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By Erika Moonin, Jim Nickerson, Claudio Cimiotti, Roberto Bono

"In response to the severe drought on the Colorado River basin and in order to preserve existing water capacity to the Las Vegas Valley, the Southern Nevada Water Authority contracted a new deep-water intake (Intake No. 3) located in Lake Mead. The current project (Contract No. 070F-01-C1) includes 5 km (3 miles) of tunnel with very difficult geological conditions and a 200- m (650-ft) deep shaft and marine works. This paper will present the current status of the design-build contract being constructed by Vegas Tunnel Constructors and the challenges and problems faced and the innovative solutions developed to handle the difficult conditions encountered during tunneling with up to 15 bars of pressure.ProjectbackgroundThe Las Vegas Valley receives the majority of its water from Lake Mead, which is located approximately 30 km (20 miles) east of the Las Vegas, NV metropolitan area. Due to the severe drought that has hit the southwest region of the United States, the water level in Lake Mead has receded from its high water level of 372 m (1,221 ft) above mean sea level (amsl) to a low of 330 m (1,076 ft) amsl in June 2015. Should the lake level continue to fall, at elevation 320 m (1,050 ft) amsl, the current water intakes will not be able to draw enough water to meet the needs of the local area. The risk of losing water capacity has prompted the construction of a new deeper intake. Not only is the new Intake No. 3 situated at a lower elevation in the lake at 262 m (860 ft) amsl, the new Intake No. 3 is also located to draw better quality (Fig. 1).Project challengesThe project has had several difficult challenges to overcome:• The work consisted of a 1.2 kt (1,300 st) structure constructed on a barge and lowered 100 m (330 ft) into Lake Mead anchored with 9,200 m3 (12,200 cu yd) of tremie concrete.• The drill-and-blast starter tunnel was impacted by three inflow events, resulting in a one-year project delay.• One of the main challenges was selecting the tunnel boring machine (TBM) and excavating the tunnel with expected hydraulic head pressure of as much as 17 bar (16 bar was the highest pressure recorded during the drive), crossing faulted areas, low rock cover and the risk of tunnel instability due to direct connection with the lake.• Extensive pre-excavation grouting with a constant head pressure ranging from 12 bar to 15 bar.• Structural repair of the cutterhead in difficult hydrogeological conditions [water inflow of approx. 800 m3/hr (4,000 gpm)].• Complete repair of the cascade sealing system for the main bearing and two replacements of the pinion bearings.• The TBM approach to the intake structure."

Jan 1, 2015

By R. L. Keiski, H. Miettunen

"The serpentinite massifs of Hitura are located in the municipality of Nivala in Central Finland. The most important sulfide minerals in the ore are pentlandite, pyrrhotite and chalcopyrite. The ore body consists of amphibolite rocks in contact with serpentinite against mica gneiss. The mean Ni grade of the ore is about 0.7%, and the highest Ni grades have been encountered in close contact. In general, the inner parts of the ore are strongly serpentinized ultramafite and some sulfides have been converted to mackinawite and valleriite. The degree of alteration varies considerably within the ore body and, correspondingly, the grain size of the sulfides varies as well. In this study, flotation tests were done with samples from different zones of the ore body. The flotation test results on the bench scale and plant scale are discussed in terms of the mineralogical features of the ore. Ores in the North Hitura zone differ from those in the South Hitura zone.IntroductionThe Hitura nickel mine, like the entire Nivala area, is part of the Bothnian Svecokarelian schist zone, where numerous Ni-Cu boulders have been discovered since the early 1930s. The Nivala area has therefore been the subject of exploration activities by the Geological Survey of Finland (GSF) and mining companies. The first period of exploration started in 1936, and the Makola nickel deposit, located 3 km south of the Hitura mine, was discovered by GSF in 1937. About 415,000 tonnes of ore were mined at Makola between 1941 and 1954. In 1937, during the exploration and development stage of the Makola mine, boulder tracing and a geophysical survey revealed a significant ultramafic body with some lowgrade Ni-Cu occurrences in the South Hitura zone.In 1961, GSF continued the exploration program in the area and discovered the North Hitura ultramafic complex and its allied Ni-Cu occurrences. In 1964, Outokumpu Oy bought the property and, after underground exploration, comprehensive mineralogical studies, process research and a feasibility study, production started in 1970 (Isohanni et al., 1985)."

