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By J. Gummer, M. Williams, S. J. Hawksworth

A common problem encountered in British coal mines is bearing failure on conveyor system idler rollers, which on occasions has led to fires. The UK Mines Inspectorate initiated a study of such failures to assess the potential for ignition of explosive atmospheres. As part of this study HSL have developed a system to measure the temperatures generated within the bearings during controlled failure. Temperatures are measured using both infrared thermal imaging and contact thermometry. The work to date has shown that temperatures well in excess of the auto-ignition temperature of methane can occur.

Jan 1, 2003

By S. Lohmeier, D. Gallhofer, B. G. Lottermoser

Reprocessing of historic gold tailings is a common activity in South Africa, while base metal tailings offer similar reprocessing potential. The historic base metal tailings of the Namib Pb–Zn mine (Erongo Region, Namibia) still contain valuable resources of Pb and Zn in carbonate-rich matter. Micro-analysis of primary ore minerals identifies some galena as argentiferous and sphalerite as the principal host of Cd. This study demonstrates that knowledge of primary ore mineralogy helps to reveal the hosts of valuable commodities (Ag, Cd) and that field-portable X-ray fluorescence tools allow precise and accurate determinations of major and minor elements like Zn and Cd in such carbonate-rich material. Although there are limitations to directly determine the contents of certain element (i.e., As, Sb, In), linear correlations allow prediction of the likely abundance of these elements. Providing that the inter-mineral and inter-element relations are understood and there is consistency in sampling and analytical methodology, portable X-ray fluorescence analysis is an effective method to evaluate the chemical characteristics of base metal tailings for a range of major and trace elements.

Sep 9, 2024

By H. Dong

This paper presents a heat conduction model to determine the erosion profile of freeze linings in a ferronickel submerged arc furnace. Kirchhoff transformation was adopted to simplify the nonlinear equation governing heat conduction. The boundary element method (BEM) and Nelder-Mead simplex optimization method were employed to solve an inverse heat conduction problem. Erosion profiles could be obtained when calculated temperatures at sensor locations agreed well with measured temperatures. The model was validated by comparing the heat loss through the linings, which was calculated by BEM and integral operation after erosion profiles were obtained, with the value calculated from industrial data such as actual power consumption, tap-to-tap time, and ferronickel output. The optimal solution for the erosion profile could be acquired when the difference in heat losses calculated by these two methods is at a minimum.

Jan 1, 2014

By J. E. Nesset

The bubble size, together with the gas rate, determines the bubble surface area flux in flotation machines and, therefore, impacts directly on the kinetics of flotation. Understanding the variables that influence bubble size is one of the keys to understanding flotation recovery. Surprisingly, these relationships are poorly understood, largely due to the difficulties associated with gas dispersion measurements in industrial environments. The McGill gas dispersion sensors (bubble size, gas rate, gas holdup) are capable of reliably making such measurements. This paper reports on a study, using the McGill sensors in a 0.8 m3 Metso RCSTM pilot cell, which investigated the effect on bubble size of frother type and concentration, gas rate, temperature and rotor speed. A Denver laboratory cell was used to investigate the effect of elevation above sea level. Frother concentration proved to have the predominant influence on bubble size, and the effect of frother type can be normalised as a function of the critical coalescence concentration (CCC). Measurements made at many plant sites worldwide are compared to the model developed using the Metso RCSTM unit.

Jan 1, 2007

By F. M. C. C. Vieira

Four mining alternatives for exploiting an ultra-deep orebody were assessed through a multidisciplinary evaluation process which involved: the generation of a 3D geological model; the design and scheduling of life-of-mine layouts; the analysis of anticipated ventilation and cooling conditions; the study of rock-related risks of mining in ultra-deep stress environments; the logistic implications of transporting men, rock and materials; and, lastly, the economic implications of each option. Once results from the integrated mine design assessment were available, mine planners were faced with an important problem to solve: how to identify the optimal mine design alternative when numerous assessment measures and multiple decision criteria needed to be considered simultaneously? To address this ‘multiple-attribute decision problem’ and arrive at the ‘optimal layout for ultra-depth’, a generic decision methodology that uses principles of ‘utility’ was applied. The methodology assumes that ‘single-value risk estimators’ do not account for the inherent variability of real conditions. Therefore, risk estimators were represented by statistical distributions of their incremental changes, where applicable. The stochastic variables, once defined, are used as inputs in the ‘utility’-based layout decision scheme. This ‘utility’-based decision methodology offers a framework for mine design decisions to be made objectively, when complex trade-offs between multiple risk domains need to be considered simultaneously. Upon applying it, one of the layouts emerged as the preferred alternative. Keywords: Utility; mine design; multiple-attribute decision; layout selection

