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By Larry A. Haas

The U.S. Bureau of Mines is investigating ways of enhancing the high-temperature softening-melting (HTSM) properties of domestic taconite pellets. These properties, which are important for determining the performance of pellets in blast furnaces, include pellet bed contraction, pressure drop, S-value (area under the pressure-temperature curve), and softening and metal-slag drainout temperatures. Experiments showed that HTSM properties were related to the physiochemical properties (fired strengths and reducibilities) of pellets containing different levels of limestone and dolomite flux. Flux additions resulted in slightly lower green and fired pellet strengths, but improved metallurgical properties, such as reducibility. The influence of reduction conditions on HTSM properties was evaluated by varying the pellet metallization starting temperature and the carbon monoxide content of the CO-N2 gas mixture. HTSM property change was more sensitive to flux addition levels when metallization was initiated at 1,100° C with 20 pct CO in the gas stream. The S-value and the metal-slag drainout temperature were found to be the best criteria for characterizing HTSM properties. The optimum flux addition level was about 8 pct (4 pct dolomite, 4 pct limestone) or a basicity of about 1. At higher flux levels, a higher metal-slag drainout temperature was obtained.

Jan 1, 2010

By Phillip W. Holland

The U.S. Bureau of Mines has developed a mass spectrometer method for determining helium in the parts-per-million to 10% range to an accuracy of ± 1%. The method employs a mass spectrometer, an inlet system utilizing a chromatographic gas-sampling valve, and an activated coconut charcoal trap cooled with liquid nitrogen. Gravimetrically prepared standards of helium in nitrogen were used to demonstrate the linearity of the method over the concentration range of 10 ppm to 10.66% helium.

Jan 1, 2010

By D. R. Tesarik

As part of its research program to investigate ways of improving resource recovery and reducing subsidence, researchers from the U.S. Bureau of Mines placed instruments in the B-North ore body of the Cannon Mine, Wenatchee, WA, to monitor cemented backfill and rock deformation during mining. The vibrating-wire gauges proved to be reliable and versatile, and approximately half of the instruments are providing data after 2 years of use. A two-dimensional, finite-element model was used to analyze the Cannon Mine's multilevel bench cut-and-fill mining method and predict rock and backfill displacements. The model accurately predicted rock displacements, but the predicted and measured displacements in cemented backfill had a correlation coefficient near zero, indicating that the model should only be used to predict rock displacements and not backfill displacements. A finite-difference model was also used to evaluate the stability of a cemented backfill pillar. Results can be used to conservatively predict backfill stresses, but on-site observation of pillar failures coupled with in situ measurements are needed to make more accurate predictions. An ongoing evaluation of the mining system has indicated that filling the primary stopes tight to the back with cemented backfill allowed these pillars to carry overburden loads soon after the cemented backfill was placed.

Jan 1, 2010

By W. P. Stroud

In this U.S. Bureau of Mines report, the conditions required for the direct reconstruction of a tomogram from observed line integrals are examined. Because of the limited access to the working faces in coal mines, the special case of access to only two opposite faces is emphasized. Classical matrix methods were used for small dimensional (2 by 2, 3 by 3, and 4 by 4) applications to determine the limitations and the requirements for a solution. The results for large (n by n) grids were then inferred and generalized from those of the smaller grids and matrices. Limited access tomography is found to be appropriate for in-seam hazard detection from seismic and microwave data, but it is shown that additional data must be added to obtain a direct solution.

Jan 1, 2010

By Robert J. Timko

In early June 1986, an underground fire of unknown origin erupted in one of several entries of a coal mine located in southwestern Colorado. For a time, mine personnel aggressively fought the fire. However, control of the fire was later lost. To prevent further damage and reduce the possibility of an explosion, all portals and shafts to the mine were sealed. The mine operator requested the U.S. Bureau of Mines' assistance in obtaining and analyzing mine fire gases taken from sampling ports placed through the mine seals, as well as down boreholes drilled after the fire. This report recounts activities within the first 2 years of the mine being sealed. It includes a description of gases analyzed and mine atmosphere status equations generated from the analyzed gases. The gases were analyzed by chromatography and included standard atmospheric gases as well as higher hydrocarbons that are found in postfire atmospheres. Nine equations were used to evaluate what was occurring within the sealed mine. Following a description of the rationale behind each equation, the 2-year trend is briefly analyzed.

