NaA type molecular sieve based on single aluminum source and preparation method and application thereof

Abstract

This invention belongs to the technical field of molecular sieve preparation and solid waste resource utilization. Specifically, it discloses a NaA-type molecular sieve based on a single aluminum source, its preparation method, and its application. The method includes the following steps: Secondary aluminum ash is sequentially subjected to water washing and desalination, high-temperature denitrification, alkaline leaching for impurity removal, amino acid chelation for heavy metal removal, and concentration, roasting, and activation to obtain an active aluminum source precursor; the active aluminum source precursor, silicon source, sodium hydroxide, and deionized water are mixed in a specific ratio and stirred until homogeneous to obtain a molecular sieve synthesis solution; the molecular sieve synthesis solution is transferred to a closed reaction vessel for static crystallization, followed by filtration, washing, and drying to obtain the NaA-type molecular sieve. This invention utilizes the above-mentioned NaA-type molecular sieve based on a single aluminum source, its preparation method, and its application to achieve the harmless and high-value treatment of secondary aluminum ash, and is suitable for industrial heavy metal wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve preparation and solid waste resource utilization technology, and in particular to a NaA-type molecular sieve based on a single aluminum source, its preparation method and application. Background Technology

[0002] NaA-type molecular sieves are aluminosilicate crystals with a cubic crystal system. They have a uniform microporous structure, a large specific surface area, and excellent ion exchange performance. They are widely used in adsorption separation, ion exchange, catalysis, and other fields, and especially show good adsorption performance in the treatment of heavy metal ion wastewater.

[0003] Traditional preparations of NaA-type molecular sieves often utilize high-purity chemical products such as sodium aluminate and aluminum hydroxide as aluminum sources. These aluminum sources have a single composition and high activity, enabling the preparation of molecular sieves with high crystallinity and stable performance. However, the high cost of raw materials and large resource consumption limit their large-scale industrial application.

[0004] Secondary aluminum ash is a hazardous solid waste generated during aluminum industry production. It is the residue left after primary aluminum ash is extracted to obtain metallic aluminum. Its main components are alumina (Al2O3, about 60%), metallic aluminum (about 10%-20%), aluminum nitride (AlN, a toxic and harmful component, about 8%~20%), and aluminum carbide (Al4C3), while also containing small amounts of fluorides, chlorides, and heavy metal oxides. Currently, secondary aluminum ash is mostly disposed of through landfill and stockpiling, which not only occupies land resources but may also cause environmental pollution due to AlN reacting with water to release NH3 and heavy metal leakage.

[0005] In the existing technology, 4A molecular sieves have been successfully prepared using cast aluminum ash and microsilica powder. However, cast aluminum ash belongs to the category of primary aluminum ash, while secondary aluminum ash has a significantly different composition and a higher AlN content. It is difficult to effectively remove impurities and activate aluminum components when used directly as an aluminum source. The preparation of molecular sieves is prone to problems such as low crystallinity and unstable performance. AlN is prone to releasing toxic NH3 when it comes into contact with water, which poses a potential pollution risk and restricts its application in the preparation of molecular sieves. Summary of the Invention

[0006] The purpose of this invention is to provide a NaA-type molecular sieve based on a single aluminum source, its preparation method and application, to achieve harmless and high-value treatment of secondary aluminum ash, which is suitable for industrial heavy metal wastewater treatment.

[0007] To achieve the above objectives, this invention provides a method for preparing NaA-type molecular sieves based on a single aluminum source, comprising the following steps: S1. The secondary aluminum ash is sequentially subjected to water washing and desalination, high-temperature denitrification, alkaline leaching for impurity removal, amino acid chelation for heavy metal removal, and concentration, roasting and activation to obtain an active aluminum source precursor. S2. Mix the active aluminum source precursor, silicon source, sodium hydroxide and deionized water obtained in S1 according to the proportion, and stir evenly at 30~40℃ and 400~600r / min to obtain molecular sieve synthesis solution. S3. The molecular sieve synthesis solution obtained in S2 is transferred into a closed reaction vessel and statically crystallized at 95~115℃ and 0.1~0.3MPa for 18~30h. After filtration, separation, washing and drying, NaA type molecular sieve is obtained.

