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By R. Mulyanto, M. Siray, A. Parhusip, F. Hartono

"PT Freeport Indonesia is preparing the Deep Mill Level Zone (DMLZ) mine to be the successor of the currently operating Deep Ore Zone (DOZ) mine. The DMLZ is block cave mine situated 500 m below the DOZ mine and approximately 1600 m depth from surface. Both of the block caving mines require draw point construction in the extraction level to extract the ore from caved area above. Learning from the experience in DOZ, the construction & maintenance of draw points in the production panels is a significant challenge in supporting consistent production.The average DOZ draw point construction duration is approximately 46 shifts per draw point. The time frame for construction is dependent on several variables; availability of the conventional forming system, material availability, and development tolerances. The repair of concrete floors and lintel sets causes production downtime. Reviewing the old DOZ draw point design, there is an opportunity to increase constructability, durability, and reliability of DMLZ draw points. This paper discusses how the DMLZ has improved draw point construction productivity and is on track to significantly reduce costs whilst increasing the quality by using the Six Sigma Improvement Method.Introduction The DMLZ Mine is part of the PT. Freeport Indonesia (PTFI) future Expansion to its underground mining complexes. It is the fourth vertical lift in the East Ertsberg Skarn System (EESS) deposit (Figure 1).Currently, it is under development phase.The DMLZ mine will be a block cave mine using an advanced undercutting method. The DMLZ extraction level will be approximately 1,600 meters below the surface on the 2570 level with column heights of roughly 500 m. The Undercut is on 2590 level, some 20 meters above the extraction level."

Jan 1, 2016

By Moreno Pescara, Luca Soldo, Piergiorgio Grasso

"Risk management in tunneling is more important today than it was a few years ago, considering increasing demands for safety and environmental and socio-economic sustainability, which are now required by citizens, owners, lenders, and insurers. Moreover, our current risk management philosophy should not only address risk avoidance and mitigation, but should also be used as a means of value creation, benefiting the overall project. Given the strategic implications of risk management, the authors intend to present, in this paper, a comprehensive overview of references and experiences from current practice—e.g., what is missing or weak, as well as possible or necessary developments that can have a key role in implementing effective risk management, particularly for a project’s design and construction phases. Therefore, as God has set some things in broad daylight; as he has given us some certain knowledge, though limited to a few things so, in the greatest part of our concernments, he has afforded us only the twilight, as I may so say, of probability (John Locke) PREFACE Many large-scale engineering and construction projects suffer millions of dollars in cost overruns, delays in design and construction, and operability troubles once finally completed (Edward W. Merrow, 2011). The undesired effects of these problems can become disastrous for large-scale megaprojects (those that typically cost US$1 billion or more), particularly considering that these are increasingly used as the preferred delivery model for infrastructure (Bent Flyvbjerg, 2014), often in public-private partnerships (PPPs). McKinsey G.I. (2015) has estimated that bridges and tunnels average 35% in cost overruns, and roads 20%. Some of the values published by Flyvbjerg (ibidem, 2014) for projects with relevant underground elements are the highest, with cost overruns from 60% to 300%. The analysis of 32 other case histories (from 1994 to 2010) given by Hartmut, R. (2011, IMIA Annual Conference, Amsterdam) indicates an average increase of costs around $55 million, with a 20-month average delay."

Jan 1, 2016

By F. Roemer, D. Goldmann, T. Elwert

Tantalum is an important minor metal for the production of high performance capacitors. Approximately 60% of the annual tantalum production is used in this application. Despite its high price of 298 US$/kg (average price 2010–2014), at the moment, no recycling from end-of-life products takes place. In the established recycling processes of waste electrical and electronic equipment (WEEE), tantalum is lost in the slags of copper smelting, where it is highly diluted. An economic recovery is not possible at that point. Although tantalum must therefore be extracted from the WEEE stream before it enters smelting, no industrial recycling processes exist. The main reasons are its low concentration in the WEEE stream, lack of information about tantalum bearing devices, technical difficulties of extraction, and conflicts of interests regarding the recycling of other valuable metals in WEEE. In this paper, the results of a cooperation research project are presented. The aforementioned challenges are addressed and a novel tantalum recycling process is developed. Small pilot scale experiments show that a mechanical processing route can produce marketable tantalum-concentrates of 30% tantalum with yields between 60 and 70%. This is reached through a manual pre-sorting of potentially tantalum bearing products followed by a combination of an optimized comminution, sieving, air classifying, eddy-current (EC), and two stage magnetic separation. Key to the implementation of this process was a detailed survey of the tantalum concentrations in different products carried out by the industrial partner.

