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By D. R. Nagaraj, Napoleon Tercero, Raymond Farinato

"Dialkyl dithiophosphinates are a unique class of collectors used in the flotation processing of Cu- Au, complex polymetallic, and precious metal ores. They are known to exhibit higher selectivity and flotation rates for Cu sulfides, galena, and precious metal values in the presence of other gangue sulfides, than the traditionally used collectors such as dialkyl dithiophosphates and xanthates. They also have an attractive HSE profile. Historically, for most reagents used in flotation, practical methods of chemical usage have preceded detailed scientific understanding of how they work; this applies also to dithiophosphinates. Recently, however, the research community has shown significant interest in this chemistry, and numerous studies have been conducted to understand the fundamentals of interactions of dithiophosphinates with several base metal sulfides and precious metals. A critical overview of fundamental studies, laboratory ore flotation, and plant practice of dithiophosphinates is given in this paper. The findings from these studies are rationalized by drawing on concepts and insights from coordination chemistry. A comparison between the interactions of dithiophosphinates and dithiophosphate analogues with various minerals and metals is also made throughout. We believe that such a critical analysis/overview will be invaluable in identifying gaps in knowledge regarding this important set of compounds, which in turn may provide a basis for the design of studies that can advance understanding of their flotation performance. INTRODUCTIONDialkyl dithiophosphinates are an important member of the class of thiophosphorus compounds that are widely used in flotation beneficiation of base metal sulfide and precious metals ores. Ore flotation studies and plant practice experience have demonstrated their unique properties compared to the traditionally used sulfide collectors such as dialkyl dithiophosphates (their closest analogues) and xanthates. The predominant dialkyl dithiophosphinate used in the industry today is sodium diisobutyl dithiophosphinate (a.k.a. DIBDTPi; AEROPHINE® 3418A1 introduced by American Cyanamid in the late 1970s; Figure 1). The widest application of AEROPHINE 3418A is found in complex polymetallic ores of Cu-Pb-Zn-Ag, Pb-Zn-Ag, and Cu-Zn where it has demonstrated improved recoveries (and flotation rates) of sulfide minerals of Cu, Pb and Ag and selectivity against sphalerite, iron sulfides, and penalty elements (Mingione, 1991). More recently, it has also been used as a collector in the processing of Cu, Cu-Ni, and Ni ores (Guitard et al., 2015) and Cu-Au ores (Dunne, 2005). In general, it is considered to possess the collecting power of xanthates together with the selectivity (against pyrite) of dithiophosphates (Hope et al., 2003a, 2003b), while requiring lower dosages than those reagents (Guitard et al., 2015). AEROPHINE® 3418A has also found an important place in several targeted formulations to improve flotation performance. Other benefits of this reagent include higher flotation rates, having a better HSE (health, safety and environmental) profile2 compared to xanthate, and exhibiting resistance to hydrolysis and oxidation (Guitard et al., 2015). Compared to diisobutyl dithiophosphate (DIBDTP), which is known to contribute significantly to frothing (often leading to over-frothing), AEROPHINE® 3418A is observed to be froth neutral (i.e. it does not alter the existing froth characteristics). As is the case for other flotation reagents, the design and application of AEROPHINE® 3418A has preceded understanding of its behavior at a fundamental level. Recently, there have been numerous fundamental and application studies designed to develop a better understanding of its interaction with sulfide minerals and precious metals. This should help in optimizing its application in flotation and provide a basis to better rationalize its unique selectivity and activity characteristics. Past studies on the interacti"

Jan 1, 2016

By Leslie Gertsch

Outline First progress report ? ?Introduction ?Non-terrestrial mining ?Near-term targets ?Stages of mining ?Study procedure Capabilities needed for non-terrestrial mining ?Mining methods ?Mining unit operations ?Typical surface mine operations sequence ?Results to date General effects of gravity ?On fragmentation ?On excavation ?On transport ?Conclusions / Recommendations

May 1, 2013

By Tassos Grammatikopoulos, Vladimiros Papangelakis, Douglass Duffy, Cheryl Washer, Srinath Garg

