The influence of design variables on the flotation of pyrite in an air-sparged hydrocyclone

Abstract

Two batches of ore, A and B, from the reclaimed dumps of ERGO Ltd on the East Witwatersrand were used to investigate the effect of design parameters on the flotation of pyrite in an air-sparged hydrocyclone (ASH). In the ASH, air is sparged radially through a porous cylinder and dispersed by the high velocity of slurry in swirl flow, countercurrent to the froth phase rising axially in the centre of the cylinder. The concentrate overflows through the vortex finder, while the tailings flow downward. A spigot where flow is restricted by a horizontal baffle, positioned 30mm above the orifice, proved to be more successful than a spigot consisting of an annular opening between a pedestal and the cylindrical wall, and a flow restricting orifice below. Pyrite from both samples A and B was difficult to float efficiently. Sample A, which contained only 0.14%S, yielded typical sulphur recoveries of 40% and associated grades of 4%S in the ASH, while batch flotation yielded recoveries of 65% and grades of 11%S. The corresponding results for Sample B with a head grade of 1.42%S, were 40% and 7.5%S in the ASH, and 56% and 6%S in batch tests. From a variety of runs, it can be concluded that flotation in the ASH is influenced mainly by the tangential velocity and the hold-up of slurry. Hence, the effective design of an ASH is critically dependent on the dimensions of the cylinder, vortex finder and the spigot. For some ASH designs, flotation performance could be improved noticeably by sealing off the lower part of the porous cylinder.