China Nonferrous Metallurgy

The milling residues from PCB (Printed Circuit Board) cutting typically contain copper and aluminum metals along with a high plastic content. The electrochemical dissolution and electrodeposition process offer an effective method for stripping copper and obtaining high-purity cathode copper from these residues. This process is characterized by its short duration, high current efficiency, and the production of high-purity copper, making it highly promising for various applications. However, the electrochemical mechanism underlying this process remains unclear.In this study, PCB-generated copper-containing solid waste was utilized as the anode, with titanium plates serving as the cathode. A series of experiments was carried out using a diaphragm electrolysis process in an NH₃-(NH₄)₂SO₄ system. These experiments included investigations into different ammonium salt systems, various electrodes in the ammonia/ammonium sulfate system, electrochemical behavior curves of different electrolyte compositions in the ammonia/ammonium sulfate system, and control steps and nucleation mechanisms of copper electroplating in the NH₃-(NH₄)₂SO₄ system. The results indicate that the starting reduction potential of copper electroplating in the ammonia/ammonium sulfate system is the lowest, resulting in low energy consumption during electroplating. Additionally, the hydrogen deposition potential in this system is negative, which helps avoid side reactions such as hydrogen evolution and enhances the cathodic current efficiency. The electroplating reaction of Cu²⁺ on the titanium electrode surface in the NH₃-(NH₄)₂SO₄ system is found to be an irreversible process and a two-electron one-step transfer process, with diffusion control as the controlling step. The nucleation mechanism of Cu²⁺ on the titanium electrode is close to instantaneous nucleation. These findings provide valuable theoretical insights for the NH₃-(NH₄)₂SO₄ system diaphragm electrolysis copper process.