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By A van Jaarsveld

Environmentally-friendly, safe and cost-effective technology for stope drilling has successfully been introduced at TauTona mine. It has enabled the problem of inadequate compressed air pressure and its downgrading impact on production capability to be overcome. The paper traces the development process which culminated in the conversion of the entire stoping operation at TauTona to electric drilling. Background work which took place at other mines is also described. Statistics of performance improvements are provided. 1. Introduction Holman?s Silver series and the Seco S215 were drills that had a measurable impact on the South African gold mining industry. It is too soon to say whether Hilti will join those great names. However, there is no doubt that the introduction of electric drills into the harsh and unforgiving world of deep level gold mining is a significant development. History has shown that being the first to enter a new technology is no guarantee of long-term success. The pain and suffering which accompany the birth of anything new can deplete the energy of the innovator while at the same time creating opportunities for competitors to leapfrog him. In addition to commitment and enthusiasm, the innovator must therefore also possess, or have access to stamina and resourcefulness to overcome the unexpected difficulties which will inevitably arise. All of these were needed for the Hilti project.

Jan 1, 2008

By F. H. Abd EL-Rahiem

A selective dispersion process is presented and the work carried out to find optimum process conditions to minimise the colouring material in ground calcium carbonate (GCC) is described. The feed material is the overflow product from a hydrocyclone which results from using a Denver Attritioning machine with semi-autogenous grinding for one hour and a 1:1 ore/water ratio. By using sodium silicate (SS), with pH 9 and pulp density 5%, the iron content (as colouring impurities) is decreased from 0.21% in the original concentrate to 0.12% in the final concentrate. The degree of whiteness reached is improved to 85% from 63% in the original material. However, by using hexametaphosphate (SHMP) at pH 10 at the same pulp density, the iron content decreased to about 0.073% and hence the whiteness degree increased to about 96%.

Jan 1, 2004

By TvS. von Moltke

Steel is a highly versatile material due to its low cost and good mechanical properties, but typically needs some or other form of corrosion protection due to its tendency to corrode when exposed to atmospheric conditions. In the case of organic coatings, the corrosion protection and functionality of the final product is critically dependent on the adhesion of the coating to the surface of the steel. In this work the effect of contaminants and the nature of the surface layers present on industrial steel products are investigated by means of paint adhesion tests, Auger electron spectroscopy (AES), and X-ray Photoelectron spectroscopy (XPS). It was found that the presence of sodium species on the surface is very detrimental to paint adhesion under wet conditions, while satisfactory adhesion may be obtained even in the presence of silicon and carbon residues. It was also found that the nature of the Fe-O layer, formed under wet conditions is labile and different from that formed in dry air, and that subtle changes in process conditions, such as changing the oxygen content of the quench water, may change the adhesion of paint to the surface of the steel. Lewis acid-base interactions are discussed as a mechanism that may determine the bonding between the steel and polymer coating.

Jan 1, 2003

By A. A. Debrah

Artisanal and small-scale mining (ASM) plays a fundamental role in the national and local economies of resource-rich countries in Africa. As such, more effort must be geared towards fostering this type of economic activity to sustain livelihoods in rural communities. Across Africa, efforts to operationalize ASM based on a sustainable development framework have been quite tedious and often ineffective. This is because most of these frameworks lacked context and an understanding of the continuum from the artisanal through small-scale and up to the junior miner, grouped under the general term ?ASM?. Driven by the need to contextualize some of the definitional issues in this niche sector, and gain a clearer understanding of their peculiar challenges, this paper aims to contribute to the debate on ASM by considering two of Africa?s resource-rich countries ? Ghana and South Africa. Since South Africa has made greater inroads in protecting the interests of small-scale miners, we thus draw comparisons from both countries? approach to ASM, outline the lessons learnt, and provide recommendations regarding the ways forward.

