Method and device for treating wastewater containing aluminum nitrate and nitric acid

Abstract

The present invention relates to a method and an apparatus for treating wastewater containing aluminum nitrate and nitric acid. The method includes: (1) a neutralization reaction step, including: reacting the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate; and subjecting the reaction product containing aluminum hydroxide and sodium nitrate to solid-liquid separation to respectively obtain aluminum hydroxide and a solution containing sodium nitrate, (2) an electrochemical membrane reactor treatment step, including subjecting the solution containing sodium nitrate obtained from step (1) to an electrochemical membrane reactor treatment with a potassium salt solution to respectively obtain a potassium nitrate solution and a sodium salt solution, and (3) a bipolar membrane electrodialysis step, including: subjecting the sodium salt solution obtained from step (2) to a bipolar membrane electrodialysis treatment to respectively obtain a sodium hydroxide solution and an acid solution. The apparatus correspondingly includes a neutralization reaction module, an electrochemical membrane reactor module, and a bipolar membrane electrodialysis module.

Description

Technical Field

[0001] The present invention generally relates to the technical field of wastewater treatment, and particularly to a method and an apparatus for treating wastewater containing aluminum nitrate and nitric acid. Background Art

[0002] In recent years, the demand for aluminum electrolytic capacitors has been increasing year by year. The stringent requirements for high capacitance, high voltage resistance, and miniaturization of aluminum electrolytic capacitors have forced the continuous improvement of electrode foil technology and quality. Improving the capacitance of electrode foils is the main process step in the preparation of electrode foils in the current electronic information industry. The capacitance of electrode foils can be improved through chemical conversion etching. The chemically converted foil is a key material affecting the performance of aluminum electrolytic capacitors. However, a large amount of strong acid waste liquid and aluminum salt wastewater are generated in the etching process of producing chemically converted foils. If not properly treated, it will cause serious environmental pollution and great waste of resources. Especially in the process of using nitric acid to etch aluminum foils, the nitric acid aluminum foil etching waste liquid contains a large amount of nitric acid and aluminum nitrate, and the total nitrogen content of the generated waste acid far exceeds the national total nitrogen wastewater discharge standard and needs to be treated to meet the standard before discharge.

[0003] Therefore, the recycling of nitric acid aluminum foil etching waste liquid has become a research hotspot in the chemically converted foil industry in recent years. Currently, the commonly used nitric acid aluminum foil etching waste liquid treatment technology in the prior art is to first carry out an acid-base neutralization reaction between the waste liquid (mainly composed of nitrate ions and aluminum ions) and an alkali solution (such as sodium hydroxide solution) to generate aluminum hydroxide precipitate and nitrate solution (such as sodium nitrate solution), filter out the aluminum hydroxide, and then subject the obtained sodium nitrate solution to softening treatment and put it into a bipolar membrane electrodialysis device for treatment, and an acid solution and an alkali solution with higher purity can be obtained. However, in such a treatment method, the loss of the equipment is relatively serious. Especially, the bipolar membrane electrodialysis device often cannot be used normally after running for 1 month and needs to be frequently replaced, resulting in higher operation and operation costs.

[0004] Therefore, there is an urgent need to provide a method and an apparatus for treating wastewater containing aluminum nitrate and nitric acid (such as nitric acid aluminum foil etching waste liquid) with high economic efficiency and environmental friendliness, which can extend the service life of the treatment equipment, thereby reducing operation and operation costs, and at the same time can recycle the wastewater to obtain products with high economic value, so as to achieve high economic efficiency. Summary of the Invention

[0005] The present invention is made in view of the above problems existing in the prior art.

[0006] In a first aspect, the present invention relates to a method for treating wastewater containing aluminum nitrate and nitric acid, comprising the following steps:

[0007] (1) Neutralization reaction step, comprising:

[0008] React the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate;

[0009] Perform solid-liquid separation on the reaction product containing aluminum hydroxide and sodium nitrate to obtain aluminum hydroxide and a solution containing sodium nitrate respectively,

[0010] (2) Electrochemical membrane reactor treatment step, including:

[0011] Perform electrochemical membrane reactor treatment on the solution containing sodium nitrate obtained from step (1) with a potassium salt solution to obtain a potassium nitrate solution and a sodium salt solution respectively. The potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and combinations thereof. The sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and combinations thereof,

[0012] (3) Bipolar membrane electrodialysis step, including:

[0013] Perform bipolar membrane electrodialysis treatment on the sodium salt solution obtained from step (2) to obtain a sodium hydroxide solution and an acid solution respectively. The acid solution is selected from hydrochloric acid solution, sulfuric acid solution, and combinations thereof.

[0014] In a second aspect, the present invention relates to an apparatus for treating wastewater containing aluminum nitrate and nitric acid, including the following modules:

[0015] (1) Neutralization reaction module, including:

[0016] A neutralization reaction unit for reacting the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate;

[0017] A solid-liquid separation unit downstream of the neutralization reaction unit for performing solid-liquid separation on the reaction product containing aluminum hydroxide and sodium nitrate to obtain aluminum hydroxide and a solution containing sodium nitrate respectively,

[0018] (2) An electrochemical membrane reactor module downstream of the neutralization reaction module, including:

[0019] An electrochemical membrane reactor unit for performing electrochemical membrane reactor treatment on the solution containing sodium nitrate obtained from the neutralization reaction module with a potassium salt solution to obtain a potassium nitrate solution and a sodium salt solution respectively. The potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and combinations thereof. The sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and combinations thereof,

[0020] (3) A bipolar membrane electrodialysis module downstream of the electrochemical membrane reactor module, including:

[0021] A bipolar membrane electrodialysis unit is used to perform bipolar membrane electrodialysis on a sodium salt solution obtained from an electrochemical membrane reactor module to obtain a sodium hydroxide solution and an acid solution respectively, and the acid solution is selected from hydrochloric acid solution, sulfuric acid solution, and combinations thereof.

[0022] In the above method and device according to the present invention, first, wastewater containing aluminum nitrate and nitric acid (for example, aluminum nitrate foil etching waste liquid) is subjected to an acid-base neutralization reaction with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide precipitate and sodium nitrate, and then the reaction product is subjected to solid-liquid separation to obtain a sodium nitrate solution. Then, the sodium nitrate solution is subjected to electrochemical membrane reactor treatment with an inexpensive potassium salt solution (i.e., potassium chloride solution, potassium sulfate solution, or combinations thereof) to obtain a sodium salt solution (i.e., sodium chloride solution, sodium sulfate solution, or combinations thereof) and a high-value and high-purity potassium nitrate solution respectively. Subsequently, the obtained sodium salt solution is subjected to bipolar membrane electrodialysis treatment to obtain a sodium hydroxide solution and an acid solution respectively. The sodium hydroxide solution and the acid solution can be further recycled and utilized.

[0023] The inventors unexpectedly found that by using the above method and device including a neutralization reaction process section, an electrochemical membrane reactor process section, and a bipolar membrane electrodialysis process section, compared with the method and device without introducing the electrochemical membrane reactor process section (i.e., only using the neutralization reaction process section and the bipolar membrane electrodialysis process section), the service life of the treatment equipment, especially the bipolar membrane electrodialysis equipment, is greatly extended, thereby effectively reducing the operation and operation costs. At the same time, high-value and high-purity potassium nitrate can be prepared from waste liquid and inexpensive potassium salts (such as potassium chloride, potassium sulfate), achieving higher economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings required for describing the embodiments will be briefly described below. It should be understood that the drawings are only for facilitating those skilled in the art to more easily understand the present invention, rather than intending to limit the scope of the present invention.

[0025] Figure 1 A schematic diagram showing an exemplary embodiment of the method according to the present invention is shown.

[0026] Figure 2 Shows Figure 1 A schematic diagram of the electrochemical membrane reactor treatment process in the method shown.

[0027] Figure 3 Shows Figure 1 A schematic diagram of the bipolar membrane electrodialysis process in the method shown. DETAILED DESCRIPTION OF THE INVENTION

[0028] To make the invention objectives, technical solutions, and beneficial technical effects of this application clearer, the following will provide a detailed description of this application. It should be noted that the various aspects, features, embodiments, and their advantages described in this application can be compatible and / or combined together.

[0029] Unless otherwise specified, the meanings of the scientific and technical terms in this specification are the same as those generally understood by those skilled in the art. Additionally, unless explicitly described to the contrary, the words "comprising", "including", or "containing" will be understood to include the stated elements, but not exclude any other elements.

