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By M. Z. Emad, A. Hassan, M. A. Raza, M. U. Khan, S. A. Saki

Digital modelling of a surface is crucial for Earth science and mining applications for many reasons. These days, high-tech digital representations are used to produce a high-fidelity topographic surface in the form of a digital terrain model (DTM). DTMs are created from 2D data-points collected by a variety of techniques such as traditional ground surveying, image processing, LiDAR, radar, and global positioning systems. At the points for which data is not available, the heights need to be interpolated or extrapolated from the points with measured elevations. There are several interpolation/extrapolation techniques available, which may be categorized based on criteria such as area size, accuracy or exactness of the surface, smoothness, continuity, and preciseness. In this paper we examine these DTM production methods and highlight their distinctive characteristics. Real data from a mine site is used, as a case study, to create DTMs using various interpolation techniques in Surfer® software. The significant variation in the resulting DTMs demonstrates that developing a DTM is not straightforward and it is important to choose the method carefully because the outcomes depend on the interpolation techniques used. In mining instances, where volume estimations are based on the produced DTM, this can have a significant impact. For our data-set, the natural neighbour interpolation method made the best predictions (R2 = 0.969, β = 0.98, P < 0.0001).

Feb 6, 2023

By V. I. Ryaboy, V. P. Kretov, I. V. Ryaboy

Attachment of collectors containing thioamide groups to sulfide minerals is interpreted as interaction between NH-acids and sulfides acting as solid bases with the formation of a donor–acceptor reagent–mineral bond. As the acid function of the reagents increases, their sorption optimum is observed to shift to a less alkaline region. The developed concept has enabled us to propose a method for calculating optimal pH values for the sorption of reagents on mineral surfaces depending on the acidity of the reagents and the pH value of the medium. Our estimates correlate well with the experimental data. We studied the spectra of the reagents containing thioamide groups and the spectra of copper salts and their surface compounds on an oxidised copper film, chalcopyrite, and pyrite using the infrared (IR) spectroscopy. Some effective applications are described of reagents containing thioamide groups in the flotation of copper, copper-molybdenum, and gold ores, both separately and in combination with other collectors. It is shown that the flotation performance is maximised by adding two- and three-component collector combinations, including collectors containing thioamide groups. In this case, the increase in the recovery of copper, molybdenum, and gold is up to 2-5% compared to conventional process conditions. A new, high-performing reagent containing a thioamide group is proposed. A commercial pilot batch of the reagent was produced and sent for flotation tests in gold ore applications. Keywords: Thioamide reagents, dialkyldithiophosphate, collectors, flotation, arsenopyrite, chalcopyrite

Jan 1, 2020

By S-J. Park

When evaluating mining investment opportunities, one should consider the risks associated with mineral exploration and development. These are commonly classified as technical, economic, and political risks, and are accounted for in the investment decision by changing the discount rate. Thus, a company may use different discount rates associated with varying risks in order to compensate for the variability of success. The discount rate has a tremendous effect on the economic evaluation of mineral projects. Even when all other factors used as inputs for calculating the NPV (net present value) are equal, the project under consideration may be accepted or rejected depending upon the discount rate. Determining a realistic discount rate for a given project is therefore the most difficult and important aspect of cash flow analysis. It should be determined with the consideration of proper technical, economic, and political conditions surrounding the specific project undergoing economic evaluation. One key problem for determining the appropriate discount rate is that it typically depends more on subjective perception of the degree of risk or other experience factors than on a systematic approach. Thus, this study aims to identify, analyse, and document the type, role, and impact of risk factors influencing the determination of discount rates, and then to determine discount rate by using the aforementioned factors.

