Smelting

Smelting is a process of applying heat to ore in order to extract out a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind. The reducing agent is commonly a source of carbon, such as coke—or, in earlier times, charcoal.[1]

The carbon (or carbon monoxide derived from it) removes oxygen from the ore, leaving the elemental metal. The carbon thus oxidizes in two stages, producing first carbon monoxide and then carbon dioxide. As most ores are impure, it is often necessary to use flux, such as limestone, to remove the accompanying rock gangue as slag.

Plants for the electrolytic reduction of aluminium are also generally referred to as aluminium smelters.

Labourers working in the smelting industry have reported respiratory illnesses inhibiting their ability to perform the physical tasks demanded by their jobs.[2]

TVA phosphate smelting furnace
Electric phosphate smelting furnace in a TVA chemical plant (1942)

Process

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 reducing substances that combine with those oxidizing elements to free the metal.

Roasting

In the case of carbonates and sulfides, a process called "roasting" drives out 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.[3] This mineral undergoes thermal decomposition to 2CuO, CO2, and H2O[4] in several stages between 250 °C and 350 °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 required temperature varies over a very large range, both in absolute terms and in terms of the melting point of the base metal. Examples:

  • Iron oxide becomes metallic iron at roughly 1250 °C (2282 °F or 1523.15 K), almost 300 degrees below iron's melting point of 1538 °C (2800.4 °F or 1811.15 K).
  • Mercuric oxide becomes vaporous mercury near 550 °C (1022 °F or 823.15 K), almost 600 degrees above mercury's melting point of -38 °C (-36.4 °F or 235.15 K).

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.

Fluxes

Metal workers use fluxes in smelting for several purposes, chief among them catalyzing the desired reactions and chemically binding to unwanted impurities or reaction products. Calcium oxide, in the form of lime, was often used for this purpose, since it could react with the carbon dioxide and sulfur dioxide produced during roasting and smelting to keep them out of the working environment.

History

Of the seven metals known in antiquity, only gold occurred regularly in native form in the natural environment. The others – copper, lead, silver, tin, iron and mercury – occur primarily as minerals, though copper is occasionally found in its native state in commercially significant quantities. These minerals are primarily carbonates, sulfides, or oxides of the metal, mixed with other components such as silica and alumina. Roasting the carbonate and sulfide minerals in 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 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.[5]

Tin and lead

In the Old World, the first metals smelted were tin and lead. The earliest known cast lead beads were found in the Çatal Höyük site in Anatolia (Turkey), and dated from about 6500 BC, but the metal may have been known earlier.

Since the discovery happened several millennia before the invention of writing, there is no written record about 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.

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 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 in stone buildings.

Tin was much less common than lead and is only marginally harder, and had even less impact by itself.

Copper and bronze

After tin and lead, the next metal smelted appears to have been copper. How the discovery came about is debated. Campfires are about 200 °C short of the temperature needed, so some propose that the first smelting of copper may have occurred in pottery kilns. 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.[5] The earliest current evidence of copper smelting, dating from between 5500 BC and 5000 BC, has been found in Pločnik and Belovode, Serbia.[6][7] A mace head found in Can Hasan, Turkey and dated to 5000 BC, once thought to be the oldest evidence, now appears to be hammered native copper.[8]

Combining copper with tin and/or arsenic in the right proportions produces bronze, an alloy that is significantly harder than copper. The first copper/arsenic bronzes date from 4200 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.

Copper–tin bronzes, harder and more durable, were developed around 3200 BC, also in Asia Minor.

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 BC, people were mining tin on purpose to produce bronze—which is amazing given that tin is a semi-rare metal, and even a rich cassiterite ore only has 5% tin. Also, it takes special skills (or special instruments) to find it and locate richer lodes. However early peoples learned about tin, they understood how to use it to make bronze by 2000 BC.