Jan 1, 2015

By S. Bentley

"Everyone has a general idea what mixing means, but describing the mixing process is not so simple. The objective of any mixing process is to distribute and blend the materials with different characteristics, different quantities as evenly as possible resulting in a homogenous mixture. Introducing proportional movement with the optimal intensity into the materials achieves effective homogeneous mixing results. A simple one directional movement with inadequate acceleration of the materials would obviously not achieve the same mixing results. This would be more like stirring than mixing. The amount of relative movement that is introduced is a decisive factor. Circumstances for successful mixing involve distribution of all materials, and achieving the highest probability that all recipe particles located in a specific position at the beginning can be found at any random location in the mixing chamber at the end of the process. This is the only way to ensure that a consistent result is achieved every time mixing is repeated.THREE-PART CYCLE The mixing cycle occurs in three phases; charging the mixer, the mixing process, and discharging. The sequence in which the individual materials to be mixed are filled into the mixer can have a huge impact on the efficiency of the mixing cycle. The mixing cycle overlaps the charging process and the discharge cycle follows the mixing cycle. To achieve optimum results, effective discharging methods should be taken into consideration to avoid risks of segregation. Costs for energy and wear should be as low as possible and finally, it is very important that the mixing cycle takes place as quickly as possible. In concrete or paste backfill production, selecting the best mixing technology is crucial for both the quality of the final product to be blended and the efficiency of the production process. The optimum mixing system is one that rapidly disperses all ingredients evenly throughout the mixing trough and completely surrounds all the course or fine aggregate particles with the slurry cement particles. Specific for paste production it’s the mixers job to also break-down unconditioned tailings to achieve consistent paste viscosity or measured spread. Many paste and concrete formulas also involve small quantities of chemical additives which also must be evenly distributed effectively. The time required per mixing cycle as well as the costs of energy, wear and maintenance will determine the economy of the concrete production."

Jan 1, 2015

By P. G. Martin

"As the speed of business has continued to increase over the last decade, the focus on real-time control of the performance of both stationary and mobile assets has become an increasing priority. Traditionally the maintenance team has been focused on the management of the availability of assets while the operations team has been focused on the throughput of those same assets. Typically operations and maintenance teams worked almost independently in spite of the fact that they were both working with the same assets. Part of the problem has been their traditional performance measures which have often been diametrically opposed. Recent advancements in the area of real-time performance measures and decision support have helped to drive higher levels of collaboration between operations and maintenance leading to real-time asset performance control and higher levels of business performance. This paper will explore the forces driving the need for changes, present an effective approach to the definition of the most appropriate business performance measures, and examine the effectiveness of contextualized real-time decision support resulting in asset performance control. TRADITIONAL APPROACHES TO ASSET PERFORMANCE MANAGEMENT In most industrial operations the phrase asset performance management is synonymous with maintenance of the industrial assets. This is the way industry has viewed asset management and asset performance management for decades. This is a very limited perspective that is serving to constrain the profitability of industrial operations. As industrial organizations began to form following the Industrial Revolution, the complexity of the operations forced an organizational design based on specialization. No single person could understand all of the aspects of an industrialized operation. This was particularly true at the plant floor level where the operation and maintenance of the industrial equipment required very different skillsets and training. To accommodate the vast differences most industrial organizations set up operations teams to run the equipment and maintenance teams to keep the equipment available to the operation. Both teams were dealing with the same industrial equipment but from very different perspectives and with very different performance measures. Typically the operations team was measured on maximizing the output of the equipment – or throughput. On the other hand the maintenance team was measured on the uptime – or availability of the equipment."

Jan 1, 2015

By P. Zhang, W. D. Xiao

"A process mineralogy study was conducted to guide the development of a process for the extraction of vanadic oxide (V2O5) and aluminum compounds from bone coal and its ash as well as the production of byproducts. Results show that to extract the targeted metals at higher recovery rates, one must find a suitable agent capable of destroying the structure of the mica and breaking down the lattices in which these metal-bearing minerals occur. For such minerals, metal extraction efficiency is usually low if the approach is simply adding an oxidant that cannot destroy the structure. In this research, a byproduct fluosilicic acid (H2SiF6) at 20 percent concentration from an operating phosphate fertilizer plant was found to be powerful and effective for the leaching of vanadium-bearing minerals such as mica. This environmentally friendly process improved the leachability of valuable constituents in the bone coal significantly, with the leaching rate of V2O5 increased to 94 percent, from 83 percent, and that of aluminum oxide (Al2O3) increased to 75 percent, from 40 percent. X-ray diffraction and chemical analyses showed that the structure of mica can be destroyed using fluosilicic acid either alone or in combination with sulfuric acid. Based on the process mineralogy study, a processing flowsheet was tested, which resulted in a final V2O5 powder product with purity of 99.2 percent and an overall recovery rate of higher than 85 percent. The flowsheet consists of leaching, ion exchange and ammonium precipitation. With this process, various byproducts could also be generated, including aluminum fluoride, cryolite, aluminum sulfate, calcium sulfate, ammonium chloride, sodium chloride and cement admixtures.IntroductionVanadium is an important rare metal broadly used in the production of steel alloys and nonferrous alloys as well as in the chemical field as a catalyst. Vanadium-bearing bone coal and clays are abundant in China, and they contain other valuable metals such as aluminum. Bone coal is a type of carbonaceous shale. The vanadium-bearing minerals mainly exist in mica, kaolin, iron oxides, tourmaline and garnet. According to previous studies (Xiao, 2007; Xu, 1989; Xu and Chen, 1991; Ji and Xu, 1991; Chen and Xu, 1992; Xu and Heng, 1992), vanadium occurs from the isomorphous substitution of V3+ for Al3+ or Fe3 + in the crystal lattices of mica, tourmaline, garnet, dolomite and aluminosilicate minerals. In iron oxide and kaolin minerals, vanadium appears as an adsorption form. The isomorphous substitution of vanadium is more stable in tourmaline, garnet and silicate minerals. Therefore, vanadium in bone coal may exist in three phases: vanadium-containing kaolin and oxides, vanadium-containing mica, and tourmaline and garnet (Xu and Chen, 1993; Xu and Zhang, 1993; Xu and Wang, 1994; Feng, et al., 2005; Lin and Fan, 2001)."

