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By Fedotov Pavel

One of the efficient means of ore disintegration during the processing is its volume breakage in such machines as roller-presses. Up to date neither the ore disintegration mechanism in roller-presses nor the reasons of their high efficiency are thoroughly investigated. In this work, the mathematical model of Finite Element Method of bad material disintegration in roller-press is discussed. The mechanism of the interparticle ore disintegration is traced.

Sep 1, 2012

By W. H. Gauvin, N. J. Themelis

I N ADDITION to its practical importance in the beneficiation of iron ores and in direct-iron processes, the study of the reduction of iron oxides involves many aspects of challenging theoretical interest. The complexity of the reduction process combined with the fact that under different experimental conditions the controlling stage for the reaction may not necessarily be the same, has led experimenters in this field to a wide diversity of opinion regarding the reaction mecl1anism. As a rule, each investigation has been restricted to the study of one or two variables over a comparative]~• narrow range of experimental conditions, and consequently, it be-comes necessary to examine the significance of each published work in the light of the results of other experimenters in the field.

Jan 1, 1962

By Saluja, Sunder S.

Man had to learn to break rocks as early as the Stone Age, when they formed his main source of raw material. He started with chipping and over the years has reached a stage where he can employ atomic blasts and break, with one blast, millions of tons of rock. In between these two extremes there have been several stages of development including fire setting, use of the expansion of water on freezing in chipped cracks in cold climates, the use of low or deflagrating explosive black powder in about the 17th century, the use of high explosives with the discovery of nitroglycerine in 1846 by Sobrero, followed by the monumental discoveries of the great Swedish scientist Alfred Nobel in the latter half of the nineteenth century.

Jan 1, 1968

By H. Itou

A mechanism of scorodite formation at ambient pressure was investigated using transmission electron microscopy (TEM). Several types of iron arsenate were obtained from Fe/As solutions (Fe/As = 1.0 and 1.5) at pH values of 1.0, 1.25 and 1.5 at 95°C. Amorphous FeAsO4.xH2O was precipitated from solutions having a higher mole ratio of Fe/As at pH l.5, even after 9 hours. A few micron sized particles were observed by SEM, but these proved to be agglomerates of 10-50 nm amorphous FeAsarxH2O particles when observed by TEM. This means that supersaturation of the solution causes the acceleration of nucleation of iron arsenate hydrate. Crystalline scorodite was obtained from a solution in which the Fe/As mole ratio was unity, at pH l.0 and pH 1.5, after 3 hours. Almond-type crystalline scorodite particles were observed by TEM and most of them showed high crystallinity. The addition of scorodite seed material enhanced the crystallization. Amorphous FeAsO4.xH2O, however, was observed at the surface of the seeds during the early stages of precipitation. It is postulated that crystalline scorodite is not directly precipitated even on crystalline scorodite seeds, but requires a certain time to crystallize on the seed material.

Jan 1, 2006

By Ke Yang

"Engineering practices have shown that the skip-fault longwall mining is frequently used when faults with offsets larger than 1 Om are present. Since the skip-fault longwall mining not only reduces the recovery rate of coal reserves, but also increases the cost due to developing another setup room on the opposite side of the fault and moves the longwall into it. The coal pillar so created induced residual stress in and thus affects the safe mining of adjacent coal seams. In order to investigate the influence on panel layout and retreat by a l 6.5m offset normal fault, the similar material simulation model was constructed based on the geological and engineering conditions of No.13 coal seam in the western district of Liuzhuang coal mine employing the down-dip longwall mining. The characteristics of deformation, movement and failure of the overlying strata and abutment pressure when the face cut through the hangingwall and footwall of a normal fault were obtained. There were significant differences between the hangingwall and footwall as conformed by the equilibrium structure model. The results showed that superposition of the tectonic stress from a normal fault of large offset and that induced by mining is one of key factors that lead the severe pressure difficult to control during panel retreating from the hangingwall to footwall. Accordingly, the technical solutions for a fully mechanized mining face directly cutting through the fault are presented and optimized, and the applications of the technical solution in Panels 171301and171303 of Liuzhuang mine enabled them to complete the mining safely and efficiently. INTRODUCTIONFaults have been one of the important technical factors in underground coal mining l1-2i. Engineering practice has shown that the methods of mining through the faults depend on the seam thickness, seam dip angle, offset of fault throw, equipment height, rock strength, and advancing direction l3-5l. In the fully-mechanized longwall mining, the face normally proceeds to cut through the fault directly if the offset of the fault less than 5m, and to skip Uump) the fault if the offset is larger than 5m. In the former case, the most important problem is to efficiently control or avoid roof fall accidents (i.e., crushing, falling, pushover, and rock burst). In the latter case, the most important problem is very expensive to drive a new setup room and move the face equipment to it. The skipped coal pillar may poses problems for mining in adjacent seams."

