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Home > Conversion of ore into oxide - Calcination and Roasting

Conversion of ore into oxide - Calcination and Roasting - (Concept)

Calcination
Calcination is the process of heating the ores below their melting points in absence of air to remove volatile impurities like water, CO2 and organic
matter etc.

For example:

\mathrm{CaCO}_{3}\: \rightarrow \mathrm{CaO}+\mathrm{CO}_{2} \uparrow
Limestone        Calcium
                       oxide

\mathrm{Al}_{2} \mathrm{O}_{3}.\mathrm{H}_{2} \mathrm{O}\: \rightarrow \mathrm{Al}_{2} \mathrm{O}_{3}+2 \mathrm{H}_{2} \mathrm{O} \uparrow
   Bauxite                 Alumina

During calcination the ore becomes porous, volatile impurities are removed and carbonate ore decomposes into oxides.

Roasting
Roasting is the process of heating the ore in excess of air in order to convert metals into their oxides and water-insoluble sulphides into water-soluble sulphates. It is also called de-electronation of ores.

For example:

2 \mathrm{FeS}+3 \mathrm{O}_{2}\: \overset{\Delta }{\rightarrow}2 \mathrm{FeO}+2 \mathrm{SO}_{2}
Pyrite

2 \mathrm{HgS}+3 \mathrm{O}_{2} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{HgO}+2 \mathrm{SO}_{2}
Cinnabar

\mathrm{ZnS\: +\: 2O_{2}\: \overset{\Delta }{\rightarrow}\: ZnSO_{4}}
Zinc Sulphide

\mathrm{PbS}+2 \mathrm{O}_{2} \stackrel{\Delta}{\longrightarrow} \mathrm{PbSO}_{4}
Lead Sulphide

During roasting volatile impurities are removed, S, As, Sb are removed as SO2, As2O3, Sb2O3 respectively and sulphides ores arc converted into their oxides.

NOTE: Both calcination and roasting occur in mainly reverberatory furnace.

Exam Chapter
MHT-CET General principles and processes of isolation of elements
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