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Professor R.F. Sandenbergh matriculated at Germiston Afrikaans High School, and then he obtained the degrees of B.Eng. (Chem.) in 1972, M.Eng. (Chem.) in 1975, and D.Eng. (Met.) in 1983-all from the University of Pretoria. Mr J.A.D. Britz matriculated in 1958 at the Roodepoort Hoerskool, and joined the mining industry in 1959 as a student mine official at the Rand Mines Training Centre. Mr J.A. Cruise matriculated at Durban High School and joined Union Corporation as a Learner Official in 1962. He was awarded a scholarship to read for B.Sc. and M.Sc. degrees in mining engineering at the University of the Witwatersrand

Jan 1, 1990

By A. Chryss, L. Pullum

Shear-thickening suspensions abound throughout the hydraulic conveying industry; at least this is the perception of many engineers running plants where hydraulic conveying is commonplace. In reality, shear thickening behaviour is limited, in the main, to high concentrations of fine particles, including colloidal and biological suspensions, at moderate to high shear rates. In the authors? experience most cases of shear-thickening behaviour have been either simple ?coarse? particle interactions, poor instrumentation techniques, or both. In some cases these were obviously heterogeneous flows, while in others flows that were homogenous, or were thought to be homogenous. Examples, which illustrate this erroneous perception are given. However, the trend towards pastes and complex suspensions that use high concentration carrier fluids means that the underlying slurries for many of these flows may now be truly shear-thickening. Unfortunately, suspensions that might exhibit shear thickening also invariably exhibit slip, or wall-particle depletion. These separate phenomena are difficult to resolve experimentally and many observations of apparent shear-thickening behaviour are in fact obscured or convoluted by slip effects. A method is presented whereby the true flow properties of these high concentration suspensions, and hence accurate prediction of pipeline flows, can be made using a parallel plate rheometer.

Jan 1, 2007

By M. J. A. Leal-Gomes

There is a set of settled ideas in the field of the mechanics of rock mass joints, that need a deep revision, after the last experimental works of several authors. In this paper, this theme is approached under several viewpoints, like the following ones: the essential influence of the mating or mismatching of rock joints on their strength (different strength models are applicable to these two situations, one leading preferably to normal scale effects, and the other to inverse scale effects); Patton's model is a bad formulation of the joint strength, whenever there is a dilation effect in the slidings (actually, the essential consideration of the amplitude of the roughess isn't made by any limit equilibrium model, like Patton's model); the joint strength increases as the width perpendicular to the sliding direction is reduced (previous works of other authors suggested the independence of the strength on that width); the reduction of the anisotropy of the roughness, as the sample symmetry and sample dimensions increase; there is no scale effect in the discontinuity mechanics, if there is no roughness heterogeneity; when only the same roughness and undulation orders are involved in the tests, shorter samples have larger peak displacements and lower shear stiffnesses than larger samples (usually, the contrary is admitted). For all these reasons, there isn't an easy correlation between the small scale tests and the natural large joint scale. Only "in situ" large scale tests have some representativeness. All the above mentioned questions are correlated to each other. Es gibt eine Menge eingewurzelter Ideen im Gebiet der Mechanik von Felsklüften, die, nach den letzten experimentellen Arbeiten von mehreren Verfassern, eine tiefe Überprüfung benötigen. In dieser Mitteilung, wird dieses Thema unter mehreren Blickpunkten angegangen, wie die folgenden: der wesentliche Einfluß des Zusammenpassens oder nicht Zusammenpassens von Gesteinsklüften auf ihre Festigkeit (verschiedene Festigkeitsmodelle sind auf diese zwei Situationen anwendbar, eins, das vorzugsweise zu normalen Maßstabseffekten führt, und das andere, das zu umgekehrten Maßstabseffekten führt); Pattons Modell ist eine schlechte Formulierung der Kluftfestigkeit, immer wenn es einen Dilatationseffekt in den Verschiebungen gibt (in Wahrheit, wird die wesentliche Berücksichtigung der Rauheitsamplitude von keinem Grenzgleichgewichtsmodell beachtet, wie Pattons Modell); die Kluftfestigkeit wächst wenn sich die Breite senkrecht zur Verschiebungsrichtung verringert (frühere Arbeiten anderer Verfasser suggerierten die Unabhängigkeit der Festigkeit von jener Breite); die Verringerung der Rauheitsanisotropìe, wenn die Probekörpersymmetrie und Probekörperabmessungen zunehmen; es gibt keinen Maßstabseffekt auf die Trennflächenmechanik, wenn es keine Rauhheitsheterogenität gibt; wenn nur die gleichen Rauheits- und Ondulationsgrößenordnungen in den Versuchen verwickelt sind, haben kürzere Probekörper größere Spitzenverschiebungen und geringere Schersteifigkeiten als größere Probekörper (gewöhnlich, wird das Gegenteil angenommen). Wegen aller dieser Gründe, gibt es keine einfache Korrelation zwischen den Versuchen im kleinen Maßstab und dem natürlichen großen Kluftmaßstab. Nur "in situ" Versuche im großen Maßstab sind einigermaßen repräsentativ. Alle die oben erwähnten Fragen hängen miteinander zusammen. Il y a un ensemble de des bien établies arrière-pensées idées dans le champ de la mécanique des discontinuités en massifs rocheux qui ont besoin d'une profonde revision, après les derniers travaux de divers auteurs. Dans cet article cette matière est abordée sous divers points de vue, comme les suivants: la signification essentiel de l'ajustement ou du désajustement des discontinuités dans leur résistance. Des différents modèles sont applicables à ces deux situations, une conduisant de préference à des effets d'échelle normaux et l'autre à des effets d'échelle inverses; le modèle de Patton est une mauvaise formulation de la résistance des joints quand il y a effet dilatant dans les glissement. En effet la contribuition essentielle de l'amplitude de la rugosité n'est pas consideré par aucun modèle d'équilibre limite comme le modèle de Patton; la résistance des joints croit au fur et à mesure que la largueur perpendiculaire à la direction de glissement est réduite. Des travaux antérieurs d'autres auteurs suggéraient que la résistance était indépendant de cette largueur; la réduction de l'anisotropie de rugosité au fur et à mesure que la symétrie et les

