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By S. R. Dismukes

Mining is likely to be targeted by The United States Environmental Protection Agency (“EPA”) as one of its key enforcement targets for fiscal year 2002-2003. Identifying the mining industry as an enforcement target, coupled with an increase in enforcement activity in recent years, places each mining operation at increased risk of receiving enforcement attention. A properly developed and implemented Environmental Management System (“EMS”) tailored for your operation is invaluable in reducing the risk of incurring liability for non-compliance. At the heart of an effective EMS is an audit program that checks the company’s compliance with environmental requirements. In addition, audit privilege (in select states), voluntary self-disclosure, and the attorney-client privilege serve as very effective tools for managing those liabilities that may arise during auditing a well-developed program. Of course, these latter tools are effective only if the auditing program is properly structured and properly managed. EPA and some states also provide varying degrees of immunity for environmental violations that are voluntarily disclosed in writing by the company. However, self-disclosure laws and policies typically prescribe stringent requirements for parties seeking to take advantage of them. For example: U.S. EPA has recently extended the time period in which to provide full written self-disclosure to 21 days. However, U.S. EPA’s revised Self-Disclosure guidance also addresses when a company obtains knowledge of a violation for purposes of triggering the 21-day clock and specifically extends the knowledge requirement to include the company’s agents and consultants. This expansion increases the difficulty companies may have in clearly defining and managing when they obtained knowledge. This difficulty increases the importance of managing factual development and the strategic use of other

Jan 1, 2001

By S. Junnikkala, K. Föhr

"Experiments were performed with plant feeds with a continuous 1,8 m3 cell at Pyhasalmi mine with Cu flotation feed in order to test the applicability of the bubble surface area flux as an indicator of the flotation rate constant. It was found that bubble surface area flux could not predict the rate constants of coarse Cu containing fractions. In the middle size fraction, the correlation coefficient in the rate coefficient estimation was higher but not statistically significant. Only the fine fraction showed a linear relationship with a moderate correlation coefficient.The bubble surface area flux was shown not to be a function of the impeller velocity above a threshold value. The flux was an almost linear function of the superficial gas rate enabling to use the superficial gas rate instead of flux if the operation of an existing cell is to be estimated.INTRODUCTIONBubble area flux seems to offer a simple way of modeling flotation. It relates the flotation rate constant with the bubble surface area flux by a simple linear equation. Due to this, there has been a considerable interest in using the bubble area flux for flotation computations. It has even caused claims that a cell producing a high bubble surface area flux automatically produces a high rate constant and therefore a high recovery.This paper discusses some of the assumptions of the relationship and gives some plant results during two sampling campaigns.The bubble surface area flux s b is describing the area of bubbles available for flotation in a cell per unit area. The bubble surface area flux is related to the superficial gas rate J, by the Sauter mean diameter as follows"

Jan 1, 2001

By M. Hancer, J. D. Miller

It is known from soluble salt flotation practice that the K, Mg double salts of kainite (KClMgSO43H2O), and carnallite (KClMgCl26H2O) are difficult to float and must be converted to other salts such as schoenite (K2SO4MgSO46H2O) and sylvite (KCl) in order to recover potash values. The flotation characteristics of these double salts have now been confirmed in some detail by carefully controlled laboratory experiments with both cationic and anionic collectors. The experimental results are discussed in view of recent experimental findings regarding the flotation characteristics of simple salts, in which the flotation response was shown to be determined by the interfacial water structure and whether the salt could be considered to be a water structure maker or a water structure breaker. The same approach can be use to explain the flotation response of the potassium double salts ; schoenite, kainite, and carnallite. In addition, the sign of the surface charge of schoenite (K2SO4MgSO46H2O), was determined as a function of pH from nonequilibrium electrophoretic mobility measurements. Schoenite appears to exhibit three charge reversals (CR) which can be explained based on surface hydrolysis reactions. The flotation behavior of schoenite is further considered based on solution chemistry calculations, electrophoretic mobility measurements, and microflotation results.