Jan 1, 2011

By P. Lenegan, R. Masethe, R. I. L. Ferreira

Underground mining in high rock-stress environments can induce unanticipated dynamic rockmass deformation, posing a serious risk to the workforce. Data collected by seismic networks are imperative for the design-as-you-mine process. Often an inappropriate assessment of the seismic hazard is done when unnecessary data are included in analytical techniques, particularly short-term time frames. Depending on the methodology or application of data analysis and interpretation, some of the information may not be relevant and even detract from the objective. By using the spatial event clusters associated with active workplaces to define the shape and size of the polygons for data selection for subsequent analysis, a problematic subjective component can be eliminated. The mining of tabular reefs in South Africa, be they gold- or platinum group metals, is very extensive, and underground workplaces are often widespread. Production stoppages are very costly, especially for marginal mines, so there is just cause not to evacuate an entire operation’s workforce following the occurrence of a large mining-induced seismic event. A rationale based on the damaging peak particle velocities (PPV) of the past seismicity can exclude the unaffected underground personnel and allow a quick orderly withdrawal where required. Micro-deformation may precede rockbursting, which can occur on-shift close to the workface. A mine-wide array of geophones suitable for the accurate location and analysis of seismicity may not be able to detect these higher-frequency emissions. Inexpensive but fit-for-purpose accelerometers, providing real-time, continuous measurement of acoustic rockmass deformation near the workplace, integrated through underground and surface communications networks, are shown to record ‘rock-talk’, clearly distinguishable from the instrument background noise, which can be in the order of hours leading up to an imminent damaging seismic event.

Jan 12, 2025

By S. Dey, C. Bhar, S. K. Mandal

Loading and hauling of ore and waste are the key operations of an opencast coal mine and entail a high operational cost. The productivity of a mine can be increased by reducing the cycle time of loading equipment as well as utilizing dumpers optimally. In this paper we discuss the impact of rock type, bucket fill factor, rock fragmentation, the height of the cut, and angle of swing of the bucket on shovel performance. A time study is conducted on shovels in an opencast coal mine with experimental blasts of rocks to assess the impact of different factors on the performance of the shovel. Based on the data, the authors applied multiple regression (MR) and artificial neural network (ANN) techniques to develop different models for the prediction of the shovel cycle time. Developed models are validated by comparing the predicted data with actual field data. With the help of the best model, the plausible fleet size is determined in order to utilize the shovel and dumper optimally and to improve the performance of shovel–dumper operation.

Oct 1, 2022

By M. Bryson, J. Taguta

The Prieska deposit, mined between 1971 and 1991, is one of the world’s top thirty volcanogenic massive sulphide (VMS) base metal deposits. The Prieska Copper Mine in the Northern Cape Province was closed by Anglovaal when underground mining had extended to depths which did not allow for safe and economic extraction of the deposit at the time. The mine has a recorded historical production of over 1 Mt of zinc and 430 k tonnes of copper from 46.8 Mt of milled sulphide ore, achieving life-ofmine metal recoveries of 85% for copper and 84% for zinc into high quality concentrates (refer ORN ASX release 15 Nov 2019). Orion Minerals Ltd is currently investigating the feasibility of developing a new mine in the footprint of the historical Prieska Copper Mine, using the extensive remaining infrastructure, with the intent of extracting the unmined zinc-copper mineralisation from the Prieska deposit. This paper reports results on the flowsheet development philosophy on the hypogene ore, and challenges encountered in the process. This study initially failed to replicate historic copper and zinc recoveries employing the historic production flowsheet and reagent conditions unmodified on bench scale, as the copper and zinc were co-floating. Flowsheet modifications were therefore made to improve differential flotation and recovery, resulting in achieving comparable saleable products and recoveries from processing the hypogene ore on bench scale. Flotation variability test work on the hypogene ore focused on the use of the original flotation procedure and reagent suite using a sodium cyanide-zinc sulphate depressant system on the copper circuit, and it generated a saleable copper product of 20-26% Cu grade at 80-86% recovery. The zinc circuit generated a saleable zinc product grading at 48-55% Zn at 80-94% recoveries. Some zinc losses were due to the deportment of some zinc in sauconite. It is recommended that further test work may further improve the copper grades and recoveries. Keywords: Prieska, flotation, hypogene ore, flowsheet development, sulphide flotation, reagents

