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By J. L. Havenga, L. J. van der Walt, J. T. Nel, H. Bissett

"SynopsisNew technologies used to manufacture high-quality components, such as direct laser sintering, require spherical powders of a narrow particle size distribution as this affects the packing density and sintering mechanism. The powder also has to be chemically pure as impurities such as H, O, C, N, and S causes brittleness, influence metal properties such as tensile strength, hardness, and ductility, and also increase surface tension during processing.Two new metal powder processes have been developed over the past few years. Necsa produces zirconium powders via a plasma process for use in the nuclear industry, and the CSIR produces titanium particles for use in the aerospace industry.Spheroidization and densification of these metal powders require remelting of irregular shaped particles at high temperature and solidifying the resulting droplets by rapid quenching. Spherical metal powders can be obtained by various energy-intensive methods such as atomization of molten metal at high temperatures or rotating electrode methods. Rapid heating and cooling, which prevents contamination of the powder by impurities, is, however, difficult when using these methods for highmelting- point metals. For this reason plasma methods should be considered.Thermal plasmas, characterized by their extremely high temperatures (3000–10 000 K) and rapid heating and cooling rates (approx. 106 K/s) under oxidizing, reducing, or inert conditions, are suitable for spheroidization of metal powders with relatively high melting points. Thermal plasmas for this purpose can be produced by direct current (DC) plasma arc torches or radio frequency (RF) inductively coupled discharges. In order to obtain chemically pure spheroidized powder, plasma gases such as N2, H2, O2, and CH4 cannot be considered, while Ar, Ne, and He are suitable. Neon is, however, expensive, while helium ionizes easily and it is therefore difficult to obtain a thermal helium plasma at temperatures higher than 3000 K. Therefore argon should be used as plasma gas. Residence times of particles in the plasma region range from 5–20 ms, but this is usually sufficient as 7–8 ms is required for heating and melting of titanium or zirconium metal particles in the 30 µm size range at 3500 K. In this study the melting and spheriodization of titanium powders was investigated by DC non-transferred arc and RF induction plasma methods. The powders were characterized before and after plasma treatment by optical microscopy and scanning electron microscopy (SEM) to observe if any melting or spheroidization had occurred."

Jan 1, 2015

By C. Dorfling, M. Tadie, M. Tucker

Electrowinning is the final step in the hydrometallurgical production of high purity copper, involving the passage of electric current through an electrolyte and consequent plating of solid copper to form cathode sheets. Key electrowinning performance indicators are the current efficiency, specific energy consumption, yield, and quality of the metal. The high energy demand and associated cost mean that determination of performance indicators is critical during operation, but ‘online’ measurement is impractical due to the nature of the measurements and corrosive environment brought about by acid mist. This research considered the development of a predictive electrowinning model as a shift towards a pre-emptive approach to attaining plant performance data. A steady-state model was created from input variables available in the industry, using a first-principles approach combining mass balances, electrochemical and thermodynamic equations, and property correlations. A circuit diagram equivalent of an electrowinning cell, containing multiple pairs of electrodes, was used as the backbone of the model. The kinetics of each electrochemical reaction were modelled including iron as a major impurity. Losses in current efficiency due to ineffective electrode contact, short circuits, and stray currents were also incorporated. The model was used to predict the current efficiencies for tests performed at varying conditions in a bench-scale electrowinning cell; the average absolute error between the measured and predicted current efficiencies was 3.2%. The model requires a unique parameter fitting approach for each industrial operation; if parameters are customised for specific plants, the model will be a useful tool to predict performance and can aid the development of effective process control systems in copper electrowinning tank houses. Keywords: Copper; current efficiency; electrowinning; modelling; plating rate

Jan 1, 2020

By R. Altındag, D. Akbay

The point load index is a simple, fast, and inexpensive method for determining rock strength and can be applied both in the field and in the laboratory. There are, however, some disadvantages and limitations to the method, and the test results can be affected by the person carrying out the test, the rock characteristics, or the test device. In this study we describe an investigation into how the point load index value is affected by the shape of the conical platens used in the test. Point load index tests were carried out using different devices fitted with conical platens of different spherical radii, and on a modified device which circumvented the limitations/disadvantages. It was seen that the point load index value increased as the platen radius increased, as expected. In the case of testing using non-standard conical platens, an equation is proposed to normalize the point load index value with respect to the standard spherical radius value.

