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By Roy A. Lindgren

SINCE the year 1643, when the first blast furnace in America for treating iron ore was built at Saugus, Mass., out of mica schist quarried in the neighboring district, the procurement of a suitable refractory for furnace lining has been a problem of concern to the operators of furnaces. The stacks built of mica schist continued to smelt iron ore until about 1836, when, according to F. H. Norton, the first firebrick were produced', at Queens Run, Pa. Other writers speak of brick having been molded and burned in Massachusetts about the year 1834. In 1841, Andrew Russell began to produce medium refractory plastic clay brick near East Liverpool, Ohio, that were used for lining blast furnaces'. The well-known Kentucky clay-producing district was not opened up until the year 1871, but since then it has produced a large percentage of the linings for iron blast furnaces. While some strides have been made by the refractories industry during the 100 years that have passed since the first firebrick were produced, it has been only during the last two decades that any real progress has been made towards bettering the product, even though the method of production had improved. Perhaps the fault lies with the user of the brick rather than with the producer, for not sooner demanding a supe¬rior product. During the past 15 years the tonnage produced per lining has increased from 500,000 gross tons to 1,000,000 gross tons, and now some furnaces are producing 1,600,000 gross tons and better on a single lining. It is true that enlarged capacity of furnaces and improved practice have accounted for some of this increase in tonnage, nevertheless better quality in firebrick must be given credit for its share. However, we are not yet ready to say that we have reached a maximum life of furnace lining. We believe that a better product can be produced and that the refractories industries of America will, through their extensive research depart-

Jan 1, 1937

By J. S. Oram

Maltby Colliery, operated by RJB Mining (UK) Ltd is successfully mining the Parkgate seam in Yorkshire at a depth of 1000m using longwall retreat. Extraction in the Parkgate seam is influenced by interaction from previous workings in the Swallow Wood Seam 160m above. The paper describes in-situ stress measurements and simple gate road convergence measurements carried out to assess the extent of the interactive influence. The stress measurements, obtained using the stress relief overcore technique, were carried out from a maingate development roadway in an area where the stress redistribution under an overlying pillar and adjacent panel goat could be measured. The measured vertical stress distribution confirmed a significant interactive influence with high imposed vertical stresses under the overlying panel edges. Simple roadway convergence monitoring stations established in the gateroads of a retreating panel and in the development gateroads of the adjacent panel, confirmed higher rates of roadway deformation relating to overlying panel edges and pillars, particularly in the areas where a vertical stress window developed during panel retreat. In addition to highlighting a close relationship between closure rate and the measured vertical stresses, the convergence monitoring proved valuable in establishing characteristic deformation behaviour under specific interactive influences and also in defining the optimum location, extent and time of installation u£ additional roadway support and reinforcement. The information from the measurement programme has enabled the Mine Management to gain a better understanding of the interactive influences on roadway behaviour and was instrumental in designing the layout of panels in an area of the North East district of the mine where previous experience had indicated the combined influence of high interactive stresses and weak roof lithology resulted in difficult strata conditions both at development and on panel retreat. The planned location of panels and gateroads took into account both mining operational considerations and the need to avoid potentially high risk interaction zones as highlighted from analysis of the monitoring results. To obtain additional data on parameters influencing roadway deformation, extended roadway convergence monitoring has been established.

Jan 1, 1997

By S. Yano, S. Takagi, Y. Nagaya, T. Akai, T. Ishida, Z. Bennour, T. Suzuki

"It is often reported that the concept of single-plane-fracture is not sufficient to account for the productivity from shale gas/oil wells. Many researchers introduce the concept of the stimulated reservoir volume to describe observed production behaviour. However, the characteristics of the stimulated reservoir volume are not well understood. In this study, to investigate the characteristics of fractures and surrounding region induced by the hydraulic fracturing, a devised hydraulic fracturing experiment was conducted using the cylindrical shale specimens in the laboratory.Two resins were prepared as the fracturing fluid for the experiments: cyanoacrylate, an instant glue, mixed with a fluorescent paint (resin A), and methyl metaacrylate, a thermosetting acrylic resin, mixed with a fluorescent paint (resin B). These resins were able to fix within the specimen after fracturing. This is because the present study aimed to only detect fractures induced by hydraulic fracturing. Cut sections of the specimens were observed under ultraviolet light irradiation. It is expected that the hydraulically induced fractures and the surrounding regions will be detected because the induced fractures filled with the resin should emit light, while the other parts will not.The specimens, which were collected from the Kushiro Coal Mine in Hokkaido, Japan at the depth around 275 m, were roughly 85 mm in diameter, 170 mm in length, and cored normal to the sedimentary planes. An injection hole with a 10-mm diameter was drilled onto the center of the specimen parallel to the sedimentary plane to simulate hydraulic fracturing in shale gas development. The experiment was conducted under a uniaxial loading condition of 3 MPa and the fracturing fluid was injected into the sealed injection hole at a constant flow rate using a syringe pump.After the fracturing experiment, the resins were fixed in the specimens and then the cut sections were observed under ultraviolet light irradiation. As a result, the hydraulically induced fractures, which were filled with the resin, are clearly observed. Detailed microscopic observations show that the main fractures are tortuous and are accompanied by many thinner ramified fractures. Additionally, fractured regions where the resin penetrates significantly are observed around the main fractures in the specimens fractured by the resin B. These induced fractures and fractured regions are considered to be the stimulated region in which permeability is improved. The necessity of estimation on the features of fracture tortuosity and ramified fractures is indicated for more accurate understanding of the well production and the stimulated reservoir volume."

