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By C. J. Van Niekerk

The study comprised of the investigation into the sensitization characteristics of AISI 409 titanium stabilized ferritic stainless steel during low heat input welding. AISI 409 is a fully ferritic stainless steel used in catalytic converters and tubing for automotive exhaust systems due to the supposition that sensitization does not occur during low heat input welding. Two plates of 2 and 4 mm were tested for sensitization during low heat input welding. The study confirmed that chromium carbide (M23C6) precipitation occurs on the grain boundaries in the heat-affected zone with consequent depletion of Cr adjacent to the grain boundaries during welding. In the 2 mm plate sensitization occurred in the heat input range of 0.1 kJ/mm to above 0.25 kJ/mm and in the 4 mm plate sensitization occurred in the heat input range of 0.2 to 0.9 kJ/mm. Ti stabilization is ineffective at the heat inputs used in this investigation due to the rapid cooling rate through the temperature region where TiC precipitates. The presence of N was found to be detrimental since it consumes Ti on cooling, forming TiN, effectively lowering the amount of Ti available for TiC formation during rapid cooling after welding. Annealing for 5 minutes at 725°C does not improve the sensitization characteristics of the welded plate. There is a linear increase in grain size as heat input increases. The resistance to pitting corrosion decreases in the sensitized, welded plate in theheat-affected zone adjacent to the fusion line of welding. Keywords AISI 409 ferritic stainless steel, sensitization, grain growth, resistance to pitting corrosion, low heat input welding.

Jan 1, 2011

By M. Bhandari, D. Norval

The bulk of plain carbon steel is produced through conventional Basic Oxygen or Electric Arc Furnace routes where the development of the AC Ladle Furnace has made it possible to also produce alloy steels. Smaller Ladle Furnaces have limitations such as lower efficiency; high electrode consumption and diminutive yields rendering them uneconomical to operate and making the processing of low carbon steel grades difficult due to carbon pick up. The demand for special steels and alloys with strict specifications is increasing while commodity prices remain competitive. The production of special steels and alloys have specific process control requirements and the development of the induction melting furnace (IMF) has made it possible to produce smaller batches economically. Refining and alloying of the melt in the IMF further enhance the efficiency. The INDUREF furnace offers increased productivity and flexibility through increased thermal efficiency and can be utilised for holding molten metal for further processing such as granulating, atomising, nitriding, alloy additions and desulphurisation of Ferro-alloys and steels. The system utilises a specially engineered ladle which is placed in an induction-heating assembly comprised of a stationary water-cooled copper coil and lamination packs. The addition of equipment for vacuum degassing and decarburisation of steels and alloys is also feasible. Benefits are: ? No electrode consumption or carbon pick-up ? Lower installation, operation and maintenance cost. ? No line-flicker facilitates operation on a weak power grid. ? Good power factor and balanced load ? No skull formation and reduced refractory consumption ? Higher yield of Fe-alloys ? Automatic controlled stirring

Jan 1, 2004

By P. Venter, N. Naude

"Coal mining is a thriving industry and 53% of the coal mined in South Africa is used for electricity generation. Mechanization has made coal mining more efficient, but fines generation has subsequently increased. Up to 6% of the run of mine material can report to the -200 µm fraction. Common problems associated with fines handling include dust formation, storage problems, and high moisture levels. A method to turn this material into a saleable product instead of stockpiling it can add value to a company.Briquetting is a pressure agglomeration method where loose material is compacted into a dense mass (FEECO International, 2014). The briquettes must be able to withstand rigorous handling and transport operations without disintegrating. This study aims to investigate the optimum binder and moisture conditions required to produce a mechanically strong briquette using two different binders - a PVA powder (binder A) and a starch powder (binder B).It was found that for binder A the optimum moisture level was 12% to 14%. At this moisture level the greatest compression strength gains were observed, and low amounts of fines produced in impact and abrasion tests. The minimum amount of binder added while still obtaining a strong briquette was 0.5% binder A. For binder B the optimum moisture level was also 12% and the minimum amount of Binder B to be added was found to be 1%. Briquettes that were dried outside reached their peak strength after about four days, whereas the briquettes that dried inside took about 20 days to reach their strength plateau. Hardly any degradation took place on the surface of the binder A film after exposure of 300 hours of artificial weathering. Thermogravimetric analysis confirmed that neither binder A nor binder B will add to the ash content of the coal fines, as both binders totally decompose above 530°C.Binder B yielded stronger briquettes after 15 days and also generated less fines. It is therefore superior to binder A and would be recommended for further use.Paper written on final year project work carried out in partial fulfilment of B.Eng degree in Coal Beneficiation"

