Editing Cement (section)

=={{anchor|Environmental and social impacts}}Environmental impacts==
{{Further|Environmental impact of concrete}}
Cement manufacture causes environmental impacts at all stages of the process. These include emissions of airborne pollution in the form of dust, gases, noise and vibration when operating machinery and during blasting in [[quarry|quarries]], and damage to countryside from quarrying. Equipment to reduce dust emissions during quarrying and manufacture of cement is widely used, and equipment to trap and separate exhaust gases are coming into increased use. Environmental protection also includes the re-integration of quarries into the countryside after they have been closed down by returning them to nature or re-cultivating them.

==={{chem|CO|2}} emissions===
[[File:Co2-emissions-by-fuel-line1800-2018.svg|right|400px|Global carbon emission by type to 2018]]
Carbon concentration in cement spans from ≈5% in cement structures to ≈8% in the case of roads in cement.<ref>{{cite journal|title=Influence of 150 years of land use on anthropogenic and natural carbon stocks in Emilia-Romagna Region (Italy)|author1=Scalenghe, R.|author2=Malucelli, F.|author3=Ungaro, F.|author4=Perazzone, L.|author5=Filippi, N.|author6=Edwards, A.C.|year=2011|volume=45|issue=12|pages=5112–5117|doi=10.1021/es1039437|pmid=21609007|journal=Environmental Science & Technology|bibcode=2011EnST...45.5112S}}</ref> Cement manufacturing releases {{CO2|link=yes}} in the atmosphere both directly when [[calcium carbonate]] is heated, producing [[lime (mineral)|lime]] and [[carbon dioxide]],<ref>{{cite web|url=http://www.eia.doe.gov/oiaf/1605/ggrpt/carbon.html|title=EIA – Emissions of Greenhouse Gases in the U.S. 2006-Carbon Dioxide Emissions|archive-url=https://web.archive.org/web/20110523061426/http://www.eia.doe.gov/oiaf/1605/ggrpt/carbon.html|archive-date=23 May 2011|publisher=US Department of Energy}}</ref><ref>{{cite journal|title=Striking a balance between profit and carbon dioxide emissions in the Saudi cement industry|author1=Matar, W.|author2=Elshurafa, A. M.|year=2017|volume=61|pages=111–123|doi=10.1016/j.ijggc.2017.03.031|journal=International Journal of Greenhouse Gas Control|bibcode=2017IJGGC..61..111M|doi-access=free}}</ref> and also indirectly through the use of energy if its production involves the emission of {{chem|CO|2}}. The cement industry produces about 10% of global [[Anthropogenic greenhouse gas|human-made {{chem|CO|2}} emissions]], of which 60% is from the chemical process, and 40% from burning fuel.<ref>{{cite web|url=http://www.pbl.nl/sites/default/files/cms/publicaties/PBL_2014_Trends_in_global_CO2_emisions_2014_1490_0.pdf|title=Trends in global {{chem|CO|2}} emissions: 2014 Report|archive-url=https://web.archive.org/web/20161014143722/http://www.pbl.nl/sites/default/files/cms/publicaties/PBL_2014_Trends_in_global_CO2_emisions_2014_1490_0.pdf|archive-date=14 October 2016|publisher=PBL Netherlands Environmental Assessment Agency & European Commission Joint Research Centre|year=2014}}</ref> A [[Chatham House]] study from 2018 estimates that the 4 billion tonnes of cement produced annually account for 8% of worldwide {{chem|CO|2}} emissions.<ref name=chathamhouse>{{Cite web|url=https://reader.chathamhouse.org/making-concrete-change-innovation-low-carbon-cement-and-concrete|title=Making Concrete Change: Innovation in Low-carbon Cement and Concrete|website=Chatham House|date=13 June 2018|access-date=17 December 2018|archive-url=https://web.archive.org/web/20181219161129/https://reader.chathamhouse.org/making-concrete-change-innovation-low-carbon-cement-and-concrete|archive-date=19 December 2018|url-status=live}}</ref>