Jan 1, 2016

By Sahendra Ram, Arnn Kr Singh, Dheeraj Kumar, Rajendra Singh

"Inherent existence of different rooms (openings) along the extraction line in a depillaring panel provides an easy path for the goaf to encroach the working area. Each of these openings in a mechanized depillaring (MD) operation along the extraction line is supported by the roof bolt-based breaker line support (RBBLS) to restrict the goaf encroachment. Different field studies by Council for Scientific and Industrial Research - Central Institute of Mining and Fuel Research (CSIR-CIMFR) found that the RBBLS works effectively during the depillaring under the shadow of stable surrounding ribs/fenders only. It is observed that, generally, these natural supports experience high value of induced stresses after a large amount of void creation inside the goaf. The induced stress creates spalling/loosening of the sides of the natural supports. Field studies also found that the positions of the RBBLS at the goaf edge need to be adjusted according to the depth of this spalling/ loosening. However, a systematic study in field for the correct positioning of the breaker line as per the spalling/loosening under different site conditions is difficult. Therefore, on the basis of the data and guidance provided by these field investigations, a detailed parametric investigation was conducted in the laboratory on simulated models for an effective design of RBBLS in a MD panel. FLAC3D is used for the simulation of the depillaring, and the available empirical formulations for Indian coalfields are used for subsequent calibration. An analysis of stress redistribution for different stages of the MD in simulated models showed the significance of the nature of overlying strata/induced stress for the RBBLS design. Discussing some results of field studies, this paper presents results of the laboratory investigations for an effective design of the RBBLS.INTRODUCTIONContinuous Miner (CM)-based mechanized depillaring (MD) is an important issue for Indian coalfields, where huge amounts of coal are locked up in standing pillars (Dixit and Mishra, 2010). Considerable variations in site conditions of these developed pillars bring a number of technical challenges into consideration during their final extraction. One of these challenges is goaf encroachment/overriding during caving of the competent roof strata. Goaf encroachment/overriding can effectively be controlled, mainly, by suitable design of natural supports (rib/snook/fender). However, there is a requirement of applied supports against the immediate roof as a considerable portion of this roof is exposed due to the presence of different openings along the line of extraction. These applied supports act as a fulcrum at the goaf edge between the working area and the goaf to facilitate the break out of the hanging roof inside the goaf. This is called breaker line support. An effective breaker line support is important for the efficiency of a depillaring operation. Generally, MD adopts roof bolt-based breaker line support (RBBLS) at the goaf edge (Singh, et al., 2014). For the first time in India, roof bolts were applied at the goaf edge as RBBLS in a CM-based MD (Leeming, 2003). In the beginning, three rows of roof bolts were installed as primary and secondary breaker lines support. On the basis of the observations of instrumented bolts, only two rows of roof bolts were used as secondary RBBLS (Ram, et al., 2014). Now, most of the MD operations in India are using only two rows of bolts as RBBLS (Table 1). However, the strata mechanics studies at different MD operations showed interesting characteristics resulting from this support (Ram, et al., 2015)."

Jan 1, 2016

By H. Ramazi, A. Amini

"This article is devoted to the introduction of a new technique of electrical resistivity data processing called residual resistivity (RR). We define RR as measured resistivity minus background resistivity. To determine the background resistivity, the data acquired from electrical resistivity measurements along a given survey line is evaluated, and then an equation is fitted to the data corresponding to a chosen measurement station as a function of current electrode spacing (or array length). The RR technique was applied to several synthetic models to compare the conventional resistivity inversion of each model with its RR-based inversion. A case study was carried out in a karstic area in Zarrinabad, Lorestan Province, western Iran, to detect the location and geometry of probable cavities by conventional resistivity inversion and RR-based inversion. The results showed that the anomalous zones are better highlighted in the RR-based inversion images in comparison with the conventional inversion images. In some cases, anomalies detected by the RR-based images were hidden in the conventional method. IntroductionThe geoelectrical resistivity method has been widely used since the early 20th century, and plays an important role in several fields such as groundwater and subsurface mineral exploration, geotechnical and environmental investigations, and archeological studies (Bayrak and Senel, 2012; Candansayar and Basokur, 2001; Fehdi et al., 2011; Hee et al., 2010; Osella et al., 2003; Wilkinson et al., 2010). The goal of geoelectrical resistivity surveys is to determine the distribution of subsurface resistivity by measuring the current-potential difference on the ground surface (Aizebeokhai et al., 2010). In the electrical resistivity method, an electrical current is injected into the ground by two electrodes, called current electrodes (AB), and the potential difference is measured between another pair of electrodes, the potential electrodes (MN). Several methods of interpretation are available for application to electrical resistivity data, the simplest being the graphical interpretation of the apparent electrical resistivity pseudo-sections along each survey line. A second method, electrical resistivity inversion, has been developed to create relatively accurate two- and threedimensional computational resistivity models of subsurface sections (Loke and Barker, 1996; Niwas and Mehrotra, 1997; Nordiana et al., 2014; Oldenburg and Li, 1994; Papadopoulos et al., 2009; Yilmaz and Narman, 2014). In the inversion method, models of subsurface objectives are mathematically inverted to reach optimal solutions subject to prescribed objective functions, constrains, and convergence criteria. A common problem when using the electrical resistivity inversion method is that the inversion model of an electrical resistivity profile may be non-unique because different inhomogeneities in the investigation media can result in the same electrical response (Smith and Vozzof, 1984)."

