Method for repairing oxidation film on surface of aluminum cathode plate and improving unsmooth stripping of cathode zinc
By using hydrogen peroxide or potassium permanganate aqueous solution for spraying and aging during the polishing process of the aluminum cathode plate, the problem of poor zinc stripping caused by corrosion of the aluminum cathode plate oxide film is solved, the oxide film is quickly repaired and the cathode zinc is smoothly stripped, which reduces costs and space requirements.
Patent Information
- Application Number
- CN202511035956.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-25
- Publication Date
- 2025-09-16
AI Technical Summary
During the wet zinc smelting process, the oxide film on the surface of the aluminum cathode plate is corroded and damaged, resulting in poor cathode zinc peeling. Existing technologies make it difficult to effectively repair or increase the thickness of the oxide film without increasing power consumption and equipment footprint.
During the polishing process of aluminum cathode plates, an aqueous solution containing hydrogen peroxide or potassium permanganate is used for spraying, combined with pressure spraying and aging or oxygen-enriched air blowing to quickly repair the oxide film and form a dense Al2O3 oxide film.
It achieves rapid repair of the oxide film, improves the stripping effect of the cathode zinc, reduces operating costs and equipment footprint, and is suitable for large-scale production.
Abstract
Description
Technical Field
[0001] The present invention belongs to wet zinc smelting, and specifically relates to a technical process for repairing the oxide film on the surface of the aluminum cathode plate and improving the poor cathode zinc peeling when pure aluminum is used as a cathode plate and zinc is electrolyzed in a zinc sulfate solution. The cathode zinc sticks to the plate and peels poorly. After the zinc is peeled and cleaned, the plate is polished and sprayed with an aqueous solution containing hydrogen peroxide or potassium permanganate for oxidation. Background Art
[0002] The electrolysis of wet zinc smelting uses pure metal aluminum plates as cathodes. During the rolling process of the aluminum cathode plate, a dense oxide film with a thickness of several μ (micrometers) is generally naturally formed on the surface of the plate. Due to the protection of this oxide film, the metal zinc and metal aluminum are prevented from forming an alloy and sticking to the plate during zinc electrolysis, which makes the cathode zinc peeling smoothly and greatly reduces the damage and consumption of the plate. However, since the zinc raw materials contain fluorine and chlorine, the zinc sulfate electrolyte contains fluorine and chlorine impurities, which will corrode and destroy the oxide film on the surface of the aluminum cathode plate, causing it to lose protection and causing the cathode zinc to form an alloy on the metal aluminum plate and stick to the plate, making the cathode zinc peeling difficult. In particular, fluoride ions exist in acidic electrolytes as H2F+ cations, and as the acidity increases, they can form H4F 3+ Or aggregate to form larger positive ion groups. Move toward the cathode in electrolysis, taking precedence over Zn 2+ Discharge on the aluminum cathode plate, corroding the aluminum oxide film to generate AlF3 or (AlF6) 3- The aluminum cathode plate loses the protection of the surface oxide film, making Zn 2+ Discharge precipitation on the metal aluminum plate forms an alloy with the metal aluminum and sticks to the plate, causing zinc stripping to be difficult. Especially when F - When the content exceeds 300 mg / L, it will seriously damage the aluminum cathode plate and cause serious zinc stripping problems.
[0003] Secondly, when nickel, cobalt, germanium, and thallium exceed the permitted levels in the electrolyte, the cathode zinc deposited during electrolysis will dissolve back in a micro-galvanic cell process, inevitably damaging the oxide film on the plate surface. A third factor that damages the surface oxide film on the aluminum cathode plate is the use and contact of the zinc stripping knife during cathode zinc stripping, which can also damage the plate surface oxide film. This is especially true during manual zinc stripping, where the impact and scraping of the zinc stripping knife can severely damage the plate surface oxide film. Therefore, protecting or repairing the surface oxide film and its integrity is key to resolving the issue of poor zinc stripping.
