A MOF modified zeolite fluorine removal agent, a preparation method and application thereof

Abstract

The application relates to the technical field of fluorine-containing wastewater treatment, and discloses a MOF modified zeolite fluorine removal agent as well as a preparation method and application thereof, which comprises the following steps: subjecting natural zeolite to carboxylation or calcination pretreatment; preparing a MOF precursor; the MOF precursor is prepared from at least two kinds of rare earth metal ions in La 3+ , Ce 3+ or Zr 4+ and an organic ligand; adding the MOF precursor into a DMF solvent, then adding the pretreated natural zeolite, and ultrasonic treatment for 5-10 min; adding the obtained mixed solution into a high-pressure reaction kettle, and reacting at 160 DEG C for 24 h; after the high-pressure reaction kettle is naturally cooled, the mixed solution in the high-pressure reaction kettle is centrifuged, the precipitate is washed with DMF for 3-5 times, and then dried at 65-90 DEG C for 18-24 h, so that the MOF modified zeolite fluorine removal agent is finally obtained. The disclosed fluorine removal agent has larger pore volume and specific surface area, and has good fluorine removal effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fluorine-containing wastewater treatment, and particularly relates to a MOF modified zeolite fluorine removal agent and a preparation method and application thereof. BACKGROUND

[0002] In the natural environment, fluorine is relatively widely distributed, and the natural fluorine content in the groundwater in some areas is relatively high. In the industrial production process, new energy, batteries, semiconductors and new pesticides industries will produce fluorine-containing waste or waste liquid, which is also an important source of fluorine pollution. Appropriate amount of fluorine can promote the formation of teeth and bones, but excessive intake can damage human health. Long-term drinking of high-fluorine water can cause dental fluorosis, and severe cases can cause bone deformation, pain, joint stiffness, tendon calcification and difficulty walking, and even paralysis. Therefore, it is particularly important to effectively remove excessive fluorine in water.

[0003] At present, the methods for treating fluorine-containing wastewater mainly include adsorption, electrocoagulation, reverse osmosis, ion exchange, chemical precipitation and coagulation sedimentation, etc., and each method has its own advantages and disadvantages. Ion exchange method removes fluorine ions by using ion exchange resin and other materials, but its selectivity is relatively low, the regeneration process is complex and the cost is high, so it is limited in practical application. Reverse osmosis method can effectively remove fluorine ions, but this method requires high operating pressure and equipment investment, and the operation cost is also high, which is not suitable for large-scale application. Chemical precipitation and coagulation sedimentation method is easy to produce a large amount of residual sludge, causing secondary pollution. The adsorption method has the advantages of low cost, simple design, convenient operation and high removal efficiency, and is a widely researched and applied fluorine ion removal technology, which has a broad application prospect in fluorine pollution problems.

[0004] Zeolite is a kind of aluminosilicate mineral, and its crystal structure is skeleton-shaped, with a large number of cavities and channels in the crystal, thus having a large specific surface area and rich pore structure, which provides a basis for its adsorption performance. Due to the diversity of silicon (aluminum) oxygen tetrahedron connection mode, zeolite exhibits adsorption separation, ion exchange and catalytic properties. Natural zeolite is a commonly used adsorbent, although natural zeolite itself has a certain degree of fluorine removal ability, due to its surface properties and structure limitations, its fluorine removal effect is not ideal, and the adsorption capacity and selectivity of fluorine ions still need to be improved.

[0005] The surface properties, pore structure and chemical composition of zeolite can be changed by modification treatment, and the fluorine removal performance of zeolite material can be improved. However, the existing modified zeolite for fluorine removal has low adsorption capacity, which cannot meet the increasingly strict requirements of fluorine-containing wastewater treatment. SUMMARY

[0006] To solve the above technical problems, the application provides a MOF modified zeolite fluorine removal agent and a preparation method and application thereof, so that the modified zeolite has a larger pore volume and specific surface area, and the fluorine removal effect of the modified zeolite is improved.

