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By J. Alexis, G. Ye, E. Burström

Over the past twenty years the 3 MW DC arc furnace at MEFOS has been frequently used for development of new processes. These processes include recovery of valuable metals from slag, sludge and dust from steel and other metallurgical industry, treatment of ashes from power plant and incinerators, smelting reduction of minerals and zinc recovery from EAF dust. The process characteristics of the DC arc furnace operation in terms of: ? selective reduction, ? total reduction, ? process stability and flexibility, ? dust carry-over, ? thermodynamic conditions provided in the hot spot area, ? precision in composing slag products These are analysed and described in this paper based on technical results from selected test campaigns over the years and thermodynamic considerations. The electromagnetic properties of DC arcs beneath the electrode have been studied by CFD simulation. The calculated result enables us to understand some interesting technical phenomena observed. The heat balance has also been considered based on data obtained from test campaigns and heat balance calculation.

Jan 1, 2004

In order to deliver a quality shotcrete and concrete product underground for the extensions to the Cullinan Diamond Mine operations it was decided to develop a new, simpler concrete product to meet underground support requirements. The aim was to develop a concrete product that not only reduced costs but also met the performance criteria of the current range of concrete products used on Cullinan Diamond Mine, a 25, 45 and 60 MPa concrete and a fibre reinforced wet shotcrete. The concrete product batching and delivery system was to be from surface as opposed to the current underground batching systems. The operational principle was to include an automated surface batching plant with delivery of the concrete product to a borehole containing suspended pipelines delivering to an underground storage facility from where the product is delivered to the working area by further pumping or agicars. Keywords: concrete, shotcrete, full flow, frictional loss, pipeline transport, positive displacment pump

Jan 1, 2006

By I. Bhattacherya

Over the last three decades, the mining industry has been moving towards underground mechanized mining methods and the number of load haul dump (LHD) vehicles utilized has increased. The growth of mechanization and automation has benefited both workers and mining companies. However, due to the design constraints with LHD vehicles and the limitations of the operating environment, restrictions to operator visibility has contributed to a number of accidents, including fatal injuries. Past researchers have used the light filament technique to collect obscuration zones around mobile equipment and have produced 2D visibility charts (shadow diagrams) of this information. The light filament method involves manually collecting visibility data, which results in errors and is time consuming, requiring around three hours to complete. This research utilizes a MENSI GS100 laser scanner along with 3D modelling software (3Dipsos) to collect and process operator visibility profiles for underground mobile equipment. Results from this test work indicate that a laser scanner can be successfully used to rapidly collect this data and utilize this information for improved mobile equipment design from a visibility perspective. Nomenclature FERIC Forest Engineering Research Institute of Canada ISO International Organization for Standardization JACK Software for digital human modelling and ergonomics LHD Load haul dump vehicle LOS Line of sight MASHA Mines and Aggregates Safety and Health Association (based in Ontario, Canada) PVD Polar visibility diagram SAMMIE3D human modelling computer aided ergonomics design system WSIB Workplace Safety and Insurance Board

Jan 1, 2006

By Glen Mc Gavigan

The roof of the Sishen cave is being mined in order to exploit 6.8Mt of high grade ore. The cavity is filled with quartzite backfill in order to support the roof in the event of collapse. The cave dips at approximately 37o, is 260m along dip and 70m along strike and has a total volume of 261,391m3. GPS and optical monitoring techniques were attempted to detect subsidence but proved to be impractical. The GroundProbe Slope Stability Radar (SSR) uses differential interferometry to measure sub millimetre movement in a rock face. The SSR was applied in a non production situation and detected subsidences of 38mm/day before visual signs of instability were detected. The rate of deformation detected was slowing as a result of the roof coming to rest on underlying backfill. Monitoring during production drilling detected a sudden subsidence of 18.6mm/hour which resulted in the evacuation of personnel from the area. Further inspection of data showed that the rate of deformation was slowing and production was allowed to continue without further incident. The SSR has helped dispel the fears of workers and has proven that subsidence can be accurately measured and delineated with the SSR.

