Efficient deep fluorine removal agent and preparation method thereof

Abstract

The invention provides an efficient 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, dropwise adding alkali liquor, stirring for reaction, and performing centrifugal separation to obtain LDH-coated fly ash; and (2) dissolving the chitosan quaternary ammonium salt in an acetic acid solution, adding a cross-linking agent, performing stirring reaction, and performing centrifugal freeze-drying to obtain the fluorine removal agent. According to the fluorine removal agent prepared by the invention, the fluorine removal effect is improved, and the stability of the fluorine removal agent is also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of defluorination materials, and particularly relates to a high-efficiency deep defluorination agent and a preparation method thereof. Background Art

[0002] With the acceleration of the industrialization process, the problem of the discharge of fluoride-containing wastewater has become increasingly prominent. Fluorine is one of the essential trace elements for the human body, but excessive intake will cause serious impacts on human health, such as fluorosis of teeth and skeletal fluorosis. Therefore, effectively treating fluoride-containing wastewater and reducing the fluoride ion concentration are of great significance for ensuring environmental safety and human health.

[0003] At present, the treatment methods of fluoride-containing wastewater mainly include adsorption method, electrocoagulation method, reverse osmosis method, ion exchange method, chemical precipitation method, coagulation sedimentation method, etc. These methods have their own advantages and disadvantages and are applicable to the treatment of fluoride-containing wastewater with different concentrations.

[0004] Although the high-efficiency deep defluorination agent has significant advantages in terms of defluorination efficiency, reaction speed, sludge volume, etc., there are still some problems: some high-efficiency deep defluorination agents have high costs due to complex compositions and cumbersome preparation processes, which limit their wide 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 a preparation method thereof. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-efficiency deep defluorination agent and a preparation method thereof, which improve the defluorination effect and also enhance the stability of the defluorination agent.

[0006] On the one hand, the present invention provides a preparation method of a high-efficiency deep defluorination agent, including the following steps:

[0007] (1) Adding activated fly ash into a nitrate solution, dropping an alkali solution, stirring and reacting, and then centrifuging and separating to obtain LDH@fly ash;

[0008] (2) Dissolving chitosan quaternary ammonium salt in an acetic acid solution, adding LDH@fly ash and a crosslinking agent, stirring and reacting, and then centrifuging and freeze-drying to obtain the defluorination agent.

[0009] Further, the preparation method of the activated fly ash includes: impregnating fly ash in a hydrochloric acid aqueous solution with a mass concentration of 10-12% for 20-24 h, filtering, washing, and drying to obtain the activated fly ash.

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

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

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

[0013] Further, the nitrate solution contains 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 method for preparing the nitrate solution is as follows: Add 36 - 40 g of La(NO3)3·6H2O, 12 - 13 g of Mg(NO3)2·6H2O, 23 - 24 g of Al(NO3)3·9H2O, and 6 - 8 g of Zn(NO3)2·6H2O to deionized water to obtain 1 L of nitrate solution.

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

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

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

[0018] Further, the reaction conditions in step (1) are as follows: Perform a water bath at 60 - 70 °C and stir at 300 - 350 rpm for 4 - 5 h.

[0019] Further, the reaction conditions in step (2) are as follows: Perform a constant - temperature water bath at 50 - 55 °C and stir and react at 200 - 240 rpm for 2 - 3 h.

[0020] On the other hand, the present invention also provides a highly efficient deep - fluoride - removing agent prepared by the aforementioned preparation method.

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

[0022] The present invention activates fly ash with hydrochloric acid to form a high - porosity carrier, and then loads La - Mg - Al - Zn four - metal LDH to achieve efficient fluoride adsorption. Hydrochloric acid dissolves silicates and aluminosilicates in fly ash, exposes internal pores and generates active hydroxyl (-OH) sites, increasing the specific surface area.

[0023] In the present invention, a synergistic adsorption mechanism of a four-metal LDH (La-Mg-Al-Zn) is constructed through nitrate coprecipitation, where La 3+ forms a strong ionic bond with F - and is the core site for fluoride ion capture; in Comparative Example 2, the defluorination rate drops sharply to 57.9% after the absence of La 3+ , indicating its irreplaceability; Mg 2+ is embedded between the LDH layers to neutralize the high positive charges of Al 3+ and La 3+ and maintain the stability of the layered structure; in Comparative Example 3, the absence of Mg 2+ results in a 31% reduction in the adsorption capacity; Al 3+ enhances the charge density of the layer board and promotes the diffusion of F - into the interlayer; in Comparative Example 4, the absence of Al 3+ reduces the regeneration efficiency to 48.8%; Zn 2+ forms a Zn-O-H bond with the hydroxyl group to enhance the interlayer binding force; in Comparative Example 5, the absence of Zn 2+ results in an increase in the residual fluoride concentration after regeneration.

[0024] In the present invention, QCS coats LDH@fly ash through electrostatic interaction to form a core-shell structure. The quaternary ammonium group of QCS neutralizes the negative charge on the surface of LDH, prevents particle aggregation, and improves the exposure rate of adsorption sites. In Comparative Example 7, the material agglomerates severely without QCS, and the regeneration efficiency is only 24.0%. QCS promotes the desorption of F - through electrostatic repulsion during the regeneration stage (NaOH elution), avoiding the occupation of active sites by residual fluoride ions. In Comparative Example 6, the regeneration efficiency decreases by 19.6% after reducing the dosage of QCS.

[0025] In the present invention, freeze-drying is used to replace high-temperature drying to retain the hierarchical pore structure. Freeze-drying forms a composite structure of macropores and mesopores through ice crystal sublimation, and the specific surface area retention rate is high. In Comparative Example 10, the pores collapse after drying at 80 °C, and the adsorption capacity decreases by 15%; moreover, the freeze-dried material maintains its integrity during 10 regeneration cycles, avoiding the collapse of layered LDH.

[0026] In the present invention, glutaraldehyde is used to replace epichlorohydrin as a cross-linking agent; glutaraldehyde cross-links with the amino group of QCS through Schiff base reaction, and the reaction efficiency is higher than that of epichlorohydrin, and toxic by-products (such as chlorinated organic compounds) are avoided. Using epichlorohydrin in Comparative Example 9 will result in an increase in the wastewater COD and a 22.1% decrease in the regeneration efficiency. Detailed implementation manners

[0027] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the protection scope of the present invention.

[0028] It should be noted that all raw materials are commercially available. In the present invention, the chitosan quaternary ammonium salt is hydroxypropyltrimethylammonium chloride chitosan, purchased from Shandong Dibek Biotechnology Co., Ltd.; the fly ash is purchased from Lue Tu Fine Chemicals Hebei Co., Ltd.

[0029] Example 1

[0030] This example provides a preparation method of an efficient deep fluoride remover, which includes the following steps:

[0031] (1) Immerse 1000 g of fly ash in a hydrochloric acid aqueous solution with a mass concentration of 11% for 22 h, filter, wash with deionized water, and dry at 100 °C for 12 h to obtain activated fly ash;

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

[0033] (3) Stir and dissolve 20 g of chitosan quaternary ammonium salt in 1 L of acetic acid aqueous solution with a volume concentration of 2.5%, add 100 g of LDH@fly ash and 0.6 g of crosslinking agent glutaraldehyde, ultrasonically disperse for 30 min, stir and react at 52 °C under a constant water bath and 220 rpm for 2.5 h, centrifuge at 8000 rpm for 10 min, and freeze-dry at -50 °C for 48 h to obtain the fluoride remover.

[0034] Example 2

[0035] This example provides a preparation method of an efficient deep fluoride remover, which includes the following steps:

[0036] (1) Immerse 1000 g of fly ash in a hydrochloric acid aqueous solution with a mass concentration of 10% for 20 h, filter, wash with deionized water, and dry at 100 °C for 12 h to obtain activated fly ash;

[0037] (2) Add 36 g of La(NO₃)₃·6H₂O, 12 g of Mg(NO₃)₂·6H₂O, 23 g of Al(NO₃)₃·9H₂O, and 6 g of Zn(NO₃)₂·6H₂O to deionized water to obtain 1 L of nitrate solution; add the activated fly ash obtained in step (1) to 1 L of nitrate solution, dropwise add 3 mol / L NaOH aqueous solution until the pH value reaches 9.5, perform water bath at 60 °C, stir at 300 rpm for 4 h, then centrifuge at 8000 rpm for 15 min, wash with deionized water 3 times, and dry at 80 °C for 6 h to obtain LDH@fly ash;

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

[0039] Example 3

[0040] This example provides a preparation method of a high-efficiency deep defluorinating agent, including the following steps:

[0041] (1) Immerse 1000 g of fly ash in 12% hydrochloric acid aqueous solution for 24 h, filter, wash with deionized water, and dry at 100 °C for 12 h to obtain activated fly ash;

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

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

[0044] Example 4

[0045] This embodiment provides a preparation method of an efficient deep defluorination agent, comprising the following steps:

[0046] (1) Immerse 1000 g of fly ash in a hydrochloric acid aqueous solution with a mass concentration of 12% for 20 h, filter, wash with deionized water, and dry at 100 °C for 12 h to obtain activated fly ash;

[0047] (2) Add 36 g of La(NO3)3·6H2O, 13 g of Mg(NO3)2·6H2O, 23 g of Al(NO3)3·9H2O, and 8 g of Zn(NO3)2·6H2O to deionized water to obtain 1 L of nitrate solution; add the activated fly ash obtained in step (1) to 1 L of nitrate solution, dropwise add 3 mol / L of NaOH aqueous solution until the pH value is 10.5, perform water bath at 60 °C, stir at 350 rpm for 4 h, centrifuge at 8000 rpm for 15 min, wash with deionized water 3 times, and dry at 80 °C for 6 h to obtain LDH@fly ash;

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

[0049] Comparative Example 1

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

[0051] Comparative Example 2

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

[0053] Comparative Example 3

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

[0055] Comparative Example 4

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

[0059] Comparative Example 6

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

[0061] Comparative Example 7

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

[0063] Comparative Example 8

[0064] The LDH@fly ash in step (2) was calcined at 500 °C for 2 h and then compounded with chitosan quaternary ammonium salt and cross-linking agent to obtain the defluorinating agent of Comparative Example 8.

[0065] Comparative Example 9

[0066] In step (3), glutaraldehyde was replaced with equimolar epichlorohydrin, and other steps were the same as in Example 1.

[0067] Comparative Example 10

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

[0069] Test Example: The performance of the highly efficient deep defluorinating agents prepared in the foregoing Examples 1-4 and Comparative Examples 1-10 was investigated.

[0070] Fluoride removal performance: Measure the sewage from the sewage treatment plant. The original fluoride ion concentration in the water is 12.1 mg / L. Add the fluoride removal agents prepared in the examples and comparative examples at a concentration of 1000 mg / L respectively, stir at 200 rpm for 2 min, then let it stand for 30 min, and take the supernatant to measure the fluoride ion content in the effluent. The detection method of fluoride is carried out 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 ion concentration of the solution, and C1 is the fluoride ion concentration in the solution after treatment with the fluoride removal agent.

[0071] Stability: Filter the above fluoride ion-adsorbed fluoride removal agent and soak it in 0.1 mol / L NaOH solution for 8 h for regeneration, then wash it with water until neutral, and finally dry it in an oven at 60 °C for 12 h. Then carry out fluoride removal again. Repeat the fluoride removal and regeneration steps 10 times respectively, and record the fluoride ion concentration C in the solution after treatment with the fluoride removal agent for the 10th time. 10 , the fluoride 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] Combined with the above data, the initial fluoride removal rates of Examples 1-4 of the present invention are all ≥94%, and still remain ≥88% after the 10th regeneration, indicating that the material has excellent adsorption capacity and stability. The key factors mainly lie in the synergistic effect of acid-activated fly ash and four-metal (La-Mg-Al-Zn) LDH, the QCS coating enhances the regeneration performance, and freeze-drying protects the structure of the material. The examples adopt freeze-drying, and the adsorption capacity is improved compared with Comparative Example 10.

