Process for the regeneration of a chromic anhydride decoppering solution for the aviation industry

Abstract

This invention provides a method for regenerating chromic anhydride copper stripping solution used in the aerospace industry, solving the current technical problem of not being able to regenerate chromic anhydride copper stripping solution while simultaneously considering economic cost, environmental protection, and meeting process requirements. The method consists of two parts: copper ion separation and hexavalent chromium regeneration. First, after experimental screening, the effectiveness of oxalate as a copper ion precipitant in a chromic acid environment was verified. Although there is a drawback that some hexavalent chromium is reduced to trivalent chromium by the precipitant, a reasonable oxidation method is subsequently proposed to fully oxidize and regenerate the total trivalent chromium in the failed solution back to hexavalent chromium, thus overcoming the drawback of the first step of copper separation. Simultaneously, it also oxidizes and regenerates the original trivalent chromium in the solution.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, and specifically relates to a method for regenerating a copper stripping solution of chromic anhydride. Background Technology

[0002] Electroplated copper layers have advantages such as softness, density, and low internal stress. In the aerospace industry, they are often used as an underlayer to prevent high-temperature adhesion of steel fasteners, and to resist nitriding, carburizing, and other plating layers. During aerospace maintenance, old copper layers and substandard copper plating on spare parts are often chemically stripped using a mixed solution of high-content chromic anhydride and sulfuric acid. The entire process has a simple formula, stable performance, and is easy to operate, and it does not corrode the steel substrate.

[0003] In industrial production, when the copper ion content in the chromic anhydride copper stripping solution reaches a certain threshold, the copper stripping efficiency decreases, and copper rust precipitates on the matrix, affecting production efficiency and product quality. Re-preparing the copper stripping solution is costly; furthermore, the treatment of high hexavalent chromium content in the waste solution is extremely costly and difficult. Therefore, the disposal of chromic anhydride copper stripping solutions not only increases production costs for enterprises but also exposes them to heavy environmental monitoring pressure. Under the concept of cleaner production, regenerating chromic anhydride copper stripping solutions is of great significance in saving costs and energy, ensuring product quality, and effectively avoiding environmental pollution.

[0004] The regeneration methods for chromic anhydride copper stripping solutions mainly involve the separation of copper ions and the regeneration of hexavalent chromium. Firstly, due to the strong oxidizing properties of hexavalent chromium and the colloidal precipitation of trivalent chromium, most copper ion precipitants are oxidized and decomposed, making it difficult to effectively separate copper ions. Secondly, after oxidizing trivalent chromium, the corresponding reduction products of most available oxidants remain in the bath, becoming components outside the process specifications. For example, the paper "Regeneration of Ineffective Copper Stripping Solution with Potassium Permanganate" (Surface Technology, 1981.01) reported a method for regenerating ineffective copper stripping solution using potassium permanganate. At high temperatures, the strong oxidizing power of potassium permanganate can oxidize trivalent chromium in the copper stripping solution to hexavalent chromium. Although this method effectively regenerates hexavalent chromium, it cannot separate copper ions; furthermore, it introduces chemical substances outside the copper stripping process specifications, threatening product quality. Thus, previous reports have not adequately addressed both of these issues, leaving the solution to this problem unresolved. Chinese patent applications CN101050175A, CN114956154A, and CN102070436A all disclose methods for precipitating copper ions in a generally acidic environment. However, it is important to note that the chromic acid environment differs from a generally acidic environment; it possesses extremely strong oxidizing properties and can oxidize and decompose the precipitant to varying degrees. This raises a new problem: if the copper ion precipitation method described in the aforementioned patents is used, how can the reduced trivalent chromium be regenerated back into hexavalent chromium without producing chemical residues? Chinese patent CN208791372U discloses a copper-containing wastewater treatment and recovery device, which uses ion exchange resin to filter out copper ions from the copper-containing wastewater, then uses a regeneration agent to elute the copper ions, and finally uses an electrolytic eluent to harvest pure copper and electrolyte, respectively. Although this scheme provides a method for recovering copper-containing wastewater, the operation is complex and the process is lengthy, which is not conducive to practical application. In summary, there is still a lack of a truly meaningful regeneration method for chromic anhydride copper stripping solutions.

