Cadmium removing solution of cyanide-free cadmium plating layer, preparation method of cadmium removing solution and cadmium removing method

Abstract

The invention discloses a cadmium removing solution of a cyanide-free cadmium plating layer and a preparation method and a cadmium removing method of the cyanide-free cadmium plating layer, and the cadmium removing solution comprises the following components in percentage by mass: 8wt%-12wt% of nitric acid; 20 wt%-35 wt% of an ammonium salt; 3 wt%-10 wt% of a buffer agent; 1 wt%-3 wt% of a corrosion inhibitor; and 0.5 wt%-2wt% of a surfactant. The corrosion inhibitor is used for preventing corrosion of the base material, and it is guaranteed that the size and mechanical performance of the base material are not affected in the deplating process; and meanwhile, side reactions generated in the dissolving process are inhibited through the corrosion inhibitor, and the deplating efficiency is improved. According to the invention, hydrogen atoms generated by dissolving the cadmium plating layer are prevented from permeating into a matrix through the surfactant, so that the hydrogen embrittlement phenomenon is reduced; and complexing of cadmium ions is realized, and dissolution of the cadmium layer is accelerated. The solution is close to neutral, corrosion to a base material is reduced, meanwhile, the hydrogen embrittlement phenomenon generated in the operation process is reduced, the stripping efficiency is effectively improved, and good practicability is achieved.

Description

Technical Field

[0001] This invention belongs to the technical field of metal surface protection, specifically relating to a cyanide-free cadmium plating removal solution, its preparation method, and the cadmium removal method thereof. Background Technology

[0002] Cadmium electroplating is a surface treatment technology widely used in aerospace, electronics, electrical engineering, and corrosion protection. Cadmium plating exhibits excellent corrosion resistance, a low coefficient of friction, and good electrical conductivity, making it crucial in demanding fields such as aerospace. However, traditional cadmium electroplating processes typically use cyanide as the main component. Cyanide is highly toxic and poses a serious threat to the environment and the health of operators.

[0003] During the production and maintenance of parts, defects or wear of the electroplated layer are inevitable, requiring rework. This typically involves removing the plating and replating. Existing methods for removing cadmium plating primarily involve using ammonium nitrate solutions. While effective, this method is limited by the fact that ammonium nitrate is a controlled chemical with explosive hazards and is difficult to procure, restricting its widespread application. Currently, if ammonium nitrate is not used, acidic substances such as chromic acid and sulfuric acid are required, which can adversely affect the dimensions and properties of the substrate, especially when processing high-precision parts, making them more susceptible to hydrogen embrittlement. Hydrogen embrittlement can cause sudden fracture of metal materials under external forces, severely impacting the reliability and lifespan of parts. Therefore, developing an environmentally friendly, safe, easy-to-operate, and non-adverse-effect-on-the-substrate cyanide-free cadmium plating removal solution is of paramount importance.

[0004] Chinese patent CN118086907A discloses an alkaline zinc / cadmium plating stripping solution, its preparation method, and its application. Under room temperature conditions, immersing steel parts with cadmium or zinc plating in the stripping solution allows for complete removal of the plating. Using sodium m-nitrobenzenesulfonate as the oxidant oxidizes zinc / cadmium into ions without oxidizing the metal plating, ensuring the surface smoothness of the substrate. Stripping in a weakly alkaline environment significantly reduces hydrogen embrittlement, making it suitable for removing zinc / cadmium plating from the surfaces of high-precision, high-strength steel parts. However, this method does not consider enhancing the slow-release effect during the stripping process.

[0005] Chinese patent CN117587408A discloses a method for stripping substandard zinc-cadmium alloy plating from high-strength steel. Sodium nitrite is used as an oxidant for the zinc-cadmium alloy plating and a corrosion inhibitor for the steel substrate; ammonium bicarbonate is used as a coordinating agent for zinc and cadmium ions and a pH buffer for the plating solution; and ammonium chloride is used as a coordinating agent for zinc and cadmium ions and a promoter for dissolving the zinc-cadmium alloy plating. If the pH of the stripping solution is too high, dilute nitric acid is used to lower the pH; if the pH is too low, sodium carbonate solution is used to raise the pH. However, this method is essentially just preparing ammonium nitrate in solution using other raw materials.

