Search Documents

To the members of The South African Institute of Mining and Metallurgy We have audited the annual financial statements of The South African Institute of Mining and Metallurgy set out on pages 357 to 366 for the year ended 30 June 2002. These financial statements are the responsibility of the Institute?s Council. Our responsibility is to express an opinion on these financial statements based on our audit. Scope We have conducted our audit in accordance with statements of South African Auditing Standards. Those standards require that we plan and perform the audit to obtain reasonable assurance that the financial statements are free of material misstatement. An audit includes: ?examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements, ?assessing the accounting principles used and significant estimates made by management, and ?evaluating the overall financial statement presentation. Audit opinion In our opinion, the financial statements fairly present, in all material respects, the financial position of the Institute at 30 June 2002 and the results of its operations and cash flows for the year then ended in accordance with South African Statements of Generally Accepted Accounting Practice. Auditors 26 July 2002 Council?s approval of the annual financial statements The annual financial statements for the year ended 30 June 2002 set out on page 357 to 366 wereapproved by the Council on 26 July 2002 and are signed on its behalf by:

Jan 1, 2002

By A. Hammel

This paper summarizes indigenous mining methods used to collectmetal ores in pre-colonial southern Africa, south of 15°S. These methods, for the purposes of discussion, are divided into sections inorder of increasing organizational complexity, from scavenging,which only required basic equipment and a relatively minimal division of labour, to underground mines, which necessitated complex planning to overcome obstacles such as the need for illumination and ventilation. Examples concerning the pre-colonial exploitation of iron, copper, tin, and gold have been taken from the archaeological literature. This review paper provides an introduction to the technology that was available to and used by miners in the past, illuminates some of the factors limiting their operations, and supports the claim to the indigenous nature of this activity

Jan 1, 2000

By W. C. Joughin

Problems with the stability and performance of rockpasses in deep-level mines are common. This paper presents the results of an investigation into the recorded performance of rockpasses in deep-level gold mines. Records relevant to the geological environment in which the passes are excavated, their excavation details, and their historical performance are not at all well documented on mines. In general, the quality of data available from mines is poor. The investigation showed that very large spans frequently developed in passes during use, and that rock mass quality, the orientation of the pass with respect to the dip of the strata, and the magnitude of the stress acting normal to the axis of the pass were the main factors of influence. From the historical information obtained, the risks of instability in rockpasses are identified.

Jan 1, 2005

By R. Zivojinovic, S. Vujic, T. Tanaskovic

The problem of determining the optimum exploitation life of machinery, namely the optimum time for machinery and equipment replacement, represents a complex and highly responsible engineering task. Taking into consideration the situation prevailing at coal pit mines in Yugoslavia, the tasks of this class are very complex and difficult. To make a decision on replacement of capital equipment and machinery, such as bucket wheel excavators within the mentioned systems, understands a management task of utmost responsibility. It requires high professional and analytical knowledge as well as the reliable arguments, based on multidisciplinary professional approach. In this paper, the authors present their views on the problem of establishing the optimum exploitation life of bucket wheel excavators, offering an algorithm, based on dynamic programming, as a solution. Keywords: Bucket wheel excavators, exploitation life of machinery, optimization, operations research, theory of replacement, dynamic programming

Jan 1, 2003

Control of flotation processes is mostly managed by plant operators, who assess the performance of the plant based on their own experience and other heuristic rules. These rules tend to be subjective or ill-defined, since most of them are concerned with the structure of the flotation froth, such as colour, bubble size and shape distributions, froth mobility and froth stability. These phenomena are very difficult to quantify objectively, and inexperience on the part of the operators, human error, etc., can lead to significant inefficiencies in plant operation. In this paper the development of a fuzzy system to support the control decisions of plant operators is described, which leads to significantly smoother control action and more stable plant operation than could be obtained with crisp sets of rules or manual control strategies. Keywords: flotation, fuzzy logic, image analysis, genetic algorithms, rule induction

Jan 1, 2000

By M. Tangstad, D. Lu, G. Tranell, S. Gaal, J. Safarian

The kinetics of MnO reduction from high carbon ferromanganese slag was investigated using a sessile drop technique at 1600 ºC. The effects of reductant type, ambient atmosphere and slag composition on the MnO reduction were illuminated. Two different types of industrial reductants (ground to a particle size of 44 to 106micron and pressed to pellets) were used as substrates for small slag droplets of varying composition, which were reacted in a CO or Ar atmosphere with the reaction studied in-situ. The cross sections of the reacted slag-carbon samples were subsequently studied by EPMA to find the extent of MnO reduction as a function of reaction time. It was found that the rate of MnO reduction is affected by both the type of reductant, the ambient atmosphere and the presence of metallic components in the slag. Higher reduction rates were obtained for charcoal than for coke as reductant while a CO atmosphere unexpectedly yielded faster MnO reduction than an Ar atmosphere. It was also found that metal prills in the initial slag will increase the rate ofMnO reduction.

