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By Preben Ingerslev

Control of the reheating of ingots is based either on surface temperature measurements using optical pyrometers or on furnace set points and reheat time determined empirically. This paper presents a real-time mathematical heat flow model, named BESTT, which calculates the temperature distribution in an ingot cross section when reheated or cooled. The model runs on a 486 PC in less than one minute for a variety of ingot cross sectional shapes such as circular, square and with some considerations octagonal and heavy-cornered square. Initial temperatures can either be uniform or nonuniform while accounting for temperature dependent thermophysical properties. The model was developed and verified using 718 alloy ingots in box type furnaces. When integrated with on-line pyrometric measurements, BESTT can provide for improved feed back in the reheating control loop. The use of BESlT will assist in reducing energy costs, and improving product quality and consistency. EPD Congress 1994 Edited by C. Warren The Minerals, Metals k Materials Sodety, 1993

Jan 1, 1994

By J. Bacho

The modern drilling fluids industry is a dynamic, evolutionary environment. It is continuously striving to satisfy and anticipate the ever-changing needs of the oil and gas industry. The predominant driving forces in the industry over the past decade have changed dramatically. Health and environmental issues, coupled with economic and performance requirements, demand innovation and change from the drilling fluids industry. Emerging drilling fluid technologies will demand environmental considerations from mined components with additional emphasis on cost and performance criteria. Drilling fluids providers continue to search for and identify environmentally sensitive components which meet or exceed the performance of their more toxic predecessors. These changes have and will impact the components of drilling fluids that are mined.

Jan 1, 1994

Structural geological information is widely used at the Mt Whaleback Mine, Newman, WA. Recent improvements in the structural understanding of Mt Whaleback are providing a very cost-effective way of reducing geological risk, improving the economics of mining, optimising pit design and addressing safety problems. The structure of the Mt Whaleback orebody is highly complex and has a significant influence not only on iron ore genesis but also on pit wall stability. A team approach between the Structural Geology and Geomechanics Groups has been providing excellent results to reduce geological risk at Mt Whaleback.

Jan 1, 1994

By P. R. Taylor

A review of the advantages and disadvantages of plasma technology for metal and mineral wastes is presented. Examples of the use of plasma systems are given and possible future uses are outlined. Among the potential uses are treatment of electric arc furnace (EAF) dusts, the vitrification of nuclear wastes and the removal of toxic metals. Over the past few decades, plasma technology has been studied for potential applications over a wide range of metals/materials processing areas. One promising area of plasma technology applications is the treatment of industrial hazardous waste. The potential generation of hazardous and toxic waste by various industries has become a matter of public and political awareness. Environmental regulations have put stringent toxicity emission limits on disposable waste streams. An intensive research effort is currently underway in the area of hazardous waste treatment.

Jan 1, 1994

By B. R. Addison

In the Spring of 1991, Georgia Marble Company of Arizona (GMCOA), acquired the Andrada Marble Company located near Vail, Arizona, approximately 32 km southeast of Tucson. The Georgia Marble Company operation consists of an open pit quarry and a recently constructed, state of the art calcium carbonate milling and processing facility. The open pit quarry exposes white, crystalline, CaCO3, Escabrosa limestone that meets our customer criteria for Consumer and Industrial Filler applications. The Georgia Marble Company Arizona Division facility is designed and engineered to produce a wide range of milled calcium carbonate that includes finely ground and coarse screened products.

Jan 1, 1994

By Pat McLaughlin

Blast design in the construction industry has often been based on past practice or powder factors. This is to some extent understandable, since construction projects do not have the longevity of mining or quarrying operations and therefore have less opportunity to pursue potential improvements. The main concern of the operator is whether or not the technique will work, and at what cost to the downstream processes. Time, not long term savings, is of the essence.

