Search Documents

By J. G. van der Watt

Due to increasing concerns of global rare earth element shortfalls in the near future, possible alternative sources of rare earth elements have recently become of economic interest. One such alternative is decanting acid mine water originating primarily from abandoned old mines in the Witwatersrand region of the Republic of South Africa. In this study, a novel way of rare earth element removal from the acid mine drainage was employed, making use of bentonite clay, which has very good adsorbent properties, as a rare earth element carrier material. The process can be economically viable only, if the elements can be selectively removed from the bentonite clay carrier material so as to yield reusable clay. Acid leaching was proposed to liberate the adsorbed rare earth elements from the bentonite clay. Accordingly, acid leaching experiments were performed to study the desorption of three commonly-found rare earth elements, namely neodymium, samarium, and dysprosium, from bentonite clay in the presence of sulphuric and hydrochloric acid. It was established that the three rare earth element species could be selectively removed as a group from iron, magnesium, and manganese metals through the careful manipulation of the pH. An investigation into the kinetic aspects of the rare earth element desorption process from the bentonite clay was also undertaken. The applicability of various kinetic models such as zero-order, pseudo first-order, pseudo second-order, elovich, parabolic diffusion, and power function were tested to describe the time-dependent desorption of rare earth elements from bentonite clay. It was determined that the pseudo second-order kinetic model represented the dissolution processes for neodymium, samarium, and dysprosium from bentonite clay the most accurately.

Jan 1, 2012

By Chris M. Haberfield, Neil D. Benson

The assessment of overall modulus (or stiffness) of a fractured weak to moderately strong rock mass is a key parameter in the design of civil engineering works in these materials. It also provides the highest level of uncertainty due to scale effects, anisotropy and the influence of joint frequency and joint stiffness. Using the example of the Melbourne Mudstone, this paper compares approaches using empirical rules based on intact rock strength, laboratory testing, in situ field testing, semi-quantitative assessment techniques based on rock mass classification and back analyses. L'évaluation du module (ou rigidité) global d’une masse rocheuse faible et fissurée a modérément forte est un paramètre principal dans la conception des travaux du génie civil dans ces types de matériaux. Elle fournit également le niveau le plus élevé d'incertitude due aux effets d’échelle, à l'anisotropie et à l'influence de la fréquence et de la rigidité des joints rocheux. En utilisant l'exemple du schiste de Melbourne, cet article compare des approches empiriques basées sur la force intacte de La roche, les essais expérimentaux au laboratoire, les essais sur site, les techniques semi-quantitatives d'évaluation basées sur la classification de la masse rocheuse et les analyses en retour. Die Schaetzung des allgemeinen Steifigkeit-Moduls des gebrochenen schwachen bis zu maessig starken Felsmassen ist eine Haupt- Annahme in dem Entwurf von Tiefbau-Projekten in diesen Materialien. Es verursacht den hoechsten Grad der Ungewissheit in Folge der Groessenordnung, Spaltorientierung und dem Einfluss der Haeufigkeit der Risse und Bruch-Steife. Unter Verwendung des Beispiels des Melbourner Tonsteine, vergleicht diese Darlegung die Anwendung der empirischen Regeln, die sich auf die Staerke des ungestoerten Fels Basieren mit Versuchen in der Material Pruefungsanstalt, Untersuchungen auf der Baustelle und halb-quantitative Schaetzungsverfahren, die sich auf die Felsmassen Klassifikation und fruehere Analysen stuetzen.

