A fly ash-based adsorbent for cationic dye wastewater treatment

Abstract

The application discloses a fly ash-based adsorbent for cationic dye wastewater treatment. The fly ash adsorbent is prepared by a method comprising the following steps: mixing alkali-modified fly ash with an anionic monomer, and performing polymerization to obtain the fly ash-based adsorbent, wherein the alkali-modified fly ash is used in an amount of 0.2-0.6% of the mass of the anionic monomer. Compared with common methylene blue adsorption materials on the market, the fly ash-based adsorbent has not only extremely high adsorption performance and removal efficiency, but also extremely fast adsorption rate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of cationic dye wastewater treatment, and particularly relates to a fly ash-based adsorbent for cationic dye wastewater treatment. BACKGROUND

[0002] Cationic dyes, also known as basic dyes and salt-based dyes, are soluble in water. Due to their complex chemical composition, they are difficult to degrade. If the water polluted by dyes is directly discharged without treatment, it will cause harm to humans and the water environment. However, at present, the use of cationic dyes in the industrial field is increasing sharply, causing more serious water pollution. Therefore, water pollution caused by dyes has attracted high attention from countries around the world. Adsorption is a good technology for removing dyes and treating industrial wastewater, which has the characteristics of simplicity, environmental protection, and adsorption of toxic pollutants, and can treat all types of dye waste, has high efficiency, and is of great economic significance, for example, document Zheng, Y., Zong, L. & Wang, X. Graphene oxide enhanced hydrogel as an adsorbent for effective removal of methylene blue. Polym. Bull. (2023) https: / / doi.org / 10.1007 / s00289-023-04920-4 discloses a P(AA-AMPS) / SA-GO composite hydrogel, but the adsorption capacity of the hydrogel for methylene blue is only 486.5 mg / g, and the adsorption rate is low.

[0003] Fly ash is a small particle of coal after high-temperature combustion, which is discharged into the atmosphere through the factory chimney or deposited on the ground. If not controlled, it will cause serious air pollution and water pollution. Due to its low surface area and crystal structure, only a small amount of fly ash can be reused in the construction industry, and a large amount of fly ash cannot be reasonably utilized. SUMMARY

[0004] Based on the above prior art, the purpose of the present application is to provide a fly ash-based adsorbent for cationic dye wastewater treatment, which has extremely high adsorption capacity and faster adsorption rate for cationic dyes, especially methylene blue.

[0005] The technical solution adopted by the present application to achieve the above purpose is as follows:

[0006] A fly ash-based adsorbent for cationic dye wastewater treatment, the fly ash adsorbent is prepared by a method comprising the following steps:

[0007] The alkali-modified fly ash is mixed with anionic monomers, and a polymerization reaction is performed to obtain the fly ash-based adsorbent, wherein the amount of alkali-modified fly ash is 0.2-0.6% of the mass of anionic monomers, preferably 0.2-0.3%.

[0008] Preferably, the anionic monomers are 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid.

[0009] Preferably, the molar ratio of 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid is 0.5-2:1, and beyond this molar ratio range, the adsorption performance of the adsorbent to cationic dyes is significantly reduced. More preferably, the molar ratio is 1.5-1.7:1, and most preferably, the molar ratio is 1.6:1.

[0010] Preferably, the mixing process comprises:

[0011] (1) dissolving an anionic monomer in water, adding sodium hydroxide for neutralization to obtain a neutralization solution, and the molar ratio of sodium hydroxide to the anionic monomer is 0.25-0.5:1;

[0012] (2) then adding alkali-modified fly ash, a crosslinking agent and an initiator to the neutralization solution.

[0013] More preferably, the molar ratio of sodium hydroxide to the anionic monomer is 0.28-0.30:1.

[0014] More preferably, the crosslinking agent is N,N-methylenebisacrylamide.

[0015] More preferably, the amount of the crosslinking agent is 0.1-2% of the molar amount of the anionic monomer, and higher than this amount range will reduce the adsorption capacity to cationic dyes. Most preferably, the amount of the crosslinking agent is 0.4-0.5% of the molar amount of the anionic monomer.

[0016] More preferably, the initiator is potassium persulfate.

