Thesis (MAppSc)--University of South Australia, 2000.

Thesis (MAppSc)--University of South Australia, 2000.

In this study the unique Magotteaux Mill® system was used to control the grinding chemical conditions, which may be adjusted by varying grinding media, purging gas and pH, during grinding. An electrochemical apparatus was used to investigate oxidation-reduction behaviour of grinding media and sulphide mineral electrodes, as well as their galvanic interaction in-situ of the Magotteaux Mill®. Galvanic interaction between the grinding media (mild steel, 15% chromium, 21% chromium and 30% chromium media) and the sulphide minerals (bornite, arsenopyrite and pyrite) was initially quantified in-situ of the mill by electrochemical techniques under different grinding atmospheres (nitrogen, air and oxygen). An innovative mathematical theoretical model was developed to describe the effect of galvanic interaction on oxidation rates of the grinding media during grinding, which was verified by the experimental data. Galvanic interaction enhanced the oxidation of the grinding media and produced more oxidized iron species in the mill discharge. It was observed that oxidized iron species (EDTA extractable iron) was linear with galvanic current between the grinding media and the sulphide minerals, in agreement with the prediction of the theoretical model. The effect of grinding conditions on pulp chemistry, surface properties and floatability was investigated by the measurement of dissolved oxygen (DO), pH, pulp potential (Eh), ethylene diamine-tetra acetic acid (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) and floatation recovery. / PhD Doctorate

Bacterial leaching utilises bacteria, ubiquitous to sulphide mining environments to oxidise sulphide ores. The sulphide mineral chalcopyrite is the most common copper mineral in the world, comprising the bulk of the known copper reserves. Chalcopyrite is resistant to bacterial leaching and despite research over the last 20-30 years, has not yet been economically bioleached. Attempts have been made to use silver to catalyse the bacterial leaching of chalcopyrite since the early seventies. The majority of reported testwork had been performed on finely ground ore and concentrates in agitated batch reactors. This project used silver to catalyse the bioleaching of chalcopyrite in shake flasks, small columns and large columns. The catalytic effect was extensively studied and experimental parameters were varied to maximise copper recovery. Silver was also used to catalyse the ferric leaching of chalcopyrite at elevated temperatures. It was noted that the leaching performance of chalcopyrite in shake flasks compared to columns was markedly different. The specific differences between shake flasks and columns were qualified and separately tested to determine which parameter(s) affected the bioleaching of chalcopyrite. It was found that the ore to solution ratio, aeration, addition of carbon dioxide, solution distribution and small variations in the leaching temperature did not significantly effect the bioleaching of chalcopyrite ore in columns. The method of silver addition to columns did significantly affect the overall copper extraction. The ore in shake flasks was subjected to abrasion between ore particles and with the base of the flask. A test was designed to mimic the shake flask conditions, without the abrasion. The low abrasion test performed similarly to a column, operated with optimum silver addition. This indicated that the inherent equipment difference between shake flask and column operation largely accounted for the difference in leaching performance. Chalcopyrite ore was biologically leached in large columns. The ore crush size and other conditions were typical of those used in the field. The biological leach achieved 65% copper extraction in 160 days. This level of copper extraction is significantly higher than any previously reported results (typically /10% copper extraction) and represents a significant advance in the bacterial leaching of chalcopyrite ore. Due to the inherent high temperature within underground stopes, it was decided to investigate the possibility of separating the leaching and the bacterial oxidation stages. The concept of separate bacterial and ferric leaching has been previously suggested, however the application to a stope, and heat exchange between the process streams was a novel approach. Large column ferric leaches at 70 oC illustrated the technical feasibility of this process. Copper extraction was rapid and high (70% in 100 days of leaching), even when a reduced level of silver catalysis was used. After leaching in large columns, samples of ore were taken for analysis by optical mineralogy. The analysis gave valuable insights into the nature of reaction passivation on chalcopyrite ore. In particular, it was discovered that the precipitation of goethite was a major limiting factor in the bioleaching and ferric leaching of chalcopyrite in columns. In addition, reduced sulphide species were detected on the surface of residual chalcopyrite, giving an indication of the sequential nature of the chalcopyrite reaction chemistry. The bacterial population was characterised using DNA techniques developed during the project. Qualitative speciation was carried out and compared between the columns, down the columns and over time in a column. Comparison of these populations enabled greater mechanistic understanding of the role of bacteria in the leaching of chalcopyrite. This work was the most comprehensive attempt to date made to delineate the complex microbiological/mineral actions using analysis of population dynamics from a mixed inoculum. It was found that the iron oxidiser Thiobacillus ferrooxidans dominated within the columns and leach solutions. The sulphur oxidiser Sulfobacillus thermosulfidooxidans was also prevalent in the columns, particularly during the period of rapid chalcopyrite oxidation. The high temperature, ferric leaching of chalcopyrite was unexpectedly poor in the first round of large columns. The reason for the low extraction was attributed to an increase in pH down the column, resulting in excessive goethite precipitation. The solution flowrate (velocity) was increased by ten times in subsequent columns. There were no operational problems (e.g. break-up of ore agglomerates). The increase in flowrate resulted in a high yield of copper. The kinetics of extraction were faster than a corresponding bacterial leach, confirming the potential advantage of a high temperature leach. The small column studies highlighted that it was important to get an even distribution of silver down the stope to enable maximum catalytic effect. If the ore were agglomerated, silver would be added with acid at that point. However, it may not always be possible to agglomerate the ore. For example, the process may be used in-situ on a fractured ore body, or on an ore that has a low fines content, and hence does not require agglomeration. Various complexing agents were tested for their ability to distribute silver at the start of the leach and to recover silver at the end of the leach. For instance when silver was complexed with thiourea and then trickled through the ore, an even distribution of silver was achieved. After leaching was completed, a thiourea wash recovered a significant amount of the silver. These two techniques minimised the amount of silver required and thus significantly added to the economic viability of the process. The success of the technical work has led to an evaluation of the process in the field. A flowsheet was developed for the high temperature, in-stope ferric leach of chalcopyrite. An economic analysis was performed that illustrated the process would be viable in certain situations. An engineering study considered issues such as acid consumption, aeration, silver distribution, silver recovery and a heat balance of the stope.

