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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 L. A. Vermeulen, D. D. Howat

New distribution functions are derived to describe the size distribution of grinding elements in ball mils. The formulations are based on the assumption that abrasive as well as impactive interactions occur during bal milling-an assumption that is supported by a large body of experimental evidence. It is shown that the functions can be used in the estimation of the magnitudes of abrasive and impactive components in the total rate of bal wear. The relative magnitudes of the wear components provide a basis for optimization of the chemical and metallurgical properties of the balls in a given milling situation. However, it is contended that these quantities are also useful indicators of the relative intensities of the abrasive and impactive interactions that are operative in the size reduction of mineral particles within ball mils. These quantities can be determined for any industrial ball mil, and their magnitudes provide practical guidelines for mil operation. The theory is used in an analysis of samples of ball charges from two industrial ball mils, and it is also applied to al the data on bal-size distributions found in the literature. The qualitative correlation between the calculated values of the wear components and the reported operating conditions is good for a variety of industrial ball mils, in conformity with the hypothesis that the relative magnitudes of the wear components are related to the milling conditions.

Jan 1, 1986

By D. F. Sinclair

It is often said in business that if you don't have a customer you don't have a business. The same rule applies to project evaluation; if you don't have customers you really don't have a viable project. It is therefore essential that in the early stages of project evaluation the following fundamental questions are addressed: ? What products will this project produce? ? Who are the potential customers? ? What are the customers' requirements with respect to grade and impurities? ? Do they have adequate capacity to take the production from the proposed project? ? Will the products introduce adverse effects in the customer's process circuits? ? Will additional waste streams requiring disposal be produced? In the past the attitude has been along the lines of the customer will take whatever we produce at the mine site. Times have now changed with customers now operating under much tighter environmental regulation with waste disposal becoming increasingly difficult. It would therefore be prudent that the principles of product stewardship be used as a tool in project evaluation. This paper will provide a general discussion on customer requirements and provide detail on case studies of the impact of mine products on smelter process circuits. It will provide examples where there were synergies between the mine product and the smelter circuit and where the mine product had adverse impacts on smelter performance.

Jan 1, 2007

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 P. J. Petit

The strategic mission of the South African mining industry is to extract the mineral assets in an energy efficient, economical and safe manner. Drilling has received particular attention in the last few years. As the operations move away from the power source, conventional and old drilling technology result in poor penetration rates, increased drilling shift lengths, slow face advances and limited stope efficiencies. The need for an alternate mining method, performed by a skilled workforce, to increase productivity, has led to the development of the electric rock drilling system for in-stope mining operations. The focus of this paper is a systematic evaluation of the electric rock drilling system as a function of production and technical parameters, in the platinum orebody. The particular electrical reticulation system is illustrated. Power usage, problems experienced, and solutions are described. The safe use of the recently developed drill is elaborated upon by describing protection devices. The testing and certification process, for approval by the recognized authorities, are documented. The testing and certification process, for approval by the recognized authorities, are documented. The human factor is also considered. Known detrimental factors of high noise exposure, vibrations levels and oil emissions are reviewed. In conclusion, recommendations on future strategies for the implementation of electric drilling technology within the mining and construction industries, is included.

Jan 1, 2006

By Y. Suzuki, H. Yoshida, K. Sakaguchi, K. Matsuki, M. Minami

To estimate three dimensional in-situ stress at great depth, Downward Compact Conical-ended Borehole Overcoring (DCCBO) technique, which is one of stress relief methods, was developed. DCCBO technique can be applied to a water-filled vertical/sub-vertical borehole. In in-situ tests, the bonding device and the cleaning system were verified to work well in a water-filled borehole with cuttings on the bottom. Um dreidimensionale in-situ Beanspruchungen in großen Tiefen abzuschätzen, wurde das Downward Compact Conical-ended Borhole Overcoring (DCCBO) Verfahren entwickelt, wobei es sich um ein diese Beanspruchungen entlastendes Verfahren handelt. Die DCCBO Technik kann auf wassergefüllte vertikale und subvertikale Bohrlöcher angewandt werden. Bei den in-situ Tests wurde die Einsatzfähigkeit der Verbindungsvorrichtung und des Reinigungssystems für wassergefüllte Bohrlöcher mit Einschnitten am Boden bestätigt. La technique de Downward Compact Conical-ended Borehole Overcoring (DCCBO) ou ‘Surcarottage par sondage à extrémité conique compact dirigé vers le bas’, qui est une méthode de détente des tensions, a été développée pour calculer les tensions in-situ à trois dimensions à grande profondeur. Cette technique peut s’appliquer à des sondages verticaux/sub-verticaux remplis d’eau. Au cours des essais in-situ il a pu être vérifié que le dispositif de liaison et le système de nettoyage fonctionnaient bien dans un trou de forage rempli d’eau avec saignées au fond.

