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By E. Pizarro, A. Videla, G. Compan

One of the main problems related to mining investment decisions is the use of accurate prediction models. Metallurgical recovery is a major source of variability, and in this regard, the Chuquicamata processing plant recovery was modelled as a function of geomining-metallurgical data and ore characteristics obtained from a historical database. In particular, the dataset gathered contains information related to feed grades, ore hardness, particle size, mineralogy, pH, and flotation reagents. A systemic approach was applied to fit a multivariate regression model representing the copper recovery in the plant. The systemic approach consists of an initial projection of the characteristic grinding product size (P80), based upon energy consumption at the particle size reduction step, followed by a flotation recovery model. The model allows for an improvement in the investment decision process by predicting performance and risk. The final geometallurgical model uses eight operational variables and is a significant improvement over conventional prediction models. A validation was performed using a recent data-set, and this showed a high correlation coefficient with a low mean absolute error, which reveals that the geometallurgical model is able to predict, with acceptable accuracy, the actual copper recovery in the plant.

Jan 1, 2015

By J. L. Viljoen

t has long been the drive of the industry and all operations to create an environment that is free of injury and illness. We have come a long way; the leaders, executives, managers, supervisors and workers are to be commended for relentlessly driving to create, what I call a ?White Flag Day Every Day?. Yet I am also aware of the huge shift we still need to create in the industry, on the operations and in the workplaces to have them free of injury and illness. Keywords People, values, care, trust, belief.

Jan 1, 2011

By M. Tangstad, B. Monsen, H. Midtgaard, R. Ishak, M. Syvertsen, I. Solheim

Charcoal is an interesting reducing agent because it is produced from growing wood which is renewable and does not contribute to global warming, provided that there is a balance between the felling of timber and growth of trees. In the biocarbon project the possibilities for using charcoal is investigated as well as other biological based and renewable reductants for ferroalloy production. The background for the project is that the Norwegian ferroalloy producers wish to contribute to reduction of CO2- emissions. This paper focuses on the use of charcoal instead of coke for the production of manganese alloys, and the consequences of doing so. Results from practical SiMn smelting experiments on a pilot scale have previously been reported, where only 12-14 % Si in the metal was obtained when charcoal was used. Recently we have attained satisfactory 18 %Si also for charcoal, but good results are indeed dependant on good furnace performance. There is no tradition for using charcoal for manganese production in Norway. A change from using mainly coke to the use of some charcoal will demand new routines for furnace operation, raw material and off-gas handling. Hence, characteristic properties of charcoal, which may cause change of furnace operation, have been measured and are compared to coke. The following results are presented: ?Thermal abrasion strength together with CO2- reactivity; important parameters for the performance of the upper part of the furnace. ?Coke-bed resistance; it will increase with the use of charcoal (a review of new results). ?Slag reactivity; a relevant method for testing slag reactivity of industrial reductants is of interest. The suggested method can serve for comparing slag reactivities towards graphite.

Jan 1, 2007

By P. I. Page

In mineral exploration the place that yields the first significant result is marked and two questions are posed immediately. Where should the next sample be drawn and how big should it be? At present the answers are arbitrary and ad hoc. They depend on personal experience and sentiment?that is hunch. The thought processes involved in reaching the decisions are unsatisfactory and unsatisfying for professionals. This paper proposes guidance on choosing sample spacing and sample size. The guidance is obtained from the grades of the samples. The grades also imply the extent of influence of each sample assay. Thus sampling and assay are integrated. The integration is achieved by changing the unit of value in which assays and grades are expressed and by exposing meanings and functions of grade beyond that of measuring rock value. The proposals are extended to guide comminution of particle size in sample size reduction and to deal with the problem of erratic high assays. Also, elucidation becomes possible of the computation of a reliable figure for average grade as a statistical weighted mean.

Jan 1, 2005

By A. Whillier

The decisive action taken by mine managements in recent years has been the main factor in bringing about the present downward trend in mine fires. A better understanding of the fundamental factors that govern the ignition and spread of fires. obtained as a result of investigations into mine fires, has provided useful guidance to production personnel. Similar investigations into fire-fighting techniques have assisted the Rescue Training Service and mines to institute more effective fire-fighting techniques. Some of the more important findings of recent investigations in these areas are outlined.

