A interação espontânea entre pirita e íons mercúrio foi acompanhada por meio de voltametria cíclica. Eletrodos de carbono grafite e parafina sólida recobertos com grãos de pirita foram mergulhados em soluções contendo íons mercúrio, retirados, lavados e introduzidos na solução de trabalho (solução tampão de ácido acético 0,25M e acetato de sódio 0,25M). Eletrodos que previamente estiveram imersos na solução contendo íons Hg(II) apresentaram um potencial de circuito aberto maior que o potencial típico da pirita na mesma solução. Com o elevado número de novos processos eletroquímicos detectados verifica-se a complexidade do sistema pirita/íons Hg(II) e que mais de uma espécie de mercúrio se deposita espontaneamente sobre o mineral. A possibilidade de formação de sulfeto de mercúrio sobre a pirita foi investigada construindo eletrodos com duas espécies de sulfeto (HgS(preto) e HgS(vermelho)). A resposta eletroquímica do HgS(preto) apresenta processos catódicos e anódicos semelhantes aos processos observados no voltamograma da pirita, após sua interação com íons Hg(II). Entretanto, o perfil eletroquímico do HgS(vermelho) não apresenta qualquer semelhança com voltamograma do sistema pirita/íons Hg(II). Realizou-se estudos para verificar a influência de variáveis químicas (concentração e pH) e físicas (tempo, temperatura e transporte de massa). Observou-se que o transporte de massa acelera o processo de adsorção de espécies de mercúrio sobre a pirita e determinou-se a melhor condição experimental de retirada de íons mercúrio. / The spontaneous interaction between pyrite and mercury ions was studied employing cyclic voltammetry. The electrodes, consisting of solid paraffin and graphite covered by pyrite particles, were immersed in solutions containing mercury ions. After mineral/mercury ions interaction, the electrode was washed and introduced in the working solution (acetic acid 0,25M and acetate of sodium 0,25M). Eletrodes which were immersed in the solution containing mercury ions, presented a open circuit potential more positive than that of the pyrite in the same solution. The high number of new electrochemical processes detected denotes the complexity of the system pyrite/mercury ions and indicates that several species of mercury may deposit spontaneously on the mineral surface. The possibility of formation of mercury sulfide on the pyrite was investigated employing electrodes constructed with HgS(Black) and HgS(red). The electrochemical response of HgS(black) presents cathodic and anodic processes similar to that observed in the voltammogram of pyrite, after interaction with mercury ions. The potentiodynamic profile of HgS(red) it does not present any similarity with the voltammogram of the system pyrite/mercury ions. Studies were carried out to verify the influence of chemical (concentration and pH) and physical variables (time, temperature and mass transport). It was observed that the mass transport accelerates the adsorption process of mercury species on the pyrite surface and the optimal experimental condition for scavenging mercury ions was determined.

