A method for preparing a MOF-based mixed matrix membrane for treating tailings wastewater

Abstract

The application relates to a preparation method of a MOF-based mixed matrix membrane for treating tailing wastewater, and relates to a preparation method of a mixed matrix membrane for treating tailing wastewater.The application aims to solve the technical problem that the existing UiO-66-based mixed matrix membrane only has a trapping effect on Sb(V) ions in tailing wastewater.The application uses the characteristics of MOF, such as super-high specific surface area, customizable structure, high adsorption capacity and good compatibility with a polymer matrix, to become a revolutionary material for tailing wastewater treatment, and through a blending modification method, monodispersed UiO-66-EDTA material is introduced into a PVDF membrane matrix, the shape and size of membrane holes can be effectively adjusted, a MOF-based mixed matrix membrane with multiple adsorption objects and high removal efficiency is prepared, the MOF-based mixed matrix membrane has a high trapping rate on heavy metals such as Sb(V), Cr(VI) and Pb(II) in tailing wastewater, has good anti-pollution performance, and can be applied to the treatment of tailing wastewater.

Description

Technical Field

[0001] This invention relates to a method for preparing a mixed matrix membrane for treating tailings wastewater. Background Technology

[0002] Tailings wastewater is a complex pollutant generated during mining and mineral processing, containing high concentrations of heavy metal ions (such as lead, cadmium, arsenic, and mercury) and acidic substances. It is characterized by high toxicity, poor degradation, and easy accumulation. According to the United Nations Environment Programme, over 10 billion tons of tailings waste are generated globally each year, of which approximately 30% seeps into soil and water bodies due to improper treatment, leading to ecosystem damage and public health risks. For example, acidic mine wastewater (AMD) can have a pH as low as 2-3 and is often accompanied by Fe... 3+ Cu 2 + Plasma migration poses a serious threat to the safety of the food chain. Traditional treatment methods such as chemical precipitation, ion exchange, and activated carbon adsorption are widely used, but they suffer from low efficiency, high cost, and secondary pollution. For example, chemical precipitation easily generates large amounts of sludge, activated carbon regeneration is difficult, and its adsorption capacity for low concentrations of heavy metals is limited. Therefore, developing a new, efficient, environmentally friendly, and recyclable treatment technology is urgently needed.

[0003] Metal-organic frameworks (MOFs) are porous crystalline materials formed by the self-assembly of metal ions / clusters and organic ligands, possessing extremely high specific surface areas (up to 7000 m²). 2 The tunable pore size structure and surface functional groups of MOFs (Metal-Oxide-Factory Formings) give them great potential in adsorption and catalysis. However, their fragility into small particles or powder limits their practical applications. In industrial processes such as catalysis and separation, these fragmented particles or dust can easily clog pipes or even cause explosions, severely hindering the widespread application of MOFs. Therefore, exploring novel processing and molding methods for MOFs is crucial. Currently, the common industrial method is to granulate MOF powder, usually using high-pressure molding or adding adhesives for shaping. However, high-pressure granulation may affect the properties of MOFs and reduce the efficiency of the molded device; while adding adhesives reduces the proportion of active components in MOFs, weakening their performance. In addition, reported MOF membranes suffer from poor stability and brittleness, and the production process is energy-intensive. However, blending MOFs with polymer materials (such as polyvinylidene fluoride) to form hybrid matrix membranes can combine the excellent properties of both, showing potential application prospects in tailings wastewater. Summary of the Invention

[0004] The present invention aims to solve the technical problem that existing UiO-66-based hybrid matrix membranes only have a retention effect on Sb(V) ions in tailings wastewater, and provides a method for preparing a MOF-based hybrid matrix membrane for treating tailings wastewater.

