Copper is refined by electrolysis using an electrolytic cell containing an impure copper anode, a pure copper cathode, and an acidified copper sulfate solution as the electrolyte. When an electric current is passed through the cell, copper from the impure anode dissolves into the electrolyte and is deposited as pure copper onto the cathode.
The Electrolytic Process Explained:
The electrolytic refining of copper is a crucial process for obtaining high-purity copper used in electrical wiring and electronics. Here's a step-by-step breakdown:
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Electrolytic Cell Setup: The process takes place in an electrolytic cell. This cell consists of:
- Anode: A large slab of impure copper.
- Cathode: A thin sheet of highly pure copper.
- Electrolyte: An aqueous solution of copper sulfate (CuSO4) acidified with sulfuric acid (H2SO4). The sulfuric acid increases the conductivity of the solution.
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Applying an Electric Current: A direct current (DC) is applied across the electrodes. The anode is connected to the positive terminal and the cathode to the negative terminal of the power supply.
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Anodic Reaction (Oxidation): At the anode (impure copper), copper atoms lose two electrons and dissolve into the electrolyte as copper ions (Cu2+):
Cu(s) → Cu2+(aq) + 2e-
Importantly, less reactive impurities (like gold, silver, and platinum) present in the impure copper anode do not dissolve. These settle down below the anode as "anode mud," which can be recovered for their valuable metals. More reactive metals (like zinc and iron), if present, will also dissolve as ions in the electrolyte.
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Cathodic Reaction (Reduction): At the cathode (pure copper), copper ions (Cu2+) from the electrolyte gain two electrons and deposit as pure copper atoms:
Cu2+(aq) + 2e- → Cu(s)
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Selective Deposition: The voltage is carefully controlled so that only copper ions are reduced at the cathode. This prevents the deposition of other metal ions (like zinc or iron) that may have dissolved from the anode.
Summary of the Electrolytic Refining of Copper:
| Component | Description | Role in Electrolysis |
|---|---|---|
| Anode | Impure copper | Source of copper that dissolves into the electrolyte. |
| Cathode | Pure copper | Surface where pure copper is deposited. |
| Electrolyte | Acidified Copper Sulfate (CuSO4) solution | Conducts electricity and provides copper ions for deposition at the cathode. |
| Anode Mud | Residue of less reactive impurities | Valuable source of precious metals (gold, silver, platinum). |
Advantages of Electrolytic Refining:
- High Purity: Produces copper with a very high degree of purity (typically >99.99%).
- Byproduct Recovery: Allows for the recovery of valuable byproducts (like gold and silver) from the anode mud.
Electrolytic refining is an efficient and economical method for obtaining high-purity copper, essential for various industrial applications.
