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Q.
The process of converting hydrated alumina into anhydrous alumina is called
AMUAMU 2002
Solution:
Calcination is a process in which the ore is heated strongly in the absence of air.
It removes volatile impurities like $CO _{2}, SO _{2}$, moisture from the ore.
It removes water from hydrated oxide ore.
$\underset{\text{bauxite (hydrated alumina)}}{Al _{2} O _{3} \cdot 2 H _{2} O} \xrightarrow{\text { Calcination }} \underset{\text{anhy.aluminium oxide}}{Al _{2} O _{3}}+2 H _{2} O$
It also removes $CO _{2}$ from a carbonate ore.
$\underset{\text { limestone }}{ CaCO _{3}} \xrightarrow{\text { Calcination }}CaO + CO _{2}$
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.