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Smelting is a process of applying heat to
ore ore – psilomelane (size: 6.7 × 5.8 × 5.1 cm) ore – galena and anglesite (size: 4.8 × 4.0 × 3.0 cm) ore (size: 7.5 × 6.1 × 4.1 cm) File:OreCartPachuca.JPG, upMinecart on display at the Historic Archive and Museum of Min ...

ore
in order to extract a base
metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts Electrical resistivity and conductivity, ele ...

metal
. It is a form of
extractive metallurgy Extractive metallurgy is a branch of metallurgical engineering wherein process and methods of extraction of metals from their natural mineral deposits are studied. The field is a materials science The interdisciplinary field of materials sc ...
. It is used to extract many metals from their ores, including
silver Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, wh ...
,
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is Abundance ...
,
copper Copper is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...
, and other
base metals A base metal is a common and inexpensive metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conduc ...
. Smelting uses heat and a chemical
reducing agent A reducing agent (also called a reductant, reducer, or electron donor) is an element or compound that loses or "donates" an electron The electron is a subatomic particle In physical sciences, subatomic particles are smaller than atom ...
to decompose the ore, driving off other elements as gases or
slag '' (slag), an 1873 wood engraving Slag is the glass-like by-product left over after a desired metal has been separated (i.e., Smelting, smelted) from its raw ore. Slag is usually a mixture of metal oxides and silicon dioxide. However, slags ca ...

slag
and leaving the metal base behind. The reducing agent is commonly a
fossil fuel A fossil fuel is a hydrocarbon In organic chemistry, a hydrocarbon is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen che ...
source of
carbon Carbon (from la, carbo "coal") is a chemical element with the Symbol (chemistry), symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—making four electrons available to form covalent bond, covalent chemical bonds. ...

carbon
, such as coke—or, in earlier times,
charcoal or soil, and firing it (circa 1890) Charcoal is a lightweight black carbon Carbon (from la, carbo "coal") is a chemical element with the Symbol (chemistry), symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent ...

charcoal
. The oxygen in the ore binds to carbon at high temperatures due to the lower potential energy of the bonds in
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalent bond, covalently double bonded to two oxygen atoms. It occurs naturally in At ...

carbon dioxide
(). Smelting most prominently takes place in a
blast furnace A blast furnace is a type of metallurgical Metallurgy is a domain of Materials science, materials science and engineering that studies the physical and chemical behavior of metallic Chemical element, elements, their Inter-metallic alloy, inter-m ...
to produce
pig iron Pig iron, also known as crude iron, is an intermediate product Intermediate goods, producer goods or semi-finished products are goods In economics Economics () is the social science that studies how people interact with value; in parti ...

pig iron
, which is converted into
steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appea ...

steel
. The carbon source acts as a chemical reactant to remove oxygen from the ore, yielding the purified metal
element Element may refer to: Science * Chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all ...
as a product. The carbon source is oxidized in two stages. First, the carbon (C) combusts with oxygen (O2) in the air to produce
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
(CO). Second, the carbon monoxide reacts with the ore (e.g. Fe2O3) and removes one of its oxygen atoms, releasing carbon dioxide (). After successive interactions with carbon monoxide, all of the oxygen in the ore will be removed, leaving the raw metal element (e.g. Fe). As most ores are impure, it is often necessary to use a
flux of \mathbf(\mathbf) with the unit normal vector \mathbf(\mathbf) ''(blue arrows)'' at the point \mathbf multiplied by the area dS. The sum of \mathbf\cdot\mathbf dS for each patch on the surface is the flux through the surface Flux describes ...
, such as
limestone Limestone is a common type of carbonate rock, carbonate sedimentary rock. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science), crystal forms of calcium carbonate (). Limestone forms ...

limestone
(or
dolomiteDolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincorp ...
), to remove the accompanying rock
gangue In mining, gangue () is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. It is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body ...
as slag. This
calcination Calcination refers to heating a solid to high temperatures in absence of air or oxygen, generally for the purpose of removing impurities or volatile substances. However, calcination is also used to mean a thermal treatment process in the absence o ...
reaction also frequently emits carbon dioxide. Plants for the
electrolytic An electrolyte is a substance that produces an conductivity (electrolytic), electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separates into cations and anions, which disperse uniformly thr ...

electrolytic
reduction of
aluminium Aluminium (aluminum in American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of America (USA), commonly known as the Unit ...

aluminium
are also generally referred to as
aluminium smelters Aluminium (aluminum in American English, American and Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common Metal, metals, at ap ...
.


