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By W. Jomaa, V. Songmene, O. Mechri, Laval Université, P. Bocher, J. Levesque

"A 2D finite element modelling (FEM), based on pure Lagrangian approach, is developed for studying the serrated chip formation during high speed machining (HSM) of 7075-T651 alloy. The solution was achieved using a commercial software package, ABAQUS/Explicit v6.13. The Johnson-Cooke (JC) constitutive equation is used to describe the work material behaviour. Moreover, the JC damage equation is implemented into the FEM to take into account for the shear localization during the serrated chip formation. Modified Coulomb friction model has been used to characterize the sliding/sticking effects on the tool-chip interface with the friction coefficient and shear flow stress determined by force calibration and machining data, respectively. The proposed FEM is validated using experimental data obtained in HSM of 7075-T651. The FEM was able to predict accurately serrated chip morphology. The intensity of chip segmentation was found to increase with cutting speed.INTRODUCTIONHigh speed machining (HSM) is one of the most used processes for manufacturing aircraft parts with aluminum alloys. For aluminum alloys, the use of HSM increases metal removal rate and reduces the formation of built up edges and burrs. However, it was found that serrated (also named segmented or sawtooth chip) and discontinuous chips can be produced during HSM of some high strength aluminum alloys, such as 7075-T6 alloy (Rao & Shin, 2001). Many parameters were found to affect the segmented/discontinuous chip formation during the machining of aluminum alloys.There are two cases in which the serrated chip can forms: the first is when machining hardened materials (Morehead, Huang, & Luo, 2007), and the second, when machining ductile materials with a cutting speed higher than a critical value (Barry & Byrne, 2002). Different theories and models were developed in order to explain the formation mechanism of such kind of chips. According to Astakhov (2006), the segmented chip formation is attributed to variations in stress and plastic deformation states, and resulting temperatures on the cutting zone. Liyao et al. (2013) stated that the segmented chip formation was mainly attributable to adiabatic shear instability/catastrophic strain localization. Others (Vyas & Shaw, 1999) suggest that the fracture/crack propagation mechanism is at the root of chip generation."

Jan 1, 2016

By D. Newman

"The U.S. stone industry is in a transition from surface quarries to single and multiple level underground stone mines. The factors driving this transition include surface quarries; ? reaching their economic stripping ratio, ? encroaching on the mineral reserve boundary where the remaining reserves are below the active pit, ? dust, noise, and blast vibration concerns as suburban neighborhoods and development move into formerly rural areas. Ground control is critical to the success of a safe and productive, mining operation. The primary focus of the ground control engineer in an underground stone mine is the stability of the roof or back, development and benched pillar stability, stability of the sill pillar between vertically adjacent mining levels, and floor stability. Roof stability begins with the selection of a stable back horizon based upon the presence of a thin shale parting, stylolite, or other discontinuities from which the production shot can easily ""peel"" away leaving a stable back stratum. Room width and the decision of whether to bolt the roof, the bolt length, bolt type, bolt diameter, and spacing of the support is controlled by the thickness, fracture spacing, jointing, and material properties of the back strata. Horizontal stress controls the header and crosscut azimuth as to avoid driving perpendicular to the maximum horizontal stress direction. Stable pillar dimensions depend upon the interaction of the; ? vertical stress resulting from overburden thickness and multiple level interaction of overlying level(s), ? mining height during development and the final mining height after floor shots are taken while benching, ? presence of faults, folds, or joints passing through the pillar, and ? stone lithology recognizing that the presence of oolitic bands, shale partings, and bentonite beds create zones of weakness that can destabilize an otherwise competent pillar. Floor stability is typically not a significant issue for underground stone mines because the bearing capacity of the stone exceeds the vertical pressure transferred through the pillar. However, floor heave can be a ground control issue where shale partings, moisture sensitive strata, weak stone bands, or horizontal stress is present. Roof stability and pillar stability problems can be initiated as the floor heave enables the pillar and roof to settle. The ground control issues for underground stone mines are most clearly presented through a series of case histories. The case histories presented in this paper are a mix of ground failures and successful mining. The focus is on the geotechnical data required for underground stone mine ground control for roof, pillar, and floor design and stability analysis."

