Search Documents

By J. D. Miller, C. L. Lin

As the techniques and resolution for 3-D spatial analysis have advanced in the last decade, it is now possible to map in detail the microstructure of multiphase materials in three-dimensional digital space. In this regard, three-dimensional x-ray microtomography offers a unique imaging capability. Spatial resolution on the order of ten microns can be achieved with the use of microfocus x-ray generators. Recently, a state-of-the-art cone beam x-ray microtomography system has been installed at the University of Utah for the quantitative analysis of multiphase materials in three dimensions. This facility has been designed to obtain 2048 x 2048 pixel reconstruction over a 10-mm diameter, while also allowing for the imaging of somewhat larger (40-mm) objects. The system is capable of handling high-density materials, even materials having a density as high as 8.0 g/cm3. This unique, one-of-a-kind, instrument will be used to obtain three-dimensional spatial reconstruction for such applications as specific examples 3D liberation analysis, pore structure analysis of particle beds during filtration and air-void system of concrete structures. The utilization of x-ray microtomography not only will allow for quantitative analysis of multiphase systems but also allow for textural characterization and the determination of phase continuity. In this paper, we present information regarding the current use of this new facility and reviewed potential applications for the advanced analytical system.

Jan 1, 2001

By A. Fred Gelding

Introduction In preparing this paper considerable time was spent attempting to find some upbeat data about the mining industry, so those of us in the field could feel somewhat better about future prospects. Much to my regret, I failed to uncover substantial evidence that our near-term or, for that matter, our long-term opportunities appear all that bright in North America. That is certainly not the kind of assessment anyone likes to hear or accept as even a possibility. Those remarks may, on the surface, appear far too pessimistic. This industry will experience a recovery and most likely will see conditions begin to improve later this year or early next. The kind and degree of recovery, however, will more than likely differ from those experienced in the past. Fundamental Changes Clearly, the fundamentals on a world scale of our business have undergone important changes. In recognizing these fundamental changes, mining authorities believe productivity advances are needed to change the direction mining has taken in recent years. The really tough question is whether increases in productivity will be enough to change the course of events that has dominated the mining sector for the past decade. Before one can provide an honest answer, an appraisal of what has and is happening now is necessary. Here are some changes and events that have taken place that effect domestic mining and will probably continue: • Mineral-rich lesser developed countries (LDCs) in Africa, South America, and Asia-Pacific have reached a point where they have developed the needed mining infrastructure to not only produce at a high rate, but in many instances, at a lower cost than fully developed countries. Just as importantly, these countries, even if they do not enjoy lower costs, will produce for world export with government subsidies because min¬ing products are key in obtaining badly needed foreign exchange. • These producing countries also have the distance advantage of lower labor, environmental, and other important regulatory costs. If that were not enough, these same countries have minerals with considerably higher grade ore and, in some cases, much lower cost accessibility. • Exporting North American commodities is impaired by a dollar that continues to strengthen against other important currencies around the world. There are other impediments to overcome, but these represent some of the realities our industry faces. Can those obstacles be overcome through improving productivity? In the past, this industry has offset the impact of these events to a sizeable degree through innovations of mining techniques, equipment and processes, and by increasing the size of its individual operations to reduce costs. Will further enhancements along these lines be enough to alter this changing balance in the future? While there is no answer, it is apparent that if we do not mount a full-scale assault in some key areas, our prospects will not be encouraging. Productivity improvements throughout the entire chain of the mining industry most certainly rates as a high priority. Every link in that chain from mine planning, equipment selections, and transportation considerations needs to be examined and reexamined to assure the lowest effective cost is developed. Quality, while oftentimes costing a little more initially, is still the most cost effective purchasing decision to make. Regulations Another area of concern is regulations, be they environmental or those that dictate what must or must not be done in running our business. Certainly, I do not suggest that we not protect our environment. However, there is an acceptable balance that has, over

