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By K. Louk, E. Gilliland, N. Ripepi, M. Karmis

"Carbon dioxide (CO2) injection in deep unmineable coal seams can enhance coalbed methane (CBM) recovery as well as effectively and permanently store the CO2. Enhanced coalbed methane (ECBM) recovery and CO2 storage capacity can be improved by altering injection parameters including the injection well locations, number of injection wells, and the time and rate of the injection. A sensitivity study was performed with sixteen different injection scenarios on a coalbed methane field in Buchanan County, Virginia to understand the influence of the injection parameters on methane production, CO2 storage and the extent of the CO2 plume. History matching was done for the gas and water production period prior to injection based on field data from an active US Department of Energy funded pilot project. INTRODUCTION The coal structure is a combination of the coal matrix and cleats. In a CBM reservoir, the methane (CH4) is stored in the matrix under adsorption properties, not as a free gas. During CH4 production, the reservoir pressure is reduced and gas is released from the surface of the coal, diffuses through the matrix and transmits to fractures (man-made or natural) via the cleat network. Fractures and cleats are the major parameters that influence gas flow capacity because deliverability of the CH4 to the production well is controlled by the cleat permeability. As gas production continues over time, CH4 desorbs from coal, and coal matrix volume starts to decrease. This volume decrease in the matrix opens up the cleats, matrix shrinkage, which leads to a permeability increase. Several emprical (Harpalani and Schraufnagel 1990a, 1990b; Harpalani and Chen 1995, 1997; Harpalani and Mitra 2010; Pan et al. 2010; Liu et al. 2012; Mitra et al. 2012) and analytical (Palmer 2009; Liu and Harpalani 2013) studies have reported this relationship between pressure and permeability. Those studies showed that permeability is an important parameter in CH4 production performance. Furthermore, during gas production, water is produced through the cleat system as well, therefore gas-water relative permeability must be also considered in evaluating production performance (Gash et al., 1991). In the CO2 injection scenario the opposite occurs because CO2 has a higher adsorption affinity than CH4. CO2 replaces CH4 in the matrix of the coal and increases the volume of the coal matrix, matrix swelling, and results in a permeability decrease. Harpalani and Mitra (2010) concluded in their experimental study that swelling of the coal matrix due to the CO2 injection is two to three times more than the sorption of CH4, resulting in large permeability changes during CO2 injection."

Jan 1, 2016

By Yoichi Shimada, Katsuyuki Nishida, Shinichi Takahashi, Yasushi Okada, Yohei Nakamichi, Kazunori Oshiro, Taichi Terui, Sigehiko Sugie

"Temporary retaining walls are ordinarily used for tunnel construction work conducted using the opencut construction method. Retaining walls in such instances are typically installed vertically. However, shoring (such as struts and king posts) is required to ensure the stability of retaining walls in cases of excavation work to depths that exceed approximately 4 m. A new design and construction method that focuses on the effectiveness of retaining walls that are installed on an incline was studied with the aim of improving construction workability by omitting shoring. The inclined braceless excavation support (IBES) method, which was developed for use with the inclined buttress method, requires no shoring, even for deep-open-cut construction work and can be applied to deep excavation work on ground with a high groundwater level. This method has been applied at six work sites in Japan in recent years. This paper introduces the IBES design and construction method and presents verification results based on the design method, a model experiment, finite element analysis, and measurements obtained during construction work.INTRODUCTIONBackgroundIn the past, temporary retaining walls used in open-cut construction work have been installed vertically, and shoring (such as struts and king posts) has typically been used to ensure the stability of these retaining walls when the excavation depth reached 3–4 m. However, shoring interferes with structures built within excavations and requires box-outs and penetration sections in the structures, as well as concrete joints that raise concerns about their impact on the watertightness and long-term durability of structures (Figure 1).Shoring also narrows the space available for conducting construction work and reduces construction work efficiency, and the installation and removal of shoring increases the construction duration and cost. As a result, there has been a demand for ways to reduce or eliminate shoring to improve the quality of structures and construction work efficiency."

