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Mill relining is a major contributor to overall plant downtime. Reducing the number of mill liner pieces removed from and replaced in the mill has a direct impact on the overall reline time and in turn, mill availability. To improve the mill availability of Ridgeway Operations' 32 foot SAG mill, a number of initiatives were implemented in terms of liner design. These included the conversion of the shell from 40 to 30 rows, reducing the number of pieces from 80 to 60 each shell reline and reducing the number of pieces from 48 to 32 per feed end reline. In addition, modifications were made to the discharge end of the mill to extend the life of the outer pulp lifter and discharge cone, thereby reducing the frequency of change out. The standard radial outer pulp lifter was converted to an angled design. The discharge cone was converted to the BullnoseTM design supplied by Bradken. This paper discusses the design changes made and the expected benefits to the Ridgeway Operations in terms of mill availability improvements.

Jan 1, 2007

By B. Talbot

How this simple plant generates a large revenue stream. The concept behind the Tailings Scavenging Plant (TSP) is simple: it is a non-complicated modular plant which is designed to be more stable than upstream plants. This, plus the use of ?high energy?, enables the plant to recover any metal missed by the upstream operation. Impala Platinum?Mineral process started pilot plant exercises in June 2003. The pilot plant ran for one year before the capital for the full-scale plant was approved. This year was used to motivate, design and cost a full-scale plant. The metal produced during the pilot and feasibility study enabled this part of the project to run at a small profit. The scale-up to full-scale was relatively simple as the pilot plant had a capacity of 180 m3/hrand the full-scale plant was designed for a capacity of 550 m3/h. The design for the full scale plant was completed in May 2003, with ground breaking taking place on 19 May 2003. The construction phase of the project went well with the commissioning of the first two modules taking place on 22 October 2003. The remaining two modules were commissioned two weeks later. The plant was at full capacity by the 20 November 2003. A review of the plants performance for the first 5 production months is as follows: the plant has required only a few minor modifications and additions, it has run well in excess of 95%availability with no major wear apparent. In addition to this, the plant has produced 3 times the metal forecast.

Jan 1, 2004

By D. S. van Vuuren

Industrial production of titanium occurs via the batch-wise reduction of titanium tetrachloride (TiCl4) with a reducing metal, being magnesium in the Kroll process, or sodium in the Hunter process. In the search for low cost titanium, the CSIR is developing a continuous process to produce titanium powder directly via metallothermic reduction of TiCl4 in molten salt, dubbed the CSIR-Ti process. The move to a continuous process has been attempted by a number of organizations, but was until now always met with failure, due in no small part to challenges inherent in the process chemistry. The reaction between TiCl4 and the reducing metal can occur directly, when TiCl4 or any titanium sub-chlorides present, comes into contact with suspended or dissolved reducing metal. The reaction can also occur indirectly, without any physical contact between the reacting species, via an electronically mediated mechanism. The reaction mechanism via electronic mediation can cause TiCl4 to react at the outlet of the feed port, rapidly causing blockages of the TiCl4 feed line. The electrical conductivity of the metal reactor can also cause the electronically mediated reaction to favour the formation of titanium sponge on the reactor walls and internals, rather than titanium powder. Various methods were investigated to overcome the problem of blockages in the TiCl4 feed line, e.g. mechanical removal, sonic velocities, dilution of the TiCl4 and the use of ceramic feed lines. This article discusses problems experienced with the continuous feeding of reagents, and various methods attempted are shown and discussed. Information is also given on the morphology, chemical composition and suitability of the final titanium powder for powder metallurgical application as presently produced by the CSIR-Ti process. Keywords Titanium dioxide, titanium nitride, carbo-thermic reduction, ilmenite, slag, tunnel kiln, residence time.

