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By H. Cevizci

"Numerical simulation of the plaster stemming method (PSM) was performed and compared with the conventional drill cuttings stemming method (DCSM). Many earlier in situ tests have proved that PSM can use the blast energy more efficiently than DCSM. Despite PSM generating more blast vibrations, it has advantages over DCSM such as better fragmentation and lower cost per unit volume of rock blasted. In this study, numerical simulation with Autodyn software using a 2D tool was employed to prove the efficiency of plaster stemming by comparing parameters such as pressure, Y-velocity, Y-force, internal energy, acceleration-Y, and compression. For example, the maximum pressure attained at the top of explosive column was 7 395 MPa for DCSM whereas it was as high as 11 945 MPa for PSM. Most of the computed parameters were significantly higher in PSM than those obtained for DCSM. This paper is the first study elucidating the efficiency of PSM by numerical simulation. It is concluded that PSM can save substantial amounts of money and effort. IntroductionThe stemming of blast-hole collars in surface mines with an inert material redirects blasting energy to the rock more efficiently, thus the blast-induced energy is utilized more effectively in breaking rock. With proper stemming, the gases should not escape due to loose stemming material. More efficient stemming with better confinement therefore increases the blast fragmentation. In addition, the distance of scatter is increased, giving rise to a looser rock pile that can be more easily loaded and transported. In order to improve the performance of a blast, stemming is used to help maintain the gas pressure over time (Konya and Konya, 2018). Proper stemming has been shown to increase the explosive efficiency by over 41% (Snelling and Hall, 1912).The most common stemming material in open pits and quarries is drill cuttings because of their ready availability at blast sites and the drill cuttings stemming method (DCSM) is a low-cost method. However, it has a major disadvantage in that dry drill cuttings eject very easily from blast-holes during an explosion, thus a great percentage of the blast energy is wasted and lost to the atmosphere. Cevizci (2012, 2014, 2013, 2017) studied blasting parameters in open pits and obtained better results with the plaster stemming method (PSM) in many limestone, basalt, and clay quarries. Moulding plaster is preferred for stemming because of the fast hardening time of 25–30 minutes."

May 1, 2019

By X. Xiang, W. Xia, J. Yin

"TiCl4 slurry containing valuable metals is an unavoidable by-product of the titanium ore chlorination process. The recovery of these valuable metals, which include titanium, niobium, tantalum, and aluminum, is an urgent issue to tackle in the titanium industry. The results of this investigation show that the valuable metallic elements can be recovered from the slurry by evaporation in a sealed container and leaching with dilute hydrochloric acid. After evaporation at 200°C for 60 minutes, nearly 99% of the titanium was recovered in the form of TiCl4, which was formed by the reaction of the TiO2 in the slurry with AlCl3. After evaporation, metals like niobium, aluminum, and tantalum remained in the residue. By leaching with 2.1 mol/L HCl at a L/S ratio of 6:1 mL/g at 80°C for 60 minutes, the soluble metals, such as aluminum, iron, and copper were all removed from the residue, and the niobium and tantalum were further enriched in the leach residue. A concentrate containing 53.40 wt% Nb and 5.57 wt% Ta was obtained by washing the leach residue with dilute aqueous ammonia under stirring. A potential waste water purifying agent containing 263.75 g/L AlCl3 was produced by purifying the leaching solution with Al(OH)3 and modified polyacrylamide. IntrodutionTitanium tetrachloride (TiCl4) is an important intermediate in titanium metallurgy that is widely used in the production of titania and titanium sponge (Akhtar, Xiong, and Pratsinis, 1991). In conventional titanium metallurgical processes, high-titanium materials such as synthetic rutile and high-titanium slag are reacted with chlorine to produce TiCl4 in a fluidized-bed furnace. Accompanying elements, such as Al, Nb, and Fe also react with chlorine to form chlorides, which are mixed with gaseous TiCl4 (Anderson, 1917). In the condensation process, gaseous TiCl4 is refrigerated and high-boiling-point chlorides are precipitated in the liquid TiCl4 to form a slurry containing 50~60 wt% TiCl4 (Wang, Xiang, and Wang, 2012).Various methods have been proposed to recover TiCl4 from the slurry, including microwave heating and spray drying (Wang, Xiang, and Wang, 2012, Wang et al., 2010a). To date, the only way to recover the TiCl4 is to return the slurry to the fluidized-bed furnace. However, this causes fluctuations in the temperature in the furnace, resulting in incomplete reaction between titanium-rich materials and chlorine. Therefore, the slurry is often rinsed with water and neutralized by adding lime, which caused serious environmental pollution and wastes a valuable resource (Roy, Bhatt, and Rajagopal, 2003)."