Jan 1, 2016

By Giorgio Höfer-Öllinger, Peter Pointner, Manfred Stadlober

"SUMMARY Investigations from tunnel face are part of risk mitigation measures during the excavation works. With the tunnel equipment, percussion drillings of up to 30-40m can be achieved. Core drillings are state of art method for investigation exceeding 50m. At Koralm base tunnel, up to 270m deep percussion drillings were performed with drilling rigs and accompanied by an intensive investigation program. These investigations consisted of monitoring during the drilling, field tests (with packer, using the preventer, borehole imaging) and in laboratory. Percussion drillings are cheaper and save time of interruption of the excavation progress. INTRODUCTION As part of a proper risk management, horizontal advance drillings during excavation of underground works can be seen as state of art and meet wide acceptance. Core drillings, deep and shallow percussion drillings can be differed. The selection of the type of drilling, meanwhile, causes intensive discussions. On the one hand, only a core drilling allows a direct investigation of the rock mass expected during later excavation works. On the other hand core drillings are expensive in both cost and time – if there is no excavation progress during the investigation measures – in construction time. Percussion drillings can be performed as rapid investigation measure with the excavation equipment (“Jumbo”) allowing two dimensional image of the ground around the cross section. There is some limitation concerning a reasonable depth of approximately 30m and a borehole diameter of 76mm. The applications of preventer, packer or borehole imaging are hardly applicable. By use of a drilling rig depths of percussion drillings of several hundred meters can be achieved relative easily and there is less limitation of the borehole diameter. Installation of a preventer is possible, as well as packer tests and borehole measurements (imaging, gyroscope, borehole geophysics). The gap of information between core and percussion drilling cannot be closed completely, but it can be reduced substantially and sufficiently by combination of an intensive program of measurements and analysis accompanying the investigation works."

Jan 1, 2016

By Xiqing Wu, Liang Dai, Tao Yue, Longsheng Yi, Ruifang Wang

Magnetic seeding flotation (MSF), i.e. adding magnetic seeds and pre-magnetization-flotation, is a new flotation technology especially for fine particles, which improves the flotation performance by enlarging the apparent size of the particles in a way of magnetic agglomeration. Both the fine coal slimes with a size of 66.68% –38µm and the pyrite slimes with a size of 73.95% –23 µm were investigated by the MSF, respectively. Flotation tests with variable of dosages of magnetic seeds and polyacrylamide were conducted, and some measurements, such as laser diffraction size analysis, magnetic susceptibility by vibrating sample magnetometer (VSM) and infrared spectroscopy (IRS), were also applied in order to probe the mechanism of the MSF. Based on the tests, measurements and calculations it was found that both the recovery of coal and the flotation kinetics of pyrite slimes increased with the additions of the magnetic seeds, and in the presence of polyacrylamide the coal flotation was further strengthened due to a synergetic effect of magnetic seeds and polyacrylamide on the flotation and a relatively larger apparent size of slimes after additions of magnetic seeds and polyacrylamide. The reason for the MSF lies in fact that the presence of the polyacrylamide intensified the adsorption of magnetic seeds on the coal particles and increased the coverage of the magnetic seeds on the coal surface from 0.2 to 1.3 wt%, resulting in increased magnetic susceptibility of coal particles from 9.13×10-9 to 22.17×10-9 m3/kg and thus a low magnetic field strength of pre-magnetization needed for the magnetic agglomeration among the coal particles from 602 to 24 mT prior to proper flotation. IRS shows that polyacrylamide chemisorbed on the surfaces of both coal particles and magnetic seeds, thus acting as the bridging media between particles and seeds.

