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By C. M. Suhr

n order to validate the borehole analysis valuation procedure commonly used in the South African gold mining industry, a simulated orebody was used to create borehole values which would serve as data for the procedure. After confirming the distribution, calculating the variance size of area relationship, estimating the block variance, and calculating a profit measurement for each set, comparisons were made to the known population parameters. Results show only one overall bias (in the estimation of the lognormal third parameter), which is carried throughout the analysis. The remainder of the analysis is unbiased, validating the procedure.

Jan 1, 1987

By G. W. Healy

The smelting of calcium carbide has always been plagued by eruptions, too often with serious injury y or loss of life. To find their causes, the author calculated an internal energy balance using 1992 data for CaC2 and CaO, and older data for the remaining items. The heat content of the charge, and that of the hot gases formed at the reduction temperature, showed that only a fraction of its heat content can be supplied by these gases. Laboratory data on the electrical resistivity of fine mixtures of coke and non-conductive solids were extrapolated to a commercial carbide charge, and then used to calculate the heat produced by current flowing through the mix from the electrode surface to the hearth, which, under favourable conditions, sufficed to bring the charge to 1900 K and higher, at which temperatures reduction could take place.

Jan 1, 1995

By G. J. Wright, M. J. Neale

As machines become more complex and vital to our way of life, any disturbance or failure of their proper functioning tends to have serious consequences. To prevent such failures, increasing attention is being paid to techniques for the monitoring of machinery condition or 'health'. Of the many methods available, examination of the lubricant and any particles it contains forms a basis for interpretation of the conditions of operation, and the rate and severity of degradation of the moving parts, in a machine. Many techniques of wear-debris analysis, such as spectrographic oil analysis and ferography, are available indicate the composition, shape, size, and concentration of contaminants in a lubricant. This paper reviews the important aspects of wear-debris analysis as an integral component of machinery condition monitoring, and gives an insight into the selection of appropriate techniques and the information that can be obtained from each.

Jan 1, 1987

By R. Meyjes, P. Davies

Keywords: Pyrometallurgy, furnace, smelter, engineering company Metix is a private smelter engineering company wholly owned by its management. Its main lines of business in the ferro-alloy industry being: - turnkey smelter projects (LSTK) - engineering, project, and construction management projects (EPCM) - specialised furnace equipment comprising: ? complete electrode columns, including forged copper pressure rings and contact shoes, as well as fail-safe slipping devices ? water-cooled roofs ? bus-tube systems ? feed systems ? cooling systems ? linings ? off-gas systems ? tap-hole drills & clay guns - furnace power supply systems - ore agglomeration & sinter plants - feasibility studies & due diligence reports - technical consulting for investment banks - project procurement & cost control Metix management experience includes around 130 combined years of contacts and experience in the South African smelter industries. Over 30 furnaces have been built, for processes including FeCr (high, medium, and low carbon), FeSi, FeMn (high and medium carbon), SiMn (ultra low carbon), Si metal, and FeV.

Jan 1, 2006

By Alan Bauer

SYNOPSIS A discussion is presented of the advances that have been made in rotary drilling in recent years and it is indicated how and why these drills have replaced percussive equipment even in the hardest formations at larger than 7 in. diameter. A method is presented showing how it is possible to estimate drill requirements and how to optimize drilling and blasting costs for a particular situation. To do this it is necessary to have, in addition to drill performance data, a knowledge of comparative explosive performance. Current methods of doing this are therefore critically appraised. As hole diameters have increased for overall drilling and blasting economies the question of fragmentation arises. In North America this has been approached on a try-it-and-see basis giving results that, in general, have been very satisfactory. The current drilling and blasting practices in North America are reviewed and reference made to the factors of importance in slope control.

