Smelting is a process of applying heat to ore to melt out a base metal. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals.
Roasting the carbonate and sulfide minerals in air converts them to oxides. Carbon monoxide was (and is) the reducing agent of choice for smelting.
It is easily produced during the heating process, and as a gas comes into intimate contact with the ore.
The carbon thus oxidizes in two stages, producing first carbon monoxide and then carbon dioxide.
As most ores are impure, it is often necessary to use flux, such as limestone, to remove the accompanying rock gangue as slag.
Plants for the electrolytic reduction of aluminium are also generally referred to as aluminium smelters.