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By Duclerc Fernandes Parra, Washington Luiz Oliani, Christiano Gianesi Bastos Andrade, Ademar Benevolo Lugão, Danilo Marin Fermino, Francisco R. Valenzuela Diaz

This work concerns the study of the effect of discarded bond paper on the mechanical behavior of polypropylene/organophilic clay nanocomposites. A brown polycationic bentonite from the state of Paraíba, Brazil, was treated with sodium carbonate to transform it into a bentonite that swells in water and then treated with hexadecyltrimethylammonium ammonium chloride to transform it into a bentonite that swells in organic liquids. Polypropylene with 3 % polypropylene graft compatibilizer (PP-g-AM) was mixed with 1 % and 2 % by weight of discarded bond paper and with 1% and 2% by weight of organophilic clay using a twin-screw extruder. The specimens were prepared by the injection process. The clay as received and after organophilization was characterized by XRD, SEM, and capacity of swelling in water and in organic solvents. The nanocomposite specimens were characterized by XRD and thermal analysis. The mechanical behavior of the injected specimens was evaluated by strength, flexural and impact tests. The nanocomposites showed improved mechanical properties compared with the polymer without filler.

Jan 1, 2015

By Joseph Licavoli, Paul Sanders, Yang Yang

"Al-Sc-Zr alloys form thermally stable L12 precipitates which provide high temperature strength. Although the overall fraction of L12 Al3Sc and Al3Zr may be increased by increasing scandium (Sc) and zirconium (Zr) content, such additions may increase primary phase fractions and do not produce desirable secondary phase morphologies. Rapid solidification techniques, such as melt spinning, increase solute atom concentration within the matrix. When the supersaturated matrix is aged, higher precipitate volume fractions at low Sc and Zr levels can be achieved improving high temperature strength. Melt spinning was used to rapidly solidify (107 k/s) a thin ribbon of Al-0.5Sc-0.4Zr at. %. The ribbon was compacted and extruded into 99.8% dense rods, and then aged using multi-step isochronal heat treatment up to 600°C. Precipitation strengthening was evaluated by ambient hardness measurement. The ambient hardness of melt-spun ribbon after precipitation hardening increased by 450 MPa (~67% increment) during isochronal heat treatment.INTRODUCTION Small Sc and Zr additions to aluminum improve strength and creep resistance above 300°C due to tri-aluminide precipitation of Al3(Sc,Zr) in L12 structures similar to ??, Ni3(Al,Ti) in nickel superalloy, but the Al3(Sc,Zr) particles have a Sc-rich core surrounded by Zr-rich shell (Figure 1). The Al3Zr shell limits atomic transport between the Al3Sc core and the matrix and reduces coherency strain. These factors reduce precipitate coarsening rate at elevated temperature (Bergner & Van Chi, 1977; Fujikawa, 1997; Knipling et al., 2011; Clouet et al., 2006).Figure 1. Simplified schematic model of precipitate Al(Sc,Zr) in Al-Sc-Zr alloy. Shell is rich of Al(Zr) intermetallic phase, particle core is rich of Al(Sc) intermetallic phase (after Voorhees, 2006). Numerous Al3(Sc,Zr) particles increase alloy strength and creep resistance as the precipitates impede dislocation glide and to a lesser extent climb. Previous work on ternary Al-Sc-Zr alloys show large strength increases versus binary Al-Sc, and Al-Zr alloys in Table 1."

