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2 microfiche in end pocket / v, 162 leaves : ill., diagrs., graphs, tables ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Economic Geology, 1978

The promoter action of mixtures of catalysts has been reported in literature to be valuable in industries. Whether mixtures of rhenium and molybdenum sulfides would have promoter actions in the hydrogenations of certain reducible organic groups was the main object of this research. Mixtures of rhenium and molybdenum sulfides of various compositions were prepared by three different methods, i.e., (a) by saturating perrhenate and molybdate with hydrogen sulfide in hydrochloric acid solutions, (b) in ammonium hydroxide solutions followed by acidification, and (c) by treating perrhenate and molybdate with thiosulfate in dilute sulfuric acids followed by extraction with toluene to remove excess sulfur. Those prepared in ammonium hydroxide solutions (greater than 2.5N) followed by acidification were found to have satisfactory yields.

The Platreef has been the site of platinum mining since the 1920’s. The reef itself comprises a series of pyroxenites, gabbronorites and norites that contain xenoliths/rafts of footwall rocks. The Platreef is irregularly mineralised with PGE, Cu and Ni, and has a greater abundance of sulphides than the Merensky Reef. The main base metal sulphides within the Platreef are pyrrhotite, pyrite, pentlandite, and chalcopyrite. Extremely varied platinum group minerals occur as tellurides, bismuthotellurides, antimonides and arsenides. This study aimed to gain a clearer understanding of the formation of sulphides within the Platreef. In order to do this, cores from both the northern and southern sectors of the Platreef were sampled. A detailed study of the sulphides within these cores was conducted to identify different styles of mineralisation and their occurrences. Four different styles of mineralisation were identified: massive, net-textured, blebby and interstitial. In general, sulphides in the southern sector of the Platreef are concentrated in the lower portion of the package, whereas in the northern sector they are concentrated in the upper part although in both sectors the sulphide occurrences are associated with metasedimentary xenoliths. Conventional and multiple sulphur isotope analyses were undertaken on sulphides from cores from both the southern and the northern sectors. This was done in order to determine the source of the sulphur. These analyses were also conducted to examine sulphur isotope variations with changing footwall. Previous sulphur isotope data predominantly obtained from the central sector of the Platreef indicated a crustal contribution to the sulphur budget but did not provide much data on footwall sulphides so the nature of the crustal component was only implied. In this thesis sulphur from an external source was identified as having contributed to the formation of sulphides in both the southern and the northern sectors of the Platreef, especially for sulphides in proximity to metasedimentary xenoliths. In the southern sector of the Platreef this source was identified as most likely being pyritic shales of the Lower Duitschland Formation. In the northern sector, Malmani dolomites, which are suggested to have collapsed from the roof of the Platreef, are the most likely source of sulphur. Importantly, in the northern sector no sulphur is thought to have come from the Archaean granite footwall. Oxygen isotope analyses were conducted on samples from the southern sector of the Platreef to verify the presence of crustal contamination. Data collected indicated that there had been a crustal oxygen component involved in the formation of silicates that led to their partial recrystallisation. When compared to oxygen isotope data from the central sector of the Platreef it appears that there are variations along strike that most likely result due to the changing footwall. This data indicates a major contribution of oxygen-, sulphur- and other volatile-rich fluids to the Platreef. This led to the partial re-crystallisation of silicates, and in areas in close proximity to sulphur-bearing metasedimentary xenoliths aided in the formation of sulphides. These volatile-rich fluids most likely originated from metasedimentary xenoliths during metamorphism that then migrated through the Platreef package. When the observations from both the southern and northern sectors of the Platreef are compared and combined with pre-existing data for the central sector, several general observations can be made. 1. The entire length of the Platreef has been affected by contamination from crustal sulphur sources to some degree. This contamination is suggested to be from volatile-rich fluids which were released from metasedimentary crustal xenoliths and footwall during metamorphism. 2. The proximity between sulphide enrichment and sulphur-bearing sediments (as footwall or xenoliths) is important and indicates the source of the sulphur which led to sulphide formation. 3. Contamination occurred on a localised scale, depending on the composition of the sedimentary lithologies and the proximity of the contaminant to the magma. In the southern sector of the Platreef the source of the sulphur is almost certainly pyritic shales of the Lower Duitschland Formation. In the central sector, sulphur has most likely come from sulphur-rich dolomites and evaporites from the Malmani dolomites. In the northern sector, sulphur-rich fluids were released from Malmani dolomite rafts that collapsed from the roof into the magma during the emplacement of the Platreef. The Archaean footwall in this area has had little or no control on the formation of the sulphides within the Platreef.

