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By John J. Sammarco

Light-emitting diodes (LEDs) are emerging as viable replacements for incandescent (INC)-based cap lamps used in mining. The photometric and energy characteristics of these light sources differ in important ways. This paper describes the performance of LED and INC sources in cap lamps in terms of correlated color temperature, color rendering, light output, electric power, ambient temperature and air flow, and light source aging. Importantly, these characteristics can influence a miner?s ability to spot mining hazards thus impacting safety. Second, some of these characteristics interact with the operating life of the cap lamp?s battery power, such that differences between LED and INC sources can be magnified toward the end of a 10-h battery discharge cycle. Empirically, we have determined that after 8 h at an ambient temperature of 25 ?C, the average light output of an INC cap lamp can decrease to about 69% of its initial value when powered by a lead-acid battery, and it can decrease to about 65% of its initial value when powered by a nickel-hydride battery. An LED-based cap lamp using a constant current drive circuit can maintain about 96% of its initial value when powered by a nickel-hydride battery. Real-world tests addressing the effects of ambient temperature and air flow on the light output of an LED and INC cap lamp were conducted in the National Institute for Occupational Safety and Health Safety Research Coal Mine. The LED cap lamp yielded a vertical average illuminance improve­ment of approximately 9.5%, and the INC cap lamp yielded a vertical average illuminance degradation of approximately 4%. The differences between LED and INC cap lamps were further quantified by the calculation of ?mesopic luminance? data that indicated for the same photopic luminance (i.e., as measured using a conventional light meter) the LED cap lamp could be up to 38% more efficient than the INC cap lamp with a lead-acid battery at the end of the 10-h driving cycle. Lastly, accelerated life tests were used to empirically determine light output depreciation as the INC light source age approached its useful life. There was about a 35% decrease in light output. This is quite considerable, particularly given that the light output will decrease an additional 30% to 45% over the period of a 10-h shift. The implications of the differences between LED and INC sources are discussed. This information is crucial in determining how visual performance could be affected for real-world conditions where batteries discharge during the work shift and as the light source ages. To date, only idealized conditions have been used for LED and INC cap lamp visual performance research.

Jan 1, 2009

By Jing Zhan

The fibrous precursor can be obtained by coordination precipitation process, using oxalate, cobalt chloride and ammonia. The composition and morphology of fibrous precursor were characterized by XRD, IR, DTA/TGA and SEM analysis. The results show that XRD pattern and composition of the precursor with fibrous morphology precipitated at pH=9.0 were different from that of ß-CoC2O4?2H2O precipitated at pH=1.0. The mechanism on the thermal decomposition of fibrous precursor was addressed. The influences of various conditions in pyrolysis, including the temperature, time, atmosphere, and the morphology of the precursor, on the morphology, average size and specific surface area of the Co powders were investigated in detailed. At last, the final product, fibrous cobalt powders with diameter about 0.3~0.5µm in size and 40~60 in aspect ratio, were produced by thermal decomposition at 400~500? in the weak reducing atmosphere. The structure of pores in cobalt powders was capillary tube with open ports and the majority was mesoporous.

Jan 1, 2009

By Hebi Yin

A coupled cellular automaton (CA) - finite element (FE) model was developed to calculate the growth of dendrites during the solidification of cubic and hexagonal metals. The model solves the conservation equations of mass, energy and solutes in order to calculate the temperature field, solute concentration and the growth morphology of dendrites, including the grain structure and the dendritic microstructure. Validation of the model was performed by comparing the simulation results with calculation results from previously published works, showing qualitatively good agreement in the dendritic morphology. Application to magnesium alloy AZ91 illustrates the difficulty of modeling dendrite growth in hexagonal systems, observed as deviations in growth direction caused by mesh-induced anisotropy. The model was applied to the simulation of small specimens with single- and multiple- equiaxed grain growths and columnar grain growth in directional solidification. The influence of cooling rate and some kinetics parameters on the grain morphology are also discussed.

Jan 1, 2009

By Hua-qing Li

Electromagnetic stirring process effectively improves the casting quality of metals. In this paper, the physical simulation experiment, in which the molten copper is displaced by mercury, was designed. The factory test parameters were determined according the simulated data. The flow behavior of the mercury to be stirred as well as the relations between the microstructure of plate blanks and the current parameters were analyzed. With an appropriate electromagnetic stirring, the inverse segregation of tin for C51900 alloy plant blank reduces from 15 % ~ 30 % to about 5 %, and the proportion of equiaxed grain rises to larger than 30%.

