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By Wolfgang Guetter, Wolfgang Weber

The upgrading project for two hydropower plants in Slovenia, Europe, requires two new pressure tunnels: Plave II (5.9 km Flysch) and Doblar II (3.6 km Limestone). It is the worldwide largest application of the Double-Shield TBM technology combined with an extremely thin-walled monoshell honeycomb lining system. The first drive has been completed by end of June 2000 achieving best performances of 50m/d and almost 1,100m/mth. In September 2000 the TBM started the second tunnel without any required adjustments due to geological or other reasons. Another 52m/d have been bored already within one production day of two 8 h shifts achieving a maximum penetration rate of more than 6m/h. The completion of the Doblar drive can be expected by February 2001.

Jan 1, 2001

By Dale Matthews

The Getchell Mine, near Winnemucca, NR, was discovered in the 1930s and was initially mined to recover gold from oxide ores. During the 1940s and 1950s, gold was recovered from the highly refractory arsenic sulfide ores using horizontal kilns to roast the ores. During the 1960s, fluid bed roasters were used to oxidize the ore and recover the gold. The mine was shut down from 1968 through 1985. In 1985, heap leaching was started on the low-grade oxide ores that were available. In 1989, a pressure oxidation circuit was started to recover gold from the higher grade sulfide ores. Flowsheet The basic plant flowsheet of the Getchell Mine are shown in Figs. 1 and 2. The plant was designed to process a nominal 2.7 kt/d (3000 stpd) of ore with about an 85% onstream availability and a gold production of 15.5 kg/d (500 oz/ day). Run-of-mine (ROM) ore is fed directly to a wet semiautogenuous grinding (SAG) mill after the +457-µm (+18in.) rock is removed on a stationary grizzly. From the SAG mill, the ore goes to a ball mill where it is ground to 80% -75 µm (-200 mesh) and is then sent to a thickener. The SAG and ball mill operate in closed circuit using cyclones.

Jan 1, 1994

By Douglas R. Shaw

Normal dodecyl mercaptan was evaluated as a collector for flotation of sulfide minerals and precious metals. The reagent is from the class of normal mercaptoalkanes (n-alkyl thiols), and is commercially available in the form of a mixture of n-dodecyl mercaptan and a dispersant, under the trade name Pennfloat(TM)3. Reported are results of bench-scale flotation experiments on many commercially treated base metal and precious metal sulfide ores. Dosages, points of addition, and flotation pH were among the uariables studied. Most notable results were increased copper, molybdenum, and precious metals recoveries. Dosages of dodecyl mercaptan on some ores were considerably lower than required for conventional collectors.

Jan 1, 1979

A series of gas inrush events occurred during development at Grosvenor mine resulting in exposure to elevated levels of methane at the production face. A total of 22 gas inrush events occurred releasing between 15 and 130 m3 of methane during each event. The presence of an undrained seam in the immediate floor, geotechnical characteristics of the floor, and the stress environment all contributed to these dynamic floor events, while the geological characteristics of the seam below, such as the seam thickness and ash content of 75%, prevented effective pre-drainage. However, events only occurred in headings mined parallel to the principal horizontal stress direction. In cut-throughs (C/Ts) perpendicular to the principal stress direction, no events occurred, and higher methane levels were observed at the production face.

Jan 7, 2020

Ten years ago, only 3% of Consol's underground coal production resulted from using the longwall mining method. Today, that figure has grown to 45% and has helped the Pittsburgh-based concern fuel an upswing in productivity. The company reported that productivity at its underground mines, excluding labor strike periods, increased 24% between 1978 and 1981. Last year, an additional 8% increase was achieved. Efforts such as improved safety, training, engineering, and maintenance programs as well as the closing of unproductive mines has contributed to these gains, according to Joseph M. Richards, Consol's executive vice president of operations. But, Richards adds, a great part of the credit goes to longwall mining. What is Longwall Mining? To fully appreciate the advantages of longwall, one needs an understanding of how mining is done by other methods. For instance, in both conventional and continuous mining, rooms or tunnels are dug in the coal seam. Pillars of coal are left standing to support the roof as mining moves forward in the seam. In conventional mining, a slot is cut in the base of the seam and holes for blasting are drilled. After blasting, the coal is loaded. A more efficient method - continuous mining - uses a machine that combines cutting and loading. Longwall mining, by contrast, works backwards from the end of a panel. Two parallel sets of tunnels (development panels) are cut into a seam with continuous mining machines, then connected with a set of crosscuts at the far end. Min¬ing then proceeds back toward the entrance. Longwall mining employs some very productive machines. Large drum shearers, for example, run on a track along the length of the coal face for some 150-180 m (500-600 ft). The shearers cut the coal which falls onto a conveyor system or pan that also runs the entire length of the face. The longwall crew works under a roof of heavy steel supports called shields. As the coal is removed, shearers, pans, and shields are moved forward by hydraulic rams. The roof is allowed to collapse behind the shields. In addition to increasing production, longwall mining is considered to be safer because the miners work under strong steel shields. New designs have made them more rugged and maintenance free, as well as more stable on soft mine floors. Early roof supports, called chocks, had gaps in the roof canopies. The new roof shields now cover the entire working area and are better able to prevent roof material from falling into the working area, thereby improving safety and productivity. Longwall mining also results in a cleaner product in many mines. If the first layer of rock over the coal seam is thin, it might have to be removed with the coal in a room-and-pillar operation so a