Nov 1, 2021

By P. Valicek

Anglo American Platinum Limited is constantly striving to improve safety and productivity. There are many different initiatives taking place within the organization in order to ensure continued safe operation and profitable ounces for the future. One of the opportunities and potential growth areas that has been identified and is being explored is that of mechanization. In order to do this, the approach that has been adopted by Anglo American Platinum is to fully understand and analyse the current mechanized mining methods. Once each configuration is fully understood, the method can then be optimized and new mining technologies and systems can be developed to overcome the current shortfalls. This paper will discuss a methodology that was developed by Anglo American Platinum (in conjunction with Cyest Corporation) and adopted to optimize the mechanized mining layout and fleet configuration, and will also present the final findings of the study. Due to the impracticability of piloting every possible option in the workplace, extensive modelling and simulation exercises were conducted to determine realistic parameters for productivity and value. The study resulted in a full understanding of mechanized mining systems and their associated layout. From the results of the study a mining / logistic layout was developed which highlighted the following opportunities: 1. Create safe operations through the reduction of personnel in the ?high-risk zone? of stopes 2. Separate machines and personnel by use of remotely operated machines 3. Create focused mining on primary development from the production stoping, thus having dedicated teams on development and stoping. 4. Develop primary development ahead of the stoping activity. This enables: a) Understanding of the geology and subsequent implementation of the correct b) technology (?fit-for-purpose?) required to mine that area based upon this geological knowledge c) Ability to install tipping points ahead of stoping, creating ?immediate stoping reserves?, thus increasing flexibility and reducing production risk d) Improved productivity by having adequate faces available and reduction in re-development to establish faces. 5. Quicker return on Investment due to recovering revenue from ?on-reef development? 6. The layout allows flexibility between stope sections enabling better ?resource sharing? 7. Optimize the long-term ratio of machine makeup of the fleet in relation to the production outputs 8. Creates an agile mining layout allowing rapid response to market pressures. The findings and work presented in this paper is currently being implemented at different test sites within Anglo American Platinum and will demonstrate that improved safety and productivity can be achieved through the adoption of mechanization.

Jan 1, 2012

By R. B. Khumalo, M. S. Nyarela, R. C. Nemathithi

Palabora Mining Company is one of the largest low-grade copper mines globally. The mine uses block caving for the extraction of the orebody. This paper enumerates the drawpoint loading strategies for the overall head grade improvements, particularly for a block that is nearing depletion. A comprehensive literature review of various considerations relating to improving productivity in block caving is presented to contextualize the draw control in caving. From this study, an optimized draw control strategy is presented, which focuses on three parameters that include grade distribution, loading compliance, and tonnage splits per sector. An empirical method based on the relational study between various parameters is used to outline the key criteria to be used in the optimization of drawpoint loading in block caving.

