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By Z. van Zyl

The southern African coal industry is facing the reality that coal reserves are becoming deeper and harder to mine than before. Alternative visions need to be considered to offset the impact of these challenges on productivity, cost, and profitability. One of the main challenges is to maintain current production levels under more difficult conditions, and improve productivity where conditions allow. There is a need to move from the reactive event-based management system towards the more adaptable and flexible process-based management system. This paper focuses on underground coal mining, but the principles are also applicable to other commodities and mining methods. This paper is based on research undertaken by the personnel from Mining Consultancy Services Pty Ltd (MCS) on trends in the underground coal mining sector, as well as practical experience over a period of 16 years in the field of electronic monitoring of mining machinery and productivity optimization.

Jan 1, 2015

By J. Alexis, G. Ye, E. Burström

Over the past twenty years the 3 MW DC arc furnace at MEFOS has been frequently used for development of new processes. These processes include recovery of valuable metals from slag, sludge and dust from steel and other metallurgical industry, treatment of ashes from power plant and incinerators, smelting reduction of minerals and zinc recovery from EAF dust. The process characteristics of the DC arc furnace operation in terms of: ? selective reduction, ? total reduction, ? process stability and flexibility, ? dust carry-over, ? thermodynamic conditions provided in the hot spot area, ? precision in composing slag products These are analysed and described in this paper based on technical results from selected test campaigns over the years and thermodynamic considerations. The electromagnetic properties of DC arcs beneath the electrode have been studied by CFD simulation. The calculated result enables us to understand some interesting technical phenomena observed. The heat balance has also been considered based on data obtained from test campaigns and heat balance calculation.

Jan 1, 2004

By M. B. Fonseca

Risk quantification in grade-tonnage curves is critical for capital investment in mining projects and can be obtained through geostatistical simulations of orebodies. A practical difficulty may arise in multi-element deposits, as the joint modelling of the related attributes using the traditional co-simulation approaches is computationally intensive and may be impractical for use in the industrial environment. This paper presents the construction of risk-integrating grade-tonnage curves for a complex copper deposit in northern Brazil, by jointly simulating its key geochemical attributes of interest: Cu, Fe and K. The joint conditional simulation of these elements is based on Minimum/Maximum Autocorrelation Factors (MAF). MAF is an approach, based on principal components, that spatially decorrelates the variables involved to non-correlated factors. MAF’sspatial decorrelation at any lag distance is the main and critical difference of this approach from the principal component approach attempted in the past. In the MAF approach, the independent factors are individually simulated and back-transformed to the conditional simulations of the correlated deposit attributes that reproduce the cross-correlations of the original variables. Keywords: Joint simulation; mini/max autocorrelation factors; grade-tonnage curves.

Jan 1, 2003

By R. P. Singh

A mine fire model gallery has been designed and constructed on the premises of the Central Mining Research Institute, Dhanbad, India to perform systematic in-depth studies on various aspects of mine fires. The gallery is 65.5 m long and 5.86 m2in cross-section and it is divided into firing and non-firing zones. It is equipped with a computer-aided online telemonitoring system that has 130 sensors, two data loggers and computer peripherals for continuous recording of various fire parameters. A fan to generate airflow through the gallery has been installed at its end. Two sliding doors and one rolling shutter were also provided for sealing and regulation of airflow. Two sets of experiments have been carried out in the model gallery maintaining air velocity of 1 and 1.5 m/s through it. In the experiments, the inner sides of the firing zone, 22 m in length, were lined with a thin layer (8?10 cm thick) of coal slabs. Two fire suppression techniques viz. flushing of liquid nitrogen (LN2) and infusion of high pressure high stability (HPHS) nitrogen foam were tried to quantify their effectiveness under dynamic fire conditions. The paper addresses important design features of the gallery, its instrumentation system, the experimental procedure adopted and important findings from the experiments. It has been observed that the intensity of the fire was very high after one hour of its initiation and continued for 3?4 hours. During the period, frequent backlash with smoke and flame was noticed. The efficacy of the fire suppression techniques has been assessed interms of reduction in temperature, generation rate of CO2and CO, and heat release rate. The study reveals that high pressure high stability (HPHS) nitrogen foam is more effective in controlling open fires than liquid nitrogen is. Keywords: Model gallery, telemonitoring system, velocity, temperature, pressure, gas concentration, intensity, liquid nitrogen, high pressure high stability nitrogen foam.

