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By J. A. de Carvalho Junior

This paper analyses the impact of the uncertainty associated with the input parameters in a mine planning optimization model. A real example was considered to aid in the building of a mathematical model that represents the coal production process with reference to the mining, processing, and marketing of coal. This model was optimized using the linear programming concept whereby the best solution was perturbed by the stochastic behaviuor of one of the main parameters involved in the production process. The analysis of the results obtained permitted an evaluation of the risk associated with the best solution due to the uncertainty in the input parameters.

Jan 1, 2012

By D. S. Richards

Computers have revolutionized the collection of data on modern mines. Never before has it been possible to collect data from all aspects of the mining value chain at rates now common. With this has come a new challenge. Deriving information from these copious amounts of data and disseminating it. This problem is being exacerbated by technical software systems, which use proprietary and binary data formats that severely inhibit the flow of data and information both across departments and the larger organization. Generally this had led to data duplication and data redundancy. The Gemcom Enterprise Mining System (GEMS) makes use of industry standard, secure and open databases for all its data objects. It manages multiple users accessing the same bits and bytes in the database, preventing data duplication and redundancy. Developed in the Microsoft BackOffice ® environment, GEMS is also able to leverage the enormous amount of tools available in this environment, whether it’s for e-mail notification, reporting or data capture. Microsoft’s® Active Server Pages are one of these tools. These are standards used to create dynamic and interactive web pages with links into databases and many other objects. The real example outlined in the text, demonstrates how a user anywhere in the world is able to login to a web page and run a query that returns a report with vector plots of performance for the user-selected time frame. As integration is tightened between the various components of the mining value chain, the importance and reliance on ASP pages will grow as the need for management information tools develops. Keywords: mines, computers, ASP, GEMS, integration, Microsoft, Management Information.

Jan 1, 2003

By A. Kale

A chlorination pilot plant having capacity to produce 5?10 kg/hr of titanium tetrachloride is in operation at the chlorination facility in Mintek. The bubbling fluid bed chlorination plant can be operated in batch and/or continuous process to study the chlorination kinetics of various feedstocks. The chlorination of titaniferrous ores to produce titanium tetrachloride (TiCl4) was carried out during the commissioning of the pilot plant and also as part of the titanium programme carried out at Mintek. TiCl4 is a basic raw material for producing commercial titanium dioxide pigment and titanium metal. This paper discusses the challenges faced during the commissioning and operation of the chlorination pilot plant. It also discusses the effect on the auxiliary facilities and instrumentation as a result of the harsh operating conditions of +1000°C and use of corrosive gases like chlorine and titanium tetrachloride. It discusses the effect of physico-chemical properties of the titanium tetrachloride and iron chlorides. The effect on the chlorinator refractory lining due to heating and cooling of the chlorinator is also discussed. Besides the special provisions made during the design of the chlorinator, this paper also discusses the operational experience and possible solutions to be implemented in future. Keywords Fluid bed chlorination, titanium ore chlorination, titanium tetrachloride (TiCl4) production using fluid bed technology.

Jan 1, 2011

By R. Abela

Heavy mineral sands are usually beneficiated in a spiral concentrator circuit prior to separation of heavy minerals into streams of zircon, rutile and ilmenite. The performance of the spiral concentrators is heavily affected by the presence of slimes in the rougher feed. The paper quantifies the effect of slimes content and discusses the beneficial effect of spiral feed de-sliming. The net effect of inefficient slimes removal can cause significant recovery losses of the heavy minerals present in the feed.

