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By Bror Nyman

Wide settlers are a way to decrease the linear velocities of advancing liquid phases. It has, however, been found unnecessary to risk a proper settler performance by building shallow settlers in order to avoid a so-called interface turbulence due to a too big difference between the linear velocities of the organic and the aqueous phase. This conclusion has been reached from tests using a large transparent settler model, where the behaviour of a clean interface between two advancing liquids has been investigated. Also in a more realistic case, making an organic in aqueous or an aqueous in organic dispersion to move between the liquid phases, no obstacle has been found to use a somewhat more deep and correspondingly ore slowly t10wing aqueous phase. Based on above findings, support can be given to a new trend to build the settlers slightly deeper than what has been typical for the so-called low-profile design. In this way, it is much easier to avoid an excessive air introduction and other severe difficulties, like those caused by crud moving from one stage to another. It is further shown, how gravity can be used to slow down and distribute a dispersion being fed into a settler of a VSF unit. Entrainment levels have been found to be reduced by a careful design of primary dispersion distributors and picket fences of the settler. Finally, it is demonstrated, how outlets from the side of the settler can be used to simplity interstage pumping and to decrease the rotation speed of any pumping device.

Jan 1, 1996

By K. L. Gabby

Since mercury is chemically similar to silver, it tends to dissolve along with the silver and gold during cyanide leaching. Ultimately mercury is recovered along with the silver as mercury/silver/gold amalgam which requires retorting to remove the mercury prior to refining the silver and gold. A possible approach to separating mercury from silver and gold in cyanide leach solutions is to take advantage of the replacement reaction between [Hg(CN)4]2- and Ag2S, which results in precipitation of mercury as HgS while dissolving silver as [Ag(CN)2]-. Results are presented demonstrating that mercury can be removed from cyanide solutions with high effectiveness, while, at the same time, recovering additional silver in solution. Initial experiments with static flasks in the laboratory showed a high degree of mercury removal could be achieved. Results using actual metallurgical plant products in bottle roll tests indicate the process works on a larger scale, but also results in significant gold losses if the solution being treated has high gold levels, such as carbon stripping pregnant eluent solution.

Feb 23, 2014

By Andy Thompson, Frank Perrone

"As part of the Metropolitan Transportation Authority’s $10.5bn East Side Access Project in New York, 3,200 m of tunnel had to be constructed in rock, mix face and soft ground conditions beneath one of the largest passenger railroad junctions in North America, handling over 780 trains per day. The use of risk based decision making tools was essential in developing the bespoke contract framework that was adopted as well as making informed decisions once excavation commenced. This paper will outline the risk management process adopted, discuss the risks and mitigation strategies adopted and comment on the impacts of this approach on the as built Project cost and schedule. In particular, the paper will outline the unique approach used to establish the baseline against which the Contractors performance would be measured as the selection of a Slurry TBM to excavate the tunnels was considered to compromise the effective use of a Geotechnical Baseline Report. BACKGROUND AND CHALLENGES Contract CQ031, Queens bored Tunnels and Structures was awarded in September 2009 to a joint venture of Granite Northeast/Traylor Brothers/Frontier Kemper (GTF JV) for $717.6m following a negotiated procurement process. A robust approach was taken with regard to the management and payment for risks associated with the construction of these tunnels. Risk assessments were carried out during the design phase and a risk register was developed prior to procurement. During the procurement phase close attention was paid to ensuring that the allocation and pricing of known risks, together with mechanisms for managing future risks were clearly defined between the MTA and GTF JV.In comparison to the excavation work in Manhattan, which was performed in competent hard Manhattan schist, the tunnels in Queens were excavated predominantly through soft ground with a high water table and complex environmental conditions. Not only did this require the use of pressurized face TBM technology, a first in New York, but also a re-evaluation of the contractual mechanisms used to manage the hard rock excavation contracts for their appropriateness to the soft ground tunnel work."

