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A201 aluminium alloy is a high strength casting alloy with a nominal composition of Al-4.6Cu-0.3Mg-0.6Ag. It is strengthened by the O(Al2Cu) phase and the ??(Al2Cu) phase during heat treatment. Further strengthening of this alloy system can be obtained through the addition of transition elements, but care must be taken as other elements might have adverse effects on the mechanical properties. The objective of this study is to determine the influence of Mn on the tensile properties of rheo-processed Al-Cu-Mg-Ag alloy A201. ThermoCalc software was used to predict the different phases that can be expected in the alloys, and scanning electron microscopy(SEM) with energy dispersive spectroscopy (EDS) was used to investigate the actual phases that formed. The influence of these phases on tensile properties is quantified. SEM and ThermoCalc revealed that there is an increased amount of the Al20Cu2Mn3 with increasing Mn. The tensile properties showed that high amounts of Mn do have adverse effects on the tensile properties of alloy A201, especially the ductility. Keywords Semi-solid metal (SSM) forming, alloy A201, intermetallics, Al20Cu2Mn3

Jan 1, 2011

By B. P. Watson

The Bushveld platinum group metal deposits are two distinct, shallow-dipping stratiform tabular orebodies which strike for many hundreds of kilometres. Mining is extensive, with depths ranging from close-to-surface to 2 300 m. The mining method is a variation of planar open stoping. Pillars are widely employed to support the open stopes. In the deeper levels, in-stope pillars are required to fail in a stable manner soon after being cut, and the residual pillar strength is used to stabilize the hanging wall. These pillars are commonly known as crush pillars. Little work has been done in the past to determine pillar peak and residual strengths, and pillars have been designed using experience and formulae developed for other hard-rock mines. This has led to over and undersize pillars with consequential loss of ore, pillar bursts and potential collapses. This paper describes a crush pillar design methodology, and provides design charts. Three mining environments were incorporated in the investigations, which included underground and laboratory measurements, analytical solutions, numerical model sand back analyses. The results of the study are suitable for the areas where the research was carried out, and may also be applied with caution in other similar environments.

Jan 1, 2010

By M. Dworzanowski

The beneficiation of fine iron ore will increase in importance in the future because most new iron ore resources will be in the form of lower grade ore deposits that will require liberation of iron ore minerals at finer sizes. Generally this fine iron ore will be beneficiated to produce a pelletizing concentrate with very strict chemical and physical specifications. In addition, because of the increasing demand for iron ore there are now more opportunities to produce by-product iron ore from mining operations producing other commodities. In the past the associated iron ore minerals would report to final tailings but now there is potential value to be realised from by-product revenue. These by-product iron ore opportunities are almost all centred on producing pelletizing concentrate. Currently pelletizing concentrates are produced mainly by various combinations of flotation and magnetic separation. The selection of the beneficiation route will depend on ore mineralogy and considerations around plant capacity and final concentrate quality. The main economic iron minerals are magnetic, haematite being paramagnetic and magnetite being ferromagnetic. This, therefore, means that magnetic separation can be applied, in principle, to all fine iron-ore beneficiation plants. While flotation has a considerable capacity advantage over magnetic separation, the real advantage of magnetic separation over flotation in fine iron-ore beneficiation is that treatment of -10 µm iron ore is possible-in flotation, the feed is deslimed at 10 µm and the -10 µm stream is considered to be final tailings, even though there is often a significant amount of contained iron ore. This paper describes a study around the recovery of fine magnetite in the form of a pelletizing concentrate. The study is based on an evaluation of an iron ore by-product opportunity from an iron oxide copper-gold (IOCG) deposit. Experiments were conducted to quantify the differences in magnetic separation performance with decrease in particle size treated. A mineralogical evaluation of all the test work products was undertaken to facilitate the interpretation of the test work results. These results were then used to propose an economically viable flowsheet for maximizing fine magnetite recovery using magnetic separation.