Coal is a combustible sedimentary rock composed of a complex heterogeneous mixture of mostly organic constituents and minor inorganic phases. Coal is a vital energy resource providing more than half of the electric power generated in the United States. However, coal combustion is responsible for a significant portion of anthropogenic release of different toxic elements including sulfur into the environment. Therefore, deciphering the residence of the different fractions of sulfur in coal is essential. In this study, eight different sulfur fractions from Pennsylvanian-age coal samples collected from the Murphysboro, Mount Rorah, Springfield (No. 5), and Herrin (No. 6) coal seams from the Illinois Basin were separated using a wet sequential chemical extraction procedure in order to evaluate the coal quality and to test the efficiency of this technique. The average weight percent of sulfur in each seam was 1.98%, 2.1%, 2.26%, and 2.4%, respectively, showing that the coal samples were of medium-sulfur-type. Among the eight different sulfur fractions extracted, kerogen sulfur was found to be the most abundant, followed by sulfate sulfur, fulvic acid sulfur, pyritic sulfur, and elemental sulfur. However, XRD and coal petrography revealed the significant amounts of pyrite still present in the coal sample even after pyritic sulfur extraction, indicating that the finely disseminated pyrite in the coal was not completely removed during the sequential extraction. The sulfur isotopic study showed the average δ34S values of pyritic sulfur and sulfate sulfur in the Murphysboro coals as 7.82 / and 2.44 / and that of Mount Rorah coals were 10.68 / and 7.87 /, respectively. The heavier δ34S values of pyritic sulfur compared to the sulfate sulfur can be explained by a bacterial sulfate reduction (BSR) model in a closed system where most of the sulfate reservoir was consumed at the top of the seam. Similarly, the average δ34S values of elemental sulfur for the same coals (8.05 / and 14.54 /, respectively) were also heavier than the sulfate sulfur which suggests the pyrite oxidation followed by disproportionation of intermediate sulfur species. The δ34S values of handpicked pyrite samples and the mercury concentration for the Herrin (No.6) and Springfield (No. 5) coals indicated at least two stages of hydrothermal inputs into these coal seams. SEM/EDS and petrographic microscopy of the Illinois coal samples revealed the presence of different syngenetic and epigenetic sulfur-containing minerals such as framboidal pyrite, euhedral pyrite, galena, anhydrite, anglesite, and also non-sulfur containing minerals such as calcite and clay. Based on these results, it can be said that sulfur in Illinois coals is present in different phases extractable by wet sequential chemical extraction however; care should be taken during each individual extraction step to obtain better results.

Submitted by Laíze Fernanda Pereira null (laize_fernandapereira@yahoo.com.br) on 2016-10-03T11:51:03Z No. of bitstreams: 1 Dissertação Laize Fernanda Pereira_versão final.pdf: 1765685 bytes, checksum: c480da42091df39cbc80f15e56710bec (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-10-05T17:05:35Z (GMT) No. of bitstreams: 1 pereira_lf_me_araiq.pdf: 1765685 bytes, checksum: c480da42091df39cbc80f15e56710bec (MD5) / Made available in DSpace on 2016-10-05T17:05:35Z (GMT). No. of bitstreams: 1 pereira_lf_me_araiq.pdf: 1765685 bytes, checksum: c480da42091df39cbc80f15e56710bec (MD5) Previous issue date: 2016-09-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O carvão é a mais importante fonte de energia não renovável de origem fóssil do planeta. Um dos maiores problemas em sua utilização como fonte energética se deve à presença de enxofre na forma orgânica e inorgânica (pirita FeS2). Durante a combustão do carvão, são lançados na atmosfera vários gases, entre eles o SO2 que causam problemas ambientais como a formação de chuva ácida além da corrosão de “boilers”, oleodutos subterrâneos, instalações metálicas e maquinários de minas. Há vários processos físicos e químicos para redução do enxofre antes da combustão do carvão, no entanto, tais métodos são dispendiosos, pois necessitam de condições extremas de temperatura e pressão. Os métodos biológicos de dessulfurização deste combustível fóssil têm demonstrado