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By B. K. Mishra, R. K. Rajamani

A numerical method known as the discrete element method (DEM) is used to track the motion of individual balls in large-diameter ball mills. As a result, the en masse motion of the charge, force distribution, fall-height distribution, and energy distribution emerges from the simulation. Hence, it is possible to investigate the effect of mill diameter, liner profile and ball size distribution on the force regime created within the mill. Simulation results for 14-, 16- and 18-ft diameter mills are shown. The proportion of energy lost in high-intensity impacts and sliding ball motion is discussed. The DEM simulation technique opens the way for a closer examination of liner profiles on ball-charge motion.

Jan 1, 1992

By N. B. Aughenbaugh

Compacted, fine-grained soils, often referred to collectively as clays, are used as permeability barriers in many mineral engineering projects such as heap leaching, containment ponds, tailings disposal and earth dams. Source materials for these liners include a variety of sand, silt and clay admixtures. These exhibit dramatically different engineering properties when densified. Therefore, it is imperative to adequately assess and characterize any soils being considered for compacted liners. The permeability and plastic properties of fine-grained soils are reviewed with respect to the state of compaction as the water content varies. Because they are weak in tension, compacted clays are susceptible to cracking when subjected to differential flexural movements. Designs of compacted clay liners also must include an evaluation of their flexibility. That is the ability of a fine-grain soil to bend plastically without cracking. This paper will also discuss the importance of flexibility with respect to soil types, compaction effort, failure mechanism and testing evaluation to the performance of clay liners in preventing seepage of pollutants from a containment site.

Jan 1, 1991

By R. E. Johnson, W. Kat, B. R. Palmer, van Sandwijk A., G. Van Weert, S. Honingh

In-plant recycling of dust from iron making BF's creates undesirable circulating loads of volatile trace elements such as zinc and lead. Disposal of such dusts creates environmental problems, hence a separate treatment is indicated. Since the bulk of the zinc and lead compounds occurs in the fine dust fraction; hydrocycloning the slurry from the BF gas cleaning operation results in upgrading the material for treatment. A process has been proposed, whereby the zinc and lead are solubilized from the fine fraction with spent hydrochloric acid from steel pickling. The stoichiometry of this autoclave oxidation process is adjusted to simultaneously precipitate, by oxyhydrolysis, most of the iron for recycling to the BF's. Lead and zinc are successively recovered from the filtrate as low chloride precipitates. This paper describes additional testwork, leading to the design of a pilot plant which was planned to begin operation in 1992.

Jan 1, 1993

By F. W. Petersen

In the precious metal industry, activated carbon is used extensively for the recovery of gold and silver from cyanide solutions, particularly from slimy pulps and unclarified solutions. However, carbon can easily become fouled by inert particles in the pulp, thus decreasing the activity or gold loading of the carbon. This paper attempts to quantify the distribution of fine inert particles in activated carbon. Furthermore, a possible mechanism for the intrusion of fines will be postulated. Precipitated silica and ground silica sand were used to simulate pulp conditions and their loadings on activated carbon were determined by ashing. The kinetics of intrusion of fines into the pores of carbon were relatively fast, and were dependent on the concentration in the pulp. Results indicated that particle size of the solids and zeta potential of the fines influenced the loading of inert species on carbon. Scanning electron microscopy and secondary ion mass spectrometry showed a decrease in solids concentration to the centre of the carbon particle.

Jan 1, 1995

By Hiromu Kusakawa, Tetsuo Kanematsu

INTRODUCTION In urbanized area with heavy street traffic and with environmental requirements to lessen construction noise and vibration, the cut-and-cover is not always a feasible method to build a small diameter tunnel for sewage, water or other utilities. That is where the use of the shield machine to bore such a small diameter tunnel should be considered as a more acceptable alternative. Although the shield machine of this type should be small enough to meet specific requirements for a given tunnel, it should be big enough to provide some working space inside of the tunnel. Recently, we have successfully developed the fully mechanized small diameter tunneling method which enables us to bore a tunnel as small as 600mm in finished diameter. This paper discusses the concept of this newly developed method, including a case history where sewage tunnels of 800mm finished diameter were constructed by using this method. OUTLINE OF METHOD Developed from the original slurry shield pipe-jacking tunneling method, this method is highly automated so that all operations inside of the tunnel can be remotely controlled. Various data including the advance rate, position and inclination of the shield are transmitted to the central control room outside of the tunnel and monitored by the CCTV and the instrument panel at all times to

Jan 1, 1981

By S. Mason

Many organizations are realizing that continual improvement in health and safety relies on addressing the potential for various forms of human error. Of these, rule violations are often the most frequent form associated with accidents. These occur when an individual (or individuals) deliberately contravenes established and known safety rules. They have been associated with up to 90% of the accidents and other incidents in some industries, and yet they rarely receive the systematic attention they deserve in the promotion of safety. This paper presents underlying motives that cause violations. These can vary significantly from mine to mine and from job to job. Managers need some measure of the attitudes of the violators to determine the underlying motives behind the violations if they are to determine effective strategies for promoting safe behavior. Questionnaires form the starting point to address attitudes and the motives behind rule violations. The choice of the most suitable questionnaire, how- ever, will vary from organization to organization. Guidelines on the choice of questionnaire are offered.

Jan 1, 2000

By Jianping Sheng, Francis Otuonye

The potential for methane and coal dust explosions in underground coal mining operations has increased in recent years with the introduction of fast coal-cutting machines. Dust explosions usually follow accidental ignition of a methane pocket. The dynamics of the explosion may be strong enough to pick up and disperse coal dust deposited on mine surfaces and ignite the mixture. A self-sustaining dust explosion can then develop and propagate at large distances. Ignition of dusts can result in a fire, and this may also lead to a dust explosion if the burning dust becomes airborne. Entrainment of dust and the resulting dust concentration in the gas stream are some factors which determine the features of the subsequent explosion and flame propagation. A model of coal dust transport in the gas stream due to the initial explosion is presented. In this model, equations for the conservation of mass, momentum and energy are coupled with the convective-diffusive model of dust transport. The system of equations is solved numerically to obtain dust concentration, convective velocity and gas pressure profiles.

Jan 1, 1989

By M. K. Gangal, E. D. Dainty

The paper describes the capabilities of a micro-computer-based real time data acquisition system for monitoring and control of mine environments. Applications of such a system for monitoring the ventilation and air quality of a mine is outlined. The paper discusses the results of running a monitoring system with various environmental sensors in a simulated mine environment. The sensors used in this study are: carbon monoxide (CO), carbon dioxide (C02), nitric oxide (NO), nitrogen dioxide (NO2), sulphur dioxide (SO2 ), methane (CH4 ), air flow, absolute pressure, temperature and relative humidity. A performance evaluation of the monitoring system and sensors is presented.

Jan 1, 1987

By Pierre M. Matheron

TRANSMANCHE-LINK is responsible for designing, developing and implementing the project for a fixed link under the English Channel, comprising two running tunnels of diameter 7.6 metres and a service tunnel of diameter 4.8 metres. The three tunnels will all be 50 km long, with 37 km bored through chalk marl at a depth of 40 metres under the sea bed. The tunnels will be driven from both sides of the channel from intermediate addits above the coastline on either side with a 55 m access shaft at Sangatte in France and two "descenderies" or inclined tunnels addits and a shaft at Shakespeare Cliff on the English side. A total of eleven tunnel boring machines will drive the 150 km of tunnels. The major part of the tunnel linings will be built of precast reinforced concrete segments, and two plants have been specially built to produce the necessary 725,000 segments. Seven million cubic metres will be evacuated on wagons along the tunnels and then lifted by belt conveyor on the English side, and by hydraulic mucking from the bottom on the French side. Preliminary work started early in 1987 with manufacture of the first boring machines, construction of five precasting plants, boring of the Sangatte shaft in preparation of the Shakespeare Cliff entrances. The principal project dates are :

Jan 1, 1987

By Bruce C. Schepens

The Balsam Meadow Hydroelectric Project is currently under construction in central California. TMCI Construction, Inc. was subcontracted to perform the shaft enlargement and lining required for the elevator, surge and power shafts. Involved in the initial work was slashing the elevator and surge shaft into a previously excavated borehole. The elevator shaft then required a reinforced concrete lining and structural steel installation. Throughout the course of construction, numerous design changes occurred, necessitating a lining in both the power and surge shafts. These changes caused TMCI to design two underground hoisting systems to install these additional linings. An analysis of the construction methods used is now given. Introduction The Balsam Meadow Project consists of an underground hydroelectric powerhouse designed to provide additional capacity and energy to the Southern California Edison system during critical peak demand periods, and has the capability for pumped storage operation. The project is located in the Sierra Nevada Mountains about 55 miles northeast of Fresno. The project will divert water presently flowing from Huntington Lake to Shaver Lake to power a single 200 megawatt turbine generator. The approach used to the shaft slashing was governed partially by the strict CAL-OSHA requirements, which became more stringent after the recent Helms' Creek accident. A scaled down sinking plant was used to minimize economic risk and to simplify the excavation and lining scheme.

Jan 1, 1987

By Jack Parker

Pillar design ought to be a matter of matching pillar strength against pillar loading conditions to come up with dimensions that will cause the pillar to behave as required - to stand forever, or for a limited time, or to fail in a controlled manner. But something has gone wrong in recent years, seriously wrong. Pillar design practices have departed from reality. The laboratory and computer have taken the place of the mind. If the mind is put to work and such pillar design practices are examined critically, it becomes obvious that they deal with conditions that do not exist in a real mine. Time, effort and money are wasted, and the end results are incorrect and misleading. These questionable pillar design practices have been passed on from generation to generation over the past 30 or 40 years. The hope here is that we can return to reality as soon as the questionable practices are generally recognized. We could then go back into the mines and define how pillars really work, and mining safety, efficiencies and costs should improve. Let us take a close look at current textbook design practices and compare them to real-life conditions. Common sense might then prevail. (At this time, we will consider only mine pillar design, but similar scrutiny should be applied to design criteria for width of openings, floor conditions and roof support systems.)

Jan 1, 1993

By D. D. Snyder, J. D. Bode, F. T. King

INTRODUCTION Only in recent years have the environmental hazards associated with mining and tunneling operations been fully acknowledged and determined remedial action undertaken. The nature of these excavation operations leads to a wide diversity of hazards spanning mechanical, electrical, chemical, environmental, and physiological. The most insidious of these are unquestionably the environmental ones which have the greatest long-term effect and are the most difficult to pinpoint and monitor. It is the atmospheric contaminants that lead to a significantly greater illness and mortality rate among miners. Dust is the most prevalent, hence most important of the atmospheric contaminants. Respirable particles lead to diseases characteristic of many mining operations: coal workers pneumoconiosis, asbestiosis, silicosis, talcosis, anthrocosis, etc. But toxic and suffocating gases can be equally insidious and the most innocuous pollutant, methane, leads to the most imminently disastrous results of all - explosion and fire. This means that truly effective monitoring of the environmental hazards in tunneling cannot be limited to a few simple standard check measurements. It must include the most precise measurements we can make for specific, documented hazards and even for factors, such as noise and heat stress, not immediately obvious as hazards. The Federal Metal and Nonmetallic Mine Safety Act and more recent Occupational Safety and Health Administration standards are clearly designed to match such effective monitoring. We must, therefore, consider not only presently available monitoring instruments and those currently under develop-

Jan 1, 1997

By J de Cuyper, S. Ramachandran, L. A. Vazquez, N. L. Grauerholz, W. Freyberger

A novel process is described for the selective flotation of scheelite from low-grade (- 0.5% W03) tungsten ores having appreciable quantities of calcareous and siliceous gangue minerals. Specifically developed for the Tempiute, Nevada facility of Union Carbide, the process yields tungsten concentrates exceeding 15 percent W03 with at least 85 percent recovery. This condition was not achieved through conventional processes. This process consists of conditioning the ore pulp with judicious amounts of lime, followed by soda ash and sodium silicate as modifiers. The scheelite is then floated using a mixture of oleic and naphthenic acids as collector. Contrary to the common observation as to the deleterious effects of calcium in fatty acid flotation systems, lime addition is found to be beneficial in achieving satisfactory results. The process has also shown excellent results on a Brazilian scheelite ore.