Jan 1, 1994

By B. G. Thomas

"Mathematical process models can be applied in several different ways to serve industry by inducing beneficial changes to process operation. This paper attempts to summarize the different uses, types, and attributes of these models, and to offer some ideas to consider when developing, using, and reporting on them. Process models range from empirical to mechanistic in nature and vary in complexity from simple analytical solutions to coupled, 3-D transient numerical simulations. They are classified here according to the way in which they are implemented in practice, viz. fully-online models, semi-online models, off-line models, and literature models. The purpose of the model should dictate how choices are made during its development. Ways to validate and compare the model with experiments are suggested. Examples are taken in the context of the author's experience in modeling the continuous casting of steel.IntroductionThe objective of this paper is to provide a partial introduction for this symposium by discussing some basic aspects of the application of mathematical process models in industry. Essentially, the aim is to explore how process models are used to benefit industry, and to offer some general comments and suggestions, based on the experience of the author, on how models can best meet this goal.This work is concerned with process models, which consist of systems of mathematical equations and constants that are solved on a computer to make quantitative predictions about some aspect(s) of the process. The specific variables required as input data and generated as output data are important features of the model. The equations often derive from a numerical solution to one or more differential equations and their boundary conditions. The model also includes the constants, which represent material properties, empirical relationships, and other knowledge about the process, and usually require considerable effort to obtain. Thus, general purpose commercial software packages, (ie. finite-element or finite-difference based codes), are not models in this context. They are useful tools, however, serving as frameworks for the development of process models."

Jan 1, 1994

By E. Hosca

Alternative tailgate loading conditions due to conventional and conventional/yield pillar combinations were evaluated to define roof loading. In order to isolate different loading situations, the tailgate entry was considered as part of the roof-pillar-floor system, which is controlled largely by the structural integrity of each member. A data bank of case studies was compiled, which contains details of roof and floor lithology, structure, support, and mining data, including any failure modes. The range of loading conditions that any tailgate can be subjected to was identified to form the basis of numerical modeling. Numerical modeling was then conducted on tailgate openings to determine roof, floor, and rib responses, including failure modes to a variety of loading conditions. Trends developed from the numerical modeling were modified using field data to form the basis for support evaluation and application. The effects of support were modeled numerically to determine optimum load capacity and points of application for reducing the potential for entry failure.

Jan 1, 1994

By E G. Prado

We have confirmed on bench scale the removal of chlorides and alkalies (+95%) and over 2/3 of the zinc, lead and cadmium from EAF dusts. This has been achieved with arrononium acetate solutions alone, or with combinations of water wash, amonia-ammonium carbonate and ammonium acetate solutions. Also confirmed are the process routes for the recovery of the aforementioned elements into marketable products. The technology involves the complete recycling of the reagents. The FAF residue is returned to the electric furnace without risk of impurities buildup. Commercial scale testing with the recycled dust was satisfactory, including quality of the slag and its behavior during the melting stage. A cursory feasibility evaluation is presented.

