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Slip-and-Fall Accidents During Equipment Maintenance in the Surface Mining Industry

Description: Report issued by the U.S. Bureau of Mines discussing mining accidents during equipment maintenance. As stated in the abstract, "this U.S. Bureau of Mines report identifies potential causes of slip-and-fall accidents occurring during surface mine equipment maintenance and describes the relative roles of direct worker behavior and machine design" (p. 1). This report includes tables, and illustrations.
Date: 1990
Creator: Albin, Thomas J. & Adams, W. P.

An Adaptive System for Process Control

Description: Abstract: Researchers at the U.S. Bureau of Mines (USBM) have developed adaptive process control systems in which genetic algorithms (GA's) are used to augment fuzzy logic controllers (FLC's). GA's are search algorithms that rapidly locate near-optimum solutions to a wide spectrum of problems by loosely modeling the search procedures of natural genetics. FLC's are rule-based systems that efficiently manipulate a problem environment by modeling the "rule-of-thumb" strategy used in human decisionmaking. Together, GA's and FLC's include all of the capabilities necessary to produce powerful, efficient, and robust adaptive control systems. To perform efficiently, such control systems require a cont element to manipulate the problem environment, an analysis element to recognize changes in the problem environment, and an adaptive element to adjust to the changes in the problem environment. The control system also employs a computer simulation of the problem environment. Details of an overall adaptive control system are discussed. A specific laboratory acid-base pH system is used to demonstrate the ideas presented; all results are from the physical laboratory system and not from a computer simulation.
Date: 1995
Creator: Karr, Charles L.; Gentry, E. J. & Stanley, D. A.

Adhesion of Diamond Films on Tungsten

Description: The U.S. Bureau of Mines has investigated the chemical vapor deposition of diamond films on tungsten substrates. The effects of deposition parameters on the adhesion of the films was determined. The films were produced using a hot filament chemical vapor deposition system. Parameters investigated were substrate temperature and methane concentration in the feed gas. Film quality, morphology, and composition were characterized by scanning electron microscopy and Raman spectroscopy. Adhesion testing was performed using an indentation technique, and the results were quantified by relating adhesion to interface fracture toughness. Diamond films with well-faceted crystalline morphology with grain size greater than 1 pm had poor adhesion properties regardless of substrate temperature or methane concentration. Diamond films with smooth morphologies consisting of rounded clusters of small (<0.2 pm) diamond crystallites and amorphous carbon phases displayed much higher adhesion, although the conditions that led to the growth of these films are not understood.
Date: 1995
Creator: Maggs, K. J.; Walkiewicz, J. W. & Clark, A. E.

Bending Fatigue Tests on Flattened Strand Wire Rope at High Working Loads

Description: Abstract: The U.S. Bureau of Mines established a wire rope research laboratory to examine the factors that affect the safety and the useful life of wire rope. In the most recent work, two 32-mm 6x27H flattened strand ropes were degraded on a bending fatigue machine. The two tests were run at constant loads of 285 and 347 kN or safety factors of 2.5 and 2. Nondestructive and tensile strength tests were performed on samples of the ropes to determine the relationship between rope deterioration and rope breaking strength. Neither the area loss nor the number of broken wires measured from nondestructive tests could be used as clear indicators of the loss of strength. However, it was found from the tensile tests for both rope specimens that the strength loss was associated with the reduction of breaking strain. This suggests that measuring the strain of many short sections of a rope in the elastic region may locate the high stress sections and thus determine the condition of the rope.
Date: 1995
Creator: Wang, Richard C. & Shapiro, David E.