Jan 1, 1981

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 J. N. Van der Merwe

The research described in the paper was aimed at providing standardized information of cases of failed and intact coal pillars in the form of databases to researchers. It also offered the opportunity to take stock of the pillar stability situation in coalmining and to review the impact of the application of the safety factor formula for pillar design. It was found that the physical parameters of coalmining have not changed substantially over the last four decades. However, changes in the controllable parameters like pillar width, pillar width-to-height ratio and percentage extraction have all moved toward the more conservative side. Scrutiny of the database indicates that of all the failures recorded, only 23 occurred in panels that were mined after 1969, when one can assume that the safety factor formula was fully applied. If the pre-1969 practices had been continued, at least 144 collapses would have been expected. There has thus been a substantial reduction of pillar collapse cases, justifying the cost paid for the formula, which has shown to be in the region of 600 million tons of coal. It is evident that that are distinct differences in the natures of the failures among different coalfields. This justifies the attempts to derive seam or coal field specific strength formulae and is a topic that should be pursued.

Jan 1, 2006

By A. M. Hefny, F. P. Siew, P. G. Ranjith

Fracture initiation and propagation, being one of the most intensive subjects in rock mechanics; contribute significantly to the deformation of jointed rock masses. An experimental study on fractured granitic rock was carried out to determine the peak strength of specimen under triaxial loading conditions. The commonly observed failure mode for rock specimens in this study was found to be the shearing of the plane of weakness. The minimum peak strength of fractured rock is observed when the joint orientation is approximately 70° to the horizontal axis. Based on experimental test data, an empirical expression was developed to accommodate the effect of joint orientation and joint trace length in estimating the peak strength of fractured rocks. The predicted values of peak strength using the proposed equation well agree with the experimental results carried out on singly fractured specimens under triaxial loading conditions. The threshold stress values of crack initiation and propagation depend on joint geometrical parameters, their degree of interconnectivity, as well as surrounding stresses on the fracture plane.

Jan 1, 2003

By A. Andrews

Paper written on project work carried out in partial fulfilment of MSc (Eng) degree Solid state sintered silicon carbide ceramics are used in aggressive environments as sealings. There exist data concerning corrosion, but there are only few data concerning their electrocorrosion behaviour. Therefore the electrochemical corrosion of solid state sintered silicon carbide (SSiC) ceramics has been studied at room temperature in acidic and alkaline environments by using potentiodynamic polarization measurements. The investigation showed a pronounced electrochemical corrosion in bases and acids. In HCl andHNO3pseudo-passivity features due to the formation of a thin layer of SiO2on the surface were observed, whereas in NaOH soluble silicate ions were observed, resulting in more pronounced corrosion. The microstructural observations of initial and corroded samples reveal that the residual carbon found in the microstructure do not dissolve preferentially. Keywords: Corrosion; SEM; SSiC; polarization test.

Jan 1, 2006

By Grant Loveday, Vincent Dieudonné, Andrew Jonkers

Bateman Minerals & Metals supplies the APIC Technologies which include the under-bed air-pulsed APIC jig and related technologies such as the JigScan controller and advanced mathematical models of the jig process. Bateman have developed a methodology for predicting process performance for jigs from simplified testing and modelling, based on batch equipment matched to industrial designs. Batch tests conducted on laboratory scale air-pulsed jigs can process small batches of material, such as those obtained from drill core samples. The novelty comes from using an advanced jig process model, ASTRAD, to link the results of batch and continuous jigs. The batch jig presented as a novelty in this paper has been designed to be hydraulically equivalent to the full-scale APIC Jig, allowing the generation of equivalent pulse shapes and using JigScan controller. Lump and fine ferrous ore material have been separated in this unit and any feed >1mm can be tested and extracted. The global test procedure and further modelling focus on the stratification of material, with emphasis on key aspects such as pulse shape, feed characteristics and residence time. The splitting of rejects from concentrates is itself more difficult to reproduce in batch jigging, however the ASTRAD model includes a separation imperfection module, and the APIC Technologies have extraction systems adapted to each type of material. Air pulsed batch jigs are available in several locations and are relocatable. They have been used to treat samples from Australia, South Africa and India as part of studies into ore processing using jigs. Each test layer is available for various physical testing procedures (density and chemical analyses). Test-work is performed on a case by case basis, and analysed using an advanced model ?now available over the internet. Some fundamentals of air-pulsed jigging are recapped along with some of the features of APIC jigs. The process of designing a ?hydraulically equivalent? batch jig test is then described. Some results from jigging tests are presented plus the results of the ASTRAD advanced jig model, which was first developed at the JKMRC with ferrous ores and coal and is now being supported and further developed and utilised by Bateman.