Jan 1, 2016

By S. Mathur

Oxide particles are commonly used as fillers in plastics, paper, rubber etc. (particulate composites). The successful fabrication of such composites is dependent upon the adhesive strength of the filler particles to the matrix. The compatibility of the matrix and the filler particles is generally enhanced by adsorption of surface modifiers such as surfactants and polymers at the particle-matrix interface. In order to develop a scientific basis for selection of appropriate modifiers it is necessary to understand their adsorption mechanism(s). Specifically, adsorption of polymeric additives is attributed to a combination of chemical and electrostatic interactions, hydrogen bonding and van der Waals forces. Hydrogen bonding has been suggested to be the primary adsorption mechanism for non-ionic polymers. However, a literature survey of Poly(ethylene oxide)(PEO)-oxide system suggested PEO, a non-ionic polymer, to be substrate specific. A systematic study was undertaken to investigate the adsorption mechanism(s) of a PEO on oxide particles. It was determined that strong Bronsted acid sites on the surface interact with the ether oxygen, a Lewis base, of PEO to induce adsorption. In this work characterization of PEO binding sites on oxides is reported and the mechanism(s) of PEO adsorption discussed.

Jan 1, 1997

By Jasna Jurjovec, David W. Blowes, Carol J. Ptacek

At the Kidd Creek site, natrojarosite residue, derived from the zinc refinery circuit, is mixed with mill tailings before final disposal in the tailings impoundment. Column experiments were conducted with fresh unoxidized mill tailings and a mixture of tailings containing the natrojarosite residue. Acidic water, simulating mine drainage water, was pumped through the columns. The effluent water geochemistry was interpreted with the assistance of MINTEQA2. The experimental results suggest that the effluent water pH was buffered by a series of acid neutralization reactions. The release of metals, including Cu, Pb and Zn, was affected by pore water pH, Eh and mineralogy of the tailings material.

Jan 1, 2000

By B. Andersen

An accurate knowledge of Interactions among mineral particles and between such particles and dissolved and precipitated species Is Important in developing efficient separation processes. In this investigation interactions in Florida phosphatic clay waste, that are relevant to dispersion and selective reagent adsorption, the two main prerequisites for selective flocculation, were studied. Initial studies with artificial slimes, consisting of pure clay and phosphate minerals, showed dispersion of artificial slimes to be relatively easy. The problems that were encountered during selective flocculation of the artificial slime were due to unselective polyacryllc acid adsorption on clay, which was caused by the presence of multivalent calcium ions on the exchangeable cation positions on the clay surfaces. This problem could be solved by exchanging calcium for sodium, which reduces the interaction between the polymer and the clay surface. This procedure, however, was not successful for mineral mixtures. Natural slimes were found to be much more difficult to disperse. This was attributed to the presence of cementing materials such as humic substances and Ai and Fe (hydr)oxide precipitates. Selective removal of these cementing materials resulted in good dispersion and partial separation. Further increase in separation of natural slime is likely determined by the presence of calcium on the clay surfaces, as was found for the artificial mixtures.

Jan 1, 1992

By F. D. S. Marquis

An investigation of the mechanisms of formation of two types of porosity-primary and secondary-their characterization, evolution during processing, and effects on the mechanical behavior (fracture, fatigue, and failure) of 7X50 and 2X24 alloys has been conducted. The mechanisms of formation of three forms of primary or cast porosity were investigated, and each form was characterized: (a) macroscopic shrinkage porosity-MSP); (b) microscopic interdendritic porosity (MIP); and (c) hydrogen gas porosity (HGP) or primary hydrogen porosity (PHP). The mechanisms of formation of four forms of secondary or thermal/thermomechanical porosity were investigated, and each form of porosity was characterized: (a) high temperature oxidation (HTO). internal hydrogen precipitation (IHP), or secondary hydrogen precipitation (SHP); (b) preheating blistering porosity (PBP); (c) eutectic melting porosity (EMP);and, (d) dissolution micro void formation (DMF). The evolution and interactions of the primary and secondary types of porosity (w.ith special emphasis on PHP and SHP) during industrial and laboratory processing and their effects on the fracture and failure behavior of both types of alloys (with special focus on fatigue crack initiation and propagation) were investigated.

