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By Natesa Jayaraman, Jon C. Volkwein, Edward D. Thimons

The Bureau of Mines has studied the impact of shuttle car movement on face ventilation. Real-time measurements of air velocity, methane gas, and respirable dust were recorded and compared with a time study of face shuttle car movement. Work was conducted in a blowing face ventilation section where a scrubber-equipped mining machine operated. Air velocities decreased by an average of 35% as the shuttle car entered the face, restricting air flow, and increased by an average of 35% as the shuttle car pulled away from the face, drawing with it additional air. Return air methane levels follow the face air flow volumes, decreasing as air volume increases. The surge of air created as the shuttle car leaves the face helps to dilute methane. Respirable dust levels, however, were found to increase as the air flow increased and decreased the scrubber capture efficiency.

Jan 1, 1989

By Jaime E. Sepúlveda

Semiautogenous grinding (SAG) operators have been realizing the very significant impact of fresh feed particle size distribution on the mill grinding capacity. In actual practice, this impact may be quite difficult to assess because of the natural process variability that may also involve- concurrently other critical factors such as ore hardness. Recognizing the limitations of the empirical approach, the current publication proposes the use of mathematical models and simulators to explore and assess the net effect of feed particle size only, independent of any other factors. The simulation analysis here reported provides a basis to claim that the size distribution of the particles being ground (simply characterized by a % - 2" or similar measurement) is one of the most relevant controlling variables of the overall mill performance, regardless of the SAG circuit configuration.

Jan 1, 2005

By C. Bazin, D. Hodouin

Dynamic experiments were performed in a continuous open-circuit 40x40-cm ball mill using a pseudo-random binary sequence of the feed rate and measuring the variations of the discharge particle-size distribution. The impulse response is calculated by a cross-correlation technique. Then a model involving a discrete transferfunction and a time-series stochastic equation is calibrated using maximum likelihood methods. Based on this empirical model, a minimum variance controller with constrained input is designed and its performances are compared, by simulation, to the performances of a conventional PID regulator.

Jan 1, 1987

By B. Bringhurst, J. J. McClelland

A filter consisting of a synthetic fibrous material has been determined to be a viable alternative to the wire mesh panels currently used in irrigated filter dust collection systems. An extensive laboratory investigation of the material showed that it removed a higher percentage of both respirable coal and quartz dust from the air entering a collector than did the flat and pleated wire mesh panel designs. This improvement in dust collection efficiency reduced the amount of coal and quartz dust discharged from the collector exhaust by approximately 44%. Since continued exposure to excessive levels (>5%) of respirable quartz dust presents a severe health hazard, this alternative filter medium could be of use to those mines required to comply with more stringent dust standards due to quartz.

Jan 1, 1992

By D. H. Warren

This presentation we hope will provide you with an orderly approach co mine and surface plant closure taken from our experience over the past several years on six different projects within the intermountain states. There is no magic to the approach. It is basic common sense and yet it is interesting how many of the specific details are overlooked due to the individual complexity of each site. Our attempt here is to share some of the issues that have confronted us on these six sites. Please recognize that it is impossible to be all inclusive. Of the six sites we have drawn from; two are mine, mill and smelter sites dating back to pre-1900, one is an industrial site dating back to the early 1900s, two are mill and concentrator sites dating from the late 1940s and one is a mining district site dating from the late 1800s.

Jan 1, 1989

By I. Iwasaki, H. Dho

The role of sodium silicate in the anionic flotation of a Florida phosphate ore was investigated using laboratory continuous flotation tests, frothabiliry tests and SEM observations. In the absence of sodium silicate, Ca I+ promoted the unwanted activation of quartz by forming calcium bearing precipitates. The addition of sodium silicate enhanced the flotation efficiency through: 1) the removal of impurity minerals and calcium-bearing precipitates from quartz surfaces by dispersion, 2) drier and more persistent froths stabilized by oily droplets containing calcium silicate precipitates, and 3) higher specific flotation rates of phosphate relative to quartz, leading to faster flotation rates and increased selectivity of separation.

Jan 1, 1991

By S. G. Malghan

This paper reviews uses of sodium sulfide in the flotation of oxide minerals of copper, lead, and zinc. The activation and depression effects of sodium sulfide are of particular importance because of their applications with oxidized lead and copper ores. In spite of its industrial importance, the nature of the heterogeneous reactions between sulfide ions in solution and the surface of oxidized minerals has not been fully understood. Hence, proposed mechanisms of the sulfide action in flotation, methods of measuring and monitoring sodium sulfide in flotation pulps, and variables influencing the sulfide addition are analyzed. Recent studies on sodium sulfide addition to flotation pulps, monitoring its concentration, and the optimum dosage control using platinum and/or sulfide specific ion electrodes are discussed.

