Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 342-353).

Thesis (Ph. D.)--University of Chicago, Dept. of the Geophysical Sciences, June 2000. / Includes bibliographical references. Also available on the Internet.

Carbon dioxide capture and storage will be necessary to mitigate the effects of global climate change. Mineral carbonation - converting carbon dioxide gas to carbonate minerals - is a permanent and environmentally benign mechanism for storing carbon dioxide. The peridotite section of the Samail Ophiolite is host to exceptionally well-developed, naturally occurring mineral carbonation and serves as a natural analog for an engineered carbon dioxide storage project. This work characterizes the geochemistry and hydrogeology of peridotite aquifers in the Samail Ophiolite. Water samples were collected from hyperalkaline springs, surface waters, and boreholes in peridotite, and recent mineral precipitates were collected near hyperalkaline springs. Samples were analyzed for chemical composition. Geochemical data were used to delineate water-rock-CO₂ reactions in the subsurface and constrain a reaction path model for the system. This model indicates that mineral carbonation in the natural system is limited by the amount of dissolved carbon dioxide in water that infiltrates deep into the aquifer. The amount of carbon dioxide stored in the system could potentially be enhanced by carbon dioxide injection into the aquifer. Reaction path modeling suggests that injection of water at saturation with carbon dioxide at 100 bars pCO₂ and 90⁰C could increase the carbonation rate by a factor of up to 16,000 and bring carbonation efficiency to almost 100%. Dissolved gas samples from boreholes were collected at in situ conditions and analyzed for chemical composition. Boreholes with pH > 10 contain millimolar levels of dissolved hydrogen and/or methane, indicating these boreholes are located near areas of active low temperature serpentinization. Serpentinization rates were calculated using groundwater flow estimates and dissolved gas concentrations, and range from 3x10⁻⁸ to 2x10⁻⁶ volume fraction peridotite serpentinized per year. Additionally, laboratory incubation experiments show dissolved hydrogen can be stored in sealed copper tubes for at least three months with neither diffusive loss nor production of hydrogen from oxidation of the copper. These experiments demonstrate that copper tubes can be practical containers for collecting and storing dissolved hydrogen in freshwater. Groundwater ages in the peridotite section of the Samail Ophiolite are investigated through analysis of tritium, dissolved noble gases, and stable isotopes. Tritium-³Helium dating was used to estimate the age of modern groundwaters (< 60 years old), and helium accumulation was used as relative age indicator for pre-bomb groundwaters (> 60 years old). Waters with pH < 9.3 have ages from 0-40 years, while waters with pH > 9.3 are all more than 60 years in age. Helium accumulation indicates pH < 10 waters contain only atmospheric and tritiogenic helium, while pH > 10 waters have accumulated 30-65% of their helium from radiogenic production or mantle helium. pH > 10 waters are thus significantly older than pH < 10 waters. Noble gas temperatures are generally around 32⁰C, close to the current mean annual ground temperature. One hyperalkaline borehole has noble gas temperatures 7⁰C cooler than the modern ground temperature, indicating the water at that site may have recharged during a glacial period. Stable isotope data (Δ¹⁸O and Δ²H) for waters with pH < 11 plot between the northern and southern local meteoric water lines, in the typical range for modern groundwater. Hyperalkaline boreholes and springs are enriched in Δ¹⁸O, which suggests they recharged when the southern vapor source dominated, perhaps during glacial periods. Lastly, the potential for in situ mineral carbonation in peridotite is investigated through reactive transport modeling of dissolved CO₂ injection into a peridotite aquifer. Injection was simulated at two depths, 1.25 km and 2.5 km, with reservoir conditions loosely based on the peridotite section of the Samail Ophiolite. The dependence of carbonation extent (mass of carbon dioxide sequestered as carbonate minerals per unit volume) on different factors - such as permeability, reactive surface area, and temperature - was explored. Carbonation extent is strongly controlled by reactive surface area (RSA), with geometric RSA models producing 10 to 770 times more carbonation than conservative RSA models with the same initial permeabilities and temperatures. The ratio of carbon dioxide supply to RSA is also a key factor. The ideal relationship between CO₂ supply and RSA appears to be from 5x10⁻⁴ to 0.2 kg CO₂ /day per m²/m³ RSA. Temperature has also has an impact on carbonation rate: for the same initial permeability, carbonation is 7-35% faster at 90⁰C than at 60⁰C. Simulations of a 50-year carbon dioxide injection show that fracture porosity and permeability do not become overly clogged and carbonation continues at a more or less constant rate. We estimate that one dissolved CO₂ injection well in peridotite could store 1.4 Mtons CO₂ in 30 years with a storage cost of $6/ton. This suggests that an engineered carbon dioxide storage project in peridotite could be both feasible and economical. In situ mineral carbonation in peridotite should continue to be investigated as a safe and permanent mechanism for carbon dioxide storage.

