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By H. J. Glass

Collection, preparation, and analysis of blasthole chippings is expensive. Frequently, interpolation of grades at unsampled locations is considered using techniques like kriging. A pre-requisite for kriging is that an experimental variogram is established. In order to assess the quality of the experimental variogram, a measure is developed in this paper. The measure is derived from analysis of the time-honoured expression relating the variance, semivariance, and covariance. It reflects the weighted average deviation of the summed semivariance and covariance from the biased variance. The proposed measure allows assessment of the influence of key variables on the quality of the variogram. Using simulated data, it follows that the quality improves with an increasing number of samples, increasing density of the sampled locations, increasing regularity of the sampling pattern, and increasing uniformity of grades in the absence of correlation. Application to real data shows that the minimum number of samples could coincide with a marked decrease in the value of the measure. Establishing a threshold value is subject to further research. Keywords: variogram, variance, covariance, semivariance, minimization, sampling.

Jan 1, 2003

By C. Machio

This paper reports the results of a study to determine the effect of process control agent (PCA) on the characteristics of Ti-Mg powders during milling. It has been shown that a 2% increase in PCA content leads to up to a 40% increase in yield of the milled powder but reduces the kinetics of the mechanical alloying process. The introduction of 4% PCA decreases the mean powder particle size by up to 30%, whereas 6% PCA increases the mean particle size by up to 230%. The characteristics of the milled powders will be discussed in relation to the role of PCA in the milling process. Keywords Titanium?magnesium, mechanical alloying, PCA.

Jan 1, 2011

By S. P. Pereira

The mechanized mining cycle using loaders and shuttle cars had it speak in terms of usage in the mining industry during 1950 through 1960. In Brazil, this system is still used at underground coal mines in southern Santa Catarina coal basin. With the aim of investigating the benefits of a new mining scheme using the room and pillar method for these local mines, a computational simulator model was developed in order to investigate the mining cycle. This paper presents the methodology used to develop the simulator and the results that the simulation shows regarding impact of the proposed new scheme on mining productivity.

Jan 1, 2012

By S. P. Pereira

The mechanized mining cycle using loaders and shuttle cars had its peak in terms of usage in the mining industry during 1950 through 1960. In Brazil, this system is still used at underground coal mines in southern Santa Catarina coal basin. With the aim of investigating the benefits of a new mining scheme using the room and pillar method for these local mines, a computational simulator model was developed in order to investigate the mining cycle. This paper presents the methodology used to develop the simulator and the results that the simulation shows regarding impact of the proposed new scheme on mining productivity.

Jan 1, 2012

By D. J. Young

Alloys used at high temperature must resist both creep and corrosion. Design for corrosion resistance is based on the formation of a slow-growing, protective oxide scale by selective oxidation of an appropriate alloy component, usually chromium or aluminium. A successful scale will exclude other corrodents, notably carbon, which can otherwise cause extremely rapid corrosion at high temperatures. Selective oxidation of an alloy component necessarily lowers the concentration of that metal in the alloy subsurface region. Under thermal cycling conditions, mechanical damage to the scale leads to renewed oxide growth and accelerated alloy depletion. Eventually, a point is reached where diffusion of a corrodent into the alloy becomes competitive with the outward diffusion of alloy metal to repair the protective scale. Two examples of alloy failure by carbon attack are considered. In the steam cracking (pyrolysis) process, centrifugally cast tubes of heat-resisting alloy are exposed to a gas stream of hydrocarbon and steam, at a carbon activity of unity. Formation and repair of the surface chromia scale causes alloy depletion, Kirkendall void formation, and subsequent internal precipitation of chromium-rich carbides. Their formation makes chromia scale formation much more difficult, and generates internal stress. Eventually, the tubes fail by creep rupture. In other processes (e.g. steam reforming, heat treatment), synthesis gases are supersaturated with carbon at intermediate temperatures. Once the alloy's protective scale is breached, carbon attacks the depleted substrate. In the case of ferritic alloys, it forms a surface scale of Fe3C. As this scale thickens, the supersaturated carbon precipitates as graphite within its outer regions. The resulting volume expansion causes disintegration of the cementite in a process known as metal dusting. In the case of austenitic alloys, no metal carbide is formed. Instead, carbon dissolves in the depleted metal to diffuse inward and precipitate as graphite within the metal matrix. Again, volume expansion causes disintegration of the alloy, and metal dusting results. Dusting occurs at an extraordinarily rapid rate, and leads to failure by section loss or even penetration.

