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By Thomas M. Barczak

This Bureau of Mines report investigates shield mechanics by describing the elastic response and interaction of shield components to applied vertical and horizontal displacements for various canopy and base contact configurations. This research provides information on generalized shield mechanics, which is applicable in describing the behavior of all two-leg shield supports. Utilizing mechanics of materials concepts and known kinematic relationships for two-leg shield supports, free-body diagrams are constructed for each shield component illustrating internal axial, shear, and bending moment responses required to maintain equilibrium for each load case evaluated. Predicted shield (component) responses are verified by controlled displacement of instrumented longwall shields in the Bureau's mine roof simulator (MRS). Conclusions drawn from these analyses include shield structural responses are significantly dependent upon canopy and base contact configurations. Applied displacements also significantly affect shield responses. Horizontal displacement produces different responses than those produced by vertical displacements. The direction of horizontal displacement is also significant in evaluating shield response. Applications of shield mechanics to in situ support monitoring are also discussed. An objective of this research program is to establish unique shield responses to identify in situ load conditions.

Jan 1, 1989

By Ryan CG, Cousens DR, Griffin WL

The proton microprobe is developing into a vital tool in the geosciences, through its high sensitivity for in-situ detection of trace elements in the ppm regime. This paper will describe the instrument at the CSIRO Heavy Ion Analytical Facility at North Ryde, including features crucial to its successful application in the geoscience. Examples of applications in the basic geoscience and mineral industry related research are described briefly. Conditions required for widescale applications in the minerals industry are Discussed.

Jan 1, 1989

By A. S. Mallicis, Li Xiawoei, P. W. Weiblen, I. Iwasakl

Platinum group metals (PGM) are often found in close association with arsenide and sulfarsenide minerals in copper-nickel bearing gabbroic rocks. Major losses of platinum in flotation have been attributed to the susceptibilities of the arsenic minerals to oxidation and subsequent losses of their recoveries in cleaner flotation stages. The use of a nitrogen atmosphere in grinding and in flotation, the effectiveness of activation for improving their floatabilities, and the role that electrochemical interactions play not only between grinding media and minerals, but also among different minerals, are discussed.

Jan 1, 1989

By H. W. Kilau

The U.S. Bureau of Mines examined the wettability of bituminous and subbituminous coals before and after exposure to ambient air atmosphere, as part of an ongoing project investigating the coal-wetting abilities of surfactant solutions intended for the suppression of dust during coal mining operations. Exposure periods were generally 7 days or less, and the changes in wetting response were measured with a capillary penetration apparatus. Wetting solutions tested included a nonionic surfactant, two anionic surfactants, and pure distilled water. After exposure, higher ranked bituminous coals treated with nonionic surfactant solution and pure water showed increased wettability, but lower ranked subbituminous coals showed decreased wettability. With the anionic surfactants, the coals demonstrated opposite responses. The wettability changes appeared to be related to the coal moisture content. These changes may be amplified by specific, but incompletely understood, interactions between surfactant polar groups, absorbed water, and the coal surface.

Jan 1, 1989

By Danell. R. E.

A drill monitoring system has been developed which measures performance characteristics of a rotary drill and relates this to the material strength and rotary specific energy. The drill monitor is computer based and is used to produce a profile of the relative in-situ material strength as a function of depth. This information has been used in determining the placement of explosive in selective loading of blastholes and estimating the amount of lump product in a particular section of an ore body.