[0030] It will be understood that although the terms "first", "second", "third", etc. may be used herein to describe various elements, components, process steps, and / or parts, these elements, components, process steps, and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, process step, or part from another. Thus, without departing from the teachings herein, the "first element", "component", "process step", or "part" discussed below may be referred to as the second element, component, process step, or part.

[0031] The present invention relates to a method and apparatus for treating wastewater containing aluminum nitrate and nitric acid.

[0032] The following will provide a specific description of the present invention.

[0033] Method for treating wastewater containing aluminum nitrate and nitric acid

[0034] In a first aspect, the present invention relates to a method for treating wastewater containing aluminum nitrate and nitric acid, comprising the following steps:

[0035] (1) Neutralization reaction step, comprising:

[0036] Reacting the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate;

[0037] Performing solid-liquid separation on the reaction product containing aluminum hydroxide and sodium nitrate to separately obtain aluminum hydroxide and a solution containing sodium nitrate,

[0038] (2) Electrochemical membrane reactor treatment step, comprising:

[0039] Treating the solution containing sodium nitrate obtained from step (1) with a potassium salt solution in an electrochemical membrane reactor to separately obtain a potassium nitrate solution and a sodium salt solution, where the potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and combinations thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and combinations thereof,

[0040] (3) Bipolar membrane electrodialysis step, comprising:

[0041] The sodium salt solution obtained from step (2) is subjected to bipolar membrane electrodialysis to obtain a sodium hydroxide solution and an acid solution respectively, and the acid solution is selected from hydrochloric acid solution, sulfuric acid solution, and combinations thereof.

[0042] The following will describe each step in detail.

[0043] Step (1): Neutralization reaction step

[0044] Step (1) includes reacting the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate.

[0045] In one or more embodiments, the wastewater containing aluminum nitrate and nitric acid is obtained from the process of etching electrode foils, especially the process of etching aluminum foils with nitric acid. For example, the wastewater containing aluminum nitrate and nitric acid is the waste liquid of aluminum foil etching with aluminum nitrate.

[0046] In one or more embodiments, in step (1), before reacting the wastewater containing aluminum nitrate and nitric acid with the sodium hydroxide solution, the wastewater containing aluminum nitrate and nitric acid is subjected to a first electrodialysis treatment to recover at least a part of nitric acid. Through this first electrodialysis treatment, the preliminary separation of the mixture of nitric acid and aluminum nitrate and the recovery of nitric acid can be achieved. The concentrated solution (nitric acid solution) preliminarily separated by electrodialysis can be returned to the front-end chemical conversion foil etching process for recycling, so as to achieve higher economic and environmental benefits.

[0047] In a preferred further embodiment, a hydrogen ion selective exchange membrane is used for the first electrodialysis treatment, and the hydrogen ion selective exchange membrane comprises:

[0048] a substrate, such as a porous substrate, such as a porous support

[0049] an anion exchange resin coating and a cation exchange resin coating on the substrate, wherein the pore size of the cation exchange resin coating is 0.8 - 1.2 Å, such as 0.8, 0.9, 1.0, 1.1, 1.2 Å or within the range defined by any two of the above values; and the pore size of the anion exchange resin coating is 2 - 10 Å, such as 2, 3, 4, 5, 6, 7, 8, 9, 10 Å or within the range defined by any two of the above values.

[0050] The inventors unexpectedly found that when using a hydrogen ion selective exchange membrane including the above structure, especially having the above pore size of the cation exchange resin coating and the anion exchange resin coating, the recovery rate of nitric acid and the retention rate of aluminum ions are both significantly improved.

[0051] In step (1), those skilled in the art can select the appropriate amount of sodium hydroxide according to actual needs. In one or more embodiments, the concentration of the sodium hydroxide solution used in step (1) is 1-5 mol / L, preferably 2 mol / L. For example, 1, 2, 3, 4, 5 mol / L or within the range defined by any two of the above values.

[0052] In one or more embodiments, in the wastewater containing aluminum nitrate and nitric acid, the concentration of nitric acid is not particularly limited and can be 3-6 wt%, for example, 3, 4, 5, 6 wt% or within the range defined by any two of the above values, based on the total weight of the wastewater containing aluminum nitrate and nitric acid.

[0053] In one or more embodiments, in the wastewater containing aluminum nitrate and nitric acid, the concentration of nitrate is not particularly limited and can be 6-12 wt%, for example, 6, 7, 8, 9, 10, 11, 12 wt% or within the range defined by any two of the above values, based on the total weight of the wastewater containing aluminum nitrate and nitric acid.

[0054] Step (1) further includes solid-liquid separation of the reaction product containing aluminum hydroxide and sodium nitrate to obtain aluminum hydroxide solid and a solution containing sodium nitrate respectively. The specific method of solid-liquid separation is not particularly limited in principle. Those skilled in the art can select a suitable solid-liquid separation method according to actual needs. For example, the solid-liquid separation can be selected from one or more of precipitation (such as flocculation precipitation), clarification, and filtration (such as multimedia filtration, ultrafiltration, and plate and frame pressure filtration). In a preferred embodiment, the solid-liquid separation includes one or more selected from flocculation precipitation, multimedia filtration, and ultrafiltration.

[0055] Through the above step (1), a relatively pure sodium nitrate solution can be obtained, and the separated aluminum hydroxide precipitate can be used as a water treatment aid in related processes or sold to a water treatment agency as a water treatment aid, which can solve the problem of solid waste disposal of aluminum hydroxide and avoid waste of by-products.

[0056] Step (2): Electrochemical membrane reactor treatment step

[0057] Step (2) includes subjecting the solution containing sodium nitrate obtained from step (1) to electrochemical membrane reactor treatment with a potassium salt solution to obtain a potassium nitrate solution and a sodium salt solution respectively. The potassium salt solution can be selected from potassium chloride solution, potassium sulfate solution, and combinations thereof, preferably potassium sulfate solution. Correspondingly, the sodium salt solution can be selected from sodium chloride solution, sodium sulfate solution, and combinations thereof, preferably sodium sulfate solution.

[0058] The electrochemical membrane reactor treatment described herein is also referred to as electrodialysis with replacement treatment. In the electrochemical membrane reactor treatment, a plurality of cation exchange membranes and anion exchange membranes are alternately arranged between the anode and the cathode to form an ion exchange membrane array. Among them, cations migrate toward the cathode side under the action of the electric field force, and anions migrate toward the anode side under the action of the electric field force. When cations encounter a cation exchange membrane during their movement, the cations can pass through. When cations encounter an anion exchange membrane during their movement, the cations are blocked and cannot pass through. When anions encounter an anion exchange membrane during their movement, the anions can pass through. When anions encounter a cation exchange membrane during their movement, the anions are blocked and cannot pass through. The electrochemical membrane reactor process utilizes this principle to redistribute the cations and anions therein, so that some products that are not convenient to produce by the double decomposition reaction method can be realized.

[0059] In one or more embodiments, in the electrochemical membrane reactor treatment, the membrane surface flow rate is controlled to be 1 cm / s to 10 cm / s, preferably 4 cm / s to 5 cm / s, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 cm / s or within the range defined by any two of the above values. When the membrane surface flow rate is within the above range, excellent salt migration efficiency can be achieved, and at the same time, the membrane stack can be protected to prevent the load of the membrane stack from being too high.

[0060] In one or more embodiments, in the electrochemical membrane reactor treatment, the current density is controlled to be 200 A / m 2 to 400 A / m 2 , preferably 300 A / m 2 to 400 A / m 2 , such as 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400 A / m 2 or within the range defined by any two of the above values. When the current density is within the above range, high production efficiency can be achieved, and the energy consumption of the equipment can be further reduced.

[0061] In one or more embodiments, in step (2), before the electrochemical membrane reactor treatment, the solution containing sodium nitrate obtained from step (1) is pretreated to remove at least a part of the impurities, wherein the pretreatment includes one or more of filtration and ion exchange, and the impurities are selected from one or more of calcium ions, magnesium ions, nickel ions, cobalt ions, manganese ions, iron ions and aluminum ions. For example, the solution containing sodium nitrate obtained from step (1) can be softened, for example, by absorbing calcium ions and magnesium ions in the solution through an ion exchange resin to obtain a high-purity sodium nitrate solution, and then the high-purity sodium nitrate solution is subjected to electrochemical membrane reactor treatment.

[0062] In one or more embodiments, in the electrochemical membrane reactor treatment, the concentration of the potassium salt solution used is not particularly limited and can be 10-20% by weight, for example, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20% by weight or within the range defined by any two of the above values.

[0063] The electrochemical membrane reactor treatment in step (2) can be carried out in a manner known to those skilled in the art. For example, the electrochemical membrane reactor treatment is carried out using a four-channel electrodialysis device as described in CN110917882A, and the content of this patent application is incorporated herein by reference in its entirety.

