Zeolite-like molecular sieve membrane for removing fluorine and chlorine in waste acid and preparation method of zeolite-like molecular sieve membrane

Abstract

The invention belongs to the technical field of waste acid treatment, and particularly discloses a zeolite-like molecular sieve membrane for removing fluorine and chlorine in waste acid and a preparation method. The molecular sieve membrane comprises a dispersed phase and a continuous phase, the dispersed phase is zeolite-like molecular sieve nanoparticles, and the continuous phase is formed by dissolving PVDF monomer particles; the zeolite-like molecular sieve nanoparticles are prepared by dissolving a metal compound in a first solvent in an ultrasonic environment, then dissolving the metal compound in a second solvent to form a mixed solution I, and then drying the mixed solution I. The preparation method comprises the following steps: preparing the PVDF molecular sieve blended membrane by a blending method, and coating and modifying the surface of the PVDF molecular sieve blended membrane. The zeolite-like molecular sieve membrane for the waste acid system is prepared through a blending method, fluorine chloride ions in waste acid can penetrate through the membrane, sulfate ions are intercepted, fluorine and chlorine are removed, the loss rate of the sulfate ions is reduced, cyclic utilization of sulfuric acid resources is achieved, and the cost is reduced. The device has the characteristics of high fluorine and chlorine removal rate, high sulfate radical retention rate, good corrosion resistance and high water production flux.

Description

Technical Field

[0001] The invention relates to the technical field of waste acid treatment, and in particular to a zeolite molecular sieve membrane for removing fluorine and chlorine from waste acid, which has high fluorine and chlorine removal rate, high sulfate retention rate, good corrosion resistance and high water production flux, and a preparation method thereof. Background Art

[0002] The main component of waste acid produced by metal smelting and smelting flue gas acid production is sulfuric acid. If the sulfuric acid in waste acid can be recycled in production, it can not only reduce production costs, but also reduce pollutant emissions. However, due to the high concentration of fluorine and chloride ions in waste acid, the corrosion resistance of devices, equipment and pipeline valves is required to be high. Therefore, the fluorine and chloride ions in the waste acid must be removed before the sulfate ions can be recycled.

[0003] At present, the main methods for removing fluoride and chloride ions from polluted acid are: physical removal, that is, through hot air stripping and nanofiltration membrane, PVDF flat ultrafiltration membrane filtration method, but the hot air stripping efficiency is low, the heat consumption is large, and the membrane filtration has the problem of high fluoride ion retention rate; chemical precipitation method, that is, by adding bismuth salts, calcium salts, rare earth removal agents, etc., to precipitate fluorine and chlorine impurities, but there are problems such as the introduction of new impurity elements, high cost and the failure to realize resource utilization of fluorine and chlorine.

[0004] In the prior art, neutralizing agents such as calcium carbonate, calcium oxide, and calcium hydroxide are added to fluorine-chlorinated waste acid to neutralize the waste acid; anionic polyacrylamide is added as a flocculant to promote the precipitation of calcium fluoride and calcium chloride; and then the fluorine and chloride ions in the waste acid are removed by preparing calcium fluoride and calcium chloride (such as patent CN111634934A). However, sulfuric acid in the waste acid is also neutralized at the same time, so that the resource reuse of sulfuric acid cannot be achieved.

[0005] To this end, there are also methods that use lanthanum chloride as a defluorinating agent and sodium sulfate as a lanthanum removal agent, which can effectively remove fluoride ions in the dirty acid without introducing other impurity ions; and the lanthanum fluoride and sodium lanthanum sulfate obtained in the defluorination and lanthanum removal process can be transformed by alkali dissolution and regenerated by acid dissolution to obtain lanthanum chloride, thereby realizing the regeneration and recycling of the defluorinating agent, and the sodium sulfate obtained by alkali dissolution can also be recycled as a lanthanum removal agent; and silver sulfate is selected as a dechlorinating agent, and after removing chloride ions from the dirty acid, high-value nano silver powder can be prepared to achieve high-value recovery of the dechlorinating agent (such as patent CN114890526B). However, since this method introduces defluorinating agents and dechlorinating agents, the alkali dissolution transformation and acid dissolution regeneration processes are lengthy and complicated to operate, and are not applicable when treating large amounts of dirty acid wastewater.

[0006] According to the shortcomings of the prior art in removing fluorine and chlorine from waste acid, the inventors proposed a concept: whether it is possible to use molecular sieve membrane separation technology to treat fluorine-containing chlorine-containing waste acid. However, since waste acid is a complex acidic liquid with multiple components and is highly corrosive, the traditional molecular sieve membrane is not suitable for fluorine-containing chlorine-containing waste acid systems. For example, the silicon-aluminum compound molecular sieve membrane, whose silicon-aluminum skeleton is easily destroyed by fluorine-containing chlorine-containing waste acid and basically loses the molecular sieve function, becomes a disposable chemical precipitation consumable that cannot be regenerated and recycled, resulting in not only high costs, but also a fluorine removal rate far lower than expected, and even adding new silicon-aluminum impurities to the waste acid and causing serious interference to the determination of fluorine.