Jan 1, 2016

By A. Röttger, W. Theisen, J. Küpferle, M. Alber

"Wear of TBM tools significantly affects tunneling advance rates. Wear-prediction models are based (amongst others) on the abrasivity of the present geology, which is determined via laboratory tests. To evaluate the results from such tests in context, this work considers the tribological system TBM tool from a materials technology perspective. In so doing, the microstructures of different application-oriented materials are presented and discussed in terms of their wear behavior and wear resistance. The significant influence of tool materials on the abrasivity of the geology and thus wear prediction models has already be identified. LCPC, Cerchar and nano-scratch experiments have been performed as confirmation. Material-dependent wear mechanisms and their correlation in terms of tunneling have shown that it is mandatory to consider the complete tribological system to estimate the wear of TBM tools. 1 INTRODUCTION Mechanized tunneling is vital to ensure necessary infrastructure development in megacities like Tokyo (Bay Tunnel), Istanbul (Eurasia Tunnel) and Mexico City (Tunnel Emisor Oriente). The use of Tunnel Boring Machines (TBMs) has been established for many years. In contrast to other methods such as boring and blasting or excavation using dredgers, tunneling with TBMs allows simultaneous excavation and removal of both the mineral and tunnel lining by tubbing segments or shotcrete. This makes tunneling more efficient, allowing for faster development of the tunnel in both hard rock and soil [1]. When budgeting such tunneling projects, precise planning and coordination in terms of tunneling technique choice (e.g. EPB or Slurry-shield), the relevant geology, and the associated penetration rates and tool wear are required. In particular, wear to TBM tools has a significant impact on tunneling progress. Due to wear, tools become dulled or lose their functionality because of brittle material behavior, thus reducing penetration rates and therefore tunneling efficiency [1]. As a result, additional tool changes are necessary, leading to higher overall costs due to down times and maintenance costs. Therefore, there is strong interest in a reliable and precise wear prediction model for TBMs. As already mentioned, the geology and associated wear of the tunneling tools define the maintenance times."

Jan 1, 2016

By Leonardo Rosas Sánchez, Darío Ángel Bulla

"The two track road sector between Cisneros-Loboguerrero (having a length of 14 km and 11 short unidirectional tunnels) is a new highway still on construction located along the existing Highway Buga – Buenaventura (Colombia). Due to the steep topography, difficult geological/geotechnical conditions, the traditional portal construction approach was impossible to be implemented in eleven (11) of the twenty two (22) portals. In this specific project, the skewed portal approach was developed as the optimal and more effective solution. The construction time and costs of portals were reduced in 21 months and 75%, respectively. At the same time, the natural equilibrium of the slopes was maintained, thus, facilitating adequate safety factors along the useful life of the project. This document pretends to show a detailed design experience (and the construction of the entry portal of tunnel 11 (left)). INTRODUCTION The Cisneros-Loboguerrero project is a 14 km length dual lane highway, connecting productive zones with the Pacific Ocean along the current Bogota-Buenaventura highway as shown in Figure 1. The project is located at the northern side of the Dagua River Valley. The preliminary design suggested constructing portals under challenging topographical conditions, i.e., slope cuts having heights between 50 to 100 m (some having slopes > 100%) requiring complex developments and having very high risks.The entry portal of tunnel 11 (left) was the first portal successfully built by implementing the skewed portal approach. Later, this approach was used as a model for the construction of the other ten (10) portal having similar topographic and geotechnical conditions. The development of this new alternative provided a considerable reduction on the construction time of portals, thus relieving a critical path in this project."

Jan 1, 2016

By C. Musingwini, A. S. Nhleko

"Since the Global Financial Crisis (GFC) in mid-2008, capital has been more difficult to access. Mining projects must contend with projects from other industries for scarce capital. A decision to invest available capital in mineral projects requires that valuation be conducted to assess the expected return on the projects. The discounted cash flow (DCF) analysis is generally applied for the valuation of mining projects, whereby future cash flows are discounted to present value using an appropriate discount rate. The discount rate significantly affects the outcome of a valuation. Economic and finance theory provides tools to calculate discount rates. The discount rate must account for factors such as the risk and stage of development of the mineral project; hence the appropriate discount rate to utilize in a project is often a subject of debate.The discount rate is the weighted sum of the cost of debt and equity. There are several methods for determining the cost of equity. This study considers the commonly applied Capital Asset Pricing Model (CAPM) and Gordon’s Wealth Growth Model because of their simplicity and availability of parameters required to estimate the cost of equity. This study explores how differences in the cost of equity obtained by these two methods can be explained for a mining environment. Data for empirical analysis were collected from the I-Net Bridge, McGregor BFA, and Bloomberg databases. It was found that Gordon’s Wealth Growth Model provides better estimates of the cost of equity compared to the CAPM under depressed market conditions. Therefore, this research recommends that Gordon’s Wealth Growth Model be used to estimate the discount rates for mining projects during periods of depressed market conditions."