Jan 1, 2015

By J. Hop, A. Støre, T. Foosnæs

The carbon cathode for aluminium electrolysis is also part of the container of the process. In order to understand the behaviour and possible failure of the cathode, detailed material properties under operating conditions are needed. The paper reports experimental studies of bath and sodium in filtration, graphitization with time, loss of strength due to sodium, sodium expansion as function of pressure, as well as creep due to the developed stresses. As an example, sodium and thermal expansion data are used to calculate strain-stress models of realistic cell designs, and possible design weakness can be pointed out. Keywords: carbon, cathodes, sodium expansion, strength, graphitization, creep

Jan 1, 2004

By S. P. Pearton

"Pumpable emulsion explosives have been available to surface and underground massive mining operations for decades, and their unique properties offer significant advantages in terms of improved safety, reliability, and performance. However, the benefits of pumpable emulsions have been unavailable to narrow-reef mining operations due to the lack of technology necessary for their successful implementation in this challenging environment. Despite efforts to promote and enhance the safety and performance of bulk emulsions for narrow-reef stoping, little research has been undertaken to advance the pump technologies required for their implementation. This has resulted in a gap in knowledge and technology, and as a consequence the successful implementation of a pumpable emulsion system has consistently eluded the narrow-reef environment.The purpose of the following investigation was to evaluate the viability of pumpable emulsion explosives for use in South African narrow-reef mining operations. By approaching the problem from multiple perspectives, this research aimed firstly to propose a theoretical framework and suite of equipment suitable for the implementation of pumpable emulsions within the narrow-reef environment. Through the development of this suite of pumpable emulsion technology, tests could be undertaken on the proposed narrow-reef emulsion formulation and pumpable emulsion technology to obtain the necessary understanding of the performance of the system under controlled operating conditions prior to its implementation in the broader mining industry."

Jan 1, 2015

By T. Tamura

It is known that the CaO-FetO-P2O5slag system has a wide liquid miscibility gap at steelmaking temperatures and this two-liquid slag phase has many advantages such as high activities of both FetO and CaO and high amount of P2O5. The phosphorus distribution ratio between the two-liquid slag and molten steel was confirmed to be higher than that between CaOsat.-FetO-P2O5slag and molten steel. The two-liquid slag may be useful for dephosphorization of molten steel and reduction of slag volume. Furthermore, the phase equilibrium of two-liquid CaO-FetO-P2O5slagsaturated with MgO was measured to determine the applicability of the two-liquid slag to dephosphorization in steelmaking process. Keywords: slag, refractories, solid solution, two-liquid phase, dephosphorization, steelmaking, phase equilibrium.

Jan 1, 2004

By F. N. F. le Roux

This paper describes the method used for excavating the upper 33m of emergency access shaft E2 for the underground single track tunnel running between Park and Rosebank station of the Gautrain Rapid Rail System. The soil was decomposed shale and diabase from the Witwatersrand Supergroup. The location was in the car park of The Wilds (a public park) in Johannesburg. The method proved very simple and required less complex plant and equipment than normal when excavating the shallow soil sections in shafts. It involves driving steel sheets ahead of the shaft sump into the soils and then excavating inside the ?tub? created by the sheets whilst supporting the sheets above with regularly spaced circular Steel Rings. It is the intent of this paper to discuss the method and design approach to the method. This will be done at the hand of experiences at E2 shaft..

