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By Robin J. Batterham, Dave J. Robinson

The most significant trend in flotation has been the ever-increasing scale of operations. There is, however, doubt that this ongoing trend is enough to maintain the economics against trends such as falling grades, increasing mining costs, pressure on water supply and demand, rising energy demands needed for mineral processing, and a focus on whole of life value and mine legacy issues. We comment on the ramifications of broader uptake of more sustainable mining for mineral processing methods and address the specific question of whether recent progress in in-place recovery will lead to a timely breakthrough. The answer proposed is that this is possible in the next 10 to 20 years, but in the meantime the focus is just as likely to be on removal of waste (beneficiation) much earlier in circuits. Either way, mineral processing and flotation as we know it will change significantly. 

By Chas. F. Jackson

INTRODUCTION This paper is one of a series dealing with mining methods and costs, prepared and published under the sponsorship of the US Bureau of Mines (USBM) and made possible through the cooperation of many mining companies in the US and foreign countries. The data presented have been obtained from papers previously published by the Bureau dealing with indi¬vidual mines, from the technical press, and from infor¬mation furnished by the mining companies. DEFINITIONS Top Slicing The term top slicing is commonly applied to that method of mining in which the ore is extracted by a series of timbered slices, beginning at the capping; the slice is caved, bringing down the capping to the floor of the slice; the succeeding lower slices are mined up to the overlying mat or gob, consisting of an accumulation of timber from the upper slices and broken capping, which follows the mining progressively downward (Fig. 1). The term has also come to be applied to the mining of ore bodies only one slice thick, by a series of tim¬bered slices one beside the other. The timbers are blasted out, bringing the capping down to the floor, suc¬ceeding slices being driven alongside those already caved (Fig. 2). In USBM classifications of mining methods, top slic¬ing has been placed under the heading caved stopes. The method differs fundamentally, however, from the cav¬ing methods of mining in which the breaking of the ore itself is accomplished by caving action induced by undercutting. In top slicing the ore is broken by the ordinary methods of drilling and blasting, and only the capping is broken up by caving. Main Levels or Haulage Levels Main or haulage levels are the main extraction levels on which the ore is hauled to the shaft. These levels and the shaft constitute the preliminary development of the mine.

Jan 1, 1982

By D. L. Kowal, P. J. Whittaker, M. A. Tuzun, N. O. Lotter

The area of flotation testing of drill-core is important in the business plan of most mining companies. Metallurgical information derived from this practice can be used to advantage in strategic decision-making. Sampling, flotation testing and subsequent Qem SCAN analysis of a mineral resource is one example of this approach. Anew resource, located in Sudbury, Ontario, is being assessed for the Sudbury Operations of Falconbridge Limited, which includes the Strathcona Mill. In this case, it was possible to improve the value of information from sampling and flotation testwork by using an improved, statistically-based test design, by sampling the resource by generic end-member ore type, and by integrating the Mineral Processing and Mineral Science disciplines into a Process Mineralogy team. In addition to producing standard metal grade and recovery information, this new approach provides more reproducible information from representative samples and flotation testing in a replicate format. Qem SCAN technology is used to produce a size by size mineral balance, including both modal percentages and liberation, from which flotation models for each ore type can be developed. As a result, a key understanding of the potential behaviour of a given ore type, if mined and then processed at the current mill operation, is gained at the 95%confidence level. The three ore types of this mineral resource were shown to have different flotation characteristics. Quantifying the mineralogy and liberation in each of the three ore types, has shown that this difference is due to changes in modal percentages of ferro-magnesium and magnesium silicate minerals such as pyroxene, talc and serpentine. Liberation across the three ore types is very similar and is therefore not responsible for variation in flotation performance.

Jan 1, 2003

By Hiroshi Himura, Shoichi Tsushima, Hiromi Goshima

This paper reports the construction of an environmentally-friendly tunnel in sedimentary soft rock near a residential area. The main tunnel, which will be used as the Onmawashi-Koen (Park) Regulating Reservoir, is a large-scale tunnel with a cross sectional area of 254.0 m2 and a lengthof 577.3 m, excavated using such support as shotcrete, rockbolts and steel H-sections. Since the large main tunnel is excavated in sedimentary soft rock, it is necessary to keep the stability of the tunnel face and the crown and to prevent surface settlement. A top heading with a length of 50 m is therefore driven as a pilot tunnel to observe the ground behavior during excavation, and to obtain information on the geological conditions based on which type of support structure is determined with consideration given to the results of field measurements and numerical analyses.

