Question

What is calcination? Explain it with reactions.

Answer 1

Hint: Calcination is the process used to convert the ore of the metal into metal oxide. The ore is heated strongly below its melting point. Calcination occurs in either absence of oxygen or a limited supply of air.

Complete step by step answer:
- Metals are usually present in ores as hydrated oxides (hydroxides), carbonates, and sulfides. Depending upon the nature of the mineral present in the ores, calcination is one of the processes used for the conversion of ores into their respective oxides.
- Calcination is the process of converting ore into its oxide by heating it strongly below its melting point either in the absence of oxygen or a limited supply of air/oxygen.
This method is commonly used to convert metal carbonates and hydroxides to their respective oxides.
During the process of calcination, the following chemical changes occur:
i)- Moisture in the ore is driven out.
ii)- Volatile impurities of S (sulfur), As (arsenic), and P (phosphorus) are removed as their volatile oxides respectively.
iii)- Water is removed from hydrated oxides and hydroxides oxides. Bauxite is converted into alumina. Limonite is converted into Ferric oxide.
$A{{l}_{2}}{{O}_{3}}.2{{H}_{2}}O\to A{{l}_{2}}{{O}_{3}}+2{{H}_{2}}O$
$F{{e}_{2}}{{O}_{3}}.3{{H}_{2}}O\to F{{e}_{2}}{{O}_{3}}+3{{H}_{2}}O$
iv)- Carbonate ores are converted into their respective oxides by loss of carbon dioxide. Limestone is converted into Calcium oxide.
$CaC{{O}_{3}}\to CaO+C{{O}_{2}}\uparrow $
Dolomite is also converted into Calcium oxide.
$CaC{{O}_{3}}.MgC{{O}_{3}}\to CaO+MgO+2C{{O}_{2}}\uparrow $
Malachite is an ore of copper and is converted into Copper oxide
$CuC{{O}_{3}}.Cu{{(OH)}_{2}}\to 2CuO+{{H}_{2}}O\uparrow +C{{O}_{2}}\uparrow $
Calamine is an ore of zinc and is converted into Zinc oxide:
$ZnC{{O}_{3}}\to ZnO+C{{O}_{2}}\uparrow $
v)- It makes the ore porous and hence easily workable in subsequent stages. Calcination is usually carried out in a reverberatory furnace.
- The concentrated ore is placed on the hearth of the furnace and heated by flames deflected from the roof.

Note: The conversion of ore of the metal into its ore is also called as De-electronation of ores. There is one more process called Roasting in which the ore is heated over the air, so don't get confused between them.