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By J. Bal, V. D. Dao, W. Li

"SynopsisThis study proposes a methodology for evaluating the risk of coal bumps in multiple-seam longwall mining. Both the stress field and the total energy release (TER) during retreat were evaluated in the specified case involving multiple-seam mining using the LaModel program. The results of numerical simulations indicated that both the peak vertical stresses on the panel edges and the peak TERs in the outby longwalls increased significantly as the horizontal offsets were reduced from 60 m to zero. With the comprehensive consideration of the stress field and TERs, a conservative offset of 60 m was ultimately adopted when developing the gateroads of the lower panel in the field. The field measurements indicated that coal bumps were avoided completely by employing the proposed design, and the maximum roof-to-floor and rib-to-rib convergences of the tailgate during retreat were only 360 mm and 576 mm, respectively.IntroductionCoal bumps – sudden, violent bursts of coal – pose a serious threat to the safe excavation of coal. Their occurrence depends on the properties of the surrounding rocks, stress field, and dynamic disturbance. The complexity of the mechanism of coal bumps is further enhanced in multiple-seam mining due to seam interaction. Multiple-seam mining is most frequently found in the coalfields in eastern China, such as Xuzhou, Xinwen, Zaozhuang, and Huainan. In the past, due to issues of availability, economics, and ignorance of the potential risk in multipleseam mining, coal seams in such conditions were mined without proper planning to account for seam interaction. Fortunately, studies published over the past three decades have raised awareness of the problems associated with multiple-seam mining, and indicated that the ground control issues induced by multiple-seam mining can be avoided and/or minimized with proper planning.A number of technical studies pertaining to the design of multiple-seam mines have been published. These studies can be divided into two groups based on their methodologies of design: empirical (Chekan and Listak, 1993; Haycocks and Zhou, 1990, Matetic et al.; 1987a, 1987b) and numerical approaches (Li et al., 2000; Maleki, 2007; Mark, 2007; Peng, 2007; Zipf, 2005). The majority of the extant studies on the interaction mechanisms in multiple-seam mining have focused on the load transfer during operation, resulting in the proposal of the pressure bulb theory (Forrest et al., 1987; Haycocks and Karmis, 1983; Peng, 2008; Peng and Chandra, 1980) and pressure arch theory (Holland, 1973; Oram and Ponder, 1997) to guide multiple-seam mine design. However, neither, of these theories can be used to evaluate the potential for coal bumps."

Jan 1, 2015

By H. A. D. Kirsten

Written contribution by L.J. Besaanst I am a Mechanical Engineering Technician (T3), and wish to further my education to at least NHD (T4) level. I read your paper in the Journal of The South African Institute of Mining and Metallurgy with great interest, and must compliment you on its brilliance. However, there are some questions I should like to ask, and certain points I should like to highlight. I should appreciate your comments. Written contribution by J.F. Curtis The comprehensive and finely detailed survey of, and proposals for, engineering education in South Africa reflects the author's wide experience in the needs for, and the provision of, such education. This paper wil make a major contribution to the enhancement of the profession of engineering and the improvement in quality of engineering activities in South Africa. Contribution by G.W. Annandalet I have studied your paper in some detail, and am of the opinion that it makes an important contribution to the topic of the development of technological manpower, which is currently being debated in South Africa at al levels. Debate on this topic has risen above the level of academic discussion; it has been discussed by the Economic Advisory Council of the President, and is being considered at Ministerial level. Author's reply to L.J. Besaans Thank you for your contribution and complimentary remarks. As you have pointed out, there are certainly many aspects that will have to be addressed in the resolution of the crisis in engineering education. I trust that the following comments satisfactorily answer the queries you have raised. Author's General Comments Since publication of the paper, attention has become focused on the provision of employment opportunities an aspect not dealt with specifically in the paper. The following comments serve to indicate some of the directions in which job opportunities will have to be developed in the numbers that will be required.

