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By David P. Lindroth

The objective of this research by the Bureau of Mines was to determine the technical feasibility and associated pilot data for drying minus 1/4-in coal with microwave energy at a frequency of 2.45 GHz. The drying data were obtained experimentally on three coal types: bituminous, subbituminous, and lignite. The experiments were performed with a custom-designed conveyorized microwave oven having a continuous power capability of 12 kW. Drying efficiencies near the theoretical maximum of 1.54 kg of water per kilowatt hour of energy input were achieved for two coals and two sizes; overall drying efficiencies averaged 77 pct.

Jan 1, 1986

By J. E. Tress

The Bureau of Mines prepared submicron tungsten powder by reducing tungsten hexachloride with hydrogen. The particle diameters of the resulting tungsten powders ranged from 0.015 to 0.046 micron. Within the limits of the variables investigated, no clear-cut correlation was found between process conditions and final size of the powder. Oxygen was the major contaminant in the product; being present both as an adsorbed gas and as suboxides of tungsten. Studies showed that the powder yielded compacts of approximately 45 per-cent of theoretical density when compacted mechanically. Low-temperature sintering produced more rapid densification in these compacts than in compacts prepared from conventional powders. Adding up to 20 percent ultrafine powder to conventional tungsten powder caused an increase in density upon compaction with maximum densification occurring at approximately 12 percent ultrafine powder.

Jan 1, 1966

By C. P. Fang, V. A. Marple, K. L. Rubow, P. H. McMurry

"It has been known for some time that sizes of aqueous particles may be affected by flow-induced relative humidity (RH) changes. The RH of air flowing through an impactor decreases as a result of pressure drop through the impactor and increases because of aerodynamic cooling within the high-speed jets, as illustrated in Figure 1. Because the sizes of aqueous particles depend on RH, the impaction stage on which such particles are collected may be different from the stage where they ought to be col¬lected, based on the particle size at the sampler inlet.Fuchs (1980) reviewed literature on water vapor condensation in impactors. The reviewed impactors operated at jet velocities of 100-250 m/s. Particle size increases ow¬ing to water vapor condensation were found in all cases. In one case (Khorguani et al., 1970), it was found that very small droplets (Dp <_ 0.02 um) containing sodium chloride and silver iodide were collected in an impactor with a cut point of 0.32 µm and a jet velocity of 100 m/s. Fuchs believed that such particles could not be captured in an impactor without having been enlarged by condensation. Winkler (1974) sampled at¬mospheric dust with a rectangular nozzle impactor that had a nozzle cross section of 0.3 x 15 mm, a cut size of 0.4 um, and an average jet velocity of 100 m/s. No adhesive was used on the impaction plate. The collection efficiency increased as air humidity was increased from 20% to 100%. The effect was especially noticeable in the increased collection efficiency for hygroscopic particles, and was attributed to condensation.Extensive theoretical and experimental research work on the distortion of the particle size distributions in impactors was done by Biswas and coworkers (1985, 1987). The impactors employed in the study were a low-pressure impactor with high jet velocity stages (Hering et al., 1978, 1979) and a conventional six-stage impactor, Sierra's model 226, operated in the incompressible regime. Ammonium sulfate aerosols were chosen for the study. In the low-pressure impactor, an orifice operating at a Mach number of 1 causes a sudden pressure drop, significantly reducing the RH in the next two stages (stages 5 and 6). This results in a 0.15-um diameter ammonium sulfate droplet shrinking to about 0.07 um at stage 5 when the inlet RH is 95%. In stage 7, the tempera¬ture drop is considerable because the jet speed is sonic. For an inlet RH of 95%, a 0.03 um droplet grows to about 0.06 um. However, the same size droplet at an inlet RH of 25% grows to only 0.04 um. For the Sierra model 226 cascade impactor that is operated with a Mach number of 0.27 at the last stage (stage VI), it was found that for an inlet RH of about 67%, particle growth would occur in stage VI. At 80% RH, both stages V and VI were affected. Biswas et al. (1987) stated that Mach number alone does not determine the size biasing; the type of aerosol, the inlet conditions, the temperature and pressure ratio, and the impactor geometry (throat length, jet-to-plate distance, etc.) must be considered for each stage in evaluating the distortion of the particle size distribution."