Jan 1, 2015

By R. Woods

"Comments on the paper ""Formation of hydrogen peroxide by chalcopyrite and its influence on flotation,""by A. Javadi Nooshabadi and K. Hanumantha Rao (Minerals & Metallurgical Processing, 2013, Vol. 30,No. 4, pp. 212-219)The formation of hydrogen peroxide from water during the grinding of chalcopyrite in a nitrogen-sparged environment, as reported by Javadi Nooshabadi and Rao (Minerals & Metallurgical Processing, 2013, Vol. 30, No. 4, pp. 212-219), is questioned on the grounds that oxidation of water by the mineral is unlikely to be thermodynamically feasible. It is argued that it is more likely that any peroxide that had been formed would have been generated from residual oxygen in the nitrogen-flushed system than from the oxidation of water.The formation of hydrogen peroxide by finely divided pyrite had been reported by a number of authors (Borda et al., 2001; Borda et al., 2003; Cohn et al., 2006; Schoonen et al., 2006; Schoonen et al., 2010; Jones et al., 2011; Javadi Nooshabadi et al., 2013). That hydrogen peroxide is formed in the presence of oxygen in solution can be comprehended from wellestablished mechanisms. Pyrite in aerated solution is known to oxidize by an anodic process that is coupled with the cathodic reduction of oxygen (Holmes and Crundwell, 2000). The latter process has been shown to occur through the formation of hydrogen peroxide (Biegler et al., 1975; Ahlberg and Broo, 1996). The pH dependence of cathodic oxygen reduction at other sulfide minerals, including chalcopyrite (Biegler et al., 1977; Rand, 1977), implies a similar mechanism at these surfaces."

Jan 1, 2015

By M. Noppé

"Dilution in underground coal operations can be underestimated by up to five times during Feasibility Studies, with disastrous economic consequences. Every 1% of stone waste introduced can reduce an in situ specific energy of 11,000 BTU/lb (25 MJ/kg) by some 110 BTU/lb (0.25 MJ/kg) and increases the abrasiveness of the run-of-mine coal. Where a wash plant is not in place, penalties imposed for not meeting contractual specifications alone can amount to some AU$1 million per year.This paper presents a method for monitoring, reporting and ultimately controlling dilution in an underground coal mining operation. The dilution trends before and after introducing the recommended controls in a continuous miner/longwall mine are presented over an eight year period. The additional information from such a dilution monitoring program can also be used to control mining horizons and plan longwall extraction heights across the face proactively, on a short-term scale with resulting improvements in productivity. INTRODUCTION Grade control, as practiced on any mine, is concerned with predicting routine quality and tonnage values for short- to medium-term mining operations, and the reconciliation of these predictions against “actual” results. For a longwall mine supplying steam coal, such routine parameters may include the proximate analyses, specific energy (SE), abrasiveness and sulphur, as well as float and sink analyses if the coal is beneficiated. In addition, grade control is concerned with identifying the mineable horizon (or horizons) in a selective-mining operation, together with monitoring how well these horizons have been extracted or adhered to. Close-spaced surface drilling can be costly for any mining venture, particularly for longwall mines operating in the deeper seams. For this reason, much of the data for short-term grade control requirements are acquired during actual bord-and-pillar development. The underground data are derived from so-called “channel” samples. These samples are cut or chipped from the coal seam, perpendicular to the mining horizon, with dimensions suitable for obtaining sufficient “representative” sample for analyses. For a 2m thick mining horizon, a channel sample 300 mm wide and 50 mm deep over the thickness of the horizon would provide some 4.5 kg of sample, sufficient for most of the necessary tests. To allow the information to be computer recorded, additional information such as seam thickness, sample co-ordinates, and the elevation of the seam (or horizon) roof or floor, may be required."

Jan 1, 2015

By H. Wen, X. Zhai

"The Jurassic coal fields which lay in west China are the major energy base and contain half of coal resources in China. Due to the gather and degeneration rules, the spontaneous combustion characteristic of Jurassic coal is distinguished with permo-carboniferous coal, which needs to be studied deeply. Programmed heating experiments of five Jurassic coal samples and three permo-carboniferous coal samples from different primal coal fields in West China were conducted to identify the characteristic parameters in the low temperature stage of oxidation and spontaneous combustion. The experiments were carried out under non-isothermal heating conditions up to 180? at the heating rate of 0.33?/min in an air atmosphere. The result showed that oxygen consumption rate, CO gas production rate and heating intensity of all coal samples increased with the rising of the temperature, which of the Jurassic coal was higher than that of Permian-carboniferous coal. The C2H4 gas of Jurassic coal generated earlier, more than that of Permian-carboniferous coal in the process of oxidation and spontaneous combustion. It indicated that the Jurassic coal was easier to be oxidized and spontaneous combustion and the index parameters of spontaneous combustion were different between the Jurassic coal and permo-carboniferous coal.INTRODUCTION Coal was the foundation of industry development, and occupied 70% of primary energy production and consumption structure in China. According to the data of the 3rd coalfield prediction, 39.6% of the total coal resources were located in northwest Jurassic coal field in China [1], where the quality of coal was excellent. The study of northwest Jurassic coal already dated from the 80s of the 20th century, about coal rock composition, coal metamorphism [2], coal-derived hydrocarbons, coal structure [3], etc. The results of these studies showed that the composition and properties of Jurassic coal was obviously different from Permian-carboniferous coal, as well as the characteristic of spontaneous combustion [4]. As a result, the spontaneous combustion characteristic of Jurassic coal particularly needed to be studied. Now more and more methods could be conducted to test the characteristics of coal spontaneous combustion, for example, thermal analysis technology [5-7], programmed heating experiment [8-10] and coal spontaneous combustion experiment [11,12]. In these methods, programmed heating experiment could be conducted to determine the oxygen consumption rate, CO gas production rate and heating intensity quickly."