[0007] Therefore, studying a molecular sieve membrane that can improve the removal rate of fluoride and chloride ions in waste acid and reduce the loss rate of sulfate ions not only has important practical significance, but also provides a new idea for removing fluoride and chloride ions from various waste acids. Summary of the invention

[0008] In view of the deficiencies in the prior art, the present invention provides a zeolite molecular sieve membrane for removing fluorine and chlorine from waste acid, which has high fluorine and chlorine removal rate, high sulfate retention rate, good corrosion resistance and high water production flux, and also provides a method for preparing the zeolite molecular sieve membrane for removing fluorine and chlorine from waste acid.

[0009] The zeolite molecular sieve membrane used for removing fluorine and chlorine from polluted acid of the present invention is realized as follows: it comprises a dispersed phase and a continuous phase, wherein the dispersed phase is zeolite molecular sieve nanoparticles, and the continuous phase is formed by dissolving PVDF monomer particles; the zeolite molecular sieve nanoparticles are prepared by first dissolving a metal compound in a first solvent and then dissolving it in a second solvent under an ultrasonic environment to form a mixed solution I, and finally drying the mixed solution I.

[0010] The preparation principle of zeolite molecular sieve nanoparticles: react a specific metal compound with a specific solvent to obtain porous zeolite molecular sieve nanoparticles with metal ions as the center and organic matter as ligands.

[0011] Furthermore, the metal compound is ZrCl4 or Zr(OH)4, the first solvent is trimesic acid or biphenyl dicarboxylic acid, and the second solvent is a deionized aqueous solution of one or any combination of ethanol, isopentyl glycol and isohexyl glycol.

[0012] Furthermore, the metal compound is any one of ZnSO4, ZnCl2, CoCl2, Co(NO3)2, CuSO4 and Cu(NO3)2, the first solvent is one or any combination of imidazole, dimethylimidazole and di-methylimidazole, and the second solvent is a deionized aqueous solution of one or any combination of ethanol, isoprene glycol and isohexanediol.

[0013] Furthermore, the metal compound is ZrCl4, Zr(OH)4 or Cr2(SO4)3, the first solvent is succinic acid, and the second solvent is a deionized aqueous solution of one or any combination of ethanol, isopentyl glycol and isohexyl glycol.

[0014] Furthermore, the mass fraction of the metal compound in the mixed solution is 2wt% to 20wt%.

[0015] Furthermore, the spatial structure of the zeolite molecular sieve nanoparticles is cage-shaped, and the gaps formed between the cages become channels with a pore size of 1 to 6 nm through which ions can pass.

[0016] The preparation method of the zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid of the present invention is achieved as follows: it includes the steps of preparing a PVDF molecular sieve blended membrane by a blending method and coating and modifying the surface of the PVDF molecular sieve blended membrane, and the specific contents are as follows: A. Preparation of PVDF molecular sieve blended membrane by blending method: PVDF monomer particles are dissolved in an organic solvent DMF with a concentration of 8wt% to 12wt%, and then the zeolite molecular sieve nanoparticles according to any one of claims 1 to 6 are added, and then monomer polymerization initiators VBC and BPO are added to prepare a mixed solvent II; then the mixed solvent II is reacted at 60 to 70°C for 7 to 9 hours under nitrogen protection to prepare a casting solution; then the casting solution is vacuum degassed and allowed to stand for 7 to 9 hours, and then the casting solution is injected into a casting template and scraped with a scraper to form a film, and then the scraped film is evaporated to remove the organic solvent, and finally the scraped film is immersed in a deionized water coagulation bath for solidification to prepare a PVDF molecular sieve blended membrane; B. Surface coating modification of PVDF molecular sieve blend membrane: The aforementioned PVDF molecular sieve blend membrane was immersed in ethanol and deionized water for 20 to 40 minutes respectively, and then immersed in dopamine hydrochloric acid buffer and stirred for 16 to 24 hours under ultrasonic environment to obtain a zeolite molecular sieve membrane for removal of fluorine and chlorine from polluted acid.

[0017] Furthermore, in the mixed solvent II of step A, the mass fraction of PVDF is 6wt% to 12wt%, the mass fraction of zeolite molecular sieve nanoparticles is 0.5wt% to 2wt%, the mass fraction of VBC is 2wt% and the mass fraction of BPO is 0.02wt%.

