Master of Science in Engineering - Engineering / The employment of an electrochemical process is an attractive alternative for the treatment of effluents. When dealing with solutions of low metal ion concentrations mass transport limitations are significant and large electrode surfaces are required. The use of a reactor containing a three-dimensional electrode is preferable as the surface area per unit volume is orders of magnitude greater than that of the familiar plate type reactor. A benchscale electrochemical reactor was designed and constructed to incorporate a cylindrical packed bed cathode. The flow of electrolyte is perpendicular to the direction of the flow of the current and the system is operated galvanostatically in a batch recirculation mode. The industrial stream selected for examination contains palladium and copper ions and a small concentration of platinum in a chloride medium containing ammines. The evolution of chlorine gas at the anode by the oxidation of the chloride ions is prevented by the inclusion of a cation exchange membrane and a separate anolyte, namely sulphuric acid, is introduced to the outer anodic chamber. Tests were conducted on both synthetic and industrial solutions and a simplified model which was derived was used to estimate the mass transfer coefficients. The concentrations of the palladium, copper and platinum in the plant effluent were approximately 150, 200 and 10 ppm respectively. The results show that the metal ions can be rapidly reduced to well below 1 ppm in each case. The separation of the palladium and copper ions is shown to occur to a limited degree during electrodeposition, with the extent of separation increasing for lower current densities. Enhanced separation may be possible during the removal of the deposited metals from the cathode either by anodic stripping or chemical treatment. A further method for the recovery of the metals is the combustion of the graphite particles. The high value of palladium, coupled with the significant recoveries shown to be achievable, suggest economic viability in addition to the environmental benefits.

Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2008.

Activated carbons used in the Platinum Group Metals extraction industry are characterised by large internal surface areas and a great affinity for platinum, palladium and ruthenium. It is therefore necessary in this study to develop a method to produce an activated carbon that is suitable and yet cost effective, for use in the extraction of PGM's. The quality of the coal-based activated carbon may not prove to be as good as activated carbon produced from other traditional sources, but the production costs involved may make South African coal a feasible alternative feedstock. The purpose of this research is to prepare activated carbon from a South African based bituminous coal by physical activation. The activated carbon produced are characterised by BET surface area, activated carbon pH and phenol adsorption studies. The results of the different characterisation methods for the prepared activated carbons are compared to the results of a commercially available activated carbon, Norit RO 0.8 (control sample). Bituminous coals from various sources including Witbank Seam 4 and New Vaal are used. The preparation method chosen is raw material activation by means of physical activation with superheated steam. The effects of process variables such as activation time (1-3 hr) and temperature (600 - 800°C) are studied in order to optimise those preparation parameters. Activated carbon surface area is characterized by means of nitrogen adsorption isotherms at 77K. BET surface area analysis showed that Witbank Seam 4 coal activated at a temperature of 800°C and activation time of 3 hours, resulted in a surface area of 340m2/g. Quality control of each sample was performed by measuring the pH of a known amount of the prepared activated carbon in distilled water over time. Results showed that the pH of some of the prepared activated carbons reached a value of 11. Phenol adsorption results for the different activated carbons prepared corresponded well to the results obtained for the Norit RO 0.8 activated carbon sample. / Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2008.

Activated carbons used in the Platinum Group Metals extraction industry are characterised by large internal surface areas and a great affinity for platinum, palladium and ruthenium. It is therefore necessary in this study to develop a method to produce an activated carbon that is suitable and yet cost effective, for use in the extraction of PGM's. The quality of the coal-based activated carbon may not prove to be as good as activated carbon produced from other traditional sources, but the production costs involved may make South African coal a feasible alternative feedstock. The purpose of this research is to prepare activated carbon from a South African based bituminous coal by physical activation. The activated carbon produced are characterised by BET surface area, activated carbon pH and phenol adsorption studies. The results of the different characterisation methods for the prepared activated carbons are compared to the results of a commercially available activated carbon, Norit RO 0.8 (control sample). Bituminous coals from various sources including Witbank Seam 4 and New Vaal are used. The preparation method chosen is raw material activation by means of physical activation with superheated steam. The effects of process variables such as activation time (1-3 hr) and temperature (600 - 800°C) are studied in order to optimise those preparation parameters. Activated carbon surface area is characterized by means of nitrogen adsorption isotherms at 77K. BET surface area analysis showed that Witbank Seam 4 coal activated at a temperature of 800°C and activation time of 3 hours, resulted in a surface area of 340m2/g. Quality control of each sample was performed by measuring the pH of a known amount of the prepared activated carbon in distilled water over time. Results showed that the pH of some of the prepared activated carbons reached a value of 11. Phenol adsorption results for the different activated carbons prepared corresponded well to the results obtained for the Norit RO 0.8 activated carbon sample. / Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2008.

