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

Chemical reduction, or smelting, is a form of extractive metallurgy. The main use of smelting is to produce a metal from its ore. This includes iron extraction (for the production of steel) from iron ore, and copper extraction and other base metals from their ores. It makes use of a chemical reducing agent, commonly a fuel that is a source of carbon such as coke, or in earlier times charcoal, to change the oxidation state of the metal ore; however, plants for the electrolytic reduction of aluminum are also generally referred to as smelters. The carbon or carbon monoxide derived from it removes oxygen from the ore to leave the metal. The carbon is oxidised, producing carbon dioxide and carbon monoxide. As most ores are impure, it is often necessary to use flux, such as limestone to remove the accompanying rock gangue as slag (also called scoria or cinder). Image File history File links Download high-resolution version (3500x2716, 755 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Smelting ... Image File history File links Download high-resolution version (3500x2716, 755 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Smelting ... This article or section does not cite any references or sources. ... A Chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. ... Look up chemical compound in Wiktionary, the free dictionary. ... ed|other uses|reduction}} Illustration of a redox reaction Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... Extractive metallurgy is the practice of extracting metal from ore, purifying it, and recycling it. ... For other uses, see Iron (disambiguation). ... For other uses, see Steel (disambiguation). ... For other uses, see Ore (disambiguation). ... The Chino open-pit copper mine in New Mexico. ... This article is about metallic materials. ... For other uses, see Ore (disambiguation). ... For other uses, see Carbon (disambiguation). ... Coke Coke is a solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. ... Charcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. ... In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... In metallurgy, flux is a substance which removes passivating oxides from the surface of a metal or alloy. ... For other uses, see Limestone (disambiguation). ... Tailings (also known as slickens[1]) are the waste left over[2] after removing the gangue from ore. ... Slag is also an early play by David Hare. ... Scoria Scoria is a textural term for macrovesicular volcanic rock ejecta. ... A cinder is a fragment of cooled pyroclastic material (lava or magma). ...

Contents

Smelting basics

The 7 metals that were known in ancient times (mercury, tin, lead, copper, silver, gold, and iron) can in principle be smelted through similar chemical reactions from their ores: This article is about the element. ... This article is about the metallic chemical element. ... This article is about the metal. ... For other uses, see Copper (disambiguation). ... This article is about the chemical element. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... For other uses, see Iron (disambiguation). ...

Mercury Oxide
2,HgO + C rarr 2,Hg + CO_2
Cassiterite
2,SnO_2 + 2,C rarr 2,Sn + 2,CO_2
Minium
2,PbO + C rarr 2,Pb + CO_2
Silver oxide
2,Ag_2O + C rarr 4,Ag + CO_2
Cuprite
2,CuO + C rarr 2,Cu + CO_2
Hematite
2,Fe_2O_3 + 3,C rarr 4,Fe + 3,CO_2

Different ores require different reactions at different temperatures, but almost always the reducing agent is carbon. The list above is sorted in increasing temperature order, so iron is the most difficult metal to smelt from the ones in the list (that's why historically iron smelting was the last to be discovered).


A common mistake is to think that the metal is obtained from the ore because at high temperature the metal just melts out of the ore. That is incorrect: if a blacksmith just heats up the ore without the proper reducing agent (carbon), he will just obtain molten ore. Also, one can smelt some ores at a temperature lower than the temperature required to melt the metal. Usually, though, these reactions happen at temperatures high enough to melt the resulting metal, so the metal can just be cast directly out of the furnace. A reducing agent (also called a reductant or reducer) is the element or a compound in a redox (reduction-oxidation) reaction (see electrochemistry) that reduces another species. ...


The exception to the previous paragraph is that some metal oxides just decompose at relatively low temperatures, so instead of trying to smelt mercury out of mercury oxide, one can just heat up mercury oxide to about 500°C, and the oxide will decompose into mercury and oxygen; as mercury boils at 357C, this will cause the oxide to decompose and boil out, producing the highly toxic gaseous mercury. This is possible only for mercury and a handful of other metal oxides; most metal oxides must be smelt with carbon as the reducing agent.


