Examine individual changes

'{{short description|Use of heat and a reducing agent to extract metal from ore}} {{Use dmy dates|date=September 2020}} [[File:TVA phosphate smelting furnace.jpg|thumb|Electric phosphate smelting furnace in a [[Tennessee Valley Authority|TVA]] [[chemical plant]] (1942)]] '''Smelting''' is a process of applying heat and a chemical [[reducing agent]] to an [[ore]] to extract a desired [[base metal]] product.<ref>{{Cite web|title=smelting {{!}} Definition & Facts|url=https://www.britannica.com/technology/smelting|access-date=2021-02-23|website=Encyclopedia Britannica|language=en}}</ref> It is a form of [[extractive metallurgy]] that is used to obtain many metals such as [[iron-making|iron]], [[copper extraction|copper]], [[silver mining#Ore processing|silver]], [[lead smelting|lead]] and [[zinc smelting|zinc]]. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or [[slag]] and leaving the metal behind. The reducing agent is commonly a [[fossil fuel]] source of [[carbon]], such as [[carbon monoxide]] from incomplete combustion of [[coke (fuel)|coke]]—or, in earlier times, of [[charcoal]].<ref name=SmeltingEB>{{cite encyclopedia |title=Smelting |url=https://www.britannica.com/technology/smelting |encyclopedia=Encyclopaedia Britannica |access-date=2018-08-15}}</ref> The oxygen in the ore binds to carbon at high temperatures as the [[Chemical energy|chemical potential energy]] of the bonds in [[carbon dioxide]] ({{CO2}}) is lower than the bonds in the ore. Sulfide ores such as those commonly used to obtain copper, zinc or lead, are [[roasting (metallurgy)|roasted]] before smelting in order to convert the sulfides to oxides, which are more readily reduced to the metal. Roasting heats the ore in the presence of oxygen from air, oxidizing the ore and liberating the sulfur as [[sulfur dioxide]] gas. Smelting most prominently takes place in a [[blast furnace]] to produce [[pig iron]], which is converted into [[steel]]. Plants for the [[electrolysis|electrolytic]] reduction of [[aluminium]] are referred to as [[aluminium smelting|aluminium smelters]]. ==Process== [[File:Karabash copper smelter.jpg|thumb|Copper smelter, Chelyabinsk Oblast, Russia]] [[File:Série de cuves d'électrolyse.jpg|thumb|[[Electrolysis|Electrolytic cells]] at an aluminum smelter in Saint-Jean-de-Maurienne, France]] Smelting involves more than just melting the metal out of its ore. Most ores are the chemical compound of the metal and other elements, such as oxygen (as an [[oxide]]), sulfur (as a [[sulfide]]), or carbon and oxygen together (as a [[carbonate]]). To extract the metal, workers must make these compounds undergo a [[chemical reaction]]. Smelting, therefore, consists of using suitable [[reduction (chemistry)|reducing substances]] that combine with those [[oxidation (chemistry)|oxidizing]] elements to free the metal. ===Roasting=== In the case of sulfides and carbonates, a process called "[[Roasting (metallurgy)|roasting]]" removes the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is usually carried out in an oxidizing environment. A few practical examples: * [[Malachite]], a common ore of [[copper]] is primarily copper carbonate hydroxide Cu₂(CO₃)(OH)₂.<ref name="mindat">{{cite web|url=http://www.mindat.org/min-2550.html|title=Malachite: Malachite mineral information and data.|publisher=mindat.org|access-date=26 August 2015|url-status=live|archive-url=https://web.archive.org/web/20150908005239/http://www.mindat.org/min-2550.html|archive-date=8 September 2015}}</ref> This [[mineral]] undergoes [[thermal decomposition]] to 2CuO, CO₂, and H₂O<ref name="asminternational">{{cite web|url=http://www.asminternational.org/documents/10192/1942082/coppermetal.pdf/86992a2a-61db-4628-b01d-c70c0338b756|title=Copper Metal from Malachite &#124; Earth Resources|publisher=asminternational.org|access-date=26 August 2015|url-status=live|archive-url=https://web.archive.org/web/20150923175352/http://www.asminternational.org/documents/10192/1942082/coppermetal.pdf/86992a2a-61db-4628-b01d-c70c0338b756|archive-date=23 September 2015}}</ref> in several stages between 250&nbsp;°C and 350&nbsp;°C. The carbon dioxide and [[water]] are expelled into the atmosphere, leaving [[copper(II) oxide]], which can be directly reduced to copper as described in the following section titled ''Reduction''. * [[Galena]], the most common mineral of lead, is primarily lead sulfide (PbS). The sulfide is oxidized to a sulfite (PbSO₃), which thermally decomposes into lead oxide and sulfur dioxide gas (PbO and SO₂). The [[sulfur dioxide]] is expelled (like the [[carbon dioxide]] in the previous example), and