If you put the Earth on a scale, its weight would be no less than 5,974,000,000,000,000,000,000,000 kilos, according to geologists. And iron accounts for no less than a third of that. Because although the element makes up ‘only’ 6 percent of the earth’s crust, the earth’s core consists almost entirely of iron.
Iron is the sixth most abundant element in the universe – the top five are hydrogen, helium, oxygen, carbon and neon. As far as metals are concerned, iron has a number 1 position: no other metal is present in such an abundance in the universe.
Iron not only forms the core of our Earth, but also that of a star that is about to explode. ‘Young stars’ consist of hydrogen, and in their core it is so hot and the pressure is so high that the atomic nuclei fuse to form helium. This process, nuclear fusion, releases energy that we can see from Earth as radiation. Helium further fuses into carbon, carbon into silicon and finally, at the end of nucleosynthesis – the element formation in stars – iron is created. And with that a tipping point is reached.
When iron atoms merge in that hot star core, energy is no longer released, but it costs the star energy. Without the nuclear fusion process, the star collapses under its own gravity and then explodes in a huge explosion. During such a so-called supernova, the ‘debris’ of the star is thrown into space – and can thus form the basis for a new planet, for example. On earth, iron can be found in the human body: in our blood.
Iron even has its own era named after it. The Iron Age followed the Bronze Age: from around 800 BC, many swords and tools were made of iron. Because although bronze is harder, it also has a number of disadvantages: as an alloy of tin and copper, the production process is more laborious. Iron is also easier to mine, precisely because it is so abundant in the earth’s crust.
It was the Hittites, who lived in present-day Turkey from around 2000 BC, who were the first to develop a process for extracting iron from iron ore: using charcoal. At first they kept their discovery secret so that only they could fight with iron weapons. After the fall of the Hittite empire, iron production expanded.
Contaminated slag
Nowadays, iron is extracted from iron ore in blast furnaces using coke: coal that is used as fuel. Through a few intermediate steps, both liquid iron and a contaminated ‘slag’ are created: a by-product consisting of undesirable substances that can ultimately be processed into cement. The pig iron initially extracted is brittle and contains a high percentage of carbon. The end product that remains after removing the slag still contains a small percentage of carbon. With less than 0.05 percent carbon it is called wrought iron, above that it is called steel (up to 2 percent) or cast iron (more than 2 percent). If desired, other metals can be added to steel as an alloy. But the fact that making steel is not a clean process is evident from the discussions around Tata Steel…