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By Jameel Menashi

Aqueous solutions of Na2Cr04 can be reduced with CO to produce hydrous Cr203 and NaHCO3/Na2CO3. CH3OH, HCOO and HCHO in the presence of CO2 also reduce Cr 6+ and yield similar products. It is shown that the rate of Cr6+ reduction can be represented by the expression -d[Cr6+]/dt=k[Cr6+)1/2[R] where [R] is the aqueous phase concentration of CH3OH, HCOO- or CO. With these three reductants, the activation energies for the reduction processes are comparable and are of the order of 100 kJ/mole. Rapid reduction rates are attained at temperatures in excess of 220°C and, with these three reductants, a green acid-insoluble readily filterable hydrous Cr203 is formed. With HCHO significant reduction of Cr6+ occurs at about 80-100°C and an acid-soluble violet modification of hydrous Cr2O3 is formed. The reduction process is reasonably selective: solutions of Na2CrO4 contaminated with Mo6+ and W6+ can be reduced to yield a Cr2O3 product with significantly reduced contaminant levels. These findings are utilized as a basis for a process for recovering chromium from secondary source materials.

Jan 1, 1984

By M. Fan

Coal has in general a wide range of density from minus 1.3 to plus 2.0 g/cm3 because of its variations in purity, rank, and porosity, etc. The coal density has great impact on froth flotation performance, but much less attention has been paid to particle density than particle size. Our previous research results demonstrated that cavitation-generated nanobubbles around 700 nm in diameter can significantly improve coal and phosphate flotation performance over a wide particle size range. In this study, the effect of nanobubble on the flotation performances of different density fractions (minus 1.3, 1.3-1.4, 1.4-1.5, 1.5-1.6, 1.6-1.8, 1.8-2.0, 2.2-2.2, and plus 2.2 g/cm3) of coal was investigated using a bank of 10-liter flotation cells, a specially designed 50-mm-inside-diameter column, and a 152-mm-inside-diameter column. It was found that nanobubble has the biggest impact on the flotation performance of 1.4-1.8 g/cm3 medium-density coal particles.

Feb 23, 2014

By Sihua Lei, Hong Zhong, Shuai Wang, Yu Gan, Zhanfang Cao

High purity MgO is widely used in various fields as an important magnesiumcompound. The separation of Mg and Ca is of great importance for the preparation of high purity MgO from dolomite. In this study, the key effects of carbonization temperature and nano-calcium carbonate agglomeration on the separation mechanism of calcium and magnesium have been investigated. The results indicated that the reaction in the carbonization process was stepwise. Precise control of the carbonization temperature was essential for the formation of Mg(HCO3)2 due to its low reaction efficiency at lower temperatures or decomposition markedly at higher temperatures. Meanwhile, there was a common-ion effect in solutions containing Mg2+ and Ca2+. Nano-CaCO3 particles were formed during carbonization and agglomerated with the prolongation of static time. A product with a purity of 99.56% MgO and 0.16% CaO was obtained under the optimized conditions: ratio of liquid–solid 30 L/g, carbonization temperature 22–25 °C, carbonization time 1 h, and refining time 4 h. This work has important guiding significance for the preparation of high purity magnesium oxide from dolomite.

Apr 21, 2020

By Shankar S. Hegde

In many areas of the United States much of the most readily minable coal is nearing depletion, while at the same time, increased national attention is being given to coal as a major alternate energy source. If some of the thinner, more erratic, deeper and lower quality coals, which comprise the great bulk of U.S. resources, are to be mined efficiently and economically, greater attention must be devoted to careful planning of mines and to preparation facilities. One of the cornerstones to careful and successful mine planning is precise knowledge of coal thickness and areal distribution, roof and floor quality, and seam quality. Data on which this knowledge is based are obtained from various borehole techniques and, in some cases, seismic methods. Despite the many technical innovations that have been made in acquiring subsurface data, little attention has been given to the problem of systematic storage and retrieval procedures of the data and assembling them in a form that can be used for various computer mapping programs now available. (See Bilter and Martin, 1977; Bryant and Zobrist, 1977 and Farrell and Wherry, 1978). The purpose of this paper is to describe a series of user oriented programs developed over the past five years which are specifically designed for precise logging of rock core, accurate storage and retrieval of this data, correlation of seams between logs, tagging seams, computer assisted data posting of maps and preparing maps and profile sections for report illustrations. The entire system stresses increased precision and speed for a series of operations which are now largely manual, time consuming and prone to error.

