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.

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.

This investigation has been carried out for the purpose of determining the effect of solid particle size distribution on the roasting and leaching of a complex sulfide ore. The effect of pulp density in the leaching process has also been studied. The oxidizing roast of the combined sulfide concentrates, prepared by bulk sulfide flotation and tabling, was conducted with a fluidized-bed kiln. The calcines were leached by dilute sulfuric acid in an autoclave. The following conclusions have been reached: 1. In the fluidized-bed roasting, the solid particles within the size range of minus 35 to plus 150-mesh would have a higher overflow rate from the fluidized bed. This inference might be effective only when the roasting is conducted under the conditions performed in this investigation. 2. In the process combining fluidized-bed roasting and dilute sulfuric acid leaching, the effect of solid particle size is significant. The solid particles within the size range of minus 65 to plus 150-mesh have the highest iron recovery, the highest copper and zinc extraction rates and the lowest sulfur content of leach residue. 3. In dilute sulfuric acid leaching there is no significant effect of pulp density within the range tested in this investigation. The general trends are: iron recovery decreases as the pulp density decreases, extraction rates of copper and zinc decrease as pulp density increases, and there is little pulp density effect on the sulfur content of leach residue. / Master of Science

This investigation deals with the application of high pressure and high-temperature leaching techniques to separate out zinc and copper from the iron constituents of a calcined sulfide ore. An important variable in this study proved to be the concentration of the leaching reagent -- sulfuric acid. The leaching temperature was varied within a range of 250°F to 550°F., and 8 cubic centimeters to 20 cubic centimeters of sulfuric acid in 2000 cubic centimeters of distilled water was employed as the leaching agent concentration. The major equipment utilized for roasting was the fluidized bed and an autoclave for leaching. After the physical and chemical treatments of roasting and leaching of the calcine, the resulting constituents were studied by means of quantitative chemical analysis. Numerical theories were used to correlate the points obtained into continuous functions of the leaching temperature, concentration of sulfuric acid and the recovery percentage. From these curves, it is concluded that the recovery of the impurities in the calcine is proportional to the leaching temperature and the concentration of the leaching agent. However, under certain circumstances, the leaching action causes loss of iron in the calcine, and the minimizing of the loss in leaching is also studied. / Master of Science

Long chain alkyl pyridinium salts have been used as collectors for the flotation of chalcopyrite and copper-activated sphalerite. For the ores tested in this study, these reagents have demonstrated improved selectivity and recovery in comparison to conventional xanthates. The best flotation results, in terms of both grade and recovery, were achieved with cetyl pyridinium chloride (CpCl). A distinct advantage of using CpCl instead of a conventional xanthate, such as sodium isopropyl xanthate (NaIpX), is that the kinetics of flotation are much faster. This may be explained by the reduction in the negative ζ-potential of the sulfide mineral upon adsorption of cetyl pyridinium ions, which, in turn, minimizes the electrostatic component of the disjoining pressure of the wetting film. CpCl has also demonstrated a remarkable selectivity despite the fact that both chalcopyrite and the silicious gangue minerals present in the ore are negatively charged. This may be explained by the premise that cetyl pyridinium ions adsorb more strongly on chalcopyrite than on the gangue. Analysis of the adsorption isotherms established for chalcopyrite and quartz supports this view. Several possible mechanisms have been suggested to explain the 'high affinity' type of adsorption observed in the CpCl-chalcopyrite system. / Master of Science

Electric field studies, electrochromism, were used to obtain excited-state data for analogous divalent sulfur compounds. The sulfides investigated were dimethyl sulfide and small cyclic sulfides including the three to six member ring compounds. The excited-state dipole moments and polarizabilities are reported for the first s, p, and d Rydberg absorption bands which occur in the near vacuum ultraviolet region from 230 to 170 nm. The excited-state data are interpreted in terms of the particular excited-state (s, p, or d) for the molecules and the bending differences due to the presence of the ring and the number of atoms in the ring. The next section describes the use of electrochromism to investigate the pressure effect of argon, carbon tetrafluoride and sulfur hexafluoride on the spectra for molecular Rydberg states.

