No description available.

Widespread arsenic contamination with adverse effects to human health is a global problem. Most previous studies on arsenic contamination in natural environments and those associated with mining and agricultural activities focused largely on arsenic-rich minerals such as arsenates, arsenites, sulfarsenides, and sulfides. Rock-forming minerals generally contain only minor or trace amounts of arsenic but, owing to their sheer abundances, are potentially important (and sometimes dominant) sources of this metalloid and can play significant roles in the attenuation and sequestration of arsenic in various environments. However, there remains a significant gap in my knowledge about the uptake and speciation of arsenic in rock-forming minerals. This thesis research is intended to bridge this gap by investigating the uptake and speciation of arsenic in selected rock-forming sulfate and phosphate minerals (i.e., gypsum, struvite and newberyite). Gypsum (CaSO4•2H2O) is a major by-product of mining and milling processes of borate, phosphate and uranium deposits worldwide and, therefore, potentially plays an important role in the stability and bioavailability of heavy metalloids, including As, in tailings and surrounding areas. Gypsum containing 1,900 and 185 ppm As, synthesized with Na2HAsO4•7H2O and NaAsO2 in the starting materials, respectively, has been investigated by synchrotron X-ray absorption spectroscopy (XAS), single-crystal electron paramagnetic resonance spectroscopy (EPR), and pulsed electron nuclear double resonance spectroscopy (ENDOR). Quantitative analyses of As K edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra show that arsenic occurs in both +3 and +5 oxidation states and the As3+/As5+ value varies from 0.35 to 0.79. Single-crystal EPR spectra of gamma-ray-irradiated gypsum reveal two types of arsenic-associated oxyradicals: [AsO3]2− and an [AsO2]2−. The [AsO3]2− center is characterized by principal 75As hyperfine coupling constants of A1 = 1952.0(2) MHz, A2 = 1492.6(2) MHz and A3 = 1488.7(2) MHz, with the unique A axis along the S-O1 bond direction, and contains complex 1H superhyperfine structures that have been determined by pulsed ENDOR. These results suggest that the [AsO3]2− center formed from electron trapping on the central As5+ ion of a substitutional (AsO4)3− group after removal of an O1 atom. The [AsO2]2− center is characterized by its unique A(75As) axis approximately perpendicular to the O1-S-O2 plane and the A2 axis along the S-O2 bond direction, consistent with electron trapping on the central As3+ ion of a substitutional (AsO3)3− group after removal of an O2 atom. These results confirm lattice-bound As5+ and As3+ in gypsum and point to potential application of this mineral for immobilization and removal of arsenic pollution. EPR spectra show that another sulfate boussingaultite is also sequestering both As5+ and As3+ at its S site. Synthesis experiments at pH from 2 to 14 also show that arsenic uptake in gypsum is pH dependent. Struvite and newberyite, common biominerals and increasingly important green fertilizers recovered from wastewater treatment plants, are capable of sequestering a wide range of heavy metals and metalloids, including arsenic. Inductively coupled plasma mass spectrometric (ICPMS) analyses show that struvite formed under ambient conditions contains up to 547±15 ppm As and that the uptake of As is controlled by pH. Synchrotron As K-edge XANES spectra measured at 20 K show that As5+ is the predominant oxidation state in struvite, irrespective of Na2HAsO4•7H2O or NaAsO2 as the source for As. Modeling of As K-edge EXAFS data suggest that local structural distortion associated with the substitution of As5+ for P5+ in struvite reaches up to 3.75 Å. Single-crystal electron paramagnetic resonance (EPR) spectra of gamma-ray-irradiated struvite disclose five [AsO3]2- radicals and one [AsO4]2- radical. These arsenic-centered oxyradicals are all readily attributed to form from diamagnetic [AsO4]3- precursors during irradiation, providing further support for exclusive incorporation and local structural expansion beyond the first shell of As5+ at the P site in struvite. Arsenic doped newberyite (MgHPO4•3H2O) obtained from the gel diffusion method has investigated by synchrotron XAS at the As K-edge (11,867 eV) at 8 K and single-crystal EPR spectroscopy at room temperature. XANES data show that As5+ is dominant and EXAFS analysis reveals a local environment typical of the arsenate species as well. Single-crystal EPR spectra of gamma-ray-irradiated newberyite contain two arsenic-associated oxyradicals: [AsO3]2− and [AsO2]2− derived from As5+ and As3+, respectively, at the P site in the newberyite structure. Elevated concentrations of arsenic have also been observed in natural newberyite from guano deposits and reflect the accumulation of this metalloid in the food chain. Therefore, struvite and newberyite can both sequester significant amounts of arsenic, and their direct use as fertilizers (irrespective of origins from guano deposits or wastewaters) is a potential source of arsenic contamination. On the other hand, the capacities of struvite and newberyite for accommodating significant amounts of arsenic in crystal lattices coupled with their simple chemistry and crystallization under ambient conditions make them attractive materials for immobilization and removal of arsenic contamination in aqueous environments.

All the warm deserts of the world exhibit gypsum crusts in favourable localities, generally areas with a source of gypsum and less than 250 mm of rainfall annually. The features, comprising loose powdery or cemented crystalline accumulations of calcium sulphate dihydrate, are found at the surface or within the uppermost 10 m of regolith. Thicknesses vary from a few millimetres to several metres and purities range from about 15% to nearly 100% gypsum. A review of the literature on gypsum soils and crusts reveals that the classification of types requires both standardizing and simplifying. A preliminary classification of crusts into three types can be made on the basis of structural and stratigraphic characteristics of examples from southern Tunisia and the Central Namib Desert. The types consist of subaerial aqueous evaporites, two subsurface and three surface forms. Detailed physical and chemical analyses justify a broadly similar genetic classification though one subsurface form is believed to be a primary pedogenic type of which the surface forms represent relics at various stages of solutional deterioration. Examples of subaerial aqueous evaporites are all products of shallow-water sedimentation in seasonally flooded chotts and sabkhas. The non-pedogenic subsurface type, croûte de nappe, is produced by displacive crystallization at the surface of a fluctuating water table. Gypsum precipitation results from either evaporation or mixing of saline waters causing saturation with respect to gypsum. Surface gypsum crusts are subsurface illuvial accretions exposed by erosion of overlying material. The gypsum is derived from solution of surface aeolian, atmospheric, colluvial or alluvial deposits by meteoric waters which percolate into the upper soil zone replenishing the antecedent soil moisture deficit. Subsurface accumulation results from displacive crystallization at host sediment grain contacts when gypsum saturated soil moisture evaporates.

The provisions to determine the deflection of gypsum wallboard (GWB) sheathed shearwalls available in the Canadian and American standards are limited to nailed shearwalls and are rudimentary compared to the wood based sheathing equations. There is currently no fastener slip model for the GWB sheathed shearwalls that are fastened with GWB screws. A main goal of this study is to improve the existing equations for nailed GWB sheathed shearwalls and develop a suitable analytical expression that can be used for GWB fastened with screws. In total, 270 GWB sheathed joints were subjected to reversed cyclic loading with variations including GWB type, thickness, fastener type, fastener size and manufacturers. The power model type is used to develop the fastener slip equations for nails and screws, which have GWB density and fastener diameter as equation inputs. The accuracy of the developed model is then validated by comparing the tested full-scale GWB sheathed shearwall deflection to the deflection calculated using the newly proposed fastener slip models. The proposed equation is a significant improvement to the existing code provisions. Component testing was performed on the fasteners (center point bending test) and the GWB (dowel bearing test). The results of these tests were used to determine the joint capacity based on the European Yield Model. It was also found that the shearwall capacity could be predicted by considering the joint level capacity while accounting for the number of joints at a panel edge. The joint level and full-scale experimental results are also validated with the use of an analysis program (SAPWood) to model the joint level hysteresis as a hysteretic spring with 10 model fitting parameters. The developed joint level hysteretic model was then used to represent the fasteners connecting the sheathing panels to the lumber framing in the construction of the full-scale shearwall model.

No description available.