Jan 1, 2003

By C. Legote

"This paper investigates the conditions leading to the indefinite termination of production in four critical primary panels at an underground coal mining operation, the observed shortcomings in the mining approach, and the proposed strategy to mine through the affected panels. Initial assessment of the abandoned panel conditions indicated time-dependent strata failure,(i.e. bolted roof failure overrunning intersections), which occurred from mere minutes to up to four weeks post-production, with and without prior warning of failure. This prompted the constant re-supporting of back areas, which raised safety and productivity concerns. Investigation of the initial mining conditions revealed that the failures were due to a critical combination of factors, the chief of which was isolated horizontal stress. Other factors that were initially overlooked by the mine (i.e. influence of hydraulic stress, misinterpretation of borehole data), resulted in the conditions being described as abnormal. Remedial actions were determined, and in so doing, a new strategic approach was formulated to thoroughly address all failure concerns. The four panels were explicitly planned to serve as the main intake and return airways for the recently commissioned secondary ventilation shaft, as well as providing access to millions of tons in proven coal reserves. It is thus imperative to mine the panels. A feasibility study showed that the proposed strategy set for implementation would be financially viable. Paper written as project work carried out in partial fulfilment for BEng(Mining Engineering) degree"

Jan 1, 2015

By G B. Gnoinski

The Skorpion Zinc Mine and Refinery is situated approximately 25 km north of Rosh Pinah, south-western Namibia. The supergene zinc oxide deposit at Skorpion is hosted in a volcano-sedimentary succession within the para-autochthonous Port Nolloth Zone of the Gariep Belt. Rock types hosting the ore deposit include altered and metamorphosed volcaniclastic and clastic sediments, limestone and rhyolite. At Skorpion, the metallurgical process is unique and the plant design requires minimal fluctuations within a selected feed grade. In addition, the presence of limestone inter-fingered with ore in some areas of the deposit results in dilution problems which may increase gangue acid consumption and therefore processing costs. Hence, selective mining is necessary to ensure the delivery of suitable ore to the processing plant, in order to keep the overall operating costs at a minimum. A complex control system is in place and is capable of a high degree of selectivity. The paper describes the grade control system in place at Skorpion Mine which ensures that the qualities of the blocks planned for mining and the material being mined meet the stringent process requirements of the refinery, i.e zinc grade, gangue acid consumption and deleterious elements that may impact on the efficiency and costs of the metallurgical process. Keywords: Skorpion zinc, zinc oxide, supergene, volcano-sedimentary, grade control

Jan 1, 2007

By G. V. R. Landman

It is self-evident that economic pressure demands that today?s mines stay ahead and stay competitive. The challenge, however, isto find fresh approaches to the pursuit of efficiency and operational effectiveness. Rather than focusing on individual activities in isolation, a process that can lead to poor investment decisions affecting other critical areas of operation, a key concept is optimization of the whole value-adding process of mining. This concept is often called ?mine to mill?. Whereas it is never easy to establish optimal conditions across a whole mining operation, the quality and consistency of the blasted rock strongly affects all operations. In many instances an inability to control rock breaking has been unchallenged, leading to significant investment in time and money to manage the consequences of poor and/or inconsistent rock breaking. This paper discusses how electronic initiation systems can play a major role in optimizing the whole mining operation. Electronically programmed detonators provide not only the ability to tightly control a key parameter, namely timing, but also the opportunity to extract blast data for a continuous improvement process. The ability to alter predictably, using feedback from the downstream processes, blasting variables such as fragmentation, throw, wall stability, and vibration, is a huge advantage. The current understanding of the effect of timing, accuracy, and scatter on rock fragmentation is reviewed and offers reasons why there is significant progress in controlling blast results. Two case studies are examined, which demonstrate the benefits of the technology on the economics of the operations under review.

Jan 1, 2010

By T. R. Curr, R. T. Jones

Keywords: Pyrometallurgy, Mintek, DC arc furnace, plasma, smelting, chromite, ilmenite, cobalt, slag, zinc fuming, dust, magnesium, laterite, ferronickel, arc modelling, Pyrosim, thermodynamics The Pyrometallurgy discipline at Mintek was initiated in the early 1970s, to support a growing ferroalloy industry in South Africa. In addition to a range of pyrometallurgical options, Mintek specialises in DC arc furnace technology and has pilot plant facilities up to 5.6 MVA, as well as a strong base in process and arc modelling. Industrial processes have been developed for ferrochromium production, ilmenite smelting, and cobalt recovery from slag. Recent work has been done on such processes as the production of ferronickel from laterite ores, the fuming and condensation of magnesium, and the recovery of platinum group metals from 'difficult' feedstocks.