Jan 1, 1991

By S. A. Villalobos, F. A. Villalobos, and L. E. Aguilera

Rockburst events have been a serious problem for many years in many mines worldwide, and in particular at El Teniente mine in Chile. El Teniente is the largest copper mine in the world, located in the Andes Cordillera where high stress levels are present due to intensing mining activity in addition to complex geology. Consequently, the study and management of the rockburst threat are necessary. In this work, the case of the Diablo Regimiento (DR) mine within El Teniente is studied. The energy capacity of dynamic support systems is determined for different tunnel geometries based on two kinetic methodologies, using data from DR. Initially, rockburst potential is determined by means of a stress analysis around different tunnel geometries through the boundary elements method. In the first methodology a yielding zone (YZ) is estimated for each excavation geometry using the finite element method FEM. The second methodology involves the definition and determination of a critical strain energy (SE) around each excavation geometry using a FEM numerical analysis. In both cases, peak particle velocity PPV is estimated by a scaling law, which is subsequently adjusted due to tunnel amplification effects. According to the results, and knowing the working energy capacity applied in DR mine, it was found that the values of energy capacity for the rock dynamic supports were better estimated by the YZ-PPV approach than by the SE approach.

Sep 1, 2022

By D. P. Roberts

This investigation aimed to simulate the experiments performed by Nic Gay (Gay, N.C.1976. Fracture growth around openings in large blocks of rock subjected to uniaxial and biaxial compression. International journal of Rock Mechanics and Minining Sciences and Geomechical Abstracts, vol. 13. pp. 231-243) on fracture growth around openings in blocks of rock subjected to uniaxial and biaxial compression, using the Elfen discrete element code. The results of the physical experiments indicated a number of trends that were successfully replicated in the numerical simulations, including crushing ahead of the face, the formation of a sub-vertical tensile fracture at centre-span, the formation of groups of fractures originating from the crushed face zone, the formation of large corner-to-corner fractures which precede sample failure, and linking of slot corner and sample corner fractures leading to sample failure. In addition, other features were apparent that were not reported by Gay. It is believed that these took the form of conjugate shear fractures (as reported by Gay in a previous paper) and other features that may have been altered or inhibited by the presence of pre-existing structure in the physical samples. It was found that the samples, though nominally made up of the same rock type, must have had significantly differing properties. The presence of pre-existing structures may have contributed to this discrepancy. Strain measurements from the physical experiments were reasonably well matched, except where the gauge lay directly in the path of advancing fractures.

Jan 1, 2012

By T. Szendrei and S. Tose

Historical approaches to the problem of flyrock based on correlation studies and regression analysis, including artificial neural networks and similar techniques, are inherently incapable of addressing two core issues – root causes of flyrock and projection velocity. A further shortcoming of correlation techniques is that they give no information on the influence of rock size and shape on the flight distance. The scaled depth of burial model for crater blasting in the collar zone and bench face does not specifically address the question of flyrock velocity. A third approach, based on flight trajectory calculations, often neglects the very significant effects of air resistance on the trajectory. Some trajectory models incorporate air resistance but use an implausible fragment velocity model that cannot propel sizeable rocks to distances much beyond 150 m. Nonetheless, trajectory calculation incorporating the effects of air drag affords the most promising approach to the prediction of flyrock range. A unique and insightful feature of the proposed realistic flight modelling is that it collapses all suspected causes of flyrock, many of which are not well understood, to just a single parameter – the launch velocity. This indicates that the root causes of flyrock lie in the mechanisms of momentum transfer to broken rock and suggests new avenues of study.

Dec 13, 2022

By D. Moses, J. A. Onyango

Carbonatites are generally competent rock masses with rock mass rating class II rating 60–74. In spite of their competency, they tend to be affected by weak features like manganese-iron veins and/or in situ rock damage due to brecciation associated with carbonatite complexes. Rock slope failure in such hard rocks is complex since such structures within the rock mass form weak links that could potentially control slope instability. In this contribution, a numerical simulation using phase2 v 7.0 was carried out to investigate the influence of in situ rock damage on the stability of mine pit walls. The outcome reveals that, the existence of breccia in the competent rock mass has the capability to reduce the slope stability performance particularly at gentle dipping angles of emplacement in close range to the slope toe. However, as the emplacement position of breccia moves away from the pit wall, the stability performance increases at gentle dipping angle <50º. On the contrary, at the dipping angle of 50° the performance of slope reduced, and at steeper angles >50° the impact becomes negligible. Thus, from a series of analyses, mine design in brecciated rock masses, the ratio of 1:5 between the breccia distance from slope toe and pit depth should be implemented to counter its impact, and if the breccia is within or close to the pit limit, a deliberate effort must be made to mine it out.