Jan 1, 2013

By A. Aitio

Sustainable development is one of the central themes of the work of the World Health Organization; chemical safety is one of its important components. For more than 25 years, WHO has had specialized units for assisting member countries in dealing with their problems in chemical safety. For one of the units involved, International Programme on Chemical Safety, a reorientation is in progress to make best use of existing resources, and to prioritise the work to optimally correspond to the needs of the member countries. The risk assessment work of IPCS, and specifically, the work on chromium and chromium compounds, are discussed.

Jan 1, 2004

By Godofredo F. Barrios

For years urethane screen surfaces have been used in a wide range of wet screening applications where openings from as fine as 100 microns and coarser have been used. The purpose of this paper is to expose the reader to new developments in both screen surface and screening equipment technologies which allow an end user to consider urethane screen surfaces for fine screening applications. These technologies allow an end user to use the inherent advantages of urethane with regards to wear resistance while also realizing the benefits that a high oper area urethane screen surface can bring. These benefits include non blinding characteristics and feed capacities that which rival that of traditional stainless steel surfaces. The paper will highlight the features of this patented urethane screen surface technology and the screening machines they are used in conjunction with. There will also be a presentation of case studies of commercial installations where these technologies are utilized. These case studies are from the base metals industry therefore relevance to the conference is direct and not inferred. Included in the paper will also be constraints which must be taken into account when considering urethane screen surfaces such as temperature and chemical attacks. This paper will expose potential end users to a possibility of using screens to achieve extremely accurate size separations in applications where screens were previously not considered. The paper will explain and demonstrate that prior concerns of screen surface blinding, high screen surface consumption rates and large screen surface area requirements can be eliminated by proper utilization of high open area urethane screen surfaces.

Jan 1, 2007

By Du Sichen, K. Mukai, S. Seetharaman

Viscosities of slags constitute an important physical property needed for an understanding of the mass transfer phenomena in metallurgical processes. Viscosity is also the key that leads to a better understanding of the structure of slags. It is well known that the viscosities of silicate slags decrease with the addition of basic oxides due to the breaking of the silicate network. The measurements of slag viscosities often pose experimental challenges, especially to the choice of materials. The keynote lecture takes up the experimental problems and the various techniques adopted. Dynamic viscosity measurement, as a powerful tool towards an understanding of the kinetics of some high temperature reactions, is brought out. A number of semi-empirical models have been developed to estimate the slag viscosities in the case of multi component slags. A critical survey of these models is presented in the lecture. Earlier models by Riboud et al., Urbain et al. and Mills et al. have been developed further into a new generation of models. Some of the current important models are (1) Model by Iida et al. (2)CSIRO model (3) Pyro research Model (4) Model by Tanaka et al. (5) Model approach by Reddy et al. and (6) KTH-model. The predictions and capabilities of the various models are compared. Estimations of viscosities from thermodynamic data and prediction of liquidus temperatures from viscosities are presented. The concept of surface viscosities with reference to slags and viscosities of two-phase mixtures are also taken up in the presentation.

