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By J. Nesset, F. Rosenblum, P. Spira

"Sulphide concentrates may exhibit self-heating to various degrees during storage or shipping, the worst cases presenting a serious hazard from fire and SO2 emission. Based on measurements of heating rates on a wide variety of concentrate samples in a special apparatus, combined with field experience, a methodology has been developed which allows concentrates to be rated for their heating potential. This has proven to be very useful in practice, for example, in deciding on the need to take preventive measures. Oxidation under ambient conditions in the presence of moisture initiates heating locally within a stockpile. In the case of highly active materials, such as those that contain abundant pyrrhotite, heating may progress through three stages to temperatures well above 5000C. However, most concentrates show little or no propensity to selfheat. Heating rates were used to estimate values of the heat output, or self-heating capacity (in joules per gram), which sustains the process at each stage. Thermal data from differential scanning calorimetry are also reported. Variables which affect self-heating are discussed and an actual case of heating control on a stockpile by covering is described. A simple apparatus which can be used to simulate stockpiling conditions has been tested successfully and is proposed as a convenient test system.INTRODUCTIONPrevious publications from this laboratory on the evaluation of self-heating in sulphides dealt with tailings backfill (Rosenblum et al. 1982) and waste rock (Rosenblum and Spira 1995). Sulphide concentrates may likewise exhibit self-heating in storage or during shipping. In a comprehensive but dated review, Kirshenbaum (1 968) pointed out the conflicting nature of information on means of controlling the problem, particularly with regard to the application of water and ventilation. Modelling by Simpson (1 97 1) of autogenous heating in stockpiled zinclead concentrate and associated field measurements by Wright et al. (1972) showed that the supply of oxygen by wind and the shape of the piles were the major factors in the development of hot spots. Simpson did not attempt to explain the complex mechanism of self-heating, simply ascribing its onset to oxidation. Pearse (1 980) investigated a potential method of testing for selfheating which consisted of (i) reaction with hydrogen peroxide and (ii) differential thermal anal sis, to characterize the response of concentrates at both ambient and temperatures above 100 C. He found the method sensitive enough to identify the need for careful handling but not to predict ignition. He recommended compacting concentrates and covering stockpiles with plastic sheeting to prevent ingress of air. All these workers recognized the key role played by oxygen and moisture in triggering self-heating."

Jan 1, 2001

By R. J. Matetic

The Bureau of Mines, as part of a program to improve mine planning and development, is currently investigating the effects of pillar load transfer, which can impact mining operations wi.thin a multiple-seam configuration. At two mine sites where such ground interactions were present, the Bureau performed a complete geological analysis and installed and monitored instrumentation to gather pertinent data on rock mechanics. Overburden depth varied dramatically in the vicinity of the study area and reached a maximum at the study site; innerburden thick-ness was less than a pillar width (40 to 4S ft); heaving was experienced in both mines where sandstone and/or shale floor units were observed; overlays of the mine layouts show pillars were not totally superpositioned; a maximum of S in of roof to floor convergence was measured; and pressure readings indicated pillar core loading only and increased to a maximum of 7,000 psig over instrument setting pressure.

Jan 1, 1987

By Dennis E. Jensen

Field studies were performed during blasting operations for strip coal mining above the room and pillar workings at Jenny mine in eastern Kentucky. The study is part of the Bureau of Mines program to develop criteria for the proximity of surface blasting to underground mines. Measurements and observations were made to identify physical changes in the mine. No change in the frequency of roof falls or any other indication of apparent damage was noted. Recordings of blast induced vibrations were made using sensors on the roof and floor of the underground mine and at the ground surface. A maximum particle velocity of 17.5 in/sec was recorded on the mine roof. The vibration data were analyzed and comparisons were made between roof vibration levels and those recorded on the mine floor and at the ground surface. Results are compared with previous blast vibration studies. Recommendations are made for further study toward developing criteria.

Jan 1, 1979

By Manuel Rapiman, Ricardo Sepulveda

The feasibility study of Escondida Norte (ENorte), recommended a slope angle design for the Final Pit. But, according to the experience obtained with the slope adjacent to the West wall of ENorte, in which Compañia Minera Zaldívar (CMZ) gained in its phase 4, a slope of similar geotechnical characteristics will be exposed in the West Wall of Phase 1 (Premine) and of the Final Pit, with an interramp angle 53º and with very good stability results. In this regard, Minera Escondida Ltd. (MEL) performed a study of the slope angles for the phases mentioned and according to this delivered the results of this evaluation, the recommendations and/or the necessary conclusions in the design to ensure that the slopes are stable enough and may enable safe operational management of them.

