Despite their broad use and importance, inherent deficiencies of the hydrocyclone have negative effects on the efficiency and economics of a processing plant. In the processing of complex metal sulfide ores, density differentials between the gangue and the various sulfide minerals generally result in a sulfide metal concentration in the re-circulation stream of a closed-mill grinding circuit, which results in overgrinding and potential metal loss (Firlh etal, 1998: Mnsher, 1999). Also, …. (Heiskanen, 1993; Wills,1997). For these reasons, the U.S. mining industry and prominent researchers have identified the need for improved classification efficiency as a major research topic in a recent publication (Anon., 2000).