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By M D. Melville, B C. T Macdonald, J Dixon

The acidic and metal rich waters that are generated from acid sulfate soil (ASS) drainage can have damaging impacts upon ecosystems. The most obvious impact has been the discolouration of water and occasional fish kills. ASSÆs produce these acidic and metal rich waters when pyrite in soil is oxidised. Land management techniques are an essential long-term requirement to minimise the amount of pyrite oxidation. Acidic water that cannot be prevented through land management can be neutralised by other techniques. Powdered lime is the most common material in agriculture that is applied directly to soils and waters. Powdered lime can be expensive and if applied dry it may aggregate. Since the aggregated particles of lime are larger they could sink rapidly in the water column and not react. In waters with high concentrations of dissolved iron and aluminium the lime particles may become coated with a metal oxy-hydroxide precipitate, which will decrease its reactivity. A unique lime-dispensing machine, the Waterways Lime Spreader, has been developed to neutralise acidic waterways. The Waterways Lime Spreader can produce a solution rich in fine lime from larger limestone fragments. The current size of the machine means only 3.5 grams per second of limestone can be emitted. This output will neutralise low acidity waters, however, for high acidity waters the time for neutralisation can be long. More reactive chemicals such as hydrated lime or increasing the size of the machine will reduce this neutralisation time. The Waterways Lime Spreader is also capable of producing slurry mixtures if powdered materials are required. Trials with the Waterways Lime Spreader were undertaken in part of the Clothiers Creek catchment located in northeast NSW, Australia. A small drain with a water volume of 4 m3 was neutralised with crushed limestone to pH 6.9 from an initial pH of 2.6 and an acidity of 902 mg/L CaCO3 in 160 minutes. In comparison a drain with a slightly larger volume of 6 m3 that had an initial pH of 3.2 and an acidity of 753 mg/L CaCO3 was neutralised with hydrated lime to pH 11.8 in five minutes. The Waterways Lime Spreader has been used successfully to neutralise water from acid sulfate soils. It is expected that future applications of the machine may be for the neutralisation of acid rock drainage or acidified lakes.

Jan 1, 2003

By R. B. Walker, R. Palmer, L. C. Bryner

The purpose of this investigation was to further study some of the factors affecting the air oxidation of sulfide minerals. Data obtained from laboratory studies on the effect of temperature, concentration of iron salts, pH, and other catalysts on the biological and nonbiological oxidation of sulfide minerals are presented. The oxidation of copper sulfide minerals and subsequent leaching of the soluble copper has long been a profitable operation. The chief oxidizing agent is oxygen from the air. This reaction is influenced by a number of different factors such as temperature, light, hydrogen ion concentration, oxidizing agents, and various catalysts. Sullivan1 found that copper sulfide minerals are slowly oxidized by the air and that dilute sulfuric acid and iron (111) increased their solubility. At that time it was not known that bacteria were involved in the oxidation of the sulfide minerals. It has been shown that pyrite, molybdenite, free sulfur, and the copper sulfide minerals found in the waste rock dumps in Bingham Canyon, Utah, are largely oxidized by chemosynthetic autotrophic microorganisms found in the leaching streams.2-6 Similar organisms have been isolated in other mining areas7,8 and from the effluents from coal rnines.9 The following are some of the questions that have arisen regarding the mechanisms of the reactions involved in the leaching process. How dependent is the leaching operation upon the biological reactions? How does the temperature effect the biological and non-biological reactions? How does the concentration of iron (II) and (111) effect the rate of oxidation of copper (II) sulfide? Does the iron act as a catalyst? Does activated carbon act as a catalyst on the oxidation of sulfide minerals? What effect does the hydrogen ion concentration (pH) have on the above reactions? The purpose of this paper is to report the results of laboratory studies on these problems. EXPERIMENTAL The apparatus used in this investigation was an air lift percolator described in our earlier work.' The percolator consisted essentially of an air lift which enabled the leaching solution and microorganisms to pass freely through a suspension of mineral (substrate) in Ottawa sand. The air lift served the additional purpose of maintaining an ample concentration of oxygen and carbon dioxide in the nutrient (leaching) solution. (See Fig. 1.) The percolators were so constructed that they could be immersed in liquid constant temperature baths for temperature studies. The thermostats were controlled to +0.5°C. The reactions were all run in the dark. The percolators were charged with one to three g of mineral, dispersed in 100 g of Ottawa sand and 100 ml of nutrient or leaching solution. The sand was purified to remove traces of iron by digesting with concentrated hydrochloric acid and washng with distilled water until free from chloride. After drying, the sand was ready for use. The compressed air supply was regulated to 5 psi and bubbled through an aerator containing distilled water, which was maintained at the same temperature as the bath used. The air was filtered through cotton plugs to maintain sterile conditions. The tops of the