Este trabalho teve como foco a preparação de compostos orgânicos de selênio, fundamentado em plataformas estruturais de moléculas pequenas que pudessem ter suas preparações viabilizadas em reduzido número de etapas, a partir de matérias primas comerciais ou de fácil preparação e economicamente viáveis. O trabalho ficou dividido em 3 partes, sendo que na primeira, optou-se por preparar compostos fundamentados em estruturas derivadas dos ácidos acético, propiônico e butírico. As estratégias de preparação ficaram centradas na geração de HSeNa ou Se2Na2, por reação de selênio e borohidreto de sódio em água ou etanol. As espécies nucleofílicas foram então submetidas a reação com cloro-acetato de sódio ou de etila, levando aos correspondentes diorgano-selenetos ou disselenetos. Também foram preparados derivados de ácido propiônico, α-hidroxilados. Para isso duas abordagens foram empregadas, sendo que em uma mantivemos a estratégia de substituição nucleofílica de um haleto terminal por reação com MeSeLi, levando ao β-metilseleno-α-hidroxipropóide. Na outra, optamos por fazer reacão de abertura de um epóxido glicídico. Neste caso observamos mistura de regioisômeros quando MeSeLi foi empregado. Quando o Grignard correspondente foi usado na reação de abertura do epoxido além de mistura de regioisômeros, também se observou como produto majoritário, o monoseleneto dimérico (provavelmente oriundo de uma de-metilação). Por fim, empregou-se também abertura da γ-butirolactona com disselenolato de sódio, levando ao disselenodi-ácido correspondente. Esses compostos foram submetidos a ensaios preliminares de atividade antioxidante. Destes, o seleno-diacetato de etila apresentou alta seletividade para reação com HOCl, mesmo frente a outras espécies oxidantes e em experimento in vitro com células Hela-60. Além disso foi preparado um seleno-diglicosídeo, também empregando hidrogenoselenolato de sódio, gerado in situ à partir de selênio elementar e borohidreto de sódio. Esse composto foi submetido a ensaios de atividade anticâncer, em associação com β-glucana, levando a ótimos resultados para os experimentos envolvendo câncer de mama e pulmão. Cabe mencionar que nesse caso foram feitos experimentos in vivo com ratos, acrescendo o derivado seleno-açucar e glucana, à dieta dos animais. Por último, foram investigadas estratégias de preparação de sais de Bunte (tiossulfatos orgânicos) de diferentes padrões de substituição. Nessa parte do estudo, tivemos como propósito investigar alguns fatores de reatividade desses compostos frente a espécies nucleofílicas e eletrofílicas de selênio e telúrio, a fim de preparar seleno- e telurosulfetos. Esses por sua vez devem ser submetidos a ensaios biológicos variados. Das estratégias investigadas observamos uma serie de subprodutos das reações envolvendo os sais de Bunte com espécies nucleofílicas de selênio, sendo o que o produto principal foi formado apenas em baixo rendimento e alguns derivados se mostraram bastante instáveis. Em contrapartida, reação bastante seletiva e bons rendimentos foram observados para os casos em que o sal de Bunte agiu como nucleófilo em reações com cátions de selênio e telúrio, gerados por clivagem do dicalcogeneto por persufato de amônio em solvente protônico. Alguns exemplos dos dicalcogenetos puderam ser preparados e caracterizados. / This work was devoted to the preparation of organic selenides, based on structural platforms of small molecules taking in account scalable synthetic procedures in a small steps numbers, from commercial raw materials or from easily prepared and economically viable starting materials. The work was divided into 3 parts, and in the first, it was decided to prepare compounds based on structures derived from acetic, propionic and butyric acids. The preparation strategies were centered on the generation of HSeNa or Na2Se2, by reaction of elemental selenium and sodium borohydride in water or ethanol. The nucleophylic species were then subjected to reaction with sodium chloroacetate, leading to the corresponding diorgano-selenides or disselenides. They were also prepared from α-hydroxylated propionic acid derivatives. For this purpose, two approaches were employed, and in one we maintained the nucleophylic substitution strategy of a terminal halide by reaction with MeSeLi, leading to β-methylseleno-α- hydroxy-propoide. In the other, we chose to perform an epoxi-glycidic opening reaction. In this case, we observed a mixture of regioisomers when MeSeLi was employed. When the corresponding seleno-Grignard was used in the epoxide opening reaction besides a mixture of regioisomers, it was also observed as a major product, the symmetric monoselenide (probably originated from a de-methylation reaction). Finally, it was also used the γ-butyrolactone opening reaction with sodium disselenolate, leading to the corresponding disseleno-diacid. These compounds were submitted to preliminary assays of antioxidant activity. The ethyl Seleno-diacetate showed high selectivity for reaction with HOCl, even in the presence of other oxidant species and in an in vitro experiment with Hela-60 cells. In addition, a Selene-diglycoside was prepared, also employing sodium hydrogen selenide, generated, in situ from elemental selenium and sodium borohydride. It was subjected to anticancer activity assays, in association with β-glucan, leading to great results for experiments involving breast and lung cancer. It is worth mentioning that inthis case experiments were made in vivo with rats, adding our seleno-sugar/glucan system to the diet of the animals. Finally, strategies for the preparation of Bunte salts (organic thiosulphates) of different substitution patterns were investigated. In this part of the study, we intend to investigate some factors of reactivity of these compounds through nucleophilic and electrophilic selenium and tellurium species, in order to prepare seleno- and telluro-sulfides. Opportunely, these compounds should be submitted to biological assays. Under the investigated reaction conditions, we observed a series of by-products of reactions involving the Bunte salts with nucleophilic selenium species, and the main product was formed only in low yield and some derivatives showed to be quite unstable. On the other hand, a fairly selective reaction and good yields were observed for cases in which the Bunte salt was used as the nucleophile in reactions with selenium and tellurium cations, generated by the cleavage of the dichalcogenide by ammonium peroxysulphate in protonic solvent. Some examples of dichalcogenides were prepared and characterized.

