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By C. Siyasiya

One of the problems that is occasionally encountered during the continuous casting of DIN 1.4003 stainless steel (hereafter referred to as 1.4003) is the side bulging effect, a problem that is generally prevalent in ferritic stainless steels. This occurs because the unconstrained narrow sides of the solidification shell are not able to withstand the ferrostatic pressure once the strand has emerged from the mould. Coupled with side bulging, there is strand width variation at high temperatures, i.e. when the steel is in the ferrite-austenite dual phase region. Both of these dimensional changes to the slab profile create some processing problems in subsequent hot rolling operations when unacceptable width variations are encountered. The strength of the solidification shell and its ability to withstand the ferrostatic pressure during continuous casting is dependent on its thickness and phase composition when exiting from the mould up to a few metres downstream. From the study of the high temperature metallurgical behaviour of this steel, it was observed that a thicker solidification shell when exiting from the mould and a higher austenite volume fraction in the steel would be favourable for the reduction of the side bulging effect during continuous casting. It was also found that as long as the d-ferrite to austenite phase ratio keeps fluctuating due to variations in chemical composition and process control in the dual phase region from cast to cast, the strand width variation problem would probably persist. The remedy to this effect lies in more strict chemical composition and process control during continuous casting of this steel. The hot ductility experiments revealed that 1.4003 exhibits good hot ductility in the strand straightening temperature range with a minimum of 75 per cent reduction in area and this was attributed to the high volume fraction of ferrite (0.2 to 0.4) in the steel. This would provide a remedy to side bulging by increasing the secondary cooling rate of the strand in order to form a thicker solidification shell without necessarily risking transverse cracking and other surface defects during unbending. Keywords: side wall bulging, resistance bending moment, applied bending moment, ferrostatic pressure.

Jan 1, 2005

By G. Hangone

Paper written on project work carried out in partial fulfilment of MSc thesis This paper investigates the effects of thiol collectors: xanthates, dithiophosphates, dithiocarbamates and mixtures of these on the froth flotation performance obtained with a bornite-rich copper sulphide ore from Okiep Copper Mine with a feed grade of 1.8%copper. Batch flotation tests were used to assess the performance in terms of mass-water recovery, sulphur grade-recovery and copper grade-recovery relationships and the Klimpel rate constant for copper recovery. The results showed that the di-ethyl-dithiocar-bamate (di C2-DTC) was the weakest collector of copper sulphide minerals. Highest copper recoveries were obtained with the di-ethyl-dithiophosphate (di C2-DTP), which were accompanied with more watery froths and lower copper grades demonstrating frothing properties in addition to collector action. Superior copper recoveries were obtained with the 90% ethyl xanthate (C2-X):10% di-ethyl-dithiophosphate (di C2-DTP) and 90% ethyl xanthate (C2-X):10%di-ethyl-dithiocarbamate (di C2-DTC) collector mixtures compared to that obtained with ethyl xanthate at an equivalent collector dosage of 0.139 mol/ton ore (a dosage equivalent to 20 g sodium ethyl xanthate per ton ore). A superior copper grade was obtained with the 90% ethyl xanthate: 10% di-ethyl-dithiocarbamate collector mixture at a dosage of 0.0695 mol/ton ore compared to that obtained with ethyl xanthate at the same equivalent dosage. Keywords: flotation, collector mixtures, copper sulphide ore

Jan 1, 2005

By C. Maree

Paper written on project work carried out in partial fulfilment of B. Eng (Chem. Eng.) This paper describes the development and use of a process simulator to optimize gypsum recovery at Afmine, a small plant near Yzerfontein on the South African West Coast. The simulator consisted of models of the major plant equipment, viz. hydrocyclones, surge bins, settling tanks, a primary sieve and a dewatering screen. Experimental data suggested that the equipment could be modelled satisfactorily from data published in the open literature. Simulation studies have indicated that gypsum losses on the plant could be reduced substantially by means of some relatively minor modifications to the plant layout. Moreover, sensitivity analyses of the plant have indicated that optimization of the settling tanks should receive priority over the other process units.

Jan 1, 2005

By G. Westcott

Impala Platinum, the second largest platinum producer in the world, is embarking on a major expansion strategy to increase its platinum output from 1.95 moz to 2.8 moz by the year 2008. The smelter complex, situated in Rustenburg, will undergo substantial modifications, and will require a solution to the capture and treatment of the smelter off-gases and dust produced during smelting and converting operations. One of the solutions explored was an integrated approach, where all the off-gases from both the primary smelting electric furnaces and the converter operations are routed to a large central gas cleaning and double catalysis, double absorption acid plant. In-line sulphur burning, utilizing a highly flexible LURO1spin cup burner with a turn down ratio of 50%, ensures that the acid plant operates independently of operating conditions at the smelter complex.

