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By S. D. Rosenthal

"This paper will share my ‘shift in career direction’ journey from corporate mine engineer, with 31 years of mining various commodities with a wide range of responsibilities in a variety of countries, to the world of academia. There are times in one’s career that a change is required, albeit perhaps not as drastic of a change as moving to teaching. This paper will share how the transition arose, the decision to make the change, the challenges of the first year in academia, and the journey within academia going into the second year. INTRODUCTION As a graduate of the Montana College of Mineral Science and Technology (Montana Tech) with a B.S. Mining Engineering degree in May of 1982, my first job with Utah International in the Farmington area took me back to my home state of New Mexico. Some of you will remember that the early 1980’s was not a period of prolific opportunities for mining engineers; given low commodity prices, especially for copper (for example, Anaconda Company had been taken over by Arco and was in the midst of closing down its Butte operations). Coal was good and the learning opportunities abounded with Utah (which became BHP and then BHP Billiton). Gold was taking off in the mid to late 1980’s thanks to use of cyanide and heap leaching technology improvements, coupled with deregulation of the gold price, so I ventured off to work in the gold industry with a (then) junior Canadian company called Barrick at a new acquisition of theirs known as Goldstrike. That same gold surge was causing a shortage of iron ore mining engineers in Australia so after a few years in Nevada, I uprooted the family and left for a little town in the Pilbara of West Australia, known as Newman, to work in the iron ore industry with BHP Iron Ore. An initial short overseas posting turned into six plus years before transferring to BHP’s Indonesian steam coal mines in Kalimantan on the island of Borneo. BHP was going through a rough period following some ill-fated projects (Magma copper purchase, Beanup and HBI) and was reviewing assets and staffing so internal opportunities became scarce. Employees were encouraged to ‘leave the company and find work elsewhere.’ So, off I go to Argentina to try copper mining in the Andes with Minera Alumbrera. This short stint in South America was followed by a move to another mining town, Morenci, Arizona, and a posting with Phelps Dodge (now Freeport McMoran). After 12+ years without living close to snow we moved to the Denver area in a new position with Newmont Mining Corporation. Along the way I became a Professional Engineer (Nevada) and completed a Masters in Project Engineering and Management. After 11 years with Newmont, I moved to Butte, Montana where I accepted a position as Assistant Professor of Mining Engineering."

Jan 1, 2015

By Darryl Amick, Keith A. Prisbrey, Lee E. Plansky

The problem addressed was to develop automated image analysis of metal welds to replace unreliable and costly 100% visual inspection. The objective was to evaluate neural networks combined with features from gray level surfaces. Photomicrographs of the welded seam in Zircaloy-4 channels used in nuclear fuel rod assemblies were examined. The methodology used was to select a set of morphological feature coefficients from Bessel Fourier morphological feature coefficients extracted from digitized photomicrographs. The selected morphological feature coefficients were then used to train a neural network. The approach was verified initially by successfully training a neural network using the known, secondary chemistry of the alloy welds. The results were good. The Bessel Fourier coefficients captured sufficient information from the metallographic images to distinguish weld quality. This approach has the combined advantages of compressing the images through Bessel Fourier coefficients and give the ability to rapidly process large amounts of data using neural networks.

Jan 1, 1993

By Robert B. Hopler

Explosives research and development has historically been motivated by coal mining. Whether to solve safety problems or to improve productivity and cost, the result has been the same: better explosives products and initiation systems. Today, this process continues at an accelerated pace due to the tools presently available to the explosives and mining industries. Background Explosives have been used in coal mining since the industry's earliest days. Black powder, introduced into metal mining in 1627, undoubtedly was introduced into coal as soon as a need to replace pick work was apparent. Until the invention of the safety fuse by William Bickford in 1832, the only initiation methods available were the straw, quill and miner's squib. Disastrous explosions underground in England brought about studies on their possible causes (Atkinson, 1886). The studies showed that, while explosives contributed to the accidents, the real villain was coal dust, since that was the agent that transmitted the disaster throughout the mine workings. To improve underground safety, research was applied in an attempt to make explosives that could be safely fired in a methane air atmosphere. The Prussian government was apparently the first to establish a testing station for coal mine explosives. This occurred in 1885 (Guttmann, 1909).

