Calcination means what?

Calcinations is the process of subjecting a substance to the action of heat, but without fusion, for the purpose of causing some change in its physical or chemical constitution. The objects of calcination are usually:

• to drive off water, present as absorbed moisture, as "water of crystallization," or as "water of constitution";
• to drive off carbon dioxide, sulphl11' dioxide, or other volatile constituent;
• to oxidize a part or the whole of the substance.

There are a few other purposes for which calcination is employed in special cases, and these will be mentioned in their propel' places. The process is often called "roasting," "firing," or "burning," by the workmen. It is carried on in furnaces, retorts, or kilns, and very often the material is raked over or stirred, during the process, to secure uniformity in the product.
The furnaces used for calcining substances vary much in their construction, but there are three general classes: muffle, reverberatory, and shaft furnaces or kilns.
 

Heating of ores in no or limited supply of air is called calcination. Calcination is usually done for carbonate ores