Sep 1, 2025

By E. K. Mutinda, D. K. Maina, R. M. Kasomo, B. O. Alunda

Assessment of blast fragment size distribution is critical in mining operations because it is the initial step towards mineral extraction. Different empirical models and techniques are available for predicting and investigating the consequences of blasting, one of which is the Kuznetsov Cunningham-Ouchterlony (KCO) model. In this paper we summarize the advances in the empirical models from inception until now, and explore the improvements that have been made so far with particular emphasis is on the most recent KCO model. Utilization of the model and the errors that arise between expected and the actual outcomes are analysed. The results indicate that the KCO model remains useful for predicting the blast fragmentation at limestone mine sites, despite the availability of other advanced prediction models. It is also a valuable instrument for pre-surveying the impact of varying certain parameters of a blast plan.

Mar 1, 2021

By N. Snyders, I. Mwandawande, S. M. Bradshaw, M. Karimi

"Computational fluid dynamics (CFD) was applied to predict the average gas holdup and the axial gas holdup variation in a 13.5 m high cylindrical column 0.91 m diameter. The column was operating in batch mode. A Eulerian-Eulerian multiphase approach with appropriate interphase momentum exchange terms was applied to simulate the gas-liquid flow inside the column. Turbulence in the continuous phase was modelled using the k-_ realizable turbulence model. The predicted average gas holdup values were in good agreement with experimental data. The axial gas holdup prediction was generally good for the middle and top parts of the column, but was over-predicted for the bottom part of the column. Bubble velocity profiles were observed in which the axial velocity of the air bubbles decreased with height in the column. This may be related to the upward increase in gas holdup in the column. Simulations were also conducted to compare the gas holdup predicted with the universal, the Schiller-Naumann, and the Morsi-Alexander drag models. The gas holdup predictions for the three drag models were not significantly different. IntroductionColumn flotation is an important concentration technology that is used in the mineral processing and coal beneficiation industries. The growing interest in the use of column flotation in mineral processing has been attributed to the simpler flotation circuits and improved metallurgical performance compared to conventional flotation cells (Finch and Dobby, 1990). Flotation columns have also found other applications outside mineral processing, such as de-inking of recycled paper (Finch and Hardie, 1999).In column flotation, a rising swarm of air bubbles generated by means of air spargers is employed to collect the valuable mineral particles and separate them from the gangue minerals in a countercurrent process. Wash water, which is continuously fed at the top of the column, is used to eliminate entrained particles and stabilize the froth. The column volume can be divided into two sections – the collection zone in which the bubbles collect the floatable mineral particles, and the cleaning zone (or froth zone) where product upgrading is enhanced through the removal of unwanted particles entrained in the water mixed with bubbles from the collection zone."

Jan 1, 2019

By D. F. Malan, D. Ile

This study explores the use of backfill in hard rock bord-and-pillar mines to increase the pillar strength and extraction ratio at depth. The use of backfill will also minimize the requirement for tailings storage on surface and the risk of environmental damage. A literature survey indicated that backfill is extensively used in coal mines, but rarely in hard rock bord-and-pillar mines. To simulate the effect of backfill confinement on pillar strength, an extension of the limit equilibrium model is proposed. Numerical modelling of an actual platinum mine layout is used to illustrate the beneficial effect of backfill on pillar stability at greater depths. The magnitude of confinement exerted by the backfill on the pillar sidewalls is unknown, however, and this needs to be quantified using experimental backfill mining sections equipped with suitable instrumentation.

May 3, 2023

By D. T. Williamson, B. P. Gilbertson

Satellite observation of mine-dump vegetation by B. P. GILBERTSON, M.Sc. (Phys.) (Visitor) and D. T. WILLlAMSON, B.A., LLB., B.A. Hons. (Visitor) NASA&apos;s first Earth Resources Technology Satellite (ERTS-I) was launched on 23rd July, 1972, and has subsequently gathered multispectral imagery of most of Southern Africa from an orbital altitude of 900 km. Images of the Witwaters rand area have been studied in an attempt to differentiate between mine dumps having varying degrees of vegetative cover. At this stage it is clear that the various mine dumps can be located and identified, and differences in vegetative cover can be seen and measured. Patterns of vegetative growth, some characteristic to particular dumps, can also be seen.

