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Iron ores are
rocks A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition and the way in which it is formed. Rocks form the Earth's oute ...
and
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (20 ...

mineral
s from which
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, el ...

metal
lic
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
can be economically extracted. The
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
s are usually rich in
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
s and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of
magnetite Magnetite is a mineral and one of the main iron ore Iron ores are rocks and minerals from which metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, po ...

magnetite
(, 72.4% Fe),
hematite Hematite (), also spelled as haematite, is a common 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 ...

hematite
(, 69.9% Fe),
goethite Goethite () is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient tim ...

goethite
(, 62.9% Fe),
limonite Limonite () is an iron ore Iron ores are rocks and minerals from which metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, sho ...

limonite
(, 55% Fe) or
siderite:''Siderite is also the name of a type of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of ...

siderite
(, 48.2% Fe). Ores containing very high quantities of hematite or magnetite (greater than about 60% iron) are known as "natural ore" or "direct shipping ore", meaning they can be fed directly into iron-making
blast furnace A blast furnace is a type of metallurgy, metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atm ...
s. Iron ore is the
raw material A raw material, also known as a feedstock, unprocessed material, or primary commodity, is a basic material that is used to produce goods In economics Economics () is the social science that studies how people interact with value; in par ...
used to make
pig iron Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel Steel is an alloy of iron with typically a few tenths of a percent of carbon to improve its strength of materials, strength and ...

pig iron
, which is one of the main raw materials to make
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
—98% of the mined iron ore is used to make steel. In 2011 the ''Financial Times'' quoted Christopher LaFemina, mining analyst at Barclays Capital, saying that iron ore is "more integral to the
global economy The world economy or the global economy is the economy of all humans of the world, referring to the global economic system which includes all economic activities which are conducted both within and between nation A nation is a community of peop ...
than any other commodity, except perhaps
oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can b ...

oil
".


Sources

Metallic iron is virtually unknown on the surface of the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wit ...
except as iron-nickel
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 ...
s from
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When th ...
s and very rare forms of deep mantle
xenolith Sierra_Nevada_(U.S.).html"_;"title="Gabbroic_xenolith_in_granite_in_Rock_Creek_Canyon,_eastern_Sierra_Nevada_(U.S.)">Sierra_Nevada,_California A_xenolith_("foreign_rock")_is_a_rock_(geology).html" ;"title="Sierra Nevada (U.S.)">Sierra Nevada, Cal ...
s. Some
iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Iron meteorite ...
s are thought to have originated from accreted bodies 1,000 km in diameter or larger. The origin of iron can be ultimately traced to formation through nuclear fusion in stars and most of the iron is thought to have originated in dying stars that are large enough to collapse or explode as
supernova (bright spot on the lower left), a type Ia supernova A type Ia supernova (read: "type one-A") is a type of supernova (bright spot on the lower left), a type Ia supernova within its host galaxy, NGC 4526 A supernova ( plural: supernova ...

supernova
e. Although iron is the fourth-most abundant element in the
Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere, a division of Earth's layers that includes the Crust (geology), ...
, composing about 5%, the vast majority is bound in
silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they unde ...
or more rarely
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 ...
minerals (for more information, see
iron cycle The iron cycle (Fe) is the biogeochemical cycle of 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 ...

iron cycle
). The
thermodynamic Thermodynamics is a branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related ent ...
barriers to separating pure iron from these minerals are formidable and energy-intensive; therefore, all sources of iron used by human industry exploit comparatively rarer iron
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 ...
minerals, primarily
hematite Hematite (), also spelled as haematite, is a common 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 ...

hematite
. Prior to the industrial revolution, most iron was obtained from widely available
goethite Goethite () is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient tim ...

goethite
or
bog ore Bog iron is a form of impure 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 t ...
, for example during the
American Revolution The American Revolution was an ideological and political revolution that occurred in British America between 1765 and 1791. The Americans in the Thirteen Colonies formed independent states that defeated the First British Empire, British in ...
and the
Napoleonic Wars The Napoleonic Wars (1803–1815) were a series of major World war, global conflicts pitting the First French Empire, French Empire and its allies, led by Napoleon, Napoleon I, against a fluctuating array of Coalition forces of the Napoleonic Wa ...
. Prehistoric societies used
laterite Laterite is both a soil and a rock type rich in 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 e ...
as a source of iron ore. Historically, much of the iron ore utilized by
industrialized Industrialisation Industrialisation (or industrialization) is the period of social and economic change that transforms a human group from an agrarian society An agrarian society, or agricultural society, is any community whose economy is based ...
societies has been mined from predominantly hematite deposits with grades of around 70% Fe. These deposits are commonly referred to as "direct shipping ores" or "natural ores". Increasing iron ore demand, coupled with the depletion of high-grade hematite ores in the United States, led after
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a World war, global war that lasted from 1939 to 1945. It involved World War II by country, the vast majority of the world's countries—including all the great ...
to development of lower-grade iron ore sources, principally the utilization of
magnetite Magnetite is a mineral and one of the main iron ore Iron ores are rocks and minerals from which metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, po ...

