Salvage and metalworking

[Thrudd]

Questions for metallurgists or smiths:

Is it possible to reforge salvaged galvanized steel, such as tools or girders or auto frames, into new things? If yes, what sort of technology or equipment would be required?

Imagine the steel found in a modern city: once it oxidizes and corrodes and returns to the earth, would it return to an iron ore state and be recoverable again in the future? Assuming, of course, there is no interference from civilization in the intervening years.

[MrZJunior]

Questions for metallurgists or smiths:

Is it possible to reforge salvaged galvanized steel, such as tools or girders or auto frames, into new things? If yes, what sort of technology or equipment would be required?

Imagine the steel found in a modern city: once it oxidizes and corrodes and returns to the earth, would it return to an iron ore state and be recoverable again in the future? Assuming, of course, there is no interference from civilization in the intervening years.

I believe it would be incredibly difficult to restore oxidized iron to a usable state. Perhaps in billions of years after the Earths crust has recycled itself some of it would be reconverted to iron ore.

[raygun goth]

Well, let's see, ore is oxidized metal - smelting's purpose is to remove the oxygen through heat and pressure. Most iron, let's say, in the United States, after a given apocalypse, would leach back into the soil as rust particles. I would imagine to get it out, you'd have to either use sand extraction (really time consuming) or go down to the southeastern states (notably the Mississippi watershed and the Florida wetlands) because as time goes on, that's where the iron would collect in big chunks, like bog iron.

[Xuc Xac]

I believe it would be incredibly difficult to restore oxidized iron to a usable state. Perhaps in billions of years after the Earths crust has recycled itself some of it would be reconverted to iron ore.

I could do it in a kitchen. Scaling it up to an industrial process in a post-apocalyptic setting might be difficult but I could produce "artisanal batches".

[BootStrapTommy]

Rust would simplly be a type of ore. It can be refined by a number of methods similar to those used with other ores.

Given it's friablity, it might be hard to collect sufficient quantities to refine on any industrial scale though...

Two come to mind:

Fe2O3 + 2Al --> 2Fe + Al2O3 (this method might induse a thermite reaction if not done properly)

2 Fe2O3 + 3 C --> 4 Fe + 3 CO2

[jqavins]

Is it possible to reforge salvaged galvanized steel, such as tools or girders or auto frames, into new things? If yes, what sort of technology or equipment would be required?
Galvanized? The rest of your post seems to be about using rust as iron ore, to which others have responded, and well; if you can find big deposits then it's a great ore and if it ends up being distributed (which is very likely) then the quality of ore depends on how rusty the stuff you can dig up is.

But galvanized is something altogether different. Galvanized iron (or steel) is coated with zinc, which protects it from corrosion. The protection is imperfect and temporary, so in a post-apocolyptic seting you'd be left with a mixture of rust and a trace of zinc oxide. When you smelt this for the iron you would get a little bit of zinc in the iron, but there would be no way of restoring it to galvanized (unless you know enough to separate the iron and zinc ores, smelt them separately, and then redo the plating.)


Fe2O3 + 2Al --> 2Fe + Al2O3 (this method might induse a thermite reaction if not done properly)
First, rust is a mixture of Fe2O3 and Fe(OH)3. Aluminum might still work, with the second equation being
2Fe(OH)3 + 2Al --> 2Fe + Al2O3 + 2H2O.
BUT, (second point) in such an environment, aluminum metal would be way, way too valuable to use for refining iron when the same thing can be done with coal or charcoal.


2 Fe2O3 + 3 C --> 4 Fe + 3 CO2
In refining with coal or charcoal, the carbon is first partialy oxidized to carbon monoxide; carbon's oxygen affinity is not as high that as CO. It's all done in one stack or pile, but the CO step is critical.
2C + O2 --> 2CO
Fe2O3 + 3CO --> 2Fe + 3CO2
2Fe(OH)3 + 3CO --> 2Fe + 3CO2 + 3H2O

[Thrudd]

Galvanized? The rest of your post seems to be about using rust as iron ore, to which others have responded, and well; if you can find big deposits then it's a great ore and if it ends up being distributed (which is very likely) then the quality of ore depends on how rusty the stuff you can dig up is.

