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By Harold L. Lovell

Problems associated with fines (minus 6 mm, 1/4-inch) production, preparation, and utilization have long plagued the coal industry and are now more acute than ever. Continuous deep mining systems create more fines which have moisture; content greater than natural levels from dust control spraying and often add substantial levels of mineral matter due to mining selectivity constraints. Frequently, during preparation, more -fines are developed to achieve improved component liberation. Coal consumers often specify small sizes whether for carbonization, combustion, or conversion. Wet beneficiation systems process fines by several' types of unit operations, but usually must also incorporate costly and complex dewatering systems to reduce the moisture content of the products. Existing pneumatic preparation systems are constrained between product equality and yield by the sharpness of separation. These limitations become more severe with decreasing particle size and increasing feed moisture content. Control of particulate emissions, both process and fugitive, during pneumatic preparation, can be forbidding. A pneumatic preparation-process which would overcome these constraints, could be most enticing. The DryFlo system is being evaluated to quantify performance characteristics as regards these constraints.

Jan 1, 1976

Tables

Jan 1, 1973

By Sergey G. Pushkin, Eugeny L. Schastlivtsev, Anatoly A. Bykov

Three years ago the authors and a group of assistants began to develop a GIs-system for integration of comprehensive eco- logical information to be linked to geographical maps of Kuzbass region. And now we have got the working system and some first results that the present paper deals with.

Jan 1, 1996

By K. Papke

Nine western states contain significant barite deposits, but most deposits are in Nevada, which has been the principal western producer for more than three decades. Nevada produces about 85% of the total United States production, but about one-half of the barite consumed in the country is imported. Approximately 95% of the barite is used in drilling muds. Sharply decreased oil and gas drilling, starting in early 1982, severely depressed the domestic barite industry. Other problems for western barite include long distances to the areas of major drilling, high railroad-freight rates, and increased barite imports. Bedded deposits, formed by submarine exhalative processes, account for almost all western production, and reserves are large.

Jan 1, 1983

By L. Frost

The establishment of a retreat system of longwall mining in this submarine coal field has been under study for many years and, although in special cases there have been limited local applications of this method of mining, there has been no attempt until quite recently to establish a uniform system of longwall retreating' in this area (see Figure 1) Where retreat walls were established, it was strictly as a result of physical, rather than economic conditions. In some of the operations- of the Corporation, where the coal was liable to spontaneous combustion- or the area subject to bumps as in No. 2 Mine of the Cumberland Railway and Coal Company in Springhills the recovery of the coal on a retreat system was more or less a necessity.

Jan 1, 1964

By Mark Springett

The problems inherent in sampling low- grade deposits have long been recognized. As economic grades become lower with increasing metals prices and improvements in recovery technology then the previously difficult sampling problem has consequently become even more demanding. The breakdown of the sample process and error is illustrated by describing in the remainder of the paper some sampling practices that have been utilized on mining and exploration properties and by describing some problems that have been encountered, providing a series of cautionary tales to those involved in any aspect of mine or exploration sampling.

Jan 1, 1983

By Hubert Erik Sherer

Determination of the best time to replace an aging unit of equipment is a recurring problem which is common to essentially all surface and underground mining operations. Virtually all mining equipment is subject to wear and the resulting deterioration that increases with equipment life. This mechanical deterioration results in lower availability and, thus, decreasing, production. Due to decreasing production and increasing repair costs, there is an optimum age at which the replacement of a given equipment unit with a new unit will result in the lowest cost per unit of production for the equipment operation in question (Figure 1). Determination of this optimum replacement age is further complicated by factors such as: possible overhaul alternatives, fleet replacement and expansion alternatives, remaining life of the mine, and technological improvements in the potential replacement or differences in the production capacities of these replacements. Determination of the optimum time to replace an equipment unit becomes more critical each successive year due to the rising capital costs of new equipment versus maintaining old equipment. An incorrect choice of the replacement age for an equipment unit can result in excessive costs to the mining operation. If a unit is replaced too early, the capital cost of the unit is not fully utilized; conversely, replacing a unit too late results in excessive maintenance costs and low production. The economic life of a piece of equipment is the equipment age that results in the lowest total discounted cost per unit of production for that piece of equipment, not considering the cost of future replacements. The economic life of a piece of equipment is usually shorter than the physical life, the maximum age at which a machine is capable of doing useful work. The optimum replacement age for a piece of mining equipment may vary from the economic life of that equipment due to the remaining life of the mine, fleet considerations, costs associated with potential replacement machines, and capital rationing constraints. For example, the equipment life of the current machine that may result in the lowest cost per unit of production might be 10 years; however, when the timing of the future replacement costs are entered into the calculation, a different life for the current machine might result in the lowest total cost per unit produced for the remaining life of the mine.

