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By R. M. S. Falcon, L. M. Falcon

The prediction of the mechanical behaviour of South African coal on the basis of current proximate and other chemical parameters gives rise to problems, and the use of ultimate analyses and inferred maceral and rank analyses, although it has improved the situation to some extent, is still not satisfactory. In an attempt to reach a new level of understanding, this paper gives an in-depth review of the fundamental petrographic characteristics of coal and compares these parameters with the main types of mechanical performance. A two-tiered system of primary and secondary parameters is proposed for the prediction of coal behaviour. The primary or inherent parameters include rank and organic composition. The secondary or extraneous factors include such parameters as mineral mater, cracks or cleats, degree of oxidation, and size. In addition, an explanation is offered of several anomalous behavioural conditions in some South African coals.

Jan 1, 1987

By G. A. Slabbert

The paper describes work undertaken to identify the influence of the matrix structure on the metal dusting rate of stainless steel alloys. Specifically, the difference in metal dusting rate between austenitic and ferritic stainless steels of similar chromium contents was investigated. The alloys were exposed to metal dusting conditions and their performance compared by weight loss, optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The specific gas mixture used for all the tests were 18.9% CO-79.1% H2-2% H2O at 650°C. For austenitic stainless steels, Types 304, 321, 316, and 316Ti were compared to two ferritic grades, namely Types 430 and 441. The resistance of the ferritic grades was found to be significantly better than that of the austenitic grades. This was attributed to greater permeability of chromium through the matrix structure to maintain the protective oxide scale. The results will be used in the development of novel alloys to combat metal dusting.

Jan 1, 2013

By I. Ngo, L. Q. Ma, J. S. Guo

Deformation of gob-side entries has always been a critical concern for ensuring stability in longwall coal mines. This paper addresses the significant deformation and support challenges that arise in thick and hard roof longwall faces (THRLF) due to dynamic pressure. The study aims to elucidate the characteristics and mechanisms of deformation during the retreat of the longwall face. The research findings indicated that the primary cause of deformation was the combination of advanced abutment stress resulting from longwall face mining and the movement of the lateral roof over the chain pillar. To mitigate this issue, we propose a deformation control method known as cutting off the lateral roof (COLR) over the chain pillar. Simulation results demonstrate a significant reduction in roof stress and deformation of the gob-side entry after implementing the lateral roof-cutting technique. These findings provide valuable guidance for effectively managing deformation in gob-side entries, particularly when dealing with thick and hard roof strata.

Aug 3, 2023

By J. H. Bulloch

The paper gives an assessment of the available data on the linear elastic fracture mechanics involved in stress corrosion cracking and in the behaviour of reactor pressure-vessel materials exposed to a simulated pressurized water-reactor environment. As a result of the different experimental techniques used in the various studies mentioned, only a few detailed conclusions can be drawn. The data from constant-displacement wedge-opening loading (WOL) tests, with the exception of one study, exhibited very limited or no crack extension during exposure periods of up to 14000 hours. The data from constant-load tests indicated evidence of crack extension, but the nature and extent of the crack extension are still unclear. When crack extension did occur, it was exclusively transgranular in nature. Certain differences in the available test data are tentatively explained in terms of the experimental procedures used, and the need for a consistent code of experimental techniques is highlighted.

Jan 1, 1987

By M. J. Southwood

SYNOPSIS Experiments carried out under atmospheric pressure and temperature (25°C) and sterile conditions show that the dissolution rate of nickel and copper from a pyrrhotite-pentlandite-chalcopyrite ore in a lixiviant of sulphuric acid is greatly enhanced in the presence of pyrite. At a pH value of 1,8 and in the presence of pyrite of equal mass to that of the ore, the recoveries of nickel and copper improved dramatically (21 and 80 per cent respectively). At a pH value of 4,0 the recovery of nickel was enhanced, but the chalcopyrite was refractory. A galvanic mechanism is probable, but cannot be proved from these experiments. The economic implications of the results are discussed.

Jan 1, 1985

By I. R. M. Chaston

A full and detailed description is given of the dense-medium cyclone plants used in Africa for the recovery of diamonds.

An investigation into the stability of large open stopes at Premier diamond mine, Culinan, South Africa, is described. The open stopes are located in a weak kimberlite orebody, directly underneath a 75 m-thick sill of gabbro. Two and three-dimensional stress analyses were carried out in a back-analysis of the stresses and failure around the first open stope created under the sill. The results were used in the prediction of the future stability of the planned open stopes, intervening pillars, and sill.

Jan 1, 1987

By S. C. Thorley, J. R. Menasce

Trackless mining in low profile (LP) and extra low profile (XLP) platinum stopes has forced equipment designers to re-evaluate their equipment profiles to match the undulating reef. Low profile equipment designed to work in conditions with smooth and flat floors will simply not function with undulating floors and roofs and will become wedged between the floor and roof, beached on undulations due to lack of ground clearance, or suffer excessive mechanical damage. Tyres, too, need special evaluation, as conventional tyres for trackless mining do not work in an extra low profile environment.

