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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 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 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.

1. Book review . Australasian coal mining practice, edited by C.H. Martin. Reviewer: R.B. MacGilIivray This book is an extremely comprehensive coverage of coal-mining practice in Australasia, the countries covered being Australia, New Zealand,and Papua New Guinea. 2. From The Institute of Metals The folowing are available from The Institute of Metals, 1 Carlton House Terace, London SWl Y 5DB. Physical and elastic characterisation, edited by M. McLean. 1989. 228 pp. £25.00. High nitrogen steels, edited by J. Foct and A. Hendry. 1989. 461 pp. £49.50. Proceedings of the First International Calcium Treatment Symposium. 1988. 116 pp. £15. New cored-wire injection techniques, particularly as Design for recyc/ability, by Michael E. Henstock. 1988. 150 pp. £15. Solidification processing. 1988. 549 pp. £45. Marine engineering with copper-nickel. 1988. 103 pp. £18. Characterisation of High Temperature Materials. 3. New journal FMJ International Publications Lid have announced a new quarterly publication, Aluminium Today. 4. Other new publications Algorithms in real algebraic geometry, edited by Denis S. Arnon and Bruno Buchberger. London, Academic Press, 1988. 274 pp. £15.95. Proceedings, Foundry and Heat Treatment 88. R150 per set of 5 volumes, or R40 per volume.

Jan 1, 1989

By S. Vorberg, B. Fischer, U. Glatzel, R. Völkl, D. Lupton, M. Wenderoth

Owing to their excellent oxidation and corrosion resistance, Pt and its alloys are being used preferentially at elevated temperatures and in aggressive environments. For example, an important application field is the glass industry. Alongside the discovery of new potential application fields, the knowledge of material properties is essential for computer simulations, design configuration, process optimization, research and development or quality assurance purposes. Due to the importance for technical applications high-temperature properties have been investigated for currently available Pt-base alloys with ongoing improvements. For the determination of tensile creep test data up to 3000°C, including precise strain measurement, special experimental equipment has been developed at the University of Applied Sciences Jena, Germany. An overview of the existing and newly obtained mechanical property data on pure Pt, solid-solution strengthened Pt-Rh alloy, oxide dispersion-hardened materials Pt DPH and Pt 10%RhDPH as well as cutting-edge results on Pt-base superalloys hardened by intermetallic precipitates will be presented and discussed. Furthermore, some important application examples for the abovementioned Pt-materials will be given.

Jan 1, 2006

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 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 A. García-Gutiérrez, A. Aragón-Jerónimo, R. Salazar-Mendoza

A theoretical analysis of a two-region solid-liquid flow system in horizontal pipes is presented, which considers a stationary bed of drill cuttings as a porous medium (-region) below of a two-phase dispersed flow (-region).The method of volume averaging was applied in this study to derive a rigorous mathematical model in which each variable is precisely defined. This model includes the volume-averaged transport equations for both the two-phase dispersed flow and the porous medium regions and terms from a macroscopic forces balance. The solution of the two-region model allowed evaluation of the behaviour of pressure gradient as a function of velocity, total volume fraction of cuttings and the relationship of the height of the stationary bed and pipe diameter. The solution is based on a backward finite difference explicit scheme. The simulated physical system is a pipe of 4.135 m in horizontal length and 0.0508 m in diameter. A one-dimensional, mesh-centred grid, consisting of 100 nodes, is used. The numerical results were compared with experimental data on slurry flows and a good agreement was found. Keywords: two-phase, cuttings transport, solid-liquid flow, drilling modelling, volume averaging.

Jan 1, 2007

By H. M. Dus, D. J. Smith

Resistivity tests indicated that, at temperatures lower than 1450°C, reducing agents alone, as well as burdens consisting of high-carbon ferrochromium and reducing agents, exhibit wide differences in resistivity. These differences are less pronounced at elevated temperatures. The resistivity of a reducing agent and the volume fraction it occupies are important factors controlling the resistivity of burdens of high-carbon ferrochromium. A mathematical model is formulated to describe the dependence of the resistivity of mixtures of conducting and insulating particles on the particle sizes and the volume fraction occupied by the conducting phase. The resistivity of burdens of high-carbon ferrochromium is high if the particle size of the reducing agent is larger than that of the other components of the burden. A number of reducing agents showed small variations in their reactivity towards chromite ore in the solid state. However, with chromite ore in the liquid state, reduction proceeded more rapidly with reducing agents occupying larger volume fractions. During the smelting of manganese ore, high initial rates of reduction were observed for reducing agents that had a high reactivity towards carbon dioxide and a high content of volatile matter, and that occupied a large volume fraction. High liq'uid-state reactivities were observed for reducing agents occupying a large volume fraction and having a Iow degree of graphitization.