Jan 1, 2009

By R. P. Jensen

This is a sampling of the papers presented at the conference, the proceedings can be bought from the SAIMM Arbitrary Lagrangian Eulerian (ALE) computational techniques allow treatment of gases, liquids and solids in the same simulation. ALE methods include the ability to treat shock waves in gases, liquids and solids and the interaction of shock waves with each other and with media from one of the other categories. ALE codes can also treat explosive detonation and the expansion of the explosive gases and their interaction with air and solids. ALEGRA is a 3-D ALE code that has been developed at Sandia National Laboratories over the past few years. ALEGRA has been applied to a 2-D simulation of presplitting using decoupled explosives in rock blasting with very interesting results. The detonation of the explosive at the bottom of the hole sends a shock wave up the borehole driven by the explosive gas expanding into air. The explosive gas compresses the air against the stemming column where it rebounds and recompresses at the bottom of the borehole. This type of ringing takes several cycles to damp out. The explosively induced expansion of the borehole is also treated by ALEGRA as well as the shock wave imparted to the rock. The presentation of this paper will include several computer animations to aid in understanding this complex phenomenon.

Jan 1, 2000

By N. B. Devi

The extraction of copper(II) from sulphate solution was investigated using LIX®984N in kerosene. The parameters that could affect the extraction, such as equilibrium pH, extractant concentration, salt concentration, various diluents, and temperature, were separately investigated. On the basis of slope analysis, the complex formed in the organic phase is proposed to be CuR2, where R is the anionic part of LIX®984N. The extraction equilibrium constant and Gibbs free energy ( G) of the extraction process were determined. The positive value of H obtained from temperature variation studies showed that the extraction process is endothermic. The extraction of copper was lowest when chloroform was used as the diluent. Separation and recovery of copper from a synthetic copper-nickel solution containing 6.35 g/L Cu(II) and 0.58 g/L Ni(II) was carried out using 20%(v/v) LIX® 984N. The separation factor ( = DCu/DNi) was found to be pH-dependent. A two-stage batch countercurrent extraction was carried out at an O:A ratio of 3:4 at equilibrium pH 1.05 for extraction of copper from copper-nickel solution, followed by copper stripping from the loaded organic phase with 15% H2SO4 at an O:A ratio of 3:1.

Jan 1, 2014

By F. N. F. le Roux

This paper describes the method used for excavating the upper 33m of emergency access shaft E2 for the underground single track tunnel running between Park and Rosebank station of the Gautrain Rapid Rail System. The soil was decomposed shale and diabase from the Witwatersrand Supergroup. The location was in the car park of The Wilds (a public park) in Johannesburg. The method proved very simple and required less complex plant and equipment than normal when excavating the shallow soil sections in shafts. It involves driving steel sheets ahead of the shaft sump into the soils and then excavating inside the ?tub? created by the sheets whilst supporting the sheets above with regularly spaced circular Steel Rings. It is the intent of this paper to discuss the method and design approach to the method. This will be done at the hand of experiences at E2 shaft..

Jan 1, 2009

By Braam Blom

PK2 Ventilation shaft is part of Paardekraal No 2 twin shaft system that is being developed to replace depleting Merensky reef production at Paardekraal shaft complex. The sinking team at this shaft faced considerable challenge of improving the total sinking cycle in order to be able to deliver the fully equipped shaft on time and on schedule. The cladding support cycle was identified as the tedious and time consuming activity in the overall shaft sinking operation. Reduction in the time required for handling and setting up the support installation equipment, and the time required for subsequent installation of the necessary support has a direct impact on the overall cycle time, and consequently the overall productivity and efficiency of the sinking operation. This reduction in support cycle was achieved by making use of machine carousel. The objective of this paper is to describe the support methodology that was used during the ventilation shaft sinking and the use of the machine carousel to reduce the cladding support cycle. The machine carousel replaces the traditional use of machine kibble in conventional vertical shaft sinking and has been designed specifically for installation of sidewall support at the shaft bottom during the sinking process.

