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By T. Marin, J. E. Seccatore, M. Cardu

The most energy-intensive process in the mining industry is particle size reduction – comminution. The first phase of this process is blasting to fragment the rock from the initial Boussinesq’s halfspace size. Scientific literature demonstrates that the output of a blast in terms of fragment size distribution can be manipulated by varying the specific charge (powder factor) and charge distribution. This study focuses on the influence of blasting on the internal resistance of the blasted fragments; in particular the influence of the spatial distribution of charges. Small-scale blasts were performed on 14 marble blocks using different powder factors and charge distributions. Three control blocks were fragmented by mechanical means for comparison. The results show the correlations between charge distributions and the specific energy of mechanical comminution. Opportunities for adjusting charge diameter and distribution in opencast blasts to improve the performancet of comminution circuits are discussed.

Aug 8, 2024

Notices THE FEDERATION OF SOCIETIES OF PROFESSIONAL ENGINEERS It is expected that the National Institute of Personnel Research will be conducting a project, at the request of the Federation, to establish the relationship, if any, between the academic and professional achievements of engineers. co-operate with the researchers. INFACON 74 The National Institute for Metallurgy, the South African Institute of Mining and Metallurgy, and the Ferro Alloy Producers' Association of South Africa will hold an International Ferro-alloys Congress in Johannesburg from 22nd to 26th April, 1974. INTERNATIONAL PLATINUM SYMPOSIUM OF THE SOCIETY OF ECONOMIC GEOLOGISTS The above symposium is to be held at the U.S. Geological Survey, Denver Federal Center, Denver, Colorado, from 13th to 17th October, 1975. Papers up to 40 doublespaced THIRD MEETING-CANADIAN HYDROMETALLURGYGROUP The Hydrometallurgy Group of the Metallurgical Society, Canadian Institute of Mining and Metallurgy, will hold its Third Annual Meeting, October 1 and 2, 1973, at Edmonton Alberta. COLLOQUIUM ON THE CONSTRUCTION OF SLIMES DAMS The Institute has arranged a two day colloquium on the above topic, to be held on November 14th and 15th, 1973, at Kelvin House. The following Programme has been arranged:

By G. O. Rading, B. O. Odera, M. J. Papo, R. Couperthwaite

"Platinum-based alloys are being developed with microstructures similar to nickel-based superalloys for potential high-temperature applications in aggressive environments. Since the chemistries of nickel and platinum are similar, Pt-based alloys can be made with gamma prime ~Pt3Al precipitates in a gamma (Pt) matrix. Currently, the Pt-Al-Cr-Ru system is one of the bases for developing Pt-based alloys, where Al allows the formation of thePt3Al precipitate and also gives protection from the alumina scale formed, Cr provides oxidation resistance and stabilization for the L12~Pt3Al phase, and Ru provides solid solution strengthening in the (Pt) matrix. Four Pt-Al-Cr-Ru-V and two Pt-Al-Cr-Ru-V-Nb alloys were made, with compositions based on a quaternary alloy, ~Pt82:Al12:Cr4:Ru2, which hadpreviously been identified as having optimum properties. Four of the as-cast alloys had the targeted two-phase structure of ~Pt3Al and (Pt), and two were single-phase ~Pt3Al. Vanadium partitioned more to (Pt) than to~Pt3Al. There was an improvement in hardness compared to the quaternary alloys. The best addition of V was ~15 at.%; higher additions resulted in brittle intermetallic phases of the Pt-V system. The effect of Nbcould not be ascertained because of its high losses."

Jan 1, 2015

By A. Andrews

Paper written on project work carried out in partial fulfilment of MSc (Eng) degree Solid state sintered silicon carbide ceramics are used in aggressive environments as sealings. There exist data concerning corrosion, but there are only few data concerning their electrocorrosion behaviour. Therefore the electrochemical corrosion of solid state sintered silicon carbide (SSiC) ceramics has been studied at room temperature in acidic and alkaline environments by using potentiodynamic polarization measurements. The investigation showed a pronounced electrochemical corrosion in bases and acids. In HCl andHNO3pseudo-passivity features due to the formation of a thin layer of SiO2on the surface were observed, whereas in NaOH soluble silicate ions were observed, resulting in more pronounced corrosion. The microstructural observations of initial and corroded samples reveal that the residual carbon found in the microstructure do not dissolve preferentially. Keywords: Corrosion; SEM; SSiC; polarization test.

Jan 1, 2006

By P. J. N. Pells

A good thing is becoming a bad thing. Rock mass classification systems, that are so excellent for communications between engineers and geologists, and that can be valuable in categorizing project experience, are emasculating engineering geology and rock mechanics. Some engineering geologists have been sucked into thinking that Q and RMR values are all that is needed for engineering purposes, and seem to have put aside what can be learned from structural geology and geomorphology. Many rock mechanics engineers seem to have forgotten the scientific method. This paper attempts to redress the situation by showing how mechanics can be used in rock engineering to design with a similar rigour to that used in the fields of structural engineering, hydraulics and soil mechanics. It also attempts to remind practitioners of what can be achieved by skilled engineering geology.

Jan 1, 2008

By L. A. Cramer

Platinum metal was first utilized by the Inca civilization in South America where it was found in alluvial deposits along the San Juan and Atrato rivers that lie between the Andean mountain range in Colombia and the Pacific Ocean. The nuggets found in these rivers average between 77% and 86%platinum, 7%?8% iron and small amounts of copper, gold and other Platinum Group Metals (PGMs). The Incas often alloyed platinum with copper to increase its workability and fabricated various ornaments from it. With the arrival of the Spanish in the early 1700s, platinum was labelled a nuisance for the Spanish in their quest for alluvial gold because it concentrated with the gold and had to be removed by either extended amalgamation or by hand sorting. It was at this time that platinum received the root of its current name for the Spanish referred to it as platina del Pinto, platina being the somewhat derogatory diminutive of plata (silver). Pinto was a river in Colombia where the Spanish first distinguished it. The English eventually adopted ?platina? and it is only in recent times that the Latin name platinum has been accepted as the metal?s common English name. From its first introduction to European scientists in 1740, platinum was unappreciated because of its brittle nature and difficulty of working and as a result had little commercial value. Its ability to be dissolved in gold did lead to some counterfeiting of gold bullion and even to the debasement of gold currency.

Jan 1, 2000

By M. W. Hildyard

The aim of this paper is to demonstrate that active seismic measurements could have an impact in helping solve rock engineering problems experienced in the South African mining industry. The paper presents a variety of experimental and numerical results where seismic waves show clear differences in wave-speed and amplitudes due to different degrees of fracturing. It presents results from the ?Omnibus? project commissioned to develop new ultrasonic technologies for diagnosing fracturing for nuclear waste repositories. This included using models to investigate assemblies of cracks where the effects of crack density and crack size on waveforms are shown to be coupled. Results indicate that these effects can be decoupled in the frequency domain, where the Fourier amplitude aids in estimating crack size, while the low frequency phase-difference has a direct relationship to crack density. Models are also shown to aid interpretation of waveforms by isolating geometric effects from the effects due to cracks. Two rock engineering problems experienced in the South African mining industry are investigated through numerical examples. These demonstrate that determining whether ?crush? pillars have failed and determining the degree of fracturing in the hangingwall of stopes, may be possible through the use of active seismic surveys.

Jan 1, 2005

By J. H. Van Reenen, H. Thiele, C. Bergman

For some time spirals have been the process equipment chosen to recover metal in the size range 0.15 to 3mm from ferrochrome and silico/ferro manganese slags. Recoveries of metal obtained using spirals are usually about 70%. Spirals are also difficult to control. By combining a novel gate on the Apic pneumatic fines jig with the recently developed Apic classifier, metal recoveries of 76% and grades of over 90% have been obtained for FeCr and SiMn slags in the size range 0.15 to 3 mm. The paper compares classifier operating performance and costs with those spirals for FeCr and SiMn metal recovery from slags. The classifier technology can also be applied to chromite and iron ores and coal fines.

Jan 1, 2004

By J. L. Viljoen

t has long been the drive of the industry and all operations to create an environment that is free of injury and illness. We have come a long way; the leaders, executives, managers, supervisors and workers are to be commended for relentlessly driving to create, what I call a ?White Flag Day Every Day?. Yet I am also aware of the huge shift we still need to create in the industry, on the operations and in the workplaces to have them free of injury and illness. Keywords People, values, care, trust, belief.

Jan 1, 2011

By A. Engelbrecht, B. North, B. Oboirien

"There is large electricity generation potential in discard coal, both in stockpiles and current arisings. Power stations with a combined capacity of up to 18 GW electrical (GWe) could be fuelled by discard coal. Modern circulating fluidized bed combustion (CFBC) boilers, with capital costs comparable to equivalent pulverized fuel (PF) boilers, are capable of utilizing discard coal at a high efficiency while reducing sulphur dioxide (SO2) emissions though the use of limestone sorbent for ‘in-situ’ capture.A detailed economic assessment of the feasibility of electricity generation from discard coal, comprising material and energy balances and the construction of a discounted cash flow (DCF) table, shows that it is also potentially attractive from an economic perspective. A base case analysis shows positive net present values (NPVs) and an internal rate of return (IRR) of 21.4%. Sensitivity analyses on critical parameters show that the economic viability is heavily dependent on parameters such as coal cost and the value of electricity. The project becomes unattractive above a coal price of approximately R300 per ton and at an electricity value below approximately 59c per kilowatt-hour (kWh).Site- and project-specific information such as the delivered cost of coal, location and efficacy of sorbents, and effective value of the electricity produced can be used as input to the economic analysis to evaluate siting options and sorbent source options for such a power station."