Jan 1, 2015

The control system of a mine winder or other variable speed drive has many component parts that must work together to provide the required functional performance of the machine, together with comprehensive safety features, reliability, maintainability, user-friendliness and efficiency. Modern winders use digital control technology extensively and hence software design is a major part of the overall system. It is not practical to simulate an entire mine winder in a single computer model because of the sheer mathematical complexity of the behaviour of many of the components. However, most component parts can be simulated quite easily, and related parts of the control system software can be simulated. Such simulations allow control software algorithms to be developed and tested in isolation from the real plant. Tests can be performed on the model without fear of injury to personnel or damage to the valuable plant. For example, speed regulator control algorithms and stability settings can be adjusted to and beyond the limits of stable operation, and near optimum settings can be found. This is particularly important, for example, when designing closed loop controls for emergency brake systems. Obviously, care must be taken to ensure that the computer model of the plant is realistic and takes into account as many non-linear features of the real plant as possible. Pure mathematical analysis of some systems is very difficult to perform when non-linear plant behaviour is involved. This paper shares a number of practical simulation experiences performed using commercially available software such as Matlab and Simulink to simulate various parts of the control system of a mine winder or other variable speed drive. Demonstrations of the operation of several different computer models are shown during the presentation of the paper.

Jan 1, 2005

By Roe-Hoan Yoon

INTRODUCTION In 1960, coal accounted for 49% of the world energy consumption, an amount that was reduced to 29% in 1973 because of the availability of cheap oil. At that time, it seemed that oil would remain available for a long time in unlimited quantities. However, this situation changed drastically in 1973/74 when a series of closely spaced price increases from $3 per to $12 per bbl by mid-1974 hit both industrialized and developing countries. Another sharp price increase in 1979/80 to the $34 to $38 per bbl level also hit the world economy hard and, at the same time, set in motion powerful technology development forces for increased coal utilization. At this point, the price of coal was approximately $1.50 per MM Btu, while that of oil approached $6.00 per MM Btu. This huge price differential offered an incentive for developing new coal technologies including liquefaction, gasification, fluidized bed combustion, coal-water mixture (CWM), etc. The CWM technology was of particular interest to the utility industry, which consumes more than 80% of the coal mined in the US for power generation. In this technology, a powdered coal is mixed with water to produce a stable slurry that can be stored for an extended period of time without settling and is readily pumpable. Various reagents in the amount of approximately 1% by weight of the coal are added to inhibit sedimentation during storage and to reduce the viscosity for atomization in burners. The coal loading is in the range of 50 to 80% solids, depending on the particle size and its distribution. With very fine particles, it is difficult to increase the coal loading above 50%, and a binomial distribution helps increase the coal loading. The presence of water consumes a relatively small amount of the heating value of the coal during combustion; for a coal-water slurry containing 30% water, less than 5% of the calorific value of coal is usually consumed due to evaporation. The major advantage of burning coal as a slurry is that many of the oil-burning furnaces can be converted to coal-burning with a minimum retrofit cost. Considering the substantial price margin between coal and oil, the pay- back period for retrofit costs can be relatively short. Nevertheless, the retrofit cost can be further reduced if low-ash coals are used as feedstocks for CWM; there will be savings in the capital cost of installing bag filters or electrostatic precipitators that are designed to remove the ash from the combustion gases. Furthermore, the use of low-ash coals can minimize derating of boilers because the velocity of the combustion gases can be maximized without creating erosion