[0006] Chinese patent CN111690933B discloses a stripping solution and method for removing substandard cadmium plating from steel parts. The method involves immersing the substandard plating parts in the stripping solution at room temperature until the plating is completely removed, followed by rinsing with water. The stripping solution does not contain highly toxic hexavalent chromium, thus solving the high pollution problem associated with existing chromic acid stripping solutions. However, this process is acidic. Summary of the Invention

[0007] The purpose of this invention is to provide a cyanide-free cadmium plating removal solution, its preparation method, and the cadmium removal method thereof, in order to solve the above-mentioned problems.

[0008] This invention is mainly achieved through the following technical solutions:

[0009] A cadmium stripping solution for cyanide-free cadmium plating, comprising the following components by mass percentage:

[0010] Nitric acid: 8wt%~12wt%;

[0011] Ammonium salt: 20wt%~35wt%;

[0012] Buffer: 3wt%~10wt%;

[0013] Corrosion inhibitor: 1wt%~3wt%;

[0014] Surfactant: 0.5wt%~2wt%.

[0015] To better realize the present invention, the ammonium salt further includes ammonium chloride and / or ammonium sulfate; the buffer includes ammonium acetate and / or ammonium borate.

[0016] To better realize the present invention, the corrosion inhibitor further includes any one or more of benzotriazole, methylbenzotriazole, and benzotetrazole.

[0017] To better realize the present invention, the surfactant further comprises any one or more of dodecylbenzenesulfonate amine, dodecyl polyoxyethylene ether, tetradecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, and octadecyl polyoxyethylene ether.

[0018] To better realize the present invention, further, based on concentration, it includes the following components:

[0019] Nitric acid: 100 mL / L;

[0020] Ammonium chloride: 150 g / L;

[0021] Ammonium acetate: 40 g / L;

[0022] Benzotriazole: 10 g / L;

[0023] Dodecylbenzenesulfonate ammonium: 10 g / L.

[0024] To better realize the present invention, further, based on concentration, it includes the following components:

[0025] Nitric acid: 120 mL / L;

[0026] Ammonium sulfate: 150 g / L;

[0027] Ammonium acetate: 50 g / L;

[0028] Methylbenzotriazole: 10 g / L;

[0029] Dodecylbenzenesulfonate ammonium: 15 g mL / L.

[0030] To better realize the present invention, further, based on concentration, it includes the following components:

[0031] Nitric acid: 120 mL / L;

[0032] Ammonium sulfate: 80 g / L;

[0033] Cadmium chloride: 70 g / L;

[0034] Ammonium borate: 50 g / L;

[0035] Benzotetrazole: 10 g / L;

[0036] Dodecylbenzenesulfonate ammonium: 20 g / L.

[0037] This invention is mainly achieved through the following technical solutions:

[0038] A method for preparing a cyanide-free cadmium plating stripping solution includes the following steps:

[0039] Step S1: Slowly add nitric acid to the ammonium salt dissolved in deionized water;

[0040] Step S2: After the solution cools, add the buffer, corrosion inhibitor and surfactant in sequence, and stir until homogeneous;

[0041] Step S3: Adjust the pH of the solution to 6.0-7.0 using ammonia.

[0042] To better realize the present invention, further, in step S2, the surfactant includes dodecylbenzenesulfonate amine, and the preparation of dodecylbenzenesulfonate amine includes the following steps:

[0043] Step T1: Sulfonyl chloride reaction:

[0044] Step T11: Add dodecylbenzene and solvent to the reaction vessel;

[0045] Step T12: Under cooling conditions, control the temperature to 0-10℃, and slowly add chlorosulfonic acid dropwise while stirring;

[0046] Step T13: Gradually raise the reaction temperature to room temperature, stir the reaction, and generate dodecylbenzenesulfonyl chloride;

[0047] Step T2: Ammoniation reaction:

[0048] The generated dodecylbenzenesulfonyl chloride solution is slowly added to cooled ammonia water or ammonia gas stream, and the reaction temperature is set to 0-10℃; the reaction is stirred to generate dodecylbenzenesulfonate amine.

[0049] This invention is mainly achieved through the following technical solutions:

[0050] A method for removing cadmium from a cadmium plating, using the aforementioned cyanide-free cadmium plating removal solution, includes the following steps:

[0051] Step A1: Maintain the temperature of the cadmium removal solution at 10–40°C;

[0052] Step A2: Adjust the pH of the cadmium removal solution to 6.5 using ammonia or nitric acid;

[0053] Step A3: Immerse the cadmium-coated parts completely in the cadmium removal solution until the cadmium plating is completely removed.

