Roasting is the process in which the ore is heated below its melting point in presence of air to oxidise the impurities. eg: carbon, sulphur etc removed as their gaseous oxides.
Calcination is the process of heating the ore below its melting point an absence of air to remove volatile impurities like arsenic etc.
Roasting vs Calcination
|One is heated in the presence of excess of oxygen or air.||one is heated in the absence or limited supply of oxygen or air|
|This method is employed for sulphide ores.||This method is employed for carbonate ores.|
|Sulphur dioxide is produced along with metal oxide.||Carbon dioxide is produced along with metal oxide.|
Example: For the ores ZnS (sphalerite) and Cu2S (chalcocite), balanced equations for the roasting are:
2ZnS+3O2-->2 Zno+ 2SO2
2 Cu2S + 3O2 → 2 Cu2O + 2 SO2
Example: ZnCO3--> ZnO+ C02