Jan 1, 2018

By Frank G. Horino, V. E. Hooker

INTRODUCTION The determination and use of mechanical properties of rock in engineering and rock mechanics are rapidly developing. Many of these properties are determined on intact rock specimens; thus, their application and repre¬sentation of rock mass properties may be limited. How¬ever, relative information often provides useful guidance in the solution to mine design and stability problems. Summarized in this chapter are some of the stan¬dardized techniques and procedures currently used to obtain these mechanical properties. Typical applications of the use of these properties are also presented. Stan¬dardized techniques include those advanced by the American Society of Testing and Materials (ASTM), International Society of Rock Mechanics (ISRM), US Bureau of Mines (USBM), Canadian Dept. of Mines and Technical Surveys, South African Institute of Min¬ing and Metallurgy, and other individual investigators. Information on the mechanical properties of rock and the behavior of the rock under a given system of stresses represents a necessary part of the information for rational engineering design for any given mining op¬eration. The mining method, the type and extent of sup¬port, the extraction ratio, the overall dimensions of the mine, and the orientation of the rooms and pillars are all decisions that are influenced by the mechanical prop¬erties of the ore, roof, and floor material under various stress systems and the magnitude and direction of the in situ stresses (Hooker, Bickel, and Aggson, 1972). Initial mechanical property information regarding a structure or mine property is generally obtained by two basic techniques: (1) static and dynamic property tests are conducted on intact and fractured rock specimens of exploratory drill core, and (2) dynamic properties are obtained by borehole logging techniques. When mining access becomes available, and as the mining horizon is expanded, additional information can be ob¬tained to verify preliminary mine design values. This chapter presents some of the standardized tech¬niques and equipment currently used in obtaining me¬chanical property data in the laboratory. The properties considered are: (1) uniaxial compressive strength of intact rock core specimens, (2) uniaxial compressive strength of rock cores containing planes of weakness, (3) triaxial compressive strength of intact rock core specimens, (4) triaxial compressive strength of cores with a plane of weakness, (5) Young's modulus, (6) Poisson's ratio, (7) density or apparent specific gravity, (8) modulus of rupture, (9) indirect tensile strength, and (10) creep characteristics. Where possible, an at¬tempt will be made to evaluate each property measure¬ment in relation to the problems of rock mechanics and application of results. TEST SPECIMENS The selection and care of drill core for laboratory testing require some consideration. It is recognized that laboratory-determined properties are not necessarily rep¬resentative of an in situ rock mass property. However, relative information between beds or zones of interest is still valuable information in selecting mining horizons and preliminary design criteria. To provide statistical data the number of drill core samples selected to repre¬sent each of the areas of interest should be from a mini¬mum of three to a maximum of ten test specimens. A judgment must also be made on site as to whether the recovered drill core should be wrapped and sealed in plastic to preserve moisture. On the one hand investiga¬tions of air-dried and saturated specimens have shown that moisture significantly affects the elastic properties and strengths of many rock materials (Obert, Windes, and Duvall, 1946; Colback and Wiid, 1965); on the other hand it is apparent that most core drilling is done with water which may saturate the specimen to a greater extent than in the in-situ condition. Whether or not the decision is made to retain the moisture, the core should be delivered to the laboratory as soon as possible after recovery for subsequent specimen preparation and testing. Specifications Shape: The shape of the specimens influences lab¬oratory testing in two ways: (1) time and cost of sam¬ple preparation and (2) strength of the material. Cy¬lindrical specimens of drill core are by far the least time-consuming to prepare for static or dynamic labora¬tory testing. In addition, the cylindrical shape lends it¬self to a more uniform stress distribution throughout the sample than other shapes, such as rectangles and hexa¬gons. The compressive strengths of various shapes have been studied (Grosvenor, 1963, and Price, 1960), and results indicate that the cylindrical specimens usually provide the highest strength for a given height-diameter ratio. However, reduction in strength from a cylindrical shape to a rectangular in situ pillar is not regarded as significant in relation to other considerations such as planes of weakness in a pillar or safety factors in the design process. Length-Diameter Ratio: The length-to-diameter ra¬tio, LID, has a significant effect on the compressive strength. Various recommendations have been made to use standard LID ratios ranging from 2 to 2.5 to 3 (ASTM, 1975c; ISRM, 1972). However, past work by others such as Obert, Windes, and Duvall (1946) has shown that excellent results can be obtained using LID ratios from 2 > (LID) > >/s. In selecting an LID ratio for testing, one should keep in mind the amount of material available for testing. In many instances, this may be limited. Thus, a shorter specimen such as 1: 1 LID may be necessary to provide enough test data for statistical analysis of results. Sec¬ond, it may be desirable to obtain elastic constants dur¬ing the test. This generally requires instrumentation such as linear variable differential transformers (LVDTs) or strain gages near the center of the specimen. In this case, an LID of 2.5 or 3 is desirable so that the instru