Jan 1, 1980

By Robert Hochscheid

When the original water-only cyclone patents were established in the 1950?s, the supplies of low cost oil and natural gas were abundant and low selling prices for metallurgical and steam coal provided little incentive for developing more sophisticated coal cleaning systems. Bituminous coal sold for less than $5.00 per ton, and in this period many domestic coal producers discarded to the slurry pond the coal finer than 0.5-mm. For many producers, the selling price would not permit the recovery of the capital and operating costs required for dewatering and drying the fine coal. Water-only Cyclones Clean Fine Metallurgical Coal The first broad interest in the water-only cyclone became evident in the mid- 19601s, and though some work was done on coarser coals, investigators were particularly interested in cleaning coal finer than 0.5-mm. Flotation was the only fine coal cleaning method that was broadly accepted, but short-comings were recognized and investigators were looking for an effective fine coal cleaning device or system. Because of the greater market value and the need for reducing pyritic sulfur in metallurgical coals, much of the development work of the 1960's was done on coking coals.

Jan 1, 1981

By Reul A. Dejú

The mineral olivine has been the subject of continued research by various authors. Paik (1967) conducted infrared and flotation studies of the adsorption of sodium alkyl benzene sulfonates on olivine. These studies are of interest from two points of view. First, in the metallurgical field it is of interest to understand the mechanism of silicate flotation using sulfonate collectors and second to a hydrologist studying the pollution of surface or subsurface waters it is of interest to study the reactions taking place when water plus sulfonates encounter a porous (silicate) medium. On the basis of Paik's study he was able to postulate a possible mechanism for the attachment of RSO3 (sulfonate radical) to the olivine surface. Parks (1969) has been studying the important influence of the structure of a silicate such as olivine on its dissolution mechanism and its related surface charge. Also Luce, a student of Parks (1964, 1965) has been studying the kinetics of dissolution of olivine using the techniques of direct solution analysis and infrared analysis. Certainly a classic in the study of silicate dissolution is the work of Murata (1940) on the reaction of orthosilicates (olivine in particular) with strong acid solutions. Many authors (Dejú and Bhappu, 1966. 1967. 1968, Dejú, 1969; Rhoades and Krueger. 1968, and Faust and blunter, 1967) have reported studies of the behavior of silicates immersed in water (especially orthosilicates) and have found that there is an exchange of cations from the silicate surface for H+ from the water. Studies by Dejú and Bhappu have also included the system olivine-water-amine.

Jan 1, 1971

By Stephen C. Tadolini, Colton Cook, Cody Hildreth, Frederick Cybulski

"Broken and jointed ground is extremely hazardous and requires unique stabilization techniques to protect worker and critical entries. Bolting techniques, even the most advanced with pre-load to create roof compression, can leave large gaps of unconfined and separated roof. This roof can also be susceptible to water inflows which only exacerbate the support problem. These types of conditions existed on long term development main entry accessing several future longwall panels. The geotechnical assessment identified well-defined jointing systems that also permitted water to flow between the roof separations, which “lubricated” the roof material and minimized any frictional advantages. Chemical injection of a Polyurethane material, Minova Carbopur WS, was placed beyond the bolted horizon to move the water to the rib lines and reinforce the fractured and broken roof. The injection material permitted the effective use of bolting patterns and helped ensure long-term stability of these critical entries. The paper describes the evaluation techniques, design patterns, basis for chemical selection and application, and results and recommendations.BACKGROUNDThe injection of mine and underground civil structures using polyurethane (PUR) has been ongoing for over 50 years. The applications in mining have included gate road stabilizations, longwall set-up and tear-down entries, and simple consolidation of coal mine roofs. PURs have also been used for roof stabilization during longwall shield recoveries. Polyurethane injection was initially developed by the Bergbau-Forshung GmbH, a German coal mine research institute, in the early 1960s (Jankowski, 1972). The product became a standard stabilization method in Germany after its commercial introduction in 1971 (Knoblauch, 1994), and was successfully manufactured at the Minova Essen, Germany location for over 50 years. With the recent closing of the German underground mines, that manufacturing facility has been closed and moved to Katowice, Poland, where production continues today Injection products are also being successfully manufactured by Minova in Australia and the United States.Polyurethane injection in underground coal mines is used in difficult ground conditions in fractured immediate and main roofs. It is also common as a rock stabilization remedy to prevent longwall face caving during shield removal. As presented in the case study, polyurethane was applied to minimize the inflow of water from beneath a stream channel while providing reinforcement and consolidation of the fractured roof that had lost confinement. Polyurethane is a two-component system (Part A and Part B) that is injected into a borehole and can chemically bond to the rock, not relying on friction or mechanical interlock to provide support. The material is injected under pressure, coupled with a low viscosity and small particle size; it flows into roof fractures and separations, which are the paths of least resistance. New developments in low viscosity PUR materials allows penetration of cracks as tight as 0.002 inch (0.05 mm) wide. This also allows for the closures of extremely small cracks to minimize the inflow of water, even if the water is under pressure. Combinations of designed expansion properties and low viscosities make the materials ideal for minimizing and stopping flows of water from underground structures."