Nearly 900&nbsp;kg of {{chem|CO|2}} are emitted for every 1000&nbsp;kg of Portland cement produced. In the European Union, the specific energy consumption for the production of cement clinker has been reduced by approximately 30% since the 1970s. This reduction in primary energy requirements is equivalent to approximately 11 million tonnes of coal per year with corresponding benefits in reduction of {{chem|CO|2}} emissions. This accounts for approximately 5% of anthropogenic {{chem|CO|2}}.<ref>
{{Cite book|last=Mahasenan|first=Natesan|author2=Smith, Steve|author3=Humphreysm Kenneth|author4=Kaya, Y.|title=Greenhouse Gas Control Technologies – 6th International Conference|chapter=The Cement Industry and Global Climate Change: Current and Potential Future Cement Industry {{chem|CO|2}} Emissions|publisher=Pergamon|isbn=978-0-08-044276-1|pages=995–1000|location=Oxford|year=2003|chapter-url=http://www.sciencedirect.com/science/article/B873D-4P9MYFN-BK/2/c58323fdf4cbc244856fe80c96447f44}}
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The majority of carbon dioxide emissions in the manufacture of Portland cement (approximately 60%) are produced from the chemical decomposition of limestone to lime, an ingredient in Portland cement clinker. These emissions may be reduced by lowering the clinker content of cement. They can also be reduced by alternative fabrication methods such as the intergrinding cement with sand or with slag or other pozzolan type minerals to a very fine powder.<ref name="Science Direct 2015">{{cite web|url=https://www.sciencedirect.com/topics/engineering/blended-cement|title=Blended Cement|work=Science Direct|date=2015|access-date=7 April 2021}}</ref>

To reduce the transport of heavier raw materials and to minimize the associated costs, it is more economical to build cement plants closer to the limestone quarries rather than to the consumer centers.<ref>{{cite web|last=Chandak|first=Shobhit|title=Report on cement industry in India|url=https://www.scribd.com/doc/13378451/Cement-Industry-In-India|publisher=scribd|access-date=21 July 2011|url-status=live|archive-url=https://web.archive.org/web/20120222124243/http://www.scribd.com/doc/13378451/Cement-Industry-In-India|archive-date=22 February 2012}}</ref>

{{As of|2019}} [[carbon capture and storage]] is about to be trialed, but its financial viability is uncertain.<ref>{{cite news|title=World's first zero-emission cement plant takes shape in Norway|url=https://www.euractiv.com/section/energy/news/worlds-first-zero-emission-cement-plant-takes-shape-in-norway/|publisher=Euractiv.com Ltd.|date=13 December 2018}}</ref>

