Table of Contents
Introduction:
Iron (Fe) is a thick metal with a silvery-white appearance and exceptional magnetic properties. It is the fourth most abundant element after oxygen, silicon, and aluminium, accounting for 5% of the Earth’s crust by weight. At 1,538 degrees Celsius, it melts (2,800 degrees Fahrenheit). Iron is allotropic, which means it exists in various forms. Depending on the temperature, its crystal structure is either body-centred cubic (bcc) or face-centred cubic (fcc).
The basic configuration in both crystallographic modifications is a cube with iron atoms at the corners. In the bcc modification, there is an extra atom in the centre of each cube, and in the centre of each face in the fcc modification. Pure iron has a bcc structure known as alpha-ferrite at room temperature; this persists until the temperature is raised to 912° C (1,674° F), at which point it transforms into a fcc arrangement known as austenite. Further heating causes austenite to persist until the temperature reaches 1,394° C (2,541° F), at which point the bcc structure reappear. This type of iron, known as delta-ferrite, is stable until the melting point is reached.
Overview
Except for iron-nickel alloys from meteorites and very rare forms of deep mantle xenoliths, metallic iron is virtually unknown on the Earth’s surface. Some iron meteorites are thought to have formed from accreted bodies 1,000 km in diameter or larger. The origin of iron can ultimately be traced back to nuclear fusion in stars, with the majority of iron thought to have originated in dying stars large enough to collapse or explode as supernovae.
Although iron is the fourth most abundant element in the Earth’s crust, accounting for about 5%, the vast majority is bound in silicate or, more rarely, carbonate minerals. Since the thermodynamic barriers to separating pure iron from these minerals are formidable and energy-intensive, all iron sources used by human industry rely on comparatively rarer iron oxide minerals, primarily hematite.
During the American Revolution and the Napoleonic Wars, the majority of iron was obtained from readily available goethite or bog ore. Laterite was used as an iron ore source by prehistoric societies. Traditionally, hematite deposits with Fe grades of around 70% were used to mine much of the iron ore used by industrialised societies. These deposits are known as “direct shipping ores” or “natural ores.” Increasing iron ore demand, combined with the depletion of high-grade hematite ores in the United States, led to the development of lower-grade iron ore sources after World War II, primarily the use of magnetite and taconite.
The methods used to mine iron ore differ depending on the type of ore being mined. Depending on the mineralogy and geology of the ore deposits, there are four main types of iron ore deposits currently being worked. Magnetite, massive hematite, titanomagnetite, and pisolitic ironstone deposits are examples.
Extraction of iron
Iron processing is the use of a smelting process to convert ore into a form from which products can be made.
Iron ore extraction
In a variety of geologic environments, iron ores can be found in igneous, metamorphic (transformed), or sedimentary rocks. Most are sedimentary, but many have been altered by weathering, making it difficult to pinpoint their precise origin. The most common iron-bearing minerals are oxides, and iron ores are primarily composed of hematite (Fe2O3), which is red; magnetite (Fe3O4), which is black; limonite or bog-iron ore (2Fe2O3·3H2O), that is brown; and siderite (FeCO3), which is pale brown. By far the most common ore types are hematite and magnetite.
It is clear that, pure magnetite contains 72.4 percent iron, hematite contains 69.9 percent, limonite contains 59.8 percent, and siderite contains 48.2 percent, the metal content of real ores is lower because these minerals never occur alone. Deposits containing less than 30% iron are commercially unattractive, and while some ores contain as much as 66 percent iron, many are in the 50–60% range. The quality of an ore is also influenced by its other constituents, which are referred to collectively as gangue. Silica (SiO2) and phosphorus-containing compounds (typically reported as P2O5) are particularly important because they alter the composition of the metal and cause additional problems in steelmaking.
Surface mining is used to extract the majority of iron ores. There are some underground mines, but surface mining is preferred whenever possible because it is less expensive.
Iron extraction process
The third and final process in metallurgy is the extraction of iron from its ore. Metal extraction and isolation take place in a few major steps:
-Ore Concentration
-Metal extraction from concentrated ore
-The purification of metal
Concentration via calcination roasting is the first step in the process. Water and other volatile impurities such as sulphur and carbonates are removed during the concentration process. This concentrated ore is mixed with limestone (CaCO3) and Coke before being fed into the blast furnace from above. The extraction of iron takes place in the blast furnace. The extraction of iron from its ore is a lengthy and laborious process that aids in the separation of useful components from waste materials such as slag.
A Blast Furnace’s purpose is to chemically reduce concentrated ore to liquid metal. A blast furnace is a massive steel stack lined with refractory brick, into which concentrated iron ore, coke, and limestone are thrown from the top and a blast of hot air is blown. The ingredients then crushed into small round pieces, mixed together, and placed on a hopper that controls the input.
Warmer air is blown from the bottom, and coke is burned to produce temperatures as high as 2200K. The majority of the heat required for this process is provided by burning coke. Coke reacts with the oxygen in the hot air to form carbon monoxide at such high temperatures (CO). The CO and heat are now moving upwards and colliding with the raw material that is running down from the top. The temperature in the upper parts of the Blast Furnace is significantly lower than the temperature at the bottom, which is 2200K. Haematite (Fe2O3)and Magnetite (Fe3O4) are reduced to Ferrous Oxide in this section (FeO).
Reactions in the blast furnace at 500 – 800 K, with lower temperatures in the upper parts:
3 Fe2O3+CO→2 Fe3O4+ CO2
Fe3O4+4CO→3Fe+4 CO2
Fe2O +CO→2FeO+ CO2
At 900 – 1500 K, in the furnace’s lower sections,
C+ CO2 →2CO
The limestone also breaks down to CaO, removing the ore’s silicate impurity in the form of Slag. It is easily separated from molten iron. Blast furnace iron contains about 3 – 4% carbon and smaller amounts of many other impurities such as sulphur, silicon, and so on. This is known as pig iron. It is a hard but brittle metal, and impurities significantly reduce its strength. Carbon appears to have a significant influence on the brittleness and hardness balance in iron. To reduce the carbon content of pig iron even further, it is melted again with scrap iron and coke and subjected to a blast of hot air. This type of iron is known as Cast Iron, and it has a slightly lower carbon content of 2 – 3 percent. This is more difficult to work with than pig iron.
Wrought iron is the clearest form of iron available commercially, and it is made by heating cast iron in a furnace lined with Haematite (Fe2O3). In cast iron, haematite interacts with carbon to produce pure iron and carbon monoxide gas, both of which escape.
Limestone is then got to add as flux, resulting in the formation of slag. Impurities such as S and Si enter the slag, which can then be easily separated to yield pure iron.
FAQs
Question 1: Why does coke used in the extraction of iron?
Answer 1: Iron oxides are the most common ores of iron, and they can be reduced to iron by heating them with carbon in the form of coke. Coke is created by heating coal in the absence of oxygen. Coke is inexpensive and serves as both a reducing agent and a heat source in the reaction.
Question 2: How was iron first made?
Answer 2: Smiths created iron objects (metalworkers). The iron was heated until it shone brightly. It was then hammered into the shape of the new object. Meteorites, which are rocks from space that crash-landed on Earth, contained pure iron.
Question 3: How is iron mined?
Answer 3: Iron ore accumulations could be found deep underground. An elevator or hoist must be installed, and a shaft must be dug from the surface. The shaft is the primary vertical channel used to transport people and ore into and out of the mine.