Jan 1, 2009

By Xie Hao

According to its raw materials orthogonal test scheme is designed and a large number of systemic experiments were carried out in order to study the sintering characteristics of three types of fine ores in Kunming Iron&Steel Co.Ltd(KISC). The effects of carbon mixture ratio and basicity on sintering time, agglomeration ratio, physical properties and utilize coefficient were researched via single factor analysis and range analysis. The experimental results show the best mixture ratio of each fine ore. Analysis found that the influence of the carbon mixture ratio is more significant than which of the basicity on the sintering process except agglomeration ratio of foreign ore.

Jan 1, 2009

By Zhang Qin

Dolomite is main impurity mineral in phosphate ores. In practice of phosphate ores production, the grade of concentrates is only containing P2O5 31-32%.In this study, even the increasing of floatation reagent consumption and decreasing of floatation recovery, economic performance is estimated high according to the decreasing of H2SO4 consumption in subsequent production of phosphate fertilizer and the increasing of products value. In floatation stage, influence factor include the synergism impacts of floatation collector, the stages, time, concentration of ore pulp, which were discussed respectively in this paper. Raw material is characterized by mineralogy, chemical analysis, the grain size analysis and milling test . The results show that the grade of concentration can reach to P2O5 36% by deeply de-magnesium oxide from phosphate ores by floatation , which yield a high added value.

Jan 1, 2009

By De-wen He

The distribution of persistent organic pollutants in the environment is studied using the multimedia environmental fugacity model, and environmental health risk assessment of POPs nearby a copper smelt enterprise is carried out. The result indicates that all are in an agreeable risk level without exception. The annual individual chronic risk index of HCB is 7.50×10-11. The annual individual risk index of 3,3',4,4'-TCB is 1.57×10-9, and the annual individual risk index of 2,3,7,8-TCDD is 6.57×10-9.

Jan 1, 2009

By H Benzer, N A. Aydogan

It is well known that the high pressure grinding rolls (HPGR) can only be operated efficiently under choke feeding conditions in which a material bed is built up between the rollers to ensure interparticle breakage. By increasing the fines amount in the material bed up to a specific level with the recycling load, a uniform material bed is created and higher pressure gradient along the roller width is obtained which results in compact flakes including more fines. Extensive test work has been carried out with an industrial HPGR unit grinding cement clinker in a cement plant in Turkey. During the test work the recycling load of the circuit was changed to achieve different ratios to the fresh feed rate in order to identify the effect of the recycling load on the circuit performance. Six different tests were performed with the circuit at steady state. For each test, samples were collected from HPGR fresh feed and discharge, and total feed, then the particle size distributions of the samples were determined and mass balances around the circuit were calculated. The conclusion was that the reduction ratio of the HPGR increased with increase in recycling load. The flake densities showed the same trend with more compacted flakes being produced for higher recycling loads.

Jan 1, 2009

Jan 1, 2009

By J. Doucet, C. Price

In an industrial setting, operational changes are continually introduced, driven by new technologies or changing economics. Because of day-to-day variability, quantifying the impact of these changes based on metallurgical performance requires long trial periods to achieve statistically significant results. Tools and techniques developed by the mineral processing group at McGill University have allowed for direct measurement of process variables (e.g., bubble size, gas and solid holdup). Two case studies are described where direct measurement techniques were used to evaluate: a) a new rotor stator mechanism; and b ), the introduction of a new frother type. Application of these methods has accelerated the evaluation of process changes and improved confidence in results.

Jan 1, 2009

By L. Patts, J. Rohrbaugh

The Mine Safety and Health Administration (MSHA) has received several reports of filters igniting when high-temperature disposable filters were used on non-cooled diesel exhaust systems in underground coal mines. Based on laboratory testing (to determine the ignition temperature of these filters, which were loaded in the field with diesel particulate matter, or DPM), MSHA determined a maximum safe operating temperature for high-temperature disposable filters. When the results of the laboratory filter ignition testing were reported to the Coal Diesel Partnership (comprised of members of the Coal Industry, Labor, NIOSH and MSHA) the Partnership charged NIOSH with investigating the safe use of high-temperature disposable filters. This paper reports on the design, fabrication and testing of a unique exhaust gas cooling device and the ability of this device to successfully lower filter inlet temperatures and thus reduce the potential for fires.

