On the role of nanobubbles in particle–bubble adhesion for the flotation of quartz and apatitic minerals

This work evaluated the influence of nanobubbles (150–200 nm, mean diameter) on the visual adhesion of microbubbles (70 μm mean diameter) and macrobubbles (1 mm mean diameter) onto selected mineral particles (quartz and apatite) and on the flotation of both minerals, at bench scale. The adhesion of bubbles to high purity grains of quartz and apatite was monitored using a specially designed photographic technique. The results showed that the highest adhesion of bubbles onto the mineral grains occurred only after “conditioning” with nanobubbles. The nanobubbles appear to adhere to hydrophobic surfaces and confined to the rough surfaces of the grains, probably due to the dissipation of the free surface energy of the solids. As a result, the nanobubbles appear to serve as nuclei for enhanced adhesion of micro and/or macrobubbles, assisting the flotation of both minerals. In the case of quartz (D50 = 290 μm), the recovery increase was about 23% compared to a standard test of flotation with macrobubbles only. Furthermore, flotation kinetics was rapid and quartz recovery, at the first min, was double that obtained in the absence of nanobubbles. In the case of a fine apatitic ore (35% < 37 μm particles), best results were obtained with a combination of nano, micro and macrobubbles, with a 500–1000 g t−1 saponified soybean oil collector and a 300–600 g t−1 gelatinized corn starch depressant of iron bearing minerals. The P2O5 recoveries increased about 9% compared to flotation with macrobubbles only, and separation also occurred at a higher rate. The total recovered phosphate (4 min standard test) was obtained in the first 1.5 min, after conditioning with nanobubbles, followed by injection of and microbubbles. Results validated the reported high potential for nanobubbles in “surface conditioning”, the first stage of mineral flotation and were explained in terms of the solution and interfacial phenomena involved.