IRON (ELEMENT): CHARACTERISTICS, CHEMICAL STRUCTURE, USES - CHEMISTRY - 2025

The iron is a transition metal belonging to Group 8 or VIIIB of the periodic table and represented by the chemical symbol Fe. Is a metal gray, ductile, malleable and high strength, used in numerous applications useful for man and society.

It constitutes 5% of the earth's crust, and it is also the second most abundant metal after aluminum. Also, its abundance is exceeded by oxygen and silicon. However, with respect to the earth's core, 35% of it is composed of metallic and liquid iron.

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Outside of the earth's core, iron is not found in metallic form, as it is rapidly oxidized when exposed to humid air. It is located in basalt rocks, carboniferous sediments and meteorites; generally alloyed with nickel, as in the mineral kamacite.

The main iron minerals used for mining are the following: hematite (ferric oxide, Fe ₂ O ₃), magnetite (ferrosomeric oxide, Fe ₃ O ₄), limonite (hydrated ferrous oxide hydroxide), and siderite (iron carbonate, FeCO ₃).

On average, man has a content of 4.5 g of iron, of which 65% is in the form of hemoglobin. This protein is involved in the transport of oxygen in the blood and in its distribution to the different tissues, for its subsequent uptake by myoglobin and neuroglobin.

Despite the many benefits of iron for humans, excess metal can have very serious toxic actions, especially on the liver, the cardiovascular system and the pancreas; such is the case of the hereditary disease hemochromatosia.

Iron is synonymous with construction, strength and wars. On the other hand, due to its abundance, it is always an alternative to consider when it comes to the development of new materials, catalysts, drugs or polymers; and despite the red color of its rusts, it is an environmentally green metal.

History

Antiquity

Iron has been processed for millennia. However, it is difficult to find iron objects of such ancient ages due to their susceptibility to corrode, which causes their destruction. The oldest known iron objects were made from that found within meteorites.

Such is the case of a kind of beads made in 3500 BC, found in Gerzah, Egypt, and a dagger found in the tomb of Tutankhamun. Iron meteorites are characterized by a high nickel content, so their provenance could be identified in these objects.

Evidence of cast iron was also found in Asmar, Mesopotamia, and Tail Chagar Bazaar, in Syria, between 3000-2700 BC. Although iron casting began in the Bronze Age, it took centuries for it to displace bronze.

In addition, cast iron artifacts were found in India, 1800 to 1200 BC, and in the Levant, about 1500 BC. It is thought that the Iron Age began in 1000 BC, as the cost of their production was reduced.

It appears in China between 700 and 500 BC, probably transported through Central Asia. The first iron objects were found in Luhe Jiangsu, China.

Europe

Wrought iron was produced in Europe through the use of so-called gala forges. The process required the use of coal as fuel.

Medieval blast furnaces were 3.0 m high, made of fireproof bricks and air was supplied by manual bellows. In 1709, Abraham Darby established a coke blast furnace to produce molten iron, replacing charcoal.

The availability of cheap iron was one of the factors that led to the Industrial Revolution. In this period began the refining of pig iron into wrought iron, which was used to build bridges, ships, warehouses, etc.

Steel

Steel uses a higher carbon concentration than wrought iron. Steel was produced in Luristan, Persia, in 1000 BC New methods of producing iron bars without carbon were devised in the Industrial Revolution, which were later used to produce steel.

In the late 1850s, Henry Bessemer devised blowing air into molten pig iron to produce mild steel, which made steel production more economical. This resulted in a decrease in the production of wrought iron.

Properties

Appearance

Metallic luster with a grayish tinge.

Atomic weight

55,845 u.

Atomic number (Z)

26

Melting point

1,533 ºC

Boiling point

2,862 ºC

Density

-Ambient temperature: 7.874 g / mL.

-Melting point (liquid): 6.980 g / mL.