Jan 1, 1989

By A. L. Mular

"IntroductionSince the mid -1960s, automatic control of grinding circuits has become the rule, to avoid losses attributable to frequent circuit upsets associated with uncontrolled disturbances such as ore hardness variations. Higher capital costs of grinding equipment and corresponding operating costs-especially with respect to energy consumption-are major factors that continue to stimulate interest in grinding control.Grinding circuit control strategies depend upon the control objectives defined by the processing plant and are subject to constraints such as: maintain final per cent solids within some range, do not transport steel ball s out of the discharge trunnion, or do not overflow or empty the pump box and so on. Constraints depend on the nature of equipment employed within the grinding circuit and may actually determine the characteristics of the control scheme. Typical control objectives are:1. Maintain final particle size at set point by ,a. manipulation of fresh feed rate with circulating load maintained by manipulation of pump box water addition rate, orb. manipulation of pump box water addition rate with circulating load maintained by manipulation of fresh feed rate, where the methodology utilized to accomplish either (a) or (b) is dependent upon equipment/circuit constraints such as the availability of a variable speed pump.2. Maintain circuit throughput at a maximum by,a. manipulation of fresh feed rate subject to constraints on final particle size and variables such as power draw, circulating load and mill overload.3. Maintain mill load at set point by a. manipulation of fresh feed rate subject to constraints such as on power draw.4. Maintain mill power draw at set point bya . manipulation of fresh feed rate subject to mill load constraints. Often, a grinding control objective is dictated by the recovery vs fineness-of-grind characteristic that exists for downstream separation circuits. When recovery is relatively insensitive to size, maximum throughput in the grinding circuit is advantageous.The purpose of this paper is to review control strategies for primary ball mill grinding circuits, rod mill/ball mill grinding circuits and semi-autogenous grinding mill circuits. Primary sensors employed are highlighted and modern trends are documented briefly."

Jan 1, 1989

By Michael D. Fenton

Detailed comprehensive assessment of the performance of Afghanistan's mineral industry during 1987 is virtually impossible, owing to the paucity of reliable published information. It was evident, however, that the level of civil disorder, now in its eighth year since the arrival of significant numbers of Soviet troops, was in actuality little removed from open civil war. Insurgents controlled substantial areas of the country and imperiled any industrial activity in many places. Assistance programs by the U.S.S.R. and other Eastern European nations were directed at developing the country's meager mineral industry, but the economy was generally viewed as chaotic. The inflation rate was somewhere between 20% and 30%; major food shortages contributed to the discontent of the population, and numerous villages were devastated by Soviet and Afghan Government campaigns to destroy the insurgents and cut their supply routes. Moreover, proposals by the Soviets and the Kabul Government aimed at reducing tensions with the rebels and scaling down the warfare seemingly were taken by the opposition as signs of weakening by the Soviet-backed Government, and rather than reducing aggressions, seemed to heighten insurrectionist activities. Efforts to entice the substantial number of Afghans who have fled to nearby areas of Pakistan and Iran to return to their country seemingly were failures, and indications near yearend that the Soviet Union might soon begin withdrawal of its occupation force of nearly 120,000 did little if any to reduce disorder.

Jan 1, 1989

By J. Rothschild

I would like to thank the Society of Mining Engineers for inviting me as well as the other distinguished panelists to spend a morning reviewing and discussing the handling and shipping of industrial minerals. I also would like to thank my management, Cometals. Inc. for permitting me to take time out from the daily hectic pace of marketing and trading to share with you some of our experiences and expertise. Cometals, Inc. is a wholly-owned subsidiary of Commercial Metals of Dallas. The transportation and handling costs of industrial minerals frequently are a major component of the value of the goods marketed and, therefore, it is only natural that close attention should be paid to them. Many of the industrial minerals require special handling to assure that the material reaches the consumer without being contaminated or getting wet. I invite you to accompany me through the various steps involved in "delivering the goods" to the consumer.

Jan 1, 1989

By A. M. Al Taweel, V. K. Kasireddy

Intensive coal cleaning usually necessitates fine grinding of the feed in order to liberate inorganic constituents from the surrounding organic matrix. This however adversely affects the ability of flotation techniques to beneficiate coal. Such difficulties are mainly attributed to the increase of particle population density, the decrease in capture efficiency, and the greater tendency of inorganic components to report with the froth. A three-pronged approach was adopted in an attempt to overcome these difficulties. The aggregative flotation technique was used to reduce particle population densities and improve capture, while unconventional spargers were used to generate a wide range of bubble sizes. Use of unagitated flotation columns allowed for the maintenance of countercurrent flows in both the recovery and washing sections. The combined effect of these parameters enabled the recovery of 92% of the carbon content of coal having an average particle size of 20.5 µ m, while rejecting 85% of the ash. This was accomplished using 2 kg of fuel oil per tonne of coal in a column 2 meters high operating at 2-3 tph/m3, a capacity which compares favourably with conventional cells.

