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By J. P. Beukes

The production of ferrochrome alloy from chromium bearing chromite ores is conducted at high temperature under highly reducing conditions. However, albeit completely unintended, it is impossible to completely exclude oxygen from all high temperature process steps, with the corresponding possibility arising for the generation of small amounts of Cr(VI) species. Certain Cr(VI) species are regarded as a carcinogenic, with specifically airborne exposure to these Cr(VI) species being associated with cancer of the respiratory system. With approximately three-quarters of the world?s viable chromite ore reserves located in South Africa, and annual ferrochrome production approaching almost half of total annual global output, aspects of Cr(VI) generation and control are of particular relevance and importance to the local industry, and naturally to the global industry at large. This paper seeks to examine theoretical and practical aspects associated with Cr(VI)generation (based largely on experience within the local South African industry, but considered to be generally encountered in the broader global industry context), together with mitigating measures that can be applied within the context of the production processes. From the discussions it is clear that significant improvements in various Cr(VI)-related aspects have been made by the South African ferrochrome industry. However, it is also evident that several areas of uncertainty still exist, which require further research in order to better quantify risks and enhance the efficacy of mitigating steps. Keywords Hexavalent chromium, Cr(VI), ferrochrome production, South Africa.

Jan 1, 2010

This paper summarises some observations regarding the way SAG and AG mills work based on the last ten years of pilot plant operation, grinding circuit design and operational reviews for various projects in Australia and overseas. The main purpose is to promote discussion on key factors influencing breakage in a SAG mill. The focus of the paper is on two questions: ? How do mill lifters and liners really work and have an effect on grinding? ? How does the mill charge composition impact on grinding performance? The focus of the paper is on observations of mill behaviour in both pilot plant trials and plant operation, particularly on Cadia ore. DEM, by others, and JKSimMet modelling of SAG mill performance have greatly assisted in forming the ideas expressed in the paper and both are valuable tools in developing our understanding of the comminution process. Put in the `extreme' form the major observations and conclusions expressed in this paper are that: ? the main purpose of mill lifters is to reduce mill liner wear and not to promote rock breakage; ? the often promoted theory that balls impacting the ?toe of the charge? is a dominant form of breakage is incorrect; and ? fines production in a SAG mill is primarily a function of the rock load mass, with a secondary dependence on ball load for any given circuit configuration.

Jan 1, 2007

By S. M. Bradshaw

In order to assess the requirements for online matching when using a transverse electric field (E-field) applicator to treat mineral ores continuously, the effect of varying load properties on matching has been investigated by simulation. The effective permittivity of the ore to be treated is expected to show variation on both short (< 1 s ) and long (minutes) time scales. By modelling the ore as a series of slices with alternating effective permittivity values, it was shown that permittivity variations on the scale of the expected particle size are attenuated significantly and matching is not required. For variations in permittivity on the length scale of the free-space wavelength, variations in reflected power are at most within ±10% of the mean. This is not considered operationally significant, as extreme permittivity variation over this length scale is unlikely, given the expected distribution of ore particle sizes to be treated. At typical ore transport speeds through the applicator, these variations occur on a time scale an order of magnitude shorter than the response time of typical industrial online matching equipment. This implies that online matching is neither required nor possible for short time scale variation. Long-term variations in dielectric properties can be adequately compensated for by current matching technologies. It is concluded that the transverse E-field applicator is robust to changes in the dielectric properties of crushed ores within the expected range of their variation.

