Method and apparatus for treating wastewater comprising aluminum nitrate and nitric acid

Abstract

The invention relates to a method and a device for treating waste water containing aluminum nitrate and nitric acid. The method comprises the following steps: (1) a neutralization reaction step: carrying out a reaction on wastewater containing aluminum nitrate and nitric acid and a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate; and (2) an electrochemical membrane reactor treatment step: carrying out electrochemical membrane reactor treatment on the sodium nitrate-containing solution obtained in the step (1) and a potassium salt solution to respectively obtain a potassium nitrate solution and a sodium salt solution, and carrying out solid-liquid separation on the reaction product containing the aluminum hydroxide and the sodium nitrate to respectively obtain the aluminum hydroxide and the sodium nitrate-containing solution. And (3) bipolar membrane electrodialysis: carrying out bipolar membrane electrodialysis treatment on the sodium salt solution obtained in the step (2) to respectively obtain a sodium hydroxide solution and an acid solution. The device correspondingly comprises 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 in particular to a method and a device for treating wastewater containing aluminum nitrate and nitric acid. Background Art

[0002] In recent years, the demand for aluminum electrolytic capacitors has been growing year by year. The stringent requirements of high capacity, high voltage resistance, and miniaturization of aluminum electrolytic capacitors have forced the electrode foil technology and quality to continue to rise. Improving the capacitance of the electrode foil is the main process in the preparation of electrode foil in the current electronic information industry. Improving the capacitance of the electrode foil can be achieved through chemical corrosion, and chemical foil is a key material that affects the performance of aluminum electrolytic capacitors. However, a large amount of strong acid waste liquid and aluminum salt wastewater will be generated in the corrosion process of chemical foil production. If not properly handled, it will cause serious environmental pollution and great waste of resources. Especially in the process of corroding aluminum foil using nitric acid, 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 waste acid generated far exceeds the national total nitrogen wastewater discharge standard, and it needs to be treated to meet the standard before it can be discharged.

[0003] Therefore, the recycling of aluminum foil etching waste liquid has become a research hotspot in the chemical foil industry in recent years. At present, the aluminum foil etching waste liquid treatment technology frequently used in the prior art is to first subject the waste liquid (mainly composed of nitrate ions and aluminum ions) and an alkaline solution (such as a sodium hydroxide solution) to an acid-base neutralization reaction to generate aluminum hydroxide precipitation and a nitrate solution (such as a sodium nitrate solution), filter and remove the aluminum hydroxide, and then put the resulting sodium nitrate solution into a bipolar membrane electrodialysis device after softening treatment to obtain an acid solution and an alkaline solution with higher purity. However, with such a treatment method, the loss of the equipment is more 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 running and operating costs.

[0004] Therefore, there is an urgent need to provide a method and apparatus for treating wastewater containing aluminum nitrate and nitric acid (for example, aluminum nitrate foil etching waste liquid) which is economically efficient and environmentally friendly, which can extend the service life of the treatment equipment, thereby reducing running and operating costs, while also being able to recycle the wastewater to obtain products with higher economic value, thereby achieving higher economic benefits. 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 comprising aluminum nitrate and nitric acid, comprising the following steps: (1) A neutralization reaction step, comprising: reacting wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate; The reaction product containing aluminum hydroxide and sodium nitrate is subjected to solid-liquid separation to obtain aluminum hydroxide and a solution containing sodium nitrate, respectively; (2) An electrochemical membrane reactor treatment step, comprising: The solution containing sodium nitrate and the potassium salt solution obtained in step (1) are subjected to electrochemical membrane reactor treatment to obtain potassium nitrate solution and sodium salt solution, respectively, wherein the potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and a combination thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and a combination thereof, (3) a bipolar membrane electrodialysis step, comprising: 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. The acid solution is selected from a hydrochloric acid solution, a sulfuric acid solution, and a combination thereof.

[0007] In a second aspect, the present invention relates to an apparatus for treating wastewater comprising aluminum nitrate and nitric acid, comprising the following modules: (1) A neutralization reaction module, comprising: 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 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, comprising: An electrochemical membrane reactor unit is used for subjecting the solution containing sodium nitrate and the potassium salt solution obtained from the neutralization reaction module to electrochemical membrane reactor treatment to obtain potassium nitrate solution and sodium salt solution respectively, wherein the potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and a combination thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and a combination thereof, (3) A bipolar membrane electrodialysis module downstream of the electrochemical membrane reactor module, comprising: The bipolar membrane electrodialysis unit is used for treating the sodium salt solution obtained from the electrochemical membrane reactor module with bipolar membrane electrodialysis to obtain a sodium hydroxide solution and an acid solution respectively, wherein the acid solution is selected from a hydrochloric acid solution, a sulfuric acid solution, and a combination thereof.

[0008] In the above-mentioned method and apparatus according to the present invention, firstly, wastewater containing aluminum nitrate and nitric acid (for example, aluminum nitrate foil etching waste liquid) is subjected to acid-base neutralization reaction with sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide precipitation 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 a cheap potassium salt solution (i.e., potassium chloride solution, potassium sulfate solution, or a combination thereof) to obtain a sodium salt solution (i.e., sodium chloride solution, sodium sulfate solution, or a combination thereof) and a high-value, 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 also be further recycled.

[0009] The inventors unexpectedly found that by using the above-mentioned method and apparatus including a neutralization reaction process section, an electrochemical membrane reactor process section and a bipolar membrane electrodialysis process section, compared with a method and apparatus without introducing an electrochemical membrane reactor process section (i.e., only using a neutralization reaction process section and a bipolar membrane electrodialysis process section), the service life of the processing equipment, especially the bipolar membrane electrodialysis equipment, is greatly extended, thereby effectively reducing the running and operating costs. At the same time, high-value and high-purity potassium nitrate can be prepared from waste liquid and low-cost potassium salts (e.g., potassium chloride, potassium sulfate), thereby achieving higher economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solution of the present invention, the following will briefly describe the drawings required for describing the embodiments. It should be understood that the drawings are only for the convenience of technicians to understand the present invention more easily, and are not intended to limit the scope of the present invention.

[0011] Figure 1 A schematic diagram of an exemplary embodiment of the method according to the invention is shown.

[0012] Figure 2 Shows Figure 1 Schematic diagram of the electrochemical membrane reactor process in the method shown.

[0013] Figure 3 Shows Figure 1 Schematic diagram of the bipolar membrane electrodialysis process in the method shown. DETAILED DESCRIPTION

[0014] In order to make the invention purpose, technical solution and beneficial technical effect of the present application clearer, the present application will be described in detail below. It should be noted that the various aspects, features, implementation methods and advantages described in the present application may be compatible and / or may be combined together.

[0015] If not otherwise specified, the meaning of the scientific and technological terms in this specification is the same as that generally understood by those skilled in the art. In addition, unless explicitly described to the contrary, the words "comprise", "include" or "contain" will be understood to include the stated elements, but do not exclude any other elements.