Jan 1, 1987

By Y. M. Jiang

From underground instrumentation data and from direct observation of longwall panels, it was demonstrated that growth of the main-roof overhang causes an extremely high roof weighting on the face supports. This can result in catastrophic effects on the supports when the roof-weighting intensity far exceeds the support capacity. In this paper, a comprehensive study was conducted on the characteristics of main-roof breakage and its effects on shields at different locations along the face. The study was based on monitored shield data, theoretical analysis and finite element analysis. With the help of theoretical analysis and numerical modeling, stress distribution and redistribution in the main roof were analyzed to define the main-roof failure modes and to understand the maximum roof-weighting intensity imposed on the shields. From this study, it was found that the effects of main-roof breakage on shields are chiefly related to the shield's initial-setting condition and to the final failure mode of the main roof.

Jan 1, 1996

By Isobel Clark

Geostatistical methods of estimating ore reserves and other spatial phenomena are becoming increasingly wide spread in their use. Properly applied, Geostatistical estimation falls into two stages -- the "modelling" of the spatial variability within the study area; and the use of this spatial model to provide an appropriate estimation technique. The first stage usually consists of construction and interpretation of semi-variogram graphs, and the second is the development of the corresponding Kriging method. Because of the apparent subjectivity inherent to the first stage of a geostatistical analysis, attempts have been made to provide methods of "testing' whether a particular semi-variogram model (say) adequately represents the study area. Increasingly, the choice of model is being justified by a process known as "Cross Validation'. With this approach, the analyst uses a partial data set to estimate values at actual sampled positions. "Real" and "estimated" values are then compared in such a way that the model can be accepted or rejected. This paper discusses the process of cross validation in some detail, using case studies as examples. Some problems with the technique are illustrated and discussed.

Jan 1, 1986

By G. R. Rao, K. A. Natarajan, P. Devasia

The role of growth conditions and adhesion of Thiobacillus ferrooxidans on the leaching of chalcopyrite was investigated. Thiobacillus ferrooxidans grown on sulfur, thiosulfate and ferrous ion substrates was used in this comparative study. Growth on sulfur, a solid substrate, requires bacterial adhesion unlike that required in the presence of soluble thiosulfate and ferrous ion in a mineral-salts medium. Solid substrate-grown cells showed higher rates of leaching than those grown in liquid media. An initial lag period noticed during leaching by solution-grown cells was absent when solid substrate-grown cells were used. Such a behavior is attributed to the presence of an inducible proteinaceous cell-surface appendage on the sulfur-grown cells. This appendage aids in bacterial adhesion onto the mineral surfaces. Such an appendage is absent in solution-grown cells, as substantiated by electrophoretic measurements. The importance of bacterial adhesion and the direct mechanism in leaching by Thiobacillus ferrooxidans are demonstrated.

Jan 1, 1997

By H. Polat, S. Chander

Relatively large amounts of hydrocarbons such as fuel oils are often needed in the flotation of low rank coals. The amount of oil can be decreased considerably by using surfactants as promoters. The reagents that are good candidates as surfactants to promote hydrophobicity can also act as emulsifying and wetting agents. Because the physical and chemical variables influence various subprocesses in different ways, their influence on the performance parameters is complex. The results of laboratory tests are presented to show that the dual role of reagents can be judiciously exploited to increase both the recovery and grade of the clean coal. The mode and order of reagent addition is critical in enhancing their efficacy as flotation promoters. The results demonstrate the benefits of proper conditioning of the pulp prior to flotation.

Jan 1, 1999

By S. Chander, A. Briceno

The properties of surface films on pyrite have been studied through electrochemical techniques of cyclic voltammetry and AC impedance, measurements. The characteristics of the surface films depend on the conditions of oxidation and the source of pyrite. At potentials near 0.0 V, some pyrites have large values of polarization resistance, showing a certain degree of passivity. Some pyrites show more passivation than others, however. On oxidation, meta- stable phases of Fe(OH)2 and Fe(OH)3 form that transform to more stable phases on aging. The growth of surface films near the corrosion potential of pyrite follows a linear kinetics that is attributed to a chemical (or an electrochemical) reaction as the rate determining step. The surface film is considered to be a hydroxide or an oxide because it is hydrophilic. This study has also demonstrated that AC impedance ,measurements can be used to study the growth characteristics of films at mineral/solution interfaces.

