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By S. Parada, P. T. Jones, M. Guo, S. Smets

The corrosion behaviour of a high-quality rebonded magnesia-chromite refractory in contact with a vacuum oxygen decarburization (VOD) slag with high Al2O3content (15?20 mass per cent) is investigated under VOD process conditions by rotating finger tests in a vacuum induction furnace. The refractory degradation mechanisms are studied by the characterization of corroded microstructures using scanning electron microscopy, equipped with energy dispersive spectroscopy. The influence on the refractory wear of the process temperature and the Al2O3content in the slag is discussed. Keywords: corrosion, magnesia-chromite refractory, VOD slags, vacuum induction furnace

Jan 1, 2004

By A. W. Dougall, T. M. Mmola

"SynopsisThe global resources and commodities market has become highly competitive. While southern Africa’s abundance of minerals resources is still unrivalled, it has lost considerable dominance in terms of production output. The sustainability of southern Africa’s mining industry is increasingly becoming dependent on its ability to manage the performance of its operations well. A valuable tool for monitoring and managing performance is the use of key performance areas (KPAs) – which are those areas of performance that are reflected explicitly or implicitly in the vision and strategies of an organization and reflect the critical success factors of the organization. This paper is a review of key performance areas in the southern African mining delivery environment. The KPAs discussed in this paper have been identified by comparing KPAs of the several mining houses engaged in surface mining operations in southern Africa and then extracting those KPAs that are common to most of them. Although the authors support the view that each organization should develop KPAs to specifically fit its needs, the study reveals that five KPAs – safety and health, costs, product quality, fleet management, and delivery should form a default list that covers the key areas that any organization should consider when choosing KPAs. KPIs are those subsets of KPAs that we measure in order to manage KPAs.IntroductionThe global resources and commodities market has become highly competitive. While southern Africa’s abundance of minerals resources is still unrivalled, it has lost considerable dominance in terms of production output. The sustainability of southern Africa’s mining industry is increasingly becoming dependent on its ability to manage the performance of its operations well. A valuable tool for monitoring and managing performance is the use of key performance areas (KPAs), which are ‘those areas of performance that are reflected explicitly or implicitly in the vision and strategies of the organization’ (Barker, 1997). The terms KPA and KPI (key performance indicator) are often used interchangeably – whether correctly or erroneously is debatable. KPIs are ‘quantifiable measurements, agreed to beforehand, that reflect the critical success factors of an organization’ (O’Neill, 2007). Each KPA probably has multiple KPIs associated with it."

Jan 1, 2015

By H. Gumede

The occurrence of fracturing due to high stress levels is a major factor in hangingwall stability in deep level gold mine stopes. However, rock falls cannot be the result of these fractures alone. Rock falls can result only from the occurrence of unstable rock blocks defined by the interaction of the stress induced fractures and naturally occurring geological planes of weakness. These planes include bedding planes and joint set planes. However, there is a general lack of information on the characteristics of these planes (orientations, spacings and lengths)?it does not appear that any such systematic and quantified information, if collected, has been published. To remedy this situation to some extent, joint mapping exercises have been carried out in several geological environments in two gold mines. The data collected on joint geometry included orientation, spacing and length, and this information is included in the paper. In addition, the paper describes the use of the data collected to evaluate the potential for rock falls and the probability of failure of stope support

Jan 1, 2007

By P. Mokwena

Paper written on project work carried out in partial fulfilment of BSc (Hons) in Chemical Engineering Diamond synthesis has attracted a great deal of interest because of its exceptional properties and various applications. In this study, the chemical catalytic vapour deposition (CCVD) method was used to synthesize diamond films using acetylene as carbon source and hydrogen as carrier gas at a temperature of 1000°C, and their thermodynamic stability was studied. Photographic analysis revealed that these products are diamond films, Ramman spectroscopy confirmed that they are graphitic while confocal laser scanning microscopic image analyses proved that these diamonds films have structural defects due to iron impurity from the catalyst precursor. The quantity of diamonds films produced is also proportional to the acetylene to hydrogen ratio but these films are larger in size at lower acetylene to hydrogen ratio. Thermogravimetric analyses showed that transformation of these materials begins at 25°C but could not be used to determine if a temperature range below 25°C exists. The stability of these CCVD-synthesized diamonds also increases below 25°C when stored at different temperatures.

