Abstract: A system operating in accordance with the method of the invention can be compared to a single stage enrichment by noting that in the single stage system, 100% (or all) of the underflow output of the first stage would go into refuse, i.e. whatever desirable product is contained in the underflow of the first stage would be lost. In contrast to this system, in accordance with invention, a middling fraction is directed back into stage 2 (along with spoil) which results in self-enriching the material undergoing separation in the second stage. Eventually the enriched coal will be contained in that portion of the overflow output of the second stage which is directed back to the first stage, and for that reason the losses going into the spoil will be reduced in comparison to the enrichment loss in the first stage.