Jan 1, 2003

A General Meeting and Colloquium was held in Kelvin House, Johannesburg on Wednesday 29th September, 1971. The theme of the Colloquium was "The Ferro-alloy Industry". Prof D. D. Howat (President) was in the Chair. The meeting was attended by 106 delegates and was opened by the President at 10.05 a.m. OBITUARY The President: "It is my sad duty to announce the death of G. C. Needham, Fellow, who joined the Institute in 1966 and passed away on 27th September, 1971. As a mark of respect to the memory of the deceased and in sympathy with the bereaved I would ask you all to rise and observe a few moments silence." MEMBERSHIP The President: "I have much pleasure in announcing that the names of the following candidates, having been published in accordance with By-Law 5.2.2, Council has elected them to membership of the Institute. Fellows: Richard Lloyd Blandy, Brian Roger Borton, Brian Teversham, Peter Donald Dickson. Members: Frederick Brian Peacock, Peter John Stacey, Kenneth Niles Thanstrom, Byron J. Hayley, Ian Flemming Buchan, Abraham Hercules le Roux. Graduate: Ian William Coy. Students: Peter Boesley J ames, Kenneth Brian Perel. TRANSFERS From Member to Fellow: Cecil Eugene Fivaz, Peter Edwards. From Student to Graduate: Roy Stavely Traviss. From Student to associate: William Mitchell. I welcome the new members to the Institute and congratulate those members who have been transferred to a higher grade. COLLOQUIUM The first paper, presented by Mr S. Selmer-Olsen, Consulting Metallurgist, Amcor Limited, on 'Trends in Ferro Alloy Production' was published in the May issue of the Journal and comprised information and data relating to new developments in ferro alloy production in various parts of the world. This was followed by a paper-'Conductivity and Viscosity Properties of Slags produced in ferro-alloy manufacture' by D. 1. Ossin et al. This was a record of laboratory test work on slags containing both lime and magnesia, corresponding with the composition of slags encountered in the production of ferro chrome alloys when a dolomite flux is employed. The third paper-'Review of the work of the Pyrometallurgical Research Group of N.I.M. and Metallurgy Department, Wits.' presented by Dr P. R. Jochens, leader of the Research Group, outlined the progress made on ten different research projects presently under way in the Department of Metallurgy. These projects range from studies of the kinetics and mechanism of the reduction of chromite ores through the determination of the activities of MnO in slags to phase studies and melting point determinations in the alloy systems Cr-Fe-Si-C and Cr-Fe-Si. A new feature of this Colloquium was the introduction of the discussion panel composed of four or five individuals known to have special knowledge or interest in the subject under duscussion. Mr J. J. Coetzee was chairman of the first panel, Professor D. D. Howat of the second and Dr R. E. Robinson of the third. During the discussion of Mr Selmer-Olsen's paper an interesting contribution was made by Mr Jack Hayley of Transalloys (Pty.) Limited who pointed out that the lowest power cost in the U.S.A. was that from the TV A at 6 mils per unit (0,43 cents S.A.) while costs from other sources were 7 to 8 mils per unit (0,50 to 0,57 cents S.A.) He also referred to the use of 'pile sintering' of ore fines plus coke at certain ferro alloy plants in the V.S. and to the recent practice of 'graphitising' the paste used for Soderberg electrodes. The last session in the afternoon was devoted to a group discussion on 'Practical problems in Arc Furnace Operation', Mr H. R. Reid of Middelburg Steel Alloys (Pty) Limited occupying the chair, members of the panel being Mr J. Meintjies (Rand Carbide Limited), Mr J. Benn (Amcor) and Mr E. J. Jackson (Transalloys (Pty.) Limited). Mr Reid initiated the discussion by talking of the design and composition of electrode shoes, mentioning the use of the 85/15 Cu/Zn alloy and the comparison of hollow shoes and shoes cooled by tubes. Mr Meintjies discussed electrode management with particular reference to breakages, and dealt with casing and fin design and the welding of fins. Mr Benn dealt with aspects of closed top furnace operation with particular reference to the control of eruptions in the furnace and indicated that preheating of the raw materials might be well worth considering together with the development of a system for the detection of the water vapour present. Mr J ackson was concerned with shells, linings, refractories and tap holes. He deprecated the use of oxygen for opening the tap hole emphasising how uncontrolled use of oxygen led to loss of shape of the tap hole and quite severe burning out of the front hole resulting in time and labour in repairs. A notable feature of the Colloquium was the free discussion 'from the floor' of the hall. Many valuable and highly pertinent contributions were made spontaneously and usually in reply to some controversial topic raised by the discussion group.

