Search Documents

By C. L. Workman-Davies

Noise is a form of pollution arising mainly from the activities of man. One such activity is mining, in which man, as in many of his other activities, uses machinery of various kinds to achieve safe, healthy, and economic production. Trackless mining makes use of an advanced state of technology over that required In traditional mining methods. One of the advantages of the former, as distinct from any disadvantages it may have, is a reduction in noise levels, the number of people exposed to noise, and the duration of their exposure to noise. This paper briefly examines why noise is a problem and what various countries are doing about it in terms of standards, codes of practice, and regulations. It also investigates the extent to which noise is a problem in mining and how trackless mining alleviates this problem. The question is then posed as to whether South Africa is not setting too high a standard at this stage of its national development by comparison with what is being done by other, more-advanced countries.

Jan 1, 1989

It is shown that, when a flat-bottomed indentor is pressed into the surface of a strong rock, the normal force necessary to cause failure of the rock is reduced substantially if a shear force is applied to the indentor. A mathematical analysis is described, which shows that higher stresses are induced in an elastic material close to the free surface of the material ahead of a punch when a shear force together with a normal force is applied to the punch. Therefore, failure of the material would occur with lower forces applied to the punch. Stress trajectories show that fractures develop in the rock along lines of maximum principal stresses.

Jan 1, 1978

By H. W. Read, L. G. D. Napier

Change is endemic in our society. Future change will be accelerated by an explosion in technology, communication, and political thought. To meet these challenges, rapid structural changes have been taking place in mining organizations both here and abroad. The management of shaft-sinking projects is a case in point. Shaft sinking is a seminal element in the sustained well-being of a deep level mining venture. Its accomplishment is fraught with risk, involves a high level of capital expenditure, and is a precursor to profitable mining investment. The purpose of this paper is to present a concise and practical picture of the concepts, methods, and techniques of professional project management as applied to shaft-sinking projects.

Jan 1, 1994

By J. N. Van der Merwe

It is shown that the safety factor as calculated traditionally by use of the tributary-area theory is not valid for high-extraction methods of coal mining. An alternative approach is suggested in which the pillar loads are calculated more realistically for the period during which pillar extraction is in progress. This safety factor, which is known as the Extraction Safety Factor (ESF), can be used in determining the effects of strong layers in the overburden on pillar sizes.

Jan 1, 1990

By E. J. Magri

This paper describes a geostatistical study of the relative merits of diamond-saw sampling and conventional chip sampling, using results from experimental work carried out on Randfontein Estates Gold Mine and Western Areas Gold Mine. The diamond-saw sampling procedure is described, and it is concluded that this is a very efficient operation and leads to good-quality sampling that is clearly an improvement over conventional chip sampling. The study principally involved the computation of the errors of estimation of the mea gold value of mining panels for the two sampling methods, revealing that, in the normal production environment, the diamond-saw sampling method is a significant improvement over conventional chip sampling, as evidenced by the reduced estimation errors achieved. The question of optimum sample spacing is discussed, and it is concluded that the required spacing for chip sampling needs to be smaller than for the diamond-saw method.

Jan 1, 1986

Currently the most widely used formula in pillar design is the power formula, which implicitly assumes a volume effect. This assumption is critically examined, and it is proposed .that a limiting strength value, the critical rock mass strength, be used for pillar design instead. A methodology is provided to determine this value. It is suggested that the effects of geometry on pillar strength are well described by a linear function and the power formula, for w/h ratios less than or equal to about 5. This approach together with the use of the critical rock mass strength, removes the volume effect. Various factors that affect pillar strength are examined. The concept of explicitly determining the stability of each component in the pillar system is briefly discussed. It is proposed that pillar design be expanded to a pillar system design procedure that incorporates the interaction of the pillar, roof and floor strata, and the loading system.