==={{chem|CO|2}} absorption===
Hydrated products of Portland cement, such as concrete and mortars, slowly reabsorb atmospheric CO2 gas, which has been released during calcination in a kiln. This natural process, reversed to calcination, is called carbonation.<ref name="pade2007">{{cite journal|last1=Pade|first1=Claus|last2=Guimaraes|first2=Maria|date=1 September 2007|title=The CO2 uptake of concrete in a 100 year perspective|url=https://www.sciencedirect.com/science/article/pii/S0008884607001317|journal=Cement and Concrete Research|volume=37|issue=9|pages=1348–1356|doi=10.1016/j.cemconres.2007.06.009|issn=0008-8846}}</ref> As it depends on CO2 diffusion into the bulk of concrete, its rate depends on many parameters, such as environmental conditions and surface area exposed to the atmosphere.<ref>{{Cite journal|last1=Xi|first1=Fengming|last2=Davis|first2=Steven J.|last3=Ciais|first3=Philippe|last4=Crawford-Brown|first4=Douglas|last5=Guan|first5=Dabo|last6=Pade|first6=Claus|last7=Shi|first7=Tiemao|last8=Syddall|first8=Mark|last9=Lv|first9=Jie |last10=Ji |first10=Lanzhu|last11=Bing|first11=Longfei|last12=Wang|first12=Jiaoyue|last13=Wei|first13=Wei|last14=Yang|first14=Keun-Hyeok|last15=Lagerblad|first15=Björn|date=December 2016|title=Substantial global carbon uptake by cement carbonation|url=https://www.nature.com/articles/ngeo2840|journal=Nature Geoscience|language=en|volume=9|issue=12|pages=880–883|doi=10.1038/ngeo2840|bibcode=2016NatGe...9..880X|issn=1752-0908}}</ref><ref name="cao2020">{{Cite journal|last1=Cao|first1=Zhi|last2=Myers|first2=Rupert J.|last3=Lupton|first3=Richard C.|last4=Duan|first4=Huabo|last5=Sacchi|first5=Romain|last6=Zhou|first6=Nan|last7=Reed Miller|first7=T.|last8=Cullen|first8=Jonathan M.|last9=Ge|first9=Quansheng |last10=Liu |first10=Gang|date=29 July 2020|title=The sponge effect and carbon emission mitigation potentials of the global cement cycle|journal=Nature Communications|language=en|volume=11|issue=1|pages=3777|doi=10.1038/s41467-020-17583-w|pmid=32728073|bibcode=2020NatCo..11.3777C|issn=2041-1723|doi-access=free|pmc=7392754|hdl=10044/1/81385|hdl-access=free}}</ref> Carbonation is particularly significant at the latter stages of the concrete life - after demolition and crushing of the debris. It was estimated that during the whole life-cycle of cement products, it can be reabsorbed nearly 30% of atmospheric CO2 generated by cement production.<ref name="cao2020" />

Carbonation process is considered as a mechanism of concrete degradation. It reduces pH of concrete that promotes reinforcement steel corrosion.<ref name="pade2007" /> However, as the product of Ca(OH)2 carbonation, CaCO3, occupies a greater volume, porosity of concrete reduces. This increases strength and hardness of concrete.<ref>{{cite journal|last1=Kim|first1=Jin-Keun|last2=Kim|first2=Chin-Yong|last3=Yi|first3=Seong-Tae|last4=Lee|first4=Yun|date=1 February 2009|title=Effect of carbonation on the rebound number and compressive strength of concrete|url=https://www.sciencedirect.com/science/article/pii/S0958946508001236|journal=Cement and Concrete Composites|volume=31|issue=2|pages=139–144|doi=10.1016/j.cemconcomp.2008.10.001|issn=0958-9465}}</ref>

There are proposals to reduce carbon footprint of hydraulic cement by adopting non-hydraulic cement, [[lime mortar]], for certain applications. It reabsorbs some of the {{chem|CO|2}} during hardening, and has a lower energy requirement in production than Portland cement.<ref>{{Cite news|url=https://www.theguardian.com/commentisfree/2007/oct/23/comment.comment|title=Response: Lime is a much greener option than cement, says Douglas Kent|last=Kent|first=Douglas|date=22 October 2007|work=The Guardian|access-date=22 January 2020|language=en-GB|issn=0261-3077}}</ref>

A few other attempts to increase absorption of [[carbon dioxide]] include cements based on magnesium ([[Sorel cement]]).<ref>{{Cite web|date=9 March 2011|title=Novacem's 'carbon negative cement'|url=https://ceramics.org/ceramic-tech-today/novacems-carbon-negative-cement/|access-date=26 September 2023|website=The American Ceramic Society|language=en-US}}</ref><ref>{{cite web|url=http://www.imperialinnovations.co.uk/?q=node/176|title=Novacem|archive-url=https://web.archive.org/web/20090803053655/http://www.imperialinnovations.co.uk/?q=node%2F176|archive-date=3 August 2009|website=imperialinnovations.co.uk}}</ref><ref>{{cite news|url=https://www.theguardian.com/environment/2008/dec/31/cement-carbon-emissions|work=The Guardian|location=London|title=Revealed: The cement that eats carbon dioxide|first=Alok|last=Jha|date=31 December 2008|access-date=28 April 2010|url-status=live|archive-url=https://web.archive.org/web/20130806151853/http://www.theguardian.com/environment/2008/dec/31/cement-carbon-emissions|archive-date=6 August 2013|df=dmy-all}}</ref>

