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Taconite

Taconite

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Taconite is a variety of iron formation
Banded iron formation
Banded iron formations are distinctive units of sedimentary rock that are almost always of Precambrian age. A typical BIF consists of repeated, thin layers of iron oxides, either magnetite or hematite , alternating with bands of iron-poor shale and chert...

, an iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

-bearing (>15% iron) sedimentary rock
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

, in which the iron minerals are interlayered with quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

, chert
Chert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...

, or carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....

. The term was coined by Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...

 State Geologist Newton Horace Winchell
Newton Horace Winchell
Newton Horace Winchell was the extremely prolific Minnesota geologist responsible for the six-volume The Geology of Minnesota: Final Report of the Geological and Natural History Survey of Minnesota, which is the work of Winchell and his assistants...

 during his pioneering investigations of the Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...

 Biwabik Iron Formation
Mesabi Range
The Mesabi Iron Range is a vast deposit of iron ore and the largest of four major iron ranges in the region collectively known as the Iron Range of Minnesota. Discovered in 1866, it is the chief deposit of iron ore in the United States. The deposit is located in northeast Minnesota, largely in...

 of northeastern Minnesota owing to its superficial resemblance to iron-bearing rocks from the Taconic Mountains
Taconic Mountains
The Taconic Mountains or Taconic Range are a physiographic section of the larger New England province and part of the Appalachian Mountains, running along the eastern border of New York State and adjacent New England from northwest Connecticut to western Massachusetts, north to central western...

 of New York, with which he was familiar.

The iron content of taconite, commonly present as finely dispersed magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

, is generally 25 to 30%.

In the late 19th and early 20th centuries, there was an abundance of iron ore of such high quality that taconite was considered an uneconomic waste product. By the end of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 much of the high-grade iron ore in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 had been exhausted and taconite became a new source of the metal.

To process taconite, the ore is ground into a fine powder, the magnetite is separated from the gangue by strong magnets, the powdered iron concentrate is combined with a binder such as bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...

 clay and limestone as a flux
Flux (metallurgy)
In metallurgy, a flux , is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time...

 and rolled into pellets about one centimeter in diameter that contain approximately 65% iron. The pellets are fired at a very high temperatures to harden them and make them durable. This is necessary to ensure that the blast furnace
Blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.In a blast furnace, fuel and ore and flux are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions...

 charge remains porous enough to allow heated gas to pass through and react with the pelletized ore. Firing the pellet oxidizes the magnetite (Fe3O4) to hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...

 (Fe2O3), an exothermic
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...

 reaction that reduces the cost of pelletizing the concentrate. E.W. Davis
Edward Wilson Davis
Edward Wilson Davis was an American engineer and inventor famous for pioneering early research into taconite. As a researcher at the University of Minnesota, Davis developed an engineering process to economically extract iron ore from hard taconite rocks, making taconite valuable as iron ore for...

 of the University of Minnesota
University of Minnesota
The University of Minnesota, Twin Cities is a public research university located in Minneapolis and St. Paul, Minnesota, United States. It is the oldest and largest part of the University of Minnesota system and has the fourth-largest main campus student body in the United States, with 52,557...

 Mines Experiment Station is credited with developing the pelletizing process. Since the commercial development of this process in the Lake Superior
Lake Superior
Lake Superior is the largest of the five traditionally-demarcated Great Lakes of North America. It is bounded to the north by the Canadian province of Ontario and the U.S. state of Minnesota, and to the south by the U.S. states of Wisconsin and Michigan. It is the largest freshwater lake in the...

 region in the 1950s, the term taconite has been used globally to refer to iron ores amenable to upgrading by similar processes.

Major producers of iron ore pellets from taconite in North America include Cliffs Natural Resources, U.S. Steel
U.S. Steel
The United States Steel Corporation , more commonly known as U.S. Steel, is an integrated steel producer with major production operations in the United States, Canada, and Central Europe. The company is the world's tenth largest steel producer ranked by sales...

, and ArcelorMittal. These processed taconite ore pellets are also referred to as "taconite". Because this is the form that is typically transported by rail and ship, and cargo of these is often discussed, this usage of the term is very common.


