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By D. Reddish

The combination of free standing steel supports, such as arches, and rock bolts (mixed support) has Frequently been in used in UK coal mine roadways when it is considered that the strata and/or environmental conditions would not be suitable for rock bolts solely. However, how such mixed support systems operate is not fully understood. Due to the differences in the support method provided by rock bolts and free standing steel, the total support generated is not simply a case of adding the contribution to the support of the roadway given by the two systems. This paper describes a numerical investigation into mixed support systems when used in coal mine roadways. A series of 2D and 3D geomechanical models are described and the method of modelling the rock bolts and steel supports in coal mine tunnels is discussed. The numerical models described include rock boltd only roadways, steel supported roadways and mixed supported roadways in a variety of geological and in-situ stress conditions. Conclusions are formed that allow an insight into mechanisms of strata reinforcement provided by the support systems modelled. Further to this, a review of the numerical modelling of pre-tensioned rock bolted systems is described identifying the contribution to support efficiency given by the adoption of tensioning in full column resin anchors. The results obtained highlight that the effectiveness of the pre-tensioned load is dependant on the rock mass quality and in- situ stress level at the site where it is to be used.

Jan 1, 2004

By S Ravn

Under platform exhaust (UPE) systems are often designed into metro stations as a means of removing heat generated by trains as they come to a halt in the platform. These systems are designed to extract heat from the brakes and brake resistors directly at the source in order to capture as much heat as possible before it can enter the public areas of the station, or contribute to the temperature build-up in the tunnels. Due to space requirements for the associated duct and air handling units, the UPE plays a significant role in the geometric design of the platform and station as a whole.In recent years questions have arisen as to the effectiveness of UPE systems. However, very little data is available for designers to use when making important decisions on the station designs for new metro systems. This is important as significant savings could be achieved by omitting or re-designing these systems for new build stations; not only due to the capital costs of space provision for the duct itself but also due to the associated operation and maintenance cost of the UPE system.This paper will present recent measurements of the UPE system of the Copenhagen metro together with one-dimensional (1D) simulations, looking at typical dispersion of heat into the station plenum box and air exchange through draught relief shafts as the train enters the station in order to evaluate the effectiveness of the UPE system. The aim of this paper is to disseminate the results of measurements and analysis to increase awareness of the issue and to provide discussion relevant to designers in their evaluation of heat removal systems in new build station designs.

Mar 8, 2011

By Metehan Erdogan, Ishak Karakaya, Fuat Erden, Emre Ergül

"The FFC Cambridge process was suggested as a promising Si production technique for the expanding solar energy industry. Direct electrochemical reduction of bulk SiO2 plates and porous SiO2 pellets in molten CaCl2-NaCl salt mixture were investigated at 750°C by applying 2.8 V potential difference. The produced Si powder was brown and found to be contaminated by the Ni and stainless steel plates used as the cathode contacting materials. The reduction rates of the bulk SiO2 plates and porous SiO2 pellets were compared from variations of current and accumulative electrical charge that passed through the cell during the electrochemical reduction. The amorphous bulk SiO2 plates were reduced slightly faster than porous pellets of crystalline SiO2. The overall reduction potential of SiO2 pellets against the graphite anode at 750°C in molten CaCl2-NaCl salt mixture was determined as 2.3 V by cyclic voltammetry. This potential was supported by calculations.IntroductionMetallurgical grade Si cannot be directly used in electronic industry and some intermediate steps are required to produce industrial solar grade silicon (SOG-Si). A promising alternative solar grade silicon production technique is the FFC Cambridge Process [1]. Production of Si by electrochemical reduction of SiO2 at 850oC in molten CaCl2 electrolyte was first studied by Nohira et.al. [2]. In their study; Si formation was observed on bulk SiO2 cathodes after 1 hour of electrolysis. Complete electrochemical reduction of porous SiO2 pellets was first reported by Jin and his coworkers [3]. The mechanism of electrochemical reduction of SiO2 to Si in molten CaCl2 was explained in another study [4]. Reduction rates of bulk SiO2 and porous SiO2 pellets were also compared previously and it was found that reduction rates for bulk plates were higher [5]. Furthermore, it was reported that mixing Si into porous SiO2 pellet increased the reduction rate [5]. Mo [2, 4-7], Ni [3, 8, 9] or Si [6] were used as cathode contacting materials in various studies. Yasuda et. al. [6] produced Si with 99.80 % purity using Si plates as cathode contacting material to reduce metal contamination."

