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By M. Dondi, M. Surracco, G. Alfano, P. Saba

Recent investigations on fine grinding with jet mill miprototypes of original design, constructed at the DIMM and Centro Studi of the National Research Council at Cagliari University, have led to the realization of a third generation micronizer characterized by large capacity and high efficiency. The new model and its distinctive features are described here and the results are presented of grinding tests on typical, high grade Sardinian minerals used for quality products. The operating principles of the jet mill are described in relation to the mechanico-elastic properties of the minerals treated. In particular the efficacy of the comminution process is demonstrated in terms of both solid treated and of impact, attrition and shearing forces generated in the micronizer. Particle size distribution of the finished products are reported, that satisfy the most stringent market specifications for the different minerals, as well as energy consumptions. The alternative operating options for solving particular grinding problems and minimizing energy consumption are discussed. Lastly, the main developments of the jet mill for a possible application at industrial scale are suggested.

Jan 1, 1995

By D. J. Torpy

With copper at its host depressed price in several years, producers are looking at every opportunity to cut costs in order to continue operating. Some of the measures that have been applied by different companies include reduction in manpower, high grading, and in some cases partial shutdowns. The most beneficial cost cutting measure implemented by Southern Peru Copper Corporation was to steepen the slope of the final pit limit from a conservative 37 degrees to an average of 48 degrees. By doing so, substantial cash outlays were saved. Southern Peru Copper Corporation (SPCC) operates two open pit copper mines and concentrators in the southern part of Peru, about 150 kilometers from the Chilean bordar. The Toquepala Mine went into production in 1960 and the Cuajone Mine in 1976. Both mines use shovel, truck and train operations. The trains, which haul ore to the crusher or waste to the dumps, are loaded either directly by shovels or by a transfer system. The Toquepala Concentrator treats an average of 43,000 tons per day and the Cuajone Concentrator an average of 55,000 tons per day. Concentrates are shipped via a 200 kilometer railroad to the port city of Ilo where the SPCC smelter is located. The annual production in the smelter from both mines is 290,000 tons of blister copper.

Jan 1, 1987

By R. Singhal

Canada's coal production is approximately 65.4 million tonnes of which 95 % is produced by surface mining methods mostly from the three Western provinces (British Columbia, Alberta and Saskatchewan). The mines are highly mechanized; productivity gains during the past few years have ranged from 60 -80%. Truck/Shovel methods are common although Saskatchewan lignite is almost exclusively mined by draglines. This paper provides an overview of Canadian Coal mining industry vis a vis surface mining. Emphasis is on application and utilization of mining equipment and associated mining methods.

Jan 1, 1994

By K. P. Chong

Fracture toughness of oil shale is an essential property in fragmentation to optimize particle sizes and permeability distributions in in-situ processes. Fracture mechanics of oil shale has been based on conventional fracture mechanics using notched samples and assuming the material to be isotropic and elastic. Oil shale is a layered material more accurately characterized as transversely isotropic. The senior author proposes to use a semi- circular core specimen with a center crack subjected to three point bending. Singular crack tip elements with isoparametric elements are used. The precracked semi-circular disk is modeled under displacement loading. The effect of crack length on the non-dimensionalized stress intensity factor is investigated by strain energy method, ellipse method, and stress method. Very close agreements are found. The fracture toughness is obtained by compressing the specimen in to failure. Parameters such as oil yield are investigated.

Jan 1, 1984

By P. J. Best

Due to its low mine production costs, competitive rail rates and low sulfur content, the Southern Powder River Basin (SPRB) now commands 30 percent of the U.S. utility coal market. In 1996, production exceeded 260 million tons, a growth of 110 million tons since 1989 and 15 million tons over 1995. Continued growth is expected as the second phase of the Clean Air Act Amendments (CAAA) looms. This growth will be the greatest in the southern part of the basin, where coal quality is higher. This article is an overview of supply and demand issues affecting markets for SPRB coal. It reviews the current markets for SPRB coal and addresses future prospects for market expansion.

Jan 1, 1998

By Duane L. Whiting

The National Environmental Policy Act of 1969 (NAPA) provides guidance for federal agencies in making informed decisions. The Act has been used to determine the potential environmental impacts from mining and other natural resource operations, primarily in the Western USA. To accomplish the purpose of the Act, a process for developing environmental documents was established. The documents (EA/EISs) evaluate environmental impacts and are produced by federal agencies through public participation and cooperating agency review. Effective interactions and up front coordination between agencies and industry is required. An abbreviated history of environmental protection in the USA leading to NEPA, the driving regulation, objectives, provisions and limitations of the Act, and select mining related NEPA projects III the Western U.S. are discussed in this paper.

