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By Lifeng Zhang, Zineb Benouahmane, Yaqiong Li

The wettability behavior of graphite with silicon is a key factor for its application as a crucible in silicon making industry. A previous study was carried out to determine the correlation between the physico-chemical behaviors of different types of graphite and the final contact angle for the graphite/silicon system. In this study, experimental vacuum annealing treatment by varying the exposure time at high temperature of 1000 °C processed by X-ray photoelectron spectroscopy and SEM analyses enabled to found a correlation between the oxygen content in the graphite and the final contact angle for the graphite/silicon system. Finally, the experimental results with and without vacuum annealing treatment have shown that a deep infiltration of silicon inside the graphite occurs in case of high level of oxygen content inside the graphite’s pores.

Mar 1, 2017

By Payne AR

The high cost of gateroad repairs and maintenance in U.K. longwall coalmining is a clear indication of the failure of permanent support systems to fulfill their prime function, i.e. control of strata movement. The main component of gateroad support is the pack, the design and materials of which have experienced an important development process during the last 10-15 years. More recently, research investigators have attempted to give a design basis to pack quality and dimension, and reference is made to two theoretical approaches. In the course of a current research programme based upon in situ monitoring, interim design recommendations have been proposed as a means of effecting improvement in support efficiency. Identification of characteristic deformation behaviour forms the basis of the recommendations made and the subsequent improvement in gateroad performance reported.

Jan 1, 1986

By D. I. Verrelli

Within the flotation community a belief has developed that some particle shapes are more ?floatable? than others. This is usually attributed to an influence of particle shape or roughness on the induction period required to achieve attachment between the particles and the air bubbles in the pulp. Up to now, such measurements have not been able to readily isolate the effect on individual flotation subprocesses. In contrast, our experimental apparatus, the CSIRO Milli-Timer, enables us to directly observe the process of particle?bubble interaction and attachment by means of a high-speed video recording, thus providing a direct measure of the induction period for attachment. To assess the influence of particle shape on induction time we used two varieties of methylated borosilicate glass particles ? spheres and angular ?frit? ? in a range of tightly-sized fractions. In doing this, we take care to account for the influence of other factors that could affect the induction time, such as the polar angle of sliding commencement, and approach velocity. These parameters are recorded as variables for each interaction, and corrected for using multiple nonlinear regression. Our results illustrate the importance of particle shape on induction period, with angular particles exhibiting induction periods that were an order of magnitude lower than those of spheres. Furthermore, the induction period was seen to decrease with increasing particle velocity, or kinetic energy on approach, but increased as the trajectory approached the limit of just grazing the bubble. Particle shape in mineral processing is a consequence chiefly of the mineral type and the type of grinding employed. The results presented herein indicate that attention should be paid to the shape of particles obtained from the grinding operation, besides particle size. Keywords: attachment, bubbles, flotation, induction period, particles, shape effects, surface roughness

Sep 1, 2012

By David I. Verrelli, Peter T. L. Koh

"Recent experimental measurements of induction time made by direct observation with the ‘Milli-Timer’ indicated that angular particles were able to attach much more rapidly than spherical particles. There was around a tenfold difference in the respective induction periods for particle-bubble attachment. For industrial application, a more holistic comparison is needed, with the induction period for attachment being just one input. Over the years, CSIRO has developed a CFD-flotation model that incorporates both rigorous hydrodynamics, to simulate real industrial cell geometries, and a detailed model of the embedded flotation process, in which the induction period is an important parameter. We conducted transient modelling of batch flotation. First, spherical particles were modelled, as a ‘baseline’, for different particle sizes and levels of hydrophobicity. In the second set of results, the induction period was decreased by a factor of up to ten, simulating flotation of angular particles. Flotation recovery was found to depend upon induction period in a complex manner. For highly hydrophobic or fine particles, the induction period for spheres was already so low that recovery was limited by other factors (e.g. bubble-particle collision frequency). Further decreases in induction period, as for angular particles, did not have a significant effect on recovery in these cases. By contrast, when weakly hydrophobic or coarse particles were modelled, the recovery was predicted to be greatly enhanced for angular particles, in comparison to spheres. For these particles the induction period was limiting recovery, so that the flotation rate constant could be improved directly by reducing the induction period. This is consistent with batch flotation experiments using Ballotini reported earlier. Therefore, when dealing with weakly hydrophobic particles or relatively large particles that are to be floated, an enhancement can be expected for more angular particle shapes. In such cases, judicious specification of the grinding circuit may improve the overall efficiency."

