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By J. D. Smit, K. C. Garner, P. C. van Aswegen

The initial results obtained from the implementation of computer-controlled strategy on the milling circuit are reported. An analysis of these results showed that a peak-power pebble-mill controller on a high throughput hardrock wet-milling circuit reduces the stability of the system. It was concluded that the milling circuit should be regarded as a single system in which the measurement of grinding efficiency, circulating load, product size distribution, and feed rate should minimize the product variance and maximize the feed rate according to the grinding power available. Work is proceeding on such a system.

Jan 1, 1980

By B. K. Cross

This paper, which adopts a philosophical approach, attempts to analyse the contribution that the computer is capable of making in geological analysis, financial evaluation, and mine project control. Also examined are some reasons for non-utilization of these capabilities. As with most computer associated problems, the cause is primarily human and not mechanical. The paper gives one numerical example of the analysis of geological data and one of the evaluation of mine-design data. The values used in the examples are intended only to emphasize certain points and are not necessarily reproducible.

Jan 1, 1980

By H. M. Friede

Discussion of the above paper by A. SIFF The steely nature of the Iron Age objects mentioned in Dr Friede's paper point to two hypotheses. (1) The African iron workers were conversant with the art of direct steel manufacture. (2) They were less knowledgeable of the art of the production of carbonless iron. In this context I cannot but quote T. A. Wertime.

Jan 1, 1980

By P. J. F. Fourie

The purpose and frequency of comprehensive performance testing and the types of tests to be included are discussed. The results obtained from a series of such tests are reviewed.

Jan 1, 1980

By D. T. Walton

In a former Spotlight articlet, Dr P. J. D. Lloyd focused attention on the shortage of locally trained mining and metallurgical graduates, and indicated that the South African Institute of Mining and Metallurgy (SAIMM) has been exerting pressure to boost the intake of undergraduates in mineral disciplines. This article reviews the recruiting activities of the South African minerals industry over the past decade, and discusses some of the programmes that are in operation at the moment, particularly those aimed at potential graduates.

Jan 1, 1980

By G. J. McDougall, M. J. Nicol, O. L. Wellington, R. G. Copperthwaites, R. D. Hancock

X-ray photoelectron spectroscopy showed that the adsorption of gold cyanide on carbon in the presence or absence of electrolytes and acids proceeds by the same mechanism. Although the identity of the gold cyanide adsorbate is not known, the mechanism appears to have an initial adsorption stage that involves the adsorption of an ion pair: Mn+[Au(CN)-2]n where Mn+ is a metal ion (for example Na+, K+ and Ca2+) that has a lower solubility than the Au(CN)-2 anion in the adsorption medium, followed by a reduction step in which either a sub-stoichiometric Au(CN)x surface species or a cluster-type compound of gold is formed.

Jan 1, 1980

By D. W. Horsfallt

The above paper gives a fair amount of information and is a useful addition to the literature on a subject of growing importance. I believe that more experimental results could have been given, together with more details of the modifications made to the plant that enabled it to operate with the success mentioned in the paper. One important omission is a definition of the word fines. As pointed out elsewhere!, this word is used very loosely.

Jan 1, 1980

By M. B. Dunn

Terminals form part of the transportation chain from producer to consumer in the world-wide conveyance of bulk commodities. As such, they are a vital link in providing a buffer between widely differing transporation modes. It is essential in the conceptual design of such terminals that an overall view of the entire system of which they form a part is taken. Only in this way can it be ensured that the system will operate smoothly and without disruption, for in the end such disruptions can have dramatic repercussions, both on the cost of the commodity in the market place and on production. In this respect, computer simulation is a useful tool in arriving at the optimum design for the system. The Richards Bay Coal Terminal provides a good example of such an approach. Commissioned in 1976 to handle 12 Mt per annum, it is now handling 24 Mt per annum, with plans for further expansion to 44 Mt per annum in the future.

