Flotation is arguably the most important mineral separation technique. It has been demonstrated that hydrophobic nanoparticles adsorbed onto hydrophilic mineral surfaces can facilitate mineral particles attachment to air bubbles in flotation process. This thesis explores the effects of nanoparticle adhesiveness, size and shape on the performance of nanoparticle flotation collectors. For this, a series of rigid polystyrene, soft shelled polystyrene-poly (n-butyl methacrylate) (PS-PB) and soft lobed polystyrene/poly (n-butyl methacrylate) (PS/PB) Janus nanoparticles were prepared and characterized. Flotation experiments with glass beads, a model for mineral particles, revealed that soft-shelled particles were more effective collectors than were hard polystyrene particles. The small (92 nm) Janus particles were particularly good flotation collectors for glass beads.
The pull-off forces required to remove nanoparticles from glass were measured by AFM and the results were compared to the abilities of the nanoparticles to induce the flotation of hydrophilic glass beads. Soft PS-PB particles were strongly adhering and were very effective nanoparticle flotation collectors. By contrast, hard PS particles were weakly adhering and were poor flotation collectors. These observations led to the hypothesis that weakly adhering nanoparticles were dislodged from the glass bead surfaces during flotation. Experimental support for this hypothesis included: (1) the coverage of nanoparticle on glass bead surfaces decreased with increased conditioning time; (2) large nanoparticles aggregates were detected in flotation pulp as well as on bead surfaces; and, (3) dislodged soft-shelled PS-PB particles left polymeric patches, we call footprints, on the glass bead surfaces. Indeed, the presence of the footprints, suggests that a nano-scale stamping process can be used to cover surfaces with hydrophobic polymer footprints.
Arguments are made that hydrodynamic forces alone were insufficient to detach the small nanoparticles from the glass bead surfaces in our experiments. Instead, it is proposed that bead-bead collisions during conditioning and flotation caused weakly adhering particles to detach; a process is termed as “nano-scale ball milling”. Furthermore, geometric arguments show that during a bead-bead encounter, larger nanoparticles are more susceptible to removal than small particles which is consistent with the experimental data.
Although all experiments were performed with model glass beads and rather simple nanoparticles, this work has for the first time explained why larger polystyrene nanoparticles are ineffective flotation collectors. The work highlights the need to consider nanoparticle/mineral adhesion when designing collectors for real mineral systems. / Dissertation / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20957 |
| Date | January 2017 |
| Creators | Dong, Xiaofei |
| Contributors | Pelton, Robert, Chemical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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