magnetite
and
taconite Taconite ( IPA: tækənaɪt is a variety of iron formation, an 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 seri ...

taconite
. Iron ore mining methods vary by the type of ore being mined. There are four main types of iron ore deposits worked currently, depending on the
mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical mineralogy, optical) properties of minerals and mineralized artifact (archaeology), artifacts. Specific stu ...

mineralogy
and geology of the ore deposits. These are magnetite,
titanomagnetite Titanomagnetite is a mineral containing oxides of titanium and iron, with the formula Fe2+(Fe3+,Ti)2O4. It is also known as titaniferous magnetite. It is part of the spinel group of minerals. The Curie temperature for titanomagnetite has been found ...
, massive hematite and pisolitic ironstone deposits.


Banded iron formations

Banded iron formation showing banded iron formation, displayed in Dresden, Saxony, Germany Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iro ...

Banded iron formation
s (BIFs) are
sedimentary rock Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentation ...

sedimentary rock
s containing more than 15% iron composed predominantly of thinly bedded iron minerals and
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
(as
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tetrahedra, ...

quartz
). Banded iron formations occur exclusively in
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologic ...

Precambrian
rocks, and are commonly weakly to intensely metamorphosed. Banded iron formations may contain iron in
carbonates 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 ...
(
siderite:''Siderite is also the name of a type of iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of ...

siderite
or
ankerite Ankerite is a calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical an ...
) or
silicates In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they unde ...
(
minnesotaite Minnesotaite is an iron silicate mineral Silicate minerals are rock-forming mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned ...

minnesotaite
,
greenalite Greenalite is a mineral 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 ...

greenalite
, or
grunerite Grunerite is a mineral of the amphibole Amphibole () is a group of Silicate minerals, inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedron, tetrahedra, linked at the vertices and generally containing ...
), but in those mined as iron ores,
oxides of rutile. Ti(IV) centers are grey; oxygen centers are red. Notice that oxygen forms three bonds to titanium and titanium forms six bonds to oxygen. An oxide () is a chemical compound that contains at least one oxygen Oxygen is the chemic ...
(
magnetite Magnetite is a mineral and one of the main iron ore Iron ores are rocks and minerals from which metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, po ...

magnetite
or
hematite Hematite (), also spelled as haematite, is a common 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 ...

hematite
) are the principal iron mineral. Banded iron formations are known as ''
taconite Taconite ( IPA: tækənaɪt is a variety of iron formation, an 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 seri ...

taconite
'' within North America. The mining involves moving tremendous amounts of ore and waste. The waste comes in two forms: non-ore bedrock in the mine (
overburden In mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. These deposits form a mineralized commodity that is of economic int ...
or interburden locally known as mullock), and unwanted minerals which are an intrinsic part of the ore rock itself (
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 ...
). The mullock is mined and piled in
waste dump A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste w ...
s, and the gangue is separated during the
beneficiation In the mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. These deposits form a mineralized commodity that is of economic ...
process and is removed as
tailings Tailings are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are distinct from overburden, which is the waste rock or other material that overlies an ore or mi ...
. Taconite tailings are mostly the mineral quartz, which is chemically inert. This material is stored in large, regulated water settling ponds.


Magnetite ores

The key parameters for magnetite ore being economic are the crystallinity of the magnetite, the grade of the iron within the banded iron formation host rock, and the contaminant elements which exist within the magnetite concentrate. The size and strip ratio of most magnetite resources is irrelevant as a banded iron formation can be hundreds of meters thick, extend hundreds of kilometers along
strike Strike may refer to: People *Strike (surname) Physical confrontation or removal *Strike (attack), attack with an inanimate object or a part of the human body intended to cause harm *Airstrike, military strike by air forces on either a suspected o ...

strike
, and can easily come to more than three billion or more tonnes of contained ore. The typical grade of iron at which a magnetite-bearing banded iron formation becomes economic is roughly 25% iron, which can generally yield a 33% to 40% recovery of magnetite by weight, to produce a concentrate grading in excess of 64% iron by weight. The typical magnetite iron ore concentrate has less than 0.1%
phosphorus Phosphorus is a chemical element with the Symbol (chemistry), symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly Reactivity (chemistry), reactive, phosphor ...

phosphorus
, 3–7%
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 less than 3%
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 ...
. Currently magnetite iron ore is mined in
Minnesota Minnesota () is a U.S. state, state in the north central region of the United States. It is known as the "Land of 10,000 Lakes". Its official motto is , French for "The Star of the North". Of the U.S. state, U.S. states, Minnesota is the List ...

Minnesota
and
Michigan Michigan () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper ...

Michigan
in the
U.S. The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country primarily located in North America North America is a continent entirely within the Northern Hemisphere and almost all ...

U.S.
, Eastern
Canada Canada is a country in the northern part of North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean, Atlantic to the Pacific Ocean, Pacific and northward into the Arctic Ocea ...