Jan 1, 2016

By P. Hickey, G. Hubert, P. Healy

"J. S. Redpath Limited, an underground contractor with a worldwide presence, has implemented innovative techniques in various projects in Canada to shorten the development cycle. Conventional methods currently used for installing primary ground support are compared with the Australian technique of bolting and meshing with jumbos equipped with twin telescopic booms, in-cycle shotcreting, and the use of two jumbos and two scissor bolters set up side by side in wide headings. Recommendations and lessons learned are presented with the aim of providing realistic expectations with regard to development advance rates in a mining environment.RÉSUMÉ J. S. Redpath Limitée, un entrepreneur minier souterrain d’envergure mondiale, a complété plusieurs projets au Canada où des techniques novatrices ont été mises en oeuvre pour raccourcir le cycle de développement. Cet article présente une comparaison entre les méthodes conventionnelles fréquemment utilisées pour le support de terrain, la technique australienne de boulonnage et d’installation de grillage au moyen de jumbos équipés de flèches télescopiques doubles, du béton projeté appliqué durant le cycle de développement et de l’utilisation de deux jumbos et deux boulonneuses côtes-à-côtes dans des galeries de grandes dimensions. Les recommandations et les leçons apprises sont présentées dans le but de fournir au lecteur des attentes réalistes quant aux taux d’avancement du développement dans un environnement minier."

Jan 1, 2016

By Olivier Kraft, Olaf Kortz

"Project-specific optimized tunnel boring machines represent the spearhead of technological progress in tunneling because with their use, very long-lasting, high quality tunnel structures in almost any geology, depth and topography can be produced with a high degree of automation. The mechanized excavation of tunnel structures ensures the greatest possible environmental protection during tunneling itself. Professional, systematic and high quality rebuilds and reuse of already proven equipment also ensures maximum efficiency in the use of materials and energy resources. It offers an enormous potential for a highly optimized environmental balance. Here the manufacturers of tunnel boring machines and their users in particular have a duty to ensure transparent, high quality and binding standards in the entire rebuild cycle and in the refurbishment management of innovative tunneling technology. This paper deals with the comprehensive processes with rebuild levels of tunnel boring machines and highlights some exemplarily implemented projects. 1 INTRODUCTION All over the world, the number of tunnel boring machines (TBM) in which equipment rebuilds from previous projects are re-used has increased over the last few years. This text presents the technical and economical aspects of this market development. It also takes a look at the practical implementation of rebuild measures. The ""ITAtech Guidelines on Rebuilds of Machinery for Mechanized Tunnel Excavation"" from 2015 lay down the requirements that the machine manufacturers must meet. 2 ECONOMICAL AND ECOLOGICAL ASPECTS OF RE-USING COMPONENTS The globalization of the construction sector and the consideration of environmental aspects promote an increased re-use of machines and machine components. Nowadays, large-scale construction projects are often carried out by international joint ventures of several individual companies that are established specifically for this purpose. After the completion of the project, the joint ventures are dissolved and they liquidate their project-specific equipment, such as tunnel boring machines. Today, it is much more uncommon for such machines to remain permanently in the possession of construction companies. Joint ventures offer TBMs on the free market, or they exercise contractually agreed repurchase options with the manufacturer. On the whole, this increases the number of re-usable components or complete tunneling systems available on the market."

Jan 1, 2016

By T. Wajima

"A novel carbonaceous adsorbent for recovery of nickel from nickel plating waste solution was prepared from rice straw using sulfur impregnation. The rice straws were cut to 1 cm pieces, and then immersed in 0.01 - 3 M K2S solution to prepare sulfur-immersed materials. The immersed-materials were heated at 100-700 ºC in nitrogen gas to produce the sulfur-impregnated carbonaceous adsorbent by pyrolysis. The contents of carbon and sulfur in the adsorbent and abilities of adsorbent to recovery nickel from aqueous solution were examined. The contents of carbon and sulfur in sulfur-immersed materials are almost same as those in raw material. In pyrolysis, with increasing the heating temperature to 200 ºC, the contents of carbon and sulfur are almost constant, and then above 300 ºC those increase. The recovery for nickel using raw material, sulfur-immersed material and the product pyrolyzed at 100 - 200 ºC are almost same, and with increasing the heating temperature to 400 ºC, that of the product increases, and above 500 ºC that of the product decreases. In immerse step, with increasing K2S concentration, the carbon content of the product at 400 ºC gradually decreases, the sulfur content of the product increases, and the recovery for nickel using the product gradually increases and then above 1 M K2S decrease. The product prepared from material immersed in 1 M K2S solution at 400 ºC indicates a maximum recovery for nickel ion. The product can adsorb nickel ion in nickel plating waste solution coexisting with phosphate ion, and adsorbed nickel ion in the product was deposited as nickel metal after heating at 1000 ºC under N2 atmosphere.INTRODUCTIONRice is the second world’s largest cereal crop after wheat, but produces large amount of straw residues, of about 330 million metric tonnes. Rice is a widely grown crop in Asia, and rice straw is produced as a by-product of rice production. In most parts of rice fields, open-field burning of rice straw is commonly practiced in the region when there is limited time to prepare a field for the next crop. However, open-field burning of crop residues is an uncontrolled combustion process during which air pollutants are emitted into atmosphere. These air pollutants have significant toxicological properties and are potential carcinogens (Gadede et al., 2009). Although wildfires are prohibited in cultivation fields of most countries, farmers usually keep on burning their crop by-products. Biomass burning is an important source of aerosol particles which may affect local and regional air quality (Gao et al., 2011), and also contribute to global climate changes."