Made available in DSpace on 2014-06-12T18:01:48Z (GMT). No. of bitstreams: 2 arquivo6300_1.pdf: 2246056 bytes, checksum: 57be7b0e6c47c2db5b0f7eee13fc1125 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2006 / A Yersinia pestis, bactéria Gram-negativa da família Enterobacteriaceae, é uma espécie muito homogênea quando observada pelos métodos fenotípicos: apresenta apenas um sorotipo, um fagotipo e um biótipo subdividido em três biovars ou variedades geográficas. Com a introdução de técnicas moleculares os estudos de tipagem em cepas de Y. pestis foram significativamente aprofundados contribuindo para rastrear a origem de novas cepas e detectar o surgimento de novos clones. Este trabalho teve como objetivo verificar a diversidade genética entre cepas de Y. pestis analisando regiões específicas do genoma desta bactéria suscetíveis a diferentes mecanismos de mutação. Para isto foram empregadas duas abordagens: 1) análise do loco pgm em três cepas altamente virulentas, isoladas de humanos e 2) análise de VNTRs (MLVA-PCR) como marcador para reconhecer e rastrear os clones circulantes de Y. pestis nos focos de peste do Nordeste do Brasil. Foram observadas diferenças na estabilidade do loco pgm das cepas estudadas (duas cepas brasileiras: P. CE 882 e P. Exu 340 e uma de outro foco sul-americano: P. Peru 375). As culturas derivadas da P. Exu 340 e P. Peru 375 apresentaram alterações no loco pgm após repiques sucessivos no meio agar vermelho Congo, enquanto que a P. CE 882 não apresentou. Nos ensaios do MLVA-PCR todos os seis locos estudados foram amplificados em todas as cepas de Y. pestis. Os locos VNTR1, VNTR5 e VNTR6 apresentaram padrões de amplificação semelhantes em todas as cepas de Y. pestis das diferentes regiões geográficas. Entretanto, os padrões dos locos VNTR2, VNTR3 e VNTR4 foram distintos para algumas cepas. Foi verificado diversidade no número de alelos por loco variando de três (para o VNTR1 e o VNTR3), quatro (para o VNTR2) e cinco (para o VNTR4), enquanto para os VNTR5 e VNTR6 o número de alelos não variou. A análise do tamanho e o número de repeats para cada VNTR permitiu identificar 23 genótipos nas 105 amostras de Y. pestis analisadas. Alguns destes genótipos apresentaram uma ampla distribuição geográfica, enquanto outros foram específicos de uma determinada região. Para verificar a estabilidade dos VNTRs in vitro , três cepas de Y. pestis foram submetidas a repiques sucessivos e as culturas derivadas foram analisadas. As cepas parentais e as culturas derivadas revelaram perfis idênticos com os seis locos estudados. Cepas de Y. pseudotuberculosis e Y. enterocolitica foram incluídas no trabalho para comparação. As cepas de Y. enterocolitica amplificaram todos os locos, com exceção do VNTR1 onde nenhum segmento foi amplificado. Com os outros locos os padrões de amplificação obtidos foram semelhantes aos encontrados nas cepas de Y. pestis. As cepas de Y.pseudotuberculosis apresentaram padrões de amplificação semelhantes aos encontrados em cepas de Y. pestis para os locos VNTR1 e VNTR3 e distintos para os demais locos. Os resultados obtidos pela análise de diferentes regiões ou locos (pgm e VNTRs) do genoma da Y. pestis demonstraram diversidade genética intraespecífica nessa espécie os quais contribuirão para estudos epidemiológicos, taxonômicos e evolutivos futuros

