Contribution to the understanding of the three-product cyclone on the classification of a dual density platinum ore

Includes bibliographical references (p. [234]-246).The detrimental effects exhibited by the conventional hydrocyclone in classifying ores that contain different density components motivated the AMIRA P9 project to look into modifications to the conventional hydrocyclone that can improve separation by component density. In this project a cyclone termed the three-product cyclone has been developed and tested. The three-product cyclone is a modification of the conventional hydrocyclone with an additional vortex finder termed the inner vortex finder inserted concentric to the existing one, termed the outer vortex finder, resulting in three products from the same hydrocyclone. The three-product cyclone produces a finer overflow stream, an intermediate overflow stream comprising fine high density particles and medium sized light particles, and a coarse underflow stream. The work presented in this thesis involved designing an overflow arrangement which allowed interchangeable inner vortex finders to be tested, and a special rig for industrial scale experiments using a 600mm diameter hydrocyclone

Investigation and modelling of the progression of zinc leaching from large sphalerite ore particles

X-ray Computed Tomography (CT) was used to follow the progression of Zn leaching in a number of individual sphalerite ore particles, which were subjected to a long-term simulated heap bioleaching environment. The ore was prepared by two different modes of comminution – HPGR at 90 bar and cone crusher – and individual particles were selected from three different size fractions. Investigation of the reacted fraction of Zn vs distance from the centre of each particle indicated that leaching from large particles leads to near complete conversion near the surface, but only partial conversion in the zones that are closer to the centre of particles. The cores of the cone-crushed particles show hardly any conversion at all, especially in the larger particle sizes. Mathematical analysis shows that leaching from the large particle does not follow the shrinking core model. It is shown that the progression can rather be described by a combined reaction-diffusion process progressing through the network of cracks and pores closer to the particle surface. Extent and depth of this network are a function of particle size and comminution method. A simplified rate model is proposed that describes the extent of leaching as a function of time in terms of a set of parameters that can all be related to just particle size and crushing mode

Investigation of particles with high crack density produced by HPGR and its effect on the redistribution of the particle size fraction in heaps

The application of comminution technology such as the High-pressure grinding rolls (HPGR), which is able to generate a high density of cracks in the ore particles, is favourable for leaching processes. Extraction of metallic values by the heap leach process, can take place on the particles with partial exposure of mineral grains, if it can provide sufficient surface front for chemical attack by leaching solution. The aim of this study was to assess the benefits of high crack density in the ore particles produced using the HPGR and how it could diminish due to inadequate percolation of the leaching agent. A zinc ore was comminuted using HPGR at three different pressure settings and with a cone crusher for the control experiment. Subsamples from the (+23/-25, +14/-16, +5.25/-6.75 mm) size fractions were characterized and packed into leach reactors. The reactors were stopped from time to time to investigate the progress of crack and micro-crack growth and its effect on metal extraction using the X-ray computed tomography (CT). The results are validated with those obtained using traditional techniques such as SEM and QEMSCAN. Investigation of the leach reactors residue indicated significant changes in the particle size distribution (PSD) of initial feed toward the fine size fraction. The residues from the reactors leaching the material prepared using the HPGR product contained more fine particles than the reactors, which were fed by cone crusher product. These differences were up to 10.3%

Mineralogical Factors Affecting the Dense Medium Separation of Nickel Sulfide Ores

Dense medium separation (DMS) is often used to reject a large portion of gangue material upfront to create cost and energy savings during processing. As lower-grade ores with complex mineralogy are being increasingly exploited, the properties of the gangue minerals begin to play a more important role in the upgrading of the ore. It is therefore important to understand these mineralogical factors to be able to select suitable processing routes for specific ore types. Two nickel sulfide deposits in southern Africa were chosen as case studies to understand differences in DMS efficiency when applied to different ores: Ore A and Ore B. Both ores showed nickel upgrades using DMS and the products were then characterized using QEMSCAN, with the aid of X-ray diffraction and electron probe microanalysis. Overall, particle density remains the main control on the separation, followed by sulfide texture, with massive and net-textured sulfides having larger grain sizes and therefore better liberation than disseminated sulfides. In addition to the concentration of sulfides, primary and secondary silicate minerals are separated by their density differences, which can affect the recovery of finely disseminated sulfides associated with them. Particle size is also important in DMS, with material near the cut-point density separating on size rather than density. The understanding of the mineralogical properties affecting DMS can aid in the prediction of the suitability of DMS for different ore types

Axial Segregation of Polydisperse Granular Mixtures in Rotating Drum Flows

Axial segregation of polydisperse granular mixtures in rotating drums have been observed in several experimental and discrete particle simulation studies reported in the literature. A common thread to both experimental and numerical studies is the formation of (alternating) bands which eventually coarsen in the long-time limit due to logarithmic merging. Models to explain the experimental observations are generally limited to bidisperse mixtures, and often unable to reproduce band coarsening. One such mechanism for bidisperse mixtures argues that the grains eventually diffuse into axial bands as a consequence of concentration fluctuations in the free surface layer caused by friction-limited mobility. We generalise this model to multi-species mixtures and show that the solution produces banding that evolves more complexly than binary mixtures, with sinusoidal-like variations of the band structure that evolves non-linearly in time. In addition, we successfully recover band coarsening with time—an observation that is generally difficult to reproduce, even experimentally. Contrary to literature findings, the configurations herein did not produce bands within bands for ternary and quaternary mixtures