Ph.D. / The two-step growth process, involving the selenization and sulfurization of sputter deposited CuInGa alloys has been identified as a commercially viable method to produce large area Cu(In1-xGax)(Se1-ySy)2 absorber films for solar cell application. The success of this method is however limited by insufficient control over the lattice parameters and band gap of the compound due to phase segregation associated with non-uniform Ga and S incorporation. This study provides an approach to overcome this limitation by investigating the influence of process parameters on the structural features of the Cu(In1-xGax)(Se1-ySy)2 films. In this approach, films were partially selenized in optimum H2Se/Ar flow to produce composite alloys comprising of a mixture of binary selenides (InSe, CuSe and GaSe) and at least one group I-III-VI ternary alloy. The subsequent reaction step in H2S/Ar produced homogeneous Cu(In1-xGax)(Se1-ySy)2 films. The lattice constants of the resulting films varied linearly with an increase in the S/(S+Se) ratio in accordance with Vegard’s law. The Raman spectra of the films were characterized by the presence of the A1-Se mode near 180 cm-1 and a low intensity, A1-S mode around 290 cm-1. With an increase in the S/(S+Se) ratio of the films, the FWHM of the A1-Se mode increased and its frequency shifted linearly towards that of A1-S mode. A corresponding increase in the value of the Urbach energy, attributed to an increase in chalcopyrite crystal alloy disorder, was observed from the analysis of the transmission and reflectance data. 0.45 cm2 area devices with conversion efficiencies between 12% and 15%, were fabricated from absorber layers with the (112) x-ray diffraction peak position between 27.1°and 27.2°, corresponding to the S/(S+Se) ratio of about 0.18 to 0.20. The process scale up was demonstrated by the fabrication of large area, (30 x 40) cm2 modules, with conversion efficiencies of 10%.

M.Sc. / CuInSe2 (CIS) is considered to be one of the most promising candidates for high efficiency thin film solar cells. The reaction of metallic alloys to a reactive selenium atmosphere (H2Se/Ar or elemental Se vapour) is a promising growth technique to produce CIS thin films of high crystalline quality. However, up to now, the control of the final film quality has been critically influenced by the loss of material and subsequent formation of detrimental binary phases during the high temperature selenization stages. In this study, it is shown that this phenomenon is strongly related to the selenization temperature and, in particular, the ramping procedure followed to the final selenization temperature. Metallic alloys which were selenized in H2Se/Ar at 400°C or slowly heated in 20 minutes to temperatures around 400°C were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) to have nonuniform surface morphologies, highly defected 0.8-2 !lm sized grains and to contain Cuselenide binary phases. Energy dispersive X-ray spectroscopy (EDS) analysis confirmed the generally reported sharp increase in the Cu/In atomic ratio for these classes of samples. In contrast, rapid heating (in 2 minutes) of identical metallic alloys to temperatures above 400°C, resulted in uniform, dense films with low defect density 1 !lm sized grains void of any evidence of secondary phases. X-ray fluorescence (XRF) Kal,2 measurements of metallic alloys at different stages of selenization revealed no evidence of material losses. XRF depth profiles, however, explained this discrepancy by revealing a pronounced segregation of In towards the Mo back contact when the samples were selenized at 400°C, or slowly heated to temperatures around 400°C. This segregation was dramatically reduced in films rapidly heated and selenized at temperatures above 400°C. For the purpose of comparison, metallic alloys were also reacted to elemental Se vapour. The structural features (grain size and preferred orientation) ofthese films differed significantly from those selenized under similar conditions in H2Se/Ar. The results from this study, including photoluminescence (PL) measurements obtained from these films, were used to affect the fabrication of CIS absorbers with excellent material properties and solar cell devices with moderate conversion efficiencies.