May 1, 2019

By E. A. van Wyk, M. R. de Villiers

"Mining companies strive to increase and maintain production, while simultaneously remaining competitive in the global economy. Furthermore, they must ensure workers’ safety and maintain good safety records. The use of virtual reality (VR) facilitates the development of tools and systems for various purposes that can improve knowledge and understanding of the work environment. VR is a rapidly growing technology that uses the ever-increasing power of computing to simulate real-world and imaginary environments and situations with a high degree of realism and interaction. The availability of 3D modelling tools and simulation programming engines that work effectively with a mid-range desktop PC and standard 3D graphics card, make VR technology viable and attractive for mainstream training applications. The design, development, and implementation of interactive VR training systems is proposed as an innovative approach to augment safety training. However, in order to assess the impact of such VR training systems it is of particular importance to determine the effectiveness of the design of such systems. This article proposes an evaluation framework for this vital purpose. This framework comprises criteria to assess VR training systems, specifically relating to usability, instructional design, VR systems design, and mining industry context-specific aspects. Although the framework was developed as an evaluation tool to assess effectiveness of the design of such systems, it can equally well be used as a set of design principles to inform the design of VR training systems for mining. IntroductionMining in South Africa has been the main driving force behind the history and development of Africa’s richest and most advanced economy (Coka, 2012). The South African mining industry is frequently criticised for its poor safety record and high fatality rate (Stoddard and Skweyiya, 2016). Inadequate or insufficient training is often cited as a root cause of accidents (Van Wyk and De Villiers, 2009; Tichon and Burgess-Limerick, 2011). Virtual reality (VR) is a rapidly growing technology that utilizes the ever-increasing power of computing to simulate real-world and imaginary environments and situations with a high degree of realism and interaction (Webber-Youngman and Van Wyk, 2013). VR is currently being used or investigated as a training solution in a variety of industries. VR technology has developed rapidly and costs have fallen to levels where it can now be considered for mainstream training applications. The availability of 3D modelling tools and simulation programming engines that work effectively with a mid-range desktop PC and a standard 3D graphics card, make VR even more attractive to mine training centres (Van Wyk and De Villiers, 2009)."

May 1, 2019

By K. Thambi

"A recent amendment to Section 36(11)(e) of the Income Tax Act, 53 of 1968 (Tax Act) now extends the allowable deduction of ‘capital expenditure’ incurred by mining companies pursuant to the Mineral and Petroleum Resources Development Act 28 of 2002 (MPRDA). In terms of the Taxation Laws Amendment Bill 2016 (TLAB 2016), the allowable deduction has been extended to include expenditure incurred on infrastructure in terms of Social and Labour Plan (SLP) requirements as per the MPRDA. Interestingly, what necessitated the amendment was the need to recognize SLP requirements and to circumvent administrative difficulties for mining companies and the South African Revenue Services (SARS) in differentiating the use of developmental infrastructure by employees or the community. The successful implementation of such a deduction hinges on a sound SLP system. However, given the challenges within the current SLP system, this amendment could be considered somewhat premature. IntroductionSection 36(11) of the Income Tax Act 58 of 1962 (Tax Act) enabled mining companies to deduct certain capital expenditure in lieu of its other sections. In particular, it made provision for mining companies to deduct capital expenditure incurred pursuant to the Mineral and Petroleum Resources Development Act 28 of 2002 (MPRDA), but excluding capital expenditure incurred in respect of infrastructure or environmental rehabilitation. As such, mining companies could only deduct such capital expenditure that related directly to their employees and not to the wider community (Clegg, 2018).In terms of the Taxation Laws Amendment Bill 2016 (TLAB, 2016) (South Africa, 2016a), the recent amendment to Section 36 extends the relief provided under section 36(11)(e) to include capital expenditure incurred on infrastructure in terms of the Social and Labour Plan (SLP) requirements of the MPRDA. In other words, the capital expenditure incurred by the mining company for the benefit of the people living in mining communities. To qualify for such a deduction, the infrastructure erected or developed by the mining company should reflect what was agreed between the mining company and the Department of Mineral Resources (DMR) as per the SLP requirements of the MPRDA (TLAB 2016)."

May 1, 2019

By F. Mwaura

"The aim of the audit was to determine whether the mining project environmental impact assessments (EIAs) in Kenya are undertaken according to international best practice. A sample of 50 EIA reports for the 2007–2016 period was evaluated using 18 criteria in the Environmental Law Alliance Worldwide (ELAW) guidelines. The findings showed that only two criteria were considered ‘excellent’ according to the ELAW guidelines, namely baseline environmental assessment and prediction of physical impacts. Six criteria were found to be ‘satisfactory’, including prediction of social impacts, analysis of alternative options, and impact mitigation. The reports were quite weak in terms of: consideration of all phases in the mining cycle, environmental regulatory framework, prediction of biological impacts, stakeholder consultation and engagement, integration of human right issues, and integration of climate change and cost-benefit analysis. It is therefore recommended that the Kenyan National Environment Management Authority (NEMA) should consider tightening the EIA terms and conditions in the approval of statutory terms of reference (ToR) for full-scale mining EIAs to ensure improved performance of EIA as a tool for environmental protection. IntroductionThe nexus between society and the environment has continued to generate interest because the environment is the source of goods and services that sustain the various needs of human beings as outlined in the UN sustainable development goals (SDGs) (Armstrong and Peart, 2000; Sutton 2004; Chakrabarti 2007; Strange and Bayley 2008). All the five generic categories of societal needs, namely physiological needs (food, water, clothing, medicines, etc.), residential and occupational needs (shelter, transport, energy, etc.), economic needs (tradeable goods and services), leisure and recreational needs (tourism), and cultural and spiritual needs (e.g. sacred resources and ecosystems) (Mwaura et al. 2016) are addressed by the environment. Consequently, a wide range of development sectors have been established around the world in order to address the above needs (Lederer, Galtung, and Antal, 1980; Rammelsberg et al., 2006; Noonan, 2014). All these development sectors rely entirely on the environment for their proper functioning, as shown in Table I."