Jan 1, 1989

By Roger L. Keller

This paper examines the aspects of differing types of blasting cuts in underground headings with consideration to the reduction of number of holes and costs. At least one comparison study is related where costs per advance meter were significantly improved. The technical aspect of the paper covers a study of the effects of various blasthole delay intervals on resulting crater volume, ground vibration, and fragmentation for six hole V-cuts.

Jan 1, 1989

By Hayward B. Oblad, Anthony G. Fonseca

Coal flotation has been practiced since about 1920 in Europe and since about 1926 in the U.S. Over 200 U.S. coal preparation plants now use the process to recover coal. Over the 60 year period, the fundamental principles upon which flotation is based have been enumerated, but the interaction between the parameters that affect flotation has not been quantified and a useful model which accounts for these parameters has not yet been developed. A comprehensive and user friendly kinetic model coupled with better process monitoring and control instrumentation would allow plant operating personnel to better predict flotation performance and better control the flotation process in coal preparation plants.

Jan 1, 1989

By P. Sergi

A method of characterizing gold ores with respect to processing is proposed. The method includes microscopical examinations to obtain qualitative and quantitative data that relate to processing. The main thrust, however, involves laboratory heavy liquid separation tests, laboratory amalgamation tests, and laboratory cyanidation tests to determine the proportions of gold that can be recovered in a conventional processing operation. Two different Brazilian gold ores: a quartz vein gold ore, and gold in metasediments were tested.

Jan 1, 1989

By R. Karl Zipf, Z. T. Bieniawski

"Fracture mechanics plays an important role in studies of geologic materials such as rock and coal. Yet fracture data are scarce for rock and most limited or unreliable for coal. A testing system was developed which can apply mixed mode loads to a crack tip in many rocks and geologic materials. It is possible to subject the test specimen to pure mode I, various mixed modes and a nearly pure mode II fracture load. The system is currently used to study the mechanics of fine fragment formation in various coals. Experimental measurements include KI and KII' fracture velocity and acoustic emission.INTRODUCTIONA major research program at The Pennsylvania State University is directed to understanding the fundamental mechanics of fine fragment formation in various coals. The program represents an effort to reduce the incidence of coal workers pneumoconiosis (black lung) in coal miners. The principal source of the respirable coal fragments is the cutting operation which forms and liberates the particles by a fracture process. Present understanding of the mechanics of the events which form and liberate these particles is meager (Cook, 1982).Current knowledge of the fundamental mechanisms of coal dust generation and entrainment in terms of the underlying fracture mechanics is critically needed to improve and possibly control the processes involved. Whether the cutting operation is done with a 'continuous miner' cutting machine, a plow or a longwall shearer, it is fundamentally a problem of mixed-mode crack propagation. When a cutting tool interacts with coal, it causes numerous cracks to propagate through the intact material. Numerous larger fragments are broken free, but another quantity of undesirable fine fragments is also created. The formation of these respirable fragments may be a direct result of the crack propagation process; hence, a thorough understanding of the fracture mechanics of coal is required to minimize production of the unwanted fine fragments.In most rock engineering applications, the rock material properties are of secondary importance to the rock mass properties; however, for rock fragmentation and rock cutting problems, it is rock material properties such as fracture toughness which are of prime interest (Bieniawski, 1980). Several rock cutting and rock failure theories have been proposed, but it is only very recently that fracture mechanics concepts have been successfully applied to the study of rock cutting mechanics. All cutting models seek to predict the cutting forces and the cutter geometry necessary to cause rock breakage and chip formation given some fundamental mechanical properties ~f the rock. Such models have wide applications in drilling, tunnel boring and mining problems. Nelson et al., (1985, 1986) has provided a very useful correlation between the laboratory measured fracture mechanics properties of rock and the performance of the disk cutters on tunnel boring machines."