Jan 1, 2006

By C. Kloppers

The aim of this investigation was to reduce the cost of primary steel de-oxidation by substitution of aluminium primary de-oxidation with a practice that uses carbon. The cost of carbon is four times lower than that of aluminium. The application of carbon would directly result in raw material cost savings. Investigations were conducted at Iscor?s Newcastle steel plant on various steel grades. Specific production aspects were emphasized to ensure that the cost savings accrued would not create secondary expenses. These production aspects entailed: ?Yields on de-oxidation elements ?De-oxidation capabilities ?Alloying yields (Mn and Si) ?Carbon-pickup ?Nitrogen-pickup ?Temperature loss during tap ?Steel cleanliness ?Slag morphology. This project proved that carbon de-oxidation, apart from reducing de-oxidation raw material cost due to cheaper raw materials being used and lower consumption rates, resulted in steel that is cleaner and has lower nitrogen concentrations. Carbon primary de-oxidation has been implemented at Iscor?s Newcastle plant on a large range of steel grades, ranging from ultra-high carbon (> 0.60% C) to ultra-low carbon (< 0.03% C) grades. A net saving of between R100 000 and R200 000 per month was achieved.

Jan 1, 2001

By F. Terblanche, M. Holton, A. Kruger

The paper presents an optimal mine planning system designed to simultaneously optimize all the underground mines of large South African gold and platinum mining corporations. The system, code named PlanIT-OPTIM, is a multi-stage solution involving the use of adetailed 3D CAD-based mine planning system (CADSmine™V4). The mine design and scheduling rules defined in CADSmine™ are responsible for simulating mining sequencing, rock mechanics, and ventilation, etcetera. Feasible production ranges generated by CADSmine™ and various high-level mathematical models are used as inputs to a mathematical optimization engine. The optimization engine produces optimal production profiles (i.e. key business indicators such as tonnages, mineral and areas extracted per time period) by maximizing net present value. Other objectives such as profit continuity, production continuity and maintaining available reserves can also be specified as optimization criteria. The final step in the PlanIT-OPTIM process is to convert the optimal production profiles into practical and attainable business plans. This is achieved through the CADSmine™ Detail Optimization Engine that modifies the original CADSmine™ schedule to match the optimal production profiles. With current methods it is an impossible task to find the best business plan for a mining corporation in any reasonable period of time should conditions change (e.g. gold prices, exchangerates, grade estimates, etcetera). The fast turn around time achieved through PlanIT-OPTIM makes it possible to do several ‘what-if’ scenarios in a reasonably short time. PlanIT-OPTIM has already been used in the gold mining industry to find optimal business plans for a mine.

Jan 1, 2003

Application of Gy?s formula is appropriate for calculation of the Fundamental Error (FE) prior to samples being collected at any stage of the minerals process, provided that sampling parameters K and a (alpha) have been determined by calibration of the ores. Two types of calibration procedure are well established in the industry, the Hetrogeneity test and the 32-piece sampling tree experiment. The sampling tree experiment uses the variance and average grade of metal analyses from four series of samples at different nominal fragment size, as the basic input data. Pierre Gy suggested the cube as an appropriate exponent of the nominal fragment size for use in his equation. More recent work suggests that this exponent is variable and characteristic of specific ores and therefore requires calibration. The method described here explains the experimental procedure of the calibration. It is then possible to calculate a sampling nomogram using the sampling parameters K and a. This allows the sampler to determine a suitable protocol for the sampling event that will ensure that the FE does not exceed a predetermined precision at any point in the sampling procedure.

