Thesis--University of Pennsylvania.

Thesis (M.S.)--University of Wisconsin--Madison, 1923. / Typescript. eContent provider-neutral record in process. Description based on print version record.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1912. / The entire thesis text is included in file. Typescript. Illustrated by authors. Title from title screen of thesis/dissertation PDF file (viewed March 2, 2009) Includes bibliographical references (p. 2).

Clair Groups and underlying basement contain cataclastic faults, cement-sealed faults/veins and open fractures. The dominant fracture cements are calcite and pyrite, although fluorite (with sulphides and native silver) occurs in minor amounts in some Clair Group fractures, marcasite is often associated with Clair Group fracture-hosted pyrite, and some basement fractures contain epidote/chlorite and quartz/feldspar/hematite. Calcite cements in many Clair Group fractures may have crystallised from porewaters whose calcium and bicarbonate were mostly remobilised from Clair Group calcretes. Many of these cements may predate Late Cretaceous/Early Tertiary oil charge. Some may have crystallised from Early Tertiary meteoric porewaters, the fluorite with which they are associated perhaps having crystallised from porewaters hydrothermally affected by local igneous activity. Calcite cements within some basement fracture may have crystallised from porewaters whose calcium and bicarbonate came from Clair Group calcretes, as may most non-ferroan calcite cement within Clair Group sandstones. Calcite cements in some Clair Group fractures contain a high proportion of non-calcrete carbonate. These cements may have crystallised after oil charge began, from Early Tertiary meteoric porewaters or meteoric/basinal-derived brine mixtures. Non-calcrete bicarbonate may have been generated via bacterial activity (organic matter oxidation and methanogenesis) within the Clair Group. Bacteria could have utilised hydrocarbons, substrates generated via aerobic hydrocarbon oxidation, or externally-sourced substrates such as acetate. Authigenic iron sulphides often predate the calcite cements. The sulphur within these was probably externally-sourced, H2S either having come direct from external sources, or having been generated in situ via bacterial sulphate reduction. Sulphur may have undergone redox cycling through contact with oxygenated meteoric water in some fractures and marcasite genesis may have resulted from this. Calcite cements within some basement fractures may have crystallised from Early Tertiary porewaters containing bicarbonate generated in situ via the oxidation of hydrocarbons, and these cements are often predated by authigenic pyrite.

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1912. / The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed April 20, 2009) Includes bibliographical references.

Thesis (MSc. (Physics)) --University of Limpopo, 2009 / Calculations were carried out on transition-metal sulphides (TMS) and transitionmetal arsenides (TMA), in both pyrite- and marcasite-type structures, using planewave (PW) pseudopotential methods within density functional theory (DFT) in the local density approximation (LDA). The structural, electronic and optical properties for both pyrite- and marcasite-type structures (naturally occurring and converted) have been investigated. The equilibrium lattice parameters were investigated and are in good agreement with the experimental values. The heats of formation calculations predict that the naturally occurring pyrite- and marcasite-type structures are more stable than the converted ones. In particular, the calculated pyrite-type RuS2 compares well to the experimental value (with energy difference of 0.381 eV/atom). The bulk modulus and elastic properties were calculated. The predicted anisotropic ratio shows that the naturally occurring pyrite- and marcasite-type structures are more stable than the converted ones. Moreover, the electronic density of states and band structure calculations reveal that most compositions shows semiconducting behaviour except for the converted pyritetype structures, i.e OsAs2 and RuAs2 where a metallic behaviour was observed. The electronic charge density and charge density difference show charge accumulation on bonding atoms, predicting the charge gain/ loss and nature of bonding to be covalent/ weak ionic between the atoms. Lastly, optical properties are computed at equilibrium and predict that naturally occurring structures have lower absorption and reflectivity than the converted structures. At different pressures ranging from -10 GPa to 10 GPa, the absorption and reflectivity spectra show a shift from the 0 GPa spectrum for all the structures / National Research Foundation

