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By James Noll, Sam Janisko

Underground miners are exposed to some of the highest levels of diesel particulate matter (DPM) in the United States. Therefore, it is important to monitor the exposure of miners to DPM, but it can be difficult because of the complex composition of DPM and the number of interferences. Currently, elemental carbon (EC) is used as a surrogate because it makes up a significant fraction of the DPM and is not affected by interferences. Standard measurement methods for EC can be time consuming and only record end of shift results. In this research, a laser absorption technique that enables one to measure EC concentration in near real time was shown to be a beneficial tool. The real time data showed that the fresh air being drawn into a stone mine was not properly reaching the working area and needed to be redirected to decrease DPM concentrations. The real time data also provided a more accurate efficiency ofan environmental cab compared to just using the standard method by detecting the opening of the cab's window and door. The EC optical monitor was also worn by researchers in a mine to show how it can give not only the average concentration for the shift but also reveal when and where a miner is exposed to DPM. Keywords: Laser absorption, diesel, elemental carbon, mining, exposure

By J. H. Rowland, A. C. Smith, K. A. Teacoach

Current regulations for fire suppression systems in underground coal mines to protect conveyor belt installations have been in place since the Coal Mine Health and Safety Act of 1969 was enacted. Over time, the coal conveyer equipment being used and ventilation conditions underground have changed significantly, particularly the width of the conveyor belts and the use of belt air at the face. The effect of these new conditions on the effectiveness of suppression systems during a fire is not known. The National Institute of Occupational Safety and Health (NIOSH) conducted a study to evaluate the effect of air velocity, water sprinkler activation temperature and a limited water application time on the effectiveness of water sprinkler fire suppression systems to extinguish large-scale conveyor belt fires. The fire tests were conducted using both new and used 1.8-m-wide, fire-resistant rubber belt that met the Mine Safety and Health Administration (MSHA) flame-resistant requirement specified in Title 30, Code of Federal Regulations, part 18, section 18.65 (also known as the 2G test). Tests were conducted using standard response sprinklers with activation temperatures of 68° C and 141° C at air velocities of 0.5 and 5.1 m/s. Two tests were conducted at both air velocities for each sprinkler activation temperature, one using a new belt and one with a used belt. The results showed that the suppression system was able to suppress the fires in ten minutes to the point that a miner could extinguish it with a fire hose. However, in several of the tests, the fire reestablished itself a few minutes after the sprinkler water supply was cut off and quickly grew out of control. This report discusses the large-scale experimental configuration, the installation specifications of the fire suppression system and the results and conclusions regarding the effect of air velocity, sprinkler activation temperature and limited water application on the suppression system performance.

Jan 1, 2010

The purpose of this work is to determine the equilibrium-state of the aqueous-solution which is produced by the leaching processes, including natural weathering of pyrite minerals. The latter can lead to acid-mine-drainage (AMD). The ferric iron species (Fe3+) resulting from bacteria-catalysed oxidation of ferrous iron (Fe2+), in the presence of water and air, is known to bring about steady-dissolution of minerals chalcopyrite (CuFeS2), sphalerite (ZnS), pyrite (FeS2), and so forth. Good-aeration, relatively high-porosity and sufficient bacterial activity tend to promote leaching in waste-rock-dumps. The composition of the aqueous-phase that accumulates in the pore-space (or in open-pits) is of practical interest as it would strongly influence the leaching of both sulfide and non-sulfide minerals. Since the reactions among the various ionic species occur relatively fast, the solution-phase may be regarded as approaching a state of virtual-equilibrium and it is possible to determine by computation the respective concentrations of the many dissolved species. For the Cu-Fe-H-O-S system, these species may include: H+, Fe2+, Fe3+, Cu2+, HSO4-, SO42-, OH-, CuSO4o, H2O, Fe(OH)+, Fe(OH)2+, Fe(OH)2+, Fe2(OH)24+, Fe(SO4)+, Fe(HSO4)+, Fe(HSO4)2+, and Fe(SO4)2-. The aqueous-system which may be constituted from appropriate mole-quantities of H2SO4, FeSO4, Fe2(SO4)3, and CuSO4 is in fact the result of various natural processes (reactions) and due respect must be accorded to the extents of these reactions. The present model computes the equilibrium molalities of the foregoing ionic and neutral aqueous species, using the iterative equilibrium constant method that ensures strict-adherence to charge-balance and elemental molar-balance constraints. The dissolving sulfide-minerals (FeS2, CuFeS2) consume Fe2(SO4)3, H2O, and O2 and yield FeSO4, H2SO4, and CuSO4 while the aqueous-phase tends to become progressively acidic (declining pH) reflecting the gradual increase in the extents of sulfide-dissolution reactions. The equilibrium-state of the solution-phase is computed for specific set of values for the extents of respective reactions. The temperature and pressure of the system are 25¦ C (298.15 K) and 101.325 kPa (1.0 atm), respectively. The mica-like minerals such as the biotite [H2K(Mg,Fe)3Al(SiO4)3] tend to consume much of the H2SO4(aq), with the extracted K+, Mg2+, Fe2+ and Al3+ ionic species accumulating in the solution. The precipitation of the jarosites (potassium, hydronium, or ammonium) contributes to the removal of ferric and ferrous species from the solution-phase. In the present work, the emphasis is on predicting the compositions of the aqueous- and condensed-phases with advancing time or increasing æextent of reactionÆ. The results of such calculations are compared to published data on raw AMD (acid-mine-drainage).