Jan 1, 2001

By Mario E. Rossi

The concept of entropy is classical in thermodynamics and information theory. Its potential use as a measure of the ordering of a spatial system is discussed. Although entropy has been discussed previously in the framework of spatial statistics and for univariate distributions, a bivariate data-based estimator has not until now been defined. Different statistical distributions maximize entropy, depending on the univariate, bivariate, or n-variate constraints applied. For bivariate distributions, with a known mean and known covariance, it can be shown that the distribution that maximizes the entropy of the system is the bivariate gaussian. A nonparametric bivariate entropy estimator is introduced, derived directly from the experimental cumulative frequency distribution. Assuming that this experimental bivariate distribution is representative of the population distribution, then a measure of departure from gaussianity can be introduced as a relative entropy estimator. Practical applications for the entropy estimator are discussed, and an example developed.

Jan 1, 1992

By Yuanping Chen, Yihui Zhao, Yunhe Hong

It is important to study the methane transport phenomenon in a longwall panel under descentional ventilation conditions. The gob area is divided into a number of rectangular percolating elements, each of which is connected with its neighbors by leakage passages, so that a network can be formed. Using the mechanics of porous media fluid flow, the mathematical model of air and gas flows can be established. Based on the existing ground pressure theories, the inhomogeneous porosity of the porous media in the gob can be given. Through computer simulation it is found that air pressure and temperature are functions of position. Air density, viscosity, and natural ventilation pressure are functions of temperature, pressure and methane concentration. It is also found that the resistance varies with air density and viscosity. Finally, the calculation results are given to show the differences between ascentional and descentional ventilation methods.

Jan 1, 1991

By S. Subramanian, K. A. Natarajan, D. N. Sathyanarayana

FTIR spectroscopy is used to study the ad¬sorption of an oxidized starch on hematite, corundum, and quart: substrates. The difference spectrum of the adsorbed starch on hematite indicates surface reactions involving -CH2OH and -COH groups and shows striking similarities with that of the ferric-starch system, suggesting chemical interaction between the iron of hematite and the starch adsorbate. The IR spectra of starch adsorbed on corundum and quart: show no evidence of chemical interaction, although hydrogen bonding is apparent. The extent of adsorption of starch on hematite. corundum, and quartz decreases along the series. The evidence for chemical interaction of starch with hematite is further obtained by the X-ray photoelectron spectra of starch adsorbed on hematite, showing noticeable decrease in peak positions of O(Is) and C(Is) of free starch. The Mössbauer spectrum of hematite with stanch adsorbed on it complements these findings.

Jan 1, 1990

By Ben H. Daud

The systems optimization approach to mine planning has led to the adoption of a number of mathematical and computer models for short, medium and long range planning of mining operations. In the realm of open pit mine planning, the most common uses of such an approach have been in the areas of optimal pit design and planning of materials handling operations. Since a truck-shovel combination is the most widely used method of materials handling in open pit mines, a number of models have been presented in the past to analyze and optimize such systems. Broadly, these models can be divided into two categories. The simulation model, which is primarily used as an aid in analyzing the performance of either an operating or a proposed haulage system under the influence of externally alterable parameters, and the linear or integer model which is used as a tool for short or medium term optimization of the system under the operating constraints. In the first part of this paper, a brief discussion is presented of the linear/integer optimization models presented in the past, and in the second part a new model is described which is actually a combination of the simulation and the integer programming models. In its bare essentials, the model consists of an integer optimization algorithm, but the constraints are regularly and dynamically updated by incorporating the conclusions drawn from a stochastic simulation model of the mine haulage system. Since the successive optimization is performed by the mine operator who manipulates the constraints to guide the model towards the optimum, the mystical black box approach is minimized and should help in adoption of the model by the mine personnel. Also, by combining the stochastic simulation model and the deterministic integer model, some of the advantages of each are acquired.