Jan 1, 1998

By Andreas G. Mueller

Gold-silver and copper-gold deposits with high-temperature wallrock alteration of Ca-Mg-Fe-Al silicates occur in ca. 3.0 Ga old greenstone belts of the Yilgarn Block, Western Australia. The deposits are hosted by amphibolite-facies komatiites, basalts and BIF, controlled by ductile shear zones and located within the contact-metamorphic aureoles of composite granodiorite-granite batholiths. Disseminated sulfides and free gold form foliation-parallel ore zones in a gangue of anhydrous silicates (garnet, clinopyroxene, olivine), hydrous silicates (amphibole, biotite) and calcite. The deposits may be classified on the basis of their dominant economic metals as: 1(1) Gold skarns with substantial silver as by-product, represented by the Marvel Loch mine (production: 2,200,000 t at 3.5 g/t Au), and characterized by the mineral association pyrrhotite, loellingite, arsenopyrite, galena, gold and magnetite. (2) Gold skarns with low silver contents, represented by the Nevoria mine (production:1,850,000 t at 3.4 g/t Au), and characterized by the mineral association pyrrhotite, chalcopyrite, arsenopyrite, gold, Bi-tellurides and magnetite. (3) Copper-gold skarns, represented by the Elverdton mine (production: 850,000 t at .7 5 Cu, 0.81 g/t Au), and characterized by the mineral association magnetite, chalcopyrite, pyrrhotite, pyrite, gold and Ag-Bi tellurides.

Jan 1, 1990

By G. Biles

The Eskay Creek Mine, a high-grade gold and silver underground mine in northwestern British Columbia started operations in late 1994. For the first three years of operation, ore was crushed to minus 2 inch; blended to satisfy smelter terms and direct shipped to smelters in Japan and Canada. Before commencing the above operations, preliminary evaluations had indicated that an extremely complex metallurgical facility, requiring a large capital investment, would be required to recover the precious and other economic metals. Subsequently markets for raw ore were identified and underground mining and ore transportation operations, at a nominal production rate of 300 tonnes per day, were commenced. Exploration diamond drilling in 1995 and 1996 discovered additional lower grade mineralized zones, which are less economic or uneconomic as direct shipping ore. Testwork demonstrated that these lower grade zones could be upgraded to marketable concentrates in a simple flotation mill. The mill was built in 1997 and has been in operation since late 1997. The mining rate now has increased to 400 tonnes per day including 250 tonnes per day of the direct shipping ore and ISO tonnes per day of the mill ore. Prime Resources Group Inc. wholly owns the Eskay Creek Mine. Homestake Canada Inc. owns 50.6% of Prime's shares and manages and operates the mine on Prime's behalf. This paper discusses the mining and milling operations as well as ore shipment and smelter contracts' administration.

Jan 1, 1999

By Hervé Le Bissonnais, Jean-Pierre Janin, Anne Bergère, Pierre Renier

"The most important impact on the environment of a tunnel excavation is the creation of surface settlements. Nowadays, the mechanized tunneling allows minimizing the settlements, applying a confinement pressure which counterbalances the ground de-confinement. It is thus essential to determine the correct amount of confinement pressure. In this paper, the authors present a 3D numerical study simulating the EPB-TBM excavation of a water tunnel, in the Flanders clays (north of France). Firstly, a simplified 3D simulation, based on the concept of instantaneous longitudinal settlement curve, was performed to predict the surface settlements for different values of heading confinement pressures. Secondly, the same pressures were tested by the EPB-TBM in a monitoring zone. The comparison between the prediction settlements and the measurements was very satisfactory and allowed validation of the numerical approach and the choice of the optimal confinement pressure value for a sensitive area of the project. INTRODUCTION The excavation of a tunnel can create displacements of the surrounding soil which may affect existing structures and generate unacceptable dysfunction. The development of the closed shield tunneling has permitted to reduce the volume loss generated around the excavation and consequently the surface settlements. In this case, as explained by different authors (Clough et al., 1985; Kastner et al., 1996; Mair and Taylor, 1997), the ground movements are influenced by the TBM works: the heading confinement pressure, the shield overcutting and conicity, the annular void grout injection parameters, the segment concrete lining rigidity, the consolidation of the grout. Hence, in the tunnel design, it is important to take into consideration these different processes of the excavation works to simulate correctly the tunneling process."

