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By S. Purushotham, Y. R. Murthy, M. Narasimha, S. K. Tripathy, M. Kumar

Spiral concentrators are gravity-based separators widely used to beneficiate coal, heavy minerals and beach sand. It consists of a helicoid trough that spirals downward in the helical configuration around an axial column. The particle segregation takes place based on size and density under the influence of gravity as the particles spiral down within the thin water layer. In the last century, most design modifications of this equipment were based on trial and error based lab-scale experimentations and empirical approach. The use of Computational Fluid Dynamics (CFD) has gained interest in the past two decades to understand the underlying flow physics in the spiral concentrators. In this paper, we used CFD to model the fluid flow and investigate the particle segregation inside a conventional LD9 spiral concentrator. Firstly, the Volume of Fluid model was used to resolve the liquid-air interface. The liquid depth and flow field predictions for varying flowrates were validated against the experimental literature data. One-way coupled VOF-LPT model was then used to describe the particle dynamics in the spiral flow field assuming dilute particulate flow. Moderate dense particulate flow (20 vol.%) was then modelled using the Algebraic Slip Mixture (ASM) model. Four particle-phases representing particles of different sizes of dual-density were simulated, and the component particle segregation was analysed. Keywords: Spiral concentrator, two-phase flow, multiphase, discrete phase model, ASM model

Jan 1, 2020

By M. J. U. T. Van Wijngaarden, R. J. Dippenaar

An electrochemical technique based on the solid oxide galvanic cel Mo / Mo + MoO2/ ZrO2-MgO / Fe + (FexO)slag + Ag / Fe was used in a determination of FexO activities in liquid slag systems. The emf measurements, scanning electron microscopy, and microprobe analysis of the cross-sections of the electrolyte tubes used in direct contact with the slag melts indicated that slag attack did not affect the open-circuit emf values during normal cell operation, The reliability of the cell was confirmed by the good agreement between the standard free energy of formation of liquid Fep obtained in the present study and those reported in the literature, The FexO activities were determined in FexO -CaO and FexO-SiO2 slags at 1673 K, and are in good agreement with those measured by the conventional gas-equilibrium technique. The experimental technique was successfully extended to the measurement of Fe2O activities in the complex slags that are used for the external desilliconization of the hot metal product of the blast furnace.

Jan 1, 1986

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

By R. H. English, N. C. Joughin

The results of trials with three stope-face cleaning systems are described. Two of these systems were based on armoured chain conveyors, and the third on a reciprocating-flight conveyor. The operational elements of each system are discussed with reference to their effectiveness, and many problems are highlighted. It is concluded that the reciprocating-flight conveyor is superior, and has the potential for being developed into a system yielding a labour productivity of more than 30 m2 per worker per month and a face advance of 15 m per month working one shift a day.

Jan 1, 1979

By J. Keyser

The realization of an Integrated Technical Resource Asset Management System (ITRAMS) has so far evaded all software developers in the mining industry. The major factors that have prevented the development of such a system are limitations on software, hardware and network systems. Several factors have come together at Venetia Mine, which has made the undertaking of such a project both possible and desirable. This has led to the formation of a strategic partnership between Venetia Mine and Gemcom Software International Inc. This partnership is dedicated to develop and provide an Integrated Technical Resource Asset Management System based on Microsoft Back Office architecture, Gemcom for Windows™ and the MinRas system. This paper will elaborate on the phased approach of the integration of systems into the core repository, mechanisms of integration, the functionality of the system, final results, techno-economic benefits and general project management issues.

