Browsing by Author "Uys, Nardus"
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- ItemFlotation of a UG2 ore in a novel pneumo-mechanical laboratory cell(Stellenbosch : Stellebosch University, 2018-03) Uys, Nardus; Burger, A. J.; Stellenbosch University. Faculty of Engineering. Dept. of Processing Engineering.ENGLISH ABSTRACT: Flotation is regarded as one of the most significant primary separation techniques in the minerals processing industry and most platinum-bearing minerals are separated from their related gangue minerals through froth flotation. The selectivity of the flotation process is influenced by many factors, amongst others, the degree of liberation of the valuable minerals and the size of the particles in the feed slurry. For a specific flotation system – and with all else being equal – the selectivity of the process drops notably below a certain particle size (e.g. 15 μm) due to decreasing efficiencies of particle-bubble attachment and increasing levels of gangue entrainment. Against this background, conventional mechanically-agitated flotation machines are generally used in the PGM industry, where they are operated to deliver relatively high energy input and high aeration rates. In search of more efficient flotation devices for this industry, a unique flotation machine was designed, built and evaluated in collaboration with a consultant from the PGM industry. In an attempt to achieve both higher valuable mineral recovery and higher concentrate grade, especially in the finer size ranges, the specific design combined the following principles: • high energy intensity at consecutive (in series) particle-bubble attachment points; • release of loaded bubbles to a non-agitated calming zone for froth separation. As such, the flotation unit contained a down-comer (similar to a Jameson CellTM), which was fitted with three internal impellers and subsequent exit ports for the sequential release of aerated slurry. This agitated down-comer represented the high-energy intensity zone for proper particle-bubble attachment, while the outer calming zone provided a non-agitated froth separation environment. The idea behind the sequential release of intensely air-contacted slurry was to establish a concentration gradient within the outer cell in an attempt to improve the concentrate grade at minimal loss of recovery. The first objective of this study was to utilize the extensive knowledge and know-how captured in literature to design and build a pneumatic flotation cell that enables: a) multi-stage energy input during aeration for improved overall particle-bubble attachment, in an attempt to maximise recovery; b) systematic, multi-stage release of the aerated pulp into a non-agitated calming zone for froth separation, in an attempt to maximise grade while minimising recovery losses. The second objective of this study was to perform a preliminary evaluation of the flotation device, with PGM ore as feed, by characterising the cell’s performance in terms of the most prominent hydrodynamic parameters, such as superficial air velocity, energy input and cell superficial slurry velocity. These objectives were achieved by answering the following key questions: • What are the key features of a flotation cell that could potentially produce PGM concentrates with higher grades and similar recoveries than the mechanical cells currently in use? • How is the flotation efficiency of the newly designed cell (as constructed for this project) typically affected by prominent hydrodynamic parameters such as aeration rate, energy input and recycling rate? • How does this newly designed cell typically perform with regards to recovery, grade and Cr2O3 rejection, compared to mechanical flotation machines used in the PGM industry? The cell was operated in batch-like mode, with tailings being recycled to simulate multiples of these flotation cells in series. This also enabled some comparison of the test results with flotation data generated in a conventional, mechanically-agitated, laboratory batch flotation cell at an operating PGM flotation plant. Chemical dosing (i.e. activator, collector and frother) and related conditioning times were in accordance to prescriptions from the consultant and similar to recipes used on the PGM plant. A notable difference from the operation at the PGM plant was that low-TDS reverse osmosis permeate was used to prepare the flotation slurry for test work. The operating conditions were: cell superficial slurry velocity (1.8-2.6 cm/s), superficial air velocity (0.8-1.2 cm/s) and mixing intensity (680-1277 rpm in a 36 mm down-comer). The froth depth was maintained at 10 mm and scraping occurred at 8 second intervals. Within this range of operating conditions and under continuous recycle, promising results could be obtained, similar to batch flotation results from the PGM plant. In a typical run with a high overall 4-element (4E) recovery of 80.8%, the cell produced an overall 4E grade of 76.4 g/t. When the system was operated to improve grade, an overall 4E recovery of 72.6% was achieved at a very high 4E grade of 153.6 g/t. Both these runs produced good chromite rejection.