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By L. G. Austin

Using an instrumented laboratory high-pressure grinding rolls mill, the grinding force, gap dimension, mass flow rate and net mill power were measured for six coals and a crystalline quartz. A technique was developed to estimate the compressive stress-strain curves for compression of the materials in the mill plus the effects of elastic decompression. To reconcile the mill power and grinding pressure results, it was necessary to allow for the energy recovery on decompression. No clear correlation was obtained between the form of the stress-strain curves or the variation of specific mill power factor with the Hardgrove grindability index (HGI), although coals with the lowest and highest HGIs (i.e., 44 and 106) gave results significantly different from the other coals. Feeds below 140 mesh (105 µm) flowed more rapidly than coarser feeds and would not build up high grinding pressures. This indicated shearing and fluidlike properties rather than compression as a locked bed.

Jan 1, 1998

By S. Jennings

The Red Dog massive sulfide deposit is located in the western Brooks Range of Alaska 100 miles north of the village of Kotzebue. It contains the largest zinc reserve in the world. Reserves were doubled in 1995 with the discovery of the Aqqaluk deposit and significantly increased in 1996, with the discovery of a deep zone of mineralization to the north. At present the global reserve and resource is 143 million tonnes of 16.1 % zinc and 4.3% lead. Red Dog is a silica + sulfide synsedimentary replacement deposit hosted in barite and black shale of the Mississippian Kuna Formation. Red Dog was thrust northward during the late Mesozoic Brookian orogeny. Understanding the setting of the deposit at the time of formation and its subsequent deformation history is critical to current exploration efforts and to future discoveries in the district.

Jan 1, 1998

By K. J. Bruxvoort

Background ground water quality is often used to drive remediation programs at sites with waters affected by mining activities. In the past these levels were sometimes chosen without rigorous statistical and geochemical analysis. A probability distribution approach was used at the Sweetwater Uranium Project to separate a large set of geochemical data into populations that represent contributions from different sources. Natural background populations were identified for major ions, metals, and radionuclides, and were submitted to the Nuclear Regulatory Commission to modify the extent of a Corrective Action Program and to establish control limits for future monitoring.

Jan 1, 1998

By D. Edward, C. Clarkson, B. A. Firth

The presence of misplaced ultrafine particles decreases the separation efficiency of unit operations used in coal preparation. Although the classification of fine coal was considered to be adequate for the needs of the coal industry during the 1970s and 1980s, it is apparent that further improvements in the yield/ash/moisture relationship achieved by coal preparation plants will require increased efficiency in this size-separation step. This paper describes the capability of current and developing techniques to address the problems that need to be overcome.

Jan 1, 1998

By R. H. Lambeth

Disposal of mine tailings in "waters of the United States" is presently prohibited even though case studies indicate that the practice may be environmentally viable. To simulate disposal in the natural environment, nine containers of tailings and sediment were instrumented and placed on the ocean floor near Juneau, AK as were ninety-six biosample containers. Pore water concentrations of five metals were determined, and biota populations were characterized for both materials. After 500 days of exposure there were no statistical macro scale differences between tailings and sediment biota populations or Cu, Pb, and Zn pore water concentrations. Tailings released slightly more Fe than sediment, but sediment released significantly more Mn than tailings. Disposal of mine tailings in marine waters may be environmentally safe.

Jan 1, 1998

By Hector M. Valenzuela, Juan H. Rojas

This paper presents a strategic plan for automation, plant integration and process management being implemented at the Chuquicamata mining and metallurgical complex of Codelco-Chile. This five-year plan considers different levels of process control and plant integration, which include instrumentation and direct control, process models and supervisory control, plant information integration, and real time process and plant wide management. The conceptual solution developed defines an architecture for the overall system and the projects to be implemented by each production unit, as part of the proposed solution for the division wide process control, plant integration and real time process management. An estimate of the cost benefit relation of the plan is also given.