Jan 1, 2015

By J. P. Ducarme, J. L. Carr, C. C. Jobes

"An average of 1.2 fatalities occur per year in underground coal mines in the United States when a miner is struck or pinned by a remote-controlled continuous mining machine. Proximity detection technology provides a means to prevent these types of accidents by disabling all machine motion when a miner is in close proximity. Researchers at the National Institute for Occupational Safety and Health (NIOSH) have developed the intelligent Proximity Detection (iPD) system, which continuously tracks the position of miners near the machine and disables only those machine motions that could cause a pinning accident. This system, previously demonstrated using non-permissible proximity detection hardware, has now been shown to be effective when implemented using an MSHA-approved system as a platform. Performance tests have shown accuracy, repeatability, and stop zone identification to be comparable to or better than the system demonstrated with non-permissible hardware. INTRODUCTION Underground coal mining room-and-pillar operations typically use Continuous Mining Machines (CMMs), such as the one shown in Figure 1. When CMMs first became available, they were operated from an on-board operator’s compartment that protected operators from roof falls and other hazards but severely restricted visibility and subjected them to machine vibration and high levels of dust and noise. To solve these problems, remote controls were developed to operate CMMs. Now CMM operators are free to position themselves for best visibility of each mining task and are no longer subjected to the rough motion of the CMM during mining operations or the dust and noise generated by the machine. However, this technological advance removed operators from the protection afforded by the operator’s compartment and exposed them to the hazard of being struck or pinned by the CMM or other large moving machines."

Jan 1, 2015

By K. Huttu, A. van Wageningen

"The Kittilä underground mine in northern Finland is extracting one of the largest known gold deposits in Europe. Kittilä achieved commercial production on May 1, 2009, becoming Agnico Eagle’s first mine to open outside of Canada. The Kittilä orebodies were initially mined from two openpits – Suuri and Roura – and underground operations were added in October 2010. The pits were mined out in November 2012, so mining is now entirely underground in the Suuri and Roura deposits. Additional, small openpits will mine any remaining near-surface reserves in the future.The Kittilä Mine is located in the Lapland region of northern Finland, approximately 900 km (560 miles) north of Helsinki and 150 km (93 miles) north of the Arctic Circle. With a mine life estimated through 2034, Kittilä is Agnico’s longest-life mine.The mine’s proven and probable reserves contain 32 Mt (4.7 million oz) at 4.6 g/t (0.13 oz/ st) gold. Ore has been mined from underground since 2010. The original 3 kt/d (3,300 stpd) operation underwent an expansion project to increase the throughput capacity of the mill by 1 kt/d (1,100 stpd), starting by the end of 2014.The region around the Kittilä Mine is underlain by mafic volcanic and sedimentary rocks of the Kittilä Greenstone Belt oriented nearly vertical. This greenstone belt is similar to those hosting Agnico Eagle’s Canadian deposits in Quebec’s Abitibi region and Nunavut. At the contact point between ironrich and magnesium-rich rocks lies a 100- to 200- m (330- to 660-ft) thick structural zone known as the Suurikuusikko Trend. This trend hosts the Kittilä deposit, where multiple mineralized zones have been traced over a strike length of more than 25 km (15 miles).Most of Agnico Eagle’s work has focused on a 4.5-km (2-mile) segment of the Suurikuusikko Trend that hosts the five main zones of the known gold reserves and resources. From south to north they are: Ketola, Etela, Suuri, Roura and Rimpi.The ore at the Kittilä Mine is refractory, making gold extraction relatively difficult because the gold is generally locked inside the two main sulfide minerals – arsenopyrite and arsenic-rich pyrite. Only about 4 percent is very fine-grained “free gold” (not locked in sulfide grains) and easier to extract. Most of this free gold is found in the outer, oxidized or eroded sections of the ore."