Jan 1, 1976

By N. A. Frazier

The technology for using limestone or lime to scrub SO2 from power-plant flue gas has significant implications to the limestone industry. A brief status report on these processes will be made, possible process requirements on the limestone properties will be reviewed, and projections on the buildup of demand with respect to time will be reviewed. Disposal problems inherent with the use of these throwaway processes will also be summarized. Given a viable technology, relations among (1) distance of power plants from low- and high-sulfur coal and limestone deposits, (2) modes of handling and transporting immense tonnages of bulk material-coal and/or limestone, and (3) regional air-quality standards are some of the factors which will ultimately determine the demand for limestone. A discussion of these factors will be presented, with the intent of identifying geographic regions where significant increases in production can reasonably be expected.

Jan 1, 1974

By K. L. Kayler

Ball clay production in 1991 amounted to about 800 kt (880,000 st), about the same as in 1990. 1992 estimates show a 5% decrease to 750 kt (827,000 st). This decrease continued a trend of reduced production that began after the peak of 900 kt (1 million st) that occurred in 1988. Use of ball clay in sanitary ware was about 2% less in 1992, although levels of use in floors and wall tile, dinner ware and pottery remained constant. Filler, extender and binder applications continued to be important end uses, accounting for about 17% of total market. Refractory uses maintained their market share of about 17 kt (18,700 st). Use of clay liners in toxic and waste dumps is an application widely found in Germany. However, its use has not been fully exploited in the United States. This could represent an opportunity for domestic clay producers. Tennessee remained the leading source of ball clays. Other producers were Indiana, Kentucky, Mississippi and Texas. Tennessee's production, however, decreased about 3% in tonnage produced and its value dropped from 68% to 65% of total production. The ceramics division of Southern Clay Products, Inc., was bought from LaPorte plc by United Clays of Texas, Inc., a US subsidiary of Watts Blake Bearne & Co. The purchase included ball clay reserves at Troup, TX. The acquisition makes United Clays the second largest ball clay producer in the United Sates. United is also the only company mining clay in Texas. Fire clay production decreased 5%

Jan 1, 1993

By J. M. Barker

Formation of commodity agreements depends mainly on the economic instability and associated mitigation measures inherent in the economic conflict between more developed and less developed nations. Five types of possible agreements exist: futures market, buffer stock, restrictive agreement, multilateral contract, and compensatory finance. Lack of market separation between sulfur consumers and producers coupled with large world production and highly concentrated export production in theory suggest a restrictive agreement as most likely. In practice, stockpiling of sulfur, an informal buffer stock, as done in Canada and perhaps the Middle East, has been the main sulfur price-supporting mechanism in the past two decades. No commodity agreements involving sulfur now exist except for multilateral contracts. Sulfur agreements apparently have existed rarely, if at all, in the past. Law (1975) refers to sulfur as one of a group of commodities where "there have been additional control efforts of various types." Clearly, sulfur was a candidate, at least conceptually in the past, for some form of commodity agreement. The following discussion centers on the world sulfur market from 1976 to 1985 in this context.

Jan 1, 1987

By Frank E. Dalton, Forrest C. Neil

INTRODUCTION The Tunnel and Reservoir Plan (TARP) (Figure 1) was adopted in 1972 as the most cost-effective way to bring Chicago area waterways up to Federal and State water quality standards. TARP will significantly reduce pollution of these waterways and provide flood relief for Chicago and 53 adjacent suburban communities. These communities, covering an area of 971 sq km (375 sq miles), are at present served by combined sewers, which carry both raw sewage and stormwater. Because porous ground surfaces have been covered over in recent years by buildings, streets, and parking lots, stormwater runoff into sewers frequently exceeds the capacity of the sewers. When this happens, sewers back-up into hundreds of thousands of basements, and the overflows on the combined sewers discharge rainwater mixed with raw sewage directly into the area's waterways at 645 overflow points. The result is severe pollution of the waterways and flooding in 53 communities. During particularly heavy rains, overloaded rivers have to be relieved by opening the locks and allowing the polluted waterways to flow into Lake Michigan, the region's water source. Goals of TARP 1. PREVENT BACKFLOWS INTO LAKE MICHIGAN. 2. ELIMINATE WATERWAY POLLUTION CAUSED BY COMBINED SEWER OVERFLOWS. 3. PROVIDE AN OUTLET FOR FLOOD WATERS.