Extraction of metals from the seafloor has been considered for decades, beginning with manganese nodules in the 1970s. Today, the targets are massive sulphide deposits rich in copper, zinc, gold, and silver that are associated with hydrothermal vents or black smoker chimneys that occur at divergent and convergent plate margins such as mid-ocean ridges and volcanic island arcs respectively. A recent objective of the mining industry is to develop industry practices that coincide with concepts of sustainability or sustainable development. This objective, known by some as sustainable mining, has indeed become an essential part of the commissioning of any new project, regardless of geographical location. While there has been much work on sustainable mining practice for terrestrial mining, these frameworks are not directly applicable to seafloor projects. There are two problems facing the development of a seabed mining industry. First, there is a regulatory vacuum when considering the mining of seabed deposits, leading to important policy issues. Second, the economic, environmental, and social impacts of a seabed mining project are theoretical, and the real impacts are unknown. Thus, the identification, characterization, and analysis of the sustainability issues facing a seabed mining project are essential steps. To assist with performing these three steps, this thesis provides a process model based on the IDEF0 (Integration DEFinition) standard to assess seafloor massive sulphide mining projects from sustainable mining perspectives. This adaptation of IDEF0 provides a clear, visual representation of a hierarchical framework that can be used to identify “go no-go” sustainability criteria to assist decision makers interested in the potential development of an ore body. / Thesis (Master, Mining Engineering) -- Queen's University, 2011-12-12 12:54:28.436

Simulation technique has been used for a feasibility study of a deep exploration project for massive sulphides in an old mining district, the Skellefte field. The outcome under very different conditions has been studied. Under the specific conditions of the well known Skellefte field it is found to be possible to even calibrate the mathematical model.It is found that when the geology is not known in detail, an outcome of the order of 50 tons per meter drillhole is to be expected under a simple drilling strategy.When a certain knowledge about the general structures down to around 1 000 m is established, it is possible to improve the outcome by a factor of 2 through an optimization of the depth of investigation. The optimal depth of investigation is in the order of 500 m.On the other hand, when a minimum ore value is introduced as a function of depth, the expected outcome will again decrease with a factor of about 3.It must be underlined, that these results are average values in a mathematical model and do not say anything about the outcome in the single exploration case. However, in exploration campaigns of the order of 40 drillholes to a depth of 1000 m an analysis shows that at least one deep seated large body was found in 25% ot the exploration campaigns.Faced with the problem whether to go or not to go into a deep exploration phase, this technique can headlight the problem and it can give an estimate about the order of costs and benefits. / digitalisering@umu

Thesis (MSc. (Physics)) -- University of Limpopo, 2016 / The stabilities of PtS to PdS and PdS to PtS were investigated using density functional theory within the generalized gradient approximation. Their structural, electronic and mechanical properties were determined to show their stability and the effect of pressure on different compositions. We found good correlation of calculations with available ex-perimental data. The lattice parameters were observed to fluctuate with increasing con-centration for both systems. Furthermore, heats of formation were calculated to deter-mine the relative structural stability of the systems. They predict that the most stable structure is Pd50S50 P42/mmc and Pt25Pd25S50 P42/mmc being the least stable. Pd12.5Pt37.5S50 P42/m is the most stable and Pd50S50 P42/m being the least stable struc-ture. The Pt37.5Pd12.5S50 P1 was said to be the most stable structure and Pd50S50 P1 be-ing the least stable. The phonon dispersion calculations show that Pt50S50 P42/mmc, Pd50S50 P42/mmc, Pd12.5Pt37.5S50 P42/m and Pt50S50 P1 (derived from P42/mmc) are me-chanically stable, consistent with calculated elastic constants. The Pt25Pd25S50 P42/mmc show soft modes, which are due to vibrations of Pt and Pd atoms in the x - y plane which suggests the instability of the structure, in agreement with C66 being negative, and consistent with heats of formation. The lattice parameters decreased steadily with increasing pressure. An anomaly was observed in Pt50S50 P1 (derived from P42/mmc), where the c lattice parameter was found to increase with increasing pressure. The elec-tronic density of states (DOS) were performed on all compositions. The DOS were sub-jected to pressure and it was generally noted that the band gap increases with increas-ing pressure. It was observed that the smaller the band gap, the more stable the struc-ture. Furthermore, phonon dispersions under pressure show that compounds with the P42/mmc and P1 (from P42/mmc) symmetries display the mixing of lower and upper en-ergy bands at pressures above 30 GPa. / National Research Foundation