[0005] In view of this, the research team of this invention has provided a method for regenerating chromic anhydride copper stripping solution through in-depth research. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problem that it is currently impossible to regenerate chromic anhydride copper stripping solution while simultaneously considering economic costs, environmental protection, and meeting process requirements, and to provide a method for regenerating chromic anhydride copper stripping solution.

[0007] To achieve the above objectives, the technical solution provided by this invention is:

[0008] A method for regenerating a copper stripping solution from chromic anhydride, characterized by the following steps:

[0009] Step 1: Add oxalic acid or oxalate to the expired chromic anhydride copper stripping solution, stir well, let stand until the layers separate, separate the supernatant from the precipitate (i.e., copper oxalate precipitate), and recover the supernatant and precipitate.

[0010] Due to the differences in reaction rate constants between different competing reactions and the significant chemical inertness of copper oxalate, in practice, oxalate ions always preferentially combine with copper ions to form a stable precipitate that is insoluble in chromic acid (Equation 1). A small portion of oxalic acid or oxalate reduces hexavalent chromium to trivalent chromium (Equation 2).

[0011] C2O4 2- +Cu 2+ →CuC2O4↓ (1)

[0012] Cr2O7 2- +3C2O4 2- +14H + →2Cr 3+ +6CO2+7H2O(2)

[0013] Step 2: Add persulfate to the supernatant recovered in Step 1 at room temperature, stir thoroughly, and continue heating to carry out the reaction (since persulfate is thermally unstable in the sulfuric acid system, any residual persulfate is decomposed and expelled from the system by continuously heating the supernatant to carry out a free radical quenching reaction, see Equation 3-5). After the reaction is completed, cool to room temperature, and then analyze the sulfuric acid content in the solution. Based on the difference between this content value and the sulfuric acid content requirement in the process, add sulfuric acid to the range required by the industry standard to obtain the regenerated chromic anhydride copper stripping solution.

[0014] S2O8 2- →2·SO4 - (3)

[0015] SO4 - +H₂O→HSO 4- +·OH (4)

[0016] ·OH + ·OH → H₂O + 1 / 2O₂ (5)

[0017] Further, in step 1, based on the total copper ion content (i.e., the total amount of substance) in the failed chromic anhydride copper stripping solution, the theoretical amount of oxalic acid or oxalate to be added is calculated. Then, oxalic acid or oxalate is added in portions to the failed chromic anhydride copper stripping solution, stirring thoroughly and allowing it to stand for at least 4 hours. (Due to the difference in reaction rate constants between different competing reactions and the significant chemical inertness of copper oxalate, in practice, oxalate ions always preferentially combine with copper ions to form a stable precipitate that is insoluble in chromic acid. When the amount of oxalic acid or oxalate added exceeds 100%, theoretically, copper ions will precipitate completely, and the excess oxalate will act as a reducing agent to reduce chromic anhydride to trivalent chromium, which contradicts the overall technical approach. Therefore, the amount of oxalic acid or oxalate added should be controlled within 95%).

[0018] Further, in step 1, the oxalate is sodium oxalate, potassium oxalate, ammonium oxalate, calcium oxalate, ammonium hydrogen oxalate, ferrous oxalate, or magnesium oxalate.

[0019] Further, in step 2, based on the total trivalent chromium content (i.e., the total amount of substance) in the supernatant recovered in step 1, the theoretical amount of persulfate to be added is calculated. Persulfate is then added in portions to the supernatant at no more than 95% of the theoretical amount (subsequent continuous heating is to decompose any potentially excessive persulfate; for ease of operation in subsequent heating, the amount of persulfate added as an oxidant should preferably not reach 100%, but should be close to the theoretical value; therefore, in this invention, it is controlled to not exceed 95% of the theoretical amount to avoid producing residual substances). After thorough stirring, the mixture is continuously heated for at least 3 hours, with the heating temperature being 40-70°C.

[0020] Furthermore, in step 2, the persulfate is ammonium persulfate, sodium persulfate, or potassium persulfate.

[0021] Furthermore, in order to effectively utilize the product and enhance its economic value, the process also includes recovering the precipitate obtained in step 1) (i.e., recovering the byproduct, which can be in the form of copper oxalate or copper oxide). The specific operation is as follows:

[0022] The precipitate recovered from step 1 is washed until it is no longer yellow, and then dried at an temperature not exceeding 100°C to obtain pure copper oxalate; however, at temperatures exceeding 100°C, some copper oxalate may be converted into forms such as copper oxide.