Jan 1, 1994

By Charles T. Steuart, Richard B. Berg

Tripoli and the related mineral commodities such as micro- crystalline silica have been mined for more than 100 years for their abrasive properties. Although abrasive and buffing compound markets are still very important, within the last 15 years the filler and extender markets in paint, plastics, rubber, adhesives, and sealants have increased substantially. Tripoli or microcrystalline silica consists almost entirely of very small quartz crystals, many less than one micrometer in length. Material mined from different districts differs in crystal shape, grain size, and texture of the rock, all of which influence markets. Most US deposits are now mined by surface methods, and both air floated and micronized products are marketed. Deposits of tripoli now mined in the United States occur in chert-bearing Paleozoic limestone in the central part of the country with producing districts in southern Illinois, central Arkansas, and eastern Oklahoma. Although deposits within each district are confined to specific formations and extend laterally within those formations, individual bodies form minable deposits that are typically several hectares in areal extent. Tripoli is white to cream to rose and characterized by high porosity and ease of disaggregation. DEFINITIONS Tripoli In the United States, tripoli was first used to describe the fine-grained, easily disaggregated material from Seneca, MO, be- cause of its similarity to a rock from the Tripoli region of North Africa (Hovey, 1894). The North African rock is actually diatomaceous earth, a material that is similar in appearance to the rock from Seneca, but is of entirely different origin having formed by the accumulation of siliceous remains of microscopic marine or fresh- water animals. Tripoli is best defined as a very fine-grained, generally porous rock that consists of microcrystalline quartz, typically formed by the alteration of a chert-bearing limestone. Tripolite A term used to describe a rock from the vicinity of Tripoli in North Africa which is diatomaceous earth (Quirk and Bates, 1978) Microcrystalline Silica Microcrystalline silica is the same material as tripoli, but the distinction between the use of these two names is dictated largely by convention and markets. Material produced from southern I1linois deposits and used in white pigment and filler applications is generally referred to as microcrystalline silica, whereas that used in abrasive applications, both from the Illinois district and from other states, is commonly called tripoli. Amorphous Silica Amorphous silica, a term formerly used to describe the material produced from the deposits in southern Illinois, is now replaced by the term microcrystalline silica. Amorphous silica came into use when even optical methods for the identification of very fine- grained quartz were not widely available and the Illinois product, composed of quartz grains too small to be seen with the unaided eye, was thought to consist of amorphous silica. The Illinois material is clearly crystalline quartz, as shown by X-ray diffraction analysis and scanning electron microscopy (Fig. 1). Novaculite Although originally used to describe a rock suitable for the manufacture of whetstones, novaculite is now defined more generally " - as a homogeneous, mostly white or light colored rock, translucent on thin edges, with a waxy or dull luster, and almost entirely composed of microcrystalline quartz" (Steuart et al., 1983). The more compact rock mined in central Arkansas from the Arkansas Novaculite is referred to as novaculite, whereas the more porous rock is referred to as tripoli. Rottenstone The commodity rottenstone is sometimes included within the general mineral commodity category of tripoli. Rottenstone is mined in Northumberland County in eastern Pennsvlvania and formed by the weathering of a siliceous shale of Devonian age (Faill, 1979, Berkheiser, private communication, 1991). This material is used as a filler and extender, but is apparently unlike tripoli both in origin and physical properties. Spiculite Spiculite is a rock consisting of siliceous sponge spicules having formed by the removal by solution of the carbonate matrix of a spicule-bearing limestone. Spiculite has been mined in Texas and, because it resembles tripoli in several aspects, is included in the discussion of deposits.

Jan 1, 1994

By P. J. Lloyd

Society is fully justified in its concern about the environment, but that concern may, at present, be too uncritical It is, for instance, essential to establish that there is a valid environmental impact, and that there is truly a causal link between a human activity and an observed shift in environmental conditions. In establishing these, it inessential to recognize that scientific proof offers consistency, but that it can never provide completeness. Thus, no amount of scientific endeavour can ever prove that mitigation of the effects of human activity will be perfect. Society normally expresses its concern through legislation. The existing legislation in South Africa is reviewed, and it is found that [>legislation regarding water is probably too stringent to be effective, >legislation regarding air and land use is probably too lax, >all the environmental legislation is too fragmented to be efficient, and the Department of Environmental Affairs is hamstrung by inter-departmental rivalry. ] It is accordingly concluded that, if means are to be found for ensuring adequate mitigation of environmental impact in the face of ongoing economic development, it is necessary to establish a Judicial Commission on Environmental Affairs advised by, but given greater powers than, the departments currently active in environmental maters. This Commission should be charged with creating, perhaps over a decade, a body of legislation that would guide development while protecting the environment in its widest sense.

Jan 1, 1994

Optimal gold recoveries largely depend on efficient liberation of the gold or gold-bearing minerals as well as on maximum access for the lixiviant. Thus, crushing and grinding may become the most costly part of gold ore processing. It may, in fact, represent 50% to 70% of a plant's operating costs (Michaelis, 1989). The increasing significance of refractory gold will require even more cost-efficient comminution of ultrafine sulfides and/or native gold. Transitional ore zones with semi refractory gold may respond to direct leaching if better particle fracturing is being achieved (Baum, 1991, 1993a). Many oxide ores have been left in the ground because they were unsuitable for heap leaching since conventional comminution could not facilitate economic gold extraction. Also, the costs of conventional bal1 mill operations did not permit the recovery of gold from many ultrafine, low-grade refractory ores. As shown by Marsden et al. (1993), the trend to treat ores with progressively lower grades will involve power-and leach-efficient grinding applications. Our current laboratory work shows that high-pressure grinding roll (HPGR) Polycom grinding may enable many mining companies to add large amounts of these "non-leachable" ores to their current heap or mill leach feeds. This finding may dramatically change the economics of many oxide gold ore operations and may add significant reserves to ores amenable to direct cyanidation.