the lead oxide is reduced as below. ===Reduction=== Reduction is the final, high-temperature step in smelting, in which the oxide becomes the elemental metal. A reducing environment (often provided by carbon monoxide, made by incomplete [[combustion]] in an air-starved furnace) pulls the final [[oxygen]] atoms from the raw metal. The carbon source acts as a chemical reactant to remove oxygen from the ore, yielding the purified metal [[Chemical element|element]] as a product. The carbon source is oxidized in two stages. First, carbon (C) combusts with oxygen (O₂) in the air to produce [[carbon monoxide]] (CO). Second, the carbon monoxide reacts with the ore (e.g. Fe₂O₃) and removes one of its oxygen atoms, releasing carbon dioxide ({{CO2}}). After successive interactions with carbon monoxide, all of the oxygen in the ore will be removed, leaving the raw metal element (e.g. Fe).<ref>{{cite web | title=Blast Furnace | website=Science Aid | url=https://scienceaid.co.uk/chemistry/applied/blastfurnace.html | ref={{sfnref | Science Aid}} | access-date=2021-10-13}}</ref> As most ores are impure, it is often necessary to use [[Flux (metallurgy)|flux]], such as [[limestone]] (or [[Dolomite (mineral)|dolomite]]), to remove the accompanying rock [[gangue]] as slag. This [[calcination]] reaction emits carbon dioxide. The required temperature varies both in absolute terms and in terms of the melting point of the base metal. Examples: * [[Iron oxide]] becomes metallic iron at roughly 1250&nbsp;°C (2282&nbsp;°F or 1523.15&nbsp;K), almost 300 degrees ''below'' iron's melting point of 1538&nbsp;°C (2800.4&nbsp;°F or 1811.15&nbsp;K).<ref>{{Cite book |last=Eisele |first=T.C. |title=Direct Biohydrometallurgical Extraction of Iron from Ore |year=2005 |doi=10.2172/877695}}</ref> * [[Mercuric oxide]] becomes vaporous mercury near 550&nbsp;°C (1022&nbsp;°F or 823.15&nbsp;K), almost 600 degrees ''above'' mercury's melting point of -38&nbsp;°C (-36.4&nbsp;°F or 235.15&nbsp;K).<ref>{{Cite web|title=Mercury processing - Extraction and refining|url=https://www.britannica.com/technology/mercury-processing|access-date=2021-02-23|website=Encyclopedia Britannica|language=en}}</ref> ===Fluxes=== Fluxes are materials added to the ore during smelting to catalyze the desired reactions and to chemically bind to unwanted impurities or reaction products. [[Calcium carbonate]] or [[calcium oxide]] in the form of [[Lime (material)|lime]] are often used for this purpose, since they react with sulfur, phosphorus, and silicon impurities to allow them to be readily separated and discarded, in the form of slag. Fluxes may also serve to control the viscosity and neutralize unwanted acids. Flux and slag can provide a secondary service after the reduction step is complete; they provide a molten cover on the purified metal, preventing contact with oxygen while still hot enough to readily oxidize. This prevents impurities from forming in the metal. ===Sulfide ores=== [[File:Cowles furnace-2.jpg|thumb|[[Electric Smelting and Aluminum Company|Cowles Syndicate]] of [[Ohio]] in [[Stoke-upon-Trent]] [[England]], late 1880s. [[British Aluminium]] used the process of [[Paul Héroult]] about this time.<ref name=Minet>{{cite book|author=Minet, Adolphe|others=Leonard Waldo (translator, additions)|title=The Production of Aluminum and Its Industrial Use|url=https://archive.org/details/productionalumi01minegoog|year=1905|page=[https://archive.org/details/productionalumi01minegoog/page/n254 244] (Minet speaking) +116 (Héroult speaking)|publisher=John Wiley and Sons, Chapman & Hall|location=New York, London|ol=234319W}}</ref>]] The ores of base metals are often sulfides. In recent centuries, [[reverberatory furnace]]s have been used to keep the charge being smelted separately from the fuel. Traditionally, they were used for the first step of smelting: forming two liquids, one an oxide slag containing most of the impurities, and the other a sulfide [[matte (metallurgy)|matte]] containing the valuable metal sulfide and some impurities. Such "reverb" [[Reverberatory furnace|furnace]]s are today about 40&nbsp;meters long, 3&nbsp;meters high, and 10&nbsp;meters wide. Fuel is burned at one end to melt the dry sulfide concentrates (usually after partial roasting) which are fed through openings in the roof of the furnace. The slag floats over the heavier matte and is removed and discarded or recycled. The sulfide matte is then sent to the [[converter (Metallurgical)|converter]]. The precise details of the process vary from one furnace to another depending on the mineralogy of the ore body. While reverberatory furnaces produced slags containing very little copper, they were relatively energy inefficient and off-gassed a low concentration of [[sulfur dioxide]] that was difficult to capture; a new generation of copper smelting technologies has supplanted them.