Is there a level of decomposition after rust? Or is there any way (either naturally or through processing) to return rusted iron to a deoxidized state?

Question

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?

In: 16

Answer 1

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).