Jan 1, 2010

By Louis E. Dalverny

U.S. Bureau of Mines research to develop diagnostic methods to locate and evaluate fires in abandoned mines and waste banks and techniques to extinguish such fires was applied to an abandoned 60-acre underground bituminous coal mine (Renton, Allegheny County, PA) to locate and extinguish three separated fire zones. Mine fire diagnostics interpret changes from baseline values in subsurface pressures, temperatures, and mine gas composition under imposed pressure gradients induced by a borehole exhaust fan. The effective gas sampling area surrounding each borehole is greatly enlarged. Sampling iterations, using a "communicating" boreholes set, provide "fire signature" information for locating both heated and cold areas. Time-dependent monitoring differentiates heating and cooling periods resulting from combustion front movement and/or fire extinguishment activities. A water injection with fume exhaustion extinguishment effort involved injecting water through boreholes to quench the heated zones while exhaust fans actively removed heated gases from the mine. The technique was ineffective as implemented, primarily because of inadequate spreading of water from the injection points. The Bureau's diagnostic method determined the fire locations and the effectiveness of the water injection with fume exhaustion extinguishment technique.

Jan 1, 2010

By R. A. Cortese

The U.S. Bureau of Mines has developed a flame-radiation-powered trigger device to explosively activate suppression barriers to quench gas and coal dust explosions. The major component of the device is a silicon solar panel, which converts radiation from the developing explosion into electrical energy to initiate an electric detonator, which releases an extinguishing agent into the advancing flame front. Solar panels that are rated to produce 20 W of electrical power when exposed to the sunlight are producing about 200 W when exposed to a full-scale dust explosion. The solar panel is electrically isolated from the detonator by a pressure-sensitive switch until the arrival of the precursor pressure pulse, which always precedes a deflagration. This combination of pressure arming and flame-powered photogenerator prevents false barrier activation and requires no external power supply.

Jan 1, 2010

By Dennis R. Dolinar

The danger to personnel, equipment, and pillar structure created by the spalling of a coal rib can be minimized by installing rib bolts. To assure that a configured support system will maintain a coal rib, the U.S. Bureau of Mines developed a rib bolt system based on a nonpreventable failure concept. A statistical equation quantitatively relates the amount of rib retained to the bolt spacing and the width of the spalled material. Laboratory test results show that the equation accurately predicts the amount of material retained and confirm the validity of the support concept. The examination of rib bolting at a coal mine experiencing rib sloughage provides evidence that the effectiveness of the support can be related to the failure pattern of the spalled material. An analysis of roof and roof support reaction to rib sloughage at the mine indicated that the rib sloughage had little effect on roof stability. Although supporting ribs might not affect roof stability, laboratory test results indicate that the material retained by the support can sustain a load up to 20 pct of the intact compressive strength of the material.

Jan 1, 2010

By Maria I. De Rosa

The U.S. Bureau of Mines performed experiments to determine the hydrogen cyanide (HCN) concentrations and smoke particle characteristics during the combustion of flexible polyurethane foams and other nitrogen-containing materials, for the development of a test parameter. The experiments were conducted in an approximately 2O-L furnace at set furnace temperatures of 250° and 1,000° C for a 14-min duration, with an airflow through the furnace of 10 L/min. The variables studied as a function of time were the gaseous and aerosol HCN concentrations, the smoke particles average diameter (dg) and particle concentration (no), and the product of the smoke particle diameter and concentration (dgno). Carbon monoxide, carbon dioxide, and oxygen concentrations, sample mass weight loss, and furnace temperatures were also studied; analyses of nitrogen and cyanate content of the material were carried out. Results show that dgno correlates directly with the HCN concentrations, which depend on the nitrogen and cyanate contents of the material.

Jan 1, 2010

By G. T. Fisher

The U.S. Bureau of Mines conducted research on calcium ferrite slags to determine the distribution of Pb and minor elements (Ag, Cd, Zn, and Co) between Pb bullion and slag. These fundamental data are required to evaluate nonferrous smelting with calcium ferrite slags as a substitute for conventional iron silicate slags. Determinations were made in 25-cm3-capacity MgO crucibles at 1,250° C for 2 h in a CO-CO2 atmosphere with an O2 potential that would retard the formation of magnetite. Calcium ferrite slag composition variables studied were from 16 to 32 wt pct CaO in 2-pct increments and Si02 ranging from 1 to 5 wt pct in 1-pct increments with equal additions of MgO. For all compositions studied, the retention of Pb in the calcium ferrite slag was less than 1 wt pct, which compares favorably to about 6 wt pct Pb in conventional iron silicate slags used in smelting of Pb concentrates. Minor element distribution was insensitive to changes in slag composition in the range studied. However, slag composition had significant impact on the melting and fluidity of the slag.

