the reaction of $\mathrm{Al}_{2} \mathrm{O}_{3}$ with coke $(\mathrm{C})$ at a temperature $>2500^{\circ} \mathrm{C}$.

the neutralization of aluminate solution by passing $\mathrm{CO}_{2}$ gas to precipitate hydrated alumina $\left(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot 3 \mathrm{H}_{2} \mathrm{O}\right)$.

the dissolution of $\mathrm{Al}_{2} \mathrm{O}_{3}$ in hot aqueous $\mathrm{NaOH}$.

the electrolysis of $\mathrm{Al}_{2} \mathrm{O}_{3}$ mixed with $\mathrm{Na}_{3} \mathrm{AlF}_{6}$ to give $\mathrm{Al}$ and $\mathrm{CO}_{2}$.

A mixture of PbS and PbO undergoes self-reduction to produce Pb and SO₂

In the extraction process of copper from copper pyrites, silica is added to produce copper silicate.

Partial oxidation of sulphide ore of copper by roasting, followed by self-reduction produces blister copper.

In cyanide process, zinc powder is utilized to precipitate gold from Na[Au(CN)₂]

Pb(NO₃)₂ and Zn(NO₃)₂

Pb(NO₃)₂ and Bi(NO₃)₃

AgNO₃ and Bi(NO₃)₃

Pb(NO₃)₂ and Hg(NO₃)₂

Hydrated Al₂O₃ precipitates, when CO₂ is bubbled through a solution of sodium aluminate.

Addition of Na₃AlF₆ lowers the melting point of alumina.

CO₂ is evolved at the anode during electrolysis.

The cathode is a steel vessel with a lining or carbon.