System and method for preparing acid and alkali based on multi-stage membrane salt separation coupled bipolar membrane electrodialysis

Abstract

The invention provides a system and a method for preparing acid and alkali based on multi-stage membrane salt separation coupled bipolar membrane electrodialysis, and the system comprises a concentrated water high-density unit which is used for treating concentrated brine of steel comprehensive wastewater to obtain concentrated water high-density produced water; the multi-medium filtering unit is used for removing large-particle impurities in the concentrated water high-density produced water to obtain multi-medium filtered produced water; the concentrated water ultrafiltration unit is used for removing small-particle impurities and colloidal substances in the multi-medium filtered produced water to obtain concentrated water ultrafiltration produced water; the acid cation bed unit is used for removing hardness ions in the concentrated water ultrafiltration produced water to obtain weak acid cation bed produced water; the multi-stage membrane salt separation system is used for separating various salts in the weak acid cation bed produced water to obtain produced water with preset salt concentration; and the bipolar membrane electrodialysis unit is used for treating the produced water with the preset salinity concentration to obtain acid and alkali. According to the method, low-value salt is converted into high-value acid and alkali through coupling of multi-stage membrane salt separation and bipolar membrane electrodialysis, so that high-value recovery and utilization of resources are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of bipolar membrane electrodialysis, and more specifically, to a system and method for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis. Background Art

[0002] Efficient treatment and recycling of industrial wastewater is a crucial approach to addressing water resource crises and controlling water pollution. Advanced industrial wastewater treatment technologies, exemplified by "zero discharge," not only significantly reduce wastewater pollutant emissions but also contribute to the efficient recovery and resource utilization of water resources. Therefore, zero wastewater discharge is an inevitable trend in the development of industries such as steel and coal chemical industry, and is crucial for alleviating water shortages and promoting high-quality business development.

[0003] In current practical applications, the commonly used processes are pretreatment, membrane concentration, and solidification. Pretreatment, including coagulation, sand filtration, and ultrafiltration, provides a preliminary removal of impurities and suspended solids from the water, laying a solid foundation for subsequent treatment. Membrane concentration, encompassing various technologies such as RO (reverse osmosis), forward osmosis, electrodialysis, and membrane distillation, utilizes different membrane separation principles to concentrate salt and other substances in the water, increasing the salt concentration for subsequent treatment. Solidification, encompassing multi-effect evaporation, MVR (mechanical vapor recompression), flue evaporation, and natural evaporation, can achieve separation of solid salt from water. However, the resulting solid salts have low added value, the divalent salt (sodium sulfate) is not highly pure, and the system consumes a lot of energy. Therefore, developing targeted operational optimization plans to address the technical challenges of these zero-emission systems is key to achieving green and low-carbon application of zero-emission processes in industrial wastewater treatment, particularly in the steel industry.

[0004] In recent years, bipolar membrane electrodialysis (BMED) has demonstrated unique advantages in the resource utilization of high-salinity wastewater. It can convert salt into alkali and acid without causing secondary pollution to water systems, offering potential economic and environmental benefits for industrial applications. Current methods for using BMED to recycle reverse osmosis (RO) brine include: adding calcium and magnesium precipitants to the RO brine for mixing and removing hardness; filtering to form a membrane to trap organic matter and sediment; adjusting the pH of the resulting aqueous solution to an acidic pH; the brine entering an electro-Fenton reactor, where it is oxidized under acidic conditions, achieving a COD removal rate of over 97%; the effluent is then finely filtered through a PP microporous filter to produce a filtrate; and the filtrate is passed through a BMED unit to generate acid and alkali under the action of an applied electric field. Through appropriate pretreatment, the RO brine is upgraded to remove COD and calcium and magnesium ions, and the majority of the brine is directly converted into acid and alkali without evaporation or crystallization.

[0005] Although the above method can remove a large amount of COD and calcium and magnesium ions, greatly reduce evaporation, and significantly reduce the overall water production cost, the following problems still exist:

[0006] 1) During the filtration process, a filter membrane is used to intercept organic matter and sediment. The filter membrane may become clogged and needs to be cleaned or replaced regularly, which increases maintenance costs and operational difficulty.

[0007] 2) While oxidation treatment under acidic conditions can achieve COD removal rates exceeding 97% in concentrated brine, controlling the acidic conditions requires additional reagent addition and adjustment, increasing treatment costs and operational complexity. Furthermore, the electro-Fenton reaction device has high equipment requirements, requiring corrosion-resistant materials and, consequently, high energy consumption. Furthermore, the reaction produces some byproducts that require further treatment.

