Academic literature on the topic 'Theses – Metallurgical engineering'

In order to study the relationship and effect of nitrogen gas in the reducing gases used in the reducibility tests of iron oxides, under isothermal conditions, a test scheme was executed using ammonia gas, such that its decomposition of the gas in the reactor produced a mixture of H2 and N2 gases. Furthermore, the addition of 6% NH3 in a 28% H2 and 68% N2 gas stream was planned to obtain a gas composition of 70% N2 and 30% H2. This would allow comparing the reducibility curves between both conditions, assuming that the possible difference between both conditions to compare the volume changes of the reduced samples. The difference to be studied will be based on the estimation and comparison of the rate of formation of metallic iron in the stages of reduction of Hematite / Magnetite / Wustite (FeO), as well as the effects of nitrogen absorbed by the fresh metallic iron produced, or present. in iron catalysts to produce ammonia, from the reducing gas mixture, on the volume change of the samples. Likewise, the catastrophic volume changes caused by nitrogen are compared by comparing sources of this gas in solid carbonaceous reducers. Keywords: Gaseous Reduction, Direct Reduced Iron, isothermal tests. References [1]O. Dam G. “The Influence of Nitrogen on the Swelling Mechanism of Iron Oxides During Reduction”. Univ. of London. PhD Thesis 1983. [2]J. Bogde. “Thermoelectric Power Measurements in Wustite. Univ. of Michigan”. 1976. [3]O. Dam G. y J. Jeffes. “Model for the Assessment of Chemical Composition of reduced iron ores from single measurements. Ironmaking and Steelmaking”. Vol. 14, N`5. 1987. [4]M. Yang. “Nitriding-Fundamentals, modelling and process optimization”. Tesis PhD. Worcester Polytech Institute. 2012. [5]EL Kasabgy. T and W-K. LU. “The Influence of Calcia and Magnesia in Wustite on the Kinetics of Metallization and Iron Whisker Formation”. Metallurgical 1980 American Society for Metals and the Metallurgical Society of AIME Volume 11b, pp. 410-414. 1980. [6]“Srikar Potnuru Studies nn the Physical Properties and Reduction Swelling Behavior of Fired Haematite Iton ore Pellets”. MSc Thesis. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2012. [7]R. Agarwal, S. Hembram. “To Study the Reduction and Swelling Behavior Iron Ore Pellets”. BSc. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2013. [8]C. Seaton., J. Foster. and J. Velasco. “Structural Changes Occurring during Reduction of Hematite and Magnetite Pellets Containing Coal Char”. Transactions ISIJ, Vol. 23, 1983, pp. [10]C. Bozco. “Interaction of Nitrogen with Iron Surfaces”. Journal of Catalysis 49. pp16-41. 1977. [11]L. Darken y R. Gurry. “Physical Chemistry of Metals”. Mc Graw hIll . 1953. [12]H. Weirdt and Z. Zwell, Trans. AIME. 229. 142. 1969. [13]J. Schulten. Trans. Soc. Faraday. 53, 1363, 1957. [14]E. Barret y C. Wood. Bureau of Mines R-I 3229. 1934

Con el objeto de estudiar la relación y efecto del gas nitrógeno en los gases reductores utilizados en los ensayos de reducibilidad de óxidos de hierro, en condiciones isotérmicas, se ejecutó un esquema de ensayos utilizando gas amoniaco, tal que la descomposición del gas en el reactor produjera un gas de H2 y N2. Además, se planifico la adición de 6% de NH3 en una corriente de gas 28% H2 y 68% N2 para obtener una composición de gas de 70% N2 y 30% H2. Esto permitiría la reinterpretación de los datos de laboratorio para comparar las curvas d reducibilidad entre ambas condiciones, asumiendo que la posible diferencia entre ambas condiciones a comparar los cambios de volumen de las muestras reducidas. La diferencia a estudiar se basará en la estimación y comparación de la velocidad de formación de hierro metálico en las etapas de reducción de hematita/magnetita/wustita (FeO), así como los efectos del nitrógeno absorbido por el hierro metálico fresco producido, partir de la mezcla de gas reductor, sobre el cambio de volumen de las muestras. Así mismo se comparan empíricamente los cambios catastróficos de volumen causados por el nitrógeno comparando fuentes de este gas en reductores carbonosos sólidos. Palabras clave: reducción gaseosa, hierro de reducción directa (HRD), catálisis, catalizador de hierro, amoniaco, hinchamiento, absorción, nitruración. ensayos isotérmicos, nitrógeno en carbón. Referencias [1]O.G. Dam . The Influence of Nitrogen on the Swelling Mechanism of Iron Oxides During Reduction. Univ. of London. PhD Thesis 1983. [2]J.D Bogde.- Thermoelectric Power Measurements in Wustite. Univ. of Michigan. 1976. [3]O.G. Dam y J. Jeffes. Model for the Assessment of Chemical Composition of reduced iron ores from single measurements. Ironmaking and Steelmaking. 1987. Vol. 14, N`5. [4]M. Yang. Nitriding-Fundamentals, modelling and process optimization. Tesis PhD. Worcester PolytechInstitute. 2012. [5]T. EL Kasabgy y W-K. LU. (1980). The Influence of Calcia and Magnesia in Wustite on the Kinetics of Metallization and Iron Whisker Formation. Metallurgical 1980 American Society for Metals and the Metallurgical Society of AIME Volume 11b, September 1980, pp. 410-414. [6]Srikar Potnuru Studies nn the Physical Properties and Reduction Swelling Behavior of Fired Haematite Iton ore Pellets. MSc Thesis. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2012. [7]R.S Agarwal y S.S. Hembram. To Study the Reduction and Swelling Behavior Iron Ore Pellets. BSc. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2013. [8]C.E. Seaton y J.S. Foster. and Velasco. Structural Changes Occurring during Reduction of Hematite and Magnetite Pellets Containing Coal Char. Transactions ISIJ, Vol. 23, 1983, pp. [10]C. Bozco. et.al. Interaction of Nitrogen with Iron Surfaces. Journal of Catalysis 49. 1977. [11]L.S. Darken y R.W. Gurry, Physical Chemistry of Metals. Mc Graw hIll . 1953. [12]H. A. Weirdt, y Z .Zwell. Trans. AIME. 229. 142. 1969. [13]J.J.S.Schulten. et al. Trans. Soc. Faraday. 53, 1363, 1957. [14]E.G.Barret y C.F. Wood. Bureau of Mines R-I 3229. 1934.

The metallurgy reactions in the weld pool were analyzed with the application of reaction kinetics. Furthermore a formula to quantificationally calculate the amount of Mg2Si was generated. By means of calculating the thermodynamic condition of the reaction and combined with the verification testing, this article indicates that the metallurgical product Mg2Si was created in the liquid weld pool but not separated out from the arborescent crystal during its solid state. This thesis summarizes the precipitation mechanism of Mg2Si and explains the configuration, amount and location where Mg2Si was separated out by analyzing the phase diagrams and constitution diagrams. Relevant data suggests that: the content of Mg2Si is slightly less than Mg.

Abstract Sealing slurries, mainly the cement-based ones, are concentrated dispersive systems, containing solid particles of considerably developed specific surface. Rheologically, such systems are very complex. This also stems from the fact that the rheological properties have a significant effect on: • additives and admixtures modifying technological properties of fresh and set slurries, • chemically complex mechanism of hydration in a slurry in a function of time. Special attention should paid to plasticizing (plasticizers PL) and liquefying (traditional and new- -generation superplasticizers SP) admixtures affecting the modification and optimization of rheological properties of fresh cement slurries as far as providing efficiency of sealing of casing pipes is concerned. Laboratory analyses were focused on proving the following thesis: properly selected type of superplasticizer [by BASF Polska Sp.z o.o. (The Chemical Company) - Admixtures for Concrete Division] advantageously affects the rheological parameters of sealing slurry based on metallurgical cement CEM III /A 32,5. The following variables were used in the analyses: • type of superplasticizer, • type of batch fluid. The laboratory experiments were made on superplasticizers produced by BASF: • SKY 501, • SKY 503, • SKY 591, • ACE 430, • Glenium 115. The superplasticizer concentration in the slurry was 0.5 wt% (as compared with mass of dry cement). Water to cement ratio for the analyzed sealing slurries was equal to 0.5. The sealing slurries were made of metallurgical cement CEM III/A 32,5 N-LH/HSR/N Lafarge Cement S.A. in Małogoszcz.

This technical note summarizes a technical comparison of common testing procedures, as well as reviewed of the UN Test N` 5, for the assessment of the self-heating properties of cargoes and materials that has shown a clear trend on maritime fire and explosions events, as well as considering of external factors that can combine self-heating and emit flammable gases to conclude in an unlikely event affecting the security of crews and ships. A high understanding of the external factors effect on the cargo materials certainly will help the application of spontaneous reactions management actions (SRMA) on board of ships during the cargo sea passage. The intended comparison is based on laboratory, industry and field observations and data, whereas the among the external factors considered are, moisture content, stockpile procedure and aging, air velocities and moderate pressures internal and externally to the cargo material. The comparison results have shown that the self-heating and the flammable gas emissions has a common pattern when reacting with any oxygen available source, regardless the reactive material chemical composition. Keywords: reactive materials, self-heating, self-ignition, direct reduced iron fines, materials handling, UN test N` 5, maritime safety, spontaneous reactions, risk management. IMSBC Code , IMO. References [1]A. M. DeGennaro, M. W. Lohry, L. Martinelli, C. W. Rowley. Uncertainty Quantification for Cargo Hold Fires. Princeton University, Princeton, NJ, 08540, USA. American Institute of Aeronautics and Astronautics. [2]L.L.Sloss Assessing and Managing Spontaneous Combustion of Coals. IEA Clean Coal Center (CCC 259). Oct. 2015. [3].A. Janes, G Marlair, D Carson, j. Chaneausx. Towards the improvement of UN Test N1 5 Method for the characterization of substances which in contact with water emit Flammable Gases. Journal of Loss Prevention in the Process Industries. Elsevier 2012, 25 (3), pp 524-534. [4]G. Rouget, B. Majidi, D. Picard, G. Gauvin, D. Ziegler, J. Mashreghi, and H. Alamdar. Electrical Resistivity Measurement of Petroleum Coke Powder by Means of Four-Probe Method. Metallurgical and Materials Transactions B. Vol. 48B, Oct. 2017-2543. [5]Y. Rubiela Hernández Puerto, M.Triviño Restrepo. El coque metalúrgico aplicado a protección catódica (Metallurgia coque applied to catodic protection). Revista del Instituto de Investigaciones FIGMMG. Vol. 10, Nº 20, 60-67 (2007) UNMSM I. [6]S. Narayan Jha, K. Narsaiah, A.L. Basediya, R.Sharma, P. Jaiswal, R. Kumar, and R. Bhardwaj. Measurement techniques and application of electrical properties for nondestructive quality evaluation of foods—a review. Food Sci Technol. 2011 Aug; 48(4): 387–411. [7]R. Fontes Araujo, J. Batisa Zonta, E. Fontes Araujo, E. Heberle, E, F. Miranda Garcia Zonta. Teste de Conductividade Eletrica para Smentes de Feijao Mungo Verde 1. Rev. Brasikleira de Sementes, Vol. 33, N` 1, pp123/130, 2011. [8]P.A. Eidem. Electric Resistivity of Coke Beds. PhD Thesis. Norwegian University of Science and Technology Faculty of Natural Sciences and Technology Department of Materials Science and Engineering. Tronheim Oct. 2008. [9]N. Birks, et.al. - Mechanism in Corrosion Induced Auto-ignition of Direct Reduced Iron. Materials Science and Engineering Department, University of Pittsburgh. [10]Monitoring Implementation of the Hazardous and Noxious Substances Convention. Report on incidents involving HNS. Submitted by the United Kingdom. IMO 85th Session, Agenda item 5- LEG 85/INF.2, 19 September 2002.