Jan 1, 2007

By J. Little

It is common practice for underground mine plans to be created sequentially, where results from one planning process form the input data for another. While this is practical for manual methods, computerized optimization techniques should consider an integrated approach to creating the global mine plan. This is because optimizing an individual mine planning process, such as stope layouts, introduces a likelihood of increasing costs or decreasing revenues associated with other areas, such as production scheduling, as harmful decisions must be balanced. Considering the interaction and influence that individual underground mine planning processes have on each other during optimization will provide more profitable results than if these are ignored. Optimization techniques for stope layouts and production scheduling are reviewed. An integer programming model is proposed that allows for either integrated or isolated optimization. Both approaches are separately applied to a block model. The results demonstrate the model?s ability to produce optimal long-term sublevel stoping mine plans and the benefits of using an integrated approach. Keywords underground mine optimization, stope layouts, underground production scheduling, integer programming, mathematical programming application.

Oct 1, 2013

By C. Birch

"A ‘geologically constrained’ orebody model has long been hailed as vital for a Mineral Resource statement that is compliant with the South African Code for Reporting of Exploration Results, Mineral Resources and Mineral Reserves (SAMREC Code). In this paper, the requirements for geological modelling as contained in the outline for the SAMREC Code are considered, and whether the new modelling software available on the market is a ‘black box’ or is better for modelling than traditional methods of wireframe creation.Implicit geological modelling is a technique that uses a radial basis function to establish and update geological models relatively quickly and efficiently from borehole data, outcrop data, manually interpreted vertical or horizontal sections, and structural data. Assays and any coded drill-hole data, such as lithology and alteration, can be interpolated.Leapfrog Geo software is an example of this new approach to geological modelling. A case study of a short training course in geological modelling for non-geologists at the University of Witwatersrand, as part of the Higher Certificate in Mineral Resource Management, is presented. The benefits of this type of geological modelling software are considered for this type of assignment as well as for mining industry applications.The use of geological models in mine planning is reviewed and a case study is presented comparing the variations in mine plan design and financial output of 13 final-year Mine Design projects from the University of the Witwatersrand School of Mining Engineering. These designs were all based on the same geological model created in the traditional way, and yet the resultant mine designs were significantly different, with very different resulting financial outlooks for the project. This raises questions as to how significant a very detailed model in the pre-feasibility and feasibility phases of projects really is, considering the huge costs involved in gathering the required data to build a SAMREC-compliant geological model."

Jan 1, 2014

By S. L. Chen

Keywords: copper, concentrate drying, steam dryer, dryers By placing additional demands on energy and gas flow, the moisture content of a copper concentrate has an adverse effect on the smelting process. Different drying technologies, such as directly heated rotary dryers, flash dryers, and steam dryers, are available to solve this problem. The energy requirements of and off-gas generated from different dryer types are compared. The performance of the steam dryer was found to be superior to that of the others. In particular, the rotary steam dryer and its benefits are discussed. Structural properties confer an advantage on the rotary steam dryer, for wear on tube elements is eliminated, and drying efficiency is improved. If steam is available, the rotary steam dryer is an excellent choice for drying copper concentrates.

Jan 1, 2006

By G. B. Quaye

The deep level gold mining environment is characterized by high stresses that give rise to intense mining induced fracturing of the rock mass surrounding the stopes. In a geologically disturbed region where the intensity of mining induced stress fracturing is high, the degree of faulting and/or the frequency of other geological features such as joints may pose serious strata control problems. Unfavourable intersection of these discontinuities namely, faults, joints and mining induced stress fractures tend to divide the immediate hangingwall into unstable keyblocks which, if not supported, may result in extensive falls of ground. Effective support strategies therefore demand detailed investigation of the predominant inclinations and orientations of these discontinuities. The orientations and inclinations of these discontinuities surrounding a deep level stope have been measured. The results are projected onto the lower hemisphere of a stereographic net to determine the factors that contribute to the falls of ground in the stope. The analyses reveal that unfavourable intersection of these discontinuities divides the immediate hangingwall into unstable wedges that may become dislodged between support units.

Jan 1, 1998

By M. Tangstad, B. Monsen, H. Midtgaard

The increased attention towards reducing emissions of fossil CO2 due to its potential global warming effect has resulted in a focus on renewable resources, as charcoal. Since charcoal is produced from growing wood it does not contribute to global warming. This paper gives a brief review of consequences of and reasons for using charcoal in the silicomanganese (SiMn) production. Results are presented from practical SiMn smelting experiments, on a pilot scale, using charcoal as reduction material and comparing with coke. As slag- and CO2-reactivity are important for furnace performance these features have also been measured.