Mar 1, 1992

By H. S. Chiang, S. S. Peng

"SummaryAir velocity distribution surveys on four mechanized longwall faces are presented and discussed. Although there are discernible patterns in the velocity distribution, there are wide differences in distribution in the cases examined. This can be attributed to differences in mining and face geometry. An important factor is air leakage into the goaf.IntroductionOver the past two years several intensive air velocity surveys have been carried out in West Virginia coal mines as part of a programme aimed at understanding dust transport mechanisms on mechanized longwall faces. These are presented here and some of the patterns of velocity distribution are discussed.Ventilation survey methodologyThe air velocity vector consists of three mutually perpendicular subvectors; the vertical subvector is directed toward the roof, one of the horizontal subvectors is parallel to the coal face and the other pointing to the gob. The air velocity which was measured in this paper is the horizontal subvector parallel to the coal face.To record the velocity distributions at the longwall faces, the surveying stations and the surveying points were established as follows.(1) The first station usually was set at the third support from the headentry T-junction. Within the first few supports, the air coming from the intake airway encounters a sharp right-angle turn at the T-junction, and forms a turbulent region close to the coal face. The intake air in this region is also influenced by the motors that drive the face conveyer. But when the air reaches the different. But for the same face the number was the same. The main air-travelling area was divided into six to 12 equally sized sub-areas, and each surveying point was situated approximately at the centre of the sub-area.The velocity survey was carried out by two persons, one reading the meter and the other taking down the readings. A complete survey at one station took about 5-8 min. Usually, the dimension of the cross-sectional area was measured during that time.A third person used the smoke tubes to observe the following: (I) the air movement patterns at different locations; (2) the extent and the direction of the air leakage; and (3) the machines' influence on the main airflow. At the same time he observed and recorded the roof conditions and the compactness of the roof-caving in the gob."

Mar 1, 1989

By Martin H. Stanczyk

The Bureau of Mines studied continuous closed-circuit attrition grinding of a coarse commercial filler-grade kaolin to produce paper-coating-grade clay having a particle size analysis of at least 70 percent minus 2-micron equivalent spherical diameter (esd). The coarse clay, containing about 12 percent minus 2-micron-esd material, was ground in a Bureau-developed 10-inch-diameter attrition grinder in closed circuit with a 5-foot-diameter bowl classifier. In the best test, a finished product containing 82.7 percent minus 2-micron-esd material was obtained when grinding 20 pounds of raw clay per hour at percent solids with a 100-percent circulating load. Energy consumption was about 341 kilowatt-hours per ton of clay feed, or 487 kilowatt-hours per ton of minus 2-micron-esd material produced. Closed-circuit grinding gave some-what greater particle size reduction and lower energy consumption than either batch or continuous open-circuit grinding.

Jan 1, 1965

By Debra A. Griffith

The U.S. Bureau of Mines currently is researching the relationship between the level of back strength and the probability of low-back injury. This report is a review of the literature and statistics on over-exertion injuries. Overexertion continues to be a significant source of injury in metal and nonmetal mining, accounting for approximately 24 pct of all injuries yearly. These injuries, particularly to the lower back, can be very expensive in human and monetary terms. An examination of the accident data on overexertion injuries is necessary to provide a background for research into prevention and/or amelioration of those in-juries. The job categories outlined in the Accident Data Analysis data base most affected are "Mechanic/Electrician" and "Mill/Plant Worker." The age group most affected is "30-39" years, and the experience group most affected is "0-.99" years. The most prevalent type of overexertion injury is "Strain/Sprain," and the trunk is the body part most often involved in an overexertion injury.