A method of calculation has been derived to assess the nitrogen estimated content in iron reduced samples. The method is based on the review of observations and laboratory measurements of relationships between the rate of reduction and the corresponding metallic iron formation during the reduction process. The metallic iron formation has been calculated from relationships that apply to a wide variety of types of ores undergoing reduction under a nitrogen-containing gas mixture in proportions above 50% by volume. The empirical correlations found between the rates of metallization, the sample swelling index, and the equilibrium nitrogen solubility in iron can be used for determined the approximate final content of nitrogen in the reduced samples from the estimated and measured final volume of the reduced specimens. It is necessary to have an accurate analysis of the starting sample as well as the reducibility information. Keywords: Iron ore, nitriding, catastrophic swelling, rate of metallization, reduction degree. [1]M. Kumar, B. Himanshu & S. Kumar. “Reduction and Swelling of Fired Hematite Iron Ore Pellets by Non−coking Coal Fines for Application in Sponge Ironmaking”. Mineral Processing and Extractive Metallurgy Review- MINER PROCESS EXTR METALL REV. 34. 10.1080/08827508.2012.656776. 2012. [2]I. Mikko, M. Olli, A. Tuomas, V. Ville-Valtteri, K. Jari, P. Timo & F. Timo. “Dynamic and Isothermal Reduction Swelling Behaviour of Olivine and Acid Iron Ore Pellets under Simulated Blast Furnace Shaft Conditions”. ISIJ International. 52. 1257-1265. 10.2355/isijinternational.52.1257. 2012. [3]M. Kumar. “Study of reduction kinectics of iron ore pellets by noncoking coal”. Thesis of Master. National Institute of technology, Rourkela. 2009. [4]O. Dam. “The Influence of Nitrogen on the Swelling Mechanism of Iron Oxides During Reduction”. PhD Thesis .Univ. of London. 1983. [5]O. Dam and J. Jeffes. “Model for the Assessment of Chemical Composition of reduced iron ores from single measurements”. Ironmaking and Steelmaking Journal. Vol. 14, N`5. 1987. [6]O. Dam. “Efecto de la descomposición de gas de amoniaco (NH3) sobre el hinchamiento de óxidos de hierro durante reducción”. UCT Journal. Vol 100, 24. May 2020. [7]R. Agarwal and S. Hembram. “To Study the Reduction and Swelling Behavior Iron Ore Pellets”. BSc. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela. May 2013 [8]Z. Chen , C. Zeilstra , J. Van der Stel , J. Sietsma & Y. Yang. “Review and data evaluation for high-temperature reduction of iron oxide particles in suspension”. Ironmaking & Steelmaking. Vol. 47. N°7. pp. 741-747. 2019.

The paper is an extensive monographic review of the literature, and also uses the results of the authors’ own experimental research illustrating the noticed developmental tendencies of the filling material based on gutta-percha. The whole body of literature proves the correctness of the research thesis that this material is the best currently that can be used in endodontics. Caries is one of the most common global infectious diseases. Since the dawn of humankind, the consequence of the disease has been the loss of dentition over time through dental extractions. Both tooth caries and tooth loss cause numerous complications and systemic diseases, which have a serious impact on insurance systems and on the well-being, quality, and length of human life. Endodontic treatment, which has been developing since 1836, is an alternative to tooth extraction. Based on an extensive literature review, the methodology of qualifying patients for endodontic treatment was analyzed. The importance of selecting filling material and techniques for the development and obturation of the root canal during endodontic treatment was described. Particular attention was paid to the materials science aspects and the sequence of phase transformations and precipitation processes, as well as the need to ensure the stoichiometric chemical composition of Ni–Ti alloys, and the vacuum metallurgical processes and material processing technologies for the effects of shape memory and superelasticity, which determine the suitability of tools made of this alloy for endodontic purposes. The phenomena accompanying the sterilization of such tools, limiting the relatively small number of times of their use, play an important role. The methods of root canal preparation and obturation methods through cold side condensation and thermoplastic methods, including the most modern of them, the thermo-hydraulic condensation (THC) technique, were analyzed. An important element of the research hypothesis was to prove the assumption that to optimize the technology of development and obturation of root canals, tests of filling effectiveness are identified by the density and size of the gaps between the root canal wall, and the filling methods used and devices appropriate for material research, using mainly microscopy such as light stereoscopic (LSM) and scanning electron (SEM). The most beneficial preparations were obtained by making a longitudinal breakthrough of 48 natural human teeth, extracted for medical reasons, different from caries, with compliance with all ethical principles in this field. The teeth were prepared using various methods and filled with multiple obturation techniques, using a virtual selection of experimental variants. The breakthroughs were made in liquid nitrogen after a one-sided incision with a narrow gap created by a diamond disc using a materialographic cutter. The best effectiveness of the root canal filling was ensured by the technology of preparing the root canals with K3 rotary nitinol tools and filling the teeth with the THC thermoplastic method using the System B and Obtura III devices with studs and pellets of filling material based on gutta-percha after covering the root canal walls with a thin layer of AH Plus sealant. In this way, the research thesis was confirmed.

During use, a scaffold support allegedly failed, causing injuries to the user when he fell. The plaintiff’s expert identified a defective weld as the cause of failure and opined that the product was improperly designed. This paper examines methods used to evaluate the circumstances of and claims made regarding the incident. A combination of engineering methodologies, including metallurgical evaluation, stress analysis, and physical testing, was used to examine the plaintiff’s claims of deficiencies in the design and fabrication of the product. The engineering methodologies refute claims made about the structural capacity of the product by the plaintiff’s expert and the fundamental cause of failure. This paper examines themes related to the presence of apparent defects/failure and the necessity of verifying postulated hypotheses. It also examines the efficacy of analysis and testing as part of implementation of the “forensic engineering method” in verifying or rejecting hypotheses en route to offering expert opinions in forensic engineering investigations.

Its highly impossible for false proofing the super structures or mechanisms or the metallurgical methods after installation so they are perfectly engineered and dispatched only after a series of quality checks which has a proper methodology. If this is the scenario with the non living structure's components if they were engineered without errors. There must be some more intensity with the living organisms. living organisms are not engineered but the engineering of the ailments or aids which support the life of living organism must be error free and perfect also must be ready to use. In this context it's pity that there is no perfect operational procedure for internal fixation of fractures this thesis Is focused on that area and aimed to derive a reliable design of internal fixation screw which is designed in contrast with conventional screw This project is stimulation out from two case studies of operational failure implant removal.

Thesis (PhD)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: The objective of this work was to achieve a completely automated fire assay system for the analysis of process control samples on a flotation plant in less than 120 minutes. With this in mind, a systems engineering approach was undertaken. The physical and chemical characteristics of the technology for each subsystem were investigated in turn and the critical factors that influenced accuracy, precision and analysis time were identified and optimised. Some of the key developments achieved during this work were: · Existing technology for the sampling, filtering, drying and grinding of flotation plant samples were evaluated and where necessary, modified for this application. · The fusion system was totally re-designed with a bottom-loading configuration called FIFA (Fast In-line Fire Assay) to make automation with a central robot possible. With the fast fusing flux developed, a quantitative collection of the platinum group elements with a fifteen-minute fusion was achieved compared to an hour for the classical method. · A robust automated separator system was developed to isolate the lead collector from the fusion in the molten state thereby separating it quantitatively from the slag. This allowed the automation of the entire fire assay process. · Methods to prepare lead standards for calibration were developed. These were used to optimise analytical protocols for the analysis of platinum group elements in lead using a spark optical emission spectrometer. This made it possible to accurately determine the quantities of platinum group elements in lead samples prepared by the automated fire assay system. · A fully automated system was developed that could meet the accuracy and precision requirements for the analysis of tailings and feed grade samples in concentrator slurry streams in less than one hour compared with the 24-72 hours required when using classical methods. The new fire assay technology including flux, FIFA system, oxygen lance and separator were all patented along with the automation vendor. This technology has made the first fully automated fire assay system a reality.
AFRIKAANSE OPSOMMING: Die hoofoogmerk van die studie was om ‘n totale geoutomatiseerde vuuressaieering stelsel te ontwerp vir die ontleding van prosesbeheermonsters van ‘n flotasieaanleg in ‘n bestek van 120 minute. Gedurende die ontwerp is ‘n ingeneursstelselbenadering gebruik. Die fisiese en chemiese kenmerke van elke deel van die tegnologie is eers afsonderlik en dan as ‘n geheel ondersoek. Die bepalende faktore wat akkuraatheid, presisie en ontledingstyd beinvloed het was geidentifiseer en geoptimeer. Die hoofpunte van die werk behels onder andere die volgende: · Bestaande tegnologie vir monsterneming, filtrasie, droging en vermaling van flotasiemonsters was ondersoek en is, waar nodig, aangepas vir die finale stelsel. · Die smeltingsisteem was in geheel herontwerp om monsters van onder in die FIFA (Fast In-line Fire Assay) sisteem te laai en sodoende die outomatisering met ‘n sentrale robot te vergemaklik. ‘n Vinnig smeltende vloeimiddel was ontwikkel wat ‘n kwantitatiewe versameling van die platinum groep elemente binne ‘n tydsduur van vyftien minute moontlik gemaak het, in vergelyke met die oorspronklike duur van die klassieke smelt metode van een uur. · ‘n Outomatiese skeier was ontwikkel waarmee die gesmelte loodversamelaar geskei kon word van die slakfase. Met die nuwe stelsel kon die hele vuuressaieerproses outomaties verloop. · Metodes is ontwikkel om loodstandaarde vir kalibrasie doeleindes te berei. Die standaarde is op hulle beurt weer gebruik om ‘n ontleding protokol daar te stel vir die analiese van die platinum groep elemente in lood, met behulp van ‘n vonkontlading-optiese-uitstraling-spektrometriese instrument. Ten einde was dit moontlik om outomaties klein hoeveelhede van die platinum groep elemente in monsters akkuraat te bepaal, na voorbereiding met behulp van die geoutomatiseerde vuuressaieering stelsel. · Die volle geoutimatiseerde stelsel was ontwikkel wat aan die akkurate en noukeurige vereistes voldoen het vir die ontleding van flotasie-uitskot-envoergraad monsters van die konsentraataanleg binne die bestek van ‘n uur. Die nuwe vuuressaieer tegnologie, insluitend die vinnig smeltende vloeimiddel, FIFA en skeier stelsels, asook die suurstof lanset is gepatenteer met die vervaardiger. Die studie het gelei tot die eerste volle geoutomatiseerde vuuressaieering stelsel wat tans gebruik word in die industrie.

