Orientadores: Bernardino Ribeiro de Figueiredo, Jaime Wilson Vargas de Mello / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-08-09T03:35:47Z (GMT). No. of bitstreams: 1 Andrade_RenatoPereirade_M.pdf: 3230376 bytes, checksum: 0c97aa2a31e60b46ab3f3d65fdda0ace (MD5) Previous issue date: 2007 / Resumo: A drenagem ácida da mina (DAM) resulta da exposição de materiais dos sulfetados à água e ao oxigênio atmosférico. Nestes ambientes, a oxidação da arsenopirita causa a liberação do arsênio (As) para o meio ambiente. Tendo em vista o grande problema ambiental que é a dissolução do arsênio nas águas subterrâneas e superficiais, este trabalho propõe-se a verificar a eficácia do uso de calcário ('CaCO IND. 3¿) para controlar a dispersão desse metalóide no ambiente. Amostras parcialmente oxidadas de materiais sulfetados provenientes de minas de ouro do Brasil foram usadas para avaliar a mobilidade do arsênio em teste de colunas. Foram feitos testes de lixiviação em colunas passando água destilada, com intervalos de 2 semanas durante 156 dias. O comportamento das amostras ao teste estático de oxidação dos sulfetos foi semelhante, valores de balanço ácido-base (BAB) positivo, caracterizando a capacidade de geração de águas ácidas pelos materiais. Nos tratamentos onde o substrato era mais ácido (sem adição de carbonatos) a concentração de As, Fe e S nos lixiviados foram altas, enquanto nos tratamentos com adição de neutralizante (pH>7) foram encontrados baixos teores para esses elementos. Não obstante, a eficácia do carbonato sobre a mobilização do As foi menor na amostra que tinha maior quantidade de goethita. A alta correlação (r=0,749) entre o Fe e As nos lixiviados sugere que o As está sendo adsorvido nos oxi-hidróxidos formados pela oxidação do material sulfetado. A presença de enxofre nos lixiviados foi aumentada com a diminuição no pH devido ao maior poder da catálise bacteriana proporcionada pelo meio ácido. A arsenopirita teve sua velocidade de oxidação aumentada em pH baixo provavelmente devido à ação de bactérias Acidithiobacillos ferrooxidans, aumentando assim a geração de águas ácidas, e conseqüentemente, dissolvendo os oxi-hidróxidos de ferro, liberando o As que estava retido na sua estrutura. Os resultados corroboraram o uso do CaCO3 para controlar a dispersão de As em ambientes afetados por DAM. Entretanto a eficácia do tratamento com carbonato parece ser dependente da presença de óxidos-hidróxidos de ferro na amostra. Estes resultados podem ser usados para a remediação de áreas afetadas por drenagem ácida de mina e mobilização de As em materiais sulfetados parcialmente oxidados / Abstract: Acid mine drainage (AMD) results from the exposure of sulfide materials to atmospheric water and oxygen. In addition to AMD, oxidation of arsenopyrite and other As bearing sulfides can release arsenic (As) into the environment. In view of the risks to living organisms due to arsenic contamination of groundwater and surface water sources this work was carried out in order evaluate the effectiveness of lime ('CaCO IND. 3) to control the dispersion of this metalloid in the environment. Partially oxidized samples of sulfide bearing materials from gold mines in Brazil were used to evaluate the arsenic mobilization by leaching tests. Columns containing ground samples, with and without liming treatments, were leached with distilled water every two weeks during 156 days. The acid-base accounting (ABA) static tests classified the samples as potential acid forming materials. In the treatments without liming, As, Fe and S concentrations in the leachates were higher than those in the treatments with carbonate. Nevertheless, the effectiveness of liming and As mobilization were less in the sample containing goethite. High correlation between Fe and As concentrations in the leachates (r=0.749) suggests that iron oxides-hydroxides retained arsenic in the solid phase. Oxidation rates of As bearing sulfides were increased at low pH, probably due to the enhanced activity of bacteria (Acidithiobacillus ferrooxidans) and decreased rate of Fe precipitation, thus reinforcing generation of acid water, and consequently releasing As. Our results corroborate the use of lime to control the dispersion of As in AMD affected environments. However the effectiveness of the liming treatment seems to be dependent on the presence of iron oxides-hydroxides in the sample. These findings can be useful to remediate areas affected by acid mine drainage and arsenic mobilization in partially oxidized sulfide materials / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