Sep 1, 2001

COUNCIL AND STANDING COMMITTEES, 1974-1975 Office Bearers : Prof. R. P. Plewman (President), Dr R. E. Robinson and Dr M. D. G. Salamon (Vice Presidents), J. K. E. Douglas (Honorary Treasurer), and P. W. J. van Rensburg (Immediate Past President). Elected Members of Council: Dr M. G. Atmore, E. Collier, G. H. Grange, Dr P. R. Jochens, Dr D. I. Legge, D. G. Malan, C. T. Shaw, L. W. P. van den Bosch, D. A. Viljoen, H. M. Wells, P. A. von Wielligh. Branch Chairmen: B. T. Hosking (Witbank-Middelburg Branch), D. A. Smith (Orange Free State Branch). Past Presidents Serving on Council: R. J. Adamson, M. Barcza (until May 1975), H. Britten, H. E. Cross, Prof. J. de V. Lambrechts (until December 1974), R. C. J. Goode, Prof. D. D. Howat, Dr J. P. Hugo, D. M. Jamieson, D. G. Maxwell, Dr J. T. McIntyre, V. C. Robinson. Ten Council meetings were held during the year, with an average attendance of 19, and the standing and sub-committees held 74 meetings. COMMITTEE CHAIRMEN Membership, Dr M. D. G. Salamon; Technical Programme-Metallurgy, D. A. Viljoen; Technical Programme-Mining, G. H. Grange ; Vacation School-Metallurgy, Dr P. R. Jochens; Vacation School-Mining, Dr M. D. G. Salamon; Awards, Prof. R. P. Plewman; Excursions, Dr D. I. Legge; Constitution, Rules and Policy, P. W. J. van Rensburg and Prof. R. P. Plewman; Mines and Works, P. A. von Wielligh; Education, P. W. J. van Rensburg. REPRESENTATIVES ON OTHER BODIES Associated Scientific and Technical Societies Members: V. C. Robinson and Prof. R. P. Plewman. Alternates : Dr R. E. Robinson and Dr M. D. G. Salamon. Federation of Societies of Professional Engineers Members : J. K. E. Douglas and P. W. J. van Rensburg. Alternates : Prof. R. P. Plewman and G. H. Grange. South African Council for Professional Engineers Member : R. C. J. Goode. Alternate : G. H. Grange. Engineers' Liaison Committee (Pretoria) Member: Dr J. P. Hugo. Alternate: P. W. J. van Rensburg. MEMBERSHIP Thirteen Fellows, seventeen Members, eleven Graduates, three Associate Members, eighteen Associ¬ates, twenty-six Students, and one Company Affiliate were elected during the year. Nine Fellows, four Members, and three Associates were admitted to retired membership. Eight Fellows were elected to Honorary Life Membership. Three Members and one Graduate were transferred to Fellows, nine Graduates and two Students to Members, six Students to Graduates, one Student to Associate, and one Associate to Associate Member. Six Fellows, ten Members, three Associates, and one Student resigned. A statement of membership as at June 30th 1975 and the end of the previous year is shown in the following tabulation: 30th - 30th June, - June, 1974 - 1975 Honorary Life Fellows - 9 - 15 Honorary Fellows 8 - 8 Life Fellows 170 - 170 Fellows 544 - 536 Members 512 - 523 Associate Members 10 -15 Graduates 130 - 133 Associates 194 - 210 Students 173 -175 Company Affiliates 70 - 71 1 820 - 1 851 [ ] OBITUARIES Your Council records with deep regret the death during the year of the following members: M. Barcza, Honorary Life Fellow and Past President of the Institute; J. A. Boyd, F. E. Keep and J. H. Taylor, Life Fellows; I. D. B. Corner, C. O'G. Deane, R. E. Gilmour, A. C. Hofmeyr, M. W. Howell, T. J. Robin and F. C. Steinhobel, Fellows; J. J. Frankel, Member; T. J. Higgs, Associate. FINANCE The annual accounts, which follow this report, indicate that income again exceeded expenditure by a margin of R21 410 (last year R28 524). This year's income of R71 184 showed a further increase compared with last year's figure of R55 025. Costs, however, also in¬creased, and it is calculated that, excluding non-recurrent costs, the cost of running the Institute in¬creased by R6 654 from R25 501 to R33 155 for the current year. The main increases were involved in secretarial fees, stationery and print¬ing, and in publication of the Journal. All indications are that costs will continue to rise, and we have been advised that the A.S. & T.S. will be increasing their secretarial fees by 25 per cent in the year ahead to meet their rising costs. This year's surplus was derived entirely from the revenue from sales of publications (R13 644) and a surplus from the 1974 Winter School (RIO 654). There can be no certainty that revenue from these sources can be repeated each year. Our funds are in a satisfactory position because of these worth¬while activities, but the administrat¬ion of the Institute should not de¬pend on them. Council will accord¬ingly have to give consideration in the year ahead to an upward adjust¬ment of subscriptions to meet rising costs.

