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By F. M. C. C. Vieira

The work described forms part of a Safety in Mines Research Advisory Committee (SIMRAC) funded project, currently an ongoing programme of research aimed at providing ?improved criteria, guidelines and the use of numerical models to design mine layouts at depth, so as to reduce seismicity and enhance worker safety?. The entire project deals with a number of distinct, albeit interrelated, research areas such as: subsidence and caving in hardrock, general numerical criteria for layout design, regional benefits of backfill, concrete pillars, strike stabilizing pillars and bracket pillars. This paper will focus on the last two items only. New considerations for the design of both stabilizing pillars and bracket pillar layouts are briefly discussed.

Jan 1, 1998

By Herbert H. Kellogg

The chemistry of sulfide roasting is analyzed to show those aspects of performance which Thecan be predicted from considerations of thermodynamic equilibrium. It is concluded that equilibrium calculations can serve as a yardstick for prediction of roaster-gas composition and sulfate formation in the calcine for fluid-bed roasting practice. A method of calculation which combines the equilibrium and stoichiometric factors is outlined, and illustrated by an example from the roasting of Cu-Fe sulfides. ON first examination the roasting of sulfides would not seem to be a process to which equilibrium calculations could be applied to yield results of practical value. The burning of sulfides is an ex-tremely spontaneous reaction, excess air is always used to obtain rapid reaction, and in most traditional roaster designs (hearth roasting) the temperature and gas composition vary widely from point to point in the roaster. These are all conditions which promote a non-equilibrium state in the roasting process. However, the introduction of the fluid-bed roaster1 has brought to roasting practice new conditions of operation, so that equilibrium calculations can be used to predict certain limited aspects of practical operation. The fluid bed is characterized by uniformity of temperature, gas composition, and calcine composition from point to point throughout the bed. These relatively uniform properties of the bed make the meaningful calculation of the equilibrium state of certain reactions in roasting possible. It is the purpose of this paper to analyze roasting from an equilibrium viewpoint, to show where the method may be expected to yield valuable information, where it fails, and to outline methods of calculation. Main Roasting Reaction The reaction MS (s) + 3/2 0, = MO (s) + SO, [I] might well be called the main roasting reaction. It adequately accounts for the well known facts that metal sulfide and air are the main reactants, and metal oxide and SO, the main products. Deviations from this simple stoichiometry will be discussed under side reactions. For all metal sulfides, Reaction 1 is strongly exothermic and the equilibrium position is far to the right. Since the reaction is exothermic, the equilibrium shifts in the right-to-left direction as the temperature is raised. However, at all practical roaster temperatures (between 500" and 1200°C), the amount of this shift is small, and the equilibrium position remains far to the right. The main roasting reaction is essentially irreversible, and the application of equilibrium considerations to this reaction will not be! a fruitful field of investigation. A knowledge of the rate of this reaction. although not the proper subject of this paper, is of great importance to the roasting process. Analysis of the factors which influence this rate shows that: 1) The rate will increase rapidly with increased temperature. 2) The rate will be proportional to the partial pressure of oxygen at the surface of the reacting particle. Because of diffusion effects, the partial pressure of oxygen at the particle surface may be considerably less than in the bulk of the roaster gas. For this reason, intimate contact between gas and solid and high relative velocity between gas and solid, such as can be obtained in a fluid bed or flash roaster, will markedly increase the rate of reaction. 3) The rate will be proportional to the surface area of metal sulfide. Therefore, smaller particle size will permit a more rapid rate per unit of weight. To achieve practical rates of roasting the partial pressure of oxygen in the roaster gases must be maintained at a finite level at all times. Even where the gas-solid contact is very good, as in the fluid-bed roaster, the oxygen content of the gas must not be allowed to drop below some limiting value (perhaps 1 pct), or the rate of the main roasting reaction will become too small for practical operation. Side Reactions in the Gas Phase The gas phase during roasting of metallic sulfides contains the elements oxygen, sulfur, nitrogen, by-

Jan 1, 1957

By Kevin Connor

During 1986, the Government continued with efforts to ease the country's almost total reliance on coffee exports for trade revenues by allocating 45% of the Government's budget to commerce and industrial projects. The collapse in coffee prices in 1985 continued to exacerbate the country's growing trade deficit, weakened currency, and dwindling reserves of foreign exchange in 1986. Amoco Burundi Petroleum Corp., a subsidiary of Amoco International Oil Co., continued with plans to drill at least two exploration wells in Lake Tanganyika in 1987. Both offshore and onshore drilling exploration was planned by Amoco Burundi. Any oil or gas finds were expected to have substantial impact on the Burundian economy, as a major portion of the country's trade deficit was directly attributable to petroleum and gas imports.

