Smelting is a form of extractive metallurgy Extractive metallurgy is the practice of extracting metal from ore, purifying it, and recycling it; its main use is to produce a metal A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by from its ore An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element. This includes iron Iron is the most common element in the earth as a whole, and the fourth most common in the Earth's crust. It is produced as a result of stellar fusion in high-mass stars, and it is the heaviest stable element produced by stellar fusion because the fusion of iron is the last nuclear fusion reaction that is exothermic. Iron is the most widely used extraction (for the production of steel Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten. Carbon and other elements act as a hardening agent, preventing) from iron ore, and copper extraction Currently, the most common source of copper ore is the mineral chalcopyrite , which accounts for about 50% of copper production. The focus of this article is on the process of copper extraction from chalcopyrite ore into pure metal. Processes for other minerals are mentioned and other base metals from their ores. Smelting uses heat and a chemical reducing agent Redox reactions describe all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in to change the oxidation state In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by integers, which can be positive, negative, or zero of the metal ore; the reducing agent is commonly a source of carbon Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of such as coke Coke is the solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. Cokes from coal are grey, hard, and porous, or in earlier times charcoal Charcoal is the dark grey residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in the absence of oxygen . The resulting soft, brittle, lightweight, black, porous. The carbon or carbon monoxide Carbon monoxide , also called carbonic oxide, is a colorless, odorless and tasteless gas which is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal biological functions derived from it removes oxygen Oxygen (pronounced /ˈɒksɨdʒɨn/, OK-si-jin, from the Greek roots ὀξύς (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter), is the element with atomic number 8 and represented by the symbol O. It is a member of the chalcogen group on the periodic table, and is a highly from the ore to leave the metal. The carbon is thus oxidized in two stages, producing first carbon monoxide and then carbon dioxide Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state. CO2 is a trace gas comprising 0.039% of the atmosphere. As most ores are impure, it is often necessary to use flux In metallurgy, a flux is a chemical cleaning agent that facilitates soldering, brazing, and welding by removing oxidation from the metals to be joined. Common fluxes are: ammonium chloride or rosin for soldering tin; hydrochloric acid and zinc chloride for soldering galvanized iron ; and borax for brazing or braze-welding ferrous metals. Different, such as limestone Limestone is a sedimentary rock composed largely of the mineral calcite . Like most other sedimentary rocks, limestones are composed of grains; however, most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and extraclasts, 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. The separation of mineral from gangue is known as mineral processing, mineral dressing or ore dressing and it is a necessary and often significant aspect of mining. It can be a complicated process, depending on the as slag Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form. While slags are generally used as a waste removal mechanism in metal.

Plants for the electrolytic In chemistry and manufacturing, electrolysis (from the Greek λύσις, and ἤλεκτρον (ɛː́lektron = amber)) is a method of using a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally occurring sources reduction of aluminium Aluminium (UK: /ˌæljʉˈmɪniəm/ AL-yew-MIN-ee-əm) or aluminum (US: /əˈluːmɨnəm/ ( listen) ə-LOO-mi-nəm) is a silvery white member of the boron group of chemical elements. It has the symbol Al and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth's crust,, while not using carbon, are also generally referred to as smelters.

Process

Smelting involves more than just "melting the metal out of its ore". Most ores are a chemical compound of the metal with other elements, such as oxygen (as an oxide An oxide is a chemical compound containing at least one oxygen atom as well as at least one other element.[citation needed] Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon monoxide and carbon dioxide. Even), sulfur (as a sulfide A sulfide is an anion of sulfur in its lowest oxidation number of −2. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors) or carbon and oxygen together (as a carbonate In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, CO2−3. The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group O=C2). To produce the metal, these compounds have to undergo a chemical reaction. Smelting therefore consists of using suitable reducing substances Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane (CH4), or it can be a complex process such as the oxidation of sugar in the human body that will combine with those oxidizing Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane (CH4), or it can be a complex process such as the oxidation of sugar in the human body elements to free the metal.