Jan 1, 1982

Researchers from the National Institute for Occupational Safety and Health's Spokane Research Laboratory installed Split-Set rock bolts instrumented with strain gauges to document the mechanical load response of the bolts in weak ground. Short-term monitoring of the bolts immediately after installation showed that some of the gauges went into tension. It was felt that the force exerted on the bolts to drive them into the hole should have caused the gauges to show compression. The tension probably resulted from the holes having crooked sections. Long-term monitoring over the course of a year also showed that the bolts were bending at some locations and that loads as high as 98 kN (22,000 Ib) were recorded along sections of the bolts. Load cells were placed on the head end of the bolts to determine head loads. Head loads up to 14.7 kN (3,300 Ib) were generated during bolt installation. In addition, closure readings were taken across the drift to determine the convergence rate responsible for bolt loading. A Rock Mass Rating (RMR) was calculated at the site to compare with bolt response. The bolts were installed as part of the rebolting process in an area being repaired because the near-vertical beds in the walls were buckling and causing the wall to fail. The instrumented Split-Set rock bolts will provide data that will lead to greater understanding of the behavior of the rocklbolt support mechanism. It may also be possible to explain the overall performance of the bolts in situ in terms of their design effectiveness. This work showed that load at the head of a Split-Set rock bolt was less than load along the interior of the bolt.

Jan 1, 2005

By McHenry Mosier

Mechanical loading, adopted long ago in open-pit, coal, and non-metal mines, was not used extensively in underground metal mines until the World War. In less than a decade it became standard practice in underground work in many mining districts. In 1924 the Missouri School of Mines and Metallurgy, in cooperation with the Federal Bureau of Mines, published a bulletin entitled "Mechanical Underground Loading in Metal Mines," which was prepared by Charles E. van Barneveld, mining engineer, Bureau of Mines.

Jan 1, 1940

By I. M. Richardson, M. Janssen, W. Geerstma, I. J. Bennett, V. A. Popovich

Avoiding wafer breakage is a big challenge in the photovoltaic silicon industry, limiting production yield and further price reduction. Special fracture strength tests suitable for thin silicon solar wafers and solar cells, to be used in combination with Weibull statistics, finiteelement (FE) modelling and digital image correlation have been developed in order to study the mechanical stability of solar wafers. The results show that removal of the saw damage significantly increases the strength of crystalline silicon wafers. Furthermore, it was found that silicon crystallinity and the location where the wafer is extracted from the cast Si ingot have a significant effect on the strength, namely samples taken from the bottom of the ingot are 30% stronger than those taken from the top. The study also showed that there is a decrease in fracture strength when an anti-reflective SiNx coating is applied, which is caused by high thermal stresses.

Jan 1, 2015

By Patrick Oriez, Chris Norris, Alain Mercusot

"Temporary mechanical ventilation is one of the fundamental requirements in guaranteeing a healthy atmosphere in underground construction works in order to protect the health of persons working on the site. It is therefore essential to conceive a system which meets the requirements of the whole of the worksite and for all phases of work which takes into account all aspects pertaining to its design, dimensioning, justification, installation, maintenance and validation. In doing so, the ventilation design and the selected apparatus to be installed shall meet with the degree of health protection and the quality of air of the worksite as defined by the legislation in force in France, through limiting the concentration of the different pollutants associated with the site activities. Consequently, when presenting a mechanical ventilation project, all of the participating parties and especially the contractor make a commitment to guarantee sufficient volumes (or airflow rates) of fresh (non-polluted and oxygenated) air and extracted (polluted) air in order to meet these limitations and maintain them in all conceivable site configurations. This article sets out the most important aspects of the implementation of a ventilation project from the initial design stage through to its application, discussing French legislation, ventilation principles, calculations and techniques with regards to underground construction sites. BASICS OF VENTILATION Mechanical ventilation studies are concerned with all of the site workstations and work phases which are sources of pollution and apply to all zones of the underground worksite with the goal of maintaining the concentration or composition of this pollution below the permitted levels and comply with the following three basic principles which are complementary to one another without being in contradiction. •,The first principle consists in eliminating or limiting as much as possible the emission of any polluting, irritant, or dangerous substances, by specifying appropriate construction techniques and equipment (use of electric motors, combustion engine equipment: filters, tanks, catalyzers, use of less polluting explosives, damping down dust with water or wetting products, damping down and diluting certain gases using water mists). •,The second principle is designed to capture residual polluting substances emitted close to the source in order to prevent them from spreading into the worksite atmosphere (extraction ventilation with ducting up to the source – upstream of the extractor fan – and use of downstream filters before expelling the polluted air to the exterior). •,The third principle involves accompanying the capture of the pollutants with additional blowing ventilation specific treatment of substances dissipated by and distant from the source of pollution (acceleration of the drift air flow in order to confine dust and better capture it, supply ventilation with ducting in order to dilute the gases emitted and discharge them to the exterior)."