Jan 1, 1980

By Ralph H. Nafziger

This paper reviews the major deposits of lower-grade chromite in the world, and a wide variety of methods used for the recovery of chromium from them. Gangue materials in more coarsely sized ores can be separated by gravity means, whereas flotation techniques are required for finer-grained materials. However, unless there is considerable Iron In the ores, physical means cannot increase the Cr/Fe ratios. Chemical techniques such as hydrometallurgical methods, chlorination, roasting and leaching, and smelting are required for this purpose. A greater understanding of the physical properties of chromites and the chemical reactions that take place in the recovery operations is required before. the recoveries from lower-grade chromites can be maximized. More efficient recovery operations can be realized If It can be shown definitively that the reduction of chromites occurs via either a gas-solld or solid-solid mechanism, for example. The effects of specific impurities on the chromite reduction reactions need to be better understood, as do reagent and pH control in the flotation of chromite.

Jan 1, 1982

By O. Fenn

Earlier work had shown that the use of water jets at moderate pressure enhances mechanical cutting in hard rock. To assess the potential of this technique for use in conjunction with free-rolling cutters, a series of laboratory tests was conducted with disc and button cutters to determine the effect of variations in the jet and cutting parameters on the cuter performance. In these tests it was found that the use of water jets at pressure in the range 5 to 40 MPa can reduce the forces on a free-rolling cuter by 40 per cent, which represents a significant improvement in cutting performance. The reduction in thrust force was found to be dependent on jet pressure: the greater the pressure, the greater the reduction. The reduction in rolling force was independent of jet pressure over the range investigated. The results indicate that no additional improvements in cutting performance of any significance are to be gained by an increase in jet pressure above 40 MPa. The most effective jet configuration for the reduction of cuter forces was found to be four coherent water jets, two lateraly disposed on each side of the cuter and directed at the arc of contact between the cutting edge and the rock.

Jan 1, 1987

By R. Tinsley

Project-finance risk assessment is mature and approached systematically. Mining industry due diligence remains fragmented with specialists addressing different aspects of the project such as reserves/JORC, environmental impact, commodity market, even financial analysis/ modelling. Each professional has a natural tendency to believe that the risk factors they have examined are the key ones necessary to be reviewed, as if their review will stand in isolation from others in the way a project materialises. By first laying out the project risk categories and risk matrices, this paper examines the due diligence process with a keen eye to the risk assessment and overlap/interaction. Some cross fertilisation of due diligence techniques from other industry sectors is placed into the mining context. Six case studies are then presented with regards to due diligence features in each project's feasibility review or financial information/ offering memorandum. A power case first shows the differences between the due diligence expectations of banks versus bond financings. Then some Australian and Indonesian mining development cases are analysed to see the due diligence learning points. Some of these were project/due diligence failures. The conclusion focuses on the value of a systematic risk assessment for project evaluation, all from the project-finance perspective.

Jan 1, 2007

By V. M. Lovell, N. P. Finkelstein

The concepts involved in flotation research are discussed and aims are presented. Three different methods of investigation can be used, all of which are applied at the National Institute for Metallurgy (N.I.M.), and these are the empirical, trial and error method, the chemical engineering method, and the physicochemical approaches. This paper is devoted to the last of these. Because of the complexity of the physicochemical interactions involved, the work has, to a large extent, been concentrated on only one aspect, viz. the interaction between the mineral surface and reagents in solution, which was considered of major importance in the understanding of the process. The aspects on which work has been done are the concentration of uranium, the reaction between salt minerals and fatty acids, mixed xanthate-cationic collector systems, and the reaction between sulphide minerals and thiol reagents. Selected problems from the first two of these are discussed in some detail and deal with the agglomeration flotation of uranium and the chemical control of the flotation process for phoscorite. A detailed discussion is also presented of the progress made in the understanding of the interaction between sulphide minerals and thiol reagents, which is of more general application. Finally, an indication is given of the future direction of physicochemical research at the N.I.M.

