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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 slags produced by the Imperial Smelting Process (ISP) are based on the system ZnO-?FeO?-Al2O3-CaO-SiO2. The slag chemistry is important to the process since it determines the fluxing practice and the operating temperature of the furnace required to produce fluid slag. The paper presents the results of the first systematic experimental investigation of these ZnO-containing slags in equilibrium with metallic iron, and provides information on the primary phase fields and liquidus temperatures in these slags over the range of compositions used in ISP practice. A feature of the slags is the presence of alumina, which has a major influence instabilizing the spinel phase. This information presented in the form of pseudo-ternary sections ZnO-?FeO?-(Al2O3+CaO+SiO2) enabling the data to be readily used by plant engineers. Keywords: liquidus temperature, ISP, EPMA, ZnO-?FeO?-Al2O3-CaO-SiO2, phase equilibria.

Jan 1, 2004

The paper deals with the results of dynamic tests carried out on a range of surface support liners consisting of combinations of mesh (various types), shotcrete, and wire rope lacing. The testing was carried out over the period 1993 to 1998. The dynamic testing method made use of drop weight impact loading of test samples which attempted to simulate realistic in situ conditions, and the range of loading imposed was equivalent to small to severe rockburst conditions. The results of the testing provide quantitative data, in the form of input energy, which is relevant for support design and for the choice of support types appropriate for situations in which significant mine-induced seismicity occurs or is expected to occur. In addition to the wire mesh and shotcrete liner systems tested, estimates of energy capacity are made for other, untested, systems.

Jan 1, 2001

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 K. Ding

The thermodynamic activity of MnO was measured in MnO-CaO-MgO-SiO2 slags that are typically encountered in the production of manganese-containing stainless steels. A gas equilibration-quenching technique was employed in measuring the activities. Activities of Mn in Pt-Mn alloys were redetermined at 1600ºC, which reconfirmed earlier results of strong negative deviations. MnO activities were then measured by equilibrating slags of various compositions based on a statistical experimental design procedure with Pt-Mn alloys under controlled partial pressure of oxygen in MnO saturated platinum crucibles at 1600ºC. Activities of MnO were found to increase with increasing concentration of MnO, basicity and CaO to MgO ratio. Two multi-coefficient regression models were developed to predict the activities and activity coefficients of MnO in slags at 1600ºC. Keywords: activity, MnO, slag

Jan 1, 2005

By S. E. Olsen, T. Færden, G. Tranell, T. Lindstad, J. Lubetsky

The authors are lead authors for chapter 4.3 ?Emissions from Ferroalloy Production? in ?2006 IPCC Guide-lines for National Greenhouse Gas Inventories, Volume 3?. The paper discusses the methods to calculate and report emissions from the production of ferrosilicon, silicon-metal, ferromanganese, silicomanganese and ferrochromium alloys, as well as the basis for the methods and choice of emission factors. CO2 is the main greenhouse gas emission from ferroalloy production, accounting for about 95 % of the total CO2-equivalents. The most accurate method of determining emissions is to base the calculations on reported amounts and analyses of reducing agents and carbonate ores used in the process. If analyses are not available, typical CO2 emission factors for the different reducing agents are recommended. If neither reliable amounts nor analyses of all reducing agents are known, default generic CO2 emission factors for the type of ferroalloy multiplied with amount produced, can be used. The CO2 produced from bio-carbon (charcoal and wood chips) should be reported but will not be accounted for in national emissions. If any bio-carbon is used, the default generic CO2 emission factors cannot be applied. CH4 accounts for less than 1 % of the total emission of CO2-equivalents. Default emissions factors for CH4 are given for the production in open or semi-closed furnaces of silicon-metal and ferrosilicon. In the production of FeMn, SiMn and FeCr in closed furnaces the gas containing CO,CO2 and volatiles can be combusted in boilers and N2O may be formed. While reporting is not required, IPCC Guidelines recommend that the N2O-content in the off-gas is measured.