Jan 10, 1975

By Luis Rudolphy, Pekka Tähkiö

"Flotation plant design, construction and start-up can be challenging tasks, because multiple factors and disciplines have to be combined in an efficient manner, in order to execute a project that meets the technical, financial and timeframe expectations. Key considerations that need to be addressed when designing a flotation plant are process requirements, equipment integrability, automation, and up- and downstream processes/designs. Furthermore, several other lifecycle factors need to be considered, such as servicing and maintainability, operational costs, future expansions and decommissioning, among others. To address these challenges, Outotec has developed a new approach to designing flotation plants that targets eliminating most of the inherent risks that can be found in these types of projects. The new Outotec® plant is a fully modular approach in which the above-mentioned challenges have been taken into consideration in the design phase. As a result, the cPlant concept can give several benefits for new and experienced companies involved in the minerals processing business, such as lower risk investments, fast and cost-efficient flotation plant delivery, faster ramp-up period, easy plant expansions, fully automated processes and operation and maintenance ease. As well, dismantling and transportation of the cPlant to a new location is easy and fast, hence the new cPlant concept makes possible to exploit small, short-lifespan ore deposits and also retreat old tailings ponds that might contain valuable minerals and where the ore quantities are limited. Furthermore, cPlant is easily implemented for brownfields and temporary expansions during bigger expansions."

Jan 1, 2015

By A. Whillier

Recommendations are given for the design of vertical cooling towers for use underground in mines and a method is given for predicting the entering and leaving water temperatures when a given amount of heat has to be dissipated.

By D. G. Krige

By use of models based on the South African gold-mining industry, analyses are made of the effects of changes in the mining tax structure on the .State's tax income from potential new mines; also on the percentage of such mines likely. to be proceeded with. The percentage is affected by the correlation between changes in taxation and in the flotation pay limits !or new mines. It is shown that the State stands to gain both directly and indirectly from raising the level of the capital allowance and from its extension to all mines; and that the reduced taxation resulting from a lowering of the discriminatory high tax formula for the gold mines, would, in respect of potential new mines, be compensated for by a significant increase in the percentage of such mines that would be proceeded with.

Jan 1, 1979

By P. Lundman, L. Rosengren, T. Brandshaug

Tunnel 99’, the Swedish National Road Administration´s (SNRA) general technical specification for road tunnels requires that the load bearing system must be designed to withstand specified design explosion loads. This paper presents the results of an SNRA study to provide a perspective of design analyses tailored to comply with the new requirement. The paper provides an example of a design analysis for assumed tunnel conditions using a numerical model. Dynamic predictions of potential damage to the rock mass and ground support system (rock bolts and shotcrete) from the specified explosion loads are presented including the nonlinear response of the shotcrete. “Tunnel 99”, qui fixe les règles de l’Administration nationale suédoise des Routes (Vägverket) concernant la conception et la construction des tunnels routiers, requiert entre autres que la structure porteuse soit capable de résister à certaines contraintes spécifiques résultant d’explosions. Cette étude présente les résultats d’une étude effectuée par Vägverket en vue d’obtenir une perspective d’analyses de conception spécialement élaborées pour se conformer aux nouvelles règles. Il contient un exemple d’analyse en fonction de conditions déterminées, basée sur un modèle numérique. Des prévisions de’études dynamiques de dommages potentiels subis par la masse rocheuse et les systèmes de soutènement (boulons d’ancrage et béton projeté) du fait des contraintes libérées par la force d’explosion spécifiée sont également présentées, y compris dans le cas d’une réaction non linéaire du revêtement en béton. “Tunnel 99” - die Vorschriften für Strassentunnel der Nationalen Schwedischen Behörde für Straßenwesen - (Vägverket) - fordern vom Tragsystem eine Auslegung in der Form, dass es spezifischen Explosionsbelastungen standhält. Dieser Artikel präsentiert die Ergebnisse einer Studie der Behörde, um einen Ausblick über konstruktive Auslegungen zu geben, die geeignet sind, die neuen Vorschriften zu erfüllen. Der Artikel zeigt ein Beispiel einer konstruktive Auslegung für eine angenommene Tunnelsituation mit Hilfe eines numerischen Modells. Voraussagen unter Beachtung der vollständigen dynamischen Berechnung zu potentiellen Schädigungen des Gebirges und des Ausbaus (Anker und Spritzbetonauskleidung) durch die spezifizierten Explosionsbelastungen, einschließlich des nichtlinearen Verhaltens der Spritzbetonauskleidung, werden gezeigt.