[0007] To achieve the above purpose, the technical scheme of the application is as follows:

[0008] A preparation method of a MOF modified zeolite fluorine removal agent, comprising the following steps:

[0009] Step 1, carboxylation or calcination pretreatment is performed on the natural zeolite;

[0010] Step 2, a MOF precursor is prepared; the MOF precursor is prepared from at least two kinds of rare earth metal ions of La 3+ , Ce 3+ or Zr 4+ and an organic ligand;

[0011] Step 3, the pretreated natural zeolite and the MOF precursor are added to a DMF solvent, and ultrasonic treatment is performed for 5-10 min;

[0012] Step 4, the obtained mixed solution is added to a high-pressure reaction kettle, and reaction is performed at 160 DEG C for 24 h; after the high-pressure reaction kettle is naturally cooled, the mixed solution in the high-pressure reaction kettle is centrifuged, and the precipitate is washed with DMF for 3-5 times, and then dried at 65-90 DEG C for 18-24 h, and finally the MOF modified zeolite fluorine removal agent is obtained.

[0013] In the above scheme, in step 1, the treatment process of carboxylation of the natural zeolite is as follows:

[0014] (1) the natural zeolite powder is taken into a beaker, hydrochloric acid solution is added according to a solid-liquid ratio of 1:10, and then the beaker is placed in a shaker and continuously shaken at room temperature for 12 h;

[0015] (2) the zeolite sample is filtered and washed with distilled water until neutral, and then placed in a muffle furnace and heated at 350-400 DEG C for 3-6 h;

[0016] (3) the treated zeolite sample and succinic anhydride are added to a mixed solution of 3-aminopropyl triethoxysilane and DMF according to a mass ratio of 1-1.5:3 and a volume ratio of 1:6-8;

[0017] (4) the obtained mixed solution is ultrasonically treated for 30 min, and then stirred with a stirrer for 24 h, and then filtered, washed with ethanol for several times and dried, to obtain the carboxylated natural zeolite.

[0018] In the above scheme, in step 1, the treatment process of calcining the natural zeolite is as follows: the natural zeolite powder is placed in a muffle furnace and heated at 400 DEG C for 5 h to obtain the calcined natural zeolite.

[0019] In the above scheme, in step 2, the organic ligand is 2-amino terephthalic acid or terephthalic acid.

[0020] In the above scheme, in step 2, the total amount of any two rare earth metal ions of La 3+ , Ce 3+ or Zr 4+ is 2-4:1-4 molar ratio to the organic ligand.

[0021] In the above scheme, in step 2, the molar ratio of La 3+ , Ce 3+ , Zr 4+ to the organic ligand is 1-2:1:1:2-5.

[0022] In the above scheme, in step 3, the mass ratio of the pretreated natural zeolite, the MOF precursor and the DMF solvent is 1:1-5:60-80.

[0023] A MOF modified zeolite fluorine removal agent prepared by the preparation method.

[0024] The application of a MOF modified zeolite fluorine removal agent in the treatment of fluorine-containing wastewater.

[0025] In a further technical solution, the application comprises the following steps:

[0026] (S1) adjusting the pH of the fluorine-containing wastewater to 3.5-6.5;

[0027] (S2) adding the MOF modified zeolite fluorine removal agent to the fluorine-containing wastewater, wherein 1.5-3 g of the MOF modified zeolite fluorine removal agent is added per 1 L of the fluorine-containing wastewater;

[0028] (S3) stirring for 15-40 min;

[0029] (S4) filtering after standing and settling for 2-5 min.

[0030] Through the above technical solution, the MOF modified zeolite fluorine removal agent, the preparation method and the application thereof provided by the application have the following beneficial effects:

[0031] 1. In the present application, a MOF modified zeolite fluoride removal agent is successfully prepared through screening of specific components and optimization of the allocation ratio of each component. When the fluoride removal agent is used to treat low-concentration fluoride-containing wastewater (fluoride ion concentration ≤ 15 mg / L), the removal rate of fluoride ions can be as high as 90% or more under the condition of stirring for 15 to 40 minutes at pH 3.5 to 6.5, showing good fluoride removal efficiency;

