Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> http://www.scielo.org.za/rss.php?pid=0038-223X20080009&lang=en vol. 108 num. 10 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Determining concentration and velocity profiles of non-Newtonian settling slurries using electrical resistance tomography</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2008000900001&lng=en&nrm=iso&tlng=en Pipelines for transporting high concentration slurries are often designed using methods applicable to homogeneous non-Newtonian laminar flow. Many industrial slurries though comprise coarse particles in a non-Newtonian carrier fluid, and existing experimental evidence from tests with such slurries demonstrates that they are not homogeneous. Under laminar shear conditions the coarse particles settle, even in statically stable carrier fluids. To understand this better, the Institute of Materials Science and Technology (IMST) at Cape Peninsula University of Technology (CPUT) is conducting ongoing research into the flow of these high concentration non-Newtonian settling slurries. Since pressure gradient and flow rate measurements alone are insufficient to adequately model the flows, an electrical resistance tomography (ERT) instrument developed by the University of Cape Town (UCT) was incorporated into the pipe test loop to determine pipe crosssection concentration and velocity profiles. The software developed to do this is modular and allows different image reconstruction and cross-correlation algorithms to be implemented and tested without significantly changing the rest of the application. At a total frame capture rate of 566 frames/sec a 2.67 GHz Intel Celeron processor with 500 MB of RAM is fast enough to calculate and display velocity profiles in 'real-time' at an update rate of one profile every two seconds. Examples of experimental concentration and velocity profiles obtained using the system are shown and some proposed improvements/extensions to the system are listed. <![CDATA[<b>Applications of electrical tomography to improve the performance of crystallization, precipitation and mixing processes</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2008000900002&lng=en&nrm=iso&tlng=en Electrical tomography has developed rapidly over the last few years in its sophistication and practical use to enable three-dimensional information on the distribution of phases within flowing mixtures to be observed1. This paper reviews the current state of application from the industrial perspective, drawing on applications case studies based on scaling studies in the laboratory right through to installations on plant. In the laboratory, applications have looked at scale-up of mixing2 processes involving gas-liquid and solid-liquid suspensions3 with a particular interest in verifying computational fluid dynamics simulations or in checking scale-up design4,5. In the processing plant, the circumstances are usually bespoke and may range from simple detection of the degree of homogeneity of a flowing mixture through to the need to measurement a sophisticated batch process such as crystallization, sedimentation, filtering and drying. Examples drawn from the chemical and pharmaceutical industries will be presented and related to the benefits that can be gained through application of the method. <![CDATA[<b>Measurement of suspension velocity in slurries and pastes using impedance imaging</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2008000900003&lng=en&nrm=iso&tlng=en Electrical impedance tomographic methods have been applied to a variety of mineral and chemical processes in the laboratory and on plant. This review paper surveys technical developments in measurement methods to enable quantitative extraction of key process information in the form of mapping of concentration profiles, mixture homogeneity and suspension velocity. The methods for determining velocity are summarized, since this is of especial interest when applied to opaque systems where most conventional optically based measurements fail. A recent significant development is the use of ultra-high speed measurement that now allows velocity vectors to be extracted for fast moving mixtures and fluids (up to several metres per second). New data are reported pertinent to low and high solids concentration flow in pipelines. Use of the methods offer improvements to design of such systems but also points to the use of tomographic electrical sensor as online flow measurement and fault detection. This offers new opportunities for applications and benefits in the design and monitoring of mineral slurries and sludges. <![CDATA[<b>Three-dimensional measurement and simulation of the dewatering behavior of flocs and sediments using X-ray microtomography</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2008000900004&lng=en&nrm=iso&tlng=en The ability to perform three dimensional imaging at micronscale resolution of real mineral floc sediments and structures using commercially available Micro X-ray Tomography (XMT) instrumentation can be used for the analysis of aggregates and granules, liberation and dewatering of sediments. This paper presents a review of recent work by the authors relevant to the mining and minerals industries. It covers three main topics: X-ray imaging of agglomerates and multi-component mineralic particles,, permeability of sediments, and dissolution of granules with potential application to heap leaching. <![CDATA[<b>Neutron and X-ray tomography at Necsa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2008000900005&lng=en&nrm=iso&tlng=en The utilization of computer assisted tomography (CT or CAT-scan) as general non-destructive examination (NDE) technique and as research tool for scientists in South Africa, is limited due to the relative unavailability or nonexistence of such specialized analytical equipment. Many medical hospitals are equipped with X-ray CT scanners for the diagnostic examination of patients but do not easily allow paleontologist or other scientist to utilize their very expensive equipment. As from 2003, Necsa hosts the South African Neutron Radiography (SANRAD) and tomography facility where neutrons from the SAFARI-1 nuclear research reactor and their penetrating power as well as X-rays as a complementing tool, are utilized in many R&D applications. This facility is being made available to HEI and specifically utilized by postgraduate students as part of their studies and/or by industry on an ad hoc commercial basis. The capability of these radiation imaging facilities at Necsa will be demonstrated in areas such as paleontology, geosciences and specifically the physical properties of rock and the distribution of minerals in borehole cores, petrophysics to predict the percentage tar/oil/water content within sandstone samples and others. The penetration capability of neutrons through specimens with a matrix of high atomic number (dense materials) and their ability to be attenuated by low atomic number material (light density) makes neutron imaging complementary to X-ray imaging. The capability of X-ray and gamma