Jan 1, 2016

By K. V. Raj, T. Bhowmick

"Control of fugitive dust in high latitude open-pit mines is challenging due to unique atmospheric phenomenon resulting in complicated flow regimes, and atmospheric inversion due to lack of adequate solar insolation during prolonged winter seasons. In this study, two idealized (One conical and one trapezoidal) three-dimensional open-pit mine geometries are simulated for differing seasonal conditions using the CRADLE-CFD package. The airflow is modeled using Standard Kappa-Epsilon Turbulence Model solved by RANS equations. The concept of particle tracking is used to predict the flow pattern of dust particles. For various climatic conditions, and two different pit geometries, fugitive dust particles varying in size (PM0.1 to PM10) and concentration are generated at various locations of a mine and dispersed by the airflow pattern inside the open-pit mine. The amount and location of dust particles inside the pit is reported at various time intervals. The development of atmospheric inversion during the winter season significantly affected the amount of dust retention inside the open-pit domain. While during the summer, airborne dust particles were transported outside the open-pit domain in a short time. INTRODUCTIONComputational fluid dynamics (CFD) modeling of open-pit mines is challenging. In a recent paper, Bhowmick et. al. [1] presented different constraints and challenges in developing a 3-Dimensional CFD model. In order to obtain realistic results from a simulation, however, appropriate values of various inputs are required. Simulation results of a 3D non-hydrostatic model by Shi et al. [2] showed that both the mechanical and thermal forcing are important mechanisms, controlling the development of the atmosphere inside an open-pit. Alvarez et al [3] used a CFD model for predicting dust dispersions in a medium sized limestone quarry, and presented several iso-surfaces of varying dust concentrations using ANSYS CFX. A similar study by Torno et al [4] introduced a more sophisticated parameterization of the dust sources. Flores et al. [5] used an OpenFOAM CFD simulation package to simulate and predict pollutant dispersion in an idealized and an actual open-pit mine in Chile with an intense insolation condition. The model was simulated for three different conditions: (i) air advection (10 m/s) driven mechanical turbulence; (ii) surface heat flux (240 W/m2) driven thermal buoyancy; and (iii) both air advection and surface heat flux driven conditions. The results of the simulations showed that the buoyant currents contribute to the removal of a large percentage of the dust particles. The buoyant currents modify the purely mechanical-turbulence induced flow pattern and reduce the particle residence time, commonly observed in a purely mechanical turbulent flow (non-buoyant case)"

Jan 1, 2015

By Tim Langmaid, Steve Skelhorn, Stephanie Robillard, Allen Mitchell

"The Port Mann Main Water Supply Tunnel project provides a critical water main crossing of the Fraser River for the owner, Greater Vancouver Water District (Metro Vancouver). The project consists of two 60-metre-deep slurry panel shafts and a 1-kilometre-long, 3.5-metre excavated diameter tunnel located near Vancouver, British Columbia, Canada. The initial tunnel lining is a precast concrete steel fiber reinforced gasketed segmental lining. The final lining is a 2.1-metre-diameter welded steel pipe. This paper describes the challenges encountered during tunnel construction and the solutions implemented. Key challenges include earth pressure balance tunnelling at up to 6 bar pressure—the highest to date in Canada—a water-crossing without surface access for the majority of the tunnel drive, ground freezing from a river platform for a critical TBM intervention, and boring through cobbles and boulders in dense glacial till. INTRODUCTION Metro Vancouver supplies drinking water to 18 municipalities, one electoral district and one treaty first nation, serving a population of more than 2.4 million residents. Water is collected in three mountainous watersheds to the north of the Greater Vancouver area, in southwestern British Columbia, Canada. To supply the growing demands of Metro Vancouver’s customers, treated water must be conveyed across two significant water bodies: the Burrard Inlet and the Fraser River. The existing Port Mann water main is one of several key links between the watersheds north of Vancouver and the municipalities south of the Fraser River. The Port Mann Main Water Supply Tunnel (PMMWST) is the first of a series of upgrades, to increase capacity, enhance scour protection, and improve seismic resilience. The new tunnel is 3.5 metres (11.5 ft) in diameter and 1 kilometre (0.6 mi) long. When completed, it will contain a new 2.1 metre (7 ft) diameter steel water main that will help ensure the continued, reliable delivery of drinking water to these municipalities, and will more than double the capacity of the existing 1.2 metre diameter main."