Jan 1, 2020

By J. J. Cilliers, J-A. Lamamy, J. N. Rasera, K. Hadler

Production of oxygen on the moon can be achieved by reduction of lunar soil. One such reduction technology, hydrogen reduction, favours a high proportion of ilmenite in the feedstock. Ilmenite is present in lunar soil as a minor mineral phase, but it can be upgraded using electrostatic separation. This study presents the results of a preliminary investigation into the operating parameters and sensitivities of a free-fall electrostatic mineral separator for lunar applications. Samples of ballotini and ilmenite as well as simple binary mixtures of the two were tribocharged on copper and passed through a uniform electrostatic field. The field is varied to change the electrostatic force acting on the particles. The proportion of material reporting to the positive electrode collectors, negative electrode collectors or the central collector was measured to determine the separation performance. The data confirmed that the charge transferred from the tribocharger to each species is in agreement with the triboelectric series; ballotini was found to charge positively on copper and ilmenite negatively. Particle-particle contacts were dominant, however, resulting in a somewhat symmetrical particle distribution in the collectors. These findings indicate that the copper tribocharger design requires optimisation in order to substantially increase particle-wall contacts. Four binary mixtures with feed grades of ilmenite ranging from 5% to 20% were prepared and tested. This study found that a higher ilmenite head grade resulted in a higher concentrate grade (26.3% from a head grade of 20%) with low recovery (3.4%). In contrast, the lower feed grade resulted in a low concentrate grade but higher recovery. The mass yield of ilmenite was 1.4 times greater for the highest-grade feed than for the lowest. A subsequent study into the reprocessing of middling fraction found a nearly constant relationship between cumulative grade and recovery. This is the first investigation into the effect of feed grade on the concentrate grade and recovery for lunar mineral processing. Keywords: Lunar resources, beneficiation, electrostatic, SRU, ISRU

Jan 1, 2020

By K. Sasaki, S. Kuroiwa, H. Miki, Y. Aoki, T. Hirajima, Y. Orii, G. P. W. Suyantara

Selective flotation to separate copper minerals from, for example, Mo- and/or As-bearing minerals is a continuing problem because the selectivity of current systems is imperfect. Selective Cu-As flotation is currently difficult, and the most common Cu-Mo selective flotation method uses NaHS; this must be done in an enclosed system because, under acidic conditions, this method produces hydrogen sulfide. In this paper, some novel alternative flotation processes that use redox reactions are discussed; these methods have a much lower environmental impact. Oxidation and reduction reactions can be used to make copper minerals more hydrophilic and Mo-bearing minerals more hydrophobic. X-ray photoelectron spectroscopy (XPS) analyses indicated that the copper minerals became hydrophilic because hydrophilic iron precipitated and several hydroxides covered the copper minerals’ surfaces, whereas the molybdenum minerals remained hydrophobic because their sulfide surfaces were not covered. Flotation experiments on these minerals after redox treatments indicated that excellent separation of Cu-minerals from Mo-minerals can be achieved. Possible mechanisms for this separation were investigated using detailed surface analyses and thermodynamic calculations. The additives used to initiate the redox reactions are easy to handle and make these new flotation procedures better than current processes because the new methods do not emit effluent gas and because they are commercially viable. Keywords: Flotation; chalcopyrite; molybdenite; oxidation; reduction

Jan 1, 2020

By C. Kirmanli

The purpose of this paper is to develop an expert system for hydraulic excavator and truck selection in surface mining. Hydraulic excavators and trucks are finding increasing applications in mining operations. Hydraulic excavators are extensively used especially when bringing electricity to rural areas is difficult and for small-scale mining. This paper describes an expert system, which selects the optimum hydraulic excavator truck configuration such that unit production cost is minimized and technical constraints such as geological, geotechnical and mining constraints are satisfied. The system has four modules: user interface, rules and an methods, databases and output module. The expert system in this study is developed within KappaPC shell. It supports object-orientated technology for the MS Windows environment. The software provides a very useful tool to practitioners, saving time and cost. Equipment selection is a recurring and expensive problem of mine planning and often involves interdisciplinary experts from different fields. It is very difficult and expensive to bring together all these experts. The capabilities of the expert system developed are illustrated in the paper. The software overcomes the difficulties of selecting the proper equipment for surface mining operations, which is very important, and results in substantial savings. Equipment databases for hydraulic excavators with 15-59 yd3 capacities and trucks with 35-360 tons are constructed and these databases are used to select the proper configuration. A case study is carried out for Soma Surface Coal mines in Turkey. Keywords: surface mining, expert systems, equipment selection, hydraulic excavators, diggability