<ref>{{cite book|author=W. G. Davenport |contribution=Copper extraction from the 60s into the 21st century |title=Proceedings of the Copper 99–Cobre 99 International Conference |volume=I—Plenary Lectures/Movement of Copper and Industry Outlook/Copper Applications and Fabrication|editor1=G. A. Eltringham |editor2=N. L. Piret |editor3=M. Sahoo |publisher=The Minerals, Metals and Materials Society |location=Warrendale, Pennsylvania |year=1999 |pages=55–79 |oclc=42774618}}</ref> More recent furnaces exploit bath smelting, top-jetting lance smelting, [[flash smelting]], and blast furnaces. Some examples of bath smelters include the Noranda furnace, the [[Isasmelt]] furnace, the Teniente reactor, the Vunyukov smelter, and the SKS technology. Top-jetting lance smelters include the Mitsubishi smelting reactor. Flash smelters account for over 50% of the world's copper smelters. There are many more varieties of smelting processes, including the Kivset, Ausmelt, Tamano, EAF, and BF. ==History== Of the [[metals of antiquity|seven metals known in antiquity]], only [[gold]] occurs regularly in its native form in the natural environment. The others – [[copper]], [[lead]], [[silver]], [[tin]], [[iron]], and [[mercury (element)|mercury]] – occur primarily as minerals, though copper is occasionally found in its [[native copper|native state]] in commercially significant quantities. These minerals are primarily [[carbonate]]s, [[sulfide]]s, or [[oxide]]s of the metal, mixed with other components such as [[silica]] and [[alumina]]. [[Roasting (metallurgy)|Roasting]] the carbonate and sulfide minerals in the air converts them to oxides. The oxides, in turn, are smelted into the metal. Carbon monoxide was (and is) the reducing agent of choice for smelting. It is easily produced during the heating process, and as a gas comes into intimate contact with the ore. In the [[Old World]], humans learned to smelt metals in [[Prehistory|prehistoric]] times, more than 8000 years ago. The discovery and use of the "useful" metals – copper and bronze at first, then iron a few millennia later – had an enormous impact on human society. The impact was so pervasive that scholars traditionally divide ancient history into [[Stone Age]], [[Bronze Age]], and [[Iron Age]]. In the [[Americas]], pre-[[Inca]] civilizations of the central [[Andes]] in Peru had mastered the smelting of copper and silver at least six centuries before the first Europeans arrived in the 16th century, while never mastering the smelting of metals such as iron for use with weapon craft.<ref name="sciencedaily.com">{{cite web|url=https://www.sciencedaily.com/releases/2007/04/070423100437.htm|title=releases/2007/04/070423100437|publisher=sciencedaily.com|access-date=26 August 2015|url-status=live|archive-url=https://web.archive.org/web/20150909222002/https://www.sciencedaily.com/releases/2007/04/070423100437.htm|archive-date=9 September 2015}}</ref> ===Tin and lead=== In the [[Old World]], the first metals smelted were tin and lead. The earliest known [[Casting|cast]] lead beads were found in the [[Çatalhöyük]] site in [[Anatolia]] ([[Turkey]]), and dated from about 6500&nbsp;BC,<ref>{{Cite journal |last=Gale |first=N.H. |last2=Stos-Gale |first2=Z.A. |date=1981 |title=Ancient Egyptian Silver |url=https://journals.sagepub.com/doi/abs/10.1177/030751338106700110 |journal=The Journal of Egyptian Archaeology |volume=67 |issue=1 |pages=103-115 |via=Sage Journals}}</ref> but the metal may have been known earlier.{{citation needed|date=September 2021}} Since the discovery happened several millennia before the invention of writing, there is no written record of how it was made. However, tin and lead can be smelted by placing the ores in a wood fire, leaving the possibility that the discovery may have occurred by accident.{{Citation needed|date=August 2023}} Recent scholarship however has called this find into question.<ref>{{Cite journal |last=Radivojević |first=Miljana |last2=Rehren |first2=Thilo |last3=Farid |first3=Shahina |last4=Pernicka |first4=Ernst |last5=Camurcuoğlu |first5=Duygu |date=2017 |title=Repealing the Çatalhöyük extractive metallurgy: The green, the fire and the ‘slag’ |journal=Journal of Archaeological Science |volume=86 |pages=101–122 |doi=10.1016/j.jas.2017.07.001}}</ref> Lead is a common metal, but its discovery had relatively little impact in the ancient world. It is too soft to use for structural elements or weapons, though its high density relative to other metals makes it ideal for [[sling (weapon)|sling]] projectiles. However, since it was easy to cast and shape, workers in the classical world of [[Ancient Greece]] and [[Ancient Rome]] used it extensively to pipe and store water. They also used it as a [[Mortar (masonry)|mortar]] in stone buildings.