Heat of fusion

13.81 kJ / mol

Heat of vaporization

340 kJ / mol

Molar caloric capacity

25.10 J / (mol K)

Ionization energy

-First ionization level: 762.5 kJ / mol (Fe ⁺ gaseous)

-Second ionization level: 1,561.9 kJ / mol (Fe ²⁺ gaseous)

-Third ionization level: 2.957, kJ / mol (Fe ³⁺ gaseous)

Electronegativity

1.83 on the Pauling scale

Atomic radio

Empirical 126 pm

Thermal conductivity

80.4 W / (mK)

Electrical resistivity

96.1 Ω · m (at 20 ºC)

Curie point

770 ° C, approximately. At this temperature, iron is no longer ferromagnetic.

Isotopes

Stable isotopes: ⁵⁴ Fe, with an abundance of 5.85%; ⁵⁶ Fe, with an abundance of 91.75%; ⁵⁷ Fe, with an abundance of 2.12%; and ⁵⁷ Fe, with an abundance of 0.28%. As ⁵⁶ Fe is the most stable and abundant isotope, it is not surprising that the atomic weight of iron is very close to 56 u.

While the radioactive isotopes are: ⁵⁵ Fe, ⁵⁹ Fe and ⁶⁰ Fe.

Structure and electronic configuration

-Allropes

Iron at room temperature crystallizes in the body-centered cubic structure (bcc), which is also known as α-Fe or ferrite (within metallurgical jargon). Since it can adopt different crystal structures as a function of temperature and pressure, iron is said to be an allotropic metal.

The allotrope bcc is common iron (ferromagnetic), the one that people know so well and is attracted to magnets. When heated above 771 ºC, it becomes paramagnetic, and although its crystal only expands, this “new phase” was previously considered β-Fe. The other allotropes of iron are also paramagnetic.

Between 910ºC and 1,394ºC, iron is found as the austenite or γ-Fe allotrope, whose structure is face-centered cubic, fcc. The conversion between austenite and ferrite has a major impact on steelmaking; since carbon atoms are more soluble in austenite than in ferrite.

And then, above 1394 ºC until its melting point (1538 ºC), the iron returns to adopt the bcc structure, δ-Fe; but unlike ferrite, this allotrope is paramagnetic.

Epsilon iron

By increasing the pressure to 10 GPa, at a temperature of a few hundred degrees centigrade, the α or ferrite allotrope evolves to the ε allotrope, epsilon, characterized by crystallizing in a compact hexagonal structure; that is, with the most compact Fe atoms. This is the fourth allotropic form of iron.

Some studies theorize about the possible existence of other allotropes of iron under such pressures, but at even higher temperatures.

-Metal link

Regardless of the iron allotrope and the temperature that "shakes" its Fe atoms, or the pressure that compacts them, they interact with each other with the same valence electrons; These are, those shown in their electronic configuration:

3d ⁶ 4s ²

Therefore, there are eight electrons that participate in the metallic bond, whether it is weakened or strengthened during allotropic transitions. Likewise, it is these eight electrons that define the properties of iron such as its thermal or electrical conductivity.

-Oxidation numbers

The most important (and common) oxidation numbers for iron are +2 (Fe ²⁺) and +3 (Fe ³⁺). In fact, the conventional nomenclature considers only these two numbers or states. However, there are compounds where iron can gain or lose another number of electrons; that is, the existence of other cations is assumed.

For example, iron can also have oxidation numbers of +1 (Fe ⁺), +4 (Fe ⁴⁺), +5 (Fe ⁵⁺), +6 (Fe ⁶⁺) and +7 (Fe ^{7 +}). The anionic ferrate species, FeO ₄ ^2-, has iron with an oxidation number of +6, since the four oxygen atoms have oxidized it to such an extent.

Likewise, iron can have negative oxidation numbers; such as: -4 (Fe ^4-), -2 (Fe ^2-) and -1 (Fe ^-). However, compounds with iron centers with these electron gains are very rare. That is why, although it surpasses manganese in this respect, the latter forms much more stable compounds with its range of oxidation states.

The result, for practical purposes, it is enough to consider Fe ²⁺ or Fe ³⁺; the other cations are reserved for somewhat specific ions or compounds.

How is it obtained?

Steel ornaments, the most important alloy of iron. Source: Pxhere.