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 of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest re ...
), sulfur (as a
sulfide Sulfide (British English British English (BrE) is the standard dialect of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, whi ...

sulfide
), or carbon and oxygen together (as a
carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystalline min ...

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 (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, K+ and permanganate, . It is a purplish-black crystalline salt, th ...
elements to free the metal.


Roasting

In the case of sulfides and carbonates, a process called "
roasting Roasting is a cooking method that uses dry heat where hot air covers the food, cooking it evenly on all sides with temperatures of at least from an open flame, oven, or other heat source. Roasting can enhance the flavor through caramelizatio ...
" 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 Malachite is a copper Copper is a chemical element with the Symbol (chemistry), symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductility, ductile metal with very high thermal conductivity, thermal and elec ...

Malachite
, a common ore of
copper Copper is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

copper
, is primarily copper carbonate hydroxide Cu2(CO3)(OH)2. This mineral undergoes
thermal decomposition Thermal decomposition, or thermolysis, is a chemical decompositionChemical decomposition, or chemical breakdown, is the process or effect of simplifying a single chemical entity (normal molecule, reaction intermediate, etc.) into two or more fra ...
to 2CuO, CO2, and H2O in several stages between 250 °C and 350 °C. The carbon dioxide and
water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts ...

water
are expelled into the atmosphere, leaving
copper(II) oxide Copper(II) oxide or cupric oxide is an inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is not ...
, which can be directly reduced to copper as described in the following section titled ''Reduction''. *
Galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a he ...

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 Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a Toxicity, toxic gas responsible for the smell of burnt matches. It is released naturally by vol ...
is expelled (like the
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalent bond, covalently double bonded to two oxygen atoms. It occurs naturally in At ...

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 Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

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 Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, ...

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 Mercury(II) oxide, also called mercuric oxide or simply mercury oxide, has a formula of Hg O. It has a red or orange color. Mercury(II) oxide is a solid at room temperature and pressure. The mineral form montroydite is very rarely found. History ...
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 Lime refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany * Austra ...
, 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 Gold is a chemical element with the Symbol (chemistry), symbol Au (from la, aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally. In a pure form, it is a brightness, bright, slightly reddish yel ...

gold
occurs regularly in native form in the natural environment. The others –
copper Copper is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

copper
,
lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate h ...

lead
,
silver Silver is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same n ...

silver
,
tin Tin is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same numbers ...

tin
,
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundance ...

iron
and
mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

mercury
– occur primarily as minerals, though copper is occasionally found in its
native state In biochemistry, the native state of a protein or nucleic acid is its properly folded and/or assembled form, which is operative and functional. The native state of a biomolecule may possess all four levels of biomolecular structure, with the seco ...

native state
in commercially significant quantities. These minerals are primarily
carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystalline min ...

carbonate
s,
sulfide Sulfide (British English British English (BrE) is the standard dialect of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, whi ...

sulfide
s, or
oxide of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest re ...
s of the metal, mixed with other components such as
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

silica
and
alumina Aluminium oxide is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by ...

alumina
.
Roasting Roasting is a cooking method that uses dry heat where hot air covers the food, cooking it evenly on all sides with temperatures of at least from an open flame, oven, or other heat source. Roasting can enhance the flavor through caramelizatio ...
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 The Old World consists of Africa Africa is the world's second-largest and second-most populous continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any ...
, humans learned to smelt metals in
prehistoric Prehistory, also known as pre-literary history, is the period of human history Human history, also known as world history, is the description of humanity's past. It is informed by archaeology Archaeology or archeology is the study ...
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 The Stone Age was a broad prehistoric Prehistory, also known as pre-literary history, is the period of human history Human history, also known as world history, is the description of humanity's past. It is informed by archaeology ...

Stone Age
,
Bronze Age The Bronze Age is a prehistoric Periodization, period that was characterized by the use of bronze, in some areas proto-writing, and other early features of urban civilization. The Bronze Age is the second principal period of the Three-age syst ...
, and
Iron Age The Iron Age is the final epoch of the three-age system, three-age division of the prehistory and protohistory of Homo sapiens, humanity. It was preceded by the Stone Age (Paleolithic, Mesolithic, Neolithic, and Chalcolithic) and the Bronze Age ...
. In the
Americas The Americas (also collectively called America) is a landmass comprising the totality of North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to East and West. ''North'' ...

