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By X. Xu, J. K. -W. Wong, J. -Y. Delenne, K. Soga

Hydraulic fracturing (HF) is a mulit-scale and multi-physics process which makes numerical modelling challenging. Conventional numerical models focus on multi-physics nature of HF but the multiscale nature is compromised by idealization of reservoir to be continuous, homogeneous and isotropic. However, natural fractures take a significant role in the success of HF for exploration of unconventional resources like Shale gas. Advancement in microseismic monitoring provides useful data for simulation in a much greater details. There is an urgent need to develop a suitable numerical tool for multi-scale threedimensional simulation to better understand the roles of discontinuities and heterogeneity in reservoir and its interaction with HF, especially to address the environmental concerns such as induced seismicity. In this paper, a simple discontinuum numerical method – Lattice Element Method (LEM) is proposed to model HF in a large scale three-dimensional model. A reservoir is modelled as a lattice network composed of 1D Hookean’s spring. Fracturing is modelled simply by removing lattices that meet a specified threshold as determined by the critical energy release rate of the rock. By introducing disorder in the model, mesh dependency in modelling fracture growth is minimized. Fluid flow is simplified as flow in pipe network and the permeability of pipe is related to fracture aperture by cubic flow law. Therefore, fracture flow and rock deformation are fully coupled. In this paper, four simulations of the same configuration except with different degrees of reservoir heterogeneity are presented. Fractures formed are diffusive and two groups of fracture are identified – connected fractures and isolated fracture without clear spatial correlation. The former forms a ‘fracture cloud’ and contributes to fluid flow and modeled by pipe network. The flow of fluid is highly tortuous and pipe network is sparely connected. The degree of reservoir heterogeneity controls the growth of ‘fracture cloud’ and pipe network. Microseismic monitoring often shows diffusive fracturing during HF on site and hence the outcome of the proposed model can be compared to such monitoring results.

Jan 1, 2015

By D. P. Ziegler

Formulas relating economic optimum busbar cross sectional areas to busbar cost, electric price and financial parameters are reviewed and revised. Application of the formulas is illustrated with discussion of the appropriate choice of parameter values and the sensitivity of the optimum to the parameters. The extension of the single busbar concept to optimization of more complicated arrangements of bus for smelting pots is complicated by the constraint of obtaining a specified current distribution. An example problem illustrates the optimization of a section of a bus network containing a fork, with the imposed limitation of achieving a specified uniformity in the current. In cases where the current in the individual conductors may vary, Kelvin's law does not apply. Further extension of the technique to a full pot set of conductors poses additional problems which are discussed, but whose solution has not yet been accomplished. Aluminium 2006 45th Annual Conference of Metallurgists ofCIM Montreal, Quebec, Canada Edited by

Jan 1, 2006

By A. Taylor

This paper considers mineral processing in zero gravity dry environments typical of asteroids or comets. The electro-dynamic separation technique using pneumatic flow systems is explored. Pneumatic delivery of solids is used because of extreme temperature changes and the possible scarcity of water. The present earth-based process and how it can be modified for these conditions is examined.

May 1, 2001

By Wei Sun, Xiangsong Meng, Xiaodong Li, Weisheng Huang, Yuehua Hu, Chonggao Cao, Haisheng Han, Wensheng Chen, Runqing Liu, Central South University

