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A project report submitted to the faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 1994. / South Africa is the largest primary producer of platinum-group metals (PGMs) in the world. It is estimated that only 2.1 per cent of the 153711 kg of total sales for 1993 was beneficiated locally. Potential value added foreign exchange earnings and employment opportunities. therefore. are being forfeited. This study identifies prospective areas of development in the major sectors of application of PGMs namely: autocatalysts; chemical and allied industries; electrical and electronics sectors; jewellery and coinage fabricators. The methodology of intensity of use (IOU) is first discussed. ThIs is followed by an analysts of South Africa's production and sales of PGMs. The body of the report is an empirical study of the IOU of platinum and palladium to establish a world outlook for these metals in their applications. Finally, the more lucrative of these applications are discussed in the light of South Africa's participiltion and competitiveness in the world market. The conclusions are firstly, that the established autocatalyst industry has the best prospect for growth and expansion. Secondly, the electrical application of platinum in fuel cells has potential depending on the level of government funding and support for a R&D programme. The third finding is that the electronics and jewellery industries have development potential on condition that resistance to market entry can be overcome by reduced public policy costs. Possible violation of GATT agreements may be avoided for these applications by world free trade co-operation.

Motivation: The health effects of platinum on the human body are a great concern. It affects the respiratory system as well as the skin. The demands for platinum have seemingly increased over the last few years due to its use in automobile exhaust gas catalysts. Thus there will be an increase in the production and processing of platinum and therefore a greater possibility of exposure to platinum compounds. This is why it is of great importance to evaluate the surface sampling methods, to ensure that they are effective for platinum use. Objectives: 1) To evaluate and compare a few different surface sampling methods for removal of platinum salts from contaminated surfaces in order to determine which one of these methods has the best retention and recovery efficiency. 2) To use the most effective method to monitor surface contamination on porous and non–porous surfaces in a platinum refinery. Methods: Two types of filters (mixed cellulose ester and polyvinyl chloride) and GhostwipesTM were evaluated and compared in this study. Platinum solution (hexachloroplatinic acid) concentrations of 50, 150 and 300 ug Pt/ml solution were used. The retention efficiency of the different sampling mediums was tested by releasing 1 ml of each concentration directly onto the sampling medium. Efficiencies were tested on a non–porous (glass) and porous surface (semi–face bricks). This was done to see how the collection efficiency of the medium will differ on these two surfaces. A total of three wipes were used per surface, however were analyzed individually. All the samples were analyzed using the Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP–AES) analytical method by an accredited laboratory. Results: The results obtained indicated the retention and recovery efficiencies of the three sampling mediums at the three platinum concentrations of 50, 150 and 300 ug Pt/ml solutions. The retention efficiency of the GhostwipesTM was 93.2% at 50 ug Pt/ml solution, 95.3% at 150 ug Pt/ml solution and 93.6% at 300 ug Pt/ml solution, whilst the mixed cellulose ester (MCE) filters and polyvinyl chloride (PVC) filters were lower than 30% at all three concentrations. The overall recovery efficiencies of all three concentrations of the GhostwipesTM and MCE filter were the highest: the GhostwipesTM with levels of 73.9 %, 84.4% and 63.5% and the MCE filters with levels of 71.4%, 84.4% and 80.2%, whilst the PVC filters did not achieve levels above 60%. The wipe materials were also evaluated in terms of the ASTM E1792 standard requirements for wipe materials. Conclusion: GhostwipesTM were found to be the most suitable sampling medium based on retention and recovery efficiencies. The GhostwipesTM also complies with all the requirements listed in the ASTM E1792 standard for wipe materials, which makes it the most suitable wipe sampling material. The MCE and PVC filters however do not comply with all the ASTM E1792 requirements. / Thesis (M.Sc. (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2011.