Jan 1, 2014

By F. Dehghani

The influence of different grinding methods on the shape characteristics of magnetite particles was investigated. Also, the effect of particle shape on the flotation of the magnetite, both alone and in the presence of quartz particles, was investigated. The shape characteristics of the magnetite particles were measured and calculated from images obtained by scanning electron microscopy via an image analysis system. The flotation tests were performed using a laboratory flotation cell. Results showed that in the -250+212 µm and -106+75 µm size fractions, ball mill products have a higher elongation value than rod mill products, while in the -150+125 µm size fraction, rod mill products have a higher elongation value. Particles with higher elongation values and lower roundness values have a higher flotation kinetic constant. Furthermore, the influence of magnetite particle shape on flotation is greater, and the flotation kinetic constant is higher, in the presence of quartz particles than in the flotation of magnetite alone Keywords shape, elongation value, flotation kinetics, magnetite.

Dec 1, 2013

By L. Kühnel, H. Lieberwirth

Confined bed comminution in High Pressure Grinding Rollers (HPGR) and Vertical Roller Mills (VRM) is gaining substantial attention in many applications. Previously used mainly for milling coal or construction materials, HPGR and VRM have started to complement or even replace tumbling mills in ore beneficiation. Materials like coal or clinker are relatively homogenous, however, in comparison to metal ores and wall rocks. This characteristic poses a new challenge to the confined bed comminution but also an opportunity. Fuerstenau and Abouzeid have investigated the selectivity in comminution of a mixture of particles of different strength in a particle bed. The median particle size and particle size distribution (PSD) of the two constituents used were kept constant. Only the proportion of the two constituents was modified. The competence of a material is, however, also a function of particle size. Smaller particles tend to be more competent than larger ones of the same material. If selective comminution is applied on ores, this size influence has to be understood. The paper presents research results on this topic based on experimental investigations with model materials as well as with natural particles, which were stressed in a piston-die press. It appeared that the comminution result depends substantially on the material characteristics and the composition of the mixture. Conclusions will be drawn for the application in future applications of selective comminution in mineral processing. Keywords: Confined bed comminution, HPGR, VRM, piston die press, particle size

Jan 1, 2020

By K. Biswas

So far, all pillar design methods or approaches consider the coal seam as a uniform structure From some mine visits in northern Appalachian Region. it is found that some coal seams have binder or parting material within the coal scan with varying thicknesses and numbers- And it has also been found that these kinds of hinder materials tire prone to weathering when exposed to ambient mine moisture In this paper an attempt has been made to study the weathering susceptibility of parting materials and coal when exposed to moisture and a two dimensional finite element analysis has been carried out to study the effect of the presence of partings on the structural integrity of the coal pillar in terms of short-term and long-term stability.

Jan 1, 1995

By C. K. Lee

The influence of passageway fires on ventilation flows was investigated in three horizontal fire tunnel s: 1. a laboratory-scale fire tunnel network, 2. a small-scale fire-plume tunnel, and 3. a large- scale simulated mine gallery. Wood was used in the first and third tunnel and gas-burners were used in the second one to generate passageway fires. Experimental measurements included gas mass flow rate, velocity, temperature and pressure in the passageways and exhaust fans. The overall and local effects of the fires were investigated by comparing these measurements obtained before and during the fires. Results show that a passageway fire essentially increases the flow resistances of the passageways of a tunnel flow network by virtue of volatile fuel mass injection and high combustion temperatures. The ventilation air flow rate is consequently throttled to lower values than that before the fire. At severe throttling, reverse flow occurs. Conditions for reverse flow are characterized by two Froude numbers based on gas velocity and density upstream of the fire, and height of the passageway. The Froude numbers and the characteristics of the passageway fire are necessary to analyze mine ventilation/fire interaction and to predict mine ventilation patterns during fires.