Americas
, pre-
Inca The Inca Empire ( qu, Tawantinsuyu,  "four parts together"), also known as the Incan Empire and the Inka Empire, was the largest empire in pre-Columbian America. The administrative, political and military center of the empire was in the c ...

Inca
civilizations of the central
Andes The Andes, Andes Mountains or Andean Mountains ( es, Cordillera de los Andes) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of Sout ...

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.


Tin and lead

In the
Old World The Old World consists of Africa Africa is the world's second-largest and second-most populous continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any ...
, the first metals smelted were tin and lead. The earliest known cast lead beads were found in the
Çatal Höyük Çatal is a Turkish word meaning "fork". It may refer to: *Çatal railway station, a station in İzmir Province, Turkey *Çatalhöyük (also Çatal Hüyük/Höyük), an archaeological site in Konya Province, Turkey ;Catal and Čatal *Čatal Česjm ...
site in
Anatolia Anatolia,, tr, Anadolu Yarımadası), and the Anatolian plateau. also known as Asia Minor, is a large peninsula in Western Asia and the westernmost protrusion of the Asian continent. It makes up the majority of modern-day Turkey. The region ...
(
Turkey Turkey ( tr, Türkiye ), officially the Republic of Turkey, is a country located mainly on Anatolia in Western Asia, with a small portion on the Balkans in Southeast Europe. It shares borders with Greece and Bulgaria to the northwest; the B ...

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 Ancient Greece ( el, Ἑλλάς, Hellás) was a civilization belonging to a period of History of Greece, Greek history from the Greek Dark Ages of the 12th–9th centuries BC to the end of Classical Antiquity, antiquity ( AD 600). This era was ...
and
Ancient Rome In historiography, ancient Rome is Roman people, Roman civilization from the founding of the Italian city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD, encompassing the Roman Kingdom (753 BC ...
used it extensively to pipe and store water. They also used it as a
mortar Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps between blocks and bind them together * Mortar and pestle, a tool pair used to crush or grind * Mortar, Bihar, a village in ...
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
kiln , Wrecclesham Wrecclesham is a village on the southern outskirts of the large town of Farnham Farnham is a market town in Surrey, England, within the Borough of Waverley Borough Council, Waverley.OS Explorer map 145:Guildford and Farnham ...

kiln
s. The development of copper smelting in the Andes, which is believed to have occurred independently of the
Old World The Old World consists of Africa Africa is the world's second-largest and second-most populous continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any ...
, may have occurred in the same way. The earliest current evidence of copper smelting, dating from between 5500 BC and 5000 BC, has been found in
Pločnik Pločnik ( sr, Плочник) is a village in the municipality of Prokuplje Prokuplje ( sr-cyrl, Прокупље, ) is a city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Pengui ...
and Belovode, Serbia. 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. Combining copper with tin and/or
arsenic Arsenic is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same num ...

arsenic
in the right proportions produces
bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (such as aluminum, manganese, nickel or zinc) and sometimes non-metals or metalloids such as arsenic, phosphorus or ...

bronze
, an
alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts Elec ...
that is significantly harder than copper. The first copper/arsenic bronzes date from 4200 BC from
Asia Minor Anatolia,, tr, Anadolu Yarımadası), and the Anatolian plateau. also known as Asia Minor, is a large peninsula A peninsula ( la, paeninsula from ' "almost" and ' "island") is a landform surrounded by water on most of its border while be ...

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 3500 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 Cassiterite is a tin Tin is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all ...

cassiterite
ore only has 5% tin. Also, it takes special skills (or special instruments) to find it and locate richer
lode In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the process ...
s. 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 The Old World consists of Africa Africa is the world's second-largest and second-most populous continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any ...
. 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 A sword is an edged and bladed weapons, edged, bladed weapon intended for manual cutting or thrusting. Its blade, longer than a knife or dagger, is attached to a hilt and can be straight or curved. A thrusting sword tends to have a straighter ...

sword
s,
dagger A dagger is a knife A knife (plural knives; from Old Norse'' knifr'', "knife, dirk") is a tool or weapon with a cutting edge or blade, often attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least ...

