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By Karl-Heinz Obst, Juergen Stradtman

The importance of the chemical and physical properties of lime has been overlooked for years although the quality of lime plays an important role in the production of steel. With the introduction of the oxygen injection process these properties have been re-evaluated. The CaO, MgO, S, and P2O5 contents of lime are important, but so are the physical properties such as granulation, reactivity with respect to slag formation, and the degree of burning. Soft burnt lime enhances de-phosphorisation and de-sulphurisation, and facilitates the smelting process in general, mainly due to its large specific surface. Special lime, prepared as briquettes from quicklime and fluxes or as pellets from limestone and various fluxes with or without binding agents, clearly accelerates lime dissolution during the slag formation process, lowers the melting point, and enhances de-phosphorisation, de-sulphurisatlon, and de-carburisation even more than soft burnt lime. The introduction of special limes in the oxygen injection process for steel production has opened up new fields for commercial exploitation of slags as well as improved operational techniques.

By R. B. MacGillivray

The No. 2 Seam at Van Dyks Drift Colliery was found to be made up of six easily recognizable bands or plies of differing qualities. Not only did the plies differ from one another in quality, but their thickness and quality varied laterally across the mine. The economic production of a Iow-ash blendcoking coal for supply to the Japanese Steel Mills called for the mining of different portions of the seam. The portions that could be extracted economically varied in thickness and position within the No. 2 Seam across the mine. A unique system of selective mining had to be developed involving the dispatch of two separate streams of coal out of the mine. Conventional American mechanized pillarand-stall mining was used, and the productivity was improved by the installation of twin conveyor belts into a double-header section. The method of grade control that was instituted to ensure efficient extraction of the available coal reserves is described.

Jan 1, 1985

By C. Chapman, M. G. Reading, M. P. Amsden

Computer control of flotation at the Ecstall concentrator By M. P. AMSDEN, C. CHAPMAN, and M. G. READING Ecstall Mining Limited, a subsidiary of Texas Gulf Sulphur Company, operates the Kidd Creek Mine, a 10000 tons per day base metal producer, near Timmins, Ontario. Two different types of ore are mined and milled: copper-zinc and silver-lead-zinc. At the highly automated Ecstall concentrator the ores are processed by selective flotation in three individual circuits. One of the most important metallurgical tools for process control is a sample system incorporating continuous on-stream X-ray analysis. Recently this system was automated further by the addition of computer control of reagents for two copper-zinc flotation circuits. The computer programs, utilizing optimum seeking methods and smelter contract terms, have increased copper recovery by 1,1 per cent, zinc recovery by 1,4 per cent, and have reduced reagent costs by 16 per cent. Although not expected, copper and zinc concentrate grades were improved slightly as well.

By G. A. Bezuidenhout

Lonmin Platinum installed a concentrated mode dual-alkali scrubber at the smelter in Marikana in 2002. The dual-alkali scrubber was the technology of choice at that time as a sulphur fixation plant, due to the perceived benefits of handling both the high SO2 concentrations of converter off-gas and the swings in SO2 concentration that are linked to Peirce-Smith operation. Owing to current and impending legislative requirements for air quality and waste, Lonmin is currently considering additions to the dual-alkali plant, but is also evaluating alternative technologies for sulphur fixation. This paper reviews the decision of Lonmin to install a concentrated mode dual-alkali scrubber and presents plant performance achieved. It also describes the important control variables and sensitivities of the plant, and the final product that is produced by the operation of the plant. The legislative requirement that drives the Lonmin technology evaluation is also discussed.

Jan 1, 2012

By B. Hayen

The principal advantages of fibre optics as compared to copper wire are well known and include almost perfect electromagnetic isolation, light weight, small size, excellent transmission security and substantially better bandwidth/distance performance. The decreasing cost of the optical fibre technology (both fibre cable and equipment) has led to another generation of private networks, which provide much larger bandwidths, very high reliability and an increase of the maximum geographical coverage. The larger bandwidth allows to transport all types of information on a single network. Typical communication requirements are speech (audio), computer data, LAN info, control information, video, etc. OTN or ‘Open Transport Network’ is a transmission system based on the latest available technology in fibre optics. It is characterized by the dual ring approach, resulting in high network availability, and the integration of different types of services in one network. As such, it can fulfil almost all transmission requirements for voice, data, LAN, video and any special service required.

