Search Documents

By A. M. Neale

Kriel Colliery has experienced some sub-standard blast results on the overburden. Blast results are considered poor when the fragmentation is too big, back break into the new highwall, capping is experienced and/or excess overburden material is thrown into the void. Poor blasting leads to lower productivity, equipment breakdowns, and poor drilling and blasting results on the adjacent blast, contamination of coal or loss of coal. A simulation was developed in Microsoft Excel to model blasting results while changing various parameters. From the simulation results, it could be seen that a change of blast design could be beneficial. As an example, smaller drilling patterns were simulated (10 m x10 m to 8 m x8 m, and 8 m x8 m to 7 m x7 m in Pit 5 and Pit 6 respectively) in combination with changes in explosives (P700 emulsion vs. ANFO) and drill bit diameter (311 mm vs. 251 mm). The results show that each of the options has a specific scenario that will be most beneficial to the mine. These results are quite specific and subject to variable inputs. The purpose of the example is to demonstrate how the simulation can be used as a tool to asses blast design variations.

Jan 1, 2010

The excavation of ramps and tunnels often requires high-speed development with (or without) the use of high-energy mining equipment such as loaders, dump trucks, TBMs and roadheaders. This high-speed development creates a challenge in terms of providing a safe and productive working environment. For example, heat from continuously exposed surrounding rock, heat from broken rock, heat generated by mining equipment, potential in flows of hot ground water, pollution from associated diesel equipment and the distance of the advancing face from fresh through-ventilation all have to be taken into account when designing ventilation systems for high-speed ramp and tunnel developments. This paper discusses methods of achieving acceptable environments at the face and along the length of the tunnel. The methodology has been successfully implemented in the development of long (up to 20 km) TBM drives in the Lesotho Highlands Project and in mining projects in hot rock using drill and blast methods as well as mechanized methods using continuous miners and roadheaders. The determination of heat loads includes calculation of the heat flow within the surrounding rock, evaluation of the operating cycle of the equipment and the contribution to the overall heat load of the broken rock as it travels out of the tunnel. The determination of heat loads from surrounding rock in new tunnels required a modification of the algorithms generally used for established excavations. The paper also examines the use of, for example, mobile duct and fan systems to ensure that fresh air is delivered to the specific areas where workers are located.

Jan 1, 2000

By Krogerus. H., P. Jokinen, T. Lintumaa

Keywords: Pyrometallurgy, furnace, coke, smelting charge, optimization, ferrochrome The main consumer of ferrochrome is stainless steel production. Stainless steel must maintain a reasonable price against other competitive materials. Therefore, the ferrochrome price must be low enough and profitable for the producers of stainless steel. The investment and operational costs of ferrochrome production are greatly dependent on the availability of the process and the production rate. Thus the furnace size and production rate in submerged electric arc furnaces will be greatly increased in the near future. The ferrochrome production per furnace, e.g. at Outokumpu?s Tornio Works, increased from 30 000 t/a to 165 000 t/a in about 35 years. The same trend will continue globally but now much more quickly. The Outokumpu ferrochrome process at Tornio Works uses sintered chromite pellets and upgraded lumpy ore as a chromite source. Metallurgical coke is used as a reductant. Reliable smelting in a large furnace demands the correct charge composition and well-known characteristics of the charge components. The quality and electrical conductivity of cokes (normally used) has the most important role for the electrical conductivity of the smelting charge. The results of the measured electrical conductivity of different cokes and the smelting charge with many controlling factors are presented here. These measurements were performed over the years for our own purposes at the laboratory of Outokumpu Research Oy (ORC), in Pori, Finland.

