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By Arthur S. Radtke

The structural setting of disseminated-replacement gold deposits of the Carlin-type and other aspects of their genesis are closely related to events which took place during the evolution of the Basin and Range province. The deposits formed as a result. of chemical and physical processes which took place at shallow depths in the roots of hot spring systems at moderate temperatures (about 200°C) and low pressures (about 25 bars) (Radtke and Dickson, 1974). Locations of Carlin-type gold deposits in the Basin and Range province are shown in Figure 1. Most of the block-faulted mountain ranges in the Great Basin formed by tectonic activity that happened since Miocene time, although faulting in some places probably began in Eocene to Oligocene time (Hamilton and Myers, 1966). The Carlin-type deposits are spatially related to Basin and Range-type faults: Many deposits, such as Getchell, Pinson, Preble, and Cortez, occur along the flanks of ranges, while other deposits, including Carlin (Radtke, 1974) occur within the ranges in areas characterized by crosscutting and intersecting high-angle or Basin and Range-type faults. The association of the ore deposits with Basin and Range-type faults is evidence that ore deposition is young, Miocene or later. The steep, high-angle faults played three roles: first, they provided deep channels for upward-flowing solutions; second, in preparing the rocks for fluid penetration by brecciation and general rock dislocation; and third, they moved sedimentary carbonate rocks, favorable for ore deposition, from deep levels to near-surface positions where the physico-chemical conditions were more suitable for the deposition of ore.

Jan 1, 1976

By R. Michael Craig

The flood basalts of the Columbia Plateau in eastern Washington State are under investigation for suitability in siting a deep geologic repository for high-level radioactive waste. To support safety and feasibility evaluations of the proposed repository construction and operation, an assessment is necessary of the potential for inflow of groundwater to the repository excavations from the surrounding saturated rock. Preliminary estimates of inflow are presented using simple models appropriate to the current understanding of available data. Both normal and bounding analyses are presented.

Jan 1, 1986

By Jon C. Jenkins

In order to plan the most efficient mine installation, a company should take advantage of all available information and tools. One of the first factors of a coal reserve that needs to be determined as accurately as possible is the quality of coal the mine will have access to during the life of the installation. With the aid of many types of well logs and computor analysis, we are investigating several methods of log correlation to determine such data as moisture, ash, sulphur, and BTU on an in place basis. It may be possible to determine this data more accurately in this manner than by using diamond drill cores for analysis and thus allow for a more profitable mine installation. The production of an underground mine is based on many factors, two of these being roof control and line water, where present either in the roof or coal seam. Using many of the same logs obtained from reserve and active mine areas, we have attempted to determine roof and floor characteristics such as strength, lithology, and moisture properties. Using data obtained from this program, we will make comments on possible length of bolt to be used, possible mining width, and pillar size as they would pertain to these reserves and active mine areas.

Jan 1, 1969

By A. Juganda, Jr. Bogin, S. A. Lolon, J. F. Brune, J. W. Grubb

"A longwall gob is mainly filled with broken rocks from the collapsed roof and becomes a porous medium where explosive methane-air mixtures can accumulate. In bleeder ventilation systems, this mixture can migrate out of the gob into the longwall face and other active areas in the mine during barometric or ventilation-induced pressure changes. When external pressures change, the gob does not perceive this disturbance instantly but with a delay due to air flow resistance in the porous gob material. The delay of gob response to outside pressure changes increases the pressure differential across the gob and may cause an outflow of explosive air mixtures from the gob into the adjacent bleeder entries. With computational fluid dynamics (CFD) modeling, researchers at the Colorado School of Mines have evaluated the impact of gob pressure fluctuations on the outgassing of the explosive gas zones (EGZs), the magnitudes and rates of pressure changes, the volumes as well as the potentials location of outgassing if it occurs. INTRODUCTION The air pressure field in underground mines is controlled by many factors such as operating fan settings, ventilation controls, surface atmospheric conditions, and other local events that can intermittently disturb mine pressure, including blasting, roof falls, or inundations. Mine fan settings are rarely changed. Mine atmospheric pressure fluctuations due to adjustments in ventilation controls occur more often during the mining process. Atmospheric conditions and barometric pressures can generate fluctuations in mine pressure on a large scale. Atmospheric pressures change regularly every day but can fluctuate abruptly and become increasingly hazardous in adverse weather conditions. Investigations conducted in coal mines in the United States, Australia, Poland, and South Africa observed higher methane emissions from the gob during periods of falling atmospheric pressures, which led to mine explosions (McIntosh, 1957; Boyer, 1964; Kissell et al., 1973; Fauconnier, 1992; Belle, 2014; Wasilewski, 2014; Lolon et al., 2015). Falling external pressures are understood to cause potential outflow of explosive mixtures from the gob, while rising pressures may push fresh air into the gob. This phenomenon is widely known as gob breathing. The actual processes that trigger gob breathing are not fully understood, nor are the parameters that contribute to the process. Other major events such as roof falls or fan failures can also change the pressure conditions in the mine. In contrast to atmospheric pressure changes, these events can change mine pressures much more rapidly or immediately. TIME LAG AND GOB BREATHING CONCEPT In a bleeder ventilation system, the pressure in the gob is designed to be lower than that of the headgate entries and the longwall face. Air from the gob and gate entries flows towards the tailgate-bleeder returns. When the external pressures are disturbed, this designed pressure arrangement may change, potentially resulting in increased outflow from or inflow into the gob."

