Tin removal process for tinned copper wires

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The descaling process for tinned copper wires: The electronics and communications industry makes extensive use of tinned copper wires. During their production and use, a large amount of waste tinned wire is generated inevitably. For this type of tinned copper wire, aside from a portion that is used in the production of bronze alloys, the tin coating on the wires needs to be removed for other applications. Therefore, selecting an appropriate descaling process that results in low investment, easy operation, good descaling efficiency, and minimal copper loss is very important for improving profitability. 1 Chemical method: The chemical method for removing tin involves utilizing the difference in chemical reactivity between tin and copper to develop a process that removes tin while retaining copper. In line with environmental protection principles, this article does not cover the tin removal process using cyanide systems. 1.1 Acidic system A: Industrial hydrochloric acid (36%): 180 – 210 L/m3; oxidant Sb2O3: 8 – 12 g/L. This process operates at room temperature and is relatively simple, but it causes significant corrosion of copper; therefore it is generally not used. B: Industrial hydrochloric acid at 80 g/L, industrial copper sulfate pentahydrate at 150 g/L, and ferric chloride hexahydrate at 150 g/L. This process is simple to operate; tin removal takes place at room temperature, and the raw materials used are relatively inexpensive, making it a viable option for reference. C: 56% glacial acetic acid, 250 – 400 L/m3; copper sulfate pentahydrate, 110 – 140 g/L; ferric chloride hexahydrate, 60 – 90 g/L. The process is carried out at room temperature. The glacial acetic acid used in this process is relatively expensive, so it should be used with caution. D: 40% fluoroboric acid at 125 L/m3, 30% hydrogen peroxide at 38 L/m3. The process can be carried out at room temperature and is simple; care must be taken when adding hydrogen peroxide to prevent copper from being oxidized. 1.2 Alkaline system: Sodium hydroxide (caustic soda) – 160 to 180 g/L; Anti-staining salt S – 70 to 80 g/L; Sodium citrate – 15 g/L. 2 Electrochemical method: Electrochemical stripping can be used to effectively remove tin plating. Stripping equipment includes drum-type strippers and basket-type strippers, and the stripping solutions can be either acidic or alkaline. 2.1 Alkaline system: Sodium hydroxide stripping solution, with a concentration of 135 g/L, temperature of 80–90°C, and voltage of 1 volt. The stripping solution needs to be heated. 2.2 Acidic system: Stripping solutions based on fluoroboric acid or silfluoric acid, with a concentration of around 150 g/L; at room temperature, and at a potential of about 1 volt, ensuring that copper is not corroded. As long as the process conditions are properly controlled, electrochemical stripping can be used without damaging the copper substrate; sponge tin can be recovered, melted after washing, and purified to obtain tin with a purity of 99.9%, which can then be used to formulate tin alloys such as solder or to produce tin-based chemical products.