Jan 1, 1998

By Spencer R. Titley

"For his pioneering contributions to the understanding of the geology of porphyry copper systems" Recipient Of The 1997 D. C. Jackling Award SPENCER R. TITLEY Introduction The subject of this lecture, a late century perspective on porphyry copper geology, is one of current interest and importance as the search for these ores remains intense. It is presented in the belief that an appreciation of our present understanding of the subject requires it to be viewed historically, thus providing a basis for evaluating appropriate directions for continued study. At the outset, it is important to note that the technology of mining and extractive metallurgy has developed ore from these low grade orebodies, starting with D. C. Jackling, and has continued to create them as copper grade and price have diminished. But the continued search for them is a geological problem that responds to growing expectations of people and societies; exploration based upon ever increasing knowledge of the habits of the ores has been very successful. This is the story of evolution of geological thought and practice in porphyry ore search across an interval of time beginning with the bulk mining of "low grade" copper ores at Bingham and ending with late Century concepts. "How did we get here?" The lecture concerns the ideas of many different people. The ideas and events discussed reflect a bias on North American thought, where the great low grade orebodies were first recognized as such and where many of the basic geological ideas were developed. A very great number of geologists have contributed to this understanding. In no sense is it meant to minimize the contributions to the story that have evolved in the study and mining of ores of the Andes, whose development and expansion has been nearly synchronous with that in North America - nor to minimized comparable contributions made in the late century from studies of the newer discoveries of deposits in other regions, especially the southwestern Pacific regions. In expansion of this topic, I have found that many important concepts are marked by appropriate publication but some are not, or I have not been able to discover documentation. Many notions appear to have become conventional knowledge without publication, mostly being geological viewpoints developed synchronously from similar observation. Thus, apologies are extended in advance to those whose work I have might have missed and to those unknown to me whose unpublished ideas may have seeped into the pool of common knowledge without appropriate recognition. The analysis here addresses events of two time segments, an older one extending from the developments at Bingham in the early 1900s through the Second World War, ending about 1950: the second period extends from that time to the present. This separation is seen in Figure 1, which traces numbers of publications through the period as extracted from some 700 publications, again with a North American bias, from an annotated bibliography of porphyry copper geology in preparation. During the early period, exploration was "immature" in North America, that is, geologists looked for new districts and sites of the deposits. Outcrops were sought that carried the signatures of former mineralization and regional controls related to structural geology were closely studied. In the later period, North American exploration had "matured" into a study of districts, rather than a search for them. As the studies of these ores intensified during the younger period concommitant with increasing demands for the metal, they did so with a broadened understanding of some habits of occurrence, of hydrothermal alteration, mineral zoning, petrology, and geochemical and geophysical signatures. Outside of North America, search remained "immature" but closely related to the

Jan 1, 1998

By L. R. Freitas, A. K. Resende, J. A. Oliveria, K. L. Gonçalves, L. F. D’Assumpção, L. R. Lage, J. D. Neto, F. Viveiros

Pará Pigmentos S.A. (PPSA) is an association between the Brazilian companies CVRD and CADAM, Mitsubishi Corporation of Japan, and the IFC (World Bank) created in 1992 in order to recover kaolin from Rio Capim deposit, northern Brazil. Commercial production at PPSA started in August 1996 using a process comprising mining and beneficiation at the mine site, pumping through a pipeline and drying/loading at the port site on the Amazon river estuary. Presently, all PPSA production is concentrated on 82% <2um, high-brightness coating clay shipped in bulk. In this paper, a detailed description of the development of PPSA beneficiation process is presented. The results of laboratory and pilot plant studies under- taken to develop alternative grades of clay, such as delaminated and calcined kaolins, are also discussed.

Jan 1, 1998

By Jan M. Mutmansky, Y. J. Wang

In the mathematical analysis of electrical networks, the electrical devices are often modeled using idealized network elements such as current sources, voltage sources and resistors. An analogous approach is outlined for the modeling of mine ventilation networks, which can be considered nonlinear resistive networks. The proposed modeling technique uses the following five basic (nonreducible) elements: H, Q, D, R and N. These elements are characterized by their pressure gain or loss, their air quantity and their pressure-vs.-quantity relationships, each of which may be known or unknown. In addition to the definition of the basic elements, the necessary conditions for which there exists a unique solution are discussed. This is performed using theoretical developments derived from electrical circuit theory and illustrated in example networks. The proposed procedures are useful in the solution and characterization of mine-ventilation networks.

