High-efficiency deep fluorine removal agent and preparation method thereof

Abstract

The application provides a high-efficiency deep fluorine removal agent and a preparation method thereof, and relates to the technical field of fluorine removal agent materials. The preparation method of the high-efficiency deep fluorine removal agent comprises the following steps: (1) adding activated fly ash into a nitrate solution, adding alkali solution dropwise, stirring and reacting, and then centrifugally separating to obtain LDH@fly ash; (2) dissolving chitosan quaternary ammonium salt in an acetic acid solution, adding a crosslinking agent, stirring and reacting, and then centrifugally freezing and drying to obtain the fluorine removal agent. The fluorine removal agent prepared by the application improves the fluorine removal effect and improves the stability of the fluorine removal agent.

Description

Technical Field

[0001] This invention relates to the field of defluorination materials technology, specifically to a highly efficient deep defluorination agent and its preparation method. Background Technology

[0002] With the acceleration of industrialization, the problem of fluoride-containing wastewater discharge has become increasingly prominent. Fluorine is one of the essential trace elements for the human body, but excessive intake can have serious effects on human health, such as causing dental fluorosis and skeletal fluorosis. Therefore, effective treatment of fluoride-containing wastewater to reduce fluoride ion concentration is of great significance for ensuring environmental safety and human health.

[0003] Currently, the main methods for treating fluoride-containing wastewater include adsorption, electrocoagulation, reverse osmosis, ion exchange, chemical precipitation, and coagulation sedimentation. Each of these methods has its own advantages and disadvantages and is suitable for treating fluoride-containing wastewater of different concentrations.

[0004] Although high-efficiency deep defluorination agents have significant advantages in defluorination efficiency, reaction rate, and sludge volume, some problems still exist: some high-efficiency deep defluorination agents have high costs due to their complex composition and complicated preparation process, which limits their widespread application; some defluorination agents are prone to deterioration during storage and use, affecting the defluorination effect. Based on this, the present invention provides a high-efficiency deep defluorination agent and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a highly efficient deep defluorination agent and its preparation method, which improves the defluorination effect and enhances the stability of the defluorination agent.

[0006] On the one hand, the present invention provides a method for preparing a highly efficient deep defluorination agent, comprising the following steps:

[0007] (1) Activated fly ash was added to nitrate solution, alkaline solution was added dropwise, and after stirring and reacting, LDH@fly ash was obtained by centrifugation.

[0008] (2) Dissolve chitosan quaternary ammonium salt in acetic acid solution, add LDH@fly ash and crosslinking agent, stir and react, then centrifuge and freeze dry to obtain the defluorinating agent.

[0009] Furthermore, the method for preparing the activated fly ash includes: immersing fly ash in a hydrochloric acid aqueous solution with a mass concentration of 10-12% for 20-24 hours, and obtaining activated fly ash after filtration, washing, and drying.

[0010] Furthermore, the ratio of fly ash to hydrochloric acid aqueous solution is 1g:(10-12)mL.

[0011] Furthermore, the ratio of activated fly ash to nitrate solution is 100-120 g / L.

[0012] Furthermore, the nitrate solution is an aqueous nitrate solution with a mass concentration of 77-85 g / L.

[0013] Furthermore, the nitrate solution comprises La(NO3)3·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O and Zn(NO3)2·6H2O in a weight ratio of (36-40):(12-13):(23-24):(6-8).

[0014] Further, the nitrate solution is prepared by adding 36-40g of La(NO3)3·6H2O, 12-13g of Mg(NO3)2·6H2O, 23-24g of Al(NO3)3·9H2O and 6-8g of Zn(NO3)2·6H2O to deionized water to obtain 1L of nitrate solution.

[0015] Furthermore, the alkaline solution is a 3-4 mol / L NaOH aqueous solution, and the pH value after adding the alkaline solution is 9.5-10.5.

[0016] Furthermore, the acetic acid solution is an aqueous solution of acetic acid with a volume concentration of 2-3%, and the ratio of the chitosan quaternary ammonium salt to the acetic acid solution is 18-22 g / L.

[0017] Furthermore, the weight ratio of the chitosan quaternary ammonium salt, LDH@fly ash, and crosslinking agent is (18-22):(90-110):(0.5-0.7).

[0018] Furthermore, the reaction conditions in step (1) are: water bath at 60-70℃ and stirring at 300-350 rpm for 4-5 hours.

[0019] Furthermore, the reaction conditions in step (2) are: stirring the reaction for 2-3 hours in a constant temperature water bath at 50-55℃ and at 200-240 rpm.