Jan 1, 2008

By P. R. Taylor

This work is concerned with the extraction of refractory metals using an electro-reduction process, in which a molten oxide melt, instead of halide, is used as the electrolyte. The process may provide an alternative method of producing refractory metals from their ores through use of a reverse-polarity direct current (DC) plasma arc heating process. In such a process, the plasma torch itself acts as an anode, and resulting liquid or solid product metals work as a cathode, whereas the molten oxide melt plays the role of an electron transfer layer. The focus of this study is: the electro-reduction of scheelite; vanadium pentoxide; and chromite. For the vanadium pentoxide, the proposed melt is mainly composed of CaO-V2O5/Li2O-B2O3-V2O5or FeO-CaO-SiO2-V2O5-Li2O with the addition of other alkali and alkaline metal oxides. In the case of scheelite ore, the SiO2-CaO-Li2O-WO3system is used as melt and metal aluminum or nickel could be used as a collecting media. As for the reduction of chromite ore, SiO2-CaO-Cr2O3-Li2O system with trace amount of CaF2is used as the melt. As a demonstration, chromium was successfully produced at a laboratory scale through the plasma driven electro-reduction process. One of the studied slags had a composition of 13.8% CaO; 4.9%CaF2; 36.4% Cr2O3; 6.9% Li2O; and 38.0% SiO2. Two observations are significant in this laboratory scale study. The first one was that the amount of Cr2O3and FeO, which were predominantly electronic conductors in the oxide melt, greatly affected the conducting mechanism of the melt. With high concentration of Cr2O3and FeO in the melt, the current efficiency was fairly low. In this case, chromium was found to be barely reduced because of electronic conducting mechanism. For example, with initial slag of 60% Cr2O3, no chromium was found reduced. With low concentration of Cr2O3and FeO in the studied melt, typically no more than 30% Cr2O3, it was observed that chromium was readily reduced due to the dominant ionic conducting mechanism. The second observation was that the addition of SiO2tothe melt helped to make the oxide melt more ionic, which was apparently desirable to the molten oxide electrolysis. However, high content of silica had a negative effect on the fluidity of the melt. This was resolved by adding trace amounts of CaF2to the melt. Therefore, by judicious selection of oxide melt, refractory metal oxides might be dissolved into it and yet the melt itself retains the required ionicity. A reverse-polarity DC plasma driven molten oxide electrolysis may prove to be a viable alternative route for the extractive metallurgy of refractory metals.

Jan 1, 2003

By R. Chen, K. Xia

In deep mining activities, blasting induced compressive stress wave would be reflected as tensile wave at a free surface around the openings, which would facilitate the tensile failure of the deep rock since it is much weaker in tension than in compression. It is thus critical to understand the dynamic tensile failure of rocks subjected to static tension for deep rock engineering applications. A modified split Hopkinson pressure bar (SHPB) system is adopted to load Brazilian disc (BD) samples statically, and then exert dynamic load to the sample through stress wave generated by impact. The pulse shaper technique is used to generate a slowly rising stress wave and thus to facilitate the stress equilibrium of samples during each test. Five groups of Laurentian granite (with tensile strength of 12.8 MPa) BD samples under the pretension stress of 0 MPa, 2 MPa, 4 MPa, 8 MPa, and 10 MPa are tested under different loading rates. The result shows that the dynamic tensile strength of the rock decreases with the increase of pre-tension stress, which is easy to understand because pre-tension stress weakens the rock sample. It is also observed that under the same pre-tension stress, the dynamic tensile strength increases with the loading rate, revealing the so-called rate dependency that is common for engineering materials. Furthermore, it is found that the loading rate sensitivity of the rock increases with the increase of pre-tension stress. A qualitative explanation for this phenomenon is that more microcracks are generated and activated under higher pretension stress, resulting in a more viscous material. Based on the results, an empirical equation is proposed to fit the data and explain the dynamic tensile behaviour of rock under pre-tension stress. A physical model is used to simulate the dependency of the dynamic tensile strength of rock on the pre-tension stress and the loading rate, which is shown to be in good agreement with the experimental results.

