Search Documents

By L. K. Smith, E. M. de Kock, J. van der Walt

A systematic approach to the analysis of alternative methods of ventilating and cooling large hot mines is presented. The important factors that have a bearing on ventilation and cooling requirements and practices, such as air flow through the mine, geographical distribution of eat loads, and micro-ventilation considerations, are dealt with. The analysis of these factors leads to definitive ventilation and cooling strategies, air and water process design, specifications of details, and designs of the associated plant and equipment.

Jan 1, 1983

By A. L. Hinde, P. J. D. Lloyd, A. R. Atkins, J. G. MacKay

The control of milling circuits by A. R. ATKINS, M.Se. (Elee. Eng.) (Visitor), A. L. HINDE, S.Se., Ph.D. (London) (Visitor), P. J. D. LLOYD, S.Se. (Chem. Eng.), Ph.D. (Cape) (Fellow) and J. G. MACKA Y, S.Se. (Chem. Eng.) (Visitor). The general behaviour of mills is described in an attempt to find a control philosophy that will permit milling circuits to produce a constant particle size. Although the experimental work has been confined to a single section of the milling circuit of one mine, it is felt that the findings are applicable to other milling circuits.

Jan 6, 1974

By M. N. James

The Fracture Research Group has been operating at the University of the Witwatersrand for some ten years and, in that period, has achieved a significant profile, both nationally and internationally, through its research publications, industrially-based technical reports, continuing short courses in engineering education, and co1Jferences. This paper outlines the activities of the Group over the past few years, emphasizing the research thrusts and the results that have been obtained, as well as highlighting areas of current and future research interest The capabilities of the Group in terms of equipment and expertise are also discussed briefly.

Jan 1, 1995

By A. B. Stewart, I. J. Barker

Traditionally it has commonly been believed that the only problem with inductive reactance in a submerged-arc furnace is that it leads to difficulties with the electricity supply as a result of the Iow power factor. This paper sets out to show that inductive reactance can also give rise to the following problems in the metallurgical operation of a furnace: (i) dead and live phases (fairly well known in openarc furnaces), (ii) lack of sensitivity to electrode movement, (iii) interactions between electrodes. These problems increase with increasing inductive reactance relative to resistance, and thus they increase with furnace size. Each of these effects is discussed in detail, and suggestions are made for their alleviation.

Jan 1, 1980

By C. Hey

The cycloned gravitated tailings backfill system, also referred to as a soft or low density fill, has been implemented at Vaal Reefs. Inhibiting the success of the system was the problem of shrinkage after placement. The problem was overcome by a pressure fill technique which eliminated settlement, contained costs and allowed remote placement. The technique involves the preinstallation of disposable pipes which are filled cyclically until a residual pressure of 0,5 bar of active support is generated in the filled paddock.

Jan 1, 1988

By G. Matheron

This paper discusses important aspects, both psychological and methodological, which have delayed the introduction of geostatistics in practice. The evolution of geostatistics is traced through three 'generations', and in conclusion some important questions are raised on the current status of the subject and possible areas of future research.

Jan 1, 1987

By K. R. Vost

This paper reviews the theoretical methods used in South Africa for the prediction of heat pick-up and air-temperature gradients along main haulages. These methods include those of Starfield, Ramsden, McPherson, and Goch and Patterson. The differences in predictions based on typical airway conditions are explained as being due to differences in the mathematical models on which the predictions are based. The largest discrepancies were found for dry airways and for airways with bulk air coolers. The errors in predictions of the effect of machines and coolers that have been running for only a few months are calculated, and the limitations of various simplified methods are discussed.

Jan 1, 1982

By R. Meyjes, P. Davies

Keywords: Pyrometallurgy, furnace, smelter, engineering company Metix is a private smelter engineering company wholly owned by its management. Its main lines of business in the ferro-alloy industry being: - turnkey smelter projects (LSTK) - engineering, project, and construction management projects (EPCM) - specialised furnace equipment comprising: ? complete electrode columns, including forged copper pressure rings and contact shoes, as well as fail-safe slipping devices ? water-cooled roofs ? bus-tube systems ? feed systems ? cooling systems ? linings ? off-gas systems ? tap-hole drills & clay guns - furnace power supply systems - ore agglomeration & sinter plants - feasibility studies & due diligence reports - technical consulting for investment banks - project procurement & cost control Metix management experience includes around 130 combined years of contacts and experience in the South African smelter industries. Over 30 furnaces have been built, for processes including FeCr (high, medium, and low carbon), FeSi, FeMn (high and medium carbon), SiMn (ultra low carbon), Si metal, and FeV.