Jan 1, 2001

By E Christodoulou, L Zoumpoulakis

The kinetics of the thermal decomposition of MgCO3 was investigated using isothermal experiments performed in a thermogravimetric analyzer under a nitrogen atmosphere at 380¦, 400¦, 450¦ and 480¦C. The weight loss data as a function of time were modified to give the fraction that reacted (ß) and the rate of reaction (dß/dt) vs. time (t). Kinetic analysis of the experimental results, using three different methods, showed that diffusion predominates the MgCO3 decomposition over the investigated temperature range, with the data being best fitted by JanderÆs equation ([1−(1−ß)1/3]2=kt). The activation energy was estimated by Arrhenius plots using both the initial reaction rates and rate constants from fitting the above equation. The values estimated were 27.1 and 171.4 kJ/mol respectively.

Jan 1, 2001

By R. J. Snoby, M. A. Short, A. Jungmann

In processing coal, the low concentrate value requires high capacity production and sharp classification/separation techniques to reduce specific production costs. The allflux separator meets these criteria with a unique two-stage design. Through a combination of rising current and fluidized bed technologies, the allflux has extended the state of the art by expanding the particle size range that can be efficiently processed. Using concepts that have proven successful in processing concrete sands, small-scale industrial testing with coal feed stocks looks very promising. Attractive applications for the allflux are projected in fine coal recovery from old settling ponds or as a retrofit in existing fines circuits.

Jan 1, 2001

By A. Broussaud, J. D. McKay

Benefits analysis of adaptive Expert control systems operating at plants in Africa and the United States are presented. Proper statistical tools and techniques are discussed. Technical and practical pitfalls of strategy comparison are also presented and illustrated with from published data. Advantages and disadvantages of a “Pay for Performance” approach to a project are reviewed.

Jan 1, 2001

By Paul C. Schmall, Thomas Tuozzolo, Arthur B. Corwin

The Lenox Avenue Reconstruction Project involved the excavation and replacement of 750 m (2,500 ft) of deteriorated subway invert concrete, 5 to 7 m (15 to20 ft) below water table in very permeable ground. The Replacement work was done over an 8 month period, while maintaining track service through this subway section. The project was dewatered with a single 125 l/s (2,000 gpm) wellpoint system,750 m (2,500 ft) in length, which was installed from inside the active tunnel structure and configured to coexist in the subway tunnel with operating trains as well as the construction activities. A thin diaphragm jet grout wall was utilized on one end of the site to cut off the flow of water across a difficult geological interface that was situated immediately below the tunnel invert. The thin diaphragm jet grout wall permitted the large 116th Street Station area to be dewatered completely with well points from outside of the excavation.

Jan 1, 2001

All minerals contain radioactive elements, from the uranium ores of the Gabon, which contained sufficient uranium to initiate a natural nuclear reactor, to the very low levels of some recent evaporites. The commonly occurring heavy minerals such as ilmenite, rutile and zircon are no exception to this and contain varying qualities of radionuclides, depending on the source. With recent changes in legislation many natural minerals may become officially classed as radioactive. Such moves can inhibit the sales and exploration of many minerals in the heavy minerals suite. The many negative perceptions associated with the word radioactivity can produce an over cautious reaction from regulators and users. This paper presents a method of managing the radioactivity issues associated with minerals such that the safety aspects of workers and public are not compromised, whilst allowing the commercial use of such minerals to continue in a sensible manner. The paper focuses mainly on the mineral zircon and its uses. However the legislation changes particularly in Europe and the USA have the potential to affect all minerals imported into or produced in those countries. The model developed for addressing the issues of zircon radioactivity may be readily applied to other minerals since legislation governing such matters is not mineral specific. There is a strong need for education of both regulators and users of minerals. Regulators are usually not aware of the specific properties or uses of individual minerals. Similarly mineral users are not aware of the radioactive nature of their materials or how to manage this property. The paper concludes by recommending strong cooperative action by both producers and users of minerals to protect the future of their industry.