Flotation operations in Sudbury, Ontario, seeking to separate pentlandite and chalcopyrite from mixed sulphide deposits, produce pyrrhotite tailings that have been disposed of in tailings ponds for over 50 years. These reactive tailings are viewed as waste, despite containing ~0.8 wt% Ni, and represent an environmental liability because of their acid mine drainage (AMD) potential. Given the large quantities of pyrrhotite currently stored in Sudbury, and declining ore grades elsewhere, these tailings have shifted from being viewed as a waste to a potential resource. Recent advances in the bioleaching of low-grade sulphide ores have raised the prospect of bioleaching as a potential low-cost processing option. However optimization of this proposed process requires a thorough understanding of the mineralogy of the pyrrhotite tailings that would be leached. The work presented here addresses the characterization of two distinct Sudbury pyrrhotite tailings, namely from the Vale and Glencore operations, using electron microprobe, XRD and QEMSCAN analysis. Particular focus is given to how the mineralogy may affect bioleaching as a processing option, through the deportment of nickel and the various phases present

Jan 1, 2015

By Roger Potvin

Abstract The demand for pure zirconium and titanium metals in Germany increased considerably during the war. Pure zirconium was used in flash bulbs, in vacuum tubes, and in time fuses for bombs, where it has a decided advantage because it gives no gas in burning. Under the form of alloy, it was used with other rare elements for making substitutes for platinum; it was also used as a scavenging agent in high-grade steels. Metallic titanium was mainly used in connection with the manufacturing of special alloys. The authors were sent to Germany by the Department of Reconstruction and have investigated the German process developed for producing these rare metals. They describe the procedure and special equipment used for their commercial production in Germany during the war. General Metallic zirconium and titanium were .produced on a commercial scale in Germany by the thermal reduction, with metallic sodium, of potassium fluozirconate and titanium chloride, respectively, using a mixed potassium and sodium chloride flux. According to the information gathered, the sole German producer of these rare metals in pure form was the Deutsche Gold und Silber Scheideanstalt (commonly called Degussa), at their Werk II, 215 Gutleutstrasse, Frankfurt/Main, which was visited by the authors on September 18th, 1945. As far back as 1934, Degussa was carrying on active research on the manufacture of zirconium, and nearly one ton of the pure metal had been produced before September, 1939. Concurrently, a quite similar process was worked out for the recovery of titanium and it was in commercial operation in the year 1938, during which the production totalled about half a ton (metric). The demand, especially for pure zirconium, increased considerably during the war, attaining a total of about 48 tons during the period October, 1939, to the end of 1944, and reaching a peak of more than 15 tons in 1943. In 1944, the plant was slowed down due to the frequent and disastrous bombing by the Allies, especially in March and September.

Jan 1, 1946

By E. Ghali, W. Zhang, G. Gabra, N. Sorour, G. Houlachi

The additives polyacrylamide, 1-Butyl-3-methylimidazolium chloride, Tetra-butylammonium bromide, Benzalkonium chloride and chitin are evaluated during zinc electrolysis from synthetic acidic sulphate electrolyte containing Mn2+ ions, in absence and in presence of 0.0055 mg dm-3 of Sb3+ ions. Galvanostatic polarization tests for 2 hours at 50 mA cm-2 and 38oC were carried out to determine the cathodic and anodic potentials, and current efficiency of the deposited zinc. Potentiodynamic polarization and cyclic voltammetry tests have also been employed to study the electrochemical behavior of each additive on the zinc deposit on aluminum electrode. Results showed that, in presence of Sb3+, adding 1 to 3 mg of 1-Butyl-3-methylimidazolium chloride increases the cell voltage by ˜0-7 mV. Current efficiency is increased by ˜4.90-6.40%; power consumption is reduced by ˜147-173 kWh t-1 by adding 1-3 mg, respectively. However, in absence of Sb3+, cell voltage is decreased by ˜7-28 mV, current efficiency is increased by ˜0.70-1.50%; power consumption is reduced by ˜41-47 kWh t-1 by adding 1-3 mg. The effect of the other additives on cell voltage, current efficiency, lead content and morphology of zinc deposit has also been examined. Surface morphology and crystallographic orientation of the deposit was studied using scanning electron microscopic (SEM) and X-ray diffraction (XRD), respectively. The content of lead in the deposit has also been measured using inductively coupled plasma spectroscopy (ICP).

