Thesis (PhD)--University of South Australia, 1995

Note:

Graduation date: 1994

No description available.

Four sphalerites (synthetic, high grade natural, moderately impure flotation concentrate and highly impure flotation concentrate) were leached in acid sulphate media without and with ferric ions present under the following conditions :- Case (i) [Fe3+]o : [H2S04]o = 0,0 Case ( ii) [Fe3+]o : [H2S04]o = 1,8 Case (iii) [Fe3+]o : [H2S04]o = 0,1 Extensive data for leaching under these conditions are tabulated. Kinetic mechanisms based on Langmuir-Hinschelwood adsorption theories were proposed, and leaching models were developed for different assumed rate limiting steps. The initial rate and overall forms of the models were tested using experimental data.Leaching under case (i) conditions Non-oxidative dissolution took place with Zn2+ and H2S the predominant reaction products. The H2S partial pressure was monitored continuously and solution samples were taken for analysis at discrete time intervals. Vibratory (i.e. attrition) milling eliminated very large differences observed in the leaching characteristics of course size fractions of the natural sphalerites. The initial rate form of a model based on a dual site reaction mechanism and on either H+ adsorption or reaction product desorption rate control was found to fit the data for the synthetic and vibratory milled forms of sphalerite. The most impure vibratory milled sphalerite adsorbed Zn2+ and H2S very strongly, and this resulted inproduct desorption rate control. Vibratory milled forms of the high grade natural sphalerite and the moderately impure flotation concentrate, exhibited virtually identical initial rate dissolution kinetics, despite large differences in their chemical compositions. Leaching under case (ii) conditions Oxidative dissolution took place with Zn2+ and elemental sulphur the predominant reaction products. Scanning electron microscope photographs of leached and unleached particles showed the sulphur present on the particle surface. These photographs, and optical microscope photographs of etched polished sections, showed that dissolution took place in a complex way. A model based on ferric ion adsorption as the rate limiting step was proposed and confirmed experimentally. The model demonstrated a proportional dependency of the rate on the area and ferricion concentration, and an inverse dependency on the hydrogen ion concentration. For a -90,0 + 63,0 um size fraction, the three natural sphalerites exhibited virtually identical dissolution rates per unit area. The effect of ball milling or vibratory milling the sphalerites fine, was to increase the rate per unit area for the most impure natural sphalerite but decrease the rate per unit area for the high grade natural sphalerite.It was shown that for course size fractions of sphalerite, the most impure sphalerite which leached slowest under case (i) conditions (i.e. adsorbed H+ poorly) leached fastest under case (ii) conditions (i.e. adsorbed Fe3+ strongly). The reverse was true for the high grade natural sphalerite. Except in the case of synthetic sphalerite leaching under case (i) conditions, no correlation was shown to exist between the way the B.E.T. measured area changed, and the way the calculated active area changed during leaching. Leaching under case (iii) conditions Oxidative and non-oxidative dissolution, as well as H2S oxidation by Fe3+ occured simultaneously. The extents to which oxidative or non-oxidative dissolution occured could be explained in terms of the hydrogen ion and ferric ion adsorption characteristics of the sphalerites.The ferric ion oxidation of H2S was studied in the absence and presence of solids, and the presence of sphalerite or activated charcoal catalysed this reaction. No advantage was gained by leaching in the presence of activated charcoal with or without Fe3+ present, unless conditions were such that H2S was formed as a product of reaction. / Thesis (Ph.D.)-University of Natal, Durban, 1977.

The isotopic composition of meteorite sulphur and sea water sulphates was investigated by means of a simultaneous collection mass spectrometer. It was found that sixteen samples of meteorite sulphur possessed identical isotope abundances within the precision of the instrument. The sulphates from various depths in the Atlantic, Pacific and Arctic Oceans, were found to be enriched in s34 compared to the meteorite base level. The overall variation in s32/s34 content was 0.39 percent for the sea water samples. / Thesis / Master of Science (MS)

A study was conducted in 2006 to investigate the long-term effects of air pollution on soil properties in the vicinity of the Arnot power station, Mpumalanga, South Africa. Fifteen sites were re-sampled and the soil chemical properties compared to baseline data gathered in 1996, resulting in a ten year period after which changes in soil properties were investigated. A spatial gradient was incorporated into the study in order to better understand the deposition of pollutants with increasing distance from the power station. The study indicates that long-term acidic deposition has led to detectable changes in soil chemical properties. Three chemical properties, namely the concentrations of calcium and magnesium in both the topsoils and the subsoils, as well as the effective cation exchange capacity in the subsoils showed a significant increase since 1996. However, five soil chemical properties, namely soil pH (K2SO4), the concentration of hydrogen and aluminium and total sulphur in both the topsoils and the subsoils, as well as extractable sulphate in the topsoils and soluble sulphate in the subsoils, all show that the soils have become more acidic over the ten years. The acidic components in the soil override the basic components, as shown by the ratio of basic cations to acidic cations in the soils. The spatial gradient generally indicates that at approximately 8 km from the power station, there is a decrease in the concentration of acidic soil properties and one explanation for this may be a reduction in the acidic components of atmospheric deposition at this site. However, this needs further investigation. Two significant relationships with distance were found, namely a significant negative relationship with soluble sulphate and a significant positive relationship with acid neutralising capacity. This research will form part of a database for other long-term monitoring programmes and will allow data to be compared to other data from this area of research. It will also provide information to important industry leaders such as Eskom.

