An axial inlet cyclone was developed and tested for wet size classification of particulate materials with the purpose of providing an alternative to the tangential inlet cyclone used traditionally in the mineral processing industry. The proposed device shared many of the fundamental features of a conventional cyclone, but had a circular opening on the roof of the cylindrical section and surrounding the vortex finder for feed entry, instead of a tangential inlet. The feed material spiraled down through that opening and generated the necessary spin for separation inside the cyclone. Experimental work was carried out on a sample of copper nickel mill tailings having a particle size of 91% passing 300 mum, and the performance of the cyclone was evaluated at different inlet pressures, feed pulp densities and vortex finder lengths. In comparison to the tangential inlet cyclone, the axial inlet cyclone provided higher throughputs, coarser cut-sizes in relatively dilute pulps, and greater flexibility and control over the cyclone separation process. (C) 2003 Elsevier Ltd. All rights reserved.