Nov 30, 2022

By J. G. M. Mukoya, B. Adebayo

"This work was carried out to determine the influence of rock properties and drilling machine parameters on the penetration rate at the SJ pit of Rössing Uranium Mine, Namibia. Rock properties (uniaxial compressive strength, tensile strength, and modulus of elasticity) of samples collected were determined in the laboratory. Drilling experiments were conducted in which feed pressure, air pressure, rotary speed, weight on the bit, and torque were varied to measure their effect on the penetration rate. The uniaxial compressive strength varied from 90–180 MPa for layered marble-quartzite and banded gneiss. Increases in feed pressure, weight on the bit, and rotary speed beyond the optimum level led to a decrease in penetration rate and caused the drill bit to ‘stall’. Results of the study revealed that penetration rate increases with an increase in the feed pressure and air pressure. After reaching a maximum value, the penetration rate begins to decrease despite increasing feed pressure. A very high torque causes the drill bit to stall, since the feed pressure is too high and the air pressure is not sufficient to remove the cuttings from blast-hole at maxium bailing velocities. The average penetration rate varied from 19 to 45 m/h for phase 2 of the pit, and from 17 to 68 m/h for phase 3. The optimum drilling machine parameters obtained in phase 2 and phase 3 were slightly lower than those currently being used at the mine. The trials of the optimum machine parameters will assist in reducing the cost of drilling, which varied from N$29.48 to N$36.31 per metre for the tricone bit. IntroductionDrilling and blasting contribute most to the operational cost in opencast mining and have the potential to influence the cost of downstream operations (Aipanda, 2011). The drillability of rocks depends not only on the rock properties, but also on the drilling tools and operational variables. In rotary drilling, rotational speed, thrust, and flushing are the operational variables, and are known as the controllable parameters. Rock properties and geological conditions are the uncontrollable parameters. Although, many attempts have been made to correlate drillability with rock properties, the rock characteristics affecting rotary drilling have not been entirely defined (Hartman, 1962; Kahraman, Bilgin, and Feridunoglu, 2003). The drill bit is forced into a rock surface from the rotary power head, hence creating stresses and cracks at the bit-rock interface. The performance of a particular bit in any formation i"

May 1, 2019

By T. Nesane, S. S. Mnyakeni-Moleele, L. C. Murulana

The effectiveness of two synthesized ionic liquids, 1-(benzyloxy)-1-oxopropan-2-aminium 4-methylbenzenesulfonate (1-BOPAMS) and 4-(benzyloxy)-4-oxobutan-1-aminium 4-methylbenzenesulfonate (4-BOBAMS), were evaluated for mild steel corrosion inhibition in 1.0 M hydro-chloric acid solution, using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and gravimetric techniques. Organic moieties responsible for the adsorption process on mild steel surface were investigated using Fourier transform infrared spectroscopy (FTIR). Gravimetric analysis revealed that the inhibition efficiency of 1-BOPAMS and 4-BOBAMS increased with concentration, with maximum inhibition values of 90.32% and 97.91%, respectively, at the highest concentration of the inhibitors. Gibbs free energy (ΔG°ads) values indicated a strong interaction between the mild steel surface and the molecules of the ionic liquids, and that the adsorption process was spontaneous. These values also show that the inhibitive nature of ionic liquids against mild steel corrosion is caused by a mixedtype of adsorption film formed on the steel surface. The Langmuir adsorption isotherm was used to describe the adsorption of ionic liquid molecules onto the mild steel surface. Polarization curves showed that 1-BOPAMS and 4-BOBAMS have a similar effect on both the anodic and cathodic half-reactions, indicating that they prevent the dissolution of mild steel through both physical and chemical process. Nyquist plots were defined by incomplete semicircle capacitive loops, showing that the charge transfer mechanism controls the corrosion of mild steel in acidic solution.

