Strip steel pickling waste mixed acid treatment system and method for removing metal ions from waste mixed acid

Abstract

The present application relates to a strip steel pickling waste mixed acid treatment system and a method for removing metal ions in waste mixed acid, the strip steel pickling waste mixed acid treatment system comprising a strip steel pickling tank, an electrolytic tank, an anode electric plate, a cathode electric plate, a filtering device, a cathode acid storage tank and an anode acid storage tank, wherein the electrolytic tank is provided with a negative ion membrane, which separates the electrolytic tank into a cathode chamber and an anode chamber, the anode electric plate is arranged in the anode chamber, the cathode electric plate comprises at least two, one of which is arranged in the cathode chamber and the other is used as a backup, so that the metal elements reduced and attached to the cathode electric plate during electrolysis can be cleaned in time by pulling out the cathode electric plate, the cathode chamber and the filtering device are connected into a circulating loop for circulating and filtering the cathode liquid to remove the precipitate in the cathode liquid, the filtering device is also connected to the cathode acid storage tank, the anode chamber is connected to the anode acid storage tank, and the cathode acid storage tank and the anode acid storage tank are respectively connected to the strip steel pickling tank. The above-mentioned waste mixed acid treatment system can realize the removal of metal ions in waste mixed acid.

Description

Technical Field

[0001] This invention belongs to the field of waste acid treatment technology, specifically relating to a waste mixed acid treatment system for steel strip pickling waste and a method for removing metal ions from the waste mixed acid. Background Technology

[0002] During the pickling process of stainless steel, metal is continuously dissolved from the substrate in the pickling tank. When the concentration of dissolved metal reaches a critical level, the dissolved metal will precipitate and form sludge / mud, which can clog pipes, valves, and pumps, thus affecting the pickling process. Simultaneously, as the concentration of metal ions in the pickling solution gradually increases, the pickling activity gradually decreases, and the pickling efficiency also gradually declines. Therefore, the generated waste liquid needs to be treated promptly. Pickling waste liquid mainly contains a certain concentration of nitric acid, hydrofluoric acid, and a large number of metal ions. It is a highly acidic and highly toxic waste liquid with extremely strong corrosiveness. Without treatment, it will cause great harm to human health and the environment.

[0003] Currently common methods for pickling stainless steel with mixed acids include acid mist roasting and resin bed acid recovery technology. However, resin bed acid recovery technology cannot recover metal salts, and the desalinated metal salt waste liquid requires further treatment. Acid mist roasting has high installation and operation / maintenance costs, and its regeneration process is complex and requires large equipment. It is suitable for the recovery of waste mixed acids in large stainless steel enterprises, but the amount of waste mixed acid generated by small and medium-sized stainless steel enterprises is insufficient to supply the normal continuous operation of the acid mist roasting system. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a waste mixed acid treatment system for steel strip pickling and a method for removing metal ions from the waste mixed acid. This will develop a stainless steel pickling waste mixed acid regeneration process technology that is advanced and reliable, easy to operate and maintain, low in processing cost, highly automated in the control system, and free from secondary pollution. It can effectively solve the problems of high acid consumption and difficulty in waste acid recovery in small and medium-sized stainless steel enterprises.