Characterization of Dredged River Sediments in 10 Upland Disposal Sites of Alabama

Description: Abstract: The U.S. Bureau of Mines, Tuscaloosa Research Center, in cooperation with the U.S. Army Corps of Engineers under interagency Agreement No. 14-09-0078-1510, conducted a comprehensive sampling program of 10 upland disposal sites along the Alabama, Black Warrior, and Tombigbee River systems in Alabama. Samples from each site were characterized according to particle size, chemical analysis, mineralogical content, and potential end use. Additionally, samples were subjected to the Toxic Characteristic Leachate Procedure to determine the presence of potentially harmful heavy metals. Based on the results of these studies, each sample was determined to have properties amenable for use as aggregate in general-purpose portland cement concretes and certain asphalt concrete applications.
Date: 1995
Creator: Smith, C. W.

Detection and Control of Spontaneous Heating in Coal Mine Pillars--a Case Study

Description: This U.S. Bureau of Mines study examined spontaneous heating episodes in coal mine pillars in an active underground coal mine. The information obtained from these incidents was then analyzed to learn which sampling methods provided the earliest indication of pillar heating. The objective of this study was to discover if the location of future events of pillar spontaneous heating could be inferred from the available information. The spontaneous heating-prone area in this evaluation involved pillars located just in by the mine portals. Several detection methods were used to determine gas levels outside as well as inside the affected pillars. It was hoped that, by incorporating external and internal sampling methods into an organized program, locations undergoing spontaneous heating could be determined more readily. This study found that by drilling small-diameter boreholes into the pillars, then obtaining gas samples from the affected pillars, the ability to locate early spontaneous heating episodes was improved. However, the ability to accurately predict future spontaneous heating events remains in question.
Date: 1995
Creator: Timko, Robert J. & Derick, R. Lincoln

Development of Coal Combustion Sensitivity Tests for Smoke Detectors

Description: Standard smoldering and flaming combustion tests using small coal samples have been developed by the U.S. Bureau of Mines as a method to evaluate the response of a smoke detector. The tests are conducted using a standard smoke box designed and constructed according to Underwriters Laboratories. The tests provide a standard, easily reproducible smoke characteristic for smoldering and flaming coal combustion, based upon a comparison of the smoke optical density and the response of a standard ionization chamber to the smoke. With these standard tests, the range of threshold limits for the response of a smoke detector and the detector's reliability can be evaluated for nearly identical smoke visibility and smoke physical characteristics. The detector's threshold response limits and reliability need to be well defined prior to the instrument's use as part of a mine fire warning system for improved mine safety.
Date: 1995
Creator: Edwards, John C. & Morrow, Gerald S.

Dust Sources and Controls for Multiple-Machine Longwall Faces

Description: Abstract: Longwall mining in lower seam heights may necessitate the use of single-drum shearers to overcome size constraints associated with standard double-drum shearers. To avoid the operational problem of clearance in the tailgate entry with one single-drum shearer, two single-drum machines can be operated on the same face, with each shearer responsible for mining a predefined portion of the face. However, utilization of two shearers on the same face necessitates the positioning of one shearer operator and a jacksetter in the return air of the upwind shearer, thus complicating respirable dust control on the longwall. In an effort to evaluate the unique dust control problems associated with this type of mining, the U.S. Bureau of Mines conducted dust surveys on two multiple-machine longwall operations. Sampling was done to quantify major sources of respirable dust and to identify potential solutions to problem areas. Sampling results indicate that the cutting sequences utilized on multiple-machine faces may have to be designed to minimize dust exposure, as opposed to optimizing productivity or facilitating operational requirements. Also, state-of-the-art dust control techniques typically found on double-drum shearer longwalls must be employed to help minimize the exposure of all face personnel to traditional dust sources.
Date: 1995
Creator: Colinet, Jay F. & Spencer, Ellsworth R.

