* Roasting is a process in metallurgy in which a sulfide ore is heated in air. The process may convert a metal sulfide to a metal oxide or to a free metal.
Example: Roasting ZnS may yield ZnO; roasting HgS may yield free Hg metal.
* Calcination is a thermal treatment process in presence of air applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The calcination process normally takes place at temperatures below the melting point of the product materials. Calcination is to be distinguished from roasting, in which more complex gas–solid reactions take place between the furnace atmosphere and the solids.
Calcination reactions usually take place at or above the thermal decomposition temperature.
For example, in limestone calcination, a decomposition process, the chemical reaction is
CaCO3 → CaO + CO2(g)