Thesis (MScIng)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: The pneumatic injection of reagent powder into molten iron has become the preferred way to carry out iron and steel desulphurisation. It is therefore essential to not only understand the thermodynamic implications, but also the kinetic principles that govern the desulphurisation process. Key variables that influence the kinetics of the procedure are the condition and composition of the top slag and the melt as well as the injection conditions. Notable injection parameters include reagent flowrate, injection-lance depth and carrier gas flowrate. Owing to sampling restrictions, the subsequent data from Saldanha Steel®, South Africa does not provide adequate insight into the kinetic behaviour of the desulphurisation process and it was therefore the focus of this research to provide an improved quantitive comprehension of the calcium carbide injection procedure at Saldanha Steel. For this purpose a one-dimensional quasi-steady state model for momentum, heat- and mass transfer in rising gas-liquid-powder plumes has been developed for conditions relevant to the Saldanha Steel refining process. Combined with a model predicting the contribution of the topslag to the process, the overall rate of desulphurisation as a function of time can be determined, thus affording the ability to quantitatively explore and analyse the influence of the afore-mentioned injection parameters, as well as the nature of both the topslag and the melt, on the kinetics of the desulphurisation process. Sensitivity analyses concluded that individual increases in the calcium carbide flowrate, the depth of injection and the amount of carry-over slag will result in a reduction in the injection time, while a decrease in the reagent particle diameter and the initial mass of iron in the ladle will have the same effect. Molten iron temperature losses brought about by prolonged injection needs to be electrically recovered within a steelmaking furnace at a high cost. Owing to the high cost of the desulphurising agent, any reduction in the required injection time, while still maintaining product specifications, will therefore result in diminishing overall production costs. Although all the results contained in this study is of particular interest to the Saldanha Steel scenario, it also provides invaluable information and insights into the important variables and parameters playing a role in injection desulphurisation processes in general, along with the influence that changing conditions can have on the end result of such a procedure.
AFRIKAANSE OPSOMMING: Die pneumatiese inspuiting van reagentpoeier is die populêrste ontswawelingsmetode in die yster- en staal bedryf. Dit is dus van groot belang dat die gepaardgaande termodinamiese en kinetiese beginsels betrokke by die ontswawelingsreaksies baie goed verstaan word. Die kondisie en samestelling van die bo-slak en die vloeibare yster, asook die inspuitingkondisies is twee van die belangrikste veranderlikes wat die kinetika van die ontswawelingsproses beïnvloed. Beperkte monsternemingsgeleenthede het veroorsaak dat die relevante data, soos voorsien deur Saldanha Staal®, nie die nodige kinetiese insig in verband met die ontswawelingreaksie weergee nie. Dit is dus die doel van hierdie werkstuk om ‘n verbeterde kwantitatiewe begrip van die ontswawelingsproses by Saldanha Staal daar te stel. Vir hierdie doeleinde is ‘n een-dimensionele, kwasi-gestadigde toestand model vir stygende gas-vloeistof pluime ontwikkel. Die model inkorporeer momentum-, hitte- en massaoordragsprinsiepe en is verteenwoordigend van die ontswawelingsproses by Saldanha Staal. ‘n Tweede model simuleer die bydrae wat die bo-slak tot die algehele ontswawelingsproses maak en saam gee hierdie twee modelle die algehele ontswawelingstempo weer as ‘n funksie van tyd. Die modelle word ook gebruik om die invloed van die bogenoemde inspuitingsveranderlikes op die proses te ondersoek. Deeglike sensitiwiteitsanalise het gewys dat ‘n verhoging in die kalsium karbied vloeitempo, asook die inspuitingsdiepte van die lans en die hoeveelheid slak wat vanaf die boogoond na die ontswawelingseenheid oorgedra word, ‘n vermindering in die vereisde inspuitingstyd te weeg bring. Verkleining in die kalsium kardied partikels se gemiddelde diameter en vermindering van die hoeveelheid yster in die torpedokarre aan die begin van die proses, het dieselfde uitwerking op die vereisde inspuitingstyd. Geweldig baie geld moet aan elektrisiteit spandeer word om die temperatuur wat verlore gaan as gevolg van onnodige lang inspuitingstye, in die staalmaakoonde te herwin. Gekombineerd met die feit dat die kalsium karbied reagent baie duur is, beteken dit dat reduksies in die vereisde ontswaweling inspuitingstyd groot besparings te weeg kan bring. Alhoewel die saamgevatte resultate van spesifieke belang is vir die Saldanha Staal proses, verskaf hierdie studie waardevolle informasie oor die belangrikheid van verskeie veranderlikes, asook die rol wat veranderende toestande op die eindresultate van die ontswawelingproses kan hê.

Thesis (MScIng)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: This thesis investigates the control of calcium and magnesium in a base metal sulphate leach solution containing nickel and cobalt. The presence of calcium and magnesium in the hydrometallurgical processing of base metals, result in a number of difficulties. These problems range from the contamination of the final product, to high energy consumption and large bleed streams during electrowinning. Calcium poses a greater problem in sulphate solutions due to the low solubility of its sulphate salts. No conventional method exists for the control of calcium and magnesium. As part of this study a review of possible control methods was conducted, which is listed within. From this list the precipitation of fluorides was selected for further investigation. The results showed that it is possible to control calcium and magnesium through the precipitation of their respective fluorides, without the co-precipitation of nickel and cobalt. For 10% stoichiometric excess of fluoride 96.5% calcium and 98.5% magnesium were removed during batch experiments. It is known that mixing and hydrodynamics plays an important role on the characteristics of the formed precipitate, making these processes inherently difficult to scale-up. To evaluate these effects on a continuous process, the three-zone model proposed by Gösele and Kind (1991) was used. A precipitate with consistent characteristics was produced while varying the mixing on the macro, meso and micro scale. Additionally, methods were investigated for the removal or possible recycling of the unreacted fluoride, for which activated alumina was identified. It was observed that activated alumina could adsorb fluoride to low levels in the presence of the base metal solution, after which it could be regenerated again. The activated alumina (AA) had a capacity of 8.65 gF/lAA at a 10 mg/l fluoride breakthrough level during column tests. Based on the experimental results a conceptual process was devised whereby only a portion of the leach stream is subjected to the fluoride precipitation process, after which it is returned to lower the overall calcium and magnesium concentrations. This method would reduce the effect of the observed dominance of magnesium precipitation, in processes where the maximum removal of both elements is not required. The fluoride precipitation process consisted of three steps being precipitation, solid-liquid separation and adsorption of the unreacted fluoride. Sufficient information is provided on the process for a cost estimation to be carried out. Should this found to be feasible, a continuation of the project is recommended. Different reactor configurations could be evaluated for precipitation. The scaling observed during the continuous experiments should also be investigated to minimise its effect. The investigation of activated alumina was only a secondary project and more work is required on optimisation, particularly for the desorption cycle to enable the recycling of the unreacted fluoride.
AFRIKAANSE OPSOMMING: Saamgestel in hierdie tesis is 'n studie van die beheer van kalsium en magnesium in 'n basismetaal-sulfaatoplossing, bevattende nikkel en kobalt. Die teenwoordigheid van kalsium en magnesium in dié oplossings veroorsaak 'n verskeidenheid van probleme, wat wissel van produkkwaliteit verlaging tot hoë energieverbruik en groot bloei strome tydens platering. 'n Groter probleem word ondervind met kalsium as gevolg van die lae oplosbaarheid van sy sulfaatsoute. Geen konvensionele metode kon gevind word vir die beheer van kalsium en magnesium gedurende die oorsig van moontlike metodes nie. Hierdie moontlike metodes is geïdentifiseer en kortliks bespreek in die tesis. Van die moontlike metodes is die presipitasie van fluoried-soute gekies vir verdere eksperimentele ondersoek. Die ondersoek het getoon dat dit moontlik is om kalsium en magnesium te beheer deur die presipitasie van fluoriede sonder om die basismetale saam te presipiteer. Vir 'n 10% oormaat fluoried toevoeging is 96.5% van die kalsium en 98.5% van die magnesium gepresipiteer gedurende die enkelladingstoetse. Dit is bekend dat vermenging en hidrodinamika 'n groot rol speel in die kwaliteit van die presipitaat wat gevorm word. Dit bemoeilik die opskalering van presipitasie prosesse. Vir die ondersoek oor die invloed van vermenging op 'n kontinu proses is die drie-sel model van Gösele en Kind (1991) gebruik. Dit is gevind dat die karakter van presipitaat relatief konstant gebly het vir variasies van vermenging op die makro, meso en mikro skaal, wat opskaling behoort te vergemaklik. Addisioneel is die verwydering of moontlike hersirkulasie van die ongereageerde fluoried ondersoek, en geaktiveerde alumina is geïdentifiseer as 'n moontlike adsorbeermiddel. 'n Eksperimentele ondersoek het getoon dat geaktiveerde alumina fluoried tot lae vlakke kan adsorbeer in die teenwoordigheid van die basismetale, waarna dit weer geregenereer kan word. Die kapasiteit van die geaktiveerde alumina (GA) was bereken as 8.65 gF/lGA by 'n 10 mg/l fluoried vlak gedurende die kolom toetse. 'n Konsep-proses is opgestel na aanleiding van die eksperimentele resultate, waarvolgens slegs 'n gedeelte van die logingstroom na die fluoried presipitasie proses gestuur word, waarna dit weer teruggevoeg word om die algehele kalsium en magnesium konsentrasie te verlaag. Dié metode sal voorkom dat magnesium presipitasie domineer vir 'n toepassing waar slegs 'n gedeelte van kalsium en magnesium verwyder word. Die fluoried presipitasie proses behels drie stappe waarvolgens die fluoriede eers gepresipiteer word, waarna dit geskei word, en dan die ongereageerde fluoried geadsorbeer word. Genoeg inligting is versamel sodat 'n kosteberaming van die proses gedoen kan word. As die koste van die proses aanvaarbaar is, word dit voorgestel dat die ondersoek voortgesit word. Verskillende reaktor konfigurasies kan vir die presipitasie stap getoets word en daar moet ook ondersoek ingestel word hoe om die korslaag wat gedurende die kontinu eksperimente geobserveer is, te verminder. Die ondersoek van geaktiveerde alumina was ondergeskik in die projek en nog werk sal gedoen moet word om dit te optimiseer, spesifiek gedurende die desorpsie siklus vir die hersirkulasie van die ongereageerde fluoried.