Jan 1, 2007

By H. Zhu

Coal desulphurization by flotation is often difficult due to the surface oxidation of coal pyrite. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were adopted to obtain detailed information about the surface oxidation of pyrite. Fresh pyrite surfaces were found to be hydrophilic, and to turn hydrophobic after initial oxidation, with oxidized products such as polysulphide FeSx and free sulphur. The oxidized products on the pyrite surface were reduced by an electrochemical method, returning the surfaces to a hydrophilic state and thus increasing the separating efficiency of coal from pyrite by flotation. Key words: surface oxidation, pyrite, SEM, XRD pattern, electrochemical modification.

Jan 1, 2002

By G. Song

"SynopsisAccording to the overlying rock strength and thickness of 10 shallow coal seams in China, the strata are classified into four types: weak and laminated strata (hereinafter referred to as WL), weak and massive strata (WM), strong and laminated strata (SL), and strong and massive strata (SM). The four types of strata, together with longwall panel height (M), panel length (L), and seam depth (H) are factors that influence the loads on hydraulic power supports. Principal component analysis was used to study the seven influencing factors. It turns out that seam depth (H) is multicollinear with WL, WM, SL, and SM. Thus the enumerated seven factors are divided into two models. In Model 1, six factors; panel height, panel length, and layer thickness of the four type strata are involved. In Model 2, three factors; panel height, panel length, and seam depth are included. Using multivariate regression analysis, two equations to calculate loads on supports are obtained for each model. The equations were applied to shallow coal seams. The equation of Model 1 is more accurate than that of Model 2, but Model 2 could be further used in deep coal seams. The equations were coded through VB programming to simplify the calculation.IntroductionTo ensure coal production in the long term, the focus of coal mining has been gradually shifted to the western areas of China in recent years due to rich coal resources in this region. Most of the coal seams in this area are shallow but the support loads are abnormally high. In these circumstances, the chock loads estimating methods used in the past do not work. If the rated working resistance of a support is larger than needed, the shield is unable to fully perform, while a lower working resistance would lead to accidents like shield crushing or even casualties. This problem is frequently found in shallow coal seams such as Shenfu-Dongsheng, Yulin, Tuha, Lingwu etc. (Zhang, 2011). Thus, to ensure safety and efficiency during mining, the estimation of support loads and selection of supports are of great significance."

Jan 1, 2015

A systematic study of groundwater conditions at eight underground mine sites exhibiting a wide range of groundwater qualities throughout Australia has been completed at the WA School of Mines. This has resulted in a new corrosivity classification for groundwater driven corrosion processes for cement grouted cable strand used in the Australian underground mining industry. The new corrosivity classification is simple to use and corrosion rates may be predicted from readily obtained in situ measurements of groundwater dissolved oxygen.

Jan 1, 2008

By C. M. Rule

Energy efficiency is currently a significant area of interest due to the Eskom power situation, which led to severe power impacts to the PGM, and indeed whole SA primary industries, in early 2008. Anglo Platinum has focused on energy efficiency for a number of years, especially in the concentrator operational area. New comminution technologies have been aggressively developed, which have shown real metallurgical efficiency gains as well as significant energy efficiency and saving potential for Anglo Platinum?s total electrical consumption as the company expands into a growing PGM demand market. This paper illustrates this programme?s activities, potential and considerable achievements to date.

Jan 1, 2009

The 102nd Annual General Meeting of The South African Institute of Mining and Metallurgy was held in the Gold Room, Transvaal Automobile Club, 60 5th Street, Lower Houghton, Johannesburg on Wednesday, 18th August, 1999. Obituaries The President announced the death, during the year, of the following members: Honorary Life Fellows and Past Presidents D.D. Howat Life Fellows O. Deane, J.S. van Zijl Fellow A.A. Hejja Retired Fellows A.L. Forder, C.B. Parker, A.C. Petersen, F.W.J. Ross Members J.S. Stanko, D.H. Gray Retired Member P.K. Bredell Retired Associate I.S. van Eyssen In memory of the deceased and in sympathy with the bereaved, all rose and observed a moment of silence.