La présente étude porte sur le problème de l'entreposage à long terme des déchets nucléaires. En France, il est prévu que les déchets radioactifs à haute activité et vie longue soient confinés dans un surconteneur en acier au carbone, puis stockés à une profondeur d'environ 450 m dans une formation argileuse (argilite). En raison de l'intense radioactivité, une température proche de 90°C est attendue à la surface de l'acier. Dans un premier temps, il a été nécessaire de synthétiser, par polarisation anodique à courant imposé, des couches de produits de corrosion susceptibles de se former en conditions de stockage. Les électrodes d’acier S235 ont été recouvertes d’une couche d’argilite broyée et immergées en solutions carbonatées. La synthèse a d’abord été effectuée à 25°C afin de déterminer les paramètres influant sur la nature des produits de corrosion, puis à 80°C de façon à se rapprocher des conditions réelles. Les composés obtenus dépendent de la concentration en NaHCO3, de la densité de courant imposée et du temps de polarisation. A 80°C, la magnétite Fe3O4 et la sidérite FeCO3 sont les principaux produits formés. La rouille verte carbonatée FeII4FeIII2(OH)12CO3.2H2O et la chukanovite Fe2(OH)2CO3 n'ont pu être détectées que localement dans certaines conditions. Des sulfures de fer, notamment la mackinawite, se forment en début d’expérience pour des densités de courants anodiques modérées. Dans la deuxième partie de l’étude, nous avons étudié l’influence des espèces sulfures sur un système constitué par l’acier et une couche de produits de corrosion modèle. Les modifications de cette couche préalablement formée, induites par les espèces sulfures, ont été plus particulièrement étudiées. Enfin, la dernière partie de notre travail de recherche a porté sur l’étude des couplages galvaniques pouvant s’établir entre deux zones de la surface de l’acier recouvertes de produits de corrosion différents. Nous avons notamment étudié les couplages impliquant la magnétite Fe3O4, principal composé conducteur susceptible de se former en conditions de stockage. / The present study relates to the problem of the long-term interim storage of nuclear wastes. In France, it is envisaged that high-level radioactive wastes will be confined in a glass matrix, stored in a stainless steel canister, itself placed in a carbon steel overpack. The wastes will then be stored at a depth of ~450 m in a deep geological disposal, drilled in a very stiff (indurated) clay (argillite) formation. A temperature as high as 90°C is expected at the steel surface because of the intense radioactivity. Anodic polarization at applied current density was used to synthetize corrosion product layers likely to be formed in storage conditions. The S235 steel electrodes were covered by a layer of argillite and dipped in carbonated solutions. The synthesis was first achieved at 25°C to determine the parameters controlling the nature of the corrosion products and then at 80°C to be closer to the real conditions. The nature of the obtained compounds proved to be dependent on NaHCO3 concentration, on current density and on polarization time. At 80°C, magnetite Fe3O4 and siderite FeCO3 were the main identified compounds. Carbonate green rust FeII4FeIII2(OH)12CO3.2H2O and chukanovite Fe2(OH)2CO3 were detected locally in some experiments. Iron sulfides, mainly mackinwaite, also formed at the beginning of the experiments with a moderate current density. In the second part of the study, the influence of sulfide species on the steel / model corrosion products layer system was investigated. The modifications of the layers previously formed by anodic polarization induced by sulfide species were more particularly studied. Finally, the last part of our research was focused on the effects of a galvanic coupling that could appear between two areas of the steel coated by different corrosion products. In particular, galvanic couplings involving magnetite Fe3O4, the main conductive compound likely to form under storage conditions, were studied.