Jan 1, 1998

By W. J. Schlitt

Introduction A major uncertainty in assessing the potential for heap-and dump-leach projects is how to determine the extraction-rate curve for the recovery of the mineral values from coarse ore. Such material could either be run-of-mine (ROM) or primary crushed ore. The problem with field testing coarse ore, especially for new projects, is the large scale and extended leach times needed to accurately determine the final extraction-rate curve. At least 5 x 103 to 5 x 104 t of representative ROM ore are typically required for a copper test heap, and much more is often used. Kennecott, for example, recently constructed a 0.9 Mt (1 million st) ROM test heap at the Bingham Canyon Mine in Utah. In such coarse ore operations, the ultimate level of extraction will require a leach cycle that can extend from several months to a few years. Quite often, project development schedules do not provide the luxury of mining such large quantities of material or running such long tests. Instead, test data are usually limited to results from column leach studies on relatively fine ore, often with a top size that does not exceed 25 mm. Maximum leach times are also short, typically less than a year before an initial decision is needed on project viability. Proposed method One approach to estimating the recovery from a coarse ore leach is to assume that the leach solution will have some ultimate penetration distance into the rock. Then, the final level of mineral extraction in this "leached rim" will equal the ultimate level of extraction identified in various testing programs. Obviously, if the radius of a given rock fragment is less than the penetration distance, that fragment will be fully leached at the end of the operation. With larger rock sizes, the percent recovery will fall off as the size increases and the fraction of unpenetrated rock mass increases. Such an approach sounds simple but is likely to be complex when applied to a real project. For example, the penetration distance will be a function of both the rock characteristics and the effective length of the leach cycle. The important rock characteristics include rock porosity, the degree of internal fracturing and the mode of mineral occurrence. With regard to the latter, penetration is likely to be greater if the leachable mineralization occurs on fracture surfaces or in veinlets, as opposed to fine grains uniformly disseminated throughout the rock mass. An estimate of penetration distance may be derived from column or heap tests by noting the depth of solution penetration into the larger rock fragments after three, six and 12 months of leaching. While the penetration rate is ore specific, something on the order of 10 to 20 mm/y may be appropriate for competent, primary copper (chalcopyrite) ore. For gold in tight quartz, the rate may be about the same. Copper oxide ores and gold that is hosted in a more porous rock matrix are likely to have penetration rates that are at least two to three times higher, and an even higher rate should be appropriate for uranium hosted in sandstone. As noted above, the length of the effective leach cycle is likely to be measured in years. On this basis, the ultimate penetration distance (dp) would vary from less than 50 to several 100 mm when a particular ore is leached to exhaustion. Several sets of mathematical manipulations are necessary to convert a rock size distribution and corresponding value of dp into an estimated extraction-rate curve. The first step is to break the ROM size distribution down into intervals and then calculate the radius for the mean rock size in each interval. This is shown in Table 1 for rock sizes up to 1.75 m (about 6 ft) in diameter. The next step is to calculate the volume of unleached core and the fraction of rock that is leached. This is done for the following three values of dp: 25, 100 and 250 mm. Results are shown in Table 2. The third step is to select the ultimate level of recovery that will be achieved in the fraction of material that is effectively leached, i.e., the outer zone that is penetrated by the leach solution. This is clearly a site-specific factor that can only come from metallurgical test results on representative ore

Jan 1, 1998

By Y. M. Jiang, D. W. Park

Longwall faces can move at high advancing rates, but many geological variations can cause unexpected instabilities and production losses. The rapid movement makes it necessary to evaluate different geologic conditions in the rock mass as fast as possible to assess their effects on the longwall face and shields. It is believed that prompt awareness of geologic conditions is the key to preventing instability at a longwall face. This paper introduces the application of fuzzy set theory for characterizing and evaluating roof conditions. Real-time monitored data coupled with fuzzy set analysis provides valuable information, such as shield leg pressure, developing load on shields, intervals of periodic weighting and the ratio of developing loads during periodic to normal times.

Jan 1, 1998

By T. E. Wilson

An exploration bore core sample of coal ought to be reduced from its original cylindrical form to a particle size distribution and particle composition that reflects, insofar as possible, a process stream of? raw? coal it represents. Often, coal cores are reduced with a laboratory crushing machine, the product of which may not match the raw coal size distribution or size fraction composition. This study employs drop-shatter impact breakage followed by dry batch tumbling in a steel cylinder rotated about its transverse axis in order to characterize the core material in terms of first-order and zeroth-order breakage rate constants. These are indices of the propensity of the coal to degrade during excavation and handling. Initial drop-shatter and dry tumbling tests were done with synthetic cores, to reduce material variables and . conserve difficult-to-obtain coal cores.? Cores of three different coal beds --Illinois No.6, Upper Freeport, and Pocahontas No. 5 -were subjected to drop-shatter and dry batch tumbling tests to determine breakage response. Comparison of coal preparation plant feed with a crushed bore core and a bore core prepared by drop-shatter and tumbling (all from the same Illinois No.6 coal mining property) indicated that the size distribution and size fraction composition of the drop-shattered/tumbled core more closely resembled the plant feed than the crushed core.