Jan 1, 2007

By K. -H. Lux, Z. Hou

ABSTRACT: It is well known in underground mining and waste disposal that the development of excavation damaged zones (EDZ), and thus, hydraulic pathways, is closely related to the excess in the corresponding damage boundary (= long-term strength) of the rock mass and the resulting damage. By integrating short-term and long-term strength, dilatancy, damage and healing into the newly extended Hou/Lux constitutive model for rock salt, it is possible to treat the tertiary creep, to identify the EDZ around underground facilities and to predict the time-dependent development of the EDZ in rock salt. Under in-situ conditions, the EDZ of a 37-year-old drift at the Sondershausen salt mine and the EDZ around a drift dam in rock salt are numerically examined. The numerical analysis gives satisfactory results. RÉSUMÉ: Dans les exploitations minières et le stockage souterrain des déchets, le développement des zones endommagées et fracturées (EDZ – excavation damaged zone), créant des chemins préférentiels pour écoulement, est étroitement lié au contexte géotechnique et à la méthode d’excavation. En intégrant la résistance court et long terme, la dilatance, l’endommagement et le colmatage, le nouveau modèle rhéologique Hou/Lux pour le sel gemme est capable de traiter le fluage tertiaire, d’évaluer l’extension de l’EDZ et de prédire l’évolution de EDZ dans temps autour des ouvrages creusés dans le sel gemme. L’EDZ d’une galerie datée de 37 ans dans la mine de sel de Sondershausen et les EDZ autour de barrage des galeries dans un sel gemme ont été modélisées. Les résultats numériques fournissent des résultats satisfaisants. ZUSAMENFASSUNG: Bekanntlich ist die Entstehung von Auflockerungszonen und damit hydraulischen Wegsamkeiten in der unmittelbaren Umgebung um bergmännische Hohlräume mit der Überschreitung der entsprechenden Schädigungsgrenze eng verbunden. Unter Berücksichtigung der Bruchfestigkeit, Schädigungsgrenze, Dilatanz, Schädigung und Verheilung kann das Stoffmodell Hou/Lux das Verhalten des tertiären Kriechens beschreiben, die Auflockerungszone im Salzgebirge ermitteln und ihre zeitabhängige Ausdehnung vorausberechnen. Mit diesem Stoffmodell werden die Auflockerungszonen einer 37jährigen Strecke in der Salzgrube Sondershausen und die Auflockerungszonen um ein exemplarisches Abdichtungsbauwerk im Salzgebirge numerisch untersucht. Dabei werden zufriedenstellende Berechnungsergebnisse erzielt.

Jan 1, 2003

By W. S. Steinberg

Keywords: Pyrometallurgy, furnace, open slag bath, Evraz, Highveld In 1963, the full-scale engineering study for the development of an Iron, Steel, and Vanadium plant was initiated. This was the birth of Evraz Highveld and its process flow as it is known today. Highveld started out as a steel works that produced steel and vanadium-bearing slag by using a titaniferous magnetite iron ore mined from its own mine site near Steelpoort. The process utilized co-current rotary kilns for pre-reduction, and submerged-arc furnaces for the production of pig iron with approximately 1.15% vanadium. Because of various technical challenges that the submerged-arc furnaces experienced over the years, a decision was taken in 2004 to convert the furnaces to Open Slag Bath (OSB) operation, in order to enable the maximum production of iron and vanadium while improving the control over operational parameters. The conversion proved to be highly successful and, since 2005, three furnaces have been converted to OSB operation. The fourth furnace will be converted in the first half of 2011. The conversion to OSB furnaces not only yields higher vanadium recovery to the metal at the iron plant, but also improves the overall throughput of the steel plant. This is the result of a higher carbon content of the liquid iron from the OSB furnaces, eliminating the need for anthracite addition to the shaking ladle process. This reduces the blowing time by approximately 60%. The conversion of the furnaces to OSB configuration is seen as an enabling technology change and a prerequisite to the implementation of other plant improvements that are envisaged. The long-term vision of EHSV is to convert five furnaces to OSB mode, and permanently decommission the two remaining submerged-arc furnaces. This will allow EHSV to maintain current steel and vanadium production but at a significantly improved overall efficiency.