Jan 1, 1993

By V. Nasri, P. Jarast, M. Bakhshi

The Montreal metro Blue Line Extension toward the northeast consists of the construction of five new underground stations. The project includes 6 kilometers of the tunnel which will be constructed using a Tunnel Boring Machine (TBM). In line with the commitment to integrating sustainability best practices, Envision verification is pursued this project. The Envision reference framework was developed to cover all the sustainable development aspects of an infrastructure project and each phase of its life cycle (planning, design, construction, operations and maintenance, and end-of-life). As a part of this endeavor, low-carbon concrete and shotcrete mixtures are proposed for the linings of TBM and SEM tunnels as well as stations and auxiliary structures. The CO2 emission of the low-carbon concrete and shotcrete mixtures were compared with their typical mixtures and the total CO2 emissions reduction related to the tunnel lining is determined. The study is of strategic significance for achieving emission reduction in the tunnel industry.

Jun 13, 2023

By Karl H. Bruemmer

1. TRENDS OF DEVELOPMENT IN THE MECHANICAL DRIVING OF UNDERGROUND EXCAVATIONS IN THE GERMAN COAL MINING INDUSTRY The demand for higher advance in underground excavations led, in the past ten years, to the development and application of various mechanical methods in the coal mining industry of the Federal Republic of Germany. Hence, a modern mine cannot operate anymore without tunneling machines for the driving of horizontal and inclined roads and shaft boring machines for the sinking of shafts. In future, boring operations will assume a high positional value in the mining industry, as the development of cutters has kept pace with the development of machines. In the past ten years, about 40 km of roadways have been bored by tunneling machines in the German coal mining industry, further 140 km will be bored by 1990, part of which are already under contract. The idea was tempting to apply the technology of horizontal tunnel borers also to the sinking of vertical shafts. The underground contractors Deilmann-Haniel GmbH of Dortmund and Thyssen Schachtbau GmbH of Mülheim/Ruhr developed already in 1970, together with Wirth of Erkelenz, a shaft boring machine working without drill pipes, capable of sinking shafts following a pilot borehole, according to the downward reaming method (Fig. 1). In the meantime, two such shaft borers are operating in coal mines with diameters of 4.50 m to 6.50 m. Recently an order was placed for a third Wirth shaft borer for diameters up to 8.50 m. Since 1971 about 3.800 m of open or blind shafts have been sunk by the reaming process (Fig. 2).

Jan 1, 1979

By Rustu S. Kalyoncu

Rainbow colors of roofing granules, adorning the roofs of buildings from single family units to largest office buildings, have their origin in the roofing shingles as burlap soaked with tar appearing as early as the 1700s. Dusting of talc and mica on the coated surfaces, to keep roofing from sticking to itself in storage, represents an early improvement to the original construction product. Sometimes, colored, natural mineral dusts were added as color pigments within the dusting material, for initial color. Prolonged exposure to sun caused the asphalt to become brittle, and it eventually cracked and leaked. Search for solutions to cracking and subsequent leaking problems eventually led to the use of crushed mineral granules on asphalt coated shingles. This provided the impetus for further growth in the asphalt roofing industry. Application of a layer of crushed mineral on the asphalt coating minimized the coating deterioration from exposure to ultraviolet light, thus significantly improving the shingle life. In the 1900s, screened waste from slate quarries was the most commonly used granule in asphalt roofing products. Records indicate the use of coarse slate screenings for asphalt roofing as early as 1906. As the asphalt roofing industry further developed, other naturally colored minerals, such as silica sand, quartz, mica, feldspar, talc, slag, granite, rhyolite, and oyster shells were used on roofing surfaces. Later on, a number of manufactured granular materials, such as crushed brick and tile, fire clay, and white porcelain were used. The first artificially colored roofing granule was produced in 1914 by running molten slag into a solution of alkaline metal silicate, which was absorbed by the porous slag. Various colors were obtained by adding pigments to the silicate coating and by subsequently heat treating the granules. In 1922, another technique was developed in which green slate granules were saturated with copper sulfate solution and heated to 760°C to form copper oxide. Since then, many other granule coloring processes have been patented, one of the most significant being the sodium silicate coatings introduced around 1975. Granules as used in construction (specifically roofing materials) are defined as natural or synthetic-mineral grains smaller than gravel and larger than sand in particle size. They are used primarily for protective and decorative purposes on the weather- exposed surface of asphalt composition roofing. Development of artificial coloring techniques has made it possible for the roofing industry to provide asphalt roofing shingles in a wide variety of colors complementing the color and style of buildings. Roofing granules, as we see today, are the products of long technological evolution.