Jan 1, 2015

By R. Le Houillier, M. Nagamori, A. J. Plumpton

"Asbestos tailings are a typical serpentine, hydrated magnesium silicate, consisting primarily of antigorite and a few per cent of unrecovered fibrous chrysotile. Serpentine has unique thermal properties in that dehydroxylating calcination at 600 to 700°C can yield an amorphous structure in which most of the magnesia is liberated from the original bond with silica and thereby rendered chemically active. The amount of activated magnesia can be quantified by selective leaching with a weak acid such as acetic acid. Many wet processes have been proposed to extract magnesium values from calcined or natural serpentine by means of various acids and their ammonium salts. However, the only commercial utilization of serpentine today is found in dry processes such as the production of fused magnesium phosphate fertilizer .The present paper reviews the physical chemistry of the dehydroxylation of serpentine and also various wet and dry processes in order to provide a general view regarding the chemical transformation of asbestos tailings.IntroductionAsbestos fibers occur as chrysotile, a serpentine polymorph. More than nine tenths of mined asbestos ores consist of massive non-fibrous serpentine, primarily the polymorph antigorite, which is discarded as tailings after fiber extraction. For many decades, Quebec has been a world leader in the production of asbestos fibers. As a result, colossal tonnages of serpentine have accumulated in the Eastern Townships'!'. Serpentine minerals are found in large deposit s throughout the world, and significant research efforts have been made, particularly in Japan and the USSR, mostly in attempts to extract magnesia or silica values therefrom.The chemical composition of serpentine (chrysotile and antigorite) may be ideally expressed as Mg3Si2Os(OH). which corresponds to 43.7% MgO and 43.3% SiO2. Natural serpentines often contain a few per cent of Ni-bearing magnetite and other impurities, and therefore the contents of MgO and Si02are both about 40% or lower.Serpentine (hydrated magnesium silicate) is virtually insoluble in weak acids. However, when dehydroxylated under controlled conditions, ' it decomposes to an amorphous state in which magnesia and silica are isolated and chemically active. The magnesia so activated is readily soluble in weak acids. This unique characteristic of calcined serpentine, first discovered in 1942,, has since attracted the attention of innumerable researchers, whence many processes have been proposed."

Jan 1, 1980

By Wang Xianzheng

For a long period of time, the Chinese Government has been attaching great importance to and supporting the rapid development of the coal industry. Particularly since more than 30 years ago, when China introduced the Reform and Opening-up policy, the reform and development of the Chinese coal industry has witnessed world-recognized achievements. National coal production increased from 618 million tonnes in 1978 to 3.52 billion tonnes in 2011. While China?s coal production accounts for 49.5% of the world?s total, its annual production growth contributes to over 80% of global production growth. China is a country utilizing coal as its main source of energy. As the Chinese Government gives support to the rapid development of new and renewable energy sources, as well as to increased coal utilization efficiency, the ratio of coal in the primary energy consumption mix will gradually decline. However, for a long period of time to come, the total volume of coal demand will keep rising modestly. The Chinese Government has been highly committed to and actively promoting the overall, coordinated and sustainable development model, which puts people first. It has put forward a strategic task to build an ecological civilization, and highlighted its resolve to uphold the basic national policy of resource conservation and environmental protection, with a view to the pursuit of sustainable development. China will incorporate its response to climate change into the national economic and social development program, and take effective measures to lower CO2 emissions 40?45% per unit of GDP in 2020 compared to 2005. At the same time, China will increase the ratio of non-fossil fuels to 15% in the primary energy consumption mix. All of the above factors have raised requirements for the Chinese coal industry, with implications for clear directions, plans and goals for the development of the coal industry.

Aug 1, 2013

By R. D. Parker

Location The Frood ore-body is expressed on surface as a prominent gossan ridge, with a total length of approximately two miles. The original Frood (the old No. 3 mine of the Canadian Copper Company) is at the southwest end of this gossan; adjoining it on the northeast is the Frood Extension (until 1929 the property of i:he Mond Nickel Company), while at the extreme northeast end is the Stobie mine. The first two of these divisions of the ridge form the Frood mine as it is known today.? This lies in lots 6 and 7 of the sixth concession, township of McKim, and is two and a half miles north of the city of Sudbury. The general elevation is 1,000 feet above sea level. The Ore-Body The Frood-Stobie parallel offset(l), as its name implies, has no connection in the field with the main mass of the Sudbury nickel eruptive-a norite. It lies one mile to the southeast of that body, and, in general, parallels it in strike. The ore occurs as a more or less tabular structure in what is known locally as the Sudbury series. They are the oldest rocks of the district, and have been placed by Collins(2) as earlier than the lower Huronian, of pre-Cambrian time. The series is comprised of sediments, volcanics (both acid and basic flows), tuffs, agglomerates, breccias, and basic intrusives, all highly metamorphosed, yet all forming a more or less regular picture. The controlling feature of the area has been the attitude of the sedimentary strata, from which has arisen the present sill-like character of the flow rocks, the basic intrusives, and the ore-body itself.

