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By J. B. Gwiazda

S.S. Peng The highlights of this paper are: The shield supports with lemniscate links will exert a tangential force on the roof strata, causing unnecessary and harmful roof movements, thus damaging the roof structure. The principal source of the tangential force is the horizontal movement of the point O, the pivotal joint between the canopy and the caving shield. When the support height is changed during setting, the point O will move along a curve upward and rearward toward the gob. As a result, it produces a vertical movement, causing the roof to move up a distance of t d, and a horizontal movement toward the gob, creating vertical fractures in the roof. The major purpose for employing the lemniscate- link system is to protect the hydraulic legs against the action of the bending moments induced by the tangential force that causes deformation or destruction of the legs. Based on these two points, the author suggested that, in order to eliminate the harmful effects of the lemniscate-link system and strengthen its advantageous features, a shield support with a new design of that mechanism has been developed. With the new design, the conventional rigid lemniscate links are replaced by hydraulic rams. When the pressure inside the rams reaches a certain level, the ram will yield.

Jan 1, 1987

A series of gas inrush events occurred during development at Grosvenor mine resulting in exposure to elevated levels of methane at the production face. A total of 22 gas inrush events occurred releasing between 15 and 130 m3 of methane during each event. The presence of an undrained seam in the immediate floor, geotechnical characteristics of the floor, and the stress environment all contributed to these dynamic floor events, while the geological characteristics of the seam below, such as the seam thickness and ash content of 75%, prevented effective pre-drainage. However, events only occurred in headings mined parallel to the principal horizontal stress direction. In cut-throughs (C/Ts) perpendicular to the principal stress direction, no events occurred, and higher methane levels were observed at the production face.

Jan 7, 2020

By E. C. Dowling, S. A. Elmquist, L. A. Kipfstuhl

The Cliffs and Associates Limited (CAL) 500,000 tpy HBI plant located in Trinidad was commissioned after modifications in early 2001. This plant employs the novel Lurgi Circored® process to reduce iron ore fines using a combination of circulating fluidized bed and conventional fluidized bed reactors in a hydrogen based. This paper will review the advantages offered by working in the Caribbean nation of Trinidad and Tobago, the Circored® processes, and plant start-up experience.

Jan 1, 2002

By Johann Engelbrecht, Stéfan de Bruyn, Petrus van den Heever

A system for the on-stream X-ray diffractometric determination of mineral phases in slurries was developed in response to the mining industry's need for process control during the beneficiation of industrial minerals. The instrumentation for and results from testwork conducted at a phosphate rock beneficiation plant in Florida are discussed. Results show that the concentrations of the minerals apatite (var. francolite) and quartz can be accurately determined every few minutes, so that adjustments to the flotation circuit can be timeously executed from the control room. The on-stream measurements can ultimately be integrated into an automated plant control strategy. Estimates of savings on reagent and staffing costs, as well as the benefits from consistent grades and greater recoveries, have shown that the investment in such a system could often be recovered in less than a year.

Jan 1, 1999

By Patrick McElhinney, Jacob Carr, Bruce Whisner, Cory DeGennaro, Jingcheng Li

Since 2016, electromagnetic interference (EMI) of personal dust monitors (PDMs) with magnetic proximity detection systems (PDSs) has been observed in underground coal mines. The EMI causes the magnetic field measurements of a PDS to change, which, in turn, alters the calculated location of the miner relative to the machine. Any altered location calculation can potentially cause the PDS to fail to warn a worker who is at an unsafe distance from the machine, arousing a serious concern on safety hazard caused by EMI in underground mines. The search for EMI mitigation strategies led to the development and use of large shielding pouches and boxes to hold the entire PDM to reduce its magnetic emission. Research on these pouches and boxes found that although they were able to reduce the emitted radiation from the PDM, they also disturbed the magnetic field of the PDS, affecting its performance. Researchers from the National Institute for Occupational Safety and Health (NIOSH) have focused on shielding internal PDM components rather than shielding the entire PDM. The PDM air pump motor is one of the PDM components that has been identified as a major source of electromagnetic radiation and has been selected for further study and tests. The measurements show that a small copper or aluminum foil enclosure can effectively reduce the magnetic emission of the motor by between 50 and 85% at 73 kHz. This study compares the test results of the air pump motor with various cost-effective shielding materials. The data provided in this paper can serve as a reference for shielding enclosure design of the PDM air pump motor to reduce its electromagnetic emission as one form of EMI mitigation strategy.