Jan 11, 1983

By Timothy P. Smirnoff, Tracy K. Lundin

INTRODUCTION The City of Phoenix, Arizona is located in the Phoenix Basin watershed which is prone to flash flooding several times each year. The runoff from these storms moves from the mountains in the north to the Salt River in the south. An extension of Interstate Highway 10 (1-10) will pass through the city east to west to form an Inner Loop through the downtown business district. PROJECT DESCRIPTION The I-10 Inner Loop extension will be a depressed roadway which would intercept the surface drainage of the Phoenix Basin and separate the watershed into two regions. To prevent flooding of the depressed roadway, runoff storm water collected from the northern half of the drainage area will be conveyed beneath the roadway to its natural outlet at the Salt River. A conveyance system composed of pressure tunnels beneath the city, shown in Figure 1, was proposed to achieve this goal . Table A presents the prominent features of each of the tunnels. This paper will describe geologic and engineering parameters specific to Phoenix which were used in the design of a series of tunnels to convey storm water from the I-10 Inner Loop to the Salt River. The design of tunnel initial and final support is described along with support and construction methods used by the Contractor.

Jan 1, 1985

By D. F. Machuca-Mory

A change of support model consists of a procedure to change a stationary histogram at a small data scale to represent a larger scale; typically a distribution of sample drill-hole data is changed to represent a chosen selective mining unit (SMU) scale. Most grade variables average arithmetically. Thus, the mean stays the same for different scales, and the variance changes according to well-established theory using average variogram values. The longstanding challenge has been to predict how the shape of the histogram changes. The discrete gaussian model is widely used because it appears reasonable and introduces few artifacts; there are no artificial minimum/maximum values and the target mean and variance are reproduced exactly. The resulting distribution shape, however, is strongly dependent on a multivariate gaussian distribution. The authors generalize the approach by taking advantage of a property of the isofactorial model, which allows one to specify where the random function falls on the spectrum between a low-entropy mosaic model and a maximum-entropy diffusion model. A measure of dissemination (MD) is computed using a ratio of the madogram and the variogram. The change of support algorithm is developed that uses a variable measure of dissemination (VMD) that is easily calculated and fit to data from the deposit. The resulting VMD change of support model is very flexible to represent different mineralization styles encountered in practice; global predictions of recoverable reserves are more accurate and decision-making is improved. A number of real examples are shown to demonstrate the approach.

Jan 1, 2008

By J. Wright

Since the 1960’s toroidal conductivity has been used to determine the Alumina to Caustic ratio of the digester discharge liquor stream. In recent years the application of ceramic materials have allowed the sensors to moved upstream to provide tighter control of the process. In the Bayer process, dissolving the aluminum contained in bauxite ore in caustic soda and converting it to aluminum oxide produces alumina. An important parameter of the process is measuring the alumina to caustic ratio in the digester discharge stream. The A/C ratio at a given caustic concentration is a measure of the degree of saturation of the alumina in the plant liquor. The aim in the process is to achieve a high A/C ratio. There is however a limit where precipitation will occur if the A/C ratio is too high. For many years conductivity has been used to determine the A/C ratio. Conductivity of discharge liquor is related to the caustic concentration. The change in the caustic concentration is in the same direction of the change of solubility of the alumina. Controlling the conductivity through adding additional bauxite ore and varying the dilution flow can increase plant yield.

Jan 1, 2001

By Dennis Ofiara

Several recent tunnel jobs have required special adaptations of hard rock TBMs. Some of the special job conditions are ?no blast? launch requirements, small shafts or launch pits, proximity to existing underground structures, and short tunnels where the TBM must be retrieved through the primary lining. This paper describes a few of these projects, and the machine adaptations that have made TBM excavation feasible.

Jan 1, 2008

By S. Schina

Part of the Imittos Western Peripheral Motorway in Athens is the twin road tunnel in the vicinity of American College, with 20m excavation diameter. In the paper, the environmental and other requirements, the geometry and the geological – geotechnical characteristics of the rock formations in the construction area are given. Information regarding the modeling and analysis methods that are used for the design of the temporary support, the final lining and the wedge and slope stability analysis is described thoroughly. Finally, the results of the analyses are compared with these of measurements and general remarks during the construction of the tunnels.