[0008] Water washing and desalination can remove soluble salts (such as sodium chloride and sodium fluoride) from secondary aluminum ash, preventing them from adsorbing onto the molecular sieve surface during subsequent crystallization and damaging the microporous structure and crystal integrity. High-temperature denitrification can decompose toxic and harmful AlN into Al2O3 and N2, eliminating the risk of NH3 pollution. If the denitrification temperature is too low, AlN decomposition will be incomplete, while if it is too high, energy consumption will increase. Alkali leaching can dissolve impurity oxides such as iron and calcium, improving the purity of the aluminum source. Amino acid chelation removes heavy metals to ensure that the heavy metal content of subsequent products does not exceed the standard and enhances the heavy metal adsorption capacity. Calcination and activation can convert the aluminum components in secondary aluminum ash into highly active γ-Al2O3, enhancing its reactivity with silicon and alkali sources.

[0009] If the silicon-to-aluminum ratio is too low, impurities are easily formed; if it is too high, the crystallinity decreases. Stirring forms a uniform, sediment-free gel-like synthetic liquid, ensuring that all components are fully mixed, and providing a stable system for the uniform crystallization of molecular sieves.

[0010] Static crystallization allows crystals to grow uniformly. Temperature and time must be strictly controlled. If the temperature is too low or the time is insufficient, crystallization will be incomplete. If the temperature is too high or the time is too long, the crystal grain size will be too large and the agglomeration will be severe.

[0011] Preferably, in S1, the Al2O3 content of the secondary aluminum ash is ≥55%, and the total heavy metal content is ≤1000mg / kg, ensuring sufficient aluminum components required for molecular sieve synthesis. After ball milling, it is passed through a 200-mesh sieve to remove large inert impurities.

[0012] Preferably, S1 is as follows: S11. Water washing and desalination: Mix secondary aluminum ash with deionized water according to the ratio, stir for 1-2 hours, filter and separate, repeat 2-3 times, and collect the filter cake. S12, High-temperature denitrification: The filter cake obtained from S11 is transferred to the furnace, heated to 450~600℃, held for 2~4 hours, and naturally cooled to room temperature to obtain denitrified aluminum ash; S13. Alkali leaching to remove impurities: Add NaOH solution to the denitrified aluminum ash obtained in S12, heat to 80~90℃, stir at 300~500r / min, react for 2~3h, vacuum filter, and collect the filtrate. S14. Amino acid chelation to remove heavy metals: Slowly introduce CO2 into the filtrate obtained in S13, stir to adjust the pH to 5-7, then add hydrolyzed amino acids, heat to 30-40℃, stir for 30-60 min, let stand for 60-90 min, vacuum filter, and collect the supernatant. S15. Concentration, roasting and activation: The supernatant obtained in S14 is transferred to a rotary evaporator and concentrated at 60~80℃ to obtain a solid product. The solid product is then transferred to a furnace and kept at 650~800℃ for 1~3 hours. After cooling, it is ground to obtain the active aluminum source precursor.

[0013] Preferably, in S11, the solid-liquid ratio of the secondary aluminum ash to the deionized water is 1g:5~10mL.

[0014] Preferably, in S13, the solid-liquid ratio of the denitrified aluminum ash to the NaOH solution is 1g:8~12mL, and the mass fraction of the NaOH solution is 20%~30%.

[0015] Preferably, in S14, the hydrolyzed amino acid is glycine, and the amount of glycine used is 3 to 5 times the molar ratio of the total heavy metal content in the filtrate.

[0016] Preferably, in S2, the silicon source is one or more of sodium silicate, water glass, or fumed silica.