Jan 1, 1968

By Ashley Woodward, S. Katharine Hammond, Mayela Padilla-Salas

This paper presents a scalable framework for worker safety assessments. The paper focuses on uranium mine reclamation in underserved communities, specifically Cove Chapter of the Navajo Nation. By integrating field observations, OSHA data analysis, systems mapping, and a hierarchical occupational health pyramid, this framework identifies site-specific hazards while addressing broader socio-cultural dynamics. The approach improves upon existing safety programs by suggesting actionable, locally sensitive solutions that prioritize higher-order controls such as hazard engineering interventions and administrative controls. This study contributes to enhanced worker safety, efficient environmental restoration, and engagement in marginalized communities with abandoned mine lands.

Feb 22, 2026

By P. D. Chamberlain, R. M. Nadkarni, D. J. Kinneberg

Introduction The relationship between precious metal miners and gold refiners has been uneasy over the years. Reasons for this uneasiness and lack of trust include technical factors, economics of scale, and cultural differences. Technical factors take two forms. First, concentrates, precipitates, and sponge produced at the mine site are notoriously difficult to sample. A nonrepresentative sample can be the cause of misunderstanding and distrust. Dote, however, is relatively homogeneous and can be correctly sampled and analyzed with greater reliability. Second, the technology and chemistry of fine gold and silver production is complex and quite different from dote production. Most mining companies are content not to be involved with additional processing steps. From the standpoint of process economies, it is easy to see why miners and refiners are separate groups. Mine location is dictated by the natural occurrence of ore bodies. Heavy capital investment requirements for infrastructure in remote locations usually limits companies to produce the first marketable product from a mine. Beyond that point, the economies of scale and large capital investments for refineries generally dictate that the outputs of several mines be combined to feed a single refinery. The refin¬ing process is so complex that refineries are generally built in larger cities with a skilled labor pool. Therefore, only the largest mines can afford to refine their own output. Lastly, there are cultural differences between the miner and the refiner. The miner, particularly the small gold miner, is by definition a risk taker in a risky business. Refineries, on the other hand, have historically been operated under legal or implied monopolies approved by the government. The government is interested in owning gold, either for currency reasons or because many national mints are major users of gold coins. It is not surprising, then, to find that miners may regard refiners as part of an unresponsive government bureaucracy or, worse, as "city slickers." It is easy for the two groups to distrust each other with these different backgrounds. The interface between miner and refiner does exist and affects nearly all precious metal mining companies and most refineries. This paper discusses the technical and economic aspects of the interface. It points out how both parties can improve the relationship. Technical interface Precious metals selectively dissolve to produce a pregnant solution. They are then recovered from solution by zinc precipitation (Merrill-Crowe process) or by absorption onto activated carbon. This is followed by stripping and electrowinning. At this point, the mining company must decide whether to ship precipitates (or sponge) to refiners or to produce a dote. Some factors the company must consider are the ability to sample precipitates, concentrates or sponge, security of storage, and production rates. An important factor is the incremental cost (capital and operating) of converting precipitates or sponge into dote at the mine. Generally, mines prefer to melt precipitates or sponge to dote to avoid prob¬lems associated with sampling them. There are three types of fur¬naces used by mining operators to melt precipitates to dote. The first and most widely used is a sil¬icon carbide crucible heated ex¬ternally with a gaseous liquid fuel. The crucible is easy to use and slag can be skimmed before pouring dote. This simple system is capable of handling 1 t/a (32,000 oz per year) gold. It could cost as little as $20,000. More complex systems could cost up to $200,000. The second type of furnace is the gas- or propane-fired rever¬beratory furnace. This is usually used only by large-scale opera¬tors in the silver business. Precip¬itates in reverberatory furnaces come in direct contact with the flame. The large volumes of flue gas can carry significant amounts of dust and fume that must be re¬moved from the gas before dis¬charging it to the atmosphere. In the days when the Rand re¬finery in South Africa used reverberatory furnaces, the silver leaving the furnace in the form of vapor and fume was estimated at 2.2% of the total silver charged to the furnace. The gold in the gases was about 0.03% of the gold charged. Most of this silver and gold was recovered in the exhaust gas scrubber system. These scrub¬ber systems can be more costly than the furnace itself.