Jan 1, 1994

By T. P. Lim, A. J. Vivyurka, N. K. Davé

Chemical and radioisotope stratification studies were carried out in an abandoned uranium tailings pile at Elliot Lake, Ontario, Canada. The tailings, with an average thickness of 7 m over an area of 16 hectares, were deposited approximately 20 years ago on a layer of black peaty material which overlays deposits of permeable glaciofluvial sands. Geohydro-chemical investigations of this tailings area have been ongoing since 1978. The radioisotope profile study was conducted on three adjacent sites. Solid core samples, collected with a split spoon sampler at various depths, were analyzed for various chemical and radioisotope constituents. The results indicated by 2 distinct zones of stratification; an upper zone, where the constituents were uniformly distributed, and a lower zone, near the peat-tailing interface, which showed increasing concentration with depth. Within the peat layer, the concentration decreased rapidly with no significant levels of contaminant penetration below the peat layers observed, though the samples were limited. The pH profile showed that the top 5 m of the tailings have been oxidized, the average soil pH in this zone was 3.4 compared to 5 .8 underneath it. The groundwater hydrology of the system was observed to be complex showing downward and lateral flow in the dry season and lateral and upward flow during the spring and periods of heavy rainfall. The results are discussed in terms of a model based on the combined segregation and settling process of the tailings fine fraction, and the geohydro-chemical interaction of the solid and liquid phases.

Jan 1, 1981

By S. K. Kawatra, S. A. Moffat, K. A. DeLa’O, T. C. Eisele

It was observed that the efficiency of some autogenous grinding circuits was dependent on temperature, with the energy-efficiency of the grinding process decreasing in the winter months, accompanied by an increase in critical-size production. Several possible causes of this phenomenon were suggested, including: • Increased brittleness of the ore during blasting in the pit at low temperatures, leading to increased levels of internal cracking that would lead to rapid breakage to critical size in the mill; •Brittleness changes of the rock in the mill; and • Changes in the durability of the rock caused by either formation of ice on the surface, or freezing of water inside the pores and cracks of the rock. To determine which mechanisms were occurring, drop tests were carried out using frozen and unfrozen rock with varying degrees of porosity, both dry and water-saturated, and which had been blasted for mining in summer and in winter. These tests showed that there was no difference between the summer-blasted ore and the winter-blasted ore, and that durability changes in dry rock over the temperature range from 25ºC to -25ºC were negligible. However, water-saturated rock showed an increased resistance to breakage upon freezing, particularly when the rock was highly porous, or when a layer of ice formed on the surface. Seasonal changes in the durability of rock in grinding are therefore due to formation of ice in and around the rock.

Jan 1, 1995

By Gabriel E. Zárate, Juan C. Guzmán

In Chile there are significant amounts of gold in flotation tailings that could be recovered, being heap leaching the most promising alternative. In order to determine the feasibility of treating these tailings by this method, a detailed study is carried out using 4 representative samples. After defining the best conditions an economic evaluation is done for a plant treating 200 tpd, sensibilizing with respect to parameters such us gold price, tailing grade and capital costs. The results show that it is technically feasible treat these gold tailings by heap leaching with gold extractions over 70 %. It is also economically feasible for gold grades higher than 0.5 g/t and gold prices over 350 US/oz.