Unfertilized or parthenogenetically non-activated porcine oocytes matured in vitro conditions are subjected to a process known as aging. During such development, porcine oocytes undergo the complex of the structural and functional changes, which can result in spontaneous parthenogenetic activation, fragmentation or lysis. After three days of culture in our condition, 23% of oocytes remained at the stage of metaphase II, 48% of oocytes were spontaneously parthenogenetically activated, 26% of oocytes were subjected to fragmentation and 3% of oocytes were lysed. The complete suppression of porcine oocyte fragmentation during the process of aging occurred during oocytes cultured in medium with sulphide donor Na2S in concentrations 150 µM and 300 µM. Inhibition of enzymes catalyzing the synthesis of hydrogen sulfide in the oocytes during the process of aging (cystathionine-gamma-lyase and cystathionine beta-synthase), iniciates earlier onset of oocytes fragmentation. The effect of both inhibitors could be completely reversed by using sulphide donor Na2S. The process of aging in porcine oocytes significantly reduces the success of the activation processes. Parthenogenetic activation occurred in 94% of pig oocytes, which were not subjected to aging. The proportion of activated oocytes after exposure to 24...

Ore specimens from the cupriferous zone of the basal Nonesuch shale at the White Pine Mine were analysed for sulphur isotopes, carbon and sulphide contents and boron. The results of the analyses were discussed in relation to a biogenic-syngenetic mineralization process for the ore body. A model, based on the δS³⁴sulphide frequency distribution, was developed to determine the δS³⁴ sulphate value of the lower Nonesuch paleoenvironment. A transmitted light microscopic examination of chlorite was undertaken in order to present a more complete picture of this proposed source for copper in the cupriferous zone of the Nonesuch shale. / Thesis / Master of Science (MSc)

<p> In the past decade, sites of hydrothermal activity along the Juan de Fuca Ridge have gained a growing amount of attention. Increased sampling has provided the materials for more detailed studies, including those collected from Axial Seamount, a large shield volcano on the central portion of the ridge. Axial Seamount is host to at least three active vent sites, one of which, along the northwest caldera wall, consists of recently active eruptive-fissures and nearby chimney-like spires. A sampled spire from this location and samples from other vent areas are described using reflected and transmitted light techniques. They have been found to consist of the sulphide phases sphalerite, wurtzite, pyrite, marcasite, chalcopyrite, isocubanite, and galena. Jordanite and tetrahedrite-tennanite are also known to precipitate at these vent sites, but were not observed here. The most dominant non-sulphide minerals are amorphous silica and barite. Native sulfur, Fe and Mn oxides and a variety of sulfosalts may also be present. The complex textures in these samples reflect precipitation and growth from higher temperature fluids that are mixing with local ambient seawater. Fluid inclusions in sphalerite have revealed salinities in the 5.6 to 7.0 weight % NaCl range, with homogenization temperatures ranging from 214.8°C to 269.4°C. Temperatures of homogenization require pressure-corrections between approximately 9.0°C and 13.0°C, to set-up a range of trapping temperatures that lie between 211.8°C and 279.4°C. Fluid inclusions are also found in wurtzite, barite, and amorphous silica however, these would yield no data. Middle Valley is a sedimented rift valley that lies at the extreme north end of the Juan de Fuca Ridge. A number of hydrothermal sulphide mounds that lie atop the sediment pile have been sampled. The mineralogy is similar to that at Axial Seamount; however, the dominant sulphide phase at Middle Valley is pyrrhotite. Textural differences between the two sites are significant, a result of the traversing of hydrothermal fluids through a thick package of hemepelagic sediment at Middle Valley. Samples from Middle Valley are found to contain no measurable fluid inclusions in the sections available for study. Mineralogical and fluid inclusion studies are important methods that can be used to help solve the complex growth history of sulfides that are and have been accumulating at mid-ocean ridge vent sites.</p> / Thesis / Bachelor of Science (BSc)