[0008] 3) The fine filtration of PP microporous filters will gradually become clogged as the use time increases, so the filter element needs to be cleaned or replaced regularly, which increases maintenance costs and operational difficulty; some fine impurities or specific pollutants cannot be completely removed during the fine filtration process, which may have a certain impact on the operation of the subsequent bipolar membrane electrodialysis device.

[0009] In order to solve the problems existing in the treatment of reverse osmosis concentrated brine by conventional bipolar membrane electrodialysis, the present invention urgently needs to provide a system and method for acid and alkali production based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis. Summary of the Invention

[0010] In view of the above problems, the purpose of the present invention is to provide a system and method for acid and alkali production based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis to solve various problems existing in the existing bipolar membrane electrodialysis method for treating reverse osmosis concentrated brine.

[0011] On the one hand, the present invention provides a system for acid and alkali production based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis, comprising: a concentrated water high-density unit, a multi-media filtration unit, a concentrated water ultrafiltration unit, a weak acid cation bed unit, a multi-stage membrane salt separation system, and a bipolar membrane electrodialysis unit, wherein:

[0012] The concentrated water high-density unit is used to sequentially add sodium hydroxide, PAC, sodium carbonate, PAM and concentrated sulfuric acid to the concentrated brine of steel integrated wastewater to obtain concentrated water high-density water;

[0013] The multi-media filtration unit is used to remove large particles of impurities in the concentrated high-density produced water to obtain multi-media filtered produced water;

[0014] The concentrated water ultrafiltration unit is used to remove small particle impurities and colloidal substances in the multi-media filtered water to obtain concentrated water ultrafiltration product water;

[0015] The acid cation bed unit is used for removing hardness ions and part of cations in the concentrated water ultrafiltration product water, so as to obtain weak acid cation bed product water;

[0016] The multi-stage membrane salt separation system is used for separating various salts in the weak acid cation bed product water by using different membranes, so as to obtain preset salt concentration product water;

[0017] The bipolar membrane electrodialysis unit is used for processing the preset salt concentration product water, so as to obtain acid product, alkali product and recycled water.

[0018] Optionally, the concentrated brine of the steel comprehensive wastewater has a pH value of 7.5-9.5, a COD content of 120-140 mg / L, a Na + content of 12000-19000 mg / L, a Cl - content of 6000-9000 mg / L, a SO4 2- content of 2000-3500 mg / L, a calcium content of 300-650 mg / L, a magnesium content of 20-120 mg / L, and a suspended substance content of 10-18 mg / L, and a total hardness of 600-700 mg / L.

[0019] Optionally, in the process of processing the concentrated brine of the steel comprehensive wastewater in the concentrated water high-density unit, the sodium hydroxide is a liquid solution with a mass concentration greater than 30%, and the sodium hydroxide is added in an amount of 600-1200 mg / L.

[0020] The PAC is a PAC aqueous solution with a mass concentration greater than or equal to 10%, and the PAC is added in an amount of 30-50 mg / L.

[0021] The sodium carbonate is a sodium carbonate solution with a mass concentration greater than or equal to 10%, and the sodium carbonate is added in an amount of 450-1300 mg / L.

[0022] The PAM is a PAM aqueous solution with a mass concentration greater than or equal to 0.1%, and the PAM is added in an amount of 4-6 mg / L.

[0023] The concentrated sulfuric acid is a concentrated sulfuric acid with a mass concentration greater than or equal to 98%, and the concentrated sulfuric acid is added in an amount of 30-80 mg / L.

[0024] The hardness of the concentrated water high-density product water is 30-50 mg / L.

[0025] Optionally, in the multi-medium filtration unit,

[0026] The multi-medium filter is used for removing large-particle impurities in the concentrated water high-density product water, so as to obtain multi-medium filtration product water, and the removal rate of the multi-medium filter to the large-particle impurities is 80-90%;

[0027] The fillers in the multi-media filter are quartz sand and anthracite from top to bottom, wherein:

[0028] The running flow rate of the packing is 6 to 12 m / h;

[0029] The particle size of the quartz sand is 0.5-2 mm, and the particle size of the anthracite is 0.8-1.8 mm.