Jan 1, 2006

By M. Pineda

Sublevel stoping (SLS) is one of the oldest and most used methods for underground mining. It relies heavily on the use of drilling and blasting techniques to remove the rock, and gravity to transport the broken rock to drawpoints located at the base of the stope, with LHDs to transport material from the drawpoints. Current SLS operations are based on the assumption of stable geometry of the stope. Thus, the stope design includes the definition of the geometry according to the orebody shape and geomechanical constraints to avoid instability, which may cause excessive dilution. Under some circumstances, dilution could enter the stope due to geotechnical instability, especially when large stope geometries are used. A review of current design and planning practices for large SLS operations indicates that no consideration is given to the material flow and the mixing that occurs after blasting. Material flow could have a large impacton the mixing of ore when grades are heterogeneous in the stope. In this paper, we discuss the influence of gravity flow on the design and planning of large sublevel stopes with and without vertical dilution, based on laboratory experiments. The outcomes of this investigation are used todevelop guidelines towards the design and planning of large SLS mines, which would complement the currently used geotechnical considerations.

Jan 1, 2015

By W. Carter, P. Chaubal, K. Spaleck, M. Schoeman, J. Bobek, W. Seegers

Keywords: Pyrometallurgy, steel, hearth, blast furnace The Mittal Steel Company operates about 36 blast furnaces on four continents. Furnaces range from 1100 m3 to 4800 m3 inner volume. The focus of the group is to push for increasing productivity and increasing campaign life. This has been especially challenging, as many of these furnaces were not equipped for long campaigns during their prior rebuilds. Monitoring and operating practices have to be modified to match the new philosophy. Mid-campaign hearth repair strategies and hearth design philosophies have had to be reconsidered. The paper describes experiences with the current hearth designs and measures taken for hearth life extension. Additionally, the philosophy of recent hearth re-designs is discussed.

Jan 1, 2006

By G. F. Vander Voort

The accident at Unit No. 2 of the Three Mile Island nuclear reactor (TMI-2) on 28 March 1979 was the worst nuclear accident in US history and crippled the nuclear industry. An international Vessel Investigation Project was formed to assess the integrity of the vessel. However, it was not possible to remove specimens from the lower head until January?March 1990. Fourteen of the fifteen specimens removed by electrical discharge machining were from under the debris pile that accumulated on the lower head due to melting of approximately 19 000 kg (45%) of the core. Specimens were previously cut from the lower head of a cancelled reactor of very similar size and design destined for Midland, Michigan. These specimens were subjected to controlled heating cycles with peak temperatures from 800°C to 1100°C for periods of 1 to 100 minutes. The initial study qualitatively compared the structures in the 15 specimens from TMI-2 to the control specimens from the Midland lower head. The writer used the same specimens and employed microindentation hardness traverses, electron microprobe analysis, and selective etching followed by quantitative metallography (by image analysis) to obtain a far more detailed description of the thermal exposure experienced.

Jan 1, 2013

By J. A. de Carvalho Junior

This paper analyses the impact of the uncertainty associated with the input parameters in a mine planning optimization model. A real example was considered to aid in the building of a mathematical model that represents the coal production process with reference to the mining, processing, and marketing of coal. This model was optimized using the linear programming concept whereby the best solution was perturbed by the stochastic behaviuor of one of the main parameters involved in the production process. The analysis of the results obtained permitted an evaluation of the risk associated with the best solution due to the uncertainty in the input parameters.

Jan 1, 2012

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

Mine wide, underground wireless communications are possible with the use of Ultra Low Frequency (ULF) technology. Due to the propagation through rock of ULF radio signals a relatively small antenna can provide communications coverage over a complete mining operation. Starting as a Personal Emergency Device (PED) for emergency messaging to miners under all circumstances, the ULF communications system has grown to include capabilities of remote control of underground equipment such as pumps and fans and centralised blasting initiation. This technology is now in use on 5 continents having lately made it onto the African mining scene. The paper and presentation will provide the audience with the benefit from international mining know-how in this technology as well as local African experiences. A recent commissioning exercise for example, is expected to pay for itself in electricity savings within a few months. These and other results from practical demonstrations and usage will be covered. This novel technology becomes an integral part of the daily operating infrastructure of a mine with immediate safety and business benefits. It is able to reduce capital expenditure and is designed for ease of routine operational use. The paper will conclude with insights into current R&D for further development of this technology.