By P. J. Suardini, T. E. Seppanen, M. J. Hanninen

In order to reduce the heat loading in the Tilden Mine kilns caused by burning coal, which in turn resulted in rapid and significant build-upon the kiln lining, internal carbon was added to the green ball prior to balling. Intensive laboratory testing led to three short-term full-scale plant tests that were successfully conducted. Appropriate environmental permits were obtained to allow Tilden to use internal carbon on a continuous basis. Findings concerning carbon addition rates, reductions in coal use, build-up reductions, fired pellet quality, and environmental issues will be discussed.

Jan 1, 2003

By B. Stewart, J. R. Warneke

The productivity of underground mines has increased dramatically since the introduction of continuous miners. A variety of new hazards have developed as a result. In the spring of 2004, Mine Health and Safety Administration (MSHA) held a workshop to brainstorm ideas to decrease the number of injuries associated with continuous miners. One of the main areas of discussion at the workshop was “trailing cable-handling injuries.” The method of handling the power cables over the years has changed very little while the technology and uses of continuous miners has advanced dramatically. This paper will discuss the main ideas brainstormed at the MSHA continuous miner (CM) trailing cable handling workshop and the history and root causes of cable-handling injuries, as well as proposed ideas developed at the National Institute for Occupational Safety and Health (NIOSH) to alleviate some of the cable handling issues.

Jan 1, 2006

By A. Covelli, A. B. Cecala

Two recent US Bureau of Mines studies evaluated workers' dust exposures in automated pallet loading processes. The first study involved a Bureau designed dust control system using a push-pull ventilation technique. The unit was shown to reduce workers' dust exposures by 76% during pallet loading at a ground silica operation. A hydraulic lift table was used to automate the bag stacking process. This kept the loading height constant throughout the entire pallet loading cycle. The second study evaluated different commercial, automated-pallet loading systems. These systems automatically stack the bags onto pallets, shrink wrap the pallets, and deliver the pallets to a fork lift pickup location. Results from a ground silica evaluation site indicated respirable dust samples taken were below the Threshold Limit Value (TLV) as established by the Mine Safety and Health Administration (MSHA).

Jan 1, 1992

By L. Xu, S Jones, R. Bhaskar, J. McKenzie

The objective of this project was to optimize the ventilation parameters of a continuous miner underboom scrubber. This would result in further control of the amount of airborne dust discharged during mining, reduce the exposure of face personnel for an exhaust brattice ventilation system, and avoid recirculation of contaminants at the face. This research was performed in an underground coal mine in Utah. The tasks performed included preliminary face ventilation evaluation, and optimization of the scrubber system to eliminate recirculation of the scrubber discharge air. Airflow tests were conducted on the currently used dust control system and the modified scrubber system. Tracer gas tests were performed to evaluate face ventilation effectiveness. Confirmatory tests of the scrubber system under actual operating conditions, modifications to the scrubber system and a comparative evaluation of the scrubber system vs. the existing system were performed. This paper presents the results of the airflow pattern tests and the respirable dust levels in the modified scrubber system and the existing system. The optimized face ventilation parameters and the developed operating guidelines may provide the benefits of dust reduction, better lace ventilation and improved visibility.