[0020] On the other hand, the present invention also provides a highly efficient deep defluorination agent, which is prepared using the aforementioned preparation method.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention utilizes hydrochloric acid to activate fly ash into a high-porosity carrier, which is then loaded with La-Mg-Al-Zn tetrametallic LDH to achieve efficient fluorine adsorption. The hydrochloric acid dissolves the silicates and aluminosilicates in the fly ash, exposing internal pores and generating active hydroxyl (-OH) sites, thereby increasing the specific surface area.

[0023] In this invention, a synergistic adsorption mechanism for four-metal LDH (La-Mg-Al-Zn) is constructed through nitrate co-precipitation, wherein La... 3+ With F - The formation of strong ionic bonds is the core site for fluoride ion capture; Comparative Example 2 lacks La. 3+ The subsequent defluorination rate plummeted to 57.9%, indicating its irreplaceability; Mg 2+ Embedded between LDH layers, neutralizing Al 3+ and La 3+ The high positive charge maintains the stability of the layered structure; Comparative Example 3 lacks Mg. 2+ This resulted in a 31% decrease in adsorption capacity; Al 3+ Increase the charge density of the laminate and promote F - Diffusion into the interlayer; Comparative Example 4 lacks Al 3+ This reduced the regeneration efficiency to 48.8%; Zn 2+ Zn forms Zn-OH bonds with hydroxyl groups, enhancing interlayer bonding; Comparative Example 5 lacks Zn. 2+ This leads to an increase in the residual fluorine concentration after regeneration.

[0024] In this invention, QCS coats LDH@fly ash via electrostatic interaction, forming a core-shell structure. The quaternary ammonium groups of QCS neutralize the negative charge on the LDH surface, preventing particle agglomeration and increasing the exposure rate of adsorption sites. In Comparative Example 7, without QCS, material agglomeration was severe, with a regeneration efficiency of only 24.0%. During the regeneration stage (NaOH elution), QCS promotes the adsorption of fly ash through electrostatic repulsion. - Desorption prevents residual fluoride ions from occupying the active sites. In Comparative Example 6, reducing the QCS dosage decreased the regeneration efficiency by 19.6%.

[0025] This invention employs freeze-drying instead of high-temperature drying to preserve the multi-level pore structure. Freeze-drying forms a composite structure of macropores and mesopores through ice crystal sublimation, resulting in a high specific surface area retention rate. In Comparative Example 10, drying at 80°C caused pore collapse and a 15% reduction in adsorption capacity; moreover, the freeze-dried material maintained its structural integrity during 10 regeneration cycles, preventing the collapse of layered LDH.

[0026] In this invention, glutaraldehyde is used instead of epichlorohydrin as a crosslinking agent; glutaraldehyde crosslinks with QCS amino groups via a Schiff base reaction, which has a higher reaction efficiency than epichlorohydrin and avoids toxic byproducts (such as chlorinated organic compounds). Comparative Example 9 showed that the use of epichlorohydrin led to an increase in wastewater COD and a 22.1% decrease in regeneration efficiency. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that all raw materials are commercially available. In this invention, the chitosan quaternary ammonium salt is hydroxypropyltrimethylammonium chloride chitosan, purchased from Shandong Dibeike Bioengineering Co., Ltd.; the fly ash was purchased from Luetu Fine Chemical Hebei Co., Ltd.

[0029] Example 1

[0030] This embodiment provides a method for preparing a highly efficient deep defluorination agent, including the following steps:

[0031] (1) 1000g of fly ash was soaked in an aqueous solution of hydrochloric acid with a mass concentration of 11% for 22h, filtered, washed with deionized water, and dried at 100℃ for 12h to obtain activated fly ash.

[0032] (2) Add 38g of La(NO3)3·6H2O, 12.5g of Mg(NO3)2·6H2O, 23.5g of Al(NO3)3·9H2O and 7g of Zn(NO3)2·6H2O to deionized water to obtain 1L of nitrate solution; add the activated fly ash obtained in step (1) to 1L of nitrate solution, add 3.5mol / L NaOH aqueous solution dropwise until the pH value is 10, perform water bath at 65℃, stir at 325rpm for 4.5h, centrifuge at 8000rpm for 15min, wash 3 times with deionized water, and dry at 80℃ for 6h to obtain LDH@fly ash;

[0033] (3) Dissolve 20g of chitosan quaternary ammonium salt in 1L of acetic acid aqueous solution with a volume concentration of 2.5%, add 100g of LDH@fly ash and 0.6g of crosslinking agent glutaraldehyde, and ultrasonically disperse for 30min. After stirring and reacting for 2.5h in a constant temperature water bath at 52℃ and 220rpm, centrifuge at 8000rpm for 10min and freeze dry at -50℃ for 48h to obtain the defluorinating agent.