<ref>{{Cite news|last=Browne|first=Malcolm W.|date=1997-12-09|title=Ice Cap Shows Ancient Mines Polluted the Globe (Published 1997)|language=en-US|work=The New York Times|url=https://www.nytimes.com/1997/12/09/science/ice-cap-shows-ancient-mines-polluted-the-globe.html|access-date=2021-02-23|issn=0362-4331}}</ref><ref>{{Cite journal|last1=Loveluck|first1=Christopher P.|last2=McCormick|first2=Michael|last3=Spaulding|first3=Nicole E.|last4=Clifford|first4=Heather|last5=Handley|first5=Michael J.|last6=Hartman|first6=Laura|last7=Hoffmann|first7=Helene|last8=Korotkikh|first8=Elena V.|last9=Kurbatov|first9=Andrei V.|last10=More|first10=Alexander F.|last11=Sneed|first11=Sharon B.|date=December 2018|title=Alpine ice-core evidence for the transformation of the European monetary system, AD 640–670|journal=Antiquity|language=en|volume=92|issue=366|pages=1571–1585|doi=10.15184/aqy.2018.110|issn=0003-598X|doi-access=free}}</ref> Tin was much less common than lead and is only marginally harder, and had even less impact by itself. ===Copper and bronze=== [[File:Tiangong Kaiwu Tripod Casting.jpg|thumb|Casting bronze ding-tripods, from the Chinese ''Tiangong Kaiwu'' encyclopedia of [[Song Yingxing]], published in 1637.]] After tin and lead, the next metal smelted appears to have been copper. How the discovery came about is debated. Campfires are about 200&nbsp;°C short of the temperature needed, so some propose that the first smelting of copper may have occurred in pottery [[kiln]]s.<ref>{{cite book|title=The Prehistory of Metallurgy in the British Isles|author=Tylecote, R F|date=1986|publisher=The Institute of Metals|publication-place=London|pages=16–17}}</ref> (The development of copper smelting in the Andes, which is believed to have occurred independently of the [[Old World]], may have occurred in the same way.<ref name="sciencedaily.com"/>) The earliest current evidence of copper smelting, dating from between 5500&nbsp;BC and 5000&nbsp;BC, has been found in [[Pločnik]] and Belovode, Serbia.<ref name="stonepages">{{cite web|url=http://www.stonepages.com/news/archives/002557.html|title=Stone Pages Archaeo News: Ancient metal workshop found in Serbia|publisher=stonepages.com|access-date=26 August 2015|url-status=live|archive-url=https://web.archive.org/web/20150924110730/http://www.stonepages.com/news/archives/002557.html|archive-date=24 September 2015}}</ref><ref name="archaeologydaily">{{cite web|url=http://www.archaeologydaily.com/news/201006274431/Belovode-site-in-Serbia-may-have-hosted-first-copper-makers.html|title=201006274431 &#124; Belovode site in Serbia may have hosted first copper makers|publisher=archaeologydaily.com|access-date=26 August 2015|url-status=dead|archive-url=https://web.archive.org/web/20120229205002/http://www.archaeologydaily.com/news/201006274431/Belovode-site-in-Serbia-may-have-hosted-first-copper-makers.html|archive-date=29 February 2012}}</ref> A mace head found in Turkey and dated to 5000&nbsp;BC, once thought to be the oldest evidence, now appears to be hammered, native copper.<ref name="google">{{cite book|title=Ancient Turkey|author1=Sagona, A.G.|author2=Zimansky, P.E.|date=2009|publisher=Routledge|isbn=9780415481236|url=https://books.google.com/books?id=QHAlOAAACAAJ|url-status=live|archive-url=https://web.archive.org/web/20160306062734/https://books.google.co.uk/books?id=QHAlOAAACAAJ|archive-date=6 March 2016}}</ref> Combining copper with tin and/or [[arsenic]] in the right proportions produces [[bronze]], an [[alloy]] that is significantly harder than copper. The first [[Arsenical bronze|copper/arsenic bronzes]] date from [[5th millennium BC|4200&nbsp;BC]] from [[Asia Minor]]. The Inca bronze alloys were also of this type. Arsenic is often an impurity in copper ores, so the discovery could have been made by accident. Eventually, arsenic-bearing minerals were intentionally added during smelting.{{citation needed|date=May 2009}} Copper–tin bronzes, harder and more durable, were developed around 3500&nbsp;BC, also in Asia Minor.<ref>{{Cite web|title=History of Bronze Infographic {{!}} About {{!}} Website {{!}} Makin Metal Powders (UK)|url=http://www.makin-metals.com/about/history-of-bronze-infographic/#:~:text=Around%203500%20BC%20the%20first,used%20to%20build%20campfire%20rings.