The high demand for copper is coinciding with a sharp decline in the grade of copper reserves, and as a result, copper scarcities are expected to arise in the coming decades. In this work, a transformative hydrometallurgical process is being developed to lower the costs of copper production and thereby sustain the use of copper throughout the global transition to renewable energy technologies. The focal point of the hydrometallurgical process is the reductive treatment of chalcopyrite, which is in contrast to the oxidative treatment more commonly pursued in the literature. Chalcopyrite may be reduced directly by the cathode of an electrochemical reactor, which is monitored by atomic absorption spectroscopy (AAS), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). The efficiency of the electrochemical reaction is optimized by adjusting the electrode materials, applied current density, and reactor design. Chalcopyrite may also be reduced by reaction with the vanadium (II) ion, which circumvents engineering challenges associated with slurry electrodes but requires the separation and electrochemical regeneration of the vanadium (II) ion. A preliminary technoeconomic analysis suggests that both reduction pathways may be competitive with the pyrometallurgical standard for copper production. The performance of vanadium redox flow batteries (VRFBs) is hindered by the diffusion and migration of the vanadium species across the separator, however the migration of vanadium species has not been accurately measured or characterized with values of the transference numbers. In this work, models based on dilute solution theory and concentrated solution theory are developed to introduce the dimensionless ratio of migration to diffusion (M/D) to the literature. It is shown that transference numbers may be measured with high accuracy and precision for experiments conducted in the migration-dominated regime. An experimental procedure is designed to measure vanadium crossover as a function of current density for vanadium-containing electrolytes of various state of charge (SOC), state of discharge (SOD), and sulfuric acid concentration. Model-guided design of experiment is used to estimate the transference number of the vanadium species in Nafion 117 with minimal uncertainty related to unknown or unmeasured physical properties. Markov Chain Monte Carlo simulations are used to quantify the relative uncertainties of the transference number estimates to be less than five percent, consistently. The transference number estimates are related to faradaic efficiency loss and capacity fade of working VRFBs operating in the migration-dominated regime. The technique used in this work may be generalized to measure salt transference numbers in novel electrochemical systems and membrane separators to inform their rational design.

Thesis(Ph.D.(Physics)) -- University of Limpopo, 2020 / Surface properties of pyrite (FeS2), chalcopyrite (CuFeS2), galena (PbS) and sphalerite (ZnS) most thermodynamically stable surfaces have been studied using first priniciples density functional theory. The most stable surfaces showed the highest surface exposure as it covered a higher percentage of the surface area on morphologies. The interaction of water with such sulphide surfaces was also investigated; the structures of sulphide minerals surfaces were changed in the presence H2O molecules. The surfaces of FeS2 and ZnS relax most while those of CuFeS2 and PbS surfaces change slightly in the presence of H2O molecules. The results on the effect of chain length of DTPs and DTCs on the enthalpies of adsorption on pyrite, galena, chalcopyrite and sphalerite have shown that an increase in chain length of the DTPs resulted in an increase in the enthalpies of adsorption trend for pyrite, galena and sphalerite. This is an important observation since the ligand is the same in all cases and therefore the effect is due to the role of the alkyl group Moreover, we noted a decrease of enthalpies of adsorption with an increase of DTCs chain lengths on pyrite, galena, chalcopyrite and sphalerite. The effect of the branching of the hydrocarbon chain length of the dithiocarbamates on the enthalpy of adsorption of pyrite was investigated. The results show that the configuration of the alkyl chain length of the same carbon number has an influence on the enthalpy of adsorption. Furthermore, the results indicate that there was minimal enthalpy of adsorption when DeDTP was dosed to galena, chalcopyrite and sphalerite minerals as compared to DeDTC and ethyl xanthate. On the other hand, the enthalpies of adsorption of DeDTP on pyrite were very high which represented a greater exothermic reaction than for any of the DeDTC and ethyl xanthate. The bond distance between thiol collector and the surface is consistent