Jan 1, 1932

By J. C. Roy, S. Couture, C. Barbeau

The chemical composition of the asbestos tailings from different mines in the Eastern Townships of Quebec are fairly uniform in composition. The serpentine minerals antigorite and chrysotile form about 85 to 90 per cent of the total. Iron oxides add another 7 to 10 per cent; magnetite represents about 70 per cent of the oxides. Chromite is present in amounts of about 0.5 per cent. The average contents of elemental magnesium, iron and nickel are 23, 6 and 0.25 per cent respectively.

Jan 1, 1972

By H. Link

"The extremely low permeability of the water-carrying beds in the nevonian formation of the potash district of Saskatchewan does not permit the injection of cement or chemicals to seal off sufficient water from the shafts to guarantee the safety of the mine. Based on many years of experience with wet shafts in the German and French potash mining industry, Alwinsal Potash of Canada Ltd. decided to have their potash mine shaft near Lanigan, Sask., which was completed in September of 1967, lined by means of an absolutely watertight lining of combined concrete and steel-plate construction.This shaft lining, consisting of two steel shells of welded construction with concrete filled in between, has proved itself before in the German coal mining industry. It guarantees a permanently dry shaft. With this type of lining, time-robbing and very often abortive injections are superfluous and the regular repair and adjusting work as well as the corrosion of conveyances and ropes can be avoided. Above all, however, the danger of a water inrush into the shaft is abolished completely."

Jan 1, 1971

By W. Gordon Muir

This paper deals with the exploration, development and current operations of the salt mine at Goderich, Ontario operated by the Sifto Salt Division of Domtar Chemical Limited. The rock salt is obtained from a bed 1,760 feet below the surface, 75 feet thick, extending under Lake Huron. Annual production is in excess of one million tons. Large mobile equipment is used. Details of this equipment, as well as the shaft layout, which permits the equipment to be lowered underground with a minimum of trouble are outlined. Mining, crushing and screening procedures' are rev1ewed. Reference is also made to productivity salt distribution and uses.

Jan 1, 1967

By C. O. Aksoy, P. M. Ozfirat, M. K. Ozfirat, C. Tatar, C. Pamukcu

"Temporal and other factors contributing to the occurrence of occupational accidents at an underground coal mine in Turkey between 1992 and 2000 have been analyzed. The time period of the study spanned the transition from hand-worked mining methods (1992 to 1996) to hand-worked mining methods and mechanized mining methods (1997 to 2000).The mine selected for the study employed an average of 5,835 men per year on three separate eight-hour production shifts for 302 d/y (Sundays are not worked, and there are 11 holiday days per year). Production on an annual basis averaged 190,000 tons per year between 1992 and 1996, and 300,000 tons per year between 1997 and 2000.The purpose of the study was to determine which, if any, of the factors studied contributed to the occurrence of accidents so that the mine could take the necessary steps to reduce the risk to the workforce. Regression analysis was used to determine the strength of the relationship between each factor studied and the number of occupational accidents.The strongest relationships observed were between the age of the employee, the day of the week, and the total yearly labour."

Jan 1, 2006

By Nordau R. Goodman

"IntroductionTHE HISTORY of Nova Scotia's gypsum industry goes back about two hundred years. The extensive deposits found in the Windsor formation, which is Lower Carboniferous, were the first discovered in North America and were known to the earliest .settlers. There has been a steady increase in production from these beds, except for minor setbacks in years of wars and depressions, but at the same time there has been a decrease in the number of operating quarries. This decrease reflects the change from the days of horse-and-cart recovery to the modern, large-scale, highly mechanized operations. In the beginning, almost any outcrop could •supply the tonnage requirements and the most •convenient were selected, but the millions of tons needed to meet present-day needs are not easily found.Despite the size and importance of the Nova Scotian deposits there has been little detailed geological work. Sir Charles Lyell, in 1843 ( 10), established that the beds are Lower Carboniferous and this was confirmed by Sir William Dawson (3) a .few years later. Both Lyell and Dawson agreed the calcium sulphate beds were an original part of a bedded series .but did not consider they resulted from a concentration of sea water. Lyell reached the conclusion that the gypsum was related to volcanic action in the form of heated vapours or hot springs. Dawson believed it was formed by the action •of sulphuric acid on calcium carbonate. The acid, derived from the oxidation •of iron pyrites which was abundant in the older formations, was carried by rivers into basins which were rich in shells."

