One of the most abundant metals on the planet, iron makes up five percent of the earth’s crust and most of the outer core and inner core, which by mass makes it the most common element on Earth. It is also a common element found in the universe, as it has been discovered both in meteorites that come to earth as well as supernovas. No matter where it comes from, iron has a variety of purposes, whether it’s for maintaining human health or for its use in steelmaking. It is vital not only for industry, but for the continued existence of the world.
With an atomic number of 26 and the symbol Fe (for ferrum, or the Latin word for iron), this metal is a part of group eight on the periodic table, or transition metals located in the d-block. Like its fellow group members ruthenium and osmium, iron has a silvery color and high melting and boiling points, although in its natural state iron ore is filled with iron oxides that can make it appear to be a variety of colors ranging from rusty red to deep purple, which makes it a material also commonly used for pigments in paints and colored coatings. In its purest form, iron is a relatively soft element, but most of the time it is found with other elements that give it a harder texture, especially when it is mined. In its natural state, iron is often found bound in silicate or carbonate materials.
Iron has a long, extensive history of being melted down and used in a variety of ancient tools that can be traced as far back as 2.6 million years ago, ranging from wrought iron in 3000 B.C. Egypt to cast iron in China in the 5th century B.C. Although the welding of copper tools predate the use of iron in history, it became much more desirable than the precious reddish metal due to its abundance. Iron was particularly desirable due to it being much easier to manipulate and shape into desired forms than other natural elements such as aluminum, which requires electricity in order to mold. In recent years, iron has been replaced by other materials such as plastic and glass fibers, but it still maintains an important place in modern society with a variety of uses across the world and remains vital as a part of commerce.
As an individual element, iron has a vital role in the maintaining of life in plants and animals, as it works with hemoglobin and myoglobin in order to facilitate oxygen transference in the blood stream for humans and animals. It also plays an important part in the cellular respiration in plant life. It can additionally be used for a variety of chemical compounds, whether it’s for purifying welding for other types of ore or forming binary compounds. It is sometimes used for scientific purposes as a measuring gauge, since iron tends to react the same way every time in experiments as opposed to other elements that lack reproducibility and stability, making it much more desirable for testing. However, for most of its practical purposes, iron is used mainly for industry and manufacturing.
Iron ore is typically found combined with oxygen, which is commonly known as iron oxide. During processing, the oxygen will typically be removed from the iron, along with other impurities, in order to obtain the pure metal.
There are sixteen iron oxides in different colors that have been identified, but there are several particular iron oxides that are the most commonly found:
- Magnetite (Fe3O4), which is approximately 72 percent iron
- Hematite (Fe2O3), which is around 70 percent iron
- Goethite (FeO(OH)), which is approximately 63 percent iron
- Limonite (FeO(OH).n(H2O)), which is up to 60 percent iron
- Siderite (FeCO3), which is around 48.2 percent iron
Any of the materials above that contain over 60 percent iron, usually magnetite and hematite, are considered to be ready for blast furnaces used to make iron in its usable forms, such as pig iron. In the past, particularly during the American Revolutionary War and Napoleonic times, it was usually goethite that was used for iron weapons and tools.
As the industrial revolution set in during the mid-1800s, hematite was the preferred source of iron, which is referred to in the industry as “natural ore,” as it can go directly from the ground into a blast furnace for smelting with very few impurities. However, in recent years, particularly since World War II, this has changed dramatically, as magnetite has a higher concentration of iron ore to other iron oxides and is now being utilized more often in smelting.
Magnetite can be found mainly in banded iron formations, which is sedimentary rock that has ore combined with quartz, and is commonly known as taconite. It is also found in magmatic deposits originating from volcanic activity as well as in some river areas. If you look very carefully, magnetite can also be found on sandy beaches in parts of California and New Zealand.
IRON TO STEEL
The most common industrial use of iron in modern times is steel. Approximately 98 percent of all iron ore that is mined in the world is used in the production of steel. This alloy, which is made up of mainly iron and carbon, has been used almost as long as pure iron has been used over the centuries. Today, it is utilized for a variety of purposes, ranging from building infrastructure to railways to appliances in the home.
Smelting, or melting material to obtain ore, has been used for centuries in the pursuit of making and casting steel. The most common technique for creating useable iron today is through the use of a blast furnace, which combines iron ore with charcoal and limestone which causes many of the impure materials, such as oxygen, in iron ore to burn off.
This helps make what is known as pig iron, which is the basis of all irons used in industry and includes about four to five percent carbon. As a result, pig iron is rather brittle and needs to be refined further in order to be utilized for steel or any other type of iron welding. From pig iron, there are several options when it comes to usage:
- The majority of carbon is reduced from the pig iron to about 0.3 percent creating wrought iron, which is rarely used today but was once utilized in gates, rails and nails.
- Two to four percent carbon in iron combined with silicon, manganese and other trace elements creates cast iron for various tools.
- When the carbon in pig iron is reduced to between 0.5 and 1.5 percent, with some other trace elements added, the ending result is low carbon steel. This is the preferred material in industries using steel where weldability, formability and additional strength are required.