Extraction is a process of obtaining metals in the free state from concentrated ores. The two main operations for working of the ore are, conversion of concentrated ore to its oxide from (oxidation or de-electronation) and conversion of oxide to the metal (reduction or de-electronation). The concentrated ore is converted to metal oxide by calcination and roasting. The oxide of the metal is converted to metallic form by using reducing agents such as C,CO or active metals (Na, K, Mg, Al, etc). The Ellingham diagrams help in choosing the better reducing agents. Some metals like gold and silver are extracted by leaching process which involves both oxidation and reduction.
What is the basic difference between calcination and roasting .

Explanation

During calcination, the concentrated ore is heated either in the absence or in the limited supply of air. But roasting is carried out in excess of air.