[0030] Among them, an optional solution is that in the concentrated water ultrafiltration unit,

[0031] The concentrated ultrafiltration water is obtained by removing small particle impurities and colloidal substances in the multi-media filtration water through an ultrafiltration membrane, wherein:

[0032] The pore size of the ultrafiltration membrane is 0.01-0.1 μm, the temperature is 15-40°C, the pressure is 0.1-0.3 MPa, and the pH value is 2-11;

[0033] The water production rate of the concentrated water ultrafiltration water is ≥90%, and the SDI of the concentrated water ultrafiltration water is ≤5.

[0034] Among them, an optional solution is that in the acid cation bed unit,

[0035] The hardness ions in the concentrated water ultrafiltration product water are removed by sodium-type weak acid cation exchange resin, and the acid in the concentrated water ultrafiltration product water is regenerated into hydrogen type, and the alkali in the concentrated water ultrafiltration product water is regenerated into sodium type; wherein the hardness of the weak acid cation bed product water is ≤1mg / L.

[0036] Among them, an optional solution is that the multi-stage membrane salt separation system includes a medium-loose nanofiltration membrane and an anion exchange membrane; wherein,

[0037] The medium-loose nanofiltration membrane is used to selectively separate sodium sulfate from the weak acid cation bed water;

[0038] The anion exchange membrane is used to selectively separate anions in the weak acid cation bed produced water.

[0039] Among them, an optional solution is that in the multi-stage membrane salt separation system, the anion is Cl - / SO4 2- ,in,

[0040] The selective separation rate of the medium-loose nanofiltration membrane for the sodium sulfate is ≥99%, the selective separation rate of the anion exchange membrane for anions is ≥25%, and the COD removal rate of the water produced at the preset salt concentration is ≥95%.

[0041] Among them, an optional solution is that the bipolar membrane electrodialysis unit includes two bipolar membranes, an anode electrically connected to one of the bipolar membranes, a cathode electrically connected to the other bipolar membrane, a cation exchange membrane and an anion exchange membrane arranged between the two bipolar membranes, wherein,

[0042] The cation exchange membrane and the anion exchange membrane form a salt chamber, the bipolar membrane electrically connected to the anode and the anion exchange membrane form an acid chamber, and the bipolar membrane electrically connected to the cathode and the cation exchange membrane form an alkali chamber.

[0043] Among them, an optional solution is that the bipolar membrane is used to decompose water into hydrogen ions and hydroxide ions;

[0044] The cation exchange membrane is used to migrate the cations in the salt chamber to the base chamber;

[0045] an anion exchange membrane for migrating anions in the salt chamber to the acid chamber;

[0046] The cathode and the anode provide a potential difference for driving the migration of the cations and the anions.

[0047] On the other hand, the present invention also provides a method for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis, wherein the system for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis is used to treat concentrated brine of steel integrated wastewater, the method comprising:

[0048] Sodium hydroxide, PAC, sodium carbonate, PAM and concentrated sulfuric acid are added to the concentrated brine of steel integrated wastewater in sequence to treat it and obtain concentrated high-density water.

[0049] Removing large particle impurities in the concentrated high-density produced water through a multi-media filtration unit to obtain multi-media filtered produced water;

[0050] Removing small particle impurities and colloidal substances in the multi-media filtered water through a concentrated water ultrafiltration unit to obtain concentrated water ultrafiltration water;

[0051] The hardness ions and some cations in the concentrated water ultrafiltration product water are removed by an acid cation bed unit to obtain weak acid cation bed product water;

[0052] Separating various salts in the weak acid cation bed produced water through different membranes of a multi-stage membrane salt separation system to obtain produced water with a preset salt concentration;

[0053] The produced water with the preset salt concentration is treated by a bipolar membrane electrodialysis unit to obtain an acid product, an alkali product and recycled water.

[0054] As can be seen from the above technical solutions, the system and method for acid and alkali production based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis provided by the present invention can achieve the following beneficial effects compared with the prior art:

[0055] (1) In the multi-stage membrane salt separation system, the present invention realizes the selective separation of ions in the concentrated brine by precisely controlling the process parameters during the salt separation process. This can avoid the tedious steps of controlling the acidic conditions and reduce the use of reagents, thereby reducing the processing cost and operational complexity. It effectively solves the problem in the prior art that the control of the acidic conditions requires the addition and adjustment of additional reagents, which increases the processing cost and operational complexity.

[0056] (2) The present invention combines a concentrated water high-density unit, a multi-media filtration unit, a concentrated water ultrafiltration unit, a weak acid cation bed unit, a multi-stage membrane salt separation system and a bipolar membrane electrodialysis unit, which not only improves the removal effect of fine impurities and specific pollutants, but also reduces the risk of membrane clogging, extends the service life of the membrane, reduces the frequency of cleaning and replacement, and reduces maintenance costs and operating difficulty.