[0018] Furthermore, the preparation method of the dopamine hydrochloric acid buffer in step B is: firstly prepare a buffer solution with a pH of 8.5 by using tris(hydroxymethyl)aminomethane and hydrochloric acid, and then dissolve DA and PEI in the buffer solution to prepare the dopamine hydrochloric acid buffer solution.

[0019] Furthermore, the mass fraction of DA in the dopamine hydrochloride buffer is 0.2wt% to 1.6wt%.

[0020] The preparation principle of PVDF molecular sieve blend membrane is: polymer and zeolite molecular sieve are blended into membrane, polymer becomes continuous phase, zeolite molecular sieve nanoparticles are dispersed phase, all zeolite molecular sieve nanoparticles constitute zeolite molecular sieve, thus solving the problem of poor compatibility between conventional molecular sieve and organic polymer matrix, avoiding the formation of clusters and interface gaps on the membrane surface and affecting separation; and zeolite molecular sieve spatial structure is mostly cage-shaped, different gaps can be formed between molecular cages to become channels for ions to pass through, playing a selective screening effect. In the formed blend membrane, the polymer is the continuous phase, and its effective pore size is equivalent to that of conventional nanofiltration membrane, and the gaps between molecular cages in the dispersed phase are less than 6nm, so as to provide fluoride and chloride ions to pass through.

[0021] Principle of surface coating modification of PVDF molecular sieve blend membrane: PVDF material is corrosion-resistant, but the presence of CF bonds makes PVDF material very hydrophobic, which makes it easy to contaminate and affect the flux of membrane materials. Although the hydrophobicity of PVDF molecular sieve blend membrane has been reduced to a certain extent, the water production flux is still low for the continuous phase PVDF, so modification is needed to improve the hydrophilicity of the continuous phase.

[0022] The beneficial effects of the present invention are: 1. The present invention prepares zeolite molecular sieve nanoparticles under an ultrasonic environment, so that the newly prepared zeolite molecular sieve nanoparticles can be suitable for highly corrosive fluorine-containing and chlorine-containing waste acid systems, and ingeniously blends the zeolite molecular sieve nanoparticles with a polymer to form a film and coats and modifies the surface through a blending method to obtain a zeolite molecular sieve membrane for the waste acid system, which can allow fluorine and chloride ions in the waste acid to pass through and intercept sulfate ions, thereby achieving efficient removal of fluorine and chloride ions in the waste acid without introducing new impurity elements and consuming heat, and can also significantly reduce the loss rate of sulfate ions, thereby realizing the recycling of sulfuric acid resources.

[0023] 2. Compared with conventional nanofiltration membranes and PVDF flat ultrafiltration membranes, the zeolite molecular sieve membrane of the present invention can not only effectively remove fluorine and chlorine in polluted acid, but also reduce the loss rate of sulfate ions in polluted acid, realize the recycling of sulfuric acid resources, and provide a new process idea for removing fluorine and chloride ions from various wastewaters.

[0024] 3. In the method for preparing zeolite molecular sieve membranes of the present invention, dopamine hydrochloric acid buffer solution is prepared in advance to perform hydrophilic modification on the PVDF molecular sieve blend membrane, so that the PVDF molecular sieve blend membrane has corrosion resistance and its hydrophobicity can be effectively reduced, thereby increasing the water production flux when filtering waste acid.

[0025] In summary, the present invention has the characteristics of high fluorine and chlorine removal rate, high sulfate retention rate, good corrosion resistance and high water production flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a partial enlarged view of the zeolite molecular sieve membrane prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] The zeolite molecular sieve membrane used for removing fluorine and chlorine from polluted acid is characterized by comprising a dispersed phase and a continuous phase, wherein the dispersed phase is zeolite molecular sieve nanoparticles, and the continuous phase is formed by dissolving PVDF monomer particles; the zeolite molecular sieve nanoparticles are prepared by first dissolving a metal compound in a first solvent and then dissolving it in a second solvent under an ultrasonic environment to form a mixed solution I, and finally drying the mixed solution I.

[0029] The metal compound is ZrCl4 or Zr(OH)4, the first solvent is trimesic acid or biphenyl dicarboxylic acid, and the second solvent is a deionized water solution of one or any combination of ethanol, isopentyl glycol and isohexyl glycol.

[0030] The metal compound is any one of ZnSO4, ZnCl2, CoCl2, Co(NO3)2, CuSO4 and Cu(NO3)2, the first solvent is one or any combination of imidazole, dimethylimidazole and di-methylimidazole, and the second solvent is a deionized aqueous solution of one or any combination of ethanol, isoprene glycol and isohexanediol.

