Search Documents

By Fred N. Kissell

Methane-flow and pressure data taken from a mine in the Pocahontas No. 3 coalbed are compared with flow rates from lump coal obtained in laboratory experiments. From this, it is concluded that the main source of gas is the intact coalbed rather than a "crushed zone" near the working face. The permeability and sorption capacity of the intact coalbed are calculated and gas emission rates are theoretically accounted for.

Jan 1, 1972

By Nancy S. Raymon

The Bureau of Mines investigated the effect of controlled additions of selected metal oxides, as well as the adjustment of the calcia-to-silica ratio on the high-temperature strength of refractory-grade periclase. Increases in the hot flexural strength of some periclase materials in the range of threefold to fourfold were obtained with additions of Zr02 and by adjustment of the CaO:Si02 ratio to the 2.5 to 3.0 level. Results show that for each periclase refractory raw material, there exists a combination of level of Zr02 addition and an adjustment to the CaO:Si02 ratio that optimizes the hot flexural strength of each of these materials. Data also indicate that the improved hot strengths can be attributed to the high-temperature secondary phases formed between the different levels of periclase impurities and the additives, resulting in improved intergranular high-temperature bond strength.

Jan 1, 1982

By Joseph B. Huvos

Said to be one of the world's most under-developed countries, Benin had a gross national product (GNP) estimated at $1 billion in 1980.2 Contribution of the mineral industry such as cement and limestone to the GNP was negligible, but exploration of mineral potential continued Minerals.-The United Nations Development Program (UNDP) conducted an investigation of three deposits from 1977 to 1980: Phosphates (Mekrou), gold (Perma), and chromite (Buem). A phosphate rock deposit containing about 4.5 million tons recover- able by opencast techniques was discovered. It was not known if the gold and chromite deposits were recoverable economically. Iron ore deposits of some 230 million tons near Loumbo-Loumbo are at present not exploitable because of lack of infrastructure in the northern part of the country. Geologic mapping with British and French assistance was also pursued in 1980.

Jan 1, 1982

By James W. Vogh

The report covers initial findings in an experimental program to identify diesel exhaust odorants and determine their contributions to diesel odor. The approach was to isolate selected component groups from exhaust and to evaluate the contribution of each group to exhaust odor. Results were obtained for those carbonyls and phenols that could be isolated from exhaust through inter-mediate conversion to oxime derivatives. Unsaturated aliphatic aldehydes and sterically hindered carbonyls were not included. Hydrocarbons intermediate in the diesel range were "also evaluated and an odor contribution was found from those of the aromatic group. The evaluated carbonyls, phenols, and hydrocarbons were found to account for about 20 pct of the total odor in exhaust from an indirect-injection engine during idle. For exhaust from the indirect-injection engine operating under load and from a direct-injection engine at no load, these compounds were found to have no significant levels of odor.

Jan 1, 1972

Enhance the critical skill of hazard recognition among miners by providing quality training that can help jot performance and lead to a higher degree of safety in the workplace. Background In mining, as in many other occupations, the safety of the worker depends on his or her ability to recognize hazards in the workplace. Some of the information needed by the miner for recognizing potential areas of danger is available in the form of visual cues found throughout the mine. One aspect of the dynamic mine environment it which the task of hazard recognition is critical for al workers is that of ground control. Regardless of job responsibilities, every worker is continuously exposed to roof rib, and floor hazards. Fatality injury data for the "underground coal" segment of the mining industry continue to show that about half of all fatalities are due to falls of ground each year. It is hypothesized that some of these accident, can be prevented if miners are better able to recognize visual cues that forewarn of potential roof and rib problems.

Jan 1, 1992

By Donald P. Tuchman, Robert P. Vinson, Linda J. McWilliams, Steven E. Mischler, Jon C. Volkwein

A personal dust monitor (PDM) was developed to measure respirable coal mine dust mass to provide accurate exposure data at the end of a work shift. Additionally, the new monitor continuously displays near-real-time dust exposure data during the shift. The PDM uses a tapered-element oscillating microbalance to measure the mass of dust deposited on a filter and continually displays the cumulative exposure concentration data. The accuracy and precision of the instrument was determined by comparison to gravimetric filter samplers in the laboratory and in four mines. Laboratory results with different coal types and size distributions showed that there is a 95% confidence that the individual PDM measurements were within ±25% of the reference measurements. Mine test results indicate that data taken with adjacent PDM and reference samplers are indistinguishable. The technology proved durable enough to successfully measure 108 shifts of data out of 115 attempts in the mines. Under these specific test conditions, the PDM demonstrated that it was convenient to wear, robust, provided accurate data, provided timely data that could be used to prevent overexposure, and was easy to use.

