Smelting: Smelting is a pyrochemical (pyre = heat) process, in which the ore is mixed with flux and fuel and strongly heated. The heat is so strong that the ore is reduced to even metal as in the case of iron (Fe), and the metal is obtained in molten state. During smelting the impurities (gangue) in the ore react with flux to form slag which is removed. For haematite (Fe2 O3 )ore, coke is used as fuel and lime stone (CaCO3 ) is used as flux. The smelting is carried out in a specially built furnace known as blast furance.
The reactions inside the furnace are:
2C(s) + O2 (g) ––––> 2CO(g)
Fuel Fe2 O3(s) + 3CO(g) ––––> 2Fe(l) + 3CO2(g)
haematite CaCO 3(s) –––> CaO(s) + CO2 (g) Limestone(flux) lime CaO(s) + SiO2(s) ––––> CaSiO
Roasting: Roasting is a pyrochemical process in which the ore is heated in the presence of oxygen or air below its melting point. The products (like metal oxide from sulphide ore) obtained in the process also are in solid state. Generally reverberatory furnace is used for roasting.
2ZnS(s) + 3O2(g) ––––> 2ZnO(s) + 2SO2(g)
Calcination: Calcination is a pyrochemical process in which the ore is heated in the absence of air. The ore gets generally decomposed in the process.
Eg: MgCO3(s) MgO(s) + CO2(g)
CaCO3(s) C aO(s) + CO2(g)
Flux: Flux is a substance added to the ore to remove the gangue from it by reacting with the gangue. If the impurity (gangue) is acidic substance like SiO2 , basic substance like CaO is used as flux and if the impurity is of basic