Jan 1, 2016

By Lauro Lacerda

Shotcrete is a highly adaptable and widely used underground construction material at infrastructure and mining projects around the world. In fact, many projects could not have been completed without its utilization. As underground projects became larger the use of mechanized wet-mix spraying gradually replaced manual dry-mix shotcrete applications. This paper details some of the reasons for that and provides information on the equipment and operational factors including safety and productivity required to successfully complete underground shotcrete projects.

Jun 13, 2021

By Brian G. White, Theodore J. Williams, Jeffrey K. Whyatt

Detailed mapping and examination of the site of a large rock burst at the Lucky Friday Mine, Mullan, ID, demonstrated conclusively that damage was caused by a splitting and buckling failure mechanism initiated by separation of rock into layers along steeply dipping metamorphic shear foliation subparallel to the affected crosscut. The thin tablular layers then buckled into the crosscut from both sides. Rigorous control of the burst by these layers suggests practical measures for avoiding bursts in crosscuts in the future by repositioning and reorienting openings so that splitting and buckling are reduced or precluded.

By Ken W. Mills

The ground movements associated with underground coal mining and, in particular, longwall mining, are recognised to include horizontal subsidence movements, but the mechanics of the processes that cause these horizontal movements are not well understood. Over the last two decades, three-dimensional subsidence monitoring has become routine in Australia and has provided a wealth of measurements of horizontal movements caused by mining subsidence. These measurements and other sub-surface observations allow the processes that cause mining-induced horizontal movements to be inferred and, subsequently, verified. In this paper, the mechanics of the processes that cause horizontal movements, particularly those in sloping topography, are described and discussed on the basis of field observations. There are several processes recognised to generate horizontal subsidence movements. In flat terrain, systematic horizontal movements cause the surface to move initially toward the newly created goaf and, subsequently, in the direction of mining. Tectonic energy stored as horizontal stress is released by mining, and, when the horizontal stresses are high, the magnitude of this horizontal stress relief movement is large enough to be perceptible for some kilometres from the panel. In sloping terrain, there is an additional component of horizontal movement that occurs in a down slope direction. This movement, sometimes referred to as valley closure movement, has a magnitude that is typically much greater than systematic or stress relief movements.

Jan 1, 2014

By W. G. Pariseau

Joints may be taken into account when using numerical modeling as an aid to mine design by embedding joints in the model. When using the popular finite element method, say UT3PC, a pre-analysis step is necessary, Step 0. This step is for the computation of equivalent properties of a representative elementary volume of jointed rock (REV) in the model. This Step 0 is taken before Steps 1, 2 and 3 for specification of a rock properties file, generation of the mesh, and model analysis are taken. A brief explanation of equivalent properties and several examples aid in explaining the details of Step 0. Focus is on procedures, input files, and output to show ease of computation. Theoretical details are relegated to references (e.g. Pariseau 2022). Comparisons of safety factor distributions about example mine excavations with direct scaling from mine observations then offer some insights concerning equivalent properties, especially strengths.