[0023] or,

[0024] The precipitate recovered from step 1 is washed with water until it is no longer yellow, and then calcined at an environment of not less than 400°C to obtain pure copper oxide.

[0025] Meanwhile, the present invention also provides a regenerated chromic anhydride copper stripping solution obtained by the above method, as well as copper oxalate or copper oxide.

[0026] The concept and principle of this invention:

[0027] In copper plating production for surface treatment, a large amount of chromic acid stripping solution is generated that fails. The costs of wastewater treatment and the cost of re-preparing the stripping solution are high. The research team of this invention analyzed the root causes of this failure as a decrease in hexavalent chromium content, a decrease in the solution's oxidizing power, and an increase in copper ion content leading to copper ion saturation. Unrestricted addition of chromic anhydride and sulfuric acid would significantly increase the solution's acidity, causing corrosion to the parts. Therefore, adhering to the concept of clean production, the recycling and regeneration of chromic acid stripping solution is of great significance. To this end, the research team of this invention explored a two-step continuous method for the chemical regeneration of failed chromic acid stripping solution. The overall approach is divided into two parts: the separation of copper ions and the regeneration of hexavalent chromium. First, after experimental screening, the effectiveness of oxalate as a copper ion precipitant in a chromic acid environment was verified. Although there is a drawback that some hexavalent chromium is reduced to trivalent chromium by the precipitant (Equation 2 above), a reasonable oxidation method was subsequently proposed (Equation 3 above and Equations 6-7 below) to fully oxidize and regenerate the total trivalent chromium in the failed solution back to hexavalent chromium (Equation 6-7 below). This overcomes the new problem introduced in the first step of copper separation—the reduction of chromic anhydride to trivalent chromium. At the same time, it can also oxidize and regenerate the original trivalent chromium in the solution.

[0028] Cr 3+ + ·SO4 - → Cr 6+ + SO4 2- (6)

[0029] Cr 3+ + ·OH → Cr 6+ + OH - (7)

[0030] In the oxidation-reduction of trivalent chromium to hexavalent chromium, generally, the oxidation potential of most organic oxidants lies between that of trivalent and hexavalent chromium. The use of organic oxidants often results in them being preferentially oxidized by the existing hexavalent chromium in the solution, making it difficult to achieve the goal of oxidizing trivalent chromium to hexavalent chromium. The use of inorganic oxidants requires consideration of the specific surface treatment requirements in aerospace production. The copper stripping process HB / Z 5069 has extremely high quality requirements, and the solution in this process only allows the presence of permitted chemical components, namely chromic anhydride and sulfuric acid. Therefore, the strategy of using inorganic oxidation to oxidize trivalent chromium to hexavalent chromium is difficult to implement. This is because after oxidizing trivalent chromium, the inorganic oxidant itself is reduced to a lower-valent inorganic salt and dissolves and remains in the solution, which is unacceptable in aerospace production. Therefore, in this invention, the oxidation of trivalent chromium is achieved by constructing a free radical chain reaction. Based on persulfate, in an acidic environment with transition metal ions (chromate), persulfate is catalyzed to generate sulfate radicals (·SO4).- The oxidation potentials of trivalent chromium (chromate) and hydroxyl radicals (·OH) are 3.1V and 2.8V respectively, which are much higher than the 1.3V of dichromate, thus making it easier to oxidize trivalent chromium. Furthermore, free radicals are short-lived; after the oxidation process, they undergo a quenching reaction (Equation 4-5 above), preventing them from remaining in the solution as chemical substances outside the copper stripping process HB / Z 5069. Therefore, this invention can truly regenerate the failed chromate copper stripping solution while fully meeting the quality requirements of the aerospace industry.

[0031] The advantages of this invention are:

[0032] 1. The regeneration method for chromic anhydride copper stripping solution provided by this invention can effectively separate copper ions separately using copper oxalate or copper oxide and regenerate functionally failed chromic anhydride copper stripping solutions. The entire process is simple and safe to operate, requires no special equipment support, has low requirements for equipment and environment, can significantly reduce raw material costs and wastewater treatment costs in the production process, has strong industrial applicability, and will not introduce chemical substances other than those specified in the HB / Z 5069 process document, greatly saving energy input, ensuring product quality, and the regeneration process does not generate waste, and has very significant economic benefits and environmental protection significance, saving energy and effectively avoiding environmental pollution.