Jan 1, 2006

By M. A. van Nierop

The Discrete Element Method (DEM) is a model that is used to simulate the motion of the media in a grinding mill. The sum of the energy that is lost in inter-media and media-wall collisions represents the power drawn by the mill. The fact that the DEM predicts the power drawn by grinding mills over a large range of diameters has been used to show the validity of the DEM. However, the power drawn by a mill is a function only of the sum of forces of the load on the shell liners. A more accurate and detailed validation of the DEM would be to measure these forces as a function of angular position as the liner moves under the load, and to compare these measurements with predictions generated using the DEM. An experimental mill has been developed to reproduce exactly what the 2-dimensional DEM simulates. The 0,55 m diameter mill has a length of 0,023 m, which is fractionally larger than the diameter of the media used in the mill. One of the lifters in the mill has been instrumented so that the forces on the lifter can be measured as the mill rotates. The DEM simulation will be used to predict these forces. This will give experimental evidence of the validity of the DEM for modelling load behaviour in rotating grinding mills.

Jan 1, 1999

The paper reviews the results emanating from an experiment conducted in Bochum?Germany in which various international rope inspection authorities were requested to assess the conditions of a corroded rope sample as well as a rope sample containing internal fatigue breaks. Both samples were of the multi-layer low rotation construction.

Jan 1, 2000

By P. C. Schutte

There have been several high-profile accidents in the South African mining industry where fatigue was identified as either causal or contributory. The risk of fatigue is inherent in any work-time arrangement involving shift work and work that is physically or mentally demanding, repetitive, or requires high vigilance. The management of fatigue is not simply a matter of correct shift scheduling. Amore comprehensive approach is needed. In order to be successful, a fatigue management programme should address the unique needs of the operation in which it will be implemented and should be integrated into normal operations. Fatigue management is a shared responsibility between the organization and its employees, and all stakeholders should participate in order to provide the safest and healthiest working environment possible.

Jan 1, 2010

By S. N. Opperman

Testwork at Goedehoop Colliery showed that fine coal, essentially?150 microns can be successfully beneficiated using froth flotation. Both conventional and column flotation were tested. It was found that the traditional stirred tank type of flotation machines used in conventional flotation produced the best recovery of fine coal. After extensive testwork it was decided to develop a flotation machine on Goedehoop Colliery that would combine stirred tank and quiescent column technology. It was thought that this design would give the best combination of recovery and selectivity. The Multicell was developed and is producing results acceptable for Witbank coal flotation. Keywords: Multicell, Witbank coal flotation, froth, stirred tank, quiescent column.

Jan 1, 2002

Rockbursts continue to be a scourge in the mining industry, being responsible for accidents and damage to mining excavations. Although the problem has been present for more than a century, and although much research has been carried out, a solution is still elusive. Determination of, firstly, the demand on the support system imposed in the rockburst and, secondly, the capacity of the support system, cannot be carried out with any confidence, and therefore rockburst support cannot be designed using a conventional design approach. In contrast with the conventional approach, observations of rockburst damage in a mine have revealed a possible alternative approach to rockburst support ? sacrificial support. It was observed, in rockburst events, that a support system consisting of concrete panels restrained by grouted cables was destroyed, and the concrete panels were ejected. However, the rock behind the panels remained apparently undamaged and in place. This behaviour reignited the concept of sacrificial support, conceived more than 20 years ago, and which is described in this paper. The remedial solution implemented on the mine, involving cables wrapped over the panels and retained by grouting into boreholes, has been subjected to rockburst loading and has confirmed the validity of the sacrificial support concept. The concept of sacrificial support may be controversial, but is deliberately presented here with the aim of generating discussions and contributions, and with the ultimate aim of improving safety and reducing rockburst damage in mines. Keywords rockburst, seismicity, seismic waves, rock support, support design.

Jul 1, 2013

By Ö. Uysal

This study deals with the presentation of the mechanized longwall mining project introduced some years ago to increase productivity and output of Aegean Lignite Establishment (ELI) owned by Turkish Coal Enterprises (TKI.) and the comparison of this method with a planned alternative new mining method called ?shortwall mining? where continuous miners will be introduced as primary coal excavation machines. Following the planning phase, production costs have been calculated for both mining methods on the basis of a panel having a height of 7.5 m. In addition to cost analysis, both methods have been evaluated using ?the multi-dimensional objective system?. In this evaluation the value synthesis has been carried out according to scoring models. Lastly, the advantages and disadvantages of both production methods have been stated by analysing them according to related criteria. In the light of outputs gathered from the analyses, it has been determined that the shortwall mining method will out perform the longwall method. Keywords: continuous miner, shortwall mining, longwall mining, multi-dimensional objective system.