[0005] The method for preparing the MOF-based hybrid matrix membrane for treating tailings wastewater according to the present invention is carried out according to the following steps:

[0006] 1. The UiO-66-EDTA composite material was dissolved in a solvent and subjected to ultrasonic treatment to obtain a suspension;

[0007] 2. Dissolve the suspension prepared in step 1 with polyvinylidene fluoride (PVDF) powder to form a casting solution, and then perform ultrasonic defoaming for 90 minutes.

[0008] 3. Apply the casting solution obtained in step 2 onto a glass plate to form a liquid film;

[0009] 4. Place the glass plate with the liquid film in the air and let it stand for 30 to 35 seconds to pre-evaporate. Then immerse it in deionized water at 27°C to 29°C and let it stand until the film is completely separated from the glass plate. Use tweezers to transfer the liquid film to another deionized water at room temperature and soak it for 24 to 25 hours to obtain the MOF-based mixed matrix membrane.

[0010] The mass of the MOF-based hybrid matrix membrane is composed of the UiO-66-EDTA composite material from step one, the solvent, and the polyvinylidene fluoride powder from step two, wherein the amount of UiO-66-EDTA composite material added is 1wt% to 6wt%, and the amount of polyvinylidene fluoride powder added is 6wt% to 11wt%.

[0011] The beneficial effects of this invention are:

[0012] Compared to UiO-66 alone, this invention incorporates EDTA into UiO-66. Due to its strong complexing properties, EDTA competes with organic ligands for binding to zirconium clusters, thereby controlling and slowing down crystal growth and filling some missing sites. This results in UiO-66 nanoparticles with a higher specific surface area and more uniform distribution, exposing more adsorption sites. This characteristic not only allows for the adsorption of more Sb(V) ions but also increases the adsorption of Cr(VI) and Pb(II) ions, enabling the adsorption of multiple metal ions. This invention utilizes the characteristics of MOF (Metallic Oriented Foil)—ultra-high specific surface area, customizable structure, high adsorption capacity, and good compatibility with polymer matrices—making it a revolutionary material for tailings wastewater treatment. By introducing monodisperse UiO-66-EDTA material into the PVDF membrane matrix through blending modification, the shape and size of the membrane pores can be effectively adjusted to prepare a MOF-based hybrid matrix membrane with multiple adsorbents and high removal efficiency. It exhibits high rejection rates for heavy metals such as Sb(V), Cr(VI), and Pb(II) in tailings wastewater, and has good anti-fouling performance, making it applicable to the treatment of tailings wastewater. Attached Figure Description

[0013] Figure 1 This is a process flow diagram of the preparation of the MOF-based hybrid matrix membrane for treating tailings wastewater according to the present invention;

[0014] Figure 2 The graph shows the water flux test data and the separation performance data of Sb(V) ions in tailings wastewater in Experiment 1. Detailed Implementation

[0015] Specific Implementation Method 1: This implementation method is a method for preparing a MOF-based hybrid matrix membrane for treating tailings wastewater, specifically carried out according to the following steps:

[0016] 1. The UiO-66-EDTA composite material was dissolved in a solvent and subjected to ultrasonic treatment to obtain a suspension;

[0017] 2. Dissolve the suspension prepared in step 1 with polyvinylidene fluoride powder to form a casting solution, and then perform ultrasonic defoaming for 90 minutes.

[0018] 3. Apply the casting solution obtained in step 2 onto a glass plate to form a liquid film;

[0019] 4. Place the glass plate with the liquid film in the air and let it stand for 30 to 35 seconds to pre-evaporate. Then immerse it in deionized water at 27°C to 29°C and let it stand until the film is completely separated from the glass plate. Use tweezers to transfer the liquid film to another deionized water at room temperature and soak it for 24 to 25 hours to obtain the MOF-based mixed matrix membrane.

[0020] The mass of the MOF-based hybrid matrix membrane is composed of the UiO-66-EDTA composite material from step one, the solvent, and the polyvinylidene fluoride powder from step two, wherein the amount of UiO-66-EDTA composite material added is 1wt% to 6wt%, and the amount of polyvinylidene fluoride powder added is 6wt% to 11wt%.