[0064] The inventors unexpectedly found that when an electrochemical membrane reactor treatment step is introduced between the neutralization reaction step and the bipolar membrane electrodialysis step, compared with the case where the electrochemical membrane reactor step is not introduced (i.e., only the neutralization reaction step and the bipolar membrane electrodialysis step are used), the service life of the treatment equipment, especially the bipolar membrane electrodialysis equipment, is greatly extended, thereby effectively reducing the operation and operating costs. At the same time, high-value and high-purity potassium nitrate can be prepared from waste liquid and inexpensive potassium salts (such as potassium chloride).

[0065] In addition, the process cost of the electrochemical membrane reactor treatment process is very low, while the equipment occupies a small area and can be independently operated by one person, and the operation is simple. Preparing potassium nitrate by the electrochemical membrane reactor treatment technology can reduce the production energy consumption. The test theoretical calculation shows that the energy consumption is reduced by more than 20%, and the product purity can reach more than 99.9%. Thus, the purification process is reduced, the production efficiency is improved, the production cost is reduced, and membrane pollution can be avoided to a certain extent. At the same time, the disposal problem of sodium nitrate obtained in the neutralization reaction step is also solved.

[0066] Step (3): Bipolar membrane electrodialysis step

[0067] Step (3) includes subjecting the sodium salt solution obtained from step (2) to bipolar membrane electrodialysis treatment to obtain a sodium hydroxide solution and an acid solution respectively, and the acid solution is selected from hydrochloric acid solution, sulfuric acid solution, and combinations thereof.

[0068] In a preferred embodiment, the sodium hydroxide solution obtained from step (3) is used as the sodium hydroxide solution used in step (1). By returning the sodium hydroxide obtained from the bipolar membrane electrodialysis treatment to the neutralization reaction step to react with the waste liquid from the etching of aluminum nitrate foil, the entire process flows in a cycle. This not only solves the disposal problem of by-products but also ensures the input and consumption of materials required for the process, forming a perfect closed loop for the process and achieving high economic and environmental benefits.

[0069] The acid solution obtained by bipolar membrane electrodialysis can be returned to the front-end etching process to prepare hydrochloric acid etchant or sulfuric acid etchant, participate in the preparation of electrode foils, or be sold as an acid solution to generate economic benefits. In a preferred embodiment, the wastewater containing aluminum nitrate and nitric acid is obtained from the process of etching electrode foils, particularly the process of etching electrode foils using nitric acid, and the acid solution obtained from step (3) is used in the process of etching electrode foils, particularly the process of etching electrode foils using nitric acid.

[0070] The bipolar membrane electrodialysis treatment in step (3) can be carried out in a manner known to those skilled in the art. For example, the bipolar membrane electrodialysis treatment can be performed using a bipolar membrane electrodialyzer as described in CN107298450B, and the content of this patent application is hereby incorporated by reference in its entirety.

[0071] By introducing the bipolar membrane electrodialysis step, the by-products sodium chloride and / or sodium sulfate in the electrochemical membrane reactor treatment step are disposed of, and acids and sodium hydroxide are prepared, producing high-value-added products. At the same time, the obtained acids and sodium hydroxide can be returned to the front-end process for recycling, forming a process closed-loop, achieving the goal of green and environmentally friendly resource-based production, and also reducing the economic cost of the entire process flow.

[0072] The following will be combined with Figures 1 to 3 An exemplary embodiment of the method for treating wastewater containing aluminum nitrate and nitric acid according to the present invention will be described.

[0073] From Figure 1 it can be seen that the entire process consists of three processes: neutralization reaction, electrochemical membrane reactor treatment, and bipolar membrane electrodialysis.

[0074] In the first process section (neutralization reaction process section), the raw materials are the mixed electrode foil etching solution of nitric acid and aluminum nitrate (the main components are nitrate ions and aluminum ions). First, the nitric acid and aluminum nitrate solution after the formation foil etching treatment are centrally collected and used as the raw water of the electrodialysis equipment for desalination and concentration treatment. In the desalination and concentration treatment, the electrode foil etching solution containing nitric acid and aluminum nitrate is introduced into the desalination liquid chamber of the electrodialysis equipment, and at the same time, pure water is added to the concentrated liquid chamber of the electrodialysis equipment. The electrode solution uses a sodium sulfate solution. The power supply is turned on, and the flow rate and pressure balance are adjusted. At this time, H +It migrates from the desalination liquid chamber to the concentrated liquid chamber through the cation exchange membrane. The concentration of nitric acid in the desalination liquid chamber decreases, and the concentration of nitric acid in the concentrated liquid chamber increases, completing the preliminary separation of the nitric acid and aluminum nitrate mixed solution. The recovery rate of nitric acid can reach about 90%. The concentrated liquid (nitric acid solution) preliminarily separated by electrodialysis is returned to the front-end forming foil etching process for use. Then, a desalination liquid with a molar ratio of 1:3 (a mixed solution of aluminum nitrate and nitric acid mainly composed of aluminum nitrate) and a sodium hydroxide solution are placed in a reaction tank to undergo a neutralization reaction, generating sodium nitrate and white aluminum hydroxide precipitate. After the reaction is fully completed, the mixed solution obtained after the reaction is added to the mixing tank of the high-density tank. A rapid mixer is placed in the mixing tank. At the same time, a coagulant is added to the mixing pond, and the rapid mixer is turned on to quickly disperse the coagulant, which is fully and evenly mixed with the raw water in the mixing tank to form small flocs. The mixed solution after pre-coagulation flows to the bottom of the draft tube in the reaction tank. The mixed solution, reflux sediment, and coagulant aid are mixed evenly from bottom to top by the stirring paddle in the draft tube, and a flocculant is placed in advance below the stirrer. At the same time, continuous external sediment reflux from the sedimentation and concentration zone to the reaction zone is carried out to maximize the concentration of the aluminum hydroxide precipitate, thereby improving the flocculation effect. The flocculant alum flowers formed in the reaction zone slowly enter the sedimentation zone, and slowing down the flow rate can avoid damage to the alum flowers. The flocculant alum flowers gather into sludge and concentrate at the lower part of the sedimentation tank. Inclined plates are arranged at the upper part of the sedimentation zone, and their function is to remove the alum flowers entrained by the rising water flow, thereby ensuring the quality of the effluent. The sedimentation and concentration zone ensures the slow flocculation required for the growth of alum flowers, and the generated alum flowers have a relatively high density. A sludge scraper is placed in the middle of the sedimentation zone. The function of the sludge scraper is to continuously scrape and sweep to promote the concentration of the sludge in the sedimentation zone, and at the same time push the sludge to the sludge hopper. A sludge pump is arranged at the bottom of the sludge hopper. Part of the concentrated sludge is sent to the inlet of the reaction tank by the sludge circulation pump in the concentration zone, and the other part of the surplus sludge is pumped out by the sludge pump and sent to the sludge dewatering room for treatment. Then, the obtained solution undergoes multi-media filtration, and the obtained sodium nitrate solution is put into the raw water tank of the ultrafiltration device. The ultrafiltration device switch is turned on to obtain a relatively pure sodium nitrate solution. At the same time, the obtained aluminum hydroxide precipitate is centrally collected for future use as a water treatment aid, or it can also be sold to some water treatment institutions for use as a water treatment aid, thus solving the problem of solid waste disposal of aluminum hydroxide and avoiding waste of by-products.