Jan 1, 2015

By H. Yen, D. E. Walsh, H. K. Lin

"Comminution circuits are widely used in nonferrous and precious metals milling. Steel crushers, grinding mills and grinding media are typically used in comminution circuits. Comminution circuit wear products, in the form of metallic iron (steel) fines, are unavoidably produced and report to undersize products in the classification circuit, i.e., flotation or leach feed, while tramp grinding steel (TGS) reports to classification oversize products and returns to the grinding mill, building up in the circulating load. In laboratory studies, TGS reduced grinding efficiency significantly, the impact being dependent upon the size of the TGS present in the mill. Because iron fines adsorb flotation reagents effectively, iron fines increase reagent consumption and reduce flotation recovery. Iron fines are also capable of reducing gold recovery in cyanidation circuits via a cementation reaction. When using filtered gold solution from the cyanidation circuit of an Alaskan gold mine, the gold concentration in solution was reduced by 0.2 to 2.6% over various reaction periods when iron fines were present in the solution.IntroductionComminution circuits are widely used in copper, lead, zinc, nickel, cobalt, molybdenum and precious metal mills. Flotation and leaching processes are usually preceded by comminution (crushing and grinding) circuits in order to liberate valuable minerals for effective separation, concentration or dissolution by the subsequent flotation or leaching processes.Steel crushers, grinding mills and grinding media are typically used in comminution circuits. Comminution circuit wear products, in the form of metallic iron (steel) powder, are unavoidably produced and report to undersize products in the classification circuit (flotation or leach feed), while tramp grinding steel (TGS) reports to oversize productions during classification and returns to the grinding mill, building up in the circulating load. Variables affecting the amount of metallic iron powder and TGS produced in a comminution circuit include ore hardness, grinding mill operating conditions, comminution circuit design and the metallurgy of the steel used for manufacturing crusher liners, mill liners and grinding media. As one example, a comminution circuit product of 80% passing 200 mesh at the Pogo Mine, AK is estimated to contain approximately 2 kg/t of metallic iron. A finer grind will generally produce a comminution circuit product with higher metallic iron fines content."

Jan 1, 2015

By J. Boisvert, E. Daniels, C. Deutsch

"INTRODUCTION Conventional mine planning is performed on a single resource model at a selective mining unit (SMU) scale deemed appropriate for the deposit and mining method. Estimation methods such as kriging and inverse distance, commonly used to construct a single model, are susceptible to histogram smoothing (Rossi & Deutsch, 2014). This can be mitigated by limiting the number of composites per estimate, therefore correctly reproducing the distribution of estimates (Boisvert & Deutsch, 2012). Search limiting techniques remedy histogram smoothing at the cost of introducing a problematic conditional bias (Isaaks, 1999) and introduces even greater spatial smoothing. Localization is an alternative, offering histogram reproduction through post processing of more robust probabilistic modeling techniques. A single localized model at the SMU scale is desirable. The correct histogram can be reproduced and a single model allows for the use of conventional mine planning and resource evaluation techniques. Despite the advertized benefits of localization, the necessary reliance on a larger panel scale as a middle step in the localization process yields unsightly “edge-effect” artifacts (Boisvert & Deutsch, 2012). Two approaches to artifact reduction are presented here. The first is a straight forward optimization approach designed to minimize an objective function that penalizes artifacts including panel edge discontinuities to generate a model free of panel edge-effects. The second approach redefines a panel in a less conventional fashion as a randomly chosen set of SMUs throughout the domain. This method produces a model void of any regular panel shape resulting in an artifact free model. Artifact reduction minimizes the obvious “edge-effect” issues of localization but local precision issues described by Boisvert & Deutsch (2012) persist. Localization is not a replacement for quantified uncertainty for comprehensive risk analysis and resource evaluation. LOCALIZATION Initially developed with Uniform Conditioning in mind, localization collapses a distribution of local uncertainty at a panel scale to an SMU scale model for mine planning (Abzalov, 2006). This process has been extended to Indicator Kriging (Hardke, 2011), Sequential Gaussian Simulation (Boisvert & Deutsch, 2012) and MultiGaussian Kriging (Daniels and Deutsch, 2014). The localization process is performed in a similar fashion regardless of which technique is chosen to create the prior model of uncertainty. Methodology There are three scales of importance considered in the localization process. The point scale, otherwise known as the data scale, is the smallest and is the scale at which experimental data is collected. The SMU or block scale is the familiar scale at which mine planning and resource evaluation takes place. Lastly, the panel scale is larger and contains a number of SMUs. Each of the three scales is illustrated in Figure 1."

Jan 1, 2015

By J. M. Ekenes, C. A. Caro

"New approaches that increase hydrometallurgical recovery from refractory minerals in below mill cutoff -grade sulfide copper ore can add significant value, improve profitability and increase ore reserves. This paper describes the development and implementation of an engineered heap (EH) approach to leaching low-grade, chalcopyritebearing ore at Freeport-McMoRan’s mine in Morenci, AZ. The technical evolution of the engineered heap concept is described together with the challenges and benefits following implementation. Introduction The Morenci ore deposit, located in eastern Arizona, has been mined for copper for 140 years. Mineralization in the Morenci district consists of sulfides and oxides. To process these ores, Morenci operates concentrator and leaching circuits. Leaching accounts for two-thirds of the copper produced in Morenci. More than one-half of this leaching-derived copper production comes from run-of-mine (ROM) stockpiles. The largest category of material moved in Morenci is destined for ROM stockpiles and waste dumps. Materials that are not economic to mill or leach are designated “waste.” However, this designation can change based on improvements in extraction technology and commodity prices. Chalcopyrite does not leach well due to its refractory nature. For predominant chalcopyrite mineralized ore, copper recovery during a typical leaching cycle may be as low as 5%. For this reason, chalcopyritedominant ores below mill cutoff grade have historically been classified as waste. By incorporating advanced leaching technology to improve metal recovery from previously leach-resistant ore types such as chalcopyrite, the Morenci Mine has been able to reclassify substantial amounts of this “waste” to “ore.” Process chemistry Chalcopyrite copper extraction is temperature, oxygen and ferric dependent. The temperature is achieved primarily by pyrite oxidation (Eq. (1)) and secondarily by oxidation of chalcopyrite itself (Eq. (2)). The regeneration of ferric in solution can be enhanced by providing the appropriate acid and oxygen levels according to Eq. (3). In the absence of microorganisms, this reaction is very slow."