Jan 1, 2017

By James H. Harmon

As the trend to deeper mines, producing from marginal ore bodies, continues, mine hoists and their associated equipment will become more sophisticated, complex, large and expensive. Over the past two decades, mine hoisting equipment and systems have moved from steam engines to static rectification of ac to dc, and electronic controls are the standard. It is the intent of this section to present what is currently available in the field of mine hoisting equipment and systems. Because the present engineer has been exposed longer and more intensively to such things as computers, electronic devices, and machine design, no attempt has been made to make this a layman's article. Contributions from the electrical design and application engineer, gearing and hearing design engineers and other specialists have been incorporated. Some material will be devoted to electrical drive systems, rectifiers and gearing design among others. These items are inherent in the design of a mine hoisting system and the subsequent selection of the correct, most reliable and most economic system. The mine hoist can be a bottleneck between the underground mine and the surface mill. Correct selection of the right type of hoist is imperative. In this vital link between mine and mill, crude estimates of hoist capacity are not good enough, and the mining engineer must design and select the right hoisting system to meet the design specifications. 15.1-MINE HOIST TYPES There are two basic types of mine hoists available anywhere in the world today: the drum hoist on which the hoist rope is actually stored during the hoisting cycle, and the friction (Koepe), which merely passes the rope over the wheel during the hoisting process. Drum and friction hoists are "generic" terms which describe the two basic categories. Within each category are variations, as below. 15.1.1-DRUM HOISTS Drum hoists, as noted, actually store the hoist rope on the drum much the same as line on a fishing reel. To accomplish this task, the drums are so designed to store, in one or more layers, the footage of wire rope equal to the total maximum hoisting distance plus sufficient rope for cutting and inspection at regular intervals and for holding to the drum (see Fig. 15-1). Usual practice in hoist drum design is to allow three turns of hoist rope for holding on the drum and three turns for inspection cuttings. 1. Single-Drum Hoists-Fig. 15-2 shows a typical single-drum hoist as manufactured by most U.S. heavy-mining-equipment companies. With the exception of some very minor features, this design configuration is standard throughout the U.S.A. Fig. 15-3 is a plan view of a typical single-drum mine hoist. This particular hoist has a single-motor drive and a double-reduction set of gearing.

