Search Documents

By W. Vorster

Bateman Engineering Project's acid-plant track record goes back to 1977. Bateman Engineering can design sulphuric plants based on gas from sulphur burners, metallurgical off gas as well as pyrite roasting systems. Bateman Engineering has a technology marketing agreement with NORAM Engineering Ltd of Canada to provide state-of-the-art, well-proven acid plant technology, and also has access to roaster technology from several sources, including Chinese technology. Utilising the Noram technology agreement, Bateman was awarded the Engineering and Procurement (EP) contract for the Ambatovy Nickel Project, Sulphuric Acid Facilities in 2007. This is the first Greenfield sulphuric acid plant Bateman has designed for many years, producing a combined 5,500tpd, and is one of the largest sulphur burning acid plants in the world. This paper gives an overview of the sulphuric acid plant for the Ambatovy Nickel Project, advantages of Noram?s unique technology on offer, an overview of work conducted on a recent study of an pyrite roasting acid plants as well as a new technology currently being developed by Bateman for the direct combustion of solid sulphur to form sulphur dioxide.

Jan 1, 2009

By V. B. Teffo

The aim of the project was to experimentally determine the coefficient of restitution, and static and rolling friction of Eskom-grade coal for discrete element modelling (DEM). These parameters will be used in further DEM studies to simulate the flow and behaviour of coal during conveyance. For the simulation to yield realistic results, the parameters for the different coal shapes identified in the samples were determined. DEM uses spherical particles, and it was found that the difference between the DEM default parameters and those measured is significantly different, by as much as 97%, which illustrates the importance of experimentally determining these parameters. The spherical particles in DEM can be used to construct the various coal shapes identified, and the parameters measured can be used to simulate realistic results. The conveyance system can then be optimized accordingly.

Jan 1, 2013

By Petrus Christiaan Pistorius, Makunga Daudet Seke

The flotation response of a Pb-Zn sulphide ore from the Rosh Pinah Mine (Namibia) was studied in the presence of inorganic depressants such as sodium cyanide and zinc sulphate. Poor flotation selective was observed in the rougher concentrate of the galena circuit despite the use of excessive amount of sodium cyanide. Batch flotation tests have shown that the use of cyanide alone is not efficient for the depression of sphalerite from the Rosh Pinah ore when milling is carried out according to the current plant particle size distribution. The use of both cyanide and zinc sulphate improved the selectivity between galena and sphalerite much better than cyanide alone. Flotation selectivity is limited by the mineralogical texture of the Rosh Pinah ore sample. Microscopic analysis has shown that the presence of sphalerite in the galena concentrate is also due to poor liberation between galena and sphalerite, especially in the middlings. Hence selectivity could be improved by regrinding the rougher concentrate prior to the cleaning stage. Keywords- Sulphide ores, Flotation, Flotation depressant, Mineralogy.

Jan 1, 2005

Recently, work was carried out by the Shotcrete Working Group to study anisotropy in steel fibre reinforced shotcrete using strain-controlled, compressive strength testing methods. The shotcrete materials used and specimen preparation procedures as well as testing methods are described. The test results are discussed and it is concluded that, because of the anisotropic nature of fibre reinforced shotcrete, it may be worthwhile investigating the degree of such anisotropy in practice using strain-controlled, strength testing techniques.

Jan 1, 2001

By M. Shahabi, M. Kashfi

This paper briefly describes the excavation procedure of a powerhouse, comprising of its incremental excavation, reinforcement measures, and the installed monitoring system. During the first phase of excavation, the data obtained from monitoring of the behavior of Mudstone layers were used to recommend extra support measures. These data are also used to design the support of the powerhouse during its extension phase. In diesen bericht wird die bohrmcthode von kraftwerk ecavation in stupenweise dargestelt, und in die richtung d.sicherung, Mit hilfe von monitoring systeme. Die monitoring in (mudstone) schichten ist an schutz in bohrung entworfen und montiert in diese methode in K.W. fase 1 schutzung das K.W. in erweiterung der K.W. das berte auserwelt worden ist Cet article décrit brièvement le procédé d'excavation d'une centrale électrique, comportant de son excavation incrémental, de mesures de renfort, et du système de surveillance installé. Pendant la première phase de l'excavation, les données obtenues à partir de la surveillance du comportement des couches de schiste ont été utilisées pour recommander des mesures supplémentaires de soutien. Ces données sont également utilisées pour la conception de la soutènement de la centrale électrique pendant sa phase d’extension.