Jan 1, 2015

By J. Pereyra, M. DeMarco

"INTRODUCTION It can be vital that bolted joints holding subassemblies together remain secure. Bolts should resist the loosening effects of vibrations and dynamic loads yet need to be easily removable during maintenance. When a threaded fastener is subjected to vibration, the rapid movement causes a lowering of friction against the threads and a subsequent loss of preload. The loss of preload allows the fastener to vibrate loose and possibly fall out. As the diameter of fasteners increase desired preload becomes increasingly more difficult to achieve. Input torque requirements for achieving proper bolt preload is exponentially related to any given fasteners diameter. This means that specialized tooling or bolting practices are usually required to attempt the tightening of fasteners to reach their required preload. Traditional methods can cause problems with joint integrity and do not provide consistent bolt load across the bolted surface. BOLTED CONNECTIONS A failed critical bolted joint can lead to high maintenance costs, machine downtime, and risk to worker safety. Control of the clamp load in a bolted joint is vital. However, when faced with a problem joint, it is not surprising that the design engineer will not have an answer if asked about the clamp load. Torque calculations must always be based on the existing conditions that often are vague. Unless all parameters are correct, the calculation will be unreliable. Examples of parameters are: • Thread condition of the fasteners • Hardness of contact surface • Material (steel, aluminium, copper, etc.) • Extra friction from a locking fastener • Extra friction from an adhesive • Lubricant on the thread • Type of bolt head (flanged, regular or serrated) • Surface coating of the bolt • New or reused fastener During tightening, bolts are subjected to both tensile and torsional stress. The total stress in a bolt can be calculated using the formula: Total stress = vsx2 + 3txy2 In order to maximize the desired tensile stress (sx) it is vital to minimize the torsional stress (txy). Tensile stress (clamp load) is achieved when the bolt is axially elongated. Unwanted torsional stress (twisting) in bolts arises during tightening due to thread friction. High thread friction increases torsional stress and causes yielding at lower clamp load levels than normal. A lubricant is necessary to minimize the malign torsional stress. However, many commonly used bolt-locking systems are based on increased thread friction (deformed nuts, adhesives, etc). To minimize thread friction and concurrently safely secure the joint has often incorrectly been considered impossible. The use of locking systems that increase thread friction is the single most common reason why the full capacity of bolted joints is not utilized. The following example illustrates the problem."

Jan 1, 2015

By H. Wen

"Taking the long flame coal, gas-fat coal and anthracite as samples, we tested the adsorption quantity to single component gas of N2, CO2 and CH4 under atmospheric pressure phase at different temperatures. Then we analyzed the adsorption characteristics and models of different metamorphic coals. The results show that metamorphic grade, temperature and gases species are main factors to adsorption quantity of coal. The higher and lower metamorphic grade of coal have greatly influence on adsorption capacity while moderate grade of coal has opposite result. The coal adsorption amount to three single component gases under the same experimental condition is CO2> CH4> N2.The simulation precision order of four adsorption models is quadratic curve model > Freundlich isotherm model> Langmuir model >logarithmic curve model. Quadratic curve model and Freundlich isotherm model both can accurately describe the adsorption behaviors of N2 and CH4, different isothermal adsorption curve of CO2 needs two kinds or more models to describe. This has a reference value to the study of adsorption characteristics and models to single component gases.INTRODUCTION Adsorption is the interfacial phenomena that concentration of single or multiple components in the interface layer is different from the bulk phase (1964). Adsorption model is mathematical models to describe the adsorption characteristics of the adsorbent, mainly reflected to fitting effect of gas adsorption isotherm, which contribute to deeply understand the adsorption characteristics of adsorbent. Many scholars have carried out extensively experimental studies of the coal adsorption process from different angles. Zhao (2010) studied the influence of coal metamorphism to pore development of coal seam through a variety of experimental methods. Zhang (2006) analyzed the adsorption capacity and the controlling factors from three aspects of the coal rank, maceral and coal mass deformation. Cheng et al., (2002) studied the influence of pore size distribution of different rank coals to adsorption constants. Zhong (2002) carried out varieties of isothermal assay and established the prediction method of coal seam adsorption affected by a variety of conditions. R. M. Bustin (1998) proposed that we could not simply describe the change law of coal adsorption capacity and maceral content by a fixed parameter, and the adsorption capacity of the same coal rank also has great change. C. R. Clarkson et al., (1997) used four different adsorption models to describe the coal methane adsorption process, and the fitting precision of adsorption models is D-A equation >D-R equation > BET equation> Langmuir equation. Gasem, K et al., (2003) found that the fitted isothermal adsorption curve of D-A equation and BET equation are better than Langmuir equation under high pressure condition, while D-R equation and BET model are better to CO2 adsorption. In recent years, scholars’ at home and abroad research achievements of coal adsorption focused on high-pressure stage (about 0~15 MPa), mainly for coalbed methane exploitation, carbon dioxide trapping and sealing technology development, but the study of coal adsorption under atmospheric pressure phase is little. In this paper, we analyzed the adsorption characteristics and models under atmospheric pressure phase, it has a reference value to the study of characteristics and models to single component gas."