Jan 1, 2004

By T. Markus, K. Hilpert

Discharge vessels of advanced light sources are made of translucent polycrystalline Al2O3(PCA).These tubes contain salt mixtures, which essentially consist of metal halides. The salt mixture is present as a melt at the coldest spot of the vessel under operating conditions and vaporizes partly. The temperatures of the coldest spot range between 1200 K and 1300 K, depending on the lamp performance. The maximum wall temperatures range up to 1500 K and for special purposes up to1700 K. Important constituents of the melt are alkali halides AX (A = Na, Cs, X= Br, I) and rare earth metal halides LnX3(Ln = Dy, Ho, Tm). Severe corrosion attack on the wall material is observed in the PCA discharge vessels. The aim of this work is to elucidate the corrosion mechanism. Annealing experiments under well defined temperatures were carried out in order to understand the complex chemical corrosion processes. Two different annealing vessels were used, one for experiments under isothermal conditions with a temperature of 1473 K and one for experiments with a linear temperature gradient from 1450 K to 1600 K. The vessels were filled with salt mixtures of different compositions and annealed for 1000 h. The corrosion attack was characterised by XRD, analytical electron microscopy, high temperature mass spectrometry, and chemical analysis of the salt melts. The results of our investigations show that the corrosion attack is caused by vapour species and by the salt melt. The most severe corrosion is observed in vessels filled with mixtures of alkali halides and rare earth metal halides. No corrosion of the alumina is practically observed if pure alkali halides or pure rare earth metal halides are present in the annealing vessel. Keywords: thermodynamic, corrosion, lamps, metal halide salt

Jan 1, 2004

By M. Moys

The use of temperature measurements for unusual applications in the analysis and control of column flotation and milling is discussed. This is followed by a review of some of the authors current research in the application of the discrete element method to the modelling of particulate processes, specifically milling, fluidized beds and chute flow.

Jan 1, 2005

By S. E. Olsen, T. Færden, G. Tranell, T. Lindstad, J. Lubetsky

The authors are lead authors for chapter 4.3 ?Emissions from Ferroalloy Production? in ?2006 IPCC Guide-lines for National Greenhouse Gas Inventories, Volume 3?. The paper discusses the methods to calculate and report emissions from the production of ferrosilicon, silicon-metal, ferromanganese, silicomanganese and ferrochromium alloys, as well as the basis for the methods and choice of emission factors. CO2 is the main greenhouse gas emission from ferroalloy production, accounting for about 95 % of the total CO2-equivalents. The most accurate method of determining emissions is to base the calculations on reported amounts and analyses of reducing agents and carbonate ores used in the process. If analyses are not available, typical CO2 emission factors for the different reducing agents are recommended. If neither reliable amounts nor analyses of all reducing agents are known, default generic CO2 emission factors for the type of ferroalloy multiplied with amount produced, can be used. The CO2 produced from bio-carbon (charcoal and wood chips) should be reported but will not be accounted for in national emissions. If any bio-carbon is used, the default generic CO2 emission factors cannot be applied. CH4 accounts for less than 1 % of the total emission of CO2-equivalents. Default emissions factors for CH4 are given for the production in open or semi-closed furnaces of silicon-metal and ferrosilicon. In the production of FeMn, SiMn and FeCr in closed furnaces the gas containing CO,CO2 and volatiles can be combusted in boilers and N2O may be formed. While reporting is not required, IPCC Guidelines recommend that the N2O-content in the off-gas is measured.

Jan 1, 2007

By F. Essrich

A quantitative rockburst hazard assessment procedure was introduced on Elandsrand Gold Mine at the end of 1994. It is currently used to evaluate the seismicity-related risk in production areas on the mine. Six parameters related to seismicity, geology, mining layout, and production are rated and results are used as a planning tool on a regular basis. The applied assessment can be considered successful in that it promotes awareness of the seismic hazard and provides an opportunity to address seismicity-related mining problems. A comparison between high risk panels and those working areas with rockburst incidents showed that high hazard ratings reliably forecast the occurrence of larger events in the following month but they do not necessarily predict those working places with rockburst-related accidents. From this one may conclude that high levels of seismicity do not coincide with high rockburst rates.