Jan 1, 2003

By A. Rejeb, A. Millard

ABSTRACT: An evaluation of the importance of the thermo-hydro-mechanical couplings (THM) on the performance assessment of a deep underground storage design has been made as part of the international DECOVALEX III project. It is a numerical study that simulates a generic repository configuration in the near field in a granite medium. The thermo-hydro-mechanical evolution of the whole configuration is simulated over a period of 100 years. The model used to represent the unsaturated behaviour of the various porous media makes allowance for moisture transfers through the effect of thermal and water gradients. The paper presents a comparison of the temperature, water pressure and stress fields obtained by TM, TH, HM and THM coupled calculations. The results demonstrate that temperature is hardly affected by the couplings. In contrast the influence of the couplings on the mechanical stresses is considerable. This is attributed to the key role that water has on bentonite swelling or shrinkage effects that are dependent on its saturation level variations. KEY WORDS: Modelling, thermo-hydro-mechanical couplings, temperature, pressure, stress. ZUSAMMENFASSUNG : Im Rahmen des internationalen Projekts DECOVALEX III wurde untersucht, wie groß der Einfluss thermisch-hydraulisch-mechanischer Kopplungen (THM) auf die Leistungsfähigkeit eines Konzeptes zur Lagerung hoch radioaktiver Abfälle zu bewerten ist. Bei dieser numerischen Behandlung wird eine generelle Lagerungskonfiguration in granitartigem Milieu simuliert. Die thermisch-hydraulisch-mechanischen Prozesse werden für eine Dauer von 100 Jahren simuliert. Bei dem Modell, mit dem das Verhalten der verschiedenen, unterschiedlich porösen Milieus in ungesättigtem Zustand dargestellt werden soll, werden die Feuchtigkeitstransporte infolge thermischer und hydraulischer Vorgänge berücksichtigt. Verglichen werden in diesem Artikel verschiedene Temperatur-, Wasserdruck- und Beanspruchungsfelder, die sich aus TM-, TH-, HM- und THM gekoppelten Berechnungen ergaben. Dabei stellte sich heraus, dass die Temperatur nur gering von den Kopplungen berührt wird. Die Einflüsse der Kopplungen auf die Mechanik sind hingegen bedeutend; ausschlaggebend dafür ist der Faktor Wasser, der den Bentonit je nach Sättigungsgrad quellen oder trocknen lässt. SCHLÜSSELWÖRTER: Modellbildung, thermisch-hydraulisch-mechanische Kopplungen, Temperatur, Druck, Beanspruchung. RESUME : Dans le cadre du projet international DECOVALEX III, une évaluation de l’importance des couplages thermo-hydro-mécaniques (THM) sur les performances d’un concept de stockage de déchets fortement radioactifs a été menée. Il s’agit d’une étude numérique simulant une configuration générique de stockage en champ proche dans un milieu granitique. L’évolution thermo-hydro-mécanique de l’ensemble est simulée sur une période de 100 ans. Le modèle utilisé pour représenter le comportement non saturé des différents milieux poreux prend en compte les transferts d’humidité sous l’effet de gradients thermiques et hydriques. L'article présente une comparaison des champs de température, de pression d’eau et de contraintes obtenues par des calculs couplés TM, TH, HM et THM. Les résultats montrent que la température est peu affectée par les couplages. En revanche, l’incidence des couplages sur la mécanique est importante; ce qui est attribué au rôle majeur joué par l’eau à travers les effets de gonflement ou de retrait de la bentonite selon la variation de son degré de saturation. MOTS-CLEFS : modélisation, couplages thermo-hydro-mécanique, température, pression, contrainte.