Jan 1, 2019

Just 104 km (65 miles) from Phoenix, AZ, Rio Tinto hopes its new Resolution Copper Mine will be a showcase for the Rio Tinto management philosophy. Its goal is to have a net positive impact. In every place that Rio Tinto mines, it wants to be able to have an overall beneficial effect on the local community, environment and economy. ?We?re constantly working to understand our impacts, to understand how to minimize our impacts and understand how to mitigate those impacts,? said Resolution Copper Mining chief executive officer David Salisbury, from the global headquarters of Rio Tinto Minerals in Green-wood Village, CO.

Jan 1, 2010

By X. Wang, Y. Luo

The propensity of coal spontaneous combustion can be evaluated using various laboratory testing methods, such as R70 adiabatic tests, thermal gravimetric analyzer (TGA) tests and critical self-heating temperature (CSHT) methods. Each of the methods has its unique characteristics and index for classifying the propensity of self-ignition of coals. Accountable relationships among the propensity indices of different methods should be established. Using the newly established R70 and TGA testing setups in our ventilation laboratory, samples from U.S. coal mines have been collected and tested. The TGA is a relatively new quantitative method. A test can be conducted in a relatively short time, within about one and a half hours, compared to the adiabatic tests. The temperature and weight of the sample can be measured with high precision and then used to determine the activation energy of the coal, which is a good indicator of the potential for self-heating. Under a specific experimental design, the TGA technique could perform the proximate analysis for determining coal quality parameters (e.g., moisture, volatile matter, fixed carbon and ash content). These parameters can be used in an empirical equation for assessing the potential for coal self-ignition. The trend of activation energies determined using TGA techniques is reasonably consistent with the trend of activation energies determined using adiabatic tests. As a case study, a comparative analysis of these two methods for determining activation energy was made on coal samples collected from Indiana. The kinetics of the spontaneous combustion mechanism has been explained. If the functional groups of a coal such as hydroxyl (-OH), carboxyl (-COOH), methyl (-CH3), etc., activate more easily with a small amount of activation energy at a relatively low temperature, the coal will have a higher potential for self-heating. With the kinetic and coal quality parameters determined by the TGA setup, it has been found that the coal with a low potential for self-ignition has low self-heating rate, a high activation energy and a high minimum self-heating temperature.

Jan 1, 2012

By Francesco Chiappalone, Miriam Piemontese, Lance Waddel, Paolo Perazzelli, Emidio Tamburri, Roberto Schuerch

The Three Rivers Protection & Overflow Reduction Tunnel is part of the Long-Term Control Plan of the City of Fort Wayne, Indiana (USA). The 4.9 m internal diameter tunnel, of length approximately 7.5 km, is excavated at a depth of approximately 40–60 m through carbonate rocks using a slurry TBM. Due to the high hydraulic conductivity of the rock mass and the high in-situ ground water pressure (up to 6.5 bar), the management of the water inflow during the TBM advance and standstills, represents the major challenge for the project. This paper outlines the geotechnical conditions and the hazards related to the large water inflows expected in the pre-excavation phase and discusses the experience gained during the construction of the first 8,224 feet (2,507 m), (first third of the total length of the tunnel).

Jun 13, 2021

By Clément F. Bernier

One of the chief sources of the world's supply of asbestos lies in a belt of ultrabasic rocks which runs northeastward through an area called the Eastern Townships, south of the St. Lawrence River in the Province of Québec. The productive portion of this belt extends from the town of Asbestos in the south, for a distance of some 9,5 km to beyond the village of East-Broughton. The first discovery of asbestos in this region was made in 1874. Only crude fibre was produced until 1888 when the first mill was erected near the town of Black Lake. Since the inception of the industry, almost 100 years ago, no less than 100 different compa¬nies have been formed and 46 different mines have been operated. There are presently 5 active companies in the area providing direct employment for 4100 workers, down from 6000 during the seventies.

