Editing Iron (section)

====Blast furnace processing====
{{Main|Blast furnace}}
The blast furnace is loaded with iron ores, usually [[hematite]] {{chem2|Fe2O3}} or [[magnetite]] {{chem2|Fe3O4}}, along with coke ([[coal]] that has been separately baked to remove volatile components) and [[Flux (metallurgy)|flux]] ([[limestone]] or [[Dolomites|dolomite]]). "Blasts" of air pre-heated to 900 °C (sometimes with oxygen enrichment) is blown through the mixture, in sufficient amount to turn the carbon into [[carbon monoxide]]:{{sfn|Greenwood|Earnshaw|1997|p=1073}}

:{{chem2 | 2 C + O2 -> 2 CO }}

This reaction raises the temperature to about 2000 °C. The carbon monoxide reduces the iron ore to metallic iron:{{sfn|Greenwood|Earnshaw|1997|p=1073}}

:{{chem2 | Fe2O3 + 3 CO -> 2 Fe + 3 CO2 }}

Some iron in the high-temperature lower region of the furnace reacts directly with the coke:{{sfn|Greenwood|Earnshaw|1997|p=1073}}
:{{chem2 | 2 Fe2O3 + 3 C -> 4 Fe + 3 CO2 }}

The flux removes silicaceous minerals in the ore, which would otherwise clog the furnace: The heat of the furnace decomposes the carbonates to [[calcium oxide]], which reacts with any excess [[silica]] to form a [[slag]] composed of [[calcium silicate]] {{chem2|CaSiO3}} or other products. At the furnace's temperature, the metal and the slag are both molten. They collect at the bottom as two immiscible liquid layers (with the slag on top), that are then easily separated.{{sfn|Greenwood|Earnshaw|1997|p=1073}} The slag can be used as a material in [[road]] construction or to improve mineral-poor soils for [[agriculture]].<ref name="Biddle" />

Steelmaking thus remains one of the largest industrial contributors of CO<sub>2</sub> emissions in the world.<ref>{{Cite journal |last1=Wang |first1=Peng |last2=Ryberg |first2=Morten |last3=Yang |first3=Yi |last4=Feng |first4=Kuishuang |last5=Kara |first5=Sami |last6=Hauschild |first6=Michael |last7=Chen |first7=Wei-Qiang |date=2021-04-06 |title=Efficiency stagnation in global steel production urges joint supply- and demand-side mitigation efforts |journal=Nature Communications |volume=12 |issue=1 |pages=2066 |doi=10.1038/s41467-021-22245-6 |issn=2041-1723 |pmc=8024266 |pmid=33824307|bibcode=2021NatCo..12.2066W }}</ref>

<gallery widths=200 heights=150>
File:Chinese Fining and Blast Furnace.jpg|17th century Chinese illustration of workers at a blast furnace, making wrought iron from pig iron<ref name="song">[[Song Yingxing]] (1637): The ''Tiangong Kaiwu'' encyclopedia.</ref>
File:Iron-Making.jpg|How iron was extracted in the 19th century
File:Geography of Ohio - DPLA - aaba7b3295ff6973b6fd1e23e33cde14 (page 111) (cropped).jpg|Iron furnace in Columbus, Ohio, 1922
</gallery>