Effects of Remote Drop and Pumpdown Placement on Cellular Concrete

Description: Abstract: The hazards to the public posed by abandoned mine shafts are well documented. As private development encroaches on previously mined areas, the potential for fatalities and serious injuries from abandoned mine shafts increases. The U.S. Bureau of Mines has conducted research into cellular concrete as a material for sealing these openings. The current work involves testing the characteristics of cellular concrete before and after it had been pumped or dropped from different heights into a simulated mine shaft. Cellular concrete was pumped vertically up to and subsequently dropped from heights of 18 and 37 m into concrete forms. Wet density measurements were made at multiple sampling points in the test circuit. Air content determinations and uniaxial compressive strength testing were conducted. Research results showed significant loss in air content and changes in the characteristics of cellular concrete during pumping or dropping from various heights. Recommendations on effective use of cellular concrete for sealing abandoned mine shafts are made.
Date: 1995
Creator: Boreck, D. L. & Miller, R. E.

Electrochemical Reduction of Titanium in Nonaqueous Solvents

Description: Abstract: Electrorefining of Ti in nonaqueous solvents has been studied by the U.S. Bureau of Mines as a method for recycling impure scrap Ti. Electrochemical behavior of Ti species was investigated using cyclic voltammetry. Research results showed that Ti metal can be dissolved in polar solvents such as dimethylformamide or dimethyl sulfoxide. However, deposition of Ti from these solvents was not successful. Several solvent systems were investigated for electrodepos.tion of Ti but no deposits were obtained. Reduction of Ti' complexes to Ti" proved to be straightforward, but reduction to lower oxidation states could not be confirmed. In dimethylformamide solutions, cyclic voltammetry results demonstrated the reduction of Ti to an oxidation state of less than three, but no Ti metal was identified. In dimethyl sulfoxide solutions containing LiCl, it was possible to deposit Li metal. After adding Ti salts to the solution, electrolysis quickly passivated the electrode. Deposition of Ti was also investigated in solutions of dimethoxyethane and propylene carbonate but, again, no reduction of Ti to oxidation states of less than three occurred. Therefore, the prospects for a nonaqueous electrorefining system for Ti metal do not appear promising.
Date: 1995
Creator: Sibrell, P. L.

Field Demonstration of Two Pneumatic Backfilling Technologies

Description: Abstract: This U.S. Bureau of Mines (USBM) report summarizes a field demonstration of pneumatic backfiling technologies conducted at the abandoned Hillside Coal and Iron Slope in Vandling, PA. Researchers demonstrated tro pneumatic backfilling technologies recently developed under the USBM's Abandoned Mine Reclamation Research Program, the Pneumatic Pipefeeder and the High-Efficiency Ejector. Both systems had previously been evaluated at the USBM's subsidence abatement investigation laboratory near Fairchance, PA. The objective of the demonstration was to fill 100% of the abandoned tunnel with backfill stone to prevent further subsidence. The Pneumatic Pipefeeder was used for 21 days, at a rate of 63 to 124 t/d (69 to 136 st/d), to fill 88% of the tunnel. The High-Efficiency Ejector was used for 2 days, at a rate of 125 to 132 t/d (138 to 146 st/d) to fill the remaining 12% of the tunnel. The backfill placed by both systems was tightly compacted. The major problem encountered was wear on the polyethylene pipeline from the abrasion of the high-velocity backfill. The use of heavier steel pipe minimized the problem. A cost analysis for the entire project is given.
Date: 1995
Creator: Dyni, Robert C.; Burnett, Mackenzie & Philbin, David

Hazards of Conveyor Belt Fires

Description: This report describes a U.S. Bureau of Mines study on the hazards of large-scale conveyor belt fires in underground coal mines, as a function of both air velocity and distance from belt surface to gallery roof. The fire hazards considered were smoke obscuration, toxic effects of carbon monoxide (CO), and elevated air temperatures downstream of the fire. All of these hazards scale with the ratio of fire intensity to ventilation airflow. These hazards were all found to be greater at the lower belt-to-roof distance, owing to the greater fire intensities that resulted. The hazards of smoke obscuration and elevated CO levels were greater at lower air velocities. Smoke obscuration was found to be the earliest hazard, reaching critical levels before the stage of belt flame spread. Critical levels of CO and downstream air temperatures were not reached until the later stages of flame spread. Fire growth rates during rapid flame spread were much greater than rates measured during the early stages of belt burning. Data were analyzed to determine the early-warning capability of fire sensors. Smoke sensors provided the earliest warning, followed closely by CO sensors. Thermal sensors did not exhibit any early warning capability.
Date: 1995
Creator: Perzak, Frank J.; Litton, Charles D.; Mura, Kenneth E. & Lazzara, Charles P.

