Impurities are removed from copper during the refining process through a series of steps that involve both physical and chemical methods. The most common method for copper refining is called electrolytic refining, which involves the use of an electrolytic cell. Here's a general overview of the process:
Blister copper: The initial material used for refining is called blister copper, which is obtained from copper ore through smelting. Blister copper contains impurities such as sulfur, iron, and other metals.
Electrolysis: The blister copper is used as an anode, and a thin sheet of pure copper is used as a cathode. Both the anode and cathode are placed in an electrolytic cell containing an electrolyte solution of copper sulfate (CuSO4) and sulfuric acid (H2SO4).
Electrolytic process: When an electric current is passed through the cell, copper ions from the blister copper anode migrate towards the cathode and get reduced, depositing pure copper onto the cathode. At the same time, impurities in the blister copper remain in the anode as sludge or dissolve into the electrolyte.
Sludge removal: Periodically, the sludge containing impurities settles at the bottom of the cell. It is then removed, and the impurities within the sludge can be further processed or treated separately.
Multiple electrolytic cycles: The electrolytic refining process is typically repeated multiple times to achieve higher purity levels. Each cycle further removes impurities from the copper, resulting in progressively purer copper.
Additional purification methods: In some cases, additional purification methods such as solvent extraction, precipitation, or other chemical treatments may be employed to remove specific impurities that are not effectively eliminated through electrolytic refining alone.
By repeating the electrolytic refining process and incorporating other purification techniques, the impurities in copper are gradually reduced, resulting in high-purity copper suitable for various applications, including electrical wiring, electronics, and other industries where high-quality copper is required.