Copper is purified through electrolysis using an electrolytic cell containing specific components and processes. Here’s a breakdown:
The Electrolytic Cell
The electrolytic cell used for copper refining consists of the following key elements:
- Anode: Large slabs of impure copper (often called blister copper) serve as the anode.
- Cathode: Thin “starter sheets” of highly pure copper foil are used as the cathode. These are placed between the anodes.
- Electrolyte: The electrolytic solution is typically composed of copper sulfate and sulfuric acid.
The Electrolysis Process
When an electric current is passed through the cell:
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At the Anode: The impure copper anode dissolves into the copper sulfate solution. Copper atoms lose two electrons and become copper ions (Cu2+). Impurities like gold and silver don't dissolve and instead form a solid "anode sludge" at the bottom of the tank.
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In the Electrolyte: Copper ions (Cu2+) migrate through the electrolyte solution.
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At the Cathode: Copper ions (Cu2+) in the solution are attracted to the cathode. Here, they gain two electrons and are deposited as pure copper atoms onto the cathode.
Cu2+(aq) + 2e- → Cu(s)
Summary Table
| Component | Description |
|---|---|
| Anode | Impure copper (blister copper) |
| Cathode | Thin sheets of pure copper |
| Electrolyte | Copper sulfate (CuSO4) and sulfuric acid (H2SO4) solution |
| Process | Anode dissolves, copper ions migrate, pure copper deposits on the cathode |
| Impurities | Form "anode sludge" containing valuable metals like gold and silver |
Practical Considerations
- The voltage applied must be carefully controlled to ensure selective dissolution and deposition of copper.
- The electrolyte composition is maintained to maximize conductivity and copper ion concentration.
- The "anode sludge" collected is a valuable byproduct because it contains precious metals that can be recovered.