[0021] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the solvent used in step one is N,N-dimethylacetamide. Everything else is the same as in Specific Implementation Method One.

[0022] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the preparation method of the UiO-66-EDTA composite material in step one is as follows:

[0023] (1) Dissolve 240 mg of zirconium chloride in 50 mL of acetone, then add 161 mg of terephthalic acid and sonicate for 15 min to obtain a homogeneous precursor solution.

[0024] (2) The precursor solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene and placed in an oven at 120°C for constant temperature crystallization for 48 hours. The reactor was then removed and allowed to cool naturally to room temperature.

[0025] (3) The obtained product was repeatedly washed with N,N-dimethylformamide and anhydrous ethanol and then placed in a forced-air drying oven and dried at 60°C for 12 hours to obtain UiO-66 powder.

[0026] (4) Dissolve 1.582 g of EDTA-2Na in 50 mL of water and stir to form a clear and transparent solution. Then add 0.1 g of UiO-66 powder and stir at 60 °C for 24 h. Filter and wash with deionized water, retain the solid portion, and finally dry at 100 °C to obtain the UiO-66-EDTA composite material. Other steps are the same as in specific embodiment one or two.

[0027] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step two, the polyvinylidene fluoride powder is fully dissolved in the suspension by magnetic stirring for 24 hours. Everything else is the same as in Specific Implementation Methods One to Three.

[0028] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the magnetic stirring speed in step two is 300 rpm. Everything else is the same as in Specific Implementation Method Four.

[0029] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the specific process of step three is as follows: Using a glass plate as the substrate, the gap between the scraper and the glass plate is set to 200 μm. The casting solution is poured onto one side of the scraper, and a uniform liquid film is quickly scraped onto the glass plate by manual operation. The experimental conditions are room temperature and humidity of 40%–50%. Everything else is the same as in Specific Implementation Method Five.

[0030] The invention was verified using the following experiments:

[0031] Experiment 1: This experiment demonstrates a method for preparing a MOF-based hybrid matrix membrane for treating tailings wastewater, specifically carried out according to the following steps:

[0032] 1. Dissolve 0.5g of UiO-66-EDTA composite material in 8.8g of N,N-dimethylacetamide solvent, and sonicate for 10min to obtain a suspension;

[0033] The preparation method of the UiO-66-EDTA composite material is as follows:

[0034] (1) Dissolve 240 mg of zirconium chloride in 50 mL of acetone, then add 161 mg of terephthalic acid and sonicate for 15 min to obtain a homogeneous precursor solution.

[0035] (2) The precursor solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene and placed in an oven at 120°C for constant temperature crystallization for 48 hours. The reactor was then removed and allowed to cool naturally to room temperature.

[0036] (3) The obtained product was repeatedly washed with N,N-dimethylformamide and anhydrous ethanol and then placed in a forced-air drying oven and dried at 60°C for 12 hours to obtain UiO-66 powder.

[0037] (4) Dissolve 1.582g of EDTA-2Na in 50mL of water and stir to form a clear and transparent solution. Then add 0.1g of UiO-66 powder and stir at 60℃ for 24h. Filter and wash with deionized water, retain the solid part, and finally dry at 100℃ to obtain UiO-66-EDTA composite material.

[0038] 2. Dissolve the suspension prepared in step 1 with 0.7g of polyvinylidene fluoride powder, stir magnetically for 24 hours at 300 rpm to form a casting solution, and then perform ultrasonic defoaming for 90 minutes.

[0039] 3. The casting solution obtained in step 2 is coated onto a glass plate to form a liquid film. The specific process is as follows: using a glass plate as the substrate, the gap between the scraper and the glass plate is set to 200μm. The casting solution is poured onto one side of the scraper. A uniform liquid film is quickly scraped onto the glass plate by manual operation. The experimental conditions are room temperature and 45% humidity.