[0017] Preferably, in S2, the proportion of each component in the molecular sieve synthesis liquid is Al2O3:SiO2:Na2O:H2O=1:1.5~2.5:3.5~5.0:130~160, measured by molar ratio.

[0018] Preferably, in step S3, the filtration separation, washing, and drying specifically involve: After cooling to room temperature, vacuum filter the solution and wash it repeatedly with deionized water until the pH of the filtrate is 8-9 and the conductivity is ≤50μS / cm. Dry the solution at 100-120℃ for 4-6 hours to obtain NaA type molecular sieve.

[0019] This invention also provides a NaA-type molecular sieve, wherein the molecular sieve has a cubic crystal structure, a particle size of 250-450 nm, and a specific surface area of ​​350-420 m². 2 / g.

[0020] This invention also provides a NaA-type molecular sieve in Ni 2+ Applications in adsorption removal.

[0021] Therefore, the present invention employs the above-mentioned NaA-type molecular sieve based on a single aluminum source, its preparation method, and its application, with the following beneficial effects: This invention uses secondary aluminum ash as a single aluminum source. Through a pretreatment process, it effectively removes impurities and activates aluminum components, adapts to the compositional fluctuations of different batches of secondary aluminum ash, decomposes toxic AlN into harmless Al2O3 and NAl2O3, blocks the pollution pathway of its release of NH3 upon contact with water, and efficiently removes impurities such as Fe, Ca, Pb, and Cd as well as heavy metals. It avoids harmful components in the raw materials from seeping into molecular sieve products or the environment, and replaces high-cost traditional aluminum sources such as sodium aluminate and aluminum hydroxide, realizing the harmless and high-value utilization of solid waste.

[0022] This invention reduces the risk of salts damaging the microporous structure of the product by water washing and desalination, and rapidly forms molecular sieve crystal nuclei through calcination. The prepared NaA-type molecular sieve has high crystallinity, large specific surface area, and excellent adsorption performance, meeting the needs of heavy metal wastewater treatment.

[0023] The preparation process of this invention is simple, suitable for large-scale industrial production, and the operating conditions during application are mild, requiring no complex equipment, thus achieving both economic and environmental benefits.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is the XRD pattern of a NaA-type molecular sieve based on a single aluminum source, its preparation method, and application example 1 of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0028] Example 1: A NaA-type molecular sieve based on a single aluminum source, using secondary aluminum ash as the single aluminum source, is prepared as follows: Water washing and desalination: Take 100g of secondary aluminum ash (Al2O3 content 58%), ball mill it through a 200-mesh sieve, mix it with 800mL of deionized water (solid-liquid ratio 1:8g / mL), stir at room temperature for 1.5h, filter and separate, repeat twice, the salt content of the filter cake is 0.4%.

[0029] High-temperature denitrification: The filter cake was transferred to a muffle furnace and heated to 500°C at a rate of 5°C / min. The temperature was maintained for 3 hours and then naturally cooled to room temperature to obtain denitrified aluminum ash with a residual AlN content of 0.3%.

[0030] Alkali leaching for impurity removal: Add 1000 mL of 25% NaOH solution (solid-liquid ratio 1:10 g / mL) to the denitrified aluminum ash, stir at 85℃ and 400 r / min for 2.5 h, vacuum filter, and collect the filtrate.

[0031] Amino acid chelation for heavy metal removal: Slowly introduce CO2 into the filtrate, stir to adjust the pH of the filtrate to 6, add glycine (molar ratio of heavy metal 4 times), stir at 35℃ for 45 min, let stand for 75 min, vacuum filter through a 0.45 μm filter membrane, and collect the supernatant.

[0032] Concentration, roasting and activation: The supernatant was transferred to a rotary evaporator and concentrated to dryness at 60°C. The solid product was placed in a muffle furnace and kept at 700°C for 2 hours. After cooling and grinding to 250 μm, an active aluminum source precursor with an Al2O3 content of 68% was obtained.