[0057] (3) The present invention combines multi-stage membrane salt separation technology with bipolar membrane electrodialysis. Different membranes are used to separate different ions during the multi-membrane salt separation process, reducing reliance on energy-intensive oxidation reactions. During bipolar membrane electrodialysis, salt is converted into acid and base under the action of an applied electric field. This process is clean, efficient, and energy-efficient, without generating significant byproducts. This reduces waste emissions and production costs.

[0058] (4) The present invention realizes the effective treatment of concentrated brine of comprehensive wastewater from steel industry by multi-stage membrane salt separation coupled with bipolar membrane electrodialysis technology, removes harmful substances, and converts low-value salt into high-value acid and alkali, thereby realizing high-value recovery and utilization of resources.

[0059] In order to achieve the above and related purposes, one or more aspects of the present invention include the features that will be described in detail later. The following description and the accompanying drawings describe some exemplary aspects of the present invention in detail. However, these aspects indicate only some of the various ways in which the principles of the present invention can be used. In addition, the present invention is intended to include all of these aspects and their equivalents. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] By referring to the following description in conjunction with the accompanying drawings, and with a more complete understanding of the present invention, other objects and results of the present invention will become more clear and easy to understand. In the accompanying drawings:

[0061] Figure 1 Schematic diagram of the logical structure of a system for acid and alkali production based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to an embodiment of the present invention;

[0062] Figure 2 This is a schematic diagram of the principle of acid and alkali production by Na2SO4-based bipolar membrane electrodialysis according to an embodiment of the present invention;

[0063] Figure 3 This is a schematic diagram of the principle of acid and alkali production using a NaCl-based bipolar membrane electrodialysis system according to an embodiment of the present invention;

[0064] Figure 4 Schematic diagram of a method for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to an embodiment of the present invention.

[0065] The same reference numerals throughout the drawings indicate similar or corresponding features or functions. DETAILED DESCRIPTION

[0066] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0067] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0068] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0069] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0070] In order to illustrate the logical structure of the acid and alkali production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis provided by the present invention, Figure 1The system logic structure for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to the embodiment of the application is shown.

[0071] As shown in the figure, Figure 1 The system for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis provided by the application mainly comprises a concentrated water high-density unit 110, a multi-medium filtration unit 120, a concentrated water ultrafiltration unit 130, a weak acid cation bed unit 140, a multi-stage membrane salt separation system 150 and a bipolar membrane electrodialysis unit 160, wherein,

[0072] The concentrated water high-density unit 110 is used for sequentially adding sodium hydroxide, PAC, sodium carbonate, PAM and concentrated sulfuric acid into the concentrated brine of the steel comprehensive wastewater to obtain concentrated water high-density produced water.

[0073] The multi-medium filtration unit 120 is used for removing large-particle impurities in the concentrated water high-density produced water to obtain multi-medium filtration produced water.

[0074] The concentrated water ultrafiltration unit 130 is used for removing small-particle impurities and colloidal substances in the multi-medium filtration produced water to obtain concentrated water ultrafiltration produced water.

[0075] The acid cation bed unit 140 is used for removing hardness ions and part of cations in the concentrated water ultrafiltration produced water to obtain weak acid cation bed produced water.

[0076] The multi-stage membrane salt separation system 150 is used for separating various salts in the weak acid cation bed produced water by using different membranes to obtain preset salt concentration produced water.

[0077] The bipolar membrane electrodialysis unit 160 is used for processing the preset salt concentration produced water to obtain acid products, alkali products and recycled water.

[0078] By using the multi-stage membrane salt separation coupled with bipolar membrane electrodialysis technology, the application realizes effective treatment of the concentrated brine of the steel comprehensive wastewater, which not only removes harmful substances but also recycles clean water, thereby improving the utilization rate of water resources.

[0079] In the concentrated water high-density unit 110, the pH value of the concentrated brine of the steel comprehensive wastewater is 7.5-9.5, the COD (Chemical Oxygen Demand) content is 120-140 mg / L, the Na + content is 12000-19000 mg / L, the Cl - content is 6000-9000 mg / L, the SO4 2-The content is 2000-3500 mg / L, the calcium content is 300-650 mg / L, the magnesium content is 20-120 mg / L, the suspended matter content is 10-18 mg / L, and the total hardness content is 600-700 mg / L.