Roasting

In the case of carbonates In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, CO2−3. The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group O=C2 and sulfides A sulfide is an anion of sulfur in its lowest oxidation number of −2. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors, a process called "roasting" drives off the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is usually carried out in an oxidizing environment. A couple practical examples:

• Malachite Malachite is a copper carbonate mineral, with the formula Cu2CO3 , a common ore of copper Copper is a chemical element with the symbol Cu (Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable, and a freshly exposed surface has a pinkish or peachy color. It is used as a thermal conductor, an electrical conductor, a building material, and a, is primarily copper carbonate (CuCO₃). This mineral undergoes thermal decomposition to CuO and CO₂ in several stages between 250°C and 350°C. The carbon dioxide is expelled into the atmosphere, leaving copper oxide which can be directly reduced to copper as shown below.
• Galena Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral, the most common mineral of lead Lead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a, is primarily lead sulfide (PbS). The sulfide is oxidized to a sulfate (PbSO₃) which thermally decomposes into lead oxide and sulfur dioxide gas. (PbO and SO₂) The sulfur dioxide (like the carbon dioxide in the example above) is expelled, and the lead oxide is reduced as below.

Reduction

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. The required temperature varies over a very large range, both in absolute terms, and in terms of the melting point of the base metal. A few examples:

• iron oxide becomes metallic iron at roughly 1250°C, almost 300 degrees below iron's melting point of 1538°C
• mercuric oxide becomes vaporous mercury near 550°C, almost 600 degrees above mercury's melting point of -38°C

Fluxes

Fluxes are used 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 or sulfur dioxide produced during roasting and smelting to keep them out of the working environment.

History

Historically, the first smelting processes used carbon (in the form of charcoal) to reduce the oxides of tin Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead, like the two possible oxidation states +2 and +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, the largest (cassiterite, SnO₂), copper (cuprite Cuprite is an oxide mineral composed of copper oxide Cu2O, and is a minor ore of copper, CuO) and lead (Lead(II) oxide Lead oxide is the inorganic compound with the formula Pb , PbO), and eventually iron (hematite Hematite, also spelled as hæmatite, is the mineral form of iron oxide (Fe2O3), one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum. Hematite and ilmenite form a complete solid solution at temperatures above 950°C, Fe₂O₃) In all these reactions the reducing agent was actually carbon monoxide, as the charcoal and oxides remained solid and therefore could not react directly with each other. For copper and lead, important ores were actually the sulfides, chalcocite Chalcocite, copper sulfide (Cu2S), is an important copper ore mineral. It is opaque, being colored dark-gray to black with a metallic luster. It has a hardness of 2½ - 3. It is a sulfide with an orthorhombic crystal system (CuS₂) and galena (PbS); these first had to be converted to oxides by roasting Roasting is a metallurgical process involving gas-solids reactions at elevated temperatures. A common example is the process in which sulfide ores are converted to oxides, prior to smelting. Roasting differs from calcination, which merely involves decomposition at elevated temperatures. A typical sulfide roasting chemical reaction takes the them in air

Silver was generally found in the form of sulfides mixed with galena; it was smelted together with lead and was afterwards separated from it by cupellation Cupellation is a metallurgical process in which ores or alloyed metals are treated under high temperatures and carefully controlled operations in order to separate noble metals, like gold and silver, from base metals like lead, copper, zinc, arsenic, antimony or bismuth, that might be present in the ore. This process is based on the principle that.

The primary source of mercury was the sulfide ore (cinnabar HgS adopts two structures, i.e. it is dimorphous. The more stable form is cinnabar, which has a structure akin to that for HgO: each Hg center has two short Hg-S bonds , and four longer Hg---S contacts (3.10, 3.10, 3.30, 3.30 Å). The black form of HgS has the zinc blende structure, HgS). This was roasted to produce the oxide HgO, which decomposed into oxygen and mercury, which both left the furnace as a (highly toxic) vapor, that was condensed in appropriate containers.

In the Old World, humans learned to smelt metals in prehistoric Prehistory is a term used to describe the period before recorded history. Paul Tournal originally coined the term Pré-historique in describing the finds he had made in the caves of southern France.[citation needed] It came into use in France in the 1830s to describe the time before writing, and the word "prehistoric" was introduced into 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 is a broad prehistoric period during which humans widely used stone for toolmaking. Stone tools were made from a variety of different sorts of stone. For example, flint and chert were shaped for use as cutting tools and weapons, while basalt and sandstone were used for ground stone tools, such as quern-stones. Wood, bone, shell,, Bronze Age The Bronze Age of a culture is the period when the most advanced metalworking in that culture used bronze. This could either have been based on the local smelting of copper and tin from ores, or trading for bronze from production areas elsewhere. Many, though not all, Bronze Age cultures flourished in prehistory, and Iron Age In archaeology, the Iron Age is the historical period in any area during which cutting tools and weapons were mainly made of iron or steel. The adoption of this material coincided with other changes in society, including differing agricultural practices, religious beliefs and artistic styles.

