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By C. A. Pickles, S. J. Splinter

Silicon oxynitride, Si2N20, has many of the intrinsic properties of a potential high temperature engineering ceramic material. Some of these properties are similar to those of silicon nitride, which has been more intensively studied. However, although silicon nitride ceramics are approaching a state of microstructural refinement for various engineering applications, silicon oxynitride has received little attention. This has been mainly due to a lack of an economical and reproducible method of producing pure crystalline Si2N2O. Several reports exist on the preparation of crystalline Si2N2O from SiO2 and Si3N4, yet very little kinetic data exist. Even less is known about the carbothermic reduction of SiO2 in a nitrogen atmosphere to produce Si2N2O. In this paper, a review of the properties and methods of preparing silicon oxynitride will be presented. In addition, results obtained by reactively sintering SiO2 and Si3N4 will be discussed. The overall reaction is as follows:

Jan 1, 1990

By Charles Banks Belt

In 1925, Niggli (1925, pp, 1-69), formulated a physico-chemical, explanation for the origin of hydrothermal ore deposits, from a concept that had appeared earlier in the literature in the writings of Von Groddeck, Stelzner, Beck, de Launay, Kemp, and Lindgren. Niggli proposed that pressure at depth could force volatiles from deep-seated magmas. The volatiles would In turn form pegmatites and then ore deposits as the fluids cooled. This is one view of a general theory of ore genesis that gained secondancy for years among such prominent geologists as Fenner (1926, p, 697) and Emmons (1936, pp. 29-70). It was, proposed that ore deposits were precipitated from solutions or fluids that had escaped or been separated from a deep-seated magma by means of liquid immiscibility or crystallization or gas transfer. This theory is based on the presence of igneous rocks close in space and age to hydrothermal ore deposits in many mining districts of the world. As is well known, there are many ore deposits apparently of hydrothermal origin that are neither spatially nor chronologically related to igneous rocks, In still other localities where there are no hydrothermal ore deposits, igneous rocks occur that are similar in composition to those in mining districts. In view of such facts, the applicability of the Niggli theory to all hydrothermal ore deposits may well be questioned. The chief purpose of this paper is to test the Niggli theory by studying the primary petrology, hydrothermal alteration, and distribution of copper and zinc in silicic igneous plutons supposedly genetically related (in the Niggli sense) to nearby hydrothermal ore deposits, Silicic Tertiary plutons in three New Mexico mining districts were chosen, the Hanover-Fierro intrusive at Hanover and Fierro, the Granite Mountain pluton at Magdalena, and the four outliers of the Lordsburg stock at Lordsburg. First, it had to be established whether the observed plutons were or were not the source of the adjacent ore deposits. This was done by studying the relation between the copper or zinc distribution-and the primary or secondary features in the plutons studied, and the time relations between instrusion and ore deposition. Primary igneous features of a pluton are defined as the minerals, texture, shape, and character of the pluton which were formed prior to the complete solidification of the rock, secondary features include all changes that took place in a pluton after solidification. They are identified by their cross cutting nature or as replacing primary minerals, Under the Niggli concept, it is proved that the ore ions did not originate from the parts of the pluton now visible as immediately adjacent to the ore deposits; it must then be established, if possible', that the ore ions were separated from deeper parts of the intrusive, Some idea as to whether the copper or zinc ions originated from a related magma at depth may be gained by a comparison between the primary (that is, pre-alteration) zinc and copper abundances found in ore localizing intrusive studied and the average abundances for copper and zinc in silicic igneous rocks most recently given in the literature. Finally, the relation between ore deposition and hydrothermal alteration was studied on a regional as well as on a local scale.