|access-date=2021-02-23|website=www.makin-metals.com}}</ref> How smiths learned to produce copper/tin bronzes is unknown. The first such bronzes may have been a lucky accident from tin-contaminated copper ores. However, by 2000&nbsp;BC, people were mining tin on purpose to produce bronze—which is remarkable as tin is a semi-rare metal, and even a rich [[cassiterite]] ore only has 5% tin. However early peoples learned about tin, they understood how to use it to make bronze by 2000&nbsp;BC.{{citation needed|date=July 2017}} The discovery of copper and bronze manufacture had a significant impact on the history of the [[Old World]]. Metals were hard enough to make weapons that were heavier, stronger, and more resistant to impact damage than wood, bone, or stone equivalents. For several millennia, bronze was the material of choice for weapons such as [[sword]]s, [[dagger]]s, [[battle axe]]s, and [[spear]] and [[arrow]] points, as well as protective gear such as [[shield]]s, [[helmet]]s, [[greave]]s (metal shin guards), and other [[body armor]]. Bronze also supplanted stone, wood, and organic materials in tools and household utensils—such as [[chisel]]s, [[saw]]s, [[adze]]s, [[Nail (fastener)|nail]]s, [[blade shears]], [[knife|knives]], [[sewing needle]]s and [[pin]]s, [[Jug (container)|jug]]s, [[cooking pot]]s and [[cauldron]]s, [[mirror]]s, and [[horse harness]]es.{{Citation needed|date=May 2009}} Tin and copper also contributed to the establishment of trade networks that spanned large areas of Europe and Asia and had a major effect on the distribution of wealth among individuals and nations.{{citation needed|date=May 2009}} ===Early iron smelting{{anchor|early_iron_smelting_anchor}}=== {{Main|Ferrous metallurgy}} The earliest evidence for iron-making is a small number of iron fragments with the appropriate amounts of carbon admixture found in the Proto-Hittite layers at [[Kaman-Kalehöyük]] and dated to 2200–2000&nbsp;[[BCE]].<ref>{{cite journal |last=Akanuma |first=Hideo |title=The significance of Early Bronze Age iron objects from Kaman-Kalehöyük, Turkey |journal=Anatolian Archaeological Studies |volume=17 |pages=313–320 |year=2008 |url=http://www.jiaa-kaman.org/pdfs/aas_17/AAS_17_Akanuma_H_pp_313_320.pdf |publisher=Japanese Institute of Anatolian Archaeology |place=Tokyo }}</ref> Souckova-Siegolová (2001) shows that iron implements were made in Central Anatolia in very limited quantities around 1800 BCE and were in general use by elites, though not by commoners, during the [[Hittites#New Kingdom|New Hittite Empire]] (~1400–1200 BCE).<ref>{{cite journal |last=Souckova-Siegolová |first=J. |title=Treatment and usage of iron in the Hittite empire in the 2nd millennium BC |journal=Mediterranean Archaeology |volume=14 |pages=189–93 |year=2001}}.</ref> Archaeologists have found indications of iron working in [[Ancient Egypt]], somewhere between the [[Third Intermediate Period]] and [[Twenty-third dynasty of Egypt|23rd Dynasty]] (ca. 1100–750&nbsp;BCE). Significantly though, they have found no evidence of iron ore smelting in any (pre-modern) period. In addition, very early instances of [[carbon steel]] were in production around 2000 years ago (around the first-century CE.) in northwest [[Tanzania]], based on complex preheating principles. These discoveries are significant for the history of metallurgy.<ref>Peter Schmidt, Donald H. Avery. [http://www.sciencemag.org/cgi/content/abstract/201/4361/1085 Complex Iron Smelting and Prehistoric Culture in Tanzania] {{webarchive|url=https://web.archive.org/web/20100409173608/http://www.sciencemag.org/cgi/content/abstract/201/4361/1085 |date=9 April 2010 }}, Science 22 September 1978: Vol. 201. no. 4361, pp. 1085–1089</ref> Most early processes in Europe and Africa involved smelting iron ore in a [[bloomery]], where the temperature is kept low enough so that the iron does not melt. This produces a spongy mass of iron called a bloom, which then must be consolidated with a hammer to produce [[wrought iron]]. The earliest evidence to date for the bloomery smelting of iron is found at [[Tell Hammeh]], Jordan ([http://www.ironsmelting.net/www/smelting/]), and dates to 930&nbsp;BCE ([[C14 dating]]). ===Later iron smelting=== {{Main|Blast furnace}} From the medieval period, an indirect process began to replace the direct reduction in bloomeries. This used a [[blast furnace]] to make [[pig iron]], which then had to undergo a further process to make forgeable bar iron. Processes for the second stage include fining in a [[finery forge]]. In the [[13th century]] during the [[High Middle Ages]] the blast furnace was introduced by China