Search Documents

In this paper, a number of novel hypotheses that provide a fresh perspective on the characterization of strata movements associated with longwall mining are developed by analyzing subsidence measurements with an influence- function-based computer program. With this influence-function technique, easily obtained surface displacements can be used to determine some of the complicated, expensive, and difficult to measure movements of the immediate roof strata in a longwall panel. The primary hypothesis developed by this analysis proposes the existence of an area of partial roof caving near the edge of a panel called the "edge effect." A second hypothesis, interrelated with the first, promotes the importance of the effect of gate-entry closure on the observed strata movements. Both the primary edge effect hypothesis and the secondary hypothesis concerning gate-entry closure are justified and quantified in an extensive analysis of surface subsidence that uses supporting information from related theories, design criteria and insitu measurements. Next, the edge effect and the gate closure hypotheses are extended further and used to provide an explanation of the complex subsidence interaction of adjacent longwall panels in what is termed a "redisturbed" effect. Finally, in the conclusions of this paper, the importance of accurately understanding these longwall strata movements for proper subsidence prediction or gate design is stressed.

Jan 1, 1986

By S. Corrent, F. A. V. Guimarães, M. G. Barbosa

"INTRODUCTION Moisture can be a villain, so new technologies have been explored to make more viable the production of high moisture iron ores. The current work presents the attempt of the utilization of a superabsorbent polymer (SAP) to aid in the screening process and in the ore handling process, such as stockpiles reclaiming and vessels/trains discharge in sub-zero temperature conditions. The results have shown that the polymer can be used in certain cases to improve productivity and increase safety in the process of handling the material (by increasing the TML). However, for size separation no advantages were found upon the use of the polymers. WATER ADSORPTION MECHANISMS The use of water in mineral processing is constant as its utilization brings an increase in the efficiency of separation. Although we have better results in the processing with water, materials with a high content of “natural” moisture can be very difficult to be treated by the conventional methods of separation. Nowadays many studies have been conducted in order to understand the effect of adsorption of water in the particles of complex minerals. Those studies have being divided in many different lines of research such as contact angle of a drop of water and the surface of the mineral to determine hydrophobicity, the particle size distribution and the porosity of particles. Mainly two forms of adsorption of water by the particles are possible: one the water is retained inside porosity of the particles. Laboratory tests developed in China have showed that capillary adsorption is faster in coarser particles that achieve the saturation degree earlier than finer particles (Xuewei Lv et al., 2011). The so called non-porous model considers the effect of water in the bulk sample of iron ores, in a physical connection when all the water works as a binder between particles as shown in the figure 1.If we take into account the compressibility of the system and compaction due to the weight of the bed over the particles, the thickness of the water film between particles is the same but the volume inside different particle size systems is much higher than in a system with particles of same size."

Jan 1, 2018

By A. L. Hinde

Ideally, mill circuits should be controlled so that excessive random disturbances are reduced in frequency and amplitude. It is difficult to derive an objective measure of the effectiveness of any chosen control strategy. Often, the response of the circuit to pulse or sinusoidal disturbances is used as a measure of the effectiveness of control, but this is not adequate in many circumstances because such disturbances bear little resemblance to those that occur in practice, and such an approach cannot be easily related to the profitability of the reduction process. A superior approach appears to be the application of the theory of stochastic processes. This theory permits both real process disturbances to be modelled accurately, and useful objective functions for control to be derived. A test of the usefulness of stochastic theory in mill control was made on the gold ore milling circuit shown in Figure 1. This circuit was fed with an ore which had a liberation characteristic such as that shown in Figure 2. It is simple to show that, for such a liberation characteristic, the recovery of valuable mineral will vary as the standard deviation of the particle mass-size distribution varies even though the mean particle mass-size is kept constant. Similarly it may be shown that excessive perturbations in the circulating load in a milling circuit such as that shown in Figure 1 can affect liberation. Figure 3 shows how, as the cyclone feed density increases and the sump water addition decreases at constant sump level, the cyclone operation becomes unstable and the discharge "ropes? with a consequent catastrophic coarsening in product size. By minimising the variance of the circulating load it is possible to reduce the probability of initiating instabilities of this nature.