Jan 1, 2012

By R. G. B. Pickering

The purpose of this report is to chronicle the interaction between Anglo Platinum and Sandvik Tamrock during the development and application of Long Hole drilling as a viable, practical method of narrow reef mining. Appendix I identifies the people from Anglo Platinum and Sandvik Tamrock who participated in the project. Experiments in long hole drilling and blasting were conducted in a number of mines during the late 1950s and early 1960s. Some of the advantages envisaged were: ? The face would require no daily examination ? No barring down or immediate face support required ? No sockets to clean ? Only a few well drilled holes rather than large numbers of short blast holes ? Avoidance of poorly-marked holes, inaccurate drilling and improper charging ? Better supervision and better face advance. Holes 50 mm in diameter were drilled parallel to the stope face by pneumatic rock drills from advance strike gullies. Holes were charged with amon gelignite cartridges. All holes were traced with detonating cord to ensure propagation of the explosive along the entire hole length. Rock was blasted onto a rolling scatter pile. A number of reasons have been cited for the failure of this mining method. The two most important were: ? problems in controlling hole deviation which was exacerbated by the fractured ground ? difficulty of charging up holes in fractured ground, due to relative movement of rocks along fracture surfaces over the hole length. The idea of drilling a few long holes parallel to the face rather than a large number of short blast holes perpendicular to the face was an attractive option to mechanize narrow reef mining. This particular project started in 1998. Initial trial The Union Section of Anglo Platinum purchased a Solo H 606 RA long hole drilling rig from Sandvik Tamrock in 1997. In order to evaluate long hole drilling as a basis for face mechanization. The Solo series of drill rig was selected because it combines high drilling performance and good drilling accuracy with high versatility with a compact size. The mining method proposed by a consultant to Anglo Platinum was based on the current trackless mining method practised by Union Section. The trackless mining method is better described as a trackless development and transport method. Reef strike drives were installed approximately 40 metres apart on dip using trackless equipment. Reef was mined using hand-held pneumatic rock drills and scraper winches and the excavation was supported by sticks and crush pillars at the top of the panel. Rock scraped from the panel was loaded by Lad Haul Dumps (LHDs), trammed to an inclined haulage, and loaded into trucks for transport to the surface. It was intended that the Solo would drill from the bottom advance strike drive to the top advance strike drive. Blasted rock would still have to be scraped from the panel. It is also difficult to understand how well the support would have survived. In the initial motivation it was stated that drilling accuracy was of the utmost importance. Previous work by Sandvik Tamrock had shown that, in other parts of the world, 20 metre long holes could be drilled with a deviation not exceeding 100 mm provided that: ? holes were collared with low thrust pressure ? operating percussion pressure was kept low -often not ? exceeding 10 MPa ? drilling was to be with tubes, not rods. In early 1998 initial trials with the Solo H 606 RA were inconclusive; attempts were made to drill 40 metre long holes from one advance strike drive to another. Difficulty was experienced in measuring hole straightness and accuracy, there was no survey of the holes, and no blasting was done to expose hole barrels. A long hole mining system was then defined, with a corresponding face mining system, which led to the design of a test programme for the Solo drilling rig. Earlier experience at Telfer The proposed face mining system was based on a mining method that is practised at Telfer Gold Mine in Western Australia. Telfer has a series of domed reefs that dip at angles of less than 20° to more than 40°. The ore bodies are all thin, with widths from 0.6 metres to 0.8 metres. Figure 1 shows the face layout. Experience at Telfer indicated the following: ? The spacing and size of the dip pillars should be based on the rock mechanics of Union Section ? The length of the face is determined by the ability to correctly position the blast holes. Positioning of blast holes is a function of hole straightness and hole direction. Blast holes in Telfer were drilled 64 mm diameter with retrac bits from Sandvik. Extension steel was T38 by 1.8 metre lengths. A guide rod was fitted immediately behind the bit. To achieve greater accuracy' operators drill at relatively low percussion and thrust pressures. Results show that very good accuracy is achieved in 20 metre stopes and only fair accuracy in longer stopes. In 34 metre long stopes 10-15% of the holes are not sufficiently accurately positioned and have to be re-drilled. All blast holes are