Jan 1, 2014

By S. Achilleoudes

This paper describes the various factors that contribute to the maximum design pressures acting on box fronts and how these factors influence the mass and economy of box front steelwork. The influence of material density, rock size and moisture content on the incidence of hang ups and mud rushes in the rock pass is also highlighted. The loads acting on any box front are a function of several different parameters. These include natural, operational and excavational parameters. A case study analysis was carried out using UG2 ore and a typical box front structure to demonstrate the relationship between the mass of the box front and the material pressures resulting from variations in the above parameters. Based on the results of this case study, the required design mass of a side mounted box front for a rock pass containing platinumUG2 increases in (close to) linear proportion to % overbreak and is also linearly proportional to the pressure on the face of the box front beyond saturated conditions. The mass of the box front structure also doubles with a 100%increase in over-break which emphasises that a box hole excavation that is as neat as possible will yield a lighter and more econimical box front structure.

Jan 1, 2005

By P M. Bradbury

The nature of aggressive process chemical requirements typically in the Platinum Refinery Industries, lend themselves to the use of Polymer Composite Glass Reinforced plastics for pipework and other associated equipment in these types of Plants. This paper discusses the basic characteristics of a Polymer Composite glass reinforced piping system and gives sample examples of applications in current present day use.

Jan 1, 2006

By H. G. Oltmann

The equilibrium nitrogen solubility in the CaO-SiO2system was studied by a slag-gas equilibration technique, in graphite crucibles at 1823K under a CO-N2 atmosphere. The nitrogen content of the slags was determined by the Kjeldahl method. A reliable technique was used to obtain an initial nitrogen content in the master slags, from the addition and pre-melting of silicon nitride. Reduction of silica by graphite was found to occur during the equilibration experiments, resulting in compositional changes of the slags. The results were extrapolated to equilibrium by kinetic evaluation of the data. The nitrogen solubility showed good agreement with the result of Suito and Sano, while Fruehan?s results were lower. However, the results of the present study do not support the maximum nitrogen solubility values found by Sano.

Jan 1, 1999

By R. M. Lamya

The kinetics of copper cementation during atmosphere leaching of a Ni-Cu matte in CuSO4-H2SO4 solution was studied as a function of initial copper ion concentration, initial acid concentration, temperature, stirring rate, particle size distribution and pulp density. It was found that all these process variables influenced the rate of cementation. A two-stage rate of reaction was observed inmost of the experiments, with the rate of cementation in the initial stage being slower than that of the subsequent second stage. The increased rate of cementation in the second stage was attributed to the enhancing effect of the surface deposit. The cementation process was found to take place by two different rate-controlling mechanisms. At a temperature range of 50?70°C, an activation energy of 74.6 kJ/mol was obtained, indicating a surface reaction controlled process. At higher temperatures (70?80°C) a lower value of activation energy was observed (18.2 kJ/mol), indicative of a process controlled by diffusion through surface layers. The structural characteristics of the cemented deposit could not be determined in the investigated system where the deposit was mixed with the leach solid residue.

Jan 1, 2005

By I. Jauhari, F. Stober, D. Fowler, B. O. Wasmund, T. Miraza, C. Nichols, A. Taofik Hidyat, K. Said

The existing PT Aneka Tambang (Antam) ferronickel smelter located at Pomalaa, Indonesia consists of two RKEF lines with reduction furnaces nominally rated at 17 MW and 18 MW, respectively. The low power densities and heat fluxes allowed both furnaces to operate with falling water film shell cooling systems. The furnace campaigns comprised a 5-yearly cold shut -down for metal taphole area rebuild and a 10-yearlysidewall and hearth perimeter repair. Towards the end of these campaigns the furnaces would typically be operated at below nominal power due to excessive sidewall temperatures. In January 2001 Hatch performed a smelter study which proposed options which indicated the possibility of a single furnace operation for the smelter, elimination of lime addition and transition to shielded-arc operation with associated efficiency and throughput gains. This paper discusses the process of uprating the second?line furnace capability from 18 MW to 32MW following the decision by Antam to implement the recommendations proposed by Hatch. It will cover the development of scaled-up furnace design basis by Hatch and Antam with the enabling application of Hatch cooling and binding technology. To optimise the capital cost and maximise Indonesian supply content and post installation support, the scope was carefully and clearly divided between Hatch and Antam. The challenges, set backs and valuable learning experiences gained during the implementation of the retrofit include; ?The support and re-use of existing roof system and challenges presented in re-use of existing crucible support steel. ?Training and technical assistance for Antam operators to perform refractory and copper cooler installation and maintenance of crucible integrity technologies. ?Hearth integrity during start-up and development of an initial charge and start-up procedure to achieve planned thermal expansion of the hearth prior to bath formation ?Implementation of a sidewall hold-down system within the refractory sidewall due to space constraints ?Existing furnace foundation reinforcement to overcome lateral forces on furnace piers during crucible support steel expansion ?Conversion of an open-loop gravity feed cooling water system to a closed loop pressurised system with integrated emergency gravity feed and backup system ?Existing water treatment system and pumping system improvement and modification to meet copper cooling system requirements ?Integration of the new instrumentation control system designed by Hatch to increase performance of the furnace monitoring system and operation ?Uprate transformer capacity from 25 MVA to 40 MVA to meet with requirement of Shielded- Arc Furnace Operation.