Jan 1, 1982

By Robert H. Hooff

The Vor-Siv Dewatering and Classifying Unit was developed by the Polish Coal Industry because of a need for a unit that would dewater and classify high volumes of solids in water slurry. To be practical, the unit needed to be relatively small in size, simple in design, involve low operating costs, and be able to give a dewatered product of less than 30% moisture. The answer to the above mentioned criteria was the Vortex Dewatering Sieve or, as we refer to it, the Vor-Siv. The original installation of the unit, as we know it today, began in 1963 when the Pols installed the unit in a full scale pilot application. By 1966, at least 30 of these units were installed throughout the Polish Coal Industry. This equipment was originally introduced in the United States in 1966 at the Fifth International Coal Preparation Meeting in Pittsburgh, Pennsylvania. The first installation in the United States was not achieved until 1970, when Mr. Fred Sachs of The Valley Camp Coal Company, Triadelphia, West Virginia, installed a Vor-Siv in a retrofit application. To date, there are 36 Vor-Sivs installed in this country and 29 in the process of being installed or delivered.

Jan 1, 1976

By T. Hollenberg, N. Nolten

The mining industry is one of the major energy consumers in Namibia. Energy costs increase the operating costs of Namibian mines, in particular, the processing plants, and result in an overall increase of production costs. A substantial part of the energy used is directly imported from South Africa. The cost of energy has been increasing rapidly in the past few years and will most likely continue to do so in the future. In 2015, the average wholesale price for energy from national power utility NamPower was US$87/MWh after rising more than 12 percent annually in the two previous years. At peak times, which are early in the morning and late in the evening, imported-energy prices are extremely high and have to be factored into the electricity tariffs. This problem is expected to intensify due to a projected 4 percent annual increase in energy demand. A major target of the Namibian mines, therefore, is to consider possible ways to address energy-saving challenges and to investigate possibilities for the mines to generate electricity internally during peak times. This is in alignment with the mines’ strategic plans and objectives to reduce total energy consumption and costs from both national and foreign electricity suppliers. In this paper, we explore addressing some of the key energy consumption and optimization challenges through process energy reuse and solar energy production to decrease demand for imported energy through a case study carried out in cooperation with Skorpion Zinc Mine and Refinery.

Jan 1, 2018

By Michael J. Hannan, Thomas F. Torries

The nature of industry structure is examined and the structure of the aluminum, copper, lead and zinc industries are described by the use of factor analysis. Capacity is defined and the relationship between industry structure and capacity utilization is examined. It is demonstrated that excess capacity is possible in industries with competitive or monopolistic characteristics, but the effects of the overcapacity are vastly different in the two cases. In a competitive industry, cycles of overcapacity with attendant fluctuating prices are expected. A change in industry structure from monopolistic to competitive characteristics over time causes profits and economic rents to be transferred from the producer to consumers of the mineral.