Jan 1, 2015

By S. K. Jena, S. Singh, B. Das, N. Dhawan, P. K. Misra, D. S. Rao

"Iron as an impurity in pyrophyllite ore affects pottery, ceramics and tile quality. We carried out the characterization of a pyrophyllite ore sample using optical microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and wet chemical analysis. The study revealed the presence of 2.15% iron oxide (Fe2O3 ) along with silica and alumina as the major components, which constituted around 90% of the total sample. We carried out the removal of iron from the pyrophyllite using magnetic separation and acid leaching and found that wet high-intensity magnetic separation (WHIMS) could remove 28% of iron values while oxalic acid leaching could remove up to 99.3%. The leaching kinetics of iron removal and the effects of pulp density, acid concentration, leaching time and temperature were also investigated. The optimum conditions for leaching were found to be leaching time of 60 minutes, temperature of 90°C, pulp density of 5%, oxalic acid concentration of 0.3 M, and particle size below 100 microns. Iron dissolution from the pyrophyllite sample can be best described by the diffusion of ions through the product layer of constant-size spherical particles. The breakdown of the pyrophyllite structure was evident from the FTIR and TGA studies. The activation energy of the leaching process over the temperature range was calculated to be 43.47 kJ/mol. IntroductionPyrophyllite is a naturally occurring phyllosilicate mineral composed of aluminum silicate hydroxide [Al2Si4O10(OH)2] as the major component and often associated with other minerals such as kaolinite, mica, quartz, rutile and epidote. It occurs in fine-grained sericite schist that is quarried as pyrophyllite (Pandit et al., 2008). In India, pyrophyllite occurs mainly in Madhya Pradesh state, Uttar Pradesh state and the Keonjhar district of Odisha state (Harpavat, 1995). Pure pyrophyllite is a highly desirable material for various applications due to its unique properties. It exhibits high refractive behavior, low thermalelectrical conductivity, low expansion coefficient, low hot-load deformation, low bulk density and high corrosion resistance to molten metal and basic slag (Rieger, 1997). It is used in the ceramics, refractory, foundry, electrical-insulation, sanitary-ware, glassmaking, pesticide and rubber fields. Compared with clay, it has lower thermal conductivity and coefficient of expansion, making it more suitable for refractory applications (Harben, 2002; The Minerals Yearbook, 2011)."

Jan 1, 2015

By D. J. A. Chambers, J. M. Wempen, K. D. Koper, M. K. McCarter, K. L. Pankow

"The EarthScope Transportable Array (TA) of broadband seismometers (www.usarray.org) was deployed across southwest Wyoming from November 2007 through May 2009. During this time period the Array Network Facility (ANF, anf.ucsd.edu) detected and located a total of six seismic events near the trona-mining district. This lack of seismicity is atypical compared to coal mines employing similar mining methods. In this study, eighteen months of continuous seismic data from several nearby TA stations are reexamined using conventional and correlation-based methods to detect seismic events. Waveform cluster analysis and epicentral locations are used to discriminate between mining induced seismicity (MIS) and seismic energy generated from surface blasts at nearby coal mines. The locations and magnitudes of the 143 newly detected MIS events are compared to regional subsidence as measured by Differential Interferometric Synthetic Aperture Radar (DInSAR). INTRODUCTION An abundance of natural resources and a favorable political climate have made southwest Wyoming home to multiple large mining operations. Among these operations are five underground trona mines located approximately 50 km west of Rock Springs, Wyoming. The trona mines employ room and pillar, longwall, and solution mining methods over an area roughly 900 km2, and produce a sizable portion of the world’s soda ash (Brown 1995). Historically, in the Rock Springs mining district, several relatively large magnitude seismic events have occurred. These events are thought to have been related to mining activity and have caused notable subsidence (Case 1997). The largest event in the region recorded by seismometers, ML 5.1, has been confirmed as the 1995 Solvay Trona Mine collapse (Pechmann et al. 1995). In addition, blasting at surface coal mines near Rock Springs produces significant amounts of seismicity; approximately 50% of all daytime seismic events in the Mountain time zone from 2007 to 2009 locate near an active surface mine in this region (Astiz et al. 2014). Much of the current research related to surface subsidence and induced seismicity focuses on wastewater impoundment (Ellsworth 2013) and hydraulic fracturing. The observable seismicity in geological injection environments is widely variable and McGarr (2014) has argued that, in such environments, the maximum amount of seismic energy that can be released is proportional to the injected volumes. Like injection environments, in extraction (mining) environments seismicity is highly variable depending on many geological and operational variables (Boltz et al. 2012; Carnec and Delacourt 2000; Fritschen 2010; Iannacchione et al. 2005; Sen 2013) and does not always correlate well spatially with subsidence, a surface expression of extraction at depth."

