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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

Caving is the lowest cost underground mining method provided that the draw point spacing, draw point size, and ore-handling facilities are designed to suit the caved material, and that the draw point horizon can be maintained for the life of the draw. In the near future, several open-pit mines that produce more than 50 kt per day will have to examine the feasibility of converting to low-cost, large-scale underground operations. Several other large scale, low-grade underground operations will experience major changes in their mining environments as large dropdowns are implemented These changes demand a more realistic approach to mine planning than in the past, where existing operations have been projected to increased depths with little consideration of the change in mining environment that will occur. As economics force the consideration of underground mining of large, competent ore bodies by low-cost methods, the role of cave mining will have to be defined In the past, caving was generally considered for rockmasses that cave and fragment readily. The ability to define cavability and fragmentation, the availability of large, robust load-haul-dump units, a better understanding of draw-control requirements, improved drilling equipment for secondary blasting, and reliable cost data have shown that competent orebodies with coarse fragmentation can be exploited by cave mining at a much lower cost than by drill-and blast methods.

Jan 1, 1994

By Q. G. Reynolds

The dual-electrode DC arc furnace, an alternative design using an anode and cathode electrode instead of a hearth anode, was studied at small scale using computational modelling methods. Particular attention was paid to the effect of two key design variables, the arc length and the electrode separation, on the furnace behaviour. It was found that reducing the arc length to brush arc conditions was a valid means of overcoming several of the limitations of the dual-electrode design, namely high voltages and arc deflection.

Jan 1, 2012

By Wm. Bleloch

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

By L. A. Vermeulen, D. D. Howat

The use of pebbles as the medium in the grinding of quartz gravel in a laboratory mil provided experimental data that were used to quantify the relationships between the feed rate of ore to the mil, the fineness of grind of the product, and the wear rate and consumption of the grinding medium. Fineness of grind is expressed as the inverse of the harmonic mean size, a quantity that is calculated from data obtained by sieve analyses. The commonly used criterion for fineness of grind (the percentage of material smaller than 75 µm in the mil product) is shown to corelate approximately linearly with the inverse of the harmonic mean size. An increase in the feed rate was found to cause the harmonic mean size of the product to increase linearly, Le. the relationship previously found for metalic grinding media is applicable to al grinding media, irespective of shape or composition. Simple expressions for the consumption and wear rate of pebbles are derived from the experimental data, and are shown to be functions of the feed rate. The expression for wear rate is a monotonicaly increasing function, while that for consumption is a hyperbolicaly decreasing function of the feed rate. In contrast, a linear relationship was found between the rate of wear of the grinding medium and the rate production of fines. The expressions that were previously developed in relation to the use of metalic grinding media are shown to be equally applicable to pebble milling.

Jan 1, 1988

By J. -M. Chautru

A geostatistical simulation of a typical mining site for polymetallic nodules in the North Pacific Ocean is presented. This is the first stage in the design of an industrial mining system. Two variables which have a major effect on the orebody's economic potential are considered, namely: the maximum slope of the ground inside a mining block of 50 x 100 m; and the average quantity of nodules on the same support. Two geostatistical problems have emerged in this study. The first is due to the lack of a change of support model for the maximum of a variable. A provisional solution, considering an experimentally accessible 'equivalent' support, is proposed. The second is due to a non-linear link between the two variables. To be able to take this into account in the simulation, we propose a new method based on the decomposition: X = E(X/Y) + Residue (X). Satisfactory results were obtained with this approach.

Jan 1, 1987

By G. Ferrara

The mathematical framework of a well-established model proposed earlier by the authors for the screening process is briefly recalled. Some numerical methods for the application of the model, concerning numerical solution of the equations and parameter estimation, are indicated. Some applications of the model to improve screening operations, sizing of screen, simulation of screening and of integrated plant operations are discussed, and the computer software to be used for these purposes is described in detail.

Jan 1, 1987

By Q. G. Reynolds

The dual-electrode DC arc furnace, an alternative design using an anode and cathode electrode instead of a hearth anode, was studied at small scale using computational modelling methods. Particular attention was paid to the effect of two key design variables, the arc length and the electrode separation, on the furnace behaviour. It was found that reducing the arc length to brush arc conditions was a valid means of overcoming several of the limitations of the dual-electrode design, namely high voltages and arc deflection.