Jan 1, 1994

By K. E. Tame

The Bureau of Mines is studying possible modifications in conventional ore-processing methods that will confine and permit controlled disposal of radioactive liquid wastes. Stream and ground water pollution from radio-active nuclides, principally radium 226 and thorium 230, in liquid wastes from uranium mills can be minimized by reusing the waste solution within the mill. Such reuse of waste solution in an acid leach-resin-in-pulp flowsheet was investigated in the laboratory. The process consists of acid leaching for dissolution of the uranium, sand-slime separation and countercurrent decantation washing for recovery of a pregnant slime slurry, and the use of ion-exchange resin for recovery of uranium from the slurry. Reuse of clarified barren effluent for washing in the simulated mill circuit was carried through 55 cycles. Dissolution of uranium from the ore averaged 97.5 percent. Washing efficiency of 99.9 percent was attained when using 4.35 volume tons4 of combined barren effluent and makeup water per ton of ore. Absorption of uranium from the pregnant slime slurry by an ion-exchange resin averaged over 99.9 percent.

Jan 1, 1962

By G. M. Martinez

A cell concept adaptable to large-scale electrowinning of zirconium metal from zirconium tetrachloride was investigated by the Federal Bureau of Mines. Tests were made in twin cells, each 12 inches in diameter by 33 inches long. Electrowinning was performed in one chamber from which the electrolyte was transferred after electrolysis to the other chamber where it was renewed by the introduction of ZrC14 by direct sublimation. The formation of a salt plug in the connecting pipe provided a seal between the chambers. Optimum electrolyte composition, with respect to quality of the metal product (91 pct meeting ASTM standards except for the oxygen content) and current-carrying capability (about 350 amp) was determined to be 16.7 wt-pct NaF-83.3 wt-pct NaCl mixture plus ZrC14 equal to about 3 wt-pct zirconium. A twin-cell design incorporating the unit operations covered by this investigation is proposed.

Jan 1, 1976

Recent Bureau of Mines research in earth grounding safety is documented in three separate papers. First, guidelines for the design of a 5- ohm borehole ground are presented. Next, an inexpensive practical means to construct a low-resistance bed in high-resistivity soil is described. Finally, a procedure that employs a commercial resistivity meter to measure shock potentials around grounded objects is explained step-by-step. These papers complement the material presented at an earlier technology transfer seminar and published as IC 8767.

Jan 1, 1985

By R. Hogg, T. F. Dumm

"Procedures for particle size analysis on respirable dust from coal mines have been evaluated. Using respirable dusts dispersed in a laboratory dust chamber, size distributions measured using cascade impactors have been compared with the results of a variety of laboratory sizing methods performed on samples collected on filters placed side-by-side with the impactors. The laboratory techniques included centrifugal sedimentation, laser diffraction/scattering and automatic particle counting. The general agreement among the various methods was very good, with systematic differences which can be attributed to the different definitions of size used. Simple conversion factors have been obtained which can be used to transform the laboratory data to equivalent aerodynamic sizes.Similar comparisons have been made on samples collected in underground coal mines. Again, the results are in quite good agreement although small discrepancies were observed in· some cases. These have been attributed to some degree of agglomeration in the airborne dust, leading to slightly coarser apparent distributions in the impactor samples INTRODUCTIONA primary goal of mine ventilation is the control of airborne dust, especially in the ""respirable"" size range, typically defined as finer than about 5 to 10 µm. It follows that determination of the amount and characteristics of the respirable dust is an important factor in evaluating the performance of ventilation systems. Particle size information on airborne dust in mines is commonly obtained by in- situ measurements using cascade impactors. However, these tend to be inconvenient for routine data collection and the alternative approach of collecting samples in the mine, on filters for example, and returning them to the laboratory for detailed analysis is very attractive. Questions have often been raised, on the other hand, as to the appropriateness of this approach. How well · do such laboratory methods describe the distribution of aerodynamic diameter of the airborne dust particles in the mine environment? The purpose of the work described in this paper was to evaluate some laboratory sizing methods and to compare the results of such measurements with the size data obtained by the direct, in-situ method."

