Search Documents

By T. V. Johnson

The microstructural relationships in dolomitic fluxed taconite pellets were studied. The influence of basicity (in the range 0.75 to 2.1) and firing temperature (to 1340°C) on the grain structure, macrostructure, and mineralogical phase relationships are described. Extensive slag bonding of hematite grains begins at temperatures between 1220 and 1230°C, and results in fundamental changes in grain structure. Successive temperature increases result in little change in grain structure until 1340°C, when extensive coalescence of the hematite grains begins.' Increasing flux additions have little effect on grain structure but greatly influence pore character. The compressive strength decreases with increasing flux addition, increases with increasing firing temperature, and is related to the macrostructure of the pellet. The compositions of the slag phases are represented on the CaO-Fe2O3-SiO2 phase diagram, and the compositional path of slag development is described.

Jan 1, 1980

Lignite is a kind of easy-to-slime and low rank coal. It is hard to be separated by the conventional wet coal beneficiation technologies. Meanwhile, in recent decades, a large amount of fine coal (-6 mm) is generated as the mechanized mining technology has been progressively deployed in coal sector, which causes a great difficult for lignite beneficiation and upgrading due to lack of efficient technology available. In this paper, a vibrated gas-fluidized bed was used to separate the -6 mm fine lignite particles. Separation experiments of -6+3 mm and -3+1 mm lignite were carried out in a laboratory-scale vibrated gas-fluidized bed. The effects of several parameters including the superficial air velocity, vibration intensity, bed height and exterior moisture content on the separation performance were experimentally studied. The results show that the optimal separation performance was achieved when the superficial air velocity is 0.3, the vibration intensity is 1.4, the bed height is 50 mm, the exterior moisture content is below 4% (-6+3 mm) and 2% (-3+1 mm). And the probably error E values of -6+3 mm and -3+1 mm size fraction of lignite are 0.202 and 0.225 respectively. The results indicate that a vibrated gas-fluidized bed can provide an effective solution for -6 mm lignite separation.

Feb 23, 2014

By L. J. Prosser, A. T. Iannacchione

From 1991 through 1995, 44 miners out of a total workforce of less than 2,000 were fatally injured in the stone industry. Of these, 12 occurred at underground mining operations with nine deaths resulting from roof or rib falls. A safer environment can be achieved by evaluating the nature of the hazardous ground and by developing more efficient and effective ground-control strategies. Roof and rib conditions were observed and assessed in 33 underground stone mines in Illinois, Indiana, Kentucky, Maryland, Missouri, Pennsylvania and West Virginia (Fig. 1). Hazard assessment indicated that the ground failures that occurred under moderate to substantial overburden, i.e., >30 m (100 ft), were caused by stress concentrations and geologic structures. Ground failures near the surface are caused by solution (water) processes. Selection of the mining horizon and mine-layout decisions

Jan 1, 1999

By S. R. Abt, J. D. Nelson, G. M. Smith

An empirical investigation was conducted to formulate a design criteria for predicting the beach profile of hydraulically deposited tailings. Field data were obtained from mining operations producing gold sulfides, silver, molybdenum, copper, platinum, and uranium. Site-specific parameters were collected that included the beach slopes, tailings soil properties, slurry properties, and the slurry distribution system characteristics. Each of the beach profiles were dimensionlessly plotted, and regression expressions were computed. It was determined that either a power expression or exponential expression closely predicted each beach slope. A general power expression and a general exponential ex¬pression were developed resulting in a design criteria. A procedure was formulated to determine which expression, power or exponential, is applicable to any specific site. A slope designation chart was developed as a function of the discharge, the tailings critical tractive shear stress, and the inertial forces exerted by the slurry on the beach.

Jan 1, 1987

By T. G. Bobick

Task analyses were conducted by the Bureau of Mines at four underground low-seam coal mines to evaluate their supply-handling systems and for use in subsequent design of laboratory simulation experiments. Items were tracked (by videotaping) from delivery to the surface storage areas to their final destinations underground. Of particular interest were those tasks that required manual handling of supplies or equipment. Analysis of the videotapes revealed that the miners handled materials while stooped over a total of 37.8 pct of the time, 31.5 pct while on both knees and 9.5 pct while kneeling on one knee. These working postures impose considerable stress on the lumbar spine and may be implicated in the high number of back injuries in this work population. This paper also discusses various mechanical-assist devices developed by the Bureau and successfully evaluated in the underground workplace. These devices can be used to minimize the manual effort and the corresponding risk of injury associated with handling supplies and equipment components in low-seam coal mines.