Jan 1, 1991

By Fred C. Bond, Jen-Tung Wang

Comminution energy is principally energy of deformation before breakage, which appears as heat An empirical equation is presented which covers the entire comminution range. The new strain-energy theory considers comminution from the known principles of mechanics and the reduction ratio. Energy requirements according to the different theories the romnnred. THE present status of the theory of comminution is extremely unsatisfactory. The amount of various ores and rock products crushed and ground annually approaches the staggering sum of perhaps one half billion tons. Yet the basic concepts underlying an operation of such magnitude are unknown, and actual knowledge of what takes place in comminution is almost entirely empirical. The responsibility for this situation cannot be charged to apathy or lack of appreciation of the importance of the problem. Many attempts have been made to evolve a workable hypothesis, but none has been completely successful. General Considerations In order to break rock, it must be subjected to a stress which strains the rock beyond its critical breaking point. The stress imparts energy to the rock, most of which is released in the form of heat when the stress and resulting strain are removed. If the strain induced exceeds the critical strain, the energy is released by breaking; if the induced strain does not reach the critical point, the energy is released with removal of the stress as energy of resilience. Rock is a brittle material and it is assumed that it breaks approximately at its yield point, so that no permanent deformation results from strains below the critical. When rock is broken the total energy input is accounted for by the heat liberated, and by the surface energy of the new surface produced. A small and probably negligible amount is released as noise. Rock is commonly broken under compression and the applied stress is ordinarily compressive. However, for breakage to occur, it is only necessary that the induced strain exceed the critical value, and this strain may represent the resultant of compressive, shearing, and tensile forces. The stress-strain diagram of rocks under compression, and the modulus of elasticity as determined therefrom, should be fundamental considerations in the development of any theories of rock breakage. Crushing in jaw or gyratory crushers results primarily from a squeezing action, and reduction in a hammer mill is the result of impact. The action in rod and ball mills is a combination of impacting, squeezing, and wearing away by attrition, or rubbing. In ordinary crushing and grinding, the forces are applied at protruding points and are not distributed evenly throughout the rock. This is one of the features of comminution which theoretical considerations have not covered adequately. Another feature is the effect of impact velocities, which may greatly influence the total energy required for breakage. Impact velocities may vary from 1 or 2 fps in crushers to 10 or 20 fps for ball mills, and as high as 100 or more for hammer mills. However, according to the findings of geophysicists, the velocity of sound and of compression waves in stone is many times greater; the primary longitudinal compression waves travel at perhaps 15,000 fps, and the secondary transverse waves, which may reach the surface and cause cracks to form thereon, travel at perhaps 5000 fps. When a crack tip forms, the total surrounding stresses are concentrated in this tip, which rapidly extends throughout the rock particle.1 It would seem that the energy required to deform the rock beyond its critical strain, resulting in the formation of a crack tip, represents practically all of the energy required. Most of the primary crack tips presumably form on the surface. A simple method of designating feed and product size is necessary for the evaluation of crushing and grinding results. Taggart's suggestion2 that the 80 pet passing size be used has been found very practical. In this paper, the square opening screen size which 80 pct of the feed passes is designated as the feed size F, and the size which 80 pct of the product passes, or the product size, is designated as P. The reduction ratio at the 80 pet passing size, or F/P is designated as n. The feed and prod-

Jan 1, 1951

By Fred C. Bond, Jen-Tung Wang

Comminution energy is principally energy of deformation before breakage, which appears as heat An empirical equation is presented which covers the entire comminution range. The new strain-energy theory considers comminution from the known principles of mechanics and the reduction ratio. Energy requirements according to the different theories the romnnred. THE present status of the theory of comminution is extremely unsatisfactory. The amount of various ores and rock products crushed and ground annually approaches the staggering sum of perhaps one half billion tons. Yet the basic concepts underlying an operation of such magnitude are unknown, and actual knowledge of what takes place in comminution is almost entirely empirical. The responsibility for this situation cannot be charged to apathy or lack of appreciation of the importance of the problem. Many attempts have been made to evolve a workable hypothesis, but none has been completely successful. General Considerations In order to break rock, it must be subjected to a stress which strains the rock beyond its critical breaking point. The stress imparts energy to the rock, most of which is released in the form of heat when the stress and resulting strain are removed. If the strain induced exceeds the critical strain, the energy is released by breaking; if the induced strain does not reach the critical point, the energy is released with removal of the stress as energy of resilience. Rock is a brittle material and it is assumed that it breaks approximately at its yield point, so that no permanent deformation results from strains below the critical. When rock is broken the total energy input is accounted for by the heat liberated, and by the surface energy of the new surface produced. A small and probably negligible amount is released as noise. Rock is commonly broken under compression and the applied stress is ordinarily compressive. However, for breakage to occur, it is only necessary that the induced strain exceed the critical value, and this strain may represent the resultant of compressive, shearing, and tensile forces. The stress-strain diagram of rocks under compression, and the modulus of elasticity as determined therefrom, should be fundamental considerations in the development of any theories of rock breakage. Crushing in jaw or gyratory crushers results primarily from a squeezing action, and reduction in a hammer mill is the result of impact. The action in rod and ball mills is a combination of impacting, squeezing, and wearing away by attrition, or rubbing. In ordinary crushing and grinding, the forces are applied at protruding points and are not distributed evenly throughout the rock. This is one of the features of comminution which theoretical considerations have not covered adequately. Another feature is the effect of impact velocities, which may greatly influence the total energy required for breakage. Impact velocities may vary from 1 or 2 fps in crushers to 10 or 20 fps for ball mills, and as high as 100 or more for hammer mills. However, according to the findings of geophysicists, the velocity of sound and of compression waves in stone is many times greater; the primary longitudinal compression waves travel at perhaps 15,000 fps, and the secondary transverse waves, which may reach the surface and cause cracks to form thereon, travel at perhaps 5000 fps. When a crack tip forms, the total surrounding stresses are concentrated in this tip, which rapidly extends throughout the rock particle.1 It would seem that the energy required to deform the rock beyond its critical strain, resulting in the formation of a crack tip, represents practically all of the energy required. Most of the primary crack tips presumably form on the surface. A simple method of designating feed and product size is necessary for the evaluation of crushing and grinding results. Taggart's suggestion2 that the 80 pet passing size be used has been found very practical. In this paper, the square opening screen size which 80 pct of the feed passes is designated as the feed size F, and the size which 80 pct of the product passes, or the product size, is designated as P. The reduction ratio at the 80 pet passing size, or F/P is designated as n. The feed and prod-

