Ore is heated strongly in absence or limited
supply of air (air is used here as carrier of heat and moisture).Calcination
process temperature is below melting point of treated ore. This
process of calcination brings about the following changes.
(1)
The Carbonate ore gets decomposed to form the oxide of the metals for example
(2) Water of crystallisation present in the hydrated
oxide ores are gets lost as moisture as
Consequence of Calcination:
(1) Volatile products like water vapour / CO2
are removed and ore become porous
(2) Organic impurities decomposes into smaller
volatile products
Note: Both calcination and
Roasting are generally carried out in a Reverbatory
furnace. In case of roasting, the air holes are kept open while they are
partially or completely closed during calcination.
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