Jan 1, 2003

The statistical methods described in the previous chapter permit the estimation of the average value p of a deposit, and the calculation of confidence limits for this value. They are based on the assumption of independence of sample values. As soon as a reasonable number of samples has been obtained from a deposit, local valuation, or estimation of blocks of ore within the mineral deposit, becomes necessary. The assumption of independence of values must then be rejected. Local valuation is possible only if there is a relationship between the value of a sample and the value of the surrounding ore, provided this relationship is a function of the position of the sample with respect to the blocks of ore to be valued. Whichever method is used for the valuation of a block of ore, the following assumptions are always made: ? The values of samples located near or inside the block are related to the value of the block. ? The values of the samples located closest to the block are most closely related to the value of the block. These assumptions will hold true only if the following assumption can also be made: ? There exists a relationship between sample values which is a function of the distance between samples. We are saying that the value x (z) of a sample centred at a point z has properties which are functions of this point. A certain spatial structure exists in the sample distribution. We are therefore dealing with a regionalized phenomenon, and we must treat x (z) as a regionalized variable. This can be done statistically by means of a model chosen to represent the spatial structure of the phenomenon. We shall see that the relationship between block values and sample values can be deduced from the relationship between sample values, and all local valuation problems can be solved using the statistical model obtained from the analysis of the sample values. It is important to realize that this statistical model is obtained by analysing the properties of known sample values, and will be used for the estimation of unknown block values. Such a statistical inference is valid only if the model developed represents the properties of both the sampled section of the ore body and the section to be valued: some stationarity conditions must be satisfied, and the model with the least restrictive conditions is preferred. In the following chapters, the most important models used in spatial geostatistics are presented. The models which can be used when there is no significant drift (trends) in values are described in Chapters 3-1 1. These models can also be used to solve some specific valuation problems when a linear drift is present. A general study of the more difficult problem of analysis of an ore body whose values present a drift is described in Chapter 12. Note that the area considered for local valuation of a block of ore is often small enough for any drift which might be present to be ignored.

Jan 1, 1978

By H. G. Mosenthal

In any mining enterprise, the extraction of the ore from the orebody is of vital importance. This activity is stoping. The gold mines of the Witwatersrand and its extensions in the Klerksdorp, Welkom, and Evander areas form the most extensive goldfield in the world. This address reviews stoping technology and improvements in this technology since the end of the Second World War. Although the reefs that make up the Witwatersrand orebody are uniquely extensive, they are not suited to mechanized mining. This is due to a number of factors such as the depth of the orebody, its narrowness, and the hardness and abrasiveness of the quartzite forming the orebody. The most notable improvements in stoping technology have been brought about because of our beter understanding of rock-engineering problems. This has resulted in beter layouts, stoping geometry, systems of aleviating rock stresses, and support systems. It has enabled the industry, at ever-greater mining depths, to maintain and even increase productivity. These improvements, based on rock engineering, have significantly reduced the accidents due to rockbursts. There are many diferences between today's stoping and that practised forty years ago. Panels are shorter, concentrated mining has superseded bench mining, and the support systems are certainly better. Yet the face scraper is still used extensively, as are pneumatic rock drills. Some innovative stoping systems that have given rise to improved productivity are discussed. Explosives technology has shown spectacular advances during the period under review. Sadly, our local industry has had little to do with this research and development, but has been most adaptive in using the new products on offer.

Jan 1, 1990

A. H. Mokken: I am pleased to have been given this opportunity to make a contribution to Dr Muller's paper tonight. The reason for this is that, at one stage in our careers, we were associates in the same undertaking. Dr Muller, then fresh from University, with a degree in pure science, had just stepped onto the first rung of the ladder, which, it was then thought, would lead him to a career in gold extractive metallurgy. However, endowed with an enquiring mind and conscious of a lack of fundamental training in general metallurgy and engineering, he felt a need for further academic study. To meet this need and, more importantly, to meet the necessary finances, he found his opportunity in steel. Armed with a bursary, he bade farewell to gold and proceeded overseas, to the University of Sheffield, to train as a steel metallurgist. The outcome of these academic efforts, which were followed by assignments in the steel industry and a further period at Sheffield, is the man we have listened to tonight-a highly qualified metallurgist who has displayed a sound knowledge of his subject. In choosing Sheffield, Dr Muller became associated with a steelmaking centre of world renown, a centre usually credited with the first systematic production of alloy steels, as far back as the 18th century. Since that time, great advances have been made in the production of alloy steels and this is especially so in the last decade or two, when major developments in civil, mechanical, electrical, aeronautical and nuclear engineering have been made possible by the development of steels with improved properties. In spite of spectacular advances in the technology of non-ferrous alloys, plastics and other materials of construction, steel has maintained its role as a pre-eminent material for engineering use. With the gradual accumulation of data on the properties of steels, and the use of thin film electron microscopy, to study the behaviour and characteristics of such phenomena as dislocations in metals and other microstructural features, the physical metallurgist appears to be approaching the stage of an exact understanding of such phenomena as strength, ductility and brittleness-a knowledge which could lead to close control of such properties and, therefore, to the attainment of the highest goals. An interesting example, illustrating the use of fundamental principles, based on physico-metallurgical research, is the development of the maraging steels developed by Bieber at the International Nickel Company. These steels have met the extreme technological requirements of the space age by providing the material for the cases of large rockets in which qualities, such as high tensile strength, toughness, workability and weldability are most important. Attractive as they might appear to be in considerations of savings of weight, cost of erection, transport of materials and foundations, the use of high strength steels has been accompanied by special problems such as brittle fracture, hydrogen embrittlement, notch-toughness and fatigue. It has been found that high strength steels, which performed acceptably in conventional tension tests, were found to undergo failure, in a brittle manner, in service. Hydrogen embrittlement has caused spectacular failures at a fraction of the normal ultimate tensile strength, and a lack of correlation between fatigue and tensile strengths has diminished the advantages to be obtained from the use of high strength steel in some applications. A new approach to the selection of materials for engineering design has resulted from a consideration of these phenomena in which strength, as such, is no longer as significant as it was previously. Parallel with the development of high strength steel has been the need for suitable techniques for joining component parts and here welding has played an