"The similar flotability of scheelite, fluorite, and calcite resulted in the difficult separation by flotation. This work revealed the effect of water glass on the flotation of scheelite by FTIR and the wettability change of the usual cleavage plane, and proved that water glass inevitably influenced the flotation of tungsten minerals to a large extend in traditional fatty acid flotation process. A new collector, benzohydroxamic acid complexes, was found to be selective for the separation of scheelite and calcium minerals with little water glass. Hence a novel flotation process was developed for the recovery of tungsten minerals in shizhuyuan mine in China. Normal temperature flotation of tungsten minerals was developed to instead of the classical “Petrov's process” for scheelite-calcite-fluorite type ores. Compared with the traditional process, the recovery was improved by 10% and the grade of scheelite concentrate was above 55%. The disappearance or decreasing of water glass contributed to improving the recovery of tungsten and fluorite and the circulation of water and reagents.INTRODUCTIONChina is rich in tungsten resources and the proved reserves accounted for 60% of the world's reserves (Cai Gaipin et al., 2009). However the wolframite has been dried up and the scheelite resource has become the main resource of the tungsten metal. Scheelite deposits were classified to scheelite-silicate type and scheelite-calcite-fluorite type based on the associated gangue minerals. Scheelite was easy to separate from the silicate minerals. Flotation separation of scheelite from calcium minerals creates difficulties because of the existence of the same cation in the minerals and similar physicochemical characteristics such as solubility, hardness, specific gravity, PZC (point of zero charge) etc.(Arnold & Warren, 1974; Yongxin & Changgen, 1983; Ozcan & Bulutcu, 1993a; Deng et al., 2015, 2016;). The conventional collectors used in the flotation of scheelite ores are generally fatty acids or fatty acid derivatives ( Yongxin & Changgen, 1983; Oliveira & Sampaio, 1988; Sivamohan, 1988; Shi et al., 2014; Bo et al., 2015). It is difficult to separate scheelite especially from calcite with these reagents because the adsorption mechanism of these collectors occurs through chemisorption of the oleate ion onto the mineral surface (Atademir et al., 1979; Changgen and Yongxin, 1983; Hiçyìlmaz et al., 1993; Hu et al., 2011). Therefore, it is almost impossible to separate them by fatty acid flotation without using any selective depressant. Although oleoyl sarcosine was used as a selective collector in the flotation of fluorite and siliceous scheelite ores (Ozcan & Bulutcu, 1993b; Ozcan et al., 1994), this selectivity is not adequate for a low-grade calcitic scheelite ore. Unfortunately, the reagents such as organic colloids (dextrine, starch), quebracho, sodium phosphates, sodium silicate solutions containing polyvalent cations (hydrosols), etc. (Yongxin and Changgen, 1983; Schubert et al., 1990; Shi et al., 2014; Bo et al., 2015) used for calcite depression also depress scheelite to a large extent."

Jan 1, 2016

By X. Gu

Mining operations, especially surface coal mines, have great impacts on the local ecosystem and the environment. However, it has been a common practice in mine design that the economic evaluation considers only the operating and capital costs, while the costs incurred due to ecological damage are left out. Such practice underestimates the total cost of mining and ignores the difference in ecological impacts between different mine design alternatives. With growing interest in sustainable development, the mining industry is under increasing pressure to operate not only based on economic and engineering principles but also on principles of sustainability. Therefore, estimating ecological costs of mining and considering such costs in the mine design process is an important step towards reducing ecological impacts at the design stage. The objective of this paper is to quantify the ecological costs of open pit coal mining and to demonstrate the influence of such costs on the ultimate pit design. The ecological costs of mining are estimated based on the areas and types of land damaged by mining activities and the carbon emission from energy consumption. Four major components of ecological cost are identified, namely, lost value of direct eco-services, lost value of indirect eco-services, prevention and restoration costs, and the cost of carbon emission from energy consumption. Necessary equations are given for estimating these costs. An algorithm is described for ultimate pit optimization in coal deposits with near-horizontal coal seams. A case study is presented in which the ultimate pits with and without ecological costs are optimized and compared to show the influence of ecological costs on the pit design outcome.

Aug 1, 2013

By Glenville A. Collins

IN 1932, Horace Onyett at Oroville, California, built a practical floating washing plant along the general lines as now known, using a 24 in. by 12 ft. trammel; it was fed with a ½ yard dragline bucket, rated then at 200 yards per day. Onyett dubbed his plant a 'Doodlebug' which name has clung to this type of operation ever since. In general, the 'Doodlebug' dredge is the outgrowth of the depression of 1929, wherein many dirt contractors had surplus idle equipment and a few of them ventured to use it for placer mining. Many such plants were impractical and poorly designed and adapted often to locations not suited to the purpose. However out of the general idea came refinements until today dragline dredging has a very definite place in the gold production of the world. Many of the early operators, being mainly contractors without mining experience or technical knowledge of gold saving, geology, or mechanical design, naturally went through stages of trial and error until a workable unit became standard practice. Credit should be given Bodenson Iron Works of San Francisco, who did a notable job of pioneering and building of floating washing plants; also, to Lord and Bishop, contractors of Sacramento, who were among the early operators, and to several others who built and rebuilt their plants until the weak spots were strengthened to take the beating required, and yet deliver a high degree of efficiency.