Jan 1, 1973

By J. R. Kadambi, C. Shingote, J. Furlan, R. Ke

"Hydrocyclone separators are widely used in various industrial applications in the oil and mining industries to sort, classify and separate solid particles or liquid droplets within liquid suspensions, which are considered to be multi-phase systems. Numerous valuable studies have been conducted in recent years to investigate the flow fields inside hydrocyclones. However, much of the information regarding the performance of cyclones in the literature has limitations, based in some part on the respective current-available theoretical models, and much of it cannot be considered as completely applicable to most real-world applications; many of the studies investigated the flow fields within extremely simplified hydraulic designs that are not representative of the complex geometries or large sizes which are typical in industry. Therefore, in this study, the two phase flow system inside the actual hydraulic geometry of a milling circuit hydrocyclone was explored with the aid of both computational and experimental techniques (Particle Image Velocimetry). In this study, the flow field with an air core has been investigated; in essence, the research was a two-phase problem, which caused some challenges on both the computational and experimental sides. Two turbulence models were used in the numerical calculations: the Reynolds Stress Model and Large Eddy Simulation. The computational studies are mainly focused on the prediction of the dimensions and shape of the air core. Different section planes of the hydrocyclone were selected as planes of interest and then were divided into several fields of view (FOV) for PIV measurements. Two dimensional experimental velocity vector maps were obtained in each of the fields of view. The computational results were validated globally using pressure and flow rate readings at the boundaries and locally by comparison to the PIV velocity vector maps and profiles. Keywords: Computational fluid dynamics (CFD); Hydrocyclone; Particle image velocimetry (PIV); Reynolds Stress Model (RSM); Large Eddy Simulation (LES). INTRODUCTION A hydrocyclone is a device used to separate a solid-liquid, liquid-liquid, solid-gas, or liquid-gas suspensions into at least two separate density or particle size components. Hence, the flow field of the hydrocyclone is generally considered a multi-phases flow system. Application of hydrocyclones have been used in numerous industries including oil, drilling, metal working, and mineral processing since 1891, when E. Bretney obtained the first patent for the predecessor design of all contemporary hydrocyclones. A modern hydrocyclone typically consists a cylindrical section at the top where the liquid is being fed tangentially, and a conical chamber attached to the bottom of the cylindrical section, as shown in Figure 1. The characteristics of the feed stream that is injected into the cylindrical chamber play a significant role in hydrocyclone operation. The inlet is tangential relative to the cylindrical chamber and hence causes a centripetal force in the flow field which is considered as the primary separation mechanism."

Jan 1, 2017

By Martín A. Encinas-Romero, GUILLERMO TIBURCIO-MUNIVE, María M. Salazar-Campoy, Patricia Guerrero-Germán, José R. Parga-Torres, Luis S. Quiróz-Castillo, JESÚS L. VALENZUELA-GARCÍA

Pressure oxidation is a hydrometallurgical oxidative pretreatment for refractory ores, such as sulfide ores. Here, simultaneous alkaline pressure oxidation and sodium cyanide leaching treatments were carried out on a pyritic ore from the Mulatos Mine located in Sahuaripa, Sonora, Mexico. Mineral characterization, agitation leaching, hot cyanidation under atmospheric pressure conditions, simultaneous moderated pressure oxidation and leaching, and kinetic testing results are shown. The modified variables were temperature, pressure, and cyanide concentration. Characterization indicated that pyrite was the main mineral. Simultaneous pressure oxidation and leaching experiments were conducted at a temperature range of 40–80 °C, oxygen pressure of 87.5–200 psi, and cyanide concentration of 0.8–1.2 wt% in a 2-L Parr pressure reactor. A dissolution rate of 81–86% was achieved under the following conditions: 87.5 psi, 80 °C, 0.8 wt% NaCN, for 1 h.

May 7, 2020

By M. Sengupta

Surface mining in arctic regions is characterized by many unique problems. Continuous and discontinuous permafrost (perennially frozen ground) occurs in most of the arctic and subarctic areas. Permafrost presents special problems of slope stability. Stability of permafrost depends on its temperature, moisture content and material type. Permafrost slope fails due to solifluction, disturbance of ice rich slopes, and liquefaction. Drilling and blasting of frozen ground present special problems. Depending on their degree of saturation with water, freezing soils and rocks have a number of important characteristics that affect blasting efficiency. Metals used in mining equipment and mining structures require special selection. At low temperatures many steels lose most of their normal ductility and toughness (resistance to brittle fracture). The paper discusses engineering solutions to unique problems of arctic mining.

Jan 1, 1986

By G. M. Li

It is shown that seriously preoxidized arsenopyrite can adsorb a large amount of copper ions as unoxidized one, but without, release of corresponding amount of Fe ions; seriously preoxidized pyrite cannot adsorb copper ions, but with release of a large amount of Fe ions. However, if the minerals are rapidly oxidized with potassium permanganate solution, both arsenopyrite and especially pyrite can adsorb a large amount of copper ions, but still without release of corresponding amount, of Fe ions. Cu adsorption (if there is any) on both oxidized arsenopyrite and pyrite is not based on the Cu-Fe exchange mechanism.