Canada
and Northern
Sweden Sweden ( sv, Sverige ), officially the Kingdom of Sweden ( sv, links=no, Konungariket Sverige ), is a Nordic countries, Nordic country in Northern Europe.The United Nations Group of Experts on Geographical Names states that the country's for ...

Sweden
. Magnetite-bearing banded iron formation is currently mined extensively in
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, ...
, which exports significant quantities to
Asia Asia () is a landmass variously described as part of Eurasia Eurasia () is the largest continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict crite ...
, and there is a nascent and large magnetite iron ore industry in
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, smal ...

Australia
.


Direct-shipping (hematite) ores

Direct-shipping iron ore (DSO) deposits (typically composed of
hematite Hematite (), also spelled as haematite, is a common 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 ...

hematite
) are currently exploited on all continents except
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oce ...

Antarctica
, with the largest intensity in
South America South America is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered fr ...

South America
, Australia and Asia. Most large hematite iron ore deposits are sourced from altered banded iron formations and rarely igneous accumulations. DSO deposits are typically rarer than the magnetite-bearing BIF or other rocks which form its main source or protolith rock, but are considerably cheaper to mine and process as they require less beneficiation due to the higher iron content. However, DSO ores can contain significantly higher concentrations of penalty elements, typically being higher in phosphorus, water content (especially
pisolite QEMSCAN mineral map of pisoids A pisolite is a sedimentary rock made of pisoids, which are concretionary grains – typically of calcium carbonate which resemble ooids, but are more than 2 mm in diameter. These grains are approximately sph ...
sedimentary accumulations) and aluminium (
clays Clay is a type of fine-grained natural soil Soil (often stylized as SOiL) is an American rock band that was formed in Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive maps of Chi ...
within pisolites). Export-grade DSO ores are generally in the 62–64% Fe range.


Magmatic magnetite ore deposits

Occasionally
granite Granite () is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools ...

granite
and
ultrapotassicUltrapotassic igneous rocks are a class of rare, volumetrically minor and generally ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous Igneous rock (derived from the Latin ...
igneous rock Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the p ...
s segregate
magnetite Magnetite is a mineral and one of the main iron ore Iron ores are rocks and minerals from which metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, po ...

magnetite
crystals and form masses of magnetite suitable for economic concentration. A few iron ore deposits, notably in
Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention ra ...
, are formed from
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continent ...

volcanic
flows containing significant accumulations of magnetite
phenocryst 300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss Swiss may refer to: * the adjectival form of Switzerland *Swiss people Places *Swiss, Missouri *Swiss, North Carolina *Swiss, West Virginia *Swiss, Wisconsin Other uses * ...
s. Chilean magnetite iron ore deposits within the Atacama Desert have also formed
alluvial Alluvium (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of t ...
accumulations of magnetite in streams leading from these volcanic formations. Some magnetite
skarn Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism Metasomatism (from the Greek μετά (change) and σῶμα (body)) is the chemical alteration of a rock by hydrothermal and other fluids. ...

skarn
and
hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC ...
deposits have been worked in the past as high-grade iron ore deposits requiring little
beneficiation In the mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. These deposits form a mineralized commodity that is of economic ...
. There are several granite-associated deposits of this nature in
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two reg ...

Malaysia
and
Indonesia Indonesia ( ), officially the Republic of Indonesia ( id, Republik Indonesia, links=yes ), is a country in Southeast Asia and Oceania between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. It consists of more than List of islands ...

Indonesia
. Other sources of magnetite iron ore include metamorphic accumulations of massive magnetite ore such as at Savage River,
Tasmania Tasmania (), abbreviated as TAS, is an island States and territories of Australia, state of Australia. It is located 240 km (150 mi) to the south of the Mainland Australia, Australian mainland, separated from it by Bass Strait. Th ...
, formed by shearing of
ophiolite , Newfoundland An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle (Earth), upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφι ...

ophiolite
ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch o ...
s. Another, minor, source of iron ores are magmatic accumulations in
layered intrusionImage:Chromitite Bushveld South Africa.jpg, 200px, Chromitite and anorthosite layered igneous rocks in Critical Zone UG1 of the Bushveld Igneous Complex at the Mononono River outcrop, near Steelpoort, South Africa A layered intrusion is a large Sill ...
s which contain a typically
titanium Titanium 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 ...

titanium
-bearing magnetite often with
vanadium Vanadium is a chemical element with the Symbol (chemistry), symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an ...

vanadium
. These ores form a niche market, with specialty smelters used to recover the iron, titanium and vanadium. These ores are beneficiated essentially similar to banded iron formation ores, but usually are more easily upgraded via and screening. The typical titanomagnetite concentrate grades 57% Fe, 12% Ti and 0.5% .