[0004] The current methods are mainly to reduce the fluoride ion content in zinc sulfate solution to <100 mg / L, or to add Al 3+ Make it with F - Producing AlF3 or (AlF6) 3- The solid fluorine or make it move towards the anode. Therefore, the production requires F in the electrolyte. -Less than 100mg / L, the lower the better, requiring Al 3+ 500~1000mg / L, acidity ≤150g / L, nickel, cobalt, germanium, thallium, arsenic, antimony and other impurities ≤1mmg / L. Secondly, it is required to artificially repair or increase the thickness of the oxide film on the surface of the aluminum cathode plate before electrolytic zinc to improve the resistance to F - However, F - In the process of electrolytic zinc production, in addition to neutralizing the iron oxide with lime, part of F - The calcium fluoride precipitate generated by reacting with calcium can remove some F - Except for the above, other processes cannot be removed by open circuit. As the production continues, it is enriched. When the concentration in the electrolyte exceeds 300 mg / L, it cannot be removed by increasing AL 3+ This is because although F - Can with Al 3+ Combined to form AlF3 or (AlF6) 3- However, since the acidity of the electrolyte is generally above 100g / L, the F - Mainly H2F + or H4F 3+ The existence of aluminum fluoride cannot generate a large amount of aluminum fluoride. 3+ Aluminum sulfate content increases electrolyte resistance, leading to higher power consumption and electrolyte temperature, which in turn increases cathode zinc dissolution. This is why adding aluminum sulfate or other aluminum salts to the electrolyte cannot completely prevent fluoride and address the problem of poor zinc stripping. Pre-treating the aluminum cathode plate, repairing the oxide film, and increasing its thickness are the primary means of addressing this problem.
[0005] At present, the repair and thickening of the oxide film on the surface of the aluminum cathode plate is mainly carried out by polishing the plate and then storing it for more than 12 hours to allow it to oxidize naturally or placing it in a place containing permanganate (MnO4 - ) or hydrogen peroxide zinc electrolytic waste liquid for immersion oxidation. The natural oxidation of plate polishing is only suitable for situations where the fluoride ion content is not high and the corrosion is slight because the oxide film is thin and the corrosion resistance is weak. Immersion oxidation in electrolytic waste liquid containing oxidants requires soaking for more than 1 hour to form a surface oxide film of several microns. However, the soaking time in the fluorine-chloride acidic solution is too long, and the plate is damaged due to the lack of cathode protection. When the production scale is large, it is necessary to set up several soaking tanks, which occupy a large area and squeeze the operating space of the electrolysis workshop.
[0006] Some people also use the method of anodizing the aluminum cathode plate in a sulfuric acid solution to obtain an oxide film with a certain thickness. This method not only requires the investment in the construction of aluminum anodizing equipment, but also because the thickness of the anodized film is generally above 10μ, and it is a porous oxide film. The porous oxide film of this thickness has poor conductivity, which will increase the Zn 2+The discharge resistance on the cathode plate increases power consumption, and the coating below 10μ is uneven, has many defects, and has weak corrosion resistance. Summary of the Invention
[0007] To overcome the shortcomings of the aforementioned methods, the present invention proposes spraying both surfaces of the aluminum cathode plates with an aqueous solution containing hydrogen peroxide or potassium permanganate while polishing them. This not only removes polishing debris but also performs a surface oxidation treatment under a certain pressure. The process is then followed by aging or drying with oxygen-enriched air. This method is simple, convenient, rapid, and large-scale in repairing the oxide film on the surface of the aluminum cathode plates. The present invention does not damage the plates, requires little investment, occupies a small area, and consumes little energy.
[0008] The technical solution of the present invention: A method for repairing the oxide film on the surface of an aluminum cathode plate to improve poor cathode zinc stripping is implemented by the following steps: Step 1. Manually clean the aluminum cathode plate from which the cathode zinc is not well peeled off, so that there are no cathode zinc spots or other debris on both surfaces of the plate; Step 2. The cleaned aluminum cathode plate from step 1 is brushed vertically on both sides using a wire drum brushing machine. While brushing, a strong oxidant aqueous solution containing hydrogen peroxide or potassium permanganate with a pH of 2-7 is sprayed onto both surfaces to perform cleaning and surface enhanced oxidation, thereby obtaining a thick, uniform, and dense Al2O3 oxide film. Step 3. Take out the aluminum cathode plate with a certain thickness of oxide film from step 2 and place it on a plate rack, age it for more than 10 hours before using it in electrolytic zinc production; or blow it with oxygen-enriched air for 0.5 to 1 hour before using it in electrolytic zinc production; Step 4. The aqueous solution of a strong oxidant containing hydrogen peroxide or potassium permanganate used in step 2 is placed in a recycling tank or tank, filtered through a mesh, and repeatedly recycled while maintaining a substantially constant concentration of hydrogen peroxide or potassium permanganate and a substantially constant pH value.
