The Effect of Comminution Mechanism on Particle Properties: Consequences for Downstream Flotation Performance

Timothy Vizcarra (2010). The Effect of Comminution Mechanism on Particle Properties: Consequences for Downstream Flotation Performance PhD Thesis, Julius Kruttschnitt Mineral Research Centre, The University of Queensland.

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Author Timothy Vizcarra
Thesis Title The Effect of Comminution Mechanism on Particle Properties: Consequences for Downstream Flotation Performance
School, Centre or Institute Julius Kruttschnitt Mineral Research Centre
Institution The University of Queensland
Publication date 2010-09
Thesis type PhD Thesis
Supervisor Dr. Elaine Wightman
Prof. N.W. Johnson
Total pages 174
Total colour pages 37
Total black and white pages 137
Subjects 04 Earth Sciences
Abstract/Summary Many particle properties critical to the flotation process originate from the comminution stage. A better understanding of how these properties are affected by the methods of particle size reduction used will help determine whether current strategies for comminuting ores can be modified to further enhance particle floatabilities. This thesis investigates how different comminution mechanisms affect the properties of ore and mineral particles and assesses how changes to these properties subsequently affect flotation performance downstream. Three ores were selected for this study: Northparkes (a low-grade, copper porphyry ore); Ernest Henry (an iron-oxide hosted copper-gold ore); and Century (a high-grade strataform zinc ore). These were each comminuted to various particle size distributions using a hammer mill and a piston-die compression unit (simulating the breakage mechanisms used by high pressure grinding rolls). Progeny particles were then characterised using the JKMRC’s mineral liberation analyser (MLA) on a size-by-size basis. It was found that size-by-size liberation properties were independent of both the mechanism used to comminute the ore samples, as well as the final size distribution of the progeny particles. This was observed for both valuable and gangue mineral phases. Variations in the liberation properties of a mineral in a given size fraction were explained in terms of the effect of mineral grade upon the statistical uncertainties of liberation measurements. Rather than being dependent on the method of breakage used to comminute an ore, liberation properties were instead found to be dependent on the mechanical properties of associated mineral phases. Where large differences existed between the mechanical properties of associated minerals, the “harder” mineral was found to be conserved during the breakage process, deporting directly to high-grade liberation classes upon size reduction without forming composite particles. These effects were not observed for “softer” minerals. The mechanism of comminution used was not found to have any effect on the liberation properties of the discharge particles. However, relationships were found between the shape properties of particles (quantified using the MLA) and the breakage devices from which they were discharged. Samples comminuted in the hammer mill were found to be comparatively more round than those discharged from the piston-die compression unit which, conversely, were more angular. This was attributed to rebreakage events during the hammer mill grinding process whereby topographical features on particle surfaces (such as sharp edges and corners) were chipped away, resulting in the production of round, spherical particles. The effect of particle angularity on flotation performance was subsequently tested by floating sized, fully liberated chalcopyrite particles that were comminuted in either the hammer mill or piston-die compression unit, and retrospectively analysing the angularity properties of the timed concentrates. It was found that, in the absence of collector, angular chalcopyrite particles exhibited faster flotation kinetics than comparatively round particles, likely due to the enhancement of particle-bubble adhesion mechanics as hypothesised by past studies. Additionally, surface chemistry analysis conducted in collaboration with the Ian Wark Research Institute also showed that the comparatively angular concentrates also had higher degrees of surface coverage by hydrophobic polysulphide species, and this is also likely to have contributed to their faster flotation kinetics. The results of this thesis clearly show that mineral liberation properties cannot be controlled by the method of breakage used. However, it is expected that the results will aid in the development of both empirical as well as fundamental mineral liberation models. Additionally, it is shown that a potential method of enhancing particle floatability during the comminution stage is through the manipulation of particle shape properties. This has important implications for the development of property-based flotation models as well as for the eventual integration of comminution and flotation models.
Keyword Mineral Liberation
High-pressure grinding rolls
Particle shape
Additional Notes Colour pages: 22,23,26,36,55,56,58,60,,61,63,69,70,71,83,84,85,86,87,88,93,94,111,119,123,124,125,126,136,139,142,144,148,151,154,156,159,160,164 Landscape pages 127-129

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Created: Thu, 31 Mar 2011, 21:43:01 EST by Mr Timothy Vizcarra on behalf of Library - Information Access Service