Jan 1, 2003

By E. M. W. Skinner

Various models of near-surface kimberlite pipe emplacement have been proposed over the years. These include a top-down, phreatomagmatic model, a bottom-up, embryonic pipe model and three top-down explosive dyke models. AU of these models consider kimberlites as essentially the same rock type. However, different kimberlites have different pipe shapes and contain different rock types with very specific mineral assemblages and textures and therefore are likely to have been emplaced by different processes. Some authors have considered local geological differences as the principal reason for the contrasting geology but others argue that, while geological differences might contribute locally the petrographic peculiarities of particular kimberlites may be due mainly to inherent compositional differences specifically in the ratios of juvenile CO2 and H2O.

Jan 1, 2010

By L. Morin, S. Mortazavi, K. Volchek, A. Demers, A. Di Feo

The objective of this paper was to investigate the possibility of reducing process (fresh) water and increasing recycled water (thickener tank overflow water). As part of the investigation, rougher flotation tests were done with the two water types and a mixture of the two (50%/50%). The effect of recycled water on the grade-recovery response and rougher recoveries was investigated. When thickener tank overflow was used (50% and 100%), the nickel+copper grade versus nickel recovery decreased. The decrease in the grade-recovery was due to higher pyrrhotite recovery. Also, there were no effects on nickel and copper recoveries, which was confirmed using multivariate statistical analysis at the 95% significance level. Keywords: Flotation, nickel, copper, water recycling, multivariate statistical analysis, MANOVA, reverse osmosis

Jan 1, 2020

By D. T. Williamson, B. P. Gilbertson

Satellite observation of mine-dump vegetation by B. P. GILBERTSON, M.Sc. (Phys.) (Visitor) and D. T. WILLlAMSON, B.A., LLB., B.A. Hons. (Visitor) NASA's first Earth Resources Technology Satellite (ERTS-I) was launched on 23rd July, 1972, and has subsequently gathered multispectral imagery of most of Southern Africa from an orbital altitude of 900 km. Images of the Witwaters rand area have been studied in an attempt to differentiate between mine dumps having varying degrees of vegetative cover. At this stage it is clear that the various mine dumps can be located and identified, and differences in vegetative cover can be seen and measured. Patterns of vegetative growth, some characteristic to particular dumps, can also be seen.

Jan 2, 1974

By P. R. Jochhens

The Past. In the past, large metallurgical companies (for example the mining houses) had the necessary infrastructure both to develop metallurgical flowsheets and to undertake the construction and project management of metallurgical plants. Effectively, the sole contribution by contracting companies was the supply, and possibly the installation, of specific items of equipment. OBITUARY: AUSTIN WHILLIER (1927 - 1981) On Thursday, 13th August, 1981, Dr. Austin Whillier passed away peacefully in Johannesburg after a long illness. This event has been a serious blow indeed, and its effects will be felt, not only by the Chamber of Mines of South Africa and the South African mining industry, but also throughout many scientific and technical spheres both in South Africa and further a field.

Jan 1, 1981

By R. Guest

Reichert cone concentrators are used successfully in many applications, but have as yet not found favour in the gold mining industry on the Witwatersrand, because, for optimum operation, the cones need to have specially designed feed-preparation and circuit details. In addition, good liberation of the valuable minerals is essential. Gravity tests, in which a pilot plant was used on refractory gold ore, showed that 94 per cent of the gold could be extracted after gravity concentration and preferential grinding, roasting, and cyanidation of the concentrate, whereas 96 per cent could be extracted by flotation followed by the same preferential treatment. However, the capital and operating costs for gravity separation are expected to be considerably lower than those for flotation.

Jan 1, 1982

By S. N. Alecsandrov, BulgakovY. F.

Putting out fires in faces is an extremely complex and dangerous operation from the technological point of view which sometimes is accompanied by human victims. The new technology of fire-extinguishing sets giving directly into a mining face has been developed at the DNTU in order to put out such kinds of fires. The technique presupposes an availability of special installation placed on ventilation and conveyor mining drift. In case of fire a special fire-extinguishing powder is delivered with the help of remote control into mining face. Subjects, allowing to determine powder delivering distance in the frame of mining workings are presented in the report. The given technology substantially increases safety of accident work which are carried out in case of fire.

Jan 1, 2003

By S. Visage

By 1984 Iscor's first direct-reduction plant will be operating at the Vanderbijlpark Works, and for the fin;t time the Corporation will have an alternative method to the blast furnace for producing iron from ore. The performance of Iscor's four-kiln plant, which will be the largest coal-based plant in the world producing sponge iron, will undoubtedly be watched with great interest by steelmakers throughout the world. Beneficiation of tin The Southeast Asia Tin Research and Development (SEATRAD) Centre is a regional oganization, formed by the Governments of Indonesia, Malaysia, and Thailand with assistance from the United Nations, to conduct, coordinate, and promote research and training in the various fields of tin production, including geology, prospecting, mining, mineral processing, and smelting.