[0054] The beneficial effects of this invention are as follows:

[0055] (1) Addressing the current limitations of using ammonium nitrate, chromic acid, and sulfuric acid for stripping cadmium plating, this invention develops an environmentally friendly, safe, and easy-to-operate cyanide-free cadmium plating stripping solution that has no adverse effects on the substrate. The solution of this invention is nearly neutral, has high stripping efficiency, exhibits excellent stripping performance on cadmium-titanium plating, and has no adverse effects on substrate dimensions or hydrogen embrittlement. Compared to traditional acidic or alkaline stripping solutions, the solution of this invention is nearly neutral (pH between 6.0 and 7.0), reducing corrosion to the substrate and minimizing hydrogen embrittlement during operation. This is particularly important for industrial applications requiring high precision and reliability. Furthermore, traditional cadmium plating stripping methods rely on ammonium nitrate, which is explosive, dangerous, and difficult to obtain. This invention, by using a chemical composition free of ammonium nitrate, avoids the use of ammonium nitrate, significantly improving operational safety and environmental friendliness.

[0056] (2) The corrosion inhibitors used in this invention (such as benzotriazole, methylbenzotriazole, etc.) can effectively prevent corrosion of the substrate, ensuring that the dimensions and mechanical properties of the substrate are not affected during the stripping process. At the same time, these corrosion inhibitors can also suppress side reactions generated during dissolution, improving stripping efficiency and demonstrating good practicality. In the solution formulation of this invention, the selection and ratio of ammonium salts, buffers, corrosion inhibitors, and surfactants have been optimized to ensure high efficiency and stability during the stripping process. For example, ammonium chloride and ammonium sulfate in the ammonium salts not only provide good dissolving power but also play a role in corrosion inhibition during the stripping process.

[0057] (3) The surfactants of this invention (such as dodecylbenzenesulfonate amine, dodecyl polyoxyethylene ether, etc.) play a key role in the stripping process, preventing hydrogen atoms generated by the dissolution of the cadmium coating from penetrating into the substrate and reducing hydrogen embrittlement. They can also complex cadmium ions, accelerating the dissolution of the cadmium layer. This innovative application significantly improves the safety of the stripping process and the reusability of the substrate, and has good practicality. Attached Figure Description

[0058] Figure 1 This is a flowchart illustrating the preparation method of the cadmium stripping solution for the cyanide-free cadmium plating of the present invention.

[0059] Figure 2 SEM images of the electroplated substrate and the electroplated substrate after the cadmium plating layer was removed in Example 1;

[0060] Figure 3 SEM images of the electroplated substrates after the cadmium plating was removed in Examples 2 and 3;

[0061] Figure 4 SEM images of the electroplated substrates after the cadmium plating was removed in Comparative Examples 1-3. Detailed Implementation

[0062] Example 1:

[0063] A cyanide-free cadmium plating stripping solution, comprising:

[0064] Nitric acid: 100 mL / L;

[0065] Ammonium chloride: 150 g / L;

[0066] Ammonium acetate: 40 g / L;

[0067] Benzotriazole: 10 g / L;

[0068] Dodecylbenzenesulfonate ammonium: 10 g / L.

[0069] The pH of the cadmium removal solution is 6.0; the temperature is 10℃.

[0070] A method for preparing a cyanide-free cadmium plating stripping solution includes the following steps:

[0071] (1) Slowly add nitric acid to ammonium chloride dissolved in deionized water;

[0072] (2) After the solution has cooled, add ammonium acetate, benzotriazole and dodecylbenzenesulfonate in sequence and stir until homogeneous;

[0073] (3) Use ammonia to adjust the pH of the solution to 6.0, and then add deionized water to the specified volume.

[0074] The preparation of dodecylbenzenesulfonate amine includes the following steps:

[0075] 1) Sulfonyl chloride reaction;

[0076] In a reaction vessel, 695g of dodecylbenzene and an appropriate amount of dichloromethane were added as solvent;

[0077] Under cooling conditions (0-10℃), slowly add 278g of chlorosulfonic acid dropwise while stirring.

[0078] The reaction temperature was gradually increased to room temperature, and stirring was continued for several hours to ensure complete reaction and produce dodecylbenzenesulfonyl chloride.

[0079] 2) Ammoniation reaction;

[0080] The generated dodecylbenzenesulfonyl chloride solution is slowly added to cooled ammonia water (or ammonia gas stream), and the reaction temperature is maintained at 0-10℃;

[0081] Continue stirring to ensure complete reaction, converting sulfonyl chloride into sulfonic acid amine.