Jan 1, 2016

By G. O. Oniyide, H. Yilmaz

The South African platinum mines in the Bushveld Complex (BC) have unique features that distinguish them from the gold mines. They have a higher horizontal stress closer to the surface, lower occurrence of seismic activity (caused mainly by pillar failure), and are sited in an area of high geothermal gradient. One of the future challenges of platinum mining is the increasing temperatures as the mining depth increases. High temperatures invariably bring about higher ventilation costs and require different approaches to human factors and ergonomics. Excavation stability would also be another area of concern due to increasing stresses. In this investigation, the effect of temperature on the physical and chemical properties of selected Bushveld rocks (chromitite, pyroxenite, norite, leuconorite, gabbronorite, mottled anorthosite, varitextured anorthosite, granite, and granofels) was studied by means of optical microscopy and scanning electron microscopy using energy-dispersive Xray spectrometry (SEM-EDX). The rock specimens were heated in a temperature-controlled oven a rate of 2°C /min to 50°C, 100°C, and 140°C and kept at temperature for five consecutive days. Samples were allowed to cool to ambient temperature (approximately 20°C) before image capturing. Micrographs of the specimens were taken before and after heat treatment. All the SEM samples were also subjected to heating and cooling on alternate days for ten days in order to observe the effect of repeated heating and cooling on the rocks. The results of the optical microscopy analyses showed minor physical changes in the rocks. The SEM images revealed that cracks initiating at lower temperatures extend with increasing temperature. The chemical analyses showed that the temperature range considered in this research is not high enough to induce changes in the chemical composition of rock samples.

Jan 1, 2016

By Alain Blouin, Mohamad Sabsabi, Aissa Harhira, Paul Bouchard, Greg Lithgow

"The objective of this study was to demonstrate the application of Laser-Induced Breakdown Spectroscopy (LIBS) to the continuous analysis of online monitoring of Al, Mg, Ni, Mn, Si and Fe in nickel ore limonite and saprolite slurry samples. Analysis was performed on slurry samples in air at atmospheric pressure. Two pure samples of limonite and saprolite were used. Mixtures of the two samples in varying proportions were used to build calibration curves, study the influence of solid/liquid ratio, and evaluate short and long term reproducibility. The LIBS measurement of these elements is independent of the water content (from 70-85%, the range allowed by our setup). Repeatability of the measurement and long term reproducibility (from day-to-day) were below 1.2 % and 2% respectively for all the elements studied in our conditions. The results obtained showed that an industrial LIBS analyzer could provide the chemical composition of the six elements Al, Mg, Ni, Mn, Si and Fe within 1-2 minutes.IntroductionThe metal-producing industry faces the major challenge of increasing productivity, reducing costs, and maximizing benefits from existing equipment. By pyrometallurgy, metal making involves the basic steps of charging the furnace, melting the charge and refining. By hydrometallurgy, the metal refining is carried out through the dissolution of the metal by chemical reaction and electrolysis. During refining either by pyrometallurgy or hydrometallurgy, it is critical that operating parameters be adjusted and controlled so that the chemistry of the melt or the solution is within predetermined limits. Presently, the complete turnaround time for sampling, sample transfer, analysis and communication of the results to the operators is often 30 minutes or more."

Jan 1, 2016

By Simon B. Blancher, Malo Rousseau, Renato Contessotto, Thomas Wallmach

The Manganese division of the ERAMET group extracts manganese ore in Gabon and produces manganese alloys for the steel industry. ERAMET has an economic interest to maximize the ore throughput without reducing the lifetime of its manganese mines. This can be achieved by means of research and development leading to innovative ore beneficiation processes. For this purpose, the ERAMET research center has designed and constructed a new pilot plant for ore beneficiation by physical separation processes. This pilot facility was erected within an infrastructural and synergetic framework, including competencies in hydrometallurgy, pyrometallurgy, numerical modelling, analyses and mineral characterization that provide ideal research conditions. After laboratory scale tests, a pilot operation of beneficiation of low grade Mn ore (around 35% Mn) was carried out by jigging of the 1-10 mm fraction. This gravity separation process exploits density differences between the various Mn-bearing minerals such as pyrolusite and lithiophorite as well as gangue minerals such as silicates and iron-hydroxides. Enrichment leads to the production of a marketable product associated with a high mass recovery (53% for the jigging step). However, 20% of pyrolusite and 30% of lithiophorite are lost in the waste. Mineral characterization has shown microtextural complexities, but grinding the ore to approach the liberation mesh was not an option due to commercially defined constraints given by the ferro-alloy industry. Recovery of the Mn-bearing minerals or adjustments of the feed grain size (6.3-10 mm) are two potential areas of process improvements identified by means of Qemscan® mineral characterization. This paper details the process tested on a pilot scale (0.5 t/h), which has led to a significant increase in the beneficiation of a low grade Mn ore.