Jan 11, 1983

By Andres Salazar, Carlos Delgado Robles, Richard K. Preece

Minera Escondida, located in the Antofagasta Region of northern Chile, is the world’s largest producer of copper as concentrate and SX-EW cathode. Projects to increase mill and flotation capacity began soon after start-up in 1990 to off-set decreasing copper grade. Subsequent projects had the objective to increase copper production through heap leach and SX-EW production and a second concentrator. The mine footprint concurrently expanded peripherally from the central high-grade enriched core of Escondida and then into the separate Escondida Norte deposit. Early in the mine life, metallurgical forecasting that was based on metallurgical composites of presumed ore types and historical plant production was adequate for operational planning, plant design, and project valuation. This approach became unreliable, however, as the increase in mine footprint was accompanied by an increased variability in key ore body characteristics such as hardness, copper-iron sulfide mineralogy, and sulfide liberation textures that were not reflected in the geological criteria used for ore type designation. The project study teams turned to small-scale physical and chemical tests to better characterize the spatial distribution of these key ore characteristics. Programs associated with capital growth projects were carried out through the mid-2000s to sample and construct a three-dimensional spatial model of hardness, copper sulfide mineralogy, and rougher flotation recovery from tests on 15-m drill core composites. Mathematical models were developed from the respective ore characteristic data to calculate throughput, flotation recovery, and concentrate copper grade. The spatial models were integrated with the concurrent mineral resource block model using standard geostatistical methods and the metallurgical process calculations were applied to the block estimates. The geometallurgical model, originally constructed on a project basis, is now managed by a dedicated team reporting to the manager of Geosciences & Resources Definition in the Escondida organization. The model has evolved with increasing complexity of the mine and processing plants and currently includes seven forecasting areas for three concentrators and four areas for two leach plants. Metallurgical forecasts of mill throughput, final flotation recovery, and concentrate copper grade still have the highest relevance to mine planning and optimization. Sample preparation, test procedures, and quality control methods are summarized for the ore characteristic tests important to these forecasts. Analytical results from recent annual sampling programs are presented for the hardness indices, rougher flotation recovery, and partial extraction copper analyses. Geostatistical analysis of the SAG mill hardness index is summarized as an example for the spatial estimation process. Mathematic models are presented for throughput (based on hardness indices), final flotation recovery (based on rougher recovery and plant calibration studies), and concentrate copper grade (based on sulfide mineralogy and empirical pyrite rejection studies).

Aug 31, 2023

The US Constitution provides for regulation by the states for protecting the public's safety, health, and welfare. Hence, in the eyes of the law of all states today, this is the sole justification for registration of professional engineers. Wyoming was the first state to register professional engineers in 1907, to correct abuses of incompetent or fraudulent practices in surveying and real estate. Public safety and health are most directly affected by civil, electrical, and mechanical engineering. Other branches of engineering have a profound effect on the public welfare, including investors, and safety and health of employees. No arguments, pro or con, are valid except in relation to the registration laws of various states. Code of Ethics Few would argue the desirability of requiring conformance with a code of ethics. A major problem lies in enforcing compliance, since protecting the public demands a high standard of competence, yet assessing competence gets confused with restraint of trade. Bidding engineering work on price competition can lead to pressure to cut corners on engineering quality, and was therefore discouraged by codes of ethics. The Supreme Court, in a suit against the National Society of Professional Engineers (NSPE), barred any engineering society from such bidding restriction. It has, however, upheld the right of states to impose codes of acceptable practice as part of registration laws. For example, Texas Canon I reads, "The engineer's paramount professional responsibility should be the safety, health, and welfare of the general public." Anything less makes the code practically meaningless, but there are potential conflicts of interest in many engineering organizations. How can conflicts be handled? Any corporation could improve its public image by adopting a policy that each employed PE should, without fear of recrimination, record in writing over his seal any problem or flaw in any design that comes to his attention. The policy should further require that his superior provide him a written reply pointing out that the "flaw" is accepted as requiring correction or as a calculated risk, or overruled as erroneous or as a difference of opinion. Errors in calculation of judgment are inevitable. Despite this, there are limits to how much time and money should be spent to eliminate them. It is difficult, however, to see any excuse for failure to conscientiously evaluate the opinion of a PE. This may be an impossible ideal, but how else can the profession or the industry have credibility? The National Council of Engineering Examiners (NCEE) has a code of ethics one presumably subscribes to by signing an application to write a Principles and Practices examination. However, NCEE has none of the power of enforcement that is available through state boards of registration. Registration Qualifications Qualifications are set by the laws of the states. In general, they require passage of an eight-hour examination in fundamentals, preferably at graduation, and, later, one in principles and practices. The examinations are compiled and distributed by NCEE. This system provides for a high degree of uniformity and reciprocity. States set the education and experience levels (typically four years after graduation) required by those desiring to write the principles and practices examination. Examinations The principles and practices examination calls for answering eight of 20 equal weight questions; one on engineering economics, 19 on engineering. Economics may enter into engineering questions, but only provided the question is not answerable by an economist without engineering training. In preparing examinations, NCEE strives to use questions that require some judgment and can be more effectively answered by someone with four years experience beyond college. The aim is to assess entry-level professional

