Conventional flotation machines are effective for fine particle size classes. However, limitations due to particle buoyancy and bubble-particle detachment restrict their effectiveness when floating coarse particles. As a result, flotation circuits are generally configured to maximize the recovery of particles finer than 150-200 micron. In fact, grinding circuits expend significant energy reducing a feed stock to a particle size range suitable for flotation.
Increasing the upper size limit of coarse particle flotation has been a long-standing challenge in the minerals processing industry, and losses of values to tailings can often be attributed not only to ultrafines, but to particles too coarse to float. Some time ago I commented on the loss of copper in the final tailings at Nchanga (posting of 21st August), and Nchanga mineralogist Fuzail Siddiqui responded, attributing these losses to chalcocite particles as large as 0.5mm which were too coarse to float. He had even recommended the introduction of a step to regrind the coarsest fraction of the feed to bring the sulphide particles in floatable size range, but this was not implemented. Instead unsuccessful attempts to float the leach reside in columns were made.
If the particle size that could be effectively recovered in a flotation cell could be increased, the product size from grinding could be significantly coarsened, resulting in a more eco-efficient flowsheet. A number of strategies that could potentially increase coarse particle flotation recovery will be discussed at Flotation ’13 by Erico Tabosa and Kym Runge, of
|The HydroFloat Separator at Metplant '13|