Thesis (PhD)--Stellenbosch University, 2008.
ENGLISH ABSTRACT: The growing need to improve accounting accuracy, precision and to standardise generally accepted measurement methods in the mining and processing industries has led to the joining of a number of organisations under the AMIRA International umbrella, with the purpose of fulfilling these objectives. As part of this venture, Anglo Platinum undertook a project on the material balancing around its largest smelter, the Waterval Smelter. The primary objective of the project was to perform a statistical material balance around the Waterval Smelter using the Maximum Likelihood method with respect to platinum, rhodium, nickel, sulphur and chrome (III) oxide. Pt, Rh and Ni were selected for their significant contribution to the company’s profit margin, whilst S was included because of its environmental importance. Cr2O3 was included for its importance in as far as the difficulties its presence poses in smelting of PGMs. The objective was achieved by performing a series of statistical computations. These include; quantification of total and analytical uncertainties, detection of outliers, estimation and modelling of daily and monthly measurement uncertainties, parameter estimation and data reconciliation. Comparisons were made between the Maximum Likelihood and Least Squares methods. Total uncertainties associated with the daily grades were determined by use of variographic studies. The estimated Pt standard deviations were within 10% relative to the respective average grades with a few exceptions. The total uncertainties were split into their respective components by determining analytical variances from analytical replicates. The results indicated that the sampling components of the total uncertainty were generally larger as compared to their analytical counterparts. WCM, the platinum rich Waterval smelter product, has an uncertainty that is worth ~R2 103 000 in its daily Pt grade. This estimated figure shows that the quality of measurements do not only affect the accuracy of metal accounting, but can have considerable implications if not quantified and managed. The daily uncertainties were estimated using Kriging and bootstrapped to obtain estimates for the monthly uncertainties. Distributions were fitted using MLE on the distribution fitting tool of the JMP6.0 programme and goodness of fit tests were performed. The data were fitted with normal and beta distributions, and there was a notable decrease in the skewness from the daily to the monthly data. The reconciliation of the data was performed using the Maximum Likelihood and comparing that with the widely used Least Squares. The Maximum Likelihood and Least Squares adjustments were performed on simulated data in order to conduct a test of accuracy and to determine the extent of error reduction after the reconciliation exercise. The test showed that the two methods had comparable accuracies and error reduction capabilities. However, it was shown that modelling of uncertainties with the unbounded normal distribution does lead to the estimation of adjustments so large that negative adjusted values are the result. The benefit of modelling the uncertainties with a bounded distribution, which is the beta distribution in this case, is that the possibility of obtaining negative adjusted values is annihilated. ML-adjusted values (beta) will always be non-negative, therefore feasible. In a further comparison of the ML(bounded model) and the LS methods in the material balancing of the Waterval smelter complex, it was found that for all those streams whose uncertainties were modelled with a beta distribution, i.e. those whose distribution possessed some degree of skewness, the ML adjustments were significantly smaller than the LS counterparts It is therefore concluded that the Maximum Likelihood (bounded models) is a rigorous alternative method of data reconciliation to the LS method with the benefits of; -- Better estimates due to the fact that the nature of the data (distribution) is not assumed, but determined through distribution fitting and parameter estimation -- Adjusted values can never be negative due to the bounded nature of the distribution The novel contributions made in this thesis are as follows; -- The Maximum Likelihood method was for the first time employed in the material balancing of non-normally distributed data and compared with the well-known Least Squares method -- This was an original integration of geostatistical methods with data reconciliation to quantify and predict measurement uncertainties. -- For the first time, measurement uncertainties were modeled with a distribution that was non-normal and bounded in nature, leading to smaller adjustments
AFRIKAANSE OPSOMMING: Die groeiende behoefte aan rekeningkundige akkuraatheid, en om presisie te verbeter, en te standardiseer op algemeen aanvaarde meetmetodes in die mynbou en prosesseringsnywerhede, het gelei tot die samwewerking van 'n aantal van organisasies onder die AMIRA International sambreel, met die doel om bogenoemde behoeftes aan te spreek. As deel van hierdie onderneming, het Anglo Platinum onderneem om 'n projek op die materiaal balansering rondom sy grootste smelter, die Waterval smelter. Die primêre doel van die projek was om 'n statistiese materiaal balans rondom die Waterval smelter uit te voer deur gebruik te maak van die sogenaamde maksimum waarskynlikheid metode met betrekking tot platinum, rodium, nikkel, swawel en chroom (iii) oxied. Pt, Rh en Ni was gekies vir hul beduidende bydrae tot die maatskappy se winsmarge, terwyl S ingesluit was weens sy belangrike omgewingsimpak. Cr2O3 was ingesluit weens sy impak op die smelting van Platinum groep minerale. Die doelstelling was bereik deur die uitvoering van 'n reeks van statistiese berekeninge. Hierdie sluit in: die kwantifisering van die totale en analitiese variansies, opsporing van uitskieters, beraming en modellering van daaglikse en maandelikse metingsvariansies, parameter beraming en data rekonsiliasie. Vergelykings was getref tussen die maksimum waarskynlikheid en kleinste kwadrate metodes. Totale onsekerhede of variansies geassosieer met die daaglikse grade was bepaal deur ’n Variografiese studie. Die beraamde Pt standaard afwykings was binne 10% relatief tot die onderskeie gemiddelde grade met sommige uitsonderings. Die totale onsekerhede was onderverdeel in hul onderskeie komponente deur bepaling van die ontledingsvariansies van duplikate. Die uitslae toon dat die monsternemings komponente van die totale onsekerheid oor die algemeen groter was as hul bypassende analitiese variansies. WCM, ‘n platinum-ryke Waterval Smelter produk, het 'n onsekerheid in die orde van ~twee miljoen rand in sy daagliks Pt graad. Hierdie beraamde waarde toon dat die kwaliteit van metings nie alleen die akkuraatheid van metaal rekeningkunde affekteer nie, maar aansienlike finansiële implikasies het indien nie die nie gekwantifiseer en bestuur word nie. Die daagliks onsekerhede was beraam deur gebruik te maak van “Kriging” en “Bootstrap” metodes om die maandelikse onsekerhede te beraam. Verspreidings was gepas deur gebruik te maak van hoogste waarskynlikheid beraming passings en goedheid–van-pas toetse was uitgevoer. Die data was gepas met Normaal en Beta verspreidings, en daar was 'n opmerklike vermindering in die skeefheid van die daaglikse tot die maandeliks data. Die rekonsiliasies van die massabalans data was uitgevoer deur die gebruik die maksimum waarskynlikheid metodes en vergelyk daardie met die algemeen gebruikde kleinste kwadrate metode. Die maksimum waarskynlikheid (ML) en kleinste kwadrate (LS) aanpassings was uitgevoer op gesimuleerde data ten einde die akkuraatheid te toets en om die mate van fout vermindering na die rekonsiliasie te bepaal. Die toets getoon dat die twee metodes het vergelykbare akkuraathede en foutverminderingsvermoëns. Dit was egter getoon dat modellering van die onsekerhede met die onbegrensde Normaal verdeling lei tot die beraming van aanpassings wat so groot is dat negatiewe verstelde waardes kan onstaan na rekosniliasie. Die voordeel om onsekerhede met 'n begrensde distribusie te modelleer, soos die beta distribusie in hierdie geval, is dat die moontlikheid om negatiewe verstelde waardes te verkry uitgelsuit word. ML-verstelde waardes (met die Beta distribusie funksie) sal altyd nie-negatief wees, en om hierdie rede uitvoerbaar. In 'n verdere vergelyking van die ML (begrensd) en die LS metodes in die materiaal balansering van die waterval smelter kompleks, is dit gevind dat vir almal daardie strome waarvan die onserkerhede gesimuleer was met 'n Beta distribusie, dus daardie strome waarvan die onsekerheidsdistribusie ‘n mate van skeefheid toon, die ML verstellings altyd beduidend kleiner was as die ooreenkomstige LS verstellings. Vervolgens word die Maksimum Waarskynlikheid metode (met begrensde modelle) gesien as 'n beter alternatiewe metode van data rekosiliasie in vergelyking met die kleinste kwadrate metode met die voordele van: • Beter beramings te danke aan die feit dat die aard van die onsekerheidsdistribusie nie aangeneem word nie, maar bepaal is deur die distribusie te pas en deur van parameter beraming gebruik te maak. • Die aangepaste waardes kan nooit negatief wees te danke aan die begrensde aard van die verdeling. Die volgende oorspronklike bydraes is gelewer in hierdie verhandeling: • Die Maksimum Waarskynlikheid metode was vir die eerste keer geëvalueer vir massa balans rekonsiliasie van nie-Normaal verspreide data en vergelyk met die bekendde kleinste kwadrate metode. • Dit is die eerste keer geostatistiese metodes geïntegreer is met data rekonsiliasie om onsekerhede te beraam waarbinne verstellings gemaak word. • Vir die eerste keer, is meetonsekerhede gemoddelleer met 'n distribusie wat nie- Normaal en begrensd van aard is, wat lei tot kleiner en meer realistiese verstellings.