serem mais eficazes para tal fim. Neste contexto o presente trabalho utilizou bactérias oxidantes de ferro e/ou enxofre, Acidithiobacillus ferrooxidans e Acidithiobacillus thiooxidans a fim de obter uma redução no conteúdo de enxofre pirítico do carvão fornecido pela Carbonífera do Cambuí. Ensaios de biolixiviação em frascos sob agitação foram conduzidos em diferentes condições com a finalidade de acompanhar a cinética de dissolução do enxofre pirítico na amostra mineral. Na fase líquida a evolução dos seguintes parâmetros foi monitorada: pH, Eh e íons ferrosos. A fase sólida foi caracterizada posteriormente através de medidas de difração de raio-X (DRX) e espectroscopia de infravermelho (FTIR). A quantificação parcial do enxofre total foi avaliada utilizando Analisador Preiser Mineco de acordo com as normas ABNT NBR 8295 e suas formas (pirítica, sulfática e orgânica) foram analisadas por normas ASTM. Os ensaios utilizando tais microrganismos obtiveram redução de 44% no teor de enxofre total e de 90% no teor de enxofre pirítico. Como resultado das análises de raio-X observou-se a redução de picos característicos da pirita e o surgimento de uma nova fase cristalina durante o tratamento biológico. Os espectros de infravermelho indicaram que os microrganismos utilizados neste estudo foram capazes de interagir apenas com a fase inorgânica do carvão. Estes ensaios de bancada forneceram parâmetros para um posterior trabalho em escala de bancada utilizando colunas de biolixiviação. / Coal is the most important non-renewable energy source of fossil origin in the world. One of the major problem in using coal as an energy source is the presence of sulfur in the organic and inorganic form (pyritic FeS2). During combustion of coal, SO2 is released in the atmosphere, causing many environmental problems such as the formation of acid rain, beside this sulfur also causes the corrosion of boilers and installations of underground metal pipelines. There are several physical and chemical processes to reduce sulfur in the coal before combustion, however, such methods are very costly, with the use of extreme temperatures and pressures. The biological method for desulfurization of the fossil fuel has proved to be more effective for such purpose. In this context, the present work evaluated the use iron and/or sulfur oxidizing bacteria, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans in order to obtain a maximum reduction in the pyritic sulfur content of the coal supplied by the Carbonífera Cambuí. For this purpose, the bioleaching tests were performed in shake flasks and conducted under different conditions in order to follow the pyritic sulfur kinetics of dissolution of the mineral sample. In the liquid phase, the following parameters such as pH, Eh and ferrous ions were monitored. The solid phase was characterized subsequently by means of measurements of X-ray diffraction (XRD) and infrared spectroscopy (FTIR). The partial quantification of total sulfur was evaluated using Preiser Mineco analyzer according to ABNT NBR 8295 standards and other forms such as pyritic, sulfatic and organic were analyzed by ASTM. The tests using such microorganisms obtained 44% reduction in total sulfur and 90% pyritic sulfur. The result of ray-X analyzes showed the reduction of characteristic peaks of pyrite and the emergence of a new crystalline phase during biological treatment. Infrared spectra indicated that the microorganisms used in this study were able to interact only with the inorganic phase coal. These bench tests provided parameters for further laboratory scale using bioleaching column.

The organic-rich mudrocks of the Jurassic Fernie Formation in British Columbia, Canada contain unusual silica concretions. The silica originated from dissolved volcanic ashes found in the Highwood Member. A lack of radial trends in d13C and internal zonation demonstrate that these concretions grew pervasively. Stable isotope data from calcite inter-grown within the silica matrix (d13C and d18O) indicate that the concretions formed during sulfate reduction and methanogenesis. The d34S revealed a suppressed sulfur fractionation and suggest that they formed in a system that became progressively closed. The Fernie concretions offer insight into the formation of siliceous concretions in marine environments.