[0034] Example 2

[0035] This embodiment provides a method for preparing a highly efficient deep defluorination agent, including the following steps:

[0036] (1) 1000g of fly ash was soaked in a 10% hydrochloric acid aqueous solution for 20h, filtered, washed with deionized water, and dried at 100℃ for 12h to obtain activated fly ash.

[0037] (2) 36g of La(NO3)3·6H2O, 12g of Mg(NO3)2·6H2O, 23g of Al(NO3)3·9H2O and 6g of Zn(NO3)2·6H2O were added to deionized water to obtain 1L of nitrate solution; the activated fly ash obtained in step (1) was added to 1L of nitrate solution, and 3mol / L NaOH aqueous solution was added dropwise until the pH value was 9.5. After water bath at 60℃ and stirring at 300rpm for 4h, centrifugation at 8000rpm for 15min was performed, and after washing with deionized water 3 times, it was dried at 80℃ for 6h to obtain LDH@fly ash;

[0038] (3) Dissolve 18g of chitosan quaternary ammonium salt in 1L of acetic acid aqueous solution with a volume concentration of 2%, add 90g of LDH@fly ash and 0.5g of crosslinking agent glutaraldehyde, ultrasonically disperse for 30min, stir and react for 2h in a constant temperature water bath at 50℃ and 200rpm, centrifuge at 8000rpm for 10min, and freeze dry at -50℃ for 48h to obtain the defluorinating agent.

[0039] Example 3

[0040] This embodiment provides a method for preparing a highly efficient deep defluorination agent, including the following steps:

[0041] (1) 1000g of fly ash was soaked in a 12% hydrochloric acid aqueous solution for 24h, filtered, washed with deionized water, and dried at 100℃ for 12h to obtain activated fly ash.

[0042] (2) Add 40g of La(NO3)3·6H2O, 13g of Mg(NO3)2·6H2O, 24g of Al(NO3)3·9H2O and 8g of Zn(NO3)2·6H2O to deionized water to obtain 1L of nitrate solution; add the activated fly ash obtained in step (1) to 1L of nitrate solution, add 4mol / L of NaOH aqueous solution dropwise until the pH value is 10.5, perform water bath at 70℃, stir at 350rpm for 5h, centrifuge at 8000rpm for 15min, wash with deionized water 3 times, and dry at 80℃ for 6h to obtain LDH@fly ash;

[0043] (3) Dissolve 22g of chitosan quaternary ammonium salt in 1L of acetic acid aqueous solution with a volume concentration of 3%, add 110g of LDH@fly ash and 0.7g of crosslinking agent glutaraldehyde, and ultrasonically disperse for 30min. After stirring and reacting for 3h in a constant temperature water bath at 55℃ and 240rpm, centrifuge at 8000rpm for 10min and freeze dry at -50℃ for 48h to obtain the defluorinating agent.

[0044] Example 4

[0045] This embodiment provides a method for preparing a highly efficient deep defluorination agent, including the following steps:

[0046] (1) 1000g of fly ash was soaked in a 12% hydrochloric acid aqueous solution for 20h, filtered, washed with deionized water, and dried at 100℃ for 12h to obtain activated fly ash.

[0047] (2) 36g of La(NO3)3·6H2O, 13g of Mg(NO3)2·6H2O, 23g of Al(NO3)3·9H2O and 8g of Zn(NO3)2·6H2O were added to deionized water to obtain 1L of nitrate solution; the activated fly ash obtained in step (1) was added to 1L of nitrate solution, and 3mol / L NaOH aqueous solution was added dropwise until the pH value was 10.5. After water bath at 60℃ and stirring at 350rpm for 4h, centrifuged at 8000rpm for 15min, washed 3 times with deionized water, and dried at 80℃ for 6h to obtain LDH@fly ash;

[0048] (3) Dissolve 18g of chitosan quaternary ammonium salt in 1L of acetic acid aqueous solution with a volume concentration of 3%, add 90g of LDH@fly ash and 0.7g of crosslinking agent glutaraldehyde, ultrasonically disperse for 30min, stir and react for 2h in a constant temperature water bath at 50℃ and 240rpm, centrifuge at 8000rpm for 10min, and freeze dry at -50℃ for 48h to obtain the defluorinating agent.

[0049] Comparative Example 1

[0050] The fly ash was not activated with hydrochloric acid, and all other steps were the same as in Example 1.