Jan 1, 2006

By C. Marais

The use of machine vision in the monitoring and control of metallurgical plants has become a very attractive option in the last decade, especially since computing power has increased drastically in the last few years. The use of cameras as a non-intrusive measurement mechanism not only holds the promise of uncomplicated sampling but could provide more consistent monitoring, as well as assistance in decision making and operator and metallurgist training. Although the very first applications of machine vision were in the platinum industry, no automated process control has been developed for platinum group metals (PGMs) as yet. One of the reasons is that to date froth features could not be related to key performance indicators, such as froth grade and recovery. A series of laboratory experiments was conducted on a laboratory-scale platinum froth flotation cell in an effort to determine the relationship between the platinum grade and a combined set of image features and process conditions. A fractional factorial design of experiments was conducted, investigating 6 process conditions, namely air flow rate (x1), pulp level (x2), collector dosage (x3), activator dosage (x4), frother dosage (x5) and depressant dosage(x6), each at levels. Videos were recorded and analysed to extract 20 texture features from each image. By using artificial neural networks (ANN), the nonlinear relationship between the image variables and process conditions and the froth flotation grades could be established. Positive results indicate that the addition of image features to process conditions could be used as sufficient input into advanced model based control systems for flotation plants. Keywords Flotation, machine vision, image analysis, neural networks.

Jan 1, 2011

By C. Lottering

Copper sulphate solutions are produced during the pressure leaching of first-stage leach residue in a typical base metal refinery process. Apart from impurities such as selenium and tellurium, this leach solution also contains other precious metals (Rh, Ru, and it) due to dissolution in the pressure leaching stage. Selenium and tellurium are removed from the leach solution by precipitation with sulphurous acid, since these elements negatively affect electrowinning. This study investigates the feasibility of modifying the Se/Te precipitation process step to achieve significant rhodium precipitation in addition to selenium and tellurium precipitation, in order to reduce the rhodium inventory of the process. Thiourea, S02, formaldehyde, formic acid, and sodium thiosulphate were evaluated to determine which of these reagents would achieve the highest Rh precipitation. Based on these screening tests, SO2 and thiourea were selected to be used as precipitation reagents in optimization tests. During these optimization tests, the operating temperature (80 to 150°C) and the amount of reagent added (80 to 140 per cent excess) were varied to evaluate the effects that these operating conditions have on the precipitation behaviour of Rh as well as Se, Te, Cu, and Ni, and to propose appropriate operating conditions. It was found that thiourea resulted in good Rh and Se precipitation (typically in excess of 90 per cent), but precipitated noticeably more copper and nickel from the solution than when SO2 was used. In addition, thiourea had poor Te removal characteristics. SO2 achieved a maximum of 70 per cent precipitation of the rhodium. Faster kinetics and a larger extent of Te precipitation were, however, observed when using SO2 compared to thiourea.

Jan 1, 2012

RME has a vision for a new grinding plant operational paradigm made possible by RME's fast, safe Mill Relining System. Some new liner designs can degrade SAG mill performance because of mill volume loss, ball strike (rotational speed limitations) and other issues often brought about by modifying liner design for maximum life and without a backward glance at metallurgical consequences. Freshly relined mills can initially produce as little as 80 per cent of their maximum throughput, that maximum occurring toward the end of the liners' wear life. RME's proposition is to see new liners designed for maximum commercial performance. This may mean more frequent mill relines but with liners designed to yield optimum grinding, metallurgical and profitability performance, not maximum life. In other words, mill liner profiles and mill relining speed become key operational controls and not simply `must do' maintenance functions. Taken to the extreme, liner profiles may prove capable of `tuning' a grinding plant for maximum profitability in any metal price environment. Following the introduction, the first section of this paper provides an update describing recent and significant developments within RME's range of Mill Relining Systems, the enabling technologies which permit more frequent liner exchange without incurring additional downtime imposts. The second section outlines RME's vision of a `liner profile versus profitability' commercial model, developed either intuitively or by using a combination of new measurement and modelling technologies. These new measurement and modelling tools provide the opportunity to predict the optimum commercial outcome, off-line in the virtual world, before committing to an expensive liner experiment.