Jan 1, 1958

By M. Gunter, M. Buzon

"Talc formed by hydrothermal alteration of preexisting carbonate rocks is known to be nearly monomineralic, and lacking in amphiboles. In southwest Montana, talc formed from hydrothermally altered dolomitic marbles, and is still actively mined. These talc deposits are typically in contact with quartzofeldspathic gneiss and marble. Accessory minerals vary between these rocks and the ore producing body; the identification and characterization of such minerals requires carefully selected analytical methods. Recent litigation and ensuing confusion over the petrology and asbestos content of these deposits challenges the talc mining industry in Montana, and elsewhere in the world. INTRODUCTION Commercial talc has been mined from the deposits in southwest Montana since the 1940s, and by 1956 the region had output 200,000 tons of talc ore (Chidester et al., 1964). Commercial talc refers to rocks containing more than 20% of the mineral talc (McCarthy et al., 2006); the ores from Montana typically contain upwards of 90% talc. This region remains the leading domestic source of talc in the U.S. partly due to the reserves in the area, and partly due to the diagnostic purity of the ore compared to that of other regions, some of which are no longer actively mined. The mineral talc, a sheet silicate, is expressed by the formula Mg3Si4O10(OH)2, and therefore can form in geologic environments that are rich in Mg, Si, O and water. The protolith for the talc deposits in southwest Montana is a dolomitic marble, but other common protoliths include ultramafic igneous, mafic igneous, and siliceous dolomites (McCarthy et al., 2006). Physical properties such as hardness of 1 on Mohs hardness scale, white streak and slippery feel are among some of the reasons why talc is so widely used as fillers in a number of industries. In decreasing order, ceramics, paper, paint, roofing, plastics, rubber, and cosmetics are the leading domestic industries that use talc despite the decreasing trend in U.S. talc use and production since 1994 (Virta, 2015). The purpose of this paper is to describe the mechanism of talc formation in southwest Montana by focusing on talc deposits and surrounding rocks in the Ruby, Greenhorn, and the Gravelly Ranges, and to relate the mechanism of formation to the composition of talc ores. The compositional data show mineral content of selected ores, and the major and trace element content of those minerals, specifically talc. Our electron microprobe (EPMA), powder x-ray diffraction (XRD) and x-ray fluorescence data for samples from five mines in these three ranges provide continued evidence of the purity of these ores despite claims made during recent litigation that these ores contain asbestos. The five mines that we discuss include the Beaverhead, Treasure, Regal, Willow Creek, and Yellowstone Mines (Figure 1.)"

Jan 1, 2016

By S. Kelkar, H. Murphy, Z. Dash

Nearly 30 estimates of the minimum earth stress were obtained from hydraulic stimulation tests in 5 boreholes at depths varying from 0.6 to 4.3 km in jointed granitic rock near the Valles Caldera in New Mexico. This site is located within the transition between the Colorado Plateau and Basin and Range provinces. Stresses were determined from open hole hydraulic fracturing experiments conducted with water at pressures up to 48.3 MPa (surface). The virgin bottomhol e temperatures ranged up to 327°C. Pressure records show no evidence of rock breakdown, indicating injection into pre-existing joints. A typical pressure response consists of an early wellbore storage period followed by linear fracture flow, which then evolves into a steady pressure, fracture extension mode. Shut-in behavior is characterized by a sharp pressure drop followed by a more gradual decay. The minimum earth stress shows a general linear trend with depth, increasing with a gradient of 19 MPa/km. A low stress anomaly occurs from 2490 to 3100 m where the minimum stresses are as much as 28 MPa lower.

Jan 1, 1986

By Arafat Ghosheh, Yousuf Abu-Rish, Darwish Amara, Mohammed Baderkhan

The Jordan Phosphate Mines Company is one of the world's major phosphate rock and phosphatic fertilizers producers (the second largest phosphate rock exporter), with ore reserves exceeding 2 billion tonnes, mainly located in the Eshidiya area. The Eshidiya phosphate deposits, 120 km north-east of Aqaba, are of sedimentary origin (as are all phosphate ore in Jordan). Three exploitable beds (Al, A2, and A3) with variable content of P205, CaO, SiO2, etc., are processed in order to produce 68-70,73-75, and 75-77% TCP grades. The A3 bed, which is characterized as the most siliceous containing 40-48% TCP, requires physical beneficiation using wet scrubbing, screening, and desliming by hydrocylone, followed by anionic conventional flotation to achieve 75- 77% TCP grade. For the last 15 years extensive laboratory and pilot tests (including physical, chemical, and mineralogical studies) were carried out. After operating the industrial plant, certain modifications were deemed necessary to adjust the operational parameters and the final flowsheet, which was followed to obtain the targeted quantity and quality of concentrate.