Jan 1, 2012

By D. D. Hawat

The locations of potential reserves of chromite ores throughout the world are discussed. Reference is made to the marked changes in international trade in chromite ores during the past ten to fifteen years, and to the change in locality of the production of ferochromium aloys, which is curently largely carried out in the country of origin of the ores. The influence of these changes has been very profound in South Africa, which has the largest smelting capacity and the largest production of ferochromium aloys in the world. A proportion of South African ore is stil exported to meet the demands for the production of chromium chemicals and refractories, including a large tonnage of foundry sands. Ferochromium smelters in South Africa have a capacity of virtualy 1 Mt of aloy per annum. Nearly al this development has taken place since the introduction of the argon-oxygen decarburization (A.O.D.) process for the smelting of stainless steels. Formerly, expensive Iow-carbon ferochromium aloys were required as raw materials, but the AO.D. process, which is being used world wide, permits the use of high-carbon ferrochromium, the main product of the smelters in this country. The production in South Africa of chromium-containing corrosion- and heat-resistant steels is stil on a relatively smal scale, but serious atention is being paid to the exploitation of low-carbon weldable feritic chromium steel.

Jan 1, 1986

Interpretation of Leached Outcrops, by Roland Blanchard. Published by Nevada Bureau of Mines, University of Nevada, Reno, Nevada, 89507, 1968, 188 pages. Price $7.50 (R5.40). This book contains a summary of the author's knowledge of leached outcrops, derived from some 30 years' experience as a geologist operating mainly in the United States of America and Australia. Part 1 of the book provides a comprehensive coverage of the various processes and substances involved in the oxidation of many minerals, under different climatic conditions, to form the final leached products. In Part 2, details are given of the appearance and composition of the oxidation products of the following minerals: pyrite, pyrrhotite, arsenopyrite, cha1copyrite, cha1cocite, bornite, tetrahedrite, oxidized copper minerals, galena, cerussite, sphalerite, molybdenite, chromite, hematite, magnetite, manganite, pyrolusite, calcite, siderite, fluorite, salite and supergene silica. The illustrations, the black and white photographs and the colour plates of oxidation products are of a high standard. The material is presented in a logical order and in terms which are not over-technical; hence it is useful to persons other than trained geologists. Despite the advances in geophysical and geochemical prospecting, the location and interpretation of gossans remains an important method of discovering ore bodies, particularly so since the correct interpretation of a leached material can prevent the fruitless and expensive prospecting of an underlying body of uneconomic concentration. Therefore it is considered that this volume will be a valuable addition to the libraries of universities, exploration companies and geologists. It is of interest to note that the author, who died in 1966, presented a paper, under the same title as this book, to the Chemical, Metallurgical and Mining Society of South Africa in 1939. For this work he was awarded the Society's Gold Medal. W.T.S.

By W. D. Grimsley, R. P. King, J. B. See

Samples (15 to 20 g) of pre-calcined Mamatwan manganese ore or pure Mn 304 smaller than 48 mesh were reacted at temperatures in the range 1000 to 1300°C with samples of spectrographically pure graphite smaller than 325 mesh. Samples (1 g) of ore or pure Mn02 smaller than 48 mesh were reacted at temperatures of 1000 and 1200°C with pure graphite fines in argon, with graphite in carbon, .'1onoxide, and with carbon monoxide alone. In each case, the loss of mass as a function of time was recorded with a hermobalance. The rate and degree of reduction were found to increase with additions of carbon and with increasing temperature up to 1300oC, when they reached their maximum. The shape of the reduction curves, together with the results obtained from examination of the products of reaction by microscopy and X-ray diffraction, were used as the basis for a postulated reduction mechanism. Some details are given of an initial kinetic model that was used to verify the proposed mechanism. It was found that the reduction of Mamatwan ore by graphite at temperatures in the range 1000 to 1300°C occurs in two stages: (i) an initial stage during which the higher oxides of manganese are rapidly reduced to MnO with concurrent formation of CaMn2O4 and (ii) a longer stage during which CaMn2O4 and MnO are reduced to carbides by carbon dissolved in the ferromanganese phase.

