A method of enhancing the recovery of useful coal or potassium chloride from screenbowl centrifuge separation operations comprising adding to the screenbowl centrifuge, from about 0.005 lbs active polymer/ton dry solids in centrifuge to about 0.70 lbs active polymer/ton dry solids in centrifuge, of an anionic copolymer, wherein said anionic copolymer is selected from the group comprising copolymers of acrylamide and acrylic acid and the known salts thereof.