Jan 1, 2011

By A. P. Squelch

The question of what stress condition exists in the hangingwall of tabular stopes remains topical and largely unanswered. Limited field data exist to quantify the situation and provide calibration for investigative computer modelling exercises. Work conducted in1989 and 1990 under a Chamber of Mines Research Organization (now the CSIR: Division of Mining Technology) programme of research into the behaviour and benefits of backfill may assist with this situation. The original work was motivated by the premise that the improved hangingwall stability in backfilled panels (identified by rockfall accident analyses) is due to a change in the hangingwall stress regime. Current, largely theoretical, studies into mechanisms of stope hangingwall behaviour and support interaction could benefit from considering these data. Keywords: Backfill, horizontal stress, stope hangingwall, hangingwall stability, support interaction.

Jan 1, 2002

By J. Böhlke, B. Friedrich, E. Hecker

The legislation for the disposal of heavy metals contaminated substances is still going to be tightened up in the future. The main criteria for the utilization or deposition of these residues are the content and the water solubility of these metals. Through this, the use of slags from the lead-and zinc-industry in road building may become limited or even not possible at all. From an economic point of view this would lead to Pb/Zn losses and costs for safe dumping. This paper investigates the feeding of the reducing agent via hollow electrode DC smelting and the yield of metal reduction. After carrying out thermodynamic calculations, the process window conditions for electric-arc furnace tests were determined. Doing this, the zinc could be reduced, evaporated and recovered as an oxidic intermediate product flue dust, while the lead was present either in flue dust or in metallic form. The zinc content in the final slag could be reduced by up to 90%. The slag product has undergone an eluation test which allows it to be used as building materials. Keywords: zinc reduction, lead reduction, hollow electrode, slag treatment, electric arc furnace

By K. Goshtasbi

The mechanical behaviour of schistose sedimentary rocks such as slate show a great amount of anisotropy. Hence, the schistocity plane is essential when investigating the mechanical behaviour of such rocks. The presence of such rocks in civil projects causes non-symmetric deformation and their behaviour is unpredictable. In this research, the anisotropic strength behaviour of slates is studied. Uniaxial and triaxial tests were conducted on specimens having orientation angles (ß) of 0, 30, 45, 60, 75 and 90 degrees. The triaxial tests were done at confining pressures of 3, 5 and 10 MPa. The effect of anisotropy on uniaxial and triaxial strength, cohesion, angle of internal friction and Hoek and Brown&apos;s m and s constants were investigated. The results indicate that the strength of slates in uniaxial and triaxial compression exhibit a U-shaped anisotropic behaviour. In-order to evaluate the most suitable criterion for predicting the anisotropic strength of rocks in uniaxial and triaxial compression, an investigation was carried out on various criteria. In uniaxial compression, the Liao and Huong and Ramamurthy criteria had good agreements with the test results. In triaxial compression the Hoek and Brown and Mc Lamore criteria had better agreements with the test results. It should be noted that in-order to utilize these criteria, a large number of tests must be carried out. However, as the Ramamurthy criterion needs fewer test results, it can be the most suitable for investigating the behaviour of anisotropic rocks in triaxial compression. Keywords: Slate, anisotropy, schistose, failure criteria

Jan 1, 2006

By D. B. Paterson

In view of decreasing head grades, the relatively high gold price, and recent developments in metal evaluation, an exercise was initiated to determine the extent of gold concentration, the mode of occurrence, and the areas of concentration within the run-of-mine milling circuits of Randfontein Estates Gold Mining Company (Witwatersrand) Limited. The total gold content of three of the thirteen run-of-mine mils in the Group was measured as a typical lock-up of approximately 200 kg per mil. The majority of this gold was concentrated either behind the grid-type body liners or within the pockets of the body liners. This paper is an account of the experimental procedure and the results obtained, and highlights possible means of limiting gold lock-up in future.