First smelting: campfires

Smelting is a chemical reaction that requires a particular ore (that sometimes look like any other common sedimentary rock), a particular content of carbon and a particular temperature in order to produce the metal. Without knowledge of chemistry, it is impossible to predict if a given rock can be smelted or not, and what it will produce. Therefore, there is continuous debate to understand how the ancient people learned how to smelt.


Probably the first smelting was done by accident by making a campfire on top of tin or lead ores. That may accidentally produce metallic tin and lead at the bottom of the campfire, as the temperatures to smelt tin and lead are easily obtained in a campfire. These metals can then be molten and cast in a campfire.


The earliest cast lead beads known today were found in the Çatal Höyük site in Anatolia (Turkey), and were dated of 6500BC. It is unclear when the earliest cast tin artifacts were made, given that tin is much more uncommon than lead, and earlier tin artifacts may have been reused to make bronze. Excavations at the South Area of Çatal Höyük Çatalhöyük (also Çatal Höyük and Çatal Hüyük, or any of the three without accent marks -- Çatal is Turkish for fork and Höyük is Turkish for mound) was a very large Neolithic and... This article is about two nested areas of Turkey, a plateau region within a peninsula. ... This article is about the metal alloy. ...


Although lead is a relatively common metal, it is too soft to be of much utility, so the first smelting of lead didn't have significant impact in the ancient world.


Copper smelting: kilns

There were in the past some arguments that copper was first smelt by accident also in campfires, but that seems improbable as campfires are about 200°C short of the temperature needed to smelt copper. A more probable path may have been through pottery kilns, invented in Iran by 6000BC. Pottery kilns produce ceramics that can be glazed with colorful earths (mostly metalic oxides) to produce colorful vases; it happens that malachite (copper oxide) is a colorful green stone, so a potter that encrusts malachite in a ceramic vase in a coal-fired kiln will produce a few droplets of metallic copper (ruining his vase). That may have set the way to smelt copper.


The first known cast copper artifact is a mace head found in Can Hasan from 5000BC.


Copper created some impact on the ancient world, as it produces good blunt weapons and reasonable armor, but it is still too soft to produce useful blade weapons. Therefore, the smelting of copper did not replace the manufacture of stone weapons, which still produced superior blades.


Bronze smelting

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

Bronze is a copper/arsenic or copper/tin alloy. The presence of arsenic and tin dramatically increased the hardness of copper, producing war-winning weapons and armor. A noble wearing bronze armor was basically impervious to the stone tools of the times, and his bronze sword kept its edge and shattered the older stone-based weapons. The knowledge of the smelting of copper allowed kings to overcome their enemies, and caused such a revolution that it marked the end of the Stone Age and the beginning of the Bronze Age. It would be millennia, though, until bronze could be used by common soldiers and townsfolk, and for a long time they were luxury items used by nobility. Image File history File links Metadata No higher resolution available. ... Image File history File links Metadata No higher resolution available. ... Song Yingxing (Traditional Chinese:宋應星; Simplified Chinese:宋应星; Wade Giles: Sung Ying-Hsing; 1587-1666 AD) was a Chinese scientist and encyclopedist who lived during the late Ming Dynasty (1368-1644). ... This article is about the metal alloy. ... For other uses, see Copper (disambiguation). ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... This article is about the metallic chemical element. ... An alloy is a homogeneous hybrid of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. ...


The first copper/arsenic bronzes date of 4200BC from Asia Minor, and were used for a long time until replaced by the modern copper/tin bronzes by 1500BC. It is unclear that if at some point in time the smiths that produced copper/arsenic bronze added arsenic oxides on purpose, or if they explored some copper lodes that happened to have arsenic as a lucky contamination. Anatolia (Greek: ανατολη anatole, rising of the sun or East; compare Orient and Levant, by popular etymology Turkish Anadolu to ana mother and dolu filled), also called by the Latin name of Asia Minor, is a region of Southwest Asia which corresponds today to...