Jan 1, 1951

By Joan T. May

The Federal Bureau of Mines investigated the potential for recovering aluminum from copper-dump leach liquors by use of single-contact ion-exchange technology. A strongly acidic ion-exchange resin was used to extract aluminum from a typical dump leach liquor and from synthetic leach liquors. Aluminum was stripped from resin with a HS04 or NaCl solution. Bench-scale experiments indicate that a single-contact ion exchange is technically feasible, but that the process is limited by the relatively low loading capacity of the resin and the excessive amount of stripping agent required. A further limitation is that significant amounts of magnesium and iron are loaded and stripped along with the aluminum.

Jan 1, 1976

By Dirk van Zyl, S. Chander

Minerals have been critical to human society from the earliest and their use has been intertwined with the development of civilization. In the Western World, the mining, processing and extractive metallurgy associated with ores was first described in detail by Agricola in the 16th century. He considered these collective activities to be the most necessary and the most profitable of professions, and wrote, "without doubt, none of the arts is older than agriculture, but that of the metals is not less ancient; in fact they are at least equal and coeval, for no mortal man ever tilled a field without implements. In truth, in all works of agriculture, as in the other arts, implements are used which are made from metals, or which could not be made without the use of metals; for this reason the metals are of the greatest necessity to man." Ours is still a materials-dependent society that relies heavily on minerals for raw materials. Today our dependence on minerals is exceptionally great. To meet the need for fuel and non-fuel minerals in a representative year, in the United States alone, about one billion tons of coal and 2.7 billion tons of ore are mined. These mineral products are essential for fertilizers, for construction materials, metals and alloys, for manufacturing household and industrial items, for transportation, and for the generation of electric power. It is instructive to consider the diversity of uses found in our society for a single mineral product - silver, for example. Experts believe that in the past 5000 years we have mined about a million tons, or 31.9 billion troy ounces of silver. In 1988, 133 million troy ounces of silver were used in the Unites States. Most of the silver used was for techno- logical, medicinal and industrial purposes, Table 1. X-ray films, for example, carry comparatively large amounts of silver to lessen patient's radiation exposure. Silver does not prevent tooth decay, but each year about two million troy ounces of silver is used for dental work in the United States. In small quantities it is used in medicine. No metal - not even copper conducts heat and electricity so efficiently as silver. Silver wires lace solar cells, and silver oxide batteries power hearing aids, calculators, submarines and satellites. Hardened with tungsten or molybdenum, miniature discs of silver pass current from wire to wire in cars, telephones and computers. A dish- washer timer alone may have 50 such electrical contacts, which open and close without excessive heat or friction. Silver is an important component of solar reflectors, since no other material reflects light so well or uniformly. In our personal lives, silver remains in high esteem to adorn our tables, provide precious objects and jewelry. In many parts of the world, silver in the form of coins, jewelry and bullion is used for financial independence and security against the vagaries of paper currency. In India, silver is used in its purest form as thin foils to decorate sweets and other edibles. It is obvious that this mineral product, silver, is of great value and utility in our society. Minerals and Environment The benefits of minerals do not come without problems. Much of the silver, for example, lies locked up in copper, lead-zinc or precious metal ores; to extract it creates vast quantities of waste material. On the average, in order to recover one ounce of silver about a quarter ton of ore must be mined. To meet the world's annual demand for silver, approximately 100 million tons of waste is generated every Year. The problem with silver is repeated with all minerals. Conversion of mineral ores into usable materials necessitates the generation of large quantities of waste products that create tremendous disposal problems. In addition to waste material discarded during mining, wastes may be generated during processing as gases, liquids or solids that must be subsequently converted into forms more acceptable for disposal. Associated with the handling, treatment and management of waste products are a number of environmental problems. Environmental problems are not new to the minerals industry. In his Geographia, Strabo (63 B.C. - 20 A.D.), gives an account of the conditions of labor under which men