Jan 1, 2016

By R. Mishra

The validity of the concept of mine resistance in ventilation systems is examined. Mine resistance is the proportionality constant relating the head generated by a fan and the quantity flowing through it when the fan is connected to a mine circuit. It is the total effect of all branches in the mine ventilation circuit. Its importance lies in the fact that for new mine projections, and in the extensions of existing mines, ventilation calculations are usually based upon adjustments of the mine resistance. In ventilation circuits with regulation, and/or with multi-fans, simple adjustments of the mine resistance curve do not lead to correct solutions. A ventilation system consists of several interconnected subsystems where one subsystem behavior affects that of the others, and the total system. Through a series of simple but realistic examples, the authors will demonstrate the importance of the systems concept in mine ventilation, and its practical application to coal mine ventilation planning.

Jan 1, 1977

By Tim Arnold

"Justified is a show on FX that takes place in Kentucky coal country. The two main characters, a cop named Raylan and a criminal named Boyd, are adversarial to the very end, yet they manage to maintain a seemingly inexplicable bond of friendship through it all. The final episode ends (spoiler alert) with Boyd asking Raylan why that is. He responds, “If I allow myself to be sentimental, there is one thing I wander back to” Boyd responds, “We dug coal together.” Fade to black.What creates these types of bonds between friends and co-workers in mining? I don’t know about you, but many of my best friends I met in mining. Certainly the people I respect the most in this world are a part of our industry. Good, honest, honorable men and women. And I am not just talking about the leaders of our industry. I am talking about great miners who taught me how to do the right thing and also be productive.I have had the pleasure to work for some great people and the misfortune of working for some of the loudest screamers. What I consider the worst butt-chewing in my life may surprise you. I once worked for a man I respected, because he showed me respect. He went on a business trip and left some instructions. For some reason, I was able to justify to myself that they applied to everybody but me, and I disobeyed them. When he returned he called me into his office and said to me: “Tim, you pissed me off when you did that.” He said it quietly and with no anger. I had lost his respect. This devastated me more than any screaming shift boss ever could have. I learned a lot about values from that conversation.Most of us will spend more time at work than we will with our families over a lifetime. It is natural that tight bonds be created at work. What I believe makes mining special is that these bonds are so strong. They are strengthened by the incredibly hard work our miners do. They work at all hours, on holidays and in all sorts of extreme weather conditions. The physical demands of the job are sometimes exhausting. Our bonds are further reinforced because the work is dangerous. Not only does management watch out for the wellbeing of their people, but each and every one of us looks out for one another. The bonds are made tight because our people are so passionate about what they do, no matter the department or profession. Finally, they are strong because of the thousands in the industry that keep doing the right thing, every day. We make great friends in this industry because of the strength of character of our people. That is why Boyd and Raylan respected one another so much."

Sep 1, 2016

By Víctor Vázquez, Guillermo Tiburcio, Martin Encinas, Jesús L. Valenzuela, Erick Montaño, Alejandro Valenzuela, José Parga

Merrill-Crowe is the primary process used for the concentration and purification of silver in a cyanide solution. The Langmuir Adsorption model for silver recovery in a cyanide solution was used for the study. The maximum adsorption capacity was 6.19 mmol/g for silver. This model properly adjusts the experimental results of the adsorption equilibrium with high correlation coefficients, which also favors the formation of a single layer of molecules adsorbed for the silver in the electrocoagulation- generated species. The thermodynamic parameters ΔG, ΔH, and ΔS were estimated, and it was found that the adsorption process is exothermic and spontaneous. For the kinetic study, the Lagergren second-order equation was used to study the adsorption speed. To characterize the solids coming from the electrocoagulation, X-ray diffraction (XRD), and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) were used; the results of this study suggest that silver is present in aluminite, hydroniumjarosite, and alunogen.