By J. D. Stone, I. D. Brumby, J. D. Inch, C. J. Beukes

A. Continuous miners, and their operation at Bosjesspruit Colliery J. D. INCH*, B.Sc. (Min.), M. I. Min. E. (Visitor) A brief description is given of the main types of continuous miner and their incidence of application in South Africa. Definitions and descriptions of the design parameters and components of the main cutting head are given. together with an outline of the modifications carried out to improve machine cutting performance. An account is given of experience with the application of water infusion to suppress airborne dust during continuous-miner operations. B. The selection and performance of continuous miners at Matla Coal by J. D. STONE, B.Sc. Eng. (Min.,) M.B.L. (Graduate) The reasons for the choice of continuous miners for the development of accesses and the winning of coal in a modern underground coal mine are discussed. It is shown that, at relatively low depths, the extraction rate as well as the costs are more favourable than those of proved total extraction methods. The selection of a continuous miner is largely dictated by factors such as production rate, capital and running costs, imported content and the extent to which local content and manufacturing are to be increased, manpower requirements, seam thickness, expected floor and roof conditions, and maximum cutting height. The present inherent shortcomings of continuous miners, such as inefficient continuous transportation of coal away from the miner and the lack of an infinitely variable traction to match the sumping speed with the feasible penetration speed, are pointed out. Specific problems encountered and the methods of solving them, as well as a planned trial with a heavy-duty continuous miner, are discussed. C. Continuous mining within the Tavistock Group of collieries I. D. BRUMBY.Dip. Min. (Visitor) The Tavistock Group of collieries is situated some 25 km south of Witbank. The three collieries comprising the Group are Tavistock Colliery, Phoenix Colliery, and South Witbank Coal Mines. Continuous mining is practised to some degree at all three collieries. This system of mining was introduced at Phoenix during 1976, South Witbank during 1978, and Tavistock during 1979. For the twelve months ended June 1979, continuous mining accounted for 1,7 Mt of the 4,5 Mt hauled from underground. All the continuous miners introduced to date have been of the rotary-drum type. D. Pillar extraction at Usutu Collieries using continuous miners by c. J. BEUKES(Visitor) In 1969 Usutu Collieries began pillar extraction with conventional mechanized equipment. This was very successful, but certain disadvantages could be eliminated if continuous miners were used instead. In 1976 the first continuous miner was introduced for this purpose; this proved so successful that a second unit was introduced in 1977, and pillar extraction by conventional equipment was discontinued. By the end of 1978, 1,3 Mt had been mined from pillar extraction by continuous miners. This paper describes the method in some detail, and indicates that the operational costs are lower than for conventional bord-and-pillar mining. Defect solid state A one-day multidisciplinary symposium entitled 'The Defect Solid State '80' will be held under the auspices of the Solid State Physics and Materials Science Subcommittee of the South African Institute of Physics at the University of the Witwatersrand on Monday, 14th July, 1980, following the Twenty-fifth Annual Conference of the South African Institute of Physics.

Jan 1, 1980

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

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

Jan 1, 2007

The Registrar has requested us to publish the following notices: COUNCIL'S POLICY REGARDING LATE APPLICATIONS IN TERMS OF SECTION 18(4) (b) OF THE PROFESSIONAL ENGINEERS' ACT, 1968 (ACT NO. 81 OF 1968) Laat aansoeke om registrasie as Professionele Ingenieurs Die Suid-Afrikaanse Raad vir Professionele Ingenieurs (SARPI) vestig die aandag daarop dat daar 'n mistasting bestaan oor die vraag of 'n persoon sonder erkende ingenieurskwalifikasies wat nie in 1969 aansoek gedoen het om registrasie as professionele ingenieur nie, nie meer aansoek mag doen nie. Diegene wat voor 14 Februarie 1969 minstens 3 jaar aanvaarbare ingenieurswerk gedoen het kan nog oorweeg word. Die werk moet egter voldoen aan die standaarde deur SARPI neergele: dit Suid-Afrikaanse Road vir Professionele Ingenieurs DIE WET OP PROFESSIONELE INGENIEURS, 1968 (WET NO. 81 VAN 1968): JAARGELD: 1972/73 BOEKJAAR Kragtens die bepalings van Artikel 18(9) (b) van die Wet verval die Registrasie van 'n persoon wat as 'n ingenieur of ingenieur-in-opleiding geregistreer is as sodanige persoon versuim om die voorgeskrewe jaargeld binne ses maande nadat dit betaalbaar word, te betaal. Aandag word ook vriendelik daarop gevestig dat persone wat kragtens Artikel 18(4) (b) van die Wet geregistreer is (dit wil se persone wat nie oor 'n erkende akademiese kwalifikasie beskik nie) en wat toelaat dat hulle registrasie verval, moontlik nie weer vir registrasie in aanmerking sal kan kom nie. Vir persone in hierdie kategorie is dit dus van kardinale belang om toe te sien dat hulle jaargeld binne die voorgeskrewe tydperk betaal word.