[0032] 2. The MOF modified zeolite fluoride removal agent according to the present application can simultaneously open the adsorption and ion exchange reaction mechanisms on the surface of the modified zeolite during contact with fluoride-containing wastewater. Specifically, the fluoride ions in the wastewater can not only adhere to the surface of the modified zeolite, but also can exchange with the OH - ions present on the surface of the modified zeolite. The synergistic effect of adsorption and ion exchange achieves efficient removal of fluoride ions, greatly improving the treatment efficiency of fluoride-containing wastewater and providing an effective solution for the purification treatment of fluoride-containing wastewater;

[0033] 3. The MOF modified zeolite fluoride removal agent according to the present application has a stable crystal structure, good adsorption performance, and efficient adsorption effect after multiple uses. The adsorbent does not undergo irreversible structural changes after adsorbing fluoride ions, and the pore structure is stable and has strong plasticity;

[0034] 4. The networked porous structure of the MOF modified zeolite fluoride removal agent and the complex active groups on its surface enable it to strongly adsorb fluoride ions, and the large specific surface area provides sufficient adsorption sites for fluoride ions, thereby improving the removal efficiency of the adsorbent for fluoride ions;

[0035] 5. The present application combines carboxylated or calcined natural zeolite with MOF precursors. Compared with untreated natural zeolite, the carboxylated natural zeolite has abundant carboxylic acid groups on its surface, which is more conducive to its compounding with MOF precursors to form a more stable crystal structure. The calcined natural zeolite has a more abundant pore structure, thereby increasing the specific surface area of the composite material and improving the fluoride removal performance of the MOF modified zeolite;

[0036] 6. The MOF modified zeolite fluoride removal agent prepared in the present application introduces a bimetallic or multimetallic MOF precursor, which can utilize the synergistic effect between metals and provide more active sites and reaction paths for the reaction, thereby improving the reaction efficiency and enhancing the adsorption capacity for fluoride ions. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description.

[0038] Figure 1 FTIR spectrum of MOF modified zeolite fluoride removal agent prepared for Example 1 of the present application.

[0039] Figure 2 SEM image of MOF modified zeolite fluoride removal agent prepared for Example 1 of the present application. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

[0041] Example 1:

[0042] The present embodiment provides a preparation method of MOF modified zeolite fluoride removal agent, comprising the following steps:

[0043] (1) Take natural zeolite powder with a particle size of 200 mesh into a beaker, and add hydrochloric acid solution with a mass concentration of 4% according to a solid-liquid ratio of 1:10, then place the beaker in a shaker and continuously shake at room temperature for 12 h;

[0044] (2) Filter the zeolite sample and wash it to neutral with deionized water, then place it in a muffle furnace and heat at 380 ℃ for 6 h;

[0045] (3) Add the treated zeolite sample and succinic anhydride with a mass ratio of 1:3 into a mixed solution of APTES (3-aminopropyltriethoxysilane) and DMF with a volume ratio of 1:7;

[0046] (4) Ultrasonically treat the mixed solution obtained in step (3) for 30 min, then stir it with a stirrer for 24 h, then filter, wash several times with ethanol and dry to obtain carboxylated natural zeolite;

[0047] (5) Add cerium nitrate hexahydrate, zirconium nitrate pentahydrate and 2-amino terephthalic acid with a molar ratio of 1:1:2 as MOF precursors into DMF and ultrasonically treat for 5 min;

[0048] (6) Add carboxylated natural zeolite to the solution obtained in step (5) according to a ratio of MOF precursors, carboxylated natural zeolite and DMF solvent of 1:1:60;

[0049] (7) Transfer the mixed turbid solution obtained in step (6) to a polytetrafluoroethylene-lined high-pressure reaction kettle and react at 160 ℃ for 24 h;

[0050] (8) After the high-pressure reaction kettle is naturally cooled, centrifuge the mixed solution in the high-pressure reaction kettle and wash it with DMF 4 times, then dry it at 70 ℃ for 24 h, and finally obtain the MOF modified zeolite fluoride removal agent.