Jan 1, 1997

By D. Tesh

The mining industry worldwide is facing a tremendous shortage of minerals engineers in all fields of specialization. For instance, in Australia the skills shortage in the mining industry has been identified as one of the top risks facing the mining industry. In Namibia most minerals engineers employed are expatriates, with some being Namibians who studied abroad. The minerals engineering programmes at the Polytechnic of Namibia are still in their infancy. These programmes were designed to meet the mining industry skills needs. Being young has its advantages in that lessons can be learnt from older minerals education institutions that went through similar challenges. However, this does not imply just copying and implementing their approaches, since the context differs and, to ensure sustainability of the minerals education programmes, curricula have to be customized to the local context. This paper reviews the interventions made by the Polytechnic of Namibia in order to ensure the sustainability of its minerals education programmes. The methodology consisted of an extensive literature review, a status quo analysis of the mining and process engineering department, identifying the gaps between the current state and desired state, and mapping the goals and strategic actions required to progress to the desired state. The following factors were identified as major threats to the sustainability of minerals education at the Polytechnic of Namibia: the quality of students, low student enrolment rates, low pass rates in science and mathematics, shortage of academic staff, dwindling government funding, and limited involvement of the mining industry. The major outcomes of this research comprise the detailed strategic actions employed by the Polytechnic of Namibia to address the threats to sustainability of its minerals education programmes.

Jan 1, 2014

By V. Tathavadkar

Worldwide TiO2is extracted from natural ilmenite, rutile, and anatase minerals via the sulphateand chloride processes. The sulphate process generates large volumes of less toxic wastes, whereas the chloride process, including the ilmenite-chloride process of DuPont, yields much lower volume of wastes, which are highly toxic and hazardous. The treatment and disposal of such hazardous chloride wastes is both expensive and difficult in terms of long-term monitoring. Besides the waste management and disposal, there is also a shortage of high-grade titanium dioxide minerals in nature, which consequently yields much larger tonnages of sulphate and chloride wastes. In the present investigation we report the results of an alternative titaniferous mineral beneficiation process based on soda ash roasting of minerals. Compared to the conventional processes for beneficiation of TiO2- ores, the alkali roasting of titaniferous offers several advantages including the zero process wastes. In the soda ash roasting process, the mineral is mixed with sodium carbonate and heated above 1023 K in air. The oxidative roasting of ores yields several complex alkali compounds, some of which produce a liquid mixture above 1123 K. In this paper, we have attempted to characterize the composition and physical chemistry of alkali-rich liquid phase. The phase equilibria in the Ti-(M:Fe)-Na-O system are evaluated and compared with the phases formed as a result of roasting reaction. The experimental results revealed that the composition of complex alkali liquid at the reaction interface plays an important role in determining the transport of O2-ions and decomposition of ilmenite. The roles of the crystal structure of mineral phases and their energetics are also emphasized in controlling their decomposition during alkali roasting. The presence of molten alkali in controlling the partitioning of water-soluble alkali salts and insoluble sodium titanate is also explained. Keywords: ilmenite, anatase, alkali roasting, phase equilibria.

Jan 1, 2004

By A. S. Macfarlane

This paper describes how knowledge of the orebody morphology and ore morphology can be used to optimize the planning, mining, and metallurgical output from an open pit copper mining operation, such as to significantly increase the stability of the whole value chain process, and increase the reliability and value of the process outputs. In the case under consideration, the orebody contains both copper and cobalt. This in itself provides a challenge, in that the two metals do not occur in consistent ratios across the orebody as a whole. Furthermore, mineralogical differences within the orebody have a significant impact on plant performance in terms of throughput rates, acid consumption, and recoveries. In order to stabilize and optimize the plant performance, it is necessary to firstly have a complete understanding of the geometallurgical factors that affect performance, and then to have a sound knowledge of how these are distributed within the orebody. These models then inform the mine planning strategy that optimizes cash flow and NPV, and also allow the development of a stockpiling strategy that not only stabilizes the plant, but also allows variations in the plant feed according to ore type and grade in volatile price scenarios. Integral to the realization of these opportunities is the establishment of an appropriate measuring, control, and reconciliation system, customized to the optimization objectives. The paper describes how all of these factors and strategies can be integrated to produce optimal value from the orebody through to final dispatched product. It also shows the significant value that can be released through such an approach.