[0033] 2. The copper stripping efficiency was compared and verified through experiments to show that the copper stripping solution after multiple regenerations was as effective as the freshly prepared copper stripping solution. Attached Figure Description

[0034] Figure 1 The images show the precipitation and separation effects of copper ions in the copper stripping solution under a series of oxalate addition amounts (from left to right: 0.01 mol, 0.025 mol, 0.05 mol, 0.075 mol, and 0.1 mol).

[0035] Figure 2 The image shows a comparison of the effects of the degraded chromic anhydride copper stripping solution and copper separation. The left image is a schematic diagram of the degraded chromic anhydride copper stripping solution, and the right image is a schematic diagram of copper separation after step 1. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the embodiments. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Steps not specifically described in the embodiments are existing technologies and will not be described in detail here. To ensure excellent performance of the regenerated solution, its sulfuric acid content can be adjusted as needed according to the process range.

[0037] A method for regenerating a copper stripping solution from chromic anhydride includes the following steps:

[0038] Step 1: Based on the total copper ion content (i.e., total amount of substance) in the expired chromic anhydride copper stripping solution, calculate the theoretical amount of oxalic acid or oxalate to be added. Add oxalic acid or oxalate to the expired chromic anhydride copper stripping solution in portions, not exceeding 95% of the theoretical amount. After stirring evenly, let stand for at least 4 hours, separate the supernatant from the precipitate (i.e., copper oxalate precipitate), and recover the supernatant and precipitate. The oxalate can be sodium oxalate, potassium oxalate, ammonium oxalate, calcium oxalate, ammonium hydrogen oxalate, ferrous oxalate, or magnesium oxalate.

[0039] Due to the differences in reaction rate constants between different competing reactions and the significant chemical inertness of copper oxalate, in situations such as Figure 1 In the operations shown (oxalate addition amounts of 0.01 mol, 0.025 mol, 0.05 mol, 0.075 mol, and 0.1 mol respectively), oxalate ions preferentially combine with copper ions to form a stable precipitate insoluble in chromic acid (Equation 1), with only a very small portion of oxalic acid or oxalate being oxidized or decomposed by hexavalent chromium (Equation 2). Figure 2 The comparison of the failed tank solution and its copper separation effect shows that the copper ion separation effect is obvious.

[0040] C2O4 2- +Cu 2+ →CuC2O4↓ (1)

[0041] Cr2O7 2- +3C2O4 2- +14H + →2Cr 3+ +6CO2+7H2O (2)

[0042] Step 2: Based on the total trivalent chromium content (i.e., total amount of substance) in the supernatant recovered in Step 1, calculate the theoretical amount of persulfate to be added. Add persulfate to the supernatant in portions not exceeding 95% of the theoretical amount, continuously heating at 40-70℃ and stirring for at least 3 hours to carry out the reaction. After the reaction is complete, cool to room temperature and adjust the sulfuric acid content in the product to the range required by the process to obtain the regenerated chromic anhydride copper stripping solution. The persulfate can be ammonium persulfate, sodium persulfate, or potassium persulfate. Since persulfate is thermally unstable in sulfuric acid systems, residual persulfate is decomposed and removed from the system by continuously heating the supernatant to initiate a free radical reaction (Equation 3-5).

[0043] S2O8 2- →2·SO4 - (3)·SO4 - +H₂O→HSO 4- +·OH (4)

[0044] ·OH + ·OH → H₂O + 1 / 2O₂ (5)

[0045] To effectively utilize the product and enhance its economic value, the precipitate recovered in step 1 is washed until it is no longer yellow and then dried (e.g., at 60°C for 5 hours) at an environment not exceeding 100°C to obtain pure copper oxalate; or, the precipitate recovered in step 1 is washed until it is no longer yellow and then calcined (e.g., at 400°C for 3 hours) at an environment not lower than 400°C to obtain pure copper oxide.

[0046] The specific implementation method is as follows:

[0047] Example 1

[0048] A method for regenerating a copper stripping solution from chromic anhydride includes the following steps:

[0049] Step 1: Take a portion of the expired chromic anhydride copper stripping solution from a 500L copper stripping tank. According to HB / Z 5091-1978, the contents of chromic anhydride, sulfuric acid, and trivalent chromium are 203.08g / L, 98.80g / L, and 28.50g / L, respectively; according to GB 4702.10, the copper ion content is 24.90g / L.