Jan 1, 2012

By Isa Nozari, Asghar Azizi

The extraction of copper from sulfate leaching liquor was investigated using Acorga M5640 commercial extractant in kerosene diluent. The effects of important factors such as the extractant concentration, contact time, liquor pH, and temperature were examined on the separation factor Cu/Fe and the extraction efficiency of copper. The results indicated that nearly 92.32% copper was extracted from the leach liquor at 10% (v/v) Acorga M5640 concentration, 1:1 aqueous/organic phase ratio, 20 min contact time, pH 2.5, and 25 °C temperature. Also, the further increase in the values determined had no positive impact on the extraction of copper. Under these conditions, the separation factor Cu/Fe was obtained about 29.64. The extraction mechanism was studied applying the plot of log(D) – 2 pH against log [extractant] and it proved the association of two moles of Acorga M5640 for the extraction of one mole of copper. McCabe–Thiele diagram was constructed and a single-step extraction process was found to obtain themaximumextraction. Additionally, thermodynamic datawere investigated and the extraction process was endothermic and non-spontaneous at 298 K (ΔH = 27.05 and ΔG = 15.52 kJ mol−1). Moreover, the loaded organic phase was stripped and 80.94% copper was recovered after 20 min using 10% sulfuric acid concentration.

Jul 31, 2020

An Investigation into the Flotation Behaviour of Pyrrhotite Present in the Merensky Orebody

Sep 13, 2010

By G. L. Gomes-Sebastiao, W. W. de Graaf

"Gomes Sand is a quarry operation that produces sand and aggregate for the construction industry. The quarry is experiencing inconsistencies in the fragmentation and poor pit conditions as a result of poor drilling and blasting practices. This results in excessive downtime in the load and haul and crushing processes.A benchmarking exercise of the blasting practices was conducted to evaluate the effect of the inconsistency on the mining cycle. After changes in the blasting practices the downtime was reduced, which improved the crushing plant utilization by 4.9%. The improved blasting practices and more consistent fragmentation decreased the average number of loads lost each month due to jaw crusher blockages from 9.2% to 3.9% of plant throughput. The change in blasting practices also improved pit conditions. IntroductionGomes Sand is a quarry operation that has been in operation since 2009, producing sand and stone for the construction industry. The quarry was experiencing unacceptable blasting results. The repercussions included uneven pit floors, large amounts of oversize rock (>500 mm), and inconsistent fragmentation.The blast results affected the load and haul operations as well as the efficiency of the crusher. This resulted in downtime in the daily operations, and consequent production and revenue losses.The crusher product should have a top size of 50 mm. A blast fragmentation of <50 mm would improve the downstream operations and the crusher throughput.An investigation into the blasting practices was carried out to assess whether the downstream delays can be eliminated by improving the blast results. The exercise included:* Assessing if the designed blast layout is adhered to on the bench* Observing the quality and control of drilling* Observing the charging procedure of the blast-holes* Benchmarking the fragmentation consistency of the blasted rock using current blast design and practices* Analysing the throughput of the crushing plant* Investigating the power consumption of the crushing plant and determine if a change in blasting practices will affect this* Evaluating the hours spent by the hydraulic hammer on secondary breaking."

Jan 1, 2017

By Bruno Bussière, Guosheng Zhan, Michel Aubertin, Vincent Martin, Robert P. Chapuis

The study evaluates the hydrological behaviour of exposed and covered waste rock dumps. The objectives were to determine the major factors influencing unsaturated flow in waste rock dumps and covers, and to improve the in-situ, laboratory and numerical modeling characterization methods. Using material properties obtained from in-situ and laboratory tests, waste rock dumps of different configurations, with and without covers, were modeled. It was found that a properly designed “Store, divert and release” (SDR) cover allows most of the water to be diverted downslope and discharged outside of the waste rock dumps. The SDR cover seems to work efficiently even in extreme storm events. The numerical modeling results show that the unsaturated hydraulic properties (e.g. air entry value and water entry value) of the materials largely control the infiltration of water into waste rock dumps.

