A fly ash adsorbent, a preparation method and application thereof

Abstract

This invention provides a fly ash adsorbent, its preparation method, and its application, belonging to the technical field of fly ash reuse and dye-containing wastewater treatment. The invention mixes sodium sulfide with fly ash in water, causing the sodium sulfide to react with heavy metal ions (such as zinc, chromium, and lead) in the fly ash, forming insoluble sulfide precipitates. This stabilizes the heavy metal ions and prevents toxic heavy metal leaching during adsorbent use. Furthermore, the resulting fly ash adsorbent has a porous structure and a large specific surface area, providing more physical adsorption sites for adsorbing dye molecules via van der Waals forces. The resulting fly ash adsorbent remains weakly alkaline, and its surface hydroxyl groups can further bind with dye molecules through electrostatic attraction or hydrogen bonding, forming surface complexes for further decolorization.

Description

Technical Field

[0001] This invention relates to the fields of fly ash reuse and dye-containing wastewater treatment, and particularly to a fly ash adsorbent, its preparation method, and its application. Background Technology

[0002] Dye wastewater refers to highly polluting industrial wastewater generated during the production of dyes and pigments and the printing and dyeing process. Its most significant characteristic is high chroma, which reduces water transparency, thus affecting the photosynthesis of aquatic organisms. Simultaneously, it absorbs light, further reducing water transparency, causing oxygen deficiency, and damaging the growth environment of aquatic organisms and microorganisms. Using only advanced oxidation and membrane separation technologies results in high sludge treatment costs and a high risk of secondary pollution. Furthermore, considering that dye wastewater is often acidic, adsorption combined with other treatment methods can be used to treat dye wastewater.

[0003] Fly ash from municipal solid waste incineration is fine particulate matter and flue gas sediment captured by the flue gas purification system during the incineration process. It contains dioxins, heavy metals (such as zinc, chromium, and lead), and soluble chlorides (8%–25%). Its heavy metal concentration far exceeds environmental standards, classifying it as hazardous waste. Most fly ash from waste incineration is alkaline, and its aqueous solution is also alkaline. Traditional solidification and landfill methods waste land resources and pose a risk of secondary pollution. While new technologies such as vacuum thermal detoxification can eliminate dioxins and heavy metals, their cost and processes still need optimization.

[0004] Currently, existing technologies utilize biomass ash mesoporous adsorbent materials prepared by acid treatment of waste incineration fly ash to adsorb dye wastewater, thereby decolorizing the wastewater while simultaneously utilizing the waste incineration fly ash as a resource. However, this method has low adsorption efficiency for dye wastewater, requiring two hours to reach adsorption equilibrium; the decolorization rate is also low, ranging from 70% to 90%. Summary of the Invention

[0005] The purpose of this invention is to provide a fly ash adsorbent, its preparation method, and its application. The fly ash adsorbent prepared by the preparation method provided by this invention has a short adsorption time and a high decolorization rate when applied to dye wastewater.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for preparing a fly ash adsorbent, comprising: Fly ash, sodium sulfide, and ultrapure water are mixed and stabilized to obtain a fly ash adsorbent.

[0007] Preferably, the mass ratio of fly ash to sodium sulfide is 1:(0.1~0.5).

[0008] Preferably, the stabilization treatment temperature is 20℃~25℃, and the stabilization treatment time is 1h~3h.

[0009] Preferably, after the stabilization treatment, the product of the stabilization treatment is subjected to solid-liquid separation, and the resulting solid product is dried and sieved in sequence.

[0010] Preferably, the solid-liquid separation is centrifugation; the centrifugation rate is 1500 r / min to 3000 r / min, and the centrifugation time is 10 min to 30 min.

[0011] Preferably, the mass ratio of fly ash to ultrapure water is 1:(2~5).

[0012] Preferably, the fly ash is waste incineration fly ash.

[0013] The present invention also provides a fly ash adsorbent prepared by the preparation method described in the above technical solution.

[0014] Preferably, the particle size of the fly ash adsorbent is 100 mesh to 400 mesh.

[0015] The present invention also provides the fly ash adsorbent prepared by the preparation method described in the above technical solution, or the application of the fly ash adsorbent described in the above technical solution in dye wastewater.