The first copper/tin bronzes date of 3200BC, again from Asia Minor. Copper/tin bronzes are harder and more durable than copper/arsenic ones, and made these obsolete. The process through which the smiths learned to produce copper/tin bronzes is once again a mystery. The first such bronzes were probably a lucky accident from tin contamination of copper ores, but by 2000BC we know that tin was being mined on purpose for the production of bronze. This is amazing, given that tin is a semi-rare metal, and even a rich cassiterite ore only has 5% tin. Also, cassiterite looks like any common rock, and it takes special skills (or special instruments) to find it and locate the richer lodes. But, whatever steps were taken to learn about tin, these were fully understood by 2000BC. Cassiterite is a tin oxide mineral, SnO2. ...


Early iron smelting

The earliest evidence to date for the bloomery smelting of iron is found at Tell Hammeh, Jordan (see also external link), and dates to 930 CalBC (C14 dating). However, based on the archaeological record of iron artifacts, it is clear that intentional reduction of iron metal from terrestrial ores (in the case of Hammeh a Haematite ore), must have started near the end of the Late Bronze Age (ca. 1600–1150 BC). Where and how iron smelting was discovered is widely debated, and remains uncertain due to the significant lack of production finds. Nevertheless, there is some consensus that iron technology originated in the Near East, perhaps in Eastern Anatolia. The history of ferrous metallurgy began far back in prehistory, most likely with the use of iron from meteors. ... A bloomery is a type of furnace once widely used for smelting iron from its oxides. ... Tell Hammeh is a relatively small tell in the central Jordan Valley, Hashemite Kingdom of Jordan, located where the Zarqa river valley opens into the Jordan Valley. ... Radiocarbon dating is the use of the naturally occurring isotope of carbon-14 in radiometric dating to determine the age of organic materials, up to ca. ... Tell Hammeh is a relatively small tell in the central Jordan Valley, Hashemite Kingdom of Jordan, located where the Zarqa river valley opens into the Jordan Valley. ... Hematite (AE) or haematite (BE) is the mineral form of Iron (III) oxide, (Fe2O3), one of several iron oxides. ... Names for archaeological periods vary enormously from region to region. ... This article is about two nested areas of Turkey, a plateau region within a peninsula. ...


In Ancient Egypt somewhere between the Third Intermediate Period and 23rd Dynasty (ca. 1100–750 BC) there are indications of iron working. Significantly though, no evidence for the smelting of iron from ore has been attested to in Egypt in any period. There are further indications of iron smelting and working in West Africa by 1200 BC[1]. In addition, very early instances of carbon steel was found to be in production around 2000 YBP in northwest Tanzania, based on complex preheating principles. These discoveries are significant for the history of metallurgy.[2] Khafres Pyramid and the Great Sphinx of Giza, built about 2550 BC during the Fourth Dynasty of the Old Kingdom,[1] are enduring symbols of the civilization of ancient Egypt Ancient Egypt was a civilization in Northeastern Africa concentrated along the middle to lower reaches of the Nile River... The Third Intermediate Period is a phrase used to refer the period of the history of Ancient Egypt from the death of pharaoh Rameses XI in 1070 BC to the foundation of the Twenty-sixth Dynasty by Psamtik I, following the expulsion of the Nubian rulers of the Twenty-fifth... The Twenty-third dynasty of Egypt was a separate regime of Meshwesh Libyan kings, who ruled ancient Egypt. ...  Western Africa (UN subregion)  Maghreb[1] West Africa or Western Africa is the westernmost region of the African continent. ... (Redirected from 1200 BC) Centuries: 14th century BC - 13th century BC - 12th century BC Decades: 1250s BC 1240s BC 1230s BC 1220s BC 1210s BC - 1200s BC - 1190s BC 1180s BC 1170s BC 1160s BC 1150s BC Events and Trends 1204 BC - Theseus, legendary King of Athens is deposed after... Carbon steel,is very fun 2 play with also called plain carbon steel, is a metal alloy, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. ...