Jan 1, 2003

By A. M. Ghodgaonkar, P. J. Bhonde, R. D. Angal

Primarily ferrochrome is used to introduce chromium into steels and alloys. Chromium enhances hardness, hardenability, corrosion, abrasion and wear resistance of the steel. High carbon ferrochrome is one the cheapest sources of chromium, which finds large consumption in foundries and steel plants. However, carbon leads to problems viz. weld decay and sensitization of steels at elevated temperature causing catastrophic failure. Thus high carbon ferrochrome which otherwise enjoys financial edge over its low carbon grade is not suitable for final alloying or adjustment of chromium content. Subsequently, its addition burdens a steel maker. Hence, metallurgists around the globe have researched on finding out suitable technique for refining of ferrochrome. Traditional production methods of low carbon ferrochrome have drawbacks i.e. high refractory consumption, losses of chromium in slag and fumes etc-. Later these were overcome by adopting relatively new methods namely, metallothermic reduction, triplex process, vacuum technique to directly produce extra low carbon ferrochrome. Authors have carried SWOT analysis of the aforementioned techniques in the literature. Key Words: Ferrochrome, carbon content, low carbon grade, chromite, sensitization

Jan 1, 2007

By Dave Capstick, Ken Garner, Jim Porter

Technologies and systems used in the management of energy consumption in the mining and metal processing industry are well understood and documented from the supply side of the business. It is our contention that in many instances, through a more complete understanding of the demand side of the business, based on the detail of the operations plan, will provide greater lead time in terms of the design, implementation and utilisation of power supply infrastructure. Thus, optimal management of demand in a proactive manner, based on production requirements, will ensure both security of supply as well as continuity of operations. This paper describes the technology and methodology that is being developed to enable the above statement to be achieved. We use a case study to demonstrate the ability of the tools and methodology and conclude by outlining the business benefits achievable as well as the future developments emanating from this initiative.

Jan 1, 2005

By Y. I. Yang, Y. -B. Tang, D. -J. Ma

Chlorine-containing minerals are commonly present in coal. Associated minerals such as pyrite can undergo exothermic reactions. Consequently, it is of great significance to study the effect of inorganic chloride on the spontaneous combustion of coal. In this study, the effects of five inorganic chlorides (sodium chloride, magnesium chloride, potassium chloride, calcium chloride, and zinc chloride) on the spontaneous oxidation of coal were investigated. Analysis of the gaseous products of coal oxidization at low temperatures (323K to 453K) showed that the presence of inorganic chlorine in coal markedly decreases O2 consumption and the generation of CO and CO2. Samples of raw coal and chlorine-loaded coal were oxidized for 36 hours under the same experimental conditions. Infrared diffuse reflectance spectroscopy results showed that inorganic chloride can inhibit the oxidative decomposition of some functional structure components (methyl, methylene, methine, and hydroxy) in the coal. The influence of inorganic chloride on the oxidation characteristics of the functional groups in coal during spontaneous combustion was investigated using benzyl alcohol and 1-phenylpropanol as model compounds, which were tested under the same experimental conditions as the coal samples. The oxygen consumption of model compounds with and without the addition of inorganic chloride further suggested that inorganic chloride may hinder the oxygenolysis of these structures during low-temperature oxidation. This phenomenon can be attributed to the radical reaction from the perspective of radical chemistry. It can therefore be concluded that inorganic chlorides play an inhibitory role in the spontaneous combustion of coal.

Jan 1, 2015

By N. R. Williams

Black Mountain, a polymetallic base metal mine located in the Northern Cape territory of South Africa has been blessed with high grade economic ore for many years. Now that the Broken Hill orebody is nearing the end of its life, a lower grade orebody (Swartberg) is being exploited to supplement production from Broken Hill. In addition, ore from stopes in the upper levels of the Broken Hill orebody is considerably tarnished (oxidized). As a natural result, the remaining ore contains a higher percentage of magnetite, pyrrhotite and pyrite than in earlier years. Bismuth, cadmium and cobalt also occur in the ore in higher quantities. The life of the mine has been lengthened with the discovery of further deeper-lying ore reserves extending from the Broken Hill orebody suitably called the Deeps section. However, to bridge the gap between development of the new reserve and the exhaustion of the old reserve, these lower grade and tarnished (oxidized) ores have to be treated. The mine has had reasonable success in identifying unfavourable or problematic ore types and stockpiling them separately to blend in small quantities with more favourable ore. Bench and plant scale tests have aided identification of the various ore types and significant improvements in flotation metallurgical results have been seen. Copper, lead and zinc metal occur as sulphides in the ore. The mill consists of a differential and sequential flotation process that extracts copper concentrate, lead concentrate and zinc concentrate respectively with silver metal recovered in the copper and lead concentrates. This paper describes the ore blending strategy employed at the mine to maximize the econo-metallurgical efficiency of the operation.

