Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> http://www.scielo.org.za/rss.php?pid=0038-223X20130012&lang=es vol. 113 num. 12 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Portfolio Potential</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200001&lng=es&nrm=iso&tlng=es <![CDATA[<b>President's Corner</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200002&lng=es&nrm=iso&tlng=es <![CDATA[<b>SANCOT and the International Tunnelling Association (ITA)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200003&lng=es&nrm=iso&tlng=es <![CDATA[<b>A review of real-time optimization in underground mining production</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200004&lng=es&nrm=iso&tlng=es Real-time monitoring makes it possible to detect any disturbance occurring in production, while decision instruments can efficiently assist decision-makers to optimize production, reduce iterative workload, obtain better solutions, and preview possible results. Technologies for the above already exist and have been proven in the process industry, i.e. refining and smelting. Optimization is also essential for profitable and stable mining production. Real-time monitoring has already taken hold in mining operations, especially in surface mining, while optimization techniques have also been widely used in underground mining, particularly for planning and scheduling. This review is limited to the hard-rock mining production of metallic ores such as gold and copper. It reviews optimization techniques developed for mine planning and scheduling, and communication technologies suitable for underground applications. It also presents control features for individual operation units, and discusses the technical viability of a mining production real-time optimization (MPRTO) system for underground mines, with possible benefits and challenges. Operational disturbances always occur in mine production. An MPRTO system can be useful to maintain operational effectiveness and efficiency by allowing quick changes to short-term plans. This paper briefly describes the MPRTO system, including the input, output, and basic algorithms. The technical prerequisites for the system specified here are already available. Further studies that are required to improve the system are discussed. <![CDATA[<b>Particle collision during the tribo-electrostatic beneficiation of fly ash based on infrared thermography</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200005&lng=es&nrm=iso&tlng=es Tribo-electrostatic beneficiation is effective for separating unburned carbon from fly ash. During the process, the fly ash particles become charged owing to friction and collision inside a tribo device. The intensity of friction and collision between particles can be deduced from the tribo device temperature field, obtained by infrared thermography. The purpose of this research was to establish whether an appropriate configuration of tribo device models can be obtained from particle collision experiments using infrared thermography. An experimental set-up was configured to study tribo devices with different arrangements and spacing of the friction rods, and the effect that this has on interparticle collision and the tribo-electrostatic beneficiation process. The experimental material was fly ash particles with a size range from 38 µm to 74 µm and loss on ignition (LOI) 12.65%. The operating conditions were electric field voltage 40 kV and the air flux ranged from 12 to 24 m³/h. The results show that the temperature inside the tribo devices is directly proportional to air flux and particle collision rate. The arrangement and spacing of the friction rods has an important effect on the temperature field distribution. An equilateral triangular arrangement with 20 mm spacing significantly increases the temperature value and collision probability. The optimum operating parameters were established through tribo-electrostatic beneficiation experiments on the fly ash, and the results (LOI of the product at the two electrodes and rate of removal of unburned carbon at the negative plate) were consistent with those of the infrared thermography experiments. A tribo device with friction rods configured in an equilateral triangle arrangement and with 20 mm spacing again yielded the best results. This approach constitutes a new technique for the optimization of tribo device design. <![CDATA[<b>Influence of particle shape on the flotation of magnetite, alone and in the presence of quartz particles</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200006&lng=es&nrm=iso&tlng=es The influence of different grinding methods on the shape characteristics of magnetite particles was investigated. Also, the effect of particle shape on the flotation of the magnetite, both alone and in the presence of quartz particles, was investigated. The shape characteristics of the magnetite particles were measured and calculated from images obtained by scanning electron microscopy via an image analysis system. The flotation tests were performed using a laboratory flotation cell. Results showed that in the -250 +212 µm and -106+75 µm size fractions, ball mill products have a higher elongation value than rod mill products, while in the -150+125 µm size fraction, rod mill products have a higher elongation value. Particles with higher elongation values and lower roundness values have a higher flotation kinetic constant. Furthermore, the influence of magnetite particle shape on flotation is greater, and the flotation kinetic constant is higher, in the presence of quartz particles than in the flotation of magnetite alone <![CDATA[<b>Towards an understanding of dynamic demand on ground support</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200007&lng=es&nrm=iso&tlng=es The proper understanding of the functioning of ground support under dynamic loading and the current approaches to designing of dynamic support are plagued by a great deal of uncertainty and lack of knowledge. This applies equally to the understanding of the support capacity as well as the demand placed onto the support due to dynamic loading. This lack of understanding currently leads to a case of design indeterminacy. This paper does not aim to solve this problem of design indeterminacy but to explore some of the issues that need consideration to obtain a better understanding of the dynamic demand on ground support systems. <![CDATA[<b>Application of ecosystem function analysis (EFA) in assessing mine tailings rehabilitation</b>: <b>an example from the Mhangura Copper Mine tailings, Zimbabwe</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200008&lng=es&nrm=iso&tlng=es The widespread environmental damage caused by slimes dam construction requires rehabilitation as one of the key management strategies towards land restoration. From the time when Mhangura Copper Mine in