Jan 1, 1996

By J J. McNee and, J Crusius, T F. Pedersen

The use of water covers is a globally-applied method for minimising acid rock drainage (ARD) and metal leaching. Although the subaqueous disposal of potentially acid-generating materials has been shown to effectively limit ARD, under certain scenarios, metal remobilisation can occur at circum-neutral pH. The following paper presents data from four case studies in which metal mobility from submerged mine waste resulted in degradation to water quality in the overlying water cover. Subcentimetre resolution profiling of dissolved constituents across the tailings-water interface (dialysis arrays), in conjunction with mineralogical information, were used to elucidate the controls governing metal mobility. The data illustrate four pathways of metal remobilisation, including: the release of zinc via the oxidative remineralisation of metal-rich organics at the tailings-water interface; enhanced remobilisation of arsenic as a result of anthropogenic eutrophication; the release of copper resulting from the pH-driven dissolution of treatment sludges; and the release of radium from uranium mill tailings due to the dissolution of radiobarite [(Ra,Ba)SO4] by sulfate-reducing bacteria. The results highlight the conclusion that the chemical stability of submerged tailings reflects both: the solid-phase characteristics of the tailings material; and the physical, chemical and biological characteristics of the depositional environment. In particular, the data illustrate that rigorous characterisation of both the waste solids and receiving environment must be performed in order to assess their compatibility. The results have relevance to the management of tailings repositories including constructed impoundments, pit lakes and natural lakes.

Jan 1, 2003

By S. Mathur

Oxide particles are commonly used as fillers in plastics, paper, rubber, etc. (particulate composites). The successful fabrication of such composites is dependent upon the adhesive strength of the filler particles to the matrix. The compatibility of the matrix and the filler particles is generally enhanced by the adsorption of surface modifiers such as surfactants and polymers at the particle-matrix interface. To develop a scientific basis for the selection of the appropriate modifiers it is necessary to understand their adsorption mechanisms. specifically, the adsorption of polymeric additives is attributed to a combination of chemical and electrostatic interactions, hydrogen bonding and van der Waals forces. Hydrogen bonding has been suggested to be the primary adsorption mechanism for nonionic polymers. However, a literature survey of the Poly(ethylene oxide) (PEO)-oxide system suggested that PEO, a nonionic polymer, was substrate specific. A systematic study was undertaken to investigate the adsorption mechanisms of PEO on oxide particles. It was determined that strong Bronsted acid sites on the surface interact with the ether oxygen, a Lewis base, of PEO to induce adsorption. In this work, characterization of PEO binding sites on oxides is reported and the mechanisms of PEO adsorption are discussed.

Jan 1, 1999

By M. P. Fahey

A significant amount of silca is recovered in the rougher stage of anionic flotation of Florida apatite. This recovery, in the past, has been attributed to both entrainment and cation activated flotation. This study shows that by using a transport factor, it is possible to determine the contribution of each mechanism towards silica recovery. Further, it is shown that the concentration of cations in the conditioning water significantly affects both the amount of silica recovered due to entrainment and true flotation. Further confirmation of this phenomenon was obtained by Ca++ doping of the conditioning water and by using a sodium silicate depressant.

Jan 1, 1996

By A. Wahab Khair

There are a number of factors, including mine geometry, local geology, geotechnical properties of overburden materials, surface topography, sequence of overburden strata, and extraction rate, affecting characteristics of surface subsidence imposed by large underground excavation. Among the factors, the first three have the major impact on magnitude and area of influence of final subsidence. Hence, a model has been developed, considering mine geometry and geologic and geotechnical properties of the associated area, to predict maximum possible subsidence and subsidence profile at any cross-section within the subsidence influence zone. Based on extensive field measurements and mechanics of strata behavior, under the action of overburden pressure in the vicinity of the large underground excavation, the vertical plane of influence zone has been divided into five areas: 1) excavated, 2) caved, 3) fractured, 4) highly deformed but continuous, and 5) subsided zones. In the final state of subsidence each area maintains a certain volume expansion/contraction, i.e. a factor which depends on geologic, geotechnical properties of overburden strata and state of stress within the subsidence trough. The cumulative volume expansion and contraction partially compensates for the extracted volume and the difference between the two is reflected as the subsided area in the form of the area within a curve defined by a probability function. The input parameters for the model are mine geometry (i.e. length and width of the panel), depth of cover, and geologic and geotechnical properties of overburden strata (i.e. percentage of hardrock, sandstone and limestone, and soft rock, shale within the overburden strata and Rock Quality Designation). The model calculates angle of draw for the site, expansion factor for each zone utilizing empirical relationships, maximum possible subsidence and plots the subsidence profile curve. The model is developed for a longwall excavation with unique characteristics of prediction of angle of draw and maximum possible subsidence for a given geologic and mining condition at any cross-section within the influence zone of subsidence.