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 swords, daggers, battle axes, and spear and arrow points, as well as protective gear such as shields, helmets, greaves (metal shin guards), and other body armor. Bronze also supplanted stone, wood, and organic materials in tools and household utensils—such as chisels, saws, adzes, nails, blade shears, knives, sewing needles and pins, jugs, cooking pots and cauldrons, mirrors, and horse harnesses. 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.

Tiangong Kaiwu Tripod Casting
Casting bronze ding-tripods, from the Chinese Tiangong Kaiwu encyclopedia of Song Yingxing, published in 1637.

Early iron smelting

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 BC.[9] Souckova-Siegolová (2001) shows that iron implements were made in Central Anatolia in very limited quantities around 1800 BC and were in general use by elites, though not by commoners, during the New Hittite Empire (∼1400–1200 BC).[10]

Archaeologists have found indications of iron working in Ancient Egypt, somewhere between the Third Intermediate Period and 23rd Dynasty (ca. 1100–750 BC). Significantly though, they have found no evidence for iron ore smelting in any (pre-modern) period. In addition, very early instances of carbon steel were in production around 2000 years before the present in northwest Tanzania, based on complex preheating principles. These discoveries are significant for the history of metallurgy.[11]

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 ([1]), and dates to 930 BC (C14 dating).

Later iron smelting

From the medieval period, an indirect process began to replace 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 and, from the Industrial Revolution, puddling. 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.

Base metals

Cowles furnace-2
Cowles Syndicate of Ohio in Stoke-upon-Trent England, late 1880s. British Aluminium used the process of Paul Héroult about this time.[12]

The ores of base metals are often sulfides. In recent centuries, reverberatory furnaces have been used to keep the charge being smelted separate 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 containing the valuable metal sulfide and some impurities. Such "reverb" furnaces are today about 40 meters long, 3 meters high and 10 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. The precise details of the process vary from one furnace to another depending on the mineralogy of the orebody.

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.[13] 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.

Environmental implications

Smelting seriously impacts the environment by producing wastewater and slag and releasing such toxic metals as copper, silver, iron, cobalt and selenium into the atmosphere.[14] It also releases gaseous sulfur dioxide, contributing to acid rain, which acidifies soil and water.[15]

See also

References

  1. ^ "Smelting". Encyclopaedia Britannica. Retrieved 2018-08-15.
  2. ^ Sjöstrand, Torgny (1947-01-12). "Changes in the Respiratory Organs of Workmen at an Ore Smelting Works1". Acta Medica Scandinavica. 128 (S196): 687–699. doi:10.1111/j.0954-6820.1947.tb14704.x. ISSN 0954-6820.
  3. ^ "Malachite: Malachite mineral information and data". mindat.org. Archived from the original on 8 September 2015. Retrieved 26 August 2015.
  4. ^ "Copper Metal from Malachite | Earth Resources". asminternational.org. Archived from the original on 23 September 2015. Retrieved 26 August 2015.
  5. ^ a b "releases/2007/04/070423100437". sciencedaily.com. Archived from the original on 9 September 2015. Retrieved 26 August 2015.
  6. ^ "Stone Pages Archaeo News: Ancient metal workshop found in Serbia". stonepages.com. Archived from the original on 24 September 2015. Retrieved 26 August 2015.
  7. ^ "201006274431 | Belovode site in Serbia may have hosted first copper makers". archaeologydaily.com. Archived from the original on 29 February 2012. Retrieved 26 August 2015.
  8. ^ Sagona, A.G.; Zimansky, P.E. (2009). Ancient Turkey. Routledge. ISBN 9780415481236. Archived from the original on 6 March 2016. Retrieved 26 August 2015.
  9. ^ Akanuma, Hideo (2008). "The Significance of Early Bronze Age Iron Objects from Kaman-Kalehöyük, Turkey" (PDF). Anatolian Archaeological Studies. Tokyo: Japanese Institute of Anatolian Archaeology. 17: 313–320.
  10. ^ Souckova-Siegolová, J. (2001). "Treatment and usage of iron in the Hittite empire in the 2nd millennium BC". Mediterranean Archaeology. 14: 189–93..
  11. ^ Peter Schmidt, Donald H. Avery. Complex Iron Smelting and Prehistoric Culture in Tanzania Archived 9 April 2010 at the Wayback Machine, Science 22 September 1978: Vol. 201. no. 4361, pp. 1085–1089
  12. ^ Minet, Adolphe (1905). The Production of Aluminum and Its Industrial Use. Leonard Waldo (translator, additions). New York, London: John Wiley and Sons, Chapman & Hall. p. 244 (Minet speaking) +116 (Héroult speaking). OL 234319W.
  13. ^ W. G. Davenport (1999). "Copper extraction from the 60s into the 21st century". In G. A. Eltringham; N. L. Piret; M. Sahoo. Proceedings of the Copper 99–Cobre 99 International Conference. I—Plenary Lectures/Movement of Copper and Industry Outlook/Copper Applications and Fabrication. Warrendale, Pennsylvania: The Minerals, Metals and Materials Society. pp. 55–79. OCLC 42774618.
  14. ^ Hutchinson, T. C.; Whitby, L. M. (1974). "Heavy-metal pollution in the Sudbury mining and smelting region of Canada, I. Soil and vegetation contamination by nickel, copper, and other metals". Environmental Conservation. 1 (2): 123–132. doi:10.1017/S0376892900004240. ISSN 1469-4387 – via Cambridge University Press.
  15. ^ Likens, Gene E.; Wright, Richard F.; Galloway, James N.; Butler, Thomas J. (1979). "Acid Rain". Scientific American. 241 (4): 43–51. doi:10.1038/scientificamerican1079-43. JSTOR 24965312.