Jan 1, 2012

By Z-P. Song, Z-B. Jiang, A-N. Jiang

"In deep excavations under conditions of high ground stress, even hard rock undergoes creep and other time-dependent effects that may result in instability. This study involves an analysis of the typical damage to the surrounding rock in the deep tunnels of the Jinchuan nickel mine in China. In order to understand the creep mechanism, triaxial creep laboratory tests were conducted under high stress. The creep characteristic curves and the Nishihara model parameters of typical rock were obtained from these tests. The numerical simulations, with which the creep model is developed, were performed using Flac3D. The creep model parameters were back-analysed on the basis of field monitoring data. Finally, appropriate support schemes for deep tunnels are suggested. The creep deformation of rock increases with time and axial load. At the same load level, the creep deformation of unloading is greater than that of loading. The simulated deformations of the surrounding rock are coincident with those from in situ monitoring, indicating the applicability of the presented rock creep model in situations of high ground stress. The results constitute a reference for support design in deep mining tunnels.IntroductionThe excavation of underground caverns can alter the natural stress field of the surrounding rock. In deep engineering projects under conditions of high ground stress, even hard rock shows obvious creep properties and time effects (Yao, 2005; Liu, 1994). The time effect of excavation not only causes decompression of the floor and increases sidewall stress, but also leads to stress concentration at the corners of the excavation, which influences the stability of the surrounding rock in a very complex manner.Many researchers have studied the creep properties of rock. ‘Griggs (1939) showed that creep occurs in sandstone, shale, and silty sandstone rock under the load of 12.5%–80% of the failure load.’ Subsequently, much research has been published on rock creep tests, including the uniaxial compressive creep test, the triaxial compressive creep test, the discontinuity rock shearing test, and field tests (Wawersik, 1974; Amadei et al., 1980; Okubo et al., 1991; Jin et al.,1995). A rheological model is used to describe the complex rheological deformation of material. This model is based on various fundamental parameters including rock elasticity, plasticity, and viscous properties, which can be combined into a constitutive model to reflect the rheological properties of various types of rocks. Wang et al. (2014) studied the creep– damage–rupture characteristics of rock salt by applying a creep-damage model. Munson (1997) developed a multi-mechanism constitutive model of creep of polycrystalline rock salt based on steady-state creep and modified it to incorporate transient creep through work hardening and recovery. An elasto-viscoplastic approach was developed to simulate the timedependent nature of the fracture zone (Malan, 1999). Rheological models were proposed to understand the collapse of iron ore mines in Lorraine by Dragan et al. (2003)."

Jan 1, 2016

By G. Dhakal, J. -I. Kodama, K. Neaupane, T. Yoneda

ABSTRACT Durability tests and evaluation of sub-zero temperature effects to some argillaceous clastic rocks were carried out. Welded tuff, limestone, sandstone and schist samples collected from different parts of Japan were tested and results are presented. Schist and dolomite from Ganesh Himal area along the higher Himalayas of Nepal were also tested, and the results are compared. The slaking tests were performed on all samples in pure water. The results reveal that the slaking index of schist from Japan is lower than that of schist from Nepal. Regarding carbonate rocks, the slaking index of limestone from Japan is higher than that of dolomite from Nepal. A tendency of decrease in slake durability with an increase in porosity is also observed. Freezing and thawing experiments conducted on welded tuff and schist reveal that crack initiates earlier but extends slower in schist than in welded tuff. It is also observed from the freeze-thaw experiment that the welded tuff deteriorates and wears faster than the schist. However, sandstone remains relatively intact for a long run of freeze-thaw cycles. Zusammenfassung Beständigkeitstests sowie die Bewertung der Auswirkungen von Minusgraden auf Tonschiefer Trümmergestein wurden durchgeführt. Dabei wurden geschweißter Tuff, Kalkstein, Sandstein und Schiefer aus verschiedenen Gebieten Japans sowie Schiefer und Dolomitgestein aus dem Ganesh Himal Gebiet, dem höheren Himalaya Nepals, untersucht und die Resultate verglichen. Für alle diese Gesteine wurden Slaking-Tests in reinem Wasser vorgenommen. Die Resultate zeigen, dass das Slaking von Schiefer aus Japan höher als das von Schiefer aus Nepal war, wohingegen bei kalkhaltigem Gestein das Slaking von Kalkstein aus Japan niedriger als das von Dolomitgestein aus Nepal ausfiel. Es wurde dabei auch eine Tendenz zur Löschbeständigkeitsverringerung bei gleichzeitig erhöhter Porosität beobachtet. Gefrier- und Tautests an geschweißtem Tuff und japanischem Schiefer zeigten, dass Risse in Schiefer schneller auftraten, aber sich langsamer ausweiteten als in geschweißtem Tuff. Bei Gefrier- und Tautests wurde ebenfalls beobachtet, dass geschweißter Tuff schneller verfällt und verschleißt als Schiefer. Sandstein hingegen blieb über lange Tau- und Gefrierzyklen intakt Résumé Des tests de solidités et l’évaluation de l’effet des températures en dessous de zéro sur les rocs argileux ont été effectués. Les rocs d’origine volcanique (cendre), les rocs calcaires, sableux et les schistes de différentes régions du Japon, ont été étudiés. Les schistes et les dolomites de la région de Ganesh Himal le long du haut Himalaya (Népal) ont été étudiés et comparés à ceux du Japon. Les tests de désintégration sur les rocs ont été effectués dans l’eau pure. Les résultats montrent que l’index de désintégration des schistes du Japon est inférieur aux schistes du Népal. En ce qui concerne les rocs carbonyles, l’index de désintégration des rocs calcaires du Japon est supérieur à ceux des dolomites du Népal. Une décroissance de la résistance à la durabilité est observée avec une plus grande porosité des rocs. Les tests de congélation-décongelation sur les schistes et les rocs d’origine volcanique (cendre) du Japon montrent une apparition précoce des fissures mais l’expansion des fissures est plus rapide dans les rocs volcaniques. Des tests similaires montrent que les rocs volcaniques (cendre) se désagrégent plus rapidement que les schistes. Cependant, les rocs sableux restent intacts après plusieurs cycles de congélation-décongélation.

