Editing Aluminium oxide (section)

==Production==

{{See also|List of countries by aluminium oxide production}}

Aluminium [[hydroxide]] minerals are the main component of [[bauxite]], the principal [[ore]] of [[aluminium]]. A mixture of the minerals comprise bauxite ore, including [[gibbsite]] (Al(OH)<sub>3</sub>), [[boehmite]] (γ-AlO(OH)), and [[diaspore]] (α-AlO(OH)), along with impurities of [[iron oxide]]s and hydroxides, quartz and [[clay minerals]].<ref>{{cite web| url = http://minerals.usgs.gov/minerals/pubs/commodity/bauxite/|publisher = USGS| access-date = 2009-05-05| title = Bauxite and Alumina Statistics and Information| archive-url= https://web.archive.org/web/20090506220703/http://minerals.usgs.gov/minerals/pubs/commodity/bauxite/| archive-date= 6 May 2009 | url-status= live}}</ref> Bauxites are found in [[laterite]]s. Bauxite is typically purified using the [[Bayer process]]:

: Al<sub>2</sub>O<sub>3</sub> + H<sub>2</sub>O + NaOH → NaAl(OH)<sub>4</sub>
: Al(OH)<sub>3</sub> + NaOH → NaAl(OH)<sub>4</sub>

Except for SiO<sub>2</sub>, the other components of bauxite do not dissolve in base. Upon filtering the basic mixture, Fe<sub>2</sub>O<sub>3</sub> is removed. When the Bayer liquor is cooled, Al(OH)<sub>3</sub> precipitates, leaving the silicates in solution.

: NaAl(OH)<sub>4</sub> → NaOH + Al(OH)<sub>3</sub>

The solid  Al(OH)<sub>3</sub> [[Gibbsite]] is then [[calcined]] (heated to over 1100&nbsp;°C) to give aluminium oxide:<ref name = azom/>

: 2&thinsp;Al(OH)<sub>3</sub> → Al<sub>2</sub>O<sub>3</sub> + 3&thinsp;H<sub>2</sub>O

The product aluminium oxide tends to be multi-phase, i.e., consisting of several phases of aluminium oxide rather than solely [[corundum]].<ref name=Paglia/> The production process can therefore be optimized to produce a tailored product. The type of phases present affects, for example, the solubility and pore structure of the aluminium oxide product which, in turn, affects the cost of aluminium production and pollution control.<ref name=Paglia/>

=== Sintering Process ===
The Sintering Process is a high-temperature method primarily used when the Bayer Process is not suitable, especially for [[ores]] with high [[silica]] content or when a more controlled product morphology is required.<ref>{{cite book |author=Alton T. Tabereaux, Ray D. Peterson |year=2014 |title=Treatise on Process Metallurgy |publisher=Elsevier |editor=Seshadri Seetharaman |chapter=Chapter 2.5 - Aluminum Production |pages=839–917 |isbn=9780080969886}}</ref> Firstly, [[Bauxite]] is mixed with additives like [[limestone]] and soda ash, then heating the mixture at high temperatures (1200&nbsp;°C to 1500&nbsp;°C) to form [[sodium aluminate]] and [[calcium silicate]].<ref>{{cite journal |last1=Bordboland |first1=Reza |last2=Azizi |first2=Asghar |last3=Khani |first3=Mohammad |year=2024 |title=Extracting Alumina from a Low-grade (Shale) Bauxite Ore using a Sintering Process with Lime-soda followed by Alkali Leaching |journal=Journal of Mining and Environment |volume=15 |issue=3 |pages=1131–1148 |doi=10.22044/jme.2024.13905.2588}}</ref> After sintering, the material is leached with water to dissolve the [[sodium aluminate]], leaving behind impurities. Sodium aluminate is then precipitated from the solution and calcined at around 1000&nbsp;°C to produce alumina.<ref>{{cite journal |last1=Sun |first1=Yue |last2=Pan |first2=Aifang |year=2023 |title=Extraction of alumina and silica from high-silica bauxite by sintering with sodium carbonate followed by two-step leaching with water and sulfuric acid |journal=RSC Advances |volume=13 |issue=33 |pages=23254–23266|doi=10.1039/D3RA03362G |pmid=37538514 |bibcode=2023RSCAd..1323254S |pmc=10394738 }}</ref> This method is useful for the production of complex shapes and can be used to create porous or dense materials.<ref>{{cite web |url=https://www.preciseceramic.com/blog/several-production-methods-of-alumina-and-their-advantages.html |title=Several Production Methods of Alumina and Their Advantages |date=Apr 3, 2024 |website=Precise Ceramics |access-date=Aug 19, 2024}}</ref>