Jan 1, 2006

By D Macdougall, J Otto

The financing of large mining projects in developing countries is often achieved, at least in part, by limited-recourse financing methods. Financing agreements are affected by the basic accord that is struck between the host government and the sponsors of the project. It is concluded that governments and project sponsors should take into account the requirements of lenders when structuring such mineral development agreements to maximise the potential for attracting project financing. Lenders are likely to be most interested in aspects such as fiscal arrangements, calculation of taxable income and general accounting rules, royalties, transferability of payments/dividends overseas, corporate structure and control, staged development, financing, loan support and state guarantees/approvals, political risk, provisions for default, product marketing, settlement of disputes and environmental issues

Aug 1, 1994

By F. F. Skiba, P. J. Root

A mathematical model has been used to investigate crossflow effects in a stratified reservoir during an idealized displacement process. A process in which one incompressible fluid displaces completely another incompressible fluid of the same density and viscosity was considered. The reservoir was assumed to be composed of homogeneous layers which are discrete but interconnected. Approximate five-spot flow geometry was simulated by arranging two pie-shaped cylindrical (two-dimensional) wedges in series. Some of the common production methods rely, for their effectiveness, on the fact that the formation consists of isolated strata. This is particularly true of selective plugging and single-zone production-injection methods. The effectiveness of these techniques for several cases in which adjacent strata are in communication has been evaluated. The usual production-injection schemes for fluid injection processes involve using the same completion interval in both the production and the injection wells. The efficiency of this, as well as alternative productioz-injection procedures has been examined for some cases involving communicating strata. INTRODUCTION The performance of many fluid injection projects is marred by early breakthrough and by production of a high percentage of the displacing phase after breakthrough. This channeling effect, if it occurs in reservoirs which have large permeability variations, is often explained on the basis of a model composed of discrete, isolated strata. Corrective or preventive measures based on this same model are also common. The behavior of stratified models has been the subject of considerable study. An excellent review of the early literature was given by Seba.1 Studies of the depletion performance have since been made for continuous, unrestricted communication between strata2-4 and for production from one permeable bed in continuous but restricted communication with an adjacent permeable bed.5,6 Model studies of displacement processes in stratified systems with crossflow also have been reprted.7-12 Finally, methods which account for crossflow have been developed for computing displacement behavior in stratified systems.13,14 Most methods for controlling or preventing channeling involve some change in the interval open to production and/or injection. Although many variations of the selective completion problem have been studied in regard to the depletion of a reservoir, little attention has been given to the behavior of a displacement process under similar conditions. Sebal used a resistance network model to study the performance of a process in which one incompressible fluid displaces an identical fluid from a linear, stratified reservoir. He investigated the possibility of improving the vertical coverage by limiting the completion interval of the production well. This investigation deals with techniques in which selective completion of the production and/or the injection wells is used in an attempt to control channeling. At one extreme, selective plugging and single-zone isolation (assuming perfect execution) should be successful if the reservoir is actually made up of independent strata. At the other extreme, they can hardly be expected to be successful if the channeling is caused by a mechanism in which stratification effects are negligible even though there are extreme variations in the formation permeability and/or the injectivity profile of the wells is not uniform. By contrast, it is difficult to anticipate the effect that the amount of communication between the beds of a stratified system will have on the efficiency of selective completion techniques. The objective of this study is the quantitative determination of the effect of communication on the behavior of some particular stratified systems which will at least lead to qualitative conclusions.

Jan 1, 1966

By AIME AIME

A REQUEST for information as to the details of activities of the Engineering Council was made by the Joint Conference Committee for the benefit of the new American Engineering Council. , This request was complied with, and the scheduled reply so succinctly sets forth the activities of the old Council as well as the scope of possible activities of ,the new Council, about whose efforts there has been much discussion, .that it' is given herewith in full, except the 'budget which is summarized.

Jan 1, 1920

This report, the third in an annual series, outlines recent trends and developments in the minerals industry. Discussed are new methods, equipment, techniques, and systems used to more, effectively extract and process minerals and fuels. Environmental considerations, reduced ore grades, and the related increased quantities of material handled were the dominent concerns of the minerals industry in 1972. Productivity increased in most mineral commodities as equipment became more mobile, versatile, and sophisticated. Increasingly, equipment designs incorporated health and safety features. There was considerable interest in the field of energy and in pollution-free metallurgy processes.

Jan 1, 1973

By Pedro Lilienfeld

This report presents a design and cost investigation for several alternative versions of a field-worthy mining machine-mounted respirable dust monitor. Three main design variations are considered: (a) light scattering sensing, (b) Beta-filter tape sensing, and (c) a combination of the two preceeding methods. Eventual instrument production coats as a function of design complexity are tabulated. Cost estimates for the development and field testing of field-worthy prototypes are also presented. A general discussion on the technical aspects of these design alternatives is included following a modular-hierarchical approach of progressive complexity. The technical background to this report has been provided by the experience and results derived from the work performed under U.S. Bureau of Mines Contracts Nos. H0166097 and H0377092.