Jan 1, 2003

By S. M. Rupprecht

"Artisanal mining is basic mining characterized by manually intensive work methods utilizing primitive or simple equipment and conducted by individuals or small groups exploiting deposits. Artisanal mining in Rwanda and Burundi is further complicated in that the techniques applied are often inadequate, resulting in low productivity and poor recoveries, and workers are paid low wages with owners reluctant to reinvest in the mining operations. A consequence of this vicious circle is often poor working conditions, with miners operating under unsafe and/or unhealthy working conditions. An additional problem is that mining is conducted in a manner that is detrimental to the environment.Artisanal mining is commonly more dangerous than large-scale modern mining operations. Artisanal operations are generally subsistence activities with the miners focusing more on immediate concerns than the long-term consequences of their activities. When miners have no other source of income, they will usually find ways to evade controls and carry on working. Machinery tends to be expensive and often far beyond the reach of most artisanal miners, and therefore there is a general tendency for workers to focus on labour intensive and riskier mining methods.This paper proposes the introduction of small-scale mechanization with labour-intensive manual mining utilizing a bench mining approach in artisanal mines operating in Central Africa. From the 1950s to the 1980s bench mining was successfully conducted in Burundi utilizing manual labour. In order to achieve a balance between job creation and project economics, the combination of manual and mechanized mining is proposed. Manual mining offers the benefit of local job creation while ensuring good mining techniques, such as minimizing mining loses and dilution. Through the introduction of mechanized loading and hauling activities, areas of high stripping ratios can be viably mined, thus increasing the amount of resources that can be exploited. The use of a loader and tractor-trailer arrangement is proposed, thereby improving throughput, productivity, and worker safety and, reducing the impact on the environment."

Jan 1, 2017

By B. P. Watson

In South Africa, the Bushveld platinum group metal deposits are unique in that they are the largest platinum group metal deposits in the world. These deposits occur as two distinct stratiform tabular orebodies and strike for many hundreds of kilometres. Mining is extensive, with depths ranging from close-to-surface to 2 000 m. The mining method is a variation of planar open stoping. Pillars are widely used to support the open stopes. Crush pillars are commonly used in this role, where the residual pillar strength provides the required support resistance to stabilize the stoping excavations. This paper describes the direct measurement of stress within these crush pillars, and describes the stress?strain behaviour of these pillars. These findings indicate that the measured pillar failure stress is too high. The implications of these findings are that roof damage and pillar bursting could occur, and some examples of this type of damage are shown. The paper concludes that this problem could be mitigated if the three dimensional pillar geometry were modified and the pillars were cut smaller.

Jan 1, 2007

By F. Lombard

We consider in this paper the use of a modified version of Hotelling?s statistic in the analysis of particle size distributions. The statistic can be adversely affected by the presence of outliers among the data. We propose a competitor to the statistic that is based on ranks, and hence is less sensitive to outlier effects. The results of a Monte Carlo study suggest that the rank test is highly competitive with the Hotelling test in its ability to detect differences between two mass size distributions. The calculation of the rank statistic is explained in detail and its application is illustrated on two sets of data.

Jan 1, 2012

By R. L. Robinson

An analytical framework is formulated to assist mining companies in assessing the relative merits of mineral exploration and acquisition strategies. The anticipated costs, risks, and returns of each strategy are conceptualised using decision trees. Economic criteria - expected net present value, expected return per unit of investment, and the probability of success - for each strategy are derived(from the appropriate decision tree network. Application of the analytical framework is illustrated using the example of a medium-size company in the Canadian base metal sector.