Jan 1, 1999

By R. J. Roman

Several research groups have spent considerable time investigating coarse ore leaching. Coarse ore leaching includes both heap and dump leaching. The term "heap leaching" will be used in this paper to mean any type of coarse ore leaching. The results of their work are generally in agreement: the progress of leaching can be described by the shrinking core model and its associated mathematics. The shrinking core model is schematically represented in Figure 1. The particle is contacted by the leach solution on its outside surface and the solution migrates inward by filling the pores on the particle. As the solution filling the pores comes in contact with grains of ore mineral the reagent chemically reacts with the ore mineral to solubilize the contained metal. The solubilized metal diffuses outward to the particle surface and is washed away by the leach solution flowing past the particle. The leaching reagent in the particle interior is replenished by the diffusion of reagent from the surface of the particle to the interior of the particle. If the chemical reaction between the leaching reagent and the ore mineral is relatively fast compared to the diffusion rate of the reagent in the solution in the pores of the particle then leaching proceeds from the outside of the particle inward resulting in a "shrinking core" of unreacted ore surrounded by a "leached shell". The rate controlling step in the reaction can initially be a chemical reaction between the reagent and the ore mineral grain, however, once the reaction has proceeded a short period of time diffusion of the leaching reagent through the leached shell will be the slow step and hence the rate controlling step in the production of metal from an ore particle.

Jan 1, 1992

By J. Stachurski, N. A. Abdel-Khalek

The objective of this investigation was to compare the results of countercurrent, column cell flotation vs. conventional (mechanical) cell flotation for the cleaning of a sulfur ore (-0.5 mm, 27.43% S) and its discrete size fractions. The tests were carried out using diesel oil as a collector and alcohol as a frother. Generally, column flotation produced concentrates of higher grade. For example, column cell flotation produced a nonwashed concentrate of 65.3% S with a recovery of 84.1%. However, conventional cell flotation produced a rougher concentrate of lower grade (57.0% S) and higher recovery (92.5%). At a superficial-wash water velocity of 0.265 cm/sec, the column product grade increased to 76.4% S, with a slightly lower recovery (80.3%). However, a concentrate with a similar recovery but a lower grade (74% S) than that of the washed product was obtained after three cleaning stages with the conventional cell. The column gave superior results for the flotation of fine and ultrafine particles.

Jan 1, 1994

By Daniel R. Walton

This paper covers several points of interest to mine engineers and planners involved in evaluating or conducting geostatistical coal reserve estimates. In particular, the ability to optimize borehole drilling locations and minimize drilling costs is addressed. Also discussed is the concept of confidence intervals for estimated coal characteristics obtained through geostatistical estimates and their importance in decision-making for mine planners. Finally, a discussion is presented on how geostatistics enables identification of invalid data points and actually forces strict attention to data editing and proper geologic interpretation.

Jan 1, 1982

By William I. Weisman

The annual consumption of fluorspar in the United States, in the last 10 years has doubled. In 1971, when 1,344,742 tons were consumed, almost 45 percent of this amount was used in the production of steel and nearly 50 percent was consumed in the manufacture of hydrofluoric acid. Of the hydrofluoric acid produced, about one-third was used in the manufacture of aluminum electrolytes for production of primary aluminum metal and the balance was consumed in the manufacture of a variety of fluorocarbons and other chemicals. A small amount of fluorspar, constituting less than five percent of total consumption, was used in the foundry industry, and in the manufacture of glass, enamel, cement and other products. It is apparent that a continuing supply of fluorspar will be required to meet the demands for these vital metals and chemicals in our expanding industrial society. Domestic fluorspar production meets only approximately 20 percent of our needs. Hence, it is essential that the United States maintain a healthy domestic fluorspar industry in order to have adequate domestic reserves available at times of emergency and to protect this country from becoming solely dependent on foreign sources for this strategic commodity.