Jan 1, 2007

By Z. Jin, Q. Yun, C. Lu

This paper presents a quantitative assessment model for the assessment of environmental load in gold production, which is based on environmental ecology, Life-Cycle Assessment and technical conditions of gold production in China. This model can make environmental assessment in terms of a set of indexes and quantitative approach by means of artificial neural network, which also improves the theory of Life-Cycle Assessment. Keywords: Artificial neural networks, Environmental load, Assessment, Utility function, Gold production

Jan 1, 2003

By K. I. Afewu

A modified approach to the implementation of Gy?s sampling theory is discussed and used to design a procedure for sampling crushed gold ore feed to metallurgical process plants. The approach involves calibration of certain ore-specific parameters. These parameters were calibrated for two different crushed gold ores en route to grinding mills in process plants. The model predictions were compared with the predictions from Gy?s original model. Far smaller masses of samples are required by the modified model than by Gy?s model at the same relative variance. The representativeness of the sampling procedure if normally distributed errors are assumed was also calculated. These procedures and evaluations lead to significant savings on cost of handling and preparation of the samples and to a quantifiable degree of confidence in the analytical results for the process plant.

Jan 1, 1998

A large number of brittleness concepts have been used in very different studies in the literature. One of them is the B1brittleness concept. In this study, the objective is to criticize the B1 brittleness concept on rotary blast hole drills. The B1 brittleness concept, the ratio of uniaxial compressive strength (sc) to tensile strength (sT), are widely used as a rock brittleness concept in the literature (Inyangand Pitt, 1990; Verhoef, P.N.W. 1993; Neil, D.M. et al.1994;Becker, et al.1984; Evans and Pomeroy, 1966; Göktan, R.M.1992; Kahraman, S. 2001; Yamaguchi, U. 1970; Verhoef, P.N.W. et al.1996; Bilgin, 1982; Howarth and Rowlands,1987; Howarth, D.F. et al. 1986). So, it was used as a rock brittleness concept in this article. The value of the B1brittleness concept is equal to the tangent of ß angle in the following graph. It was seen that more meaningful relationships could be obtained with the B2 brittleness, the under ?Area?(= 1/2(scxsT) = B2) under the curve, instead of tangent ß, (=B1), of the curve.

Jan 1, 2003

By M. K. Elmouttie, G. V. Poropat

Mapping of exposed rock walls provides data on geological features such as joints, bedding planes, faults etc critical to the economics and the safety of mine operations. Traditional, manual methods of mapping can be time consuming, error prone and limited in their coverage. New methods have been developed to map exposed faces remotely and safely however the benefits of these methods are only fully realised when exposed structures can be quickly and easily mapped using automated methods. This paper describes the application of an automated method of analysis of 3D images that provides users with the capacity to map exposed structures automatically. The method is based on the use of vector classification methods used in some neural network systems and provides rapid and reliable identification of exposed planes. CSIRO Exploration and Mining is applying these methods to 3D images for a range of applications from pit mapping to machine automation.

Jan 1, 2006

By J. C. Vreugdenburg, B. A. Dippenaar, J. Muller, T. L. de Vries

Iron ore fines are agglomerated to produce sinter, which is an important feed material for blast furnaces worldwide. A model of the iron ore sintering process has been developed with the objective of being representative of the sinter pot test, the standard laboratory process in which the behaviour of specific sinter feed mixtures is evaluated. The model aims to predict sinter quality, including chemical quality and physical strength, as well as key sinter process performance parameters such as production rate and fuel consumption rate. The model uses the finite difference method (FDM) to solve heat and mass distributions within the sinter pot over the height and time dimensions. This model can further be used for establishing empirical relationships between modelled parameters and measured sinter properties. Inputs into the model include the feed material physical properties, chemical compositions, and boundary conditions. Submodels describe relationships between applied pressure differential and gas flow rate through the bed of granulated fine ore particles, combustion of carbonaceous material, calcination of fluxes, evaporation and condensation of water, and melting and solidification. The model was applied to typical sinter test conditions to illustrate the results predicted, and to test sensitivities to parameters such as feed void fraction, feed coke percentage, and the fraction of combustion heat transferred to the gas phase. A model validation and improvement study should follow, ensuring sinter test results are free from experimental errors by conducting repeated tests.