No description available.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1984. / Bibliography: leaves 219-236. / Microfiche. / xviii, 236 leaves, bound ill. 29 cm

Thesis (Ph. D.)--Open University. BLDSC no. DX227301.

Epithermal vein and carbonate replacement deposits in Cunningham Gulch are located within the western San Juan Tertiary volcanic field in southwestern Colorado. The Pride of the West epithermal vein system is hosted within the intracaldera facies of the Sapinero Mesa Tuff, a voluminous ash-flow tuff that erupted from and resulted in the formation of the San Juan Caldera at 28 mybp. The Pride of the West vein system is developed along a radial fracture formed during resurgence of the San Juan Caldera prior to eruption of the Crystal Lake Tuff (27.5 mybp). This eruption led to the concomitant collapse of the Silverton Caldera, nested within the larger San Juan Caldera. The Pride of the West, Osceola, and Little Fanny mines are positioned near the intersection of the Pride radial fracture system and the buried structural margin of the San Juan Caldera, suggesting that ore concentration was controlled by this structural setting. Large limestone blocks of the Mississippian Leadville Formation are incorporated into the intracaldera fill volcanics in the mine area. These blocks appear to have been engulfed within mudflow breccias of the Tertiary San Juan Formation (32.1 mybp). They were then emplaced in their present structural position within a caldera-collapse breccia which caved from the oversteepened margin of the San Juan Caldera. Regional propylitic alteration of the hosting volcanics to a chlorite-calcite-pyrite assemblage preceded vein-associated alteration and mineralization. The veins are enveloped by a narrow phyllic alteration assemblage of quartz, sericite, illite, kaolinite, and pyrite. The veins are comprised of sphalerite, galena, chalcopyrite, pyrite, hematite, magnetite, quartz, pyroxmangite, calcite, and minor barite. Substantial bodies of replacement ore are present where the vein structures intersect the limestone blocks; the mineral assemblages of the replacement deposits are identical to those of the feeding vein structures. Commonly, replacement textures are spectacular concentrations, especially the "zebra ore" which primarily consists of regularly spaced, alternating bands of sulfides and quartz. These "zebra" laminations are stratigraphically controlled and appear to represent replacement of a depositional or diagenetic fabric. Main ore-stage mineralization began with widespread deposition of quartz with or without pyrite, followed by sphalerite, chalcopyrite, and galena. Post ore-stage brecciation and silicification events are evident and were followed by deposition of calcite and minor barite during the waning stages of the hydrothermal system. The distributions of Fe, Mn, Pb, and Ca suggest a lateral component of fluid flow from northwest the southeast, away from the structural margin of the Silverton Caldera. Fluid inclusion data from both vein and replacement-type sphalerite and quartz indicate that mineral deposition occurred over a range of 200 to 312°C (mean 243°C) from solutions containing 1 to 5% total salts. The high base metal to precious metal content of the ore, the phyllic alteration assemblage, and the temperature and composition of the ore-forming fluid indicate that the mine workings are within the lower portion of a fossil geothermal system. / text