Jan 1, 2006

By M. J. Gouws, T. P. Knoetze

The spontaneous combustion of coal and the explosion of coal dust are two phenomena that were identified by the South African mining industry as requiring investigation. Research contracts were awarded to the G.P. Badenhorst Research Facility of the CSIR and the Department of Mining Engineering of the university of the Witwatersrand by the now defunct National Energy Council. Both projects entailed tests on numerous coal samples in specially designed apparatus. Since the completion of the project, attempts have been made to predict experimental results without incurring the cost of performing experiments. This paper describes predictive indices, based on routine laboratory tests, that were developed by the different research teams for their particular projects. A comparison of the results obtained by applying the spontaneous combustion liability index and the explosibility index to common coal samples indicates that, in general, propensity to spontaneous combustion and explosibility exhibit an inverse relationship. A brief overview is given of some major South African coal-mine disasters.

Jan 1, 1995

By J. P. Kirsch

This paper sets out to clearly identify all elements that make up an effective furnace feed system. These are outlined and the more common types of technology are listed. These technologies all play an important role in the final delivery of all feed materials to the furnace.

Jan 1, 2008

The aspect ratio (mill diameter/mill length) of autogenous and semi autogenous mills varies widely and can be as high as three or as low as 0.5. The literature on the subject of what effect aspect ratio has on grinding mill performance or energy efficiency is almost non-existent. However, at the design stage of many grinding circuits the subject is often vigorously debated amongst metallurgists. In this paper the performance characteristics of mills with different aspect ratios are examined to determine whether process performance characteristics are a function of aspect ratio and whether high aspect ratio mills are any more or less energy efficient than low aspect ratio units. Data from both pilot and full-scale mills are used for this purpose in open and closed circuit configurations.

Jan 1, 2007

By L. A. Vermeulen

Electronic circuits were developed and successfully utilized to record, store, and continuously transmit to a remote station physical information relating to the impacts of pebbles on the shell liners of an industrial pebble mill, and of electrical conduction in the mineral pulp. The information was obtained by the instrumentation of some of the bolts that are used to clamp the liner blocks and litter bars to the mill shell. The features associated with the impact and conduction signals have been interpreted, and it is shown that such signals can lead to continuous measurements of the volume of the load in an industrial mill. Information is given regarding the angular distribution of direct impacts of the pebbles onto the shell liners, the power required to promote impacts, the amount of material in flight, the impact velocity, and the average number of direct impacts with the shell liner that any given pebble undergoes in unit time in the given mill.

Jan 1, 1984

By C. Chapman, M. G. Reading, M. P. Amsden

Computer control of flotation at the Ecstall concentrator By M. P. AMSDEN, C. CHAPMAN, and M. G. READING Ecstall Mining Limited, a subsidiary of Texas Gulf Sulphur Company, operates the Kidd Creek Mine, a 10000 tons per day base metal producer, near Timmins, Ontario. Two different types of ore are mined and milled: copper-zinc and silver-lead-zinc. At the highly automated Ecstall concentrator the ores are processed by selective flotation in three individual circuits. One of the most important metallurgical tools for process control is a sample system incorporating continuous on-stream X-ray analysis. Recently this system was automated further by the addition of computer control of reagents for two copper-zinc flotation circuits. The computer programs, utilizing optimum seeking methods and smelter contract terms, have increased copper recovery by 1,1 per cent, zinc recovery by 1,4 per cent, and have reduced reagent costs by 16 per cent. Although not expected, copper and zinc concentrate grades were improved slightly as well.

In Chapter 1 we mentioned that up to three components are considered to represent the variability of regionalized variables : a deterministic component, a correlated component, and a random component. In Chapter 2 we considered some of the models based on the assumption of randomly distributed values: the random component was assumed to be the only one present. In Chapters 3 to 11, more general but also more complex models were described, based on the assumption that the values were correlated with the possible presence of random noise. In this chapter we introduce a model used to analyse non- stationary data, for which a deterministic component (or drift) must be assumed. This model will be used for estimation purposes, and the corresponding optimal linear estimation procedure is known as universal kriging. The theory of universal kriging is much more complex than the theory of kriging. Fortunately, in the majority of mine valuation problems the drift can be ignored and the simpler form of kriging can be used.

Jan 1, 1978

By K. F. Lane

Mine planning is a complex function and also a vital one. The quality of the planning has a profound effect on the efficiency and the economics of every mining operation. It is therefore important that the function should not be reliant upon only a few techniques but should have command of an orchestra of them. Then the most appropriate can be selected for each application or, if it is advantageous, a group can be employed in concert. This paper introduces peripheral algebra as a set of techniques which should be included in the mine planning orchestra. Its objective is primarily to stimulate more development not only of these techniques but also others of a similar kind which will increase the effectiveness of mine planning.

