Browsing by Author "Ghorbani, Yousef"
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- ItemOpen AccessInvestigation and modelling of the progression of zinc leaching from large sphalerite ore particles(Elsevier, 2013-01) Ghorbani, Yousef; Petersen, Jochen; Becker, Megan; Mainza, Aubrey Njema; Franzidis,Jean-PaulX-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.
- ItemOpen AccessInvestigation of particles with high crack density produced by HPGR and its effect on the redistribution of the particle size fraction in heaps(Elsevier, 2013) Ghorbani, Yousef; Petersen, J; Becker, Megan; Mainza, Aubrey Njema; Franzidis, Jean-Paul; Kalala, JTThe 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%.
- ItemOpen AccessInvestigation of the effect of mineralogy as rate-limiting factors in large particle leaching(Elsevier, 2013-10) Ghorbani, Yousef; Becker, Megan; Petersen, J; Franzidis, Jean-PaulAlthough heap leaching is by now well established in the mining industry, the process remains limited by low recoveries with different rate-limiting factors that are not clearly understood. In this study, three large particle size classes (+19/-25, +9.5/-16, +4.75/-5 mm) were prepared from a sphalerite ore by two different methods of comminution (HPGR and cone crusher). The particles were then packed into leach reactors that were operated continuously for eleven months with well-mixed internal circulation of the leach solution. Characterization of the residue of the leach reactors indicated that there are areas within the ore particles where although sphalerite grains are accessible to the solution, they remain unreacted. X-ray tomography and QEMSCAN® analysis of the selected samples before, during and after leaching, showed increased leaching of sphalerite grains associated with pyrite due to galvanic interactions. Mineral chemistry (Fe, Mn content of sphalerite) and jarosite precipitation were also investigated as factors influencing sphalerite leaching.
- ItemRestrictedLarge particle effects in chemical/biochemical heap leach processes – A review(Elsevier, 2011) Ghorbani, Yousef; Becker, Megan; Mainza, Aubrey; Franzidis, Jean-Paul; Petersen, JochenThe application of heap leach technology to recovery of economically important metals, notably copper, gold, silver, and uranium, is wide-spread in the mining industry. Unique to heap leaching is the relatively coarse particle size, typically 12–25 mm top size for crushed and agglomerated ores and larger for run-ofmine dump leaching operations. Leaching from such large particles is commonly assumed to follow shrinking core type behaviour, although little evidence for the validity of this assumption exists. This review investigates the current state of knowledge with respect to the understanding of the characteristics and mineralogy of large particles and how these influence leaching in a heap context and the tools to characterize these. This includes the study of ore and particle properties, visualization techniques for ore characterization, the connection between comminution and leaching behaviour, as well as particle models within heap leach modelling. We contend that the economics of heap leaching are strongly governed by the trade-off between the slow rate and limited extent of leaching from large particles and the cost of crushing finer. A sound understanding of the underlying large particle effects will therefore greatly inform future technology choices in the area of heap leaching.
- ItemOpen AccessOn the progression of leaching from large particles in heaps(2012) Ghorbani, Yousef; Petersen, JochenAlthough heap leaching is by now a well-established technology choice in the mining industry, the process remains limited by low recoveries and long extraction times. It is becoming increasingly clear that the successful application of heap leaching technology will ultimately depend on having a comprehensive understanding of the underlying fundamental processes for optimisation to take place...The subject of this research was, therefore, to understand more clearly the diffusion reaction phenomena of reagents through large particles and to provide true and reliable physical parameters to formulate the relevant modelling approaches to large particle leaching. A combination of standard optical microscopy, SEM, QEMSCAN and X-ray CT techniques has been used for the characterization of crack networks and mineral dissemination in the ore particles, which are important characteristics that determine the diffusion of reagents into and out of particles and the reactions within.
- ItemRestrictedUse of X-ray computed tomography to investigate crack distribution and mineral dissemination in sphalerite ore particles(Elsevier, 2011) Ghorbani, Yousef; Becker, Megan; Petersen, Jochen; Morar, Sameer H; Mainza, Aubrey; Franzidis, J-PAs the trends in mineral processing move towards the beneficiation of finer grained and more complex ore bodies, so too do the methods needed to understand and model these processes. During the heap leaching of low-grade ore bodies, the crack distribution and mineral dissemination in ore particles are important characteristics that determine the performance of sub-processes, such as the diffusion of reagents in and out of particle pores. Recent developments in X-ray computed tomography (CT) as an advanced diagnostic and nondestructive technique have indicated the potential for the technology to become a tool for the acquisition of 3-D mineralogical and structural data. The spatial distribution of cracks and mineral dissemination in particles derived from a sphalerite ore in the Northern Cape, South Africa, was characterized using a high-resolution industrial X-ray CT system. This paper describes the use of image analysis techniques including image segmentation, which uses a combination of thresholding and other methods to characterize and quantify crack and mineral dissemination in the sphalerite particles. The results are validated with those obtained using traditional techniques such as physical gas (with N2) adsorption, mercury intrusion porosimetry, SEM and QEMSCAN. A comparison of the effect of different comminution devices (HPGR and Cone crusher) on crack generation is also given.