===Heavy metal emissions in the air===
In some circumstances, mainly depending on the origin and the composition of the raw materials used, the high-temperature calcination process of limestone and clay minerals can release in the atmosphere gases and dust rich in volatile [[heavy metal (chemistry)|heavy metals]], e.g. [[Thallium#Thallium pollution|thallium]],<ref>{{cite web|url=http://www.epa.gov/safewater/pdfs/factsheets/ioc/thallium.pdf|access-date=15 September 2009|title=Factsheet on: Thallium|url-status=live|archive-url=https://web.archive.org/web/20120111232626/http://www.epa.gov/safewater/pdfs/factsheets/ioc/thallium.pdf|archive-date=11 January 2012|df=dmy-all}}</ref> [[cadmium]] and [[mercury (element)|mercury]] are the most toxic. Heavy metals (Tl, Cd, Hg, ...) and also [[selenium]] are often found as trace elements in common metal [[sulfide]]s ([[pyrite]] (FeS<sub>2</sub>), [[Sphalerite|zinc blende (ZnS)]], [[galena]] (PbS), ...) present as secondary minerals in most of the raw materials. Environmental regulations exist in many countries to limit these emissions. As of 2011 in the United States, cement kilns are "legally allowed to pump more [[toxins]] into the air than are hazardous-waste incinerators."<ref>{{cite web|last=Berkes, Howard|title=EPA Regulations Give Kilns Permission To Pollute : NPR|work=NPR.org|access-date=17 November 2011|date=10 November 2011|url=https://www.npr.org/2011/11/10/142183546/epa-regulations-give-kilns-permission-to-pollute|url-status=live|archive-url=https://web.archive.org/web/20111117112612/http://www.npr.org/2011/11/10/142183546/epa-regulations-give-kilns-permission-to-pollute|archive-date=17 November 2011|df=dmy-all}}</ref>

===Heavy metals present in the clinker===
The presence of [[heavy metals]] in the clinker arises both from the natural raw materials and from the use of recycled by-products or [[alternative fuels]]. The high pH prevailing in the cement porewater (12.5 < pH < 13.5) limits the mobility of many heavy metals by decreasing their solubility and increasing their sorption onto the cement mineral phases. [[Nickel]], [[zinc]] and [[lead]] are commonly found in cement in non-negligible concentrations. [[Chromium]] may also directly arise as natural impurity from the raw materials or as secondary contamination from the abrasion of hard chromium steel alloys used in the ball mills when the clinker is ground. As [[Chromate ion|chromate]] (CrO<sub>4</sub><sup>2−</sup>) is toxic and may cause severe [[skin allergies]] at trace concentration, it is sometimes reduced into trivalent Cr(III) by addition of [[ferrous sulfate]] (FeSO<sub>4</sub>).

