Flotation separation of mixtures of coal and silica particles falling onto a moving water surface

Flotation is used extensively in mineral processing to separate valuable minerals from unwanted gangue material. Typically, the solids are suspended in the pulp and captured by bubbles which then rise to the surface to form a froth concentrate. In flotation, much of the energy utilization is directed into the creation of fine bubbles to increase collision efficiency and product recovery. This study was aimed at quantifying the flotation performance of mixtures of hydrophobic and hydrophilic particles being dropped directly onto a moving water surface. Mixtures of coal and silica particles (0-100 wt% coal), with diameters 180-212 micrometers, were dropped from 300 millimetres above the water surface at a surface loading of approximately 0.03kg/m²•s, corresponding to 0.11m² particles/m² water surface per second. The grade and recoveries of the coal product were found to be 90-92% and 96-100%, respectively, and corresponded well with the theoretical prediction of fall height where the coal particles float while the silica particles sink. It seems, therefore, that the modelling for single particle interaction with a free surface is broadly applicable to different particle mixtures