| Description |
In this dissertation research, Molecular Dynamics Simulation (MDS), Sum Frequency Vibrational Spectroscopy (SFVS), and contact angle measurement have been used to investigate the wettability and interfacial water structure at selected mineral surfaces. The primary objective is to provide fundamental understanding of the hydrophobic surface state, a state of special interest in particle separations by froth flotation. First, MDS interfacial water features, including water number density profile, water residence time, water dipole orientation, and hydrogen bonding analysis, at selected hydrophobic mineral surfaces (graphite (001) surface and octadecyltrichlorosilane (OTS) monolayer on quartz) and at selected hydrophilic mineral surfaces (quartz (001), sapphire (001), and gibssite (001) surfaces) have been evaluated and compared to the corresponding SFVS experimental results. A "water exclusion zone" of 3 A accounts for the "free OH" vibration (from both MDS water dipole orientation analysis and SFVS spectrum) at hydrophobic surfaces. In addition, a water residence time of less than 10 ps and about 2 hydrogen bonds have been found for surface water molecules at the selected hydrophobic mineral surfaces. Sessile drop wetting characteristics of the hydrophobic molybdenite (001) surface and the hydrophilic quartz (001) surface have been examined by MDS and by contact angle experiments to determine the effect of drop size, advancing/receding contact angles, and spreading time on wettability. In addition, film stability and bubble attachment at the hydrophobic molybdenite (001) surface and the hydrophilic quartz (001) surface have been studied by MDS for the first time and the results compared with corresponding experimental captive bubble contact angles. At the hydrophobic molybdenite (001) surface, the water film is unstable and ruptures, while the water film at the hydrophilic quartz (001) surface does not. Finally, the wettability and interfacial water features of sulfide/telluride mineral surfaces have been described with MDS for the first time. The interfacial water features of selected sulfide/telluride mineral surfaces under anaerobic conditions have been 2 + examined, as well as Cu activated sphalerite (110) and oxidized pyrite (100) surfaces, to determine which interfacial water features best identify the wetting characteristics of the selected mineral surfaces. In summary, it has been found that "water exclusion zone" and "free OH" vibration present for hydrophobic mineral surfaces, whereas, for hydrophilic mineral surfaces, the interfacial water is characterized by hydrogen bonding with the surface and relatively long water residence time. The interfacial water analysis of the selected mineral surfaces increases our fundamental understanding of the flotation chemistry associated with the mineral systems and is expected to provide a foundation for improved flotation technology in the future. |