Jan 1, 1980

By John C. LaScola

The Bureau of Mines investigated coal storage silos to determine how gassy coal must be for methane accumulations in a silo to become hazardous and where such accumulations are likely to occur. Methane concentrations were measured in the open space above the stored coal pile, in the pile, and in the reclaiming area. No methane layering was found in closed-top silos. Reclaiming areas were as gassy as the top part of the silos. Coal samples were collected from the conveyors entering the silos in order to assess the gassiness of the coal. No simple correlation was found between the gassiness of the coal stored and the measured methane concentrations. However, at mines where the average 24-hour gas emission from the conveyor belt samples was 14 ft3/ton or more, fans or open tops were used. It appears that a large fraction of the methane released during storage remains in the void space between the coal particles.

Jan 1, 1980

By Robert T. Davis

An award is a form of recognition given for superior performance in a special field of endeavor. Each year awards are given by the Joseph A. Holmes Safety Association and the National Safety Council to the coal-mining industry's underground and open-pit mines that have worked a specific number of man-hours without a lost-time injury. These awards have a dual significance in that they prove efficiency can be attained without injury to persons. Safety awards do not result from luck or good fortune but do result from sincere desire coupled with sufficient effort and cooperation to achieve a desired goal.

Jan 1, 1964

By Frank G. Horino

Drill cores from 18 exploratory holes that were drilled into the unleached saline beds were tested for mechanical properties by the Bureau of Mines. Test cores were primarily selected from zones L4B, R4B, L3, and R3A in the Piceance Creek Basin, Rio Blanco County, Colo. Regression analysis techniques were tried in an attempt to relate kerogen yield or apparent specific gravity to the parameters compressive strength, Young's modulus, and Poisson's ratio. Correlation coefficients were very poor, indicating that this type of analysis was not amenable to these data. Analysis of variance techniques were tried using a division of either greater than or less than 10% nahcolite together with the requirement of less than 3% dawsonite. Results showed that a larger percentage of nahcolite tended to lower the compressive strength and to increase Young's modulus. A second analysis was made using a division of less than 3% dawsonite and greater than 3% dawsonite together with the requirement of less than 1% nahcolite. For this analysis, a larger per-centage of dawsonite tended to increase compressive strength, Young's modulus, and Poisson's ratio. Mean compressive strength values were determined for the mining horizons of interest. Average physical properties for design purposes were also determined for the horizons of interest and for a proposed adit based only on logged geologic depths to these horizons. No consideration was given to percentages of nahcolite and dawsonite. Creep data obtained from nahcolite-and dawsonite-rich oil shales provides a best fit to a modified power equation.

Jan 1, 1978

By C. Bachmann, M. J. Laurila, A. J. Widenman, A. Klein

Elemental analysis of slurry streams using X-ray fluorescence (XRF) has long been employed. However, detector technology has limited the application of XRF devices. Using detector technology employed on NASA's Mars Pathfinder to analyze soil samples, Process Control, Inc. has developed an on-line analyzer to mount on a sampling system. The prototype XRF elemental analyzer was installed at Detroit Edison's Monroe Power Plant in January, 1998 and has been employed to monitor feedstock quality. A slurry system has been developed for flotation control. This paper describes the testing of the analyzer using the new, draft ISO standard for evaluating the performance of online analyzers (ISO/DIS15239).

Jan 1, 1999

By C. E. Rork

This paper discusses various mechanical improvements that have been gradually incorporated in the copper-willing plants of the Southwest daring the past 14 years, power plants for concentrators, use of large-size units of equipment, and the effect of plant capacities on costs. The improvements in mechanical equipment and plant design have contributed in the reduction of operating costs; in some instances a saving in the capital cost per ton of daily capacity milled has resulted.

Jan 1, 1935

By Richard C. Rice

Laboratory and field data for wire ropes typical of constructions used in underground mine hoisting were obtained, screened, encoded and analyzed statistically. The statistical analysis of data for hoist ropes retired from service showed that rope remaining strength (or, conversely, strength loss) can be predicted with good accuracy if several nondestructive measures of rope damage are assessed. Found to be most important was the outer-wire corrosion rating, the electromagnetic (EM) nondestructive-inspection technique used for predicting strength loss, and the rope diameter reduction. Signs of rope deterioration such as broken wires or damage were also important indicators of strength loss. Based on the results of this investigation, a number of recommendations are presented that promise to yield better rope inspection and retirement criteria which will in turn lead to improved safety and efficiency in underground mine-hoist systems.

Jan 1, 1983

By Andrew Cecala

The Bureau of Mines performed tests to compare the effectiveness of steam and of water sprays to reduce respirable dust levels at mineral processing plants. By applying 0.22 wt pct water vapor as steam to product material, a 64-pct respirable dust reduction was recorded. By applying the same amount of moisture with water sprays, only a 25-pct dust reduction was recorded. By increasing the moisture content up to0.5 pct using water sprays, the dust reduction was increased to 55 pet, which was still less than the dust reduction achieved by adding less than half that amount of water in the form of steam.