Jan 1, 1989

By Luis E. Vallejo

The strength measured by the uniaxial compression test is a parameter that is widely used for the engineering classification of rocks. Sedimentary rocks such as shales, however, are difficult to evaluate by uniaxial compression tatting because the rocks slake during the preparation of the standard samples required for the tests. Indirect methods such as the point load test have been proposed to determine the unconfined compressive strength of shales and other soft rocks. It is current practice to use 24 as the conversion factor between the point load strength, Is, and the unconfined compressive strength, sf (sf = 24 Is). The present study investigated index-to-strength conversion factors for shales and sandstones obtained from surface coal mining sites in the Appalachian region. Regression analyses indicate that a conversion factor of 12.5 best correlated the strengths obtained from the point load and unconfined compression tarts in the case of shales. For the sandstones, a value of 17.4 best correlated the strengths.

Jan 1, 1989

By Deepak Malhotra

Rosario Dominicana, S.A., operates a gold processing complex at Pueblo Viejo, northwest of Santo Domingo (Dominican Republic). The plant processes approximately 10,000 mtpd of oxide gold-bearing ore with a work index of 11 kWh/mt. The ore hardness has increased to about 17 kWh/mt. Metallurgical auditing of the plant was conducted? to find ways to modify the circuit to process hard ore without sacrificing throughput. In addition, unit operations were optimized to increase recovery and reduce operating cost,. The results of modifications made in the plant are discussed in this paper.

Jan 1, 1989

By Mark E. Hammele

A number of new thoughts have recently emerged concerning the role of air decks, stemming, gas confinement and gross motion in specific blasting environments and applications. Field research in full-scale production environments is based on the theoret ical work f i rst proposed at the Universi ty of Maryland’s Fracture Mechanics Laboratory.

Jan 1, 1989

By James W. Reil, Douglas A. Anderson

Blast vibration monitoring has generally been regarded as a necessary evil. New instrumentation and computer programs can change this. Rather than the usual trial and error methods to control vibration problems, an integrated, intelligent approach is possible. There is also the possibility of diagnosing problems with the blast vibrations.

Jan 1, 1989

By David L. Shearer

INTRODUCTON James Howden first secured an order for two Service Tunnel Boring machines in November 1986. These Tunnel Boring machines were 5.7 and 5.4 metres in diameter and the full length including back up was 215 metres. Manufacture commenced in December 1986 at the Glasgow factories of James Howden & Company with the deliveries to site of the machines in September 1987 and March 1988 respectively. In December 1987 two further orders were secured for the land running tunnels at 8.7 metres diameter. This paper presents some of the challenges in building tunnel boring machines for the Eurotunnel project between Britain and France. The general specifications of the Tunnel Boring machines and length of drives are shown in Appendix 1. DESIGN PARAMETERS The specification given by the Consortium TML on behalf of their client Eurotunnel cleary indicated that cutting of the face should be concurrent with the building of the precast concrete lining rings. In order to do this a telescopic machine was thought to be the best solution. Ground conditions were described as chalk marls of homogeneous nature with the possibility of friable areas and some revelling. A shielded type TBM with open cutter head was chosen together with a telescopic section and a rear

Jan 1, 1989

By Yoginder P. Chugh

Subsidence may be observed above partial extraction shallow room-and-pillar mines where the coal seam(s) is associated with weak and thick claystone in the floor. This paper presents results of subsidence studies at such a mine. During the 26-month study period, a time dependent subsidence causing a maximum vertical movement of 50 mn was observed. After a subsidence rate of 6.0-6.5 m/month for the first two months after development of mine workings, the rate decreased to 0.8-0.9 mm/month after 17 months. However, presumably due to settlement of barrier pillars, it increased therafter to 1.7 mm/month for the next 9 months. Angle of draw, based on zero subsidence, was calculated to be about 29 degrees. Maximum tensile strain and compressive strain values observed were 0.040 pct and 0.039 pct respectively. A hypothesis was fomlated to correlate surface subsidence movements with observed underground movments. The data collected to date fits reasonably well within the formulated hypothesis.