Mine tailings

For every 1 ton of iron ore concentrate produced approximately 2.5–3.0 tons of iron ore
tailings Tailings are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are distinct from overburden, which is the waste rock or other material that overlies an ore or mi ...
will be discharged. Statistics show that there are 130 million tons of iron ore discharged every year. If, for example, the mine tailings contain an average of approximately 11% iron there would be approximately 1.41 million tons of iron wasted annually. These tailings are also high in other useful metals such 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
,
nickel Nickel 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 ...

nickel
, and
cobalt Cobalt 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 numbe ...

cobalt
, and they can be used for road-building materials like pavement and filler and building materials such as cement, low-grade glass, and wall materials. While tailings are a relatively low-grade ore, they are also inexpensive to collect as they don't have to be mined. Because of this companies such as Magnetation have started reclamation projects where they use iron ore tailings as a source of metallic iron. The two main methods of recycling iron from iron ore tailings are magnetizing roasting and direct reduction. Magnetizing roasting uses temperatures between 700 and 900 °C for a time of under 1 hour to produce an iron concentrate (Fe3O4) to be used for iron smelting. For magnetizing roasting it is important to have a reducing atmosphere to prevent oxidization and the formation of Fe2O3 because it is harder to separate as it is less magnetic. Direct reduction uses hotter temperatures of over 1000 °C and longer times of 2–5 hours. Direct reduction is used to produce
sponge iron Direct reduced iron (DRI), also called sponge iron, is produced from the direct Reduction (chemistry), reduction of iron ore (in the form of lumps, pellets, or fines) to iron by a Reducing agent, reducing gas or elemental carbon produced from natura ...
(Fe) to be used for steel making. Direct reduction requires more energy as the temperatures are higher and the time is longer and it requires more reducing agent than magnetizing roasting.


Extraction

Lower-grade sources of iron ore generally require
beneficiation In the mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. These deposits form a mineralized commodity that is of economic ...
, using techniques like crushing,
milling Milling may refer to: * Milling (grinding), breaking solid materials into smaller pieces by grinding, crushing, or cutting in a mill * Milling (machining), a process of using rotary cutters to remove material from a workpiece * Milling (military tra ...
, gravity or heavy media separation, screening, and silica
froth flotation of the froth surface. Froth flotation is a process for selectively separating hydrophobic In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, m ...
to improve the concentration of the ore and remove impurities. The results, high-quality fine ore powders, are known as fines.


Magnetite

Magnetite Magnetite is a mineral and one of the main iron ore Iron ores are rocks and minerals from which metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, po ...

Magnetite
is
magnetic Magnetism is a class of physical phenomena that are mediated by magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in ...

magnetic
, and hence easily separated from the
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 ...
minerals and capable of producing a high-grade concentrate with very low levels of impurities. The grain size of the magnetite and its degree of commingling with the silica
groundmass The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ord ...
determine the grind size to which the rock must be comminuted to enable efficient magnetic separation to provide a high purity magnetite concentrate. This determines the energy inputs required to run a milling operation. Mining of banded iron formations involves coarse crushing and screening, followed by rough crushing and fine grinding to the ore to the point where the crystallized magnetite and quartz are fine enough that the quartz is left behind when the resultant powder is passed under a magnetic separator. Generally most magnetite banded iron formation deposits must be ground to between 32 and 45 micrometers in order to produce a low-silica magnetite concentrate. Magnetite concentrate grades are generally in excess of 70% iron by weight and usually are low phosphorus, low aluminium, low titanium and low silica and demand a premium price.


Hematite

Due to the high
density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its mass per unit volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter Rho (letter), rho), although the L ...

density
of
hematite Hematite (), also spelled as haematite, is a common 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 ...

hematite
relative to associated
silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they unde ...
gangue, hematite beneficiation usually involves a combination of beneficiation techniques. One method relies on passing the finely crushed
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
over a slurry containing
magnetite Magnetite is a mineral and one of the main iron ore Iron ores are rocks and minerals from which metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, po ...

magnetite
or other agent such as
ferrosilicon Ferrosilicon is an alloy of iron and silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalen ...

ferrosilicon
which increases its density. When the density of the slurry is properly calibrated, the hematite will sink and the
silicate mineral Silicate minerals are rock-forming mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs na ...
fragments will float and can be removed.


Production and consumption

Iron is the world's most commonly used metal—steel, of which iron ore is the key ingredient, representing almost 95% of all metal used per year.Iron ore pricing emerges from stone age
''Financial Times'', October 26, 2009
It is used primarily in structures, ships, automobiles, and machinery. Iron-rich rocks are common worldwide, but ore-grade commercial
mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. These deposits form a mineralized commodity that is of economic interest to t ...