Jan 1, 1977

By James E. Lawver

Response surface methodology is a well-known and powerful technique for determining optimum conditions in flotation systems. One disadvantage is the onerous task of the numerical calculations and curve platting. This paper describes a system in which the investigator simply selects the range of several flotation variables after which the design of the experiment, data analysis, generation of response surface equations, and response surface plats are automatically carried out using a digital computer and a computer-driven curve plotter. Several typical response surfaces of important variables in phosphate flotation are presented as examples. An overview of the flow charting of the system is provided in the addendum.

Jan 1, 1978

By Maria S. Adusmilli, Bhaskara A. Rao, Jorge G. C. Barros, Augusto F. Mendonca

Lateritic gold has been the object of study only for a very few years, though nuggets have been mentioned in earlier works even as early as 1984 by Hartt in Brazil. In Mato Grosso State, lateritisation is intense, as is common in all tropical forest areas of the world. Exploration has revealed the presence of recoverable "nugget gold" of variable sizes (30 - 200 gms) but frequently of good size (0 - 40 gms), especially near Cuiaba and Alta Floresta regions. In both of them the host system is a lateritised breccia indicative of a fault or shear zone breccia, though in different lithological domains. The Cuiaba occurrences are phyllitic and show a profile as follows, from top to bottom: 1) Compact ferralite crust. 2) Oolitic to pisolitic compact crust (+ some gold). 3) Mottled concretionary laterite crust. 4) Lateritised "eluvial material" (gold nuggets). 5) Mottled patchy to banded laterite. 6) Banded lateritised phyllite with lenticular to banded goethite. 7) Altered red goethitic phyllite, with quartz veins (+ fine gold). 8) Unaltered grey phyllite with quartz veins (Protore). The Alta Floresta-Juruena River occurrences are volcano-sedimentary and show a profile as follows: 1) Deep brown siltitic, argillaceous and arenaceous material with organic matter (+ gold). 2) Modular and concretionary laterite, compact and indurated, with arsenophyrite in quartz fragments (gold nuggets). 3) Band with silty-clayey matrix and arenaceous in nature. 4) Bedrock meta-arcosian arenite. 5) Volcano-sedimentary with rhyodacites and andesitic basalts, with intercalations of arkosic and greywacke nature. Breccias and quartz veins, and granites associated in different portions (Protore).

Jan 1, 1988

By Glenn Melchert, Paul Eger, Jon Wagner, Dave Antonson, John Folman

Current approaches to reclaiming acid generating tailings include permanent water cover or encapsulation with various synthetic liners and/or clay. Although these methods can be effective, some ongoing maintenance will be required in perpetuity to ensure that water levels are adequately maintained or that the integrity of any capping system is protected. The successful creation of wetlands in tailings basins offers the possibility of creating a stable environment for the tailings with minimal maintenance. Acid-generating tailings from a massive zinc sulfide deposit in Winston Lake, Ontario, were placed in small cylindrical tanks to examine the feasibility and effectiveness of creating wetlands and mitigating acid and metal release. Two uncovered controls were established in addition to the five treatments, which were done in duplicate. Each wetland tank was 117 cm in diameter and contained 6 1 cm of tailings. Treatments included 61 cm cover of wetland soil, 61 cm of glacial till, 61 cm of tailings, and two tanks with 71 cm of water. One of the water covers included the aquatic macrophytes: Elodea canadensis, Potamegeton sp., and Ceratophyllum demersum. Cattails (Typha latifolia) were planted in the plots with substrate cover, and the initial water level was set at ten centimeters. The pH within the tailings in the treated tanks generally ranged between 6.0 and 6.5 and zinc concentration ranged from 0.02 to 0.1 mg/L. The drainage from the controls had an average pH of 3.3, and 7,700 mg/L of zinc.