Jan 1, 2001

By Charles Vaught, Belinda Sue Mills, Henry P. Cole, William J. Wiehagen

This study reports the results of a survey of organizations that used problem-solving simulation exercises to support mine health and safety training. The exercises are designed to teach judgment and decision-making skills within two broad domains: (1) how miners respond to mine emergencies (e.g., first aid, self-rescue, and escape) and (2) how miners integrate safety concepts within the context and performance of routine production work. The simulation exercises were distributed by the Mine Safety and Health Administration's National Mine Health and Safety Academy near Beckley, WV. The present study focused on those organizations that ordered the exercises from the Academy over a 2-year period (1995-96). Researchers assessed how the materials were used and trainer perceptions of the impact of these materials on annual mine health and safety training . A total of 147 organizations ordered the exercises over the 2-year period. Survey responses were obtained from 52 of these organizations. Sixty percent of the respondents rated the exercises as more useful than traditional instructional materials, 40% as equally useful, and 0% as less useful. Most trainers (79%) felt that the exercises help them to make better use of workers’ knowledge and experience during training. Many (71%)also reported that the simulations helped to improve the effectiveness of their instruction and promoted a problem-solving approach to their training. Fifty of the fifty-two respondents reported that they would like to have new simulations developed. A large majority showed a proactive interest in helping to develop and field test new exercises. Ninety-four percent of the trainers judged the exercises as a good value; 92% planned to order more simulations in the future. Based on this study, recommendations are offered for the continuation and expansion of simulation exercises as one method for occupational health and safety training.

Jan 1, 2001

By C Li

Removal of gangue minerals from ilmenite concentrates can be accomplished by relatively low temperature roasting in controlled gas atmospheres to selectively enhance the magnetic separation characteristics of the ilmenite. At roasting temperatures below 800¦C the magnetising reactions are often not consistent with phase equilibria considerations. Metastable phases can nucleate and control the roasting products. In weathered ilmenites the phase assemblages and microstructures in the altered ilmenite grains can influence the roasting reactions. In this paper we give an overview of the phase chemistry of chemically weathered ilmenites and of metastable phases formed by low temperature roasting. We also report the results of roast experiments conducted in a neutral gas atmosphere. Major increases in magnetic properties after short roasting times at low temperatures were obtained for a range of ilmenite concentrates. For example heating a secondary ilmenite concentrate from Western Australia for 15 minutes in nitrogen at 600¦C gave an increase in the three kilogauss magnetic fraction from three to 92 wt per cent. The solid state phase changes accompanying the inert atmosphere roasts were characterised by combining elemental analyses with quantitative phase analyses of the ilmenite concentrates and their roast products. It was found that the phase reaction that is principally responsible for the increase in the magnetic properties of weathered ilmenites involves a transformation of disordered ferrous-containing pseudorutile to an ordered ilmenite-hematite solid solution containing typically ten to 35 mole per cent of the hematite component. Examples are given of the application of the inert atmosphere roast to effect separations of ilmenite from gangue minerals.

Jan 1, 2001

By R. Owen

The vision-based approach to process control involving fine particles in harsh on-line environments is discussed in this paper. The sensor equipment at the process location, consisting of a light source and a CCD camera provides RS-170 B&W video output. The video can be seen on a process monitor in the control room and is sent to a computer based Vision Processor. The Vision Processor contains a video digitizer and Canty developed software that extracts process information. The iron mine application controls thickener agent feed rate and thus settling pond overflow clarity. The sensor is mounted in the overflow flume of the outdoor settling pond and is used year around in the Minnesota weather. Alternate control system needs a low flow water sample which is subject to freezing in winter. The computer based vision processor provides 4-20 mA analog outputs for real time control as well as file archive for a history record.

Jan 1, 2001

By A. Vien

Over the past several years, Svedala has developed a continuous charge monitor (CCM) for tumbling mills. It consists of a strain gauge embedded into a rubber lifter and associated electronics. This paper describes the results of a research program to evaluate the technical and economical merits of such a device on a SAG mill. The evaluation includes validation through discrete element modelling and comparison to measured static volumetric load. Inclusion of the measurement into a control strategy and its potential for condition monitoring is discussed.