Jan 1, 1984

By William D. Mayercheck

Beginning in 1974, the Bureau of Mines, U.S. Department of the Interior, sponsored R & D efforts related to further development and use of continuous face haulage in underground coal mines (Cowan, 1975). The U.S. Department of Energy continued this effort as of October 1977. This paper represents an update of an article previously published in Mining Engineering magazine (Mayercheck, 1979). Development progress is summarized for a variety of prototype systems or components now being built, surface tested, or tried underground.

Jan 1, 1981

By J. F. T. Agapito

Stability in Exxon's Colony Pilot Mine in the Piceance Creek Basin, Colorado has been monitored by periodic pillar stress-determinations End roof-to-floor convergence measurements since 1971. Pillar failure has caused marginal stability in some areas of the mine. Measurements taken during the process of failure provided valuable information on the in-situ pillar strength and long-term behavior of the mine structure. Four pillars were reinforced by 32 mm (1-1/4 in) diameter tensioned grouted bolts to increase long-term stability in the northern area of the mine. Stability of this area is necessary because future plans envision its use as an exit/access and ventilation exhaust. Computer analyses were performed to help evaluate the effect of pillar reinforcement on long-term stability. Results indicate that bolting is particularly useful in stabilizing failed pillars, but its effects are significant only in the immediate area of the pillar. The projected significant decrease in deformation of two extensively failed pillars near a main entry indicates that bolting reinforcement will assist the long-term stability of the opening.

Jan 1, 1985

By Nick Tessitore, Ryan Marsters, Alex Warren, Dylan Fawaz

The West Gates Deicing Industrial Waste Pond Expansion project at Denver International Airport seeks to expand utilities to accommodate additional terminal gates. The project includes six tunnel crossings beneath taxiways and runways with lengths ranging from 239 to 2,025 linear feet. Excavation methods include shielded tunnel boring machines and steerable auger boring. Designed initial support includes liner plate, steel ribs and lagging, steel casing, and Fiberglass Reinforced Pipe and ranges in size from 24" to 132". This paper will discuss challenges associated with the overall layout and design of the project, including contingencies to protect critical infrastructure. In addition, a construction update is provided.

Jun 23, 2024

By James P. Ludwig

While we are all aware of the need for reclamation of mine sites, few managers and engineers seem to be aware that good reclamation begins with the earliest plans for mining and processing of ores. Far too often the attitude that reclamation is an add-on to worry about at the end of the mining process dominates the thinking of mine engineers and management, A common result is that the reclamationist can be faced with mining and waste disposal designs that are nearly impossible to deal with effectively from an ecological perspective. Everyone of us has been victimized by the down time and maintainence cost that resulted from the purchase of an outwardly attractive, but poorly designed piece of equipment. When confronted by design defects in equipment, a distraught owner can always trade it in, call a consumer advocate, or follow up one of the "lemon laws" at either the federal or state level. A poorly designed mine for reclamation purposes usually cannot be treated either with ease or cost effectiveness. Good reclamation can be effectively prevented by the designs used when the mine was planned. The purpose of this paper is to share some of the experiences our firm has had with reclamation projects at mines in the Upper Midwest as these were influenced or controlled by mine design decisions. My aim is to sensitize mine planners and managers to planning processes they should consider, and hopefully use, early in the mining process to assure successful reclamation during and after mining. Many of the examples I will cite are from experience gained at the recently closed Jackson County Iron Company taconite operation at Black River Falls, Wisconsin. I am particularly grateful to Mr. Vern Metzger, mine manager at JCIC, for his unflagging support of good reclamation practices, employee training programs (which have included reclamation techniques), and his forebearance to put up with our group of ecologists. I realize that this was a time when there were significant internal and external pressures to cut all costs including reclamation efforts. The collaboration has been successful as you will soon see.

Jan 1, 1984

By Y. Luo

Although considerable progress has been made in the last decade in predicting surface subsidence over longwall panels, a number of important issues deserve further studies in order to improve the techniques and accuracy of subsidence predictions. Some of the problems are: (1) subsidence over the chain pillars between mined longwall panels; (2) subsidence development process after face stop due to either a vacation or the completion of a longwall panel; and (3) subsidence initiation and development process over the setup entry area in the initial stage of mining a longwall panel. In this paper, the measured data related to the targeted problems are presented, the data analysis techniques are briefly introduced, and some of the prediction methods developed based on the collected data are proposed. The proposed methods can be used as supplemental tools for the existing subsidence prediction models to improve their prediction accuracy.