[0005] The technical solution of this invention is: a strip steel pickling waste mixed acid treatment system, including a strip steel pickling tank, an electrolytic cell, an anode plate, a cathode plate, a filter device, a cathode acid storage tank, and an anode acid storage tank. The strip steel pickling tank is used to pickle the strip steel to remove the oxide scale on the surface of the strip steel, correspondingly forming waste mixed acid after cleaning. The electrolytic cell is equipped with an anion exchange membrane, which divides the electrolytic cell into a cathode chamber and an anode chamber. The anode plate is arranged in the anode chamber. The cathode plate includes at least two, at least one of which is inserted in the cathode chamber for electrolysis, and the other at least one is not inserted for backup, so that when the cathode plate inserted in the cathode chamber is pulled out, the backup cathode plate can be inserted into the cathode chamber. Electrolysis continues, allowing metal ions in the waste mixed acid to be reduced during the electrolysis process. The metal elements attached to the cathode plate are removed and cleaned in time, achieving uninterrupted electrolysis. The cathode chamber is connected to the filtration device to form a circulation loop, used to circulate and filter the cathode liquid to remove precipitates. The filtration device is also connected to the cathode acid storage tank, and the anode chamber is connected to the anode acid storage tank. After electrolysis, the solution in the cathode chamber is introduced into the filtration device for filtration and then enters the cathode acid storage tank, while the solution in the anode chamber enters the anode acid storage tank. The cathode acid storage tank and the anode acid storage tank are respectively connected to the steel pickling tank, so that the solutions in the cathode acid storage tank and the anode acid storage tank can enter the steel pickling tank.

[0006] A method for removing metal ions from mixed acid in steel strip pickling waste is provided, and the aforementioned mixed acid treatment system for steel strip pickling waste is disclosed. The removal method includes the following steps:

[0007] (1) The stainless steel strip is pickled in the strip pickling tank, and the resulting waste mixed acid is coarsely filtered to remove particulate matter from the waste mixed acid.

[0008] (2) Place the filtered waste mixed acid into the cathode chamber and the low-concentration nitric acid solution into the anode chamber;

[0009] (3) A cathode plate is placed in the cathode chamber and an anode plate is placed in the anode chamber. Electrolysis is started. Free nitrate ions in the waste mixed acid pass through the anion exchange membrane into the anode chamber, while fluoride ions remain in the cathode chamber. During electrolysis, metal ions in the waste mixed acid are reduced and attached to the cathode plate. The cathode plate is pulled out to clean the metal elements and metal oxides on it. When the cathode plate is pulled out, a spare cathode plate is placed into the cathode chamber. The cathode plates are replaced periodically in this way to achieve uninterrupted electrolysis.

[0010] (4) During electrolysis, the liquid in the cathode chamber is circulated and filtered through a filter device to remove the precipitate formed in the cathode chamber.

[0011] Furthermore, including (5), after electrolysis, the liquid in the cathode chamber is introduced into a filter device for filtration and then enters the cathode acid storage tank, and the liquid in the anode chamber is introduced into the anode acid storage tank.

[0012] Further, including (6), the solution from the cathode acid storage tank and the solution from the anode acid storage tank are placed into the steel pickling tank in the specified amounts.

[0013] Furthermore, in (4), the filtration process uses an external filter press, and both the chamber plate and the filter cloth are made of acid-resistant material.

[0014] Furthermore, the cathode plate is made of stainless steel, copper, or lead, and the anode plate is made of lead dioxide or platinum.

[0015] Furthermore, in (4), the precipitate obtained is a metal oxide and a metal hydroxide, and the precipitate is subjected to centrifugal dehydration treatment.

[0016] Compared to existing technologies, this invention provides a stainless steel pickling waste mixed acid treatment system. The electrolytic cell is divided into an anode chamber and a cathode chamber, separated by an anion exchange membrane. The waste mixed acid is passed into the cathode chamber, while a certain concentration of nitric acid solution is passed into the anode chamber. During electrolysis, nitrate ions pass through the anion exchange membrane into the anode chamber. Metal ions in the waste mixed acid are reduced and adhere to the cathode plate. The cathode plate can be removed to promptly clean the metal elements, and a spare cathode plate can be placed when replacing the cathode plate, improving electrolysis efficiency. Metal ions in the stainless steel pickling waste mixed acid are recovered through cathode reduction during electrolysis. Both free and combined metal ions can be removed simultaneously, resulting in a high metal ion removal rate and high purity of the obtained metal elements, metal oxides, and metal hydroxides, which are recyclable. The entire process is simple, with a short operation time. While removing metal ions, it also recovers nitric acid and hydrofluoric acid from the waste mixed acid, achieving resource reuse and significantly reducing wastewater treatment volume. Specifically, the technical effects include the following:

[0017] (1) The method for removing and recovering metal ions in stainless steel pickling waste mixed acid of the present invention reduces free and complexed metal ions to metal elements by cathode reduction in electrolysis, while releasing more free acid components.