Jan 1, 1989

By Frank G. Horino, V. E. Hooker

INTRODUCTION The determination and use of mechanical properties of rock in engineering and rock mechanics are rapidly developing. Many of these properties are determined on intact rock specimens; thus, their application and repre¬sentation of rock mass properties may be limited. How¬ever, relative information often provides useful guidance in the solution to mine design and stability problems. Summarized in this chapter are some of the stan¬dardized techniques and procedures currently used to obtain these mechanical properties. Typical applications of the use of these properties are also presented. Stan¬dardized techniques include those advanced by the American Society of Testing and Materials (ASTM), International Society of Rock Mechanics (ISRM), US Bureau of Mines (USBM), Canadian Dept. of Mines and Technical Surveys, South African Institute of Min¬ing and Metallurgy, and other individual investigators. Information on the mechanical properties of rock and the behavior of the rock under a given system of stresses represents a necessary part of the information for rational engineering design for any given mining op¬eration. The mining method, the type and extent of sup¬port, the extraction ratio, the overall dimensions of the mine, and the orientation of the rooms and pillars are all decisions that are influenced by the mechanical prop¬erties of the ore, roof, and floor material under various stress systems and the magnitude and direction of the in situ stresses (Hooker, Bickel, and Aggson, 1972). Initial mechanical property information regarding a structure or mine property is generally obtained by two basic techniques: (1) static and dynamic property tests are conducted on intact and fractured rock specimens of exploratory drill core, and (2) dynamic properties are obtained by borehole logging techniques. When mining access becomes available, and as the mining horizon is expanded, additional information can be ob¬tained to verify preliminary mine design values. This chapter presents some of the standardized tech¬niques and equipment currently used in obtaining me¬chanical property data in the laboratory. The properties considered are: (1) uniaxial compressive strength of intact rock core specimens, (2) uniaxial compressive strength of rock cores containing planes of weakness, (3) triaxial compressive strength of intact rock core specimens, (4) triaxial compressive strength of cores with a plane of weakness, (5) Young's modulus, (6) Poisson's ratio, (7) density or apparent specific gravity, (8) modulus of rupture, (9) indirect tensile strength, and (10) creep characteristics. Where possible, an at¬tempt will be made to evaluate each property measure¬ment in relation to the problems of rock mechanics and application of results. TEST SPECIMENS The selection and care of drill core for laboratory testing require some consideration. It is recognized that laboratory-determined properties are not necessarily rep¬resentative of an in situ rock mass property. However, relative information between beds or zones of interest is still valuable information in selecting mining horizons and preliminary design criteria. To provide statistical data the number of drill core samples selected to repre¬sent each of the areas of interest should be from a mini¬mum of three to a maximum of ten test specimens. A judgment must also be made on site as to whether the recovered drill core should be wrapped and sealed in plastic to preserve moisture. On the one hand investiga¬tions of air-dried and saturated specimens have shown that moisture significantly affects the elastic properties and strengths of many rock materials (Obert, Windes, and Duvall, 1946; Colback and Wiid, 1965); on the other hand it is apparent that most core drilling is done with water which may saturate the specimen to a greater extent than in the in-situ condition. Whether or not the decision is made to retain the moisture, the core should be delivered to the laboratory as soon as possible after recovery for subsequent specimen preparation and testing. Specifications Shape: The shape of the specimens influences lab¬oratory testing in two ways: (1) time and cost of sam¬ple preparation and (2) strength of the material. Cy¬lindrical specimens of drill core are by far the least time-consuming to prepare for static or dynamic labora¬tory testing. In addition, the cylindrical shape lends it¬self to a more uniform stress distribution throughout the sample than other shapes, such as rectangles and hexa¬gons. The compressive strengths of various shapes have been studied (Grosvenor, 1963, and Price, 1960), and results indicate that the cylindrical specimens usually provide the highest strength for a given height-diameter ratio. However, reduction in strength from a cylindrical shape to a rectangular in situ pillar is not regarded as significant in relation to other considerations such as planes of weakness in a pillar or safety factors in the design process. Length-Diameter Ratio: The length-to-diameter ra¬tio, LID, has a significant effect on the compressive strength. Various recommendations have been made to use standard LID ratios ranging from 2 to 2.5 to 3 (ASTM, 1975c; ISRM, 1972). However, past work by others such as Obert, Windes, and Duvall (1946) has shown that excellent results can be obtained using LID ratios from 2 > (LID) > >/s. In selecting an LID ratio for testing, one should keep in mind the amount of material available for testing. In many instances, this may be limited. Thus, a shorter specimen such as 1: 1 LID may be necessary to provide enough test data for statistical analysis of results. Sec¬ond, it may be desirable to obtain elastic constants dur¬ing the test. This generally requires instrumentation such as linear variable differential transformers (LVDTs) or strain gages near the center of the specimen. In this case, an LID of 2.5 or 3 is desirable so that the instru

Jan 1, 1982

By R. L. Wiegel

Several mineral process modeling and simulation packages are currently available for use in evaluating the performance of alternative process flow schemes. A critical link that has been missing from these packages is the ability to quantitatively model the effect of size reduction on the liberation of the valuable and waste minerals in the ore being processed. Although there have been several approaches taken to this problem over the past 25 years, none of them has led to a satisfactory conclusion. A technique was developed for measuring the effective liberation characteristics of magnetic taconite ores, and a program was constructed that makes use of these liberation characteristics in simultaneously simulating both size reduction and mineral liberation as it occurs in tumbling mills. This is an especially important step in the modeling of magnetic taconite processes, where magnetic rejection of low-grade wastes between grinding stages mandates that a predictive capability be available. The current application is specific to magnetic taconite, but it is possible that a similar approach could be used for other types of mineral systems. Key words: Modeling and simulation, Size reduction, Mineral liberation, Taconite, Magnetic concentrator

Jan 1, 2003

By Violetta Pavlova

Knowledge of geometrical properties of blocks in a hard jointed rock among other things is of considerable importance for prediction of rock mass behavior and for its exploitation. This paper presents a new approach to obtain the information about percentage of blocks with desirable geometrical properties in a jointed rock mass extending through a large region of interest. A model of a rock mass separated by finite number of systems of parallel plane discontinuities which form discrete blocks is discussed. A computational procedure has been derived to analyze the volume and shape distribution of blocks in the rock mass.

Jan 1, 1992

By Evans U. Jegbefume

A plane strain two-dimensional finite element model employing the method of negative reaction loading has been used to model roof collapse and subsidence resulting from the underground gasification of coal in regions of soft overburden such as that found in Texas. The model included dry zones of rock around the cavity. Roof collapse was included by considering the final state of stress in the elements and removing those that had undergone tensile failure. The two-dimensional plane strain model was extended to include thermal loading and thermal softening of the roof rock. Roof collapse initiation and growth of the cavity were modelled by examining the portion of the rock immediately above the cavity under thermal and hydrostatic load. The model was extended to include linear creep using the method of incremental strains. The overburden was modelled as a generalized Kelvin material.

Jan 1, 1982

By F. A. Kruse, R. J. Madrid, P. L. Hauff

Sub-microscopic gold grains in disseminated gold deposits in Nevada are often directly associated with the clay mineral illite. Delineation of gold ore-zones can be improved by accurate characterization of the associated illite varieties or polytypes. X-ray diffraction studies of clay minerals from several disseminated gold deposits demonstrate that illite polytypes reflect lateral and vertical zonation around the ore bodies. Polytypes act as geothermometers indicating temperatures of ore deposition and proximity to hypogene and supergene fluids. Visible/near infrared spectral measurements using a field-portable reflectance spectrometer provide a reconnaissance technique for mapping the in-situ distribution of illites. Changes in the visible/near-infrared reflectance spectra are observed as illites progress from the lower temperature, less ordered 1 M variety to the higher temperature 2M type. The combination of the reflectance spectroscopy with the X- ray diffraction data creates a powerful tool for detailed mineralogic mapping for gold exploration.

Jan 1, 1989

By H. B. Comstock

This paper reviews the trends in supply and consumption of the principal magnesium compounds in the United States in relation to domestic requirements and world resources. The data are confined to these principal magnesium compounds: Magnesium chloride, magnesium hydroxide, precipitated magnesium carbonate, and magnesium oxide (commonly referred to as magnesia). The properties and uses of magnesium compounds are shown in various chapters of' the 2nd edition of Industrial Minerals end Rocks. 3/ The third edition of this reference is in preparation. A more recent description of properties, uses and sources of magnesium compounds appears in a Bureau of Mines publication.4/ The American Iron and Steel Institute and the Refractories Institute have published comprehensive data on the properties and uses of basic refractories. Many magnesium compounds are prepared by the producers to meet specifications set by individual consumers.

Jan 1, 1960

By K. R. Weller, U. J. Sterns, P. S. B. Stewart

Complex sulphide ores usually require very fine grinding of the whole ore stream to achieve adequate liberation. Recent improvements to DSM screens have made this device appear competitive with cyclones in circuits treating these ores. A DSM screen and cyclones were tested in pilot-scale grinding of a copper, lead, zinc ore and the resultant data were used to establish a multi-component simulation model. The model was used to assess the influences of mill environment, circuit flows and pulp densities, final product properties (size, relative size and SG of the values, and liberation characteristics) and a second grinding circuit on capacity and product size distributions, and hence define conditions for which one device is better than the other.