[0051] As shown in Figure 1 , the FTIR spectrum of the MOF modified zeolite fluoride removal agent prepared in this embodiment shows asymmetric internal T-O stretching vibration of TO4 tetrahedron (T = Si or Al) of zeolite framework structure and stretching vibration of -COOH, and characteristic peaks of Ce-O and Zr-O bonds and C=C framework stretching vibration of benzene ring. As shown in Figure 2 , the surface of the MOF modified zeolite fluoride removal agent prepared in this embodiment can be observed to have rich wrinkle and micropore structure by SEM, which increases the possibility of contact between the adsorbent and fluoride, making it more potential for fluoride removal.

[0052] Example 2:

[0053] Compared with Example 1, in step (5), lanthanum nitrate hexahydrate, cerium nitrate hexahydrate and 2-amino terephthalic acid with a molar ratio of 1:1:1 are added to DMF as MOF precursors, and other steps are the same as those in Example 1.

[0054] Example 3:

[0055] Compared with Example 1, in step (5), lanthanum nitrate hexahydrate, zirconium nitrate pentahydrate and 2-amino terephthalic acid with a molar ratio of 1:1:2 are added to DMF as MOF precursors, and other steps are the same as those in Example 1.

[0056] Example 4:

[0057] Compared with Example 1, in step (5), lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, zirconium nitrate pentahydrate and 2-amino terephthalic acid with a molar ratio of 2:1:1:4 are added to DMF as MOF precursors, and other steps are the same as those in Example 1.

[0058] Example 5:

[0059] The present embodiment provides a preparation method of a MOF modified zeolite fluoride removal agent, comprising the following steps:

[0060] (1) The natural zeolite powder with a particle size of 200 mesh is placed in a muffle furnace and heated at 400 ℃ for 5 h to obtain a calcined natural zeolite;

[0061] (2) Lanthanum nitrate hexahydrate, cerium nitrate hexahydrate and terephthalic acid with a molar ratio of 1:1:1 are added to DMF as MOF precursors, and ultrasonic treatment is performed for 5 min;

[0062] (3) adding the calcined natural zeolite powder to the solution obtained in step (2) in a mass ratio of MOF precursor, calcined natural zeolite powder and DMF solvent of 1:1:60;

[0063] (4) The mixed turbid liquid obtained in step (3) was transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 160°C for 24 h;

[0064] (5) After the reactor was cooled naturally, the mixed liquid in the reactor was centrifuged and washed with DMF four times, and then dried at 70 °C for 24 h to finally obtain the MOF-modified zeolite defluoridant.

[0065] Comparative Example 1:

[0066] Compared with Example 1, in step (5), aluminum nitrate nonahydrate and 2-aminoterephthalic acid in a molar ratio of 1:1 were added to DMF as MOF precursors, and the other steps were the same as those in Example 1.

[0067] Comparative Example 2:

[0068] Compared with Example 1, in step (5), lanthanum nitrate hexahydrate and 2-aminoterephthalic acid in a molar ratio of 1:1 were added to DMF as MOF precursors, and the other steps were the same as those in Example 1.

[0069] Comparative Example 3:

[0070] Compared with Example 1, in step (5), lanthanum nitrate hexahydrate and 2-aminoterephthalic acid in a molar ratio of 1:1 were added to DMF as MOF precursors, and the other steps were the same as those in Example 1.

[0071] Comparative Example 4:

[0072] Compared with Example 5, in step (3), the calcined natural zeolite powder was added to the solution obtained in step (2) in a mass ratio of MOF precursor, calcined natural zeolite powder and DMF solvent of 9:1:300, and the heating temperature in step (4) was 120°C. The other steps were the same as in Example 5.

[0073] A sodium fluoride solution was prepared with deionized water as the fluoride-containing water to be treated, with a fluoride ion concentration C0 of 15 mg / L. The pH was adjusted to 4 with dilute hydrochloric acid. 1 L of the fluoride-containing water to be treated was added to a beaker, followed by 2 g of the defluoridating agents prepared in the Examples of the present invention and the Comparative Examples. The mixture was stirred for 20 minutes and allowed to settle for 2 minutes. The supernatant was filtered and the fluoride ion concentration C1 after treatment was measured using a PXSJ-216F ion meter. The fluoride removal rate η was calculated as (C0 - C1) / C0. The results are shown in Table 1.