Jan 1, 2001

By J. P. Harrison

ABSTRACT: The significant effect of fracture surface morphology on the mechanical behaviour of rock masses is well known and has been studied by many people. For linear profiles taken from fracture surfaces, short- and long-period variation has traditionally been described using the descriptors ‘roughness’ and ‘waviness’, with Fourier series analysis being perhaps the most commonly used technique to distinguish between the two attributes. However, the mathematical procedure is involved and the assumptions that have to be made may not be appropriate for rock fracture surfaces. In this paper, an alternative method is presented that enables us to distinguish between roughness and waviness of a linear profile by performing only one straightforward analysis. In our technique, surface morphology is studied in terms of the distribution of unit normal vectors to the profile. The statistical analysis of the distribution is performed using Riemannian, rather than the customary Euclidean, geometry, and from this the 1D Riemannian dispersion parameter (DR1) is obtained, which quantifies the geometry of the profile. The method is applied at different scales to both synthetic sinusoidal profiles and real rock profiles. The results show how periodic behaviour of the profile is revealed at scales where DR1 is substantially equal to zero. RESUME: L’influence significative de la morphologie des épontes sur le comportement mécanique des massifs rocheux est bien connue et a fait l’objet de nombreuses études. Pour les profils lineraires, les variations de courtes et longues périodes sont traditionnellement décrites par les indicateurs “rugosité” et “ondulation” qui sont le plus couramment distingués à l’aide d’une analyse en series de Fourrier. Cependant, la méthode de calcul utilisée et les hypothèses faites ne sont pas appropriées dans le cas des épontes rocheuses. Cet article présente une méthode alternative qui permet de distinguer la rugosité de l’ondulation d’un profil en réalisant une seule analyse directe. Avec notre technique, la morphologie de l’éponte est étudiée comme une distribution spatiale de vecteurs normaux au profil. L’analyse de cette distribution est réalisée à l’aide de la géométrie Riemannienne plutôt que la géométrie classique Euclidienne et permet d’identifier la dispersion Riemanienne en 1D (DR1) qui quantifie la géométrie du profil. Cette méthode est appliquée à différentes échelles sur des profils artificiels sinusoïdaux et des épontes naturelles. Les résultats montrent que le comportement périodique du profil est révélé à des échelles où DR1 est essentiellement égal à zéro. ZUSAMMENFASSUNG: Der signifikante Effekt von Bruchoberflaechen Morphologien auf das mechanische Verhalten von Gesteinsmassen ist gut bekannt und von vielen Bearbeitern untersucht worden. Traditionel lineare Profile von Bruchflaechen sind mit kurz und lang periodischen Variationen, die auch als “Rauhigkeit” und “Welligkeit” bezeichnet worden sind, beschrieben worden. Hierbei ist wohl die Fourier Serien Analyse das wichtigste Hilfsmittel zur Unterscheidung der beiden Attribute gewesen. Hierfuer wird jedoch ein mathematisches Prozedere verlangt und Vorraussetzungen gemacht, die vielleicht nicht fuer Gesteinsbruchflaechen zutreffend sind. In dieser Publikation wird eine andere Methode vorgestellt, die uns mit Hilfe nur einer einfachen Analyse erlaubt zwischen “Rauigkeit” und “Welligkeit” bei einem linearen Profil zu unterscheiden. In unserer Methode wird die Gesteinsoberflaeche unter zu Hilfenahme der Verteilung von Einheitsnormalvektoren beschrieben. Die statistische Analyse der raeumlichenVerteilung dieser Vektoren wird mit Hilfe der Riemannschen, anstatt der ueblicherweise benutzten Euklidischen, Geometrie durchgefuehrt. Von ihr wird der Riemannsche Dispersions Parameter (DR1) abgeleitet, der die Geometrie des Profils quantifiziert. Diese Methode ist bei verschiedenen Masstaeben sowohl auf rein harmonische (sinusoidale), syntetische Profile als auch auf Gesteinsprofile angewendet worden. Die Ergebnisse zeigen, dass bei Masstaeben bei denen DR1 nahe Null ist periodische Characteristika der Profile hervortreten.