[0016] This invention provides a method for preparing a fly ash adsorbent, comprising: mixing fly ash, sodium sulfide, and ultrapure water, followed by stabilization treatment to obtain the fly ash adsorbent. In this invention, sodium sulfide and fly ash are mixed in water, causing the sodium sulfide to react with heavy metal ions (such as zinc, chromium, lead, etc.) in the fly ash, forming insoluble sulfide precipitates, thus stabilizing the heavy metal ions and preventing toxic heavy metal leaching during adsorbent use. Furthermore, the stabilized fly ash retains a high specific surface area, microporous / mesoporous structure, Si-O-Al framework, and active sites such as surface hydroxyl groups and iron oxide, further providing more physical adsorption sites for adsorbing dye molecules via van der Waals forces. The resulting fly ash adsorbent remains weakly alkaline, and its surface hydroxyl groups can further bind with dye molecules through electrostatic attraction or hydrogen bonding to form surface complexes, thereby further decolorizing. Example results show that the fly ash adsorbent provided by this invention, when used for treating dye wastewater, achieves a removal rate of 99.9% and a decolorization rate of 100% within 1 hour. Attached Figure Description

[0017] Figure 1 The decolorization rate diagrams are for application examples 1-5 of this invention; Figure 2 Photographs of the fly ash adsorbents used in Application Examples 1-2 and 4 before adsorption of methylene blue solution; Figure 3 The images show the fly ash adsorbents used in Examples 1-5 adsorbing methylene blue solution for 1 hour. Detailed Implementation

[0018] This invention provides a method for preparing a fly ash adsorbent, comprising: Fly ash, sodium sulfide, and ultrapure water are mixed and stabilized to obtain a fly ash adsorbent.

[0019] In one embodiment of the present invention, the fly ash can be waste incineration fly ash. The present invention, by limiting the fly ash to waste incineration fly ash, utilizes its porous structure and large specific surface area, enabling it to adsorb dye wastewater and simultaneously achieve resource utilization of waste incineration fly ash.

[0020] In one embodiment of the present invention, the fly ash may be composed of NaCl, KCl, CaClOH, SiCl4, CaSO4, SiO2, Ca(OH)2, and CaCO3.

[0021] In one embodiment of the present invention, the mass ratio of fly ash to sodium sulfide can be 1:(0.1~0.5). In embodiments of the present invention, the mass ratio of fly ash to sodium sulfide can specifically be 1:0.1, 1:0.25, or 1:0.5. The present invention ensures that the sodium sulfide reacts fully with the heavy metal ions (such as zinc, chromium, lead, etc.) in the fly ash to form insoluble sulfide precipitates, thereby stabilizing the heavy metal ions.

[0022] In one embodiment of the present invention, the mass ratio of fly ash to ultrapure water can be 1:(2~5). In embodiments of the present invention, the mass ratio of fly ash to ultrapure water can specifically be 1:2, 1:3, 1:4, or 1:5. The present invention limits the mass ratio of fly ash to ultrapure water to the above range to ensure that fly ash and sodium sulfide are fully mixed to form a slurry.

[0023] The present invention does not have any special limitations on the mixing of fly ash, sodium sulfide and ultrapure water, and any mixing method known in the art can be used.

[0024] In this invention, during the stabilization treatment, sodium sulfide reacts with heavy metal ions (such as zinc, chromium, lead, etc.) in fly ash to form insoluble sulfide precipitates, thereby stabilizing the heavy metal ions. As one embodiment of this invention, the stabilization treatment temperature can be 20-25°C, and the stabilization treatment time can be 1-3 hours. In specific embodiments of this invention, the stabilization treatment time can be 1 hour, 2 hours, or 3 hours. Setting the stabilization treatment parameters within the above range ensures a more complete reaction between sodium sulfide and heavy metal ions in fly ash.

[0025] As one embodiment of the present invention, the stabilization process can be performed under oscillating conditions.

[0026] After the stabilization treatment is completed, the present invention preferably performs solid-liquid separation on the product after the stabilization treatment, and then dries and sieves the obtained product in sequence to obtain fly ash adsorbent.

[0027] In one embodiment of the present invention, the solid-liquid separation can be centrifugation. In another embodiment, the centrifugation rate can be 1500 r / min to 3000 r / min; the centrifugation time can be 10 min to 30 min. In specific embodiments of the present invention, the centrifugation rate can be 1500 r / min, 2000 r / min, 2500 r / min, or 3000 r / min. In specific embodiments of the present invention, the centrifugation time can be 10 min, 20 min, or 30 min.