Jan 1, 1991

By Palmer C. Sweet

Mining-related wastes, which are increasing, are being utilized more and more as valuable resources in Virginia. The Environmental Protection Agency (EPA) divides mining-related wastes into two categories: those generated from mineral extraction and beneficiation and those generated from mineral processing. Materials from both categories are produced in Virginia, where waste (by-product) materials are present at a variety of mining sites and processing plants; some of which have been exploited for various uses in the past and/or present. These materials include: used concrete recycled for roadbase material; pyrite coated with magnetite for use in portland cement; minor amounts of fly ash for use in concrete block, lightweight aggregate, and flowable structural fills; granite and diabase quarry fines for use as agricultural and asphalt filler; lime kiln dust for use in neutralizing and stabilizing coal refuse; soapstone aggregate for use in terrazzo heat retention panels; kaolin for use as a filler product and as an ingredient in white cement; slate quarry fines used as landcover and combined with aggregate for crusher run and as a filler in asphalt; and coal refuse for use as fuel in a lightweight aggregate plant. There are some materials available that have never been utilized, although several ideas were investigated to turn them into usable commodities. One such material is a high-alumina scrap produced as a by-product at a ferrovanadium processing plant. However, large quantities of waste materials from metal mining, industrial mineral, and fossil fuel operations remain to be disposed of in an environmentally safe and economic manner. In 1989, almost one million tons of fly ash were produced from burning of coal at eight coal-fired power plants in Virginia. Present uses for this waste such as an ingredient in concrete block, concrete aggregate, and in structural fills cannot dispose of all the available material; however, increased use of fly ash as a soil/rock substitute for structural fills and embankments may solve the problem of its disposal. Another waste material is calcium carbonate precipitate paste produced at a lithium carbonate processing plant and presently being used for back filling an on-site inactive underground limestone mine. Flue gas desulfurization (FGD) wastes in the form of CaS04 will probably increase threefold. If this material contains a minimum of 95 percent gypsum and negligible chloride, it may have a value to a wallboard manufacturer as we move toward the year 2000. Thought must be given how this increasing waste can be disposed of in an environmentally safe manner.

Jan 1, 1995

By R. C. Hopper, A. A. Mathews, T. A. Lang

DESCRIPTION OF PROJECT The Straight Creek Tunnel site is located approximately sixty (60) miles west of Denver, Colorado, on Interstate Route 70 in the vicinity of Loveland Pass, in the Rocky Mountains. The ultimate project will consist of dual two-lane vehicular tunnels with a building at each portal to house mechanical ventilation equipment and other installations. The tunnels run virtually east-west on an ascending 1.64 percent grade for a distance of approximately 8,900 feet, and will pass beneath the Continental Divide at an elevation of about 11,000 feet above sea level. The maximum cover is 1,450 feet and each tunnel is approximately 48 feet wide by 50 feet high as excavated. The work now under construction consists of the North Tunnel, which initially will have two-way traffic. Ultimately it will be the west bound lanes for Interstate 70. The completion of the North Tunnel will be the fulfillment of a long felt need for better communication through the high Rocky Mountains of central Colorado and is a vital link in Interstate Route 70. The early planning for a vehicular tunnel through the Continental Divide began in the late 1930's and between November, 1941 and May, 1943 an exploratory pioneer tunnel

Jan 1, 1997

By Ehsan Alavi, Brian Hagan, Colin LaVassar, Glen Frank, Derek Dugan, Rick Capka, Lisa Mori