High-Temperature Cyanide Leaching of Platinum-Group Metals from Automobile Catalysts--Pilot Plant Study

Description: From abstract: The U.S. Bureau of Mines Reno Research Center investigated, developed, and patented a high temperature cyanide leaching process for recovering platinum-group metals (PGM) from automobile catalysts. A batch pilot plant was constructed at the center and operated to demonstrate this technology to industry.
Date: 1995
Creator: Kuczynski, R. J.; Atkinson, G. B. & Dolinar, W. J.

Human Factors Analysis of Roof Bolting Hazards in Underground Coal Mines

Description: Abstract: The U.S. Bureau of Mines conducted a human factors analysis of hazards associated with roof bolting activities in underground coal mines. Emphasis was placed on hazards related to the movement of the drill-head boom or mast of a roof bolting machine. The objective was to identify hazards and recommend solutions. The data-collection effort consisted of analysis of U.S. Mine Safety and Health Administration accident data; visits to underground mines and interviews with experienced roof bolting machine operators; discussions with roof bolting machine manufacturers; interviews with workers injured while performing roof bolting tasks; and reviews of research on roof bolting safety. A set of recommendations to increase the safety of roof bolting operations was developed. In particular, the following list of recommendations was presented in ranking order: (1) use an interlock device to cut off power to controls when an operator is out of position,,(2) place fixed barriers at pinch points, (3) provide appropriate control guarding, (4) reduce fast-feed speed, (5) use automatic cutoff switches at pinch points, (6) redesign control bank to conform to accepted ergonomic principles, and (7) use resin insertion tools and resin cartridge retainers.
Date: 1995
Creator: Turin, Fred C.

Improved Grindability of Taconite Ores by Microwave Heating

Description: The 11.S. Bureau of Mines has conducted studies to utilize rapid microwave heating to stress fracture ore samples. Iron ores containing hematite, magnetite, and goethite were subjected to microwave energy in batch operations at 3 kW and heated to average maximum temperatures between 840 and 940 *C. Standard Bond grindability tests showed that microwave heating reduced the work index of iron ores by 10 to 24 pct. In a microwave chamber designed to simulate a continuous throughput operation at 3 kW, the grindability of a tacon-te ore was improved by 13 pct at a bulk temperature of 197 *C. Because stress cracking occurred at a lower temperature, less energy was consumed. To further improve the economics of microwave fracturing, higher powers up to 16 kW were used to rapidly heat samples to relatively low temperatures in a continuous, belt-fed applicator. A significant improvement of grindability was obtained with a larger rod mill feed size in comparison to a minus 6-mesh Bond feed.
Date: 1995
Creator: Walkiewicz, John W.; Lindroth, David P. & Clark, Andrea E.

Improved Performance of Linear Coal Cutting Compared with Rotary Cutting

Description: From abstract: The linear cutting system, developed by the U.S. Bureau of Mines, uses geometric principles developed by Cardan to produce a nearly constant cut depth. The new system has been extensively tested in a synthetic material under laboratory conditions to verify mechanical capability and to identify operational characteristics. This report details the improved performance versus rotary cutting.
Date: 1995
Creator: Roepke, Wallace W.; Hanson, B. D.; Olson, R. C.; Wingquist, C. F. & Myren, T. A.