[0075] In the second process section (electrochemical membrane reactor treatment process section, the specific process is as Figure 2 shown), the sodium nitrate solution obtained by ultrafiltration in the first process section is added to a water quality filtration device filled with ion exchange resin. The resin fully absorbs calcium ion and magnesium ion impurities in the solution, and the solution is softened to obtain a pure sodium nitrate solution. At this time, the sodium nitrate solution already meets the conditions for being introduced into the electrochemical membrane reactor equipment for testing. As Figure 2As shown in the figure, the sodium nitrate solution and the prepared potassium chloride solution and / or potassium sulfate solution with the same concentration and volume as the sodium nitrate solution are respectively added into the No. 7 circulation tank and the No. 9 circulation tank of the electrochemical membrane reactor equipment. At the same time, equal volumes of pure water are added into the No. 6 circulation tank and the No. 8 circulation tank respectively. After all the solutions and water are added, open all the circulating water pump valves. The pure water in the No. 6 circulation tank is pumped into chamber 2, the sodium nitrate solution in the No. 7 circulation tank is pumped into chamber 3, the pure water in the No. 8 circulation tank is pumped into chamber 4, and the potassium chloride and / or potassium sulfate solution in the No. 9 circulation tank is pumped into chamber 1, 5. Turn on the DC power supply 10 to apply a DC current to the membrane stack of the electrochemical membrane reactor equipment, and adjust the rectifier so that the intermembrane voltage of the entire membrane stack is less than or equal to 10V, and the output current remains constant at 8A until the end of the entire process. At this time, K in chamber 1 + enters chamber 2 through the cation exchange membrane CEM, and NO3 in chamber 3 - enters chamber 2 through the anion exchange membrane AEM. At this time, NO3 - and K + react to form potassium nitrate (KNO3) and flow back to circulation tank 6; at the same time, Na in chamber 3 + enters chamber 4 through the cation exchange membrane CEM, and Cl in chamber 5 - and / or SO4 2- enter chamber 4 through the anion exchange membrane AEM. At this time, Na in chamber 4 + and Cl - react to form sodium chloride (NaCl) and / or Na + and SO4 2- react to form sodium sulfate (Na2SO4), and flow back to circulation tank 8. Thus, a set of reactions is completed, and every four chambers form a set of reaction units. During the treatment process of the electrochemical membrane reactor, control the membrane surface flow rate at 4 cm / s to 5 cm / s. At this time, a higher treatment efficiency can be achieved without increasing the load of the membrane stack. At the same time, control the current density to remain at 350 A / m 2, it is found that the current efficiency of the electrochemical membrane reactor treatment is the best at this time, reaching the maximum production efficiency. The control of the above two key parameters solves the production efficiency problem caused by unbalanced flow rate or uneven current, and further reduces the energy consumption of the equipment. By introducing the second process section, the service life of the treatment equipment can be extended, thereby reducing the operation and operation costs. At the same time, high-value potassium nitrate products can be produced using low-value potassium chloride or potassium sulfate, achieving higher economic benefits. In addition, the process cost of this section is very low, the equipment occupies a small area, and one person can operate independently, with simple operation. The low-concentration potassium chloride solution or low-concentration potassium sulfate solution on the fresh water side after the electrochemical membrane reactor treatment can be returned to the salt dissolution stage of potassium chloride solid salt or potassium sulfate solid salt to dissolve potassium chloride solid salt or potassium sulfate solid salt. Continuing to reuse in this way also avoids the problem of disposal of low-concentration fresh water, reduces the amount of pure water used, and avoids the problems of resource waste and cost increase; the sodium nitrate solution generated on the fresh water side after the reaction can be returned to the reverse osmosis device for concentration treatment, and the concentrated sodium nitrate solution is then returned to the electrochemical membrane reactor equipment to participate in the reaction to produce potassium nitrate and sodium chloride or sodium sulfate, forming a process closed loop. In this way, the disposal problem of low-concentration sodium nitrate on the fresh water side is also solved.

[0076] In the third process section (bipolar membrane electrodialysis process section, the specific process is as Figure 3 shown), using the by-product sodium chloride (NaCl) solution and / or sodium sulfate (Na2SO4) solution obtained from the second process section as production raw materials, hydrochloric acid (HCl) and / or sulfuric acid (H2SO4) and sodium hydroxide (NaOH) are prepared through a bipolar membrane electrodialysis device. As Figure 3 shown, first, the sodium chloride solution and / or sodium sulfate solution obtained from the second process section are added to the 12th circulation tank of the bipolar membrane electrodialysis device, and at the same time, equal volumes of pure water are added to the 11th circulation tank and the 13th circulation tank. After all the solutions and water are added, open all the circulating water pump valves. At this time, the liquid in the circulation tank enters the membrane stack. First, based on the flow rate and pressure of the sodium chloride solution and / or sodium sulfate solution side, adjust the pressure of each path to be balanced with the salt solution side. At this time, turn on the DC power supply 19 and adjust the rectifier to keep the output current at a constant current of 12.6A throughout the process, and control the intermembrane voltage to be less than or equal to 20V. At this time, the sodium chloride solution or sodium sulfate solution in the 12th circulation tank enters the 16th chamber and decomposes into Na + and Cl - and / or Na + and SO4 2- , Na + enters the 17th chamber through the cation exchange membrane (CEM), and Cl - and / or SO4 2-It enters chamber 15 through the anion exchange membrane (AEM). Since opposite-direction voltages are applied to both sides of the bipolar membrane (BP) stack by a DC power supply, charged ions diffuse to the outside through the anion exchange membrane and the cation exchange layer respectively, causing a high potential gradient to form in the hydrophilic layer and starting the electrolysis of water to produce H + and OH - , H + Under the action of the electric field force, it migrates to the outer chamber 15(18) and reacts with Cl - therein to produce hydrochloric acid (HCl) and / or reacts with SO4 2- therein to produce sulfuric acid (H2SO4). OH - Under the action of the electric field force, it migrates to the outer chamber 17(14) and reacts with Na + therein to produce sodium hydroxide (NaOH). The hydrochloric acid (HCl) and / or sulfuric acid (H2SO4) produced by bipolar membrane electrodialysis returns to the front-end etching process section to prepare hydrochloric acid etchant and / or sulfuric acid etchant, participates in the preparation of electrode foils, and can also be sold as an acid solution to generate economic benefits; the produced sodium hydroxide (NaOH) can be used to return to the first process section to react with the waste etching solution of aluminum nitrate foil. The entire process flows in a cycle in this way, which not only solves the problem of by-product disposal but also ensures the input and consumption of materials required for the process, and the process forms a perfect closed loop.

[0077] Device for treating wastewater containing aluminum nitrate and nitric acid

[0078] In a second aspect, the present invention relates to a device for treating wastewater containing aluminum nitrate and nitric acid, comprising the following modules:

[0079] (1) Neutralization reaction module, comprising:

[0080] Neutralization reaction unit, which is used to react the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate;

[0081] Solid-liquid separation unit downstream of the neutralization reaction unit, which is used to perform solid-liquid separation on the reaction product containing aluminum hydroxide and sodium nitrate to obtain aluminum hydroxide and a solution containing sodium nitrate respectively,

[0082] (2) Electrochemical membrane reactor module downstream of the neutralization reaction module, comprising:

[0083] Electrochemical membrane reactor unit, which is used to perform electrochemical membrane reactor treatment on the solution containing sodium nitrate obtained from the neutralization reaction module and a potassium salt solution to obtain a potassium nitrate solution and a sodium salt solution respectively. The potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and combinations thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and combinations thereof,

[0084] (3) The bipolar membrane electrodialysis module downstream of the electrochemical membrane reactor module includes:

[0085] The bipolar membrane electrodialysis unit is used to perform bipolar membrane electrodialysis treatment on the sodium salt solution obtained from the electrochemical membrane reactor module to obtain a sodium hydroxide solution and an acid solution respectively, and the acid solution is selected from hydrochloric acid solution, sulfuric acid solution, and their combinations.

[0086] Each module will be described in detail below.

[0087] Module (1): Neutralization reaction module

[0088] The device according to the present invention includes module (1), that is, the neutralization reaction module.

[0089] Module (1) includes a neutralization reaction unit, which is used to react the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate.

[0090] In one or more embodiments, the device according to the present invention further includes a corrosion electrode foil module upstream of the neutralization reaction module, and the corrosion electrode foil module is used to provide the wastewater containing aluminum nitrate and nitric acid.

[0091] In one or more embodiments, the neutralization reaction module further includes a first electrodialysis unit upstream of the neutralization reaction unit, and the first electrodialysis unit is used to perform first electrodialysis treatment on the wastewater containing aluminum nitrate and nitric acid before reacting the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to recover at least a part of nitric acid. Preferably, the device according to the present invention further includes a pipeline connecting the first electrodialysis unit and the corrosion electrode foil module, which is used to supply the nitric acid obtained from the first electrodialysis unit to the corrosion electrode foil module. The concentrated solution (nitric acid solution) preliminarily separated by electrodialysis can also be returned to the front-end formation foil corrosion process for recycling, so as to achieve higher economic and environmental benefits.

[0092] In a preferred further embodiment, the first electrodialysis unit includes a hydrogen ion selective exchange membrane for performing the first electrodialysis treatment, and the hydrogen ion selective exchange membrane includes:

[0093] A substrate, such as a porous substrate, such as a porous support

[0094] An anion exchange resin coating and a cation exchange resin coating on the substrate, wherein the pore size of the cation exchange resin coating is 0.8 - 1.2 Å, such as 0.8, 0.9, 1.0, 1.1, 1.2 Å or within the range defined by any two of the above values; and the pore size of the anion exchange resin coating is 2 - 10 Å, such as 2, 3, 4, 5, 6, 7, 8, 9, 10 Å or within the range defined by any two of the above values.