who had been using it since as early as 200 b.c during the [[Qin dynasty]]. [https://www.britannica.com/summary/blast-furnace#:~:text=Blast%20furnaces%20were%20used%20in,century%2C%20replacing%20the%20bloomery%20process.] [[Puddling (metallurgy)|Puddling]] was also Introduced in the [[Industrial Revolution]]. Both processes are now obsolete, and wrought iron is now rarely made. Instead, mild steel is produced from a [[Bessemer converter]] or by other means including smelting reduction processes such as the [[Corex Process]]. ==Environmental and occupational health impacts== Smelting has serious [[human impact on the environment|effects on the environment]], producing [[wastewater]] and [[slag]] and releasing such toxic metals as [[copper]], silver, iron, [[cobalt]], and [[selenium]] into the atmosphere.<ref>{{Cite journal |last1=Hutchinson |first1=T.C. |last2=Whitby |first2=L.M. |date=1974 |title=Heavy-metal pollution in the Sudbury mining and smelting region of Canada, I. Soil and vegetation contamination by nickel, copper, and other metals |journal=Environmental Conservation |volume=1 |issue=2 |pages=123–13 2 |doi=10.1017/S0376892900004240 |s2cid=86686979 |issn=1469-4387}}</ref> Smelters also release gaseous [[sulfur dioxide]], contributing to [[acid rain]], which acidifies soil and water.<ref>{{Cite journal |last1=Likens |first1=Gene E. |last2=Wright |first2=Richard F. |last3=Galloway |first3=James N. |last4=Butler |first4=Thomas J. |date=1979 |title=Acid Rain |jstor=24965312 |journal=Scientific American |volume=241 |issue=4 |pages=43–51 |doi=10.1038/scientificamerican1079-43|bibcode=1979SciAm.241d..43L }}</ref> The smelter in [[Flin Flon|Flin Flon, Canada]] was one of the largest point sources of [[Mercury (element)|mercury]] in North America in the 20th century.<ref name=":0">{{Cite journal |last1=Wiklund |first1=Johan A. |last2=Kirk |first2=Jane L. |last3=Muir |first3=Derek C.G. |last4=Evans |first4=Marlene |last5=Yang |first5=Fan |last6=Keating |first6=Jonathan |last7=Parsons |first7=Matthew T. |date=2017-05-15 |title=Anthropogenic mercury deposition in Flin Flon Manitoba and the Experimental Lakes Area Ontario (Canada): A multi-lake sediment core reconstruction |url=http://www.sciencedirect.com/science/article/pii/S0048969717302875|journal=Science of the Total Environment |volume=586 |pages=685–695 |doi=10.1016/j.scitotenv.2017.02.046 |pmid=28238379 |bibcode=2017ScTEn.586..685W |issn=0048-9697}}</ref><ref>{{Cite web |last=Naylor |first=Jonathon |title=When the smoke stopped: the shutdown of the Flin Flon smelter |url=http://www.thereminder.ca/news/local-news/when-the-smoke-stopped-the-shutdown-of-the-flin-flon-smelter-1.9955169 |access-date=2020-07-06|website=Flin Flon Reminder|date=21 February 2017 }}</ref> Even after smelter releases were drastically reduced, landscape [[Volatility (chemistry)|re-emission]] continued to be a major regional source of mercury. Lakes will likely receive mercury contamination from the smelter for decades, from both re-emissions returning as rainwater and [[Leaching (chemistry)|leaching]] of metals from the soil.<ref name=":0" /> ===Air pollution=== Air pollutants generated by [[aluminium smelter]]s include [[carbonyl sulfide]], [[hydrogen fluoride]], [[polycyclic compound]]s, lead, [[nickel]], [[manganese]], [[polychlorinated biphenyl]]s, and [[Mercury (element)|mercury]].<ref>{{cite web |title=Primary Aluminum Reduction Industry |website= National Emission Standards for Hazardous Air Pollutants (NESHAP) |url=https://www.epa.gov/stationary-sources-air-pollution/primary-aluminum-reduction-industry-national-emission-standards |date=2022-05-25 |publisher=U.S. Environmental Protection Agency (EPA) |location=Washington, D.C.}}</ref> Copper smelter emissions include arsenic, [[beryllium]], [[cadmium]], [[chromium]], lead, manganese, and nickel.<ref>{{cite web |title=Primary Copper Smelting |website=NESHAP |url=https://www.epa.gov/stationary-sources-air-pollution/primary-copper-smelting-national-emissions-standards-hazardous-air |date=2022-02-01 |publisher=EPA}}</ref> Lead smelters typically emit arsenic, [[antimony]], cadmium and various lead compounds.<ref>{{cite web |title=Primary Lead Processing |website=NESHAP |url=https://www.epa.gov/stationary-sources-air-pollution/primary-lead-processing-national-emission-standards-hazardous-air |date=2022-04-07 |publisher=EPA}}</ref><ref>{{cite journal | title=Potentially toxic elements pollution in road deposited sediments around the active smelting industry of Korea| year=2021| pmc=8012626| last1=Jeong| first1=H.| last2=Choi| first2=J. Y.| last3=Ra| first3=K.