Oct 30, 2021

By Enrico Pavese, Tim Kearney, Stefan Lemke

Watertightness is of central importance in hydraulic and underground structures but has always been associated with a risk, as demonstrated by the very high impact that water inflows have on the damage of linings and infrastructure (Howard, 1991; Sandrone and Labiouse, 2011). Concrete is vulnerable to groundwater and chemical contaminants in the soil. These can leach into the pores and cracks of the concrete and degrade its integrity, causing spalling and corroding the reinforcing steel. Moisture migrating into the building can also degrade structural elements over time and lead to mold and other hazards to occupants’ health. In this connection, the demands placed on the setup and detailed design of the seal depending on the negative influence by water on the one hand and on the other hand on the function of a construction in view to its watertightness classification. Thus, the reliable functioning of a seal is of particular significance in the case of traffic tunnels, which are not easily accessible for all subsequent repairs after the construction in seepage water and especially when located in a pressure water zone (risk–cost assessment). Requirements for the long-term efficiency and quality of underground structures have increased in recent decades. Today, the standard lifetime requirement for an underground infrastructure project is 100 to 120 years and, in some cases, even higher. This calls for high increased attention to the durability of the whole structure and of each individual element. Standards, which started as application guidelines given by the manufacturers, are available in the market since the 1980s and are constantly adapted to the current developments in various technical committees. Differentiations are made between: Manufactures application guidelines, case studies or published articles Test standards for the laboratory to guideline the testing procedures (air temperature, type of test equipment, dimensions, test speed, test duration, concentration, type of liquids, monitoring, tolerances, interpretation of results, documentation, etc.), developed by committees based on material and laboratory experts Application standards, which include test standards but also the related minimum performance requirements (values) for material, processing, and quality assurance (practical tolerances), developed by committees based on a wide range of experts (e.g., designers, construction companies, applicators, manufactures, owners, test institutes, quality engineers) and therefore also based on a wide field of experience, different views and up-dated case studies. In the following there are some examples of guidelines and published information’s, ranked according to the year of issue, which are relevant for the development of waterproofing specifications in the tunnel industry:

Jun 13, 2023

By Vasilis Androulakis, Caroline Gerwig, Zach Agioutantis

Mining operations that involve caving of the overlying strata are designed so that caving occurs in a controlled manner by progressive overburden failure. However, there are many cases where the overlying strata bridge over the caved area for longer periods than anticipated and desired. As the caved area expands with the advance of the mining panel, excessive amounts of energy accumulate in the roof strata which will be rapidly released when the overburden eventually fails.

By David A. Zegeer

Since 1980, more than 40 miners have lost their lives by being trapped and suffocating in stock-piles, bins, silos, and similar facilities. Mine Safety and Health Administration (MSHA) is concerned about these accidents, most of which could be prevented if management and miners appreciated the hazard. In February 1986, the coal industry had a suffocation accident that drew national attention. A group of engineers were standing on a coal stockpile. It gave way under their feet. Five of the engineers were buried in the coal and suffocated. As with all fatal accidents, MSHA investigated the cause of this tragedy. I also asked my staff to look into the history of similar accidents. I found out it is rare to have multiple fatalities due to suffocation in material. But, over the years, there has been a long series of individual fatalities from this type of accident. Here are some examples. In Oct. 1985, a coal mine employee in Virginia entered a hopper to collect a coal sample. The feeders were started while he was standing in the hopper. He sank into the coal and suffocated. In Sept. 1985, an employee at a Texas sand company climbed onto a surge pile, to check a problem with sand flow. When other employees found him, the sand had swallowed him. Only his face and one hand were showing. Though the victim's face was clear of the sand, he suffocated before rescuers could free him. Many people do not realize you can suffocate in this kind of situation, though your head is free. Every time you exhale, the material has room to shift and press harder against your chest. Then you have less room to inhale. If this goes on long enough, it gets to the point where you cannot inhale at all. That is what happened to the victim in this accident. In May 1985, a plant operator at a Wisconsin sand and gravel operation purposely slid into the drawhole of a surge pile. He tried to break up large rocks that were clogging the drawpoint. Material piled on the side of the surge pile slid down and buried him. The operator was wearing a safety belt and line. But he was covered by 3 to 3.7 m (10 to 12 ft) of material and could not be pulled free. This incident illustrates another point. A safety line can help. But it is not enough. Workers should never put themselves in a position where loose material can fall on them from above. In Jan. 1985, a young Utah coal miner was waiting for a ride home from a co-worker whose job was at the tipple. A jam developed in the coal bin. The men could not clear the jam from the outside. So the young miner jumped into the bin. He started digging with a shovel at the toe of the coal pile. It caved in on him and he suffocated. The young miner had only three months of mining experience. He had not been trained for work around the coal bin. Since 1980, 16 coal miners and 26 nonmetal miners have lost their lives in loose-material suffocation accidents. Suffocation accidents occur in many areas around mines - bins, hoppers, stockpiles, surge piles, and silos, among others. One recent accident occurred at a surface coal mine in Illinois. The victim was walking over an area that had been drilled and blasted the week before. He fell into a void that had been crusted over with earth. He too suffocated. And many materials have been involved in suffocation accidentscoal, crushed stone, sand, salt, different kinds of ore, ammonium nitrate pellets used in blasting, and a powdery byproduct of iron ore milling called calcine. In addition to fatal accidents, there are near misses. We do not know how many. Most of them are not reported. A person who gets trapped in material, but is rescued, is usually unhurt. MSHA sometimes hears about these accidents by chance, or because they are reported in the local media. We do know that near misses are happening far more often