Jan 1, 2004

By J. J. Bezuidenhout

The waste-heat boiler is used within the Sulphide flash smelting process as the main dust and energy recovery unit. The large volume of off-gas discharged from the flash smelter is at a very high temperature (1350°C) and contains a significant dust load that subjects the downstream waste-heat boiler to tough and demanding conditions. The boiler cavity is especially prone to dust accretions, fouling, and corrosion caused by accumulation of molten particles and precipitation of sulphuric acid. Computational fluid dynamics (CFD) is applied within a qualitative study to model the flow and heat transfer distribution throughout the waste-heat boiler. The commercial CFD package, Fluent 6.2.16, was applied to a modified waste-heat boiler (23 m ×11 m ×5.4 m) within the Outokumpu flash smelting process. This investigation focuses on the geometric modifications to the typical boiler design, which includes elevation of the ceiling, placement of flow-obstructing baffles and radiation plates parallel within the flow path. Also investigated were various boiler operating conditions such as the circulation of process off-gas, air leakage from the dust discharging hoppers and variation in inlet gas composition. The geometric modifications had the desired effect of increasing the volumetric utilization and therefore enhancing heat transfer between the boiler surface and the gas stream and dust segregation. Introducing circulated off-gas at a rate of 20 m/s and at a 45° angle to the front of the waste boiler further enhanced cooling while reducing the high impact of the furnace-uptake gas-stream on the boiler ceiling. The placement of radiation plates was found to be very effective in enhancing the heat transfer surface and distributing gas flow within the boiler. These results present recommendations towards an improved waste-heat boiler design. Keywords: flash smelting, waste-heat boiler, CFD simulation, off-gas cooling.

Jan 1, 2008

By Org de Wet

This paper summarises the strategy for selection between a two module coal plant incorporating large, but less equipment, and a three module coal plant with more but smaller equipment. The two options were evaluated in terms of three main categories: ? Size ? size of the equipment and the effect on the process efficiency as well as the difference in physical dimensions of the plant to accommodate the larger equipment; ? Cost ? capital savings between a two and a three module plant, processing the same ROM (run-of-mine) tons per hour (t/hr); and ? Practicality ? in terms of constructability of the plant, safety of using larger equipment and maintainability of the equipment. Decisions that were taken to reduce the risk associated with size, cost and practicality on the chosen option of a two module plant will be highlighted.

Jan 1, 2006

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 G. van den Berg

Anglo Platinum has initiated a project to investigate hydraulic hoisting technology for platinum mines. Hydraulic hoisting systems are categorized as pumping, fluidizing feeder or displacement feeder systems. Positive displacement piston diaphragm pumps are most suitable for pumping systems but they require that the ore be milled prior to pumping. Fluidizing feeders are unsuitable for platinum ore applications due to the large percentage of fines in the ore. The three-chamber pipe displacement feeder has been most widely used for hydraulic hoisting and is the most suitable technology for platinum mines. Eight hydraulic hoisting applications covering pumping and displacement feeder technologies are reviewed. The key factors to be assessed in selecting a hydraulic hoisting system for a platinum mine are discussed. A typical platinum mine configuration will comprise an ore preparation plant (to produce -15mm material through screening or crushing), motive water pump on surface, high pressure water pipeline from surface to underground, ore slurrification plant, three-chamber displacement feeder, and a high pressure slurry pipeline to surface. The water and slurry pipelines are housed in a purpose drilled borehole. A hydraulic hoisting system selection chart is presented. A 150mm diameter system with a 25 MPa pressure rating is required to hoist 60 000 t/m from a depth of 1 200 m. Generic capital and operating costs are presented. A major potential advantage of hydraulic hoisting is that the fines, which contain a high percentage of PGMs, are captured underground and transported directly to the concentrator. Hydraulic hoisting technology is ideally suited to providing supplementary hoisting capacity to existing shafts that have reached the skip hoisting capacity limit. The main advantage for new shafts is the potential to significantly simplify underground rock handling and transportation. All hydraulic hoisting system components are proven. The only risk area is the wear rates of the valves and piping. Current estimates are based on gold ore. The business cases investigated show that the financial viability of the installations are not sensitive to wear rate. Hydraulic hoisting is technically feasible and financially attractive for platinum mines. Keywords: hydraulic hoisting, slurry