Jan 10, 1986

By James Corcoran, Richard McLane, Joseph DeMello, Eric Carlson, Hans van de Vrugt

The Los Angeles County Transportation Authority’s Purple Line Extension Phase 1 is a $3.12 billion (USD) design-build, underground heavy rail project, connecting an existing station at Wilshire Boulevard and Western Avenue and extending west 3.92 miles under Wilshire Boulevard and terminating approximately 550 feet west of Wilshire/La Cienega Station. The project alignment runs through the heart of the world famous La Brea Tar Pits and one of the world’s largest urban oil elds. This paper presents a case history of the planning, design, and construction efforts to achieve successful construction of the bored tunnels through Reach 3 of the alignment. Further, this paper outlines the proactive partnership between the owner, Los Angeles County Metro (Metro), the Design Builder, Skanska-Traylor-Shea oint enture (STS), and Southwest Geophysics who provided the geophysical services. Specically, the project included background review of historic site data (e.g., oil eld maps, building foundation plans, historic aerial photographs, etc.), geophysical demonstration testing to ascertain the capability of borehole magnetics to detect oil wells, directional drilling of thousands of feet of horizontal and vertical boreholes, collection of high resolution magnetic gradiometer data along vertically and horizontally cased boreholes as well as the collection of surface magnetometer data, discovery (“ground truthing”) of detected geophysical anomalies, and abatement of potential obstructions within the tunnel alignment.

Jun 23, 2024

By Charles L. Kimbell

The year 1979 was a period of increased activity for the world's mineral industry, distinctly in contrast with 1978 when estimated world crude mineral output value declined slightly and most phases of the industry's activity were somewhat curtailed. In 1979, most major mineral commodities recorded significant gains in output, with a substantial number achieving new record highs; details on trade levels for 1979 were not available, but increases over those of 1978 were expected on the basis of partial data. Consumption of most commodities edged higher; in some cases the higher demand levels were met largely through draw-downs of stocks accumulated in recent years, while in other cases notable output increases were required to meet demand. Actually, 1978 was not a bad year for all elements of the mineral industry if changes in output levels of the various commodities are considered as a measure of performance. There were far more individual commodities registering production increases between 1977 and 1978 than registered declines, but some of those reported as declining were relatively major commodities (bauxite, aluminum, copper and zinc were notable), Moreover, the upturn in productive activity in 1978 was not matched by increases in profits. However, 1979 was unquestionably a year of renewed expansion efforts, although some commodity areas, most notably the steel industry component, were still experiencing difficulties.

Jan 1, 1981

By S. McGinn

The Brunswick Mine Diesel Particulate Filter Study was one of several research projects initiated by the Diesel Emissions Evaluation Program (DEEP). The study was carried out at Noranda?s Brunswick Mine in Bathurst, New Brunswick by Noranda Technology Centre and Brunswick Mine personnel with the collaboration of Natural Resources Canada - Canada Centre for Minerals and Energy Technology (CANMET), National Institute of Occupational Safety and Health (NIOSH), Andreas Mayer of VERT, and diesel particulate filter (DPF) system suppliers. The study began in early 2000. Field evaluations continued for 20 months. The final report?authored by Sean McGinn?was submitted to DEEP in the Autumn of 2003.