Jan 1, 2003

By P. van Dorssen

In South African metalliferous mines, stoping operations are largely confined to narrow, tabular orebodies making mechanization extremely difficult. Limited flexibility in terms of stope width has necessitated drilling by means of handheld, pneumatic rock drills at most of our operations. As the largest producer of platinum in the world, we drill in excess of forty million stope blast holes per annum. Cleaning of the broken ore is also done by conventional means?utilizing scrapers and scraper winches. Conventional methods such as these carry high costs in terms of risk exposure as well as labour intensity. The purpose of this paper is to describe the development of a long hole stoping system suitable for the narrow platinum reefs. The new system had to be substantially safer and more cost effective than conventional mining. We selected a site that was conducive to mechanized mining and set out the parameters that we considered would meet our requirements. We then conducted a feasibility study to evaluate the conceptualized long hole stoping system in terms of specific goals. An analysis of the proposed system identified the Key Performance Indicators (KPIs). One of the most critical goals was to be able to create a man-free stope. This would mitigate the safety risk associated with normal stoping operations, as well as the inefficiency cost previously referred to.

Jan 1, 2002

By O. Acaroglu

Selection of the most suitable roadheaders (boom type tunnelling machines) for the galleries/tunnels to be excavated in certain rock and under known project conditions is important for avoiding problems during application. This research utilized a multiple attribute decision-making method and studied how this will be applied for the selection of boom-type excavation machines. The Cayirhan Coal Basin was used for selecting roadheaders using the analytical hierarchy process, which is one of the multiple attribute decision-making methods. To conclude, this study reveals that decision-making methods can be used in the process of selecting roadheaders for the excavation of galleries. Keywords: roadheaders, multiple attribute decision-making, analytical hierarchy process.

Jan 1, 2006

By D. G. Hulbert, D. J. Oosthuizen, D. de V. van der Spuy

Expert Online, as a software system, is aimed at providing plant operators in the minerals industry with effective training and on-the-job assistance. It incorporates a number of features to achieve this goal, of which the most important is its ability to explain the dynamics of the plant and control system in simple language, mimicking an informed plant expert who has online access to the inner workings of the plant and control system. This is made possible by a novel form of Artificial Intelligence, called the Interpreting Expert System. Previous implementations of the IES were only capable of explaining controller actions. Expert Online will extend this capability to also perform the more difficult task of explaining process behaviour. Expert Online will implement three main processes, namely the accumulation of data from the controllers and plant models, the interpretation, processing and filtering of that data and lastly communicating the relevant information to the user, both as written messages and in other audio-visual forms. Although Expert Online is aimed at the operator, other plant personnel, like supervisors and plant managers, will also benefit from it. This paper focuses on the structural and functional design of Expert Online for implementation on the latest version of Mintek’s open control platform, PlantStar, highlighting advances and additions since the previous implementations of the Interpreting Expert System and concluding with an example illustrating some of the principles.

Jan 1, 2003

Following a short review of selected literature, a back analysis of stress measurements of stress regeneration in a closed mini-longwall is shown. The agreement is good, lending confidence to the parameters used in the proposed numerical model. Foundation yielding was modelled in the absence of total stope closure. A ?Prandtl? wedge was formed, coinciding with the yield point of the pillar/foundation system. Some theoretical work is used as a starting point for the formulation of a new design methodology for strike or dip stabilizing pillar/foundation systems in deep level goldmines. The existing guideline for the stability of foundations (APS< 2.5UCS) is critically examined. Finally, the advantages of the new approach, and the work required to substantiate the proposed new design methodology, are outlined.

Jan 1, 1998

By J. Daavittila

In the latter part of the 1980s Outokumpu Chrome in Tornio, Finland, was in a situation when its twenty-year-old ferrochrome plant was becoming too inefficient to sustain economically sound production. The company made extensive studies on the then available processing methods to find out the best possible processing route. As a result, the whole plant was practically rebuilt and expanded. When equipment was proven in practical operation, an application for FeMn production was developed. Now as the Tornio FeCr-plant is considering expansion, the same type of exercise is to be performed with today?s challenges, which will be discussed in the paper. These challenges include increasing costs or decreasing quality of raw materials, increasing energy costs, stricter environmental regulations and demand for better working conditions. The possibilities of resolving to these challenges will be discussed in the paper. The future and continuing development with FeCr includes the better utilization of process dusts and a lower consumption of energy. By adapting the latest automation tools to better control the process, even higher efficiencies can be achieved with present technology. New processes are considered for development in the future and some possible technologies will be described.