Jan 1, 2004

Use water-jet-assisted cut-ting technology to reduce the exposure of mi ne workers' to respirable dust. Approach Install water-jet-assist on mining machines and evaluate its impact on respirable dust. How It Works Water-jet-assisted cutting involves a mechanical cutting bit working in combination with a moderate pressure (generally up to 10,000 psi) water jet directed just in front of, or through, the bit tip. One of its advantages is reduced dust generation because the jet wets the face of the material being cut more efficiently than a conventional low-pressure water spray, thus capturing much of the dust before it ever becomes airborne. It also removes loose cuttings ahead of the bit before they are pulverized by the bit into respirable dust. Total water consumption is about the same as for conventional low pressure dust control water spray systems. However, there is some increase in power consumption because of the energy needed to provide the high pressure water.

Jan 1, 1987

Control dust generated during overburden drilling at surface coal mines using either wet suppression or dry collection systems. Approach For the wet suppression systems, a range of water flow rates was tested over a number of holes. Each hole was drilled at a specific and constant flow rate. A recording flow meter was mounted in the water line near the control system pump. For the dry collection systems, each drill was tested with the front of the shroud set at different heights above the ground. Because of the irregularity of the ground surface, all height measurements were taken at the front of the shroud. Background Wet drilling systems consist of a water tank mounted on the drill from which water is pumped into the downhole air line. The water droplets in the bail air conglomerate dust particles as they travel up the the annular space of the drilled hole, thus controlling dust as the air bails the cuttings from the hole.

Jan 1, 1987

Provide optimum visibility of mining operations while maintaining protection and comfort for machine operators. Approach A cab with hydraulically powered variable-height control was developed and used on a loading machine in underground operations. How It Works The cab is attached to the vehicle on a horizontal trunnion located near the forward end of the cab. A hydraulic cylinder, controlled by the operator from inside the cab, pivots the cab about the trunnion providing variations of up to 16 inches in elevation. The nominal tramming position of the cab is with its underside 6 inches above the mine bottom. From this position the cab can be pivoted up, or down, so that its back end is elevated 10 inches, or lowered to the floor. (See Figure 1.) The cab encloses the operator for protection against both overhead and lateral obstructions, and it raises or lowers, allowing the operator to select the most advantageous cab height. The cab is angled inboard 30 degrees to the machine line of direction. The operator's seat swivels to allow view of the conveyor during loading. All controls are located within the cab and move up and down with it.

Jan 1, 1978

By C. M. McCulloch

A series of geological surveys were completed in six coal mines in connection with a Bureau of Mines research program on methane control. The aim of these surveys was twofold: First, to study the overall geology of the coalbed, and second to use the resulting data to evaluate the influence of the geological characteristics of the coalbed on safe and efficient coal extraction. This report explains the advantages of geologic maps and fence diagrams in coal mining, and how the knowledge gained from such geologic investigations of mines can help control many underground problems.

Jan 1, 1975

By B. W. Madsen

As part of a program to maintain an adequate supply of minerals and metals to meet national economic and strategic needs, the Bureau of Mines conducted research to determine the diffusion coefficients for ferric ions in synthetic copper leach solutions. Determination of ferric ion diffusion coefficients in typical dump leach solutions is necessary for predicting leaching rates of copper from large-scale leaching operations and for optimizing concentrations of ferric iron in solutions to maximize leaching efficiency. Derivative chronopotentiometry, an electroanalytical technique, was used to determine ferric ion diffusion coefficients. The diffusion coefficient decreased dramatically with increasing concentration of iron in solution. An empirical model was used to relate the ferric ion diffusion coefficient to the total amount of sulfate in solution. Measuring the diffusion coefficient dependence on temperature yielded an activation energy of 5.5 kcal/mole of ferric ion. Activity coefficients of ferric ions as a function of concentration were calculated from diffusion coefficient data.

Jan 1, 1981

By David C. Oyler, Winton J. Gale, Jinsheng Chen, Christopher Mark

A collaborative project between RAG Emerald Mine, NIOSH, and SCT Operations was conducted to investigate ground behaviour, reinforcement performance, and stress redistribution in a coal mine entry subjected to a severe horizontal stress concentration. Field measurements indicated that the stresses applied to the study site nearly doubled during longwall mining, resulting in roof deformations extending to a height of 4.8 m (16 ft) above the entry. This paper focuses on the computer simulation that was undertaken to provide more insight into the roof behaviour and rock bolt interaction during mining. The model’s input rock properties were derived from extensive laboratory testing, and the model itself simulated a broad range of failure mechanisms. The effects of different bolt patterns on roadway behaviour were evaluated. Comparison between the model results and the field measurements indicated that that the model effectively simulated the critical elements of the actual roadway’s behaviour. With the confidence gained, the model was used as a baseline for additional simulations that evaluated the expected performance of alternative roof support systems. The study will also provide a benchmark data set for future applications of numerical modelling to U.S. coal underground mining.

