calcium oxide

Calcium oxide is usually made by the thermal decomposition of materials, such as limestone or seashells, that contain calcium carbonate (CaCO₃; mineral calcite) in a lime kiln. This is accomplished by heating the material to above {{convert|825|C|F}},Merck Index of Chemicals and Drugs, 9th edition monograph 1650{{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 }} a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO₂), leaving quicklime behind. This is also one of the few chemical reactions known in prehistoric times.{{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}}

: CaCO₃(s) → CaO(s) + CO₂(g)

The quicklime is not stable and, when cooled, will spontaneously react with CO₂ from the air until, after enough time, it will be completely converted back to calcium carbonate unless 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.{{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}}

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.{{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 }}

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.

File:09. Гасење вар како силно егзотермен процес.webm reaction occurs ("slaking of lime"). The temperature can reach up to some {{convert|300|C|F}}.]]

• The major use of quicklime is in the basic oxygen steelmaking (BOS) process. Its usage varies from about {{convert|30|to(-)|50|kg|round=5||}} per ton of steel. The quicklime neutralizes the acidic oxides, SiO₂, Al₂O₃, and Fe₂O₃, to produce a basic molten slag.
• Ground quicklime is used in the production of aerated concrete such as blocks with densities of ca. {{cvt|0.6-1.0|g/cm3|g/cuin||}}.
• Quicklime and hydrated lime can considerably increase the load carrying capacity of clay-containing soils. They do this by reacting with finely divided silica and alumina to produce calcium silicates and aluminates, which possess cementing properties.
• Small quantities of quicklime are used in other processes; e.g., the production of glass, calcium aluminate cement, and organic chemicals.
• Heat: Quicklime releases thermal energy by the formation of the hydrate, calcium hydroxide, by the following equation:Collie, Robert L. "Solar heating system" {{US patent|3955554}} issued May 11, 1976

::CaO (s) + H₂O (l) {{eqm}} Ca(OH)₂ (aq) (ΔH_r = −63.7{{nbsp}}kJ/mol of CaO)

: As it hydrates, an exothermic reaction results and the solid puffs up. The hydrate can be reconverted to quicklime by removing the water by heating it to redness to reverse the hydration reaction. One litre of water combines with approximately {{convert|3.1|kg}} of quicklime to give calcium hydroxide plus 3.54 MJ of energy. This process can be used to provide a convenient portable source of heat, as for on-the-spot food warming in a self-heating can, cooking, and heating water without open flames. Several companies sell cooking kits using this heating method.{{cite web|last1=Gretton|first1=Lel|title=Lime power for cooking - medieval pots to 21st century cans|url=http://www.oldandinteresting.com/fireless-cooking-with-quicklime.aspx|website=Old & Interesting|access-date=13 February 2018}}