Jan 1, 1999

By R Ratlou

Increased contamination due to sand in spiral feed has had a negative effect on the efficiency of spiral concentrators at Navigation Plant. The no. 1 seam at Kromdraai opencast, which was previously mined by underground bord and pillar methods, is now susceptible to spontaneous combustion because of air ingress into the old workings which are exposed in the opencast high wall. This posed a risk in the loss of reserves to burnt coal. As solutions, buffer blasting of the preceding cut to collapse bords and soft overburden dressing of un-collapsed bords were implemented to prevent air entering the workings. The latter remedy resulted in increased contamination due to addition of sand in Run of Mine. After evaluating alternatives, a low capital option was selected. The 110t/hr Teetered Bed Separator (TBS) has been installed, primarily to desand and upgrade the feed to the spiral concentrators. The unit indicated an upgrade with a yield increase of 0.4% during test work and is currently showing an overall plant yield increase of 0.97%.

Jan 1, 2006

By H. T. Ozkahraman

It is important to know the breakage mechanism in materials since this knowledge influences the results of subsequent grinding operations. There are two distinct failure mechanisms in breakage: one is tensile micro crack generation at low stresses, which leads to macroscopic failure by disintegration, and the other is formation of shear zones under heavier dynamic impact forces, which generates more fines as seen in crush zones in blasting. Tensile fracturing simply breaks the material into fragments. It is seen as the disintegration of the specimen into two or more separate fragments. This happens under the absence of lateral stresses and the material is free to expand. On the other hand, compressive-shear breakage produces finer fragments due to shear stresses. The first mechanism is observed in laboratory tensile and bending strength tests and the second mechanism is observed both in laboratory brittleness tests and in situ blasting operations under dynamic impact forces. The friability of rocks and ores can be determined by a brittleness test. A test apparatus to determine the friability value has been designed to suit limestone strength characteristics used in cement production. The friability and stored strain energy values of barite, marble, limestone and bauxite have been determined and compared with the corresponding Bond work index (Wi) and grindability index (G) of these materials. The physico-mechanical properties of the tested materials have also been determined to investigate their effect on friability and grinding. The relationships obtained between the indices were in surprisingly good agreement, with high correlations (0.99 and 0.97). The Bond work index and grindability index can therefore be estimated from the friability value, which can be determined more rapidly than the Bond test. But for certain rock types such as andesites the relationships does not hold. Key words: comminution, tensile stress, shear forces, brittleness test, strain energy.

Jan 1, 2010

By P. M. Cole

An unprecedented expansion of the global zinc industry is currently under way. While most new projects and plant upgrades remain committed to traditional processing technologies, recent advances in zinc solvent extraction (SX) have created opportunities for new process routes for both primary and secondary materials. The first commercial plant to use zinc SX for the mainstream processing of a low-grade ore is under construction and promises to become one of the lowest cost zinc producers. Several other oxide and sulphide projects in various stages of feasibility are considering the inclusion of SX in their process flowsheet. Zinc SX has also proved advantageous in the reprocessing of secondary materials, particularly for the treatment of zinc residues and furnace dusts. This review focuses on recent installations and projects underdevelopment that feature zinc SZ as the key separation step.

Jan 1, 2002

By P. J. N. Pells

A good thing is becoming a bad thing. Rock mass classification systems, that are so excellent for communications between engineers and geologists, and that can be valuable in categorizing project experience, are emasculating engineering geology and rock mechanics. Some engineering geologists have been sucked into thinking that Q and RMR values are all that is needed for engineering purposes, and seem to have put aside what can be learned from structural geology and geomorphology. Many rock mechanics engineers seem to have forgotten the scientific method. This paper attempts to redress the situation by showing how mechanics can be used in rock engineering to design with a similar rigour to that used in the fields of structural engineering, hydraulics and soil mechanics. It also attempts to remind practitioners of what can be achieved by skilled engineering geology.