"Tunnel face instability is one of the most common issues in EPB tunneling. The evaluation of an ideal face support pressure is a critical element in the design and construction phases of EPB tunneling. In this study, measured tunnel face pressures in three EPB tunneling projects (University Link U230 and U220 projects and the Northgate Link Extension N125 Project) for Sound Transit in Seattle, WA are compared with the calculated analytical methods. This comparison shows that the analytical methods generally overestimate the required tunnel face support. The best practice for managing the face pressure in EPB tunneling operation is discussed based on the experience gained through these projects. Furthermore, the algorithm that is developed for identifying ground loss in these projects is addressed. INTRODUCTION Earth pressure balanced tunneling relies on using muck within the chamber to support the face. Muck is pressurized by controlling the advance rate of the tunnel boring machine and the speed of the screw conveyor. Target face pressure is typically calculated by using the geotechnical assumptions in the geotechnical baseline report. The concept behind EPB tunneling is that the application of sufficient face support pressure will prevent tunnel face instability and the resultant over excavation. Tunnel face instabilities caused by a lack of sufficient face support can lead to ground loss and surface settlement (Anagnostou & Kovári 1996, Kirsch 2010). A certain support pressure must be achieved to counteract water and earth pressure with an adequate factor of safety. While the water pressure can be predicted accurately, the determination of the resultant earth pressure on the face is less precise. This becomes manifested in the relatively high partial safety factors on the earth pressure."

Jan 1, 2016

By Scott G. Britton

Today's coal mines are turning more and more to belt haulage as the key system to transport coal out of the mine. The advantages of using belt for both intermediate and main haulage are numerous. Belts are reliable high capacity haulage mediums that can be utilized at low operating costs. They are adaptable to rolls in the coal seam and can handle relatively steep grades. They are not noisy, operate with a minimum amount of labor, and are easily extended and retracted. Belts require the least power of any haulage medium, are easily controlled by push- buttons and interlocks, and present low fire and safety hazards. Belt haulage can also be the largest source of operational problems for mine management when not installed correctly. This chapter and Chap. 6 concentrate on proper installation of both the static and dynamic components of efficient belt haulage. This chapter looks at the static system component, composed of the belt drive, its installation and operation, as well as belt takeup and transfer point construction. These components do not change readily over the life of the installation, hence the term static system. Chap. 6 discusses the dynamic system of belt line construction, which includes belt splicing, breaking down and reanchoring the tailpiece, and extending the belt line, plus operational and maintenance items for belt operation. This chapter is divided into three major topics. The first is a general discussion covering the points necessary for designing an efficient haulage system; the second looks at installing belt drives, head rollers, and takeups, and the third discussion centers on installing efficient and effective transfer points along the haulage system. Each will address the design and construction issues facing the engineer or construction supervisor in charge of installing the system. Before looking at the static system, it may be useful to review some of the basic design factors and considerations of all belt haulage systems. The material usually carried on an underground belt is a mixture of raw coal and rock, commonly known as run-of-mine (ROM) coal. This mixture has certain material characteristics that guide the mining engineer to the final and proper belt selection. The characteristics looked at most frequently are: 1) Angle of Repose is the angle at which the material will freely make a pile. Most ROM coal averages a 35"-39" angle of repose. 2) Angle of Surcharge is the angle a pile will assume on a moving conveyor. This ranges from 5" to 15" less than the angle of repose in most materials. For ROM coals, 25" is the average angle of surcharge. 3) Flowability, which determines the maxi- mum cross-sectional area needed to carry any given material on a belt. It is measured by the angles of repose and surcharge of a material and also serves as an index of the safe incline angle for the belt line. These characteristics, plus practical engineering research and development work are defined by an organization called the Conveyor Equipment Manufacturers Association (CEMA) for most bulk materials. CEMA also provides a code for each classified material depending on the characteristics above and the subjective considerations of the average size to be encountered, the abrasiveness of the material, and any miscellaneous characteristics (oil resistive, corrosive, etc.) which may be important. For coal, CEMA (composed of member companies in-