This thesis is submitted as a portfolio of peer-reviewed publications. / For many geochemical systems, reaction kinetics determines the system's current status and evolution. It might also be the key to unraveling their thermal history. In metal sulfide systems, kinetic studies have been carried out on four sets of solid-state transitions/transformations in Fe-Ni-S and Ni-S systems. In this work, a new kinetic model, the Refined Avrami method, has been developed to account for reactions involving changes in reaction mechanisms. Nonstoichiometric compounds are commonly present in these reactions. The exsolution of pentladite from the monosulfide solid solution (mss) is an important reaction in the formation of nickel ores. For near equimolar mss compositions, the reaction rate is rapid even in the low temperature ranges. For bulk composition Fe₀.₇₇ Ni₀.₁₉ S, the experimental results show the reaction rates ( mss → pentlandite ) vary from 1.6x10⁻⁵ to 5.0x10⁻⁷ s⁻¹ at 200 °C and from 9.4x10⁻⁵ to 4.1x10⁻⁷ s⁻¹ at 300 °C. The activation energy, E [subscript a], varies during the course of reaction from 49.6 kJ.mol⁻¹ at the beginning of reaction (nucleation mechanism is dominant) to 20.7 kJ.mol⁻¹ at the end (crystal growth mechanism is dominant). Monosulfide solid solution (mss) is a common intermediate phase observed during the oxidation of nickel ores, such as violarite and pentlandite. The investigation of mss oxidation is of benefit in understanding the thermal behavior of economically important metal sulfides during smelting. The oxidation products of mss vary in our samples depending on their compositions. Apart from the common oxidation products hematite and Ni₁ ₇ S₁₈, Fe₂ (SO₄) ₃ was observed during the oxidation of Fe₇ . ₉ S₈ and pentlandite for Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ . The activation energy was determined using a model-free method. The oxidation of Fe₆.₄ Ni₁.₆ S₈ exhibited a higher E [subscript a] than Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ over the course of the reaction. The E [subscript a] increases with reaction extent (y) from 67.1 to 103.3 kJ.mol⁻¹ for mss composition Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ and from 76.1 to 195.0 kJ.mol⁻¹ for Fe₆.₄ Ni₁.₆ S₈ . The kinetic study of the α - Ni₁₋ ₓ S → β - NiS transition shows that initial compositions of α - Ni₁₋ ₓ S plays an important role in the kinetics of the transition. The activation energy ( E [subscript a] ) for this α - to β - phase transition is 16.0 ( ± 0.5 ) kJ.mol⁻¹ for NiS in the temperature range 70 to 150 °C, and 13.0 (± 0.5) kJ.mol⁻¹ in the temperature range 250 to 350 °C. For Ni₀. ₉₇ S, however, E [subscript a] deceases from 73.0 ( ± 0.5 ) to 17.0 ( ± 0.5 ) kJ.mol⁻¹ over the course of the reaction in the temperature range 300 to 320 °C. The relationship between E [subscript a] and extent of transition (y) for the initial bulk Ni₀. ₉₇ S was derived using the Refined Avrami method. For Ni deficient compositions, α - Ni₁₋ₓ S, the transformation to β-NiS is accompanied by the exsolution of either a progressively more Ni deficient α-Ni₁₋ₓ S and Ni₃ S₄ , and the reactions become more sluggish for more metal deficient compositions. The study of oxidation kinetics of α-NiS is of metallurgical interest, as α-NiS related phases may occur when nickel ores are flash smelted to produce nickel matte. In an open air environment, the oxidation mechanisms of α-NiS are constant at 670 and 680 °C, dominated by the direct oxidation of α-NiS → NiO. The dominant oxidation mechanism changes to a chain reaction : α-NiS → [superscript k] ₁ Ni₃ S₂ → [superscript k] ₂ NiO at 700 °C. Therefore, different kinetic models need to be applied to these two distinct reaction mechanisms. Activation energy for the oxidation, α-NiS → NiO, in the temperature range 670 to 680 °C was calculated to be 868.2 kJ.mol⁻¹ using Avrami/Arrhenius method. Rate constant k₁ and k₂ are approximated to be 3 x 10⁻⁴ s⁻¹ and 5 x 10⁻⁴ s⁻¹ for the first part and second part of the chain reaction respectively at 700 ° C. The study of the variation in reaction rate with oxidation time illustrates the optimum oxidation time zone for each temperature, where NiO can be produced at the fastest rate. / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2005.

Graduation date: 2004

Bibliography: leaves 192-193. / ix, 214, ix leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The focus of the thesis is to investigate the fundamental kinetics of the pyrite-nitric acid system. Particular attention is paid to the formation and oxidation of elemental sulfur. The study aims to elucidate the chemistry of the sulfide oxidation and of elemental sulfur formation and oxidation. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1997?