<p>In this work we have investigated the intercalation of electron-donors between NbS₂ slabs in Nb-based layer sulfides.</p><p>Two series of Sr substituted Nb-based misfit sulfides belonging to the 1.5Q/1H and 1Q/1H series of misfit layer compounds have been synthesised. For large lanthanides (Ln=La, Ce), only the 1Q/1H compounds formed whereas for smaller lanthanides and yttrium, both types of phases can be obtained. The crystal structure of misfit sulfide (Pr_0.55Sr_0.45S)_1.15NbS₂ has been refined using the composite approach. In the Q-slab, Pr-atoms are partly replaced by Sr with a random distribution over one cation position. The crystal structure of misfit sulfide [(Sm_1/3Sr_2/3S)_1.5]_1.15NbS₂ belonging to the 1.5Q/1H series have also been determined. The obtained results suggest a preferred occupancy of the cation positions in the slab where Sr atoms mainly occupy positions on the exterior of the slab while Sm atoms are in the center of the slab. The (La_1-xSr_xS)_1.15NbS₂ solid solution (0.1<x<0.9) has also been studied. It was found that the maximum value of Sr substitution is 40-50% and therefore, the minimal value of charge transfer to stabilize this structure type is about 0.6ē per Nb atom. </p><p>An attempt to synthesize Sr_xNbS₂ (0.1≤x≤0.5) intercalates was made but single phases were not obtained and increasing the temperature from 1000^оС to 1100^оС leads to the decomposition of these intercalates. Single crystals of Sr_0.22Nb_1.05S₂ and Sr_0.23NbS₂ were found and their structures were determined. The structures belong to two different types of packings with statistical distribution of Sr between layers.</p><p>A new superconducting sulfide, "EuNb₂S₅", was investigated by ED and HREM and its structure model consisting of Nb₇S₁₄ and (Eu₃S₄)₂ slabs alternating along the c-axis is suggested. An attempt to suggest a model for the structure of "SrNb₂S₅" by means of X-ray single crystal diffraction was made. The proposed structure consists of two types of slabs: a Nb₇S₁₄ and a [Sr₆(NbS₄)₂S] slab with niobium in tetrahedral coordination. It is shown that "SrNb₂S₅" and "EuNb₂S₅" are have similar structures.</p><p>For the first time, single crystals of the complex sulfide BaNb_0.9S₃ have also been studied by means of X-ray single crystal diffraction. The single crystal refinement and EDX analysis showed the existence of cation vacancies at the niobium position. BaNb_0.9S₃ has also been studied by ED and no superstructure was found which implies that and the vacancies are statistically distributed.</p><p>No improvement of the magnetic properties of the studied compounds was observed in comparison to NbS₂.</p>

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