Jan 1, 2016

By C. Musingwini, A. S. Nhleko, M. J. Mahase

"In an environment like the mining industry, which is characterized by different stakeholders with multiple objectives, multi-criteria decision analysis (MCDA) is a useful approach for optimal decision-making. The application of MCDA techniques in the mining industry has predominantly been in mine planning and related problems, although no comprehensive survey has previously been undertaken to establish the application trends. A survey of the use of MCDA techniques was therefore conducted using case studies from the literature. It was noted that often two or more methods are applied to the same problem in order to increase confidence in the solution derived. As the number of criteria and alternatives increases, some methods become inefficient. A combination of the analytic hierarchy process (AHP) method with other MCDA techniques was the most frequently used approach, indicating the efficiency of the AHP method, especially when evaluating problems with more criteria and fewer alternatives. A combination of fuzzy theory with AHP or other methods incorporates uncertainty. The findings from the survey will benefit users applying MCDA techniques to solve mine planning and related problems.IntroductionA country’s natural resources serve the needs of different groups of people within the country. These different groups are collectively known as stakeholders (Herath and Prato, 2006). Stakeholders have different needs, preferences, and expectations, which describe and define the criteria to be considered in decision-making. The options available as solutions describe the alternatives in decisionmaking theory. The criteria and alternatives have to be evaluated simultaneously when making decisions, and this is when multicriteria decision analysis (MCDA) techniques become invaluable (Herath and Prato, 2006) because the human mind is considered to be limited when solving complex and intangible problems with several criteria and alternatives (Saaty, 2007). MCDA techniques belong to a broad group of techniques called multi-criteria decision-making (MCDM) techniques. The other group of techniques within MCDM comprises the multi-objective decision-making (MODM) techniques. MODM techniques are generally used to solve problems with an infinite number of alternatives, while MCDA techniques are generally used to solve problems with a finite number of alternatives (Musingwini, 2010)."

Jan 1, 2016

By M. Shriwas, F. Calizaya

"Controlled recirculation may be considered as a beneficial means in mines of cold climate, where heating of air is required, and in deep or extensive mines, where cooling of air is required. Controlled recirculation can be designed by proper sizing of the booster fans with respect to main fan. Intuitively, it seems that the buildup of methane at the face will cease when a steady state condition is attained, and also that, at that same time, the maximum concentration at the face will remain same as in the return air. This supposition is proved by mathematical analysis that considers uniform mixing of methane in air in successive cycles of recirculation. This study includes two scenarios to show the effect of controlled recirculation on methane concentration in a sample network. Firstly, when recirculation crosscut exists near the working face; secondly, when recirculation crosscut exists away from the working face. The later scenario shows lesser buildup of methane concentration than the former one. INTRODUCTION The controlled recirculation is designed purposefully to allow a partial fraction of used air that increases the air velocity due to increased quantity of air and consequently allows effective dilution of contaminants to improve local ventilation condition at the working face. It can be designed by proper sizing of booster fan with respect to main fan in a ventilation network. Controlled recirculation may be categorized as crosscut, in-line or combined system based upon the configuration of the booster fan locations in a district ventilation network. Research on controlled recirculation has shown numerous benefits of controlled recirculation especially in deep or extensive underground mines, where further heating or cooling is required (Calizaya 1990; McPherson 1993 and Jones, 1987). However, fear of buildup of concentration has misled the mining communities to view the controlled recirculation as a hazard and deprived the mining industry to derive benefits from recirculation. Intuitively, it seems that the buildup of methane at the face will cease when a steady state condition is attained, and also that, at that same time, the maximum concentration at the face will remain same as in the return air. This supposition is proved by mathematical analysis that considers uniform mixing of methane in air in successive cycles of recirculation. This study includes two scenarios to show the effect of controlled recirculation on methane concentration in a sample network. Firstly, when recirculation crosscut exists near the working face; secondly, when recirculation crosscut exists away from the working face. The later scenario result shows the less buildup of methane concentration than former scenario result."