Bibliography

  • 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.
Aluminium smelting

Aluminium smelting is the process of extracting aluminium from its oxide, alumina, generally by the Hall-Héroult process. Alumina is extracted from the ore bauxite by means of the Bayer process at an alumina refinery.

This is an electrolytic process, so an aluminium smelter uses prodigious amounts of electricity; they tend to be located very close to large power stations, often hydro-electric ones, and near ports since almost all of them use imported alumina. A large amount of carbon is also used in this process, resulting in significant amounts of greenhouse gas emissions.

Asarco

ASARCO LLC (American Smelting and Refining Company) is a mining, smelting, and refining company based in Tucson, Arizona, which mines and processes primarily copper. The company is a subsidiary of Grupo México.

Its three largest open-pit mines are the Mission, Silver Bell and Ray mines in Arizona. Its mines produce 350,000,000 to 400,000,000 pounds (160,000,000 to 180,000,000 kg) of copper a year. Asarco conducts solvent extraction and electrowinning at the Ray and Silver Bell mines in Pima County, Arizona, and Pinal County, Arizona, and operates a smelter in Hayden, Arizona. Before its smelting plant in El Paso, Texas, was suspended in 1999 and then demolished in April 13, 2013, it was producing 1,000,000,000 pounds (450,000,000 kg) of anodes each year. Refining at the mines as well as at a copper refinery in Amarillo, Texas, produce 375,000,000 pounds (170,000,000 kg) of refined copper each year.

Asarco's hourly workers are primarily represented by the United Steelworkers.

Asarco has 20 superfund sites across the United States, and it is subject to considerable litigation over pollution. In 2008 it made a settlement with the government of $1.79 billion for contamination at various sites; the funds were allotted to the Environmental Protection Agency (EPA) for cleanup at 26 sites around the country.