Jan 1, 2016

By C. R. Kato, G. Proulx

"Within the continuous scenario of reduced aluminium price and plants production costs increase, the energy consumption optimization in the aluminum electrolytic pots continues as the main focus for the producers. Energy consumption was chosen as a key performance indicator to drive the efforts and actions for improvements. Alcoa improved the energy consumption by approximately 3% from 2005 to 2015. This improvement was a result of best practices implementation, new technologies introduction, strategic actions with plant curtailments and management practices. The main objective of this paper is to highlight the importance of the management practices for planning and operational improvements beyond the technology changes. About 10 years ago, Alcoa reorganized its approach to retain knowledge in the Smelters by using a Best Practices format. For each specific subject, a skilled team defined the minimum requirements and the Best Practices for several aspects of operation and maintenance, which affect the environment, safety, cost, customers and performance. These Best Practices were deployed to all Smelters combined with training sessions to process and operation professionals. We will describe how the Best Practices were organized, the deployment strategy used, and the approach to measure the plants’ success. We will describe the management approach that includes Manufacturing Analyses focused on 3-year potential, annual planning, and weekly monitoring of plant stability. A manufacturing analysis is organized at select plants with cross-functional participation of specialists from technical, operational, procurement and finance. The output of a manufacturing analysis includes a roadmap of enablers to improve energy efficiency. A quarterly follow-up of enabler deployment is held with the plant and resources that participated in the analysis. Annually, there is a Planning Process where energy consumption enablers are selected to be implemented during the next 3 years for each plant. A monthly critical analysis is made by the plants with regional best practice support. On a weekly basis, key performance indicators are reviewed with determination of a stability index for each plant. Any deviation signal of unstable condition is alerted and supporting resources are diverted to the plant to reverse trend with countermeasures.INTRODUCTIONDue to factors like excess aluminum in the market and lower consumption in China, the LME price is declining along the last years, as showed in Figure 1. In 2011, the price peaked at US$ 2,400/ton and since then, continues to trend down and approaching the lowest level at US$ 1,500/ton in the last 5 years."

Jan 1, 2016

By L. A. Cornish, J. W. van der Merwe

"The hydrofluoric acid (HF) industry in South Africa uses normalized mild steel (SA 516 Gr 70) for the storage and distribution of its technical-grade product (70% HF). The technical-grade acid is split from the anhydrous hydrogen fluoride (AHF) product during distillation just after HF is produced, in a stainless-steel-lined kiln, from the reaction of calcium fluoride (CaF2) with sulphuric acid (H2SO4). Uniform corrosion of the storage tanks is mitigated during commissioning by contacting the steel with 70% HF. A corrosive reaction takes place (2H+ + 2F- + Fe - H2 + FeF2) to form scale inside the tank which diminishes the attack of the steel by fresh HF, thus prolonging the service life expectancy of the vessels. This iron fluoride scale in the vessel grows continually, resulting in corrosion of the vessels continuing at a predictable rate (approx.0.5 mm/a) since the first commissioning of the tanks at Necsa in 1993. In early 2012, an increase in the average corrosion rate of the tanks to 3 mm/a measured at and below the liquid band in the storage vessels was noted. Three months later the corrosion rate had increased to 30 mm/a, just before the first leak from the tank was detected. The tanks were decommissioned shortly afterwards and an investigation revealed that the rapid corrosion was due to the presence of increased levels (>50 ppm) of nitric acid (HNO3) in the tanks, which attacked the fluoride layer protecting the steel.The oxidation characteristics of high concentrations of HNO3 with low concentrations of HF on stainless steel surface treatment are well documented. The effects of low levels of nitric acid on the corrosion of steels in sulphuric acid are also known, but no suitable published data currently exists on corrosion by high HF concentrations with low HNO3 concentrations. Establishing the rate and mechanism of corrosion by HNO3 (0.1 to 1%) in 70% HF is currently a high priority for the HF industry in South Africa and will become increasingly important in the near future due to depleting fluorite reserves and cheaper, but less efficient, processes producing H2SO4 with higher impurity levels, which were not anticipated in the original plant design. The aim of this study is to simulate the corrosion conditions in the plant on a laboratory scale in order to establish the corrosion characteristics of the steels used in the HF plant, which are increasingly exposed to the HNO3 impurities that tend to concentrate in the final technical-grade HF acid product."