Jan 1, 2011

By D. F. Malan, R. P. Els

The limit equilibrium model, used in displacement discontinuity codes, is a popular method to simulate pillar failure. This paper investigates the use of physical modelling to calibrate this model. For the experiments, an artificial pillar material was prepared and cubes were poured using the standard 100 mm × 100 mm civil engineering concrete moulds. The friction angle between the cubes and the platens of the testing machine was varied by using soap and sandpaper. Different modes of failure were observed depending on the friction angle. Of interest is that significant loadshedding was recorded for some specimens which visually remained mostly intact. This highlights the difficulty of classifying pillars as failed or intact in underground stopes where spalling is observed. The laboratory models enabled a more precise calibration of the limit equilibrium model compared to previous attempts. Guidelines to assist with calibration of the model are given in the paper. The limit equilibrium model appears to be a useful approximation of the pillar failure as it could simulate the stress-strain behaviour of the laboratory models.

May 3, 2023

By J. S. Contreras, E. Córdova, I. Gottreux, A. Anani, A. Ferrada

Cave mining is an underground mass mining technique. The largest projects, which are known as ‘super caves’, produce hundreds of thousands of tons of ore per day, which involves large footprints with considerable column height, and have a life of mine of over 20-40 years. These operations are typically located deep, under high stresses and in competent rock masses, making initiation and propagation of the caving process harder to manage. These challenges must be confronted by optimizing the fragmentation of the orebody to achieve smaller size blocks that will result in consistent caving and improved flow of the ore from the drawpoints. To achieve better performance from the drawpoints, preconditioning is applied to fragment and damage the material required to cave. We present a proposed design for preconditioning in underground mines, considering the challenges that these large-scale mines are already facing, based on a comprehensive analysis of current design parameters, case studies, and sensitivity analyses using numerical models.

Feb 2, 2021

By P. Gonzalez

Minera La Parreña, S.A. de C.V., Milpillas operation is an underground mine designed to process 8 352 tons of ore per day for the recovery of copper through crushing, heap leaching, solvent extraction and electrowinning facilities. In order to optimize copper recovery during leaching, the ore is crushed to 13 mm and subjected to primary sampling every 15 minutes for metallurgical accounting. At the same particle size, primary sample goes to secondary sampling and then, the secondary sample is crushed to 2 mm before tertiary sampling. The tertiary sample is sent to laboratory where a final sample is obtained and pulverized to 106 microns for copper assay. This paper shows a review of sampling strategy focused on minimizing or eliminating sampling errors and an experiment designed to determine copper head grade profile as well as the best sampling frequency.

Jan 1, 2009

By B. Moritz, W. Schubert, E. A. Button

ABSTRACT: Geological conditions associated with alpine environments in combination with high overburden in many tunnelling projects lead to squeezing behaviour. The main problems associated with such conditions include large deformations, overstressing of supports, and lack of face stability. In the past during Alpine tunnelling the problem of large displacements incompatible with rockbolt – shotcrete support systems have been solved by leaving gaps in the lining to accommodate excessive deformations. In the late nineties, yielding elements have been developed, which are integrated into the lining. The paper deals with the basic concept, the design and the application of that system, which has been successfully used in several Alpine tunnels. ZUSAMMENFASSUNG: Die geologischen Verhältnisse in den Alpen führen bei großer Überlagerung häufig zu starken Deformationen während des Baues von Tunneln. Die großen Verformungen führen in vielen Fällen zu einer Überbeanspruchung des Ausbaues und Problemen mit der Ortsbruststabilität. Früher ist man dem Problem der Unverträglichkeit des Ausbaues mit den hohen Dehnungen durch Freilassen von Deformationschlitzen im Spritzbeton begegnet. Vor etwa 10 Jahren wurden duktile Stahlelemente entwickelt, welche in die Spritzbetonschale integriert werden. Der Beitrag beschäftigt sich mit dem Konzept, der Planung und der Ausführung. RÉSUMÉ: Les conditions géologiques dans les Alpes conduisent fréquemment lors d'un grand recouvrement à des déformations fortes pendant la construction des tunnels. Les grandes déformations conduisent dans beaucoup de cas à une surtension du revêtement et à des problèmes avec la stabilité de front de taille. On a fait face plus tôt au problème de l'incompatibilité du revêtement avec les extensions élevées par libérer des rainures dans le béton projeté. Il y a environ 10 ans, des éléments sidérurgiques ductiles qui sont intégrés dans le béton projeté ont été développés. La contribution s'occupe de concept, de planification et de mise en oeuvre.