Jan 1, 2005

By George J. Karcas, Raimo Kuusisto, Pertti Pekkala

Ongoing Outokumpu development in Solvent Extraction and Electrowinning Technology, involving all aspects of process chemistry, equipment and control, extends over a period of close to 30 years. The development in SX started with molybdenum and rhenium, continued with zinc, manganese, cobalt and nickel and is now focusing on copper. The OutoCompact VSF? SX concept, which has been recently introduced, is a honed version of earlier VSF? technology. The Outokumpu VSF? ("Vertical Smooth Flow") SX package includes the DOP ("Dispersion Overflow Pump") units, the Spirok Mixers, the OutoCompact Settlers including their DDG ("Dispersion Depletor Gate") fences and tank farm equipment such as the LOS ("Loaded Organic Scrubbing") tank as well as the CEP ("Copper Electrolyte Purifying") tank. Although the VSF? SX package can be implemented according to several optional lay-outs, the so-called Track version has lately been introduced to the advantage of new plants. The new OutoCompact SX technology decreases the footprint of future VSF? plants. The lay-out, including plant size flexibility, have further been improved by Outokumpu?s new OutoReverse settler technology. Two of several SX plants currently under construction rely on reverse settlers in order to maximize their performance. The Outokumpu EW technology includes process know-how as well as proprietary equipment. The copper EW package consists of permanent stainless steel cathodes based on wax-less technology and lead anodes utilising polymer concrete cells with the double contact bus bar system and ventilation hoods fitted for efficient mist control. The lifting of cell hoods, as well as cathode washing, is done by the cathode pulling crane. Proper electrolyte flows and matching current density further ensure high productivity of LME grade copper cathodes.

Jan 1, 2005

By P. C. Carrasco

Knowing the origin of the relevant and irrelevant components of the nugget effect is essential to optimize the process under study. This paper describes the causes of the nugget effect and, its dependency on the sample support, sampling density, and on the QA/QC procedures. Several examples of natural and ?human? nugget effect are given. A method to estimate the magnitude of the relevant and irrelevant components is suggested. Finally, the economic consequences of misunderstanding the nugget effect are analysed.

Jan 1, 2010

By K. Lombard

"‘Roof support awaiting time’ (RSAT) is a term used at Goedehoop Colliery’s Simunye Shaft to describe the potential production time lost due to the continuous miner (CM) standing idle waiting for roof support to catch up. Investigations revealed that in 2013, Simunye Shaft had approximately1400 hours of RSAT, which suggests that the mine could have potentially produced an additional 280 000 t of coal. This project consisted of two parts. Firstly, the causes of the high RSAT and means to improve the situation were investigated. Secondly, as insisted by mine management, the CM cutting sequence was investigated as a possible cause of high RSAT. Machine-related challenges due to the roofbolter installing support too slowly, geological conditions (mostly hard roof conditions and slips),logistical challenges pertaining to the CM cutting sequence, man-related challenges related to operator fatigue, re-support, operator inexperience, and the absence of support targets were identified as main contributors to RSAT. Furthermore, results showed that the roofbolters in the sections at Simunye Shaft are slower than the CMs. A target of 28% reduction in RSAT was set. Experts from Kennametal and Fletcher were consulted to find solutions for the identified causes. In total, eight solutions for RSAT were identified, but the solution that contributed most significantly to reducing RSAT was to use hard roof drill bits as a standard product at Simunye Shaft. Calculations showed that by using hard roof drill bits, RSAT can be reduced by 43%, which is more than the specified 28% target. The cutting sequences at Kriel, Greenside, and Simunye Shaft, togetherwith three newly developed cutting sequences, were simulated using the UCMS (Underground Coal Mining Simulation) program. A re-aligningprinciple was incorporated into the newly developed cutting sequences toalign the cutting sequences to general support work and to reduce RSAT. A decision matrix revealed that a cutting sequence in which boxing takesplace in R3 (third road to the right of the belt road) and in which the re-aligning principle has been incorporated will be the best option for Simunye Shaft. The recommended cutting sequence will lead to a 5% increase in production.The work presented in this paper was carried out as partial fullfilment for the degree BEng (Mining Engineering)"

Jan 1, 2015

By D. E. Ng?andu

The experience of Mufulira concentrator, of the Zambia Consolidated Copper Mines Limited, with underground mine drainage water, which is used in milling operations is discussed. It is shown that the underground mine water has a deleterious effect on flotation performance. The adverse effect of the underground water was successfully negated by adding lime into the primary ball mills and increasing the pH of the slurry, from a ?natural? pH of 8 to the flotation pH of 10.5. Traditionally, the pH modifier, quicklime, had been added downstream of the milling. Changing the lime addition point further reduced lime consumption by 50%,?a key issue as lime accounted for over 60% of the Mufulira flotation reagent costs. The nature of the effect of the underground water at Mufulira, particularly the sensitivity of the flotation to the pH at which the milling was conducted, characterized galvanic interaction. A large-scale plant situation is presented in which the desired electro-chemical response in the flotation was achieved, by a deliberate manipulation of the milling environment. The experience provides practical testimony of a more fundamental role for the milling process, other than the mere physical preparation, i.e. size reduction and liberation, of mineral particles prior to flotation.