Jan 1, 1988

By Christopher Mark

This proceedings volume contains papers presented at W U.S. Bureau of Mines (USBM) technology transfer seminars on New Technology for Longwall Ground Control. These seminars were conducted in Washington, PA, on April 12, 1994, and Denver, CO, on May 10, 1994. The papers herein describe several new, highly practical USBM technologies now available for ground control in longwall mines, including lie Coal Mice Roof Rating (CMRR), cable bolts, the MULSIM/NL model, and the Wood Crib Performance Model. Other significant topics addressed include longwall panel layout, coal pillar design, horizontal stress in longwall mines, roof support selection for gate entries, and ground control monitoring.

Jan 1, 1994

By M. A. Grossman

THE hardenability of most steels can be predicted within 10 to 15 per cent provided the complete chemical composition is known, including "incidental" elements; and provided the as quenched grain size is known; and provided, finally, that the composition and heating temperatures for hardening are such as to result in austenite free from carbide particles. In method proposed herein, the steel is considered as having a base hardenability due to its carbon content alone (the hardenability of a "pure steel" of the given carbon content, without any other elements), and this base hardenability is multiplied by a multiplying factor for each chemical element present. After multiplying all these together, the final product is the hardenability. Grain size may be taken into account either in the base hardenability or after the multiplication. Hardenability is stated in terms of "ideal critical diameter"; namely, the diameter of bar, in inches, that will just harden all the way through (absence of unhardened core) in an "ideal" quench, and the calculation may also be related to the Jominy test. The data bring out certain features rather clearly. For example: I. It is quite useless to attempt to predict hardenability unless all elements, including "incidentals," are known; thus an "incidental" chromium content of o.-2o per cent increases the hardenability by about 50 per cent. 2. The relative effectiveness of different alloys is sometimes unexpected; thus molybdenum when calculated in this way appears to be of the same order of effectiveness as manganese, rather than much more powerful as would appear to be common experience; observe that an increase from no manganese to 0.20 per cent Mn provides a multiplying factor of 1.67, and an increase from no molybdenum to 0.2o per cent Mo provides a factor of 1.63, an increase of over 6o per cent in each case. However, if to a steel containing 0.50 per cent Mn there is added "20 points of manganese," the factor is raised from 2.65 (for 0.50 per cent Mn) to 3.35 (for 0.70 per cent Mn), or an increase of only 26 per cent. Thus the first small addition of an element has a much more powerful percentage effect than an equal further addition when some is already present, and in most cases the effect of molybdenum is considered in relation to a steel in which molybdenum is absent. 3. If two elements are equally effective, a greater harden ability will be obtained by using, for example, o.5 per cent of each than by using 1.0 per cent of either of them alone. 4. A knowledge of the as-quenched grain size is essential for precise work, since a difference of only one grain size number (say No. 7 instead of No. 6) makes a difference of almost 10 per cent in hardenability (in these units); this, however, does not apply to certain steels of high hardenability. It should be emphasized that in chromium steels (over 0.30 per cent Cr) and chrome-molybdenum and chrome-vanadium steels, undissolved carbides are likely to be present in the steel as quenched, and that in such cases the charts can indicate only a maximum possible hardenability, whereas the extent of hardening actually obtained may be much less. Thus tests on a number of chrome-molybdenum steels have indicated a degree of hardening amounting to only 50 to 65 per cent of the maximum possible, and in chromium steels from full hardening (100 per cent) down to as low as 70 per cent. On the other hand, when the amount of such elements is small (Cr under 0.30 per cent, Mo up to 0.25 per cent in the absence of Cr, and V up to 0.04 per cent), the charts provide reasonable approximations. The precise figures on the charts are suggested as tentative, subject to some modification as more data accumulate, but the fundamental concept appears to be supported by tests made on a wide variety of steels, a few of the correlations being shown in Fig. I.

