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By R. T. Jones

DC arc furnaces are widely used for steel scrap melting as well as for reductive smelting of ore fines. Industrial smelting applications include the smelting of chromite to produce ferrochromium, the smelting of ilmenite to produce titania slag and pig iron, and the recovery of cobalt from nonferrous smelter slags. A number of myths and misconceptions are widely held, especially regarding: the age of the technology, the use of a hollow electrode, arc stability and shape, arc and bath radiation, interaction between the arc and molten slag, electrical behaviour of arcs and slags, a comparison between AC and DC furnaces, DC reactors, the lifespan of bottom electrodes, and the applicability of DC arc furnaces to various metallurgical systems.

Jan 1, 2011

A localized nonlinear recoverable resource estimate technique has been applied using typical feasibility or new mining drilling data configurations drawn from a massive database from a mined-out area on a hydrothermal gold deposit. The results were then compared with the corresponding 8 m x 5 m grid grade-control data in order to determine the efficiency of the approach and the validity of the recoverable resource estimates for mine planning and financial forecasts.

Jan 1, 2014

By E. Laine

Rock density determinations are necessary for ore resource evaluations from estimated block grades in g/t. Rock density depends on the mineral composition and, thus, it is specific for each rock type. The rock density distributions for different rock types are often symmetric. Hence, the arithmetic mean is a good approximation for the average density for lithological units. However, there may exist spatial variation in density values due to alteration, fracturing and original heterogeneities such as layering. This study compares the kriged density model with the one with constant density values for different lithological units in the evaluation of metal amounts in rock blocks. The case study consisted of rock densities measured from the drill cores at Ahmavaara PGE deposit in northern Finland. The used Ni contents were simulated in accordance with the spatial distribution of rock densities. The Ni amounts in 2x2x2 m3blocks are higher for the kriged densities than for the average densities. The difference is increasing with the increasing metal amounts due to the nonlinear correlation between Ni content and rock density. The final effect on the resource estimation depends on the cutt off grade and prices of the metal, for example, for a very valuable metal the small differences are significant

Jan 1, 2003

By M. Natarajan, C. J. Cutler, E. Mponda

Keywords: Pyrometallurgy, furnace, KCM Nkana, Zambia The Nkana smelter was initially commissioned in 1931, with two reverberatory furnaces, two Peirce-Smith converters, and blister copper casting facilities. Reverberatory furnaces were the mainstay of production up until 1994, when an El Teniente Converter (CT) was installed to upgrade reverberatory furnace matte to white metal, prior to converting in conventional Peirce-Smith (PS) converters. In 2000, a decision was taken to increase the proportion of concentrate smelted in the CT by introduction of bone-dry concentrate injection through the tuyeres. A flash dryer with a nominal capacity of 1 200 metric tons per day of dry product, and associated tuyere injection system was commissioned in March 2004. Based on the projected concentrate arisings from the KCM mines into the future, as seen in 2004, it was decided to develop the CT to be the primary smelting vessel at Nkana, to handle a minimum of 1 250 tons per day of concentrate, and to operate only one reverberatory furnace in slag-cleaning mode pending a full evaluation of alternative slag-cleaning technologies. The anticipated cathode production from Nkana was to be in the range 140 to 150 000 tons per annum. This paper details the outcomes from trials that were carried out in August and September 2004, using two reverberatory furnaces for slag cleaning. The results of these trials, plus further work in October and November, provided confidence to move to one reverberatory furnace for slag cleaning in December 2004. With the advent of Vedanta as the majority shareholder in KCM at the end of 2004, the approach has been to maximize the available smelting capacity. Currently, two reverberatory furnaces and the CT are on-line, with the higher silica concentrates going to the reverberatory furnaces with an appropriate amount of pyrite, and the cleaner concentrates going to the CT. Expansion of the smelter is currently under investigation.

Jan 1, 2006

By D. J. Adams, W. K. Rymon-Lipinski

Rock engineering plays a crucial role in contributing to sustainable development in South African mining. A framework for this has been created through legislation and structures to encourage the mining industry to have a long and prosperous future. However, rock engineering input is an essential element to achieving success. The most accessible deposits have been mined in South Africa and although large reserves still remain, many of these are difficult to access and will require excellent rock engineering knowledge and skill in the future. This is borne out by the fact that more than 50 % of fatal accidents are related to rock engineering issues. Many of these may be addressed with rock engineering solutions which are not beyond current rock engineering technology. A reduction in fatalities and injuries contributes to a sustainable mining industry.