Jan 1, 2007

By M. du Plessis

This paper describes the evaluation of a limit equilibrium model to simulate the behaviour of crush pillars in platinum mines. An analytical model was derived to calculate the residual average pillar stress (APS) values of the crush pillars. The values predicted by this model were compared to the numerical values obtained from TEXAN simulations. In general, the limit equilibrium model appears to be very attractive for simulating pillar failure as the gradual crushing of the outside of the pillar and the transfer of stress to the intact core can be replicated. The value of the TEXAN crush pillar model was further demonstrated by simulating an idealized layout with crush pillars between two adjacent panels. The simulations illustrated that oversized pillars will not crush close to the face and this may lead to seismic failure in the back area. An important finding of the study is that closure measurements may prove to be a very valuable diagnostic measure in crush pillars layouts. Distinct differences in magnitudes of closure were simulated for a scenario where the pillars crush as expected, compared to the scenario where an oversized pillar is left. Experimental closure data collected in a crush pillar stope provided further evidence regarding the value of closure measurements in these layouts.

Jan 1, 2011

By André de Jager, Henk Ludik

Navachab Mine experiences difficulties with pit wall stability in certain areas of the mine. The main reason for the instability is the fact that the geology comprises many joints and faults. Blasting, without impacting negatively on the stability of the pit walls, poses a major challenge. The mine has installed a technologically advanced seismic monitoring system with monitoring sensors positioned at various locations and depths throughout the pit. The electronic data recording system records all relevant information on a continuous basis with early warning signals in cases of potential danger. From the information recorded by this micro-seismic system it was established that the energy release into the high-wall is predominantly influenced by the mining rate, water content and mining tempo and to a lesser extent by the blasting operations. To limit the negative effects of blast vibrations, the use of Electronic Delay Detonators (EDDs) was introduced. The optimal delays were determined through signature trace analysis. The vibrations obtained during blasts initiated by means of electronic delay detonators were monitored and compared to those traditionally obtained when standard pyrotechnic delay detonators had been used. The measured vibration data indicated an improvement of 25% to 100% drop in vibration amplitude compared. The accuracy and programmability of EDDs presented huge potential for blast optimization in terms of limiting the vibrations without compromising fragmentation. The whole project was conducted over a twelve week period with some 4000 EDDs. The average size of a blast was in the order of 350 holes using about 40kg explosives per hole, which equates to 14,000 kg explosives over 12 different blasts. The paper deals in detail with the blast optimization process with regard to: - determining the rock response time; - establishing the signature traces; - analyzing the wave interference patterns; - predicting the direction of constructive and destructive wave interferences; - optimizing of the inter-hole and inter-row delay periods; - measuring the ground vibrations. The results obtained during electronic blasting are compared to those obtained during pyrotechnic blasting. Comparisons are being made with regard to the following: - ground vibration measurements; - pit wall stability measurements; - blast safety.