By R. M. Spang

Abstract Between the German city of Dresden and the Czech capital Prague a 4-lane highway is under con-struction. At the outskirts of Dresden it will cross the narrow and deeply eroded Weißeritz Valley by a bridge. Two twin tube tunnels under oblique angles join the bridge out of the rocky valley flanks. The different geotechnical conditions of these 4 tunnel portals, their design and construction are described within this publication. The two southern portals of the tunnel Dölzschen are situated within a vertical 65 m high former quarry slope, 25 m above the valley floor. The slope proved instable due to toppling failure and exposed serious rockfall risks. Systematic anchoring, scaling, rock bolting, netting and filling under extreme access conditions eliminated these risks. Tunnel excavation started from the slope surface without any pre-cut or conventional portal construction. The opposite northern portals of the tunnel Coschütz are situated in more gentle rock slopes. After removal of debris, excavation of the eastern tunnel started in a 30° slope striking oblique to the driving direction, without any precut, too. Because of the gentle slope inclination the cross section was not earlier completely covered by rock than 30 m behind. The western tunnel started from an optimized short, narrow and steep precut. Its flanks were stabilized by reinforced shotcrete and rock bolts. Because of the small distance between the tubes rock bolts were drilled into the cross section of the neighboring tunnel. Tunnel excavation was made by drill and blast operation, preliminary support consisted of steel arches, reinforced shotcrete and radial rock bolts. Thorough survey of the bolt’s coordinates and direction prevented them from meeting each other. Rock bolts were of the permanent type to prevent the final lining from being obliquely loaded. Systematically arrayed measuring devices checked deformations of slopes and tunnels. Zusammenfassung Der Neubau der Bundesautobahn A 17 wird Dresden und Prag miteinander verbinden. Die vierspurige Autobahn quert westlich von Dresden das enge und tief eingeschnittene Tal der Wilden Weißeritz mit einer Brücke. An beide Brückenwiderlager schließen mit schiefwinkligem Anschnitt doppelröhrige Tunnel an, deren Portale in den felsigen Talflanken liegen. Die unterschiedlichen geotechnischen Verhältnisse, die Überlegungen für einen jeweils optimalen Entwurf und der Bau der portalnahen bergmännischen Tunnelabschnitte sind Gegenstand dieser Veröffentlichung. Die Südportale des Tunnels Dölzschen liegen in einer vertikalen, 65 m hohen Felswand, 25 m über dem Talgrund. Die Felswand erwies sich als global kippgefährdet, außerdem lagen flächig verteilte erhebliche Steinschlag- und Felssturzrisiken für Bau und Betrieb vor. Die Kippgefahr wurde durch ein Systemraster aus vorgespannten Felsankern, die Steinschlag- und Felssturzrisiken durch bergsteigerisches Beräumen mit dem Brecheisen, Felsnägel und Steinschlagschutznetze eliminiert. Der Tunnelausbruch begann von einer Vorschüttung direkt in der Felswand ohne Voreinschnitt im Schutz einer kurzen Luftbogenstrecke. Die gegenüberliegenden Nordportale des Tunnels Coschütz befinden sich in wesentlich flacheren Hängen. Nach dem Aushub einer mehrere Meter dicken Abraumhalde begann der Tunnelausbruch der östlichen Röhre asymmetrisch mit einer Luftbogenstrecke in einer spitzwinklig zur Vortriebsrichtung streichenden, 30° mit dem Vortrieb steigenden Felsfläche, ebenfalls ohne Voreinschnitt. Wegen der flachen Neigung der Böschung war der Tunnelquerschnitt erst nach 30 m vollständig überdeckt. Für den Vortrieb der westlichen Tunnelröhre mussten erst eine zwischen den Röhren vorhandene Felsnase teilweise abgetragen, die westlich anschließende zurückspringende Felswand vertikal gestellt und gesichert und Felsaushub in der rechten Flanke getätigt werden. Der damit entstehende Voreinschnitt wurde so kurz wie möglich und ohne seitliche Arbeitsräume ausgeführt. Die Sicherung der Böschungen erfolgte mit bewehrtem Spritzbeton und Felsnägeln. Wegen des geringen Abstands der beiden Röhren wurden die unteren Lagen der radialen Ausbruchsicherung durchgeankert. Der Tunnelvortrieb begann im Schutz eines geankerten Portalkranzes und ebenfalls von einer Luftbogenstrecke aus.