Jan 1, 1994

By Murray Hughes, Neil Brown, John Carran

"A control system architecture has been developed using the Ward-Mellor structured analysis techniques for real-time applications. This approach has produced several advantages over traditional control system implementation methods including:•,partitioning of the control system into discrete control functions.•,easy identification of the interaction between individual control functions and the rest of the system including the impact of changes at the control system boundary (i.e. additional inputs or outputs).•,simplified control software testing.•,a closed loop design, implementation and documentation process.This paper describes a generic control application in which the process specification and control system design are logically linked. Both components are used by process engineers for on-going development.IntroductionAluminium is reduced from alumina in multiple electrochemical semi-batch reactors. Raw material additions and molten metal withdrawal are made at discrete intervals ranging from seconds to days. The electrolytic reduction process is continuous, despite the semi-batch nature of the material inputs and outputs. The chemical and physical processes that occur within each reactor are complex and interdependent, therefore simple methods used for the control of many chemical processes are impractical. The process control system is required to optimise operating efficiencies within the safe operating zone.The process control of aluminium reduction cells is heavily biased towards calculation of process variables with relatively few measured sensors. Each cell is controlled independently of the other cells, although changes to process conditions and raw material . quality will affect all cells. The process responds relatively slowly and with significant time lags. Measurements and process variable calculations occur each second, however the accuracy and precision of actuator response and sensor sampling are measured 111 milliseconds. Time-based scheduling is a significant component of reduction cell control."

Jan 1, 1994

By King D, Dickinson S. B, Matheson R. S

Commencing in 1956, Rio TInto Australian Exploration Pty Limited in association with Electrolytic Zinc Co of Australasia, Limited, has been carrying out a mineral prospecting program in North-West Tasmania over an area of about 4000 square miles.The program has comprised extensive airborne geophysical surveys, detailed geological mapping, ground geophysical and geochemical investigations. Out of the wealth of new data, and the examination of previous records, has emerged a new structural concept of regional ore control and distribution in North-West Tasmania. This roncept stems from the discovery of an ancient 'fossil' rift valley (graben), named the Owen Rift Valley, along which are located the major mines of the area and numerous well-known prospects. The known mines and prospects from north to south include Mt Bischoff (tin); the Pinnacles (zinc, lead, ropper); the Chester (pyrites); Rosebery-Hercules (lead, zinc, ropper, silver, gold); Mt Tyndall (lead, ropper, zinc); Comstock and Tasman (copper, lead, zinc); Mt Lyell (copper, pyrites, gold); Mt Jukes and Mt Darwin (ropper). The identification of the West Coast (Owen Conglomerate) Range as a fossil rift valley is due to Or B Campana, who carried out extensive geological mapping and interpretation work, and who, with S B Dickinson, are the senior authors of this paper.S B Dickinson, who introduced B Campana to the geological problems of West Tasmania, had previously investigated the Mt Lyell and Rosebery mining fIeld, to which reference is made in this work.D King assisted in the regional mapping and in providing numerous data on the mineral distribution of the area.R S Matheson rontributed to the fmdings on ore emplacement and rontrol in the discussions held on this subject. They are accordingly included as joint authors of this paper.Credit is also due to E McCarthy, who interpreted the geophysical results, and to J H Rattigan, who compiled the preliminary geological maps from published documents and by photo-geological methods.G Hall and V H Cottle, of the Electrolytic Zinc Co in Rosebery, provided invaluable geological data and suggestions in the course of the survey, and made a constructive criticism of the manuscript of this work. The airborne geophysical survey carried out by the Adastra-Hunting Geophysics Ltd company, furnished useful data which substantiated many of the fIndings on the stratigraphic and structural relationship. The Mines Department of Tasmania and S W Carey, Professor of Geology at the University of Tasmania, were instrumental in initiating the regional survey and provided the published and unpublished geological literature on the area.The authors also wish to acknowledge the invaluable assistance received from the Mt Lyell Mining and Railway Co in Queenstown, which made available the more recent geological and mining documents rompiled by M L Wade and M Solomon.