Jan 1, 1998

By G. A. Wiebols, N. G. W. Cook, N. C. Joughin

Introductory remarks Dr N. G. W. Cook: This paper was published in your Journal in May of this year and you will, therefore, have had the opportunity of reading it over the past six months. I can state that experience has shown that the paper is substantially correct, but a number of questions have to be answered. The first question, Mr President, that I would be happy to answer, is how is it that one is able to cut hard, abrasive quartzite with a strength some six times greater than that of good concrete? The essence of the answer is that there is a tremendous difference between abrasion, or scratching, and cutting, or chipping. For example, it is well known that a diamond will scratch or abrade almost anything. It is also relatively easy to chip, crack or crush a diamond. As a demonstration I have here an ordinary bench grinder, and with the bench grinder I also have a piece of tool steel. The wheel on this bench grinder is a silicon carbide wheel, which is an extremely hard material, and the tool steel is much softer. In rock-cutting we use tungsten carbide for cutting the quartzite. The quartzite and the tool steel have roughly the same hardness. You can sharpen tungsten carbide with a silicon carbide wheel. In fact, this is done. It won't surprise any of you, therefore, when I show you that tool steel can be sharpened with silicon carbide. Now, what I propose to do is to change the configuration of this experiment and use the soft tool steel to cut silicon carbide, and if I can do that, I think you will agree that I have gone some way to being able to cut quartzite, which is about as hard as tool steel, with tungsten carbide, which is harder than quartzite. Let me do this. (Demonstrates.) That, I think, is a very clear demonstration of how it is possible, with a metal, to cut an extremely hard and brittle material. What, essentially, is the difference that we have here? In the first case, I held the tool with a relatively low force against the hard silicon carbide wheel. This generated a relatively low average stress, which was insufficient to fracture the carbide wheel. Nevertheless the protuberances on the silicon carbide wheel indented the tool steel and abraded it at a multiplicity of points, and quickly reduced the section of the tool steel that I held against the wheel. By changing the configuration and clamping my tool steel in a firm post, against the silicon carbide wheel, I changed these conditions very extensively. I now had a high force. I had to exert a considerable moment on that lever. The tool was anchored so that it could sustain these high forces, and they generated high stresses, which were adquate to fracture the silicon carbide. Now, what about wear? It so happens that, in these two experiments I have just done, the power I was using was about the same-a small fraction of a horse power.

May 1, 1968

By D. R. Hardman

South Africa is the third-largest supplier of coal on the world's export markets after Australia and the USA, and the second-largest supplier of bituminous steam coal following Australia. There are many Similarities between the coal industries of South Africa and those of Australia and the USA, in contrast to the coal industries in Europe. For South Africa to maintain a competitive position on the export markets, it must continue to compete against these two countries. It is therefore important that the performance of the loca1 coal industry should against that of the Australian and US coal industries. Although financial performance is the major criterion, financial information is not easily obtained, and the paper therefore uses employee productivity in the form of tonnes per man year as a means of comparison. The paper reviews recent trends in the level of production and numbers of employees prior to review1ng the productivity. The influence on productivity of some mining methods is highlighted. It is realized that published information (information available within the public domain) can contain anomalies, but every effort is made to compare data of a similar type. Notwithstanding possible inaccuracies, it is shown that South African coal-De productivity lags far behind that of Australia and the USA. The significance of the difference is that the South African coal industry is able to apply overseas practices and procedures that have been shown to give improved performance, and that the increased use of more productive extraction techniques has limited application.

Jan 1, 1996

By G. T. van Rooyen

Materials for Winding Plant Components By Prof. G. T. van Rooyen (ScD) (MIT). Materials for critical applications such as winding plant components are reviewed in terms of the basic requirements which have to be complied with. It is shown that tensile testing alone is not sufficient and that impact testing also is necessary if the incidence of brittle fracture is to be avoided. As a criterion it is suggested that the brittle transition temperature (B.T.T.) determined by impact testing should in all cases be well below the lowest anticipated service temperature. A number of steels were evaluated by impact testing and it is shown that a small ferrite grain size, obtained either by chemical means such as by the use of appropriate alloying elements in the steel or by means of a quenching heat treatment, is effective in attaining a Iow B.T.T. The speed of strain aging as well as the influence of strain aging on the B.T.T. was also evaluated. On the basis of the results obtained it is recommended that steels for critical applications must conform to an appropriate grade and class of steel according to BS 4360 specification. It is further recommended that such steels be exempted from the customary six-monthly heat treatment prescribed by the Mines and Work Act, Regulation 16,18.

By Z. T. Bieniawski

Estimating the strength of rock materials by Z. T. BIENIAWSKI, Pr.Eng., D.Sc.(Eng.) (Visitor) A practical approach for estimating the strength behaviour of rock materials is presented. The demand for data on rock properties in engineering design is considered, and it is shown that, based on the trends observed in the South African mining industry during the last twenty years, simple and easy-touse methods for the estimation of the uniaxial and triaxial strength of rock materials are needed. It is shown that the uniaxial compressive strength of rock can be conveniently determined from the pointload strength index, which is obtained underground on unprepared rock cores. The triaxial strength of rock can be estimated for most practical purposes from empirical strength criteria. Two such criteria are proposed that allow estimation of the triaxial strength for rock materials to about 10 per cent. The only input required for these criteria is the uniaxial compressive strength. The validity of the practical approach outlined in this paper is confirmed from the experimental tests conducted on some 700 rock specimens representing five rock types. A practical example for the prediction of rock strength is given.