Feb 1, 2023

By Yvette Heritage

"The risk of fatalities from rib failure is still prevalent in the coal mining industry. This risk has prompted further research to be conducted on rib deformation in order to understand the mechanisms of rib failure, with the long-term objective being to improve rib support design. This paper presents the results of ACARP research project C25057, which investigated the mechanics and drivers of rib failure. The results of rib deformation monitoring at three different mines in Australia provides rib deformation characteristics for overburden depths ranging from 160 m to 530 m. Monitoring includes deformation during development drivage conditions and during the longwall retreat abutment stress environment. The rib deformation monitoring covered three different seams: the Goonyella Middle Seam, Ulan Seam, and Bulli Seam in the Bowen Basin, Western Coalfield, and Southern Coalfield, respectively. The observed mechanisms driving the rib deformation ranged from bedding shear failure along weak claystone bands to vertical shear fractures to kinematic failures driven by shear failure dilation. The variation in mechanisms of rib failure, together with the seemingly consistent method of rib support design, prompts the question: What exactly is the role of rib support?INTRODUCTIONThe current risk of rib fatalities in the coal mining industry has prompted further research into understanding the mechanisms of rib failure. Three Australian mines assisted further research by providing sites for rib deformation studies as part of the Australian Coal Association Research Program (ACARP) project C25057. The mines included in this study were Moranbah North Mine, Ulan West Mine, and Appin Mine. This paper provides key results of the rib deformation monitoring relevant to assessing the mechanisms of rib deformation.The approach of monitoring rib deformation and rib support loads was used to measure and characterise the dynamic rib deformation present in both development and longwall retreat stress environments. The characterisation of rib deformation, together with rock failure modelling, was used to determine the mechanisms for failure within the rib and to assess the interaction of rib support with the failure process. The mechanisms of rock failure are considered an important factor in understanding the drivers for the failure. Consideration of the site-specific failure mechanisms can provide for a more tailored support design."

Jan 1, 2018

By Douglas R. Piteau, Dennis C. Martin

Instability of rock slopes may occur by failure along pre- existing structural discontinuities, by failure through intact material or by failure along a surface formed partly along discontinuities and partly through intact material. Although certain fundamental failure modes are recognized, the mechanisms of slope failure are varied and complex. Such mechanisms are governed by the engineering geology conditions of the rock mass, which are almost always unique to a particular site. An understanding of failure mechanisms requires a knowledge of the physical, mechanical and strength properties of the intact material and discontinuities which make up the rock mass, as well as the structural geology and hydrogeology. These engineering geology parameters also must be evaluated with respect to the slope geometry to determine failures which are kinematically possible. Only after obtaining a reasonable appreciation of the possible failure modes can a rational mechanical stability analysis be carried out. Both two-dimensional and three-dimensional failure mechanisms should be considered in assessing the design of rock slopes. Simple analyses methods are used initially to identify those possible failures which could control slope stability. More complex and detailed analyses usually are required for a few critical failure modes which could control stability, or where a more complex type of failure mechanism is envisaged. Complex failure mechanisms are usually identified when assessing previous slope failures. More detailed information concerning slope geometry and engineering geology parameters must be acquired where analyses must be more rigorous.

Jan 1, 1983

By A Buckingham, R M. Hancock

The underground Sunrise Dam gold mine commenced in October 2003 to extract ore from a series of orebodies with various dips, widths, and ore grades over a strike length of 1.5 km. To successfully operate flat stopes it was identified that a means to extract ore left behind after blasting in stopes with dips ranging from 15 to 40 degrees was needed. Various options were available, which included a bulk water cannon, hand held high-pressure water jet, remote controlled small dozer, several mini excavators and finally a specialised remote controlled excavator from the demolition industry. Trials were commenced for the bulk water cannon option in 2006 that proved that the concept worked, however, the system was too cumbersome to set up for use in cycle with production. Hand washing down using mine (low pressure) water with a two-inch bullhose proved of limited value. The small, one metre high remote controlled dozer as used in South Africa was reviewed, but the steepness of most of the stopes precluded this machine. The hand held high-pressure water jet option is still being investigated; with safety factors still being addressed. Several mini excavators were trialled to clean out the flat stopes with generally poor results, the machines being either too large to fit in the drives and pull ore down or too small with too short reach to effectively and efficiently pull ore out of the stope. In early 2007 a Brokk 330 remote controlled excavator was trialled on site with the low profile of the machine and unique arm configuration proving an effective tool for pulling ore from the footwall of short, flat stopes. A Brokk 330 remote controlled excavator was purchased in late 2007 and is currently in operation.

