Surface chemistry aspects of flourite and bastnaesite flotation systems.

摘要

In this dissertation research, the surface chemistry aspects of the alkaline earth semisoluble salt mineral fluorite (CaF2) and the rare earth (RE) semisoluble mineral bastnaesite ((Ce, La) CO 3F) were investigated. The primary objective is to provide fundamental understanding of the surface chemistry features for both fluorite and bastnaesite minerals including the wetting characteristics, electrokinetic features as well as collector adsorption properties.;First, the surface chemistry aspects of fluorite were examined with particular interest in investigating the effect of crystal structure differences on the wettability as well as the surface charge characteristics. Results from contact angle measurements, MD simulations and sum frequency vibrational spectroscopy (SFVS) analysis indicate that the different fluorite surfaces (111, 100 and 110) exhibit different wettability features. The 111 surface exhibits moderate hydrophobicity, while the 100 and 110 surfaces are hydrophilic. Flat plate streaming potential measurements at the different fluorite surfaces show that cleaning procedure has a significant effect on the surface charge of fluorite surfaces. The controversial zeta potentials at different fluorite surfaces might be due to the different cleaning methods.;Then the surface chemistry features of bastnaesite including wetting characteristics, electrokinetics and hydroxamate adsorption at low concentrations were investigated. Effect of CO2 pressure on the stability diagram of bastnaesite was considered and the surface charge properties from electrophoresis measurements were explained using the stability diagram. Bastnaesite was found to be naturally hydrophilic from both contact angle measurement and MD simulations. The adsorption isotherm at low levels of hydroxamate adsorption was established by the solution depletion technique and contact angle measurements. The relationship between hydrophobicity and adsorption density was examined by MD simulations for the first time. The SFVS spectra indicate a well-ordered monolayer was formed at a hydroxamate concentration of about 1 x10-4 M.;It is expected that the findings for this dissertation will provide fundamental understanding of the flotation chemistry for fluorite and bastnaesite, make improvements in procedures for the strategy of flotation chemistry and provide a foundation for improved flotation technology in the future.