Jan 1, 1980

By J. Alatalo

Autogenous grinding is a process of reducing the particle size distribution of an extracted ore by using the ore itself as the grinding media. It is a process that is difficult to control and there is a lack of knowledge of the events occurring inside the mill. To find out more about how the mill behaves under different processing conditions, a full factorial test was performed with iron ore in a pilot-scale pebble mill at the LKAB R&D facility in Malmberget. To complement this work, a strain gauge detector was embedded in one of the mill?s rubber lifters, the Metso Minerals continuous charge measurement (CCM) system, and was used to get more information about the charge dynamics. The data from the experiments has been analyzed. For production purposes, an increase in the number of particles smaller than 45 µm can be regarded as a probable increase in the production rate. The analysis shows that there will be an increase in fines at 65% of critical speed, especially when the mill is 45% full. This setting will also increase the power consumption, but improves the grindability of the ore even more. The deflection of the lifters is smaller for lower critical speeds. A higher degree of filling also gives a smaller toe angle and a higher shoulder angle as expected.

Jan 1, 2011

By J. Alatalo

Autogenous grinding is a process of reducing the particle size distribution of an extracted ore by using the ore itself as the grinding media. It is a process that is difficult to control and there is a lack of knowledge of the events occurring inside the mill. To find out more about how the mill behaves under different processing conditions, a full factorial test was performed with iron ore in a pilot-scale pebble mill at the LKAB R&D facility in Malmberget. To complement this work, a strain gauge detector was embedded in one of the mill?s rubber lifters, the Metso Minerals continuous charge measurement (CCM) system, and was used to get more information about the charge dynamics. The data from the experiments has been analyzed. For production purposes, an increase in the number of particles smaller than 45 µm can be regarded as a probable increase in the production rate. The analysis shows that there will be an increase in fines at 65% of critical speed, especially when the mill is 45% full. This setting will also increase the power consumption, but improves the grindability of the ore even more. The deflection of the lifters is smaller for lower critical speeds. A higher degree of filling also gives a smaller toe angle and a higher shoulder angle as expected.

Nov 1, 2011

By B. K. Mohapatra

Small manganese ore bodies in south Odisha, India occurs both as stratiform and stratabound ore bodies. These two ore bodies show contrasting mineralogical, petrographical and chemical characteristics. Stratiform type of Mn-ores consists of manganese, iron and silicate- phases in approximately same proportion. In contrast, stratabound ore bodies contain a high proportion of manganese oxides, silicates and phosphorus phases. Phosphorus is found within apatite in the stratabound ore bodies while in the stratiform ore it occurs as an adsorbed state with iron phase (goethite). Both ore bodies are low-grade (17-23% Mn) therefore do not have a market value. However, the stratabound ores are enriched in phosphorus (P2O5: >1%) compared to the stratiform ores. Both the ore types were processed through gravity, magnetic and roast reduction followed by magnetic separation techniques. The strata bound ore could be upgraded to 33% Mn from a feed of 23% by combination of dry and wet magnetic separation methods. But the phosphorus content also suits up (P2O5: 1.2%) in the processed product making it unsuitable for further use. The stratiform ores do not respond to either gravity or magnetic separation because of close association of manganese with iron phases. However, this could be beneficiated through roast reduction followed by magnetic separation. An ore with 17% Mn content could be upgraded to 40% Mn with a 42% yield and 78% recovery. The goethite, having phosphorus, converts to magnetite and is retained within the magnetic fraction, thereby reducing the concentration of phosphorus in the non-magnetic fraction, which becomes the product. This report demonstrates the influence of ore petrology in determining the up-gradational potential of manganese ore in the southern Odisha, India. Keywords: manganese ore, physical beneficiation, phosphorus rich ore

Sep 1, 2012

By P. Randall, J. Ickes, S. Chattopadhyay

This study was undertaken as a part of developing treatment alternatives for waste materials, primarily waste rock and roaster tailings, from sites contaminated with mercury (Hg) mining wastes. Leaching profiles of waste rock over a range of different pH and oxidation-reduction (Eh) conditions were performed. Since iron (Fe) is present in large quantities in mining wastes, the effect of Fe on leaching of Hg was also determined. Results show that the Hg concentration increased as the pH of the suspension increased until a pH value of 10.65. Thereafter, the Hg concentration decreased sharply. The Hg concentration, in presence of Fe decreased significantly (1/10thto 1/100th). Kinetics results show a relatively slow rate of leaching in presence of ferric ions. The results obtained from the present study are being used to predict the fate and stability of Hg present in the environment, and will therefore, be useful in dictating the nature and suitability of any remediation treatment.