Jan 1, 1987

By 1980, the US mining community had reached a broad consensus regarding coal pillar design. The pillar load could be estimated from tributary area theory, and the pillar strength could be estimated from empirical formulas and laboratory coal strength testing. Then the growth of longwall mining required new thinking. Recently, powerful design methods have emerged from analysis of large databases of real-world pillar successes and failures. These include the analysis of retreat mining pillar stability (ARMPS), the analysis of longwall pillar stability (ALPS), the Mark-Bieniawski rectan¬gular pillar strength formula and guidelines for preventing massive pillar collapses. Sophisticated numerical models have also helped transform the pillar design landscape. In the process, the understanding of pillar mechanics has been greatly enriched. A new paradigm identifies three categories of pillars according to the types of failure that are associated with them. These categories are slender pillars (w/h < 3.0), which are subject to sudden collapse; intermediate pillars, in which pillar squeezes seem to be the most common failure mode; and squat pillars (w/h > 10), which are dominated by entry failure (rib, roof or floor) and coal bumps.

Jan 1, 2000

By Greg Bold, Mahmood Khwaja, Yuannian (Jerry) Wan, Michael S. Schultz, William Simcoe

Beaver Creek Clean River Project will satisfy the consent decree requirements by capturing and treating combined sewage overflows. The project consists of, approximately, 2,700 feet of 30-inch trenchless pipe installation, a new screening/disinfecting facility, an expansion of an existing diversion structure, and a 72-inch internal diameter, 530-foot long mined tunnel. The tunnel portions are being progressed as early release packages. This paper presents the geotechnical exploration program and the subsurface conditions encountered; interpretation of the geotechnical conditions; and, approach to developing stand-alone packages for the tunnels to mitigate construction and schedule risks and continue to advance the project.

Jun 13, 2021

By Osamu Nishikokura, Jumpei Yamashita, Darrell Liebno, Malcolm Sheehan

"The Eglinton-Scarborough Crosstown Project builds a 19km LRT corridor that includes a 10km underground portion, between Keele Street and Laird Drive. The West Tunnel Contract (ECLC1-15) includes 6.5km of twin EPB TBM bored tunnels with a 5.75m internal diameter precast concrete segment lining (PCTL), between Keele Street and Yonge Street. This paper summarizes the overall scope of work, the technical challenges faced and innovative solutions developed by the contractor during the TBM move across an existing subway tunnel using state of the art high capacity strandjack gantry crane.1. PROJECT OVERVIEW The Greater Toronto and Hamilton Area (GTHA) is Canada’s largest urban region, populated with over 6 million people, and is one of the most rapidly growing regions in North America. One forecast estimates that the population of this region will increase to 8.6 million by the year 2031. In September 2008, Metrolinx, an agency of the Government of Ontario, launched a 25-year regional transportation plan named “The Big Move” to cope with the expected increase in transportation demand. The Eglinton-Scarborough Crosstown, one of the projects included in “The Big Move”, is a light rail transit (LRT) that will run across Toronto in an east-west direction between Mount Dennis and Kennedy along Eglinton Avenue. In October 2012, the West Tunnel Contract of the Crosstown LRT (ECLC1-15) was awarded to Crosstown Transit Constructors (CTC), a joint venture between Obayashi Canada Ltd., Kenny Construction Company, Kenaidan Contracting Ltd. and Technicore Underground Inc. The project includes approximately 6.2 km long twin bored tunnels, 9 cross passages, 1 emergency exit building, 7 sets of station headwalls, and an intermediate pair of extraction and launch shafts. Each of 6.5 km long twin tunnels are divided by the existing subway station into two drives: the first half from the launch shaft LS-1 (west of Keele Station) to the extraction shaft ES-1 (west of Eglinton West Station), and the second half from the launch shaft LS-2 (east of Eglinton West Station) to Yonge Station, as shown in Figure-1. The TBMs are extracted at ES-1 and moved to LS-2 over the existing Yonge-University Subway Line at Eglinton West Station before resumption of tunneling at LS-2."

Jan 1, 2016

By W. M. Ma, Daniel W. H. Su, K. Centofanti, Yi Luo, W. L. Zhong, Syd S. Peng

6.1 INTRODUCTION A surface structure will suffer damage when the additional stresses induced by ground deformations associated with surface subsidence, plus the original stress introduced by construction de¬sign, exceed the strength of the structural elements. In this con¬text, there are two methods available for preventing and control¬ling surface structural damage: one is to strengthen the structure and the other is to design the mining operations such that ground deformations at the structure site can be reduced to an acceptable level. Mining operations include panel layout and mining tech¬niques. These methods are detailed in this chapter. It must be noted that most prevention/control methods men¬tioned in this chapter are used in the countries where the reference papers are cited. In the United States, the coal operators are not required to take those measures mentioned in this chapter. Some of the methods described in this chapter cannot be implemented with¬out changes in the current mining practice as permitted by laws. In addition cost of implementing those methods are not considered here. 6.2 PANEL LAYOUT As shown in Figs. 2.9, 2.10, and 2.11, permanent ground deformations in a subsidence basin mainly concentrate near the edges of the underground opening, and can be divided into four zones. A structure located in different zones will be subjected to different types and magnitudes of ground deformations. In laying out the panels, Table 5.1 and Figs. 2.9, 2.10, and 2.11 could be taken into consideration. Attempts could be made to avoid placing the structure on a location where the ground deformation to which that structure is sensitive is at its maximum. Therefore rational design of the panel is the simplest way to reduce structural defor¬mations. Panel design involves the determination of panel dimension, panel edge location, direction of face advance, and use of yield chain pillars. A. Panel Dimension Since longwalls in the US employ a multiple-entry system, where rows of chain pillars are left unmined, subsidence over those chain pillars is usually smaller. Therefore, whenever possi¬ble, the panel dimension could be designed such that a major structure or structures are over those unmined chain pillars, be¬tween adjacent panels, or some distance beyond both ends of the panels. At the center of the supercritical final subsidence basin, a structure will not be subjected to any final or permanent ground deformations. In order to create such a condition, the panel width must be such that the structure will be located beyond the major influence zone of the final subsidence basin, the minimum dimen¬sion of which must be: [ ] where L is the width or length of the final mined out gob, t is the width or length of the structure to be protected, h is mining depth and [ ] s is the angle of full subsidence. B. Panel Edge Location Wherever there is a permanent panel edge, there are large ground deformations induced on the surface on both sides of the permanent panel edge. Therefore whenever possible the panel di¬mension should be designed such that the permanent panel edges could be located in the areas with the least impacts. In terms of permanent edge location, it is best to eliminate any permanent panel edge under a structure or groups of structures. If this cannot be done, the panel should be lengthened to reduce the number of permanent panel edges, or narrower multiple panels advancing in the same direction in a staggered manner could be employed. If the structures are located in Zones II and III, the longer dimension of the structure must be parallel to the nearest perma¬nent edge (Fig. 6.1). But in Zone IV, the longer dimension should be tangential to the corner of the permanent panel edge. If the structure is inclined to the permanent panel edge, it will be sub¬jected to twisting and shearing. C. Direction of Face Advance The direction of face advance should be parallel to the long axis of the structure. But if the structure is to be located at or close to the center of the final subsidence basin, the direction of face advance should be perpendicular to the long axis of the structure. Careful choice of the direction of multiple face advance is the most effective way to reduce structural deformation and thus dam¬age. This applies the principle of overlapping and cancellations of ground deformations, due to multiple face advance, at the right time and at the right intensity, e.g., opposing tilts, concave and convex curvatures, tensile and compressive strains are induced simultaneously on the structure to be protected by two or more faces. D. Use of Yield Chain Pillars In US longwall panels there are generally two or three rows of stiff chain pillars between the panels. The combined width of the chain pillars ranges from 100 to 350 ft(30 to 107m). depending on mining depth. In general, surface movement above the chain pil¬lars after the panels on both sides have been extracted is much smaller, as compared to that in panel center. Thus in order to create critical or supercritical width of opening and eliminate sur¬face bumps over the chain pillars, yield chain pillars may be em¬ployed (Jarosz and Karmis, 1986). However if yield pillars are to be used, it must be designed such that it yields totally right after the panels on both sides have been extracted. Unfortunately cur¬rent yield pillar design techniques cannot predict when and how much it will yield. In summary, whenever possible attempts could be made to lay out the panel in such a way that surface structures are located above chain pillars between panels or above solid coal beyond both ends of the panels. In those areas the surface structures will most likely be unaffected, or if affected, the damage is so minor that no remedial measures are necessary. 6.3 CONTROLLED MINING TECHNIQUES Several mining techniques are available for reducing the sur¬face ground deformations of specific types. Regardless of tech-