Jan 1, 1989

By Jean M. Kenney

Frequencies of haulage-related accidents in metal and nonmetal surface mines for the years 1988 through 1990 were investigated and compared with those of non-haulage-related accidents. This study was part of the U.S. Bureau of Mines program to improve mining haulage safety. Data were obtained through the U.S. Bureau of Mines Accident Data Analysis (ADA) program. The chi-square test was used to compare frequencies of haulage-related and non-haulage-related accidents for each of the following variables: degree of injury, age, total number of years of mining experience, and shift time. Significance was determined for degree of injury between haulage-related and non-haulage-related accidents. Age of injured did not vary significantly between haulage-related and non-haulage-related accidents, but total number of years of mining experience was found to be significant. Shift time for the accident proved to vary significantly between haulage-and non-haulage-related accidents. Events causing injury for haulage-related accidents were tabulated, and the most frequent determinants of haulage-related accidents were identified. Accident descriptions for both fatalities and permanent disabilities were studied, and the primary causes of these accidents were identified. These findings suggest that haulage-related jobs are among the most dangerous when considering accidents experienced by all workers in the metal and nonmetal surface mining work force.

Jan 1, 1993

By Charles B. Carpenter

When a drilling well strikes a horizon in which there is a large volume of petroleum or natural gas under high pressure, danger of a blowout with disastrous results is imminent unless proper precautionary measures are taken. The history of oil-swell drilling has been marked by many blow-outs and wild wells, some of which-have caught fire and burned for long periods. Such incidents nearly always make headline news, but ordinarily few persons realize that what to them is an interesting newspaper item may entail great financial loss to the operator and frequently loss of life or personal injury to members of the drilling crew and others in the vicinity of the well. The blow-out, wild well, and crater are dreaded specters to every thoughtful person in the oil industry because of danger to life and property, underground damage to surrounding wells, dissipation of reservoir energy, and waste of irreplaceable natural resources that blow to the air or migrate to barren formations. Every operator drilling in high-pressure fields must be on the alert always to forestall any conditions that may lead to a blow-out, and his vigilance must not cease until a well is completed and oil, gas, or both are flowing to storage or market.

Jan 1, 1937

By R. V. Lundquist

The compound 2Na2O?3CaO?5Al2O3 occurs as a minor phase in lime-soda sinters prepared for extracting aluminum from siliceous aluminum-bearing materials. About 99 percent extraction of sodium and aluminum from synthesized 2Na2O.3CaO.5Al2O3 was obtained in solutions of NaOH-Na2CO3 at leaching temperatures of 50° C and above. Extractions in water were low because insufficient NaOH was generated by hydrolysis. Extractions in NaOH solutions were limited to about 80 percent owing to the precipitation of hydrated calcium aluminates. Rapid extractions of 100 percent were obtainable in NaaC03 solutions, but the subsequent rapid precipitation of alumina trihydrate caused losses in alumina recovery.