Jan 1, 2015

By D. G. Krige

For the purpose of determining confidence limits for ore grade estimates, an extensive simulated data base was used, which included 1728 ore blocks with ‘actual’ grades and the corresponding estimates based on ordinary and simple kriging. The practical results show that conditional unbiasedness is essential and that acceptable confidence limits can then be set using Normal theory for the simulated error distribution based on the logarithms of the ratios of ‘actuals’/estimates with a variance related to the kriging variance. The mean of the data used to prepare the variogram and the estimated block grade are to be used properly in this approach. A practical analysis was also done of the actual point and block data from a very large mined out Carbon Leader area. The distributions of the actual grades for two levels of block sizes with different levels of variability were fitted using three models, ie. 2-. 3- and compound-lognormal. The trends of tonnages, grades and relative profits for a range of pay limits, as well as the usual tonnage-grade curves, show a practical insensitivity for the choice between the three lognormal models considered.

Jan 1, 2003

By Darelle T. Janse van Rensburg

Some of the more recent developments in Paint Technology are solvent free materials. These coatings have mainly been formulated to overcome the negative attributes of solvent-based coatings, i.e. environmental, safety and health risks, potential for solvent entrapment and osmotic blistering, as well as the formation of micro-pores during the curing process. Two solvent free liquid epoxy coatings have been used extensively on power generation plant. However, very little is known regarding their long-term performance under different exposure conditions, as well as whether these coatings actually perform better than their solvent-borne counterparts. In addition, solvent free materials are generally used where outage periods are restricted and coatings need to be applied within a very short period. Though these materials have reportedly much shorter curing times than other conventional solvent-borne coatings, little is known regarding their limits with respect to maximum film thicknesses and being put into service while still being wet/partially uncured. The latter has become common practice at many power stations in the past two years or so. In addition, the application and curing methods of solvent free materials are different to that of solvent-borne materials, and may require equipment and application process changes. This paper covers the application and performance properties of solvent free coatings in comparison to solvent-borne materials primarily intended for immersion service. Numerous coatings were evaluated under immersed static and cyclic hydrostatic pressures. Other tests included short curing / early immersion tests, dry-to-touch and dry-through curing times, adhesion tests, surface tolerance tests, etc. The results show that the solvent free materials have clear benefits with respect to safety, health, environmental and long-term performance, but will be more difficult to apply compared to solvent-borne materials.

Jan 1, 2006

By D. M. MacHunter, M. K. Palmer

Refinement of design parameters and features has resulted in the development and commercialization of spiral separator models that offer enhanced performance for a number of application areas. Examples of recently developed spiral separator models include the enhanced performance (EP)spiral and the HC (high capacity) series. Comparative performance data for appropriate applications are presented for each of these new model spiral separators. The utilization of spiral separators providing improved performance offers significant cost and operational benefits for process plants. Examples of process flowsheet changes that have resulted from the incorporation of recently developed spiral separators include the reduction of the number of process stages and the achievement of high density tailings by the utilization of a dewatering arrangement in the spiral tailings splitter system.

Jan 1, 2003

By M. Le Roux

Fine coal (-500 µm) is notoriously difficult to dewater. It is not uncommon for a dewatered product to have a moisture content as high as 30 per cent after vacuum filtration. This poses several handling and financial problems to such an extent that a lot of fine coal is discarded onto slurry waste ponds. A novel way of dewatering fine coal was developed at North-West University. It entails deliberately damaging the filter cake during dewatering to allow for an increased flow of air through the cake at the expense of the applied pressure differential. This method resulted in an average improvement in final cake moisture of between 3 per cent and 5 percent when executed in the laboratory under controlled conditions. A device was designed that could be fitted onto existing belt filters that would damage the filter cake as it passes by. This device was tested on a vacuum belt filter installation at a coal beneficiation operation in the Waterberg coal field in South Africa. The results showed a 3 per cent reduction in final moisture of the cake, proving the validity of the method at full industrial scale.

Jan 1, 2012

In the 1980s and?90s the gold mining industry in South Africa came under pressure from the continued poor dollar gold price and escalating Rand based costs, furthermore the external impacts on the industry were changing. Thus, the Chamber of Mines (COM) shifted its focus away from many historical areas of support towards the new industry challenges in safety and health, labour markets, environmental responsibility, mineral rights legislation and social responsibility. During 1997 the lack of funds and the changes facing the tertiary institutions were often subjects of discussion at the various sub-committee meetings. The Metallurgical Sub-committee of the Chamber Education Fund or the Sub-committee of Consulting Metallurgists as it was known identified the need for the funding structure to change with the times. Up to this time the Chamber of Mines operated an Education Fund that supported mining industry academic departments at various South African tertiary institutions; these funds were derived exclusively from the country?s gold and coal mines the basis of Chamber membership. Funds of less than R5 million per annum were available for distribution by the three disciplinary sub-committees of mining, metallurgy and geology.