Mining activities, particularly coal mining, lead to the excavation of large volumes of pyrite rich soils. When exposed to air (oxygen) and water these pyrite complexes are oxidised to form highly acidic and corrosive wastewaters collectively termed acid mine drainage (AMD). Containing elevated levels of sulphates (SO42-) and toxic dissolved heavy metals, AMD seeping from mining sites, active or abandoned, poses a major environmental risk to aquatic bio-systems – not only in South Africa but globally. Chemical neutralization of AMD is expensive and often challenging. Biological sulphate reduction provides a promising and cheaper alternative to the treatment of sulphate rich wastewaters. Little, however, is known about the microbial communities involved in biological treatment systems and the effect of external factors thereon. Studying microorganisms in their natural environment is extremely difficult. The limitations of culture-based methods only provide a limited insight into the bacterial diversity of natural habitats and the microbial communities present. With the progressive advances in molecular biology, non culture-based tools such as DGGE, FISH and more recently t-RFLP allow easier and much more accurate studies of microbial communities within their natural as well as man-made environments. This study specifically investigated the use of t-RFLP to study microbial communities and dynamics within sulphate removing bioreactors. The set up and optimization of a t-RFLP system to specifically study microbial communities from sulphate removing bioreactors were investigated and the applicability of t-RFLP demonstrated. Copyright / Dissertation (MSc)--University of Pretoria, 2009. / Microbiology and Plant Pathology / unrestricted

Carbon matrix composite (CMC) electrode and surface conducting (SC) electrode have been developed to study the copper-activation and the subsequent xanthate adsorption on insulating sphalerite. Fabricating CMC electrode involves embedding sphalerite particles in carbon to form a carbon matrix composite; and SC electrode is designed by contacting a platinum wire to the sphalerite surface. When these electrodes are activated by heavy metal ions such as copper, a conducting layer is formed on the mineral surfaces that allows dynamic electrochemical studies to be conducted. Voltammetric studies on the copper activated CMC:ZnS electrodes in inert electrolytes show that although the activation product and kinetics may differ with pH, copper-activation occurs at all pH ranges. At acidic pH, a Cu2S-like activation product was formed at open circuit. When activation was conducted at near neutral and alkaline pH at open circuit, the surface products formed were identified to be CuS-like. It was also established that the amount of copper uptaken by sphalerite is strongly dependent on the time of activation and on the electrochemical potential applied during activation. Activation at potentials positive of the rest potential decreases the amount of copper on the surface. Indeed, activation at potentials of 50 to 100 mV more positive of the rest potential in the activating solution completely inhibits copper activation. This result is consistent with the anodic stripping voltammetry that shows copper can be removed from the surface of sphalerite at oxidizing potentials. Activation at potentials mildly negative of the rest potential causes a progressive increase in the amount of copper on the surface, consistent with the diffusion controlled reduction process between ZnS and Cu2+ ions observed in the activating solution. At very low potentials, however, elemental copper is formed, which may worsen the selectivity of the sphalerite flotation. Controlled potential contact angle measurements showed that xanthate adsorption does occur on copper-activated sphalerite at all pH ranges. However, the contact angles and flotation recovery decrease at near neutral pH. This problem is caused by the adsorption of the copper-hydroxy species on the activated sphalerite surface. It was found that addition of small amount of complexing reagent can improve the flotation recovery at the near neutral pH. The results obtained in the present work show that potential control of the activation process can provide a means of controlling copper uptake and, hence, the selectivity and recovery of sphalerite flotation. The development of CMC:ZnS and SC:ZnS electrodes provides a practical and reliable way to quantitatively estimate the amount of copper uptake on sphalerite surface after activation. / Ph. D.

