Is it possible to make iron shavings to be dust? 
I'm considering how to separate iron shavings from iron. In the picture, there are some iron chunk and iron shavings. The problem is iron shavings are not dust. I want to make the iron shavings to be dust and fall through the holes. Even I don't know well, In my thinking, when pressure is be higher, the iron shavings could be dust. I'm not sure.. anybody can help me??
 A: If your question is about how to reduce small particles of iron into smaller particles, I would try using some form of grinder designed for very small particle output. Possibly some form of conical burr grinder similar to the hand cranked ceramic burr ones used for grinding coffee beans. A possible problem is that too much heat caused by grinding will result in chemical reaction between air and iron, probably creating ferric oxide (rust) when oxygen combines with the iron. If you are doing this at home, I would freeze the iron particles prior to grinding and avoid grinding too fast.
If your question is about how to separate small enough particles (dust)of iron from larger but still small particles, I recommend using airflow through a screen under a pile of iron particles, with a vacuum at the top to capture the dust. The smaller the particle is, the more easily air will lift it up for vacuum capture. Adjusting air flow will alter the size of particles captured.
If you need to separate iron from non-iron, a quick way is using an electromagnet. Don't use a permanent magnet, since getting the iron off the magnet afterward will be difficult.
A: I presume that you wish to avoid grinding the lumps of iron into dust.
The difficulty with your proposal is finding some way of grinding the shavings to dust without also grinding the lumps of iron.  If you can find some way to separate them first that would work - but then the problem would be solved without any need for grinding.
To separate them you must use some difference between the physical or chemical properties of the lumps and the shavings.  
The grinding process might work because the 'shavings' seem to be clumps of fine particles and might disintegrate under a small applied force.  You could perhaps shake them together violently so that the harder lumps grind the softer clumps without getting broken up themselves.
If the shavings are clumps of dust they might have a lower density than the solid lumps and might float in heavy oil whereas the lumps sink.  For the same reason shavings would sink more slowly than the lumps, so you could separate them by tipping them all into a tall column of water or oil and removing the lumps from the bottom before the shavings reached the bottom.
The difficulty of finding a liquid of intermediate density can be overcome by  using fine particles (of iron, preferably, otherwise sand) and vibrating them to simulate a fluid.  The 'density' of this fluid can be varied by altering the frequency and amplitude of vibration.  At some point the clumps may 'float' while the lumps sink.  Then you can scrape off the top layers of clumps and fine particles and sieve the bottom layers of fine particles and lumps.
Unless this is a process which you will repeat on a large scale, the simplest solution is to pick the lumps out by hand.  They seem to be easily distinguishable from the clumps.  Even if you intend to repeat this process it is worth comparing the cost (also effectiveness, reliability, etc) of paying someone to do this mundane job with the cost of installing, operating and servicing complicated machinery to do the job (which might break down).