[0095] The inventor unexpectedly found that when using a hydrogen ion selective exchange membrane including the above structure, especially a cation exchange resin coating and an anion exchange resin coating having the above pore size dimensions, both the recovery rate of nitric acid and the rejection rate of aluminum ions are significantly improved.

[0096] Module (1) further includes a solid-liquid separation unit downstream of the neutralization reaction unit, which is used to perform solid-liquid separation on the reaction product containing aluminum hydroxide and sodium nitrate to obtain aluminum hydroxide and a solution containing sodium nitrate respectively. The specific equipment of the solid-liquid separation unit is not particularly limited in principle, and those skilled in the art can select appropriate solid-liquid separation equipment according to actual needs. For example, the solid-liquid separation unit may include one or more selected from precipitation equipment (such as high-density ponds), clarification equipment, and filtration equipment (such as multi-media filters, ultrafilters, and plate-and-frame filters). In a preferred embodiment, the solid-liquid separation unit includes one or more selected from high-density ponds, multi-media filters, and ultrafilters.

[0097] Through the above module (1), a relatively pure sodium nitrate solution can be obtained, and the separated aluminum hydroxide precipitate can be used as a subsequent water treatment aid or sold to a water treatment agency as a water treatment aid, which can solve the problem of solid waste disposal of aluminum hydroxide and avoid waste of by-products.

[0098] Module (2): Electrochemical membrane reactor module

[0099] The device according to the present invention includes module (2), that is, an electrochemical membrane reactor module (also called a displacement electrodialysis module) downstream of the neutralization reaction module.

[0100] Module (2) includes an electrochemical membrane reactor unit, which is used to perform electrochemical membrane reactor treatment on the solution containing sodium nitrate obtained from the neutralization reaction module and a potassium salt solution to obtain a potassium nitrate solution and a sodium salt solution respectively. The potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and combinations thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and combinations thereof.

[0101] The electrochemical membrane reactor unit may include an electrochemical membrane reactor device (also known as a permselective electrodialysis device), such as the four-channel electrodialysis device described in CN110917882A. The electrochemical membrane reactor device may have a structure known to those skilled in the art. The electrochemical membrane reactor device generally includes an electrochemical reaction membrane stack. The main components of the electrochemical membrane reactor device are membrane sheets (anion exchange membranes and cation exchange membranes), spacers, electrode plates, foaming materials, compression plates, frames, and locking (or hydraulic locking) devices. The membrane stack may include anion exchange membranes and cation exchange membranes, where the anion exchange membranes and cation exchange membranes are alternately arranged to form intermembrane chambers. In the electrochemical membrane reactor device, a plurality of cation exchange membranes and anion exchange membranes are alternately arranged between the anode and the cathode to form an ion exchange membrane array. Among them, cations migrate toward the cathode side under the action of the electric field force, and anions migrate toward the anode side under the action of the electric field force. When cations encounter a cation exchange membrane during migration, the cations can pass through. When cations encounter an anion exchange membrane during migration, the cations are blocked and cannot pass through. When anions encounter an anion exchange membrane during migration, the anions can pass through. When anions encounter a cation exchange membrane during migration, the anions are blocked and cannot pass through. A solution containing sodium nitrate and a potassium salt solution perform ion exchange in the ion exchange membrane array.

[0102] In one or more embodiments, the electrochemical membrane reactor module further includes a pretreatment unit upstream of the electrochemical membrane reactor unit, which is used to pretreat the solution containing sodium nitrate obtained from the neutralization reaction module before performing the electrochemical membrane reactor treatment to remove at least a part of the impurities. The pretreatment unit includes one or more of a filter and an ion exchange resin, and the impurities are selected from one or more of calcium ions, magnesium ions, nickel ions, cobalt ions, manganese ions, iron ions, and aluminum ions.

[0103] The inventors unexpectedly found that when the electrochemical membrane reactor module is introduced into the neutralization reaction module and the bipolar membrane electrodialysis module, compared with the case where the electrochemical membrane reactor module is not introduced (i.e., only the neutralization reaction module and the bipolar membrane electrodialysis module are used), the service life of the treatment equipment, especially the bipolar membrane electrodialysis equipment, is greatly extended, thereby effectively reducing the operation and operating costs. At the same time, it is also possible to prepare high-value and high-purity potassium nitrate from waste liquid and inexpensive potassium salts (such as potassium chloride).

[0104] In addition, the electrochemical membrane reactor equipment occupies a small area and can be independently operated by one person with simple operation. Using the electrochemical membrane reactor module to prepare potassium nitrate can reduce production energy consumption. The theoretical calculated energy consumption in the test is reduced by more than 20%, and the product purity can reach more than 99.9%. This can reduce the purification process, improve production efficiency, lower production costs, and to a certain extent avoid membrane pollution. At the same time, it also solves the problem of the disposal of sodium nitrate obtained from the neutralization reaction module.

[0105] Module (3): Bipolar membrane electrodialysis module

[0106] The device according to the present invention includes module (3), that is, a bipolar membrane electrodialysis module downstream of the electrochemical membrane reactor module.

[0107] Module (3) includes a bipolar membrane electrodialysis unit for performing bipolar membrane electrodialysis treatment on the sodium salt solution obtained from the electrochemical membrane reactor module to respectively obtain a sodium hydroxide solution and an acid solution, and the acid solution is selected from hydrochloric acid solution, sulfuric acid solution, and combinations thereof.

[0108] The bipolar membrane electrodialysis unit may include a bipolar membrane electrodialysis device, such as the bipolar membrane electrodialyzer described in CN107298450B. The bipolar membrane electrodialysis device may have a structure known to those skilled in the art. The bipolar membrane electrodialysis device generally includes a bipolar membrane stack. The bipolar membrane stack is the core component of the device and is generally composed of a cation exchange layer, an anion exchange layer, and an interfacial hydrophilic layer therebetween.

[0109] In a preferred embodiment, the device according to the present invention further includes a first pipeline connecting the bipolar membrane electrodialysis module and the neutralization reaction module, and this first pipeline is used to supply the sodium hydroxide solution obtained from the bipolar membrane electrodialysis module to the neutralization reaction module. By returning the sodium hydroxide obtained from the bipolar membrane electrodialysis module to the neutralization reaction module to react with the nitric acid aluminum foil etching waste liquid, the entire process flows in a cycle. This not only solves the problem of the disposal of by-products, but also ensures the input and consumption of materials required for the process, and the process forms a perfect closed loop.

[0110] In a preferred embodiment, the device according to the present invention further includes: a corrosion electrode foil module upstream of the neutralization reaction module, which is used to provide wastewater containing aluminum nitrate and nitric acid; and a second pipeline connecting the bipolar membrane electrodialysis module and the corrosion electrode foil module, and this second pipeline is used to supply the acid solution obtained from the bipolar membrane electrodialysis module to the corrosion electrode foil module.

[0111] By introducing a bipolar membrane electrodialysis module, the by-products sodium chloride and / or sodium sulfate of the electrochemical membrane reactor module are disposed of, and acids and sodium hydroxide are prepared, producing high-value-added products. At the same time, the obtained acids and sodium hydroxide can be returned to the front-end process for recycling, forming a process closed-loop, achieving the goal of green and environmentally friendly resource-based production, and also reducing the economic cost of the entire process flow.

[0112] Example

[0113] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following examples are used to further elaborate on the present invention in detail. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0114] In the following text, unless otherwise stated, the contents or concentrations mentioned are in terms of mass.

[0115] I. Evaluation experiment of running time

[0116] Experimental equipment and operating conditions:

[0117] The main experimental equipment and operating conditions used in the following Example 1 and Comparative Example 1 are as follows:

[0118] 1. The first electrodialysis equipment

[0119] Model CH-0, purchased from Hangzhou Jiangrongdao Environmental Technology Co., Ltd.,

[0120] Basic operating conditions:

[0121] Operating temperature 25°C - 35°C, given current density 300 - 400 A / m 2 , the intermembrane voltage per pair of membranes is less than or equal to 0.5 V; the membrane surface flow rate is 7.5 - 10 cm / s.

[0122] 2. Electrochemical reactor equipment

[0123] Model CHE-0, purchased from Hangzhou Jiangrongdao Environmental Technology Co., Ltd.,

[0124] Basic operating conditions:

[0125] Operating temperature 25°C - 35°C, given current density 200 - 400 A / m 2 , the intermembrane voltage per pair of membranes is less than or equal to 0.5 V; the membrane surface flow rate is 5 - 10 cm / s.