Jan 1, 2005

By M. J. Nicol, R. P. Colborn

An investigation into the kinetics and mechanism of the oxidation of iron (11) by oxygen in aqueous chloride solutions By R. P. COLBORN Pr. Eng., Ph.D. (Natal) and M. J. NICOLt B.Sc. Hons., Ph.D. (Rand) A reaction mechanism for the oxidation of ferrous chloride by molecular oxygen is developed. and the appropriate constants are evaluated. The effect of a number of cations and anions on the rate of oxidation has been tested.

The aim of this research was to study the absorption characteristics of thermally dried fine coal from South African collieries. After milling to ?150 µm and pressure filtration, the samples were subjected to either air drying or thermal drying at 150°C. The samples were then put into a climate box at 28°C and at three different relative humidity levels, namely 30, 60 and 94 per cent. It was found that the equilibrium moisture content of thermally dried coal at a specific relative humidity was lower than that of air dried coal. The relationship between the equilibrium moisture content and relative humidity is described by 1 ? RH = exp (-KTMen). There was no relationship between the volatile matter content and equilibrium moisture content, but there was an increase in the equilibrium moisture content of the coal with an increase in mineral content. The moisture uptake rate increased with an increase in temperature and a decrease in particle size. A model is discussed that fitted the experimental data and gave a good prediction for changes in the conditions. There was no evidence of greater moisture absorption by thermally dried coal. Keywords: Fine coal, thermal drying, drainage, South Africa, drying

Jan 1, 2002

By M. S. P. Rampedi

The paper reports on a vacation work project conducted at Khuseleka No. 1 Shaft, Anglo Platinum, where there was a need to optimize the transport of personnel to level 15 and below. Approximately 900 men per hour need to travel between the shaft and the start of the current chairlift system. Time studies were used as the major indicator of the extent of the current problem, and it is recommended that a new chairlift system be installed to cover the distance from the vertical shaft station at level 15 to the chairlift decline station on level 15. A capital cost of approximately R10 million is necessary to carry out the proposed recommendation. Khuseleka No. 1 Shaft has the capacity to wind 1070 people per hour, and the current labour complement going to the level 15 shaft station stands at 1570 employees; thus at optimum efficiency the proposed chairlift system could transport the entire shift to the start of the current chairlift system in only 1 hour and 45 minutes. Reducing the distance walked at the start of the shift may also have an impact on productivity.

Jan 1, 2012

By M. C. Bhulose

Paper written on project work carried out in partial fulfilment of B. Eng (Mining Engineering) degree The purpose of this project was to identify constraints that could occur in the current sub-decline shaft at Turffontein Shaft should an increase in production take place. Particular attention was to be paid to the transportation of men and materials and to the broken rock and ventilation capacity of the shaft. This project is an in-depth evaluation of the logistic capacity of the sub-decline system at Turffontein Shaft in order to determine by how much production can be increased in this area to replace tonnages from the vertical shaft area, where ore reserves are rapidly becoming depleted.

Jan 1, 2004

By M. Karmis

The determination of the surface area which may be impacted by underground mining is an important consideration in subsidence engineering. A number of parameters have been utilized to identify this influence area, most notably the angles of draw and break. This paper discusses the implications of selecting an appropriate "damage angle" for defining a potential damage area due to mining, within which surface structures may be impacted Furthermore, the influence of both mining and geological factors, such as mining width and depth and overburden lithology, on this angle is examined, using the Surface Deformation Prediction System (S.D.P.S) software. Finally, recommendations are given for applying these concepts in subsidence control.

Jan 1, 1994

By R. Shamsodini, A. Poor Zaeif Doost, H. Haji Amin Shirazi, M. R. Garmsiri

"With columns being installed in rougher section at Miduk Copper Complex, the rougher feed mainly reports to rougher-scavenger cells. To evaluate the efficiency of regrinding circuit, we conducted flotation experiments on samples of the feed and the products of the regrinding circuit. The grade difference of these products at 85% recovery was considered as the efficiency index. Results show that, with weight recovery of the rougher-scavengers the efficiency of the circuit increases. Exclusion of the rougher-scavenger concentrate from the feed to the regrinding circuit, resulted in an increase in the efficiency index from 10.12 to 17.6%.INTRODUCTIONThe flotation circuit at Miduk Copper Complex consists of five flotation columns as roughers and ten mechanical cells as rougher-scavengers. According to design criteria, 75% of the final product was expected to be produced by the rougher columns, while most of the feed consisting of liberated valuable particles is introduced into rougher-scavengers. To liberate locked particles, the rougher-scavengers concentrate is introduced into the regrinding circuit (see Figure 1 below). The regrind mill is in reversed closed circuit with a secondary hydrocyclones cluster, and the cyclone overflow is introduced into three parallel cleaner columns. Cleaners concentrate reports to concentrate thickener and the column tailings is introduced into six mechanical cleaner-scavenger cells. The cleaner-scavengers concentrate reports to the regrind circuit(Figure 1)."