Apr 1, 2021

1. Book review Technology of metal powders- recent developments, edited by L. H. Yaverbaum. New Jersey, Noyes Data Corporation, 1980. 400 pp. (Reviewer: B. K. Loveday) 2. New books The use of microprocessors, by M. Aumiaux. New York, Wiley, 1980. 176 pp. $25,50. Aluminium smelter technology, a pure and applied approach, by K. Grojtheim and B. J. Welch. Diisseldorf, Aluminium-Verlag GmbH (P.O. Box 1207, D-4000, Federal Republic of Germany). 146 pp. DM48. Coal-bridge to the future. New York, Harper & Row, 1980. $35. System modeling and response.. theoretical and experimental approaches, by O. Doebelin. New York, Wiley, 1980. 576 pp. $26. Environmental and climatic impact of coal utilization, edited by J. J. Singh and A. Deepak. New York, Academic Press, 1980. 646 pp. $39,50. Proceedings of the Third European Conference on Mixing, York, England, April 1979, edited by H. S. Stephens and C. A. Stapleton. BHRA Fluid Engineering (Cranfield, Bedford Mk43 OAJ, U.K.), 1980. 2 volumes. 500 pp. $50. Lignite technology, edited by P. Nowacki. New Jersey, Noyes Data Corporation, 1980. 228 pp. $42. The application of rock mechanics to cut-and jill mining. London, Institution of Mining and Metallurgy, 1980. Papers presented at the Fifth International Symposium on Jet Cutting Technology, Hanover, Federal Republic of Germany, June 1980, edited by H. S. Stephens and B. Jawis. BHRA Fluid Engineering (Cranfield, Bedford Mk 43 OAJ, U.K.), 1980. 438 pp. £38. World coal resources.. methods of assessment and results, by G. Fettweis. Amsterdam, Elsevier, 1979. 425 pp. $80,50. Geophysical and geochemical techniques for exploration of hydrocarbons and minerals, edited by M. Sittig. New Jersey, Noyes Data Corporation, 1980. 300 pp. $40. Financial Times mining international year book 1980. Longman Group Ltd (Periodicals and Directories Division, Longman House, Burnt Mill, Harlow, Essex CM20 2JE, England). £24 surface, £34 airmail. National Symposium on the Availability of Strategic Minerals, edited by M. J. Jones. London, Institution of Mining and Metallurgy, 1980. 109 pp. 3. NIM reports Report No. 1941 The recovery of chromite and platinum from the UG-2 Upper Chromitite Layer .of the Bushveld Complex at the Pandora Mine (first published 10th Mar., 1978). Report No. .2012 A mineralogical investigation of borehole cores from the Trompsburg Complex (first published 6th Apr., 1979). Report No. 2038 The leaching of sphalerite in acidic ferric sulphate media in the absence of elemental oxygen. Report No. 2052 An investigation of the impurities in native gold by neutron-activation analysis. Report No. 2056 The mineralogy and geochemistry of the copper, lead, and zinc sulphides of the Otavi Mountainland. Report No. 2058 A n elementary introduction to image analysis - a new field of interest at the National Institute for Metallurgy. Report No. 2059 Distributed computer control of industrial processes. Report No. 2060 The analysis, by atomic-absorption spectrophotometry, of activated charcoal.

Jan 1, 1980

By S. Bradshaw, A. Mabentsela

"Physical and numerical modelling methods were followed to identify mechanism(s) for tundish slag entrainment in a bare tundish and one with a flow control device (FCD).The physical and numerical models made use of water and paraffin to model steel and slag respectively. Observations from the physical model showed that the steel-slag interface remains immobile in both cases. Entrained paraffin formed droplets approximately 1 mm in diameter. Results from both models (numerical and physical) showed that in both cases (bare and FCD case), areas of high entrained slag concentration exist near the inlet region. The entrained slag concentration decreases towards the tundish endwalls.Flow patterns and velocities tangential to the steel-slag interface from the numerical model showed that slag entrainment in both the bare tundish and tundish with a FCD possibly takes place via two mechanisms. First, the slag moves across the steel-slag interface via mass transfer; secondly small velocities tangential to the interface at depths greater than 10 mm below the interface carry the already ‘entrained’ slag into the bulk steel phase. These tangential flow patterns are dominant in the inlet region, hence the high concentration of entrained slag in this region. IntroductionThe tundish serves as the last metallurgical vessel through which steel passes before solidifying in the moulds. It is in the tundish that the last traces of non-metallic inclusions should be removed, otherwise the inclusions carry over to the moulds and cause defects in the steel product. In the tundish, the slag is less dense than the melt and thus resides on the top of the melt. The slag provides a sink into which the non-metallic inclusions float to and dissolve. The slag also protects the melt from air and heat loss. However, when slag is entrained in the melt as a result of increased turbulence or shearing at the steel-slag interface, slag can become a source of nonmetallic inclusions.Numerous studies on flow patterns in the tundish have been carried out since the introduction of the tundish. These studies were aimed at improving the flow characteristics in the tundish (Chattopadhyay, Isac, and Guthri, 2010; Cloete, 2014; Jha, Dash, and Kumar, 2001; Jha, Rao, and Dewan, 2008;"