Jan 1, 2007

In extracting base metals from orebodies, sulphide as well as oxide, the main environmental concern is sulphur, whether in the form of sulphurous gases or sulphate in liquid form. Generally sulphur is in over supply in developed countries mainly because of strict legislation to capture it. In developing countries, on the other hand there is usually a shortage of sulphur because of less strict environ-mental legislation. Africa falls in this second category and the African continent imports substantial amounts of sulphur, despite the fact that large quantities of sulphur are emitted by smelters, thermal power stations, coalmines, fertilizer manufacturers and others. Other than making acid from gaseous emissions, existing methods to capture sulphur from gaseous and liquid effluents are uneconomical and it ends up in the environment either as ammonium sulphate (from gaseous effluents) or as gypsum (from liquid effluents). The CSIR?s Environmentek and Key Structure Holdings have developed a process whereby gaseous sulphur emissions and sulphates in liquid effluents can be economically captured and converted into elemental sulphur and metal carbonates. The elemental sulphur is of high purity as it is precipitated from a gas stream and is readily marketable. The metal carbonates (barium or calcium) can be recycled back to the process or marketed. The only harmful by-product of the process is carbon dioxide. Should natural gas or methane be available, the carbon dioxide could be reduced by about one third. Should solar, wind or hydro energy be available to generate hydrogen, the carbon dioxide emissions would be zero. Employing this technology could make Africa independent of sulphur imports and furthermore reduce the impact of acid rain and seepage of sulphate from gypsum and other waste dumps into the environment.

Jan 1, 2005

By L. R. C. Cairncross

In this study, the general case of semi-batch precipitation of nickel hydroxide, Ni(OH)2, is modelled. In practical terms, this precipitation may occur at high ionic strengths, and therefore the model for solution chemistry requires a thermodynamic model that is applicable for these non-ideal systems. The activity coefficient model used is the ELEC-NRTL. The simulation of the solution chemistry is performed using AspenPlusTM, which is a steady-state process simulation program. This allows for rigorous evaluation of the solution speciation, and hence the degree of supersaturation which dictates the precipitation kinetics. The solution chemistry provides the basis for predicting the formation of solids. The model consists of a solution chemistry part and a solids formation part. The inputs to the model include the initial concentrations of the streams entering the reactor, kinetic parameters for the precipitation processes, and a particle size distribution obtained from experiments. The solids formation part of the model employs the method of moments for the evaluation of the population balance. The population balance accounts for total particle number, and the formation and increase in size of particles across the entire particle size range. This balance requires kinetic parameters for the processes of nucleation, growth and agglomeration. Using optimization routines inherent in AspenPlusTM, parameters for the rate of nucleation, growth and agglomeration may be extracted from experimental particle size distributions. These are then used in the model to extrapolate to other conditions. Once an understanding of the kinetics of the precipitation processes is gained, the model provides a predictive tool for optimization of these kinetics, in order to increase the overall particle size and therefore improve solid-liquid separation. The work is deemed to be significant as it sheds some light on solids formation processes involved in precipitation?including nucleation, growth and aggregation?and develops a predictive modelling tool applicable to solutions of high ionic strength. We argue that this dewatering of suspensions is affected significantly by particle size distribution and surface properties of the solids formed by precipitation. This modelling tool should facilitate the design of solids formation processes where downstream dewatering is enhanced.