Jan 1, 1965

By N. S. Dalal, B. Jafari, F. Y. H. Green, V. Vallyathan

"Using electron spin resonance (ESR) spectroscopy we have carried out a systematic study of the measurement of concentrations of organic free radicals in freeze-dried lung tissue. Sixty-six tissue samples were obtained from the National Coal Workers' Autopsy Study (NCWAS). The samples were characterized in terms of the concentration per gram of the free radicals, and examined in relationship to the histopathological parameters such as age, numbers of years in the mining atmosphere, the degree of disease, and smoking history. Preliminary results indicate a positive correlation between the free radicals in the lung tissue and the severity of pneumoconiosis.IntroductionThis paper summarizes our electron spin resonance (ESR) measurements of the concentration of organic free radicals in the freeze-dried lung tissue of autopsied coal miners. This work was undertaken because it is well known that most coals contain carbon-centered organic free radi¬cals,(1,2) and recent studies from our laboratories indicated that reactive free radicals might play a role in the biochemi¬cal mechanism of coal workers' pneumoconiosis (CWP) (3) Thus we obtained 144 lung-tissue samples from the Nation¬al Institute for Occupational Safety and Health (NIOSH) in Morgantown. The samples came from the data bank of the National Coal Workers' Autopsy Study (NCWAS). This selection was unique because fairly detailed histopathologi¬cal information was available for each sample.Other recent studies in this field are those of Ohta et al (4) who conducted ESR measurements on black dust deposited in autopsied human lungs, but no coal miner was included therein. Earlier Retcofsky (2) had examined one lung-tissue sample via ESR spectroscopy and had concluded that the free radicals in the lung tissue reflected simply the fusain (narrow component) ESR signals. The present study was thus undertaken to complement the earlier work (2-4) and the results indicate a positive correlation with the disease severity fairly strongly."

Mar 1, 1989

By Frank C. Andreuzzi

The Division of Environmental Activities, U.S. Bureau of Mines, conducted a solid waste demonstration project on a burning coal refuse bank. The primary objective of this project was to develop and evaluate an efficient method of extinguishing burning coal refuse and moving it. A series of tests were performed using water monitors and related apparatus to quench the burning material and, at the same time, using earth-moving equipment to transport, spread, and compact the extinguished material. The method found to be most effective consisted of water-quenching the surface material to a workable depth, ripping, and removing the quenched material with a bulldozer and tractor-scraper. The total cost was estimated to be $0.44 per cubic yard.

Jan 1, 1970

By P. L. Swanson

Over a recent 20-month observation period, the U.S. Bureau of Mines obtained seismogram records from a single vertical-component, short-period seismometer installed at the surface of a metal mine in northern Idaho. The seismic events were analyzed for local (Richter) magnitude (M), time of occurrence, location, and relation to rock bursting and production blasting. Approximately 150 seismic events with -0.5 = M = 2.9 were located within the mine, yielding a b value (slope of the logarithm of the number of events with magnitude greater than M versus M) of 0.5. Event locations were constrained using a dense underground array of high-frequency accelerometers. Twenty of the surface-recorded events, with 0.5 = M = 2.9, were associated with rock bursts that produced damage requiring at least 1/2 day of cleanup and/or repair. Other possibly hazardous rock bursts, with magnitudes as small as -1.1, were numerous but were not associated with significant structural damage. Approximately 60 pct of the seismic events with M > -0.5 and 75 pct of damaging rock bursts occurred within 45 min of blasting. Estimates of characteristic rupture dimensions for rock bursts with -1.1 = M = 2.9, based on a conventional dislocation shear-slip model of failure, range from 3 to 300 m.