Jan 1, 1988

By G. H. Lind

Research into the safe and economic extraction of underground coal pillars in the Witbank and Highveld coalfields of South Africa highlighted that future practices will have to consider pertinent risks associated with this least safe of all underground coal mining methods conducted in South Africa. To this end, a computer-based program called A-PEP (Analysis for Pillar Extraction Potential) was developed to assess three aspects of this mining practice, viz. risks associated with the physical attributes, operational risk attributes and economic attributes. This intelligent tool can thus be used when planning to conduct underground pillar extraction to ensure that all pertinent risk elements and legislative requirements are considered to conduct this mining method safely before a submission is made to the Department of Minerals and Energy. Keywords: operational risk management, mine planning, underground coal mining, pillar extraction.

Jan 1, 2003

[COUNCIL FOR 1991/92 President R.D. Beck President Elect JP. Hoffman Vice Presidents Senior Junior Dr H. Scott-Russell J.A. Cruise Immediate Past President Honorary Treasurer H.G. Mosenthal J.A. Cruise Members of Council Dr N.A. Barcza G.A. Brown B.R. Broekman Prof. RJ. Dippenaar B.R. Fleetwood* J.S. Freer P.R. Janisch P.J. Knottenbelt Dr J. Lurie R.P. Mohring *Co-opted K.C. Owen P.D.K. Robinson D.A.J. Ross-Watt P. Smith K.A. van Gessel DJ. van Niekerk P. van Schaardenburgh* CJ.C.J. van Vuuren* P.M.T. White]

Jan 1, 1992

By C. Musingwini, A. S. Nhleko

"Since the Global Financial Crisis (GFC) in mid-2008, capital has been more difficult to access. Mining projects must contend with projects from other industries for scarce capital. A decision to invest available capital in mineral projects requires that valuation be conducted to assess the expected return on the projects. The discounted cash flow (DCF) analysis is generally applied for the valuation of mining projects, whereby future cash flows are discounted to present value using an appropriate discount rate. The discount rate significantly affects the outcome of a valuation. Economic and finance theory provides tools to calculate discount rates. The discount rate must account for factors such as the risk and stage of development of the mineral project; hence the appropriate discount rate to utilize in a project is often a subject of debate.The discount rate is the weighted sum of the cost of debt and equity. There are several methods for determining the cost of equity. This study considers the commonly applied Capital Asset Pricing Model (CAPM) and Gordon’s Wealth Growth Model because of their simplicity and availability of parameters required to estimate the cost of equity. This study explores how differences in the cost of equity obtained by these two methods can be explained for a mining environment. Data for empirical analysis were collected from the I-Net Bridge, McGregor BFA, and Bloomberg databases. It was found that Gordon’s Wealth Growth Model provides better estimates of the cost of equity compared to the CAPM under depressed market conditions. Therefore, this research recommends that Gordon’s Wealth Growth Model be used to estimate the discount rates for mining projects during periods of depressed market conditions."

Jan 1, 2016

By S. Kitamura

In recent years, the amount of ferritic stainless steel production has increased. However, the rust formation by the salt spray test was pointed out in the past. At the centre of the circular rust zone, pitting corrosion where water-soluble nonmetallic inclusions were embedded was observed. These inclusions originated from the suspended refining slag and consisted of multi-phase oxides and sulphides. By the experiments and thermodynamic consideration of the water-solubility, not only CaO or CaS, but also lime rich calcium-aluminates or calcium-silicates have shown large water-solubility. The composition of oxide phase in the inclusions was almost the same among the samples from molten steel, slab, or cold rolled sheet. On the contrary, CaS was clearly observed around the oxide in the sample of cold rolled sheet, although it was not found in the molten steel or slab samples. The enrichment of sulphur occurred from the desulphurization reaction of the suspended slag particles in the molten steel and also occurred from the diffusion of sulphur to the oxide inclusions during the heating of the slab. The optimization of refining slag composition has lead to produce the ferritic stainless steel without rust formation. Keywords: stainless steel, rust, calcium aluminates, calcium sulphides, water-solubility, refining slag, composition control of inclusions.