Jan 1, 1945

By S. S. Teal, W. W. Weber

"AS THE TITLE implies, this paper will deal with the unusual rather than the standard practices as employed . at the property of North Rankin Nickel Mines, Limited. Fortunately •the mining, with the exception of permafrost conditions, and the milling practices, are the normal approaches dictated by the size, type, and character of the orebody. The unusual aspects are linked directly or indirectly to the isolated location and are •principally ancillary requirements or services covering a broad range from climate to supplies and from finance to entertainment. It is our intent to cover the more salient points of interest together with a brief description of the general operation.To understand the primary motivation of the mine, it must be made clear that North Rankin was conceived as a foothold in the Canadian North, that region embracing 40 per cent of the Dominion which ex-tends north of the commercial tree-line and which includes nearly 50 per cent of the Precambrian Shield, our mainstay of Canadian mining. Secondly, this project was born in an atmosphere of premium sales in the nickel markets, assuring a rapid pay-back of the heavy •capital expenditures. And finally, it has •been coddled through the stark reality of a competitive metal market with the hope and trust that the experiences and achievements will lead over the bill to a bigger and better mine in this virgin territory. This is the briefest story of the mine's history, but it pays tribute to the many people who, in thirty years since .discovery, have championed this project."

Jan 1, 1959

By A. Villanueva

The effect of High Pressure Grinding Rolls (HPGR), as a preceding stage to a conventional ball mill circuit at PT Freeport Indonesia?s C1/C2 concentrators, has been studied in terms of downstream grinding efficiency and circuit performance. When milling the product from the HPGR, mill capacity increased by 21% for the same product grind size, when compared to processing similar ore from a conventional crushing circuit. This achievement is a result of several reasons, among them: reduction in feed size (F80), fines generation beyond the proportional reduction in F80, reduction in ore hardness induced by HPGR comminution mechanism, optimization of the recycle system of the HPGR and ball string optimization in the ball mill circuit given the new feed to the mill.

Jan 1, 2012

By Jaeheon Lee, Junmo Ahn, Doyun Shin

"Many alternative leaching systems including bacterial leaching have been introduced to avoid passivation on the surface of chalcopyrite and to increase the leaching efficiency of copper from chalcopyrite. Recently, glycine, one of the simplest amino acids, has been emerging as an efficient and environmental-friendly lixiviant to recover copper. In the present study, an alkaline glycine–peroxide lixiviant system was used to leach copper from chalcopyrite concentrate and the leaching mechanisms were also investigated by a suite of kinetic studies under different conditions. The chalcopyrite concentrate contains 28.8% copper with 30.8% sulfide sulfur. The effect of concentration of glycine and hydrogen peroxide of the leaching solution was investigated. Glycine concentration was varied from 0.5 to 1.0 M and the hydrogen peroxide concentration was changed between 3 to 5%. Leaching time and pulp density were also varied. Hydrogen peroxide is an oxidant of the system and the leaching efficiency with periodic additions of the peroxide was also studied. A mineralogical study was performed using XRD and SEM. To investigate the surface of the residue materials, XPS was used to see if any passivating layer was formed during the leaching. Detailed results from mineralogical, chemical, and metallurgical studies will be presented and discussed.INTRODUCTION The greatest global resource of copper is low-grade chalcopyrite and heap bioleaching may be the only economic option for its processing. However, formation of a passivating layer on the surface of chalcopyrite slows down the oxidation reaction and reduces the efficiency of the process."