Jan 1, 2016

By F. S. Knoll

GENERAL INTRODUCTION Electrostatic separation has found a number of applications since its initial installation as a processing method. Three broad types of electrostatic installations are discussed in order to provide a practical guide for three widely divergent uses of electrostatic separation. Only operating and installation data are covered in detail. A detailed technical treatment on the various types of electrostatic separation described in this paper can be found in the literature by F. S. Knoll, J. B. Taylor and J. E. Lawer.8, 9 ELECTROSTATIC SEPARATION OF IRON ORE: WABDSH MINES, CANADA Introduction Electrostatic roll-type separator technology which had been in use in various forms since the 1920's evolved in the late 1940's when this separation process was developed and applied to the extraction of titanium bearing minerals from beach sands by J. H. Carpenter. Equipment design and industrial flowsheets developed for the recovery of rutile and ilmenite found new application in iron ore by chance in the year, 1956. From the time of the first beach sands plant, Carpco had developed other technology, gravity and magnetic separation to better serve the beach sands industry. It was in the fall of 1956 that an iron ore producer from the upper Michigan Peninsula sent a sample of jaspilite (fine-grained specular hematite in a jasper matrix) to Carpco's laboratory for the purpose of determining if a new high-intensity magnetic separator would be beneficial. Process Development W. P. Dyrenforth, while presenting a paper on the subject in the fall of 1957, recounts the laboratory tests. "High-intensity magnetic separators have been employed (for the beneficiation of iron ore) with some success and are still being investigated. Magnetic separation is a natural field of investigation, since iron and magnetism have been almost synonymous since ancient times. As a matter of fact, when Carpco first began investigating the possibilities of upgrading specular hematite, the first thought was in terms of magnetic separation; and the second thought was in terms of gravimetric separation. It was found

Jan 1, 1986

The knowledge of aggregate size under various chemical and hydrodynamic conditions is very important for selective agglomeration, flotation and water clarification processes. Traditionally, aggregate size measurements are conducted using an ex-situ technique or in a diluted suspension. In either case, the measurement occurs in an environment that does not resemble the actual conditions under which the aggregates are formed. In this study, an on-line scanning laser microscope has been used to study the coagula size of micronized coal suspensions as a function of pH, solids concentration and agitation intensity. A maximum aggregate size of 310 µ m was obtained under relatively quiescent conditions and at pH values near the iso-electric point (iep) of the coal. The aggregate size results compare well with the coagulation efficiency measurements obtained under the same pH conditions.

Jan 1, 1994

By O. A. Velasquez, A. R. Kumar

"Dust generated on underground mechanized coal mining faces is a health and safety hazard. Continuous miners deployed underground usually have an integrated flooded-bed dust scrubber mounted onto the machine that arrests the generated dust from close to the face and cleanses the air around it. However, the impingement screen might get clogged depending on the coal seam being worked. This necessitates the cleaning of the screen which in turn, reduces the overall availability of the scrubber and, hence the continuous miner. A novel non-clogging screen has been developed at the Department of Mining Engineering, University of Kentucky. The proposed impingement screen is built up of three individual aluminum screen units 1.5 mm thick and separated by 3 and 2 mm respectively. The screens have long vertical slits measuring 6 mm. A water spray continuously keeps the screen wet and provides for the filter element to arrest the dust particles. The slits force the dust-laden air to make sharp turns. The dust particles cannot change directions rapidly, impact one of the three screens and are separated out based on their momentum. Preliminary computational fluid dynamics (CFD) models have indicated significant cleaning efficiencies in the respirable range at the expense of much lower pressure drops. Results indicated by CFD models and supported by laboratory experiments have been discussed in this paper.ACKNOWLEDGEMENT The authors acknowledge the National Institute for Occupational Safety and Health (NIOSH) for funding this research. Dr. Thomas Novak, Professor of Mining Engineering, is also acknowledged for his continued support and encouragement. INTRODUCTION Continuous miners are ubiquitous in coal mining around the world. The miners are operated against bling headings, ensuring adequate flow of air at the face could be difficult. The minimum requirement of ventilation airflow quantities at those coal faces are legislated to dilute dust generated to harmless levels. New dust rules promulgated recently have further called for lower exposure levels of personnel working underground (Courtney) (MSHA, 2014) (NIOSH, 2010). Water sprays are also installed at strategic locations and serve as powerful air-movers. The sprays capture some amount of dust generated while cutting. In addition to this, usually, all continuous miners are equipped with a flooded-bed dust scrubber as shown in Figure 1 to capture the dust from close to the extraction drum (Chao & De-sheng, 2000) (Wala, Vytla, Huang, & Taylor, 2008) (Organiscak & Beck, 2010)."

