The role of gas nucleation and cavitation in flotation has been systemically studied. It was shown theoretically that about a 10 m high recovery zone is required to ensure at least one collision between a particle less than 10 $ mu$m and a bubble, under conventional column flotation conditions, indicating that the collision is the rate limiting step for fine particle flotation. Direct formation of small bubbles on the hydrophobic particle surfaces and in slurry by gas nucleation and cavitation has, therefore, been exploited as a way to accelerate the fine particle collection rate. / Experimentally, the existence of gas nuclei in water was demonstrated from coagulation, sedimentation and filtration tests of fine coal (d$ sb{50} approx 5 mu$m) and silica (d$ sb{50} approx 3.5 mu$m) particles. Small bubbles are generated, from the expansion of the pre-existing gas nuclei, by hydrodynamic cavitation induced by flow of liquid through a nozzle at a velocity of 8-15 m/s, depending on nozzle diameter and length. This velocity of bubble initiation is reduced 5-7 m/s when the liquid is gas-supersaturated. Surfactants do not affect the on-set of bubble formation by cavitation, but increase the amount of bubbles formed. The addition of a small amount of hydrophobic particles in gas-supersaturated systems increases the quantity of bubbles generated, while the presence of hydrophilic particles reduces bubble formation. / Dissolved air (or carbon dioxide) flotation of fine silica (d$ sb{50} approx 1.6 mu$m) has shown that recovery increases with the slurry flow velocity, regardless of the saturation pressures applied (102-310 kPA). Releasing the gas-supersaturated slurry into a solution gives a higher recovery than releasing the gas-supersaturated slurry into a slurry. These observations suggest that bubble nucleation is a better mechanism for enhancing particle collection compared with the direct particle-bubble contact. / Flotation results using a newly designed flotation reactor indicate that adding a cavitation tube and a small amount of air in the feed stream increases recovery significantly, and that bubbles formed by hydrodynamic cavitation play a role in improving flotation kinetics, even in the absence of added gas in the stream.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.40477 |
| Date | January 1996 |
| Creators | Zhou, Zhi-ang. |
| Contributors | Xu, Zhenghe (advisor), Finch, J. A. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Mining and Metallurgical Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001536643, proquestno: NN19790, Theses scanned by UMI/ProQuest. |
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