Jan 1, 2004

By O. L. Papendorf

The method presented in this paper can be used, instead of lengthy cash-flow determinations, for the calculation of present values in the face of physical growth and inflation.

Jan 1, 1981

By J. O. Jensen

A method is described for the determination of cyanide in gold slurries, based on amperometry. The measured current is proportional to the concentration of cyanide, and is not effected by pH or by the concentration of oxygen in solution. It is also unaffected by other ions that may be present in gold-leaching solutions, including sulphide, thiocyanate, and thiosulphate. The current depends on the temperature, and an activation energy of 17,9 kJ/mol was determined Since the current is controlled by the mass transfer of cyanide to the anode, it depends on the conditions of agitation. In tests on an operational gold plant, slurry was pumped directly from the top of the leaching tank, through the measuring cell and back into the tank. The results indicate that the instrument is a promising alternative to the instruments currently available. The readings from the instrument remained in calibration for at least two days, showing that the instrument would need to be re-calibrated by the operating staff at regular periods.

Jan 1, 1994

When designing coal mine roof support, it is necessary to account for the uncertainties and variability that inherently exist within the rock mass and support elements. The performance of a support system is affected by these uncertainties, which are not taken into account in the current deterministic design methodologies used in South Africa. The key to the design of a roof support system is a better understanding of roof behaviour and uncertainties that can been countered during extraction. This paper sets out to develop a method that takes all uncertainties that exist within the rock mass and the mining process into account and provides a quantitative risk-based design methodology.

Jan 1, 2009

By E. C. Stoltz

Note: An electric tin smelter for the processing of Iow-grade tin concentrates in South Africa by E. C. STOLTZ, Pr. Eng., B.Sc. Eng. (Rand) Gold Fields of South Africa Limited is the largest producer of tin in the form of concentrates in South Africa, more than 55 per cent of the South African tin production being produced by the tin mines of the Group. Most of these concentrates are exported to be custom-smelted in overseas smelters, but the modern tendency is for tin-mining countries to establish their own smelters.

Jan 11, 1976

By A. M. Bauristhene

Ti-64, which accounts for more than 50% of the worldwide titanium tonnage, has found commercial importance in industries requiring components with high specific strength and resistance to corrosion. Investment casting is the preferred production method due to the difficult machinability of the alloy. This study was aimed at investigating the mechanism and the extent of alpha case formation on Ti-64 components cast using the investment casting method with YFSZ (yttria fully-stabilized zirconia) shell moulds after vacuum induction melting. The extent of the reaction between the mould hot face and the molten metal has been studied by varying parameters such as soaking temperature and mould hot face composition, and examining their effects on the reaction with the mould. An increase in the soaking temperature had an effect on the alpha case, both in appearance and hardness, but had no effect on contamination levels by carbon, oxygen, and nitrogen. The depth of alpha case increased with soaking temperature, increasing from 35 µm to 161 µm with an increase in temperature from 1200°C to 1400°C. The micro-hardness profiles provided insight into the effect of the alpha case on the mechanical properties of the Ti-64 alloy by displaying hardness values of 1000 HV0.1 and above, but could not be solely utilized to determine the alpha case penetration depth due to microstructural differences in the unaffected Ti-64, in particular the martensitic microstructure that formed with a fast cooling rate from a higher temperature. Levels of expected contaminants such as Zr, Y, 0, and C were low. The addition of the colloidal zirconia binder affected the interfacial reactions. YFSZ proved to be a thermodynamically stable refractory material, with the alpha case possibly forming as a result of segregation.

Jan 1, 2013

Rock fall accidents continue to be the main causes of fatalities in the mining industry. The occurrence of rock falls in supported stopes implies a failure of the support system. The failure of the support system in turn implies a failure in design. In this paper, ethical issues associated with engineering design are discussed, with particular relevance to stope support design. A risk approach is introduced that will allow designs to be carried out that are compatible with the acceptable risk defined by the mining company management. The implementation of this approach would overcome the ethical shortcomings of current support design practices.