[0009] Furthermore, the poor cathode zinc stripping in step 1 refers to the cathode zinc sticking to the plate, and both mechanical stripping and manual stripping may cause a smooth process, including slight and severe stripping.
[0010] Furthermore, the hydrogen peroxide solution in step 2 is an aqueous solution containing 20-30% by volume of hydrogen peroxide, and the potassium permanganate solution is an aqueous solution containing 10-20 g / L by mass of potassium permanganate.
[0011] Furthermore, the spray washing in step 2 is performed by multi-tube side-by-side spray washing using stainless steel tubes or plastic tubes installed on both sides of the brush plate of the brush machine, 20 to 30 mm below the wire roller, 30 to 50 mm away from the plate surface, and with a diameter of 10 to 15 mm or 4 to 6 inches; the spray pressure is 0.2 to 0.5 kg / m2, and the temperature of the spray solution is room temperature or the natural temperature when the solution is prepared.
[0012] Furthermore, the aging in step 3 refers to taking out the aluminum cathode plate that has been polished and spray-oxidized to repair the surface oxide film, placing it on a cathode plate rack with a spacing of 10 to 20 mm between the plates, and naturally aging it in air at room temperature and pressure; or using oxygen-enriched air with an oxygen content of 30 to 40% for blowing and drying.
[0013] Principle of the present invention: The present invention utilizes a plate brushing machine to clean impurities and oxide film defects from the surface of the aluminum cathode plate while simultaneously performing pressure spraying with an aqueous solution containing hydrogen peroxide or potassium permanganate. This strengthens oxidation of the fresh surface of the plate, repairs oxide film defects, and produces an AL203 oxide film with a thickness of 5 to 10 μm. The redox potentials of hydrogen peroxide and potassium permanganate are 1.77 V and 1.52 V, respectively, second only to fluorine and ozone among strong oxidants. They exhibit high oxidation strength and rapid oxidation speed, enabling the required oxide film thickness of 5 μm or greater to be achieved in a short period of time. Furthermore, the use of a pH value of 1 to 10 makes the process extremely convenient. Because aluminum metal and its oxide film exhibit both acidic and alkaline properties, the present invention utilizes an aqueous solution with a pH of 2 to 7 for spraying, minimizing corrosion of the aluminum plate and oxide film under both highly acidic and alkaline conditions. This also reduces the risk of the spraying solution to the plate brushing machine and circulation system.
[0014] The so-called aging is to place the polished and oxidizing liquid sprayed electrode plates on the electrode rack, so that the residual oxidizing liquid can continue to play an oxidizing role in the pores of the generated aluminum oxide film, thereby thickening the oxide film. The traditional method requires that the electrode plates be polished by a plate brush, placed on the electrode rack, and subjected to natural air oxidation for more than 12 hours before use. Therefore, the aging of the present invention does not increase the equipment and technical process operations, and does not cause inconvenience to the electrolytic zinc production and worker operation. In order to shorten the aging time, the present invention can also use oxygen-enriched air to blow and dry the electrode plates sprayed with an oxidant aqueous solution, which can achieve the purpose of rapid aging and thickening the aluminum oxide film.
[0015] The beneficial effect of the present invention is that the aluminum cathode plate with poor zinc stripping can better repair the oxide film on the plate surface, improving the problem of poor cathode zinc stripping; at the same time, it has the characteristics of simple operation, small space occupation, low repair cost, and large-scale production. DETAILED DESCRIPTION
[0016] The present invention will be further described below by way of examples.
[0017] A method for repairing the oxide film on the surface of an aluminum cathode plate to improve poor cathode zinc stripping is implemented by the following steps: Step 1. Manually clean the plate where the cathode zinc is not peeling smoothly to remove any cathode zinc lumps or other debris from the surface. Poor cathode zinc peeling refers to the phenomenon that the cathode zinc sticks to the plate when peeling mechanically or manually, and must be peeled slowly or with force using a zinc peeling knife.