Jan 1, 2008

By I. Ngo, L. Q. Ma, J. S. Guo

Deformation of gob-side entries has always been a critical concern for ensuring stability in longwall coal mines. This paper addresses the significant deformation and support challenges that arise in thick and hard roof longwall faces (THRLF) due to dynamic pressure. The study aims to elucidate the characteristics and mechanisms of deformation during the retreat of the longwall face. The research findings indicated that the primary cause of deformation was the combination of advanced abutment stress resulting from longwall face mining and the movement of the lateral roof over the chain pillar. To mitigate this issue, we propose a deformation control method known as cutting off the lateral roof (COLR) over the chain pillar. Simulation results demonstrate a significant reduction in roof stress and deformation of the gob-side entry after implementing the lateral roof-cutting technique. These findings provide valuable guidance for effectively managing deformation in gob-side entries, particularly when dealing with thick and hard roof strata.

Aug 3, 2023

By A. Kurkov

Flotation process is based on the formation of primary collector-based supramolecular associates at the mineral surface and within the pulp. Supra molecular chemistry allows studying within a common framework, all kinds of molecular associates, from dimers to large assemblies, resulting from spontaneous association of a large number of interacting components of the flotation system, where the collective action of non covalent bonds can have an important role. Self-organization of supra molecular assemblies in the flotation process can be controlled by modifying the chemical structure of the collector, the nature and arrangement of functional group in it, by introducing secondary agents (SA) into the process, to adjust the interaction between the collector and the surface and to control the hydrophobicity of the adsorption bed. This offers broad opportunities to build supramolecular assemblies to improve the efficiency of flotation. Besides, the more complex is the system, the weaker are the interactions, that determine its behavior. This powerful factor still is not employed deliberately to control the flotation process. Organophosphorus compounds (OPC) - dialkyl phosphoric acids whose radicals contain ethoxylated groups ? are considered as nanocompounds, that can be used in building supramolecular assemblies. The presence in an OPC molecule of functional groups (P=O, P (O) O-, P (O) OH), ethoxylated groups, and aromatic rings is the basis for the formation of stable supramolecular associates. Gross formula: C54H94KO16P. Molecular weight is 1069.39. Phosphoryl anion has a regular tetrahedral structure with the angle of 109.5°. Lengths of -P-O- bonds in a PN molecule are 1.7345Å; length of the hydrocarbonic radical C42-C72 = 33.942Å. In an alkaline environment, PN is in the form of the anion, in an acidic environment ? in the form of the polycation due to protonation of the oxygen in the EO group. Chem Office software suite was used to generate three-dimensional images of an OPC molecule in acidic and alkaline environments, to reveal the OPC geometry (bond lengths, valence angles, aliphatic radical length), to identify the collector's binding sites with the mineral surface, to find the most stable and energy-efficient molecular conformations of an OPC molecule and its complexes with minerals under various conditions. Mechanisms of interaction between OPCs and the mineral surfaces are different. In ores whose minerals are dominated by ionic bonds (fluorite), the interaction mainly involves the anionic form of the collector; in ores, whose minerals are dominated by covalent bonds - the oxygen of the phosphoryl group (donor-acceptor interaction) and the oxygen of the ethoxylated groups. This difference is responsible for the formation of spatial associates with different surface layer structures. Introduction of supramolecular chemistry concepts into the analysis of flotation phenomena and mechanisms can become an effective tool for better understanding the flotation process and offers new means of consistently improving its effectiveness.