===Use of alternative fuels and by-products materials===
A cement plant consumes 3 to 6 [[Gigajoule|GJ]] of fuel per tonne of clinker produced, depending on the raw materials and the process used. Most cement kilns today use coal and petroleum coke as primary fuels, and to a lesser extent natural gas and fuel oil. Selected waste and by-products with recoverable [[calorific value]] can be used as fuels in a cement kiln (referred to as [[co-processing]]), replacing a portion of conventional [[fossil fuels]], like coal, if they meet strict specifications. Selected waste and by-products containing useful minerals such as calcium, silica, alumina, and iron can be used as raw materials in the kiln, replacing raw materials such as clay, [[shale]], and limestone. Because some materials have both useful mineral content and recoverable calorific value, the distinction between alternative fuels and raw materials is not always clear. For example, sewage sludge has a low but significant calorific value, and burns to give ash containing minerals useful in the clinker matrix.<ref>{{cite web|url=http://www.wbcsd.org/DocRoot/Vjft3qGjo1v6HREH7jM6/tf2-guidelines.pdf|title=Guidelines for the selection and use of fuels and raw materials in the cement manufacturing process|archive-url=https://web.archive.org/web/20080910015447/http://www.wbcsd.org/DocRoot/Vjft3qGjo1v6HREH7jM6/tf2-guidelines.pdf|archive-date=10 September 2008|publisher=World Business Council for Sustainable Development|date=1 June 2005}}</ref> Scrap automobile and truck tires are useful in cement manufacturing as they have high calorific value and the iron embedded in tires is useful as a feed stock.<ref>{{cite web|url=https://www.ifc.org/wps/wcm/connect/cb361035-1872-4566-a7e7-d3d1441ad3ac/Alternative_Fuels_08+04.pdf|title=Increasing the use of alternative fuels at cement plants: International best practice|publisher=International Finance Corporation, World Bank Group|date=2017}}</ref>{{rp|p. 27}}

Clinker is manufactured by heating raw materials inside the main burner of a kiln to a temperature of 1,450&nbsp;°C. The flame reaches temperatures of 1,800&nbsp;°C. The material remains at 1,200&nbsp;°C for 12–15 seconds at 1,800&nbsp;°C or sometimes for 5–8 seconds (also referred to as residence time). These characteristics of a clinker kiln offer numerous benefits and they ensure a complete destruction of organic compounds, a total neutralization of acid gases, sulphur oxides and hydrogen chloride. Furthermore, heavy metal traces are embedded in the clinker structure and no by-products, such as ash or residues, are produced.<ref>{{cite web|url=https://cembureau.eu/media/1229/9062_cembureau_cementconcretecirculareconomy_coprocessing_2016-09-01-04.pdf|title=Cement, concrete & the circular economy|archive-url=https://web.archive.org/web/20181112223510/https://cembureau.eu/media/1229/9062_cembureau_cementconcretecirculareconomy_coprocessing_2016-09-01-04.pdf|archive-date=12 November 2018|website=cembureau.eu}}</ref>

The EU cement industry already uses more than 40% fuels derived from waste and biomass in supplying the thermal energy to the grey clinker making process. Although the choice for this so-called alternative fuels (AF) is typically cost driven, other factors are becoming more important. Use of alternative fuels provides benefits for both society and the company: {{chem|CO|2}}-emissions are lower than with fossil fuels, waste can be co-processed in an efficient and sustainable manner and the demand for certain virgin materials can be reduced. Yet there are large differences in the share of alternative fuels used between the European Union (EU) member states. The societal benefits could be improved if more member states increase their alternative fuels share. The Ecofys study<ref>de Beer, Jeroen et al. (2017) [https://cembureau.eu/media/2lte1jte/11603-ecofys-executive-summary_cembureau-2017-04-26.pdf Status and prospects of co-processing of waste in EU cement plants] {{Webarchive|url=https://web.archive.org/web/20201230172551/http://www.cembureau.eu/media/2lte1jte/11603-ecofys-executive-summary_cembureau-2017-04-26.pdf |archive-url=https://web.archive.org/web/20200923223026/http://cembureau.eu/media/2lte1jte/11603-ecofys-executive-summary_cembureau-2017-04-26.pdf |archive-date=23 September 2020 |url-status=live |date=30 December 2020 }}. ECOFYS study.</ref> assessed the barriers and opportunities for further uptake of alternative fuels in 14 EU member states. The Ecofys study found that local factors constrain the market potential to a much larger extent than the technical and economic feasibility of the cement industry itself.