Jan 1, 2007

By M. Gericke

Over the past few decades the commercial application of heap bioleaching technology for the extraction of base metals has become increasingly important, due mainly to the depletion of high-grade ore reserves. Heap bioleaching is widely used for the extraction of copper from secondary copper sulphide ores. The design and engineering aspects of the process have received considerable attention, but issues related to the microbiology of the process have been subjected to less rigorous scrutiny. The major role of micro-organisms in bioleaching processes is to catalyse the regeneration of ferric iron and protons, from ferrous iron and by sulphur oxidation respectively. It is accepted that even the most carefully engineered heaps are heterogeneous in terms of temperature, pH, the presence of anaerobic pockets, irrigation efficiency, and dissolved solutes. Since interactions between solution chemistry, mineralogy, and microbial populations exist in heaps, a better understanding of the correlation between microbial numbers and types with changes in these chemical and physical profiles with time would be beneficial during process design and operation of heaps, and could result in faster start-up times and higher metal recoveries. This paper reviews the role of microbiology in heap bioleaching processes. Aspects such as microbial diversity, identification and monitoring of cultures, inoculation strategies, colonization behaviour, and tolerance to metals and salts are discussed, and the potential contribution of the knowledge to the improvement of the operation and design of heap bioleach processes assessed. Conclusions are drawn with respect to the role of genetic engineering, heap inoculation practises, and remaining areas for future heap bioleaching research and development.

Jan 1, 2012

By S. K. Lahiri, K. C. Ghanta

Design of industrial slurry pipelines is usually performed by applying semi-empirical procedures, requiring a significant experimental study for each project. The mechanisms of suspension flow are not yet completely understood and existing predictive models cover only some aspects of uniform or closely graded particle slurry flows. This paper presents a computational technique for prediction of the velocity and concentration profile in slurry pipelines based on computational fluid dynamics. This model gives numerical solutions for the concentration and velocity distributions in the pipeline cross-section. The model prediction and experimental concentration and velocity profiles were found to be in good agreement. Keywords: pressure drop; concentration profile; particle diffusivity; slurry flow.

Jan 1, 2007

By R. L. Castro

Currently, in several caving operations, the spacing between the drawpoints is determined by consulting Laubscher's design guide (Laubscher 1994, 2000), a methodology based on the gravity flow characteristics of the caved rock. Laubscher's methodology is based upon the height of interaction between adjacent flow zones, but does not allow calculation of primary recovery for a given layout. In this paper the authors present a technical and economic methodology based on the flow that occurs near the drawpoint and the associated development costs to estimate the optimal spacing. The flow model at the drawpoint was validated at the El Teniente mine, which extracts coarse caved rock. To validate the flow model, small-scale simulations using drawpoint clusters were conducted and results compared to extracted grades, marker recovery, and drill holes to determine ore remnants that are part of the production control programme at the mine. The results indicate that primary recovery depends on the height of interaction, which varies with the friction angle of the caved rock and the spacing between adjacent drawpoints. Primary recovery estimations indicate values from 85 per cent to 97 per cent depending on the drawpoint spacing used. Extrapolations were then conducted to estimate the primary recovery for different drawpoint configurations planned to be used in the New Mine Level of the mine. The results indicate that the optimal drawpoint spacing is 32 m x 20 m with a through length of 18 m. The methodology developed may be used to estimate optimal drawpoint spacing for block caving mines under different metal prices and mine cost conditions.

Jan 1, 2012

By K. Koruyan

Although remote sensing technology has been available for many years, it has rarely been used for monitoring mining activity. Recent studies indicate that remote sensing is also a valuable tool for managing and planning certain aspects of the mining operation. In this paper, we examine areal expansion of marble quarries and the affected vegetation over a period of 10 years in the Mugla region in Turkey, using geographic information system (GIS) and remote sensing (RS) techniques. Images captured by ASTER Level 3A01 (3D Ortho Data Set), Landsat 5, and Landsat 7 satellites between 2001 and 2009 were used for the analysis. Changes in the natural vegetation as a function of the production level in the marble quarry were calculated using the normalized difference vegetation index. According to the study results, land cover and natural vegetation decreased by less than 3 per cent and 1 per cent respectively between 2001 and 2009, following an upsurge in mining activity in the region.

Jan 1, 2012

By J. M. Stewart

The purpose of my few comments is to try to create a healthy perspective to constructively link considerations of the sessions to follow to those of the earlier sessions. I propose to do this by considering some of the issues and priorities related to the development of backfill systems and technology for South African gold mines.

Jan 1, 1988

The results of small-scale resin-in-pulp pilot-plant investigations at Grootvlei Proprietary Mines Ltd, President Brand Gold Mining Co. Ltd, and Western Areas Gold Mine Co. Ltd are reported. At each mine, a pulp was fed simultaneously to a carbon-in-pulp plant, allowing a direct comparison of the metallurgical performance of the two processes. With the Grootvlei pulp, gold was extracted more efficiently by resin than by carbon owing to the Iow concentration of competing base-metal cyanide complexes in solution. With the Western Areas pulp, the reverse was true because of the high concentrations of copper and nickel in solution. Finally, with the President Brand pulp, resin-inpulp was significantly superior to carbon-in-pulp owing mainly to the inherently slow rate of gold extraction from calcine by activated carbon. Results are presented that show the efficiency of the elution of gold and other elements with a variety of reagents from the loaded resins arising from these three campaigns. At Western Areas, a detailed investigation enabled a preliminary cost evaluation to be made of three techniques for the elution of strong-base resins.

Jan 1, 1984