Thèse ou mémoire avec insertion d’articles / La susceptibilité à la lixiviation de l'or associé à la pyrrhotite issue de calcines de pyrite a été étudiée en mettant l'accent sur les effets des conditions/environnement de grillage et des contacts galvaniques durant la cyanuration. La première partie du travail a examiné le traitement thermique de la pyrite sous différentes atmosphères oxydantes et non-oxydantes, et les résultats ont montré que le grillage à l'air favorisait la coexistence de plusieurs pyrrhotites, tandis que les environnements d'hélium, de CO₂ et de vapeur donnaient à chaque fois une seule stoechiométrie de pyrrhotites hexagonales avec une carence croissante en fer et une porosité décroissante. La deuxième partie du travail s'est orientée à l'utilisation d'une cellule de lixiviation à double couche pour contrôler les contacts électrochimiques entre la poudre d'or et la pyrite brute/grillée pendant la cyanuration. Il a été constaté que la topologie de la pyrrhotite et des oxydes de fer était influencée par le type de traitement de rôtissage, ce qui pouvait avoir un impact sur la cinétique de dissolution de l'or, notamment dans les cas impliquant de l'or réfractaire ou une récalcitrance au prég-robbing du minerai. Par conséquent, lorsqu'il s'agit d'extraire de l'or encapsulé associé à de la pyrite réfractaire qui nécessite un traitement thermique, le grillage à l'air était la plus efficace pour la lixiviation de l'or des calcinés, surpassant à la fois les environnements inertes et oxydatifs doux. De plus, la présence de CO₂ (et/ou d'humidité) dans l'atmosphère de grillage pour imiter la combustion de matière carbonée pourrait améliorer modérément la récupération de l'or, et cela, indépendamment de la présence ou non de contact galvanique avec la pyrite grillée. / The susceptibility of gold associated with pyrrhotite in roasted pyrite calcines to leaching was investigated, with emphasis on the effects of the roasting environment and galvanic contacts under cyanidation conditions. The first part scrutinized the thermal treatment of pyrite under different oxidizing and non-oxidizing atmospheres, and demonstrated that air roasting promoted the coexistence of multiple pyrrhotites, while He, CO₂, and steam environments resulted in single hexagonal pyrrhotites with increasing iron deficiency and decreasing porosity. The second part employed a bilayer leach cell to control the electrochemical contacts between gold powder and raw/roasted pyrite during cyanidation, and found that the topology of pyrrhotite and iron oxides was influenced by the type of roasting treatment, which could impact the kinetics of gold dissolution, particularly in cases involving refractory gold or ore preg-robbing recalcitrance. Therefore, when it comes to extracting encapsulated gold associated with refractory pyrite that requires heat treatment, air roasting was the most effective for leaching gold from calcine, outperforming both inert and mild oxidative environments. In addition, the presence of CO₂ (and/or moisture) in the roasting atmosphere to mimic the combustion of carbonaceous material could moderately enhance gold recovery regardless of whether or not there was galvanic contact with the roasted pyrite.

Dans la région de Trois-Rivières, de nombreuses résidences ont été construites sur une fondation de béton incorporant des granulats riches en sulfures de fer, notamment de la pyrrhotite et de la pyrite. Plus de trois cents échantillons ont été prélevés au sein de seize fondations de maisons montrant différents degrés d’endommagement, de très faible à très élevé, afin de les analyser et de contribuer à une meilleure compréhension des mécanismes en cause. Plusieurs types d’essais pétrographiques, mécaniques et chimiques ont ainsi été effectués sur ces échantillons, tant sur le terrain qu’en laboratoire. Le suivi de l’expansion et du développement de la fissuration sur des blocs prélevés au sein de fondations résidentielles a permis de démontrer le potentiel résiduel d’endommagement du béton lorsque soumis aux conditions climatiques naturelles. De plus, les résultats des travaux effectués sur les blocs suggèrent que la méthode de l’indice de fissuration est un bon outil du suivi l’évolution de l’endommagement du béton. Finalement, les résultats des travaux effectués en laboratoire suggèrent que le Damage Rating Index et le Stiffness Damage Test ont la capacité de quantifier l’état d’endommagement des bétons détériorés fabriqués avec des granulats incorporant des sulfures de fer. / In the Trois-Rivières area, many houses were built on a concrete foundation made with aggregates containing large amounts of iron sulfides, such as pyrrhotite and pyrite. To allow for a better understanding of the oxidation mechanism, more than three hundred samples were extracted from sixteen foundations, showing different degrees of damage. A variety of petrographic, mechanical and chemical tests were conducted on these samples, in the laboratory as well as in the field. The monitoring of the development of expansion and cracking in the concrete blocks taken from residential foundations demonstrated a potential for residual concrete deterioration when exposed to natural environmental conditions. Furthermore, results of experiments performed on the blocks suggest that the cracking index method is a good indicator of the evolution of damage. Finally, laboratory testing suggests that the Damage Rating Index and the Stiffness Damage Test can potentially quantify damage suffered by deteriorated concrete made with aggregates incorporating iron sulfide minerals.