[0077] In addition, the fluoride removal rate of Comparative Example 1 is only 75%, and the regeneration efficiency drops significantly, indicating that acid activation is crucial for the porosity and active sites of fly ash. After omission, the initial fluoride removal rate decreases by 19.7%, and the regeneration efficiency drops by 38.6%. The fluoride removal rate of Comparative Example 2 drops to 57.9%, confirming that the specific coordination of La 3+ to fluoride ions is irreplaceable, and the efficiency drops suddenly after regeneration. Because the Mg / Al / Zn system cannot stably bind fluoride ions, La 3+ is a key component for the synergy of four-metal LDH. Its absence leads to the initial fluoride removal rate dropping to 57.9%, and the regeneration efficiency is only 29.8%. In Comparative Example 3, the absence of Mg 2+ leads to the destruction of the charge balance between the layers of LDH and the decrease in the stability of the layered structure. Mg2+ Maintain the LDH structure through charge balance. After deletion, the adsorption capacity decreases by 31%, and the regeneration efficiency is only 43.0%. In Comparative Example 4, Al 3+ deletion leads to insufficient charge density of the lamellar, weakening the ability of fluoride ions to intercalate. Al 3+ Optimize the intercalation adsorption of fluoride ions, and the regeneration efficiency drops to 48.8%. In Comparative Example 5, Zn 2+ deletion reduces the interlayer stability of LDH, and the structure is prone to collapse during regeneration; Zn 2+ Enhance the interlayer binding force. Its deletion leads to the regeneration efficiency dropping to 66.1%, and the fluoride residue concentration is much higher than that in Example 1. In Comparative Example 6, the dosage of QCS is halved, resulting in incomplete coating of QCS, weakening of flocculation and regeneration functions; insufficient dosage of QCS leads to a 19.6% reduction in regeneration efficiency. In Comparative Example 7, the lack of the electrostatic flocculation effect of QCS makes the material prone to agglomeration and insufficient regeneration sites; the coating of QCS is the key to improving the regeneration efficiency and sludge sedimentation performance. Its deletion leads to a sharp drop in the regeneration efficiency to 24.0%. In Comparative Example 8, high-temperature calcination destroys the layered structure of LDH, and the defluorination rate drops to 66.9%. In Comparative Example 9, glutaraldehyde is replaced by epichlorohydrin. Epichlorohydrin has low cross-linking efficiency and toxicity; after replacement, the regeneration efficiency decreases by 22.1%, and the wastewater COD increases. In Comparative Example 10, drying at 80°C is used instead of freeze-drying. Drying causes pore collapse. Freeze-drying is a necessary process to retain the porous structure. After drying, the adsorption capacity decreases by 15%, and the regeneration efficiency is only 73.6%.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and do not limit the technical solutions described in the present invention; those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced; and all technical solutions and their improvements that do not depart from the spirit and scope of the present invention should be covered by the scope of the claims of the present invention.

Claims

1. A preparation method of an efficient deep defluorination agent, characterized in that, It includes the following steps: (1) Add activated fly ash into a nitrate solution, dropwise add an alkali solution, stir and react, and then centrifuge and separate to obtain LDH@fly ash; (2) Dissolve chitosan quaternary ammonium salt in an acetic acid solution, add LDH@fly ash and a crosslinking agent, stir and react, and then centrifuge and freeze-dry to obtain the defluorinating agent.

2. The preparation method of an efficient deep defluorination agent according to claim 1, characterized in that, The preparation method of the activated fly ash includes: impregnating fly ash in a hydrochloric acid aqueous solution with a mass concentration of 10-12% for 20-24 h, filtering, washing, and drying to obtain activated fly ash.

3. The preparation method of an efficient deep defluorination agent according to claim 2, characterized in that, The dosage ratio of the fly ash to the hydrochloric acid aqueous solution is 1 g:(10-12) mL.

4. The preparation method of an efficient deep defluorination agent according to claim 1, characterized in that, The dosage ratio of the activated fly ash to the nitrate solution is 100-120 g / L.

5. The preparation method of an efficient deep defluorinating agent according to claim 1, characterized in that, The nitrate solution is a nitrate aqueous solution with a mass concentration of 77-85 g / L.

6. The preparation method of an efficient deep defluorination agent according to claim 1, characterized in that, The nitrate solution includes La(NO3)3·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O, and Zn(NO3)2·6H2O with a weight ratio of (36-40):(12-13):(23-24):(6-8).

7. The preparation method of an efficient deep defluorination agent according to claim 2, characterized in that, The alkali solution is a 3-4 mol / L NaOH aqueous solution, and the pH value after dropping the alkali solution is 9.5-10.

5.

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

9. The preparation method of an efficient deep defluorination agent according to claim 1, characterized in that, The weight ratio of the chitosan quaternary ammonium salt, LDH@fly ash, and the crosslinking agent is (18-22):(90-110):(0.5-0.7).

10. An efficient deep defluorination agent, characterized in that, It is obtained by using the preparation method of the high-efficiency deep defluorinating agent according to any one of claims 1-9.

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