Jan 1, 2007

By David Norval

The increased tendency to use hydrometallurgy as an extraction step towards final refining following a pyrometallurgical smelting process requires melts which have to be cast and or comminuted which can then be taken up into solution or leached. To generate surface area for optimal leaching, a common process is to granulate and in many cases mill, which is a general practice with friable material with properties associated with higher sulphur, carbon and silicon levels. However, in the case of metallic melts milling can be unfeasible due to the ductility of the granulated particles. Water solidification is capable of producing either fine particles by means of granulation or atomisation. Atomisation however, can produce particles as fine as 40 microns without a milling circuit.

Jan 1, 2005

By B. Samanta

This paper investigates the performance of the neural network technique in a placer deposit situated at the Nome district in Alaska. Initially a single neural network model was constructed to estimate the gold grade. However, at a later stage, an ensemble model consisting of multiple networks was also constructed via the Adaboost algorithm. The reason behind the use of the ensemble model of the Adaboost algorithm was to examine if the ensemble model provided superior performance to the single neural network. As indicated by other studies, Adaboost did not have a better performance than a single neural network in this specific application. This may be due to the high noise inherent in the gold data used in this project. Consequently R2 values of gold prediction are also poor for both the single and multiple networks.

Jan 1, 2005

There has been disappointingly little development in the analysis of rock slopes in open pit mines over the past 30 years. A brief review of literature shows that the application of numerical stress analysis methods to open pit mine slope stability has become only relatively common in recent times, and that there are as yet no standardized approaches. The lack of development in general, and of robust, standardized approaches in particular, is surprising in view of the ?ultra? deep open pit mines that are being developed to depths in excess of 1000 m. In this paper, the results of a substantial programme of two dimensional and axisymmetric analyses of open pit slopes are described. Variations in the following parameters were taken into account in this programme: slope angle, slope height and horizontal to vertical in situ stress ratio. The evaluation of the data has concentrated on the tensile stresses and the extension strains in the slopes. This is believed to be the first publication dealing with strain distributions in slopes. The occurrence of zones of tensile stress was very limited. These zones occur in the crests of slopes, except in the case of low horizontal to vertical stress ratios, in which case the tensile zone is in the floor of the pit. In contrast, very large zones of extension strain can occur, and this finding represents a significant new aspect in slope stability that has not been considered before. The greatest magnitudes of extension strain occur near the toe of the slope, either in the slope itself, or in the floor of the pit. The magnitudes of the strains are considered to be large enough to result in fracturing of intact rock, and the fracture orientations predicted are adverse for slope stability. The large zone in which such extension failure could potentially occur in a 1200 m deep pit is typically more than 100 m horizontally behind the toe and about 400 m up the face from the toe. Fracturing that is extension in nature is common in competent, brittle rocks and often develops with some violence and little or no warning. Such ?strain bursting? produces easily measurable seismicity, events often being audible as well. In the slope situation, the expected physical manifestation of this behaviour would be popping off of rock slabs and plates of rock from slope surfaces and popping up of the pit floor, as well as the formation of new fractures within the rock mass. Such behaviour may cause overall slope failure, or may initiate failure, which may then be driven to overall slope failure by other influencing factors or combinations of factors. In addition to instability resulting from the fracture surfaces themselves, all induced fracture surfaces could interact with natural geological structures to facilitate formation of a significant failure surface. With suitably orientated joints, extension strains are likely to manifest themselves in the opening up of such joints and hence in the loosening of the rock mass in a preferential orientation, with potential effects on groundwater flow patterns.

Jan 1, 2003

In surface mining operations, ultra-heavy trucks operate on haul road networks which are typically from 10?40 km in length. These road networks are often not optimally designed and maintained and as a result, identifying and remediating road functional defects is problematic. Most surface mine operators agree good roads are desirable, but find it difficult to translate this into an effective road maintenance system. This paper presents a haul road maintenance management system which utilizes an assessment of rolling resistance based on a functional performance evaluation of a haul road, together with mine haul truck operating cost models to derive the optimal frequency of road maintenance. A typical application is presented which illustrates the potential of the technique to manage maintenance as and where needed with resultant reduction in total road user costs and an improvement in service provided for the road user. Keywords: Haul road, surface mining, road maintenance, transportation, pavement design

Jan 1, 2003

Council for 2002/2003 President S.J. Ramokgopa President-elect T.R. Stacey Vice-presidents Senior F.M.G. Egerton Junior W.H. van Niekerk Immediate Past-president A.A.B. Douglas Honorary Treasurer J.A. Cruise

Jan 1, 2003

By S. Sarac

In this study, graphical and mathematical methods used to determine operating points in single or multiple fan ventilation systems are summarized. The problem is mathematically formulized for parallel connected fans in which analytical solutions are not possible. For n number of parallel connected fans, a non-linear equation system that consists of n number of non-linear equation sis derived. The Newton-Raphson method, which is a numerical analysis method, is adapted to solve this non-linear equation system and the solution steps are given as an algorithm. A computer program based on this algorithm is written and its applicability is proved.

