Search Documents

By M. B. Cortie, J. H. Potgieter

An account is given of the production of three types of experimental high-chromium duplex stainless steel. The alloys had chromium contents of 22, 29, and 35 per cent. The partitioning of the main alloying elements between the austenite and ferite phases was determined, and the effect of the alloying elements chromium, nickel, and molybdenum on the mechanical properties and corrosion resistance of the duplex stainless steels is summarized. The phase compositions of the different duplex stainless steels were measured by different techniques, and the values obtained were correlated. The cracking occasionally observed during the thermo mechanical processing of these alloys was studied, and is explained as being the result of known embritlement processes.

Jan 1, 1990

By H. Krogerus, P. Jokinen, T. Lintumaa

The energy consumption and recovery of chromium are important economic factors in ferrochrome production. Outokumpu has a lot of experience of the reduction behavior of the sintered pellets in industrial-scale furnaces and also on the grounds of numerous laboratory and pilot-scale investigations. Sintered pellets have shown a superiority over lumpy ore and briquettes made of the same chromite grade. The good performance of the pellets has also resulted in investigations on the reasons for such a performance. In this study, the factors affecting pellet behavior in smelting furnace were investigated. This study is divided into two sections, i.e. the investigations were on the factors affecting solid state reduction and on the factors affecting reduction under melting. These tests were performed by means of thermo gravimetry and by smelting tests. The correlation between the pellet characteristics and reduction behavior was shown and its influence on industrial-scale furnaces was discussed. Factors worth of consideration are for instance, the extent of oxidation during sintering, slag formation and chemistry in respect of molten state reduction, and the grain size of the chromite mineral in the raw material in respect of kinetic reasons (retention time in smelting).

Jan 1, 2007

By P. Falcão Neves

A detailed analysis of the geomechanical behaviour in rock cutting with a diamond saw is provided to obtain a better understanding of the mechanisms involved in the process. The energy of elastic deformation (before failure) and plastic deformation (post failure) was determined in uniaxial compression tests as well as the energy consumed per unit volume in the cutting process. The test samples are White and Ruivina marbles from Borba - Vila Viçosa in Portugal. Correlations between total deformation specific energy and cutting specific energy, normal and tangential forces and diamond indentation are analysed, and some conclusions are presented.

Jan 1, 2012

By Merete Tangstad, Kai Tang

The primary aim of the present investigation is to develop a model which permits to calculate/predict the viscosities of ferromanganese slags, typically focus on the MnO-SiO2-Al2O3-CaO-MgO-FeO multicomponent system. The present viscosity model emphasizes the ability of prediction, i.e. using the binary parameters to extrapolate the viscosities in ternary and higher order systems. To this end, a physical sound model is essential. Temperature dependence of viscosity is described by the Eyring?s formalism. The well-known cell model is used to define the SiO44- tetrahedra in the silicate melts. Composition dependence is expressed in term of viscous activation energy, which is characterized by the binary structural units. The viscosities in ternary and higher order systems are hence predicted using the binary activation parameters. The model has been used to calculate the viscosities in the whole liquid composition range of ferromanganese slag.

Jan 1, 2007

By A. Sissing

Paper written on project work carried out in partial fulfilment of M.Sc. (Chemical Engineering) degree Thermophilic bioleaching, conducted at temperatures in excess of 65°C, provides considerable benefit over mesophilic bioleaching, particularly through extending the extent of leaching of base metal minerals such as chalcopyrite. Thermophilic bioleaching is facilitated through a group of micro-organisms known as the Archae, well adapted to extreme environment. In order to maximize the space time utilization of the stirred tank reactor in the thermophilic bioleaching process, it is desirable to maximize the loading of the finely divided mineral phase present while not adversely affecting the microbial performance. In this paper, the effect of the loading of the solid particulate phase on the bioleaching performance of Sulfolobus metallicus was studied in a stirred tank reactor. Emphasis was placed on the effect of the concentration of the finely divided solid phase (35 ? 75 µm). A model system comprised of 3% (w/v) pyrite in the presence of varying quantities of quartzite in the range 0 to 24% (w/v) was used to obtain the different solids concentrations. The bioleaching experiments revealed similar bioleaching performance in the presence of 3 to 18% (w/v) total solids. Above 18% (w/v) total solids (15% quartzite loading), bioleaching was impaired progressively with increasing solids concentration. At the highest solids loading studied of 27% (w/v), bioleaching was still observed. In terms of mass transfer, oxygen transfer potential was not significantly influenced in the bioleaching process over the range of solids investigated.