Jan 1, 2003

By J Taguta, B. McFadzean, P. E. Ngoepe, M. G. Mulaudzi

Computational modelling methods and isothermal titration calorimetry (ITC) were employed to investigate the interaction of a pyrite surface with thiol collectors. Modelling work was conducted in the presence and absence of water. Microcalorimetry was employed to investigate the resultant energy of interaction pyrite as a result of mineral-collector interactions. Sodium ethyl xanthate (SEX), diethyldithiocarbamate (DTC) and diethyl dithiophosphate (DTP) were investigated in this study. The results showed that the calculated surface energies and morphologies for FeS2 showed that (100) and (111) are the most stable surfaces. The morphology also indicated the appearance of the (100) and (111) surface facets and no presence of others. The calculated adsorption energies between thiol collectors and the pyrite surface were always more exothermic than the experimentally determined ones. When comparing different ligand types with the same alkyl chain length, the heat of adsorption of diethyl-DTC was greater than that of ethyl xanthate and diethyl-DTP for pyrite. Experimentally, the diethyl DTP barely adsorbed onto the pyrite surface and this may be due to a different mechanism of action. In computational calculations, water adsorption was found to reduce the reactivity of the Fe atom for the interaction with thiol collectors, and bring the adsorption energies closer to the magnitude of the experimental values. Keywords: Computational modelling, microcalorimetry, experimental and thiol collectors, adsorption energies

Jan 1, 2020

By F. Diot, S. K. Tripathy, L. O. Filippov, I. Filippova

Among different pre-treatment methods, a high voltage electric pulse was recently developed and is gaining popularity due to multi-benefits such as pre-weakening along the grain boundaries, as well as size reduction to improve the liberation characteristics. In this paper, the pre-treatment using high voltage electric pulse of lithium-bearing granite ore was studied to understand the morphology through texture, as well as the friability of the particles. To understand the phenomena, SELFRAG, a laboratory facility used for generating high voltage electric pulse and key operating variables were varied. The role of applied voltage (94.5-195.5 kV), number pulse (3-87), and the frequency of pulse (1.3-4.7 Hz) was varied to understand the liberation characteristics as well as energy consumption. Characterisation tools such as optical, and electron microscopy were used to describe the pre-weakening phenomena through textural features. Further, the energy required to break the particle to finer sizes as well as friability were determined and described. Keywords: Pre-treatment, high voltage electric pulse, lithium, liberation, grinding

Jan 1, 2020

By L. A. Cornish, I. A. Mwamba, R. A. Couperthwaite

"In previous work by the authors, it was established that additions of 0.2 at.% Ru to an Fe-40 at.% Al alloy improved the corrosion and oxidation resistance of the alloy. The alloy was produced by mechanical alloying and spark plasma sintering and the work showed that nonequilibrium processing was able to significantly refine the grain size of the material. The sintered material had a higher hardness than the as-cast material and the change in grain size did not significantly affect the oxidation and corrosion. In the present research, the mechanically alloyed powder was coated onto a mild steel substrate using cold-spray coating at a gas pressure of 10 bar and a temperature of 500°C. The coatings were found to be 5–10 um thick, although thicknesses of up to 30 um were observed. The coated materials were subjected to oxidation and corrosion tests to determine the effectiveness of the coating in increasing the oxidation and corrosion resistance of mild steel. This was done to determine the effectiveness of cold-spray coating as a technique to coat these mechanically alloyed powders. IntroductionPrevious work conducted by Mintek (Couperthwaite et al., 2013, 2015) investigated the effect of precious metal additions on the structure, oxidation and corrosion properties of an Fe-40 at.% Al (Fe- Al) alloy. Initial work determined that additions of more than 0.5 at.% precious metal did not improve the oxidation and corrosion properties of the materials and in some cases even decreased the resistance to corrosion. Further work identified Pt and Ru as beneficial additions to the FeAl alloy. Four alloys were then produced by mechanical alloying and sintering (FeAl–0.2 at.% Pd, FeAl–0.2 at.% Ru, FeAl–0.5 at.% Ag, FeAl–0.5 at.% Pt). These alloys were all successfully produced by melting and casting and mechanical alloying sintering and it was found that the nonequilibrium processing greatly decreased the grain size of the materials compared to the ascast materials. It was found that the additions of Ru and Pt were still the most beneficial to the oxidation and corrosion properties, with Ru being considered the most beneficial."