Influence of Environmental Factors on Spark Ignition Probability

Description: Abstract: In past years, the U.S. Bureau of Mines has been involved in safety research that could ultimately relate the conditions of spark testing and actual use by estimating the simple ignition probability of a circuit in question. A major problem in estimating this probability is that results show a significant variability, even though gas mixtures and electrical parameters may be closely controlled. Some researchers have suggested that the ambient environmental conditions of the testing may influence the results. A series of tests were conducted using a spark test apparatus to simulate a failing electrical circuit. By independently adjusting the temperature, pressure, or relative humidity of the combustible gas mixture, multiple test environments were examined. At each ignition, a computer recorded the temperature, pressure, and relative humidity of the gas immediately prior to the explosion. These data were then used to establish the effect of the test environment on the ignition probability and to create a mathematical model of the test environment's synergistic effects. The analysis indicated that these effects were not as significant as previously expected. No general algorithm was found that could be used to predict these effects across the range of circuits tested.
Date: 1995
Creator: Peterson, Jeffrey Shawn

Investigation of Acid Production, Leaching, and Transport of Dissolved Metals at an Abandoned Sulfide Tailings Impoundment: Monitoring and Physical Properties

Description: Abstract: Researchers at the U.S. Bureau of Mines conducted a long-term groundwater monitoring and site characterization program at an abandoned 10-ha, acid-producing, copper-gold tailings impoundment in north-central Washington State. The purpose was to investigate contaminant release and transport, and attenuation mechanisms in the tailings, sediments below the tailings, and gravels downgradient of the impoundment. This report summarizes the monitoring results and physical properties of the tailings, the sediments below the tailings, and the groundwater system associated with the tailings. Water samples from the vadose and saturated zones of the impoundment were analyzed for 15 constituents. Concentrations of the same constituenta were determined in water samples up to 3 m beneath the impoundment and in the shallow colluvium and deep bedrock at 76, 335, and 550 m downgradient and 168 m upgradient. Constituent concentrations within the tailings are quite variable and are influenced by pH, depth of oxidation, grain-size differential (surface area), hydraulic gradient, groundwater mixing, and the presence of hardpan layers, carbonaceous material, and organic matter. Most of the metal constituents decreased to background or near-background concentrations in the farthest downgradient well.
Date: 1995
Creator: Stewart, Bill M.; Williams, B. C. & Lambeth, R. H.

Investigation of Optimum Thrust, Cutting Speed, and Water Pressure for Tungsten Carbide and Polycrystalline Diamond Compact Roof-Bolt Drill Bits

Description: Abstract: Laboratory tests were conducted at the U.S. Bureau of Mines to determine the effects of roof-bolt drilling parameters on penetration rate in sandstone using tungsten carbide alloy (WC-Co) and polycrystalline diamond compact (PDC) drill bits. During the tests, water pressure of 552 kPa was found to be adequate for removing the cuttings from the tops of drill holes. Test results show that for both types of bits, penetration rate increased when thrust was raised from 227 to 1,588 kg. When water pressure rose from 554 120 to 1,344 350 kPa, the effect on penetration rate was not significantly different. Conventional WC-Co bits became dull when one or two holes were drilled, after which the penetration rate dropped dramatically. Microscopic examination shows that the cutting edges of PDC bits also become somewhat dull, but at a much lesser rate than WC-Co tips. Microscopic examination also reveals that the wear mechanism of WC-Co and PDC bits is quite different, which may explain the longer life of the PDC bits.
Date: 1995
Creator: Sundae, Laxman S.; Smelser, Thomas W. & Howie, Wayne L.

A Kinetic Model for Conventional Flotation of Coal

Description: The U.S. Bureau of Mines has developed a computer model to 'describe a flotation process. Coal data from conventional flotation has been converted to a simple, two-parameter kinetic model developed by Reuter and van Deventer (j,2 3. Each set of coal data was represented by two constants, a and a, and an average flotation rate. The success of the model was demonstrated when the calculated and experimental recoveries showed good correlation. The two-parameter model allows complex data to be defined much more efficiently than traditional knowledge-based models.
Date: 1995
Creator: Susko, Frank J. & Stanley, Don A.