Jan 1, 1954

By Michael Chender

Emerging Equity Sources ? Larger IPOs ? China Inc. ? Other sovereign wealth funds ? New funds and higher allocations ? Private equity

May 1, 2010

By Martin Junker

This Notwithstanding all the debates on climate change and renewable energy, coal remains the world's no.1 primary energy source even in the 21st century. In 2011 alone, total output rose from 420 million t to around 6.6 billion t. Similar growth rates are also expected for the next few years. In order to meet demand, new seams are being tapped and others mined far more extensively. In most cases, this means a move from open-cast to deep mining, and extracting coal from ever greater depths. At the same time, extraction processes such as the room and pillar method are being replaced by longwall mining, which significantly increases seam yield and therefore output. The depth of extraction with new, modified mining methods is increasing rapidly around the world - in most countries, much more rapidly than the corresponding expertise. A trade in mining expertise has therefore developed alongside the coal trade proper. Germany relies on coal imports, but can export mining industry services and advanced mining equipment. Geological conditions in the Ruhr and Saar coalfields forced Germany to drive forward development of deep working for hard coal years ago. For 30 years now, Germany has been mining hard coal at depths of over 1,000 m, and excavation is now at depths up to 1,600 m. Deeper extraction and more extensive excavation posed new challenges for both miners and equipment. Intelligent logistics, modern roadway development methods and longwall mining with ploughs or shearers combined with optimised process coordination offered pioneering solutions - solutions to enable costeffective coal extraction in the long term without compromising safety. Countries such as Russia, the Ukraine, China and the Czech Republic, where extraction is now reaching similar depths, can now benefit from this experience: they do not need to go through the same process of trial and development, but can draw on Germany's findings and ultimately save on costs. Now, Germany is offering this knowledge and experience on the international market on a client- and deposit-specific basis to continue providing mining countries with safe and cost-effective coal mining solutions and secure the energy supply. The presentation gives a number of examples of how international mining companies have used expertise from Germany to better meet the challenges of deep mining.

Aug 1, 2013

By Hyung Sup Choi

The preparation of high-purity zirconyl compounds was studied in order to develop an economical process for obtaining pure zirconium via the caustic fritting of zircon sand. The direct dissolution of caustic frits with concentrated hydrochloric or nitric acid at 80c. followed by the addition of a small amount of acidified gelatin, gave high-purity zirconyl chloride or nitrate. The addition of a small amount of gelatin caused a mutual flocculation between colloidal silica and gelatin. The precipitation of this silica floc markedly lowered the content of silica in the product. The silica content of the compounds (or solution) so produced, generally less than 100 ppm., was sufficiently low for tributyl phosphate extraction for nitrate solutions. It was found that the degree of purification de-pends not only on the procedures employed but also on the nature of the frit itself. Silica was more effectively eliminated from the fritted product produced at higher temperatures, and less silica was present in the com-pound prepared from the frit produced in a shorter heating time. In order to ascertain the nature of the

Jan 1, 1965

By I. Filzwieser, A. Filzwieser

The Peirce Smith converter is the key metallurgical vessel in the majority of copper smelters. During the two step process, oxygen enriched air is injected through a row of tuyeres into the matte received from a primary smelting unit. Additionally, in the first step the iron content is oxidized into a fayalite slag by the addition of silica. During the second step, the remaining copper sulphide is converted into blister copper with a final sulphur content of approximately 200 ppm. The overall efficiency of this process is determined by the total reaction time, the slag quality and quantity, and the chemistry of the final blister copper. To increase the reaction kinetics during both stages, the METTOP Process Control and Regulation (MPCR) system was developed, which consists of four elements: OPC - Optical product control ACR - Automatic computer regulation GCU - Gas control unit GIS - Gas injection system The OPC system from SEMTECH records the optical spectrum emitted by the off gas flame providing immediate, detailed process information. Using this online data, additional gas can be automatically injected into the converter through a gas injection system opposite the tuyere zone. An improved oxygen distribution in the melt and the accurate determination of the process end point results in a significant reduction in the process cycle time. Furthermore, by maintaining the reaction closer to the equilibrium the final sulphur and oxygen content can be reduced compared to the conventional process. In particular, the final sulphur content can be lower than 70 ppm, eliminating the need for an oxidation step in the anode furnace.