Jan 1, 1986

By E. D. Gardner

The Synthetic Liquid Fuels Act (58 Stat., 190; 30 U.S.C. Sup., Secs. 321- 325) was approved by Congress April 5, 1944; it directed the Bureau of Mines to build demonstration plants to produce synthetic liquid fuels from coal, oil shale, and agricultural products. The most important oil-shale de- posits in the United States are in the Green River formation of Colorado, Utah, and Wyoming. The oil shale of western Colorado generally is more amenable to exploitation, more persistent, and apparently richer than elsewhere in the Rocky Mountain Region. It occurs at the top of a high plateau surrounded by bold, nearly vertical escarpments 500 to 600 ft in height. The top 400 to 500 ft of these escarpments comprises an oil-shale measure that averages 15 gal of shale oil per ton; the bottom 70 to 100 ft of the measure, called the Mahogany Ledge, averages over 30 gal per ton. The full measure in a 1000-square-mile area is estimated to contain 300 billion barrels of shale oil;' the Mahogany Ledge is estimated to contain 100 billion barrels of oil. These estimates are based on numerous surface samples and on core-drill holes drilled by the Government and by private enterprise. The oil-shale beds are undisturbed and lie nearly horizontal. The name

Jan 1, 1949

By L. Sandbak

The Turquoise Ridge Joint Venture (TRJV) is located in northern central Nevada, and is situated within the Basin and Range province, near the northeast end of the Osgood Mountains (see Figure 1). The TRJV mine consists of typical Carlin type- gold mineralization characterized by low strength rock of altered limestones, siltstones, and mudstones. The weak nature of the ground facilitates the underhand cut and fill mining methods. TRJV has been working to optimize ground support and mechanize top cut drift sizes and eliminate operating hazards associated with jackleg drilling. Safety Factor analysis based on bolt strengths has allowed us to pursue larger sized top cut drifts and to evaluate bolt length sizes and spacing. Switching from jackleg sized drifts of 10?W x 10?H to a mechanized 12?H x12?W top cut drift design has the potential to decrease overbreak, provide more uniform drift design sizes and bolt patterns, and increase ore production by at least 38%.

Feb 23, 2014

By John Newby, Edward Kennedy, Ulf Gwildis

Alluvial deposits of major rivers often provide relatively uniform tunneling conditions. However, these conditions pose specific challenges due to the tunneling behavior of the granular soils as flowing ground, if unsupported. This paper describes the design considerations and construction experiences gained during the Tunnel Boring Machine (TBM) drives for the Annacis Island WWTP New Outfall System in the Vancouver, B.C. metropolitan area. Meeting the design criteria for connecting two (2) deep on-land shafts with an in-river riser manifold required advancing a 5-meter-diameter slurry TBM through the Fraser Rivers sands and at a tunnel invert elevation with a baseline hydrostatic head of 3.4 bar.

Dec 1, 2022

By Werner Burger, Marcus Lübbers

TBM development in recent decades has been dominated by increased face pressures, larger diameters and multi-mode functionality paving the way to realize projects deemed impossible before. In addition, the trend towards digitalization does not stop at the tunnel portal. A shortage of skilled personnel and the ever-present wish to increase workplace safety, quality and system performance automation, operatorassist or even autonomous systems have become key development targets. The paper will present the current state of the art in light of these special conditions.

Jun 13, 2023

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

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

Jan 1, 2016

By R. Sakthivel

Blue dust is a high grade soft haematite material containing 96.14% Fe2O3 transformed into magnetite (Fe3O4), when it is subjected to planetary ball milling in the presence of iron powder as reducing reagent. X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM) and Laser particle size analyser have been employed to characterize various samples collected at various milling times to know the phase evolution, particle size distribution and morphology of particles. X-ray diffraction studies reveal the formation of magnetite phase at the optimum milling time of 40 hours. Vibrating sample magnetometry (VSM) study demonstrates, that sample obtained at 40 hours of milling time exhibits saturation magnetisation of 14.757 emu/g whereas the starting material used in this study shows only 1.0425 emu/g. Keywords: Blue dust, reaction milling, magnetite, saturation magnetization

Sep 1, 2012

By G. Ferrara

The paper describes the new design criteria and control strategies for multi-density dense medium separation (DMS) circuits. The role of the multi-density separation is discussed, and it is emphasized that for many processing problems -related to minerals and coals -it may be very important to perform two or more cuts at different densities in order to obtain a remarkable improvement in quality of products, process efficiency and economy. The two-density separation by dense medium cyclones was generally performed using two dense medium plants in sequence. In contrast to the former technology, the multi-density separation can now be performed by using a single medium circuit composed of different interconnected medium sumps. The sumps, one for each density, are fed with different medium streams selected according to their density, size composition and content in non-magnetic contaminant in such a way that the rheological properties of the media are optimized. This new technology is based on dynamic systems to density the medium, on the size-density segregation of the medium in the cyclones and separating devices and on accurate control systems for the density, viscosity and stability of the dense media of the different sumps. The present paper reports on the theoretical basis for the new, advanced medium circuits and on the systems for the control of the densities and of the rheological properties of the dense media. A typical circuit for a two-density separation is also described, and some industrial applications reported and discussed.

Jan 1, 1994