[0017] More preferably, the amount of the initiator is 0.1-1.1% of the molar amount of the anionic monomer, and higher than this amount range will cause the polymerization reaction to be too fast, thereby reducing the adsorption capacity to cationic dyes. Most preferably, the amount of the initiator is 0.2-0.3% of the molar amount of the anionic monomer.

[0018] More preferably, the temperature of the polymerization reaction is 60-80℃, and the time is 5-10 min.

[0019] Preferably, the alkali-modified fly ash is obtained by heating and refluxing fly ash in a sodium hydroxide solution.

[0020] More preferably, after heating and refluxing, the alkali-modified fly ash is subjected to washing and drying treatment.

[0021] More preferably, the temperature of heating and refluxing is 105℃, and the time is 12 h or more.

[0022] More preferably, the concentration of the sodium hydroxide solution is 2-5 mol / L.

[0023] Application of the above fly ash-based adsorbent in cationic dye wastewater treatment.

[0024] Preferably, the cationic dye is methylene blue.

[0025] Advantages:

[0026] The adsorbent prepared by the application has a methylene blue adsorption capacity of 4000 mg / g or more, and a removal rate of 96% or more for a 500 mg / L methylene blue solution within 60 min. Compared with common methylene blue adsorption materials on the market, the adsorbent has extremely high adsorption performance and removal efficiency, and extremely fast adsorption rate. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The infrared spectra of fly ash before and after alkali modification.

[0028] Figure 2 The electron microscope image of the adsorbent prepared in Example 2.

[0029] Figure 3 The physical image of the adsorbent after absorbing methylene blue. DETAILED DESCRIPTION

[0030] The technical solutions of the application are further described in combination with examples.

[0031] The fly ash-based adsorbent for cationic dye wastewater treatment is prepared by a method comprising the following steps:

[0032] The alkali-modified fly ash is mixed with an anionic monomer to obtain the fly ash-based adsorbent by polymerization, wherein the mass ratio of the alkali-modified fly ash to the anionic monomer is 0.6-1:1.

[0033] In the application, the anionic monomers are 2-acrylamide-2-methylpropanesulfonic acid (CH2=CHCONHC(CH3)2CH2SO3H) and acrylic acid (CH2=CHCOOH), which can provide a large number of carboxyl and sulfonic acid functional groups.

[0034] The alkali-modified fly ash and the anionic monomer are mixed in an aqueous solvent, and a crosslinking agent for enhancing the stability of the polymer and an initiator for controlling the reaction rate are also added during the mixing.

[0035] Specifically, the mixing process comprises:

[0036] (1) The anionic monomer is dissolved in water, sodium hydroxide is added, and neutralization is performed to obtain a neutralization liquid, wherein the molar ratio of sodium hydroxide to the anionic monomer is 0.25-0.5:1.

[0037] (2) Then, the alkali-modified fly ash, the crosslinking agent, and the initiator are added to the neutralization liquid.

[0038] The alkali modification can remove the impurities in the micropores inside the fly ash. Moreover, as shown in the infrared spectrum of Figure 1 the fly ash (SF) after the alkali modification (SF-OH), the characteristic peak at 3418 cm -1 is obviously enhanced, indicating that the number of hydroxyl groups on the surface of the modified fly ash is increased, which is effective in enhancing the fixing effect of the anionic polymer on the fly ash.

[0039] The micropores inside the alkali modified fly ash and the rich hydroxyl groups on the surface can enhance the adsorption performance of the anionic polymer on the cationic dye.

[0040] Example 1

[0041] Preparation of the alkali modified fly ash: 4 g of fly ash was added into a 4 mol / L NaOH solution and stirred, and then refluxed at 105℃ for 18 h. After centrifugal washing, the supernatant was adjusted to pH 7. After drying, the product was ready for use.

[0042] Preparation of the fly ash-based adsorbent: 13.5852 g of 2-acrylamido-2-methylpropanesulfonic acid was dissolved in water to obtain a solution; the obtained solution was mixed with 3 g of acrylic acid; the mixed solution was placed in a three-necked flask and stirred; nitrogen was introduced into the three-necked flask; 1.2236 g of sodium hydroxide was added into the mixed solution for neutralization; 0.0488 g of alkali modified fly ash was added into the neutralized solution; then 0.1347 g of N,N-methylenebisacrylamide and 0.0650 g of potassium persulfate were added into the system; and the system was heated to 70℃ for reaction for 8 min. The obtained product was washed with anhydrous ethanol, dried at 60℃ and crushed to obtain an adsorbent particle with a size of 20-40 mesh.