[0033] Preparation of the synthesis solution: Take 20g of active aluminum source precursor, add 35g of sodium silicate (SiO2 content 28%), 22g of sodium hydroxide and 800mL of deionized water, stir at 35℃ and 500r / min for 75min to obtain the molecular sieve synthesis solution (the molar ratio of each component in the molecular sieve synthesis solution Al2O3:SiO2:Na2O:H2O=1:2.0:4.0:145).

[0034] Crystallization reaction: The molecular sieve synthesis solution was transferred to a closed reaction vessel and statically crystallized at 105℃ and 0.2MPa for 24h. After cooling to room temperature, it was vacuum filtered and washed with deionized water until the pH of the filtrate was 8.5 and the conductivity was ≤50μS / cm. It was dried at 110℃ for 5h and ground through a 300-mesh sieve to obtain NaA type molecular sieve.

[0035] NaA-type molecular sieves have a cubic crystal system, a particle size of 280 nm, and a specific surface area of ​​410 m². 2 / g,Ni 2+ The adsorption capacity was 124.3 mg / g, the adsorption removal rate was 97.5%, and the XRD pattern of the product was as follows. Figure 1 As shown.

[0036] Example 2: A NaA-type molecular sieve based on a single aluminum source, using secondary aluminum ash as the single aluminum source, is prepared as follows: Water washing and desalination: Take 100g of secondary aluminum ash (Al2O3 content 60%), ball mill it through a 200-mesh sieve, mix it with 1000mL of deionized water (solid-liquid ratio 1:10g / mL), stir at room temperature for 1.5h, filter and separate, repeat 3 times, the salt content of the filter cake is 0.3%.

[0037] High-temperature denitrification: The filter cake was transferred to a muffle furnace and heated to 500°C at a rate of 5°C / min. The temperature was maintained for 3 hours and then naturally cooled to room temperature to obtain denitrified aluminum ash with a residual AlN content of 0.3%.

[0038] Alkali leaching for impurity removal: Add 1000 mL of 25% NaOH solution (solid-liquid ratio 1:10 g / mL) to the denitrified aluminum ash, stir at 85℃ and 400 r / min for 2.5 h, vacuum filter, and collect the filtrate.

[0039] Amino acid chelation for heavy metal removal: Slowly pass CO2 into the filtrate, stir to adjust the pH of the filtrate to 7, add glycine (5 times the molar ratio of heavy metals), stir at 35℃ for 45 min, let stand for 75 min, vacuum filter through a 0.45 μm filter membrane, and collect the supernatant.

[0040] Concentration, roasting and activation: The supernatant was transferred to a rotary evaporator and concentrated to dryness at 60°C. The solid product was placed in a muffle furnace and kept at 700°C for 2 hours. After cooling and grinding to 250 μm, an active aluminum source precursor with an Al2O3 content of 72% was obtained.

[0041] Preparation of the synthesis solution: Take 18g of active aluminum source precursor, add 30g of water glass (SiO2 content 30%), 20g of sodium hydroxide and 750mL of deionized water, stir at 35℃ and 500r / min for 75min to obtain the molecular sieve synthesis solution (the molar ratio of each component in the molecular sieve synthesis solution Al2O3:SiO2:Na2O:H2O=1:2.2:4.5:150).

[0042] Crystallization reaction: The molecular sieve synthesis solution was transferred to a closed reaction vessel and statically crystallized at 105℃ and 0.2MPa for 24h. After cooling to room temperature, it was vacuum filtered and washed with deionized water until the pH of the filtrate was 8.5 and the conductivity was ≤50μS / cm. It was dried at 110℃ for 5h and ground through a 300-mesh sieve to obtain NaA type molecular sieve.

[0043] NaA-type molecular sieves have a cubic crystal system, a particle size of 320 nm, and a specific surface area of ​​385 m². 2 / g,Ni 2+ Adsorption capacity: 115.2 mg / g; Adsorption removal rate: 95.8%.