[0031] The metal compound is ZrCl4, Zr(OH)4 or Cr2(SO4)3, the first solvent is succinic acid, and the second solvent is a deionized water solution of one or any combination of ethanol, isopentyl glycol and isohexyl glycol.

[0032] The mass fraction of the metal compound in the mixed solution is 2wt% to 20wt%.

[0033] The spatial structure of the zeolite molecular sieve nanoparticles is cage-shaped, and the gaps formed between the cages become channels with a pore size of 1 to 6 nm for ions to pass through.

[0034] The mixed solution I is dried at conventional low temperature to obtain zeolite-like molecular sieve nanoparticles.

[0035] The method for preparing a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid of the present invention comprises the steps of preparing a PVDF molecular sieve blended membrane by a blending method and coating and modifying the surface of the PVDF molecular sieve blended membrane, and the specific contents are as follows: A. Preparation of PVDF molecular sieve blended membrane by blending method: PVDF (polyvinylidene fluoride) monomer particles are dissolved in an organic solvent DMF (dimethylformamide) with a concentration of 8wt% to 12wt%, and then the zeolite molecular sieve nanoparticles according to any one of claims 1 to 6 are added, and then the monomer polymerization initiator VBC (p-chloromethylstyrene) and BPO (benzoyl peroxide) are added to prepare a mixed solvent II; then the mixed solvent II is reacted at 60 to 70°C for 7 to 9 hours under nitrogen protection to prepare a casting solution; then the casting solution is vacuum degassed and allowed to stand for 7 to 9 hours, and then the casting solution is injected into a casting template and scraped with a scraper to form a film, and then the scraped film is evaporated to remove the organic solvent, and finally the scraped film is immersed in a deionized water coagulation bath for solidification to prepare a PVDF molecular sieve blended membrane; B. Surface coating modification of PVDF molecular sieve blend membrane: The aforementioned PVDF molecular sieve blend membrane was immersed in ethanol and deionized water for 20 to 40 minutes respectively, and then immersed in dopamine hydrochloric acid buffer and stirred for 16 to 24 hours under ultrasonic environment to obtain a zeolite molecular sieve membrane for removal of fluorine and chlorine from polluted acid.

[0036] In the mixed solvent II of step A, the mass fraction of PVDF is 6wt% to 12wt%, the mass fraction of zeolite molecular sieve nanoparticles is 0.5wt% to 2wt%, the mass fraction of VBC is 2wt% and the mass fraction of BPO is 0.02wt%.

[0037] The preparation method of the dopamine hydrochloric acid buffer in step B is: firstly prepare a buffer solution with a pH of 8.5 by using tris(hydroxymethyl)aminomethane and hydrochloric acid, and then dissolve DA (dopamine) and PEI (polyethyleneimine) in the buffer solution to prepare the dopamine hydrochloric acid buffer solution.

[0038] The mass fraction of DA in the dopamine hydrochloride buffer is 0.2wt% to 1.6wt%.

[0039] In the step B, the mixture is immersed in dopamine hydrochloride buffer and stirred conventionally for 16 to 24 hours under an ultrasonic environment.

[0040] Example 1 S100: Under an ultrasonic environment, 6 parts of ZrCl4 are first dissolved in 44 parts of diphenyl dicarboxylic acid, and then the above solution is dissolved in a second solvent of 30 parts of deionized water, 10 parts of ethanol and 10 parts of isohexanediol to form a mixed solution I (wherein the mass fraction of ZrCl4 is 6wt%). Finally, the mixed solution I is dried to obtain zeolite molecular sieve nanoparticles.

[0041] S200: dissolving PVDF (polyvinylidene fluoride) monomer particles in an organic solvent DMF (dimethylformamide) with a mass concentration of 10%, then adding the zeolite molecular sieve nanoparticles prepared above, and then adding VBC (p-chloromethylstyrene) and BPO (benzoyl peroxide) to prepare a mixed solvent II, wherein the mass fraction of PVDF is 6%, the mass fraction of zeolite nanoparticles is 0.5%, the mass fraction of VBC is 2%, and the mass fraction of BPO is 0.02%; Subsequently, the mixed solvent II was reacted at 65°C for 8 hours under nitrogen protection to obtain a casting solution; the casting solution was vacuum degassed and allowed to stand for 8 hours, and then the casting solution was injected into a casting template and scraped with a scraper to form a film, and then the scraped film was evaporated to remove the organic solvent, and finally the scraped film was immersed in a deionized water coagulation bath for solidification to obtain a PVDF molecular sieve blend membrane.