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 P. K. Sahoo, C. R. Ray, S. S. Rao

This paper deals with various factors affecting the strength of chromite briquettes which plays a vital role in the smelting of charge chrome / ferro chrome production. Appropriate briquetting parameters like molasses and lime binder level, molasses quality, particle size distribution and segment condition etc. are essential to guarantee quality briquettes in the successful use of briquette and chromite ore fines. In developing a technology for briquetting of chromite ores, it is important not only to study the grain size characteristics of the chrome ore fines but also to make an informed choice of the type and quality of the binder and the condition for producing a physically and chemically competent green and cured briquette. This paper also describes the effect of strength of briquettes on various parameters of charge chrome production as the use of quality briquettes in the production of high carbon ferrochrome alloys has a number of operational, metallurgical and economic advantages. It is also a requirement for submerged arc furnace operation that the charge be adequately porous to allow gaseous products of the reduction reaction to escape from the furnace charge burden without hindrance. Otherwise, furnace material would erupt causing electrodes and furnace other equipments damage and risking the safety of the work force. The briquette, because it replaces lumpy charge but has an advantage of smaller size, allows for an uniform and porous charge so that the ascending gaseous products can escape freely. Finally this paper deals with furnace operational results with varying proportion of briquettes having same strength.

Jan 1, 2007

A diverse selection of rockbolt designs and resin anchors are available for use in underground mines. Research in recent years at the UNSW Mining Research Centre led to the construction of a rockbolt pull-testing facility. This facility has subsequently been upgraded, commissioned and initial test work has been completed to verify the pull-test process. A test program has been completed with the objective to understand the load transfer mechanism and improve the general performance of rockbolts. This paper describes the results of this research. Une sélection diverse de dessins du rockbolt et ancres de la résine est disponible pour usage dans les mines de métro. Faites des recherches ces dernières années à l'UNSW que le Centre de la Recherche Minier a mené à la construction d'une facilité de l'essai de la traction du rockbolt. Cette facilité a été améliorée par la suite, le travail de l'épreuve en commission et initial a été complété pour vérifier le processus de la traction-épreuve. Un programme de l'épreuve a été complété avec l'objectif comprendre le mécanisme du transfert de la charge et améliorer la performance générale de rockbolts. Ce papier décrit les résultats de cette recherche. Eine verschiedenartige Auswahl an rockbolt-Designs und Harzankern ist dafür verfügbar, benutzen Sie in unterirdischen Bergwerken. Forschung in letzten Jahren beim UNSW-Bergbau Forschung Zentrum führte Ruckerprobung-Einrichtung zur Konstruktion eines rockbolt. Diese Einrichtung ist anschließend befördert worden, ist beauftragt worden und wird abgezeichnet, prüfen Sie, die Arbeit ist vervollständigt worden, um den Ruckprüfung-Prozeß zu verifizieren. Ein Prüfungsprogramm ist mit dem Objektiv vervollständigt worden, den Lastübertragungsmechanismus zu verstehen und die allgemeine Aufführung von rockbolts zu verbessern. Dieses Papier beschreibt die Ergebnisse dieser Forschung.

Jan 1, 2003

By M. Nete

Qualitative analysis of three mineral samples from northern Mozambique was accomplished by X-ray diffraction (XRD), microscopy, scintillation, and magnetic determination. Chemical characterization was accomplished using ICP-OES and pressed powder XRF after dissolution using microwave-assisted digestion and flux fusion. The samples consisted of a mixture of minerals with tantalite as the major component, with minor amounts of microlite, quartz, mica, accessory garnet, and tourmaline. Incomplete dissolution was obtained using microwave digestion, with maximum recoveries of 90.25 ± 0.06% and 88.90 ± 0.04% for Nb2O5 and Ta2O5 respectively. Complete dissolution using Li2B4O7 resulted in recoveries of 98.5 ±0.2% Nb2O5 and 100.4 ± 0.3% Ta2O5.

Jan 1, 2012

By D. P. Roberts

The stoping of platinum orebodies in the Bushveld has in the past been accomplished by using in-stope pillars to ensure stability of the workings. In the future, the use of continuous mining machines to mine the platinum orebodies is probable. It is not envisaged that such machines will cut in-stope pillars. This paper describes the alternative support systems that will replace the pillars and the stope geometries that will be required for this type of mining. The paper describes how the support resistance provided by in-stope pillars in current mining was determined and then evaluates support systems that can substitute for these pillars. Conceptual layouts based on existing breast mining layouts are presented. The layouts consist of panels of up to 100 m face length between rigid strike stabilizing pillars. A number of design charts are then proposed that allow for the design of appropriate support systems.