Jan 1, 1997

By E. V. Lilford

Equity investors and project sponsors have divergent views about expected or minimum returns that should be generated by a mineral project. Irrespective of their views, the fundamental estimation of the corporate cost of capital remains singularly determinable, with additive components of risk and uncertainty often incorporated in the final analysis. This paper discusses and details the fundamental, numerical determination of the corporate cost of capital.

Jan 1, 2006

By M. Castelli, C. Scavia, S. Marello, A. Allodi

ABSTRACT – This paper investigates the possibility of interpreting the shear band evolution in hard soils and soft rocks as the result of shear propagation from pre-existing natural defects. Thesis done through the application of the principles of Fracture Mechanics, a Slip-Weakening Model(SWM) being used to simulate the non-linear zone at the tips of the discontinuity. Experimental observations have been carried out on prismatic samples of Beaucaire marl through biaxial compression tests in plane strain conditions. A numerical simulation confirms the validity of the proposed approach. RÉSUMÉ – Cet article présente la possibilité d’interpréter l’évolution des bandes de cisaillement dans les roches tendres et les sols raides comme le résultat de la propagation pour cisaillement à partir d’un défaut préexistant. Le Slip-Weakening Model (SWM) a été employé pour modéliser la zone non linéaire a l’extrémité d’une discontinuité. Nous présentons des observations expérimentaux obtenues à travers des essais de compression en déformation plane sur des échantillons prismatiques de marne. La simulation numérique d’un essai confirme la validité de la méthode proposée. KURZFASSUNG – Die vorliegende Arbeit versucht die Ausbreitung von Scherzonen in(bindigen) Böden und im Lockergestein anhand der Entwicklung von Scherrissen ausgehend vonexistierenden Schwachstellen zu erklären. Die Umsetzung erfolgte mit Hilfe der Bruchmechanik,für die Modellierung der nichtlinearen Zone an den Rissenden wurde ein Slip-Weakening-Modell(SWM) eingesetzt. Es wurden zweiaxiale Druckversuche an prismatischen Probekörpern vonBeaucaire Mergel unter der Bedingung eines ebenen Verzerrungszustandes durchgeführt. Dienumerische Untersuchungen bestätigten die Annahmen der untersuchten Theorie.

Jan 1, 2003

By P. A. Olubambi

The leaching of zinc and copper from Nigerian bulk sulphide ore with sulphuric acid in the presence of hydrogen peroxide was studied. The aim of the study was to investigate the effectiveness of hydrogen peroxide as an oxidant for the sulphuric acid leaching of zinc and copper from a complex sulphide ore. Distribution of elementals within the various particle sizes was initially determined by ICP-OES and XRF to provide a basis for explaining the dissolution process. The effects of concentration of hydrogen peroxide, particle size, stirring speed, and leaching time at a constant temperature of 298K were studied. There were variations in elemental and mineralogical composition within the different sizes. The concentrations of zinc and copper reduced as particle size decreased while silica, sulphur, iron and lead contents increased. Dissolution results showed that the leaching rate of copper was lower than that of zinc. The highest recoveries of zinc and copper were obtained at a leaching time of 180 minutes, stirring speed of 160 rpm, particle size of 75 µm and a concentration of 1M H2SO4/1MH2O2. It was observed that the leaching rate of zinc and copper increased with increasing hydrogen peroxide concentration. Increased stirring speed had a negative leaching effect as it promotes hydrogen peroxide decomposition. Keywords: Nigerian sulphide ore, zinc, copper, hydrometallurgy, sulphuric acid, hydrogen peroxide.

Jan 1, 2006

By P. A. Olubambi

The leaching of zinc and copper from Nigerian bulk sulphide ore with sulphuric acid in the presence of hydrogen peroxide was studied. The aim of the study was to investigate the effectiveness of hydrogen peroxide as an oxidant for the sulphuric acid leaching of zinc and copper from a complex sulphide ore. Distribution of elementals within the various particle sizes was initially determined by ICP-OES and XRF to provide a basis for explaining the dissolution process. The effects of concentration of hydrogen peroxide, particle size, stirring speed, and leaching time at a constant temperature of 298K were studied. There were variations in elemental and mineralogical composition within the different sizes. The concentrations of zinc and copper reduced as particle size decreased while silica, sulphur, iron and lead contents increased. Dissolution results showed that the leaching rate of copper was lower than that of zinc. The highest recoveries of zinc and copper were obtained at a leaching time of 180 minutes, stirring speed of160 rpm, particle size of 75 µm and a concentration of 1M H2SO4/1MH2O2. It was observed that the leaching rate of zinc and copper increased with increasing hydrogen peroxide concentration. Increased stirring speed had a negative leaching effect as it promotes hydrogen peroxide decomposition. Keywords: Nigerian sulphide ore, zinc, copper, hydrometallurgy, sulphuric acid, hydrogen peroxide.