Small organic ‘collector’ ligands play an important role in the recovery of platinum group minerals (PGMs) from the industrial platinum mining process via the froth flotation process, which separates finely ground minerals on the basis of relative hydrophobicity. Design of novel ligands to improve PGM recovery is an ongoing industrial interest. This thesis involves the application of computational chemistry techniques to gain a first-principles understanding of simple mineral-collector ligand interactions, with a view to applying this understanding to the design of novel collector ligands. Experimental techniques are also used, where appropriate, to validate computational modelling in order to gauge the applicability of computational chemistry to this field. Sperrylite (PtAs2), the world’s most common PGM, was used as a model for a typical platinum group sulfide mineral. Pentlandite ((Fe,Ni)9S8) and pyrite (FeS2), two base metal sulfide minerals commonly associated with PGMs, were used as competitor surfaces to gauge collector selectivity. α-quartz (SiO2) was used as to model silicaceous waste material, and pure platinum (Pt) as an internal standard to gauge Pt-collector interactions. Chapter 1 provides an overview of PGM mining with particular focus on the froth flotation process. A brief overview of the computational methods applied in this work is provided in Chapter 2. Chapter 3 presents modelling work based on assessing the various mineral and metal surfaces upon which ligands adsorption is modelled. Stable ‘working surfaces’ are defined by calculating surface energies for various low Miller index cleavages of the bulk unit cells of these solids. Surface stability with respect to slab depth is also assessed. A number of methods, including application of the virtual crystal approximation, a pairwise cluster expansion and explicit site modelling, are used to resolve the issue of positional disorder of the metal sites in pentlandite. This leads to the observation that pentlandite slabs with a higher concentration of Ni atoms at the mineral/vacuum interface are more stable. A global minimum energy bulk unit cell of pentlandite is described. Chapters 4 and 5 deal with the adsorption of collector and aqua ligands onto these surfaces, with Chapter 5 also reporting attempts at rational in-silico ligand design. A novel method for calculating the binding energy of anionic species in periodic systems via a work-function based correction is described and tested for both mono- and dianionic species. Modelling of ethyl xanthate (H5C2OCS2-) and xanthate-based analogues (H5C2XCS2-, where X=N, NH, NC2H5, S, CH, CH2) shows a trend of increased binding strength upon formation of dianionic species. Whilst this observation was supported (to a lesser degree) by geometrical parameters, the extension of the work-function based correction to deal with dianionic species tended to significantly overbind these ligands and so the work function correction was found to be inappropriate for use in models with a charge state greater than -1. Modelling of heterocyclic ligands on selected surfaces shows weaker adsorption than non-heterocyclic species due to unfavourable electronic effects of the delocalised heterocycle on the R-CS2- head group. Efforts in ligand design focussed on optimising the electronic properties of the tail group in the xanthate structure to provide maximum electron density to the CS2- system. The output from this process was p-methoxyphenyl dithiocarbamate (H2CO-C6H4-N=CS2²-), which performed well in computational models. Synthesis of this ligand, as well as protonated Nethyl dithiocarbamate (H5C2NHCS2-) failed, however, due to the intrinsic instability of monosubstituted dithiocarbamates. Attempts to validate modelling results using two experimental techniques are reported in Chapter 6. Firstly, cyclic voltammetry experiments using sperrylite, pentlandite and platinum working electrodes suspended in collector solutions of concentration 1x10-3 M are reported, which show some correlation between the order of calculated binding energies and the relative position of the oxidation potential for the formation of disulfide oxidation products, a process which is affected by surface adsorption. Correlation is best for ethyl xanthate and diisobutyl dithiophospinate, but poor for N,N-diethyl dithiocarbamate ((H5C2)2NCS2-). Secondly, microflotation experiments for the recovery of sperrylite, pentlandite and pyrite using various collector ligands were conducted. Results broadly agree with prior microflotation literature, but show no simple correlation between ligand binding energies and flotation recovery, suggesting that more complex factors than simple ligand/mineral adsorption are involved.