Jan 1, 1976

By Steven J. Stokowski, Frederick M. Bodycomb

This chapter deals with the use of industrial minerals in insulating materials used to control our thermal and acoustical environment. There are numerous products on the market used for thermal and acoustical insulation; they consume substantial quantities of a variety of industrial minerals. Following is a brief review of the theory and function of insulating materials. Acoustics is the science of sound, and architectural acoustics deals with sound in buildings. If this definition is broadened to include transportation vehicles, it is this end use for which acoustical insulations are primarily manufactured. Sound is defined as the auditory sensation in the ear, or the disturbance in a medium which causes this sensation. Acoustical insulation is used to reduce or eliminate noise, defined as unwanted sound. Noise control may be accomplished by the reduction of sound radiation at the source, by utilizing sound reducing construction methods such as staggered studs, etc., to control sound transmission, or by using sound absorbing material on walls, ceilings, and floors (Rossing, 1985). Acoustical insulation functions by absorbing the energy in sound waves in a porous material. As the sound waves penetrate the pores, they are dissipated by reducing the amplitude of vibration of the air molecules by contact with the pore walls, with subsequent conversion of the sound energy to heat energy. Acoustical insulation is generally highly porous, 1.3 cm or greater in thickness, and has interconnected pores. Acoustical insulating materials include fibrous vegetable or mineral matter and cellular organic and inorganic material, such as natural or manufactured foams (Sabine and Moulder, 1979). Acoustical materials are most commonly porous boards and tiles, which are often composite materials with perforated facing. Roof insulation board and lightweight concrete can also contribute to the absorption of noise. Thermal insulation is defined as material used to control the flow of heat. It may be used for heat control from low cryogenic temperatures (below -100°C) to in excess of 2 200°C for applications such as ablative shields for spacecraft. Heat transfer occurs by conduction, convection, or radiation. Conduction is the transfer of heat without the movement of the conducting medium, as through a metal. Heat convection through a liquid or gas takes place by movement of the medium. Forced convection is the basis for heating and cooling equipment, utilizing pumps or blowers to transfer the thermally conditioned fluid. Free or natural convection occurs due to density differences in the fluid. Radiation is the transfer of energy in space (Eckert, 1985). Conduction of heat through a solid is reduced by insulating the body with foams, or fibrous or small celled granular material. Heat transfer through a gas (convection) is controlled by creating many small pores which inhibit the movement of the fluid, substituting a gas of low thermal conductivity, or evacuating the space. Heat radiation can be reduced by the use of materials that reflect or absorb the energy (Glaser, 1967). Thermal insulating materials may be vegetable or mineral fibers, organic or inorganic particles, or foams with small pores, generally used to form a low density thermal barrier. They may be blocks, poured lightweight cementitious materials, bricks, etc.

Jan 1, 1994

By Erik Westman, Enji Sun, Xu Ma, Ben Fahrman

"Shale gas has become an increasingly important clean energy, which has been explored worldwide in recent decades. Supercritical CO2 acts as fracturing fluid for shale gas production. The safety monitoring is essential to prevent any kinds of leakage from the reservoir as the supercritical CO2 physically stored hundred kilometres underground. Seismic tomography is an imaging technique that uses induced seismic waves to create three dimensional images of the subsurface. It is an effective monitoring method to evaluate the caprock integrity in the carbon dioxide sequestration storage (CCS). In this experimental research, a simulated uniaxial compressive load is applied on a granite sample to analyze the stress redistribution for long-term in-situ caprock integrity during CO2 injection. The induced seismic waves are recorded and seismic events are traced based on the Geiger algorithm. The frequency of seismic events correlates with the caprock failure evolution. The acquired seismic data is divided into four regimes based on the frequency of seismic events and the failure process to examine the failure evolution. Furthermore, the travel time and distance is plotted to analyze the variation of velocity. Finally, the double difference tomography (TomoDD) algorithm using arrival time is adopted to recalculate the locations of seismic events and velocity structure in each regime. The results indicate that the passive seismic system can map the caprock stress distribution and allow for imaging of the caprock integrity. TomoDD exhibits sound improvements to relocate seismic events both in relative and absolute locations as well as to characterize the local velocity structure. The study further reveals that seismic monitoring along with TomoDD could evaluate the caprock failure accurately in the CCS.Introduction To reduce the CO2 concentration in the atmosphere, CO2 capture and sequestration (CCS) has been suggested to as a means of continuing to use fossil fuel resources while offsetting their negative environmental impacts (Eiken et al 2011). A positive CCS project should retain 99% of the injected supercritical CO2 (pressure is greater than 7.38 MPa and temperature is above 31.04? and a density is of about 700 kg/m3) over at least 100 years (Davidson et al 2005). As large quantities of supercritical carbon dioxide are being injected into full scale storage projects, caprock stress is redistributing and the leakage could occur anywhere over a wide storage area (Hou et al 2012). Acoustic waves are emitted from the caprock, as it fractures due to the CO2 injection, which can be detected by passive seismic sensors (Shitashima et al 2013). Tomography techniques are advantageous for imaging the integrity of the caprock in the CCS projects. Velocity tomography uses waves to model entities based on the arrival time of waves (Westman et al 2001, Westman 2004, Luxbacher et al 2008). Seismic tomography is a data inference technique that exploits information contained in seismic records to constrain 2D or 3D models of the Earth's interior. It generally requires the solution of a large inverse problem to obtain a heterogeneous seismic model that is consistent with field observations (Kudryavtsev et al 2012)."