Jan 1, 2014

By H. Kose

In this research, a model quarry with an annual production capacity of 1 000 000 tonnes has been studied for both pit and hillside quarry cases with constant overall slope angle and variable bench slope angle, considering road grades of 8 per cent and 10 per cent. First, technical requirements have been determined and then the effect of production parameters, such as hole diameter, type of quarrying (pit or hillside) and road grade, on the cost has been investigated to determine bench height. Based on the results, it has been concluded that hole diameter has to be kept large in both pit and hillside quarrying to reduce drilling unit costs. In addition, in order to take advantage of gravity and reduce transportation cost, it has been suggested that bench height and road grade have to be kept high and low respectively in the case of hillside quarrying (downhill transportation) while, in the case of pit quarrying (uphill transportation), bench height and road grade have to be kept low and high respectively, in order to transport the blasted material to a lower height and distance, to save energy, thus decreasing the transport cost. Keywords: Quarry, pit, hillside, road grade, bench height

Jan 1, 2005

By P. Goosen, A. Paterson, E. Paulsen

Ticor South Africa is currently involved in the mining and processing of a heavy mineral oredeposit at Hillendale Mine on the KwaZulu-Natal north coast. The orebody is characterized by a high ultra fine fraction (-45µm) that has a variable rheological behaviour when subjected to shear and hydration. Experience at Hillendale has shown that the ultra fine mineral tailings are sensitive to shear history in terms of shear intensity and shear duration as well as hydration history. This phenomenon expresses itself right through the primary beneficiation process influencing the mineral separation, but is especially prevalent on the residue disposal i.e. slurry transport and deposition on the tailings impoundment. Tube viscometer test work was conducted on the flocculated fine tailings that indicated that there was a change in rheology as a result of shear. This paper presents the results of the on-site test work conducted at the mine to measure the rheology at various stages in the process.

Jan 1, 2003

By J. C. van Dyk

The objectives of this study were firstly to characterize and quantify the inorganic material in the Secunda gasification feedstock. Secondly, the effect of washing on coal properties and sulphur content was investigated. Coal from a single source and a coal blend from 6 different mines were tested. Composite samples were visually sorted by a geologist in the groups containing roof, floor, C-shale, pyrite, carbonates and siltstone material. Inorganic mineral types from the single source and coal blends were characterized separately. Characterization results indicate that the average mineral matter distribution (mass %) of the coal tested was as follows: carbonates (6%), carbon-shale (19%), pyrite (12%), roof (18%), floor (46%) and siltstone (22%). The roof, floor, pyrite, carbon-shale, carbonates and siltstone in the single source and coal blend have similar chemical properties and characteristics, except for the ash melting temperatures of pyrite and kaolinite in the siltstone. By implementing selective mining and increasing mining management practices, the percentage discard in the run of mine coal can be significantly reduced, by up to 45%, if the mining of roof and floor material can be avoided. No significant impact of mining practices on sulphur content is expected in this case due to the low concentrations of sulphur in the roof and floor material. In summary, selective mining practices will probably result in almost45% decrease in the discard content in the run of mine to gasification, an increase in the carbon content from 55.0% to 58% (air dry basis) and a decrease in sulphur content from 1.1% to 0.9% (air dry basis). It is clear from this study that the main source of sulphur is not in the high ash-content mineral types (e.g. floor and roof), but in situ in the coal structure. Keywords: inorganic material, effect of washing, roof, floor, pyrite, C-shale, carbonates and siltstone