Jan 1, 2003

By M. J. Little

Potgietersrust Platinums Ltd (PPRust) is Anglo Platinum?s only open pit operation. The major slope stability concern at PPRust is rapid, small-scale brittle failure on the west wall of Sandsloot open pit. In order to improve safety and mine more economically, a comprehensive slope monitoring strategy has been implemented. In the last 3 years four new state-of-the-art monitoring systems have been installed namely an ISSI microseismic monitoring system, a GeoMoS automated prism monitoring system, prismless Riegl laser scanners and a GroundProbe slope stability radar (SSR). Groundwater monitoring and visual monitoring have also been improved over the same time period. To complement the visual inspections, SiroVision digital photogrammetry is now used for predicting where future failures may occur. All these monitoring tools provide primary monitoring which is used to identify high risk areas. The SSR is then set up in that area to provide early warning of failure so evacuation can be successfully done. Fault tree analysis has proved that with this comprehensive slope monitoring strategy the geotechnical risk at PPRust is greatly reduced, allowing mining to continue safely and economically in challenging conditions.

Jan 1, 2006

By M. B. Fonseca

Risk quantification in grade-tonnage curves is critical for capital investment in mining projects and can be obtained through geostatistical simulations of orebodies. A practical difficulty may arise in multi-element deposits, as the joint modelling of the related attributes using the traditional co-simulation approaches is computationally intensive and may be impractical for use in the industrial environment. This paper presents the construction of risk-integrating grade-tonnage curves for a complex copper deposit in northern Brazil, by jointly simulating its key geochemical attributes of interest: Cu, Fe and K. The joint conditional simulation of these elements is based on Minimum/Maximum Autocorrelation Factors (MAF). MAF is an approach, based on principal components, that spatially decorrelates the variables involved to non-correlated factors. MAF’sspatial decorrelation at any lag distance is the main and critical difference of this approach from the principal component approach attempted in the past. In the MAF approach, the independent factors are individually simulated and back-transformed to the conditional simulations of the correlated deposit attributes that reproduce the cross-correlations of the original variables. Keywords: Joint simulation; mini/max autocorrelation factors; grade-tonnage curves.

Jan 1, 2003

By G. V. R. Landman

In the early days of underground coal mining, the use of explosives to break coal resulted in a large number of disastrous methane and coal dust explosions and consequential loss of life. Research by the British, French, US authorities, amongst others, introduced many practices that significantly reduced the occurrence of such incidences. The use of explosives designed to be safe in a methane atmosphere, plus the creation of a second free face were two such practices which became commonly used in coal mines all over the world including southern Africa. With its associated coal cutting equipment and labour, the cost of creating a second free face is significant and this, together with the constant drive to reduce mining costs in a competitive market, causes mine management to regularly question the need for the second free face. Also, the safety and nature of permitted explosives has changed considerably since the days of black powder and nitroglycerine-based explosives with the introduction of water-based explosives. In southern Africa mining regulations pertaining to the blasting of coal has its origins in British research which was largely done in the first half of the twentieth century. More recent research by the US Bureau of Mine has resulted in a deeper understanding of some of the mechanisms of methane ignition by explosives and suggests that some of the earlier regulations can be relaxed to a certain extent without compromising safety. This paper gives an overview of the original research done in Europe and the more recent work in the USA, to give mine management and regulatory authorities a deeper understanding of the important safety issues when using explosives in a methane atmosphere. It also suggests that blasting off the solid is no less safe than using a second free face providing certain safety procedures are followed.