Jan 1, 2015

By W. C. Hudson

"The Miami-West Palm Beach belt of silica sand, which may be suitable for the manufacture of high-grade glass, extends 65 miles northward from the neighborhood of Miami to the vicinity of West Palm Beach, The sand presumably originated in the host rocks constituting the oceanward slope of the Appalachian Mountains and the Piedmont Plateau of Georgia and the Carolinas. The sand now lies in a long, narrow, and probably thin belt that forms a dune-capped terrace marking a previous stage of submergence. The highest dune crests appear to be no more than 30 feet above sea level, and the water table is about 10 or 15 feet below the general level of the terrace.The width of the belt in several places is known to be more than a mile, and the thickness of the clean glass sand sampled ranged from 4 to more than 7 feet. Visual inspection and the meager data indicate the existence of bodies of glass sand large enough to supply foreseeable markets.Analyses of three samples indicate that beneficiation would make the sand suitable for the better grades of ordinary and flint glass.The prospective grade and quantity of sand, an available market in Florida for glassware, and the expectation of postwar expansion of the new industry of glass producing justify more detailed exploratory work and beneficiation testing.U. S. Route No. 1, Old Dixie Highway, the Seaboard Railway, and the Florida East Coast Railway, all substantially parallel and usually within a width of a mile or two, run along parts of the belt or between it and the coast. In addition to many streets and unpaved roads, a paved road crosses the belt at right angles about every 5 miles. Numerous towns are situated within or near the belt. Any area selected for a mining, processing, and manufacturing plant would be near a railroad, a highway, and water and also accessible to public utilities.The subtropical climate, famous for its pleasantly warm winters, would preclude seasonal interruption of plant operations."

Apr 1, 1946

By T. S. Plaskett

A striated structure perpendicular to the growth axis was observed by the copper-decoration tech-nique in dislocation-free, .float-zoned silicon crystals. The striations, which were spaced about 100 p apart, fitted the relationship d = f/u , where d is the spacing, f is the growth rate, and u is the crystal rotation rate. Each stria was resolved into an UNDOPED silicon crystals pulled from quartz crucibles by the Czochralski technique usually exhibit a striated structure perpendicular to the growth axis.'-' This structure has been attributed to oxygen segregation, with the oxygen being introduced from the quartz crucible. If the crucible is rotated, the level of oxygen contamination has been reported as high as 10° atoms per cu cm.10 These striations are similar to solute striations commonly observed in doped Czochralski-grown crystals. The periodic nature of the striations is caused by a periodic variation in the growth rate",12 which is attributed mainly to thermal gradients in the melt.13 A finer striated structure14 attributed to constitutional supercooling is sometimes observed between the coarse striae. The oxygen striations have been observed by infrared transmission techniques,' by the copper-decoration technique,' by X-ray diffraction microscopy,6-8 and by 9 p absorption measurements3 on crystals pulled from the melt both with and without dislocations. In this investigation float-zoned dislocation-free crystals were examined by the copper-decoration technique. The level of oxygen for float-zone material is less than 1016 atoms per cu cm the lower limit of detection by 9 p absorption measurement. EXPERIMENTAL TECHNIQUE The crystals were grown by the float-zone process with the rf heating coil outside of the quartz envelope containing the silicon. All float zoning was done under an atmosphere of purified helium. The Dash technique15 was used to grow the crystal dislocation-free. This involves growing the crystal initially with a diameter between 2 and 3 mm and at array of starlike precipitates of copper. The strucLure was not .found at the surface tor a depth of about 1.5 mm, or in a region of similar width ahead of a dislocation network. The structure is postulated to consist of vacancy clusterings or dislocation loops. very rapid rates, about 20 mm per min, for a distance of about 3 cm. The diameter of the crystal is then increased to the diameter of the source of silicon, which in this case was about 19 mm. Because of the arrangement of the apparatus, the zone was passed downward rather than upward, contrary to the standard float-zoning practice. Also, the source was rotated rather than the seed. ziegler17 has made dislocation-free crystals by a similar technique but has passed the zone upwards. The starting material was zone-refined and had a p-type resistivity of 150 ohm-cm. The major impurity was boron; the total impurity excluding the boron was reported by the supplier (Dow-Corning) to be typically less than 2 x 1013 atoms per cu cm. The crystals were examined by the Dash copper-decoration technique18'19—a method in which about 10" atoms per cu cm of copper are diffused at a temperature between 900" and 1000°C into silicon which is then quenched to room temperature. On quenching, the copper precipitates on crystalline defects which are then visible when viewed by transmission infrared microscopy. The photomicrographs shown were taken either of the infrared image tube screen or directly on infrared film. All sections prior to decorating were chemically polished and, for some sections, given a sirtlZ0 dislocation etch-pit examination. After decorating, the samples were mechanically polished. RESULTS A photomicrograph, taken in transmission of a decorated cross section, is shown in Fig. 1. The portion of the section shown is near the surface of the crystal. The entire cross section showed no dislocation etch pits after being given a Sirtl etch treatment. It is seen that the copper precipitated randomly. Each precipitate, as has been reported by others, was found to have a starlike structure.