Jan 1, 1991

By Michael Hood

Subsidence profiles above two adjacent panels in Illinois are compared with pro- files predicting subsidence behavior obtained using the (i) National Coal Board (NCB, 1975) method, (ii) the profile function method and (iii) the influence function method. The NCB method predicts the maximum subsidence values at the center of the troughs accurately, but, the overall shapes of these predicted profiles do not match the profiles from the measured data well. Consistent values for the angles of draw were measured but these angles were different in the transverse (average value 43 degrees) and in the longitudinal (average value 17.5 degrees) directions. Time dependent subsidence effects are shown to be small but measurable. These displacements continue at a linear rate for at least a 12 month period. A comparison of measured horizontal distances, interpreted as horizontal strain, and the NCB predictions for strain shows that the peak measured strains are greater by a factor f about four than the predicted strains. The relationship between surface curvature and strain is investigated. Problems associated with calculation of surface curvatures from vertical displacement data are highlighted and a recommendation is made for future studies to consider direct measurement of this parameter. Surface curvatures above a moving face are found to be about three times less than the curvatures at the stationary end of the panel. On the other hand, a hyperbolic tangent profile function is shown to serve as an accurate predictive tool for subsidence behavior in two adjacent longwall panels at Old Ben Number 24 mine in Illinois. This function predicts not only the vertical displacements but also the surface curvatures above both panels. Influence functions are shown to be more problematic, although potentially more flexible, in their application than the profile functions.

Jan 1, 1982

By P. Rusin

A new bacterium, Thiobacillus cuprinus, can extract copper from chalcopyrite as rapidly as T. ferrooxidans. On solution with and without nutrient amendments and bacterial growth media were supplemented with T. ferrooxidans or T. cuprinus in shake flask studies. Both species extracted -42% of the copper using growth media. In one case, T. cuprinus solubilized approximately twice as much copper as T. ferrooxidans utilizing a seeded On solution. Thiobacillus prosperus also oxidizes chalcopyrite and tolerates high chloride concentrations. These sulfide-oxidizing bacteria are representatives of the mixed microbial community found in sulfide dumps. Rates of biological copper extraction from sulfide ores, using the native microbes, have been significantly enhanced by amending On solution with PGM.

Jan 1, 1994

By Paul E. Rosten

This paper describes some of the latest improvements that have been incorporated or planned by the Cleveland-Cliffs Iron Company to reduce operating costs and improve pellet quality. The Cleveland-Cliffs Iron Company operates and manages mining, beneficiation, and pelletizing operations in Michigan, Canada, and Western Australia. This paper deals with the grate-kiln pelletizing operations at Republic, Humboldt, Tilden, Empire, and Pioneer in Michigan, and the Adams and Sherman in Ontario, Canada. Table I characterizes .each operation in regard to location, ore type, pellet capacity and date that pellets were first produced. All of the operations with the exception of Pioneer and Tilden, utilize downdraft-two-pass grate cycles of drying followed by preheating. Pioneer utilizes an all-downdraft, three-pass grate cycle which consists of three drying zones followed by the preheat zone. The Pioneer and Tilden cycles have been described previously. (1) (2)(3) Tilden utilizes a three-pass grate cycle with a stage of updraft drying, followed by two downdraft drying stages. Recuperation systems which supply hot gases to a drying zone from second stage cooling were designed and furnished for Tilden I. Tilden II will be identical. Empire IV will also be furnished with a recuperation system. The Adams grate-kiln system was retrofitted with a recuperation system. This paper will summarize some of the efforts that are in effect or planned for grate-kiln pelletizing systems to (1) reduce operating and maintenance costs, (2) reduce energy requirements, (3) improve product quality, and (4) meet environmental standards.

Jan 1, 1977

By Shiou-Chuan Sun

The froth flotation of coal, differing greatly from that of most minerals1-5, is not improved but rather impaired by temperatures higher than room temperature6-10 This phenomenon has long taunted us for an explanation. Gayle and Associates 8,9 reported the lack of relationship between their contact angle measurements and their flotation of American coals under various temperatures. Bailey and Whelan6 stated that the viscosity of flotation reagents, offering some clue for their flotation of British coals at low temperatures, could not be put forward as an explanation either in whole or in part for the effect of temperatures on coal-flotation. In this paper, a froth hypothesis is proposed to explain the flotation behavior of coals under various pulp temperatures. Test work involved the flotation of coals and the frothing of reagents.

Jan 1, 1966