Jan 1, 2016

By J. T. Liu, G. H. Han, W. C. Chai, Y. F. Huang

"In beneficiation process, metal ions could adsorb onto clay mineral surfaces or interact with flotation chemicals, and then result in the flotation behavior changing of desired minerals. Al(III) is the dominating ion existing in the bauxite flotation system. In this research, the adsorption behaviors of Al(III) on two silicate clay minerals (including bentonite and kaolin) were investigated by means of UV-Vis spectra, zeta potential testing and scanning electron micrograph analysis. The adsorption experiment results show that the adsorption capacity of clays for Al(III) ions increases with the initial Al(III) concentration, contact time and solution pH. There are some different adsorption behaviours for two clays. Increasing the clay concentration decreases the adsorption capacity of bentonite, while increases first then decreases for kaolin. Higher temperature favours the adsorption of Al(III) on bentonite but goes against for kaolin. The adsorption capacities of bentonite and kaolin for Al(III) respectively reach 12.48 and 0.875 mg/g at initial solution pH 5. Zeta potential results show that the adsorption of Al(III) on two clays is characterized by electrostatic attraction mechanism.INTRODUCTIONIn beneficiation process, there is inevitably a wide variety of metal ions generated from mineral crushing, mineral dissolution and water chemistry conditions. Metal ions adsorb on the mineral surfaces or interact with the beneficiation agents, affecting the flotation efficiency of desired minerals (DiFeo et al., 2001; Parolis et al., 2008; Shackleton et al., 2012; Shengo et al., 2014). Therefore, it is necessary to have a detailed investigation on the adsorption behaviour of metal ions on clay minerals.Having good ion exchange capacity and negative surface charge, the clay minerals could take up various metal ions from the mineral-water system. Bentonite and kaolin are very common aluminosilicate clays in the mineral processing system. These two clays both hold a permanent negative charge, =X- on the basal surfaces, and a smaller variable charge, =SiOH on the mineral edges (Gu & Evans, 2008; (Gu et al., 2010). Adsorption experiments are usually used to study the adsorption affinity of metal ions for clay minerals (Sen & Bhattacharyya, 2012). The adsorption of Zn(II), Cu(II) and Pb(II) onto natural bentonite showed that the adsorption amounts of metal ions increase with contact time, solution pH and metal ion concentration, but decreases with adsorbent concentration and system temperature (Sen & Gomez, 2011; Melichova & Hromada, 2013). Cr(III) adsorption on bentonite was significantly pH dependent. The adsorption process followed pseudo-second-order model and the equilibrium adsorption was consistent with Freundlich isotherm (Lollino et al., 2015). The adsorption behaviours of Pb(II), Cd(II), Ni(II) and Cu(II) onto kaolin indicated that increasing pH favoured the adsorption of metal ions (Jiang et al., 2010). The adsorption of Cd(II), Cu(II), Pb(II) and Zn(II) onto kaolin showed that an ion-exchange reaction occurred at pH<7.0 and inner-sphere surface complexes were prone to form at higher pH (Srivastava et al., 2005)."

Jan 1, 2016

By Romel Villanueva L.

"Peru does not produce ammonium nitrate; nevertheless it is a large consumer of both, porous prill (PP) and high-density (HD) varieties. Explosives cost is an important preoccupation in Peru, due tofluctuations of the imported ANFO grade Ammonium Nitrate (AN). The use of Gasified Emulsion (GE)-manufactured with much cheaper HDAN- has become an alternative to reduce such costs. However, some problems were reported in the application of pure GE, including explosive percolation in highly fractured rock and lack of sensitivity by the effect of hydrostatic pressure in very deep holes. It was, hence, proposed to have an explosive based on GE too, but more robust and capable to keep the shape of the explosive column into the blast hole, by minimizing the leakage into the cracks. This could be achieved by adding limited amounts of lower priced HDAN, at the same time of providing gas pressure benefits. Other alternative is to add a low-density material, such as polystyrene prills, into the GE, although it reduces the explosive energy. The chemical gassing controls the density of GE, thus it can be obtained a wide range of densities."