Jan 1, 2007

By I. C. Spangenberg

The status of sampling practices in the gold mining industry in Africa was determined as an initial step in a process to standardize sampling practices in the mining industry. Twenty-one gold mines, twenty metallurgical plants, and thirteen laboratories were rated for the potential influence of the relevant sampling errors on each component of the particular sampling system. The findings of the study on the status of equipment, standards, procedures, and management principles were presented in a dissertation (Spangenberg, 20121) and are now used by AngloGold Ashanti?s mines in the quest for correct sampling practices. The information is also used to compile a guideline on leading practice procedures for sampling methods in gold mining. This article is an overview of sampling best practice found in African mining Keywords theory of sampling, best practise, sampling errors, sampling standards.

Jan 1, 2014

By A. P. N. Sutherland

Pipelines for transporting high concentration slurries are often designed using methods applicable to homogeneous non-Newtonian laminar flow. Many industrial slurries though comprise coarse particles in a non-Newtonian carrier fluid, and existing experimental evidence from tests with such slurries demonstrates that they are not homogeneous. Under laminar shear conditions the coarse particles settle, even in statically stable carrier fluids. To understand this better, the Institute of Materials Science and Technology (IMST) at Cape Peninsula University of Technology (CPUT) is conducting ongoing research into the flow of these high concentration non-Newtonian settling slurries. Since pressure gradient and flow rate measurements alone are insufficient to adequately model the flows, an electrical resistance tomography (ERT) instrument developed by the University of Cape Town (UCT)was incorporated into the pipe test loop to determine pipe cross-section concentration and velocity profiles. The software developed to do this is modular and allows different image reconstruction and cross-correlation algorithms to be implemented and tested without significantly changing the rest of the application. At a total frame capture rate of 566 frames/sec a 2.67 GHz Intel Celeron processor with 500 MB of RAM is fast enough to calculate and display velocity profiles in ?real-time? at an update rate of one profile every two seconds. Examples of experimental concentration and velocity profiles obtained using the system are shown and some proposed improvements/extensions to the system are listed.

Jan 1, 2008

By J. W. van der Merwe, A. Palazzo

"Owing to the corrosiveness of the untreated brackish cooling water typically used for steel mills (and other environments), it is important to treat the water and monitor corrosion in such systems. Generally, corrosion rates are monitored with corrosion probes inserted into a pipeline or vessel. This has been standard practice for many years, and is widely accepted in industry. Typically, two kinds of probes are used - electrical resistance and linear polarization resistance (LPR) probes.In this study, the effectiveness and accuracy of the LPR technique was evaluated by comparing the electrochemical measurements with the results of mass loss tests using corrosion coupons. The corrosivity of the environment, a synthetic brackish water, was varied by varying the calcium hardness and alkalinity, and to simulate actual plant conditions temperatures of 35°C and 45°C were used. In addition to the corrosion rate measurements, the iron concentration was measured, as well as the imbalance from the probe.The corrosion rates obtained by LPR were from 57% lower to 385%higher than those from the immersion tests. Most probe measurements were higher than the immersion results, and 50% of the probe results were50% or more higher than the immersion results. The best correspondence between the two methods was obtained at low calcium levels, except for one measurement that was 93% higher than the coupon results. There was no clear correlation between parameters such as temperature and total alkalinity and the difference between the results. It would therefore appear that LPR measurements can differ significantly from immersion results, and LPR results should therefore be used with caution in industrial applications."

Jan 1, 2015

By Y. He

Early research showed that the separation of particles based upon their density was not possible in steadily rising air streams. The terminal velocities of moving spheres are determined by their aerodynamic characteristics. This prevents particle separation by density in standard air classifiers. Passive pulsing air classifiers have accelerated airflow in certain regions, which achieves density-dominant separation. Numerical simulation of airflow within passive pulsing air classifiers was done to estimate airflow patterns near a damper. Analysis of those results shows the significant acceleration of the airflow above the damper. Laboratory trial separations have shown that passive pulsing classifiers are superior to standard air classifiers. Keywords: pulsing airflow, passive, simulation of airflow models, acceleration effect, density