Jan 1, 2010

By D. L. Yopps

In research conducted by the U.S. Bureau of Mines, platinum-group metal (PGM) flotation concentrate from the Stillwater Complex, MT, was subjected to biooxidation using Thiobacillus ferrooxidans in an effort to break down the sulfide minerals and liberate the associated PGM's for subsequent chemical leaching. Bacterial preleaching oxidized up to 94 pct of the sulfide present, destroyed the PGM-bearing pentlandite [(Ni,Fe)9S8] mineralization, and dissolved most of the nickel in the concentrate. Cyanidation at 80° C proved to be the most attractive chemical leachant, removing 34 pct of the platinum, 76 pct of the palladium, 94 pct of the rhodium, and 97 pct of the gold from the biooxidized concentrate. Research also indicated that increased sulfide oxidation during the preleach phase led to improved PGM recovery in the subsequent chemical leaching phase.

Jan 1, 2010

By P. Comba

The U.S. Bureau of Mines investigated a hydrochloric (HC1)-calcium fluoride (CaF2) leaching procedure to treat domestic manganese (Mn)-bearing silicate resources. The proposed process is an alternative to high-temperature and energy-intensive extractive techniques. Single-stage leaching with a stoichiometric amount of HCl and a F-Mn mole ratio of 0.2 extracted 96 pct of the Mn when the leach conditions were 50° C, 3 h, and 35 pct solids. Ninety-eight percent of the Mn was extracted during countercurrent leaching at similar conditions. A process flowsheet was developed that incorporated HC1-Cab leaching, excess leach acid utilization, fluoride (F) recycle, and Mn recovery. When the domestic manganese silicate ore was processed, 98 pct of the Mn was extracted, 99 pct of the Cab was reclaimed, and a leach residue was produced that passed the Environmental Protection Agency (EPA) Extraction Procedure (EP) Test for nonhazardous waste.

Jan 1, 2010

Laboratory tests were conducted by the U.S. Bureau of Mines to determine respirable dust reduction effectiveness of and interaction between face airflow and water sprays for a continuous miner. Increases in exhausting face ventilation from 3,000 to 9,000 cfm, in waterflow from 15 to 35 gpm, and in water nozzle operating pressure from 80 to 200 psi were evaluated. Results indicated that airflow had the greatest individual impact on reducing dust levels, with concentrations at return and operator sampling locations reduced by as much as 57% and 99%, respectively. Regression modeling was utilized to predict dust concentrations over the range of values tested for the control parameters. Interactions between the control parameters were significant and often defined an optimum level where further increases in that parameter failed to produce additional dust reductions. Increasing airflow to 8,400 cfm, waterflow to 25 gpm, and water pressure to 140 psi typically reduced dust concentrations at operator and return locations. Application of a control parameter above these levels can provide additional dust reductions if used in conjunction with appropriate levels of the other two control parameters. Otherwise, higher operator dust levels may result and can be attributed to increased rollback and/or airflow turbulence.

Jan 1, 2010

By P. D. Kovscek

The performance of a novel prototype kerf-cutting impact mining machine was evaluated under a cooperative agreement between the U.S. Bureau of Mines and RAMEX Systems, Bellevue, WA, while operating under conditions typical of normal tunnel entry development. Selected operating parameters were monitored concurrently to determine baseline operating conditions and to study relationships between operating parameters. Using the data obtained, the specific energy requirements of the impact mining machine were calculated and compared to specific energy requirements of tunnel boring machines cutting in rock having similar hardness. Tests results indicate that the kerf-cutting impact mining machine can provide a mechanical means for mining very hard rock that cannot be effectively mined using commercially available mechanical excavators.

Jan 1, 2010

By K. E. Hjelmstad

During an underground mine fire, air can be rapidly depleted of oxygen and contaminated with smoke and toxic fire gases. Any delay in warning miners could have disastrous consequences. Unfortunately, present mine fire alarm systems, such as stench, audible or visual alarms, telephones, and messengers, are often slow, unreliable, and limited in mine area coverage. Recent research by the U.S. Bureau of Mines has demonstrated that ultra low frequency electromagnetic signaling can be used for an underground mine fire alarm. In field tests of prototype equipment at five mines, electromagnetic signals from 630 to 2,000 Hz were transmitted through mine rock for distances as great as 1,645 m to an intrinsically safe receiver. The prototype system uses off-the-shelf components and state-of-the-art technology to insure high reliability and low cost. When utilized, this. technology would enable simultaneous and instantaneous warning of all underground personnel, regardless of their location or work activity, thereby increasing the likelihood of their successfully escaping a mine disaster. This report presents the theoretical basis for through-the-rock ultra low frequency electromagnetic transmission, design of the prototype transmitter and receiver, and the results of in-mine tests of the prototype system.

Jan 1, 2010

By John C. Edwards

To increase the capability to predict the effectiveness of a flame arrester in the cooling of hot combustion gases expelled through a flame arrester, the U.S. Bureau of Mines developed an equilibrium. model and one-and three-dimensional transient thermal models of a flame arrester, which were used to predict the temperature evolution within the arrester and the maximum temperature at the external surface of the arrester. The models account for convective and conductive heat transport within the arrester and radiative losses at the exit surface. The gas flow through the arrester is established from an empirically derived relationship between the gas velocity and the pressure gradient across the arrester. Lateral heat loss from the arrester to the enclosure wall is accounted for in the three-dimensional model. The model calculations for maximum outside surface temperature of the arrester showed an approximate agreement with measured values for vent-area-to-enclosure-volume ratios between 12 and 28 in2?ft-3.

Jan 1, 2010

By Jennifer Riefenberg

The U.S. Bureau of Mines has long recognized the hazards associated with rock burst activity in underground mines. Concern over lost lives and resources prompted this study to further characterize rock burst occurrence as related to microseismicity and mining. A period of over 1,079 days of mining with 101 bursts, where microseismicity rates and blasting were recorded, was used in this study. Statistical analyses investigated relationships between (1) rock burst occurrence versus blasting, (2) rock burst size versus damage, (3) rock burst occurrence versus average micro seismicity rates, and (4) rock burst occurrence versus local mine geometry. Statistical analyses showed that 91% of all rock bursts occur with blasting while only 3% of all rock bursts occur, apparently, independent of blasting. Additionally, the long-term average daily micro seismicity rates appear to dictate when blasting will trigger rock bursts. Time series analysis on the daily microseismicity resulted in model equations that may be used to forecast the daily microseismic activity.

Jan 1, 2010

By Charles P. Lazzara, Charles D. Litton, Frank J. Perzak

This U.S. Bureau of Mines report details the results of a series of large-scale experiments where small coal fires were used to ignite the conveyor belt at air velocities ranging from 0.76 to 6.1 m/s. In the tests, electrical strip heaters imbedded within a pile of coal were used to heat the coal to a point of flaming ignition. The flaming coal subsequently ignited the conveyor belt located approximately 5 to 10 cm above the coal pile. During the tests, temperature, CO, and smoke levels were continuously measured in order to determine both alarm time and level as the fire intensity progressed through the stages of smoldering coal, flaming coal, and flaming coal plus flaming belt. Analysis of the data leads to certain conditions of air velocity and sensor alarm levels that are required for early detection of conveyor belt entry fires. Two nomographs are presented, which define sensor alarm levels and sensor spacings as a function of belt entry cross-sectional area and belt entry air velocity.

Jan 1, 1991

By Charles D. Litton

This U.S. Bureau of Mines report details the results of a series of large-scale experiments where small coal fires were used to ignite the conveyor belt at air velocities ranging from 0.76 to 6.1 m/s. In the tests, electrical strip heaters imbedded within a pile of coal were used to heat the coal to a point of flaming ignition. The flaming coal subsequently ignited the conveyor belt located approximately 5 to 10 cm above the coal pile. During the tests, temperature, CO, and smoke levels were continuously measured in order to determine both alarm time and level as the fire intensity progressed through the stages of smoldering coal, flaming coal, and flaming coal plus flaming belt. Analysis of the data leads to certain conditions of air velocity and sensor alarm levels that are required for early detection of conveyor belt entry fires. Two nomographs are presented, which define sensor alarm levels and sensor spacings as a function of belt entry cross-sectional area and belt entry air velocity.

Jan 1, 2010

By S. P. Sandoval

Previous research by the U.S. Bureau of Mines demonstrated that nonionic surfactants increased the leaching rate of copper in the flask leaching of chalcopyrite with ferric sulfate if sufficient ferric sulfate was present. This research was continued by the Bureau in Part 2 to further explore the application of nonionic surfactants to the dump leaching of chalcopyrite. A polyoxyethylene lauryl ether was selected as the superior nonionic surfactant tested at 25° and 50° C. The addition of the surfactant increased copper leaching by 116 pct at 25° C and 1.0 pct solids and by 61 pct at 50° C and 0.5 pct solids at Fe 3+ concentrations greater than 1 g/L. At 0.1.0 g/L Fe 3+ and below, the addition of the surfactant produced as much as a 35 pct decrease in leaching. Each of the nonionic surfactants studied was found to be heavily adsorbed by a typical chalcopyrite ore, which poses a serious barrier to the application of nonionic surfactants in an actual chalcopyrite dump.

Jan 1, 2010