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By K. Nong, H. F. Fuls

The quality of Pregnant Leach Solution (PLS) at Skorpion Zinc is of utmost importance for efficient operation of the Solvent Extraction (SX) Plant. Suspended solids in the PLS forms CRUD in the settlers, resulting in reduced zinc transfer capacity and increased impurity carry over to Electrowinning. The Ishigaki Fibre-Wakishimizu filter (fibre media rapid filtration equipment) has been identified as polishing filter that potentially could remove solids from the PLS of Skorpion Zinc. A pilot unit with 20m³/h capacity was tested on site over a period of 9 months under plant operating conditions in the refinery. The FW filter produces a clear filtrate, acceptable for the Solvent Extraction. Turbidity is improved by 72%. Gravimetric analysis indicates a 47% removal of solids. However, the gravimetric method is biased by a co-precipitation of saturated salts during the analysis. Filter media is blinded by the Skorpion Zinc PLS solution, as result of suspended solids and process chemistry. The media could not be regenerated to acceptable conditions. Further testwork to investigate the impact of process solution chemistry modification on blinding is undertaken. Based on the outcome of this investigation a final decision on the FW filter can be taken.

Jan 1, 2007

By M .. Hori, H. Onishi, Y. Goda

The split-lining structure was newly developed for the air-tight lining of the underground compressed air storage cavern. This structure consists of separated reinforced concrete (RC) segments and air-tight membrane. It is most important for the Compressed Air Energy Storage Gas Turbine (CAES-G/T) system to develop the economical lining. In order to verify the applicability of split-lining structure, CAES-G/T pilot plant was constructed and operated for 6 months. We confirmed the practical usefulness and safety of this system through the operation. This paper presents the mechanical behaviour of surrounding rock mass and the lining structure observed through the operation of CAES-G/T pilot plant. Nous avons mis au point une structure de revêtement modulaire pour le revêtement des cavernes souterraines hermétiques à pression. Ce revêtement est composé de segments de béton armé et de membranes hermétiques. Il était très important, pour le CAES-G/T (Compressed Air Energy Storage Gas Turbine), de développer un revêtement économique. Afin de vérifier l’aptitude d’application de notre revêtement modulaire, nous avons construit un système pilote CAES-G/T et nous avons effectué des essais de fonctionnement pendant six mois. Ces essais nous ont permis de confirmer l’utilité et la sécurité du système. A travers le présent rapport, nous rendons compte de la structure de ce nouveau type de revêtement et du comportement mécanique de la masse rocheuse environnante que nous avons pu observer au cours desdits essais. Als luftdichter Druckbehälter wurde eine gegliederte Belagsstruktur für tief unterirdisch liegende Felshöhlungen entwickelt. Diese Struktur ist aus Stahlbetonabdeckung und luftdichter Plane aufgebaut. Bei der Entwicklung des Pressluftgasturbinen – Stromerzeugungssystems (CAES-G/T) war es die wichtigste Aufgabe, einen wirtschaftlichen Belag zu entwickeln. Deswegen wurde zum Nachweis der Effektivität der gegliederten Belagsstruktur eine Pilotanlage errichtet und 6 Monate lang betrieben. Durch den Betrieb konnten wir die Praktikabilität und Sicherheit des Systems bestätigen. Dieser Aufsatz ist ein Bericht über das Verhalten der durch Betrieb der CAES-G/T Pilotanlage beobachteten Belagsstruktur und umliegenden Felsmasse.

Jan 1, 2003

By I. McDougall

The matte/slag tidal zone in a nickel-copper-iron-sulphide matte smelting furnace is subject to severe process conditions that can lead to premature failure of the lining. The MgO-FeO-SiO2 slag is aggressive to refractory bricks, while the Ni-Cu-Fe-S matte is aggressive to water-cooled copper cooling elements, and can penetrate and sulphidize refractory bricks. A novel approach to the lining design was taken at a PGM smelting furnace, where an indirectly-cooled graphite ring was applied in the matte/slag tidal zone, with refractory bricks on the hot face. The graphite was cooled by the copper cooling elements in the slag zone, obviating the need for copper cooling elements in the tidal zone. In this paper the effectiveness of different lining designs utilizing varying degrees of cooling in the slag zone and slag/matte tidal zones is compared. In comparison to water-cooled copper in various configurations, cooled graphite shows promise as an indirect refractory cooling system in the tidal zone area of furnaces. Keywords PGM smelting, graphite, refractory lining, copper cooling elements, submerged arc furnace.