Jan 1, 2004

By TvS. von Moltke

Steel is a highly versatile material due to its low cost and good mechanical properties, but typically needs some or other form of corrosion protection due to its tendency to corrode when exposed to atmospheric conditions. In the case of organic coatings, the corrosion protection and functionality of the final product is critically dependent on the adhesion of the coating to the surface of the steel. In this work the effect of contaminants and the nature of the surface layers present on industrial steel products are investigated by means of paint adhesion tests, Auger electron spectroscopy (AES), and X-ray Photoelectron spectroscopy (XPS). It was found that the presence of sodium species on the surface is very detrimental to paint adhesion under wet conditions, while satisfactory adhesion may be obtained even in the presence of silicon and carbon residues. It was also found that the nature of the Fe-O layer, formed under wet conditions is labile and different from that formed in dry air, and that subtle changes in process conditions, such as changing the oxygen content of the quench water, may change the adhesion of paint to the surface of the steel. Lewis acid-base interactions are discussed as a mechanism that may determine the bonding between the steel and polymer coating.

Jan 1, 2003

By A. W. Dougall, T. M. Mmola

"SynopsisThe global resources and commodities market has become highly competitive. While southern Africa’s abundance of minerals resources is still unrivalled, it has lost considerable dominance in terms of production output. The sustainability of southern Africa’s mining industry is increasingly becoming dependent on its ability to manage the performance of its operations well. A valuable tool for monitoring and managing performance is the use of key performance areas (KPAs) – which are those areas of performance that are reflected explicitly or implicitly in the vision and strategies of an organization and reflect the critical success factors of the organization. This paper is a review of key performance areas in the southern African mining delivery environment. The KPAs discussed in this paper have been identified by comparing KPAs of the several mining houses engaged in surface mining operations in southern Africa and then extracting those KPAs that are common to most of them. Although the authors support the view that each organization should develop KPAs to specifically fit its needs, the study reveals that five KPAs – safety and health, costs, product quality, fleet management, and delivery should form a default list that covers the key areas that any organization should consider when choosing KPAs. KPIs are those subsets of KPAs that we measure in order to manage KPAs.IntroductionThe global resources and commodities market has become highly competitive. While southern Africa’s abundance of minerals resources is still unrivalled, it has lost considerable dominance in terms of production output. The sustainability of southern Africa’s mining industry is increasingly becoming dependent on its ability to manage the performance of its operations well. A valuable tool for monitoring and managing performance is the use of key performance areas (KPAs), which are ‘those areas of performance that are reflected explicitly or implicitly in the vision and strategies of the organization’ (Barker, 1997). The terms KPA and KPI (key performance indicator) are often used interchangeably – whether correctly or erroneously is debatable. KPIs are ‘quantifiable measurements, agreed to beforehand, that reflect the critical success factors of an organization’ (O’Neill, 2007). Each KPA probably has multiple KPIs associated with it."

Jan 1, 2015

By P. L. Duncanson, J. D. Toth

Since 1995, when "freeze lining" refractory systems were introduced to the ferroalloy industry, they have gained in popularity, due to the freeze lining?s reputation for reliability, safety, and the contribution it makes to profitability. As with many popular and effective technologies, however, the freeze lining has spawned low-cost pretenders that claim the "freeze lining" name. On the surface they appear to contain some of the components of the technology, such as thermally conductive materials, but they fail to incorporate all of the principles that define a true Freeze Lining. The term "freeze lining" refers to the refractory system?s ability to maintain a temperature profile that is low enough to freeze a layer of process material on its hot face, which insulates the refractory and prevents direct contact with molten metal and slag. In doing so, the common wear mechanisms found in the submerged arc furnace - chemical attack, erosion, and thermal stress - can be prevented. These wear mechanisms are all related to high temperature; thus, they are prevented by maintaining low temperatures. Certain refractory properties and design concepts are absolutely necessary for the lining system to function as a true Freeze Lining. The paper explains these requirements and why they are important - the Truth of freeze linings - and further explains why systems that ignore one or more of these requirements cannot claim to be freeze linings, thereby exposing the Myths.