Jan 1, 2016

By G. C. Lindeque

"A downward trend in tyre life on haul trucks at an open pit iron ore mine prompted an investigation into the current tyre management strategy in order to improve tyre life. ‘Best practice’ was compared to the current tyre management strategy at the mine to determine aspects that could be improved. Aspects that showed significant room for improvement included employee tyre awareness, tyre pressure maintenance, and road conditions. For each of these aspects a plausible alternative was suggested.A new tyre management strategy was formulated as a step-by-step guide on how to implement the proposed changes. Each step introduces new initiatives but at the same time builds on the previous step’s success. A sensitivity analyses was performed to determine the impact of the proposed changes, with the variables being the reduction in the percentage of premature tyre failure, and the reduction of the site wear rate.The ‘most likely’ scenario showed an increase in tyre life of 41% for the Komatsu 730 trucks and 105% for the CAT 777 trucks if the entire tyre management model is implemented. This would result in a possible annual saving related to tyre usage of R9.2 million. OverviewThe study focused on the tyre life on the main haul fleet at an open pit iron ore mine. The haul fleet consisted of 17 Komatsu 730 (180 t) haul trucks and 12 CAT 777 (90 t) haul trucks.The haulage operation consists entirely of tyre-based haul trucks. Five per cent of the total mining budget is related to tyre costs. Since 2012 there has been a steady decrease in tyre life as measured in operating hours (Figure 1) due to the high percentage of tyres that fail prematurely. In 2014 a total of 41% of all tyres failed prematurely and 61% were classified as ‘worn out’."

Jan 1, 2016

By Samuel Rigert, Marco Bettelini

"INTRODUCTION AND OBJECTIVES Long rail tunnels require in most cases powerful mechanical ventilations. Besides requirements related to normal operation and maintenance, operational safety always requires a high level of smoke management. Identifying the optimum ventilation concept is essential for achieving proper performance and safety while keeping investment and operational cost at a reasonable level. For the purpose of the present paper, long tunnels have a length of typically 20 km or more. This is related to the European classification of trains (TSI 1303/2014), where the maximum distance from the portals to a firefighting point and between firefighting points is limited to 20 km (only category B passenger rolling stock allowed) or 5 km (general case). From TSI 1303/2014 it can be concluded, that tunnels over 20 km require in any case emergency stations with complex mechanical ventilations. Based on the experience arising from a number of recent projects in the European area, including in particular Gotthard (GBT), Lötschberg, Lyon-Tourin (LTF), Brenner (BBT) and Gibraltar, safety-relevant issues related to the ventilation of long railways tunnels are reviewed in this paper. Amberg Engineering is directly involved in these challenging design tasks and can provide first-hand experience and know-how. As a particular highlight, special attention is devoted to the longest tunnel worldwide, the 57 km long Gotthard Base Tunnel, which will be commissioned in 2016. THE GOTTHARD BASE TUNNEL Overview The Gotthard Base Tunnel will be commissioned in 2016 (official inauguration on the 1st of June and beginning of regular operation on the 11th of December) and will be the worldwide longest tunnel. Its complex and powerful ventilation system is very representative for many other long tunnels and is used as reference in this paper. Therefore, a few key characteristics of the Gotthard Base Tunnel and its ventilation system will be described in some detail in this initial chapter. The Gotthard Base Tunnel (GBT) consists of two single-track tunnel tubes with connecting galleries every 312 meters. Two so-called multi-functional stations (MFS), located at roughly 1/3 and 2/3 of the tunnel length, host the key equipment for normal and for emergency operation. At these locations, double crossovers allow trains to switch from one tunnel tube to the other. An emergency station is located in each multifunctional station, allowing trains to stop in case of emergency. The general layout of the GBT is presented in Figure 1."