Jan 1, 1992

By G. F. Ayakwah

Point load strength (Is50) and slake durability (ID2) indices provide a measure of the strength and durability of rock fragments and are related to the alteration intensity and frictional resistance of the materials. Samples were collected from the rock piles, alteration scars and debris flows at the Questa mine with the purpose of examining relationships between Is50 and ID2, mineralogy, chemistry, weathering, hydrothermal alteration, and other geotechnical parameters. The Is50 from the various rock piles ranges from 0.6-8.2 MPa and the ID2 ranges from 80.9-99.5%. The Is50 and ID2 results indicate that the samples from the debris flows are stronger (average Is50= 4.0 MPa and ID2= 98.4%) than the rock-pile samples and that the alteration scar samples are weaker (average Is50 = 2.8 MPa and ID2 = 89.2%) than the rock-pile samples, but still most of these rocks are strong in terms of their Is50 and ID2. The Is50 decreases as the degree of alteration increases in some rock pile and alteration scar samples, but not in all. However, the majority of the rock fragments within the rock piles still indicate high strength, even after 25-40 years of weathering.

Jan 1, 2009

By E. D. Attanasi

The US mining industry finished the traumatic 1980s with a strong economic performance. Worldwide economic growth and capital spending led to tight metal markets. So, 1989 metals prices were generally higher than average 1988 prices. Financial markets&apos; volatility resulted from US junk bond defaults, heavy US savings and loan losses and effects on the US budget deficit, higher energy prices, and the seemingly intractable problems of some debtor countries. Moreover, the events in Eastern Europe promise fundamental changes in the world economic system for the 1990s. US mining companies that survived the decade had weathered economic changes that, at one point, reduced industry employment by 40%, drove oil companies to divest or liquidate recently acquired mineral subsidiaries, and led to substantial write-offs of reserves. Canadian and other international minerals firms experienced similar industry upheavels. The forced modernization and capacity rationalization produced an internationally competitive US industry. For example, even though 1989 US copper production was 27% greater than in 1980, industry employment was less than half the 1980 level. The steel industry and other minerals industries showed similar productivity improvements.

Jan 1, 1990

By Chuck R. McLendon

A new face ventilation system was needed at the Allied Chemical Trona mine, near Green River, Wyoming. The development of an exhaust manifold face ventilation system came from a need to reduce the dust and noise concentration level while maintaining methane control at the continuous miner working face. Dust laden air from a heading being driven by a continuous miner was contaminating the intake air in the mine around the roof bolter operator and adjacent headings. Each working heading was exhausted into the last open crosscut by a face fan. A face fan would contaminate the adjacent downstream heading with dust-laden air until a high dust concentration developed in the final entry before the returns. A face ventilation system was needed to give the exhaust of each heading an individual path to the return air. In addition, the system could not interfere with the present room and pillar mining process. A manifold system of rigid duct ventilation tubing was designed using the existing fans in a parallel arrangement. Each system was to consist of the rigid duct tubing in three headings junctioned together at the last open crosscut and exhausted at a common branch in the return air. Each heading was to have its own damper (or valve) so that air could be directed where it was most needed. The system was installed using both round and oval rigid duct ventilation tubing to minimize head loss and to allow proper ground clearance for mining machinery. Two fans in parallel were used to exhaust three headings. By adjusting the valves at each heading, up to 18.0 kcfm (9.36 cu m per sec) could be exhausted from one heading and still keep the methane level controlled in the other two headings. The manifold exhaust system has proven to be an efficient, long lasting ventilation system at the Alchem Mine. It has reduced the dust and noise exposure levels at the working faces while keeping the methane level under control.