Jan 1, 1988

By W. C. Patrick

The Spent Fuel Test-Climax (SFT-C) was con- ducted to evaluate the feasibility of retrievable deep geologic storage of commercially generated spent nuclear-reactor fuel assemblies. One of the primary aspects of the test was to measure the thermomechanical response of the rock mass to the extensive heating of a large volume of rock. Instrumentation was emplaced to measure stress changes, relative motion of the rock mass, and tunnel closures during three year of heating from thermally decaying heat sources, followed by a six month cooldown period. The calculations reported here were performed using the best available input parameters, thermal and mechanical properties, and power levels which were directly measured or inferred from measurements made during the test. This report documents the results of these calculations and compares the results with selected measurements made during heating and cooling of the SFT-C.

Jan 1, 1986

By X. Shi, F. -Y. Wang

Automation and robotics are the keys to new intelligent autonomous mining systems that can remove operators from hazardous and stressful mining environments and provide the tools for greater productivity. This paper presents the components necessary for an Intelligent Task Control System (ITCS) for machine control in dynamic unstructured mining environments. In particular, the design details of a controller for an automated excavator are developed. The excavator controller uses fuzzy logic to interpret forces and torques gathered from a wrist mounted force/ torque sensor during the excavation process. This approach enables the transfer of human heuristics and expert knowledge to the controller. Several excavation tests using the fuzzy logic controller are described. These experimental results represent the first step toward an integrated approach that uses force/torque, vision and other sensor data to perform generic tasks in uncertain mining environments.

Jan 1, 1995

By Evans U. Jegbefume

A plane strain two-dimensional finite element model employing the method of negative reaction loading has been used to model roof collapse and subsidence resulting from the underground gasification of coal in regions of soft overburden such as that found in Texas. The model included dry zones of rock around the cavity. Roof collapse was included by considering the final state of stress in the elements and removing those that had undergone tensile failure. The two-dimensional plane strain model was extended to include thermal loading and thermal softening of the roof rock. Roof collapse initiation and growth of the cavity were modelled by examining the portion of the rock immediately above the cavity under thermal and hydrostatic load. The model was extended to include linear creep using the method of incremental strains. The overburden was modelled as a generalized Kelvin material.

Jan 1, 1982

By X. Wu, M. G. Karfakis, K. Y. Haramy, B. T. Brady

A quantitative evaluation of damage caused by ground motions associated with strong roof caving is presented. The strong roofs are modeled as either cantilevering or bridging beams over continuous elastic foundations that are subject to an exponentially distributed vertical stress. Major factors influencing roof caveability and strain-energy buildup are identified and investigated. A methodology for the evaluation of strain-energy accumulation caused by, an overhanging roof is presented. The potential for mine tremors is determined in terms of the local Richter magnitude (ML), which depends on the seismic energy transformed from the stored strain energy that is released when the roof fails. A particle-velocity model is applied to estimate the damage area associated with roof collapse. A case study from a Utah coal mine shows that estimations of bump severity and the damage area agree well with field observations.

Jan 1, 1997

By S. S. Peng, V. Z. Sun

One of the major concerns of ground control in a coal mine is the prevention of roof, pillar and floor failures of the mine entry. To better design and evaluate the stability of a mine entry within a certain level of confidence, a reliability approach is introduced. The advantage of using the reliability approach, rather than the conventional safety-factor (SF) method, is that it not only takes variability of both rock/coal properties and stress into consideration but also assesses the stability of each component and the mine entry as a whole. Therefore, it is anticipated that by using this approach the current ground-control technology in a coal mine will convey a better sense of confidence. The results of a case study show that there is a significant difference in mine entry stability between the current design method and the reliability approach.