[0018] Step 2. Use a wire roller brush to brush the aluminum cathode plate that has been cleaned in step 1 on both sides of the plate, and spray an aqueous solution containing hydrogen peroxide or potassium permanganate on both surfaces for 1 to 2 minutes while brushing. The aqueous solution containing hydrogen peroxide or potassium permanganate is an aqueous solution containing 20 to 30% by volume of hydrogen peroxide or 10 to 20 g / L of potassium permanganate by mass, with a pH of 2 to 7. The spraying is relative to both sides of the plate, 20 to 30 mm below the wire roller, 30 to 50 mm away from the surface of the plate, and multiple Φ10 to 15 mm (4 to 6 inch) stainless steel or plastic nozzles are installed in parallel, and the spray washing is carried out with a pump at a pressure of 0.2 to 0.5 kg / m 2 .
[0019] Step 3. Remove the plates that have been spray-washed and oxidized in Step 2 and place them on a plate rack, spacing them 10-20 mm apart. Allow them to age for at least 10 hours before use. Alternatively, allow them to be air-blown with oxygen-enriched air at natural temperature for 0.5-1 hour before use. Aging refers to allowing them to oxidize naturally in air at room temperature and pressure. The oxygen-enriched air contains 30-40% oxygen, and the natural temperature is the temperature of the oxygen-enriched air at the time of use.
[0020] Step 4. The hydrogen peroxide or potassium permanganate aqueous solution used in step 2 is set up in a recycling tank (tank) and is repeatedly recycled under the condition of filtering through a screen and maintaining H2O2 or KMnO4 and pH value basically unchanged. Example
[0021] Example 1. After the zinc sulfate leachate of a certain enterprise was neutralized and oxidized to remove iron, and the zinc powder was purified to remove copper, cadmium, nickel and cobalt, the zinc sulfate solution still contained 320 mg / L of fluorine. After 24 hours of electrolytic zinc stripping, about 1 / 5 of the cathode zinc could not be peeled off smoothly. Among them, about 50% were slightly sticky to the plate, about 30% could be peeled off in one piece with a zinc stripping knife, about 10% were seriously sticky and had to be peeled off manually with a zinc stripping knife, and about 10% were difficult to peel off. The remaining cathode zinc spots had to be cleaned with a hammer and a scraper. The aluminum cathode plate that was not peeled off smoothly was manually cleaned and then polished with a plate brush machine. While polishing, 20% of the pH=3 hydrogen peroxide solution was sprayed on both surfaces of the plate for 1.5 minutes, and the spraying pressure was 0.5 kg / m 2Then, remove the plate and place it on a plate rack with a 10mm plate spacing. Aged in air at room temperature and pressure for about 18 hours. When the electrolytic zinc is removed from the tank and the plates are replaced, add it to the electrolytic tank for zinc sulfate electrolysis for 24 hours before removing it from the tank. When stripping the zinc, the cathode zinc can be smoothly stripped. Use a zinc stripping knife to gently tap the plate to create cracks, which can be easily stripped.
[0022] Example 2. After cleaning the residual zinc from the cathode zinc stripping plate using the cleaning method described in Example 1, the plate was polished with a brush and sprayed with a 10g / L potassium permanganate solution at pH 6.5 for 2 minutes. The plate was then removed and placed on a rack, spaced 50mm apart, and air-blown from both sides with 30% oxygen-enriched air at room temperature for 0.5 hours. The plate with the repaired surface oxide film was immediately added to an electrolytic cell for electrolysis. After 12 hours, the plate was removed and the cathode zinc stripping process was performed. No problem with stripping was observed using a mechanical zinc stripper.
[0023] Example 3. Plates with poor cathode zinc stripping were tested with a film thickness meter. The oxide film thickness at the plate sticking site was 2-3μm, and the oxide film thickness at the zinc spots was zero. The remaining oxide film thickness was 4-5μm. After manual cleaning, the plates were brushed with a brushing machine. Parts of the plates were sprayed with a 30% by mass hydrogen peroxide solution at pH 5, and part of the plates were sprayed with a 20g / L potassium permanganate solution at pH 2. The spray pressure was 0.2 kg / m 2 , the spraying time is 2 minutes. Then take it out and age it for 10 hours and blow it with oxygen-enriched air containing 30% oxygen for 40 minutes. The thickness of the oxide film is measured respectively with a film thickness meter. The average thickness of the oxide film on the surface of the plate sprayed with hydrogen peroxide before aging or blowing with oxygen-enriched air is 5~8μ, and 8~10μ after aging for 10 hours. The thickness of the oxide film blown with oxygen-enriched air is 7~9μ. The thickness of the oxide film before aging sprayed with potassium permanganate aqueous solution is 4~6μ, after aging it is 7~8μ, and after blowing with oxygen-enriched air it is 8~9μ. The above experiments show that the present invention can repair the damaged oxide film on the surface of the aluminum cathode plate to a thickness of 5~10μ, thereby improving the problem of poor cathode zinc peeling.