But galvanized is something altogether different. Galvanized iron (or steel) is coated with zinc, which protects it from corrosion. The protection is imperfect and temporary, so in a post-apocolyptic seting you'd be left with a mixture of rust and a trace of zinc oxide. When you smelt this for the iron you would get a little bit of zinc in the iron, but there would be no way of restoring it to galvanized (unless you know enough to separate the iron and zinc ores, smelt them separately, and then redo the plating.)


First, rust is a mixture of Fe2O3 and Fe(OH)3. Aluminum might still work, with the second equation being
2Fe(OH)3 + 2Al --> 2Fe + Al2O3 + 2H2O.
BUT, (second point) in such an environment, aluminum metal would be way, way too valuable to use for refining iron when the same thing can be done with coal or charcoal.


In refining with coal or charcoal, the carbon is first partialy oxidized to carbon monoxide; carbon's oxygen affinity is not as high that as CO. It's all done in one stack or pile, but the CO step is critical.
2C + O2 --> 2CO
Fe2O3 + 3CO --> 2Fe + 3CO2
2Fe(OH)3 + 3CO --> 2Fe + 3CO2 + 3H2O

That's great, thanks. What if the galvanized steel was not completely corroded yet, you find a pile of old girders. Would anything prevent them from being melted down and used for something else (not to maintain the galvanization, just to reuse the steel)? Would it still be steel, or would only the iron remain after it was melted?

Would post apocalyptic dark ages society be able to use old steel components to forge tools and armor and weapons? Or would it require higher level technology or complete oxidation/decay.

[jqavins]

Girders, tools, and car frames are rarely if ever galvanized to begin with. Galvanized steel is used most often in sheet metal, and often in nails, and not so often in much of anything else. Is there a particular reason that you're fixated on galvanized?

One detail I forgot earlier is that zinc will evaporate at a lower temperature than iron melts. Smelting by charcoal actually doesn't involve melting the iron, so the zinc may survive as I said, amd you would probably end up with some zinc disolved in the iron, but very little. And I should have added that melting intact galvanized steel will cause the zinc to evaporate, and zinc vapor is quite dangerous. (Imagine inhaling and finding that your airway has been zinc plated by the vapor deposition process.)

Leaving galvanized behind, steel can be melted and it's still steel. Forget paper, glass, and soda cans; steel is the most recycled material on the panet. There are many different kinds of steel, with different amounts of included carbon, and a wide range of other metal elements added. Some, like most stainless aloys (which have a lot of chromium) take a higher temperature to melt than "regular" carbon steel, but a mixed pile could potentially all melt together because the stainless might disolve.

Without advanced methods, you prretty much wouldn't know exactly what you've got as far as aloying elements and carbon content, and it's amazing how a 1% change in some element or other can alter a steel's properties. Could you make tools, weapons, and armor out of it? Sure. Could you make good tools, weapons, and armor out of it? Only if you're an expert or get your material from one. When I wrote earlier "advanced methods," those could include the finely calibrated hands and eyeballs of very experienced artisans who know that the, just for example, the blue ore is good for tools but lousey for armor and for armor you need the green, but they're talking about super subtle shades of color in what 99.9% of us just see as rust red.

The intricacies of metalurgy are deep, complicated, and sometimes arcane. I'm not a metalurgist, just an EE who likes chemistey and has read a decent bit about this stuff. Enough to know that there are tons more I don't know.

[Jendekit]

I don't know about galvanized, but there's a program called Forged in Fire where modern day blacksmiths compete. The first round involves taking a piece of steel (in one episode they had to pick from scrap pieces of steel, in another they used large ball bearings, etc.) and making a knife blade & tang out of it.

So recycling scrap metal in a post-apocalyptic setting is certainly feasible.