Roasting is a process used in metallurgy to convert an ore into its oxide by heating it below its melting point in the presence of excess air or oxygen). Roasting is mostly used for converting sulfide ores, and it involves solid-gas thermal reactions, which can include oxidation, reduction, sulfation, chlorination, and pyrohydrolysis). During roasting, moisture and non-metallic impurities are released in the form of volatile gases. The process of roasting is exothermic and releases large amounts of acidic, metallic, and other toxic compounds, which can cause harm to the environment).

Roasting is different from calcination, which is a process in which ore is heated in the absence of air or air might be supplied in a limited quantity. Calcination involves the thermal decomposition of carbonate ores, while roasting is carried out mostly for sulfide minerals. The main purpose of roasting is to convert sulfide ores into oxides, and then metals are extracted.

In summary, roasting is a process used in metallurgy to convert sulfide ores into oxides by heating them below their melting point in the presence of excess air or oxygen. The process involves solid-gas thermal reactions, which can include oxidation, reduction, sulfation, chlorination, and pyrohydrolysis. Roasting is different from calcination, which is a process used to decompose carbonate ores.