Blast furnace

A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. Blast refers to the combustion air being "forced" or supplied above atmospheric pressure.In a blast furnace, fuel (coke), ores, and flux (limestone) are continuously supplied through the top of the furnace, while a hot blast of air (sometimes with oxygen enrichment) is blown into the lower section of the furnace through a series of pipes called tuyeres, so that the chemical reactions take place throughout the furnace as the material falls downward. The end products are usually molten metal and slag phases tapped from the bottom, and waste gases (flue gas) exiting from the top of the furnace. The downward flow of the ore and flux in contact with an upflow of hot, carbon monoxide-rich combustion gases is a countercurrent exchange and chemical reaction process.In contrast, air furnaces (such as reverberatory furnaces) are naturally aspirated, usually by the convection of hot gases in a chimney flue. According to this broad definition, bloomeries for iron, blowing houses for tin, and smelt mills for lead would be classified as blast furnaces. However, the term has usually been limited to those used for smelting iron ore to produce pig iron, an intermediate material used in the production of commercial iron and steel, and the shaft furnaces used in combination with sinter plants in base metals smelting.

Bloomery

A bloomery is a type of furnace once used widely for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which is usually consolidated and further forged into wrought iron. The bloomery has now largely been superseded by the blast furnace, which produces pig iron.

Chalcolithic

The Chalcolithic (English: ), a name derived from the Greek: χαλκός khalkós, "copper" and from λίθος líthos, "stone" or Copper Age, also known as the Eneolithic or Aeneolithic (from Latin aeneus "of copper") is an archaeological period which researchers usually regard as part of the broader Neolithic (although scholars originally defined it as a transition between the Neolithic and the Bronze Age). In the context of Eastern Europe, archaeologists often prefer the term "Eneolithic" to "Chalcolithic" or other alternatives.

In the Chalcolithic period, copper predominated in metalworking technology. Hence it was the period before it was discovered that adding tin to copper formed bronze (a harder and stronger metal). The archaeological site of Belovode, on Rudnik mountain in Serbia has the oldest securely-dated evidence of copper smelting, from 7000 BP (c. 5000 BC).The Copper Age in the Ancient Near East began in the late 5th millennium BC and lasted for about a millennium before it gave rise to the Early Bronze Age.

The transition from the European Copper Age to Bronze Age Europe occurs about the same time, between the late 5th and the late 3rd millennia BC.

Copper extraction

Copper extraction refers to the methods used to obtaining copper from its ores. The conversion of copper consists of a series of physical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors.

As in all mining operations, the ore must usually be beneficiated (concentrated). The processing techniques depend on the nature of the ore. If the ore is primarily sulfide copper minerals (such as chalcopyrite), the ore is crushed and ground to liberate the valuable minerals from the waste ('gangue') minerals. It is then concentrated using mineral flotation. The concentrate is typically then sold to distant smelters, although some large mines have smelters located nearby. Such colocation of mines and smelters was more typical in the 19th and early 20th centuries, when smaller smelters could be economic. The sulfide concentrates are typically smelted in such furnaces as the Outokumpo or Inco flash furnace or the ISASMELT furnace to produce matte, which must be converted and refined to produce anode copper. Finally, the final refining process is electrolysis. For economic and environmental reasons, many of the byproducts of extraction are reclaimed. Sulfur dioxide gas, for example, is captured and turned into sulfuric acid — which can then be used in the extraction process or sold for such purposes as fertiliser manufacture.

Oxidised copper ores can be treated by hydrometallurgical extraction.

Crucible

A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles historically were usually made from clay, they can be made from any material that withstands temperatures high enough to melt or otherwise alter its contents.

Economy of Iceland

The economy of Iceland is small and subject to high volatility. In 2011, gross domestic product was US$12.3bn; by 2017 that had increased to a nominal GDP of US$24bn. With a population of 350,000, this is $50,000 per capita, based on purchasing power parity (PPP) estimates. The financial crisis of 2007–2010 produced a decline in GDP and employment that has since been reversed entirely by a recovery aided by a tourism boom starting in 2010. Tourism accounted for more than 10% of Iceland's GDP in 2017. After a period of robust growth, Iceland's economy is slowing down according to an economic outlook for the years 2018–2020 published by Arion Research in April 2018.Iceland has a mixed economy with high levels of free trade and government intervention. However, government consumption is less than other Nordic countries. Hydro-power is the primary source of home and industrial electrical supply in Iceland.In the 1990s Iceland undertook extensive free market reforms, which initially produced strong economic growth. As a result, Iceland was rated as having one of the world's highest levels of economic freedom as well as civil freedoms. In 2007, Iceland topped the list of nations ranked by Human Development Index and was one of the most egalitarian, according to the calculation provided by the Gini coefficient.From 2006 onwards, the economy faced problems of growing inflation and current account deficits. Partly in response, and partly as a result of earlier reforms, the financial system expanded rapidly before collapsing entirely in a sweeping financial crisis. Iceland had to obtain emergency funding from the International Monetary Fund and a range of European countries in November 2008.