Jan 2, 1984

By G. P. Tomaino

Talc is a layered, hydrous magnesium silicate mineral. It has a soft, soapy feel and typically a smooth texture. Talc is also known for its insulation, heat resistance, chemical stability, oil absorption and strong covering quality. Talc, Mg3Si4O10 (OH)2, has a theoretical chemical composition of MgO at 31.7 percent, SiO2 at 63.5 percent, and H2O at 4.8 percent. However, talc’s chemical and mineralogical composition can vary depending on its geological history/parent rock association. These mineral associations and variable levels are usually chlorite and carbonates (magnesite, calcite and dolomite). Two key elemental substitutions that can occur in the talc crystal structure are iron for magnesium and fluorine for hydroxyl. These compositional differences may limit or enhance the talc’s usage in specific market niches. The United States remains self-sufficient in most grades of talc.

Jan 1, 2005

By K. Norrena

Grade control in open pit mining requires the specification of dig limits that account for mineral grades, economic costs, and selectivity of mining equipment. Visual identification of ore rock types is ideal, but this is not always possible in lower grade disseminated deposits where ore/waste contacts are not visually discernible. In this case, conventional grade control practice consists of a two-step procedure (1) create a map of mineral grades at some selective mining unit scale, and (2) determine practical ore-waste boundaries or dig limits on the basis of the gridded block grades or assay information. This procedure is laborious, depends on a subjective assessment of where the boundary should be, and may be economically sub-optimal. We pose the determination of dig limits as an optimization problem and solve that problem with the technique of simulated annealing. Simulated annealing has the unique advantage of being able to combine multiple non-linear constraints into a single objective function. We use maximum profitability and the ability of the equipment to mine the proposed dig limits as constraints in the determination of optimal dig limits. We require a map of expected profit for eah block. Geostatistical techniques are recommended, for mapping expected profit but not necessary. Geostatistics will provide a quantification of the uncertainty in the grades within rock types using all available blasthole samples and exploration drilling. Some variant of L-optimal estimation or kriging can be used to determine the block-by-block classification that is economically optimum. We also need the expected profit for each block. It is unrealistic to assume free selection, that is, each block cannot be extracted independently of its neighbors. The optimal balance of ''accepting dilution'' and ''wasting ore'' is achieved to maximize profit subject to equipment constraints.

Jan 1, 2001

By R. L. Virta

Twenty-three companies mined kaolin in nine States in 2004. Production was estimated to be 7.6 Mt (8.3 million st) valued at $912 million, based on preliminary data. This was a slight decrease from 7.68 Mt (8.46 million st) valued at $939 million in 2003.Georgia was the leading producer state with an estimated 6.5 Mt (7.1 million st) in production. It was followed, in decreasing order of tonnage, by South Carolina, Alabama, California, Texas, Arkansas, Nevada, Florida and North Carolina. Georgia accounted for nearly the entire domestic water-washed, delaminated, and pigment-grade calcined kaolin production. Consumption Sales to the paper industry accounted for 49 percent of domestic sales and 64 percent of total sales. Other major markets for domestic sales were refractory products (10 percent), paint (5 percent), fiberglass (4 percent), catalysts (3 percent) and rubber (2 percent).Paper coating and filler markets accounted for about 87percent of export sales of kaolin.