Jan 1, 2000

By J. E. Davidsen, M. Honstad

"A well-maintained tap-hole channel is important in order to achieve good and stable furnace operation over time. A worn or short tap-hole channel can lead to more violent flow, significantly increasing the fume emissions during tapping and leading to more metal being mixed with and lost to the slag. Over time, a worn tapping channel might cause side channels and damage to the lining around the tap-hole area. This can result in a burn-through which is a considerable safety risk and will cause significant production losses. At Eramet Norway Porsgrunn, tap-hole maintenance has been done regularly with electrode paste for over three decades with good results. This article summarizes some of the experiences obtained from this practice on a 33 MW SiMn furnace, as well as a change to a coal tar pitch-free binder. IntroductionA well-maintained tap-hole channel is important in order to achieve good and stable furnace operation over time. Metal and slag are regularly tapped from the furnace and may cause a lot of wear on the tapping channel, increasing the risk of lining damage and ultimately leading to a burn-through. On furnace 10 at Eramet Norway Porsgrunn, the tap-hole area is the part of the lining that has been by far the most prone to burn-through since the startup of the furnace.Experience shows that almost all lining problems have started with burn-through in the tap-hole area or in close proximity to the tap-hole. During tap-hole repairs, side channels with metal and slag have also been observed emanating from the main tapping channel. In addition, a shorter tapping channel will cause more violent flow. This can lead to more metal droplets being entrained in the slag, and increase the risk of the furnace not being closed properly at the end of the tap.As a burn-through is a considerable safety risk, and also causes significant production losses, systematic work has been performed over the years to maintain the tapping channel in order to prevent burn-through."

Jun 1, 2019

By D. M. MacHunter, T. Lawson, D. K. Henderson

The development and commercialization of new generation high tension electrostatic separators has provided a basis for simplifying mineral separation plant circuitry. The inclusion of new design features including insulated plate electrodes that have resulted insignificantly improved separation efficiencies in electrostatic separators are described. The increase in separation efficiency has resulted in a reduction in the number of treatment stages required to produce final high grade mineral products. Comparative performance data on different feed types are presented. A comparison between mineral separation plant flowsheets using both conventional and new generation high tension electrostatic separation technology is presented. A 55% reduction in the number of installed electrostatic separators and a 36% reduction in plant area was achieved through the use of this new electrostatic separation technology.

Jan 1, 2003

By Mauri Kauppi, Pekka Niemelä

World HCFeCr production is 6.0 million tonnes. Correspondingly 1.1-1.6 t slag / t FeCr is produced depending on the raw material basis. Essentially all FeCr is produced in submerged arc furnaces, while the role of competitive technologies like DC is limited. In all furnaces fluxes are used to optimize the slag composition. Vital characteristics are smelting point, electric conductivity and viscosity. The main components of FeCr slag are SiO2, Al2O3 and MgO. Additionally it consists of Cr-, Fe-oxides and CaO. Granulated slag and/or classified slag products are produced depending on the production process. The slag products are mainly marketed in road and civil construction purposes but also in producing refractories. Normally crushed and screened slags are produced simultaneously when recovering alloy. The leachate of slag products is low and performance results are excellent. Slag products successfully replace natural sand and macadam. Generation of waste is essentially reduced. Producing and using slag products are described as BAT-technology and it is an essential environmental aspect. Outokumpu Tornio Works produces 320 000 t FeCr-slag/a. This paper deals with formation of slag in smelting process, its chemical composition, physical and structural characteristics, utilization and product specifications as well as environmental aspects. The slag products are standardized and CE marked. Additionally the role of slag in smelting and alloy recovery is reviewed in this paper.

Jan 1, 2007

By J. A. Theron

"This paper provides guidelines on performing mass and energy balance modelling involving coal and coal derivatives. Usually, the inputs to a pyrometallurgical process would be specified in terms of elements and compounds. Reliable thermochemical data is more widely available for species involving uniquely defined, relatively smaller molecules. However, in the case of coal, the molecules are extremely large and not uniquely defined. Consequently, modelling processes involving coal and its derivatives involve several potential pitfalls. These are outlined in the present paper.It was found that coal proximate analysis should not be regarded as absolute; it could vary with several parameters, including heating rate. For modelling, the use of ultimate analyses should be considered a preferable option to proximate analyses, where ‘fixed carbon’ and ‘volatiles’ are not defined in terms of chemical composition. Significant errors could be incurred if the larger molecules are neglected during calculation of the calorific value (CV) of coal gas (the gas liberated when coal is heated in the absence of oxygen).For elemental analysis determination, the oxygen content (which is calculated by balance) should be checked to ensure it is within the expected range. For representation of sulphur in coal, one should avoid doublecounting due to SO3 in the ash analysis.Potentially, oxygen in coal could be represented as O2, H2O, CO, or CO2.However, use of some of these species without considering the experimentally determined gross CV leads to significant errors in the energy balance. If coal enthalpy is calculated from elemental analyses without correction, representation of coal oxygen as H2O(l) gives reasonable accuracy. Coal volatiles could be represented by a complex mixture of compounds, even using different oxygen-containing species than these four, provided the enthalpy is corrected.It is recommended that an ‘enthalpy correction value’ be incorporated in energy balances involving combustion, devolatilization, or conversion of coal and coal derivatives, e.g. coke, char, or tar. That would imply that proximate analysis, elemental analysis, as well as the gross CV would be required for all solid or liquid coal-derived substances being modelled. No other correction due to carbon being present in a form other than graphite should be used, as that would imply double-counting some effects."