Jan 1, 2006

By Rodney Ishak, Merete Tangstad

In the HC FeMn production, better utilisation of coke and electric power is vital for reducing the production costs. The higher manganese oxides in the charge are reduced to MnO in the prereduction zone, where also the Boudouard reaction is active. These gas-solid reactions are to a large extent decisive for the total consumption of both coke and electrical power in ferromanganese production. In the present work formulas for calculating the Degree of prereduction have been developed for industrial practice. It shows that the typical Degree of prereduction is between 10-40%, but it may in good periods be as high as 60%. Statistical analysis has been done in order to find how various operational parameters influence the Degree of prereduction. A few parameters were observed to have an effect on the prereduction. Comilog ore definitely had a positiveinfluence on the prereduction, Comilog sinter and Mamatwan ore probably had a positive influence on the prereduction, all in relation to the average prereduction in the selected periods. Meanwhile, As man ore definitely, % H2O in raw materials and increasing Hd probably, had a negative influence on the prereduction. The findings for these raw materials were very much in coherence with the results of laboratory scale experiments performed, where the CO-reactivity of different ore materials was studied.

Jan 1, 2007

By Nielen van der Merwe

Mr Janisch' s comment' in the August issue on Dick Stacey's remarks about safety factors indeed requires wider debate. The example he quoted to illustrate the successful application of the safety factor concept in coal mining, namely the Salamon formula, is to my knowledge the only recognized application of that concept. Not only that, but that particular formula should be used only for what it was intended, namely to prevent major disasters. It was never intended to indicate long-term pillar stability, and it should not be used for that.

Jan 1, 1993

In recent years several mine researchers have studied the optimization of cutoff grade with the purpose of maximizing Net Present Value (NPV). The best and most popular one is the Lane algorithm. Based upon the Lane algorithm it is possible to calculate the optimum cutoff grade for mine, mill, and refinery capacities for single metal deposits with variable grades. The Lane algorithm cannot be used in multiple metal deposits. The reason is that, while in single metal deposits six points are possible candidates for the optimum cutoff grade, in multiple metal deposits an infinite number points are possible candidates for the optimum cutoff grades and objective function evaluation of these infinite points is impossible. In this study the Golden Section search method was used to calculate optimum cutoff grades of multiple metal deposits for the same conditions as Lane assumed in single metal deposits. Based on this method, grade-tonnage distribution uncertainty space of problem is guessed. In the next step, by selecting test points in uncertainty space and evaluating the objective function at these points, a part of uncertainty space will be eliminated. The procedure is then repeated until the uncertainty space has been sufficiently reduced to ensure that the optimum cutoff grades have been located to the required accuracy. Key words: Optimum cutoff grades, Optimization, Net Present Value (NPV), Golden Section search method

Jan 1, 2003

By D. Whittles, C. J. Lea, T. X. Ren, A. Kelsey

A methodology for the simulation of methane drainage combining geotechnical modelling and computational fluid dynamics (CFD) will be described. Geotechnical modelling was used to predict the development of stress and strain due to mining. The results from the geotechnical modelling were combined with empirical expressions for the variation in permeability with stress of coal measure rocks and assumptions on fracture behaviour. This allowed the permeability, as affected by mining, to be specified in CFD simulations. Flow of methane through strata, with and without methane drainage, was then simulated to examine the effects of methane drainage.

Jan 1, 2003

The modelling of lithological domains is a critical step in mineral resource and reserve evaluation. Deterministic models rely on an interpretation of the available drill hole data and expert knowledge, but do not account for the uncertainty in the spatial extent of the lithological domains. Instead, probabilistic models based on conditional simulation can be used to map the probabilities of occurrence of the domains within the deposit, which reflect the uncertainty in their presence or absence at unsampled locations. The mineral grade model is then obtained by weighting the predicted grades associated with each lithological domain by the probability of occurrence of this domain. Such an approach accounts for the continuity of the grades proper to each lithological domain and for the uncertainty in the spatial extent of these domains within the deposit. An application to a porphyry copper deposit is presented. Keywords: spatial uncertainty; plurigaussian simulation; geological control; kriging; geostatistics.

