From my understanding, iron veins in mines are spotted by their bright red color due to rust on the exposed surface. Then when it’s refined, the rust separates as slag and is discarded, leaving the pure iron behind.
Is this accurate? Or does the refining process deoxidize iron while separating impurities?
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Assuming the steel/iron was completely rusted and no metallic iron remained, you could simply heat the iron oxide to drive off moisture, producing a mixture of hematite and magnetite, which are it on oxide minerals. These are the most important and widely used ores of iron. Such material can be smelted back into irin and steel within the same methods used with mined iron ore.
A convenient way to reduce the iron oxide would be to mix it with powdered aluminum or magnesium metal. Those metals have a much higher affinity for oxygen and are more electropositive. Meaning they are more eager to donate electrons to other atoms than iron. You can ignite the mixture producing a thermite reaction. In this reaction aluminum or magnesium donates electrons to iron producing a puddle of molten iron metal, aluminum oxide, and a lot of heat. This is known as a “single replacement” reaction where the aluminum or magnesium replaces the iron.
This isn’t widely done industrially, though, because aluminum is more expensive than steel from other methods is. It has the advantage that it’s fast and produces intense heat so it’s sometimes used to weld train rails together. Another method that can be used is by preheating natural gas to about 700- 800°C. The hot natural gas can then react with the oxygen producing H2O, CO (carbon monoxide), CO2, and fine iron powder. You can then melt the iron powder mix with certain other ingredients and cast at into whatever shape. You could also blend the iron with other metal powders and some carbon, then use it in certain 3D printing methods like powder bed laser sintering.
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