[0042] S300: First, tris(hydroxymethyl)aminomethane and hydrochloric acid are prepared into a buffer solution of pH 8.5, and then DA (dopamine) and PEI (polyethyleneimine) are dissolved in the buffer solution to prepare a dopamine hydrochloric acid buffer solution with a mass concentration of 0.2%; The PVDF molecular sieve blend membrane prepared above was then placed in ethanol and deionized water for 30 minutes each, and then placed in dopamine hydrochloric acid buffer and stirred for 20 hours under ultrasonic environment to obtain a dopamine modified molecular sieve membrane, that is, a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid.

[0043] In this example, the prepared zeolite molecular sieve membrane was subjected to a test for the removal of fluorine and chlorine from polluted acid. The purpose of the test was to study the volumes of fresh water and concentrated water obtained after the removal of fluorine and chlorine, as well as the concentrations of fluoride, chloride ions and sulfate ions in the fresh water and concentrated water, and then to obtain the fluorine removal rate, chlorine removal rate and sulfate retention rate of the molecular sieve membrane.

[0044] Different batches of waste acid were sampled and tested, then mixed and subjected to a waste acid fluorine and chlorine removal test. The main indicators are shown in Table 1.

[0045] Table 1 Sampling test results of different batches of waste acid The average value in Table 1 was used as the final sampling data of the waste acid. The mixed waste acid of this batch was subjected to two consecutive waste acid fluorine and chlorine removal tests using the prepared zeolite molecular sieve membrane. The test results are shown in Table 2.

[0046] Table 2 Results of two consecutive tests on the removal of fluorine and chlorine from polluted acid

[0047] Primary fluorine and chlorine removal: Use zeolite molecular sieve membrane to remove 10L of mixed polluted acid to obtain primary concentrated water and primary fresh water. Secondary fluorine and chlorine removal: Take 10L of primary concentrated water for secondary removal to obtain secondary concentrated water and secondary fresh water.

[0048] After processing the data in Table 2, the defluorination rate in the first-stage defluorination chlorine reaches 65.87%, and the dechlorination rate is 72.63% at this time; the defluorination rate in the second-stage defluorination chlorine reaches 40.63%, and the dechlorination rate is 78.36%; after two removals, the first and second-stage comprehensive defluorination rate reaches 79.96%, the dechlorination rate reaches 94.08%, and the sulfate retention rate reaches 79.14%. In this embodiment, the concentrated water is regarded as defluorination chlorine water, and the recovery rate of defluorination chlorine water reaches 49%, and the fresh water is high-fluorine chlorine waste liquid, which is used for other purposes.

[0049] Example 2 S100: Under an ultrasonic environment, 5 parts of Zr(OH)4 are first dissolved in 40 parts of trimesic acid, based on the same mass of each part, and then the above solution is dissolved in a second solvent of 25 parts of deionized water, 15 parts of ethanol, 10 parts of isopentyl glycol and 5 parts of isohexyl glycol to form a mixed solution I (wherein the mass fraction of Zr(OH)4 is 5wt%), and finally the mixed solution I is dried to obtain zeolite molecular sieve nanoparticles.

[0050] S200: The content is the same as step S200 in Example 1, except that: PVDF monomer particles are dissolved in an organic solvent DMF with a mass concentration of 8%, and the mass fraction of PVDF in the obtained mixed solvent II is 12%, and the mass fraction of zeolite nanoparticles is 2%; the mixed solvent II is reacted at 70°C for 7 hours under nitrogen protection to obtain a casting liquid; then the casting liquid is vacuum degassed and allowed to stand for 9 hours.

[0051] S300: The content is the same as that of step S300 in Example 1, except that: a dopamine hydrochloride buffer solution with a mass concentration of 1.6% is prepared, and the PVDF molecular sieve blend membrane is immersed in ethanol and deionized water for 20 minutes each, and then immersed in the dopamine hydrochloric acid buffer solution and stirred for 24 hours under an ultrasonic environment, and finally a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid is prepared.

[0052] The mixed waste acid treated in this example is the same as that in Example 1. The zeolite molecular sieve membrane prepared is used to carry out two consecutive tests for waste acid fluorine and chlorine removal. The test results are shown in Table 3.

[0053] Table 3 Results of two consecutive tests on the removal of fluorine and chlorine from polluted acid

[0054] After processing the data in Table 3, the defluorination rate in the first-stage defluorination chlorine reaches 43.64%, and the dechlorination rate is 63.33% at this time; the defluorination rate in the second-stage defluorination chlorine reaches 36.47%, and the dechlorination rate is 65.32%; after two removals, the first and second-stage comprehensive defluorination rate reaches 58.46%, the dechlorination rate reaches 85.24%, and the sulfate retention rate reaches 90.95%. In this embodiment, the concentrated water is regarded as defluorination chlorine water, and the recovery rate of defluorination chlorine water reaches 52.57%.

