Answer
$Calcination$ is the heating of an ore in order to decompose it and drive off a volatile product.
Work Step by Step
For example, when carbonate minerals are heated, carbon dioxide is driven off, for example:
$PbCO_{3}(s)\rightarrow^{heat} PbO(s) + CO_{2}(g)$
Many minerals occur in a hydrated form (that is, they contain water). Calcination can also drive off water:
$Fe_{2}O_{3}. 2 Fe(OH)_{3}(s) \rightarrow^{heat}2 Fe_{2}O_{3}(s) + 3 H_{2}O(g)$
Heating that causes a chemical reaction between the furnace atmosphere (the gases in the furnace) and the mineral is called $roasting$ . Roasting is particularly important in processing sulfide ores. The ores are heated in the presence of oxygen, converting the sulfide into an oxide and emitting sulfur dioxide. For example, the roasting of lead(II) sulfide occurs by the reaction:
$2 PbS(s) + 3 O_{2}(g)\rightarrow^{heat}2 PbO(s) + 2 SO_{2}(g)$
In some cases, especially with the less active metals such as mercury, roasting the sulfide produces the pure metal:
$HgS(s) + O_{2}(g)\rightarrow^{heat}Hg(g) + SO_{2}(g)$
When roasting forms a liquid product, which makes separation easier, it is called $smelting$ . For example, the smelting of zinc oxide occurs as follows:
$ZnO(s) + C(s) \rightarrow^{heat} Zn(l) + CO(g)$
The gaseous carbon monoxide separates from the liquid zinc, allowing the metal to be readily recovered.