Jan 1, 2016

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

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

Jan 1, 2016

By P. W. Conrad, C. Todd, N. West, R. Kramer

"Surface subsidence caused by both underground room-and-pillar mining operations and solution mining operations have each been studied separately, but never combined. In 2008, FMC Minerals began using solution mining at its Westvaco Mine as a secondary extraction method in an area that had been previously mined using the room-and-pillar mining method. Mining regulations require that subsidence associated with underground mining activities be monitored and measured annually. Researchers at Montana Tech were able to develop a relationship between measured surface mine subsidence and solution mining that can be used at the Westvaco Mine to estimate the production of trona from solution mining operations. PROJECT BACKGROUND FMC Minerals (FMC) has increased the production of trona from its Westvaco Mine near Green River, Wyoming, using solution mining as a secondary extraction method in an area previously mined using the room-and-pillar method. The area of interest was mined until 2001 with the use of a borer miner at a depth of approximately 1,600 feet. Currently, FMC determines the amount of trona produced using its solution mining operations by measuring the dissolved solids pumped from the mine. This approach, however, does not account for the location from which the trona was removed. The location from which the trona was removed and the size of the cavern created by the solution mining operations is important to FMC’s mine planning. FMC believed that with proper investigation of the subsidence at the Westvaco test site, a correlation might be found that would allow for the use of surface subsidence measurements to estimate the amount and location of trona production from the solution mining activities. The primary goal of this project, conducted by Montana Tech, was to find a relationship between the measured subsidence and the solution mining activities. The project attempted to model the relationship between the measured subsidence and the solution cavern using Salt_Subsid, an existing subsidence software package from the Solution Mining Research Institute (SMRI), to determine the program’s usefulness for locating and developing the cavern created by solution mining activities. The project also attempted to develop an equation that could be used to predict solution trona production based on measured subsidence. The data used in this study were collected over a seven year period, 2008 through 2014."

Jan 1, 2016

By R. Roufail

"Energy consumption in stirred mills has been studied, in the last couple of decades, on a macro scale. Effective operation and meeting particle size required for downstream operations used to be the main objectives behind energy utilization of stirred mills. In this paper, three energy terms are defined to assist in understanding the breakage mechanism for various types of minerals versus mill operation. The types of minerals studied had diverse physical and mechanical properties that are summarized as specific gravity, hardness and crystal structure. The minerals utilized in this study were quartz and galena. The effect of quartz and galena mix has been addressed as well as Lead-Zinc ore sample from SAG mill discharge. The energy input to the mill is function of the agitator speed, therefore three agitator speeds were evaluated, 1000, 1500 and 2000 RPM, respectively. The energy terms studied are specific energy (kWhr/ton). Effective energy is the ratio between net energy and total energy consumed by the mill. Last type of energy is the specific breakage energy, which is the net energy consumed by the mill per one-micron breakage. Results showed that specific energy and specific breakage rate are functions of mineral type, while effective energy is only function of mill input power (agitator speed).INTRODUCTIONGrinding is the largest energy consuming component of a mineral processing operation and typically consumes about 50% of the total energy used at a mining operation (Botin, 2009). Over the last two decades, stirred mills have been extensively utilized in mineral processing operations due to increased mineralogical complexity of ore bodies. Stirred mills grind particles to less than 10 µm by applying a high power intensity. The technology has been the focus of several research studies to investigate mill energy and grinding mechanisms. Becker, et. al. (2001) studied the relationship between different types of energy including input energy, specific energy, volume/mass specific energies, to stress intensity and final product particle size. Other studies such as by Kwade (1999), Kwade and Schwedes (2002), Blecher et al (1996), Partyka and Yan (2007), Stender et al (2004), focused on mill design and/or stress intensity distribution. Peukert (2004) studied the effect of mechanical properties of the grinding media and ground material on the comminution process."

Jan 1, 2016

By L. V. Kin, V. V. Lodeischikov, A. V. Byvaltsev, IRGIREDMET JSC, O. D. Khmelnitskaya, S. V. Petrov

"Irgiredmet Institute carried out the study on the development of gold recovery technology from refractory ore from a Russian deposit. The ore contained 1.1 g/t Au, 1.5% of pyrite and 2.4% of pyrrhotite. The recovery of gold achieved was 84.7% using gravity with generation of high grade recoverable gold concentrate and gravity middling. In the course of lime treatment, cyanidation of the middling followed by tailings detoxification the consumption of reagents was 13.0 kg/t CaO, 95 kg/t NaCN and 72 kg/t Ca(OCl)2 of the concentrate. This was capital intensive.In order to decrease the consumption of reagents, magnetic separation of the middling of the concentrates from gravity separation was added to this flow sheet. Pyrrotite recovered to magnetic fraction, which did not contain gold in accordance to this advanced flow sheet. The mass yield of pyrite goldbearing non-magnetic fraction decreased down to 1.5 times in relative to gravity middling. The slurry filtration prior to and after cyanidation allowed the organization of cyanide solution recycling.The results of pilot plant tests using the developed flow sheet showed that the content of pyrrhotite in the non-magnetic fraction decreased from 59.1% to 11.3%. The reagents consumption was 12 kg/t CaO, 3 kg/t NaCN and 16 kg/t Ca(OCl)2 of the pyrite concentrate. The total gold recovery using this flow sheet was 83.4%. Due to a decreased consumption of reagents, cost efficiency of the process was achieved. Based on the results of this research, a project design criteria was developed. A processing plant with the annual throughput of 2.6 million tonnes of ore is being designed."