Jan 1, 2005

By C. Musingwini, A. S. Nhleko

"Since the Global Financial Crisis (GFC) in mid-2008, capital has been more difficult to access. Mining projects must contend with projects from other industries for scarce capital. A decision to invest available capital in mineral projects requires that valuation be conducted to assess the expected return on the projects. The discounted cash flow (DCF) analysis is generally applied for the valuation of mining projects, whereby future cash flows are discounted to present value using an appropriate discount rate. The discount rate significantly affects the outcome of a valuation. Economic and finance theory provides tools to calculate discount rates. The discount rate must account for factors such as the risk and stage of development of the mineral project; hence the appropriate discount rate to utilize in a project is often a subject of debate.The discount rate is the weighted sum of the cost of debt and equity. There are several methods for determining the cost of equity. This study considers the commonly applied Capital Asset Pricing Model (CAPM) and Gordon’s Wealth Growth Model because of their simplicity and availability of parameters required to estimate the cost of equity. This study explores how differences in the cost of equity obtained by these two methods can be explained for a mining environment. Data for empirical analysis were collected from the I-Net Bridge, McGregor BFA, and Bloomberg databases. It was found that Gordon’s Wealth Growth Model provides better estimates of the cost of equity compared to the CAPM under depressed market conditions. Therefore, this research recommends that Gordon’s Wealth Growth Model be used to estimate the discount rates for mining projects during periods of depressed market conditions."

Jan 1, 2016

By L. Mabiza

Keywords: Pyrometallurgy, furnace, sulphur, SO2, off-gas, Zimplats Zimplats embarked on an off-gas sampling campaign in December 2009 to characterise the concentration of SO2 in the off-gas from their 13 MW furnace. In excess of forty isokinetic samples (US EPA Method 8) were taken over seven days. The aim of the sampling campaign was to increase the understanding of factors that influence sulphur release from sulphide concentrates in an electric furnace. Specifically, detailed monitoring was conducted over various operating conditions to evaluate: ? The relationship between SO2 and feed rate (i.e. furnace power) ? The relationship between SO2 and ingress (i.e. furnace freeboard pressure) ? The impact of concentrate bed thickness on SO2 (i.e. blacktop) ? The effect of events such as tapping and converter slag return on SO2 ? The desulphurization reactions that take place in the blacktop A model was developed to predict the SO2 content in furnace off-gas for a particular set of operating conditions. In order to evaluate the impact of random, uncorrelated changes in concentrate composition, ingress and power (feed rate) on the SO2 content of the off-gas, a Monte Carlo approach was adopted whereby concentrate composition, power, and ingress were allowed to vary randomly around selected set-points. The model is primarily based on the release of ?labile? sulphur from the partial thermal dissociation of sulphide minerals with an over-stoichiometric sulphur content (e.g., Fe7S8 decomposition to FeS and S). The main findings of this work suggest that labile sulphur does not fully account for the measured SO2 content of the off-gas, and that limited oxidation of sulphides during melting also contributes to the SO2 content. Details of sulphide oxidation reactions in the furnace remain unclear, and it is currently not possible to provide a theoretical framework for the relationship between the extent of oxidation and variables such as temperature, gas composition, particle size, and residence time in the furnace black top. Through the use of the Monte Carlo model it was, however, possible to constrain the extent of sulphide oxidation to about 1%. This work has shown in practice what was expected in concept, that SO2 in off-gas is proportional to furnace power and ingress rate. The model that was developed consistently slightly under-predicts the quantity of SO2 generated. It also highlights that more work is required to better understand the analytical methods used to analyse for SO2 in off-gas.