[0074] Table 1 Fluoride ion concentration C1 and fluoride removal rate η after treatment

[0075]

[0076] As can be seen from Table 1, the MOF modified zeolite fluoride removal agent prepared according to the technical solution provided in the present application has good fluoride removal effect, and can reduce the fluoride ion concentration to below 1 mg / L, reaching the fluoride-containing wastewater discharge standard. The fluoride removal effect of the fluoride removal agent prepared in Comparative Examples 1-4 is obviously not as good as that of Examples 1-5.

[0077] The above description of the disclosed embodiments enables one skilled in the art to make or use the application. Numerous modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Therefore, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a MOF-modified zeolite defluoridant, characterized in that: The steps include: Step 1, pre-treating the natural zeolite by carboxylation or calcination; Step 2, preparing a MOF precursor; the MOF precursor is composed of La 3+ 、Ce 3+ or Zr 4+ It is prepared from at least two metal ions and organic ligands; Step 3: Add the MOF precursor to DMF solvent, ultrasonicate for 5-10 min, and then add the pretreated natural zeolite; Step 4: adding the obtained mixed solution to a high-pressure reactor and reacting at 160° C. for 24 hours; after the high-pressure reactor is naturally cooled, the mixed solution in the high-pressure reactor is centrifuged, and the precipitate is washed with DMF 3 to 5 times, and then dried at 65 to 90° C. for 18 to 24 hours to finally obtain a MOF-modified zeolite defluoridant; In step 2, the organic ligand is 2-aminoterephthalic acid or terephthalic acid; In step 3, the mass ratio of the pretreated natural zeolite, MOF precursor and DMF solvent is 1:1~5:60~80.

2. The method for preparing a MOF-modified zeolite defluoridant according to claim 1, wherein: In step 1, the process of carboxylating natural zeolite is as follows: (1) Place natural zeolite powder in a beaker, add hydrochloric acid solution at a solid-liquid ratio of 1:10, and then place the beaker in a shaker and shake continuously at room temperature for 12 h. (2) Filter the zeolite sample and wash it with distilled water until it is neutral, then heat it in a muffle furnace at 350-400 °C for 3-6 h; (3) adding the treated zeolite sample and succinic anhydride in a mass ratio of 1 to 1.5:3 to a mixed solution of 3-aminopropyltriethoxysilane and DMF in a volume ratio of 1:6 to 8; (4) The resulting mixture was ultrasonically treated for 30 min and then stirred with a stirrer for 24 h. It was then filtered, washed several times with ethanol, and dried to obtain a carboxylated natural zeolite.

3. The method for preparing a MOF-modified zeolite defluoridant according to claim 1, wherein: In step 1, the natural zeolite is calcined as follows: natural zeolite powder is placed in a muffle furnace and heated at 400° C. for 5 h to obtain calcined natural zeolite.

4. The method for preparing a MOF-modified zeolite defluoridant according to claim 1, wherein: In step 2, La 3+ 、Ce 3+ or Zr 4+ The molar ratio of the total amount of any two metal ions to the organic ligand is 2~4:1~4.

5. The method for preparing a MOF-modified zeolite defluoridant according to claim 1, wherein: In step 2, La 3+ 、Ce 3+ 、Zr 4+ The molar ratio of the organic ligand is 1~2:1:1:2~5.

6. A MOF-modified zeolite defluoridant prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the MOF-modified zeolite defluoridant according to claim 6 in the treatment of fluorine-containing wastewater.

8. The use according to claim 7, characterized in that The steps include: (S1) adjusting the pH of fluoride-containing wastewater to 3.5-6.5; (S2) adding a MOF-modified zeolite defluoridant to the fluoride-containing wastewater, wherein 1.5 to 3 g of the MOF-modified zeolite defluoridant is added to each liter of the fluoride-containing wastewater; (S3) Stir for 15-40 min; (S4) After settling for 2 to 5 minutes, filter.

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