Collection of raw materials

We must proceed to the location of the ores of the most appropriate minerals for the mining of iron. The minerals most used to obtain it are the following: hematite (Fe ₂ O ₃), magnetite (Fe ₃ O ₄), limonite (FeO · OH · nH ₂ O) and siderite (FeCO ₃).

Then the first step in the extraction is to collect the rocks with the iron ore ores. These rocks are crushed to break them into small pieces. Subsequently, there is a phase of selection of the fragments of the rocks with iron ore.

Two strategies are followed in the selection: use of a magnetic field and sedimentation in water. The rock fragments are subjected to a magnetic field and the mineral fragments are oriented in it, thus being able to be separated.

In the second method, the rocky fragments are dumped into the water and those that contain iron, because they are heavier, settle at the bottom of the water, leaving the gangue in the upper part of the water because it is lighter.

Blast furnace

Blast furnace where steel is produced. Source: Pixabay.

The iron ores are transported to blast furnaces, where they are dumped together with coking coal, which has the role of fuel and carbon supplier. In addition, limestone or limestone is added, which fulfills the function of flux.

The blast furnace, with the previous mixture, is injected hot air at a temperature of 1,000 ºC. Iron is melted by the combustion of coal that brings the temperature to 1,800 ºC. Once liquid, it is called pig iron, which accumulates at the bottom of the oven.

Pig iron is removed from the furnace and poured into containers to be transported to a new foundry; while the slag, an impurity located on the surface of the pig iron, is discarded.

Pig iron is poured through the use of casting ladles into a converter furnace, along with limestone as flux, and oxygen is introduced at high temperatures. Thus, the carbon content is reduced, refining the pig iron to turn it into steel.

Subsequently, the steel is passed through electric furnaces for the production of special steels.

Applications

-Metal iron

Iron bridge in England, one of the many constructions made with iron or its alloys. Source: No machine-readable author provided. Jasonjsmith assumed (based on copyright claims).

Because it is a low-cost, malleable, ductile metal that has become resistant to corrosion, it has become the most useful metal for man, under its different forms: forged, cast and steel of different types.

Iron is used for the construction of:

-Bridges

-Basics for buildings

-Doors and windows

-Boat hulls

-Different tools

-Piping for drinking water

-Tubes for collecting wastewater

-Furniture for the gardens

-Grille for home security

It is also used in the production of household utensils, such as pots, pans, knives, forks. In addition, it is used in the manufacture of refrigerators, stoves, washing machines, dishwashers, blenders, ovens, toasters.

In short, iron is present in all objects that surround man.

Nanoparticles

Metallic iron is also prepared as nanoparticles, which are highly reactive and retain the magnetic properties of the macroscopic solid.

These spheres of Fe (and their multiple additional morphologies) are used to purify waters of organochlorine compounds, and as drug carriers delivered to select regions of the body through the application of a magnetic field.

They can also serve as catalytic supports in reactions where carbon bonds, CC, are broken.

-Iron compounds

Oxides

Ferrous oxide, FeO, is used as a pigment for crystals. Ferric oxide, Fe ₂ O ₃, is the base for a number of pigments ranging from yellow to red, known as Venetian red. The red shape, called rouge, is used to polish precious metals and diamonds.

Ferro-ferric oxide, Fe ₃ O ₄, is used in ferrites, substances with high magnetic accessibility and electrical resistivity, usable in certain computer memories and in the coating of magnetic tapes. It has also been used as a pigment and polishing agent.

Sulfates

Ferrous sulfate heptahydrate, FeSO ₄ · 7H ₂ O, is the most common form of ferrous sulfate, known as green vitriol or coppera. It is used as a reducing agent and in the manufacture of inks, fertilizers and pesticides. It also finds use in the electroplating of iron.

Ferric sulfate, Fe ₂ (SO ₄) ₃, is used to obtain iron alum and other ferric compounds. It serves as a coagulant in the purification of wastewater, and as a mordant in the dyeing of textiles.

Chlorides

Ferrous chloride, FeCl ₂, is used as a mordant and reducing agent. Meanwhile, ferric chloride, FeCl ₃, is used as a chlorinating agent for metals (silver and copper) and some organic compounds.