Jan 1, 2016

By C Jincheng, L. Liang, L. Wenjun

"Considering overgrinding in a grinding process, the grinding characteristics of comminuted hematite products using a HPGR and a conventional CC were comparatively studied. The major properties including particle size, grinding kinetics and grinding technical efficiency (Et) were investigated. Individual size distributions (ISDs) of -2.0mm in a HPGR product showed a more significant “double-peak” characteristic than a CC product. As a result, HPGR products were finer and had a wider full-size distribution because of the greater proportion of fines. The parameters m and zi in m-th order grinding kinetics were analyzed by the partial-derivative method and the critical time tc(tc = exp (1/ zi)) was obtained. zi mainly affected the breakage rate when t < tc; otherwise, m mainly affected the breakage rate. In these tests, tc was considerably higher than the grinding times, and HPGR products yielded a higher zi-value than the CC product for the same sieve size. This indicated that HPGR products had a higher breakage rate and needed a shorter grinding time for a certain grinding fineness. Et was calculated by simulating the size distributions of batch grinding products. HPGR products gave a lower Et at a decreasing rate than the CC products for -2.0 mm feed and -0.5mm feed, and then showed a slightly higher Et for -2.0+0.5 mm feed. This indicated that overginding in HPGR full-size products was more serious under the condition of coarse grinding, whereas the efficiency was higher and overgrinding weakened significantly in HPGR coarse products because of screening-out fines. Based on the above research, a new process of “ultra-crushing in HPGR – classified grinding” was advanced, reducing ores tonnage into first stage ball mill significantly, improving grinding efficient and weakening overgrinding in the whole grinding process.INTRODUCTIONIn mineral processing, comminution accounts for a substantial portion (approximately 60~70%) of the energy consumed in plants. As an ultra-fine crushing equipment,the application of the HPGR for industrial comminution has been paid close attention because of its low specific energy, low steel consumption, high capacity and high ratio of reduction, among others (Schonert, 1998; Norgate & Weller, 1994; Fuerstenau & Kapur, 1995). HPGRs comprise two counter-rotating rolls that draw feed material into the roll gap. One roll is fixed to the mainframe, while the other movable roll is mounted on slides and positioned by hydraulic rams. The specific pressing force (SPF) (i.e., total force divided by projected roller area) is typically in the range of 3~9 N/mm2 depending on the application, while pressures of up to 1000 N/mm2 have been measured within the operating gap (Maxton , Morley, & Bearman , 2003)."

Jan 1, 2016

By Rainer Antretter

"THE CHALLENGE The 14km long, Arlbergtunnel, closed for public traffic during summer 2015, receiving a comprehensive and substantial renovation from 2015 to 2017. The main works discussed here, carried out during 2015, comprise 37 drill and blast SEM/NATM emergency escape tunnels from road level to the ventilation duct plenum have to be constructed as well as eight additional lay-by niches and three transformer tunnels. This presentation comprises the construction ventilation design, designed according to national regulations, suitable for 150 employees working 24/7 simultaneously at more than 40 single working sites lined up along the tunnel. The ventilation-system chosen was utilising two existing shafts for intake/discharge and a cross passage to surface, to handle a total fan power of 1.600kW. DESCRIPTION OF RENOVATION WORKS Linking Tyrol and Vorarlberg, two Federal States of Austria, the Arlbergtunnel is a single tube two-way road tunnel with vent duct plenum, constructed in the mid-1970s. According to latest EU legislation, additional escape exits have become obligatory. The existing seven cross passage links to the adjacent Arlberg Railway Tunnel, with average spacing of about 1.500m constructed in 2007, an additional upgrade to shorter escape spaces of approx. 400m was now required to comply with the updated legislation. Additional transformer tunnels, lay-by niches and small niches for emergency maintenance use, cleaning and other purposes, as well as a the installation of a new fire main in the invert, coupled with the simultaneous replacement of virtually the entire power and signaling cables, generated several dozen small and large single sites distributed along the 14km of tunnel.Purpose of the 37 walkable emergency escape tunnels is to reach the “upper deck” of the Arlbergtunnel, the vent duct plenum. These have an 180deg curve in plan, inclined at 10% and approx. 60m (65yd) long tunnels, excavated using drill and blast method starting from road level and working upwards to the level of an “intermediate soffit”, the vent duct plenum in the crown of the tunnel. The vent duct plenum is separated into a fresh air part and an exhaust air part, shown in Figure 1. The escape tunnels end with a pressure door in the fresh air section of the ventilation duct plenum. From there illuminated signs show the shortest escape route to the safe area between the road tunnel and the railway tunnel, as shown in Figure 2."