By A. O. Filmer

An account is given of a study on the non-oxidative dissolution in aqueous acidic solutions of nickel sulphides of different stoichiometric composition, in which a rotating ring-disc electrode was used. The rate of dissolution was found to depend on the potential of the sulphide and the nickel-to-sulphur stoichiometric ratio. A maximum rate for the dissolution of nickel from nickel sulphides containing an excess of nickel was recorded at potentials around -0,2 to -O,3V. The rate decreased markedly at more anodic potentials. For nickel-deficient nickel sulphides, the nonoxidative dissolution rate increased with a cathodic shift in potential. Under open-circuit conditions, a nickel sulphide of a composition approximating Ni ,S. reacted most rapidly. The dissolution rate was controlled by either a chemical or an electrochemical reaction at the electrode surface, had an activation energy of between 50 and 65 kJ.mol-1, and was independent of stirring speed.

Jan 1, 1980

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 A. Ball

This paper addresses the need for a unifying model that will permit the selection and design of optimum materials for a given wear situation. With this objective in view, the characteristics of the various forms of abrasive, adhesive, and erosive wear are described in terms of localized stress, strain, strain rate, and frictional heating. The measured performance of a variety of metallic, ceramic, and polymeric materials and coated or surface treated materials are described briefly. These results were obtained under conditions of dry-particle abrasion, abrasion in conjunction with corrosion, cavitation erosion in liquids, erosion by particles in low- and high-velocity gas streams, and erosion by particles in a liquid stream. Electron microscopy was used extensively, together with microhardness profiles, in the determination of the modes of material detachment and the underlying deformations and structural changes. As a result of the experimental work, a model based upon a critical strain to microfracture is presented. The microstructural features and materials properties that determine wear resistance are discussed.

Jan 1, 1986

By N. Kernahan, T. Zaniewski

Threshold blasting involves the use of small amounts of high explosive to break and fragment hard rock without having to evacuate mining personnel. The method is easily assimilated and effective in rockbreaking, but requires rigid control on drilling, charging and timing. Current underground trials are aimed at fine-tuning the amount of explosive energy and blast hole geometry to allow the firing of multiple sets of shot holes in a continuous manner. Through correct procedures, the after-blast fumes, dust and fly rock can be contained so as to provide a safe working environment. Threshold blasting hugely reduces the volumes of explosives used in mining and brings to maturity the potential of the process begun by Alfred Nobel when he introduced nitroglycerine, and later dynamite, to mining. Its key contribution is its enabling of continuous mining operations with well understood and relatively low cost technologies. The use of batch blasting, employing large burdens holds the greatest potential for delivering high flow rates of ore at minimal cost. There is good potential for rapid evolution of the concept.

Sep 1, 2001

By R. G. B. Pickering

The Faculty of Engineering at the University of the Witwatersrand and the Mining Technology Division of the CSIR have co-operated to define the problems associated with deep level mining and in this paper they will identify what they consider to be the critical areas requiring technological solutions. This perspective will then be applied to work currently being carried out by both the organizations and gaps for additional developments will be identified. Finally the Co-operative Research Centre methodology operating in Australia is described. The purpose of this CRC is to provide a vehicle for R&D co-operation to develop and implement technologies which will increase the competitiveness of the mining industry. A further objective is to develop an appropriately skilled human resource base.

Jan 1, 1996

By R. E. Gürtunca, D. J. Adams

Writen contribution by J.F.Curtls The subject mater of the paper is interesting in that, instead of 'numerical modeling based on elastic theory' being used for the prediction of energy release rate (ERR) in relation to various types of stope support, including backfil, use is made of stresses in the backfil in an atempt to corect the numerical modeling. Authors' reply to J. F. Curtis We thank Mr Curtis for his contribution to our paper. First of al, it should be emphasized that the object of the paper is not to address the validity of ERR as a tool for the assessment of seismic events or rockbursts, but to determine an in situ modulus for the rockmass with the aid of backfil measurements. Writen contribution by T.R. Stacey Although the authors of the above-mentioned paper have presented some good and interesting information, the title of the paper, and the recommendation that such an in situ modulis should be used for calculations of energy release rate (ERR), are viewed with some concern. The reasons for this concern are as follows. Authors' reply to T.R. Stacey Dr Stacey's comments on our paper are appreciated; we should like to address his concerns as follows.