Jan 1, 2017

By W. J. Kempson

In recent years, substantial progress has been made with respect to the definition and control of the primary energy requirements in underground mines. Little has, however been done to develop a more detailed understanding of how to limit the various pressure losses which are intrinsic to shaft systems. This is in spite of the fact that more than half of the pressures generated by the ventilation fans in deep level mines are dissipated as pressure losses within the shaft system. This paper presents research which has been completed to optimise the pressure losses which occur in shaft systems as a result of the ventilation air flowing through them. In this regard, the response of various shafts to the ventilation air flowing through them was measured. These results were evaluated against the current theory for the calculation of shaft pressure losses. Finally the results of the measurements and calculations were used to calibrate a Computational Fluid Dynamics model of the shaft systems. This model was then iterated to allow meaningful conclusions as to the specific make up of the shaft equipment which contributes the most to pressure losses in shaft The results of the above analysis demonstrated that the current theory used for the evaluation of these pressure losses is deficient. The paper discusses these conclusions and the specific ramifications of the analysis. Finally, the understandings gained with regards to the above research are applied to the design and layout of equipment in mine shafts. In this regard, the shape and orientation of the shaft steelwork is evaluated and it specific interaction with the piping and conveyance is evaluated. Coming out of this evaluation are specific recommendations for the design of future shaft systems. These recommendations are based on the above models and offer specific savings on the lifetime operating costs of shaft systems.

Aug 1, 2013

By J. Cayouette, C. Bolduc, P. Blatter

"The LaRonde mill was commissioned in 1988 and began treating ore from the Penna shaft in 2000. The mill has been expanded to accommodate 7,500 t/day, but ramped down to 6,000 t/day since the deep extension began. The process recovers gold, silver, and base metals. In 2008, the Goldex plant began trucking gold-pyrite concentrate to a treatment plant feeding pulp to the LaRonde mill, increasing gold output by 40,000 oz. In 2009, the high-grade Lapa ore processing facilities were annexed to the LaRonde plant, increasing gold output by 120,000 oz. This paper outlines the metallurgical considerations related to the treatment of different ore types.RÉSUMÉ Le concentrateur de la mine LaRonde a été mis en service en 1988 et a commencé à traiter le minerai du puits Penna en 2000. La capacité du concentrateur a augmenté afin de permettre le traitement de 7 500 tonnes de minerai par jour, capacité qui est retombée à 6 000 tonnes par jour (tpj) depuis le début de l’extension en profondeur de la mine. Ce procédé permet de récupérer de l’or, de l’argent et des métaux communs. En 2008, l’usine de traitement Goldex a commencé à transporter par camion du concentré de pyrite et d’or vers une usine de traitement alimentant en pulpe le concentrateur de LaRonde, augmentant ainsi la production d’or de 40 000 onces. En 2009, les installations de traitement du minerai à haute teneur de Lapa ont été annexées à l’usine de traitement de LaRonde, augmentant la production d’or de 120 000 onces. Cet article passe en revue les considérations métallurgiques liées au traitement de différents types de minerai.INTRODUCTIONThe LaRonde metallurgical plant in the Abitibi region of Quebec, Canada, evolved into a mature milling site following expansions in 2000–2003, thanks to improved processes, manpower, and water treatment capabilities that better accommodate the complex constituents of the LaRonde ore. The ore requires a sequence of grinding, copper- lead and zinc flotation, and precious metals leaching, ending with a carbon-in-pulp (CIP) gold recovery. A portion (35%) of the tailings is sent back underground as paste backfill after being treated with the SO2-air cyanide destruction process. The tailings area has a dedicated cyanide destruction and metal precipitation area through which the used water passes before returning as recycled water. A biological water treatment plant was built in 2004 to address water toxicity in the final effluent. The water toxicity was the result of the high sulfide content of the LaRonde ore (from thiocyanate or stable cyanide species buildup) and the use of 90% recirculated water in the mill. The water treatment plant uses bacteria to transform thiocyanate into nitrates and precipitate phosphorus from the water before it is discharged into the environment."