[0082] 3) Solvent extraction and purification;

[0083] After the reaction is complete, the reaction mixture is cooled.

[0084] Dodecylbenzenesulfonate amine is extracted using a solvent (such as methanol or ethanol);

[0085] Unreacted impurities and byproducts are removed by filtration, and the filtrate is collected.

[0086] The solvent was evaporated from the filtrate to obtain pure solid dodecylbenzenesulfonate amine.

[0087] A method for removing cadmium from a cadmium coating involves using the aforementioned cyanide-free cadmium coating removal solution, maintaining the temperature of the removal solution at 10°C and the pH at 6.0, and completely immersing the cadmium-coated parts in the removal solution until the cadmium coating is completely removed.

[0088] Example 2:

[0089] A cyanide-free cadmium plating stripping solution, comprising:

[0090] Nitric acid: 120 mL / L;

[0091] Ammonium sulfate: 150 g / L;

[0092] Ammonium acetate: 50 g / L;

[0093] Methylbenzotriazole: 10 g / L;

[0094] Dodecylbenzenesulfonate ammonium: 15 g mL / L.

[0095] The pH of the cadmium removal solution is 7.0; the temperature is 25°C.

[0096] A method for preparing a cyanide-free cadmium plating stripping solution includes the following steps:

[0097] (1) Slowly add nitric acid to ammonium sulfate dissolved in deionized water;

[0098] (2) After the solution has cooled, add ammonium acetate, methylbenzotriazole and dodecylbenzenesulfonate in sequence and stir until homogeneous;

[0099] (3) Use ammonia to adjust the pH of the solution to 7.0, and then add deionized water to the specified volume.

[0100] The preparation method of dodecylbenzenesulfonate amine is the same as that in Example 1, so it will not be described again.

[0101] A method for removing cadmium from a cadmium coating involves using the aforementioned cyanide-free cadmium coating removal solution, maintaining the temperature of the removal solution at 25°C and the pH at 7.0, and completely immersing the cadmium-coated parts in the removal solution until the cadmium coating is completely removed.

[0102] Example 3:

[0103] A cyanide-free cadmium plating stripping solution, comprising:

[0104] Nitric acid: 120 mL / L;

[0105] Ammonium sulfate: 80 g / L;

[0106] Cadmium chloride: 70 g / L;

[0107] Ammonium borate: 50 g / L;

[0108] Benzotetrazole: 10 g / L;

[0109] Dodecylbenzenesulfonate ammonium: 20 g / L.

[0110] The pH of the cadmium removal solution is 6.5; the temperature is 40°C.

[0111] A method for preparing a cyanide-free cadmium plating stripping solution includes the following steps:

[0112] (1) Slowly add nitric acid to ammonium sulfate dissolved in deionized water;

[0113] (2) After the solution has cooled, add cadmium chloride, ammonium borate, benzotetrazole and dodecylbenzenesulfonate in sequence, and stir until homogeneous;

[0114] (3) Use ammonia to adjust the pH of the solution to 6.5, and then add deionized water to the specified volume.

[0115] The preparation method of dodecylbenzenesulfonate amine is the same as that in Example 1, so it will not be described again.

[0116] A method for removing cadmium from a cadmium coating involves using the aforementioned cyanide-free cadmium coating removal solution, maintaining the temperature of the removal solution at 40°C and the pH at 6.5, and completely immersing the cadmium-coated parts in the removal solution until the cadmium coating is completely removed.

[0117] Comparative Example 1:

[0118] A cadmium removal solution, comprising:

[0119] Ammonium nitrate: 80 g / L;

[0120] Temperature: 10℃.

[0121] Preparation steps for cadmium removal solution: Add ammonium nitrate to deionized water and stir until homogeneous.

[0122] Instructions for using cadmium removal solution: Keep the temperature of the cadmium removal solution at 10°C, and completely immerse the cadmium-coated parts in the solution until the cadmium plating is completely removed.

[0123] Comparative Example 2:

[0124] A cadmium removal solution, comprising:

[0125] Ammonium nitrate: 100g / L

[0126] Temperature: 25℃

[0127] Preparation steps for cadmium removal solution: Add ammonium nitrate to deionized water and stir until homogeneous.

[0128] Instructions for using cadmium removal solution: Keep the temperature of the cadmium removal solution at 25°C, and completely immerse the cadmium-coated parts in the solution until the cadmium plating is completely removed.