Jan 1, 2004

By A. Kapito

The formation of bainite in steel is dependent on the size of the casting, the heat treatment, and the alloying elements. It is difficult to obtain a fully bainitic microstructure in steels during heat treatment because of its close proximity to the martensite (a?) reaction. The ferrite (a) and pearlite reactions in steels are also rapid and shield the bainite reaction. Alloying elements therefore need to be added to separate the bainite reaction. Boron (B) and molybdenum (Mo) are key elements added to bainitic steels because of their ability to retard the a reaction. Other elements used in the production of bainitic steels are silicon (Si), chromium (Cr), manganese (Mn), and titanium (Ti). In this paper we investigate the effect of alloying elements on the bainite reaction through the use of dilatometry. Dilatometry is a technique that determines phase transformations in the steel and through which continuous cooling transformation (CCT) curves can then be developed. Some initial results are presented of an ongoing study on the development of bainitic steels for railway wheel applications.

Jan 1, 2013

By P. Rosario

The application of high pressure grinding rolls (HPGR) has been growing in the mining industry for the last 10 to 15 years. The major benefits supporting this trend are better energy efficiency, improved grinding capacity, and higher metal recovery in downstream processes such as heap leaching and flotation. In general there is limited quantitative knowledge on the true benefits of HPGRs relative to SAG mills in comminution, and about which situations one deals with better than the other. This paper will present a structure for comparison of the energy requirements for HPGR versus SAG mill considering complete circuits for comminution of precious and base metals hard ores. The work presented is from the design of four complete circuits based on ore data from two sites.

Jan 1, 2010

Sishen Iron Ore Mine previously used only A-grade material (>60% Fe in situ value) from the pit for beneficiating in the DMS plant to a final product grade of 66% Fe in lump and 65% Fe fine ore. The B-grade (between 50% and 60% Fe) and C-grade material (between 35% and 50% Fe) were stockpiled separately, owing to the inability of the existing DMS plant to beneficiate material at densities higher than 3600 kg/m3. The ability to beneficiate the B-grade material at densities higher than 3600 kg/m3 was evaluated, and air-pulsed jigs were found to be techno-economically feasible and value maximizing. The beneficiation of B-grade material would add to the existing DMS production of 28 Mt/a, with no additional mining cost and only limited costs for the handling of waste and B-material. The objective of the Sishen Expansion Project (SEP), i.e. the jig plant, was to produce 10 Mt/a of saleable product with six modules to the set physical and chemical specifications by 2009. During the start of construction, it was decided to add another two jig modules to the plant to increase production to 13 Mt/a. During commissioning and ramp-up the shortcomings and advantages of the jigs were fully experienced and understood, resulting in many changes to optimize jigging performance..

Jan 1, 2014

Experimental results are presented that test the hypothesis that the descaling behaviour of stainless steel slabs following reheating is controlled by interfacial roughening at the scale-steel interface. In this investigation, two stainless steels were considered: type 304 (austenitic, with 18% Cr and 8% Ni) and type 412 (ferritic/martensitic, with 11.6% Cr). It was found that the entanglement that arises at the scale-steel interface was in fact effective in maintaining scale-steel adhesion, under the mechanical descaling conditions used. In the case of type 304, descaling proceeded by fracture along chromite layers, which formed (by internal oxidation) on the austenite grain boundaries; for this steel, the extent of descaling depends most strongly on austenite grain structure, and not primarily on the conditions in the reheating furnace. In contrast, type 412 samples descaled only at the edge of the entangled zone, and showed a greater sensitivity to the reheating conditions; specifically, higher free oxygen in the reheating gas and longer reheating times were found to increase the residual scale thickness. Key words: stainless steel, reheating, scale, entanglement, descaling, fayalite, internal oxidation, grain structure, free oxygen.