Jan 1, 2017

By M. Mirnezami, J. A. Finch, S. Uddin

A fast, reliable and practical way of measuring zeta potential using sedimentation potential method is proposed. A cell was designed along with the instrument control software to determine the required variables simultaneously i.e. sedimentation potential, specific conductivity, volume fraction of solid as well as pH. High purity alumina and silica powders were used as test samples. Measured zeta potential using the proposed technique was comparable with the results by electrophoresis.

Jan 1, 2009

By Lloyd W. Trevoy

Syncrude Canada Limited is presently studying commercial production of heavy minerals from plant tailings of the openpit A lhabasca tar sands operation. When tar sands are processed and upgraded to synthetic crude oil, heavy minerals can be removed f rom the extraction circuit and beneficiated to provide concentrates of zircon and titanium minerals. Calculated recovery rates indicate that crude oil production capabilities of 105,000 barrels per day would provide 26,000 tonnes of zircon and 114,000 tonnes of titanium minerals annually. The titanium minerals concentrate is a mixture of ilmenite, leucoxene and rutile; it could be used as recovered or upgraded to synthetic rutile. With the consrruction of further synthetic crude oil plants in Western Canada, a large reserve of heavy minerals will become available.

Jan 1, 1984

By G. Ergin

The interactions taking place between Al-Mg alloys and the bed media during aluminum filtration are not yet well understood. These interactions were studied using the infiltration technique. The reaction interface was analyzed using different techniques such as SEM and TEM. Only spinel formation was observed at the interface regardless of the type of alumina and contact time. This paper discusses the results of the study.

Jan 1, 2004

By J-S. Marois, F. Cappucitti, Y. Dodier, D. Downey, G. Matton

"The flotation processes of the Niobec Mine have been affected by a seasonal loss of recovery and a significant increase in reagent consumption over the past few winters. This paper discusses the problem-solving methodology that was used to identify the root causes, to develop solutions and to implement changes that resolved the problem to restore the process to summer-like conditions year-round. Mainly, it was found that the process water was contaminated by phosphates ions, which adversely affected the carbonate pre-flotation, and caused detrimental effects on the subsequent niobium flotation. The phosphate ions were being generated by the process itself, but were consumed by algae in summer conditions. It was determined in laboratory studies that concentrations as low as 5 ppm were enough to affect the circuit and that the multiple additions of process water throughout the circuit was worsening the effect. Also, temperature was found to have an impact on the reagent performance. The performance of the plant was restored by implementing a natural treatment of our process water with a simple cost-free rearrangement of our circuit streams. In addition to that, our extensive geometallurgical program was used to provide ore to the plant restricting phosphate generation in the process. Also, a modification of the collector was developed and introduced in the carbonate pre-flotation that provided improved performance during the periods of low pulp temperature.INTRODUCTION Niobec is one the three major global producers of niobium presently in operation. Situated in the Saguenay-Lac-St-Jean region of Quebec and in operation since 1976, the site produces ferroniobium (FeNb) to be used mainly in High Strength Low Alloy (HSLA) steel, which is known to have better mechanical properties than carbon steel. The Niobec operation consists of an underground mine, a concentrator and a converter plant. The concentrator concentrates niobium-bearing minerals, mainly pyrochlore and columbite, to produce a high-content Nb2O5 concentrate which is then converted to FeNb in the converter plant by an aluminothermic reaction. The Niobec concentrator flowsheet, which has gone through many expansions and optimisation over the years, consists of grinding, desliming, flotation and leaching steps. The flotation steps are numerous, sensitive and difficult to operate due to the non-selective nature of oxide mineral collectors. Thus, the pyrochlore concentration process at Niobec still faces many challenges and is constantly going through periods of continuous improvement."