[0080] Among them, in the concentrated water high-density unit 110, during the treatment of concentrated brine of steel integrated wastewater, sodium hydroxide is a liquid solution with a mass concentration greater than 30%, and the amount of sodium hydroxide added is 600-1200 mg / L; PAC (PolybasicAluminumChloride) is a PAC aqueous solution with a mass concentration of ≥10%, and the amount of PAC added is 30-50 mg / L; sodium carbonate is a sodium carbonate solution with a mass concentration of ≥10%, and the amount of sodium carbonate added is 450-1300 mg / L; PAM (Polyacrylamide) is a PAM aqueous solution with a mass concentration of ≥0.1%, and the amount of PAM added is 4-6 mg / L; concentrated sulfuric acid is concentrated sulfuric acid with a mass concentration of ≥98%, and the amount of concentrated sulfuric acid added is 30-80 mg / L; the hardness of the concentrated water high-density product is 30-50 mg / L.

[0081] It should be noted that lime milk can be used instead of sodium hydroxide, or other flocculants such as PFS (Polymericferric sulfate) can be used instead of PAC. In specific applications, appropriate alternatives can be selected according to actual conditions.

[0082] In the multi-media filtration unit 120, large impurities in the concentrated high-density produced water are removed by a multi-media filter to produce multi-media filtered produced water. The multi-media filter has a large impurity removal rate of 80-90%, and large impurities here generally refer to suspended matter. The fillers in the multi-media filter are quartz sand and anthracite, respectively, from top to bottom, with an operating flow rate of 6-12 m / h. The particle size of the quartz sand is 0.5-2 mm, and the particle size of the anthracite is 0.8-1.8 mm. In specific applications, different types of filter materials (such as activated carbon, ceramic sand, or other synthetic materials) can be used instead of quartz sand and anthracite to improve the filtration effect or adapt to specific water qualities.

[0083] Among them, in the concentrated water ultrafiltration unit 130, small particulate impurities and colloidal substances in the multi-media filtration water are removed by ultrafiltration membrane to obtain concentrated water ultrafiltration water. The pore size of the ultrafiltration membrane is 0.01-0.1μm, the temperature is 15-40°C, the pressure is 0.1-0.3Mpa, and the pH value is 2-11; the water production rate of the concentrated water ultrafiltration water is ≥90%, and the SDI (silt density index) of the concentrated water ultrafiltration water is ≤5.

[0084] In the acid cation bed unit 140, sodium-type weak acid cation exchange resin removes hardness ions from the concentrated ultrafiltration water. The acid in the concentrated ultrafiltration water is regenerated to hydrogen type, and the alkali in the concentrated ultrafiltration water is regenerated to sodium type. The hardness of the weak acid cation exchange bed water is ≤1 mg / L. In specific applications, other types of weak acid cation exchange resins, such as macroporous resins or high-performance resins, can be used as needed to increase exchange capacity and service life.

[0085] The multi-stage membrane salt separation system 150 includes a medium-porosity nanofiltration membrane and an anion exchange membrane; wherein the medium-porosity nanofiltration membrane is used to selectively separate sodium sulfate from the weak acid cation bed water; the anion exchange membrane is used to selectively separate anions from the weak acid cation bed water. - / SO4 2- The selective separation rate of medium-loose nanofiltration membrane for sodium sulfate is ≥99%, the selective separation rate of anion exchange membrane for anions is ≥25%, and the COD removal rate of water produced at the preset salt concentration is ≥95%.

[0086] The bipolar membrane electrodialysis unit 160 includes two bipolar membranes, an anode electrically connected to one of the bipolar membranes, a cathode electrically connected to the other bipolar membrane, and a cation exchange membrane and an anion exchange membrane disposed between the two bipolar membranes. The cation exchange membrane and the anion exchange membrane form a salt chamber, the bipolar membrane electrically connected to the anode and the anion exchange membrane form an acid chamber, and the bipolar membrane electrically connected to the cathode and the cation exchange membrane form an alkaline chamber. The bipolar membranes are used to decompose water into hydrogen ions and hydroxide ions; the cation exchange membrane is used to transfer cations in the salt chamber to the alkaline chamber; the anion exchange membrane is used to transfer anions in the salt chamber to the acid chamber; and the cathode and the anode provide a potential difference to drive the migration of cations and anions.

[0087] The bipolar membrane electrically connected to the anode is the first bipolar membrane, the bipolar membrane electrically connected to the cathode is the second bipolar membrane, the first bipolar membrane and the anode membrane form an alkaline chamber, and the second bipolar membrane and the cathode membrane form an acid chamber.