By Zdenek Kunicky

Kovohute Pribram is a plant recycling lead wastes, lead acid batteries in particular. Relevant new recycling technologies are being gradually developed. Outdated technology of smelting lead plates has been replaced by a new technology based on processing of entire batteries in a blast furnace according to the process developed by know-how of German Varta company. The classical Harris refining has been substituted by the oxygen refining. New technologies aimed at utilization of related wastes arising from refining lead bullion in Kovohute Pribram are being developed in house. At present, a new technology of utilization of spent battery acid for extracting zinc from various wastes has been developed. Zinc oxide dross from alkaline refining of lead bullion, during which residual zinc from the preceding vacuum de-zincing is removed as well as waste zinc galvanic sludges (a product of neutralizing precipitation of metals from industrial wastewaters with lime) were treated. In this study, the new developed technology yielding basic zinc carbonate - a valuable raw material for zinc electrowinning, is described together with the first experience of applying the developed method to processing zinc wastes on a pilot scale. Most of the equipment used in the past to regenerate alkali solutions originating from Harris refinery was utilized in the practical realization of this new technology.

Jan 1, 2008

By Wm. Bleloch

SYNOPSIS The feasibility of rejection of nitrogen from stack gas by recycling of top-gas with cold-blast 95 to 98 per cent oxygen is assessed. It is concluded that nitrogen could be removed to a level below 3 per cent of the stack-gas using recycled cleaned cold top-gas and 95 to 98 per cent oxygen produced by a single-column air separation plant with liquid-air reflux instead of liquid nigroten reflux. The partial pressure of carbon monoxide in the stack-gas could be doubled without top pressure and the deposition of carbon and reduction of iron oxides by the stack gas could be markedly increased. It is concluded that rate of stock descent could be doubled compared with present-day practice and an iron make of 4400 kg/m 2 of hearth area/hour may be attainable with a working volume of 129 m2/m hearth diameter by this method. Oxygen consumption is estimated at possibly 280 m2 (0.4 t)/t iron made and carbon consumption at possibly 280 kg/t iron. Power consumption for oxygen including auxiliaries is estimated at 304 kWH/t 100 per cent oxygen as 95 to 98 per cent gas. The air separation cycle due to Schuftan is discussed in some detail, and the components of a 1 600 metric ton/day separation plant are briefly discussed. The paper is a theoretical essay.

By T. R. Twiddle

The sequential flotation of copper, lead, and zinc in that order is practised at the Broken Hill Concentrator of the Black Mountain Mineral Development Company (Pty) Limited. The minerals of economic importance are chalcopyrite, galena, and sphalerite, with associated silver. The targets for recovery and grade in the lead and zinc circuits were reached quite readily after start-up, but the copper circuit failed to meet the performance requirements with respect to both recovery' and grade. The original circuit for copper is described, together with the subsequent investigations and modifications that were required to produce acceptable metallurgical results. Circuits for semi-bulk and bulk flotation were tried, and the effect of the oxidation state of the pulp was investigated extensively and found to be all important. Tests were conducted on the depression of lead in the cleaning circuit by the use of sodium dichromate, and on heating with the addition of sulphurous acid. The latter technique was ultimately the more successful. The proportion of fresh to recycle water entering the circuit was shown to be important. The original reagent regime was altered and augmented. A more recent problem has been the contamination of the ore with cemented backfill. The changes that this new condition necessitated are described. Success has been measured by a continuous improvement in the economics of the copper recovery.