[0016] 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 element, component, process step or part. Therefore, without departing from the teachings herein, the "first element", "component", "process step" or "part" discussed below may be referred to as a second element, component, process step or part.

[0017] The present invention relates to a method and an apparatus for treating wastewater containing aluminum nitrate and nitric acid.

[0018] The present invention will be described in detail below.

[0019] Process for treating wastewater containing aluminum nitrate and nitric acid

[0020] In a first aspect, the present invention relates to a method for treating wastewater comprising aluminum nitrate and nitric acid, comprising the following steps: (1) A neutralization reaction step, comprising: reacting wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate; The reaction product containing aluminum hydroxide and sodium nitrate is subjected to solid-liquid separation to obtain aluminum hydroxide and a solution containing sodium nitrate, respectively; (2) An electrochemical membrane reactor treatment step, comprising: The solution containing sodium nitrate and the potassium salt solution obtained in step (1) are subjected to electrochemical membrane reactor treatment to obtain potassium nitrate solution and sodium salt solution, respectively, wherein the potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and a combination thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and a combination thereof, (3) a bipolar membrane electrodialysis step, comprising: 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. The acid solution is selected from a hydrochloric acid solution, a sulfuric acid solution, and a combination thereof.

[0021] Each step is described in detail below.

[0022] Step (1): Neutralization reaction step Step (1) comprises reacting wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate.

[0023] In one or more embodiments, the wastewater containing aluminum nitrate and nitric acid is obtained from a process of etching electrode foil, in particular, a process of etching aluminum foil using nitric acid. For example, the wastewater containing aluminum nitrate and nitric acid is nitric acid aluminum foil etching waste liquid.

[0024] 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 portion of the nitric acid. Through the first electrodialysis treatment, the nitric acid and aluminum nitrate mixed solution can be initially separated and the nitric acid can be recovered. The concentrated solution (nitric acid solution) initially separated by electrodialysis can be returned to the front-end chemical foil etching process for recycling, thereby achieving higher economic and environmental benefits.

[0025] In a preferred further embodiment, the first electrodialysis treatment is carried out using a hydrogen ion selective exchange membrane comprising: a substrate, such as a porous substrate, such as a porous support, 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 0.8-1.2Å, such as 0.8, 0.9, 1.0, 1.1, 1.2Å, or within a range defined by any two of the above values; and the pore size of the anion exchange resin coating is 2-10Å, such as 2, 3, 4, 5, 6, 7, 8, 9, 10Å, or within a range defined by any two of the above values.

[0026] The present inventors unexpectedly found that when 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, is used, the recovery rate of nitric acid and the retention rate of aluminum ions are significantly improved.

[0027] 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.

[0028] In one or more embodiments, in the wastewater containing aluminum nitrate and nitric acid, the concentration of nitric acid is not particularly limited and may 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.

[0029] In one or more embodiments, in the wastewater containing aluminum nitrate and nitric acid, the concentration of nitrate ions is not particularly limited and may 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.

[0030] Step (1) further comprises subjecting the reaction product comprising aluminum hydroxide and sodium nitrate to solid-liquid separation to obtain aluminum hydroxide solid and a solution comprising sodium nitrate, respectively. The specific method of solid-liquid separation is not particularly limited in principle, and those skilled in the art can select a suitable solid-liquid separation method according to actual needs, for example, solid-liquid separation can be selected from one or more of precipitation (e.g., flocculation precipitation), clarification and filtration (e.g., multi-media filtration, ultrafiltration and plate and frame filter press). In a preferred embodiment, solid-liquid separation includes one or more selected from flocculation precipitation, multi-media filtration, and ultrafiltration.

[0031] 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, and can also be sold to water treatment institutions for use as a water treatment aid, thereby solving the solid waste disposal problem of aluminum hydroxide and avoiding the waste of by-products.

[0032] Step (2): Electrochemical membrane reactor treatment step Step (2) comprises subjecting the solution containing sodium nitrate obtained from step (1) and the potassium salt solution to electrochemical membrane reactor treatment to obtain potassium nitrate solution and sodium salt solution, respectively. The potassium salt solution can be selected from potassium chloride solution, potassium sulfate solution, and a combination thereof, preferably potassium sulfate solution. Accordingly, the sodium salt solution can be selected from sodium chloride solution, sodium sulfate solution, and a combination thereof, preferably sodium sulfate solution.

[0033] The electrochemical membrane reactor treatment described herein is also referred to as displacement electrodialysis 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, wherein the cations are subjected to the electric field force to migrate toward the cathode side, and the anions are subjected to the electric field force to migrate toward the anode side. When the cations encounter the cation exchange membrane while traveling, the cations can pass through, and when the cations encounter the anion exchange membrane while traveling, the cations are blocked and impermeable. When the anions encounter the anion exchange membrane while traveling, the anions can pass through, and when the anions encounter the cation exchange membrane while traveling, the anions are blocked and impermeable. The electrochemical membrane reactor process utilizes this principle to achieve the redistribution of the anions and cations therein, thereby enabling the realization of some products that are not convenient for the production of the double decomposition reaction method.

[0034] In one or more embodiments, in the electrochemical membrane reactor process, 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 while protecting the membrane stack and preventing the membrane stack from being overloaded.

[0035] In one or more embodiments, in the electrochemical membrane reactor process, the current density is controlled to be 200A / m 2 Up to 400A / m 2 , preferably 300A / m 2 Up to 400A / m 2 , for example 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, further reducing the energy consumption of the equipment.

[0036] In one or more embodiments, in step (2), before the electrochemical membrane reactor treatment, the solution containing sodium nitrate obtained in step (1) is pretreated to remove at least a portion 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. For example, the solution containing sodium nitrate obtained in step (1) can be softened, such as 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.

[0037] In one or more embodiments, in the electrochemical membrane reactor treatment, the concentration of the potassium salt solution used is not particularly limited and may be 10-20 wt %, for example, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 wt % or within the range defined by any two of the above values.

[0038] 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, the contents of which are incorporated herein by reference in their entirety.

[0039] The inventors unexpectedly discovered that when an electrochemical membrane reactor treatment step is introduced between the neutralization reaction step and the bipolar membrane electrodialysis step, the service life of the treatment equipment, especially the bipolar membrane electrodialysis equipment, is greatly extended compared to 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), thereby effectively reducing the running and operating costs, while also being able to prepare high-value and high-purity potassium nitrate from waste liquid and inexpensive potassium salts (e.g., potassium chloride).

[0040] In addition, the process cost of the electrochemical membrane reactor treatment process is very low, and the equipment occupies a small area. One person can operate it independently, and it is easy to operate. The preparation of potassium nitrate with electrochemical membrane reactor treatment technology can reduce production energy consumption. The experimental theoretical calculation shows that the energy consumption is reduced by more than 20%, and the product purity is improved. The purity can reach more than 99.9%, thereby reducing the purification process, improving production efficiency, reducing production costs, and avoiding membrane pollution to a certain extent. At the same time, it also solves the disposal problem of sodium nitrate obtained in the neutralization reaction step.