Thesis (MScIng)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: This thesis details results obtained in an experimental study conducted to determine the effects of operating temperature, oxygen partial pressure, bulk chromium oxide content and bulk FeOx/MgO ratio on the solubility of chromium oxide in melter type slags in the platinum industry. Two PGM-containing layers in the Bushveld Complex in South Africa, the Merensky and UG2 reefs, are currently being mined for the extraction of base metals and platinum group metals (PGM). While the Merensky reef is a pyroxenitic layer, the UG2 reef is a platiniferous chromitite seam. Due to a gradual depletion in Merensky ore reserves, platinum producers have been moving towards the processing of more UG2 concentrates, which are higher in chromium oxide content. The technical difficulties associated with the smelting of concentrates with high chromium oxide contents is a matter of concern. The formation of chromite spinels in melts increases liquidus temperatures and viscosities and subsequently hampers tapping of slags and mattes from furnaces. Bottom build-up from the smelting of high chromium oxide containing concentrates could reduce effective furnace volume. From the literature reviewed it was found that very few published investigations covered melt compositions and oxygen partial pressures similar to those encountered in the platinum industry. Relevant studies were found to deal with significantly lower bulk chromium oxide and iron oxide contents. It became clear that a need exists for information on the behaviour of chromium oxide and its effects on phase chemistry and stability in melter slags. It was decided to study the phase equilibria through drop-quench experiments using six synthetic slags with bulk FeOx/MgO ratios between 0.6 and 1.9 and bulk chromium oxide contents between 1.2 and 7 wt%. Temperatures investigated were 1400, 1500 and 1600°C. The oxygen partial pressure was varied between 6.8x10-10 atm at 1400°C to8.3x10-5 atm at 1600°C. Experiments were conducted in a sealed vertical tube furnace and the required oxygen partial pressure in the furnace tube was maintained by controlling the flow rates of purified CO and CO2 gas mixtures through the tube. Reaction products were quenched after a reaction time of between 20 and 24 hours, depending on temperature, and the phase compositions were analysed by microprobe. The experimental study revealed that chromium oxide partitions very strongly into the spinel phase relative to the liquid phase, especially at lower temperatures, and higher oxygen partial pressures and bulk chromium oxide contents. The solubility of chromium oxide in the liquid phase was found to increase with increasing temperature and decreasing oxygen partial pressure. An increase in bulk chromium oxide contents of 1 wt%, under otherwise constant conditions, resulted in an increase in slag liquidus temperature of approximately 100°C over the range of temperatures investigated. At 1500°C and bulk chromium oxide contents of 3.7 and 6.4 wt% a reduction in oxygen partial pressure from 1.1x10-5 to 1.1x10-7 atm resulted in increases in soluble chromium oxide of 0.9 and 2.0 wt%, respectively. A further decrease in oxygen partial pressure to 6.7x10-9 atm resulted in increases in soluble chromium oxide of 2.8 and 4.7 wt%, respectively. Experimental results were compared to values predicted by the multi-phase equilibrium (MPE) model developed by CSIRO, and found to agree well. Slag basicity was not varied experimentally and therefore the model was used to predict its effect on the solubility of chromium oxide in the liquid phase and the stability of crystalline phases. At constant temperature, an increase in basicity resulted in a decrease in the solubility of chromium oxide in the liquid phase as well as stabilisation of the spinel phase. It was concluded that practicable combinations of one or more of four main factors, namely increased operating temperature and decreased bulk chromium oxide content, slag basicity and oxygen partial pressure, should be applied and evaluated in a plantenvironment to optimise furnace operation. The MPE model would be a valuable tool in predicting the outcomes of such investigations.
AFRIKAANSE OPSOMMING: Hierdie tesis detaileer die resultate wat verkry is uit ‘n eksperimentele studie uitgevoer om die effek van bedryfstemperatuur, die parsiële druk van suurstof, die algehele chroomoksied inhoud en die algehele FeOx/MgO verhouding op die gedrag van chroomoksied in smelter slakke in die platinum industrie te bestudeer. Twee PGM-bevattende ertslae in die Bosveldkompleks in Suid Afrika, die Merensky en UG2 riwwe, word huidiglik gemyn vir die ekstraksie van basismetale en platinumgroep metale (PGM). Die Merensky rif is ‘n piroksenitiese laag terwyl die UG2 rif ‘n platinumbevattende chromitiet laag is. As gevolg van ‘n geleidelike afname in reserwes van Merensky erts beweeg platinumprodusente al meer na die verwerking van groter hoeveelhede UG2 erts. Die tegniese probleme wat gepaard gaan met die smelting van konsentrate met hoë chroomoksied inhoud kan ‘n rede tot kommer wees. Die vorming van chromiet spinelle in die slak- en matfases verhoog likuidus temperature en viskositeite en bemoeilik die tap van hierdie fases uit oonde. Die opbou van soliede fases verlaag ook die effektiewe oondvolume. Uit die literatuurstudie is gevind dat gepubliseerde studies waarin slak samestellings en parsiële suurstofdrukke wat betrekking het op die platinumindustrie bespreek is, baie beperk is. Dit is gevind dat relevante navorsing gedoen is met aansienlik laer algehele chroom- en ysteroksied konsentrasies. Gevolglik het dit duidelik geword dat ‘n behoefte bestaan vir inligting oor die gedrag van chroomoksied in oonde en die effekte daarvan op fasechemie en –stabiliteit in smelter slakke. Daar is besluit om eksperimente uit te voer deur die gebruik van ses sintetiese slakke met algehele FeOx/MgO verhoudings tussen 0.6 en 1.9 en algehele chroomoksied konsentrasies tussen 1.2 en 7.0 % (op ‘n massabasis). Temperature van 1400, 1500 en 1600°C en suurstof parsiële drukke tussen 6.8x10-10 atm by 1400°C en 8.3x10-5 atm by 1600°C is ondersoek. Eksperimente is uitgevoer in ‘n geseëlde vertikale buisoond en dievereiste suurstofdruk in die oond is gehandhaaf deur beheer van die vloeitempos van gesuiwerde CO en CO2 gas deur die oond. Reaksieprodukte is in water geblus na ‘n reaksietyd van tussen 20 en 24 ure, afhangende van die reaksietemperatuur. Fasesamestellings is bepaal deur mikrosonde analises. Die eksperimentele studie het bewys dat chroomoksied baie sterk in die spinelfase konsentreer relatief tot die vloeistoffase, veral by laer temperature, suurstofdrukke en algehele chroomoksied konsentrasies. Dit is gevind dat die oplosbaarheid van chroomoksied in die vloeistoffase toeneem met toenemende temperatuur en afnemende suurstofdruk. ‘n Toename in die algehele chroomoksied konsentrasie van 1 massa%, onder andersins onveranderde toestande, het ‘n toename van ongeveer 100°C in likuidus temperature veroorsaak tussen 1400 en 1600°C. By 1500°C en algehele chroomoksied konsentrasies van 3.7 en 6.4 massa%, het ‘n verlaging in suurstofdruk vanaf 1.1x10-5 tot 1.1x10-7 atm respektiewelike toenames in die chroomoksied oplosbaarheid van 0.9 en 2.0 massa% veroorsaak. ‘n Verdere verlaging in suurstofdruk tot 6.7x10-9 atm het respektiewelike toenames in chroomoksied oplosbaarheid van 2.8 en 4.7 massa% veroorsaak. Eksperimentele resultate is vergelyk met waardes wat voorspel is deur die multifase ewewigsmodel (MPE), ontwikkel deur CSIRO, en goeie ooreenstemming is gevind. Verskillende slak basisiteite is nie eksperimenteel ondersoek nie en daarom is die model gebruik om die effek daarvan op die oplosbaarheid van chroomoksied in die vloeistoffase asook die stabiliteit van kristallyne fases te bepaal. By konstante temperatuur het ‘n toename in slak basisiteit ‘n afname in chroomoksied oplosbaarheid veroorsaak en die spinelfase gestabiliseer. Die aanbeveling is gemaak dat ‘n kombinasie van een of meer van vier hooffaktore, naamlik hoër bedryfstemperature en laer algehele chroomoksied konsentrasies, slak basisiteit en suurstofdruk, in die praktyk toegepas en geëvalueer moet word om sodoendeoptimum bedryfkondisies te bepaal. Die multifase ewewigsmodel is ‘n nuttige instrument wat gebruik kan word om die resultate van sulke ondersoeke te voorspel.

Thesis (PhD)--Stellenbosch University, 1992.
ENGLISH ABSTRACT: The dissolution of gold from refractory ores is a complex kinetic problem involving a number of chemical, mass transport and mineralogical factors. In most Witwatersrand ores in South Africa more than 97 % of the gold is dissolved in cyanide medium after a residence time of about 16 hours in pachuca tanks. This high percentage may be the reason why so little fundamental research has been done into the mechanism and kinetics of the leaching process. With the increasingly lower grades of ore mined, the introduction of backfill mining, and the reduction of profit margins, it has become imperative to increase the efficiency of gold dissolution. The effects of the chemistry and particle size on the dissolution of gold in each sample of ore were studied in detail. The emphasis in this study is on the effect of the leaching behaviour of various ore constituents on the rate of gold dissolution. Interferences with the leaching of gold in contact with other minerals or metals could be attributed to the galvanic interaction (electrical conductivity) between the gold and the mineral and to the formation of a surface film on the gold surface. Sulphide minerals and their oxidation products cause the largest decrease in gold dissolution rate. Galena enhances the rate of gold dissolution owing to dissolved Pb(II)-ions. Gold in contact with conductive minerals passivates as a result of the enhanced magnitude of the cathodic cu1Tent. In all experiments the rotating disc of gold passivated so that the rate of dissolution was much slower than that predicted by a mass-transport limiting model. The various films that form on the surface of the gold and associated minerals, as well as the galvanic interaction, depend largely on the pretreatment of the ore. Pre-elimination of host minerals from the gold bearing ore increases the dissolution rate of gold, and explains the kinetics of reaction on the gold surface to a large extent. The selective destruction of the various minerals with oxidative acid leaches destroys and/or decomposes certain minerals which may form films on the gold surface by precipitation. The chemical composition of these films and precipitates depends on the mineralogy of the sample. These films may be oxides, sulphides, carbonates and cyanide complexes. The complexes can be destroyed, depending on the nature of the film, by interstage dilute acid and/or cyanide washes in an agitated vessel. The destruction of the films exposes the gold surface for cyanidation. A simple distribution function similar to the King liberation model is proposed and tested to describe the dissolution step in the multi-step leaching mechanism. For the King model, good agreement is shown with experimental results. For the liberation results obtained by leaching in this study, the trend is co1Tect, but calibration is required for a close fit. A potentially important use for the liberation model by leaching is to predict the leachable or free gold in an ore from the free gold in the complete sample. This approach for studying the leaching behaviour of different gold bearing minerals has provided reasons why some ores leach better than others.
AFRIKAANSE OPSOMMING: Die loging van goud vanuit weerbarstige ertse is 'n komplekse kinetiese probleem wat verskeie faktore soos massa-oordrag, chemiese aspekte en mineralogiese ingeweefdheid insluit. Goud ekstraksies so hoog as 97 % in sianied oplossings in Pachuca reaktore na ongeveer 16 uur logingstyd word behaal in die meeste Witwatersrand ertse in Suid-Afrika. Hierdie hoë ekstraksies mag dalk die rede wees vir die min fundamentele navorsing oor die ekstraksie van goud vanuit minerale in 'n spesifieke erts. Die dalende erts grade, die verlaging van winsgrense en die terugplaas van geloogde erts in die myn noodsaak verbeterde goud ekstraksie. Verkeie faktore nl., chemie, diffusie, partikelgrootte en oplosbaarheid van goud in elke monster erts is in hierdie studie ondersoek. Die sentrale tema was om die logingsgedrag van goud vanuit verskeie minerale in 'n erts te bepaal. Galvaniese interaksie (hou verband met elektriese geleidingsvermoeë) en film vorming is die belangrikste faktore wat die loging van goud in kontak met minerale nadelig beïnvloed. Sulfied minerale en hul oksidasie produkte speel die grootste rol in die verlaging van die tempo van goudloging. Galena verhoog die tempo van goudloging as gevolg van die Pb (II)- ione in oplossing. Goud in kontak met geleidende minerale passiveer as gevolg van die verhoogde katodiese stroomdigtheid. In alle eksperimente met die roterende skyf (goudskyf) apparaat, passiveer die goudskyf in so 'n mate dat die logingstempo baie stadiger is as wat voorspel word met die massa-oordrags model. Die onderskeie films wat vorm op die goud- en geassosieerde minerale se oppervlaktes, asook die galvaniese interaksies, is 'n funksie van die voorafbehandeling van die erts. Die selektiewe eliminering van minerale vanuit 'n gouddraende erts verhoog die tempo van goudloging drasties en dit beskryf die kinetika van goudloging op die goudoppervlak in 'n groot mate. Die selektiewe eliminering van minerale deur gebruik te maak van oksiderende suurlogings, vernietig sekere van die minerale wat films op die goudoppervlakte kan veroorsaak deur middel van presipitasie. Die chemiese samestelling van hierdie films hang af van die mineralogie van die monster. Dit bestaan meestal uit oksiedes, sulfiedes, karbonate en sianiedkomplekse en hulle kan vernietig word deur middel van inter-stadia verdunde suur-en/of sianied wasse. 'n Eenvoudige distribusiefunksie, soortgelyk aan die King bevrydingsmodel word voorgestel en eksperimenteel getoets om die logingstap in die multi-stadia logingsmeganisme te beskryf. Vir bevryding deur loging, is die neiging van King se model korrek, maar kalibrasie word benodig vir goeie passing. 'n Potensiele gebruik van die aangepaste model is om vrye of loogbare goud in 'n spesi fieke partikel grootte fraksie van 'n erts te voorspel as die vry goud in die totale fraksie bekend is. Die resultate uit hierdie studie kan gebruik word om die logingsgedrag van gouddraende minerale te voorspel en te beskryf, en dus veduidelik hoekom goud uit sekere ertse beter loog as uit ander.