Jan 1, 1942

By Joseph Nawrocki, Margaret Hettinger, Dr. Catherine Johnson

"Optimized rock fragmentation is essential for minimizing downstream costs to mining operations.Photographic fragmentation analysis, vibration monitoring, and high-speed video all providemeasurements of blast effectiveness and supply data that allows operations to modify blasts to achieve downstream goals."

Jan 1, 2016

By Mark I. Copeland

The Bureau of Mines investigated the effect of up to 1 wt-pct of copper and silicon on the heat treatment response and hardness, tensile, and impact properties of hot-rolled medium-carbon steels. The steels were prepared by induction melting and fabricated into plates by forging and rolling. The tensile strength of 0.2-wt-pct carbon steels containing 0.3 wt-pct silicon was affected significantly by copper in both the hot-rolled and heat-treated (600° C) conditions, whereas the tensile strength of the 0.3-wt-pct carbon steels was less affected. A 600° C treatment was considered optimum as a post-rolling treatment to strengthen the steels by copper precipitation. Strengthening of 0.2-wt-pct carbon steels by silicon was reduced by increasing copper contents.. Optimum impact strengths occurred at about 0.3 wt-pct silicon in 0.2-wt-pct carbon steels containing 0.6 and 0.8 wt-pct copper. The impact strengths were lowest for 0.2-wt-pct carbon steels containing over 0.8 wt-pct copper and greater than 0.3 wt-pct silicon, especially in the heat-treated condition. Copper and silicon solutes and copper precipitates strengthened the steels. This effect was augmented slightly by strengthening through grain refinement by these solutes.

Jan 1, 1973

By Jackson de Brito Simões

As ligas com memória de forma (LMF) apresentam características funcionais de recuperação de deformações plásticas aparentes e mudança de suas propriedades mecânicas quando submetidas a variações de temperatura, proporcionando um crescente interesse para aplicações de engenharia e originando uma nova maneira de projetar sistemas mecânicos. Nesse contexto, é importante desenvolver novos métodos de fabricação de componentes e dispositivos a partir de LMF. Infelizmente essa fabricação pode ser ainda extremamente complexa e dispendiosa, principalmente para LMF do sistema Níquel-Titânio (Ni-Ti). No final do século XX, a fundição de precisão se tornou uma alternativa eficaz para a conformação de componentes de titânio e suas ligas em aplicações de alta tecnologia. Entretanto, não existem informações da utilização desse processo para fabricação de componentes mecânicos de LMF. Assim, o objetivo deste trabalho foi avaliar o processo de fundição de precisão para o desenvolvimento de novos, produtos principalmente miniatuadores ativos de LMF Ni-Ti. Para isso, foi realizada a fabricação de diferentes formatos de miniatuadores de LMF Ni-Ti (de composição nominal em peso de 54,9Ni-45,1Ti) pelo processo de fundição de precisão com molde sólido, e ainda sua caracterização térmica e por ensaios não destrutivos. Foram obtidos quatro miniatuadores distintos, nos formatos de minitubo duplo, arruela Belleville, mola e parafuso, com bom acabamento superficial. A presença da transformação de fase característica das LMF foi avaliada por técnicas de calorimetria diferencial exploratória (DSC) e resistência elétrica em função da temperatura (RET) nos quatros tipos de miniatuadores. As técnicas não destrutivas de raios X e tomografia computadorizada foram empregadas para avaliar a qualidade dos miniatuadores produzidos, sendo importantes na detecção da presença de defeitos de processo. Ficou evidente a eficiência do novo processo proposto, porém ainda se faz necessário mais investigações principalmente com relação ao comportamento termomecânico dos miniatuadores obtidos por esse processo.