Jan 1, 2017

By B. T. McKenna, H. Nirschl, P. Morsch, B. Fränkle

Generally, filter media used in filter presses have a limited operational life. Besides mechanical damage, there is a growing deposition of fine particles with increasing filtration cycles, the so-called blinding, inside the filter cloth. The resulting decreasing pore diameters not only affect the efficiency of the filtration process itself by increasing the filter medium resistance, but also make it more difficult to regenerate the filter press between the individual cycles, e.g. leading to an insufficient cake discharge. Since tailings filtration requires handling of large process flows containing a significant fraction of particles in the lower micrometer range, an investigation into media rejuvenation is of interest. Keywords: Tailings filtration, filter fabric resistance, filter media regeneration, filter cleaning, intraweave contamination

Jan 1, 2020

By A. R. Javadi

Pyrite (FeS2), chalcopyrite (CuFeS2), sphalerite (ZnS) and galena (PbS) generate hydrogen peroxide (H2O2) when placed in water, with pyrite generating the most amount of H2O2. The order of these minerals for generating H2O2 in water is: pyrite > chalcopyrite > sphalerite > galena. In previous research, the methods of generation of H2O2 in the grinding mill were studied. In this study, data from experiments were included by using MODDE 9 software for six parameters composed of water, grinding media, particle size; adding collector to the grinding, and adding depressant and pH. Finally the optimal condition was achieved. According to the results, most of the recovery is related to the particle 75 μ size and when using processed water, adding 100% collector and without depressant and pH 10. The most recovery of lead in the case of the use of fresh water is in the case of 100% collector, without depressant, pH 10 and 150 μ particle size. Maximum recovery in fraction size 45 μ in the case of water process is 100% collector, without depressant and pH 10. Maximum depressant of pyrite will be the fraction size 75 μ, distilled water, without collector, 100 depressant. Keywords: Sulfide mineral, hydrogen peroxide, flotation, oxidation

Jan 1, 2020

By J. de Korte, Z. Loubser

"SynopsisThe aim of a blending stockpile is to minimize the natural variation in properties of a material. Two simulation models were written, for coneshell and chevcon stacking, and used to investigate the influence of different stockpile parameters on blending efficiency. The coneshell model is used to show that blending efficiency is highly sensitive to stacked height, with lower output variances observed for higher capacities. Output variance in both models also decreased when the stacker movement increment was decreased. For chevcon stacking, increasing stacker speed significantly increases the blending efficiencies. Increasing the length of the blending tail also reduces output variation, but this parameter would need to be weighed against the accompanying decrease in buffer capacity.IntroductionEven in the most uniform deposit of materials in nature, material properties will vary. The degree of variation can be measured, and usually resembles a normal distribution. The aim of blending and homogenization operations is to minimize the standard deviation of this normal distribution (De Wet, 1994). In general, the reduction in variation will result in a more efficient and cost-effective downstream process. Cement plants need a precise blend of raw materials to ensure desired kiln performance; boilers used in power generation are optimized for fuels of a constant specification; and even though the separation density in a coal washing plant can be adjusted, a constant product quality cannot be produced from highly variable feed (Denny and Harper, 1962). The process efficiency, product quality, and environmental compliance depend on consistency of characteristics in the material fed (Kumral, 2005) Many industries involved in"