mining
operations are dominated by the countries listed in the table aside. The major constraint to economics for iron ore deposits is not necessarily the grade or size of the deposits, because it is not particularly hard to geologically prove enough tonnage of the rocks exist. The main constraint is the position of the iron ore relative to market, the cost of rail infrastructure to get it to market and the energy cost required to do so. Mining iron ore is a high-volume, low-margin business, as the value of iron is significantly lower than base metals.Iron ore pricing war
''Financial Times'', October 14, 2009
It is highly capital intensive, and requires significant investment in infrastructure such as rail in order to transport the ore from the mine to a freight ship. For these reasons, iron ore production is concentrated in the hands of a few major players. World production averages two billion metric tons of raw ore annually. The world's largest producer of iron ore is the Brazilian mining corporation Vale, followed by Anglo-Australian companies
Rio Tinto Group Rio Tinto Group is an Anglo-Australian multinational and the world's second largest metals and mining corporation, behind BHP, producing iron ore, copper, diamonds, gold and uranium. The company was founded in 1873, when a multinational consor ...
and then
BHP BHP, formerly known as BHP Billiton, is the trading entity of BHP Group Limited and BHP Group plc, an Anglo-Australian multinational mining, metals and petroleum dual-listed public company A public company, publicly traded company, publi ...
. A further Australian supplier,
Fortescue Metals Group Fortescue Metals Group Ltd (Often referred to as FMG) is an Australian iron ore company. As of 2017, Fortescue is the fourth largest iron Ore, iron ore producer in the world after BHP, Rio Tinto Group, Rio Tinto, and Vale (company), Vale. The co ...

Fortescue Metals Group
Ltd, has helped bring Australia's production to first in the world. The seaborne trade in iron ore—that is, iron ore to be shipped to other countries—was 849 million tonnes in 2004. Australia and Brazil dominate the seaborne trade, with 72% of the market. BHP, Rio and Vale control 66% of this market between them. In
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, smal ...

Australia
iron ore is won from three main sources: pisolite " channel iron deposit" ore derived by mechanical erosion of primary banded-iron formations and accumulated in alluvial channels such as at Pannawonica, Western Australia; and the dominant metasomatically-altered
banded iron formation showing banded iron formation, displayed in Dresden, Saxony, Germany Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iro ...

banded iron formation
-related ores such as at Newman, the Chichester Range, the
Hamersley Range The Hamersley Range is a mountainous region of the Pilbara region of Western Australia Western Australia (abbreviated as WA) is a States and territories of Australia, state occupying the western percent of the land area of Australia excludi ...
and Koolyanobbing, Western Australia. Other types of ore are coming to the fore recently, such as oxidised ferruginous hardcaps, for instance
laterite Laterite is both a soil and a rock type rich in 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 e ...
iron ore deposits near Lake Argyle in Western Australia. The total recoverable reserves of iron ore in India are about 9,602 million tonnes of
hematite Hematite (), also spelled as haematite, is a common 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 ...

hematite
and 3,408 million tonnes of
magnetite Magnetite is a mineral and one of the main iron ore Iron ores are rocks and minerals from which metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, po ...

magnetite
. Chhattisgarh, Madhya Pradesh, Karnataka, Jharkhand, Odisha, Goa, Maharashtra, Andhra Pradesh, Kerala, Rajasthan and Tamil Nadu are the principal Indian producers of iron ore. World consumption of iron ore grows 10% per annum on average with the main consumers being China, Japan, Korea, the United States and the European Union. China is currently the largest consumer of iron ore, which translates to be the world's largest steel producing country. It is also the largest importer, buying 52% of the seaborne trade in iron ore in 2004. China is followed by Japan and Korea, which consume a significant amount of raw iron ore and metallurgical coal. In 2006, China produced 588 million tons of iron ore, with an annual growth of 38%.


Iron ore market

Over the last 40 years, iron ore prices have been decided in closed-door negotiations between the small handful of miners and Steelmaking, steelmakers which dominate both spot and contract markets. Traditionally, the first deal reached between these two groups sets a ''benchmark'' to be followed by the rest of the industry. In recent years, however, this benchmark system has begun to break down, with participants along both demand and supply chains calling for a shift to short term pricing. Given that most other Commodity, commodities already have a mature market-based pricing system, it is natural for iron ore to follow suit. To answer increasing market demands for more transparent pricing, a number of financial exchanges and/or clearing houses around the world have offered iron ore swaps clearing. The CME group, SGX (Singapore Exchange), London Clearing House (LCH.Clearnet), NOS Group and ICEX (Indian Commodities Exchange) all offer cleared swaps based on The Steel Index's (TSI) iron ore transaction data. The CME also offers a Platts-based swap, in addition to their TSI swap clearing. The ICE (Intercontinental Exchange) offers a Platts-based swap clearing service also. The swaps market has grown quickly, with liquidity clustering around TSI's pricing. By April 2011, over US$5.5 billion worth of iron ore swaps have been cleared basis TSI prices. By August 2012, in excess of one million tonnes of swaps trading per day was taking place regularly, basis TSI. A relatively new development has also been the introduction of iron ore options, in addition to swaps. The CME group has been the venue most utilised for clearing of options written against TSI, with open interest at over 12,000 lots in August 2012. Singapore Mercantile Exchange (SMX) has launched the world first global iron ore futures contract, based on the Metal Bulletin Iron Ore Index (MBIOI) which utilizes daily price data from a broad spectrum of industry participants and independent Chinese steel consultancy and data provider Shanghai Steelhome's widespread contact base of steel producers and iron ore traders across China. The futures contract has seen monthly volumes over 1.5 million tonnes after eight months of trading. This move follows a switch to index-based quarterly pricing by the world's three largest iron ore miners— Vale, Rio Tinto (corporation), Rio Tinto and
BHP BHP, formerly known as BHP Billiton, is the trading entity of BHP Group Limited and BHP Group plc, an Anglo-Australian multinational mining, metals and petroleum dual-listed public company A public company, publicly traded company, publi ...
—in early 2010, breaking a 40-year tradition of benchmark annual pricing.


