Attachment, Coalescence, and Spreading of Carbon Dioxide Nanobubbles at Pyrite Surfaces

Recently, it was reported that using CO₂ as a flotation gas increases the flotation of auriferous pyrite from high carbonate gold ores of the Carlin Trend. In this regard, the influence of CO₂ on bubble attachment at fresh pyrite surfaces was measured in the absence of collector using an induction timer, and it was found that nitrogen bubble attachment time was significantly reduced from 30 ms to less than 10 ms in CO₂ saturated solutions. Details of CO₂ bubble attachment at a fresh pyrite surface have been examined by atomic force microscopy (AFM) measurements and molecular dynamics (MD) simulations, and the results used to describe the subsequent attachment of a N₂ bubble. As found from MD simulations, unlike the attached N₂ bubble, which is stable and has a contact angle of about 90°, the CO₂ bubble attaches, and spreads, wetting the fresh pyrite surface and forming a multilayer of CO₂ molecules, corresponding to a contact angle of almost 180°. These MDS results are complemented by in situ AFM images, which show that, after attachment, CO₂ nano-/microbubbles spread to form pancake bubbles at the fresh pyrite surface. In summary, it seems that CO₂ bubbles have a propensity to spread, and whether CO₂ exists as layers of CO₂ molecules (gas pancakes) or as nano-/microbubbles, their presence at the fresh pyrite surface subsequently facilitates film rupture and attachment of millimeter N₂ bubbles and, in this way, improves the flotation of pyrite.