The electronic spectra of sulfide minerals can be complex, and their features difficult to assign. Often, therefore, they are interpreted using electronic-structure models obtained from quantum-chemical calculations. The aim of this study is to provide such models for the minerals sphalerite, wurtzite, pyrite, marcasite, and chalcopyrite. All are important minerals within a mining context, either as a source for their component metals or as a gangue mineral. They are also semiconductors. Each is the structural archetype for a particular class of semiconductors, and so a knowledge of their electronic structures has wider applicability. / PhD Doctorate

The relative reactivities of pulverized samples (100-200 mesh) of 3 marcasite and 7 pyrite specimens from various sources were determined at 25°C and pH = 2.0 in ferric chloride solutions with initial ferric iron concentrations of 10⁻³ molal. The rate of the reaction: FeS₂ + 14Fe³⁺ + 8H₂O = 15Fe²⁺ + 2SO₄²⁻ + 16H⁺ was determined by calculating the rate of reduction of aqueous ferric ion from measured oxidation-reduction potentials. The reaction follows the rate law: -d m_Fe³⁺ / dt = k (A/M) m_Fe³⁺ where m_Fe³⁺ is the molal concentration of uncomplexed ferric iron, k is the rate constant and A/M is the surface area of reacting solid to mass of solution ratio. The measured rate constants, k, range from 1.0x10⁻⁴ to 2.7x10⁻⁴ sec⁻¹ ±5%, with lower-temperature/early diagenetic pyrite having the smallest rate constants, marcasite intermediate, and pyrite of higher-temperature hydrothermal and metamorphic origin having the greatest rate constants. Geologically, these small relative differences between the rate constants are not significant, so the fundamental reactivities of marcasite and pyrite are not appreciably different. The activation energy of the reaction for a hydrothermal pyrite in the temperature interval of 25 to 50°C is 92 kJ mol⁻¹. The BET-measured specific surface area for lower-temperature/ early diagenetic pyrite is an order of magnitude greater than that for pyrite of higher-temperature origin. Consequently, since the lower-temperature types have a much greater A/M ratio, they will appear to be more reactive per unit mass than the higher temperature types. / Master of Science

Technetium is the lightest element whose isotopes are all radioactive. Among them, 99Tc (hereafter simply referred as technetium or Tc) is the most abundant and raises great environmental concern due to its relatively long half-life of 2.14×105 years and the high mobility of pertechnetate, Tc(VII)O4, its most stable form under aerobic conditions. The reduction from Tc(VII) to Tc(IV) is one of the most successful strategies for Tc immobilization; however, the mechanism of this redox reaction is not yet fully understood. This presents a large gap in the general knowledge of technetium chemistry and a significant obstacle for the modeling of its reactivity in contexts like a nuclear waste repository. This thesis was developed in the frame of the BMWi funded VESPA II project, and it studies the surface-mediated reduction of 99Tc(VII) using a combination of fundamental chemistry and its application for remediation and nuclear waste management. First, spectro-electrochemical methods (cyclic voltammetry, rotating disk electrode, chronoamperometry coupled with UV-vis, Raman microscopy and nuclear magnetic resonance) were employed to study the reduction mechanism of 0.5 mM KTcO4 in non-complexing media (2 M NaClO4) in the pH range from 2.0 to 10.0. It was found that the mechanism depends on the pH. At pH 2.0 it splits into two steps: Tc(VII) gains 2.1 ± 0.3 electrons and becomes Tc(V) that rapidly reduces to Tc(IV) with the transfer of further 1.3 ± 0.3 electrons. In contrast, at pH ≥ 4.0 there is a direct transfer of 3.2 ± 0.3 electrons. The complete reduction of Tc(VII) yielded a black solid that was successfully characterized by NMR and Raman microscopy as Tc(IV) regardless of the initial pH at which the reaction occurred. Unfortunately, it was not possible to observe the Tc(V) species at pH 2.0 by the spectroscopic tools used. Second, the reductive immobilization of Tc(VII) by pure pyrite and a synthetic mixture marcasite-pyrite 60:40 (synthetic FeS2, with both minerals being polymorphs) was studied by a combination of batch sorption experiments (Tc-removal was studied varying pH, contact time, ionic strength and Tc concentration) and several spectroscopies and microscopies such as Raman microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and VIII X-ray absorption spectroscopy. It was found that both pyrite and the synthetic FeS2 promote the reduction of Tc(VII) to Tc(IV). In the case of pure pyrite, the Tc-removal is complete after one day in contact at pH ≥ 5.5. The spectroscopic analysis showed at pH 6.0 an inner-sphere complex between Tc(IV) dimers and hematite formed as secondary mineral on the pyrite surface. In contrast, at pH 10.0 Tc(IV) gets incorporated into surficial magnetite by replacing Fe3+ in octahedral position, with Fe2+ providing reasonable charge compensation for Tc4+. The presence of marcasite made the process slower and less efficient since the synthetic FeS2 was capable to remove 100% Tc from solution only after seven days in contact at 6.0 < pH ≤ 9.0 while the Tc-removal at pH 10.0 was only around 80%. At pH 6.0 the formation of hematite was also observed, suggesting that the formed Tc(IV) species at the surface is the same as with pure pyrite. However, at pH 10.0 the formation of sulfate minerals evidences a change of redox active species: S2- instead of Fe2+. This, combined with the fact that in both solids the formation of TcSx species was detected by XPS at pH 10.0, shows the potential of sulfur as another reducing agent for Tc(VII). The effect of polymorphism on the Tc removal is remarkable and this work shows the relevance of more studies on the interaction of radionuclei with other mineral polymorphs. Regardless of the kinetics of the Tc removal, both pyrite and synthetic FeS2 hindered the re-oxidation of Tc(IV) when exposed to ambient atmosphere for two months. This feature makes them good candidates for the remediation of technetium from contaminated waters. Moreover, natural attenuation effects can be expected for technetium in the near and far field of nuclear waste repositories wherever iron sulfide is present. The results presented in this work contribute to a better understanding of the fundamental aqueous chemistry of technetium and confirm pyrite, a ubiquitous mineral, as a very good candidate for technetium scavenging even in the presence of marcasite. These results close important gaps in thermodynamic databases that are needed for the safety assessment, i.e. modeling of fission products.