Jan 1, 2012

By M. C. Harris

"Excess Gibbs energy is a thermodynamic parameter which quantifies the difference between the value of the Gibbs energy for a real mixture and that for an ideal mixture. More specifically the partial molar excess Gibbs energy of a species (i) in a mixture is indicated by the change in the overall excess Gibbs energy of the solution as the number of moles of species (i) changes while keeping temperature, pressure and the number of moles of all other species in the solution constant. Generally it is obtained from the activity coefficient which in turn can be obtained for a species in a mixture using a variety of models. The most widely used method is to use UNIFAC. Flotation is probably the most important process in the concentration of minerals and requires the use of reagents such as collectors and frothers. There is abundant experimental data which illustrates that collectors of different alkyl chain lengths will change the contact angle and that frothers of different structures and molecular weights will result in changes in key flotation properties such as froth behavior, surface tension and critical coalescence concentration. In this paper it is shown that there is a strong linear relationship between measured parameters such as froth volume/height, surface tension, critical coalescence concentration and contact angle and the partial molar excess Gibbs energy of the molecules used. Proposals are made to explain these correlations.INTRODUCTIONAs is well known froth flotation is arguably the most widely used process in the separation of minerals. In broad terms the process relies on the use of reagents known as collectors to adsorb onto a mineral surface and thus render the mineral particle hydrophobic. Alkyl thiolates are very commonly used for this purpose. The hydrophobicity is induced as a result of the alkyl group’s molecular structural properties which results in it forming a non-ideal mixture with the process water. Surfactants (or frothers) are typically alcohols and are known to lower the surface tension of the system and also inhibit bubble coalescence and reduce bubble size. Since alcohols are polar they will also form a non-ideal mixture with water. The hydrophobic mineral attaches to the bubble and rises to the froth phase where the valuable mineral is recovered as a concentrate. Frothers have often been characterized using the so-called HLB (hydrophobic-lipophilic balance) number but recently it was shown that the use of activity coefficients (?) or excess Gibbs energy (G ex ), which is calculated using equation (1) is a much more appropriate way to describe the behavior of these reagents in non-ideal mixtures with water (Corin and O’Connor, 2014)."

Jan 1, 2016

By Megan Becker, Cyril O’Connor, Jenny Wiese, Gaynor Yorath

The effect of particle shape on true flotation has been widely reported. The present paper presents results obtained in investigating the effect of particle shape on the entrainment of particles during the flotation process. Different hydrophilic minerals with particles of varying aspect ratios were used and their shape determined using rheological tests and QEMSCAN. Their entrainment properties showed a close relationship to their shape with the recovery due to entrainment increasing as the aspect ratio of the particles increased. The effect of surface charge, by changing pH, and size of particles showed that the effect of shape was sustained at different pHs and particle sizes. Proposals are made to explain these observations in terms of the known relationships between drag coefficients and terminal velocities and shape. Since it has been previously reported that different milling procedures can affect particle shape, these results indicate that it is possible that such different procedures may result in increased entrainment of hydrophilic minerals.

Jan 1, 2014

By J. P. Sairrlon, K. G. Wheeland, K. J. Mintz, B. J. Kiener

Iwenty-one ore dusts of varying mineralogy, sulphur content and reputed in-mine explosibility were selected from eight mines. After chemical and mineralogical analysis and sieving into two size fractions (+45/ -63 microns and -45 microns), these sarrples and seven pure minerals were tested for explosibility in oxygen in a Harbnann chamber. '!he maximum explosion pressures and maximum rates of pressure do not correlate with sulphur content alone; the types of minerals are also .important. Residues were analyzed to check the combustion reactions. Further comparisons between laboratory and mine results are planned to improve predictability.