Thesis (MScIng)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: Physical systems encountered in process engineering are invariably ill-defined, multivariate, and exhibit complex nonlinear dynamical behaviour. The increasing demands for better process efficiency and high product quality have led to the development and implementation of advanced control strategies in process plants. These modern control strategies are based on the use of a mathematical model defined for the process. Traditionally, linear models have been used to approximate the dynamics of processes whereas most processes are governed by nonlinear mechanisms. Since linear systems theory is well-established whereas nonlinear systems theory is not, recent developments in nonlinear dynamical systems theory present opportunities for improved approaches in modelling these process systems. It is now known that a nonlinear description of a process can be obtained from using time-delayed copies reconstructed from measurements taken from the process. Due to low signal to noise ratios associated with measured data it is logical to exploit redundant information in multivariate time signals taken from the systems in reconstructing the underlying dynamics. This study investigated the extension of univariate nonlinear time series analysis to the situation where multivariate measurements are available. Using simulated data from a coupled continuously stirred tank reactor and measured data from a flotation process system, the comparative advantages of using multivariate and univariate state space reconstructions were investigated. With respect to detection of nonlinearity multivariate surrogate analysis were found to give potentially robust results because of preservation of cross-correlations among components in the surrogate data. Multivariate local linear models showed a deterministic structure in both small and large neighbourhood sizes whereas for scalar embeddings determinism was defined only in smaller neighbourhood sizes. Non-uniform multivariate embeddings gave local linear models that resembled models from a trivial reconstruction of the original state space variables. With regard to global nonlinear modelling, multivariate embeddings gave models with better predictability irrespective of the model class used. Further improvements in the performance of models were obtained for multivariate non-uniform embeddings. A relatively new statistical learning algorithm, the least-squares support vector machine (LSSVM), was evaluated using multilayer perceptrons (MLP) as a benchmark in modelling nonlinear time series using simulated and plant data. It was observed that in the absence of autocorrelations in the variables and sparse data LSSVMs performed better than MLPs. Simulation of trained models gave consistent results for the LSSVMs, which was not the case for MLPs. However, the computational costs incurred in training the LSSVM model was significantly higher than for MLPs. LSSVMs were found to be insensitive to dimensionality reduction methods whereas the performance of MLPs degraded with increasing complexity of the dimension reduction method. No relative merits were found for using complex subspace dimension reduction methods for the data used. No general conclusions could be drawn with respect to the relative superiority of one class of models method over the other. Spatiotemporal structures are routinely observed in many chemical systems, such as reactive-diffusion and other pattern forming systems. We investigated the modelling of spatiotemporal time series using the coupled logistic map lattice as a case study. It was found that including both spatial and temporal information improved the performance of the fitted models. However, the superiority of spatiotemporal embeddings over individual time series was found to be defined for certain choices of the spatial and temporal embedding parameters.
AFRIKAANSE OPSOMMING: Fisiese stelsels wat in prosesingenieurswese voorkom is dikwels nie goed gedefinieer nie, multiveranderlik en vertoon komplekse nie-lineˆere gedrag. Toenemende vereistes vir ho¨e prosesdoeltreffendheid en produkgehalte het gelei tot die ontwikkeling en implementering van gevorderde beheerstrategie¨e vir prosesaanlegte. Hierdie morderne beheerstrategie¨e is gebaseer op die gebruik van wiskundige prosesmodelle. Lineˆere modelle word gewoonlik ontwikkel, al is die onderliggende prosesmeganismes in die algemeen nie-lineˆere, aangesien lineˆere stetselteorie goed gevestig is, en nie-line¨ere stelselteorie nie. Onlangse verwikkelinge in die teorie van nie-lineˆeredinamiese stelsels bied egter geleenthede vir verbeterde modellering van prosesstelsels. Dit is bekend dat ‘n nie-lineˆere beskrywing van ‘n progses verkry kan word deur tydvertraagde kopie¨e van metings van die prosesse te rekonstrueer. Met die lae seintot- geraasverhoudings wat met gemete data geassosieer word, is dit logies om die oortollige informasie in meerveranderlike seine te benut tydens die rekonstruksie van die onderliggende prosesdinamika. In die tesis is die uitbreiding van enkel-veranderlike nie-lineˆere tydreeksontleding na meer-veranderlike stelsels ondersoek. Met data van twee aaneengeskakelde gesimuleerde geroerde tenkreaktore en werklike data van ‘n flottasieproses, is die meriete van enkel- en meerveranderlike rekonstruksies van toestandruimtes ondersoek. Meerveranderlike surrogaatdata-ontleding het nie-lineariteite in die data op ‘n meer robuuste wyse ge¨ıdentifiseer, a.g.v. die behoud van kruis-korrelasies in die komponente van die data. Meerveranderlike lokale lineˆere modelle het ‘n deterministiese struktuur in beide klein en groot naasliggende omgewings ge¨ıdentifiseer, terwyl enkelveranderlike metodes dit slegs vir klein naasliggende omgewings kon doen. Nie-uniforme meerveranderlike inbeddings het lokale lineˆere modelle gegenereer wat soos globale modelle afkomstig van triviale rekonstruksies van die data gelyk het. M.b.t globale nie-lineˆere modellering, het meerveranderlike inbedding deurgaans beter modelle opgelewer. Verdere verbetering in die prestasie van modelle kon verkry word d.m.v. meerveranderlike nie-uniforme inbedding. ‘n Relatief nuwe statistiese algoritme, die kleinste-kwadrate-steunvektormasjien (KKSVM) is ge¨evalueer teenoor multilaag-perseptrons (MLP) as ‘n standaard vir die modellering van nie-lineˆere tydreekse, deur gebruik te maak van gesimuleerde en werklike aanlegdata. Daar is gevind dat die KKSVM beter presteer het as die MLPs wanneer die opeenvolgende waarnemings swak gekorreleer en min was relatief tot die aantal veranderlikes. Die KKSVMs het beduidend langer geneem as die MLPs om te ontwikkel. Hulle was ook minder sensitief vir die metodes wat gevolg is om die dimensionaliteit van die data te verlaag, anders as die MLPs. Ook is gevind dat meer komplekse metodes tot die verlaging van die dimensionaliteit weinig nut gehad het. Geen algemene gevolgtrekkings kan egter gemaak word m.b.t die verskillende modelle nie. Ruimtelik-temporale strukture word algemeen waargeneem in baie chemiese stelsels, soos reaktiewe diffusie e.a. patroonvormende sisteme. Die modellering van ruimtelik-temporale stelsels is bestudeer aan die hand van ‘n gekoppelde logistiese projeksierooster. Insluiting van beide die ruimtelike en temporale inligting het tot beduidend beter modelle gelei, solank as wat di´e inligting op die regte wyse ontsluit is.