Abundance by country


Available world iron ore resources

Iron is the most abundant element on earth but not in the crust. The extent of the accessible iron ore reserves is not known, though Lester R. Brown, Lester Brown of the Worldwatch Institute suggested in 2006 that iron ore could run out within 64 years (that is, by 2070), based on 2% growth in demand per year.


Australia

Geoscience Australia calculates that the country's "economic demonstrated resources" of iron currently amount to 24 Tonne#Derived units, gigatonnes, or 24 billion tonnes. Another estimate places Australia's reserves of iron ore at 52 billion tonnes, or 30 per cent of the world’s estimated 170 billion tonnes, of which Western Australia accounts for 28 billion tonnes. The current production rate from the Pilbara region of Western Australia is approximately 430 million tonnes a year and rising. Gavin Mudd (RMIT University) and Jonathon Law (CSIRO) expect it to be gone within 30–50 years and 56 years, respectively. These 2010 estimates require on-going review to take into account shifting demand for lower-grade iron ore and improving mining and recovery techniques (allowing deeper mining below the groundwater table).


United States

In 2014 mines in the United States produced 57.5 million metric tons of iron ore with an estimated value of $5.1 billion. Iron mining in the United States is estimated to have accounted for 2% of the world's iron ore output. In the United States there are twelve iron ore mines with nine being Open-pit mining, open pit mines and three being reclamation operations. There were also ten pelletizing plants, nine concentration plants, two direct-reduced iron (DRI) plants and one iron nugget plant that were operating in 2014. In the United States the majority of iron ore mining is in the Iron Range, iron ranges around Lake Superior. These iron ranges occur in
Minnesota Minnesota () is a U.S. state, state in the north central region of the United States. It is known as the "Land of 10,000 Lakes". Its official motto is , French for "The Star of the North". Of the U.S. state, U.S. states, Minnesota is the List ...

Minnesota
and Michigan which combined accounted for 93% of the usable iron ore produced in the United States in 2014. Seven of the nine operational open pit mines in the United States are located in Minnesota as well as two of the three tailings reclamation operations. The other two active open pit mines were located in
Michigan Michigan () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper ...

Michigan
, in 2016 one of the two mines shut down. There have also been iron ore mines in Utah and Alabama; however, the last iron ore mine in Utah shut down in 2014 and the last iron ore mine in Alabama shut down in 1975.


Canada

In 2017 Canadian iron ore mines produced 49 million tons of iron ore in concentrate pellets and 13.6 million tons of crude steel. Of the 13.6 million tons of steel 7 million was exported, and 43.1 million tons of iron ore was exported at a value of $4.6 billion. Of the iron ore exported 38.5% of the volume was iron ore pellets with a value of $2.3 billion and 61.5% was iron ore concentrates with a value of $2.3 billion. Forty-six per cent of Canada's iron ore comes from the Iron Ore Company of Canada mine, in Labrador City, Newfoundland, with secondary sources including, the Mary River Mine, Nunavut.


Brazil

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, ...
is the second largest producer of iron ore with
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, smal ...

Australia
being the largest. In 2015 Brazil exported 397 million tons of usable iron ore. In December 2017 Brazil exported 346,497 metric tons of iron ore and from December 2007 to May 2018 they exported a monthly average of 139,299 metric tons.


Ukraine

According to the US Geological Survey's 2021 Report on iron ore, Ukraine is estimated to have produced 62 million tons of iron ore in 2020 (2019: 63 million tons), placing it as the seventh largest global centre of iron ore production, behind Australia, Brazil, China, India, Russia and South Africa. Producers of iron ore in Ukraine include: Ferrexpo, Metinvest and ArcelorMittal Kryvyi Rih.


Smelting

Iron ores consist of oxygen and iron atoms bonded together into molecules. To convert it to metallic iron it must be smelting, smelted or sent through a Direct reduced iron, direct reduction process to remove the oxygen. Oxygen-iron bonds are strong, and to remove the iron from the oxygen, a stronger elemental bond must be presented to attach to the oxygen. Carbon is used because the strength of a carbon-oxygen bond is greater than that of the iron-oxygen bond, at high temperatures. Thus, the iron ore must be powdered and mixed with coke (fuel), coke, to be burnt in the smelting process. Carbon monoxide is the primary ingredient of chemically stripping oxygen from iron. Thus, the iron and carbon smelting must be kept at an oxygen-deficient (reducing) state to promote burning of carbon to produce not . *Air blast and charcoal (coke): 2 C + O2 → 2 CO *Carbon monoxide (CO) is the principal reduction agent. **Stage One: 3 Fe2O3 + CO → 2 Fe3O4 + CO2 **Stage Two: Fe3O4 + CO → 3 FeO + CO2 **Stage Three: FeO + CO → Fe + CO2 *Limestone calcining: CaCO3 → CaO + CO2 *Lime acting as flux: CaO + SiO2 → Calcium silicate, CaSiO3


Trace elements

The inclusion of even small amounts of some elements can have profound effects on the behavioral characteristics of a batch of iron or the operation of a smelter. These effects can be both good and bad, some catastrophically bad. Some chemicals are deliberately added such as flux which makes a blast furnace more efficient. Others are added because they make the iron more fluid, harder, or give it some other desirable quality. The choice of ore, fuel, and flux determine how the slag behaves and the operational characteristics of the iron produced. Ideally iron ore contains only iron and oxygen. In reality this is rarely the case. Typically, iron ore contains a host of elements which are often unwanted in modern steel.


