A fractional factorial design was carried out to determine the relative effects of various design and operating parameters on the performance of a 46 mm diameter Air-Sparged Hydrocyclone (ASH) in treating a sample of fines from a South African (Witbank) Colliery. The effect of (feed) pulp density was also investigated. The overall results indicated that the ASH beneficiated the coal successfully at capacities of up to 300 times those possible in conventional (batch) flotation, and in the region of 1500 times those achieved using the same coal in a column cell. The underflow configuration was found to be the most important design parameter; better results were achieved using an orifice with a horizontal baffle located above it as opposed to the conventional pedestal and annular opening configuration. ASH performance was also significantly affected by the cyclone length and by the A∗ ratio (overflow area to underflow area). Q∗ (air rate to slurry rate) was found to have a minor effect on the performance of ...