Jan 1, 2018

By E. Ghali, N. Sorour, G. Houlachi

"The binary Fe53Mo47 and ternary Fe54Mo30P16 coatings have been electrodeposited from citrate-based electrolyte on mild steel (MS) substrates. The electrodeposition has been conducted for 6 hours at 20 mA cm-2 and 30°C. The electrochemical tests were carried out in chlorate solutions containing 300 g L-1 NaCl and 4 g L-1 K2Cr2O7 at pH 6.4 and 80°C. A number of surface characterization techniques such as SEM-EDS, XRD and EMP were used to study the microstructure of the alloys. The electrocatalytic activity of these coatings was investigated using steady-state polarization and galvanostatic technique. This study revealed that the Fe-Mo-P coating could be considered as a promising cathode material for the hydrogen evolution reaction (HER). The results showed an important decrease of hydrogen overpotential for Fe-Mo-P alloy as compared to that of Fe-Mo and especially MS which is a traditional cathode in chlorate industry. The HER overpotential for Fe54Mo30P16 at current density of 250 mA cm-2 was decreased by 30% in comparison to that of MS (1029 mV), and by 16.5% to that of Fe53Mo47 coating (857 mV).INTRODUCTIONSodium chlorate is used for manufacturing of several daily consumption products. This chemical is mainly employed for the production of chlorine dioxide (ClO2) that is a bleaching agent used in the pulp and paper industry. The ClO2 is also consumed for generation of perchlorates, chlorites and other chlorates, as an herbicide and in uranium processing (Cornell, 2002). Sodium chlorate is produced industrially via following overall formula in un-divided electrochemical cell (Nylén & Cornell, 2009):"

Jan 1, 2016

By Atulya Verma, Samantha Espley, Nashel Kalaka

Numerical modelling simulations of proposed mining sequences are used to evaluate mining induced stress concentrations and their migration associated with the progress of mining. This analysis is a standard practice for most prospective mining projects at various levels of feasibility study. The studies are usually initiated at the beginning of the mining cycle, on a global scale, and are maintained and updated throughout the life of mine (LoM) to identify or address local issues and the required remedies as and when needed. Developments in numerical modeling techniques along with advancements in computing technology and data storage/management capacity have given rock engineers access to a huge volume of data that needs to be analyzed and assessed. The most common approach to numerically evaluate stress concentrations and migrations in underground mines is to select the points of interest in a given volume such as the back of an excavation or points within pillars around critical infrastructure, and plot the stresses or a derivative of stresses over time to represent life of mine concentrations and migrations of stresses. The problem with this approach is the sharp gradient of stresses close to excavation boundaries. Slight changes in the location of selected points can change the stress concentration and migration patterns substantially and all generalized statements about LoM risk can be challenged in one way or another. For global stresses, the most common current approach of data analysis is by viewing series of pictures representing stress contours. In this approach, it is easy to overlook some critical detail and/or be masked by personal preferences of contour/picture representation. To overcome the problem of representing and analyzing huge volume of stress simulation data, the authors, through their experience at different mining operations, developed a volume-based technique to reliably evaluate mining-induced stress concentrations and migrations. The volume-based approach is for risk-based assessments of adjacent regions in the rockmass, in and around planned stoping excavations. The volume of interest is the entire ore body that is planned to be mined, but it could be just a part of the ore body depending on the specific use case. The risk identifiers are the induced stresses as compared to the strength of the rockmass. Over the LoM, the risk identifiers are tracked versus the corresponding excavation ratio of the zone. This approach is very effective in identifying the stages of mining that are contributing the most to the mining induced stress risk and the results can be used for proactive planning and mitigations measures such as alternative mining sequences, or stope sizes, or extraction methods. The approach has also been very successful in application at mature mines, particularly in assessing the re-initiation of mining in zone that has been dormant for some time. The volume-based approach allows for an assessment of the current state of the rockmass and the identification of future risks when planning resumption of mining activities.

Jan 1, 2023

By G. O. Oniyide, H. Yilmaz.