Silicon

Silica () is almost always present in iron ore. Most of it is slagged off during the smelting process. At temperatures above some will be reduced and form an alloy with the iron. The hotter the furnace, the more silicon will be present in the iron. It is not uncommon to find up to 1.5% Si in European cast iron from the 16th to 18th centuries. The major effect of silicon is to promote the formation of grey iron. Grey iron is less brittle and easier to finish than white iron. It is preferred for casting purposes for this reason. reported that silicon also reduces shrinkage and the formation of blowholes, lowering the number of bad castings.


Phosphorus

Phosphorus (P) has four major effects on iron: increased hardness and strength, lower solidus temperature, increased fluidity, and cold shortness. Depending on the use intended for the iron, these effects are either good or bad. Bog ore often has a high phosphorus content . The strength and hardness of iron increases with the concentration of phosphorus. 0.05% phosphorus in wrought iron makes it as hard as medium carbon steel. High phosphorus iron can also be hardened by cold hammering. The hardening effect is true for any concentration of phosphorus. The more phosphorus, the harder the iron becomes and the more it can be hardened by hammering. Modern steel makers can increase hardness by as much as 30%, without sacrificing shock resistance by maintaining phosphorus levels between 0.07 and 0.12%. It also increases the depth of hardening due to quenching, but at the same time also decreases the solubility of carbon in iron at high temperatures. This would decrease its usefulness in making blister steel (cementation), where the speed and amount of carbon absorption is the overriding consideration. The addition of phosphorus has a down side. At concentrations higher than 0.2% iron becomes increasingly cold short, or brittle at low temperatures. Cold short is especially important for bar iron. Although bar iron is usually worked hot, its uses often require it to be tough, bendable, and resistant to shock at room temperature. A nail that shattered when hit with a hammer or a carriage wheel that broke when it hit a rock would not sell well. High enough concentrations of phosphorus render any iron unusable . The effects of cold shortness are magnified by temperature. Thus, a piece of iron that is perfectly serviceable in summer, might become extremely brittle in winter. There is some evidence that during the Middle Ages the very wealthy may have had a high-phosphorus sword for summer and a low-phosphorus sword for winter . Careful control of phosphorus can be of great benefit in casting operations. Phosphorus depresses the liquidus temperature, allowing the iron to remain molten for longer and increases fluidity. The addition of 1% can double the distance molten iron will flow . The maximum effect, about 500 °C, is achieved at a concentration of 10.2% . For foundry work Turner felt the ideal iron had 0.2–0.55% phosphorus. The resulting iron filled molds with fewer voids and also shrank less. In the 19th century some producers of decorative cast iron used iron with up to 5% phosphorus. The extreme fluidity allowed them to make very complex and delicate castings. But, they could not be weight bearing, as they had no strength . There are two remedies for high phosphorus iron. The oldest, easiest and cheapest, is avoidance. If the iron that the ore produced was cold short, one would search for a new source of iron ore. The second method involves oxidizing the phosphorus during the fining process by adding iron oxide. This technique is usually associated with puddling in the 19th century, and may not have been understood earlier. For instance Isaac Zane, the owner of Marlboro Iron Works did not appear to know about it in 1772. Given Zane's reputation for keeping abreast of the latest developments, the technique was probably unknown to the ironmasters of Virginia and Pennsylvania. Phosphorus is a deleterious contaminant because it makes steel brittle, even at concentrations of as little as 0.6%. Phosphorus cannot be easily removed by fluxing or smelting, and so iron ores must generally be low in phosphorus to begin with.


Aluminium

Small amounts 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 ...
(Al) are present in many ores including iron ore, sand and some limestones. The former can be removed by washing the ore prior to smelting. Until the introduction of brick lined furnaces, the amount of aluminium contamination was small enough that it did not have an effect on either the iron or slag. However, when brick began to be used for hearths and the interior of blast furnaces, the amount of aluminium contamination increased dramatically. This was due to the erosion of the furnace lining by the liquid slag. Aluminium is difficult to reduce. As a result, aluminium contamination of the iron is not a problem. However, it does increase the viscosity of the slag ( and ). This will have a number of adverse effects on furnace operation. The thicker slag will slow the descent of the charge, prolonging the process. High aluminium will also make it more difficult to tap off the liquid slag. At the extreme this could lead to a frozen furnace. There are a number of solutions to a high aluminium slag. The first is avoidance; don't use ore or a lime source with a high aluminium content. Increasing the ratio of lime flux will decrease the viscosity .