Jan 1, 2003

By A. Kotze, D. Messina, E. Nagels, Y. Cryns, S. Arnout

The FlashPhos process aims to recover white phosphorus (P4) from sewage sludge by drying, flash combustion/gasification, and carbothermic refining steps. This study evaluates the material behaviour of sewage sludge ash melting and reduction in a refining furnace for the novel FlashPhos process. Thermodynamic modelling in FactSage 8.2 is combined with experiments from a tube furnace to determine the possible phosphorus recovery and minor element behaviour. For the two studied sludges, a yield of 40% and 75% white phosphorus is achieved after 1 hour at 1600°C, corresponding with a 60% and 25% loss to the metal phase. This is slightly above the calculated equilibrium yield of 28%–73%, which depends mainly on the Fe/P ratio of the sludge. Temperature is found to have a significant influence on the final phosphorus yield when leading to incomplete melting of the ash. A clean slag is produced in the process free of heavy metals making it suitable to be used as a cement-like binder material. The main heavy metals that co-evaporate with the phosphorus are Zn, Pb, As, Sb, and Sn. Additional processing steps will be required to remove these to produce a pure P4 product. The metal alloy consists of mostly Fe and P with smaller amounts of other components such as Mo, Cr, Cu, Mn, Sn, Sb, and V. The final slag consists of CaO, SiO2, MgO, and Al2O3 with virtually complete removal of P and heavy metals.

Oct 2, 2025

By L. Bam, R. Machaka, S. Chikosha, N. S. Muchavi

"Parts manufactured through power metallurgy (PM) typically contain pores that can be detrimental to the final mechanical properties. This paper explores the merits of 3D X-ray computed tomography over traditional microscopy for the characterization of the evolution of porosity in metal injection moulding (MIM) and direct powder rolling (DPR) products. 17-4 PH stainless steel (as-moulded, as-debound and sintered) dog-bone samples produced via MIM and Ti-HDH strips (as-rolled and sintered) produced via DPR and were analysed for porosity. 3D microfocus X-ray tomography (XCT) analysis on specimens from both processes revealed spatial variations in densities and the existence of characteristic moulding and roll compaction defects in agreement with traditional microscopic microstructural analysis. It was concluded that micro-focus XCT scanning can be used to study MIM and DPR parts for the characterization of the amount, position and distribution of porosity and other defects. However, the majority of the sub-micron sized pores could not be clearly resolved even at the highest possible instrument resolution. Higher-resolution scans such as nano-focus XCT could be utilized in order to fully study the porosity in MIM and DPR parts. IntroductionMetal injection moulding (MIM) is a novel process, which combines the advantages of powder metallurgy (PM) and plastic injection moulding. MIM has found widespread applications in the cost-effective production of high-sintered density small parts with complicated shapes and mechanical properties equivalent to those of wrought materials (German and Bose, 1977; Machaka and Chikwanda, 2015; German, 2013). There are four basic processing steps involved in MIM, namely; feedstock preparation, injection moulding, debinding and sintering. These steps are discussed in greater detail elsewhere (Machaka, Seerane and Chikwanda, 2014; German and Bose, 1977; Machaka and Chikwanda, 2015; German, 2013).Feedstock preparation involves mixing metal powder with a carefully selected composition of polymeric binder materials at a specific temperature. The feedstock is then granulated and injected into a predefined mould die with the desired shape. The part produced during the moulding step is referred to as a ‘green’ component. The green component typically contains no porosity since the spaces between adjacent powder particles are readily filled with the binder materials (German and Bose, 1977; Li, Li and Khalil, 2007). Debinding is the systemic removal of the binder components by chemical, catalytic, or/and thermal means while maintaining the shape of the component. The part produced after the debinding step is referred to as a ‘brown’ component. Debinding is known to be the source of porosity in brown components (Ji et al., 2001; Tsai and Cen, 1995). Finally, the brown debound part is sintered to full or nearfull density (Sotomayor, Varez and Levenfeld, 2010). The sintering step and associated densification closes up the majority of the pores. Sintered MIM parts are typically sintered to high density (95–99%) and retain an irreducible amount of residual porosity (Barriere, Liu and Gelin, 2003; German, 1990)."

