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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Sure. You can separate the oxygen out and get iron back. Pre typically isn’t the metal at all, it’s some mineral containing iron. The heat breaks the mineral down to release metallic iron. Carbon present also helps to strip oxygen from the iron.
Try not to think about it as decomposition. It’s oxidation on a molecular level, not decomposition on a macro/organism level. So it can be reversed, removing the oxygen. In fact, you can buy the chemicals necessary from a hardware store.
The smelting process for iron is essentially that. You melt the ore (not the same as pure iron), the molten state and heat will make it so that the unwanted elements like oxygen, etc. either end up as a gas, react with something else like carbon in the case of oxygen or separate out as slag.
EDIT: As for is there a level of decomposition after rust? Not really. You have different oxides possible like FeO, Fe2O3, and Fe3O4. There are also other minerals that have iron in them, but aren’t solely iron and oxygen. Iron oxide is usually what you’ll get when iron and steel rusts, but in nature, you can find other compounds with iron in them that formed at different temperature and pressure conditions.
I wouldn’t call it decomposition. It’s more that the iron is reacting with something and losing the properties of the original material.
> Is there a level of decomposition after rust?
You can bind up iron in other molecules. I dunno of any naturally occuring reactions though.
The iron element is stable though and doesn’t have a halflife.
>Or is there any way (either naturally or through processing) to return rusted iron to a deoxidized state?
Sure. An oven in a vacuum will essentially cook out the oxygen. It’s not worth it though, so no, this isn’t part of the mining / refining process.
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.
Not sure if you are interested in theory or practical application, but you can use electrolysis to move rust from one piece of iron to another. Running direct current through a solution with another piece of sacrificial iron (like rebar) which collects the rust. Google will give you the details.
A more simple effect that I think people are overlooking is that iron expands when it rusts. This is why rusty metal starts to flake off. The forces that hold it together get weaker too. When the atoms of iron become oxidized molecules, they break free from the surrounding iron atoms. In short, when iron rusts you can’t just put it back exactly how it was by removing the oxygen. You can melt it back down and separate the iron and oxygen through various processes (mostly involving high temperatures or electricity).
Rust is more or less end stage in nature, it will physically break down into smaller bits. Maybe a plant will absorb it at some point.
Iron ore is basically rust and rock. The refining process removes the impurities and kicks the oxygen off leaving the iron behind. So yes rust can be turned back into pure iron.
Basically what you are mining out of the ground when you mine “iron ore” is rust. The red colour isn’t just surface rust, it’s rust all the way. The process of smelting does two things. First, what you dig out of the ground isn’t pure rust (iron oxide), it has a bunch of other stuff, essentially dirt, mixed with it. That is what is turned into slag. The other process is to rip the oxygen out of the rust, converting it from rust to iron. (There are other subsequent processes to make it into more useful things like steel, but that’s not important.)
Way back when the earth formed, there was a lot of iron around. It was just metal. This is because the atmosphere at the time was mostly carbon dioxide and methane, and iron requires oxygen to rust. At some point after the very first life evolved, a special kind of bacteria, cyanobacteria, evolved, that had the clever trick of combining water and carbon dioxide, in the presence of sunlight, into sugar molecules, and a bit of spare oxygen was released. When this happened, all the iron that was just sitting around as part of the rocks, on becoming exposed to oxygen, began to rust.
In the course of several million years, two things happened. One was that life evolved to, first, survive in oxygen, and then to depend on it. The second was that all the iron, every last bit of it, rusted (well all the iron in the crust). When we dig up iron ore today, that’s where it came from.
Rust is stable in an oxygenated atmosphere (like the air we live in). It has decomposed all the way it will, and can sit, unchanging for literally billions of years (the Great Oxygenation Event that caused it to rust in the first place was about 2.4 billion years ago, and since then, all the rust has just sat there doing nothing in particular).
Decomposition is the wrong word, because the iron is just fine.
Also all of the iron you mine is rust. Not just the surface.
You just break down the rocks the iron ore is found in, and heat them with something that will want the oxygen from the oxidised iron more than the iron. Usually that’s carbon.
And carbon and oxygen gives carbon oxides, which just leave as gasses. Thus the slag is solely the accompanying rocks in the material you mined.
If you smelted pure ironoxides rather than iron ore, there would be no slag.
Slag is just molten rock, mostly silicates, a similar to glass.
Basically all iron in the ground has at some point been oxidised. We mine the rocks that contain that oxidised iron, and then use carbon to separate the oxygen and iron.
So no iron can’t rust further under natural circumstances. However you can react rust with stronger oxidants than oxygen like fluorine, and then get oxygen gas and iron fluorides, this doesn’t happen naturally though, cause there no free fluorine gas around.
Rust IS iron. Just a salt of iron.
The slag has nothing to do with being part of the rust. It’s just the rocks you found the rust veins in.
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