By P. K. Van Manen

Anglo Platinum's Polokwane Smelter is situated outside Polokwane, in the Limpopo Province of South Africa. Wet concentrate is received from various concentrators along the Eastern Bushveld Complex. Approximately 60% of the total concentrate received is from UG2 Reef, and 40% is from Merensky Reef. The concentrate is dried in two flash dryers, and smelted in a single 168 MVA furnace. A PGM-rich nickel-copper matte is cast, crushed and transported to Rustenburg for converting. The plant was commissioned in March 2003. The wet concentrate, containing 12-18% moisture, is weighed, sampled by one of two auger samplers, and off-loaded into a concentrate shed, either directly through a grizzly into a hopper, or onto the floor. From the shed the concentrate is conveyed to 12 concrete silos. Each of the two identical flash dryers can be fed from six silos. From the flash dryers concentrate is transported pneumatically to a 3 000-ton dry concentrate storage silo. The flash dryers are rated at a nominal 66 tph of dry concentrate at 14% moisture, while the furnace can smelt 90 tph of dry concentrate. Therefore both flash dryers are required to operate when the furnace runs at design throughput. Each flash dryer consists of a hot gas generator (HGG), a disintegrator and drying column, and a section for gas/solids separation. In the HGG, gas heated up to 700° C is produced from the combustion of coal peas in a fluidized sand bed. The hot gas and wet concentrate are introduced to the disintegrator at the bottom of the drying column. The disintegrator breaks up any lumps of concentrate, and throws the concentrate up into the drying column, where it travels co-currently with the hot gas. A fan draws the hot gas from the drying column and through the gas/solids separation section, which consists of three primary cyclones, a multiclone and a high-temperature bag house. The dry concentrate reports to a 450-ton dry concentrate storage bin. A portion of dry concentrate is recycled to the wet concentrate feed in a paddle mixer, so that concentrate that is too wet does not enter the disintegrator. The drying column outlet temperature is controlled at 120° C. Coal is received by road, screened for oversize and conveyed to a 400-ton concrete silo. From here it is pneumatically conveyed to a small feed bin at each of the HGG' s. The optimization work consists of process control improvements relating to the HGG outlet temperature, to control the drying column temperature during the ramp-up of the HGG outlet temperature and bag filters. Furthermore a heat balance is used to evaluate options to increase the instantaneous drying capacity of the existing equipment. The coal consumption derived from the heat balance is compared with the actual coal consumption. The purpose of the optimization work is to achieve an operating schedule for the flash dryers such that they operate simultaneously for as short time as possible. Most of the time one flash dryer should operate, allowing maintenance to be done on the other flash dryer, while drawing down the dry concentrate stock. Keywords: Anglo Platinum, Polokwane Smelter, pyrometallurgy, metallurgy, platinum, platinum group metals (PGM), base metals, flash drying, fluidized bed.

Jan 1, 2006

By M. I. Brittan

Discussion Dr R. E. Robinson (Fellow): The author must be congratulated on a very meticulous and self-contained piece of work. It is indeed a pleasure to read a paper that is so clearly and systematically laid out, and where the conclusions and the testwork conducted have been so clearly described. The paper is complete in itself, which makes it very difficult for someone who is not intimately involved in the whole Torco project to make any comments on its content. However, two points that, strictly speaking, fall outside the scope of the paper are of considerable interest. The first relates to the particle size of the material treated. In the paper, the testwork is confined to one standard particle size (minus 60 plus 100 mesh). The essential feature of the paper is to indicate that the rate-controlling reaction in the whole segregation process is the rate of reaction of the ore particles with the reducing agent and the hydrogen chloride. One wonders, therefore, to what extent this relatively slow rate of reaction is affected by the particle size of the ore itself. One imagines that the reaction must take place by contact of the hydrogen chloride with the surface of the mineral particles, and it is reasonable to suspect that the rate of diffusion of the copper ions to the surface is a relatively slow process and is thus the limiting factor in this particular rate of reaction. It is possible, for example, that the improvement obtained, when the ore is subjected to reducing conditions before the chlorination, is due to a breakdown in the crystal structure of the original particle. This breakdown is brought about by the reduction and by the consequent increase in surface area available for reaction with hydrogen chloride. Can the author indicate whether any work has been done along these lines, and whether it has been established that the reaction depends on the surface area available? The second point relates to the application of this kinetic study to the actual operation of a Torco reactor. It was once planned to feed the sodium chloride, together with the reducing agent, into the top of the segregation chamber. In the paper, the author mentions that it has now been established that the segregation chamber behaves, to all intents and purposes, as a fluidized bed, and that there is, therefore, a rapid evolution of gas in the lower regions of the chamber, which, it is imagined, displaces the gas phase rapidly. Since the reaction between sodium chloride, water vapour, and the aluminium silicates in the ore is extremely rapid, one wonders how much of the hydrogen chloride produced is removed from the reaction zone before it has had time to react with the copper minerals. The extremely low consumption of sodium chloride (which is a vital feature of the Torco process) must depend on an extremely rapid circulation of the hydrogen chloride gas to all the ore particles in the segregation chamber. One wonders, therefore, if a system for the introduction of the sodium chloride into the bottom regions of the chamber might not result in even greater efficiency in the utilization of sodium chloride. ProC D. D. Howat (Fellow): All of us who have been concerned with the study of chemical reactions at high temperatures are keenly interested in kinetics and are well aware that this is not an easy study experimentally. Dr. Brittan is to be congratulated on the development of neat experimental methods and for his full discussion of the results obtained. Although the segregation process for the extraction of copper from oxide and silicate ores has been known for almost fifty years, the fundamental chemical and physical changes involved have been little understood and the fundamental data are very scanty. The work now in progress at A.A.R.L., together with that sponsored by the Anglo American Corporation in other research institutions throughout the world, is bound to produce new fundamental data and a much more complete understanding of this rather fascinating process. It is already apparent that some of the old and well-worn chemical reactions that were postulated to occur, just cannot take place in the way which was formerly accepted. Dr Brittan's work, carefully conducted and thoroughly analyzed as it has been, still leaves us with one great outstanding problem. The thermodynamic data and the possible reactions set out in Table I (page 281) of his paper leave us asking, in complete despair, how can copper be converted into a volatile chloride in the presence of HCl, CO and carbon at temperatures about 800°C? The thermodynamics all combine to show that copper should be reduced to metal as the first step in the process. This brings us right up against the second problem. If copper were reduced to the metal how would HCI convert it to the volatile chloride? On top of these problems is the unknown reason for the very high speed of reaction between CO, HCI and the ground copper ore. Still further into the region of the unknown is the reaction by which gaseous hydrochloric acid is produced in the actual process. Perhaps Dr Brittan is feeling grateful that he doesn't have to try to explain this reaction-at this stage of the research programme at least. The results very clearly show that both CO and HCl gas are essential for rapid production of the volatile copper chloride. Dr Brittan states that 18 minutes were required to attain 83 per cent extraction with HCl gas alone and this was reduced to 4 minutes when CO was