Jan 1, 1992

By Jr. Stokowski

Topsoil for revegetation projects is in demand in many urban areas. In this case history, a large aggregate producer manufactured a topsoil from three waste materials. The topsoil was produced in a 200,000 m2 (50-acre) abandoned gravel pit that still had additional gravel under 10 m (30 ft) of overburden uneconomic to strip directly. The topsoil was produced by rotary mixing of sludge, overburden, and a lime admixture; solar drying; and stripping and stockpiling of the product. A major problem was an increase of topsoil drying times for stripping from 40 to over 100 hours when it was rewet by storms. The problem was solved by a research project that evaluated over 50 formulations and over 20 waste materials. . The final formula dried in 15 hours and contained 3-parts sandy mine spoil, 1-part sewage sludge, and 2 % spent-bed, a granular quick-lime produced during power-plant flue-gas desulfurization.

Jan 1, 1988

By David T. Kao

The energy situation the world faced during the decade of the Seventies resulted in actions throughout the free world to reduce its dependence on OPEC oil. Many nations heeded the indicators early in that decade and commenced efforts to reduce their oil requirements. Those nations which did not heed these warnings had the message brought to them more emphatically in the last portion of the decade with the further rapid and continuing rise in prices of OPEC oil. Furthermore, the demonstrated unstable nature of large oil-producing countries has made it clear to all free world nations that their energy demands of the future must be provided for by some more stable and assured supply. Now, early in the decade of the Eighties, we see the need for expanded use of coal as an energy supply to be essential. The result in 1980 and 1981 has been a great increase in demand for steam coal worldwide. In essence, a new business for the United States has developed in steam coal export. In the United States, the large growth in foreign demand for our steam coal is now well recognized and documented. A major impediment in meeting this growing demand became abundantly clear in 1980. This impediment is the congestion existing at U.S. coal export ports. With the recognition of this constraint, a plethora of activity has been observed in announcements for alleviating the problem by improving and expanding current export port facilities. In addition to improvement and expansion, an abundance of totally new facilities has been announced in an effort to find ways to meet this large demand in the new business of steam coal export. This is needed; and hopefully, many of these plans will be translated into action. While total implementation of all stated plans is not expected, much of the implementation depends upon large- scale dredging, large waterside ground storage sites, and improved handling equipments in the conventional type of export ports. The time and capital required for implementation is great, and environmental problems associated with dredging are substantial. Host significantly, and unfortunately, implementation that does include dredging our ports will still not permit use of the truly large colliers of 140,000 DWT and greater, which are evolving as the "state of the art" in long-distance sea transport.

Jan 1, 1981

By Ralf Winterberg, Axel G. Nitschke

"Macro synthetic fiber reinforced concrete or shotcrete is seen by many design engineers as offering a viable alternative to steel reinforcement in tunnel linings. The technology is now commonplace for primary and permanent ground support in both mining and civil tunnel applications. It has for instance become the standard form of reinforcement in the Australian mining industry, and has been used for a majority of permanent tunnel linings in recent tunnel construction in Norway. Similarly, macro synthetic fibers are becoming a standard solution for the initial lining in the USA.The use of macro synthetic fiber offers innovative solutions, yielding robust and sustainable tunnel lining designs. Citing recent research and actual projects, this paper presents state-of-the-art design considerations for fiber reinforced tunnel linings relating to structural and long-term performance. Topics include seismic resistance, crack width control, corrosion and durability, as well as sustainment of performance with age.INTRODUCTIONMacro synthetic fiber reinforced concrete (MSFRC) and shotcrete (MSFRS) has reached maturity as an engineered material and is widely used in all forms of tunnel linings, for temporary as well as permanent ground support in both, mining and civil tunnel applications. In the Australian underground mining industry, it became the standard form of reinforcement, where 2014 literally marked the end of steel fiber use in shotcrete [1], and has been used for over 80 percent of permanent tunnel linings in recent tunnel construction in Norway. Similarly, macro synthetic fibers are becoming a standard solution for tunnel initial linings in the USA. Recent examples in civil tunneling are the Devil’s Slide Tunnel and Caldecott Fourth Bore Tunnel in California or the Anacostia River Tunnel Intershaft Connector Tunnel in Washington D.C. In addition, an increasing number of tunnels are adopting shotcrete permanent linings using macro synthetic fibers. Examples include the A3 Hindhead tunnel near Guildford in the UK and the North Strathfield Rail Underpass in Sydney, Australia [2, 3]."

Jan 1, 2016