Jan 1, 2000

By John A. Cordes, John J. Schanz

INTRODUCTION The economic structures of industrialized countries require a continuous supply of reasonably priced and appropriately processed nonfuel minerals. As a result, national policy makers are sensitive to real or perceived threats to the effective operation of these commodity markets. Their most persistent concerns can be subsumed into the related political economy issues of supply availability and marketplace stability. These concerns are not new. For over a century the "global struggle" for mineral resources has influenced national policies and international relations (Eckes, 1979). During the past two decades the complexity of these issues, if not their place on national political agendas, has increased. Dramatic changes in the structure of mineral industries and in the nature of international economic relations have redefined policy needs and response options. This paper focuses on how selected OECD countries have responded to nonfuel mineral industry issues over the past twenty-five years. Particular emphasis is placed on the impact these policy decisions have had on the size and location of productive capacity and its utilization rates. The results, perhaps, are not surprising for this group of market- oriented economics. While individual cases of significant impact are easy to identify at various times in most countries, the overall importance of policy decisions has not been great. This is especially true for the past decade when excess capacity reached unusual highs of magnitude and duration. Macroeconomic forces and market structure changes played much more important roles. PERSPECTIVES ON THE ISSUES OECD nations dominate the international nonfuel minerals marketplace as producers, consumers and traders. In 1986, these twenty-four countries accounted for 75 percent of the Western world's export trade value in minerals, ores and metals. They imported 88 percent of the total value. During 1966, the respective percentages were 70 and 94. Japan was the world's largest importer in 1986 followed by the US, FRG, UK and France. The same five countries led the 1966 list except that, then, Japan was ranked fourth. Table 1 ranks the fifteen largest Western exporting nations in the two specified years. It also indicates the growth in current export dollars earned in 1986 compared to 1966.

Jan 1, 1989

By D. E. Ranta, Stephen W. Thomas, Clancy J. Wendt

One of the most difficult tasks associated with placer mining is the sampling of the deposit. More placer projects have failed due to inaccurate assessment of the reserves than to any other reason. Within the realm of placers, those containing valuable minerals with a high unit value are more difficult to sample than those with larger bulk, lower unit value minerals. Some items to consider when sampling a placer deposit are as follows: A. A relatively large sample is needed for accurate valuation of the ground being tested. Placers are composed of many sizes of gravel which makes a representative sample difficult to obtain. B. When sampling placers for high unit value minerals such as gold, any error in mineral content of the sample will be magnified in the calculation of reserves. C. Values are usually erratically distributed within the gravel mass. Therefore, some placers with a more uniform value distribution may be adequately assessed with a minimum number of samples whereas a deposit with a highly erratic distribution of values may not be adequately sampled regardless of how many samples are taken. D. The investigation of a placer deposit should be made by, or be under the direction of, a person experienced in the art of placer sampling. F) During a sampling program, items that must be observed and noted in addition to the sample size and valuable mineral content should include boulder size and number, clay content, bedrock conditions, water, frozen ground, false bedrock, and any other physical characteristics that would affect mining of the deposit.

Jan 1, 1992

By William J. Cavanaugh

In 1967, Lone Star Industries, Incorporated, established a program to carry out the necessary Research and Development work to bring the Snyder Process to commercial application. The purpose of this paper, is to present the detailed metallurgical results gathered in comparing the Snyder Process of Comminution to conventional grinding techniques for the milling and beneficiation of certain ores and other materials. The ore primarily dealt with in this paper is a fine-grained magnetite ore, containing approximately 23% acid-soluble iron, from the Lake St. Joseph ore body of Steep Rock Iron Mines, Ltd., (Canada). This particular example was selected for presentation in this paper because extensive comparative results with conventional methods of grinding were available. Also briefly described in the paper are the comminution of other ores and materials such as porphyry copper ore and alumina.

Jan 1, 1973

By Fred L. Myers

The use of finite element programs for evaluating large grinding mill shells is becoming increasingly popular. However, large scale, detailed analysis can become a burdensome task when one is required to manually prepare the necessary data to be entered into the program, while evaluating the voluminous results is even more devastating. Although available computerized finite element analyses can reduce computation time from years to months or even weeks, additional pre and post processors can reduce the time for data preparation and result evaluation to hours, while simultaneously reducing the probability of human error. Examples of the uses of these processors are presented as well as typical modeling techniques.

Jan 1, 1979

By Joseph C. Rota, Charles E. Ekburg

Introduction The Gold Quarry gold deposit is the largest bulk tonnage epithermal gold deposit in northeastern Nevada to be developed by Newmont Gold Co., formerly known as Carlin Gold Mining Co. Exploration and development of the deposit extended over a period of nearly 50 years before bulk tonnage mining became economically feasible. Proven reserves at Gold Quarry are currently estimated at more than 255 t (8.2 million oz.) of gold, accounting for more than 40% of the total Carlin Trend mineable reserves for 1986. Milling began in late 1985; dump leaching of lower grade ores began in May of 1986. The mill has exceeded the initial design throughput rate of 6.3 kt/d (7000 stpd) and is now processing more than 8 kt/d (9000 stpd). The dump leach facility will process more than 7.3 Mt (8.1 million st) of lower grade ores in 1986. The Gold Quarry ore body is to be developed by an open pit that will eventually be 1830 m (6000 ft) long, 1220 m (4000 ft) wide and 300 m (1000 ft) deep. The mine currently produces 77 kt/d (85,000 stpd) on a 24-hour-a-day, seven-day workweek. Planned pit production will increase to nearly 168 kt/d (185,000 stpd) in 1988. Production equipment currently includes one Demag H-/285, three Komatsu PC-1500 hydraulic shovels, two Cat 992C loaders and 21 90 to 135 t (100 to 150 st) haul trucks. Mining is conducted on 8 m (20 ft) benches within the Paleozoic