[0018] (2) Through the integrated electromechanical mode, the cathode plate can be freely switched and lifted out for cleaning, and the obtained high-purity iron powder or iron oxide powder can be recycled.

[0019] (3) The operation time is short, the process is simple, the operation and maintenance are simple and convenient, and the processing cost is low. The processing cost is reduced by electrolytic reduction, and the metal ion removal rate is high.

[0020] (4) The waste mixed acid after metal ion removal can be reused after electrolytic treatment without secondary pollution. This achieves the effect of making full use of resources and saving energy and protecting the environment. Attached Figure Description

[0021] Figure 1This is a structural diagram of the steel strip pickling waste mixed acid treatment system of the present invention;

[0022] Figure 2 To adopt Figure 1 The flowchart shown is a method for removing metal ions from waste mixed acid in the strip pickling waste system.

[0023] Figure 3 This is a schematic diagram of the electrolytic cell in the steel strip pickling waste mixed acid treatment system of the present invention.

[0024] The annotations in the attached figures are explained as follows:

[0025] 1-Steel strip pickling tank; 2-Electrolytic cell; 3-Filtering device; 4-Cathode acid storage tank; 5-Anode acid storage tank; 21-Anion exchange membrane; 22-Cathode chamber; 23-Anode chamber; 24-Cathode plate; 25-Anode plate; 6-Metallic element. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] like Figure 1As shown, a strip steel pickling waste mixed acid treatment system includes a strip steel pickling tank 1, an electrolytic cell 2, a filter device 3, a cathode acid storage tank 4, and an anode acid storage tank 5. The strip steel pickling tank 1 is used to pickle the strip steel to remove the oxide scale on the surface of the strip steel, correspondingly forming waste mixed acid after cleaning. The electrolytic cell 2 is provided with an anion exchange membrane 21, which divides the electrolytic cell 2 into a cathode chamber 22 and an anode chamber 23. The electrolytic cell 2 also includes cathode plates 24 and anode plates 25. The anode plates 25 are disposed in the anode chamber 23. The cathode plates 24 include at least two, at least one of which is inserted into the cathode chamber 22 for electrolysis, and the other at least one is not inserted for backup, so that after the cathode plate 24 inserted in the cathode chamber 22 is pulled out, the backup cathode plate 24 can be inserted into the cathode chamber 22 to continue electrolysis, so that during electrolysis... During the process, metal ions in the waste mixed acid are reduced and the metal element 6 attached to the cathode plate 24 is removed and cleaned in time to ensure uninterrupted electrolysis in the electrolytic cell 2. The cathode chamber 22 is connected to the filter device 3 to form a circulation loop to circulate and filter the solution (also known as catholyte) in the cathode chamber 22 to remove the precipitate in the catholyte. The filter device 3 is also connected to the cathode acid storage tank 4, and the anode chamber 23 is connected to the anode acid storage tank 5. After electrolysis, the solution in the cathode chamber 22 is introduced into the filter device 3 for filtration and then enters the cathode acid storage tank 4. The solution in the anode chamber 23 enters the anode acid storage tank 5. The cathode acid storage tank 4 and the anode acid storage tank 5 are respectively connected to the steel pickling tank 1 to allow the solution in the cathode acid storage tank 4 and the anode acid storage tank 5 to enter the steel pickling tank 1, so as to realize the recycling of waste mixed acid.