Jan 1, 2010

By Z. Zhiqun, V. A. Marple, B. Y. H. Liu

"IntroductionIt is commonly understood that aerosol particles may be injurious to human health if they are of a size that enables them to enter the respiratory tract. Coal Workers' Pneumoconiosis (CWP) is one disease known to be caused by coal mining related particles.The location in the respiratory tract where the particles are deposited is primarily a function of the equivalent aerodynamic diameter (EAD) of the particle. The equivalent aerodynamic diameter is the diameter of a spherical particle with a density of 1.0 gm/cm3 with the same falling speed as the particle in question. For a spherical particle the calculation is rather simple in that the equivalent aerodynamic diameter is simply the diameter of the particle in question multiplied by the square root of the density of the particle. For irregularly shaped particles, such as coal particles, there is no simple way to make the EAD calculation. For example, Figure 1 is only one of an infinite variety of particle shapes that can be found in practice and the aerodynamic size of this particle and, therefore, its deposition location in the respiratory tract would be nearly impos-sible to estimate accurately.The normal method for determining the aerodynamic diameter of particles has been to experimentally measure the size of the particles in a settling chamber or with an inertial classifier such as an impactor, cyclone or a centrifuge, since inertial classifiers have the property of classifying the particles according to their aerodynamic diameters."") However, these devices can only give limited information on the EAD of a single particle with a specific shape. Impactors and cyclones, for example, collect particles in size ranges and not at a specific size, so the determination of the EAD of a specific particle is not possible. A centrifuge, on the other hand, can measure the EAD of a specific particle but the equipment is costly and procedure laborious, and it may not be possible to disperse a particle of a specific shape into the centrifuge. The centrifuge can be used to determine the EAD of clusters of spheres in various arrays, but introducing particles of a specific irregular shape may not be feasible. Furthermore, the EAD is a function of the orientation of an irregularly shaped particle and the orientation of a particle in an inertial classifier is unknown. The orientation may also vary as the particle passes through the classifier.Because of the difficulty in determining the EAD of an irregularly shaped particle, we have undertaken a program to apply theoretical numerical methods to calculate the EAD of any shape particle. In our laboratory we have, for some time, been using numerical methods to determine the flow field of air within instruments such as impactors, (2) inlets, (3) and virtual impactors (4) Recently, this technique has been expanded into the three-dimensional regime, and the flow fields and particle motion characteristics within cyclones (5) and glove boxes have been studied. We have now begun to use these numerical three-dimensional flow programs to study the flow field around irregularly shaped particles to determine their drag coefficients, falling speed, and thus, their EAD."

Mar 1, 1989

By R. L. Crosby, L. W. Higley

Magnesium- rich magnesium- aluminum- zirconium alloys in the cast and in the extruded and heat- treated condition were studied to identify the phases present and to determine phase distribution . In cast alloys , two intermetallic compounds were identified : ZrAla by X- ray diffraction ; and Mg₁ Al₁₂ by microscopical observation . Based on microscopical comparisons between the known phases in the cast structures and the phases in the structures of extruded and heat - treated rods , ZrAl₂ and Mg1 , Al12 were identified in the structure of the latter . The presence of these intermetallic compounds in rod specimens could not be confirmed by X- ray diffraction . ZrAl₂ was observed in the structure of extruded and heat - treated rod specimens containing as little as 0.01 weight - percent zirconium . The presence of aluminum restricts the solubility of zirconium in magnesium because of the strong tendency to form ZrAla . This intermetallic compound segregated in clusters of small particles in the matrix of cast alloys , and only slight improvement in distribution was noted when the alloying techniques were varied .

Jan 1, 1964

By Steven J. Page

Longwall double-drum shearers frequently have difficulty complying with the 2.0 mg/m3 dust standard and, therefore, require the use of effective dust controls. However, before dust controls can be implemented effectively, the major individual dust sources must be determined and their relative severity evaluated. The Bureau of Mines has recently developed a sampling strategy, based upon short-term gravimetric sampling, that can identify the major dust sources contributing to the shearer operator&apos;s exposure. This technique utilizes approved gravimetric sampling equipment already available to all mine operators and can be performed by two people in 2 days. Five examples, including data analysis, are discussed with respect to various cutting sequences. In addition, typical dust source contributions obtained from studies of double-drum shearer operations regularly in compliance are included. Mine operators can thereby compare their dust source evaluation results with those from these longwalls.

Jan 1, 1982

By John W. Frey

This paper presents one of a series of digests of foreign mining legis- lation and court decisions, which is being prepared in advance of a general re- port relative to the rights of American citizens to explore for minerals and to own and operate mines in various foreign countries. This interpretation of the laws governing the Portuguese overseas possessions, prepared from the best avail- able information in Washington, has been slightly amplified in accordance with suggestions transmitted through the courtesy of the Department of State by Fred Morris Dearing, American Minister at Lisbon.

Nov 1, 1929