Jan 1, 2009

By H. Möhle

Premier Mine is a large underground diamond mine, situated at Cullinan in the Gauteng Province of South Africa. The mine hoists over 3 millions tons of diamond bearing kimberlite per year, from a modern, mechanized panel retreat block cave mining operation. Troughs sited at the base of the cave are developed into the overlying caved ore, allowing loading access to the ore through draw points. Trough opening is therefore a vital aspect of the mining operation. Most of the production is dependent on fast, reliable and safe trough opening. Successful trough openings are achieved under difficult mining conditions due to restricted void, long up-holes and the inherent properties of kimberlite?soft, elastic rock with a high swell factor. Early in 1998, Premier Mine undertook a joint development project (with an electronic initiation system supplier) to determine whether the use of a fully programmable electronic detonator system would enhance the mining cycle in the trough opening process. Blasting commenced in February 1998, initially with blasts of a similar size and duration to those that had been previously blasted with shock-tube systems, to confirm the operational capabilities of the blasting system. The accuracy, reliability and flexibility of the electronic delay detonators (EDDs) minimized associated risks for re-engineering of the trough opening process. Further, as blast timing was optimized, larger blasts were successfully initiated. To date over 20 troughs have been opened successfully with the use of EDDs. Not only did it take less time to open troughs, but also drilling and blasting operations have been optimized, as well as an overall improvement in safety. This paper details the benefits that EDDs have delivered to Premier Mine in this area. The logic followed is: ?Review of the original trough opening practices ?Re-engineering of the trough opening process ?Implementation of EDDs ?Evaluation of improvements and conclusions.

Jan 1, 2000

By L. Mpolokeng, J. P. Labuschagne, H. Yilmaz

"An investigation into pillar cutting was carried out at a platinum mine on the western limb of the Bushveld Complex. The focus was on crush pillar design and implementation in order to ultimately improve the compliance percentage for pillar cutting. The major findings from the investigation suggest that the pillar cutting problem lies with the implementation of the design rather than the design itself. Observations of the practical issues underground that prevent good pillar cutting were made. After these issues had been identified, recommendations to rectify these problems and a few other issues identified during the investigation were provided. The recommendations are aimed at improving the pillar cutting compliance and reducing the likelihood of pillar bursts or pillar runs, which will ultimately create a safer mining environment. Paper written on project work carried out in partial fulfilment of BSc. Eng. (Mining Engineering)"