Jan 1, 2016

By Christopher E. Dianora, Matthew Sorrell, Eileen Test

"Constructed between 1939 and 1945, the Rondout-West Branch Tunnel (RWBT) portion of the Delaware Aqueduct is 45 miles (72 km) long. The New York City Department of Environmental Protection (NYCDEP) first identified suspected areas of leakage from the RWBT in the 1990s. A $1 billion project is underway to mitigate the leakage through the construction of a bypass tunnel around the area of most severe deterioration, a 2.5-mile (4 km) section located beneath the Hudson River. Two shafts, 800 and 900 feet (244 and 274 m) below the ground surface, are being sunk to support the tunnel construction. The deep shafts will be subjected to high groundwater pressures and have been designed to accommodate multiple tunnel portals. This paper discusses the engineering decisions and analyses leading up to the final design. INTRODUCTION Project Background The New York City Department of Environmental Protection (NYCDEP) provides over 1 billion gallons (3.7 billion liters) of water to over 9 million residents of the City of New York and surrounding communities each day. This water is stored in upstate reservoirs and conveyed to the City via a system of aqueducts and tunnels. Water is delivered to the City almost completely by gravity and consists of three systems: the Croton, the Catskill, and the Delaware. The Delaware System is the largest of the three and supplies between 50% and 70% of the City’s daily water supply. In the 1990s, the NYCDEP discovered leaks in the central 45-mile-long (72 km) portion of the Delaware Aqueduct known as the Rondout-West Branch Tunnel (RWBT). The leaks release between 15 and 35 million gallons per day (MGD) (132.5 million liters per day) and are concentrated in two areas near Wawarsing and Roseton, New York. As part of the Rondout-West Branch Bypass Tunnel and Wawarsing Repairs Project (Bypass Tunnel Project), the leaks in the Wawarsing area will be repaired by grouting from inside the existing RWBT, and the leaks in the Roseton area will be mitigated by constructing a bypass tunnel parallel to and 1,750 feet (533 m) north of the leaking portion of the existing RWBT. Two deep shafts will be excavated on either side of the Hudson River: Shaft 5B in Newburgh and Shaft 6B in the Town of Wappinger."

Jan 1, 2016

By J. D. Miller

"It is now possible to use 3D X-ray tomography analysis for plant-site characterization of coarse particles at a sampling rate of about 3 kg/min for particles which range in size from 150 mm to 1 mm at a voxel resolution of about 150 microns. This is quite a significant advance in X-ray tomography technology and should be useful for plant-site coarse particle characterization (size, shape, composition, density, texture, grain exposure, mineral liberation) with a response time of minutes after receiving the sample. Applications in the mineral industries are discussed including the coal industry, aggregate industry, metal mining and the processing of industrial minerals. INTRODUCTION Plant-site characterization of coarse particles at coal preparation plants, crushed stone/aggregate plants, and mineral processing plants is needed to improve plant capacity, product quality, and/or process efficiency. Not much on-line coarse particle characterization is done at these plants. Some limited information regarding particle size is obtained on-line from reflected light images using systems such as the OPSA, Split, and WipFrag analyzers. Even laboratory analysis of coarse particles has been difficult because of the large amount of sample required to insure statistical significance of the results. During the past decades laboratory 3D characterization of particles from energy and mineral resources by X-ray tomography has been demonstrated and used to good advantage [1, 2]. 3D X-ray tomographic analysis had its origin in the medical services industry; it is used to provide internal images of the human body and now has also been developed for non-medical applications [3]. Figure 1 shows a schematic diagram for the cone-beam geometry micro-CT system. In our case X-rays from a microfocus X-ray generator are partially attenuated by the sample (a packed bed of particles) that is made to rotate in equal steps in a full circle about a single axis of the particle sample. At each rotational position, the surviving X-ray photons are detected by a planar two-dimensional array (image intensifier) large enough to contain the shadow of the specimen. These two dimensional projection images are collected using conventional video technology. The video signal for each projection is then converted to a two-dimensional digital array by an image processing system. Finally, a three-dimensional image is reconstructed from the collected set of projection images. With the availability of automated high speed X-ray tomography [4] it now seems possible to do plant-site particle characterization at a sampling rate of about 3 kg/min for particles which range in size from 150 mm to 1 mm at a voxel resolution of about 150 microns. This is quite a significant advance in X-ray tomography technology and should be useful for plant-site particle characterization (size, shape, composition, density, texture, grain exposure, mineral liberation) with a response time of minutes after receiving the sample. Applications in the mineral industries are discussed including the coal industry, aggregate industry, metal mining, and the processing of industrial minerals"

Jan 1, 2016

By G. Hoffmeyer, I. Ream

"Several copper projects exclusively utilizing in-situ recovery methods are currently under development in Arizona. Favorable conditions for In-Situ Copper Recovery (ISCR) include a saturated orebody, fracture hosted mineralization, hydraulic conductivity sufficient to effectively inject and recover solutions using wells, and a relatively flat background hydraulic gradient. Safe operation of an ISCR project requires that the operator have the ability to induce and maintain localized hydraulic gradients, thereby controlling the movement of injected and recovered solutions. Benefits of ISCR include reduced initial capital, and a greatly reduced environmental footprint. THE ISCR METHOD EXPLAINED The method chosen to extract a mineral from a deposit is driven by characteristics such as its size, grade and depth of burial. Large lower grade deposits that require significant excavation to access using surface methods are potential candidates for in-situ recovery. ISCR may also be ideal for smaller deposits due to the lower initial capital. However, regardless of the size of the deposit, certain hydrogeologic conditions must be present for ISCR to be successful. In-situ recovery methods do not require excavations of rock from the surface or underground, resulting in a dramatic reduction in surface disturbance when compared to conventional mining. With the ISCR method, what is visible above ground is the processing plant, well heads, piping, process solution impoundments and evaporation ponds. There are no waste rock piles, tailings impoundments, leach pads, or impacts associated with blasting and hauling. Other benefits include reduced initial capital, reduced dust and noise, and lower water use. Early testing of the in-situ copper recovery method by Occidental on the Van Dyke deposit east of Phoenix and by Kennecott at Safford Arizona in the 1970s produced encouraging results, but the permitting regime for a large-scale operation was not yet in place. Additional testing and commercial application of in-situ copper recovery techniques have expanded since the 1980s, most commonly in conjunction with open pit or underground mining operations. For example, several operations in Arizona (San Manuel, Miami East and Tohono) have used in-situ techniques to extract additional copper following conventional mining from parts of the deposits adjacent to open pits or underground workings. Where the rock has been broken up by conventional methods, the method is called “in-place” leaching. The US government has also been involved in assessing in-situ techniques. For example, joint research was conducted by the US Bureau of Mines and industry on the Santa Cruz deposit in Arizona; and both federal and state agencies have been involved to establish the comprehensive permitting regime that exists today. Currently there are several projects in Arizona being evaluated as stand-alone ISCR operations."

Jan 1, 2016

By Zorigtkhuu Davaanyam, Fisher Wang, Bern Klein, Amit Kumar

"The High Pressure Grinding Roll (HPGR) is an increasingly popular energy efficient solution for comminution of competent ore deposits that primarily competes with conventional crushers and tumbling mills. A significant barrier to increased adoption of HPGRs is the requirement for large amounts (one tonne or more) of sample for pilot testing which may not be feasible for most early staged projects.Various researchers have worked towards developing piston-die and JK drop weight tests to model and predict the energy requirements for an HPGR. Two small scale laboratory test procedures (the SMC test (Morrell, 2009) and the piston press tests (Davaanyam, 2015)) have been developed in recent years to provide necessary information to size an HPGR.These two methods were used to estimate the required specific energy for an HPGR unit and compared to HPGR pilot scale test results from a copper deposit. The comparison provides insight into the benefits and limitations of these tests.INTRODUCTIONHigh pressure grinding rolls (HPGR) have gained popularity in recent years because of their energy efficiency in comminution. Various researchers have suggested that approximately 50–80% of the total energy consumed in a mineral processing plant is used by the comminution equipment (Haque, 1999; Abouzeid & Fuerstenau, 2009; Wang, 2013). Haque (1999) showed that the efficiency of grinding equipment can be as low as 1%. Due to the energy intensive nature of comminution, mining industry has been forced to explore alternative energy efficient processes.An HPGR based circuit has been shown to be 10–25% more energy efficient than a conventional SABC circuit (Von Michaelis, 2009; Wang, 2013). A significant barrier to the increased adaptation of HPGRs is the requirement for a large amount of sample for pilot testing (up to 5 tons), even on a prefeasibility level. Numerous studies have been performed to utilize piston press test to analyze the performance of the HPGR circuit and to predict the energy consumption for an industrial application. This paper uses two small scale laboratory test procedures, the SMC test and a piston press test, to compare the energy requirement to the pilot HPGR data."

Jan 1, 2016

By Aydin Shaterpour Mamaghani, Cemal Balci, Nuh Bilgin, Mucahit Namli, Hanifi Copur

"It is expected that more than 10 Billion USD will be spent in Istanbul in coming years on tunnel boring especially with EPB-TBMs. However, the geology of Istanbul is very complex. Geologic formations changing from Paleozoic to Cenozoic ages cause tremendous problems due to frequently changed rock formations and andesite and diabase dykes. This paper summarizes a universal model to predict the performance of EPB-TBMs which is created upon the data base collected from several projects. The model first is based on predicting field specific energy and power consumed of TBMs using geo-mechanical properties of the excavated material and TBM diameter. Later net production rate is calculated using field specific energy and power consumed by TBM. A methodology to predict machine utilization factor permits to calculate daily advance rates. The validity of the model is tested using the data obtained from two recent metro tunnel projects. 1. INTRODUCTION It is expected that in a near future a total length of 400 km will be excavated in Istanbul in a complex geology. Selecting proper tunneling equipment, organizing an effective operational management with the right tunneling crew will be a major concern for an efficient scheduling of the future projects necessitating to create a model to estimate daily advance rates. Several TBM performance prediction models with few on the prediction of machine utilization time were realized in the past. However, there is quite limited number of research studies on predicting the performance of EPB TBMs. Specially predicting daily advance rates in complex geology, in mixed face, in fractured rocks, in transition zones etc. are in big concern (Namli et al. 2013, 2014). The first experiences in Istanbul with a gripper type TBM was a nightmare, roof collapses caused big delays in tunnel excavation (Bilgin 1993). A typical example to EPB-TBM was Kadikoy-Kozyatagi tunnel, changing TBM from opened mode to closed mode with few modifications on the cutterhead resulted a tremendous increase in the daily advance rates (Bilgin et al. 2009). The data collected from several tunnelling projects served a basis to create a model to predict daily advance rates of EPB TBMs. Within the frame of a research program the validity of the model was tested in Uskudar-Umraniye–Cekmekoy-Sancaktepe metro project and very recently in Mecidiyekoy-Mahmutbey project."

Jan 1, 2016

By M. Leahy

"Very little is known about the large scale fluid dynamics and associated distribution of copper in an operating electrowinning cell, yet they will have a major influence on mass transfer and plating quality. The CFD model in this work is used to simulate an entire EW cell with 60 cathodes and 61 anodes, or 121 anode–cathode pairs, elucidating for the first time the three-dimensional (3D) flow and copper distribution in an industrial cell. Two methods for the distribution of electrolyte are modelled:1. Downcomer method: electrolyte is fed by a downcomer at one end of the cell, overflowing at the opposite end.2. Manifold method: a horizontal manifold pipe runs the whole length of the cell and feeds electrolyte via small holes in the top of the manifold pipe.The recirculation that develops within each anode-cathode pair, driven by oxygen bubble generation on the anode, is similar to that seen previously in two-dimensional models of single anode–cathode gaps. However a more complex 3D flow recirculation is established, which involves flow of electrolyte down the side gaps (being a path of low resistance for return flow) as well as the usual return flow down the cathode side of each pair gap. The bubble-driven flow is not influenced by the mode of electrolyte distribution.The electrolyte flow due to the manifold and downcomer is somewhat secondary to the bubble driven flow. In the case of the downcomer distribution mode, the high injection velocity causes a very turbulent flow in the first 1–2 m down the cell from the downcomer, with several large vortices developing. This may lead to some sludge particles being entrained into the bulk of the cell.In the manifold pipe case, the jet from each hole is dissipated very quickly, within the first 10–20 cm. The jets are directed into the downward flowing zone of the bubble-driven recirculation, which leads to unstable and periodic behaviour on a large spatial scale.In both the manifold and downcomer cases, there is a marked two-zone vertical stratification in copper concentration."

Jan 1, 2016

By Gregory E. Smith

"Tensionable headed roof bolt systems are common in the U.S. mining industry. In the last 15 years or so, they have made a comeback as a hybrid system where a mechanical anchor is used in conjunction with resin. When such a system is used, it is common to use a spherical washer to comply with the requirements of 30 CFR Part 75.204(f)(8). This standard requires an angle-compensating device be used in installations where the bearing plate is offset from the roof bolt axis by an angle greater than five degrees. This paper evaluates system performance of four different traditional angle-compensating device/plate combinations including a new patented extruded plate/extruded washer system that improves overall load capacity and stretch.INTRODUCTIONA large western U.S. underground coal mine was using a fully grouted headed rebar system as their primary support. They had developed their component specifications over many years of working with suppliers to improve and optimize these components to integrate well as a system. As shown in Figure 1, the components included a patented 7 /8"" -diameter Grade 60 headed rebar bolt with a flange capable of full bar load (Walker, 2009) and a patented 8 in x 8 in Grade 3 extruded hole bearing plate manufactured by DieMatic Corporation.The mine decided to pursue a fully grouted tensionable system using a mechanical anchor as the tensioning device. Their primary goal was to eliminate the need for the roof bolt operator to secure (hold) the bolt during resin set time. An additional benefit was the increased initial tension on the bolt. To comply with the requirements of 30 CFR Part 75.204(f)(8), regarding tensioned roof bolts, they were required to include an angle-compensating device because a share of the bolt population would be installed at angles greater than five degrees from the perpendicular to the bearing plate. Also, to improve cycle time and torque/tension consistency, the mine desired to have the washers and anchors assembled at the factory. This required the use of a bearing plate with a center hole large enough to accommodate the 1-3/8-in-diameter mechanical anchor to pass though it during assembly by the roof bolt operator. The mine wanted to continue to use an extruded hole bearing plate in the tensionable system, and EMS was asked to propose a plate and angle-compensating device."

Jan 1, 2016

By J. C. Barry, J. H. van Laar, P. L. Crouse, H. Bissett, I. J. van der Walt

"Plasma-assisted spheroidisation of metal powders offers several technical advantages with respect to both the ease of materials handling and powder-metallurgical item manufacturing. Advantages include improved flowability, increased powder packing density, elimination of internal component cavities and fractures, changes in morphology resulting in decreased friction between particles and contamination during pneumatic transport and enhanced particle purity. In this empirical study, spherical iron particles were produced using a microwave plasma operating at atmospheric pressure and characterized using optical microscopy and SEM techniques. Iron powders were fed into the system at fixed operating conditions, resulting in particles with spherical structures. The theoretical estimate of the time required for melting to occur is 1.6 ms, an order of magnitude smaller than the actual residence time. IntroductionParticle design and functionalization has become an increasingly popular aspect of materials synthesis and powder-metallurgical item manufacturing. One such technique involves the spheroidisation and densification of feed materials, typically in the form of chemical powders with wide particle size distributions. The major benefits of powder spheroidisation include improved powder flowability, increased powder packing density and powder purity, reductions in internal voids and defects, as well as the ability to manipulate the particles surface morphologies (Boulos, 2004). Thermal plasma processing has the potential for scale-up and for producing industrial quantities of spheroidised powder.Thermal plasma technologies offer a wide spectrum of material synthesis and treatment options, amongst others the synthesis and spheroidisation of nano-sized ceramic and metal particles (Kumar and Selvarajan, 2006). The spheroidisation process occurs within the plasma discharge via in-flight heating and melting of the powder feed material, given high enough plasma temperatures (Fridman, 2008, p. 495). Surface tension in the molten droplets results in spherical, or nearly, spherical, powder particles being formed upon exiting the plasma discharge where the droplet undergoes rapid cooling and freezes. Quite often, the bulk density of these spherical particles is higher than that of the starting material (Boulos, Fauchais and Pfender, 2013, p. 42). The different plasma spheroidisation techniques reported include radio frequency (RF) induction thermal plasmas (Jiang and Boulos, 2006; Karoly and Szepvolgyi, 2005; Yuming, Junjie and Yanwei, 2013), nontransferred direct current (DC) thermal plasmas (Chaturvedi et al., 2014; Kumar and Selvarajan, 2008; Suresh, Selvarajan and Vijay., 2008) and microwave-assisted plasma processing methods (Chen, Gleiman and Phillips, 2001; Vanamu et al., 2004; Weigle et al., 2004)"

Jan 1, 2016

By M. Saghaeian, R. Hejazi, Fakoor Sanat Tehran Company, H. Abedini, M. Zare

"Dewatering of final tailings is one the biggest issues in iron ore processing plants. Because of the fine and hydrophilic particles in the iron ore tailings, dewatering of such material is difficult and, in most of the cases, needs to be processed using expensive and complicated equipment. In this study, a novel method based on classification of small and large particles has been proposed to improve the dewatering performance of iron ore tailings. In the proposed method, a hydrocyclone has first been used to separate the fine and coarse fraction of iron ore tailings. Then, the coarse fraction (hydrocyclone underflow) is easily dewatered by using vacuum belt filter. Then, the fine fraction (hydrocyclone overflow) is primarily dewatered by using a high rate thickener. Finally, the thickener underflow is added to the bed of solids on the same belt filter, which is used for dewatering of hydrocyclone underflow. The efficiency of this method has been compared with other solutions for tailings dewatering including changing vacuum filtration parameters, using fabric with larger pore size, and using pressure filtration, all through laboratory scale experiments on the tailings of an iron ore processing plant in Iran. The results indicated the superiority of this method compared to the other ones, which increased the specific filtration capacity of the tailings by around 46%.INTRODUCTIONWet beneficiation of minerals requires a substantial amount of water to enhance the efficiency of the process. Used water should be recovered at the end of process to minimize shipping costs, meet contract specifications, and reuse process water (Wills and Napier-Munn, 2006). Dewatering equipment is usually divided into sedimentation (thickening) and filtration (pressure and vacuum) equipment, the choice of which depends on particle size, solid content of slurry, and material nature (Mular et al., 2002)."

Jan 1, 2016

By Karsten Zimmermann, Peter Cain

"To receive regulatory approval for a new coal mining operation in North America, extensive investigations of feasibility and potential environmental impacts, including ground deformations, are required. Figure 1 shows pictures from mine sites and an example mine map with the planned panel layout for one seam of the multi-seam longwall operation considered.The cumulative mined coal thickness of 22 meters in some areas of the operation requires a comprehensive forecast of expected ground movements and subsidence impacts (e.g., subsidence, slope, displacement, curvature and strain). In the frame of the impact study, the prediction of these impact factors was conducted by DMT using the computer program SPS 4D, based on the Ruhrkohle modeling method by Ehrhardt and Sauer (1961).This paper briefly presents the modeling method and explains the benefits and possibilities for its international application. Information gathered from literature studies on subsidence in North America were incorporated into the initial model parameterization. The article shows the ways in which the observed influences of mountainous topography on surface displacements and deformations can be considered by an extension of the subsidence prediction model and integration of DEM information.SUBSIDENCE MODELFor the calculation of mining-induced subsidence and deformation, DMT has developed subsidence prediction software SPS 4D, which is built according to the stochastic prediction model by (Ehrhardt and Sauer, 1961). The model is based on the subsidence theory by (Knothe, 1953) with a specific parametrization of the stochastic influence function and includes enhancements for dynamic subsidence calculations after (Sroka, 1978). In Europe, mainly in Germany and Poland, the model is approved by the authorities as a standard model for subsidence prediction in mining areas. However, extensive research within R&D activities has shown the possibility to predict mining-induced subsidence considering the specific mining conditions in North America (Zimmermann and Fritschen, 2007)."

Jan 1, 2016

By M. Walawalkar, C. K. Nichol, G. Azimi

Rare earth elements (REEs) are essential to the production of technologically advanced products, including wind turbines, electric and hybrid cars, automotive catalytic convertors, hand held electronic devices, and military defense systems. Their application in environmentally beneficial technologies puts them at a high priority for ameliorating environmental concerns. Because of their increasingly high demand and limiting resources, it is highly beneficial to find new sources for them. The present study is focused on leaching REEs from a phosphate based fertilizer by-product, known as phosphogypsum (PG). Global estimated world production of PG is about 240 million tonnes that is stored in the form of wet stacks adjacent to fertilizer production facilities, occupying vast amounts of land. PG also contains trace metals, which are detrimental to the environment, and hence it is crucial to monitor these stacks. We obtained our PG sample from Agrium Inc. (a fertilizer manufacturing company in Canada). We performed a comprehensive characterization of the PG sample and found that it predominantly contains Y, La, Ce, Nd, and Sm. For leaching purposes, we used hydrometallurgical acid leaching techniques. We investigated three acids over a range of operating conditions such as acid concentration, temperature, solid-to-liquid ratio, and residence time. We achieved an average leaching of 81% with hydrochloric acid as leachant using operating conditions that can be easily replicated in industrial settings. If our process is implemented, not only will it reduce the size of the existing PG stacks (mitigating their environmental risks), but also enable the development of new innovative routes for extracting REEs, making countries like Canada less vulnerable to supply disruptions.

Jan 1, 2016

"The main purpose of geometallurgy is to develop a model to predict the variability in the mineral processing performance within the ore body. Geometallurgical tests used for developing such a model need to be fast, practical and inexpensive and include as an input data relevant and measureable geological parameters like elemental grades, mineral grades and grain size. Important in each geometallurgical program is to define the number of samples needed to be sent for geometallurgical testing to enable reliable metallurgical forecast. This is, however, a complicated question that does not have a generic answer.To study the question on sampling a simulation environment was built including a synthetic ore body and sampling & assaying module. A synthetic Kiruna type iron oxide - apatite deposit was established based on case studies of Malmberget ore. The synthetic ore body includes alike variability in rock types, modal mineralogy, chemical composition, density and mineral textures as its real life counterpart. The synthetic ore body was virtually sampled with different sampling densities for a Davis tube testing, a geometallurgical test characterising response in magnetic separation. Based on the test results a forecast for the processing of the whole ore body was created. The forecasted parameters included concentrate tonnages, iron recovery and concentrate quality in terms of iron, phosphorous and silica contents.The study shows that the number of samples required for forecasting different geometallurgical parameters varies. Reliable estimates on iron recovery and concentrate mass pull can be made with about 5-10 representative samples by geometallurgical ore type. However, when the concentrate quality in terms of impurities needs to be forecasted, the sample number is more than 20 times higher. This is due to variation in mineral liberation and shows the importance of developing techniques to collect qualitative information on mineral and ore textures in geometallurgy."

Jan 1, 2016

By Minghao Hu, Hongbo Zhao, Jun Wang, Wenqing Qin, Rui Liao, Central South University

"In the present work, X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) analysis and electrochemical analysis were carried out to investigate the intermediate species and electrochemical dissolution process of chalcopyrite in the presence of sulfur and iron oxidizing microorganisms. For bioleaching of chalcopyrite by the sulfur oxidizing microorganism Acidithiobacillus caldus, the redox potential was always lower than the appropriate value and chalcopyrite was mainly directly oxidized to polysulfide (Sn 2-), thus resulting in low copper extraction. As for bioleaching of chalcopyrite by the iron oxidizing microorganism Leptospirillum ferriphilum, chalcopyrite was mainly directly oxidized to polysulfide at the initial stage where redox potential was lower than the appropriate value and resulted in low dissolution rate. At the middle stage where redox potential was appropriate (about 350–480 mV vs. Ag/AgCl), chalcopyrite was mainly transformed to intermediate species of Cu2S rather than polysulfide, thus resulting in high dissolution rate. At the later stage where redox potential was higher than the appropriate value, chalcopyrite was mainly directly oxidized to polysulfide which caused the later passivation of chalcopyrite. Finally, a model of electrochemical dissolution process of chalcopyrite in the presence of sulfur and iron oxidizing microorganisms was provided.INTRODUCTIONBiohydrometallurgy is considered as one promising mineral processing technique in processing low grade ores due to the advantages of simplicity, low cost and eco-friendly. Chalcopyrite (CuFeS2) is the most abundant copper-bearing resource, accounting for appropriately 70% of the known reserves in the world, while is recalcitrant to bio-hydrometallurgy mainly due to the coated passivation layer (Klauber, 2008; Li, Kawashima, Li, Chandra, & Gerson, 2013). However, the detailed dissolution and passivation mechanisms of chalcopyrite bioleaching are still uncertain. The microorganisms assisting chalcopyrite dissolution can be mainly classified into three types, including mesophilic microorganisms (e.g., Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans), moderately thermophilic microorganisms (e.g., Acidithiobacillus caldus, Sulfobacillus thermosulfidooxidans and Leptospirillum ferriphilum), and extremely thermophilic microorganisms (e.g., Metallosphaera sedula, Sulfolobus sp., Acidianus sp., and Sulfurcoccus mirabilis). Moderately thermophilic microorganisms have a better prospect in the future industrial application of chalcopyrite bio-hydrometallurgy (Olson, Brierley, & Brierley, 2003; Rohwerder, Gehrke, Kinzler, & Sand, 2003). Hence, investigating the detailed dissolution and passivation mechanisms of chalcopyrite bioleaching by moderately thermophilic microorganisms is of important significance, which will provide essential information for promoting chalcopyrite bioleaching by moderately thermophilic microorganisms in laboratory or industrial plant."

Jan 1, 2016