Jan 1, 2005

By M. Superfesky, P. Michael

Introduction The US Office of Surface Mining (OSM) is proposing changes to the Code of Federal Regulations in the interest of minimizing the adverse effects of excess-spoil-fill construction on the “prevailing hydrologic balance, fish, wildlife and other environmental values” (70 FR 35112). The proposed changes will require: (1) minimization the amount of excess spoil generated at a mine site; (2) minimization of the size of the fills constructed; (3) consideration of alternative configurations for disposal; and (4) development of a disposal plan that would minimize adverse impacts to the environment.1 To achieve those objectives, mining companies operating in steep-sloped Appalachia will likely build excess spoil fills (also called valley fills) that toe out at higher elevations in the hollows (i.e. to prevent or limit burial of streams). Consequently, the slopes of fill foundations will generally be steeper. Whereas the authors of this paper support these measures to protect the hydrologic balance and general environment, we wish to point out that placement of fills on steeper foundations can negatively impact the stability of the fills if proper care is not taken during their construction. It is important to note that in addition to impairing human safety, valley fill instability can negatively impact streams, the riparian habitat etc., and thus defeat the very purpose of the spoil minimization measures proposed. We do not, however, propose additional regulatory requirements pertaining to valley fill stability. Rather, we intend to emphasize the importance of engineering requirements already on the books, especially as they apply to the predominant type of valley fill constructed: the durable rock fill. We believe that the practice of restricting valley fills, to higher elevations in the watershed leaves less room for error in the design and construction of stable structures. This paper gives a quick review of the nature of excess spoil generation; methods and requirements of excess spoil fill construction, and the to-date stability record of the fills. The interest in excess spoil minimization and how it affects valley fill construction is also discussed. Most importantly, we will review long-standing issues pertaining to proper design and construction measures with respect to durable rock fills and discuss how they will become more critical as spoil minimization is practiced.

Jan 1, 2007

By C. Rodriguez, T. BoBo

Comminution, being the energy intensive part of a mining operation receives much scrutiny by cost controllers, CEO’s, investors and others as the mining industry goes “back to basics” to reverse the decline in productivity which occurred during the mining super cycle. Blasting is the first and lowest cost per ton stage in the comminution value chain. The basic principle that effective blast design can optimize fragmentation from the Run of Mine (ROM) ore muck pile to improve productivity through digging, loading and crushing to grinding and increase mine site profits has been well documented. Benefits of controlling fragmentation in the blast include reduced wear on equipment, faster loading, increased truck loads while detecting oversize rocks at the muck pile can reduce the frequency of a blocked primary crusher. A second basic principle is a measure of particle size distribution (PSD) at each unit operation in the comminution cycle allows engineers to manage blast design to produce fragmentation in the ROM ore most suitable to optimize downstream unit processes to improve mine site productivity and profits. Split-Online® systems have measured PSD of rocks on conveyors from the primary crusher to the SAG mill for over 20 years. Split-Engineering partnered with various mining companies to develop Split-ShovelCam® to automatically measure fragmentation from shovels and excavators working the ROM muck pile. This paper takes the reader “Back to Basics” by discussing the use of real time fragmentation analysis at the muck pile as an important parameter to optimize energy factors required for each blast. Case studies are given. INTRODUCTION The basics of mining are: • Explore for and find economic resources of valuable minerals • Mine rocks containing valuable minerals using blasting • Crush and grind rocks to liberate valuable minerals (comminution) • Recover valuable minerals for sale Comminution is an energy intensive process which accounts for a major proportion of mine site costs. Effective blasting can improve comminution and deliver significant reductions to mine site unit costs, (CEEC, 2016). Engineers, scientists, builders and even philosophers have long promoted the phrase “measure to manage”; the premise being “you can’t improve what you don’t measure”. Blast Engineers measure fragmentation in ROM ore for feedback to manage energy input in the design of blast patterns to optimize the ROM product size for downstream operations, whether they be for ROM Leach or feed into the primary crusher.