Jan 1, 2015

By Dick Minnitt

Large-scale variability in process plants and process control can be identified and controlled through disaggregating the overall variability in a process stream. Conventional statistics and Statistical Process Control (SPC) fail to address the concept of stream heterogeneity, therefore fail to identify and distinguish between the various sources of variability in a process stream. A modified set of 445 data from a process plant is used as an example to explain the benefits of variography in process control. Large-scale variability, usually in the form of product composition cycles and chemical cyclic variations may be manifest throughout a sampling system or a process plant, but this type of variability is most easily discernable in one-dimensional process streams. The Moving Average is a powerful tool for identifying large and small scale variability and cyclical behaviour in process streams, while the variogram is a custom built tool that allows the components of variability to be identified and resolved. The positions in the variogram at which the different variance can be read and the nomenclature of these types of variability is described. The transfer of variances converted to standard deviations to the Control Charts, allows an operator to appreciate the appropriateness of Upper and Lower control and specification limits. The overall contribution of the various sources of variability is represented in a pie diagram.

Jan 1, 2007

By F. Hörtkorn, Y. Narainsamy

Rather quietly, a new generation of European norms dealing with earthworks has been developed over the past few years, in particular a part of EN 16907 pertaining to extractive waste. Whereas the majority of the parts deal with routine geotechnical aspects, one part deals specifically with tailings dams. The standard is currently in draft form but if this becomes a European Standard, members of the European Union are bound to comply with the regulations. As such, the standard has the capacity to influence mining in Europe and potentially in South Africa. In this paper we review the standard and compare it to the South African standard on mine residues and the recently published Global Industry Standard on Tailings Management (GISTM). We conclude found that although the European norm makes great strides towards increasing tailings dam safety, there is room for improvement. The current South African standard has served well since its inception, but can be improved by using concepts from the European and global tailings standards.

Jun 2, 2022

By I. Çinar

Cappadocia is not only a region of Turkey with historical and touristic importance. During the cutting and processing of volcanic tuff, quarries in this region release large amounts of tuff into the environment that is viewed as waste. The release of this waste constitutes an economic loss and contributes to environmental pollution. However, through experimentation with deformation, weight per unit of volume, water absorption, uniaxial compression strength, modulus of elasticity, and point load strength index, volcanic tuff and marble dust composite materials can be produced for use in the building sector. In this study it was observed that, as the percentage of volcanic tuff dust in the mixture increased, the water absorption rate of the material increased, and uniaxial compression strength and point load strength decreased. The produced composite samples used in this study were kept for a predetermined number of times per day, and no deformation in the surface characteristics of the materials was observed. In a statistical parameter analysis, averages, variances, standard deviations, coefficients of variation, and skewness coefficients were calculated. Covariance changes between experimental parameters were also determined. In this study, two types of volcanic tuff dust, that is, yellow and red, were produced during the production of tuff-marble dust composite material. When the percentage of either type of volcanic tuff dust was increased, an increase in water absorption was observed. It was also observed that when the percentage of volcanic tuff dust was increased, uniaxial compressive strength and point load strength decreased. Furthermore, the physical and mechanical properties of the materials obtained by mixing different colored tuff powders and marble powders in different proportions were evaluated using statistical parameter analysis.

Mar 5, 2025

By J. S. C. Joubert

The Koidu Kimberlite Project is situated in the Kono District of Sierra Leone, approximately 330 km east of the capital city, Freetown. The mining lease area is 4 km2 and comprises 2 kimberlite pipes, 4 dyke zones and a number of blows off the dykes. Koidu Holdings established on the property and began dewatering and the removal of silt from the existing 30 m excavation of the No.1 Pipe in 2003. While the original planning for the pipes included conventional open pit operations, mitigating factors such as the proximity of the town, the presence of houses close to the perimeter of the pipe, the size of the pipe and the planned open pit depth with relevant stripping ratios, as well as uncertainties on the grades in respect of an underground operation, lent itself to the vertical pit concept. The vertical pit was established using an A-frame headgear for the hoisting arrangement, with sidewall support comprising a combination of 20 m and 40 m long cable anchors, rock bolts, wire mesh and pneumatically applied concrete. The pit reached steady state production in January 2007 and produced some 26,000 tonnes of head feed per month until August 2007 when mining reached a depth of 74 m below the pit collar (approximately 126 m below surface). Mining was suspended following a sidewall failure that disrupted operations. Now that the grades in No.1 Pipe have been validated, focus has been switched to an underground operation taking account of both No. 1 Pipe and No. 2 Pipe. While the mining costs for the vertical pit have been higher than for a conventional open pit, the concept did circumvent the social implications, the issue of grade consistency and diamond value at depth, as well as providing the time frame to carry out a full underground mining study.