Motivation: The health effects of platinum on the human body are a great concern. It affects the respiratory system as well as the skin. The demands for platinum have seemingly increased over the last few years due to its use in automobile exhaust gas catalysts. Thus there will be an increase in the production and processing of platinum and therefore a greater possibility of exposure to platinum compounds. This is why it is of great importance to evaluate the surface sampling methods, to ensure that they are effective for platinum use. Objectives: 1) To evaluate and compare a few different surface sampling methods for removal of platinum salts from contaminated surfaces in order to determine which one of these methods has the best retention and recovery efficiency. 2) To use the most effective method to monitor surface contamination on porous and non–porous surfaces in a platinum refinery. Methods: Two types of filters (mixed cellulose ester and polyvinyl chloride) and GhostwipesTM were evaluated and compared in this study. Platinum solution (hexachloroplatinic acid) concentrations of 50, 150 and 300 ug Pt/ml solution were used. The retention efficiency of the different sampling mediums was tested by releasing 1 ml of each concentration directly onto the sampling medium. Efficiencies were tested on a non–porous (glass) and porous surface (semi–face bricks). This was done to see how the collection efficiency of the medium will differ on these two surfaces. A total of three wipes were used per surface, however were analyzed individually. All the samples were analyzed using the Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP–AES) analytical method by an accredited laboratory. Results: The results obtained indicated the retention and recovery efficiencies of the three sampling mediums at the three platinum concentrations of 50, 150 and 300 ug Pt/ml solutions. The retention efficiency of the GhostwipesTM was 93.2% at 50 ug Pt/ml solution, 95.3% at 150 ug Pt/ml solution and 93.6% at 300 ug Pt/ml solution, whilst the mixed cellulose ester (MCE) filters and polyvinyl chloride (PVC) filters were lower than 30% at all three concentrations. The overall recovery efficiencies of all three concentrations of the GhostwipesTM and MCE filter were the highest: the GhostwipesTM with levels of 73.9 %, 84.4% and 63.5% and the MCE filters with levels of 71.4%, 84.4% and 80.2%, whilst the PVC filters did not achieve levels above 60%. The wipe materials were also evaluated in terms of the ASTM E1792 standard requirements for wipe materials. Conclusion: GhostwipesTM were found to be the most suitable sampling medium based on retention and recovery efficiencies. The GhostwipesTM also complies with all the requirements listed in the ASTM E1792 standard for wipe materials, which makes it the most suitable wipe sampling material. The MCE and PVC filters however do not comply with all the ASTM E1792 requirements. / Thesis (M.Sc. (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2011.

Durability of carbon-supported platinum nanoparticle is one of the limiting factors for PEM fuel cell commercial applications. In our research work, we applied both experimental and mathematical simulative tools to study the mechanisms of Pt/C catalyst degradation. An accelerated catalyst degradation protocol by cycling the cathode potential in a square-wave profile was applied to study the losses of cell performances, catalyst ORR activity, and Pt active surface areas. Post-mortem analyses of cathode Pt particle size by X-ray diffraction and platinum distributions in CCMs by SEM/EDS were also conducted. Increased cell temperature and relative humidity was found to accelerate the cathode catalyst degradation. High membrane water contents or abundant water/ionic channels within the polymer electrolyte were believed to accelerate Pt ion transport and cathode degradation. After degradation tests, significant amount of Pt loss into the membrane forming a Pt "band" was observed through cathode platinum dissolution and chemical reduction of soluble Pt ions by permeated hydrogen from the anode. Platinum deposition was confirmed at a location where the permeated hydrogen and oxygen had the complete catalytic combustion over the deposited Pt clusters/particles as the catalyst. A cathode degradation model was built including the processes of platinum oxidation, dissolution/replating, diffusion of Pt ions and Pt band formation in electrolyte. A simplified bi-modal particle size distribution was applied with equal numbers of small and large type particles uniformly distributed in the cathode initially. Processes of Pt mass exchange between two types of particles were demonstrated to cause the overall particle growth. This was due to the particle size effect that platinum dissolution from the small type particles and replating of Pt ions onto the large particles was favored. Parametric study found the increased upper cycling potential was the dominated factor to accelerate the catalyst degradation. Also high frequency of potential cycle and low surface oxide coverage accelerated the degradation rate. Pt dissolution and oxidation processes in perchloric acid were preliminary investigated, and both chemical and electrochemical processes of oxidation and dissolution were believed to be involved under closed-circuit fuel cell conditions with oxygen presence at cathode.

