In Pyro-metallurgical extraction of metal, thermal energy is one of the important inputs. Different unit processes like roasting, smelting, converting and refining require large amount of thermal energy. This lecture discusses roasting.
Roasting
Roasting is the oxidation of metal sulphides to give metal oxides and sulphur dioxide. Typical examples are:
In addition other reactions may take place: formation of and metal sulphates and formation of complex oxides such as .
Typically,sulphide ores of copper, zinc and lead are roasted either partially or completely. Copper sulphide ores are roasted partially; whereas ores of lead and Zinc are roasted completely into oxides for subsequent treatment. This is then a byproduct.
Roasting is usually carried out below the melting points of the sulphides and oxides involved, usually below. Both reactants and products are in the solid state.
In roasting ore concentrate is mixed with for oxidation. Normally excess air is used for roasting. Fuel may or may not be used.
Sources of energy
Different sources of thermal energy are
Heat of reaction: Combustion of S to releases and of thermal energy respectively. Several oxidation reactions like and so on releases thermal energy. These energies can be calculated from the heat of formation. Heat of formation of some compounds is
and metal sulphates and formation of complex oxides such as 
.
is then a byproduct.
. Both reactants and products are in the solid state.
releases 
and 
of thermal energy respectively. Several oxidation reactions like 
and so on releases thermal energy. These energies can be calculated from the heat of formation. Heat of formation of some compounds is 