Jan 1, 1973

By Greg Watson, Dennis Ofiara

"TBMs have been used in mining in decades past, but their use has been limited and sporadic, due to both perceived and actual application difficulties. With new technology and mounting success stories, this is changing. For both coal and metals mining, deep ore bodies require long access tunnels, and an efficient and economical method of reaching those deposits. Today, mining engineers are considering TBMs as part of the overall mine development plan. Planned TBM mine drifts are not only longer, but have more complicated trajectories. Mine development TBMs will have to cope with varying geology, potential for high water inflows, steep gradients, and high temperatures. TBM systems are being planned to cope with such difficulties. TBM systems will be considered and increasingly deployed for mine development, even if commodity prices remain low. TBMs can satisfy the need for increased productivity, better life of mine infrastructure, and safety. Effective conveyor systems are essential to support TBM operation in many mining applications. Many mine development tunnels are slopes, driven down at the steepest practical gradient to reach the deep ore body. Conveyors are often the only safe and effective way to haul the TBM muck form such tunnels. This paper will review the historical use of TBMs in mining, and will discuss the 2015 status of TBMs and conveyor systems in mining, and the special requirements and adaptable features needed in order to make efficient TBMs a reality in mines worldwide.HISTORICAL USE OF TBMS IN MINING APPLICATIONS The first successful hard rock TBM was invented in 1954. Over the next decades, TBMs have been used in many mining applications: Mine access drifts in several Spanish mines •,White Pine Copper Mine, USA •,Selby Coal mine drift, UK •,Coal slopes in Appalachia, USA •,German coal mines accdess drifts, several mines •,Magma Copper San Manuel, USA •,Cape Bretton Undersea Coal Slopes, Canada •,Stillwater Mines, USA"

Jan 1, 2016

By Louise H. Michaud

An interactive mine planning system that employs recent advances in 3D computer graphics capabilities and 3D geologic modelling to aid with the tasks involved in producing dragline mine plans was developed. As well as offering large potential saving in the time required to carry out the planning tasks, the system offers immediate visual feedback to the planning engineer. This can greatly aid in the conceptual understanding of complex geology and mine plans. The package incorporates the generation of a three dimensional Gridded Seam Model (GSM) as the basis for the development of the geologic database. This modelling method is capable of accurately representing rugged topography and multiple coal seams, including folding and faulting. The GSM is then integrated with an interactive graphics mine planning system in order to develop one model and one database for the generation of the mine design, the depletion of the coal resources and the movement of spoil material. The gridded structure of the model also provides the foundation on which all mine and spoil pile volumes are calculated.

Jan 1, 1992

By F. Warnaars

Historically, this area produced gold and silver from many well-known vein deposits, like Tayoltita, Topia, and San Jose de Gracia. Modern exploration identified three categories of deposits: 1) low grade porphyry golds in shallow level dacite porphyries; 2) batholith-related deposits; and 3) those formed in volcanic sequences of Late Cretaceous to Late Tertiary. At least four porphyry golds have been identified, of which Metates is best known. These are formed by and within dacite porphyries, associated hydrothermal breccias and sometimes within surrounding metasediments. Their ages are from mid-Cretaceous to Early Tertiary. Precious metal deposits associated with batholiths occur as veins, contact haloes in metasediments or volcanics, skarns, tectonic breccias, hydrothermal tourmaline breccias, dacite dikes or as disseminated or stockwork deposits such as La Fortuna. Several new gold discoveries were made in older Early Tertiary Volcanic Sequences and in the younger Tertiary volcanics within prominent structures exceeding 3 to 5 km in lengths. Some of these are open-pittable but most have to be mined by underground methods.

Jan 1, 1999

By R. Sivamohan, F. Huang

A mineral processing strategy developed for the finely and complexly interlayered calcite rich wollastonite, microcline, and iron-garnet ore of Jokkmokk, northern Sweden, gives an overall calcite recovery of 89.4% at a grade of 90.7% CaCO3. The wollastonite product assays 53.0% Ca- SiO3 at a recovery of 92.2%. The significant elements of the developed strategy are stepwise grinding, wet high intensity magnetic separation (WHIMS), reverse flotation and starvation flotation. Stepwise grinding avoids the overgrinding of soft calcite. WHIMS removes the colored iron-garnet impurity and thereby increases the whiteness of the product. Reverse flotation enables a simple flotation circuit and starvation `flotation helps to optimize the physicochemical conditions in cleaner flotation by giving rougher products of narrow particle size distributions. Moreover, with the reagent scheme developed in this work only one cleaner stage is necessary for the various rougher flotation products to be upgraded to give the foregoing results. In this paper, the strategy is presented in detail along with appropriate results.

