- Title
- Fast flotation in a reflux flotation cell
- Creator
- Jiang, Kaiqi
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The research undertaken in this study was based on a novel flotation device, the Reflux Flotation Cell (RFC). This system consists of multiple parallel inclined channels positioned below a vertical chamber. The inclined channels provide an effective increase in the cross-sectional area of the vessel, thus permitting enhanced bubble-liquid segregation efficiency when the bubbles are conveyed into the inclined channels. In this thesis, fast flotation is defined as simultaneously maximising three fundamental flotation aspects: the kinetics for particle collection by bubbles, the supply of bubble surface area flux for particle extraction, and the segregation of the fine bubbles from the tailings flow. Only one or two aspects can be addressed effectively using conventional flotation systems, hence those systems are constrained by the rate limiting aspect. The RFC, however, offers the potential to achieve increases in all three areas, meaning the concept of Fast Flotation can be achieved, delivering very high flotation rates per unit of vessel area. The study firstly addressed the hydrodynamics of the RFC. Drift flux theory was used to describe the performance of the conventional vertical flotation column, predicting the theoretical gas flux, liquid flux, and the bubble surface area flux under the flooding condition. The capacity advantage, developed from the Reflux Classifier to describe the enhanced processing rate using inclined channels, is utilised to estimate the enhancement of bubble surface area flux. The theory showed the bubble surface area flux of the RFC could be increased to well beyond the typical levels of conventional flotation systems under flooding condition. A series of experiments was conducted using the laboratory RFC based on the bubble-liquid system. The experimental work achieved a bubble surface area flux of about 600 m²/m²/s, more than an order of magnitude larger than achieved in conventional flotation. Another series of experiments, having the same operating conditions as in the RFC system, involved the use of a vertical column. Extreme gas fluxes of up to 5.5 cm/s, and feed fluxes of up to 16 cm/s were applied, significantly higher than the conventional operating ranges. The results showed the inclined channels greatly enhanced the bubble-liquid segregation, preserving the fraction of feed liquid reporting to overflow to well below 24%. By comparison, 50% to 80% of the feed liquid was conveyed to the overflow using the vertical column, driven by the need to prevent bubbles reporting to the underflow, thus exhibiting very inefficient segregation. Hydrodynamic investigation of the RFC system showed great potential to achieve fast flotation. Thus the second part of the study involved the processing of low pulp density fine coal slurries collected from the overflow of the hydrocyclone in a coal preparation plant. Three slurry pulp densities of 0.34 wt%, 3.0 wt%, and 5.2 wt% were processed. Very high feed fluxes in the range of 10 to 12 cm/s, more than ten times higher than the typical level of conventional flotation, and high gas fluxes from 2 to 6 cm/s were used. Combustible recoveries between 66% and 78% were obtained for the extremely low feed pulp density of 0.34 wt%. A near complete recovery of 98% was achieved for the coarser particles above 38 µm. By increasing the feed pulp density, the overall combustible recoveries were largely maintained, reaching up to 86%, while there was a decline in the recovery of the particles above 38 µm. The underflow discharging rate, affecting the overflow rate and the overflow liquid split (fraction of feed liquid reporting to overflow), determined the amount of gangue particles transported to product. The product ash was reduced by increasing the underflow rate, leading to a product ash of 18%, well below the feed ash of about 50%. The rejection of the mineral matter increased almost linearly as the overflow liquid split was decreased. The final part of the thesis was concerned with the flotation kinetics within a single channelled downcomer. The drift flux model was utilised to analyse the bubble volume fraction of the two-phase downward flow by varying the gas flux and the liquid flux. Graphical analysis of the drift flux curve and operating lines showed the bubble volume fraction in the flow was reduced with an increase in the liquid flux and a decrease in the gas flux. The flotation performance of three downcomer channel gaps of 2 mm, 4.5 mm, and 9 mm, were experimentally examined using a clean coal feed. The bubble-particle interaction in the downcomer was affected by the shear rate and the fluid turbulence inside the downcomer channel for a given gas flux and feed flux. The investigation of partition numbers showed that the particle recovery for a given particle size was improved with increasing gas flux, and decreasing feed flux for the narrower downcomer channel gaps of 2 mm and 4.5 mm. For a given feed flux and gas flux in the downcomer, higher particle recovery was achieved using the downcomer channel gaps of 2 mm and 4.5 mm. The first-order kinetic constant in the downcomer was obtained using a plug flow model. The downcomer kinetic constant was related to the particle size, the gas flux and feed flux in the downcomer. The correlations of the downcomer kinetic constant with the particle size, the downcomer gas flux and the downcomer feed were developed to provide a consistent basis for assessing the recovery performance for the three downcomer channel dimensions. The 2 mm and 4.5 mm channelled downcomers showed superiority for a wide range of feed fluxes when using high gas fluxes.
- Subject
- flotation; bubble surface flux; fine particle flotation; fast flotation; desliming flotation; coal tailing; inclined channels; segregation; reflux flotation cell; flotation kinetics; bubble–liquid segregation; bubble interfacial flux; coal
- Identifier
- http://hdl.handle.net/1959.13/1342434
- Identifier
- uon:28966
- Rights
- Copyright 2017 Kaiqi Jiang
- Language
- eng
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