Jan 1, 2017

By Carl Eschman

Productivity from large walking draglines is primarily dependent on operator skills. This machine may be in operation three shifts a day, 364 days a year, and its output is directly related to coal uncovered and mine profitability. Dragline operators must have highly developed manual skills and be knowledgeable in mine planning and working strategies. When using equipment costing more than $25 million, some formal training is usually required before an operator is allowed to assume complete con¬trol; however, dragline operators rarely receive any structured training before operating these giant excavators. A form of apprenticeship is usually followed where an operator candidate progresses from a groundsman to an oiler position. As an oiler, he is permitted to operate the dragline for short periods under supervision. After apprenticeship, the operator is considered sufficiently prepared to operate the largest, most powerful machine at the mine. The apprenticeship training method has obviously provided the surface mining industry with skilled dragline operators; however, conditions are arising that require a realistic and effective training tool that can be accessed by mining companies. New mines -either planned, under construction, or recently opened in the West-do not have access to a pool of experienced operators and oilers as do Midwest mines. As coal mining activities increase in both the West and Midwest, demand for trained dragline operators could be required in a short amount of time. Also, the more productive techniques along with sound basics of strip mining are sometimes lost in the informal "OJT" training method. Modern draglines are the pacemakers of the strip mine, and are simply too expensive to be used as a training device where lost productivity and susceptibility to damage can directly affect mine output. The Dragline Training System is a logical first step in formally educating or retraining operators. The program, started by the US Bureau of Mines and continued by McDonnell Douglas Electronics Co. under contract with the US Department of Energy, was installed and evaluated at DOE's Carbondale Mining Technology Center in Carterville, IL, last year. It is now being operated by Southern Illinois University at Carbondale. System Description The Dragline Training System addresses specific environments and work practices encountered during an actual mining operation at a midwestern US surface mine. This area was chosen because of its high number of strip mines using large walking draglines. Most draglines in the region are Bucyrus-Erie 1370, 1450, and 2570 models, so the dragline trainer was patterned after the company's 1370 machine. Operating and emergency controls are sufficiently standardized for most large walking draglines, and peculiar dynamics and responses from any specific dragline can be programmed into the computer system. The computer simply prompts the user to select the manufacturer and any peculiar response or rate changes needed. A 46-m3 (60-cu yd) bucket is simulated, but for closer simulation, various bucket configurations can be provided. Dragline Trainer The dragline trainer uses the TV-model simulation technique. A scaled model of the dragline is positioned in a model mine. A television camera is positioned at the operator's theoretical eyepoint, and the view captured is projected into a large screen in full scale. The screen is positioned in front of the operator seated in a full-size cab at Bucyrus-Erie controls. By manipulating the controls, the trainee can operate the model dragline and observe its reaction in the television display. In addition to housing dragline controls and consoles, the wooden, oversized cab contains the digital computer, terminal, video recorder and monitor, power switch box, air conditioner, and has enough room for the instructor and five student observers. The 50:1 scaled dragline model contains servo-controlled functions for hoist, drag, swing, delta swing, and longitudinal and lateral position. The delta swing provides bucket lag during swing and a realistic pendulum action when the swing is terminated. The over-responsive second order servo system is designed to provide hoist, drag, and swing rates exceeding present draglines. In all cases, position servos are used for better control and sta¬bility. The normal rate operation of an actual dragline is computed for the specific machine and presented to the servo amplifiers as iterative position commands increasing or decreasing