Jan 1, 2000

By J. B. Oosthuizen

Mechanical rock breakers are used in block caving operations to reduce the size of ore fragments which are too large to pass through grizzlys at the load-haul-dumper tipping points. Several layouts of grizzly, rock breaker and ore pass are possible. The authors evaluated three different layouts at the Premier Mine Division of De Beers Consolidated Mines. The first layout consisted of a 15m surge bin before the breaker, which was located 15 m below the production level. The second layout had a 43 m longs urge bin, with the breaker located 43 m below the production level. The third layout did not have a surge bin, the breaker was located on the production level and operated at the tip. The ore throughput, availability and utilisation, delays, costs and operational experience with each system are discussed. It was found that the rock breakers did not represent a bottleneck in the ore transfer system and a surge bin did not significantly improve the production capacity. The mine has decided to make use of rock breakers situated on the production level, breaking rocks at the tip.

Jan 1, 1997

By S. Jiansheng, H. Nakayama, D. Lu, A. Wang

ABSTRACT: New techniques and methods for 3D geo-mechanical model test are presented in this paper. The new model material NIOS with high density and low cost; the so-called DPSS (Discrete Principal Stress Surface) loading concept, the loading and monitoring system for the generation of the 3D initial stress field of the model test, also the special techniques and apparatuses for modelling the excavation of caverns located deep inside the model material, are developed and introduced. By adopting those new techniques, a very large 3D geo-mechanical model test with high comparability for a newly designed underground powerhouse has been successfully fulfilled. Key Words: 3D model test, underground group caverns, excavation process modeling. ZUSAMMENFASSUNG: Neue Techniken und Methoden für 3D geomechanischen Modellversuch wurden in diesem Artikel vorgestellt. Ein neues Modellmaterial mit hocher Dichte und niedrigem Preis, ein sogenanntes DPSS (Discrete principal stress surface) Ladenkonzept, ein Laden- und Überwachungssystem für die Erzeugung des 3D primären Spannungsfelds und überdies spezielle Techniken und Maschinen für das Ausbruch der tief in dem Versuchsmodell liegenden Kaverne wurden entwickelt. Bei Anwendungen dieser neuen entwickelten Techniken wurde ein sehr großer 3D Modellversuch mit großem Maßstab für ein geplantes unterirdisches Kraftwerk erfolgreich durchgeführt. Stichworte: 3D Modellversuch, unterirdischen Gruppekaverne, Ausbruchsmodellierung Résumé: le test de modèl de Nouvelles techniques et méthodes pour la géo-mécanique 3D est figuré dans ce papier. Le nouveau modèle de matériels NIOS avec la haute densité et le coût bas; la conception proposée de chargement DPSS (Discrete Principal Stress Surface), le système de chargement et de moniteur pour la génération de champs de stress initial du test de modèle, ainsi que les techniques et appareils spéciaux pour modeler les excavations de cavernes profondément localisées dans l’intérieur du matériel de modèle, sont développés et introduits. A travers l’adoptation de ces nouveaux techniques, le test de modèle de la géo-mécanique très large 3D avec la haute comparabilité pour actualiser une nouvelle étude de la centrale électrique sous-terraine a déjà accompli avec succès. Mots de clé: test de modèle 3D, groupes de cavernes sous-terraines, processus de modèle d’excavation

Jan 1, 2003

By R. G. Cawthorn

The earliest authenticated scientific report of the occurrence of platinum in rocks from the Bushveld Complex appears to be by William Bettel on 10 November 1906. Thereafter, prospecting of the chromite-rich rocks for platinum proved frustrating. I suggest that the resurgence of interest shown by Dr Hans Merensky in 1924 resulted from his realization that newly panned platinum had a different grain size from that in the chromite layers and indicated a different source rock, which he located, and it became known as the Merensky Reef.