May 1, 2019

By P. P. Kim, M. Tangstad, T. A. Larssen

"The kinetics of MnO and SiO2 reduction in SiMn slags based on Assmang/Comilog ore and HCFeMn (highcarbon ferromanganese) slag were investigated between 1500 and 1650°C under a CO atmosphere. The results showed that charges containing HCFeMn slag had relatively faster reduction rates than those without. The difference in the driving force for MnO reduction was insignificant among the SiMn slags at 1500°C, which implies a low contribution of the driving force for reduction rate. The slag viscosities were also rather similar, around 1 poise at 1500°C, which could not explain the different reduction rates. Instead, the different charges containing various sulphur contents are believed to give rise to the varying reduction rates. The estimated activation energies for MnO reduction were around 500–920 kJ/mol for charges containing HCFeMn slag, and between 250–300 kJ/mol for those without. Based on the estimated kinetic parameters, the considered rate models were able to describe the reduction of MnO and SiO2 in SiMn slags between 1500 and 1650°C. IntroductionManganese ferroalloys such as ferromanganese (FeMn) and silicomanganese (SiMn) are important ingredients in steel production due to the beneficial effects of manganese on the physical properties of steel. Mn enhances the strength, toughness, and hardness of steel products, and both Mn and Si are used as deoxidizers to prevent the development of porous structures (International Manganese Institute, 2014; Olsen, Tangstad, and Lindstad, 2007; Subramanyam, Swansiger, and Avery, 1990; Tomota et al., 1987).The thermodynamic background of manganese ferroalloys is well established (Olsen, Tangstad and Lindstad, 2007), but kinetic information is rather scarce, especially for the SiMn process (Tranell et al., 2007; Tore-Andre Skjervheim, 1994). The absence of kinetic information makes it more difficult to understand the reduction mechanisms of MnO and SiO2. It is not clear how different raw materials affect the SiMn process. The main metal-producing reactions in the SiMn process are described by Equations [1] and [2]:"

May 1, 2019

By A. Sokolov, M. Demsky, E. Hasikova, V. Gostilo

"Previously, we upgraded and implemented two gamma activation assay (GAA) systems designed to analyse the gold content in raw ores at Zarafshan laboratory, Uzbekistan, and achieved a detection limit of less than 0.05 g/t under actual industrial conditions. Having started to design a fully modern, industrial GAA system for mining companies, this paper analyses the advantages, disadvantages, and special features of all major system components that can influence the sensitivity and accuracy of the analysis. The results of a study to optimize the detector geometry and sample size are presented and the performances of the linear electron accelerator, detector array, and sample transportation system of a modern, industrial GAA system for analysing gold, silver, and rare earth elements are considered. IntroductionGamma activation analysis (GAA) has considerable potential as a future replacement for traditional fire assay analysis in gold mining (Hoffman, Clark, and Yeager, 1998; Morse, 1977; Bourmistenko, 1986, 1981; Sammut, 2016; Tickner et al., 2017). The essence of GAA is to irradiate ore samples with high-energy gamma quanta generated by an electron linear accelerator (LINAC) and then to use a gamma spectrometer to detect the induced activity of the excited gold nuclei. The advantages of this method are discussed in detail elsewhere (Hoffman, Clark, and Yeager, 1998; Morse, 1977; Bourmistenko, 1986, 1981; Sammut, 2016; Tickner et al., 2017), where it is shown that GAA is uniquely suited to analysing ore samples when mining for gold, other precious metals, and accompanying elements.These advantages were realized in three industrial GAA laboratories that were commissioned in Zarafshan, Uzbekistan in 1977, in Magadan, Russia in 1979, and in Batagay, Russia in 1986 (Bourmistenko, 1986; Nii Tekhnicheskoy Fiziki I Avtomatiki, n.d). In 1989, a fourth industrial GAA laboratory was commissioned at a gold mine in Tommot, Russia. However, the project was subsequently halted due to economic reasons (Moshkov and Tjamisov, 2017). Currently, only the laboratory of the Muruntau mine in Zarafshan, Uzbekistan is in operation. The gamma activation method for gold determination is widely applicable at this mine owing to its high productivity and low cost of analysis. An outstanding aspect is the performance of more than one million analyses per year."