[0055] Example 3 S100: Under an ultrasonic environment, based on the same mass of each part, 14 parts of ZnSO4 are first dissolved in 30 parts of dimethylimidazole, and then the above solution is dissolved in a second solvent of 50 parts of deionized water and 6 parts of ethanol to form a mixed solution I (wherein the mass fraction of ZnSO4 is 14wt%), and finally the mixed solution I is dried to obtain zeolite-like molecular sieve nanoparticles.

[0056] S200: The contents are the same as those of step S200 in Example 1, except that: PVDF monomer particles are dissolved in an organic solvent DMF with a mass concentration of 12%, and the mass fraction of PVDF in the obtained mixed solvent II is 8%, and the mass fraction of zeolite nanoparticles is 1%; the mixed solvent II is reacted at 60°C for 8 hours under nitrogen protection to obtain a casting liquid; then the casting liquid is vacuum degassed and allowed to stand for 8 hours.

[0057] S300: The content is the same as step S300 in Example 1, except that a dopamine hydrochloric acid buffer solution with a mass concentration of 1.0% is prepared, and the PVDF molecular sieve blend membrane is immersed in ethanol and deionized water for 40 minutes each, and then immersed in the dopamine hydrochloric acid buffer solution and stirred for 16 hours under an ultrasonic environment, and finally a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid is prepared.

[0058] The mixed waste acid treated in this example is the same as that in Example 1. The zeolite molecular sieve membrane prepared is used to carry out two consecutive tests for waste acid fluorine and chlorine removal. The test results are shown in Table 4.

[0059] Table 4 Results of two consecutive tests on the removal of fluorine and chlorine from polluted acid

[0060] After processing the data in Table 4, the fluorine removal rate in the first-stage fluorine removal chlorine reaches 54.88%, and the chlorine removal rate is 70.62% at this time; the fluorine removal rate in the second-stage fluorine removal chlorine reaches 51.45%, and the chlorine removal rate is 68.32%; after two removals, the first and second-stage comprehensive fluorine removal rates reach 78.09%, the chlorine removal rate reaches 90.69%, and the sulfate retention rate reaches 78%; in this embodiment, the concentrated water is regarded as the fluorine-free chlorine water, and the recovery rate of the fluorine-free chlorine water reaches 53.15%.

[0061] Example 4 S100: Under an ultrasonic environment, 4 parts of CuSO4 are first dissolved in 35 parts of imidazole, based on the same mass of each part, and then the above solution is dissolved in a second solvent of 25 parts of deionized water, 15 parts of ethanol, 11 parts of isopentyl glycol and 10 parts of isohexyl glycol to form a mixed solution I (wherein the mass fraction of CuSO4 is 4wt%), and finally the mixed solution I is dried to obtain zeolite molecular sieve nanoparticles.

[0062] S200: The contents are the same as those of step S200 in Example 1, except that the mass fraction of PVDF in the prepared mixed solvent II is 6%, and the mass fraction of zeolite nanoparticles is 2%; the mixed solvent II is reacted at 60°C for 8 hours under nitrogen protection to obtain a casting liquid; the casting liquid is then vacuum degassed and allowed to stand for 9 hours.

[0063] S300: The content is the same as step S300 in Example 1, except that a dopamine hydrochloric acid buffer solution with a mass concentration of 1.2% is prepared, and the PVDF molecular sieve blend membrane is immersed in ethanol for 20 minutes and deionized water for 40 minutes in turn, and then immersed in the dopamine hydrochloric acid buffer solution and stirred for 22 hours under an ultrasonic environment, and finally a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid is prepared.

[0064] The mixed waste acid treated in this example is the same as that in Example 1. The zeolite molecular sieve membrane prepared is used to carry out two consecutive tests for waste acid fluorine and chlorine removal. The test results are shown in Table 5.

[0065] Table 5 Results of two consecutive tests on the removal of fluorine and chlorine from polluted acid

[0066] After processing the data in Table 5, the fluorine removal rate in the first-stage fluorine removal chlorine reaches 57.17%, and the chlorine removal rate is 71.43% at this time; the fluorine removal rate in the second-stage fluorine removal chlorine reaches 53.64%, and the chlorine removal rate is 67.49%; after two removals, the first and second-stage comprehensive fluorine removal rates reach 80.14%, the chlorine removal rate reaches 92.88%, and the sulfate retention rate reaches 68.90%; in this embodiment, the concentrated water is regarded as the fluorine-free chlorine water, and the recovery rate of the fluorine-free chlorine water reaches 45.09%.

[0067] Example 5 S100: Under an ultrasonic environment, 8 parts of Cr2(SO4)3 were first dissolved in 51 parts of succinic acid, based on the same mass of each part, and then the above solution was dissolved in a second solvent of 30 parts of deionized water and 11 parts of ethanol to form a mixed solution I (wherein the mass fraction of Cr2(SO4)3 was 8wt%). Finally, the mixed solution I was dried to obtain zeolite-like molecular sieve nanoparticles.

