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Hundreds of years ago, the world as we know it came to an end for various reasons. Mass death, mass agricultural failure, a complete breakdown of all economies and transportation networks along with essentially all nations seeking to function as nations.

But humanity survived, the descendants of the survivors have lost most the technology their ancestors had (but not all!). Would it be plausible for them to dig up the remains buildings, vehicles and so on in order to recycle the raw materials? I have read that iron, and possible other metals, can be recycled simply by melting them down and skimming off the impurities. Would it still be possible after this amount of time? Is there any challenge to this that I'm missing? Once they start doing this, would recyclable materials be depleted very quickly?

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    $\begingroup$ Even with readily-available metals to work with, it takes lots of energy to melt/re-refine metals. If the survivors have large sources of energy, recycling metals is fairly straightforward. But if energy (coal, oil natural gas, nukes, etc.) is in short supply, your survivors will have real problems! $\endgroup$ – Catalyst Nov 29 '16 at 14:04
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    $\begingroup$ @Catalyst Does melting and refining scrap take more energy than mining, melting, and refining ore? Digging up shallowly-buried hulks seems easier than tunneling through stone for bits of ore, and the rest of the process is as old as metalworking; I'd think they could work something out as long as they had wood to burn. $\endgroup$ – Phasma Felis Jul 20 '17 at 0:08
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This is not only feasible but preferable. If I was living in that world and needed to mine and process metals, I would get them out of the ruins and leftover items from those ancient times.

First, as to how long the metal will last. We are still finding metal coins from the Roman Empire. It is amazing how long metal will last. Some of it might be unusable, but even with medieval technology, you could smelt metal ore with a lot more impurities than what you would find in say the ruins of a skyscraper. Mind you, a lot of the ore that is pulled out of mines is combined with other elements or is Iron Oxide (Fe2O3). Pulling the oxygen off is part of the smelting process, so rusty iron, is just fine for smelting.

As to safety, I would rather mine a collapsed building or beached aircraft carrier than mine into the side of a mountain. Dangerous, absolutely, but mining for ore is far more so.

And the melting temperature of steel (1370 C) is actually lower than the melting temperature of iron you would dig out of the ground (1510 C), which is a bigger part of the reason that recycling can be profitable. If you could mine and process iron ore in medieval times, you will be able to mine and process steel from ruined buildings, beached ships, etc.

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  • $\begingroup$ It might be fun to note some estimates place some landfills as currently being viable mining targets. $\endgroup$ – user25818 Nov 18 '16 at 20:36
  • $\begingroup$ @notstoreboughtdirt your username is appropriate for a mining discussion $\endgroup$ – Marshall Tigerus Nov 18 '16 at 21:01
  • $\begingroup$ Additionally, it is safe to think that almost all the easily available ore is already mined and that you will need equipment that no longer exists to mine more (not only to break / extract the ore, but in underground mines also to get down to the rock and also to operate ventilation pumps). $\endgroup$ – SJuan76 Nov 18 '16 at 21:41
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Reducing oxidized (rusted) iron to usable iron metal is the function of a blast furnace. These were developed in China around two millennia ago, so it's definitely within reach of post-apocalyptic technology.

All you would need is coal/charcoal, ceramics (clay) to create the body of the furnace, and a means to create bellows (wood and leather?).

Bloomeries are even simpler and can be used to create wrought iron.

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It is very possible.

Ideally you would first look for material which is in a useful state as it is. Steel would be a high priority for making tools etc and while steel can corrode quickly in the wrong conditions it is entirely plausible that heavier sections in sheltered locations could still be sound after several centuries. A good target would be machine tools and plant where high quality steel parts would be well protected inside the body of the machine and also covered in oil or grease.

Indeed it is not entirely implausible that a significant number of machines may still be restorable condition. There are plenty of 100+ year old lathes and milling machines still in operation.

Many common and useful non-ferrous metals are very easy to recycle and can just be melted in a crucible at fairly moderate temperatures which are easy to achieve with say a charcoal furnace. This includes bronze, brass, lead aluminium and copper. This process is sufficiently obvious that it is entirely plausible that it could be done with relatively little specialist knowledge or experience.

Remelting cast iron is a bit more difficult as some care needs to be taken to maintain the proper carbon content but it can be done with pretty simple equipment if you understand the process.

There is a fair chance that the amount of metal currently in circulation would keep a severely depleted population going for a long time without needing to start smelting ferrous metals from ore (or severely corroded stock)

Global annual steel production is in the order of hundreds of millions of tons so there is a lot of it about so you only need a small proportion to be accessible and in reasonably good condition to have very large stocks available and without large scale industrial projects and facilities there is a limit to the amount you are going to be able to use. Indeed before you even need to start recycling there will be plenty just stacked up in warehouses and rail yards.

A relatively simple forge using a medieval level of technology could effectively recycle most metals, although remelting steel is a bit beyond this setup it is entirely possible to forge weld assorted bits of scrap into usable billets without needing to melt it.

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humans have been recycling old material forever. taking the stone off of buildings, melting down statues, ect. they will likely recycle a lot more than metal, modern glass would be valuable, and concrete and asphalt can be cut into blocks, as long as the things exist they will find uses for them. and digging the debris off old cities would be a lot easier than searching for bog iron much less digging a mine in solid rock.

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