Jan 1, 2003

By M Muzammil, S. Mukerjee, S. Saran, M. Bharathi

"This paper presents the results of in-situ tests conducted on a set of under-reamed piles in a silty sand deposit. Three piles (i.e. vertical, vertical with one bulb and vertical with two bulbs) of diameter 0.2 m were cast upto a depth of 5 m. The pile cap had four foundation bolts cast into it so that a mechanical oscillatormotor assembly could be mounted centrally on it. The oscillator-motor assembly was used to generate purely sinusoidal dynamic forces, in either horizontal or vertical directions. For both horizontal and vertical vibration cases, it was observed that (i) the natural frequencies decreased with an increase in the excitation force level, (ii) for the same excitation level, the natural frequencies as well as the maximum amplitude of vibration are almost the same irrespective of the pile geometry i.e. number of bulbs in the pile, indicating that the full pile length is not being excited. For the vertical vibration case, the soil-pile stiffness at frequencies, before resonance, were observed to be higher than those at frequencies after resonance. In the horizontal vibration case, the stiffness of the soil-pile system was found to be decreasing with an increase in the excitation force level. The damping ratio was found to be increasing with an increase in the excitation force level.INTRODUCTIONUnder-reamed piles are piles, normally upto a depth of 6 m, with one or more bulbs along the pile stem. These have been used for structures like transmission towers, structures on expansive soils etc. for a very long time, however it is only in the last 30 years that dynamic response of a pile has been studied. Evaluation of dynamic soil-pile interaction is a very complex problem as the conditions and properties of soil are highly variable and unpredictable. Various models and approaches have been suggested by various investigators for evaluating the dynamic soil-pile interaction problem, but most of them are based on the assumptions that the behaviour of soil is linear and the soil surrounding the pile is strongly adhered to it. But in practice, it is not so. The soil surrounding the pile is always somewhat loosened and undergoes some deformation when a sinusoidal load is applied. This causes the soil-pile system to behave nonlinearly.In earlier studies by Novak, (1974), Novak and Aboul-Ella, (1978) etc. a linear elastic behaviour of soil was assumed. This approach was very useful in understanding the mechanism of soil-pile interaction to a large extent. Subsequently various models were suggested like the lumped mass models with nonlinear discrete springs, dashpots and friction elements Matlock et al. (1978), weak cylindrical zone around the pile model Novak and Sheta, (1980), ideal boundary zone model with non-reflective interface, Han and Sabin, (1995) etc. These approximate solutions give an idea about the mechanism of dynamic pile-soil interaction to a large extent. However, in reality both separation and slippage can occur due to the formation of a weak bond at the contact surface between the soil and the pile when a dynamic load is applied. In addition, the soil column adjacent to the pile experiences large deformations under dynamic loads and thus behaves nonlinearly.Some computer aided model studies on the dynamic response of under-reamed piles have been reported, however, very few insitu dynamic tests on under-reamed piles are reported. Dynamic tests on piles were carried out by Novak and Grigg (1976) on small scale single piles and pile groups in the field. Similar field tests on small scale piles were conducted to study the nonlinear behaviour of a single pile and a pile group under strong harmonic excitation by Han and Novak (1988), Han and Vaziri (1992), Burr et al. (1997), Manna and Baidya (2010) etc. The majority of these experimental studies were focussed on the response of the specific pile groups and compared with the results of a single pile. Hence there was a need to study the influence of pile g"

Jan 1, 2015

By Michael DiMatteo, Michael D. Gardner, Eric F. Perry, John K. Felbinger, Robert S. Evans