Jan 1, 2011

By Vinay Kumar Agrawal, Rama Nath Praharaj

IMFA Group is the largest producer of Charge chrome not only in India but also in Asia. This Group has plants situated at Therubali and at Choudwar. They also have a Thermal power plant at Choudwar which not only caters to the power requirement of Choudwar plant but also supplies power to Therubali. The plants are fed for Chromite ore through the captive mines namely Nuasahi Chromite mines (40.47 Ha) , Bangur Chromite mines(37.34Ha), Sukinda chromite mines (116.76 Ha), Mahagiri Chromite Mine(73.777 Ha) and Chingudipal Chromite mines (26.62 Ha). Nuasahi Chromite Mine, which is situated in Keonjhar district, is an underground mine and is based upon best technological advancements in the industry. The underground mining operation is certified under ISO-9002, ISO-14001and OHSAS 18001. This not only shows the concern for the quality, environment but also for the health of the employees. The Nuashahi is the first chromite mine to backfill the opencast excavations created during the last 50 years and carry out the production from underground area below the opencast workings. This paper deals with the state of art technology of sub-level open stopping in thin ore bodies. The under-ground mine openings was started in the year 1997. In next four years the production of chromite from underground was started.(2001). At present the mine is in a good shape with several running stopes. Today it is producing around 10,000 Mt per month of chromite. The development of the mine is carried out with an average of 200 mtr per month of tunneling. The mine is having a mechanical ventilator having a capacity of24000 M3 per hour at 50mm water gauge, thus feeding sufficient air for the persons working in underground. The mine is being dewatered through a most modern positive suction sump, having a capacity of 500 cum and operated with 120 HP pumps. After commissioning of this sump in the year 2003, the mine has taken a quantum jump in production with remarkable saving in power consumption.

Jan 1, 2007

By E. Pizarro, A. Videla, G. Compan

One of the main problems related to mining investment decisions is the use of accurate prediction models. Metallurgical recovery is a major source of variability, and in this regard, the Chuquicamata processing plant recovery was modelled as a function of geomining-metallurgical data and ore characteristics obtained from a historical database. In particular, the dataset gathered contains information related to feed grades, ore hardness, particle size, mineralogy, pH, and flotation reagents. A systemic approach was applied to fit a multivariate regression model representing the copper recovery in the plant. The systemic approach consists of an initial projection of the characteristic grinding product size (P80), based upon energy consumption at the particle size reduction step, followed by a flotation recovery model. The model allows for an improvement in the investment decision process by predicting performance and risk. The final geometallurgical model uses eight operational variables and is a significant improvement over conventional prediction models. A validation was performed using a recent data-set, and this showed a high correlation coefficient with a low mean absolute error, which reveals that the geometallurgical model is able to predict, with acceptable accuracy, the actual copper recovery in the plant.

Jan 1, 2015

By S. Z. Pethö

Pillar extraction at shallow depths with small pillars that were not originally intended for secondary extraction can provide a huge benefit to the coal mining industry in those areas where a significant percentage of the remaining coal reserves are locked up in small pillars at shallow depths and where opencast mining methods are simply not as cost-effective and practical to implement. A system considering all of the pertinent geotechnical and mining aspects for the safe and efficient pillar extraction of small pillars at shallow depths at Xstrata Coal South Africa (XCSA) has been further developed and implemented as part of an ongoing improvement process addressing all of the relevant legal and associated risk aspects. This work follows on from the previous pillar extraction work carried out at the ATC, Boschmans, and Spitzkop Collieries. The process involved a number of in-house workshops and sessions arranged with all key personnel from Tavistock Colliery, and also included Professor Nielen van der Merwe of the University of the Witwatersrand, a world renowned authority on pillar extraction, towards reviewing and developing the Modified NEVID pillar extraction system employed previously at Boschmans Colliery. The system is currently being employed at Tavistock Colliery with success and no major accidents, with around 655 000 t of coal having been successfully extracted from the pillar extraction panels.

Jan 1, 2012

By J. Dienenthal

Automatic Charging and Stoking Machines for use at ferroalloy furnaces are in operation for more than 20years. Dango & Dienenthal Maschinenbau GmbH (short: DDS) has developed several machine generations. Today advanced solutions help to achieve better charging and stoking results to minimize cost and to improve the working environment around the furnaces. Three different alternatives can be considered: Rail-mounted solution The machine(s) travel(s) on an overhead monorail to one or several furnaces and is locked in the desired working position from where charging and stoking is performed. Mobile solution This machine travels on the charging platform and is also locked at the respective working position to perform charging and stoking. Automation of a standard mobile charging and stoking machine A standard charging and stoking machine can be adapted for automation. A reliable navigation system is included. Charging and stoking is performed with the moving machine. Advantage versus other solutions: considerable lower investment cost and possibility to upgrade the mobile charging and stoking machine for later automation. Overall, automatic charging and stoking can save up to 10 per cent of the specific smelting energy. A better and more consistent furnace operation can be achieved. Different programs are used to cope with different furnace conditions and changing raw materials. All machine movements can be recorded and correlated to other furnace parameters. Working environment on the charging platform is greatly improved.