Sep 1, 2012

By Sadatoshi Ohmori, Karen Shinoda, Nobuharu Isago

Method of tunnel excavation is generally classified such as full-face excavation, bench-cut excavation, diaphragm with center pillar excavation, center drift advancing excavation and so on. These excavation methods should be selected properly in terms of ground condition, the area of tunnel section, the arrangement of construction. Center drift advancing excavation method in mountain tunnel construction, is often applied under quite weak ground condition, prior to the main tunnel widening excavation. Recently, the advancing drift is for the excavation of extreme larger section in main tunnel to confirm the stability of face. In addition, we make advancing deformation occur in drift when the construction was done in poor ground like squeezing and swelling ground, and the force occurred in main tunnel was expected to reduce by the effect of ‘dodging’ for support structure. Mechanical relation between drift and main tunnel has been mainly grasped on past experiences in Japan. However, the characteristic of tunnel enlargement was partially discussed by using the three dimensional analysis and the result was grasped by past experiences on the basis of each tunnel construction. It is considered that the natural ground stress is normally released as the advance displacement, but it was released after the main tunnel widening, causing a displacement and deformation increase. Up to now, the construction practice has shown the reduced displacement during the main tunnel widening excavation by the drift, and the numerical analysis agreed with above observation. However, there is no report found that the displacement and deformation at the time of widening excavation of the main tunnel become larger in case of a drift application. In Kyusyu area, western part of Japan, the northern part of Yoshinomoto tunnel was applied an advancing bench-cutting method for a center drift for the purpose of obtaining the geological information for support selection of the main tunnel in widening excavation. The shape of center drift was a perfect circle with a diameter of 4.0 m or 6.0 m and the same temporary support regardless of the geological situation. As a result, the displacement and deformation of the main tunnel after widening excavation were larger than the section where the center drift was not applied. Furthermore, the displacement and deformation of the main tunnel after its widening excavation was considered larger in the section where the cross-section of the center drift with 4.0 m diameter was applied than one with 6.0 m. Therefore, the center drift with a high rigidity support structure had the effect of suppressing the advancing deformation prior to the main tunnel widening excavation.

Jun 13, 2021

By J. A. Finch, M. Mimezami, M. S. Hashemi A.

The adsorption of magnesium and calcium ions on sphalerite and pyrite is discussed. These ions are common in process water and often considered be detrimental in sulphide flotation. The study attempts to characterize the adsorption mechanism, which has been less studied than the oxide system. Generally for oxides metal ion uptake occurs when cations are hydrolyzed. Our findings reveal that magnesium and calcium adsorb on sulphides at pH below hydrolysis, but adsorption is not chemical. At higher pH, charge reversal occurs that does correspond to presence of hydrolysis products. Advances

Jan 1, 2009

By Onal G, Celik MS, Dogan MZ

Chromite tailings assaying 21.2 per cent Cr2O3 was upgraded to 48.7 per cent Cr2O3 at a recovery of 72.0 per cent using column flotation with a mixture of anionic collectors at pH 11. Electrokinetic methods were used to elucidate the mechanism of collector adsorption and correlate the findings with the optimum flotation conditions. Multivalent constituent ions such as Cr3+, A13+, Fe2+ and Mg2+ were found to adsorb on chromite surface and shift the zpc of chromite in the direction of oxide form of the mineral. The anionic collectors also imparted a negative charge to chromite in the entire pH region. The higher zeta potentials obtained upon adding the anionic collectors is ascribed to the adsorption of anionic surfactant onto the positively charged chromite surface. The positive sites are generated through formation of significant amount of hydroxy complexes of magnesium at pH 11. Complementary infrared data reveal the absence of a shift in the spectra indicating the possibility of physical adsorption in the system.

Jan 1, 1993

By L. Klinger, T. Werber, LA Levin, A Katsman

"The process of catastrophic carburization known as ""metal dusting"", whereby a solid metallic material is converted into fine particles in a carburizing atmosphere, was analyzed. It was shown that this conversion is the result of plastic deformation and subsequent fracture accompanying diffusional phase formation in the near-surface layer. The process is controlled by internal stresses arising during phase transformation. Competition between stress generation and relaxation may result in the attaining the ultimate strength in the near-surface layer and its fracture. Such a mechanism of metal disintegration may occur in a certain temperature interval depending on the kinetic and geometrical parameters of the system - the diffusivities of the alloy's components, the ratio between specific volumes of the new and the old phases, and the ultimate plastic strain. The temperature interval for disintegration of carbon steel, the rate of disintegration, and the period of the disintegration cycle, were evaluated and compared with experimental data. IntroductionCatastrophic carburization, known as ""metal dusting"", consists in conversion of a solid metallic material into fine particles. The process occurs in a carburizing atmosphere at elevated temperatures. The corrosion product, usually named ""coke"", consists of metallic particles dispersed in a loose carbon matrix. Under industrial conditions metal dusting takes place, for example, in a gas mixture of CO and H2 or in hydrocarbon environments. Steels, nickel- and cobalt alloys are susceptible to this kind of wastage in the temperature range 400-800°.A mechanism of metal dusting in steels was proposed by Hochman [1] and later developed by Grabke and coworkers [2-5]. According to the proposed model, the process consists of the following reaction steps:"

Jan 1, 1996