Sep 1, 2001

By S. Maluadzi, D. Rocchi, S. Luyckx, S. S. Potgieter-Vermaak, C. Machio, J. H. Potgieter

The aim of this work was to compare the corrosion behaviour of thermal spray WC ? based coatings before and after annealing. X-ray diffraction (XRD) was used to determine the phases present in the coatings at various stages. The corrosion resistance of the coatings was measured using electrochemical and immersion corrosion tests. The results obtained from electrochemical corrosion (quantified by corrosion current density) and immersion corrosion tests showed that annealing appears to decrease the corrosion resistance of the coatings. From the XRD results it was determined that the phases that corroded preferentially were cobalt (Co), eta (Co6W6C) and W2C. Keywords: Corrosion, thermal spray, coatings, hardmetals.

Jan 1, 2006

By M. U. Ozbay

The stability of pillars is analysed on the assumption that pillars shed load in a stable manner if the slope the strata load-deformation relation is steeper than that of pillars in the post-peak regime. Concepts of local stiffness, mine structural stiffness, and critical stiffness are discussed. Procedures are described for the determination of strata stiffness for various pillar layouts by use of the available boundary-element computer programs. The postpeak stiffness of pillars is assessed from the available data relating to the post-peak load-deformation relationship and width-to-height ratio. Stability analyses are carried out by the contrasting of strata stiffness with post-peak pillar stiffness. It is shown that the strata stiffness becomes unacceptably small for a stable yield-pillar layout when the span exceeds about 5 times the depth. The strata stiffness is found to increase, thereby increasing the stability, as the span-to-depth ratio, number of pillars, and percentage extraction are decreased. It is also found that the stability in a yield pillar becomes difficult to achieve when al the pillars in a layout are in the descending part their post-peak load-deformation curve

Jan 1, 1989

By E. J. Margi

Deep gold exploration such as is used for Witwatersrand gold deposits is both expensive and time-consuming. This paper provides quantitative guidelines as to the economic optimum number of boreholes and deflections within each borehole for a certain reef characterized by its variability pattern and depth below surface in order to maximize the level of confidence for a fixed drilling budget or to minimize the total drilling cost for a given level of confidence. Portions of the Basal, Vaal, and Elsburg Reefs that show a wide range of variability (sample logarithmic variances of 0,63, 1,05, and 2,06 respectively) are examined at depths below surface ranging from 1000 m to 4000 m over a simulated mining property covering 7000 ha (7000 m by 10000 m). It is concluded that four intersections per borehole are optimum in al the cases considered, which cover the majority of current Witwatersrand exploration, with the exception of the highly variable Elsburg Reef at depths of 1000 m and 2000 m, where boreholes with one and two intersections respectively should be preferred.

Jan 1, 1987

By S. M. Spottiswoode, A. J. Jager, N. C. Gay, J. A. Ryder

The South African mining industry is at present planning to extract orebodies at depths of up to 4 km. To do this cost effectively and, at the same time, ensure safe working conditions for mining, the personnel will require both the development of new strategies and the implementation of current rock-engineering technological developments on a wide scale. This paper covers most of the technological developments likely to be required for mining at very high stresses, but it is clear that improved regional support systems will need to be developed to ensure defective stability of the rockmass during mining operations. Similarly, it is clear that improved strategies for mining in large-scale geologically disturbed areas, where slip on faults or dykes can result in wide-spread rockburst damage, will have to be addressed

Jan 1, 1995

By G. C. Howell, H. A. D. Kirsten

The mining-induced effects around narrow tabular stopes have traditionally been evaluated in terms of elastic continuum analyses. An understanding of the phenomenological behaviour of the rock surrounding deep-level gold mines has accordingly been developed on the basis of such analyses. However, elastic analyses do not afford reliable representations of the behaviour of rock in which failure may occur on discontinuities. This paper describes investigations that show how the stress and stiffness characteristics of a rockmass are affected under such circumstances for representative ranges of values for the relevant parameters (depth, span, support stiffness, field stress ratio, and discontinuity strength). These investigations afford a substantially different understanding of the mechanical behaviour of rock that is subject to failure. Instead of forming an arch across the abutments, the rock in the hangingwall bears directly across the stope onto the footwall and, instead of being subjected to tension, the nether hangingwall is clamped in compression in the horizontal direction.

Jan 1, 1993

By C. J. Fauconnier

The main purpose of the paper is to determine the contribution of fluctuations in barometric pressure to flammable gas explosions in South African mines. For this purpose, the barometric-pressure patterns preceding each of the 59 major explosions in South African gold and coal mines over the past 20 years were analysed. It is concluded that diurnal fluctuations in pressure do not have a major influence on the accumulation of gas in the underground workings, but that pressure drops associated with cyclonic weather systems moving across the country over a number of days are the major factor contributing to gas explosions in mines. To illustrate some of the points made in the paper, the Hlobane Colliery explosion of September 1983 is used as a case study. In the final section, several general conclusions are drawn and recommendations put forward as to how mines should recognize and react to meteorological phenomena that may lead to an increased probability of gas explosions in underground workings.