[0041] Step (3): Bipolar membrane electrodialysis step Step (3) comprises subjecting the sodium salt solution obtained from step (2) to bipolar membrane electrodialysis to obtain a sodium hydroxide solution and an acid solution, respectively, wherein the acid solution is selected from a hydrochloric acid solution, a sulfuric acid solution, and a combination thereof.

[0042] In a preferred embodiment, the sodium hydroxide solution obtained from step (3) is used for the sodium hydroxide solution used in step (1). The sodium hydroxide obtained by bipolar membrane electrodialysis is returned to the neutralization reaction step to react with the aluminum foil etching waste liquid with nitric acid, and the entire process flow is circulated in this way. This not only solves the problem of disposal of by-products, but also ensures the input and consumption of materials required for the process. The process forms a perfect closed loop and achieves higher economic and environmental benefits.

[0043] The acid solution obtained by bipolar membrane electrodialysis can be returned to the front-end etching process to prepare hydrochloric acid etching solution or sulfuric acid etching solution to participate in the preparation of electrode foil, or it can 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 foil, especially the process of etching electrode foil using nitric acid, and the acid solution obtained from step (3) is used in the process of etching electrode foil, especially the process of etching electrode foil using nitric acid.

[0044] 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 carried out using a bipolar membrane electrodialyzer as described in CN107298450B, the contents of which are incorporated herein by reference in their entirety.

[0045] By introducing the bipolar membrane electrodialysis step, the sodium chloride and / or sodium sulfate by-products of the electrochemical membrane reactor treatment step are disposed of, and acid and sodium hydroxide are prepared to produce high value-added products. At the same time, the obtained acid 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 reducing the economic cost of the entire process.

[0046] The following will be combined Figures 1 to 3 An exemplary embodiment of a method for treating wastewater containing aluminum nitrate and nitric acid according to the present invention is described.

[0047] from Figure 1 It can be seen that the whole process consists of three stages: neutralization reaction, electrochemical membrane reactor treatment and bipolar membrane electrodialysis.

[0048] In the first process section (neutralization reaction process section), the raw materials are nitric acid and aluminum nitrate mixed electrode foil etching solution (mainly composed of nitrate ions and aluminum ions). First, the nitric acid and aluminum nitrate solutions after the chemical foil etching treatment are 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 passed into the desalting liquid chamber of the electrodialysis equipment, and pure water is added to the concentration liquid chamber of the electrodialysis equipment. The polar liquid uses sodium sulfate solution, the power is turned on, and the flow pressure balance is adjusted. At this time, H +The nitric acid migrates from the desalting liquid chamber to the concentrating liquid chamber through the cation exchange membrane. The nitric acid concentration in the desalting liquid chamber decreases, while the nitric acid concentration in the concentrating liquid chamber increases, completing the preliminary separation of the nitric acid and aluminum nitrate mixture. The recovery rate of nitric acid can reach about 90%. The concentrated solution (nitric acid solution) initially separated by electrodialysis is returned to the front-end chemical foil corrosion process for use. Then, the desalting liquid (aluminum nitrate and nitric acid mixture mainly composed of aluminum nitrate) and sodium hydroxide solution with a molar ratio of 1:3 are placed in a reaction tank to cause a neutralization reaction to generate 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, the rapid mixer is placed in the mixing tank, and the coagulant is added to the mixing pond at the same time. The rapid mixer is turned on to allow the coagulant to disperse quickly and be fully and evenly mixed with the raw water in the mixing tank to form small flocs; the pre-coagulated mixed solution flows to the bottom of the diversion barrel in the reaction tank, and the mixed solution, reflux precipitation and coagulant aid are evenly mixed from bottom to top by the stirring paddle in the diversion barrel, and the flocculant is placed in advance under the agitator; at the same time, continuous external precipitation reflux is carried out from the precipitation concentration area to the reaction area, so that the concentration of aluminum hydroxide precipitation reaches the maximum value, thereby improving the flocculation effect; the flocculants formed in the reaction zone The alum flocs enter the sedimentation zone slowly, slowing down the flow rate to avoid damage to the alum flocs. The flocculated alum flocs gather into sludge and concentrate in the lower part of the sedimentation tank. An inclined plate is set at the upper part of the sedimentation zone to remove the alum flocs carried by the rising water flow, thereby ensuring the quality of the effluent. The sedimentation concentration zone ensures the slow flocculation required for the growth of the alum flocs, and the generated alum flocs have a higher density. A scraper is placed in the middle of the sedimentation zone. The scraper can continuously scrape and 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 set at the bottom of the sludge hopper. Part of the concentrated sludge is pumped to the entrance of the reaction tank by the sludge circulation pump in the concentration zone, and the other part of the remaining sludge is pumped out by the sludge pump and sent to the sludge dehydration room for treatment. Then the obtained solution is subjected to multi-media filtration, and the obtained sodium nitrate solution is put into the raw water tank of the ultrafiltration device, and the switch of the ultrafiltration device is turned on to obtain a relatively pure sodium nitrate solution. At the same time, the aluminum hydroxide precipitate obtained can be collected and retained as a water treatment additive in the future, or it can be sold to some water treatment institutions for use as a water treatment additive. This solves the solid waste disposal problem of aluminum hydroxide and avoids the waste of by-products.

[0049] In the second process section (electrochemical membrane reactor treatment process section, the specific process is as follows Figure 2 As shown in ), the sodium nitrate solution obtained by ultrafiltration in the first process stage is added to a water quality filtration device filled with ion exchange resin, and 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 is ready to be passed into the electrochemical membrane reactor equipment for testing. Figure 2As shown in , the sodium nitrate solution and the prepared potassium chloride solution and / or potassium sulfate solution of the same concentration and volume as the sodium nitrate solution are added to the No. 7 and No. 9 circulation boxes of the electrochemical membrane reactor device, respectively, and the same volume of pure water is added to the No. 6 and No. 8 circulation boxes, respectively. After all the solutions and water are added, all the circulating water pump valves are opened, the pure water in the No. 6 circulation box is pumped into chamber 2, the sodium nitrate solution in the No. 7 circulation box is pumped into chamber 3, the pure water in the No. 8 circulation box is pumped into chamber 4, and the potassium chloride and / or potassium sulfate solution in the No. 9 circulation box is pumped into chambers 1 and 5. The DC power supply 10 is turned on to apply a DC current to the membrane stack of the electrochemical membrane reactor device, and the rectifier is adjusted so that the inter-membrane voltage of the entire membrane stack is less than or equal to 10V. The output current is maintained at a constant 8A until the entire process is completed. At this time, the K in chamber 1 is + The NO3 in chamber 3 enters chamber 2 through the cation exchange membrane CEM. - Enters chamber 2 through the anion exchange membrane AEM. At this time, NO3 - and K + The potassium nitrate (KNO3) generated by the reaction flows back to the circulation box 6; at the same time, the Na + The Cl in chamber 5 enters chamber 4 through the cation exchange membrane CEM. - and / or SO4 2- Entering into chamber 4 through anion exchange membrane AEM, at this time, Na in chamber 4 + and Cl - The reaction produces sodium chloride (NaCl) and / or Na + and SO4 2- The reaction generates sodium sulfate (Na2SO4) and flows back to the circulation box 8. At this point, a group of reactions is completed. Each four chambers form a group of reaction units. During the electrochemical membrane reactor treatment process, the membrane surface flow rate is controlled at 4cm / s~5cm / s. At this time, a higher treatment efficiency can be achieved without increasing the load on the membrane stack. At the same time, the current density is controlled to be maintained at 350A / m 2, and found that the current efficiency of the electrochemical membrane reactor treatment is optimal at this time, achieving 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 processing equipment can be extended, thereby reducing the running and operating costs. At the same time, low-value potassium chloride or potassium sulfate can be used to produce high-value potassium nitrate products, achieving higher economic benefits. In addition, the process cost of this section of the process is very low and the equipment occupies a small area. One person can operate independently, and the operation is easy. The low-concentration potassium chloride solution or low-concentration potassium sulfate solution on the fresh water side after treatment by the electrochemical membrane reactor 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. Such continued reuse also avoids the disposal problem of low-concentration fresh water and reduces the amount of pure water used, avoiding resource waste and cost increase problems. The sodium nitrate solution produced 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 continues to return 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, so that the disposal problem of low-concentration sodium nitrate on the fresh water side is also solved.