Jan 1, 1992

By J. M. Eriksen, T. Rosenqvist, H. Elstad, S. Seim, A. Hildal

The titanium industry demands high titanium feedstock for their processes. As rutile resources are limited, ilmenite has become the most important titanium source. Ilmenite smelting is an important part of upgrading ilmenite to high titanium feedstock. In the year 2005, upgrading of ilmenite by smelting, producing a slag with 80-90% Ti02, accounted for approximately 40% of the feedstock to the Ti02 pigment industry. In ilmenite smelting molten iron is produced together with a slag, which in addition to titanium oxide contains iron oxide as well as various impurity oxides of manganese, magnesium, silicon, aluminium, etc. Titanium is present mainly as Ti02 but partly also as Ti203. It is known that the concentration of Ti203 increases with decreasing concentration of FeO, but this dependency is affected by the nature of the impurity oxides. Sigurdson and Moore1 showed that slags high in CaO and MgO had a lower concentration of Ti203 than slags high in Si02 for the same amount of FeO. Pistorius2 showed in 2002 that if the impurity oxides MnO and MgO are counted, on a molar basis, as FeO, and Cr203, V203 and part of the A1203*), as Ti203, industrial slags will have a composition close to that of the M305 phase, where M denotes the elements Ti, Fe, Mn, etc, and which has the pseudobrookite structure. However, for equilibrium with liquid metallic iron he computed, by means of a computer program FACT, that the slag equilibrium composition is represented by a curved line in the ternary phase diagram FeTi03-TiO2-Ti2O3, but with a significantly higher concentration of trivalent titanium than actually observed in the industrial slags, and he discussed various mechanisms by which the slag during solidification could change its composition to a lower Ti203 content, but the possibility that the computed compositions might be wrong was not mentioned. Trane113 found in her research on titaniferous silicate slags a lower Ti3+/ Ti4+ ratio than that which is computed by the FACT program. The purpose of the present investigation was to study the equilibrium composition of Fe-Ti-O slag in equilibrium with liquid metallic iron, as well as the effects of impurities such as Si02, CaO and MgO on the slag composition. Industrial slags from TINFOS Titan and Iron KS (TTI) will also be discussed and their compositions will be plotted in the ternary phase diagram. These are slags produced from Tellnes ilmenite, quite high in magnesium and iron. Experimental In the past, equilibrium studies of the Fe-Ti-O slag system were difficult when it came to producing the slag. It was difficult to find a suitable crucible for the meltings. The highly corrosive slag would attack all known refractories, and the metal would attack metallic crucibles such as those made of platinum and molybdenum. In the present investigations the slag-metal combination was prepared in a high-frequency induction furnace with a vertically segmented water-cooled copper crucible. The crucible is shown in Figures 1 a and 1b. It was designed by the Australian Nuclear Science and Technology Organisation (ANSTO) with power from a 75 kVA high-frequency generator (750 kHz) supplied by Farfield Electronics Pty, Ltd, Australia. This enabled the slag-metal combination to be melted with turbulent stirring and is expected to be isothermal. The entire temperature gradient

Jan 1, 2007

By David C. Grant

In situ uranium mining offers the advantages of minimal environmental disturbance, low capital and operating costs, and reduced mining development time. It is becoming an increasingly attractive mining method for the recovery of uranium from secondary ore deposits. In order to better understand the process, a laboratory technique was developed and used to study and simulate both the chemical and physical phenomena occurring in ore bodies during in situ leaching. The laboratory simulation technique has been used to determine effects of leaching variables on permeability uranium recovery, and post-leach aquifer restoration. This report describes the simulation system and testing procedure in sufficient detail to allow the construction of the system, and to perform the desired leaching tests. With construction of such a system, in situ leaching of a given ore using various leach conditions can be evaluated relatively rapidly in the laboratory. Not only could optimum leach conditions be selected for existing ore bodies, but also exploitation of new ore bodies could be accelerated.

Jan 1, 1985

By R. A. Wood, R. I. Jaffee, H. R. Ogden, D. N. Williams

Dispersion-containing titanium-copper alloys were prepared having mean free paths varying from 1.0 to 9.7 P. Tensile studies at room temperature and at 1000°F showed that little or no strengthening occurred when the mean free path exceeded 3 p. However, at lower values of mean free path appreczable strengthening was observed. A considerable amount of strengthening also resulted from copper in solid solution. DURING the past several years, an increasing amount of study has been devoted to dispersion hardening, an alloying process in which increased strength is obtained through the addition of a ran-