Jan 1, 2016

By M. Rhodes

The Sukari project, which is owned by Centamin Egypt Ltd, is located in southern Egypt, 770 km south of Cairo but close to the Red Sea. The project is the first new gold development in Egypt and was commissioned in the middle of 2009. In 2007, Centamin purchased the CIL plant from the Kori Kollo mine in Bolivia. This plant was originally designed to treat 6.5 Mtpa of oxide ore. The Sukari deposit contains an oxide zone close to surface with a thick zone of mixed oxide and sulphides below this. The sulphides contain relatively coarse pyrite and arsenopyrite with fine <10 µm gold inclusions. Eventually, the sulphide ore will be mined from underground. Metplant Engineering Pty Ltd, a subsidiary of Bateman Engineering Pty Ltd was contracted to design modifications and additions to the Kori Kollo plant to enable it to treat the Sukari ores. The plant was designed to treat the three ore types in stages. Throughput was set to 4 Mtpa, dueto Sukari ore being harder, at a head grade of 1.7 g/t to produce 200 000 oz of gold. The oxide circuit was based on the use of the Kori Kollo plant and the difference with mixed ore was that the oxide circuit would treat flotation tailings rather than ore. This circuit has a leach capacity of 26 000 m3 and residence time of 24 hrs The main feature of the upgraded mixed ore plant was the addition of a flotation circuit to produce a concentrate which would be reground and treated in a separate leach and elution circuit. Ore is crushed in a gyratory crusher and the comminution circuit uses a conventional SABC producing a product with a P80 of 150 microns. The throughput of 580 tph of oxide ore and 500tph of mixed ore was set to match the mills from Kori Kollo, with the addition of the pebble crusher to accommodate the more competent Sukari ore. The flotation circuit comprises a single rougher circuit to maximize recovery. The concentrate is thickened prior to regrinding which is carried out in a tower mill and two SMD mills operating in series. The final product, with a P80 of 12 microns, from the regrind circuit is leached in a CIL circuit with a total capacity of 2 550 m3. Gold is recovered through a conventional pressure Zadra circuit. Tailings from both circuits report to separate tailings thickeners and are pumped to a tailings storage facility. The circuit is designed to maximize the recovery of water. The project lies in one of the driest deserts in the world and a feature of the operation is the use of sea water from the Red Sea. This water is pumped 25 km from the coast.

Jan 1, 2009

By M. Faure

The experiment with backfill at Harmony was mainly an attempt to improve the ground conditions in a particularly tricky section of the mine. A deslimed tailings system was selected for financial reasons, ease of installation, ease of operation and its low level of mechanization. The design of the system has three aspects: firstly, to define the parameters of the backfill material itself; secondly, to design a reliable plant which could consistently produce the desired material in sufficient quantities; and, thirdly, to design a fill distribution system for maximum reliability in the shaft, minimum pipe line velocity, pressure and cost in the horizontal sections and consistency and reliability at the delivery end. The system was successfully constructed and commissioned in a short space of time at a relatively low cost. It has now reached its full potential, and very encouraging results have been achieved with regard to cost savings, ground conditions, ventilation and accident statistics.

