Physical processes involved in metallurgy doesn't require any chemical reaction.
Some common chemical reactions involved in process of metallurgy are:
1. In roasting:
Ores when heated in excess of air.
2ZnS + 3O2 → 2ZnO + 2SO2
2CuS + 3O2 → 2PbO + 2SO2
Ores when heated in limited supply of air.
ZnCO3 → ZnO + CO2
CuCO3 → CuO + CO2
3. Reduction through electrolysis:
Al2O3 ⇔ 2Al+3 + 3O2-
At Cathode: 2Al+3 + 6e- → 2Al
At Anode : 3O2- - 6e- → 3[O] → 3O2 (gas)
4. Reduction by reducing agents:
ZnO + C → Zn + CO
Fe2O3 + 3CO → 2Fe + 3CO2
2PbO + C → 2Pb + CO2
CuO + CO → Cu + CO2
5. Reduction through thermal decomposition
2HgO → 2Hg + O2