[0126] 3. Bipolar membrane electrodialysis equipment

[0127] Model BP-0, purchased from Hangzhou Jiangrongdao Environmental Technology Co., Ltd.,

[0128] Basic operating conditions:

[0129] The operating temperature is 25°C - 35°C, and the given current is 600 - 800 A / m 2 , the voltage between membranes is between 1.2 V - 1.8 V for each pair of membranes, and the flow rate on the membrane surface is 5 cm / s.

[0130] Example 1

[0131] Take the mixed corrosion solution of nitric acid and aluminum nitrate (mainly composed of nitrate ions and aluminum ions) after forming foil corrosion treatment as the raw material and undergo the following three-stage process (neutralization reaction, electrochemical reactor, and bipolar membrane electrodialysis process) treatment.

[0132] In the first-stage process, collect the mixed corrosion solution of nitric acid and aluminum nitrate after forming foil corrosion treatment and conduct desalination and concentration treatment as the raw water of the first electrodialysis device. In this desalination and concentration treatment, pass the above-mentioned corrosion solution into the desalination liquid chamber of the first electrodialysis device, and at the same time add pure water to the concentrated liquid chamber of the first electrodialysis device. The electrode solution uses sodium sulfate solution, turn on the power supply, and adjust the flow rate and pressure balance. At this time, H +It migrates from the desalination liquid chamber to the concentrate chamber through the cation exchange membrane. The concentration of nitric acid in the desalination liquid chamber decreases, and the concentration of nitric acid in the concentrate chamber increases, completing the preliminary separation of the mixed solution of nitric acid and aluminum nitrate. The recovery rate of nitric acid reaches about 90%. The concentrate (nitric acid solution) preliminarily separated by the first electrodialysis is returned to the front-end forming foil corrosion process for use. A desalination liquid (a mixed solution of aluminum nitrate and nitric acid mainly composed of aluminum nitrate) with a molar ratio of 1:3 and a sodium hydroxide solution are placed in a reaction tank to undergo a neutralization reaction, generating sodium nitrate and white aluminum hydroxide precipitate. After the reaction is fully completed, the mixed solution obtained after the reaction is added to the mixing tank of the high-density tank, and a rapid mixer is placed in the mixing tank. At the same time, a coagulant is added to the mixing pond, and the rapid mixer is turned on to quickly disperse the coagulant, which is fully and evenly mixed with the raw water in the mixing tank to form small flocs. The mixed solution after pre-coagulation flows to the bottom of the guide barrel in the reaction tank. The mixed solution, recycled precipitate, and coagulant aid are mixed evenly from bottom to top by the stirring paddle in the guide barrel, and a flocculant is placed in advance below the stirrer. At the same time, continuous external precipitation reflux from the precipitation concentration area to the reaction area is carried out to make the concentration of aluminum hydroxide precipitate reach the maximum value, thereby improving the flocculation effect. The flocculent alum flowers formed in the reaction area slowly enter the precipitation area. Slowing down the flow rate can avoid damage to the alum flowers. The flocculent alum flowers gather into sludge and concentrate at the lower part of the sedimentation tank. Inclined plates are set at the upper part of the sedimentation area, and their function is to remove the alum flowers entrained by the rising water flow, thus ensuring the quality of the effluent. The precipitation concentration area ensures the slow flocculation required for the growth of alum flowers, and the generated alum flowers have a higher density. A sludge scraper is placed in the middle of the sedimentation area. The function of the sludge scraper is to continuously scrape and sweep to promote the concentration of sludge in the sedimentation area, and at the same time push the sludge into the sludge hopper. A sludge pump is set at the bottom of the sludge hopper. Part of the concentrated sludge is sent to the inlet of the reaction tank by the sludge circulation pump in the concentration area, and the other part of the surplus sludge is pumped out by the sludge pump and sent to the sludge dewatering room for treatment. Then the obtained solution undergoes multi-media filtration, and the obtained sodium nitrate solution is put into the raw water tank of the ultrafiltration device again. The ultrafiltration device switch is turned on to obtain a relatively pure sodium nitrate solution. At the same time, the obtained aluminum hydroxide precipitate is collected centrally and reserved as a water treatment aid.

[0133] In the second-stage process, the sodium nitrate solution obtained from the first-stage process is added to a water quality filtration device filled with ion exchange resin. The resin fully absorbs the calcium and magnesium ion impurities in the solution, and the solution is softened to obtain a pure sodium nitrate solution. The sodium nitrate solution and the prepared potassium chloride solution or potassium sulfate solution with the same concentration and volume as the sodium nitrate are respectively added to two raw water circulation tanks of the electro-chemical reactor equipment. At the same time, pure water with the same volume is added to the two product water circulation tanks respectively. After all the solutions and water are added, open all the circulating water pump valves, adjust the circulating flow rate and pressure to be stable, and then turn on the DC power supply to apply a DC current to the membrane stack of the electro-chemical reactor equipment. Adjust the rectifier so that the inter-membrane voltage of the entire membrane stack is less than or equal to 10V, and the output current remains constant at 8A until the end of the entire process. At this time, K + passes through the cation exchange membrane, and NO3 - passes through the anion exchange membrane, and the two react to form potassium nitrate (KNO3) with a purity of 99.5%; at the same time, Na + passes through the cation exchange membrane, and Cl - or SO4 2- passes through the anion exchange membrane, and the two react to form sodium chloride (NaCl) or sodium sulfate (Na2SO4).

[0134] In the third-stage process, using the by-product sodium chloride (NaCl) solution or sodium sulfate (Na2SO4) solution prepared in the second-stage process as the production raw material, hydrochloric acid (HCl) or sulfuric acid (H2SO4) and sodium hydroxide (NaOH) are prepared through a bipolar membrane electrodialysis device. First, add the sodium chloride solution or sodium sulfate solution obtained from the second-stage process to the salt solution circulation tank of the bipolar membrane electrodialysis device. At the same time, add pure water with the same volume to the acid solution circulation tank and the alkali solution circulation tank. After all the solutions and water are added, open all the circulating water pump valves. At this time, the feed liquid in the circulation tank enters the membrane stack. First, focus on the flow rate and pressure on the salt solution (sodium chloride or sodium sulfate solution) side, adjust the pressure of each path to be balanced with the salt solution side. At this time, turn on the DC power supply, adjust the rectifier so that the output current remains constant at 12.6A in a constant current operation throughout the process, and control the inter-membrane voltage to be less than or equal to 20V. At this time, the sodium chloride solution or sodium sulfate solution enters the chamber and decomposes into Na + and Cl - or Na + and SO4 2- , Na + passes through the cation exchange membrane (CEM), and Cl - and / or SO4 2- passes through the anion exchange membrane. Since opposite voltages are applied to both sides of the bipolar membrane (BP) membrane stack by the DC power supply, the charged ions diffuse to the outside through the anion exchange membrane and the cation exchange layer respectively, causing the hydrophilic layer to form a high potential gradient and start electrolyzing water to produce H +and OH - ,H + Under the action of the electric field force, it migrates to the peripheral chamber and reacts with Cl therein - to form hydrochloric acid (HCl) or reacts with SO4 therein 2- to form sulfuric acid (H2SO4). OH - Under the action of the electric field force, it migrates to the peripheral chamber and reacts with Na therein + to form sodium hydroxide (NaOH).

[0135] Comparative Example 1

[0136] The same mixed etching solution of nitric acid and aluminum nitrate (mainly composed of nitrate ions and aluminum ions) after forming foil etching treatment as in Example 1 was used as the raw material and treated through the following two-stage processes (neutralization reaction and bipolar membrane electrodialysis process).