Jan 1, 1983

By Jon C. Volkwein

The U. S. Bureau of Mines investigated a method of using inert gas to prevent the formation of explosive gas mixtures in auger highwall mining of coal. A combination of gasoline and diesel engine exhaust gases was introduced into the auger drill hole using a short section of pipe located at the collar. Gas samples were taken and analyzed on site with infrared detectors for oxygen, carbon dioxide, methane, and carbon monoxide. Evacuated bottle samples were also taken and analyzed by gas chromatography at the Pittsburgh Research Center. These gas results were analyzed for explosibility. Personal exposure to carbon monoxide was also monitored. The highest methane level observed was 9.55 pct. The Inert gas levels, (carbon dioxide and nitrogen) were sufficiently high to prevent any ignition of the methane. Results showed that for all conditions during mining, gas concentrations were non-explosive. The maximum personal time weighted average sample for carbon monoxide was 20 ppm. This system provides a safe, inexpensive, simple method for preventing explosions during auger mining. INTRODUCTION The auger highwall mining method is an effective method to recover coal from a reserve when removal of the overburden by surface mining equipment becomes uneconomical. In this method of mining, a horizontal auger enters the coal seam from the surface mine bench under the highwall and the coal is drilled in a series of parallel holes. Historically, coal mined from the surface is relatively shallow, and over time, methane associated with the coal has dissipated through the surface. In most circumstances, little methane has been found associated with auger mining. However, mining technology has enabled surface mining of deeper reserves of coal. Furthermore, environmental constraints have forced the highwall extraction method to be used to remove coal under wetlands, further increasing the chances of encountering methane. Recently incidents of methane explosions at a few auger mining operations have resulted in injuries and increased testing for methane at the collars of auger holes. The fuel source of the reported explosions was not necessarily limited to methane, but may also have involved coal dust. The Mine Safety and Health Administration (MSHA) met with the Bureau to discuss what technology might be available to enable the safe resumption of mining. The discussion included the difficulty of ventilating through the solid shafts of the augers, that steel bits probably created the ignition source, and that perhaps inerting the holes with low oxygen and high carbon dioxide concentrations from the machine's diesel exhaust was a potential solution. Considering the ventilation aspects of the problem, it was not clear If ventilation could be reliably established. If some degree of ventilation to the front of the mining head is achieved, it may combine with methane to bring the hole atmosphere from a rich, nonexplosive mixture to an explosive mixture. Furthermore, it may not prevent a dust explosion in such a mining configuration. Lack of access through the shafts of auger type mining machines further limits the ability to add water or air to cool bits to prevent an ignition source from developing. Either of these approaches would also be expensive. The process of mining coal In an inert atmosphere has been considered in the past, but to our knowledge, never implemented (Department of Interior, 1970). Clearly, implementation in underground mining would be more complicated. On a mine bench open to the atmosphere, however, adding inert gas to the mining head could provide a quick, feasible method to prevent explosions at auger highwall mining operations. Also the problem of how to move the inert gas to the cutting head of the machine had to be considered. Preventing explosions on auger mining machines using inert gas requires three primary considerations: first is the source of inert gas; second, placing the inert gas at the cutter head; and third, monitoring the hole atmosphere. Any gas source having an effective inert gas concentration of 34 volume pct or greater will prevent methane from Igniting (Zabetakis, 1965). Sources of inert gas considered for this application included liquid nitrogen, modified shipboard inert gas generators (for hydrocarbon shipping and transfer), jet turbine engine (Paczkowski, et. al., 1982), the auger's diesel engine and a gasoline engine. Operation cost, purchase cost and availability limited our testing to the diesel and gasoline engines. This work tested each engine, separately and combined. To ensure effectiveness, both company and enforcement personnel need to know how to monitor the condition of the inerted hole. Measurements at depth inside the hole are possible by remote sampling through rigid tubing, but this method is Impractical for routine monitoring. Continuous monitoring of the exhaust gas stream is an alternative. The U. S. Bureau of Mines evaluated an inert gas system at an auger mining operation at a surface mine near Owensboro, KY. Coal was mined from the Number 9 Coalbed in Henderson Co. KY. Tests were conducted in January and March of 1992.

Jan 1, 1993

By A. T. Yu

Bulk sampling is define' as the ?process of extracting a small fraction of material from a large bulk ...sufficiently representative ...for the intended purpose.? (ref. 1). Today's pressing need for simple, effective and reliable sampling systems is intensified by the growing demand for quality control as a means to cope with inflation, competition and rapidly increasing consumption of raw materials. Much has been written on bulk sampling (ref. 2 thru 9). It involves a wide range of subjects cutting across the domains of physics, chemistry, geology, mining, materials handling and processing, as well as probability and statistics. Since the problem itself is complex, any in-depth treatment cannot avoid a somewhat lengthy coverage. Of all of the related topics. Arbitrary, haphazard studies, on the other hand, can leave out important details and obscure or confuse the issue.