Aug 16, 2017

Mining One (M1) is often challenged with the task of evaluating deposits considering open cut and/or underground (UG) mining methods. In many near surface deposits a combination of both methods results in the optimum economic means of exploitation. As common as it is to have open pit mines eventually develop into underground mines, theory associated with determining the optimum underground/open pit interface location continues to be subject to refinement. With recent developments in underground software packages, the generation of rudimentary underground mining stopes from basic economic inputs is not only fast, it provides a practical underground mining solution. The determination of the open pit/underground interface is not new to Gemcom's Whittle 4X (Whittle). However, its solution has only ever claimed to be indicative, mainly due the rudimentary nature of how Whittle represents any potential underground mining. The efficient generation of the aforementioned underground mining solution has provided mining engineers with a unique opportunity. Underground mining can now be represented within the Whittle environment to allow the open pit/underground mining scenario to be modelled with increased accuracy. Providing Whittle with the ability to now consider mineable underground stopes combined with the consideration of time value of money (discounting), has delivered a solution with higher credibility than ever before.This paper will elaborate on the potential value gains associated with improved accuracies in the modelling of any potential underground mining in the Whittle environment. Furthermore, it will explain the importance of incorporating time value of money in the optimisation process to provide a consistent solution through to pit selection and final analysis.

Dec 6, 2010

By Robin B. Dill, Mark Pelletier, Daniel J. Dobbels, Subodh Bhaumik, Daniel J. VanRoosendaal

Although primarily cut-and-cover excavations are required for replacement of the existing elevated I-93 interstate highway through the heart of Boston for the Central Artery/Tunnel (CA/T) project, some mined tunnel construction was also undertaken. The mined tunneling conducted was the 22-m-wide northbound roadway structure which passed below a 20-m-deep operating underground subway station that was built in 1913. The innovative underpinning scheme used to support the subway station during construction resulted in the successful mining beneath the subway station with negligible vertical settlement. Two grouting galleries were carefully mined below the subway structure, and pre-grouting of the granulary, pervious glacial soils and weathered bedrock was carried out from these galleries. The reinforced concrete walls of the underpinning structure were constructed within three stacked drifts that were sequentially mined below each grouting gallery. After 11 cross adits were mined between the grouting galleries, cast-in-place post-tensioned girders that spanned between the stacked-drift walls were constructed to support the subway station. The stacked-drift walls also provided lateral support for the 22-m wide by 29-m long by13-m high opening beneath the girders.

Jan 1, 2001

By R. Sankey, L. Gatty, F. Bizzozero, G. F. Shannon, F. Savaglio, L. McDonald

State mining regulations in Queensland stipulate that a mine be provided with an earth installed on surface and that all underground equipment that needs to be earthed should be connected via a copper conductor to this surface grounding point. The regulations further require that all exposed metal surfaces in underground substations be connected to an earth. In a study of earthing conditions at Mount Isa mine it was found that the physical anchoring of metal work at substations (with rockbolts and associated steel mesh) also provides an excellent electrical connection to the country rock. It was established that not only is the mine's earthing system grounded at numerous underground locations but also that such anchor points offer, in general, a path to ground with lower resistance than does the legally required grounding point on the surface. It is recommended that metalliferous mines should utilise a multiple-earth system and not a run earth connected to a single, above-ground earth point

May 1, 1991

By N. J. Grant, K. M. Zwilsky, J. T. Blucher

DISPERSION strengthening has been studied in a number of metal-metal oxide systems. To date those pure metals available as fine particles (less than about 5 p) have received most of the attention whereas solid solution alloys, generally unavailable as fine powders, have not been examined in detail. The present work was undertaken as a preliminary study to evaluate combined effects of solid solution and dispersion strengthening. The technique used was that of dry mixing of elemental powders with the oxide, followed by a diffusion treatment to obtain the solid solution. The average particle size of the powders used was: Ni, 3.2 p (1nco B); Mo, 1.3 p (Fansteel Metallurgical Corp.); and y alumina, 0.027 \i (G. L. Cabot, Inc.). The particle size of the metal powders was determined by Fisher subsieve measurements while the size of the alumina was calculated from a surface area determination. Prior diffusion studies on small compacts pressed from mixtures of nickel and molybdenum powders with and without 7.5 vol pct A1203 indicated that diffusion was complete after sintering for 100 hr at 1800" , or 50 hr at 2250", or 20 hr at 2550° F. The progress of diffusion was followed by microstructural examination and micro-hardness measurements. Two observations made during the diffusion experiments were: 1) That diffusion proceeded faster in the presence of alumina, confirming similar findings by Seith and Loepman on "SAP'';4 2) That diffusion at temperatures above 1800°F resulted in coarsening of the alumina in agreement with results of other authors reporting on the growth of alumina in nickel above 1800"F. Similar experiments in the Ni-Cr system using 6 and 20 p Cr powders of 0.7 and 0.025 pct 0, respectively, did not result in significant solid solution formation even after long time exposures at 2550° F. It must be concluded that chromium oxide films around individual particles interfere with normal diffusion. A nickel alloy containing 5 wt pct Mo and 7.5 vol pct alumina was fabricated by dry mixing of powders, isostatically compacting at 30,000 psi, diffusing for 120 hr in dry hydrogen at 1800" F, and extruding at 1950"~ with a 30 to 1 reduction of area ratio. The resulting structure, presented in Fig. 1

