The effect of agitation on the flotation of platinum ores

Flotation is routinely used for the beneficiation of platinum ores for which the bulk of world production is from South Africa. Most South African platinum concentrators use mechanically agitated flotation cells which operate with power intensities higher than the typical industrial range of 1.0-2.0 kW/m3. This is due to the general philosophy in the platinum industry that increasing power intensity is beneficial to the flotation of finer particles. This paper investigates the influence of agitation on flotation with reference to results from tests on two pilot-scale mechanical flotation cells on South African platinum concentrators. Flotation tests were conducted on a 60 l forced-air flotation cell and a bank of four 150 l induced-air flotation cells over a range of impeller speeds, air flow rates and feed types. Flotation results demonstrate that increasing the level of agitation generally has a beneficial effect on the rate of flotation of platinum ores but that this is accompanied by significant decreases in concentrate grade. These decreases may be due to increases in entrainment or in the rate of flotation of poorly liberated (low grade) particles or floatable gangue. However, since platinum ores are measured in parts per million, relatively small amounts of additional gangue reporting to concentrate will impact significantly on concentrate grade.