Plants for the electrolytic reduction of aluminium are also generally referred to as aluminium smelters.There can be associated health risks with smelting, one of them being respiratory problems causing reduced physical capacity, for those who work in smelting factories.In the case of carbonates and sulfides, a process called "roasting" drives out the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced.
In the Old World, the first metals smelted were tin and lead.
The earliest known cast lead beads were found in the Çatal Höyük site in Anatolia (Turkey), and dated from about 6500 BC, but the metal may have been known earlier.
Since the discovery happened several millennia before the invention of writing, there is no written record about how it was made.
However, tin and lead can be smelted by placing the ores in a wood fire, leaving the possibility that the discovery may have occurred by accident.
The required temperature varies over a very large range, both in absolute terms and in terms of the melting point of the base metal.
Examples: Flux and slag can provide a secondary service after the reduction step is complete: they provide a molten cover on the purified metal, preventing contact with oxygen while still hot enough to readily oxidize.
Calcium oxide, in the form of lime, was often used for this purpose, since it could react with the carbon dioxide and sulfur dioxide produced during roasting and smelting to keep them out of the working environment.
Of the seven metals known in antiquity, only gold occurred regularly in native form in the natural environment.
The reducing agent is commonly a source of carbon, such as coke—or, in earlier times, charcoal.