Jan 1, 2005

By P. Rice, A. Photolo, A. C. Barnard

Introduction -Sampling Tool Project (STP) -History -Results to date -Costs -Questions

Jan 1, 2005

By J. Little

It is common practice for underground mine plans to be created sequentially, where results from one planning process form the input data for another. While this is practical for manual methods, computerized optimization techniques should consider an integrated approach to creating the global mine plan. This is because optimizing an individual mine planning process, such as stope layouts, introduces a likelihood of increasing costs or decreasing revenues associated with other areas, such as production scheduling, as harmful decisions must be balanced. Considering the interaction and influence that individual underground mine planning processes have on each other during optimization will provide more profitable results than if these are ignored. Optimization techniques for stope layouts and production scheduling are reviewed. An integer programming model is proposed that allows for either integrated or isolated optimization. Both approaches are separately applied to a block model. The results demonstrate the model?s ability to produce optimal long-term sublevel stoping mine plans and the benefits of using an integrated approach. Keywords underground mine optimization, stope layouts, underground production scheduling, integer programming, mathematical programming application.

Oct 1, 2013

By A. Bothma

The Impala No. 1A ventilation shaft is located approximately 15 kms north of Rustenburg and is accessed via the R510road from Rustenburg to Northam/Thabazimbi. This situation is shown on the location plan in Figure 1. The geology at the site consists of an upper layer of black turf of about 1 metre in thickness, grading into weathered norite. The depth of weathering is generally less than 5 metres. Zones of deeper weathering may occur along fracture zones associated with faults and dykes. Groundwater occurs mainly within the weathered/fractured aquifer system. The ventilation shaft is a 5.1 m diameter upcast shaft ,and forms part of a system of ventilation shafts to complement the existing infrastructure as mining progresses down the new twin decline extension of Impala 1 shaft. The principal reason for these shafts is to lessen the risk of an extended RAW and also to counter the effects of the heat build-up as the mining goes deeper, with the resultant effect that the existing cooling centre (fridge plant) becomes more remote from activities. The No. 1A shaft (upcast) is positioned approximately 1,2 km on down dip from the main shaft and the No. 1Bshaft (downcast) approximately 1,2 km further. Geological information was used from a borehole 1,2 km away on strike from the upcast shaft. The first shaft (1A) is a 5,1 m diameter hole to be fitted with two 2,2 MW fans, whilst the second shaft (1B) is 4,1 m diameter to accommodate a 7MW fridge plant.

Jan 1, 2001

By M. Mabuza

Two Rivers Platinum Mine (TRP) is a 55:45 joint venture between African Rainbow Minerals and Impala Platinum, respectively. TRP is situated on the farm Dwarsrivier 372KT, in the southern sector of the eastern limb of the Bushveld Complex. Dwarsrivier is underlain by rock formations of the Critical Zone (Winterveld norite-anorthosite) and the Main Zone (Winnarshoek norite- anorthosite). Two economically significant PGE-bearing layers namely the Merensky Reef and the UG2 chromitite are found within the upper Critical Zone. These are approximately 140 m vertically apart, separated by a series of barren norites and anorthosites. At Two Rivers Platinum, only the UG2 chromitite layer is currently being mined for PGEs. The UG2 sub-outcrops north/south along the Klein Dwarsrivier river valley with a very gentle dip to the west of 7º?10º. At Two Rivers the UG2 averages about 120 cm in thickness, overlain by a waste pyroxenite parting about 20 cm thick, above which is a leader seam about 20 cm in thickness. The mineable cut consists of the leader seam, the waste pyroxenite parting, the UG2 chromitite layer including 25 cm of pegmatoidal pyroxenite footwall, below the UG2 reef to a minimum of 185 cm trackless mining cut. The mining method is a mechanized bord and pillar layout, which will yield a total of 185 000 tons at full run of mine production from the underground UG2 mine.

Jan 1, 2007

By J. P. Piguet, Y. Wileveau

ABSTRACT : An experimental programme for damage assessment was performed in the vicinity of the main shaft of Andra’s Underground Research Laboratory, currently under construction in the East of France, when the shaft is crossing the Kimmeridgian marls between 80 and 100 m depth. The mechanical behaviour was analysed by mean of convergence and displacement measurements. The disturbance into the wall was assessed using numerous methods such as measurement of sonic velocities, permeability measurement and VSP measurement in radial boreholes. The intensity of the damaged zone is low, and its extension does not exceed 0.5 time the radius of the shaft. It does not seem to depend on blasting patterns. ZUSAMMENFASSUNG : Ein Forschungs- und Versuchsprogramm wurde aufgestellt, um die beschädigte Zone im Bereich der Kimmeridgemergel zwischen 80 und 100 Meter Tiefe beim Zugangsschacht des im Bau befindlichen Andralabors im Osten Frankreichs zu berechnen. Das mechanische Verhalten der Formationen wird auf der Grundlage von Konvergenz- und Verschiebungsmessungen ermittelt. Verschiedene Messmethoden, wie z.B. mikroseismische Geschwindigkeite Messungen, Permeabilitäs- und Beschleunigungsbestimmungen in strahlenförmigen Bohranordnungen, erlaubten die Ermittlung des Beschädigungscharakters der Schachtwand. Die Intensität der beschädigten Zone ist niedrig, ihre Ausdehnung übersteigt nicht die Hälfte des Radius des Zugangsstollens und scheint unabhängig vom Schema der Sprengstoffanordnungen zu sein. RESUME : Un programme expérimental visant à évaluer la zone endommagée autour du puits d’accès du Laboratoire de Recherche Souterrain de l’Andra actuellement en construction dans l’Est de la France a été mis en œuvre lors de la traversée des marnes du Kimméridgien entre 80 et 100 m de profondeur. Le comportement mécanique des formations est évalué à partir de mesures de convergence et de déplacements. La mise en œuvre de nombreuses méthodes, telles que des mesures microsismiques, des mesures de perméabilité et d’accélérométrie en forages radiaux, a permis de caractériser l’endommagement en paroi du puits. L’intensité de la zone endommagée est faible et son extension ne dépasse pas 0,5 fois le rayon du puits. L’endommagement semble indépendant des schémas de tirs testés.