Jan 6, 1982

By A. Ballester, F. Gonzalez, M. L. Blázquez

Pyrometallurgical process are usually used to recover valuable metals from metal sulphide concentrates. However, their use is diminishing as the cost of energy rises and pollution controls become strictes. An alternative method of treatment sulphides could be bacterial leaching due its simplicity and negligible contamination (1-2). This process is presently used commercially to re cover metals such as Cu and U from low grade ore concentrates. In spite of numerous researchs during recent years (3-5) there exists very little kinetic data concerning the speed of bioleaching process. The kinetic analysis of bacterial activity is related with the metabolism and growth of microox ganisms . This fundamental information permits ma- king the best utilization of bacterial oxidation and to suggest techniques which might increase the production of the products desired. However, bio- kinetic models are especially complicated due to the existence of many metabolic routes and parallel reactions which are important for the life of the bacteria. Microbiological oxidation of a mineral substrate is influenced by its own inicial concentration: This influence can be determined by means of a kinetic study. In a medium with sufficient concentration of nutrients (nitrogen, phosphorous and potassium) and an adequate supply of 0, and CO2, as the only & L source of carbon for the biochemical synthesis, the substrate concentration would remain the only limitation in the rate of leaching. In this case the Michaelis-Menten model could be applied (6). The model is based on an association of the enzyme (El with the substrate (S) with consequent decomposition of the latter into enzyme and products [ ] The rate of dissolution is defined by the equation : [ ] Were V is the rate of metal extraction (mg 1-1 1 h-1 ) ; S is the pulp density Mn is the maximum rate for metal extraction (mg 1-1 h-1) and K is the constant of Michaelis (concentration of substrate that yields Vm/2). This method is applicable only when the rate of bacterial growth is similar to the rate of metal extraction. It would therefore be sufficient to control the concentration of metal in the medium over the period of time. In the present work a systematic study of the kinetics of ZnS and CuFeS bioleaching in sphalerite and complex ore concengrates was carried out. The rate of dissolution of the Zn and Cu as function of the pulp density and temperature was determined. However, most oxidations of sulphide dissolution take place with a very slow kinetic; but, this can be accelerated considerably by the addition to the solution of suitable catalytic ions, as was Suggested many years ago by Bjorling (7). Such ions can exercise an important influence on the rate of the oxidation-reduction reactions, both homogenous and heterogenous, which take place during the leaching of sulphides; they also affect the nature of the reaction products. The action of catalytic ions has been fully developed in aqueous systems, but in the absence of bacteria (8 - 11) although the actual machanisms is not totally known. The mechanisms proposed as hypotheses in the literature (8) indicate that, in the case of ZnS, the catalyst ion act through an electrochemical mechanism according to the reactions: [ ]

Jan 1, 1989

By R. G. Lundquist

The idea that fragmentation for mineral processing results from some tradeoff between increased drilling and blasting and increased load on the primary crusher is well known. In a previous paper (Lundquist and Konya, 1963) the authors reported on the results of a laboratory scale study which attempted to quantify this tradeoff in energy terms. If we look only at the production of new surface area, blasting is 1700 times as energy efficient as crushing. On an energy cost basis, crushing is 57 times as expensive per unit surface produced as blasting with dynamite and more than 700 times as expensive as blasting with ANFO. The comminution process at an open pit operation starts with the drilling of blast holes and ends after the material has gone through the fine grind circuit. Operators usually break the process into several separate operations and do their cost analysis based on this approach. Often drilling and blasting is considered as one system and crushing and grinding are considered as one or two separate and independent systems. Operators will independently optimize each system. The cost for the drilling and blasting system is obvious in operations which use contract drillers to do the drilling and either contract the blasting to a distributor or do the blasting themselves. The cost of rock breaking in this manner is readily available since the contract driller will supply a monthly drilling cost to the operation and either the distributor who is contracting the blasting or the distributor who is supplying the powder to the blasting operation will also supply a monthly billing. In either case, the costs can easily be seen on a monthly or per ton basis. They are not difficult to compute even when drilling and blasting are done entirely in-house.

Jan 1, 1985

The engineering company's participation in quality assurance in the mining industry is twofold. Not only must it have such a program to ensure the necessary high standards for its own design and construction of a minerals processing plant, but it is also responsible as the "engineer" for both the selection and the quality of purchased equipment which goes into that plant. It is in this latter role that the engineer finds the most difficulty, or controversy, since while it is relatively easy to control his own performance, this is not ncessarily so when dealing with companies, all with their own ideas or standards. The engineer has perhaps rather reluctantly become more involved with the quality assurance of purchased equipment. This is because he has been used to writing performance type specifications and expecting the equipment manufacturer to provide the degree of quality, and control of that quality, for the product to meet the specified operating conditions. However, this has sometimes placed the manufacturer in a difficult position since to remain competitive in today's market conditions, he cannot always insist on product improvements or options which may in the long run be vital to reliable operation of the equipment.