[0028] As one embodiment of the present invention, the supernatant after centrifugation can be used for the recovery and reuse of soluble salts.

[0029] In one embodiment of the present invention, the drying method can be freeze-drying. In another embodiment, the freeze-drying temperature can be -60°C; the freeze-drying time can be 24h to 48h. The present invention does not impose any particular limitation on the sieving method; any sieving method well-known in the art can be used.

[0030] This invention mixes sodium sulfide with fly ash in water, causing the sodium sulfide to react with heavy metal ions (such as chromium, cadmium, lead, etc.) in the fly ash, forming insoluble sulfide precipitates, thus stabilizing the heavy metal ions and preventing toxic heavy metal leaching during adsorption. Furthermore, the stabilized fly ash retains its high specific surface area, microporous / mesoporous structure, Si-O-Al framework, and active sites such as surface hydroxyl groups and iron oxide, providing more physical adsorption sites for adsorbing dye molecules via van der Waals forces. The resulting fly ash adsorbent remains weakly alkaline, and its surface hydroxyl groups can further bind with dye molecules through electrostatic attraction or hydrogen bonding to form surface complexes, thereby further decolorizing.

[0031] The present invention also provides fly ash adsorbent prepared by the preparation method described in the above technical solution.

[0032] The fly ash adsorbent provided by this invention has a porous structure, a large specific surface area, and good adsorption properties.

[0033] The present invention also provides the application of the fly ash adsorbent prepared by the preparation method described above in dye wastewater.

[0034] In one embodiment of the present invention, the dye wastewater may be containing cationic dyes.

[0035] The fly ash adsorbent provided by this invention has a short adsorption time, high decolorization rate, and no heavy metal leaching when applied to dye wastewater.

[0036] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0037] Example 1 A method for preparing a fly ash adsorbent is as follows: The fly ash from waste incineration, sodium sulfide, and ultrapure water were mixed and stabilized by shaking at 25°C for 2 hours. Then, the mixture was centrifuged at 3000 r / min for 20 minutes. The resulting product was freeze-dried at -60°C for 24 hours and then sieved to obtain a fly ash adsorbent with a particle size of 100-200 mesh. The mass ratio of fly ash to sodium sulfide was 1:0.25, and the mass ratio of fly ash to ultrapure water was 1:2.

[0038] Example 2 The difference between this embodiment and Embodiment 1 is that the fly ash adsorbent obtained after sieving has a particle size of 200-400 mesh.

[0039] Example 3 The difference between this comparative example and Example 1 is that the sieving process is omitted, while the rest is the same as Example 1.

[0040] Example 4 The difference between this comparative example and Example 1 is that the fly ash adsorbent obtained after sieving has a particle size of 400 mesh or larger.

[0041] Example 5 The difference between this comparative example and Example 1 is that the fly ash adsorbent obtained after sieving has a particle size of less than 100 mesh.

[0042] Application Example 1 2g of fly ash adsorbent prepared in Example 1 was mixed with 20mL of 20mg / L methylene blue solution and placed in a constant temperature shaker, and shaken at 300r / min for 24h.

[0043] Application Example 2 2g of fly ash adsorbent prepared in Example 2 was mixed with 20mL of 20mg / L methylene blue solution and placed in a constant temperature shaker, and shaken at 300r / min for 24h.

[0044] Application Example 3 2g of fly ash adsorbent prepared in Example 3 was mixed with 20mL of 20mg / L methylene blue solution and placed in a constant temperature shaker, and shaken at 300r / min for 24h.

[0045] Application Example 4 2g of fly ash adsorbent prepared in Example 4 was mixed with 20mL of 20mg / L methylene blue solution and placed in a constant temperature shaker, and shaken at 300r / min for 24h.

[0046] Application Example 5 2g of fly ash adsorbent prepared in Example 5 was mixed with 20mL of 20mg / L methylene blue solution and placed in a constant temperature shaker, and shaken at 300r / min for 24h.

[0047] Samples of 2 mL were taken at 1 h, 2 h, 4 h, 6 h, 12 h and 24 h corresponding to cases 1 to 5, respectively. After centrifugation, the supernatant was divided into two parts. The concentration of methylene blue in one part was determined three times using a UV-Vis spectrophotometer, and the results are shown in Table 1. The concentration of heavy metal pollutants in the other part was determined by ICP-MS after refrigeration for 24 h, and the results are shown in Table 2. The residue obtained by centrifugation was freeze-dried for 36 h and the content of heavy metal pollutants was determined by ICP-MS, and the results are shown in Table 3.

