Vibration and gravity, gold having a much higher density. Mercury amalgamation is another way, extremely efficient, but you'll have to distillate the mercury for recovering the gold. Not difficult, but mercury is toxic so this should be done in a special equipement, not in air.

Alain

http://www.goldrushnuggets.com/figore.html

http://www.elmergates.com/by_others/mgovern_pure_gold.pdf

http://www.recyclingsecrets.com/free-reports/refining-precioius-metals-waste-cm-hoke.pdf

If you're trying to separate gold from common dust just get one of those bagless vacuum cleaners and modify it. They're even clear so you can watch the gold particles separate. They're cheaper than anything else you could make too.

@Dudley: Can you please elaborate your method?

I liked Alain's method of using Hg for quantification and separation of gold but it can be risky also.

@Ali: I even like your ideas but they are time consuming. I am still reading your third link and this one seems interesting. Hopefully i can get some insights out of it.

@Everyone: Also is there any means by which, given a sample of the dust generated in our industry, we can estimate the % gold present in it quickly?

Thanks in advance!

Adapted from Dudleys idea, weigh the amount of dust on a balance, blow gently the dust away and determine the residue.