Jan 1, 1992

By D. D. Howat, J. van der Colf

This paper is the first in a series of three dealing with this subject and also with the rate of oxygen removal from the slags in the presence of solid carbon and with the physicochemical properties of the reduced slags. For selected members of the system, the melting temperatures and primary crystallization products were determined. as were the viscosity and the electrical resistivity of the corresponding melts. All the experiments were conducted in a neutral atmosphere. Where determined, the primary phase was found to be either perovskite or magnesium aluminium titanate. The composition variable exerting the most pronounced influence on viscosity or resistivity was found to be the basicity expressed as the mass ratio (CaO + MgO)jSiO,. The ratio CaOjMgO became important only at Iow basi<:ity values. Although generally there is a direct proportionality between log (viscosity) and log (resistivity), slags h&apos;lving either a very high silica content or a very high titania content have anomalously Iow electrical resistance.

Jan 1, 1979

By N. Birtek, R. P. King

The washability characteristics of fine South African coals were measured and were found to be well characterized by an M-curve having the equation Z = aQb exp(cQ) x dQ, where Z is the ash content per 100 units of total feed and 0 is the mass yield. Parameters a, b, c, and d were determined for 23 different samples of coal from important coal seams in the main South African coalfields in the size range 0,0025 to 1 mm. The relationship between ash content and relative density was determined and correlated by means of two linear relationships. This characteristic behaviour was explained in terms of the liberation of macerals and the different association between the mineral mater and the two major macerals vitrinite and inertinite. The results obtained in this study can be used to calculate the expected performance of an ideal separation process, and can also be used as input for the simulation of real beneficiation plants. An example is worked through in detail to illustrate the method of calculation.

Jan 1, 1990

By Austin Whillier, Duncan Mitchell

The problem of heat stress underground in the gold mines is approached on the basis of the heat transfer between the human body and the underground environment. Experimental measurements of radiant and convective heat transfer and a theoretical calculation of maximum evaporative heat transfer enable the maximum cooling power of an environment to be calculated in terms of the dry-bulb and wet-bulb temperature, the mean radiant temperature, the wind speed and the barometric pressure. For most underground applications the cooling power can be expressed as a function of wet-bulb temperature and wind speed only. The relative importance of wind speed and wet-bulb temperature can be assessed: in working places where wind speed is low additional cooling of workmen can be achieved better by increased wind speed than by decreased wet-bulb temperature. The wet kata reading proves to be of limited value as an index of heat stress because environments with equal wet kata do not necessarily have the same cooling power. Finally, thermal equilibrium with the environment is possible when cooling power equals or exceeds the rate of metabolic heat generation. The rates of metabolic heat generation for various underground tasks are indicated.

By J. D. Salter

Most diamonds are liberated from their ores by crushing. Diamond and other coarse grained mineral ores require carefully optimised crushing circuits. Recent advances in computer technology have made possible the on-line capture of crushing plant performance data and, hence, the accurate empirical modelling of the crushing process. Such models are used in simulation studies to determine the optimum operating conditions for a given plant. A system is described which allows operating data from mineral treatment processes to be logged. Up to 16 channels of data may be recorded simultaneously at sampling rates in the kiloHertz range per channel. A data storage and analysis procedure is described which allows the system to make full use of its sampling capabilities.

Jan 1, 1987

Edward J. Stephenson. Extractive metallurgy. Recent advances. Park Ridge (New Jersey), Noyes Data Corporation. James L. McCall and P. M. French (eds.). Interpretive techniques for microstructural analysis. 1977. Institution of Mining and Metallurgy. Prospecting in areas of glaciated terrain. London, the Institution, 1977. £16 ($D.S. 30). NIM reports Report no. 1928 A liquid-nitrogen monitor for lithium-drifted germanium detectors. (21st Nov., 1977). Report no. 1931 The equilibrium between the slag and the metal in the production of low-carbon ferromanganese. (14th Nov., 1977). Report no. 1934 The spectrometric analysis of chromium-bearing materials with particular reference to ferrochromium slags and chromite ores. (30th Nov., 1977). Report no. 1935 The construction and testing of a small mixer-settler for use in the laboratory. (30th Nov., 1977). Report no. 1933 The determination of trace elements by thin-film X-rayfluorescence spectrometry, and its application to zirconium. (30th Nov. 1977). Report no. 1942 The accuracy of assays for platinum -group metals and gold. (30th Nov., 1977). Courses on geostatistics In view of the continuing demand, the University of Leeds will offer two further courses on geostatistics in 1978, each covering ten working days (3rd to 14th April, and 3rd to 14th July).