The reduction and stabilization of atmospheric CO2 concentration is currently one of the most challenging problems being investigated. Carbon mineralization has recently received much attention as one of the most promising options for CO2 sequestration. The engineered weathering of silicate minerals as a means of permanent carbon storage has unique advantages such as the abundance of naturally occurring calcium and magnesium-bearing minerals and the formation of environmentally-benign and geologically stable solids via a thermodynamically favored carbonation reaction. However, several challenges need to be overcome to successfully deploy carbon mineralization on a large-scale. The current limitation of the carbon mineralization scheme for permanent storage of anthropogenic CO2 is the slow reaction kinetics, since the natural weathering of silicate minerals occurs on geological time-scales. Another problem of mineral carbonation is that the cost of the carbon mineralization process for sequestration is dominated by up front energy costs during the mineral processing and carbonation. In this study, chemically enhanced mineral dissolution via various chelating agents was investigated to accelerate the overall reaction rate of ex-situ and in-situ mineral carbonation. To reduce the overall cost of the carbon mineralization process, the utilization of solid products as value-added materials, e.g. precipitated magnesium carbonates (PMC) and precipitated calcium carbonates (PCC), was studied. Wollastonite (CaSiO3) and antigorite, which is a kind of serpentine (Mg3(OH)4(Si3O5)) group minerals, were selected for this work. They are representative of calcium silicate minerals and magnesium silicate minerals, respectively. This work starts with development of an experimental framework for the systematic investigation of mineral dissolution and carbonation behaviors with mineral pre-processing considerations (e.g., the removal of fines (< 5 μm) to standardize the reaction surface of the minerals), experimental set-up (e.g., syringe pump reactor for the investigation of mineral dissolution and high temperature, high pressure batch reactor for the study of direct aqueous mineral carbonation) and post reaction analyses (e.g., the evaluation of various carbon analysis techniques for the accurate estimation of the extent of carbon mineralization). Accelerated wollastonite weathering is experimentally studied first. For large scale carbon mineralization, generally Mg-bearing silicate minerals such as serpentine or olivine (Mg2SiO4) are the most suitable minerals due to not only their significant abundance in nature but also their high capacity. New York State, however, has one of the largest deposits of wollastonite in the United States and is considered to be a suitable place to adapt CO2 mineralization using Ca-bearing minerals as a CO2 storage option. Moreover, the technologies developed for enhancing carbonation of Ca-bearing minerals can also be applied to the industrial wastes with similar chemistry, such as steel slag and cement kiln dust. The effect of various types of chelating agents on the dissolution rate of wollastonite minerals is explored to accelerate its weathering rate. It is found that chelating agents such as acetic acid and gluconic acid can significantly improve the dissolution kinetics of wollastonite even at a much diluted concentration of 0.006 M by complexing with calcium in the mineral matrix. Calcium extracted from wollastonite is then reacted with a carbonate solution to form PCC, and the study shows that by controlling the reaction temperature, the morphological structure of the synthesized PCC can be tuned for various applications (i.e., paper fillers, plastic fillers and construction materials). Microbial and chemical enhancement of ex-situ and in-situ antigorite carbonation is investigated as well as synthesis of PMC to mimic commercially available CaCO3-based filler materials. The effect of various chelating agents, including volatile fatty acids produced via anaerobic digestion of food waste, on antigorite dissolution is investigated in a syringe pump reactor. It is found that oxalate performs best among over fifteen kinds of chelating agents on accelerating dissolution rate of antigorite minerals. Among the volatile fatty acids, valerate works best on antigorite dissolution followed by acetate. The concentration of valerate, however, is very low in the produced mixture of volatile fatty acids via anaerobic digestion. On the other hand, acetate is the dominant component in the mixture, so it is considered as the most valuable product of anaerobic digestion of food waste. Magnesium extracted from antigorite is then reacted with carbonates to form precipitated magnesium carbonates. The effects of various chelating agents, reaction time, reaction temperature and pH on the mean particle size, particle size distribution, composition, and particle morphological structures of precipitated magnesium carbonates are systematically studied. Finally, the effect of volatile fatty acids on direct aqueous mineral carbonation is studied in a high temperature, high pressure batch reactor with antigorite and olivine minerals to predict the effect of volatile fatty acids on in-situ mineral carbonation. Volatile fatty acids can enhance the overall reaction rate via direct aqueous mineral carbonation route slightly. Volatile fatty acids may be not good enough for accelerating ex-situ direct aqueous mineral carbonation. However, they may be suited to in-situ mineral carbonation, which takes years.

Growth and dissolution of the mineral calcite is important for prediction and control of surface and subsurface water quality, calculation of past sea-surface temperatures using paleoenvironmental proxies, and sequestration of contaminants through engineered calcite precipitation. At high concentrations of strontium, calcite growth is known to be inhibited, but the mechanism by which strontium inhibits growth is not well understood. Seeking to better understand this mechanism, atomic force microscopy is used with a flow-through fluid cell to measure real time growth rates of the obtuse and acute monomolecular step orientations on the calcite surface. Growth was measured at two saturation indices as a function of the ratio of the concentrations of aqueous calcium-to-carbonate and varying aqueous strontium concentration. It was found that the amount of strontium required to inhibit growth correlated with the aqueous calcium concentration, but did not correlate with carbonate concentration. This suggests that strontium inhibits attachment of calcium, but not carbonate, during growth. Analytical models of nucleation and propagation of steps are expanded from previous studies to capture multiple saturation indices.

Thesis (M.A.)--University of Texas at Austin, 1984. / Vita. Includes bibliographical references (leaves 119-124).