Jan 1, 2008

By K. Thambi

The court in Baleni v Minister of Mineral Resources [2019] 2 SA 453 GP and [2020] 4 All SA 374 (GP), deliberated on the protection of rights of a community holding informal land tenure under Customary Law. The contention related to the necessary level of consent needed to acquire a mining right over such land. Moreover, whether consultations with such communities (Section 23, Mineral and Petroleum Resources Development Act 28 of 2002 (MPRDA) or consent (Section 2, Interim Protection of Informal Land Rights Act, No. 31 of 1996 (IPILRA)) was required to acquire such right. The case has a significant bearing on the granting of mining rights in South Africa, and the discretion of the Minister of Mineral Resources (the Minister) in this regard. However, the objectives of the MPRDA and IPILRA do not dovetail, therefore consultation and consent are not mutually exclusive (Tlale, 2020). This note argues that, despite the resounding victory of this case, the peripheral basis surrounding the decision and the various levels of engagement require serious deliberation. Equally, the degree of reliance on the IPILRA requires clarity to avoid aborting the fundamental objectives of the MPRDA. This paper provides considerations and recommendations that may reduce or eliminate the tensions between the statutory and socio-economic rights in the application of the two statutes.

Sep 1, 2022

By S-J. Park

When evaluating mining investment opportunities, one should consider the risks associated with mineral exploration and development. These are commonly classified as technical, economic, and political risks, and are accounted for in the investment decision by changing the discount rate. Thus, a company may use different discount rates associated with varying risks in order to compensate for the variability of success. The discount rate has a tremendous effect on the economic evaluation of mineral projects. Even when all other factors used as inputs for calculating the NPV (net present value) are equal, the project under consideration may be accepted or rejected depending upon the discount rate. Determining a realistic discount rate for a given project is therefore the most difficult and important aspect of cash flow analysis. It should be determined with the consideration of proper technical, economic, and political conditions surrounding the specific project undergoing economic evaluation. One key problem for determining the appropriate discount rate is that it typically depends more on subjective perception of the degree of risk or other experience factors than on a systematic approach. Thus, this study aims to identify, analyse, and document the type, role, and impact of risk factors influencing the determination of discount rates, and then to determine discount rate by using the aforementioned factors.