Jan 1, 2019

By Duane A. Smith

They are gone now. Gone like that long ago generation that gave them birth. The Homestake Mine, nestled in the northern Black Hills, closed in 2001 after 125 years, the longest run of any major American gold mine. The Homestake Mining Co., which guided its destiny for those many years, is gone too. It merged with Barrick Gold. The Hearst family, which guided the early destiny of both, has long since gone beyond its mining heritage and into the national and even international spotlight. The mine and the company passed from the scene with as little fanfare as heralded their birth, amid the Black Hills gold rush of the 1870s. They both grew into American mining legends, as did the town they sired and nurtured, Lead. In a real sense, the mine and the company symbolized one of the last links to a vanished world and a mining era.

Jan 1, 2003

By Richard E. Gray

The Office of Surface Mining Reclamation and Enforcement (OSM) is preparing an Abandoned Mined Lands Reclamation Control Technology Hand- book. (l) GAI Consultants, Inc. , recently prepared Chapter 2 on Mine Subsidence Control which contains a summary of subsidence abatement measures plus two new decision matrices for evaluating the subsidence abatement options that might be considered for a particular problem. These decision matrices are presented for information. Review of the subsidence abatement methods resulted in identification of items where research may impact the current state of technology in mine subsidence control. These research needs are presented to stimulate discussion of their importance in subsidence abatement and to encourage funding agencies, researchers, and practitioners to work on them.

Jan 1, 1982

By Dan Martz, Bill Moler, David Young, Wally Chen, Matthew Crow, Steve Norris, Tolga Togan

Two 610 m (2000 ft) long tunnels were driven through water bearing silts, sands and clays beneath the Sacramento River using a 4.59 m (15.1 ft) diameter Earth Pressure Balance Tunnel Boring Machine (EPBM). Four sheet pile shored shafts were sunk with and without dewatering. The pre-cast concrete segmentally lined and grouted tunnels were driven down at 6% grades beneath the river flood protection levees, buildings, roads, a railroad and adjacent to a Freeway Viaduct. Details of the schedule, cost, shaft construction, TBM, tunnel construction, and installation methodology for the twin1.676 m (66 in) steel force main pipes and environmental constraints are provided.

Jan 1, 2007

By Richard M. Chamberlin

Perlite is an altered rhyolitic glass with 2 to 5 wt % water that expands or "pops" when heated quickly to plasticity while evolving steam to form lightweight, glass foam. Commercial perlite deposits in New Mexico are well-developed zones of chemical weathering (hydration) superimposed on highly permeable and thick glassy zones at the chilled upper surface and toes of high-silica-rhyolite lava flows and lava domes. The maximum tonnage of glass in these volcanoes was predetermined by their unique eruptive histories. New Mexico perlite production (80% of US production of 571,00 st) is mostly from the 3.9 Ma high-silica-rhyolite lava flows at the No Agua Peaks volcanic center. The primary vent at No Agua is defined by a 900 ft-high rubidium-rich composite lava dome, known as West Peak, that contains minor perlite reserves. Slightly less rubidium-rich lava squeezed out from under the west flank of the dome to form relatively thin (250 ft) but highly vesicular lobate flows that now consist of about 50 % recoverable perlite. Finally, rubidium-poor lavas were extruded from a radial dike on the northeast flank of the dome. These thicker (400 ft) flow lobes contain about 20 % recoverable perlite. The largest mass of lava does not always contain the most perlite. The thinner (west) flow at No Agua yields the largest perlite reserves rather than the large composite lava dome or thicker (east) flow.