Jan 1, 1965

By C. W. Spencer, J. T. Smith

GRAIN-BOUNDARY surfaces are penetrated by a liquid phase when the liquid-solid interfacial tension is less than one-half the tension of the grain-boundary surfaces. Grain growth may occur in the presence of this liquid phase. burke1 reports that grain growth of this nature has been observed in two-phase ceramic systems. He suggests that the presence of a grain-boundary liquid may accelerate or decelerate the

Jan 1, 1963

By Smith T

Bacterial oxidation is often attributed with the advantage that a high level of gold recovery can be obtained at a relatively low level of sulphur oxidation. This is sometimes attributed to the bacteria "tunneling" towards gold inclusions, however it is often due to the presence of two or more sulphides of differing gold content which leach at different rates. Gold is liberated from the individual sul- phides linearly with oxidation. The distribution of gold between pyrite and arsenopyrite in two samples taken from a prospective gold resource was examined. The two samples showed differing responses to bacterial oxida tion and it was shown that this was due to differing intrinsic gold grades in the mineral phases and differing proportions of the minerals in the two samples.

Jan 1, 1991

By J. Paraszczak

Application of teleoperated and automated (or ?autonomous?) mobile equipment in underground metal mines represents a promising avenue for overcoming some of the challenges facing the industry. This paper addresses the overall effectiveness of autonomous loading and haulage equipment compared with conventional human-operated machines. Factors affecting availability, utilization, and production rate are explored, and an emphasis is placed on some problems and risks not present in conventional human-operated systems, as well as on the character and criticality of autonomous equipment. The need for a more in-depth analysis of factors affecting overall autonomous equipment effectiveness is stressed; these factors should be taken into consideration at the stage of feasibility studies. The paper concludes with recommendations and directions for future research.

Aug 1, 2010

By W. Randolph Van Lewis

In determilling the relative rate and in fi~lding the point where different inlpurities containecl in copper-matte are eliminated during the process of a converter-blow, the follo~ving results were obtainecl : A converter was selected which was starting on its sccolld charge. The first charge after lining had finished its copper " hot," and conseqaently no copper was adhering to the sides of the lining. All the copper and granulated slag from the previous charpc mcrc dumped, thus removing ally possibility of " salting " the matte to be tested. The coliverter worked fast and well during the entire test. Periods of ten minutes were selected. The converter mas brought from the stack to secure each sanlple of matte to be

Jan 1, 1904

By G. D. Schena

The issue of evaluating the economic impact of large mineral projects in developing countries was studied by the use of econometric models. The evaluating system is demonstrated by its application to an example from Namibia. Three-dimensional graphics are used to illustrate the procedures leading to an assessment of the economic effects of the mineral development. The analysis allows the assessment of the overall economic consequences of mineral developments where there is a need to incorporate in the evaluation issues that are broader in scope than the pure financial objectives. Sets of technical coefficients are exploited for the development of input-output models of the productive structure of an economy. The models are refined to incorporate country-specific behaviours. The increased flexibility of the enhanced semi-input-output model permits a more confident investigation of the economy wide effects associated with a new project in the mineral sector of a developing country. Synthetic measures of profitability at market and shadow prices are introduced, and the cost/benefit ratio is used to rank mineral projects according to their economic profitability. The cost is the capital mobilized for the development of the project and for increasing the productive capacity of the related satellite industries. The benefits are identified with the economy-wide increase in value added induced by the project. 80th costs and benefits are initially valued at market prices. Their ratio is likely to be an index of economic profitability superior to measures that concentrate exclusively on the benefit side of projects. To allow for market distortions, the concept of shadow prices is introduced, and accordingly project-related costs and benefits are re-evaluated. A new cost/benefit ratio at shadow prices is recalculated, which is more meaningful to the policy-maker than decision-making based on socio-economic issues.