Jan 1, 1978

Underground mining and particularly dipping narrow tabular orebodies are difficult to mechanize appropriately, given the low gold price and other external factors. Particularly in the deep level mines in South Africa, there is little choice left but to mechanize if the industry is to remain competitive and a significant global player. This paper presents a design philosophy for appropriate mechanization intended to generate solutions that can be implemented using the people currently employed in South Africa mines. The design philosophy is based on the ability of high-pressure water (hydropower technology) to deliver enhanced performance to users and on simplicity in the eyes of the user. Four examples of systems and equipment are described to illustrate the approach to Appropriate Mechanization. These include: • The Development End System, • The Monorail Raise Climber, • Automatic Pump Control Valves, and • The Energy Recovery Pump. The equipment is presented with the following critical issues foremost in mind: Safety, Working Environment, Performance, Cost effectiveness and Implementation. Although the appropriate mechanization approach is described in the context of the South African underground mining industry, much of the Appropriate Mechanization equipment has worldwide applications. Key Words: Hydropower, Mechanization, Tunnel Development, Raise Development, Monorail, Raise Climber, Pump Control Valve, and Energy Recovery

Sep 1, 2001

By Y. Mitani, M. Zhang, M. Takeda, T. Esaki

Despite their inadequacy, assumptions of isotropy and homogeneity are often applied to the analyses of in situ permeability tests. In this paper, we exam the effects of anisotropy and heterogeneity on Pressure Pulse Test (PPT) and Constant Head Injection Test (CHIT) by means of numerical approaches. Some new findings that offer practical considerations in properly interpreting in-situ permeability tests are presented. Malgré leur manque de précision inhérente, les assomptions d&apos;anisotropie et d&apos;hétérogénéité sont souvent utilisées lors de test de perméabilité in situ. Dans cette étude, nous examinons les effets de l&apos;anisotropie et de l&apos;hétérogénéité sur le test par pression pulsée et le test à injection à charge hydraulique constante par le biais de la simulation numérique. Des nouveaux résultats permettant une interprétation pratique et claire des test de perméabilité in-situ sont présentés. Trotz ihrer inhärenten Ungeeignetheit werden häufig Annahmen über Isotropie und Homogenität auf Analysen von in-situ Permeabilitätstests angewendet. In diesem Papier untersuchen wir die Effekte von Anisotropie und Heterogenität auf Durck-Impuls-Test (PPT) und Konstant-Kopf-Einspritztest (CHIT) mit numerischen Ansätzen. Einige neue Befunde, die zu praktischen Erwägungen zur richtigen Interpretation von in-situ Permeabilitätstests führen, werden vorgestellt.

Jan 1, 2003

ERRATA-AUTHOR&apos;S REPLY IN SEPTEMBER, 1970, JOURNAL: PAGE 52 I. Left half of the page, 4th paragraph, fifth line from the bottom: for 22 / 5 1/2 %, read 22 / 5 1/2 %. 2. Right half of the page, fifth paragraph from the bottom, third line from the bottom: for N(l - p), read N(1 - p)x. 3. Right half of the page, fourth paragraph from the bottom, second line: for: at time t after time zero, read: at time x after time zero. NOTICE TO ALL STUDENT MEMBERS OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY The Institute offers each year for competition among Student Members of the Institute a prize, or prizes, should entries so warrant it, of up to the value of R100 to be awarded to the Student Member or Members who submit the best paper or dissertation on a topic appropriate to the interests of the Institute. In the case of Student Members who are in full time study at a university the dissertation or thesis which they may have to write in part fulfilment of their university curriculum may be accepted provided it is presented in a manner and on a topic suitable for publication in the Journal. The closing date for the receipt of papers shall be 31st December each year.

By L. Wade

Laboratory testing of the self-heating propensity of coal, using crossing-point temperature and differential thermal analysis techniques, involves the frequent recording of several temperatures. The volume of data and the desire for high accuracy of measurements motivates an automated recording system. The data which are recorded must be adjusted for calibration factors and the results presented in both graphical and tabular form. The paper describes hardware and software features of a computerised system which is being used to establish the relative propensity to self-heating of a wide variety of coals.

Jan 1, 1987