[0040] 4. After the glass plate with the liquid film is placed in the air and allowed to pre-evaporate for 30 seconds, it is immersed in deionized water at 28°C. After standing for 5 minutes, the film is completely separated from the glass plate. The liquid film is transferred to another deionized water at room temperature with tweezers and soaked for 24 hours to obtain a PVDF / UiO-66-EDTA mixed matrix membrane.

[0041] The mass of the PVDF / UiO-66-EDTA mixed matrix membrane is composed of the UiO-66-EDTA composite material from step one, the solvent, and the polyvinylidene fluoride powder from step two, and is 10g.

[0042] Experiment 2: The difference between this experiment and Experiment 1 is that the amount of UiO-66-EDTA composite material added in step 1 is 0.6g, and the amount of polyvinylidene fluoride powder added in step 2 is adjusted to 0.6g. All other conditions are the same as in Experiment 1.

[0043] Experiment 3: The difference between this experiment and Experiment 1 is that the amount of UiO-66-EDTA composite material added in step 1 is 0.4g, and the amount of polyvinylidene fluoride powder added in step 2 is adjusted to 0.8g. All other conditions are the same as in Experiment 1.

[0044] Experiment 4: The difference between this experiment and Experiment 1 is that the amount of UiO-66-EDTA composite material added in step 1 is 0.3g, and the amount of polyvinylidene fluoride powder added in step 2 is adjusted to 0.9g. All other conditions are the same as in Experiment 1.

[0045] Experiment 5: The difference between this experiment and Experiment 1 is that the amount of UiO-66-EDTA composite material added in step 1 is 0.2g, and the amount of polyvinylidene fluoride powder added in step 2 is adjusted to 1g. All other conditions are the same as in Experiment 1.

[0046] Experiment Six: The difference between this experiment and Experiment One is that the amount of UiO-66-EDTA composite material added in step one is 0.1g, and the amount of polyvinylidene fluoride powder added in step two is adjusted to 1.1g. All other conditions are the same as in Experiment One.

[0047] Experiment 7: The difference between this experiment and Experiment 1 is that UiO-66 was used to replace UiO-66-EDTA in step 1, resulting in a PVDF / UiO-66 mixed matrix membrane. All other conditions are the same as in Experiment 1.

[0048] Experiment 8: The difference between this experiment and Experiment 2 is that in step one, UiO-66 was used to replace UiO-66-EDTA, resulting in a PVDF / UiO-66 mixed matrix membrane. All other conditions were the same as in Experiment 2.

[0049] Experiment Nine: The difference between this experiment and Experiment Three is that in step one, UiO-66 was used to replace UiO-66-EDTA, resulting in a PVDF / UiO-66 mixed matrix membrane. All other conditions are the same as in Experiment Three.

[0050] Experiment 10: The difference between this experiment and Experiment 4 is that UiO-66 was used to replace UiO-66-EDTA in step one, resulting in a PVDF / UiO-66 mixed matrix membrane. All other conditions were the same as in Experiment 4.

[0051] Experiment 11: The difference between this experiment and Experiment 5 is that in step one, UiO-66 was used to replace UiO-66-EDTA, resulting in a PVDF / UiO-66 mixed matrix membrane. All other conditions are the same as in Experiment 5.

[0052] Experiment Twelve: The difference between this experiment and Experiment Six is ​​that in step one, UiO-66 was used to replace UiO-66-EDTA, resulting in a PVDF / UiO-66 mixed matrix membrane. All other conditions were the same as in Experiment Six.

[0053] The preparation method of the aforementioned UiO-66 is as follows:

[0054] (1) Dissolve 240 mg of zirconium chloride in 50 mL of acetone, then add 161 mg of terephthalic acid and sonicate for 15 min to obtain a homogeneous precursor solution.

[0055] (2) The precursor solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene and placed in an oven at 120°C for constant temperature crystallization for 48 hours. The reactor was then removed and allowed to cool naturally to room temperature.