Jan 1, 1990

By Ruoming Gong, Arindam Samanta, Ragula Bhaskar

Three studies conducted at the University of Utah relating to the effect of scrubbers on face airflow patterns, the resulting dust exposure of operators and the development of a throat scrubber for continuous miners are summarized in this paper. The first study involved full-scale laboratory tests to determine the potential dispersion patterns and transport of dust at a continuous miner face, using different ventilation configurations and a scrubber. Concentration maps were developed and potential exposures at operator positions were examined. The second study involved the development of a 3-D numerical model to predict airflow patterns generated by a scrubber at a continuous miner face. The model was designed to evaluate the role of various face parameters on airflow patterns at a miner face and to complement the full-scale testing. The third study involved the design and fabrication of a low profile hydraulically powered continuous miner throat scrubber. The scrubber uses three hydraulic motors and small diameter fans to draw about 3000 cfm (1.42 m3/s) of air and uses a flooded bed scrubber to filter dust particles.

Jan 1, 1993

By Brad C. Lewis

The coal mining industry has experienced a general trend toward longwall operations. An increasing percentage of underground coal is being mined by longwalls. And productivity in longwalls is likewise increasing. Operators of longwalls, however, have not yet reached a state of mining euphoria. Competitiveness within the industry and from alternate fuel sources is forcing continued pursuit of higher productivities and lower costs. [Figures 1, 2 and 3] present trends in the industry. Longwall mines, as defined here, are those reportedly having longwall installations in each of the respective years. Production from both the continuous miner and longwall units is included in the longwall mines. Nonlongwall mines are all other underground mines. Productivity calculations are based on total employee-hours associated with the operation. Annual percent increases in productivity appear to have peaked in the 1985-1987 time frame. This was due, in part, to implementation of technological advancements and improvements in management-labor relations. The results shown in [Fig. 3] aroused the author's curiosity. The first question was "Have technological advancements to increase productivity peaked?" It does not appear so.

Jan 1, 1990

By George A. Lawrence

A new super-large 100 m3 (3500 ft3) pneumatic mechanical flotation cell is now available to meet today's mineral processing challenges. Several innovative design concepts represent a marked departure from conventional flotation cell designs. The radial discharge from the pump action rotor and the overhung vane type stator is contained in a conical bottom round tank with no dead comers. Peripheral launders collect froth overflowing the entire circumference of the tank and these launders are of a hexagonal design permitting cells to be nested together in a honeycomb fashion. The mechanism drive is either a customized right angle gear reducer or a conventional Vee belt drive. Both drive systems are available with an optional variable frequency control system that permits infinite speed adjustment of the rotor in each flotation cell or group of cells. Results of side-by-side comparative testing between three major manufacturers of super-large pneumatic mechanical flotation cells are discussed. These results were obtained at a large copper concentrator in Chile during several weeks of commercial scale testing.

Jan 1, 1995

By J. A. Baicker

A 2 1/2 inch diameter probe containing a high resolution gamma ray spectrometer was developed for downhole ore grade assays to depths of 6,000 feet. Tests have been conducted on the characteristics of this tool for in-situ determinations of uranium by means of natural gamma ray counting, and of copper, silver, gold, iron and coal quality by means of neutron-induced gamma rays. Application of the technique for improved carbon-oxygen logging in oil fields is promising. The probe contains a cryogenically cooled high purity germanium detector and a 4,000 channel spectrum analyzer. Gamma ray spectra are digitally transmitted up the cable to the truck-mounted data processing system. We found that uranium can be assayed directly in different types of formations independently of the degree of geochemical disequilibrium by counting the relatively weak 1.001 MeV gamma ray of protactinium-234m. Neutron activation work shows that in-situ determinations of copper, silver, iron and coal quality are technically feasible. In carbon-oxygen oil well logging the technique allows an accurate determination of carbon, oxygen, hydrogen, chlorine, silicon, calcium and iron, and shows promise of providing an improved oil/water differentiator.