Jan 1, 1999

By R. A. Lohnes, S. M. Levorson

As part of research to develop a coal handleability index that predicts the ease with which coal will flow through a handling system, comparative tests were conducted with a Johanson Indicizer and a low-stress triaxial apparatus on 12 coals at a variety of gradations and moisture contents. The lndicizer test provides a rapid method for generating data associated with coal handling characteristics. The arching index measured with the Indicizer is a function of the geometry of the apparatus as well as the properties of the coal. The handleability index determined from triaxial data is a more direct measure of coal characteristics. The handleability index shows a wider range of values than the arching index and, therefore, appears to be more sensitive to coal variations. Neither the arching index nor the ratholing index, as measured with the Indicizer, agreed well with the handleability index. This is attributed to differences in sample preparation as well as to the tests themselves.

Jan 1, 1993

By M. H. Foroughi

In this paper, the compressive strengths, failure modes and acoustic emission behaviors of cubic coal specimens containing bedding planes at various inclinations are considered. Test results showed that the compressive strengths and the modes of failure of coal specimens depend on the inclination of the bedding planes. From the acoustic emission (AE) measurements, the count rate detected through a low-pass window (AE (L)) was compared with that through a high-pass window (AE (H)) in each test. The results of accumulated AE history were compared with AE signatures of others. It is shown that the AE signature of coal depends on the inclination of the bedding planes, and the AE signatures can be classified into three groups. Each group corresponds to a particular mode of failure, namely, slip on the bedding planes, fracture across the bedding planes and fracture extension through the bedding planes. The parameter r, defined as the ratio of AE (L)/ [AE (L) + AE (H)], is plotted against the stress for each test. Test results showed that r also depends upon the inclination of the bedding planes.

Jan 1, 1999

By Roshan B. Bhappu

In situ mining and extraction is one of the Frontier Technologies that is destined to play an increasingly important role in the recovery of metals and minerals in the future. This premise is based on increasing costs of labor and energy, increasing awareness of environmental considerations and decreasing ore grades in the United States. Up to now, in situ mining has been successfully applied to a few favorable situations for the extraction of some evaporites, copper and uranium. However, because of its unique technical, environmental and economic advantages, this versa tile technology will find broader applications for the recovery of above commodities as well as for others which are currently extracted by hydrometallurgical means. This paper traces the development of in situ mining and extraction; stresses its dependence on interdisciplinary science and engineering; discusses its theoretical, practical and economic aspects; and finally presents potential applications of this Frontier Technology.

Jan 1, 1985

By Neville G. W. Cook, John Kemeny

Utilizing the principles of elastic-brittle fracture mechanics, stress-displacement relationships are derived for an elastic solid containing a slip plane consisting of various configurations of collinear arrays of cracks. These models take into account the heterogeneous nature of slip planes as observed in the lab and in the field, and are relevant to the behavior of rock containing faults, joints, bedding planes, and fractures. All of our models exhibit slip weakening behavior, and show regimes of both stable (aseismic) and unstable (seismic) deformation. For given configurations of cracks and applied boundary conditions, our results show explicit ly the energy released through unstable crack growth. For instance, it is found that two equal length cracks growing together release more seismic energy than, say, a large crack growing into a small crack. Also, by allowing cracks to coalesce, our models show multiple stick-slip events without crack healing or other geochemical means.

Jan 1, 1986

By Norbert Patzelt, Johann Knecht, Wolfgang Baum

High pressure roll grinding (HPGR) is a mature but still expanding comminution technology. In the metals mining industry, HPGR is slowly gaining acceptance as a cost-efficient, high-throughput alternative for plant optimization. The increasing need to treat ores with progressively lower grades, complex mineralogies, refractory metal occurrence and variable rock types requires an energy-efficient comminution technology that reduces metallurgical problems inherent in conventional crushing and grinding, while stabilizing leach and flotation circuits and increasing metals extraction. This paper will summarize our latest HPGR pilot test results for gold and copper projects in the United States and South America and their confirmation through the first HPGR operation in copper mining. This paper will also stress the use of the high pressure grinding roll as a metallurgical tool. The application of HPGR for the treatment of heap leach SX-EW ores, semi-refractory gold ores, waste rock material and concentrator feeds will be illustrated.