Jan 1, 1987

By S. Maluadzi, D. Rocchi, S. Luyckx, S. S. Potgieter-Vermaak, C. Machio, J. H. Potgieter

The aim of this work was to compare the corrosion behaviour of thermal spray WC ? based coatings before and after annealing. X-ray diffraction (XRD) was used to determine the phases present in the coatings at various stages. The corrosion resistance of the coatings was measured using electrochemical and immersion corrosion tests. The results obtained from electrochemical corrosion (quantified by corrosion current density) and immersion corrosion tests showed that annealing appears to decrease the corrosion resistance of the coatings. From the XRD results it was determined that the phases that corroded preferentially were cobalt (Co), eta (Co6W6C) and W2C. Keywords: Corrosion, thermal spray, coatings, hardmetals.

Jan 1, 2006

By V. P. Kolosyuk, A. M. Bryukhanov

Occurrences of hazardous events (explosions of methane or coal dust, fires, outbursts) have been investigated and presented as a flow of events in time. It has been shown that flows of hazardous events in a long time span are homogeneous, stationary and no-after effect flows and can be considered as stationary Poisson flows. A flow of CH4/coal dust explosions that had happened for the last 27 years in Ukraine was analyzed. The explosions have been statistically processed. Practicability of agreement of statistical and theoretical data on mathematical expectation and mean square deviation of time interval between explosion and the explosion intensity has been stated. Probability of an emergency event in time is expressed through an exponential function, while mathematical expectation of an accident and mean square deviation of time interval between successive explosions are in inverse proportion to the accident intensity. Accident probability for practical purposes can be determined as a product of accident intensity by calculated time interval.

Jan 1, 2003

By J. T. Collins, C. J. Cloete

Secunda Collieries forms part of Sasol Coal, the coal division of the Sasol Group of companies, and already produces 29 Mt of coal per annum from its four collieries: Twistdraai, Brandspruit, Bosjesspruit, and Middelbult. The successful establishment of this mining complex was achieved only through a unique team spirit in which the central services and the decentralized teams under the leadership of the mine management of each of the four mines played an important role. The Secunda mining complex has now reached the optimization phase, during which the mining cost, productivity, safety, and quality of work become as important as production. The setting of priorities and problem solving over the long, medium, and short term are essential for improving the performance of the four collieries. Management had to adapt to the fast-changing environment during the enormously fast build-up of production. The major challenges in the environment were posed by the frequent dolerite intrusions, the extremely hard cutting conditions caused by carbonated nodules and thin sandstone intrusions in the coal seam, and excessive roof and face pressure in some areas due to semi-massive sandstone formations in the rock strata.

Jan 1, 1986

A brief overview is given of the issues regarding the processing of waste electrical and electronic equipment (WEEE). The printed circuit board component of WEEE is an exceptionally complex feed to possible recycling processes. Scrap printed circuit boards were selectively smelted at 1 200°C to produce a metallic alloy. Iron and aluminium were found not to be part of the alloy. The alloy was characterized by SEM-EDS, and three phases were identified: alpha and delta bronzes, and a lead-rich phase. Calculations show that about 56 mass per cent of the alloy is the alpha phase, 35 per cent delta phase and 9 per cent lead phase. A simplified approach using appropriate binary phase diagrams was used to derive a phase composition for the alloy. This was further backed by FactSage calculations, which showed that the simplified approach was appropriate for this alloy. The experimental findings and theory were found to agree well.

Jan 1, 2009

The kinetics of adsorption of gold di-cyanide onto activated carbon has been investigated extensively over the past two decades. These studies have demonstrated that both film and intra-particle mass transfer affect the kinetics. The dominant mechanism of intra-particle mass transfer has not yet been identified. In the work described, surface diffusion and pore diffusion are considered as possible rate-determining mechanisms of intra-particle mass transfer. Mathematical models are described that incorporate film mass transfer and the respective intra-particle mass transfer mechanism with equilibrium described by a Freundlich isotherm. Rate constants of film mass transfer and pore or surface diffusivities were estimated by the fitting of the respective models to experimental carbon adsorption data. The estimated pore diffusivities, after they had been corrected for the porosity and tortuosity of the carbon, were found in most instances to be higher than the molecular diffusivity of dilute gold di-cyanide in aqueous solution. This situation is not physically viable. The surface diffusion mechanism acting in parallel with the pore-diffusion mechanism is thus responsible for the intra-particle transportation of most of the gold.

Jan 1, 1996