Question

What is the basic purpose of roasting and Calcination? Compare these two processes.

Answer 1

The main purpose of Calcination and Roasting, are used to convert the Carbonate ores and Sulphide ores into its pure metals

Calcination:- The process in which , ore is heated in absence of air or limited supply of air strongly, below its fusion temperature .it is carried out in the case of carbonated ores or hydrated oxides.

i) Hydrated oxide ore undergo calcination in order to remove moisture

• It is a decomposition process ( removal of moisture or carbon-dioxide gas)

Example:-${\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O}(\mathrm{bauxite})\stackrel{∆}{\to }{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{alumina}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{water}\right)$

ii) carbonate ores undergo calcination in order to remove carbon-dioxide as-

${\mathrm{CaCO}}_3(\mathrm{lime}\mathrm{stone})\stackrel{∆}{\to }\mathrm{CaO}(\mathrm{quick}\mathrm{lime})+{\mathrm{CO}}_2(\mathrm{carbon}\mathrm{dioxide})$

Roasting:- The process in which , ore is heated either alone or with some material but the excess of oxygen (air)is the essential Condition. it is carried out for Sulphide ore .

• It is oxidation process (addition of oxygen)

$2\mathrm{PbS}\left(\mathrm{Galena}\right)+3{\mathrm{O}}_2\left(\mathrm{oxygen}\right)\stackrel{∆}{\to }2\mathrm{PbO}(\mathrm{Lead}\mathrm{II}\mathrm{oxide})+2{\mathrm{SO}}_2\left(\mathrm{sulphurdioxide}\right)$

Therefor the main purpose of Calcination and Roasting, are used to convert the Carbonate ores and Sulphide ores into its pure metals.