[0088] exist Figure 2 In the embodiment shown, the salt chamber contains Na2SO4 solution, and the Na + Migrate to the alkaline chamber through the cation membrane, the first bipolar membrane is electrically connected to the cathode and ionizes OH in the alkaline chamber - , Na is formed in the base chamber + With OH - Combined NaOH alkaline solution; SO4 in Na2SO4 solution 2- Migrate to the acid chamber through the anion membrane, the second bipolar membrane is electrically connected to the anode, and ionizes H in the acid chamber + , H is formed in the acid chamber + With SO4 2- Combined H2SO4 acid solution.

[0089] exist Figure 3 In the embodiment shown, the salt chamber contains NaCl solution, and the Na + Migrate to the alkaline chamber through the cation membrane, the first bipolar membrane is electrically connected to the cathode and ionizes OH in the alkaline chamber - , Na is formed in the base chamber + With OH - The combined NaOH alkaline solution; Cl in the NaCl solution - Migrate to the acid chamber through the anion membrane, the second bipolar membrane is electrically connected to the anode, and ionizes H in the acid chamber. + , H is formed in the acid chamber + With Cl - Combined HCl acid solution.

[0090] comprehensive Figure 2 and Figure 3 In the embodiment shown, the bipolar membrane is the core component of the system. Under the action of the DC electric field, the bipolar membrane can decompose water into hydrogen ions (H + ) and hydroxide ions (OH-). A cationic membrane is a cation exchange membrane, and an anionic membrane is an anion exchange membrane. A cation exchange membrane only allows cations to pass through while blocking the migration of anions, that is, preventing anions in the salt chamber from entering the base chamber. An anion exchange membrane, on the other hand, only allows anions to pass through while blocking cations, that is, preventing cations in the salt chamber from entering the acid chamber. In an embodiment of the present invention, salt is converted into acid and base under the action of an applied electric field, and the acid-base concentration is ≥6%.

[0091] On the other hand, the present invention also provides a method for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis. Figure 4 The flow chart of the method for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to an embodiment of the present invention is shown.

[0092] like Figure 4 As shown, the present invention also provides a method for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis, which uses the above-mentioned system for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis to treat concentrated brine of steel integrated wastewater, and the method comprises:

[0093] S1: Sodium hydroxide, PAC, sodium carbonate, PAM and concentrated sulfuric acid are added to the concentrated brine of steel integrated wastewater in sequence for treatment to obtain concentrated high-density water;

[0094] S2: Remove large particle impurities in concentrated high-density produced water through a multi-media filtration unit to obtain multi-media filtered produced water;

[0095] S3: The concentrated water ultrafiltration unit removes small particle impurities and colloidal substances in the multi-media filtration product water to obtain concentrated water ultrafiltration product water;

[0096] S4: removing hardness ions and some cations in the concentrated water ultrafiltration product water through the acid cation bed unit to obtain weak acid cation bed product water;

[0097] S5: Separating various salts in the weak acid cation bed produced water through different membranes of the multi-stage membrane salt separation system to obtain produced water with a preset salt concentration;

[0098] S6: The produced water with a preset salt concentration is treated by a bipolar membrane electrodialysis unit to obtain an acid product, an alkali product and recycled water.

[0099] In S6, the bipolar membrane electrodialysis unit 160 includes two bipolar membranes, an anode electrically connected to one of the bipolar membranes, a cathode electrically connected to the other bipolar membrane, and a cation exchange membrane and an anion exchange membrane disposed between the two bipolar membranes. The cation exchange membrane and the anion exchange membrane form a salt chamber, the bipolar membrane electrically connected to the anode and the anion exchange membrane form an acid chamber, and the bipolar membrane electrically connected to the cathode and the cation exchange membrane form an alkaline chamber. The bipolar membranes are used to decompose water into hydrogen ions and hydroxide ions; the cation exchange membrane is used to transfer cations in the salt chamber to the alkaline chamber; the anion exchange membrane is used to transfer anions in the salt chamber to the acid chamber; and the cathode and the anode provide a potential difference to drive the migration of cations and anions.

[0100] Among them, the bipolar membrane is the core component of the system. Under the action of the DC electric field, the bipolar membrane can decompose water into hydrogen ions (H + ) and hydroxide ions (OH-). A cationic membrane is a cation exchange membrane, and an anionic membrane is an anion exchange membrane. A cation exchange membrane only allows cations to pass through while blocking the migration of anions, that is, preventing anions in the salt chamber from entering the base chamber. An anion exchange membrane, on the other hand, only allows anions to pass through while blocking cations, that is, preventing cations in the salt chamber from entering the acid chamber. In an embodiment of the present invention, salt is converted into acid and base under the action of an applied electric field, and the acid-base concentration is ≥6%.

