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By John Turner, James Lamb

The Minnesota Department of Transportation (MNDOT) has an extensive project to improve driving conditions and reduce hazards to motorists on US Highway 61 between Duluth, MN, and Canada along the north shore of Lake Superior. In 1991, the Lafayette Bluff Tunnel was completed just north of Two Harbors, MN, through a joint venture of Johnson Brothers Corporation of Litchfield, MN, and Obayashi Corporation of San Francisco, CA.

Jan 1, 1994

By Louis J. Trostel

Refractories, called the Hidden Industry by The Refractories Institute, provide the temperature and chemically resistant linings for the multitude of vessels that are used today in high temperature processes ranging from giant iron-making blast furnaces to industrial incinerators to petrochemical cracking units to the smallest furnaces used by the jewelry trade. While these refractory linings are absolutely essential to the proper functioning of these processes, the linings are almost always on the inside of the vessels and thus hidden from the eyes of the public. Refractories are defined in Standard C71 of the American Society for Testing and Materials (ASTM), titled "Standard Definitions of Terms Relating to Refractories," as "nonmetallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 1 000°F (538°C)." This criterion of ability to withstand exposure to environments above 538OC is the critical distinction separating refractories from other ceramics, fibers, and coatings applicable only at lower temperatures. In addition to resisting temperature, the refractories must with- stand abrasion, chemical and slag attack, resist thermal shock, and carry sustained structural stresses at high operating temperatures for as long as years. The most common methods of classifying refractories are by forming method and composition. First are the traditional formed and fired bricks, batts, and the associated multitude of special shapes. These refractories are usually formed at room temperature, dried, and then fired to high temperatures to develop the final properties desired. Other formed refractories are chemically bonded or resin or tar bonded. To complete the formed refractory matrix, some fired refractory bricks and shapes are subsequently impregnated with resins or tars. Physical dimensions of these formed refractories are classified into two general categories: standard sizes and special shapes. The standard sizes are those in common usage in the United States described in ASTM Standard C909 "Dimensions of a Modular Series of Refractory Brick and Shapes" based on the 38 mm basic module as described in ASTM Standard C861 "Determining Metric Dimensions of Standard Series Refractory Brick and Shapes." The most common size is the "9-inch straight" 228 x 114 x 64 mm (9 x 4 ½ x 2 ½ in.) of the "2 ½ -inch" series or 228 x 114 x 76 mm (9 x 4 ½ x 3 in.) of the "3-inch" series. Bricks of nonstandard sizes are referred to as special shapes. Their use is required in specific furnaces for particular requirements or applications. In addition there is the large and growing group of refractories sold as unshaped mixtures that may be formed into their final shapes at the application site. These unshaped mixtures are sometimes referred to as specialties. The mixtures are prepared to be hydraulically cast, plastic or wet rammed, dry rammed, or dry vibrated into their final shapes. Some are designed to be projected through nozzles (or gunned) onto their forms. The refractory mortars used to lay up the shaped refractories fall into this group referred to as specialties. Prepared refractory grains also are sold. These are usually calcined or fused materials that are subsequently crushed and sized to a variety of specific carefully controlled grain sizes or size distributions. These grains include calcined fire clay, dead burned magnesite, periclase (fused magnesia), dead burned dolomite, kyanite, tabular and fused aluminas, fused zirconia, fused mullite, and calcined alumina-magnesia spinel. The primary composition groups of refractories are the 1) alumino-silicate refractories made largely from fire clay and high- alumina materials, 2) silica refractories made from quartzites and ganisters, and 3) basic refractories from magnesia (or magnesite) and chromia (also referred to as chrome ore), alone and in combination, and dolomite. Special refractories include carbon, zirconia, zircon, high purity alumina, mullite, silicon carbide, silicon nitride, and some borides. In addition there are groups of special insulating refractories.

Jan 1, 1994

By E. M. Williams

The U.S. Bureau of Mines is investigating the use of in-seam seismic methods to monitor stress-induced changes in coal near the working face of longwall mines. Seismic surveys performed through a longwall panel and pillars near the face can provide valuable information on geologic anomalies, high stress regions, tailgate support performance and other conditions that could endanger miners or interrupt production. This paper describes the details of the equipment and data analysis techniques used, and the significant results obtained and their implications for ground control. Using seismic tomography, it is possible to conduct measurements on the pillar and reconstruct an image representing the internal velocity distribution. Successive measurements over several days identify changes in velocity attributable to changes in stress. Several field measurements were conducted at a western U.S. longwall mine to observe stress induced changes within the panel and pillars during mining. A permissible data acquisition system was designed to meet mine safety requirements for operation in gassy air. Certification from the Mine Safety and Health Administration (MSHA) was obtained, and this approved system was used to monitor stress changes in several pillars as the longwall face passed during first panel mining. Tomographic surveys were completed across the longwall panel to map the apparent abutment stresses ahead of mining. Velocity distributions show an increase in vertical stress across the panel from the headgate to the tailgate. Additionally. a yield zone along the face near the tailgate and the forward abutment approximately 100 feet outby the face in the tailgate side of the panel were detected. These results agree well with data obtained from other instrumentation emplaced in the panel near the tailgate. Using velocities for both compressional and shear waves, the Poisson's ratio was calculated for the panel.

Jan 1, 1994

By Claude Cunningham

Ths oonoept of precise. eooursts timing with Elsotronic Delay Detonators (EDD’s) was first ssriously sddresssd in ths mid 80’s end much wss made of the cheapness end profusion of digital wstohes in terms of the likelihood of EDD’s also being cheap and essyto produce. Ten years Iater. with every major explosives group end many elsotronios groups having instituted projects to capitalize on the promise of these devices, production devices are still to come into asneral use.

Jan 1, 1994

By L. C. Morales

Mexico has an area of about 2 million km2 (772,260 sq miles), with volcanic activity, large shores and mountainous areas reaching as high as 6000 m (19,680 ft) above sea level. These conditions are favorable for most mineral deposits, some of commercial value and others as a source of mineral samples. In addition to its vast mineral wealth, Mexico has another valuable asset in its people. Even before the discovery of America, natives were successfully mining metals. During the colonial days, the mineral deposits were mined to increase the wealth of Spain. All this experience was passed from generation to generation. It created a tradition of mining and minerals processing engineers that currently accounts for about 182,000 people supported by mining-related activities. Nonmetallic minerals in Mexico have been mined by natives since the early days. They knew the value of kaolin clays for pottery, as evidenced by archeological findings. This experience was also passed from generation to generation and has become recognized worldwide as ceramic wares of high quality. The Talavera ceramic from Puebla is an example of family traditions many generations old.

Jan 1, 1994

By E. E. Bauer

Oversize boulders in mines and quarries must be broken for waste disposal or further processing of ore. Early methods involved drilling and "shooting" or using a drop ball of sufficient weight to accomplish the purpose. The first "high-energy" hammers for breaking concrete or boulders were pneumatically operated. Blow energy was limited by valving and air pressure. However, smaller boulders of lower compressive strength could be broken. A hydraulic excavator-backhoe type machine was required for either a drop ball or hammer. Standard practice was to break oversize boulders in the pit before hauling to the grizzly or crusher. Generally, quarry boulders were not valuable enough for further processing. Quarry roads were lined with oversize boulders. As safety requirements were advanced, "drill and blast" for boulders was ruled out.

Jan 1, 1994

By J. Groff

The Getchell and Twin Creeks mines are located along a north-northeast trending structural zone in Humboldt county, Nevada approximately 40 miles northeast of the town of Winnemucca. Gold mineralization at the Getchell mine is represented principally by sulfide-rich ores, which contain significant amounts of realgar and\ orpiment, with the gold being recovered through processes which involve pressure oxidation. In contrast, oxide ores are currently being mined and processed at the Twin Creeks mine although large reserves of sulfide ores, some of which contain orpiment-realgar-stibnite, have been defined (Bloomstein et al., 1990). The Getchell and Twin Creeks mines represent major gold orebodies but very little has been published pertaining to mineral paragenesis and the characteristics of ore-forming fluids for these deposits.

Jan 1, 1994

By Brennan D. J

The trend worldwide is for increasingly stringent control of sulphur dioxide emissions to the environment. It is therefore likely that Australian industry will be placed under increased pressure to restrict such emissions, and this will have implications for Australian smelters of mineral sulphide ores. Traditional outlets for sulphur dioxide emissions have been in sulphuric acid manufacture, but Australian demand for sulphuric acid has declined markedly in recent years. This paper examines the balance of supply and demand for sulphur and related products in Australia, the shifts occurring in that balance and the underlying causes of those trends.

Jan 1, 1994

By P. Rusin

A new bacterium, Thiobacillus cuprinus, can extract copper from chalcopyrite as rapidly as T. ferrooxidans. On solution with and without nutrient amendments and bacterial growth media were supplemented with T. ferrooxidans or T. cuprinus in shake flask studies. Both species extracted -42% of the copper using growth media. In one case, T. cuprinus solubilized approximately twice as much copper as T. ferrooxidans utilizing a seeded On solution. Thiobacillus prosperus also oxidizes chalcopyrite and tolerates high chloride concentrations. These sulfide-oxidizing bacteria are representatives of the mixed microbial community found in sulfide dumps. Rates of biological copper extraction from sulfide ores, using the native microbes, have been significantly enhanced by amending On solution with PGM.

