Question

The process of converting hydrated alumina into anhydrous alumina is called

• A. smelting
• B. roasting
• C. calcination
• D. dressing

Answer 1

Answer: (C)

Calcination is a process in which the ore is heated strongly in the absence of air.
It removes volatile impurities like $C{O}_2,S{O}_2$, moisture from the ore.
It removes water from hydrated oxide ore.
$\underset{\text{bauxite (hydrated alumina)}}{A{l}_2{O}_3\cdot 2H_{2}O}\stackrel{\text{ Calcination }}{\to }\underset{\text{anhy.aluminium oxide}}{A{l}_2{O}_3}+2H_{2}O$
It also removes $C{O}_2$ from a carbonate ore.
$\underset{\text{ limestone }}{CaC{O}_3}\stackrel{\text{ Calcination }}{\to }CaO+C{O}_2$
Therefore, the process of converting hydrated alumina into anhydrous alumina is called calcination.
1. Roasting is a process in which the sulphide ore is heated strongly in the presence of air. In roasting the ore is converted into its oxide.
2. Smelting is a process in which the oxide ore in the fused state is reduced by carbon to the free metal.
3. Dressing: There are many impurities like soil, stones, clay, etc., present in the ore. These impurities are called gangue. The removal of these impurities from ore is called dressing.