PNNL

Abstract

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 AFM measurements and MD simulations, and the results used to describe the subsequent attachment of an N2 bubble. As found from MD simulations, unlike the attached N2 bubble, which is stable and has a contact angle of about 90 degrees, the CO2 bubble attaches, and spreads, wetting the fresh pyrite surface and forming a multi-layer of CO2 molecules, corresponding to a contact angle of almost 180 degrees. These MDS results are complemented by in-situ AFM images, which show that after attachment, CO2 nano/micro bubbles 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 or as pancake nano/micro bubbles, 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. The U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences, funded the work performed by L.X.D.