• It is a food additive used as an acidity regulator, a flour treatment agent and a leavener.{{cite web |title=Compound Summary for CID 14778 - Calcium Oxide |url=https://pubchem.ncbi.nlm.nih.gov/compound/Lime |publisher=PubChem}} It has E number E529.
• Light: When quicklime is heated to {{convert|2400|C|F}}, it emits an intense glow. This form of illumination is known as a limelight, and was used broadly in theatrical productions before the invention of electric lighting.{{cite journal |last=Gray |first=Theodore |date=September 2007 |title=Limelight in the Limelight |journal=Popular Science |page=84 |url=http://www.popsci.com/node/9652 |access-date=2009-03-31 |archive-date=2008-10-13 |archive-url=https://web.archive.org/web/20081013235058/http://www.popsci.com/node/9652 |url-status=dead }}
• Cement: Calcium oxide is a key ingredient for the process of making cement.
• As a cheap and widely available alkali. About 50% of the total quicklime production is converted to calcium hydroxide before use. Both quick- and hydrated lime are used in the treatment of drinking water.
• Petroleum industry: Water detection pastes contain a mix of calcium oxide and phenolphthalein. Should this paste come into contact with water in a fuel storage tank, the CaO reacts with the water to form calcium hydroxide. Calcium hydroxide has a high enough pH to turn the phenolphthalein a vivid purplish-pink color, thus indicating the presence of water.
• Chemical pulping: Calcium oxide is used to make calcium hydroxide, which is used to regenerate sodium hydroxide from sodium carbonate in the chemical recovery at kraft pulp mills.
• Plaster: There is archeological evidence that Pre-Pottery Neolithic B humans used limestone-based plaster for flooring and other uses.{{Cite news|author=Tel Aviv University|title=Neolithic man: The first lumberjack?|url=https://phys.org/news/2012-08-neolithic-lumberjack.html|date=August 9, 2012 |access-date=2023-02-02|website=phys.org|language=en}}{{Cite journal | doi = 10.1017/S006824540000006X| title = Neolithic Lime Plastered Floors in Drakaina Cave, Kephalonia Island, Western Greece: Evidence of the Significance of the Site| journal = The Annual of the British School at Athens| volume = 103| pages = 27–41| year = 2011| last1 = Karkanas | first1 = P. | last2 = Stratouli | first2 = G. | s2cid = 129562287}}Connelly, Ashley Nicole (May 2012) [https://beardocs.baylor.edu/xmlui/bitstream/handle/2104/8320/Ashley_Connelly_HonorsThesis.pdf?sequence=1 Analysis and Interpretation of Neolithic Near Eastern Mortuary Rituals from a Community-Based Perspective] {{Webarchive|url=https://web.archive.org/web/20150309143945/https://beardocs.baylor.edu/xmlui/bitstream/handle/2104/8320/Ashley_Connelly_HonorsThesis.pdf?sequence=1 |date=2015-03-09 }}. Baylor University Thesis, Texas Such Lime-ash floor remained in use until the late nineteenth century.
• Chemical or power production: Solid sprays or slurries of calcium oxide can be used to remove sulfur dioxide from exhaust streams in a process called flue-gas desulfurization.
• Carbon capture and storage: Calcium oxide can be used to capture carbon dioxide from flue gases in a process called calcium looping.
• Mining: Compressed lime cartridges exploit the exothermic properties of quicklime to break rock. A shot hole is drilled into the rock in the usual way and a sealed cartridge of quicklime is placed within and tamped. A quantity of water is then injected into the cartridge and the resulting release of steam, together with the greater volume of the residual hydrated solid, breaks the rock apart. The method does not work if the rock is particularly hard.{{cite book|last1=Walker|first1=Thomas A|author-link=Thomas A. Walker|title=The Severn Tunnel Its Construction and Difficulties|url=https://archive.org/details/severntunnelits01walkgoog|date=1888|publisher=Richard Bentley and Son|location=London|page=[https://archive.org/details/severntunnelits01walkgoog/page/n160 92]}}{{cite journal|title=Scientific and Industrial Notes|journal=Manchester Times|date=13 May 1882|page=8|location=Manchester, England}}US Patent 255042, 14 March 1882
• Disposal of corpses: Historically, it was mistakenly believed that quicklime was efficacious in accelerating the decomposition of corpses. The application of quicklime can, in fact, promote preservation. Quicklime can aid in eradicating the stench of decomposition, which may have led people to the erroneous conclusion.{{cite journal |last1=Schotsmans |first1=Eline M.J. |last2=Denton |first2=John |last3=Dekeirsschieter |first3=Jessica |last4=Ivaneanu |first4=Tatiana |last5=Leentjes |first5=Sarah |last6=Janaway |first6=Rob C. |last7=Wilson |first7=Andrew S. |title=Effects of hydrated lime and quicklime on the decay of buried human remains using pig cadavers as human body analogues |url=https://www.researchgate.net/publication/51748334 |journal=Forensic Science International |date=April 2012 |volume=217 |issue=1–3 |pages=50–59 |doi=10.1016/j.forsciint.2011.09.025|pmid=22030481 |hdl=2268/107339 |hdl-access=free }}
• It has been determined that the durability of ancient Roman concrete is attributed in part to the use of quicklime as an ingredient. Combined with hot mixing, the quicklime creates macro-sized lime clasts with a characteristically brittle nano-particle architecture. As cracks form in the concrete, they preferentially pass through the structurally weaker lime clasts, fracturing them. When water enters these cracks it creates a calcium-saturated solution which can recrystallize as calcium carbonate, quickly filling the crack. {{citation|url=https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106 |journal=MIT News | date=January 6, 2023|title=Riddle solved: Why was Roman concrete so durable? }}
• The thermochemical heat storage mechanism is greatly impacted by the sintering of CaO and CaCO₃. It demonstrates that the storage materials become less reactive and denser at increasing temperatures. It also pinpoints particular sintering processes and variables influencing the efficiency of these materials in heat storage.

In 80 BC, the Roman general Sertorius deployed choking clouds of caustic lime powder to defeat the Characitani of Hispania, who had taken refuge in inaccessible caves.{{citation|author=Plutarch|author-link=Plutarch|title=Parallel Lives|chapter=Sertorius 17.1–7|chapter-url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A2008.01.0062%3Achapter%3D17%3Asection%3D1}} A similar dust was used in China to quell an armed peasant revolt in 178 AD, when lime chariots equipped with bellows blew limestone powder into the crowds.{{citation | editor=Philip Wexler | author=Adrienne Mayor | entry=Ancient Warfare and Toxicology | title=Encyclopedia of Toxicology | edition=2nd | volume=4 | publisher=Elsevier | year=2005 | pages=117–121 | isbn=0-12-745354-7}}

Quicklime is also thought to have been a component of Greek fire. Upon contact with water, quicklime would increase its temperature above {{convert|150|C|||}} and ignite the fuel.{{cite book|url=https://books.google.com/books?id=MQMGhInCvlgC&pg=PA128|page=128|title=Chemical and biological warfare: a comprehensive survey for the concerned citizen|author=Croddy, Eric |publisher=Springer|year=2002|isbn=0-387-95076-1}}