Jan 1, 2015

By W. Lin, H. Endo, M. Kwasniewski, A. Kamei, M. Takahashi

Uniaxial tension tests were conducted on specimens of eleven granitic rocks which came from eastern Japan, and included a granite, four granodiorites, four tonalites and two gabbros. The axial and transversal deformability of these rocks was determined based on strain measurements using wire strain gauges. The experimental test results revealed that deformational properties of the rocks investigated varied depending on their petrographic features. However, the axial strain and the lateral strain characteristics showed a similar trend for all the rocks, i.e. the stress-strain curves were non-linear throughout the whole stress range from the initial point of loading to the point of ultimate failure. Moreover, the tangent Young's modulus and the ratio of the lateral strain to the axial strain decreased monotonously with the increasing of the axial stress. Still, the deformational properties were different for individual rocks in a quantitative sense. In particular, the difference in the lateral strains among different rocks was more distinct than that in the axial strains. For example, the Poisson's ratio at a stress level equal to 50% of the ultimate strength of a granodiorite was very low, close to zero. Furthermore, the Poisson's ratio of a tonalite was lower than that of a granodiorite, and assumed a negative value. This effect occurred because the lateral strain became positive as it changed from contraction at the initial stage of loading to extension at higher stress levels. There is no ready explanation for this phenomenon; it is believed, however, that it occurs due to microcracks pre-existing in rock materials and/or weak bonds between the adjacent mineral grains. Les essais de traction directe ont été conduits sur les échantillons de onze roches granitiques provenant de la région Est du Japon: un granit, quatre granodiorites, quatre tonalites et deux gabbros. Déformabilité axiale et transversale de ces roches s’était déterminée en utilisant des jauges extensométriques à fil. Les résultats obtenus à partir des essais montrent que la déformabilité des roches examinées varie selon leurs propriétés pétrographiques. Cependant, à partir des essais, une tendance semblable était observée dans les paramètres de la déformation axiale et la déformation latérale de toutes les roches; c'est-à-dire chaque courbe de contrainte-déformation était non-linéaire dans tout l'intervalle de contraintes à partir de l’état initial jusqu’à l’état d’une rupture finale au cours du chargement. De plus, le module tangent de Young et le rapport de la déformation latérale sur la déformation axiale a diminué de manière monotone avec l'augmentation de la contrainte axiale. Cependant, les différences quantitatives de propriétés de déformation sous traction étaient observées entre des roches individuelles. Particulièrement, la différence de déformations latérales était plus notable que celle-là de déformations axiales entre des roches différentes. Par exemple, le coéfficient de Poisson à un niveau de contrainte égal à 50 % de la résistance d'un granodiorite était très bas, près du zéro. En outre, le coéfficient de Poisson de la tonalite était inférieur que celui du granodiorite et a assumé une valeur négative. Cet effet est apporté parce que la déformation latérale est devenue positive en passant de la contraction dans l'étape de chargement initiale à l'extension sous les contraines plus hautes. Il n'y a aucune explication prête de ce phénomène; on prétend, cependant, qu'il est induit par des microfissures préexistantes dans des matériaux rocheux et/ou des joints faibles entre les grains minéraux adjacents. Einaxiale Zugversuche wurden auf Probestuecke von elf frischen, in Ostjapan vorkommenden, granitartigen Gesteinen durchgefuehrt, welche einen Granit, vier Granodiorite, vier Tonalite und zwei Gabbros umfassten. Die axiale und transversale Verformbarkeit von diesen Gesteinen wurde durch Verformungsmessungen mit Drahtdehnungsmessstreifen geklaert. Die experimentellen Versuchsergebnisse offenbarten, dass Verformbarkeitseigenschaften des untersuchten Gesteins in Abhaengigkeit von ihren petrographischen Eigenschaften variierten. Jedoch zeigten die axialen und die lateralen Spannungsdehnungslinien eine aehnliche Tendenz bei allen Gesteinen, d.h. die Verformungskurven waren nicht linear im ganzen Bereich vom Ausgangspunkt des Belastens bis zum Punkt des entgueltigen Bruchs. Ausserdem verringerten sich das tangentiale Elastizitaetsmodul und das Verhaeltnis der lateralen Verformung zur axialen Verformung monoton mit der Erhoehung der axialen Spannung. Dennoch waren die Verformbarkeitseigenschaften der einzelnen Gesteine in der quantitativen Wahrnehmung unterschiedlich. Insbesondere war der Unterschied bezueglich der lateralen Verformungen zwischen verschiedenen Gesteinen eindeutiger, als der in den axialen Verformungen. Z.B. war die Querkontraktionszahl auf einem Spannungsniveau, das 50% der Zugfestigkeit eines Granodiorits entspricht, sehr niedrig und nah an Null. Ausserdem war die Querkontraktionszahl eines Tonalits negativ und deshalb niedriger als die eines Granodiorits. Dieser Effekt trat auf, weil die laterale Verformung, als sie sich von der Kontraktion am Ausgangsstadium des Belastens bis hin zur Ausdehnung auf den hoeheren Spannungsniveaus aenderte, positiv wurde. Es gibt keine fertige Erklaerung fuer dieses Phaenomen; es wird jedoch angenommen, dass es wegen der Mikrorisse auftritt, die vorher im Gesteinsmaterial und/oder in den schwachen Bindungen zwischen den angrenzenden Mineralkoernern existieren.

Jan 1, 2003

By Ö. Erdem

The investment decision making process in the insurance and finance industries is affected by new advances such as simulation techniques. These advances have improved the discounted cash flow method (DCF). In DCF, a dynamic and flexible model construction is not possible because it does not consider uncertain conditions. Each project should be evaluated taking into account the related uncertainties because the related uncertainties determine the characterization of the project. Related uncertainties can be processed in dynamic DCF, which is applicable to both financial and non-financial industries with different kind of uncertainties, such as power generation and petroleum projects. The dynamic DCF method can estimate net present value (NPV) while managing related project uncertainties with a simulation method like Monte Carlo Simulation. The simulation method is preferred because its output is unbiased. Therefore, a more realistic financial evaluation of the project can be concluded. In spite of the improvement of dynamic DCF, this project evaluation method is not used frequently in mining industry. However, the mining industry is ideally suited to this concept because it is highly dependent on estimations such as orebody size and ore grade. During the project evaluation stage, these uncertainties can be included with the dynamic DCF method. This study aims to contribute to increasing the usage of this method in mining projects. A copper reserve in Turkey is selected as a case study to apply uncertainty assessment for the evaluation of NPV.

