Given that your input stream of plastic waste contains a very large number of toxic inputs, burning it without releasing toxic outputs seems pretty much impossible. It seems a similar level of problem: burning it without releasing toxins and recycling it without incorporating toxins.
Most of it is hydrocarbons, which a sufficiently thorough decomposition process ought to be able to turn into CO2 and H2O. (And maybe HCl in the case of the chlorinated plastics? I guess that's neutralized with a base to make a salt?)
I don't know a ton about this, but it looks like plasma gasification plants achieve something like this -- producing syngas (mostly H, CO), metal nodules, and a slag material (which seems to roughly be, "igneous rocks or sand, but man made"). I'm curious about the composition of the output products. But it seems to usually be net-energy-positive. This seems like a good intro:
I wonder if there are methods from physics that could be used (even if not now cost effectively) to more thoroughly isolate the various elements rather than having the (it seems not totally understood?) chemical reaction of the various components of the plasma as it cools? Like a big industrial scale mass spectrometer? Like the cyclotron scheme to separate isotopes of uranium in the Manhattan Project? Then you could know, "all the lead is in this beam over here" and "all the mercury is in this beam over here", and so on... That'd be neat. Have some plasma physicists working on recycling instead of on fusion...
(At this point I Google more...)
Interesting, so here they separate copper from zinc using a plasma centrifuge:
Is there a burn-temperature above which everything dangerous is basically rendered inert?
I.e., you make stuff so hot that whatever survives is perma-bonded to oxygen, carbon, chlorine, fluorine, etc., and has almost zero chance of reacting with living creatures?
you need to clean up the syngas to get rid of dioxins with a charcoal filter or something like that. The plasma torch is supposed to convert the organic materials in municipal waste (e.g. food waste, plastic, wood) to syngas and then vitrify the remainder as glass particles that trap toxic heavy metals (you could use it as a material for roads and buildings.) Allegedly you can burn the syngas to make enough electricity to run the torch and still sell some to the grid. I guess you'd want to try to capture mercury before it goes up the stack.
They built a few small (like 5 MW) plants to test the idea but attempts to scale up to 50 MW. For a long time the technology belonged to one of Westinghouse's ghosts (like the one that owns the AP1000) but they are still ordering AP1000s but nobody is ordering plasma torches for municipal waste.
I asked my local waste disposal company why they don't buy a plasma gasification system and they told me that the plants require so much trash as fuel that to keep them fed they'd have to haul trash from three states. It wasn't affordable to buy one just for local operation. Here's the history of attempts and current projects:
These are definitely large scale, large area systems and there have been some engineering problems. A few seem to be operating successfully. Even if the net energy production is zero that's better than it being negative. Financing has been a problem also. It still produces CO2 also, so there is that to consider. It greatly reduces hazards in the waste stream though, so it seems better than a landfill. I'm not sure it would be a good idea to turn the glass plus heavy metals that is produced into building or road materials.