[0050] Step 2: Based on the measured copper ion content, the total amount of copper ions in the bath solution is calculated to be 196.06M.

[0051] Step 3: Stir the tank liquid and add sodium oxalate in 15 portions, with a total amount of 186.26M, to carry out the reaction.

[0052] Step 4: After stirring continuously for 100 minutes, let it stand overnight. After it separates into layers, filter the supernatant using a filter with a filter diameter of 5μm, and transfer the clear filtrate to a clean copper stripping tank.

[0053] Step 5: The contents of chromic anhydride, trivalent chromium, and copper ions in the supernatant were 195.50 g / L, 36.1 g / L, and 3.11 g / L, respectively. The total amount of trivalent chromium in the supernatant was calculated to be 347.12 M.

[0054] Step 6: Add 989.28M of ammonium persulfate in 15 portions, stir the solution thoroughly, and then heat the supernatant to 40-50°C using a steam heating pipe to allow for a full reaction.

[0055] Step 7: After heating for 3 hours, stop heating and allow it to cool naturally to room temperature.

[0056] Step 8: The contents of chromic anhydride and trivalent chromium were 232.60 g / L and 1.31 g / L, respectively.

[0057] Step 9: Adjust the sulfuric acid content to the process range specified in HB / Z 5069.

[0058] Step 10: Wash the copper oxalate precipitate with water until no yellow color remains; dry at 60°C for 5 hours, then calcine at 400°C for 3 hours to obtain copper oxide.

[0059] Example 2

[0060] A method for regenerating a copper stripping solution from chromic anhydride includes the following steps:

[0061] Step 1: Take a portion of the expired chromic anhydride copper stripping solution from a 500L copper stripping tank. According to HB / Z 5091-1978, the contents of chromic anhydride, sulfuric acid, and trivalent chromium are 228.11g / L, 58.81g / L, and 22.23g / L, respectively; according to GB 4702.10, the copper ion content is 22.53g / L.

[0062] Step 2: Based on the measured copper ion content, the total amount of copper ions in the bath solution is calculated to be 177.40M.

[0063] Step 3: Stir the tank liquid and add 168.53M oxalic acid in 20 portions to carry out the reaction.

[0064] Step 4: After stirring continuously for 120 minutes, let it stand overnight. After it separates into layers, filter the supernatant using a filter with a filter diameter of 5μm, and transfer the clear filtrate to a clean copper stripping tank.

[0065] Step 5: The contents of chromic anhydride, trivalent chromium, and copper ions in the supernatant were 209.58 g / L, 41.55 g / L, and 1.13 g / L, respectively. The total amount of trivalent chromium in the supernatant was calculated to be 399.53 M.

[0066] Step 6: Add sodium persulfate in 15 portions at a concentration of 1138.66 M, stir the solution thoroughly, and then heat the supernatant to 50-60°C using a steam heating pipe to allow for a complete reaction.

[0067] Step 7: After stirring continuously for 5 hours, stop heating and allow to cool naturally to room temperature.

[0068] Step 8: The contents of chromic anhydride and trivalent chromium were analyzed to be 248.11 g / L and 2.85 g / L, respectively.

[0069] Step 9: Adjust the sulfuric acid content to the range specified in the process.

[0070] Step 10: Wash the copper oxalate precipitate with water until no yellow color remains, then dry it at 60°C for 5 hours to obtain pure copper oxalate.

[0071] Example 3

[0072] A method for regenerating a copper stripping solution from chromic anhydride includes the following steps:

[0073] Step 1: Take a portion of the expired chromic anhydride copper stripping solution from a 500L copper stripping tank. According to HB / Z 5091-1978, the contents of chromic anhydride, sulfuric acid, and trivalent chromium are 199.45g / L, 33.23g / L, and 33.56g / L, respectively; according to GB 4702.10, the copper ion content is 21.66g / L.

[0074] Step 2: Based on the measured copper ion content, the total amount of copper ions in the bath solution is calculated to be 170.55M.

[0075] Step 3: Stir the tank liquid and add potassium oxalate in 10 portions, each containing 162.02 M of the substance, to carry out the reaction.