The Mesabi Iron Range
Mesabi Range
The Mesabi Iron Range is a vast deposit of iron ore and the largest of four major iron ranges in the region collectively known as the Iron Range of Minnesota. Discovered in 1866, it is the chief deposit of iron ore in the United States. The deposit is located in northeast Minnesota, largely in...

 region of the American state of Minnesota is a major production area. The taconite iron ore pellets are hauled by railroad through the ports of Silver Bay
Silver Bay, Minnesota
Silver Bay is a city in Lake County, Minnesota, United States. The population was 1,887 at the 2010 census. The city was founded on May 1, 1954 after previously being known as the Beaver Bay housing project...

, Two Harbors
Two Harbors, Minnesota
As of the census of 2000, there were 3,613 people, 1,636 households, and 953 families residing in the city. The population density was 1,120.7 people per square mile . There were 1,631 housing units at an average density of 505.9 per square mile...

 and the Twin Ports
Twin Ports
The Twin Ports of Duluth, Minnesota and Superior, Wisconsin are located at the western part of Lake Superior and together are considered the largest freshwater port in the world. They are twin cities and seaports, connected to the Atlantic Ocean through the Great Lakes and the St. Lawrence...

 of Duluth, Minnesota
Duluth, Minnesota
Duluth is a port city in the U.S. state of Minnesota and is the county seat of Saint Louis County. The fourth largest city in Minnesota, Duluth had a total population of 86,265 in the 2010 census. Duluth is also the second largest city that is located on Lake Superior after Thunder Bay, Ontario,...

 and Superior, Wisconsin
Superior, Wisconsin
Superior is a city in and the county seat of Douglas County, Wisconsin, United States. The population was 26,960 at the 2010 census. Located at the junction of U.S. Highways 2 and 53, it is north of and adjacent to both the Village of Superior and the Town of Superior.Superior is at the western...

, all on Lake Superior
Lake Superior
Lake Superior is the largest of the five traditionally-demarcated Great Lakes of North America. It is bounded to the north by the Canadian province of Ontario and the U.S. state of Minnesota, and to the south by the U.S. states of Wisconsin and Michigan. It is the largest freshwater lake in the...

. The ore is generally shipped by lake freighter
Lake freighter
Lake freighters, or Lakers, are bulk carrier vessels that ply the Great Lakes. The best known was the , the most recent and largest major vessel to be wrecked on the Lakes. These vessels are traditionally called boats, although classified as ships. In the mid-20th century, 300 lakers worked the...

s to locations on the lower Great Lakes
Great Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...

. Many steelmaking centers are located near Lake Erie
Lake Erie
Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...

. Due to increased international demand, Taconite is now shipped to Mexico and China.

The cargo of the SS Edmund Fitzgerald
Edmund Fitzgerald
Edmund Fitzgerald may refer to:*SS Edmund Fitzgerald, a freighter that sank on Lake Superior in 1975 with all hands aboard**"The Wreck of the Edmund Fitzgerald", a song about the shipwreck by Gordon Lightfoot...

, which sank in Lake Superior on November 10, 1975, consisted of approximately 26,116 long tons of taconite pellets.

Taconite and human health


The Minnesota Department of Health has launched a study to determine whether fibrous minerals in taconite and taconite dust can cause or exacerbate lung conditions similar to asbestosis
Asbestosis
Asbestosis is a chronic inflammatory and fibrotic medical condition affecting the parenchymal tissue of the lungs caused by the inhalation and retention of asbestos fibers...

, pleural mesothelioma
Mesothelioma
Mesothelioma, more precisely malignant mesothelioma, is a rare form of cancer that develops from the protective lining that covers many of the body's internal organs, the mesothelium...

 and other pleural conditions which occur following asbestos exposure. Because these conditions can be triggered by industrial asbestos
Asbestos
Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

, which was also used in taconite mining and processing, the study will attempt to determine what, if any, influence naturally occurring fibrous minerals in taconite may have played. This will be the second study of the issue that the MDH has conducted. A 2003 study of taconite miners concluded that the most likely cause of 14 of the 17 cases of mesothelioma was contact with asbestos. However, since the conclusion of that study, 35 additional cases of the disease have been diagnosed. Mesothelioma occurs at twice the expected rate in the northeastern region of Minnesota, including the Iron Range
Iron Range
The Iron Range is a region that makes up the northeastern section of Minnesota in the United States. "The Range", as it is known by locals, is a region with multiple distinct bands of iron ore...

.

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