Jan 1, 1994

By Etienne Simode

When a fire breaks out in a mine access road, the hot smoke, due to heat transfer with the surrounding strata, progressively cools as it moves forward. Depending upon the resulting temperature distribution, the density of the fluid changes. This change will bring about: Firstly, a variation in the resistance of the roads, a static factor which will affect ventilation flow rates; Secondly, the appearance of extensive aerodynamic driving loads in the vertical and angled roads, a dynamic factor which can have an extensive impact on ventilation. Because of the appearance of combustion and distillation products, the vaporization of water, which wets the timbering and strata, and the expansion of gases, fluid rates can at times be increased tenfold in the area of the fire. These disturbances may cause explosions and ventilation inversions, which fill other working areas with smoke toxic to workers, and which can come up upon rescue teams from behind. Due to the progressive heating of the surrounding rocks, which will slow down heat transfer, these dangerous conditions change over time. At the Lorraine Basin Coal Mines, programs have been set up and employed for the computer simulation of these phenomena over time. They serve to anticipate or to understand such phenomena, the input data being the characteristic parameters of the mine ventilation network, the operating curve of the main fans, and measurements or estimates of some temperatures. Two programs, employed together, have been developed for these studies: One program, called RESO, calculates the distribution of flow rates and pressures throughout the entire network; The other, called FEUMIN, determines smoke temperatures over their entire path.

Jan 1, 1980

By W. J. Deutsch, W. J. Martin, R. J. Serne

At the termination of mining, the quality of ground water in the ore-zone aquifer must be returned to a condition predetermined by the permitting agency. To immobilize the redox-sensitive elements (e.g., uranium, arsenic, selenium, molybdenum), it has been suggested that a reducing agent be circulated through the leached ore zone. We have conducted laboratory experiments to test the ability of sodium sulfide as such a reducing agent. Sodium sulfide lowered the redox potential of the effluent such that insoluble minerals containing the redox-sensitive elements should be stable. The uranium concentration of the solution decreased by more than three orders of magnitude. In column experiments, by the time 10 pore volumes of the sulfide solution had flowed through, sulfide minerals were forming. The experimental results indicate that the addition of sodium sulfide should cause chemical reduction of the leached sediments, thereby producing long-term stability of the ground-water/sediment system.

Jan 1, 1988

By Gordon F. Revey, Dan Harrison

Hanging Lake Joint Venture recently excavated two conventional 12.8 m (42 foot) diameter highway tunnels in the difficult ground conditions of Glenwood Canyon, Colorado. This paper outlines the type and success of the various Controlled Blasting Techniques that were used to minimize overbreak in the portal and tunnel excavations. The different Smoothwall and Cushion Charge loads used in the different ground types are described in detail. Delay Timing and Drilling Pattern variations are also discussed.

Jan 1, 1991

By Steve Kral

The domestic mining industry may be in the doldrums but there appears to be hope, at least from a regulatory standpoint. At least one US senator believes that the events of Sept. 11, 2001 made many citizens see the need for the country to become more self-reliant on its growing energy needs. Even before that tragic day, however, the Bush administration was making a strong push to open up more public land for energy and natural resource development.

Jan 1, 2002

By D. Duvris

The main objective of this work was to quantitatively investigate exhaust emission levels relative to maintenance (service) intervals during the operation of diesel-powered equipment at an underground bauxite mine in Greece. Such emissions depend on a great number of parameters, including the type of engine (technology) and its tuning, the type of work performed (as related to the engine workload), the suggested maintenance intervals, the altitude, the temperature and humidity of the atmosphere in the underground mine, the properties of the fuel and the operator's training and experience levels. The necessary ventilation quantities were calculated based on exhaust gas-concentration measurements and site-specific relationships between pollutants and adjusted air-quality indices. Diagrams comparing the necessary and recommended airflow for several equipment groups, featuring two engine types and different maintenance intervals, are presented.

Jan 1, 2000

By Morgan M. Sears, Gamal Rashed, Michael M. Murphy, Brent Slaker

In this study, a parametric study was conducted using FLAC3D numerical models to examine the impact of oblique loading, generated from seam dip, on the strength and the failure propagation pattern of a stone pillar using two simplified geometry types. In type 1, the sidewalls of the pillars were assumed to be perpendicular to the roof and the floor, while in type 2, the sidewalls of pillars were assumed to be vertical. The complex pillar geometry in dipping mines was frequently modeled using these two geometries. To capture a complete picture of the effect of seam dip on pillar stability, the modeled width-to-height (W/H) ratio of the pillars, in situ stress field, and pillars roof/floor interfaces were systematically varied to account for the potential distribution of values for these parameters across the underground stone mines in USA. Results from the numerical modeling indicate that dipping pillars have reduced strength compared with horizontal pillars. Also, an asymmetric failure propagation pattern could be obtained depending on an interaction between the W/H ratio, seam dip, in situ stresses, and pillar geometry.