Aug 1, 2013

By Y. Mao, D. Xie

The viscosity of TiO2-containing blast furnace slags may increase rapidly (commonly referred to as thickening) under strong reducing conditions in the blast furnace. To elucidate the mechanisms for slag thickening, measurements have been made of changes in the composition and rheological properties of TiO2-CaO-SiO2-Al2O3-MgO slags during the reduction process. The slag composition covered the range of 17–33 wt% TiO2, 9–19% Al2O3, 8–16% MgO and theCaO/SiO2from 0.8 to 1.4. The viscosities were measured using the rotating cylinder method at temperatures up to 1550ºC and the fusibility temperatures were determined from ‘breaks’ in the viscosity-temperature curves. The reduction of the slag was carried out in graphite crucibles at1500ºC for 2–6 hours The rheological properties of the slags during reduction were predominantly influenced by the slag basicity (CaO/SiO2), and the effect of other components depended largely on basic or acidic behaviour of the oxide. The reduction of TiO2in the slag by carbon was initially fast to formTi2O3, followed by further reduction to TiO and TiC. Correspondingly, the viscosity showed initially a slight decrease, followed by a gradual and then rapid increase. The thickening was found to be accelerated by an increase in TiO2content and a decrease in the CaO/SiO2in the slag. In addition to the existence of 1~3 wt% TiC, the thickened slags also had a significant amount of TiO (3~7 wt%), suggesting that TiO may play an important role in the ‘thickening phenomena’ ,possibly by forming solid solutions with TiC to significantly increase the number of solid particles in the heterogeneous slag. Keywords: TiO2slags, viscosity

Jan 1, 2004

By C. E. Hales

In an effort to improve efficiencies and reduce costs, AngloGold has embarked on a process to develop and deliver consistent, high quality, tailings based support or construction products to stopes and tunnels on request. A three-phase approach of product conceptualisation, design and delivery has been adopted. To date a substantial amount of laboratory development has taken place with promising results, indicating that the project aims are achievable. Dans un effort pour améliorer le rendement et réduire les coûts, AngloGold s’est embarqué dans une opération qui vise à développer et fournir aux chantiers d’extraction et tunnels, sur demande, des produits de construction ou de support basés sur rejets qui sont réguliers et de haute qualité. Une méthode à trois volets a été adoptée : conception, création et livraison. A ce jour, un développement important en laboratoire s’est produit, avec des résultats pleins de promesses, qui semblent indiquer que les buts du projet peuvent être atteints. In der Bemühung, die Effizienz zu steigern und Kosten zu verringern, hat AngloGold begonnen ein Verfahren zu entwickeln welches auf Anfrage konsistent hochqualitative auf Haufwerk basierender Unterstützung oder Bauprodukte für Abbaustellen und Tunnels entwickelt und liefert Eine Dreiphasenplan zur Produktkonzeptualisierung, Design und Lieferung wurde adoptiert. Bis jetzt hat eine substantielle Anzahl an Laborentwicklung mit vielversprechenden Resultaten stattgefunden und aufgezeigt, daß die Projektziele erreichbar sind.

Jan 1, 2003

Konkola No 3 shaft experienced severe mining-induced stress and time-related deterioration in ground conditions in an area where an over-cut and bench (OCB) mining method was used to extract a shallow dipping wide orebody. This caused an unacceptable risk for safe mining operations to sustain the required levels of production. After a review of the conditions it was decided to change the mining method to CASCADE to recover ore in the affected area and modify the OCB method and use a modified over-cut and bench method (MOCB) for new mining sections. This paper describes the geotechnical criteria included to derive the mining standards for the MOCB. The geotechnical risks are identified and taken into account to develop stope design parameters, stoping sequences and support requirements. A monitoring programme to assess conditions as mining progresses is also discussed.

Jan 1, 2005

By O. Naiker, T. Riley

Keywords: Pyrometallurgy, furnace, Xstrata, ferrochromium, Premus Technology The presentation will give a basic overview of Xstrata Alloys. Included will be a brief history of the Alloys division as well as of each plant within the division. The Xstrata chrome plants utilise a wide variety of production processes, including Xstrata's Premus process, the Outokumpu process, and the conventional process. Xstrata?s Lion Project is underway, with commissioning expected in the third quarter of 2006. The new smelter will utilize Xstrata?s patented Premus process, and the competitiveness of the Premus process is discussed.