Jan 1, 2015

By J. Rogans

This paper discusses the comparative performances of the three activated carbon adsorption circuits at the West Wits operations of Anglogold. These circuits consist of two pump-cell circuits (at Two Plant, formerly Elandsrand and at Three plant) and a conventional counter-current adsorption circuit (at Mponeng plant). The implications of the improved performance of the pump-cell plants are discussed.

Jan 1, 2002

By M. Karsten

Platinum mines in the Bushveld Complex are located in areas with a high geothermal gradient. This means that, compared to, for example, gold mines of the Witwatersrand region, high rock temperatures are encountered at relatively shallower depths. Thus air cooling and refrigeration need to be considered at early stages in mine development. Another factor that influences air cooling and ventilation requirements is the use of trackless diesel equipment for loading and hauling broken rock. At shallower depths it will be more cost-effective to locate the cooling and ventilation equipment on surface, whereas for deeper mines the more cost-effective option is to locate cooling equipment underground. For intermediate depths, trade-off studies need to be undertaken to determine the optimum mix between more cooling and less air or more air and less cooling, as well as the optimum location for this cooling equipment. Factors that are taken into account include power requirements, positional efficiency, and additional infrastructure requirements. Traditionally the approach has been to ventilate ?all of the mine all of the time?. However, with increasing power costs and growing pressure to ensure sustainability, this strategy must be modified to apply ventilation and cooling on demand. In other words, both cooling and ventilation equipment should be operated only when needed and should be adjusted to the demand at the time. Obviously there will be areas that will need to be ventilated (and cooled) continuously (for example, for dilution of flammable gases), but this can be built in to the overall strategy. In addition, in devising ventilation on demand (VoD) strategies, occupational criteria relating to exposure to gases, noise, and heat need to be taken into account. This paper discusses options available for implementing energy-efficient ventilation and cooling systems and suggests ways of changing traditional thinking in the overall ventilation and cooling of mines. Efficient ventilation and cooling designs can play a major role in improving sustainability and reducing energy costs and carbon footprint.

Jan 1, 2012

By D. P. Roberts

The stoping of platinum orebodies in the Bushveld has in the past been accomplished by using in-stope pillars to ensure stability of the workings. In the future, the use of continuous mining machines to mine the platinum orebodies is probable. It is not envisaged that such machines will cut in-stope pillars. This paper describes the alternative support systems that will replace the pillars and the stope geometries that will be required for this type of mining. The paper describes how the support resistance provided by in-stope pillars in current mining was determined and then evaluates support systems that can substitute for these pillars. Conceptual layouts based on existing breast mining layouts are presented. The layouts consist of panels of up to 100 m face length between rigid strike stabilizing pillars. A number of design charts are then proposed that allow for the design of appropriate support systems.

Jan 1, 2005

By W. G. Huang

To recover the coal resources of high-sulphur anthracite in Jincheng Mining Area, underground coal gasification (UCG) of No. 15 seam in Fenghuangshan Coal Mine was proposed. The feasibility of the project was confirmed by investigations of occurrence conditions, coal properties, and roof conditions, as well as experimental studies and theoretical analysis. It was found that UCG technology is appropriate to be adopted in the mining of the No. 15 seam, due to the stable rock conditions, simple geological structure and hydrogeology, the high carbon content of the coal, non-cohesiveness, medium-thermal stability, high ash fusion temperature, and weak reactivity with CO2. Further factors are the characteristics of the immediate roof, which consists of 9.11 m of limestone and mudstone with a compact structure and low permeability, and 4.27 m of dominantly mudstone with low permeability.

Jan 1, 2012

By P Papanastasiou, J Hadjigeorgiou, E Kyriakou

The south west area of Cyprus has a long history of slope instability problems. The location and extent of these landslides has been influenced by ground morphology, geological structure and the presence of weak rocks and cohesive soils. The main triggering mechanisms have been precipitation and/or seismic events. Landslides have contributed to the decision to relocate villages and considerable efforts have been put into maintaining the integrity of the local transportation network. This paper uses a recent case study of road embankment failure near Pentalia in southwest Cyprus to review the available tools for the analysis of slope instability. It further demonstrates how the shear strength reduction technique can be used in a finite element analysis to better visualise the slope instability mechanism of a road embankment and provide a reliable tool in selecting appropriate remedial measures.