[0076] Step 4: After stirring continuously for 120 minutes, let it stand overnight. After it separates into layers, filter the supernatant using a filter with a filter diameter of 5 μm, and transfer the clear filtrate to a clean copper stripping tank.

[0077] Step 5: The contents of chromic anhydride, trivalent chromium, and copper ions in the supernatant were analyzed to be 185.77 g / L, 50.68 g / L, and 2.01 g / L, respectively. The total amount of trivalent chromium in the supernatant was calculated to be 487.31 M.

[0078] Step 6: Add 1388.83M of potassium persulfate in 20 portions, stir the solution thoroughly, and then heat the supernatant to 60-70°C using a steam heating pipe to allow for a full reaction.

[0079] Step 7: After stirring continuously for 6 hours, stop heating and allow to cool naturally to room temperature.

[0080] Step 8: The contents of chromic anhydride and trivalent chromium were 230.18 g / L and 1.98 g / L, respectively.

[0081] Step 9: Adjust the sulfuric acid content to the process range specified in HB / Z 5069.

[0082] Step 10: Wash the copper oxalate precipitate with water until no yellow color remains, dry it at 60°C for 5 hours, and then calcine it at 400°C for 3 hours to obtain copper oxide.

[0083] To verify the effectiveness and practicality of the regeneration method of this invention, the research team also conducted experiments on the copper removal efficiency after multiple regenerations of the chromic anhydride copper removal solution. The specific data are shown in Table 1:

[0084] Table 1. Copper stripping efficiency of regenerated copper stripping solution and virgin copper stripping solution with the same concentration.

[0085]

[0086] As can be seen from Table 1, the copper stripping efficiency of the regenerated copper stripping solution is comparable to that of the newly prepared copper stripping solution, further proving the feasibility of the regeneration method of the present invention. This method is not only environmentally friendly and meets the requirements of process standards, but also does not introduce any chemical substances other than those specified, and can significantly reduce the regeneration cost, making it highly applicable to industrial applications.

[0087] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for regenerating a copper stripping solution of chromic anhydride used in the aerospace industry, characterized in that, Includes the following steps: Step 1: Add oxalic acid or oxalate to the expired chromic anhydride copper stripping solution, stir well, let stand until the layers separate, separate the supernatant from the precipitate, and recover the supernatant and precipitate. Based on the total copper ion content in the failed chromic anhydride copper stripping solution, calculate the theoretical amount of oxalic acid or oxalate to be added, and add oxalic acid or oxalate to the failed chromic anhydride copper stripping solution in portions, not exceeding 95% of the theoretical amount. After stirring evenly, let stand for at least 4 hours. Step 2: Add persulfate to the supernatant recovered in Step 1 at room temperature, stir thoroughly, and continue heating to carry out the reaction. After the reaction is completed, cool to room temperature, and then analyze the sulfuric acid content in the solution. Based on the difference between the value of this content and the sulfuric acid content required in the process, add sulfuric acid to the range required by the industry standard to obtain the regenerated chromic anhydride copper stripping solution. Based on the total trivalent chromium content in the supernatant recovered in step 1, calculate the theoretical amount of persulfate to be added, and add persulfate to the supernatant in portions not exceeding 95% of the theoretical amount. After thorough stirring, continue heating for at least 3 hours, with the heating temperature being 40-70℃.

2. The regeneration method of the chromic anhydride copper stripping solution for the aerospace industry according to claim 1, characterized in that: In step 1, the oxalate is sodium oxalate, potassium oxalate, ammonium oxalate, calcium oxalate, ammonium hydrogen oxalate, ferrous oxalate, or magnesium oxalate.

3. The regeneration method of the chromic anhydride copper stripping solution for the aerospace industry according to claim 2, characterized in that: In step 2, the persulfate is ammonium persulfate, sodium persulfate, or potassium persulfate.

4. The regeneration method of the chromic anhydride copper stripping solution for the aerospace industry according to any one of claims 1-3, characterized in that: This also includes recovering the precipitate obtained in step 1), specifically as follows: The precipitate recovered in step 1 was washed with water until no yellow color remained, and then dried at an environment not exceeding 100°C to obtain pure copper oxalate. or, The precipitate recovered from step 1 is washed with water until it is no longer yellow, and then calcined at an environment of not less than 400°C to obtain pure copper oxide.

5. A recycled chromic anhydride copper stripping solution for the aerospace industry obtained by the method described in any one of claims 1-3.