[0137] In the first-stage process, the mixed etching solution of nitric acid and aluminum nitrate after forming foil etching treatment was collected centrally, and then it was placed in a reaction tank with sodium hydroxide solution to carry out a neutralization reaction, generating sodium nitrate and white aluminum hydroxide precipitate. After the reaction was fully completed, the resulting mixed solution was added to the mixing tank of the high-density tank, and a rapid mixer was placed in the mixing tank. At the same time, a coagulant was added to the mixing pond, and the rapid mixer was turned on to quickly disperse the coagulant, which was fully and evenly mixed with the raw water in the mixing tank to form small flocs; the pre-coagulated mixed solution flowed to the bottom of the draft tube in the reaction tank, and the mixed solution, reflux precipitate, and coagulant aid were mixed evenly from bottom to top by the agitator paddle in the draft tube, and a flocculant was placed in advance below the agitator; at the same time, continuous external sediment reflux from the sedimentation concentration area to the reaction area was carried out to maximize the concentration of aluminum hydroxide precipitate, thereby improving the flocculation effect; the flocculent alum flowers formed in the reaction area slowly entered the sedimentation area, and slowing down the flow rate could avoid damage to the alum flowers. The flocculent alum flowers gathered into sludge and were concentrated at the lower part of the sedimentation tank; inclined plates were set at the upper part of the sedimentation area, and its function was to remove the alum flowers entrained by the rising water flow, thereby ensuring the quality of the effluent; the sedimentation concentration area ensured the slow flocculation required for the growth of alum flowers, and the generated alum flowers had a relatively high density. A sludge scraper was placed in the middle of the sedimentation area. The function of the sludge scraper was to continuously scrape and sweep to promote the concentration of sludge in the sedimentation area, and at the same time push the sludge to the sludge hopper. A sludge pump was set at the bottom of the sludge hopper. Part of the concentrated sludge was sent to the inlet of the reaction tank by the sludge circulation pump in the concentration area, and the other part of the remaining sludge was pumped out by the sludge pump and sent to the sludge dewatering room for treatment. Then, the resulting solution was subjected to multi-media filtration, and the obtained sodium nitrate solution was put into the raw water tank of the ultrafiltration device, and the ultrafiltration device switch was turned on to obtain a relatively pure sodium nitrate solution.

[0138] In the second-stage process, the sodium nitrate solution obtained from the first-stage process is added to a water quality filtration device filled with ion exchange resin. The resin fully absorbs calcium and magnesium ion impurities in the solution, and the solution is softened to obtain a pure sodium nitrate solution. Then, the obtained sodium nitrate solution is fed into a bipolar membrane electrodialysis device, and pure water of equal volume is added to the concentrate circulation tank at the same time. After all the solution and water are added, open all the circulating water pump valves. At this time, the liquid in the circulation tank enters the membrane stack. Taking the sodium nitrate side flow rate and pressure as the main parameters, adjust the pressures of each path to be balanced with the salt solution side. Then, turn on the DC power supply and adjust the rectifier to keep the output current at 12.6 A in constant current operation throughout the process, and control the intermembrane voltage to be less than or equal to 20 V. At this time, the sodium nitrate solution in the salt solution circulation tank enters the chamber and decomposes into Na + and NO3 - . Since opposite voltages are applied to both sides of the bipolar membrane (BP) membrane stack by the DC power supply, charged ions diffuse to the outside through the anion exchange membrane and the cation exchange layer respectively, causing a high potential gradient to form in the hydrophilic layer and starting to electrolyze water, generating H + and OH - . Under the action of the electric field force, H + migrates to the outer chamber and reacts with the NO3 - therein to form nitric acid. OH - migrates to the outer chamber under the action of the electric field force and reacts with the Na + therein to form sodium hydroxide.

[0139] Evaluation results of running time

[0140] Measure the hydrolysis voltage and bursting strength of the bipolar membrane electrodialysis device in Example 1 and Comparative Example 1 at the initial stage of the process, after 7 days of operation, after 14 days of operation, and after 30 days of operation respectively, and summarize the measurement results in Table 1 below.

[0141] The measurement method of the hydrolysis voltage used is as follows:

[0142] 1. Prepare materials and equipment:

[0143] Ion exchange membrane in the bipolar membrane electrodialysis device

[0144] Electrolytic cell

[0145] DC power supply

[0146] Voltmeter and ammeter

[0147] Electrodes (such as platinum electrodes)

[0148] Electrolyte solution (such as Na2SO4)

[0149] 2. Assemble the electrolytic cell:

[0150] Place the ion exchange membrane in the middle of the electrolytic cell to separate the anode and cathode chambers.

[0151] Add an equal amount of 100 ml of electrolyte solution on both sides.

[0152] 3. Connect the circuit:

[0153] Insert the electrodes into the anode and cathode chambers respectively, and connect the DC power supply, voltmeter and ammeter.

[0154] 4. Apply voltage:

[0155] Gradually increase the voltage, observe the change of current, and record the voltage and current values.

[0156] 5. Observe the hydrolysis phenomenon:

[0157] When the voltage reaches the hydrolysis voltage, bubbles (such as H2 and O2) will be generated on the electrodes and the current will increase significantly.

[0158] 6. Record data:

[0159] Record the voltage value when hydrolysis occurs, that is, the hydrolysis voltage.

[0160] The measurement method of the bursting strength used is as follows:

[0161] 1. Prepare materials and equipment:

[0162] Ion exchange membrane in the bipolar membrane electrodialysis equipment

[0163] Bursting strength tester

[0164] Jig

[0165] Pressure source (such as air pump)

[0166] Pressure sensor

[0167] 2. Sample preparation:

[0168] Cut the membrane into a size suitable for the jig to ensure no damage.

[0169] 3. Install the sample:

[0170] Fix the membrane in the jig of the tester to ensure good sealing.

[0171] 4. Apply pressure:

[0172] Gradually increase the pressure and observe the change of the membrane.

[0173] 5. Record data:

[0174] When the membrane ruptures, record the pressure value at this time, that is, the bursting strength.

[0175] 6. Repeat test:

[0176] Test multiple samples and take the average value.

[0177] Table 1 Evaluation results of running time

[0178]

[0179] As can be seen from the results in Table 1 above, in Example 1 where the chemical conversion foil corrosion waste liquid is treated using a three-stage process (neutralization reaction, electrochemical reactor, and bipolar membrane electrodialysis process), the hydrolysis voltage and bursting strength remain stable after 30 days of operation, and the equipment operates normally and stably. While in Comparative Example 1 where the chemical conversion foil corrosion waste liquid is treated using a two-stage process (neutralization reaction and bipolar membrane electrodialysis process), the hydrolysis voltage of the bipolar membrane increased by 297% and the bursting strength decreased by 3.8% after 7 days of operation, and the equipment could no longer be used normally after 30 days of operation. It can be seen that by introducing the electrochemical reactor for treatment, the service life of the equipment is extended, thereby reducing the operation and operation costs. At the same time, the chemical conversion foil corrosion waste liquid is recycled to obtain potassium nitrate products with high value and high purity.

[0180] Evaluation experiment of hydrogen ion selective membrane

[0181] Experimental equipment and operating conditions:

[0182] The experimental equipment and operating conditions used in the following Example 2 and Example 3 are as follows:

[0183] Equipment model: Electrodialysis equipment, model CH-0, purchased from Hangzhou Jiangrongdao Environmental Technology Co., Ltd.;

[0184] Membrane stack information: In Example 2, a hydrogen ion selective cation membrane + hydrogen blocking membrane purchased from Asahi Glass is used. The model of the hydrogen ion selective cation membrane is HSFN, which has an anion exchange resin coating with a pore size of 2 - 10 Å and a cation exchange resin coating with a pore size of 0.8 - 1.2 Å. The model of the hydrogen blocking membrane is AAVN; In Example 3, a hydrogen ion selective cation membrane + hydrogen blocking membrane purchased from PCA is used. The model of the hydrogen ion selective cation membrane is PC FH, and the pore size on the membrane surface is 10 - 15 Å. The model of the hydrogen blocking membrane is AAVN;

[0185] Current density: Both are maintained at 300 A / m 2 Continuous operation;

[0186] Intermembrane voltage: Both are controlled within 5 V;

[0187] Temperature: The water temperature on the desalination side and the concentration side is adjusted within the range of 25 °C (±2 °C) using a chiller;

[0188] Operating requirements: Continuously supplement the corrosion solution of nitric acid and aluminum nitrate on the desalination side to ensure that the intermembrane voltage is less than or equal to 5V;

[0189] Experiment end point: The experimental duration reaches 168 hours.

[0190] Example 2

[0191] Initially, add the corrosion solution with a nitric acid concentration of 200.57 g / L and an aluminum ion concentration of 11 g / L to the desalination side water tank of the electrodialysis device (using a hydrogen ion selective cation membrane + hydrogen barrier membrane purchased from Asahi Glass), add 2 L of pure water to the concentration side water tank, the electrode solution is 3% Na2SO4 solution, start the three-way circulation pumps simultaneously, adjust the desalination side flow rate to 250 L / h, adjust the pressures of the other two paths to be the same as that of the desalination side, record the flow rates and pressures of the three-way circulation pumps, turn on the rectifier, pass in direct current, and operate at a constant current of 6.3 A. Control the intermembrane voltage of the membrane stack within 5V. During the experiment, when the intermembrane voltage is close to 5V, continuously pump the raw water of the nitric acid and aluminum nitrate corrosion solution into the desalination side, control the intermembrane voltage to be less than or equal to 5V to keep the device running stably. When the conductivity of the concentrated solution side shows a downward trend, continuously pump pure water into it to balance the conductivity and prevent back migration. After running for 168 hours, the experiment ends, and record the acid concentration in the concentrated solution, the aluminum ion concentration in the concentrated solution, the volume of the concentrated solution, the acid concentration in the raw water, the aluminum ion concentration in the raw water, and the volume of the consumed raw water. Calculate the acid recovery rate and aluminum rejection rate according to the following formulas:

[0192] Acid recovery rate = Acid concentration in the concentrated solution × Volume of the concentrated solution / Acid concentration in the raw water × Volume of the consumed raw water;

[0193] Aluminum rejection rate = 1 - Aluminum ion concentration in the concentrated solution × Volume of the concentrated solution / Aluminum ion concentration in the raw water × Volume of the consumed raw water.