Jan 1, 1978

By J. D. Austin

Currency fluctuations affect the rand revenues of all exports of mineral commodities, as well as influencing their price on local markets. Of the more than 50 mineral commodities produced by South Africa, about 75 per cent derive 40 to 100 per cent of their revenues from exports. . Although supply and demand are largely beyond its control, management can maximize its revenues despite fluctuating overseas prices and exchange rates by using the right market at the right time. Management can operate in the futures markets, which involve a specific commitment to deliver a specific quantity of a standardized commodity at a set time in the future and at a price that is determined on a futures exchange in open auction; or management can use the options market, in which a producer can insure against the risk of a falling price by taking out a put-option, which gives the holder the right (but not the obligation) to sell the commodity at a stated price at an agreed time in the future. In the forward markets, management has three available tools; forward currency transactions, trading of currency options, and money market hedges. Revenues, currencies of exchange earnings, purchasing power of the rand, and world price trends are shown in over 40 diagrams and tables for the main mineral commodities produced in South Africa.

Jan 1, 1984

By Donald Sir Tebbit

To have been invited to deliver this second CMMI lecture is an honour that I deeply appreciate. But, when I contrast my qualifications for delivering it, with those of Sir Alistair Framet, who delivered the inaugural lecturet in the series, or with those of other members of the Council, I feel rather an imposter. Far from having been a miner al my life, I have been associated with the mining industry on a part-time basis for a mere eight years. However, I encourage myself with two recollections. The first is the admission of the great Sherlock Holmes that he was often guided to the truth by the erroneous opinions expressed to him by Dr Watson. I may be able to perform a similar service for you. Secondly, I recall that, when I was a member of the Diplomatic Service, I was quite often asked to address representative gatherings of such professional people as the police, architects, dress designers, teachers, doctors, funeral directors, bird fanciers, and so on. Since it would have been pointless to pretend that I was expert in any of their businesses, I used to resort to the technique of announcing as my theme' A diplomat looks at the police' or whatever profession it was. They fortunately took it as a compliment that their profession was apparently one that diplomats spent a lot of time brooding over. They could also afford to laugh of any criticism that I might make because it could be ascribed to ignorance rather than informed malice. I hope that you will do the same.

Jan 1, 1988

By T. A. Silva, A. C. Bragança

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

Jan 1, 2007

By J. Lamb

Project managers must juggle many aspects to bring their project in on time, on budget, and in accordance with the aims of the project owner. Whether the project is a mining feasibility study, a technology implementation or a construction project, it falls to the project manager and his or her team to deal with risk from two standpoints, which may be at odds with one another. First, a project team must deal with risks to the project itself - that is, risks to on-time, on-spec and on-budget delivery against the value promise made to the customer. Second, there is the management of risks within the subject matter of the project, undertaken on behalf of the customer. The project manager cannot dodge this responsibility; yet there is a tendency (particularly in smaller, in-house studies) to avoid digging too deep, possibly for fear of what may be uncovered! This paper investigates the responsibilities of project teams in regard to risk management and reporting. It examines ownership of project risk; the nature of risk management activities undertaken by the team during the course of a project; and outlines some controls to ensure that the two opposing arms of project risk are reconciled for the benefit of both the project team and the project owner.

Jan 1, 2007

Newmont is one of the few remaining large mining companies that was established in the early nineteen hundreds. The company has a long, colourful and enviable history. This paper provides highlights of Newmont?s business and technical history since its inception in 1916, its transition to a ?gold only? company in the early 1990s and progress since that time up until the present day. Details of Newmonts current gold operations and its gold production profile for 2008 are also provided in the paper Over the last 50 years Newmont has developed a host of innovative gold technologies to meet the challenges of treating the complex refractory gold ores, found at the company owned mines in the Carlin region and around the world. Details of the technologies are provided and they include chlorination, roasting, bacterial and pressure leaching, leaching gold with thiosulphate and thiocyanate, N2Tech flotation, HPGR treatment of hard and abrasive ores and, finally, the use of Hydro-Jex technology for improving gold recovery from heaps.