Jan 1, 1982

By Theodore M. Gurr, James J. Bartels

Phosphate produced fertilizers provide the phosphorous nutrients required by plant life to sustain significant growth, thus improving the production of food for the world's population. Phosphorous replenishment of soil currently can be obtained efficiently by no other means than by direct application of phosphate fertilizer to the soil. Phosphate products are also utilized in animal feeds, detergent, and various industrial processes. Thirty-three countries are presently mining phosphate rock for the production of fertilizers, and its process byproducts. The major phosphate rock producers are the United States, the former Soviet Union, Morocco, and China [(Table 1)]. Phosphate rock is generally defined as a rock material that contains phosphate minerals which are sufficient for commercial usage. Phosphate minerals are found in sedimentary igneous and metamorphic rocks. Economic resources of phosphates are primarily developed from sedimentary rock sources. The apatite mineral family comprises the majority of phosphate constituents from both sedimentary and igneous rocks. Igneous phosphate rocks are generally composed of fluroapatite whereas sedimentary rocks are generally composed of carbonate fluroapatite, or chlorapatite. Phosphate rock is mined by a multitude of processes, including surface and underground mining. The mined rock requires mechanical and chemical processing to liberate the phosphate for utilization as fertilizer. Approximately 85% of the world's phosphate production uses sulfuric acid, with the remaining processes utilizing nitric and phosphoric acids. Ammonia is also introduced in the manufacture of liquid fertilizer, ammonium phosphate and ammonium polyphosphate. GEOLOGY Mineralogy and Chemical Properties Phosphate most commonly is derived from the mineral apatite, which is chemically described as CA5(F,Cl,OH)(PO4)3. Apatite is also broken up into the composite apatite minerals which are fluroapatite Ca5F(PO4)3, chlorapatite Ca5Cl (PO4)3 and hydroxyl-apatite Ca5(OH)(PO4)3. Carbonate CO3 can substitute for PO, forming carbonate apatite, called francolite. The guano phosphate (bird excrement) mineralogy commonly occurs as brushite CaHP04.2H20, monetite CaHPO4, whitlockite Ca3(PO4), and dahlite Ca10(PO4)6(OH)2. Apatite minerals form from igneous sources where they are developed deep in the earth's crust; and the cooling processes are slow, producing long, hexagonal prismatic to tabular crystals. The termination of the crystal can be basal plans or pyramids. In some instances, the crystals are bipyramids. Faster cooling, or sedimentary derived apatites are more commonly cryptocrystalline. Collophane is a name given to cryptocrystalline apatite found in phosphate rock in fossil form. Apatite minerals are relatively soft and are used to describe the 5 hardness on the Mohs scale. Cleavage is poor and develops along the C(0001). The color of apatite minerals varies from colorless, to violet, and blue, but are predominantly green or brown; luster is vitreous to subresinous. Collophane's physical appearance is often opaline, dense, with colloform structure and sometimes concretionary, nodular or pulverulent. Phosphate Bearing Materials Origins Phosphate deposits of igneous and metamorphic origins have been well defined. Sedimentary origins have been defined, but with a greater degree of uncertainty. Research in the 1980s proved out some of these processes through studies of real time deposition in Chile, Peru, and Australia. Igneous intrusive alkali rock and associated contact metamorphic rocks, provide approximately 20% of the world's phosphate. Fluorine containing apatite minerals are the most common materials containing phosphorous. Fluorapatite occurs in most igneous rocks. Fluorapatite and fluorine hydroxylapatite, together with carbonate varieties of these, are important members of the group. Where an essentially pure chlorapatite, carbonate apatite, and hydroxylapatite are rare and restricted in occurrence, the fluorine containing types occur in most all igneous rocks as early formed accessory mineral, usually in microscopic crystals, and may occur as extremely large bodies as magmatic segregations from alkalic igneous rocks. Apatite is also found crystallized in pegmatitic faces of both acidic and basic types of igneous rocks. More specifically, apatite is associated with magnetite deposits, in hydrothermal veins, especially those formed at relatively high temperatures, and in veins of the Alpine type. Apatite is common in both regionally and contact metamorphosed rocks, especially in the crystalline limestones where it is associated with sphene, zircon, pyroxine amphibole, spinel vesuvianite, phlogopite, talc, chloride schists, and as a contact metamorphic mineral.