Treatment of Fe ³⁺ with the hexocyanoferrate ion ^-4 produces a blue precipitate, called Prussian blue, used in paints and lacquers.

Iron foods

Clams are a rich food source of iron. Source: Pxhere.

In general, an iron intake of 18 mg / day is recommended. Among the foods that provide it in the daily diet are the following:

Shellfish provide iron in heme form, so there is no inhibition in intestinal absorption of it. The clam provides up to 28 mg of iron per 100 g of it; therefore, this quantity of clam would be enough to supply the daily requirement of iron.

Spinach contains 3.6 mg of iron per 100 g. Beef organ meat, for example veal liver, contains 6.5 mg of iron per 100 g. The contribution of blood sausage is likely to be somewhat higher. Blood sausage consists of portions of the small intestine, stuffed with beef blood.

Legumes, such as lentils, contain 6.6 mg of iron per 198 g. Red meat contains 2.7 mg of iron per 100 g. Pumpkin seeds contain 4.2 mg per 28 g. Quinoa contains 2.8 mg of iron per 185 g. The dark meat of turkey contains 2.3 mg per 100 g. Broccoli contains 2.3 mg per 156 mg.

Tofu contains 3.6 mg per 126 g. Meanwhile, dark chocolate contains 3.3 mg per 28 g.

Biological role

The functions that iron fulfills, especially in vertebrate living beings, are innumerable. It is estimated that more than 300 enzymes require iron for their function. Among the enzymes and proteins that use it, the following are named:

-Proteins that have the heme group and do not have enzymatic activity: hemoglobin, myoglobin and neuroglobin.

-Enzymes with the heme group involved in electron transport: cytochromes a, b, and f, and cytochrome oxidases and / or oxidase activity; sulfite oxidase, cytochrome P450 oxidase, myeloperoxidase, peroxidase, catalase, etc.

-Proteins containing iron-sulfur, related to oxyreductase activities, involved in energy production: succinate dehydrogenase, isocitrate dehydrogenase and aconitase, or enzymes involved with DNA replication and repair: DNA-polymerase and DNA-heliclases.

-Non-heme enzymes that use iron as a cofactor for their catalytic activity: phenylalanine hydrolase, tyrosine hydrolase, tryptophan hydrolase and lysine hydrolase.

-Non-heme proteins responsible for the transport and storage of iron: ferritin, transferrin, haptoglobin, etc.

Risks

Toxicity

Risks from exposure to excess iron can be acute or chronic. One cause for acute iron poisoning can be excessive intake of iron tablets, in the form of gluconate, fumarate, etc.

Iron can cause irritation of the intestinal mucosa, the discomfort of which manifests immediately after ingestion and disappears after 6 to 12 hours. The absorbed iron is deposited in different organs. This accumulation can cause metabolic disturbances.

If the amount of iron ingested is toxic, it can cause intestinal perforation with peritonitis.

In the cardiovascular system, it produces hypovolemia that can be caused by gastrointestinal bleeding, and the release by iron of vasoactive substances, such as serotonin and histamine. Ultimately, massive necrosis of the liver and liver failure can occur.

Hemochromatosia

Hemochromatosia is a hereditary disease that presents an alteration in the body's iron regulation mechanism, which is manifested in an increase in the blood concentration of iron and its accumulation in different organs; including the liver, heart and pancreas.

The initial symptoms of the disease are the following: joint pain, abdominal pain, fatigue and weakness. With the following symptoms and subsequent signs of the disease: diabetes, loss of sexual desire, impotence, heart failure and liver failure.

Hemosiderosis

Hemosiderosis is characterized, as its name implies, by the accumulation of hemosiderin in the tissues. This does not cause tissue damage, but it can evolve to damage similar to that seen in hemochromatosia.

Hemosiderosis can be caused by the following causes: increased absorption of iron from the diet, hemolytic anemia that releases iron from red blood cells, and excessive blood transfusions.

Hemosiderosis and hemochromatosia could be due to an inadequate functioning of the hormone hepcidin, a hormone secreted by the liver that is involved in the regulation of body iron.

References

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