Jan 1, 1987

By P. G. Terrazas Prado

This paper presents the results of research on the development and application of a custom-made truck cycle and delay automated data collection system (TCD-ADCS) in a surface coal mining. Truck cycle and delay field data are locally stored in trucks and then synchronized and replicated through a wireless network into a centralized server containing an already-developed integrated production management system (IPMS). The system relies on motion sensing and distance travelled in order to automatically define the cycle starting/ending points, cycle time, position, and delay time. Connectivity and communication between loading equipment and trucks are also established. Communication between the equipment operators and TCD-ADCS system is via a user-friendly graphic interface. The hardware used for the development of this system consists of a rugged touch-screen personal computer, 2.4 GHz radio transmitter antenna, and a commercial GPS receiver. The system was developed, tested, and deployed at a surface coal mine in the USA. Keywords surface coal mining, truck and shovel, data collection, information systems.

Nov 1, 2013

By J. Tikka, E. Bäcklund, N. -O. Lindfors

Tornados are the most violent weather events in the world, and we have all seen the forces and phenomena created by tornados in nature. Airgrinder AB has been working with a material treatment technology, which most easily could be described as an artificial tornado. The process consists principally of one air fan providing a high-velocity airstream that enters a mechanical cyclone. When the gas enters the cyclone, an outer vortex is created. This outer vortex rotates next to the cyclone wall, and at the bottom of the cyclone funnel the gas stream is turned and an inner vortex is created. The control of the air flow is tuned by a special device on top of the cyclone. The gas outlet is at the top of the cyclone and the material outlet at the bottom. The material is fed through a feeding device into the air stream channel prior to the inlet into the cyclone. The process is basically an improved grinding and dehydrating system, which is very efficient and environmentally friendly and can even be employed with very sticky materials. Also due to its rotating comminution, the material particles become rounded during grinding, hence more free flowing and easier to handle. MEFOS has already tested more than 30 different applications in the pilot equipment. The materials tested range from metallurgical slags containing 2?3% moisture to sludges with up to70% moisture. This technology has a potentially strong impact on mineral beneficiation, including the drying of sticky fine-grained materials, improved and selective gas scrubbing and the manufacture of free flowing powders.

Jan 1, 2007

By Kevin Peacocke

The future of Gravity ? Primary mineral recovery ? Enhancement of existing process efficiency ? Pre-Concentration ? Alternative? or ?New? production

Jan 1, 2006

By Lene Hansen

Sulphuric acid plants now and then see unexpected increases in SO2 emissions. Our experience is that it is not always easy for the acid plants to pin point the exact reason for the SO2 increase. Sometimes a catalyst bed is sacrificed even though reliable emperature readings and gas analyses could have verified satisfactory activity, hence the leaking heat exchanger is never discovered and after the shutdown the SO2 emissions are still too high. This paper will look into some basic catalyst management tools: Good record keeping is a necessity for collection of representative catalyst samples, reliable operating data is an inevitable starting point for all analysis and trending of operating data is a must for plant optimisation and troubleshooting. In addition these catalyst management tools will give a continuous updated knowledge of the catalyst status in each bed providing the basis for a more effective replacement strategy. The most typical reasons for increasing SO2 emissions will be presented together with easy guidelines for cross-checking of operating data, temperature optimisation and good record keeping.

Jan 1, 2009

By P. J. Petit

The strategic mission of the South African mining industry is to extract the mineral assets in an energy efficient, economical and safe manner. Drilling has received particular attention in the last few years. As the operations move away from the power source, conventional and old drilling technology result in poor penetration rates, increased drilling shift lengths, slow face advances and limited stope efficiencies. The need for an alternate mining method, performed by a skilled workforce, to increase productivity, has led to the development of the electric rock drilling system for in-stope mining operations. The focus of this paper is a systematic evaluation of the electric rock drilling system as a function of production and technical parameters, in the platinum orebody. The particular electrical reticulation system is illustrated. Power usage, problems experienced, and solutions are described. The safe use of the recently developed drill is elaborated upon by describing protection devices. The testing and certification process, for approval by the recognized authorities, are documented. The testing and certification process, for approval by the recognized authorities, are documented. The human factor is also considered. Known detrimental factors of high noise exposure, vibrations levels and oil emissions are reviewed. In conclusion, recommendations on future strategies for the implementation of electric drilling technology within the mining and construction industries, is included.

Jan 1, 2006

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 southernsector 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 UG2chromitite 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 theUG2 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 UG2chromitite 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 000tons at full run of mine production from the underground UG2 mine.