Jan 1, 1994

By Harlan L. Kebel

Gypsum, the dihydrate form of calcium sulfate, has a history of usefulness to man dating back several thousand years, and a worldwide industry has been built on the mining and processing of this versatile industrial mineral. However, anhydrite, the other prin¬cipal calcium sulfate mineral, has very limited use, so much so that separate statistics for it are not always kept, but are usually included with those for gypsum. Although often found in close association, the two minerals have important chemical differences in that anhydrite is the anhy¬drous form of calcium sulfate (CaSO4) whereas gypsum is the dihydrate (CaSo4.2H20). These two molecules of combined water result in significant differences in hardness, density, and solubility of the two minerals. Of most importance, however, is the difference in thermal properties wherein gypsum, upon the application of a modest amount of heat, can be converted to the hemihydrate of calcium sulfate (CaSO4 '21H20) or plaster of paris, an intermediate product upon which is based over 90% of the value of all calcium sulfate end products. Anhydrite, on the other hand, is inert at these temperatures and its uses have been limited to only those few cases where calcium sulfate in the anhydrous form may have an advan¬tage. The earliest known use of gypsum plaster dates back some 5000 years to the time of the Pharaohs of Egypt who had discovered that gypsum rock, when exposed to fire, broke down into a powder which, when mixed with water, would form a putty that could be plastered on a rough mud brick or stone wall to make a smooth finish. It was used down through the centuries in a limited way for ornamental purposes, but did not achieve wide acceptance because of the quick (25 to 30 min) setting or hardening time which made it difficult to use. The first real understanding of gypsum chemistry was developed in France about 1755, and the gradual growth of its present utilization dates from that time. In the United States, the first utilization of gypsum was to grind it to a fine material for use as a soil conditioner at about the time of the Revolutionary War, and the term land plaster for ground gypsum was coined and has remained in use. Another cementitious material-lime or calcium oxide-had become the usual plastering material, but by about 1870 a method for retarding the set of gypsum plaster was discovered; today it has almost completely replaced lime as a plastering material. In recent years, gypsum products sold in the United States have reached a total valuation of approximately $2 Gpy as illustrated in [Table 1].

Jan 1, 1994

By R. Nilsson

In the present work the sulphide capacities of Ca0-Mn0-Si0, ternary slags have been measured in the temperature range 1798 - 1873 K by equilibrating the slag with a gas-mixture containing CO, CO,, SO, and Ar. The results are compared with the data reported in literature. A theoretical model has been developed in the present work where the sulphide capacity is expressed as a function of the slag composition and temperature. The model enables the estimation of sulphide capacities of complex slags with a knowledge of the capacities of simpler systems.

Jan 1, 1994

By H. Kung, T. R. Jervis, M. Nastasi, T. E. Mitchell

"A systematic study of the structure-mechanical properties relationship is reported for nanolayered composites of MoSh-SiC, Mo-MoSh, Mo-MoShNx, MoSi2-MoSi2Nx, and Mo-MoShMoSi2Nx (x=3-4) synthesised by sputtering techniques. These composites have been studied by nano-indentation and cross-sectional TEM as a function of annealing temperature. As-deposited layers are amorphous except for Mo. With increasing annealing temperature, first MoSh and then SiC crystallize, while the hardness progressively increases until the layers start to spheroidize and grain growth sets in at 900ºC. For the case of Mo-MoSi2, the layers react and the composite deteriorates rapidly. However, MoSi2Nx remains amorphous up to 1000ºC, suggesting that it could act as a diffusion barrier between Mo and MoSi2. In fact the Mo. MoSi2Nx, MoSi2-MoSi2Nx and Mo-MoSi2-MoSi2Nx nanolayers are found to remain stable up to such temperatures. IntroductionMolybdenum dislicide, MoSh, is a potential matrix material for high temperature structural composites due to its high melting point and good oxidation resistance at elevated temperature [1]. The two major drawbacks for structural applications are inadequate high temperature strength and poor low temperature ductility. Silicon Carbide (SiC) being hard and thermally compatible with most ceramics and intermetallic compounds, has been found to be suitable for second phase reinforcement in various structural applications and, in particular, the addition of SiC whiskers improves the high temperature yield strength of MoSi2 [2]. While most of the research in MoSb-SiC composites has been on the particulate form of SiC, laminated composites may offer unique properties. It has been shown that synthetic multilayers with alternating layers of metal and/or compounds may exhibit interesting mechanical properties [3]. Enhancement in mechanical properties by decreasing the wavelength of multilayer spacing has been studied extensively. In general, two types of strengthening have been proposed: (1) Hall-Petch strengthening [4,5], where the strength increase is inversely proportional to the square root of the layer thickness; (2) Koehler modulus strengthening [6], which increases with modulus difference and decreasing layer thickness. In the present study, we have performed a systematic study of the relationship between strength and structure in a number of different nanolayered systems based on MoSh. Layer thicknesses have been varied and their nanostructures have been varied by heat treatment. Previous work on MoSi2-SiC is summarized [7]. In an attempt to improve fracture toughness, MoSh-Mo nanolayered materials have been prepared but are found to react and deteriorate. Previous work has shown that nitrided MoSi2 (MoSi2Nx with x=3-4) is highly stable [8] and so nanolayered composites of MoSi2-MoSi2Nx and Mo-MoSi2-MoSi2Nx have been prepared to assess the' stability and mechanical properties of these composites. Preliminary results are presented."