dagger
s,
battle axe A battle axe (also battle-axe, battle ax, or battle-ax) is an axe (tool), axe specifically designed for combat. Battle axes were specialized versions of utility axes. Many were suitable for use in one hand, while others were larger and were dep ...

battle axe
s, and
spear A spear is a pole weapon A pole weapon or pole arm is a close combat Close combat means a violent physical confrontation between two or more opponents at short range.''MCRP 3-02B: Close Combat'', Washington, D.C.: Department Of The Navy, H ...

spear
and
arrow s and nock. An arrow is a fin-stabilized projectile launched by a bow and arrow, bow. A typical arrow usually consists of a long, stiff, straight ''shaft'' with a weighty (and usually sharp and pointed) ''arrowhead'' attached to the front end, m ...

arrow
points, as well as protective gear such as
shield Wall painting depicting a Mycenaean Greek "figure eight" shield with a suspension strap at the middle, 15th century BC, National Archaeological Museum, Athens -The faces of figure eight shields were quite convex. The cited "strap" may be the ri ...

shield
s,
helmet File:Tour du Doubs 2014 - Pontarlier - Jérémy Leveau.jpg, French cyclist Jérémy Leveau wearing a bicycle helmet A helmet is a form of protective gear worn to protect the Human head, head. More specifically, a helmet complements the skull in ...

helmet
s,
greave 225px, Greek greaves of “Denda”, c. 500 BCE, Staatliche Antikensammlungen (Inv. 4330) A greave (from the Old French ''greve'' "shin, shin armour") or jambeau is a piece of armour that protects the human leg, leg. Description The primary purp ...
s (metal shin guards), and other
body armor Body armor, also known as body armour, personal armor/armour, or a suit/coat of armour, is protective clothing designed to absorb or deflect physical attacks. Historically used to protect military personnel Military personnel are members of the ...
. Bronze also supplanted stone, wood, and organic materials in tools and household utensils—such as
chisel A chisel is a tool A tool is an object that can extend an individual's ability to modify features of the surrounding environment. Although many animals use simple tools, only human beings, whose use of stone tool A stone tool is, in the ...

chisel
s,
saw A saw is a tool A tool is an object that can extend an individual's ability to modify features of the surrounding environment. Although many animals use simple tools, only human beings, whose use of stone tools dates back hundreds of mil ...

saw
s,
adze An adze (; alternative spelling: adz) is an ancient and versatile cutting tool similar to an axe but with the cutting edge perpendicular to the handle rather than parallel. They have been used since the Stone Age. Adzes are used for smoothing or ...

adze
s,
nail Nail or Nails may refer to: In biology * Nail (anatomy), toughened protective protein-keratin (known as alpha-keratin, also found in hair) at the end of an animal digit * Nail (beak), a plate of hard horny tissue at the tip of some bird beaks O ...
s, ,
knives A knife (plural knives; from Old Norse Old Norse, Old Nordic, or Old Scandinavian was a North Germanic languages, North Germanic language that was spoken by inhabitants of Scandinavia and their Viking expansion, overseas settlements fro ...

knives
,
sewing needle A sewing needle, used for hand- sewing, is a long slender tool with a pointed tip at one end and a hole (or ''eye'') at the other. The earliest needles were made of bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes p ...

sewing needle
s and
pin A pin is a device used for fastening objects or material together, and can have three sorts of body: a shaft of a rigid inflexible material meant to be inserted in a slot, groove, or hole (as with pivots, hinges, and jigs); a shaft connected to ...
s, jugs,
cooking pot Cookware and bakeware are food preparation vessels used in kitchen A typical Hoosier cabinet of the 1920s A kitchen is a room or part of a room used for cooking Cooking or cookery is the art, science, and craft of using heat to Outline ...
s and
cauldron A cauldron (or caldron) is a large cast iron Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fr ...

cauldron
s,
mirror Grange, East Yorkshire, UK, from World War I. The mirror magnified the sound of approaching enemy Zeppelins for a microphone placed at the Focus (geometry), focal point. A mirror is an object that Reflection (physics), reflects an image. Lig ...

mirror
s, and
horse harnessHorse harness is a device that connects a horse The horse (''Equus ferus caballus'') is a domesticated odd-toed ungulate mammal. It belongs to the taxonomic family Equidae and is one of two Extant taxon, extant subspecies of wild horse, ''Equus ...
es. 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.