Jan 1, 2003

By A. V. Z. Brink, D. M. O’Connor

Recent research into the prediction of mining-induced seismic events by the monitoring of small microseismic events at Western Deep levels Gold Mine is described. Measurement and interpretation techniques and results are presented. It was found that the occurrence of the larger events near longwall faces on the Carbon leader reef is preceded for some hours by an increased rate of microseismic emission and spatial concentration of the microseismic events in the zone of eventual failure. The research is currently being expanded with the aim of producing a practical rockburst early-warning system.

Jan 1, 1983

By M. Nakamura, T. Akamatsu

Embankment dams are often constructed on soft rock foundations in Japan, so it is important to precisely predict deformation of the foundations due to fill placement at the design stage. In order to accurately evaluate the settlement and the strain of the rock foundation surface during construction, the influence of the scattering of the deformability of foundations on the deformation behaviour should be investigated. In this paper, a method of evaluating the settlement and the strain of the rock foundation surface during construction was studied with stochastic deformation analysis considering the scattering of the deformability of the dam foundation. Based on the analytical results, a dam foundation design using the deterministic method considering the scattering of its deformability was discussed. Da in Japan Uferdämme of auf weichen Felsfundamenten gebaut werden, ist es wichtig, die Verformung der Fundamente auf Grund der Platzierung der Aufschüttungen bereits in der Planungsphase genau vorherzusagen. Im Zusammenhang mit einer genauen Beurteilung der Senkung sowie der Belastung der Felsfundamentoberfläche während der Bauarbeiten sollte auch der Einfluss der Streuung der Verformbarkeit der Fundamente auf das Verformverhalten untersucht werden. In der vorliegenden Studie wurde die Bewertungsmethode zur der Senkung sowie der Belastung der Felsfundamentoberfläche während der Bauarbeiten mit Hilfe von Wahrscheinlichkeitsanalysen der Verformung unter besonderer Berücksichtigung der Streuung der Verformbarkeit der Dammfundamente untersucht. An Hand dieser analystischen Ergebnisse wurde das Design der Dammfundamente dann enthusiastisch mittels deterministischer Methoden hinsichtlich der Streuung der Verformbarkeit diskutiert. Comme les barrages en remblai sont souvent construits sur des fondations rocheuses tendres au Japon, il est essentiel de prévoir précisément les déformations des fondations causées par la mise en place du remblayage durant la phase de conception. Afin d’évaluer avec exactitude le tassement et la déformation de la surface du rocher de fondation durant la construction, l’effet de la dispersion de la déformabilité des fondations sur le comportement de déformation doit être étudié. Dans cette étude, l’auteur a étudié la méthode d’évaluation du tassement et de la déformation de la surface du rocher de fondation durant la construction en procédant à une analyse aléatoire/stochastique de la déformation et en prenant en considération la dispersion de la déformation des fondations du barrage. En se basant sur les résultats de l’analyse, la conception des fondations de barrage avec la méthode déterministe considérant la dispersion de sa déformabilité a été activement discutée.

Jan 1, 2003

By J. Meintjes

by I. J. BARKER and A. B. STEWART J. MEINTJES I read the above paper with considerable interest. I would like to point out, however, that it is fallacious to conclude that the adverse effects of a high inductive reactance on furnace operation can be cancelled by connecting capacitors in series - or for that matter, in shunt - with the power supply.