Jan 1, 2001

By K A. Pericieous

"Magnetic fields have many actual applications in the metals processing industry. Externally applied magnetic fields give rise to electromagnetic (Lorentz) forces formed by the cross product JxB, between the induced current density J and the magnetic field density B. When the metal is in liquid form, the Lorentz force generates motion in the fluid which in applications of practical interest becomes turbulent. In modelling terms, the Lorentz force appears as a source in the momentum equations. In addition, the induced current generates heat (Joule heating) in the metal that is in proportion to J2, with a corresponding source of heat in the energy equation. Whether as heat or as a force, these effects represent action at a distance - a most useful attribute when dealing with hot metal. The Lorentz force is used to stir solidifying alloys, pump liquid metal in conduits, dampen the flow in the meniscus of a continuous caster, levitate metal drops, induce artificial gravity conditions in suspensions or contain liquid metal. Elsewhere, the Lorentz force may be a by-product of some other operation, so leading to wave excitation in aluminium electrolysis cells, or altering the shape of the weld pool in arc welding. Joule heating is most commonly used with applied AC fields, to melt metal in induction furnaces.The author and his colleagues have been involved in the modelling of most of these processes in the past decade. Modelling is not however straightforward, since most of the examples mentioned represent genuine multi-physics challenges. There is a strong coupling between the flow field and electromagnetic field. The addition of a dynamically varying metal free surface and the moving solidus front means the flow, heat and electromagnetic fields need to be computed simultaneously. In situations involving metal containment, the metal free surface position is governed by the interplay of gravity, Lorentz force, surface tension and fluid inertia. Since all the interesting effects often happen in thin boundary layers at the surface due to the skin effect, mesh generation and mesh control during the computation become non trivial problems that need to be addressed. This paper presents a review of numerical methods used to model droplet levitation, semi-levitation melting and cold crucible induction melting of metals. The first method is based on spectral collocation techniques and the second is the traditional FV approach. Steps taken to validate the computations and typical transient results are also given."

Jan 1, 2001

By Robert J. Whiteley, Colin Parker

Two major tunnel projects with a combined value of about $US700 million have been recently completed in Sydney using both soft ground and hard rock Tunnel Boring Machines. The first of these and the main entry in Australia for the Year 2000 Olympics was the New Southern Railway. This is 10 km of mainly soft ground tunnel linking the Sydney’s International Airport with the Central Business District. The second tunnel was designed to alleviate major stormwater pollution of Sydney Harbour and involved construction of the Northside Storage Tunnel. This is19 km of hard rock tunnel at depths exceeding 90 m that connects many of the northern Sydney suburbs of Sydney with the North Head Ocean Outfall. Case studies of these projects describe the use of innovative geophysical technologies comprising gravity and seismic tomographic imaging with geotechnical testing at the feasibility and design stages. This approach minimised construction and financial risk by effectively quantifying the significant geological and hydrogeological issues along these tunnel routes that exerted major controls on these projects.

Jan 1, 2001

By M. M. Botz

There are currently more that 460 mines worldwide that utilize cyanide for gold and silver extraction. Despite this large number of cyanide-related mining operations, there have been no published accounts during the previous 25 years of the death of humans due to cyanide as a direct consequence of major mining-related environmental incidents. All published accounts of human deaths due to mining-related environmental incidents have been the result of physical inundation with tailings or waste rock materials. It appears that major mining-related environmental incidents have not been concentrated in any geographic location, are likely to occur regardless of the size of the mining company and do not occur more frequently with a specific type of mining activity. Several cyanide treatment and recovery technologies have been widely demonstrated to reliably control cyanide levels in mining solutions. With proper use of these technologies, tailings cyanide concentrations can be maintained at levels protective of wildlife while reducing the potential for adverse environmental incidents. The development of an international cyanide code of practice or management plan is recommended and should take into consideration the adoption of a weak-acid-dissociable (WAD) cyanide standard that maintains the levels entering a tailings impoundment below 50 mg/L.