[0050] In the third process section (bipolar membrane electrodialysis process section, the specific process is as follows Figure 3 In the process shown in FIG. 1 , the byproduct sodium chloride (NaCl) solution and / or sodium sulfate (Na2SO4) solution obtained in the second process stage are used as production raw materials to prepare hydrochloric acid (HCl) and / or sulfuric acid (H2SO4) and sodium hydroxide (NaOH) through a bipolar membrane electrodialysis device. Figure 3 As shown in , the sodium chloride solution and / or sodium sulfate solution obtained in the second process section is first added to the No. 12 circulation box of the bipolar membrane electrodialysis equipment, and an equal volume of pure water is added to the No. 11 circulation box and the No. 13 circulation box. After all the solutions and water have been added, all the circulating water pump valves are opened. At this time, the feed liquid in the circulation box enters the membrane stack, and the flow rate and pressure on the side of the sodium chloride solution and / or sodium sulfate solution are mainly adjusted to balance the pressure of each line with the salt solution side. At this time, turn on the DC power supply 19, adjust the rectifier so that the output current is maintained at a constant current of 12.6A 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 in the No. 12 circulation box enters the No. 16 chamber, and is decomposed into Na under the action of the DC electric field. + and Cl - and / or Na + and SO4 2- , Na + Entering chamber 17 through the cation exchange membrane (CEM), Cl - and / or SO4 2-The charged ions enter the chamber 15 through the anion exchange membrane (AEM). Since the DC power supply applies voltages in opposite directions to both sides of the bipolar membrane (BP) stack, the charged ions diffuse to the outside through the anion exchange membrane and the cation exchange layer, respectively, forming a high potential gradient in the hydrophilic layer and starting to electrolyze water, producing H + and OH - , H + Under the action of the electric field, it migrates to the peripheral chamber 15 (18) and the Cl - Reacts to produce hydrochloric acid (HCl) and / or SO4 2- The reaction produces sulfuric acid (H2SO4). - Under the action of the electric field, it migrates to the peripheral chamber 17 (14) and interacts with the Na + The reaction generates sodium hydroxide (NaOH). The hydrochloric acid (HCl) and / or sulfuric acid (H2SO4) produced by bipolar membrane electrodialysis are returned to the front-end etching process to prepare hydrochloric acid etching solution and / or sulfuric acid etching solution, participate in the preparation of electrode foil, and can also be sold as an acid solution to generate economic benefits; the generated sodium hydroxide (NaOH) can be used to return to the first process stage to react with nitric acid aluminum foil etching waste liquid, and the entire process flow is circulated in this way, which solves the problem of by-product disposal, and also ensures the input and consumption of materials required for the process, and the process forms a perfect closed loop.

[0051] Apparatus for treating wastewater containing aluminum nitrate and nitric acid

[0052] In a second aspect, the present invention relates to an apparatus for treating wastewater comprising aluminum nitrate and nitric acid, comprising the following modules: (1) A neutralization reaction module, comprising: 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 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, comprising: An electrochemical membrane reactor unit is used for subjecting the solution containing sodium nitrate and the potassium salt solution obtained from the neutralization reaction module to electrochemical membrane reactor treatment to obtain potassium nitrate solution and sodium salt solution respectively, wherein the potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and a combination thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and a combination thereof, (3) A bipolar membrane electrodialysis module downstream of the electrochemical membrane reactor module, comprising: The bipolar membrane electrodialysis unit is used for treating the sodium salt solution obtained from the electrochemical membrane reactor module with bipolar membrane electrodialysis to obtain a sodium hydroxide solution and an acid solution respectively, wherein the acid solution is selected from a hydrochloric acid solution, a sulfuric acid solution, and a combination thereof.

[0053] Each module will be described in detail below.

[0054] Module (1): Neutralization reaction module The device according to the present invention comprises a module (1), namely a neutralization reaction module.

[0055] Module (1) comprises a neutralization reaction unit, which is used to react wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate.

[0056] In one or more embodiments, the apparatus according to the present invention further comprises a corrosion electrode foil module upstream of the neutralization reaction module, wherein the corrosion electrode foil module is used to provide wastewater containing aluminum nitrate and nitric acid.

[0057] 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 a 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 portion of the 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 chemical foil corrosion process for recycling, thereby achieving higher economic and environmental benefits.

[0058] In a preferred further embodiment, the first electrodialysis unit comprises a hydrogen ion selective exchange membrane for performing the first electrodialysis treatment, the hydrogen ion selective exchange membrane comprising: a substrate, for example a porous substrate, such as a porous support, 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 0.8-1.2Å, such as 0.8, 0.9, 1.0, 1.1, 1.2Å, or within a range defined by any two of the above values; and the pore size of the anion exchange resin coating is 2-10Å, such as 2, 3, 4, 5, 6, 7, 8, 9, 10Å, or within a range defined by any two of the above values.

[0059] The present inventors unexpectedly found that when 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, is used, the recovery rate of nitric acid and the retention rate of aluminum ions are significantly improved.

[0060] 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 suitable solid-liquid separation equipment according to actual needs. For example, the solid-liquid separation unit may include one or more selected from a precipitation device (such as a high-density tank), a clarification device, and a filtration device (such as a multi-media filter, an ultrafilter, and a plate-and-frame filter press). In a preferred embodiment, the solid-liquid separation unit includes one or more selected from a high-density tank, a multi-media filter, and an ultrafilter.

[0061] 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 additive, and can also be sold to water treatment institutions for use as a water treatment additive, thereby solving the solid waste disposal problem of aluminum hydroxide and avoiding the waste of by-products.

[0062] Module (2): Electrochemical membrane reactor module The device according to the invention comprises a module (2), namely an electrochemical membrane reactor module (also called displacement electrodialysis module) downstream of a neutralization reaction module.

[0063] Module (2) includes an electrochemical membrane reactor unit, which is used to subject the solution containing sodium nitrate and the potassium salt solution obtained from the neutralization reaction module to electrochemical membrane reactor treatment to obtain potassium nitrate solution and sodium salt solution respectively, wherein the potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and a combination thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and a combination thereof.

[0064] The electrochemical membrane reactor unit may include an electrochemical membrane reactor device (also referred to as a displacement electrodialysis device), such as a 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 a diaphragm (anion exchange membrane and cation exchange membrane), a partition, an electrode plate, a foaming material, a pressing plate, a frame, and a locking (or hydraulic locking) device. The membrane stack may include an anion exchange membrane and a cation exchange membrane, wherein the anion exchange membrane and the cation exchange membrane are alternately arranged and form an intermembrane chamber. 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, wherein the cations are subjected to an electric field force to migrate to the cathode side, and the anions are subjected to an electric field force to migrate to the anode side. When the cations encounter the cation exchange membrane while traveling, the cations can be penetrated, and when the cations encounter the anion exchange membrane while traveling, the cations are blocked and impermeable. When the anions encounter an anion exchange membrane during their travel, the anions can pass through, and when the anions encounter a cation exchange membrane during their travel, the anions are blocked and cannot pass through. The solution containing sodium nitrate and the potassium salt solution are ion exchanged in the ion exchange membrane array.

[0065] 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 electrochemical membrane reactor treatment to remove at least a portion of impurities, wherein 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.

[0066] The inventors unexpectedly discovered that when an electrochemical membrane reactor module is introduced into a neutralization reaction module and a bipolar membrane electrodialysis module, the service life of the processing equipment, especially the bipolar membrane electrodialysis equipment, is greatly extended compared to the case where no electrochemical membrane reactor module is introduced (i.e., only the neutralization reaction module and the bipolar membrane electrodialysis module are used), thereby effectively reducing the running and operating costs, while also being able to prepare high-value and high-purity potassium nitrate from waste liquid and inexpensive potassium salts (e.g., potassium chloride).

[0067] In addition, the electrochemical membrane reactor equipment occupies a small area and can be operated independently by one person, which is easy to operate. The use of electrochemical membrane reactor modules to prepare potassium nitrate can reduce production energy consumption. The experimental theoretical calculation shows that the energy consumption is reduced by more than 20%, and the product purity is improved. The purity can reach more than 99.9%, thereby reducing the purification process, improving production efficiency, reducing production costs, and avoiding membrane pollution to a certain extent. At the same time, it also solves the disposal problem of sodium nitrate obtained from the neutralization reaction module.

[0068] Module (3): Bipolar membrane electrodialysis module The device according to the invention comprises a module (3), namely a bipolar membrane electrodialysis module, downstream of an electrochemical membrane reactor module.

[0069] The module (3) comprises a bipolar membrane electrodialysis unit, which is used to subject the sodium salt solution obtained from the electrochemical membrane reactor module to bipolar membrane electrodialysis treatment to obtain a sodium hydroxide solution and an acid solution, respectively. The acid solution is selected from a hydrochloric acid solution, a sulfuric acid solution, and a combination thereof.

[0070] 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 a core component of the device, generally composed of a cation exchange layer, an anion exchange layer and an interface hydrophilic layer therebetween.

[0071] In a preferred embodiment, the device according to the present invention further comprises a first pipeline connecting the bipolar membrane electrodialysis module and the neutralization reaction module, and the 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 flow is circulated in this way, which not only solves the problem of 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.

[0072] In a preferred embodiment, the device according to the present invention 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; and 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.

[0073] By introducing a bipolar membrane electrodialysis module, the sodium chloride and / or sodium sulfate by-products of the electrochemical membrane reactor module are disposed of, and acid and sodium hydroxide are prepared to produce high value-added products. At the same time, the obtained acid and sodium hydroxide can be returned to the front-end process for recycling, forming a closed process loop, achieving the goal of green and environmentally friendly resource-based production, and reducing the economic cost of the entire process.

[0074] Example

[0075] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0076] Hereinafter, unless otherwise specified, the contents or concentrations mentioned are all based on mass.

[0077] 1. Evaluation Experiment of Running Time Experimental equipment and operating conditions:

[0078] The main experimental equipment and operating conditions used in the following Example 1 and Comparative Example 1 are as follows: 1. The first electrodialysis equipment The model is CH-0, purchased from Hangzhou Jiangrongdao Environmental Technology Co., Ltd. Basic operating conditions: Operating temperature 25℃-35℃, given current density 300-400A / m 2 , the inter-membrane voltage for each pair of membranes is less than or equal to 0.5V; the membrane surface flow rate is 7.5-10cm / s.

[0079] 2. Electrochemical reactor equipment The model is CHE-0, purchased from Hangzhou Jiangrongdao Environmental Technology Co., Ltd. Basic operating conditions: Operating temperature 25℃-35℃, given current density 200-400A / m 2 , the inter-membrane voltage for each pair of membranes is less than or equal to 0.5V; the membrane surface flow rate is 5-10cm / s.

[0080] 3. Bipolar membrane electrodialysis equipment The model is BP-0, purchased from Hangzhou Jiangrongdao Environmental Technology Co., Ltd. Basic operating conditions: Operating temperature 25℃-35℃, given current 600-800A / m 2 The inter-membrane voltage of each pair of membranes is between 1.2V-1.8V, and the membrane surface flow rate is 5cm / s.

[0081] Example 1

[0082] The mixed etching solution of nitric acid and aluminum nitrate (mainly composed of nitrate ions and aluminum ions) after the chemical foil etching treatment is used as a raw material to undergo the three-stage process (neutralization reaction, electrochemical reactor and bipolar membrane electrodialysis process) as described below.

[0083] In the first process, the mixed etching solution of nitric acid and aluminum nitrate after the etching treatment of the chemical foil is collected and used as the raw water of the first electrodialysis device for desalination and concentration treatment. In the desalination and concentration treatment, the above-mentioned etching solution is passed into the desalting liquid chamber of the first electrodialysis device, and pure water is added to the concentration liquid chamber of the first electrodialysis device. The polar liquid is sodium sulfate solution, the power is turned on, and the flow pressure balance is adjusted. At this time, H + The nitric acid migrates from the desalting liquid chamber to the concentrating liquid chamber through the cation exchange membrane, the nitric acid concentration in the desalting liquid chamber decreases, and the nitric acid concentration in the concentrating liquid chamber increases, completing the preliminary separation of nitric acid and aluminum nitrate mixed solution, and the recovery rate of nitric acid reaches about 90%. The concentrated solution (nitric acid solution) initially separated by the first electrodialysis is returned to the front-end chemical foil corrosion process for use, and the desalting liquid (aluminum nitrate and nitric acid mixed solution mainly composed of aluminum nitrate) and sodium hydroxide solution with a molar ratio of 1:3 are placed in a reaction tank to cause a neutralization reaction to generate 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, the rapid mixer is placed in the mixing tank, and the coagulant is added to the mixing tank at the same time. The rapid mixer is turned on to allow the coagulant to disperse quickly and be fully and evenly mixed with the raw water in the mixing tank to form small flocs; the pre-coagulated mixed solution flows to the bottom of the diversion barrel in the reaction tank, and the mixed solution, reflux precipitation and coagulant aid are evenly mixed from bottom to top by the stirring paddle in the diversion barrel, and the flocculant is placed in advance under the agitator; at the same time, continuous external precipitation reflux is carried out from the precipitation concentration area to the reaction area, so that the concentration of aluminum hydroxide precipitation reaches the maximum value, thereby improving the flocculation effect; the flocculent aluminum hydroxide formed in the reaction area The alum flocs enter the sedimentation area slowly, slowing down the flow rate to avoid damage to the alum flocs. The flocculated alum flocs gather into sludge and concentrate in the lower part of the sedimentation tank; an inclined plate is set at the upper part of the sedimentation area, which can remove the alum flocs entrained by the rising water flow, thereby ensuring the quality of the effluent; the sedimentation concentration area ensures the slow flocculation required for the growth of the alum flocs, and the generated alum flocs have a higher density. A scraper is placed in the middle of the sedimentation area. The function of the scraper is to continuously scrape and promote the concentration of the sludge in the sedimentation area, and at the same time push the sludge to the sludge hopper. A sludge pump is set at the bottom of the sludge hopper. Part of the concentrated sludge is pumped to the entrance of the reaction tank by the sludge circulation pump in the concentration area, and the other part of the remaining sludge is pumped out by the sludge pump and sent to the sludge dehydration room for treatment. Then the obtained solution is subjected to multi-media filtration, and the obtained sodium nitrate solution is put into the raw water tank of the ultrafiltration device, and the switch of the ultrafiltration device is turned on to obtain a relatively pure sodium nitrate solution. At the same time, the obtained aluminum hydroxide precipitate is collected and reserved as a water treatment additive.

[0084] In the second process, the sodium nitrate solution obtained in the first 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 sodium nitrate are respectively added to the two raw water circulation tanks of the electrochemical reactor equipment, and an equal volume of pure water is added to the two produced water circulation tanks. After all the solutions and water are added, open all the circulating water pump valves, adjust the circulation flow rate and pressure to stabilize, then turn on the DC power supply to apply DC current to the membrane stack of the electrochemical 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 is maintained at a constant 8A until the entire process is completed. At this time, K + Through the cation exchange membrane, NO3 - Through the anion exchange membrane, the two react to produce potassium nitrate (KNO3) with a purity of 99.5%; at the same time, Na + Through the cation exchange membrane, Cl - or SO4 2- Through the anion exchange membrane, the two react to form sodium chloride (NaCl) or sodium sulfate (Na2SO4).

[0085] In the third process, the sodium chloride (NaCl) solution or sodium sulfate (Na2SO4) solution prepared as a byproduct of the second process is used as a production raw material to prepare hydrochloric acid (HCl) or sulfuric acid (H2SO4) and sodium hydroxide (NaOH) through a bipolar membrane electrodialysis device. First, the sodium chloride solution or sodium sulfate solution obtained in the second process is added to the salt solution circulation box of the bipolar membrane electrodialysis device, and an equal volume of pure water is added to the acid circulation box and the alkali circulation box. After all solutions and water are added, all circulating water pump valves are opened. At this time, the feed liquid in the circulation box enters the membrane stack, and the flow rate and pressure on the salt solution (sodium chloride or sodium sulfate solution) side are mainly used to adjust the pressure of each line to balance with the salt solution side. At this time, the DC power supply is turned on, and the rectifier is adjusted so that the output current is maintained at 12.6A cross-flow operation throughout the process, and the inter-membrane voltage is controlled to be less than or equal to 20V. At this time, the sodium chloride solution or sodium sulfate solution enters the chamber and is decomposed into Na under the action of the DC electric field. + and Cl - Or Na + and SO4 2- , Na + Through the cation exchange membrane (CEM), Cl - and / or SO4 2-Since the DC power supply applies voltages in opposite directions to both sides of the bipolar membrane (BP) stack, the charged ions diffuse to the outside through the anion exchange membrane and the cation exchange layer, respectively, forming a high potential gradient in the hydrophilic layer and starting to electrolyze water, producing H + and OH - , H + Under the action of the electric field, the Cl - Reacts to generate hydrochloric acid (HCl) or SO4 2- The reaction produces sulfuric acid (H2SO4). - Under the action of the electric field, the Na + The reaction produces sodium hydroxide (NaOH).

[0086] Comparative Example 1

[0087] The same nitric acid and aluminum nitrate mixed etching solution (mainly composed of nitrate ions and aluminum ions) that has been subjected to chemical foil etching treatment as in Example 1 is used as a raw material and subjected to the two-stage process (neutralization reaction and bipolar membrane electrodialysis process) as described below.

[0088] In the first process, the mixed etching solution of nitric acid and aluminum nitrate after the corrosion treatment of the chemical foil is collected and then placed in a reaction tank with a sodium hydroxide solution to cause a neutralization reaction to generate 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 the 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 allow the coagulant to disperse quickly and mix fully and evenly with the raw water in the mixing tank to form small flocs; the pre-coagulated mixed solution flows to the bottom of the diversion barrel in the reaction tank, and the mixed solution, reflux precipitation and coagulant aid are mixed evenly from bottom to top by the stirring paddle in the diversion barrel, and the flocculant is placed in advance under the agitator; at the same time, continuous external precipitation reflux is carried out from the precipitation concentration area to the reaction area, so that the concentration of aluminum hydroxide precipitation reaches the maximum value, thereby improving the flocculation effect; the flocculent aluminum hydroxide formed in the reaction area The alum flocs enter the sedimentation area slowly, slowing down the flow rate to avoid damage to the alum flocs. The flocculated alum flocs gather into sludge and concentrate in the lower part of the sedimentation tank; an inclined plate is set at the upper part of the sedimentation area, which can remove the alum flocs carried by the rising water flow, thereby ensuring the quality of the effluent; the sedimentation concentration area ensures the slow flocculation required for the growth of the alum flocs, and the generated alum flocs have a higher density. A scraper is placed in the middle of the sedimentation area. The function of the scraper is to continuously scrape and promote the concentration of the sludge in the sedimentation area, and at the same time push the sludge to the sludge hopper. A sludge pump is set at the bottom of the sludge hopper. Part of the concentrated sludge is pumped to the entrance of the reaction tank by the sludge circulation pump in the concentration area, and the other part of the remaining sludge is pumped out by the sludge pump and sent to the sludge dehydration room for treatment. Then, the obtained solution is subjected to multi-media filtration, and the obtained sodium nitrate solution is put into the raw water tank of the ultrafiltration device, and the switch of the ultrafiltration device is turned on to obtain a relatively pure sodium nitrate solution.

[0089] In the second process, the sodium nitrate solution obtained in the first 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 obtained sodium nitrate solution is then put into a bipolar membrane electrodialysis device, and an equal volume of pure water is added to the concentrate circulation box. After all the solutions and water have been added, all the circulating water pump valves are opened. At this time, the feed liquid in the circulation box enters the membrane stack, and the flow rate and pressure on the sodium nitrate side are mainly adjusted to balance the pressure on the salt solution side. At this time, turn on the DC power supply, adjust the rectifier so that the output current is maintained at 12.6A cross-flow operation throughout the process, and control the inter-membrane voltage to be less than or equal to 20V. At this time, the sodium nitrate solution in the salt solution circulation box enters the chamber and is decomposed into Na under the action of the DC electric field. + and NO3 -Since the DC power supply applies voltages in opposite directions to both sides of the bipolar membrane (BP) stack, the charged ions diffuse to the outside through the anion exchange membrane and the cation exchange layer, respectively, forming a high potential gradient in the hydrophilic layer and starting to electrolyze water, producing H + and OH - , H + Under the action of the electric field, NO3 migrates to the peripheral chamber and - The reaction generates nitric acid. - Under the action of the electric field, it migrates to the peripheral chamber and interacts with the Na + The reaction produces sodium hydroxide.

[0090] Run time evaluation results

[0091] The hydrolysis voltage and burst strength of the bipolar membrane electrodialysis devices in Example 1 and Comparative Example 1 were measured at the initial stage of the process, after the 7th day of operation, on the 14th day of operation, and on the 30th day of operation, respectively, and the measurement results are summarized in Table 1 below.

[0092] The hydrolysis voltage used was measured as follows: 1. Prepare materials and equipment: Ion exchange membranes in bipolar membrane electrodialysis equipment Electrolyzer DC Power Supply Voltmeter and Amperemeter Electrode (such as platinum electrode) Electrolyte solution (such as Na2SO4) 2. Assemble the electrolytic cell: The ion exchange membrane is placed in the middle of the electrolytic cell to separate the anode and cathode chambers.

[0093] Add equal amounts of 100 ml of electrolyte solution to both sides.

[0094] 3. Connect the circuit: Insert the electrodes into the cathode and anode chambers respectively and connect the DC power supply, voltmeter and ammeter.

[0095] 4. Apply voltage: Gradually increase the voltage, observe the current changes, and record the voltage and current values.

[0096] 5. Observe the hydrolysis phenomenon: When the voltage reaches the hydrolysis voltage, bubbles (such as H2 and O2) are generated on the electrode and the current increases significantly.

[0097] 6. Record data: Record the voltage value when hydrolysis occurs, i.e., the hydrolysis voltage.

[0098] The burst strength measurement method used is as follows: 1. Prepare materials and equipment: Ion exchange membranes in bipolar membrane electrodialysis equipment Burst Strength Tester Fixture Pressure source (such as an air pump) Pressure Sensors 2. Sample preparation: Cut the membrane to size that fits the jig, making sure there is no damage.

[0099] 3. Install the sample: Secure the membrane in the tester's clamps, ensuring a good seal.

[0100] 4. Apply pressure: Increase the pressure gradually and observe the changes in the membrane.

[0101] 5. Record data: When the membrane ruptures, record the pressure value at that time, i.e., the bursting strength.

[0102] 6. Repeat the test: Test multiple samples and take the average value.

[0103] Table 1 Run time evaluation results

[0104] As can be seen from the results in Table 1 above, the hydrolysis voltage and burst strength of Example 1, which uses a three-stage process (neutralization reaction, electrochemical reactor and bipolar membrane electrodialysis process) to process the electroplating foil corrosion waste liquid, remain stable after 30 days of operation, and the equipment operates normally and stably, while the hydrolysis voltage of the bipolar membrane of Comparative Example 1, which uses a two-stage process (neutralization reaction and bipolar membrane electrodialysis process) to process the electroplating foil corrosion waste liquid, increases by 297% and the burst strength decreases by 3.8% when it is operated for 7 days, and the equipment can no longer be used normally after 30 days of operation. It can be seen that by introducing the electrochemical reactor process, the service life of the equipment is extended, thereby reducing the running and operating costs, and the electroplating foil corrosion waste liquid is also recycled to obtain a potassium nitrate product with high value and high purity.

[0105] Evaluation experiment of hydrogen ion selective membrane Experimental equipment and operating conditions:

[0106] The experimental equipment and operating conditions used in the following Examples 2 and 3 are as follows: Equipment model: Electrodialysis equipment, model CH-0, purchased from Hangzhou Jiangrongdao Environmental Technology Co., Ltd.; Membrane stack information: In Example 2, a hydrogen ion selective cationic membrane + a hydrogen barrier membrane purchased from Asahi Glass were used. The model of the hydrogen ion selective cationic membrane was HSFN, which had an anion exchange resin coating with a pore size of 2-10Å and a cation exchange resin coating with a pore size of 0.8-1.2Å, and the model of the hydrogen barrier membrane was AAVN; In Example 3, a hydrogen ion selective cationic membrane + a hydrogen barrier membrane purchased from PCA were used. The model of the hydrogen ion selective cationic membrane was PC FH, the pore size of the membrane surface was 10-15Å, and the model of the hydrogen barrier membrane was AAVN; Current density: maintained at 300A / m 2 Continuous operation; Inter-membrane voltage: controlled within 5V; Temperature: Use a chiller to adjust the water temperature on the desalting side and the concentration side to 25°C (±2°C); Operation requirements: Continuously add nitric acid and aluminum nitrate corrosive solution on the desalination side to ensure that the inter-membrane voltage is less than or equal to 5V; Experimental endpoint: The experimental duration reached 168 hours.

[0107] Example 2

[0108] Initially, a corrosive solution with a nitric acid concentration of 200.57 g / L and an aluminum ion concentration of 11 g / L was added to the desalination side water tank of the electrodialysis equipment (using a hydrogen ion selective cation membrane + a hydrogen barrier membrane purchased from Asahi Glass), and 2 L of pure water was added to the concentration side water tank. The polar liquid was a 3% Na2SO4 solution. The three circulation pumps were started at the same time, and the flow rate on the desalination side was adjusted to 250 L / h. The pressures of the other two routes were adjusted to be consistent with the pressure on the desalination side. The flow rates and pressures of the three circulation pumps were recorded, the rectifier was turned on, direct current was passed, and the constant current was 6.3 A. The voltage between the membranes of the membrane stack was controlled within 5 V. During the experiment, when the inter-membrane voltage is close to 5V, nitric acid and aluminum nitrate corrosive solution are continuously pumped into the desalination side to control the inter-membrane voltage to be less than or equal to 5V to allow the device to operate stably. When the conductivity of the concentrate side shows a downward trend, pure water is continuously pumped into it to balance the conductivity and prevent back migration. The experiment ends after running for 168 hours, and the acid concentration in the concentrate, the aluminum ion concentration in the concentrate, the volume of the concentrate, the acid concentration in the raw water, the aluminum ion concentration in the raw water, and the volume of the raw water consumed are recorded. The acid recovery rate and aluminum retention rate are calculated according to the following formula: Acid recovery rate = acid concentration in concentrate × concentrate volume / acid concentration in raw water × raw water volume consumed; Aluminum retention rate = 1 - aluminum ion concentration in concentrate × concentrate volume / aluminum ion concentration in raw water × raw water volume consumed.

[0109] Example 3

[0110] The experiment was carried out under exactly the same procedure and conditions as in Example 2, and the acid recovery rate and aluminum retention rate were calculated using the same method. The only difference was that the hydrogen ion selective cationic membrane + hydrogen barrier membrane purchased from PCA was used instead of the hydrogen ion selective cationic membrane + hydrogen barrier membrane purchased from Asahi Glass.

[0111] The experimental results of Example 2 and Example 3 are summarized in Table 2 below.

[0112] Table 2 Experimental results of different hydrogen ion selective membranes

[0113] It can be seen from the results in Table 2 above that, under the same experimental duration (168 hours) and the same experimental parameter conditions, compared with Example 3 using a hydrogen ion selective membrane with a pore size of 10-15Å, Example 2 using a hydrogen ion selective membrane having an anion exchange resin coating with a pore size of 2-10Å and a cation exchange resin coating with a pore size of 0.8-1.2Å achieved significantly higher acid recovery and aluminum ion retention.

[0114] The above is only an exemplary embodiment of the present invention. It should be noted that, for those skilled in the art, without departing from the inventive concept of the present invention, improvements can be made to the present invention, but these all belong to 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) A neutralization reaction step, comprising: reacting wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution to obtain a reaction product containing aluminum hydroxide and sodium nitrate; The reaction product containing aluminum hydroxide and sodium nitrate is subjected to solid-liquid separation to obtain aluminum hydroxide and a solution containing sodium nitrate, respectively; (2) An electrochemical membrane reactor treatment step, comprising: The solution containing sodium nitrate and the potassium salt solution obtained in step (1) are subjected to electrochemical membrane reactor treatment to obtain potassium nitrate solution and sodium salt solution, respectively, wherein the potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and a combination thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and a combination thereof, (3) a bipolar membrane electrodialysis step, comprising: 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. The acid solution is selected from a hydrochloric acid solution, a sulfuric acid solution, and a combination thereof.

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 for 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 an electrode foil etching process.

4. The method for treating wastewater containing aluminum nitrate and nitric acid as claimed in claim 3, wherein the acid solution obtained from step (3) is used for an electrode foil etching process.

5. A method for treating wastewater containing aluminum nitrate and nitric acid as claimed in claim 1 or 2, wherein in step (1), the wastewater containing aluminum nitrate and nitric acid is subjected to a first electrodialysis treatment to recover at least a portion of the nitric acid before reacting the wastewater containing aluminum nitrate and nitric acid with a sodium hydroxide solution.

6. The method for treating wastewater containing aluminum nitrate and nitric acid according to claim 5, wherein the first electrodialysis treatment is performed using a hydrogen ion selective exchange membrane, the hydrogen ion selective exchange membrane comprising: Base material, 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 0.8-1.2Å, and the pore size of the anion exchange resin coating is 2-10Å.

7. 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 membrane surface flow rate is 1 cm / s to 10 cm / s.

8. 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 current density is 200 A / m 2 Up to 400A / m 2 .

9. The method for treating wastewater containing aluminum nitrate and nitric acid as claimed in claim 1 or 2, wherein in step (1), solid-liquid separation comprises one or more selected from flocculation precipitation, multimedia filtration, and ultrafiltration.

10. A method for treating wastewater containing aluminum nitrate and nitric acid as described in claim 1 or 2, wherein in step (2), before being subjected to electrochemical membrane reactor treatment, the solution containing sodium nitrate obtained in step (1) is pretreated to remove at least a portion of impurities, wherein the pretreatment comprises 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.

11. An apparatus for treating wastewater containing aluminum nitrate and nitric acid, comprising the following modules: (1) A neutralization reaction module, comprising: 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 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, comprising: An electrochemical membrane reactor unit is used for subjecting the solution containing sodium nitrate and the potassium salt solution obtained from the neutralization reaction module to electrochemical membrane reactor treatment to obtain potassium nitrate solution and sodium salt solution respectively, wherein the potassium salt solution is selected from potassium chloride solution, potassium sulfate solution, and a combination thereof, and the sodium salt solution is selected from sodium chloride solution, sodium sulfate solution, and a combination thereof, (3) A bipolar membrane electrodialysis module downstream of the electrochemical membrane reactor module, comprising: The bipolar membrane electrodialysis unit is used for treating the sodium salt solution obtained from the electrochemical membrane reactor module with bipolar membrane electrodialysis to obtain a sodium hydroxide solution and an acid solution respectively, wherein the acid solution is selected from a hydrochloric acid solution, a sulfuric acid solution, and a combination thereof.

12. The apparatus for treating wastewater containing aluminum nitrate and nitric acid as claimed in claim 11, further comprising a first pipeline connecting the bipolar membrane electrodialysis module and the neutralization reaction module, the first pipeline being used to supply the sodium hydroxide solution obtained from the bipolar membrane electrodialysis module to the neutralization reaction module.

13. The apparatus for treating wastewater containing aluminum nitrate and nitric acid according to claim 11 or 12, further comprising a corrosion electrode foil module upstream of the neutralization reaction module, the corrosion electrode foil module being used to provide wastewater containing aluminum nitrate and nitric acid.

14. The apparatus for treating wastewater containing aluminum nitrate and nitric acid according to claim 11 or 12, further comprising a second pipe connecting the bipolar membrane electrodialysis module and the corrosion electrode foil module, the second pipe being used to supply the acid solution obtained from the bipolar membrane electrodialysis module to the corrosion electrode foil module.

15. An apparatus for treating wastewater containing aluminum nitrate and nitric acid as claimed in claim 11 or 12, wherein 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 a 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 portion of the nitric acid.

16. The apparatus for treating wastewater containing aluminum nitrate and nitric acid according to claim 15, wherein the first electrodialysis unit comprises a hydrogen ion selective exchange membrane to perform the first electrodialysis treatment, the hydrogen ion selective exchange membrane comprising: Base material, An anion exchange resin coating and a cation exchange resin coating on a substrate, wherein the pore size of the cation resin coating is 0.8-1.2Å, and the pore size of the anion exchange resin coating is 2-10Å.

17. The apparatus for treating wastewater containing aluminum nitrate and nitric acid as claimed in claim 11 or 12, wherein the solid-liquid separation unit comprises one or more selected from a high-density tank, a multimedia filter, and an ultrafilter.

18. An apparatus for treating wastewater containing aluminum nitrate and nitric acid as described in claim 11 or 12, wherein 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 electrochemical membrane reactor treatment to remove at least a portion of impurities, wherein 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.

Images