Jan 1, 2006

A shortage of technical skills in all areas of the mining industry is being experienced worldwide. This has significant consequences for design, operations, productivity and safety and, therefore, needs to be seriously addressed, both in the short and longer term. It is therefore both a strategic and a tactical issue. Importantly, however, since mining is a long-term business, the shortage of skills must be dealt with from a strategic point of view to ensure the supply of the necessary skills for future mining. This paper will deal specifically with the provision of high level technical skills, that is, university graduates in mining engineering, and the outlook for the institutions that are currently producing such graduates.

Jan 1, 2008

By F. M. C. C. Vieira

The DEEPMINE Research Programme sought to develop the technology and competence to mine gold safely and profitably at depths of 3 to 5 km. Among the many issues addressed was the stability and support of rockpasses at ultra-depth. It was found that high virgin and mining-induced stresses could cause the walls of rockpasses to spall, leading to the deterioration and failure. A comprehensive programme of numerical modelling was conducted to investigate alternative mining layouts and sequences to ameliorate the problem.

Jan 1, 2005

By J. T. Nel

The establishment of a pilot plant for the continuous production of titania pigment and nano-titania is discussed. The plant was designed, constructed and operated on the Necsa site. The TiO2 production capacity is 7?10 kg.h-1 by the reaction of TiCl4 and O2at>1000°C. Liquid TiCl4 is sprayed under pressure into a plasma reactor where it evaporates and reacts with O2 to form TiO2. Process optimization has allowed for continuous production without any clogging or blockages. The primary advantage of the plasma-assisted process is the possibility to recover and recycle the chlorine values in high yield as Cl2 for use in the manufacture of TiCl4. The HCl formed in most conventional fossil-fuelled processes makes Cl2 recovery and recycling much more difficult. Particle size distribution analysis of the fine, white product revealed a d50= 125 nm. The raw product consisted of 60% rutile that could be increased to 80?100% rutile by post-annealing. The specific surface area (SSA) of the pigment was 8?20 m2?g-1(BET). According to the CIE colour index the ?whiteness? (L*>95) of the plasma-produced pigment was better than that of several commercially available pigments. The particle size could be manipulated by controlling the TiCl4 feed rate, gas flowrates, and the particle quench rate and residence time. Nano-sized TiO2 powders with a particles size (d50) as small as 50 nm were also successfully produced in this way.

Jan 1, 2010

By J. D. Steenkamp

In a paper presented at the Heavy Minerals Conference 2001 a laboratory scale investigation on the beneficiation of an ilmenite containing waste stream by magnetizing roasting was reported1.This waste stream contained a high concentration of ilmenite, which was contaminated by chromite and other gangue minerals. Interpretation of the results of the investigation was based on the assumption that during magnetizing roasting of an ilmenite concentrate, under the oxidizing conditions, the magnetic properties of the chromite would remain constant. In this article the following hypothesis was tested: The magnetic susceptibility of chromite would remain constant during magnetizing roasting of an ilmenite concentrate under the oxidizing conditions reported by Gouws and Van Dyk1. The results of this study indicated that the hypothesis is not true. The increase in the magnetic susceptibility is not significant though and it is expected that it will not influence the final ilmenite quality to a large extent. Based on the assumptions that the bulk magnetic susceptibility of the waste stream samples represents that of the ilmenite in the waste stream, and the bulk magnetic susceptibility of UG1 chromite that of the chromite in the waste stream, the results also served to confirm that the waste stream with a high chromite content should be roasted under oxidizing conditions, in a reactor with a well-defined retention time distribution (i.e. a fluidized bed reactor), at a roasting temperature of 750°C (rather than the higher temperature ranges of 800°C and 850°C).