Jan 1, 1985

By Herman O. Ankenbruck

Analyses of statistical data indicate that haulage accidents are one of the largest sources of injuries and fatalities in underground coal mines, and that the rate of accidents in transportation has been increasing during the past few years. These previous analyses were performed by correlating accident or fatality data at a rather high level of miner activity. In this present investigation, underground surveys were made by observing conditions and activities in some detail at a rather low level of activity in an attempt to understand factors contributing to hazards in the specific situations observed. The aim of the current study was to derive preventive measures that might obviate the hazardous conditions and unsafe acts observed; and, following this, to provide recommendations for additional research and development to reduce accident potential in underground transportation. The major project tasks are diagrammed together with the task outputs in figure 1-1. Initially, a preliminary study of ell underground haulage operations was performed in order to establish the kinds of data needed and to provide the rationale leading to the data requirement. At the same time, the various types of haulage equipment used for each operation were defined. A preliminary analysis of each type of haulage operation was performed in order to establish the sequence of tasks required to operate haulage equipment. These tasks were transferred directly onto observation forms, and were used in developing interview forms. In parallel with the task analysis, a review was made of accidents and hazards that might occur during each type of operation.

Jan 1, 1975

By Rudolf E. Greuer

This report contains a theoretical study on the usefulness of fighting mine fires with inert gases. Four introductory chapters review the role of fires in the mining industry; the conventional fire fighting techniques, the influence of inert gases on the burning of gases and solids, and the well established inert gas fire extinguishing systems for buildings and machinery. A large chapter describes the use which inert gas has found so far for fighting mine fires in major mining countries. More applications have occurred than generally expected and the inert gas method has in the last years become routine in Czechoslovakia and the USSR. This chapter is based on an evaluation of the extensive literature as well as on personal information obtained from leading experts.

Jan 1, 2012

By R. O. Dannenberg

The Bureau of Mines conducted laboratory batch and small-scale continuous tests to remove traces of dissolved molybdenum from water simulating waste discharged from a molybdenum concentrator, Molybdenum concentrations, initially ranging from 2 to 10 ppm, were decreased to 0.5 ppm or less by coprecipitation of the molybdenum with freshly precipitated ferric hydroxide" The precipitate was separated as a froth by dissolved-air flotation for subsequent disposal. Although the treated water met current environmental standards for contained molybdenum, contained particulate iron might have to be removed by filtration for the water to be acceptable. Estimated costs for treating concentrator effluent water were 55 cents, 57 cents, and 64 cents per 1,000 gal at initial molybdenum concentrations of 2, 4, and 10 ppm, respectively.

Jan 1, 1982

By R. Loots

High temperature creep resistant alloys are used in power plants as steam pipes and headers where they have to withstand super heated steam temperatures of up to 600ºC for the lifetime of the plant. Frequently certain portions of pipes may be subjected to excessive temperatures and consequently suffer from creep damage. Damaged portions then have to be replaced by welding new steel to the service exposed steel. Such welds will have to be subjected to a post weld heat treatment (PWHT) to relieve residual stress. During such a PWHT it is then possible for the steel to crack in the heat affected zone (HAZ) by what is known as Reheat Cracking (RHC), also known as stress relief cracking. For the present purpose the RHC susceptibility of service exposed steel was compared with that of new steel by reproducing the temperature cycle to which the HAZ will be subjected during welding in a weld simulator. This was followed by PWHT where the influence of residual stress was studied by applying a constant stress to such a weld-simulated specimen in a creep testing machine. A sharp spiral was machined along the length of the cylindrical specimen to simulate the presence of a possible weld defect. In this way it is possible to subject all portions of the simulated HAZ to the same stress intensity. For the purpose of the investigation 1/2Cr-1/2Mo-1/4V steel known to be susceptible to RHC was chosen. During testing a constant tensile stress was maintained while the temperature was increased to follow the thermal cycle prescribed for PWHT. It was found that the new steel in all instances failed by RHC along the grain boundaries in the high temperature heat affected zone. In the case of the service exposed steel the creep strength of parent metal was lower than that of new steel as a result of exposure to a steam temperature of 540°C for about 15 years. Consequently, all of the failures during testing occurred in a ductile manner by necking outside the HAZ rather than by RHC. When service exposed steel is welded to new material, it is expected that the creep strain associated with stress relaxation will mostly be concentrated in the parent steel outside the HAZ. Accordingly, it should probably not be necessary to make any extra allowance for reheat cracking during repair of steam pipes manufactured from 1/2Cr-1/2Mo-1/4V steel other than that applicable for welding new steel.

Jan 1, 2004