Jan 1, 1963

By Thomas J. Crocker, Douglas B. Uthus

Tunnel Boring Machines (TBM) have gained worldwide acceptance in the construction field and are being employed in ever increasing numbers to drive underground transit lines, drainage systems, etc. However, TBM utilization in the mining industry, and more specifically coal mining, has been very limited. This paper reviews past and present applications of TBMs to coal mining and examines the needs of the industry in an attempt to offer some insight as to what a TBM system must provide if the excavation potential demonstrated in civil works projects is to be realized in coal operations. EUROPEAN EXPERIENCE Germany The Germans recognized long ago the potential of mechanized drivage for coal mine entry development. Early in the 1960's experimental runs were made with a full-face Wohlmyer roadheader at the Westerholt Mine and trials were conducted on a roller bit armed full-face Bade roadheader. But because of problems with penetrating the various carboniferous strata occurring in changing sequence and hardness, these first attempts were soon terminated. After viewing later successes in the construction industry with improved TBMs, new attempts were initiated by the German mining industry in 1971 to mechanize drivage of their development entries. Four TBMs of two different types were placed in operation.

Jan 1, 1976

By G. T. Fisher

The material requirements of carbide cutting tools for machining steel and cast iron are dependent on WC bonded with Co, with additions of TaCand TiC. The Bureau of Mines is conducting research to devise substi-tute materials, based on Ni-alloy-bonded TiC, for C-5-grade cutting tool applications. This substitution would result in less dependence on foreign sources for Co, Ta, and W, and use of lower cost materials. In this preliminary study, the Bureau investigated the effects of composition and processing variables on the transverse rupture strength and hardness of Ni-alloy-bonded TiC to identify compositions that exhibit promising mechanical properties. Further systematic modification of these compositions by soild-solution strengthening additions would subsequently be evaluated to obtain cutting tool materials with requisite properties and performance for C-5 applications. Compositions for evaluation were prepared by a powder metallurgy method of cold-pressing and liquid-phase sintering. Complementary analysis of compositions included chemical analysis, X-ray diffraction, energy-dispersive X-ray spectro-scopy, and density measurements. Based on results of this investigation, promising compositions were determined to be 59.37TiC-25Ni-5Mo-lO.63Mo2C, 59.68TiC-25Ni-3.33Mo-1.77Mo2C-6.67W-3.55WC, and 59.35TiC-25Ni-l.67Mo-3.54Mo2C-3.33W-7.1WC.

Jan 1, 1987

By Richard H. Bares

This report describes the purpose and application of seventeen statistical and mathematical procedures used in a series of studies made in the project ?A Systems Approach to the Reclamation of Strip-Mined Areas in North Dakota". The objective is to help readers better understand the utility of these procedures.