Jan 1, 1980

By D. P. Enright, D. D. Howat

Austenitic manganese-steel castings are very widely used in crushing and grinding in the' gold-mining industry in South Africa, The service life of a casting in a short-head crusher is difficult to predict because there are no clear-cut criteria by which such a judgement can be made, The addition of molybdenum and zirconium to the castings for crushers failed to result in improved performance, The results of extensive tests with through-hardened steel castings were very disappointing, mainly because of a design factor in the bowl liner. The design of the bowl liner is an important determinant of the life and performance of these castings. The extent to which the material in a crusher is reduced in size has profound effects on the consumption of metal and power, and on the effective life of a casting. Tests on manganese-steel castings in an 8 ft by 12 ft rod mill provided data on the total consumption of metal, and on the variations in the pattern and rates of wear of liners over lengthy periods. Progressive changes in the wear profiles of the lifter bars and the other liner components showed unexpected features. There are clear indications that, whereas a set of lifter bars will at first lift the charge strongly with relatively little slippage, there is a later period characterized by more slippage and greater wear on all the liner components.

Jan 1, 1980

The exciting history of gold mining in South Africa haR been told in many different ways - in books, plays, and films, and on radio. But now, there's a new and far more lively way to find out about it and that is by actually participating in living history. Your invitation to go back in time will not take you much further from the centre of Johannesburg than the late-afternoon stretch of the shadows of the skyscrapers. The Gold Mine Museum - a new venture by the Chamber of Mines - brings back all the colour and romance of mining a century ago, and reminders of some of the hardships too. This is not an ordinary museum, but one of the most modem attempts in the world to make the past come to life.

Jan 1, 1980

By P. R. Jochens

South Africa depends to a considerable measure on the exploitation of mineral reserves and the processing of these minerals. One of the prime requirements for the mining and metallurgical industry to continue in this vital role is access to sufficient energy in a suitable form. Hence, four important questions are discussed: Does South Africa have sufficient energy for the processing of its minerals and metals! Will the cost of energy allow South Africa's minerals and metals to compete on world markets? Can mining and metallurgical processes become more energy-efficiency Can mining and metallurgical processes be adapted to the various forms of energy that may have to be utilized in the future? It is concluded that about 26 per cent of the extractable reserves of coal would be required in the mining and processing of 50 per cent of South Africa's reserves of gold, platinum-group metals, copper, iron, ferrochromium, and ferromanganese. However, the reducing agents required exceed the extractable reserves but not the total estimates of mineable in situ resources of metallurgical coal and anthracitic coal. Even under the severe constraint that coal could become virtually the sole source of energy, only about three-quarters of the extractable reserves of coal would have been consumed by the year 2025. The reasonably assured resources of uranium metal that can be recovered at less than $80 per kilogram are considerable and, at current conversion efficiencies to electricity, are equivalent to one-fifth of the extractable reserves of coal. The rate of exportation of energy in the form of U30. was about five times that of coal in 1978. It is pointed out that the price of energy has a direct effect on the competitiveness of metals, and, although constituting only a small proportion of the selling price of precious metals, it represents a significant proportion of the selling price of copper and metals recovered from oxide ores. The scope for the conservation of energy appears to be greater in the extraction and conversion of primary energy-carriers to electrical energy than in other mining or metallurgical fields. Provided that alternative sources of energy can be converted to electrical energy, they can be applied to the mining and metallurgical industries. The decision as to which type of energy should be used in specific mining and metallurgical situations is complicated, and is likely to be subjected to closer scrutiny than in the past. The hope is expressed that the tentative conclusions reached will give rise to more-quantitative analyses from those qualified to undertake such an exercise. Inevitably, the questions asked at the outset give rise to more questions, and the more interesting ones are posed in the context of each conclusion.

Jan 1, 1980

By P. J. van der Walt, P. J. F. Fourie, L. M. Falcon

Various methods for the beneficiation of minus 0,5 mm coal are examined briefly, and tests are described on a cyclone of 150 mm diameter operating with magnetite as the medium. It was found that, for sharp separations, at least 50 per cent of the magnetite should be finer than 1Oµm. At that size, the ash content of the product was about 7 per cent at yields of 59 to 64 per cent, and the loss of medium was reasonable (about I kg per ton of fines treated).

Jan 1, 1980

By D. W. Horsfall

The coal-preparation techniques used in South Africa over the past ten years are reviewed, the term preparation being taken to refer to processes involving beneficiation techniques. The success of the preparation methods adopted can be gauged from the fact that, although South African coals are generally of a fairly low quality, the country is producing coals both that are used locally for the raising of steam and for metallurgical purposes, and that compete successfully on world export markets.