Jan 1, 2008

By S. Asokan, CVGK Murty, R. Upadhyay

The principal mineral sources of titanium are rutile, anatase (both TiO2), ilmenite (FeTiO3) and leucoxene (a weathered ilmenite of variable concentration of TiO2 but similar to pseudorutile Fe2Ti3O9). These titaniferous minerals along with their value added products like Synthetic Rutile and TiO2 slag constitute ?Titanium Feed-stocks? for TiO2 pigment, Ti metal and welding electrodes industries. Unlike in other industries, the demand driver for titanium minerals is not the metal, but the TiO2 pigment ?a specialty chemical. Of the total titanium feedstocks usage in the world, about 93 % is consumed in TiO2pigment, with only about 3 % is utilized in metal production. India?s heavy mineral sands resources are among the largest and also one of the richest grades in the world. The country?s Ilmenite resource base stands at 348 million tonnes of Ilmenite (18% of the total world reserves)along with 18 million tonnes of Rutile, 21 million tonnes of Zircon, 8 million tonnes of Monazite, 107 million tonnes of Garnet and 107 million tonnes of Sillimanite. Though the grades (Total Heavy Minerals (THM) present in the sand) of Indian deposits are relatively rich, the contained ilmenite are termed as sulphate grade with 50-53% TiO2 (Chavra deposit of Kerala and Ratangiri deposit of Maharastra are an exception with 60% of TiO2). While superior grades with adequate reserves lead to a cost advantage in ilmenite production, the lower TiO2 percentage allows the direct use of Indian ilmenite only in the production of TiO2 pigment through sulphate route and for the chloride pigment production; such ilmenite is required to be upgraded either to Synthetic Rutile (SR) or TiO2 slag. However, in order to produce TiO2 slag in India at a globally competitive cost, the issues like high power tariff, inadequate infrastructure, expensive logistics, less enthusiastic market preferences, supply-demand gaps are to be adequately addressed. This paper deals with some of the above issues and possible solutions thereto in production of TiO2 slag from Indian ilmenite.

Jan 1, 2007

By D. S. van Vuuren

Over the last 60 years many different processes were conceived to reduce the cost of titanium produced by the Kroll process. However, success eluded all previous efforts, which were consequently terminated in periods of economic downturn. Recently, the grow thin demand for titanium and the high cost of producing the metal again sparked renewed attempts in various parts of the world to replace the antiquated Kroll process with a more efficient route. The different options to produce titanium are reviewed, classified and evaluated in terms of the fundamentals underlying the technologies, and it is shown that the options considered to be the most likely to replace the Kroll process, are continuous processes to reduce TiCl4 metallo-thermically to titanium powder. Of these, continuous magnesio-thermic reduction of TiCl4 would conceptually result in the lowest-cost and highest-value product. However, when considering by-product salt removal from the titanium product and recycling of the salt as well, sodio-thermic reduction of TiCl4 is better.

Jan 1, 2009

By O. Naiker, T. Riley

Keywords: Pyrometallurgy, furnace, Xstrata, ferrochromium, Premus Technology The presentation will give a basic overview of Xstrata Alloys. Included will be a brief history of the Alloys division as well as of each plant within the division. The Xstrata chrome plants utilise a wide variety of production processes, including Xstrata's Premus process, the Outokumpu process, and the conventional process. Xstrata?s Lion Project is underway, with commissioning expected in the third quarter of 2006. The new smelter will utilize Xstrata?s patented Premus process, and the competitiveness of the Premus process is discussed.