To improve efficiency in producing clarified water from mineral and metallurgical processing streams containing suspended particles. Approach Particles suspended in mineral and metallurgical processing streams are filtered out by granular magnesium oxide (MgO) used as the medium in deep bed filters. How It Works MgO is substituted for the silica sand or garnet sand currently used in conventional deep bed filters. These filters presently consist of a 24- to-48-inch-deep layer of either silica sand or mixed media, consisting of a stratified combination of anthracite coal, silica sand, and garnet sand. As waste water containing fine solids is percolated through the granular bed, the suspended particles become attached to the filter grains. When MgO replaces sand as a filter medium, the overall filter capacity is generally increased 50 to 80 percent, and no equipment modifications are necessary for filter operation. MgO is unique because it has a positive surface charge in water while most suspended materials are negative. The attraction of these negatively charged suspended particles to MgO enhances filtering performance. As is necessary for all good media, MgO is insoluble and nontoxic.

Jan 1, 1983

By Sarah P. Guerrino

This chapter summarizes data on crude nonfuel mineral production for the United States, its island possessions, and the Commonwealth of Puerto Rico. Included also are the tables that show the principal nonfuel mineral commodities exported from and imported into the United States and that compare world and U.S. mineral production. The detailed data from which these tables were derived are contained in the individual commodity chapters of Volume I and in the State chapters of Volume II of this edition of the Minerals Yearbook. Although crude mineral production may be measured at any of several stages of extraction and processing, the stage of measurement used in this chapter is what is normally termed ?mine output.? It usually refers to minerals or ores in the form in which they are first extracted from the ground, but customarily includes the output from auxiliary processing at or near the mines.

Jan 1, 1987

By J. P. Baur

The sensitivity of radiochemical techniques makes possible the study of the initial-stage sulfuric acid leaching kinetics of chalcopyrite and other copper sulfide minerals. This Bureau of Mines study of the initial leaching of chalcopyrite used techniques to evaluate the molecular and electrochemical processes. High-grade Transvaal chalcopyrite was neutron-irradiated in a TRIGA reactor4 to produce radioisotopes copper-64, iron-59, and sulfur-35. Dissolution rates were measured in the time interval zero to 60 minutes, during which time significant anomalies were observed. First was an initial period of rapid dissolution lasting a few minutes; second, an arrest or ?plateau? region usually lasting from 6 to 10 minutes; third, a second period of dissolution of lesser rate than the first. The effects of solution variables such as pH, oxygen partial pressure, and ferric ion concentration at different temperatures were measured.

Jan 1, 1974

The extrapolation of results from reconstructed laboratory soil columns to field conditions is difficult because of the limitations of laboratory experiments. Permeability and elution tests performed in the laboratory differed from the natural state in that the soil was sieved through 1/4 inch screen to remove large stones and roots, its density was controlled by tamping the soil into two-inch I.D. tubes instead of normal weathering, and water and latex were applied with a constant head of liquid. Tube wall effects are important in interpreting data. Conversely, interpretation of field results were confounded by non-homogeneities within the sample tested, a soil profile with gradation of permeability and density with depth, and uncontrolled weather conditions and seasonal changes that affected the results. Nevertheless, both laboratory and field tests showed that a specific latex did perform as a soil sealant. In view of these facts a soil box experiment was designed to overcome some of the disadvantages associated with the small laboratory soil columns and the field experiments. Two wood soil boxes 5 ft x 5 ft x 5 ft were built in the greenhouse at the Uniroyal Research Center. They were lined with plastic PVC sheeting provided with tubes every six inches of depth on one side of each box to measure water removal rates under saturated conditions. Tensiometer gauges were placed at depths of 6, 12, 18, 24, 36 and 48 inches and Bouyoucos blocs and resistance thermometers were positioned at 6, 24 and 48 inch depths. Each box was filled with a uniform sub-soil obtained from Ogdensburg, N. J. The texture of this soil was determined to be a sandy loam by the ASTM Hydrometer method, as shown below: [ ] The boxes were thoroughly wetted by sprinkling to abet settling and allowed to dry by draining to check seepage ports and functioning of tensiometers.