Thesis (PhD)--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: The availability of vast deposits of high-grade ore bodies are rapidly becoming something of the past in the modern mining and metallurgical scenario. Apart from the lower grade content of these ore bodies, complex mineralogy are an even greater obstacle in the recovery of valuable metal species. The development of new technology to deal with these type of ore bodies is therefore critical and worth investigating, as the world's easily exploitable high grade ore deposits are decreasing. Valuable species can be recovered from sparingly soluble solids, which slightly dissociate to give traces of the valuable ions in solution, with the use of ion-exchange resins in a slurry mixture. A dissociation equilibrium exists between the dissolved ions in solution and the solid ore body. Jf the dissolved ions are removed from the solution by ion-exchange, the solid / liquid dissociation equilibrium is continually displaced. According to Le Chatelier's principle further dissolution of the sparingly soluble solid is required to restore the equilibrium concentration of the valuable species in solution. It is possible to recover valuable metal species from metal precipitates, such as metal sulphides, by contacting a slurry of the precipitate with a suitable ion-exchange resin. The resulting ion exchange reaction between the valuable metal species and counter ions creates electrolyte solutions that may facilitate the further dissolution of the metal precipitate. These counter ion electrolyte solutions may easily become significantly concentrated. This occurs in the event of a Resin-in-Leach (RIL) mixture that results in a continuous ion-exchange reaction taking place due to the continually changing electrolyte composition of the mixture, which significantly changes the activities and hence the solubility of the valuable metal species in solution. Complete dissolution and liberation of the metal precipitate can often be achieved provided that a sufficient amount of a suitable high capacity ion-exchange resin is used in a properly engineered Resin-in- Leach (RIL) circuit. The simultaneous dissolution and adsorption of various base metal precipitates were tested. Various interactions that take place in the slurry at molecular level as well as the effects of various variables on the "adsorption by dissolution process" are discussed through the development of fundamental thermodynamic models. These thermodynamic mathematical models are developed for the three phase system that exists in a Resin-in- Leach mixture, i.e. the solid ore body, the electrolyte solution and the ion-exchange resin, and can be used for possible other applications such as the recovery of rare earths from low grade ores in the minerals processing industry. A typical example of an industrial process for the recovery of rare earth species is the percolation leaching of rare earths from low-grade kaolinitic ores, which continually shifts the solid / liquid dissociation equilibrium condition. The rare earth content of these ores is usually between 0.05%and 0.3 %, which is very low by any modern industrial extraction and refining standards.
AFRIKAANSE OPSOMMING: Die beskikbaarheid van ryk mineraal ertsneerslae is spoedig besig om iets van die verlede te word in die huidige mineraalontginning en metallurgiese veredelings industrie. Afgesien van die lae graad van die huidige mineraal ertsneerslae, blyk die komplekse mineralogiese samestelling van hierdie neerslae In veel groter struikelblok te wees in die herwinning en veredeling van die edelmetale teenwoordig in hierdie ertse. Die ontwikkeling van nuwe veredelings en ekstratiewe tegnologie vir die herwinning van edel metale, vanuit hierdie lae graad mineraal ertsneerslae, word dus benodig wat verdere navorsing in hierdie gebied regverdig. Dit is wel moontlik om metaal spesies afkomstig van ertse met 'n baie lae oplosbaarheid in waterige oplossings te herwin met ioon-uitruilings harse vanweë die feit dat die metaal spesies wel teen baie lae konsentrasies in die waterige oplossings teenwoordig is. Die metaal spesies los op in die waterige oplossings volgens hulle karakteristieke oplossings termodinamika. Indien die opgeloste metaal spesies vanuit die waterige oplossing verwyder word, sal die vaste stof / vloeistof ewewigs balans weer herstel word deurdat die vaste stof verder saloplos as gevolg van Le Chatelier se beginsel. Dit is dus moontlik om metaalagtige spesies, soos metaal sulfiedes, te herwin deur 'n waterige oplossing wat die metaal erts bevat in kontak te bring met 'n ioon-uitruilings hars. Die daaropvolgende ioon-uitruilings reaksie tussen die metaalagtige spesies en die spesies teenswoordig op die ioon-uitruilingshars het tot gevolg dat die elektrolitiese samestelling van die waterige oplossing verander. Dit is die gevolg van die migrasie van spesies aanvanklik teenswoordig op die hars wat in die waterige fase eindig. Die veranderende samestelling van die waterige oplossing mag verder tot gevolg hê dat die oplosbaarheid van die metaalagtige spesie verder verhoog mag word. Die gevolg van bogenoemde reaksies is dat die waterige oplossing ionies sterk gekonsentreerd kan word soos meer en meer spesies aanvanklik teenswoordig op die hars migreer na die oplossing. Die ioniese verandering van die waterige oplossing van 'n suiwer waterige fase tot 'n ionies sterk gekonsentreerde oplossing vind plaas tydens die oplos van erste in 'n hars-inpulp (HIP) oplossing. Die nuwe ioniese aktiwiteit in die oplossing kan die oplosbaarheid van die vaste stof drasties verander. Die volledige oplossing van 'n bepaalde kwantiteit van die vaste stof kan bereik word deur die genoegsame toevoeging van 'n geskikte hars tot die waterige oplossing wat die vaste stofbevat. Die gelyktydige oplossing en absorpsie van die metaalagtige vastestowwe vanuit waterige oplossings met behulp van ioon-uitruilings harse is eksperimenteel getoets vir die doeleindes van hierdie werkstuk. Verskeie interaksies wat op molekulêre vlak in die pulp plaasvind asook die adsorpsie proses van die spesies vanuit die waterige oplossing op die harse word bespreek en gemodelleer. Wiskundige modelle wat die termodinamika van die verskillende fases wiskundig verteenwoordig is ontwikkel vanaf bestaande termodinamiese beginsels. Die drie verskillende fases wat in ag geneem is, is die waterige fase met opgeloste metaal spesies, die vaste stof fase wat as die erts in bostaande paragrawe beskryf is en die ioon-uitruilings fase wat 'n komplekse vastestof en water fase gekombineerd is. Die doel van die werkstuk is om die basis te skep vir die ontwikkeling van modelle wat gebruik kan word om die herwinning van skaars-aarde mertale vanuit lae oplosbare erstse te modelleer en beskryf. 'n Tipiese industriële voorbeeld is die herwinning van skaars-aarde metale van lae-graadse kalkagtige erste deur gebruik te maak van perkolerende logings reaksies wat geduring die vastestof / vloeistof ewewig versteur. Die konsentrasie van die skaars-aarde metale in hierde erts gesteentes kan wissel vanaf so laag as 0.05% tot 0.3% per massa. Hierdie konsentrasies is uiters laag gesien vanuit enige industriële herwinnings proses oogpunt.

Thesis (MScEng)--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: Metallurgical processes are often high dimensional and non-linear making them difficult to understand, model and control. Whereas the human eye has extensively been used in discerning temporal patterns in historical process data from these processes, the systematic study of such data has only recently come to the forefront. This resulted predominantly from the inadequacy of previously used linear techniques and the computational power required when analysing the non-linear dynamics underlying these systems. Furthermore, owing to the recent progress made with regard to the identification of non-linear systems and the increased availability of computational power, the application of non-linear modelling techniques for the development of neural network models to be used in advanced control systems has become a potential alternative to operator experience. The objective of this study was the development ofa non-linear, dynamic model of an autogenous mill for use in an advanced control system. This was accomplished through system identification, modelling and prediction, and application to control. For system identification, the attractor was reconstructed based on Taken's theorem making use of both the Method Of Delays and singular spectrum analysis. Modelling consisted of the development of multi-layer perceptron neural network, radial basis function neural network, and support vector machine models for the prediction of the power drawn by an autogenous mill. The best model was subsequently selected and validated through its application to control. This was accomplished by means of developing a neurocontroller, which was tested under simulation. Initial inspection of the process data to be modelled indicated that it contained a considerable amount noise. However, using the method of surrogate data, it was found that the time series representing the power drawn by the autogenous mill clearly exhibited deterministic character, making it suitable for predictive modelling. It was subsequently found that, when using the data for attractor reconstruction, a connection existed between the embedding strategy used, the quality of the reconstructed attractor, and the quality of the resulting model. Owing to the high degree of noise in the data it was found that the singular spectrum analysis embeddings resulted in better quality reconstructed attractors that covered a larger part of the state space when compared to the method of delays embeddings; the data embedded using singular spectrum analysis also resulting in the development of better quality models. From a modelling perspective it was found that the multi-layer perceptron neural network models generally performed the best; a multi-layer perceptron neural network model having an appropriately embedded multi-dimensional input space outperforming all the other developed models with regard to free-run prediction success. However, none of the non-linear models performed significantly better than the ARX model with regard to one-step prediction results (based on the R2 statistic); the one-step predictions having a prediction interval of 30 seconds. In general the best model was a multi-layer perceptron neural network model having an input space consisting of the FAG mill power (XI), the FAG mill load (X2), the FAG mill coarse ore feed rate (X3), the FAG mill fine ore feed rate (X4), the FAG mill inlet water flow rate (X7) and the FAG mill discharge flow rates (X9, XIO). Since the accuracy of any neural network model is highly dependent on its training data, a process model diagnostic system was developed to accompany the process model. Linear principal component analysis was used for this purposes and the resulting diagnostic system was successfully used for data validation. One of the models developed during this research was also successfully used for the development of a neurocontroller, proving its possible use in an advanced control system.
AFRIKAANSE OPSOMMING: Metallurgiese prosesse is gewoonlik hoogs dimensioneel en nie-lineêr, wat dit moeilik maak om te verstaan, modelleer, en te beheer. Alhoewel die menslike oog alreeds wyd gebruik word om temporale patrone in historiese proses data te onderskei, het die sistematiese studie van hierdie tipe data eers onlangs na vore gekom. Dit is hoofsaaklik na aanleiding van die onvoldoende resultate wat verkry is deur van voorafgaande lineêre tegnieke gebruik te maak, asook die beperkende berekenings vermoë wat beskikbaar was vir analise van onderliggend nie-lineêre dinamiese stelsels. 'n Verder bydraende faktor is die onlangse vordering wat gemaak is met betrekking tot die identifikasie van nie-lineêre stelsels en die toename in beskikbaarheid van rekenaar-vermoë. Die toepassing van nie-lineêre modellerings tegnieke vir die ontwikkeling van neurale netwerke om gebruik te word in gevorderde beheerstelsels, het 'n potensiële alternatief geword tot operateur ondervinding. Die doelwit van hierdie studie was die ontwikkeling van 'n gevorderde beheerstelsel vir 'n outogene meul gebaseer op 'n nie-lineêre, dinamiese model. Dit is bereik deur middel van stelsel-identifikasie, modellering en voorspelling, en laastens implementering van die beheerstelsel. Vir stelsel-identifikasie is die attraktor van die stelsel bepaal soos gebaseer op Taken se teorema deur gebruik te maak van beide die metode van vertraging en enkelvoudige spektrum analise. Modellering van die stelsel vir die voorspelling van krag-verbruik deur die outogene meul het bestaan uit die ontwikkeling van multilaag-perseptron-neurale netwerke, radiaalbasisfunksie-neurale netwerke, en steunvektor-masjien-modelle. Die beste model is daarna gekies vir validasie deur middel van toepassing vir beheer. Dit is bereik deur 'n neurobeheerder te ontwikkel en te toets deur middel van simulasie. Die aanvanklike inspeksie van proses data wat gebruik sou word vir modellering het egter getoon dat die data 'n aansienlike hoeveelheid geraas bevat. Nietemin, deur die gebruik van 'n surrogaat-data-metode, is dit bevind dat die tyd-reeks wat die krag verbruik van die outogene meul beskryf, duidelik deterministiese karakter toon en dat dit dus wenslik is om 'n nie-lineêre voorspellings-model, soos 'n neurale netwerk te gruik. Gevolglik is gevind dat, wanneer die data vir attraktor hersamestelling gebruik word, 'n verband bestaan tussen die ontvouing-strategie wat gebruik word, die kwaliteit van die gerekonstrueerde attraktor, en die kwaliteit van die daaropvolgende model. As gevolg van die geraas in die data is gevind dat die ontvouing gebaseer op enkelvoudige spektrum analise 'n beter kwaliteit attraktor hersamestelling lewer. So ook is gevind dat 'n groter deel van die toestandruimte gedek word in vergelyking met die metode van vertraging-ontvouing. Deur gebruik te maak van enkelvoudige spektrum-analise, het die dataontvouing ook beter kwaliteit modelle opgelewer. Vanuit 'n modellerings-perspektief is gevind dat die multilaag-perseptron-neurale netwerk-modelle in die algemeen die beste gevaar het. 'n Multilaag-perseptronneurale netwerk met 'n gepaste ontvoude multidimensionele invoer-spasie het die beste gevaar van al die ontwikkelde modelle met betrekking tot vryloopvoorspellings. Geen van die nie-lineêre modelle het egter beduidend (op 'n R2 basis) beter gevaar as die ARX model wanneer daar na die eenstap-voorspellings (oor 'n 30 sekonde interval) gekyk word nie. Die multilaag-perseptron-neurale netwerk met 'n invoer-spasie bestaande uit die meul krag-verbruik (XI), die meullading (X2), die meul growwe-erts voertempo (X3), die meul fyn-erts voertemp ('4), die meul inlaat-water vloeitempo (X7) en die meul uitlaat vloeitempo's (X9, XIO) het in die algemeen die beste gevaar. Aangesien die akkuraatheid van emge neurale netwerk afhanklik is van die data waarmee dit aanvanklik opgestel is, is 'n diagnostiese proses modelontwikkel om die proses-model te vergesel. Lineêre hoofkomponent analise is vir hierdie doel aangewend en die gevolglike diagnostiese stelsel is suksesvol aangewend vir datavalidasie. Een van die modelle ontwikkel gedurende hierdie navorsing is ook suksesvol gebruik vir die ontwikkeling van 'n neurobeheerder wat dien as bewys dat die model goed gebruik kan word in 'n gevorderde beheerstelsel.