Jan 1, 1984

By A. Kijko, C. W. Funk

Methods for the analysis of seismic hazards in mines are reviewed as illustrations of the techniques that are being used in some South African mines. The classical parameters that describe a hazard are the seismic activity rate, ?, the Gutenberg-Richter value, b, and, occasionally, the maximum regional magnitude, mmax The activity rate is calculated readily owing to the inherent simplicity of its definition. The evaluation method presented for the Gutenberg-Richter b value takes into account the presence of mmax Three statistical procedures are described for the assessment of mmax which the maximum observed magnitude, Xmax a crucial role. Often, the configuration of mine seismic networks is changed, or the networks are improved, which inevitably gives rise to changes in the completeness of the seismic catalogues. The routine analysis of seismic hazards must account for these time dependent changes. A method for the evaluation of hazards is reviewed that accommodates varying levels of quality in the catalogues. Finally, the concept of the volume of ground motion (VGM) is presented. This is a technique that allows for most aspects of seismic hazards in mines. The advantage of the VGM is that a hazard can be described by one physically significant value: the volume of rock (cumulated over a time period) in which the ground motion exceeds some critical particle velocity. Data from the gold mining region in South Africa known as the Far West Rand is used in a demonstration of the discussed methods of hazard analysis.

Jan 1, 1994

By P. Horrell, K. Rhodes, G. Harrison, J. Dean, D. Sammons, M. Stander

Anglo Platinum have perceived a need to increase the rate of reef development both for new mechanised stoping technology and on conventional new developing mines. The Research and Development Division of Anglo Platinum therefore initiated an experimental reef raise project with a tunnel boring machine (TBM) at Bafokeng Rasimone Platinum Mine (BRPM). The scope of the trial was for the boring of a reef raise 340 metres in length on the Merensky Reef. The boring phase of the trial took place over six months and the average rate of penetration of the TBM was 0,47 metres/hour. TBM utilisation was 22%. The TBM used in the trial was a Jarva MK6 manufactured in 1972 and its design with its backup system was not considered to be an ideal machine for reef development. However it was the intention of the trial to prove the concept of developing with a TBM on reef. In this respect the trial was unequivocally a success. There were many problems and long delays did occur during the boring phase. Nevertheless there is every confidence that a new TBM can be designed specifically for this type of work that will achieve high rates of advance up to (say) 400metres/month and with a more flexible steering system in order to negotiate reef changes. It can therefore be expected that TBMs will be used in the future for reef development on South African platinum mines.

Sep 1, 2001

By T. A. Silva, A. C. Bragança

Lime has been added to the iron ore slurry transported by the Samarco pipeline since its operation start-up in 1977.Initially, internal corrosion was the main concern therefore the reagent was used only for pH correction. Over the last ten years, though, transport of more complex slurries demanded a significantly higher dosage of lime to guarantee adequate rheology control. Several other reagents have been tested for the same purpose yet none has proven to be as effective regarding technical performance, environmental impact and cost. However, an alternative was sought so that the slurry rheology could still be controlled in case lime addition became impracticable. The objective of this paper is to present a technical solution for this matter, which takes into account environmental aspects. It consists of adding soda for pH correction and an organic coagulant as a rheology modifier. The latter is a quaternary ammonium salt which affected the slurry transport properties in the same manner as lime when tested in a laboratory. It showed no plug formation and allowed solid particles to settle, forming a loose sediment after rest. These results indicate a low probability of plug occurrence in the pipeline and the formation of a readily reslurryable sediment upon shutdown of the pumping system. Industrial tests should be performed in order to validate the laboratory results.

Jan 1, 2007

By P. A. Botha

The production of iron and steel generates various types of waste materials containing oxides, carbon, and flux material. Usually, these materials are land-filled at the plant site or are hauled away for disposal. Some of these waste materials are hazardous, and they must therefore be recycled or disposed of properly. The influence of different waste materials in iron-ore sinter blends on the quality and operational parameters in sinter production is described. The recycling of waste materials such as dolochar, scrap fines, mill scale, electric-arc furnace slag, basic-oxygen-furnace mud via the sintering process can achieve a saving in the cost of the raw materials (for example, fuels and flux) and a reduction in pollution. A comparison of a typical sinter with a sinter produced through the utilization of waste materials shows a distinct correlation between certain types of waste material and some metallurgical properties and operational parameters. Dolochar (and arc-furnace slag) in a sinter blend acts as part of the fuel and flux that are normally added to a sinter mix. In general, dolochar improves the quality of the sinter and decreases the consumption of coke. Other waste materials adversely influence the quality of the sinter, but not necessarily the operational parameters such as the production rate. At Vanderbijlpark, approximately 15 kt of various waste materials per month are successfully recycled in the sinter plant. Investigations into the handling and recycling of other waste materials may indicate that even more waste materials can be utilized.

Jan 1, 1993