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Vinte e oito bovinos machos inteiros da raça Brangus foram utilizados para se determinar os efeitos da estabilidade oxidativa no músculo e no fígado, comparando a utilização de fonte orgânica e inorgânica de selênio e extrato de alecrim, com base na análise da concentração de selênio no fígado e no soro, na análise da atividade da enzima glutationa peroxidase, da enzima superóxido dismutase e da catalase no fígado, e na análise de TBARS (substâncias reativas ao ácido 2-tio-barbitúrico) no músculo. Os tratamentos foram: 1) Controle - sem suplementação de selênio ou de extrato de alecrim; 2) Se IN - 2 mg de selênio/kg de matéria seca na forma de selenito de sódio; 3) Se - 2 mg de selênio/kg de matéria seca, na forma de selênio-metionina; e 4) Alecrim - 1400 mg de extrato de alecrim/kg de matéria seca. O ganho de peso foi maior com a suplementação de selênio inorgânico (P<0,05) em relação ao tratamento controle, mas não apresentou diferença em relação aos outros tratamentos. A eficiência alimentar foi maior em todos os tratamentos quando comparados ao controle (P<0,05). A ingestão de matéria seca não foi alterada pelos tratamentos (P>0,05). A concentração de selênio no fígado foi maior no tratamento selênio inorgânico (P<0,05) do que no tratamento controle, entretanto os tratamentos alecrim e selênio orgânico não apresentaram diferença entre si (P>0,05). A concentração de selênio no soro foi maior nos tratamentos selênio orgânico e inorgânico em relação ao controle por todo o período (P<0,05). O perfil de ácidos graxos na carne não foi alterado pelos tratamentos (P>0,05). A atividade da glutationa peroxidase foi maior no tratamento selênio inorgânico em relação ao controle (P<0,05). A atividade da superóxido dismutase foi menor no tratamento alecrim (P<0,05). Tanto a atividade da enzima catalase quanto a análise de TBARS não apresentaram diferença entre os tratamentos (P>0,05). / Twenty eight Brangus males were used to determine the oxidative stability of muscle and liver in order to compare organic and inorganic selenium source and rosemary extract based on the analysis of selenium concentration in the liver and in the serum, on the analysis of glutathione peroxidase, superoxide dismutase and catalase activities in the liver and also based on TBARS analysis (substances related to 2-thiobarbituric acid) in the muscle. Treatments were: 1) Control . without selenium or rosemary extract; 2) Se IN . 2 mg selenium/kg dry matter, as sodium selenite; 3) Se . 2 mg selenium/kg dry matter, as selenium-methionine and 4)Rosemary . 1400 mg rosemary extract/kg dry matter. Weight gain was greater when inorganic selenium was used (P<0.05) in comparison with control, however there was no difference regarding the other treatments. Feed efficiency was higher than control for all treatments (P<0.05). Dry matter intake was not affected by treatments (P<0.05). Selenium concentration in the liver was greater for inorganic selenium (P<0.05) than for control, in spite of that rosemary and organic selenium did not differ between themselves (P<0.05). Selenium concentration in the serum was higher for organic and inorganic selenium treatments than for control during all the period (P<0.05). Fatty acid profile in the meat was not affected by the treatments (P<0.05). Glutathione peroxidase activity was greater for inorganic selenium treatment when compared to control (P<0.05). Superoxide dismutase activity was lower for the rosemary treatment (P<0.05). Neither catalase activity nor TBARS analysis differ among treatments (P<0.05).