Jan 1, 1989

By M. G. Ayat, B. C. Scott

J. Dasher Having an interest in coal slurry pipelines from a decade of arguments with Ed Wasp and crew at Bechtel about pumping thicker slurries slower, I immediately read this article and found nothing in it pertinant to the title. Ayat and Scott pumped five unidentified coals at 9% solids (50%-60% is the area of interest) in a 25-mm (1-in.) pipe around two square elbows through a 76-mm (3-in.) cyclone for up to 60 minutes and sized a large number of samples of unstated size on an unidentified wet screening device. They did not measure power consumption, discharge pressure, flow rate, or give pump tip speed or impeller diameter. They siad the cyclone had a "high" pressure drop (unmeasured) and did much of the degradation (measured) but more or less per unit of energy expended? Hargrove was not measured, so there are no data as to whether it would correlate with degradation. The authors conclude, with no attempt, correlation is "hard to establish." Please experiment before concluding. I am at a loss to know what "increasingly smaller size" means, much less what theory says such particles take "exponentially larger quantities of energy," which the authors neglected to measure. If such experiments without pertinent data or justified conclusions must be published, please attach a pertinant title. reply by M. G. Ayat The first and the last criticism of this paper is that the work is not pertinent to the title. Anybody who reads this article will immediately realize that the work describes the breakage of coal particles to finer sizes in coal slurry pipes and pumps. If this is so, why not title the work "Degradation process in coal slurry pipelines"? What could be more pertinent to this title than the investigation concerning the degradation phenomenon of coal particles in a pipe carrying a coal slurry? Mr. Dasher complains that he does not understand the meaning of the term "increasingly smaller size." The first sentence of this article defines the degradation process as "the breakage of coal particles to increasingly finer sizes." The term "increasingly finer sizes" here means successive breakage of a fine particle to finer and finer sizes. According to Hukki (Hukki, 1975), the probability of breakage is high for large particles and rapidly diminished for fine sizes. We apologize for being brief about some of these definitions. The degradation process, breakage of particles to increasingly finer sizes, is so widespread in the mineral industry that we did not feel it necessary to bore the reader with lengthy definitions of some simple terms. Mr. Dasher states that the coals examined and their original size consist are unidentified. Please look at Table I and Table 2 in the paper again where you will find the original size consist of the coals examined and their full specifications. We only named the coals A, B, C, D, and E to avoid identifying the coal seams that were more susceptible to degradation. Not identifying the name of the wet screening device used in this work has also been criticized. In our opinion, wet screening operation is such a routine and standard procedure that naming the device by which the screening is performed would serve no purpose but to promote a sales approach. This was not our intention. We did not conclude that the correlation between the degradation process and Hardgrove Grindability Index is hard to establish as Mr. Dasher writes in his letter. We stated, not concluded, that "It is reasonable to assume that some relationship between the extent of degradation and its physical properties, such as Hardgrove Grindability Index, does exist. However, any definite correlation is difficult to establish." This statement is based on other researchers work, which are clearly referenced in the article. The conclusions of this paper were based solely on the findings of the experimental work. As for the theory of comminution that Mr. Dasher asks, we would like to refer him to some basic comminution books and articles where various theories are clearly described. For example, Hukki (Hukki, R.T.,"The Principles of Comminution; An Analytical Summary," Eng. Min. 176, 106, 1975) suggests that the relationship between energy and particle size is a composite form of three laws (Bond's law, Kick's law, and Rittinger's law). A comprehensive analysis of coal breakage processes is also performed by Broadbent and Callcott (S.R. Broadbent, and T.G. Callcott, "Coal Breakage Processes, I. - A New Analysis of Coal Breakage Processes;" and "Coal Breakage Processes, II. - A Matrix Representation of Breakage," Journal of the Institute of Fuel, pp. 524-539, December 1956). These and many other relevant publications explain the relationship between the particle size and energy much better that what can be said in this short reply. We will, however, agree with Mr. Dasher on one particular point. We, too, believe that if the investigation concerning the degradation process in coal slurry pipeline were to be pursued further, one could choose to determine one or more of the variables available in the process, such as discharge pressure, power consumption, percent solid, pipe diameter, etc.

Jan 1, 1989