[0044] Example 3: A NaA-type molecular sieve based on a single aluminum source, using secondary aluminum ash as the single aluminum source, is prepared as follows: Water washing and desalination: Take 100g of secondary aluminum ash (Al2O3 content 55%), ball mill it through a 200-mesh sieve, mix it with 500mL of deionized water (solid-liquid ratio 1:5g / mL), stir at room temperature for 1.5h, filter and separate, repeat twice, the salt content of the filter cake is 0.5%.

[0045] High-temperature denitrification: The filter cake was transferred to a muffle furnace and heated to 500°C at a rate of 5°C / min. The temperature was maintained for 3 hours and then naturally cooled to room temperature to obtain denitrified aluminum ash with a residual AlN content of 0.3%.

[0046] Alkali leaching for impurity removal: Add 1000 mL of 25% NaOH solution (solid-liquid ratio 1:10 g / mL) to the denitrified aluminum ash, stir at 85℃ and 400 r / min for 2.5 h, vacuum filter, and collect the filtrate.

[0047] Amino acid chelation for heavy metal removal: Slowly pass CO2 into the filtrate, stir to adjust the pH of the filtrate to 5, add glycine (3 times the molar ratio of heavy metals), stir at 35℃ for 45 min, let stand for 75 min, vacuum filter through a 0.45 μm filter membrane, and collect the supernatant.

[0048] Concentration, roasting and activation: The supernatant was transferred to a rotary evaporator and concentrated to dryness at 60°C. The solid product was placed in a muffle furnace and kept at 700°C for 2 hours. After cooling and grinding to 250 μm, an active aluminum source precursor with an Al2O3 content of 66% was obtained.

[0049] Preparation of the synthesis solution: Take 22g of active aluminum source precursor, add 38g of fumed silica, 25g of sodium hydroxide and 850mL of deionized water, stir at 35℃ and 500r / min for 75min to obtain the molecular sieve synthesis solution (the molar ratio of each component in the molecular sieve synthesis solution Al2O3:SiO2:Na2O:H2O=1:1.8:3.8:140).

[0050] Crystallization reaction: The molecular sieve synthesis solution was transferred to a closed reaction vessel and statically crystallized at 105℃ and 0.2MPa for 24h. After cooling to room temperature, it was vacuum filtered and washed with deionized water until the pH of the filtrate was 8.5 and the conductivity was ≤50μS / cm. It was dried at 110℃ for 5h and ground through a 300-mesh sieve to obtain NaA type molecular sieve.

[0051] NaA-type molecular sieves have a cubic crystal system, a particle size of 380 nm, and a specific surface area of ​​360 m². 2 / g,Ni 2+ Adsorption capacity: 119.5 mg / g; Adsorption removal rate: 95.5%.

[0052] Experimental testing: The NaA-type molecular sieves prepared in Examples 1-3 were used for Ni in water. 2+ Adsorption removal test. Adsorption conditions: adsorption temperatures of 25 and 45℃, solution pH of 5 and 7, adsorption time of 120 min, and NaA molecular sieve dosage of 0.5, 1.0, 1.5 and 2.0 g / L. The results are shown in Table 1.

[0053] Table 1 Adsorption Results

[0054] In summary, the adsorption conditions are: adsorption temperature 25~45℃, solution pH 5~7, adsorption time 60~120min, and NaA type molecular sieve dosage 0.5~2.0g / L; for Ni 2+ The adsorption capacity is ≥115 mg / g, for Ni with an initial concentration of 50~200 mg / L. 2+ The aqueous solution exhibits an adsorption removal rate of ≥95%, demonstrating excellent performance.

