How to Separate Wood from Plastic?

Try a "Static" charged surface.

Maybe you could soak the bead and wood particle mixture in a water-based ferrofluid. The idea being that the wood particles will absorb the ferrofluid, while the plastic beads would not. Then you could use a magnet to separate the now-magnetic wood chips from the plastic beads.

Here's a link to a Wiki article on ferrofluids: http://en.wikipedia.org/wiki/Ferrofluid

Depending on the density difference, you mgiht be able to seperate them with an air stream. Blow the wood chips up, and away from the granules.

"My guess is that the wood is from the pellets."

My guess is you mean pallets, not pellets.

This may not be feasible, but I'll throw it out anyway. I don't know if you're getting the beads from one source or many. If they are coming from one source, the most cost effective solution may be to track the beads back to the source, find out what the source of the wood chips is, and eliminate it there, before they get to you.

Sounds like a seeds-and-stems separation problem. Maybe food processing has a solution. The plastic granulated beads will roll, but the wood fragments are not spherical so they will drag. So pour the mix down a gently sloping dry screen and see if the wood fragments stick to the screen while the beads roll to the bottom where they can be collected.