[0024] Example 4. Aluminum cathode plates from Example 3 that had poor cathode zinc stripping were manually cleaned and then immersed in a flowing zinc electrolysis wastewater solution containing 3.5 g / L permanganate and 150 g / L H₂SO₄ for 1.5 hours. The plates were then removed and subjected to oxide film repair tests using the same aging time and oxygen-enriched air blowing conditions as in Example 3. The results are as follows. The average oxide film thickness after immersion was 4-5 μm, 6-7 μm after 12 hours of aging, and 7-8 μm after one hour of oxygen-enriched air blowing. Compared to Example 3, the oxide film on the plates with poor cathode zinc stripping was also repaired, but the degree of repair was lower than that achieved by pressure-spraying with hydrogen peroxide or potassium permanganate aqueous solution.
[0025] The aluminum cathode plate with poor zinc stripping of the present invention can better repair the oxide film on the surface of the plate and improve the problem of poor cathode zinc stripping; at the same time, it has the characteristics of simple operation, small space occupation, low repair cost and large-scale production.
[0026] The above examples are only used to further illustrate the present invention, and the present invention is not limited thereto.
Claims
1. A method for repairing the oxide film on the surface of an aluminum cathode plate to improve the poor cathode zinc stripping, characterized by: Follow these steps to implement: Step 1. Manually clean the aluminum cathode plate from which the cathode zinc is not well peeled off, so that there are no cathode zinc spots or other debris on both surfaces of the plate; Step 2. The cleaned aluminum cathode plate from step 1 is brushed vertically on both sides using a wire drum brushing machine. While brushing, a strong oxidant aqueous solution containing hydrogen peroxide or potassium permanganate with a pH of 2-7 is sprayed onto both surfaces to perform cleaning and surface enhanced oxidation, thereby obtaining a thick, uniform, and dense Al2O3 oxide film. Step 3. Take out the aluminum cathode plate with a certain thickness of oxide film from step 2 and place it on a plate rack, age it for more than 10 hours before using it in electrolytic zinc production; or blow it with oxygen-enriched air for 0.5 to 1 hour before using it in electrolytic zinc production; Step 4. The aqueous solution of a strong oxidant containing hydrogen peroxide or potassium permanganate used in step 2 is placed in a recycling tank or tank, filtered through a mesh, and repeatedly recycled while maintaining a substantially constant concentration of hydrogen peroxide or potassium permanganate and a substantially constant pH value.
2. A method for repairing the oxide film on the surface of an aluminum cathode plate to improve poor cathode zinc stripping as claimed in claim 1, characterized in that: The poor cathode zinc peeling in step 1 refers to the cathode zinc sticking to the plate. Both mechanical peeling and manual peeling will cause poor peeling, including slight and severe poor peeling.
3. A method for repairing the oxide film on the surface of an aluminum cathode plate to improve poor cathode zinc stripping as claimed in claim 1, characterized in that: The hydrogen peroxide solution in step 2 is an aqueous solution containing 20-30% by volume of hydrogen peroxide, and the potassium permanganate solution is an aqueous solution containing 10-20 g / L by mass of potassium permanganate.
4. A method for repairing the oxide film on the surface of an aluminum cathode plate to improve poor cathode zinc stripping as claimed in claim 1, characterized in that: The spray washing in step 2 is performed by multiple parallel spray washing using stainless steel or plastic tubes with a diameter of 10 to 15 mm or 4 to 6 inches, which are installed on both sides of the brush plate of the brush machine, 20 to 30 mm below the wire roller and 30 to 50 mm away from the plate surface; the spray pressure is 0.2 to 0.5 kg / m2, and the temperature of the spray solution is room temperature or the natural temperature when the solution is prepared.
5. A method for repairing the oxide film on the surface of an aluminum cathode plate to improve poor cathode zinc stripping as claimed in claim 1, characterized in that: The aging in step 3 refers to taking out the aluminum cathode plate that has been polished and spray-oxidized to repair the surface oxide film, placing it on the cathode plate rack with a spacing of 10 to 20 mm between the plates, and naturally aging it in air at room temperature and pressure; or using oxygen-enriched air with an oxygen content of 30 to 40% for blowing and drying.