Jan 1, 2009

By F. Roelofse, D. Grobler, and M. Purchase, C. Gauert, E. Kotze

Scandium is an important industrial metal for which demand is projected to increase in the future. Although many Sc deposits are secondary, Sc is scavenged by clinopyroxene during fractional crystallization of primary, mafic-ultramafic magmas. Sc may thus occur in sub-economic concentrations in mafic-ultramafic intrusions. In this work, we present new data on the concentration of Sc in the Bushveld Complex (BC) of South Africa. The eastern and western limbs of the BC are considered to be largely pristine, primary magmatic deposits, whereas the northern limb shows evidence of largescale, localized crustal contamination. Samples from the primary magmatic cumulates of the eastern limb, from the mineralized Flatreef of the northern limb, and from the crustal-contaminated Footwall Assimilation Zone (FAZ) of the Flatreef were analysed for Sc. Despite the FAZ containing abundant clinopyroxene, interpreted to have recrystallized from the original cumulates in the presence of melted sedimentary rocks, no significant differences are seen in the concentration of Sc compared to other cumulate rocks of the BC containing less-abundant clinopyroxene. The concentration of Sc in the analysed samples is mainly controlled by mineralogy, with anorthosites, chromitites, and harzburgites containing under 20 ppm, and norites and pyroxenites containing 20–40 ppm. The parapyroxenites of the FAZ are less enriched in Sc than expected, suggesting that Sc may have been lost during alteration and recrystallization.

Sep 1, 2022

By J. Zhang, A. J. S. Spearing, L. Ma

Ore deposits are becoming more complex to mine as a result of the exhaustion of surface and other easily mined deposits. There is also increasing socio-political pressure to design more environmentally sound, sustainable, and safe mining practices. Wang and Ma designed a mining method for coal, similar to a modified drift and fill using a continuous miner to take sequential cuts (rooms) that are subsequently backfilled. The authors have modified the concept to make it more autonomous, safer, and less costly using highwall coal mining techniques, modified and adapted for underground applications. The method is more flexible than longwall mining and the percentage extraction would seem to be in the same range. In addition because of the backfilling, surface subsidence would not be a major issue and could be more effectively managed.

Feb 2, 2021

By V. van der Merwe, C. W. Siyasiya

"A petrochemical company experiences premature thermal fatigue failure of the casting moulds used in catalyst production. The aim of the project was to find an alternative alloy that would outperform the current low-alloy cast steel used for the moulds. Based on their thermo-fatigue properties, 3CR12 ferritic stainless steel and H11 tool steel were chosen for testing and comparison with the currently used BS3100 B7 cast steel. Samples of each material were subjected to temperature cycling in a Gleeble 1500TM thermo-mechanical processing simulator, followed by surface analyses. The main parameters derived from the test work were the total true strain, the hot strength of the materials, and the number of cycles to failure. Additionally, the coefficient of thermal expansion for each material was measured using a Bähr dilatometer. H11 tool steel yielded the best performance by way of having the fewest surface cracks, the lowest total true strain per cycle, the most cycles to failure, the highest hot strength, and the lowest coefficient of thermal expansion.IntroductionThe Catalyst Manufacturing Plant (CMP) is a dusty environment with temperatures higher than ambient. Molten mill scale (magnetite, Fe3O4) is tapped from the electric arc furnace into the casting moulds at temperatures close to 1600°C. After 10 seconds the magnetite is quenched with a water spray for 50 seconds to a minimum temperature of 400°C. Sometimes there is residual water in the pans from the cooling fog process (water sprays) in the empty mould. In a typical plant, the factory produces 40–44 batches a day containing between 150–300 moulds, depending on the time required for the specific batch (Buchholz, 2014). The typical batch in the CMP usually weighs about 6 t. The thickness of the tap, speed of the casting belt, and tilting angle all affect the number of moulds per batch.One of the main problems faced during the molten mill scale casting is the premature failure of the casting moulds. Cracks initiate on the surface of the mould, which is in contact with the hot catalyst, and propagate into the interior of the mould. Cracks are generally concentrated in the middle area of the mould where the catalyst makes first contact with the mould, and which experiences the highest temperature fluctuations. This suggests that the cracks are caused by thermal fatigue during the casting process."