Jan 1, 1982

By Paul D. Chamberlin

There are many unit operations applicable to the processing of gold/copper ores. Deciding which are most applicable to your ore can be done using a series of tree diagrams. The diagrams show generalizations, not definitive rules. And the listing of process alternatives on the diagrams is very limited although there are dozens to choose from. Three questions help point the way to proper process selec-tion: 1. How much gold is in the ore? 2. How much copper is in the ore? 3, What is the cyanide consumption when leaching the ore?Halogens can also effectively leach gold ores and gold/cop

Jan 1, 1996

By W. A. Rickelton, A. J. Robertson

The ability of triisobutylphosphine sulfides to selectively recover silver from acidic sulfate solutions containing zinc and copper is described. Selectivity is explained in terms of the concept of hard and son Lewis acids and bases. Silver is stripped from the solvent using a novel strip feed (thiosulfate salt), and the recovery of metallic silver from the strip liquor by electrolysis or cementation is suggested. The high selectivity of extraction for silver and the utility of the stripping reagent are demonstrated in continuous, countercurrent, mini-plant tests. Important reagent properties, such as hydrolytic stability and low aqueous solubility, are discussed.

Jan 1, 1988

By Chris C. Sundberg, Ronald E. Heuer, Stanley L. Paul, Peter M. Douglass

Use of prestressed concrete cylinder pipe (PCCP) for pressure tunnel liners is gaining popularity with contractors, engineers, and owners. This paper presents loading considerations and a beam-spring computer model approach to tunnel liner analysis, together with ultimate strength (US) and service load (SL) procedures for liner design. The US procedure is best suited to check for adequate liner strength under extreme loading conditions. The SL procedure, based on conventional pipeline design practice, is considered more appropriate when addressing crack control and serviceability under normal working load conditions. Other design and construction considerations are discussed and a design example is presented.

Jan 1, 1987

By M. P. Meehan

The purpose of this paper is to present the key elements in a system; study of the electrical system for a timing and/or tilling operation. The ability of an electrical system to function in a reliable fashion at its proper levels is essential for an operation to be successful. A system study consists of a load study for determining the capability of the electrical network to provide power to the various loads and a short circuit study for determining the capability of the electrical protective equipment to properly protect against fault conditions. The sequence of events in a system study is data acquisition, determining the electrical parameters and analyzing the ability of the system to meet these requirements. If the system is small, herd calculations will be the manner in which the study will be conducted; if it is large then commuters will be used. A load study has as its objectives the determination of the capability and reliability of the source of power, transformers and conductors to satisfactorily deliver power to the loads at an acceptable voltage level. The Information required is a single line diagram showing the source, transformers, conductors and loads.

Jan 1, 1980

By Neil Jagger, Ian Arbuthnot, Mitchell Gordon

Ultra high density underflow is required in many thickener applications and in mineral processing is typically required for tailings to improve the thickened slurry rheology for either tailings dam development or for paste backfill applications. The improved liquid-solid separation resulting from the production ofultra high density underflow has both environmental and process benefits in the gold industry. Additional cyanide is recovered in the thickener overflow thus reducing plant cyanide costs and perhaps more significantly, a reduced quantity of cyanide is discharged to the tailings thus reducing either the toxic effect on the environment or the costs of cyanide destruction. Many gold and other mineral processing plants are situated in arid regions where the cost of water is high and the quantity often very restricted. Ultra high density thickened underflow results in increased recycle of tailings process water to the plant. In Countercurrent Decantation circuits, the wash efficiency is very dependent on the degree of liquid-solid separation in each thickener stage and the benefits ofultra high density underflow are either increased efficiency or decreased equipment costs as it may be possible to reduce the number of stages in the circuit.

Jan 1, 1995

By Richard Kolada

If the emission of methane into any particular area of an underground coal mine remains constant, then the calculation of ventilation requirements is relatively simple. This is also true if the ventilation system is recirculatory. However, the emission of methane into a working area can vary considerably. There is always a risk that the ventilation will not be able to dilute the emission of methane to acceptable levels, because there are often short-lived peaks of emission which are very large. The ventilation design must therefore consider what is an acceptable level of risks and calculate the airflow requirements to meet this level. The acceptable level of risk can be calculated by examining the historical variation in methane emission into the area to be ventilated. For example, consider that an acceptable level occurs when methane emission peaks only exceed the capability of the ventilation one day in twenty. Then, from the history of methane emission, it is possible to calculate the necessary ventilation requirements. This method has been used since the early 1980s for conventionally ventilated districts. This paper examines the application of this technique to districts ventilated by recirculatory ventilation.

Jan 1, 1987