"This paper presents the result of the research done on the effect of temperature on the dilatancy of rocks from the Bushveld Igneous Complex (BIC), where the South African Platinum mines are located. The BIC has higher virgin rock temperature (VRT) than the gold mines of the ‘Witwatersrand Basin Complex’. If the platinum mines advance to ultra-deep levels as the gold mines, since the Merensky Reef has been reported to extend beyond 5km, then the virgin rock temperature at 5 km below surface would be approximately 140oC. Hence, there is a need for the investigation of rock behaviour at high temperatures. Five different rock types (norite, leuconorite, mottled anorthosite, pyroxenite and chromitite) were tested in a 2600 kN servo-controlled multi-purpose triaxial testing machine. The tests were done at a constant strain rate of 5 x 10-1 S-1 and a confining pressure of 10 MPa within temperature range of 20 °C (ambient temperature) to 140 °C. The results show a general strength reduction and increasing dilation angles with increasing temperatures. The results also demonstrate that dilation angle is close to the internal friction angle at lower temperatures; however, they are greater at higher temperatures.INTRODUCTIONMany challenges are faced with increasing depth of mining in underground mines. The most obvious are heat, in-situ stresses and those associated with logistics. Issues related to underground heat have mainly focused on the side effect of heat on workers' health, increasing production costs as a result of higher cost of ventilation. The effect of increasing temperature with increasing depth on the behavior of rock has not been given much consideration. Generally, gold mines in South Africa are deeper than the platinum mines but the latter have higher temperature gradient, which makes the platinum mines to be warmer at similar mining depths. Although the study of the effect temperature on the behaviour of rock can be beneficial to both gold and platinum mines, the focus of the research is limited to the platinum mines because of their higher temperature gradient. Donoghue (2004) stated that the virgin rock temperatures (VRT) and air temperatures increase with depth, due to the geothermal gradient and auto-compression, that is, compression of air by its own weight."

Jan 1, 2015

By M. du Plessis, D. F. Malan

"Crush pillars are designed to be in a crushed state whilst being formed at the mining face. The residual stress state of these failed pillars provides a local support function in mining stopes and is used in the majority of the intermediate depth South African platinum mines. On mines utilising crush pillars, the pillar dimensions are selected to achieve a width to height ratio of approximately two. This is not achieved in most cases as a result of practical mining problems and poor pillar-cutting discipline. Furthermore, pillar dimensions are seldom adjusted to compensate for the various factors governing crush pillar behaviour. The pillars should, however, be in a crushed state whilst being formed or whilst still in close proximity to the mining face to prevent potential damaging seismicity.An underground investigation was conducted into the behaviour of the crush pillars in a trial site on the Merensky Reef at Lonmin Plc. The aim of this investigation was to examine the mechanism of pillar crushing and the related rock mass behaviour. The underground test results and pillar behaviour are compared to a limit equilibrium model to investigate if the model provides a useful approximation of the behaviour of the crush pillars. This paper details some of the preliminary findings.INTRODUCTIONOn most mining operations, the design of crush pillars is based on trial and error. As the pillar strength is unknown, the pillar sizes are adjusted to obtain the correct behaviour. Crush pillar dimensions are generally selected to give a width to height ratio (w:h) of approximately 2:1, (Ryder and Jager, 2002). Several factors affect the behaviour of the crush pillars and in many cases satisfactory pillar crushing is not achieved. This results in a seismic hazard in many of the mines using crush pillars. If pillar crushing is not initiated whilst the pillar is being formed at the mining face, as the mining face advances and the pillars move to the back area of a stope, some pillars may burst while oversized pillars may punch into the footwall. If pillars are designed in such a way that they are fractured during cutting by the face abutment stresses so that the pillars will already have yielded and reached their residual strength, further compression of the pillars will be associated with an increase in load and stability will be ensured, (Ozbay and Roberts, 1988). The stiffness of the strata must therefore be greater than the post-peak stiffness of the pillar (Figure 1) or violent pillar failure and hanging wall instability will occur. The pillar design should be aimed at determining pillar dimensions for which the post-peak curve of the pillar is as flat as possible."

Jan 1, 2015

By J. G. Lang

"This paper gives an outline of the principles used in E.M. wire rope testing, showing the practical application of the device and its value in industry and in mining operations.It presents: case histories involving deterioration, such as corrosion, peening and broken wires; anomalies indicating conditions peculiar to drum hoists and friction hoists; tests of locked coil ropes; low-frequency testing; and experiments and development."

Jan 1, 1969