Jan 1, 1988

By David McGregor, Ashoke SenGupta, Jerry Darlington

The stability of bentonite clay suspensions against flocculation in the presence of certain anionic polymers was investigated. These polymers included a purified sodium lignosulfonate, a sodium oxylignosulfonate, a potassium salt of humic acid, and a sodium polyacrylate. The polymers differed from one another in molecular weight as well as in carboxylic, phenolic, and sulfonate group contents. The scope of this study is in evaluating the extent of thinning achievable in a bentonite clay suspension in the presence of these anionic polymers under varying electrolyte concentration, presumably as a result of deflocculation of the clay platelets by the polymers. Under certain conditions of polymer dosage and electrolyte concentration, the lignosulfonate seemed to have flocculated the clay suspension, while the other polymers served fairly well as a deflocculating/dispersing agent. The lignosulfonate, however, showed some deflocculating ability when the electrolyte concentration of the suspending medium (water) was increased by adding sodium chloride to the clay suspension. Among the four polymers tested, the polyacrylate was found to be the most effective in deflocculating clay particles, followed by the humate and the oxylignosulfonate.

Jan 1, 2003

By Eleanor Kentish, Edward Batty, Alan Skarda

"The design of the tunnels at Bond Street Station includes a final sprayed concrete fireproofing layer. The performance of this layer was verified by a program of testing to Crossrail’s KT24 specification, which proved that a dosage of 1kg/m³ polypropylene fibers and a layer thickness of 50mm would be sufficient to limit spalling in the event of a fire. Application of this thin layer was achieved using a state of the art spraying robot, with the ability to scan the profile and automatically apply a uniform layer of concrete. To provide assurance and calibrate this spraying robot, BFK developed a bespoke survey system for checking SCL thicknesses in the field. This provided an instant independent check of the spraying robot and allowed areas of inadequate thickness to be rectified without risk of cold joints. This paper describes the practical application of the fireproofing layer and how design compliance was ensured. INTRODUCTION Fire is one of the most serious risks to a tunnel. The nature of tunnels — being long enclosed spaces — can increase the intensity of a fire, and make fire-fighting and rescue operations difficult. The damage that can be caused has been demonstrated by a number of historic tunnel fires, such as the Channel Tunnel fires of 1996 and 2008, and the Mont Blanc Tunnel fire in 1999. Without any intervention, the high temperatures in a fire create thermal stresses and a build-up of vapor pressure within the pores of concrete, which eventually exceed the tensile strength and trigger explosive spalling. Spalling exposes the core of the section to severe temperatures, leading to a loss of concrete and steel reinforcement strength or further spalling of successive layers. The concrete used in tunnel linings is particularly susceptible to explosive spalling, due to its low permeability achieved by the addition of microsilica (Bailey 2011). The sprayed concrete lined (SCL) tunnels on Crossrail have been designed to resist the worst anticipated fire in operation, in order to prevent collapse and minimize damage to the structure. The design called for a system of passive fire protection, the efficacy of which was validated by the contractor through a testing regime. It was critical that the application on site reflected the test conditions, which demanded special control of the profile and thickness of the lining. In order to meet these constraints on tolerances and quality, BAM Ferrovial Kier joint venture (BFK) developed a reliable method of working with the Meyco Logica spraying robot, and a bespoke survey system for accurately checking thicknesses in the field. These innovations are the focus of this paper."

Jan 1, 2016

By Jianmin Qin, Raja V. Ramani

In this paper, the results of a research study on airborne dust transport in a full scale simulated longwall face are presented. The simulated longwall face was set up in the Lake Lynn Laboratory mine of the U.S. Bureau of Mines to conduct experiments under controlled conditions. The controlled parameters in the experiments were the dust dispersion rate, dust size distribution, density of the dust, air velocity, and the rate of travel of the dust generating source. The analyses of the experimental results on mass concentrations, particle size distributions, and real-time respirable dust concentrations are discussed. There are definite spatio-temporal trends between the location of the shearer, the concentration at any location in the face, and the dust generation rates. The size-consist and density characteristics of the source dust, the air velocity in the face, and the air leakage into the gobs all affect the concentration.