Jan 1, 2015

By Aidan Giblett

"It is important to make a clear distinction on the scope of work of the Global Mining Standards and Guidelines (GMSG) guideline for sampling grinding circuits. Many mineral processing practitioners are familiar with the sampling and surveying of comminution circuits, in particular grinding circuits, for performance diagnosis and the identification of optimization potential. These surveys often provide information for population balance modelling of individual comminution and classification unit processes, and consequently require a large amount of information to calibrate and validate the unit models. As a result, these surveys are labour intensive, somewhat expensive, depending on internal capabilities of the mine site or company and have a long time span from initial planning to final reporting. They also require a high level of expertise to process the survey data, simulate the circuit and make sensible recommendations on follow up actions.As a result of these factors, full grinding circuit surveys are not a common occurrence at a large number of processing facilities, and several years may pass before follow up surveys are conducted. In the ensuing gap between surveys, the efficiency of the grinding circuit must often be taken on faith, and this is considered an unacceptable lapse in an environment of strained natural resources and low commodity prices.To support the rapid and productive energy efficiency analysis being promoted by the ICE working group, a much simplified survey and analysis process is required. The process reflected in the GMSG guideline is indeed more conducive to frequent analysis, at a skill level that is well within the capabilities of the average plant metallurgist. As a result, it becomes feasible to conduct mini-surveys of plant performance, which can be used to quickly and precisely diagnose the high level impact of process changes. These methods can also be manipulated by an experienced practitioner to provide sufficient information for modelling of the circuit to estimate the impact of process changes, allowing an initial rate and rank exercise to focus plant optimization efforts."

Jan 1, 2015

By A. Noble

"In coal and mineral processing, several numeric parameters are used to quantify the separation performance of unit operations. For density-based separations, the partition curve is used as the starting point for many stages of diagnostic analyses. The curve is often quantified by its midpoint slope sharpness, and this single value is subsequently used for technical evaluation, benchmarking, and comparison. While this analytical approach does depict misplacement by relative density class, it inherently prioritizes middling separation and does not consider process economics or the micro-price value of individual classes. Alternatively, the organic efficiency parameter does consider process economics; however, it does not reveal information on the root cause of lost revenue or misplacement. In this paper, a new analytical approach is introduced which reconciles the technical misplacement data derived from the partition curve with the economic data derived from micro-pricing. The result is a new analytical procedure which reflects a better use of performance data. INTRODUCTION Partition curves are commonly used in the characterization, evaluation, and simulation of various physical separators. In mineral processing, partition curve analysis is routinely applied to hydrocyclones, screens, and density separators. Graphically, the partition curve depicts the recovery of particles as a function of a physical property on which the separation is based (e.g. particle density, size, magnetic susceptibility, etc.). Given the probabilistic nature of many real separators, the partition curve often exhibits a characteristic “S” shape (Fig. 1), similar to a cumulative normal distribution. Other geometric features of the curve are also depicted in Fig. 1, including the high and low closeout (or bypass) values, the midpoint slope, and the separation cut point (property value with 50% recovery). Partition curve analysis was originally proposed to evaluate coal washability (Tromp, 1937). Given the limited computational resources at the time, the analytical methods relied heavily on graphical construction and interpretation of the curve. Owing to the simplicity of the calculation and interpretation, many of these graphical approaches are still widely used for performance analysis today. The most common calculations are based on the slope of the partition curve at the midpoint. Increased slopes correspond to enhanced separation performance, since a perfect separation exhibits a stepwise transition from 0 to 1 at the desired cut point (i.e. an infinitely large slope). One common formulation of this slope, the Ecart Probable (Ep), is derived by evaluating the slope between the 25% and 75% recovery points:"

Jan 1, 2015

By S. Peng, N. Vayenas, A. Farah

"While genetic algorithms have been widely adopted in ore grade estimation and optimization, mine design, and production scheduling in the mining engineering field, reliability and maintainability analysis of mining equipment using genetic algorithms has been a relatively new research area in recent years. This paper presents an application of genetic algorithms using case studies with seven underground scoop trams whose maintenance records have been collected over a period of 12 months from an underground mine in the Sudbury mining area. Based on the assumption that various factors that contribute to machine failures resemble the biological evolution process, the authors have developed an in-house PC software application called GenRel which adopts genetic algorithms in its programming. In this study, the authors feed the historical maintenance data into GenRel in order to predict future maintenance characteristics of mining equipment in a time period of three months. Then the predicted maintenance characteristics are compared to the actual maintenance records in the same time period. A statistical study is then used to examine the similarity between the predicted data and the recorded data.INTRODUCTION Today maintenance costs of sophisticated engineering systems are so high that maintainability draws great attention from scientific researchers to operations managers. For instance, a study by [1] shows that American manufacturers spend more than 300 billion U.S. dollars on plant maintenance and operations. Therefore it is understandable that the main objectives of applying maintainability principles to engineering systems are to reduce projected maintenance costs, to use maintainability data to estimate system or equipment availability/unavailability and to determine labor-hours and other related resources needed to perform the projected maintenance. A system with better maintainability would inherently provide the benefit of lower maintenance costs, less time to recover with lower breakdown frequency (design for simplicity), less complexity of maintenance tasks and relatively reduced man-hours [2]. Most maintainability functions use the Time To Repair (TTR) as the independent variable. It is common to use probabilistic or statistical concepts to define a maintainability function, for example, the probability density function. Let t denote the time. Assuming a repair starts at t=0 and completes at time T, the maintainability can be mathematically defined [3] as in Equation (1)."

Jan 1, 2015