Zimbabwe was shut down in 2000 due to viability problems, no follow-up studies were carried out on the slimes dams to assess their development with respect to ecosystem function and long-term recovery. The ecosystem function analysis (EFA) method was thus employed to achieve this end. EFA is a monitoring procedure that establishes how well an ecosystem functions as a biophysical system through the use of rapidly assessed field indicators. The field procedure makes use of simple visual indicators that are related to various soil surface processes. Conventional sampling methods are used to collect the vegetation data. The data was first analysed using landscape function analysis (LFA) software packages and then with various multivariate statistical techniques. In total 27 species were recorded from 14 families; 21 of them occurring in the acacia woodland and only 8 on the slimes dams. Hyparrhenia sp. was the dominant grass on Dam 5 and Imperata cylindrica dominated Dam 6. Acacia saligna was the most abundant tree species on the dams. The tree layer on the slimes dams was not as developed as the grass layer. The rehabilitated slimes dams converged with the natural woodland for the LFA indices of stability, nutrient cycling, and infiltration, which suggested a high level of functionality. The main factors affecting the sustainability of the rehabilitation are postulated to be fire, grazing, and tree harvesting. The study contributed to the importance of, and methods used for, assessing ecosystem function on rehabilitated slimes dams in Zimbabwe, which are often ignored as most efforts focus on the establishment of vegetation on the dams. <![CDATA[<b>Optimizing shaft pressure losses through computational fluid dynamics modelling</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200009&lng=es&nrm=iso&tlng=es As a result of the rising electrical energy costs in South Africa, a method was sought to reduce the overall electrical consumption of typical shaft systems. A typical shaft configuration was analysed and the primary energy consumers were identified. The ventilation fans for this system were found to consume 15% of the total energy of the shaft system. It was calculated that more than 50% of this energy is consumed by the shaft itself, more specifically, by the pressure losses that occur in the shaft as the ventilation air passes through it. In order to ensure that the theory being used for the evaluation of these shaft systems is accurate, a total of five shafts were instrumented and the actual pressure losses over the shafts plotted against time. These shafts were then analysed from a theoretical perspective. Finally, in order to ensure a thorough understanding of the behaviour of the ventilation air in shaft systems, the systems were simulated using computational fluid dynamics (CFD) techniques. There were significant discrepancies between the theoretical analysis and the CFD simulation during the initial comparisons. This discrepancy lessened as the complexity of the CFD models increased, until when the complete shaft was modelled using the full bunton sets, the pipes, and the flanges, the difference between the theoretical evaluation and the CFD simulation was small. This result demonstrates that the theory is insufficient and that the interrelated effect of the buntons and fittings has not been fully appreciated by current theory. The final phase of the work presented here was to evaluate the cost-effectiveness of using different bunton shapes and shaft configurations. It is shown that the increase in the pressure losses and therefore the direct operating costs of the shaft can vary by as much as 80%, depending on the bunton configuration chosen. The placement of the piping in the shaft can increase the pressure losses, and therefore the direct operating costs of the shaft, by as much as 12%, depending on the placement of the piping in the shaft; this effect includes the use of flanges. The use of fairings on a large cage can reduce the resistance that the cage offers to the ventilation flow by as much as 30%. This, however, does not translate into a direct saving because as the cage moves through the shaft, the overall effect is transitory. These savings can be significant when the items highlighted in this work are applied correctly. <![CDATA[<b>A study on the effect of coke particle size on the thermal profile of the sinters produced in Esfahan Steel Company (ESCO)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200010&lng=es&nrm=iso&tlng=es The aim of this research was to investigate the effect of coke particle size on the thermal profile of the charge bed in the sintering process of iron ore. Six different ranges of coke particle size that could be used in practice in the sintering line of Esfahan Steel Company (ESCO) were used while parameters such as ratios and particle sizes of other ingredients, ignition temperature, and suction power were kept constant. Thermal profiles were obtained by measuring the temperature changes at three points in the sintering bed. The influence of coke particle size on rate of temperature rise, maximum temperature of the sintering bed, and the flame front velocity of the sintering bed was determined by analysing the thermal profiles. Moreover, the cold strengths of the sinters were measured using the Tumbler method. The results indicated that the coke particle size has a significant impact on the thermal properties of the sintering bed. Based on the results, a coke particle size between 0.212 mm and 3.350 mm was determined as the optimal range for the specific conditions in the sintering line of ESCO. <![CDATA[<b>World Gold 2013</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-223X2013001200011&lng=es&nrm=iso&tlng=es The aim of this research was to investigate the effect of coke particle size on the thermal profile of the charge bed in the sintering process of iron ore. Six different ranges of coke particle size that could be used in practice in the sintering line of Esfahan Steel Company (ESCO) were used while parameters such as ratios and particle sizes of other ingredients, ignition temperature, and suction power were kept constant. Thermal profiles were obtained by measuring the temperature changes at three points in the sintering bed. The influence of coke particle size on rate of temperature rise, maximum temperature of the sintering bed, and the flame front velocity of the sintering bed was determined by analysing the thermal profiles. Moreover, the cold strengths of the sinters were measured using the Tumbler method. The results indicated that the coke particle size has a significant impact on the thermal properties of the sintering bed. Based on the results, a coke particle size between 0.212 mm and 3.350 mm was determined as the optimal range for the specific conditions in the sintering line of ESCO.