Jan 1, 2009

By B. Samanta, S. Bandopadhyay

Ore grade modeling of a placer gold deposit is considered a challenging problem even today. Typically, gold-bearing deposits show extremely erratic and unpredictable grade variation. This is principally because of isolated occurrences of gold metal within a few high-grade pockets. Because of sporadic fluctuation of high-gold-grade distribution, the overall spatial continuity of the deposit becomes poor. This type of variation is often described by a lognormal or highly skewed frequency distribution, and the spatial continuity of the deposit is characteristically represented by a variogram model that exhibits a high nugget component. Further complicating the matter is the sparse availability of drillholes to capture such erratic variation. Due to the prohibitive cost of drilling, gold grade and reserve estimations are typically carried out using insufficient exploratory data. Use of a traditional estimation technique on limited data often produces an unreliable ore grade model. Kriging and its nonlinear variation, lognormal kriging, are frequently used in gold deposit modeling (Rendu, 1979; Journel, 1980); however, kriging is flawed by the smoothing effect. Moreover, though kriging is known to be globally unbiased, it is not free from conditional bias. As a result, if a deposit is modeled using the traditional kriging technique, a high-grade zone can be predicted to be a low-grade zone and vice versa. Predicting high grade as low grade results in a missed opportunity to exploit profitable ore. On the other hand, prediction of low-grade ore as high-grade ore might result in financial loss for a mining operation. Thus, the use of kriging for ore grade mapping of a gold deposit may not be recommended. Estimation techniques (including kriging) can produce an estimate with minimum error in a minimum-error variance sense. However, no matter which estimation technique is used for grade modeling of a highly erratic deposit like gold, the error margin is bound to be high. Therefore, any grade prediction made for an unknown location is associated with high uncertainty. Since various mine-planning operations, including derivation of grade tonnage curve, pit design and economic analysis of the deposit, are based on estimated grade rather than true grade, a mining project evaluation that depends upon estimation will be subject to considerable risk. Thus, the successful design of a mining project not only depends upon accurate grade estimates, but also upon accurate assessment of uncertainty, for predictive grade is equally important. Although the kriging standard deviation is used as an indicator of uncertainty for prediction, it is flawed by characteristics related to a data-independence property. This study, therefore, investigates the stochastic simulation technique of conditional simulation for ore grade modeling of a placer gold deposit at Nome, Alaska. It is expected that the research will provide a better solution to ore-grade deposit modeling than the kriging technique because (1) conditional simulation preserves spatial continuity as well as reproduces the data histogram, thus avoiding the smoothing problem; and (2) generation of multiple realizations helps to accurately quantify the uncertainty about grade values in the deposit.

Jan 1, 2009

By M. R. Hieb, J. R. Britt, S. P. Harteis, M. J. Sapko, E. S. Weiss, R. K. Zipf

The design requirements for mine ventilation seals have undergone a radical transformation in recent years, and these revisions have greatly increased the cost of the seal designs and their construction. For example, in the past two years, new federal regulations have increased the minimum design requirement to withstand explosion pressures from 138 kPa (20 psig) to 345 kPa (50 psig) or 827 kPa (120 psig), depending on whether the sealed mine volume is monitored continuously or not. Moreover, there is still a possibility that under certain conditions (such as detonations), even higher pressure requirements may be necessary. The ability of a monolithic, stand-alone mine seal to reliably withstand the full range of possible explosion pressures is becoming increasingly difficult and expensive. In an effort to develop a practical alternative, the West Virginia Office of Miners’ Health Safety and Training (WVOMHST) and the National Institute for Occupational Safety and Health (NIOSH) have collaborated in a research effort to develop a practical, economic and safe mine sealing technique that can enable mine seals to meet the full range of new explosion pressure design requirements. The basic idea is to use a barrier of common mine gob and rubble, in combination with a conventional mine seal, so that the pressure resulting from a gas explosion is reflected, absorbed and attenuated, and the pressure on the ventilation seal is reduced. This paper discusses some concepts and preliminary test results for a “passive mine blast attenuator” (PMBA) that can provide a useful alternative to increasingly larger and stronger stand-alone mine seals. Numerical models and full-scale experiments conducted at the NIOSH Lake Lynn Laboratory Experimental Mine (LLEM) show that the use of a PMBA can signficantly reduce the blast pressure and impulse on conventional ventilation seals.