Ferrous metallurgy

Ferrous metallurgy is the metallurgy of iron and its alloys. It began far back in prehistory. The earliest surviving iron artifacts, from the 4th millennium BC in Egypt, were made from meteoritic iron-nickel. It is not known when or where the smelting of iron from ores began, but by the end of the 2nd millennium BC iron was being produced from iron ores from Sub-Saharan Africa to China. The use of wrought iron (worked iron) was known by the 1st millennium BC, and its spread marked the Iron Age. During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel.

Steel (with a carbon content between pig iron and wrought iron) was first produced in antiquity as an alloy. Its process of production, Wootz steel, was exported before the 4th century BC from India to ancient China, Africa, the Middle East and Europe. Archaeological evidence of cast iron appears in 5th-century BC China. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. During the Industrial Revolution, new methods of producing bar iron by substituting coke for charcoal were devised and these were later applied to produce steel, creating a new era of greatly increased use of iron and steel that some contemporaries described as a new Iron Age. In the late 1850s, Henry Bessemer invented a new steelmaking process, that involved blowing air through molten pig iron to burn off carbon, and so to produce mild steel. This and other 19th-century and later steel making processes have displaced wrought iron. Today, wrought iron is no longer produced on a commercial scale, having been displaced by the functionally equivalent mild or low carbon steel.The largest and most modern underground iron ore mine in the world is located in Kiruna, Norrbotten County, Lapland. The mine which is owned by Luossavaara-Kiirunavaara AB, a large Swedish mining company, has an annual production capacity of over 26 million tonnes of iron ore.

Flash smelting

Flash smelting (Finnish: Liekkisulatus, literally "flame-smelting") is a smelting process for sulfur-containing ores including chalcopyrite. The process was developed by Outokumpu in Finland and first applied at the Harjavalta plant in 1949 for smelting copper ore. It has also been adapted for nickel and lead production.A second flash smelting system was developed by the International Nickel Company ('INCO') and has a different concentrate feed design compared to the Outokumpu flash furnace. The Inco flash furnace has end-wall concentrate injection burners and a central waste gas off-take, while the Outokumpu flash furnace has a water-cooled reaction shaft at one end of the vessel and a waste gas off-take at the other end. While the INCO flash furnace at Sudbury was the first commercial use of oxygen flash smelting, fewer smelters use the INCO flash furnace than the Outokumpu flash furnace.Flash smelting with oxygen-enriched air (the 'reaction gas') makes use of the energy contained in the concentrate to supply most of the energy required by the furnaces. The concentrate must be dried before it is injected into the furnaces and, in the case of the Outokumpu process, some of the furnaces use an optional heater to warm the reaction gas typically to 100–450 °C.The reactions in the flash smelting furnaces produce copper matte, iron oxides and sulfur dioxide. The reacted particles fall into a bath at the bottom of the furnace, where the iron oxides react with fluxes, such as silica and limestone, to form a slag.In most cases, the slag can be discarded, perhaps after some cleaning, and the matte is further treated in converters to produce blister copper. In some cases where the flash furnaces are fed with concentrate containing a sufficiently high copper content, the concentrate is converted directly to blister in a single Outokumpu furnace and further converting is unnecessary.

The sulfur dioxide produced by flash smelting is typically captured in a sulfuric acid plant, removing the major environmental effect of smelting.Outotec, formerly the technology division of Outokumpu, now holds Outokumpu's patents to the technology and licenses it worldwide.