Jan 1, 1998

By V. J. Matta, A. A. Pincheira, I. A. Reghezza, Ch. J. Vergara

The growth of solvent extraction in Chile has been astonishing during the last years and has been established as a very successful technology. However, there are still limitations that must be improved, mainly, the problem of carry over from one phase to the other and the losses of organic reagent associated with the crud formation. These are problems that our company has been taking care, solving them with high efficiency and low costs, allowing important increases in the copper output of our plants and capital savings by means of the optimization of the use of nonproductive units in the SX plants.

Jan 1, 1998

By F. F. Peng, D. C. Yang, G. Yanief, E. H. Cho

This study deals with carrier flotation of cerium dioxide, a surrogate of plutonium oxide, which is the major contaminant at the Nevada Test Site (NTS). The objective of this study was to determine the feasibility of using carrier flotation for remediation of the site. In this study, a - 200-mesh fraction of pure cerium dioxide was used. Oleic acid was used as the collector, while calcium carbonate was used as the carrier. Mechanical-cell tests were conducted to float the surrogate from a mixture containing uncontaminated NTS soil, both in the absence and presence of the carrier. It was found that the addition of the carrier drastically enhanced the flotation recovery of cerium dioxide. The flotation recovery of the surrogate increased from 34% to 65% by adding only 0.5% calcium carbonate (-150 mesh). The recovery further increased to 95% by adding 10% calcium carbonate. The flotation method utilizing a carrier of calcium carbonate seems to have a high potential for the remediation of the soil contaminated with radionuclides at the NTS.

Jan 1, 1998

By S. Mafi

The Broken Aro project is associated with a 1910 abandoned underground mine complex that has been discharging aeid mine drainage from entries, seeps and springs. The Ohio Department of Natural Resources(ODNR), R&F Coal Company (R&F) and American Electric Power (AEP) are involved with this unique project that will remine the abandoned underground complex and install a mine seal constructed of fixated flue gas desulfurization (FGD) material. The goal of the project is to eliminate or reduce the acid mine drainage that is discharging into the watershed. This paper discusses remining, installation of the FGD mine seal, government financed reclamation projects and future application to active and abandoned mining sites.

Jan 1, 1998

By S. C. Tadolini

The use of resin-grouted cable supports to control large ground movements in several types of underground mines has increased substantially since being introduced in 1991. Cables offer several advantages over traditional support systems, having large support capacities coupled with the flexibility to be used in low openings. Cable slings have been designed to be installed on-cycle using no-spin technology or a two-piece unit that can be placed with hand-held drilling equipment. Additionally, yielding cable supports have been developed and are being used to control large amounts of movement in coal and evaporite deposits.

Jan 1, 1998

By R. W. Smith, S. A. Davis, A. M. Raichur, M. Misra

The flocculation of coal is typically accomplished by the addition of commercially available polymeric flocculants. Recently it was shown that biopolymers derived from microorganisms can also be used. The biopolymers flocculate coal efficiently and make the coal more hydrophobic. This increase in hydrophobicity can be utilized to separate coal flocs and can be used for reducing the moisture content of the flocculated coal. In this regard, flocculation and settling tests using biopolymers and synthetic flocculants were performed on fine coal. The experimental results are discussed and a transport model is presented for the time-dependent settling of fine coal.

Jan 1, 1998

By H. J. Chen, Y. Luo, S. S. Peng

Surface subsidence resulting from underground coal mining can cause problems for buried pipelines. In this paper, a technique for assessing the level of stress on a subsidence-affected pipeline is introduced. The main contributors to the stress are identified, and mitigation techniques for reducing the stress are proposed. The proposed mitigation techniques were then successfully tested.

Jan 1, 1998

By G. Chi, M. C. Fuerstenau, R. C. Bradt, A. Ghosh

With increased emphasis on controlled blasting, which is the first and least-costly stage of comminution, ore grindability and plant throughput can be increased by 5% to 10%, and energy savings of up to 10% appear possible. Crushing and grinding efficiencies are presented for ore blasted under regular and adjusted field conditions. An economic analysis of drilling and blasting through crushing and grinding is presented, suggesting that cost savings approaching 10% may be achieved.

Jan 1, 1998

By R. P. King, S. Middlemiss

A method is developed to convert a measured distribution of fracture energies to the equivalent work index. The method assumes that the energy required to grind the material from the feed size distribution to the product size distribution is equivalent to the sum of the impact energies that are required to reduce the feed material by successive single impacts to the required product size. The method was tested by measuring the fracture energy distributions for quartz and comparing the resulting calculated value of the work index with the work index for this material measured using the conventional Bond laboratory procedure.

Jan 1, 1998