Jan 1, 1980

By A. Koursaris, Y. N. Turan

This paper reports the results of a literature review carried out on nitrogen-alloyed austenitic stainless steels and their properties. It was found that a large volume of work has been carried out on the subject, particularly with regard to the more common stainless steels such as types 304 and 316. No work appears to have been conducted on the highly alloyed steels such as type 310S. Nitrogen has been found to increase the stability of the austenite in stainless steels and to impart significant improvements in the mechanical and corrosion properties of these alloys. Importantly, nitrogen appears to increase both the ductility and the strength of austenitic stainless steels over a wide range of temperatures.

Jan 1, 1993

By W. A. Gericke, B. Olmstead, I. Mc Dougall, C. F. R. Smith

A finite element model was generated of a Søderberg electrode in a ferromanganese smelter. In this model, the casing and fins were modelled explicitly, and temperature-dependent material properties were included. A two-stage analysis procedure was used, the first part being a coupled thermal-electrical analysis using an applied DC current. As the casing material was non-magnetic, the DC current was deemed sufficiently accurate for this initial analysis. The proximity effect was not considered. Thermal boundary conditions based on assumed temperature distributions in the furnace were applied. Calculated temperatures agreed well with measured values. The joule heat calculated in this step was applied as a load to a coupled thermalstress analysis. The model was applied to a comparative study of alternative materials for the casing and fins. A number of different combinations of materials for the casing and fins were evaluated in a comparative study. The position of the baking zone was used as the criterion for evaluating the potential of each material combination. Based on this analysis, some material combinations were discarded as being entirely unsuitable, whilst the two most suitable combinations will be tested experimentally in the furnace. The stress analysis was performed on the most suitable option. The practical advantage of this analysis was that a number of what-if scenarios could be evaluated and discarded prior to embarking on expensive experimental work, thus limiting the amount of experimental effort required. A mathematical model allows for the comparison of options under controlled conditions, where parameters of interest can be varied individually, with all other parameters remaining the same, a condition which is difficult to achieve in an operating furnace.

Jan 1, 2004

Mining plants operating in dunes north of Richards Bay have uncovered Iron Age archaeological material that spans the greater part of the past 2000 years. This was announced by archaeologists Gavin Whitelaw of the Natal Museum's Institute of Cultural Resource Management (ICRM), and Len van Schalkwyk and Mlungisi Ngubane of the KwaZulu Monuments Council (KMC), who are currently contracted by Richards Bay Minerals (RBM) to assess the cultural resources exposed during mining activities.

Jan 1, 1995

By H. M. Friede

Notes on the composition of pre- European copper and copper-alloy artefacts from the Transvaal by H. M. Friede. Ph.D. (Visitor) Seven copper artefacts (five ingots and two ornaments) found at prehistoric sites in the Transvaal were submitted to analysis. All the artefacts showed a high copper content and a relatively Iow level of impurities. A little-known ingot type from the Limpopo Valley ('nail' ingot) is described, and its analysis is given. The analysis of two copper ornaments that come from sites dated to the 5th Century AD. and the 11th Century AD. showed the constancy of the composition of copper articles over long periods. The well-known 'Blaauwberg Ingot' was re-analysed, and the results showed that this ingot cannot be regarded as a true bronze. Analytical values for the composition of three brass artefacts from Bambandyanalo (Mapungubwe), Northern Transvaal, are given. Some aspects of pre-European bronze manufacture and brass smelting, and of early metal trade from the East Coast into the interior of South Africa, are discussed.

Jan 2, 1975

By R. Hart

In this paper, problems that have been experienced with the rockpass system at Kloof Mine No. 3 Shaft are described. Actions that have been taken to overcome the problems are also described. These include the use of slugshots to remove hang-ups, the abandonment and waste filling of passes, and design criteria adopted for an alternative pass system.