[0056] (3) The obtained product was repeatedly washed with N,N-dimethylformamide and anhydrous ethanol, and then placed in a forced-air drying oven and dried at 60°C for 12 hours to obtain UiO-66 powder.

[0057] Comparative Experiment: The difference between this experiment and Experiment 1 is that the amount of UiO-66-EDTA composite material added in step 1 is 0, and the amount of polyvinylidene fluoride powder added in step 2 is adjusted to 1.2g, ultimately yielding a PVDF membrane. All other conditions are the same as in Experiment 1.

[0058] Ultrafiltration experiments were conducted on the membranes prepared for experiments one through twelve and the comparative experiment. Flux was measured using pure water, specifically as follows: The membrane was fixed in an ultrafiltration cup, 50 mL of deionized water was added, and after sealing, an air compressor and the ultrafiltration cup were connected. The membrane was pre-pressed for the first time at a pressure of 2 bar. After pre-pressing, the volume of liquid permeating through the membrane per unit time was measured using a stopwatch and a graduated cylinder. The water flux was calculated using the following formula:

[0059]

[0060] In Equation 1: J is the flux L / (m 2 ·h·bar), T is the test time (h), V is the volume of aqueous solution permeating the membrane during time T (L), and A is the effective membrane area (m²). 2 ).

[0061] Tailings wastewater from Fujian Zijin Mining Co., Ltd. was collected, containing Sb(V) at a concentration of 8 mg / L, Cr(VI) at a concentration of 10 mg / L, Pb(II) at a concentration of 12 mg / L, and pH 5.6. Retention tests were conducted, and the retention rate is an important parameter for evaluating the separation performance of the membrane.

[0062]

[0063] In Equation 2: R is the retention rate (%), C p C represents the concentration of ions in the feed solution (mg / L). f The concentration of ions in the permeate (mg / L).

[0064] The difference between the rejection rate test and the pure water flux test is that after the pure water flux test, 20 mL of tailings wastewater is added, and the filtrate is collected and its concentration is measured after all of it has passed through the membrane.

[0065] Based on Formulas 1 and 2 above, the pure water flux of each membrane at 1 bar pressure and the rejection rate of tailings wastewater (containing Sb(V), Cr(VI), and Pb(II) ions) can be calculated. The specific results are shown in Tables 1 and 2.

[0066] Table 1. Membrane rejection rate of Sb(V) ions and pure water flux

[0067]

[0068] Table 1 shows that the PVDF / UiO-66 mixed matrix membrane can only achieve a maximum Sb(V) ion rejection rate of 41.5% in tailings wastewater, while the PVDF / UiO-66-EDTA mixed matrix membrane can achieve a rejection rate of 93.4%. Furthermore, while the PVDF / UiO-66-EDTA mixed matrix membrane achieves a higher rejection rate, its water flux is not significantly lower than that of the PVDF / UiO-66 mixed matrix membrane. Therefore, the PVDF / UiO-66-EDTA mixed matrix membrane is more advantageous in treating tailings wastewater containing Sb(V) ions.

[0069] Table 2 PVDF / UiO-66-EDTA hybrid matrix membrane

[0070]

[0071] The PVDF / UiO-66 mixed matrix membrane only retains Sb(V) ions in tailings wastewater, i.e., it has an adsorption effect, while it has almost no adsorption capacity for other metal ions (this is common knowledge). Combining the data in Tables 1 and 2, it can be seen that the PVDF / UiO-66-EDTA mixed matrix membrane has a retention effect on Sb(V), Cr(VI), and Pb(II) ions, overcoming the disadvantages of the PVDF / UiO-66 mixed matrix membrane in terms of its single adsorption target and poor adsorption effect. Furthermore, even with a retention rate exceeding 90%, the water flux can still be maintained at 850 Lm³. -2 h -1 bar -1 This represents a significant breakthrough for membrane treatment of tailings wastewater.

[0072] In summary, the UiO-66-EDTA hybrid matrix membrane has advantages in treating tailings wastewater.