Jan 2, 1970

By H. J. R. Way

Dr H. J. R. Way: In his reply to my queries Mr Bath still adheres to his statement that it may be possible to replace the estimated R200 million reduction in gold revenue in 1980 by exports of ferro-chromium, and apparently based his conclusion on a growth rate in demand for corrosion resistant steels of 10 per cent per annum in the next few years. As I pointed out at the previous discussion at Middelburg this would entail a production of about one million tons of ferro-chromium in 1980. Exact statistics of South African ferro-chromium production are not available, a fact which is very much to be regretted. But statistics of exports of ferro-chromium are available from "Foreign Trade Statistics" of the Customs and Excise. These show that South Africa exported 99,580 short tons in 1967. The quantity of ferro-chromium consumed in South Africa in 1967 was fairly small and we can therefore assume that the production was 99,580 tons. For this amount to grow to 1,000,000 tons in 1980 would require a growth rate of 19.4 per cent per annum. At 10 per cent this would grow to 344,000 tons and at 7 per cent 240,000 tons. The following growth rates in the form of average trends are pertinent: STEEL - Per annum World steel ingot production - 1957-67 – 6.8 per cent Free-world ingot production - 1957-67 – 6.0 per cent Consumptions of crude steel by four major Free-world Consumers - 1957-67 - 5.6 per cent CHROMITE World production - 1952-67 - 2.5 per cent South African total sales - 1948-67 – 5.4 per cent South African exports - 1948-67 – 3.9 per cent United States consumption, very irregular, but - 1962-67 – 6.5 per cent FERRO-CHROMIUM - Per annum United States consumption - 1952-67 - 6.5 per cent South African exports - 1957-62 - 25.2 per cent South African exports - 1962-66 - 41.9 per cent South African exports - 1966-68 - 21.2 per cent These figures show that exports of ferro-chromium have been growing at a very high rate varying from 21.2 per cent to 41.9 per cent since 1957, but in view of the market situation it seems somewhat doubtful if that high rate can be maintained up to 1980. Of our 1966 exports U.S.A. took 63 per cent which was 53 per cent of their total imports. Their average consumption is trending at a growth rate of 6.5 per cent per annum from 1952-67, but the growth from 1964-66 was 5- 2 per cent and 1966-67, -12 per cent!

Mar 1, 1968

By D. Duncanson, R. J. Davidson, C. G. S. Schmidt, G. A. Brown, J. D. Taylor, N. W. Hanf

The development of a cyanidation route for the treatment of gold-plant gravity concentrates is described. This work was carried out as a natural consequence of earlier improvements to the recovery of gold in the gravity sections of existing gold plants. Concern about the environmental aspects of the conventional amalgamation process was further motivation in the development of an alternative procedure. It was found that the partial pressure of oxygen in solution was the most critical reactionrate determining factor. The rate of gold dissolution was shown to be controlled by the reaction rate below approximately 25°C and by diffusion above that temperature. Thus, the efficiency of pulp agitation and oxygen partial pressure permitted a high degree of control over the rate of gold dissolution. The use of oxygen rather than air significantly increased the dissolution rate of both gold and silver. The solubilities of sodium, calcium, and potassium aurocyanide complexes under simulated reaction conditions were studied, and it was established that the values for the sodium and calcium complexes were limited, requiring the use of lower pulp densities and higher reaction temperatures for the treatment of very high-grade concentrates. The presence of excessive amounts of tramp iron in such concentrates of up to 25 per cent by mass was found to result in poor gold dissolution owing to the cementation of gold under certain reaction conditions. The maintenance of high oxygen partial pressures, together with high cyanide concentrations, high pH levels, and the presence of calcium in the system, all aided in passivating the tramp iron. Copper, gold, and iron were shown to be the main cyanide-consuming elements. Optimum gold dissolution was obtained in a closed bench-scale reactor incorporating a flotation-machine type of agitator for effective pulp agitation and oxygenation, the oxygen being recirculated. The reactor was designed to operate under a very small positive pressure. After reaction times of 2 to 6 hours at temperatures in the region of 30°C, both the gold and the silver dissolution averaged 99,S per cent. In the case of very high-grade concentrates, it was shown that gold could be floated in the same reactor by drawing off the flotation concentrate through a port in the reactor. A flotation recovery of 87,4 per cent of the gold in 3,9 per cent by mass was obtained. The recovery of osmiridium from cyanide-leach residues and the electrowinning of gold from the pregnant liquors were also considered as processing aspects in the treatment of gold-plant belt concentrates. Final table tailings with a gold concentration of 10to 12 gft were obtained. The results of the investigation strongly suggested that an alternative cyanidation route for the treatment of gold-plant concentrates was technically feasible, provided the system included effective agitation and oxygenation. In the case of lower-grade concentrates, cyanidation followed by the electrowinning of gold appears to be the simplest route, while, for high-grade concentrates, flotation and smelting of the concentrate followed by cyanidation of the flotation tailings are suggested. The use of oxygen rather than air for sparging the pulp would depend largely on the grade of material to be treated. A preliminary comparison of the costs related to the amalgamation and cyanidation processes for the recovery of gold from such concentrates indicated very similar capital and operating costs. It was concluded that other considerations, e.g. toxicity, safety, and lower labour requirements, were more important than such small cost differences. Furthermore, the 'opening' of the gold-plant gravity circuit, which would be made possible by a cyanidation route, would further reduce the operating costs because of the subsequent decrease in the tonnage to be treated.