with the corresponding calculated adsorption energies. The Mulliken population of S-Fe/S-Pb/S-Zn bond for the adsorption of eX on CuFeS2 surface are high compared to PbS and ZnS surfaces, which indicated that there is a strong covalent bond between S and Fe atoms as compared to S-Pb and Pb-Zn bonds. Such observations are consistent with results of other thiol collectors. It was seen that the Mulliken atomic charges populations of CuFeS2, PbS and ZnS surface layers are different before and after DTPs adsorption. The charges of Fe atom reduce, which indicates that the Zn and Pb atoms become more positive and the Fe atom becomes more negative. In addition, there are changes in the charges of S atoms in ZnS and PbS surface layers before and after H2O absorption, suggesting that the presence of water would affect the adsorption of thiol collector. The densities of states (DOS) of the thiol collectors on surfaces of sulphide minerals have shown a strong hybridisation between the S 3p-orbital HOMO, metals (Fe, Pb, Zn) 3d-orbital for pyrite and chalcopyrite, 6p-orbital for galena and (3d and 4s)-orbitals for sphalerite. The collector S 3p-orbital reduces to zero states on the surfaces of Fe, Pb and Zn atoms. The Fe-S bond population for DeDTP is lower than that of DispDTP and DbDTP in pyrite, respectively. For chalcopyrite the DeDTP Fe-S population is higher than both DispDTP and DbDTP: similar trends were observed for Pb-S and Zn-S, however, the Pb-S bonding was less covalent as compared to the Fe S in chalcopyrite. The DTPs Fe-S bond population is generally higher in chalcopyrite than in pyrite. Mulliken charges analysis indicated that the DTPs S atoms lost charges and the metals gained with a decreasing DTPs chain length for pyrite: a similar trend was observed for chalcopyrite. The DTPs gained electrons from galena and sphalerite surface. For DTCs pyrite and chalcopyrite surface Fe atoms gain more electrons in the presence of DeDTP than other DTPs, while galena and sphalerite lost most electrons in the presence of DbDTC than other DTCs. As for xanthate, the Mulliken bond charges indicated that the S atoms and the metals lost charges, suggesting that some charges reside at the internuclear region between the metals and sulphurs (M– S). These show that electron charges are collector and mineral dependent; collector would be an electron acceptor or donor depending on the mineral makeup. A comparison of the computational results, isothermal titration calorimetry (ITC) and microfloatation experiments for the interaction of DeDTP, DeDTC and eX with pyrite and galena was made. The calculated adsorption energies between thiol collectors and mineral surfaces were always more exothermic than the experimentally determined ones. In computational calulations, water adsorption was found to reduce the reactivity of Fe and Pb atom for the interaction with thiol collectors and bring the adsorption energies closer to the magnitude of the experimental values. FeS2 (100) surface heat of adsorption depict similar trends to experimental recoveries from microfloation for DeDTP, DeDTC and eX, while FeS2 (111) heats of adsorptions for DeDTP and DeDTC are consistent with ITC experimental results. Lastly, calculated DeDTP and DeDTC adsorptions on the PbS (100) are also consistent with experimental recoveries. / National Research Foundation (NRF), South African Minerals of Metal Institution (SAMMRI) and University of Limpopo (UL)

<P> The occurrence of silver in galena, chalcopyrite, sphalerite, and pyrite as well as tailings from Cart Lake, Cobalt Ontario were investigated to compare with the undetectable ( <10^-11 g/g) Ag found in runoff water from the Cobalt area. </p> <p> Silver was detected at very low levels: 0.012 wt% ± 0.009 wt%, 0.015 wt% ± 0.01 wt%, and 0.0062 wt% ±0.02 wt% for pyrite, galena and chalcopyrite, respectively. </p> <p> Attempts to characterize the mineralogical associations of silver were not successful. The silver sequence of pyrite> galena> chalcopyrite is contrary to results from other studies. This may be due to the maximum thermal stabilities of the minerals in relation to the ions available for replacement. </p> / Thesis / Bachelor of Science (BSc)

The rates of oxidation of arsenopyrite and chalcopyrite by Fe³⁺ at concentrations of 10⁻² to 10⁻⁵ molal with a pH near 2 and temperatures of 0 to 60°C, conditions similar to those found in weathering sulfide ore deposits, have been determined. The rate equations for 25°C are: dn_Fe3+/dt = 1.9±0.4 x 10⁻⁷ (A) (m_Fe3+)_0.43±0.01 dn_Fe3+/dt = 1.5±0.4 x 10⁻³ (A) (m_Fe3+)_0.94±0.04 for chalcopyrite and arsenopyrite respectively. The E_a of chalcopyrite is 63±2 kJ mol⁻¹ (40 - 60°C). The E_a of arsenopyrite varied with temperature from 18±2 kJ mol⁻¹ (0 - 25°C) to -6±2 kJ mol⁻¹(25 - 60°C). / M.S.

A mina Cuajone é uma jazida de tipo pórfiro de cobre (porphyry copper), localizada na Província Cuprífera do Pacífico, nos flancos ocidentais da Cadeia Andina, no estado de Moquegua, sul do Perú, em coordenadas 17° 02\'(S) e 70° 42\'(W) e altitudes entre 3100 e 3830 m. A região é caracterizada pela ocorrência, na base, de derrames vulcânicos (andesitos e riolitos) cretácicos do Grupo Toquepala, que s~ao invadidos por um complexo intrusivo (quartzo monzonitos - quartzo latitos) associado à mineralização. Fluxos vulcânicos mais recentes, compostos principalmente por traquitos, tufos e aglomerados traquíticos e conglomerados riolíticos das Formações Huaylillas e Chuncatala recobrem todo o conjunto. A análise petrográfica de 77 amostras representativas de 22 testemunhos de furos de sondagem distribuídos em três perfis da jazida de Cuajone permitiu a caracterização das seguintes rochas: andesitos, riolitos, quartzo latitos, latitos, micro-granodioritos porfiríticos, microtonalitos porfiríticos, pórfiros-I (micro quartzo monzonitos - micro monzogranitos (?)), pórfiros- II (micro tonalitos - micro leucoquartzo dioritos (?)) e micro-brechas. Estas rochas encontram-se afetadas por alterações hidrotermais em graus variáveis, identificando-se oito tipos ou combinações de tipos principais: potássica, potássica-propílica, propílica-potássica, potássica-propí?lica/fílica, propílica, propílica-fílica, fílica-propílica e fílica. O exame microscópico em detalhe sob luz refletida das fases sulfetadas demonstrou que a pirita (py), o sulfeto mais abundante, apresenta freqüentemente inclusões diminutas de calcopirita, cp, (X0,0 e 0,X ?m), quase sempre acompanhada de pirrotita (po), cubanita (cb) e mackinawita (mck), que aparecem formando intercrescimentos tí?picos. Estas inclusões apresentam formas arredondadas, ovais ou mesmo idiomórficas que, devido às suas dimensões, quase sempre não são reconhecidas em exames convencionais ao microscópio. Os intercrescimentos identificados foram classificados de acordo com a sua morfologia, utilizando-se para tanto de nomenclatura específica, e suas abundâncias relativas. Os resultados mostram que os mais abundantes são: tipo cp/po:1b (calcopirita + pirrotita, morfologia de tipo 1b) e py/po:1e na zona de alteração potássica, py/po:1e e cp/mck:4f nas zonas potássicapropílica e propílica-potássica, cp/mck:4f e py/po:1e na zona propílica e cp/po:1b e cp/mck:4f nas zonas de alteração potássica-propílica/fílica, propílica-fílica, fílica-propílica e zona de alteração fílica. A análise de distribuição das inclusões/intercrescimentos indica que a sua mineralogia pode ser correlacionada com a tipologia da alteração hidrotermal, particularmente quando se consideram as freqüências e/ou abundâncias relativas. Assim, observa-se que a pirrotita ocorre em todos os tipos de alteração, porém sua freqüência é notadamente superior nas amostras com alteraçãao potássica. A cubanita, ainda que seja pouco abundante, é freqüente nas zonas onde há contribuição da alteração fílica. Apesar de ser encontrada também nas zonas potássica-propílica e propílica-potássica, a sua freqüência é praticamente insignificante quando comparada com a das demais fases encontradas, enquanto a mackinawita apresenta freqüência significativamente superior nas rochas afetadas pela alteração propílica. A tipologia e a distribuição das inclusões/intercrescimentos, aliadas às informações experimentais disponíveis para o diagrama de fases Cu-Fe-S, são compatíveis com temperaturas entre ca. 180 e 500 °C para a origem da mineralização de Cu (calcopirita, cubanita). / The Cuajone mine is a porphyritic copper deposit (porphyry copper), located in the Pacific Copper Province, eastern flanks of the Andean Cordillera, state of Moquegua, south of Peru, with geographic coordinates 17 ° 02 \'(S) and 70 ° 42 \'(W) and altitudes between 3100 and 3830 m. The region is characterized from base to top by cretaceous volcanics (andesites and rhyolites) from Toquepala Group, which are invaded by a intrusive complex (quartz monzonites-quartz latites) associated to the ore deposits. Covering these units there are more recent volcanic flows composed mainly by trachyte, trachytic tuff, rhyolitic conglomerates and trachytic agglomerate from Huaylillas and Chuncatala Formations. Petrographic analysis of 77 samples representing 22 drilling cores distributed in three profiles of Cuajone Mine allowed the identification of the following lithotypes: andesite, rhyolite, quartz latite, latite, porphyritic micro-granodiorite, porphyritic micro-tonalite, porphyry-I (micro quartz monzonites-monzogranites (?)), porphyry-II (micro tonalites-micro leucoquartz diorites (?)) and micro-breccias.These rocks are affected by variable degrees of hydrothermal alteration with predominance of eight types or combinations of the following main types: potassic, potassic-propylitic, propylitic-potassic, potassic-propylitic/phylic, propylic, propylitic-phylic, phylic and propylitic-phylic. Detailed microscopic investigation under reflected light revealed that among the sulphide phases, pyrite (py) is the most abundant, with frequent chalcopyrite (cp) tiny inclusions (X0, 0 and 0, X ?m), almost always accompanied by pirrotite (po), cubanite (cb) and mackinawite (mck), occurring as typical intergrowths. These inclusions show round to oval or idiomorphic shapes and are commonly overlooked during conventional microscopic analyses due to their small dimensions. The intergrowths identified during petrographic analysis were classified according to their morphology, using specific nomenclature and relative abundances. The results show that the most abundant types are: cp/po:1b (chalcopyrite + pirrotite, morphology type 1b) and py/po:1e in the potassic alteration zone, py/po:1e and cp/mck:4f in areas of potassic-propylitic and propylitic-potassic alteration, cp/mck:4f and py/po:1e in the propylitic zone and cp/po:1b and cp/mck:4f in potassic-propylic/phylic alteration zones; propylitic-phylic, phylic-propylitic and phylic zones. The distribution pattern of inclusions/intergrowths indicates that their mineralogy can be correlated with the type of hydrothermal alteration. This is particularly evident when considering frequency and/or relative abundance. Thus, pirrotite occurs in all types of alteration, although its frequency is especially higher in samples with potassic alteration. Cubanite is more characteristic in the potassic-propylic and propylic-potassic zones, while mackinawite is significantly more frequent in rocks affected by propylic alteration. The type and distribution of inclusions/intergrowths, allied to current experimental results for the Cu-Fe-S system, are compatible with temperatures between ca. 180 and 500 ° C for the genesis of the studied copper deposits (chalcopyrite, cubanite).

A mina Cuajone é uma jazida de tipo pórfiro de cobre (porphyry copper), localizada na Província Cuprífera do Pacífico, nos flancos ocidentais da Cadeia Andina, no estado de Moquegua, sul do Perú, em coordenadas 17° 02\'(S) e 70° 42\'(W) e altitudes entre 3100 e 3830 m. A região é caracterizada pela ocorrência, na base, de derrames vulcânicos (andesitos e riolitos) cretácicos do Grupo Toquepala, que s~ao invadidos por um complexo intrusivo (quartzo monzonitos - quartzo latitos) associado à mineralização. Fluxos vulcânicos mais recentes, compostos principalmente por traquitos, tufos e aglomerados traquíticos e conglomerados riolíticos das Formações Huaylillas e Chuncatala recobrem todo o conjunto. A análise petrográfica de 77 amostras representativas de 22 testemunhos de furos de sondagem distribuídos em três perfis da jazida de Cuajone permitiu a caracterização das seguintes rochas: andesitos, riolitos, quartzo latitos, latitos, micro-granodioritos porfiríticos, microtonalitos porfiríticos, pórfiros-I (micro quartzo monzonitos - micro monzogranitos (?)), pórfiros- II (micro tonalitos - micro leucoquartzo dioritos (?)) e micro-brechas. Estas rochas encontram-se afetadas por alterações hidrotermais em graus variáveis, identificando-se oito tipos ou combinações de tipos principais: potássica, potássica-propílica, propílica-potássica, potássica-propí?lica/fílica, propílica, propílica-fílica, fílica-propílica e fílica. O exame microscópico em detalhe sob luz refletida das fases sulfetadas demonstrou que a pirita (py), o sulfeto mais abundante, apresenta freqüentemente inclusões diminutas de calcopirita, cp, (X0,0 e 0,X ?m), quase sempre acompanhada de pirrotita (po), cubanita (cb) e mackinawita (mck), que aparecem formando intercrescimentos tí?picos. Estas inclusões apresentam formas arredondadas, ovais ou mesmo idiomórficas que, devido às suas dimensões, quase sempre não são reconhecidas em exames convencionais ao microscópio. Os intercrescimentos identificados foram classificados de acordo com a sua morfologia, utilizando-se para tanto de nomenclatura específica, e suas abundâncias relativas. Os resultados mostram que os mais abundantes são: tipo cp/po:1b (calcopirita + pirrotita, morfologia de tipo 1b) e py/po:1e na zona de alteração potássica, py/po:1e e cp/mck:4f nas zonas potássicapropílica e propílica-potássica, cp/mck:4f e py/po:1e na zona propílica e cp/po:1b e cp/mck:4f nas zonas de alteração potássica-propílica/fílica, propílica-fílica, fílica-propílica e zona de alteração fílica. A análise de distribuição das inclusões/intercrescimentos indica que a sua mineralogia pode ser correlacionada com a tipologia da alteração hidrotermal, particularmente quando se consideram as freqüências e/ou abundâncias relativas. Assim, observa-se que a pirrotita ocorre em todos os tipos de alteração, porém sua freqüência é notadamente superior nas amostras com alteraçãao potássica. A cubanita, ainda que seja pouco abundante, é freqüente nas zonas onde há contribuição da alteração fílica. Apesar de ser encontrada também nas zonas potássica-propílica e propílica-potássica, a sua freqüência é praticamente insignificante quando comparada com a das demais fases encontradas, enquanto a mackinawita apresenta freqüência significativamente superior nas rochas afetadas pela alteração propílica. A tipologia e a distribuição das inclusões/intercrescimentos, aliadas às informações experimentais disponíveis para o diagrama de fases Cu-Fe-S, são compatíveis com temperaturas entre ca. 180 e 500 °C para a origem da mineralização de Cu (calcopirita, cubanita). / The Cuajone mine is a porphyritic copper deposit (porphyry copper), located in the Pacific Copper Province, eastern flanks of the Andean Cordillera, state of Moquegua, south of Peru, with geographic coordinates 17 ° 02 \'(S) and 70 ° 42 \'(W) and altitudes between 3100 and 3830 m. The region is characterized from base to top by cretaceous volcanics (andesites and rhyolites) from Toquepala Group, which are invaded by a intrusive complex (quartz monzonites-quartz latites) associated to the ore deposits. Covering these units there are more recent volcanic flows composed mainly by trachyte, trachytic tuff, rhyolitic conglomerates and trachytic agglomerate from Huaylillas and Chuncatala Formations. Petrographic analysis of 77 samples representing 22 drilling cores distributed in three profiles of Cuajone Mine allowed the identification of the following lithotypes: andesite, rhyolite, quartz latite, latite, porphyritic micro-granodiorite, porphyritic micro-tonalite, porphyry-I (micro quartz monzonites-monzogranites (?)), porphyry-II (micro tonalites-micro leucoquartz diorites (?)) and micro-breccias.These rocks are affected by variable degrees of hydrothermal alteration with predominance of eight types or combinations of the following main types: potassic, potassic-propylitic, propylitic-potassic, potassic-propylitic/phylic, propylic, propylitic-phylic, phylic and propylitic-phylic. Detailed microscopic investigation under reflected light revealed that among the sulphide phases, pyrite (py) is the most abundant, with frequent chalcopyrite (cp) tiny inclusions (X0, 0 and 0, X ?m), almost always accompanied by pirrotite (po), cubanite (cb) and mackinawite (mck), occurring as typical intergrowths. These inclusions show round to oval or idiomorphic shapes and are commonly overlooked during conventional microscopic analyses due to their small dimensions. The intergrowths identified during petrographic analysis were classified according to their morphology, using specific nomenclature and relative abundances. The results show that the most abundant types are: cp/po:1b (chalcopyrite + pirrotite, morphology type 1b) and py/po:1e in the potassic alteration zone, py/po:1e and cp/mck:4f in areas of potassic-propylitic and propylitic-potassic alteration, cp/mck:4f and py/po:1e in the propylitic zone and cp/po:1b and cp/mck:4f in potassic-propylic/phylic alteration zones; propylitic-phylic, phylic-propylitic and phylic zones. The distribution pattern of inclusions/intergrowths indicates that their mineralogy can be correlated with the type of hydrothermal alteration. This is particularly evident when considering frequency and/or relative abundance. Thus, pirrotite occurs in all types of alteration, although its frequency is especially higher in samples with potassic alteration. Cubanite is more characteristic in the potassic-propylic and propylic-potassic zones, while mackinawite is significantly more frequent in rocks affected by propylic alteration. The type and distribution of inclusions/intergrowths, allied to current experimental results for the Cu-Fe-S system, are compatible with temperatures between ca. 180 and 500 ° C for the genesis of the studied copper deposits (chalcopyrite, cubanite).

L’une des solutions proposées pour la diminution du coût par watt d'électricité produite par le photovoltaïque est de réduire la quantité des matériaux semiconducteurs entrants dans la fabrication de la cellule solaire. La 3ème génération des cellules solaires en couches minces nanostructurées vient pour répondre à cette exigence. Les matériaux CIGS sous leurs structures chalcopyrites, sont de nouveaux matériaux semiconducteurs fortement recommandés pour la fabrication des cellules solaires à base de couches minces. La synthèse par la méthode de pulvérisation cathodique et la caractérisation de ces derniers matériaux ont été l’objectif général de cette thèse. Toutes les couches ont été déposées grâce à une seule cible constituée par des grains nanométriques de CIGS, ces derniers ont été obtenus par la voie solvothermale. Dans la première partie de ce travail, nous avons étudié l’effet des différents paramètres de synthèse (température, durée de synthèse, le traitement thermique et l’effet du taux molaire de gallium et d’indium) sur les propriétés des nanoparticules CIGS, les mécanismes réactionnels mis en jeu ont été aussi étudié. Les conditions de synthèse optimales sont une température et une durée de synthèse égale à 220 °C et 24 heures. Après un traitement thermique, les nanoparticules de CIGS sont cristallisées suivant la structure chalcopyrite, avec l’absence des pics correspond aux phases secondaires, les diamètres des grains varie entre 15 et 30 nm. Dans la deuxième partie, Nous sommes intéressés à l’élaboration et la caractérisation des couches absorbantes ternaire et quaternaire de type CIS et CIGS (x = 0 et x = 0.3) obtenues par pulvérisation cathodique en variant la puissance de dépôt de 60 à 100 W. Toutes les couches élaborées présentent la phase chalcopyrite avec (112) comme axe d’orientation préférentiel de croissance. La taille moyenne des grains a le même ordre de grandeur que les poudres initiales. Les couches de CIGS sont généralement de type de conduction p avec des faibles valeurs de résistivités. Les caractérisations optiques des couches présentent une bonne absorption de l’ordre de 95 % dans la gamme de visible et le proche infra-rouge. La variation du coefficient d’absorption en fonction de l’énergie du photon, nous a permis de déterminer l’énergie du gap optique. Les valeurs obtenues pour les différentes couches sont cohérentes avec l’optimum pour la conversion photovoltaïque. / One of the proposed solutions for reducing the cost of electricity produced by the photovoltaic is to reduce the amount of incoming semiconductor materials in the manufacture of the solar cell. The 3rd generation solar cells based on nanostructured thin film come in response to this requirement. CIGS under their structures chalcopyrite are highly recommended for the manufacture of this solar cells type. The synthesis of these materials using sputtering method and their characterization were the overall goal of this thesis. All films were deposited onto glass substrates from single target composed trough nanoparticles of CIGS, which are obtained by the solvothermal route. In the first part of this work, we studied the effect of different synthesis parameters (temperature, synthesis time, the heat treatment and the effect of the molar ratio of gallium and indium) on the properties of CIGS nanoparticles. The reaction mechanisms were also studied. The optimum synthesis conditions are a temperature and a synthesis time equal to 220 ° C and 24 hours. After heat treatment, the nanoparticles are crystallized according CIGS chalcopyrite structure, with the absence of the peaks corresponding to the secondary phases, grain size between 15 and 30 nm. In the second part, we are interested in the deposition and characterization of ternary and quaternary absorbent thin film CIS and CIGS (x = 0 and x = 0.3) obtained by sputtering deposition by varying the power of pulverization from 60 to 100 W. All layers have crystallized in the chalcopyrite structure with the preferential orientation in the (112) plane were obtained. The average grain size has the same order of magnitude as the initial powders. All films are generally p-type conduction with low resistivity values. Optical characterizations of the layers exhibit a good absorption in the visible range and the near infrared. The variation of the absorption coefficient as a function of photon energy enabled us to determine the energy of the optical gap. The values obtained for the different layers are consistent with the optimum for the photovoltaic conversion.

Hydrometallurgical processing of sulphide concentrates is an attractive method for the selective extraction of valuable metals. The dissolution of minerals in a leaching process involves several electrochemical parameters that need to be investigated• to ensure the development and growth of the base metal industry in South Africa. A study has been carried out to elucidate the leaching mechanism of a nickel-coppercobalt sulphide concentrate in an oxidative pressure-acid medium. The sulphide concentrate studied in this research, comprises mainly of the minerals pyrrhotite, (Fe1_xS) with x = 0 to 0.2, pentlandite, (Ni,Fe)9S8 and chalcopyrite, (CuFeS2). The leaching behaviour of these minerals was successfully studied by means of Atomic Absorption (AA) measurements, Scanning '•Electron Microscopy (SEM) and Moss bauer spectroscopy, after leaching took place in an oxidative pressure-acid medium. The dissolution of the valuable metals was achieved effectively with recoveries of well over 90% for nickel, copper and cobalt under the specific conditions studied. Mechanical activation by means of ultra fine milling improved metal extraction with an average of approximately 40%, after a leaching period of 150 minutes. The most suitable conditions for the oxidative pressure-acid leaching of the mechanically treated nickel-copper-cobalt sulphide concentrate in a dilute sulphuric acid medium were found to be: particle size 80% - 10J.Lm; temperature l10°C; oxygen partial pressure 10 bar; sulphuric acid concentration 30 kg/ton; solids content 15% by mass and an impeller agitation rate of 800 r/min. The values of the apparent activation energies of nickel, copper and cobalt, extracted from the sulphide concentrate, were found to be 20.6 (± 4.4) kJ/mol K, 33.6 (± 4.2) kJ/mol K and 17.4 (± 3.5) kJ/mol K respectively. / Thesis (MIng (Chemical Engineering))--Potchefstroom University for Christian Higher Education, 2001