In the Americas, the Incas The Inca civilization began as a tribe in the Cuzco area, where the legendary first Sapa Inca, Manco Capac founded the Kingdom of Cuzco around 1200. Under the leadership of the descendants of Manco Capac, the Inca state grew to absorb other Andean communities. In 1442, the Incas began a far-reaching expansion under the command of Patchacuti. He and other civilizations of the Andes The Andes are the world's longest continental mountain range. It is a continuous chain of highland along the western coast of South America. The range is over 7,000 km long, 200 km (120 mi) to 700 km (430 mi) wide (widest between 18° to 20°S latitude), and of an average height of about 4,000 m (13,000 ft) had mastered the smelting of copper and bronze by the time the first Europeans arrived in the 16th century.^{[citation needed]}

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 Çatal Höyük was a very large Neolithic and Chalcolithic settlement in southern Anatolia, which existed from approximately 7500 BC to 5700 BC. It is the largest and best preserved Neolithic site found to date site in Anatolia Anatolia is a geographic and historical term denoting the westernmost protrusion of Asia, comprising the majority of the Republic of Turkey. The region is bounded by the Black Sea to the north, Georgia to the northeast, Armenia to the east, Mesopotamia to the southeast, the Mediterranean Sea to the south and the Aegean Sea to the west. Anatolia (Turkey Turkey , known officially as the Republic of Turkey ( Türkiye Cumhuriyeti (help·info)), is a Eurasian country that stretches across the Anatolian peninsula in western Asia and Thrace (Rumelia) in the Balkan region of southeastern Europe. Turkey is one of the six independent Turkic states. Turkey is bordered by eight countries: Bulgaria to the), 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, we have no evidence about how it was made. However, tin and lead can be smelted by placing the ores in a wood fire, so it is possible that the discovery may have occurred by accident.

Although lead is a common metal, its discovery had relatively little impact in the ancient world. It is too soft to be used for weapons (except possibly as sling projectiles) or for structural elements. However, being easy to cast and shape, it came to be extensively used in the classical world of Ancient Greece and Ancient Rome for piping and storage of water. It was also used as a mortar in stone buildings, and as a writing material for commemorative plaques and curses.

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

Copper and bronze

After tin and lead, the next metal to be smelted appears to have been copper. How the discovery came about is a matter of much debate. Campfires are about 200 °C short of the temperature needed for that,^{[citation needed]} so it has been conjectured that the first smelting of copper may have been achieved in pottery kilns. The earliest known instances in Europe and the Near East were found in Persia, dated about 6000 BC.^{[citation needed]} The first smelted copper artifact was thought to be a mace head found in Can Hasan, Turkey and dated to 5000 BC. However, this now appears to be hammered native copper.^[1] The earliest current evidence of copper smelting, dating from between 5500 BC and 5000 BC, has been found in Pločnik and Belovode, Serbia ^[2][3].

The development of copper smelting in the Andes, which is believed to have occurred independently of that in the Old World, may have occurred in the same way.^{[citation needed]}.

By combining copper with tin and/or arsenic in the right proportions one obtains bronze, an alloy which is significantly harder than copper. The first copper/arsenic bronzes date of 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; but eventually arsenic-bearing minerals were intentionally added during smelting.^{[citation needed]}

Copper/tin bronzes, harder and more durable, were developed around 1500 BC or 3200 BC,also in Asia Minor.^{[citation needed]}

The discovery of copper smelting and bronze manufacture had a significant impact on the history of the Old World. The metal was hard enough to make weapons, which were heavier, stronger, and more resistant to impact-related damage than their wood, bone, or stone equivalents. For several millennia, bronze was the material of choice for weapons such as swords, daggers, battle axes, spear and arrow points, as well as protective gear such as shields, helmets, shin guards, and other body armor. Bronze also supplanted stone, wood and organic materials in all sorts of tools and household utensils, such as chisels, saws, adzes, nails, blade shears, knives, sewing needles and pins, jugs, cooking pots and cauldrons, mirrors, horse harnesses, and much more.^{[citation needed]} In turn, bronze tools brought about an increase in the quantity, quality, and complexity of manufactured products, from buildings to leather goods.^{[citation needed]} Tin and copper also contributed to the establishment of trade networks spanning large areas of Europe and Asia, and had a major effect on the distribution of wealth among individuals and nations.^{[citation needed]}

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 2000 BC 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 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 2000 BC.

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