Jan 1, 1972

To more rapidly and economically prepare solutions for chemical analysis, of a wide range of ores, slags, minerals, and metals. Approach A Simple pressure-dissolution system was devised using an inexpensive, heavy wall plastic bottle containing a sample in an acid medium. Using the technique, a complex silicate sample can be dissolved in less than 1 hour. How It Works A weighed portion of a sample, ground to minus 100-mesh, is placed into a polycarbonate or polysulfone plastic bottle. A mixture of hydrochloric acid, nitric acid, and hydrofluoric acid then is added. The bottle threads are wrapped with a layer of Teflon tape to prevent leakage, and the bottle cap is screwed on tightly. The sealed bottle is placed in a balling water bath. In the hot water, the plastic bottle acts as a pressure vessel to contain the pressure generated inside it. This technique should only be used by trained experienced people who are familiar with the hazards of hot acids under pressure. After being cooled in cold water, the resulting solution is brought to the final volume by adding 1.5 weight-percent boric acid solution to the bottle. The cap is replaced, and the bottle and solution is reheated. Precipitated fluorides, as well as any residue, are dissolved by the fluoride-boric acid reaction. The resulting clear solution then is suitable for spectro-photometric examination or other analysis.

Jan 1, 1980

Improve the reliability and accuracy of subsurface images using constrained tomography with enhanced ray-tracing capabilities. Background Geophysical tomography is a technique for imaging the structure of a rock mass using seismic or radio waves, in the same way that medical CAT scans image human tissue using X-rays. Tomography has found numerous practical applications related to mining, including lithologic and structural characterization, fracture detection and fluid monitoring, void detection, and evaluation of stress state and integrity of mine structures. Problems Two fundamental problems have largely prevented geophysical tomography from enjoying the tremendous success achieved by medical tomography. The first is a consequence of practical limitations on the placement of sources and receivers of wave energy: ideal resolution can be attained only when the region being imaged is entirely surrounded by sources and receivers, so that it is crossed by rays traveling in all possible directions. When such coverage is impossible or impractical, the inversion becomes underdetermined: there id not enough information in the measured data to provide a mathematically unique solution. The second major problem in geophysical tomography is the necessity for detailed ray tracing. Commercial software, as well as previous U.S. Bureau of Mines (USBM) software, employs a ray-shooting algorithm that may be unable to model some ray paths when velocity contrasts are larger than about 100%. These ?shadow zones" result in loss of data and degradation of reconstructed images.

Jan 1, 1994

By D. N. Nilsen

The U.S. Bureau of Mines investigated the use of unsupported liquid emulsion membranes (LEM's) for the extraction of copper from relatively dilute aqueous solutions (=0.3 and 2.5 g/L Cu), The performance characteristics of the three main unit operations of an LEM circuit (emulsion generation, metal extraction, and emulsion breaking) were assessed in laboratory-scale batch tests. In single-stage extraction tests using 2.5-g/L Cu feed solution, emulsion membranes extracted up to 94 pct of the copper from solutions without pH adjustment and 99.7 pct when the pH was maintained at about 2.5. Simulated two-stage crosscurrent and countercurrent circuits extracted all but 3 and 4 ppm of the original copper content, respectively. Extraction data from solutions containing mixtures of metals indicated a strong preference for Cu2+ extraction when oxime-type extractants were used in the LEM; however, some coextraction of Fe 3+ and Zn2+ was experienced. An electrostatic coalescer was used to break the copper-loaded emulsions for separation of the component phases. Up to 96 pct of the contained stripping solution (internal solution) containing the extracted copper was separated from the organic phase of the emulsion membrane. The recovered organic phase was recycled without apparent problems.

Jan 1, 2010

By John C. Edwards

Chapman-Jouguet detonation calculations were carried out for pentaerythri-tol tetranitrate (PETN), TNT, and ammonium nitrate-fuel oil (AN-FO) explosives using the compressibility form of an equation of state of hard spheres based upon Percus-Yevick (PY) theory, and a chemical equilibrium detonation code called TIGER. Similar calculations were also carried out with the Becker-Kistiakowsky-Wilson (BKW) equation of state. For PETN, the BKW equation gives somewhat better agreement with experimental values of detonation velocity and pressure. However, in terms of experimental temperatures and concentrations of the minor product species (NO), the predictions of the PY equation are shown to be more satisfactory. Similar comparisons of experimental and theoretical results for TNT and AN-FO indicate that the PY equation has general utility in predicting the detonation properties of condensed explosives at moderate loading densities (Po < 1.3 g/cm3).

Jan 1, 1974