Jan 1, 1998

By R. Hogg, R. H. Weiland, P. Bunnaul

The dewatering of flocculated clay suspensions by compression in a centrifugal field was investigated. The results were analyzed with respect to the direct applicability of centrifugal dewatering (as in solid-bowl centrifuges) and indirect applications to gravity sedimentation systems. An important objective of the study was to evaluate the self-weight effect using centrifugal forces to simulate consolidation of deep sediments. Experiments were conducted in which the sediment mass and initial structure were maintained constant while the effective sediment weight was varied by centrifuging at different speeds. The relationship between the limiting sediment density and the applied consolidation stress was found to be the same for both gravity and centrifugal consolidation, indicating that small-scale laboratory tests can be used to predict consolidation in deep beds. The effects of the initial structure were also studied using controlled variations in flocculation conditions. The results imply that, for the flocculated suspensions studied, the longterm consolidation behavior is relatively insensitive to the actual extent of flocculation.

Jan 1, 1995

By D. R. Nagaraj

Secondary Ion Mass Spectroscopy (SIMS) was used to study copper ion adsorption, and its effect on subsequent sulfide collector adsorption, on pyrite and pyroxene minerals under flotation related conditions. Copper was found to adsorb on both of these minerals and cause enhanced sulfide collector adsorption. The distribution and depth profile of copper and collector on these mineral surfaces were obtained by using SIMS in the imaging mode. The results of this study have provided a valuable insight to understanding pyrite and gangue flotation observed frequently in operating plants.

Jan 1, 1995

By Eugene F. Eisemann

This paper is concerned principally with the competition between fuels for industrial use in the United States. Total energy consumption in the U. S. is allocated between industrial and other uses The industrial volume is divided into two classifications (1) where-there is competition between fuels and (2) where there is no competition. The pattern of fuel consumption by electric utilities was studied because there, is competition between fuels and because it is the fastest-growing industrial market. Electric utilities fuel consumption is discussed by geographic area. The growth of each fuel in several areas is investigated. The analysis of these areas, includes the study of the relationship between prices where fuels are in, competition:- (1) on the East Coast where price competition occurs between oil and coal, and (2) in the southeastern states where competition exists between coal and gas..

Jan 1, 1961

By Colin Lawrence

The Port of New York and New Jersey is one of the most heavily used transportation arteries in the world, handling nearly 40 per-cent of the North Atlantic shipping trade and directly providing nearly 230,000 jobs to the local economy. In 2004, $100 billion worth of consumer goods moved through the port. To accommodate future cargo volumes in the port, which are expected to double over the next decade and possibly quadruple in 40 years, deeper shipping channels are needed to provide access for a new generation of cargo mega-ships with drafts exceeding 13.7-m (45-ft) when loaded. Current channels within the harbor range in depths up to 13.7-m (45-ft), thus preventing carriers from using these larger ships, or requiring significant reductions in cargo to achieve lesser drafts to operate safely within the harbor. As part of the Harbor Deepening Project, the Anchor-age Channel would be deepened to 15.2 m (50 ft) below mean low water (MLW), for a length of 5,790 m (19,000 ft). The New York City Department of Environmental Protection (NYCDEP) owns, operates and maintains two existing water siphons in the harbor. Due to their shallow depth, both existing siphons must be relocated before dredging of the Anchorage Channel can be completed. Tom Costanzo, manager of capital programs for the Port Authority of New York and New Jersey (PANYNJ), says that ?While the re-location of the existing siphons under the Anchorage Channel is vital to the success of the deepening program, it is also a story of cooperation among key agencies at different levels of government resulting in improvements that will benefit the people of this region greatly.?

Jun 1, 2010

By D. Scott Barr

The Zarafshan/Newmont Joint Venture operates the Muruntau heap leach project, located in the Kyzylkum desert of central Uzbekistan. The mine produces more than 12.4 t/a (400,000 oz/year) of gold from low-grade oxide ore stockpiles adjacent to the Muruntau open pit. It is op¬erated by the Navoi Mining and Metallurgical Combine and is one of the largest gold resources known (Fig. 1). Since commissioning in 1995, total heap leach production has exceeded 21 t (675,000 oz). The joint venture uses four-stage crushing and screening to produce a final product for heap leaching, Merrill-Crowe processing and local refining.

Jan 1, 1998