Jan 1, 2016

By M. Raffaldi, J. Johnson, M. Stepan, D. Benton

"The Office of Mine Safety and Health Research (OMSHR), Spokane Mining Research Division (SMRD), is continuing its High-Energy High-Displacement (HEHD) testing of field-scale shotcrete panels. A test program was developed to determine the relationship between applied force, displacement, and energy for both unreinforced and reinforced shotcrete panels. Reinforcement options consisted of synthetic macro-fibers, sprayed polyurea liners, chain-link fence, welded-wire mesh, and combinations of these products. During testing, photogrammetry was used to measure the geometric changes of the panels, including volume changes and panel cracking. These measurements were correlated with the load and displacement data, allowing visual observation to be related to the applied force and displacement. The test results provide a comparison of the mechanical performance of the various panel types and can be used by the practicing engineer to evaluate installed support based on visual observation of cracking and deformation. Visual assessment of the loading cycle and strength capacity of shotcrete in underground excavations will improve mine safety by providing a means to quantify the stability of installed shotcrete support. INTRODUCTION The National Institute for Occupational Safety and Health (NIOSH), Office of Mine Safety and Health Research (OMSHR), Spokane Mining Research Division (SMRD) is continuing research on the behavior of shotcrete when used as the surface support component in mining ground support systems. Ground control safety often depends on supporting, or at least containing, the ground between the rockbolts. Shotcrete and mesh, in various combinations and with other components, are often used to accomplish this (see Figure 1). Maintaining support pressure during ground deformation is key to the performance of these systems, and to ensuring miner safety. However, the toughness of a ground support system–the ability to maintain strength over large deformations–is difficult to quantify. Researchers at SMRD have responded to this deficiency by designing a full-scale test device, described previously by Martin et al. [2015a], and beginning a testing program to assess the behavior of shotcrete surface support reinforced with a variety of products including: fibers, chain-link mesh, welded-wire mesh, spray-on polyurea liners, and combinations of these products. This paper presents the findings of these tests."

Jan 1, 2016

By M. Maccagni, J. Nielsen

"Engitec developed the EZINEX® Technology some years ago to recover zinc from oxidized secondary sources. This process works at neutral pH and can take into solution any kind of metal, but iron is rejected and remains in the leach residue. Engitec has also developed the FLUOBORATE System, which is able to recover lead and copper from relevant concentrates. Some iron is leached into solution, but it is controlled through a solution purification bleed treatment. In this paper, we present the two above mentioned technologies. They are very different with regards to the chemical environments and the methods used to control the build-up of iron in solution, but both systems are suitable to treat iron bearing feeds.INTRODUCTIONIn the design of hydrometallurgical processes, the most important issues are the water balance, the filtration and the control of impurities. This is particularly important when the process includes an electrowinning unit. Iron has been one of the most problematic elements to remove, especially in acidic environments.Engitec Technologies has developed several hydrometallurgical processes divided in two different electrolyte lines: the Fluoborate Technology for the recovery of lead and copper from primary and secondary sources and the Ammonium Chloride System based on a chloride electrolyte for the recovery of different non-ferrous metals, among which zinc and lead are the most important. In both cases, iron is present in the feed and needs to be eliminated from the solution. It is not a problem for the quality of the metal produced, but when present in solution, it consumes the basic electrolyte reducing its free concentration which is very important both for both the leaching and electrowinning unit operations. Both process systems are very peculiar, the fluoborate case being much more intriguing."

Jan 1, 2016

By L. J. Bryson, C. A. Biley

"Anglo American Platinum’s Rustenburg Base Metals Refiners (RBMR) produces Ni and Cu cathode from slow cooled converter matte after Platinum Group Metals (PGMs) are magnetically separated for further processing. In 2010, execution of the RBMR expansion project was commenced to increase the production capacity to 33 ktpa Ni. The expansion, which is currently still in a ramp-up stage, brought about several fundamental changes to the circuit chemistry, including the installation of a dedicated Pressure Iron Removal (PIR) autoclave. This provided an independent outlet for iron from the refinery, which previously deported to the residue from the leach circuit and was toll refined. At the same time as changes in the circuit associated with the RBMR expansion were being made, the plant experienced a significant increase in iron and copper units per nickel unit in the feed. The decoupling of the leaching and iron removal process steps has had significant advantages for the robustness and control of the overall circuit, in particular pertaining to the preparation of a nickel electrolyte of sufficient purity to produce LME grade nickel. This paper details the primary changes to the RBMR circuit chemistry with a particular focus on iron deportment and the benefits derived from the installation of the PIR autoclave.INTRODUCTIONAnglo American Platinum mines and refines Platinum Group Metals (PGMs) through a complex processing pipeline in its South African operations. Mined ore is first treated through several mineral processing stages, geared to the recovery of base metals and associated PGMs, followed by smelting and refining operations that aim to separate base metals from PGMs and recover the value components to purified, saleable products. The focus of this paper is the Rustenburg Base Metals Refiners (RBMR) complex which receives a PGM-containing converter matte, then physically separates PGMs and base metals, and recovers nickel and copper to cathode by utilising leaching, precipitation and electrowinning processes.With new mining operations coming online and the continued increase in PGM ore arisings, it was necessary to undertake an expansion project at the Base Metal Refinery (BMR) to increase production capacity from 21 ktpa to 33 ktpa Ni. Complicating the expansion project was the requirement of continued production through all stages of design, construction and implementation and, due to stringent capital constraints, the utilisation of all existing equipment installed during a previous expansion in 1981. Against this backdrop, the expanded BMR flow sheet involved significant changes to the chemistry, especially iron management. These changes in iron management allowed for the separation of iron and copper residues and significantly increased the robustness of the plant to changes in feed mineralogy as well as the potential to increase production duties of the existing equipment."