[0043] Adsorption performance test: different amounts of the adsorbent were used in 100 ml of methylene blue solution at pH 11. At 60 min, the adsorption of the adsorbent on the methylene blue reached a substantially stable state, and the removal rate of the methylene blue at this time was determined.

[0044] Adsorption performance of the obtained adsorbent: the adsorption amount of the adsorbent on the methylene blue was 4812 mg / g, and the removal rate of the 500 mg / L methylene blue solution was more than 99%.

[0045] Example 2

[0046] The example 2 is basically the same as the example 1, except that the mass of the N,N-methylenebisacrylamide was adjusted from “0.1347 g” to “0.0687 g”.

[0047] Adsorption performance of the obtained adsorbent: the adsorption amount of the adsorbent on the methylene blue was 5108 mg / g, and the removal rate of the 500 mg / L methylene blue solution was more than 99.9%.

[0048] The electron microscope image of the adsorbent prepared in Example 2 is shown in Figure 2 .

[0049] The actual image of the adsorbent before and after adsorbing methylene blue is shown in Figure 3 .

[0050] Example 3

[0051] The preparation method of Example 1 is basically the same, except that the mass of the potassium persulfate is adjusted from "0.0650 g" to "0.1181 g".

[0052] The adsorption performance of the obtained adsorbent: the adsorption amount of methylene blue is 4383 mg / g. The removal rate of the 500 mg / L methylene blue solution is more than 98%.

[0053] Example 4

[0054] The preparation method of Example 1 is basically the same, except that the mass of the 2-acrylamide-2-methylpropanesulfonic acid is adjusted from "13.5852 g" to "6.7926 g".

[0055] The adsorption performance of the obtained adsorbent: the adsorption amount of methylene blue is 4172 mg / g. The removal rate of the 500 mg / L methylene blue solution is more than 96%.

[0056] From the above examples, it can be seen that the adsorbent prepared by the present application has extremely high adsorption performance and faster adsorption rate, and has broad application prospects.

[0057] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the present application has been described in detail with reference to the foregoing examples, for those skilled in the art, it still can be modified to the technical solutions recorded in the foregoing embodiments, or equivalent replacement of some technical features. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A fly ash-based adsorbent for treating cationic dye wastewater, characterized in that: The fly ash adsorbent is prepared by a method including the following steps: Alkali-modified fly ash is mixed with anionic monomers and polymerized to obtain the fly ash-based adsorbent, wherein the amount of alkali-modified fly ash is 0.2-0.6% of the mass of the anionic monomers. The anionic monomers are 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid; the molar ratio of 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid is 0.5~2:1; The mixing process includes: (1) Dissolve the anionic monomer in water, add sodium hydroxide, neutralize, and obtain a neutralized solution. The molar ratio of sodium hydroxide to anionic monomer is 0.25~0.5:

1. (2) Then add alkali-modified fly ash, crosslinking agent and initiator to the neutralization solution.

2. The fly ash-based adsorbent according to claim 1, characterized in that: The molar ratio of 2-acrylamide-2-methylpropanesulfonic acid to acrylic acid is 1.5~1.7:

1.

3. The fly ash-based adsorbent according to claim 1, characterized in that: The crosslinking agent is N,N-methylenebisacrylamide, and the amount of crosslinking agent used is 0.1~2% of the molar amount of the anionic monomer.

4. The fly ash-based adsorbent according to claim 1, characterized in that: The initiator is potassium persulfate, and the amount of initiator used is 0.1~1.1% of the molar amount of the anionic monomer.

5. The fly ash-based adsorbent according to claim 1, characterized in that: The polymerization reaction is carried out at a temperature of 60-80℃ for 5-10 minutes.

6. The fly ash-based adsorbent according to claim 1, characterized in that: The alkali-modified fly ash is obtained by heating and refluxing fly ash in a sodium hydroxide solution.

7. The use of the fly ash-based adsorbent according to any one of claims 1-6, characterized in that, Application of the fly ash-based adsorbent in the treatment of cationic dye wastewater.

8. The use according to claim 7, characterized in that: The cationic dye is methylene blue.

Images