Jan 1, 1982

The relationships between backfill-transportation parameters (solids concentration, velocity, and pipe diameter) and the wear rate of backfill-transportation pipelines is well understood. However, the degree of wear experienced by a pipeline depends not only on the transportation parameters, but also on the characteristics of the solids making up the backfill, i.e. the particle-size distribution, hardness, shape, and sharpness of the particles. Therefore, unless data corresponding to the specific wear rate of the solids are available, the determination of the wear rate for pipes transporting an uncharacterized backfill is largely guesswork. This paper describes an evaluation of particle characteristics with special reference to particle sharpness so that pipe wear rates can be correlated with solids of different size distributions and sharpnesses.

Jan 1, 1993

By P. C. Seligmann

Primary fracture from an array of shotholes by c. M. LOWNDS. B.Sc. Hons. (Rhodes). Ph.D. (Cape) (Visitor) and P. C. SELIGMANN. B.Sc. (Witwatersrand) (Visitor) The effects of stress on the directions of cracks that are propagating in a brittle medium are described. It is shown that the superimposition of stress fields from the holes of an array always adversely affects fragmentation. Consequently, the best fragmentation will result when holes are fired far enough apart in space or time for each to develop its whole crack pattern without disturbance from the others. This concept leads to a philosophy for the design of more effective blasting patterns, which has been verified on model scale and which explains many published, empirical results.

Jan 1, 1976

By A. G. W. Knock

Logistic curves are used in the prediction of the primary production of tin metal from estimated worldwide resources. Such curves are asymptotic to the total cumulative reserves, which are a function of prevailing metal prices and total resources. The figures for tin resources are based on the findings of Robertson and of Brobst and Pratt, the latter authors including estimates of undiscovered deposits. It is suggested that tin production will slump from the present level to 100000 long tons per annum by the end of the century, but will reach a new peak of 200 000 long tons some thirty years later. It appears that production will never exceed 300000 long tons per annum unless substantial new resources, excluding those predicted, are discovered.

Jan 1, 1979

By D. J. Adams, R. G. Gürtunca

In situ measurements and numerical modeling based on elastic theory showed that backfill stresses are considerably higher than originally thought. This has led to a change in understanding of rockmass behaviour. After describing previous work on the behaviour of the rockmass, this paper discusses possible reasons for the high stresses measured in backfil, and identifies the rockmass mechanisms possibly generating these stresses. It is concluded that the joints and the geological stratigraphy can lead to increased elastic convergence, and that the inelastic behaviour of the rockmass is also partly responsible for the increased closure measured in backfill. The use of an in situ modulus is suggested as an interim solution until a new computer model that allows for joints, different layers, and inelastic closures becomes available.

Jan 1, 1991

By A. W. Bryson, J. D. le Roux, B. D. Young

Several rate models for the adsorption of gold cyanide from aqueous solution onto activated carbon are given in the literature. The purpose of this study is to critically examine their ability to simulate the adsorption process over a wide range of conditions. An account is given of a comprehensive set of experimental work on the kinetics of gold adsorption onto a coconut shell- based activated carbon. Equilibrium isotherms were also determined. It is concluded that the homogeneous surface-diffusion model fits the experimental data reasonably well and provides a good balance between simplicity and descriptive accuracy. The model contains two parameters: the extra-particle mass-transfer coefficient and an effective intraparticle surface-diffusion coefficient. Both can be evaluated readily from simple adsorption experiments.

Jan 1, 1991

By H. J. E. Hamel

Some aspects of the deformation behaviour and temperature rise during instantaneous compression loading of high purity aluminium By H. J. E. HAMEL The influence of deformation speed on the deformation behaviour of high purity aluminium was investigated. By varying the initial height-to-diameter ratio a considerable influence on the deformation behaviour could be noticed. Lubrication of the specimen end faces was found to have an influence on the flow behaviour and on the roughness of the specimen interface at pressing platens. The results of temperature measurements during deformation agree with work-hardening behaviour of the specimens. Flow curves calculated with the measured temperature rises do not agree with results obtained at lower strains by other workers. The possible reasons are discussed.

By B. Jack, A. Vervoort

During pillar extraction, sidewall fracturing and spalling at some collieries constitute a severe stratacontrol problem. In order to obtain a better understanding of this phenomenon, a survey of pillar corner conditions before and during pillar extraction was conducted at one particular site. For the various successive mining steps, the vertical stresses on the pillar corners were calculated by use of a three-dimensional boundary element program. A significant correlation was found between the calculated vertical stress prior to the extraction of the panel and the sidewall conditions. During the extraction of the panel, a significant deterioration of the sidewall conditions at a pillar occurred only when the adjacent pillar was mined, causing an increase in vertical stress on the remaining pillar.

Jan 1, 1992