Jan 1, 1991

By P. R. Labrum, H. A. D. Kirsten

The literature on shotcrete is reviewed with the object of identifying aspects that have not been addressed specifically in terms of its structural performance and manufacture as applied to underground mines. The programme and results of a series of full-scale tests on mesh- and fibre-reinforced shotcrete panels are presented, from which it is concluded that fibre-reinforced shotcrete is competent, especialy at large deformations, and is equivalent in structural performance to mesh-reinforced shotcrete for a fibre content of 3 per cent by mass: furthermore, that the support design systems developed for mesh-reinforced shotcrete are directly applicable to fibre-reinforced shotcrete. The Q-NATM system for the design of temporary tunnel support is presented briefly as one such system. It provides for the integrity of the excavation to be considered in terms of its competence and displacement determinateness, and represents the first systematic procedure for the design of temporary tunnel support. Finally, the support designed on the basis of the Q-NATM system for the main and cross-cut tunnels on the production level in the proposed BA5 block cave at Premier Mine is presented as a practical example of the design of fibre-reinforced shotcrete as part of an overall support system.

Jan 1, 1990

This paper presents a quantitative approach to the problem of determining design capacity and field dimensions of underground coal mines using room- and-pillar mining systems. In evaluating these design variables, relationships among mining costs, number of production sections in mines, location of central shafts, mine field dimensions, section production, mine output, and cost of production losses due to underground man-traveling are analyzed. Thereby the unit cost of coal is expressed as a function of the design variables as well as input parameters such as seam angle, seam thickness, seam depth, underground traveling speed of men, mine recovery and plant recovery. The problem is then formulated as a nonlinear optimization model in terms of minimizing the unit cost of coal subject to a set of constraints and solved analytically for flat seams and numerically for inclined seams. Sensitivity analysis of the variables is also included in the paper.

Jan 1, 1987

By D. Limpitlaw

As coal mining often results in the generation of acid mine drainage (AMD), careful planning and management of the water on such mines is required. A colliery in Mpumalanga recently sponsored independent research into the pollution-ameliorating potential of a natural wetland that has been receiving AMD for at least two decades. Samples of the sediment collected in the wetland were subjected to nine stages of sequential extraction in a determination of the distribution of the metal species present. The samples were then analysed for aluminium, iron, and manganese. The concentrations of sulphate-reducing bacteria (SRB) were also determined. The SRB concentration was found to increase with distance downstream (away from the source of pollution). An analysis of the sediment speciation data indicated that metal immobilization may be optimal in areas where the organic adsorption of metals is at its greatest. The analysis also provided evidence of the biogeochemical improvement of the water quality as the AMD passed through the wetland environment. The metal species present did not correlate strongly with the SRB populations; nor did the soluble species correlate with the species formed over long periods of time.

Jan 1, 1996

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.

The kinetics of cyanide loss were found to be first order under any given set of conditions, allowing rate constants to be easily determined. At room temperature and in the absence of activated carbon, some cyanide is lost by hydrolysis to hydrogen cyanide, but this does not occur to any significant extent at pH values higher than about 10. A higher rate of hydrolysis occurs when air agitation is used. When activated carbon is present, an additional carbon-catalysed oxidation reaction is responsible for a fairly high loss of cyanide. The evidence indicates a reaction mechanism that consumes oxygen and produces cyanate ion. Some of the cyanate thus produced decomposes to form a mixture of ammonia, carbonate, and urea, depending on the solution conditions. Additional cyanide is lost as a result of the adsorption of sodium cyanide by the activated carbon. At high temperatures, an additional hydrolysis reaction, which involves the formation of ammonium formate as an intermediate, occurs an/j is responsible for. a high loss of cyanide, leading ultimately to the formation of ammonia, hydrogen, and carbon dioxide. The presence of activated carbon has no effect on the rate of this reaction.