Jan 1, 1994

By C. L. Karr

The efficient management of the distribution of goods and services is important throughout the minerals industry. From the scheduling of processing plant operations, to the routing of work crews in mines, to the planning of product development, vast amounts of time, energy, and money are wasted due to poor planning and scheduling. Thus, the U.S. Bureau of Mines is investigating computational algorithms that can be used to minimize the economic losses related to scheduling and allocating resources. Although there is commercial software available for tackling many scheduling problems, there has been little relief provided for solving the difficult traveling salesman with time windows problem (TSTW). The TSTW problem is a "derivative" of the classic traveling salesman problem, and can be used to minimize the distance traveled by vehicles or personnel to visit all points on a tour, with the additional constraint that each point on the tour must be visited within a specified time window. This paper is a survey of published work in which genetic algorithms have been used to efficiently solve the traveling salesman problem and its more difficult derivative, the TSTW problem. A genetic algorithm is a search algorithm based on the mechanics of natural genetics, and has been used to solve a broad spectrum of engineering optimization problems. Results indicate that the versatility, searching power, and simplicity of genetic algorithms can be used to provide substantial improvement in the area of scheduling and resource allocation.

Jan 1, 1994

By Y. Xi, T. M. Yegulalp

An availability approach for determining the capacity of a major Bucket Wheel Excavator (BWE) system to be used in the Yuabaoshan Surface Coal Mine in China is presented in this paper. Based on previous studies on other BWE systems for delay times due to internal and external causes and a four-level maintenance and repair schedule, a model was developed, taking into account all random failures, to present a fast and simple solution to this highly complex problem. A procedure employing the Markov renewal theory for determination of the distribution of random failure times and failure rate of the whole system, as well as some other factors useful for calculation of the overall system capacity, are discussed.

Jan 1, 1994

Valuers will often intuitively express the probability that property value will exceed a certain amount . . . 'I think the chances that the value will exceed $50 million are excellent. The chances that they will exceed $80 million are poor'. This paper shows how it is possible to combine the uncertainties of the value of several key items to provide an estimate of the probability of a certain overall value being achieved. The valuation of a large copper/gold deposit was naturally influenced by uncertainties in the base assumptions of costs and metal prices. Potential acquisition of the property through share purchase raised the issue of what was a reasonable intrinsic value for the shares. Market considerations could be used to appropriately adjust the intrinsic value. After a range of possible metal prices and operating costs were determined, estimates were made of their probable distributions. By combining these probabilities in a random selection, a range of property values was calculated. Each value had its respective probability of occurrence. This allowed a most likely value of shares to be calculated. This paper demonstrates how the valuer's intuition is complemented by numerical analysis.

Jan 1, 1994

By Derek V. Ellis

A stepwise implementation of seven criteria for screening the physical, chemical and environmental suitability of submarine tailing disposal (STD) at coastal mines is presented. It is expected that similar criteria would be relevant to future deepwater mining. A reconnaissance level study of four preliminary criteria: mine location; coastal bathymetry; feasible outfall locations; and potential for chemical contamination can support or eliminate the prospects for STD. If supportive, detailed, and far more time-consuming hence costly surveys of: environmental background information including oceanography and waste discharge characteristics; projected impacts on other resource uses plus regulatory and community concerns will be essential for environmental protection and to secure the necessary approvals. This review of STD systems on which the proposed screening criteria were based was undertaken by a Cooperative Agreement of the U.S. Bureau of Mines, Alaska Field Operations Center with the University of British Columbia.

Jan 1, 1994

By Deepak Malhotra

Following a severe recession in the early 1980's, mining companies have taken significant steps to improve metallurgy and reduce operating costs. They do not view chemical reagents and the long-term relationship with reagent producers the same way they did two decades ago. This paper discusses the general perspective of changes that have taken place over the years, especially with respect to cost of production, selling price and environmental constraints. A cooperative program between the consumers and producers of chemical reagents is recommended to understand each other's problems and identify the present and future needs of the mining industry. This approach will be beneficial to the long-term survival of both parties.