Jan 1, 2001

By K. Kohli

A case study involving a historic structure undermined by longwall mining is presented in this paper. The location of this study is in South Western-Pennsylvania; USA. The structure is 150-years old and subsided 4.5 feet. This paper discusses the mitigation measures taken to reduce the subsidence damage and its effectiveness.

Jan 1, 2002

By H. Sarvamangala

Biomineralization of manganese on titanium condenser material exposed to seawater has been illustrated. Biom-ineralization occurs when the fouling components, namely, the microbes, are able to oxidize minerals present in water and deposit them as insoluble oxides on biofilm surfaces. Extensive biofilm characterization studies showed that an alarmingly large number of bacteria in these biofilms are capable of oxidizing manganese and are, thereby, capable of causing biomineralization on the condenser material exposed to seawater. This paper addresses studies on understanding the exact role of the microbes in bringing about oxidation of manganese. The kinetics of manganese oxidation by marine Gram-positive manganese oxidizing bacterium Bacillus spp. that was isolated from the titanium surface was studied in detail. Manganese oxidation in the presence of Bacil-lus cells, by cell free extract (CFE) and heat-treated cell free extract was also studied. The study confirmed that bacteria mediate manganese oxidation and lead to the formation of biogenic oxides of MnO2, eventually leading to biomineralization on titanium surface exposed to seawater.

Jan 1, 2008

By L. R. Moore

Arsenic is among the list of major contaminants in mining aqueous waste streams. Though the elemental form is toxic, the aqueous oxyanions are more so. The most common forms of arsenic released during mining processes are arsenate and arsenite. The common treatment technologies to date can be summed up in these major categories: oxidation, coagulation, absorption, and media filtration. These methods can often involve many expensive processing steps that may also be limited by variables, such as total dissolved solids, other cations and anions, and the oxidation state of the arsenic. An innovative technology, falling in the absorption category, was developed that can successfully reduce such aqueous forms to a level below the EPA recommendations. This new technology offers a unique and viable solution which is transparent to the above mentioned limitations.

Jan 1, 2012

By H. K. Lin

Deepwater discharges of sulfide flotation tailings have been practiced for several decades. Oxygen penetration and organic matter content in such environments are the two major factors that determine their reduction-oxidation condition and hence the rate of sulfide mineral dissolution under such discharge environments. In this study, the effects of solution redox potential and pH on the dissolution of some heavy metals from sulfide flotation tailings were examined. Zn, Pb and Cu concentrations in solution were all higher at a higher redox potential and lower pH. Dissolved Zn concentrations reached 100 ppm even at a low redox potential of 105 mV and near neutral pH after 33 days. Pb concentrations were below 2 ppm at 105 mV and near neutral pH after 165 days. At 105 mV, the Cu concentrations were below 0.2 ppm at near neutral pH after 165 days. At pH 2.3, the Fe concentrations were higher at 420 mV than at 105 mV. But at pH 6.8, the Fe concentrations were lower at 420 mV than at 105 mV, due to the oxidation of Fe2+ to Fe3+ and the subsequent precipitation of ferric hydroxide. Arsenic concentrations in solution were all less than 0.002 ppm. For Zn, Cu and Fe, no significant differences were observed between the tests in solutions prepared using seawater and those using distilled water. However, Pb concentrations reached higher levels in solutions prepared using seawater.

Jan 1, 2009

By F. Freme

Coal production in the United States increased in2004 by 36 Mt (39.7 million st) to end the year at 1 Gt(1.11 billion st), according to the U.S. Energy Information Administration (EIA). This was a 3.7-percent in-crease from 2003’s 971.6 Mt (1.07 billion st) (Table 1).(All percentage change calculations are done at the short-tons level.) Although U.S. coal consumption rose in 2004, not all coal-consuming sectors had increased consumption for the year. Coal consumption increased in the electric power sectors by 1 percent and declined slightly in the other industrial sector, while coking coal consumption dropped by 2.4 percent. U.S. coal exports rose for the second consecutive year, while coal imports again increased to record levels. Coal stocks declined during the year, as electric generators used their stockpiles to helpmeet increased demands and missed shipments. Coal producers used their stockpiles to supplement their production levels.

Jan 1, 2005

By Eldon L. Abbott, Rebecca K. Bolan

The Florida Department of Transportation, Florida’s Turnpike Enterprise is studying the feasibility of a 1128 meter (3,700 foot) vehicular tunnel to provide direct access for Port of Miami traffic to/from I-395, I-95, SR-836 (Dolphin Expressway) and Miami International Airport. Both Bored and Immersed Tube tunnels were evaluated and re-evaluated for constructing two, two-lane, 11.9 meter (39-foot) diameter tunnels beneath the Main Shipping Channel lying between Watson Island and the Port of Miami on Dodge Island in Biscayne Bay, Miami, Florida, USA. Bedrock Geology of South Florida is predominately very permeable, vuggy limestone with sand seams and occasional voids. Groundwater inflows in deep cut-and-cover excavations, tunnel buoyancy, grouting, maintenance of Port operations and potential/possible environmental impacts to Biscayne Bay were significant issues.

Jan 1, 2005

By B. Farshadi, B. Asi, M. J. Habibian

"Dare-Zereshk deposit is one of the deposits supplies ore for Taft copper Complex in Iran Yazd province. This deposit is situated underneath a village the same name. Prior to mining activities, the village and its agricultural lands should be dislocated and deserted. This paper discusses about sustainability factors in this area including: Social and environmental effects of mining, dislocation and substitution of communities, created and lost jobs, financial and economic factors, quality of life index, infrastructures and post-mining land use. Studies have been performed by coupling Geographical Information System (GIS) with decision support tools such as Multi Attribute Decision Making (MADM), Through these studies revealed that considering the infrastructures developed for mine and plants, earned incomes and changing the community, mining activity in this area not only increases the social and regional sustainability but also improves it to a higher level."

Jan 1, 2011

New developments in the non-invasive and real-time measurement of the velocity profile of slurry flow in horizontal pipes will be described. This information can be used to determine the approach and onset of solid deposition on the bottom of the pipe. Having this information in real time can enable operation at lower velocities or higher solids concentration or both while avoiding solids deposition or plugging and their associated operational costs. In addition, advances have been made in the measurement and trending of pipewear on slurry lines. In contrast to manual methods, CiDRA?s system uses a permanently or semi-permanently installed ring of conformable ultrasonic transducers clamped onto the outside of the pipe. These transducers are used to measure the thickness of the pipe under their respective locations. This results in better repeatability, accuracy, and failure prediction, along with reduced labor costs. The benefit is significantly improved pipe wear monitoring in pipelines with abrasive solids. This provides an improvement in the ability to insure safe operation and avoidance of costly operational and environmental damage due to leaks caused by pipe wear.

Jan 1, 2009

By J. Wagner, P. Eger, G. Melchert

In 1991, LTV Steel Mining Company decided to close an open pit taconite mine in northeastern Minnesota, using a passive treatment approach consisting of limiting infiltration into the stockpiles and wetland treatment to remove metals. Over 50 million metric tons of sulfide-containing waste had been stockpiled adjacent to the mine during its 30 years of operation. Drainage from the stockpiles contained elevated levels of copper, nickel, cobalt and zinc. Nickel is the major trace metal in the drainages, and prior to closure annual median concentrations ranged from 1.5-50 mg/L. Copper, cobalt and zinc are also present but are generally less than 5% of the nickel values. Median pH ranges from 5.0 to 7.5, but most of the stockpile drainages have pH greater than 6.5. Based on the chemical composition of each stockpile, a cover material was selected. The higher the potential a stockpile had to produce acid drainage, the lower the permeability of the capping material required. Covers ranged from overburden soil removed at the mine to a flexible plastic liner. Predictions of the reduction in infiltration ranged from 40% for the native soil to over 90% for the plastic liner. Five constructed wetlands have been installed since 1992, and have removed 60-90% of the nickel in the drainages. Total capital costs for all the infiltration reduction and wetlands exceeded $6.5 million, but maintenance costs are less than 1% of those for an active treatment plant. Since mine drainage problems can continue for over a hundred years, the lower annual operating costs should pay for the construction of the wetland treatment systems within seven years.

Jan 1, 1999

By Luzheng Chen

Pulsating high-gradient magnetic separation (PHGMS) of fine hematite from tailings was studied using a pilot PHGMS separator to investigate the possibility of its application in industry. The results of this investigation indicate that PHGMS is effective for recovering fine hematite from the tailings and greatly improved the separation performance compared with the conventional high-gradient magnetic separation at the same conditions. By applying the pilot separator with a 1-mm rod matrix to a tailings containing 28.76% Fe, a concentrate assaying 54.35% Fe with 35.89% recovery was achieved. It was found that the separation performance of the pilot separator closely correlates with the main pulsating parameters, i.e., pulsating stroke and frequency. It was also found that a change in the wire diameter of the rod matrix from 2 to 1 mm causes a weak drop in concentrate grade but results in a considerable rise in recovery. This finding proves that the improved performance achieved by the pilot separator is attributed to the pulsating of slurry and to the use of a 1-mm rod matrix. When the first commercial SLon-2500 PHGMS separator with a 1-mm rod matrix was applied to recover fine hematite from the tailings, the results duplicated those achieved with the pilot PHGMS separator.

Jan 1, 2009