Acid mine drainage is a well known environmental pollutant, not only in South Africa, but throughout the world, and the use of microbial processes in the treatment of these wastes has been the subject of investigation over past decades. Lignocellulose packed-bed reactors have been used in passive treatment systems, and, although effective initially, they show early decline in performance while the packing material remains largely un-utilized. Little is known about this phenomenon which remains a severe constraint in the development of efficient passive mine water treatment systems. It has been proposed that the degradation pathways of the complex lignocellulose substrate may be limited in some way in these systems during the manifestation of this effect. This study has addressed the problem using a molecular microbial ecology methodology in an attempt to relate trophic functions of the microbial population to the physico-chemical data of the system. A field-scale lignocellulose packed-bed reactor located at Vryheid Coronation Colliery (Northern Kwa-Zulu Natal province, South Africa) was monitored for six years and the results showed the classic profile of performance decline related to a slowdown in sulphate reduction and alkalinity production. The reactor was decommissioned , comprehensive samples were collected along the depth profile and the microbial populations investigated by means of 16S rRNA gene methodology. The population was found to include cellulolytic Clostridia spp., CytophagaIFlavobacterlBacteroidetes, Sphingomonadaceae and as yet uncultured microorganisms related to microbiota identified in the rumen and termite gut. These are all known to be involved as primary fermenters of cellulose. Oesulphosporosinus was present as sulphate reducer. A comparison of substrata sampling and population distribution suggested that spatial and temporal gradients within the system may become established over the course of its operation. Based on these findings, a laboratory-scale reactor was constructed to simulate the performance of the packed-bed reactor under controlled experimental conditions. The laboratory-scale reactor was operated for 273 days and showed comparable performance to that in the field in both biomolecular and physicochemical data. Clearly defined trophic niches were observed. These results suggested that a sequence of events does occur in lignocellulose degradation over time. Based on the spatial and temporal column studies, a descriptive model was proposed to account for these events. It was found that fermentative organisms predominate in the inlet zone of the system using easily extractable compounds from the wood, thus providing feedstock for sulphate reduction occurring in the succeeding compartments. Production of sulphide and alkalinity appears to be involved in the enhancement of lignin degradation and this, in turn, appears to enhance access to the cellulose fraction. However, once the readily extractables are exhausted, the decline in sulphide and alkalinity production leads inexorably to a decline in the overall performance of the system as a sulphate reducing unit operation. These observations led to the proposal that with the addition of a limited amount of a readily available carbon source, such as molasses, in the initial zone of the the reactor, the ongoing generation of sulphide would be sustained and this in turn would sustain the microbial attack on the lignocellulose complex. This proposal was tested in scale-up studies and positive results indicate that the descriptive model may, to some extent, provide an account of events occurring in these systems. The work on sustaining lignocellulose degradation through the maintenance of sulphate reduction in the initial stages of the reactor flow path has led to the development of the Degrading Packed-bed Reactor concept and that, has subsequently been successfully evaluated in the field.

Ce travail de thèse avait pour objectif de développer une méthode basée sur l’étude de la composition isotopique du soufre (δ 34S) permettant de déterminer l’origine, biotique/abiotique, des sulfures de fer au sein des couches de produits de corrosion (CPC). Puis, il s’agissait d’appliquer la méthodologie développée à des systèmes réels afin de déterminer les mécanismes de formation de ces sulfures de fer. Des méthodes d’analyse isotopique du soufre adaptées aux liserés de sulfures de fer micrométriques observés dans les systèmes réels ont été développées en nanoSIMS et ToF-SIMS. L’étude de sulfures de fer formés en milieu carbonaté anoxique en présence, ou non, de bactéries sulfato-réductrice a permis de valider l’emploi de ces méthodes pour la détermination de l’origine des sulfures de fer. L’application de ces méthodes isotopiques couplées à la caractérisation des sulfures de fer dans les systèmes réels a mis en évidence 2 faciès. Le faciès 1 pour lequel les sulfures de fer sont situés en externe de la CPC. Ils résultent de la migration des ions Fe2+ produits au niveau du métal jusqu’aux zones riches en ions S2- d’origine biotique. Les vitesses de corrosion y sont inférieures à 20 μm/an pour les systèmes de laboratoire et à 5 µm/an pour les objets archéologiques. Et le faciès 2 pour lequel la forte présence de phases conductrices dans la CPC entraîne une délocalisation des électrons, conduisant à la migration des ions S2- d’origine biotique vers le métal où ils précipitent sous forme de sulfures de fer. Ce faciès présente de fortes avancées de corrosion locales (200 µm) qui seraient dues à l’accumulation de phénomènes de corrosion par les chlorures et de biocorrosion. / The first goal of this project was to develop a methodology based on the study of the sulfur isotopic composition enabling the determination of iron sulfides origin, biotic or abiotic, within the corrosion products layers (CPL). Then, the aim was to apply this methodology to real corrosion systems in order to determine the mechanisms of iron sulfides formation. Sulfur isotopic analyses methodologies, adapted to micrometric iron sulfides layers observed in real corrosion systems, were developed in nanoSIMS and ToF-SIMS. The study of iron sulfides formed in anoxic carbonated medium with or without sulphate-reducing bacteria validated the use of these methods for the determination of iron sulfides origin. The application of these methods coupled with the precise characterization of irons sulfides formed in the real corrosion systems show two kind of corrosion pattern. In pattern 1, the iron sulfides are localized in the external part of the CPL. They result from the Fe2+ migration from the metal surface to areas rich in biotic S2-. In this pattern, corrosion rates are lower than 20 μm/year for laboratory systems, and lower than 5 μm/year for archaeological objects. In pattern 2, the large presence of conductive phases in the CPL results in the delocalization of electrons, and so a disequilibrium of the charges at the metal’s surface. That leads to the migration of biotic S2- in the CPL till the metal where they precipitate in iron sulphides. This pattern shows high corrosion rates (~100 μm/an) that might be resulting from the accumulation of biocorrosion and chloride corrosion mechanisms.

