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I am trying to separate small dark particles from bright white ATH (alumina tri-hydrate) to avoid visual defects when casting solid surface product sheets.   Particle size of contaminate can be smaller than the particle size of the ATH.   I need to sort clean ATH at a rate of 100 lbs/min for production requirements.   Any ideas would be appreciated.

Do you know what the dark particles are?  Are they metallic..ie. attracted to a magnet?  If the substance isn't metallic, you'll need to determine what it is and you may have to consider a chemical (rather than mechanical) means of separation.  Where are the particles coming from in the first place?

Thank you for your response.  I considered the possiblity of magnetic separation however, the majority of the dark partiulates do not adhere to a magnet.  Since the ATH is a refined bauxite ore, I suspect some of the off-color particulates are organic contaminates called "hubites".  I also find traces of material that appears to be a by-product of the manufacturing process, dried lubricant from equipment bearings, possible shavings from contact fit machine components, etc.   The main reason to separate these impurities is visual, regardless of their composition.  Can you point me in the direction of a chemical separation method you mentioned?  Any info is appreciated.

         I don't know of any specific resources and I'm not sure if you'd have much luck yourself.  I recommend some testing to find a solvent that dissolves the "hubites", but not the ATH.  You'll need to consider other issues such as drying the product after separation and disposal (or recycling) of the solvent.  I really don't see an easy answer here, it just takes some good old-fashioned research to solve this problem.  Of course, you could contact someone else in this industry and ask if they've ever come across this problem.  I certainly wish you luck...I guess this is why the world has engineers!