Jan 1, 2004

By R. D. Pehke, J. F. Elliott

The solubility of nitrogen in liquid pure iron has been measured as a function of pressure and temperature. Sieverts' Law is obeyed at all pressures up to 1 atm and the temperature coefficient of solubility is 8 x 106 %/°C. The solubility of nitrogen in liquid iron alloys has been studied by the Sieverts' method and by the sampling method. The solubility is decreased by Al, C, Co Cu, Ni, 0. Si atzd Sn, and it is increased by Cr, Cb, Mn, Mo, Ta, W, and V. Interaction coefficients eN, for the effect of these elements on nitrogen dissolved in liquid iron, are reported. 1 HE effect of nitrogen upon the properties of steel may be desirable or not, depending upon the composition, processing treatment, and the use of the product. To understand the behavior of nitrogen in the various steelmaking processes, it is necessary to have reliable fundamental data pertaining to the solubilities, rates of solution, and chemical reactions of nitrogen in steel, particularly in the liquid state. In an effort to extend our knowledge in these areas, an investigation of the thermodynamics and kinetics of the solubility of nitrogen in liquid iron alloys was undertaken. The thermodynamic aspects of the study are presented in this paper. The solubility of nitrogen in liquid pure iron has received the attention of several investigators whose results are summarized in Table I. Reasonable agreement among the more recent researches1-l8 is found for the solubility of approximately 0.044 wt pct at 1600°C and 1-atm pressure of N,, for the temperature coefficient of solubility being small but positive, and for adherence to Sieverts' law for pressures up to 1 atm. The solubility of nitrogen in a number of binary liquid iron alloys has been studied: Fe-A1,3 Fe-As,16 Fe-C,3, 71 18, 19, 20 Fe-Cr ,5,7, 10, 11, 15 21 Fe-Co,'4, '6 Fe-Cu,'6 Fe-Mn,10, 11, 18 Fe-Mo,13, 16 Fe-Ni,10, 11, 13, 15, 16 Fe-O,16, 17, l9 Fe-p,7 Fe-S,l6 Fe-Sb,16 Fe-Se,lg Fe-Si,4) 97 '77 187 19>2° Fe-Sn,16 and Fe-v.51 '3 A few ternary systems have been studied, most of which were reviewed by ~angenberg" who applied the methods suggested by WagnerPz3 Chipman,24 Darken and G~rry, and Morris and Buehl26 for predicting solubilities in multicomponent alloys. Langenberg22 and Humbert and Elliott15 compared the solubilities computed from simple binary alloy systems with experimental measurements of nitrogen solubilities in liquid iron containing two or more alloying elements. The interaction coefficients for nitrogen in

Jan 1, 1961

By H. A. Doerner

"Statistics show3 that in 1927 the United States consumed 60 per cent of the world's production of chromite and produced none. The uses of chromium are rapidly expanding, and a dependable supply is essential to our industries. Since the political and commercial control of our supply of chromite is now in foreign hands it is prudent to determine how this nation can best prepare to supply its need for chromium if the imports were cut off or restricted and whether it is now possible and desirable to stimulate production of chromium from domestic deposits. We have only small amounts of chrome ore of high enough grade to meet present trade requirements. Therefore the Bureau of Mines is making a study of methods for beneficiating our low-grade ores.Chromite (Cr203.Fe0), is the only commercial source of chromium. For refractories, a minimum of 40 per cent Cr203 and a low silica content (5 to 8 per cent) is usually specified. In most instances bricks or lumps having a physical structure that will not crack when heated are required. The only way an inferior ore could be adapted to this use world be to concentrate it and develop a satisfactory binder to make bricks out of the concentrates.For making ferrochrome the requirements are a minimum of 45 per cent Cr203 and an iron content not exceeding one-third of the chromic oxide. On some low-grade ores gravity concentration will give a product meeting these requirements; other ores yield concentrates containing too much iron or other impurities to be saleable."