| journal=Scientific Reports| volume=11| issue=1| page=7238| doi=10.1038/s41598-021-86698-x| pmid=33790361}}</ref><ref>{{cite journal | url=https://pubag.nal.usda.gov/catalog/7503323 | title=Heavy Metal Pollution Assessment in Stream Sediments from Urban and Different Types of Industrial Areas in South Korea| year=2021| doi=10.1080/15320383.2021.1893646| last1=Jeong| first1=Hyeryeong| last2=Choi| first2=Jin Young| last3=Ra| first3=Kongtae| journal=Soil and Sediment Contamination| volume=30| issue=7| pages=804–818| s2cid=233818266}}</ref> {{Expand section|Description of air pollution emissions and control options|date=September 2021}} ===Wastewater=== Wastewater pollutants discharged by iron and steel mills includes gasification products such as [[benzene]], [[naphthalene]], [[anthracene]], [[cyanide]], [[ammonia]], [[phenol]]s and [[cresol]]s, together with a range of more complex [[organic compound]]s known collectively as [[polycyclic aromatic hydrocarbon]]s (PAH).<ref name="EPA ironsteel">{{cite report |date=2002 |title=Development Document for Final Effluent Limitations Guidelines and Standards for the Iron and Steel Manufacturing Point Source Category |chapter=7. Wastewater Characterization |chapter-url=http://www.epa.gov/eg/iron-and-steel-manufacturing-effluent-guidelines-documents |publisher=EPA |pages=7–1ff |id=EPA 821-R-02-004}}</ref> Treatment technologies include recycling of wastewater; [[settling basin]]s, [[clarifier]]s and filtration systems for solids removal; [[oil skimmer]]s and filtration; [[chemical precipitation]] and filtration for dissolved metals; [[Adsorption#Activated carbon|carbon adsorption]] and biological oxidation for organic pollutants; and evaporation.<ref>{{cite report |title=Development Document for Effluent Limitations Guidelines, New Source Performance Standards and Pretreatment Standards for the Iron and Steel Manufacturing Point Source Category; Vol. I |url=https://www.epa.gov/eg/iron-and-steel-manufacturing-effluent-guidelines-documents |date=May 1982 |publisher=EPA |pages=177–216 |id=EPA 440/1-82/024a}}</ref> Pollutants generated by other types of smelters varies with the base metal ore. For example, aluminum smelters typically generate [[fluoride]], [[benzo(a)pyrene]], antimony and nickel, as well as aluminum. Copper smelters typically discharge cadmium, lead, [[zinc]], arsenic and nickel, in addition to copper.<ref>EPA (1984). "Nonferrous Metals Manufacturing Point Source Category." ''Code of Federal Regulations,'' {{USCFR|40|421}}.</ref> Lead smelters may discharge [[antimony]], asbestos, cadmium, copper and zinc, in addition to lead.<ref>{{cite report |title=Development Document for Effluent Limitations Guidelines and Standards for the Nonferrous Metals Manufacturing Point Source Category; Volume IV |url=https://www.epa.gov/eg/nonferrous-metals-manufacturing-effluent-guidelines-documents-1990-amendment |date=May 1989 |publisher=EPA |pages=1711–1739 |id=EPA 440/1-89/019.4}}</ref> ===Health impacts=== Labourers working in the smelting industry have reported [[Respiratory disease|respiratory illnesses]] inhibiting their ability to perform the physical tasks demanded by their jobs.<ref>{{Cite journal |last=Sjöstrand |first=Torgny |date=1947-01-12 |title=Changes in the Respiratory Organs of Workmen at an Ore Smelting Works1 |journal=Acta Medica Scandinavica |volume=128 |issue=S196 |pages=687–699 |doi=10.1111/j.0954-6820.1947.tb14704.x |issn=0954-6820}}</ref> ===Regulations=== In the United States, the [[Environmental Protection Agency]] has published pollution control regulations for smelters. * Air pollution standards under the [[Clean Air Act (United States)|Clean Air Act]]<ref>{{cite web |title=Clean Air Act Standards and Guidelines for the Metals Production Industry |url=https://www.epa.gov/stationary-sources-air-pollution/clean-air-act-standards-and-guidelines-metals-production-industry |date=2021-06-01 |publisher=EPA}}</ref> * Water pollution standards ([[effluent guidelines]]) under the [[Clean Water Act]].<ref>{{cite web |title=Iron and Steel Manufacturing Effluent Guidelines |url=https://www.epa.gov/eg/iron-and-steel-manufacturing-effluent-guidelines |date=2021-07-13 |publisher=EPA}}</ref><ref>{{cite web |title=Nonferrous Metals Manufacturing Effluent Guidelines |url=https://www.epa.gov/eg/nonferrous-metals-manufacturing-effluent-guidelines |date=2021-07-13 |publisher=EPA}}</ref> <!