Jan 2, 1974

By S. Visage

By 1984 Iscor&apos;s first direct-reduction plant will be operating at the Vanderbijlpark Works, and for the fin;t time the Corporation will have an alternative method to the blast furnace for producing iron from ore. The performance of Iscor&apos;s four-kiln plant, which will be the largest coal-based plant in the world producing sponge iron, will undoubtedly be watched with great interest by steelmakers throughout the world. Beneficiation of tin The Southeast Asia Tin Research and Development (SEATRAD) Centre is a regional oganization, formed by the Governments of Indonesia, Malaysia, and Thailand with assistance from the United Nations, to conduct, coordinate, and promote research and training in the various fields of tin production, including geology, prospecting, mining, mineral processing, and smelting.

Jan 1, 1982

Prof C T O&apos;Connor holds the degrees of BSc, BSc Hons, University of Cape Town (UCT), where he started his academic Lecturer in the Department of Physical Chemistry in 1976. Mr P Smith, educated in England and the former Southern Rhodesia, joined Gold Fields of South Africa in 1966 as a Metallurgical Learner Official. After obtaining a BSc Eng at the University of the Witwatersrand in 1972, he returned to Gold Fields. Mr P D K Robinson was born in Zimbabwe, and was educated at Dale College in Kingwilliamstown, matriculating in 1952. He holds a Mine Surveyor&apos;s Certificate obtained in 1961) and a Mine Manager&apos;s Certificate (obtained in 1966), as well as an EDP from the University of the Witwatersrand.

Jan 1, 1991

COUNCIL The following served on Council during the year under review Office Bearers Dr J. P. Hugo (President), P. W. J. van Rensburg and Professor R. P. Plewman (Vice-Presidents), Professor D. D. Howat (Immediate Past-President), and D. G. Maxwell (Honorary Treasurer). Ordinary Members of Council H. P. Carlisle (until February), R. C. Espley-Jones, G. H. Grange, Dr D. I. Legge, W. W. Malan, J. B. Mudd, Dr R. E. Robinson, Dr M. D. G. Salamon, L. W. P. van den Bosch, D. A. Viljoen (co-opted May 1973), and P. A. von Wielligh. Branch Chairmen A. Bain (Witbank-Middelburg Branch), C. J. Isaac (O.F.S. Branch). Past Presidents Serving on Council R. J. Adamson, M. Barcza, H. Britten, J. K. E. Douglas, R. C. J. Goode, P. Lambooy, Professor J. de V. Lambrechts, Dr J. T. McIntyre, J. F. Reid, and V. C. Robinson. Ten Council meetings were held during the year, with an average attendance of 18, and the standing committees held 29 meetings. MEMBERSHIP Twelve Fellows, ten Members, twenty-one Graduates, eleven Associates, thirty-one Students, and forty-two Company Affiliates were elected during the year. One Member was reinstated. Eight Fellows, two Members, and two Associates were admitted to retired membership. Four Graduates were transferred to Members, one Associate to Member, three Students to Members, one Graduate to Associate, two Students to Graduates, and one Student to Associate. Your Council records with deep regret the death during the year of the following : D. R. Campbell, J. Daniel, M. J. Dennehy, and F. S. C. Rogers (Life Fellows) ; W. T. balling and T. Pryor (Life Members); C. Boocock, W. Drake R. J. Moore, M. P. Pearse, J. M Pike, W. A. Schwezoff, A. I. Suss man, and L. G. S. Wright (Fellows) ; A. F. Chalmers (Member) ; and W. R. Gerry and G. T. Rimmer(Associates). A comparative statement of membership as at 30th June, 1973, and the end of the previous year it shown in the following tabulation: 30th - 30th June, - June, 1972 - 1973 Honorary Life Fellows 5 - 4 Honorary Fellows 13 - 9 Life Fellows 181 - 177 Fellows 541 - 536 Members 479 - 487 Graduates 115 - 128 Associates 182 - 186 Students 162 - 183 Company Affiliates 24 - 64 1 702 - 1 774 JOURNAL The papers that were published in the Journal during the year are listed below: August, 1972 The effects of chromium oxide, iron oxide, and calcium oxide on the liquidus temperatures, viscosities, and electrical conductivities of slags in the system MgO-Al2O3-SiO2, by M. S. Rennie, D. D. Howat, and P. R. Jochens A study of the dust exposure of South African white gold miners, by R. J. Page-Shipp and Elizabeth Harris A forecast of the coal and uranium requirements for electric power generation in South Africa, by E. J. Maunders September, 1972 Mine management by objectives, by A. A. Hazell Some aspects of the deformation behaviour and temperature rise during instantaneous compression loading of high purity aluminium, by H. J. E. Hamel Computer control of flotation at the Ecstall concentrator, by M. P. Amsden, C. Chapman, and M. G. Reading Optimizing the public gains from the exploitation of mineral resources, by A. Azis and J. Zwartendyk October, 1972 Presidential Address: Nuclear energy: its interactions with mining and metallurgy, by J. P. Hugo Presidentsrede: Kernenergie: sy wissel-werkinge met mynbou en metallurgic, deur J. P. Hugo Raise-boring experiences in the gold mines of the Anglo American Corporation Group, by J. W. Wilson and P. C. Graham November, 1972 Materials for winding plant components, by G. T. van Rooyen An analytical solution to the batch-comminution equation, by R. P. King A new approach to the study of human factors in stope productivity, by A. C. Lawrence Fundamental studies of the flotation process: the work of the National Institute for Metallurgy, by N. P. Finkelstein and V. M. Lovell Growing use of deionised water in surface coating techniques, by W. F. Lorch December, 1972 The development and application of a computer system to aid in the planning of production in mines, by F. H. Deist, L. F. Duvel, J. D. Austin, and H. D. Small PERT, and how PERT techniques can be used in modern mine management, by E. J. Boome and A. C. Schmidt A critical comparison of specific cooling power and the wet kata thermometer in hot mining environments, by J. de V. Lambrechts January, 1973 Liquidus temperatures in the Cr-Fe-Si system in the composition range representative of ferrochromium-silicide produced in South Africa, by J. C. M. Wethmar, D. D. Howat, P. R. Jochens, and O. A. W. Strydom Platinoids in the Witwatersrand System, by C. A. Cousins The development of a continuous recording scintillation counter mounted on a cyclometer, by P. D. Teens and D. Visser February, 1973 Computer analysis, modelling, and optimisation of gold recovery plants of the Anglo American Group, by M. I. Brittan and E. J. J. van Vuuren The significance of the mineralogical and surface characteristics of gold grains in the recovery process, by C. E. Feather and G. M. Keen Statistical valuation of diamondiferous deposits, by H. S. Sichel March, 1973 The effect of the reactivity of lime on desulphurisation efficiency in the basic oxygen furnace, by A. A. Hejja, D. D. Howat, and P. R. Jochens A review of real-time particle size analysers, by A. L. Hinde In situ measurements of the surface heat transfer coefficient in underground airways, by K. R. Vest April, 1973 An investigation into the kinetics and mechanisms of the oxidation of iron (II) by oxygen in aqueous chloride solutions, by R. P. Colborn and M. J. Nicol Electric smelting at Rustenburg Platinum Mines Limited of nickel-copper concentrates containing platinum-group metals, by J. C. Mostert and P. N. Roberts Metallurgical considerations in the