Jan 1, 2007

By I. Matsunaga, K. Aoki, W. -j. Jung

Blasting is widely used in mining and basic construction because of its speed and economy to destroy the rocks. Blasting has the advantages of reduced excavation costs and shorted construction time when compared to the use of heavy machinery for excavation and cutting such as that with a tunnel boring machine. There are numerous problems with blasting, including the noise, vibration and fly rock. So it is necessary to accurately evaluate fracture mechanics of rocks on the dynamic loading condition to control the fracture process of the blasting. The tests using Hopkinson's effect for the dynamic condition using the precise detonators were performed for various strain rates on three different kinds of rocks. In the tests using Hopkinson's effect for the dynamic condition, the high-speed camera was used to observe the fracture process of the test sample rocks. As the results of experiments there was an increase in the tensile strength of rock with an increase in the strain rate for three kinds of rock on the dynamic loading. The tensile strength of rocks with high porosity on the water saturation condition was decreased on the both static and dynamic condition. It is clear that the strain rate and water saturation were influenced to the tensile strength of the rocks.

Jan 1, 2003

By S. O. Bada

Fine phosphate feed is considered to be slime and normally disposed of as a discard in settling ponds or dumped as landfill. The purpose of this research was to establish whether commercially acceptable qualities and yields could be obtained from this material using dry separation methods. The results obtained from the electrostatic separation of <105 µm phosphate ore are presented. An existing separator was upgraded in order to improve on product and flotation concentrate recovery, to test different mineral, and to reduce particle residence time between the charging chamber and the separating zone of the separator. The operating conditions were varied according to the charges imparted to the particles in the electric field, and according to other device parameters. Parameters such as splitter position, charge reversal, rotation speed, charging voltage and separating voltage. The <105 µm phosphate feed was concentrated under both triboelectrification and inductive charging. The use of inductive charging and charge reversal resulted in a significant increase in grade for <105 µm phosphate feed, with the P205 grade increasing from about 12 per cent to 20.50 per cent, and a recovery of 26.30 per cent under a single stage of separation. It was found that better separation was achieved at rotation speed of 6000 r/min, -8 kV charging voltage, and 25 kV separating voltage.

Jan 1, 2012

By B. S. Xakalashe

Keywords: Pyrometallurgy, silicon, solar cells Silicon has been the dominant material in the photovoltaic (PV) industry since its application in the space industry in 1958. This review focuses on crystalline silicon solar cells, primarily due to their dominance in the photovoltaic industry, omitting other photovoltaic cell technologies such as second generation (e.g. thin films) and third generation (e.g. nano-structured solar cells). The value chain for the production of crystalline silicon solar cells has been reviewed. The primary processing steps for the production of silicon solar cells from quartz are as follows: bulk production of metallurgical-grade silicon via carbothermic reduction in a submerged furnace, refining of metallurgical-grade silicon via the chemical means to polycrystalline silicon, or through the metallurgical route to solar-grade silicon, wafer manufacturing, and, lastly, silicon solar cell manufacturing. During downstream processing, solar cells are interconnected and encapsulated into solar modules (panels), which can be used individually or incorporated into a photovoltaic system for electricity generation and supply. The cost for crystalline silicon based solar cells is approaching one US dollar per watt peak ($1/Wp), while the most cost-effective solar modules in industry have reported costs below $1/Wp, and are based on CdTe thin films. Solar cell energy conversion efficiencies as high as 22% have been reported in industry for crystalline silicon solar cells.