[0048] Table 1. Methylene blue concentration data for Application Examples 1-5 at 1h, 2h, 4h, 6h, 12h, and 24h.

[0049] As shown in Table 1, in Application Examples 1-5 of the present invention, the methylene blue removal rate can reach 99.7% after 1 hour, and the methylene blue removal rate still remains at 99.6% after 24 hours, indicating good stability.

[0050] Table 2. Heavy metal concentration data in the supernatant of Application Examples 1-5 at 1h, 2h, 4h, 6h, 12h, and 24h.

[0051] Note: Unit is μg / L.

[0052] As shown in Table 2, the concentrations of various heavy metals in the supernatant were at low levels during the shaking period of 1 h to 24 h. This indicates that after the fly ash adsorbent was stabilized with sodium sulfide, the heavy metals inside it had formed insoluble sulfide precipitates, with almost no additional leaching. Furthermore, the adsorption process did not damage the stable structure of the heavy metals, and there would be no secondary release of heavy metals due to the adsorption of dye molecules. This meets the technical objective of "non-toxic heavy metal leaching" and can be safely used for dye wastewater treatment.

[0053] Table 3. Heavy metal concentration data in residues at 1h, 2h, 4h, 6h, 12h, and 24h for Application Examples 1-5.

[0054] Note: Units are mg / kg.

[0055] As shown in Table 3, the heavy metal concentrations in the residue of Application Examples 1-5 were approximately the same at 1h, 2h, 4h, 6h, 12h, and 24h. This indicates that after treatment with sodium sulfide, most of the heavy metals in the fly ash were fixed in the adsorbent in the form of precipitation and did not enter the water body. This shows that the adsorbent's fixation effect on heavy metals was stable during the adsorption process, and no heavy metal desorption phenomenon occurred.

[0056] The decolorization effect was characterized using a UV-Vis spectrophotometer at 1h, 2h, 4h, 6h, 12h, and 24h for test cases 1-5, and the decolorization rate was obtained as follows: Figure 1 As shown in the figure, in Application Examples 1-5 of the present invention, the methylene blue decolorization rate was above 99.62% at 1h, 2h, 4h, 6h, 12h and 24h.

[0057] The fly ash adsorbent used in Examples 1-2 and Application Example 4 was photographed before adsorption of methylene blue solution, as shown in the image. Figure 2 As shown in the figure, the fly ash adsorbents used in Examples 1-2 and 4 produce a deep blue color in the solution before adsorption of methylene blue solution.

[0058] The images were taken after 1 hour of adsorption of methylene blue solution using fly ash adsorbents corresponding to test cases 1-5 on a mobile phone. Figure 3 As shown in the figure, when the fly ash adsorbents from Examples 1-5 adsorbed the methylene blue solution for 1 hour, the solution became clear.

[0059] In summary, the fly ash adsorbent prepared by the method provided by this invention has a short adsorption time and high decolorization rate when applied to dye wastewater, and there is no toxic heavy metal leaching.

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a fly ash adsorbent, comprising: Fly ash, sodium sulfide, and ultrapure water are mixed and stabilized to obtain a fly ash adsorbent.

2. The production method according to claim 1, characterized by, The mass ratio of fly ash to sodium sulfide is 1:(0.1~0.5).

3. The production method according to claim 1, characterized by, The stabilization treatment is performed at a temperature of 20-25°C for 1-3 hours.

4. The preparation method according to claim 1, characterized in that, After the stabilization treatment, the product of the stabilization treatment is subjected to solid-liquid separation, and the resulting solid product is dried and sieved in sequence.

5. The preparation method according to claim 5, characterized in that, The solid-liquid separation is performed by centrifugation; the centrifugation rate is 1500 r / min to 3000 r / min, and the centrifugation time is 10 min to 30 min.

6. The preparation method according to claim 1, characterized in that, The mass ratio of fly ash to ultrapure water is 1:(2~5).

7. The preparation method according to claim 1, characterized in that, The fly ash mentioned is fly ash from waste incineration.

8. The fly ash adsorbent prepared by the preparation method according to any one of claims 1 to 7.

9. The fly ash adsorbent according to claim 8, characterized in that, The particle size of the fly ash adsorbent is 100 mesh to 400 mesh.

10. The application of the fly ash adsorbent according to any one of claims 8 to 9 in dye wastewater.

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