Jan 1, 2018

By R. W. Lake

The decision to develop an ore body can lead to multi-million dollar profits, or equally substantial losses. Accordingly, the effort required to adapt a valuation model to the specific proposal at hand, or even the development of a new model from basic principles, is clearly warranted. In the formulation of a model of this nature, one is faced with some major questions. For example, with the long term obligations that it implies, on what basis should a decision to initiate mining operations be made? Furthermore, how can the vagaries of inflation and the uncertainties that shroud the future be accommodated? Beyond the general principles by which mineral deposits are evaluated, specific cost behaviour is a function of the geology of the deposit, and of the mine design. Moreover, mine design, during the life of the mine, must be a continuing process somewhat akin to dynamic programming. An initial, apparently optimal, design is selected and mining commences. With production, a continual process of information updating leads to revisions. Thus if the maximum value is to be obtained, the mine design must be adjusted to conform to the changed conditions.

Jan 1, 1977

By B. Kyslinger

"In underground mining, machine design is predominantly dictated by mine conditions and individual customer desires. In partnership with Foresight Energy, J. H. Fletcher & Company was tasked to design and manufacture a new roof bolting machine with six independent drilling apparatus on board capable of drilling and bolting the roof and ribs with material handling. This is the first Fletcher® six head machine to be designed and built for the mines in the United States. The machine is intended to work in the Illinois Coal Basin. The objective was to produce a machine capable of drilling and installing six bolts simultaneously with a limited number of operators. The goal of the mine is to decrease the time to bolt a cut to improve the safety level of the current roof bolting method, improve efficiency and to improve the bottom line cost of entry development. The customer wanted four mast feed drills at the front of the machine dedicated to installing roof bolts and then another two mast feed drills behind them dedicated to rib bolts. This dictated the requirement of latched controls, which would allow the operator to start drilling one hole and then latch the controls to be able to move on to the next. To accomplish this, we developed a unique hydraulic latch circuit to maintain operator safety and compliance. Guarding was added to prevent an operator from coming into accidental contact with a latched drill. The result of the design is a machine with a single platform and six independent masts with drillheads: four masts strictly for drilling and installing roof bolts on the front of the platform and then two masts on the back of the platform for rib bolts. The feed and rotation controls at each operator’s station include a latch control for drilling. The latch control will allow the operator to lock in the feed and rotation once the hole has been collared, allowing the operator to move on to the next hole. The rear of the machine is equipped with material handling. There are two material pods with winch controls as well as a mesh rack that includes mesh lift, mesh tilt and mesh sump. The six-head roof bolter allows fewer operators to drill and install roof and rib bolts, which in turn lowers the miners’ roof exposure per cut. This design reduces the operator’s exposure from the inherent pinch points and rotary hazards once he has engaged the latch drilling. Therefore the machine will help to decrease the time to bolt a cut, improving productivity while enhancing the ability to operate the machine safely. INTRODUCTION When mining underground it is necessary to support the roof quickly to prevent it from collapsing after an area has been mined. Since the 1950s, the primary method for supporting the roof has been the installation of roof bolts. Roof bolting is one of the most basic functions yet one of the dangerous jobs in the underground mining operation (1). The Mine Safety and Health Administration’s (MSHA) Health and Safety Accident Classification injury database showed an average of 660 roof bolter operator accidents per year over a 5-year period (1999-2003) (2). The numbers show that roof bolting is the most hazardous machine-related job in underground mining. It represents 39 percent of all machine-related accidents in underground coal mines. In 1993, the U.S. Bureau of Mines conducted a study that has shown the activity of drilling as the most hazardous job task performed by a roof bolter operator, accounting for 31 percent of all roof bolting injuries (3). Almost half (46%) of these drilling injuries were due to falling rocks or coal from the roof. All of these injuries occurred under supported roof. The majority of these injuries (about 99%) are not caused by a major roof collapse but from falls of smaller rock from the immediate roof. This type of roof failure has also been termed “skin fall.”"