May 1, 2019

By Phil Jones

"Dilution — planned and unplanned – remains a significant cost impairment in the mining process. A series of trials were held over a sixmonth period in fiscal year 2018 (FY18) that established the cost-benefit of new technology as it applies to the alignment accuracy of production drilling rigs in underground mining, thus confirming its ability to limit drilling as one of the causes of dilution. The trials identified three underlying factors affecting drilling accuracy, measurable by blast-hole deviation surveys of planned versus actual toe data. These were rig alignment error, collar location change/ error and in-hole deviation.The trials involved a comparison of existing rig setup processes and technology, with the new technology (Minnovare’s Production Optimizer system). The trials were undertaken in the same environment: the Cracow gold mine, an operating underground mine. The comparison first revealed the extent to which rig alignment impacts blast-hole deviation. Secondly, the new technology was proven to limit rig alignment error, thereby reducing average blast-hole deviation and increasing the number of holes drilled within tolerance by 160 percent.The increased accuracy reduced stope dilution by reducing over-break of subgrade ore. The new technology was implemented at Cracow during the latter half of 2018. Despite utilizing the new technology for just six months of the year, the mine recorded a 5 percent overall reduction in dilution for the full year compared to the previous year (FY17); from 22 percent down to 17 percent (a net decrease of 22.7 percent). Mine management attribute a significant proportion of this reduction to the new technology, along with sequencing and planning improvements. This opinion is backed by detailed stope reconciliation data taken during the trial from 28 stopes — representing 20 percent of the total tonnes mined during FY18. The data identified that stopes drilled using the new technology recorded 62.6 percent less average dilution."

May 1, 2019

By R. W. O. Kersten

"The aim was to investigate stable pillar design procedures currently in use on chrome and platinum mines, subject them to a critical appraisal, and review some of the alternatives proposed in the literature. It is concluded that these pillar design methodologies suffer from drawbacks that can be detrimental to the mining industry and that an improvement is essential.It was decided that the increased availability of analytical models and failure criteria could be exploited to update the empirical to an analytical/empirical method. The proposed methodology adopted FLAC2D simulations using the Hoek-Brown failure criterion to calculate full stress-deformation curves for typical pillars. The mine stiffness concept was introduced to determine the pillar load, integrating the influence of the pillar and strata stiffness and mining geometry.The proposed methodology was calibrated by comparing experimental and predicted deformations and failure depth of pillars in one hard-rock mine. The conclusion was that the methodology is an improvement over the one currently in use. An improved factor of safety is given by the intersection point of curves for the stiffness of the system and the pillar strength. IntroductionThe paper describes part of the findings of a PhD thesis (Kersten, 2016) on an alternative stable pillar design methodology. This publication contains sufficient information to implement the method for further interpretation and testing. A detailed comparison of measured and predicted data is dealt with in the thesis, and the results show that there is promise in the methodology.The design of stable pillars in mining is of fundamental importance, not only in the Bushveld Complex mines but throughout the mining industry. Wherever mining occurs, pillars are formed at some stage and it is essential to predict their behaviour, i.e. whether they will burst, yield, or remain stable. Although of crucial importance, pillar design still suffers from major shortcomings and weaknesses."

May 1, 2019

By Edgar Roque, Edwin Cereceda

El presente trabajo pone en evidencia las ventajas de emplear el método de explotación por Bench and Fill, en lo que respecta a costos y rentabilidades. Dada la importancia de atender al control de la dilución y fragmentación tomando en consideración las variables generadas en la voladura, este artículo explica a los planificadores de minería —antes de diseñar, perforar y cargar un bloque de producción— cómo predecir y optimizar los efectos de la voladura en los costos de operación evaluando el comportamiento del macizo rocoso y zonificando los niveles a minar.

Apr 30, 2019

By M. J. Voigt, R. A. Govender, A. Mainza, L. Bbosa

"Mineral texture is a critical factor which controls ore variability and is an important attribute in geometallurgy. In relation to downstream processes, it affects the fracture pattern during breakage, where rock strength is inherently a function of mineral texture. Because of the subjective nature of mineral texture, it has not been easy to quantify, especially in the context of a measurement suitable for use in geometallurgical programmes. The aim of this paper is to present the first steps in developing a 3D mineral texture quantification method for drill core and to assess its sensitivity to differences in rock strength using a case study. The methodology includes classifying the textural information using the 3D grey level co-occurrence matrices (GLCM) and X-ray computed tomography (XCT) coupled method. Rock strength tests were performed using the split Hopkinson pressure bar (SHPB). The case study investigates a heterogeneous polymetallic sulphide deposit and a homogeneous shale subdivided into three ’mineral textural types’. The variability is largely captured by the GLCM matrices, and preliminary trends can be observed where the shale is finer grained and has a higher yield strength in comparison with the coarser grained polymetallic sulphide ore. IntroductionModern mining requires the exploitation of lower grade and more complex, heterogeneous orebodies to address the growing industry demands. Historically, processing plants were designed and built based on average ore characteristics and therefore are relatively inflexible when facing the full spectrum of ore variability in heterogeneous orebodies (Lamberg, 2011; Lotter, 2011; Schouwstra et al., 2013). The practice of geometallurgy represents an opportunity to manage ore variability in the mining industry (Powell 2013; Baum, 2014; Yildirim et al., 2014; Nguyen, 2013). It focuses on quantifying the relationships between ore characteristics and their downstream mining and processing responses, often starting with small-scale laboratory testing. The purpose of geometallurgy is linked to maximizing the net present value (NPV) of an orebody by minimizing technical and operational risk – where ‘ore variability’ is considered one of the most significant technical risks."