INCO was acquired by Brazil's Vale in 2006.

Lead smelting

Plants for the production of lead are generally referred to as lead smelters. Primary lead production begins with sintering. Concentrated lead ore is fed into a sintering machine with iron, silica, limestone fluxes, coke, soda ash, pyrite, zinc, caustics or pollution control particulates. Smelting uses suitable reducing substances that will combine with those oxidizing elements to free the metal. Reduction is the final, high-temperature step in smelting. It is here that the oxide becomes the elemental metal. A reducing environment (often provided by carbon monoxide in an air-starved furnace) pulls the final oxygen atoms from the raw metal.

Lead is usually smelted in a blast furnace, using the lead sinter produced in the sintering process and coke to provide the heat source. As melting occurs, several layers form in the furnace. A combination of molten lead and slag sinks to the bottom of the furnace, with a layer of the lightest elements referred to as speiss, including arsenic and antimony floating to the top of the molten material. The crude bullion and lead slag layers flow out of the 'furnace front' and into the 'forehearth', where the two streams are separated. The lead slag stream, containing most of the 'fluxing' elements added to the sintering machine (predominantly silica, limestone, iron and zinc) can either be discarded or further processed to recover the contained zinc.

The crude lead bullion, containing significant quantities of copper will then undergo 'copper drossing'. In this step elemental sulphur, usually in solid form is added to the molten crude lead bullion to react with the contained copper. A "matte" layer forms in this step, containing most of the copper originating from the crude lead bullion and some other impurities as metal sulfides. The speiss and the matte are usually sold to copper smelters where they are refined for copper processing.

The lead from the blast furnace, called lead bullion, then undergoes the drossing process. The bullion is agitated in kettles then cooled to 700-800 degrees. This process results in molten lead and dross. Dross refers to the lead oxides, copper, antimony and other elements that float to the top of the lead. Dross is usually skimmed off and sent to a dross furnace to recover the non-lead components which are sold to other metal manufacturers. The Parkes process is used to separate silver or gold from lead.

Finally, the molten lead is refined. Pyrometallurgical methods are usually used to remove the remaining non-lead components of the mixture, for example the Betterton-Kroll process and the Betts electrolytic process. The non-lead metals are usually sold to other metal processing plants. The refined lead may be made into alloys or directly cast.People who operate or work in such plants are also referred to as smelters.

Metallurgy in pre-Columbian America

Metallurgy in pre-Columbian America is the extraction and purification of metals, as well as creating metal alloys and fabrication with metal by Indigenous peoples of the Americas prior to European contact in the late 15th century. Indigenous Americans have been using native metals from ancient times, with recent finds of gold artifacts in the Andean region dated to 2155–1936 BCE, and North American copper finds dated to approximately 5000 BCE. The metal would have been found in nature without need for smelting techniques and shaped into the desired form using heat and cold hammering techniques without chemically altering it by alloying it. To date "no one has found evidence that points to the use of melting, smelting and casting in prehistoric eastern North America." In South America the case is quite different. Indigenous South Americans had full metallurgy with smelting and various metals being purposely alloyed. Metallurgy in Mesoamerica and Western Mexico may have developed following contact with South America through Ecuadorian marine traders.

Mitsui

Mitsui Group (三井グループ, Mitsui Gurūpu) is one of the largest keiretsu in Japan and one of the largest corporate groups in the world.

The major companies of the group include Mitsui & Co. (general trading company), Sumitomo Mitsui Banking Corporation, Sapporo Breweries, Toray Industries, Mitsui Chemicals, Isetan Mitsukoshi Holdings, Sumitomo Mitsui Trust Holdings, Mitsui Engineering & Shipbuilding, Mitsui O.S.K. Lines and Mitsui Fudosan.