Sulfur

Sulfur (S) is a frequent contaminant in coal. It is also present in small quantities in many ores, but can be removed by calcining. Sulfur dissolves readily in both liquid and solid iron at the temperatures present in iron smelting. The effects of even small amounts of sulfur are immediate and serious. They were one of the first worked out by iron makers. Sulfur causes iron to be red or hot short . Hot short iron is brittle when hot. This was a serious problem as most iron used during the 17th and 18th centuries was bar or wrought iron. Wrought iron is shaped by repeated blows with a hammer while hot. A piece of hot short iron will crack if worked with a hammer. When a piece of hot iron or steel cracks the exposed surface immediately oxidizes. This layer of oxide prevents the mending of the crack by welding. Large cracks cause the iron or steel to break up. Smaller cracks can cause the object to fail during use. The degree of hot shortness is in direct proportion to the amount of sulfur present. Today iron with over 0.03% sulfur is avoided. Hot short iron can be worked, but it has to be worked at low temperatures. Working at lower temperatures requires more physical effort from the smith or forgeman. The metal must be struck more often and harder to achieve the same result. A mildly sulfur contaminated bar can be worked, but it requires a great deal more time and effort. In cast iron sulfur promotes the formation of white iron. As little as 0.5% can counteract the effects of slow cooling and a high silicon content . White cast iron is more brittle, but also harder. It is generally avoided, because it is difficult to work, except in China where high sulfur cast iron, some as high as 0.57%, made with coal and coke, was used to make bells and chimes . According to , good foundry iron should have less than 0.15% sulfur. In the rest of the world a high sulfur cast iron can be used for making castings, but will make poor wrought iron. There are a number of remedies for sulfur contamination. The first, and the one most used in historic and prehistoric operations, is avoidance. Coal was not used in Europe (unlike China) as a fuel for smelting because it contains sulfur and therefore causes hot short iron. If an ore resulted in hot short metal, ironmasters looked for another ore. When mineral coal was first used in European blast furnaces in 1709 (or perhaps earlier), it was coke (fuel), coked. Only with the introduction of hot blast from 1829 was raw coal used.


=Ore roasting

= Sulfur can be removed from ores by Roasting (metallurgy), roasting and washing. Roasting oxidizes sulfur to form sulfur dioxide (SO2) which either escapes into the atmosphere or can be washed out. In warm climates it is possible to leave Pyrite, pyritic ore out in the rain. The combined action of rain, bacteria, and heat Oxidation, oxidize the sulfides to sulfuric acid and sulfates, which are water-soluble and leached out . However, historically (at least), iron sulfide (iron pyrite ), though a common iron mineral, has not been used as an ore for the production of iron metal. Natural weathering was also used in Sweden. The same process, at geological speed, results in the gossan
limonite Limonite () is an iron ore Iron ores are rocks and minerals from which metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, sho ...

limonite
ores. The importance attached to low sulfur iron is demonstrated by the consistently higher prices paid for the iron of Sweden, Russia, and Spain from the 16th to 18th centuries. Today sulfur is no longer a problem. The modern remedy is the addition of manganese. But, the operator must know how much sulfur is in the iron because at least five times as much manganese must be added to neutralize it. Some historic irons display manganese levels, but most are well below the level needed to neutralize sulfur . Sulfide inclusion as manganese sulfide (MnS) can also be the cause of severe pitting corrosion problems in low-grade stainless steel such as SAE 304 stainless steel, AISI 304 steel. Under oxidizing conditions and in the presence of moisture, when sulfide oxidizes it produces thiosulfate anions as intermediate species and because thiosulfate anion has a higher equivalent electromobility than chloride anion due to its double negative electrical charge, it promotes the pit growth. Indeed, the positive electrical charges born by Fe2+ cations released in solution by Fe oxidation on the Anode, anodic zone inside the pit must be quickly compensated / neutralised by negative charges brought by the Electrokinetic phenomena, electrokinetic migration of anions in the capillary pit. Some of the Electrochemistry, electrochemical processes occurring in a capillary pit are the same than these encountered in capillary electrophoresis. Higher the anion electrokinetic migration rate, higher the rate of pitting corrosion. Electrokinetic phenomena, Electrokinetic transport of ions inside the pit can be the rate-limiting step in the pit growth rate.


See also

*Bog iron *Iron ore in Africa *Ironstone


Notes


References

* * * Ramanaidou, E. R. and Wells, M. A. (2014). 13.13 - Sedimentary Hosted Iron Ores. In: Holland, H. D. and Turekian, K. K. Eds., Treatise on Geochemistry (Second Edition). Oxford: Elsevier. 313–355. * * * *


External links


History of the Iron Ore Trade on the Great Lakes

"Pioneers of the Cleveland iron trade" by J. S. Jeans 1875

Iron Ore Price and Historical Chart

Iron Mines of NY/NJ


{{DEFAULTSORT:Iron Ore Economic geology Articles containing video clips Iron ores,