Jan 1, 1970

By Bahne C. Cornilsen, X. Shan, David H. Carlson, John H. Johnson

The air in three U.S. underground coal mines has been sampled. The data developed show the relative importance of the various pollutants and quantify the need for control. Total respirable particulate matter (TRPM) was found to be the critical pollutant (the one requiring the most dilution for control). TRPM is considered to be "respirable coal dust" by procedures approved for sampling in U.S. underground coal mines. However, this "respirable coal dust" also includes diesel particulate matter (DPM) and particulate from other sources. While "respirable coal dust" was the critical pollutant, Raman spectroscopic analysis showed that more than half of this "respirable coal dust" was DPM. The DPM in the samples ranged from 22 to 152% of the 2 mg/m3 limit for respirable coal dust. Thus DPM was the critical pollutant using the 2 mg/m3 respirable coal dust limit. SO2 gas produced by the combustion of diesel fuel containing sulfur was the second-most critical pollutant. Characteristic curve slope (CCS) values were calculated to determine the quantitites of the various pollutants generated per unit of diesel haulage activity. Mine 1 had the highest TRPM CCS values with 29 mg/m3/%C02 for the Ramcar and 57 mg/m3/%C02 for the Haulageway location. The highest coal particulate CCS measured was 30 mg/m3/%CO2 and the highest diesel particulate CCS measured was 27 mg/m3/ %C02. Both of these high values were measured in the Mine 1 haulageway location. Calculations were made to determine the controlling CO2 concentrations (CCC) at which all other measured pollutants would be within their limits. These CCC values, which, for the mines sampled, were based on TRPM, varied from a low of about 0.07% for the Mine 1 haulageway location, to a high of about 0.15% for the Mine 2 Ramcar and haulageway locations. Weekly average CO2 concentrations measured in these mines ranged from 0.09 to 0.11 % for the Ramcar, from 0.05 to 0.09% for the haulageway, and from 0.08 to 0.11 % for the return. The concentrations of TRPM ranged from 1 and 2 mg/m3 in mine areas frequented by personnel, and to greater than 4 mg/m3 in returns where personnel are not exposed.

Jan 1, 1991

By John W. Scott

INTRODUCTION The design criteria for a particular concentration and dewatering project will provide the formal basis for design of the process, equipment and facilities. These criteria will specify the required capacities and operating schedules for the equipment, as well as the quantity and quality of the feed to be processed and products obtained. The general climatic and geographical conditions at the site, specific information on soil or rock conditions; and applicable design standards and codes will also be included. The design criteria will generally be based on an interpretation of testwork carried out on the particular ore and site, and will thus parallel in detail and completeness this testwork. As the project moves from the early conceptual phases through to final detailed design, the design criteria will be developed and become more detailed as information is generated and made available for use. The design criteria are critical to the design effort as the formal specification to the designer of what and how much is to be processed, what and how much is to be produced, and where and under what conditions. The actual design criteria will be a formal tabulation of the design basis information developed for the project in question. For a preliminary study, this may consist of a single page of data; for a feasibility study several pages and for a detailed design up to several hundred pages and multiple volumes. Depending on the complexity of the process and the level of detail included, each project will be unique to some degree. The design process for a project normally progresses from preliminary conceptual phases through to a final detailed design. The criteria used for the initial concepts are generally developed from rough data and preliminary testwork on the ore in question. Regardless, the plant throughput and products are defined, thus giving a scope and definition to the study phase. In some studies a range of throughputs may be analyzed in order to arrive at the most economically attractive size for the proposed operation. This optimum size is then used as the design throughput for the more detailed design phases. Similarly as more testwork results are available and the ore characteristics and process become more well defined a continuous updating of the design criteria is undertaken.

Jan 1, 1986

By James G. Tilton

Subsidence resulting from mining operations, has been the object of sporadic study for many years. Reports have shown that subsidence has ranged from minor settlement detected only by precise measurements to great slips where buildings are destroyed, roads disrupted, and large fissures opened at the surface. For years, a controversy has raged over the question of whether there is a positive or negative angle-of-draw. None of these questions can be given a flat answer for the variables controlling, subsidence are infinite. Generalizations can be made for various situations and areas but some means of control must be executed.