May 11, 1988

Common brattice cloths in use in Australian coal mines are compared by permeability measurements. The respective advantages of twill weave and tarpauling* weave cloths are listed, and the improvements to be obtained in the ventilation of a mine by using tarpauling cloths instead of the commonly used twill cloths are stressed. Plastic cloths are widely used overseas and are briefly discussed.INTRODUCTIONThe onset of extensive full-scale mechanization in Australian coal mines during the past few years has increased attention given to the ventilation of working places. Many inadequacies of the present system have been brought to light and not the least of these is connected with the use of brattice cloth, both in directing the flow of air around the face and in acting as a temporary sealing mechanism. A well-constructed line of brattice will only provide fair ventilation for a distance of 100 ft. Beyond this point the volume or air reaching the face falls off rapidly.Some of the shortcomings associated&apos; with the use of brattice cloths are:1. Hurried installation, necessitated by a rapid advance, often results in poor workmanship with, consequently, an excessively high leakage rate.2. High places caused by falls of roof are difficult and time-consuming to seal.3. Curtains, in lines of brattice crossing transport routes, are difficult to maintain.4. Lines of brattice interfere with rock-dusting and clean-up of fine coal.5. Repair and maintenance of brattice consumes much...

Jan 1, 1959

By Keith A. Heasley, Lee W. Saperstein

This paper investigates the use of backfill zones and yielding pillars for subsidence control. The investigation begins by choosing an appropriate subsidence predictive technique to simulate the proposed subsidence-control schemes. Two case studies are performed in order to delineate the accuracy and utlility of the chosen predictive technique and then the results of these case studies are used to establish appropriate sets of regional site parameters. Next, a detailed analysis of the major variables affecting the outcome of the subsidence-control simulations is conducted and graphical displays of the exact sensitivity of the surface subsidence to these variables are given. Finally, alterations to the surface subsidence that are expected from using two major subsidence-control techniques are presented. The first technique to be assessed is a backfilled pillar centered longitudinally in a panel. With this arrangement, a minimal amount of backfill material can produce substantial decreases in vertical displacements. The second technique to be assessed is the use of yielding gate pillars to reduce the sinuosity of the transverse subsidence over adjacent panels. With proper design, this technique can greatly curtail surface strains and help minimize remedial drainage control.

Jan 1, 1986

By Harold Gibson

The mechanisms leading to the impact of airborne dust particles onto bluff flow obstacles have been extensively reported [1] and widely applied in dust measuring instruments (e.g., impactors) and in dust collecting devices (e.g., filters and scrubbers). If the human head is regarded as a bluff body, particles from dusty flowing air can impact onto the face by virtue of those mechanisms. While a great deal has been researched and written on the nuisance caused to human beings by the entry of dust particles into the body by inhalation through the nose and mouth, there appears to be nothing reported in the scientific literature about the irritation which can be caused by the impact of dust onto the face. And yet there is sufficient evidence to suggest that in certain working environments and under certain conditions, the problem is indeed a real (albeit subjective) one. In the coal mining industry, underground workers are exposed to conditions, involving dust-creating production and handling processes on the one hand and high ventilation rates demanded by the gassy nature of the environment on the other, in which the problem can exist. At the coal face, for example, the movement of powered roof supports ("chocks") can release bursts of dust formed by the crushing action of the supports, which in turn is entrained into the moving air and impacts onto the faces of miners working just downstream. The dust in question contains a large proportion of coarse particles which, while still fine enough to remain airborne for appreciable distances downstream of the point of release, are coarse enough to produce sen¬sation on impact with the skin. Adverse subjective response of workers to such irritation could damage morale and productivity. We have performed laboratory and field experiments to investigate the psychophysical and physiological responses of human subjects to dust impacting onto the face and into the eyes. Since this appears to be the first systematic investigation into these questions, the aim has been to construct a useful scientific framework from which to allow characterisation of the problem of such "fly-dust", and, ultimately, the development of methods for monitoring and controlling it. The main results of our research are given here; the theoretical and experimental details will be presented at greater length elsewhere.

Jan 1, 1980

By J. L. Vanderbeek

Investigations have been conducted at Chino Mines Company into the effect that SAG mill recycle material (critical size) exerts on SAG mill throughput and specific energy requirements. Tests were conducted on the laboratory, pilot, and plant scales, to evaluate the merits of alternative treatment options. Removing critical size material from the SAG mill circuit has been shown to improve new feed rates by 34% with a reduction in specific energy (kWh/ton) of 33%. Test results obtained to date are presented.

Jan 1, 1985