Jan 1, 2006

By A. M. Hearn, J. G. Roos

Energy consumption, being a large proportion of the input of the ferroalloy production process, can be measured in terms of the efficiency with which the energy is utilized and the effectiveness with which it is used. The efficiency of the usage of energy revolves around the specific consumption of the energy for the production of the alloy, which encompasses the thermodynamic aspects of the process and is more of a metallurgical function that will not be addressed further in this paper. The effectiveness with which the energy is utilized is determined by the optimisation of the electricity supply from the utility (in this case Eskom). The South African electricity supply industry is on the brink of considerable restructuring, implying changes in ownership, structure and regulation. In other countries, however, restructuring has often seen higher prices. Owing to the diversity of growth prospects in South African markets, Eskom is turning to new market management and generation strategies. In future, Eskom will develop pricing strategies to increase demand from attractive customer segments such as paper & pulp, iron & steel, aluminium, and other metallurgical industries. There will be a broader spectrum of product offerings, including dynamic pricing options and demand-side management incentives. In a future electricity market that will become more dynamic and demanding, it will become increasingly important for electricity consumers to optimise their electricity supply. There are many facets in optimising the electricity supply, which include optimal utilisation of the tariff, integrating energy cost management into the production planning process, implementation of demand-side management actions, modelling, scenario planning (.what-ifs?.), optimisation, maintenance scheduling coordinated with the tariff periods, etc. This paper gives consideration to the status of the development of technology at the manganese alloy works of Samancor at Meyerton, South Africa in order to increase the effectiveness with which energy is utilized.

Jan 1, 2004

The results of a series of physical model studies of the stability of jointed rock slopes carried out some years ago are described. These models were tested under centrifugal loading. Four ?geological? structures were tested; all had the same joint orientations and strengths, but the relative spacing of the joints was different. The results showed that the mechanisms of failure of the slopes varied for the different models, and the gravitational loads at which failure developed also varied. The following conclusions are drawn from the results of the physical model tests: ?the mechanism of slope failure is by progressive deformations throughout the slope ?the ratio of the spacings between the different sets of discontinuities exerts considerable influence on the slope failure ?in the models tested, the intact material strength had no noticeable influence on the stability of the jointed rock slopes(note that for hard rock, similitude conditions indicate a prototype slope height of 300 to 400 m, and therefore intact rock failure might not be expected under simple gravity conditions, i.e. no tectonic stresses) ?rock slope failures are three-dimensional and in general are not amenable to two-dimensional simplification ?knowledge of the orientations of discontinuities in the slopes does not allow prediction of a unique failure surface, nor of a volume of failure. The volume of failure is determined to a large extent by the plan configuration of the slope.

Jan 1, 2006

By F. Essrich

A quantitative rockburst hazard assessment procedure was introduced on Elandsrand Gold Mine at the end of 1994. It is currently used to evaluate the seismicity-related risk in production areas on the mine. Six parameters related to seismicity, geology, mining layout, and production are rated and results are used as a planning tool on a regular basis. The applied assessment can be considered successful in that it promotes awareness of the seismic hazard and provides an opportunity to address seismicity-related mining problems. A comparison between high risk panels and those working areas with rockburst incidents showed that high hazard ratings reliably forecast the occurrence of larger events in the following month but they do not necessarily predict those working places with rockburst-related accidents. From this one may conclude that high levels of seismicity do not coincide with high rockburst rates.

Jan 1, 1997

By Md. Amanullah

A novel triple action load cell assembly (LCA) was developed to determine three index parameters reflecting compressive, tensile and shear characteristics of mudcakes. The results indicate that the tensile, compressive and torsional behaviour of mudcakes are strongly influenced by the physics and chemistry of the mud additives. Eine neuartige dreifach wirkende Druckkammer zur Bestimmung der drei Indexparameter Druck, Zug, und Scherung von Spülungskuchen wurde entwickelt. Die Ergebnisse weisen auf einen starken Einfluss der physikalischen und chemischen Spülungszusätze auf Druck, Zug, Scherung hin. Un assemblage d'une nouvelle cellule a triple action (LCA) a été développée pour déterminer trois paramètres caractérisant la compression, la contrainte en traction et la résistance á la fracture des cakes. Les résultats indiquent que les comportements tensile, compressif et de torsion des argiles sont fortement influencés par la chimie et la physique des additifs des boues.