Jan 1, 2003

By M. Nyoka

Historically bauxite-based refractories have been used in applications where andalusite-based refractories could work. Bauxite-based refractories were chosen over andalusite-based refractories mainly because of the availability of low-cost Chinese bauxite and also because many furnaces were designed by international companies that cannot easily access high-quality products. Currently, the availability of low-cost bauxite is under threat as a result of high export duties and tariffs as well as restrictions on the amount of material that China allows to be exported. South Africa is a major producer of andalusite, and this guarantees stability with respect to both availability and price. Refractories based on andalusite have an added economic advantage over bauxite-based refractories in that unlike bauxite, which requires high-temperature calcination before use, andalusite is used in its raw state. This paper constitutes a literature study of the merits, both technical and economic, of using refractories based on andalusite compared to bauxite-based refractories. Keywords bauxite, andalusite, refractory, furnaces, calcination.

Aug 1, 2013

The paper examines the design issues associated with the integration of mineral processing within underground mining systems. It demonstrates conceptual integrated system design options appropriate to a range of geological scenarios. Particular reference is then given to a case study of stoping in narrow base metal veins. The performance of such integrated systems in terms of productivity, economic and environmental criteria is demonstrated by means of simulation. Particular attention is given to the potential benefits to mine waste management. Processing technologies appear to offer genuine potential benefit, whilst underground mining methods may need to evolve further to facilitate full integration. This paper is based on industry supported research aimed at developing selective and clean underground mining systems.

Jan 1, 2003

By A. J. Geldenhuys

This paper will focus on two topics, namely (1) an innovative process for the neutralization and partial sulphate removal of acid streams produced during coal mining and processing and (2)optimization of this integrated neutralization process by adding small amounts of synthetic organic polymers. The integrated lime and limestone process has been developed to neutralize acid mine water and to remove sulphate (to less than1 200 mg/l), magnesium and metals. Limestone and lime treatment is the most cost-effective technology for neutralization and partial sulphate removal of acidic/sulphate-rich water to sulphate levels of less than 1 500 mg/l due to precipitation of magnesium and removal of the associated sulphate fraction (through gypsum crystallization). Neutralized mine water of this quality may be suitable for irrigation. The process consists of the following stages: 1. Limestone (CaCO3) neutralization to raise the pH to 7 and CO2-production. 2. Lime (Ca(OH)2) treatment to pH 12 for Mg(OH)2precipi-tation and gypsum (CaSO4.2H2O) crystallization. 3. pH adjustment with CO2recovered from stage 1 and CaCO3 precipitation. Retention times of 1 hour, 4 hours and 1/2an hour were required by stages 1, 2, and 3 respectively. The sulphate level was reduced to 1 094 mg/l, which is less than the original aim of 1 200mg/l. Chemical costs associated with neutralization, using limestone instead of lime, are reduced by 69% in the integrated limestone/lime process. The overflow water from the clarifier of each of the above stages generally contains a wide variety of colloidal impurities that may cause the water to appear turbid or may impart colour. This results in very slow sludge settling rates that cause overflow water with a high degree of turbidity and colour. There are a number of successive or simultaneous stages involved in the agglomeration of particles. To get optimum neutralisation of the acid water and partial sulphate removal to below the saturation level of gypsum (i.e. 1 500mg/l), maximum sludge recovery is needed. The higher the concentration of seed crystals, the larger the surface area. Therefore, effective removal of suspended and colloidal matter from the overflow of each stage is required and can be achieved by coagulation and flocculation. The polymers PAC6 and 3095 were effectively used as coagulant and flocculant respectively. The addition of these polymers resulted in a clear overflow in each of the above stages with a very low turbidity.

Jan 1, 2003

By D. Peatfield

The design and operation of coal preparation plants are governed by the inherent quality of the raw coal to be processed, market specifications and the saleable tonnage requirements. Topography influences the layout of the plant but does not affect the process design. The coal market comprises many sectors, each having specific requirements with respect to both size and quality. In turn, these have led to different levels of preparation and the development of specific types of coal preparation plant design. Developments in processing techniques and processing equipment have also influenced the design and now give the preparation engineer numerous permutations in process and equipment selection. This paper gives an overview of the coal industry in general and summarizes some of the developments in the design of plants and technical developments in the areas of dense medium processing, fine coal treatment and equipment design.