Jan 1, 2006

By M. Hopf, E. Rossouw

Keywords: Pyrometallurgy, furnace, copper coolers, freeze lining, monitoring, Saveway The use of water-cooled copper components as sidewall elements of submerged arc furnaces and other pyrometallurgical applications has become increasingly common. The high cooling efficiency of copper has made it possible to increase the service life of furnace refractories when compared to conventional refractory linings. However even the self-healing effect of ?freezing? worn areas of the lining does not necessarily protect the copper coolers against wear or corrosion completely. In order to avoid furnace explosions, various methods have been used to monitor the wear of coolers. Unfortunately, these have not been able to consistently identify localized wear. Thos Begbie (South African) and SAVEWAY (German) jointly developed technology to embed a line sensor into the copper cooler during the casting process. This system allows an exhaustive monitoring of the copper cooler. A SAVELINE sensor is placed inside the copper-cooling panel between the water-cooling passage and the hot face of the panel. The sensor follows the meandering shape of the cooling water channels. In the first instance, the sensor provides analogue information as the thickness of the copper reduces. Secondly, this wear signal will be confirmed by a signal of interruption if the sensor is washed away. Because of the structure of the sensor, a self-diagnosis is possible and indications can be confirmed (double proofed). Subsequent to the manufacture of some test pieces, coolers for a large submerged arc furnace were manufactured. The sensorized coolers have been installed at the intermittent surface (slag line) where the largest amount of corrosion has been encountered. The system has been operating since December 2005 in what is considered one of the largest submerged arc furnaces in South Africa.

Jan 1, 2006

By Q. G. Reynolds

Keywords: Pyrometallurgy, furnace, DC, reverse polarity, dual-electrode The dual-electrode direct current (DC) arc furnace uses two graphite electrodes, one connected as cathode, and one as anode. Such an arrangement avoids some of the design difficulties associated with the anode hearth traditionally used in single electrode and twin-cathode DC furnaces, but can introduce other design and operational difficulties including deflection of the arcs toward the furnace walls. Counter-intuitively, both arc jets in a dual-electrode furnace travel from the electrode down to the bath surface, despite carrying electric current in opposite directions ? this is suggested in the theory of the governing equations of arc formation, and confirmed by experiments using high-speed photography. The dual-electrode arc system at small pilot-plant scale is studied using a transient magneto-hydrodynamic model capable of predicting arc deflection and interaction from first principles, and the results are compared to the behaviour of twin-cathode systems at similar power. Finally, a simple arrangement of the furnace busbars, M configuration, is shown to provide some passive protection against arc deflection.

Jan 1, 2011

By D. Schreuder

Conditions in the South African market relating to atmospheric emission control has changed dramatically over the last 10 years. Companies have become more responsible, environmentally aware, and have to comply to more stringent environmental limits set by legislation. This paper describes briefly the current best available atmospheric pollution abatement technologies relating to particulates, acid gases, NOx, acid mists, aerosols, mercury, dioxins and furans. Mention is also made as to the best practices for product work-up and waste product disposal.

Jan 1, 2006

By K. Blaski

his paper reports an investigation aimed at optimizing the compaction of granulated hard-metal powder for the production of cutting tool inserts. The optimal compaction is that which yields optimal shrinkage during sintering, i.e. minimum porosity in the sintered part. Extensive compaction tests on 23 different hard-metal powders have been carried out and have shown that the ideal ?green density? of a hard-metal compact, i.e. the density after compaction, increases linearly with the apparent density of the powder. On the basis of this result, an equation has been derived, which allows one to predict the optimal shrinkage that a hard-metal compact undergoes during sintering once the following data are known: the required sintered density, the volatile content of the powder and the apparent density of the powder. Since these data are available to the tooling designer, this equation allows one to design tooling for the compaction of hard-metal, which leads to optimal shrinkage

Jan 1, 2007

By L. Arnberg, E. Ott

The microstructure of ferrosilicon is important since it controls the disintegration of the material during crushing and thus the generation of fines. Therefore a study of the microstructure formation during solidification of pure FeSi(75wt%Si) and FeSi(75wt%Si) containing 1.2wt%Al and 0.2wt%Ca has been initiated. The material has been cast into rods of 8mm diameter, which have been remolten by induction heating and directionally solidified in a Bridgman apparatus. This allows the temperature gradient and the growth rate to be controlled independently. The temperature history during solidification has been recorded by a thermocouple in the melt. Growth rates have been varied between 5 and 400µms-1 and temperature gradients between 3 and 14°Kmm-1. The microstructures show a large dependence on the solidification conditions. The crack formation in the alloys has been studied and found to be strongly related to the microstructure.

Jan 1, 2004