[0101] From the above technical solutions, the system and method for producing acid and base based on multi-stage membrane salt separation coupled bipolar membrane electrodialysis provided by the application realize effective treatment of concentrated brine of steel comprehensive wastewater through multi-stage membrane salt separation coupled bipolar membrane electrodialysis technology, not only remove harmful substances, but also convert low-value salt into high-value acid and base, so as to realize high-value recovery and utilization of resources; the salt produced in the wastewater treatment process can be reused through further processing, thereby reducing waste discharge and production cost. The application effectively removes harmful components such as heavy metal ions and organic pollutants in wastewater, thereby reducing environmental pollution. Compared with the traditional treatment method, the application has low energy consumption in the wastewater treatment process, reduces the emission of greenhouse gases such as carbon dioxide, and is helpful to environmental protection. The system and method of the application reduce the cost of wastewater treatment, especially through recycling resources, further reducing operating expenses; in addition, the acid and base produced by electrodialysis can be sold as by-products to increase economic benefits. The multi-stage membrane salt separation technology used in the application can effectively separate various ions in wastewater, thereby improving water quality purification efficiency; the characteristics of the bipolar membrane are used to decompose water into acid and base under the action of a direct current electric field, and this method has high conversion rate and selectivity. Each unit in the application can realize automatic operation, thereby simplifying the operation process and reducing labor cost; the unit design of the system makes daily maintenance simpler, thereby prolonging the service life of the equipment. The system and method provided by the application can adapt to different types of wastewater treatment, have strong flexibility and wide applicability.

[0102] The above embodiments are preferred embodiments of the application, but the embodiments of the application are not limited by the above embodiments, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the application shall be equivalent replacement modes and shall be included in the protection scope of the application.

Claims

1. A system for acid and alkali production based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis, characterized in that: include: Concentrated water high-density unit, multi-media filtration unit, concentrated water ultrafiltration unit, weak acid cation bed unit, multi-stage membrane salt separation system and bipolar membrane electrodialysis unit, among which, The concentrated water high-density unit is used to sequentially add sodium hydroxide, PAC, sodium carbonate, PAM and concentrated sulfuric acid to the concentrated brine of steel integrated wastewater to obtain concentrated water high-density water; The multi-media filtration unit is used to remove large particles of impurities in the concentrated high-density produced water to obtain multi-media filtered produced water; The concentrated water ultrafiltration unit is used to remove small particle impurities and colloidal substances in the multi-media filtered water to obtain concentrated water ultrafiltration product water; The acid cation bed unit is used to remove hardness ions and some cations in the concentrated water ultrafiltration product water to obtain weak acid cation bed product water; The multi-stage membrane salt separation system is used to separate various salts in the weak acid cation bed water using different membranes to obtain water with a preset salt concentration; The bipolar membrane electrodialysis unit is used to treat the produced water with the preset salt concentration to obtain an acid product, an alkali product and recycled water.

2. The acid-base production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to claim 1, characterized in that: The pH value of the concentrated brine of the steel comprehensive wastewater is 7.5-9.5, the COD content is 120-140 mg / L, and the Na + The content is 12000~19000mg / L, Cl - Content is 6000~9000mg / L, SO4 2- The content is 2000-3500 mg / L, the calcium content is 300-650 mg / L, the magnesium content is 20-120 mg / L, the suspended matter content is 10-18 mg / L, and the total hardness is 600-700 mg / L.

3. The acid-base production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to claim 1, characterized in that: In the process of treating the concentrated brine of the steel integrated wastewater by the concentrated water high-density unit, the sodium hydroxide is a liquid solution with a mass concentration greater than 30%, and the amount of the sodium hydroxide added is 600-1200 mg / L; The PAC is a PAC aqueous solution with a mass concentration of ≥10%, and the amount of the PAC added is 30-50 mg / L; The sodium carbonate is a sodium carbonate solution with a mass concentration of ≥10%, and the amount of sodium carbonate added is 450-1300 mg / L; The PAM is a PAM aqueous solution with a mass concentration of ≥0.1%, and the added amount of the PAM is 4-6 mg / L; The concentrated sulfuric acid has a mass concentration of ≥98%, and the amount of concentrated sulfuric acid added is 30-80 mg / L; The hardness of the concentrated high-density water is 30-50 mg / L.