[0129] Comparative Example 3:

[0130] A cadmium removal solution, comprising:

[0131] Ammonium nitrate: 120 g / L;

[0132] Temperature: 40℃.

[0133] Preparation steps for cadmium removal solution: Add ammonium nitrate to deionized water and stir until homogeneous.

[0134] Instructions for using cadmium removal solution: Keep the temperature of the cadmium removal solution at 40°C, and completely immerse the cadmium-coated parts in the solution until the cadmium plating is completely removed.

[0135] The experimental results of the comparative examples above are shown in Table 1.

[0136] Comparative Examples 1-3 use commonly used ammonium nitrate solutions for cadmium removal. As shown in Table 1, when the coating is not passivated, the cadmium removal times of Examples 1-3 and their corresponding Comparative Examples 1-3 are similar. The difference in time can be attributed to the different reaction rates caused by different temperatures. When the coating is passivated using a hexavalent chromium passivation process, the conventional ammonium nitrate removal speed in Comparative Examples 1-3 is very slow, generally requiring more than 60 minutes to completely remove the cadmium coating. However, using the solutions of Examples 1-3 with added novel surfactants, the cadmium coating removal time is significantly shortened. This is because the surfactants can accelerate the destruction of the passivation film. After the cadmium coating is completely removed, the use of novel surfactants and corrosion inhibitors in Examples 1-3 greatly enhances the corrosion resistance of the substrate.

[0137] like Figure 2 As shown, (a1)-(a3) are SEM images of the electroplated substrate; (b1)-(b3) are SEM images of the electroplated substrate after the cadmium plating layer was removed in Example 1. Figure 3 As shown, (c1)-(c3) are SEM images of the electroplated substrate after the cadmium plating layer was removed in Example 2; (d1)-(d3) are SEM images of the electroplated substrate after the cadmium plating layer was removed in Example 3. Figure 4As shown, (e1)-(e3) are SEM images of the electroplated substrate after cadmium plating removal in Comparative Example 1; (f1)-(f3) are SEM images of the electroplated substrate after cadmium plating removal in Comparative Example 2; and (i1)-(i3) are SEM images of the electroplated substrate after cadmium plating removal in Comparative Example 3. Comparison revealed that the removal effects of Examples 1-3 were all better than those of Comparative Examples 1-3, exhibiting higher structural retention and stronger corrosion resistance after removal.

[0138] Table 1

[0139]

[0140] Example 4:

[0141] This embodiment is an optimization based on Embodiments 1-3. The dodecylbenzenesulfonate amine is a novel, non-commercial substance with the molecular formula: C 18 H 29 SO3NH2; structural formula: H3C-(CH2) 11 -C6H4-SO3NH2, specifically includes the following functional groups:

[0142] a1. Hydrophilic head group: sulfonic acid group (SO3H), which has strong hydrophilicity and ionic interaction;

[0143] a2. Lipophilic tail chain: contains a twelve-carbon chain (C 12 It provides sufficient hydrophobicity and interfacial activity;

[0144] a3. Functional groups: Introducing benzene rings and amine groups into the middle of the carbon chain to increase the interaction with the cadmium coating, accelerate the dissolution of the cadmium coating, and reduce the adhesion of hydrogen to the substrate.

[0145] The preparation method of dodecylbenzenesulfonate amine includes the following steps:

[0146] Step T1: Sulfonyl chloride reaction:

[0147] In a reaction vessel, add an appropriate amount of dodecylbenzene and a solvent (such as dichloromethane);

[0148] Under cooling conditions (0-10℃), slowly add chlorosulfonic acid dropwise while maintaining stirring;

[0149] The reaction temperature was gradually increased to room temperature, and stirring was continued for several hours to ensure complete reaction and produce dodecylbenzenesulfonyl chloride.

[0150] The equation for the above reaction is: C 12 H 25 C6H5 + ClSO3H → C 12 H 25C6H4SO2Cl+HCl.

[0151] Step T2: Ammoniation reaction:

[0152] The generated dodecylbenzenesulfonyl chloride solution is slowly added to cooled ammonia water or ammonia gas stream, and the reaction temperature is maintained at 0-10℃. The mixture is continuously stirred to ensure complete reaction, converting the sulfonyl chloride into sulfonic acid amine, and generating dodecylbenzenesulfonic acid amine.

[0153] The equation for the above reaction is: C 12 H 25 C6H4SO2Cl + NH3 → C 12 H 25 C6H4SO2NH2+HCl.