Jan 10, 1973

By Mike de Wit

Of the approximately 6,500 kimberlites known to date, less than 3% are diamondiferous and less than half of those are economically viable. Admittedly, this is a global figure and varies from area to area much depending on geological, logistical, and political circumstances. The number of diamond-bearing kimberlites is an important geobarometer, and an age-frequency profile has been compiled in order to identify diamond metallogenic epochs and provinces. Four primary diamond clusters have been recognized: Siberia (332-370Ma), Kaapvaal South(114-144Ma), Kaapvaal Southwest(84-95Ma), and Slave (52-55Ma). In addition, three secondary clusters are the Kaapvaal Central (S06-S38Ma), the Man Craton (139-lS3Ma) and the Kasai Craton (120-130Ma). The Kaapvaal is the only area where kimberlites with diamonds were discovered between 1870 and 1925, except for the Prairie Creek discovery in North America in 1906 and Colossus in Zimbabwe in 1907. Between 1906 and 1940 no major diamondiferous kimberlites were discovered, but many of Africa&apos;s alluvial deposits were found and exploited in that period. Advances in scientific prospecting in the 1940&apos;s rapidly accelerated the discovery rate that peaked in the 1990&apos;s; 39 diamondiferous occurrences were found in the 1980&apos;s, of which 8 became mines and 5 are in feasibility, and nearly 450ha of kimberlite was added to the global resource base. Despite the accelerated exploration expenditure, the last decade (e.g. 2000-2009) has been the leanest since the 1940&apos;s. The most important reason for this decline in exploration success is that any undiscovered deposits are largely buried by younger cover. Understanding complex and geophysical noisy basement geology, as well as decomposition of path-finder minerals are major challenges to further exploration success. Major investments in basic geological expertise and field research will have to be made in order to secure future diamond resources. Integrated geophysical studies, geochemistry diamond forensics, and improved imaging of Earth&apos;s upper mantle are perhaps foremost in this requirement, but the costs of these activities are such that government support will be required if countries are to sustain their diamond mining industry.