Pig iron

Pig iron is an intermediate product of the iron industry, also known as crude iron, which is first obtained from a smelting furnace in the form of oblong blocks. Pig iron has a very high carbon content, typically 3.8–4.7%, along with silica and other constituents of dross, which makes it very brittle and not useful directly as a material except for limited applications. Pig iron is made by smelting iron ore into a transportable ingot of impure high carbon-content iron in a blast furnace as an ingredient for further processing steps. The traditional shape of the molds used for pig iron ingots was a branching structure formed in sand, with many individual ingots at right angles to a central channel or runner, resembling a litter of piglets being suckled by a sow. When the metal had cooled and hardened, the smaller ingots (the pigs) were simply broken from the runner (the sow), hence the name pig iron. As pig iron is intended for remelting, the uneven size of the ingots and the inclusion of small amounts of sand caused only insignificant problems considering the ease of casting and handling them.

Quriwayrachina, Anta

Quriwayrachina or Quri Wayrachina (Quechua quri gold, wayrachina a special oven for smelting metal, "oven for smelting gold") is an archaeological site with agricultural terraces in Peru. It is situated in the Cusco Region, Anta Province. The terraces lie about 4 kilometres (2.5 mi) north of the terraces of Zurite.Hiram Bingham III visited the site in April 1915, and by Paul Fejos in 1940

Slag

Slag is the glass-like by-product left over after a desired metal has been separated (i.e., smelted) from its raw ore. Slag is usually a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and elemental metals. While slags are generally used to remove waste in metal smelting, they can also serve other purposes, such as assisting in the temperature control of the smelting, and minimizing any re-oxidation of the final liquid metal product before the molten metal is removed from the furnace and used to make solid metal.

Southeast Missouri Lead District

The Southeast Missouri Lead District, commonly called the Lead Belt, is a lead mining district in the southeastern part of Missouri. Counties in the Lead Belt include Saint Francois; Crawford; Dent; Iron; Madison: Reynolds; and Washington. European lead mining started in 1720, by Philip Francois Renault of France, who led a large exploratory mission in 1719 and started mining operations in Old Mines and Mine La Motte. The town of Sainte Genevieve was founded as a river port for transportation of lead out of the area. Moses Austin started large-scale mining and smelting, at Potosi, originally known as Mine a Breton, and founded Herculaneum as his shipping point on the Mississippi. This lead was originally used as a roofing material. Bonne Terre has large subterranean mines, now used commercially for recreational scuba diving.

The area of mining has changed over the years. The Old Lead Belt is centered on Park Hills and Desloge, while the New Lead Belt or Viburnum Trend is near Viburnum. The Irish Wilderness in Ripley and Oregon Counties has significant lead ore; however, this is a protected wilderness area. Significant among Missouri's lead mining concerns in the district was the Desloge family and Desloge Consolidated Lead Company in Desloge, Missouri and Bonne Terre—having been active in lead trading, mining and smelting from 1823 in Potosi to 1929. Lead mining operations consolidated under the control of St. Joe Lead.

Teck Resources

Teck Resources Limited known as Teck Cominco until late 2008, is a Canadian metals and mining company. Canada's largest diversified resources company, it was formed from the amalgamation of Teck and Cominco in 2001.Teck's principal products at 2017 are coal, copper, zinc, with secondary products including lead, silver, gold, molybdenum, germanium, indium and cadmium.

Zinc smelting

Zinc smelting is the process of converting zinc concentrates (ores that contain zinc) into pure zinc. Zinc smelting has historically been more difficult than the smelting of other metals, e.g. iron, because in contrast, zinc has a low boiling point. At temperatures typically used for smelting metals, zinc is a gas that will escape from a furnace with the flue gas and be lost, unless specific measures are taken to prevent it.

The most common zinc concentrate processed is zinc sulfide, which is obtained by concentrating sphalerite using the froth flotation method. Secondary (recycled) zinc material, such as zinc oxide, is also processed with the zinc sulfide. Approximately 30% of all zinc produced is from recycled sources.

Mineral processing
(by physical means)
Pyrometallurgy
(by heat)
Hydrometallurgy
(by aqueous solution)
Electrometallurgy
(by electricity)
Co-products

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.