Jan 1, 2012

By J. Sjöberg, P. Lundman, E. Nordlund, C. Quinteiro

Abstract In the Kiirunavaara underground mine, crude ore is transported through ore passes from the production levels to the main haulage level. Failure and stability problems have occurred in some of these ore passes, with increasing frequency as mining depths increase. In this paper, selected results are presented from a research project run by LKAB. The presentation focuses specifically on stability analysis. Numerical models were used to identify failure mechanisms, in conjunction with empirical data and engineering judgment. The most important controlling factors governing failure and damage in ore passes were quantified. A causative model was established in which failure mechanisms and failure development were described. This model was used to formulate a prognosis of future ore pass stability, and for recommending remedial measures. Résumé Le transport du minerai entre les niveaux de production et le niveau principal de transport, à la mine de fer de Kiruna, se fait par des passes à minerai. Avec la profondeur d'extraction grandissante, les problèmes de stabilité au niveau de ces passes à minerai se sont multipliés. Les résultats d'un programme de recherche sur la stabilité des passes à minerai à la mine de fer de Kiruna sont présentés dans cet article. Les mécanismes de rupture ont été identifiés à l'aide de modèles numériques, de données de terrain et du jugement empirique des ingénieurs. Les facteurs principaux controllant l'instabilité des passes à minerai ont aussi été quantifiés. Un modèle a été établi dans lequel les mécanismes de rupture et le développement des dommages ont été décrits. Ce modèle a été utilisé à fins prédictives et remédiatives. Zusammenfassung In der Grube Kiirunavaara wird das gewonnene Erz über Sturzschächte von den Abbauebenen zu der Hauptförderebene gefördert. Mit zunehmender Tiefe des Abbaus sind vermehrt Standsicherheitsprobleme in den Sturzschächten aufgetreten, die teilweise zu Verbrüchen geführt haben. In dem vorliegenden Beitrag werden ausgewählte Ergebnisse einer Forschungsarbeit des LKAB präsentiert. Dabei wird der Schwerpunkt auf die Standsicherheitsuntersuchungen gelegt. Zur Ermittlung der Bruchmechanismen wurden numerische Modelle in Verbindung mit empirischen Daten angewendet. Die wichtigsten Einflußfaktoren für das Versagen der Sturzschächte wurden ermittelt. Es wurde ein Modell zur Beschreibung der Bruchmechanismen und des Versagensablaufs aufgestellt. Dieses Modell wurde verwendet, um die Standsicherheit zukünftiger Sturzschächte zu prognostizieren und um Sanierungsmaßnahmen zu erarbeiten.

Jan 1, 2003

By David J. Blackwell

The challenge; to design production facilities and in particular separation equipment which have the ability to deal effectively with the ever changing composition of well fluids, over the life time of the field in which it is operating, ensuring maximum uptime of the asset coupled with consistently effective separation. Design engineers are, however, continually confronted with a dilemma when selecting materials of construction for Oil/Gas separation equipment, since they are generally obliged to select an acceptable material of construction, based on ?predicted? operating conditions, at the lowest acceptable cost. Consequently many designs are somewhat basic and do not take into account the constantly varying dynamics of the well fluids being released into the separator. As oil fields mature, oil companies endeavour to maximize revenue by maintaining oil and gas throughputs. This often results in an associated increase in water and sand volumes and, in order to maintain efficient separation, an increase in operational temperature and pressure; subjecting the equipment to operational conditions for which it was never designed. In reality, therefore, the limitations and constraints placed upon new construction design often result in Maintenance Engineers having to solve the ensuing problems in difficult ?in-field? environments. Should refurbishment or upgrade be required then the status of the platform and that of the vessel during shutdown will dictate how this is achieved. Hotwork on the vessel is generally not preferred due to the requirement for post weld heat treatment and re-classification of the pressure vessel, not to mention the added risk in terms of safety. Unfortunately, until recently, there have been few alternatives to conventional ?hotwork? repair and protection systems, especially since the performance of cold curing polymer based repair and coating systems, for use in oil and gas process equipment, has, until recently, been limited by their resistance to temperature and pressure in immersed conditions. In line with the continued development of high temperature / high pressure oil and gas fields however, recent breakthroughs in polymer technology can now offer both repair and protection solutions which are able to function effectively at temperatures up to 180°C in immersed conditions combined with resistance to the destructive forces of explosive decompression from pressures in excess of 90 bar. This paper will look at recent work that has been undertaken to determine the suitability of modern polymer based repair and protection systems as an alternative to hotwork; thus enabling newly designed and upgraded internals to be cold bonded into position and further protected with temperature resistant coatings, in order to minimize the downtime of the asset and further to protect the vessel internals from the Erosive Corrosive environment.