Jan 1, 1980

By J. Meintjest

As you pointed out, furnace power factor (and consequently transformer MVA rating) depends upon the inductive reactance, and so it is desirable to design for the lowest possible value of this parameter. The further introduction on the primary side of the transformer of capacitors, whether in shunt or in series, increases the network power factor but does not alter the furnace power factor; that is, the phase angle between electrode to- hearth voltage and current remains unchanged. Corrigenda The following amendments should be made to the article entitled 'Coal-preparation routes for maximum coal recovery', which was published in the August issue (vol. 80, no. 8) of this Journal:

Jan 1, 1980

By P. King

In considering the available reserves of coal, the author points to the importance of improved recovery, and defines three extraction ratios: the geological extraction ratio (or exploitation factor), the economic extraction ratio (or mining factor), and the geometrical extraction ratio (or volumetric extraction factor). He discusses the factors affecting each of these ratios, and concludes that, although geological factors cannot be considered in isolation from technical and economic factors, the geological extraction factor is the most significant criterion of whether the best use is being made of coal resources.

Jan 1, 1980

By A. J. Jager, G. R. Adams

The pattern of mining-induced fractures ahead of stope faces in deep-level gold mines, as revealed by petroscopic observations, is described. It is shown that there are zones of fractured and unfractured rock ahead of the face, which are about I m wide and continue as discrete entities for at least 12 m parallel to the face and at least 5 m vertically. These zones do not form continuously as mining progresses, but develop from time to time, leaving a solid zone between the fractured zones. The maximum depth of fracturing ahead of the face depends on the rate of energy release.

Jan 1, 1980

A description is given of a simple, cheap device that enables the intact shear strength of rock to be determined quickly and inexpensively. Thin rock plates, prepared with a diamond saw, are tested in double shear by a linear punching action. By varying the direction of the diamond-saw cut in a number of specimens, the change in shear strength can be measured for different orientations relative to the rock fabric.

Jan 1, 1980

By M. H. Moys

The capacity of grinding mills can be maximized by use of measurements of mill power and bearing pressures. The criterion is as follows. If the derivatives with respect to time of the power and bearing pressure signals have the same sign, the volume of the mill load is smaller than the optimum value; if they have different signs, the volume of the mill load is greater than the optimum value. Few attempts have been made to use measurements of bearing pressure in the estimation of absolute values for the parameters that define the state of the mill load (e.g, mass, volume, and dynamic angle of repose) because the bearing-pressure signal is a complex function of these and other parameters. This paper gives a mathematical model that relates bearing pressures to these parameters. The theoretical values obtained from this model are compared with experimental values, and it is concluded that the model constitutes a good description of experimental reality. If accurate measurements of the load supported by each bearing are available, the model can be used in the estimation of the mass of the load in the mill. If independent estimates of the volume of the load or the dynamic angle of repose are available, the other parameter can be estimated from measurements of the bearing loads.

Jan 1, 1980

By J. A. C. Diering

The determination of stresses and displacements close to tabular excavations is of considerable importance in the planning of tunnels and of remnant and pillar layouts. This paper gives a description of a simple yet effective method for the achievement of improved values from an analogue or MINSIM type of analysis. Essentially, closures and rides (the movement of hanging-wall relative to footwall) in mined-out areas are assumed to vary in a piecewise linear fashion as opposed to a piecewise constant fashion. As the former fashion more closely resembles the true variation, it is possible for the stresses and displacements at points close to the excavations to be calculated with much better accuracy.

Jan 1, 1980

By M. J. Nicol

This paper ,examines the kinetics of the extraction of uranium from acid sulphate solutions by strongbase anionexchange resins. Parameters such as the concentration of uranium in solution. the agitation of the resin beads in solution. the size of the resin beads. and the degree of cross-linking within the resin matrix were varied. and the effec ts on the kinetics are reported. The applicability, of various empirical kinetic models to the description of the data is assessed, and an attempt is made at the modelling of the rate data in terms of established theories about the diffusion of ions through films of stagnant liquid and through spherical beads of resin.

Jan 1, 1980