Loess has a metastable structure and undergoes structural hydrocollapse when loaded and wetted, leading to subsidence and damage of overlying structures, which presents enormous engineering problems in many countries in the world. This problem is a focus of much research on both the nature of the phenomenon and the means. of overcoming its negative consequences. However, there remains a need for fundamental experimental and theoretical studies aimed at understanding the many uncertainties involved in the hydrocollapse phenomenon. An experimental programme has been conducted to study the fundamental nature of the hydrocollapse phenomenon in loess, and the primary features of the metastable structure controlling it. High quality disc-shaped specimens were prepared from natural undisturbed, very soft and slightly cemented loess soils using two simple devices which were designed and manufactured in the laboratory. Artificial loess materials were prepared by mixing pure silt particles of different geometrical characteristics (crushed sand, ballotini glass balls) with various clay types (kaolinite, bentonite) to produce mixes with different clay/silt ratios. Soil specimens of metastable structure were created from natural and model loess materials using the air-fall technique, which allowed full control over the critical variables. The index properties of the materials were determined experimentally, together with their geometrical characteristics from scanning electron microscope (SEM) studies. The compressibility characteristics and hydrocollapse behaviour were measured via one-dimensional (oedometer) compression tests. Two testing methods were used: the single oedometer test and the double oedometer test. The results indicated that the experimental approach used in this research can be used successfully to investigate the hydrocollapse problem of loess deposits. The small-clay loess model was constructed and examined. The results proved that this model is valid. The collapse behaviour of reconstituted and undisturbed loess specimens prepared from the same material was qualitatively similar, although the reconstituted materials exhibited greater collapsibility, particularly under low normal effective stresses. Specimens prepared from pure silt revealed very little collapse in spite of relatively high initial voids ratios (e ≤ 0.9). The existence of bonding materials, such as clay minerals at the points of particle contact, is thus apparently essential for hydrocollapse to occur. Specimens prepared from pure silt-bentonite mixtures exhibited low hydrocollapse values in comparison with those for pure silt-kaolinite mixtures. It was observed that there is an optimum clay mineral content for maximum hydrocollapse and it depends on the type of clay mineral and the level of applied stress. Higher values of hydrocollapse were obtained with smooth, spherical glass balls as the silt fraction, thus confirming that the geometrical properties of the silt particles also have a significant effect on the hydrocollapse behaviour of loess deposits. The position and distribution (mixing method) of clay particles inside the soil structure were equally found to have a significant effect on the hydrocollapse behaviour. The index properties of Libyan loess were found to be very similar to those of other loess deposits world-wide. The Tripoli loess can be classified as silty loess with high susceptibility to structural hydrocollapse in the same manner as other better known loess deposits in the world.

The State Intervention in the Minerals Sector Report emerged as a resolution during the 3rd National General Council Resolution on Economic Transformation held in 2012, during which the Council stated that: “The ANC’s approach to economic transformation of the South African economy should always be holistic and comprehensive, covering all sectors of the economy. In this regard, the ANC should ensure greater state involvement and control of strategic sectors of the economy, such as mining, energy, the financial sector and others.” It was for this reason that the National General Council mandated the National Executive Committee to ensure that further work be done on ways in which the African National Congress can implement economic transformation in sectors such as the mining industry. It was suggested that methods including research, study tours and discussions be conducted to gather the required information. As a result of the research, The State Intervention in the Minerals Sector Report emerged. In The State Intervention in the Minerals Sector Report, the mineral sectors of developed as well as developing countries are compared with each other. The developing countries compared included Botswana, Zambia, Ghana, Liberia and Sierra Leone, and these countries have also been selected for the purpose of comparison in the present research. The goal of this study is to analyse the recommendations made in The State Intervention in the Minerals Sector Report regarding State involvement in the minerals sector. To determine whether the economic situation in South Africa is comparable to the five other African countries, an analysis based on demographic indicators, the history of the minerals sector in the various countries, its contribution to the fiscal regime of that country, its economic contribution, as well as the extent of involvement from Government and the model implemented for its involvement, is conducted. According to a work paper published by the World Bank on the world development indicators for 2014, control over metal supply to the economy has been considered vital for political and economic reasons in most societies. It further states that most State-owned mining companies have over the years and, in particular, in developing countries, not been able to operate successfully, leading to privatisation. Poor performance is, however, not necessarily the reason for State ownership. Areas not addressed by this thesis include the Gold Mining industry in South Africa and the Diamond mining industry in Botswana.

No description available.