Jan 1, 2015

By Antoine F. Mulaba

Introduction Copper and cobalt oxide mineral deposits formed by the atmospheric weathering of near surface sulphide deposits are commonplace in the Democratic Republic of Congo. The most common route for the extraction of these metals is a hydrometallurgical one in which the base metal oxides are dissolved in sulphuric acid and then concentrated further by solvent extraction. However, as many of these deposits are relatively low grade (i.e. 0.5-1.8%Co and 2-4% Cu) and can also contain large amounts of acid consuming gangue minerals (i.e. dolomitic, micaeous, and/or siliceous), the hydrometallurgical route becomes uneconomic due to the excessive acid leaching costs. Some means of pre-concentration ahead of leaching is then desirable to improve the process economics. Apart from the small scale mining (Pan. Afr. News Agency, 2000) handpicking, although not easy, oxide concentration by flotation has been suggested. For the flotation process, the two most common approaches are controlled potential sulphidisation (CPS) and the fatty acid flotation method. The preferred method is dictated by the nature of the mineral makeup of the gangue. Being secondary deposits, the gangue associated with these ores is often complex and can play a significant role in the overall flotation efficiency. Laboratory flotation experience gained from the testing of a number of different ores of this type has revealed that it is not possible to prescribe a set method for the flotation of various ore types. Each ore needs to be analysed very carefully before and after laboratory flotation on an individual basis in order to arrive at an acceptable flotation technique Laboratory flotation testwork was carried out on three different samples from the DRC in attempts to isolate some of the more important variables affecting the flotation of copper and cobalt oxide minerals from these weathered deposits. This paper describes some early results achieved and experiences gained with these different ores ahead of a more detailed flotation test program which will follow in the near future on receipt of a significant quantity of a more representative sample. Controlled Potential Sulphidisation (CPS) was used in an attempt to achieve acceptable recoveries of both copper and cobalt.

Jan 1, 2005

By H. Yavuz

Closed form solutions assume opening shape to be circular to simplify the calculation of the ground response curve for the design of underground openings. However, in mining and civil engineering works, non-circular openings are commonly excavated. Therefore, there is a need to estimate the ground response curve for such openings. In this respect, a simple model for circular, arch and rectangular shape underground openings subject to a hydrostatic stress field is the aim of this study. A comprehensive numerical modelling, using the finite difference method, based on numerical modelling code FLAC version 4.0, was carried out. In addition to shape of an opening, the effect of rock mass strength, opening size, in situ stress on strain (tunnel deformation to tunnel radius) of the opening in response to applied support pressures was investigated parametrically by developing models for each specific condition. The strain results for each excavation shape obtained from this large number of models against the normalized strength of rock mass and internal support pressure with in situ stress magnitude were evaluated by multiple regression analysis. As a result, a model that was well correlated to data was developed for an overall estimate of the ground response curve depending on relevant effecting parameters. The regression coefficients of the model were given for estimating both roof and sidewall response curve of each excavation shape. The model was verified by statistical tests and by an analytical solution. Diagrams were also established to highlight the influence of relevant parameters and to estimate the support pressure for a stable opening staying within the acceptable limits of strain. Strains occurring in a rectangular opening are found to be larger than those in the arch and circular openings for the other fixed parameters. In the mean time, larger strains occur around an arch shape opening than a circular opening.

Jan 1, 2006