Jan 1, 1978

"Chairman: Professor E. P. PFLEIDER Rapporteur: Mr P. R. JANISCHPapers:Optimum design of an open pit by D. A. PhillipsAn open pit design system for stratiform ore bodies by L. A. J. Pronk van Hoogeveen, J. R. Cutland and M. WeirAn open pit design model by R. H. Robinson and N. B. PrennThe Chairman in opening the session highlighted the current situation in the United States of America where some 85 to 90 per cent of all mining (except for coal) is done by open pit methods, and where some 40 per cent of the coal is mined by open pit. The South African industry is, of course, dominated by the deeper level underground gold mines; however, with the aid of an extensive open-pit technology developed in other countries, South African companies arc continuing to explore possibilities of open-pit exploitation of base mineral, coal and diamond deposits. Several successful ventures are already in operation at Phalabora, Optimum Colliery, Kimberley and elsewhere, and South Africa is undoubtedly benefitting in this regard by drawing on the experience of others.The papers of this session were therefore particularly pertinent, particularly when viewed in conjunction with those presented at an earlier South African conference devoted specifically to open pit mining.Two themes dominated the discussion which followed presentation of the three papers at this session. The first related to the practicability of using the reported techniques as a tool for management, and their acceptability as such to mine management. This was, of course, not peculiar to this particular session, but rather the major point of debate over the entire conference.The second theme concerned the reliability of the initial drill hole data on which any open-pit design must necessarily be based. This gave added emphasis to the problem of practicability, for no management is likely to accept an elaborate pit design unless confidence can be placed in the ore reserve assessment.In noting these two features of the discussion, it should be remembered that all the three papers dealt largely with design and pre-planning; there was an unfortunate lack of papers or discussion on the subject of controlling the day-to-day mining of open pits, and this is an area where the potential impact which can be made by the computer is even greater.In introducing his paper, Mr D. A. Phillips pointed out that it was concerned only with optimization, and that it therefore assumed, firstly, an adequate subdivision of the orebody into ore blocks characterized by grade, rock type, structure, etc., and, secondly, an acceptable forecast of costs and mineral prices in order to generate a suitable profit matrix. However, programs dealing with these problems for both massive, disseminated and stratiform ore bodies are available to Roan Consolidated Mines. The method of optimization which he had described had been used on a region split into 28 000 blocks, for which the program used three hours of C.P.U. time on an IBM 360/40 computer. The computer design had provided a three per cent improve¬ment on a normal design of the same area."

Jan 1, 2014

"Chairman: Mr R. A. PLUMBRIDGE Rapporteur: Dr D. M. HAWKINSPapers:The relevance of computer methods to the economics of the mineral industry by R: A. PerlmanDynamic control of a mining enterprise by R. G. CoyleAn economic model of the mineral sands industry by G. P. A. HoweMr M. Splaine, in opening the discussion on Mr Perlman's paper, asked whether the model, as fitted by data up to 1963, predicted the rise in the price of copper in 1967, and whether the model could be used to capitalize on short-term price fluctuations.Answering the second question first, Mr Perlman said that the horizon used is six months to one year. In the very short term the activities of speculators obscured the effect of the fundamental econometric variables. This effect, however, was removed if one moved to a longer term, say, quarterly. In 1963 the model had predicted a price rise in 1964 and 1965 and a drop in price in 1966. The rise in 1967 had been caused by a strike, and imponderables such as large strikes were difficult to include in the model since they were unpredictable. Model simulation can be used to show the effect of strikes on price and the effect of small strikes is small.Mr B. R. van Rooyen said that because models are both calibrated and tested on historical data a bias was introduced which gave rise to an overoptimistic estimate of the accuracy of the forecasts. To this Mr Perlman replied that there seemed to be no alternative to the use of historical data for calibrating and testing models, and thus little hope of avoiding the bias. A second point made by Mr. van Rooyen was that manage¬ment tended to be suspicious of complex models and that frequently more heuristic models were sufficiently accurate and preferable for investment decisions. He added that if management were not involved in the model building the econometrician might easily go astray, Mr Perlman replied that symbiosis between data analysts and users of the model was essential and that the experience of the practitioner must be reflected in the model.Mr M. R. Fuller-Good remarked that a clear understanding of future price trends was essential for effective capital planning, and asked, first, how one went from the compiled data on supply and demand to the determination of their effect on price, record, whether necessary data, for example, capacities, could be obtained timeously, and, third, when strikes restricted supply, whether stockpiling by consumers induced large price fluctuations."

