Flotation of quartz particles assisted by nanobubbles

•The quartz particle flotation assisted by nanobubbles (200–720 nm) was investigated.•The nanobubbles increased the contact angle at the quartz/water interface.•The nanobubbles improved the flotation recovery of the ultrafine quartz fractions.•Main mechanisms were enhancement of hydrophobicity and aggregation of ultrafine quartz particles.

Experimental studies of flotation of quartz particles, under various conditions and cells (setups), are presented. Pure and well-characterized quartz samples were treated with a commercial alkyl ether monoamine as flotation collector with bubbles in various sizes: coarse bubbles (400–800 μm); nanobubbles (200–720 nm); and their mixtures. The nanobubbles were generated by selective separation from microbubbles, which are formed together after depressurizing-cavitation of the saturated water in air (as in pressure flotation or dissolved air flotation), at 66.1 psi saturation pressure. Flotation with single nanobubbles was not effective due to their very low lifting power or practically nil buoyancy. Yet, size-by-size flotation recoveries with coarse plus nanobubbles, compared with coarse bubbles, enhanced by 20–30 % the very fine quartz fractions by 20–30% (8–74 μm; Sauter diameter—D32) and slightly lowered the recoveries of coarse particles (67–118 μm; D32 diameter). Flotation of quartz samples (composites) having wide particle size distribution and results in a mechanical cell validated the overall recovery enhancement of the fines. Fine particle capture (nanobubbles enhanced the contact angle of quartz) and aggregation of the quartz ultrafines (proved with micrographs) by the nanobubbles are the main mechanisms responsible for the higher recoveries. The effect on flotation of the coarser quartz fractions, at bench scale, may be explained in terms of a reduced rising velocity of the coarse bubbles, in the presence of nanobubbles, decreasing the degree of bubble carryover. It is expected that the use of collector-coated nanobubbles (tailor-made “bubble-collectors” and flocculants) will broaden options in fine mineral flotation. The future sustainable forms (cheaply produced) of nanobubble generation on a large scale and their injection in cells are envisaged.

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