[0051] Comparative Example 2

[0052] In step (2), La(NO3)3·6H2O was not added as a raw material. Instead, 38g of La(NO3)3·6H2O was replaced with Mg(NO3)2·6H2O, Al(NO3)3·9H2O and Zn(NO3)2·6H2O in a weight ratio of 12.5:23.5:7. All other steps were the same as in Example 1.

[0053] Comparative Example 3

[0054] In step (2), Mg(NO3)2·6H2O was not added as a raw material. Instead, 12.5g of Mg(NO3)2·6H2O was replaced with La(NO3)3·6H2O, Al(NO3)3·9H2O and Zn(NO3)2·6H2O in a weight ratio of 38:23.5:7. All other steps were the same as in Example 1.

[0055] Comparative Example 4

[0056] In step (2), Al(NO3)3·9H2O was not added as a raw material. Instead, 23.5g of Al(NO3)3·9H2O was replaced with La(NO3)3·6H2O, Mg(NO3)2·6H2O and Zn(NO3)2·6H2O in a weight ratio of 38:12.5:7. All other steps were the same as in Example 1.

[0057] Comparative Example 5

[0058] In step (2), Zn(NO3)2·6H2O was not added as a raw material. Instead, 7g of Zn(NO3)2·6H2O was replaced with La(NO3)3·6H2O, Mg(NO3)2·6H2O and Al(NO3)3·9H2O in a weight ratio of 38:12.5:23.5. All other steps were the same as in Example 1.

[0059] Comparative Example 6

[0060] In step (3), the amount of chitosan quaternary ammonium salt was adjusted to 10g, and the other steps were the same as in Example 1.

[0061] Comparative Example 7

[0062] Step (3) is omitted, and the LDH@fly ash prepared is the defluorinating agent of Comparative Example 7.

[0063] Comparative Example 8

[0064] The LDH@fly ash from step (2) was calcined at 500℃ for 2 hours and then combined with chitosan quaternary ammonium salt and crosslinking agent to obtain the defluorinating agent of Comparative Example 8.

[0065] Comparative Example 9

[0066] In step (3), glutaraldehyde is replaced with an equimolar amount of epichlorohydrin, and the other steps are the same as in Example 1.

[0067] Comparative Example 10

[0068] In step (3), drying at 80°C is used instead of freeze drying, and the other steps are the same as in Example 1.

[0069] Experimental example: The performance of the high-efficiency deep defluorination agents prepared in Examples 1-4 and Comparative Examples 1-10 was investigated.

[0070] Defluoridation performance: Wastewater from the wastewater treatment plant with a raw fluoride concentration of 12.1 mg / L was collected. Defluoridating agents prepared in the examples and comparative examples at 1000 mg / L were added, stirred at 200 rpm for 2 min, and then allowed to stand for 30 min. The supernatant was then used to determine the fluoride content of the effluent. The fluoride detection method was performed according to GB7484-87 "Determination of Fluoride in Water - Ion Selective Electrode Method". The fluoride removal rate ρ = (C0 - C1) / C0 × 100%; where C0 is the initial fluoride concentration in the solution, and C1 is the fluoride concentration in the solution after treatment with the defluoridating agent.

[0071] Stability: The above-mentioned defluorinating agent adsorbing fluoride ions was filtered and soaked in 0.1 mol / L NaOH solution for 8 hours for regeneration. It was then washed with water until neutral, and finally dried in an oven at 60°C for 12 hours before defluorination again. This process was repeated 10 times. The fluoride ion concentration C in the solution after the 10th treatment was recorded. 10 Fluorine removal rate ρ=(C0-C 10 ) / C0×100%.

[0072] The performance test results are shown in Table 1 below:

[0073] Table 1

[0074]

[0075]

[0076] Based on the above data, the initial defluorination rates of Examples 1-4 of this invention are all ≥94%, and they still maintain ≥88% after the 10th regeneration, indicating that the material has excellent adsorption capacity and stability. The key factors are mainly the acid-activated fly ash, the synergistic effect of the tetrametallic (La-Mg-Al-Zn) LDH, the QCS coating to enhance regeneration performance, and freeze-drying to protect the material structure. The examples used freeze-drying, and the adsorption capacity was improved compared to the control example 10.