Jan 4, 1988

By David B. Crouch

Wastes in various forms have always been a part of mining, and management of mine waste has evolved from the early days of "push it over the side and down the creek" to today's highly engineered waste facilities. Changes have been brought about not only by technological advances in the ?3M?s? - mining, milling, and metallurgy - but also by environmental awareness and changing social values that have been manifested in an ever-growing maze of regulations. This is a dynamic era, and the debate goes on. So it is that planners have to anticipate permit and regulatory requirements in the site-selection process along with the traditional criteria. The McLaughlin gold project is an example of how one company, Homestake, has met this planning challenge. In August of 1980, Homestake Mining Company announced a major gold discovery in northern California known as the McLaughlin Project. The property is approximately 80 air miles northeast of San Francisco near the junction of Lake, Napa, and Yolo Counties. This is an area where mercury has been mined off and on for over 100 years; gold has never been mined in the area. The gold is microscopic and finely dispersed in a complex geologic setting. Reserves are estimated at approximately 20 million tons at a grade of approximately 0.16 ounces per ton.

Jan 1, 1983

By Yadong Xue, Fei Wang, Hongwei Huang, Yan Sun

"Increasing attention to subway tunnel maintenance is being paid with the high speed development of urban rail transit system in China. A novel moving tunnel inspection equipment based on machine vision is developed in this paper. High resolution image acquisition system is proposed for tunnel crack and leakage inspection. The main components of this image acquisition system includes high speed CCD cameras, linear lights and high performance computer. To inspect the crack less than 0.3mm with a 3-5km/h speed in subway tunnel, we need to consider resolution and line rate of camera, pixels of cameras, range of inspection and illumination intensity of lights simultaneously. The optimization design is proposed to make the equipment more convenient for tunnel use. Entire tunnel situation can be detected and recorded in a single inspection process. This equipment has already been verified in Shanghai subway tunnel for defects inspection.1. INTRODUCTION In China, the quantity of subway tunnel has reached a large scale in recent years. Until 2014, there had been more than 2300km of subway tunnel in China which accounted for nearly three quarters of Chinese urban railway system (Zhang Chen,2015). In some metropolises like Beijing and Shanghai, most of the metro tunnels has already run over 20 years which within maintenance phase. This has brought about plenty of inspection work and maintenance work to guarantee the tunnel under the serviceability limit states. The increase of running mileage of subway tunnels in China has been displayed in Fig 1."

Jan 1, 2016

By John W. Stevenson

At the No. 4 Mine of Jim Walter Resources in Tuscaloosa County in the North Central part of the State of Alabama, the Mary Lee and Blue Creek coal beds lay 2000 feet below the surface. The quantity of methane gas stored within the coal bed reservoir at this depth and released during development mining necessitates that each coal producing section be ventilated using large air quantities approaching 100,000 cfm. In order to meet coal contractural commitments in the early stages of mine development by installing the necessary number of continuous mining machine units and to develop the mine to projected air shaft sites, high pressure, large volume mine ventilating fans were required. This presentation discusses the installation start-up and changeover procedures when two size GAF 31.5-28-1 TLT-Babcock 3500 Horsepower fans with adjustable pitch in flight blades were put on line while phasing out two Jeffrey Mining Machine Company 8HUA 117 Fans. A graph will be presented to depict the most economic diameter shaft size under 2000 feet of cover with different air quantity requirements.