Jan 1, 2003

By M. C. Harris

Float-sink analysis has wide application in the coal laboratory. This paper evaluates the established methods used for the float-sink analysis of fine coal, and then describes a new method and apparatus that can be used for material down to a few micrometres in size. The method is rapid and accurate, and requires only a small amount of sample. The results presented show close agreement with the float-sink analyses obtained by the more classical technique using separating columns. The new centrifugal method reduces the time required for the analysis by a factor of ten.

Jan 1, 1986

By J. P. Coetzee

There is an ample supply of all the raw materials required for the future development of the industry, with the possible exception of coking coal. Improved methods of coke production are being developed. It is anticipated that steel production will reach eight million tons per annum by 1980. New techniques and equipment for refining steel will be installed, together with new processing equipment. The most serious problem now facing the industry is the acute shortage of labour.

NEW BOOKLET FOR POTENTIAL ENGINEERS A new booklet "Professional Careers in Engineering" for issue to high school students who are considering engineering as a profession has been prepared for general distribution. The booklet is intended to help high school students to decide whether a career as a professional engineer would appeal to them, and to tell them how to set about becoming a professional engineer. Copies of the booklet may be obtained free of charge by writing to: The Federation of Societies of Professional Engineers, P.O. Box 5907, Johannesburg.

By G. R. Drennan, N. J. Wagner, M. J. T. Sebola

The Soutpansberg Coalfield hosts South Africa's hard coking coal reserves. However, coals in this region are understudied compared to other coalfields in the country. This study characterizes the properties of fine-float fraction samples extracted from a wide diameter borehole core in the Makhado Project, Tshipise sub-basin, Soutpansberg coalfield. Conventional analyses were used to determine the coal quality, petrographic composition, mineralogy, geochemistry (including trace element and rare earth element composition), and free swelling index of samples from six coal horizons and three partings from the economic No.6 Seam. The coal samples are classified as medium rank bituminous C coals (0.88 %RoVmr, 0.92 %Rmax) and are highly vitrinitic in composition (97 vol% mineral matter free (mmf)). The samples show strong caking potential (FSI of 9). The total rare earth concentrations range between 570 and 3193 ppm in the ash samples. Preliminary analysis show all but two samples are promising sources of rare earth elements as the total concentrations exceeded the 1000 ppm cut-off grade. Further research is required to confirm these preliminary findings.

Aug 2, 2022

By S. A. Ghoreishi-Madiseh, F. P. Hassani, H. Rafezi, H. R. Manouchehri, A. Shadic, A. P. Sasmito

Weakening rocks by taking advantage of microwave-induced microcracks is a promising solution for comminution processes. This paper investigates the effects of microwave treatment of the rock/or samples in single and multi-mode cavities. Based on the experimental results of using a 2.45 GHz microwave generator, the performance of different cavity setups and their impact on the energy effectiveness of the microwave irradiation was examined. Physical interpretations were drawn from multiple experiments with a relatively wide range of power rates and exposure times. Both basalt and kimberlite samples were used in experiments, and their results were systematically compared. For single-mode cavity tests, a microwave applicator waveguide antenna was placed at different distances from the samples to evaluate the effects of sample positioning on microwave heating, both numerically and experimentally. Eventually, cavity performance was assessed by using calorimetric test results, and strength decay was documented based on the spallation of the samples. It was found that the singlemode cavity setup has unique properties that can significantly improve the electromagnetic heating and therefore, strength degradation process. Keywords: Microwave, fragmentation, energy effectiveness, calorimetry, mine-to-mill