Jan 1, 2016

By Anthony J. Konya

"This paper was written during part of the author’s student co-op with Cargill Salt at its Avery Islandunderground salt mine in Louisiana. Blasting salt is a unique type of blasting that is different than blasting other rock types. The plastic nature of salt, along with its large swell factor make salt a challenge to blast. The Cargill salt mines use and have tested a variety of different methods for breaking salt in an efficient manner, however these blasting methods are rarely used in other operations nor talked about today."

Jan 1, 2016

By Nickvinder Bhath, Johnson Matthey Plc, Jamie Baker, Daniel Kim, Jeff Lucht, Shijie Wang

"Precious metals (PM) in copper anode slimes are traditionally recovered by pyrometallurgical processes. Due to the compliance with increasingly stringent environmental regulations, it has made hydrometallurgical processing an attractive method for recovery of precious metals, including relatively inert metals such as gold and platinum group metals (PGMs). In this paper, a new method to recover PGM from complex and difficult feed streams is described. Using a proprietary Advanced Ion Exchange (AIX) adsorbent which has a high selectivity for PGMs over other metals and can achieve high PGM mass loadings with a series of incredible pilot test data plus the business case generated from the study results are also presented in the paper.INTRODUCTIONPrecious metals in copper anode slimes are traditional recovered by pyrometallurgical processes. Due to the compliance with increasingly stringent environmental regulations, it has made hydrometallurgical processing an attractive method for recovery of many metals, including relatively inert metals such as gold and platinum group metals (PGMs). Fully hydrometallurgical processes for extraction and recovery of gold and silver from copper anode slimes were employed in major copper refineries since 1995, which was first developed at Rio Tinto Kennecott Utah Copper.In Rio Tinto KUC process, the wet chlorination and gold solvent extraction were utilized to enable recovery of gold and silver as well as other metal compounds. The availability of water and the interaction and amenability of gold processing in water-based solution makes it possible that gold and silver are produced in only five days, compared with a traditional pyrometallurgical process that took 45 days. Most copper refineries are still following the tradition, but the use of hydrometallurgical technologies is increasing as the world demand for metals increases, energy utilization, and environmental viability."

Jan 1, 2016

By Jan Drzymala, Przemyslaw B. Kowalczuk

Froth flotation is widely used for upgrading of ores and other materials. Efficiency of flotation depends on many parameters, including type, chemical structure and dose of flotation reagents. Selection of a proper frother in flotation depends on the material used, necessary dose of frother and its selectivity. The selectivity of flotation can be characterized by proper separation factors and indices. In this paper separation selectivity and power of frothers were evaluated basing on separation data for a given material and frother, plotted as the recovery of the useful component in the concentrate versus the recovery of the remaining components in the tailing. Such a plot is called the Fuerstenau upgrading curve. The selectivity was defined as the location of the whole upgrading curve in relation to no and ideal separation lines, expressed on the scale from 50 (no separation) to 100% (ideal separation). In turn, the flotation power was defined as the dose of frother to reach a certain upgrading level at which recoveries of the useful and unwanted components are equal. The power and selectivity of frothers were determined for the Kupferschiefer stratiform copper ore floated in the presence of a fixed amount of xanthate and varying doses of frothers using a laboratory flotation machine. Basing on the separation results for different poly(propylene glycol) (CnH2n+1O(C3H6O)mH, CnPm) and poly(ethylene glycol) (CnH2n+1O(C2H4O)mH, CnEm) alkyl ethers, it was found that the concentrate yield and recovery of copper as the useful component in the concentrate were greatly influenced by the type and dose of frother. However, the same results plotted in the form of the Fuerstenau upgrading curve clearly indicated that the selectivity of frothers was similar, while their power was different. It proves that both selectivity and power of frothers are useful parameters for characterizing flotation systems.