Jan 1, 2007

By M. Rylatt, E. Legault-Seguin, C. Mohns

"With energy costs increasing and ore grades diminishing, the role of preconcentration in hard-rock mining operations has gained greater interest. Dense medium separation is a process that can be conducted at particle sizes from 250 to 0.50 mm with high separation efficiency, depending on liberation characteristics of the valuable minerals. Pilot-plant case studies conducted at the SGS Lakefield site are presented, including mineral systems such as spodumene, sulfide-bearing gold ores, and complex sulfide ores. These case studies demonstrate that, for amenable ores, mass rejection of 20–60% is possible while maintaining recoveries of greater than 90%.RÉSUMÉ Au vu de la hausse des coûts liés à l’énergie et du déclin de la teneur des minerais, le rôle de la préconcentration dans les exploitations minières en roche dure présente un intérêt croissant. La séparation (ou concentration) en milieu dense est un processus pouvant être mené sur des calibres de grains de 250 à 0.50 mm avec un rendement élevé de séparation, en fonction des caractéristiques de libération des constituants des minéraux métallifères. Sont présentées dans cet article des études de cas menées dans des usines pilotes du site de Lakefield de SGS, lesquelles incluent des systèmes de minéraux tels que le spodumène, les minerais aurifères sulfurés et les minerais sulfurés complexes. Ces études de cas montrent que pour les minerais présentant les caractéristiques de libération appropriées, il est possible d’atteindre un rejet en masse de 20 à 60 %, tout en maintenant des récupérations supérieures à 90 %.INTRODUCTIONPreconcentration is the process of rejecting gangue minerals while ensuring recovery of valuable minerals prior to more intensive, downstream processing. Preconcentration has been practiced in the industry for many years, and is gaining greater interest as the industry copes with processing lower grade, more difficult ores, which typically require finer grind sizes and incur higher energy costs.The benefits of preconcentration are:• lower mining costs, which allows for nonselective mining;• lower process capital and operating costs (e.g., resulting from reduced grinding, flotation, and fines disposal stages);• increased ore reserves, which provides the potential to treat lower grade ore;• increased mine production without expansion of the existing plant or concentrator;• reduced overall tailings impoundment by converting the reject into a byproduct (e.g., underground backfill or aggregate);• improved efficiency of downstream processes (e.g., silica removal in electric arc furnace feed, removal of softer sliming minerals prior to grinding);• potential application to brownfield operations and greenfield projects; and• a “green” process option, which reduces processing energy consumption;– reduces mill feed;– increases stage metal recovery (higher grade feed);– increases mill metal output per tonne processed;– reduces surface plant, tailings dump, and tailings pond requirements because the plant has a small footprint and can be installed underground; and– can be applied to retreatment of old tailings dumps to recover metal values and reduce environmental impacts (e.g., dissolved metal runoff, acid drainage)."

Jan 1, 2017

By Yoginder P. Chugh

This paper discusses an ongoing field study in southern Illinois (USA) that focuses on: 1) Identifying mechanisms of instability in the set-up rooms (SR) and their T-junctions with headgate and tailgate entries, 2) Developing alternate 3-entry and 4-entry set-up rooms geometry using 3-D numerical analyses, 3) Implementing developed geometries in cooperation with mining professionals and regulatory agencies, and 4) Demonstrating performance of implemented geometries through field monitoring. Illinois longwall mining operations typically experience ground control problems (roof falls, rib sloughing, floor heave, etc.) within SR layouts and around the T-junctions of SR. These occur around the areas where the SR for adjacent longwall face (to be mined) connect with the SR of the previously mined face, and around the tail-gate entries of the mined-out longwall face and around the T-junctions of SR. The problems manifest as highly fractured immediate roof strata, major shear zones in the roof, horizontal displacements within the excavations that result in shearing off the heads of the bolts, floor heave and severe rib sloughing. Similar observations have also been made in longwall mining in Utah.

Aug 1, 2013

By A. Baydusa, K. Barron

A theory for cutter roof failure in coal mines has been developed. It is shown that the key parameters influencing the likelihood of cutter roof failure are the rock strength, the vertical stress (depth) and the horizontal to vertical stress ratio. The support force necessary to prevent the development of this mode of failure is, in most cases, so high as to make it impractical to apply a force of such magnitude. It is, therefore, better to allow the failure to occur and to design a bolting system to support the dead weight load of the failed block. This is probably best achieved by using a yielding bolt system (such as split set bolts) which is anchored well beyond the top of the potential failure block. The maximum potential caving height determined from this theoretical approach compares favourably with field observations reported in the literature.

Jan 1, 1999