South Africa is renowned for its mining industry. The period over which the polluted waters from the existing and abandoned mines will require treatment has driven research into the development of passive treatment systems. These waters are characterised by a low pH, high concentrations of heavy metals, high levels of sulphate salts and low concentrations of organic material. The biological treatment of these waters has been a subject of increasing focus as an alternative to physicochemical treatment. The utilisation of lignocellulose as a carbon source has been restricted by the amount of reducing equivalents available within the lignocellulose matrix. After a few months of near 100% sulphate reduction, it was found that although there was a large fraction of lignin and cellulose remaining, sulphate reduction was reduced to less than 20%. The present study demonstrated that lignocellulose can be utilised as a carbon source for sulphate reduction. It was established that lignocellulose degradation was enhanced under biosulphidogenic conditions and that lignin could be degraded by a sulphate reducing microbial consortium. It was established using lignin model compounds synthesized in our laboratory, that the bonds within the lignin polymer can be cleaved within the sulphidic environment. The presence of cellulolytic enzymes, using CMCase as a marker enzyme, was detected within the sulphate reducing microbial consortium. Based on the results obtained a descriptive model was formulated for the degradation of lignocellulose under biosulphidogenic conditions. It was determined that the initial reduction in sulphate observed using lignocellulose as a carbon source was due to the easily extractable components. The degradation of which resulted in the production of sulphide, which aided in the degradation of lignin, allowing greater access to cellulose. Once the easily extractable material is exhausted, the cycle is halted, unless the sulphide production can be maintained. This is the focus of an ongoing project, testing the hypothesis that an easy to assimilate carbon source added after exhaustion of the easily extractable material, can maintain the sulphide production.

Porphyry copper deposits represent one of the largest copper reserves on Earth. They typically contain large, low-grade reserves of primary ore and higher-grade, supergene enrichment blankets of sulfide and oxide ores. Understanding the mineralogy of porphyry copper ores and ores related to porphyry copper systems is exceedingly important for several reasons, foremost of which are the information provided by ore mineral parageneses, assemblages, and mineral chemistry on evolution of these magmatic-hydrothermal systems, and information on mineral processing characteristics of the ores. The focus of this work is to better understand the mineralogy of supergene copper sulfides in porphyry copper systems and hypogene base metal lodes related to porphyry copper systems, and use this mineralogical knowledge to improve our understanding of the processes responsible for ore formation. The objectives of this study are accomplished by two means: focusing on the crystallography and crystal chemistry of minerals, and then applying this mineralogical knowledge to a supergene sulfide enrichment blanket and hypogene massive sulfides from base metal lodes in southeastern Arizona. The discovery of a new mineral, natropalermoite, NaSr2Al4(PO4)4(OH)4, provided the opportunity to use single-crystal X-ray diffraction to solve a crystal structure, and electron-probe microanalysis (EPMA) to study the crystal chemistry of natropalermoite and how the accommodation of Na in the structure changes lengthens the unit cell along [010] and shortens it along [100] and [001] compared to its lithium analogue, palermoite. Solution of the crystal structure of the mineral nickelskutterudite, (Ni,Co,Fe)As3, allowed for the investigation of anion deficiency in minerals of the skutterudite group, a problem whose solution has eluded researchers for nearly 100 years. Two skutterudite (CoAs3) and two nickelskutterudite samples were analyzed using single-crystal X-ray diffraction, EPMA, and procrystal electron density. The results showed fully-occupied anion sites and a cation surplus, which was accommodated in the icosahedral site, proving that minerals of the skutterudite group are not anion deficient. This mineralogical knowledge was applied to the supergene enrichment blanket in the Western Copper section of the Morenci mine, Greenlee County, and hypogene massive sulfide deposits associated with a porphyry copper deposit at Bisbee, Cochise County, Arizona. This is one of very few studies of supergene sulfide blankets ever completed. One drill hole through the supergene blanket at Western Copper was examined using ore microscopy and EPMA. Results showed dominant (Cu+Fe):S ratios of 1.80 ± 0.05, 1.92 ± 0.03, and 1.10 ± 0.10, with higher (Cu+Fe):S dominant high in the blanket and low ratios dominant near the base of the blanket. These values were interpreted to be controlled by activity of Cu2+, Fe2+, and Fe3+ in solution. Massive sulfide deposits at Bisbee were investigated using ore microscopy and EPMA in order to correct the previous conflicting reports of the mineralogy and paragenesis of this famous district and interpret constraints on conditions of ore-forming fluids. Results show four types of ore: chalcopyrite-rich with hematite and/or pyrite, bornite-rich, chalcocite-rich, and a Zn-Pb association. Chalcopyrite-rich ores formed first, followed by bornite-rich and chalcocite-rich ores. All ores were formed at relatively shallow depths from oxidized, moderately sulfur-rich fluids; early fluids were higher temperature and later fluids were lower temperature and considerably more sulfidized. Zinc-lead ores formed early and were continuously dissolved and reprecipitated distal to Cu-mineralization. These patterns are similar to many other base-metal lode districts worldwide, however Bisbee contains more Zn-Pb ore than other districts with hematite-containing ores and less than those without hematite.