This thesis is missing page 89, no other copy of the thesis has this page. -Digitization Centre / The vanadium mediated electrolysis of hydrogen sulphide has been demonstrated in a bench top pilot plant. The first step in the process is the absorption of hydrogen sulphide from a sour gas stream into an carbonate buffered liquor, pH 9. In the presence of citrate ion, the vanadium (V) in the liquor is reduced to vanadium (IV) by (hydro) sulphide ion, which is oxidized to yellow elemental sulphur. The vanadium (IV) rich solution is then pumped to an electrolysis cell where the vanadium (IV) is reoxidized to vanadium (V) and protons are reduced to elemental hydrogen. The reoxidized liquor is then returned to the absorber. The oxidation of vanadium (IV) to vanadium (V) in the liquor was found to be electrochemically irreversible. The current efficiency for vanadium (IV) oxidation exceeded 90 percent. The voltametric half-wave potential at platinum, was 0.34 v (vs Ag/AgCl, sat. KC1). With the slippage of sulphide or polysulphide ion into the electrolysis cells, the electrodes became passivated with electrodeposited sulphur. This resulted in an increased anode potential demand which may promote the electrosynthesis of oxygen and sulphate ion. The oxidation of vanadium (IV) at the anode releases 4 protons and acidifies the solution adjacent the electrode surface. This may induce carbon dioxide evolution and inhibit the discharge of vanadium (IV). The inhibition appears as a suppressed current and an anodic shift in the voltametric half-wave potential. This inhibition can be minimized at high pH levels in the liquor, buffer capacity., and citrate concentration. The irreversibility of the vanadium (IV/V) couple allows electrolysis cells to be constructed without a cell membrane. This is a significant advantage which will offset the cost of large electrolysis cells. Large cells will enable high energy efficiencies to hydrogen production to be realized. Energy efficiencies greater than 0.28 m3 /kwhr may be indicated. This study features a critical review of sulphide electro-oxidation, a factorial designed voltametric experiment, and a newly identified catalytic response in the polarographic analysis of sulphide ion. / Thesis / Master of Science (MS)