Jan 1, 2011

By Z. Gxowa, L. H. Chown, U. Curle, G. Govender

This work evaluates the deformation behaviour, at warm working temperatures, of green particle-reinforced aluminium composites produced by powder blending in a high-energy ball mill. The work focuses on metal matrix composites (MMCs) based on the 2124-Al alloy, reinforced with 10 or 15 vol.% SiC and metal matrix nanocomposites (MMNCs) based on the 2124-Al alloy, reinforced with 5 or 10 vol.% Al2O3. Three batches for each powder were blended and powder properties such as particle size distribution (PSD) and shape were consistent after blending. It was observed that a more uniform distribution of the reinforcement phase in the aluminium alloy matrix was achieved in 2124-Al/Al2O3 than in 2124- Al/SiC composites. The powders (unreinforced 2124-Al and blended) were initially over-aged at 350°C for 2 hours to reverse any natural ageing that may have occurred prior to use. The over-ageing was incorporated to improve compressibility of the powders with the aim of achieving green compacts with higher integrity. Uniaxial compression tests performed at ambient temperature on a Gleeble® 3500 thermomechanical simulator were unsuccessful as the green compacts fragmented. Engineering stress-strain curves showed that green compacts of unreinforced 2124-Al, 10%SiC MMC and 5%Al2O3 MMNC deformed in a similar manner at ambient temperature and had the same compressive fracture stress of approximately 170 MPa. When the deformation temperature was increased from ambient to warm working temperatures (170–280°C) it was observed that electrical resistance heating (the heating mode of the Gleeble®) of unreinforced Al alloy, MMC and MMNC green compacts did not occur. This was attributed to the high electrical conductivity of aluminium, which resulted in poor heat generation due to the low electrical resistance in the samples. It was presumed that the small sample size (d=8 mm, h=12 mm) also caused rapid heat loss. After further experimentation, the green compacts were heated successfully by insulating the samples to retain heat. It was found that at 280°C, increasing the soaking time from 6 to 20 minutes decreased flow stress and improved plastic flow in the 2124-Al/10%SiC green compact.

Jan 1, 2016

A Special General Meeting, followed by the February General Meeting of the Institute, was held in Kelvin House, Johannesburg, on 18th February, 1970, at 4.30 p.m. Mr J. K. E. Douglas (President) was in the Chair. There were also present 24 Members: Messrs A. R. C. Fowler, R. C. J. Goode, Prof D. D. Howat, Messrs D. G. Maxwell, J. A. Nixon, P. W. J. van Rensburg (Council Members), C. A. Border, J. C. Fritz, E. K. Gibson, P. L. Grimbeek, S. D. Hill, D. A. Immelman, P. J. Uoyd, M. Mrost, C. S. Macphail, D. G. Malan, W. D. Ortlepp, R. S. Pearson, A. J. H. Pole, Dr W. S. Rapson, L. W. P. van den Bosch, R. A. von Maltitz and Dr A. Whillier. Eight Associate Members: Dr M. I. Brittan, Messrs J. Brett, I. E. Clarke, C. L. de Jongh, W. B. Evans, D. Loubser, R. C. More O'Ferrall and G. R. Still. One Graduate: Mr T. J. Kotze. One Student: Mr J. A. Cruise. Nine Visitors: including Dr N. G. W. Cook, Messrs M. D. Labuschagne, A. Nicoll, S. Sadowski, Dr A. M. Starfield and Dr H. Wagner. Secretary: Mr D. C. Visser. Total present: 45. SPECIAL GENERAL MEETING The President: "You will have received notices of the Special General Meeting and I declare it duly constituted. In keeping with the trend of overseas and local institutes, your Council recommends that we should change our membership classification as indicated in the notes of the meeting. The new grades are proposed to replace those presently in the Constitution and By-Laws. In terms of Clause 4.8 of the Constitution a special general meeting must be held for the purpose of considering and, if approved, adopting with or without amendments, the revision of the undermentioned clauses of the Constitution, which Council now recommends should read as follows. Clause 2.2 'Corporate Members shall comprise the grades of Honorary Life Fellow, Fellow and Member', these being the equivalent of Honorary Life Member, Member and Associate Member. Clause 2.6. 'Non-Corporate Member shall comprise the grade of Honorary Fellow, Graduate, Associate and Student.' Are there any questions in regard to this proposal? If not would someone propose that these clauses be amended and adopted?" Proposer: Mr A. J. Nixon. Seconder: Prof D. D. Howat. The motion was then adopted. The President: "It is recommended that Clause 2.15 should read, 'A Corporate of the Member of the Institute shall be entitled to use the following authorised letters designating the grade of Membership in Honorary Life Fellow and Fellow, F.S.A.I.M.M. and Member, M.S.A.I.M.M.' Previously we used the letters M.S.A.Inst.M.M. and your Council considered that we should adopt the simpler lettering. Could I ask someone to propose that this amendment be adopted?" Proposer: Mr R. C. J. Goode.