Pyrrhotite (Fe(1-x)S) is one of the most commonly occurring metal sulfide minerals and is recognised in a variety of types of ore deposits. Since the principal nickel ore mineral, pentlandite, almost ubiquitously occurs with pyrrhotite, the understanding of the behaviour of pyrrhotite during flotation is of fundamental interest. For many nickel processing operations, pyrrhotite is rejected to the tailings in order to control circuit throughput and concentrate grade and thereby reduce excess sulfur dioxide smelter emissions. For the platinum group element processing operations however, pyrrhotite recovery is targeted due to its association with the platinum group elements and minerals. Therefore, the ability to be able to manipulate pyrrhotite flotation performance is of importance. It can be best achieved if the mineralogical characteristics of the pyrrhotite being processed are known and their relationship to flotation performance is understood. Pyrrhotite is known to naturally occur in different forms that have varying physical and chemical attributes. These different pyrrhotite forms are commonly known as magnetic (Fe7S8) and non-magnetic pyrrhotite (Fe9S10, Fe10S11, Fe11S12) and as a result of their varying properties are expected to show some difference in their reactivity towards oxidation and flotation performance. Yet the accounts in the literature are inconsistent as to which of the pyrrhotite types is more reactive. Similarly, there appears to be little agreement in the literature as to which of the pyrrhotite types is more floatable. It is probable that this lack of agreement arises from the fact that previous studies have not given due consideration to the effect of the mineralogy of the samples examined. The success of the discipline of process mineralogy as a whole however, has been to gain an understanding of how the mineralogy of an ore affects its processing properties. The objective of this process mineralogy study was to develop the relationship between pyrrhotite mineralogy and flotation performance based on a thorough characterisation of pyrrhotite from selected nickel and platinum group element ore deposits in terms of their crystallography, mineral association, mineral chemistry and mineral reactivity. This was achieved through the characterisation of the mineralogy and mineral reactivity of pyrrhotite samples obtained from the Sudbury ore in Canada, Phoenix ore in Botswana and the Merensky Reef and Nkomati ores in South Africa. Based on the linkage of these characteristics to flotation performance, an understanding of the relationship and mechanisms that cause pyrrhotite mineralogy to influence pyrrhotite flotation performance has been gained. Mineralogical characterisation of the pyrrhotite samples in this study was performed using ore petrography, x-ray diffraction and mineral chemistry analysis. On the basis of these results pyrrhotite samples were classified as: single phase magnetic 4C Fe7S8 pyrrhotite, single phase non-magnetic 5C Fe9S10 pyrrhotite; two phase magnetic 4C Fe7S8 pyrrhotite intergrown with non-magnetic 5C Fe9S10 pyrrhotite and as two phase non-magnetic 6C Fe11S12 pyrrhotite intergrown with 2C FeS troilite. Nickel was identified as the main trace element impurity in the pyrrhotite structure and the amount of solid solution nickel in the pyrrhotite structure was correlated with whether the pyrrhotite was magnetic or non-magnetic, and whether it coexisted with another pyrrhotite phase. All pyrrhotite samples investigated showed a strong association to pentlandite that occurred in both granular and flame pentlandite forms. These key features of pyrrhotite mineralogy were in turn shown to be controlled by the bulk composition and cooling history of the monosulfide solid solution (MSS) from which pyrrhotite is derived. The reactivity of the different pyrrhotite samples towards oxidation was determined using open circuit potential, cyclic voltammetry and oxygen uptake measurements at both pH 7 and 10. Non-magnetic Sudbury Copper Cliff North pyrrhotite was the most unreactive of the samples examined, whereas magnetic Sudbury Gertrude West pyrrhotite was the most reactive. The magnetic Sudbury Gertrude West pyrrhotite was so reactive that open circuit potential and oxygen uptake measurements showed it was already passivated and likely covered with hydrophilic ferric hydroxides. The magnetic Phoenix pyrrhotite was slightly less reactive than the magnetic Sudbury Gertrude West pyrrhotite. The reactivity of the Nkomati Massive Sulfide Body (MSB) mixed pyrrhotite was in between that of the non-magnetic Sudbury Copper Cliff North and magnetic Phoenix pyrrhotite, due to the combined contribution of intergrown magnetic and non-magnetic pyrrhotite to its reactivity. The flotation performance of the different pyrrhotite samples was investigated at both pH 7 and 10 using microflotation tests. A variety of different reagent conditions was also investigated that included the use of different chain length xanthate collectors (sodium isobutyl xanthate (SIBX), sodium normal propyl xanthate (SNPX)) and the use of copper activation. The collectorless flotation of the non-magnetic Sudbury Copper Cliff North pyrrhotite was the greatest of the samples investigated. Only with the addition of flotation reagents were differences in the floatability of the other pyrrhotite samples identified. Magnetic Phoenix pyrrhotite showed good flotation performance whereas the flotation performance of the magnetic Sudbury Gertrude and Gertrude West pyrrhotite was very poor. The Nkomati MSB mixed pyrrhotite only showed good flotation performance at pH 7. All pyrrhotite samples generally showed improved flotation performance with the use of the longer chain length SIBX collector than the shorter chain length SNPX, whereas the efficiency of copper activation was influenced by pyrrhotite mineralogy, pH and collector chain length. Differences in the flotation performance of the pyrrhotite samples investigated were linked to their reactivity towards oxidation. Although not directly measured, the formation of hydrophilic ferric hydroxides on pyrrhotite surfaces due to oxidation was inferred as the reason for the poor flotation performance of some of the pyrrhotite samples. Key features interpreted to influence both pyrrhotite reactivity and flotation performance were pyrrhotite crystallography, mineral chemistry and mineral association. It has been proposed that differences in the amount of vacancies in the pyrrhotite crystal structure influence the oxidation rate and similarly the greater proportion of ferric iron in the magnetic pyrrhotite structure was argued to account for its greater reactivity relative to non-magnetic pyrrhotite. Differences in the solid solution nickel content and trace oxygen in the pyrrhotite structure were also proposed as additional characteristics influencing pyrrhotite oxidation rate and flotation performance. Depending on the degree of association of pyrrhotite to pentlandite, its flotation performance could be affected by the liberation characteristics and flotation of composite particles containing abundant locked flame pentlandite, although this could be manipulated by changing the grind size. The presence of nickel ions derived from the flame pentlandite in these composite particles could also assist in the activation of pyrrhotite and further improvement of its flotation performance. Some guidelines are also presented as to which simple mineralogical and mineral reactivity measurements have been of the most use in developing the relationship between mineralogy and flotation performance. / Thesis (DPhil)--University of Pretoria, 2009. / Materials Science and Metallurgical Engineering / unrestricted