Jan 1, 2016

By O. A. Olaseinde

The 2101 lean duplex stainless steel has wide potential application in storage, heat exchangers, and in the oil and gas industries. This work investigates the electrochemical behaviour of 2101 duplex stainless steel with an addition of 0.15 wt% ruthenium, using potentiodynamic techniques in 1M H2SO4 at 25º, 40º, 60º, and 80ºC. The microstructures of samples were characterized using optical metallography and scanning electron microscopy. The results showed that the ruthenium addition moved the corrosion potential of alloy 2101 to a more positive potential. All samples containing ruthenium displayed longer passive regions at 25°C and 80°C compared to those without ruthenium. Alloys without ruthenium had higher critical current density (icrit) values when compared to the alloys with ruthenium. Ruthenium additions decreased the passive current densities and inhibited anodic dissolution. At room temperature the corrosion rate of alloys with ruthenium was lower than these without ruthenium.

Jan 1, 2012

By H. Gercek, M. Genis

In this paper, the effects of dynamic loads on the geometry of the failure zone occurring around underground openings, excavated in deep and massive rock masses, have been investigated. Following an elasto-plastic stress analysis of a two-dimensional underground opening under static conditions, dynamic loads have been applied. In the static and dynamic analyses, FLAC2D computer program has been utilized. Maximum ground acceleration value is selected as an input parameter. An index determining the relative size of the yield zone around the opening has been used for comparison of instabilities. In diesem Bericht wurden die Auswirkungen von dynamischen Lasten, auf die Geometrie der Bruchzone in der Umgebung von Untertagehohlräumen, die in tiefen und massiven Gebirge aufgefahren wurden, untersucht. Nach einer elasto-plastischen Spannungsanalyse eines zwei-dimensionalen Untertagehohlraumes unter statischen Beanspruchungen, wurden dynamische Lasten aufgebracht. Für die statischen und dynamischen Analysen wurde das FLAC2D Computer Programm verwendet. Die maximale Bodenbeschleunigung wurde als Eingabe Parameter gewählt. Zum Vergleichen der Unstabilitäten wurde ein Index verwendet, der die relative Grösse der Bruchzone in der Umgebung des Hohlraumes bestimmt. Dans ce papier, l’influence des chargements dynamique sur la géométrie de la zone en rupture observée autour des cavités profondes excavées dans des massifs rocheux ont été étudiées. Des chargements dynamiques ont été appliqués, dans le cas d’une modélisation bi-dimensionnelle de l’excavation d’une cavité profonde, sur la base d’une analyse élastoplastiques des contraintes en conditions statiques. Le code de calcul FLAC2D a été utilisé pour les analyses statiques et dynamiques. La valeur maximale de l’accélération du sol est choisie comme paramètre d’entrée. Un indice déterminant la taille relative de la zone sollicitée autour de la cavité a été utilisé pour comparer les différentes instabilités.

Jan 1, 2003

By N. A. Barcza

INFACON 7, the seventh International Ferro Alloys Congress, took place in Trondheim, Norway, in June 1995. The main aim of the Congress, which was held under the auspices of Euroalliages and the Norwegian Ferroalloy Research Organization, was to present the challenges facing the ferro-alloys industry on the road to the 21st century. Halyard Tveit, Chairman of the Technical Committee, summarized these as: ? the transition to a single global market economy ? new demands with regards to quality arising from customer needs, and ? increased awareness of the global environment. In the Plenary Sessions Kouichi Nakamura (Nippon Steel) outlined, from the steel industry's point of view, the relationship between technical advances in the products and more demanding ferro-alloy specifications. Advances in steel manufacturing technology and higher product quality have been supported in the past by raising the quality standards of ferro-alloys. Future requirements are bound to bring about more severe standards, and these need to be established by common agreement between both industries.