Jan 1, 2006

By J. Wills

The use of drilling rigs to increasingly mechanize stope drilling has been acknowledged as important for the S.A. mining industry in it ís efforts to tackle the challenges of low productivity, AIDS and an ageing driller workforce. The spin-offs of increased safety, cost-effectiveness and better mining performance provide advantages to all?from the driller to the shareholder. However, implementation or product rollout has varied from outright success to dismal failure. A study of various cases by Novatek and Anglogold TDS showed clear reasons for these differences. Whereas the successes were characterized by clear objectives, accountability, user buy-in, a commitment to make the technology work and no-nonsense reporting, these were typically absent in failed implementations. The attitude at unsuccessful mines was to ?trial? the equipment?even subconsciously, a ?trial? is a test where failure becomes an acceptable outcome. During the study it became clear that mining management are not adequately trained to manage the often-tricky rollout process. They are often also not empowered or clearly mandated to deal with the organizational, human and technical issues that must dovetail to create a success. The output of the study was to develop a basic rollout process that could be used to formally manage the implementation of new drilling technology. Creating an alignment between the mine, workforce and supplier promotes a win-win situation that will not otherwise spontaneously arise.

Jan 1, 2002

By N. B. Devi

The extraction of copper(II) from sulphate solution was investigated using LIX®984N in kerosene. The parameters that could affect the extraction, such as equilibrium pH, extractant concentration, salt concentration, various diluents, and temperature, were separately investigated. On the basis of slope analysis, the complex formed in the organic phase is proposed to be CuR2, where R is the anionic part of LIX®984N. The extraction equilibrium constant and Gibbs free energy ( G) of the extraction process were determined. The positive value of H obtained from temperature variation studies showed that the extraction process is endothermic. The extraction of copper was lowest when chloroform was used as the diluent. Separation and recovery of copper from a synthetic copper-nickel solution containing 6.35 g/L Cu(II) and 0.58 g/L Ni(II) was carried out using 20%(v/v) LIX® 984N. The separation factor ( = DCu/DNi) was found to be pH-dependent. A two-stage batch countercurrent extraction was carried out at an O:A ratio of 3:4 at equilibrium pH 1.05 for extraction of copper from copper-nickel solution, followed by copper stripping from the loaded organic phase with 15% H2SO4 at an O:A ratio of 3:1.

Jan 1, 2014

By S. Kahraman

The correlations between the modulus ratio and penetration rate of rotary and percussive drills were statistically investigated using the raw data obtained from the experimental works of different researchers. An inverse power law was found between the modulus ratio and the penetration rate of rotary and diamond drills. The penetration rate of rotary drills and diamond drills decrease with an increasing modulus ratio. The penetration rates of percussive drills increase with an increasing modulus ratio. There are significant linear correlations between the penetration rates of percussive drills and the modulus ratio. In one of the cases of percussive drilling, a strong correlation between the penetration rate and the modulus ratio was found for the rocks having a porosity value lower 1.23 %. It can be concluded that the modulus ratio might be a representative measure of rock drilling efficiency. However, further study is necessary to check the validity of the derived equations for other rock types. The effect of porosity on the correlations between the modulus ratio and penetration rate needs to be further investigated.

Jan 1, 2003

NIM reports Report No. 1615 Fluorspar pellets. A survey of the world market and an assessment of future South African production. Report No. 1621 Correction for matrix effects in the analysis of solutions by X-ray-fiuorescence spectrometry. Notices Questionnaire on Technicians The Department of National Education's committee of enquiry into the education, training, utilization, and status of engineering technicians in the Republic of South Africa was established as a result of Resolution 6.3 taken at the Sixth Conference on Engineering Education: The Education and Training of Engineering Technicians. Vraelys oor Tegnici Die Departement van Nasionale Opvoeding se komitee wat ondersoek instel na die opleiding, gebruik en status van ingenieurstegnici in die Republiek van Suid-Afrika is gestig as gevolg van Besluit 6.3 wat geneem is tydens die Sesde Konferensie oor Ingenieursopleiding: Die Opleiding van Ingenieurstegnici. Competition for Student Members of the South African Institute of Mining and Metallurgy Each year the Institute offers a prize (or prizes should the entries warrant it) of up to R100 for the best paper or dissertation on a topic appropriate to the interests of the Institute. The competition is open to all Student Members of the Institute.

