.2 10.0 8 13.4 9.8 9 13.6 10.0 10 13.8 10.1 11 14.0 10.1

[0063] The time required for the complete reaction of the third mixture refers to the time when all the raw materials used to prepare the magnetic composite material in the third mixture are completely reacted and the third mixture no longer produces the magnetic composite material.

[0064] As Figure 3 shown, as the pH value of the third mixture changes, the time for the complete reaction of the third mixture is a curve. As the pH value increases, the time required for the reaction generally gradually decreases. However, when the pH value rises to a certain extent, the time required for the reaction will instead increase slightly.

[0065] When the pH value is 13.4, it is a trough of the above curve. At this time, the time required for the magnetic composite material is the shortest and the production efficiency of the magnetic composite material is the highest. By controlling the pH value of the reaction, the purpose of shortening the reaction time and improving the production efficiency of the magnetic composite material is achieved.

[0066] Thus, it can be seen that controlling the pH value can improve the material production efficiency, and the pH value of 13.4 is the optimal preparation pH value for preparing the magnetic composite material.

[0067] Example 5

[0068] The reaction time of the fourth mixture will affect the adsorption performance of the material. After the third mixture starts to react, the time needs to be strictly controlled and the reaction continues for 0.5 - 1 h. Then, SmCl3, CoCl2, and NaBH4 are added. If they are added when it is less than 0.5 h, the adsorption performance of the prepared material will deteriorate; if it is greater than 1 h, it will affect the combination between SmCo5, Fe3O4, and Na2Al2Si2O8, and the yield rate of the material will be low. The reaction time of the fourth mixture on the material adsorption performance is shown in Table 3.

[0069] Table 3 The influence of the reaction time of the fourth mixture on the material adsorption performance

[0070] Serial number Reaction time of the fourth mixture Equilibrium adsorption concentration of ammonia nitrogen (mg / g) Qualified rate of magnetic composite material (%) 1 10 min 12.5 75.2 2 20 min 15.0 82.5 3 30 min 39.8 86.5 4 40 min 40.5 98.1 5 50 min 40.5 98.5 6 60 min 40.5 98.8 7 70 min 40.6 97.8 8 80 min 40.6 97.5 9 90 min 40.6 97.5

[0071] Table 4 shows that for the magnetic composite material formed by SmCo5, its magnetic susceptibility is improved, the proportion of Na2Al2Si2O8·4.5H2O with adsorption performance increases, and the adsorption performance is improved. The comparison difference data of the ammonia nitrogen equilibrium adsorption concentration, the yield rate of the magnetic composite material, and the magnetic susceptibility between SmCo5 - Fe3O4 / Na2Al2Si2O8·4.5H2O and Fe3O4 / Na2Al2Si2O8·4.5H2O are shown in Table 4.

[0072] Table 4 Comparison difference table of two materials

[0073]

[0074] The above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit. 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 terms of 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 the chemical formula of Na2Al2Si2O8·nH2O, SmCo5 particles and Fe3O4 particles existing in the pores of the porous carrier, where n≥0, and the mass percentages of SmCo5, Fe3O4 and the porous carrier are 0.4-10%: 30-50%: 50-70%; the pore diameter of the pores is 0.35-0.45 nm.

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

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

4. The preparation method of the magnetic composite material according to claim 1, wherein It includes the following steps: S1. Mix FeCl2, FeCl3 and pure water to form a first mixture; S2. Add metakaolin to the first mixture and mix evenly to form a second mixture; S3. Add a NaOH solution to the second mixture to adjust the pH of the reaction system to 13-14, and then react at a temperature of 70-100 °C for 0.5-1 h to form a third mixture; S4. Then add SmCl3, CoCl2 and NaBH4 to the third mixture for hydrothermal reaction, control the reaction temperature to be 60-100 °C, the pH to be 13-14, and the reaction time to be 6-10 h. The obtained solid product is the magnetic composite material; Among them, the reactions in steps S1-S4 are all carried out under the protection of an inert gas.

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

6. The preparation method according to claim 4, characterized in that: After step S4, there is also step S5; S5. Screen and separate the magnetic composite material by magnetic separation, and wash and dry 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 supplementing NaOH to the third mixture.

9. The preparation method according to claim 4, characterized in that: The pH value is controlled at 13.4 in step S4.

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

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