[0194] Example 3

[0195] Conduct the experiment with exactly the same procedures and conditions as in Example 2 and calculate the acid recovery rate and aluminum rejection rate in the same way. The only difference is that the hydrogen ion selective cation membrane + hydrogen barrier membrane purchased from PCA is used instead of the hydrogen ion selective cation membrane + hydrogen barrier membrane purchased from Asahi Glass.

[0196] The experimental results of Example 2 and Example 3 are summarized in Table 2 below.

[0197] Table 2 Experimental results of different hydrogen ion selective membranes

[0198]

[0199] As can be seen from the results in Table 2 above, under the conditions of the same experimental duration (168 hours) and the same experimental parameters, Example 2 using a hydrogen ion selective membrane with an anion exchange resin coating having a pore size of 2 - 10 Å and a cation exchange resin coating having a pore size of 0.8 - 1.2 Å achieved significantly higher acid recovery rates and aluminum ion rejection rates compared to Example 3 using a hydrogen ion selective membrane with a pore size of 10 - 15 Å.

[0200] The above are only exemplary embodiments of the present invention. It should be noted here that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, improvements can still be made to the present invention, but these all fall within the protection scope of the present invention.

Claims

1. A method for treating wastewater containing aluminum nitrate and nitric acid, comprising the following steps: (1) Neutralization reaction step, including: Reacting the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate; Performing solid-liquid separation on the reaction product containing aluminum hydroxide and sodium nitrate to obtain aluminum hydroxide and a solution containing sodium nitrate respectively, (2) Electrochemical membrane reactor treatment step, including: Performing electrochemical membrane reactor treatment on the solution containing sodium nitrate obtained from step (1) with a potassium salt solution to obtain a potassium nitrate solution and a sodium salt solution respectively. The potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and combinations thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and combinations thereof, (3) Bipolar membrane electrodialysis step, including: Performing bipolar membrane electrodialysis treatment on the sodium salt solution obtained from step (2) to obtain a sodium hydroxide solution and an acid solution respectively. The acid solution is selected from hydrochloric acid solution, sulfuric acid solution, and combinations thereof, Wherein in step (1), before reacting the wastewater containing aluminum nitrate and nitric acid with the sodium hydroxide solution, the wastewater containing aluminum nitrate and nitric acid is subjected to a first electrodialysis treatment to recover at least a part of nitric acid, and the first electrodialysis treatment is performed using a hydrogen ion selective exchange membrane, which comprises: A substrate, An anion exchange resin coating and a cation exchange resin coating on a substrate, wherein the pore size of the cation exchange resin coating is and the pore size of the anion exchange resin coating is 2. The method for treating wastewater containing aluminum nitrate and nitric acid according to claim 1, wherein the sodium hydroxide solution obtained from step (3) is used as the sodium hydroxide solution used in step (1).

3. The method for treating wastewater containing aluminum nitrate and nitric acid according to claim 1 or 2, wherein the wastewater containing aluminum nitrate and nitric acid is obtained from a process for corroding electrode foils.

4. The method for treating wastewater containing aluminum nitrate and nitric acid according to claim 3, wherein the acid solution obtained from step (3) is used in the process for corroding electrode foils.

5. The method for treating wastewater containing aluminum nitrate and nitric acid according to claim 1 or 2, wherein in the electrochemical membrane reactor treatment, the membrane surface flow rate is 1 cm / s to 10 cm / s.

6. The method for treating wastewater containing aluminum nitrate and nitric acid as claimed in claim 1 or 2, wherein in the electrochemical membrane reactor treatment, the current density is 200 A / m 2 to 400 A / m 2 .

7. The method for treating wastewater containing aluminum nitrate and nitric acid according to claim 1 or 2, wherein in step (1), the solid-liquid separation includes one or more selected from flocculation precipitation, multi-media filtration, and ultrafiltration.

8. The method for treating wastewater containing aluminum nitrate and nitric acid according to claim 1 or 2, wherein in step (2), before performing the electrochemical membrane reactor treatment, the solution containing sodium nitrate obtained from step (1) is pretreated to remove at least a part of impurities, wherein the pretreatment includes one or more of filtration and ion exchange, and the impurities are selected from one or more of calcium ions, magnesium ions, nickel ions, cobalt ions, manganese ions, iron ions, and aluminum ions.

9. An apparatus for treating wastewater containing aluminum nitrate and nitric acid, comprising the following modules: (1) Neutralization reaction module, including: A neutralization reaction unit, which is used to react the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate; A solid-liquid separation unit downstream of the neutralization reaction unit, which is used to perform solid-liquid separation on the reaction product containing aluminum hydroxide and sodium nitrate to obtain aluminum hydroxide and a solution containing sodium nitrate respectively, (2) An electrochemical membrane reactor module downstream of the neutralization reaction module, including: An electrochemical membrane reactor unit, which is used to perform electrochemical membrane reactor treatment on the solution containing sodium nitrate obtained from the neutralization reaction module and a potassium salt solution to obtain a potassium nitrate solution and a sodium salt solution respectively. The potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and their combinations. The sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and their combinations, (3) A bipolar membrane electrodialysis module downstream of the electrochemical membrane reactor module, including: A bipolar membrane electrodialysis unit, which is used to perform bipolar membrane electrodialysis treatment on the sodium salt solution obtained from the electrochemical membrane reactor module to obtain a sodium hydroxide solution and an acid solution respectively. The acid solution is selected from hydrochloric acid solution, sulfuric acid solution, and their combinations, wherein the neutralization reaction module further includes a first electrodialysis unit upstream of the neutralization reaction unit. The first electrodialysis unit is used to perform first electrodialysis treatment on the wastewater containing aluminum nitrate and nitric acid before reacting the wastewater containing aluminum nitrate and nitric acid with sodium hydroxide solution to recover at least a part of nitric acid. And the first electrodialysis unit includes a hydrogen ion selective exchange membrane to perform the first electrodialysis treatment. The hydrogen ion selective exchange membrane includes: A substrate, An anion exchange resin coating and a cation exchange resin coating on a substrate, wherein the pore size of the cation resin coating is and the pore size of the anion exchange resin coating is 10. The device for treating wastewater containing aluminum nitrate and nitric acid according to claim 9, which further includes a first pipeline connecting the bipolar membrane electrodialysis module and the neutralization reaction module. The first pipeline is used to supply the sodium hydroxide solution obtained from the bipolar membrane electrodialysis module to the neutralization reaction module.

11. The device for treating wastewater containing aluminum nitrate and nitric acid according to claim 9 or 10, which further includes a corrosion electrode foil module upstream of the neutralization reaction module. The corrosion electrode foil module is used to provide wastewater containing aluminum nitrate and nitric acid.

12. The device for treating wastewater containing aluminum nitrate and nitric acid according to claim 9 or 10, which further includes a second pipeline connecting the bipolar membrane electrodialysis module and the corrosion electrode foil module. The second pipeline is used to supply the acid solution obtained from the bipolar membrane electrodialysis module to the corrosion electrode foil module.

13. The device for treating wastewater containing aluminum nitrate and nitric acid according to claim 9 or 10, wherein the solid-liquid separation unit includes one or more selected from high-density ponds, multi-media filters, and ultrafilters.

14. The device for treating wastewater containing aluminum nitrate and nitric acid according to claim 9 or 10, wherein the electrochemical membrane reactor module further includes a pretreatment unit upstream of the electrochemical membrane reactor unit. The pretreatment unit is used to pretreat the solution containing sodium nitrate obtained from the neutralization reaction module before performing electrochemical membrane reactor treatment to remove at least a part of impurities. The pretreatment unit includes one or more of filters and ion exchange resins. The impurities are selected from one or more of calcium ions, magnesium ions, nickel ions, cobalt ions, manganese ions, iron ions, and aluminum ions.

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