Jan 1, 2001

Recent studies on the physico-chemical properties of molten slags and oxide solid solutions of interest are reviewed. The review covers redox and phase equilibria in slags, viscosity, diffusivity, electrical conductivity, kinetics of interfacial reactions between slags and CO-CO2, interfacial properties and phenomena. Some highlights from ongoing work on modelling phase diagrams, component activity, viscosity and electrical conductivity of multi component slags will be presented and results compared with published experimental data on slags with or without suspended solid phases.

Jan 1, 2004

By Steven Rupprecht

"The South African Code for the Reporting of Exploration Results, Mineral Resources and Mineral Reserves (the SAMREC Code or the Code) sets out minimum standards, recommendations and guidelines for public reporting of exploration results, mineral resources and mineral reserves in South Africa. The Code is being rewritten and updated, with work on-going since 2013. The revision is being undertaken to ensure the Code remains relevant, incorporates developments within the international mining industry and keeps abreast of technology. Some of the changes and their reasons are discussed. INTRODUCTION The South African Code for the Reporting of Exploration Results, Mineral Resources and Mineral Reserves (the SAMREC Code or the Code) sets out minimum standards, recommendations and guidelines for public reporting of Exploration Results, Mineral Resources and Mineral Rreserves in South Africa. The Code is being rewritten and updated, with work on-going since 2013. The proposed 2016 update is not significantly different from previous versions of the Code. The revision is being undertaken to ensure the Code remains relevant, incorporates developments within the international mining industry and keeps abreast of technology. The Code sets out minimum standards, recommendations and guidelines for public reporting. However, reporting may be unclear, ambiguous, selective, obscure, distorted or unintelligible. Part of the purpose of the update is to provide better guidelines to Competent Persons (CPs) to ensure that the material information is being reported and that reporting is transparent in accordance with the guidelines of the Code. The information provided should, as required by the Code, be adequate to inform the “reader/investor or potential investor to make a reasonable and balanced assessment of the significance of the information”. The Committee for Mineral Reserves International Reporting Standards (CRIRSCO) highlights the importance of the reporting Codes, as provided from a quote from their website (www.crirsco.com): The mining industry is a vital contributor to national and global economies. It is a truly international business that depends on the trust and confidence of investors and other stakeholders for its financial and operational well-being. Unlike many other industries, it is based on depleting mineral assets, the knowledge of which is important prior to the commencement of extraction. It is therefore essential that the industry communicates the risks associated with investment effectively and transparently in order to earn the level of trust necessary to underpin its activities."

Jan 1, 2015

By L. Jeffrey

The Waterberg Coalfield has vast potential to become a significantmining and industrial centre in South Africa. Its future developmenthinges on a number of critical decisions that must be made jointly by government, power utilities and industry, and on some technical and economic challenges that must initially be overcome. Sufficient water is the primary key to enabling exploitation, together with an adequate market for the large volumes of low-grade coal. As the most likely consumer of this coal will be either a power station or a petrochemical complex, the need for additional energy will be a driving force in the development of this coalfield. Conventional mining methods can exploit the shallow coal resources in both the Grootegeluk and the Vryheid formations, but alternative technologies such as coalbed methane extraction and underground coal gasification are the only currently known technologies that may be able to exploit the deep Grootegeluk Formation resources. However, extensive research is still required into these procedures, particularly with respect to the Waterberg coals. Transport infrastructure to the region is currently not sufficiently well developed to support large-scale exploitation of the region?s coal resources. In particular, the railway line would have to be extensively upgraded to allow the increased export of coal. Alternative transport methods such as pipelines would also have to be pursued to serve a large Sasol-type petrochemical complex or coal gas extraction. The road network would also require improvement, as only the roads between the main commercial centres are currently tarred. Dr Con Fauconnier, Kumba CEO, concluded his presentation to the Investing in African Mining Conference 2004 with the words: Again, it?s all about infrastructure? when it?s there, it enables the development of bulk mining projects which attract the resultant economic benefits for the region and country as a whole. These words aptly sum up one of the stumbling blocks to the future development of the Waterberg Coalfield.

Jan 1, 2005