Jan 1, 1987

By Richard L. Bullock

At the beginning of the previous chapter, variation in the types of room-and-pillar stopes were briefly identified so that the reader could begin to understand the extensive application of this mining system. These same variations will be reviewed and elaborated upon in this chapter while discussing the methods by which the material is extracted. FULL-FACE SLICING BY DRILLING AND BLASTING When the entire mineralized thickness is taken in one pass of mining, it is known as full-face slicing. There is no mineral of economic value intentionally left either in the floor or the back. Theoretically, there is no limit as to how high the face could be in a single pass. But there are practical limitations to equipment size, pillar stability, and control of local loose slabs on the face, roof, and pillars that dictate current practices. The range of face height of the 15 typical room- and-pillar mines covered in Table 8 (Sec. 1, Subsec. 7) from the Dravo report, 1974 was 1.7 m (5.5 ft) to 9.8 m (32.1 ft), the average being 5.2 m (17.1 ft). In the Gaspe copper mine, Murduchville, Que., the drill jumbos were constructed with an extendable tower for full-face mining up to 15.2 m (49.9 ft) if necessary. However, a more common practice at that mine is to take the ore in multiple slices (Hall, 1959). In many metal mines the normal practice when starting stoping is to drive a single development drift into the ore zone a distance that will allow at least four or five rooms to be opened on each side of the initial drift. Since this opening will probably serve as the main haulage drift, it should be kept as straight and as level as possible. As to the other criteria for the stope developments, it might be well at this point for the mine planner to review the remarks presented earlier (Sec. 1, Subsec. 7) on drifts, entries, and crosscuts for production. After the initial drift is driven, it should be slabbed to the full room width if it is not that wide already. Next, the future pillars should be marked on the ribs and the rooms driven between them. If the ore extends beyond the length of the initial drift and is to be mined in the normal sequence of mining, care should be taken in a random room-and-pillar system to see that the extension of the initial roadway remains straight. If pillar "spotting" is left to the shift foreman or to the miners, they probably will not realize the importance of maintaining a uniform pillar line next to the roadway, and of keeping the line straight. Invariably, a pillar will end up in the middle of the future drift extension resulting in a "dogleg" in a possible main haul- age road. While this error is not catastrophic, too much weaving in and out of pillars will certainly slow down future production haulage and needlessly increase costs. Face or Breast Drilling and Blasting Practices To drill and blast the initial advances into the rock, usually some form of cut pattern must be used. In room-and-pillar mining, when a pattern is drilled in a face and that face is the only exposed surface to which all of the rock must be broken, the pattern is known as a "face round" or "swing." The face to which the rock must be broken is referred to as a "free face." Thus the most common way to advance a room into virgin rock with only one free face is by drilling swings. If, after breaking around a pillar, taking down back, or taking up bottom, there is a second (or third) face exposed, a group of holes drilled nearly parallel to a free face and breaking to it is known as a "slab round" or "slabbing." In some mining districts it is also known as "slashing." Obviously, because two faces exposed offer less resistance to fragmentation than a single face, slabbing requires less drilling and fewer explosives than required to break the same tonnage with the same degree of fragmentation with swings. Therefore, it behooves the driller (or supervisor) to plan the combination of