Jan 1, 1988

By B. Zlender

ABSTRACT: The paper presents investigation of carboniferous slates from the Trojane hilly area performed on series of samples of equal material. The results of static loading tests show that carboniferous slate is heterogeneous and yields on slate layers. Where that kind of heterogeneity is distinctive the strength results are essentially lower of commonly tests results. The results of dynamical loading tests show that the slate surfaces have the essential meaning for the stability of the material. When those surfaces are moistened the material become unstable. RÉSUMÉ: L&apos;article présente une épreuve des ardoises carbonifères de la région montagneuse de Trojane sur une série des échantillons des matériaux identiques. Les résultats des tests de charge statique montrent que l&apos;ardoise carbonifère est hétérogène et qu&apos;elle cède sur les couches d&apos;ardoise. Quand l&apos;hétérogénéité est distinctive, les résultats de stabilité sont essentiellement plus bas que les résultats obtenus par des tests ordinaires. Les résultats des tests de charge cyclique montrent que les surfaces d&apos;ardoise sont très importantes pour la stabilité du matériel. Quand ces surfaces sont mouillés, le matériel devient instabile. ZUSAMMENFASSUNG: Der Artikel präsentiert die Forschung von Karbonschiefersteinen im Bereich des Bergland Trojane, ausgeführt durch Serien von Proben aus den gleichen Erdmaterial. Die Resultate der statischen Belastungsprüfungen zeigen, das die Karbonschiefersteine heterogen sind und die Schieferflächen nachlassen. Wo bei dieser Art der Heterogenität die Festigkeitsergebnisse wesentlich niedriger sind als bei gewöhnlichen Testergebnissen. Die Ergebnisse der zyklischen Belastungsprüfungen zeigen das die Schieferflächen eine wesentliche Bedeutung für die Stabilität des Erdmaterials haben. Wen diese Schieferflächen befeuchtet sind, wird das Erdmaterial unstabil.

Jan 1, 2003

By A. Pareek, V. S. Masampally, V. Runkana

Mineral processing plants, in general, consist of comminution and separation circuits. Rougher flotation is considered as the heart of the separation circuit with concentrate grade and mineral recovery being the key productivity and quality parameters that affect the downstream operations and profitability. Online prediction of these parameters can help improve process performance in real-time. Past efforts to predict flotation cell performance have focused on building physics-based or machinelearning (ML) based models. Although physics-based models are popular in process design applications, ML models are more appropriate for online monitoring, control and optimisation due to their lower computational requirements. Deep learning (DL) is gaining prominence nowadays for application in industrial operations where a large amount of data is available. We have developed a DL model based on long short-term memory (LSTM) neural networks to forecast the two key performance indicators (KPIs), namely, mineral recovery and concentrate grade in a mineral processing plant. Rougher feed characteristics such as mineral grade and particle size distribution, upstream measurable disturbances such as throughput of the comminution circuit and pulp density, and control variables such as aeration rate, pH, and collector addition rate are considered as explanatory variables to train the model. The model was tested with data from an industrial mineral processing plant. For real-time dynamic predictions, the trained model appropriately accounts for mismatch in measurement frequency of real-time process data and off-line laboratory analysis data. Such a time series model can be used as a state observer in model predictive control techniques for optimal control of unit operations in a mineral processing plant. Keywords: Mineral processing, flotation, time-series, dynamic modelling, deep learning

Jan 1, 2020

By H. J. Le Roux, W. B. Drummond

1. INTRODUCTION We have a moral responsibility towards the world to reduce the harmful deposits we emit into the environment arising from beneficiation technologies. Industry has not willingly spent money to limit these emissions because it affected their profit margin with the end result of emitting harmful elements into the environment. Governments have thus rightly stepped in and enforced systematic reduction of these emissions through legislation. In the past beneficiation of sulphur bearing ores was typically done through hydro-metallurgical concentration, smelting, followed by Sulphur removal by converting processes like the Pierce Smith converter. The latter two processes emitted substantial quantities of Sulphur into the atmosphere. Spiralling costs and legislation have resulted in the quest to develop more efficient and environmentally friendly processes to achieve the same end results. New hydro-metallurgical processes like the ActiVox process has completely eliminated the pyro-metallurgical processes. Kansanshi are also operating a similar process. It however elicits other ground water and spillage pollution hazards and problems of it?s own. Various improvements has also been made to the pyro-metallurgical stages, examples being combined smelting and converting with the Noranda reactor, the Codelco CMT furnace, one step flash smelting/converting or the Mitsubishi continuous smelting, converting and slag cleaning process. The new converting processes are also normally enhanced using oxygen leading to higher SO2 gas strength with only a marginal increase in off-gas volume. These processes have led to better efficiencies and a more controlled environment that reduces pollution, but does not eliminate it completely. The fact that there are still more than 70 existing Pierce Smith converter plants throughout the world that needs to be replaced or upgraded at tremendous capital cost, means that we will have the environmental problems for some time to come. The need thus exists to cost effectively get these existing plants into a state where they meet the new environmental regulations, community and safety requirements. This paper will concentrate on just one aspect of this quest, i.e. reduction/removal of off-gasses emanating from the converting of non ferrous sulphur mattes to achieve higher or specialised grades of refined metals.

Jan 1, 2005

By K. Lomberg

In this paper the process of sampling and assaying as it relates in particular to the platinum group elements (PGEs) is presented. A discussion of the geology of PGE deposits is included to provide an understanding of the mineralization that is considered necessary prior to sampling, as this has a direct bearing on the mineral resource estimate and also the selection of an appropriate mining cut. The discussion includes the selection of the sampling technique (drilling or face sampling), the size of the sample relating to the requirements of the laboratory, the potential mining cut, as well as a reference to sampling theory. The selection of an assay technique that is appropriate and will yield the optimal result based on sample turnaround, precision, accuracy, and cost is then considered. Examples are drawn from work undertaken on the Bushveld Complex (Merensky Reef, UG2 Chromitite Layer, Platreef) and Great Dyke (Main Sulphide Zone). A discussion of the appropriate QA/QC programme includes the chain of custody, CRM selection and the QA/QC process. Keywords sampling, assaying, QA/QC, platinum group elements.

Jan 1, 2014

By C. Birch, J. Perold

"Due to the challenging geological environment of the Postmasburg Manganese Field (PMF), a study was conducted to determine if any benefits would derive from the inclusion of resistivity data during threedimensional (3D) modelling of the manganese resource. This was achieved by estimating manganese resources from 2011/2012 drilling data and comparing them with manganese resources estimated from the same drilling data and resistivity data collected during 2013 and 2017.Both models were adjusted to limit their extent to the same 3D modelling space. Significant volume and tonnage differences were observed for all lithological units. The greatest differences were noted in the manganiferous zones of alteration – 7.200 Mt for the geological model versus 3.700 Mt for the geoelectric model.This study showed that the inclusion of resistivity data can reduce exploration costs significantly, as a direct consequence of the resistivity data allowing more accurate siting of boreholes. This decreases the number of boreholes, samples, and analyses required due to the 3D electrical delineation of mineralized areas prior to drilling.An additional benefit is the ability to more correctly forecast the net present value of an operation due to more accurate estimation of manganese resources and stripping ratios. This is clearly demonstrated by the estimated gross profit estimation of R409 million for the geological resource model versus R264 million for the geoelectric resource model.The addition of resistivity data can, therefore, reduce exploration costs and can increase confidence in geological and financial modelling. It would be reasonable to conclude that this approach could also be used for karsthosted massive sulphide deposits. IntroductionAccording to Corathers (2014) and Gajigo, Mutambatsere. and Adjei (2011), South Africa holds between 75–80% of global manganese reserves, followed by Ukraine (10%), Australia (3%), India (3%), and Gabon (2%). The known, land-based, manganese resources located elsewhere are estimated at 2%.The majority of economically important sedimentary manganese ore deposits in South Africa are situated in the Northern Cape Province (Gutzmer, 1996). Manganese ores of the Postmasburg Manganese Field (PMF) were discovered in 1922, and the Kalahari Manganese Field (KMF) in 1940. According to Astrup and Tsikos (1998) and Gutzmer (1996), mining of manganese ore from the PMF ceased during 1989 in favour of the superior quality of manganese ore from the KMF."

Mar 1, 2019

By D. R. Tesarik, F. M. Jones, J. B. Seymour

As part of safety and stability studies at three underground mines in the United States, researchers installed earth pressure cells and embedment strain gauges in cemented rockfill to measure stress and strain changes as mining progressed and the rockfill was loaded. Data from these instruments were used to calculate the in situ modulus of the rockfill for two of the mines. A three-dimensional numerical model of a cemented rockfill cap was validated with data from extensometers anchored in the mine roof and sill; this model was then used to estimate deformation modulus at the third mine because the earth pressure cells and embedment strain gauges recorded negligible changes. Rockfill binder used at these mines ranged from 4 to 8 per cent of the dry components by weight, the water-to-cement ratio was from 0.42 to1.0, and the largest aggregate size in the three mixes ranged from 5 to12 cm (2 to 4.7 in). The range of the calculated in situ deformation modulus values was large, but as expected, it was bracketed by modulus values for cemented tailings and roller-compacted concrete with similar cement contents and water-to-cement ratios. Dans le cadre d’études sur la sécurité et la stabilité de trois mines souterraines situées aux États-Unis, les chercheurs ont installé des palpeurs de pression des terres et des extensomètres d’encastrement dans les remblais cimentés afin de mesurer les variations relatives à l’effort et à la déformation des terrains durant l’exploitation minière et le chargement du remblai. Les données recueillies à l’aide de ces instruments ont servi au calcul du module in situ du remblai dans deux de ces mines. Le modèle numérique tridimensionnel de la semelle d’un remblai cimenté a été validé à partir des données recueillies par les extensomètres ancrés dans la voûte et dans la semelle de ces mines; ce modèle a ensuite été utilisé pour estimer le module de déformation à la troisième mine, étant donné que les palpeurs de pression des terres et les tensiomètres enfouis avaient relevés des variations négligeables. La matière d’agrégation de l’enrochement utilisée dans ces mines comportait entre 4 % et 8 % des composantes sèches par poids; le rapport eau-ciment se situait entre 0,42 et 1,0; et la taille des agrégats les plus gros dans ces trois mélanges était de 5 cm à 12 cm (2 po à 4,7 po). L’écart entre les valeurs calculées des modules de déformation in situ était grand, mais comme on s’y attendait, cet écart a été compensé par les valeurs modulaires des résidus cimentés et du béton tassé au rouleau avec des teneurs en ciment et des rapports eau-ciment semblables. Als Teil der Sicherheits- und Stabilitätsstudien an drei Bergwerken in den Vereinigten Staaten von Amerika installierten Forscher Erddruckgeber und Einbindungsdehnungsmesser in zementierter Steinschüttung, um Spannungs- und Dehnungsveränderungen während der fortlaufenden Bergarbeiten und der Belastung der Steinschüttung zu messen. Daten von diesen Instrumenten wurden dazu verwendet, das In-Situ-Modul der Steinschüt-ung für zwei Gruben zu berechnen. Ein dreidimensionales numerisches Modell einer zementierten Steinschüttungsschwelle wurde mit den Daten von den im Grubendach und in der Schwelle verankerten Extensometern validiert; dieses Modell wurde dann dazu eingesetzt, um das Deformationsmodul in der dritten Grube zu schätzen, da die Erddruckgeber und Einbindungsdehnungsmesser nur geringfügige Messabweichungen feststellten. Das in diesen Gruben verwendete Steinschüttungsbindemittel variierte zwischen vier und acht Prozent an Trockenkomponenten nach Gewicht, der Wasser-Zementfaktor betrug zwischen 0,42 und 1,0 und die größte Zuschlagstoff-größe in den drei Mischungen schwankte zwischen fünf und zwölf Zentimetern. Die Reichweite der berechneten Werte des In-Situ-Deformationsmoduls fiel etwas breit aus, aber es fand erwartungsgemäß eine Klammerung der Modulwerte zwischen den Zemen-trückständen und dem durch Walzen verdichteten Beton mit ähnlichem Zementanteil und Wasser-Zementfaktor statt.

Jan 1, 2003

By Xiaoxu Sun, Jianchao Yao, Qiheng Zhu, Dubo Wang, Jiancheng He, Shijie Lu

Tower mill is considered to have a better regrinding and fine grinding effect compared with ball mill, and its application is much broader. The spiral agitator of the tower mill is driven by the motor. Media inside the mill is under the combined actions of the spiral mechanism, the cylinder, and media nearby, and these parameters are key factors affecting the grinding effect. However, it is not possible to obtain detailed information of kinematic law of media based only on traditional laboratory experiments, let alone the relationship between parameters of kinematic law of media and grinding effect. Experimentation is the only way to develop industrial equipment. However, this is time-consuming and costly, which hampers the further research of the tower mill’s grinding mechanism. The paper selects two structural parameters (gap between the edge of the spiral agitator and the cylinder wall, ratio between the diameter of cylinder and that of the spiral shaft.) and three operating parameters (diameter of media, filling ratio, the speed at the edge of the spiral agitator) as variables to do an orthogonal designed experiment of five factors, four levels, and thereby obtaining change law of grinding indicators of different parameters. Experimental equipment may be simplified to enable an applicable simulation strategy. Simulation based on a discrete element method is conducted to obtain the change law of the speed of media, collision frequency, normal force, and radial force. The relational curve between parameters of kinematic law of media and energy consumption of grinding is clarified, and key factors affecting grinding efficiency are determined. Those factors will be used for optimising the design and operating process. The research result of this paper obtained from laboratory experiments and computer simulation provides data support and theoretical bases, and has directive meaning and applicable value for tower mill’s optimisation and large-sized design. Keywords: Tower mill, discrete element method, kinematic law of media, energy consumption of grinding

Jan 1, 2020

By T. E. Oates, W. Spiteri

In 2015, after amendments to the explosives regulations, stemming became a mandatory activity for all South African mining operations. There are, however, circumstances in which it is thought stemming has an adverse impact on the blasting outcome. Some of these circumstances include blasting in hot holes, in reactive ground, or when blasting a pre-split. In order to determine when stemming is necessary, its role in the control of adverse blasting phenomena and impact on explosive performance were reviewed. Stemming was found to play a significant role in the fragmentation process and burden movement. Additionally, stemming significantly influences the control of flyrock, air-blast, and toxic fume generation. The review of the literature indicates some motivation for not using stemming for presplit, trim, hot hole, and reactive ground blasting, provided the benefits associated with not stemming the holes outweigh the risks of stemming them. Best practice for stemming from the literature indicates a stemming length of 0.7 × burden is best for larger hole diameters, and 20 to 30 × Ø for smaller hole diameters. Crushed aggregate appears to be the most effective stemming material. The South African explosives regulations pertaining to stemming were found to be consistent with those of Australia and the USA.

Aug 1, 2021

By Karl-Heinz Obst, Juergen Stradtman

The importance of the chemical and physical properties of lime has been overlooked for years although the quality of lime plays an important role in the production of steel. With the introduction of the oxygen injection process these properties have been re-evaluated. The CaO, MgO, S, and P2O5 contents of lime are important, but so are the physical properties such as granulation, reactivity with respect to slag formation, and the degree of burning. Soft burnt lime enhances de-phosphorisation and de-sulphurisation, and facilitates the smelting process in general, mainly due to its large specific surface. Special lime, prepared as briquettes from quicklime and fluxes or as pellets from limestone and various fluxes with or without binding agents, clearly accelerates lime dissolution during the slag formation process, lowers the melting point, and enhances de-phosphorisation, de-sulphurisatlon, and de-carburisation even more than soft burnt lime. The introduction of special limes in the oxygen injection process for steel production has opened up new fields for commercial exploitation of slags as well as improved operational techniques.