Editing Calcium oxide (section)

==Preparation==
Calcium oxide is usually made by the [[thermal decomposition]] of materials, such as [[limestone]] or [[seashell]]s, that contain [[calcium carbonate]] (CaCO<sub>3</sub>; mineral [[calcite]]) in a [[lime kiln]]. This is accomplished by heating the material to above {{convert|825|C|F}},<ref name="merck">Merck Index of Chemicals and Drugs, 9th edition monograph 1650</ref><ref>{{Citation |last1=Kumar |first1=Gupta Sudhir |title=Lime Calcination |date=2007 |url=http://link.springer.com/10.1007/978-1-59745-173-4_14 |work=Advanced Physicochemical Treatment Technologies |volume=5 |pages=611–633 |editor-last=Wang |editor-first=Lawrence K. |place=Totowa, NJ |publisher=Humana Press |language=en |doi=10.1007/978-1-59745-173-4_14 |isbn=978-1-58829-860-7 |access-date=2022-07-26 |last2=Ramakrishnan |first2=Anushuya |last3=Hung |first3=Yung-Tse |series=Handbook of Environmental Engineering |editor2-last=Hung |editor2-first=Yung-Tse |editor3-last=Shammas |editor3-first=Nazih K.|url-access=subscription }}</ref> a process called [[calcination]] or ''lime-burning'', to liberate a molecule of [[carbon dioxide]] (CO<sub>2</sub>), leaving quicklime behind. This is also one of the few chemical reactions known in [[prehistoric]] times.<ref>{{Cite web|url=https://www.lhoist.com/lime-throughout-history|title=Lime throughout history {{pipe}} Lhoist - Minerals and lime producer|website=Lhoist.com|access-date=10 March 2022}}</ref>
: CaCO<sub>3</sub>(s) → CaO(s) + CO<sub>2</sub>(g)

The quicklime is not stable and, when cooled, will [[Spontaneous process|spontaneously react]] with CO<sub>2</sub> from the air until, after enough time, it will be completely converted back to calcium carbonate unless [[Slaking (geology)|slaked]] with water to set as [[lime plaster]] or [[lime mortar]].

Annual worldwide production of quicklime is around 283 million tonnes. China is by far the world's largest producer, with a total of around 170 million tonnes per year. The United States is the next largest, with around 20 million tonnes per year.<ref>{{cite book|first=M. Michael|last=Miller|chapter=Lime|title=Minerals Yearbook|page=43.13|publisher=[[U.S. Geological Survey]]|year=2007|url=http://minerals.usgs.gov/minerals/pubs/commodity/lime/myb1-2007-lime.pdf}}</ref>

Approximately 1.8{{nbsp}}t of limestone is required per 1.0{{nbsp}}t of quicklime. Quicklime has a high affinity for water and is a more efficient [[desiccant]] than [[silica gel]]. The reaction of quicklime with water is associated with an increase in volume by a factor of at least 2.5.<ref name="a">{{citation | author=Tony Oates | contribution=Lime and Limestone | title=[[Ullmann's Encyclopedia of Industrial Chemistry]] | edition=7th | publisher=Wiley | year=2007 | pages=1–32 | doi=10.1002/14356007.a15_317| isbn=978-3527306732 }}</ref>

Hydroxyapatite's free CaO content rises with increased calcination temperatures and longer times. It also pinpoints particular temperature cutoffs and durations that impact the production of CaO, offering information on how calcination parameters impact the composition of the material.