[0028] When using the above-mentioned strip pickling waste mixed acid treatment system, the method for removing metal ions from the waste mixed acid includes the following steps:

[0029] (1) The strip steel pickling tank 1 pickles the strip steel to remove the oxide scale on the surface of the strip steel, and correspondingly forms the waste mixed acid after cleaning. The waste mixed acid is coarsely filtered to remove the particulate matter in the waste mixed acid. In this embodiment, the waste mixed acid after coarse filtration contains 20-200 g / L of nitric acid, 0-50 g / L of hydrofluoric acid, and 20-200 g / L of metal ions.

[0030] (2) Place the coarsely filtered waste mixed acid into the cathode chamber 22 and place a low-concentration nitric acid solution at the same level into the anode chamber 23; the initial concentration of the dilute nitric acid is 0-80 g / L.

[0031] (3) Cathode plate 24 is placed in cathode chamber 22, and anode plate 25 is placed in anode chamber 23. Electrolysis is started, and free NO3 in the mixed acid is released. - F passes through anion exchange membrane 21 and enters anode chamber 23. - Remaining in cathode chamber 22, NO3 - and F -Separation: During the electrolysis process, metal ions in the waste mixed acid are reduced and attached to the cathode plate 24. The cathode plate 24 is pulled out to clean the metal element 6 or the metal oxide formed by the metal element 6. When the cathode plate 24 is pulled out, a spare cathode plate 24 is placed into the cathode chamber. The cathode plate 24 is replaced periodically in this way to achieve uninterrupted electrolysis in the electrolytic cell 2.

[0032] Specifically, please refer to the following: Figure 3 The cathode chamber 22 contains a cathode plate 24, and the anode chamber 23 contains an anode plate 25. The cathode plate 24 can be made of stainless steel, copper, lead, etc., and the anode plate 25 can be made of lead dioxide, platinum, etc. When the electrolytic cell is energized, the current flowing through the cathode plate 24 and the anode plate 25 is 500-5000 A / m. 2 The temperature inside the tank is 30–80℃, and the electrolysis time is 8–24 hours. Through the reducing atmosphere of the cathode chamber 22, free metal ions are reduced to elemental metal 6, which adheres to the cathode plate 24, thus removing metal ions from the waste mixed acid. Simultaneously, as the concentration of metal ions decreases, they react with NO3-. - F - The chelated metal ions will gradually dissolve, releasing free metal ions, thus achieving continuous reduction, attachment, and removal of metal ions. Meanwhile, free NO3... - Recovery and enrichment are achieved in anode chamber 23, yielding a high-concentration nitric acid solution. Additionally, with the addition of NO3... - As the metal ions migrate continuously, the pH of the solution in cathode chamber 22 gradually increases, and some of the metal ions in the mixed acid form hydroxide precipitates. When the amount of elemental metal 6 adhering to cathode plate 24 reaches a certain limit, the voltage of electrolytic cell 2 will rise sharply. After reaching the rated voltage, the current begins to drop rapidly. At this time, cathode plate 24 needs to be lifted out of cathode chamber 22 for cleaning of the adhering substances. At the same time, another spare cathode plate 24 is placed into the solution. The cleaned cathode plate can be lifted back into cathode chamber 22 for reuse, and so on. Furthermore, the installation of cathode plate 24 in electrolytic cell 2 adopts a clamping structure. When replacement is needed, the button is activated to open the clamping valve, allowing cathode plate 24 to be lifted out and moved to a fixed position for cleaning. At the same time, a spare set of cathode plates 24 is replaced in electrolytic cell 2 for electrolysis.

[0033] Cathode chamber 22 is affected by metal ions and free NO3. - As the concentration gradually decreases, the metal ions and acid radicals that are in a combined state gradually decompose, releasing free NO3. - F - Due to the selective permeability of the anion exchange membrane 21, NO3 - Priority passage, NO3 - A large amount entered the anode chamber 23, F -A large amount of hydrofluoric acid remains in cathode chamber 22, causing a significant increase in the concentration of hydrofluoric acid and a substantial decrease in the concentration of metal ions. The solution in cathode chamber 22 can be essentially considered a hydrofluoric acid solution containing a small amount of metal ions. Correspondingly, a high concentration of nitric acid will be obtained in the solution in anode chamber 23, thus achieving NO3-. - and F - The separation and recovery of combined acids and free acids are also achieved simultaneously.