Jan 1, 2003

This paper reviews the history of refractory materials, highlights the development of refractory technology over the years, draws attention to the technology behind these materials, and comments on future developments in this field. By walking the path with refractory materials, from their initial uses in BC times, to the composite materials that are used nowadays, and the nanotechnology developments that are currently taking place in this field, the reader will come to agree that refractory materials are indeed very ?cool?! Keywords: refractory materials; bricks; monolithic materials.

Jan 1, 2008

By S. G. Ercelebi

In surface mining operations, truck haulage is the largest item in the operating costs, constituting 50 to 60% of the total. In order to reduce this cost, it is necessary to allocate and dispatch the trucks efficiently. This paper describes shovel and truck operation models and optimization approaches for the allocation and dispatching of trucks under various operating conditions. Closed queuing network theory is employed for the allocation of trucks and linear programming for the purpose of truck dispatching to shovels. A case study was applied for the Orhaneli Open Pit Coal Mine in Turkey. This approach would provide the capability of estimating system performance measures (mine throughput, mean number of trucks, mean waiting time, etc.) for planning purposes when the truck fleet is composed of identical trucks. A computational study is presented to show how choosing the optimum number of trucks and optimum dispatching policy affect the cost of moving material in a truck-shovel system. Keywords: Open pit mine, equipment selection, dispatching, linear programming, closed queuing network theory

Jan 1, 2009

By S. K. Murphy, S. M. Spottiswoode, A. M. Milev, D. Geyser

A portable, stand-alone instrument especially designed for recording strong ground motion was used in this study to create a large database of peak particle velocities measured underground. A total number of 39 sites located in stopes mining Carbon Leader and Ventersdorp Contact Reefs were investigated. Peak particle velocities whith values up to 3 m/s were recorded at some sites. The data recorded on the skin of the excavations were compared to the data recorded by the mine seismic networks to determine the site response. The maximum site response was obtained for source radii of between 5 m and 30 m and events locating within 200 m of the site. The extreme values of peak particle velocities were obtained in cases were the face-area lay within the source radius. Un instrument portable unique spécifiquement conçu pour enregistrer les mouvements dynamiques des terrains, a été utilisé dans cette étude pour créer une base de données importante sur la vélocité maximum des particules, mesurée en souterrain. Un nombre total de 39 sites situés dans les excavations exploitant les récifs appelés ‘Carbon Leader et Ventersdorp Contact Reefs’, a été investigué. Une vélocité maximale avec des valeurs allant jusqu’ à 3 m/s a été enregistrée sur certains sites. Les données enregistrées sur le bord de l’excavation ont été comparées aux données enregistrées par les réseaux séismiques de la mine pour déterminer la réponse du site. La réponse maximum du site a été obtenue pour des sources de rayons entre 5 m et 30 m et des évènements situés dans les 200 m du site. Les valeurs extrêmes de vélocités maximales ont été obtenues pour les cas où la zone de face se trouve à l’intérieur du rayon de la source. Ein mobiles, alleinstehendes Instrument, speziell entworfen um starke Formationsbewegungen aufzuzeichnen, wurde in dieser Studie verwendet um eine große Datenbank von Partikelspitzengeschwindigkeiten, die Untertage gemessen wurden, aufzuzeichnen. Eine Gesamtanzahl von 39 Aufstellungsorten in den Schichtabbauorten vom Carbon Leader und Ventersdorp Contact Reef wurden untersucht. Partikelspitzengeschwindigkeiten mit Werten bis zu 3 m/s wurden an einigen Standorten aufgezeichnet Die an der Oberfläche des Grubenraumes aufgezeichneten Daten wurden mit jenen Daten verglichen, die vom seismischen Netzwerk der Grube notiert wurden, um die örtliche Reaktion des Standortes zu bestimmen. Die maximale Standortreaktion wurde für Ursprungsradien von zwischen 5 m und 30 m erhalten und Ereignissen die sich innerhalb von 200 m vom Standort befanden. Die extremen Werte der Partikelhöchstgeschwindigkeiten wurdenin jenen Fällen erreicht wo sich der Abbaubereich innerhalb des Ursprungsradiuses befand.