Jan 1, 1961

By J. B. F. Champlin

The continuing development of the nuclear industry in the United States requires a program of waste disposal that insures against the release of large amounts of radioactivity to the environment. This paper describes research on one proposed means of disposal of this waste, that of injection into geologic formations at depth. Nuclear production plant wastes were simulated and injected into samples of sedimentary rock obtained from outcrops, quarries, and deep wells. Changes in the chemical and physical characteristics of the rocks caused by the interaction of ions and suspended particles in the waste solutions with the cementing material and claylike particles in the rock are discussed. Laboratory tests show that nuclear wastes can be injected into many natural porous, permeable geologic formations. Injectivity can be maintained over a longer period by monitoring the ionic balance and particle-size distribution of waste streams. The combination of permeability and porosity with low cation-retention capacity, as exhibited by most sandstones, would satisfy the engineering requirements for the subsurface disposal of nuclear waste. Shales and clays with their low permeability and high cation-retention capacity would make excellent confining formations. The amount of cation retained by sedimentary rocks increases with increasing valence or concentration of the cation or decreasing brine concentration. The use of rock cores as model reservoirs had proved successful in determining some of the parameters that need to be considered in full-scale field disposal of wastes.

Jan 1, 1967

By L. A. Panek

Research on roof bolting has developed significant information with respect to the functions that can be performed by properly installed bolts and the methods that can be used to ensure that effective installation has been achieved. The present paper brings together results that are pertinent to the design of a bolting system for reinforcing horizontally stratified mine roof with vertical bolts. The design approach is based on the use of bolts to decrease the maximum bending stress within an arbitrary sequence of roof strata (see Fig. 2) in which the only loads are the weights of the individual beds. The use of rock bolts to achieve other objectives, such as to stabilize a fractured rock mass on the periphery of a mine opening,3 is excluded from consideration herein. Reinforcing effect of bolts consists of a friction effect and a suspension effect in combination. "Friction effect" refers to reduction of bending in a stratified roof due to clamping action of tensioned bolts, which compress the strata, thereby creating frictional resistance to displacement along planes of stratification. (The flexure of a sequence of strata is necessarily accompanied by horizontal displacement of each bed with respect to its neighbor, along mutual surfaces of contact.) Although the sliding of the beds tends to exert a shearing effect on the bolts, tests show that this has negligible influence on the bending stresses, probably because the bolts are so far apart. "Suspension effect" refers to the transfer of part of the weight of the weaker or thinner strata to one or more thick strata, which occurs when strata with differing tendencies to deflect are constrained to have equal deflection. The term "suspension" is used irrespective of whether the thin strata are above or below the thick strata, because tests show that the supporting effect of the flexurally more rigid roof strata is for practical purposes independent of their position in a bolted sequence of strata. An earlier paper4 dealt with a bolted unit in which all strata had equal flexural rigidity; bolting could develop a friction effect but no suspension effect. The present paper deals primarily with a bolted unit in which all strata do not have equal flexural rigidity, so that bolting can develop both a friction effect and a suspension effect. The reinforcing effect of the bolts was determined by a combination of experimental and theoretical stress analysis.4'6'7 The experimental method consisted of loading a model by rotating it in a centrifuge to simulate the gravity forces exerted about an underground excavation. Models were made from two different limestones, although the results are independent of the material because the elastic constants were taken into account in the data analysis. Electric resistance strain gages were bonded to the highest and lowest members of the bolted unit to determine the outer-fiber bending strains at the center and at the supports. The quantitative results presented herein are based on tests of 56 different models, which included a range of values for the structural parameters. Each model was tested several times, with different combinations of spacing and tension of the bolts. DESIGN EQUATIONS The effects of friction and suspension on the flexure of a bolted stratified roof can be expressed by the following equations, which give the maximum bending stress, the deflection, the friction effect, the suspension effect and the transferred load for any (the i-th) member of the bolted unit in terms of the structural parameters:

Jan 1, 1964

By William S. Pintz, William A. Vogely, Charles J. Johnson

This chapter on the role of minerals in developing economies is oriented toward economic policy issues. The discussion and analysis cut across the technical, economic, legal, and policy fields. The goal of this chapter is to pro- vide relevant background information important to individuals involved with the minerals sector in developing countries. Where possible, trends are shown to provide a basis for understanding the evolving role of minerals in developing economies. This chapter is divided into the following five sections: (1) characteristics of developing countries (which presents selected statistical comparisons); (2) government objectives in developing countries; (3) government policy formulation in developing countries; (4) determinants of future trends, and (5) a summary of the chapter's major points combined with the authors' view. CHARACTERISTICS OF DEVELOPING COUNTRIES There are 155 nations in the world categorized as "developing countries." In total these nations represent about one third of the value of the world's mineral production, three quarters of the world's population, and over half of the world's land surface area. The group of so-called developing countries is quite diverse and there are exceptions to almost any general observation about the group as a whole. Most definitions of the term "developing country" are based on levels of per capita income. However, if per capita income is the sole criterion used in categorization, then several oil-exporting countries would jump from the category of developing country to the category of developed country.a Obviously, this results in a poor fit with respect to other measures. In general, the majority of developing countries can be characterized by relatively low per capita income, high population growth rates, high levels of unemployment, low levels of education, short average life ex- pectancies, income distribution skewed toward the highest 20% of the population, and a large share of exports represented by primary commodities. b For the purposes of this chapter a slightly modified version of the widely used World Bank system of classification (shown in Table 1.2.1) is used. As summarized in Table 1.2.1, developing countries are divided into three main groups based on estimated gross national product (GNP) per capita. It should be noted that the high- income, oil-exporting countries have characteristics of both developing and industrialized countries; however they are included for most statistical comparisons within the group of developing countries. Of the 155 developing countries in the world, approximately half produce minerals other than common building materials, and only 32 account for more than five percent of world pro-