Jan 1, 1995

By W. L. Fourney, D. C. Holloway, J. W. Dally

Introduction Improvements in the process of rock excavation by blasting involves better control of one or more phases of the fracture process immediately after detonating the ex- plosive charge. Total control of the process involves individual control of (1) The number of fracture planes. (2) The crack initiation sites. (3) The direction of crack propagation (usually radial). (4) The stress field driving the fracture front. Fracture plane control is usually accomplished today by using the smooth wall blasting method; however, investigations by the authors (1) indicate several areas where this method could be improved. These improvements include: a) generation of stress concentration factors at the location of the initiation sites; b) protection of the remaining region of the borehole wall to inhibit initiation of any cracks not associated with the fracture plane and fragmentation pattern; c) limit peak detonation pressures to avoid borehole crushing and maintain by stemming residual gas pressure in the bore- hole during the crack propagation period. This paper describes experiments con- ducted with a charge holding device fabricated from thin-wall steel tubing which was partially slit at fracture locations. The tube lined the bore-hole in laboratory tests to simulate smooth wall blasting. Results showed close control could be achieved relative to both the number and the location of the fracture initiation sites.

Jan 1, 1977

By Jacek Kolacz, Knut Lyng Sandvik

Fine grinding in an air swept and a grate discharge ball mill working in closed circuit with a forced vortex air classifier has been investigated in continuous laboratory scale. Minerals with different physical properties were ground down to 40, 20, and 10 micron top size. The shape of the product particle size distribution curve was investigated and specific surface (BET) was measured. During production of material with top size of 40 microns in an air swept mill, the capacity was up to 25% higher when compared to a grate discharge mill. This difference dropped to 180A during production of 10 micron top size material. A corresponding decrease in power consumption was observed. An important finding is that by regulation of the air flow rate through the mill, it is possible to achieve products with different specific surfaces and particle size distribution curve steepness. During production of the 10 pm material, the specific surface could be varied in the range 3 to 4.5 m2/g. Such powders could hardly be produced in a grate discharge mill because fine particles coated the grinding media and the lining. On the other hand the internal classification in the air swept mill kept the size distribution of the mill content relatively free of fines. This prevented a similar slowing-down of the air swept grinding process.

Jan 1, 1995

By A. D. Davis, C. J. Webb, T. V. Durkin

This project took a watershed approach in the evaluation of water-quality impacts from past mining activities and current restoration projects in the Bear Butte Creek basin, a small and well-defined drainage in a heavily mined area of the northern Black Hills. The basin contains numerous inactive and abandoned mines, as well as a heap-leach surface gold mine. Bear Butte Creek normally loses all of its discharge to sinkholes in the Madison Limestone aquifer. Thus, it can affect the water quality of this regionally important water resource. Water-quality data were analyzed, stream surveys were conducted and two abandoned-mine restoration projects were monitored to evaluate the effectiveness of the watershed approach and to identify practical remediation techniques that could be applied to other watersheds. A geographic information system (GIS) was developed to organize information on stream quality, abandoned mine locations, and other geologic and hydrologic data. The watershed approach toward assessing and reclaiming abandoned mines appears to be effective when compared to a point-source approach that might improve water quality at specific sites but not result in significant overall improvement to the watershed because of adjacent sources.

Jan 1, 2000

By David J. Brown, Richard C. Fountain, Marc V. Hurst

The Central Florida Phosphate District, one of the most productive phosphate districts in the world, has been mined principally within Polk and Hillsborough Counties, Florida. Recent development is extending the district southward into Hardee, Manatee, and DeSoto Counties. This area is known as the Southern Extension. The combined area of these two phosphate-bearing areas encompasses about 2,000 square miles. Structurally, the district and its Southern Extension lie at the southern end of the Ocala Arch and are flanked by the Hillsborough High to the northwest. South of this area is the South Florida Embayment. The Osceola Low lies to the east. The phosphorite within the Central Florida Phosphate District generally dips very gently (<0.1°) to the south. The boundaries of the central Florida Phosphate District are generally defined by thinning of the phosphorite due the adjacent structurally high areas to the north, west, and east, and by increased clay, CaO, and MgO content reflecting lithologic differences to the east and south. The Bone Valley Member of the Peace River Formation and reworked sediments of more recent age were the primary ore-bearing horizon in the Polk-Hillsborough County area. As those reserves are depleted, the less desirable phosphorites of the Peace River Formation are being exploited in the Southern Extension.

Jan 1, 1993

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