Jan 1, 2003

By J. Gholamnejad

The aim of short-term production scheduling is to decide which blocks of ore and waste to mine in which time period (shift, days, weeks or months) so that several operational and geometrical constraints can be satisfied simultaneously. Since 1960s several mathematical programming approaches were developed for solving production scheduling problems that are based on a combination of various operational research approaches such as linear programming (LP), integer programming (IP), dynamic programming (DP), etc. A number of models have been developed in the past three decades but some models have limited application especially to geometrical mining constraints. One of the geometrical constraints is block accessibility. All blocks must be accessible to mining equipments on the same bench. In this paper a binary integer programming model is developed in order to incorporate block accessibility constraints in an efficient manner. This mathematical model insures that each block has been open and can be loaded and transported easily by shovels and trucks.

Jan 1, 2008

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

Jan 1, 2003

By J. L. Human, N. Fernandes

The rockfall hazard is the major contributing agency to fatal accidents in South African platinum mining operations. The majority of these accidents occur in close proximity to the working stope face. The collapse of fractured or blocky ground between individual temporary support units or the closest permanent support line to the stope face has not yet been adequately addressed. A large-scale stope support system testing facility funded by the Safety in Mines Research Advisory Committee (SIMRAC), has been designed and constructed to test support systems and stimulate innovative thinking by mining personnel, support manufacturers and suppliers by providing a facility where the interaction of stope support systems, a rigid stope face and a discontinuous hangingwall beam can be observed during quasi-static and dynamic conditions. Tests have been carried out on various types of stope support systems, focusing on the temporary support systems used in the immediate stope face area. The interlinking of the temporary support units with mesh or safety netting has been explored in the prevention of falls of ground between support units during gravity driven falls of ground. These tests illustrate the facility?s ability to be used to stimulate innovative thinking and provide a testing ground for the development of temporary support systems in order to reduce the risk off all of ground injury to mining personnel at the stope face.

Jan 1, 2004

By M. Maleki

Variogram analysis and kriging lack robustness in the presence of outliers and data with long-tailed distributions, which often arises when estimating grades in precious metal deposits. The capping technique, consisting of truncating the data to some top-cut grade, is widely used in order to mitigate the influence of the values in the upper tail of the distribution. However, this procedure omits part of the grade variability and is likely to provoke a bias in the estimates. To avoid these issues, a recently proposed approach is to decompose the grade of interest into three components (the truncated grade, a weighted indicator above the top-cut grade, and a zero-mean residual) and jointly estimate the truncated grade and the indicator by cokriging. This approach is attractive as it provides unbiased grade estimates, allows choosing the ?optimal? top-cut value, and essentially works with truncated and indicator data, thus avoiding the use of outlying values for calculating sample variograms and performing spatial interpolation. This work presents an application of this approach to a disseminated gold deposit that has been identified through exploration drilling. The effect of using an indicator covariate is assessed through leave-one-out cross-validation, by comparing the grade estimates with the true grades and with the grade estimates obtained with the conventional capping approach, which considers only the truncated grade as the variable of interest. As a result, cokriging the truncated grade and the indicator above top-cut grade outperforms the conventional capping approach, yielding significantly more accurate estimates. A few complementary guidelines are provided for validating the model hypotheses and for the implementation of cokriging.

Jan 1, 2014

By V. C. Kelessidis

The interaction between rock and drill bit during drilling has been modeled for many years, but a complete understanding of the phenomena occurring has yet to materialize. Successful models will allow the prediction of rate of penetration in a given environment and optimal selection of drill bit and drilling parameters, thus minimizing exploration costs. In most rock-drilling models the value of the unconfined compressive strength of the rock (UCS) is used in the predictive equations, within the concept of specific energy, and the value of UCS is the percentage of the value of the stress applied on the drilling bit in order for the bit to advance. While the exact percentage depends on the model used and it is not known with certainty, good knowledge of UCS is nevertheless required before any decent prediction can be made on rate of penetration. Determination of UCS, normally done via destructive testing, requires not only the availability of sound rock core samples but also expensive testing and significant time for the test, which frequently are not available for routine drillability predictions. Hence, a multitude of methods and techniques has been proposed for estimating UCS from various indirect and/or non-destructive measurements, or combination of measurements with neural networks, such as point load index, block punch index, unit weight, and apparent porosity, water absorption by weight, sonic velocity, and Schmidt hardness. The many proposed approaches are critically reviewed and the results are compared, and what becomes apparent is that after many years, not only in mining but also in oil-well drilling, accurate indirect determination of UCS is still an elusive goal. An equation to predict UCS from sonic velocity data is suggested based on several data sets reported in the literature. Use of the specific energy equation with UCS or sonic data and utilization of drilling data allows an estimation of the efficiency of energy transfer from the bit to the rock and of the friction coefficient. Analysis of data reported in the literature, both from laboratory and field studies, has shown that this approach is sound and enables the determination of energy transfer efficiencies and friction coefficients, which for the cases studied range between 15 and 30% and 0.15 and 0.30 respectively. Thus, the suggested data analysis approach allows drillers to focus on inefficiencies and optimize drilling practices in future campaigns. Keywords Rock drillability, unconfined compressive strength, prediction.