Jan 1, 1994

By J. D. Morgan

Demand for nonfuel minerals depends on the overall state of the economy, which steadily improved each quarter in 1984. New housing starts rose to 1.8 million units. Automakers turned out about 15% more cars (7.8 million) and 30% more trucks (3.1 million) than in 1983. Nevertheless, many domestic mineral operations experienced difficulties in 1984. This resulted from import competition greater use of newer engineered materials, emphasis on multi-unit housing and downsizing of motor vehicles. About 15% of our energy was imported. This in cluded $36 billion worth of crude oil and $22 billion in refined products This added significantly to the overall merchandise trade deficit of $12; billion. On the bright side for mining, coal production rose 14% to 810 Mt (890 mil lion st). Three-fourths o: the coal was burned to generate electricity and more than half of our electricity was derived from coal-burning plants. With the exception of a few large-bulk, low-value raw minerals, most minerals move relatively freely in world trade. The strong dollar encouraged imports and made exporting more difficult. Consequently, our nonfuel minerals trade deficit rose 60% to $19 billion, reflecting imports of $39 billion and exports of $20 billion. There were increased pressures from some major segments of the minerals industry for some form of import protection. But President Reagan said, "Our goal is a system of free and fair trade in goods, services, and capital. We will work toward this goal through both bilateral and multilateral trading agreements." The US minerals industry consists of domestic mines, concentrators, smelters, refineries, mineral manufacturing plants, and recyclers. It also includes many wholly- or partially-owned operations in many parts of the world, providing employment and income for US citizens and others as well. Compared with 1983, the value of US raw nonfuel mineral output rose 8%, to $23 billion. The $253 billion worth of goods processed from this crude mineral output was a 14% increase. Major Metals Raw steel production - a major indicator of both material use and mineral production-rose 10%, to 84 Mt (93 million st). This stimulated a 36% rise in domestic iron ore production, to 52 Mt (57 million st), about 98% pelletized. Iron ore imports rose 44%, to 14 Mt (15 million st). Despite the increase of steel production, output remained well below levels of just a few years ago. For example, 1984 production was still 23% less than in 1981. Raw steelmaking capacity remained steady at 122 Mt (135 million st). The industry continued to cite steel imports as a major reason for low domestic capacity. In December, pacts with seven leading steel exporting nations were announced. This is an effort to reduce import penetration to about 18.5% of the domestic market. Domestic producers of bulk ferroalloys of chromium, manganese, and silicon operated at about 50% capacity. The US mined no manganese or chromium. Only a small quantity of ferronickel was produced from domestic laterite mining in Oregon. Molybdenum production, at 45 kt (49,500 st), rose threefold. Mine shipments of tungsten, another mineral tied to steel