David Hume, in his History of England, recounts that early in the reign of Henry III, the English Navy destroyed an invading French fleet by blinding the enemy fleet with quicklime.{{cite book|url=http://www.gutenberg.org/files/19212/19212-h/19212-h.htm#2H_4_0002|title=History of England| volume=I|author=David Hume|author-link=David Hume|year=1756}} Quicklime may have been used in medieval naval warfare – up to the use of "lime-mortars" to throw it at the enemy ships.Sayers, W. (2006). "The Use of Quicklime in Medieval Naval Warfare". The Mariner's Mirror. Volume 92. Issue 3. pp. 262–269.

Limestone is a substitute for lime in many applications, which include agriculture, fluxing, and sulfur removal. Limestone, which contains less reactive material, is slower to react and may have other disadvantages compared with lime, depending on the application; however, limestone is considerably less expensive than lime. Calcined gypsum is an alternative material in industrial plasters and mortars. Cement, cement kiln dust, fly ash, and lime kiln dust are potential substitutes for some construction uses of lime. Magnesium hydroxide is a substitute for lime in pH control, and magnesium oxide is a substitute for dolomitic lime as a flux in steelmaking.{{cite web|url=https://prd-wret.s3-us-west-2.amazonaws.com/assets/palladium/production/atoms/files/mcs-2019-lime.pdf|title=Lime|page=96|website=Prd-wret.s3-us-west-2.amazonaws.com|access-date=2022-03-10|archive-date=2021-12-19|archive-url=https://web.archive.org/web/20211219004903/https://prd-wret.s3-us-west-2.amazonaws.com/assets/palladium/production/atoms/files/mcs-2019-lime.pdf|url-status=dead}}

Because of vigorous reaction of quicklime with water, quicklime causes severe irritation when inhaled or placed in contact with moist skin or eyes. Inhalation may cause coughing, sneezing, and labored breathing. It may then evolve into burns with perforation of the nasal septum, abdominal pain, nausea and vomiting. Although quicklime is not considered a fire hazard, its reaction with water can release enough heat to ignite combustible materials.{{Cite web|url=http://ww25.hazard.com/msds/mf/baker/baker/files/c0462.htm?subid1=20230203-0103-092e-9982-d576d3e248aa |url-status=usurped |archive-url=https://web.archive.org/web/20120501110853/http://hazard.com/msds/mf/baker/baker/files/c0462.htm |archive-date=May 1, 2012 |access-date=2023-02-02|website=ww25.hazard.com|title=Hazards |date=December 8, 1996 |author=Mallinckrodt Baker Inc. - Strategic Services Division }}{{better source needed|date=June 2023}}

Calcium oxide is also a separate mineral species (with the unit formula CaO), named 'Lime'.{{cite web|url=http://cnmnc.units.it/|title=List of Minerals|website=Ima-mineralogy.org|date=21 March 2011}}{{cite journal |last1=Fiquet |first1=G. |last2=Richet |first2=P. |last3=Montagnac |first3=G. |title=High-temperature thermal expansion of lime, periclase, corundum and spinel |journal=Physics and Chemistry of Minerals |date=Dec 1999 |volume=27 |issue=2 |pages=103–111 |doi=10.1007/s002690050246 |bibcode=1999PCM....27..103F |s2cid=93706828 |url=https://doi.org/10.1007/s002690050246 |access-date=9 February 2023|url-access=subscription }} It has an isometric crystal system, and can form a solid solution series with monteponite. The crystal is brittle, pyrometamorphic, and is unstable in moist air, quickly turning into portlandite (Ca(OH)₂).{{Cite journal |last=Tian, Lin, Yan |first=X. K., S. C., J., & Zhao, C. Y. |date=2022 |title=Lime |url=https://doi.org/10.1016/j.cej.2021.131229 |access-date=10 March 2022 |website=Mindat.org|doi=10.1016/j.cej.2021.131229 |url-access=subscription }}

{{Reflist}}

{{Commons category|Calcium oxide}}

• [http://minerals.usgs.gov/minerals/pubs/commodity/lime/index.html#myb Lime Statistics & Information] from the United States Geological Survey
• [http://www.cheresources.com/quicklime.shtml Factors Affecting the Quality of Quicklime]
• [http://www.americanscientist.org/issues/feature/dating-ancient-mortar American Scientist] (discussion of ¹⁴C dating of mortar)
• [https://web.archive.org/web/20080217232600/http://scifun.chem.wisc.edu/CHEMWEEK/Lime/lime.html Chemical of the Week – Lime]
• [https://web.archive.org/web/20120501110853/http://hazard.com/msds/mf/baker/baker/files/c0462.htm Material Safety Data Sheet]
• [https://www.cdc.gov/niosh/npg/npgd0093.html CDC – NIOSH Pocket Guide to Chemical Hazards]

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