Jan 1, 2010

By R. W. O. Kersten

"The aim was to investigate stable pillar design procedures currently in use on chrome and platinum mines, subject them to a critical appraisal, and review some of the alternatives proposed in the literature. It is concluded that these pillar design methodologies suffer from drawbacks that can be detrimental to the mining industry and that an improvement is essential.It was decided that the increased availability of analytical models and failure criteria could be exploited to update the empirical to an analytical/empirical method. The proposed methodology adopted FLAC2D simulations using the Hoek-Brown failure criterion to calculate full stress-deformation curves for typical pillars. The mine stiffness concept was introduced to determine the pillar load, integrating the influence of the pillar and strata stiffness and mining geometry.The proposed methodology was calibrated by comparing experimental and predicted deformations and failure depth of pillars in one hard-rock mine. The conclusion was that the methodology is an improvement over the one currently in use. An improved factor of safety is given by the intersection point of curves for the stiffness of the system and the pillar strength. IntroductionThe paper describes part of the findings of a PhD thesis (Kersten, 2016) on an alternative stable pillar design methodology. This publication contains sufficient information to implement the method for further interpretation and testing. A detailed comparison of measured and predicted data is dealt with in the thesis, and the results show that there is promise in the methodology.The design of stable pillars in mining is of fundamental importance, not only in the Bushveld Complex mines but throughout the mining industry. Wherever mining occurs, pillars are formed at some stage and it is essential to predict their behaviour, i.e. whether they will burst, yield, or remain stable. Although of crucial importance, pillar design still suffers from major shortcomings and weaknesses."

May 1, 2019

By K. Moxham, A. Smit, R. Pickering

Since the early 1970s research has been ongoing to develop a cost-effective way of continuously mining the narrow reef, hard rock, typical of South African gold and platinum mines. In the late1980s it was shown that impact ripping was a practical solution for the deep gold mines. In March2001 Lonmin and Sandvik agreed to co-operate in an endeavour to design and manufacture a prototype narrow reef mining machine with the ultimate aim of producing such a machine on a commercial basis that would enable Lonmin to create a safer and more productive environment within its mines and for Sandvik to enhance its leading position as a supplier of a new generation hard rock cutting machine. This paper describes the developed technology, the current progress of the delivery of the required objectives and the optimum mining layout for the roll-out of the mining method.

Jan 1, 2006

By J. C. Vreugdenburg, B. A. Dippenaar, J. Muller, T. L. de Vries

Iron ore fines are agglomerated in the sintering process to produce sinter: an important feed material for blast furnaces worldwide. A model of the iron ore sintering process has been developed with the objective of being representative of the sinter pot test, the standard laboratory process in which the behaviour of specific sinter feed mixtures is evaluated. The model aims to predict sinter quality, including chemical quality and physical strength, as well as key sinter process performance parameters such as production rate and fuel consumption rate. The model uses the finite difference method (FDM) to solve heat and mass distributions within the sinter pot over the sinter bed height and time dimensions. This method can further be used for establishing empirical relationships with measured sinter properties. Inputs into the model include the feed material physical properties, chemical compositions, and boundary conditions that vary over time. Sub-models describe relationships between applied pressure differential and gas flow rate through the bed of granulated fine ore particles, combustion of carbonaceous material, calcination of fluxes, evaporation and condensation of water, and melting and solidification. Four sinter pot tests were performed and the model predictions validated against temperatures measured at depths of 100, 230, and 420 mm. Differences between predicted and measured temperatures indicated the need for optimization of some model parameters that are uncertain. Optimization resulted in an improvement in the correlation between the predicted and measured temperatures for all tests, although an acceptable level of agreement was not achieved in all cases. Using these parameter values, reasonable agreement was found in terms of typical performance parameters for three out of the four tests.