Jan 1, 2007

The compilation of the sampling nomogram is an essential tool in the optimization of a sampling protocol and allows the operator to track the change in relative variance of the sampling error (the Fundamental sampling error) during steps of comminution and mass reduction in the process of recovery of the aliquot for analysis. The data required for the compilation of the nomogram are centred on the sampling constant K and the exponent, alpha (a) of the nominal fragment size. Five methods for establishing K have been identified, but two of them, the duplicate sampling analysis method and the heterogeneity test method purport to provide such constant. The step by step procedure for each of these two methods was examined using broken ores from three mines, Mponeng mine, Kloof mine, and Lily mine. Two of these mines (Mponeng and Kloof) are typical Witwatersrand-type gold mines, and the third is an Archaean-type shear related gold deposit situated in the Barberton Greenstone belt. The results suggest that the factor K derived using the heterogeneity test is very accurate, but applies only to a single size fraction in the spectrum of comminuted materials. The calculation of gold grain sizes using this method appear to be too small and do not conform with the results from detailed mineralogical studies. The factors K and alpha derived using the duplicate series analysis are appropriate for use across a wide spectrum of comminution sizes and also provide realistic gold grain sizes, comparable with the equivalent circular diameter of gold grains identified in mineralogical studies of the ores.

Jan 1, 2010

By I. Mc Dougall

Finite element models were generated of two submerged arc furnaces of different geometries. A 48MW circular furnace and a 68MW 6-in-line rectangular furnace were studied. The electrodes, raw material, slag and molten metal were included in the model. ANSYS/Multiphysics was used to predict the current density distribution in the electrodes, raw material, slag and molten metal as a result of the three phase AC current. The effect of the electrode immersion on the current path was studied. The ?proximity effect? caused a pronounced asymmetry in the electrode currents in the circular furnace, whilst the electrode currents in the rectangular furnace exhibited radial symmetry. The current distribution in the melt in both furnaces indicated that the bulk of the current flows between phases. The current density is greatest between electrodes. Results were compared to qualitatively similar published work, operating experience and results of furnace dig-outs.

Jan 1, 2007

By J. D. Steenkamp

Southern Africa has a history rich in the pyrometallurgical processing of ores. Two of the alloys produced are high-carbon ferromanganese (74?83 per cent Mn) and silicomanganese (59?67 per cent Mn and 14?31 per cent Si). The largest land-based manganese ore deposit in the world is based in the Northern Cape Province of South Africa. In 2010, 6.3 Mt of ore from the deposit was exported, mainly to China, Norway, Japan, and India, and an estimated 1.1 Mt beneficiated locally to produce manganese ferroalloys. In southern Africa the producers of manganese ferroalloys are Metalloys and Assmang, and of silicomanganese Transalloys, Mogale Alloys, and Match Corporation. Submerged arc furnace technology is utilized in the production of high-carbon ferromanganese (HCFeMn) and silicomanganese, applying the discard slag practice in both instances. The carbon content of HCFeMn is reduced using converter technology and that of SiMn using the Perrin process. Ninety per cent of the world?s manganese ferroalloys production is consumed by the steel industry. The consumption (and production) of manganese ferroalloys therefore closely follows worldwide steel production. From 2001 to 2010, the doubling of the worldwide production of manganese ferroalloys can be attributed to an increase in production capacity in Asia and Oceania, with the largest increase in the production of SiMn. Manganese ferroalloys produced in Asia and Oceania are mainly for the local market, with North America, Europe, Russia, and Turkey the major markets for alloys from southern Africa. The major challenges faced by the southern African manganese ferroalloy producers are increasing electricity tariffs and productivity of labour, which require a concerted effort by all parties involved to achieve a satisfactory solution. Keywords manganese ferroalloys, ferromanganese, silicomanganese, southern Africa, South Africa, manganese ore, high-carbon ferromanganese, refined ferromanganese, refined silicomanganese.

Aug 1, 2013