Jan 1, 1990

The block caving mining method is used to mine large orebodies in weak rock types. The layout for block caving requires that a considerable amount of development is carried out on the extraction drives and drawpoints at the bottom of the caving block. The development further weakens the rock mass, and stability problems arise in the extraction drives and extraction pillars. This paper describes the application of three-dimensional boundary element models in analysing alternative extraction level layouts for a block caving mine. The objectives were to establish whether the use of lateral pillars between drawpoints was warranted, and whether the lateral pillars should be offset or not. The stability of the rock mass within the pillars as well as the stability of the extraction drives were taken into account. The results showed that after undercutting, the horizontal and vertical stresses in the extraction level would be reduced. The lateral pillars would significantly improve the stability of the extraction pillars and extraction drives. There would be a minor improvement in stability if the lateral pillars were offset.

Jan 1, 1987

By M. Akyüzlü

The equilibrium between carbon-saturated Fe-Cr-Si-C alloys and SiO2-CaO-MgO-A2O3-CrO2-FeOy slags was studied under atmospheres of argon and carbon monoxide at temperatures of 1500 and 1600°C. The equilibrium distribution of chromium, silicon, and iron between the slag and the metal phases was determined for different compositions of both phases under different atmospheres and temperatures. It is shown that silicon transfer from the slag to the metal increases with increasing temperature, decreasing carbon monoxide partial pressure, decreasing carbon content of the metal, increasing chromium-to-iron ratio of the metal, increasing silica content of the slag, and decreasing lime-to-alumina ratio of the slag. Some activity calculations were made for the experiments conducted at 1600OC in a carbon monoxide atmosphere. It is also shown that a decrease in the iron content and an increase in the slag basicity decrease the chromium content of the slag. A major proportion of the chromium present in the slag was found to be in the divalent state under the highly reducing conditions prevailing in the experiments. The chromous capacities of these slags were calculated and were found to decrease with increasing basicity.

Jan 1, 1992

By P. J. van Staden, T. W. Walker

The Minfurn is a novel carbon-regeneration furnace developed at Mintek. It combines the advantages of direct resistive heating in a vertical-tube furnace with those of continuous operation, in a furnace whose capital, operating, and maintenance costs compare favourably with those of conventional rotary kilns. After successful tests under experimental conditions on carbons containing different contaminants, a 3 kg/h unit was installed on the carbon-in-pulp (CIP) plant at the Klipwal Gold Mine near Piet Retief, where it has been operating at, on average, 123 per cent of its design capacity. Since the installation of the Minfurn, monthly average losses of dissolved gold of less than 0,02 p.p.m. have been maintained for several successive months for the first time since January 1989. It is also possible that the monthly average residue values have been reduced. Further improvements to the carbon circuit are possible, and the possibility of making further savings by a reduction in the carbon-throughput rate still needs to be investigated. The mathematical modeling of the furnace has progressed to the stage where the future scale-up and design of the Minfurn can be carried out by simulation of the performance of different designs, and choosing the design that yields the desired performance.

Jan 1, 1993

By P. J. Lloyd

Society is fully justified in its concern about the environment, but that concern may, at present, be too uncritical It is, for instance, essential to establish that there is a valid environmental impact, and that there is truly a causal link between a human activity and an observed shift in environmental conditions. In establishing these, it inessential to recognize that scientific proof offers consistency, but that it can never provide completeness. Thus, no amount of scientific endeavour can ever prove that mitigation of the effects of human activity will be perfect. Society normally expresses its concern through legislation. The existing legislation in South Africa is reviewed, and it is found that [>legislation regarding water is probably too stringent to be effective, >legislation regarding air and land use is probably too lax, >all the environmental legislation is too fragmented to be efficient, and the Department of Environmental Affairs is hamstrung by inter-departmental rivalry. ] It is accordingly concluded that, if means are to be found for ensuring adequate mitigation of environmental impact in the face of ongoing economic development, it is necessary to establish a Judicial Commission on Environmental Affairs advised by, but given greater powers than, the departments currently active in environmental maters. This Commission should be charged with creating, perhaps over a decade, a body of legislation that would guide development while protecting the environment in its widest sense.

Jan 1, 1994