Filtration of fine mineral particles assisted by nanobubbles

Abstract

This study investigates the effect of nanobubbles (NBs) on the filtration rate of quartz and iron ore tailings (fine and coarse samples) using a bench-scale press filter operating at 8 bar. The NBs dispersion was generated through hydrodynamic cavitation in a needle valve after 25 min of air saturation in water at constant pressure (Psat = 2.5 bar). To assess the influence of particle size and hydrophobicity (amine conditioning) on the filtration rate, quartz samples with varying particle size distributions were employed. Subsequently, fine (Dm = 7 µm) and coarse (Dm = 90 µm) tailings were examined as a case study. These tailings were collected from the desliming hydrocyclone (prior to the flotation stage) and the floated product (silica and silicate particles) from the reverse cationic flotation of a Brazilian iron ore mill. Filtration tests were conducted with the quartz samples after treatment with 180 g t−1 of dodecyl-ether-amine at pH 7.5. The results revealed that NBs significantly improved the filtration rate (approximately 20%) for fine (Dm = 7 µm) and medium-sized quartz samples (Dm = 129 µm). Conversely, no substantial effect was observed with the coarse material (Dm = 307 µm), due to its higher porosity. The enhanced filtration rate was validated with fine iron tailings, where NB conditioning reduced the filtration time by about 30%. Similar to the results with quartz, this positive effect diminished when fines were mixed with coarse tailings because of the enhanced porosity of the resulting cake. The underlying operating mechanism seems to be the enhancement of mineral particle hydrophobicity induced by the NBs. In addition, theses bubbles reduce the capillary forces responsible for retaining liquid within the cake's porous section, allowing a more rapid flow of the filtrate. This technique appears to hold substantial potential for tailings management in the iron mineral industry, and extended trials at a pilot scale will be scheduled.