Jan 1, 2016

By F. Dong, F. Yang, J. Wang, Z. Wang, D. Mingxia

Antimony oxide ores are important antimony resources, but their recovery is still a problem. In this paper, the adsorption behaviour and mechanism of dodecamine and quaternary ammonium salt on the surface of cervantite and quartz were investigated. The flotation behaviour of cervantite and quartz using quaternary ammonium salts and dodecylamine as collectors was studied by single mineral flotation experiments. The adsorbed amount was measured and infrared spectroscopy was used to study the ability of several cationic collectors to float cervantite and quartz. The results show that quaternary ammonium salts can simultaneously float the cervantite and quartz. It is difficult to achieve separation of the two minerals using quaternary ammonium salts as collectors. At pH>10, dodecylamine can float quartz but not cervantite, which can achieve reverse flotation separation of the two minerals. The difference between the abilities of quaternary ammonium salts and dodecylamine to float cervantite and quartz lies in the different ionisation properties of the two reagents. Quaternary ammonium salt is a strong electrolyte that is completely ionised in the pulp and exists mainly in the form of quaternary ammonium ions. Dodecylamine is a weak electrolyte and predominantly forms molecules under alkaline conditions. Keywords: Cervantite, quartz, dodecylamine, quaternary ammonium salts, flotation

Jan 1, 2020

By J. R. Bredell, J. Branehog, C. Coetzee, J. J. van Tonder

A nutating grinding mill, exemplified by the commercial HICOM mill, achieves efficient particle size reduction through the accelerated motion of the material charge within the nutating chamber. This design, characterised by high particle velocities and rapid charge circulation, offers a compact solution compared to tumbling mills. There have been concerns regarding the mechanical reliability of kinetic joints for certain specialised mining applications. Recognising the need to model internal forces in such systems, this study focuses on the uncoupled simulation using multibody dynamics and the discrete element method. The investigation employed a small-scale experimental test mill, referred to as the NuMILL, featuring a cylindrical chamber (140 mm internal diameter, 245 mm height, 6° nutation angle). Instrumented with an array of sensors, the NuMILL provided internal load data for validating the simulations. Experiments were conducted with an empty chamber or filled with charge material. Charge materials included coarse sand or steel pellets with a charge-to-chamber mass ratio of 0.25. The mill speed ranged between 100 to 700 RPM. Multibody dynamics modelled resultant inertial and frictional loads within 5%, while the discrete element method simulated the internal material contact loads with accuracies ranging from 1% to 19%. The combined simulation approach predicted the resultant forces in the critical kinetic joint within a 20% margin. Representing the charge using rigid lumped mass elements was also studied. The presented simulation techniques, validated against experimental data, offer a robust foundation for analysing larger systems, including the industrial-scale HICOM.