Jan 1, 2020

By M. Frenzel, K. Bachmann, M. Rudolph, R. Tolosana-Delgado, E. Schach, M. Buchmann, L. Pereiraa, K. G. van den Boogaart, N. Kupka

Geometallurgy - the science of predicting the behaviour of ores along the value chain based on their geological and mineralogical characteristics - has barely moved beyond process minerology studies. These studies typically link process behaviour to the mineralogical and microstructural characteristics of pristine or processed ores in a qualitative or semi-quantitative manner. Eventually, a trial-and-error optimisation of the operation is achieved. However, to deliver on its promise, geometallurgy should progress beyond this current approach to a fully quantitative understanding of process behaviour, including the various uncertainties involved, namely predictive geometallurgy. One of the barriers currently hindering this development is the neglect of most ore characterisation data obtained in geometallurgical studies. This is mostly due to the large extent of this information exceeding the capacity of conventional software. To address this challenge, we developed a data mining platform consisting of an SQL database, an R front-end in-house package, and back-ends to interpret data from several analytical instruments. This platform enables the use of the statistical and data mining power of the R open-source environment for any geometallurgical study. Potential applications range from ore characterisation to process understanding and forecasting, and from geostatistical prediction to operational control and optimisation. The scripting abilities of R allow for the: 1) processing of many streams in loops, thus freeing the user from repeating tedious click-and-drop tasks; 2) computation of virtually any derivate or aggregate quantity from the data; 3) distribution of the work among several processor clusters; and 4) keeping of a log file for the calculations done. This contribution presents the building blocks of this platform, and illustrates with several examples its potential to enable predictive geometallurgy. Keywords: Data mining, entropy, kernel methods, LASSO regression, predictive geometallurgy

Jan 1, 2020

It is well understood that to develop wagon wheels with higher abrasion resistance, fracture toughness, and fatigue resistance, steels with lower amounts of inclusions need to be used. Clean steels are produced with technologies that minimize the amount of inclusions in the microstructure. The demand for cleaner steels is high, and lowering of non-metallic oxide inclusions and controlling their morphology, composition, and size distribution is vital. Reduction of residual impurity elements such as sulphur, phosphorus, hydrogen, nitrogen, and trace elements is essential in the production of cleaner steel. Material cleanliness is vital for fatigue endurance, since oxide inclusions may act as stress concentrators and initiation points for fatigue cracks. To better understand the relationship between the cleanliness and toughness of the 34-inch cast wagon wheels, two samples of different levels of cleanliness were supplied for investigation. This paper presents the results of metallurgical analysis using scanning electron microscopy(SEM), energy-dispersive spectrometry (EDS), and mechanical tests for the pearlitic high-performance cast rail wagon wheel (identified as Class B) that are currently being used. The Charpy V-notch impact test results for the three samples from wagon wheels were compared. With the aid of SEM/EDS analysis system, non-metallic inclusions in these steels were detected, and it was possible to determine the position, size, shape, and composition of each particle. Alumina and manganese sulphide inclusions could be identified as the dominant inclusion types in the investigated samples. Fracture surface analysis of the Charpy specimen with high inclusions indicated that transgranular cleavage was the predominant fracture mode. Fractography of fracture surfaces of Charpy impact test samples also showed improvement of toughness properties on the clean sample.

Jan 1, 2013

By S. Mohanty, K. Sarangi, S. Dash, P. P. Patra

Industrial effluent from various industries contains heavy metals that are a serious threat to humans, flora and fauna in water bodies, and the environment. The heavy metals are dumped after precipitation, which has serious environmental consequences. In this paper, a 2D axi-symmetry CFD model has been developed to study the extraction of chromium ion from industrial effluent, in a hollow fibre membrane, using Alamine 336 as the carrier and kerosene as the diluent. The Navier Stokes equation was used to predict the velocity profile of the aqueous and organic phases, and species transport equation, which considers both convective and diffusive mass transfer, was used to predict the concentration profile of the chromium ion in the computational domain. The distribution coefficient was experimentally determined at a pH 4, which was found to be the optimum pH. Numerical simulations were performed considering 11.11 mol/m3 of initial feed concentration for chromium ions and extractant concentration of 0.2 M. Simulations were carried out with various aqueous and organic flow rates, and validated with experimental data. Keywords: CFD, metal extraction, hollow fibre membrane, heavy metals