Jan 1, 1996

By S. Krishnannair

Singular Spectrum Analysis (SSA) is an effective data-adaptive multimodal tool for monitoring chemical processes. However, monitoring multiscale signals using principal component analysis obtained from the multilevel decomposition of process signals using basic SSA assume the upper control limits of monitoring charts (" ) to have a Gaussian distribution. This assumption deteriorates the performance of basic SSA when applied to the monitoring of nonlinear processes. To address the issue in this paper, the kernel density estimation (KDE) was used to estimate upper control limits of monitoring charts for basic SSA based nonlinear process monitoring techniques. The monitoring performance of the resulting basic SSA-KDE approach was then compared with a basic SSA approach of which upper control limits of the monitoring charts were determined based on a Gaussian distribution. Application on nonlinear dynamic simulated process and base metal flotation plant chemical processes showed that the SSA-KDE approach provided better overall performance than the SSA approach with Gaussian assumption-based upper control limits for its monitoring charts. Keywords: Fault detection, singular value decomposition, singular spectrum analysis, kernel density estimation

Jan 1, 2020

A physical modelling study has been carried out to simulate the slag-metal dispersion induced by a high-strength bottom gas injection. Water and kerosene were utilized to simulate metal and slag respectively. A water model of CLU (Creusot-Loire Uddeholm) vessel was used with three different nozzle orientations, namely, off-centre, triangular off-centre and centre. The gas flow rates changed from 0.00599m3/sec to 0.01081m3/sec. Height of heavy and light phases was kept fixed at 0.23 m and 0.02 m respectively. The dispersed phase holdup was determined at various axial and radial distances, gas flow rates, and tuyere configurations. The observations revealed that at a fixed gas injection rate, as the vertical distance increased in the centerline, straight off-centre orientation resulted in greater dispersed phase hold up values than those of the centre configuration and the triangular off-centre orientation. The dispersed phase holdup was found to increase with gas injection rate and decreased with axial distance. The variation of the dispersed phase hold up with the dimensionless axial distance and the gas injection rate was correlated by using the Modified Froude Number. The experimental values of the dispersed phase holdup were found to be in good agreement with the correlated values obtained from the modelling equations. The findings of the present study may be utilized in the ferroalloy refining vessels in terms of designing tuyere locations for optimum processing conditions.

Jan 1, 2004

By J. -P. Gisiger

On the basis of laboratory test results a comparison of various parameters (unconfined compressive strength, CERCHAR and LCPC abrasivity indexes, mineralogy) is presented and discussed in order to outline certain correlations between them. Samples cover a wide range of lithological types coming from various sites of tunnels. A partir de résultats d’essais de laboratoire, une comparaison de divers paramètres (résistance à la compression simple, indices d’abrasivité CERCHAR et LCPC, minéralogie) est présentée et discutée dans le but d’en tirer certaines corrélations. Les échantillons couvrent un large éventail de types lithologiques provenant de plusieurs sites de tunnels. Basierend auf Laborversuchen, werden verschiedene Gesteinseigenschaften (Druckfestigkeit, CERCHAR und LCPC Abrasionsindexe) präsentiert und Korrelationen aufgezeigt. Die untersuchten Proben verschiedenster Lithologien stammen aus mehreren Tunnelprojekten.

Jan 1, 2003

By Y. Qin, L. Han, P. Gao, Y. Han, Y. Lia

In the present study, an innovative comminution technology of high-voltage pulse discharge was proposed for galena to weaken the mechanical property. The results of pre-treatment experiments indicated that the optimal operating conditions of spherical gap spacing 25 mm, pulse numbers 120, and loading voltage 25 kV were obtained, where the relative grindability of pretreated products was improved significantly, although with the prolonging of grinding time, the superiority of high-voltage electric pulses was gradually weakened. The galena ores were subjected to a high-voltage pulse discharge, and then the crack generating along the boundary between galena and gangue was observed under an optical microscope, and the surface burning which appeared in the ores. The scanning electron microscope (SEM) results indicated that the pretreated products were in a state of melting and then condensation, accompanied by some pore formation. Pulsed discharge pre-treatment not only produced more micro-cracks and cracks in the sample but also extended the original crack. Keywords: High-voltage pulse discharge; galena; relative grindability; micro-crack