Jan 1, 2017

By Howard Brown

High purity, high brightness limestone deposits in the San Bernardino Mountains and Mojave Desert region occur in upper Paleozoic carbonate rocks which are part of an upper Precambrian and Paleozoic sequence that unconformably overlies crystalline basement. The Paleozoic strata are divided into formations and members, and correlated with strata of the inner Cordilleran miogeocline. The region has been affected by multiple Mesozoic intrusive, contact, and regional metamorphic events. Structure is complex, and includes polyphase Mesozoic folding and thrusting, and complex Cenozoic structures. The area continues to be seismically active. High brightness (white), high purity crystalline limestone deposits are uncommon because their formation is dependent on several geologic processes which include; 1) depositional environment, 2) contact and or regional metamorphism, 3) folding and faulting, 4) uplift and erosion, and 5) preservation through geologic time. The complex geologic history of the San Bernardino Mountains and Mojave Desert region has allowed the formation of several large high brightness, high purity limestone deposits which are currently being mined or will be mined in the future. Specialty Minerals, Inc. (formerly Ptizer), Pluess-Staufer (California), Inc. and Partins Limestone, Inc. produce high brightness, high purity limestone from several quarries in the San Bernardino Mountains. These active mines combined with undeveloped deposits controlled by Pluess-Staufer in the San Bernardino Mountains, New York Mountains, and Bristol Mountains in the Mojave area, contain proven and or indicated reserves sufficient to sustain production through the 21st century Detailed geologic mapping, intimate knowledge of stratigraphy, recognition of complex structures, sampling, drilling and assay data, are proven tools in the discovery and delineation of high brightness, high purity limestone deposits in the San Bernardino Mountains and Mojave Desert region of southern California.

Jan 1, 1995

Since it was first introduced, the Coal Mine Roof Rating (CMRR) has been widely accepted as a tool for geologic characterization and mine planning. This paper discusses the application of the CMRR to another practical ground control problem. Extended cuts (cuts greater than 6 m (20 ft) in length) are commonly used with remote control continuous miners. Extended cuts can greatly increase productivity, but they have been associated with a number of fatal roof fall accidents. When extended cuts are attempted in weak roof, the roof may collapse before it can be bolted, causing hazardous conditions. Until now, it has not been possible to predict where conditions may not be suitable for extended cuts. In this study, data on the CMRR and extended cut experience were collected at 36 mines in 7 states. It was found that when the CMRR was greater than 55, deep cuts were routine in nearly every case. When the CMRR was less than 37, extended cuts were almost never taken. Between 38 and 55, extended cuts were feasible sometimes but not others. The data also shows that extended cuts are less likely to be stable if either the entry span or the depth of cover increases.

Jan 1, 1998

By J. Drelich

The adsorption of oleate at the surface of titanium dioxide from aqueous solutions was examined by Fourier transform infrared (FT -IR.) spectroscopy using a germanium internal reflection element coated with a thin film of TiO2. This thin film, with a thickness of 100-200 A, was deposited on the surface of a germanium single crystal by RFIDC magnetron reactive sputtering. It was found that significant adsorption of oleate from a 0.02-0.03 mM aqueous solution on the surface of TiO2 thin film occurs at neutral pH, from about pH=5.5 to pH=7.7. Adsorption of oleate at the surface of the amorphous TiO2 thin film appeared to be reversible, involving soap-acid dimers.

Jan 1, 1997

By D. Hong

The leaching behavior of rhenium in ammonium iodide solutions with iodine as oxidant has been studied. Experiments were carried out in an autoclave. The effect of stirring speed, temperature, pH of the solution, iodine and iodide concentrations on the dissolution of rhenium was investigated. It was found that high temperature and high pH of the solutions were essential for the efficient leaching of rhenium. The dissolution rate was found to be dependent upon the concentration of iodine and iodide. It was concluded that the dissolution of rhenium under the conditions studied was controlled by mass transfer of iodine with an apparent activation energy of 15.77 kJ/mole.

Jan 1, 1997

By H. M. Breza

Recovery of phosphate concentrate has received increased attention as the existing mine and plant production capacity limitations of the Texasgulf Inc. Aurora, North Carolina Mine are reached. Improved mining techniques and mineral processing of waste streams offer a potential to increase overall phosphate production without major expansion of the Mining facility. Innovative processes have been or are being identified to maximize pit mining recovery and to minimize losses in waste streams, resulting in more effective use of the valuable phosphate natural resource. This paper will describe the various continuous recovery improvement programs being implemented to achieve this goal.

Jan 1, 1994

By G. L. Brooke

At present, there are two known cobalt deposits in the 48 contiguous states. This paper is a brief description of one of these deposits. It is a Mississippi Valley type deposit, but somewhat atypical in that the metal of greater interest is cobalt as opposed to lead, zinc, and copper. The history and present work are outlined along with a discussion of the geology and mineralogy.

Jan 1, 1981