Dusts are obtained by macerating their respective ores, all ores apart from Coal, give 2 pieces of Dust when macerated. Metal Dusts can then be smelted into ingots of their respective metal (but using an EE transmutation tablet to change the dusts into their respective ingots is much cheaper than smelting them) and Coal Dust can be crafted into Raw Carbon Fibers. Macerating ores before smelting them will give you 200% of your normal ore yield, at the cost of the energy to macerate each ore before smelting.
If you macerate Refined Iron, you will end up with a piece of Iron Dust, which can then be smelted to become an iron ingot. This is useful if you have a surplus of Refined Iron and wish to make non-Industrial items that need iron.
Refined Iron dust exists in the game, but can be only obtained by getting a Rotary Macerator and placing iron in the first slot and coal in the second slot (and by powering it, of course).