Jan 1, 2006

By J. Kuijpers

Failure and fracturing are often regarded as synonymous. While this is obviously true in an environment dominated by tensile stresses, it is still not clear how failure and macro fracturing are related in a compressive stress environment. Excavations at great depths are typically subjected to compressive stresses only. The fracturing observed around such excavations is therefore commonly assumed to be induced by such compressive stresses. The physics of such a phenomenon have unfortunately never been explained properly, so that the formation of these so-called extension fractures still remains a mystery. As the presence of fractures is an important factor affecting the stability of underground excavations, it is of practical relevance to understand their formation. In this paper, a possible explanation is proposed. It is argued that fracturing in a compressive stress environment is a secondary effect. Primary failure, in the form of micro fracturing and associated damage is assumed to precede the major fracture processes. The fractures are thus generated in response to material failure and may not directly be the cause of failure. The implications for material response and behaviour are discussed. Keywords: micro fracturing, macro fracturing, extension fractures, failure, compressive stresses, damage, excavations.

Jan 1, 2000

By G. Denton, P. den Hoed, A. Luckos

The potential application of fluidized beds in several sectors of the ferroalloy industry is promising. They can be used in the direct reduction of iron ores to produce a feed for steelmaking, in the reduction of manganese dioxide to produce a lesser oxide for feeding to smelters, in the preheating of chromite for the production of ferrochrome, and in the calcining and pre-reduction of nickel laterites for the production of ferronickel. This paper discusses the potential of fluidized beds in theses processes and highlights the advantages of the technology over other technologies, such as rotary kilns. Two primary advantages?(1) that fluidized beds can treat fine materials and (2) that fluidized beds can be integrated with smelters in a way that allows for more efficient use of energy?may well see the technology gain prominence as more deposits of lower grade are mined and industries strive to use their resources more efficiently. In discussing the potential of the technology in the ferroalloy industry, this paper focuses on the application of fluidized beds in the smelting of chromite, nickel laterites, and manganese ores. Central to the successful operation of this technology is a knowledge of how particle properties influence the behaviour and design of fluidized beds.

Jan 1, 2007

By J. R. Cole-Baker

An independent technical audit by a consultant is part of the accountability process of publicly owned or publicly quoted companies when raising finance through share issues or loans or the sale of equity, and of banks or development funds when granting loans. Africa is undergoing a renaissance in investment in its mining industry. It is forecast that capital investment, in major mining projects in Africa, will be over US$ 4.4 billion, in the next few years. Most, if not all, of the capital to be raised will require an independent technical audit. The aim of this paper is to assist the management of mining companies seeking finance in appreciating the role of such technical audits. The reasons for such audits, especially to attract international investment, are listed. The role of the audit is explained in assessing the underlying robustness of the company as ?a going concern? and the viability of any ?expansion plans?. Its use is emphasised in establishing the underlying value of the company based on the mine life as supported by the mineral reserves. The independent consultant role is stressed as a representative of the parties in a finance deal who cannot, in practice, carry out their own detailed and specialized technical due diligence. The various components of a typical audit are examined with examples of critical matters which may require resolution. The definitions, which are used commonly in audits, in respect of competence and reserves and resources, as stated by various regulatory bodies, are compared.

Jan 1, 1998