Editing Smelting (section)

===Reduction===
Reduction is the final, high-temperature step in smelting, in which the oxide becomes the elemental metal. A reducing environment (often provided by carbon monoxide, made by incomplete [[combustion]] in an air-starved furnace) pulls the final [[oxygen]] atoms from the raw metal. The carbon source acts as a chemical reactant to remove oxygen from the ore, yielding the purified metal [[Chemical element|element]] as a product. The carbon source is oxidized in two stages. First, carbon (C) combusts with oxygen (O<sub>2</sub>) in the air to produce [[carbon monoxide]] (CO). Second, the carbon monoxide reacts with the ore (e.g. Fe<sub>2</sub>O<sub>3</sub>) and removes one of its oxygen atoms, releasing carbon dioxide ({{CO2}}). After successive interactions with carbon monoxide, all of the oxygen in the ore will be removed, leaving the raw metal element (e.g. Fe).<ref>{{cite web | title=Blast Furnace | website=Science Aid | url=https://scienceaid.co.uk/chemistry/applied/blastfurnace.html | ref={{sfnref | Science Aid}} | access-date=2021-10-13}}</ref> As most ores are impure, it is often necessary to use [[Flux (metallurgy)|flux]], such as [[limestone]] (or [[Dolomite (mineral)|dolomite]]), to remove the accompanying rock [[gangue]] as slag. This [[calcination]] reaction emits carbon dioxide.

The required temperature varies both in absolute terms and in terms of the melting point of the base metal. Examples:

* [[Iron oxide]] becomes metallic iron at roughly 1250&nbsp;°C (2282&nbsp;°F or 1523&nbsp;K), almost 300 degrees ''below'' iron's melting point of 1538&nbsp;°C (2800&nbsp;°F or 1811&nbsp;K).<ref>{{Cite book |last=Eisele |first=T.C. |title=Direct Biohydrometallurgical Extraction of Iron from Ore |year=2005 |doi=10.2172/877695|url=https://digital.library.unt.edu/ark:/67531/metadc880305/ }}</ref>
* [[Mercuric oxide]] becomes vaporous mercury near 550&nbsp;°C (1022&nbsp;°F or 823&nbsp;K), almost 600 degrees ''above'' mercury's melting point of -38&nbsp;°C (-36.4&nbsp;°F or 235&nbsp;K), and also above mercury's ''boiling'' point.<ref>{{Cite web|title=Mercury processing - Extraction and refining|url=https://www.britannica.com/technology/mercury-processing|access-date=2021-02-23|website=Encyclopedia Britannica|language=en}}</ref>