Mar 5, 2025

By A. Tosun

"The size distribution of the muckpile formed as a result of open pit blasting operations has a considerable effect on the efficiency of loading, hauling, and crushing. Various researchers have developed specialized computer software that uses image analysis methods for determining the size distribution of the muckpile. However, these methods have some limitations. One of the most important of these limitations is that the very fine fragments in the muckpile cannot be used in the size distribution calculation. In this study, 18 test blasts in total were carried out in two limestone quarries belonging to Batiçim Corp. in Izmir, Turkey. A new model was developed in order to ensure that very fine fragments are used in the size distribution calculation. The size distributions of the test blasts were calculated by both the Wipfrag computer program and the new model. Correlations were established between the muckpile size distributions determined by both methods and the parameters determining the efficiency of the loader. IntroductionThe size distribution of the muckpile formed as a result of open pit blasting operations has a considerable effect on the efficiency of loading, hauling, and crushing. Various researchers have established certain correlations for predicting the efficiency of the operations according to the muckpile size distribution so that production can be carried out economically (Tunstall and Bearman, 1997; Nielsen and Kristiansen, 1996; Workman and Eloranta, 2004; Michaud and Blanchet, 1996; Frimpong, Kabongo, and Davies, 1996; Osanloo and Hekmat, 2005; Molotilov et al., 2010). In these studies, the 50% passing size (X50) is generally used. These methods rely on the correct measurement of the size distribution of the muckpile formed by the blast. The most reliable measurement method would be to subject the entire muckpile to a sieve analysis, but this is obviously impracticable. Therefore, computational method based on image analysis have been developed. These include IPACS (Dahlhielm, 1996), Tucips (Havermann and Vogt, 1996), Fragscan (Schleifer and Tessier, 1996), Cias (Downs and Kettunen, 1996), GoldSize (Kleine annd Cameron, 1996), Wipfrag (Maerz, Palangio, and Franklin, 1996), Split Desktop (Kemeny, 1994), PowerSieve (Chung and Noy, 1996), and Fragalyst (Raina et al., 2002). In these methods, the size limits of the fragments forming the material are determined by image analysis on photographs of the muckpile. However, the computer software has some limitations. It does not take into account the third dimension of the muckpile, nor the size distribution of very fine fragments. In particular, the fragment size ranges below 2.5 to 3 cm cannot be determined, and therefore these cannot be included in the muckpile size distribution. However, the muckpile formed by a bench blast contains a wide range of particle sizes (Tosun et al., 2015)."

Oct 1, 2018

By Z. Botha

Sheryl Sandberg, the COO of Facebook, published a book titled 'Lean In', where she invites women to sit at the table. In summary, to 'sit at the table' entails not only embracing opportunity, but to actively seek out opportunities in leadership positions. Sandberg points out that, unfortunately, apart from institutional obstacles, a woman's own perceived limitations have a negative impact on her leadership ambitions. To create an environment where diversity will flourish, where everyone has a seat at the table and everyone has a voice, safety must be established first. To establish safety within a diverse team, there is power in relationships and connections. This study will first and foremost review theories in literature as to why diversity and inclusion are so important and the value that diversity brings to our industry. The study also recommends a few focus areas for improving diversity and inclusion in the industry.

Sep 1, 2022

By S. M. H. Haddad, M. Saghaeian, R. Hejazi, V. Sheikhzadeha, A. H. Baladastian, A. Dehghani Ahmadabadi

Sulfide impurities in iron ore concentrates play an important role in designing pelletising and steel making plants. Therefore attempts are made to keep the sulfur content of the final concentrate produced by the plants as low as possible. Generally, in the beneficiation process of iron ore concentrate, the removal of sulfur is performed through magnetic separation systems, followed by reverse flotation. The sulfide content of the iron ore concentrates originated from two main sources, including pyrite and pyrrhotite. In this research, in order to compare the floating capability of these two types of sulfide minerals, two iron ore concentrates with different sulfide constituents, pyrite or pyrrhotite, were selected. Reverse flotation tests were done separately on these samples under similar conditions. Process parameters considered for the tests included pH (2, 4, 6, 8 and 10), collector consumption (150, 200, 250, 300 and 350 g/t) and frother consumption (40, 50, 60, 70 and 80 g/t). Potassium Amyl Xanthate (PAX) and Methyl Isobutyl Carbinol (MIBC) were the collector and frother used in the tests, respectively. For modelling and optimising process parameters, the Central Composite Design (CCD) method was applied to the test results. Empirical coded equations were obtained for responses involving weight recovery, Fe recovery, Fe grade and S grade. Finally, comparison of test results revealed that the elimination recovery of pyrite sulfides was far greater than pyrrhotite sulfides, and it was possible to remove 84% sulfur content of the pyrite sample compared to minus 30% for the pyrrhotite sample. Keywords: Reverse flotation, pyrite and pyrrhotite, sulfur removal, iron ore concentrate, beneficiation plant

Jan 1, 2020

By J. P. Harrison, J. A. Hudson.