Jan 1, 2003

By M. Kahn

This paper traces the rise of South Africa's mining industry in the context of the different state forms that oversaw its development. It commences with the mining-led industrial revolution through four periods of conflict, each of which contributed to a deepening of the industrial base, with constant battles between domestic and foreign capital and labour, and the rise of both Afrikaner and African nationalism. The role of state-owned enterprises has been crucial in shaping this dynamic so that at its peak the public sector and leading mining houses constituted two massive centres of power. This was followed by a thirty-year period of neo-liberal experimentation. The current debate on the 'developmental state' is an attempt to reconstruct the state as a counterweight to capital. It is argued that while the country has moved toward inclusive political and economic institutions, these are both limited by deep 'extractive' characteristics. This transformation failure provides a fertile ground for populism that presents one of the biggest threats to inclusive growth. Cited examples point to the many ways that states have sought to deal with the bonanza that conversion of mineral non-resources into resources brings. Such greenfield resources on state land, or in areas where the state holds monopoly rights, do not present ownership issues. It is suggested that this is the route that South Africa should follow, as the alternative will be conflictual.

Jan 1, 2013

By D. J. Young

Alloys used at high temperature must resist both creep and corrosion. Design for corrosion resistance is based on the formation of a slow-growing, protective oxide scale by selective oxidation of an appropriate alloy component, usually chromium or aluminium. A successful scale will exclude other corrodents, notably carbon, which can otherwise cause extremely rapid corrosion at high temperatures. Selective oxidation of an alloy component necessarily lowers the concentration of that metal in the alloy subsurface region. Under thermal cycling conditions, mechanical damage to the scale leads to renewed oxide growth and accelerated alloy depletion. Eventually, a point is reached where diffusion of a corrodent into the alloy becomes competitive with the outward diffusion of alloy metal to repair the protective scale. Two examples of alloy failure by carbon attack are considered. In the steam cracking (pyrolysis) process, centrifugally cast tubes of heat-resisting alloy are exposed to a gas stream of hydrocarbon and steam, at a carbon activity of unity. Formation and repair of the surface chromia scale causes alloy depletion, Kirkendall void formation, and subsequent internal precipitation of chromium-rich carbides. Their formation makes chromia scale formation much more difficult, and generates internal stress. Eventually, the tubes fail by creep rupture. In other processes (e.g. steam reforming, heat treatment), synthesis gases are supersaturated with carbon at intermediate temperatures. Once the alloy's protective scale is breached, carbon attacks the depleted substrate. In the case of ferritic alloys, it forms a surface scale of Fe3C. As this scale thickens, the supersaturated carbon precipitates as graphite within its outer regions. The resulting volume expansion causes disintegration of the cementite in a process known as metal dusting. In the case of austenitic alloys, no metal carbide is formed. Instead, carbon dissolves in the depleted metal to diffuse inward and precipitate as graphite within the metal matrix. Again, volume expansion causes disintegration of the alloy, and metal dusting results. Dusting occurs at an extraordinarily rapid rate, and leads to failure by section loss or even penetration.

