magnetic separator

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.