By K D. Wilkes

The WEMCO Heavy Media Drum Separator was first introduced by WEMCO in California in the 1940`s, initially from their base in San Francisco and later when the company moved to Sacramento. The WEMCO Company became a part of EIMCO Process Equipment in 1985, and in 2002 EIMCO became a part of the GL&V Group when Dorr-Oliver EIMCO was created. Throughout this period of time the WEMCO Drum has been installed on a variety of different applications and is now operating at the heart of many of the world?s largest Minerals and Coal Processing Plants, as well as being used by many smaller producers and metal re-cycling operations. This paper looks at the practical aspects of using WEMCO Drums in a representative range of processing applications.

Jan 1, 2006

By Jeremy Bosman, Johan de Korte

Traditionally the feed to coal preparation plants was de-slimed at 0,5 mm. The +0,5 mm size fraction was processed via dense-medium cyclones and the -0,5 mm size fraction was beneficiated with froth flotation, water-only cyclones or spirals. With the introduction of large diameter cyclones, the aperture sizes of de-sliming screens have progressively increased to about 3 mm in the belief that the larger cyclones are not able to effectively beneficiate coal which has a particle size below the ?breakaway? size. The efficiency of separation in the large dense-medium cyclones is improved by presenting a coarser feed to the units. At the same time, the capacity of the de-sliming screens is increased due to the larger screen apertures and in effect, the throughput capacity of the dense-medium section is increased. The 3 x 0,5 mm size fraction, which was previously processed in the dense-medium cyclones, is now added to the fine coal size fraction and processed by water-only methods such as Teetered Bed Separators (TBS) and spirals. Whether this practice is the most economical way to process the 3 x 0,5 mm size fraction requires further thought since the best processing route for the 3 x 0,5 mm size fraction will depend on a number of factors, amongst which are: o The washability of the coal and the amount of near-density material o Processing efficiency o Specification of the required product o The price paid by the customer for the product o The cost of processing the coal Breakaway size The ?breakaway? size is defined as the particle size below which the Epm of the smaller particles starts to decrease significantly. Bosman1 provides an approximate breakaway size versus cyclone diameter (Figure 1). It should be kept in mind though that the Epm of the small particles is a function not only of the cyclone diameter but also of feed pressure, medium density, medium viscosity, particle shape and density, top-size of particles in the feed, etc.

Jan 1, 2006

By D. S. van Vuuren

Titanium bearing resources can selectively be chlorinated at temperatures below 200°C if the Ti02 in the feed is nitrided before chlorination. However, the nitriding reaction is highly endothermic, requires highly reducing conditions, is only thermodynamically favourable at elevated temperatures, and is affected by mass and heat transfer restrictions. At the required processing conditions, problems might also be experienced with sintering and with melting of slag forming components in the raw materials. A test programme was undertaken to study the effects of raw material type, temperature, gas composition, bed depth, carbon to raw material ratio and residence time in order to simulate conditions required for scaling up a nitriding process. In contrast to previous experience with low-grade titanium-bearing slag containing about 30% Ti02, ilmenite and chlorinateable slag do not form melting phases under the studied nitriding conditions and hardly sintered at all. Both feed materials can readily be nitrided with conversions in excess of 90% at temperatures around 1300°C and using bituminous coal as reducing agent with fixed carbon in excess of 1.1 times the stoichiometric requirement. The conversion decreases as the bed depth of the feed material increases and the N2/CO ratio in the gas decreases. Analysis of the relative rates of mass and heat transfer into the reacting beds of ilmenite and slag showed that the heat transfer rates are more limiting than the mass transfer rates. In order to increase the throughput that can be achieved in a kiln, it would be necessary to take special measures to enhance the heat transfer rates into the mass of reacting material. One such a measure is to pre-form the mass of reacting material into thin-walled, hollow brick shapes prior to introducing it into a kiln. Depending on bed depth, temperature and N2/CO ratio, required residence times in the high temperature zone of the kiln can vary between about 6 and 10 hours. Keywords Titanium dioxide, titanium nitride, carbo-thermic, reduction, ilmenite, slag, tunnel kiln, residence time.

Jan 1, 2011