Jan 1, 1994

By M. P. Hoffman

The U.S. Bureau of Mines is developing a roof bolter with a computer-controlled drill head that will increase the safety of roof bolting in underground coal mines by allowing miners to be relocated to a safe area. To ensure secure anchorage, acceleration and strain data are broadcast from an instrumented drill steel to a data acquisition system. These data are analyzed, correlated, and transformed to pro-vide information about roof strata, then are sent to a supervisory computer executing National Institute of Standards and Technology's real-time control software. The supervisory computer sends setpoint commands to proportional-integral-derivative control loops to control drill thrust, position, revolutions per minute, and torque.

Jan 1, 1994

By L. D. Smith

"The economic evaluation of a mineral project requires a great deal of diverse information to be brought together in one place. The greatest concern is that there will be an error by omission, so it is useful to have a detailed list of what one needs to know in order to make a thorough evaluation. The list that is presented below is intended to act as a checklist for the person who develops and reviews an evaluation, and as a shopping list for the persons gathering data at the project site.There are varying degrees of detail required at the different stages of evaluation in a project, from the ""quick and dirty"" overview, to the pre-feasibility study, to a full detailed feasibility study, to a due diligence review. This list addresses most of the economic variables in a project and can be used for all levels of studies. Its purpose is to identify a variable or issue and to raise a question, which the reviewer can then pursue in more detail using increasingly more comprehensive checklists for each topic. While developed from the point of view of a new project, this list is equally valid for an ongoing operation."

Jan 1, 1994

By S. J. Ristorcelli

Historically, geologic data has not been adequately considered in resource estimation. More recently, with the use of computers and sophisticated estimation algorithms and geostatistical justifications, geology has been downplayed further. Many reasons are given for not using geology including cost, time and irrelevance. None are valid. Boundaries defining mineral domains should be used in computer-generated resource estimates. Selected case histories show how the failure to honor geology has caused discrepancies in resource estimates of actual in-place resources. After-the-fact differences have included decreases in tonnage of up to 50% and increases up to 300%; partial to complete recategorization of material; and 50% decreases in grade. The costs of gathering and using geology are trivial compared to the potential consequences.

Jan 1, 1994

By N. A. Barcza

DC plasma-arc technology using a hollow graphite electrode (cathode) has been successfully implemented in the primary metallurgical industry in South Africa up to the 30 MW scale. Mintek has applied its expertise base, established over the past fifteen years, to testing the treatment of metallurgical wastes such as carbon- and stainless-steel plant dusts, lead- and zinc-containing slags, and residues from the base-metal industry. Favourable results have been achieved, and disposable products were produced. The evaluation of numerous wastes indicates that recovery of zinc as metal gives the best economic return from these sources. Direct recovery via a splash condenser or electrolytic zinc extraction from fume are the two preferred alternatives under review. In both instances dehalogenation is an important issue, but can be achieved by suitable treatment processes. The Enviroplas technology provides a flexible, commercially viable approach to the treatment of a wide variety of wastes. Mintek, together with its associate Pyromet CC, are installing a plasma- arc pilot-plant facility with both an ISP lead-splash condenser of about 5 t/d condensed zinc capacity and a combustion chamber to burn zinc vapour to zinc oxide. This will demonstrate the suitability of the Enviroplas technology for treating specific metallurgical wastes, so that customized industrial plants can be engineered based on large-scale testwork.

Jan 1, 1994

This report on the Venezuelan coal industry is the seventh in a series of studies on coal exporting countries requested by the House Appropriations Committee, The committee asked that the basic differences in mining costs for U.S, and foreign mines be identified, especially those costs incurred in complying with health, safety, and environmental regulations.1 Basic costs in extracting raw coal are analyzed in this report for surface operations, This report also provides a limited analysis of the relative market competitiveness of selected Venezuelan and U,S. steam coal mines in three electric utility markets: New England and the east coast of Florida in the United States, and western Europe. Although some Venezuelan coal has coking characteristics, all coal-producing regions of Venezuela sell coal in steam markets.

Jan 1, 1994

By I. Gaballah

The chalcopyrite ore's anodic and cathodic electrodissolution are studied using a Porous Pulsed Percolated Electrode (3PE) reactor. Stationary solid electrode experiments are also performed to explore the mechanism of electrochemical dissolution of chalcopyrite. Experiments with a low - grade natural ore have been carried out at 25 "C in solutions containing 1 M NaCl and 1 M HCl. Galvanostatic and potentiostatic conditions are employed. The influences of current and potential on selectivity of the chalcopyrite ore dissolution are assessed. Anodic oxidation of this ore leads to a preferential dissolution of iron bearing minerals, whereas cathodic reduction is more selective with respect to chalcopyrite. However, in both cases the electrochemical dissolution is incomplete and the current efficiency is low. Design of the actual reactor has to be modified to increase the bed conductivity and to allow continuous experimentations.

Jan 1, 1994