Jan 1, 2011

By A. M. Milev

A simulated rockburst was conducted underground at Kopanang Mine, previously called Vaal Reefs No. 9 Shaft. The rockburst was simulated by means of a large blast detonated in solid rock close to a crosscut sidewall. The simulated rockburst involved the design of the seismic source, seismic observations in the near and far field, high-speed video filming, a study of rock mass conditions such as fractures, joints, rock strength etc. Knowledge of the site conditions before and after the simulated rockburst was also gained. Some of the important findings are listed below: ?Two areas of damage were identified on the blasting wall: (i) an area of high-intensity damage in which ground velocities of 3.3 m/s were recorded by an accelerometer, which was subsequently ejected in a block of rock, (ii) an area of low-intensity damage where ground velocities of 1.6 m/s were recorded by an accelerometer which remained on the tunnel wall. ?High-speed filming revealed rock fragments being ejected from the wall at velocities in the range of 0.6 m/s to 2.5 m/s. The measurements were taken in the area of low-intensity damage. As planned, no gas pressure was directly involved in damaging the wall of the tunnel. ?The attenuation of peak particle velocities for the main blast in the near field (6 m to 30 m), as a function of distance R, was found to be proportional to R-1.7. ?The simulated rockburst was recorded as a local magnitude ML= 1.3 by the Klerksdorp regional seismic network. ?Peak particle velocities from nearby blasting, recorded on the tunnel wall after the simulated rockburst, were about six times greater then peak particle velocities recorded from the same source area before the simulated rockburst.

Jan 1, 2001

By C. Birch

"A ‘geologically constrained’ orebody model has long been hailed as vital for a Mineral Resource statement that is compliant with the South African Code for Reporting of Exploration Results, Mineral Resources and Mineral Reserves (SAMREC Code). In this paper, the requirements for geological modelling as contained in the outline for the SAMREC Code are considered, and whether the new modelling software available on the market is a ‘black box’ or is better for modelling than traditional methods of wireframe creation.Implicit geological modelling is a technique that uses a radial basis function to establish and update geological models relatively quickly and efficiently from borehole data, outcrop data, manually interpreted vertical or horizontal sections, and structural data. Assays and any coded drill-hole data, such as lithology and alteration, can be interpolated.Leapfrog Geo software is an example of this new approach to geological modelling. A case study of a short training course in geological modelling for non-geologists at the University of Witwatersrand, as part of the Higher Certificate in Mineral Resource Management, is presented. The benefits of this type of geological modelling software are considered for this type of assignment as well as for mining industry applications.The use of geological models in mine planning is reviewed and a case study is presented comparing the variations in mine plan design and financial output of 13 final-year Mine Design projects from the University of the Witwatersrand School of Mining Engineering. These designs were all based on the same geological model created in the traditional way, and yet the resultant mine designs were significantly different, with very different resulting financial outlooks for the project. This raises questions as to how significant a very detailed model in the pre-feasibility and feasibility phases of projects really is, considering the huge costs involved in gathering the required data to build a SAMREC-compliant geological model."

Jan 1, 2014

By T. Tholana

South Africa hosts some of the world?s largest known resources and reserves of minerals that are strategically important to the global economy. The country?s mining industry contributes significantly to the national economy in terms of gross domestic product, export earnings, corporate tax receipts, remuneration earnings, and employment. Platinum, gold, and coal are significant minerals because they make the largest individual contributions to these economic indicators. Several factors impact the cash cost performance of operations that mine these minerals, thus affecting the future sustainability of these operations, which are generally ?price-takers?. It is therefore important that the cash cost performance of operations for these key minerals is analysed. Commercially available industry cost curves can be used for such analysis. However, some companies may not be able to afford to purchase these curves. This paper presents a simple Microsoft Excel® algorithm for constructing the curves. It also demonstrates how the constructed industry curves were used to analyse the cash cost performance of South African mining operations for the three selected minerals for the period 2007 to 2011, which included the 2008 global financial crisis. The analysis revealed that the operations were affected by several global and local factors during the review period. The work reported in this paper is part of an MSc research study at the University of the Witwatersrand. Keywords cost curve algorithm, economies of scale, cash cost performance

Jun 1, 2013