Jun 1, 1930

By E. L. Singleton

This Bureau of Mines investigation was initiated to study and establish some of the chemical and physical characteristics of the condensed Mno-Si02 system. To prevent oxidation of the manganous ion, I atmosphere of purified helium was used in the furnaces. Solidus-liquidus curves and invariant points were established from melting-point determinations and were supplemented from data obtained by the static-quenching method. Experimental findings and data are for the intermediate compounds of tephroite and rhodonite with their respective eutectics represented at 25.5 and 37.2 weight-percent silica. Tephroite melts congruently at 1,347° C., and rhodonite melts incongruently at 1,286° 8.. A metastable transformation was determined to exist at the 1,347° C. isotherm, the congruent melting point of tephroite. A composite X-ray-diffraction pattern was formulated for synthetic rhodonite. This investigation contributes fundamental data leading toward a better understanding of the more complex slag systems.

Jan 1, 1962

By Kot F. Unrug

In the premining stage of engineering design, the only available data are obtained from core drilling. It is often not sufficient for a realistic design of strata control. During the development, an access to the geological formation is created, enabling in situ testing. Obtained data can be utilized accordingly to improve preliminary design. The available methods for testing are described with emphasis on their application for a longwall system. The optimum design ensuring continuous operation of the high output longwalls is critical because their downtime is very expensive. Optimization of ground control measures also has the potential for substantial savings by elimination of unnecessary support.

Jan 1, 1994

A mineral grain finder is described which is easily constructed to fit onto the stage of a standard reflected light ore microscope.The device is most useful in relocating particular grains or mineral associations on 30 mm diameter polished sections. The use of the grain finder in the teaching of ore microscopy is outlined.

Jan 1, 1988

By A. Baydusa, K. Barron

A theory for cutter roof failure in coal mines has been developed. It is shown that the key parameters influencing the likelihood of cutter roof failure are the rock strength, the vertical stress (depth) and the horizontal to vertical stress ratio. The support force necessary to prevent the development of this mode of failure is, in most cases, so high as to make it impractical to apply a force of such magnitude. It is, therefore, better to allow the failure to occur and to design a bolting system to support the dead weight load of the failed block. This is probably best achieved by using a yielding bolt system (such as split set bolts) which is anchored well beyond the top of the potential failure block. The maximum potential caving height determined from this theoretical approach compares favourably with field observations reported in the literature.

Jan 1, 1999

By CLARENCE WM. POY

THE most common difficulty faced by an engineer or mine operator when opening a new property in a new field is the lack of roads and of cheap transportation. This one item often swings the balance of success or failure in starting a project. In Alaska, as elsewhere, such problems are more or less serious. In the boom days around the Valdez district, as well as in other parts of this territory, freighting was accom¬plished by dog teams or horses, or even by men that were willing to put their shoulders into harness, because there were virtually no roads. More important, there was only one time when supplies could be transported, and that was when there was suffi¬cient snow on the ground following a heavy wind. Then, and only then, could one depend on the snow to support horses and sleighs, and be sure that the gulleys, streams, and crevices in the glaciers were filled with snow to avoid pitfalls. These methods were used when one had no roads, no streams in the summer to float a barge, or even a trail for a pack train. If the snow was deep and soft, trans