Jan 1, 2014

Dr T. F. Muller (Honorary President): "Mr President, gentlemen. May I congratulate the Institute on its 75th birthday, and your President on his comprehensive review of the Institute's 75 years. It is an interesting commentary on the affairs of the Institute that your President should refer to a speech made by a founder member 25 years ago on the occasion of your 50th Anniversary and then say there is no need to repeat what was given there, but that he would confine his remarks to bringing the Institute's history up to date. To me this suggests a remarkable continuity of thought and ideals-a welcome island of stability in an ever-changing world. One can somehow picture another future President, perhaps one of the younger and tougher members here today, doing the same thing in 25 years when you celebrate your centenary-and again someone doing the same in the year 2094 when your Institute is 200 years old! I hope they will recognise their debt to the early pioneers of the Institute gathered here today. In any event, this review of the fine achievements of the past 75 years is certain of an honoured place in the annals of the society. Here is a record of the onward march of technology in South Africa and a tribute to a long line of mining engineers, of chemists, metallurgists and geologists who made a greater contribution to the well-being and the prosperity of South Africans than South Africans generally are aware. Your Institute started off as a 'gold and cyanide club', peopled largely by chemists and metallurgists who made a signal contribution to the industry from the earliest times. Despite the addition to their ranks of ever-growing numbers of mining engineers, the metallurgist members have continued to make notable contributions. One recalls, for example, the manner in which they rose to the occasion to resolve the problems associated with the establishment of the uranium industry in this country. The creation of a major industry based on the existence of low grade uranium ores in the conglomerate reefs of our low grade goldfields is a classic example of the manner in which a new large industry can be rapidly created through the combined endeavours of all concerned. I noted with pleasure your remark, Mr President, that members of the Institute would like to keep up to date with recent progress in nuclear fuel matters and that members should be given the opportunity to study developments in their journal. I am sure that the National Institute of Metallurgy which conducts fuel research on behalf of the Atomic Energy Board and of the Uranium industry, and NUFCOR, which co-ordinates the uranium research programme, would be glad to co-operate if invited by the Institute to make periodical contributions to its journal. You have referred to the building up of our research organization and its dynamic approach to mining problems. I understand that the expenditure of the mineral industries on research exceeds one-third of the entire research expenditure of the private sector. South Africa is in the forefront of mining development and the focus of world attention is on the achievements of our scientists and mining engineers. We can look forward to continued advances in mining technology based on their vision and expertise. I share your disappointment, Mr President, that the Base Metals Division has ceased to exist; and that there is a resultant dearth of papers offered to the Institute on these important sections of mining and metallurgy. We are seeing some remarkable developments in the mining and beneficiation of base minerals, and it is in this area that I see the greatest potential for future expansion. If we can grasp the opportunities

By E. Dadzie

This paper will review some methods used to manage geotechnical risk at Damang Pit Cutback. The pit depth is designed up to 250m with push back on the eastern and western walls of the existed and depleted Railway Cutback (RCB) pit. The geotechnical design was presented by SRK Perth, focussing on the optimisation of the bench face angle which finally evolved with ?steep slope strategy?; 24m at 800 and 24m at 750 on the eastern and western walls respectively. The east wall was designed strategically to optimise the proximity of the tailings dam to the final pit crest of the push back. The pit has experienced failure in the weathered profile transgressing through the transitional material into the fresh rock at different location of the east wall since development in July 2005. To ensure stability and to minimise ore loss, the east wall has been redesigned using 700 batter angles and reduced berm width of 4m compared to 800 and 8.5 berm width of 24m bench height. The paper will also discuss how slope failures to the east wall had been sustained, managed and monitored to enhance production. Emphasis is placed on slope management at Damang which includes the principles of wall control blast, visual inspection, slope depressurisation and the state-of-the art of slope monitoring using Autoslope automated prism monitoring. Future slope monitoring is considering the use of 3D Laser and Radar to provide early warning so that evacuation could be effected. The intension is to provide mine personnel the means to identify risk areas during mining activities.

Jan 1, 2008

By Y. -L. Chiang

Paper written on project work carried out in partial fulfilment of BSc (Eng) (Chemical) The generation and control of manganese sulphide particle size distribution using various mixing configurations were investigated. Specifically, this paper discusses how varying mixing intensities on a macro and micro scale affect the resultant manganese sulphide particle size distribution (PSD) at a constant concentration. The mixing variations were achieved using various Y- and T-mixers as premixing devices into a jacketed, agitated vessel. The reagents used to generate the seeds were aqueous manganese sulphate and sodium sulphide solutions. The results showed that the absence of micromixing resulted in very poor control of the particle size distribution, the particle size and the number of particles produced. This was due to the fact that the macromixing time is much greater than the corresponding precipitation time, resulting in different mixing regions existing within the reactor. From the micromixing experiments, the T?mixer was found to be the most effective mixing device at lower concentrations due to the T-mixer providing a faster mixing time than the other mixing configurations, thereby effectively localizing the supersaturation and hence controlling the precipitation. The results obtained from the direct addition without the extension pipe (i.e. short mixing time) indicated a general increase in mean particle size and decrease in total particle number at reagent concentration of 0.007 mol.dm-3as compared to the corresponding micromixing experiments. The phenomenon may be due to incomplete crystallization at the immediate exit of the mixing device. Further experiments need to be conducted before any conclusions can be drawn about the precipitation mechanisms.