[0154] Step T3: Solvent extraction and purification:

[0155] After the reaction is complete, the reaction mixture is cooled; dodecylbenzenesulfonate amine is extracted using a solvent (such as methanol or ethanol); unreacted impurities and byproducts are removed by filtration, and the filtrate is collected; the solvent is evaporated from the filtrate to obtain pure dodecylbenzenesulfonate amine solid.

[0156] The other contents of this embodiment are the same as those of Embodiments 1-3, so they will not be repeated here.

[0157] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A cadmium stripping solution for cyanide-free cadmium plating, characterized in that, Calculated by mass percentage, it includes the following components: Nitric acid: 8wt%~12wt%; Ammonium salt: 20wt%~35wt%; Buffer: 3wt%~10wt%; Corrosion inhibitor: 1wt%~3wt%; Surfactant: 0.5wt%~2wt%.

2. The cadmium stripping solution for cyanide-free cadmium plating according to claim 1, characterized in that, The ammonium salt includes ammonium chloride and / or ammonium sulfate; the buffer includes ammonium acetate and / or ammonium borate.

3. The cadmium stripping solution for cyanide-free cadmium plating according to claim 1, characterized in that, The corrosion inhibitor includes any one or more of benzotriazole, methylbenzotriazole, and benzotetrazole.

4. The cadmium stripping solution for cyanide-free cadmium plating according to claim 1, characterized in that, The surfactant includes any one or more of dodecylbenzenesulfonate amine, dodecyl polyoxyethylene ether, tetradecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, and octadecyl polyoxyethylene ether.

5. A cadmium stripping solution for cyanide-free cadmium plating according to any one of claims 1-4, characterized in that, Based on concentration, it includes the following components: Nitric acid: 100 mL / L; Ammonium chloride: 150 g / L; Ammonium acetate: 40 g / L; Benzotriazole: 10 g / L; Dodecylbenzenesulfonate ammonium: 10 g / L.

6. The cadmium stripping solution for a cyanide-free cadmium plating according to any one of claims 1-4, characterized in that, Based on concentration, it includes the following components: Nitric acid: 120 mL / L; Ammonium sulfate: 150 g / L; Ammonium acetate: 50 g / L; Methylbenzotriazole: 10 g / L; Dodecylbenzenesulfonate ammonium: 15 g mL / L.

7. The cadmium stripping solution for a cyanide-free cadmium plating according to any one of claims 1-4, characterized in that, Based on concentration, it includes the following components: Nitric acid: 120 mL / L; Ammonium sulfate: 80 g / L; Cadmium chloride: 70 g / L; Ammonium borate: 50 g / L; Benzotetrazole: 10 g / L; Dodecylbenzenesulfonate ammonium: 20 g / L.

8. A method for preparing a cadmium stripping solution for cyanide-free cadmium plating, characterized in that, Includes the following steps: Step S1: Slowly add nitric acid to the ammonium salt dissolved in deionized water; Step S2: After the solution cools, add the buffer, corrosion inhibitor and surfactant in sequence, and stir until homogeneous; Step S3: Adjust the pH of the solution to 6.0-7.0 using ammonia.

9. The method for preparing a cadmium stripping solution for a cyanide-free cadmium plating according to claim 8, characterized in that, In step S2, the surfactant includes dodecylbenzenesulfonate amine, and the preparation of dodecylbenzenesulfonate amine includes the following steps: Step T1: Sulfonyl chloride reaction: Step T11: Add dodecylbenzene and solvent to the reaction vessel; Step T12: Under cooling conditions, control the temperature to 0-10℃, and slowly add chlorosulfonic acid dropwise while stirring; Step T13: Gradually raise the reaction temperature to room temperature, stir the reaction, and generate dodecylbenzenesulfonyl chloride; Step T2: Ammoniation reaction: The generated dodecylbenzenesulfonyl chloride solution is slowly added to cooled ammonia water or ammonia gas stream, and the reaction temperature is set to 0-10℃; the reaction is stirred to generate dodecylbenzenesulfonate amine.

10. A method for removing cadmium from a cadmium coating, using the cadmium removal solution for cadmium coatings without cyanide as described in any one of claims 1-7, characterized in that, Includes the following steps: Step A1: Maintain the temperature of the cadmium removal solution at 10–40°C; Step A2: Adjust the pH of the cadmium removal solution to 6.5 using ammonia or nitric acid; Step A3: Immerse the cadmium-coated parts completely in the cadmium removal solution until the cadmium plating is completely removed.

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