Improved flotation of PGM tailings with a high-shear hydrodynamic cavitation device

Abstract Fine liberated valuable particles are often lost to flotation tailings due to inefficient collection by air bubbles, and passivation of their surfaces by oxidation products and slimes when reclaimed from tailings dams. Extensive research covering a diverse range of technologies has been undertaken over the years to find feasible solutions to this problem, with only relatively minor success at an operations scale. A more recent and practical prospect which has already found application in the mining industry is the use of hydrodynamic cavitation devices (HCDs), causing the nucleation of ultrafine (nano) bubbles (NBs) on the surfaces of fine valuable particles, thus aiding their agglomeration and subsequent recovery by micro-bubbles (MBs) and normal sized (macro) flotation bubbles. This paper details investigations that have been undertaken on the Mach HCD reactor, using rougher, cleaner and recleaner feed samples sourced from a UG2 Platinum Group Metal (PGM) tailings operation. The results suggest that the formation of NBs and MMBs, together with enhanced cleaning of particle surfaces, were the dominant mechanisms. This not only lead to activation of valuable mineral surfaces but also depressed the recovery of gangue. The flotation kinetics were analysed using the modified Kelsall model, showing significant improvements in the maximum (fitted) recovery Rmax, together with a reduction in mass pull, for the optimum number of passes of the various feed samples through the reactor. The contributions to the increased recovery due to additional liberation of PGMs from the chromite grains and the increased gas holdup, are being investigated further.