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Separating rubber that is mixed in with stone?

  1. Aug 5, 2007 #1
    Just looking for a few idea for me to explore.

    Basically I have a lump of material that is little bits of stone and rubber stuck together that I need to separate.

    Any ideas welcome

  2. jcsd
  3. Aug 6, 2007 #2


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    I would say heat it up till the rubber flows, then either push it through a sieve or let it set until the rocks sink to the bottom, and cut the bottom part off.
  4. Aug 6, 2007 #3


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    Welcome to PF, Shakermaker.
    Lurch's suggestion is a good one in some ways, but might fall short in others. Primarily, I think that it would depend upon what sort of 'rubber' is involved. I've personally never seen any that would lose enough viscosity under heating to flow through a sieve. There's also the density to consider; it might or might not separate from the rocks due to either floating or sinking.
    My first thought was actually to go the opposite way. If you freeze the mass, the 'rubber' should become brittle while the rocks remain unchanged. You could then whap it a few times with a hammer to get smaller chunks, then run it through a grinding mill with teeth that are made out of something just slightly stronger than the frozen rubber. They should pulverize it, while leaving the rocks intact.
    Having seen Lurch's post, though, I believe that the two could be combined. If you use his process first, it would make the 'freeze separation' a lot easier.
    A couple of things that you didn't specify is how large this mass is, and whether you have to salvage the rubber, the rocks, or both. If you only have to keep the rocks, for instance, I'd just burn the rubber off completely with a torch or kiln. If you have to keep only the rubber, or both, I'd use Lurch's heating method alternating with freezing and grinding. Eventually you should end up with little balls of rubber that are small enough to fall through a coarse screen that will stop the rocks.
    This is just a first impression, though. Some more thought needs to go into it.
  5. Aug 8, 2007 #4


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    If the rubber is thermoplastic, you could melt it. If it is a thermoset (most likely) it will never melt again... only char. I have used strong acid (methane sulfonic) to decompose rubber. If the stone is relatively immune to acid, this treatment would work regardless of the type of rubber you have. If the stone is limestone based, the stone would be decomposed along with the rubber.

    You could also apply a chemical solvent that would swell the rubber. Look up the solvent compatibility of the rubber you have and choose one that is incompatible. Acetone or methylene chloride come to mind. This would destroy the bond between the stone and the rubber and allow the release of the stone. Only the exposed stone will come away easily. A gentle grinding of the swelled rubber would expose the encapsulated rock, allowing it to fall out as well.
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