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Comment by newyankee | Hacker News Reader

Can rusted parts be recycled by reversing the process using energy ?

There are ways to turn rust back to iron, but what you get back is not the original strong steel piece, it is a spongy form of iron that immediately rusts in air.

Can it be smelted into proper iron?

Yes, I don't know if it's done commercially but the general idea is to heat and melt the rusted parts in a reducing atmosphere.

What can be done commercially for rusted stuff (cars and such) is to apply rust converters that convert the iron oxide layer on the outside into a stable primer so it seals the outside of the metal from oxidizing further.

The problem with that is that there will probably be rust and moisture deeper down underneath the new paint that will continue the rust process, cracking the paint and allowing more water, salt and air in

Molar mass of Iron Fe =55.845 g/mol

Molar mass of Rust Fe2O3 =159.7 g/mol

Rust weighs in around 3x more than bare metal, so that makes this primer one expensive fuel guzzling choice.

That is why I always go to the toilet before driving

Once it’s been converted to primer it’s not rust anymore. Still probably heavier than the metal, but eh. Get a haircut.

More but not three times as much according to your molecular weights (there are two iron atoms in the rust molecules)

Yup. While I failed chemistry, I still remember most relevant stuff.

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