No abstract available. / Dissertation (LLM)--University of Pretoria, 2013. / Centre for Human Rights / unrestricted

Please read the abstract in the 00front part of this document / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

The P2 reverse fault in the metasedimentary basement rocks of the eastern Athabasca Basin is the main structural control of the world-class McArthur River uranium deposit. The earliest preserved assemblage along the fault is oxy-dravite, rutile, quartz, pyrite and graphite. This assemblage formed at temperatures of up to 890 °C, during regional metamorphism or a thermal event at ~1.75 Ga. The exhumation and surface exposure of the rocks was accompanied by paleo-weathering, and the deposition of the Athabasca sandstones. Diagenetic fluids of the sandstones altered the basement rocks to form Sr-Ca-SO42- rich aluminum phosphate sulfate (APS) minerals + hematite ± kaolin. The onset of hydrothermal activity along the basement and the P2 fault is recorded by local anatase at 1569 ± 31 Ma. Uraniferous fluid formed an assemblage of sudoite illite, magnesio-foitite and LREE+P rich APS minerals (rims earlier diagenetic-type APS minerals) along the entire P2 fault. Magnesio-foitite exhibits a high X-site vacancy (0.70 – 0.85 apfu) and contains high Al in its Y-site (0.70 – 1.12 apfu), suggesting that magnesio-foitite likely replaced kaolin. The REE pattern of magnesio-foitite is similar to that of uraninite (CeN<YN), likely due to their co-crystallization with LREE-rich APS minerals. APS minerals show variably high S/P ratios (0.05 - 0.21) in proximity to the deposit and low ratios (0.11 - 0.13) far from the deposit along the P2 fault, indicating reducing conditions in the ore zone. Low values of δD (-41 to -98 ‰) and high values of δ11B (+13.1 to +23.2 ‰) for magnesio-foitite suggest that groundwater interacted with carbonates or evaporites and was progressively enriched in 11B through interaction with illite and kaolin minerals. This work demonstrates that i) the P2 fault was a site of extensive fluid-rock interaction, ii) mineralizing fluids travelled along the entire P2 fault in the basement, iii) the deposition of the McArthur River deposit was controlled by the availability of a reducing fluid through the P2 fault, and iv) mineral chemistry (tourmaline and APS minerals) may help identify fertile faults in exploration for uranium deposits.