Jan 1, 2006

By E. A. Brinkmann

A kinetic model framework for single particle kinetics in combined diffusion and adsorption processes is presented. The framework applies to the general case in which both diffusion and the adsorption reaction play important roles in determining the overall rate in processes where the migrating species can both adsorb and accumulate. The technique, which should be applicable to a wide range of reaction mechanisms, consists of an iterative integration procedure for the coupled diffusion and reaction equations. The case of a reversible linear adsorption reaction rate is developed. In order to verify the technique as a legitimate method of model development, an analytical solution for the identical case is derived and compared to the numerical solution. Excellent agreement exists between the two solutions.

Jan 1, 1987

"Chairman: Dr DeV. HarrisRapporteur: Mr A.H. MunroPapers:Corporate exploration strategies by MacKenzie, B.W.The Engel Simulator and the search for uranium by Griffiths, J.C. and Singer, D.A.The Chairman opened the session by tracing the changes which have taken place in the exploration field since the days of the lone prospector who relied upon his individual skills and to a large extent on luck. The deposits which now remain to be discovered are better covered and are of lower grade. A much greater team effort, involving geoscientists and engineers, is required. The gamble is thus much greater -not only are the probabilities of failure still significant but the consequences are more severe. A recent Canadian survey indicated that expenditures of between two and nine million dollars on regional exploration programs are required to locate one significant deposit.The Chairman went on to say that these facts have led companies to regard exploration as another form of investment and to treat it accordingly. This had placed exploration in the context of corporate strategics and structures, which was the subject of the first paper of the session.In introducing his paper, Dr B. W. MacKenzie said that the paper suggested a decision framework for exploration planning. Initially the environment is analyzed to define observable and relevant economic characteristics. The terms of reference for exploration planning and the appropriate allocation of capital and skills are then established in the light of corporate objectives and growth alternatives. With the aid of this information and in the light of profit and corporate risk criteria, exploration strategies can be selected.Dr MacKenzie went on to say that the usefulness of the concept and criteria outlined in his paper depended critically upon three characteristics of any particular economic environment, namely, the return resulting from an economic discovery, the unit discovery Cost and the probability of making an economic discovery. He then showed by means of a case history relative to the Canadian Shield and Cordilleran areas that these three characteristics could, in fact, be evaluated for regions with reasonable histories of mineral activity.The first contributor to the discussion of the paper, Mr Alfred Weiss, mentioned that his group had been involved in exploration modelling for some ten years and were thus particularly interested in the paper. He went on to say that they had experienced greatest difficulty with reconnaissance programs and that he sensed that these difficulties were also present with the methodology which had been outlined. Mr Weiss asked Dr MacKenzie how he would deal with such situations when no information was available but where there was the potential for both exploration and discovery. Dr Mackenzie agreed that the lack of information was a very severe limitation and said that at the present time his methodology probably did not provide a basis for breaking down the broad geological regions he considered into areas for further assessment."

Jan 1, 2014

By G. Ferrara

The mathematical framework of a well-established model proposed earlier by the authors for the screening process is briefly recalled. Some numerical methods for the application of the model, concerning numerical solution of the equations and parameter estimation, are indicated. Some applications of the model to improve screening operations, sizing of screen, simulation of screening and of integrated plant operations are discussed, and the computer software to be used for these purposes is described in detail.

Jan 1, 1987

By P. J. Petit

Financial evaluation is necessary to investigate the viability of implementing and/or utilising new technology in mining projects. It establishes a techno-economic base for decision-making and justifies capital expenditure. This paper aims to present a monetary appraisal of the electric rock drilling system in a typical feasibility project, whose purpose is to increase the production rate. The in situ environment is a platinum orebody, and the stoping operations occur in UG2 reef. The results are a function of production requirements, technical parameters and financial outlay of the drills. The costs involved in implementing and operating electric rock drills are assessed to the current method of drilling, namely the compressed air operation. A comparison of the electric and pneumatic rock drills in terms of financial outlays for drilling and service requirements, peripheral equipping and training is discussed. Other factors that affect the business case are technical advantages, safety and risk management and the environmental objective of the company.

Jan 1, 2006

By M. K. Matthews

The use of backfill has important environmental control implications which, although frequently overlooked, can be both beneficial and problematical. Where backfill is widely used, the reduction in stope heat load and improved air utilization influence the overall mine ventilation and refrigeration requirements significantly. A programme of work examining in detail all the environmental consequences of backfilling is currently underway at the Environmental Engineering Laboratory of the Research Organization of the Chamber of Mines. This paper gives an overview of the work and presents some findings. In so doing, the environmental implications to be considered when backfilling are highlighted.

Jan 1, 1988