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 
BCE Common Era (CE) is one of the year notations used for the Gregorian calendar The Gregorian calendar is the calendar used in most of the world. It was introduced in October 1582 by Pope Gregory XIII as a minor modification of the Julian c ...

BCE
. 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 New Hittite Empire (∼1400–1200 BCE). Archaeologists have found indications of iron working in
Ancient Egypt Ancient Egypt was a civilization of Ancient history, ancient North Africa, concentrated along the lower reaches of the Nile, Nile River, situated in the place that is now the country Egypt. Ancient Egyptian civilization followed prehistoric ...

Ancient Egypt
, somewhere between the
Third Intermediate Period Third or 3rd may refer to: Numbers * 3rd, the ordinal form of the cardinal number 3 * fraction (mathematics), , a fraction that is one of three equal parts * ¹⁄₆₀ of a ''second'', or ¹⁄₃₆₀₀ of a ''minute'' Places * 3rd Street ( ...
and
23rd Dynasty The Twenty-third Dynasty of Egypt (notated Dynasty XXIII, alternatively 23rd Dynasty or Dynasty 23) is usually classified as the third dynasty of the ancient Egyptian Third Intermediate Period of Egypt, Third Intermediate Period. This dynasty cons ...
(ca. 1100–750 BCE). Significantly though, they have found no evidence for iron ore smelting in any (pre-modern) period. In addition, very early instances of
carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 3.8 per cent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...
were in production around 2000 years ago (around the first century CE.) in northwest
Tanzania Tanzania (;This approximates the Kiswahili pronunciation. However, is also heard in English. ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes regi ...

Tanzania
, based on complex preheating principles. These discoveries are significant for the history of metallurgy. Most early processes in Europe and Africa involved smelting iron ore in a
bloomery A bloomery is a type of furnace A furnace, referred to as a heater or boiler in British English, is a heating unit used to heat up an entire building. Furnaces are mostly used as a major component of a central heating system. The name de ...
, 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 Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag Inclusion (mineral), inclusions (up to 2% by weight), which gives it a ...
. The earliest evidence to date for the bloomery smelting of iron is found at
Tell Hammeh Tell Hammeh ( ar, تل حمة) is a relatively small Tell (archaeology), tell in the central Jordan Valley (Middle East), Jordan Valley, Hashemite Kingdom of Jordan, located where the Zarqa River valley opens into the Jordan Valley. It is the site ...
, Jordan

, and dates to 930 BCE ( C14 dating).


Later iron smelting

From the medieval period, an indirect process began to replace direct reduction in bloomeries. This used a
blast furnace A blast furnace is a type of metallurgical Metallurgy is a domain of Materials science, materials science and engineering that studies the physical and chemical behavior of metallic Chemical element, elements, their Inter-metallic alloy, inter-m ...
to make
pig iron Pig iron, also known as crude iron, is an intermediate product Intermediate goods, producer goods or semi-finished products are goods In economics Economics () is the social science that studies how people interact with value; in parti ...

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 (metallurgy), 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

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 (metallurgy), matte containing the valuable metal sulfide and some impurities. Such "reverb" Reverberatory furnace, 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 (Metallurgical), 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 Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a Toxicity, toxic gas responsible for the smell of burnt matches. It is released naturally by vol ...
that was difficult to capture; a new generation of copper smelting technologies has supplanted them. 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 impacts

Smelting has serious human impact on the environment, effects on the environment, producing wastewater and slag and releasing such toxic metals as
copper Copper is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

copper
, silver, iron, cobalt and selenium into the atmosphere. Smelters also release gaseous
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a Toxicity, toxic gas responsible for the smell of burnt matches. It is released naturally by vol ...
, contributing to acid rain, which acidifies soil and water. 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. 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.


Air pollution


Wastewater

Wastewater pollutants discharged by iron and steel mills includes gasification products such as benzene, naphthalene, anthracene, cyanide, ammonia, phenols and cresols, together with a range of more complex organic compounds known collectively as polycyclic aromatic hydrocarbons (PAH). Treatment technologies include recycling of wastewater; settling basins, clarifiers and filtration systems for solids removal; oil skimmers and filtration; chemical precipitation and filtration for dissolved metals; Adsorption#Activated carbon, carbon adsorption and biological oxidation for organic pollutants; and evaporation. 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.


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.


See also

*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


References


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.


External links

{{Authority control Smelting, Firing techniques Metallurgical processes de:Verhüttung