[0055] Therefore, this invention employs the aforementioned NaA-type molecular sieve based on a single aluminum source, its preparation method, and its application to achieve harmless and high-value treatment of secondary aluminum ash, which is suitable for industrial heavy metal wastewater treatment.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A process for the preparation of NaA type molecular sieve based on a single aluminum source, characterized in that, Includes the following steps: S1. The secondary aluminum ash is sequentially subjected to water washing and desalination, high-temperature denitrification, alkaline leaching for impurity removal, amino acid chelation for heavy metal removal, and concentration, roasting and activation to obtain an active aluminum source precursor. S2. Mix the active aluminum source precursor, silicon source, sodium hydroxide and deionized water obtained in S1 according to the proportion, and stir evenly at 30~40℃ and 400~600r / min to obtain molecular sieve synthesis solution. S3. The molecular sieve synthesis solution obtained in S2 is transferred into a closed reaction vessel and statically crystallized at 95~115℃ and 0.1~0.3MPa for 18~30h. After filtration, separation, washing and drying, NaA type molecular sieve is obtained.

2. The method for preparing NaA type molecular sieve based on a single aluminum source according to claim 1, characterized in that, In S1, the Al2O3 content of the secondary aluminum ash is ≥55%, and the total heavy metal content is ≤1000mg / kg.

3. The method for preparing NaA type molecular sieve based on a single aluminum source according to claim 1, characterized in that, S1 specifically refers to: S11. Water washing and desalination: Mix secondary aluminum ash with deionized water according to the ratio, stir for 1-2 hours, filter and separate, repeat 2-3 times, and collect the filter cake. S12, High-temperature denitrification: The filter cake obtained from S11 is transferred to the furnace, heated to 450~600℃, held for 2~4 hours, and naturally cooled to room temperature to obtain denitrified aluminum ash; S13. Alkali leaching to remove impurities: Add NaOH solution to the denitrified aluminum ash obtained in S12, heat to 80~90℃, stir at 300~500r / min, react for 2~3h, vacuum filter, and collect the filtrate. S14. Amino acid chelation to remove heavy metals: Slowly introduce CO2 into the filtrate obtained in S13, stir to adjust the pH to 5-7, then add hydrolyzed amino acids, heat to 30-40℃, stir for 30-60 min, let stand for 60-90 min, vacuum filter, and collect the supernatant. S15. Concentration, roasting and activation: The supernatant obtained in S14 is transferred to a rotary evaporator and concentrated at 60~80℃ to obtain a solid product. The solid product is then transferred to a furnace and kept at 650~800℃ for 1~3 hours. After cooling, it is ground to obtain the active aluminum source precursor.

4. The process for preparing NaA type molecular sieve based on a single aluminum source according to claim 3, characterized in that, In S13, the solid-liquid ratio of the denitrified aluminum ash to the NaOH solution is 1g:8~12mL, and the mass fraction of the NaOH solution is 20%~30%.

5. The method for preparing NaA-type molecular sieves based on a single aluminum source according to claim 3, characterized in that, In S14, the hydrolyzed amino acid is glycine, and the amount of glycine used is 3 to 5 times the molar ratio of the total heavy metal content in the filtrate.

6. The method of claim 1, wherein the method is characterized by: In S2, the silicon source is one or more of sodium silicate, water glass, or fumed silica.

7. The method of claim 1, wherein the method is characterized by: In S2, the proportion of each component in the molecular sieve synthesis liquid is Al2O3:SiO2:Na2O:H2O=1:1.5~2.5:3.5~5.0:130~160 according to the molar ratio.

8. The method of claim 1, wherein the method is characterized by: In S3, the filtration separation, washing, and drying specifically refer to: After cooling to room temperature, vacuum filter the solution and wash it repeatedly with deionized water until the pH of the filtrate is 8-9 and the conductivity is ≤50μS / cm. Dry the solution at 100-120℃ for 4-6 hours to obtain NaA type molecular sieve.

9. A NaA-type molecular sieve prepared by the method for preparing NaA-type molecular sieves based on a single aluminum source as described in any one of claims 1 to 8.

10. Use of a NaA-type molecular sieve as claimed in claim 9 in the adsorptive removal of CO2. 2+ from a gas stream.

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