Jan 1, 1993

The declining grades of surface deposits have re-confirmed the need for greater production rates. Large scale production requires increased investments in expensive and sophisticated equipment. The key to successful operations can depend entirely on proper equipment utilisation and in this program of research at the Department of Mining and Metallurgical Engineering, University of Queensland, much emphasis has been placed on the analysis and improvement of this aspect of a load-haul-dump operation. For a model to be successfully integrated into a mine engineering function and readily accepted by mine operating personnel, it has to offer more than just results. The concepts used in its design and construction must include sufficient detail to enable engineers to apply it usefully and with confidence.

Jan 1, 1979

By N. M. Langdon

It is now about, two years since we began wing concentrates from Port Henry magnetic-ores in the blast-furnaces of Witherbee, Sherman & Co. During this time we have had the usual ups and downs incident to blast-furnace practice, and have used the concentrates in

Jan 1, 1892

By C. Ptacek, D. Hiller, J. L. Janbor, H. Mccreadie

Between 1991 and 1994, metallurgical residues from a pressure-oxidation autoclave at the Campbell Au-quartz mine at Red Lake, northern Ontario, were neutralized with dolomite-rich flotation tailings and were deposited in a polyethylene-lined disposal area. Mineralogical analysis indicates that most of the As occurs as a crystalline ferric sulfarsenate, and some is associated with Fe oxides and with K-H3O jarosite. Field pore-water geochemical data from 1994 and 1995 showed increases in Fe(II) and As(III) concentrations, suggesting that the sulfarsenate and jarosite are dissolving; none of the discrete As phases included in a thermodynamic database limit dissolved-As concentrations, and these concentrations may continue to increase. These results demonstrate the potential for Fe and As loading through groundwater systems.

Jan 1, 1998

By V. E. Ross

A computer program was developed that incorporates a novel analysis of the behaviour of the froth in full-scale cells to predict the performance of the froth over a wide range of operating conditions. The program has the distinct advantage that it can be easily implemented on a microcomputer, which allows rapid computation and processing of the results. The program utilizes experimental data obtained in flotation-plant and laboratory testwork to provide parameters for the froth model under an initial set of operating conditions. These parameters can then be used in conjunction with a model describing the transfer of material from the pulp to the froth to predict the performance of the cell when its dimensions and operating variables are changed during scale-up.

Jan 1, 1987

By Jaczkowski B. M, Cox T. J, Domfeh I. A, Stalker I

Mining and treatment of gold ore in the Ashanti region at Obuasi, Ghana has been continuous for more than 100 years. Earlier production from this world class deposit can be traced far into the history of West Africa's gold trade. As part of a general development and expansion program, Ashanti Goldfields Corporation (Ghana) recently undertook a program to heap leach oxidized near surface ore. Kappes, Cassiday & Associates was given a major role in the design, equipment supply, installation and start-up management of the 3000 tonne/day heap leach. Unusual conditions included a high annual rainfall and an ore which could be characterized as a soft, decomposed, water saturated schist. Production began in March 1990. Startup problems and their solutions are discussed.

Jan 1, 1991

By Allan M. Hale

The paper discusses past trends in phosphate reclamation, indicating advantages and disadvantages of land and lakes, sand tailings capped with overburden, phosphate slimes capped with overburden, and overburden fill reclamation. In addition, new techniques of reclamation such a clay settling-pond disposal and wetland restoration are discussed.

Jan 1, 1983

By P. J. G. duToit

The continually growing shortage of skilled underground miners, the escalating costs of labor, supplies and equipment, and the indisputable example of "what can be done" by our friends in the space-travel field, seem to be catalysts that are accelerating improvements in underground mining technology. The search for an economic, automated continuous excavation method that would produce rock at the mining face in sizes suitable for automated transportation directly into the rod-, ball-, or autogenous grinding mills is continuing. New mining methods and techniques were devised and many improvements on old methods and techniques came forth at an increasing pace that reflected a widely spreading policy among mining men to shun the shackles of conservatism and to forge ahead and venture into newer ideas.

Jan 2, 1967

By William L. Rice

Geochemical humus sampling techniques were used by the Bureau of Mines in investigating a potential large, low-grade gold deposit in the Orogrande district, Idaho. Conifer needle humus samples were processed by ashing and fire assay-atomic absorption analysis. An area bearing anomalous concentra¬tions of gold and silver was outlined by the geochemical method.

Jan 1, 1970