Jan 1, 1982

By P. Amelunxen

Over the past several years, the combination of higher energy and steel costs and the recent commercial deployment of high-pressure grinding rolls (HPGR) technology in hard rock mining have led many multinational mining companies to evaluate the suitability of HPGR technology for their particular comminution circuits. HPGR technology is perceived to require a higher capital investment while delivering lower long-term operating costs. This paper undertakes a critical evaluation of this perception. By evaluating the capital and life-of-mine operating costs of competing circuit designs for soft, medium and hard ores, the HPGR break-even point can be identified, at which the incremental capital cost of an HPGR circuit is equivalent to the net present value of the projected operating cost reductions. For ores with hardness parameters above the break-even point, HPGR circuits could offer economic benefits, while for softer ores, SAG mill/ball mill/pebble crushing (SABC) circuits are likely to be more economical and energy efficient. This evaluation considers both an SABC reference circuit and a traditional stage crushing configuration. Other influential factors are also discussed.

Jan 1, 2011

By B. K. Cantrell

The use of diesel equipment in underground coal mines is controversial because "whole diesel exhaust" is regarded as "a potential occupational carcinogen" by the National Institute for Occupational Safety and Health (NIOSH). Threshold limit values (TLVs) are recommended for the gaseous pollutants; CO, CO2, NO, NO2, SO2' and some hydrocarbons emitted in diesel exhaust. There is, however, no TLV recommended for diesel exhaust aerosols (DEA) nor is there a standard method for sampling these aerosols. The University of Minnesota and the Bureau of Mines have collaborated to develop a personal diesel exhaust aerosol sampler (PDEAS) which utilizes size selective, inertial impaction and gravimetric analysis. During the field tests of this sampler, numerous air quality measurements were conducted in underground coal mines using diesel equipment. The objective of this report is to present these data and to assess the impact of diesel face haulage equipment on mine air quality.

Jan 1, 1991

A case study of a systematic approach to grinding circuit steady-state optimization is presented. After overall review of the flowsheet, two circuits were prepared for detailed testing. Functional performance analysis was chosen as the primary modelling system, and on this basis a quality assurance program for data gathering was implemented. A number of circuit design and operating variables were experimented with statistical analysis of plant test results revealed relationships previously unquantifiable by any other modelling technique. Improvements in classification system and mill grinding efficiencies were demonstrated and significant energy cost savings thus realized.

Jan 1, 1998

By V 9. 0 / 300 dpi

In the time period from the early 1980's to the present, longwall roof support technology has evolved tremendously. Chock supports and caliper shields were replaced by 2-leg or 4-leg lemniscate shields. The lemniscate linkage for which the support is named offers numerous advantages to the sup-port both as a fabricated structure and to its performance in the mining application. The hydraulic system, which is the dynamic element of the roof support, was essentially unchanged in early lemniscate shields with the exception of the complexity of additional hydraulic circuits to power a canopy tilt cylinder and canopy side-seals. The control of these fluid-powered functions was provided by direct manual control of valves energizing individual functions onboard the roof-support or the adjacent roof-support. This control valve-gear was comprised of multiple individual valves arranged in a "bank" or integrated into a single hydraulic distribution block with a single operating handle to select any independent function.

Jan 1, 1993

The segregation process has been known for many years and applied industrially for the treatment of various refractory copper ores. The principles of the process are briefly reviewed; the process was tested in the laboratory on two copper-cobalt oxide ores from Gecamines, Shaba Province, Zaire. Various parameters of the process, such as segregation temperature, dosage of reducing and chloridizing agents and flotation conditions were inyestigated. Experimental results have shown that the segregation of copper could proceed satisfactorily at low temperature (1000° K) but that of cobalt required higher temperature and higher additions of reducing and chloridizing agents.

Jan 1, 1992

By C. H. Cheh

The amount of fines in run-of-mine coal has been increasing and coal quality has been deteriorating as a result of the increased use of mechanized and continuous mining methods. Removing the mineral matter and pyritic sulfur from coal prior to combustion will lower transportation costs, improve power plant performance and reduce sulfur dioxide emissions. Since physical cleaning methods can only remove individual particles of mineral matter and pyrite, it is necessary to crush and grind coal to fine sizes to separate these contaminants so they can be removed by deep cleaning processes. The increased portion of fines in run-of-mine coal together with attempts to increase the mineral matter removal efficiency have stimulated interest in fine coal cleaning technology. However, there are many problems to be solved before fine coal cleaning can be applied to power plant coals. These problems include: 1. coal cleaning plant capacity is reduced when conventional cleaning circuits are modifies to deep clean coals; 2. existing equipment and technology is not suitable for cleaning fine coal; 3. coal recovery is reduced; and 4. fine coal is difficult to dewater, dry, handle, transport and store.

Jan 1, 1982