Jan 1, 2003

By N. Fardin, O. Stephansson, L. Jing

A pair of silicon rubber replicas of size 250 mm by 250 mm, from a natural rock joint, was used to produce several high strength concrete fracture replicas of different sizes, from 50 mm by 50 mm to 200 mm by 200 mm. The morphology of the concrete fracture replicas were digitized at the laboratory using a 3D-laser-scanning machine with high accuracy and resolution. The scale dependency of the geometrical properties, including surface roughness and aperture, of the samples were investigated using fractal method. The investigation was extended to study the scale effect on the mechanical properties of the concrete fracture replicas. Four concrete replicas having same geometry from each sampling size were sheared under four different normal loads. The results show that normal and shear stiffness and peak shear strength decrease with increasing sample size and decreasing normal stress. It is concluded that for accurate determination of geometrical and mechanical properties of rock joints in the laboratory and field scales, samples with size equal to or larger than stationarity limit are required. Silikongummiabdrücke der Größe 250 mm x 250 mm einer natürlichen Kluft dienten als Vorlage für mehrere Hochfestbeton Rissreplikas verschiedener Größe. Die Morphologie der Beton Rissreplikas wurde mittels eines 3D-Laserscanners hoher Genauigkeit und Auflösung im Labor digitalisiert. Die Skalenabhängigkeit der geometrischen Eigenschaften, dies inklusive Oberflächenrauhigkeit und Öffnungsweite, wurden mittels Fraktalen bestimmt. Die Studie wurde durch die Untersuchung der mechanischen Eigenschaften der Betonrepliken erweitert. Hierbei wurden vier Betonrepliken der selben Geometrie jeder Probengrösse unter vier verschiedenen normalen Belastungen abgeschert. Die Ergebnisse zeigen das sowohl Normal- und Schersteifigkeit als auch die Spitzenscherfestigkeit mit zunehmender Probengrösse und abnehmender Normalspannung abnehmen. Es hat sich gezeigt, daß für eine genaue Bestimmung der geometrischen und mechanischen Eigenschaften von Felsklüften im Labor und im Feld Proben einer Größe gleich oder größer des stationären Limits verlangt werden. Deux répliques en gomme de silicone d’une fracture naturelle, de dimension 250 mm par 250 mm, ont été utilisées pour produire des répliques en béton de haute résistance de dimensions allant de 50 mm par 50 mm à 200 mm par 200 mm. La morphologie de ces répliques a été digitalisée au laboratoire à l’aide d’un laser-scanner 3D haute résolution et haute précision. L’influence de l’échelle des propriétés géométriques, incluant rugosité et ouverture, a été étudiée en utilisant la méthode des fractales. Des essais complémentaires ont été réalisés afin d’étudier l’effet d’échelle sur les propriétés mécaniques des répliques de fracture en béton. Quatre répliques béton de même géométrie pour les différentes tailles d’échantillons ont été cisaillées sous quatre valeurs de contrainte normale. Les résultats montrent que la rigidité normale et tangentielle ainsi que la résistance de pic diminuent en proportion de l’augmentation de la taille de l’échantillon et de la diminution des contraintes normales. On peut en conclure que, pour une détermination précise des propriétés géométriques et mécaniques des fractures au laboratoire et sur le terrain, des échantillons de taille égale ou supérieure à la limite stationnaire sont nécessaires.

Jan 1, 2003

By J. H. Cloete, S. M. Bradshaw, D. K. Chibwe

"Modern tundishes have evolved as vessels to serve as the final step in refining of molten steel by removing inclusions and promoting thermochemical homogeneity.In this study the flow behaviour in a four-strand tundish was investigated by means of a ½-scale water model as well as numerical modelling. The numerical and physical models were used to characterize residence time distribution and calculate properties pertaining to tundish flow regime. Three different tundish configurations were investigated: a bare tundish with no flow control devices, a tundish with a turbulence inhibitor, and a tundish with both a turbulence inhibitor and a dam.The physical and numerical models showed that a tundish without flow control devices is prone to significant short-circuiting. A tundish with a turbulence inhibitor was shown to be successful in preventing shortcircuiting and provided surface-directed flow that might assist the removal of inclusions from the melt. However, it was also observed that the upward-directed flow caused the maximum turbulence kinetic energy near the surface to increase dramatically. The potential for slag entrainment should therefore be considered during the design and operation of tundishes with turbulence inhibitors."

Jan 1, 2015