Jan 1, 2005

By A. Golshani, M. Oda, K. Suzuki, T. Takemura

Anisotropic behaviours of OhshimaOshima granite were investigated by carrying out uniaxial compression tests, together with observations of microcracks under an optical microscope. The elastic modulus tensor of Oshima granite at 10 per cent strength,E10, were calculated using theoretically formulation of elastic modulus tensor in terms of the second-rank crack tensor for pre-existing open microcracks. Furthermore, with the assumption of orthorhombic elasticity, the nine moduli of Oshima granite E10were determined by uniaxial compression test. Twenty-onemoduli of samples, calculated without assuming any symmetry, also showed orthorhombic features. Direction of the symmetry axes agreed well with the orientation of preexisting cracks. Comparison of crack tensor-based formulation results with the experimentally determined one show that the anisotropy of elasticity of Oshima granite is caused by pre-existing open microcracks, not by pre-existing healed microcracks and also crack tensor formulation can be used, as a first-order approximation at least, to describe the anisotropy of Oshima granite induced by pre-existing open microcracks. ZUSAMMENFASSUNG: Das anisotrope Verhalten des Oshima-Granits wurde mit Hilfe voneinachsigen Kompressionstests und durch die Betrachtung von Mikrorissen unter einem optischenLichtmikroskop untersucht. Das Elastizitätsmodul von Oshima-Granit bei 10 Prozent Kraft E10wurde berechnet, indem man die Formulierung des Elastizitätsmodultensors, ausgedrückt alsRisstensor zweiter Ordnung theoretisch auf bereits existierende Mikrorisse angewandt hat.Außerdem wurden die neun Module des Oshima-Granits unter der Annahme orthorhombischerElastizität E10mit einem einachsigen Kompressionstest bestimmt. Einundzwanzig Stichproben,die ohne die Annahme irgendeiner Symmetrie genommen wurden, zeigten ebenfallsorthorhombische Merkmale. Die Richtung der Symmetrieachsen stimmte mit der Orientierungbereits vorhandener Risse überein. Der Vergleich der Ergebnisse der auf dem Risstensorbasierenden Formulierung mit der experimentell bestimmten Formulierung zeigt, dass dieAnisotropie der Elastizität von Oshima-Granit von bereits vorhandenen offenen Mikrorissenverursacht wird, und nicht von vorhandenen vernarbten Mikrorissen, und dass dieRisstensorformulierung auch zumindest für eine Annäherung erster Ordnung benutzt werdenkann, um die durch vorhandene offene Mikrorisse induzierte Anisotropie des Oshima-Granits zubeschreiben. RESUME: Les comportements anisotropes du granit d’Oshima ont été étudiés en réalisant destests de compression simple, et en observant les microfissures au microscope optique. Le tenseurdu module d’élasticité du granit d’Oshima sous une résistance de 10 pourcents, E10, a été calculéen se servant de la formule théorique du tenseur de module d’élasticité basé sur le tenseur defissures de second ordre des microfissures ouvertes préexistantes. En outre, sur base del’hypothèse de l’élasticité orthorhombique, les neuf modules du granit d’Oshima ont étédéterminés par des tests de compression simple. Vingt et un modules d’échantillons, calculés endehors de toute hypothèse de symétrie, ont aussi montré des caractéristiques orthorhombiques. Ladirection des axes de symétrie correspondait bien à l’orientation des fissures préexistantes. Lacomparaison des résultats de la formule basée sur le tenseur de fissures avec les résultatsdéterminés expérimentalement montrent que l’anisotropie de l’élasticité du granit d’Oshimaprovient des microfissures ouvertes préexistantes, et non de microfissures préexistantes referméeset que la formule du tenseur de fissures peut servir, au moins comme première approximation, àdécrire l’anisotropie du granit d’Oshima marqué par des microfissures ouvertes préexistantes.

Jan 1, 2003

By D. K. Chibwe, P. Taskinen

"This investigation consists of a numerical and physical modelling exercise on flow patterns, mixing, solid-liquid mass transfer, and slag-matte phase distribution in a 0.2-scale cold model of an industrial Peirce-Smith converter (PSC). Water, kerosene, air, and sintered benzoic acid compacts were used to simulate matte, slag, injected gas, and solid additions into the PSC. The 2D and 3D numerical simulations were carried out using volume of fluid (VOF) and realizable k-e (RKE) turbulence models to account for the multiphase and turbulence nature of the flow respectively. These models were implemented using the commercial computational fluid dynamics numerical code FLUENT.Numerical and physical simulations were able to predict, in agreement, the mixing and dispersion characteristics of the system in relation to various blowing conditions. Measurement of mass transfer indicated that fluid flow in the PSC is stratified. Blowing configurations and slag volume both had significant effects on mixing propagation, wave formation, and splashing.As a potential process alternative to increase conversion efficiency, we propose a combined blowing configuration using top lance and lateral nozzles. The numerical simulations were conducted on combined as well as lateral blowing conditions, and the results of the combined concept are encouraging."

Jan 1, 2015