Jan 8, 1974

Contribution by W.D. Ortlepp? The authors are to be commended for publishing their interesting view of an aspect of deep-level mining technology that is becoming increasingly topical and vitally important. This is the second paper in the journal within four months to deal with the crucial needs of highly stressed tunnel construction, the other being the paper on the design and testing of rockburst support in the February 1994 issue. Both papers re-examine important innovative ideas that are more than a quarter of a century old, but that have not yet been implemented by the industry. It is to be hoped that they will now, taken together, serve as a new starting point for a definitive examination of what constitutes proper tunnel-support design. There can be no question that the need to develop a design approach that will solve the problems of tunnelling at depths of 4000 m or more has now become crucial. Contribution by A.M.J. Vervoort* Although the overall paper is very interesting and the future research (comparison between numerical simulations and underground measurements) will be very challenging, I would like to make some remarks regarding the set-up of the numerical model and the interpretation of the elastic results.

Jan 1, 1995

Actual observations of rockburst damage, together with some theoretical considerations, strongly suggest that conventional approaches to the design of tunnel support are inappropriate where there is a significant seismic risk. The present widely used support systems, which are based on stiff, fully grouted re-bars, are inadequate where rock displacement velocities exceed 1 m/s. It is shown by means of a simple conceptual model that yielding of the support elements is essential to ensure their survival when they are subject to the high strain rates typical of severe rockbursts. The model proposes that the total load in the element is an impulsive tensile force imposed and sustained by a single 'tributary' block ejected from the tunnel wall. The stability of the system is determined from a comparison of the kinetic energy developed by the block with the energy of deformation absorbed by a grouted steel tendon. A novel test procedure was developed for the validation of this approach, and for an examination of the energy-absorbing capacity of stiff and yielding tendons. The results of an initial series of tests showed that the recently developed cone-bolt is an effective yielding device. It absorbs twenty times more impulsive-load energy than is consumed by the complete fracture of grouted re-bar of equivalent strength, and it remains totally unscathed. Importantly, the results demonstrate that the ejection model is not merely an explanatory concept, but can be used as a representative and valid design method.

Jan 1, 1994

By G. Song, S. Yang

"SynopsisThe development of techniques and equipment for single-pass high-seam longwall mining in China is reviewed. Some methods used to obtain the fractured zone height are discussed. The boundary between the caved and fractured zones is generally not clear, but one important difference that distinguishes the two zones is that horizontal compressional forces exist only between blocks of fractured zone. Based on this, a theoretical method is presented to investigate the destabilizing modes of the main roof (by sliding or rotation) and is used to determine if the main roof is in the caved or fractured zone. This method considers the mining height, immediate roof thickness, bulking factor, main roof thickness, main roof strength, main roof periodic weighting interval, and vertical stress in the overlying strata. To verify the method, a representative physical model of Wangzhuang coal mine is developed. The movement of overlying strata and fractured zone height are thus obtained. According to the results, the total collapsed height of the strata reaches about 70 m above the coal floor; the first main roof bending interval is 45 m and periodic bending distance is 10–15 m; the maximum strata subsidence is around 62 mm; and the presence of a three-hinged arch causes the fluctuation of subsidence in the same stratum level. Based on the theoretical and experimental analysis, the middle of the main roof is considered the boundary between caved and fractured zone; the caved and fractured zone heights are about 21 and 49 m respectively.IntroductionThick coal seams (>3.5 m) account for about 44% of the coal rescource/reserves and more than 40% of the total annual production in China (Zhao 2004; Wang 2009). Three mining methods – slice mining, top coal caving, and single-pass high-seam longwall mining – are frequently used in underground thick-seam operations. Compared with slice mining and top coal caving, high-seam single-pass longwall mining significantly simplifies the mining processes, reduces roadway excavation, and improves coal production, productivity, and recovery. The favourable economics, high production, and technical simplicity make high-seam single-pass longwall mining one of the most popular underground mining methods for thick coal seams in China."

Jan 1, 2015