Jan 1, 1980

By Mulong Yu, Yosry A. Attia

Beneficiation of high magnesium Florida phosphates requires ultrafine grinding to liberate the dolomite (the main source of magnesium), and a separation process capable of dealing with ultrafine sizes such as selective flocculation. The objective of this study was to investigate the feasibility of separating dolomite from apatite ultrafines by selective flocculation. To achieve this objective, selective polymeric reagents to either dolomite or apatite must be first designed and synthesized. This challenging task was accomplished by carefully selecting complexing/chelating agents which are selective to either the Ca or Mg ionic sites on the minerals, and incorporating these reagents into the structure of long chain water soluble polymers to obtain either selective flocculants (with high molecular weight, MW, polymers), or selective dispersants (with low MW polymers) to either the dolomite or the apatite particles. Synthesis and testing of these polymers on individual and mixed mineral slurries, and on a sample of natural high magnesium phosphate ore, have been attempted and the results are described in the paper. The preliminary results showed encouraging signs for the feasibility of selective flocculation separation of dolomite from apatite.

Jan 1, 1993

By Karl J. Benecke

Though the first patent on a bucket wheel excavator was granted in 1881 in the U.S. this technology was developed in Germany to the high standards of today. However, this development was only possible in parallel with the development of shiftable belt conveyors and boom stackers. The combination of these three types of equipment in the open pits of the Federal Republic of Germany has made lignite the cheapest energy source for power generating, despite the low heating value of German lignite in the order of 8500 kJ/kg (3600 BTU/lb) only. Comparing the costs for fuels used in power generating on the basis of their heating value, the relation between lignite, high quality black coal, and imported crude oil is in the order of 1 to 1.5 to 2.5, hence highly in favour of lignite. These cost advantages for lignite in Germany are due mainly to the concentration of lignite mining in a few high-output open pit mines. The largest one, Fortuna Mine in the Cologne district, produced a, total of 45 000 000 t lignite in 1976. That equals the annual fuel need of a 5750 MW power plant running 7000 hours per year at full capacity. Altogether 95 200 000 bank m3 equal to 200 000 000 t overburden had to be removed to accomplish this lignite output. The largest BWE (Fig. 1) ever built is working in the Fortuna Mine, too. At a digging height of 51 m above crawler level, the total vertical reach in relation to the face conveyor level is 98 m by means of its conveying bridge and loading unit. The hourly output is 10 400 bank m3. Its weight in operation is 13 000 t, its wheel diameter 21.6 m, as high as a 7-storey building.

Jan 1, 1977

By R. Trottier, B. H. Kaye

Characterizing the structure of such open-structured dusts such as diesel soot and those present in welding fumes plus any other dusts which were initially formed by precipitation or agglomoration of subsidiary units in a flame process has always been a difficult task. Recently, scientists have been able to use the concepts of fractal geometry to model the growth of diesel soot and fume fine particles and characterize their structure using fractal dimensions. The measured fractal dimension of a diesel exhaust at various levels of scrutiny can be used to study the health hazards posed by the soot. Thus, the fractal dimensions of the overall structure can be related to the dynamics of the dust both empirically and theoretically. In this communication, the use of fractal dimensions to describe the structure of smoke and fine particles which pose a respirable hazard are reviewed. Experimental studies linking the measured fractal dimensions of the fine particles to dynamics of the fine particles in respirators and in the lung are outlined.

Jan 1, 1987

By C. Abbruzzese, L. Piga, P. Fornari, S. Ubaldini, R. Massidda

The effects of certain variables on the extraction of gold by thioureation have been investigated on a quartzose gold-bearing ore using a statistical multifactorial strategy. The factors taken into consideration were milling time (which corresponds to a given grain size), oxidant concentration, thiourea concentration and liquid/solid ratio. The influence of these four variables was ascertained first by a full factorial design at two levels for each variable (16 runs). This permitted the estimation of first-order effects of the factors affecting the process. Then 9 runs were added whose levels were both in the centre of and outside the axes of the previous plan thus originating a central composite design. This permitted estimation both of second-order effects of the factors involved and of parameters of a second-order polynomial model. The results show that extraction of gold depends only on milling time and oxidant concentration, at least in the experimental range considered. The equation fitting experimental data, as calculated by the least squares method, allows a response surface to be drawn. Due to the low gold grade of the ore (6 ppm) statistical analysis could lead to contradictory results, hence strict observance of Gy&apos;s rules for sampling and very accurate and precise chemical analyses were required.

Jan 1, 1995