Jan 5, 1985

By L Baumgardner, A. V. Castelli

Barite In 1987, United States mine production of barite increased 15.870, consumption (sold or used by grinding plants) increased by 6.97, and imports are estimated to have fallen by 19.57. World mine production decreased by 137, according to the US Bureau of Mines. The value of US produced barite, fob mine, decreased 1.4%, according to the Bureau. The declared value for cif US port of all imported unground barite during the first 10 months of 1987 decreased from $39.02/t ($35.40 per st) to $37.16/t ($33.71 per st), the Bureau stated. Nevada continued to be the leading US producer of' barite with 637r of the total. It is followed by Georgia, Missouri, California, Tennessee, and Montana. The Bureau of Mines estimates 657 of the US mine production was used as a weighting agent in drilling fluids. The remaining 35°/r was used in barium chemicals, glass or as a filler. Most of the production from Missouri, Georgia, and Tennessee was used in the non-oilfield sector. This sector continued to increase. Of the total consumption (used by grinding plants and chemical manufacturers), it is estimated that 8070 was used in drilling fluids and 2017( in the non-oilfield sector - barium chemicals and fillers in paper, plastics, and glass. The tonnage consumed in the drilling fluids market increased slightly. But the average number of rotary rigs operating decreased from 964 in 1986 to 936 in 1987. This is the lowest number of operating rigs reported since 1949. The increase in consumption in this sector is due to an increase of rigs operating in the US Gulf and other higher consumption areas over 1986. Crude barite imports were estimated to be down by 19.5% in 1987. Still, they accounted for 637 of the barite consumed in the US. During the first 10 months, China continued to be the leading exporter to the US with 86.970, followed by Mexico with 10.997, and Morocco 2.107(. About 5Y of the imported ore was used in the nonoilfield sector. Ground barite imports dropped from 19.8 kt to 8.8 kt (21,800 st to 9800 st) in 1987. Of this amount, 1.4 kt (1598 st) was used in drilling muds and the remainder of the non-oilfield use. During 1987, a few more grinding plants that supplied the drilling fluid market were closed. Along the US Gulf Coast, there are 13 operating plants versus a high of 31 in 1981. Cameron Offshore reopened its grinding plant at Cameron, LA. New Riverside Ochre Co. of Cartersville, GA, purchased a jigging-washing plant in Missouri and plans to place it in operation this year on a new deposit near Cartersville, GA. Milpark purchased Hughes Drilling Fluid in 1987 and operates under Milpark. US mine production will probably stay about the same as 1987. Price increases in the 10 % range for imported ore are expected due to water freight and the weak dollar. Baker Hughes estimates the average number of operating rotary rigs at 1070. A slight increase is expected in the non-drilling fluid market (chemicals, glass, and filler). Bauxite and alumina L. Baumgardner, US Bureau of Mines Domestic bauxite production in 1987, expressed as dried equivalent, was 581 kt (640,400 st), a 14% increase over 1986. US mine production amounted to less than 170 of total world production. Virtually none of the domestic bauxite was consumed in the production of primary alumina metal. About 30% of the bauxite produced by US mines was calcined to produce 117 kt (128,970 st) for use in abrasives, catalysts, chemicals, proppants, and refractories. Most of the uncalcined bauxite was refined to specialty aluminum oxide (alumina) forms. Metallurgical grade bauxite was imported from 10 countries in 1987. Principal suppliers of the 9.8 Mt (10.8 million st) were Guinea (4270), Jamaica (3501,), Australia (127), and Brazil (57). The average value, delivered U.S. ports, cif, as reported to US Customs Service, was $29.50/t ($26.76 per st). Calcined refractory grade baux-

Jan 6, 1988

By S. E. Valji

Clay slurries are normally dewatered using flocculents like sulfuric acid or aluminum sulfate. This type of flocculation is based on the electrolytic mechanism. For certain clay dewatering applications, this method of flocculation is unsatisfactory. Flocculation, based on the bridging mechanism, using organic polymers has been utilized to overcome such problem situations. This method of flocculation offers solutions not possible by previous methods. Normally these flocculents are used to assist dewatering. In this case, not only is dewatering promoted, but also further processing is assisted by a change in the dilatant character of the filter cake that is formed. Discharge of filter cake is easier, extrusion of filter cake on to conveyor dryer is possible or improved, and heat transfer and drying rates of the extruded filter cake are substantially higher. Both natural and synthetic organic polymers have been utilized for this purpose. Selection, application techniques, and economics are described.