Jan 1, 2004

By David Colloby, Darelle T. Janse van Rensburg

Premature coating failures of new and refurbished structural steelwork of clarifiers have been a common occurrence at power generation plant in recent years. Several of these failures have ended in disputes regarding which party was actually to blame for the early degradation of the coating system, i.e. quality of the power station?s water, poor application, substandard materials, outdated corrosion protection specifications, etc. Having investigated several of these premature failures, it is clear that the corrosion protection of clarifier steelwork is a highly complicated process and that the painting work needs to be closely monitored in order to ensure long-term protection by whichever product that is applied. The need for quality control inspections during the painting of the plant is often underrated during the project planning stage, also the importance of detailed corrosion protection specifications that consider not only the practical application of the materials, but also the quality control responsibilities of the Contractor, End User and Third Party Inspectorates that may be involved. This paper considers the application constraints of coatings to clarifier structural steelwork and importance of stringent quality control procedures in order to ensure the long-term performance of the corrosion protection systems.

Jan 1, 2006

By M. Ksiazek

Keywords: Thermal conductivity, thermal diffusivity, flash method, specific heat capacity, manganese ore Manganese ferro-alloys manufacturing involves a combination of quality raw materials and an energy source to produce high-quality products with low energy consumption. The thermal properties of manganese raw materials such as ores, sinters, and briquettes, are among the many factors that determine the amount of energy needed for processing. Thermal expansion, thermal diffusivity, conductivity, and apparent specific heat capacity of solid samples and compacted powder samples of manganese ores were examined from room temperature to 1000 °C. The effect of porosity (of the materials used) on the thermal properties was also investigated. The laser flash method and a pushrod dilatometer were used.

Jan 1, 2011

By F. Russo-Bello

TauTona Mine (the renamed Western Deep Levels East) is using a longwall mining method with stability pillars to extract the Carbon Leader Reef at a depth ranging from 2097 metres to 3456 metres below surface. Seismic activity and the complexity and hazards associated with negotiating geological features at great depth pose the most severe hazard to deep level gold mining in South Africa. It impacts negatively on safety and the profitability of the mining. The critical success factors in longwalling at depth are: ?Sound mining strategies and face shape control ?Ensuring follow behind development infrastructure is kept up to date ?Support system design as a strategy to effectively limit the serious effects of damaging seismicity. This paper describes the following: ?Implementation of the required mining strategies ?The evolution of a new stope support system and problems associated with its development and implementation. How this support system was adapted for the successful negotiation of major geological features with known seismic potential and problems encountered ?Current initiatives to optimize follow behind development infrastructure ?Current initiatives in designing a new gully support system and problems experienced with its development and implementation. Finally, this paper will deal with the way forward, briefly covering areas like the above-mentioned gully support system, the proposed phased introduction of technology, and the use of alternative mining layouts.

Jan 1, 2000

By D. F. Malan

This paper presents an overview of work conducted over several years to investigate the continuous stope closure profiles recorded in tabular excavations and the use of this data as a hazard indicator. In spite of the brittle nature of the rock, measurements in gold mines and intermediate depth platinum mines revealed a significant time-dependent closure component. Various approaches to simulate the time-dependent closure have been investigated. Viscoelastic theory is able to simulate the time-dependent closure behaviour, but there are subtle problems with the use of this theory as it cannot simulate the failure processes in the rock. To overcome these problems, continuum and discontinuum elasto-viscoplastic models were developed by the authors. Discontinuum models have the advantage of being able to simulate the creep behaviour of prominent discontinuities. Development of these models has led to useful insights into rock mass deformation and has made the numerical simulation of parameters, such as rate of mining, possible for the first time. A number of practical applications for the mining industry have been developed from this study. Among these are the delineation of geotechnical areas using closure data, use of the data as a hazard indicator and to give warning of large collapses in the platinum mines, identification of areas to be preconditioned in the gold mines, measurement of the effectiveness of preconditioning and improved da

Jan 1, 2007

By M. W. Hildyard

A blast was engineered close to a tunnel in a deep-level mine with the purpose of studying the wave interaction with the tunnel. Numerical modelling of seismic wave propagation was used in both the forward planning and the back-analysis of this experiment. This paper presents the forward analysis. A likely model for a propagating blast was investigated and developed. This model predicts the influence of the velocity of detonation of the blast and the rise-time of the blast on the radiation pattern, and hence on the expected positions of maximum velocity at the tunnel surface. An attempt was made to quantify the parameters of the blast model, using waveform data from two other blast experiments. The blast model caused particle velocities which were an order of magnitude lower than these measured velocities. Large values for blast pressure were required to match the amplitudes of the recorded velocities. An alternative ?effective? source with a similar mechanism but increased diameter was proposed to account for the higher velocities. It was established that distant velocities scale with the square of the borehole diameter. A calibration blast at the experimental site was also modelled. Agreement in the waveforms was not sufficient for conclusive statements to be made about the validity of the source model. However, the modelled waveforms show an encouraging correspondence with some measured waveforms. This gave confidence that the model could be used to examine wave propagation around the tunnel, and allowed a scaled source to be developed for forward analysis of the main experiment.