Jan 1, 2016

By C. Birch

"A mineral resource royalty is payment to the holder of mineral rights for the utilization of the mineral resource. In South Africa, this payment is made to the State as holder of the mineral rights (The Mineral and Petroleum Resources Royalty Act of 2008). The principle purpose of this research paper is to identify if the State is benefitting from the mineral resource royalty by considering its impact on seven individual Witwatersrand gold mines.For this study, a simple financial optimiser model was created in Microsoft Excel that links the ore flow, block listing and the cash flow (excluding or including the cost of the mineral resource royalty). Mixed integer linear programing (the Excel Solver function) is utilised to optimise either profit or NPV (at 9% and 12%) by adjusting the cut-off grade.The impact on each of the seven mines mine was different but overall R7.9 billion is estimated to be paid in mineral resource royalty over their expected remaining lives. Due to the cost of the mineral resource royalty and increasing the cut-off grades, the total revenue decreases by R10 billion. A significant portion of this lost revenue would have been paid to the State in the forms of other taxation including company income tax which decreases by R2.8 billion. It is recommended that an industry wide investigation be conducted to determine if the resource royalty is adding to the State’s revenue, or destroying value including premature job losses. IntroductionTaxation of mining companies has become a very topical subject in the context of the postapartheid South African economy. There have been increasing calls for equitable re-distribution of mineral asset wealth for the benefit of all South African citizens and not just to an elite few. As part of the Mineral and Petroleum Resources Development Act (MRDPA) of 2002, the Mineral and Petroleum Resources Royalty Act of 2008 was introduced and came into effect in 2010 (South African Revenue Services, 2008). A mineral royalty is payment to the holder of mineral rights for the utilization of the mineral resource. In the case where the holder of the mineral right is the State, then this payment is made to the State (Cawood, 1999). Studies on the potential impact of the mineral resource royalty on the minerals industry have been conducted during the formulation of the Act and subesquently. These include Cawood and Macfarlane (2003), who suggested a cap of no more than 3% (Cawood and Macfarlane, 2003), as well as Cawood (2011), who predicted rising cut-off grades and thus reducing mineral reserves. In 2013, Grobler completed a Masters in the Faculty of Economic and Management Sciences at the University of Pretoria and concluded that the impact of the mineral resource royalty on the economy is positive. She stated that the royalty has caused operating expenses to increase, but this does not appear to be significant. Furthermore, she stated that the royalty has not affected the way the mining industry operates (Grobler, 2014)."

Jan 1, 2016

By Elbasher M. E. Ahmed, Indresan Govender

"A mechanistic model of axial charge segregation in rotating drums is presented. We show that granular material composed of different frictional properties diffuse into axial bands as a consequence of concentration fluctuations in the free surface layer that is caused by friction-limited mobility. A Bagnoldian stress assumption ensures an asymmetric free surface profile thereby providing the essential ingredients for the evolution of axial bands and the subsequent band coarsening observed in the literature. The formulation is sensitive to the boundary conditions of tumbling mills, including particle size and density, mill speed, inter-particle bulk friction, end wall friction and drum geometry (length and diameter).INTRODUCTIONA mechanism to fully describe the axial segregation of charge in a rotating drum remains elusive to the mineral processing industry. With regard to low aspect ratio mills (like ball mills), current thinking favours the use of closed circuit mills with correspondingly low residence times to offset the completely random contact probabilities between particles and balls (Wills & Napier-Munn, 2006). Conical end caps are argued to exploit the centrifugal force to achieve a regular gradation of ball size along the mill with larger sizes at the feed end and smaller ones closer to the discharge. However; segregation along the length has been observed in the absence of conical end caps (Oyama, 1939; Levine, 1999): In these investigations, sufficient differences in the particle’s mechanical properties (particle size, density, shape, surface roughness) was enough to successfully achieve axial segregation. Figure 1 shows the segregation of a bimodal distribution (by size) into bands of larger (darker colour) and smaller (lighter colour) particles."