Jan 1, 2006

By G. A. Harrison

The introduction of extra low profile (XLP) mechanized equipment within Anglo Platinum is aligned with the overall New Mining Technologies strategy to focus on continuing modernization of our mining operations` incorporating injury-free production and cost-effective mining technologies. The method allows for the introduction of a suite of ultra-low profile equipment in narrow reef (1.2 m) stoping operations. For the first time it is now possible to achieve total trackless mechanization at these widths and indications are that XLP mining has the potential to add more value when benchmarked with conventional mining and low profile (1.8 m) room and pillar methods. Various mine layouts were tested at different sites within Anglo Platinum and the XLP breast mining layout proved to be the most effective. This paper describes the results of the trials at Waterval Shaft and concludes with recommendations on our future strategy on implementation of XLP technology within Anglo Platinum.

Jan 1, 2006

By M. G. Senyur

This study aims at investigating the structural characteristics of backfilling material. In this regard, spatial arrangement of solid particles and associated voids in a unit mass of coal mine refuse as backfilling material were tested. The materials were produced from coal mine refuse of Zonguldak Colliery, Turkey. The experimental procedures were developed to determine their void ratio (or its equivalent porosity), bulk density and the shape properties of constituent particles. The orientation fabric and the co-ordination number were the other two fabric elements determined. The filling materials were sieved and their particle size distributions were found. The results obtained by experiments were related to the particle size distribution parameters, namely, the coefficient of uniformity and the effective size. It was concluded that mean value of void ratio is correlated with coefficient of uniformity. The standard deviation of porosity as an index of fabric heterogeneity is clearly correlated to effective size. By an original experiment, the frequency distribution of coordination number was observed as binomial in uniformly graded materials. Also, the co-ordination numbers of test mixtures were calculated by the Marsal method and results obtained showed a good correlation between the minimum particle size and number of contacts per unit area.