Jan 1, 2011

By L. D. van Dyk

The extraction of iron and lead from their oxides with a volatile organic ligand such as acetylacetone in the gas phase offers potential advantages of lower energy consumption, recycling of the extractant, recovery of pure metals, and a reduced environmental impact compared with conventional extraction processes. The influence of reaction temperature, ligand flow rate, and metal oxide levels on the extraction and rates of reaction of iron and lead from single metal oxide (synthetic haematite (Fe2O3) and synthetic massicot (PbO)) systems in a fluidized bed was studied. It was found that at the investigated acetylacetone flow rates, the influence of mass transfer was limited, but that the reaction suffered from reactant starvation. When the metal load increased the effect of starvation on the rate of reaction also increased. The reaction kinetics increased with an increase in temperature for both systems. At low metal oxide concentrations more that 80 per cent of the iron and lead could be extracted from their respective metal oxides after only four hours.

Jan 1, 2012

By C. Thiart

Kriging is an interpolation technique for predicting unobserved responses at target locations from observed responses at specified locations. Kriging predictors are best linear unbiased predictors (BLUPs) and the precision of the BLUP is assessed by the mean square prediction error (MSPE), commonly known as the kriging variance. Both the BLUP and the MSPE depend on the covariance function describing the spatial correlation between locations and on specific parameters. The parameters are usually treated as known, whereas in practice they invariably have to be estimated and the empirical BLUP (that is, the EBLUP) so obtained. The empirical or estimated mean square prediction error (EMSPE), or the so called ?plug-in? kriging variance estimator, underestimates the true kriging variance of the EBLUP, at least in general. In this paper five estimators for the kriging variance of the EBLUP are considered and compared by means of a simulation study in which a Gaussian distribution for the responses, an exponential structure for the covariance function, and three levels of spatial correlation ? weak, moderate, and strong ? are adopted. The Prasad-Rao estimator obtained using restricted or residual maximum likelihood (REML) is recommended for moderate and strong spatial correlation and the Kacker-Harville estimator for weak correlation in the random fields.

Jan 1, 2014

By L. D. van Dyk

The extraction of iron and lead from their oxides with a volatile organic ligand such as acetylacetone in the gas phase offers potential advantages of lower energy consumption, recycling of the extractant, recovery of pure metals, and a reduced environmental impact compared with conventional extraction processes. The influence of reaction temperature, ligand flow rate, and metal oxide levels on the extraction and rates of reaction of iron and lead from single metal oxide (synthetic haematite (Fe2O3) and synthetic massicot (PbO)) systems in a fluidized bed was studied. It was found that at the investigated acetylacetone flow rates, the influence of mass transfer was limited, but that the reaction suffered from reactant starvation. When the metal load increased the effect of starvation on the rate of reaction also increased. The reaction kinetics increased with an increase in temperature for both systems. At low metal oxide concentrations more that 80 per cent of the iron and lead could be extracted from their respective metal oxides after only four hours.

Jan 1, 2012

By Jeffrey C. Hillman

The need to recruit locally produced engineers by the South African Mining Industry led to the Engineering Faculty at the University of the Witwatersrand developing a number of academic bridging initiatives for educationally disadvantaged students. The graduation rate achieved during the initial five years of operation by the most successful of these programmes has been on a par with that of al other students but the performance of subsequent intakes has declined to such an extent that the continuance of this scheme could now be at risk. One reason for this reduction in throughput is that many of the applicants for the increasing number of mining bursaries have been more interested in the bursary than the profession and have either failed or dropped out due to a lack of application and motivation. This will have serious consequences for both Wits and the Industry if it continues and some method of identifying unsuitable or suspect applicants needs to be introduced as a mater of urgency. It is recommended that an introductory course be set up at a working mine that would be run under the auspices of Wits, as a joint venture with industry, and include a level of academic input that would provide both bridging needs and certain first year credits. The final form of this course will require extensive consultation with al parties but needs to be completed before the end of 1996. It is further recommended that the advertising and promotion of mining careers be expanded and much improved.

Jan 1, 1996