A hydrologically isolated surface coal mine was reclaimed using acid material handling, alkaline addition and ground-water management techniques. Eight pit floor drains were installed during reclamation to intercept ground-water flow in the mine backfill and minimize water table buildup. All drains began flowing within six months of installation. Water quality and ground-water discharge have been monitored for four years after mine closure. A thin water table aquifer about five to seven feet thick has developed in minespoil about 20 to 40 feet thick. Ground-water flow direction is largely controlled by geologic structure and the drains. Median ground- water discharge is about 0.43 gallons per acre per minute, and varies an order of magnitude between wet and dry seasons. About 19 % of precipitation enters the aquifer as recharge. Seven of the eight drains typically discharge net alkaline water. Alkalinity is produced continuously and concentrations are highest during dry periods. Conversely, sulfate and acidity concentrations increase during wet periods as slugs of accumulated acid products are leached. Overall water quality is controlled principally by minespoil geochemistry and added alkaline material. The drains have successfully directed ground-water to a planned discharge area. Without the drains, a ground-water mound was expected to form against a buried highwall and discharge over a large area.

Jan 1, 2000

By D. A. Rice, R. L. Stone

Studies of the possible effect of plant water chemistry on the strength of unfired iron ore pellets apparently have not been reported in the literature. Naturally occurring soluble salts were removed from magnetic concentrate filter cakes obtained from several iron ore concentrators. Laboratory balling tests showed that unfired pellets made from these "clean" filter cakes were 50-100% stronger than the usual unfired pellets containing the salts. The fact that certain chemical additives dissolved in the water used for balling "clean" concentrates decreased the strength of unfired pellets indicates that salts in the plant process water may be responsible for lower strengths. According to chemical analyses of plant process waters at these plants, calcium and magnesium are probably the most detrimental salts in the plant circuits. It is suggested that calcium, magnesium, and other polyvalent cations in the mill process waters ion-exchange for lower-valence cations in the bentonite and thereby destroy the electrostatic-charge bonding in the green pellet. Some practical guidelines are also included for plant balling practices.

Jan 1, 1973

By D. J. McAdam, G. W. Geil, R. W. Mebs

AS shown in previous papers by the authors 9-l7† the resistance of a metal to fracture, like its resistance to plastic deformation, is a function of all three principal stresses.‡ A technical cohesion limit is the technically determined resistance to fracture under a specific stress system. The technical cohesive strength thus comprises an infinite number of technical cohesion limits corresponding to the infinite number of possible combinations of the principal stresses. The technical cohesive strength, therefore, may be represented by a surface in a diagram with the three principal stresses as coordinates. As shown in previous papers, 9-I8 the technical cohesive strength increases with plastic deformation, with decrease in temperature, and with increase in the strain rate. The technical cohesion limit, therefore, is affected by the same factors that affect the flow stress, § namely, the stress system, plastic deformation, temperature, and the strain rate. More- over, the influence of each of these factors on the technical cohesion limit has been shown to be qualitatively similar to the influence of the same factor on the flow stress.9-18 Advance of knowledge about the conditions determining fracture, of metals has been retarded by the reluctance of some investigators to abandon preconceived ideas about how metals "should" behave. The incorrect idea is still prevalent that the conditions determining resistance to fracture are very different from those determining the flow stress. Attempts are still being made to express resistance to fracture in terms of a single parameter, such as a limiting value of the greatest principal stress, the maximum shearing stress, or the volume stress (one-third the algebraic sum of the three principal stresses). In these attempts, a sharp distinction is sometimes made between a ductile or "plastic fracture " and a "brittle fracture." In making this distinction, however, the meaning attached to the term "brittle fracture" sometimes is not made clear. The term could mean fracture after very little plastic deformation or it could be used to designate the type of fracture. An ordinary fracture of a ductile metal at room temperature starts as a cleavage, generally transverse to the direction of the greatest principal stress, but eventually changes to a shearing fracture. In some conditions, however, the metal fractures entirely by cleavage, with no evidence of plastic deformation during the fracture; the surface of such a fracture may have a

Jan 1, 1947

By Nigel Marx

In order to understand (and ultimately to predict) the friction reduction resulting from the use of polymer solutions, the rheological properties of model polymer solutions have been measured over a wide range of shear rates. Both temporary and permanent shear thinning have been observed. By using base fluids of different viscosities it has been shown that permanent shear thinning depends more closely on the shear stress experienced by the fluid than on the strain rate. Hydrodynamic measurements have been made on the polymer solutions using a compliant ball on flat lubricated contact that operates in isoviscous-elastic conditions. The measured friction values can only be predicted with reasonable accuracy if the measured shear thinning properties of the lubricant are taken into account in the hydrodynamic model.