Jan 1, 2014

By N. Snyders, I. Mwandawande, S. M. Bradshaw, M. Karimi

"Flotation columns are normally operated at optimal superficial gas velocities to maintain bubbly flow conditions. However, with increasing superficial gas velocity, loss of bubbly flow may occur with adverse effects on column performance. It is therefore important to identify the maximum superficial gas velocity above which loss of bubbly flow occurs. The maximum superficial gas velocity is usually obtained from a gas holdup versus superficial gas velocity plot in which the linear portion of the graph represents bubbly flow while deviation from the linear relationship indicates a change from the bubbly flow to the churn-turbulent regime. However, this method is difficult to use when the transition from bubbly flow to churn-turbulent flow is gradual, as happens in the presence of frothers. We present two alternative methods in which the flow regime in the column is distinguished by means of radial gas holdup profiles and gas holdup versus time graphs obtained from CFD simulations. Bubbly flow was characterized by saddle-shaped profiles with three distinct peaks, or saddle-shaped profiles with two near-wall peaks and a central minimum, or flat profiles with intermediate features between saddle and parabolic gas holdup profiles. The transition regime was gradual and characterized by flat to parabolic gas holdup profiles that become steeper with increasing superficial gas velocity. The churn-turbulent flow was distinguished by steep parabolic radial gas holdup profiles. Gas holdup versus time graphs were also used to define flow regimes with a constant gas holdup indicating bubbly flow, while wide gas holdup variations indicate churn-turbulent flow. IntroductionTwo types of flow can be distinguished in gasliquid flows in bubble columns: bubbly flow and churn-turbulent flow. The bubbly flow regime is characterized by uniform flow of bubbles of uniform size. Churn-turbulent flow, on the other hand, is characterized by a wide variation in bubble sizes with large bubbles rising rapidly and causing liquid circulation.Flotation columns are normally operated in the bubbly flow regime, which is the optimal condition for column flotation (Finch and Dobby, 1990; Yianatos and Finch, 1990; Ityokumbul, 1992). However, it has been generally observed that flotation column performance deteriorates when the superficial gas velocity is increased beyond a certain limit where the flow regime changes from bubbly flow to churn-turbulent flow (Xu, Finch, and Uribe-Salas, 1991). The identification of this critical or maximum superficial gas velocity is therefore important for optimal operation of flotation columns."

Feb 1, 2019

By D. F. Malan, R. P. Els

The limit equilibrium model, used in displacement discontinuity codes, is a popular method to simulate pillar failure. This paper investigates the use of physical modelling to calibrate this model. For the experiments, an artificial pillar material was prepared and cubes were poured using the standard 100 mm × 100 mm civil engineering concrete moulds. The friction angle between the cubes and the platens of the testing machine was varied by using soap and sandpaper. Different modes of failure were observed depending on the friction angle. Of interest is that significant loadshedding was recorded for some specimens which visually remained mostly intact. This highlights the difficulty of classifying pillars as failed or intact in underground stopes where spalling is observed. The laboratory models enabled a more precise calibration of the limit equilibrium model compared to previous attempts. Guidelines to assist with calibration of the model are given in the paper. The limit equilibrium model appears to be a useful approximation of the pillar failure as it could simulate the stress-strain behaviour of the laboratory models.

May 3, 2023

By A. M. Bauristhene

Ti-64, which accounts for more than 50% of the worldwide titanium tonnage, has found commercial importance in industries requiring components with high specific strength and resistance to corrosion. Investment casting is the preferred production method due to the difficult machinability of the alloy. This study was aimed at investigating the mechanism and the extent of alpha case formation on Ti-64 components cast using the investment casting method with YFSZ (yttria fully-stabilized zirconia) shell moulds after vacuum induction melting. The extent of the reaction between the mould hot face and the molten metal has been studied by varying parameters such as soaking temperature and mould hot face composition, and examining their effects on the reaction with the mould. An increase in the soaking temperature had an effect on the alpha case, both in appearance and hardness, but had no effect on contamination levels by carbon, oxygen, and nitrogen. The depth of alpha case increased with soaking temperature, increasing from 35 µm to 161 µm with an increase in temperature from 1200°C to 1400°C. The micro-hardness profiles provided insight into the effect of the alpha case on the mechanical properties of the Ti-64 alloy by displaying hardness values of 1000 HV0.1 and above, but could not be solely utilized to determine the alpha case penetration depth due to microstructural differences in the unaffected Ti-64, in particular the martensitic microstructure that formed with a fast cooling rate from a higher temperature. Levels of expected contaminants such as Zr, Y, 0, and C were low. The addition of the colloidal zirconia binder affected the interfacial reactions. YFSZ proved to be a thermodynamically stable refractory material, with the alpha case possibly forming as a result of segregation.

Jan 1, 2013