Jan 3, 1974

By A E. Paterson

General aluminium corrosion charts based on 1100 alloy listing product and temperature have been developed by AFSA, mainly from available sources. The categories of corrosion expectation are fairly wide. As a result the charts are more useful in indicating what is not suited as distinct from what is. The question of how to develop useful information is assessed. Having discarded improbable options one is left with the need to refine the possible. Within each alloy group corrosion potential differs. From an engineering application point of view, the corrosion resisting marine alloys, the 5xxx series show increasing corrosion as the percentage of Magnesium increases. An important issue is that as the welding filler used for 5xxx series is Mg rich (to avoid hot cracking), the filler is likely to show the weakest resistance. In addition, when subjected to fatigue loading, the preference for critical joints is to dress the joint to the level of the base material. Overheating of the weld extends the HAZ zone and weakens the material as Mg moves to the grain boundaries. Indicator chart refinement approaches suited to aluminium use in commercial transport are discussed.

Jan 1, 2006

By J. P. G. Pretorius

The size effect in tests of the compressive strength of coal specimens differs from predictions based on the Weakest Link theory. Predictions of the size effect in tensile tests on lengths of cotton yarn and glass fibre, the behaviour of which is analogous to the weak link process, also differ from observations. This discrepancy is shown to be caused by the correlation between the strengths of the unit lengths in a composite specimen. The Weakest Link theory is reformulated as the Weakness Correlation theory to account for such correlation. It is shown that weakness correlation is found in rock and it is concluded that at least part of the discrepancy between the predicted and observed size effect in rock strength tests could be attributed to this correlation.

By S. V. Rungan

The modern mining industry is increasingly being tasked to comply with various legal, industry and social prerequisites. In addition to complying with these, the mining industry is further expected to effectively report on their compliance. Although there are many models that aid the mining industry in compliance and reporting, it is perhaps opportune for a new model to be introduced. The Compliance Spindle is postulated as a new and alternative model which is easy to understand and has the possibility of implementation in South Africa and other jurisdictions as well. The Compliance Spindle is also an effective tool to educate future compliance officers. The new model provides for all aspects of compliance and reporting and can be easily modified to take account of new developments in the mining compliance and reporting arena.

Jan 1, 2010

By M. Kumral

One of the most significant elements in solving the co-kriging equations is the matrix solver. In this paper, the singular value decomposition (SVD) as an equation solver is proposed to solve the co-kriging matrices. Given that other equation solvers have various drawbacks, the SVD presents an alternative for solving the co-kriging matrices. The SVD is briefly discussed, and its performance is compared with the banded Gaussian elimination that is most frequently used in co-kriging matrices by means of case studies. In spite of the increase in the memory requirement, the SVD yields better results.

Jan 1, 2012

By P. K. Van Manen

Anglo Platinum's Polokwane Smelter is situated outside Polokwane, in the Limpopo Province of South Africa. Wet concentrate is received from various concentrators along the Eastern Bushveld Complex. Approximately 60% of the total concentrate received is from UG2 Reef, and 40% is from Merensky Reef. The concentrate is dried in two flash dryers, and smelted in a single 168 MVA furnace. A PGM-rich nickel-copper matte is cast, crushed and transported to Rustenburg for converting. The plant was commissioned in March 2003. The wet concentrate, containing 12-18% moisture, is weighed, sampled by one of two auger samplers, and off-loaded into a concentrate shed, either directly through a grizzly into a hopper, or onto the floor. From the shed the concentrate is conveyed to 12 concrete silos. Each of the two identical flash dryers can be fed from six silos. From the flash dryers concentrate is transported pneumatically to a 3 000-ton dry concentrate storage silo. The flash dryers are rated at a nominal 66 tph of dry concentrate at 14% moisture, while the furnace can smelt 90 tph of dry concentrate. Therefore both flash dryers are required to operate when the furnace runs at design throughput. Each flash dryer consists of a hot gas generator (HGG), a disintegrator and drying column, and a section for gas/solids separation. In the HGG, gas heated up to 700° C is produced from the combustion of coal peas in a fluidized sand bed. The hot gas and wet concentrate are introduced to the disintegrator at the bottom of the drying column. The disintegrator breaks up any lumps of concentrate, and throws the concentrate up into the drying column, where it travels co-currently with the hot gas. A fan draws the hot gas from the drying column and through the gas/solids separation section, which consists of three primary cyclones, a multiclone and a high-temperature bag house. The dry concentrate reports to a 450-ton dry concentrate storage bin. A portion of dry concentrate is recycled to the wet concentrate feed in a paddle mixer, so that concentrate that is too wet does not enter the disintegrator. The drying column outlet temperature is controlled at 120° C. Coal is received by road, screened for oversize and conveyed to a 400-ton concrete silo. From here it is pneumatically conveyed to a small feed bin at each of the HGG' s. The optimization work consists of process control improvements relating to the HGG outlet temperature, to control the drying column temperature during the ramp-up of the HGG outlet temperature and bag filters. Furthermore a heat balance is used to evaluate options to increase the instantaneous drying capacity of the existing equipment. The coal consumption derived from the heat balance is compared with the actual coal consumption. The purpose of the optimization work is to achieve an operating schedule for the flash dryers such that they operate simultaneously for as short time as possible. Most of the time one flash dryer should operate, allowing maintenance to be done on the other flash dryer, while drawing down the dry concentrate stock. Keywords: Anglo Platinum, Polokwane Smelter, pyrometallurgy, metallurgy, platinum, platinum group metals (PGM), base metals, flash drying, fluidized bed.