Jan 1, 2009

By T. Puhakka

Simulation is a way to obtain quickly today future information on how planned systems will most likely behave in various selected situations. This information may then be used to optimize the system and its components and maximize the performance and output. Simulation is a way to fine-tune the layout, match the mobile fleet and optimize the schedule and the way of working to meet the desired production requirements. Simulation provides a glimpse of the upcoming operation, ‘future today’ and helps to predict its restrictions and sensitivity to various aspects. OptiMine™, the Sandvik Tamrock Corp. and CyberCube Oy developed simulation tool is designed to simulate underground rock flow and match suitable technology with various layout options. This tool can be used to view what-if situations and determine what kind of impact mastered changes have to production. The findings of critical points in the layout and working procedures at an early stage of a new mine can help to optimize the layout and material flow. OptiMine™is modular based simulation tool that combines the supplier machine knowledge and traffic guidance with mine operational know-how and mine environment. It is developed to work in a way that an effect of an individual incident, such as the effect of one additional turn in a continuous loading cycle to the daily capacity can be identified. The reported output can be used for economical impact evaluation of selected options. This paper discusses the use of simulation in general and the way the OptiMine™ simulation tool operates and how it may be used for operation, technology and material flow optimization.

Sep 1, 2001

The general standard of engineering in South Africa will, it is believed, reach new heights after the establishment of the S.A. Council for Professional Engineers (SACPE) in February, 1969. The Council is being created to establish standards for professional engineers in this country and ensure that the quality of engineering is maintained at a high level. In terms of the Act of Parliament under which the new Council will operate, all consulting engineers will have to be registered if they wish to remain in private practice. While engineers who are not in private practice cannot be compelled to register, it will be in their interests to do so, according to a statement issued by Mr M. R. Gericke, chairman of a Shadow Council which is at present preparing for registration and drafting the requirements for registration. Registration is seen as an important move towards maintaining the quality of engineering in South Africa. Engineers will be encouraged to strive for professional status by gaining the necessary qualifications and the varied range of experience required by the Council before registration. All work done by registered professional engineers will have to conform to certain minimum standards. A spokesman for the Council has urged all engineers to ensure that they apply for registration when the Act comes into force in February. The Council is also anxious to gain the co-operation of employers in ensuring that the holders of professional engineering posts will be registered. Full information regarding registration will be sent to engineers throughout South Africa early this year, and announcements will appear in the press.

By J. Levin, I. J. Corrans

Wet high-intensity magnetic separation (WHIMS) for the concentration of gold and uranium was tested on many Witwatersrand cyanidation residues, and on some ores and flotation tailings. The results varied, but many indicated recoveries of over 60 per cent of the gold and uranium. The main source of loss is the inefficiency of WHIMS for material of smaller particle size than 20fLm. The recoveries in the continuous tests were lower than those in the batch tests. The continuous tests indicated an operational difficulty that could be experienced in practice, namely the tendency for wood chips and ferromagnetic particles to block the matrix of the separator. It was decided that a solution to the problem lies in the modification of the separator to allow continuous removal of the matrix for cleaning. A system has been developed for this purpose and is being demonstrated on a pilot-plant scale. Promising results were obtained in tests on a process that combines a coarse grind, gravity concentration, and WHIMS. In the gravity-concentration step, considerable recoveries, generally over SO per cent, of high-grade pyrite. were obtained, together with high recoveries of gold and moderate, but possibly important, recoveries of uranium. A simple model describing the operation of the WHIMS machine in terms of the operating parameters is described. This should reduce the amount of empirical test work required for the optimization of operating conditions and should provide a basis for scale-up calculations. The economics of the WHIMS process is discussed.

Jan 1, 1979

By L. C. Stilwell

The paper will attempt to identify the threats, however obscure, that could confront the South African platinum industry. South Africa has the largest reserves of platinum group metals in the world, and is the largest producer of those metals. This situation is no different from that which existed in the gold sector fifty years ago. Since then South Africa?s share of world gold production has dwindled, and the gold mining industry has lost its dominance. Unlike gold, platinum has widespread use as an industrial commodity. Its investment value is a minor portion of its total value. It is therefore subject to different market forces. The sheer magnitude of the industry in South Africa obscures the fact that it is a wasting industry, and that South Africa exports almost all its production as a refined metal in the form of autocatalyst. Since Hotelling published his seminal work The economics of non-renewable resource in 1931,the science of mineral economics has developed exponentially. The paper will present a background of mineral economic theory and compare to this the development of the South African platinum industry. Of particular concern to a mineral exporting country is the question of mineral rent?its definition and employment. This will be the mail theme of the paper.

Jan 1, 2006