La propriété Lac Trieste comprend des formations de fer intercalées avec des paragneiss du Complexe de Laguiche, déformées et métamorphisées au faciès des amphibolites. La minéralisation aurifère se trouve dans des blocs erratiques de formations de fer métamorphisées. Les affleurements et les blocs de formations de fer comportent des bandes d’hédenbergite-grenat-hornblende et d’arsénopyrite-löllingite-pyrrhotite disséminées alternant avec des bandes de quartz. Les arséniures, plus abondants dans les blocs, sont caractérisés par des grains d’arsénopyrite (dénotée Apy2) avec un centre de löllingite comportant des inclusions d’arsénopyrite (Apy1). La löllingite se forme par remplacement de Apy1 (0,02 à 3,5 ppm Au) durant le métamorphisme prograde à plus de 700 °C, où l’or est enrichi dans la structure de la löllingite (0,1 à 12,4 ppm Au). L’or natif précipite au contact löllingite-arsénopyrite durant le remplacement de la löllingite par Apy2 appauvrie en or (0,0002 à 0,2 ppm Au) au cours du métamorphisme rétrograde entre 420 °C et 560 °C. La pétrologie et la géochimie indiquent que la source des blocs est locale. / The Lac Trieste mineral property is underlain by iron formations intercalated with paragneiss of the Laguiche Group, deformed and metamorphosed to amphibolite-facies and deformed. Gold mineralization is hosted in boulders of banded iron-formations. Outcrops and boulders of iron-formations comprise bands of hedenbergite-garnet-hornblende with disseminated loellingite-arsenopyrite-pyrrhotite alternating with bands of quartz. Arsenides, more abundant in the boulders, are characterized by grains of arsenopyrite (Apy2) with a core of loellingite comprising inclusions of arsenopyrite (Apy1). Loellingite formed by replacement of gold-bearing Apy1 (0.02 to 3.5 ppm Au) during prograde metamorphism above 700 °C, where gold is enriched within the structure of loellingite (0.1 to 12.4 ppm Au). Native gold formed at arsenopyrite-loellingite grain boundaries during replacement of loellingite by Apy2 depleted in gold (0.0002 to 0.2 ppm Au) during retrograde metamorphism between 420 °C and 560 °C. Petrology and geochemistry indicate that the origin of the boulders is local.