Jan 1, 2006

By P. Altounyan

Techniques used to safely control the roof in UK coal mines for some 10 years have been applied to a South African coal mine. This new approach known in the UK as advanced rockbolting technology, is based on applying four fundamental principles: ?Understanding the roof failure mechanisms ?Using an effective roof support system ?Designing this support using measurement ?Monitoring the performance of the system. The paper summarizes the approach in detail and describes how it is being applied by Anglo Coal, giving results obtained to date. Investigations at a number of South African coal mines, including stress measurements at two Anglo Coal mines, have confirmed that the mode of roof failure (lateral shearing due to horizontal stress) is the same as in other coalfields worldwide, and aspects of current world best practice, including the use of advanced technology rockbolting, are therefore relevant in South Africa. The stress measurements indicated a high level of stress field anisotropy and further investigation of stress conditions in South African coal mines is recommended. The most effective bolting system to resist shear failure is one with high bond strength and stiffness. Short encapsulation pull testing of existing South African systems confirmed that they have low bond strength and stiffness. An improved rockbolt system with the required performance, and features allowing rapid installation and installation quality and performance audit, has been developed and is currently under full-scale trial. Design by measurement and routine monitoring procedures including the use of a rotary telltale device are also under trial. It is anticipated that South African coal mines will be able to obtain significant safety and productivity benefits from the application of this technology.

Jan 1, 2001

By J. Kuijpers

Failure and fracturing are often regarded as synonymous. While this is obviously true in an environment dominated by tensile stresses, it is still not clear how failure and macro fracturing are related in a compressive stress environment. Excavations at great depths are typically subjected to compressive stresses only. The fracturing observed around such excavations is therefore commonly assumed to be induced by such compressive stresses. The physics of such a phenomenon have unfortunately never been explained properly, so that the formation of these so-called extension fractures still remains a mystery. As the presence of fractures is an important factor affecting the stability of underground excavations, it is of practical relevance to understand their formation. In this paper, a possible explanation is proposed. It is argued that fracturing in a compressive stress environment is a secondary effect. Primary failure, in the form of micro fracturing and associated damage is assumed to precede the major fracture processes. The fractures are thus generated in response to material failure and may not directly be the cause of failure. The implications for material response and behaviour are discussed. Keywords: micro fracturing, macro fracturing, extension fractures, failure, compressive stresses, damage, excavations.

Jan 1, 2000

By X. Goso

Laboratory-scale tests were conducted at Mintek for the production of titanium powder from particulate Kroll sponge by the hydrogenation-dehydrogenation (HDH) process. The aim of this work was to produce titanium powder for powder metallurgical consolidations. The work involved the production of titanium powder at optimized conditions, which included hydrogenation in a horizontal tube furnace at 600°C for 2 hours, milling using planetary and roller mills, and dehydrogenation in a vacuumed retort fitted in a muffle furnace running at 700°C for 36 hours. The titanium powder produced in this project matched the elemental specifications of commercially available titanium powder, except for high carbon content. Nevertheless, the powder has been tested further in mechanical alloying and has been found suitable for the production of powder metallurgical compacts. Keywords Powder metallurgy, titanium components, HDH process, ball milling.

Jan 1, 2011

By Noel C. Joughin

In making judgements on tolerable levels of risk in industry, and in all spheres of life, it needs to be understood that every action gives rise to risk. Without risk, nothing can be done. Without risk, no economy could be advanced. There is a strong tendency to emphasize the risk at work, but persons who are not working are exposed to a different set of risks. Often persons who are not working face greater risks than persons who are working. Simply, in being alive, one is exposed to the risk of an accident, the risk of contracting a disease, and an extremely diverse variety of other risks. According to the Health and Safety Executive of the UK, it is not possible to have a state of zero risk, because ?a state of zero risk does not exist?. Because zero risk is a physical impossibility, it is not possible to design for a state of zero risk in all engineering design. While the strategic target of achieving zero risk is laudable it does not provide any practical guidance to engineers as to what acceptable limits of risk should be. This causes a significant and real problem in the design for and the management of risk. Without meaningful guidelines, engineers, managers and the authorities often find themselves in disagreement. Thus, it has become essential to establish criteria for tolerable levels of risk and unacceptable levels of risk in order to design and manage engineering systems properly.

Jan 1, 2011