Jan 1, 1935

By B. Haimson

A new loading apparatus was fabricated and used to conduct true-triaxial compression tests on KTB amphibolite, a crystalline basement rock. Tests in dry jacketed samples reveal that the intermediate principal stress has a significant effect on the onset of dilatancy and on rock strength, contrary to the implicit assumption made by Mohr-type failure criteria. Failure is induced through a shear fracture that dips steeply in the direction of the least principal stress. Experimental results lead to a new generalized strength criterion in terms of all three principal stresses. Unjacketed KTB amphibolite specimens, exposed to confining fluid, are considerably weaker than the jacketed ones, despite the negligible porosity and permeability. Failure is facilitated by several closely spaced subparallel tensile cracks normal to the least stress direction. SEM analysis suggests that microcracks developed upon dilatancy onset are penetrated and extended by the confining fluid, bringing about the unexpected rock failure mechanism at reduced stress levels. Un nouveau dispositif à chargement fut fabriqué et utilisé afin de réaliser un vrai essai de compression tri-axial sur KTB amphibolite, une roche cristalline du sous-sol. Les essais effectués sur échantillons enveloppés et secs révèlent que les contraintes principales intermédiaires affectent considérablement le début de la dilatance et la résistance de la roche, contrairement à la supposition fondée sur le critère de rupture de Mohr. La rupture est produite grâce à une cassure de cisaillement très incliner en direction où la contrainte principale est moindre. Ces résultats expérimentaux indiquent un nouveau critère de rupture général en fonction des trois contraintes principales. Les échantillons de KTB amphibolites sans enveloppe, exposés à un liquide confiné, sont considérablement plus faibles que ceux enveloppés, malgré la porosité et la perméabilité négligeable. La rupture est facilitée par plusieurs fissures de traction adjacentes et sub-parallèles, normales à la plus petite contrainte principale. L’analyse SEM suggère que les micro-fissures développent suivant le début de la dilatance, elles sont pénétrées et agrandies par le liquide confiné, produisant un mécanisme de rupture de roche inattendu, ceci à un niveau de contrainte réduit. Ein neuer Ladungsapparat wurde hergestellt um real - triaxiale Druckfestigkeitsversuche in KTB Amphibolit, einem kristallinen Grundgebirgsgestein, durchzuführen. Messungen in trockenen, bedeckten Proben zeigen that die mittlere Hauptspannung eine bedeutende Wirkung auf das Einsetzen von Dilatanz und auf die Stärke des Gesteins hat, im Gegensatz zu der impliciten Annahme auf Grund von Mohr-ähnlichen Versagungskriterien. Versagen ist induziert durch eine Scherfraktur die sich steil in die Richtung der geringsten Haupspannung nach unten senkt. Messergebnisse führen zu einem neuen, verallgemeinerten Stärke Kriterium dass auf alle drei Hauptspannungen basiert ist. Unbedeckte KTB Amphibolit Proben, die unmittelbar den umgebenden Fluiden ausgesetzt sind, sind wesentlich schwächer als bedeckte, trotz geringfügiger Permeabilität und Porosität. Versagen wird gefördert durch mehrere, nebeneinander liegende, sub-parallele Spannungsbrüche, normal zu der geringsten Spannungsrichtung. SEM Analyse lässt vermuten dass Mikrobrüche, die sich beim Überschreiten der Dilatanzschwelle entwickeln, durch die umgebenden Fluiden fortgepflanzt und weiter verbreitet werden, und unerwartet, auf Grund der reduzierten Spannungswerte, den Versagungsmechanismus des Gesteins einleiten

Jan 1, 2003

By Felipe De Lucio Pezet

El presente texto describe la importancia del oro como metal precioso -en tanto sus propiedades permiten que se lo convierta con facilidad, pulverizar y se lo vuelve fundir, a diferencia de otros metales que requieren de instalaciones complicadas para extraerlos. Asimismo, su distribución es homogénea ya que sus yacimientos no están concentrados en pocos países como sucede con el cromo o estaño. De otro lado, el brillo, color y la forma de esta metal genera una belleza particular entre los hombres. En cuanto su uso en la minería , solo una séptima parte es industrial o cotidiana, mientras que el resto es guardado en las bóvedas del banco. Finalmente, la producción del oro en el Perú proviene de una cuarta parte de los lavaderos de Madre de Dios y de una quinta parte de la fundición de La Oroya que lo rescata al fundir minerales de muchas minas que tienen el oro como subproducto.