Longwall Gate Road Stability in a Steeply Pitching Thick Coal Seam with a Weak Roof

Description: The U.S. Bureau of Mines (USBM) conducted ground pressure analysis of a wide abutment-type chain pillar in a two-entry gate road of a Western U.S. coal mine with an extremely weak immediate roof. About 15 m of fragile, low-strength mudstone lies between the seam and the lowest competent roof member. Three- and two-entry gate road designs with several pillar sizes and various secondary support systems have been employed to improve tailgate-entry stability, with varying results. This report discusses gate road layout and performance and secondary support effectiveness. The results of the pillar pressure study are compared to pillar loading predicted by a widely used pillar design method and to similar studies in other mines. A stability evaluation of the most recent longwall headgate, using the USBM Analysis of Longwall Pillar Stability (ALPS) method, indicates marginal stability in first-panel mining and instability in second-panel mining. The ALPS method and the USBM Coal Mine Roof Rating system are used to evaluate tailgate-mining stability of the previous gate roads and to determine pillar and entry width and top coal thickness criteria for tailgate stability in future panels.
Date: 1995
Creator: Barron, Lance R. & DeMarco, Matthew J.

Numerical Modeling Analysis of Stress Transfer Modification Concepts for Deep Longwall Mines

Description: Abstract: This U. S. Bureau of Mines (USBM) report evaluates three stress-transfermodification concepts for their potential in reducing longwall gate road stresses and closures. In each of the three concepts - packwalling, gob infilling, and entry filling - support structures are constructed on the headgate side of the panel parallel with or inby the face line. When the headgate becomes the tailgate of the adjacent panel, these structures are in place to accept stresses transferred from the mined-out panel. Using the USBM nonlinear boundary-element program MULSIM/NL, baseline models of typical longwall stress transfer behavior were developed for both intermediate depth and deep mining conditions. These models were verified by comparing model results with field measurements and observations. The stresstransfer-modification concepts were then incorporated into the deep baseline model to quantify the effects of each concept on tailgate closure. Modeling results indicated that entry filling is the most effective concept in reducing tailgate escapeway closure. Using only 18 m3 of a weak fill per meter of face advance (7.3 yd3 per ft of face advance), tailgate escapeway closure was reduced by 33%. By improving the quality of the fill, similar results were achieved using 50% less volume.
Date: 1995
Creator: Vandergrift, Thomas L. & Jude, Charles V.

Petrographic and Geochemical Analyses of Leach Samples from Artillery Peak, Mohave County, Arizona

Description: Abstract: The first step in determining whether Mn can be recovered by in situ leaching is to develop and test a selective lixiviant. Two column leach tests and one core leach test were conducted by the U.S. Bureau of Mines on Mn oxide ore using aqueous sulfur dioxide (SO2) as the lixiviant. The column tests showed that aqueous SO2 could selectively dissolve available Mn oxides from calcite-rich ore in a heap leach system. However, the core test showed that calcite gangue side reactions can have pronounced negative effects on the likelihood of successful in situ leaching of a calcite-rich ore with aqueous SO2. Petrographic and geochemical analyses showed that both Mn (IV, II) oxides and calcite were dissolved. The abundance of dissolved Ca caused precipitation of gypsum. Acid consumption by calcite dissolution caused a rise in pH that caused the S02/S species to shift to SO32- (sulfite), which hindered reductive dissolution of Mn oxide. Gypsum precipitation did not affect complete leaching of the rock fragments in the column tests; however, it plugged the natural permeability in the core. Manganese recoveries were high for the column tests and low for the core test.
Date: 1995
Creator: Brink, Susan; Blake, Rolland & Marozas, Dianne