Jan 1, 2020

By D. D. Howat

In the field of high temperature smelting processes there have been two dramatic changes in the past twenty years. These are, first, the application of tonnage oxygen for direct injection for the refining of molten iron and other metals and to provide the means of enriching air used for the combustion of fuel. Second, the application of electric power for the generation of high temperatures in place of the combustion of fossil fuels. Of these two developments the application of tonnage oxygen for the refining of molten iron has virtually revolutionised the steel industry throughout the world. The magnitude of this development is exemplified by the fact that less than 5 per cent of the world's steel production in 1960 was made by this process or 16 million tons out of a total of 350 million tons of steel produced, while in 1970 over 40 per cent of the world steel production was made by this process, ie, 251 million tons out of 628 million tons total. In the same period the proportion of steel produced by the old-established open-hearth process has shrunk from 75 per cent to 38 per cent. In the whole history of the development of high temperature metallurgical smelting processes there has never been anything remotely approaching this. The other development, the application of electric power for the generation of high temperatures has not had the impact of the oxygen injection process but I believe that what we should call the electric smelting revolution in metallurgical processes has very far-reaching ramifications for steel production and other pyrometallurgical processes. This may seem a bold and brash statement but it must be remembered that the oxygen injection process constitutes a link in the chain critically dependent upon the production of vast tonnages of molten iron from very large modern blast furnaces. The Achilles heel of this chain of processes, upon which such a large percentage of the world's supply of steel depends, is the availability of metallurgical coke in turn dependent on natural resources of coking coal. Without any exception each industrial country in the world faces a shortage of resources of coking coal and in some cases a critical shortage. Certainly within the present century the major iron and steel producing countries of the world will face this critical shortage of coking coal and major modifications to steel making processes will become inevitable. W. F. Cartwright (Deputy Chairman of B.S.C) said recently that there are considerable doubts as to whether the world will be able to provide enough coking coal to meet world steel demands from the late 1970's onwards if the B.F.remains the main means for making iron from ore. This is one of the supreme ironies of the world metallurgical situation to-day when the technology of iron and steel production has reached an extremely high peak of technical efficiency. The newest modern iron blast furnace capable of producing 6 000 to 8 000 tons per day of molten iron represents probably the most efficient piece of high temperature metallurgical plant and operation known to man. The conversion of this molten iron into steel by the oxygen injection process has made available to the engineering industry steel of a quality and at a price which is quite remarkable. Yet this vast metallurgical pyramid rests on the completely insecure and uncertain foundation of inadequate world resources of coking coal. The shortage of reserves of coking coal in this country is acute and it is possible that these resources will be exhausted within the next twenty years. Yet unless some completely unexpected catastrophe occurs the demand for steel in this country will probably rise at a faster rate than in the Western world due to the expansion of the Bantu population and the increased standard of living. To offset the inevitable shortage of coking coal are our much greater resources of bituminous coal which although of low grade provide a suitable fuel for electric power generation. The geographical disposition of the coal fields in relation to the great industrial areas of the Transvaal makes it inevitable that the development of the pyrometallurgical industries must depend heavily on electric power. The position in this country with regard to electrical power generation and consumption is rather anomalous. Per capita consumption of electric power is high - in 1964 almost twice the world average of 870 KWH and twenty-five times the average of 34 KWH for the Continent of Africa. In 1964 fifty-four per cent of the total world electric power was used in industry - the ratio being approximately 1/9 mining to manufacturing uses. As shown in Table I in 1969 67.2 per cent of the total output of electric power from ESCOM was used for mining and other industrial uses but almost in the ratio 6/4 mining to industrial uses. These figures emphasise the enormous importance of the mining industry to the economy of this country and underline the major contribution made by the gold mining industry. What is of very significant importance is that although the mining industry remains by far the largest single consumer of electrical power the consumption of power for industrial uses is rising rapidly as shown in Table II.