Jan 1, 1985

By Kenneth R. Hancock

Iron oxides are unique in that they are the only significant colored mineral found in a natural state suitable for use as a pigment after being pulverized to pigmentary size. The current world production of iron oxide pigments is estimated by the author to be between 499 and 590 kt (550,000 and 650,000 st) based on 1979 data. The fact that highly colored natural deposits of iron ore are found throughout the world accounts for its use in prehistoric man's artistic cave paintings. These early artists did not realize that they had established man's first paint test fence which now has some 20,000 years of exposure. In addition to abundance, constituting about 7 % of the earth's crust, iron oxides have the advantages of low cost, permanency, and are not toxic. Through the centuries, succeeding civilizations have utilized iron oxides as a major source for decoration and protection when coloring was desired. In the last century the chemical industry has improved on nature by developing a complete range of synthetic iron oxide pigments which surpass the pigments produced from natural iron ores in uniformity, color quality, and chemical purity. In the United States alone, the combined production of natural and synthetic iron oxides produced sales of over $28,000,000 in 1970 (Stipp, 1970) and increasing to $97 million by 1980 (Spinrad, 1980). Nomenclature With the increasing importance of the synthetic iron oxides it is necessary to make a distinction between the natural or mineral pigments and the synthetic pigments. Natural pigments are those products which are derived from selected ores and should not be confused with iron ores mined for steel production. Iron ores that are mined for steel must be capable of being mined and reduced to iron on a commercial basis. These ores are selected on the basis of iron content and processing economics. It is therefore unusual when iron ores for steel production are suitable for use as mineral pigments. Natural pigment ore sources are selected for their special physical-chemical properties and can command a premium price. Synthetic pigments, and in this instance iron oxides, are those pigments produced from basic chemicals. Through chemical synthesis pigmentary sized particles are produced as opposed to comminution, the major procedure common to all natural iron oxide pigments. Classification An important characteristic of a pigment is its color and, therefore, a logical separation can be made on this basis. A. Yellow Iron Oxide Pigments 1. Natural mineral origin a) Goethite b) Lepidocrocite c) Ochres d) Siennas e) Limonite 2. Synthetic pigments a) Goethite B. Red Iron Oxide Pigments 1. Natural mineral origin a) Hematite b) Siderite (calcined) c) Pyrites (calcined) 2. Synthetic pigments a) Hematite C. Brown Iron Oxide Pigments 1. Natural mineral origin a) Umbers b) Limonite (calcined) c) Siderite (calcined) d) Goethite (bog ore or sulfur mud) 2. Synthetic pigments a) Blends of hematite, goethite, and magnetite

Jan 1, 1983

By W. W. Adams

The year 1937 was signalized by increased employment in the metal-and nonmetal-mining 4 industry of the United States. Measured by the number of men working, there was a 17-percent gain in employment compared with 1936. In total number of man-hours worked at all mines, the gain was slightly over 18 percent. Hazards connected with mining resulted in more accidents to the workers than in 1936, but the increase in number of accidents caused only a slight rise in the accident rate because of the much larger increase in the number of man-hours worked. In fact, the fatality rate per million man-hours of exposure was lower in 1937 than in 1936, but the rate for nonfatal injuries increased slightly.