In industrial environments, boiler units are widely used to supply heat and electrical power. At an integrated steel mill, industrial boilers combust a variable mixture of metallurgical gases combined with additional fuels to generate high-pressure superheated steam. Most tangentially fired boilers have experienced water wall tube failures in the combustion zone, which are thought to be caused by some deficiency in the combustion process. The challenge faced in this present process is that there are very limited means to observe the boiler operation. In this study, a three-dimensional Computational Fluid Dynamics (CFD) modeling and simulation of an industrial tangentially fired boiler firing metallurgical gases was conducted. Simulation results obtained from the assembled CFD model were validated by industrial experiments. A quick comparison of the flame shape from the simulation to the actual flame in the boiler showed a good agreement. The flow field and temperature distribution inside the tangentially fired boiler were analyzed under the operation conditions, and a wall water tube overheating problem was observed and directly related to the flow characteristics.

Laser Powder Deposition (LPD) is an additive manufacturing process used for solid freeform fabrication, surface modification, and part repair or remanufacture. This technology offers some significant advantages over traditional manufacturing processes, such as reduced post-process machining and reduced material waste. Most importantly, LPD offers increased flexibility in order to meet the demands of diverse markets. However, the connection between deposition parameters, thermal gradients, and final part quality is not sufficiently understood. The research discussed here shows how radiometric temperature measurements provide insight into the connection between process parameters and final part quality. These measurements can be used to augment the research and development process while maintaining process flexibility. Radiometric thermal data was collected during the deposition of ASTM/SAE 1045, 4130, and 4140 steel thin-wall samples. Several thermal zones were identified by radiometric analysis, and compared to post-process metallographic and dimensional inspection.

Offshore industry has evolved to meet numerous challenges, e.g. deep water, high currents, high pressure and high temperature (HPHT), and sour reservoirs, facing deepwater exploration. The trend in flowline specifications for deepwater offshore fields is a consequence of complex oil-gas field conditions, such as HPHT and developments in design criteria (i.e. limit state design), welding and laying technologies. The technological evolution exhibits a trend towards an increasing wall thickness (WT) to provide sufficient resistance for the very high operating pressures. Furthermore, the pipelay operations, especially when linepipes are installed by means of the reel laying method, cause repeated plastic bending and straightening deformation cycles. These cyclic loads affect final material stress-strain properties. Reeling is currently applied to an increasing range of pipe geometries, being the present limit given by pipes with 16″ outer diameter (OD) and 30 mm wall thickness (WT). Other pipeline installation techniques, for example, J-lay, S-lay and steep S-lay also introduce plastic strain. All previous factors mentioned before and adding one more variable when exploring and producing in regions alike to the Artic where low temperatures implied several material challenges calls for high performance seamless pipes tailored to the specific application required by the oil and gas industry. In this paper, a description is given of the results of latest fundamental studies on high-strength heavy-wall steel materials manufactured by Q&T processing. This work is part of an on-going development program on high performance heavy wall seamless pipes for special applications such as HPHT, low temperature design criteria, sour requirements and studying the material under the strain based design criteria involving metallurgical modeling, laboratory tests, industrial trials and advanced metallographic examinations. The most recent findings and overall conclusions are reported hereafter, these results have been exploited by Tenaris to manufacture a limited production seamless pipes in a wall thickness range from 40 mm to 48 mm in steel grade X65 Sour Service.

In the hot stamping process, the temperature evolution drives the metallurgy, as well as the metallurgical transformation influences the temperature evolution through the exothermic nature of the austenite to martensite transformation. This heat release has already been highlighted by previous experimental work. This heat release leads to a source term in the heat equation in the blank. This source term must be quantified in order to accurately predict blank temperature evolution. Moreover, the end of the heat release corresponds to the end of the metallurgical transformation. It allows the determination of the minimum quenching time, relevant information for industry to minimize the process time. This paper presents a method to quantify the heat released by the metallurgical transformation during the hot stamping of Usibor 1500P® ArcelorMittal steel, solving inverse conduction problems. It allows the determination of this heat release as a function of temperature or time. Then, integrating it, the latent heat of the transformation can be estimated. This can be done for different contact pressures between tool and blank. Finally, it can be linked to the martensite proportion to estimate it as a function of time or temperature and determine the Koistinen-Marburger model parameters. These results should improve the accuracy of numerical simulations of the hot stamping process.

Abstract High energy density welding processes like laser and electron beam welding are capable of welding dissimilar plates with much ease due to high power density and low heat input in spite of the varying thermos-physical properties of the used alloys. The present work is aimed to check the feasibility of joint prepared with laser welding of SS 316L and Inconel 718 plates. The experiments are designed to study the effect of welding speed on the mechanical and metallurgical behavior of the joints without any offset to joint line. The formation of laves phases is confirmed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) phase analysis. These laves phase are micro-segregation of Nb, Fe, C and Cr, which is because of high temperature in a small area of fusion zone (FZ) due to intense heat of laser source. Micro-segregation of different elements has led to micro-fissures, which is detrimental for the joints operating at elevated temperature. Cooling rate and peak temperature during welding play the significant role in obtaining a sound quality joint. The present work gives an insight on feasibility of laser welded joint of SS 316L and Inconel 718 with suitable selection of welding speed during laser welding.

Abstract The root cause of a series of similar failures in SA-213 T91 Superheater tubes of an Heat Recovery Steam Generator (HRSG) is investigated using a combination of engineering analysis and review of process data. The HRSG at the Combined Cycle Gas Turbine (CCGT) Power Plant power plant in question had suffered from frequent tube-to-header fatigue failures over the past 10 years. Metallurgical analyses had never identified any sign of creep damage in, or near, any of the failure locations. Recently, the Gas Turbine (GT) exhaust gas flow pattern upstream of the SH tubes changed slightly. Subsequently there were a large number of HPSH tube to header failures (> 10) on one side of the gas duct. Metallurgical analysis showed that the tube-to-header welds failed by creep-fatigue damage; analyses of tubes from the left-hand side of the boiler did not show any signs of similar damage being present. Further investigation confirmed that the root cause was identified as higher temperatures resulting from small changes in the GT outlet flow pattern.

Abstract In recent years, ship hulls have become larger. And the welding has become more important technology in ship building. In other word, welding has become more important technology in shipbuilding. In Japanese shipbuilding, multiple electrode butt welding has been performed with large current and high speed to increase construction efficiency. However, the multiple electrode welding method may cause a hot cracking. X-ray or ultra sonic wave inspection and repair welding are necessary due to the generation of hot cracking. These will increase the production cost. Therefore, it is important to prevent hot cracking. It is known that hot cracking is generated by both metallurgical and mechanical factors. The authors propose a new evaluation method of hot cracking based on the modeling of both mechanical and metallurgical behaviors. In the developed method, from the metallurgical point of view, solidification growth direction is determined from the temperature gradient obtained by the heat conduction analysis to predict the position of hot cracking. Moreover, from the mechanical point of view, the possibility of the generation of hot cracking is assessed using plastic strain increment in Brittleness Temperature Range (BTR). In order to show the validity of the developed method, the developed method is applied to the analysis of hot cracking on automatic tandem butt welding through the comparison with experimental results. As a result, it is demonstrated that the hot cracking can be evaluated by using the developed method.

The new generation of value-added low carbon-low manganese-niobium microalloyed structural steels for both low and high yield strength, energy absorption, fatigue and fracture resistant applications is under development for offshore and arctic materials engineering applications. These materials engineering considerations are shifting designers to consider new lower cost and more robust construction materials even for low yield strength applications require improved fatigue, fracture arrest and toughness performance. The civil engineering and end user community demand structural reinforcing bars, shapes, beams and plates with improved energy absorption and fatigue properties. With more severe climatic conditions evolving every day, demands also necessitate improved fire and seismic resistance, yield-to-tensile ratio consistency, improved bendability and weldability. These attributes are difficult to obtain from steel producers today with their current higher carbon microalloyed steel approaches and hot rolling practices. There is a global shift in motion to low C-Nb-Mn bearing construction steels displacing traditional materials. The technological and metallurgical advancements of value-added niobium (Nb) microalloyed thermo-mechanical controlled process (TMCP) plate steels have been further developed to meet more demanding fatigue, fracture and low temperature toughness end user requirements. Niobium enables achievement of substantial grain refinement and grain size uniformity when the plate is rolled with the proper reduction, thermal schedule and process metallurgical operational practices. The effects of microalloying elements on the continuous cooling transformation behavior must be carefully controlled during the process metallurgy of the reheating and rolling process to successfully achieve the desired mechanical properties. TMCP applications have been successfully developed in numerous product sectors with thickness exceeding 120 mm. Since the very fine grained microstructure improves toughness and increases the yield strength, this Nb-TMCP process enables the required tensile properties with the growing trend to leaner chemical composition designs (less than 0.10%C) and excellent toughness properties. From an operational cost perspective, in today’s very competitive market environment, there exists a huge opportunity for structural offshore and arctic plate producing steel mills to improve their profitability by thoroughly assessing a shift to lower carbon and manganese steels in their product mix. Through the adoption of these lower carbon Nb-containing structural materials, several design and/or manufacturing companies are initiating new offshore steel designs that will further provide improved overall lifetime and cost performance at reduced maintenance expense. These high strength plate steels offer the opportunity to manufacture complex heavy-lift and fatigue-critical components for larger offshore structures without increasing the weight of the platforms.

The first CANDU (CANadian Deuterium Uranium) pressurized heavy water reactor (PHWR) went into operation in July 1971. Today, there are several units in operation at the Pickering, Bruce, and Darlington sites in Ontario, Canada. The steam generator tubing materials were manufactured from Monel 400, Inconel 600, and Incoloy 800 for the Pickering, Bruce, and Darlington respectively and are subjected to different operating conditions. This paper presents a review of some of the various types of degradation mechanisms that have been observed on these tubing materials over the operating period of the respective plants. The results presented are based on the metallurgical examination of removed tubes. The mechanisms that have been observed include pitting, stress corrosion cracking, intergranular attack, fretting, and erosion corrosion. The nature of the flaws and causative factors (if known) are discussed.

Canadian nuclear standard CSA N285.4 requires the periodic metallurgical examination of removed ex-service steam generator tubes. This paper describes the practices used for the characterization and structural integrity tests of ex-service steam generator tubes at Ontario Power Generation (OPG). It shows that there is no degradation in mechanical properties of Monel 400 tubes after 7 to 18 Effective Full Power Years (EFPY) of operation and Incoloy 800 tubes after more than 10 EFPY of operation.