Jan 1, 1982

By Timo Niitti

Within the minerals industry, flotation is the predominant method when processing sulphide ores. There is hardly any competition in this area because of the high efficiency and low costs of flotation. When processing other ore types magnetic or gravity• methods are commonly used and sometimes leaching methods are selected. The wide variation of the properties of gold (high value, low ore grades, softness, high specific gravity etc.) sets challenging requirements to the processing methods and particu­larly for flotation machines, which should be able to effectively recover free fine gold, coarse gold and gold bearing minerals throughout the full size range. In gold processes the amount of concentrate is usually low, but in some cases large amounts of gold bearing sulphides e.g pyrites has to be recovered. In gold processing seldom does only one method provide the optimum results, but the recovery is usually made using several complementary technologies: gravity separation, leaching and flotation are the most common ones. Mineralogy is the determin­ing factor when selecting the method or methods to be used.

Jan 1, 1995

By Neville T. Moxen, Stuart K. Nicol, Malcolm D. Engel

Ion flotation is a process in which ions of interest are complexed with a suitable surfactant molecule. A dilute solution containing these complexes is then aerated, under which circumstance the surface-active complex concentrates at the air-water interface and is transferred to a froth. The present work describes some of the phenomenology of this process and experimental work leading up to the design and use of a pilot scale laboratory facility. Early experiments suggest that selective recovery of gold can be obtained in a manner at least equivalent to conventional CIP processing at low capital cost. Under favourable conditions, upgrade ratios of gold ions of the order of 180: l have been achieved from reclaimed residue dam water with as low an initial gold level as 0.2ppm. Successful development of countercurrent ion flotation for concentrating solids-free gold solutions may offer a lower cost alternative to existing gold ore processing technologies, or in more secondary applications such as concentrating dilute gold solutions or heap leach runoff. The technology may also have more generalised applications to other heavy metal processing.

Jan 1, 1990

By Gregory Owen Lewis

The use of gravity concentration as a means of recovering the 'free' gold component from alluvial and milled ore products is widely used and is receiving increasing attention, particularly with the introduction of the centrifugal-type concentrating units. Because of ever-increasing mining and processing costs and a decline in the gold price, it has become important that the recov­ery efficiency from concentrates is improved so as to increase the yield of bankable gold from this primary recovery step. This paper outlines an alternative hydrometallurgical approach aimed at achieving overall gold recoveries in excess of 98%, together with the elimination of any secondary residue streams which, in the case of conventional treatment methods, require re-processing. An adaptation to the Minataur™ Process technology is being applied with the proposed method, incorpo­rating the pre-treatment of the concentrate, oxidative leaching of the pre-treatment residue, followed by precipitation of a high­purity gold. This route is seen to have application in all scales of operation. Selected results from laboratory-scale testwork are presented to highlight the discussion.

Jan 1, 1998

By E. M. Hill, D. E. Walsh, J. T. Hollow, H. K. Lin

Fairbanks Gold Mining, Inc. (FGMI) began blending and processing True North ore at their Fort Knox mill on April 12, 2001.Gold extraction subsequently dropped from 88% to 71% during the last week of April 2001. 25% of the gold values remaining in the leach tailings were gravity recoverable free gold. Significant quantities of stibnite and arsenopyrite were also identified in the tailings. In laboratory bottle roll tests, the gold extraction from a composite of leach circuit feed collected during the same period was 72.6%, when leached at an average NaCN concentration of 0.16 g/kg. The extraction increased to 82.4% and 91.7% with 0.5 g/kg NaCN, and 0.5g/kg NaCN plus 0.075 g/kg Pb(NO3)2, respectively. A passivating layer surrounding liberated gold particles and resulting from sulfide mineral dissolution, likely contributes to reduced gold recovery, which can be substantially increased by the addition of lead nitrate. Lead species remain in the solid residues after leaching and were not mobilized using Meteoric Water Mobility Procedure.

Jan 1, 2003

By William R. Groseclose, Kenneth D. Schoeman

The Buckskin Mountains Tunnel is a key link in the Bureau of Reclamation's Central Arizona Project. The 22-foot (6.7-m) diameter tunnel is being bored in a north-northwesterly direction through volcanic rock near Lake Havasu in western Arizona. The 6.9-mile (11-km) conveyance tunnel will carry up to 3,000 cfs (85 cu m per sec) of water through the Buckskin Mountains as part of the Granite Reef Aqueduct. The water for the project will be drawn from Lake Havasu behind Parker Dam on the Colorado River and pumped some 800 feet (244 m) above the lake to the inlet portal of the free flow tunnel where it begins its 190-mile (300-km) journey to Phoenix, Arizona, and beyond into Orme Reservoir (figure 1). Precast concrete segments are being used as a single system initial support and final lining in the tunnel being excavated by a tunnel boring machine specially designed and built for the job by The Robbins Company. J. F. Shea Company, Inc., of Walnut, California, is constructing the tunnel for the Bureau of Reclamation.

Jan 1, 1976

By M. R. Yalamanchili, W. H. Jang, Y. Ye, J. D. Miller

Typically, rougher molybdenite flotation and recovery from bulk copper/molybdenum concentrates involves the use of alkalisulfides, Nokes reagents, cyanides, oxidants, and/or thermal treatment to depress copper sulfide minerals. The bulk copper/molybdenum feed generally varies from 0.2% Mo to 1.0% Mo, and with traditional reagents the single-stage rougher flotation recovery of molybdenite varies between 40% and 90% at a concentrate grade of 5% to 10% Mo. With ozone conditioning for copper depression, however, improved separations appear to be possible, as demonstrated by tests with Cu/Mo concentrates from both the Phelps Dodge Morenci Operations and the Kennecott Copperton Operations. Single-stage rougher flotation after ozone conditioning can provide a molybdenum concentrate at a recovery of more than 90% and a rougher concentrate grade higher than 20% Mo in some cases. Subsequent cleaner flotation with additional ozone conditioning resuIts in relatively copper-free molybdenum concentrates containing as much as 52% Mo. Preliminary analysis indicates that, with a multistage ozone conditioning/fotation strategy, the process is technically and economically viable and should be suitable for industrial ap¬plication.

Jan 1, 1991

By D. V. Professor Keller

The production of premium coal-based fuels (<3% ash) and ultra clean coals (<1% ash) using the process of selective agglomeration requires proper selection of raw coal, rough preparation procedures, milling equipment, product coal size distribution, water purity, agglomerants, agglomeration equipment and operational procedures. Each of the variables can contribute a small fraction to the impurity load in the product coal or limit the ability of the process to separate mineral matter-free coal. Each of the variables and their importance will be examined from data produced at the bench by batch and continuous agglomeratons as well as the results from pilot plant and tonnage production units. The results are discussed which have indicated that some standard commercial coals can be produced with ash contents as low as 0.2 % ash (batch/bench) and several tonnage lots of 0.6% ash in as 200 lb/hr pilot plant. In most cases iron pyrite released from the coal matrix and with proper pH control is rejected from the product coal agglomerates.

Jan 1, 1995

By D. Dolinar, T. P. Mucho

Horizontal stresses are caused by global platetectonic forces. During 1995 alone they were largely responsible for the closing of two longwall mines in the United States. This paper presents six case histories from Pennsylvania, West Virginia, Kentucky and Alabama. In each case, a mine encountered roof falls or difficult ground conditions at the headgate caused by horizontal-stress concentrations. The problems are detailed, and the control measures adopted are described. In most cases, nearby longwall panels without stress concentrations were trouble free. The paper also discusses detailed measurements that were made at two adjacent Pennsylvania longwalls. One headgate was oriented to avoid a horizontal-stress concentration, and the other was not. Eliminating the stress concentration dramatically reduced roof support loads and roof deformation. The paper concludes that proper panel orientation and sequence is the key to maintaining headgate ground control. The optimum orientation is not parallel to the maximum horizontal stress, as previously thought, but rather it is 20o in the stress shadow of the gob. Other stress-control techniques, including artificial support, are briefly discussed

Jan 1, 1999