Thermodynamic extraction (carbon reduction and zone refining) (Metal oxide + Carbon → Metal + CO; Zone refining: impurity segregates into molten zone)
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Metal oxide + Carbon → Metal + CO; Zone refining: impurity segregates into molten zone, swept to end
What each symbol means
| Symbol | What it stands for |
|---|---|
| C | Coke/carbon as reducing agent |
| M | Extracted metal |
| MO | Metal oxide (e.g., ZnO, Fe₂O₃, SnO₂) |
When to use this
Carbon reduction works for metals whose oxide line lies above the C line on the Ellingham diagram (i.e., ΔG°(oxide) is less negative than ΔG°(CO) at that temperature). Zone refining exploits the difference in solubility of impurity in solid vs liquid phase (distribution coefficient k < 1) — used for ultrapure Ge, Si, Ga, In.