Jan 1, 2006

By J. Gholamnejad

Determination of the optimum cut-off grades is one of the most important aspects of mine production planning. A cut-off is a grade below which we choose not to process material. This material is treated as waste and dumped. Dumping waste is accompanied by the rehabilitation cost which will affect the overall cost of final production and also the optimum cut-off grade. Rehabilitation cost is the cost per ton of rehabilitating material of a particular type of rock after it has been dumped as waste. One of the most popular algorithms for determination of the optimum cut-off grade is Lane?s method. Lane formulated the cut-off grade optimization, but he did not consider rehabilitation cost during the optimization process. This cost item should be evaluated first, and then considered during the cut-off grade optimization process. In this paper the rehabilitation cost is inserted directly into the cut-off grade optimization process using Lane?s theory. The cut-off grades obtained using the suggested method will be more realistic than ones using the original form of Lane?s formulations.

Jan 1, 2009

By Lene Hansen

Sulphuric acid plants now and then see unexpected increases in SO2 emissions. Our experience is that it is not always easy for the acid plants to pin point the exact reason for the SO2 increase. Sometimes a catalyst bed is sacrificed even though reliable emperature readings and gas analyses could have verified satisfactory activity, hence the leaking heat exchanger is never discovered and after the shutdown the SO2 emissions are still too high. This paper will look into some basic catalyst management tools: Good record keeping is a necessity for collection of representative catalyst samples, reliable operating data is an inevitable starting point for all analysis and trending of operating data is a must for plant optimisation and troubleshooting. In addition these catalyst management tools will give a continuous updated knowledge of the catalyst status in each bed providing the basis for a more effective replacement strategy. The most typical reasons for increasing SO2 emissions will be presented together with easy guidelines for cross-checking of operating data, temperature optimisation and good record keeping.

Jan 1, 2009

By C. Fiore, A. Kok, W. C. Coningsby

Quarrying is a comparatively simple process which is open to certain economic pitfalls, One of these is the appropriate size of the equipment needed to meet demand.

Jul 1, 1970

By B. Kenealy

A typical deep shaft is President Steyn No. 2 in the Free State, where 9 tonnes of ore are hoisted at about 15 metres per second from 2378 metres below surface. The skips and attachments each weigh 7 tonnes and they are connected by 43 tonnes of rope, so that to hoist the 9 tonnes of payload, a total of 66 tonnes is accelerated from stand still to 55 km/h for each cycle, using an average of 3185 kilowatts of power in the process. The cycle time for the hoisting is 3.22 minutes. The peak power consumption is 6954 kilowatts, which determines the size of the motor used. Is this the right approach? Are larger skips moving at higher speeds the answer? Is there another way?

Jan 1, 1996

By D. A. Viljoen

While coal can be used as a chemical feedstock instead of oil for the production of the petrochemical based commodities that are so important to our modern way of life, the impact that coal is going to make on the world-energy scene is without doubt its more important role in the short- to medium-term. After inflation, energy is probably today's most talked-about and controversial economic issue. It is a plentiful supply of energy that has permitted each of us to live a life of convenience that is matched only by the most fortunate of the aristocracy in history.

Jan 1, 1979