Jan 1, 1940

By L. R. Mabson, F. M. Russell

INRODUCTION Roan Consolidated Mines Limited (RCM) operates five underground mines - Mufulira, Luanshya, Baluba, Chambeshi and Chibuluma (figure 1) . Associated metallurgical plants provide for the operations of milling, smelting two refineries for copper and a cobalt plant. Primarily a producer of high quality copper (242,000 tonnes during 1980) the Company is also the world's second largest producer of cobalt metal. RCM's remaining ore reserves at 31st March 1980 were 275 million tonnes at 2.84% copper. Monthly ore production is in excess of 1.2 million tonnes. Sublevel open stoping was the choice of mining method for the first underground operations on the Copperbelt for ore with dips steeper than 30 degrees. This was for use at the Roan Antelope mine, subsequently to be called Luanshya mine. The sublevel open stoping system was planned based on the methods used in many of the iron mines of Michigan and New York and in the copper mines of Tennessee. Peterson (Ref. 1) gave the following reasons for employing sublevel stoping, reasons which are still valid today: (1) the working place could always be barred and made safe, and the sublevel exit was always at hand; (2) the working conditions were similar day by day and drilling operations were repetitive; (3) pillar spacing can be varied as conditions demand; and (4) stoping operations could be shut down completely or opened up to full capacity at short notice, without affecting grade or causing wastage of reserves. Such was the success of the method that it was adopted as the basic mining method at all the RCM mines in their initial stages. Although cut and fill, block caving, and sub- level caving methods have been used, sublevel open stoping in its many variants still accounts for nearly 90% of total ore production in the Company. The following descriptions outline some of the applications of sublevel open stoping within RCM. LUANSHYA Geology There are two main ore deposits at Luanshya: the Roan (Luanshya Mining Area), in which mining began in 1930, and Baluba, in which mining production started in 1973 (figure 2). Both orebodies occur in synclinal and variably folded basins. These basins are underlain and completely surrounded by much older schists and granites. The ore formation, an argillite, lies near the base of the sediments and is underlain by conglomerates, quartzites and arkoses. Copper mineralisation is mainly found in two well defined zones, separated by a varying thickness of pyrite mineralisation. In the eastern part of the Roan deposit only the upper orebody is present, but west of 18 shaft and at Baluba the lower orebody predominates. Locally the subjacent quartzites of the footwall formation are also mineralised with copper. The copper mineralisation is found princi- pally as disseminated sulphides, mainly chalcocite, bornite and chalcopyrite. Near the surface the sulphides have been changed to oxides. At Baluba the cobalt mineral carrollite is found with the sulphides. Mining methods Sublevel open stoping is the basic mining method. In its standard form this method is best suited to steeply inclined orebodies, with simple structures and with a strong foot- wall and hangingwall. In recent years, as more complex folding and flatter dipping orebodies have been encountered, considerable variations have been introduced. Stope drilling is effected with drifters and extension steel.

Jan 1, 1981

By Jorge D. Vier, Raúl B. Rebak, Alicia E. Ares, Natalia S. Zadorozne

Recent worldwide demand has driven nickel and molybdenum prices to record high values. Alloys containing significant amounts of nickel and molybde- num, such as the austenitic and duplex grades, have experienced significant price increases and some spot shortages have resulted in some regions. With low or no nickel content and reasonable molybdenum content, super-ferritic stainless steels are now proving to be the most cost effective corrosion resistant materials. The electrochemical behavior APMT® (Fe–21Cr–5Al–3Mo–0.04C) and 4C54® (Fe–26.5Cr–0.8Mn–0.5Si) super-ferritic stainless steel in NaCl solutions has been studied using open circuit potential measurements, potentiodynamic polarization curves, and electrochemical impedance spectroscopy. The aim is to compare the behavior of these materials with austenitic stainless steel alloy 316 (Fe–18Cr–10Ni– 2.5Mo). The results indicate that the APMT alloy presents a better performance than the AISI 316 stainless steel, while 4C54® does not, especially at anodic potentials. The good behavior of APMT® may be attributed to Al and Mo content in its composition.

Mar 1, 2017

By W Lindlief, Cyril Stanley Smith

Several investigators, mainly concerned with the mechanical properties of the alloys, have studied the so-called aluminum bronzes after various quenching and reheating treatments. Of these works, perhaps the most complete is that of Bouldoires, who studied changes of length, electrical conductivity, thermoelectric force, hardness and micro-structure on tempering quenched alloys containing 5 to 20 per cent of aluminum, although the work of Carpenter and Edwards,² Curry13 Greenwood,4 Braesco,5 Matsuda,67 Grard8 and others has added much to our knowledge of the changes occurring during tempering. The so-called acicular ß decomposes on tempering at temperatures between 350" C. and the eutectoid, giving rise to a Widmanstätten structure of a needles in a matrix of 6 or fine a + 6, associated with an increase in hardness and almost complete loss of ductility. Matsuda studied the eutectoid transformation by means of dilatation and electrical conductivity measurements during cooling at different rates. He found that on cooling at the rate of 10" C. per minute there was a decrease in electrical resistance and in length instead of the usual increase which occurred with slow rates of cooling. On tempering the rapidly cooled samples, the increase commenced at about 400" C. and at 520" C. the resistance and length had reached the equilibrium values. These peculiarities he accounted for as being due to a transitional phase ß' being formed, ß' having an electrical resistance and volume less than either ß or a + 6. Obinata9 published some electrical conductivity curves for copper-aluminum alloys showing a double break at the eutectoid temperature,

Jan 1, 1933