[0073] Since Sb(V) ions are the main research object, and it is convenient for comparison and simplification, Figure 2 The removal performance of MOF-based hybrid matrix membranes for tailings wastewater treatment is based on the Sb(V) ion rejection rate, i.e., the removal rate (right ordinate), as the reference standard. Figure 2 The middle bar chart corresponds to the pure water flux (left vertical axis), and ■ and ★ correspond to the removal rate of Sb(V) ions (right vertical axis).

Claims

1. A method for preparing a MOF-based hybrid matrix membrane for treating tailings wastewater, characterized in that, The preparation method is carried out according to the following steps:

1. The UiO-66-EDTA composite material is added to a solvent and subjected to ultrasonic treatment to obtain a suspension after thorough dispersion; The preparation method of the UiO-66-EDTA composite material is as follows: (1) Dissolve 240 mg of zirconium chloride in 50 mL of acetone, then add 161 mg of terephthalic acid and sonicate for 15 min to obtain a homogeneous precursor solution. (2) The precursor solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene and placed in an oven at 120°C for constant temperature crystallization for 48 hours. The reactor was then removed and allowed to cool naturally to room temperature. (3) The obtained product was repeatedly washed with N,N-dimethylformamide and anhydrous ethanol and then placed in a forced-air drying oven and dried at 60°C for 12 hours to obtain UiO-66 powder. (4) Dissolve 1.582g of EDTA-2Na in 50mL of water and stir to form a clear and transparent solution. Then add 0.1g of UiO-66 powder and stir at 60℃ for 24h. Filter and wash with deionized water, retain the solid part, and finally dry at 100℃ to obtain UiO-66-EDTA composite material.

2. Dissolve the suspension prepared in step 1 with polyvinylidene fluoride powder to form a casting solution, and then perform ultrasonic defoaming for 90 minutes.

3. Apply the casting solution obtained in step 2 onto a glass plate to form a liquid film; 4. Place the glass plate with the liquid film in the air and let it stand for 30-35 seconds to pre-evaporate. Then immerse it in deionized water at 27℃-29℃ and let it stand until the film is completely separated from the glass plate. Use tweezers to transfer the liquid film to another deionized water at room temperature and soak it for 24-25 hours to obtain the MOF-based mixed matrix membrane. The MOF-based hybrid matrix membrane described above was used to adsorb Sb(V), Cr(VI) and Pb(II) from tailings wastewater. The rejection rate of Sb(V) was 93.4%, the rejection rate of Cr(VI) was 96.4%, and the rejection rate of Pb(II) was 94.7%. The casting solution is composed of the UiO-66-EDTA composite material from step one, a solvent, and the polyvinylidene fluoride powder from step two, wherein the amount of UiO-66-EDTA composite material added is 1wt%~6wt%, and the amount of polyvinylidene fluoride powder added is 6wt%~11wt%.

2. The method for preparing a MOF-based hybrid matrix membrane for treating tailings wastewater according to claim 1, characterized in that... The solvent mentioned in step one is N,N-dimethylacetamide.

3. The method for preparing a MOF-based hybrid matrix membrane for treating tailings wastewater according to claim 1, characterized in that... In step two, the polyvinylidene fluoride powder is fully dissolved in the suspension by magnetic stirring for 24 hours.

4. The method for preparing a MOF-based hybrid matrix membrane for treating tailings wastewater according to claim 3, characterized in that... In step two, the magnetic stirring speed is 300 rpm.

5. The method for preparing a MOF-based hybrid matrix membrane for treating tailings wastewater according to claim 1, characterized in that... The specific process of step three is as follows: using a glass plate as a substrate, setting the gap between the scraper and the glass plate to 200μm, pouring the casting liquid onto one side of the scraper, and quickly scraping a uniform liquid film onto the glass plate by manual operation. The experimental conditions are room temperature and humidity of 40%~50%.

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