Jan 1, 2003

By T. J. Kolokoto

This paper is based on a project conducted at Khomanani 2 shaft, Anglo American Platinum Limited. The main objective was to find an alternative support element in stopes to address the falls of ground (FOG) problem experienced at this shaft. Literature review was the major method used in the investigations. Resin bolts or any 1.5 m in-stope roofbolts were considered. The shaft was making use of 0.9 m long friction bolts, and these could not prevent the FOG experienced. Observations indicated that the FOG resulted in fall-out thicknesses averaging to 1.1 m, which is greater than the supported length of the friction bolts. The implementation of 1.5 m long bolts was recommended as a result of the project. These bolts will be able to address the fall-out thickness and provide sufficient support resistance to mitigate FOG. The chosen support element will result in a relatively small increase in support costs.

Jan 1, 2013

By S. O. Bada

Coal samples taken from the No. 2 Seam and No. 4 Seam in a South African colliery were tested in a rotary triboelectrostatic separator. The two-stage triboelectrostatic separation results using the -177 µm size fraction reduced No. 2 Seam coal containing about 30.4 per cent ash to a clean product of 8.9 per cent and 13.1 per cent ash with combustible recoveries of 9.6 per cent and 30.7 per cent respectively. The same separation approach on No. 4 seam feed coal, which contained 36 per cent ash, produced a clean coal product with 10.8 per cent ash at a combustible recovery of 6.0 per cent. Petrographic tests show a significant improvement in the vitrinite content and a reduction in visible minerals encountered when using the triboelectrostatic separator, with about 53 per cent vitrinite reporting to the clean fraction for No. 2 Seam compared to the feed content of 21 per cent, and a 54 per cent vitrinite in the clean No. 4 Seam from a feed content of 21 per cent. Significant sulphur reductions were also observed after separation in both coal samples, with a better separation in the second-stage coal products.

Jan 1, 2012

By B. J. Buys

Rock bolt integrity is a critical issue for the mining industry because of its influence on the safety of mining operations. Guided ultrasonic wave testing of the defects associated with resin-anchored rock bolts was investigated. Axisymmetrical and three-dimensional finite element models were built, one of a partially encapsulated bolt and the other of a bolt with a simulated local corrosion crack. Experimental bolts were then installed in a testing block and typical responses were compared to finite element models of different defect scenarios. Encouraging results were obtained for the smaller axisymmetrical and three-dimensional finite element models, as well as during the experimental investigation. It is recommended that software with energy-absorbing elements should be utilized to consider higher frequencies and longer bolts. Once the integrity of models such as these has been established, the models could in principle be used to train neural networks for use in commercial equipment to determine the integrity of the installed bolt.

Jan 1, 2009

By E. Pardo-Igúzquiza, R. A. Olea

The bootstrap is a computer-intensive resampling method for estimating the uncertainty of complex statistical models. We expand on an application of the bootstrap for inferring semivariogram parameters and their uncertainty. The model fitted to the median of the bootstrap distribution of the experimental semivariogram is proposed as an estimator of the semivariogram. The proposed application is not restricted to normal data and the estimator is resistant to outliers. Improvements are more significant for data-sets with less than 100 observations, which are those for which semivariogram model inference is the most difficult. The application is illustrated by using it to characterize a synthetic random field for which the true semivariogram type and parameters are known.

Jan 1, 2015

By M. S. Raseroka

An experimental rig has been constructed to produce chloride stress corrosion cracks in Type 304L stainless steel tube samples. The samples are to be used to test possible in situ repair methods in future work. The factor which influences the time to failure most strongly is the sample temperature; the distribution of cracks within the sample is affected by local temperature variations and by the position of the water line. Low-frequency oscillations in stress, caused by the on-off temperature controller, did not appear to influence cracking in these tests.

Jan 1, 2009