Jan 1, 2020

By C. Righi, R. Carli

In modern steel continuous casting technologies mould fluxes are well-known to assure lubrication required by tribological system of mould-solidifying strand shell, and to provide crystalline phase solid film, contributing to control heat extraction between strand and mould wall. Actual cooling rates during normal continuous casting mould operations are far higher than critical cooling rate of the liquid slag. Indeed, DTA measurements point out that even relatively small cooling rates of 30?50 K/min are high enough to give exiguous formation of crystals. In this paper, contribution of devitrification in defining crystalline phase formation of industrial basic mould slag, used in continuous casting of crack-sensitive steel grades, has been investigated by means of non-isothermal experiments study. Devitrification has proved to play a major role in mould flux crystallization in a working environment explaining the higher amount of crystalline phase formed in plant sample in comparison with lab sample from DTA analysis with typical cooling rate of 5?20 K/min. The amount of crystalline phases formed ranks as follow: Cuspidine > Combeite > Gehlenite. Kinetic analysis of DTA non-isothermal experiments has provided kinetic parameters through Kissinger and Ozawa methods, as Avrami constant resulting to be n ?2 and activation energy of Cuspidine crystallization resulting to be EC= 315 kJ/mole. The effect of addition to the parent material of oxides as MnO, TiO2, ZrO2, Al2O3 and Fe2O3near to saturation point has proved to affect, in certain cases, crystallization behaviour of mold flux. In particular, MnO, TiO2, ZrO2oxides produce a relevant dump of crystallization of Combeite and Gehlenite phases, while Al2O3and Fe2O3do not appreciably affect crystallization. Key words: Mould flux, crystallization, devetrification, DTA non-isothermal analysis, Kissinger and Ozawa methods.

Jan 1, 2004

By S. H. Yi, J. R. Kim, Y. S. Lee

The viscosities of CaO-SiO2-Al2O3-MgO-FeO slags were measured under conditions ofCaO/SiO2=1.15–1.6, 10–13 percent Al2O3, 5–10 percent MgO and 5–20 percent FeO. Slag viscosity decreased with increasing FeO content at a fixed basicity (CaO/SiO2) of slag. Slag viscosity at low FeO (<7.5 percent FeO) exhibited a minimum value by increasing MgO content in slag. Viscosity decreased with increasing slag basicity up to 1.3 while it increased as slag basicity increased from 1.3 to 1.5. Thus, it was proposed that the driving force for the decreases of slag viscosity would be an increase in depolymerization of silicate network at C/S=1.3, while the viscous behaviour at C/S>1.3 would be increased with increasing the chemical potential of primary solid phase e.g. dicalcium silicate. A thermodynamic approach for the activity of primary solid phase in molten slags resulted in a reasonable relationship between viscosity and slag components. Therefore, it was confirmed that slag viscosity in basic slags system (C/S>1.3) could be determined by the chemical potential of dicalcium silicate. Keywords: viscosity, basicity, bosh slag, blast furnace, slag structure, FT-IR

Jan 1, 2004

By R. J. Gordon, N. J. Keys, N. F. Peverett

Photometric sorting of ore on a South African gold mine by N. J. KEYS. B.E. Met. (Queensland) (Visitor). R. J. GORDON. (Visitor). And N. F. PEVERETT. B.Sc. (Eng.) (Wits) (Fellow) This paper concerns the development and application of a high-throughput, multi-stream photometric sorting machine developed for the South African gold mines. It is now believed that this sorter and its progeny may be found suitable for a large proportion of all possible sorting applications. A laser-light source and sensitive photomultiplier are employed in a scanning system to detect light reflected from the surfaces of rocks passing through the sorting zone. Electronic circuitry then analyses the photomultiplier signal, which represents the varying intensity of the reflected light, and produces control signals to actuate the appropriate valves of an array of air-blast rejection devices to remove from the feed certain particles selected by the analysing process. Typical throughput per machine ranges from 50 t/h for a minus 60mm plus 30mm feed to 200 t/h for minus 150mm plus 70mm material.

