Column rougher flotation of fine niobium-bearing particles assisted with micro and nanobubbles

Abstract

Rougher column flotation pilot plant (80 kg h−1 of solids) studies, recovering pyrochlore (fine and ultrafine samples), compared separation parameters with and without the injection of nano and microbubbles. An aqueous dispersion of those bubbles, generated in a surfactant solution using a centrifugal multiphase pump coupled to a needle valve, was added to the column cell as dilution water (0.1 m3 h−1), after the conditioning stage. The results showed that, for the fine sample (D32 = 15 µm; D50 = 38 µm and about 5–5.8 % Nb2O5 feed grade), the injection of micro and nanobubbles enhanced the Nb2O5 recovery by 1.4% at similar concentrate grades. For the ultrafine and poorer feed grade sample (D32 = 1.5 µm; D50 = 4 µm and 1.9–2.3 % Nb2O5 feed grade), the flotation efficiency was higher, increasing the Nb2O5 recovery by about 4.8% while improving the concentrate grade by 30%(enrichment ratios varying from 5.2 to 6.6). The results are explained by the interfacial mechanisms involving the enhanced capture of particles by a combination of nano (30–800 nm diameter), micro (30–100 µm diameter), and coarse bubbles (>600 µm diameter). This appears to confirm the multi-sized bubbles concept and importance in flotation whereby the finest bubbles seem to attach rapidly to the pyrochlore particles acting as “seeds” for the coarser bubbles to adhere. This alternative was proved at high flow-rate pilot scale in long trials, permitting to conclude its high potential in the recovery of fine and ultrafine minerals by flotation, especially in these valuable low grade niobium-bearing particles.