There has been an increased awareness of the inter-dependence between man and the environment since the 1960’s. Environmental awareness has evolved from representing fairly radical views opposing all development, to a current emphasis on sustainable development between development and the environment. Life Cycle Assessment (LCA) is defined as the identification and quantification of the environmental impacts of a product, process or service during the entire life cycle being studied. The life cycle starts at the extraction of raw materials and the production of energy used to create the product through the use and final disposal of the product. LCA therefore considers the production, use and disposal of a product, which constitutes the life cycle of the product. LCA can be combined with methodologies that study other parameters such as costs in order to optimise the benefits from LCA. It is suggested that cost implications of processes to reduce environmental impacts should be included in a methodology used for a Platinum LCA. A comment that is consistently raised in the case studies is that the minerals industry regards LCA as an effective tool to determine the impacts of the industry, however extraction & beneficiation of minerals are often grouped together, with accurate data not being available, and databases either not available or not updated. The case studies indicated several benefits from the various LCA’s conducted. A Platinum LCA should clearly define and group the environmental impacts being studied into categories such as greenhouse gas emissions, global warming, acidification, and resource consumption. A Platinum LCA will be resource- and time intensive due to the large scale of the processes involved. It is suggested that a Platinum LCA firstly focuses on the production phase, i.e. cradle-to-gate, with potential future work done on the use and end-of-life stages. It is suggested that individual facility-based LCA’s for AMPLATS and other platinum producers are conducted in order to get a true reflection of the environmental burden of each company, and then selectively share technological improvements to reduce the environmental burden without disclosing sensitive information. The benefit of LCA in the case of platinum will be optimised if it can be used to make business decisions, together with consideration of financial and production benefits in addition to anticipated environmental benefits of alterations to processes. It is essential that LCA is seen as a business tool that will assist the company to make informed business decisions about process improvements, as well as new projects and design of new facilities. LCA on its own will not determine which product or process is the most cost effective or works best. The information developed in a LCA study should be used as one component of a more comprehensive decision making process assessing the trade-offs with cost and performance. The results from a LCA could be used to make informed decisions about optimisation between costs and reduced environmental impacts. / Thesis (M. Environmental Management)--North-West University, Potchefstroom Campus, 2011.

There has been an increased awareness of the inter-dependence between man and the environment since the 1960’s. Environmental awareness has evolved from representing fairly radical views opposing all development, to a current emphasis on sustainable development between development and the environment. Life Cycle Assessment (LCA) is defined as the identification and quantification of the environmental impacts of a product, process or service during the entire life cycle being studied. The life cycle starts at the extraction of raw materials and the production of energy used to create the product through the use and final disposal of the product. LCA therefore considers the production, use and disposal of a product, which constitutes the life cycle of the product. LCA can be combined with methodologies that study other parameters such as costs in order to optimise the benefits from LCA. It is suggested that cost implications of processes to reduce environmental impacts should be included in a methodology used for a Platinum LCA. A comment that is consistently raised in the case studies is that the minerals industry regards LCA as an effective tool to determine the impacts of the industry, however extraction & beneficiation of minerals are often grouped together, with accurate data not being available, and databases either not available or not updated. The case studies indicated several benefits from the various LCA’s conducted. A Platinum LCA should clearly define and group the environmental impacts being studied into categories such as greenhouse gas emissions, global warming, acidification, and resource consumption. A Platinum LCA will be resource- and time intensive due to the large scale of the processes involved. It is suggested that a Platinum LCA firstly focuses on the production phase, i.e. cradle-to-gate, with potential future work done on the use and end-of-life stages. It is suggested that individual facility-based LCA’s for AMPLATS and other platinum producers are conducted in order to get a true reflection of the environmental burden of each company, and then selectively share technological improvements to reduce the environmental burden without disclosing sensitive information. The benefit of LCA in the case of platinum will be optimised if it can be used to make business decisions, together with consideration of financial and production benefits in addition to anticipated environmental benefits of alterations to processes. It is essential that LCA is seen as a business tool that will assist the company to make informed business decisions about process improvements, as well as new projects and design of new facilities. LCA on its own will not determine which product or process is the most cost effective or works best. The information developed in a LCA study should be used as one component of a more comprehensive decision making process assessing the trade-offs with cost and performance. The results from a LCA could be used to make informed decisions about optimisation between costs and reduced environmental impacts. / Thesis (M. Environmental Management)--North-West University, Potchefstroom Campus, 2011.