[0077] Furthermore, Comparative Example 1 showed a defluorination rate of only 75%, with a significant decrease in regeneration efficiency, indicating that acid activation is crucial for fly ash porosity and active sites. Omitting acid activation reduced the initial defluorination rate by 19.7% and the regeneration efficiency by 38.6%. Comparative Example 2 showed a defluorination rate of 57.9%, confirming that La... 3+ The specific coordination to fluoride ions is irreplaceable, and the regeneration efficiency drops sharply because the Mg / Al / Zn system cannot stably bind fluoride ions. 3+ It is a key component in the synergistic effect of tetrametallic LDH; its absence leads to an initial defluorination rate of only 57.9% and a regeneration efficiency of only 29.8%. In Comparative Example 3, Mg... 2+ The absence of LDH leads to the disruption of the interlayer charge balance, a decrease in the stability of the layered structure, and Mg2+ Maintaining the LDH structure through charge balance resulted in a 31% decrease in adsorption capacity and a regeneration efficiency of only 43.0% after its loss. In Comparative Example 4, Al... 3+ The absence of these features leads to insufficient charge density in the laminates, weakening the intercalation ability of fluoride ions and reducing Al content. 3+ Optimization of fluoride ion intercalation adsorption reduced the regeneration efficiency to 48.8%. (Comparative Example 5: Zn) 2+ The absence of Zn reduces the interlayer stability of LDH, making the structure prone to collapse during regeneration; 2+ The lack of enhanced interlayer bonding resulted in a regeneration efficiency of 66.1%, with a fluoride residue concentration significantly higher than in Example 1. In Comparative Example 6, the QCS dosage was halved, leading to incomplete QCS coating and weakened flocculation and regeneration functions; insufficient QCS dosage resulted in a 19.6% reduction in regeneration efficiency. In Comparative Example 7, the lack of QCS electrostatic flocculation caused material agglomeration and insufficient regeneration sites; QCS coating is crucial for improving regeneration efficiency and sludge settling properties, and its absence caused a sharp drop in regeneration efficiency to 24.0%. In Comparative Example 8, high-temperature calcination damaged the LDH layered structure, reducing the fluoride removal rate to 66.9%. In Comparative Example 9, glutaraldehyde was replaced with epichlorohydrin, but epichlorohydrin has low crosslinking efficiency and is toxic; after replacement, the regeneration efficiency decreased by 22.1%, and the wastewater COD increased. In Comparative Example 10, drying at 80°C replaced freeze-drying; drying caused pore collapse, while freeze-drying is a necessary process for preserving the porous structure; after drying, the adsorption capacity decreased by 15%, and the regeneration efficiency was only 73.6%.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a highly efficient deep defluorination agent, characterized in that, Includes the following steps: (1) Activated fly ash was added to nitrate solution, alkaline solution was added dropwise, and after stirring and reacting, LDH@fly ash was obtained by centrifugation. (2) Dissolve chitosan quaternary ammonium salt in acetic acid solution, add LDH@fly ash and crosslinking agent, stir and react, then centrifuge and freeze dry to obtain the defluorination agent; The method for preparing activated fly ash includes: immersing fly ash in a hydrochloric acid aqueous solution with a mass concentration of 10-12% for 20-24 hours, and then filtering, washing, and drying to obtain activated fly ash. The nitrate solution comprises La(NO3)3·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O and Zn(NO3)2·6H2O in a weight ratio of (36-40):(12-13):(23-24):(6-8); The weight ratio of chitosan quaternary ammonium salt, LDH@fly ash, and crosslinking agent is (18-22):(90-110):(0.5-0.7). The crosslinking agent is glutaraldehyde.

2. The method for preparing a high-efficiency deep defluorination agent according to claim 1, characterized in that, The ratio of fly ash to hydrochloric acid aqueous solution is 1g:(10-12)mL.

3. The method for preparing a high-efficiency deep defluorination agent according to claim 1, characterized in that, The ratio of activated fly ash to nitrate solution is 100-120 g / L.

4. The method for preparing a high-efficiency deep defluorination agent according to claim 1, characterized in that, The nitrate solution is an aqueous nitrate solution with a mass concentration of 77-85 g / L.

5. The method for preparing a high-efficiency deep defluorination agent according to claim 1, characterized in that, The alkaline solution is a 3-4 mol / L NaOH aqueous solution, and the pH value after adding the alkaline solution is 9.5-10.

5.

6. The method for preparing a high-efficiency deep defluorination agent according to claim 1, characterized in that, The acetic acid solution is an aqueous solution of acetic acid with a volume concentration of 2-3%, and the ratio of chitosan quaternary ammonium salt to acetic acid solution is 18-22 g / L.

7. A highly efficient deep defluorination agent, characterized in that, It is obtained using the preparation method of the high-efficiency deep defluorination agent according to any one of claims 1-6.

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