Dissolved air flotation (DAF) of fine quartz particles using an amine as collector

Experimental studies concerning the dissolved air flotation (DAF) of fine (d(p) < 100 pm) quartz particles, using two different flotation cells (setups), are presented. Pure and well characterised quartz samples were treated with a commercial amine as collector prior to notation and bubbles were characterised by the LTM-BSizer technique. Bubble size distribution showed 71% (by volume) and 94% (by number) of the bubbles having sizes (d(b)) lower than 100 mu m (i.e. microbubbles). The Sauter and arithmetic mean diameters were 79 mu m and 56 mu m, respectively, for the bubbles generated at 300 kPa (gauge) saturation pressure (after 30 minute saturation time). Quartz particle size distribution (obtained by laser diffraction) showed a volume-moment diameter of 13 mu m. The Rosin-Rammler-Bennett, Gates-Gaudin-Schumann and log-normal distribution functions were well fitted (R-2 > 0.96) to the bubble size distribution and quartz particle size distribution data. Values of total quartz recovery ranging from 6% to 53% (by mass) were obtained for the DAF experiments under different collector concentrations (up to 2 mg g(-1)). with an optimal collector concentration found at 1 mg g(-1). These results are significant considering that 27% (by volume) of the quartz particles are ultrafine (d(p) < 5 mu m), demonstrating the widely-known efficiency of DAF to remove small particles when applied in the field of water and wastewater treatment. The true flotation behaviour, as a function of particle diameter (d(p)), exhibits a local minimum when particles are approximately 3-5 mu m in size. The results contribute to the discussion in the literature about the existence Of Such a minimum, which is generally interpreted as a change in the mechanism of particle collection from convection (collision) to diffusion at lower particle sizes. (C) 2008 Elsevier B.V. All rights reserved.