Jan 1, 1981

By Michel Grenier, Gopal Kunchur, Stephen Hardcastle

This paper presents the findings of a dust study in a typical fluorspar processing plant. The primary purpose of this study was to identify employees and occupational groups exposed to high dust levels and determine compliance with personnel regulations for regular and extended work shifts. The range of airborne concentration of respirable silica and fluoride compounds in specific areas and on personnel was determined. State of the art dust monitoring equipment and tracer gas techniques were used to measure dust concentration, pinpoint dust sources and map major airflow trends in the mill. Results of the survey indicated silica dust concentrations in excess of permissible limits being produced mainly by crushers at the south end of the building. Tracer gas releases and gas chromatographic analysis further showed that prevailing south to north air currents tended to carry and spread dust produced by the crushing operations throughout the process plant. Airborne concentrations of fluoride compounds measured during the study were always well below the prescribed threshold limit value (TLV) for the contaminant. Recommendations, including a mechanical exhaust ventilation system on crushers and transfer points, scheduled preventive maintenance on existing bar sprays and wearing of personal protective equipment were made which significantly improved the work environment. Further testing conducted after Installation of the dust extraction system revealed significant improvements in most areas of the mill.

Jan 1, 1991

By Mark S. Stagg, Michael J. Nutting, Douglas R. Barlet

Single-row bench blasts at a reduced scale in the field were used to study the effects of delay time on fragmentation. Nine shots with a spacing of 21 in. and a burden of 15 in. (S/B = 1.4) and nine shots with a spacing of 30 in. and a burden of 15 in. (S/B = 2.0) were completely screened to determine particle size distributions. Delay intervals between holes ranged from 0 to 45 msec, corresponding to effective delay intervals ranging from 0 to 36 msec per foot of burden. Each shot was instrumented with strain and pressure gages to measure in situ blast dynamics and to evaluate interactions between blastholes. Finer overall fragmentation was produced for shots with delay intervals between 1 and 17 msec per foot of burden. Only for shots within this optimum delay range was it observed that the strains induced by stress waves constructively interacted with strains induced by gas pres- sure from an earlier detonated hole. Coarsest fragmentation resulted at delay intervals less than 1 msec/ft, where stress waves from each hole were observed to interact destructively, and at delay intervals greater than 24 msec/ft, where no inter- action between holes was observed, indicating a condition that can be considered as the firing of single hole shots independently.

Jan 1, 1986

By Donald K. Sparling, C. Edwin Baker

The White Mesa uranium/vanadium mill is six miles south of Blanding, UT, on the Colorado Plateau, which has historically spawned more than 200 uranium mines. As uranium prices approached an all-time high during the mill planning period, Energy Fuels Nuclear Inc. anticipated the reopening of many of these mines, whose low grade ore suddenly looked economic. The company located the White Mesa mill close to these mines, to minimize hauling distances to the mill and give vendors added incentive to reopen or expand mine operations. A receptive local community, a relatively unencumbered trip through the regulatory maze, and some mill circuit innovations all helped to make the White Mesa mill a well functioning reality. From a strategic standpoint, and to begin ore stockpiling as early as possible, Energy Fuels constructed two ore buying stations and began receiving ore in early 1977. The buying stations were located at Hanksville and at what is now the Blanding mill site. Ore receipts at Hanksville did not materialize as anticipated and the facility has since been closed. The Blanding ore buying station is now an integral part of the milling operation. All ores, whether company, vendor, or for toll milling, are received at the Blanding station. The Blanding site was central to the plateau mines, and was well received by area residents, who encouraged the introduction of industry to the area. Residents viewed mill construc¬tion as an economic blessing and were prepared to accept the associated im¬pacts. Energy Fuels hired as many local people as possible for mill opera¬tions.

Jan 4, 1981