Jan 1, 1994

By John Eggert, Paul Benford

"Since 1982, Placer Dome Inc. -Dome Mine has steadily increased mill throughput. Tonnage has increased from a nominal design capacity of 3000 short tons per day, attained in 1985, to 4130 stpd by the end of 1992. Many minor and major circuit adjustments were tried to maximize tonnage.Having utilized most conventional means of increasing tonnage, further increases required a newer approach. This paper discusses the Dome experience in the development and implementation of an expert system.The Comdale/C system was chosen for a controlled trial. The criteria for acceptance were: increased tonnage had to be sufficient to pay for the system; the increase had to be visibly sustainable and the mill operators had to be willing to accept the system.The criteria for purchase were met during the trial and the system was purchased. The system continues to perform well. The tonnage throughput increase has been sustained while operator acceptance remains high.IntroductionPlacer Dome Inc. -Dome Mine is Canada's oldest operating gold mine. The mine was among the first established in the Porcupine camp in what is now Timmins, Ontario. The City of Timmins is located approximately 500 miles or 800 kilometres north of Toronto. Figure 1 shows a map of the province of Ontario and the mine location.In 1912, milling began at a rate of 350 short tons per day. With two minor exceptions, milling has been continuous since this time. The first of these shut downs was in 1918 during the first world war. The war created labour shortages which forced the mine to stop production for more than a year. The second was in 1930 when fire destroyed the mill."

Jan 1, 1994

By R. A. Plumbridge

The Honourable Mr Molefe, Premier of the North- West Province; Or Scot-Russel, Chairman of the CMMI's XV Congress; Mr Loton, Chairman of the CMMI; distinguished guests, ladies and gentlemen. At the outset may I express my sincere appreciation to the organisers of this Congress for their kind invitation to me to participate in the plenary session. May I also thank the CMMI for inviting me to be their fifth distinguished lecturer. This is a signal honour and one which is sincerely appreciated by my Group and myself. The subject of gold is a very emotive one. It conjures up different images in the minds of a wide variety of people. For many of us it is very simply the ultimate metal. In ancient times gold was sought after and treasured; it was the chosen metal for adornment and many of the best preserved artefacts of that time were hand-fashioned from gold which had been won by primitive mining techniques. Gold's rarity and its value was recognised by those who fashioned the earliest gold coins thus underlining gold's special place as a store of value.

Jan 1, 1994

By G. T. Homce

Most electric motor predictive maintenance methods have drawbacks that limit their effectiveness in the mining environment. The U.S. Bureau of Mines is developing an alternative approach to detect winding insulation breakdown in advance of complete motor failure. In order to evaluate the analysis algorithms necessary for this approach, the USBM has designed and installed a system to monitor 120 electric motors in a coal preparation plant. The computer-based experimental system continuously gathers, stores, and analyzes electrical parameters for each motor. The results are then correlated to data from conventional motor-maintenance methods and in-service failures to determine if the analysis algorithms can detect signs of insulation deterioration and impending failure. This paper describes system design and implementation. At this writing, however, installation is still underway, and field data analysis results are not yet available.

Jan 1, 1994