ABSTRACT: When considering the rock stress component of rock mechanics design, the basic procedure is to consider the pre-existing stress-state in the rock mass and then estimate the disturbance to this stress state as a result of engineering excavation. Failure criteria are applied to the final stress state to establish whether failure will occur. However, during the evolution of the stress state, the failure locus may be reached before the anticipated failure state and, in this case, failure will occur unexpectedly. This indicates that the complete stress path (defined as the variations in magnitudes and orientations of the stress tensor components resulting from engineering-induced or natural changes) must be considered. We list a set of stress path principles with their corollaries and then introduce a new and powerful method for simultaneously illustrating changes in the six independent components of the stress tensor. This method plots the magnitudes of the principal stresses above their orientational paths on the hemispherical projection, to provide a three-dimensional stress path locus for each of the three principal stress components. In connection with this presentational device, we illustrate a number of concepts associated with the stress path in rock engineering. For example, we show how the minor principal stress approaches zero at an unsupported excavation face, the interchange of the trajectories of two principal stresses when their magnitudes become equal, and the influence of the bounds on the principal stresses given by strength criteria. RESUME: Si on s’interesse à la composante “contrainte” lors d’un dimensionnement en mécanique des roches, la méthode de base consiste à considérer l’état de contrainte pré-existant dans le massif rocheux, puis d’estimer la perturbation à cet état générée par l’excavation projetée. Des critères de rupture sont appliqués à l’état de contrainte final pour établir si une rupture va se produire. Cependant, lors de l’évolution de l’état de contrainte, la surface critique peut être atteinte ce qui provoquera une rupture anticipée et, dans ce cas, cette dernière sera inattendue. Cela indique que le chemin de contrainte complet (défini par les variations de l’intensité et de l’orientation des composantes du tenseur des contraintes liées à des causes anthropiques ou naturelles) doit être pris en compte. Nous présentons un ensemble de règles pour les chemins de contraintes ainsi que leurs corollaires et, ensuite, nous introduisons une méthode, nouvelle et puissante, pour présenter simultannement les changements des six composantes du tenseur des contraintes. Cette méthode consiste à tracer l’intensité des contraintes principales sur le chemin d’orientation des contraintes à l’aide d’une projection hémisphérique afin d’obtenir le lieu, en trois dimensions, de chaque contrainte principale. En relation avec cet outil de représentation, nous illustrons certains concepts associés au chemin de contrainte en ingénierie au rocher. Par exemple, nous montrons comment la contrainte mineure tend vers zero à la surface d’une excavation sans soutenement, le changement de direction des deux contraintes principales quand leur intensité deviennent égales, et l’influence des conditions aux limites sur les contraintes fournies par un critère de rupture. ZUSAMMENFASSUNG: Bei ingenieurmassigen Taetigkeiten in Felsgesteinen ist es noetig die ungestoerten Gesteins Stress Componenten, die vor einem anthropogen Eingriff im Gestein vorhanden waren, zu kennen und erst dann Vorhersagen ueber Stoerung des Stress Zustandes, der durch einen ingenieurmaessigen Eingriff hervorgerufen wird, herzuleiten. Kriterien fuer das Versagen werden im letzten Stadium, des Stress Zustandes angewendet, um zu erfahren ob ein Versagen wohl eintreten wird. Es ist jedoch zu beachten, dass waehrend des Stress Aufbaus ein oertliches Versagen eintreten kann, welches vor dem eigentlichen, erwarteten Versagens Zustand auftritt. Diese Moeglichkeit weist darauf hin, dass der gesammte “Stress Path” (definiert durch die Variationen der Stress Tensor Komponenten in Richtung und Groesse, hervorgerufen durch ingenieurmaessig hervorgerufene oder natuerlich Vorgaenge) betrachtet werden muss. Wir fuehren eine Liste der “Stress Path” Prinzipien auf und stellen dann eine neue und wirksame Methode zur gleichzeitigen Darstellung der sechs unabhaegigen Komponenten des Stress Tensors vor. Diese Methode stellt die Groesse der “Principal Stresses” in Abhaengigkeit von ihrem rauemlichen Weg auf einer hemispherischen Projektion dar und erlaubt hiermit eine drei dimensionale Darstellung fuer jeden Ort des “Stress Path’s” in die drei Haupt Stress Komponenten. Im Zusammenhang mit der hier gegebenen Darstellungsart, verdeutlichen wir eine Reihe von Konzepten in der Felsmechanik. Wir zeigen zum Beispiel, wie der “Minor Principal Stress” Null zustrebt an einer Wand von einer nicht abgestuetzten Ausschachtung, den Austausch von Trajektorien zweier “Principal Stresses” wenn ihre Groessen sich gleichen, und den Einfluss der Groesse von “Principal Stresses” bei gegebenen Kriterien des Festgkeits Versagens.