Jan 1, 1998

By M. Ghoreychi, X. Daupley

ABSTRACT: The paper is devoted to two major aspects related to the abandonment of salt mines: 1)- Long-term risk associated with the mechanical instability of surface and its consequences for public security and properties. 2)- Long term dissolution and transport of salt resulting from its communication with groundwater. Basic characteristic features of salt deposits and mining methods are presented through the studies already undertaken on French mines. This analysis allows to identify major hazards encountered in different traditional salt mines and solution-mining cavities. In particular, the role of overburden (presence and thickness of salt layer in exploitation roof, presence of clayey rocks or hard rocks e.g. dolomite or anhydrite), presence of water-bearing strata and possibly natural brine levels, discontinuities, etc. are discussed. In the second part, the main features of mechanical behaviour of salt (creep, damage) as well as transfer processes of this material are presented. The influence of these aspects on the long term evolution of abandoned salt mines is then analysed. KEY WORDS: exploitation, abandonment, salt, mechanical, stability, transport, solution, brine. ZUSAMMENFASSUNG: Der Artikel bezieht sich auf zwei bedeutende Aspekte beim Salzabbau: 1)-Das langsfristige Risiko zur Bodenoberflächeunbeständigkeit und sein Einfluss über Mensch= und Gütersicherheit. 2)-Die langsfristige Auflösung und Beförderung des Salz beruhen sich auf Studien über französiche Bergbauen. Diese Analyse emöglicht es, die bedeutendesten Risiken in verschiedenen Salzgruben zu identifizieren, bzw. Traditionellen oder durch Auflösung abgebauten. Insbesondere wird die Rolle des Deckgebirges (Vorhandensein und Dicke von Salzschicht am Dach des Grube, Beisein von Tanlager oder hartem Gestein wie Bitterkalk oder Anhydrid), Beisein von wasserhaltigem Boden und/oder gesalzenen Wasserflächen, Trennflächen, usw… erötert. Im zweiten Teil werden die haupsächlichen Eigenschaften des Salzverhaltens (Kriechen und Beschädigung) beschrieben. Ihr Einfluss über das Verhalten von stillgelegten Bergwerken lässt sich analysieren. SCHLÜSSELWÖRTER: Bergwerksbetrieb, Stilllegung, Mechanik, Beständigkeit, Ausbreitung, Aussolung, Solewasser. RESUME: L’article est consacré à deux aspects majeurs liés à l’abandon d’exploitations de sel : 1)- Le risque d’une instabilité à long terme de la surface du sol et son incidence sur la sécurité des personnes et des biens. 2)- La dissolution à long terme et le transport de sel sous l’effet d’une communication avec des eaux souterraines. Les principales caractéristiques de gisements et d’exploitations de sel sont présentées en s’appuyant sur les études antérieures réalisées sur les exploitations en France. Cette analyse permet d’identifier les risques majeurs rencontrés dans différentes mines de sel traditionnelles ou exploitées par dissolution. En particulier, le rôle du recouvrement (présence et épaisseur d’un banc de sel au toit de l’exploitation, présence de terrains argileux ou de roches dures telles que la dolomie ou de l’anhydrite), présence de terrains aquifères ou de nappes salées éventuelles, discontinuités, etc. sont discutées. Dans la deuxième partie, les principaux traits du comportement mécanique du sel (fluage, endommagement) ainsi que les processus de transport de ce matériau sont présentés. L’influence de ces aspects sur le comportement à long terme d’exploitations abandonnées de sel est ensuite analysée. MOTS CLES: exploitation, abandon, mécanique, sel, stabilité, transport, dissolution, saumure.

Jan 1, 2003

By O. Naiker

Xstrata has modified and improved on the solid state reduction of chromite (SRC) process that was pioneered by Showa Denko in Japan and previously used at Xstrata?s Lydenburg plant. The history of pre-reduction is a long one, with the SRC process being the first and only commercially successful one prior to Premus. Krupp developed the chromite direct reduction and the rotary hearth for the pre-reduction of chromite. However, these processes have not been successfully commercialised. The are a number of significant differences between Xstrata?s patented Premus and the original Consolidated Metallurgical Industries (CMI) process. These include, the use of lower cost anthracite fines as the reductant source together with the use of unactivated bentonite as the binding agent. In addition the use of oxygen as an energy source is used in Premus but not in the original CMI process. There was a fundamental change in the operational philosophy of the process in that while the original CMI process aimed to maximize metallization of the pellets, the Premus process seeks to maximize the energy output from the kiln while still achieving the required efficiencies and hence increasing furnace output. Premus is designed to reduce electrical energy consumption, provide high recoveries of metallic oxides, and utilizes low cost reductant and energy sources such as anthracite and oxygen respectively. Due to the fact that Premus is one of the most technologically advanced and competitive processes used today in the production of ferrochrome it was the process selected for Xstrata?s new ferrochrome facility, Project Lion, that is due to be commissioned in the third quarter of 2006 in the Steelpoort Valley in Mpumulanga, South Africa.

Jan 1, 2007

By J. N. Van der Merwe

Due to the approaching depletion of reserves in the Witbank Coalfield, and the fact that the Waterberg Coalfield is as yet under developed, there is increasing pressure to extend the lives of the operating coal mines in the Witbank Coalfield. One potential source of coal is the old pillars, often small and at shallow depth, that were not left with secondary extraction in mind. At face value, some of these pillars appear to be suitable for secondary mining due to their high safety factors. However, it is known that over time, these pillars have scaled and the current sizes are smaller than the as-mined dimensions. It is also known that at shallow depth, the overburden is often less likely to fail during secondary mining, resulting in high abutment loads on the unmined pillars. The paper proposes a systematic method to pre-evaluate those old pillars for the possibility of stooping. The method consists of elements of fundamental methods and newly developed technology. In essence, it revolves around using empirical methods to estimate current pillar dimensions, followed by numerical modelling to investigate the probability of progressive pillar failure and then fundamental methods to determine the limits of applicability of the numerical model.

Jan 1, 2012