Jan 1, 2016

By Shingo Morimoto, Toru Sasaki, Masato Shinji

"1. INTRODUCTIONTunnel face stability is one of the most important consideration in New Austrian Tunneling Method. In general, if all of the material properties of ground can be obtained through the field investigations, the tunnel face behavior can be predicted using numerical simulation prior to tunnel construction. However, estimating the safety of a tunnel face is difficult, especially in cases where the ground is very weak such as in an urban area.In this study, numerical analyses of tunnel excavation in very weak ground conditions, such as a low cohesion and low internal friction angle, were carried out. The relationship between the average shear strain distribution on the tunnel face and the overburden was analyzed. This relationship estimates the shear strain of the tunnel face relative to the critical shear strain obtained by the ground properties. The critical shear strain was defined as an allowable value for the maximum shear strain. We proposed the allowable overburden as tunnel face stability index (TFI) that satisfies the critical shear strain criterion of ground. Finally, a design chart of the allowable overburden for various cohesion values and friction angles of ground was created. This chart is useful in the preliminary tunnel design stage to judge the necessity of additional counter measures against normal tunnel support design.2. WEAK GROUND MODELING AND ANALYSIS PROCEDURE2.1 Setting material propertiesWith reference to a past study1), the material properties were adopted on the basis of material properties in the standard worst rock classification case called “DII”2) for standard support pattern of weak ground in Japan. The typical material properties for “DII” are listed in Table 1. In addition, Fig.1 shows the distribution of the representative weak ground according to cohesion and internal friction angle. When the internal friction angle is relatively high and the cohesion is weak, the ground is categorized as sandy ground. Furthermore, when the internal friction angle is low and the cohesion is strong, the ground is categorized as clayey ground."

Jan 1, 2016

By Shengliyang Yang, Jinghu Yang, Jiachen Wang, Xiaomeng Li

"Safe and efficient mining of extremely inclined thick coal seams less than 20m thick is one of the new challenges in China coal industry. In recent years, the extremely inclined thick coal seams have been encountered in some old mines and western China, and currently the top coal caving longwall mining method has been successfully applied to this kind of coal seams. Accordingly, this paper studies the roof movement and its impact on shield supports of top-coal caving longwall mining in extremely inclined thick coal seams. The structure of main roof before failure was simulated by the fix-ended beam, and provided the solutions for determination of maximum compressive stress of the bottom beam end and maximum tensile stress of the top beam end. The failure mode on the upper end of working face is mainly a combination of compression and shearing, while that for the bottom end is tension and shearing. Roof fracture begins at the upper end of working and propagates downward. The shape of collapsed roof strata can be described as parabolic and divided into three segments from top to bottom, including no filling, uneven filling and densely filling segments. The roof loading conditions of no filling segment is more likely to have dynamic burst impacts.INTRODUCTIONExtremely inclined thick coal seam refers to that the dip angle of coal seam is greater than 45° and the thickness is greater than 3.5m (Wang and Zhang, 2015a; Wang and Zhang, 2015b; Wang, 2005; Xie, Gao, and Shangguan, 2005; Wu, et al., 2014; Deng and Wang, 2014; He, et al., 2015). This type of coal seams can be divided into three categories: 1. The extremely inclined thick coal seam, of which the thickness is less than 5m and the dip angle is less than 60°, is usually mined by fully-mechanized longwall mining method. 2. The extremely inclined thick coal seam, of which the thickness is 5 m-20m, is usually mined by top coal caving longwall method. And 3. When the thickness of extremely inclined thick coal seam is greater than 20m, it is mined by the horizontal section top coal caving longwall method. For example, the average angle ofWudong coal mine in Xinjiang province is 45°, and the thickness is 27m. Wudong coal mine is applying the horizontal section top coal caving longwall mining, producing 3 million tons annually per working face (Figure 1)."

Jan 1, 2016