[0068] S200: The contents are the same as those of step S200 in Example 1, except that the mass fraction of PVDF in the prepared mixed solvent II is 12%, and the mass fraction of zeolite nanoparticles is 0.5%; the mixed solvent II is reacted at 70°C for 6 hours under nitrogen protection to obtain a casting liquid; the casting liquid is then vacuum degassed and allowed to stand for 8 hours.

[0069] S300: The content is the same as step S300 in Example 1, except that a dopamine hydrochloric acid buffer solution with a mass concentration of 0.8% is prepared, and the PVDF molecular sieve blend membrane is immersed in ethanol for 30 minutes and deionized water for 20 minutes in turn, and then immersed in the dopamine hydrochloric acid buffer solution and stirred for 19 hours under an ultrasonic environment, and finally a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid is obtained.

[0070] The mixed waste acid treated in this example is the same as that in Example 1. The zeolite molecular sieve membrane prepared is used to carry out two consecutive tests for waste acid fluorine and chlorine removal. The test results are shown in Table 6.

[0071] Table 6 Results of two consecutive tests on the removal of fluorine and chlorine from polluted acid

[0072] After processing the data in Table 6, the fluorine removal rate in the first-stage fluorine removal chlorine reaches 60.39%, and the chlorine removal rate is 68.44% at this time; the fluorine removal rate in the second-stage fluorine removal chlorine reaches 53.27%, and the chlorine removal rate is 62.16%; after two removals, the first and second-stage comprehensive fluorine removal rates reach 81.45%, the chlorine removal rate reaches 88.06%, and the sulfate retention rate reaches 70.62%; in this embodiment, the concentrated water is regarded as the fluorine-free chlorine water, and the recovery rate of the fluorine-free chlorine water reaches 51.77%.

[0073] Comparative Example 1 The experimental steps are exactly the same as those in Example 1, and the batch of waste acid treated is the same, except that step S300 is no longer performed. The effect of surface coating modification of the blended membrane on the fluorine and chlorine removal rate and sulfate retention rate of the prepared molecular sieve membrane is studied. The test results are shown in Table 7.

[0074] Table 7 Comparative Example 1: Test results of removal of fluorine and chlorine from polluted acid

[0075] After processing the data in Table 7, it can be seen that the zeolite membrane obtained by the uncoated modified blend membrane has a fluorine removal rate of 62.63%, a chlorine removal rate of 70.66%, and a sulfate retention rate of 88.66%. In this comparative example, the concentrated water is produced water, and the produced water flux through the membrane reaches 24.35%.

[0076] In Example 1, the comprehensive fluorine removal rate of the zeolite molecular sieve membrane reached 79.96%, the chlorine removal rate reached 94.08%, the sulfate retention rate reached 79.14%, and the fluorine-free chlorine water recovery rate reached 49%.

[0077] By comparing Example 1 with Comparative Example 1, it can be concluded that the coating modification of the blended membrane can increase the removal rate of fluoride and chloride ions, greatly improve the recovery rate of fluoride-free chlorine water, make the PVDF molecular sieve blended membrane corrosion-resistant, reduce its hydrophobicity, and increase the water production flux.

[0078] Comparative Example 2 The same batch of waste acid treated in Example 1 was used in this comparative example to conduct a fluorine and chlorine removal test on the waste acid using a PVDF flat ultrafiltration membrane. The purpose of the test was to study the concentrations of fluorine, chloride ions and sulfate ions in fresh water and concentrated water after fluorine and chlorine removal, and then to obtain the fluorine removal rate, chlorine removal rate and sulfate retention rate of the ultrafiltration membrane. The test results were compared with those in Example 1. See Table 8.

[0079] Table 8 Comparative Example 2: Test results of removal of fluorine and chlorine from polluted acid

[0080] After processing the data in Table 8, it can be seen that the fluoride removal rate of the ultrafiltration membrane is 0.4%, the chlorine removal rate is 0.2%, and the sulfate retention rate reaches 0%.

[0081] Conclusion: Ultrafiltration membrane is not suitable for removing fluoride and chloride ions from polluted acid and retaining sulfate ions.

[0082] Comparative Example 3 The same batch of waste acid treated in Example 1 was used in this comparative example to conduct a fluorine and chlorine removal test on the waste acid using a completely unmodified conventional nanofiltration membrane. The purpose of the test was to study the concentrations of fluorine, chloride and sulfate ions in fresh water and concentrated water after fluorine and chlorine removal, and then to obtain the fluorine removal rate, chlorine removal rate and sulfate retention rate of the conventional nanofiltration membrane, which were compared with those in Example 1. The test results are shown in Table 9.