Jan 1, 2013

By T. O. Hagan

Analyses of accident records show that a better understanding of very basic strata control principles and practices, by production personnel, will improve worker safety. Workers, lack of knowledge, with respect to aspects of strata control, increases their exposure to such strata control risks. The primary objective of the Safety in Mines Research Advisory Committee (SIMRAC) project 02 02 07 was to develop tools for the transfer of strata control knowledge. Four such tools were developed, three of which focused on illiterate underground mine team members who are not yet able to take advantage of the Mining Qualifications Authority (MQA) learning process (see project outcomes 2, 3 and 4 below). The tools were designed to equip these workers with sufficient knowledge and ability to work safely underground until such time as they can take advantage of the MQA system. Project outcomes: 1 A four-minute video using animation to illustrate the causes and prevention of falls of roof in South African collieries. 2 Software to demonstrate the capability of reconstructing, interactively, accident scenes and actions that have taken place underground in stopes. 3 A strata control bridging course for illiterate mine team workers. 4 Small-scale wooden models that will be used to design life-size mock-up facilities to assist with the above mentioned bridging course. 5 Workshops and presentations to demonstrate the outcomes 1to 4 above.

Jan 1, 2005

By A. M. Hearn, J. R. Henning, A. S. J. Van Rensburg

The lining, together with the electrodes, forms the heart of the operation of a submerged arc furnace. Subsequent to a lining failure on M12 furnace during the early 1980s, Metalloys was active in investigating the concept of thermally efficient ?freeze? linings for its furnaces. The theory revolved around that, not only would, thermally efficient linings result in significant cost savings, but they would also last longer as a result of being subjected to less harsh operational conditions. After having proved the concept on the .smaller. furnaces, Metalloys decided to implement the concept on its largest submerged arc furnace, M12 Subsequent to having recovered from an impending failure of a lining installed in 1981 in M12 in the mid 1980s, Metalloys managed, through rigid lining management, to extend the life of this lining to 1999. At the end of 1999 the decision to replace the lining in the furnace with a ?freeze? lining was made and planning and design proceeded in earnest. This paper discusses the options considered in making the final decision. The features of the design of the lining are also discussed. Consideration is given to the furnace shell cooling system as a result of its importance in maintaining the thermal equilibrium in the lining. Note is made of the fact that the purchase of a .freeze. lining is an expensive exercise but that the time savings in the installation of the lining and the efficiency improvements during operation far outweigh the additional capital cost. The experience on M12 has been that the payback period of the marginal capital expenditure is less than three years. As a result of the opportunity to reline a furnace the size of M12 not presenting itself very often, the learning points from the installation of the lining and the operational advantages and disadvantages are significant. Finally, the point is made that the project had its pros and cons but overall the success of the project has been evident and, as such, the ?freeze? lining is likely to become the norm at Metalloys.

Jan 1, 2004

By N. Z. Jovanovic

Irrigation of agricultural crops may be a cost-effective option for the utilization of gypsiferous minewater as it may also create an opportunity to produce crops during the dry winter season on farm sin South Africa, such as in Mpumalanga. In this study, intensive field monitoring systems were developed and implemented to assess the feasibility and sustainability of irrigation with gypsiferous mine water. Soil water and salt balance components, as well as crop yields, were monitored in field trials carried out at Kleinkopjé and New Vaal Collieries (Anglo Coal), and at Syferfontein (Sasol). Field measurements indicated that high crop and pasture yields can be obtained, provided fertilization and irrigation water management are appropriate. Soil water and salt balances indicated that considerable amounts of minewater can be used and considerable masses of salts can be removed through precipitation of gypsum in the soil profile. With appropriate management, water and salt runoff and salt leaching can be intercepted, thereby minimizing the impact on groundwater. The SWB model is being validated through on-going monitoring. This will allow the use of the SWB model at other sites to predict the long-term impact of irrigation with mine water on soil and groundwater, as well as to run scenario simulations in order to recommend sustainable management of irrigation with minewater.

Jan 1, 2004

This paper provides an overview of possible approaches for structuring the ventilation systems for mines that will become operational within the next decade. Features addressed in the paper include: aspects of airway design and layout in the absence of centralized vertical return shafts, the impact of using diesel-powered trackless equipment in conjunction with conveyor belts in the development and production phases of the project, and the need to balance increasing electrical power costs against the requirement for reduced capital expenditure. The paper provides brief descriptions of the strategies employed in real-life situations and presents an overview of various operational parameters affecting the design of ventilation systems that will be used as ?platforms? for much deeper mines in the future.

Jan 1, 2007