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By A. Noble, R. Q. Honaker, J. Werner

Recovery of rare earth elements (REE) from coal-related resources has recently received significant interest due to supply concerns and their key roles in critical industries and defense-related technologies. An integrated flowsheet consisting of sorting, crushing/grinding, physical separation, acid leaching, solvent extraction, and selective precipitation was designed to achieve continuous production of rare earth products from various coal-related resources such as coarse refuse and acid mine drainage. A pilot plant was constructed that enabled continuous testing of the circuitry on a range of different coal-based feedstocks. Despite achieving significant success in producing high-grade rare earth oxide products, low REE recovery values and high operational costs necessitated a re-evaluation of the process flowsheet. This article describes the circuitry improvements that were based on both laboratory and pilot plant test results. Roasting as a pre-leach treatment was found to significantly improve the leaching rate and overall REE recovery values. After roasting West Kentucky No. 13 and Fire Clay coal refuse materials at 600 °C, REE recovery increased by 60 and 40 absolute percentage points, respectively. Rare earth concentration in the pregnant leachate solution (PLS) was increased to around 700 ppm prior to solvent extraction using a staged precipitation method. REEs in the precipitate were re-dissolved, purified, and extracted from the PLS using solvent extraction and selective precipitation to values of around 80%. As a result of the improvements, chemical consumption in the acid leaching and solvent extraction processes was significantly reduced. A techno-economical assessment of the improved flowsheet indicated significant commercialization potential.

By Erich J. Jacob

In the past 15 years the enforced improvement of the public traffic systems caused a boom in urban tunnel construction. In 1961 the City of Paris started to build the Express-Metro. Of the 47 km long double-track line crossing the city center, nearly 45 km are in operation since 1971. Still missing is here only an about 2.6 km long connecting stretch, which is under construction now. From 1963 to 1969 the 21.8 km long Victoria Line was built in London as extension of the existing network,. A little later, in the years 1965 to 1973, the City of Hamburg supplemented its subway network by the construction of a 16.8 km long line between the Boroughs of Billstedt and Stellingen. Also in 1965 the City o Munich started to build a subway system of 54 km f length. Thereof a stretch of 16.2 km could be taken into operation in 1972 shortly before the Olympic Games. These are only some of the better known projectsas examples of the activities in European cities. In nearly all cities with more than about ½ million inhabitants subsurface traffic lines were begun or supplemented. Furthermore, numerous undercuts or other subsurface structures were built. The Ij Tunnel in Amsterdam and the new Elbe Tunnel in Hamburg may be mentioned, both structures finding international attention.

Jan 1, 1976

By James J. Kabat, James A. McDonald

Impregilo/SA Healy JV recently completed this Project using the first slurry shield TBM’s in the United States. The Project used two TBM’s to mine 18,000 feet in sands, gravels, and silty alluvial materials under the Willamette River and downtown Portland, Oregon. This paper discusses alignment and geological conditions, equipment selection and plant setup, and tunnel excavation means and methods, parameters, and results. Extensive hyperbaric operations were required and will also be discussed.

Jan 1, 2007

The MineSight Schedule Optimizer (MSSO) is a new production scheduling tool developed by Mintec, Inc. using mixed integer linear programming (MILP) techniques. This tool was developed to solve the short- and medium-term schedule problems for surface and underground mining operations that involve multiple mining areas, multiple processes, multiple destinations and blending requirements. MSSO finds the optimum schedule in each period that achieves the objective while satisfying comprehensive product quality and quantity requirements as well as physical and technical constraints. Using the MineSight Planning Database (MSPD) as a central data hub, MSSO seamlessly works with MineSight 3-D (MS3D) block models and third-party data, MineSight Interactive Planner (MSIP), MineSight Haulage (MSHaulage) and MineSight Activity Planner (MSAP) to prepare data, formulate MILP models, calculate, report, fine-tune, save and visualize schedules. This paper presents the features and capabilities of MSSO. A case study is also given to demonstrate the applications of this new tool.

Jan 1, 2009

By Z. T. Bieniawski, José Miguel Galera, Benjamín Celada

TBM case histories from over 400 tunnel sections are analyzed presenting a comprehensive application of the Rock Mass Excavability (RME) index (Bieniawski et al.2006). The paper introduces two new adjustment factors, called the Factor of Tunnel Length and the Factor of Crew Effectiveness, which were established to represent more realistically the interaction of the rock mass characteristics, the TBM parameters and the performance of the crew operating the machine. A new correlation is provided for predicting the average rate of advance of double-shield TBMs working specifically in the double-shield mode.

Jan 1, 2007

By Mohamed A. Younis, Paul J. Headland, Paul H. Madsen, Vojtech Gall

INTRODUCTION A 100 ft long, 20 ft high and 18 ft wide NATM tunnel was excavated through grouted clean sands beneath a busy city street, including a variety of existing utility lines. The new tunnel associated with a hospital expansion will serve as a pedestrian tunnel connecting a parking structure with a new hospital facility. Tunnel construction started on December 15, 2005 when drilling for the grouting program started and was completed on May 26, 2006 when the tunnel final lining was completed. The tunnel was constructed by Kiewit Construction Company as a tunnel subcontractor to The Christman Company who is constructing the hospital facility for Spectrum Health in Grand Rapids, Michigan. URS was the project designer. GallZeidler Consultants, LLC were the contractor’s NATM consultant. PROJECT DESCRIPTION The Michigan Street Pedestrian Tunnel is a component of the Michigan Street Development located along the north side of Michigan Street NE between Coit Avenue NE and North Division Avenue in the downtown area of the Grand Rapids, Michigan. The Michigan Street Development includes a parking deck and four new towers to be constructed over the proposed parking deck. The tower planned furthest east is being developed by Spectrum Health as the Lemmen-Holton Cancer Pavillion. The purpose of the pedestrian tunnel is to connect the proposed Lemmen-Holton Cancer Pavillion with the future Spectrum building to be located on the south side of Michigan Street NE. The southern end of the tunnel was constructed with a bulkhead until the future Spectrum building is constructed at which time interconnection will be required. The tunnel site plan and profile are shown in Figure 1, Site Plan, and Figure 2, Tunnel Profile. Several challenges were faced during the design and construction of the Michigan Street Pedestrian Tunnel. These challenges included compressed design and construction schedule, maintenance of traffic and protection of old underground utilities. The tunnel was being constructed as part of the Michigan Street Development and coordination with other concurrent construction activities was required. The tunnel was constructed within a specified window of time to allow other associated construction activities to take place without compromising the overall project schedule. The design started in June 2005 and construction was completed by June 2006.

Jan 1, 2007

The more than 40,000 mining industry professionals that are expected to attend the National Mining Association’s(NMA) MINExpo International2000 trade show and conference will be treated to the exhibition’s largest display ever. The exhibit is expected to cover more than 60,385 m2(650,000 sq ft) and feature more than 1,300 exhibitors. The event is set for Oct. 9-12, 2000 at the Las Vegas Convention Center in Las Vegas, NV. Richard L. Lawson, NMA’s president and chief executive officer, said, “MINExpo 2000 will showcase everything that mining is proudest of. This is the largest premier mining exposition in the world.” MINExpo is held every four years.

Jan 1, 2000

By Paul Eger

The use of wetlands to treat mine drainage has become increasingly common, particularly as more information is available on their operation and construction. However, the lifetime of each system is still, at best, an estimate. Treatment lifetime depends on the types of processes that provide the majority of the metal removal. Anaerobic systems (vertical flow systems) rely primarily on sulfate reducing bacteria, which reduce sulfate to sulfide and generate alkalinity. Metals can be precipitated as sulfides, and acidity is neutralized. These systems can remove over 90% of the metals and increase pH from around 4 to over 7. The bacteria will remain active as long as the system remains anaerobic and contains an adequate supply of sulfate and small chain organics. Although estimates of lifetime made on the total carbon in the system suggest that lifetime should exceed 20 years, data from field and laboratory studies show that the rate of sulfate reaction decreases with time, and that after several years rates decreased substantially. To maintain acceptable treatment, either additional organic material must be added or the total metal and acid load to the system would need to be reduced substantially. Aerobic systems (overland flow wetlands) can effectively remove metals from neutral mine drainage by reactions with organic material in the substrate. Over 90% of the copper and nickel have been removed in aerobic systems treating mine drainage in Minnesota. The primary removal processes in these systems include adsorption, ion exchange and complexation, which are finite; removal will cease unless new removal sites are generated. Two wetlands built in Minnesota have been successfully treating mine drainage for 12 years. At one of the wetlands, the annual production of new removal sites has been estimated to be equal to the annual metal input, and, as a result, metal removal should theoretically continue indefinitely.

Jan 1, 2005

By Verya Nasri

The proposed Second Avenue Subway Project in New York City is approximately 8.5 miles long, up to a depth of 120 feet beneath grade and runs the length of the eastern side of the island of Manhattan from Harlem in the north to the financial district in the south. It will reduce overcrowding and delays on the existing parallel line, improving travel for both city and suburban commuters, and upgrading access to mass transit for residents of the East Side of Manhattan. This subway line will have 16 new stations providing transfers to the existing Metro-North commuter rail service and to New York City Transit subway lines and bus services. The first phase of construction includes two TBM rock tunnels 2.4 miles long and two new large and shallow rock cavern stations with clear span openings ranging from 70 to 100 feet and length in excess of 1000 feet with 615 feet center platform, coupled with low rock cover ranging from 20 feet to 40 feet. The design methodology for these large and shallow rock caverns consists of using well known empirical methods for initial estimate of support requirements and then two and three dimensional continuum and discontinuum analyses for verification of the selected excavation sequence and support system. This paper describes the analysis and design methodologies used for the two large and shallow rock caverns with insight into how to overcome the design complexities and construction challenges of the urban underground.

Jan 1, 2008

By W. David Tyler

Any mining or engineering-construction excavation that extends below the water table must be dewatered. In many situations, the ground is of low permeability or the workings extend only a short distance below the water table. So water removal can be handled easily and economically by using mobile centrifugal pumps. However, there is an increasing number of mines that have a continuous high flow of water into the workings. Controlling this flow can significantly increase the cost of ore production. Successful implementation of any major dewatering scheme will ultimately rely on a clear understanding of the local geology. This understanding is necessary before an interpretation of ground water conditions can be made. It will dictate which dewatering methods are feasible. Once the geology and the ground water system are known, the scope and timing of the dewatering measures can be varied with the mine plan. Ground water modeling can assist in optimizing the dewatering system, though the precise objective of each model should be clearly defined. Production wells must be sited and drilled so that individual well efficiencies are high. Any lost efficiencies will translate into higher operating costs. Each well must be designed for maximum long-term control of the water table, and pumps sized to operate under continually changing heads. Finally, the investment in each production well must be protected during the mining process.

Jan 1, 1991

? The economic health and national security of the U.S. depends on the continued availability of, and access to, reliable and affordable energy and mineral resources. However, America is hindered by a costly, inefficient and often redundant regulatory structure that thwarts domestic investment, expansion and job creation. The annual cost of federal regulations in the U.S. increased to more than $1.75 trillion in 2008; averaging $8000 per employee.(The Impact of Regulatory Costs on Small Finns, SBA, 2010) ? The complexity, uncertainty and delays within the current permitting system places the U.S. at a competitive disadvantage with many other countries that have both abundant mineral resources and a more welcoming business and regulatory climate. As a result, American and international mining companies often move overseas or across borders to invest capital, create local employment, and produce the critical minerals America must then import at higher cost, while sacrificing employment and economic stimulus. ? According to Behre Dolbear, the U.S. is ranked lowest globally due to the lengthy permitting period required before mine development can commence. (Where not to Invest, 2010).

Jan 1, 2011

By António Fiúza, Anthony Danko, Patrícia Leitão, Aurora Futuro, Cristina Vila, Lurdes Dinis

The average global recovery rates for processing scheelite ores by physical methods are normally in the range 50 to 70%, and it is problematic to attain a minimum grade of 60% WO3 in the concentrates without penalizing further this yield. Direct hydrometallurgical processing of low-grade concentrates or medium- to high-grade ores may become an interesting global economic alternative as it allows increasing the recovery rate, avoiding major penalizations due to the grade of the concentrate and increasing the added value of the final product. Leaching of scheelite by sodium carbonate presents several advantages such as its selectivity regarding the dissolution of troubling metals like iron and aluminium, allowing for a simple and flexible process diagram. However, it has the disadvantage that it is performed at high temperature and pressure with a high consumption of reagents. The feasibility of leaching is appraised by the extraction yield and selectivity, but also by the operating cost. Considering these aspects, a relevant objective of the research was to transform alkaline pressure leaching into a feasible processing alternative directly applicable to both medium- and high-grade ores and simultaneously to low- and high-grade concentrates produced by physical methods. The research used ore samples and low-grade concentrates from a typical skarn orebody as well as high-grade concentrates from a chalcopyrite-scheelite orebody. Different operating conditions were tested. Temperature, pressure and reagent concentration showed to be fundamental, but not exclusive, in determining the leaching behaviour. The operating conditions are milder than the ones generally proposed in the literature or currently in use in industry, but with higher carbonate consumptions. The research was oriented towards potential industrial implementation allowing for the application of optimization methods and straight scale-up to pilot-plan design and project.

By C. Slotta, F. Charlier, P. Blomen

"Within the energy concept of the German government, the operating time of nuclear power plants was initially extended from about 8 to 14 years. It is planned, however, that every power plant will gradually be decommissioned until 2025 and that simultaneously the amount of renewable energies will successively be expanded. According to the political state, nuclear energy is a discontinued model. Looking at the global energy market, though, an obviously opposed development can be observed. At the moment, 443 nuclear power plants are running worldwide and further 62 facilities are being built. These about 500 nuclear power stations have to be supplied with nuclear fuel right now and in the future. The present paper will describe the worldwide use of nuclear energy, the extraction of the nuclear fuel uranium and in detail the available and predicted resources of uranium. The conclusion of the paper is the statement that uranium as nuclear fuel is no scarce resource but sufficiently available."

Jan 1, 2011

By W. L. Jacobsen, T. L. Dyer

Cortez Gold Mines is completing a Feasibility Study for a new open pit gold mine in north central NV. The production schedule calls for a peak in material movement. This schedule is based on current operational efficiencies and equipment parameters observed at the company’s existing open pit operation. To mitigate risks of over/under predicting production, simulation modeling was used to validate the loading and haulage requirements during the peak production period. The advantage of simulation is the ability to provide a realistic model of a mining operation based on scheduled, and unscheduled random events during the period under analysis.

Jan 1, 2006

By Rameshwar Sah, Bharath Kumar Shanmugam, Govinda Raj Mandela, Marutiram Kaza, Harsha Vardhan, Harish Hanumanthappa

Iron ores obtained from different sources differ in their chemical and physical properties. These variations make the process of grinding a difficult task. The work carried out in this context focuses on three different samples of iron ore, viz., high silica high alumina, low silica high alumina, and low silica low alumina. The grinding process for all the three iron ores is carried out individually in Bond’s ball mill and the total retention time taken by each iron ore sample is calculated. The present investigation focuses on utilizing the calculated retention time of the iron ore as a standard grinding reference time to the laboratory ball mill for optimizing the grinding time of each ore. The desired P80 (150 μm) with an acceptable range of hematite liberation (> 75%) was obtained in the laboratory ball mill after reducing 6 min from the total retention time taken in the Bond ball mill.

By W. K. Hitchcock

Anecdotal evidence suggests that re-entering a sealed heating poses a significant hazard, whereby the original heating is rejuvenated at an accelerated rate forcing withdrawal and re-sealing of the area. Bulk-scale laboratory experiments using a two-metre column confirm these mine site observations. A high volatile bituminous coal from New South Wales, Australia was allowed to develop a significant hot spot before being inerted with nitrogen and allowed to cool. Air was then allowed back into the coal after the nitrogen was turned off and a hot spot developed almost immediately at the same location as the original hot spot before it quickly migrated towards the air source within a day. Two more re-entries were simulated. Each successive re-entry developed a broader hot spot and took longer to reach thermal runaway. These results clearly show the behaviour that can be expected when trying to recover a section of an underground coal mine that has been sealed due to a spontaneous combustion event.

Jan 1, 2009

By J. M. Somers

Methane is a powerful greenhouse gas and the principal component of natural gas. Coal seams often contain significant quantities of methane, and underground coal mines must ensure that methane released into the mine during coal extraction does not build to dangerous levels. This is accomplished in part through the use of large-volume ventilation systems that remove methane from the mine and release it to the atmosphere. Although the methane concentration exhausted is quite low (typically <1 percent), the volume of air that ventilation systems move is so great that they actually constitute the largest source of methane emissions from underground coal mines. Each year underground coal mines throughout the world emit more than 500 billion cubic feet of methane from their ventilation systems. An air pollution control technology, thermal oxidation using a flow-reversal reactor (TFRR), has emerged as a potential solution to ventilation air methane (VAM) emission mitigation. One manufacturer of TFRRs has demonstrated its oxidizer design (the VOCSIDIZER?) at coal mines in the United Kingdom and Australia. These demonstrations tested the technology?s effectiveness at oxidizing low-concentration methane, as well as its ability to tap the excess heat to produce steam for electric power generation. In early 2007, the first U.S. demonstration of this technology began operation at an abandoned mine in West Virginia. The project is designed to prove the technology?s operational robustness, its ability to reliably oxidize methane at concentrations typical of mine exhausts, and its safety. If the technology is employed at active underground coal mines, it offers the potential to mitigate substantial quantities of global methane emissions. This paper discusses global VAM emissions, options for the recovery and utilization of VAM, and existing projects such as WestVAMP in Australia and the ongoing U.S. VAM demonstration project.

Jan 1, 2009

By B. Oraee

Tunnels as any other structures are affected by different loads and stresses. Generally, the loads on tunnels consist of both static and dynamic loads. These loads must both be considered in the tunnel design process. In this paper, the stability state of Jiroft water-transform tunnel is evaluated. Firstly, the in-situ stresses and then using Kirsch?s equations the induced stresses due to static loads in walls and crown of tunnel are calculated. Consequently, the strain caused by probable earthquake without considering the interaction between the concrete lining of tunnel and rock mass using seismic analysis is calculated based on free-field deformation. When the strain is determined, the simplified method of closed-form solution, Wang?s equations and Penzien?s equations are used to estimate the applied forces on the tunnel due to earthquake such as axial force and bending moment on a tunnel section taking into account the interaction of the tunnel concrete lining and rock mass. Results of this study show that the loads applied to the tunnel as a result of earthquake waves can be affect the stability of underground structures, especially long structures such as tunnels.

Jan 1, 2011

By Rameshwar Sah, Bharath Kumar Shanmugam, Govinda Raj Mandela, Marutiram Kaza, Harsha Vardhan, Harish Hanumanthappa

Iron ores obtained from different sources differ in their chemical and physical properties. These variations make the process of grinding a difficult task. The work carried out in this context focuses on three different samples of iron ore, viz., high silica high alumina, low silica high alumina, and low silica low alumina. The grinding process for all the three iron ores is carried out individually in Bond’s ball mill and the total retention time taken by each iron ore sample is calculated. The present investigation focuses on utilizing the calculated retention time of the iron ore as a standard grinding reference time to the laboratory ball mill for optimizing the grinding time of each ore. The desired P80 (150 μm) with an acceptable range of hematite liberation (> 75%) was obtained in the laboratory ball mill after reducing 6 min from the total retention time taken in the Bond ball mill.

By P. C. Fletcher, E. Kaya

The Bond grindability testing procedure has been standardized to measure the same grindability values, i.e. Bond work index (BWi), for the same ore when tests are performed in different laboratories or by different operators. This is accomplished by the standardization of mill dimensions, tumbling speed, grinding ball charge weight and distribution, sample ore charge weight in the mill and operating practice. The results of this investigation reveal that the Bond work index grindability values may differ substantially with different standard Bond ball mills. This paper will review the results.

Jan 1, 2002