radiation for relatively easy penetration through specimens of low atomic number allows for viewing of imbedded high atomic number materials and density variation. X-ray micro focus radiography is capable of resolving objects of micro scale size that are micro distances apart whereas Xray phase contrast radiography utilizes the wave properties of the electromagnetic spectrum of X-rays to clearly define edges of the specimen under investigation. Many applications with neutrons as imaging probe are successfully applied at several facilities across the globe such as at NIST in USA, Neutra at PSI in Switzerland, and ANTARES at FRM2 in Germany, etc, are documented4-9, through world conferences on neutron radiography, for example. This is achieved through very well thought through and implemented instrumentation from the production of neutrons to their detection and interpretation of the images. The need arose at Necsa to upgrade the current facility from 42-year-old technology, which was successfully applied in neutron imaging over the past 10 years, to state-of-the-art technology found at European facilities. This initiative started under the auspices of an IAEA-TC programme for the period 2007-2010. <![CDATA[<b>Estimating the modulus of elasticity of the rock material from compressive strength and unit weight</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2008000900006&lng=en&nrm=iso&tlng=en The modulus of elasticity of rock material (Ei) is an important rock property that is used as an input parameter in the design stage of engineering projects such as dam and tunnel constructions, mining excavations, and so forth. However, determination of the modulus of elasticity is sometimes difficult to obtain by laboratory tests because high-quality cores are required. For this reason, empirical methods for predicting the modulus of elasticity of rock material have been popular research topics in recently published literature. In this study, the relationships between the uniaxial compressive strength (UCS), unit weight (y) and modulus of elasticity for different types of rocks were analysed by using 177 data obtained from laboratory tests carried out on cores obtained from drill holes within the area of the Kadıköy-Kartal Metro line (Istanbul, Turkey). <![CDATA[<b>Strategic factors and a model of enterprise restructuring in the coal industry in Europe with emphasis on experiences in a Slovenia-Velenje coal mine case</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2008000900007&lng=en&nrm=iso&tlng=en The main purpose of this paper is to introduce the main strategic restructuring aspects of companies that are directly (coalmines) or indirectly (companies that depend on coalmines) linked to coalmining. An attempt is also made to determine the principal factors required for the successful execution of a restructuring process in companies focused on the basic activities of coalmining, such as companies that provide supporting activities. The restructuring process exerts an influence on the whole area that relies on coalmining. So coordination of activities among the government, the local community, and the coalmine is very important. This is the major premise of this paper. The first section of the paper focuses on identifying and analysing the key factors in restructuring and a selection of key methods, drawing on past and present practice. The key factors to be considered in a model of enterprise restructuring in the coalmining sector are considered. The second section is dedicated to the actual design of the model of enterprise restructuring in the coal industry. The proposed model is based on positive experiences in the restructuring of coalmining companies in Europe, with an emphasis on Slovenia, successful approaches to crisis management in corporations, and identifying key areas in bringing about a strategic turnarounds in company operation. To support the argument for the key business areas, a brief summary of empiric findings has been included to demonstrate the applicability of the proposed model and the restructuring process. The summary is based on the survey done in both Slovenian coalmining companies (especially in Velenje Coal Mine) and their subsidiaries. The conclusion integrates key findings and outlines issues for further consideration and discussion. <![CDATA[<b>Selection of plant location in the natural stone industry using the fuzzy multiple attribute decision making method</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2008000900008&lng=en&nrm=iso&tlng=en Determining the most convenient plant location is one of the most commonly encountered problems in engineering applications. This paper presents a fuzzy multiple attribute decision making (FMADM) model which is developed for the selection of the optimum plant location for natural stone factories in the mining industry. The criteria affecting the decision making process in natural stone industry were determined to solve the plant location problem in the FMADM model. To determine the optimum plant location for a new natural stone factory, which is planned to be established by a mining firm located in the Eskisehir region of Turkey, an analysis was carried out by incorporating the method and the analytic hierarchy process (AHP) method. The analysis shows that the Yager's method can easily be applied to the selection of plant location in the natural stone and mining industry when the difficulties encountered in the application process of the AHP method is taken into account. <![CDATA[<b>Slope modification of open pit wall using a genetic algorithm - case study: southern wall of the 6th Golbini Jajarm bauxite mine</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2008000900009&lng=en&nrm=iso&tlng=en In this paper a genetic algorithm is used in a heavily jointed rock mass in order to investigate the critical circular slip surface and modification of slope surface. This method was applied to the southern wall of the 6th Golbini Jajarm bauxite mine. The mine is the largest bauxite deposit in Iran, located to the northeast of the town of Jajarm in the Khorasan province. Estimated reserve of bauxite in this deposit is about 160 million tonnes. Field and laboratory investigations were conducted in order to determine rock mass behaviour. A genetic algorithm code that uses the Simplified Bishop method as an objective function was developed for finding the safety factor of circular slip surfaces. Sensitivity analysis was applied to determine the optimum values of the genetic algorithm variables, such as population size, selection method, crossover and mutation rates. After finding the critical circular slip surface, slope modification is carried out by removing unstable sections from marked critical slip surfaces, and this process is repeated until the last unsafe section is removed. Based on this code, modification occurred during 7 steps, by reaching a safety factor of 1.3 in the last step. Finally, the modified slope angle of the southern wall of the 6th Golbini Jajarm bauxite mine was determined to be 48.44 degrees.