This question cropped up in this less serious thread here:
In a scenario where humans survive but our material culture is nearly destroyed outright, I would think metal would become difficult to get at. There’d be some things, like gold and copper, which would survive. But iron would become very hard to find.
Chain of reasoning: iron rusts and in any case all metal items will wear down. Any exposed metal (and with structures collapsing over time, it will all become exposed eventually) will go to waste over time. We won’t be able to easily mine it without good technology, because we’ve exhausted the surface deposits. The fact that we’ve mined it in the past shouldn’t matter, because that will go to waste while a few remaining humans try desperately to survive.
Eh, I was more going for a general discussion of whether we can conveniently get at large amounts of metal without modern machines, and how long it would take for existing stocks of metal to vanish into the dirt.
Your basic premise is unsound. Iron, in the form of oxides, is found commonly in the Earth’s crust; as a child I used to find loose rock in the Ozarks quite frequently with a high enough iron content to be detectable from casual observation (weight, ferromagnetic response, presence of identifiable surface oxides) from which iron could no doubt be extracted. Similarly, metals like zinc and copper are found widely, albeit often in concentrations that do not make them financially viable for commercial extraction.
With regard to corrosion, this is not as much of an issue you indicate. Metals can only corrode in the presence of a polar solvent (most commonly water with basic contaminants) in contact with the surface, hence why the thin ungalvanized carbon steel sheet metal bodies of automobiles can disintegrate by flaking apart, but more solid artifacts like forged iron nails, steel weapons, and cast iron pots can survive for hundreds of years with only modest amounts of surface rust. The Iron Pillar of Delhi has survived for at least a couple thousand years with only minor amounts of surface corrosion. Corrosion can severely impact the structural capability of steel structures like bridges and buildings, but that isn’t because the member literally rusts away across the thickness of parent material, but rather because stress corrosion cracking (crack growth due to corrosion cells of a member under constant tensile load) compromises the capability of joints to distribute loads.
In most metals, corrosion in atmosphere actually produces a protective oxide layer, as seen with aluminum and copper. As long as this layer isn’t disturbed by abrasion or erosion and there is no galvanic circuit (caused by the presence of a solvent or contact between metals of dissimilar electronegativities), the rate at which corrosion will intrude into an unloaded structure is tiny. So we’d expect structures in marine environments to corrode rapidly (and they do) but those in desert climes to survive eons.
Even in the case of corrosion, the material doesn’t disappear but returns to the environment in the form of oxides, which will eventually accumulate in groundwater and be deposited at silting points. Most oxides are readily recoverable, so even in the very long term–hundreds of thousands of years–we wouldn’t expect metals to disappear, even as the artifacts and structures constructed with them become unrecognizable.
Your main misconception appears to be that rusted metals are wasted or useless in some way, and we’ll have to dig deeper into the ground to get useful metal. Iron ore (or, really, any other ore) is just iron oxides mixed with rock. It’s rusted metal. The process of smelting removes the oxygen and purifies the metal. So a hulking chunk of rusted metal on the surface (formerly some building or machine) is easier to get to than it was when it was deposited near the surface, and probably purer too.
Easier to get to, yes, but the smelting would require considerable power sources, yes? Granted, enough coal might do it if you can then get to the coal, or the oil or whatnot. Can you actually do that with wood-burning ovens?
The context, of course, was a world in which government and society has more or less collapsed, so that travel and trade and technology are hard-pressed by society resources. Classical bootstrapping problem.
Right. I was starting to think about, when civilization falls and everybody is dressed like a Mad Max movie, how will disaffected not-too-bright teen males show their faux-rebellion?
Yeah!
I was envisioning something like the videos for:
Motley Crue’s Looks That Kill
Megadeth’s Peace Sells
Scorpions - Rock you like a Hurricane
Kiss’ Lick it Up
Anyone else?
Charcoal was the only fuel that could be used in iron production for a very long time, it wasn’t until late 18th century that people came up with methods(the Puddling process was the most successful) that could use mineral coal instead.
Technology might not be gone. One intact encyclopedia set (like the one I have in my house) or science books or even a small library can really boost technology. Even garbage dump excavations would yield metals and knowledge. I think with my small book collection alone can get up to WW2 level metal refining technology. (Love that Bessemer process…)
Oh and remember the United States is the worlds second producer of coal. There is a lot of coal out there.
At the place where I grew up, you could trail a magnet through the dirt and pick up a load of pebbles with high iron content. I don’t think finding iron ore will be a problem.