Jan 1, 1966

By A. J. Lynch, M. J. Lees

Introduction The design of wet grinding circuits may vary considerably according to the duty which is to be performed. Grinding machines which are commonly used in these circuits are rod mills, ball mills, autoge¬nous mills, and pebble mills while size separation machines commonly used are vibrating and wedge-wire screens, hydrocyclones, and rake classifiers. In some circuits, such as those producing feed to cement kilns, all the ore entering the circuit is discharged in a single product stream. In others, such as those operating on magnetite-taconite ores, the feed entering the circuit leaves in two or more streams. Grinding circuits in flotation plants normally include sections in which either the concentrate or the tailings from the primary flotation circuit is reground and these additional sections should be regarded as an inte¬gral part of the grinding circuit. A typical circuit is shown in Fig. 18. Problems in achieving maximum efficiency may occur at three stages: 1) At the design stage when the optimum size reduction flow¬sheet must be selected with respect to the types, numbers, and sizes of processing units. 2) At the operating stage when the correct selection of values must be made for those variables which may be altered while the circuit is off-line but which are constant while the circuit is on-line, for instance the vortex finder diameter of the cyclones. 3) Under conditions of continuous operation when changes in the circuit feed or in the mechanical operation of the circuit may cause undesirable changes in the circuit product. The first two prob¬lems are concerned with optimization, that is, with making the best choice from many possibilities, and the last with control. Optimization Problems. The main purpose of a wet grinding circuit is to produce particles with a sizing distribution which will ensure optimum performance of the later chemical reaction or physical concentration circuits, because it is on the efficiency of these later circuits that the economics of the total mineral treatment process depend. The size distribution of the product from a grinding circuit may be affected by many variables, some concerned with the arrange¬ment and operation of the machines and some concerned with the ore characteristics, and it is important that these should be recognized in the design and operation of the circuit. For instance, in a simple ball mill-cyclone circuit the variables which affect the product size even for constant feed characteristics are shown in Fig. 19. In addition, the rate, size, hardness, and mineralogical composition of the feed will affect the performance of the circuit and the product size. When the circuit contains more than one mill, both the number of choices available and the complexity of the problem are increased consider¬ably. Consequently, one type of problem which is to be solved if an optimum product is to be obtained from an existing grinding circuit is that of circuit design, and this includes arrangement of processing units and selection of those operating conditions which cannot be altered when the circuit is operating, such as mill speed and cyclone inlet and outlet dimensions. The other major problem in optimization is encountered at the design stage when a choice must be made about the type, number, and size of processing units. For instance, for a typical high-capacity size reduction operation, should two circuits each containing one rod mill and two ball mills or three circuits each containing one rod mill and one ball mill be used? Alternatively, should ball mills only be used and if so, how many, what size, and what arrangement?

Jan 1, 1985

By Paul E. Epstein

Despite the controversies that have surrounded asbestos over the past 20 to 30 years, no knowledgeable authority has doubted the usefulness of this material. Were it not for the health risks associated with the manufacture and use of asbestos products, its physical and chemical characteristics would continue to be hailed as an undeniable boon to mankind. However, it has become clear over the past 30 years that like other major contributors to our modern industrialized society, asbestos must be handled responsibly and with the full understanding that lack of care can lead to injury, suffering and death. In this sense, asbestos shares characteristics with nuclear power, pesticides and even motor vehicle usage. It is unlikely that modern society would be willing to walk away from the benefits bestowed by any of these valuable resources. Rather, the appropriate response to the identification of danger is to define the type of risk, quantify its incidence, search for methods of decreasing the risk and implement programs to achieve the goal of minimization of risk. We should recognize at the outset that the risk cannot be diminished to zero without elimination of the material entirely from our midst. The concept of acceptable risk is a complex issue involving medical, legal, financial, moral and even psychological factors that defy precise quantification. In essence, the major danger produced by exposure to asbestos is its potential effects on the respiratory system. Despite the fact that asbestos workers have constant skin contact with the material and porbably swallow it in the course of their activities, inhalation of the fibers is recognized as the major health risk associated with its use. Aerosols of asbestos are inhaled not only by miners, millers and fabricators but also by urban dwellers who have no direct occupational contact with the material. This occurs because asbestos has been applied to our buildings and has been used in a wide variety of products that touch our daily lives. While it is estimated that three to four million people in the United States have been occupationally exposed to asbestos, the number who have been non-occupationally exposed is many times that number.

Jan 1, 1984