Jan 1, 2007

By N. Kornelius

In recent years there has been an increased focus on corporate governance matters worldwide. The duties and responsibilities of directors of companies have come under close scrutiny, with shareholders increasing their demands for greater responsibility and accountability. Media attention and pressure groups have also had their effect. Governmental actions have supported these demands and directors have witnessed sweeping legislative changes imposing more onerous duties and liabilities than formerly imposed upon them at common law and in terms of the Companies Act. At the same time, the power of regulatory bodies has been increased to enforce this legislation and make someone pay to remedy an alleged infringement. Breach of such duties may incur personal or criminal liability, or both. Environmental protection legislation has become a particularly prevalent feature in this regard, and the number and complexity of statutes concerning the environment have increased over the past few years. Directors of South African companies will be familiar with relevant acts such as the National Environmental Management Act 107 of 1998; Conservation of Agricultural Resources Act 43 of 1983;Hazardous Substances Act 15 of 1973, as well as the National Water Act 36 of 1998. Now the directors of mining companies are faced with the Mineral and Petroleum Resources Development Act 28 of 2002.

Jan 1, 2003

By A. Lane

The socio economic risks of mining in South Africa have been emerging for some time now, and have been brought into sharp relief by recent events in the platinum sector. The slow pace of social upliftment in the country has lead to widespread social unrest with consequent calls for different forms of resource nationalism. Fundamentally, the key stakeholders are not fully aligned, and are not engaging productively. This poses significant above-the-ground risk to mining companies. Measuring social impact, deploying inclusive solutions and engaging effectively with stakeholders are three ways in which mining companies can mitigate this risk. Keywords platinum, mining, community, socio-economic impact, stakeholders, conflict, labour unrest, social licence to operate, investment, Africa.

Mar 1, 2013

By M. Dhainaut

This paper presents computations of the electric field inside a furnace. We first look at the effect of contact between two coke particles from an electrical point of view. We give values for the amount of contact resistance in the total resistance of the system formed by the two coke particles. We show that the effect of contact resistance decreases rapidly with increasing contact area. We then look at the complete electric field inside a full scale furnace. The aim is to evaluate the amount of current that short-cuts the metal bath for different vertical positions of the electrodes. We show that electrodes high above the metal bath are undesirable since they offer a larger surface of conductive charge materials where current can flow through. On the other hand, deeper electrodes force the current to go the whole way down to the metal bath. Ohmic heating along this path ensures a high temperature of coke and slag that are beneficial for metal recovery.

Jan 1, 2004

To the members of The South African Institute of Mining and Metallurgy We have audited the annual financial statements of The South African Institute of Mining and Metallurgy set out on pages 483 to 496 for the year ended 30 June 2004. These financial statements are the responsibility of the Institute?s Council. Our responsibility is to express an opinion on these financial statements based on our audit. Scope We have conducted our audit in accordance with statements of South African Auditing Standards. Those standards require that we plan and perform the audit to obtain reasonable assurance that the financial statements are free of material misstatement. An audit includes: ?examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements, ?assessing the accounting principles used and significant estimates made by management, and ?evaluating the overall financial statement presentation. We believe that our audit provides a reasonable basis for our opinion. Audit opinion In our opinion, the financial statements fairly present, in all material respects, the financial position of the Institute at 30 June 2004 and the results of its operations and cash flows for the year then ended in accordance with South African Statements of Generally Accepted Accounting Practice. Auditors 30 July 2004 Council?s approval of the annual financial statements The annual financial statements for the year ended 30 June 2004 set out on pages 483 to 496 were approved by the Council on 30 July 2004 and are signed on its behalf by:

Jan 1, 2004

By V. I. Zhuchkov, L. A. Smirnov, E. I. Arzamastsev, A. A. Babenko

A brief analysis is given for state-of-the-art of manganese and chromium ferroalloy production in Russia and their consumption by metallurgy plants. The main causes of low output of manganese and chromium ferroalloys, and ways to resolve the issue of ferroalloy production development are considered.

Jan 1, 2004