Abstract Sulfide-poor deposits of platinum-group elements (PGE) occur in two main types: silicate-type and oxide-type. In the silicate-type mineralization PGE form discrete platinum-group minerals (PGM) that occur as inclusions in various silicate minerals. In the oxide-type mineralization PGM may have different modes of occurrence. They may be associated with silicates or they may occur as inclusions in chromite, magnetite or ilmenite, for example. In some cases they may even be associated with base metal sulfides. The approach chosen in this work is mainly a mineralogical one. PGM parageneses, their modes of occurrence and associations with other minerals were studied from different deposits. These are then compared to some well-recorded examples of PGE deposits. The case studies presented, the Duluth Complex in Minnesota, U.S.A., the Hanumalapur Complex in Karnataka, India, and the Penikat Layered Intrusion in northern Finland, are examples that illustrate the multitude of possibilities regarding PGE mineralization versus the traditional approach where any significant quantities of PGE are supposed to occur only in association with base metal sulfides. As the traditional orthomagmatic and hydrothermal models cannot explain the genesis of some sulfide-poor PGE occurrences, a new theory of PGE mineralization was developed. This “redox theory” is an attempt at explaining the association of PGE with various oxide minerals, most importantly chromite.

Corrosion problems of copper waffle coolers are experienced in Platinum Group Metals (PGM’s) smelting furnaces. The copper cooler wear mechanism was studied through a post-mortem analysis of the refractory corrosion products that were removed from a PGM smelter. Post-mortem samples were characterised using Scanning Electron Microscopy (SEM), X-Ray Fluorescence Spectroscopy (XRF) and X-Ray Powder Diffraction (XRD). On visual inspection of the refractory wall it was observed that at the slag-feed interface the front refractory (mag-chrome) brick was completely corroded and only the freeze lining (frozen slag) formed a barrier between the copper cooler and the feed. At the bottom section of the slag zone the front refractory brick was still intact. Base metal sulphides and element sulphur were the major phases observed at the copper cooler-freeze lining interface while at the copper cooler-front brick interface only covellite (CuS) and element sulphur were observed. It was concluded that wear proceeded through two mechanisms: Reaction of copper with base metal sulphides which infiltrated the freeze lining and gaseous attach of copper by sulphur forming covellite. Front mag-chrome refractory bricks are replaced by graphite blocks in the latest furnace wall designs. A post-mortem graphite block was analysed with SEM, XRD and Inductively Coupled Plasma (ICP) to determine the phases associated with copper cooler corrosion. Base metal sulphides were observed at the copper cooler-graphite block (cold face) interface. Good agreement was found between the phases in the graphite block and the phases in the post-mortem sample where the refractory brick was used. Laboratory experiments were carried out to determine the effect of corrosive gas composition and copper cooler surface temperature on the corrosion rate and morphology of the corrosion products. Tests were performed on copper foils at temperatures from 80°C to 140°C. Corrosive gases included H2S, S2 and S2 with HCl. It was found that when a copper foil is exposed to sulphur the sulphides that form are covellite at 80°C, covellite and yarrowite (Cu9S8) at 110°C, yarrowite and digenite (Cu1.8S) at 140°C. Linear corrosion rate behaviour was observed between 80°C and 110°C since the sulphide scales are not passivating and they poorly adhere to the copper foil. Average corrosion rates of copper foil by sulphur vapour was 54 mm/y at 80°C and 80 mm/y at 110°C, above 112°C the corrosion rate decreased to 5 mm/y. Additions of HCl enhance the corrosion rate at temperatures above the melting point of sulphur (112°C). Chalcocite (Cu2S) forms when copper is exposed to H2S. It was concluded that the corrosion rate and the morphology of the corrosion product are functions of temperature and the corrosive gas composition. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted