Made available in DSpace on 2014-10-09T12:44:00Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:53Z (GMT). No. of bitstreams: 1 06542.pdf: 8087147 bytes, checksum: d612ed1a7213f89e107e4ab6f9b66638 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Quimica, Universidade de Sao Paulo - IQ/USP

M.Tech. (Extraction Metallurgy) / The techniques for the flotation of mixed copper and cobalt bearing oxide ores using the sulphidization method in order to recover the oxidized copper and cobalt bearing minerals have been well documented by previous researchers. These processes have been successfully implemented in many of the metallurgical plant operations in the Democratic Republic of Congo (DRC). The mixed copper and cobalt oxidised ores from this region present significant chal-lenges to metallurgists. Ore grades and gangue mineral constituents can vary quite significantly from one mine to another. Ore grades can also change substantially on an individual mine over a relatively short time period. These rather sudden ore feed grade changes can result in reduced flotation plant efficiency and hence losses in income. The prime objective of the project, to selectively recover and concentrate cobalt oxi-dized minerals by froth flotation, was not fully achieved on the ores tested. Very ac-ceptable cobalt recoveries were however achieved on three of the ores tested but it was invariably with an accompanying high copper recovery as well. Some valuable insights into the behaviour of both the cobalt and copper oxidized minerals in the froth flotation of these oxidized ores were observed and documented.

No description available.

The homogeneous hydrogenation of arenes with functional groups was studied with allylcobalt complexes containing the bulky chelating diphosphines dippp (1,3-bis(diisopropylphosphino)propane and dippcyp (trans-(±)-l,2-bis(diisopropylphos-phino)cyclopentane). The results indicated that these catalyst precursors were unsuitable for the hydrogenation reactions, being too sensitive to the nature of the substrate. From these hydrogenation reactions, the intermediates (η⁵-cyclohexadienyl)Co(dippcyp) (10) and (η⁴-2-methoxynaphthalene)Co(H)(dippcyp) (11) were isolated and structurally characterized, thus providing some insight into the mechanism of the hydrogenation reaction. The production of binuclear hydrides such as [(dippp)CoH₂]₂ (4) and [(dippcyp)CoH₂]₂ (9) was observed to lead to the end of the catalysis. An X-ray structural characterization of the blue hydride [(dippp)CoH₂]₂ (4) showed that in the solid state it is binuclear. Although the complex is diamagnetic in the solid state (6-280 K), in solution its paramagnetic behaviour could only be attributed to an equilibrium with a second species proposed to be mononuclear, (dippp)CoH₂. In addition, a cyclic voltammogram of the complex in solution indicated that the predominant species still was the binuclear compound [(dippp)CoH₂]₂ (4). One of the syntheses of [(dippp)CoH₂]₂ (4) gave a product identified as (dippp)CoH₃ (5). Based on variable-temperature spin-lattice relaxation time (T₁) measurements and an electrochemical study, this red hydride complex appeared to contain an η²-H₂ ligand. The relationship of this complex with the blue hydride apparently involves the mononuclear species, (dippp)CoH₂. Independent pathways led to the formation of both the blue and red hydrides, and these pathways are discussed in terms of possible mechanisms. / Science, Faculty of / Chemistry, Department of / Graduate

Single crystals of cobalt have been deformed in tension over the temperature range 20°C to 600°C. On heating a transformation from the hexagonal close packed (hep) structure to the face centred cubic (fee) structure occurs at 430°C. The deformation behaviour in the hep phase has been compared to that for other hep metals, and it has been shown that only basal slip occurs even in unfavourable orientations. Twinning may occur, but has not been found to be associated with an increase in the work hardening rate. Similarly the properties in the fee phase have been compared to those of fee metals. The effect of deformation on the transformation has been studied on specimens which have been thermally cycled through the transformation during tensile tests. It has been found that the (111)/ (0001) transformation habit plane may be controlled by deformation. Recrystallisation may occur if two slip systems operate, but this is a function of crystal orientation. Slip may be induced on an unfavourably orientated glide plane in the fee phase, and this indicates that deformation dislocations on the (0001)[subscript: h], /(111)[subscript: c] plane are not affected by the transformation. However, glide dislocations on any {111} plane, which does not form the basal plane on cooling do not affect the work hardening behaviour in the hep phase. In previously deformed specimens, the flow stress is a function only of the deformation history, i.e. the yield point in the hep phase may be raised by a factor of 10 or the yield point in the fee phase may be lowered by a factor of 3. However, the work hardening rate depends only on the crystal structure and is always higher (by 20 to 100 times) in the fee phase than in the hep phase. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The nuclear magnetic resonance technique has been used to study the effect of deuteration on the Neel temperature of CoCl₂•6H₂0 single crystals. The Neel temperature varies with a period of 180° as the external magnetic field is rotated about the b-axis⊥ the a-c plane. On deuteration, the Neel temperature rises for all orientations, the more deuterium being introduced the higher the transition point. The maximum increase of approximately 6% in Neel temperature is obtained with a 92% concentration of deuterium. In addition, the anisotropy in TN decreases from approximately 0.08°K for 0% deuteration to slightly less than 0.05°K for 92% deuteration. Further, the orientation-averaged Neel temperature seems to vary linearly with the cube root of relative concentration of deuterium. In the vicinity of H₀ = 4,000 gauss, the Neel temperature increases with an increase in the external magnetic field [formula omitted] being ⊥ c-axis. This unusual behaviour is common to deuterated as well as non-deuterated samples and has not yet been explained. Following Haseda's conjecture, a semi-empirical attempt is made to establish a connection among the change in Neel temperature upon deuteration, the super-exchange parameter and the potential of a proton in a hydrogen bond. The picture presented is that the Neel temperature rises on deuteration because of a change in the average of the super-exchange parameter over the ground vibrational state of the hydrogen atom. An x-ray analysis shows that at room temperature the CoCl₂•6H₂0 and CoC1₂•6D₂0 crystals have the same symmetry and their cell dimensions do not differ by more than 0.2%. The infra-red spectrum of CoC1₂•6D₂0 has been used to determine the value of electrostatic field gradient at the deuteron sites. This value is consistent with the observed quadrupole splitting of the n.m.r. spectrum of the deuterons. The n.m.r. lines belonging to deuterons in the water molecules not forming a square configuration around cobalt ions have been identified. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The interaction between sublesions produced by neutrons [p(66)/Be and d(16)/Be] and ⁶⁰Co γ-rays was investigated using mammalian cells, meristematic cells and human lymphocytes. The quality of each radiation source was quantified in terms of molecular yield per unit dose absorbed in a ferrous sulphate xylenol orange solution and was found to vary inversely with the mean LET of the radiation field. Inactivation parameters determined for mammalian and meristematic cells were not significantly different following simultaneous or sequential exposures to d(16)/Be neutrons and ⁶⁰Co γ-rays. Synergistic interaction was observed to be most pronounced in a radiation mixture consisting of about one part neutrons and three parts photons and appeared to be optimal at approximately 5 Gy. This phenomenon led to dose enhancement ratios that increase with radioresistance. Multi-target parameters indicated that on a per gray basis, priming doses of p(66)/Be neutrons and ⁶⁰Co γ-rays induce comparative levels of sublethal damage. However, non-parametric analysis of the survival data showed that mammalian cells regard a priming dose of neutrons as somewhat less effective than an iso-effective photon dose. A greater measure of synergy was observed between photons and priming doses of neutrons with less build-up. This is however mainly due to higher levels of biological damage induced with a more potent configuration of secondary charged particles. Interaction factors compared at levels of iso-effect tend to be smaller when the LET of the priming dose was increased. Split-doses of neutrons in the absence of build-up resulted in "negative" repair. The validity of proposed biophysical models was tested using meristematic cells, as the response of these cells show an apparent absence of intertrack damage. Contrary to expectations, synergistic interaction was observed for both growth delay measurements and micronuclear formations. Chromosome aberrations showed synergy between neutron and photon damage in human lymphocytes, as predicted by interaction functi ons. However, the synergistic interaction noted with micronuclear formation in binucleate cells was at variance with predictions based on biophysical models.

No description available.

A dissertation submitted to the Faculty of Engineering and the Built Environment at the University of Witwatersrand, Johannesburg, in part fulfillment of the requirements for the degree of Master of Science in Engineering, 17 May 2018 / Traditionally, copper and cobalt are extracted from oxidised ores via hydrometallurgical processing route. The ore is leached in sulphuric acid in reducing conditions. This method co-extracts impurity metal values like iron and manganese, necessitating downstream solution purification, which causes significant valuable losses. Pregnant leach solution purification is performed through step-wise oxidation and acid neutralisation of the leach solution. Cobalt is the most affected component in this process due to high losses incurred during the precipitation stages. Moreover, because the lixiviant is not recycled, the method consumes ominously high quantities of sulphuric acid. As a result, the process must be accompanied by readily available and cost-effective acid-making plant. In the event of an increase in the price of sulphuric acid raw materials or a decline in the ore grade, a source of 50% of the world’s cobalt might be rendered impracticable. This work investigates the viability of using ammoniacal solution as an alternative lixiviant to sulphuric acid. Ammoniacal solution forms soluble complexes with copper and cobalt at pH and potential where iron, manganese and other impurities tend to form precipitates. Because of the preferential leaching, downstream solution purification can be circumvented, thereby reducing valuable losses. Furthermore, because there is no solution altering, multi-step solution purification required, the leach solution retains its initial pre-leaching properties, making it fully recyclable. The recyclable nature of the lixiviant thus reduces lixiviant costs. Furthermore, an advantage of leaching in ammonia is lower equipment costs because ammonia is less corrosive than acid. The feed material used in this study was an oxidised copper-cobalt ore sourced from Katanga Region in the DRC. A size fraction analysis was undertaken in order to determine the deportation of the copper and cobalt metals in the feed material. In the leaching tests conducted, the effect of particle size, temperature, concentration of the reducing agent and concentrations of ammonia and ammonium carbonate were investigated. The results showed that a +63-75μm size fraction had the highest grade of copper and cobalt and was thus used for all the experiments undertaken. The results also indicated that cobalt and copper extraction was highly influenced by temperature. It was found that working at ambient temperature results in poor extraction of the value metal species while raising the temperature to 80°C significantly improves the extraction of both value metals if premature depressurising of the leach vessel is avoided. The results also showed that there was no significant extraction advantage gained from milling finer than -63μm. Moreover, it was found that at 80°C, 2.0M ammonia solution, 0.4M ammonium carbonate, 300rpm, 0.4M reducing agent and 60 minutes pre-treatment and leach time, a peak extraction of 90% could be realised for copper. It was also noted that even better extraction efficiencies could be obtained for copper in the absence of a reducing agent. Optimum cobalt extraction of 85% was obtained at 80°C, 2.0M ammonia solution, 2.0M ammonium carbonate solution, 0.4M ammonium sulphite, 60 minutes pre-treatment time and 60 minutes leaching time. This compares well to about 40-60% recovery reported when leaching in acid. These findings point to the conclusion that ammoniacal solution is a viable alternative to sulphuric acid for hydrometallurgical processing of the copper-cobalt ore. / MT 2018

No description available.