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 has to be consolidated with a hammer. A bloomery is a type of furnace once widely used for smelting iron from its oxides. ...


Later iron smelting

From the medieval period, the process of direct reduction in bloomeries began to be replaced by an indirect process. In this a blast furnace was used to make pig iron, which then had to undergo a further process to make forgeable bar iron. Further details of this will be found in the article on the blast furnace. Processes for the second stage include fining in a finery forge and from the Industrial Revolution puddling. However both processes are now obsolete, and wrought iron is now hardly made. Instead, mild steel is produced from a bessemer converter or by other means. The history of ferrous metallurgy began far back in prehistory, most likely with the use of iron from meteors. ... Blast furnace in Sestao, Spain. ... Two weights used in the theatre and made of pig iron; because of this, they are dubbed pig weights or simply pigs. ... Blast furnace in Sestao, Spain. ... Iron tapped from the blast furnace is pig iron, and contains significant amounts of carbon and silicon. ... A Watt steam engine, the steam engine that propelled the Industrial Revolution in Britain and the world. ... Puddle may refer to: Puddle, an acculmulation of water on a surface. ... For other uses, see Steel (disambiguation). ... Bessemer Converter, Schematic Diagram The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron. ...


Base metals

Cowles Syndicate of Ohio in Stoke-upon-Trent England, late 1880s. British Aluminium used the process of Paul Héroult about this time.
Cowles Syndicate of Ohio in Stoke-upon-Trent England, late 1880s. British Aluminium used the process of Paul Héroult about this time.[3]

The ores of base metals are often sulphides. In recent centuries, reverberatory smelters (sometimes called cupolas) have been used. These keep the fuel and the charge being smelted separate. Traditionally these were used for carrying out the first step: formation of two liquids, one an oxide slag containing most of the impurity elements, and the other a sulfide matte containing the valuable metal sulfide and some impurities. Such "reverb" furnaces are today about 40 m long, 3 m high and 10 m wide. Fuel is burned at one end and the heat melts the dry sulfide concentrates (usually after partial roasting), which is fed through the openings in the roof of the furnace. The slag floats on top of the heavier matte, and is removed and discarded or recycled. The sulfide matte is then sent to the converter. However the precise details of the process will vary for one metal to another. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... This article is about the companies owned by the inventors of an electric smelter. ... This article is about the U.S. State. ... The city of Stoke-on-Trent (also known as The Six Towns and The Potteries) is a city in The Midlands, United Kingdom. ... For other uses, see England (disambiguation). ... The Laggan Dam was constructed in 1934 to provide hydro-electric power for refining aluminium The aluminium producer British Aluminium Ltd was originally formed as the British Aluminium Company Ltd on 7 May 1894 and was subsequently known as British Alcan Aluminium Plc (1982-1996). ... The French scientist Paul (Louis-Toussaint) Héroult (1863-1914) was the inventor of the aluminium electrolysis and of the electric steel furnace. ... A reverbatory furnace is a metallurgical or process furnace which characteristically isolates the material being processed from contact with the fuel, but not from contact with the combustion gases. ... Slag is also an early play by David Hare. ... This article or section does not cite its references or sources. ... A furnace is a device for heating air or any other fluid. ... Metallurgical converter is a vessel used in the operation of converting (metallurgy). ...


References

  1. ^ How Old is the Iron Age in Sub-Saharan Africa? - by Roderick J. McIntosh, Archaeological Institute of America (1999)
  2. ^ Peter Schmidt, Donald H. Avery. Complex Iron Smelting and Prehistoric Culture in Tanzania, Science 22 September 1978: Vol. 201. no. 4361, pp. 1085 - 1089
  3. ^ Minet, Adolphe (1905). The Production of Aluminum and Its Industrial Use, Leonard Waldo (translator, additions), New York, London: John Wiley and Sons, Chapman & Hall, via Google Books scan of University of Wisconsin - Madison copy, 244 (Minet speaking) +116 (Héroult speaking). Retrieved on 2007-10-28. 

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 301st day of the year (302nd in leap years) in the Gregorian calendar. ...

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.

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