This study was designed to understand the possible impact of carbon dioxide on different reservoir rocks in south-central Mississippi. Eight samples, including six from the Heidelberg field (Mississippi), were exposed to carbon dioxide under simulated subsurface conditions of elevated temperature and pressure and then analyzed using thin section petrography, scanning electron microscopy, X-ray diffraction, and focused ion beam-SEM. Three of the eight samples showed dissolution in calcite and corrosion in smectite. SEM and EDS analysis of treated sample 5 (Se-5/shaly-sandtsone) and sample 8 (S-8/dolomitic-limestone) revealed newly precipitated lath- and fibrous-like crystals composed of sulfur (S), oxygen (O), and calcium (Ca), thus interpreted as gypsum. Three-dimensional analysis using FIB of dolomitic limestone samples (Smackover Formation) revealed that gypsum crystals fill fracture porosity. This study significantly contributes to the understanding of carbon dioxide impact on reservoir rock and promotes better management of natural gas resources.

Flue gas desulfurization (FGD) is utilized by the coal-powered generating industry to safely eliminate sulfur dioxide. A FGD vessel (scrubber) synthetically creates gypsum crystals by combining limestone (CaCO3), SO2 flue gas, water and oxygen resulting in crystalline gypsum (CaSO4 ∙ 2H2O), which can be sold for an economic return. Flat disk-like crystals, opposed to rod-like crystals, are hard to dewater, lowering economic return. The objectives were to investigate the cause of varying morphologies, understand the environment of precipitation, as well as identify correlations between operating conditions and resulting unfavorable gypsum crystal growth. Results show evidence supporting airborne impurities due to the onsite coal pile, the abundance and size of CaCO3 and high Ca:SO4 ratios within the scrubber as possible factors controlling gypsum crystal morphology. In conclusion, regularly purging the system and incorporating a filter on the air intake valve will provide an economic byproduct avoiding costly landfill deposits.

No / A prototype instrument, under development at the University of Leicester, for the future European Space Agency (ESA) ExoMars mission, was used for the analysis of microbial pigments within a stratified gypsum crust from a hypersaline saltern evaporation pond at Eilat (Israel). Additionally, the same samples were analysed using a miniaturized Raman spectrometer, featuring the same 532 nm excitation. The differences in the position of the specific bands, attributed to carotenoid pigments from different coloured layers, were minor when analysed by the ESA prototype instrument; therefore, making it difficult to distinguish among the different pigments. The portable Delta Nu Advantage instrument allowed for the discrimination of microbial carotenoids from the orange/green and purple layers. The purpose of this study was to complement previous laboratory results with new data and experience with portable or handheld Raman systems, even with a dedicated prototype Raman system for the exploration of Mars. The latter is equipped with an excitation wavelength falling within the carotenoid polyene resonance region. The ESA prototype Raman instrument detected the carotenoid pigments (biomarkers) with ease, although further detailed distinctions among them were not achieved.

Cross-section profiles of gypsum rillenkarren, obtained from a quarry near Gypsumville Manitoba, reveals a series of recently developed features. Statistical analysis of crest rillenkarren indicates a high degree of variability in the shape and size of the rills. In addition, abnormal differences between upper and lower rills can not be explained, but it is believed that the surrounding area may affect rill development. Comparing this study to previous rillenkarren studies, we find that rills from the quarry are undersized. This is due to many factors, chief of which may be the climatic conditions of central Manitoba and the relatively young age of the gypsum outcrops. / Thesis / Candidate in Philosophy

Intensive tillage practices in the Mississippi Delta degrade soil health, impacting downstream water quality. To address this, two experiments were conducted from 2019 to 2021 and 2020 to 2022 to evaluate the impact of sugarcane biochar and flue gas desulfurization (FGD) gypsum on nutrient leaching losses and soil properties in cotton and soybean cropping systems. Study I applied four biochar rates (0, 10, 20, and 40 Mg ha-1) to cotton and found improvements in soil properties and subsurface quality, with reduced nutrient leaching losses, except for sulfate and sodium ions. Study II evaluated biochar (10 and 25 Mg ha-1) and FGD gypsum (2.24 and 6.72 Mg ha-1) application rates in soybean, resulting in reduced nitrate leaching losses and soil property improvements, mostly observed in the second year. These findings suggest that reevaluating management practices with biochar and gypsum can improve soil health and water quality, but may require a lag time to realize benefits.