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

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.

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.

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: &#945;&#957;&#945;&#964;&#959;&#955;&#951; 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

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.[3]

# 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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