Jan 1, 2001

By Alok Garg, Rajeev Kumar Dayal

The Himalayan ranges have complex geological formation induced with locked up tectonic stresses and squeezing ground conditions. High overburden, steep slopes, perennial snow, and forest cover restricts accurate prediction of geological features, resulting in surprises during excavation. The tunnel planning under high altitude, extreme climatic, and unfavorable approachability conditions requires elaborate detailing. The construction technique and working faces for excavation are influenced by site accessibility/high overburden conditions, restricting the provision of access tunnel or shaft. The paper discusses site constraints influencing construction method and working faces for 8.9 km long highway tunnel at elevation 3,000 m under 1,900 mover burden through quartz-mica-schist formation.

Jan 1, 2001

By Siegmund Babendererde, Jan O. Babendererde

Extruded Concrete Lining combines technological and financial advantages. The tunnel lining is reliably embedded in the surrounding ground as the fluid concrete is extruded at constant pressure directly behind the TBM supporting the exposed surface. Ground deformation from the TBM passage can be compensated and the ground will be pre-stressed by the extrusion process. Developments in concrete technology permit high speed tunneling by use of a slip formwork attached to the TBM. Realised projects in Milano (Italy), Lyon (France), Frankfurt (Germany) and Akima (Japan) will be demonstrated.

Jan 1, 2001

By W. G. Davenport

Chapter 1 showed that flash smelting is a key step in extracting copper from sulfide ores. It also showed that there , are two versions of flash smelting: (a) Outokumpu flash smelting, which uses oxygen-enriched air blast and injects dry feed downwards into a hot furnace (b) lncoflash? smelting, which uses industrial oxygen blast and injects dry feed horizontally into a hot furnace. This chapter describes Outokumpu flash smelting.

Jan 1, 2001

By S. K. Kawatra, S. J. Ripke

During 1998, 62 million tons of iron ore pellets valued at $1.7 billion were shipped from U.S. mines. These pellets are the primary source for domestic iron and steel production. During pelletization, binders are required to improve the green strength of the pellets. Each year, bentonite binder costs a typical plant from $3 million to $5 million. Reducing the bentonite dosage has the advantages of significant cost savings while producing higher quality, lower silica pellets. The authors have recently identified a new and important bentonite binding mechanism, the fiber theory. During this study, procedures were developed that took advantage of the ability of bentonite to form fibers, and resulted in a dramatic decrease in the necessary bentonite dosage. Acceptable quality pellets were produced with the bentonite dosages reduced in half from 14 lb/lt (0.66%) to 7 lb/lt (0.33%).

Jan 1, 2001

By Vaughan R. Voller

"The wide range of length and time scales found in solidification processes are outlined and discussed. Methods for Direct Microstructure Simulation (DMS) are introduced. Key features in sharp interface and phase field models are presented. Concepts in micro-macro solidification modeling are covered. Basic details of microstructure and segregation models are provided. A description of a recent segregation micro-macro model is presented in detail.IntroductionA solidification process involves the containment of a liquid region, which, due to cooling, transforms over time to form a fully solid product. The development of the solid microstructure and the segregation of solute components during this transformation are controlled by phenomena that occur across a wide range of length and time scales. A ""successful"" model of a given solidification process needs to account for these phenomena. Standard models of solidification employ a discrete grid of node points and associated volume elements in the special domain, with a discrete time step to track the transient changes of nodal values, describing the composition and microstructure. Through the use of such models significant progress has been made towards a complete understanding of solidification process and phenomena (see the conference proceedings in Refs [1-9]). As solidification models become more sophisticated, however, they all run into the problem of resolving the full range of disparate space and time scales.Two approaches can deal with this problem1. Direct Microstructure Simulation (DMS) where the grid size and time step are chosen to scale with the smallest length and time scales of the given problem.2. Micro-macro modeling where the grid size and time step scale with the macroscopic process scale and phenomena at smaller scales are accounted for via sub-grid modeling and volume averaging.Currently full DMS of solidification is beyond the reach of available computer power and the application and development of micro-macro models is an important and critical research area."

Jan 1, 2001