By R. S. J. Toit

Discussion: T. L. Gibbs,* (Honorary Vice-President and Fellow): In terms of the Pneumoconiosis Compensation Act of 1962, a Pneumoconiosis Risk Committee was established whose function it is to estimate (by whatever means the committee deems fit) in respect of every controlled mine the pneumoconiosis risk to which persons employed in a dusty atmosphere at that mine are exposed. In estimating such risk the committee may estimate different risks in respect of individual mines or parts of mines or classes or groups of mines or occupations or localities at mines. The pneumoconiosis risk may be reviewed and re-estimated at any time. The Act provides further that the General Council for Pneumoconiosis Compensation shall apportion the levy imposed on owners of controlled mines on the basis of the pneumoconiosis risk determined by the risk committee and the numbers of persons employed in a dusty atmosphere. The task of the risk committee is a most responsible one and also a very difficult and complex one in view of the many different types of mines, rock formations, dust conditions, etc. Quite obviously, comparisons between mines cannot be made on dust concentrations alone as different mineral dusts have different toxicity or pneumoconiosis response factors. However, with its present knowledge, the risk committee is satisfied that the risk at mines, other than coal mines, is related to the mean quartz-equivalent dust concentration to which persons are exposed and the estimation of risks is based on this relationship. From the above, it will be clear that the work done by Dr du Toit on the problem of basing the current rate of levies to provide for pneumoconiosis compensation on the current dust hazard at mines has been of immense value to the risk committee. Up to now the risk committee has not been able to obtain complete and accurate information on the dust exposure of persons at all mines - and, in fact, it is doubtful whether it will be economic or practicable to obtain this in the foreseeable future - but reasonable assessments have been possible from routine dust sampling in some cases and from periodic comprehensive dust surveys in others. As a temporary measure the risks of some mines were estimated initially on a group basis relating to average dust conditions and the type of rock and mineral mined, but as more information became available, differentiation between individual mines became possible. It is the aim of the risk committee to eventually apply such a differentiation in all cases and to ensure that within the bounds of practicability each mine pays for its risk and for its risk only. In this connection, the relationship between the levies and the amounts actually paid out in compensation are examined regularly. In conclusion, I wish to add my congratulations to the author on his excellent paper. His findings will assist materially in the just administration of that very important piece of beneficial legislation, the Pneumoconiosis Compensation Act. G. K. Sluis Cremer MD (Visitor): Dr du Toit has made a valiant attempt to relate dust hazard and the rate of collecting funds for the purpose of paying compensation for Pneumoconiosis. In doing so he has had to make a number of assumptious, some of which touch on the medical aspects of pneumoconiosis. It is worth discussing whether these assumptions are justifiable. Pneumoconiosis is defined in our Pneumoconiosis Act as permanent disease of the cardio-respiratory organs which is caused by the inhalation of mineral dust. To a non-medical person this definition has probably a clear cut meaning. The doctors however have to deal with such conditions as silicosis and asbestosis where there is a well defined dose response relationship to the inhalation of quartz and asbestos respectively and on the other hand chronic bronchitis where the relationship to dust inhalation is poorly defined and where certainly no clear dose response relationship has emerged after many investigations in this country and overseas. Nevertheless since 1953 about half of our certifications for Pneumoconiosis are on the grounds of chronic bronchitis i.e. the X-rays show no evidence of silicosis, asbestosis or other relevant disease. This fact must affect Dr du Toit's computations. The next assumption we should examine is the manner in which toxicity factors have been allocated to the various mineral species. These allocations have in part been based on a restricted number of animal experiments carried out overseas but mostly in South Africa by Webster at the Pneumoconiosis Research Unit. To extrapolate the findings in a relatively small number of animal experiments to the expected reactious in man is a notoriously dangerous exercise. Furthermore the bracketing together of all silicates (except asbestos) and the insoluble metal oxides is entirely unacceptable. Talc (a hydrated silicate of magnesium) and muscovite mica (a silicate of aluminium and potassium) cause pneumoconiosis in their own right. On the other hand

Jan 3, 1970