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: It is widely accepted that sulphide is the carrier and concentrator of PGEs during magmatic mineralization episodes in the Merensky Reef (MR). PGE concentration peaks and sulphide volume percent peaks are very closely correlated. Koegelenberg, (2011), showed in an experimental investigation that sulphide movement through a cumulate silicate and cumulate oxide pile behave in such a way that sulphide melt gets trapped in chromitite layers. When looking at the compositional distribution of sulphide within the MR it is noted that not only does the sulphide volume percent varies with MR stratigraphy but also the sulphide composition. Sulphide composition is more Cu-rich in the chromitite layers and more Fe and Ni dominated in the hanging wall to the chromitite layers. Until now the more Cu-rich assemblage of the chromitite layers are accepted to be of a sulphide melt composition compared to the Fe and Ni dominated Monosulphide Solid Solution or MSS composition in the hanging wall. In this study we used an experimental approach with a sulphide starting composition thought to exist as the parental sulphide composition of the MR to investigate the phase relations with changing temperature. It is found that the sulphide composition in the chromitite layers represent a sulphide melt composition at 1000 ± 50ºC. At 1000ºC, 50% of the sulphide system would exist as a melt. This Cu-rich melt would have segregated from the MSS and be trapped in the chromitite layer. Also at 1000ºC the partitioning of the Pt would have induced a secondary enrichment step of the Pt concentration in melt through the partitioning of Pt between a sulphide melt and a sulphide solid phase. The experimental evidence in this study points towards a possible source for the parental sulphide magma to the MR, which could have been a slightly Cu enriched mantle sulphide composition. Also, the secondary enrichment of Pt through sulphide melt fractionation at 1000ºC plays an important role in the shaping of the ore body. / AFRIKAANSE OPSOMMING: Dit word wydliks aanvaar dat die sulfied fraksie van die Merensky Rif (MR) die draer en die konsentrasie agent is vir Platinum Groep Elemente (PGE`s) gedurende mineralisasie episodes. PGE konsentrasie en sulfied volume persentasie is op `n hoogtepunt by gelyke stratigrafiese posisies in the MR. Koegelenberg, (2011), het deur middel van eksperimente bewys dat `n sulfied smelt deur `n voorafbestaande kumulaat laag kan beweeg en dat veranderende fisiese eienskappe tussen sulfied smelt en silikaat kristal en sulfied smelt en chromiet kristal, die sulfied smelt sal opsuig en verhoud om verder deur te suipel. Dit is egter oplettend dat nie net die sulfied volume persentasie varieer as `n funksie van die MR stratigrafie nie, maar ook die sulfied samestelling. Die meer Cu-ryke sulfied samestelling in die chromiet lae word aanvaar as `n sulfied smelt fraksie en die meer Fe en Ni dominerende sulfied samestelling in die oorhangende wandgesteentes verteenwoordig die Monosulfied Vaste Oplossing (MVO) soliede fase. In hierdie studie maak ons gebruik van eksperimentele petrologie tesame met `n begin samestelling verteenwoordigend van die oorsprong sulfied samestelling van die MR, om die fase verwantskappe van hierdie spesifieke samestelling te ondersoek. Dit word gevind dat die fraksionering tydens die vorming van die MR plaasgevind het by ongeveer 1000 ±50 C. By hierdie temperatuur is 50% van die sisteem teenwoordig as `n smelt fase. Hierdie Cu-verykte smelt was daartoe instaat om deur die silikaat laag te suipel, geskei te raak van die Fe en Ni dominerende MVO en vasgevang te word in die chromiet lae. Hierdie fraksionering van die sulfied smelt het ook `n sekondêre effek gehad op die verspreiding van Pt tussen sulfied smelt en sulfied soliede fases. Hierdie eksperimentele bewyse dui eerstens op die moontlikheid van `n sulfied smelt in die MR wat sy oorsprong vanuit `n effense Cu-verykte mantel bron kan hê, en tweedens op die belangrikheid van `n sekondêre proses vir Pt re-distribusie tydens die vorming van die MR.

The Neoarchaean Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, within the Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton, Western Australia, contains several world-class, komatiite-hosted, nickel-sulphide ore bodies. These are commonly associated with felsic volcanic successions, many of which are considered to have a tonalite-trondhjemite-dacite (TTD) affinity. The Cosmos greenstone sequence lies on the western edge of the AWB and this previously unstudied mineralised volcanic succession contrasts markedly in age, geochemistry, emplacement mechanisms and probable tectonic setting to that of the majority of the AWB and wider EGS. Detailed subsurface mapping has shown that the footwall to the Cosmos mineralised ultramafic sequence consists of an intricate succession of both fragmental and coherent extrusive lithologies, ranging from basaltic andesites through to rhyolites, plus later-formed felsic and basaltic intrusions. The occurrence of thick sequences of amygdaloidal intermediate lavas intercalated with extensive sequences of dacite lapilli tuff, coupled with the absence of marine sediments or hydrovolcanic products, indicates the succession was formed in a subaerial environment. Chemical composition of the non-ultramafic lithologies is typified by a high-K calc-alkaline to shoshonite signature, indicative of formation in a volcanic arc setting. Assimilation-fractional crystallisation modelling has shown that at least two compositionally distinct sources must be invoked to explain the observed basaltic andesite to rhyolite magma suite. High resolution U-Pb dating of several units within the succession underpins stratigraphic relationships established in the field and indicates that the emplacement of the Cosmos succession took place between ~2736 Ma and ~2653 Ma, making it significantly older and longer-lived than most other greenstone successions within the Kalgoorlie Terrane. Extrusive periodic volcanism spanned ~50 Myrs with three cycles of bimodal intermediate/felsic and ultramafic volcanism occurring between ~2736 Ma and ~2685 Ma. Periodic intrusive activity, related to the local granite plutonism, lasted for a further ~32 Myrs or until ~2653 Ma. The Cosmos succession either represents a separate, older terrane in its own right or it has an autochthonous relationship with the AWB but volcanism initiated much earlier in this region than currently considered. Dating of the Cosmos succession has demonstrated that high-resolution geochronology within individual greenstone successions can be achieved and provides more robust platforms for interpreting the evolution of ancient mineralised volcanic successions. The geochemical affinity of the Cosmos succession indicates a subduction zone was operating in the Kalgoorlie Terrane by ~2736 Ma, much earlier than considered in current regional geodynamic models. The Cosmos volcanic succession provides further evidence that plate tectonics was in operation during the Neoarchaean, contrary to some recently proposed tectonic models.