Jan 1, 2009

By C. V. Deutsch, O. Babak

A longstanding problem in geostatistics is that kriging usually assigns significantly greater weights to end samples in strings of data than it does to central samples. These weights are theoretically valid, but suboptimal estimates may result when there are geological trends in the variable near contacts, that is, large weights may be applied to samples that are systematically lower or higher than average. A number of ad-hoc corrections exist, each with pros and cons; none are fully automatic with a well-defined measure of optimality. A new method for estimation in a finite domain is proposed. This method is referred to as finite domain kriging. The method is based on kriging with a successively larger number of data. The total number of relevant data (n) is established, and then n kriging matrices are solved. The first matrix has the closest single data value (n-1 weights are set to zero); the second has the two closest data (n-2 weights are set to zero) and so on. The final matrix has all n data. The kriging weights used for estimation are the average of the weights from the n successive kriging runs. Each kriging run is optimal, yet with different smoothing and a different treatment of data at the end of the strings. The result is a set of weights that does not give undue influence to data values at the end of strings. The methodology is developed with examples. Cross validation shows that finite domain kriging outperforms conventional kriging.

Jan 1, 2009

By L. E. Eary

Many of the major international gold mining companies provide data on rates of greenhouse gas (GHG) emissions as part of their environmental reporting commitments. These data are evaluated by an index defined as the annual GHG emission rate in metric tons, divided by the annual amount of gold produced in grams, and referred to as GHGgold. This paper examines ranges of GHGgold values for a cross section of gold mines as a function of mining method (openpit, underground and combined operation) and ore-processing method (mill, heap leach and combined methods) for reported ranges of operational data, including annual total tons mined, ore processed and gold grade. The evaluation shows that ranges and distributions of rates of GHG emission are approximately similar across different mining methods and ore-processing methods. The data presented in this paper provide the context needed to make comparisons of GHG emissions reported in companies’ annual reports to the ranges reported for the overall gold mining industry.

Jan 1, 2009

By J. Brune, P. J. Coleman, L. Martini

Research in the field of mining safety and health in the United States plays an important part in protecting the lives of miners. The National Institute for Occupational Safety and Health (NIOSH) Mining Program conducts surveillance, studies and developmental work aimed at improving the safety and health of miners. With recent reviews of the Mining Program by the National Academy of Sciences and the Mining Program response (NIOSH, 2008), the importance of setting goals, conducting high quality engineering and scientific research and evaluating the outputs, outcomes, relevance and impacts of these projects has been reemphasized. Surveillance of reported injuries is a first step in deciding on research directions and in designing specific projects. Groups of injuries often share features and attributes that suggest common causes and may respond to similar preventive efforts. Identifying groups of injuries also serves to prioritize intervention efforts. The Mine Safety and Health Administration (MSHA) Accident and Injury database (MSHA, 2008) provides individual case reports of mining injuries, illnesses and certain no-injury accidents (events such as roof falls that stop mine production or miners’ activities for more than one hour). This database is an indispensable resource for researchers and stakeholders needing information on the statistics of these events. From an epidemiological perspective, research projects target groups of miners at risk due to specific patterns of work, equipment, mine settings and the management of safety and health in their mines. Incidence rates are provided by the MSHA data for selected variables, such as surface/underground location, standard industrial classification and state. While incidence rates are the preferred measure for all variables, denominators are not typically available; for example, to more clearly understand the data about injury by occupational type, it would be necessary to conduct demographic surveys. A current survey of the demographics of the mining industry should be complete by 2010, which will allow incidence rates to be developed for a number of variables such as age, occupation and experience. This survey will provide the first update of its kind since the first survey was conducted in 1985. This report describes an alternative method of analyzing and presenting MSHA data for the purpose of identifying high-cost, high-severity injuries and illnesses. Researchers at the NIOSH Spokane Research Laboratory (SRL) developed programs to find the top five most frequent accident classes, natures of injury, types of accidents and other selected variables from the MSHA database. Studying these variables gives a cross-sectional snapshot of the most frequent groups of injuries within a commodity, regional group or time period, and allows researchers to quickly understand developing patterns for new research projects. The primary benefit of this approach is to

