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

Recently, it was reported that using CO 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 CO 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 CO saturated solutions. Details of CO 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 N bubble. As found from MD simulations, unlike the attached N bubble, which is stable and has a contact angle of about 90°, the CO bubble attaches, and spreads, wetting the fresh pyrite surface and forming a multilayer of CO molecules, corresponding to a contact angle of almost 180°. These MDS results are complemented by in situ AFM images, which show that, after attachment, CO nano-/microbubbles spread to form pancake bubbles at the fresh pyrite surface. In summary, it seems that CO bubbles have a propensity to spread, and whether CO exists as layers of CO molecules (gas pancakes) or as nano-/microbubbles, their presence at the fresh pyrite surface subsequently facilitates film rupture and attachment of millimeter N bubbles and, in this way, improves the flotation of pyrite.