Jan 1, 2007

By Stephen Yirenkyi

The mining industry remains the backbone of many economies in the developing world. Its resurgence in Ghana since 1989 was driven by the global paradigm which emphasizes private sector-led development as the engine of economic growth in developing countries. The historical importance of mining in the economic development of Ghana is evident in the country?s colonial name, Gold Coast (Akabzaa T. and Darimani A., 2001). Ghana earned $2.5 billion from mineral exports in 2007. 20,000 people are employed in large-scale mining whilst 500,000 are employed in the small-scale sector. Mining contributes about 7% of Ghana?s total corporate tax earnings, 41% of total exports, 12% of revenue collected by the Internal Revenue Service and 5% of Gross Domestic Product (Ghana Chamber of Mines, 2008). Gold dominates the mining sector and the country is Africa?s second largest gold producer after South Africa. Surface Mining, which refers to a method of extracting minerals from the earth by their removal from an open pit or borrows, requires a large tract of land for its operations (Wikipedia, 2008). There is therefore a continuous divergence of interest between land required for surface mining and other land uses such as farming and housing, among others. In recent years, surface mining has been promoted in many mining countries because of the following reasons: ?Cost considerations compared to underground mining; ?Safety considerations, compared to underground mining; ?Low grade ore which requires processing huge quantities; ?Location of the ore bodies; and ?Competition among gold producing countries for investors. This paper looks at the socio-economic impacts and challenges of surface mining by using Gold Fields Ghana Ltd. Tarkwa, Ghana as a case study. The company has a concession of about 208 sq km located in the heart of the Wassa communities in the Western Region of Ghana and undertakes surface mining like most of the other mining companies in the country. Gold Fields, Tarkwa mine produces 700,000 ounces of gold a year with the potential of increasing this output to 800,000 ounces after its current expansion programme. Some of the effects of surface mining identified were: 1. Relocation/Resettlement of host communities and its negative effects; 2. Disturbance to Flora and Fauna; 3. Disturbance to Sacred Places; 4. Land Degradation; 5. Noise and Air Pollution; and 6. Water Pollution. This paper sought to investigate the measures put in place by the government and the Gold Fields Ghana Ltd. to mitigate the above effects in order to ensure peaceful coexistence between the mining company and its host communities. It concludes that most mining companies presume the provision of socio-economic development in mining communities will lead to the company securing a social license to operate. This however is not true but rather effective community relations combined with socio-economic development. According to Gold Fields Ghana Ltds. model, this involves continuous community engagement, conflict resolution and comprehensive environmental monitoring programme which will all lead to effective community relations. The strategies to ensure socio-economic development involves community development programme, livelihood restoration programme and community training and employment. All these will then lead to sustainable development which will ensure the company?s social license to operate. Gold Fields? model is in line with the principles of responsible mining. With this model, the community feels they are part of the company and the social license of the company is guaranteed. Gold Fields? model, which has been tried and tested for the past five years, could serve as a template with suitable modification for local conditions for other mining countries where surface mines operate.

Jan 1, 2008

By W. A. Hustrulid

CONTENTS PART I The theory of percussive rockdrill operation. Blow frequency Piston impact velocity and blow energy Thrust requirements Prediction of penetration rate Drillsteel life Bit wear PART II Measurements of percussive rockdrill performance Thrust-penetration rate measurements Blow frequency Piston impact velocity and blow energy Prediction of penetration rates The effects of hole diameter Thrusts applied by men Bit wear Appendix I Experimental procedure and rockdrill and drill steel specifications Appendix II Piston impact velocities and energies PART III Practical implications. Provisions of adequate thrust Conclusions INTRODUCTION In South African gold mines some 100 million tons of rock are broken each year by drilling and blasting. Only minor improvements to this method of rockbreaking have been made since the general introduction of pneumatic rockdrills for stoping 50 years ago and, more recently, of drillsteels tipped with tungsten carbide. The combined total cost of drilling and blasting amounts to almost R0,50 per ton of rock broken, which is just short of one quarter of the direct cost of stoping or development. Rockdrilling accounts for about R0,25 of the total cost of rockbreaking, of which RO,12 represents labour costs and R0,13 the cost of drillsteels, rockdrill spares and power. Mine air compressors use over 7 X 108 kWh of electric energy a year, amounting to 7 percent of the total electric power used by the gold mining industry. The efficiency of percussive rockdrilling is, therefore, of considerable significance to mining costs. Over the past four years the Mining Research Laboratory of the Chamber of Mines of S.A. has been engaged in experimental studies of percussive drilling. These experiments were conducted at test sites on Robinson Deep Gold Mine and Vlakfontein Gold Mine, made available by Gold Fields of South Africa, Limited. Three rockdrills, designated types A, Band C, of different manufacture, were used in the experiments which involved the measurement of the following operating characteristics: 1. Throttle air pressure 2. Applied thrust 3. Penetration rate 4. Air consumption 5. Blows per minute 6. Drill steel revolutions per minute. The results of these investigations are presented in three parts. Part I, "The theory of percussive rockdrill operation" which provides a concise, mathematical description of the performance of a percussive rockdrill in terms of its principal mechanical dimensions and operating conditions, and an analysis of the bit and gauge wear of drillsteels. Part II, "Measurements of percussive rockdrill performance" in which the experimental results are presented in terms of thrust-penetration rate curves at different throttle air pressures and throttle pressure-air consumption curves, which are shown to agree well with the predictions of theory. In addition, data relating gauge wear on the drillsteel and penetration rate to the distance drilled are discussed. Part III, "Practical implications" in which an analysis of the status of thrusting devices is made and the benefits that would derive from using uptimum thrusts are discussed.