Jan 1, 1994

By D. H. Carlson, J. H. Johnson, C. F. Renders

Introduction Diesel-powered vehicles are used extensively in underground mines throughout North America. The bulk of the diesel vehicles found in underground mining operations are used for loading and ore haulage, as well as for transportation of personnel and supplies. Along with the advantages of using diesels underground is the disadvantage associated with diesel-tailpipe particulate-matter emissions (DPM). The concentration of DPM in the ambient air of US underground metal mines is not now regulated by the Federal Mine Safety and Health Administration (MSHA). However, recent studies have shown DPM to be mutagenic (National Institute of Occupational Safety and Health, 1988), and the American Conference of Governmental Industrial Hygienists (ACGIH) has recommended that the exposures of per¬sonnel to DPM be limited to an 8-hr time-weighted average concentration (threshold limit value or TLV) of 0.15 mg/m3 (Anon., 1995). The authors, while making measurements in a number of US underground mines that use diesel haulage equipment, found mine air DPM concentrations ranging from 0.2 to 2.36 Mg/M3 (McCawley and Cocalis, 1986; Watts et al., 1989; Cantrell et al., 1991; Haney, 1992; US Bureau of Mines, 1992; Watts, 1992; Watts et al., 1995). If the proposed DPM TLV were to be adopted as a permissible exposure limit (PEL) for US underground mines, the proposed limit of 0.15 mg/m3 PEL would be lower than any of the concentrations measured in the earlier studies and would represent more than a 15-fold reduction from the maximum 2.36 mg/m3 concentration. A 0.15 mg/m3 PEL would also represent a 4.5-fold reduction from the average 0.68 mg/m3 measured mine ambient air DPM concentration reported in this paper. Other diesel tailpipe emissions that are now regulated underground include carbon monoxide (CO), with a PEL of 50 ppm; nitrogen dioxide (NO,), with a PEL of 5 ppm; nitric oxide (NO), with a PEL of 25 ppm; and sulfur dioxide (SO,) with a PEL of 5 ppm. Because the concentrations of these gaseous pollutants and DPM are affected by the state-of-maintenance (Waytulonis,1992), it is important that a means be developed to measure emissions from engines that are now in service to determine when maintenance is needed. The current study was the result of an inquiry by mine¬maintenance personnel who had been receiving complaints about high concentrations of diesel soot (DPM) in mine headings from load-haul-dump (LHD) vehicle operators. Mine-maintenance personnel were searching for an objective test to determine if the diesel tailpipe particulate emitted was excessive. The mine was also evaluating electronically controlled, two-cycle, naturally aspirated, direct-injection diesel engines on some of their JCI (John-Clark Inc.) load-haul-dump (LHD) vehicles. These LHD vehicles were used to haul freshly blasted ore from mine headings to a feeder breaker. The feeder breaker breaks down the larger chunks and feeds the broken ore onto a conveyor. Michigan Technological University, in past studies, developed an emissions-measurement apparatus (EMA) ca¬pable of measuring diesel vehicle tailpipe pollutant concentrations (Chan et al., 1992; Chan et al., 1993; Carlson et al., 1994). At the time of the study reported here, most of the mine's LHD vehicles used a 12-cylinder, four-cycle, naturally aspirated prechamber diesel engine. The study was undertaken in cooperation with mine maintenance supervisors from late 1992 through July 1993. The objectives were to compare diesel exhaust emissions between the 6-cylinder, two-cycle, electronically controlled, direct-injected diesel engine and the 12-cylinder, four-cycle, prechamber diesel engine and to, then, use the data collected, in conjunction with mine ambient air measurements, to demonstrate the application of the "deterioration factor" (Chan et al., 1992), which is a measure of the state-of-maintenance of mine-vehicle engines that are now in service. The information would be used to identify vehicles that need maintenance to reduce emissions. The data reported here are unique in the sense that they combine underground diesel vehicle ambient and tailpipe

Jan 1, 1999

By S. M. Smouse

Total world energy consumption is projected to continue its strong growth of recent years. Because coal is the most abundant fossil fuel, it will likely remain an important energy source, particularly for power generation, into at least the early years of the next millennium. Clean coal technologies are available today that can economically reduce air pollution, primarily SO2 NOx and particulates, and for the higher efficiency technologies, CO2, from power generation. U.S. Department of Energy analyses show that the adoption of clean coal technologies could decrease carbon emissions worldwide while creating a strong export market with attendant creation of jobs in the U.S.

Jan 1, 1998