4. The acid-base production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to claim 1, characterized in that: In the multimedia filter unit, The multi-media filter is used to remove large particle impurities in the concentrated high-density produced water to obtain multi-media filtered produced water, and the removal rate of the multi-media filter for the large particle impurities is 80-90%; wherein, The fillers in the multi-media filter are quartz sand and anthracite from top to bottom, wherein: The running flow rate of the packing is 6 to 12 m / h; The particle size of the quartz sand is 0.5-2 mm, and the particle size of the anthracite is 0.8-1.8 mm.

5. The acid-base production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to claim 1, characterized in that: In the concentrated water ultrafiltration unit, The concentrated ultrafiltration water is obtained by removing small particle impurities and colloidal substances in the multi-media filtration water through an ultrafiltration membrane, wherein: The pore size of the ultrafiltration membrane is 0.01-0.1 μm, the temperature is 15-40°C, the pressure is 0.1-0.3 MPa, and the pH value is 2-11; The water production rate of the concentrated water ultrafiltration water is ≥90%, and the SDI of the concentrated water ultrafiltration water is ≤5.

6. The acid-base production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to claim 1, characterized in that: In the acid cation bed unit, The hardness ions in the concentrated water ultrafiltration product water are removed by sodium-type weak acid cation exchange resin, and the acid in the concentrated water ultrafiltration product water is regenerated into hydrogen type, and the alkali in the concentrated water ultrafiltration product water is regenerated into sodium type; wherein the hardness of the weak acid cation bed product water is ≤1mg / L.

7. The acid-base production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to claim 1, characterized in that: The multi-stage membrane salt separation system includes a medium-porosity nanofiltration membrane and an anion exchange membrane; wherein, The medium-loose nanofiltration membrane is used to selectively separate sodium sulfate from the weak acid cation bed water; The anion exchange membrane is used to selectively separate anions in the weak acid cation bed produced water.

8. The acid-base production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to claim 7, characterized in that: In the multi-stage membrane salt separation system, the anion is Cl - / SO4 2- ,in, The selective separation rate of the medium-loose nanofiltration membrane for the sodium sulfate is ≥99%, the selective separation rate of the anion exchange membrane for anions is ≥25%, and the COD removal rate of the water produced at the preset salt concentration is ≥95%.

9. The acid-base production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to claim 1, characterized in that: The bipolar membrane electrodialysis unit includes two bipolar membranes, an anode electrically connected to one of the bipolar membranes, a cathode electrically connected to the other bipolar membrane, a cation exchange membrane and an anion exchange membrane arranged between the two bipolar membranes, wherein: The cation exchange membrane and the anion exchange membrane form a salt chamber, the bipolar membrane electrically connected to the anode and the anion exchange membrane form an acid chamber, and the bipolar membrane electrically connected to the cathode and the cation exchange membrane form an alkali chamber.

10. The acid-base production system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis according to claim 9, characterized in that: The bipolar membrane is used to decompose water into hydrogen ions and hydroxide ions; The cation exchange membrane is used to transfer the cations in the salt chamber to the base chamber; The anion exchange membrane is used to migrate anions in the salt chamber to the acid chamber; The cathode and the anode provide a potential difference for driving the migration of the cations and the anions.

11. A method for producing acid and alkali based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis, characterized in that: The concentrated brine of steel integrated wastewater is treated using a system based on multi-stage membrane salt separation coupled with bipolar membrane electrodialysis for acid and alkali production according to any one of claims 1 to 10, the method comprising: Sodium hydroxide, PAC, sodium carbonate, PAM and concentrated sulfuric acid are added to the concentrated brine of steel integrated wastewater in sequence to treat it and obtain concentrated high-density water. Removing large particle impurities in the concentrated high-density produced water through a multi-media filtration unit to obtain multi-media filtered produced water; Removing small particle impurities and colloidal substances in the multi-media filtered water through a concentrated water ultrafiltration unit to obtain concentrated water ultrafiltration water; The hardness ions and some cations in the concentrated water ultrafiltration product water are removed by an acid cation bed unit to obtain weak acid cation bed product water; Separating various salts in the weak acid cation bed produced water through different membranes of a multi-stage membrane salt separation system to obtain produced water with a preset salt concentration; The produced water with the preset salt concentration is treated by a bipolar membrane electrodialysis unit to obtain an acid product, an alkali product and recycled water.

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