Road construction through sulfidic materials in Virginia has resulted in localized acid rock drainage (ARD) that threatens water quality, fill stability, integrity of building materials, and vegetation management. The objectives of this study were: i) to develop a state-wide sulfide hazard rating map based on characterization of the geologic formations associated with acid roadcuts, ii) to estimate depth to sulfidic sediments in the Coastal Plain based on landscape relationships, and iii) to evaluate potential acidity testing procedures on diverse materials. Geologic formations associated with acid roadcuts were characterized by potential peroxide acidity (PPA) and S content, and grouped into four categories. Listed in order of increasing severity, these formations included: the Tabb Formation (Coastal Plain), the Lynchburg Group of the Ashe Formation (Blue Ridge), the Chesapeake Group and Lower Tertiary deposits (Coastal Plain), the Millboro shale, Marcellus shale, Chatanooga shale and Needmore Formation (Valley and Ridge), and the Quantico Formation (Piedmont). Evaluation of landscape parameters near Richmond, Virginia, indicated that the likelihood of encountering sulfidic materials within a given depth at a specific location was related to elevation and mapped soil types. Elevation and soil map units were assigned to risk classes to indicate the likelihood of encountering sulfides within a depth of 9 m. Comparison of PPA and S content for 296 diverse samples indicated that S may serve as a screening tool to evaluate materials without carbonates. Comparison of PPA and conventional Acid-Base Accounting (ABA) for 14 diverse samples indicated that PPA and ABA were highly correlated, with PPA yielding 0.60 to 0.95X the amount of acidity as ABA. Potential acidity by Soxhlet extraction and PPA were equivalent for 3 of 4 diverse samples. Average acidity and metal contents of leachate from Soxhlet extractors were correlated with acidity and metals of road drainage. Sulfide hazard analysis should be an essential step in the pre-design phase of highway construction and other earth-disturbing activities. / Ph. D.

Although mining is essential to life in our modern society, it generates huge amounts of waste that can lead to acid mine drainage (AMD). Most of these mine wastes occur as large piles that are open to the atmosphere so that air and water vapor can circulate through them. This study addresses the reactions and transformations of the minerals that occur in humid air in the pore spaces in the waste piles. The rate of pyrite oxidation in moist air was determined by measuring over time the change in pressure between a sealed chamber containing pyrite plus oxygen and a control. The experiments carried out at 25?C, 96.8% fixed relative humidity, and oxygen partial pressures of 0.21, 0.61, and 1.00 showed that the rate of oxygen consumption is a function of oxygen partial pressure and time. The rates of oxygen consumption fit the expression (dn/dt=(3.31x10^-7)(P^0.5)(t^-0.5) It appears that the rate slows with time because a thin layer of ferrous sulfate + sulfuric acid solution grows on pyrite and retards oxygen transport to the pyrite surface. The transformation of efflorescent sulfate minerals (the reaction products of iron sulfide oxidation) from a pyrrhotite-rich massive sulfide is explained using a systematic analysis of their stoichiometry and thermodynamics. Their stabilities are controlled by oxygen partial pressure, relative humidity, and activity of sulfuric acid and can be visualized using log activity of oxygen-log activity of water and log acitvity of sulfuric acid-log activity of water diagrams developed during this study. Samples from the field site were analyzed in the laboratory to determine mineralogy, equilibrium relative humidity, chemical composition, and acid generation potential. Dissolution experiments showed that fibroferrite-rich samples had the highest acid producing potential, followed by copiapite-rich samples and then halotrichite-rich samples. The most abundant metals in solutions produced by dissolving the salts were magnesium, aluminum, zinc, copper, calcium, and lead. The molar concentrations of the metals varied with mineralogy. However, all of these minerals release metals and acid when they dissolve and therefore represent a significant environmental threat. / Ph. D.