Jan 1, 2001

By R. M. Goktan

Rock brittleness plays an important role in the cutting action of picks on rock surfaces. It controls the ease with which cracks can propagate through the rocks. Although rock brittleness is known as a property that contributes to the cuttability of rocks, despite considerable research effort, there is still much uncertainty about the relation between rock brittleness and rock cutting efficiency. This fact can be attributed to the lack of a universally accepted brittleness concept and a brittleness measurement method. The existing publications of some researchers have, in a way, tended to confuse the understanding of brittleness in the general field of rock excavation where it is expected that the energy consumption of cutting should decrease with increasing brittleness of rock, other conditions being equal. However, this sometimes conflicts with the brittleness concept commonly used in rock mechanics, where the more brittle the rock the higher its mechanical strength. The ratio of rock compressive strength to tensile strength is considered by many authors to give a valuable brittleness index for drag pick operations. Hence, in this contribution the ratio of uniaxial compressive strength to tensile strength BI is considered as an index of rock brittleness, and a new methodology is proposed for its use in rock cutting efficiency analyses of drag tool operations. Validation of the suggested approach is supported by available experimental data in the literature. Contrary to the conclusions reached previously by other authors, it is shown that an increase in rock brittleness is accompanied by an increase in the cutting efficiency, other conditions being equal. Keywords: brittleness index, rock brittleness, cutting efficiency, specific energy, rock excavation.

Jan 1, 2005

By A. M. Milev

A stand-alone instrument especially designed for recording strong ground motions was used in this study to create a large data base of peak particle velocities measured on stope hangingwalls. A total number of 58 sites located in stopes mining the Carbon Leader Reef, Ventersdorp Contact Reef, Vaal Reef and Basal Reef were monitored. The peak particle velocities were measured at the surface of the excavations to identify the effect of the free surface and the fractures surrounding the underground mining. From the monitoring results obtained, the velocity criterion of 3 m/s will bean adequate value that support systems have to sustain during a rockburst in most cases. However, PPVs in excess of this criterion were recorded, and some PVDs were damaged or irretrieveable, a consequence of which was that possible extreme events were not recorded. The data recorded on the skin of the excavations were compared to the data recorded by the mine seismic networks to determine the site response, defined as the ratio of the measured peak ground velocity to the peak ground velocity inferred from the mine seismic data. The site response measured at all mines studied was found to be 9 ±3 times on average. Values of the site response did not vary significantly with seismological parameters such as peak ground velocity, hypocentral distance and source radius.

Jan 1, 2005

By M. Ng

As part of a long-term study of titanium minerals processing being undertaken by the Julius Kruttschnitt Mineral Research Centre, techniques have been developed to measure the resistivity of ilmenite, rutile, zircon and other associated minerals. The techniques have proven reproducible and have allowed the measurement of resistivity under conditions of varying temperature, surface condition and surface moisture adsorption. The measured values can be linked to the separability of the minerals in the dry plant, and hence are useful as a diagnostic test for existing plants when performance deteriorates, or for greenfield sites to investigate potential problems. One of the major problems in electrical separation of titanium minerals is surface coating on the mineral grains. Coatings can make normally conductive minerals such as ilmenite and leucoxene behave much more like non-conductors. Electrical separation of surface contaminated ilmenite from non-conductors then becomes extremely difficult unless the surface contaminant is first removed. The resistivity measurement technique was used to evaluate the effect of surface cleaning on the resistivity of ilmenite and zircon from a Western Australian deposit which will shortly be in production. Ten different attritioning methods were evaluated, ranging from simple rinsing inwater to chemical attritioning in sulphuric acid combined with ultrasonic leaching. A roasting and quenching step was also investigated. As would be expected, the gentler treatments, such as rinsing in water or Calgon, had only amoderate effect on the ilmenite surface coatings. Ilmenite resistivity decreased by about 1 order of magnitude from 5.6 x108?m to between 2.5 and 4.4 x107?m. More intense treatments had a much more pronounced effect. The most effective, reduced ilmenite resistivity to 6.5 x105?m or three orders of magnitude. Zircon was relatively unaffected by any of the attritioning methods, with only a small increase in resistivity observed from 8.0 x1012?m to 2 x1013 ?m. The results show that measurement of mineral resistivity allows the effect of surface treatments to be easily quantified in a way that has benefits for greenfield site development where only small samples are available for testing. The effect of surface moisture has also been investigated using resistivity measurements. Measurements were made on zircon in an environmental chamber in which both humidity and temperature could be closely controlled. Zircon resistivity at 60 deg C decreased from 6 x1011?m at 5% relative humidity to 8 x108?m at 95% humidity. Moisture content and moisture re-adsorption from dry of zircon and number of other minerals were measured using a Mettler moisture analyser. Zircon adsorbed the least amount of surface moisture (0.05–0.09%) but re-adsorbed moisture from dry the fastest, reaching 98% of the original level in 10 minutes. Leucoxene adsorbed the most moisture (0.67%), but was much slower re-adsorbing this moisture from the dry state, reaching only 63% of the original level in 10 minutes. The difference was attributed to the surface characteristics of the grains, the leucoxene being much more porous than the zircon examined. The resistivities and differing rates of moisture adsorption can be used to quantify the effects of changes in atmospheric conditions of the performance of electrical separation in dry plants.