Jan 1, 2009

By A. G. Mayton, D. H. Ambrose, C. C. Jobes, N. K. Kittusamy

In a systematic study, the National Institute for Occupational Safety and Health (NIOSH) evaluated seat designs in low- and mid-seam shuttle cars during production operations at two underground coal mines in southern West Virginia. The purpose was to support, with additional data, earlier findings that NIOSH ergonomic seat designs (featuring viscoelastic foam padding and lower-back support) may help reduce health risks to operators of coal mine shuttle cars. Eight shuttle car operators evaluated seven seat designs (one already in use in each vehicle and five NIOSH designs) relative to perceived and measured whole-body vibration (WBV) exposure (including vehicle jarring/jolting) and discomfort. Operators’ perceptions using a visual analog scale (VAS) and questionnaire ratings were compared with International Standards Organization (ISO) 2631-1:1985 fatigue-decreased proficiency (FDP) limits and measured WBV levels on low- and mid-seam shuttle cars. Objective and subjective data results indicated that NIOSH seat designs (with added adjustability, lower-back support and improved seat padding) performed better to reduce vehicle jarring/jolting levels and that shuttle car operators favored them over existing seat designs. The NIOSH low- and mid-seam shuttle car seats showed 45 to 77 percent better performance in FDP and 9 to 60 percent better performance overall in operators’ ratings. Considering the VAS results for low- and mid-seam shuttle cars under no-load conditions, operators rated the level of jarring/jolting 18 to 89 percent lower with the NIOSH seats. Reductions in measured vehicle jarring/jolting were 19 to 46 percent for the three-directional vector sum accelerations relative to the existing seats on the low- and mid-seam shuttle cars. Questionnaire responses indicated that operators for both shuttle car models rated NIOSH seat designs as more comfortable overall. Vehicle operators most frequently suggested adding armrests to improve the seats on the mid-seam shuttle car. A suggested improvement for the low-seam shuttle car was to make the seat a better fit for the operator compartment, which would enhance clearance between the operator and vehicle controls and allow for better seat adjustment and operator visibility.

Jan 1, 2009

By Bradford F. Townsend, Marc R. Kritzer, Michael F. Roach, Dennis Ofiara

All Rights Reserved. Printed in the United States of America. Information contained in this work has been obtained by SME, Inc. from sources believed to be reliable. However, neither SME nor its authors guarantee the accuracy or completeness of any information published herein, and neither SME nor its authors shall be responsible for any errors, omissions, or damages arising out of use of this information. This work is published with the understanding that SME and its authors are supplying information but are not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Any statement or views presented here are those of the authors and are not necessarily those of SME. The mention of trade names for commercial products does not imply the approval or endorsement of SME.

Dec 1, 2008

By John A. Organiscak

Enclosed cabs are a primary means of reducing equipment operators? silica dust exposure at surface mines. The National Institute for Occupational Safety and Health experimentally investigated various factor effects on cab air filtration system performance. The factors investi­gated were intake filter efficiency, intake air leakage, intake filter loading (filter flow resistance), recirculation filter use, and wind effects on cab particulate penetration. Adding an intake pressurizer fan to the filtration system was also investigated. Results indicate that intake filter efficiency and recirculation filter use were the two most influential factors on cab penetration performance. Use of the recirculation filter reduced cab penetration by usually an order of magnitude over the intake air filter alone because of the multi­plicative filtration of the cab interior air. Intake air leakage and filter loading affected the cab penetration to a lesser extent, while wind had the least impact on cab penetration between the calm and 10-mph wind velocities tested. Adding an intake pressurizer fan notably increased intake airflow and cab pressure with only minor changes to cab penetration. A mathematical model was developed that describes cab penetration in terms of intake filter efficiency, intake air quantity, intake air leakage, recirculation filter efficiency, recirculation filter quantity, and wind penetration.

Nov 1, 2008

By Orlando Gallardo

El presente texto describe la implementación del software ADS (Sistema de Despliegue Activo) a los sistemas de control supervisor de los diferentes procesos del complejo metalúrgico a nivel administrativo -en tanto replica los archivos gráficos y de base de datos. Este servidor además de concentrar en su red de campo redundante data de controladores e instrumentos de campo, puede compartir información con clientes usuarios y clientes de visualización dentro de la planta. En ese sentido, el objetivo es simplificar la producción y uso de datos únicos y garantizar la fiabilidad de estos a tiempo real para todos los niveles de supervisión a nivel administrativo, al tiempo que se planea y optimiza los recursos con la toma de decisiones apropiada.

Sep 24, 2008