Nanolithography is a rapidly evolving field that requires new combinations of techniques to improve patterning and to assist in fabricating electromechanical devices. An increasing number of applications require surfaces with defined regions of different chemical functionality. In our previous project optimum conditions for lithographic patterning were determined and potential blockers were identified to reduce force on the tip. This work is focused on identifying good chemical modifications that will allow better control of basic patterning and to investigate the minimum force of patterning required while using each chemical system. The primary aim is to gain better control of basic pattern techniques in order to create more intricate patterns such as interdigitated arrays, which can subsequently be used in sensors. An atomic force microscope (AFM) is used to pattern the prepared colloid-coated glass slides. Several compounds were used in the investigation, including sodium sulphate, potassium sulphate, magnesium sulphate, sodium fluoride, sodium chloride, sodium bromide, and sodium iodide, potassium chloride, potassium bromide, potassium iodide, potassium dihydrogen phosphate, and potassium hydrogen phosphate. In Summary, the following were found as a result of this work:  The groups of sulphates were determined to require minimum patterning forces as indicated. Sodium sulphate took a force of 49 n Potassium sulphate took a force of 45 nN Magnesium sulphate took a force of 744.4 nN  The group of sodium and potassium halides were determined the minimum patterning forces as indicated. Sodium fluoride took a force of 8.42 nN Sodium chloride and potassium chloride took a force of 20.19 and 61.9nN Sodium bromide and potassium bromide took a force of 601.4 nN and 37.2 nN, respectively Sodium iodide and potassium iodide took a force of 953.7 nN and 47.2 nN, respectively  The phosphates were determined to require the minimum patterning forces as indicated. Potassium hydrogen phosphate took a force of 25nN Potassium dihydrogen phosphate took a force of 43 nN

This work aimed to evaluate long-term changes of selected chemical and physical parameters of rainwater from their own rain gauge stations Stropnicko. Chemical and physical parameters influence the rate of loss of substance in the landscape through the soil environment. In particular, the amount and concentration of dissolved sulphates and nitrates, affecting the value of the current pH. Samples were taken from their own rain gauge stations Stropnicko. Names of stations from which samples were taken are Horní Stropnice, Nakolice, Paseky and Nové Hrady. Rainfall were measured between the years 2005-2011 and were subjected to chemical analysis.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2005. / 199 leaves single sided printed, preliminary pages i-vii and numbered pages 1-191. Includes bibliography, list of figures and tables. Digitized using a Hp Scanjet 8250 Scanner to pdf format (OCR). / ENGLISH ABSTRACT: This study provided scientific proof of the precipitation of iron and other metal species in the HAL circuit at the Mineral Separation Plant of Namakwa Sands. Iron and aluminium hydroxides were the most abundant precipitate complexes that formed in the HAL circuit. Sulphates formed bridges with the iron complexes. It was found that precipitation of iron in the HAL circuit was a function of the pH, ferric ion concentration and temperature of the process water. Experimental work provided abundant evidence that the precipitated iron hydroxide and other species adsorb to the surfaces of zircon and rutile mineral particles due to opposite zeta potentials of the mineral particles and iron hydroxide. These adsorbed species altered the electrostatic potential of the mineral surfaces, which reduced the electrostatic separation efficiency of these minerals. It was determined that an improvement of 7% could be expected if the precipitation and attachment of iron could be minimised. Based on the experimental results, conceptual processes were developed and iterative simulations were set up to determine the optimum solution that would maximise the removal of dissolved iron. This solution would ensure clean mineral surfaces free of any adsorbed precipitates. This process circuit was constructed in May to August 2004 at a total capital cost of R4.8m and removed 99.97% of the total dissolved iron prior to caustic addition. Prime zircon recoveries were increased by 3-7%. / AFRIKAANSE OPSOMMING: Hierdie studie het wetenskaplike bewyse gelewer dat yster en ander spesies neerslae vorm in die HAL proses van die Mineraal Skeidings Aanleg van Namakwa Sands. Yster- en aluminium hidroksiede was die vernaamste neerslag komplekse wat gevorm het in die HAL proses. Sulfaat spesies het verbindings gevorm met die yster komplekse. Die neerslag van yster was ‘n funksie van pH, ferric ioon konsentrasie en temperatuur van die proses water. Eksperimentele werk het genoegsame bewyse gelewer dat die yster hidroksied neerslag en ander spesies adsorbeer op die oppervlaktes van sirkoon en rutiel minerale weens teenoorgestelde zeta potensiale van die mineraal partikels en yster hidroksiede. Hierdie geadsorbeerde spesies het die elektrostatiese potentiaal van die mineraal oppervlaktes verander wat sodoende die elektrostatiese skeidingsvermoë van hierdie minerale verminder het. ‘n Verbetering van 7% in elektrostatiese skeiding van sirkoon en rutiel minerale kan verwag word indien die neerslag en adsorbsie van yster minimiseer word. Konseptuele prosesse, gebasseer op die eksperimentele resultate, is ontwikkel. Itteratiewe simulasies is opgestel om die optimum proses te bepaal wat sodoende die maksimum verwydering van die opgeloste yster sou verseker. Hierdie oplossing sou skoon mineraal oppervlaktes, vry van enige geadsorbeerde neerslae, verseker. Hierdie prosesaanleg was opgerig in Mei tot Augustus 2004 teen ‘n kapitaalkoste van R4.8m en dit het 99.97% van die totale opgeloste yster verwyder voordat natrium hidroksied bygevoeg is. Primêre sirkoon opbrengste het sodoende toegeneem met 3-7%.