Apr 1, 2019

By N. Baloyi, P. Popoola, M. Tlotleng, S. L. Pityana

"The advantages of using Nb and Ti-Nb coatings for improving the hardness and corrosion resistance of Ti6Al4V were investigated. It has been reported that Ti6Al4V used in orthopaedic implants tends to release toxic Al and V ions into the surrounding tissue. Thin layers of Nb and Ti-Nb were deposited on Ti6Al4V substrates using a laser metal deposition technique. The deposited material was analysed using optical microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, and X-ray diffraction. The corrosion behaviour of the deposited layers was investigated using a Metrohm Autolab PG Stat101 compact potentiostat at 25°C in simulated body fluid. A Vickers hardness system was used to study the mechanical properties. Both Nb and Ti-Nb coatings exhibited good metallurgical bonding with the substrate. The microstructure and the XRD analyses for the Nb system showed that the ??-Nb phase was most dominant, while the Ti-Nb system comprised a mixture of the ?? and ?? phases. The average hardness of the Ti6Al4V substrate was 350 HV0.3, with a slight increase for the Nb coating (363 HV0.3) and a much higher hardness from the Ti-Nb coating at 423 HV0.3. The corrosion results show that the deposited Nb was more corrosion-resistant in the solution than either the Ti6Al4V substrate or the Ti-Nb coating. IntroductionMetals such as CoCrMo, 316L stainless steel, and NiTi alloy are used for manufacturing biomedical implants because of their distinct properties, including low Young’s modulus and resistance to corrosion (Ryan, Pandit, and Apatsidis, 2006). These implants are required to remain in the body of the patient for many years. Due to a favourable combination of mechanical and corrosion properties, titanium (Ti) and its alloys have emerged as the material of choice for biomedical implants. Nevertheless, their use is not entirely without challenges. For example, in total hip replacement, surface degradation and release of metal debris from metal erosion caused by friction limit the service life of the implant (Oldani and Dominguez, 2012; Manivasagam, Dhinasekaran, and Rajamanickam, 2010). Ti6Al4V is generally regarded as the material of choice, but it has been found that over extended periods of time, the combination of surface corrosion and erosion releases toxic aluminium (Al) and vanadium (V) ions into the body (Khan, Williams, and Williams, 1996). This has led to the investigation of titanium alloys containing niobium (Nb), zirconium (Zr), tantalum (Ta), and molybdenum (Mo) as substitutes for the aluminium- and vanadium-containing Ti6Al4V (Okazaki et al., 1997)."

Apr 1, 2019

By Nick Rose, Mathieu Veillette, Matthew King

"The Teck Highland Valley copper (THVC) mine is located approximately 55 km (34 miles) southwest of Kamloops and approximately 20 km (12 miles) west of Logan Lake, BC, Canada (Fig. 1). Mining at THVC is conducted at three openpit operations comprised of Valley, Lornex and Highmont with a total annual output on the order of 300 kt (330,000 st) copper concentrate and 5 kt (5,500 st) of molybdenum concentrate. The Phase 8 pushback in the Valley Pit (Fig. 2) was mined from 2011 to 2016. Successful slope steepening occurred in the later stage of the pushback with the implementation of presplit blasting in 2015 and 2016.This article summarizes the investigation and design approach including: structural analysis, kinematic assessments of bench breakback potential, development of discrete fracture networks (DFNs) to characterize discontinuity fabric, rockfall modelling, 2D anisotropic limit equilibrium and 2D distinct element modelling, assessment of potential kinematic failure modes affecting double benches with 3D distinct element modelling and improved blasting techniques using e-dets. THVC is currently undertaking a mine life expansion involving the pushback of the west wall of the Valley Pit above Phase 8 to extend the mine life to 2029. Engineering geologyThe east wall slope in the Valley Pit is comprised of a 350-m (1,148-ft) thick sequence of glacial valley sediments that occur along the Highland Valley (Fig. 2), exposing an overburden slope up to about 225-m (740-ft) high below the crest of the ultimate east wall. The glacial overburden units consist of pro-glacial outwash and glaciofluvial deposits, glacial outwash sands and gravels interbedded with till and alluvial fans consisting of cross-bedded sands and sandy-gravels. Lacustrine sediments occur within the mid to lower portion of the glacial sequence and contain intervals of low-shear-strength clays and silts. Two large (1.3 and 7 Mt or 1.4 and 7.7 million st) waste rock buttresses were required to maintain slope stability using slot-cut and fill mining methods, as described in Fortin et al. (2011).The Valley porphyry deposit occurs in the central portion of the late Upper Triassic Guichon Creek Batholith, which intrudes assemblages of the Permian Cache Creek and Upper Triassic Nicola groups. The Valley deposit occurs in an area of intense fracturing near the intersection of the northerly trending Lornex Fault and the northwest to westerly trending Highland Valley Fault."

Apr 1, 2019

By G. Coetzer

"Prior to operating a non-recovery coke pilot plant, it was critical to ascertain coal cake stability during the loading of a 1 m3 coal cake into the oven. Various compaction parameters were verified and established on a small laboratory-scale compaction machine to obtain a coal cake of acceptable stability. These parameters include cake density, cake surface moisture, transverse strength (force applied perpendicular to the original compacted coal cake layers), and applied force to the coal cake. This work determined the behavioural characteristics of the coal while being compacted either with a full-sized or a 1/3-sized compaction plate in a 9 kg capacity mould. Two different coals were evaluated, namely Waterberg semi-soft coking coal (sscc) and Oaky North hard coking coal.The target wet cake density of 1 100 kg/m3 (79% of 1 400 kg/m3 relative density) was achieved for Waterberg sscc, with a particle size d50 varying between 0.6 mm and 1 mm, utilizing the 1/3-sized compaction plate in the laboratory-scale set-up, with 11.6% surface moisture and 92.2 t/m2 commercial equivalent applied force. For Oaky North hard coking coal, a wet cake density of 1 189 kg/m3 (85% of 1 400 kg/m3 relative density) was achieved at a surface moisture content of 12.3% and at a lower applied force than that for Waterberg sscc, i.e. 78.5 t/m2.Coal cakes of acceptable strength, and therefore sufficient stability for further processing, were obtained for all materials evaluated during this study.Further studies should be conducted to determine the effect of zeta potential during the compaction of coals.IntroductionExxaro Resources has successfully installed and commissioned a world-class stamp-charging horizontal 1 t electrically-heated pilot-scale coke oven at its Metallurgy Services facility. Prior to operating the coke non-recovery pilot plant, it is essential to ascertain coal cake stability during the loading of a 1 m3 coal cake into the oven. The design of Exxaro’s pilot plant is such that the coal cake is pushed inside the oven by means of a pusher plate, rather than through a ‘spoon’ feed mechanism, such as is found in industrial horizontal coke ovens. The pusher plate loading mechanism dictates that the coal cake should possess high stability and inherent strength during loading into the oven, owing to frictional forces exerted by the oven floor. In order to obtain a coal cake of acceptable stability, various compaction parameters needed to be verified and established on a small laboratory-scale compaction machine."

Apr 1, 2019

By F. P. Janse van Rensburg, P. J. Le Roux

"There are numerous factors that affect open stope stability and often result in falls of ground. These falls of ground can be attributed to factors such as beam failure due to a larger than normal roof area (hydraulic radius too large), adverse ground conditions, seismicity, the stress-strain environment, absence of support, and poor drill-and-blast practices. The effect of time on the stability of open stopes is sometimes underestimated and is relatively unknown, especially on Target Mine. Actual data was collected from open stopes at Target and analysed to show the effect of time on open stope stability. The benefits of this analysis will include improved understanding of time-dependent failure, which can assist in reducing dilution and the risk of sterilization of future mining blocks. IntroductionTarget Mine is situated adjacent to the town of Allanridge, some 20 km from Welkom in South Africa’s Free State Province, and is the most northerly mine in the Welkom Goldfields area (Figure 1). The mine consists of a single surface shaft system with a sub-shaft (Target 1C shaft) and a decline. Ownership was attained by Harmony Gold Mining Company Limited in May 2004 (Harmony Gold Mining Company Limited, 2010). Before discussing the selection of open stopes for the back-analyses, a brief explanation of open stoping as practiced at Target Mine will be given. The orebody is some 180 m in thickness and 270 m wide and comprises multiple reefs overlying one another. The 180 m thick reef package is termed the Eldorado Reefs, as shown in Figure 2. The Eldorado Reefs suboutcrop against the Dreyerskuil Reefs, as shown in Figure 3. The dip of the reef varies from as low as 10° in the west to 75° in the east.Compared with most Australian and Canadian open stoping mining operations, Target Mine is unique. In most Australian and Canadian mining operations the hangingwall and footwall of the open stopes comprise waste rock, and the orebody dips relatively steeply. Due to the depth of Target Mine, some 2300 m to 2500 m below surface, a destress slot (Figure 4) is mined to create an artificial, shallow mining environment whereby the field stress is managed and kept at values of around 60 MPa. The destress slot comprises a narrow tabular stope with an average width of 1.5 m, and is mined on the Dreyerskuil Reefs.At Target Mine the hangingwall, sidewalls, and footwall of the open stopes all comprise reef of different grades, except for the EA1, where the EB footwall is waste rock. If a stope, for example, is mined alongside an existing old stope, the western sidewall of this stope will consist of backfill. The general mining direction of open stopes is from the lowest position of the reef on the west, progressing up towards the east as shown in Figure 5."

Apr 1, 2019

By G. Coetzer

"Prior to operating a non-recovery coke pilot plant oven, it was essential to ascertain coal cake stability during the loading of a 1 m3 (1 m × 1 m × 1 m) coal cake into the cold pilot-plant oven by a pusher mechanism. Previously established laboratory-scale compaction parameters, to obtain coal cakes with sufficient stability, were employed during the loading tests of the coal cakes. Two different coals were evaluated, namely Waterberg semi-soft coking coal (sscc) and Oaky North hard coking coal.It was demonstrated that lower applied compaction forces (14%) can be utilized during 1 m3 compaction, in comparison to laboratory-scale tests, to obtain similar wet cake densities, owing to differences in the effect of frictional forces. Wet cake densities for Waterberg sscc improved slightly (3%) to 1.13 t/m3 when utilizing 79 t/m2 applied force for a 1 m3 coal cake, in comparison to laboratory-scale tests. Similar results were obtained for Oaky North hard coking coal, with a 6% density increase to 1.27 t/m3 at a similar applied force. Porosities decreased by 13% and 32% for Waterberg sscc and Oaky North coal, respectively, when 1 m3 compaction was compared to laboratory-scale tests. An opportunity exists to further decrease the porosities of Waterberg sscc during compaction, whereas acceptable compaction parameters were achieved for Oaky North hard coking coal. Most major vertical cracks and the partial collapse of coal cakes were mitigated, and high-stability coal cakes were obtained that could be successfully loaded into the pilot-plant coke oven by a pusher mechanism.Factors contributing to the instability of the coal cake during loading into the oven, such as vertical cracks, are (i) the cubic geometry (1 m3) of the coal cake, (ii) friction exerted by the oven floor, and (iii) mechanical problems, such as a misalignment between the pusher machine feeder plate and the oven floor. IntroductionOperation of the stamp-charging horizontal 1 t electrically heated coke pilot-plant oven at Exxaro Resources requires coal cake stability during the loading of a 1 m3 compacted coal cake into the oven. In this case, a pusher plate is utilized to push the coal cake into the oven over the oven floor. This is in contrast to a ‘spoon’ or bottom plate feeding mechanism as found in industrial horizontal coke ovens. The pusher plate loading mechanism dictates that the coal cake should possess high stability and inherent strength owing to frictional forces exerted by the oven floor. In order to obtain a coal cake of acceptable stability for the 1 t coke oven, various compaction parameters need to be verified and established."

Apr 1, 2019

"The management of outlier grades in positively skewed gold distributions is a contentious issue. Incorporating outliers in standard ordinary kriging (OK) estimation procedures in a way that honours the data without smearing extreme grades into surrounding areas has been problematic. Cutting or capping of outliers to mitigate their influence in estimation techniques is common practice, while methods that manipulate the OK system of equations fail to honour the data. We propose a method of post-processing of kriging weights that provides realistic OK estimates and mitigates smearing without manipulating kriging equations or changing the original grades. The method requires that the data is not clustered, is approximately equally spaced, and is of the same support. Positively skewed data is ordered on attribute grade and nonlinearly transformed to a Gaussian histogram of categorical bins whose frequency is based on their likelihood of occurrence and location in the sample distributions. Factors that restrict kriging weights are calculated by dividing the percentage frequency of data in each bin by the percentage frequency of data in the bin with the highest frequency. Restriction factors applied to the kriging weights in the OK estimation restrict the range of influence in proportion to their probability of occurrence in the distribution. Smear reduction post-processing is easy to implement and addresses issues arising from negative kriging weights while considering the spatial location of samples, the sample grades, and their probability of occurrence. The method mitigates both smoothing and conditional bias.IntroductionOutliers are sample observations that deviate considerably from the standard or expected (Hawkins, 1980). These deviations can be high or low in grade depending on the distribution. The presence of outliers in a mine sampling campaign could provoke mixed reactions. Mining engineers might view high-grade outliers as a promise of achieving higher grades, while the geostatisticians view outliers as affecting the accuracy and precision of the overall estimate, among other issues. Having identified outliers, the geostatistician must decide how to account for their presence and treat them so that true underlying estimates are not distorted. Advanced knowledge of the deposit allows the geostatistician to identify and treat outliers acceptably, especially where samples are limited in number and the true grade distribution is uncertain. If ignored, or treated incorrectly, outliers are likely to lead to smearing of extreme grades into the surrounding estimates, thereby steering regions towards potential under- or over-estimation."