Jan 1, 1985

WHEN the writer resided at Zeehan, qn the West Coast of Tasmania, some years ago, he took a keen interest in the geology of the district and availed himself of the opportunity to investigate occurrences, of the varied minerals in which the field abounds. The following notes were compiled as a result of one of his periodical visits to the outlying mining districts, when an examination was made of the bindsay Reward tin mining property, which has an area of 140 acres. This is most easily reached from Renison Bell, the centre of the North Dundas tin-fields, on the Emu Bay railway, 'about' eight miles north east of Zeehan. Thence a pack track some 14 -miles long connects with the mine, crossing the Piemah River by a fine suspension bridge.The mine itself is situated on the main south leading spot of the Parson's Hood Range, at an altitude of some 1600 ft. above sea level. The Parson's Hood Range is composed of granite and is an extension of the rugged Meredith Range. A remarkable feature is the uniform topography of the surrounding country when viewed from the peaks. Except where dissected by the rivers and creeks, the surface is practically level and, indeed, affords a striking illustration of an ancient uplifted peneplain.The mine has been opened by means of trenches and adits, and the ore-body proved to extend for a length of 30 chains, with an average width of about 100 ft. Its general trend is west-north-west, and its dip, which is steep, corresponds to that of the country-rocks. These latter, which are of sedimentary origin and generally regarded as of pre-Silurian age, have been tilted at high angles, consequent, no doubt, on the crustal movements produced by the intrusion of the huge granitic masses which now form the high ranges in the vicinity.It may be here remarked that it is not Within the scope of this paper to deal with the sequence of events leading to the geological structure...

Jan 1, 1923

By Louis H. Berkelhamer

"INTRODUCTION In the present war, with increasing demands on foundrymen for speedy production of sound castings, the role of sand in foundries has paramount importance.Foundry sands include both molding sands and core sands. Molding sands are those used in making molds, whereas core sands include those used for ""cores"" that fill the parts of the mold intended to be openings or hollow spaces in the casting. Core sands are, as a general rule, relatively coarse-grained as compared to molding sands. Coarse-grained sands, however, are required in making molds for large castings.Owing to the intimate relationship between properties of the sand and casting defects, it is necessary (for most efficient foundry work) to keep a close check on the molding sands used and to properly select and prepare a sand for a specific job. A mold is essentially an unfired refractory composed to meet specific requirements as to strength, permeability, and resiliency. Good green strength is important in preparing and handling the mold. Low dry and hot strengths contribute to cutting and washing, whereas high strengths cause difficult shake-out, with subsequent loss of sand. When molten metal is poured into the mold: a dried skin is attained, and gases from moisture and combustibles are driven off. Excessive moisture necessary for the proper working of a sand, as well as poor venting due to low permeability, are factors responsible for producing such defects as blows and pinholing. The skin of the mold, upon contact with molten metal, first expands and later contracts; these conditions are favorable for producing scab defects. Contact with the molten metal sometimes causes the skin of the mold to sinter or fuse and may produce a sand burn on the casting. Then again, the mold may develop excessive hot strength rapidly, thereby causing a cracked casting. Experienced foundrymen can other such relationships, too numerous to be included here."

Sep 1, 1944

By J. Kern, T. F. Torries

Identifying high value areas of unmined coal when large quantities of coal are available relative to annual markets is difficult because of the uncertainty of when the coal is to be mined. A GIS based methodology developed to value reserve coal in a producing coal region for the purpose of ad valorem taxation also identifies high value areas for mining investment. The methodology is unique in that it accounts for most mining, environmental, and market factors to determine when specific properties are to be mined. The methodology and data base are useful for directing regional exploration and acquisition activities toward most favorable areas.

Jan 1, 1999

By Yataro Shimomura

La alza de precios, salarios y las restricciones impuestas por los controles de la contaminación ambiental produjo un aumento en los costos de minado, generando que las operaciones nacionales mineras sean cada más difíciles. Sin embargo, la industria minera logró superarlos, mejorando la tecnología del minado, mecanización y racionalización de sus operaciones. De otro lado, el uso de métodos de minado por cuartos y pilares ha disminuído, mientras que los de corte y relleno y de subniveles se han incrementado. A esto se suma que la utilización de brocas "TC" y del "AN-FO", mejoraron la eficiencia del minado y redujeron los costos. En este sentido, el presente texto señala los últimos avances en tecnología minera a partir de los métodos de extracción, perforación, así como el empleo de relleno de tajeos con relaves de flotación, logrando un desarrollo en la seguridad y eficiencia de la minería subterránea.

Nov 20, 1972