Jul 31, 2018

By V. Labiouse, R. Gärber

The paper aims at clarifying the up-to-now misappreciated role taken by pore water on the design of deep tunnels in saturated porous media. Numerical simulations with a non-dimensional FEM-model emphasise the influence of pore water characteristics (in situ pressure and compressibility) and boundary conditions (lining permeability) on the short and long term underground-structure equilibrium states. These results cannot be achieved by means of monophasic total stress analyses. Dieser Beitrag untersucht den Einfluss des Porenwassers auf die Dimensionierung von tiefen Tunnelbauwerken in wassergesättigtem Untergrund. Numerische Simulationen mittels eines dimensionslosen FEM-Modells betonen den Einfluss der Porenwassereigenschaften (in-situ Druck und Kompressibilität) und der hydraulischen Randbedingungen (Tunnelausbaudurchlässigkeit) auf Kurz- und Langzeitverhalten des Untergrund-Ausbau Gleichgewichts. Diese Ergebnisse können nicht ermittelt werden anhand von Einphasen- und Totalspannungsmodellen. L’article s’intéresse au rôle méconnu de l’eau interstitielle dans le dimensionnement de tunnels profonds creusés dans des milieux poreux saturés. Des calculs adimensionnels par éléments finis soulignent l’influence des caractéristiques de l’eau interstitielle (pression in situ et compressibilité) ainsi que des conditions aux frontières (perméabilité du revêtement) sur les équilibres court et long terme de l’ouvrage. Ces résultats ne peuvent pas être obtenus par des calculs en contraintes totales.

Jan 1, 2003

By Priyadharshini M. R., Premalatha K

"Abstract With the development in the construction of heavily loaded structures, the necessity of pile foundations has increased. For the transfer of heavy loads, it is mandatory that the piles need to be socketed in the underlying rock strata. The load transfer in bored rock socketed piles is by end resistance or the combination of shaft and end resistance which in turn depends on the length of the rock socket. The determination of socketing length of the pile at present is mostly based on a few factors which affect the pile load transfer mechanism. The effect of all the possible factors involved, need to be studied in proposing guidelines for the design of rock socketing length of the pile. Analyses are carried out using finite element analysis software (PLAXIS 3D Foundation) to understand the influence of the thickness of overlying strata for different socket lengths of piles in weak rock. From the load settlement curves, the influence of the overlying soil on the rock socket length isobserved and an effective rock socket length is proposed.IntroductionThe determination of socketing length of the pile at present is mostly based on a few factors affecting the pile load transfer mechanism, which sometimes give a better design and sometimes an uneconomical design. Too much socketing length results in more construction time and higher costs. Therefore, the effect of all possible factors involved need to be studied in proposing guidelinesfor the design of t h e r o c k socket length of the pile.The factors that affect the termination criteria of the rock socketed pile are the capacity requirement, thickness and properties of the overlying soil, characteristics of the founding strata, drilling tools used, roughness of the rock socket and nature of loading.A comprehensive study was performed to understand all the above mentioned factors in different types of rocks. In this paper discussion is made on the settlement results, specifically the influence of overlying sand of different densities above a weak rock. The influence of stress developed is not discussed, keeping in mind the size of the paper under study."

Jan 1, 2014

By J. P. Van Dillen

Continuing interest in processes that will effect separations in the fine particle size range has prompted intense interest in the use of high gradient magnetic separation (HGMS) for beneficiation of uranium ores. Some of the uranium minerals are paramagnetic and hence are amenable to concentration by HGMS. This paper presents a brief review of the problems associated with uranium ores beneficiation, a description of the HGNS process, and the effects of the parameters--pulp velocity, field strength, matrix loading and magnetic field gradient on product recovery and grade. Unsatisfactory separation of uranium minerals by HGHS is related to ore specific properties such as lack of liberation, fine dissemination of uranium minerals, uniform distribution of magnetic minerals throughout the ore matrix and interference of micron sized slimes. Experimental techniques to identify and resolve some of these problems are outlined.

Jan 1, 1982