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The amount of metal that gets thrown out and ends up in landfill must be huge. There must be a way of separating this metal that is cost comparable to mining. I am currently on holidays in a former tin mining town which has inspired this idea.
My idea is to use a magnetic field to perform the separation.
Using a magnet to separate ferrous metal from rubbish is obvious and well known. There is also a method of separating non-ferrous metal using magnets; my idea is a variation on this method.
The already known method of separating non-ferrous metal is to quickly pass (drop) the mix through a gradient magnetic field. The magnetic field produces eddy currents (and hence an opposing magnetic field) in the metal which deflects the metal sideways and thus separated. (sorry, can't provide links; using a rudimentary phone to post this).
This is a pretty good method, but has a few drawbacks. Firstly, the rubbish would need to be an approximately uniform size to be deflected: too big (or small?) and it won't work. Secondly, it only works on a narrow stream of rubbish.
My idea is to *slow* rather than deflect the metal. So drop the rubbish from the top of a tower (evacuated of air) with magnetic field running through it. The non- metal objects reach the bottom before the metal objects. Use a timed capture mechanism to get metal objects.
(?) Belt-type eddy-current separator
Eddies in the spacetime continuum. [MaxwellBuchanan, Jan 01 2010]
US patent 4,070,278
vaguely similar [xaviergisz, Jun 10 2010]
||ah, the internet ate half my idea. I've rewritten the lost bit (its a bit terse; I'm worried it might happen again).
||The problem would be (if I understand) that it would not be
suitable for continuous operation - you need to drop the
objects singly or in small batches.
||Industrial eddy-current belt-type separators seem to handle
stuff of a reasonable range of sizes. In any case, you'd
probably want to be shredding the input material in order to
recover maximum material from mixed-material items, no?
||Yep, the rubbish would be dropped in batches, but this would be frequent (every few seconds).
||The rubbish could be sorted iteratively: the slow to fall rubbish would be shredded and dropped again.
||The thing is, modern manufacturing sticks other
materials into and on the metals making them harder
to get a clean recovery product. The smaller the
material is chewed the more likely there will be only
metal to put through your non-ferrous spectrometer.