Jan 1, 2016

By Troy Williams, Chris Preston, Ian Lipchak

"Underground blasting operations are challenging from the standpoint of the distribution of explosivesenergy representative of ring blasting. Energy from both shock and pressure regimes of commercialexplosives may appear concentrated in the collar region of a typical ring blast and diluted at the toes of holes due to the oblique geometries of blastholes. The non-homogenous nature of ore in whichexplosives are distributed via drillholes, adds to the complexities of generating particulate profiles from fragmented material with consistencies that are predictable from blast pattern to blast pattern - well suited for specific underground handling equipment and mill processing. In an ideal world, it would be the blasting operations themselves that represent the primary crushing mechanism, or at least mitigate mechanical crushing that can comprise a large component of the cost in generating suitable muck. This paper presents a dynamic break view in 3D that allows a planner to visualize the potential break zone around a blasthole generated by an explosive load using a Kleine field. Simple as it sounds, this methodology provides information that can be used in conjunction with cavity monitoring surveys (CMS) to potentially judge dilution due to overbreak as well as recovery for a typical blast. As examples, there are two break geometries that are examined regarding circular breaks and elliptical breaks around blastholes. Using a Kleine field to define break, a planner generated isosurface can be generated and compared to CMS data for calibration and prediction, using AEGIS 3D ring design software."

Jan 1, 2016

By R. C. Gilmore, S. A. Lolon, G. E. Bogin, S. A. Saki, J. F. Brune, J. W. Grubb

"Gob ventilation boreholes (GVBs) are widely used in underground coal mines for longwall gob degasification purposes. GVBs are often drilled within 10 to 30 m above the top of the coal bed into the fractured zone, completed with 20 cm (8 in.) diameter casing and 60 m of slotted pipe at the bottom. The purpose of this completion strategy is to create a pressure sink to capture the emissions before they can enter into the underground workplace. For GVBs to work effectively, they must be drilled close enough to the working areas to capture methane from the fractured zone while the setting depth must be kept above the caved zone to minimize the amount of ventilation air that is drawn into the GVBs. Well completion parameters are important for creating safe working conditions. In this paper, computational fluid dynamics (CFD) studies will be presented to analyze the effect of different practices for GVBs completion parameters for methane extraction, formation of explosive gas zones in the gob and methane concentrations at the longwall face and tailgate. Authors have identified the optimum completion parameters for GVBs, which can maximize the benefit and minimize fire and explosion risk. INTRODUCTION Coal mines may be considered gassy based on the presence of CH4. Gas from the mined coalbed or from rider seams above or below the mined coalbed can migrate into the gob and then potentially move towards the working areas. In longwall coal mines with high methane emissions, sufficient ventilation and additional methane control measures are usually required to reduce the methane concentration in working areas to below statutory levels. Several techniques or combinations of techniques are available to control the methane hazard. These may include mine face ventilation to dilute methane, coal bed degasification, nitrogen injection into the gob to render a methane atmosphere inert and the use of gob ventilation boreholes (GVBs). Longwall face ventilation and dilution alone can only handle methane emissions up to a certain amount. When methane emissions exceed the face ventilation capacity, additional control measures are required. Drilling horizontal or vertical methane drainage holes into the coal seams as well as gob ventilation boreholes from the surface into the gob area to extract methane are common practices. GVBs are usually drilled from the surface above the longwall panel ahead of mining. When the face moves outby the GVBs and the gob begins to form, methane production starts from the boreholes. It is important to control the performance of GVBs to maintain a safe working environment in the mine. The performance of GVBs depends on multiple factors, including borehole location, length and diameter of slotted casing, setting depth of casing above the coal seam being mined, wellhead vacuum pressure, and permeability of caved-fractured zones."

Jan 1, 2016

By C. Dodds, R. S. Ferrari-John, The University of Nottingham, G. Dimitrakis, J. Katrib, A. R. Batchelor

"Sorting technologies have the potential to reduce energy use in comminution by rejecting uneconomic ore before feed material enters the mill. However, a major challenge for sorting porphyry copper ores is providing a basis of discrimination between valuable and non-valuable fragments, due to their complex mineralogies and textural features. Microwave heating in combination with infra-red detection (MW-IR) has been shown to provide upgraded feedstock for certain ores at bench scale. Selective heating of copper sulphide minerals compared to the gangue leads to an increased thermal response for valuable fragments, providing the basis for sorting.Rapid scale up of MW-IR from bench scale to a 100 t/h continuous pilot plant facility has been facilitated by the design of microwave choking structures to allow continuous operation at industrially meaningful throughputs, whilst meeting health and safety and electromagnetic compliance standards, and the integration of materials handling with electromagnetic systems.Laboratory batch testing on a pilot scale microwave system has been undertaken to investigate the thermal response of copper ores under industrial conditions, at microwave energy inputs up to 1 kWh/t. These results provided the operating window and recommended test conditions for the continuous pilot plant. Sortability curves predicted in the laboratory are in good agreement with separations achieved during continuous pilot plant operations. The potential microwave sortability of a number of ores has been studied, allowing informed decisions to be made about potential ore candidates based on mineralogy. Future development of the technology will be underpinned by the creation and validation of scale up concepts for 1000 t/h operations. Understanding the value proposition for individual sites/applications will be central to unlocking the potential economic and environmental benefits of microwave sorting."

Jan 1, 2016