Jan 1, 2003

By D. Paktunc, S. P. du Preez, J. P. Beukes, P. G. van Zyl, A. Jordaan

"The chromium (Cr) content of stainless steel originates from recycled scrap and/or ferrochrome (FeCr), which is produced mainly by the carbothermic reduction of chromite ore. The oxidative sintered pellet production process is one of the most widely applied FeCr processes. The supplier of this technology specifies that recycling of chromite-containing dust collected from the pellet sintering off-gas and fines screened out from the sintered pellets (collectively referred to as pre-oxidized chromite fines) should be limited to a maximum of 4 wt% of the total pellet composition. However, the results presented in this paper suggest that recycling of such fines up to a limit of 32 wt% of the total pellet composition may improve the compressive and abrasion strengths of the cured pellet. In addition, electron microprobe and quantitative X-ray diffraction (XRD) analyses demonstrate that chromite grains present in the pre-oxidized chromite fines consist, at least partially, of crystalline phases/compounds that will improve the metallurgical efficiency and specific electricity consumption (i.e. MWh/ton FeCr produced) of the smelting process. Introduction Stainless steel is a vital modern-day alloy that is well-known for its corrosion resistance, which is mainly due to the inclusion of chromium (Cr) (ICDA, 2013). Stainless steel is mostly produced from recycled scrap and ferrochrome (FeCr), a relatively crude alloy of Cr and iron (Fe). FeCr is predominantly produced by the carbothermic reduction of chromite, a mineral belonging to the spinel group characterized by the unit formula [(Mg,Fe2+)(Al,Cr,Fe3+)2O4] (Haggerty, 1991; Paktunc and Cabri, 1995; Tathavakar, Antony, and Jha, 2005). Although Cr can occur in 82 different minerals, chromite is the only source of new Cr units that can be exploited in commercial volumes (Motzer and Engineers, 2004). Approximately 95% of mined chromite is used in the production of various FeCr grades, of which high-carbon and charge grade FeCr are the most common (ICDA, 2013)."

Feb 1, 2019

By R. B. Khumalo, M. S. Nyarela, R. C. Nemathithi

Palabora Mining Company is one of the largest low-grade copper mines globally. The mine uses block caving for the extraction of the orebody. This paper enumerates the drawpoint loading strategies for the overall head grade improvements, particularly for a block that is nearing depletion. A comprehensive literature review of various considerations relating to improving productivity in block caving is presented to contextualize the draw control in caving. From this study, an optimized draw control strategy is presented, which focuses on three parameters that include grade distribution, loading compliance, and tonnage splits per sector. An empirical method based on the relational study between various parameters is used to outline the key criteria to be used in the optimization of drawpoint loading in block caving.

Nov 30, 2022