Jan 9, 1974

By O. Bazhko, F. D. L. Uahengo, Y. R. S. Hara

Although the conventional acid-reductive leaching method effectively extracts copper (Cu) and cobalt (Co) from Cu–Co oxide ores, efforts to enhance hydrometallurgical performance are ongoing. This study evaluates the influence of sulphuric acid (H2SO4) and sodium metabisulphite (Na2S2O5) on metal extraction from Zebesha Cu–Co oxide ore using ferrous sulphate heptahydrate (FeSO4·7H2O) and ferric sulphate (Fe2(SO4)3) as lixiviants. Ore samples (<150 μm) were leached at ambient temperature for two hours, and metal concentrations were determined via X-ray fluorescence analysis. In the FeSO4·7H2O system, Co, Mn, and Ni recoveries increased w=ith Na2S2O5 concentration, reaching a maximum of approximately 80% Co at 150 kg/t, while Cu recovery remained below 5%. Conversely, with Fe2(SO4)3, Cu recovery peaked at 88% at 50 kg/t Na2S2O5, then declined to 79% at 150 kg/t. The addition of H2SO4 improved metal recoveries in both systems. Notably, 60 kg/t H2SO4 yielded 92% Cu extraction in Fe2(SO4)3, while Co, Ni, and Mn remained below 40%. However, in FeSO4·7H2O, Co recovery improved from 40% to 84%. These findings suggest Na2S2O5 is more effective for cobalt extraction with FeSO4·7H2O, whereas H2SO4 enhances copper extraction in Fe2(SO4)3.

Oct 24, 2025

By N. Anacleto, S. Ganguly

Reduction of Groote Eylandt (Australia) and Wessels (South Africa) manganese ores using CH4-H2-Ar gas mixture was investigated in a fixed bed laboratory reactor in the temperature range 1000?1200oC. The extent and kinetics of manganese ore reduction as a function of gas composition and temperature were determined by on-line off-gas analysis using mass-spectrometer and dew point sensor. Morphology of ores and its change in the course of reduction was examined by optical and scanning electron microscopy. Phases of raw materials and reduced samples were analysed by XRD and EPMA. Manganese oxides were reduced to carbide Mn7C3. High extent and rate of reduction by methane-containing gas in comparison with carbothermal reduction were attributed to high carbon activity in the reducing gas, which was in the range 15 - 50 (relative to graphite). The reduction rate of Wessels manganese ore increased with increasing temperature. Reduction rate and extent of Groote Eylandt manganese ore achieved maximum at 1050oC. The decrease in rate and extent of reduction of Groote Eylandt ore at higher temperatures, particularly at 1150-1200oC, was due to sintering and formation of semi-liquid silicate slag. The optimum conditions for the reduction of manganese ores were established as follows: a) temperature: 1150-1200oC for Wessels and 1050-1100oC for Groote Eylandt ores, b) methane concentration: 10-15 vol%, c) hydrogen concentration: above 30 vol%, (d) size: 1-3 mm. An addition of lime (10-15 wt% CaO) to the Groote Eylandt manganese ore increased melting temperature of slag and significantly increased the rate and extent of reduction at elevated temperatures.

Jan 1, 2004

1. Book review . Australasian coal mining practice, edited by C.H. Martin. Reviewer: R.B. MacGilIivray This book is an extremely comprehensive coverage of coal-mining practice in Australasia, the countries covered being Australia, New Zealand,and Papua New Guinea. 2. From The Institute of Metals The folowing are available from The Institute of Metals, 1 Carlton House Terace, London SWl Y 5DB. Physical and elastic characterisation, edited by M. McLean. 1989. 228 pp. £25.00. High nitrogen steels, edited by J. Foct and A. Hendry. 1989. 461 pp. £49.50. Proceedings of the First International Calcium Treatment Symposium. 1988. 116 pp. £15. New cored-wire injection techniques, particularly as Design for recyc/ability, by Michael E. Henstock. 1988. 150 pp. £15. Solidification processing. 1988. 549 pp. £45. Marine engineering with copper-nickel. 1988. 103 pp. £18. Characterisation of High Temperature Materials. 3. New journal FMJ International Publications Lid have announced a new quarterly publication, Aluminium Today. 4. Other new publications Algorithms in real algebraic geometry, edited by Denis S. Arnon and Bruno Buchberger. London, Academic Press, 1988. 274 pp. £15.95. Proceedings, Foundry and Heat Treatment 88. R150 per set of 5 volumes, or R40 per volume.

Jan 1, 1989