[0034] (4) During electrolysis, the liquid in the cathode chamber 22 is circulated and filtered through the filter device 3 to remove the precipitate formed in the cathode chamber 22. The cathode chamber 22 is connected to the filter device 3, and the filtered liquid flows back to the cathode chamber 22 to realize the circulated filtration of the waste acid in the cathode chamber 22. The filter adopts an external filter press, and the chamber plate and filter cloth are made of acid-resistant material, so that the precipitate continuously generated in the cathode chamber 22 can be removed.

[0035] Further, including step (5), after electrolysis, the catholyte in cathode chamber 22 is introduced into filter device 3 for filtration and then pumped into cathode acid storage tank 4 to obtain a high-purity hydrofluoric acid solution with a concentration of 10-100 g / L. The anolyte in anode chamber 23 is introduced into anode acid storage tank 5 to obtain a high-purity nitric acid solution with a concentration of 50-400 g / L. The final waste mixed acid in cathode chamber 22 contains 0-10 g / L of metal ions and 10-100 g / L of hydrofluoric acid, which can be returned to the mixed acid tank as a high-purity hydrofluoric acid solution.

[0036] Further, including step (6), the solution in the cathode acid storage tank 4 and the solution in the anode acid storage tank 5 are mixed in the correct amount and placed into the mixed acid tank, and the mixed acid in the mixed acid tank is placed into the steel strip pickling tank 1 to realize the recycling of waste mixed acid from the steel strip pickling line.

[0037] Furthermore, the high-purity metal oxides obtained from the cleaning process and the high-purity metal hydroxides obtained from filtration are centrifuged and dehydrated for recycling.

[0038] In summary, the steel strip pickling waste mixed acid treatment system provided by this invention has an electrolytic cell divided into an anode chamber and a cathode chamber, separated by an anion exchange membrane. The waste mixed acid is passed into the cathode chamber, while a certain concentration of nitric acid solution is passed into the anode chamber. During electrolysis, nitrate ions pass through the anion exchange membrane into the anode chamber. Metal ions in the waste mixed acid are reduced and adhere to the cathode plate. The cathode plate can be removed to promptly clean the metal elements, and a spare cathode plate can be placed when replacing the cathode plate, improving electrolysis efficiency. The metal ions in the stainless steel pickling waste mixed acid are recovered through cathode reduction during electrolysis. Both free and combined metal ions can be removed simultaneously, resulting in a high metal ion removal rate and high purity of the obtained metal oxides and metal hydroxides, which are recyclable. The entire process is simple, with a short operation time. While removing metal ions, it can also recover nitric acid and hydrofluoric acid from the waste mixed acid, achieving resource reuse and significantly reducing the amount of wastewater to be treated.

[0039] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are also included in the same way.