Jan 1, 2003

By J. P. Germiquet

"Rock properties have a material impact on mining processes, including drilling performance. An investigation using point loaded index (PLI) data converted to uniaxial compressive strength (UCS) has revealed that a direct relationship between grain size and UCS exists at Mogalakwena Mine. This correlation is best seen in unaltered rock, with lower correlations for altered rock types. Measurements from the new RockMa system installed on drill rigs can be used to obtain rock strength data to validate the current rock strength domains and create additional data for the next benches below. An investigation of penetration rates in different lithologies shows that rock composition plays an important role in determining drill performance. Additionally, there is an inverse relationship between rock strength and drilling penetration rate – a measure of how efficiently a hole is drilled.The domaining of grain-size-adjusted UCS at Mogalakwena Mine will allow more accurate scheduling of drill rigs through increased knowledge of rock strength in various areas. Successful rock strength domaining has the potential to be incorporated into blast indexing and predicting crushing/milling performance.IntroductionThe optimization of mining and processing through geometallurgical characterization of ore are key drivers of value realization (Deutch, 2013). Rock strength is one such property and is affected by, among other variables, composition, texture, and grain size (Ozturk, Nasuf, and Kahraman, 2014). Mogalakwena Mine is exploiting the intrusive Platreef PGE (platinum group element)-bearing orebody which forms part of the northern limb of the Bushveld Complex. This complex orebody exhibits areas of metasomatic alteration, metamorphism, and sporadic mineralization of the footwall and hangingwall (Nex et al., 2006). Understanding this variability is paramount due to the implications for rock strength and hardness, which in turn affect crushing, milling, and liberation efficiency. These variables must be known prior to blasting in order to optimize mine and plant processes using in-situ variables. This necessitates predictive modelling (Deutch, 2013). Geological and geotechnical data was sourced from the Overysel (OY) exploration database for the study. Point load testing was done for each borehole and the results converted to uniaxial compressive strength (UCS) (Akram and Bakar, 2007). The relationship of lithology, texture, and grain size with UCS revealed an inverse relationship between grain size and UCS in unaltered rock. The relationship was not present in altered rock types. A comparison of mean strength and hardness results indicated that Bond work index and UCS may be related. Drilling performance is affected by UCS (Bourgoyne et al., 1986), and this was proven using recent measurements obtained during drilling. Lastly, grain-sizeadjusted UCS values were applied to a 3D model for the OY property."

Jan 1, 2016

By M. G. Maruma

The effect of the amount of cold reduction and annealing temperature on the evolution of the texture of AISI 441 steel is reported. The steel was cold rolled by 62%, 78%, and 82%, followed by isothermal annealing of each sample at 900°C, 950°C, and 1025°C for 3 minutes. The crystallographic texture was determined by Phillips X?Pert PROMPD texture diffractrometer. Microstructures were characterized using optical microscopy and scanning electron microscopy (SEM).The results show that sample that received 78% cold reduction and annealing at 1025°C presented the highest Rm-value and lowest ?R-value, which would enhance its deep-drawing capability. In addition, this sample showed the highest intensity of shifted ?-fibre, notably {554}<225> and {334}<483>. It can therefore be concluded that the ?-fibre, which favours deep drawing, is optimal after 78% cold reduction and annealing at 1025°C.

Jan 1, 2013