Jan 1, 1965

By L. S. Hansen

Organized efforts toward the prevention of injuries and occupational diseases have been of comparatively recent origin in the mining industry, dating generally from the beginning of this century. Mining-and particularly underground mining- is more hazardous in many respects than most other major industries, and continual and increasing attention has been given to its health and safety aspects. The importance of the physical well-being of those engaged in mining was recognized by Agricola, who, after describing the hazards encountered in 16th century mining operations, stated that "Some of these evils, as well as certain other things, are the reason why pits are occasionally abandoned." In the past 50 yr particularly, mine managements and labor organizations, separately or collectively, have mounted productive efforts toward the prevention of accidents and industry-associated diseases and illnesses. A statistical study of this period indicates that increasing awareness coupled with the endeavors of all concerned agencies has resulted in decreasing frequency of occurrences of injuries and illnesses. In recent years particularly the mining industry has used the services of safety engineers, industrial hygienists, inspectors, ventilation engineers and other specializing in locating and correcting deficiencies affecting the welfare of employees. Concurrently, the labor movement has incorporated into its organization individuals working in the fields of health and safety, many devoting full time to these responsibilities. Others serve in behalf of their fellow workmen as on-the-job safety representatives. Most authorities agree that accidents are caused by (1) unsafe acts, (2) unsafe conditions and, exceptionally, (3) Acts of God. The "unsafe act" often is cited as the prime cause. but many accidents, and attendant injuries, are the result of a blend of "unsafe acts" and "unsafe conditions," with each chargeable in varying proportions. It therefore is necessary to consider both the physical elements of the mine plant and the training, mental attributes and actions of all personnel involved. Analysis of an accident, if based on hasty reconnaissance and unduly hurried questioning, seldom will disclose more than surface causes and consequently will result in inadequate measures to prevent repetition. Mining involves unavoidable and calculated risks, as in all facets of life. It is most important then that men employed in mining be schooled in the hazards and develop fully the ability to evaluate and minimize risks. The environment, of underground mining often is harsh and strange compared to the more natural surface conditions man has learned to cope with as a part of established life patterns. The miner. therefore, must adapt to unusual situations and conditions and must develop a mental attitude permitting acceptance of change. 3.1-INDUSTRY-AFFILIATED SAFETY AGENCIES L. S. HANSEN There are many organizations primarily interested in health and safety. In addition to industry and labor groups, there are many private and governmental

Jan 1, 1973

By Paul Richardson

This paper will review several projects completed during the period from 1976 through 1984 which have been carried out utilizing big hole drilling concepts. The projects discussed will be from various industries to demonstrate the extent that big hole drilling methods are being used along with the current state of development. There will be a discussion of projects planned for the future where big hole drilling methods are the only technology being considered. Also included in the discussions will be an overview of the most recently completed heavy oil recovery project. During the next decade, big hole drilling methods will be used more and more in all industries where underground access is required. The safety, speed and economics associated with shaft sinking using drilling methods are becoming more and more recognized and the technology is rapidly becoming an accepted shaft sinking method.

Jan 1, 1985

This paper was developed as part of an effort by the National Institute for Occupational Safety and Health (NIOSH) to identify risk factors associated with bumps in the prevention of fatalities and accidents in highly stressed, bump-prone ground conditions. Changes of failure mechanism with increasing confinement, from extensional- to shear-dominated failure, are widely observed in the rupture of intact specimens at the laboratory scale and in rock masses. In the previous analysis conducted in 2018, both unconfined and triaxial compressive tests were conducted to investigate the strength characteristics of some specimens of a Utah coal, including the spalling limits, the ratio of apparent unconfined compressive strength (AUCS) to unconfined compressive strength (UCS), the damage characteristics, and the post-yield dilatancy. These mechanical characteristics were found to be strongly anisotropic as a function of the orientation of the cleats relative to the loading direction.

Jan 7, 2020

By Victor F. Paterno

In December of 2007, a joint venture of J.F Shea, Skanska and Schiavone referred to as S-3II, was awarded a $1.15 billion (? 886,880,000) contract to construct the run-ning tunnels and station structures for the Number 7 Line Extension Project in New York City by the Metropolitan Transportation Authority Capital Construction (MTACC) and New York City Transit (NYCT). As part of the contract, a technically complex and critical connection of the new tunnel to the existing, operational 7 Line subway was required. This paper describes the innovative design approach that was conceived to carry out the underpinning and excavation works both within the east-west 7 Line subway tunnel and beneath the north-south, 4 track, 2 level Times Square Station for the A, C & E trains. This underpinning provided temporary support to the subway substructure as the grade of the tunnel invert was lowered up to 10 feet (3 meters) into the rock sub-grade to allow the future subway to pass under the basement of the world?s busiest bus terminal. In addition, the creation of a new portal connecting the existing subway tunnel and the subterranean level of the Port Authority Bus Terminal by means of underpinning structural footings and horizontal spiling/poling of existing ground will be discussed.