Feb 5, 2021

By William E. Foreman

The results of the electrokinetic study of the activation of quartz by divalent cations showed that the charge reversal was related to the point at which the cation hydrolyzed. The reversal was not due to the presence of solid hydroxide at the surface of the quartz but due to the charged ions in the solutions. The charge reversal for beryllium at a log molar concentration of 1x10-4 was observed at pH 5 and 9. The quartz was positively charged between a pH reading of 5 to 10. Magnesium at the same log molar concentration did not show a charge reversal from pH 2 to 12. The probable cause of the charge reversal was due to the ionized Be3 (OH)3+3 or Mg (OH)+ . Variations in the electrokinetics of quartz were minimized by heating the sample to 300° C.

Jan 1, 1968

By G. Belardi, G. Marruzzo, P. Plescia

This paper presents the results of grinding tests performed on magnetite from Kiruna (Sweden) and on chromite from Skoumtza (Macedonia. Greece). Stresses were measured by XRD, which determined the variations in the characteristic structural spacings of the minerals both before and after, grinding in a HSM/250 Herzog laboratory ring mill. Anal Isis of the magnetite and c hromite crystallinstallin was performed hi measuring the broadening of the strongest diffraction peak (311). .Also, structural analysis on chromite was carried out using the Mikheev model. Ultrafine-grinding tests on the magnetite and chomite demonstrated that this type of treatment can induce profound variations m the surface-stress state. These included plastic variations of the cell followed by "chemical" stress with oxidation front the stricture to form hydroxide or carbonate, films. This can have a great influence on the mineral reactivity to flotation reagents

Jan 1, 1996

By E. R. Reeves

The mining industry has recognized the importance of engineering controls as a primary means of preventing hearing loss. The noise control treatments most commonly observed on drills and bolters during this study were windshields, sound absorbing material, and hydraulic motor covers. These controls were evaluated on machines at underground metal mines to determine the amount of noise reduction achieved by each control. The results indicate that absorbing material has very little effect on the noise level. The noise reduction attributable to the motor covers was dependent on the material used to create the cover. Properly installed windshields were the most consistent control.

Jan 1, 2004

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

Flotation tests were carried out on six coal samples of different rank as well as their oxidized samples. A mixture of diesel oil and alcohols was used in these tests. Surface oxidation caused a distinct decrease during flotation recovery with some improvement in the grade. The reduction in the recovery increased with increasing concentration of the oxidizing agent. The floatability of low rank coals was affected by oxidation to a higher degree than the floatability of medium and high rank coals. The recovery-size curves of oxidized samples were similar in shape to the recovery-size curves of non-oxidized coals.

Jan 1, 1991

By Scott Brien, O&apos

Cyclones have become standard unit operations in mineral processing for both dewatering mineral slurries and for making separations at given particle sizes. Conventional cyclones are normally able to make moderately sharp cuts. However, the limited ability to control water flow out of the apex means that cyclones have difficulty handling fluctuations in feed. Underflow-regulated cyclones are cyclones with a rubber boot attached to the underflow. This boot acts as a non-return valve and restricts flow out of the apex of a cyclone. Normally, this type of restriction on a cyclone causes severe difficulties in cyclone operation. However, by adding a siphon arm to the overflow, water flow can be controlled. The siphon arm creates a vacuum that reduces or eliminates the air core, permitting better control of the ratio of water flow out of the overflow and underflow. A Linatex-developed underflow-regulated cyclone was compared to a conventional cyclone for its ability to dewater a sand slurry. The underflow-regulated cyclone produced slurries with solids contents as high as 80% in the underflow. Conventional cyclones produced lower solids content in the underflow under similar conditions.

Jan 1, 1997