Editing Bauxite (section)

==Aluminium production==
{{See also | Aluminium#Production and refinement}}
[[File:CaboRojoDRBauxite.jpg|thumb|upright=1.3|Bauxite being loaded at Cabo Rojo, [[Dominican Republic]], to be shipped elsewhere for processing; 2007]]
[[File:Bauxite being digested by washing with hot Sodium Hydroxide.webm|thumb|Bauxite being digested by washing with a hot solution of sodium hydroxide at {{convert|175|C}} under pressure at National Aluminium Company, Nalconagar, India.]]
{{As of|2010}}, approximately 70% to 80% of the world's dry bauxite production is processed first into [[alumina]] and then into aluminium by [[electrolysis]].<ref>{{Cite web|url=http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/periodictable/electrolysisrev3.shtml|title=BBC - GCSE Bitesize: Making aluminium|language=en-GB|access-date=2018-04-01|archive-url=https://web.archive.org/web/20180225224144/http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/periodictable/electrolysisrev3.shtml|archive-date=2018-02-25|url-status=dead}}</ref> Bauxite rocks are typically classified according to their intended commercial application: metallurgical, abrasive, cement, chemical, and refractory.<ref>{{Cite web |last=Australia |first=Geoscience |date=2023-12-19 |title=Bauxite |url=https://www.ga.gov.au/scientific-topics/minerals/mineral-resources-and-advice/australian-resource-reviews/bauxite |access-date=2024-03-06 |website=Geoscience Australia |language=en}}</ref><ref>{{Cite web |title=Bauxite and Alumina Statistics and Information {{!}} U.S. Geological Survey |url=https://www.usgs.gov/centers/national-minerals-information-center/bauxite-and-alumina-statistics-and-information |access-date=2024-02-08 |website=www.usgs.gov}}</ref>

Bauxite ore is usually heated in a pressure vessel along with a [[sodium hydroxide]] solution at a temperature of {{cvt|150|to|200|°C|-1|}}. At these temperatures, the [[aluminium]] is dissolved as [[sodium aluminate]] (the [[Bayer process]]). The aluminium compounds in the bauxite may be present as [[gibbsite]] (Al(OH)<sub>3</sub>), [[boehmite]] (AlOOH) or [[diaspore]] (AlOOH); the different forms of the aluminium component will dictate the extraction conditions. The undissolved waste, [[bauxite tailings]], after the aluminium compounds are extracted contains [[iron oxides]], [[silica]], [[calcia]], [[Titanium dioxide|titania]] and some un-reacted [[alumina]]. After separation of the residue by filtering, pure gibbsite is precipitated when the liquid is cooled, and then seeded with fine-grained [[aluminium hydroxide]]. The gibbsite is usually converted into [[aluminium oxide]], Al<sub>2</sub>O<sub>3</sub>, by heating in rotary kilns or fluid flash calciners to a temperature in excess of {{cvt|1000|°C||||}}. This aluminium oxide is dissolved at a temperature of about {{cvt|960|°C||||}} in molten [[cryolite]]. Next, this molten substance can yield metallic aluminium by passing an [[electric current]] through it in the process of electrolysis, which is called the [[Hall–Héroult process]], named after its American and French discoverers.

Prior to the invention of this process, and prior to the [[Deville process]], aluminium ore was refined by heating ore along with elemental [[sodium]] or [[potassium]] in a [[vacuum]]. The method was complicated and consumed materials that were themselves expensive at that time. This made early elemental aluminium more expensive than [[gold]].<ref>{{cite web|url=http://www.worldwidewords.org/articles/aluminium.htm |title=Aluminium versus aluminum | author=Michael Quinion |publisher=Worldwidewords.org |date=2006-01-23 |access-date=2011-12-19}}</ref>