Apr 1, 2019

By T. Grewar

"South Africa is a water-scarce country, rated as one of the 30 driest countries in the world. Worryingly, government expects water demand to outstrip supply as early as 2025. The South African government believes that substantial volumes of water can be made available through the reuse of treated mining-impacted water. Currently, however, large volumes of treated mining-impacted water are produced, often with no end use in mind other than discharge or disposal, when these treated effluents may have further uses in applications which are currently and unnecessarily using high-quality water. Treating the wastewaters to levels that meet ’fitness-for-use’ guidelines for alternative applications such as agriculture, sanitation, or industrial processes will reduce the treatment cost burden compared to potable water production. The primary conclusion of this review is that the most suitable option for re-using treated mine-impacted water is in agriculture, for irrigation of crops (food, forage, or energy crops), which currently and unnecessarily makes use of the majority of South Africa’s high-quality resources or potable water. Other findings include the realization that although guidelines and legislation for water re-use in South Africa exist and are readily available, they tend to be contradictory and confusing in many cases. It is imperative that these ambiguities and incongruities in the available guidelines and legislation for water re-use be clarified and updated swiftly IntroductionSouth Africa is a water-scarce country and is currently rated as one of the 30 driest countries in the world, with an average rainfall of 490 mm/a, approximately half of the global average. As an indicator of the degree of regional variability in South Africa’s water supply, it has been shown that 70% of all runoff is from approximately 20% of the land area. Regardless of the water scarcity faced in South Africa, our water conservation track record is poor, with an average consumption of 280 L/d per person, almost 60% more than the global average of 175 L/d per person. Around 40% of this allocation is utilized in watering lawns and gardens (Zhuwakinyu, 2017).The South African government predicts water demand to outstrip supply as early as 2025. On an international scale, the situation appears just as dire, with the United Nations High Level Panel on Water (HLPW) expecting a 40% water shortfall by 2030, which may affect up to 1.8 billion people based on current water demand trajectories (Zhuwakinyu, 2017)."

Mar 1, 2019

By V. Ross

"Bench-scale flotation tests play a major role in the geometallurgical process value chain. Despite their apparent simplicity, these tests pose pitfalls in terms of operation, as well as the interpretation and modelling of results. In this paper we highlight key aspects to consider in generating accurate and reproducible experimental results, and critically review some assumptions relating to the estimation of entrainment and froth recovery. We subsequently focus on first-order equations to model kinetics and propose a method that accounts more realistically for the decay in kinetics over the duration of a float, and the contributions of froth stability and hence mass pull. The method was applied to three case studies on platinum group metal (PGM) ores and matched or outperformed first-order, two-component models. Also, it allows for a deeper analysis of the integrity of the bench-scale flotation results. IntroductionGeometallurgy is a structured, multidisciplinary approach that integrates key data from the geological, mining, mineralogical, and metallurgical aspects of the value chain to construct spatial models of an ore deposit such that the overall economic benefit and sustainability of an operation can be optimized. Process geometallurgy is aimed primarily at enhancing metallurgical efficiency and plant throughput by the application of appropriate mining and processing strategies, as well as supporting production planning and operational strategies to reduce the impact of highly variable ores. With flotation being the dominant concentrating process in the mineral value chain, the bench-scale flotation test is an important characterization tool – a relatively cheap, simple, and rapid way to obtain key information about the ore and its amenability to economic extraction of valuable minerals. This includes the evaluation of different ore types and the implications of mineralogical composition and texture for comminution and floatability, the effect of the grinding environment on the liberation of minerals, the electrochemical environment in the pulp (Bradshaw et al., 2006), the screening of reagents to improve floatability (Ekmekci et al., 2003), and the role of hydrodynamics in the recovery of valuables and the entrainment of gangue (Amini et al., 2016; Wang et al., 2016). It is also a critical tool in auditing the performance of a flotation plant by hot floats, paving the way for concept and feasibility studies and providing essential data on kinetics for the purposes of scale-up, optimization, and simulation of flotation circuits."

Mar 1, 2019

By Steve Kral

"Each January, tunneling and underground professionals gather in New York City for the George A. Fox Conference. The one-day event offers attendees the opportunity to listen to their peers outline what’s new in the underground construction industry, get updates on major projects in North America and have a chance to catch up of old friends.The conference is put on by the Underground Construction Association of SME. This latest conference attracted about 370 specialists in the industry. The theme for this year’s event was “Water Tunnels, Past, Present and Future.”The technical session included talks focused on major tunneling projects, including the massive California Water Fix program and the Massachusetts Water Resources Authority (MWRA) Metropolitan tunnel redundance program in Boston. The conference also included an update on the Gateway Project from Phil Rice from WSP and Mahammed Nasim of Amtrak as well as a Tunnel Industry update.The following is a sample of a few of the presentations. Technical presentationsDEP’s Tunneling Program Evolution. James Mueller is the agency chief engineer of New York City’s Department of Environmental Protection (DEP). Its mission is to plan sustainable infrastructure investments for the future of clean water and the environment in the city and its watersheds, he said. The agency’s goals are to synthesize information across bureaus within DEP to allow data-driven decision-making. It is also to optimize internal agency processes and systems related to the implmenation of engineering programs within a structured assessment process. The agency also prioritizes projects and funding within a structured integrated planning process. And it standardizes project performance and delivery to meet the needs of the agency in alignment with industry standards and market capabilities."

Mar 1, 2019