Jan 1, 2003

By I. Benning

Since the dismal performance of the Rand Mines management was called to account by its shareholders in 1994, the waves of change have continued to ripple across the South African mining industry .The number of listings on the gold board of the Johannesburg Stock Exchange, that once numbered 40 or 50-odd, have now dwindled to no more than a handful as unprecedented restructuring has taken place. The redefining of the industry has not been limited to the gold sector, but across the base metal, coal, diamond, platinum and industrial mineral sectors as well. At the same time the Mining Houses began to reconsider their funding strategies. Originally established in the early part of the century to ensure the long-term sustainability of their group mining operations by providing substantial financial muscle and technical support, the Mining Houses were faced with a rapidly changing political environment, which proved to be a critical catalyst in giving momentum to the change. Furthermore, the significant development costs and increasing risk profile for new projects, coupled with pressure from shareholders demanding respectable returns, opened the door to opportunities for banks to begin providing external debt by the way of project finance. However, the provision of long-term debt to the South African mining industry had generally not been common since mining companies had financed new projects with equity, or with the cash flows from existing operations. Those banks that had the appetite for exposure to the perceived high risks of the mining sector rapidly built up specialist resource banking divisions capable of addressing the increasing demands of the industry. The application of project finance, the principles of which were developed in the 1970s specifically for infrastructure projects and privatization, is now commonly applied in the financing of greenfield and brownfield mining projects. This paper outlines the approach that lending banks would typically adopt when arranging or providing mining project finance, their usual areas of concern and the way in which the finance is structured to mitigate the many inherent risks.

Jan 1, 2000

The paper reviews the results emanating from an experiment conducted in Bochum?Germany in which various international rope inspection authorities were requested to assess the conditions of a corroded rope sample as well as a rope sample containing internal fatigue breaks. Both samples were of the multi-layer low rotation construction.

Jan 1, 2000

By P. T. Slatter

The efficient and accurate design of pipe and pumping plant for non-Newtonian mineral slurries remains a problem. The objective of this paper is to present the development of the Balanced Beam Tube Viscometer (BBTV), an instrument which could facilitate more accurate design for these slurries. The background of rotational and tube viscometry is reviewed and the fundamental principles and inherent advantages of the BBTV are given. The design, data acquisition and processing techniques are introduced and results showing the reliability of the new instrument are presented and discussed. It is concluded that the BBTV is a reliable and versatile instrument for both routine analyses and research work, and has the potential to provide data for the refinement of the design procedure for mineral slurry pipe and plant design.

Jan 1, 1998

The coal-based power generation industry faces increased pressure from all sectors to improve its environmental performance. This is due to increased awareness of and concerns regarding greenhouse-and acid-gas emissions, toxic metal releases (to both air and water) and water availability. A methodology to assess this industry?s environmental performance is needed. Such a methodology should assess all environmental impacts accurately, recognizing the irspatial and temporal dependence, and taking into account the social acceptability of technologies employed. Here, we develop a methodology to determine the environ-mental impact associated with solid wastes generated by this industry, and apply this to the specific case of ash management. More specifically, the case study compares the environmental footprint of an ash deposit for a number of operational water management scenarios. The methodology considers leachate generation processes from ash impoundments to obtain a time-dependent concentration profile of mobile constituents at the interface between the ash impoundment and the surrounding environment. This leachate prediction modelling is subsequently linked to plume dispersion modelling tools to determine the fate and transport of leached components, predominantly salts, into groundwater. Together, these provide a measure of the extent to which a land mass is affected by leachate migration from the deposit. To determine the exact boundary between regions of acceptable and unacceptable risk to the environment, we use Ecological Risk Assessment concepts. In this way it is possible to obtain a time dependent affected land footprint which could be used as an indicator of the environmental impact of solid waste management practices. This information can be included in a set of environmental criteria which form the basis of an overall environ-mental impact assessment, using tools such as Life Cycle Assessment (LCA). The value of LCA is that its structure is consistent with accepted models of environmental decision making, where different approaches to valuation in impact assessment assist in prioritizing impacts on the basis of their perceived significance. The proposed ?affected land footprint? metric represents a significant improvement over current LCA impact indicators for solid waste management practices. Keywords: Environmental Impact Assessment, Environmental Risk Assessment; Life Cycle Assessment; coal ash; leachability; salinity

Jan 1, 2002