6.14 Giving examples, differentiate between ‘roasting’ and ‘calcination’.

Roasting is the process of converting sulphide ores to oxides by heating the ores in a regular supply of air at a temperature below the melting point of the metal. For example, sulphide ores of Zn, Pb, and Cu are converted to their respective oxides by this process. 

2 Zns + 3O2  2ZnO + 2SO2Zinc blende2 Pbs + 3O2   2 PbO + 2SO2Galena2Cu2S + 3O2   2 Cu2O + 2SO2Copperglance

On the other hand, calcination is the process of converting hydroxide and carbonate ores to oxides by heating the ores either in the absence or in a limited supply of air at a temperature below the melting point of the metal. This process causes the escaping of volatile matter leaving behind the metal oxide. For example, hydroxide of Fe, carbonates of Zn, Ca, Mg are converted to their respective oxides by this process. 

Fe2O3.3H2OΔFe2O3+3H2O

Limonite

ZnCO3sΔZnOs+CO2g

Calamine

CaMgCO32ΔCaOs+Mgos+2CO

Dolomine