Jan 1, 1982

By C. A. Horne

"The transportation of mineral solids in the form of slurry is a subject most of us are associated with and, in fact, live with on a daily basis. The design parameters of slurry systems and most important the prime movers or cent¬rifugal pumps, are frequent and often controversial subjects due to the lack of practical guidelines which, if known and followed, can increase both reli¬ability and service life of the equipment.In this talk, emphasis has been placed on the practical side or rule-of-thumb approach to applications which, in turn, has been related to successful field results. The theoretical content and complex design criteria associated with actual equipment design has consequently been held to a minimum in the following discussions.I. BASIC SLURRY PUMP DESIGN CONSIDERATIONSFirst, to better understand how a centrifugal pump performs work, a basic description of the operating principles are in order.A. Operation In a pump, mechanical energy is transformed into pressure energyby virtue of the centrifugal force exerted by the rotating impeller. The liquid is discharged by centrifugal force at a velocity required to generate a given head and the volute collects the liquid so useful work can be done by the conversion of kinetic energy to pressure energy."

Jan 1, 1976

Narrow vein mining, with enough challenge and also where the cutting edge technology can be applied, is still a very important and exciting portion of the mining industry. Based on the deposit characteristics, the most flexible mining method, cut and fill, has been being tested mining this high grade Northern Nevada property, Hollister, since the year of 2008. In the last three years, 254,000 tons of ore were hauled out of the portal and 23,000 feet of development were excavated underground with the winning of several safety and environmental awards. Together with mine geology, the essential segments include mining cycle, ground control, ventilation, grade control and backfill method in cut and fill stopes were covered in this paper.

Jan 1, 2012

By T. H. Etsell, P. C. Holloway

Vanadium is concentrated in the fly ash which is produced as a solid waste from oil sands operations in northern Alberta. Although a process flowsheet using sodium chloride as a roasting reagent has been developed at the University of Alberta, recent studies examine the p otential o f p otassium o r c alcium s alts a s alternative reagents for roasting Suncor fly ash to recover vanadium. Suncor fly ash was roasted with CaO, Ca(OH)2, CaCO3, CaSO4.2H2O and KC1 at 750, 850 and 950°C. Water leach extractions for the calcium compounds were low (<45%); leaching with 100 g/L Na2CO3 gave maximum extractions of 56 to 69% at 950°C. Ash roasted with KCI behaved similarly to ash roasted with NaCl. These tests indicate that similar roasting conditions (25 to 30% KCI, 850°C, and 2 to 4h) could be used to achieve similar water leach extractions (75 to 85%). However, the lower solubility of KVO3 in solution, compared to NaVO3, would make the use of KCI instead of NaCl less attractive from a process and economic standpoint. Mineralogically, leucite (KAlSi3O8) was the predominant phase in ash roasted with KCl while, in crystalline samples of ash roasted with calcium compounds, anorthite (CaAl2Si2O8) and pseudobrookite (Fe2TiO5) were identified. Ash roasted below 950°C with the calcium compounds remained poorly crystalline.

Jan 1, 2004

By A. Adu-Acheampong

Stope instability at Ashanti Goldfields Company Ltd. (AGC) is a major concern. Using information from field mapping, major discontinuity sets were defined, Rock Quality Designation (RQD) was determined. The stability of wedges in the stope walls was assessed using the commercially available computer program UNWEDGE(Rock Science, 1992). Analytical results indicate that the presence of graphite infilling in joints contributes to instability, while steeply dipping joints control wedge slabbing and wedge toppling in the hanging wall. Stable stope widths and dimensions were determined to range from8.1 to 30 meters (m).

Jan 1, 2003

By Gary L. Seider

Helical screw piles are used in various applications including the underpinning of distressed foundations and as deep foundations for new structures. At present, maximum design loads range between 12.5 and 50 tons. Helical piles installed with in-situ grouting of the central steel shaft are a relatively new type of deep foundation, which have extended the present maximum design loads to the 100-ton range. Vickars & Clemence discussed this new foundation system in a paper presented at GEO-Denver 2000 in Denver, CO. Over the past three years, grouted shaft helicals have been used successfully on remedial and new construction projects all across North America. The authors have studied several construction projects in a variety of soil conditions to compile a list of practical design guidelines. Those guidelines include installability of grouted shaft helicals based on soil type, equipment requirements, grout selection, and theoretical vs. actual load capacity. In a number of cases, full-scale, field load tests were conducted in both granular and cohesive soils and the results broken down between tip resistance on the helix bearing plates and friction resistance on the grouted shaft. Data is presented which will further efforts to develop a design model and method to accurately predict the axial and lateral capacity of grouted shaft helicals.

Jan 1, 2003