[0083] Table 9: Test results of removal of fluorine and chlorine from polluted acid in comparative example 3 After processing the data in Table 9, it can be seen that the fluoride removal rate of the conventional nanofiltration membrane is 3.19%, the chlorine removal rate is 9.07%, and the sulfate retention rate reaches 99.25%.

[0084] Conclusion: Compared with Example 1, the removal rate of fluoride and chloride ions by conventional nanofiltration membranes is lower, and both fluoride and chloride ions and sulfate ions are difficult to separate from the pores of conventional nanofiltration membranes.

[0085] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid, characterized in that: The invention comprises a dispersed phase and a continuous phase, wherein the dispersed phase is zeolite molecular sieve nanoparticles, and the continuous phase is formed by dissolving PVDF monomer particles; the zeolite molecular sieve nanoparticles are prepared by first dissolving a metal compound in a first solvent and then dissolving it in a second solvent under an ultrasonic environment to form a mixed solution I, and finally drying the mixed solution I.

2. The zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid according to claim 1, characterized in that: The metal compound is ZrCl4 or Zr(OH)4, the first solvent is trimesic acid or biphenyl dicarboxylic acid, and the second solvent is a deionized water solution of one or any combination of ethanol, isopentyl glycol and isohexyl glycol.

3. The zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid according to claim 1, characterized in that: The metal compound is any one of ZnSO4, ZnCl2, CoCl2, Co(NO3)2, CuSO4 and Cu(NO3)2, the first solvent is one or any combination of imidazole, dimethylimidazole and di-methylimidazole, and the second solvent is a deionized aqueous solution of one or any combination of ethanol, isoprene glycol and isohexanediol.

4. The zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid according to claim 1, characterized in that: The metal compound is ZrCl4, Zr(OH)4 or Cr2(SO4)3, the first solvent is succinic acid, and the second solvent is a deionized water solution of one or any combination of ethanol, isopentyl glycol and isohexyl glycol.

5. The zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid according to any one of claims 1 to 4, characterized in that: The mass fraction of the metal compound in the mixed solution is 2wt% to 20wt%.

6. The zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid according to claim 5, characterized in that: The spatial structure of the zeolite molecular sieve nanoparticles is cage-shaped, and the gaps formed between the cages become channels with a pore size of 1 to 6 nm for ions to pass through.

7. A method for preparing a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid, characterized in that: The method includes the steps of preparing a PVDF molecular sieve blended membrane by a blending method and coating and modifying the surface of the PVDF molecular sieve blended membrane, and the specific contents are as follows: A. Preparation of PVDF molecular sieve blended membrane by blending method: PVDF monomer particles are dissolved in an organic solvent DMF with a concentration of 8wt% to 12wt%, and then the zeolite molecular sieve nanoparticles according to any one of claims 1 to 6 are added, and then monomer polymerization initiators VBC and BPO are added to prepare a mixed solvent II; then the mixed solvent II is reacted at 60 to 70°C for 7 to 9 hours under nitrogen protection to prepare a casting solution; then the casting solution is vacuum degassed and allowed to stand for 7 to 9 hours, and then the casting solution is injected into a casting template and scraped with a scraper to form a film, and then the scraped film is evaporated to remove the organic solvent, and finally the scraped film is immersed in a deionized water coagulation bath for solidification to prepare a PVDF molecular sieve blended membrane; B. Surface coating modification of PVDF molecular sieve blend membrane: The aforementioned PVDF molecular sieve blend membrane was immersed in ethanol and deionized water for 20 to 40 minutes respectively, and then immersed in dopamine hydrochloric acid buffer and stirred for 16 to 24 hours under ultrasonic environment to obtain a zeolite molecular sieve membrane for removal of fluorine and chlorine from polluted acid.

8. The method for preparing a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid according to claim 7, characterized in that: In the mixed solvent II of step A, the mass fraction of PVDF is 6wt% to 12wt%, the mass fraction of zeolite molecular sieve nanoparticles is 0.5wt% to 2wt%, the mass fraction of VBC is 2wt% and the mass fraction of BPO is 0.02wt%.

9. The method for preparing a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid according to claim 7, characterized in that: The preparation method of the dopamine hydrochloric acid buffer in step B is: firstly prepare a buffer with pH 8.5 by using tris(hydroxymethyl)aminomethane and hydrochloric acid, and then dissolve DA and PEI in the buffer to prepare the dopamine hydrochloric acid buffer.

10. The method for preparing a zeolite molecular sieve membrane for removing fluorine and chlorine from polluted acid according to claim 8, characterized in that: The mass fraction of DA in the dopamine hydrochloride buffer is 0.2wt% to 1.6wt%.

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