-- * Need explanation that solid wastes from smelters that are listed as "Special Wastes" under RCRA & not regulated as hazardous wastes --> The RMI Conformant Smelter Program As [[conflict mineral]] use grows, numerous initiatives have been launched to counteract the problem. They encourage responsible mineral sourcing practices in regions under circumstances of conflict, human rights abuse, or labour exploitation. The Responsible Mineral Initiative, RMI, has developed a set of ideals and guidelines for smelter, including the Conformant Smelter Program. The program is a third-party audit and certification program that assesses the performance of smelters in the responsible sourcing of minerals.<ref>{{cite web |title= Standards |url=https://www.responsiblemineralsinitiative.org/minerals-due-diligence/standards/ |date=2023-05-14 |publisher=Responsible Mineral Initiative}}</ref> This program adheres to the Organization for Economic Co-operation and Development, OECD, guidelines. Published in the OECD Due Diligence Guidance for Responsible Supply Chains of Minerals from Conflict-Affected and High-Risk Areas. The OECD is a body focused on policies for bettering global practices.<ref>{{cite web |title= About the OECD |url=https://www.oecd.org/about/ |date=2023-05-14 |publisher=OECD}}</ref> The focus of the program is evaluating smelters on: *Sourcing practices: Demonstrating sourced minerals do not contribute to active conflict, human rights issues, or environmental damage *Due Diligence: Establishing a due diligence process to mitigate risks in the supply chain *Transparency: Information being transparent about their sourcing *Environmental and social performance: Minimizing the environmental impact and respecting workers' rights<ref>{{cite web |title= RMI conformant smelters |url=https://www.getenviropass.com/rmi-conformant-smelters/ |date=2023-05-22 |publisher=Enviropass}}</ref> Smelters that meet the RMI standards gain recognition on the RMI Conformant Smelter & Refiner Lists. This is not the only program regulating the smelting industry, additional auditing programs include: *The London Bullion Market Association, LBMA, focuses on gold, silver, platinum, and palladium. With successful smelters gaining recognition on the Good Suppliers List.<ref>{{cite web |title= About good delivery |url=https://www.lbma.org.uk/good-delivery/about-good-delivery |date=2023-05-22 |publisher=LBMA}}</ref> *Responsible Jewellery Council, RJC, promotes responsible practices in the jewellery supply chain. Successful smelters gaining recognition on the RJC members registry.<ref>{{cite web |title= About |url=https://responsiblejewellery.com/about/ |date=2023-05-23 |publisher=RJC}}</ref> Similarly, to the RMI Conformant Smelter Program these entities comply with OECD guidelines and promote ethical and environmental supply chain management. However, the named organizations have varying additional guidelines therefore the only cross recognized audits with the RMI are: *LBMA Responsible Gold Guidance *RMI Responsible Minerals Assurance Process Gold Standard *RJC Chain-of-Custody (CoC) Standard (provision 1 only) *RJC Code of Practices (COP) Standard (provision 7 only)<ref>{{cite web |title= RMAP cross-recognition |url=https://www.responsiblemineralsinitiative.org/minerals-due-diligence-container/recognized-standards-or-programs/audit-cross-recognition/ |publisher=Responsible Minerals Initiative}}</ref> ==See also== {{colbegin}} *[[Cast iron]] * [[Ellingham diagram]], useful in predicting the conditions under which an ore reduces to its metal * [[Copper extraction techniques]] *[[Clinker (waste)|Clinker]] *[[Cupellation]] *[[Lead smelting]] *[[Metallurgy]] *[[Pyrometallurgy]] *[[Wrought iron]] *[[Zinc smelting]] {{Colend}} ==References== {{Reflist|30em}} ==Bibliography== {{refbegin}} *'''Pleiner, R.''' (2000) ''Iron in Archaeology. The European Bloomery Smelters'', Praha, Archeologický Ústav Av Cr. *'''Veldhuijzen, H.A.''' (2005) Technical Ceramics in Early Iron Smelting. The Role of Ceramics in the Early First Millennium Bc Iron Production at Tell Hammeh (Az-Zarqa), Jordan. In: Prudêncio, I.Dias, I. and Waerenborgh, J.C. (Eds.) ''Understanding People through Their Pottery; Proceedings of the 7th European Meeting on Ancient Ceramics (Emac '03)''. Lisboa, Instituto Português de Arqueologia (IPA). *'''Veldhuijzen, H.A. and Rehren, Th.''' (2006) Iron Smelting Slag Formation at Tell Hammeh (Az-Zarqa), Jordan. In: Pérez-Arantegui, J. (Ed.) ''Proceedings of the 34th International Symposium on Archaeometry, Zaragoza, 3–7 May 2004''. Zaragoza, Institución «Fernando el Católico» (C.S.I.C.) Excma. Diputación de Zaragoza. {{refend}} ==External links== {{Wiktionary}} {{Commons category|Smelting}} {{Extractive metallurgy}} {{Authority control}} [[Category:Smelting| ]] [[Category:Firing techniques]] [[Category:Metallurgical processes]] [[de:Verhüttung]]'