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No description available.

Metal chalcogenides (sulfides, selenides and tellurides) are materials of current interest due to their peculiar properties such as optoelectronic, magnetooptic, thermoelectric and piezoelectric displays. These semiconducting materials have potential applications in solar cell devices, infrared detectors and ambient thermoelectric generators. Previously, these materials have been deposited by multiple-source precursor route with several problems associated with this technique. This work describes the synthesis of metal complexes (Zn, Cd, Fe, Ni, Pd, Pt) using the imidodichalcogenodiphosphinate ligand (Woollins ligand). Their thermal decomposition together with structural and spectroscopy analysis was carried out. The complexes were used as single source precursors for the deposition of cadmium selenide, cadmium phosphide, cadmium sulfide, zinc selenide, iron selenide and the tellurides of nickel, palladium, platinum and iron as thin films and powders. These were deposited by AACVD and pyrolysis. The deposited thin films and powders were characterised by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), X-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID). The cadmium complexes [Cd{iPr2P(Se)NP(Se)iPr2}2] and [Cd{iPr2P(S)NP(Se)iPr2}2] deposited the mixture of hexagonal CdSe and monoclinic Cd2P3 films at the flow rate of 160 sccm at 475 and 500 °C. At the flow rate of 240 sccm, only hexagonal CdSe was deposited from [Cd{iPr2P(Se)NP(Se)iPr2}2] at all temperatures. Hexagonal CdS and the mixture of orthorhombic Cd6P7/cubic Cd7P10 were deposited from [Cd{iPr2P(S)NP(S)iPr2}2]. The zinc complexes [Zn{iPr2P(Se)NP(Se)iPr2}2] and [Zn{iPr2P(S)NP(Se)iPr2}2] both deposited cubic ZnSe at all temperatures with the flow rates of 160 and 240 sccm. The iron complexes [Fe{(SePPh2)2N}2] and [Fe{(SePPh2NPPh2S)2N}2] deposited orthorhombic FeSe2 mixed with monoclinic Fe3Se4 by pyrolysis at 500 and 550 °C. An unresolved pattern was observed from the complex [Fe{(SePPh2NPPh2S)2N}2] at 550 °C. XPS analysis of the deposited FeSe2 showed the surface oxidation of the material, while the magnetic measurements on the sample using SQUID confirmed its ferromagnetic properties. The telluride complexes of nickel, palladium, platinum and iron deposited the metal telluride respectively as: hexagonal NiTe, hexagonal PdTe, hexagonal PtTe2 (mixed with rhombohedral PtTe) and hexagonal FeTe2. Conductivity studies on NiTe and PdTe revealed them to be insulators, while the magnetic measurements on FeTe2 indicated its antiferromagnetic behaviour.

Conversion of renewable energy resources (such as solar and wind) through water splitting to hydrogen and oxygen has attracted increasing attention. The sole product of hydrogen combustion is water, rendering a carbon-neutral energy cycle. Water splitting consists of two redox half reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Both of these two transformations involve multi- electron/proton movement and thus are kinetically sluggish. In order to accelerate the reaction rates for practical application, efficient catalysts are needed. State-of-the-art catalysts for water splitting are usually composed of noble metals, such as platinum, ruthenium, and iridium, whose scarcity and high cost limit their wide employment. Consequently, it is of critical importance to develop competent and non-precious catalysts via low-cost preparation. Owing to the thermodynamic convenience and potential application in proton exchange membrane and alkaline electrolyzers, traditionally, most HER catalysts were developed under strongly acidic conditions while OER catalysts under strongly alkaline conditions. In order to accomplish overall water splitting, the coupling of HER and OER catalysts in the same electrolyte is mandatory. This thesis will summarize our recent efforts towards developing 1st-row transition metal-based sulfides and phosphides for electrocatalytic water splitting under ambient conditions.