Claims

1. A system for treating mixed acid waste from steel strip pickling, characterized in that: The system includes a steel strip pickling tank, an electrolytic cell, an anode plate, a cathode plate, a filter, a cathode acid storage tank, and an anode acid storage tank. The steel strip pickling tank is used to pickle steel strip to remove oxide scale from its surface, correspondingly forming waste mixed acid after cleaning. The electrolytic cell is equipped with an anion exchange membrane, dividing the cell into a cathode chamber and an anode chamber. The anode plate is disposed in the anode chamber. At least two cathode plates are included, at least one of which is inserted into the cathode chamber for electrolysis, while the other at least one is not inserted for backup. This backup cathode plate is inserted into the cathode chamber to continue electrolysis after the cathode plate inserted in the cathode chamber is removed, ensuring that during the electrolysis process… Metal ions in the waste mixed acid are reduced and the elemental metals attached to the cathode plate are removed and cleaned in time to achieve uninterrupted electrolysis in the electrolytic cell. The cathode chamber and the filter device are connected to form a circulation loop to circulate and filter the cathode liquid to remove the precipitate in the cathode liquid. The filter device is also connected to the cathode acid storage tank, and the anode chamber is connected to the anode acid storage tank so that after electrolysis, the solution in the cathode chamber is introduced into the filter device for filtration and then enters the cathode acid storage tank, and the solution in the anode chamber enters the anode acid storage tank. The cathode acid storage tank and the anode acid storage tank are respectively connected to the steel pickling tank so that the solution in the cathode acid storage tank and the anode acid storage tank can enter the steel pickling tank. The anion exchange membrane has selective permeability, NO3. - Priority passage, NO3 - A large amount of F enters the anode chamber. - A large amount remains in the cathode chamber, where filtered waste mixed acid is placed, and a low-concentration nitric acid solution is placed in the anode chamber, the initial concentration of which is below 80 g / L.

2. The strip steel pickling waste mixed acid treatment system according to claim 1, characterized in that: The cathode plate is installed in the electrolytic cell using a clamping structure, so that when replacing it, the clamping valve can be opened by pressing the start button to lift the cathode plate out, move it to a fixed position for cleaning, and at the same time replace it with a spare cathode plate to be electrolyzed in the cathode chamber.

3. A method for removing metal ions from waste acid in steel strip pickling, characterized in that: The system for treating mixed acid from steel strip pickling waste as described in claim 1 or 2 is provided, and the removal method includes the following steps: (1) The stainless steel strip is pickled in the strip pickling tank, and the resulting waste mixed acid is coarsely filtered to remove particulate matter from the waste mixed acid. (2) The filtered waste mixed acid is placed in the cathode chamber and a low-concentration nitric acid solution is placed in the anode chamber. The initial concentration of the low-concentration nitric acid solution is below 80 g / L. (3) A cathode plate is placed in the cathode chamber and an anode plate is placed in the anode chamber. Electrolysis is started. Free nitrate ions in the waste mixed acid pass through the anion membrane into the anode chamber, while fluoride ions remain in the cathode chamber. During electrolysis, metal ions in the waste mixed acid are reduced and attached to the cathode plate. The cathode plate is pulled out to clean the metal elements and metal oxides on it. When the cathode plate is pulled out, a spare cathode plate is placed into the cathode chamber. The cathode plates are replaced periodically in this way to achieve uninterrupted electrolysis. (4) The liquid in the cathode chamber is circulated and filtered through a filter device to remove the precipitate formed in the cathode chamber.

4. The method for removing metal ions from waste acid in steel strip pickling as described in claim 3, characterized in that: The process further includes step (5), in which the liquid in the cathode chamber is introduced into a filter device for filtration and then enters the cathode acid storage tank, and the liquid in the anode chamber is introduced into the anode acid storage tank.

5. The method for removing metal ions from waste acid in steel strip pickling as described in claim 4, characterized in that: The process further includes step (6), in which the solutions from the cathode acid storage tank and the anode acid storage tank are placed into the steel pickling tank in the correct amounts.

6. The method for removing metal ions from waste acid in steel strip pickling as described in claim 3, characterized in that: In step (4), the filtration is performed using an external filter press, and both the chamber plate and the filter cloth are made of acid-resistant material.

7. The method for removing metal ions from waste acid from steel strip pickling as described in claim 3, characterized in that: The cathode plate is made of stainless steel, copper or lead, and the anode plate is made of lead dioxide or platinum.

8. The method for removing metal ions from waste acid in steel strip pickling as described in claim 3, characterized in that: In step (4), the precipitates obtained are metal oxides and metal hydroxides, and the precipitates are subjected to centrifugal dehydration treatment.

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