Jan 1, 2006

By J. Bakken, M. Th. Jonsson, G. Sævarsdottir

A typical three-phase submerged-arc furnace for production of silicon metal and ferrosilicon has arc currents ~100 kA, phase voltages ~100 V and total furnace power ~10 - 60 MW. The arcs burn in gas filled cavities or "craters", where the main atomic components of the plasma mixture are silicon, oxygen and carbon. Two quite different simulation models for high-current AC arcs have been developed: the simple Channel Arc Model (CAM), and the more sophisticated Magneto-Fluid-Dynamic Model (MFD). These models have been described extensively and results reported at INFACON-8 and INFACON-9, respectively. The coupling between the arcs and the AC power source is described by a complete three-phase Electric Circuit Model. Recent numerical modelling studies of industrial AC arcs show that the boundary conditions at the cathode and anode are critical for the simulation results. A novel Cathode/Anode Sub-Model for high-current AC arcs that treats both cathode and anode indicates a completely different cathode behaviour than previously assumed. A cathode spot which serves a high-current electric arc is shown to be dominated by the energy impact from the arc. This leads to lower cathode fall voltage than obtained from previously developed models. The anode fall voltage is negative, as the main function of the potential barrier is to repel plasma electrons. The cathode spot is diffuse in the sense that the arc in fact contracts away from the cathode. Simulation results are compared to measurements on both industrial furnaces and smaller scale pilot furnaces. An important conclusion, supported by our arc studies, is that the arc length in silicon metal and ferrosilicon furnaces does not exceed 15 cm and the arc may burn anywhere on the electrode, not necessarily beneath the electrode tip.

Jan 1, 2004

By Antonio Karzulovic, Ricardo Sepulveda, Manuel Schellman

Mantoverde Division of Empresa Minera Mantos Blancos S.A., Anglo American Chile, developed an open pit mine to exploit copper oxide ore. Mantoverde mine is located in the Province of Chañaral, Northern Chile, about 1,020 Km far from Santiago. Currently, the East wall of the mine is reaching the condition of final pit. To evaluate the possibility of a pit optimization on this wall a geotechnical study was performed, including slope stability analyses by limit equilibrium and numerical methods. As a result of this geotechnical evaluation, it was decided to allow a probability of failure of 12% for instabilities affecting up to 600,000 tonnes, and use steeper slopes on the East Wall of the mine. This paper describes this geotechnical evaluation and how the results of the stability analyses were used to define a flexible slope design, which allows modification if the observed slope behaviour deviated from the expected one.

Jan 1, 2006

By C. Musingwini

The Bushveld Complex is economically significant and strategically important to South Africa, thus it is imperative that optimal extraction of platinum group metal (PGM) resources on the Bushveld Complex is achieved. Optimal extraction broadly requires that the maximum amount of ore is extracted by excavating and hauling the minimum amount of waste in the shortest possible time, at the least cost, and in the safest and most environmentally acceptable manner. In open-pit mine planning this entails among other things, minimizing the waste stripping ratio, whereas in underground mine planning it includes minimizing the metres of waste development. In conventional mining, the main development that is in waste or partly in waste and defines the mining grid pattern includes levels and raises. It was prudent to consider optimizing level and raise spacing in conventional mining because the method is a prevalent mining method on the Bushveld Complex accounting for nearly 70% of platinum production.

Jan 1, 2010

By M. Hopf, E. Rossouw

Keywords: Pyrometallurgy, furnace, copper coolers, freeze lining, monitoring, Saveway The use of water-cooled copper components as sidewall elements of submerged arc furnaces and other pyrometallurgical applications has become increasingly common. The high cooling efficiency of copper has made it possible to increase the service life of furnace refractories when compared to conventional refractory linings. However even the self-healing effect of ?freezing? worn areas of the lining does not necessarily protect the copper coolers against wear or corrosion completely. In order to avoid furnace explosions, various methods have been used to monitor the wear of coolers. Unfortunately, these have not been able to consistently identify localized wear. Thos Begbie (South African) and SAVEWAY (German) jointly developed technology to embed a line sensor into the copper cooler during the casting process. This system allows an exhaustive monitoring of the copper cooler. A SAVELINE sensor is placed inside the copper-cooling panel between the water-cooling passage and the hot face of the panel. The sensor follows the meandering shape of the cooling water channels. In the first instance, the sensor provides analogue information as the thickness of the copper reduces. Secondly, this wear signal will be confirmed by a signal of interruption if the sensor is washed away. Because of the structure of the sensor, a self-diagnosis is possible and indications can be confirmed (double proofed). Subsequent to the manufacture of some test pieces, coolers for a large submerged arc furnace were manufactured. The sensorized coolers have been installed at the intermittent surface (slag line) where the largest amount of corrosion has been encountered. The system has been operating since December 2005 in what is considered one of the largest submerged arc furnaces in South Africa.

Jan 1, 2006