The primary focus of this study was to compare the efficiency of six filter samplers in the collection of inhalable soluble platinum (Pt) salts at a South African base metal refinery. Inhalation remains the major route of occupational exposure to platinum groups metals (PGMs). South Africa would benefit from the study since it’s amongst the major countries where PGMs are produced and hence, monitoring of worker exposure with the most efficient sampler is of utmost importance. The IOM is currently being used in routine exposure monitoring although no studies have been carried out to compare its performance to that of the other samplers under the actual base metal refinery conditions. Method: The button, closed face cassette (CFC), Gesamtsstaubprobenhome (GSP), (Institute of Medicine) IOM, PAS-6 and seven hole (SH-sampler) samplers were randomly allocated to six different positions in presumably high exposure areas. The samplers were moved around in the subsequent sampling days and the process repeated 3 times. The average dust mass and Pt concentrations were used as a basis of sampler performance and comparisons from which sampler hierarchies were determined. Results: The average relative humidity ranged between 37% and 43% and the average dry bulb temperature of 22.4°C was measured. Comparison of the dust mass concentrations revealed no statistically significant differences amongst the six filter samplers tested. The SH-sampler and CFC however collected the highest and lowest dust mass and Pt concentrations respectively. Discussion: The SH-sampler was found to be a sampler with more reliability than the the IOM for the collection of dust mass and soluble Pt. The IOM collected 98% of the SH-sampler dust mass and Pt concentrations. This was in spite of the larger variations indicated by the highest relative standard deviations and confidence intervals shown by the IOM than the other samplers. The GSP sampler, however, showed better precision than all the other samplers in the collection of platinum. The seven 4 mm orifices of the SH-sampler sampler allow for uniform distribution of sampled particles onto the filter supporting its better precision than the IOM which has only one 4 mm opening. The worst performing sampler was the CFC sampler since it collected the lowest dust mass and Pt concentrations. The CFC and the PAS samplers have downward facing inlets that are affected by gravity especially in lower wind speeds which, therefore, influences their efficiency. The GSP sampler concentrations placed it as 4th and 3rd best in Pt and dust mass hierarchies respectively even though it showed better precision than SHS in the sampling of Pt. The button sampler did not perform as well as would have been expected considering that its many evenly spaced orifices and the stainless steel are meant to reduce sample losses. Conclusion: The sampler hierarchy according to dust mass concentrations was in the following order: SH-sampler, IOM, PAS, GSP, button and CFC. The hierarchy obtained from Pt concentrations gave the order as SH-sampler, IOM, GSP, button, PAS and CFC. Similar studies have to be undertaken in primary and secondary platinum workplaces to validate the study results. Such studies should compare better performing samplers (SHS, IOM, Button and GSP) as well as incorporate particle size determination and distribution in those areas. / MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2014

The primary focus of this study was to compare the efficiency of six filter samplers in the collection of inhalable soluble platinum (Pt) salts at a South African base metal refinery. Inhalation remains the major route of occupational exposure to platinum groups metals (PGMs). South Africa would benefit from the study since it’s amongst the major countries where PGMs are produced and hence, monitoring of worker exposure with the most efficient sampler is of utmost importance. The IOM is currently being used in routine exposure monitoring although no studies have been carried out to compare its performance to that of the other samplers under the actual base metal refinery conditions. Method: The button, closed face cassette (CFC), Gesamtsstaubprobenhome (GSP), (Institute of Medicine) IOM, PAS-6 and seven hole (SH-sampler) samplers were randomly allocated to six different positions in presumably high exposure areas. The samplers were moved around in the subsequent sampling days and the process repeated 3 times. The average dust mass and Pt concentrations were used as a basis of sampler performance and comparisons from which sampler hierarchies were determined. Results: The average relative humidity ranged between 37% and 43% and the average dry bulb temperature of 22.4°C was measured. Comparison of the dust mass concentrations revealed no statistically significant differences amongst the six filter samplers tested. The SH-sampler and CFC however collected the highest and lowest dust mass and Pt concentrations respectively. Discussion: The SH-sampler was found to be a sampler with more reliability than the the IOM for the collection of dust mass and soluble Pt. The IOM collected 98% of the SH-sampler dust mass and Pt concentrations. This was in spite of the larger variations indicated by the highest relative standard deviations and confidence intervals shown by the IOM than the other samplers. The GSP sampler, however, showed better precision than all the other samplers in the collection of platinum. The seven 4 mm orifices of the SH-sampler sampler allow for uniform distribution of sampled particles onto the filter supporting its better precision than the IOM which has only one 4 mm opening. The worst performing sampler was the CFC sampler since it collected the lowest dust mass and Pt concentrations. The CFC and the PAS samplers have downward facing inlets that are affected by gravity especially in lower wind speeds which, therefore, influences their efficiency. The GSP sampler concentrations placed it as 4th and 3rd best in Pt and dust mass hierarchies respectively even though it showed better precision than SHS in the sampling of Pt. The button sampler did not perform as well as would have been expected considering that its many evenly spaced orifices and the stainless steel are meant to reduce sample losses. Conclusion: The sampler hierarchy according to dust mass concentrations was in the following order: SH-sampler, IOM, PAS, GSP, button and CFC. The hierarchy obtained from Pt concentrations gave the order as SH-sampler, IOM, GSP, button, PAS and CFC. Similar studies have to be undertaken in primary and secondary platinum workplaces to validate the study results. Such studies should compare better performing samplers (SHS, IOM, Button and GSP) as well as incorporate particle size determination and distribution in those areas. / MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2014

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy