- Title
- Gravity separation and desliming using inclined channels subject to different G-forces
- Creator
- Carpenter, James Lachlan
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The separation of ultrafine particles is a difficult and costly process. Low particle inertia and the viscous effects of clay – type slimes reduce the recovery of valuable particles and leads to further issues in downstream processing such as materials handling and dewatering. It is therefore common practise to implement a desliming stage, usually consisting of hydrocyclones, to remove these problematic ultrafines. With this comes an inherent loss of valuable particles. Current desliming processes also demonstrate an incomplete removal of the slimes, thus, downstream processing is still hindered by their presence. As the minerals industry explores lower grade deposits, it is of increasing interest to develop new technologies to remove slimes at the finest sizes, and in doing so, improve the recovery across all particle sizes. This thesis investigates the issues of ultrafine separations and desliming from two standpoints; a quantitative study of the effects of slimes on separation performance, and the development of a new technology capable of high throughput desliming. An initial systematic series of experiments was performed in the REFLUX™ Classifier using a high-grade iron ore feed containing a high concentration of slimes. The separation performance was quantified by the solids yield to underflow and Fe recovery across the entire size range. Variations to the solids throughput, through both the solids concentration and volumetric flowrate, revealed the performance to increase for more dilute feeds. At a throughput of 7 t/(m2 h), a feed of 36.5 wt.% solids achieved a low recovery and yield of approximately 30 %. By halving the solids concentration, and simultaneously doubling the flowrate to maintain the same throughput, the recovery and yield both doubled to nearly 60 %. Further reductions in the solids concentration showed no further improvement. Thus, a sharp transition in system behaviour occurred at approximately 18.5 wt.%. Additional experiments were conducted with the inclined channel spacing halved, thus inducing a higher shear rate within the channels. A high solids concentration experiment achieved an Fe recovery and yield of approximately 50 %, roughly double that of an identical experiment with the wider channels. Thus, it was shown the performance could be improved without altering feed conditions. Rheological experiments performed on the overflow solids from the REFLUX™ Classifier experiments showed the slimes to have both a strong shear thinning behaviour and strong dependence on the particle volume fraction. A sharp increase in viscosity with increasing solids fractions corresponded well with the transition in separation performance at 18.5 wt.% solids. A comparison of the slimes viscosity data to an ‘ideal’ solids model of Krieger & Dougherty (1959) indicated that the slimes effectively occupied a volume 5.5 times larger than their actual solids volume. The second part of this research involved the novel REFLUX™ Graviton, which subjects inclined channel modules to a centrifugal force, thus combining the hydrodynamic advantage of the inclined channels with the G-Force advantage. An initial series of experiments using a fine silica feed determined the effects of different variables on the continuous system and confirmed the significant throughput advantage discovered in earlier semi-batch studies. This silica work showed the solids rate to underflow to be critical in providing sharp and fine size separations. A range of iron ore feeds, extending up to particle sizes of 1000 µm, were then investigated using the Graviton. This work showed the Graviton to be remarkably effective at desliming, especially when operated as a two – stage process. By removing the ultrafine particles, significant upgrades in the sub 20 µm size fraction were observed. From a feed grade of 55 wt.% Fe, this process achieved product grades of up to 64 wt.% Fe. Thus, desliming in the Graviton proved effective in upgrading an ultrafine waste stream to a saleable product. Finally, the high-grade, high-slimes feed used in the REFLUX™ Classifier experiments was deslimed in the Graviton at approximately 10 µm, achieving a high yield and Fe recovery of over 90 %. The deslimed product was then processed in the REFLUX™ Classifier. At high solids concentrations, the deslimed runs showed recoveries up to 55 % Fe, roughly double that achieved in the original experiments, however at low solids concentrations the results were much closer. A comparison of selected experiments for the original, narrow channels, and deslimed experiments showed very similar results. Thus, the viscous effects of the slimes could be practically eliminated through the use of dilution, high shear rates, and by highly efficient desliming at approximately 10 microns. Rheological experiments conducted on the deslimed overflow solids were far closer to the ideal model case of Krieger & Dougherty (1959), with the sharp increase in viscosity not evident until much higher particle volume fractions. Hence, the viscous issues predominantly came from these ultrafine slimes. In summary, two classifier units were used to investigate the separations of ultrafine particles and slimes. Experiments in the REFLUX™ Classifier, supported by rheology, examined the separation performance in the presence slimes. Dilution and high shear rates proved effective in reducing the viscous effects of slimes, greatly improving the separation performance. Experiments in the REFLUX™ Graviton demonstrated an effective, high-throughput desliming process. With high yields and recoveries, removal of the ultrafines also resulted in high product grades.
- Subject
- beneficiation; desliming; gravity separation; inclined channels; REFLUX Classifier; enhanced gravity
- Identifier
- http://hdl.handle.net/1959.13/1421146
- Identifier
- uon:37691
- Rights
- Copyright 2021 James Lachlan Carpenter
- Language
- eng
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