Dr Jingyi Wang and Mr Lei Xie - Student Seminar Presentation - May 12 2015

C5MPT Student Seminars

Dr. Jingyi Wang and Mr. Lei Xie

University of Alberta,

Chemical and Materials Engineering

May 12, 2015 | ETLC 6-060

9:30 am




Flotation is an important and versatile mineral processing step used to achieve selective separation of minerals and gangue, which generally rely on the surface interactions (mainly hydrophobic interactions) between air bubbles and mineral surfaces. Fully solving the challenging issues involved in sulfide mineral flotation highly relies on a fundamental understanding of the interfacial (physical and chemical) properties as well as the intermolecular and surface interactions involved in the respective mineral systems.

(Jingyi WANG) The interactions between xanthate treated sphalerite particles and air bubbles were examined using induction time measurement, which revealed that the salt ions could inhibit the adsorption of xanthate on sphalerite due to the competitive adsorption, but also could compress the electrical double layer at mineral/water interface, and the water composition (e.g. Ca2+, Mg2+) could play an important role in the bubble–particle interaction. The hydrophobicity, chemical composition, and charge property of PAX treated sphalerite surfaces were characterized using contact angle measurement, Cryo-X-ray photoelectron spectroscopy (Cryo-XPS) and zeta potential determination, respectively, which support the inhibition effect of salt ions on the xanthate adsorption on sphalerite. In the case of saline water, the xanthate decomposition products were confirmed by XPS, which could further lower the hydrophobicity of the treated sphalerite.

(Lei XIE) An atomic force microscope (AFM) bubble probe technique was employed, for the first time, to directly measure the interaction forces between an air bubble and sphalerite mineral surfaces of different hydrophobicity (i.e., sphalerite before/after conditioning treatment) under various hydrodynamic conditions. The direct force measurements demonstrate the critical role of the hydrodynamic force and surface forces in bubble−mineral interaction and attachment, which agree well with the theoretical calculations based on Reynolds lubrication theory and augmented Young−Laplace equation by including the effect of disjoining pressure. The hydrophobic disjoining pressure was found to be stronger for the bubble−water−conditioned sphalerite interaction with a larger hydrophobic decay length, which enables the bubble attachment on conditioned sphalerite at relatively higher bubble approaching velocities than that of unconditioned sphalerite. Increasing the salt concentration (i.e., NaCl, CaCl2) leads to weakened electrical double layer force and thereby facilitates the bubble−mineral attachment, which follows the classical Derjaguin−Landau−Verwey−Overbeek (DLVO) theory by including the effects of hydrophobic interaction.